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TANAKA Senku

    Department of Energy and Materials　Associate Professor
Last Updated :2024/04/25

Researcher Information

Degree

  • Ph. D.（The Graduate University for Advanced Studies）

URL

ORCID ID

J-Global ID

Research Interests

  • 光電子分光   有機薄膜太陽電池   organic semiconductor interface   

Research Areas

  • Nanotechnology/Materials / Thin-film surfaces and interfaces
  • Nanotechnology/Materials / Organic functional materials
  • Nanotechnology/Materials / Applied materials

Academic & Professional Experience

  • 2019/04 - Today  Kindai UniversityFaculty of Science and TechnologyAssociate Professor
  • 2018/03 - Today  Kindai UniversityResearch Institute for Science and Technology（兼任）
  • 2013/04 - 2019/03  Kinki UniversityFaculty of Science and Engineering, Department of Electric and Electronic EngineeringLecturer
  • 2009/03 - 2013/03  Shimane UniversityInterdisciplinary Faculty of Science and Engineering, Department of Physics and Materials ScienceAssistant Professor
  • 2004/09 - 2009/02  Shimane UniversityInterdisciplinary Center for Science ResearchResearch Associate
  • 2007/09 - 2008/03  The University of Texas at DallasThe Alan G MacDiarmid NanoTech InstituteVisiting Research Scholar
  • 2003/05 - 2004/08  Nagoya UniversityResearch Center for Materials ScienceResearch Scientist

Education

  • 2000/04 - 2003/03  The Graduate University for Advanced Studies  The School of Mathematical and Physical Science  Department of Structural Molecular Science
  •        - 2000  Osaka City University  Graduate School, Division of Engineering
  •        - 2000  Osaka City University  工学研究科  応用物理学
  •        - 1998  Osaka City University  Faculty of Engineering
  •        - 1998  Osaka City University  Faculty of Engineering  応用物理学

Association Memberships

  • THE JAPANESE SOCIETY FOR SYNCHROTRON RADIATION RESEARCH   THE JAPAN SOCIETY OF APPLIED PHYSICS   The Institute of Electronics, Information and Communication Engineers   

Published Papers

  • Ryo Amasaki; Maho Kitahara; Senku Tanaka; Yoshitane Imai
    European Journal of Inorganic Chemistry Wiley 1434-1948 2024/01 [Refereed]
     
    Abstract High‐performance optoelectronic materials require luminescent materials capable of intense photoluminescence (PL). However, controlling the optical properties of luminescent materials requires complex synthesis and purification procedures. Herein, we propose a simple method for obtaining circularly polarized luminescence from achiral inorganic quantum dots. This method involves applying north‐up and south‐up 1.7 T magnetic fields at 25 °C to five types of achiral antimagnetic perovskite‐Pb‐quantum dots in a solution state. The wavelengths of magnetic circularly polarized luminescence (MCPL) and PL of achiral perovskite‐Pb quantum dots were successfully controlled according to the type and composition ratio of halogen ions. The magnitude of MCPL, gMCPL, was on the order of |gMCPL|=10−3 in a wavelength range of 406–697 nm. Although the perovskite‐Pb‐quantum dots were achiral, the rotation direction of the MCPL could be controlled by varying the direction of the applied magnetic field.
  • Tomoki Nishiyama; Hirotaka Kitoh-Nishioka; Senku Tanaka; Masahiko Maekawa; Takayoshi Kuroda-Sowa; Masaki Yoshida; Masako Kato; Takashi Okubo
    Dalton Transactions Royal Society of Chemistry (RSC) 1477-9226 2024 [Refereed]
     
    A photoconductive luminescence coordination polymer having an infinite two-dimensional (2D) structure containing copper(i) thiocyanate and a nitrogen-containing π-conjugated ligand.
  • Kouichi Matsumoto; Kazuhiro Yamashita; Yuuki Sakoda; Hinata Ezoe; Yuki Tanaka; Tatsuya Okazaki; Misaki Ohkita; Senku Tanaka; Yuki Aoki; Daisuke Kiriya; Shigenori Kashimura; Masahiko Maekawa; Takayoshi Kuroda-Sowa; Takashi Okubo
    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY WILEY-V C H VERLAG GMBH 2021 (33) 4620 - 4629 1434-193X 2021/09 [Refereed]
     
    New star-shaped non-fullerene acceptors (5Z,5 ' Z,5 '' Z)-5,5 ',5 ''-((benzo[1,2-b : 3,4-b ' : 5,6-b '']trithiophene-2,5,8-triyltris(4-octylthiophene-5,2-diyl))tris(methaneylylidene))tris(3-octyl-2-thioxothiazolidin-4-one) (1: BTT-OT-ORD) and 2,2 ',2 ''-((5Z,5 ' Z,5 '' Z)-((benzo[1,2-b : 3,4-b ' : 5,6-b '']trithiophene-2,5,8-triyltris(4-octylthiophene-5,2-diyl))tris(methaneylylidene))tris(3-octyl-4-oxothiazolidine-5,2-diylidene))trimalononitrile (2: BTT-OT-OTZDM) with a benzotrithiophene core, alkyl-thiophen units, and acceptor units were designed and synthesized. The HOMO-LUMO levels of 1 and 2 were determined by photoemission spectroscopy and UV-Vis absorption spectroscopy. Binary blend and ternary blend bulk heterojunction (BHJ) organic solar cells with non-fullerene acceptors 1 and 2 were fabricated with the inverted device structures of glass/ITO/ZnO/active_layer/MoO3/Ag. Both binary blend BHJ solar cells with 1 and 2 show lower J(SC) and larger V-OC values than P3HT : PCBM solar cells. On the other hand, ternary blend BHJ organic solar cells, including 10 % of 1, exhibited a larger power conversion efficiency than P3HT : PCBM solar cells because the J(SC) value was largely improved.
  • 義富卓也; 高田謙; 谷合伯斗; 安東秀峰; 松本浩一; 田中仙君
    電気学会論文誌 C 138 (11) 1298‐1304(J‐STAGE)  0385-4221 2018 [Refereed]
  • Hideo Ando; Senku Tanaka; Kouichi Matsumoto; Yoshihide Nakao
    CHEMICAL PHYSICS LETTERS ELSEVIER SCIENCE BV 687 60 - 65 0009-2614 2017/11 [Refereed]
     
