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. WO/BiVO 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 BiVO layer to sensitize WO 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 BiVO) or backside (through WO) irradiating photoanodes with different BiVO layer thickness demonstrate that irradiation through BiVO is beneficial for charge separation. Optimized electrodes irradiated through BiVO show 40% higher photocurrent density compared to backside irradiation.