A multilayer thin film radiative cooling device based on photonic crystal sidebands

Abstract

A multilayer thin film radiation refrigeration device based on photonic crystal sideband relates to a radiation refrigeration device. The multilayer thin film is sequentially provided with an impedance matching layer, a high-loss metal titanium layer, a one-dimensional photonic crystal, a phase compensation layer, a uniform optical thick reflective film and a supporting substrate layer from top to bottom; the one-dimensional photonic crystal is composed of infrared transparent dielectric materials with high and low refractive indexes; the sideband of the photonic crystal is used to realize wideband wide-angle high reflection, the high-loss metal titanium layer and the impedance matching layer are used to excite wideband response and improve the absorption rate, the phase compensation layer is used to control the change of the propagation phase, the wideband wide-angle absorption characteristics of the atmospheric transparent window are formed, and the passive radiation refrigeration function is realized. Compared with others, the present application can be made in a large area without photolithography, and has high radiation refrigeration power.

Description

Technical Field

[0001] This invention relates to radiative cooling devices, and more particularly to a multilayer thin-film radiative cooling device based on photonic crystal sidebands, which has a wide-bandwidth, wide-angle, high emissivity in an atmospheric transparent window (8-13µm) and high radiative cooling power at night. Background Technology

[0002] Radiative cooling primarily achieves temperature reduction through the radiation of an object's own surface. The universe provides an ideal, extremely low-temperature cold source for this process. Objects prevent their temperature from rising by reflecting sunlight off their surfaces, and they also transfer heat to outer space through atmospheric windows (8–13 μm) for radiative heat exchange, thus achieving radiative cooling. This cutting-edge technology is based on the principle of optical modulation of functional materials, utilizing thermal radiation to distribute heat into space. It is an extremely energy-efficient, noiseless, and environmentally friendly cooling method with broad application prospects in various fields, including space applications and industrial production.

[0003] To achieve radiative cooling, many researchers have made significant contributions and explored different technical methods. For example, based on multilayer dielectric photonic structures, Raman et al. were the first to use multilayer thin-film radiative cooling materials for radiative cooling. They designed a radiative cooling material composed of seven hafnium dioxide and silicon dioxide films of different thicknesses alternately deposited on a silver sheet. This material exhibited strong emissivity in the 8-13 μm atmospheric transparency window band, and experimental measurements showed that the structure had an emissivity of approximately 40.1 W / m² at the same ambient temperature. 2 The net cooling power of the material was measured. Based on a multilayer polymer photonic structure, a radiative cooler was fabricated by combining a polymer with a metal reflective substrate. Kou et al. used 10 μm polydimethylsiloxane (PDMS) as the top layer and a silver layer as the bottom reflector to deposit a double-layer coating in a high-vacuum environment using electron beam evaporation. This successfully prepared a simple polymer material. Performance tests showed that at an ambient temperature of 26 °C, the net cooling power of this material was 127 W / m². 2 However, the biggest problem with polymer materials is their susceptibility to degradation and failure in outdoor environments. Based on metamaterial micro / nano photonic structures, unlike natural materials, metamaterials are primarily fabricated in laboratories, and their properties are determined by their artificial structure. Therefore, certain special electromagnetic properties can be obtained by periodically adjusting their internal macroscopic structure. For example, conical metamaterials, gradient metasurfaces, and multicellular metamaterials have been proposed for radiative cooling. Hossain et al. first proposed and fabricated a conical anisotropic metamaterial structure composed of alternating aluminum and chromium layers. These conical metamaterial cylindrical structures exhibit a high W / m² at ambient temperature. 2It has extremely high cooling power; however, the metamaterial structure formed by the multi-scale mode is complex and difficult to process, which limits its further application.

[0004] Compared to metamaterials and polymers, multilayer thin-film radiation cooling materials have greater potential for practical applications in radiation cooling due to their large-area and easily fabricated characteristics. Research shows that one-dimensional photonic crystals possess broadband wide-angle sidebands; we utilize this property to design infrared broadband high-emissivity radiation cooling devices. By stacking different types of thin films, we expand the spectral absorption band range and obtain a more superior emission spectrum. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing radiation cooling technology and to propose a multilayer thin-film radiation cooling device that achieves wide-angle, high-efficiency cooling and is suitable for large-scale production.

