Characterization of pulsed laser deposited WO thin films for 3 electrochromic devices

Thin films of tungsten oxide were deposited on SnO2:F coated glass using pulsed laser deposition. The structure, morphology, composition of the films and thus the electrochromic properties are strongly dependent on the conditions of deposition. Emphasis is being made on both the influence of the oxygen pressure and the temperature of deposition. Crystallized films are obtained when deposited at 4008C with an oxygen pressure of 10y1 mbar while an oxygen pressure of 10y2 mbar leads to amorphous films whatever the substrate temperature is. For the lower oxygen pressure, blue colored and conductive films are deposited whereas colorless insulator films are obtained for an oxygen pressure of 10y1 mbar at room temperature RT.. The estimated optical band gaps for the films were found to be 3.2 eV when deposited at RT and 2.8 eV when deposited on a 4008C substrate while having an oxygen pressure of 10y1 mbar. Using Raman spectroscopy, the decrease of the optical band gap was ascribed to a decrease of the W5OrO–W–O ratio correlated to an increase of the cluster size of tungsten oxide with crystallinity. By IR spectroscopy, we were able to relate the better electrochromic properties of the colorless films deposited at RT in an oxygen pressure of 10y1 mbar, to the presence of water. q1999 Elsevier Science B.V. All rights reserved.