Improving radiative cooling performance via strong solar reflection by dense Al₂O₃ particles in a polymeric film

Radiative cooling (RC) technology has attracted a lot of attention due to its spontaneity and sustainability for cold energy generation. One of the primary objectives of enhancing RC performance is to prevent the absorption of incoming radiation. In particular, absorbing solar irradiance on an RC surface is known as a hazardous obstruction of the radiative cooling effect of the surface. This paper proposes a polymer-based RC film with dense aluminum oxide (Al₂O₃) microparticles to achieve high solar reflection. We have developed a fabrication recipe for densely dispersing Al₂O₃ particles in the polydimethylsiloxane (PDMS) medium to utilize a scattering effect as much as possible. As a result, the fabricated film contains 36.2% of Al₂O₃ by volume, and the resulting solar reflection is more than 94%. Additionally, both theoretical and experimental investigations are done to determine the cooling power and temperature of the fabricated film. The calculated cooling power of the proposed RC film is about 90 W/m² under a standardized weather condition. Especially, an outdoor experiment is demonstrated to measure the RC film's cooling temperature. Under cool weather conditions, the resulting temperature is measured to be approximately 3.5 ^∘C, which is 6.3 ^∘C cooler than a conventional white-colored surface.