Grey, brown and blue coloring sol-gel electrochromic devices

Abstract

Pure and doped niobium oxide (Nb2O5) layers are electrochromic (EC) materials which change their colour 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 colouration (DeltaOD = 0.3) and a longterm stability of more than 55000 switching cycles. Large area EC-devices (30 cm x 40 cm) show a transmittance change between 60% and 25% at 550 nm after galvanostatic colouration and bleaching for 3 min and a colouration efficiency of 27 cm²/C. The results obtained with blue and brown colouring Nb2O5 EC-layers and a comparison with blue coloring WO3 layers are also presented.