Papers - KADOYA Tomofumi
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Accumulated charge measurement using a substrate with a restricted-bottom-electrode structure Reviewed
Toshiaki Tanimura, Hiroyuki Tajima, Akinari Ogino, Yuta Miyamoto, Tomofumi Kadoya, Takeshi Komino, Tokuji Yokomatsu, Kazusuke Maenaka, Yuka Ikemoto
Organic Electronics 74 251 - 257 2019.11
© 2019 Elsevier B.V. Accumulated charge measurement (ACM) is a new experimental technique for organic semiconductors to evaluate the charge injection barrier at the semiconductor–metal interface directly using a metal–insulator–semiconductor–metal (MISM) capacitor. In this technique, the precise estimation of the electrostatic capacity of the insulator layer (CI) is required for the analysis. The information of this parameter is, in principle, included in the ACM data; however, it is not directly evaluated because of the error resulting from the charge-spreading effect in an organic MISM capacitor with an unrestricted electrode structure. Therefore, the CI in previous ACM experiments has been independently estimated from the area of the electrode. In this study, a novel design of a substrate with a restricted-bottom-electrode structure is reported. Using the newly designed substrate, it was possible to suppress the charge-spreading effect and successfully estimate precise values of CI directly from the ACM data. Subsequently, it was possible to evaluate the injection barriers at the metal-free phthalocyanine (H2Pc)–Ag and pentacene–Au interfaces, which were 0.4 and 0.15 eV, respectively. The built-in potentials in the semiconductor layer were also determined for the samples used in the measurement.
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New pi-extended catecholate complexes of Pt(II) and Pd(II) containing a benzothienobenzothiophene (BTBT) moiety: synthesis, electrochemical behavior and charge transfer properties Reviewed International journal
K. Tahara, Y. Ashihara, T. Higashino, Y. Ozawa, T. Kadoya, K. Sugimoto, A. Ueda, H. Mori, M. Abe
Dalton Trans. 48 ( 21 ) 7367 - 7377 2019
Benzothienobenzothiophene (BTBT) and derivatives have received increasing attention as organic field-effect transistor materials and molecular conductors. This report presents the first synthesis of metal complexes involving a BTBT moiety, which was achieved by complexation of 2,2'-bipyridyl complexes of Pt(ii) and Pd(ii) with dihydroxy-substituted BTBT (1) as a new π-extended catecholato ligand (tBu2Bpy = 4,4'-di-tert-butyl-2,2'-dipyridyl). The resulting complexes M(tBu2Bpy)(O2BTBT) (M = Pt (3Pt) and Pd (3Pd)) were characterized by UV-vis spectroscopy, density functional theory (DFT) calculations, and cyclic voltammetry. The electron donating ability of BTBT was substantially enhanced upon including two oxygen substituents followed by metal coordination. This enabled chemical oxidation of 3Pt and 3Pd with a mild chemical oxidant (ferrocenium hexafluorophosphate) and formation of the one-electron-oxidized state. While 3Pt and 3Pd exhibited an absorption band originating from a catecholate → Bpy ligand-to-ligand charge transfer transition typical of this class of catecholato complexes, the radical cations exhibited a unique π-π* intramolecular charge transfer (ICT) transition absorption in which the π and π* orbitals were the newly incorporated benzothienothiophene-based donor and semiquinonato-based acceptor, respectively. The BTBT+ skeleton was electronically divided into two sites by the present chemical modification. The ICT properties of the complexes were found to be modulated by varying the metal ions. These findings offer a new approach to molecular design for (semi)conducting materials using optical properties.
DOI： 10.1039/c8dt05057k
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T. Kadoya, R. Oki, Y. Kiyota, Y. Koyama, T. Higashino, K. Kubo, T. Mori, J. Yamada
J. Phys. Chem. C 123 ( 9 ) 5216 - 5222 2019
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Mott Transition Coupled to Molecular Motion in a Quasi-Two-Dimensional Organic Material Reviewed
Ryosuke Takehara, Kohei Nakada, Kazuya Miyagawa, Tomofumi Kadoya, Jun-ichi Yamada, Kazushi Kanoda
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 87 ( 9 ) 094707 2018.9
Publisher：PHYSICAL SOC JAPAN
We performed resistivity and H-1-NMR measurements of a quasi-two-dimensional organic material, beta-(BDA-TTP)(2)I-3, to investigate its electronic and magnetic properties across the Mott transition. The NMR spectra and spin-lattice relaxation rate, T-1(-1), show a commensurate antiferromagnetic order in a Mott insulating phase at low pressures and a strongly discontinuous Mott transition around 8 kbar. In the metallic state, the resistivity shows Fermi liquid behavior at low temperatures, whereas (T1T)(-1) is weakly temperature-dependent in the same temperature range. The temperature profile of T-1(-1) indicates that the Mott transition is associated with a marked change in molecular dynamics, suggesting the strong coupling of the Mott transition to the intramolecular degrees of freedom, which is very probably associated with a structural transition.
