摘要： Perovskite solar cells (PSCs) have attracted considerable attention in the photovoltaic field. However, most efficient mixed-cation mixed-halide perovskite in PSCs suffers from phase instability and large flux of trap states by existing methods, which limits the device performance. Herein, a facile intermediate engineering technique of the MAI-PbI2 intermediate layer via FABr solution is employed to get high-quality mixed perovskite films. The results illustrate that the proposed approach can improve the grain size, morphology, crystallization, consequently reducing defect density of the perovskite layer. The devices which treated with FABr exhibit much-enhanced performance in comparison to the pristine and traditional mixed-cation mixed-halide devices. Consequently, a champion PSC with the best power conversion efficiency of 20.08% is obtained. Moreover, the devices based on the developed FABr-treatment technique also shows much-improved stability than the mixed perovskite-based devices fabricated from the traditional method. Therefore, this approach provides a simple technique to produce high-quality mixed perovskite film and subsequently may facilitate the commercialized production of high-performance PSCs in the future.