    In poly(3-hexylthiophene) (P3HT), it is suggested that bromination disturbs the pi conjugation and reduces the carrier mobility. To investigate the deconjugation mechanism, we theoretically studied a key flexibility of the Br-P3HT backbone, namely inter-ring S-C-C-S dihedral torsion, in terms of potential energy curve, geometry-based aromaticity index, and decomposed energies of inter-monomer interaction. The linkage between bromination and the excitation energy was also investigated. We concluded that steric repulsion due to bulky bromo group can cause out-of-plane S-C-C-S torsion of Br-P3HT and consequent shortening of the conjugation length, not electronic substituent effect, leads to blue shift of the S-0 -> S-1 excitation energy. (C) 2017 Elsevier B.V. All rights reserved.
  • Hironobu Ishibashi; Mikimasa Katayama; Senku Tanaka; Toshihiko Kaji
    SCIENTIFIC REPORTS NATURE PUBLISHING GROUP 7 (1) 2045-2322 2017/07 [Refereed]
     
    For the search of new metal-halide perovskite solar cell materials, tolerance factors are calculated from the ionic radius of each site and are often utilized as the critical factors to expect the materials forming perovskite structure. As one of such amine hydrohalides, guanidine hydroiodide (GI) is reported not to react with PbI2. However, in this paper, we report the product of GI and SnI2 reaction, its visible light absorption, X-ray diffraction, and its solar cell operation, in spite of the more disadvantageous tolerance factor of SnI2 than PbI2. We also report the thermal stability of GI, enabling precise control of vacuum deposition, and utilization of co-evaporant induced crystallization method during the vacuum evaporation of the SnI2 film, which resulted in enlarging the SnI2 crystals and improving the short circuit current density of the solar cell.
  • Senku Tanaka; Siti Khadijah Binti Rosli; Ken Takada; Norito Taniai; Takuya Yoshitomi; Hideo Ando; Kouichi Matsumoto
    RSC ADVANCES ROYAL SOC CHEMISTRY 7 (74) 46874 - 46880 2046-2069 2017 [Refereed]
     
    We examined the effects of delocalized pi-electrons in poly(3-hexylthiophene) (P3HT) on the photovoltaic properties of a bulk heterojunction (BHJ) solar cell. The pi-conjugated length of P3HT was controlled by modification of P3HT through partial bromination at the 4-position of thiophene units. We investigated correlation between the degree of P3HT bromination (2, 11, 22, 37, 66, 84, 100%) and the photovoltaic properties of Br-P3HT:phenyl-C-61-butyric acid methyl ester (PCBM) BHJ solar cells. The power conversion efficiency of the 11% Br-P3HT:PCBM solar cell decreased to 56% of that of a pristine P3HT:PCBM solar cell. The main factor contributing to this decrease was lower short circuit currents. The photo absorption spectrum and the X-ray diffraction pattern of the 11% Br-P3HT film showed only slight differences to those of pristine P3HT, indicating the interchain pi-stacking of the polymers was almost unaffected by the 11% bromination. These results suggest that an intrachain pi-conjugation across more than 10 thiophene rings in the P3HT backbone is necessary to realize efficient charge transport in polymer domains. The 37% Br-P3HT:PCBM cell showed only weak photovoltaic properties; both inter- and intrachain delocalization of pi-electrons were disturbed by bromination.
  • Mamoru Kitaura; Senku Tanaka; Minoru Itoh; Akimasa Ohnishi; Hiroko Kominami; Kazuhiko Hara
    JOURNAL OF LUMINESCENCE ELSEVIER SCIENCE BV 172 243 - 248 0022-2313 2016/04 [Refereed]
     
    Excitation spectra for 5d-4f photoluminescence (PL) bands of Ce3+ and Eu2+ ions doped in SrGa2S4 crystals have been measured at room temperature in the energy region up to 25 eV. These spectra allow us to investigate the excitation process of luminescent ions under host excitation with vacuum ultraviolet (VUV) photons. A gentle increase in intensity is commonly observed at around 16.5 eV in the excitation spectra. Optical constant spectra were obtained from measurements of reflectivity and absorption edge spectra of undoped SrGa2S4 crystals. These data were compared with the results of a relativistic DV-X alpha calculation, to clarify the electronic structure of SrGa2S4. Ultraviolet photoelectron spectroscopy (UPS) has been carried out under the excitation with photons in the 12-20 eV range. The detailed analysis of UPS spectra reveals that the multiplication of electronic excitations (MEEs) occurs above 16.5 eV. The excitation process of Ce2+ and Eu2+ ions is discussed together with the processes of MEEs. (C) 2015 Elsevier B.V. All rights reserved.
  • Dynamics of surface photo-voltage in GaAs systems studied with time-resolved photoelectron spectroscopy
    Masao Kamada; Junpei Azuma; Senku Tanaka; Kazutoshi Takahashi
    3 (1) 2016/02 [Refereed]
  • Mamoru Kitaura; Senku Tanaka; Minoru Itoh
    JOURNAL OF LUMINESCENCE ELSEVIER SCIENCE BV 158 226 - 230 0022-2313 2015/02 [Refereed]
     
