Research progress on colored radiative cooling materials

Radiative cooling is a passive cooling technology that radiates heat directly to outer space through an atmospheric window. Traditional radiant cooling materials are mostly white or silver white, and the color is single, which is difficult to meet the dual requirements of aesthetics and energy saving in scenes such as building envelope and personal thermal management. Therefore, finding a balance between high cooling performance and color control has become a key issue in this field. This paper reviews the basic principles, design strategies and latest developments of color radiative cooling materials. Its optical requirements are as follows: the solar band needs high reflectivity to suppress photothermal absorption, and the atmospheric window band needs high emissivity to achieve radiative cooling. According to the coloring mechanism, the existing schemes are generally divided into two categories: photonic structure type (using structural color) and optical material type (relying on optical material coloring). By comparing the gains and losses of these two strategies in presenting color and maintaining refrigeration performance, and further introducing dynamic modulation materials, the application potential of thermochromic, phase change materials, humidity response and other mechanisms is discussed. Color radiant cooling materials have shown good prospects in building enclosures, personal thermal management, and urban heat island mitigation. However, color diversity, environmental stability and large-scale preparation are still the main obstacles.