Synthesized Cs-rich Cs0.7FA0.3PbI2Br perovskite film by two-dimensional to three-dimensional phase transition

Stability of perovskite is the main limitation of the commercialization of perovskite solar cells . Recent studies have shown that FA-Cs perovskites are expected to achieve ideal crystal structures with outstanding stability when FA content is 30 %. And its bandgap can be adjusted to 1.8 eV, making it suitable for a top battery in the tandem cell. However, when the content of Cs ions in the component exceeds 30 %, phase separation occurs. In this study, a Cs-rich Cs 0.7 FA 0.3 PbI 2 Br perovskite film was synthesized by using a 2D to 3D phase transition method. Through the high orientation of the 2D CsPbI 3 -FAI alloy-like phase and the anisotropic volatilization of FA, a well-oriented α-Cs 0.7 FA 0.3 PbI 2 Br perovskite phase is obtained. The α-Cs 0.7 FA 0.3 PbI 2 Br shows excellent thermal and UV stability and improved humidity stability. Meanwhile, the fabricated Cs 0.7 FA 0.3 PbI 2 Br perovskite solar cell achieved a competitive power conversion efficiency of 14.87 % successfully breaking the world record for this perovskite system. This further advances the research progress of Cs-rich perovskites in highly efficient and stable solar cells.