Recent advance in phase transition of vanadium oxide based solar reflectors and the fabrication progress

Vanadium dioxide (VO₂) as a phase-change material controls the transferred heat during phase transition process between metal and insulator states. At temperature above 68°C, the rutile structure VO₂ keeps the heat out and increases the IR radiation reflectivity, while at the lower temperature the monoclinic structure VO₂ acts as the transparent material and increase the transmission radiation. In this paper, we first present the metal-insulator phase transition (MIT) of the VO₂ in high and low temperatures. Then we simulate the meta-surface VO₂ of metamaterial reflector by Ansys HFSS to show the emittance tunability (Δε) of the rutile and monoclinic phase of the VO₂. In next section, we will review the recent progress in the deposition of thermochromic VO₂ on glass and silicon substrate with modifying the pressure of sputtering gases and temperature of the substrate. Finally, we present the results of the in-situ sputtered VO_x thin film on thick SiO₂ substrate in different combination of oxygen and argon environment by V₂O₅ target at temperature higher than 300°C and then, analyze it with x-ray diffraction (XRD) method. The thermochromic VO₂ based metamaterial structures open a new route to the passive energy-efficient optical solar reflector in the past few years.