Flexible electrochromic energy-saving windows with fast switching and bistability based on a transparent solid-state electrolyte

A transparent solid-state electrolyte (T-SE) consisting of polymethacrylate (PMMA), polyoxypropylene glycol (PPG), and lithium perchlorate (LiClO4) was prepared. Subsequently, using perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and 5,5′′′-di(methylbenzoate)-2,2′:5′,2′′:5′′,2′′′-quater(3,4-ethylenedioxythiophene) (4EDOT-2B-COOCH3) as the electrochromic active materials, electrochromic devices (ECDs) (including rigid and flexible ECDs) based on T-SE were fabricated. ECDs possessed a sandwich structure consisting of an indium tin oxide (ITO) glass (or ITO polyethylene terephthalate (PET))/PTCDA (or 4EDOT-2B-COOCH3) film/T-SE/ITO glass (or ITO PET). The ECDs exhibited a fast switching speed and high optical contrast. The doping/dedoping switching times of flexible ECDs (ITO PET/PTCDA film/T-SE/ITO PET and ITO PET/4EDOT-2B-COOCH3 film/T-SE/ITO PET) were 2.4 s/5.6 s and 5.2 s/2.6 s, respectively; their optical contrast values were 61.0% and 48.6% at 700 nm, respectively. Notably, the flexible ECDs (ITO PET/PTCDA film/T-SE/ITO PET and ITO PET/4EDOT-2B-COOCH3 film/T-SE/ITO PET) also showed suitable bistability (open-circuit memory); they could retain 81.5% and 74.7% of their original optical contrast at 700 nm after removing the drive voltage for 12 hours, respectively. Furthermore, the flexible ECDs also exhibited similar electrochromic properties under bending conditions.