In Situ Self‐Elimination of Defects via Controlled Perovskite Crystallization Dynamics for High‐Performance Solar Cells

Abstract Understanding and controlling crystallization is crucial for high‐quality perovskite films and efficient solar cells. Herein, the issue of defects in formamidinium lead iodide (FAPbI₃) formation is addressed, focusing on the role of intermediates. A comprehensive picture of structural and carrier evolution during crystallization is demonstrated using in situ grazing‐incidence wide‐angle X‐ray scattering, ultraviolet–visible spectroscopy and photoluminescence spectroscopy. Three crystallization stages are identified: precursors to the δ‐FAPbI₃ intermediate, then to α‐FAPbI₃, where defects spontaneously emerge. A hydrogen‐sulfate‐based ionic liquid additive is found to enable the phase‐conversion pathway of precursors → solvated intermediates → α‐FAPbI₃, during which the spontaneous generation of δ‐FAPbI₃ can be effectively circumvented. This additive extends the initial growth kinetics and facilitates solvent–FA⁺ ion exchange, which results in the self‐elimination of defects during crystallization. Therefore, the improved crystallization dynamics lead to larger grain sizes and fewer defects within thin films. Ultimately, the improved perovskite crystallization dynamics enable high‐performance solar cells, achieving impressive efficiencies of 25.14% at 300 K and 26.12% at 240 K. This breakthrough might open up a new era of application for the emerging perovskite photovoltaic technology to low‐temperature environments such as near‐space and polar regions.