Preparation of amorphous electrochromic tungsten oxide and molybdenum oxide by plasma enhanced chemical vapor deposition

Abstract

Preliminary experiments have been performed to probe the feasibility of using plasma enhanced chemical vapor deposition (PE–CVD) to prepare electrochromic thin films of tungsten oxide and molybdenum oxide by plasma reaction of WF6, W(CO)6, and Mo(CO)6 with oxygen. Thin films produced in a 300 W, electrodeless, radio-frequency (rf), capacitive discharge were found to be electrochromic when tested with either liquid or solid electrolytes. Optical spectroscopy was performed on two electrochromic coatings after Li+ ion insertion from a propylene carbonate liquid electrolyte. Broad absorption peaks at ∼900 nm for WO3 and 600 nm for MoO3 were observed. Optical results for PE–CVD MoO3 films differ from those reported for evaporated MoO3 films which have an absorption peak at ∼800 nm. The shorter wavelength absorption in the PE–CVD MoO3 films offers the potential for fabricating electrochromic devices with higher contrast ratios and less color change. Optical emission spectroscopy, Auger, and x-ray diffraction analyses indicate these thin film deposits to be predominantly amorphous tungsten and molybdenum oxides.