Papers - AKIYAMA Tsuyoshi

Improvement of the photoelectric conversion efficiencies of a half-photocell using electrodeposited poly(2,2!-bithiophene) through the incorporation of meso-tetra(3- thienyl)porphyrin and electrodeposited poly(3,4-ethylenedioxythiophene) Reviewed

Kengo Kanbe, Yu Kumagawa, Shuya Hirata, Takeo Oku, Tsuyoshi Akiyama

Japanese Journal of Applied Physics   63   12005   2024.12

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DOI： 10.35848/1347-4065/ad95d2

Fabrication and photocurrent generation properties of C60-ethylenediamine adduct microparticles film modified with poly(3-hexylthiophene-2,5-diyl) Reviewed

Moyu Tanaka, Kengo Kanbe, Shoto Banya, Takeo Oku, Tsuyoshi Akiyama

Molecular Crystals and Liquid Crystals   768 ( 13 )   541 - 551   2024.5

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DOI： 10.1080/15421406.2024.2353978

Other Link： https://doi.org/10.35848/1347-4065/ad95d2

Enhancement of photochromic molecule decolorization by coating a thin Ti(O) layer over gold nanoparticles Reviewed International coauthorship

Suguru Higashida, Ryota Toku, Genta Nakano, Ryo Mizutsu, Ryosuke Asato, Marine Louis, Tsuyoshi Akiyama, Tsuyoshi Kawai

Chemistry Letters   53   upad002   2023.12

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DOI： 10.1093/chemle/upad002

Fabrication and photoelectric conversion of densely packed C60–ethylenediamine adduct microparticle films-modified electrode covered with electrochemically deposited polythiophene thin-films Reviewed

Shoto Banya, Yu Kumagawa, Daisuke Izumoto, Moyu Tanaka, Kengo Kanbe, Takeo Oku and Tsuyoshi Akiyama

RSC Advances   13   31244 - 31251   2023.10

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DOI： 10.1039/d3ra05150a

Photothermal therapeutic ability of copper open-shell nanostructures that are effective in the second biological transparency window based on symmetry breaking-induced plasmonic properties Reviewed

Kosuke Sugawa, Arisa Suzuki, Jotaro Honda, Taiku Yabuki, Yutaro Hayakawa, Masato Furuya, Hiroki Ikake, Hironobu Tahara, Tsuyoshi Kimura, Yasuhiro Kosuge, Satoshi Kurumi, Tsuyoshi Akiyama, Kouichi Takasea and Joe Otsuki

Journal of Materials Chemistry B   11   6837 - 6852   2023.8

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DOI： 10.1039/d3tb00443k

Photocurrent Generation Properties of Half-Photocell Consisting of Electropolymerized Hierarchical Polythiophene Thin Films as Photoexciting Electron Donor and C60 as Electron Acceptor Reviewed

Kengo Kanbe, Tsuyoshi Akiyama, Takeo Oku

ECS Advances   2   020505   2023.6

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DOI： 10.1149/ 2754-2734/acdf72

Dye fluorescence enhancement by plasmonic nanostructured gold–titania film composites obtained by the combination of electrodeposition and surface sol-gel process Reviewed

Akiyama T., Aiba K., Otsuki T., Koyama N., Oku T., Sugawa K., Yamada S.

Journal of Sol-Gel Science and Technology   104 ( 3 )   666 - 672   2022.12

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Plasmonic nanostructured gold–titania film composites were fabricated and evaluated their dye fluorescence enhancement properties. The plasmonic nanostructured gold was fabricated by electrodeposition. The ragged and overlapped particle structures were observed in the nanostructured-gold. The sizes of the deposited structures varied from several tens of nanometers to the submicrometer level. Titania thin films were prepared via the self-assembly of thiols on the nanostructured-gold and a surface sol-gel process. Formation of the plasmonic nanostructured gold–titania film composites was confirmed by X-ray photoelectron spectroscopy. Porphyrin dye was deposited as a fluorescent probe on the outermost layer of the titania film. The degrees of ground-state excitation of porphyrin dye by plasmonic electric fields were evaluated in various composites with different numbers of repetitions (1–40 times) of surface sol-gel processes for titania layer formation. The enhancement ratios of porphyrin varied with the thickness of the titania film, which functioned as a spacer. In particular, apparent fluorescence enhancement of the porphyrin dye was observed at wavelengths longer than 550 nm using the composites. [Figure not available: see fulltext.].

DOI： 10.1007/s10971-022-05828-7

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Electrochemical fabrication of hierarchical thin films consisting of different polythiophenes and change in photoelectric conversion properties with film thickness Reviewed

Kanbe K., Akiyama T., Kumagawa Y., Hirata S., Tsujiai T., Oku T.

Japanese Journal of Applied Physics   61 ( 6 )   2022.6

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Hierarchical polybithiophene/poly(3,4-ethylenedioxythiophene) films with polybithiophene layers of various thicknesses were prepared on an indium tin oxide glass transparent electrode by sequential electrochemical polymerization. In the presence of methyl viologen as a sacrificial electron acceptor, cathodic photocurrents were generated under monochromatic light irradiation. The irradiation light wavelength dependence of the incident photon-To-electron conversion efficiency changed drastically with the thickness of the polybithiophene layer. The main reason for the change in the photoelectric conversion properties was light absorption by the polybithiophene layer.

DOI： 10.35848/1347-4065/ac6408

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Preparation of silver-nanoparticle-loaded C60-ethylenediamine adduct microparticles and their application to photoelectric conversion Reviewed

Matsuoka K.I., Banya S., Hosoi I., Koyama N., Suzuki K., Jeyadevan B., Oku T., Fujita K., Yamada S., Akiyama T.

Applied Physics Express   14 ( 6 )   2021.6

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We report here new types of suprastructure products consisting of C60-ethylenediamine microparticles and silver nanoparticles that were loaded onto the surfaces of the microparticles by electrostatic adsorption. The suprastructure products could be deposited on the surface of an indium tin oxide electrode by electrostatic deposition. These modified electrodes generated cathodic photocurrents in the presence of ascorbic acid and oxygen. The photocurrent generation behavior implies an ensemble of the electron-transfer processes of silver-nanoparticle-mediated electron transfer acting in the cathodic direction and plasmon-induced charge separation acting in the anodic direction.

DOI： 10.35848/1882-0786/abff9f

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Fabrication and surface-enhanced Raman scattering properties of thin-film assemblies of classified silver nanoparticles Reviewed

Koyama N., Akiyama T., Oku T.

Japanese Journal of Applied Physics   60 ( 2 )   2021.2

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The classification of citrate-stabilized silver nanoparticles was performed by a combination of centrifugation and redispersion. Repeated classification processes led to a convergence of similarly sized nanoparticles, which in turn decreased their size deviations. This tendency corresponds to the change in the zeta potentials of the silver nanoparticles. Densely packed sphere-shaped silver nanoparticle thin-film assemblies were fabricated by a liquid-liquid interfacial precipitation process using appropriately classified silver nanoparticles. The surface-enhanced Raman scattering efficiencies of these thin-film assemblies of silver nanoparticles were varied and could be optimized by the number of classification processes.

DOI： 10.35848/1347-4065/abd36c

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One-pot synthesis of visible-light-responsive titanium oxide photocatalyst with embedded silver nanoparticles Reviewed

Higashida S., Yoshida S., Koyama N., Suzuki K., Oku T., Akiyama T.

Journal of Sol-Gel Science and Technology   2021.1

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A composite powder of titanium oxide and silver nanoparticles was obtained by using a combination of the sol–gel process and ultraviolet light induced reduction of silver ion via one-pot synthesis. After calcination, silver nanoparticles were embedded in an anatase crystalline titanium oxide matrix, as revealed by transmission electron microscopy. Silver nanoparticles with sizes ranging from a few nanometers to several tens of nanometers were observed in the titanium oxide matrix. The crystalline titanium oxide-silver nanoparticle composite powder decomposed the methylene blue dye upon visible light irradiation. The decomposition rate of the dye using the crystalline titanium oxide-silver nanoparticle composite powders was considerably faster than that in the case of the reference titanium oxide powder without silver nanoparticle. Thus, plasmon-induced charge separation from the silver nanoparticle to the conduction band of titanium oxide expected to occur, and holes on silver nanoparticles or induced active oxygen decomposed methylene blue in the solution or adsorbed on titanium oxide. [Figure not available: see fulltext.]

DOI： 10.1007/s10971-021-05510-4

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Open-shell singlet diradicaloid difluoreno[4,3-b:3',4'-d]furan and its radical cation and dianion Reviewed

Mori S., Akita M., Suzuki S., Asano M.S., Murata M., Akiyama T., Matsumoto T., Kitamura C., Kato S.I.

Chemical Communications   56 ( 44 )   5881 - 5884   2020.6

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Difluoreno[4,3-b:3',4'-d]furan (DFFu) was preparedviaa short, scalable, multi-step synthesis, and characterized by crystallography, spectroscopic measurements, and theoretical calculations. Even though the results revealed an open-shell singlet diradical character, DFFu is stable under ambient conditions. The radical cationic and dianionic species of DFFu were also synthesized and characterized.

DOI： 10.1039/d0cc01638a

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Fabrication and surface-enhanced Raman scattering properties of two- dimensional gold and silver nanoparticle mixed assemblies by liquid–liquid interfacial precipitation method Reviewed International journal

Natsuki Koyama, Shoto Banya, Tsuyoshi Akiyama, Kosuke Sugawa, Takeo Oku

Applied Physics Express   13   055001-1 - 055001-4   2020.4

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We fabricated two-dimensional assemblies of gold and silver nanoparticles on polycation coated substrates by a liquid–liquid interfacial precipitation method. The assembling of the metal nanoparticles on the substrate was evaluated by absorption spectroscopy and scanning electron microscopy. Raman scattering signals of Rhodamine 6G were detected on the metal nanoparticle-modified substrates. In particular, the intensities of the Raman scattering signals of the mixed gold and silver nanoparticle-modified substrates were larger than the intensities expected from a simple proportional sum of the Raman scattering signals of the individual assembly films composed of only gold or silver nanoparticles.

DOI： 10.35848/1882-0786/ab8965

Fabrication and photocatalytic behavior of titanium oxide–gold nanoparticles composite ultrathin films prepared using surface sol–gel process Reviewed

Mitsukawa S., Akiyama T., Hinoue M., Shima K., Takishita T., Higashida S., Koyama N., Sugawa K., Ogawa M., Sakaguchi H., Oku T.

Journal of Sol-Gel Science and Technology   2020.1

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© 2020, Springer Science+Business Media, LLC, part of Springer Nature. Abstract: Ultrathin films consisting of titanium oxide and gold nanoparticles were prepared using a combination of the surface sol–gel process and liquid/liquid interfacial precipitation. The composite films had a titanium oxide/gold nanoparticle layer/titanium oxide film structure, comprising a gold nanoparticle thin-film layer sandwiched within titanium oxide films of nanometer-order thickness. Upon heating the titanium oxide–gold nanoparticle composite films to 450 °C, they underwent a phase change from the amorphous to the anatase phase, which was confirmed via Raman scattering analysis. It was observed that, even after heating, the plasmonic absorption band due to the presence of gold nanoparticles was maintained in the composite films. The photocatalytic degradation efficiencies of methylene blue dye were evaluated in films under 520 nm light irradiation. The results suggested that the sandwich-like structure of this titanium oxide/gold nanoparticle layer/titanium oxide is promising for the visible-light-induced degradation of methylene blue dye. [Figure not available: see fulltext.]

DOI： 10.1007/s10971-019-05214-w

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Infrared wire-grid polarizer with an ultrathin photoimprinted polymer film Reviewed

Itsunari Yamada, Tsuyoshi Akiyama

Optical Engineering   2019.5

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DOI： 10.1117/1.OE.58.5.057104

Development of fullerene thin-film assemblies and fullerene-diamine adducts towards practical nanocarbon-based electronic materials Reviewed

Akiyama T.

Bulletin of the Chemical Society of Japan   92 ( 7 )   1181 - 1199   2019.1

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Fullerenes are attractive spherical aromatic molecules with good electron acceptor capabilities and good utility as an n-type organic semiconductor. By using a fullerene-amine addition reaction, it was possible to fabricate ultrathin-film assemblies of fullerene on the surface of substrates, which were confirmed by photoelectric conversion applications. Addition reactions between fullerenes and primary aliphatic diamines can also occur to form insoluble adduct particles consisting of fullerenes and diamines. In one example, C -ethylenediamine adduct particles can be solubilized by addition of alkylacid chloride to residual amino groups of the adducts. Spin-coated or dip-coated thin-films of C -ethylenediamine adducts from their solutions are useful as n-type organic semiconductors which was confirmed with solar cell application. In this account, the history of the fabrication and application of fullerene thin-film assemblies and fullerene-diamine adducts using the fullerene-amine addition reaction is introduced and summarized from the early studies to more recent developments. 60 60

DOI： 10.1246/bcsj.20190079

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Fabrication and photovoltaic properties of an invert-type organic thin-film solar cells incorporation of phosphorescent material into electron transport layer Reviewed International journal

Yusuke Matsumiya, Tsuyoshi Akiyama, Itsunari Yamada, Takeo Oku

AIP Conference Proceedings   2019.1

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DOI： 10.1063/1.5089446

Precise Control of Localized Surface Plasmon Wavelengths Is Needed for Effective Enhancement of Triplet−Triplet Annihilation- Based Upconversion Emission International journal

Shota Jin, Kosuke Sugawa, Naoto Takeshima, Hironobu Tahara, Shuto Igari, Satoshi Yoshinari, Yuri Kurihara, Shiryu Watanabe, Masami Enoki, Kenta Sato, Wataru Inoue, Kyo Tokuda, Tsuyoshi Akiyama, Ryuzi Katoh, Kouichi Takase, Hiroaki Ozawa, Toshiya Okazaki, Takayuki Watanabe, and Joe Otsuki

ACS Photonics   2018.11

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DOI： 10.1021/acsphotonics.8b01292

Time-dependent non-linear size change of C<inf>60</inf>-ethylenediamine adduct particles in formation process Reviewed

Akiyama T., Ono Y., Miyamura H., Saito J., Kimura K., Higashida S., Oku T.

Journal of Nanoparticle Research   20 ( 9 )   2018.9

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© 2018, Springer Nature B.V. Addition reaction between C60and ethylenediamine occurred at room temperature in an ambient condition. C60-ethylenediamine adduct particles were prepared by mixing toluene solutions of C60and ethyelenediamine. Average diameter of the C60-ethylenediamine adduct particles was changed non-linearly according to the reaction time, which were observed using transmission electron microscopy. Early stage of the reaction, the diameter of the adduct particles was changed from about 250 to about 430 nm. Then, the size of the adduct particles was converged to about 300 nm. During this addition reaction, the crystalline sizes of adduct particles were constant about 2–3 nm, regardless of the sizes of the adduct particles, which were determined by X-ray diffraction measurement. [Figure not available: see fulltext.].

DOI： 10.1007/s11051-018-4353-9

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Insertion effect of spin-coated films of C60-ethylenediamine adduct on organic thin-film solar cells Reviewed

Atsutaka Yamada, Daisuke Izumoto, Tsuyoshi Akiyama*, Katsuhiko Fujita, Atsushi Suzuki, and Takeo Oku

AIP Conference Proceedings   1929   020020-1 - 020020-5   2018.1

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Insertion effect of spin-coated films of C<inf>60</inf>-ethylenediamine adduct on organic thin-film solar cells Reviewed

Yamada A., Izumoto D., Akiyama T., Fujita K., Suzuki A., Oku T.

AIP Conference Proceedings   1929   2018.1

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C -ethylanediamine adduct particle (C P) were prepared by simply mixing of C and ethylenediamine (EDA) in toluene. C P was dissolved into EDA to obtain C P-EDA. C P-EDA can be diluted by ethanol, 2-methoxyethanol or water. Thin films of C P-EDA were prepared from these diluted solutions of C P-EDA by spin-coating. Such thin-films were used as a part of organic thin-film solar cells. 60 60 60 60 60 60 60 60

DOI： 10.1063/1.5021933

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Effect of gold nanoparticles in titanium oxide layer on the photovoltaic performance of inverted-type organic thin-film solar cells Reviewed

Tsuyoshi Akiyama*, Hiroki Sakata, Taisuke Matsumoto, Shota Mitsukawa, Hiroshi Sakaguchi, and Takeo Oku

Molecular Crystals and Liquid Crystals   653   50 - 56   2017.11

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Effect of gold nanoparticles in titanium oxide layer on the photovoltaic performance of inverted-type organic thin-film solar cells Reviewed

Akiyama T., Sakata H., Matsumoto T., Mitsukawa S., Sakaguchi H., Oku T.

Molecular Crystals and Liquid Crystals   653 ( 1 )   50 - 56   2017.8

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© 2017 Taylor & Francis Group, LLC. Gold nanoparticle/titanium oxide composite materials were prepared at low temperature and were used as electron-transport layers for inverted-type organic thin-film solar cells. The application of gold nanoparticle/titanium oxide composite materials led to an improvement in the photoelectric conversion efficiency of the solar cells under simulated sunlight irradiation.

DOI： 10.1080/15421406.2017.1348843

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Morphological change of crystalline polymer films by annealing: substrate- and heating/cooling-rate-dependent surface roughness Reviewed

Uto Y., Mizobata K., Maurya S., Akiyama T., Nakajima T.

Surface and Interface Analysis   49 ( 7 )   577 - 583   2017.7

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Copyright © 2017 John Wiley & Sons, Ltd. We study the morphological change of crystalline polymer films by annealing using atomic force microscope, X-ray diffraction, and Fourier transform infrared spectroscopy techniques. As typical samples, we employ high-density and low-density polyethylene films prepared by the cast method. After annealing at 135 °C for 4 h, the surface roughness of polyethylene films by the atomic force microscope significantly increases, and the crystallite size by the X-ray diffraction also shows some increase, while the Fourier transform infrared spectroscopy spectrum hardly exhibits any change. This can be well explained as a result of the growth of crystal structure by recrystallization during annealing. More interestingly, we find that the choice of the substrate and also the heating/cooling rates for annealing significantly influences the surface roughness of the films. Copyright © 2017 John Wiley & Sons, Ltd.

DOI： 10.1002/sia.6195

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Development of Plasmonic Cu<inf>2</inf>O/Cu Composite Arrays as Visible- and Near-Infrared-Light-Driven Plasmonic Photocatalysts Reviewed

Sugawa K., Tsunenari N., Takeda H., Fujiwara S., Akiyama T., Honda J., Igari S., Inoue W., Tokuda K., Takeshima N., Watanuki Y., Tsukahara S., Takase K., Umegaki T., Kojima Y., Nishimiya N., Fukuda N., Kusaka Y., Ushijima H., Otsuki J.

Langmuir   33 ( 23 )   5685 - 5695   2017.6

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We describe efficient visible- and near-infrared (vis/NIR) light-driven photocatalytic properties of hybrids of Cu O and plasmonic Cu arrays. The Cu O/Cu arrays were prepared simply by allowing a Cu half-shell array to stand in an oxygen atmosphere for 3 h, which was prepared by depositing Cu on two-dimensional colloidal crystals with a diameter of 543 or 224 nm. The localized surface plasmon resonances (LSPRs) of the arrays were strongly excited at 866 and 626 nm, respectively, at which the imaginary part of the dielectric function of Cu is small. The rate of photodegradation of methyl orange was 27 and 84 times faster, respectively, than that with a Cu O/nonplasmonic Cu plate. The photocatalytic activity was demonstrated to be dominated by Cu LSPR excitation. These results showed that the inexpensive Cu O/Cu arrays can be excellent vis/NIR-light-driven photocatalysts based on the efficient excitation of Cu LSPR. 2 2 2 2

DOI： 10.1021/acs.langmuir.7b01052

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Effects of PBr3 Addition to Polysilane Thin Films on Structures and Photovoltaic Properties Reviewed International journal

Junya Nakagawa, Takeo Oku, Atsushi Suzuki, Tsuyoshi Akiyama, Masahiro Yamada, Sakiko Fukunishi, Kazufumi Kohno

Green and Sustainable Chemistry   2017.2

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Cathode buffer composed of fullerene-ethylenediamine adduct for an organic solar cell Reviewed

Kimoto Y., Akiyama T., Fujita K.

Japanese Journal of Applied Physics   56 ( 2 )   2017.2

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We developed a fullerene-ethylenediamine adduct (C P-DC) for a cathode buffer material in organic bulk heterojunction solar cells, which enhance the open-circuit voltage (V ). The evaporative spray deposition using ultra dilute solution (ESDUS) technique was employed to deposit the buffer layer onto the organic active layer to avoid damage during the deposition. By the insertion of a C P-DC buffer layer, V and power conversion efficiency (PCE) were increased from 0.41 to 0.57 V and from 1.65 to 2.10%, respectively. The electron-only device with the C P-DC buffer showed a much lower current level than that without the buffer, indicating that the V increase is caused not by vacuum level shift but by hole blocking. The curve fitting of current density-voltage (J-V) characteristics to the equivalent circuit with a single diode indicated that the decrease in reversed saturation current by hole blocking increased caused the V . 60 oc 60 oc 60 oc oc

DOI： 10.7567/JJAP.56.021601

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Doping effects of transition metal elements to titanium dioxide for perovskite solar cells Reviewed

Saito J., Suzuki A., Akiyama T., Oku T.

