Optical and Electrochromic Properties of Sol-Gel Deposited Mixed MoO3-WO3 Thin Films

Abstract

Mixed molybdenum-tungsten oxides of varying stoichiometry (MoxW1-xO3, 0 < x <1) were prepared by sol-gel deposition from peroxo-polymolybdotungstate solutions onto conductive fluorine doped tin oxide (FTO) coated glass substrates. The compositional and structure properties were characterized for MoxW1-xO3 films annealed at 450°C using energy-dispersive spectroscopy and X-ray diffraction measurements. The optical transmittance of the films were recorded with respect to air in the reference beam in a UV-Vis-NIR spectrophotometer. The transmittance modulation of the mixed oxide films were enhanced compared to the pure WO3 film and very broad spectral modulation features were observed for mixed oxide. Cyclic voltammetry and chronoamperometry measurements were conducted to estimate ion storage capacities and reversibility of the films during the coloring/bleaching process for the mixed metal oxide films in an electrolyte solution of lithium perchlorate in propylene carbonate. The subtle interplay between structural and compositional properties due to the uniform mixing of Mo and W oxide components shows that electrochromic and lithium ion transport properties are moderately enhanced relative to those of single-component WO3.