Effects of oxygen addition to the electrochromic properties of WO3 − z thin films sputtered on flexible PET/ITO substrates

An investigation was conducted on electrochromic properties of WO3 − z (tungsten oxide) thin films sputtered on 60 Ω/□ flexible PET (polyethylene terephthalate)/ITO (indium tin oxide) substrates at various oxygen flow rates. A metallic W target, sputtered by radio frequency (r.f.) power with argon gases and reacted with oxygen gases at room temperature (23 °C), was proven to provide extraordinary electrochromic properties. Cyclic voltammetry measurement demonstrated that only low driving voltages from − 1 V to 1 V were needed to provide Li+ ion insertion and extraction to and from a working electrode. The flexible PET/ITO/WO3 − z film was mounted on the working electrode and dipped in a 0.1 M LiClO4–PC (propylene carbonate) electrolyte. The electrochromic properties of flexible PET/ITO/WO3 − z were investigated by cyclic potentiostatic switching and ultraviolet (UV)–visible spectroscopy. An oxygen flow rate of 0.71 sccm with a low O/W-ratio of 2.916, an oxygen deficiency z of 0.084 and an insertion coefficient x of 0.150 can offer an excellent light modulation of up to 73.1% of transmittance variation, optical density change of 0.89 and color efficiency of 62.4 cm2/C at a wavelength of 650 nm in 14 s of Li+ insertion and extraction.