Electrochromism in some thin-film transition-metal oxides characterized by x-ray electron spectroscopy

Abstract

Qualitative results of an x-ray photoelectron and optical investigation of three thin-film transition-metal oxides, namely, WO3, MoO3, and V2O5 are reported. Data were obtained on films that were not colored and colored by an electrochromic process. The particular electrochromic coloration process used is electrolytic in nature and employs a sandwich-structure electrochromic cell and electrolyte pool. The optical spectra show increased absorption in the visible (red) and near-infrared spectral regions upon coloration. The photoelectron spectra for colored films exhibit a small band near the Fermi level and asymmetric band shapes for metal core-level bands which are absent in films that are not colored. The new band and the asymmetric band shapes are attributed to the presence of a reduced-state species caused by the presence of trapped electrons and metal bronze formation. Results from coloration with different electrolyte pools, i.e., H+, Li+, Na+, K+, Cs+, and Mg2+ electrolytes, are reported.