AIP Conference Proceedings   1807   2017.1

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Organic-inorganic hybrid heterojunction solar cells containing perovskite CH NH PbI using Nb, Ta, or V-doped TiO as electron-transporting layers were fabricated and characterized. By Nb doping, the conductivity and carrier density of the TiO increased, and its flat-band potential showed a positive shift. The short-circuit current density and power conversion efficiency of perovskite solar cells were improved by using Ti Nb O compared to undoped TiO . 3 3 3 2 2 0.95 0.05 2 2

DOI： 10.1063/1.4974792

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Fabrication and electrochemical properties of insoluble fullerene-diamine adduct thin-films as buffer layer by alternate immersion process Reviewed

Saito J., Akiyama T., Suzuki A., Oku T.

AIP Conference Proceedings   1807   2017.1

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Insoluble fullerene-diamine adduct thin-films consisting of C and 1,2-diaminoethane were easily fabricated on an electrode by an alternate immersion process. Formation of the C -diamine adduct films were confirmed using transmission absorption spectroscopy and atomic force microscopy. An inverted-type organic solar cells were fabricated by using the C -diamine adduct film as the electron transport layer. The resultant photoelectric conversation performance of the solar cells suggested that photocurrent is generated via the photoexcitation of polythiophene. The result suggests that the present insoluble fullerene-diamine adduct films worked as buffer layer for organic thin-film solar cells. 60 60 60

DOI： 10.1063/1.4974799

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Retardation of sol–gel titanium oxide with imprinted grating structure Reviewed International journal

Itsunari Yamada, Yoshiro Ishihara, Tsuyoshi Akiyama

Optical Engineering   56 ( 1 )   017108   2017.1

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DOI： 10.1117/1.OE.56.1.017108

Cathode buffer composed of fullerene–ethylenediamine adduct for an organic solar cell Reviewed International journal

Yoshinori Kimoto, Tsuyoshi Akiyama, Katsuhiko Fujita

Japanese Journal of Applied Physics   56   021601   2017.1

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Fabrication and Characterization of PCBM: P3HT-based Thin-film Organic Solar Cells with Zinc Phthalocyanine and 1,8-Diiodooctane Reviewed International journal

Haruto Maruhashi, Takeo Oku, Atsushi Suzuki, Tsuyoshi Akiyama, Yasuhiro Yamasaki

Chemical and Materials Engineering   5 ( 1 )   1 - 7   2017

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DOI： 10.13189/cme.2017.050101

Fabrication and electrochemical properties of insoluble fullerene-diamine adduct thin- films as buffer layer by alternate immersion process Reviewed International journal

Jo Saito, Tsuyoshi Akiyama, Atsushi Suzuki, Takeo Oku

AIP Conference Proceedings   1807   020017   2017

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Doping effects of transition metal elements to titanium dioxide for perovskite solar cells Reviewed International journal

Jo Saito, Atsushi Suzuki, Tsuyoshi Akiyama, Takeo Oku

AIP Conference Proceedings   1807   020010   2017

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Efficient Photocurrent Enhancement from Porphyrin Molecules on Plasmonic Copper Arrays: Beneficial Utilization of Copper Nanoanntenae on Plasmonic Photoelectric Conversion Systems Reviewed International journal

Kosuke Sugawa, Daisuke Yamaguchi, Natsumi Tsunenari, Koji Uchida, Hironobu Tahara, Hideyuki Takeda, Kyo Tokuda, Shota Jin, Yasuyuki Kusaka, Nobuko Fukuda, Hirobumi Ushijima, Tsuyoshi Akiyama, Yasuhiro Watanuki, Nobuyuki Nishimiya, Joe Otsuki, Sunao Yamada

ACS Applied Materials and Interfaces   9   750 - 762   2016.12

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DOI： 10.1021/acsami.6b13147

Extraordinary enhancement of porphyrin photocurrent utilizing plasmonic silver arrays Reviewed

Sugawa K., Uchida K., Takeshima N., Jin S., Tsunenari N., Takeda H., Kida Y., Akiyama T., Otsuki J., Takase K., Yamada S.

Nanoscale   8 ( 34 )   15467 - 15472   2016.9

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We demonstrate up to ∼630-fold enhancement of the photocurrent from a porphyrin monolayer on a plasmonic Ag-array electrode showing plasmon absorption in the Q-band region relative to that on a planar Ag electrode. The photocurrent obtained by the Q-band excitation in the plasmonic electrodes even exceeded that obtained by the Soret-band excitation in a normal, nonplasmonic electrode.

DOI： 10.1039/c6nr03158g

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Extraordinary enhancement of porphyrin photocurrent utilizing plasmonic silver arrays Reviewed International journal

Kosuke Sugawa*, Koji Uchida, Naoto Takeshima, Shota Jin, Natsumi Tsunenari, Hideyuki Takeda, Yuki Kida, Tsuyoshi Akiyama, Joe Otsuki, Kouichi Takase, Sunao Yamada

Nanoscale   8   15467 - 15472   2016.7

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Fabrication and Photocurrent Generation Properties of Insoluble Hierarchical Polythiophene Thin Films Prepared by Sequential Electrochemical Polymerization Reviewed International journal

Yu Kumagawa, Tsuyoshi Akiyama*, Yuki Nishimura, Koji Goto, Atsushi Suzuki, Takeo Oku

Bulletin of the Chemical Society of Japan   89   700 - 704   2016.6

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Low-temperature synthesis of titanium oxide/gold nanoparticle composite powders using a combination of the sol–gel process and ultraviolet light irradiation Reviewed

Matsumoto T., Akiyama T., Banya S., Izumoto D., Sakaguchi H., Oku T.

Journal of Sol-Gel Science and Technology   78 ( 3 )   692 - 697   2016.6

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Abstract: Amorphous titanium oxide/plasmonic gold nanoparticle composite powders were synthesized by a combination of the sol–gel process and ultraviolet light irradiation using light-emitting diode at room temperature. The resultant composite powders were dried at ~50 °C. These amorphous titanium oxide/gold nanoparticle composite powders were heated to 450 °C to obtain crystalline titanium oxide/gold nanoparticles. The formation and microstructure of the titanium oxide/gold nanoparticle composite powders were confirmed by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, thermo gravimetry–differential thermal analysis, and optical absorption measurements. A clear plasmonic absorption band due to typical plasmonic gold nanoparticle was observed in both composite powders. Graphical Abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s10971-016-3990-7

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Low-temperature synthesis of titanium oxide/gold nanoparticle composite powders using a combination of the sol–gel process and ultraviolet light irradiation Reviewed International journal

Taisuke Matsumoto, Tsuyoshi Akiyama*, Shoto Banya, Daisuke Izumoto, Hiroshi Sakaguchi, Takeo Oku

Journal of Sol-Gel Science and Technology   78   692 - 697   2016.3

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Fabrication and characterization of perovskite-type solar cells with Nb-doped TiO<inf>2</inf> layers Reviewed

Saito J., Oku T., Suzuki A., Akiyama T.

AIP Conference Proceedings   1709   2016.2

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Organic-inorganic hybrid heterojunction solar cells containing perovskite CH NH PbI using Nb-doped TiO as an electron-transporting layer were fabricated and characterized. Nb-doped TiO layer showed an improvement of the short-circuit current density and power conversion efficiency using Ti Nb O . 3 3 3 2 2 0.95 0.05 2

DOI： 10.1063/1.4941226

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Fabrication and photovoltaic properties of ZnO nanorods/perovskite solar cells Reviewed

Shirahata Y., Tanaike K., Akiyama T., Fujimoto K., Suzuki A., Balachandran J., Oku T.

AIP Conference Proceedings   1709   2016.2

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ZnO nanorods/perovskite solar cells with different lengths of ZnO nanorods were fabricated. The ZnO nanorods were prepared by chemical bath deposition and directly confirmed to be hexagon-shaped nanorods. The lengths of the ZnO nanorads were controlled by deposition condition of ZnO seed layer. Photovoltaic properties of the ZnO nanorods/CH NH PbI solar cells were investigated by measuring current density-voltage characteristics and incident photon to current conversion efficiency. The highest conversion efficiency was obtained in ZnO nanorods/CH NH PbI with the longest ZnO nanorods. 3 3 3 3 3 3

DOI： 10.1063/1.4941217

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Fabrication and photocurrent generation properties of insoluble hierarchical polythiophene thin films prepared by sequential electrochemical polymerization Reviewed

Kumagawa Y., Akiyama T., Nishimura Y., Goto K., Suzuki A., Oku T.

Bulletin of the Chemical Society of Japan   89 ( 6 )   700 - 704   2016.1

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Insoluble hierarchical polybithiophene/poly(ethylenedioxythiophene) thin films with a double-layered structure were prepared on an indium tin oxide transparent electrode by sequential electrochemical polymerization. The formation of the hierarchical structure was supported by the transmission absorption spectra and Raman scattering spectra of the doublelayered polythiophene thin films. In the presence of residual oxygen as an electron acceptor, light irradiation on the polythiophene-modified electrodes generated stable cathodic photocurrents. A broad peak at approximately 440 nm corresponding to the absorption of neutral polythiophene was observed in the incident photon to current conversion efficiency profile of the polybithiophene/poly(ethylenedioxythiophene)- modified electrode. The photocurrent density of the polybithiophene/poly(ethylenedioxythiophene)-modified electrode was higher than that of the poly(ethylenedioxythiophene)- modified electrode.

DOI： 10.1246/bcsj.20160025

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Effect of Gold and Silver Nanoparticle in Poly(3,4-Ethylenedioxythiophene)-Poly(Styrene Sulfonate) layer on Inverted-Type Organic Thin-Film Solar Cells Reviewed International journal

Yutaro Yagi, Tsuyoshi Akiyama*, Taisuke Matsumoto, Hiroshi Sakaguchi, Takeo Oku

Transactions of the Materials Research Society of Japan   40   331 - 334   2015.12

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Photocurrent enhancement of porphyrin molecules over a wide-wavelength region based on combined use of silver nanoprisms with different aspect ratios Reviewed International journal

Kosuke Sugawa*, Naoto Takeshima, Koji Uchida, Hironobu Tahara, Shota Jin, Natsumi Tsunenari, Tsuyoshi Akiyama, Yasuyuki Kusaka, Nobuko Fukuda, Hirobumi Ushijima, Yuji Tsuchido, Takeshi Hashimoto, Takashi Hayashita, Joe Otsuki

Journal of Materials Chemistry C   3   11439 - 11448   2015.11

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Formation of thin films of densely packed [60]fullerenediaminoethane adduct microparticles at a liquid/liquid interface and their photoelectrochemical applications（共著） Reviewed

Banya, Shoto; Akiyama, Tsuyoshi*; Izumoto, Daisuke; Suzuki, Atsushi; Oku, Takeo.

Chemistry Letters   44   489 - 491   2015.4

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Effects of triphenylborane addition to decaphenylcyclopentasilane thin films（共著） Reviewed

Oku, Takeo*; Hibi, Naoki; Suzuki, Atsushi; Akiyama, Tsuyoshi; Yamada, Masahiro; Fukunishi, Sakiko; Kohno, Kazufumi.

JJAP Conference Proceedings   3   011404(1) - 011404(6)   2015.3

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Fabrication and characterization of silicon naphthalocyanine/fullerene-based photovoltaic devices with inverted structures（共著） Reviewed

Maruhashi, Haruto; Oku, Takeo*; Suzuki, Atsushi; Akiyama, Tsuyoshi.

JJAP Conference Proceedings   3   011405(1) - 011405(7)   2015.3

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Fabrication and Characterization of Inverted Organic Solar Cells using Shuttle Cock-Type Metal Phthalocyanine and PCBM:P3HT（共著） Reviewed

Suzuki, Atsushi*; Furukawa, Ryo; Akiyama, Tsuyoshi; Oku, Takeo.

AIP Conference Proceedings   1649   107 - 112   2015.2

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Fabrication and characterization of P3HT:PCBM-based thin film organic solar cells with zinc phthalocyanine（共著） Reviewed

Maruhashi, Haruto; Oku, Takeo*; Suzuki, Atsushi; Akiyama, Tsuyoshi; Yamasaki, Yasuhiro.

AIP Conference Proceedings   1649   89 - 95   2015.2

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Fabrication and Characterization of Organic Solar Cells using Metal Complex of Phthalocyanines（共著） Reviewed

Kida, Tomoyasu; Suzuki, Atsushi*; Akiyama, Tsuyoshi; Oku, Takeo.

AIP Conference Proceedings   1649   102 - 106   2015.2

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Fabrication and characterization of inverted organic solar cells using shuttle cock-type metal phthalocyanine and PCBM:P3HT Reviewed

Suzuki A., Furukawa R., Akiyama T., Oku T.

AIP Conference Proceedings   1649   107 - 112   2015.1

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Inverted organic solar cells using shuttle cock-type phthalocyanine, semiconducting polymer and fullerenes were fabricated and characterized. Photovoltaic and optical properties of the solar cells with inverted structures were investigated by optical absorption, current density-voltage characteristics. The photovoltaic properties of the tandem organic solar cell using titanyl phthalocyanine, vanadyl phthalocyanine, poly(3-hexylthiophene) (P3HT) and [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) were improved. Effect of annealing and solvent treatment on surface morphologies of the active layer was investigated. The photovoltaic mechanisms, energy levels and band gap of active layers were discussed for improvement of the photovoltaic performance.

DOI： 10.1063/1.4913553

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Formation of thin films of densely packed [60]fullerene-diaminoethane adduct microparticles at a liquid/liquid interface and their photoelectrochemical applications Reviewed

Banya S., Akiyama T., Izumoto D., Suzuki A., Oku T.

Chemistry Letters   44 ( 4 )   489 - 491   2015.1

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Thin films of [60]fullerene1,2-diaminoethane adduct microparticles (C<inf>60</inf>P) were fabricated via a liquid/liquid interface precipitation. The energy level of the lowest unoccupied molecular orbital (LUMO) of the C<inf>60</inf>P was evaluated by electrochemical analysis. The additional tetraphenylporphyrin substantially enhanced the photocurrent from the C<inf>60</inf>P-thin-film-modified electrode.

DOI： 10.1246/cl.141153

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Fabrication and characterization of P3HT:PCBM-based thin film organic solar cells with zinc phthalocyanine Reviewed

Maruhashi H., Oku T., Suzuki A., Akiyama T., Yamasaki Y.

AIP Conference Proceedings   1649   89 - 95   2015.1

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[6,6]-phenyl C -butyric acid methyl ester and poly(3-hexylthiophene) bulk heterojunction solar cells added with zinc-tetra-tertiary-butyl-phthalocyanine (ZnPc) were fabricated and characterized. The photovoltaic properties of the solar cells with an inverted structure were improved by the ZnPc addition, which were investigated on the bases of current density-voltage characteristics, incident photon to current conversion efficiency. 61

DOI： 10.1063/1.4913550

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Fabrication and characterization of organic solar cells using metal complex of phthalocyanines Reviewed

Kida T., Suzuki A., Akiyama T., Oku T.

AIP Conference Proceedings   1649   102 - 106   2015.1

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Fabrication and characterization of organic solar cells using shuttle-cock-type phthalocyanines were carried out. Photovoltaic properties of the solar cells with inverted structures were investigated by current density-voltage characteristics. Effects of phase transition between H and J aggregates on the photovoltaic and optical properties were investigated. The photovoltaic mechanisms, energy levels and band gap of active layers were discussed.

DOI： 10.1063/1.4913552

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Photocurrent enhancement of porphyrin molecules over a wide-wavelength region based on combined use of silver nanoprisms with different aspect ratios Reviewed

Sugawa K., Takeshima N., Uchida K., Tahara H., Jin S., Tsunenari N., Akiyama T., Kusaka Y., Fukuda N., Ushijima H., Tsuchido Y., Hashimoto T., Hayashita T., Otsuki J.

Journal of Materials Chemistry C   3 ( 43 )   11439 - 11448   2015.1

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We succeeded in controlling the wavelength range in which the photocurrent of porphyrin is enhanced by tuning as well as expanding the wavelength ranges in which the localized surface plasmon resonance (LSPR) occurs. We fabricated photoelectric conversion systems consisting of 5,10,15,20-tetrakis(p-carboxyphenyl)porphyrin (TCPP) and silver nanoprisms with small (SAgPRs) and large (LAgPRs) aspect ratios as plasmonic nano-antennae. Their photocurrents were much larger than those from TCPP-modified Ag planar electrodes at the specific wavelengths corresponding to their LSPR bands (SAgPRs: 460-610 nm; LAgPRs: 610-690 nm). The maximum enhancement factors (EFs) for the SAgPRs and the LAgPRs were 37 and 35, respectively. In order to enhance the photocurrents, we expanded the LSPR bands by the combined use of SAgPRs and LAgPRs. The system consisting of the mixture (MAgPRs) showed enhancement of the photocurrent over the entire Q-band region (480-690 nm). Finally, the total EFs of the photocurrents were evaluated by irradiation with AM1.5G sunlight through a long-pass filter of 480 nm and the results revealed that the EFs were in the order of MAgPRs > SAgPRs > LAgPRs. Furthermore, the system showed stability without loss of the enhancement property for at least 10 min under the solar irradiation.

DOI： 10.1039/c5tc02606g

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Particle size dependence of the surface-enhanced Raman scattering properties of densely arranged two-dimensional assemblies of Au(core)-Ag(shell) nanospheres Reviewed

Sugawa K., Akiyama T., Tanoue Y., Harumoto T., Yanagida S., Yasumori A., Tomita S., Otsuki J.

Physical Chemistry Chemical Physics   17 ( 33 )   21182 - 21189   2014.12

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We investigated the dependence of the surface-enhanced Raman scattering (SERS) activity of densely arranged two-dimensional assemblies of spherical Au(core)-Ag(shell) nanoparticles (Au/AgNSs) on the nanoparticle diameter. The size-controlled Au/AgNSs were synthesized using the Au nanosphere seed-mediated growth method without any bulky stabilizers. The diameters of the Au/AgNSs were 38, 53, and 90 nm and the ratio of the total diameter to the Au core diameter was adjusted to ca. 2.0. Extinction spectra of the colloidal solutions of these nanoparticles exhibited the prominent peak of the localized surface plasmon resonance (LSPR) of Ag and therefore the Au/AgNSs exhibited LSPR properties almost the same as Ag nanospheres. It was confirmed from SEM observation that the organic solvent-mediated liquid-liquid interface assembly technique easily generated densely arranged two-dimensional assemblies of the nanospheres. The extinction spectra of all the assemblies exhibited a prominent broad peak ranging from 500 nm to the near-infrared region, which is assigned to the longitudinal LSPR mode of the coupling nanospheres. The extinction intensity increased with increasing nanosphere diameter. The SERS activities of these assemblies were investigated using p-aminothiophenol as a probe molecule. The result revealed that the enhancement factor (EF) of the Raman signal dramatically increased upon increasing the particle diameter. The maximum EF obtained with a laser excitation wavelength of 785 nm was 1.90 × 10 for a nanosphere diameter of 90 nm. This renders the two-dimensional assemblies of the plasmonic Au/AgNSs promising for the development of highly sensitive SERS sensor platforms due to their strong electromagnetic effect. 6

DOI： 10.1039/c4cp05058d

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Facile Fabrication and Photovoltaic Application of [60]Fullerene Assembly Films Formed by Reaction between Fullerene and Amines（共著） Reviewed

Banya, Shoto; Akiyama, Tsuyoshi*; Matsumoto, Taisuke; Fujita, Katsuhiko; Oku, Takeo.

Bulletin of Chemical Society of Japan   87   1335 - 1342   2014.12

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Selective Implantation of Gold Nanoparticles onto One Side Surface of Self-Standing Polymer Film（共著） Reviewed

Akiyama, Tsuyoshi; Yoshida, Kazuhiro; Yamada, Sunao*.

RSC Advances   4   62375 - 62379   2014.11

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Effect of annealing on photovoltaic properties and microstructure of conventional and inverted organic solar cells using active bilayer based on liquid-crystal semiconducting polymer and fullerene（共著） Reviewed

Suzuki, Atsushi*; Suzuki, Hisato; Maruhashi, Haruto; Banya, Shoto; Akiyama, Tsuyoshi; Oku, Takeo.

International Journal of Energy Research   38   1541 - 1550   2014.10

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Effect of annealing on photovoltaic properties and microstructure of conventional and inverted organic solar cells using active bilayer based on liquid-crystal semiconducting polymer and fullerene Reviewed

Suzuki A., Suzuki H., Maruhashi H., Banya S., Akiyama T., Oku T.

