Heterogeneous Nucleation-Induced Upward Crystallization for Perovskite Solar Cells

Formation of monolithic perovskite grains with low grain boundary defects is crucial for achieving high-performance perovskite solar cells (PSCs). Inclusion of two-dimensional (2D) perovskite seeds at the bottom surface is a facile method to induce an upward-directional crystallization that forms monolithic grains. However, the large organic cations in 2D perovskites can hinder carrier transfer at the bottom interface. Here, we demonstrate that inclusion of multidentate potassium pyrophosphate (PPH) at the perovskite bottom surface can induce formation of monolithic perovskite grains with reduced defects. We find that the PPH modifier can decrease the Gibbs free energy barrier for heterogeneous perovskite nucleation, leading to a faster nucleation at the bottom surface. This faster heterogeneous nucleation facilitates an upward-directional crystal growth of 3D perovskites, leading to significant defects suppression and effective carrier transfer at the bottom surface. Based on this approach, the PSC achieves a power conversion efficiency of 25.3% with improved thermal stability, maintaining 81% of its initial power conversion efficiency at 85 °C for 1100 h.