    This paper reports on the optical properties of cerium-doped lutetium oxyorthosilicate (LSO:Ce) crystals. The reflection and X-ray photoelectron spectra are measured, and compared to the electronic structure calculated by a discrete variational X alpha method. A sharp exciton band originating from O 2p -> Lu 5d transition is observed at 7.27 eV at 6 K, with the band-gap energy of 7.52 eV. Luminescence measurements have also been performed in a wide temperature range of 6-300 K. The intensity of Ce luminescence arising from the 5d -> 4f transition is temperature-independent under the direct excitation of Ce3+ ions, but it is enhanced at around 50 K under the excitation of host LSO crystals. This enhancement is found to anti-correlate with a thermal quenching of the intrinsic luminescence due to self-trapped excitons. The present results provide a piece of evidence that thermally-activated energy transfer from host to activator takes place efficiently in LSO:Ce. (C) 2014 Elsevier B.V. All rights reserved.
  • Senku Tanaka; Tomohiro Otani; Ken Fukuzawa; Koji Ogawa; Junpei Azuma; Isamu Yamamoto; Kazutoshi Takahashi; Masao Kamada; Ichiro Hiromitsu
    APPLIED PHYSICS LETTERS AMER INST PHYSICS 104 (19) 193304  0003-6951 2014/05 [Refereed]
     
    Photoelectric emission from organic and metal thin films is generally observed with irradiation of photon energy larger than 4 eV. In this paper, however, we report photoelectric emission from Ag on a zinc-phthalocyanine (ZnPc) layer at a photon energy of 3.4 eV. The threshold energy for this photoelectric emission is much smaller than the work function of Ag estimated by conventional photoelectron spectroscopy. The photoelectric emission by low-energy photons is significant for Ag thicknesses of less than 1 nm. Photoelectron spectroscopy and morphological study of the Ag/ZnPc suggest that the anomalous photoelectric emission from the Ag surface is caused by a vacuum level shift at the Ag/ZnPc interface and by surface plasmons of the Ag nanoparticles. (C) 2014 AIP Publishing LLC.
  • Takuya Nishimura; Tomotaka Furuyama; Masaru Miyazaki; Senku Tanaka; Ichiro Hiromitsu
    Applied Physics Letters 103 (22) 223306  0003-6951 2013/11 [Refereed]
     
    Internal electric field of the Schottky-barrier solar cells ITO/pentacene/H2-phthalocyanine (H2Pc)/In/Al (cell A) and ITO/H2Pc/In/Al (cell B) was studied by electroabsorption spectroscopy under white light illumination. The H2Pc films in the two cells have different crystal orientations. Under short-circuit condition, the average internal field in the H2Pc layer of cell A is increased by 2.5 times by an illumination of 40 mW/cm2 white light, which is due to a trapping of photogenerated holes and a resulting dipole layer formation at the H2Pc/In interface, while that of cell B is not affected by the white light illumination. © 2013 AIP Publishing LLC.
  • Shinsei Mizuta; Masatoshi Iyota; Senku Tanaka; Ichiro Hiromitsu
    THIN SOLID FILMS ELSEVIER SCIENCE SA 520 (17) 5761 - 5769 0040-6090 2012/06 [Refereed]
     
    Photocurrent generation in an indium-tin oxide (ITO)/iodine-doped Ni-phthalocyanine (NiPc-I-x)/C-60/In/Al heterojunction device with x similar to 1 was studied. By keeping the device in air after preparation, the device slowly reached a stationary state in which the sign of the photocurrent is opposite to that of a non-doped ITO/NiPc/C-60/In/Al device although the rectification direction for the dark current is the same. By a simulation of incident photon-to-current conversion efficiency spectra and a measurement of internal electric field by electroabsorption spectroscopy, it was elucidated that, in the doped device, the band bending near the phthalocyanine/C-60 interface is absent and the photocurrent is generated by a weak Schottky barrier at the C-60/In interface. It is also shown that the C-60 film encapsulates the doped iodine into the NiPc-I-x layer to stabilize the doping level and prevent the reaction of iodine with In. (C) 2012 Elsevier B.V. All rights reserved.
  • Ichiro Hiromitsu; Ayana Kawami; Senku Tanaka; Shigekazu Morito; Ryo Sasai; Takahisa Ikeue; Yasuhisa Fujita; Makoto Handa
    CHEMICAL PHYSICS LETTERS ELSEVIER SCIENCE BV 501 (4-6) 385 - 389 0009-2614 2011/01 [Refereed]
     
    Photoluminescence (PL) properties of meso-tetraphenylporphine-4,4'4 '',4'''-tetracarboxylic acid (H(2)TPP (COOH)(4)) bound to ZnO nanoparticle were studied. With 1.2 H(2)TPP(COOH)(4) molecules per ZnO particle, the PL intensity of H(2)TPP(COOH)(4) with a 325 nm excitation was increased to a 3.2-times larger value by the conjugate formation with ZnO. The excitation spectrum of PL gave an evidence of an emission of H(2)TPP(COOH)(4) by an energy transfer from ZnO. An analysis based on the Frster theory gave a reasonable value of 1.8 nm for the average distance between H(2)TPP(COOH)(4) and emissive surface defects on the ZnO particle. (C) 2010 Elsevier B. V. All rights reserved.
  • Senku Tanaka; Toshiyuki Hanada; Koji Ono; Kazuya Watanabe; Katsumi Yoshino; Ichiro Hiromitsu
    APPLIED PHYSICS LETTERS AMER INST PHYSICS 97 (25) 253306_1-3  0003-6951 2010/12 [Refereed]
     
    Improvement of power conversion efficiency of a zinc phthalocyanine (ZnPc)/C-60 heterojunction solar cell was achieved by inserting a lithium phthalocyanine (LiPc) layer at the indium-tin oxide (ITO)/ZnPc interface. The results of photoelectron spectroscopy suggest that the barrier height for the hole transport at the ITO/ZnPc interface is reduced by the LiPc layer. A similar improvement of the power conversion efficiency by the insertion of a LiPc layer was also observed in M-phthalocyanine (M=H-2, Cu, and TiO)/C-60 cells. (C) 2010 American Institute of Physics. [doi:10.1063/1.3529452]
  • Hiroaki Ishihara; Toyotsugu Kusagaya; Senku Tanaka; Ichiro Hiromitsu
    JAPANESE JOURNAL OF APPLIED PHYSICS JAPAN SOC APPLIED PHYSICS 49 (8) 081602_01-05  0021-4922 2010/08 [Refereed]
     