International Journal of Energy Research   38 ( 12 )   1541 - 1550   2014.10

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Conventional and inverted organic solar cells of poly[9,9-dioctyl-fluorene-co-bithiophene] (F8T2) as liquid-crystal semiconducting polymer and fullerene as electron acceptor were fabricated and characterized. An effect of thermal treatment of the films on annealing condition near glass transition was investigated for tuning optimization and improving the photovoltaic and optical properties. Annealing treatment below the glass transition improved the photovoltaic performance and carrier diffusion in crystal growth of active layer. The X-ray diffraction patterns indicate a crystalline structure with molecular order of F8T2 in crystal index, 100 as a layer distance between sheets of F8T2 chains. The photovoltaic properties were based on molecular interactions with molecular ordering in active layer at crystal state. As the photovoltaic mechanisms, the F8T2 thin film as p-type semiconducting polymer worked for electron-donor layer to support light-induced generation, carrier diffusion and charge transfer near interface in active layer.

DOI： 10.1002/er.3170

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Fabrication and characterization of organic solar cells using titanylphthalocyanine as hole transport layer（共著） Reviewed

Iwase, Makoto; Suzuki, Atsushi*; Akiyama, Tsuyoshi; Oku, Takeo*.

physica status solidi (a)   211   2861 - 2864   2014.10

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C60–ethylenediamine adduct thin-film as a buffer layer for inverted-type organic solar cells（共著） Reviewed

Ono, Yuji; Akiyama, Tsuyoshi*; Banya, Shoto; Izumoto, Daisuke; Saito, Jo; Fujita, Katsuhiko; Sakaguchi, Hiroshi; Suzuki, Atsushi; Oku, Takeo.

RSC Advances   4   34950 - 34954   2014.8

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Effects of Au nanoparticle addition to hole transfer layer in organic solar cells based on copper naphthalocyanine and fullerene（共著） Reviewed

Nagata, Akihiko; Oku, Takeo*; Akiyama, Tsuyoshi*; Suzuki, Atsushi.

Progress in Natural Science: Materials International   24   179 - 183   2014.6

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Fabrication and Characterization of TiO2/CH3NH3PbI3-based Photovoltaic Devises（共著） Reviewed

Zushi, Masahito; Suzuki, Atsushi*; Akiyama, Tsuyoshi; Oku, Takeo*.

Chemistry Letters   43   916 - 918   2014.6

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Microstructures and photovoltaic properties of Zn(Al)O/Cu <inf>2</inf> O-based solar cells prepared by spin-coating and electrodeposition Reviewed

Oku T., Yamada T., Fujimoto K., Akiyama T.

Coatings   4 ( 2 )   203 - 213   2014.6

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Copper oxide (Cu O)-based heterojunction solar cells were fabricated by spin-coating and electrodeposition methods, and photovoltaic properties and microstructures were investigated. Zinc oxide (ZnO) and Cu O were used as n- and p-type semiconductors, respectively, to fabricate photovoltaic devices based on In-doped tin oxide/ZnO/Cu O/Au heterojunction structures. Short-circuit current and fill factor increased by aluminum (Al) doping in the ZnO layer, which resulted in the increase of the conversion efficiency. The efficiency was improved further by growing ZnO and Cu O layers with larger crystallite sizes, and by optimizing the Al-doping by spin coating. 2 2 2 2

DOI： 10.3390/coatings4020203

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Effect of gold nanoparticle in hole-transport layer on inverted organic thin-film solar cell performance（共著） Reviewed

Akiyama, Tsuyoshi*; Nishida, Takuji; Matsumoto, Taisuke; Sakaguchi, Hiroshi; Suzuki, Atsushi; Oku, Takeo.

physica status solidi (a)   211   1645 - 1650   2014.5

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Fabrication and characterization of PCBM:P3HT:silicon phthalocyanine bulk heterojunction solar cells with inverted structures（共著） Reviewed

Oku, Takeo*, Hori, Satoru; Suzuki, Atsushi; Akiyama, Tsuyoshi; Yamasaki, Yasuhiro.

Japanese Journal of Applied Physics   53   05FJ08(1) - 05FJ08(5)   2014.4

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Microstructures, optical and photoelectric conversion properties of spherical silicon solar cells with anti-reflection SnOx:F thin films（共著） Reviewed

Oku, Takeo*, Kanayama, Masato; Ono, Yuji; Akiyama, Tsuyoshi; Kanamori, Youichi; Murozono, Mikio.

Japanese Journal of Applied Physics   53   05FJ03(1) - 05FJ03(7)   2014.4

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Fabrication and Characterization of Phthalocyanine-Based Organic Solar Cells（共著） Reviewed

Iwase, Makoto; Suzuki, Atsushi*; Akiyama, Tsuyoshi; Oku, Takeo*.

Materials Sciences and Applications   5   278 - 284   2014.4

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Microstructures and Photovoltaic Properties of Zn(Al)O/Cu2O-Based Solar Cells Prepared by Spin-Coating and Electrodeposition（共著） Reviewed

Oku, Takeo*; Yamada, Tetsuya; Fujimoto, Kazuya; Akiyama, Tsuyoshi.

Coatings   4   203 - 213   2014.3

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Synthesis of crystalline Cu2O nanoparticles using long chained alcohol（共著） Reviewed

Nishimura, Kenta; Huaman, Jhon L Cuya; Miyamura, Hiroshi; Akiyama, Tsuyoshi; Oku, Takeo; Jeyadevan, Balachandran.

Materials Research Express   1   015032(1) - 015032(13)   2014.3

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Synthesis of crystalline Cu<inf>2</inf>O nanoparticles using long chained alcohol Reviewed

Nishimura K., Huaman J., Hiroshi M., Akiyama T., Oku T., Jeyadevan B.

Materials Research Express   1 ( 1 )   2014.3

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The successful synthesis of highly crystallized cuprous oxide nanoparticles using long chained alcohol reduction method is reported. The purity of copper oxide obtained by this method greatly depends on the synthesis conditions such as reaction temperature, reaction duration, and hydroxyl ion concentration that assist the reduction kinetics. By optimizing the above parameters, cubic cuprous oxide with particle sizes controllable in the range of 10-30 nm were synthesized. The x-ray diffraction analysis confirmed the single-phased nature of Cu O crystal. Furthermore, the ratio between copper and oxygen atoms in the product was determined to be 1.96 using the Rietveld analysis and confirmed the purity of Cu O nanoparticles. In addition, I-V characteristics suggested that the nanoparticles function as semiconductor and indicated the use of these cuprous nanocrystals as a functional material for the preparation of solar devices. 2 2

DOI： 10.1088/2053-1591/1/1/015032

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Photovoltaic Properties and Morphology of Organic Solar Cells based on Liquid-crystal Semiconducting Polymer with Additive（共著） Reviewed

Suzuki, Atsushi; Zushi, Masahito; Suzuki, Hisato; Ogahara, Shinichi; Akiyama, Tsuyoshi; Oku, Takeo.

AIP Conference Proceedings   1585   164 - 170   2014.2

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Fabrication of dense two-dimensional assemblies over vast areas comprising gold(core)–silver(shell) nanoparticles and their surface-enhanced Raman scattering properties（共著） Reviewed

Sugawa, Kosuke*; Tanoue, Yoshimasa; Ube, Takuji; Yanagida, Sayaka; Yamamuro, Takahiro; Kusaka, Yasuyuki; Ushijima, Hirobumi; Akiyama, Tsuyoshi*.

Photochemical & Photobiological Sciences   13   82 - 91   2014.1

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C<inf>60</inf>-ethylenediamine adduct thin film as a buffer layer for inverted-type organic solar cells Reviewed

Ono Y., Akiyama T., Banya S., Izumoto D., Saito J., Fujita K., Sakaguchi H., Suzuki A., Oku T.

RSC Advances   4 ( 66 )   34950 - 34954   2014.1

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Thin films of a C -ethylenediamine (EDA) adduct were prepared from an EDA solution of the adduct particles. An inverted-type organic thin-film solar cell using the thin film of the C -EDA adduct as a buffer layer was fabricated. The solar cell performance suggested that the C -EDA adduct thin film functioned as an electron-transporting layer, similarly to the titanium oxides in typical inverted-type organic thin-film solar cells. © 2014 the Partner Organisations. 60 60 60

DOI： 10.1039/c4ra03965c

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Effects of Au nanoparticle addition to hole transfer layer in organic solar cells based on copper naphthalocyanine and fullerene Reviewed

Nagata A., Oku T., Akiyama T., Suzuki A.

Progress in Natural Science: Materials International   24 ( 3 )   179 - 183   2014.1

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Organic solar cells based on copper naphthalocyanine (CuNc) and fullerene (C ) were fabricated, and their photovoltaic properties were investigated. C and CuNc were used as n-type and p-type semiconductors, respectively. In addition, the effect of Au nanoparticle addition on a hole transfer layer was investigated, and the power conversion efficiency of the devices was improved after blending the Au nanoparticles into the hole transport layer. Nanostructures of Au nanoparticles were investigated by transmission electron microscopy and X-ray diffraction. Energy levels of molecules were calculated by molecular orbital calculations, and the nanostructure and electronic properties were discussed. 60 60

DOI： 10.1016/j.pnsc.2014.04.002

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Effect of gold nanoparticle in hole-transport layer on inverted organic thin-film solar cell performance Reviewed

Akiyama T., Nishida T., Matsumoto T., Sakaguchi H., Suzuki A., Oku T.

Physica Status Solidi (A) Applications and Materials Science   211 ( 7 )   1645 - 1650   2014.1

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Inverted-type bulk-heterojunction organic thin-film solar cells with incorporated gold nanoparticles were fabricated and evaluated. Gold nanoparticles were incorporated into the hole-transport layer, and subsequently positioned behind the photoactive layer, away from the light-facing side of the solar cell. Incorporation of gold nanoparticles was confirmed by scanning electro microscopy, atomic force microscopy, and transmission absorption spectra. The incorporation of the gold nanoparticles improved the performance of the photovoltaic device, even gold nanoparticles were aggregated in the hole-transport layer. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssa.201330674

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Fabrication and characterization of organic solar cells using titanylphthalocyanine as hole transport layer Reviewed

Iwase M., Suzuki A., Akiyama T., Oku T.

Physica Status Solidi (A) Applications and Materials Science   211 ( 12 )   2861 - 2864   2014.1

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Organic solar cells using titanylphthalocyanine as a hole transport layer (HTL) were fabricated and characterized. Photovoltaic properties of the solar cells with inverted structures were investigated by optical absorption and current density-voltage (J-V) characteristic. The titanylphthalocyanine was mainly used as a buffer layer instead of PEDOT:PSS, and worked as HTL protecting the active layers.

DOI： 10.1002/pssa.201431068

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Facile fabrication and photovoltaic application of [60]fullerene assembly films formed by reaction between fullerene and amines Reviewed

Banya S., Akiyama T., Matsumoto T., Fujita K., Oku T.

Bulletin of the Chemical Society of Japan   87 ( 12 )   1335 - 1342   2014.1

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[60]Fullerene assembly films consisting of C and 1,2-diaminoethane (ethylenediamine) were fabricated on an amino-group-modified substrate and were characterized. An inverted-type organic solar cell was fabricated using the C -assembly film as the acceptor layer in the photoactive layer of the solar cell. The resultant photoelectric conversion performances of the solar cells were studied using the photocurrent and photovoltage via the photoexcitation of polythiophene. Controlling the energy levels of the C -assembly film and optimizing the thickness of each layer in the solar cell may play an important role in obtaining efficient photoelectric conversion properties and organic electronic materials. The fabricated C -assembly films may accelerate the development of organic photoelectric conversion devices as novel n-type fullerene-based materials and organic electronic materials. 60 60 60 60

DOI： 10.1246/bcsj.20140121

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Fabrication of dense two-dimensional assemblies over vast areas comprising gold(core)-silver(shell) nanoparticles and their surface-enhanced Raman scattering properties Reviewed

Sugawa K., Tanoue Y., Ube T., Yanagida S., Yamamuro T., Kusaka Y., Ushijima H., Akiyama T.

Photochemical and Photobiological Sciences   13 ( 1 )   82 - 91   2014.1

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Fabrication of dense two-dimensional assemblies consisting of gold(core)-silver(shell) nanoparticles and the resulting peculiar surface-enhanced Raman scattering (SERS) activity are reported. The assemblies were prepared via assembly at air-toluene interfaces by drop-casting toluene solutions containing the nanoparticles protected with octadecylamine molecules onto glass plates. This simple process, which does not require special apparatus or significant fabrication time, leads to uniform assemblies over vast areas (∼34 cm ). In the SERS measurements, the high spatial reproducibility of the SERS signals from p-aminothiophenol adsorbed on the assemblies over vast areas demonstrates that this method is useful for the quantitative investigation of SERS mechanisms. Under 532 nm laser excitation, the difference in the enhancement factors of the SERS signals at the a mode between assemblies consisting of gold, silver, and core-shell nanoparticles can be explained by the degree of overlap of the excitation wavelength with their plasmon coupling modes. In contrast, under 785 nm excitation, even though the plasmon band of the core-shell nanoparticle assemblies does not significantly overlap with the excitation wavelength as compared with that of gold nanoparticle assemblies, the enhancement factor from the core-shell nanoparticle assemblies was stronger than those from the gold nanoparticle assemblies. Therefore, we have demonstrated that the gold(core)-silver(shell) nanoparticle assemblies are excellent SERS active materials, which have strong electromagnetic mechanism (EM) as well as chemical mechanism (CM) effects due to the silver shells. © 2014 The Royal Society of Chemistry and Owner Societies. 2 1

DOI： 10.1039/c3pp50281c

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Fabrication and characterization of TiO<inf>2</inf>/CH<inf>3</inf>NH <inf>3</inf>PbI<inf>3</inf>-based photovoltaic devices Reviewed

Zushi M., Suzuki A., Akiyama T., Oku T.

Chemistry Letters   43 ( 6 )   916 - 918   2014.1

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TiO /CH NH PbI -based photovoltaic devices were fabricated by a spin-coating method using a mixture solution. Photovoltaic properties of the solar cells were investigated by optical absorption, current densityvoltage characteristics, and incident photon to current conversion efficiency. Effects of TiO addition and hole-transport layers were also investigated. Microstructures of the cells were investigated by transmission electron microscopy, which indicated a nanoparticle structure of TiO , and atomic arrangements of Pb atoms in the CH NH PbI crystal were also directly observed. © 2014 The Chemical Society of Japan. 2 3 3 3 2 2 3 3 3

DOI： 10.1246/cl.140127

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Fabrication and characterization of PCBM:P3HT:silicon phthalocyanine bulk heterojunction solar cells with inverted structures Reviewed

Oku T., Hori S., Suzuki A., Akiyama T., Yamasaki Y.

Japanese Journal of Applied Physics   53 ( 5 SPEC. ISSUE 1 )   2014.1

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[6,6]-phenyl C -butyric acid methyl ester and poly(3-hexylthiophene) bulk heterojunction solar cells doped with silicon phthalocyanine (SiPc) were fabricated and characterized. The photovoltaic properties of the solar cells with an inverted structure were improved by the SiPc addition, which were investigated on the bases of current density-voltage characteristics, incident photon to current conversion efficiency, and internal quantum efficiency. The solar cell with the inverted structure also showed good stability in air compared with the normal stacking devices. The microstructure of the solar cells was investigated by X-ray diffraction and transmission electron microscopy, and the carrier separation and transfer of the solar cells were discussed. © 2014 The Japan Society of Applied Physics. 61

DOI： 10.7567/JJAP.53.05FJ08

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Microstructures, optical and photoelectric conversion properties of spherical silicon solar cells with anti-reflection SnO<inf>x</inf>:F thin films Reviewed

Oku T., Kanayama M., Ono Y., Akiyama T., Kanamori Y., Murozono M.

Japanese Journal of Applied Physics   53 ( 5 SPEC. ISSUE 1 )   2014.1

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The microstructures and optical and photoelectric conversion properties of spherical silicon (Si) solar cells were investigated and discussed. The surface of the spherical Si with a pn junction provided high crystallinity, and the lattice constant of the center of Si spheres is larger than that of the surface, which would be due to the lattice distortion by defect structures at the center of Si. The conversion efficiencies of spherical Si solar cells coated with SnO :F anti-reflection thin films were improved by annealing. The optical absorption and fluorescence of the solar cells increased, and the lattice constants of SnO :F anti-reflection layers decreased after annealing. The mechanisms of chemical reactions at the Si/metal interface were also discussed. © 2014 The Japan Society of Applied Physics. x x

DOI： 10.7567/JJAP.53.05FJ03

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Selective implantation of gold nanoparticles onto the surface on one side of a self-standing polymer film Reviewed

Akiyama T., Yoshida K., Yamada S.

RSC Advances   4 ( 107 )   62375 - 62379   2014.1

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A novel method of highly-selective implantation of gold nanoparticles onto one surface of a polymer thin film with sub-micrometer thickness is demonstrated. The poly(methyl methacrylate) (PMMA) film of about 270 nm thickness, where gold nanoparticles (AuNPs) of ∼20 nm diameter were exclusively implanted on one surface, was successfully fabricated. The preparation was carried out by using a water-organic interface at room temperature. The resultant film was self-standing in a loop of as large as about 3 cm diameter. AuNPs were located only at the surface on one side of the PMMA film, which is confirmed using transmission absorption spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. After annealing the PMMA film incorporating AuNPs in hot water, only the surface on one side of the film, where AuNPs were located, became conductive.

DOI： 10.1039/c4ra09553g

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Photovoltaic properties and morphology of organic solar cells based on liquid-crystal semiconducting polymer with additive Reviewed

Suzuki A., Zushi M., Suzuki H., Ogahara S., Akiyama T., Oku T.

AIP Conference Proceedings   1585   164 - 170   2014.1

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Bulk heterojunction organic solar cell based on liquid crystal semiconducting polymers of poly[9,9-dioctylfluorene-co-bithiophene] (F8T2) as p-type semiconductors and fullerenes (C ) and [6,6]-phenyl-C -butyric acid methyl ester (PCBM) as electron donor and acceptor has been fabricated and characterized for improving photovoltaic and optical properties. The photovoltaic performance including current voltage curves in the dark and illumination of the F8T2/C conventional and inverted bulk heterojunction solar cells were investigated. Relationship between the photovoltaic properties and morphological behavior was focused on tuning for optimization of photo-voltaic performance under annealing condition near glass transition temperature. Additive-effect of diiodooctane (DIO) and poly(3-hexylthiophene-2,5-diyl) (P3HT) on the photovoltaic performance and optical properties was investigated. Mechanism of the photovoltaic properties of the conventional and inverted solar cells will be discussed by the experimental results. 60 61 60

DOI： 10.1063/1.4866636

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Effects of phosphorus addition to poly-methyl-phenyl-silane based photovoltaic devices Reviewed

Oku T., Nakagawa J., Suzuki A., Akiyama T., Yamada M., Fukunishi S., Kohno K., Sasaki M.

Physica Status Solidi (C) Current Topics in Solid State Physics   10 ( 12 )   1832 - 1835   2013.12

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Effects of phosphorus addition to poly-methyl-phenyl-silane (PMPS) were investigated for spin-coating thin films. Microstructures of the PMPS thin films were investigated by X-ray diffraction and atomic force microscopy. PMPS thin films doped with phosphorus (P) had an amorphous structure after annealing at 300 °C. Decrease of fluorescence intensity of PMPS was observed by phosphorus doping. Desorption of phenyl and methyl groups in doped PMPS thin films was observed after annealing at 300 °C from Raman scattering measurements and theoretical calculations. Solar cells with PMPS (P)/poly[3-hexylthiophene] bulk heterojunction and heterojunction structures were fabricated, and provided a photovoltaic behavior. Formation mechanism and carrier transport mechanism of the doped PMPS thin films were proposed. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.201300368

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Microstructure analysis and properties of spherical silicon solar cells with anti-reflection thin films Reviewed

Oku T., Kanayama M., Akiyama T., Kanamori Y., Murozono M.

Physica Status Solidi (C) Current Topics in Solid State Physics   10 ( 12 )   1840 - 1843   2013.12

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Structure and properties of spherical silicon solar cells with anti-reflection thin films were investigated and discussed. Conversion efficiencies of spherical Si solar cells coated with F-doped SnO anti-reflection films were improved by annealing. Optical absorption and fluorescence of the solar cells increased after annealing. Lattice constants of F-doped SnO anti-reflection layers, which were investigated by X-ray diffraction, decreased after annealing. Mechanisms of atomic diffusion in SnO and reactions at the Si/metal interface were discussed. The present work indicated a guideline for spherical silicon solar cells with higher efficiencies. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. 2 2 2

DOI： 10.1002/pssc.201300372

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Fabrication and characterization of PCBM: P3HT bulk heterojunction solar cells doped with silicon naphthalocyanine Reviewed

Oku T., Yoshida K., Suzuki A., Akiyama T., Yamasaki Y.

Physica Status Solidi (C) Current Topics in Solid State Physics   10 ( 12 )   1836 - 1839   2013.12

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[6,6]-phenyl C -butyric acid methyl ester: poly(3-hexylthiophene) bulk heterojunction solar cells doped with silicon naphthalocyanine were fabricated and characterized. Photovoltaic properties of the solar cells with inverted structures were investigated by optical absorption, current density-voltage characteristic, incident photon to current conversion efficiency, and internal quantum efficiency. The silicon naphthalocyanine blended as the third component absorbed near-infrared light. Microstructure of the solar cells was investigated by X-ray diffraction, and energy levels of the solar cells were discussed. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. 61

DOI： 10.1002/pssc.201300369

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Mixing effect of gold and silver nanoparticles on enhancement in performance of organic thin-film solar cells Reviewed

Akiyama T., Yamamoto T., Oku T., Yahiro M., Kurihara T., Adachi C., Yamada S.

