Papers - KADOYA Tomofumi
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Semiconductor Properties of π‐Extended 2‐(Thiopyran‐4‐ylidene)‐1,3‐benzodithiole (TP‐BT) Analogs
Hiroshi Nishimoto, Tomofumi Kadoya, Takeshi Kawase, Jun‐ichi Nishida
Asian Journal of Organic Chemistry 12 ( 12 ) 2023.12
Publisher：Wiley
Abstract
Despite having an asymmetric structure, 2‐(thiopyran‐4‐ylidene)‐1,3‐benzodithiole (TP‐BT) is a good p‐type semiconductor containing isotropic three‐dimensional (3D) intermolecular interactions. Moreover, its π‐extended analogs can potentially work as organic electronic materials. Herein, a fused‐type π‐extended analog containing an extra benzene ring on the benzodithiole unit, i. e., 2‐(thiopyran‐4‐ylidene)‐1,3‐naphtho[2,3‐d]dithiole (TP‐NT), and three σ‐bonded‐type π‐extended analogs, i. e., phenyl‐, naphthyl‐, and anthryl‐substituted analogs (Ph‐TP‐BT, Nap‐TP‐BT, and Ant‐TP‐BT, respectively), were prepared and their molecular arrangements and organic field‐effect transistor (OFET) properties were investigated. TP‐NT formed a herringbone arrangement with 3D intermolecular interactions similar to that of the parent TP‐BT. Meanwhile, Ant‐TP‐BT formed a bilayer‐type layered herringbone arrangement. Since the highest occupied molecular orbital and the lowest unoccupied molecular orbital are located on the TP‐BT and anthracene units, respectively, a unique donor–acceptor separated network was formed. In OFETs prepared via a vapor deposition method using the σ‐bonded‐type analogs, slightly lower mobilities (0.1 to 8×10<sup>−3</sup> cm<sup>2</sup>/Vs) than that of TP‐NT (0.1 cm<sup>2</sup>/Vs) were observed. Upon photo‐irradiation, the OFET of Ant‐TP‐BT exhibited a larger threshold voltage shift and an increase in the off current compared with TP‐NT. The σ‐bonded‐type analogs showed a larger photo‐response effect than TP‐NT derived from the donor–acceptor molecular structure. -
Measurement of electron injection barriers in OS/Au (OS=phthalocyanine and pentacene) using accumulated charge measurement Reviewed
Takeshi Oda, Koji Yamaguchi, Tomofumi Kadoya, Hiroyuki Tajima
Organic Electronics 120 106827 - 106827 2023.9
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Hiroyuki Tajima, Takeshi Oda, Tomofumi Kadoya
Magnetochemistry 2023.7
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Sonomi Arata, Yuna Kim, Norihisa Hoshino, Keishiro Tahara, Kiyonori Takahashi, Tomofumi Kadoya, Tomonori Inoue, Takayoshi Nakamura, Tomoyuki Akutagawa, Jun‐ichi Yamada, Kazuya Kubo
European Journal of Inorganic Chemistry 2023.2
Publisher：Wiley
Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/ejic.202300017
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Boundary research between organic conductors and transistors: new trends for functional molecular crystals Reviewed
Tomofumi Kadoya, Toshiki Higashino
CrystEngComm 2023
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Tomofumi Kadoya, Masaharu Shishido, Shiori Sugiura, Toshiki Higashino, Keishiro Tahara, Kazuya Kubo, Takahiko Sasaki, Jun-ichi Yamada
Chemistry Letters 51 ( 7 ) 683 - 686 2022.7
Authorship：Lead author, Corresponding author Publisher：The Chemical Society of Japan
DOI： 10.1246/cl.220148
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Hiroshi Nishimoto, Tomofumi Kadoya, Rikyu Miyake, Takeshi Oda, Jun-ichi Nishida, Kazuya Kubo, Hiroyuki Tajima, Takeshi Kawase, Jun-ichi Yamada
CrystEngComm 2022
Authorship：Corresponding author Publisher：Royal Society of Chemistry (RSC)
We report the synthesis of P-BT and TP-BT and their OTFT properties based on electronic dimensionality and access resistance (R<sub>acc</sub>). TP-BT can suppress R<sub>acc</sub> due to its 3D electronic structure.
