Suppression of charge carrier recombination in a Ta3N5 photoanode via defect regulation: a theoretical investigation

Abstract

Defect-induced charge carrier recombination in a photoanode significantly restricts the efficiency of solar-driven water splitting. By systematically investigating the photoexcited charge carrier recombination dynamics of Ta₃N₅ with intrinsic defects, charge states, oxygen (O) impurities, and metal doping based on density functional theory (DFT) calculations and nonadiabatic molecular dynamics (NAMD) simulations, we propose two strategies to mitigate defect-induced charge carrier recombination: ionizing nitrogen (N) vacancies and magnesium (Mg) doping. Our results show that tantalum (Ta) reduction induced by N vacancies is the primary factor in reducing the carrier lifetime of the Ta₃N₅ photoanode. Ionizing N vacancies and Mg doping can tune the charges of reduced Ta species near the N vacancies, thus extending the recombination lifetime. By contrast, charge-balanced metal and O impurities co-doping in Ta₃N₅ photoanodes cannot significantly increase the lifetime. Our investigation sheds new light on understanding the charge carrier recombination mechanism and provides dependable strategies to improve the water-splitting performance of the Ta₃N₅ photoanode.