Theoretical treatment of semiconductor heterojunctions for photocatalysis: the WO₃/BiVO₄ interface

The valence and conduction band (CB) alignments and the nature of the WO₃/BiVO₄ heterojunction have been analysed in detail based on hybrid functionals density functional theory calculations. The WO₃/BiVO₄ junction is widely studied in photocatalysis for its capability to reduce electron-hole recombination and to improve efficiency. This is assumed to be due to a favourable band alignment of the junction's components, which generates a flow of negative charge carriers towards WO₃, and positive ones towards BiVO₄. This conclusion is often based on the properties of the two isolated, non-interacting units. Here, we propose an explicit interface model where the (0 0 1) surface of WO₃ is put in contact with the (0 1 0) surface of BiVO₄ rotated by about 45°, which leads to a small strain and a favourable cation-anion matching. The interface displays a moderate charge transfer and a small interface dipole. This leads to only moderate effects on the band alignment, which remains qualitatively similar to that obtained from the two independent oxides. We also considered in detail the role of the amount of exact exchange used in the description of the heterojunction, and in particular of the BiVO₄ component, for which rather different hybrid functional approaches have been proposed in the literature.