Controlling Charge Carrier Trapping and Recombination in BiVO4 with the Oxygen Vacancy Oxidation State.

The lack of an in-depth understanding of the intrinsic oxygen vacancy (OV) defect properties in the photoanode BiVO4 limits the further improvement of its photoelectrochemical water splitting performance. To address this issue, nonadiabatic molecular dynamics simulations are performed to study the impact of OV on charge carrier lifetimes in BiVO4. The simulations show that a neutral OV gives rise to local structural distortions due to the formation of V-O-V bonds, forcing the electrons trapped on the nearer of the two V atoms to form two deep polaron-like V4+ hole traps. These localized midgap states greatly accelerate nonradiative electron-hole recombination compared to that of pristine BiVO4, reaching a time scale of several nanoseconds in good agreement with experiments. The ionized OV state restores the bandgap to its value in pristine BiVO4 and restores the charge carrier lifetimes due to the fast loss of coherence time. Our study reveals the mechanism of the detrimental role of OV in BiVO4 and provides valuable insights for improving the performance of the BiVO4 photoanode by ionizing the oxygen vacancy.