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

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