[0006] The multilayer thin-film radiative cooling device proposed in this invention comprises, from top to bottom, an impedance matching layer, a high-loss titanium layer, a one-dimensional photonic crystal, a phase compensation layer, a uniformly thick reflective thin film, and a supporting substrate layer. The impedance matching layer and the high-loss titanium layer are used to excite a broadband response and improve the absorption rate. The one-dimensional photonic crystal is used to generate a broadband wide-angle reflection sideband. The phase compensation layer is used to control the change in the propagation phase. The uniformly thick reflective thin film is used to couple and form a broadband absorption, improving selective absorption and absorption efficiency without affecting thermal stability. In summary, it forms a broadband wide-angle absorption characteristic with an atmospheric transparent window.

[0007] The impedance matching layer is made of infrared transparent dielectric material. The real part n of the infrared transparent dielectric material is a real number greater than 0, and the imaginary part n is 0. It is a lossless medium with a thickness of 550-800 nm and a refractive index of 2.5-4.

[0008] The high-loss titanium metal layer has broadband infrared absorption characteristics and a thickness of 40–140 nm.

[0009] The one-dimensional photonic crystal is composed of stacked unit lattices, which consist of a high-refractive-index infrared transparent dielectric material film and a low-refractive-index infrared transparent dielectric material film. The thickness of the unit lattice is 300-400 nm, and the number of unit lattices is 5-7.

[0010] The phase compensation layer is made of infrared transparent dielectric material with a thickness of 100-250 nm and a refractive index of 1-5.

[0011] The uniform, thick reflective thin film is prepared using precious metals with stable physicochemical properties and high reflectivity, whose resonance absorption peaks can be flexibly controlled, such as Ag, Au, Al, Cu, etc., and has a thickness greater than 100 nm.

[0012] The working principle of this invention is as follows: broadband wide-angle high reflectivity is achieved by utilizing the sideband of a photonic crystal; broadband response and absorptivity are excited by utilizing a high-loss titanium metal layer and an impedance matching layer; and the propagation phase is controlled by utilizing a phase compensation layer and a uniformly thick reflective thin film, thereby forming a broadband wide-angle absorption characteristic of an atmospheric transparent window, thus realizing passive radiative cooling function.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0014] 1. The multilayer thin-film radiative cooling device proposed in this invention exhibits a higher average absorptivity in the operating wavelength range (8–13 μm) and higher reflectivity in other wavelength ranges compared to previous devices. This absorber maintains a high absorption rate of over 90% within the incident angle range of 0°–50°. Beyond 50°, the average absorptivity decreases slowly with increasing angle, but still maintains a high overall average absorptivity. It possesses broadband wide-angle absorption characteristics and has significant application potential in radiative cooling.

[0015] 2. The multilayer thin-film radiative cooling device proposed in this invention exhibits good polarization independence. While the absorption characteristics show slight differences when light of different polarizations is incident, all exhibit excellent performance. The angle has a slightly greater impact on TE-polarized light incident light than on TM-polarized light incident light; however, under TE-polarized light incident light conditions, an average absorption rate of over 80% can still be achieved within the range of 0–60°.

[0016] 3. The multilayer thin-film radiative cooling device proposed in this invention uses conventional materials, which are easy to implement. It has a simple structure and can be fabricated over large areas without photolithography, avoiding complex micro-nano processes, thus improving fabrication efficiency and reducing fabrication costs.

[0017] 4. The multilayer thin-film radiative cooling device proposed in this invention can achieve high emissivity in an atmospheric transparent window and can be used in radiative cooling devices to achieve high-power nighttime radiative cooling. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the device structure of the present invention.

[0019] Figure 2 This is the average absorption spectrum of Embodiment 1 of the present invention.

[0020] Figure 3 This is a cooling power diagram of Embodiment 1 of the present invention.

[0021] Figure 4 The average absorption spectrum of Embodiment 1 of the present invention at different incident angles is shown.

[0022] Figure 5 The average absorption spectrum of Embodiment 1 of the present invention is shown in the range of 0 to 80° under different polarized light incident conditions.

[0023] Figure 6 This is the absorption spectrum of Embodiment 2 of the present invention when light is incident perpendicularly.

[0024] Figure 7 This is the absorption spectrum of the impedance matching layer thickness when light is incident perpendicularly, according to Embodiment 2 of the present invention.

[0025] Figure 8 This is the absorption spectrum of the impedance matching layer refractive index when light is incident perpendicularly, according to Embodiment 2 of the present invention.

[0026] Figure 9 This is the absorption spectrum of the number of unit lattice cells when light is incident perpendicularly, according to Embodiment 3 of the present invention.

