Dye sensitized photocathodes for solar energy applications

Abstract:
One way of improving the efficiency of dye-sensitized solar cells is to use two photoelectrodes in a tandem device, one harvesting the high energy photons, and the other harvesting the low energy photons.1 This enables the photovoltage to be increased, whilst maximizing light harvesting across the solar spectrum. Despite their promise, a tandem cell with a higher efficiency than the state-of-the-art “Grätzel” cell has not yet been achieved. This is because the performances of photocathodes are significantly lower than TiO2-based anodes, and the p-type concept has been largely unexplored since the first device was prepared in 1999.2 The small potential difference between the valence band of the NiO, p-type semiconductor, and the redox potential of the electrolyte and the faster charge-recombination reactions compared to the TiO2 system limits the efficiency. Our success in increasing the efficiency by developing new panchromatic dye molecules will be presented.3 In parallel we are investigating the charge-transfer processes to determine the mechanism and limitations to efficiency.4-6 Our efforts to understand the redox processes at the dye/electrolyte and NiO/electrolyte interfaces will be discussed.7 As will recent work to expand the applications to photoelectrochemical water splitting for energy storage.