RF reactive sputtering of tungsten oxide thin films for application in electrochromic devices

This research was focused on the electrochromic behaviour of RF-sputtered thin films of tungsten trioxide (WO3). These thin films, which exhibit cathodic coloration under lithium ion/electron double injection, have a fairly high mixed ion-electron conductivity. Films of various thickness were deposited on conductive glass. The method of reactive sputtering of a tungsten target in the presence of oxygen as the reactive gas was used. The influence of the technological conditions during deposition, and the consequent thermal treatment have been studied. The technological parameters were optimized to obtain films of good optical quality. Using Raman spectroscopy to studying the vibrational properties, the films' crystalline modifications and chemical bonds have been identified. VIS-UV spectrophotometry showed high visible transmittance of the RF-sputtered WO3 films, which could assure good initial transparency of an electrochromic device, using WO3 as the functional layer. The films have also been characterized by ellipsometric analysis, using multiangle four zone null ellipsometry. The purpose of the research is the investigation of the structure and electrochromic behaviour of WO3 thin films. Electrochromic experiments were done and the films showed reversible coloration upon Li intercalation.