Thermal control properties of radiative cooling foil based on transparent fluorinated polyimide

The low heat dissipation efficiency will cause damage to the electronic devices. Here, we proposed a radiative cooling foil with simple double-layer structure composed of a transparent fluorinated polyimide embedding SiO2 microspheres and a silver layer(FPI@SiO2/Ag). The foil was prepared by a simple in-situ polymerization, and the thermal analysis shows that the foil has an outstanding thermal stability with the glass transition temperature of 194 degrees C. We experimentally and theoretically performed the investigation of spectra, thermal radiative property, and cooling performance at different condition. We demonstrated that the 3 wt% FPI@SiO2/Ag foil can achieve radiative cooling to 4.6 +/- 0.2 degrees C under direct sunlight. The foil shows a strong broadband thermal radiation with emissivity approaching 0.94 +/- 0.03 at 8-13 mu m wavelengths and 0.92 +/- 0.03 at 2.5-25 mu m wavelengths, yet ultralow solar absorptivity with 0.07 +/- 0.02. The radiative cooling foil that can withstand high temperature is very attractive to apply regardless of the terrestrial structure and the space lander.