New electrochromic thin-film materials

Abstract

New transition metal oxyhydroxides containing one or two metals such as W, Nb and Ti have been recently synthetized by "soft chemistry". All these materials have a crystal structure that allows further ionic insertion reactions. Moreover, the reduction of W⁶⁺, Nb⁵⁺ and Ti⁴⁺ during electrochemical insertion may lead to a colored material. For these reasons, the electrochromic properties of thin films of some of these oxyhydroxides, obtained by vacuum evaporation from bulk materials, have been investigated. This presentation will describe the method of preparation of thin films obtained from H₂Ti₃O₇, HNbWO₆, H₂0 and from mixtures of these two metal oxyhydroxides. Their composition are determined. The electrochromic properties in aqueous acid electrolyte and in lithium electrolyte will be presented and compared to those of amorphous W0₃ films. It will be shown that the coloration efficiency of these films may be improved by coevaporating mixtures of two oxyhydroxides. Moreover, the presence of Ti and Nb in the films has been shown to be directly connected to the nature of the oxyhydroxides precursors.