Flexible Self‐Cleaning Janus Emitter for Transparent Radiative Cooling in Enclosed Spaces

Abstract Passive daytime radiative cooling is a sustainable and cost‐efficient strategy that works by reflecting solar radiation and emitting heat to the cold universe through infrared radiation. However, cooling enclosed spaces that retain heat due to the greenhouse effect remains a significant challenge, particularly for transparent radiative coolers. Here, the Janus Transparent Radiative Cooler (JTRC) is introduced, which simultaneously achieves strong solar spectrum reflectivity, high infrared emissivity, and high heat absorptivity within enclosed spaces, all while maintaining transparency for practical real‐world applications. Uniquely functioning as a Janus device, with one side acting as a selective emitter and the other as a broadband emitter, this design effectively extracts internal heat while blocking external heat. As a result, it minimizes heat accumulation in enclosed spaces, effectively addressing the greenhouse effect. During the daytime, the JTRC achieved a temperature reduction of 20 °C compared to a conventional transparent radiative cooling method. This transparent, flexible, self‐cleaning, and high‐performance cooler demonstrates significant advancements over conventional designs and highlights its potential for practical applications in vehicles, buildings, and electronic devices requiring thermal management.