Controlled Grain Growth Deposition for Enhanced Bulk and Interfacial Defect Passivation in Vacuum‐Deposited FAPbI ₃ Perovskite Solar Cells

ABSTRACT Vacuum deposition of perovskite thin films offers superior conformality and precise control over solution‐based methods. However, non‐uniform nucleation and island‐like growth produce columnar grains, voids, and trap states at the electron‐transport layer (ETL)/perovskite interface, causing non‐radiative recombination. In conventional co‐deposition, volatile formamidinium iodide (FAI) reaches the SnO 2 surface first, undergoes island‐like growth in the early stages of deposition, creating pinholes and voids that act as interfacial trap sites. We present a controlled grain growth deposition (CGGD) method using FAPbI 3 components. An ultrathin 3.5 nm PbI 2 layer is pre‐deposited on atomic layer deposited SnO 2. This sacrificial nucleation template is fully converted during subsequent FAI/PbI 2 co‐evaporation, enabling uniform nucleation and laterally coherent grain growth without excess residual PbI 2 . CGGD suppresses island‐like FAI growth and promotes uniform interfacial nucleation, yielding 18.6% larger grains while reducing both bulk and interfacial trap densities. The resulting FAPbI 3 films exhibit a 34% reduction in trap‐state density and nearly twofold longer carrier lifetimes, evidencing superior structural quality and suppressed non‐radiative recombination. Implementing CGGD in perovskite solar cells delivers a stabilized power conversion efficiency (PCE) of 19.9%. This nucleation‐controlled deposition route provides a general pathway to high‐quality vacuum‐deposited films by improving bulk crystallization and ETL/perovskite interfacial defect passivation, facilitating scalable optoelectronic devices.