Preparation and properties of electrochemically deposited tungsten oxide films

Tungsten oxide films of thicknesses 1095 nm have been cathodically deposite d onto ITO coated glass substrates kept at room temperature, at a rate of 1 3 nm/min. The electrolyte solution has been prepared by adding 0.025 M tung sten (dissolved in 30% H2O2) to 0.25 M H2SO4. XRD observations showed that all films are amorphous. The film resistivity at room temperature was found to be 9 x 10(6) Omega cm, and from the resistivity-temperature dependence, the thermal activation energy was obtained as 0.29 eV. The refractive inde x, n, and the extinction coefficient, k, have been computed from the correc ted transmittance and reflectance over the spectral range 400 to 800 nm. Ab sorption versus photon energy curves give an indirect transition with optic al energy gap of 3.25 and 3.36 eV for the as-deposited and coloured states, respectively. The electrochromic properties of the prepared films have bee n investigated in situ and both solar transmittance and optical density hav e been evaluated in the coloured and bleached states. The electrochemical c oloration and bleaching were performed in an electrolyte of 0.4 M H2SO4 sol ution. The coloration efficiency has been evaluated as 50 cm(2)/C at lambda = 600 nm, which is comparable with the results obtained from films prepare d by other methods.