Electrochromic properties of nanocrystalline tungsten oxide thin films

Tungsten trioxide films formed of aggregates in the nanometric range have been deposited by thermal evaporation and condensation method. From the atomic force microscopy study, the aggregate dimensions were found to be in the range between 350 nm and 450 nm. The optical, structural and electrochromic performance of these films under lithium intercalation is studied in detail and their properties are compared to those of continuous films of tungsten trioxide. The films show a slightly elevated diffuse reflectance in the lower wavelength range and a very high transmission in the solar and visible wavelengths. Under lithium intercalation, the films exhibit a very good degree of electrochromic optical modulation in both these spectral ranges and hence, are very suitable for electrochromic device application. The high degree of change between the clear state and the colored state render such nanocrystalline films more efficient in their electrochromic performance than the conventional continuous films. (C) 1998 Published by Elsevier Science S.A. All rights reserved.