Microstructured flexible polymer films with embedded phosphor for multifunctional passive radiative cooling

Passive daytime radiative cooling schemes are of much interest because of their attractive potential to reduce energy consumption. However, the structural conditions for designing and fabricating efficient radiative cooler limit their optical diversity and hinder their practical utilization (e.g. light-emitting cooling panels, smart window systems, smart signboards, or anticounterfeiting). Here, multifunctional passive radiative cooling films are demonstrated by simultaneously implementing speckle image holography disordered microstructures and phosphor particles into the radiative polymer layer. The as-obtained multifunctional film exhibits high total reflectivity in the sunlight region (∼89%) and strong infrared emissivity (∼91%) within the atmospheric window band (8–13 μm), thus achieving subambient cooling of ∼4.1 °C under direct sunlight in a nonvacuum setup. Interestingly, the multifunctional structural films can be acted as light-emitting films under violet or blue illumination and also can be easily patterned by drawing, cutting or pixelating. The multifunctional structured films demonstrated here can be utilized for potential UV resistance, smart window displays, anticounterfeiting cooling systems, roofing materials and certain aesthetic purposes.