Optical properties of mixed-oxide WO3/MoO3 electrochromic films

Abstract

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.