A Scalable Microstructure Photonic Coating Fabricated by Roll-to-Roll Defects for Daytime Subambient Passive Radiative Cooling

The deep space's coldness (& SIM;4 K) providesa ubiquitousand inexhaustible thermodynamic resource to suppress the cooling energyconsumption. However, it is nontrivial to achieve subambient radiativecooling during daytime under strong direct sunlight, which requiresrational and delicate photonic design for simultaneous high solarreflectivity (>94%) and thermal emissivity. A great challenge ariseswhen trying to meet such strict photonic microstructure requirementswhile maintaining manufacturing scalability. Herein, we demonstratea rapid, low-cost, template-free roll-to-roll method to fabricatespike microstructured photonic nanocomposite coatings with Al2O3 and TiO2 nanoparticles embedded thatpossess 96.0% of solar reflectivity and 97.0% of thermal emissivity.When facing direct sunlight in the spring of Chicago (average 699W/m(2) solar intensity), the coatings show a radiative coolingpower of 39.1 W/m(2). Combined with the coatings'superhydrophobic and contamination resistance merits, the potential14.4% cooling energy-saving capability is numerically demonstratedacross the United States.

Automated summary

We have successfully fabricated spike microstructured photonic nanocomposite coatings using a rapid, low-cost, template-free roll-to-roll method. These coatings possess high solar reflectivity (>94%) and thermal emissivity (97.0%), and can achieve subambient radiative cooling during daytime under strong direct sunlight. When facing direct sunlight in the spring of Chicago, the coatings show a radiative cooling power of 39.1 W/m(2), and have a potential energy-saving capability of 14.4%.