MASCN Surface Treatment to Reduce Phase Transition Temperature and Regulate Strain for Efficient and Stable α-FAPbI 3 Perovskite Solar Cells.

The fabrication of α-FAPbI 3 perovskite films usually requires high temperature annealing above 150 °C, and the residual tensile strain in the films seriously affects the stability of α-FAPbI 3 by converting to δ-phase FAPbI 3 . Here, we use MASCN surface treatment of FAPbI 3 films to induce a rotation of the coplanar octahedron [PbI 6 ] 4- to the metric octahedron for the strong interaction of SCN - with Pb 2+ , converting δ-FAPbI 3 into α-FAPbI 3 highly crystalline films at room temperature. The optimized FAPbI 3 films have high stability due to releasing residual tensile strains after MASCN treatment. The efficiency of the MASCN-treated unannealed FAPbI 3 PSC is 19.03%, while the optimized FAPbI 3 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 FAPbI 3 achieves a PCE of 15.32% on a PSC module with an effective area of 9.6 cm 2 and maintains an initial efficiency of 94.1% after 100 days of ageing at 85 °C and 85% humidity.