Weatherable, solvent-soluble, paintable and transparent fluoropolymers for daytime radiative cooling

A fluoropolymer, LUMIFLONTM (LF), with high transparency at solar wavelengths is reported for use in efficient daytime radiative cooling (RC). The RC property is even present in thin films (similar to 50 mu m -thick). The fluoropolymer is weatherable, solvent-soluble, and paintable. The RC property stems from vibrations of the carbon-fluorine bond at 7.8 - 10 mu m (1000 - 1300 cm-1). As LF is transparent, it can be used for the painting of objects and buildings without changing their appearance. It is also promising for the refrigeration of solar cells without using electricity. An analysis evaluating RC materials was established by in-house measurements, in which liquid nitrogen was used as a refrigerant. RC materials such as LF and poly(dimethylpolysiloxane) were explored. Further, field RC measurements were performed and the results were analyzed. It was found that LF shows high RC efficiency in practical use.