Thin paints for durable and scalable radiative cooling

Passive daytime radiative cooling（PDRC） is environment-friendly without energy input by enhancing the coating's solar reflectance(Rsolar) and thermal emittance(εLWIR) in the atmosphere's long-wave infrared transmission window.However,high Rsolar is usually achieved by increasing the coating's thickness,which not only increases materials' cost but also impairs heat transfer.Additionally,the desired high Rsolar is vulnerable to dust pollution in the outdoors.In this work,a thin paint was designed by mixing hBN plates,PFOTS,and IPA. Rsolar=0.963 and εLWIR=0.927 was achieved at a thickness of 150 μm due to the high backscattering ability of scatters.A high through-plane thermal conductivity(～1.82 W m-1 K-1) also can be obtained.In addition,the porous structure coupled with the binder PFOTS resulted in a contact angle of 154°,demonstrating excellent durability under dust contamination.Outdoor experiments showed that the thin paint can obtain a 2.3℃ lower temperature for sub-ambient cooling than the reference PDRC coating in the daytime.Furtherly,the above-ambient heat dissipation performance can be enhanced by spraying the thin paint on a 3D heat sink,which was 15.7℃ lower than the reference 1D structure,demonstrating excellent performance for durable and scalable PDRC applications.