Transparent Glass Surfaces with Silica Nanopillars for Radiative Cooling

Abstract

The increasing global use of cooling systems and the need of reducing greenhouse effect are pushing the emergence of more efficient cooling methods. In particular, passive radiative cooling technology extracts heat from objects by tailoring their optical emissivity using surface micro- and nanostructuring. Being capable of increasing thermal emissivity is especially relevant for widespread glass structures and devices, e.g., displays, car and building windows, and solar cells. In this paper, we propose a scalable lithography-free nanostructuring method to increase the infrared (IR) emissivity of glass by reducing the high reflection associated with the SiO2 Reststrahlen band around 9 μm wavelength. Furthermore, we show that with an additional thin polymer coating the scattering (haze) in the visible due to the deep nanostructures can be dramatically reduced while maintaining the large IR emissivity. We experimentally prove that our nanostructured surface can extract more heat via radiation emission than the bare glass substrate, while keeping full transparency.

Designer SiO2 Metasurfaces for Efficient Passive Radiative Cooling

“…For example, soda-lime glass and borosilicate glass are two common types of glass that are made with SiO 2 as their principal component, but they differ in their composition of added minerals and impurities, which results in variations of the optical properties. While fused silica is highly reflective in the atmospheric window region (≈70%), the added impurities in soda [ 54] Experimental 7 --Zhang et al ( 2019) [ 55] Experimental ---Ishii et al (2020) [ 56] Experimental 5.9 0.85 -Zhao et al (2019) [ 36] Silica fibers Numerical --178 Yalçın R A et al (2020) [ 57] Experimental 6.0 0.90 112 Tsai et al (2023) [ 28] 1D gratings Numerical 31.4 --Zhu et al ( 2013) [ 58] Numerical --114 Blandre et al (2020) [ 59] Numerical -> 0.90 98 Liu et al ( 2021) [ 60] Experimental 3.6 0.91 -Zhao et al (2022) [ 61] 2D micropatterns Experimental 13 --Zhu et al (2015) [ 62] Experimental 2 -600 Long et al (2019) [ 63] Numerical 9 ≈1.0 121 Li et al (2022) [ 64] Experimental 7 0.952 -Pinto et al ( 2023) [ 52] Numerical 17.6 ≈1.0 -Zhu et al ( 2014) [ 45] Experimental -> 0.96 -Lu et al (2017) [ 65] Experimental 9.2 > 0.98 -Fathabadi et al ( 2021) [ 38] Experimental 3 0.977 -Akerboom et al (2022) [ 39] Experimental 7.1 0.95 143 Ding et al (2022) [ 37] Experimental -0.947 -Arrés Chillón et al (2022) [ 66] Microspheres Experimental -> 0.94 -Atiganyanun et al (2018) [ 67] Experimental ≈6.9 --Fan et al (2020) [ 68] Numerical 73 --Whitworth et al (2021) [ 53] Experimental 19 >0.98 350 Fernandez et al (2019) [ 40] Experimental 5 0.946 -Lin et al (2022) [ 69] Numerical -0.916 80 Chen et al (2021) [ 70] lime glass reduce the reflectance in the reststrahlen band resulting in a relatively lower reflectance in the desired region (≈30%), compared to that of pure fused-SiO 2 . Various photonic techniques also have been utilized to enhance th...…”

A Perspective for Radiative Cooling Materials

“…One example of a scalable lithography-free nanostructuring method to increase the IR emissivity of glass by lessening the high reflection related to the SiO 2 Reststrahlen band λ ∼ 9 μm is proposed by ref . Their nanostructured RC glass is proposed in Figure .…”

“…(c) Top to bottom, experimental optical absorption spectra of flat FS (black line) and randomly distributed NPs on FS (red line) in the IR optical range, simulated optical absorption spectra of flat FS (black line), and a perfect array of NPs (red line) with h ∼ 1250 nm, bottom ϕ ∼ 307 nm, top ϕ ∼ 172 nm, and P ∼ 410 nm, and finally, atmospheric optical transmission in the IR optical range from 5 to 25 μm. Reproduced from ref . Copyright 2022 American Chemical Society.…”

Progress on Natural and Sustainable Materials for Daytime Radiative Cooling

“…Furthermore, these PAN nanofibers, referred to as nano-PAN, can be employed to cool surfaces with relatively low solar reflectance. Arrés Chillón and colleagues introduce an effective and scalable technique for nanostructured glass whose aim is to enhance its IR emissivity by mitigating the strong reflectance caused by the SiO 2 Reststrahlen band at approximately 9 μm wavelength. By applying a thin polymer coating onto the nanostructured surface, one can diminish the visible light scattering (haze) significantly resulting from the deep nanostructures while preserving the heightened IR emissivity.…”