Sub-ambient full-color passive radiative cooling under sunlight based on efficient quantum-dot photoluminescence

Daytime radiative cooling with high solar reflection and mid-infrared emission offers a sustainable way for cooling without energy consumption. However, so far sub-ambient daytime radiative coolers typically possess white/silver color with limited aesthetics and applications. Although various colored radiative cooling designs have been pursued previously, multi-colored daytime radiative cooling to a temperature below ambient has not been realized as the solar thermal effect in the visible range lead to significant thermal load. Here, we demonstrate that photoluminescence (PL) based colored radiative coolers (PCRCs) with high internal quantum efficiency enable sub-ambient full-color cooling. As an example of experimental demonstration, we develop a scalable electrostatic-spinning/inkjet printing approach to realize the sub-ambient multi-colored radiative coolers based on quantum-dot photoluminescence. The unique features of obtained PCRCs are that the quantum dots atop convert the ultraviolet-visible sunlight into emitted light to minimize the solar-heat generation, and cellulose acetate based nanofibers as the underlayer that strongly reflect sunlight and radiate thermal load. As a result, the green, yellow and red colors of PCRCs achieve temperatures of 5.4-2.2 °C below ambient under sunlight (peak solar irradiance >740 W m^-2), respectively. With the excellent cooling performance and scalable process, our designed PCRC opens a promising pathway towards colorful applications and scenarios of radiative cooling.