Triple Planar Heterojunction of SnO2/WO3/BiVO4 with Enhanced Photoelectrochemical Performance under Front Illumination

The performance of a BiVO4 photoanode is limited by poor charge transport, especially under front side illumination. Heterojunction of different metal oxides with staggered band configuration is a promising route, as it facilitates charge separation/transport and thereby improves photoactivity. We report a ternary planar heterojunction photoanode with enhanced photoactivity under front side illumination. SnO2/WO3/BiVO4 films were fabricated through electron beam deposition and subsequent wet chemical method. Remarkably high external quantum efficiency of ~80% during back side and ~90% upon front side illumination at a wavelength of 400 nm has been witnessed for SnO2/WO3/BiVO4 at 1.23 V vs. reversible hydrogen electrode (RHE). The intimate contact between the heterojunction films enabled efficient charge separation at the interface and promoted electron transport. This work provides a new paradigm for designing triple heterojunction to improve photoactivity, particularly under front illumination, which would be beneficial for the development of tandem devices.