A transparent radiative cooling photonic structure with a high NIR reflection

Buildings or vehicles with transparent envelope can be heated up by sunlight, causing energy consumption for cooling and in extreme cases leading to vehicular heatstroke in a hot climate. Because only visible light for illumination is essential for these applications, the NIR solar radiation should be reflected to reduce heat gain and the infrared radiation emission should be enhanced for further cooling by using the sky as a heat sink. With a high NIR reflection, a transparent radiative cooling photonic structure consisting of 2D silica gratings atop ZnO/Ag/ZnO is demonstrated for energy-saving and safety. With 81% visible light transmitted, 57% NIR solar radiation reflected and 90% thermal infrared radiation emitted, a synthetical cooling is realized by the photonic structure. Theoretically, the total power of reflected solar irradiance and radiative cooling in infrared of this structure is more than double that of a planar silica. The field test shows that with this structure, the temperature rise of a sealed chamber covered by planar silica can be cooled down by 53.7%. This work shows that the concept of daytime radiative cooling can be applied in combination with the utilization of visible light, indicating a great practical application.