Flexible electrochromic and thermochromic hybrid smart window based on a highly durable ITO/graphene transparent electrode

A flexible smart window with electrochromic (EC) and thermochromic (TC) properties is fabricated on a highly durable transparent indium-tin oxide (ITO)/graphene/polyethylene terephthalate (PET) electrode. An amorphous WO3 film and crystalline VO2 film are used as the EC and TC material, respectively, in the device. The ITO film deposited via atomic layer deposition acts as a protective layer and suppresses the plasma-induced damage of graphene, which typically occurs during the sputtering process. In this device, the amorphous WO3 film undergoes cathodic electrochromic reactions with high coloration efficiency, while the crystalline VO2 film shows characteristic thermochromic behavior. Thus, the flexible EC–TC hybrid smart window shows the controlled transmission of optical and solar energies according to the surrounding temperature and the applied voltage, allowing selective modulation of the visible and near-infrared light. The flexible EC–TC hybrid device is also very stable under mechanical bending, owing to the robust adhesion of the ITO film on the graphene support and the reduced plasma-induced damage of graphene. The fabricated high-performance, durable ITO/graphene/PET transparent electrode can pave the way for next-generation flexible optoelectronic devices as well as multifunctional flexible smart windows.