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.