Mechanistic Insights into Defect-Assisted Carrier Transport in Bismuth Vanadate Photoanodes

Understanding defect-assisted carrier transport is critical for optimizing the performance of solar water splitting devices. Here we analyze the mechanism of two distinct types of point defects, oxygen vacancies and hydrogen donors, in defining carrier transport and thus the photoelectrochemical (PEC) behavior in bismuth vanadate (BiVO4). While the conventional hydrogen annealing brings hydrogen donors as a dominant defect, we introduce a novel carbon monoxide treatment that does not introduce hydrogen but only generates more oxygen vacancies. Combined with PEC and solid-state transport characterizations, it is revealed that oxygen vacancies are more effective than hydrogen donor to improve electron transport both within BiVO4 domains and along structural boundaries, thus yielding larger front-illuminated photocurrent, larger film conductivity, and smaller polaron hopping barrier. This study provides mechanistic insights into defect engineering that can guide novel approaches to overcoming charge transport limitations in low-mobility semiconductors.