Abstract
Amorphous and crystalline WO 3 films show electrochromic properties by means of double injection of cations and electrons. Absorption by small polaron transitions has been hypothesised to explain the coloration mechanism in amorphous WO 3 films and the most reliable model was found by Zhang, who proposed that a WO 3− x bleached virgin film ( x<0.4) consists mainly of W 6+ and W 4+, whereas in the coloured state W 5+ is also present. In this work, amorphous WO 3 films have been deposited by a thermal evaporation technique on glass and c-Si substrates. Electrical, optical and IR properties of these samples have been studied. A hopping mechanism with mobility activation has been hypothesised to justify the discrepancies between electrical and optical properties. Furthermore, our careful analysis of the typical IR absorption peaks in the range 500–1000 cm −1 confirmed the Zhang theory on the coloration mechanism.
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