Thermally Driven Point Defect Transformation in Antimony Selenosulfide Photovoltaic Materials

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 Sb2 (S,Se)3 solar cell films is presented. A top-efficiency Sb2 (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 Sb2 (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.