Preparation of highly adhesive urethane–acrylate-based gel-polymer electrolytes and their optimization in flexible electrochromic devices

Gel-polymer electrolytes are attractive for applications in flexible electrochromic devices (ECDs). Among such electrolytes, UV-curable gel-polymer electrolytes are particularly advantageous because they can be cured in a short time and suffer less deformation from heating due to low-temperature treatment. In this study, we developed a polyurethane-acrylate-based UV-curable gel-polymer electrolyte with excellent adhesion, optical transparency, and high ion conductivity by optimizing the urethane acrylate mixing ratio. The use of urethane acrylate conferred high adhesion to these gel-polymer electrolytes, and an electrolyte with high ion conductivity was developed by optimizing the ratio of urethane acrylate (oligomer) and poly(ethylene glycol) methyl ether methacrylate (monomer). The optical properties of the ECDs fabricated using the optimized electrolytes were compared. In the case of the glass-type ECDs, upon adding 33.2 wt% urethane acrylate, the coloring transmittance was observed to be 8.54%; the bleaching transmittance was 62.96%; and the change in transmittance reached 54.42%. By conducting a switching cycle test for approximately 45 times on a flexible electrochromic device made of indium tin oxide on a polyethylene terephthalate (ITO-PET) film, 43% change in transmittance was confirmed. These gel-polymer electrolytes are expected to be useful for the commercialization of flexible ECDs.