Light Harvesting and Direct Electron Injection by Interfacial Charge-Transfer Transitions between TiO2 and Carboxy-Anchor Dye LEG4 in Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSC) have attracted much attention as a promising candidate for next-generation solar cells. Recently, the solar-to-electrical energy conversion efficiency of DSSC was improved up to ca. 14%. Nevertheless, further improvement of the solar energy conversion is required for practical applications of DSSC. The performance of DSSC is limited by energy loss larger than ca. 0.3 eV in the electron injection from photoexcited dyes to TiO2. Interfacial charge-transfer transitions (ICT) between TiO2 and dyes provide a direct electron-injection mechanism with internal quantum efficiency of 100% and without energy loss. Recently, we demonstrated efficient photoelectric conversion due to ICT transitions between TiO2 nanoparticles and 2-anthracenecarboxylic acid. In this paper, we report that ICT transitions between TiO2 nanoparticles and a donor–acceptor organic dye called LEG4 bearing a carboxy anchor group extend the spectral sensitivity of the LEG4-based DSSC to the near IR region. Our research reveals the important role of ICT transitions in the improvement of the solar energy conversion of DSSC.