Unraveling the electronic structure of CuSbS2 thin film photocathodes for solar-driven hydrogen evolution

Copper antimony sulfide (CuSbS2) is a p-type semiconductor that has an appropriate band gap of 1.5 eV and a large optical absorption coefficient (>105 cm(-1)), rendering it an emerging candidate for photoelectrochemical (PEC) watersplitting to produce green H-2. However, the current understanding of the essential electronic structure of CuSbS2 and its correlation with PEC activity are limited, but it is very important to devise strategies for further PEC property improvements. Here, we report on the synthesis of CuSbS2 thin films with high quality and achieve a record-high photocurrent density of 6.3 mA cm(-2) at 0.0 V vs. reversible hydrogen electrode with an F-doped tin oxide/CuSbS2/CdS/Pt photocathode. More importantly, a synergistic combination of Xray photoemission spectroscopy and optical spectroscopy was used to unravel the electronic structure of CuSbS2. Our results show that the valence band of CuSbS2 consists of strongly hybridized states of S 3p and Cu 3d, to a lesser extent, affected by Sb 5p/5s. The implication of the electronic structure on the PEC activity and strategies for further improvement by using n-type CdS to construct a built-in electric field to facilitate photogenerated carrier transportation, are discussed.