Electronic Properties and Defect Investigation of MASnX₃ (X = Cl, Br, and I) Perovskite Structures

Tin-based organic–inorganic halide perovskites have emerged as promising lead-free candidates for photovoltaic applications due to their favorable optoelectronic properties. However, their practical deployment is limited by intrinsic instability arising from the native defect formation. In this work, we systematically investigate the defect chemistry of MASnX 3 (MA = CH 3 NH 3 +; X = I, Br, Cl) using a combination of density functional theory (DFT) calculations and experimental analysis. Formation energy calculations identify Sn vacancies and halide interstitials as the most thermodynamically favorable defects. Among the series, MASnCl 3 exhibits the highest structural stability, attributed to its reduced tendency to form Sn vacancies. Furthermore, Cl doping in MASnI 3 is shown to increase the formation energy of Sn vacancies, thereby mitigating defect-induced degradation. These findings offer critical insights into the defect tolerance of tin halide perovskites and highlight effective strategies for enhancing their stability and performance in solar cell applications.