Dual‐Functional Ionic Liquid Additive Enables High‐Performance Perovskite Solar Cells by Suppressing Ion Migration and Passivating Defects

ABSTRACT Perovskite solar cells (PSCs) have emerged as a promising next‐generation photovoltaic technology owing to their exceptional optoelectronic properties. Nevertheless, defect states within perovskite films lead to significant non‐radiative recombination and ion migration, which substantially constrain both the power conversion efficiency (PCE) and operational stability of the devices. In this work, a dual‐functional benzimidazole‐based ionic liquid (IL) additive, 1‐phenyl‐1H‐imidazol‐3‐ium trifluoromethanesulfonate (PIT), was incorporated into the perovskite precursor solution to regulate the crystallization, passivate defect states, and stabilize the crystal structure. The PIT anion, possessing a strong electron‐donating ability, exhibits strong defect passivation capability by interacting with Pb ²⁺ and FA ⁺ /MA ⁺ cations through coordination bonds and hydrogen bonds. Meanwhile, the PIT cation with a conjugated aromatic structure is enriched on the top surface of the perovskite film, effectively slowing down the crystallization rate of perovskite and increasing grain size by increasing steric hindrance. Additionally, the cation forms electrostatic interactions with I ⁻ , effectively suppressing ion migration and the formation of iodine‐related defects. Under the synergistic effect of both anions and cations, the PIT‐modified PSCs achieve a champion PCE of 25.94%. Moreover, the PIT‐based device demonstrates enhanced stability, retaining 97% of its initial efficiency after 2,064 h of continuous storage in a nitrogen atmosphere.