Electrochromic performance of WOxCy films deposited onto 60 Omega/square flexible PET (polyethylene terephthalate)/ITO (indium tin oxide) substrates by low temperature plasma-enhanced chemical vapor deposition (PECVD) was investigated. It was proven that extraordinary electrochromic performance was provided when the precursor [tungsten carbonyl, W(CO)(6); TC] vapor, carried by argon gas, was mixed with air gas and synthesized by radio frequency (r.f.) power at room temperature (23 degrees C). Cyclic voltammetry switching measurements found that only low driving voltages from -1 V to 1 V were needed to provide reversible Li+ ion intercalation and de-intercalation. The light modulation with up to 63.6% of transmittance variation at a wavelength of 650 nm was obtained for 150 cycles of Li+ intercalation and de-intercalation in a 0.1 M LiClO4-PC (propylene carbonate) electrolyte. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.