Synthesis of multicolor Nb2O5 coatings for electrochromic devices

Thin films of Nb2O5 were obtained by a sonocatalytic sol-gel method using chloroalkoxides as precursors. They were deposited using the dip-coating technique and calcined at different temperatures. Precipitates were characterized by X-ray diffraction, DSC, FTIR and the films by SEM. The films of Nb2O5 present a good electrochemical response under Li ions insertion. Depending on the treatment temperature, the films change their color from transparent to brown or blue. The efficiency of coloring was estimated to be 22 cm(2) C-1 at 600 nm for a 300 nm thick film with a change in optical transmission from 80% to 15%. The cathodic and anodic charges exchanged at a velocity of 50 mV s(-1) were about 15 mC cm(-2) and the process is fully reversible. The values measured up to 100 cycles are constant, indicating good chemical stability of the films.