The electrochromic properties of mesoporous WO3–polythiophene film devices with composite electrolytes

We prepare the mesoporous polythiophene–WO3 film through in situ polymerization which is initiated by WO3, and fabricate the electrochromic device with the composite film. The influences of the electrolyte ions, film morphologies and counter electrode on the electrochromism of the devices are explored by UV–Vis transmittance spectra and cyclic voltammetry tests. With the aim to enhance the contrast optical transmittance, we develop the binary composite electrolytes of LiClO4 and N(C4H9)4ClO4 solution which can promote intercalation/deintercalation process. Besides that, we use polyethylene oxide as pore-forming agent on the polythiophene–WO3 films, so that it will be easier for electrolyte ions to diffuse in the porous film. A NiO layer also has a complementary effect on the cathodic coloration films and increases the contrast optical transmittance remarkably. Equipped with the binary electrolyte and the NiO layer as the counter electrode, the film device exhibits high performance with the contrast optical transmittance (ΔT) of 62 % and the coloration efficiency of 212.6 cm2/C.