Yutaka Moritomo

University of Tsukuba

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Effect of temperature on carrier formation efficiency in organic photovoltaic cells

Applied Physics Letters (2014)

Yutaka Moritomo Kouhei Yonezawa Takeshi Yasuda

The internal quantum efficiency (ϕIQ) of an organic photovoltaic cell is governed by plural processes. Here, we propose that ϕIQ can be experimentally decomposed into carrier formation (ϕCF) and carrier transfer (ϕCT) efficiencies. By combining femtosecond time-resolved and electrochemical spectroscopy, we clarified the effect of temperature on ϕCF in a regioregular poly(3-hexylthiophene) (rr-P3HT)/[6,6]-phenyl C61-butyric acid methyl ester blend film. We found that ϕCF (=0.55) at 80 K is the same as that (=0.55) at 300 K. The temperature insensitivity of ϕCF indicates that the electron-hole pairs at the D/A interface are seldom subjected to coulombic binding energy.

Quantum Efficiency

10.1063/1.4892611

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Citations (9)

Dynamics of charge-transfer pairs in the cyano-bridgedCo2+−Fe3+transition-metal compound

Physical Review B (2008)

Hayato Kamioka Yutaka Moritomo Wataru Kosaka Shin‐ichi Ohkoshi

Dynamics of the charge-transfer (CT) pairs has been investigated for the cyano-bridged ${\mathrm{Co}}^{2+}\text{\ensuremath{-}}{\mathrm{Fe}}^{3+}$ particles grown in a hydrophilic cavities of Nafion 117 film. We decomposed the differential absorption spectra into the fast and slow components. We ascribed the fast and slow components to the Frank-Condon state and the CT $({\mathrm{Co}}^{3+}\text{\ensuremath{-}}{\mathrm{Fe}}^{2+})$ pairs with lattice relaxation, respectively. We found that the lifetime ${\ensuremath{\tau}}_{\mathrm{CT}}$ of the pairs at $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ increases with the absorbed photon density $n$ from ${\ensuremath{\tau}}_{\mathrm{CT}}\ensuremath{\approx}2\phantom{\rule{0.3em}{0ex}}\mathrm{ns}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}\ensuremath{\approx}6\phantom{\rule{0.3em}{0ex}}\mathrm{ns}$, reflecting the attractive interaction between the pairs.

Lattice (music)

10.1103/physrevb.77.180301

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Citations (21)

Direct Observation of Charge Transfer in Double-Perovskite-LikeRbMn[Fe(C

Physical Review Letters (2003)

Kenichi Kato Yutaka Moritomo Masaki Takata Makoto Sakata Masafumi Umekawa

The charge density distribution has been determined for a transition metal cyanide, RbMn[Fe(CN)(6)], by means of the maximum entropy-Rietveld method combined with the highly angularly resolved synchrotron radiation x-ray powder diffraction at SPring-8 BL02B2. We directly observed a charge transfer from the Mn site to the Fe site in the low-temperature phase. On the basis of a local density approximation calculation, we discuss the origin for the anisotropic bonding electron distribution around the Mn3+ ion in the low-temperature phase.

Rietveld Refinement

Charge density

10.1103/physrevlett.91.255502

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Citations (91)

Critical behavior of a photodisordered spin system in doped manganite

Physical review. B, Condensed matter (2001)

X. J. Liu Yutaka Moritomo Arao Nakamura Hidekazu Tanaka Tsuyoshi Kawai

Dynamics of the spin system has been investigated in a ferromagnetic ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ film by means of a time-resolved pump-probe method. In a weak excitation condition, the relaxation time $\ensuremath{\tau}$ increases critically on approaching the critical temperature ${T}_{\mathrm{C}}(=262$ K) from the low-temperature side as $\ensuremath{\tau}\ensuremath{\propto}|{T/T}_{\mathrm{C}}\ensuremath{-}1{|}^{\ensuremath{-}1.39}$ for $T\ensuremath{\gtrsim}200$ K. Surprisingly, the same scaling relation holds even after strong excitation in a much wider temperature range down to $\ensuremath{\sim}10$ K. We will discuss these behaviors in terms of photoinduced growth of the charge-ordering fluctuations.

