A molecular route to fluoro-perovskite materials: synthesis of CsCaF3 films through a sol-gel/spin-coating process

Fluoride perovskites have recently attracted great attention due to their unique optical properties. The present study reports for the first time the fabrication of fluoride-based perovskite, CsCaF3, in form of thin films through a combined sol-gel/spin-coating approach using beta-diketonate fluorinated precursors. The entire sol-gel process has been carried out in ethanol solution under acid-catalyzed conditions starting from the beta-diketonate complexes, Cs(hfa) and Ca(hfa)2 center dot diglyme center dot H2O (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme = 2-Methoxyethylether), which act as single sources for metal ions and fluorine. A careful optimization of the process parameters, such as molar ratio of the starting mixture, aging time and annealing temperature, has allowed to produce for the first time, selectively and reproducibly, transparent and pure CsCaF3 films. Field-emission scanning electron microscopy and energy dispersive X-ray analyses highlight the formation of films with compact morphologies having a 1:1 stoichiometric ratio of Cs:Ca, uniform throughout the film and compatible with the CsCaF3 phase identified through X-ray diffraction analysis.