Solid electrolyte containing a colorless redox couple for electrochromic device

A hybrid system in which the counter electrode is exchanged with a redox couple dissolved in the electrolyte is an alternative to a "sandwich" type electrochromic (EC) device. We have developed a solid redox (tetramethylthiourea/tetramethylformaminium disulfide dication TMTU/[TMFDS](2+)) electrolyte based on organically modified silane matrix. The EC device employing a solid electrolyte colors homogeneously, visible transmittance (T-vis) changes from 60% to 5%, at -1.5 V within less than 5 min when 240 nm cubic WO3 layer is employed. The results show that solidification of the electrolyte does not affect coloring kinetic, but the reduction of [TMFDS](2+) to TMTU at the Pt electrode significantly slows bleaching and reduces the self-bleaching of the device. Moreover, the EC device employing solid electrolyte colors homogeneously and is colorless in the bleached state (C, a and b values are below 10).