Tohoku University · Materials Science
Professor S. Yamamoto's research lab specializes in organic and hybrid electronic materials, with a focus on optoelectronic devices such as polymer solar cells, organic field-effect transistors, and neuromorphic systems. The lab investigates charge carrier dynamics, energy level alignment, and device physics in bulk heterojunction systems using advanced spectroscopic techniques like transient absorption spectroscopy. A key research direction involves engineering the interface and morphology of organic semiconductors to enhance device performance, particularly in external quantum efficiency and long-term stability. The lab also explores the integration of ionic and electronic transport in organic electrochemical transistors for bio-inspired computing and neuromorphic applications.
Figures are computed from collected data and may differ slightly.
Abstract The origin of open‐circuit voltage ( V OC ) was studied for polymer solar cells based on a blend of poly(3‐hexylthiophene) (P3HT) and seven fullerene derivatives with different LUMO energy levels and side chains. The temperature dependence of J – V characteristics was analyzed by an equivalent circuit model. As a result, V OC increased with the decrease in the saturation current density J 0 of the device. Furthermore, J 0 was dependent on the activation energy E A for J 0 , which is rel
Abstract Photogenerated charge carriers for blend films of poly[2‐methoxy‐5‐(3,7‐dimethyloctyloxy)‐1,4‐phenylenevinylene] (MDMO‐PPV) and [6,6]‐phenyl‐C 61 ‐butyric acid methyl ester (PCBM) have been investigated by transient absorption spectroscopy. The blend film with a low PCBM fraction (<10 wt %) exhibits a wide absorption that ranges from 900 to 1000 nm, which is characteristic of the MDMO‐PPV hole polaron and PCBM radical anion. On the other hand, the blend film with a higher PCBM fracti
An exact analysis is made for the shielded coupled strip transmission line with three center conductors. By means of the immittance matrices presented, the electrical behavior of the coupled strip transmission line of this type may be completely described. Design formulas which enable one to evaluate the cross-section dimensions from the desired values of characteristic immittances are derived for the two kinds of the line configurations. Equivalent circuits of the two-port networks for various
The charge carrier dynamics in blend films of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was studied by transient absorption spectroscopy in order to address the origin of limited external quantum efficiency (EQE) of this solar cell compared to that of a benchmark solar cell composed of regioregular poly(3-hexythiphene) (RR-P3HT) and PCBM. Upon photoexcitation, PCPDTBT s
4500 km optical fibre transmission at 5 Gbit/s was successfully carried out using 138 erbium-doped fibre amplifiers. However, the long term performance measurement shows BER fluctuation. It is found that such BER fluctuation can be correlated to the fading of the optical signal-to-noise ratio presumably due to the polarisation effect.
We examine the neuromorphic behavior of organic electrochemical transistors (OECTs) based on polymer blends of a mixed conductor (PEDOT:PSS) and an ion conductor (PSSNa). We show that the addition of an ionic conductor into PEDOT:PSS decreases the information retention time in paired-pulse depression (PPD) experiments and speeds up the response in dynamic filtering experiments. Detailed studies of transient properties demonstrate that the relevant time scales for the neuromorphic response are de
Using forward error correction (FEC) technology and erbium-doped fibre amplifiers (EDFAs), 5 Gbit/s optical transmission terminal equipment provides better than −40dBm receiver sensitivity at a BER of 10-11. The experiments focused on the FEC feature of the removal of the BER floor together with long-distance repeaterless transmission.
Theory and applications of coupled nonuniform transmission lines are described. Matrix representations of a general coupled nonuniform transmission line are presented, by means of which the behavior of any coupled nonuniform transmission line maybe completely described. Among a wide variety of applications of coupled nonuniform transmission lines, two typical networks, one the coupled nonuniform transmission-line folded all-pass network and the other the coupled nonuniform transmission-line dire
This paper describes an optical waveguide isolator that utilizes the unidirectional guided-radiation mode coupling in a magnetooptic/anisotropic slab guide. The basic structure is the semileaky-type waveguide that has been previously used as a polarization mode filter. Specific features of the proposed device are its compact one-section form resulting from the inherent polarization-discrimination property and the relaxed dimensional tolerance due to the automatic phase-matching of coupled modes.
We demonstrate growth control of Cu-based metal-organic framework (MOF) (HKUST-1) thin films assembled by the layer-by-layer technique on polymer films. The crystallinity and crystal face of MOF thin films were found to be controlled by reaction sites in polymer films such as hydroxy groups (the (100) crystal face), carbonyl groups (the (111) crystal face), and amide groups (the (100) crystal face). The HKUST-1 film growth amount is highly correlated with the polar component of the surface free
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