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 (FAPbI₃) 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 FAPbI₃, 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 FAPbI₃; 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-FAPbI₃ perovskites. Herein, the recent progress on the development of efficient and stable FAPbI₃ PSCs is summarized with a focus on the different phase stabilization strategies. In addition, the challenges and possible directions for future study are proposed.