Synergistic Stabilization and Defect Passivation of CsPbI₃ Perovskite Solar Cells Enabled by an In Situ Polymerized...

CsPbI₃ perovskite has emerged as a promising material for photovoltaic applications owing to its thermal stability and near-ideal bandgap. However, its tendency to transition from photoactive black phase to yellow phase and the processing-induced defects pose significant challenges to its photovoltaic performance. In this study, we propose an innovative in situ polymerization strategy to overcome these limitations by incorporating a multifunctional polymer into CsPbI₃ perovskite films. Specifically, 2,2,3,4,4,4-hexafluorobutyl acrylate monomers are employed to modify the perovskite film surface, where they undergo in situ polymerization during thermal annealing to form an integrated protective network. The resulting polymer modifier exhibits multiple synergistic functions: the carbonyl groups passivate undercoordinated Pb²⁺ defects and the -CFH- groups interact with I^- species to suppress ion migration, while the hydrophobic fluorinated chains enhance moisture resistance. Furthermore, the existence of the polymer could increase the steric hindrance of octahedral distortion to enhance the stability of black-phase CsPbI₃. Notably, the polymer-modified perovskite exhibits improved film quality with reduced defects, which facilitates efficient charge transport and extraction. As a result, the optimized CsPbI₃ perovskite solar cells achieve a power conversion efficiency of 15.23%, along with substantially improved storage stability. Meanwhile, this polymer-modification strategy effectively mitigates lead leakage, providing a valuable route toward more environmentally friendly CsPbI₃ perovskite solar cells.