Solution-Processed Bi₂S₃ Photoresistor Film To Mitigate a Trade-off between Morphology and Electronic Properties

Bismuth sulfide (Bi₂S₃) is an attractive 2D layered, visible-light-absorbing semiconductor composed of nontoxic, abundant elements. Improving the quality of a Bi₂S₃ film for device applications while maintaining its intrinsic electronic properties is a challenge, as conventional film fabrication processes require a trade-off due to the uncontrolled nucleation and growth steps. We report a novel procedure for Bi₂S₃ film formation involving spin-coating of a precursor solution of bismuth acetate and thiourea, followed by crystallization under diluted H₂S gas. This two-step process produced a large-grained (<400 nm), smooth (surface roughness = 1.7 nm), and highly pure Bi₂S₃ film with a layer-stacked structure on a substrate. Most importantly, the film exhibited a moderate Hall effect electron mobility (∼7 cm² V^-1 s^-1) and excellent performance as a photoresistor with improved photoconductance and on-off ratio compared with those prepared by conventional methods. Our approach provides a versatile route for the development of metal sulfide semiconductors for optoelectronic devices.