Electrochromic study on amorphous tungsten oxide films by sputtering

•Amorphous WO3 films are deposited by DC sputtering under different O2 flow rates.•Higher oxygen flow rate (> 10 sccm) assures the deposition of amorphous WO3 films.•Both potentiostat and cyclic voltammetry make WO3 films switch its color.•An optimal electrochromic WO3 is to make films close to its stoichiometry.

Tungsten oxide films under different oxygen flow rates are deposited by DC sputtering. The voltage change at target and analyses for the deposited films by X-ray diffraction, scanning electronic microscope, X-ray photoelectron spectroscopy and ultraviolet–visible-near infrared spectroscopy consistently indicate that low oxygen flow rate (5 sccm) only creates metal-rich tungsten oxide films, while higher oxygen flow rate (10–20 sccm) assures the deposition of amorphous WO3 films. To explore the electrochromic function of deposited WO3 films, we use electrochemical tests to perform the insertion of lithium ions and electrons into films. The WO3 films switch between color and bleach states effectively by both potentiostat and cyclic voltammetry. Quantitative evaluation on electrochemical tests indicates that WO3 film with composition close to its stoichiometry is an optimal choice for electrochromic function.