Japanese Journal of Applied Physics   52 ( 12 )   2013.12

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Bulk-heterojunction organic thin-film solar cells incorporating gold and silver nanoparticles were fabricated and evaluated. These nanoparticles were embedded in the hole-transport layer of the solar cells. Plasmonic absorption peaks of isolated gold and silver nanoparticles were confirmed from extinction spectra even in the hole-transport material. The incorporation of gold and silver nanoparticles increased the photoelectric conversion efficiency of organic thin-film solar cells, whose enhancement ratio was further increased by mixing gold and silver nanoparticles. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.122301

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Effects of phosphorus addition to poly-methyl-phenyl-silane based photovoltaic devices（共著） Reviewed

Oku, Takeo*; Nakagawa, Junya; Suzuki, Atsushi; Akiyama, Tsuyoshi; Yamada, Masahiro; Fukunishi, Sakiko; Kohno, Kazufumi; Sasaki, Muneo.

physica status solidi (c)   10   1832 - 1835   2013.12

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Microstructure analysis and properties of spherical silicon solar cells with anti-reflection thin films（共著） Reviewed

Oku, Takeo*; Kanayama, Masato; Akiyama, Tsuyoshi; Kanamori, Yoichi; Murozono, Mikio.

physica status solidi (c)   10   1840 - 1843   2013.12

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Fabrication and characterization of PCBM:P3HT bulk heterojunction solar cells doped with silicon naphthalocyanine（共著） Reviewed

Oku, Takeo*; Yoshida, Kazumi; Suzuki, Atsushi; Akiyama, Tsuyoshi; Yamasaki Yasuhiro.

physica status solidi (c)   10   1836 - 1839   2013.12

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Effects of phosphorus addition to poly-methyl-phenyl-silane based photovoltaic devices（共著） Reviewed

Oku, Takeo*; Nakagawa, Junya; Suzuki, Atsushi; Akiyama, Tsuyoshi; Yamada, Masahiro; Fukunishi, Sakiko; Kohno, Kazufumi; Sasaki, Muneo.

physica status solidi (c)   10   1832 - 1835   2013.12

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Microstructure analysis and properties of spherical silicon solar cells with anti-reflection thin films（共著） Reviewed

Oku, Takeo*; Kanayama, Masato; Akiyama, Tsuyoshi; Kanamori, Yoichi; Murozono, Mikio.

physica status solidi (c)   10   1840 - 1843   2013.12

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Fabrication and characterization of PCBM:P3HT bulk heterojunction solar cells doped with silicon naphthalocyanine（共著） Reviewed

Oku, Takeo*; Yoshida, Kazumi; Suzuki, Atsushi; Akiyama, Tsuyoshi; Yamasaki Yasuhiro.

physica status solidi (c)   10   1836 - 1839   2013.12

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Metal-enhanced fluorescence platforms based on plasmonic ordered copper arrays: Wavelength dependence of quenching and enhancement effects Reviewed

Sugawa K., Tamura T., Tahara H., Yamaguchi D., Akiyama T., Otsuki J., Kusaka Y., Fukuda N., Ushijima H.

ACS Nano   7 ( 11 )   9997 - 10010   2013.11

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Ordered arrays of copper nanostructures were fabricated and modified with porphyrin molecules in order to evaluate fluorescence enhancement due to the localized surface plasmon resonance. The nanostructures were prepared by thermally depositing copper on the upper hemispheres of two-dimensional silica colloidal crystals. The wavelength at which the surface plasmon resonance of the nanostructures was generated was tuned to a longer wavelength than the interband transition region of copper (>590 nm) by controlling the diameter of the underlying silica particles. Immobilization of porphyrin monolayers onto the nanostructures was achieved via self-assembly of 16-mercaptohexadecanoic acid, which also suppressed the oxidation of the copper surface. The maximum fluorescence enhancement of porphyrin by a factor of 89.2 was achieved as compared with that on a planar Cu plate (CuP) due to the generation of the surface plasmon resonance. Furthermore, it was found that while the fluorescence from the porphyrin was quenched within the interband transition region, it was efficiently enhanced at longer wavelengths. It was demonstrated that the enhancement induced by the proximity of the fluorophore to the nanostructures was enough to overcome the highly efficient quenching effects of the metal. From these results, it is speculated that the surface plasmon resonance of copper has tremendous potential for practical use as high functional plasmonic sensor and devices. © 2013 American Chemical Society.

DOI： 10.1021/nn403925d

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Mixing Effect of Gold and Silver Nanoparticles on Enhancement in Performance of Organic Thin-Film Solar Cells（共著） Reviewed

Akiyama, Tsuyoshi*; Yamamoto, Tomoki; Oku, Takeo; Yahiro, Masayuki; Kurihara, Takashi; Adachi, Chihaya; Yamada, Sunao.

Japanese Journal of Applied Physics   52   1222301(1) - 1222301(4)   2013.11

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Densely arranged two-dimensional silver nanoparticle assemblies with optical uniformity over vast areas as excellent surface-enhanced Raman scattering substrates Reviewed

Tanoue Y., Sugawa K., Yamamuro T., Akiyama T.

Physical Chemistry Chemical Physics   15 ( 38 )   15802 - 15805   2013.10

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Dense two-dimensional assemblies of silver nanoparticles were fabricated over vast areas (∼19 cm ) by utilizing a simple liquid-liquid interface assembly technique. The Raman signal for p-aminothiophenol immobilized on the assemblies was drastically enhanced by plasmon coupling-induced hot spots, and the enhanced signal showed high spatial reproducibility. © 2013 the Owner Societies. 2

DOI： 10.1039/c3cp52400k

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Fabrication and characterization of fullerene-based solar cells containing phthalocyanine and naphthalocyanine dimers（共著） Reviewed

Takeda, Akihiro; Oku, Takeo*; Suzuki, Atsushi, Akiyama, Tsuyoshi; Yamasaki, Yasuhiro.

Synthetic Metals   177   48 - 51   2013.8

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Fabrication and characterization of ZnO/Cu<inf>2</inf>O solar cells prepared by electrodeposition Reviewed

Fujimoto K., Oku T., Akiyama T.

Applied Physics Express   6 ( 8 )   2013.8

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Cuprous oxide (Cu O)-based solar cells containing zinc oxide (ZnO) were fabricated on F-doped tin oxide (FTO) by electrodeposition. Cu O layers were deposited from a pH-adjusted electrolyte consisting of LiOH, NaOH or KOH. A photovoltaic device based on a FTO/ZnO/Cu O/Au heterojunction structure was prepared using LiOH, and it gave a power conversion efficiency of 1.43% under air mass 1.5 illumination. © 2013 The Japan Society of Applied Physics. 2 2 2

DOI： 10.7567/APEX.6.086503

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Densely arranged two-dimensional silver nanoparticleassemblies with optical uniformity over vast areas asexcellent surface-enhanced Raman scattering substrates（共著） Reviewed

Tanoue, Yoshimasa; Sugawa, Kosuke*; Yamamuro, Takahiro; Akiyama, Tsuyoshi*.

Physical Chemistry Chemical Physics   15   15802 - 15805   2013.7

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Fabrication and Characterization of ZnO/Cu2O Solar Cells Prepared by Electrodeposition（共著） Reviewed

Fujimoto, Kazuya; Oku, Takeo*; Akiyama, Tsuyoshi.

Applied Physics Express   6   086503(1) - 086503(4)   2013.7

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Fabrication and characterization of fullerene-based solar cells containing phthalocyanine and naphthalocyanine dimers Reviewed

Takeda A., Oku T., Suzuki A., Akiyama T., Yamasaki Y.

Synthetic Metals   177   48 - 51   2013.7

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Fullerene-based solar cells with normal and inverted structures containing phthalocyanine and naphthalocyanine dimers were fabricated by vacuum evaporation. Power conversion efficiencies were measured under simulated sunlight conditions. Fabricated devices exhibited high stability in air and a wide optical absorption from 320 to 800 nm. A carrier transport mechanism is proposed based on the energy level diagram. © 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.synthmet.2013.06.011

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Preparation and photovoltaic application of fullereneporphyrin composite micropowder Reviewed

Kimura K., Oku T., Akiyama T.

Chemistry Letters   42 ( 7 )   694 - 696   2013.7

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C fullerene and 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAPP) composite micropowder was prepared by simply mixing C and TAPP in an organic solvent under ambient conditions. The composite micropowder contributed to photoelectric conversion, which was confirmed by a semi-wet-type photovoltaic application. © 2013 The Chemical Society of Japan. 60 60

DOI： 10.1246/cl.130114

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Microstructures and photovoltaic properties of C<inf>60</inf> based solar cells with copper oxides, CuInS<inf>2</inf>, phthalocyanines, porphyrin, PVK, nanodiamond, germanium and exciton diffusion blocking layers Reviewed

Oku T., Takeda A., Nagata A., Kidowaki H., Kumada K., Fujimoto K., Suzuki A., Akiyama T., Yamasaki Y., Osawa E.

Energy Materials: Materials Science and Engineering for Energy Systems   8 ( 1 )   21 - 39   2013.6

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Organic solar cells have a potential for use in lightweight, flexible, inexpensive and large scale solar cells. However, significant improvements of photovoltaic efficiencies are mandatory for use in future solar power plants. One of the improvements is donor-acceptor proximity in the devices, which are called bulk heterojunction solar cells. Bulk heterojunction is an efficient method to generate free charge carriers, and the charge transfer is possible at the semiconductor interface. The purpose of the present work is to fabricate and characterise C based solar cells with copper oxides, CuInS , phthalocyanines, porphyrin, poly-vinylcarbazole, nanodiamond, germanium and exciton diffusion blocking layers. In the present work, C and fullerenol [C (OH)10-12] were used for n-type semiconductors, and metal copper oxides, metal phthalocyanine derivative, porphyrin and poly-vinylcarbazole were used for p-type semiconductors. In addition, nanodiamond and germanium based molecules were added into the active layers of the solar cells. The novel aspect of the research is to investigate the relation between properties and microstructures of the solar cells using transmission electron microscopy, X-ray diffraction and electronic structure calculation. The impact of the research concerns the study of organic solar cells by means of microstructural analysis, property measurements and theoretical calculations. © 2013 W. S. Maney & Son Ltd. 60 2 60 60

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Incorporation Effect of Silver Nanoparticles on Inverted Type Bulk-Heterojunction Organic Solar Cells（共著） Reviewed

Matsumoto, Taisuke; Oku, Takeo; Akiyama, Tsuyoshi*.

Japanese Journal of Applied Physics   52   04CR13(1) - 04CR13(5)   2013.4

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Fabrication of C60 assembly films via an fullerene-amine addition reaction by using stepwise immersion（共著） Reviewed

Banya, Shoto; Matsumoto, Taisuke; Oku, Takeo; Akiyama, Tsuyoshi*.

Journal of Physics: Conference Series   433   012007(1) - 012007(5)   2013.4

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Effects of phosphorous doping to poly (methylphenyl silane) and fabrication of thin film solar cells（共著） Reviewed

Nakagawa, Junya; Oku, Takeo; Suzuki, Atsushi; Akiyama, Tsuyoshi; Tokumitsu, Katsuhisa; Yamada, Masahiro; Nakamura, Mika.

Journal of Physics: Conference Series   433   012026(1) - 012026(7)   2013.4

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Fabrication and characterization of silicon naphthalocyanine,gallium phthalocyanine and fullerene-based organic solar cellswith inverted structures（共著） Reviewed

Oku, Takeo; Nose, Shigefumi; Yoshida, Kazumi; Suzuki, Atsushi; Akiyama, Tsuyoshi; Yamasaki, Yasuhiro.

Journal of Physics: Conference Series   433   012025(1) - 012025(7)   2013.4

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Fabrication and characterization of copper oxide-zinc oxidesolar cells prepared by electrodeposition（共著） Reviewed

Fujimoto, Kazuya; Oku, Takeo; Akiyama, Tsuyoshi; Suzuki, Atsushi.

Journal of Physics: Conference Series   433   012024(1) - 012024(7)   2013.4

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Fabrication and characterization of polymer tandem solar cells（共著） Reviewed

Marsuhashi, Haruto*; Suzuki, Atsushi; Akiyama, Tsuyoshi; Oku, Takeo.

Journal of Physics: Conference Series   433   012023(1) - 012023(6)   2013.4

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Photochemical half-cells using mixture films of fullerene-ethylenediamine adduct microparticles and polythiophene（共著） Reviewed

Akiyama, Tsuyoshi*; Matsumura, Satoshi; Matsuoka, Ken-ichi; Oku, Takeo; Yamada, Sunao.

Journal of Physics: Conference Series   433   012010(1) - 012010(6)   2013.4

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Fabrication of C60 assembly films via an fullerene-amine addition reaction by using stepwise immersion（共著） Reviewed

Banya, Shoto; Matsumoto, Taisuke; Oku, Takeo; Akiyama, Tsuyoshi*.

Journal of Physics: Conference Series   433   012007(1) - 012007(5)   2013.4

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Effects of phosphorous doping to poly (methylphenyl silane) and fabrication of thin film solar cells（共著） Reviewed

Nakagawa, Junya; Oku, Takeo; Suzuki, Atsushi; Akiyama, Tsuyoshi; Tokumitsu, Katsuhisa; Yamada, Masahiro; Nakamura, Mika.

Journal of Physics: Conference Series   433   012026(1) - 012026(7)   2013.4

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Fabrication and characterization of silicon naphthalocyanine,gallium phthalocyanine and fullerene-based organic solar cellswith inverted structures（共著） Reviewed

Oku, Takeo; Nose, Shigefumi; Yoshida, Kazumi; Suzuki, Atsushi; Akiyama, Tsuyoshi; Yamasaki, Yasuhiro.

Journal of Physics: Conference Series   433   012025(1) - 012025(7)   2013.4

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Fabrication and characterization of copper oxide-zinc oxidesolar cells prepared by electrodeposition（共著） Reviewed

Fujimoto, Kazuya; Oku, Takeo; Akiyama, Tsuyoshi; Suzuki, Atsushi.

Journal of Physics: Conference Series   433   012024(1) - 012024(7)   2013.4

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Fabrication and characterization of polymer tandem solar cells（共著） Reviewed

Marsuhashi, Haruto*; Suzuki, Atsushi; Akiyama, Tsuyoshi; Oku, Takeo.

Journal of Physics: Conference Series   433   012023(1) - 012023(6)   2013.4

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Photochemical half-cells using mixture films of fullerene-ethylenediamine adduct microparticles and polythiophene（共著） Reviewed

Akiyama, Tsuyoshi*; Matsumura, Satoshi; Matsuoka, Ken-ichi; Oku, Takeo; Yamada, Sunao.

Journal of Physics: Conference Series   433   012010(1) - 012010(6)   2013.4

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Microstructure Analysis and Properties of Anti-Reflection Thin Films for Spherical Silicon Solar Cells（共著） Reviewed

Kanayama, Masato; Oku, Takeo*; Akiyama, Tsuyoshi; Kanamori, Youichi; Seo, Satoshi; Takami, Jun; Ohnishi, Yoshimasa; Ohtani, Yoshikazu; Murozono, Mikio.

Energy and Power Engineering   5   18 - 22   2013.4

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Fabrication and Characterization of PCBM:P3HT Bulk Heterojunction Solar Cells Doped with Germanium Phthalocyanine or Germanium Naphthalocyanine（共著） Reviewed

Yoshida, Kazumi; Oku, Takeo*; Suzuki, Atsushi; Akiyama, Tsuyoshi; Yamasaki, Yasuhiro.

Materials Sciences and Applications   4   1 - 5   2013.4

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Microstructure Analysis and Properties of Anti-Reflection Thin Films for Spherical Silicon Solar Cells（共著） Reviewed

Kanayama, Masato; Oku, Takeo*; Akiyama, Tsuyoshi; Kanamori, Youichi; Seo, Satoshi; Takami, Jun; Ohnishi, Yoshimasa; Ohtani, Yoshikazu; Murozono, Mikio.

Energy and Power Engineering   5   18 - 22   2013.4

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Fabrication and Characterization of PCBM:P3HT Bulk Heterojunction Solar Cells Doped with Germanium Phthalocyanine or Germanium Naphthalocyanine（共著） Reviewed

Yoshida, Kazumi; Oku, Takeo*; Suzuki, Atsushi; Akiyama, Tsuyoshi; Yamasaki, Yasuhiro.

Materials Sciences and Applications   4   1 - 5   2013.4

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Incorporation effect of silver nanoparticles on inverted type bulk-heterojunction organic solar cells Reviewed

Matsumoto T., Oku T., Akiyama T.

Japanese Journal of Applied Physics   52 ( 4 PART 2 )   2013.4

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A series of bulk-heterojunction organic solar cells incorporating silver nanoparticles was fabricated and evaluated. Silver nanoparticles were incorporated in the hole-transport layer of the solar cells. Plasmonic absorption and the generation of localized surface plasmon resonance of silver nanoparticles were confirmed by absorption and surface enhanced Raman scattering spectra even in the hole-transport material. The incorporation of silver nanoparticles increased photoelectric conversion efficiencies, whose enhancement properties were varied by the incorporation amount of silver nanoparticles. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.04CR13

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Microstructures and photovoltaic properties of polysilane-based solar cells Reviewed

Oku T., Nakagawa J., Iwase M., Kawashima A., Yoshida K., Suzuki A., Akiyama T., Tokumitsu K., Yamada M., Nakamura M.

Japanese Journal of Applied Physics   52 ( 4 PART 2 )   2013.4

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Polysilane-based organic solar cells with bulk heterojunction and heterojunction structures were fabricated by spin-coating using a mixture solution. Microstructures of the solar cells were investigated by X-ray diffraction analysis and transmission electron microscopy, which indicated a nanocomposite and amorphous structure. The effects of phosphorus and boron doping into polysilanes were investigated by electrical measurements, Raman scattering analysis and Hall effect measurements. Here, we discuss the photovoltaic properties and microstructures of the solar cells. Energy levels in the present solar cells are also discussed. © 2013 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.52.04CR07

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Fabrication and characterization of polysilane: PCBM bulk heterojunction solar cells（共著） Reviewed

Yoshida, Kazumi; Oku, Takeo*; Suzuki, Atsushi; Akiyama, Tsuyoshi; Tokumitsu, Katsuhisa; Nakamura, Mika; Yamada Masahiro.

Central European Journal of Engineering   3   165 - 169   2013.4

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Microstructures and photovoltaic properties of polysilane-based solar cells（共著） Reviewed

Oku, Takeo*; Nakagawa, Junya; Iwase, Makoto; Kawashima, Atsushi; Yoshida, Kazumi; Suzuki, Atsushi; Akiyama, Tsuyoshi; Tokumitsu, Katsuhisa; Yamada, Masahiro; Nakamura, Mika.

Japanese Journal of Applied Physics   52   04CR07(1) - 04CR07(5)   2013.3

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Microstructures and photovoltaic properties of C60 based solar cells with copper oxides, CuInS2, phthalocyanines, porphyrin, PVK, nanodiamond, germanium and exciton diffusion blocking layers Reviewed

Materials Technology   28 ( - )   21 - 39   2013.3

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DOI： 10.1179/1753555712Y.0000000042

Facile Solubilization and Photovoltaic Application of C60 Fullerene-Ethylenediamine Adduct Reviewed

Tsuyoshi Akiyama, Taiki Ueda, Yuji Ono, Kento Kimura, Ken-ichi Matsuoka, Sunao Yamada, and Takeo Oku

Chemistry Letters   42 ( 2 )   177 - 179   2013.2

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DOI： 10.1246/cl.2013.177

Preparation and Photovoltaic Application of Fullerene–Porphyrin Composite Micropowder（共著） Reviewed

Kimura, Kento; Oku, Takeo; Akiyama, Tsuyoshi*.

Chemistry Letters   42   694 - 696   2013.2

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Effects of phosphorous doping to poly (methylphenyl silane) and fabrication of thin film solar cells Reviewed

Nakagawa J., Oku T., Suzuki A., Akiyama T., Tokumitsu K., Yamada M., Nakamura M.

Journal of Physics: Conference Series   433 ( 1 )   2013.1

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Effects of phosphorus bromine (PBr ) doping to polysilane were investigated for spin-coating thin films. Phosphorus doped poly (methylphenyl silane) (PMPS) provided n-type semiconductor behavior, which was confirmed by Hall effect measurements. Desorption of phenyl and methyl groups in doped PMPS thin films was observed after annealing at 300 °C from Raman scattering measurements and theoretical calculations. The band gap energy of PMPS was measured to be 3.2 eV. Decrease of photoluminescence intensity of PMPS was observed by phosphorus doping. Microstructures of the doped PMPS thin films were investigated by using X-ray diffraction, which indicated doped PMPS had an amorphous structure after annealing. A solar cell with PMPS(PBr ):poly[3-hexylthiophene] bulk-heterojunction structure was fabricated, and provided a photovoltaic behavior. Formation mechanism and carrier transport mechanism of the doped PMPS thin films were proposed. 3 3

DOI： 10.1088/1742-6596/433/1/012026

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Fabrication of C<inf>60</inf> assembly films via an fullerene-amine addition reaction by using stepwise immersion Reviewed

Banya S., Matsumoto T., Oku T., Akiyama T.

