Interface-controlled BiVO4 thin films via selective rinsing for balanced front-back illumination performance

Abstract Bismuth vanadate (BiVO 4 ) has emerged as a leading photoanode material for solar-driven water splitting due to its visible-light absorption, favorable band edge positions, and chemical stability. However, BiVO 4 performance is often limited by poor charge transport and a strong disparity between front- and back-side illumination, arising from the short hole diffusion length. Here, we report a facile rinsing strategy to overcome this challenge. Bi was first electrodeposited on fluorine-doped tin oxide (FTO) substrates and subsequently rinsed to selectively remove weakly adhered Bi particles, leaving a compact, strongly anchored precursor layer. After thermal conversion, the resulting BiVO 4 electrodes exhibited uniform morphology, improved transparency, and robust adhesion. Remarkably, these rinsed BiVO 4 films delivered nearly identical photocurrents under both front and back illumination, in contrast to the conventional behavior of BiVO 4 electrodes. This symmetry indicates enhanced charge separation and reduced recombination losses across the film thickness. Stability tests further confirmed excellent durability under continuous operation. Compared with approaches involving doping, nanostructuring, or cocatalyst loading, the proposed rinsing step represents a simple, scalable, and cost-effective method to fabricate direction-independent BiVO 4 photoanodes, offering new opportunities for practical photoelectrochemical hydrogen production.