OPTIMIZATION OF PREPARATIVE AND PERFORMANCE PARAMETERS ON ELECTROCHROMIC PROPERTIES OF ELECTROCHEMICALLY DEPOSITED TUNGSTEN-OXIDE FILMS

Tungsten oxide films of 240-1080 nm thickness were deposited on indium tin oxide (ITO) coated glass substrates using an electrochemical depo sition technique. All films were amorphous, as proved by X-ray diffrac tion (XRD), and had an electrical resistivity of 10(6) Ohm.cm and spec tral transmittance exceeding 75% in the visible region. The electrochr omic (EC) properties were measured in situ during colouration and blea ching cycles. The EC parameters, T-sol(b), T-sol(c), Delta T-sol and D elta(OD)(sol) and the solar colouration efficiency eta(sol) were evalu ated 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 c olouration potentials greater than or equal to 2 V, the solar colourat ion efficiency is almost constant whereas the active sites are transfo rmed 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 conce ntration = 0.4 M. The corresponding EC parameters are: Delta T-sol = 0 .458, Delta(OD)(sol) = 0.632 and eta(sol) = 34 cm(2)/C.