Journal of Physics: Conference Series   433 ( 1 )   2013.1

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Fullerene C thin films were successfully fabricated on the surface of amino-substituted substrates via a reaction between C and an NH group of 1,2-diaminoethane (DAE) using simple immersion processes. The maximum thicknesses of the fullerene assembled films increased with the number of immersions into the fullerene solution. Layered fullerenes were obtained by a series of repeated processes. The aggregated C thin films were evaluated using transmission absorption measurements, transmission electron microscopy, and atomic force microscopy. These analyses suggest the presence of C -DAE aggregates on the substrates. 60 60 2 60 60

DOI： 10.1088/1742-6596/433/1/012007

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Fabrication and characterization of silicon naphthalocyanine, gallium phthalocyanine and fullerene-based organic solar cells with inverted structures Reviewed

Oku T., Nose S., Yoshida K., Suzuki A., Akiyama T., Yamasaki Y.

Journal of Physics: Conference Series   433 ( 1 )   2013.1

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Fullerene/phthalocyanine solar cells with inverted structures were fabricated, and the photovoltaic properties, optical absorption and microstructrues were investigated. Silicon naphthalocyanine, gallium phthalocyanine, and poly(3-hexylthiophene) were used for donor materials, and 6,6-phenyl C -butyric acid methyl ester was also used as an acceptor material. The solar cells with the inverted structure provided higher conversion efficiencies by addition of silicon naphthalocyanine, and had more stability compared to that with normal structure in the air. Nanostructures of the solar cells were investigated by transmission electron microscopy, which indicated the dispersion of nanocrystals in the active layers. Energy levels of the molecules were calculated, and a carrier transport mechanism was proposed. 61

DOI： 10.1088/1742-6596/433/1/012025

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Fabrication and characterization of polysilane: PCBM bulk heterojunction solar cells Reviewed

Yoshida K., Oku T., Suzuki A., Akiyama T., Tokumitsu K., Nakamura M., Yamada M.

Central European Journal of Engineering   3 ( 2 )   165 - 169   2013.1

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Polysilane/fullerene bulk heterojunction solar cells were fabricated on indium tin oxide electrodes by a spin-coating method, and performance and microstructures of the solar cells were investigated. Decaphenylcyclopentasilane (PDPS), polymethlyphenylsilane (PMPS) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) were used for the solar cells. The conversion efficiencies of PDPS:PCBM solar cells were higher than those of PMPS:PCBM devises. Transmission electron microscopy and X-ray diffraction indicated that PDPS:PCBM layer had a nanocomposite structure.

DOI： 10.2478/s13531-012-0057-6

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Fabrication and characterization of polymer tandem solar cells Reviewed

Maruhashi H., Suzuki A., Akiyama T., Oku T.

Journal of Physics: Conference Series   433 ( 1 )   2013.1

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Polymer tandem solar cells were fabricated and characterized. Copolymer poly(3-hexylthiophene-2,5-diyl) (P3HT) and poly((4,4-octyldithieno(3,2-b:20,30- d)silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl) (PSBTBT) were used as p-type semiconductors, and [6,6]-phenyl-C -butyric acid methyl ester (PCBM) was used as an n-type semiconductor. The open circuit voltage was improved up to 0.69 V by using the tandem structure of P3HT:PCBM and PSBTBT:PCBM layers as compared with those of P3HT:PCBM and PSBTBT:PCBM single cell of 0.53 V and 0.10 V, respectively. Absorption of the tandem cell was in the range of 400 to 800 nm, which corresponded to a sum of those in P3HT:PCBM and PSBTBT:PCBM single cells. 61

DOI： 10.1088/1742-6596/433/1/012023

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Fabrication and characterization of copper oxide-zinc oxide solar cells prepared by electrodeposition Reviewed

Fujimoto K., Oku T., Akiyama T., Suzuki A.

Journal of Physics: Conference Series   433 ( 1 )   2013.1

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Copper oxide-based heterojunction solar cells were fabricated by electrodeposition, and the electronic and optical properties were investigated. ZnO was used as an n-type semiconductor, and copper oxides were used as p-type semiconductors. A photovoltaic device based on an FTO/ZnO/Cu O heterojunction structure provided short-circuit current density of 2.7 mAcm and open circuit voltage of 0.28 V under an air mass 1.5 illumination. Microstructures of the solar cells were investigated by scanning electron microscope and X-ray diffraction, which indicated formation of copper oxides and ZnO. Energy levels of the solar cells were discussed. 2 -2

DOI： 10.1088/1742-6596/433/1/012024

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Photochemical half-cells using mixture films of fullerene-ethylenediamine adduct microparticles and polythiophene Reviewed

Akiyama T., Matsumura S., Matsuoka K., Oku T., Yamada S.

Journal of Physics: Conference Series   433 ( 1 )   2013.1

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In this study, C fullerene-ethylenediamine adduct microparticles were prepared. Mixture films of these microparticles and polythiophene were fabricated on indium-tin-oxide transparent electrodes by spin-coating. Incorporation of C -ethylenediamine microparticles was verified by scanning electron microscopy (SEM) measurements. The coverage values of these microparticles were approximately 3-17%, which were calculated from SEM images of modified electrodes. Fluorescence spectra of modified electrodes indicated that the emission intensity of polythiophene in these mixture films was apparently quenched by these C -ethylenediamine microparticles as compared with a polythiophene film without these microparticles. In the presence of methylviologen, these modified electrodes generated stable photocurrent. The photoexciting species was polythiophene, which was verified by profiles of photocurrent action spectra. The C -ethylenediamine microparticles substantially enhanced the photocurrent signals generated by the polythiophene-modified electrode. 60 60 60 60

DOI： 10.1088/1742-6596/433/1/012010

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Metal-Enhanced Fluorescence Platforms Based on Plasmonic Ordered Copper Arrays: Wavelength Dependence of Quenching and Enhancement Effects（共著） Reviewed

Sugawa, Kosuke*; Tamura, Takahiro; Tahara, Hironobu; Yamaguchi, Daisuke; Akiyama, Tsuyoshi; Otsuki, Joe; Kusaka, Yasuyuki; Fukuda, Nobuko; Ushijima, Hirobumi.

ACS Nano   7   9997 - 10010   2013.1

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Fabrication and characterization of heterojunction solar cells of hexadecafluorophthalocyanine/metal phthalocyanine Reviewed

Suzuki A., Mizuno A., Oku T., Akiyama T., Yamasaki Y.

Proceedings of SPIE - The International Society for Optical Engineering   8409   2012.12

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Fluorophthlocyanine thin films were used as n-type semiconductor in organic solar cell. Heterojunction solar cells of cupper hexadecafluorophthalocyanine (F CuPc) / copper phthalocyanine (CuPc) and F CuPc / zinc phthalocyanine (ZnPc) deposited with PEDOT-PSS on ITO as electrode were fabricated and characterized. Comparison between CuPc and ZnPc as p-type semiconductor on photovoltaic performance was studied. Light-induced charge separation and charge transfer was investigated by current density and optical absorption. Internal microstructure in active layer was measured by transmission electron microscopy, X-ray and electron diffractions. The F CuPc thin film in the deposited active layer worked for electron-accepting layer as n-type semiconductor. The photovoltaic performance was original in charge transfer from CuPc to F CuPc in active layer. © 2012 SPIE. 16 16 16 16

DOI： 10.1117/12.921210

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Fabrication and Characterization of Bulk Heterojunction Solar Cells Based on Liquid-Crystal Semiconductive Polymer Reviewed

Atsushi Suzuki, Shinichi Ogahara, Tsuyoshi Akiyama, Takeo Oku

Energy and Power Engineering   4 ( - )   459 - 464   2012.11

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DOI： 10.4236/epe.2012.46060

FABRICATION AND EVALUATION OF CuO/ZnO HETEROSTRUCTURES FOR PHOTOELECTRIC CONVERSION Reviewed

Hiroki Kidowaki, Takeo Oku & Tsuyoshi Akiyama

International Journal of Research and Reviews in Applied Sciences   13 ( 1 )   67 - 72   2012.10

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Fabrication and Characterization of Poly[Decaphenylcyclopentasilane]-Based Solar Cells Reviewed

Makoto Iwase, Takeo Oku, Atsushi Suzuki, Tsuyoshi Akiyama, Katsuhisa Tokumitsu, Masahiro Yamada, Mika Nakamura

Advances in Materials Physics and Chemistry   2 ( 3 )   121 - 125   2012.9

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DOI： 10.4236/ampc.2012.23020

Fabrication and characterization of tetracyanoquinodimethane/phthalocyanine solar cells Reviewed

Atsushi Suzuki, Takahiro Ohtsuki, Takeo Oku, Tsuyoshi Akiyama

Materials Science and Engineering: B   177 ( 11 )   877 - 881   2012.6

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DOI： 10.1016/j.mseb.2012.03.052

Electropolymerized Polythiophene Photoelectrodes with Density-Controlled Gold Nanoparticles Reviewed

Yukina Takahashi, Sakiko Taura, Tsuyoshi Akiyama, and Sunao Yamada

Langmuir   28 ( - )   9155 - 9160   2012.6

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DOI： 10.1021/la300227j

Facile Fabrication and Raman Scattering Enhancement Properties of Mixed Gold and Silver Nanoparticle Layers Reviewed

Tsuyoshi Akiyama

e-Journal of Surface Science and Nanotechnology   10 ( - )   157 - 160   2012.4

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DOI： 10.1380/ejssnt.2012.157

Tuning Optical Properties of Two-Dimensional Ordered Arrays of Silica/Gold and Silver Core/Shell Structured Nanoparticles in Near-Infrared Region Reviewed

Kosuke Sugawa, Tatsuya Sakai, Daido Tanaka, and Tsuyoshi Akiyama

Japanese Journal of Applied Physics   51 ( - )   04DH04-1 - 04DH04-5   2012.4

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DOI： 10.1143/JJAP.51.04DH04

Organic Solar Cells Based on Electrodeposited Polyaniline Films Reviewed

Kei Inoue, Tsuyoshi Akiyama, Atsushi Suzuki, and Takeo Oku

Japanese Journal of Applied Physics   51 ( - )   04DK10-1 - 04DK10-4   2012.4

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DOI： 10.1143/JJAP.51.04DK10

Fabrication and characterization of poly[diphenylsilane]-based solar cells "jointly worked" Reviewed

M. Iwase, T. Oku, A. Suzuki, T. Akiyama, K. Tokumitsu, M. Yamada, M. Nakamura

Journal of Physics: Conference Series   352   012018-1 - 012018-5   2012.3

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Microstructure analysis of spherical silicon solar cells coated with anti-reflection films "jointly worked" Reviewed

Y. Ono, T. Oku, T. Akiyama, Y. Kanamori, Y. Ohnishi, Y. Ohtani, M. Murozono

Journal of Physics: Conference Series   352   012023-1 - 012023-5   2012.3

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Fabrication and characterization of CuO/ZnO solar cells "jointly worked" Reviewed

H. Kidowaki, T. Oku, T. Akiyama

Journal of Physics: Conference Series   352   012022-1 - 012022-5   2012.3

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Fabrication and characterization of polysilane/C60 thin film solar cells "jointly worked" Reviewed

J. Nakagawa, T. Oku, A. Suzuki, T. Akiyama, K. Tokumitsu, M. Yamada and M. Nakamura

Journal of Physics: Conference Series   352   012019-1 - 012019-5   2012.3

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Microstructures and photovoltaic properties of fullerene-based organic-inorganic hybrid solar cells "jointly worked" Reviewed

T. Oku, A. Takeda, A. Nagata, K. Fujimoto, T. Akiyama, A. Suzuki

Journal of Physics: Conference Series   352   012024-1 - 012024-9   2012.3

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Effects of Film Thickness on the Photocurrent Generation from Polythiophene-Fullerene Thin Films Containing Silver Nanoparticles "jointly worked" Reviewed

Jing You, Yukina Takahashi, Hiroaki Yonemura, Tsuyoshi Akiyama, Sunao Yamada

Japanese Journal of Applied Physics   51   02BK04-1 - 02BK04-4   2012.2

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Photocurrent enhancement tuned with plasmonic resonance in self-assembled monolayers fabricated on regularly arrayed gold nanostructures Reviewed

Kosuke Sugawa, Shuichi Hirono, Tsuyoshi Akiyama and Sunao Yamada

Photochemical & Photobiological Sciences   11 ( 2 )   318 - 322   2012.2

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DOI： 10.1039/c1pp05229b

Effects of film thickness on the photocurrent generation from polythiophene-fullerene thin films containing silver nanoparticles Reviewed

You J., Takahashi Y., Yonemura H., Akiyama T., Yamada S.

Japanese Journal of Applied Physics   51 ( 2 PART 2 )   2012.2

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We have investigated the incident-photon-to-current conversion efficiency (IPCE) of thin films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl- C -butyric acid methylester (PCBM) as a function of film thickness, in the presence or absence of silver nanoparticles (AgPs) between the films and the indium-tin-oxide (ITO) electrode. The thickness of the film was evaluated by atomic force microscopy. The absorption and photocurrent action spectra of the films were measured to investigate the effect of the thickness of the P3HT:PCBM film. The results show that IPCE increased steeply in thinner films and the optimal range of thicknesses of the P3HT:PCBM film was 50-120 nm. In this optimal range, the IPCEs were 1.5- 1.8 times larger in the presence of AgPs. © 2012 The Japan Society of Applied Physics. 61

DOI： 10.1143/JJAP.51.02BK04

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Fabrication and characterization of CuO/ZnO solar cells Reviewed

Kidowaki H., Oku T., Akiyama T.

Journal of Physics: Conference Series   352 ( 1 )   2012.1

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Cuprous oxide (CuO) and zinc oxide (ZnO) heterojunction solar cells fabricated on indium tin oxide-coated glass were studied. CuO and ZnO films were deposited using a galvanostatic method. Structural, morphological and optoelectronic properties of the CuO/ZnO heterojunction were studied by using X-ray diffraction, atomic force microscopy and light current-voltage characteristics. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/352/1/012022

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Microstructures and photovoltaic properties of fullerene-based organic-inorganic hybrid solar cells Reviewed

Oku T., Takeda A., Nagata A., Fujimoto K., Akiyama T., Suzuki A.

Journal of Physics: Conference Series   352 ( 1 )   2012.1

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C -based bulk heterojunction solar cells were fabricated, and the electronic and optical properties were investigated. C were used as n-type semiconductors, and copper oxides, CuInS and diamond were used as p-type semiconductors. Electronic structures of the molecules were investigated by molecular orbital calculation, and energy levels of the solar cells were discussed. Nanostructures of the solar cells were investigated by transmission electron microscopy, electron diffraction and X-ray diffraction, which indicated formation of mixed nanocrystals. © Published under licence by IOP Publishing Ltd. 60 60 2

DOI： 10.1088/1742-6596/352/1/012024

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Microstructure analysis of spherical silicon solar cells coated with anti-reflection films Reviewed

Ono Y., Oku T., Akiyama T., Kanamori Y., Ohnishi Y., Ohtani Y., Murozono M.

Journal of Physics: Conference Series   352 ( 1 )   2012.1

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Microstructures of spherical silicon solar cells were investigated by transmission electron microscopy and X-ray diffraction. Optical absorption and photoluminescence of the solar cells were also measured by UV-visible and fluorescence spectroscopy. F-doped SnO anti-reflection coating layers were investigated by XRD, and the nanostructures and grain sizes were determined. The present work indicated a guideline for spherical silicon solar cells with higher efficiencies. © Published under licence by IOP Publishing Ltd. 2

DOI： 10.1088/1742-6596/352/1/012023

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Fabrication and characterization of polysilane/C<inf>60</inf> thin film solar cells Reviewed

Nakagawa J., Oku T., Suzuki A., Akiyama T., Tokumitsu K., Yamada M., Nakamura M.

Journal of Physics: Conference Series   352 ( 1 )   2012.1

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Polysilane/fullerene bulk heterojunction solar cells were fabricated on indium tin oxide electrode by a spin-coating method, and performance and microstructures of the solar cell were investigated. Poly-methyl-phenylsilane, poly-phenylsilane, deca-phenyl-cyclopentasilane and [6,6]-phenyl C -butyric acid methyl ester (PCBM), poly[3-hexylthiophene] (P3HT) were used for the present cells. A device based on the P3HT and PCBM provided better efficiency, fill factor, and short-circuit current compared to those of a device based on P3HT and fullerene. © Published under licence by IOP Publishing Ltd. 61

DOI： 10.1088/1742-6596/352/1/012019

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Fabrication and characterization of poly[diphenylsilane]-based solar cells Reviewed

Iwase M., Oku T., Suzuki A., Akiyama T., Tokumitsu K., Yamada M., Nakamura M.

Journal of Physics: Conference Series   352 ( 1 )   2012.1

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Poly[diphenylsilane] (PDPS)-based photovoltaic cells were fabricated by using mixture solution of PDPS, phosphorus and boron. An influence of phosphorus and boron doping into PDPS on the performance of the photovoltaic device was investigated. The solar cell using fluorine doped tin oxide glass plates provided short-circuit current density of 0.12 mA/cm and open-circuit voltage of 0.28 V under simulated sunlight. Energy levels, formation mechanism and microstructure of the solar cells were discussed. © Published under licence by IOP Publishing Ltd. 2

DOI： 10.1088/1742-6596/352/1/012018

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Fabrication and Characterization of CuO-based Solar Cells "jointly worked" Reviewed

Hiroki Kidowaki, Takeo Oku, Tsuyoshi Akiyama, Atsushi Suzuki Balachandran Jeyadeva, Jhon Cuya

Journal of Materials Science Research   1   138 - 143   2012.1

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Effects of Au nanoparticle addition to hole transfer layer in organic photovoltaic cells based on phthalocyanines and fullerene Reviewed

Nagata A., Oku T., Akiyama T., Suzuki A., Yamasaki Y., Mori T.

Journal of Nanotechnology   2011.12

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Phthalocyanines/fullerene organic photovoltaic cells were fabricated and characterized. Effects of Au nanoparticle addition to a hole transfer layer were also investigated, and power conversion efficiencies of the photovoltaic cells were improved after blending the Au nanoparticle into PEDOT:PSS. Nanostructures of the Au nanoparticles were investigated by transmission electron microscopy and X-ray diffraction. Energy levels of molecules were calculated by molecular orbital calculations, and the nanostructures and electronic property were discussed. Copyright © 2011 Akihiko Nagata et al.

DOI： 10.1155/2011/869596

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Effects on Au Nanoparticle Addition to Hole Transfer Layer in Organic Photovoltaic Cells Based on Phthalocyanines and Fullerene "jointly worked" Reviewed

A. Nagata, T. Oku, T. Akiyama, A. Suzuki, Y. Yamasaki, T. Mori

Journal of Nanotechnology   2011   869596-1 - 869596-6   2011.12

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Photocurrent enhancement tuned with plasmonic resonance in self-assembled monolayers fabricated on regularly arrayed gold nanostructures "jointly worked" Reviewed

Kosuke Sugawa, Shuichi Hirono, Tsuyoshi Akiyama, Sunao Yamada

Photochemical & Photobiological Sciences   11   318 - 322   2011.11

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Structures and photovoltaic properties of copper oxides/fullerene solar cells Reviewed

Oku T., Motoyoshi R., Fujimoto K., Akiyama T., Jeyadevan B., Cuya J.

Journal of Physics and Chemistry of Solids   72 ( 11 )   1206 - 1211   2011.11

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Copper oxide (CuO ) thin films were produced by spin-coating and electrodeposition methods, and their microstructures and photovoltaic properties were investigated. Thin film solar cells based on the Cu O/C and CuO/C heterojunction or bulk heterojunction structures were fabricated on F-doped or In-doped SnO , which showed photovoltaic activity under air mass 1.5 simulated sunlight conditions. Microstructures of the CuO thin films were examined by X-ray diffraction and transmission electron microscopy, which indicated the presence of Cu O and CuO nanoparticles. The energy levels of the present solar cells were also discussed. © 2011 Elsevier Ltd. All rights reserved. x 2 60 60 2 x 2

DOI： 10.1016/j.jpcs.2011.06.014

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Structures and photovoltaic properties of copper oxides/fullerene solar cells "jointly worked" Reviewed

T. Oku, R. Motoyoshi, K. Fujimoto, T. Akiyama, B. Jeyadevan, J. Cuya

Journal of Physics and Chemistry of Solids   72   1206 - 1211   2011.11

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Effects of capping layers on the photoelectrochemical property of silver nanoparticle-modified indium-tin-oxide electrode "jointly worked" Reviewed

Ken-ichi Matsuoka,HironobuTahara,TsuyoshiAkiyama,SunaoYamada

Journal of Photochemistry and Photobiology A: Chemistry   221   239 - 243   2011.6

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Effects of capping layers on the photoelectrochemical property of silver nanoparticle-modified indium-tin-oxide electrode Reviewed

Matsuoka K.I., Tahara H., Akiyama T., Yamada S.

