Stable δ-FA(Cs)PbI3 Intermediate Enables Fabrication of Large-Area Perovskite Solar Modules in Ambient Air

• • Introduction of 2-iodoimidazole (IIZ) into the perovskite precursor yields an air-stable pure δ-phase intermediate, which upon annealing fully converts to a highly oriented α-phase film, eliminating competing crystallization and reducing defect variability. • • Achieved a stabilized power conversion efficiency (PCE) of 20.9% on a large-area perovskite solar module of 927.5 cm2, demonstrating high reproducibility and addressing the typical PCE drop in upscaling. • • Encapsulated modules passed the stringent IEC61215:2021 standards, including thermal cycling from −40 to 85 °C and damp heat at 85 °C and 85% relative humidity, confirming industrial-level stability. • • The method enables ambient-air fabrication of large-area modules, removing the need for inert-gas processing and post-treatments, thus reducing manufacturing cost and complexity.