Suppressing Se Vacancies in Sb2Se3 Photocathode by In Situ Annealing with Moderate Se Vapor Pressure for Efficient Photoelectrochemical Water Splitting

Abstract Sb 2 Se 3 emerges as a promising material for solar energy conversion devices. Unfortunately, the common deep‐level defect V Se (selenium vacancy) in Sb 2 Se 3 results in a low solar conversion efficiency. The post selenization process has been widely adopted for suppressing V Se . However, the effect of selenization on suppressing V Se is often compromised and even more V Se are induced due to defect‐correlation. Herein, high‐quality Sb 2 Se 3 films are prepared using an unconventional selenization process, with precisely regulating in situ annealing Se vapor pressure. It is found that moderate Se vapor pressure annealing can efficiently suppress V Se by overcoming defect‐correlation, as well as promotes grain growth and forms a better heterojunction band alignment. Consequently, the Sb 2 Se 3 photocathode shows a high‐level photocurrent of 19.5 mA cm −2 at 0 V RHE , an onset potential of 0.40 V RHE and a half‐cell solar‐to‐hydrogen conversion efficiency of 1.9%, owing to the inhibited charge recombination, excellent charge transport and interface charge extraction. This work provides a significant insight to suppress deep‐level defect V Se by adjusting Se vapor pressure for efficient Sb 2 Se 3 photocathode.