Journal of Photochemistry and Photobiology A: Chemistry   221 ( 2-3 )   239 - 243   2011.6

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Photoelectrochemical properties of indium-tin-oxide (ITO) substrate modified with silver nanoparticles (AgNPs) and effects of surface capping layer of AgNP were investigated in the water/acetonitrile (H O/MeCN) electrolyte solutions with the presence of oxygen as an electron acceptor. The modified ITO substrate showed photocurrent response mainly driven by the photoinduced electron transfer from ITO substrate to AgNPs. In addition, its photoelectrochemical property significantly depended on the solvent composition of electrolyte solution which was in correlation with surface status of AgNPs. Combination of photoelectrochemical measurements and spectroscopic analysis suggested that presence of considerable amount of MeCN in the electrolyte solution triggered partial displacement of capping citrate ions to activate photocurrent generation. © 2011 Elsevier B.V. All rights reserved. 2

DOI： 10.1016/j.jphotochem.2011.03.015

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Fabrication and characterization of copper oxides/fullerene solar cells prepared by an electrodeposition method "jointly worked" Reviewed

Kazuya FUJIMOTO, Takeo OKU, Tsuyoshi AKIYAMA

Journal of the Ceramics Society of Japan   119   402 - 404   2011.6

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An influence of monomeric porphyrin structure on the electropolymerized photoactive electrode for polymer solar cells Reviewed

Takechi K., Takahashi N., Shiga T., Akiyama T., Yamada S.

Molecular Crystals and Liquid Crystals   538   10 - 14   2011.6

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We have fabricated and compared photocurrent generation properties of electropolymerized films consisting of 2,2'-bithiophene and a porphyrin derivative, 5,10,15,20-tetra(3-thienyl)-21H,23H-porphyrin or 5,10,15,20-tetra(2-thienyl)-21H,23H-porphyrin. It was found that the location and the concentration of porphyrin moieties in the films were different between the two porphyrin monomers, and the polymer film with the former porphyrin gave larger photocurrent than the latter. The result indicates that the molecular design of the polymer electrode is very important for effective photocurrent generation. Copyright © Taylor & Francis Group, LLC.

DOI： 10.1080/15421406.2011.563206

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An Influence of Monomeric Porphyrin Structure on the Electropolymerized Photoactive Electrode for Polymer Solar Cells "jointly worked" Reviewed

Kensuke Takechi, Naoko Takahashi, Tohru Shiga, Tsuyoshi Akiyama, Sunao Yamada.

Molecular Crystals and Liquid Crystals   538   10 - 14   2011.5

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Electrochemical Modulation of the Optical Property of Polythiophene-Gold Nanorod Composite Films "jointly worked" Reviewed

K. Sugawa, T. Akiyama and S. Yamada

Molecular Crystals and Liquid Crystals   539   341 - 344   2011.5

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Fabrication and photocurrent generation of multilayer assemblies consisting of silver-nanoparticles, polydiacetylene, and polyions Reviewed

Akiyama T., Masuhara A., Matsuda Y., Arakawa T., Munaoka T., Onodera T., Oikawa H., Yamada S.

Japanese Journal of Applied Physics   50 ( 4 PART 2 )   2011.4

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The fabrication of silver nanoparticle and polydiacetylene nanocrystal multilayer assemblies was successful on indium-tin-oxide transparent electrodes by repeating electrostatic layer-by-layer deposition. Adsorbed amount of silver nanoparticles and polydiacetylene nanocrystals was confirmed by visible absorption spectroscopy. The surface conditions and morphologies of the assemblies were investigated by scanning electron microscopy. In the presence of a sacrificial reagent, these multilayer assemblies generated a stable photocurrent. It has become apparent that polydiacetylene nanocrystals are not also photoexciting material in the present system, but also act as an electron relay or transport material. Therefore, photocurrent generation is assisted under the co-existence of polydiacetylene nanocrystals in the assemblies. © 2011 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.50.04DH15

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Silver-nanoparticle-assisted photocurrent generation in polythiophene-fullerene thin films Reviewed

You J., Arakawa T., Munaoka T., Akiyama T., Takahashi Y., Yamada S.

Japanese Journal of Applied Physics   50 ( 4 PART 2 )   2011.4

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We have investigated the effect of silver nanoparticles (AgPs) on the photocurrent generation of a polyphiophene-fullerene photovoltaic film. Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C -butyric acid methylester (PCBM) were used for the electron donor and acceptor, respectively. First, AgPs were electrostatically deposited upon the surface of an indium tin oxide (ITO) electrode via a polycation. Then, a film of P3HT or a mixture of P3HT and PCBM was prepared by spin coating. The thickness of the film was evaluated by atomic force microscopy. Absorption and fluorescence spectral measurements were carried out to investigate the effects of AgPs. Photocurrent spectra were also measured, and the effects of AgPs on photocurrent enhancement were verified. © 2011 The Japan Society of Applied Physics. 61

DOI： 10.1143/JJAP.50.04DK22

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Silver-Nanoparticle-Assisted Photocurrent Generation in Polythiophene-Fullerene Thin Films （共著） Reviewed

Jing You, Taichi Arakawa, Takatoshi Munaoka, Tsuyoshi Akiyama, Yukina Takahashi, Sunao Yamada

Japanese Journal of Applied Physics   50   04DK22-1 - 04DK22-4   2011.4

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Fabrication and Photocurrent Generation of Multilayer Assemblies Consisting of Silver-nanoparticles, Polydiacetylene, and Polyions "jointly worked" Reviewed

50   04DH15-1 - 04DH15-4   2011.4

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Electrochemical modulation of the optical property of polythiophene-gold nanorod composite films Reviewed

Sugawa K., Akiyama T., Yamada S.

Molecular Crystals and Liquid Crystals   539   1/[341] - 4/[344]   2011.1

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In order to electrochemically modulate the optical property of transparent films, we have fabricated composite films consisting of gold nanorods having strong absorption bands in near infrared region and polythiophene exhibiting electrochemical activity. On applying electrochemical potentials of 800 and 0mV repeatedly, the plasmon band showed irreversible but consecutive changes due to the proceeding of aggregation of the nanorods in the film, while the absorption of polythiophene around 540nm changed reversibly. It was found the composite film could electrochemically modulate the color of the film, by utilizing the aggregation of gold nanorods in the electrochemically reversible polythiophene film. Copyright © Taylor & Francis Group, LLC.

DOI： 10.1080/15421406.2011.566021

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Fabrication and characterization of copper oxides/fullerene solar cells prepared by an electrodeposition method Reviewed

Fujimoto K., Oku T., Akiyama T.

Journal of the Ceramic Society of Japan   119 ( 1390 )   402 - 404   2011.1

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Copper oxide based solar cells with fullerene (C ) were fabricated on indium tin oxide (ITO) by an electrodeposition method. Cell performance of the solar cells with the Cu O/C and CuO/C structures was investigated. A photovoltaic device based on an ITO/Cu O/C heterojunction structure provided short-circuit current density of 67μA cm and open circuit voltage of 0.20Vunder an air mass 1.5 illumination. The microstructures of the Cu O and CuO layers were examined, and the energy levels of the present solar cells were also discussed. © 2011 The Ceramic Society of Japan. 60 2 60 60 2 60 2 -2

DOI： 10.2109/jcersj2.119.402

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Effects of hole transport layer on photoelectrochemical responses from polythiophene-porphyrin composite polymer electrode Reviewed

Takechi K., Shiga T., Akiyama T., Yamada S.

Applied Physics Express   3 ( 12 )   2010.12

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The effect of a hole transport layer on the photoelectrochemical responses from an organic solar cell consisting of a composite polymer film of 5,10,15,20-tetra(3-thienyl)-21H,23H-porphyrin and polythiophene was investigated. The polyalkylthiophene layer that was inserted between the above-described photoactive polymer film and a transparent electrode acted as the hole transport layer. This layer remarkably suppressed the recombination of separated charge carriers generated in the composite polymer film and substantially improved both photocurrent and conversion efficiencies. © 2010 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.3.122301

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Effects of Hole Transport Layer on Photoelectrochemical Responses from Polythiophene-Porphyrin Composite Polymer Electrode （共著） Reviewed

Kensuke Takechi, Tohru Shiga, Tsuyoshi Akiyama, Sunao Yamada

Applied Physics Express   3   122301-1 - 122301-3   2010.12

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A Z-scheme type photoelectrochemical cell consisting of porphyrin-containing polymer and dye-sensitized TiO2 electrodes "jointly worked" Reviewed

Kensuke Takechi, Tohru Shiga, Tsuyoshi Akiyama, Sunao Yamada

Photochemical & Photobiological Sciences   9   1085 - 1087   2010.8

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Selective formation and structural properties of rhombic dodecahedral [70]fullerene microparticles formed by reaction with aliphatic diamines Reviewed

Matsuoka K.I., Akiyama T., Yamada S.

Langmuir   26 ( 6 )   4274 - 4280   2010.3

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We have accomplished the selective formation of rhombic dodecahedral microparticles on the submicrometer to micrometer scale by the reaction of [70]fullerene (C ) with primary aliphatic diamines. The morphology of the resultant microparticles was analyzed by scanning electron microscopy, powder X-ray diffraction, and other spectroscopic methods, demonstrating that the resultant particles held a rhombic dodecahedral shape having a simple cubic lattice structure and that primary aliphatic amines were mostly trapped inside the particles through electronic interaction between C and amines. Furthermore, we have discovered interesting structural characteristics in which the incorporated amines could be removed from the C microparticles or exchanged with other primary aliphatic diamines. © 2010 American Chemical Society. 70 70 70

DOI： 10.1021/la903355e

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Selective Formation and Structural Properties of Rhombic Dodecahedral [70]Fullerene Microparticles Formed by the Reaction with Aliphatic Diamines（共著） Reviewed

Matsuoka, Ken-ichi; Akiyama, Tsuyoshi*; Yamada, Sunao*.

Langmuir   26   4274 - 4280   2010.3

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A Z-scheme type photoelectrochemical cell consisting of porphyrin-containing polymer and dye-sensitized TiO<inf>2</inf> electrodes Reviewed

Takechi K., Shiga T., Akiyama T., Yamada S.

Photochemical and Photobiological Sciences   9 ( 8 )   1085 - 1087   2010.1

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A Z-scheme type photoelectrochemical cell consisting of an electrochemically polymerized photoactive electrode and a dye-sensitized TiO electrode is demonstrated. Nearly 1 V of open circuit voltage (V ) was achieved by the cooperation of a couple of photoactive electrodes toward uphill electron pumping. © 2010 The Royal Society of Chemistry and Owner Societies. 2 OC

DOI： 10.1039/c0pp00086h

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Enormous enhancement in photocurrent generation using electrochemically fabricated gold nanostructures Reviewed

Akiyama T., Aiba K., Hoashi K., Wang M., Sugawa K., Yamada S.

Chemical Communications   46 ( 2 )   306 - 308   2010.1

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A self-assembled monolayer of porphyrins fabricated on the surface of an electrochemically deposited gold nanostructure exhibits enormous enhancement of photocurrent due to porphyrin excitation, especially in the near-infrared region, where localized surface plasmon resonance was responsible. © 2010 The Royal Society of Chemistry.

DOI： 10.1039/b913284h

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Enormous Enhancement in Photocurrent Generation Using Electrochemically Fabricated Gold Nanostructures（共著） Reviewed

Akiyama, Tsuyoshi*; Aiba, Kenta; Hoashi, Kazuko; Wang, Meng; Sugawa, Kosuke; Yamada, Sunao.

Chemical Communications   46   306 - 308   2010.1

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Enhanced absorption and emission in a copper phthalocyanine-gold nanoparticle system assisted by localized surface plasmon Reviewed

Sugawa K., Kawahara T., Akiyama T., Kobayashi M., Takahara A., Yamada S.

Chemistry Letters   38 ( 4 )   326 - 327   2009.7

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Localized surface plasmon resonance leads to an increase in the degree of photon absorption and concomitant emission in copper phthalocyanine-gold nanoparticle systems. Copyright © 2009 The Chemical Society of Japan.

DOI： 10.1246/cl.2009.326

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Effects of silver nanoparticles on photoelectrochemical responses of organic dyes Reviewed

Arakawa T., Munaoka T., Akiyama T., Yamada S.

Journal of Physical Chemistry C   113 ( 27 )   11830 - 11835   2009.7

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The electrostatic layer-by-layer adsorption technique was used to fabricate silver nanoparticle (AgP)-organic dye composite films on indium-tin-oxide (ITO) electrodes. The degree of immobilization for the AgPs on the ITO electrode could be controlled by changing the immersion time of the electrode in the AgP aqueous colloidal solution. Porphyrin and phthalocyanine were selected as the dye molecules here because the former has a strong absorption band around the plasmon band of isolated AgPs, while the latter has one around the plasmon band of aggregated AgPs (interparticle plasmon coupling). Remarkable enhancement in the photocurrent action and fluorescence excitation spectra was observed for both dyes when considerable amounts of AgPs were deposited onto the ITO electrode. The Raman scattering measurements suggested the effects of enhanced electric fields resulting from localized surface plasmon resonance and light scattering on the photocurrent enhancement. © 2009 American Chemical Society.

DOI： 10.1021/jp9018525

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Effects of Silver Nanoparticles on Photoelectrochemical Responses of Organic Dyes Arakawa, Taichi; Munaoka, Takatoshi; Akiyama, Tsuyoshi; Yamada, Sunao. （共著） Reviewed

Arakawa, Taichi; Munaoka, Takatoshi; Akiyama, Tsuyoshi; Yamada, Sunao.

The Journal of Physical Chesmitry C   113   11830 - 11835   2009.6

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Photocurrent generation properties of electrochemically polymerized terthiophene-linked fullerene film Reviewed

Akiyama T., Fukuyama T., Sugawa K., Yoneda H., Yamada S.

Synthetic Metals   159 ( 9-10 )   965 - 968   2009.5

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Terthiophene derivative of C fullerene was synthesized. The polymerized film of this fullerene analog was prepared on an indium-tin-oxide electrode by electrochemical polymerization at +1.4 V versus a Ag wire. The absorbance of the polymerized film was increased by increasing the electrochemical polymerization time. The polymerized film generated stable photocurrents in the presence of triethanolamine. Optimization of the amount of adsorbed polymerized film for improving the photoelectric conversion performance was achieved by controlling the polymerization time. © 2009 Elsevier B.V. All rights reserved. 60

DOI： 10.1016/j.synthmet.2009.02.019

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Facile fabrication and photocurrent generation properties of electrochemically polymerized fullerene-poly(ethylene dioxythiophene) composite films Reviewed

Akiyama T., Yoneda H., Fukuyama T., Sugawa K., Yamada S., Takechi K., Shiga T., Motohiro T., Nakayama H., Kohama K.

Japanese Journal of Applied Physics   48 ( 4 PART 2 )   2009.4

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Fullerene-poly(ethylene dioxythiophene) (polyEDOT) composite films consisting of 3,4-ethyeledioxythiophene (EDOT) and a thiophene derivative of C fullerene (ThC ) or C fullerene were fabricated on a transparent indium-tin-oxide (ITO) electrode by electrochemical polymerization of the electrolyte solution of ThC (or C ) and EDOT. Incorporation of the C fullerene moiety in the polythiophene film was strongly suggested from absorption spectra of the composite film. We have found a higher degree of incorporation of the C fullerene moiety into the ThC -polyEDOT film, as compared with the C -polyEDOT film. In the presence of methylviologen as an electron acceptor, the as-prepared C -polyEDOT and ThC -polyEDOT composite films generated stable cathodic photocurrents in the 400-700nm region with broad peaks. The photocurrent intensity and the internal photon-to-current quantum efficiency of the ThC -polyEDOT composite film were considerably larger than those of C -polyEDOT and polyEDOT films. The thiophene unit of ThC was confirmed to be quite effective for a stable incorporation of the C fullerene moiety in the film and a higher photocurrent generation. © 2009 The Japan Society of Applied Physics. 60 60 60 60 60 60 60 60 60 60 60 60 60 60 60

DOI： 10.1143/JJAP.48.04C172

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Structural characterization and photoelectrochemical properties of gold nanoparticle multistructures prepared by layer-by-layer deposition Reviewed

Sugawa K., Kawahara T., Akiyama T., Yamada S.

Japanese Journal of Applied Physics   48 ( 4 PART 2 )   2009.4

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Surface plasmon, which is induced by the oscillation of free electrons at the surface of a metal, generates remarkable enhancement of localized electric field owing to its interaction with the incident light field, which is called localized surface plasmon resonance (LSPR). In this study, we have fabricated densely packed multistructures of gold nanoparticle films by a layer-by-layer approach using polyions and films of LSPR-active gold nanoparticles prepared at the liquid-liquid interface. The structure and the optical properties of the multistructure were evaluated by transmission absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and quartz crystal microbalance (QCM) measurements. In addition, the photoelectrochemical investigations of these films verified the anodic photocurrent generation due to photoexcitation of the gold nanoparticles. © 2009 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.48.04C132

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Structural Characterization and Photoelectrochemical Properties of Gold Nanoparticle Multistructures Prepared by Layer-by-Layer Deposition （共著） Reviewed

Sugawa, Kosuke; Kawahara, Tomoaki; Akiyama, Tsuyoshi; Kobayashi, Motoyasu; Takahara, Atsushi; Yamada, Sunao*.

Japanese Journal of Applied Physics   48   04C132(1) - 04C132(5)   2009.4

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Facile Fabrication and Photocurrent Generation Properties of Electrochemically Polymerized Fullerene-Poly(ethylene dioxythiophene) Composite Films（共著） Reviewed

Akiyama, Tsuyoshi*; Yoneda, Hiroyuki; Fukuyama, Toshihide; Sugawa, Kosuke; Yamada, Sunao; Takechi, Kensuke; Shiga, Tohru; Motohiro, Tomoyoshi; Nakayama, Hideki; Kohama, Keiichi.

Japanese Journal of Applied Physics   48   04C172(1) - 04C172(4)   2009.4

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Photocurrent generation properties of electrochemically polymerized terthiophene-linked fullerene film（共著） Reviewed

Akiyama, Tsuyoshi*; Fukuyama, Toshihide; Sugawa, Kosuke; Yoneda, Hiroyuki; Yamada, Sunao.

Synthetic Metals   159   965 - 968   2009.4

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Plasmon-enhanced photocurrent generation from self-assembled monolayers of phthalocyanine by using gold nanoparticle films Reviewed

Sugawa K., Akiyama T., Kawazumi H., Yamada S.

Langmuir   25 ( 6 )   3887 - 3893   2009.3

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The effect of localized electric fields on the photocurrent responses of phthalocyanine that was self-assembled on a gold nanoparticle film was investigated by comparing the conventional and the total internal reflection (TIR) experimental systems. In the case of photocurrent measurements, self-assembled monolayers (SAMs) of a thiol derivative of palladium phthalocyanine (PdPc) were prepared on the surface of gold-nanoparticle film that was fixed on the surface of indium-tin-oxide (ITO) substrate via a polyion (PdPc/AuP/polyion/ITO) or on the ITO surface (PdPc/ITO). Photocurrent action spectra from the two samples were compared by using the conventional spectrometer, and were found that PdPc/AuP/polyion/ITO gave considerably larger photocurrent signals than PdPc/ITO under the identical concentration of PdPc. In the case of the TIR experiments for the PdPc/AuP/polyion/ITO and the PdPc/AuP/Glass systems, incident-angle profiles of photocurrent and emission signals were correlated with each other, and they were different from that of the PdPc/ITO system. Accordingly, it was demonstrated that the photocurrent signals were certainly enhanced by the localized electric fields of the gold-nanoparticle film. © 2009 American Chemical Society.

DOI： 10.1021/la803831c

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Characterization of copper phthalocyanine nanoparticles formed by laser ablation in poor solvents Reviewed

Leonard K., Tun M.T., Kurawaki J., Akiyama T., Yamada S.

e-Journal of Surface Science and Nanotechnology   6   312 - 316   2008.12

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Laser irradiation of Copper phthalocyanine tetrasulfonate (CuPcTs) microcrystals in some poor solvents has produced CuPcTs nanoparticles with 15-112 nm in diameter. Field emission scanning electron microscopy (FESEM) images have shown densely packed nanoparticles of CuPcTs formed in methanol and acetone. The mean diameter of CuPcTs nanoparticles obtained from TEM images in methanol, 2-methy-2-propanol, ethanol, tetrahydrofuran, and acetone were determined to be 26, 36, 35, 86, and 78 nm, respectively. The size and surface morphology of CuPcTs nanoparticles have been correlated with solvent parameters such as polarity and thermal diffusivity. © 2008 The Surface Science Society of Japan.

DOI： 10.1380/ejssnt.2008.312

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Shape control of fullerene microparticles by using ethylenediamine Reviewed

Matsuoka K.I., Matsumura S., Akiyama T., Yamada S.

