Selective thermal emitters for high-performance all-day radiative cooling

Abstract

Passive radiative coolers (PRCs), which pump excess heat to cold exterior space via thermal radiation, have emerged as a promising energy-free technology in cooling buildings, thermal power plants, and photovoltaics. However, designing a ‘daytime’ PRC is challenging due to the simultaneous requirement of high reflectance in the solar spectral regime (0.3–2.5 µm) and high emissivity in the atmospheric transmittance window (8–13 µm). Here, we present a large-area compatible and lithography-free nanoscale multilayer design of daytime PRC based on two pairs of tandem silicon dioxide–aluminium nitride dielectric layer cascaded to a silver ground metal placed over a silicon substrate. We theoretically achieve near-perfect reflectance (97.3%) over the solar spectral regime while maintaining high emissivity (80%) in the atmospheric transmittance window. During the daytime under direct sunlight, the cooling power of the proposed structure is reported to be 115 W m − 2 with a temperature reduction up to 15 K below the ambient temperature, when the effect of convection and conductive heat transfer is considered. Our design is polarization-independent and angle-insensitive up to 70 degrees of angle of incidence. An excellent match between our theoretical and simulation results validates our findings. The fabrication tolerance study reveals that the cooling performance of our robust design is unlikely to degrade much during experimental realization. The figure of merit calculation indicates that our PRC can outperform recently reported daytime PRCs.

Temperature Self-Adaptive Ultra-Thin Solar Absorber Based on Optimization Algorithm

“…The proposed super-surface device design method based on the optimization algorithm not only maximizes the light-to-heat conversion efficiency but also provides new ideas for designing absorbers under different operating conditions. In addition, this design method also has potential applications such as selective emitters [21] and infrared stealth [22].…”

Radiative cooling: structure design and application

“…One of the methods to achieve this is to use a variety of materials to form multi-layer structures. [23][24][25] The special design of the material structure based on the optical properties of various materials can realize the emissivity spectrum required by radiative cooling. As shown in Fig.…”

Performance of passive daytime radiative cooling coating with CaSiO3 enhanced solar reflectivity and atmospheric window emissivity

“…In practical application, sub-ambient cooling can be achieved if solar heating is overwhelmed by heat dissipation through the atmosphere's long-wave infrared transmission window. Therefore, materials for PDRC are required to have solar reflectance and infrared emittance as high as possible [7,8].…”