Recent Progress on the Phase Stabilization of FAPbI3 for High‐Performance Perovskite Solar Cells

With the advantages of narrow bandgap and excellent thermal stability, fomamidinium lead triiodide (FAPbI 3 ) perovskite holds the promise to boost the power conversion efficiency (PCE) of perovskite solar cells (PSCs) to over 25%. However, such a promise is blurred by the poor structural stability of the black α‐phase FAPbI 3 , as it can spontaneously transform into photoinactive δ‐phase at room temperature and this process can be accelerated by the ambient moisture. The incorporation of small ions such as cesium (Cs + ), methylammonium (MA), and bromide (Br − ) into the perovskite lattice is proven to be successful in stabilizing the α‐phase FAPbI 3 ; however, the resultant mixed perovskites suffer the phase segregation problem, which inevitably undermines the long‐term stability of the corresponding PSCs. Therefore, continuous efforts are made to realize stable and pure‐phase α‐FAPbI 3 perovskites. Herein, the recent progress on the development of efficient and stable FAPbI 3 PSCs is summarized with a focus on the different phase stabilization strategies. In addition, the challenges and possible directions for future study are proposed.