Electrochromic devices (EC), which dynamically change colour under applied potential, are widely studied for use in energy-efficient smart windows. To improve the viability of smart windows, many researchers are utilizing nanomaterials, which can provide electrochromic devices with improved coloration efficiencies, faster switching times, longer cycle lives, and potentially reduced costs. The flexible electrochromic films are promising film for applications in automobiles, buildings, etc.

Here, we synthesized nanostructured tungsten trioxide (WO₃) particles for electrochromic materials. The thin layers with nanostructured materials of WO₃ inks were coated at room temperature, solution-processed method. For comparing the effects of electrolyte, electrochromic devices were fabricated with various kind of electrolyte, which can be optimized to obtain higher performances. Two types of polymer based electrolytes were fabricated and characterized. The operation voltages were controlled with electrolyte types and compositions. Ionic liquid based electrolyte showed higher ionic conductivity than liquid type or polymer type electrolyte. Also EC with the liquid electrolyte exhibited 40% of coloring/bleaching efficiencies and EC with the polymer gel electrolyte 60%. All solid EC could be fabricated with the polymer gel electrolyte, which exhibited the higher coloring / bleaching efficiencies than that with the liquid. The effects of composition and process variables will be discussed.