High switching speed and coloration efficiency of titanium-doped vanadium oxide thin film electrochromic devices

Titanium (Ti)-doped vanadium oxide thin films were fabricated by electrochemical deposition on linear polyethylenimine (LPEI)-modified indium tin oxide-coated glass from mixed vanadium oxide and titanium oxide solutions with different Ti concentrations. The as-prepared films were investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The electrochemical behaviour of the films was studied using cyclic voltammetry (CV) in 1.0 M LiClO₄/propylene carbonate solution. Electrochromism of the oxide films upon Li-ion intercalation/ deintercalation was investigated by transmittance measurements during the CV process. The charge transfer resistance of the Ti-doped vanadium oxide film was systematically analyzed with electrochemical impedance spectroscopy (EIS). The amorphous Ti-doped vanadium oxide film containing 4 mol% Ti exhibited the highest transmittance contrast (Δ%T = T_max - T_min) of ca. 51.1%T, and coloration efficiency of 95.7 cm² C^-1 at 415 nm. By increasing the Ti content to 10 mol%, the Ti-doped vanadium oxide film exhibited high switching speed and good cycling reversibility reaching 80% of colouring and bleaching time of 5 and 6 s, respectively. Furthermore, the transmittance contrast drops by only 10% after 600 cycles in a two-electrode system.