Enhanced efficiency of the honeycomb-structured film WO₃ composed of nanorods for electrochromic properties

To reduce solar heat and glare from visible light, the color of window panes need to be controlled by electronic energy. Metal oxides deposited on these "smart" windows such as WO₃, Nb₂O₅, and NiO can change the color of the glass by absorbing visible rays. It is important to control the chemical and physical characteristics of the surface of films and to apply a uniformly thin film to obtain a superior product. In this study, we generated templates as nanostructured WO₃ monolayers in nanorods with 400 nm-sized polystyrene (PS) beads. Honeycomb structures were prepared from the well-ordered monolayer template with PS beads that were synthesized by wet chemistry. We investigated the enhanced electrochromic (EC) properties of a honeycomb structured WO₃ thin films which were composed of WO₃ nanostructures. Nanoarchitectural properties like morphology of films, crystalline phases and the structures of WO₃ nanoparticles were examined by Field Emission Scanning Electron Microscopy, X-ray diffraction and Transmission Electron Microscopy. And EC standards such as the variation of transmittance, reaction time and efficiency of redox reactions called by "coloration efficiency" were measured by UV–Vis spectrophotometer, and cyclic voltammetry. The electrochromic reaction rate of honeycomb structured WO₃ thin films was fast (coloration time: 5.86 s and bleaching time: 6.65 s) but, the variation of light transmission (Δ85.04% at 700 nm wavelength) was comparable to that of flat WO₃ film with the similar thickness of about 300 nm. These results suggested that the surface area enlarged by the honeycomb structure induced by PS templating caused the simultaneous redox reaction in the entire WO₃ film. - Highlights: • We investigated the effect of patterned WO₃ film on electrochromic (EC) properties. • Non-patterned WO₃ film showed similar ΔTransmittance with patterned WO₃ film. • The patterned WO₃ film showed faster EC reaction than a flat WO₃ film. • Extended surface area allowed the electrolyte to be diffused with shortened pathway.