In Operando Photoelectrochemical Femtosecond Transient Absorption Spectroscopy of WO3/BiVO4 Heterojunctions

The WO3/BiVO4 heterojunction is a promising photoanode architecture for water splitting applications. Here, the photoinduced charge carrier dynamics occurring in this system in operando photoelectrochemical conditions, i.e., under an applied anodic potential, are studied through femtosecond transient absorption spectroscopy to unveil the effects of an applied bias on the early charge carrier dynamics following WO3/BiVO4 excitation. Electrochromic measurements on BiVO4 suggest the presence of intraband gap (IBG) states in this oxide, which play an important role in the charge carrier dynamics in the heterojunction. The differences observed in WO3/BiVO4 with respect to individual BiVO4 electrodes are rationalized in terms of the electron equilibration between the two oxides at the heterojunction, dominated by the WO3/BiVO4 interfacial electric field arising from their band energy offset, and the bias-dependent alteration of the IBG states, both determining the rate of hole transfer and accumulation at the BiVO4 surface.