Photoinduced Charge-Transfer Dynamics in WO₃/BiVO₄ Photoanodes Probed through Midinfrared Transient Absorption Spectroscopy

Abstract

The dynamics of photopromoted electrons in BiVO₄, WO₃, and WO₃/BiVO₄ heterojunction electrodes has been directly probed by transient absorption (TA) midinfrared (mid-IR) spectroscopy in the picosecond to microsecond time range. By comparison of the dynamics recorded with the two individual oxides at 2050 cm^-1 with that of the heterojunction system after excitation at different wavelengths, electron-transfer processes between selectively excited BiVO₄ and WO₃ have been directly tracked for the first time. These results support the charge carrier interactions which were previously hypothesized by probing the BiVO₄ hole dynamics through TA spectroscopy in the visible range. Nanosecond mid-IR TA experiments confirmed that charge carrier separation occurs in WO₃/BiVO₄ electrodes under visible-light excitation, persisting up to the microsecond time scale.