Suppressing Se Vacancies in Sb 2 Se 3 Photocathode by In Situ Annealing with Moderate Se Vapor Pressure for Efficient Photoelectrochemical Water Splitting

Sb₂Se₃ emerges as a promising material for solar energy conversion devices. Unfortunately, the common deep-level defect V_Se (selenium vacancy) in Sb₂Se₃ 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 Sb₂Se₃ 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 Sb₂Se₃ 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 Sb₂Se₃ photocathode.