High-Thermal-Conductivity Radiative Cooling Films for Enhanced Passive Daytime Cooling.

Passive daytime radiative cooling (PDRC) technology relies on reflecting solar visible light that carries high energy and radiating surface heat to a low-temperature cold background in the long-wave infrared band, thereby achieving clean energy-saving cooling. However, the irreversibility of high flux heat flow is often present in practical applications, resulting in the inability to maximize the cooling effect produced by radiative cooling. In this study, we developed an integrated radiative cooling (RC) film with high thermal conductivity for efficient cooling (DPHA film) by strategically constructing internal thermal channels within the RC interface. Compared to the indoor chamber temperature, the DPHA film, with its superior optical properties (reflectivity ∼ 0.96, emissivity ∼ 0.98), yielded a maximum temperature difference of 17.5 °C and an average difference of 13.2 °C under solar intensity of 977 W m. The cooling effect was 8.5 °C lower than commercially available highly reflective aluminum paint and 5.2 °C lower than a comparable cooler. Thermal conductivity tests showed that the DPHA film possessed high out-plane thermal conductivity (0.755 W m K), which facilitated the radiative dissipation of surface heat via forming a thermal gradient with the environment. After 30 days of continuous strong UV irradiation experiments, the obtained film showed favorable optical properties and aging resistance. DPHA film as a new radiative cooler effectively improves the overall performance of the cooling, with good potential and scalability for outdoor applications. This provides a new way to develop radiative cooling materials that are efficient, cost-effective and easy to mass produce.