Thermally Driven Point Defect Transformation in Antimony Selenosulfide Photovoltaic Materials

Abstract Thermal treatment of inorganic thin films is a general and necessary step to facilitate crystallization and, in particular, to regulate the formation of point defects. Understanding the dependence of the defect formation mechanism on the annealing process is a critical challenge in terms of designing material synthesis approaches for obtaining desired optoelectronic properties. Herein, a mechanistic understanding of the evolution of defects in emerging Sb 2 (S,Se) 3 solar cell films is presented. A top‐efficiency Sb 2 (S,Se) 3 solar‐cell film is adopted in this study to consolidate this investigation. This study reveals that, under hydrothermal conditions, the as‐deposited Sb 2 (S,Se) 3 film generates defects with a high formation energy, demonstrating kinetically favorable defect formation characteristics. Annealing at elevated temperatures leads to a two‐step defect transformation process: 1) formation of sulfur and selenium vacancy defects, followed by 2) migration of antimony ions to fill the vacancy defects. This process finally results in the generation of cation–anion antisite defects, which exhibit low formation energy, suggesting a thermodynamically favorable defect formation feature. This study establishes a new strategy for the fundamental investigation of the evolution of deep‐level defects in metal chalcogenide films and provides guidance for designing material synthesis strategies in terms of defect control.