Managing Crystallization and Phase Distribution via 2D Perovskite Seed Crystals for 2D‐3D Tin‐based Perovskite Solar Cells

Abstract Various popular large organic cations have been extensively used as the essential additives in the perovskite precursor solution due to their satisfactory passivation effect but may produce the low‐n value (n ≤ 2) 2D perovskite phases with undesired distribution. Meanwhile, the remaining easy oxidation of Sn 2+ and the p‐type self‐doping in the perovskites are also detrimental to the ultimate photovoltaic properties and stability of tin (Sn)‐based perovskite solar cells (PSCs). Here, 3AMPYSnI 4 crystals (3AMPY = 3‐(aminomethyl)pyridinium)) are designed and applied to adjust the crystallization process and the phase distribution of the Sn‐based perovskite. Consequently, the strong coordination interaction between 3AMPY 2+ and 3D perovskite components and the introduced nucleation sites by 3AMPYSnI 4 crystals not only decreases the low‐n value 2D phase and increases 3D perovskite phase, but also inhibits the oxidation of Sn 2+ and the self‐p‐doping in the Sn‐based perovskites, resulting in lower trap density and non‐radiative recombination loss, faster carrier extraction and transfer, and higher stability for 2D‐3D Sn‐based PSCs. As a result, the optimized devices deliver an increased power conversion efficiency from an initial 10.91% to 13.28% and retain 96.0% of their original performance for more than 3000 h in the nitrogen (N 2 ) atmosphere.