Controlled Grain Growth Deposition for Enhanced Bulk and Interfacial Defect Passivation in Vacuum-Deposited FAPbI₃...

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 SnO₂ 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 FAPbI₃ components. An ultrathin 3.5 nm PbI₂ layer is pre-deposited on atomic layer deposited SnO_2. This sacrificial nucleation template is fully converted during subsequent FAI/PbI₂ co-evaporation, enabling uniform nucleation and laterally coherent grain growth without excess residual PbI₂. 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 FAPbI₃ 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.