    Metal-free phthalocyanine (H(2)Pc) was deposited on an indium tin oxide (ITO) substrate with a pentacene buffer layer, and the effect of polishing of the ITO surface on the molecular orientation of H(2)Pc was studied By rubbing the ITO surface 10,000 times with a plastic eraser, the average surface roughness of ITO was decreased to 1 0 nm from its initial value of 2 0 nm, and the (31 (3) over bar) X-ray diffraction peak of alpha-form H(2)Pc became significantly large Rocking curves and optical absorption spectra indicated that, by polishing the ITO surface, the disorder in the orientation of the stacking axis (b-axis) of H(2)Pc was reduced A Schottky barrier cell of H(2)Pc with a highly ordered molecular orientation showed a lower photovoltaic performance than that with a disordered orientation (C) 2010 The Japan Society of Applied Physics
  • S. Tanaka; A. A. Zakhidov; R. Ovalle-Robles; Y. Yoshida; I. Hiromitsu; Y. Fujita; K. Yoshino
    SYNTHETIC METALS ELSEVIER SCIENCE SA 159 (21-22) 2326 - 2328 0379-6779 2009/11 [Refereed]
     
    We demonstrate a semitransparent organic photovoltaic (OPV) cell with two transparent electrodes: a multi-wall carbon nanotube (MWCNT) sheet and a Ga-doped ZnO (GZO) are used as a transparent anode and cathode, respectively. As an active layer, we used a bulk heterojunction structure with poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). The photovoltaic cell has a GZO/P3HT:PCBM/poly(3,4-ethylene-dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/MWCNT/PEDOT:PSS structure. For comparison, an OPV cell with a MWCNT-sheet anode and an indium tin oxide (ITO) cathode were also fabricated. The OPV cell with the GZO cathode showed better performance than that with the ITO cathode. owing to the lower work function of the former. The semitransparent OPV cell with GZO cathode demonstrated a short-circuit current of 3.4 mA/cm(2), open-circuit voltage of 0.51 V, and efficiency of 0.45%. (C) 2009 Elsevier B.V. All rights reserved.
  • Yuki Yoshida; Senku Tanaka; Yasuhisa Fujita; Ichiro Hiromitsu
    JOURNAL OF APPLIED PHYSICS AMER INST PHYSICS 106 (6) 064510  0021-8979 2009/09 [Refereed]
     
    The photovoltaic properties of a Ga-doped ZnO (GZO)/3,4,9,10-perylene-tetracarboxyl-bis-benzimidazole (PTCBI)/Zn-phthalocyanine (ZnPc)/Cu heterojunction cell (cell A) and a GZO/ZnPc/Cu Schottky-barrier cell (cell B) were investigated. The energy conversion efficiency eta of cell A was only 0.02% immediately after the device preparation but improved to 0.46% after aging for 24 days in air. To elucidate the mechanism of this aging effect, photocurrent action and electroabsorption spectra were measured for cell B. The results reveal that a Schottky barrier exists at the ZnPc/Cu interface which blocks the transport of photogenerated holes to the Cu electrode, and the barrier height is reduced by a white-light illumination of the device after aging. The change in barrier height is attributed to the formation of electron traps at the surface of the ZnPc layer on aging that trap photogenerated electrons. (C) 2009 American Institute of Physics. [doi:10.1063/1.3226880]
  • Ichiro Hiromitsu; Takahisa Ikeue; Kazuhiro Karino; Takatsugu Ohno; Senku Tanaka; Hideo Shiratori; Shigekazu Morito; Yasuhisa Fujita; Makoto Handa
    CHEMICAL PHYSICS LETTERS ELSEVIER SCIENCE BV 474 (4-6) 315 - 319 0009-2614 2009/06 [Refereed]
     
    The optical absorption and photoluminescence measurements were carried out for ZnO nanoparticle-tetraphenylporphyrin (TPP) systems made of four kinds of TPP's with and without p-aminophenyl groups. The ZnO particles were treated with L-cysteine in order to make a ZnO-(L-cysteine)-TPP binding. However, this binding was not formed because of an absence of the ZnO-(L-cysteine) binding. In the case of metal-free TPP's, the central hydrogen atoms of the TPP ring were replaced by a Zn atom during an aging of 2-4 weeks. An energy transfer from photoexcited ZnO to TPP occurs by a collision between ZnO and TPP in the dispersed medium. (C) 2009 Elsevier B.V. All rights reserved.
  • S. Tanaka; K. Mielczarek; R. Ovalle-Robles; B. Wang; D. Hsu; A. A. Zakhidov
    APPLIED PHYSICS LETTERS AMER INST PHYSICS 94 (11) 113506  0003-6951 2009/03 [Refereed]
     
    We demonstrate an organic photovoltaic cell with a monolithic tandem structure in parallel connection. Transparent multiwalled carbon nanotube sheets are used as an interlayer anode electrode for this parallel tandem. The characteristics of front and back cells are measured independently. The short circuit current density of the parallel tandem cell is larger than the currents of each individual cell. The wavelength dependence of photocurrent for the parallel tandem cell shows the superposition spectrum of the two spectral sensitivities of the front and back cells. The monolithic three-electrode photovoltaic cell indeed operates as a parallel tandem with improved efficiency.
  • Senku Tanaka; Masaya Toba; Takuya Nakashima; Tsuyoshi Kawa; Katsurni Yoshino
    JAPANESE JOURNAL OF APPLIED PHYSICS JAPAN SOC APPLIED PHYSICS 47 (2) 1215 - 1218 0021-4922 2008/02 [Refereed]
     
