D‐Isoascorbic Acid Endows Formamidinium Iodide With Robust Storage Stability and Wide‐Bandgap Perovskite With Reduced Phase Segregation

ABSTRACT Halide components phase segregation arising from the iodine‐related defects is the culprit for the deterioration of the photovoltaic performance and stability in wide‐bandgap (WBG) perovskite solar cells (PSCs). It is crucial to suppress the oxidation of I − to I 2 during the storage of formamidinium iodide (FAI) perovskite raw materials for preparing stable WBG perovskite films, which is always neglected. Here, a novel recrystallization strategy for FAI is proposed, and the D‐isoascorbic acid (IAA) aqueous solution, which possesses strong reducing ability, is utilized to synthesize I 2 ‐free FAI crystals. It is found that IAA can interact with FAI and suppress the generation of I 2 impurities, ensuring the high quality of FAI crystals during long‐term storage in a dry box. Accordingly, the perovskite films prepared by the 30‐day‐aged FAI crystals recrystallized from IAA solution display splendid crystallization quality and decreased halide components phase segregation effect, which is benefited from a significant decline in the iodine‐related defect density. Notably, the corresponding PSCs yield an impressive power conversion efficiency (PCE) of 23.03% with negligible hysteresis effect, and the unencapsulated devices maintain 88% of their initial PCE after 1400 h storage in air.