Hideo Ohkita

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The charge generation and recombination dynamics in blend films of a poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) were comprehensively studied by transient absorption spectroscopy in the wavelength region from 450 to 1650 nm under various excitation intensities and different excitation wavelengths. In homogeneously mixed blend(More)
The bimolecular recombination dynamics in blend films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) has been studied by transient absorption spectroscopy. On a microsecond time scale, two polaron bands were observed at 700 and 1000 nm and exhibited different bimolecular recombination dynamics. The 700-nm band(More)
We report herein a comparison of the photophysics of a series of polythiophenes with ionization potentials ranging from 4.8 to 5.6 eV as pristine films and when blended with 5 wt % 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]C61 (PCBM). Three polymers are observed to give amorphous films, attributed to a nonplanar geometry of their backbone while the other(More)
The formation dynamics of polaron pairs, polarons, and triplet excitons in regiorandom and regioregular poly(3-hexylthiophene) (RRa-P3HT and RR-P3HT) films was comprehensively studied by transient absorption spectroscopy over the wide wavelength region from 500 to 1650 nm under various excitation intensities. In both RRa-P3HT and RR-P3HT films, polaron(More)
Perovskite solar cells exhibit improved photovoltaic parameters with increasing perovskite grain size. The larger photocurrent is due to the enhanced absorption efficiency for thicker perovskite layers. The larger open-circuit voltage (VOC ) is ascribed to the reduced trap-assisted recombination for the larger grains. As a result, the power conversion(More)
A crucial issue facing polymer-based solar cells is how to manage the energetics of the polymer/fullerene blends to maximize short-circuit current density and open-circuit voltage at the same time and thus the power conversion efficiency. Here we demonstrate that the use of a naphthobisoxadiazole-based polymer with a narrow bandgap of 1.52 eV leads to high(More)
Singlet exciton diffusion plays a central role in the photovoltaic conversion in organic photovoltaics (OPVs). Upon light absorption, singlet excitons are promptly generated in organic materials instead of charge carriers because the dielectric constant (εr) is small (∼3-4), which is in sharp contrast to inorganic and perovskite solar cells. In order to(More)
Multi-colored dye-sensitized polymer/fullerene solar cells with two different near-IR dyes, silicon phthalocyanine bis(trihexylsilyl oxide) (SiPc) and silicon naphthalocyanine bis(trihexylsilyl oxide) (SiNc), enhanced power conversion efficiency up to 4.3%, compared to that of the individual ternary blend solar cells with a single dye under AM1.5G(More)
Enhancement of the light-harvesting efficiency in poly(3-hexylthiophene)/fullerene derivative (P3HT/PCBM) bulk heterojunction solar cells has been demonstrated by the introduction of near-infrared phthalocyanine molecules as the third component at the P3HT/PCBM interface. The introduction of silicon phthalocyanine derivative (SiPc) increased the(More)
Ternary-blend polymer solar cells can be effectively improved by incorporating a heterostructured near-IR dye, which has a hexyl group compatible with the polymer and a benzyl group compatible with the fullerene. Because of the compatibility with both materials, the heterostructured dye can be loaded up to 15 wt% and hence can boost the photocurrent(More)