Novel UV‐Shielding Ionic Liquid Enables All‐Air‐Processed Flexible Perovskite Solar Cell

ABSTRACT Flexible perovskite solar cells ( f ‐PSCs) are highly susceptible to ultraviolet (UV) degradation and mechanical brittleness during ambient‐air fabrication, hindering their commercialization. Herein, we engineer an anti‐UV ionic liquid (1‐vinyl‐3‐[3‐(trimethoxysilyl)propyl]imidazolium chloride, IL‐SiO‐2) featuring a tailored C═C‐imidazolium hybrid architecture to address these challenges. The conjugated C═C bonds effectively enable UV shielding to suppress precursor degradation while retarding PbI 2 segregation and I 3 − generation in perovskite film, thereby preventing f ‐PSC device deterioration. Simultaneously, the ionic liquid IL‐SiO‐2's adaptive molecular structure enhances mechanical compliance, enabling robust integration with flexible substrates under bending stress. Ultimately, IL‐SiO‐2 synergistically enables UV‐resistant fabrication of defect‐suppressed perovskite films and stabilized f ‐PSC in air, reducing Young's modulus to 2.58 GPa and grain boundary density by ∼10%, achieving exceptional mechanical durability with 92% power conversion efficiency (PCE) retention after 3,000 bends at R = 2 mm. Remarkable ambient‐air stability and humidity resistance are also attained. The fully air‐processed f ‐PSC delivers a negligible hysteresis (0.004) and retains 80.0 ± 1.1% PCE after 360 h in a damp heat test. This work pioneers a multifunctional ionic liquid strategy to concurrently boost UV tolerance, mechanical resilience, and efficiency of f ‐PSC, charting new pathways for air‐compatible fabrication of durable flexible photovoltaics.