Comparison between electrochromic and photochromic coloration efficiency of tungsten oxide thin films

We investigated the photochromic (PC) and electrochromic (EC) behavior of sputtered tungsten oxide (WO3-y) films with different oxygen deficiency y. It was found that both the PC and EC coloration efficiency increase with increasing oxygen deficiency in tungsten oxide. For PC efficiency, this behavior is consistent with the model of photochromism developed recently. A recently developed model based on the small polaron transition between W5+ and W4+ states has been used to explain the dependence of EC coloring efficiency on the oxygen deficiency in tungsten oxide films. This new mechanism also revealed a close relationship between PC and EC. (C) 1997 Published by Elsevier Science Ltd.