I/Pb Ratio Control in the Solid Perovskite Films toward Efficient and Stable Two-Dimensional Perovskite Solar Cells

Compositional engineering of perovskite precursors has been widely implemented to elevate the performance of perovskite solar cells (PSCs). Nevertheless, there is a lack of studies on the relationship between the I/Pb ratio and the solid perovskite film. In this work, iodine (I2) was employed to tune the perovskite crystallization and control the I/Pb ratio of a two-dimensional (2D) perovskite film. A high-quality 2D (ThMA)2(MA)4Pb5I16 perovskite film with well-aligned phase alignment was obtained at the optimal I/Pb ratio of 3.02. We achieved a champion device performance of 17.3% and an impressive open-circuit voltage (Voc) of 1.19 V, which is one of the highest [power conversion efficiency (PCE)/Voc] for thiophene spacer-based 2D Ruddlesden–Popper PSCs. Moreover, the optimized device with encapsulation demonstrated long-term operational stability, retaining 90% PCE after 500 h in dark high-humidity conditions.