Defective Interfaces between BiVO ₄ Photoelectrodes and TiO ₂ Protective Layers

The performance of photoelectrodes for water splitting depends on multiple factors, including their stability against photocorrosion. Protective layers are widely used to prevent corrosion, yet the design and optimization of the interface between the photoelectrode and their protective layer remain poorly understood. Here we focus on bismuth vanadate (BiVO 4 ), a promising photoanode material, and we investigate its interface with titania (TiO 2 ) protective layers, specifically the role of oxygen vacancies in controlling charge transfer and band alignment. Using first-principles calculations, we show that the role of oxygen vacancies in hole transfer depends on the thickness of the TiO 2 layer: the absence of vacancies is more favorable for hole transfer in thin TiO 2 layers, whereas the presence of vacancies is more favorable for thick TiO 2 layers. Hence our results provide guidelines for defect engineering depending on the thickness of the protection layer. In addition, our findings demonstrate that the impact of interfacial oxygen vacancies cannot be solely inferred from bulk defect properties, highlighting the crucial role of atomistic interface modeling in the design of heterojunction photoelectrodes.