Controllable Distribution of Oxygen Vacancies in Grain Boundaries of p-Si/TiO Heterojunction Photocathodes for Solar Water Splitting.

Silicon is a promising photocathode material in photoelectrochemical water splitting for hydrogen production, but it is primarily limited by photocorrosion in aqueous electrolytes. As an extensively used protective material, crystalline TiO could protect Si photoelectrode against corrosion. However, a large number of grain boundaries (GBs) in polycrystalline TiO would induce excessive recombination centers, impeding the carrier transport. This paper describes the introduction of oxygen vacancies (O ) with controllable spatial distribution for GBs to promote carrier transport. Two kinds of O distribution, O along GBs and O inside grains, are compared, where the latter one is demonstrated to facilitate carrier transport owing to the formation of tunneling paths across GBs. Consequently, a simple p-Si/TiO /Pt heterojunction photocathode with controllable O distribution in TiO shows a +400 mV onset potential shift and yields an applied bias photon-to-current efficiency of 5.9 %, which is the best efficiency reported among silicon photocathodes except for silicon homojunction.