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The fabrication of α-FAPbI3perovskite films usually requires high temperature annealing above 150 °C, and the residual tensile strain in the films seriously affects the stability of α-FAPbI3by converting to δ-phase FAPbI3. Here, we use MASCN surface treatment of FAPbI3films to induce a rotation of the coplanar octahedron [PbI6]4-to the metric octahedron for the strong interaction of SCN–with Pb2+, converting δ-FAPbI3into α-FAPbI3highly crystalline films at room temperature. The optimized FAPbI3films have high stability due to releasing residual tensile strains after MASCN treatment. The efficiency of the MASCN-treated unannealed FAPbI3PSC is 19.03%, while the optimized FAPbI3annealed 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 FAPbI3achieves a PCE of 15.32% on a PSC module with an effective area of 9.6 cm2and maintains an initial efficiency of 94.1% after 100 days of ageing at 85 °C and 85% humidity.