DOI： 10.1039/d2ce00644h
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Toby J. Blundell, Alexander L. Morritt, Elizabeth K. Rusbridge, Luke Quibell, Jakob Oakes, Hiroki Akutsu, Yasuhiro Nakazawa, Shusaku Imajo, Tomofumi Kadoya, Jun-ichi Yamada, Simon J. Coles, Jeppe Christensen, Lee Martin
Materials Advances 3 ( 11 ) 4724 - 4735 2022
Publisher：Royal Society of Chemistry (RSC)
Six new BEDT-TTF salts with tris(oxalato)gallate or -iridate anions including two new superconductors β′′-(BEDT-TTF)<sub>4</sub>[(H<sub>3</sub>O)Ga(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub>]·guest (bromobenzene or iodobenzene) and a novel 5 : 1 metal–insulator β′′-(BEDT-TTF)<sub>5</sub>Ir(C<sub>2</sub>O<sub>4</sub>)<sub>3</sub> ethanol.
DOI： 10.1039/d2ma00384h
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Synthesis and electron-transport properties of N-trifluoromethylphenyl-phthalimides containing selenophene substituents Reviewed
Jun-ichi Nishida, Yoshiki Morikawa, Akito Hashimoto, Yasuyuki Kita, Hiroshi Nishimoto, Tomofumi Kadoya, Hiroyasu Sato, Takeshi Kawase
Materials Advances 2 7861 - 7868 2021.10
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Thermal and non-thermal equilibrium processes of charge extraction in accumulated charge measurement (ACM) Reviewed
Hiroyuki Tajima, Tomofumi Kadoya, Koji Yamaguchi, Yuichi Omura, Takeshi Oda, Akinari Ogino
Journal of Applied Physics 130 ( 19 ) 195501 2021.10
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Kazuya Kubo, Mamoru Sadahiro, Sonomi Arata, Norihisa Hoshino, Tomofumi Kadoya, Tomoyuki Akutagawa, Reizo Kato, Jun-ichi Yamada
Crystals 11 ( 10 ) 1154 - 1154 2021.9
Publisher：MDPI AG
The effects of substituents on the arrangement of metal–dithiolene complexes based on π-conjugated systems, which are extensively used to synthesize various functional materials, have not been studied adequately. New donor-type nickel–dithiolene complexes fused with bulky cycloalkane substituents [Ni(Cn-dddt)2] (C5-dddt = 4a,5,6,6a-pentahydro-1,4-benzodithiin-2,3-dithiolate; C6-dddt = 4a,5,6,7,8,8a-hexahydro-1,4-benzodithiin-2,3-dithiolate; C7-dddt = 4a,5,6,7,8,9,9a-heptahydro-1,4-benzodithiin-2,3-dithiolate; and C8-dddt = 4a,5,6,7,8,9,10,10a-octahydro-1,4-benzodithiin-2,3-dithiolate) were synthesized in this study. All the complexes were crystallized in cis-[Ni(cis-Cn-dddt)2] conformations with cis-oriented (R,S) conformations around the cycloalkylene groups in the neutral state. Unique molecular arrangements with a three-dimensional network, a one-dimensional column, and a helical molecular arrangement were formed in the crystals owing to the flexible cycloalkane moieties. New 2:1 cation radical crystals of [Ni(C5-dddt)2]2(X) (X = ClO4− or PF6−), obtained by electrochemical crystallization, exhibited semiconducting behaviors (ρrt = 0.8 Ω cm, Ea = 0.09 eV for the ClO4− crystal; 4.0 Ω cm, 0.13 eV for the PF6− crystal) under ambient pressure due to spin-singlet states between the dimers of the donor, which were in accordance with the conducting behaviors under hydrostatic pressure (ρrt = 0.2 Ω cm, Ea = 0.07 eV for the ClO4− crystal; 1.0 Ω cm, 0.12 eV for the PF6− crystal at 2.0 GPa).
