Enhanced electrochromism from non-stoichiometric electrodeposited tungsten oxide thin films

Nanocrystalline structure tungsten oxide (nc-WO3; WO3·2H2O) thin films were deposited on fluorine-doped tin oxide (FTO) substrates via a facile electrochemical deposition (ECD) method. The X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR) spectrum, and scanning electron microscope (SEM) results confirmed the gradual temperature dependent structural transitions from nanocrystalline tungsten oxide (nc-WO3) to amorphous tungsten oxide (a-WO3) at 200 °C. Electrochromic (EC) performances of the films were examined in an aqueous solution of 0.5 M H2SO4 by cyclic voltammetry tests integrated in-situ transmittance measurements. The results showed that the EC properties of WO3 films were closely correlated to its structural arrangements of –OH groups and the structural water molecules present in the WO3 matrix. A fast-switching speed (5 s for coloration and 3 s for bleaching), a significant optical modulation (above 89 % at 632 nm), a high coloration efficiency of 51.1 cm2/C and cycling stability of more than 1000 cycles were achieved for nc-WO3 film. Additionally, an EC device was successfully assembled using NiO film prepared by chemical bath deposition as a complementary electrode and exhibited fascinating performance.