Analysis of the influence of the gas pressure during the deposition of electrochromic WO3 films by reactive r.f. sputtering of W and WO3 target

Tungsten trioxide is the most accepted material for electrochromic devices. In the work thin films of WO3 were deposited by reactive r.f. sputtering o f both metallic (W) and ceramic (WO3) targets to study the correlation betw een the electrochromic properties and the structures of the films. Samples were grown at different pressures of Ar + O-2 in order that the energy regi mes of the sputtered particles on the condensing surface could be set eithe r below or above the thermalisation diffusion limit. Lithium ions were inte rcalated in the films in an aprotic electrolyte and the colouring/bleaching behaviour as a function of the intercalated amount of lithium was detected in the 1st and 10th cycle. From these measurements, the electrochromic pro perties of the films were worked out. The optical and morphological charact eristics were analysed respectively, by spectrophotometric and X-TEM measur ements. The amount of water present in the films, detected by IR spectrosco py, turned out to be well correlated to the film morphology and also to the porosity. (C) 1999 Elsevier Science B.V. All rights reserved.