Electrochromic devices with tunable infrared radiation can meet the steadily growing demands in energy saving and thermal camouflage applications. Here, a mid-infrared radiation modulator based on flexible multilayer graphene thin films gated by nonvolatile ionic liquid on both rigid and flexible substrates is designed. The thermal emissivity of the device decreases nearly 80% within 2 s with the accumulation of anions in the multilayer graphene. The effective reduction of the emissivity results from the dramatic decrease in film's intraband absorption of graphene according to the Drude model. It has been demonstrated that with electrical control the film's mid-infrared radiation is capable of adapting to different backgrounds for thermal camouflage applications. Moreover, a sandwiched structure with stacked graphene films is designed to realize structural flexibility and double-sided radiation control for a wide range of potential applications, including energy-efficient buildings, infrared sources, and electrochromic displays.
Keywords: camouflage; graphene; ionic liquid; mid-infrared; radiation modulator.