Phase-Pure α-FAPbI₃for Perovskite Solar Cells

Because of the narrow bandgap and superior thermal stability, FAPbI₃is considered the most promising perovskite material for high-performance single-junction PSCs. Nevertheless, the metastable properties of the photoactive α-FAPbI₃becomes a primary obstacle for the development of FA-based PSCs. The main reasons for the instability of α-FAPbI₃are the rotation disorder of the FA cation and large anisotropic lattice strain, which lead to the high formation energy of α-FAPbI₃. In this Perspective, we review various strategies for preparing phase-pure α-FAPbI₃, such as engineering, intermediate phase engineering, and dimensionality engineering. These strategies can stabilize α-FAPbI₃by reducing the system energy, regulating the phase transition process and energy barrier, reinforcing the lattice structure, and passivating film defects.