High contrast electrochromic tungsten oxide layers

The electrochromic response time and the chemical and electrochemical stability of amorphous tungsten oxide layers have been found to be adversely affected by the degree of porosity and hydration of the oxide layers (1,2), thus complicating the preparation of stable high speed electrochromic films. Based on our investigation of the microstructure of thermally evaporated tungsten oxide films we could overcome this problem by preparing high density (p=6.4 g cm E-3) tungsten oxide layers by fly ash evaporation or by reactive dc sputtering. In spite of the higher packing densite (reduced free volume) which increases the electrochemical stability remarkably, the electrochromic response times of thin layers could be reduced to 50 ms, which is comparable to that of sputtered iridium oxide films. Even with 1.6 my thick dc sputtered tungsten oxide layers a response time of 400 ms for a contrast ratio of 1:2 and a response time of 5 s for a contrast ratio of 1.1000 could be achieved. (IAF)