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Electrochromic thin films of tungsten oxide (WO 3 ) were prepared on transparent conducting oxide substrates, i.e., fluorine doped tin oxide coated (FTO or SnO 2 :F) glass and microscopic glass substrates by the electron beam evaporation technique using pure WO 3 (99.99%) pellets at various substrate temperatures (i.e., T sub = room temperature (RT, 30 • C), 100 • C and 200 • C). The films were prepared under vacuum of the order of 1 × 10 −5 mbar. The room temperature prepared films were further post-heat-treated (T anne ) at 200 and 300 • C for about 1 h in the vacuum environment. The prepared films are in monoclinic phase. The chemical composition has been characterized by using the XPS technique. The W 4f and O 1s core levels of WO 3 films have been studied on the samples. The obtained core level binding energies revealed the WO 3 films contained six-valent tungsten (W 6+ ). The electrochemical nature of the films was studied by a three-electrode electrochemical cell in the configuration of FTO/WO 3 /H 2 SO 4 /Pt, SCE, using the cyclic voltammetry (CV) technique. Electrochromic devices (ECDs) of the general type FTO/WO 3 /electrolyte/FTO were studied. The films produced at higher substrate temperature show smaller modulation of the visible spectrum, compared with the films produced at lower temperatures. The significant chemical bonding nature associated with the coloring/bleaching process which follows the H + ion incorporation in the film is studied by FTIR analysis. The W-O-W framework peak was observed at 563 cm −1 and confirms the stability of the films in the electrochemical analysis. The results obtained from cyclic voltammetry technique and ECD cell characterization are used to emphasize the suitability for some applications of the solar control systems.

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