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Dihedral-Angle Dependence of Intermolecular Transfer Integrals in BEDT-BDT-Based Radical-Cation Salts with θ-Type Molecular Arrangements Invited Reviewed
Tomofumi Kadoya, Shiori Sugiura, Toshiki Higashino, Keishiro Tahara, Kazuya Kubo, Takahiko Sasaki, Kazuo Takimiya, Jun-ichi Yamada
Crystals 11 ( 8 ) 868 - 868 2021.7
Authorship：Lead author, Corresponding author Publisher：MDPI AG
We report the structural and physical properties of a new organic Mott insulator (BEDT-BDT)AsF6 (BEDT-BDT: benzo[1,2-g:4,5-g′]bis(thieno[2,3-b][1,4dithiin). This AsF6 salt has the same structure as the PF6 salt. Although the anions are disordered, the donor molecules form a θ-type arrangement. The temperature dependence of the resistivity exhibits semiconducting behavior. The static magnetic susceptibility follows Curie–Weiss law over a wide temperature range; however, below 25 K, the magnetic susceptibility is in agreement with a one-dimensional chain model with the exchange coupling J = 7.4 K. No structural phase transition was observed down to 93 K. At 270 K, the Fermi surface calculated by the tight-binding approximation is a two-dimensional cylinder; however, it is significantly distorted at 93 K. This is because the dihedral angles between the BEDT-BDT molecules become larger due to lattice shrinkage at low temperatures, which results in a smaller transfer integral (t1) along the stack direction. This slight change in the dihedral angle gives rise to a significant change in the electronic structure of the AsF6 salt. Radical-cation salts using BEDT-BDT, in which the highest occupied molecular orbital does not have a dominant sign throughout the molecule, are sensitive to slight differences in the overlap between the molecules, and their electronic structures are more variable than those of conventional θ-type conductors.
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Aoi Hori, Yuna Kim, Keishiro Tahara, Tomofumi Kadoya, Jun‐ichi Yamada, Kazuya Kubo
European Journal of Inorganic Chemistry 2021 ( 11 ) 1023 - 1027 2021.3
Publisher：Wiley
Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/ejic.202001014
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Aoi Hori, Yuna Kim, Keishiro Tahara, Tomofumi Kadoya, Jun‐ichi Yamada, Kazuya Kubo
European Journal of Inorganic Chemistry 2021 ( 11 ) 1014 - 1014 2021.3
Publisher：Wiley
Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/ejic.202100134
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Sunao Shimomoto, Tomofumi Kadoya, Toshiaki Tanimura, Kazusuke Maenaka, Tokuji Yokomatsu, Takeshi Komino, Hiroyuki Tajima
The Journal of Physical Chemistry C 125 ( 3 ) 1990 - 1998 2021.1
Authorship：Corresponding author Publisher：American Chemical Society (ACS)
This study investigates the charge injection barrier at the phthalocyanine (H2Pc)/Pd using accumulated charge measurement (ACM). Because the hole injection barrier is relatively small, the voltage oscillation method in ACM is achieved at the highest occupied molecular orbital/Pd interface, and the hole injection barrier was determined to be 0.26 eV. A negative offset voltage was applied to determine the electron injection barrier at the lowest unoccupied molecular orbital (LUMO)/Pd interface. However, when the electron injection barrier was significantly large, the charge-injected thermal equilibrium state (CITES) could not be achieved at the interface, and an accurate injection barrier could not be determined. Surprisingly, by applying a positive offset voltage, a CITES of electrons was obtained at the LUMO/Pd interface, and the band gap was determined to be 2.75 eV. Furthermore, the electron injection barrier was found to be 2.49 eV. By applying a positive offset voltage, band bending occurred at the H2Pc/Pd interface, thereby reducing the depletion layer in the LUMO and enabling the determination of the band gap and electron injection barrier.
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Toby J. Blundell, Michael Brannan, Hiroshi Nishimoto, Tomofumi Kadoya, Jun-ichi Yamada, Hiroki Akutsu, Yasuhiro Nakazawa, Lee Martin
Chemical Communications 57 ( 44 ) 5406 - 5409 2021
Publisher：Royal Society of Chemistry (RSC)
<p>Synthesis of a chiral molecular metal which shows metallic behaviour down to at least 4.2 K.</p>
DOI： 10.1039/d1cc01441b
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Keishiro Tahara, Yuya Ashihara, Takashi Ikeda, Tomofumi Kadoya, Jun-ichi Fujisawa, Yoshiki Ozawa, Hiroyuki Tajima, Noriaki Toyoda, Yuichi Haruyama, Masaaki Abe
Inorganic Chemistry 59 ( 24 ) 17945 - 17957 2020.12
Publisher：American Chemical Society (ACS)
Chemical modification of insulating material surfaces is an important methodology to improve the performance of organic field-effect transistors (OFETs). However, few redox-active self-assembled monolayers (SAMs) have been constructed on gate insulator film surfaces, in contrast to the numerous SAMs formed on many types of conducting electrodes. In this study, we report a new approach to introduce a pi-conjugated organic fragment in close proximity to an insulating material surface via a transition metal center acting as a one-atom anchor. On the basis of the reported coordination chemistry of a catecholato complex of Pt(II) in solution, we demonstrate that ligand exchange can occur on an insulating material surface, affording SAMs on the SiO2 surface derived from a newly synthesized Pt(II) complex containing a benzothienobenzothiophene (BTBT) framework in the catecholato ligand. The resultant SAMs were characterized in detail by water contact angle measurements, X-ray photoelectron spectroscopy, atomic force microscopy, and cyclic voltammetry. The SAMs served as good scaffolds of 7c-conjugated pillars for forming thin films of a well-known organic semiconductor C8-BTBT (2,7- dioctyl[1]benzothieno[3,2-b][1]benzothiophene), accompanied by the engagements of the C8-BTBT molecules with the SAMs containing the common BTBT framework at the first layer on SiO2. OFETs containing the SAMs displayed improved performance in terms of hole mobility and onset voltage, presumably because of the unique interfacial structure between the organic semiconducting and inorganic insulating layers. These findings provide important insight into creating new elaborate interfaces through installing coordination chemistry in solution to solid surfaces, as well as OFET design by considering the compatibility between SAMs and organic semiconductors.
