Anomalous Conductivity Tailored by Domain-Boundary Transport in Crystalline Bismuth Vanadate Photoanodes

Carrier transport in semiconductor photoelectrodes strongly correlates with intrinsic material characteristics including carrier mobility and diffusion length, and extrinsic structural imperfections including mobile charged defects at domain boundaries, which collectively determines the photo-electrochemistry (PEC) performance. Here we elucidate the interplay between intrinsic carrier transport, domain-boundary-induced conductivity, and PEC water oxidation in the model photoanode of bismuth vanadate (BiVO4). In particular, epitaxial single-domain BiVO4 and c-axis-oriented multidomain BiVO4 thin films are fabricated using pulsed laser deposition to decouple the intrinsic and extrinsic carrier transport. In addition to the low intrinsic conductivity that is due to the small-polaron transport within BiVO4 domains, we identify anomalously high electrical conductivity arising from vertical domain boundaries for multidomain BiVO4 films. Local domain-boundary conduction compensates the inherently poor electron transport by shortening the transport distance for electrons diffused into the domain-boundary region, therefore suppressing the photocurrent difference between front and back illumination. This work provides insights into engineering carrier transport through coordinating structural domain boundaries and intrinsic material features in designing modulated water-splitting photoelectrodes.