Absorptivity Control Over the Visible to Mid-Infrared Range Using a Multilayered Film Consisting of Thermochromic Vanadium Dioxide

Vanadium dioxide (VO2) is a phase transition material that exhibits metallic or insulating characteristics depending upon its temperature. In this study, a multilayered film consisting of VO2, silicon dioxide (SiO2) and gold was proposed as a metamaterial that switches its absorptivity over a broad wavelength range depending on the ambient temperature as a fundamental element of a building pigment. At high temperatures, the multilayer showed a high absorptivity at mid-infrared wavelengths, promoting radiative cooling. Simultaneously, the multilayer presented a low absorptivity in the visible and near-infrared wavelengths, enhancing sunlight absorption. The daily average heat flux can possibly be suppressed in summer in comparison with a gray body whose emissivity was 0.8. Conversely, at a lower temperatures, the multilayer showed opposite absorptivity in both the mid-infrared and visible ranges, and its daily average heat flux increased in winter. The metal-insulator phase transition of VO2 caused a drastic shift of the resonant wavelength related to surface phonons and surface plasmons at an infrared wavelength, and optical interference at a visible wavelength, originating at the interface of the SiO2 layer. Thus, the radiative heat flux for both sunlight absorption and radiative cooling was simultaneously controlled depending on the temperature of VO2.

Automated summary

In this study, a multilayer film consisting of VO2, SiO2, and gold was proposed as a metamaterial that can switch its absorptivity based on the ambient temperature. It showed high absorptivity in mid-infrared wavelengths at high temperatures for radiative cooling, and low absorptivity in visible and near-infrared wavelengths for sunlight absorption. The metal-insulator phase transition of VO2 controlled the radiative heat flux for both sunlight absorption and radiative cooling.