Self-trapped excitons at the surface of BiVO4

Abstract

In recent years, BiVO4 has emerged as one of the most promising photocatalysts for use in solar-driven water-splitting applications. Its favourable placement of band edges close to the redox potentials of water, together with the physical stability of the material, makes it stand out from many of its competitors. However, previous studies have demonstrated that the bulk structure of BiVO4 suffers from considerable charge localisation, with reduced charge mobility and worsened photocatalytic properties as a result. This study aims to continue these investigations by analysing the formation of localised states at the material-vacuum interface. Using hybrid density functional theory, simulations are performed on two different surface structures in order to identify the most commonly appearing charge localisations, as well as compute their respective formation energies. For both surfaces, several different localised states are found, with self-trapped excitons appearing both in the direct vacuum interface and in the layer immediately below. By effectively lowering the band gap of BiVO4, these localisations are shown to potentially hamper the overall capability of the material to drive the redox reaction.