Optimization of SnCl2:NH4F-Derived Sols for Preparation of Thin Transparent Conductive Crystallized SnO2 Films

Transparent conductive SnO2 films, promising for application in electronic engineering, were obtained by sol–gel synthesis via mixing SnCl2∙2H2O and NH4F solutions, followed by deposition onto glass substrates by centrifugation and heat treatment at 450 °C. The physicochemical processes of SnO2 crystallization in water–alcohol solutions of SnCl2 were analyzed depending on the concentration of the crystallization initiator NH4F and the alcohols used. The sol–gel processing of the thin films was investigated using a Latin square approach. Three factors affecting the film formation conditions were varied at three levels to determine the best combination of film properties involving the maximum transparency and lowest specific electrical resistance. The effect of solvent type (ethanol, 1-butanol and isopropanol), the amount of introduced fluorine (5, 10, and 15 at. %) and the number of deposited layers (10, 15, and 20) on the composition, morphology, crystallization features, transparency and specific surface resistance of the synthesized thin films was studied. The obtained films of ~200–340 nm thickness exhibited ~78%–95% transparency in the visible spectrum range and specific surface resistance (ρs) from ~109 to >1012 Ω/sq. The optimal combination of thin (~250 μm) SnO2<Sn> film target performances including transparency 84% and specific surface resistance ~109 Ω/sq. was achieved in the case of their preparation in isopropanol with an average concentration of NH4F (10 at. % F) and spin-on deposition of 20 layers.