Influences of Electron-Withdrawing Groups of Organic Dyes on Spectral Property and Photovoltaic Performance in Dye-sensitized Solar Cells Application

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We synthesized five donor--\pi-spacer--acceptor type organic photosensitizers bearing different types of electron-withdrawing groups (EWGs); trifluoromethyl, o-nitrophenyl, p-nitrophenyl, cyano, and carboxyl groups, on their acceptor part in the aim of observing an influence of the EWGs on spectral and photovoltaic properties from viewpoints of steric structure and \pi-conjugation. The EWG possessing smaller dihedral angle between the EWG and dye skeleton exhibited larger bathochromic shift in absorptions. Highly planer cyano group presented the most red-shifted absorption at 464 nm, and the highest conversion efficiency of 5.69% was obtained. In contrast, highly distorted o- and p-nitrophenyl groups exhibited blue-shifted absorption at 416 and 422, respectively; however, despite of resemble spectral properties, o- and p-nitrophenyl gave second best and the worst conversion efficiencies of 4.05 and 2.51%, respectively. By combination with computational chemistry, it was indicated that the configuration of the EWG and distance between TiO2 surface and the EWG dominated electron injection efficiency.
2012-10-25