Active Passivation of Anion Vacancies in Antimony Selenide Film for Efficient Solar Cells

Binary antimony selenide (Sb₂Se₃) is a promising inorganic light-harvesting material with high stability, nontoxicity, and wide light harvesting capability. In this photovoltaic material, it has been recognized that deep energy level defects with large carrier capture cross section, such as V_Se (selenium vacancy), lead to serious open-circuit voltage (V_OC) deficit and in turn limit the achievable power conversion efficiency (PCE) of Sb₂Se₃ solar cells. Understanding the nature of deep-level defects and establishing effective method to eliminate the defects are vital to improving V_OC. In this study, a novel directed defect passivation strategy is proposed to suppress the formation of V_Se and maintain the composition and morphology of Sb₂Se₃ film. In particular, through systematic study on the evolution of defect properties, the pathway of defect passivation reaction is revealed. Owing to the inhibition of defect-assisted recombination, the V_OC increases, resulting in an improvement of PCE from 7.69% to 8.90%, which is the highest efficiency of Sb₂Se₃ solar cells prepared by thermal evaporation method with superstrate device configuration. This study proposes a new understanding of the nature of deep-level defects and enlightens the fabrication of high quality Sb₂Se₃ thin film for solar cell applications.