Ultra-Broadband Thermal Emitter for Daytime Radiative Cooling with Metal-Insulator-Metal Metamaterials

A novel thermal emitter with metal-insulator-metal design is proposed to realize efficient daytime radiative cooling. It can achieve ultrahigh absorption of 99.67% in the first atmospheric window and strong reflection of 94.86% in solar band. Analysis on the cooling performance with different real and imaginary parts of refractive index is carried out to provide a guide line in the material choice. As a case study, three inorganic materials are substituted to get enhanced absorption and it is verified that the refractive index matching is desirable to obtain high absorption. In addition, such high emissivity persists under different incident angles in both TE and TM modes. A net cooling power of 96.39 W/m² is achieved in the daytime with the incorporation of convection coefficients. Finally, this thermal emitter achieves an average temperature drop of 5.1 °C based on the solution of conduction equation at 300 K. Therefore, our design with an excellent cooling ability can further bolster development in managements of radiative cooling or thermal radiation.