Hybrid-Functional Study of Native Defects and W/Mo-Doped in Monoclinic-Bismuth Vanadate

Monoclinic scheelite (ms) BiVO4 is recognized as one of the most promising photocatalyst materials due to its band gap as well as band-edge positions. Several theoretical and experimental works have been dedicated to improving the photocatalytic activity of ms-BiVO4. It has been reported that doping ms-BiVO4 with either W or Mo can enhance its photocatalytic activity compared to the undoped one. Further, codoping with W and Mo can improve the photocatalytic activity. Here, we systematically investigate all native and W/Mo-related defects in ms-BiVO4 by using density functional theory with hybrid functional. For undoped ms-BiVO4, we reveal that vacancies are the most dominant intrinsic defects and these defects compensate themselves leading to moderate n-type conductivity in O-poor growth condition. For W/Mo-doped ms-BiVO4, W and Mo are likely to substitute for V atom under all crystal growth conditions. While WV defect is a shallow donor, MoV defect creates a defect level below the conduction band edge. This implies that doping with W can gain more photocatalytic efficiency, which agrees well with experiment. Interestingly, we find that two donors, i.e., WV and MoV defects, prefer to form a complex defect becoming a shallow double donor. This can improve the electrical conductivity of W/Mo-codoped ms-BiVO4, which helps enhance its photocatalytic performance. In addition, the formation of donor–donor complexes is quite stable and helps improve material property.