Grey, brown and blue coloring sol–gel electrochromic devices

Pure and doped niobium oxide (Nb2O5) layers are electrochromic (EC) materials which change their color by insertion of Li+ ions from transparent to brown, grey or blue depending on the crystallinity of the layer. EC-devices with the configuration K-glass/EC-layer/composite electrolyte/ion-storage (IS) layer/K-glass, were produced using different Nb2O5 EC-layers, a (CeO2)x(TiO2)1−x (x = 0.45) IS-layer and an inorganic–organic composite electrolyte to which a small amount of water (up to 3 wt.%) was added. The grey coloring all-solid-state sol–gel devices fabricated with Nb2O5 : Mo coatings show a high reversible coloration (ΔOD = 0.3) and a long-term stability of more than 55 000 switching cycles. Large area EC-devices (30 × 40 cm) show a transmittance change between 60% and 25% at 550 nm after galvanostatic coloration and bleaching for 3 min and a coloration efficiency of 27 cm2/C. The results obtained with blue and brown coloring Nb2O5 EC-layers and a comparison with blue coloring WO3 layers are also presented.