Tungsten oxide–titania composite thin films with different W/Ti atomic ratios were prepared and characterized in this study. Surface morphology, composition and structure of the composite thin films were investigated by scanning electron microscope with an energy dispersive spectrometer, X-ray diffraction and atomic force microscope analyses. Electrochromic properties including transmittance modulation ability, coloration efficiency and coloring/bleaching response time of these thin films were examined using cyclic voltammetry and double-potential-step experiment with in-situ ultraviolet–visible spectroscopy measurement. The presence of titania in the composite thin film could inhibit the crystal growth of tungsten oxide, which enhances the transmittance modulation ability and coloration efficiency but prolongs the coloring/bleaching response time of the composite thin film. The tungsten oxide–titania composite thin film (WTi-30) with a W/Ti atomic ratio of 78/22 exhibited better transmittance modulation ability (57.5%) and coloration efficiency (49.2 cm2/C) than a pristine tungsten trioxide thin film (53.6%, 36.2 cm2/C).