    The photoresponsive change in the electronic structure of photochromic diarylethene, 1,2-bis(5-(2,4-diphenylphenyl)-2,4-dimethyl-3-thienyl) perfluorocyclopentene (DAE) is observed by photoelectron spectroscopy. UV and visible light irradiation introduce clear differences in the spectral shape of photoelectron spectra of the DAE thin film. In the photoelectron spectrum after UV light irradiation, the highest occupied molecular orbital (HOMO) of the DAE film appears at around 1.5 eV below the Fermi level. In contrast, under visible light irradiation, the HOMO of the DAE film has higher binding energy. The variation of the HOMO peak can be reproduced repeatedly by UV and visible light irradiation. These differences correspond to the difference in the electronic structure between the closed-ring and the open-ring isomer of DAE. The molecular orbitals of the DAE isomers are calculated with the density functional theory, and the results are in good agreement with the photoelectron results. Cyclic voltammetry measurement of the closed-ring isomer shows the first oxidation waves at 0.6 V (vs Ag/Ag+) whereas the open-ring isomer shows the first oxidation wave at 1.1 V. The consistency between the photoelectron results and other methods suggests that photoelectron spectroscopy has a powerful potential to reveal the electronic structure of photochromic molecules.
  • Yuki Yoshida; Senku Tanaka; Ichiro Hiromitsu; Yasuhisa Fujita; Katsumi Yoshino
    JAPANESE JOURNAL OF APPLIED PHYSICS JAPAN SOC APPLIED PHYSICS 47 (2) 867 - 871 0021-4922 2008/02 [Refereed]
     
    The photovoltaic properties of Zn-phthalocyanine (ZnPc)/3,4,9,10-perylene-tetracarboxyl-bis-benzimidazole (PTCBI) heterojunction solar cells using Ga-doped ZnO (GZO) film as a transparent electrode are studied. When GZO is the electrode in contact with the donor layer, i.e., ZnPc, the energy conversion efficiency eta is only 1/4 of that for the cell using indium-tin-oxide (ITO) as the electrode. When GZO is the electrode in contact with the acceptor layer, i.e., PTCBI, on the other hand, the cell has a three times larger eta than the cell using ITO. These results are explained by the work function of GZO being lower than that of ITO. When GZO, or ITO, is used as an electrode for PTCBI, an interesting aging effect is observed. For example, by keeping the GZO-based cell in open air for 6 days in the dark, the energy conversion efficiency and the short-circuit current are increased by factors of 1.67 and 1.36, respectively.
  • Senku Tanaka; Yuki Yoshida; Makoto Nonomura; Katsumi Yoshino; Ichiro Hiromitsu
    THIN SOLID FILMS ELSEVIER SCIENCE SA 516 (6) 1006 - 1011 0040-6090 2008/01 [Refereed]
     
    The effects of the insertion of a thin bathocuproine (BCP) layer at the Au/Zn-phthalocyanine (ZnPc) interface on the energy level alignment and morphology of each layer are investigated using photoelectron spectroscopy, atomic force microscopy and X-ray diffraction. The energy differences between the highest occupied molecular orbital (HOMO) of ZnPc and Fermi level of An (E-F(Au)) and between the HOMO of BCP and E-F(Au) are about 0.7 eV and 2.4 eV, respectively. The HOMO level of ZnPc on Au is shifted to higher binding energies with increasing ZnPc thickness. The HOMO level of ZnPc on BCP, however, indicates an energy shift in the opposite direction to the lower binding energies as the thickness of ZnPc increases. Atomic force microscopy reveals that the roughness of the ZnPc surface is reduced by the insertion of the BCP layer. X-ray diffraction patterns show that the existence of the thin BCP layer promotes crystallization of ZnPc over the layer and the molecular planes of ZnPc are perpendicular to the BCP surface. (C) 2007 Elsevier B.V. All rights reserved.
  • Ichiro Hiromitsu; Shin-Ichiro Mada; Ayumi Inoue; Yuki Yoshida; Senku Tanaka
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS INST PURE APPLIED PHYSICS 46 (11) 7241 - 7246 0021-4922 2007/11 [Refereed]
     
    The internal electric field in a heterojunction solar cell made of poly(5-(2'-ethylhexyloxy)-2-methoxy-1,4-phenylenevinylene) (MEH-PPV) as a donor and 3,4,9,10-perylene-tetracarboxyl-bis-benzimidazole (PTCBI) as an acceptor is studied by electroabsorption (EA). The 1 omega-EA signal detected at the fundamental electric-field-modulation frequency 0) comes from the bulk of the film for MEH-PPV but from the interface of the film for PTCBI. The bias dependence of the bulk electric field for MEH-PPV is correlated with that of the photocurrent generated by MEH-PPV excitation, indicating that the electric field has an essential role in carrier photogeneration. An analysis of the photocurrent action spectrum indicates that the photocurrent-active region in the MEH-PPV layer changes its location depending on the applied bias voltage. This suggests that the region of strong electric field in the MEH-PPV layer changes its location along with the active layer.
  • Yuki Yoshida; Makoto Nakamura; Senku Tanaka; Ichiro Hiromitsu; Yasuhisa Fujita; Katsumi Yoshino
    SYNTHETIC METALS ELSEVIER SCIENCE SA 156 (18-20) 1213 - 1217 0379-6779 2006/11 [Refereed]
     
    The photovoltaic properties and distribution of inner electric field were studied for ZnO/Zn-phthalocyanine (ZnPc)/Au solar cells, the ZnO films of which were prepared by the metal organic chemical vapor deposition (MOCVD) method. The photocurrent is generated only by the excitation of ZnO, and the excitation of ZnPc does not contribute to the photocurrent generation. An electroabsorption (EA) study indicated that the inner electric field only exists in the ZnO layer. The absence of the inner electric field in the ZnPc layer results in the absence of photocurrent with ZnPc excitation. (c) 2006 Elsevier B.V. All rights reserved.
  • M Nonomura; Hiromitsu, I; S Tanaka
    APPLIED PHYSICS LETTERS AMER INST PHYSICS 88 (4) 042111  0003-6951 2006/01 [Refereed]
     
