Electron injection, recombination, and halide oxidation dynamics at dye-sensitized metal oxide interfaces

Time-resolved infrared measurements indicate ultrafast, <350 fs, electron injection from (4,4'dcb)(2)Ru(NCS)(2) (1) and (5,5'dcb)(2)Ru(NCS)(2) (2) to nanostructured TiO2 electrodes (where 4,4'dcb = 4,4'-(COOH)(2)-2,2'-bipyridine). Although rapid, the injection from 2 apparently occurs with a lower quantum yield than that from 1, explaining a lower overall photon-to-current efficiency for 2/TiO2 solar cells. Transient visible spectroscopy reveals similar rates of both halide oxidation and injected electron-oxidized dye recombination for the two sensitizers. Substituting SnO2 for TiO2 increases the electron injection yield from 2 in the case of transparent metal oxide films and improves the photon-to-current efficiency. Results indicate a wavelength-dependent electron injection yield.