Highly optically selective polyethylene porous films as versatile optical shields for daytime radiative cooling applications

Radiative cooling technology holds great promise in reducing energy consumptions for cooling and is perceived as a geoengineering approach to fight climate change as well. Stringent requirement on high solar reflectance and high infrared emissivity limits the selections of radiative cooling materials. Here, we developed a thin HDPE porous film with a simple thermal scraping method to act as an optical shield for radiative cooling devices. The polyethylene porous film shows 98.3% solar weighted reflectivity and 92.5% infrared transmittance which is the highest among all the optical shields reported. The film achieved a maximum cooling more than 5 C under 950 W/m2 direct sunlight without optimizing the infrared emitting material and thermal insulation design. The preparation method has the potential to achieve continuous large-area production and the produced PE porous film will greatly broaden the selections of infrared emitters and provides more freedom for designing even better infrared emitting structures.