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

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.