VO2-based thermochromic films with passive radiative properties for spacecraft thermal control

VO₂ film is expected to be used in smart radiation devices (SRD) due to changes in infrared reflection caused by semiconductor-to-metal transition (SMT). In this work, a tunable thermal emitter which consisted of Al layer, CaF₂ layer and VO₂ layer was designed to achieve variable emittance with temperature. The variation of dielectric parameters of VO₂ shell caused by temperature change was used to regulate the absorption characteristics of the structure, to realize the positive emittance-switching performance of the thermal emitter device. It was found that the total emittance of the device could reversibly change from 0.03 at 30℃ to 0.72 at 90℃ with an emittance variability of 0.69 in 4-14 µm. In addition, the influence of the thickness of CaF₂, VO₂ layers and the intermediate layer material on the emittance variation of the device was studied. These results shown that the device has the best VO₂ and CaF₂ layer thicknesses of 20nm and 1000nm, respectively. Particularly, too high refractive index of the intermediate layer material will cause the device to produce multiple resonance peaks at high temperature, which will reduce the average emissivity of the entire band, resulting in a smaller change in the emissivity of the thermal emitter.