Interfacial Oxide Formation Limits the Photovoltage of α‐SnWO4/NiOx Photoanodes Prepared by Pulsed Laser Deposition. Issue 9 (14th January 2021)

• Record Type: Journal Article
• Authors: Schnell, Patrick; Kölbach, Moritz; Schleuning, Markus; Obata, Keisuke; Irani, Rowshanak; Ahmet, Ibbi Y.; Harb, Moussab; Starr, David E.; van de Krol, Roel; Abdi, Fatwa F.
• Is Part Of: Advanced energy materials. Volume 11:Issue 9(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-01-14
• Subjects: DFT -- HAXPES -- interface -- photovoltage -- pulsed laser deposition -- α‐SnWO4; Energy harvesting -- Materials -- Periodicals; Energy conversion -- Materials -- Periodicals; Energy storage -- Materials -- Periodicals; Photovoltaics -- Periodicals; Fuel cells -- Periodicals; Thermoelectric materials -- Periodicals; 621.31
• DOI: 10.1002/aenm.202003183
• Languages: English
• ISSNs: 1614-6832

Abstract

Abstract: α‐SnWO4 is a promising metal oxide photoanode material for direct photoelectrochemical water splitting. With a band gap of 1.9 eV, it ideally matches the requirements as a top absorber in a tandem device theoretically capable of achieving solar‐to‐hydrogen (STH) efficiencies above 20%. It suffers from photoelectrochemical instability, but NiO x protection layers have been shown to help overcome this limitation. At the same time, however, such protection layers seem to reduce the photovoltage that can be generated at the solid/electrolyte junction. In this study, an extensive analysis of the α‐SnWO4 /NiO x interface is performed by synchrotron‐based hard X‐ray photoelectron spectroscopy (HAXPES). NiO x deposition introduces a favorable upwards band bending, but also oxidizes Sn 2+ to Sn 4+ at the interface. By combining the HAXPES data with open circuit potential (OCP) analysis, density functional theory (DFT) calculations, and Monte Carlo‐based photoemission spectra simulation, the presence of a thin oxide layer at the α‐SnWO4 /NiO x interface is suggested and shown to be responsible for the limited photovoltage. Based on this new‐found understanding, suitable mitigation strategies can be proposed. Overall, this study demonstrates the complex nature of solid‐state interfaces in multi‐layer photoelectrodes, which needs to be unraveled to design efficient heterostructured photoelectrodes for solar water splitting. Abstract : Understanding complex interfaces in multilayer photoelectrodes, such as α‐SnWO4 /NiO x photoanodes, is critical to maximize the attainable photoelectrochemical performance. Synchrotron‐based hard X‐ray photoelectron spectroscopy measurements, combined with theoretical calculations and simulations, reveal that NiO x deposition introduces a thin interfacial oxide layer. The presence of this layer is responsible for the reduced photovoltage and represents a key limitation in the α‐SnWO4 /NiO x photoanodes.