On the substrate wettability of a tungsten sol for the preparation of WO3 thin films

In this work، WO3 thin films have been deposited on optical glass and transparent conducting oxide substrates using aqueous and organic sols by means of dip coating followed by post annealing at 400 oC. The wetting of applied substrates by the prepared sol has been simply studied by observation and photography. The prepared thin films were also studied by various techniques including scanning electron microscopy، X-ray diffraction، and cyclic voltammetry in H2SO4 solution. The results showed that aqueous sols showed undesired wetting while aqueous-alcoholic sols could splendidly wet both glass and TCO substrates. However، the use of ethyl alcohol resulted in the degradation of the films during the drying process whereas this problem could be overcome by the introduction of heavy alcohols. Aqueous-alcoholic sols prepared from Lauryl Alcohol andperoxytungstic acid which was previously synthesized from sodium tungstate precursors were optimized as the dipping sol. Results showed that the presence of Lauryl alcohol reduces the size of the crystallites and grains in the prepared thin films. The monoclinic phase of WO3was transformed to triclinic phase by the addition of Lauryl alcohol to the prepared sol. The cyclic voltametery analyses also verified the improved electrochromic properties of the prepared layers in the presence of Lauryl alcohol.