The design of all-dielectric metasurface for selectively blocking Near-Infrared region of solar spectrum

Abstract

Blocking near-infrared region (NIR) is indispensable for saving energy consumed to maintain an interior temperature in buildings. The methods of blocking NIR are divided into two types. One is blocking NIR without visible light for applying to windows. The other is blocking the overall solar spectrum including visible light because the visible light accounts for 45% in the solar spectrum. Thus, we designed the metasurface of two types, respectively. In the transparent metasurface blocking NIR, simultaneously enhancing transmission in visible light and blocking in NIR remains challenging. Here, we demonstrate the trans-parent all-dielectric metasurface selectively blocking the NIR by using TiO2 nanocylinder and ITO layer. The ITO layer is implemented as a back reflector because the ITO is trans-parent in visible light whereas the ITO becomes reflective materials in the long-wavelength region (λ > 1500 nm). The designed metasurface exhibits a high average transmittance of 70% in visible light and high solar energy rejection (SER) of 90% in NIR. Furthermore, the performance of the designed metasurface is maintained over a wide range of an incident angle of light. Therefore, the metasurface gives an advanced guide-line for design energy-saving applications. In the opaque metasurface blocking NIR, the previous all-dielectric metasurfaces have difficulty in reflecting overall NIR because the reflection region is too narrow. Here, we demonstrate the all-dielectric metasurface blocking almost overall NIR by using amor-phous Si (a-Si) and SiO2. Since amorphous Si has a high refractive index (~3.3) and high extinction coefficient in NIR, the designed metasurface exhibits high reflection (1050 nm ≤ λ ≤ 2320 nm) as well as high absorption (λ < 1040 nm), thereby leading to high solar energy rejection (SER) of 94% in NIR. The performance of the designed metasurface is independent over a wide range of incident light. Furthermore, a-Si substrate constituting the metasurface can be readily deposited on other materials such as glass and plastic film, so the proposed metasurface has high applicability for a large-area fabrication rather than crystalline Si and GaAs.