Dry lithiation study of nanocrystalline, polycrystalline and amorphous tungsten trioxide thin-films

The electrochromic (EC) performance, reversible coloration of certain materials under double injection of ions and electrons, of transition metal oxides (TMO) such as tungsten trioxide (WO,) depends strongly on the nature and structure of these materials. In this work, the electrochromic performance of tungsten trioxide films deposited under different conditions leading to nanocrystalline, polycrystalline and amorphous films has been studied by dry lithiation method. A comparative study of the EC coloration of these three types of films has been carried out. The techniques of spectrophotometry and atomic force microscopy have been employed for this study. Each type of tungsten trioxide (WO,) film exhibits a special nature of coloration indicating the potential for its specific application. The nanocrystalline films seem to exhibit a higher overall selective optical modulation, more efficient in the near infrared region and less in the visible, compared to the polycrystalline or amorphous films. These films also exhibit a superior normal state transmission in the clear state. Hence, these films may be of more interest for smart windows from the point of view of energy efficiency due to their highly selective optical modulation. The amorphous films and even the polycrystalline films under high degree of lithiation, may be more suited for large and small area display device application due to their efficient coloration in the visible region of the spectra. (C) 2001 Elsevier Science B.V. All rights reserved.