    A thin C-60 or bathocuproine (BCP) layer of 5 nm thickness is inserted to the Au/Zn-phthalocyanine (ZnPc) interface of a Au/ZnPc/In/Al Schottky-junction cell, and the effect of the insertion on the dark current is investigated. The forward dark current density is increased from 0.5 mA/cm(2) to 9.7 and 9.2 mA/cm(2) by the insertions of the C-60 and BCP layers, respectively. The increase is not attributed to a change in the barrier height for the hole injection, but to a decrease of the concentration of trapped negative charges on the ZnPc surface. (c) 2006 American Institute of Physics.
  • Kazuhiko Seki; Toshio Nishi; Senku Tanaka; Tadanobu Ikame; Hisao Ishii; Kanamc Kanai
    Materials Research Society Symposium Proceedings 871 293 - 298 0272-9172 2005/12 
    In various organic electronic devices, interfaces formed by organic layers can play important roles. We have been studying various organic interfaces for clarifying their structure and electronic structure. In this talk, we will report our recent study of the effect of various types of doping for a variety of dopants - residual impurity, atmospheric gases, and metallic and organic intentional dopants. In particular, detailed and quantitative information about the effect of oxygen from the viewpoint of electronic structure was obtained for titanyl phthalocyanine (TiOPc), and the results corresponded well with the recent report of atmospheric effect on organic field effect transistor. © 2005 Materials Research Society.
  • S Tanaka; E Kawabe; K Kanai; T Iwahashi; T Nishi; Y Ouchi; K Seki
    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA ELSEVIER SCIENCE BV 144 533 - 536 0368-2048 2005/06 [Refereed]
     
    The effect of n-type doping of hexadecafluorophthalocyaninatozinc (F16ZnPc) with an electron-donating organic molecule tetrathianaphthacene (TTN) was investigated by ultraviolet photoemission spectroscopy (UPS). We measured the UPS spectra over a wide range of the film thickness for pristine F16ZnPc, pristine TTN, and TTN-doped F16ZnPc. From the change of the energy of the vacuum level (VL), we could deduce the energy level alignment at organic/metal interfaces. The results for pristine F16ZnPc showed (1) abrupt shift of VL at small thickness corresponding to dipole layer formation, and (2) more gradual shift of VL, which might correspond to the band bending to align the Fermi level by residual impurity acting as unintentional dopant. For F16ZnPc doped with TTN, the region (2) is merged into the region (1), indicating that the thickness of the band-bending region of the doped F16ZnPc was much reduced from that of pristine F16ZnPc. This demonstrates that F16ZnPc was effectively doped with carriers from the TTN molecules. It was also found that the energy of the highest occupied molecular orbital of F16ZnPc was shifted to higher binding energy by doping TTN molecules. These results suggest that TTN acts as a good donor in F16ZnPc. (c) 2005 Elsevier B.V. All rights reserved.
  • S Tanaka; K Kanai; E Kawabe; T Iwahashi; T Nishi; Y Ouchi; K Seki
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS JAPAN SOC APPLIED PHYSICS 44 (6A) 3760 - 3763 0021-4922 2005/06 [Refereed]
     
    The n-type doping ability of the electron-donating organic molecule tetrathianaphthacene (TTN) was examined by ultraviolet photoemission spectroscopy (UPS) for two kinds of matrix organic semiconductors, hexadecafluorophthalocyaninatozinc (F(16)ZnPc) and tris(8-hydroxyquinoline)aluminum (Alq(3)). The observed dependence of the UPS spectra suggests that TTN acts as a good donor in F(16)ZnPc, while the effect was not so significant for Alq(3). These results and the consideration of the energy parameters of these molecules indicate that a close match between the highest occupied molecular orbital of the dopant and the lowest unoccupied molecular orbital of the matrix is important for efficient n-type doping.
  • S Tanaka; SD More; K Takahashi; M Kamada
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN PHYSICAL SOC JAPAN 72 (3) 659 - 663 0031-9015 2003/03 [Refereed]
     
    Core-level photoelectron spectroscopy with the combination of synchrotron radiation and laser light was used for exploring the dynamics of the surface photovoltage (SPV) effect on a p-GaAs (100). It was found that a temporal profile of the SPV is very different in microsecond range between room temperature and 90 K. The results can be explained with the recombination of photoexcited carriers via thermionic and tunneling processes. The SPV effects and its temporal profiles on the negative electron-affinity (NEA) surface were also studied. It was observed that the SPV effect is suppressed on the NEA surface. which may be due to the escape process of the photoexcited carriers.
  • Tanaka, S; More, SD; Takahashi, K; Kamada, M; Nishitani, T; Nakanishi, T
    Surface Review and Letters 9 (2) 551 - 556 0218-625X 2002/04 [Refereed]
  • S. Tanaka; S. D. More; J. Murakami; M. Itoh; Y. Fujii; M. Kamada; M. Kamada
    Physical Review B - Condensed Matter and Materials Physics 64 (15) 1553081 - 1553086 0163-1829 2001/10 [Refereed]
     
    The surface photovoltage (SPV) effect on laser-excited p-GaAs (100) has been investigated using core-level photoelectron spectroscopy with synchrotron radiation (SR). The energy shift of the Ga 3d photoelectrons due to the SPV effect was remarkably dependent on the sample temperature and the laser photon flux. The dependence in each case was well interpreted on the basis of a simple SPV formula derived from the band-bending scheme with excess photocarriers. The magnitude of the band bending was about 0.8 Ev for clean p-GaAs (100) surfaces having no electrodes. Similar core-level shifts were observed in the Ga 3d and Cs 4d spectra of Cs/GaAs (100), indicating an unpinned behavior of the electronic states of the Cs surface layer. The time response of the SPV effect was also investigated in the nanosecond range using a pump-probe method with SR and the laser.
  • S Tanaka; SD More; J Murakami; M Itoh; Y Fujii; M Kamada
    PHYSICAL REVIEW B AMER PHYSICAL SOC 64 (15) 155308  2469-9950 2001/10 [Refereed]
     
