Sensitisation of semiconducting electrodes with ruthenium-based dyes

Abstract

Practical photoelectrolysis of water by sunlight requires the development of suitable semiconductor electrodes. One approach is the photosensitisation of wide-bandgap oxide semiconductors by the chemical attachment of a suitable dye to the surface. We report on the photosensitisation of n-TiO₂, n-SrTiO₃ and n-SnO₂ with chemically attached Ru(bipy)₂(bpca) in which the 2,2′-bipyridine-4,4′ dicarboxylic acid (bpca) is chemically attached to the semiconductor surface by two ester linkages. Kinetic analysis reveals a surprisingly low quantum efficiency (η_e≈ 0.25%) for electron injection from the photoexcited dye into the semiconductor and a low rate constant for reoxidation of the dye. A suggestion is made how the dye molecule might be designed to improve the situation radically. Some deterioration in performance was observed after illumination of the sensitised electrode for many hours.