Electrochromic properties of sol-gel derived WO 3 coatings

Abstract

Amorphous tungsten oxide layers are deposited via the sol-gel route. Aqueous solutions of tungstate salts (Na2WO4) or chioroalkoxides (WOC12(OPr')2) provide cheap and suitable precursors for the synthesis of W03, nH2O colloidal solutions. Layers of large area can be deposited by spray or dip-coating. They exhibit electrochromic properties and could be used for making display devices or smart windows. Their elecirochromic properties depend on the structure of the oxide network and the amount of water of the W03, nH2O layers. Switching time and stability decrease when n increases due to faster ion diffusion. Optical absorption arising from electron delocalization varies with the crystalline structure of the oxide network. Both the structure and the hydration state of the layers depend on the experimental procedure. It is therefore possible to optimize the electrochromic properties of sol-gel derived layers.