Passivating Crystal Boundaries with Potassium‐Rich Phase in Organic Halide Perovskite

Recently, considerable researches have reported that the incorporation of potassium cation (K + ) in lead halide perovskites obviously improves the performance of perovskite solar cells. The recent finding indicates that the interstitial occupancy position of K + in perovskite lattice can increase ion‐migration barrier, which dramatically suppresses the hysteresis of the device. However, the enhancement of photoluminescence (PL) as well as bandgap variation cannot be interpreted by K + interstitial state in perovskite. Considering this discrepancy, it has been found out that potassium‐rich phase grows in three dimensional (3D) perovskite crystal grain boundary through both experiments and theoretical simulations, which can efficiently passivate the grain boundaries on the 3D crystal surface and decrease trap states. Meanwhile, the dielectric confinement effect between potassium‐rich phase and 3D perovskite crystal, contributing to improvement of radiative recombination in perovskite absorber, can further support the enhancement and red‐shift of photoluminescence (PL) spectrum. Therefore, a power conversion efficiency of 20.4% has been achieved in K + doped halide perovskite solar cell, and still maintains 90% initial efficiency after stored in 30% humidity at room temperature for 1000 h. These findings offer a new path for the structural manipulation by incorporating multi cations in perovskite materials.