Improvement in electrochromic response for an amorphous/crystalline WO3 double layer

Amorphous WO3 films have been deposited by E-beam evaporation technique at a substrate temperature of 80 degreesC using different base pressure values. The best results have been obtained starting from a mild base pressure (1 x 10(-5) Torr) probably due to the presence of water and oxidative atmosphere in the evaporation chamber. TEM investigations have shown that thermally evaporated WO3 films have an amorphous metastable structure, which subjected to energetic solicitations changes towards a nanocrystalline phase. The amorphous material subsequently annealed at a temperature of 500 degreesC exhibits a fully crystalline structure. Also, in this case good electrochromic properties have been observed. Afterwards a WO3 double layer structure has been realised depositing an amorphous him upon a crystalline layer. The amorphous/crystalline structure properties have been compared with the amorphous and crystalline single layer ones. The colouration response and the transmittance asymptotic value during the bleaching phase have been better for the double layer. (C) 2001 Elsevier Science Ltd. All rights reserved.