Effects of Doping on the Crystal Structure of BiVO4

The search for efficient photoelectrochemically active materials has led to several studies on BiVO4, which has shown higher photocurrent than most typical semiconductors under photoelectrochemical (PEC) operation. BiVO4 can be stabilized in different crystal structures, yet high PEC efficiency is found only for n-type doped monoclinic phase. The theoretical description of the monoclinic polymorph is difficult because of spontaneous transformation to a tetragonal phase. The cause of such instability of the monoclinic phase has yet to be resolved. Using first-principles calculations based on density functional theory, we explore how the concentration of excess electrons in this material affects its phase stability. We analyze the unit-cell structure, local bonding, and band structure of BiVO4 at different concentrations of excess electrons. We find that as the concentration of excess electrons increases, the tetragonal phase spontaneously transforms into the monoclinic phase, suggesting a crucial role of doping in the structure and, thus, the photoelectrochemical performance of BiVO4.