Direct Nanocrystal Seeding Enables Buried Interface Passivation and Enhanced Crystallization for FAPbI₃ Solar Cells

FAPbI₃-based perovskites are regarded as promising absorber materials owing to their near-ideal optical bandgap. However, lattice strain and intrinsic phase instability of FAPbI₃ 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 CsPbBr₃ 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 CsPbBr₃ 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 PbBr₂ (23.68%). Moreover, the encapsulated devices retain over 80% of their initial efficiency after 1000 h of continuous maximum power point tracking under illumination.