    The surface photovoltage (SPV) effect on laser-excited p-GaAs (100) has been investigated using core-level photoelectron spectroscopy with synchrotron radiation (SR). The energy shift of the Ga 3 d photoelectrons due to the SPV effect was remarkably dependent on the sample temperature and the laser photon flux. The dependence in each case was well interpreted on the basis of a simple SPV formula derived from the band-bending scheme with excess photocarriers. The magnitude of the band bending was about 0.8 eV for clean p-GaAs (100) surfaces having no electrodes. Similar core-level shifts were observed in the Ga 3d and Cs 4d spectra of Cs/GaAs (100), indicating an unpinned behavior of the electronic states of the Cs surface layer, The time response of the SPV effect was also investigated in the nanosecond range using a pump-probe method with SR and the laser.
  • M Kamada; S Tanaka; K Takahashi; Y Doi; K Fukui; T Kinoshita; Y Haruyama; S Asaka; Y Fujii; M Itoh
    NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT ELSEVIER SCIENCE BV 467 1441 - 1443 0168-9002 2001/07 [Refereed]
     
    Combined systems for photoelectron spectroscopy using synchrotron radiation (SR) and laser have been constructed at BL5A and BL6A2 in the UVSOR facility, Okazaki. The systems consist of photoelectron spectrometers with high performance, mode-locked lasers, and timing electronic circuits. The laser pulses with repetition frequency of 90 MHz are synchronized with the SR pulses. An upgrade project to install a micro-ESCA at BL6A2, which is now in progress, is also reported. (C) 2001 Elsevier Science B.V. All rights reserved.
  • SD More; S Tanaka; S Tanaka; T Nishitani; T Nakanishi; M Kamada
    SPIN 2000 AMER INST PHYSICS 570 916 - 919 0094-243X 2001 [Refereed]
     
    Difference in NEA activation processes on GaAs(100) has been investigated with high resolution photoemission spectroscopy. It was found that the NEA surface produced by different activation processes can be classified into three phases having characteristic chemical reactions of Cs and Oxygen with GaAs. A schematic phase diagram is presented to understand NEA activation processes.
  • S Tanaka; SD More; T Nishitani; K Takahashi; T Nakanishi; M Kamada
    SPIN 2000 AMER INST PHYSICS 570 1000 - 1002 0094-243X 2001 [Refereed]
     
    Photoelectron spectroscopy with the combination of synchrotron radiation and laser has been used for exploring the surface photovoltage effect of GaAs photocathodes. It has been observed that the laser induced surface photovoltage causes core-level shifts of photoelectron spectra without any spectral change. The surface photovoltage effects for core-levels and its temporal profiles on clean and negative electron-affinity surfaces of GaAs (100) and GaAs/GaAsP superlattice are reported.
  • S More; S Tanaka; S Tanaka; Y Fujii; M Kamada
    SURFACE SCIENCE ELSEVIER SCIENCE BV 454 161 - 165 0039-6028 2000/05 [Refereed]
     
    The electronic states during different stages of the NEA surface formation of the GaAs(100)-O/Cs coadsorption system have been investigated with photoemission using synchrotron radiation at RT and 100 K. It was found that the core level peak shifts for early steps of NEA surface formation differ between the two temperatures. An analysis of the core level peak shifts and the increase in peak height during the oxidation of Cs monolayers shows that the observed values are comparable with those of bulk Cs and Cs layers on other substrates. Later steps of NEA surface formation do not differ between experiments carried out at RT and 100 K. (C) 2000 Elsevier Science B.V. All rights reserved.
  • M Kamada; J Murakami; S Tanaka; SD More; M Itoh; Y Fujii
    SURFACE SCIENCE ELSEVIER SCIENCE BV 454 525 - 528 0039-6028 2000/05 [Refereed]
     
    The photo-induced change in the semiconductor-vacuum interface on GaAs(100) and Cs/GaAs(100) has been investigated with core-level photoelectron spectroscopy using synchrotron radiation and a mode-locked Nd:YAG laser. Both Ca-3d and As-3d photoelectron peaks showed transient energy shifts under the laser irradiation without any spectral change. The amounts of energy shift were strongly dependent on the sample temperature and laser photon flux. It is shown that the experimental results can be fitted to a theoretical curve which was derived from the photo-induced band bending scheme in the surface layer of the semiconductor. (C) 2000 Elsevier Science B.V. All rights reserved.

Conference Activities & Talks

  • 亜鉛フタロシアニン/C60界面における光起電力の光電子分光法による観測  [Not invited]
    第25回日本放射光学会年会・放射光科学合同シンポジウム  2012
  • 有機/有機界面での光起電力と太陽電池の開放電圧との相関  [Not invited]
    第59回応用物理学関係連合講演会  2012
  • Photoinduced Effects on the Electronic Structure of the Organic/Organic and Organic/Metal Interfaces  [Not invited]
    2011 MRS Fall Meeting  2011
  • 光照射による有機薄膜の電子構造変化と光電変換特性との相関  [Not invited]
    第72回応用物理学会学術講演会  2011
  • 金属ドーピングした光電変換層を持つ有機薄膜太陽電池  [Not invited]
    第72回応用物理学会学術講演会  2011
  • 銀/亜鉛フタロシアニン/銀サンドイッチ型セルにおける光電流特性  [Not invited]
    第57回応用物理学関係連合講演会  2010
  • リチウムフタロシアニン挿入層をもちいたフタロシアニン/C60系太陽電池の効率改善 II  [Not invited]
    第56回応用物理学関係連合講演会  2009
  • 有機薄膜太陽電池における有機層/電極界面障壁のLiPc挿入層による低減  [Not invited]
    第70回応用物理学会学術講演会  2009
  • 亜鉛フタロシアニン/インジウム界面における界面準位の形成  [Not invited]
    第70回応用物理学会学術講演会  2009
  • リチウムフタロシアニン挿入層をもちいたフタロシアニン/C60系太陽電池の効率改善  [Not invited]
    第69回応用物理学会学術講演会  2008
  • フォトクロミックジアリールエテン分子薄膜の光電子スペクトルにおける光応答変化  [Not invited]
    第68回応用物理学会学術講演会  2007

MISC

Industrial Property Rights

Research Grants & Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2018/04 -2021/03 
    Author : TANAKA Senku
     
