Tailoring the Crystallographic Orientation of a Sb₂S₃ Thin Film for Efficient Photoelectrochemical Water Reduction

Antimony sulfide (Sb 2 S 3 ) is an emerging earth-abundant semiconductor for photoelectrochemical (PEC) water reduction. The anisotropic nature of Sb 2 S 3 is responsible for its direction-dependent carrier transport efficiency. In general, photogenerated carriers transfer more efficiently along the [ hk 1] orientation than along the [ hk 0] orientation. However, the synthesis of a Sb 2 S 3 film with precisely controlled [ hk 1] orientation is still very challenging. Herein, a completely [ hk 1]-oriented Sb 2 S 3 film is prepared by sulfurizing an Ag/Sb bimetallic precursor film deposited using dual-source electron-beam evaporation. A sliver-induced crystal growth model is proposed to elucidate the formation mechanism of the [ hk 1]-oriented Sb 2 S 3 film. Mechanistic studies reveal that the [ hk 1]-oriented Sb 2 S 3 film has a lower defect density, a lower bulk and surface recombination, and better carrier transport efficiency in comparison to those of a randomly oriented Sb 2 S 3 film. As a result, a photocathode based on the [ hk 1]-oriented Sb 2 S 3 film delivers a high photocurrent density of 9.4 mA cm –2 at 0 V versus RHE and a high applied bias photon-to-current efficiency of 1.2% in a neutral electrolyte. Our work not only demonstrates the effectiveness of the crystal orientation of a Sb 2 S 3 film for PEC water splitting but also provides a strategy for crystal orientation engineering of stibnite-type semiconductors for solar energy conversion applications.