Molecular Engineering of Imidazole Ionic Liquids to Suppress Ion Migration in Perovskite Solar Cells

Ion migration in perovskite solar cells is a key factor limiting their thermal stability and long-term operational performance. Suppressing ion migration is therefore critical for durable devices, yet strategies to control ion migration at the molecular level remain limited. Here, we introduce a rational molecular design using imidazole-based ionic liquids to inhibit ion migration and enhance the device stability. By systematically replacing butyl and methyl with allyl and vinyl on the imidazole ring (the ability of electron donating gradually weakens from butyl to vinyl), we reduce electron density and increase electrostatic potential, tuning its interactions with perovskite components. Spectroscopic analyses indicate weakened coordination with Pb²⁺ and strengthened interactions with I^-, which play a critical role in mitigating ion migration. Among the derivatives, 1-butyl-3-vinyl imidazole (VBIM) most efficiently inhibits ion migration under light, electric bias, and an elevated temperature. Solar cell devices incorporating VBIM achieve a champion efficiency of 26.13% and exhibit dramatically improved thermal stability, demonstrating the critical role of ionic-liquid-mediated ion migration suppression for efficient and durable cells.