Crystallization Process for High-Quality Cs0.15FA0.85PbI2.85Br0.15 Film Deposited via Simplified Sequential Vacuum Evaporation

Abstract

Multiple-source thermal evaporation is emerging as an excellent technique to obtain perovskite (PVK) materials for solar cell applications due to its solvent-free processing, accurate control of stoichiometric ratio, and potential for scalability. Nevertheless, the currently reported layer-by-layer deposition approach is afflicted by long processing times caused by the multiple repetitions of thin films, which hinder industrial uptake. On the other hand, the coevaporation entails higher complexity due to the challenges of controlling the sublimation of multiple sources simultaneously. In this work, we propose a simplified approach consisting of a single-cycle deposition (SCD) of three thick precursor layers to obtain high-quality Cs0.15FA0.85PbI2.85Br0.15 (CsFAPbIBr) films. After annealing, the optimized PVK film exhibits comparable properties to the one deposited by multicycle deposition in terms of crystal structure, in-depth uniformity, and optoelectrical properties. Also, the formation and evolution of SCD PVK during annealing are investigated. We found that, in the competitive processes of precursor diffusion and reaction, the presence of cesium bromide can assist precursor mixing driven by the annealing treatment, demonstrating a reaction-limited process in the PVK conversion. With this simplified SCD approach, a PVK film is obtained with expected optical and opto-electronic properties, providing an appealing way for future thermally evaporated PVK device preparation.