Transient Interphase Assisted Crystallization of Antisolvent‐Free Perovskite for Enhanced Device Performance

ABSTRACT Antisolvent‐free perovskite solar cells (PSCs) are a promising technology for scalable manufacturing. Due to a more complicated crystallization process, a key factor limiting device performance is phase segregation induced by the varying crystallization rates of the various components. Herein, we propose a transient interphase strategy to manipulate the nucleation process and crystal growth for enhanced device performance without an antisolvent. We found that tetramethylurea (TMU) induces instantaneous nucleation with a Cs‐rich component and forms a transient interphase, which balances the integrated crystallization for the formation of α ‐Cs X FA 1−X PbI 3 phase. This approach enhances device performance with an efficiency up to 25.63% and a module efficiency of 19.62%. Crucially, suppressed phase segregation endows exceptional stability: devices show negligible degradation after 1700 h (ISOS‐L‐1) and retain 90% of their initial efficiency after 3500 h. It represents the longest reported MPPT stability for antisolvent‐free Cs X FA 1−X PbI 3 ‐based PSCs to date.