Formation and Passivation of Surface Defects in Lead-Free Tin Halide Perovskites

Lead-based hybrid perovskite materials are promising candidates for photovoltaic applications, but concerns about the toxicity of lead motivate the exploration of lead-free alternatives. In this study, we examined surface defect formations in formamidinium tin iodide (FASnI3), methylammonium tin iodide (MASnI3), and mixed cation formamidinium-methylammonium tin iodide (FAMASnI3) perovskite materials as lead-free options. We systematically investigated a wide range of defect structures, such as vacancies, interstitials, and antisites to identify detrimental defects that can impact device performance. We found that iodine interstitial, FA antisite, and iodine vacancy are harmful defects with low formation energy and charge traps in the bandgap. Also, we were able to eliminate these charge traps using cationic passivating agent molecules. Our findings provide a critical foundation for understanding the surface and defect interaction landscape in these materials, which could guide experimental efforts in synthesizing and optimizing stable, efficient, and environmentally friendly perovskites for photovoltaic applications.