Cover shields for sub-ambient radiative cooling: A literature review

Radiative cooling emits infrared thermal radiation to the outer space through the atmospheric transparent window (8–13 μm), without energy consumption and environmental pollution. In recent years, this technology has developed rapidly and the cooling performance has been gradually improved. To achieve higher temperature reduction, it is necessary to isolate the cooling device from the surroundings with an IR-transparent cover shield, thereby reducing the negative non-radiation heat exchange for sub-ambient conditions. Meanwhile, some selective cover shield reflects solar radiation while transmitting infrared thermal radiation, further increasing the cooling power and mitigating the demands for solar-reflecting emitters. This paper aims to provide a comprehensive understanding of the cover shield. Fundamental principles of the influence of cover shield on radiative cooling were analyzed. Material properties and application performance were summarized according to the spectral selectivity. Additionally, the barriers and the theoretical potential of the cover shield were also discussed. It is anticipated that this review will promote great cooling performance and a large application scale for radiative cooling.