Defect passivation in CH3NH3PbI3 films using alkali metal fluoride additives for highly efficient perovskite solar cells

Solution-processed organic/inorganic hybrid halide perovskites are a class of very promising photovoltaic materials because of their extraordinary optoelectronic properties. However, numerous intrinsic defects formed within perovskite films limit the performance enhancement of perovskite solar cells (PSCs). Herein, we introduce three different alkali metal fluoride additives in perovskite precursor to modulate the defect behaviors. The addition of alkali metal fluorides, especially KF, significantly passivates grain boundaries and point defects within bulk perovskite films, contributing to increased carrier lifetime and reduced defect state density. By optimizing the concentration of additives, the PSC device with addition of 1% KF has realized significantly enhanced power conversion efficiency (PCE) of 20.11% and ignorable hysteresis.