Impact of Organic Cation Matrices on Crystallization Regulation and Photovoltaic Performance of CsPbI ₃ Thin Films

Abstract Dimethylamine cation (DMA⁺) is widely used as an additive to regulate crystallization processes of CsPbI ₃ perovskite films and stabilize its phase structure. However, systematic comparisons between DMA⁺ and other organic cations in terms of their effects on crystallization behavior and film quality in inorganic CsPbI ₃ perovskite systems remain scarce. In this study, a series of organic cation iodides with varying carbon chain lengths, branching structures, and numbers of amino groups are investigated for the fabrication of pure inorganic CsPbI ₃ perovskite films. It demonstrates that the introduction of cations larger than Cs⁺ can lower the phase transition temperature required for the formation of black perovskite phase, while increased branching or additional amino groups can elevate the phase transition temperature. The reaction processes of different organic cations are systematically investigated and elucidated their role in regulating crystallization. Among all the tested cations, DMA⁺ yielded excellent film quality and stability, attributed to its minimal lattice strain. Consequently, the assembled cells incorporating DMA⁺ achieved a remarkable power conversion efficiency (PCE) of 21.45%, an open‐circuit voltage ( V _oc ) of 1.268 V, and a V _oc deficit of 0.462 V. These findings provide valuable insights into the role of organic cations in optimizing the crystallization and performance of inorganic perovskite films.