Boosting the Efficiency and Stability of Perovskite Solar Cells via A-Site Quintuple-Cation Engineering

A mixture of A-site cations can improve the stability and performance of organic–inorganic hybrid perovskite solar cells. Although MA+, FA+, and Cs+ are the most commonly used A-site cations in perovskite research, they are thermodynamically unstable at room temperature and tend to crystallize from the α-phase to the δ-phase. Meanwhile, the introduction of Rb+ can promote the growth of perovskite films, but its relatively small ionic size often inhibits the formation of the perovskite phase. Here, we introduced the larger dimethylammonium (DMA) cation at the A-site and fabricated organic–inorganic hybrid metal halide perovskite materials containing five distinct A-site cations. It was found that the incorporation of DMA cations can compensate for the small size of rubidium cations, thereby maintaining the average tolerance factor of the perovskite lattice. Furthermore, this approach effectively modulates the crystallization orientation of the perovskite and promotes grain growth. Ultimately, through A-Site Quintuple-Cation Engineering, the champion device achieved a power conversion efficiency (PCE) of 23.69%, significantly improved from the baseline of 22.60%. Moreover, the unencapsulated device retained approximately 84% of its initial efficiency after 1000 h of aging under air conditions at 65 °C and 35 ± 5% relative humidity.