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H. Akutsu, S. Ito, T. Kadoya, J. Yamada, S. Nakatsuji, S. S. Turner, Y. Nakazawa
Inorg. Chim. Acta 482 654 - 658 2018
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Hiroyuki Tajima, Naoto Yasukawa, Hisaki Nakatani, Seiichi Sato, Tomofumi Kadoya, Jun-ichi Yamada
ORGANIC ELECTRONICS 51 162 - 167 2017.12
Publisher：ELSEVIER SCIENCE BV
Hole injection barriers at the regioregular-poly-3(hexylthiophene) (RR-P3HT)/metal (Cu or Ag) interface were investigated using the accumulated charge measurement (ACM). Thermal annealing of RR-P3HT at 55 degrees C decreased the injection barrier. RR-P3HT thermally annealed in N-2 forms an ohmic contact with Ag and a Schottky contact with Cu. The obtained values of the injection barriers, phi(B) were well expressed by the Mott-Schottky rule, i. e., phi(B) = IE - W-m', where IE is the ionization energy of RR-P3HT and W-m' is the work function of the metal electrode in air. The effect of the large vacuum level shift, reported in UPS studies conducted under ultrahigh vacuum, was not observed. (C) 2017 Elsevier B.V. All rights reserved.
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Hiroyuki Tajima, Kesuke Yoshida, Seiichi Sato, Tomofumi Kadoya, Jun-ichi Yamada
JOURNAL OF PHYSICAL CHEMISTRY C 121 ( 27 ) 14725 - 14730 2017.7
Publisher：AMER CHEMICAL SOC
The effect of the offset bias voltage on the threshold voltage of the hole injection into the organic-semiconductor (OS) layer was examined in detail in the accumulated charge measurement (ACM) for the n-type Si/SiO2/OS/Ag (OS = zinc phthalocyanine [ZnPc] or metal-free phthalocyanine [H2Pc]) capacitor. The threshold highly depends on the offset bias voltages, when the OS layer is in the hole depletion regime. On the contrary, the threshold was nearly constant when the OS layer operated in the hole-accumulation regime. The hole injection barrier of the Ag/OS interface was obtained by the threshold in the accumulation regime. The obtained values were 0.41 and 0.05 eV for H2Pc/Ag and ZnPc/Ag interfaces, respectively. The study revealed that accurate estimation of the injection barrier is possible by examining the offset voltage dependence in the ACM.
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Ryonosuke Sato, Masaki Dogishi, Toshiki Higashino, Tomofumi Kadoya, Tadashi Kawamoto, Takehiko Mori
JOURNAL OF PHYSICAL CHEMISTRY C 121 ( 12 ) 6561 - 6568 2017.3
Publisher：AMER CHEMICAL SOC
n-Channel organic transistors with excellent air stability are realized on the basis of charge-transfer complexes, (BTBT)(TCNQ), (BTBT)(F(2)TCNQ), (BSBS)(F(2)TCNQ), and (BTBT)(F(4)TCNQ), where BTBT is benzothieno[3,2-b]benzothiophene, BSBS is benzoseleno[3,2-b]benzoselenophene, and F(n)TCNQ (n = 0, 2, and 4) are fluorinated 7,7,8,8-tetracyanoquinodimethanes. These complexes consist of mixed stacks of essentially neutral molecules, and the transistors are air stable even after several-month storage in ambient conditions.
