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

Abstract

AbstractNarrow 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.