As a component part of an electrochromic device, WO₃ layers are understood to be the main responsible of the color change of this devices when cationic ions are inserted in its crystalline lattice. In the search of a suitable all solid electrochromic device, the light should be inserted into the structure in one run process. In this work Li⁺ ions were incorporated on the WO₃ layer from a gas phase during the deposition process.

Electrochromic WO₃ thin films were deposited on fused silica and silicon substrates by physical vapor deposition techniques. The substrate temperature during the WO₃ deposition process was kept at 150ºC and the oxygen pressure was 5·10^–4mbar. In order to improve the performance of this one run doping method series of samples, with Li to W atomic ratio ranging from 0 to 0.4, were prepared to study the effect of the Li content on the optical properties of the WO₃ thin films.

A complete optical characterization in the ultra violet, visible and infrared range was carried out using ultra violet–visible transmittance, ultra violet–visible multichannel spectroscopic ellipsometry and FTIR spectroscopy. A clear dependence of the optical properties on the level of Li was observed. It was also analyzed the atmospheric evolution of the optical properties for a sample with an specific Li to W ratio.

These results are a first step to achieve a better understanding of some problems related to the doping of the electrochromic layers with lithium ions, such as irreversibility, stoichiometry effects, correlation between optical an electrical properties and optical absorption modeling.