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Tomofumi Kadoya, Masato Otsuka, Akinari Ogino, Seiichi Sato, Tokuji Yokomatsu, Kazusuke Maenaka, Jun-ichi Yamada, Hiroyuki Tajima
JOURNAL OF PHYSICAL CHEMISTRY C 121 ( 5 ) 2882 - 2888 2017.2
Publisher：AMER CHEMICAL SOC
The charge-injection barrier from metal electrodes to thin-film pentacene is investigated using accumulated charge measurements. When a gold electrode is deposited on a pentacene film, the interface forms a Schottky contact with a hole-injection barrier of 0.2 eV. However, interfacial carrier motion is reversible between charge injection and discharge. The result suggests that the reported electrical hysteresis in typical pentacene transistors is caused by carrier traps that are localized primarily in the SiO2/pentacene interface. The Ag/pentacene junction has a large barrier height of 0.5 eV. The barrier height is significantly reduced, and an Ohmic contact is realized by using molybdenum oxide (MoO3) as a buffer layer.
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Ambipolar organic transistors based on isoindigo derivatives Reviewed
Minoru Ashizawa, Naoaki Masuda, Toshiki Higashino, Tomofumi Kadoya, Tadashi Kawamoto, Hidetoshi Matsumoto, Takehiko Mori
ORGANIC ELECTRONICS 35 95 - 100 2016.8
Publisher：ELSEVIER SCIENCE BV
Structural and transistor properties of isoindigo derivatives are investigated. The unsubstituted isoindigo affords two polymorphs in addition to the reported brickwork structure; one has a stacking structure analogous to indigo, and another consists of nonplanar molecules. The unsubstituted isoindigo exhibits ambipolar transistor properties with the hole and electron mobilities more than 0.01 cm(2)/Vs, and 6.6 '-diphenylisoindigo shows ambipolar transistor properties with the hole/electron mobilities of 0.037/0.027 cm(2)/Vs. Isoindigo derivatives with electron withdrawing groups show only electron transport, indicating that the lower limit of the HOMO level showing the hole transport is -5.7 eV. (C) 2016 Published by Elsevier B.V.
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Yasuhiro Kiyota, Tomofumi Kadoya, Kaoru Yamamoto, Kodai Iijima, Toshiki Higashino, Tadashi Kawamoto, Kazuo Takimiya, Takehiko Mori
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 138 ( 11 ) 3920 - 3925 2016.3
Publisher：AMER CHEMICAL SOC
On the basis of an excellent transistor material, [1]benzothieno[3,2-b][1]benzothiophene (BTBT), a series of highly conductive organic metals with the composition of (BTBT)(2)XF6 (X = P, As, Sb, and Ta) are prepared and the structural and physical properties are investigated. The room temperature conductivity amounts to 4100 S cm(-1) in the AsF6 salt, corresponding to the drift mobility of 16 cm(2) V-1 s(-1). Owing to the high conductivity, this salt shows a thermoelectric power factor of 55-88 mu W K-2 m(-1), which is a large value when this compound is regarded as an organic thermoelectric material. The thermoelectric power and the reflectance spectrum indicate a large bandwidth of 1.4 eV. These salts exhibit an abrupt resistivity jump under 200 K, which turns to an insulating state below 60 K. The paramagnetic spin susceptibility, and the Raman and the IR spectra suggest 4k(F) charge-density waves as an origin of the low-temperature insulating state.
DOI： 10.1021/jacs.6b01213
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Chika Fujisue, Tomofumi Kadoya, Toshiki Higashino, Ryonosuke Sato, Tadashi Kawamoto, Takehiko Mori
RSC ADVANCES 6 ( 58 ) 53345 - 53350 2016
Publisher：ROYAL SOC CHEMISTRY
It has been known that organic charge-transfer complexes with a mix-stacked structure show transistor properties, and particularly complexes containing 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) show air-stable n-channel transistor properties in thin-film transistors, though ambipolar properties have been reported in a few single-crystal transistors. Here we report, when TCNQ is replaced by 2,5-dimethyl-N, N'-dicyano-p-quinonediimine (DMDCNQI), the dibenzopyrrolo[3,2-b]pyrrole (DBPP) complex exhibits ambipolar properties even in the thin-film transistor. The ambipolar operation is stable in air after several weeks. In addition, the transistor shows a very small difference in the electron and hole threshold voltages.