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Ferrocene on Insulator: Silane Coupling to a SiO2 Surface and Influence on Electrical Transport at a Buried Interface with an Organic Semiconductor Layer Reviewed International journal
Takashi Ikeda, Keishiro Tahara, Tomofumi Kadoya, Hiroyuki Tajima, Noriaki Toyoda, Satoshi Yasuno, Yoshiki Ozawa, Masaaki Abe
Langmuir 36 ( 21 ) 5809 - 5819 2020.6
Publisher：American Chemical Society (ACS)
A silane coupling-based procedure for decoration of an insulator surface containing abundant hydroxy groups by constructing redox-active self-assembled monolayers (SAMs) is described. A newly synthesized ferrocene (Fc) derivative containing a triethoxysilyl group designated FcSi was immobilized on SiO2/Si by a simple operation that involved immersing the substrate in a toluene solution of the Fc silane coupling reagent and then rinsing the resulting substrate. X-ray photoelectron spectroscopy (XPS) measurements confirmed that the Fc group was immobilized on SiO2/Si in the Fe(II) state. Cyclic voltammetry measurements showed that the Fc groups were electrically insulated from the Si electrode by the SiO2 layer. The FcSi on SiO2/Si structures were found to serve as a good scaffold for formation of organic semiconductor thin films by vacuum thermal evaporation of C8-BTBT (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene), which is well-known as an organic field-effect transistor (OFET) material. The X-ray diffraction profile indicated that the conventional standing-up conformation of the C8-BTBT molecules perpendicular to the substrates was maintained in the thin films formed on FcSi@SiO2/Si. Further vacuum thermal evaporation of Au provided an FcSi-based OFET structure with good transfer characteristics. The FcSi-based OFET showed pronounced source-drain current hysteresis between the forward and backward scans. The degree of this hysteresis was varied reversibly via gate bias manipulation, which was presumably accompanied by trapping and detrapping of hole carriers at the Fc-decorated SiO2 surface. These findings provide new insights into application of redox-active SAMs to nonvolatile OFET memories while also creating new interfaces through junctions with functional thin films, in which the underlying redox-active SAMs play supporting roles.
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Steric effect of halogen substitution in an unsymmetrical benzothienobenzothiophene organic semiconductor Reviewed
Tomofumi Kadoya, Shotaro Mano, Aoi Hori, Keishiro Tahara, Kunihisa Sugimoto, Kazuya Kubo, Masaaki Abe, Hiroyuki Tajima, Jun-ichi Yamada
Organic Electronics 78 105570 - 105570 2020.3
Authorship：Lead author, Corresponding author Publisher：Elsevier BV
We report a crystal structure analysis of an unsymmetrical organic semiconductor 2-bromo-7-butyl[1]benzothieno[3,2-b][1]benzothiophene (Br-BTBT-C ) and its transistor characteristics. Unlike the parent compound 2-butyl-[1]benzothieno[3,2-b][1]benzothiophene (BTBT-C ) forming a bilayer-type structure composed of head-to-head herringbone packings, Br-BTBT-C forms a dense head-to-tail herringbone packing arranged so as to avoid the steric hindrance between bromine atoms. The intermolecular transfer integrals in Br-BTBT-C suggest its advantage for carrier transport; however, the transistor characteristics of Br-BTBT-C and BTBT-C were found to be almost the same. This is because BTBT-C has a higher crystallinity than Br-BTBT-C in vacuum deposited thin films. 4 4 4 4 4 4 4 4
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Tomofumi Kadoya, Shiori Sugiura, Keishiro Tahara, Toshiki Higashino, Kazuya Kubo, Takahiko Sasaki, Kazuo Takimiya, Jun-ichi Yamada