Manganite

Atmospheric temperature range

10.1103/physrevb.64.100401

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Citations (36)

Na⁺ diffusion in Na_xCo[Fe(CN)₆]_0.90 film as investigated by transmission image

Japanese Journal of Applied Physics (2022)

Hiroki Iwaizumi Takayuki Shibata Yutaka Moritomo

Abstract Diffusion of alkali metal ions plays an important role in the rate property of the battery. Here, we investigated macroscopic Na + diffusion in a thin film of Na x Co[Fe(CN) 6 ] 0.90 (NCF90) by means of transmitted light intensity image at 540 nm. The distribution of the Na + concentration ( x ) was determined against the elapsed time ( t ). We found that the diffusion constant ( D ) for Na + shows x -dependence as D = 6.0 × 10 −8 − (1.6 − x ) 6.0 × 10 −8 cm 2 s −1 . The average D value (=3.0 × 10 −8 cm 2 s −1 ) is much larger than the reported value (=0.5 × 10 −10 cm 2 s −1 M. Takachi, Y. Fukuzumi, and Y. Moritomo, Dalton Trans . 45 , 458 (2016)) of Na x Co[Fe(CN) 6 ] 0.88 ( x = 0.8) determined by the electrochemical impedance spectroscopy. The large D value evaluated in the present investigation is ascribed to the fast intergrain Na + diffusion process.

10.35848/1347-4065/aca267

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Citations (0)

Scaling Relations in Charge and Spin Excitations of CMR Manganites

APS March Meeting Abstracts (1998)

Nobuo Furukawa Yutaka Moritomo Kazuma Hirota Y. Endoh

Source

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On-off optical switching of the magnetic and structural properties in a spin-crossover complex

Applied Physics Letters (2007)

Kenichi Kato Masaki Takata Yutaka Moritomo Akio Nakamoto Nobuhiko Kojima

A photoexcitation is one of the promising external fields to control the material phases. Here, the authors have demonstrated that the magnetic and structural properties of a spin-crossover complex, Fe(phen)2(NCS)2 (phen=1,10-phenanthroline), can be reversibly switched by the on-off action of the continuous photoexcitation at the same temperature. The structural data suggest that the density of the high-spin Fe2+ in the photoinduced phase is about 0.88. Suppressed atomic vibrations of the photoinduced phase exclude the conventional heating effect as the origin for the observed optical switching.

Photoexcitation

Spin Crossover

10.1063/1.2736213

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Citations (27)

Thermal Conductivity of Organic Solutions Against Solute Concentration

Journal of the Physical Society of Japan (2024)

Kaisei Nishitani Yutaka Moritomo

10.7566/jpsj.93.045002

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Citations (0)

Oxidization Process of Fe–Ni Mixed Prussian Blue Analogue Investigated by Valence-Differential Spectroscopy

Japanese Journal of Applied Physics (2011)

Ayako Omura Yutaro Kurihara Manabu Ishizaki Masato Kurihara Yutaka Moritomo

The oxidization process of the Fe–Ni mixed Prussian blue analogue (Fe0.2Ni0.8)[Fe(CN)6]0.67·zH2O was investigated by means of valence-differential spectroscopy. The spectroscopy revealed that the oxidization process selectively starts from the intermediate clusters. With a further increase in the oxidization level, all intermediate clusters are oxidized, and then Fe-rich clusters begin to be oxidized. On the basis of these results, we will discuss the redox process of the Ni–Fe cyano mixed crystal.

Prussian blue

Oxidation process

10.7567/jjap.50.032401

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Citations (1)

High-Pressure Structural Analysis of Fe₃O₄

Journal of the Physical Society of Japan (2002)

Akira Kuriki Yutaka Moritomo Yasuo Ohishi Kenichi Kato Eiji Nishibori

Dept. of Crystalline Materials Science, Nagoya University, Nagoya 464-8603 Dept. of Applied Physics, Nagoya University, Nagoya 464-8603 SPring-8/JASRI, 1-1-1 Koto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198 Faculty of Science and Technology, Science University of Tokyo, Chiba 278-8510 ISSP, University of Tokyo, Kashiwa 277-8581 Dept. of Physics, Saitama University, Saitama 338-8570 SPring-8/JAERI, 1-1-1 Koto, Mikazuki-cho, Sayo-gun, Hyogo 679-5198

10.1143/jpsj.71.3092

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Citations (18)