Crystallization Regulation for Air-Processed, Efficient, and Stable Perovskite Solar Cells via In Situ Polymerization-Assisted Intermediate-Phase Transition

Employing additives to regulate the intermediate phase configuration and their formation pathway is imperative for mitigating moisture interference on perovskite crystallization and structural perfection. Herein, we propose an in situ polymerization-assisted intermediate-phase transition strategy via incorporation of polymerizable ionic liquid 1-vinyl-3-ethylimidazolium bromide (VEImBr), which effectively shields perovskite crystallization from moisture interference. Thermodynamic analysis confirms a dynamic intermediate phase evolution from PbI₂ (lead iodide)-VEImBr-<i>N</i>, <i>N</i>-dimethylformamide to PbI₂-VEImBr and PbI₂-is-(VEImBr) adducts during thermal annealing. This engineering favors perovskite nucleation and crystal growth kinetics while offering additional thermodynamics for α-phase perovskites. Moreover, the is-(VEImBr) polymer adheres to perovskite grain boundaries via hydrogen bonding and coordination interactions, reducing the defect density and improving the film performance. Consequently, the is-(VEImBr)-modified perovskite solar cells fabricated under open-air conditions deliver the champion efficiency of 22.57%, with the encapsulated devices maintaining 80% of its initial efficiencies after 900 h under damp-heat accelerated aging test (85 °C and 85% relative humidity).