Enhanced Charge Carrier Separation in WO₃/BiVO₄ Photoanodes Achieved via Light Absorption in the BiVO₄ Layer

Photoelectrochemical (PEC) water splitting converts solar light and water into oxygen and energy-rich hydrogen. WO₃/BiVO₄ heterojunction photoanodes perform much better than the separate oxide components, though internal charge recombination undermines their PEC performance when both oxides absorb light. Here we exploit the BiVO₄ layer to sensitize WO₃ to visible light and shield it from direct photoexcitation to overcome this efficiency loss. PEC experiments and ultrafast transient absorption spectroscopy performed by frontside (through BiVO₄) or backside (through WO₃) irradiating photoanodes with different BiVO₄ layer thickness demonstrate that irradiation through BiVO₄ is beneficial for charge separation. Optimized electrodes irradiated through BiVO₄ show 40% higher photocurrent density compared to backside irradiation.