Analysis of the interfacial characteristics of BiVO4/metal oxide heterostructures and its implication on their junction properties

Abstract

The formation of heterostructures has proven to be a viable way to achieve high photoelectrochemical water splitting efficiencies with BiVO₄ based photoanodes. Especially, cobalt and nickel based oxides are suitable low cost contact materials. However, the exact role of these contact materials is not yet completely understood because of the difficulty to individually quantify the effects of surface passivation, charge carrier separation and catalysis on the efficiency of a heterostructure. In this study, we used photoelectron spectroscopy in combination with in situ thin film deposition to obtain direct information on the interface structure between polycrystalline BiVO₄ and NiO, CoO_x and Sn-doped In₂O₃ (ITO). Strong upwards band bending was observed for the BiVO₄/NiO and BiVO₄/CoO_x interfaces without observing chemical changes in BiVO₄, while limited band bending and reduction of Bi and V was observed while forming the BiVO₄/ITO interface. Thus, the tunability of the Fermi level position within BiVO₄ seems to be limited to a certain range. The feasibility of high upwards band bending through junctions with high work function (WF) compounds demonstrate that nickel oxide and cobalt oxide are able to enhance the charge carrier separation in BiVO₄. Similar studies could help to identify whether new photoelectrode materials and their heterostructures would be suitable for photoelectrochemical water splitting.