All‐Solid‐State Variable Emissivity Devices with Excellent Smart Thermal Control Performance

Variable emissivity devices (VEDs) are capable of controlling changes in emissivity through an external electric field, which has great application prospects in the field of smart thermal management and multispectral camouflage. However, the narrow working band, limited emissivity modulation, and high solar absorptivity of VEDs hinder their applications. Herein, an all‐solid‐state VED with an Ag/HfO2/ITO Fabry‐Perot (F‐P) cavity structure is designed and fabricated with a low solar absorptivity (0.19 at 250–2500 nm), a high infrared (IR) emissivity modulation (0.33 at 2.5–25 µm). Meanwhile, it has a wide temperature control range (265–346 K) and (317–405 K) on the back and sunny side, respectively. The device's temperature regulation can be greatly improved by expanding the emissivity control amplitude and lowering the emissivity value. Maintaining a low absorptivity in the solar band can expand the application possibilities and usage scenarios of VEDs. This VED provides opportunities for applications such as infrared camouflage and smart thermal control of spacecraft.