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

Vanadium dioxide (VO 2 ) is a phase transition material that exhibits metallic or insulating characteristics depending upon its temperature. In this study, a multilayered film consisting of VO 2 , silicon dioxide (SiO 2 ) 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 VO 2 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 SiO 2 layer. Thus, the radiative heat flux for both sunlight absorption and radiative cooling was simultaneously controlled depending on the temperature of VO 2 .