Influence of the substrate on the electrochromic characteristics of lithiated α-WO3 layers

The influence of the substrate on the electrochromic properties of electrochemically lithiated α-WO3 layers is investigated by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and laser Raman scattering measurements. The oxide films have been evaporated on three different substrates: ITO (In2O3:Sn) coated glass (the most common electrode used in electrochromic arrays), aluminium-foil (very often used as a flat conductive support for surface sensitive spectroscopies) and Al thin film deposited on a glass sheet. It is demonstrated that the substrate determines the microstructure of the evaporated films which consequently influences the number of “active” lithium ions necessary for coloration, as well as the coloration stability during exposure to the atmosphere. A homogeneous distribution of lithium was observed at the oxide layer deposited on ITO, while in the case of the films deposited on Al-foil and on Al/glass sheets a considerable amount of lithium atoms was concentrated on the films surface, where the self-bleaching procedure was accelerated due to the contact with atmospheric oxygen.