CrystEngComm 22 ( 36 ) 5949 - 5953 2020
Authorship：Lead author, Corresponding author Publisher：Royal Society of Chemistry (RSC)
<p>We have succeeded in developing a two-dimensional radical–cationic Mott insulator that does not contain a 1,3-dithiol-2-ylidene moiety.</p>
DOI： 10.1039/d0ce00878h
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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)
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High performance ambipolar organic field-effect transistors based on indigo derivatives Reviewed
Oratai Pitayatanakul, Toshiki Higashino, Tomofumi Kadoya, Masaki Tanaka, Hirotaka Kojima, Minoru Ashizawa, Tadashi Kawamoto, Hidetoshi Matsumoto, Ken Ishikawa, Takehiko Mori
JOURNAL OF MATERIALS CHEMISTRY C 2 ( 43 ) 9311 - 9317 2014.11
Publisher：ROYAL SOC CHEMISTRY
A bio-inspired organic semiconductor 5,5'-diphenylindigo shows excellent and well-balanced ambipolar transistor properties; its hole and electron mobilities are 0.56 and 0.95 cm(2) V-1 s(-1), respectively. The enhanced performance is attributed to the extended pi-pi overlap of the phenyl groups as well as the characteristic packing pattern that is a hybrid of the herringbone and brickwork structures. The ambipolar transistor characteristics are analyzed considering its operating regions, where a large unipolar saturated region appears due to the difference of the electron and hole threshold voltages.
DOI： 10.1039/c4tc01563k
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Energy-Level Engineering in Self-Contact Organic Transistors Prepared by Inkjet Printing Reviewed
Tomofumi Kadoya, Sumika Tamura, Takehiko Mori
JOURNAL OF PHYSICAL CHEMISTRY C 118 ( 40 ) 23139 - 23146 2014.10
Publisher：AMER CHEMICAL SOC
Organic field-effect transistors with chemically doped source/drain electrodes are fabricated by selectively transforming the active layer to the conducting material, organic charge-transfer (CT) complex, using inkjet printing. The formation of the CT complex is investigated by X-ray diffraction and Raman spectroscopy, and the resulting CT complex is conducting enough to realize satisfactory transistor performance. The solvent of the ink is a key factor to achieve the optimal chemical doping to form a well-ordered CT complex. In such a manner, we can obtain semiconductor-specific electrodes that significantly reduce the schottky barrier at the electrode/semiconductor interface, because ideal energy-level engineering is automatically attained between the same type of molecules.
DOI： 10.1021/jp5070819
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An Organic Metal Derived from a Selenium Analogue of Benzothienobenzothiophene Reviewed
Toshiki Higashino, Tomofumi Kadoya, Shohei Kumeta, Kohei Kurata, Tadashi Kawamoto, Takehiko Mori
EUROPEAN JOURNAL OF INORGANIC CHEMISTRY 24 ( 24 ) 3895 - 3898 2014.8
Publisher：WILEY-V C H VERLAG GMBH
Benzothieno[3,2-b]benzothiophene (BTBT) is an excellent organic transistor material, and its charge-transfer salt (BTBT)(2)PF6 is an organic metal that exhibits conductivity as high as 1500 S cm(-1) at room temperature. Here, we report a charge-transfer salt of the selenium analogue, benzoseleno[3,2-b]benzoselenophene (BSBS). (BSBS)(2)TaF6 is a one-dimensional metal isostructural to (BTBT)(2)PF6. The resistance jump temperature is reduced from 150 to 90 K, and the increase of the low-temperature resistivity is largely diminished. However, the spin susceptibility shows an obvious drop below 50 K, which implies that the low-temperature ground state is essentially a singlet state.
