Fabrication and Characterization of FAxCs1−xPbI3 Polycrystal Perovskite Solar Cells

FA x Cs 1− x PbI 3 perovskites were considered promising candidates to accomplish the goals of high photoelectric conversion efficiency with great stability. Limited by the phase separation during fabrication through the conventional one‐step method, the FA x Cs 1− x PbI 3 perovskites with the x ratio lower than 0.7 were barely studied. Herein, the full‐scale mixed cation‐doped FA x Cs 1− x PbI 3 perovskites are synthesized and studied. The bandgap of FA x Cs 1− x PbI 3 perovskites gradually decreases from 1.69 to 1.58 eV with x increasing from 0.15 to 0.75, along with phase structure changes from tetragonal (β) to cubic (α). Under humidity or UV irradiation, the FA x Cs 1− x PbI 3 perovskites phase separates to FA 0.92 Cs 0.08 PbI 3 perovskite and δ‐CsPbI 3 . The FA 0.60 Cs 0.40 PbI 3 perovskite solar cells exhibit more stable efficiency, the champion device reaches a power conversion efficiency of 20.40%. Meanwhile, the unencapsulated devices keep 90% of the initial efficiency when stored in air for 30 days, showing the potential for high stability photovoltaic devices.