  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.