Chemistry Letters   37 ( 9 )   932 - 933   2008.9

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[60,70]-Fullerene-ethylenediamine microparticles with sub-μn size were obtained by simply mixing fullerene and ethylenediamine in organic solvents under ambient condition. Amazingly, well-defined rhombic dodecahedral particles were obtained for C -ethylenediamine adducts only in the mixing ratio of C :ethylenediamine = 1:1000. Copyright © 2008 The Chemical Society of Japan. 70 70

DOI： 10.1246/cl.2008.932

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Enhanced photocurrent generation in self-assembled monolayers formed at plasmonic gold nanostructures Reviewed

Akiyama T., Nakada M., Sugawa K., Yamada S.

Macromolecular Symposia   270 ( 1 )   171 - 176   2008.8

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The effect of localized surface plasmon resonance (SPR) appearing at the surfaces of gold nanoparticles (AuPs) was successfully applied for the enhancement of photocurrents from porphyrin (Po) immobilized on AuPs. The electrode consisting of AuPs with different sizes (∼15 or ∼35 nm) was prepared using the AuP film formed at the liquid/liquid interface, and then Po was self-assembled on the gold surface. The SPR effect for the AuP film was verified from the attenuated total reflection SPR and absorption measurements. Photocurrents from the modified electrodes were compared with the corresponding planar electrode. Appreciable enhancement of photocurrents was observed. Copyright © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.

DOI： 10.1002/masy.200851020

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Step-by-step fabrication of porphyrin-fullerene supramolecular assemblies and their photoelectrochemical properties Reviewed

Matsuoka K.I., Akiyama T., Yamada S.

Journal of Physical Chemistry C   112 ( 17 )   7015 - 7020   2008.5

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Porphyrin-fullerene C multilayered films have been successfully fabricated on an indium-tin-oxide (ITO) substrate by step-by-step, self-assembling, and surface sol-gel processes. First, cysteamine was self-assembled on the ITO surface, and then a C layer was formed via N-H addition reaction. The layered C further underwent another N-H addition with 1,2-diaminoethane to enable formation of the subsequent C layer, giving a double-layered C film. Meanwhile, the layered C was treated with 2-aminoethanol to implant hydroxy groups on the C layer, which was essential to promote the surface sol-gel reaction with titanium-(IV) butoxide for implanting the titanium oxide layer. Then tetracarboxyphenylporphyrin was superimposed on the titanium oxide layer by the subsequent surface sol-gel reaction. By repeating these surface sol-gel reactions, the porphyrin layer was further assembled on the outermost layer. Accordingly, the porphyrin and C multilayered films could be fabricated by the series of above-described step-by-step reactions. Absorption, fluorescence, quartz crystal microbalance, and photoelectrochemical investigations were carried out. Considerable photoinduced electron transfer between photoexcited porphyrin to C was verified, even in the presence of the titanium oxide linking layer. Appreciable photocurrent generation from the multilayered films was observed, and its mechanism is described. © 2008 American Chemical Society. 60 60 60 60 60 60 60 60 60

DOI： 10.1021/jp711180m

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Fabrication of densely packed gold nanoparticle films and their fluorescence enhancement effect Reviewed

Akiyama T., Kawahara T., Arakawa T., Yamada S.

Japanese Journal of Applied Physics   47 ( 4 PART 2 )   3063 - 3066   2008.4

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Stable and densely packed two-dimensional films of gold nanoparticles (AuPs) were fabricated on a glass substrate, in which the gold nanoparticle film (AuPF) formed at a liquid/liquid interface was sandwiched between titanium oxide [Ti(O)] layers; the Ti(O) layer was prepared by a surface sol-gel process. The structure of AuPF on the substrate was measured and evaluated by absorption spectroscopy, quartz crystal microbalance (QCM) measurement, and scanning electron microscopy (SEM). Without the Ti(O) layer, the deposited gold nanoparticles moved to form aggregates on the substrate surface, as was verified from SEM measurements. A clear plasmon band due to AuPs was observed in the deposited AuPF both on the bare and Ti(O)-modified substrates. Tetratolylporphyrin (TTP) was cast on the surface of AuPFs. The excitation efficiencies of TTP on the as-described modified substrates were compared. The use of the Ti(O) layer was quite effective both for preserving the morphology of AuPF as well as for reducing the quenching effect of the photoexcited TPP by Au. © 2008 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.47.3063

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Preparation and characterization of porphyrin-polythiophene stacked films as prepared by electrochemical method under stirring condition Reviewed

Sugawa K., Akiyama T., Yamada S.

Thin Solid Films   516 ( 9 )   2502 - 2506   2008.3

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Porphyrin-polythiophene (pTh) stacked films consisting of meso-tetrathienylporphyrin (TThP) and bithiophene (BiTh) were prepared on transparent indium-tin-oxide (ITO) electrodes by sequential electrochemical scanning of applied potential between 0 and + 2 V vs Ag wire in the electrolyte solution of BiTh and TThP under stirring condition. First, the pTh films were prepared by electrochemical polymerization and then TThP was incorporated into the as-prepared pTh film by subsequent electrochemical scanning as described above in the TThP solution. The operation of solution stirring during electrochemical scanning achieved the formation of robust stacked films. UV/Vis and fluorescence spectra confirmed that the amount of TThP moiety increased with increasing the number of electrochemical scanning cycles in the TThP solution. In order to evaluate the incorporation profile of TThP, surface analyses and depth profiles of stacked films were carried out by XPS spectroscopy. The results suggested that all films formed porphyrin-polythiophene stacked structure precisely, and that TThP was exclusively incorporated around the outermost region of the pTh film. © 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2007.04.142

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Fabrication of a novel photoelectric conversion device consisting of a poly-3-dodecylthiophene film and C <inf>60</inf> fullerene-ethylenediamine nanoparticles Reviewed

Matsuoka K.I., Seo H., Akiyama T., Yamada S.

Chemistry Letters   36 ( 7 )   934 - 935   2007.7

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A novel photoelectric conversion device was fabricated by using poly-3-dodecylthiophene film and nanoparticles consisting of C fullerene and ethylenediamine on a transparent electrode. Incorporation of the nanoparticles substantially enhanced the photocurrent from the polythiophene film. Copyright © 2007 The Chemical Society of Japan. 60

DOI： 10.1246/cl.2007.934

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Characterization and evaluation of role of porphyrin moiety in meso-tetrathienylporphyrin-polythiophene composite film Reviewed

Sugawa K., Kakutani K., Akiyama T., Yamada S., Takechi K., Shiga T., Motohiro T., Nakayama H., Kohama K.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers   46 ( 4 B )   2632 - 2635   2007.4

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Porphyrin-polythiophene (pTh) composite films consisting of meso-tetrathienylporphyrin (TThP) and 2,2'-bithiophene (BiTh) were fabricated on transparent indium-tin-oxide (ITP) electrodes by the electrochemical polymerization of TThP and BiTh in solution. The incorporation of a porphyrin moiety to the pTh chain was confirmed by absorption and X-ray photoelectron spectroscopies. In the case of tetraphenylporphyrin (TPP), instead of TThP for electrochemical polymerization, no clear evidence of the incorporation of the porphyrin moiety into the pTh chain was obtained. In the presence of methylviologen and oxygen as electron acceptors, light irradiation on the TThP-pTh composite films generated stable cathodic photocurrents. A broad peak at approximately 420 nm corresponding to the Soret band of the porphyrin moiety was clearly observed in the photocurrent action spectrum of the TThP-pTh composite films. The photocurrent intensity of the TThP-pTh composite films was larger than that of the pTh film. The incorporation of TThP to the composite films was quite effective for generating larger photocurrents. © 2007 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.46.2632

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Facile fabrication of gold nanoparticle-titanium oxide alternate assemblies by surface sol-gel process Reviewed

Arakawa T., Kawahara T., Akiyama T., Yamada S.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers   46 ( 4 B )   2490 - 2492   2007.4

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Multistructured assemblies consisting of gold nanoparticles and titanium oxide were alternately fabricated by a surface sol-gel process. First, a quartz glass substrate was immersed into an organic solution of titanium butoxide [Ti(OBu) )]. Then, the substrate was rinsed with water, and dried in air, giving ultra-thin titanium oxide [Ti(O)]-modified quartz glass substrate. This modified glass substrate was immersed into an aqueous colloidal solution of gold nanoparticles (AuPs) that were stabilized with citrate ions, giving a AuP-Ti(O)-modified glass substrate. By repeating these surface sol-gel processes, the multistructured assemblies of AuPs and Ti(O), [AuP/Ti(O)] /Glass (n = 1-4) were fabricated. Plasmon band intensity increased with the number of surface sol-gel process cycles. The resultant assemblies were stable even after 11 days, or after treatment with an aqueous electrolyte solution. The alternate assembling of AuPs and Ti(O) was confirmed by quartz crystal microbalance measurements and absorption and X-ray photoelectron spectroscopies. Accordingly, we have succeeded in the preparation of stable AuP-Ti(O) composite films on the substrates. © 2007 The Japan Society of Applied Physics. 4 n

DOI： 10.1143/JJAP.46.2490

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Solar cells using iodine-doped polythiophene-porphyrin polymer films Reviewed

Takechi K., Shiga T., Motohiro T., Akiyama T., Yamada S., Nakayama H., Kohama K.

Solar Energy Materials and Solar Cells   90 ( 9 )   1322 - 1330   2006.5

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Wet-type organic solar cells containing 5,10,15,20-3-tetrathienylporphyrin (TThP) and polythiophene (PTh) films were fabricated. The TThP/PTh film was prepared on indium-tin-oxide (ITO) glass using an electrochemical polymerization method in an n-Bu NPF /CH Cl solution. It was found that a small amount of iodine doping of the film improved the incident photon-to-electron conversion efficiency (IPCE) of a solar cell consisting of a TThP/PTh film and an aqueous electrolyte. A HOMO level measurement suggested that a modified HOMO level of the low iodine-doped TThP/PTh film allowed a fast electron transfer from PTh to a porphyrin moiety. To obtain further improvement, a sandwich-type solar cell using a 5% (w/w) aqueous solution of acetonitrile containing 0.05 M iodine and 0.5 M lithium iodide as an electrolyte was then fabricated. The solar cell absorbed light in the 300-800 nm wavelength range, converting this to a cathodic photocurrent with a maximum IPCE of 32% at 430 nm under irradiation of 5.0×10 photon cm s . This value is about 10 times higher than that of the solar cells using an aqueous electrolyte. The total energy conversion efficiency (η) of the solar cell under simulated sunlight reached 0.12% for 2.59 mW cm at AM1.5 and 0.05% for 100 mW cm at air mass 1.5. © 2005 Elsevier B.V. All rights reserved. 4 6 2 2 14 -2 -1 -2 -2

DOI： 10.1016/j.solmat.2005.08.010

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Facile fabrication and photolectrochemical properties of porphyrin-fullerene assemblies by self-assembly and surface sol-gel processes Reviewed

Akiyama T., Matsuoka K.I., Arakawa T., Kakutani K., Miyazaki A., Yamada S.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers   45 ( 4 B )   3758 - 3761   2006.4

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Ultrathin photoelectric conversion films consisting of a porphyrin-fullerene photoredox pair were fabricated by the combined use of room-temperature covalent-bonding and surface sol-gel processes. First, cysteamine was self-assembled on an indium-tin-oxide (ITO) electrode. The cysteamine-modified electrode was then immersed in C solution, giving immobilization of C via bond formation between the amino group of cysteamine and C . Next, the C -modified electrode was dipped in 2-ethanolamine solution to implant the hydroxy group to the immobilized C via the bond formation between C and the amino group; thus, the hydroxy group was exposed as the outermost layer. Then, Ti(OBu) and tetracarboxyporphyrin (TCPP) were alternately assembled on the C layer by the surface sol-gel process, to give an assembly of TCPP, titanium oxide species [Ti(O)], and C on the ITO electrode. The double layering of TCPP-Ti(O) was possible. The spectral characterization of the films was carried out. In the presence of sacrificial reagents, anodic photocurrents were generated from these modified electrodes. The incorporation of the C layer resulted in the substantial enhancement of the photocurrents as compared with that of the TCPP layer alone, suggesting effective electron-transfer reactions between TCPP and C that contribute to the photocurrent increase. The photocurrents increased by the double layering of the TCPP and Ti(O) layers. ©2006 The Japan Society of Applied Physics. 60 60 60 60 60 60 4 60 60 60 60

DOI： 10.1143/JJAP.45.3758

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Molecular logic devices using mixed self-assembled monolayers Reviewed

Nitahara S., Terasaki N., Akiyama T., Yamada S.

Thin Solid Films   499 ( 1-2 )   354 - 358   2006.3

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We have developed a photoelectric conversion device which functioned as molecular logic gates. It consisted of a mixed self-assembled monolayer (SAM) of tris(2,2′-bipyridine)ruthenium(II)-viologen linked thiol and phthalocyanine thiol compounds. Photocurrents from the SAM could be controlled by an excitation wavelength as well as an applied potential. As molecular logic devices, two kinds of light emitting diodes (LEDs) were used as light sources. Photocurrents at E = 0 V clearly responded as the XOR logic gate whereas those at - 0.2 V as the OR logic gate. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tsf.2005.07.014

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Photocurrent enhancement in a porphyrin-gold nanoparticle nanostructure assisted by localized plasmon excitation Reviewed

Akiyama T., Nakada M., Terasaki N., Yamada S.

Chemical Communications   ( 4 )   395 - 397   2006.1

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The nanostructured assembly of porphyrin and gold nano-particles exhibits distinct enhancement of photocurrents from porphyrin in the longer wavelength region, where the localized plasmon resonance was responsible. © The Royal Society of Chemistry 2006.

DOI： 10.1039/b511487j

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Solid-state solar cells consisting of polythiophene-porphyrin composite films Reviewed

Akiyama T., Matsushita M., Kakutani K., Yamada S., Takechi K., Shiga T., Motohiro T., Nakayama H., Kohama K.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers   44 ( 4 B )   2799 - 2802   2005.4

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Sandwich-type solid-state solar cells using polythiophene-porphyrin composite films were fabricated. A spin-coated film of poly(3-dodecylthiophene) (P3DT) was fabricated on a old electrode. Next, an electropolymerized polythiophene film was superimposed on the surface of the spin-coated P3DT film by electrochemical polymerization of bithiophene (BiTh) with repeated redox cycles in the 0-+2 V region. Then, tetrathienylporphyrin (TThP) was further assembled on the polythiophene-modified electrode by using the same electrochemical polymerization procedure (1 or 10 cycles), to obtain polythiophene-porphyrin modified gold electrodes. Finally, an aluminum electrode was deposited on the polythiophene-porphyrin modified gold electrode by vacuum deposition, forming the sandwich-type solid-state solar cells. The morphological characterizations of the films were carried out by scanning electron microscopy. The thickness of the organic layer decreased from ∼5 μm to ∼3 μn by performing TThP polymerization. The amount of porphyrin moiety in the composite film was larger for the modified electrode after 10 cycles of electrochemical TThP polymerization than for that after 1 cycle of TThP polymerization. The resultant photocurrent increased with scanning cycle of TThP polymerization in the 400-600 nm region. The combination of polythiophene and porphyrin in the electrochemically modified electrode is one of the useful systems for photocurrent generation. © 2005 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.44.2799

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Structural characterization and photocurrent properties of cis-di(thiocyanato)-bis(4,4′-dicarboxy-2,2′-bipyridine) ruthenium(II) monolayers on the gold surfaces Reviewed

Terasaki N., Nitahara S., Akiyama T., Yamada S.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers   44 ( 4 B )   2795 - 2798   2005.4

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A self-assembled monolayer of cis-di(thiocyanato)-bis(4,4′-dicarboxy- 2,2′-bipyridine) ruthenium(II) (denoted as N3) was prepared on a gold electrode. Immobilization of N3 on the gold electrode through Au (electrode)-S (NCS ligands in N3) bonding was confirmed from electrochemical and X-ray photoelectron spectroscopy (XPS) measurements. In an acetonitrile solution containing methylviologen (MV) and oxygen as electron acceptors, the cathodic photocurrent, based on the photoexcitation of N3, was clearly observed, and the incident photon-to-current conversion efficiency (IPCE) was estimated to be ∼0.1% at 520 nm. Photocurrent responses were compared between the nanostructured gold electrode prepared from gold nanoparticles and the planar electrode; the former gave larger photocurrents than the latter, especially in the longer wavelength region around the localized surface plasmon bands of gold nanoparticles. © 2005 The Japan Society of Applied Physics.

DOI： 10.1143/JJAP.44.2795

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A photoelectronic switching device using a mixed self-assembled monolayer Reviewed

Nitahara S., Akiyama T., Inoue S., Yamada S.

Journal of Physical Chemistry B   109 ( 9 )   3944 - 3948   2005.3

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A cathodic-anodic biway photoelectronic device has been successfully constructed using a self-assembled monolayer (SAM). The SAM consists of two kinds of photofunctional thiol derivatives, a ruthenium complex-viologen linked compound (RuVS) and a phthalocyanine derivative (PcS), on a gold electrode. Structural characterization of the SAM has been carried out by absorption spectroscopy, cyclic voltammetry, and differential pulse voltammetry. Photocurrent responses were measured in the presence of methyl viologen (MV ) and oxygen as electron acceptors and triethanolamine (TEOA) as a sacrificial reagent. For the SAM of RuVS alone, intramolecular electron transfer (ET) was superior to intermolecular ET, resulting in anodic photocurrents even in the presence of MV and oxygen at 0 V vs Ag/AgCl. On the contrary, only cathodic photocurrents were observed at 0 V for the SAM of PcS alone. Photocurrents from the mixed SAM of RuVS and PcS were roughly the sum of individual photocurrents from RuVS and PcS. In fact, photocurrents from the mixed SAM of RuVS and PcS were observed in the anodic direction below ∼550 nm, and in the cathodic direction above ∼550 nm at 0 V vs Ag/AgCl. In the case of the mixed SAM of RuS (ruthenium complex disulfide) and PcS, only cathodic photocurrents were observed at 0 V vs Ag/AgCl, due to the lack of an intramolecular ET pathway. The results indicate that in the mixed SAM of RuVS and PcS both dyes can individually function for opposite photocurrent generation. We have also applied the mixed SAM as a photoelectronic logic device by using two LEDs (470 and 640 nm). The system clearly operated as an XOR logic device. © 2005 American Chemical Society. 2+ 2+

DOI： 10.1021/jp046776u

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Facile fabrication of morphology-controlled gold nanoparticle architectures by electrolyte-induced agglomeration and their photoelectrochemical applications Reviewed

Akiyama T., Inoue K., Kuwahara Y., Niidome Y., Terasaki N., Nitahara S., Yamada S.

Langmuir   21 ( 2 )   793 - 796   2005.1

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The morphology-controlled gold nanoparticles architectures was facile fabricated by electrolyte-induced agglomeration and their photoelectrochemical applications. The multistructures consisting of gold nanoparticles and sulfur-containing porphyrin or ruthenium complexes were alternatively fabricated, by using gold-sulfur self-assembling, to achieve three-dimensional networks of gold nanoparticles and dyes via covalent bonding. A planar gold electrode was prepared by vacuum deposition of titanium followed by gold onto a glass plate at 300°C. An anodic photocurrents were generated from the RuVS-modified electrodes in the 0.4 to 0.4 V region of applied voltage, in the presence of 0.05 mol dm TEOA. -3

DOI： 10.1021/la048135w

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Bi-directional photocurrent generation dependent on the wavelength of irradiation of a mixed monolayer assembly Reviewed

Akiyama T., Nitahara S., Inoue S., Yamada S.

Photochemical and Photobiological Sciences   3 ( 1 )   26 - 28   2004.1

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A mixed self-assembled monolayer consisting of a ruthenium tris-bipyridine complex linked to viologen and a palladium phthalocyanine derivative was fabricated on a gold electrode by means of pendant thiol groups. The direction of the photocurrent which is induced in the electrode when it is irradiated depends on the wavelength of the light used. © 2004 The Royal Society of Chemistry and Owner Societies.

DOI： 10.1039/b313362a

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Fabrication and photoelectrochemical properties of polythiophene-porphyrin composite films Reviewed

Akiyama T., Kakutani K., Yamada S.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers   43 ( 4 B )   2306 - 2310   2004.1

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Polythiophene-porphyrin composite films consisting of bithiophene and meso-tetrathienylporphyrin were prepared on transparent indium tin oxide (ITO) electrodes. First, a polythiophene film was fabricated on the ITO electrode by electrochemical polymerization in the bithiophene solution with repeated oxidation-reduction cycles in the 0-+2 V region. Then, porphyrin was assembled on the polythiophene-modified electrode by using the same electrochemical polymerization in the porphyrin solution, to give polythiophene-porphyrin modified electrodes. The amount of porphyrin increased with increasing number of scanning cycles for electrochemical polymerization. In the presence of oxygen, irradiation of the polythiophene-porphyrin modified electrodes resulted in stable cathodic photocurrents. Photocurrent increased with increasing amount of porphyrin. Large cathodic photocurrents were observed in the negatively applied potentials. The photocurrent action spectra of modified electrodes strongly suggested the photochemical cooperation of porphyrin and polythiophene for photocurrent generation. The combination of polythiophene and porphyrin in the electrochemically modified electrode is quite effective for generating large photocurrents.