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All-organic self-contact transistors Reviewed
Sumika Tamura, Tomofumi Kadoya, Takehiko Mori
Applied Physics Letters 105 ( 2 ) 023301 - 023301 2014.7
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Self-contact thin-film organic transistors based on tetramethyltetrathiafulvalene Reviewed
Sumika Tamura, Tomofumi Kadoya, Tadashi Kawamoto, Takehiko Mori
APPLIED PHYSICS LETTERS 102 ( 6 ) 063305 - 063308 2013.2
Publisher：AMER INST PHYSICS
Carrier injection from organic contacts to tetramethyltetrathiafulvalene (TMTTF) is investigated in the thin-film transistors. When 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) is patterned on a TMTTF film, the resulting (TMTTF)(TCNQ) works as highly conducting source and drain electrodes. Such self-contact transistors, in which the organic material constructing the active layer is selectively transformed to the contacts, have achieved low contact resistance and high performance. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4792704]
DOI： 10.1063/1.4792704
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A highly conducting organic metal derived from an organic-transistor material: benzothienobenzothiophene Reviewed
Tomofumi Kadoya, Minoru Ashizawa, Toshiki Higashino, Tadashi Kawamoto, Shohei Kumeta, Hidetoshi Matsumoto, Takehiko Mori
PHYSICAL CHEMISTRY CHEMICAL PHYSICS 15 ( 41 ) 17818 - 17822 2013
Publisher：ROYAL SOC CHEMISTRY
BTBT ([1]benzothieno[3,2-b][1]benzothiophene) is an organic semiconductor that realizes high mobility in organic transistors. Here we report that the charge-transfer (CT) salt, (BTBT)(2)PF6, shows a high room-temperature conductivity of 1500 S cm(-1). This compound exhibits a resistivity jump around 150 K, but when it is covered with Apiezon N grease the resistivity jump is suppressed, and the metallic conductivity is maintained down to 60 K. Owing to the very high conductivity, the ESR signal shows a significantly asymmetric Dysonian lineshape (A/B congruent to 3) even at room temperature. Since most organic conductors are based on strong electron donors, it is remarkable that such a weak electron donor as BTBT realizes a stable and highly conducting organic metal.
DOI： 10.1039/c3cp52881b
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Organic Field-Effect Transistors Based on Small-Molecule Organic Semiconductors Evaporated under Low Vacuum Reviewed
Takuto Takahashi, Sumika Tamura, Yuto Akiyama, Tomofumi Kadoya, Tadashi Kawamoto, Takehiko Mori
APPLIED PHYSICS EXPRESS 5 ( 6 ) 061601 - 061603 2012.6
Publisher：IOP PUBLISHING LTD
Basic small-molecule organic electron acceptors and donors such as dicyanoquinonediimine (DCNQI), tetracyanoquinodimethane (TCNQ), and tetramethyltetrathiafulvalene (TMTTF) do not smoothly form thin films by vacuum evaporation owing to the high vapor pressures. The thin films are, however, fabricated by low-vacuum evaporation, and the resulting organic thin-film transistors have exhibited remarkably improved performance. (C) 2012 The Japan Society of Applied Physics
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Nanoparticles of organic conductors: synthesis and application as electrode material in organic field effect transistors Reviewed
Dominique de Caro, Kane Jacob, Hanan Hahioui, Christophe Faulmann, Lydie Valade, Tomofumi Kadoya, Takehiko Mori, Jordi Fraxedas, Lydie Viau
NEW JOURNAL OF CHEMISTRY 35 ( 6 ) 1315 - 1319 2011
Publisher：ROYAL SOC CHEMISTRY
Stabilization of TTF center dot TCNQ nanoparticles is studied by varying the ionic liquid nature and solvent medium. The best dispersion is obtained in an acetonitrile/acetone mixture and the smaller size by using [BMIM][BF(4)], as a stabilizing ionic liquid. Applications of well-dispersed TTF center dot TCNQ nanoparticles (mean diameter of about 35 nm) as electrode material in organic field-effect transistors are also reported.
DOI： 10.1039/c0nj00858c
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Charge injection from organic charge-transfer salts to organic semiconductors Reviewed
Tomofumi Kadoya, Dominique de Caro, Kane Jacob, Christophe Faulmann, Lydie Valade, Takehiko Mori
JOURNAL OF MATERIALS CHEMISTRY 21 ( 45 ) 18421 - 18424 2011
Publisher：ROYAL SOC CHEMISTRY
Highly conducting films of organic charge-transfer (CT) salts are fabricated by a solution process from the dispersions stabilized by poly(vinylpyrrolidone). This method provides a general way to obtain conducting films of nonvolatile organic cation-and anion-radical salts with inorganic counter ions. Carrier injection from organic CT salts to organic semiconductors is investigated by using these films as electrodes in organic field-effect transistors. Efficient hole injection is observed not only from organic cation-radical salts but also from anion-radical salts to pentacene and sexithiophene. Electron injection is dominant from both types of CT salts to C-60, but hole injection and ambipolar characteristics are observed for cation-radical salts. The Fermi levels of the CT salts are discussed on the basis of these observations.
DOI： 10.1039/c1jm12783g