High‐Quality α‐FAPbI3 Film Assisted by Lead Acetate for Efficient Solar Cells

The α‐phase formamidinium lead triiodide (α‐FAPbI 3 )‐based perovskite solar cells (PSCs) exhibit potential high efficiency due to their narrow bandgap, but the fabrication of a stable α‐FAPbI 3 film still is challenging. Herein, a strategy is devised to achieve a stable α‐FAPbI 3 film, in which lead acetate (PbAc 2 ) is added to the perovskite precursor solution. The Ac − ions are involved in the formation of the lead halide octahedra, which effectively promotes the entry of FA + into the lead halide octahedra to stabilize the α‐phase of FAPbI 3 . Furthermore, the Ac − will gradually leave during the annealing process, thus the addition of PbAc 2 cannot introduce other components in the FAPbI 3 . The crystallinity and crystal orientation of the perovskite films are also improved by the PbAc 2 additive to obtain low trap density films, leading to an increase in charge carrier collection. The champion solar cell based on the α‐FAPbI 3 film presented a power conversion efficiency (PCE) of 21.24% with negligible hysteresis. After 500 h of storage under ambient conditions, the devices still maintained more than 90% of their initial efficiency.