Enhanced Charge Carrier Separation in WO(3)/BiVO(4) Photoanodes Achieved via Light Absorption in the BiVO(4) Layer

[Image: see text] Photoelectrochemical (PEC) water splitting converts solar light and water into oxygen and energy-rich hydrogen. WO(3)/BiVO(4) 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(4) layer to sensitize WO(3) 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(4)) or backside (through WO(3)) irradiating photoanodes with different BiVO(4) layer thickness demonstrate that irradiation through BiVO(4) is beneficial for charge separation. Optimized electrodes irradiated through BiVO(4) show 40% higher photocurrent density compared to backside irradiation.