Flexible electrochromic organo-tungsten-iron oxide (WFexOyCz) films are rapidly deposited onto flexible (60 Omega/square polyethylene terephthalate/indium tin oxide; PET/ITO) substrates by a low temperature-atmospheric pressure-plasma polymerization method with an atmospheric pressure plasma jet (APPJ) for a short exposed duration of 48 s. The precursor vapors of tungsten hexacarbonyl [W(CO)(6)] and biscyclopentadienyl iron [ferrocene; Fe(C5H5)(2)] are mixed with O-2 gases at various gas flow rates, injected into air plasma jet and sprayed onto PET/ITO substrates at room temperature (similar to 23 degrees C) and at atmospheric pressure (1.013 x 10(5) Pa). Flexible electrochromic WFexOyCE films are synthesized with a specific addition of oxygen gases with superior lithium electrochromic properties as demonstrated by a potential sweep alternating between -1 V and 2 V at a scan rate of 40 mV/s in a 1 M LiClO4-propylene carbonate electrolyte. With amorphous WFexOyCz films produced with an APPJ by adding oxygen gases at a specific flow rate of 0.5 sccm, a high value in oxygen deficiency up to 0.189 allows more Li- ions to intercalate into and deintercalate out of the film. Significant coloration and bleaching are proven by the high values in optical transmittance modulation (Delta T) of up to 70.3%, optical density (Delta OD) up to 0.77 and color efficiency (eta) up to 61.3 cm(2)/C, at a wavelength of 800 nm, respectively.