Optical properties of mixed‐oxide WO3/MoO3 electrochromic films

The electrochromic optical absorption of mixed‐oxide WO3/MoO3 amorphous films occurs at higher energy than either pure oxide alone. The systematics of the energy shifts as a function of MoO3 concentration and coloration density is determined. The data is explained by the intervalency charge‐transfer model if we assume that electrons trapped at Mo6+ ions lie 0.73 eV deeper than electrons on W6+ ions. Measurements of electron diffusion in mixed oxides support this hypothesis. The maximum absorption peak of mixed oxides is 2.15 eV compared with 1.4 eV for WO3. This is close to the peak in eye sensitivity, thereby leading to improved electrochromic display devices.