Photogenerated electron-hole charge separation in oxide perovskite [001] surfaces

Perovskite oxides such as SrTiO₃ have garnered much interest owing to their high photocatalytic efficiency and favorable interfacial interactions with water, two important features that drive solar water splitting. Understanding their behavior in aqueous environments is critical to improving their performance in energy applications. In this work, we focus on the overall water splitting reaction at SrTiO₃ [001] surfaces initiated by photogenerated electron-hole pairs. Using a combination of first-principles simulations and experiments, we elucidate the relation between spatial electron-hole charge separation and photocatalytic activity on the surface. Since [001] SrTiO₃ surfaces present two different terminations, namely TiO₂ and SrO, we identify which one is better suited for a photo-oxidation or reduction. This provides crucial insight into the nature of water-splitting reactions occurring at a water-oxide interface. We consider explicitly the effect of an excess electron (resp. hole) by introducing electron (resp. hole)-rich dopants at Ti-sites. We find that the preferential migration of a charge carrier is strongly determined by the specific surface site as well as the surface termination of the site.