Managing thermal emission using ENZ polar dielectrics for self-cooling window application

Area of Science:

• Materials Science
• Nanotechnology
• Optics

Background:

• Passive radiative cooling leverages thermal emission within the atmospheric transparency window (8-13 µm) to enhance energy efficiency.
• Epsilon-near-zero (ENZ) materials exhibit unique optical properties, including the Berreman mode, enabling angle-dependent thermal emission.

Purpose of the Study:

• To design and characterize a broadband thermal emitter for efficient radiative cooling applications.
• To investigate the potential of polar dielectric materials as ENZ materials for enhanced thermal emission.
• To evaluate the performance of the designed emitter for self-cooling windows and other energy-saving technologies.

Main Methods:

• Fabrication of a multilayered thermal emitter using SiO/SiN/Al2O3/Ta2O5 polar dielectrics on an ITO-coated polycarbonate substrate.
• Characterization of the emitter's thermal emission properties, focusing on emissivity in the 8-13 µm range at various angles and polarizations.
• Assessment of optical properties, including visible spectrum transparency and near-infrared (NIR) reflection.
• Quantification of radiative cooling power density under nighttime and daytime conditions.

Main Results:

• The designed emitter exhibits high emissivity in p-polarization at large oblique angles (70°-80°), covering the 8-13 µm atmospheric transparency window.
• The structure demonstrates over 70% transparency in the visible spectrum and significant reflection in the NIR region.
• Optimized structures achieved a radiative cooling power density of up to 199 W/m² at night and a mean daytime value of 60 W/m².
• The emitter's angle-dependent emission, due to the Berreman mode in ENZ materials, facilitates directional heat dissipation.

Conclusions:

• The developed broadband thermal emitter is a promising candidate for energy-saving applications, particularly for self-cooling windows in buildings.
• The directional emission capability enhances heat dissipation efficiency, even with obstructions.
• The material's properties suggest potential applications in photovoltaic systems, waste heat management, and information encryption.