[0027] Figure 10 This is the absorption spectrum of the unit lattice thickness when light is incident perpendicularly, as shown in Embodiment 3 of the present invention.

[0028] Figure 11 This is the absorption spectrum of Example 4 of the present invention when light is incident perpendicularly.

[0029] Figure 12 This is the absorption spectrum of Example 5 of the present invention when light is incident perpendicularly.

[0030] Figure 13 This is the absorption spectrum of the phase compensation layer thickness in Embodiment 5 of the present invention when light is incident perpendicularly.

[0031] Figure 14 This is the absorption spectrum of the phase compensation layer refractive index when light is incident perpendicularly, according to Embodiment 5 of the present invention. Detailed Implementation

[0032] The present invention will now be described with reference to specific embodiments and accompanying drawings, but the scope of protection of the present invention is not limited to the following embodiments. Those skilled in the art can readily modify the following embodiments and apply the general principles to other embodiments without inventive effort. Therefore, all modifications and improvements made to the present invention by those skilled in the art based on the description provided are within the scope of protection of the present invention, and are protected by the appended claims.

[0033] like Figure 1 As shown, the multilayer thin-film radiative cooling device based on photonic crystal sidebands comprises, from top to bottom, an impedance matching layer 1, a high-loss titanium layer 2, a one-dimensional photonic crystal 3, a phase compensation layer 4, a uniform thickness reflective thin film 5, and a supporting substrate layer 6. Specific embodiments of the present invention are as follows:

[0034] Example 1

[0035] The multilayer thin-film radiative cooler includes a 640nm impedance matching layer made of silicon with a refractive index of 3.47; a high-loss titanium layer with a thickness of 90nm, the relative permittivity of which can be described by the Drude model; a one-dimensional photonic crystal with unit lattice materials of zinc sulfide and chromium, with refractive indices of 2.2 and 4 respectively, each 180nm thick, using a total of 6 unit lattice layers; a phase compensation layer made of silicon with a thickness of 160nm; a uniform optical thickness reflective thin film made of silver with a thickness of 100nm; and a supporting substrate layer that is not included in the experimental calculations. The average absorption spectrum of the above device is shown in the figure. Figure 2 As shown by the black solid line, it basically matches the atmospheric infrared transparency window (gray solid line), and the average absorption rate in the 8-13μm working band from 0 to 80° is 83.8%.

[0036] The radiant cooling power of the radiant cooler in Example 1 under no sunlight is as follows: Figure 3 As shown, under ideal conditions, assuming an ambient temperature of 300K, four cases with thermal conductivity coefficients Q = 0, 1, 3, and 6.9 W / m² / K are selected to discuss the radiative cooling performance of the absorber. Calculations reveal the net cooling power P of the ideal heat sink and the cooling device in this embodiment. net The relationship with temperature Tr. In the absence of a non-radiative heat transfer coefficient, the cooling power of the radiative cooling device in this embodiment is close to that of an ideal heat sink. At an ambient temperature of 300K, i.e. under natural light, P... net It can reach as high as 126.4W / m 2 Around, even at Q = 6.9 W / m 2 At a temperature of / K, the equilibrium temperature is 286K, which is 14K lower than the ambient temperature, indicating good radiative cooling performance.

[0037] The absorption spectrum of Example 1 at multiple angles is shown below. Figure 4 As shown, when the incident angle θ increases from 0° to 30°, the absorption spectrum of the radiation cooling device in the working band (8-13µm) remains basically unchanged, and the average absorptivity reaches over 90%. When the incident angle is 50°, the average absorptivity of the device reaches 90.2%. When the incident angle exceeds 50°, the average absorptivity decreases slowly with the increase of the angle, but still maintains a high average absorptivity overall.

[0038] Example 1 shows the absorption spectra under different polarizations as follows: Figure 5 As shown, the absorption characteristics differ slightly when incident with different polarized light, but all exhibit good performance, with average absorptivity reaching 82.2% and 85.4% respectively in the range of 0–80°.

[0039] Example 2

[0040] Based on Example 1, the thickness of the top impedance matching layer silicon was modified for separate implementations. Figure 6 This shows the detailed variation of absorbance at thicknesses of 0 nm, 550 nm, 600 nm, 650 nm, and 700 nm. The relationship between the absorber's spectrum and its thickness is shown in the figure below. Figure 7 As shown, modifying the thickness of the top dielectric layer affects the absorbance. The absorbance of weak absorption peaks decreases, while the right band broadens towards longer wavelengths. Experiments show that broadband absorption can be achieved in the range of 550–800 nm, with the best effect observed at a thickness of 640 nm. The relationship between the absorber's spectrum and the refractive index of the impedance matching layer is shown in the figure. Figure 8 As shown, good results can be achieved in the refractive index range of 2.5 to 4.

