Multifunctional Ionic Liquid Assisted Crystallization Regulation and In Situ Defect Passivation for High‐Performance Perovskite Solar Cells

Abstract Perovskite solar cells (PSCs) have become a highly anticipated research direction in the field of next‐generation photovoltaic technology due to their excellent photoelectric conversion performance. One core issue for high‐performance PSCs is to suppress the non‐radiative recombination caused by defects in the perovskite layer and at the interfaces. In this work, a novel functionalized sulfonate‐based ionic liquid, 1‐ethyl‐3‐methylimidazolium methyl sulfonate (EMIM‐MS), is introduced for in situ defect passivation during the perovskite crystallization process. For the anionic part of EMIM‐MS, the ‐SO 3 − group can form coordination with Pb 2+ , and the ‐CH 3 groups can form hydrogen bonds with I−. Coupled with the formation of hydrogen bonds between EMIM‐MS and formamidinium (FA + ), high‐quality perovskite films with large crystal size and low defect density are achieved. In addition, due to its large molecular size, EMIM‐MS can be squeezed to the surface during annealing, playing an important role in passivating defects at the interfaces. Therefore, the efficiency of PSC based on EMIM‐MS is significantly improved to 25.48% from the controlled 22.24%, and the long‐term storage and wet heat stability are also improved. This strategy provides valuable insights for defect passivation and helps promote the industrialization of PSC.