Optimisation of Preparative and Performance Parameters on Electrochromic Properties of Electrochemically Deposited Tungsten Oxide Films

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Abstract
Tungsten oxide films of 240–1080 nm thickness were deposited on indium tin oxide (ITO) coated glass substrates using an electrochemical deposition technique. All films were amorphous, as proved by X-ray diffraction (XRD), and had an electrical resistivity of 106 Ω·cm and spectral transmittance exceeding 75% in the visible region. The electrochromic (EC) properties were measured in situ during colouration and bleaching cycles. The EC parameters, T sol b, T sol c, ΔT sol and Δ(OD)sol and the solar colouration efficiency ηsol were evaluated at different preparation and performance parameters. The results showed that at small film thickness, the solar colouration efficiency changes linearly and tends toward saturation at larger thickness. At colouration potentials ≥2 V, the solar colouration efficiency is almost constant whereas the active sites are transformed to colour centres. In contrast, the efficiency has an exponential dependence on electrolyte concentration. The optimum values are: film thickness = 1080 nm, colouration potential - 2 V and electrolyte concentration = 0.4 M. The corresponding EC parameters are: ΔT sol =0.458, Δ(OD)sol=0.632 and ηsol=34 cm2/C.