In Situ Polymerization Strategy for Improving the Stability of Sn-Based Perovskite Solar Cells

Sn-based perovskite solar cells (Sn-PSCs) have received increasing attention due to their nontoxicity and potentially high efficiency. However, the poor stability of Sn²⁺ ions remains a major problem in achieving stable and efficient Sn-PSCs. Herein, an in situ polymerization strategy using allyl thiourea and ethylene glycol dimethacrylate as cross-linking agents in the Sn-based perovskite precursor is proposed to improve the device performance of Sn-PSCs. The C═S and N-H bonds of the cross-linkers are able to coordinate with SnI₂ and inhibit the oxidation of Sn²⁺, thereby reducing defect density and improving the stability of Sn-based perovskite films. The high quality of the perovskite film induced by the in situ polymerization strategy delivers an improved power conversion efficiency (PCE) from 7.50 to 9.22%. More importantly, the unpackaged device with cross-linkers maintained more than 70% of the initial PCE after 150 h of AM 1.5G light soaking in a nitrogen atmosphere and 80% of the initial PCE after 1800 h in dark conditions. This work demonstrates that the in situ polymerization strategy is an effective method to enhance the stability of Sn-based perovskite films and devices.