[0041] Example 3

[0042] Based on Example 1, the number of unit lattice cells in the one-dimensional photonic crystal was modified to 4, 5, 6, 7, and 8. The absorption spectrum of the device is shown below. Figure 9 As shown, the broadband and sidebands are significantly affected by the period. The absorption band redshifts and the sidebands increase with increasing period. When the period is 6, the broadband perfectly covers the working wavelength and has a high average absorptivity. The relationship between the absorption spectrum and the thickness of the unit lattice is shown in the figure. Figure 10 As shown, the broadband absorption effect is better in the 300-400nm range, especially the effect is best at 360nm.

[0043] Example 4

[0044] Based on Example 1, the thickness of the high-loss titanium layer was modified for different implementations, and the spectra of the absorbers are shown below. Figure 11 As shown in the figure, experiments have shown that good broadband absorption can be achieved in the range of 40-140nm, with the best effect when the thickness is 90nm.

[0045] Example 5

[0046] Based on Example 1, the phase compensation layer silicon was removed, and the comparison with the original absorber at different angles was compared. Figure 12 As shown, the silicon layer, acting as a phase compensation layer, influences the redshift of the photonic crystal's edge bands to counteract the blueshift caused by changes in the incident angle. The absorption spectrum varies with the thickness of the phase compensation layer as follows: Figure 13 As shown, the broadband absorption effect is significant in the thickness range of 100–250 nm, covering the working wavelength. The variation of the absorption spectrum with the refractive index of the phase compensation layer is as follows. Figure 14 As shown, good results can be achieved in the refractive index range of 1 to 5.

[0047] The above embodiments are merely preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A multilayer thin-film radiative cooling device based on photonic crystal sidebands, characterized in that... From top to bottom, it comprises an impedance matching layer, a high-loss titanium layer, a one-dimensional photonic crystal, a phase compensation layer, a uniformly thick reflective thin film, and a supporting substrate layer. The impedance matching layer and the high-loss titanium layer are used to excite a broadband response and improve the absorptivity. The one-dimensional photonic crystal is used to generate a broadband wide-angle reflective sideband. The phase compensation layer is used to control the change in the propagation phase. The uniformly thick reflective thin film is used to couple and form a broadband absorption, improve selective absorptivity and absorption efficiency without affecting thermal stability, and form a broadband wide-angle absorption characteristic of an atmospheric transparent window, thereby realizing passive radiative cooling.

2. The multilayer thin-film radiative cooling device based on photonic crystal sidebands as described in claim 1, characterized in that... The impedance matching layer is prepared using an infrared transparent dielectric material. The real part n of the infrared transparent dielectric material is a real number greater than 0, and the imaginary part k is 0. It is a lossless dielectric with a thickness of 550-800 nm and a refractive index of 2.5-4.

3. The multilayer thin-film radiative cooling device based on photonic crystal sidebands as described in claim 1, characterized in that... The high-loss titanium metal layer has broadband infrared high absorption characteristics and a thickness of 40–140 nm.

4. The multilayer thin-film radiative cooling device based on photonic crystal sidebands as described in claim 1, characterized in that... The one-dimensional photonic crystal is composed of several stacked unit lattices. Each unit lattice consists of a high-refractive-index infrared transparent dielectric material film and a low-refractive-index infrared transparent dielectric material film. The thickness of each unit lattice is 300-400 nm, and the number of unit lattices is 5-7.

5. The multilayer thin-film radiative cooling device based on photonic crystal sidebands as described in claim 1, characterized in that... The phase compensation layer is made of infrared transparent dielectric material with a thickness of 100-250 nm and a refractive index of 1-5.

6. The multilayer thin-film radiative cooling device based on photonic crystal sidebands as described in claim 1, characterized in that... The uniform, thick reflective thin film is prepared using a noble metal whose resonance absorption peak can be flexibly controlled.

7. The multilayer thin-film radiative cooling device based on photonic crystal sidebands as described in claim 1, characterized in that... The uniform, thick reflective film is made of Ag, Au, Al, and Cu, and has a thickness greater than 100 nm.

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