A Low-Temperature Atmospheric Pressure CVD Process for Growing Thin Films of MoO3 and MoO3-WO3 for Electrochromic Device Applications

Thin films of MoO3 and mixed Mo/W oxides have been obtained by atmospheric pressure (AP)CVD, using pyrolytic decomposition of metal carbonyls. The correlation between film structure and optical properties is studied by applying techniques such as Raman spectroscopy (RS), Fourier transform infrared (FTIR) spectroscopy, and UV-vis spectrophotometry. The transmittance in the visible range of films deposited on glass substrates is about 80 %, but when deposited on conductive glass (e.g., SnO2:Sb/glass) the films have 60 % transmittance. After annealing, the optical transmittance of the single oxide films improves, while for the mixed oxide films it slightly decreases. The electrochromic (EC) properties of MoO3 and mixed Mo/W oxide films have been investigated by cyclic voltammetry. Deep-blue coloring of all the EC films appears only in the cathodic range, minimizing the visible-light transmittance. In the anodic regime, the EC film starts bleaching and becomes transparent. Devices fabricated with a solid polymeric-type electrolyte and a functioning layer of mixed oxide films exhibit good reversibility of the effect, and an optical modulation of about 30 % is obtained.