Direct Nanocrystal Seeding Enables Buried Interface Passivation and Enhanced Crystallization for FAPbI ₃ Solar Cells

FAPbI 3 ‐based perovskites are regarded as promising absorber materials owing to their near‐ideal optical bandgap. However, lattice strain and intrinsic phase instability of FAPbI 3 often generate severe interfacial defects, which act as nonradiative recombination. This consequently limits device performance and stability. Herein, a facile and effective strategy is demonstrated by directly blending CsPbBr 3 nanocrystals (NCs) into the precursor solution. This simple addition achieves the simultaneous modulation of crystallization and defect passivation. Quasi‐in‐situ monitoring reveals that the introduced CsPbBr 3 NCs partially ionize, leading to the coexistence of undissolved NCs acting as seeds for bottom‐up crystallization control and ionized species that particularly passivate the buried interface. This results in the production of high‐quality and stable perovskite films. Corresponding solar cells deliver a champion power conversion efficiency of 24.63%, significantly outperforming control devices (22.89%) and those with equivalent concentrations of CsBr and PbBr 2 (23.68%). Moreover, the encapsulated devices retain over 80% of their initial efficiency after 1000 h of continuous maximum power point tracking under illumination.