An Ultrathin Transparent Radiative Cooling Photonic Structure with a High NIR Reflection

Abstract With a high NIR reflection, a transparent radiative cooling photonic structure consisting of 2D silica gratings atop ZnO/Ag/ZnO is conceived and demonstrated. With 77% visible light transmitted, 57% NIR solar radiation reflected and 91% thermal infrared radiation emitted, a synthetical cooling is realized by this photonic structure. The theoretical total cooling power of this structure is more than double that of a planar silica and is 63.3% higher than that of a typical NIR reflecting filter, that is, ZnO/Ag/ZnO film. The field test facing the sunlight shows that the air temperature inside a chamber sealed with this structure is 12.5 and 2.5 °C lower than that sealed with planar silica and ZnO/Ag/ZnO, respectively. This work shows that the concept of daytime radiative cooling can be applied in combination with the utilization of visible light and the proposed ultrathin photonic structure shows potentials for passive radiative cooling of transparent applications.