Theoretical Insight into the Oxyacid Anions Boost Tin‐Based Perovskite Toward the Oxygen Contamination Avoidance and Charge Carrier Lifetime Extension

Abstract Tin (Sn)‐based perovskite solar cells (PSCs) stand out as a promising low‐toxicity alternative to lead (Pb)‐based PSCs. However, their progress is hindered by oxygen‐induced degradation and inherent crystal defects, challenging their efficiency and durability. Through density functional theory (DFT) calculations, it is found that oxyacid anions including HCOO − , HSO 3 − , and H 2 PO 2 − can strongly coordinate with the SnI 2 precursor to form adducts. These complexes help inhibit Sn 2+ /Sn 4+ oxidation in the precursor solution, slow down the crystallization process, and ultimately improve the crystal quality of CsSnI 3 . Moreover, these oxyacid anions bind to the iodine vacancies (I V ) and alloy within the crystal lattice, thereby preventing oxygen molecules from generating detrimental superoxide ions at these sites. Electron structure analysis and nonadiabatic molecular dynamics (NAMD) simulations show that these anions not only eliminate trap states by disrupting the 5p‐5p orbitals interaction of Sn atoms near I V , but also reduce the oscillation of key energy states and weaken nonadiabatic coupling (NAC). These effects collectively contribute to the extended lifetime of charge carriers. Notably, the charge carrier lifetime in the system passivated with H 2 PO 2 − is extended by more than 15 times. Consequently, the oxyacid anions are seen to synergistically enhance the performance of Sn‐based PSCs.