Phase‐Pure α‐FAPbI₃ Perovskite Solar Cells via Activating Lead–Iodine Frameworks

Abstract Narrow bandgap cubic formamidine perovskite (α‐FAPbI₃) is widely studied for its potential to achieve record‑breaking efficiency. However, its high preparation difficulty caused by lattice instability is criticized. A popular strategy for stabilizing the α‐FAPbI₃ lattice is to replace intrinsic FA⁺ or I⁻ with smaller ions of MA⁺, Cs⁺, Rb⁺, and Br⁻, whereas this generally leads to broadened optical bandgap and phase separation. Studies show that ions substitution‐free phase‐pure α‐FAPbI₃ can achieve intrinsic phase stability. However, the challenging preparation of high‐quality films has hindered its further development. Here, a facile synthesis of high‐quality MA⁺, Cs⁺, Rb⁺, and Br⁻‐free phase‐pure α‐FAPbI₃ perovskite film by a new solution modification strategy is reported. This enables the activation of lead–iodine (Pb─I) frameworks by forming the coated Pb⋯O network, thus simultaneously promoting spontaneous homogeneous nucleation and rapid phase transition from δ to α phase. As a result, the efficient and stable phase‐pure α‐FAPbI₃ PSC is obtained through a one‐step method without antisolvent treatment, with a record efficiency of 23.15% and excellent long‐term operating stability for 500 h under continuous light stress.