Advanced electrochromic devices based on WO3 thin films

We present work on the development of advanced materials suitable for use as electrochromic thin films (EC), ion storage layers and transparent conductors (TC) in electrochromic devices. These thin him layers were prepared in our laboratory by thermal evaporation and electron gun deposition. They were incorporated into electrochromic devices, which were subsequently characterized by optical and electrochemical techniques such as transmission spectroscopy, cyclic voltammetry and galvanostatic intermittent titration. WO3 films 300-600 nm thick have been used as EC layers. They are amorphous and near-stoichiometric with a packing density of about 0.8. We have also developed textured WO3 films. Their structure enhances Li+ intercalation into the oxide matrix, thus doubling the diffusion coefficient. V2O5 ion storage thin films were Li+ doped both electrochemically and in Vacuum leading to a 23% increase of the EC device coloration efficiency. We have fabricated electrochromic devices with ZnS/Ag/ZnS coatings as TCs. The use of multilayer ZnS/Ag/ZnS films was found to improve the electrical characteristics and to lower the emittance of the devices. All the devices described above can withstand more than 5000 coloration-bleaching cycles and have an open-circuit memory of several days. They are suitable for advanced glazing and other switching applications. (C) 2001 Elsevier Science Ltd. All rights reserved.