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 (O_V) 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 O_V on charge carrier lifetimes in BiVO₄. The simulations show that a neutral O_V 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 O_V 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 O_V in BiVO₄ and provides valuable insights for improving the performance of the BiVO₄ photoanode by ionizing the oxygen vacancy.