Spectrally Selective Nanoparticle Mixture Coating for Passive Daytime Radiative Cooling.

Area of Science:

• Materials Science
• Nanotechnology
• Thermal Engineering

Background:

• Passive daytime radiative cooling (PDRC) offers a sustainable thermal management solution by rejecting heat to outer space.
• Existing PDRC devices, such as multilayer and photonic structures, often involve complex fabrication processes.
• There is a need for simpler, yet effective, PDRC technologies with high cooling efficiency.

Purpose of the Study:

• To develop a facilely fabricated radiative cooler using a nanoparticle mixture.
• To investigate the optical properties, specifically infrared emissivity and solar absorptivity, of the nanoparticle mixture.
• To evaluate the cooling performance of the developed radiative cooler under direct sunlight.

Main Methods:

• Fabrication of a radiative cooler by one-step spin coating of a mixture of Al2O3, SiO2, and Si3N4 nanoparticles.
• Characterization of the selective infrared emission and low solar absorption of the nanoparticle mixture.
• Experimental measurement of surface and space cooling under direct sunlight, comparing with a silver film.

Main Results:

• The nanoparticle mixture exhibits highly selective infrared emission within the atmospheric transparency window.
• The fabricated radiative cooler demonstrates a low solar absorption of 4% and high emissivity of 88.7%.
• The nanoparticle cooler achieved subambient cooling of 2.8 °C (surface) and 1.0 °C (space), outperforming a silver film.

Conclusions:

• A simple, one-step fabrication method for a nanoparticle-based radiative cooler was successfully demonstrated.
• The synergistic optical properties of the nanoparticle mixture enable efficient passive daytime radiative cooling.
• This technology presents a promising, scalable solution for thermal management applications requiring subambient temperatures.