Journal
MATERIALS
Volume 14, Issue 10, Pages -Publisher
MDPI
DOI: 10.3390/ma14102637
Keywords
passive radiative cooling; silica film; surface mode
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Passive radiative cooling has attracted attention for its ability to cool items without electrical input. Silica is commonly used in radiative coolers for its high emissivity, but bare silica film has poor performance due to an emitting dip in the mid-infrared region. By sculpturing structures on the silica film, its emissivity can be improved, leading to over 90% emissivity at 8-13 µm. Two cooler designs, a silica deep grating and a silica cylinder array, have been proposed with high emissivity and insensitivity to polarization angle.
Passive radiative cooling, which cools an item without any electrical input, has drawn much attention in recent years. In many radiative coolers, silica is widely used due to its high emissivity in the mid-infrared region. However, the performance of a bare silica film is poor due to the occurrence of an emitting dip (about 30% emissivity) in the atmospheric transparent window (8-13 mu m). In this work, we demonstrate that the emissivity of silica film can be improved by sculpturing structures on its surface. According to our simulation, over 90% emissivity can be achieved at 8-13 mu m when periodical silica deep grating is applied on a plane silica film. With the high emissivity at the atmospheric transparent window and the extremely low absorption in the solar spectrum, the structure has excellent cooling performance (about 100 W/m(2)). The enhancement is because of the coupling between the incident light with the surface modes. Compared with most present radiative coolers, the proposed cooler is much easier to be fabricated. However, 1-D gratings are sensitive to incident polarization, which leads to a degradation in cooling performance. To solve this problem, we further propose another radiative cooler based on a silica cylinder array. The new cooler's insensitivity to polarization angle and its average emissivity in the atmospheric transparent window is about 98%. Near-unit emissivity and their simple structures enable the two coolers to be applied in real cooling systems.
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