MASCN Surface Treatment to Reduce Phase Transition Temperature and Regulate Strain for Efficient and Stable α-FAPbI3 Perovskite Solar Cells

The fabrication of α-FAPbI₃ perovskite films usually requires high temperature annealing above 150 °C, and the residual tensile strain in the films seriously affects the stability of α-FAPbI₃ by converting to δ-phase FAPbI₃. Here, we use MASCN surface treatment of FAPbI₃ films to induce a rotation of the coplanar octahedron [PbI₆]^4- to the metric octahedron for the strong interaction of SCN^- with Pb²⁺, converting δ-FAPbI₃ into α-FAPbI₃ highly crystalline films at room temperature. The optimized FAPbI₃ films have high stability due to releasing residual tensile strains after MASCN treatment. The efficiency of the MASCN-treated unannealed FAPbI₃ PSC is 19.03%, while the optimized FAPbI₃ annealed at 100 °C shows a maximum PCE of 21.95% on a small area. The solar cell stability for humidity, light, and thermal stability are significantly improved. The MASCN treated FAPbI₃ achieves a PCE of 15.32% on a PSC module with an effective area of 9.6 cm² and maintains an initial efficiency of 94.1% after 100 days of ageing at 85 °C and 85% humidity.