A gel-based electrochromic device towards fast response and high coloration efficiency for low-power consumption smart window applications

Immobilization of viologen derivatives in the solid electrolyte can improve significantly the electrochromic performance and stability of a viologen-based electrochromic device (ECD). Here, we successfully developed a bis(3-hydroxyethyl) viologen dibromide-immobilized PVA/CMC/Borax gel-based ECD with high coloration efficiency, fast response, and long optical memory through an easy immobilization strategy. The bis(3-hydroxyethyl) viologen dibromide was immobilized in a borax-crosslinked polyvinyl alcohol/carboxymethyl cellulose (PVA/CMC/Borax) gel electrolyte. With borate crosslinking, PVA and CMC existed in an interpenetrating polymer network (IPN), which lowers the crystallinity and glass transition temperatures of each polymer. This increase in mobility of ions through gel electrolyte leads to fast response and high coloration of ECD. The ECD exhibited fast response and high contrast ratio with a maximum contrast ratio of 98% with applying −2.5 V for a very short time of 10 s. The ECD showed a high coloration efficiency of 1280 cm2 C−1 at a switching voltage of −2.5 V, which is a high coloration efficiency value for viologen-based ECD reported so far.