Manipulating Atomic and Microstructure of Sb ₂ (S,Se) ₃ Thin Films via a Novel Post‐Treatment for Efficient Solar Cell Application

Abstract Antimony selenosulfide (Sb 2 (S,Se) 3 ), an emerging light‐harvesting material, exhibits a high light absorption coefficient, low toxicity, and phase stability. However, Sb 2 (S,Se) 3 films deposited via the conventional hydrothermal method fail to achieve desirable optoelectronic properties and crystallinity, which ultimately hinders their applications in photovoltaic devices. In this study, an innovative post‐treatment process is developed, wherein the Sb 2 (S,Se) 3 absorber is soaked in a mixed aqueous solution containing ammonia, sodium citrate, and cadmium sulfate, followed by annealing, resulting in multi‐dimensional optimization. It is revealed that the synergistic interaction in this strategy leads to the formation of cadmium selenide and cadmium sulfide on the surface and the infiltration of cadmium ions into the bulk phase. This outcome finally optimizes the atomic structure by passivating the deep‐level defects such as Se and S vacancy, while also increasing the crystallinity through a strong chemical bonding effect. Furthermore, the slight etching of the surface by ammonia reduces the content of antimony oxide, increases phase purity, and optimizes interfacial contact in the device, thereby facilitating carrier transport. With these advantages, a high power conversion efficiency of 10.5% for Sb 2 (S,Se) 3 solar cell is achieved. This study provides a one‐stone‐for‐three‐birds strategy for improving the photoelectric performance of antimony‐based chalcogenide compounds.