Crystallization Process for High-Quality Cs_0.15FA_0.85PbI_2.85Br_0.15 Film Deposited via Simplified Sequential Vacuum Evaporation

Multiple-source thermal evaporation is emerging as anexcellenttechnique to obtain perovskite (PVK) materials for solar cell applicationsdue to its solvent-free processing, accurate control of stoichiometricratio, and potential for scalability. Nevertheless, the currentlyreported layer-by-layer deposition approach is afflicted by long processingtimes caused by the multiple repetitions of thin films, which hinderindustrial uptake. On the other hand, the coevaporation entails highercomplexity due to the challenges of controlling the sublimation ofmultiple sources simultaneously. In this work, we propose a simplifiedapproach consisting of a single-cycle deposition (SCD) of three thickprecursor layers to obtain high-quality Cs(0.15)FA(0.85)PbI(2.85)Br(0.15) (CsFAPbIBr) films. After annealing,the optimized PVK film exhibits comparable properties to the one depositedby multicycle deposition in terms of crystal structure, in-depth uniformity,and optoelectrical properties. Also, the formation and evolution ofSCD PVK during annealing are investigated. We found that, in the competitiveprocesses of precursor diffusion and reaction, the presence of cesiumbromide can assist precursor mixing driven by the annealing treatment,demonstrating a reaction-limited process in the PVK conversion. Withthis simplified SCD approach, a PVK film is obtained with expectedoptical and opto-electronic properties, providing an appealing wayfor future thermally evaporated PVK device preparation.