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 TiO 2 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 /TiO 2 solar cells. Transient visible spectroscopy reveals similar rates of both halide oxidation and injected electron-oxidized dye recombination for the two sensitizers. Substituting SnO 2 for TiO 2 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.