Crystallization Kinetics Regulation for Strain and Morphology Management Enables Efficient Tin Perovskite Solar Cells

Abstract Strain effects in polycrystalline perovskite films significantly impact the performance of perovskite solar cells (PSCs). For environmental‐friendly tin (Sn)‐based perovskites, the relationship between their ultra‐fast crystallization and intrinsic strain remains unclear, and the strain engineering targeted for Sn‐based perovskites is lacking. Herein, based on in situ photoluminescence and ultraviolet‐visible absorption spectroscopies, how the various stages in Sn‐based perovskite crystallization affect intrinsic compressive strain and surface morphology of the films is investigated. Two stages of Sn‐based perovskite crystallization are identified: Stage I, synchronization of nucleation and crystallization; Stage II, evaporation of residual solvents with further crystal growth. Prolongation of Stage I can reduce the sub‐grain domains and grain boundaries where intrinsic compressive strain concentrates. Sufficient duration of Stage II can mitigate the disordered degree of grain regrowth and aggregation of perovskite clusters, avoiding the formation of grain stacking and pinholes. The 1,2‐dichlorobenzene (DCB) as an antisolvent is found to achieve the optimal durations of two stages. The resultant film exhibits suppressed nonradiative recombination due to alleviated compressive strain, and efficient interfacial carrier transfer benefited from improved surface morphology. Consequently, a 14.85%‐efficiency Sn‐based PSC with a high fill factor of 79.32% is achieved.