An Ultrathin Transparent Radiative Cooling Photonic Structure with a High NIR Reflection

Abstract

What's more, to make the DPRC devices economical and manufactured in large scale, polymers and microspheres are applied. [15,[19][20][21][22] General DPRC applications should selectively emit thermal radiation in the atmospheric window and minimize solar absorption, simultaneously. However, for transparent applications (e.g., transparent electrode, [23,24] display device, [25][26][27] and window [28][29][30][31] ), only visible light (0.38-0.78 µm) is allowed for view or illumination. The rest of the solar radiation (mainly NIR: 0.78-2.5 µm), if transmitted will cause overheating or additional energy for cooling.Many transparent NIR filters are proposed to block the NIR solar radiation in recent years. [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41] However, several NIR filters block the NIR solar radiation by absorption, [28][29][30][31][32][33][34][35][36] for example, W 18 O 49 , [28] Cu 2−x S/SiO 2 [29] and (NH4) x WO 3 , [32] which will increase the additional heating load as well. [33] To reduce the heating load, it is important to filter the NIR solar radiation by reflection. [33][34][35][36][37][38][39][40][41] Such NIR reflecting filters can be realized by a conductive layer, [33][34][35][36][37][38][39][40][41] for example, ITO [37,40] and dielectric/metal/ dielectric (D/M/D) structure. [38,39,41] However, these NIR reflecting filters will also show high reflections (low emissions) within mid-infrared (MIR) bands, which suppress the radiative cooling. [37][38][39][40][41][42][43][44] As the radiative cooling power in 8-13 µm is significant, [1][2][3][4][5][6] the MIR radiation heat transfer between the cold sky and a NIR filter shouldn't be neglected. To realize high visible transmission, NIR reflection and MIR emission, simultaneously, one can combine a NIR reflecting filter (e. g., D/M/D [38][39][40][41][42][43][44] or ITO [37] ) and a transparent MIR emitting structure (e. g., SiO 2 [45,46] or PDMS [37,47] ). As a common visible transparent NIR reflecting film in energy saving, a D/M/D structure is often used as a spectrally selective filter that can transmit most of the visible light and reflect NIR solar radiation. [38][39][40][41][42][43][44][45][46] Dielectric layers can enhance visible transmission due to a destructive multi-reflective interference and a thin metal layer is responsible for NIR reflection, [38][39][40][41][42][43][44][45] which is higher than that of an ITO structure. [38] As a polymer, PDMS will age especially under sunlight [48,49] and it is much thicker than a SiO 2 based emitter. [45,46] As a potential material for transparent radiative cooling, silica is stable with high transmittance over most of the solar wavelength range and also exhibits a strong phononpolariton resonance in the wavelength range of 8-13 µm. [45,46] However, there is an emission dip within 8-13 µm for a silica layer. [45] With 2D silica photonic crystals [45] or gratings, [46] silica can show enhanced MIR emission. As a result, it is expected With a high NIR reflection, a transparent radiativ...

Deep learning-based inverse design of microstructured materials for optical optimization and thermal radiation control

“…The design of selective emitters for radiative thermal management systems depends on two photonic wavelength (λ) spectrums: the visible (VIS) to near-infrared (NIR) and the mid-infrared (MIR) 1 , 4 . Passive cooling structures—materials that can passively cool beneath ambient temperatures—are surfaces engineered from materials such as polymers 2 , 3 , 9 , composites 10 – 12 , and graphene 13 , 14 to maximize thermal emission in the MIR and minimize absorbed solar radiation (λ = 300–2500 nm) by increasing reflected solar radiation. Methods such as nanostructuring 15 , corrugated structures 6 , 16 , core–shell materials 17 , 18 , and periodic gratings 16 , 19 can be used to induce the opposite effect and increase thermal absorption by enhancing a surface’s anti-reflective behavior.…”

High-Performance Transparent Radiative Cooler Designed by Quantum Computing

“…(B) Cross-sectional images of the fabricated TRC: (left) scanning electron microscope image of the TRC (41 μm PDMS/1.2 μm PML), (middle) transmission electron microscope image, and (right) energy-dispersive X-ray spectroscopy map of the PML. (C) The transmitted irradiance through the TRC designed with the QA-active learning scheme (experiment and simulation), the reported TRC in ref , UV-fused silica (measured), and TLSC . The yellow shade presents the solar spectral irradiance.…”

“…21,22 It has been demonstrated that emitters with unity emission efficiency across the whole M/LWIR regime can be more beneficial than AW-selective emitters for radiative cooling. 22−25 In recent years, there have been several material systems proposed for TRCs, such as stacked multilayers of hydrogenated amorphous Si and SiO 2 ; 26 SiO 2 micropillars fabricated on ZnO/Ag/ZnO films; 27 SiO 2 nanoparticles dispersed in polydimethylsiloxane (PDMS) films; 28 and stacked layers of metal oxide, glass, polymer and hydrogel. 29 However, their designs are mainly based on conventional domain-knowledge-driven design strategies, and their performances are far from that of the ideal TRC.…”

“…In the meantime, it should allow visible photons to pass through with maximal transmission efficiency to enable a clear field of vision (Figure A). Furthermore, the TRC should have high emission efficiency in the mid/long-wavelength infrared (M/LWIR) regime to achieve optimal radiative cooling performance via the AW (Figure A). , It has been demonstrated that emitters with unity emission efficiency across the whole M/LWIR regime can be more beneficial than AW-selective emitters for radiative cooling. − In recent years, there have been several material systems proposed for TRCs, such as stacked multilayers of hydrogenated amorphous Si and SiO 2 ; SiO 2 micropillars fabricated on ZnO/Ag/ZnO films; SiO 2 nanoparticles dispersed in polydimethylsiloxane (PDMS) films; and stacked layers of metal oxide, glass, polymer and hydrogel . However, their designs are mainly based on conventional domain-knowledge-driven design strategies, and their performances are far from that of the ideal TRC.…”

“…We have also compared the optimized TRC with one of the best commercial glasses with the triple-layer silver coating (TLSC), , which are developed to maintain transparency while blocking unwanted photons in the nonvisible bands of the solar spectrum. The transmitted irradiance through our TRC is shown in Figure C together with that of the TLSC, the best-performing TRC in the literature, and UV-fused silica glass. It is found that our optimized TRC outperforms the TLSC if the FOM of the present study is used as the comparison metric (Figure D; see Supporting Information).…”