Electrochromic tungsten oxide thin films were synthesized by plasma-enhanced chemical vapor deposition. Film density and electrochromic performance were controlled by the degree of ion bombardment. A moderate degree of ion bombardment was optimal, and the refractive index was shown to be a sensitive indicator of electrochromic performance. Chrono-amperometry and optical transmission were used to determine diffusion and absorption coefficients, using both H+- and Li+-containing electrolytes. The absorption coefficients were similar for both ions, scaling with the degree of intercalation to 50,000/cm in the opaque state. The diffusion coefficients for optimized films were found to be relatively insensitive to the degree of ion intercalation, with values of ~10−9 and ~10−10cm2/s for H+ and Li+, respectively. These values were about an order of magnitude greater than those reported for vacuum-deposited films. This was attributed to a low relative density of the plasma-enhanced chemical vapor deposited films.

Characterization of Ion Diffusion and Transient Electrochromic Performance in PECVD Grown Tungsten Oxide Thin Films. M.Seman, C.A.Wolden: Solar Energy Materials and Solar Cells, 2004, 82[4], 517-30