High-Quality (FA)_x(MA)_1-xPbI₃ for Efficient Perovskite Solar Cells via a Facile Cation-Intermixing Technique

The quality of perovskite light-absorbing materials plays a vital role in the photovoltaic performance of perovskite solar cells. Herein, we present a facile surface engineering technique through post-treating pure MAPbI₃ films with formamidinium iodide (FAI) solution, leading to mixed-cation FA_xMA_1-xPbI₃ perovskite with substantial grain dimensions and a compact and uniform morphology. It is noted that the film post-treated with 20 mg·mL^-1 FAI solution produces a highly crystalline and stable lattice structure with the features like the decreased defect density, improved electron transport, and long carrier lifetime. The optimized device based on the FA_xMA_1-xPbI₃ obtained from the cation-intermixing technique shows a promising power conversion efficiency of 20.21%, which is even superior than that of the device based on the mixed-cation perovskite from the traditional method without post-treatment (19.08%). Moreover, the device based on the developed method also shows a better stability. These findings provide a simple procedure to fabricate high-quality mixed-cation perovskite layers for high-performance devices via controlling the crystallization and reducing density of defect states.