DOI： 10.1039/c6ra10606d
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<sup>1</sup>H-NMR study in organic conductor β-(BDA-TTP)<sub>2</sub>I<sub>3</sub> under hydrostatic pressure
Nakada Kohei, Miyagawa Kazuya, Kadoya Tomofumi, Yamada Junichi, Kanoda Kazushi
Meeting Abstracts of the Physical Society of Japan 71 1713 - 1713 2016
Publisher：The Physical Society of Japan
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Thermoelectric power of oriented thin-film organic conductors Reviewed
Ryonosuke Sato, Yasuhiro Kiyota, Tomofumi Kadoya, Tadashi Kawamoto, Takehiko Mori
RSC ADVANCES 6 ( 47 ) 41040 - 41044 2016
Publisher：ROYAL SOC CHEMISTRY
The temperature dependence of thermoelectric power is investigated down to low temperatures for oriented thin films of organic conductors. In addition to the evaporated films, highly oriented films consisting of nanoparticles are fabricated by the solution method for tetrathiafulvalene: tetracyanoquinodimethane (TTF)(TCNQ) and (TTF)[Ni(dmit)(2)](2) (dmit: 1,3-dithiole-2-thione-4,5-dithiolato). The resulting films show n-type thermoelectric power, whose temperature dependence is similar to the single-crystal result along the most conducting axis. Owing to the ordered orientation and nanostructures, the thermoelectric power factor is considerably improved in comparison with the ordinary organic films.
DOI： 10.1039/c6ra04455g
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Enantiopure and racemic radical-cation salts of B(malate)(2)(-) anions with BEDT-TTF Reviewed
Jordan R. Lopez, Lee Martin, John D. Wallis, Hiroki Akutsu, Yasuhiro Nakazawa, Jun-ichi Yamada, Tomofumi Kadoya, Simon J. Coles, Claire Wilson
DALTON TRANSACTIONS 45 ( 22 ) 9285 - 9293 2016
Publisher：ROYAL SOC CHEMISTRY
We have synthesized the first examples of radical-cation salts of BEDT-TTF with chiral borate anions, [B(malate)(2)](-), prepared from either enantiopure or racemic bidentate malate ligands. In the former case only one of two diastereoisomers of the borate anion is incorporated, while for the hydrated racemic salt one racemic pair of borate anions containing a R and a S malate ligand is incorporated. Their conducting and magnetic properties are reported. The tight-binding band calculation indicates that the chiral salt has an effective half-filled flat band, which is likely to be caused by the chiral structural feature.
DOI： 10.1039/c6dt01038e
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Toshiki Higashino, Masaki Dogishi, Tomofumi Kadoya, Ryonosuke Sato, Tadashi Kawamoto, Takehiko Mori
JOURNAL OF MATERIALS CHEMISTRY C 4 ( 25 ) 5981 - 5987 2016
Publisher：ROYAL SOC CHEMISTRY
A new donor molecule 3,8-dimethoxy-[1] benzothieno[3,2-b][1] benzothiophene ( DMeO-BTBT) is synthesized and the charge-transfer complexes with fluorinated 7,7,8,8-tetracyanoquinodimethane (F-n-TCNQ; n = 0, 2, and 4) are prepared. All complexes (DMeO-BTBT)(F-n-TCNQ) have mixed stack structures, and the thin-film and single-crystal organic transistors show n-channel transistor performance both in vacuum and in air even after one-year storage. Although the performance and stability of the thin-film transistors are improved according to the acceptor ability of F-n-TCNQ, all single-crystal transistors exhibit similar performance and excellent air stability, among which the (DMeO-BTBT)(F-2-TCNQ) transistor exhibits the highest mobility of 0.097 cm(2) V-1 s(-1).
DOI： 10.1039/c6tc01532h
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Suppression of access resistance using carbon electrodes in organic transistors based on alkyl-substituted thienoacene Reviewed
Tomofumi Kadoya, Oratai Pitayatanakul, Takehiko Mori
ORGANIC ELECTRONICS 21 106 - 110 2015.6
Publisher：ELSEVIER SCIENCE BV
Contact resistance of bottom-contact organic transistors based on dihexyl-substituted dibenzo[d,d'] thieno[3,2-b; 4,5-b'] dithiophene is reduced substantially using carbon electrodes. In the Au top-contact transistors, the contact resistance increases proportionally to the semiconductor thickness owing to the access resistance, whereas the performance of the carbon-electrode transistors does not depend strongly on the active-layer thickness. This is attributed to the lateral charge injection from the side of the thick carbon electrode. (C) 2015 Elsevier B.V. All rights reserved.