    We studied to improve the efficiency of semi-transparent organic solar cells. Our initial goal was to increase efficiency using a ternary-mixed layer (a layer in which appropriate molecules are doped into the bulk hetero-junction organic semiconductor layer). We found that the heat treatment during the device fabrication process significantly degraded the cell performance. We investigated the process and device configuration to avoid this problem. However, we were unable to find a definitive solution during the research period. On the other hand, by investigating the relationship between light-irradiation direction on semi-transparent solar cells and their photovoltaic characteristics, we could gain insight into the charge transfer characteristics under operating conditions.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2014/04 -2017/03 
    Author : TANAKA Senku
     
    The improvement of power conversion efficiency of organic solar cells are important problem for its practical application. The electronic structure of organic molecules in the organic solar cells is a crucial information to understand the photo current generation in organic solar cells. In this research, we studied a measurement method for the electronic state of organic molecules under operating condition of organic solar cells. By using the photoelectron spectroscopy under light irradiation and the electroabsorption spectroscopy under irradiation with white light, a change in the electronic states of the organic thin film caused by the light irradiation effect was observed. A fabrication method of semitransparent organic solar cells, which is suitable for the elecrtoabsorption method, was established. Furthermore, it was found that a lead halide perovskite film was able to fabricate by the vacuum deposition method using the perovskite single crystal as a deposition source.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2012/04 -2015/03 
    Author : HIROMITSU ICHIRO; HANDA Makoto; TANAKA Senku
     
    Internal electric field and photovoltaic performance of the Schottky-barrier solar cells made of a Zn-phthalocyanine(ZnPc) thin film were studied. By an insertion of a NTCDA buffer layer between the ZnPc film and transparent electrode, the short-circuit current increased to a 6 times larger value. When PTCBI was used for the buffer layer, an interesting phenomenon was observed, i.e. the photocarrier-generation efficiency in the PTCBI layer was anomalously high. A new experimental technique, Electroabsorption under White Light Illumination(EAWL), was developed, which enabled the measurement of the internal electric field in the device under operation.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2012/04 -2014/03 
    Author : TANAKA Senku; HAYASHI Taisuke
     
    Photoelectric emission from organic and metal thin films is generally observed with irradiation of photon energy larger than 4 eV. In this research, however, we report photoelectric emission from Ag on a zinc-phthalocyanine (ZnPc) layer at a photon energy of 3.4 eV. The threshold energy for this photoelectric emission is much smaller than the work function of Ag estimated by conventional photoelectron spectroscopy. The photoelectric emission by low-energy photons is significant for Ag thicknesses of less than 1 nm. Photoelectron spectroscopy and morphological study of the Ag/ZnPc suggest that the anomalous photoelectric emission from the Ag surface is caused by a vacuum level shift at the Ag/ZnPc interface and by surface plasmons of the Ag nanoparticles.
  • Investigation of electronic structures of the organic photovoltaic cells under the operating conditions
    The Murata Science Foundation：Research grant
    Date (from‐to) : 2011/10 -2012/09 
    Author : TANAKA Senku
     
    The electronic structure of the organic electronics devices has attracted much interest since it affects the performance of the devices. Many researches are reporting the electronic structure of the organic layers of the organic solar cell for understanding and controlling the photovoltaic properties. One of the powerful tools to investigate the electronic structure of the organic layer is the photoelectron spectroscopy. The electronic structure of the organic layer in the devices can be inferred from the photoelectron spectra of the organic thin films. In the present study, photoinduced effects on the electronic structure of the donor/acceptor interface has been investigated by using the photoelectron spectroscopy under the light irradiation.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2010 -2011 
    Author : TANAKA Senku
     
    The effect of the light irradiation on the electronic structure of a donor/acceptor(DA) heterojunction interface was investigated by using the photoelectron spectroscopy. Under the light irradiation, the photoelectron spectrum was shifted corresponds to the polarity of the photovoltage of the DA heterojunction photovoltaic cell. The shift of photoelectron spectrum was caused by the photo-generated holes(electrons) in the donor(acceptor) layer. The shift value was, however, smaller than the typical value of open-circuit voltage of the DA heterojunction photovoltaic cell. The present results imply that the development of an electromotive force in an organic photovoltaic cell is closely related to a presence of semipermeable membranes for the photo-generated charges in the photovoltaic cell.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2009 -2011 
    Author : HIROMITSU Ichiro; HANDA Makoto; TANAKA Senku
     
    In the thin film of one-dimensional polymer phthalocyanine GaPcF deposited on ITO substrate, the polymer axes usually lie parallel to the substrate. In the present study, however, it has been succeeded to obtain a highly ordered alignment in which the polymer axes stand on the substrate. This made it possible to produce an organic thin film solar cells with no bottleneck for hole transport. However, the solar cells thus produced showed no improvement in the photovoltaic characteristics. This suggests that the resistance at the surface of the GaPcF film was increased by the alignment.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2005 -2008 
    Author : KAWAI Tsuyoshi; HASEGAWA Yasuchika; YUASA Junpei; NAKASHIMA Takuya; TANAKA Senku
     
    フォトクロミック分子によるπ共役系スイッチングを目指して、さまざまなπ共役系を有するフォトクロミック分子の開発とその評価を行った。フォトクロミックターアリーレンの中央のアリール部に対してπ共役ユニットを導入したところ、π共役系の拡張に伴って吸収の長波長シフトが見出された。さらにフォトクロミック反応前後の吸収波長はそれぞれの構造におけるπ共役系の広がりに対応して変化することが見出され、ターアリーレン系フォトクロミック分子においてπ共役系の方向切り替えが可能であること明らかになった。一方、光によりπ共役分子ワイヤーの形成を目指して、光照射に伴って安定な芳香族ユニットが形成する新しい光化学反応の開発に成功した。この分子では光反応後に形成する中間体から、自発的にメタノールが脱離し、安定な芳香族分子を形成し、さらにπスタックによる超分子集合体を形成することが見出された。類似の反応は従来は酸素などの酸化剤の存在が必要であったらが、脱離ユニットを安定なアルコールとすることで、自発的な光脱離反応が可能となった。

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