Reduced Defects of MAPbI3 Thin Films Treated by FAI for High-Performance Planar Perovskite Solar Cells

Organolead trihalide perovskite films with a large grain size and excellent surface morphology are favored to good-performance solar cells. However, interstitial and antisite defects related trap-states are originated unavoidably on the surfaces of the perovskite films prepared by the solution deposition procedures. The development of post-growth treatment of defective films is an attractive method to reduce the defects to form good-quality perovskite layers. Herein, a post-treatment tactic is developed to optimize the perovskite crystallization by treating the surface of the one-step deposited CH3NH3PbI3 (MAPbI(3)) using formamidinium iodide (FAI). Charge carrier kinetics investigated via time-resolved photoluminescent, open-circuit photovoltage decay, and time-resolved charge extraction indicate that FAI post-treatment will boost the perovskite crystalline quality, and further result in the reduction of the defects or trap-states in the perovskite films. The photovoltaic devices by FAI treatment show much improved performance in comparison to the controlled solar cell. As a result, a champion solar cell with the best power conversion efficiency of 20.25% is obtained due to a noticeable improvement in fill factor. This finding exhibits a simple procedure to passivate the perovskite layer via regulating the crystallization and decreasing defect density.