RADIATIVE COOLING BY USING A SLAB OF HEXAGONAL BORON NITRIDE
We propose to use a slab of hexagonal boron nitride (hBN) coated on the back side with a silver film for radiative cooling. Numerical results show that the radiative cooling power can reach 63 W/m2 at room temperature and under AM 1.5 solar irradiation, when the thicknesses of the hBN slab and the silver film are 200 μm and 200 nm, respectively. With the radiative cooler, its temperature can theoretically reach about 12 °C below ambient temperature in the daytime under direct solar irradiation. The underlying mechanism is that the imaginary part of the permittivity of hBN in the AM 1.5 solar spectrum is much smaller than that in the atmospheric transparency window, which results in the absorbed solar energy much smaller than the emitted energy from the structure. We also investigate the impact of the hBN thickness on the cooling performance, the results show that the cooling power is sensitive to the hBN thickness. This proposed structure may have potential practical applications in radiative cooling due to its simplicity.