Resonant optical absorption and defect control in Ta3N5 photoanodes

In this study, we explore resonance-enhanced optical absorption in Ta3N5 photoanodes for water splitting. By using a reflecting Pt back-contact and appropriate Ta3N5 film thickness, the resonance frequency can be tuned to energies just above the bandgap, where the optical absorption is normally weak. The resonance results in a significant improvement in the photoanode's incident photon-to-current efficiency. The Ta3N5 films are made by high-temperature nitridation of Ta2O5. The nitridation time is found to be critical, as extended nitridation result in the formation of nitrogen vacancies through thermal reduction. These insights give important clues for the development of efficient (oxy)nitride-based photoelectrodes.