Fabrication and Characterization of FA (x) Cs1-x PbI3 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 FFA(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 (beta) to cubic (alpha). 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 delta-CsPbI3. 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.