Preparation of nanostructured tungsten trioxide thin films by high pressure sublimation and condensation

Thin films of tungsten trioxide (WO3) have gained increasing importance due to their interesting chromogenic properties and for their high application potential in electrochromic devices. It is very well known that their electrochromic switching properties depend very sensitively on their nanostructure. Hence, a vast majority of the research work carried out in this domain at present is dedicated to the various techniques of controlled inducing of a nanostructure in these WO3 thin films in order to enhance their electrochromic performance. In the present work we have carried out a systematic study of the nanostructured WO3 thin films by using a novel technique of varying the source substrate distance in a high pressure sublimation and condensation method. This technique has been found to be very efficient in controlling the grain size and thus the nanostructure of the deposited films. A correlation is established between the optical and electrochromic properties of the WO3 films and the induced nanostructure. The electrochromic properties are studied by a dry lithiation process developed in our laboratory. The results indicate a strong dependence of the film nanostructure on the source substrate distance which influences quite sensitively the electrochromic properties. These results are expected-to help design electrochromic devices suitable for different applications. (C) 2015 Elsevier B.V. All rights reserved.