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Benzobisthiadiazole-based conjugated dono-racceptor polymers for organic thin film transistors: effects of pi-conjugated bridges on ambipolar transport Reviewed
Yang Wang, Tomofumi Kadoya, Lei Wang, Teruaki Hayakawa, Masatoshi Tokita, Takehiko Mori, Tsuyoshi Michinobu
JOURNAL OF MATERIALS CHEMISTRY C 3 ( 6 ) 1196 - 1207 2015
Publisher：ROYAL SOC CHEMISTRY
A new series of benzobisthiadiazole (BBT)-based donor-acceptor copolymers, namely, PBBT-FT, PBBT-T-FT, and PBBT-Tz-FT, with different pi-conjugated bridges have been developed for polymer thin film transistors (TFTs). It was found that inserting different pi-conjugated bridges into the backbone of the polymer allowed tailoring of opto-electrical properties, molecular organizations, and accordingly, ambipolar transport of TFTs. The UV-vis-NIR spectra of all three polymers were similar with the low band gaps of around 1.1 eV. While the lowest unoccupied molecular orbital (LUMO) energy levels were also similar (around -3.8 eV), the highest occupied molecular orbital (HOMO) energy levels varied from -5.05 to -5.42 eV because of the different pi-conjugated bridges; moreover, their TFTs exhibited different ambipolar transport. p-Type dominant TFT performances with the hole mobility (eta(h)) reaching 0.13 cm(2) V-1 s(-1) were observed for the prototype polymer PBBT-FT. However, the device based on PBBT-T-FT with thiophene bridges displayed lower but more balanced hole (mu(h)) and electron (mu(e)) mobilities of 6.5 x 10(-3) and 1.2 x 10(-3) cm(2) V-1 s(-1), respectively. The device based on PBBT-Tz-FT with the thiazole units exhibited more evenly balanced hole and electron mobilities (mu(h)/mu(e) = 0.45) along with a significantly enhanced mu(e) similar to 0.02 cm(2) V-1 s(-1). These different semiconducting features were ascribed to different molecular orientations and film morphologies revealed by wide-angle X-ray scattering (WAXS) and atomic force microscopy (AFM).
DOI： 10.1039/c4tc02273d
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Ambipolar Organic Field-Effect Transistors Based on Indigo Derivatives Reviewed
Oratai Pitayatanakul, Kodai Iijima, Tomofumi Kadoya, Minoru Ashizawa, Tadashi Kawamoto, Hidetoshi Matsumoto, Takehiko Mori
ENGINEERING JOURNAL-THAILAND 19 ( 3 ) 61 - 73 2015
Publisher：CHULALONGKORN UNIV, FAC ENGINEERING
In order to improve the ambipolar performance of indigo-based semiconductors, we have investigated halogen-substituted (1 - 4) and phenyl-substituted (5) indigo derivatives at the 5-position. We show that introduction of iodine atoms, namely 5,5'-diiodoindigo (4), leads to the strong halogen-halogen interaction (iodine-iodine interaction) that gives a significant effect on the molecular packing. Thanks to the supramolecular network coming from the extra iodine-iodine interaction, the molecules are arranged approximately perpendicular to the substrate in the thin film. This results in remarkable transistor performance of the maximum hole and electron mobilities (mu(h)/mu(e)) = 0.42/0.85 cm(2)V(-1)s(-1), which are one of the highest among small-molecule ambipolar organic transistors. Furthermore, introducing phenyl groups, 5 improves the transistor performances up to the maximum mobilities mu(h)/mu(e) = 0.56/0.95 cm(2)V(-1)s(-1). We have found that the phenyl groups destroy the standard molecular packing of indigo to achieve a unique structure that is a hybrid of the herringbone and brickwork structures.
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21aAS-6 Conductivity and Thermopower of organic conductors (BTBT)_2X (X: PF_6,AsF_6,SbF_6,TaF_6)
Kiyota Y., Kadoya T., Iijima K., Higashino T., Kawamoto T., Takimiya K., Mori T.
Meeting Abstracts of the Physical Society of Japan 70 1789 - 1789 2015
Publisher：The Physical Society of Japan (JPS)