MACl-Induced Intermediate Engineering for High-Performance Mixed-Cation Perovskite Solar Cells.

Recently, mixed-cation perovskites have been extensively used for high-performance solar cells. Nevertheless, the mixed-cation perovskite based on formamidinium methylammonium lead tri-iodide (FAMAPbI) fabricated through the existing methods often suffers from phase stability and trap density. Herein, we demonstrate a facile intermediate engineering approach to improve the quality of the mixed-cation perovskite based on FAMAPbI. Varying concentrations of methylammonium chloride (MACl) are used to treat the FA-MA-PbI-solvent intermediate. It is noted that MACl has a strong impact on the crystallization kinetics and charge carrier dynamics as well as the defect density of the obtained perovskite. The mixed-cation perovskite treated with 20 mg mL MACl yields a large grain size, highly uniform morphology, and better crystalline stability. Subsequently, the device with an acquired high-quality mixed-cation perovskite shows a high efficiency of 20.40%, which is obviously higher than that obtained from the traditional nontreated method. Moreover, the device prepared through the developed method could retain over 85% of the initial efficiency after 860 h at room temperature.