Vacuum Filtration-Prepared Reduced Graphene Oxide Membranes Empower High-Speed Electrochromic Devices

Graphene-based electrochromic devices have garnered significant attention owing to their rapid response and broad band tunability. The performance of such devices is highly dependent on the thickness of the graphene film. However, the fabrication of uniform multilayer graphene films with desired thicknesses in the tens of nanometers via chemical vapor deposition remains challenging to date. In this study, reduced graphene oxide (rGO) membranes with tailored thicknesses were prepared using a vacuum filtration method, and the performance of electrochromic devices based on ionic liquid intercalation into these as-prepared rGO membranes was systematically investigated. It was found that the transmittance modulation depth (%) is dependent on the thickness of the rGO membranes, with the maximum value reaching 34.72% in a wavelength range of 0.45–1.10 μm, which corresponds to a membrane thickness of 32 nm. Through careful optimization of the preparation process, the devices exhibited enhanced switching speeds (typically, a charging time of 0.7 s and a discharging time of 0.2 s), which are faster than those reported for devices using graphitic films, and the underlying mechanism is proposed. Besides, the reflectance modulation depth reached 52.83% in a wavelength range of 2–16 μm. Our approach overcomes the existing limitations associated with the preparation of uniform multilayer graphene films with desired thicknesses for electrochromic applications using the chemical vapor deposition method. This work also holds great promise for the development of high-speed switching and flexible smart windows as well as for applications in dynamic optical camouflage.