DOI： 10.1143/JJAP.43.2306

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Fabrication of a photoelectrochemical cell using a self-assembled monolayer of tris(2,2′-bipyrisine)ruthenium(II)-viologen linked thiol on multistructured gold nanoparticles Reviewed

Terasaki N., Otsuka K., Akiyama T., Yamada S.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers   43 ( 4 B )   2372 - 2375   2004.1

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A novel photoelectrochemical cell consisting of a modified electrode with a self-assembled monolayer of a tris(2,2′bipyridine)ruthenium(II)-viologen linked thiol on the surfaces of a gold-particle multistructure, an indium-tin-oxide (ITO) electrode, and an aqueous electrolyte solution containing hydroxymethylferrocene, has been fabricated. The modified electrode was constructed by the precipitation of gold nanoparticles on a planar gold electrode, and by subsequent self-assembling of the thiol compound on the surfaces of the multistructure. The spatial separation between the modified electrode and the ITO electrode was as small as ∼12 μm, which was determined from the thickness of a polyimide film used for electrical insulation. The performance of the photoelectrochemical cell was investigated. Photocurrents and photovoltages increased with increasing number of immobilized molecules.

DOI： 10.1143/JJAP.43.2372

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A double-driven photoelectrochemical cell Reviewed

Terasaki N., Kakutani K., Akiyama T., Yamada S.

Synthetic Metals   139 ( 2 )   511 - 514   2003.9

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A novel photoelectrochemical cell consisting of a set of organic thin films which generate photocurrents in opposite directions was fabricated. The polythiophene film containing 5,10,15,20-tetraphenylporphyrin (TPP) and fullerene (C ) generated anodic photocurrents in the presence of ferrocene, while that containing TPP alone generated cathodic photocurrents under aerobic condition. The combination of these two film-modified electrodes showed a better cell performance than the simple sum of these two independent photoelectrochemical cells. A push-pull type, double-driven photoelectrochemical cell is proposed in this paper. © 2003 Elsevier B.V. All rights reserved. 60

DOI： 10.1016/S0379-6779(03)00234-0

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Fabrication and photoelectrochemical properties of electron donor-acceptor assemblies via titanium oxide interlayers Reviewed

Nitahara S., Terasaki N., Akiyama T., Yamada S.

Thin Solid Films   438-439   230 - 234   2003.8

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Ultrathin molecular films consisting of electron donor (D)-acceptor (A) pairs via titanium oxide coordinative bonding have been fabricated on an indium-tinoxide electrode, by using the techniques of self-assembly and surface sol-gel process. Porphyrin and tris (2,2′-bipyridine) ruthenium (II) were used as D, while viologen as A, respectively. The degree of assembling of D and A were characterized by electrochemical and absorption measurements. In the case of the porphyrin-viologen pair, photocurrent generation based on photoinduced electron-transfer was realized, and multilayer formation of porphyrin increased the photocurrents. On the other hand, the ruthenium (II) complex-viologen pair showed very poor photocurrent responses, probably due to much poorer light absorptivity as compared with porphyrin. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0040-6090(03)00779-X

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Gold nanoparticle-porphyrin self-assembled multistructures for photoelectric conversion Reviewed

Yamada S., Tasaki T., Akiyama T., Terasaki N., Nitahara S.

Thin Solid Films   438-439   70 - 74   2003.8

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Multistructure assemblies consisting of porphyrin and gold nanoparticles have been fabricated on an indium-tin-oxide electrode by using alternate gold-sulfur self-assembling. Structural and morphological characterizations of the assemblies have been carried out by absorption spectra and scanning electron micrographs. The results verified that the degree of each self-assembling was considerably lower than monolayer level. The assemblies exhibit clear photocurrent responses ascribing to photoexcitation of porphyrin in the presence of oxygen as a sacrificial electron acceptor. The photocurrent was larger for higher number of assembling cycles. © 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0040-6090(03)00765-X

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Particle-size effects on the photocurrent efficiency of nanostructured assemblies consisting of gold nanoparticles and a ruthenium complex-viologen linked thiol Reviewed

Akiyama T., Inoue K., Kuwahara Y., Terasaki N., Niidome Y., Yamada S.

Journal of Electroanalytical Chemistry   550-551   303 - 307   2003.7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Electroanalytical Chemistry  

Photoelectrochemical assemblies consisting of gold nanoparticles and a tris(2,2′-bipyridine)ruthenium(II)-viologen linked disulfide derivative ([RuVS] ) were constructed on gold electrodes, by a combination of salting-out and self-assembly processes. Structural characterization of the nanostructured assemblies was carried out by scanning electron microscopy and cyclic voltammetry. The adsorbed amount of the tris(2,2′-bipyridine)ruthenium(II)-viologen linked moiety (RuVS) was fairly well correlated with the ratio of the total gold surface area of the nanostructured electrode. Nanostructured assemblies consisting of ∼50 to ∼ < 100 nm particles showed high photocurrent efficiencies. © 2003 Elsevier B.V. All rights reserved. 2

DOI： 10.1016/S0022-0728(03)00152-9

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Structural characterization and photoelectrochemical properties of the self-assembled monolayers of tris(2,2′-bipyridine)ruthenium(II)-viologen linked compounds formed on the gold surface Reviewed

Terasaki N., Akiyama T., Yamada S.

Langmuir   18 ( 22 )   8666 - 8671   2002.10

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Steady-state spectroscopic studies of tris(2,2′-bipyridine)ruthenium(II)-viologen (Ru -V ) linked thiol derivatives with different spacer-chain lengths (denoted as RuC VC S, where (n, m) = (11, 2), (7, 6), (7, 2), and (3, 6)) and different number ratios of Ru :V = 1:2, Ru(C VC S), have been carried out, together with the corresponding reference compounds without Ru or V . Absorption and cyclic voltammetric (CV) measurements indicated no appreciable electronic interactions between the two chromophores (Ru and V ) in the ground state. While luminescence spectral measurements revealed the occurrence of efficient photoinduced electron transfer from the photoexcited Ru (*Ru ) to V . The electron transfer efficiency was also better for the 1:2 complex as compared with the corresponding 1:1 complex. Self-assembled monolayers (SAMs) of these compounds were fabricated on a gold electrode. XPS and CV measurements revealed immobilization of the compounds on the gold surface via gold-sulfur bonding. In the presence of triethanolamine, all modified electrodes with the Ru -V linked compounds showed clear anodic photocurrents. The presence of the V moiety was crucial for obtaining larger photocurrents A shorter spacer-chain length between the V moiety and the terminal thiol group (m = 2) afforded a larger photocurrent, while a moderate spacer-chain length between the Ru and the V moieties was also a key for obtaining a larger photocurrent. A possible mechanism for photocurrent generation is discussed. 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ n m 7 6

DOI： 10.1021/la025936v

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Novel photoelectrochemical cell using a self-assembled monolayer of a ruthenium (II) tris(2,2′-bipyridine) thiol derivative Reviewed

Akiyama T., Inoue M., Kuwahara Y., Yamada S.

Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers   41 ( 7 A )   4737 - 4738   2002.1

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A novel thin-layer two-electrode photoelectrochemical cell consisting of a self-assembled monolayer of a ruthenium (II) tris(2,2′-bipyridine) thiol derivative on a transparent indium tin oxide (ITO) electrode and a bare ITO electrode was fabricated, and exhibited satisfactory performance as a photocell. A ruthenium (II) tris(2,2′-bipyridine)-viologen (electron donor-acceptor) pair yielded a higher performance of the photocell than the ruthenium complex (donor) moiety alone. Photoinduced electron transfer from the photoexcited ruthenium complex moiety to the viologen moiety was quite effective for generating larger photocurrents.

DOI： 10.1143/jjap.41.4737

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Facile fabrication of photoelectrochemical assemblies consisting of gold nanoparticles and a tris(2,2′-bipyridine)ruthenium(II)-viologen linked thiol Reviewed

Kuwahara Y., Akiyama T., Yamada S.

Langmuir   17 ( 19 )   5714 - 5716   2001.9

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Facile fabrication of a modified electrode with gold nanoparticles and a tris(2,2′-bipyridine)ruthenium(II)-viologen linked thiol (RuVS) is described. First, the gold nanoparticles (14 ± 1 nm) were precipitated onto the gold electrode in an aqueous solution. Then, this electrode was immersed into a acetonitrile solution containing RuVS, to immobilize it via Au-S bonding. Scanning electron micrographs show agglomeration and island formation of the gold particles on the electrode and 1-3 μm thickness of the deposition. In cyclic voltammetry, a redox couple due to one-electron reduction of the viologen moiety was clearly observed and its intensity increased with increasing the extent of deposition. The anodic photocurrent from the modified electrode ascribed to ruthenium-complex-sensitized redox cycles was clearly observed and was more than 15-fold larger as compared with that of the flat electrode (without gold particles).

DOI： 10.1021/la010566g

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Construction of gold nanoparticle-ruthenium (II) tris(2,2′-bipyridine) self-assembled multistructures and their photocurrent responses Reviewed

Kuwahara Y., Akiyama T., Yamada S.

Thin Solid Films   393 ( 1-2 )   273 - 277   2001.8

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Three-dimensional multistructure assemblies consisting of gold nanoparticles and a sulfur-containing ruthenium (II) tris(2,2-bipyridine) derivative were fabricated on an ITO electrode by their alternate self-assembling. Absorption spectra of the assemblies showed immobilization of the gold surface and the ruthenium complex. Broadening and red shift of the plasmon band were observed by increasing the number of assembled layers, which revealed the presence of interparticle plasmon coupling. In the presence of triethanolamine as a sacrificial reducing agent, photocurrent responses from the multistructure assemblies were clearly observed in the anodic direction. The photocurrent increased with increasing the number of assembled layers. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0040-6090(01)01085-9

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Fabrication of porphyrin-titanium oxide-fullerene assemblies on an ITO electrode and their photocurrent responses Reviewed

Akiyama T., Miyazaki A., Sutoh M., Ichinose I., Kunitake T., Yamada S.

Colloids and Surfaces A: Physicochemical and Engineering Aspects   169 ( 1-3 )   137 - 141   2000.1

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A porphyrin-fullerene assembly via titanium oxide coordinative bonding was constructed on an ITO electrode, by using the techniques of self-assembly and the surface sol-gel process. In the presence of triethanolamine, clear photocurrent responses from the modified electrode were observed in the anodic direction, and they were much larger than the electrodes modified with the porphyrin or the fullerene alone. It is suggested that the photocurrent is ascribed to photoinduced charge separation between the porphyrin and the fullerene moieties. (C) 2000 Elsevier Science B.V.

DOI： 10.1016/S0927-7757(00)00426-X

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Facile construction of an ultra-thin [60]fullerene layer from [60]fullerene-homooxacalix[3]arene complexes on a gold surface Reviewed

Hatano T., Ikeda A., Akiyama T., Yamada S., Sano M., Kanekiyo Y., Shinkai S.

Journal of the Chemical Society. Perkin Transactions 2   ( 5 )   909 - 912   2000.1

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A hexacationic homooxacalix[3]arene-[60]fullerene 2:1 complex can be deposited on an anion-coated gold surface as a monolayer (or at least as a monolayer-like ultra-thin film); as expected, this membrane efficiently shows a redox response in cyclic voltammetry and a photoelectrochemical response under visible light irradiation.

DOI： 10.1039/b000022l

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Preparation and photoelectrochemical properties of a self-assembled monolayer of a ruthenium tris(2,2′'-bipyridine)-viologen 1:2 linked compound Reviewed

Terasaki N., Akiyama T., Yamada S.

Chemistry Letters   ( 6 )   668 - 669   2000.1

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A ruthenium tris(2,2′-bipyridine)-viologen 1:2 linked disulfide was prepared. A gold electrode modified with this compound showed a higher efficiency of photocurrent as compared with a corresponding 1:1 linked compound.

DOI： 10.1246/cl.2000.668

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Effects of spacer-chain length on the photoelectrochemical responses of monolayer assemblies with ruthenium tris(2,2′-bipyridine) - viologen linked disulfides Reviewed

Koide Y., Terasaki N., Akiyama T., Yamada S.

Thin Solid Films   350 ( 1 )   223 - 227   1999.8

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Photochemical and photoelectrochemical properties of ruthenium tris(2,2′-bipyridine) (Ru )-viologen (V ) linked disulfides [RuCnVC S] (n (number of methylene groups) = 3, 7) with different spacer-chain lengths and Ru disulfides [RuC S] (m = 13, 17) were compared. The luminescence intensity in CH CN was in the order of [RuC S] ≈[RuC S] >[RuC VC S] ≫[RuC VC S] , implying efficient photoinduced electron-transfer between Ru and V moieties in the linked compounds. The monolayer assembly of the compound was fabricated on a gold surface. In the presence of triethanolamine, the anodic photocurrent was clearly observed from the RuC VC S/Au (n = 3, 7) electrode (gold electrode modified with [RuCnVC S] ), and its intensity was substantially larger for n = 7 than for n = 3. Photocurrent action spectra for the RuC VC S/Au (n = 3, 7) electrodes were well correlated with the corresponding electronic absorption spectra in solution. The photocurrent from the RuC VC S/Au electrode was reduced more effectively by the coexistence of a water-soluble viologen as compared with the RuC VC S/Au electrode. The photocurrent from the RuC S/Au (m = 13, 17) electrode was very small. The results suggest that the spacer-chain length between the Ru and the V moieties profoundly affects the Ru -sensitized photocurrent. 2+ 2+ 2+ 2+ 2+ 2+ 2+ 2+ 6 2 m 2 3 13 2 17 2 7 6 2 3 6 2 n 6 6 2 n 6 7 6 3 6 m

DOI： 10.1016/S0040-6090(99)00228-X

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Organic photoelectrochemical cell mimicking photoinduced multistep electron transfer in photosynthesis: Interfacial structure and photoelectrochemical properties of self-assembled monolayers of porphyrin- linked fullerenes on gold electrodes Reviewed

Imahori H., Ozawa S., Ushida K., Takahashi M., Azuma T., Ajavakom A., Akiyama T., Hasegawa M., Taniguchi S., Okada T., Sakata Y.

Bulletin of the Chemical Society of Japan   72 ( 3 )   485 - 502   1999.1

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Self-assembled monolayers (SAMs) technique has been applied to porphyrin-linked fullerene systems to mimic supramolecular photoinduced charge-separation (CS) events in photosynthesis. Porphyrin-linked C molecules with a sulfide group were designed to self-assemble on a gold surface using S-Au interaction. The structure of the SAMs formed on gold electrodes was investigated by spectroscopic methods including X-ray photoelectron spectroscopy (XPS), ultraviolet (UV)-visible spectroscopic ellipsometry, UV-visible absorption spectroscopy, and Fourier transform infrared (FTIR) spectroscopy as well as electrochemical studies. These results indicate that the SAMs have loosely packed structure; the porphyrin- C molecules are tilted and nearly parallel onto the gold surface. Short- circuit photocurrent with a level of sub-μA cm was observed for the photoelectrochemical cell in the presence of methylviologen (MV) under illumination with ca. 4 mW cm . The maximum intensity of the photocurrent in free-base porphyrin-C system is five times larger than that in the corresponding free-base porphyrin system, indicating that C is an effective mediator in multistep electron transfer (ET) processes. A possible mechanism for the photocurrent generation is discussed in terms of the photodynamics of porphyrin-linked fullerenes in solution. 60 60 60 60 -2 -2

DOI： 10.1246/bcsj.72.485

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Structure and photoelectrochemical properties of porphyrin-linked fullerenes on gold surface using self-assembled monolayer technique Reviewed

Imahori H., Azuma T., Ushida K., Takahashi M., Akiyama T., Hasegawa M., Okada T., Sakata Y.

Proceedings of SPIE - The International Society for Optical Engineering   3142   104 - 111   1997.12

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of SPIE - The International Society for Optical Engineering  

Self-assembled monolayers (SAMs) have recently attracted much attention as a new methodology among a variety of thin film preparation. There have been several reports of fullerene SAM. These fullerene thin films seem to be the most promising candidates for realizing photovoltaic and optoelectronic devices at the nano-scale level. We have applied this technique to donor-linked fullerene systems and have developed supramolecular porphyrin-C molecules that are designed to be self-assembled on gold surface. Such systems are expected to mimic supramolecular photoinduced charge-separation events in photosynthesis. Porphyrin-linked C bearing a methylthio group was prepared by 1,3-dipolar cycloaddition of the azomethine ylide porphyrin with C . SAM was formed by soaking Au electrode into a CH Cl solution of the porphyrin-C dyad. Structure of the SAM was investigated by spectroscopic methods including X-ray photoelectron spectroscopy (XPS) and ellipsometry and electrochemical studies. The large photocurrent with a level of sub-μA/cm was observed for the photochemical cell in the presence of methyl viologen under illumination with ∼10 mW/cm . Possible mechanism for the photocurrent generation is discussed in terms of the photodynamics of porphyrin-linked fullerenes. 60 60 60 2 2 60 2 2

DOI： 10.1117/12.279246

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MOLECULAR ASSEMBLIES OF PORPHYRINS ON GOLD SURFACE AND THEIR PHOTOPHYSICAL PROPERTIES

Tsuyoshi AKIYAMA

1997.3

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Language：English   Publishing type：Doctoral thesis  

Control of electron transfer and its utilization Reviewed

Sakata Y., Imahori H., Tsue H., Higashida S., Akiyama T., Yoshizawa E., Aoki M., Yamada K., Hagiwara K., Taniguchi S., Okada T.

Pure and Applied Chemistry   69 ( 9 )   1951 - 1956   1997.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Pure and Applied Chemistry  

In order to get information on the controlling factors of photosynthetic electron transfer and to apply the principle for the construction of artificial photosynthesis and molecular electronics, we have so far prepared various model compounds from which particular factors can be extracted. Among them our recent results on 1) mutual orientation effect, 2) effect of the nature of intervening bonds, 3) effect of inserted π-system, 4) effect of coordination bond between a redox pair, 5) size and shape effect of an acceptor, are described. In order to utilize charge separated state, C60-linked porphyrin with SMe group at the terminal position was synthesized and fixed it on gold surface using S-Au bond as self-assembled monolayer. When the sample was irradiated, photocurrent was observed.

DOI： 10.1351/pac199769091951

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The small reorganization energy of C<inf>60</inf> in electron transfer Reviewed

Imahori H., Hagiwara K., Akiyama T., Aoki M., Taniguchi S., Okada T., Shirakawa M., Sakata Y.

Chemical Physics Letters   263 ( 3-4 )   545 - 550   1996.12

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Chemical Physics Letters  

Porphyrin-linked fullerene 1 and porphyrin-linked quinone 2 have been designed and synthesized to evaluate the size and shape effect of fullerene in electron transfer. For evaluation of such an effect C and benzoquinone with comparable reduction potentials have been chosen and linked with a porphyrin, where a relatively rigid spacer ensures similar separation distance and nature of the intervening bonds between the redox pair. Accelerated charge separation and decelerated charge recombination were observed in 1 compared with 2 by picosecond fluorescence lifetime measurements and time-resolved transient absorption spectroscopy. They may be explained by the smaller reorganization energy in C compared with those in small acceptors. 60 60

DOI： 10.1016/s0009-2614(96)01244-4

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Linkage and solvent dependence of photoinduced electron transfer in zincporphyrin-C<inf>60</inf> dyads Reviewed

Imahori H., Hagiwara K., Aoki M., Akiyama T., Taniguchi S., Okada T., Shirakawa M., Sakata Y.

Journal of the American Chemical Society   118 ( 47 )   11771 - 11782   1996.11

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of the American Chemical Society  

Four different kinds of C -linked zincporphyrins have been prepared by changing systematically the linking position at meso-phenyl ring from ortho to para and their photophysical properties have been investigated. Regardless of the linkage between the two chromophores, photoinduced charge separation (CS) and subsequent charge recombination (CR) were observed in a series of zincporphyrin-C dyads by picosecond fluorescence lifetime measurements and time-resolved transient absorption spectroscopy. In THF the CS occurs from both the excited singlet state of the porphyrin and the C moieties, implying that the increase of the absorption cross section by both the chromophores results in the efficient formation of the ion pair (IP) state. On the other hand, in benzene the IP state generated by the photoinduced CS from the excited singlet state of the porphyrin to the C produces or energetically equilibrates with the locally excited singlet state of the C . Both the CS and CR rates for the metaisomer are much slower than those for the other porphyrin-linked C . Linkage dependence of the electron transfer (ET) rates can be explained by superexchange mechanism via spacer. These results demonstrate that C is a new promising building block as an acceptor in artificial photosynthetic models. 60 60 60 60 60 60 60

DOI： 10.1021/ja9628415

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Synthesis and self-assembly of porphyrin-linked fullerene on gold surface using S-Au linkage Reviewed

Akiyama T., Imahori H., Ajawakom A., Sakata Y.

Chemistry Letters   ( 10 )   907 - 908   1996.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Chemistry Letters  

Porphyrin-linked fullerene bearing methylthio group was prepared by 1,3-dipolar cycloadditon of the azomethine ylide, generated in situ using N-methylglycine and a formylporphyrin, with C . Self-assembled monolayer was formed by soaking Au electrode into a solution of the porphyrin-C dyad. The photocurrent was observed for the photochemical cell in the presence of electron carrier under illumination. 60 60

DOI： 10.1246/cl.1996.907

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