Disordered and densely packed ITO nanorods as an excellent lithography-free optical solar reflector metasurface for the radiative cooling of spacecraft

Abstract

Optical Solar Reflectors (OSRs) form the physical interface between the spacecraft and space and they are essential for the stabilization and uniform distribution of temperature throughout the spacecraft. OSRs need to possess a spectrally selective response of broadband and perfect electromagnetic wave absorption in the thermal-infrared spectral range, while strongly reflecting the solar energy input. In this work, we experimentally show that disordered and densely packed ITO nanorod forests can be used as an excellent top-layer metasurface in a metal-insulator-oxide cavity configuration, and a thermal-emissivity of 0.97 is experimentally realized in the spectral range from 2.5 to 25 μm. The low-loss dielectric response of ITO in the solar spectrum, from 300 nm to 2.5 μm range limited the solar absorptivity to an experimental value of 0.167. These make our proposed design highly promising for its application in space missions due to combining high throughput, robustness, low cost with ultra-high performance.