Interfacial Oxide Formation Limits the Photovoltage of ??SnWO ₄ /NiO <i> _x </i> Photoanodes Prepared by Pulsed Laser Deposition

?-SnWO4 is a promising metal oxide photoanode material for direct photoelectrochemical water splitting. With band gap of 1.9 eV, it ideally matches the requirements as top absorber in tandem device theoretically capable achieving solar-to-hydrogen (STH) efficiencies above 20%. It suffers from instability, but NiOx protection layers have been shown to help overcome this limitation. At same time, however, such seem reduce photovoltage that can be generated at solid/electrolyte junction. In study, an extensive analysis ?-SnWO4/NiOx interface performed by synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES). deposition introduces favorable upwards bending, also oxidizes Sn2+ Sn4+ interface. By combining HAXPES data with open circuit potential (OCP) analysis, density functional theory (DFT) calculations, and Monte Carlo-based photoemission spectra simulation, presence thin layer suggested responsible limited photovoltage. Based on new-found understanding, suitable mitigation strategies proposed. Overall, study demonstrates complex nature solid-state interfaces multi-layer photoelectrodes, which needs unraveled design efficient heterostructured photoelectrodes solar