Spectrally Selective Inorganic-Based Multilayer Emitter for Daytime Radiative Cooling

Area of Science:

• Materials Science
• Thermodynamics
• Optics

Background:

• Daytime radiative coolers offer energy-free heat dissipation into space.
• Enhancing radiative cooling performance requires selective emission in the atmospheric window and low solar absorption.

Purpose of the Study:

• To design and optimize an inorganic daytime radiative cooler.
• To maximize thermal emission in the 8-13 μm atmospheric transparency window.
• To minimize solar absorption for improved cooling efficiency.

Main Methods:

• A multilayer structure of Al2O3, Si3N4, and SiO2 was designed.
• Particle swarm optimization was used to determine layer thickness and stacking sequence.
• Emissivity and absorptivity were measured, and experimental cooling was performed.

Main Results:

• The fabricated cooler demonstrated an average emissivity of 87% in the 8-13 μm range.
• Average solar absorptivity was 5.2% in the 0.3-2.5 μm range.
• Experimental tests showed a temperature reduction of up to 8.2 °C under direct sunlight.

Conclusions:

• The optimized inorganic radiative cooler effectively achieves daytime cooling.
• The material selection and structural design are crucial for high performance.
• This technology presents a promising solution for passive cooling applications.