Micro/Nanostructural Analyses of Efficient and Stable Perovskite Solar Cells via KF Doping

The migration of ionic defects in grain boundaries plays a critical role in the stability and efficiency of organic–inorganic perovskite solar cells. Furthermore, the ionic defects of perovskites also contribute to the generation of hysteresis. Herein, we alloy KF with perovskites to passivate ionic defects, leading to the improved stability and performance. We obtain a power conversion efficiency of 21.2% by alloying KF with triple cation perovskites [Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3]. With KF, the current–voltage hysteresis of solar cells becomes negligible, and the trap density of the device is reduced. Photostability and thermal stability of the devices were also improved. Approximately 90% of the initial efficiency was maintained after 1200 h under 1 sun illumination, and ∼80% for 2000 h at 85 °C/85% relative humidity. This study confirmed that K+ ions bond to halide ions in the alloyed perovskite and suppress the ionic defects, thereby reducing the trap density and metallic lead impurities resulting in the improved stabilities.