Cs<sub>4</sub>PbI<sub>6</sub>‐Mediated Synthesis of Thermodynamically Stable FA<sub>0.15</sub>Cs<sub>0.85</sub>PbI<sub>3</sub> Perovskite Solar Cells
Zhipeng Shao, Hongguang Meng, Xiaofan Du, Xiuhong Sun, Peiliang Lv, Caiyun Gao, Yi Rao, Chen Chen, Zhipeng Li, Xiao Wang, Guanglei Cui, Shuping Pang
Abstract
Abstract The stability issue is still one of the main limitations of the commercialization of perovskite photovoltaics. The mixed cation FA x Cs 1 −x PbI 3 has shown great promise owing to its improved thermal and moisture stability. However, the study of FA x Cs 1 −x PbI 3 is concentrated on formamidine (FA)‐rich perovskite, whereas cesium (Cs)‐rich FA x Cs 1 −x PbI 3 perovskites are barely studied due to the inevitable phase separation when Cs > 30 mol%. Here, a Cs 4 PbI 6 ‐mediated method is developed to synthesize Cs‐rich FA x Cs 1 −x PbI 3 perovskites. It is demonstrated that Cs 4 PbI 6 intermediate phase has a low Cs cation diffusion barrier and therefore offers a fast ion exchange with the preformed FA‐rich perovskite phase to finally form the Cs‐rich FA x Cs 1 −x PbI 3 perovskite. The results indicate that ≈15% alloying with organic FA cations can sufficiently stabilize the perovskite phase with excellent phase and UV‐irradiation stability. The FA 0.15 Cs 0.85 PbI 3 perovskite solar cells achieve a champion power conversion efficiency of 17.5%, showing the great potential of Cs‐based perovskites for efficient and stable solar cells.