Efficient radiative cooling emitter adopting the wavelength conversion of giant CdSe/ZnS core-shell nanocrystals

Daytime radiative cooling is an eco-friendly, temperature-cooling mechanism that uses the inherent properties of a material without energy consumption. To realize a high daytime radiative cooling ability, it is necessary to minimize light absorption in the solar spectrum (0.3–2.5 μm) and maximize the emissivity in the atmospheric transmittance window (8–13 μm). Currently, the solar reflective layer of a radiative cooling material has the limitation of absorbing UV light, which can reduce the cooling performance. We attempted to solve this problem via UV-to-visible wavelength conversion using CdSe/ZnS giant core-shell structures. By applying this strategy, a wavelength conversion-type radiative cooling emitter (WC-RCE) was fabricated using “giant” CdSe/ZnS core-shell nanocrystals embedded into a polymeric membrane to establish minimized absorption within the UV and short-visible regions, which constitute up to 17.28% of the total solar spectrum. The applied g-NCs have a high photoluminescence quantum yield and a large Stokes shift, and can resolve the absorption in reflective layers, such as silver, by re-emitting the wavelength of the absorbed UV rays into the visible region. Compared with a conventional RCE, the WC-RCE achieves further cooling by 0.38 °C on average from outdoor measurements. Thus, a wavelength conversion strategy was confirmed for efficient daytime radiative cooling.