Transparent directional radiative refrigeration material and method of making same

Abstract

The present application relates to a kind of transparent directional radiation refrigeration materials and preparation method thereof, the transparent directional radiation refrigeration material is assembled by the sawtooth grating film of infrared reflection layer deposition and impedance matching layer filled sawtooth structure:The infrared reflection layer is transparent metal oxide layer;The transparent directional radiation refrigeration material satisfies: the average transmittance of visible light band is ≥65%; The average emissivity difference between high emissivity side and low emissivity side in mid-infrared band is ≥40%.Compared with prior art, the radiation cooling material in the present application has high transmittance in visible light band, and has asymmetric directional high emissivity in mid-infrared band, which can improve the radiation refrigeration effect of building facade transparent enclosure structure, make up the problem that the radiation refrigeration performance is limited due to the omnidirectional high emissivity of traditional glass building facade, and can improve the energy-saving effect of facade window.

Description

Technical Field

[0001] This invention relates to the field of radiation cooling technology, and in particular to a transparent directional radiation cooling material and its preparation method. Background Technology

[0002] In recent years, with global warming, the emission of large amounts of greenhouse gases and the generation of large amounts of waste heat from human production and daily life have exacerbated this phenomenon, and high temperatures have occurred frequently. This has led to increasing energy consumption of building air conditioning, and windows, as the least energy-efficient part of a building, consume a large amount of building air conditioning energy.

[0003] Radiative cooling is a zero-energy cooling technology that lowers the surface temperature of an object by radiating heat into outer space. This process requires no energy input. Existing transparent radiative cooling materials typically have high emissivity at any angle; however, most windows in buildings are on the facade. Therefore, when windows are combined with traditional transparent radiative cooling materials, only the view towards the sky can effectively radiate heat into outer space, while the view towards the ground and environment absorbs heat radiation from the ground and environment, thus inhibiting the cooling effect.

[0004] CN113527740A discloses a radiation-cooling thin film with a periodic micro / nano structure on its surface and its preparation method. The thin film includes a periodic micro / nano structure layer, a polymer film layer, and a reflective coating. However, the technical solution in this patent document still has certain limitations. First, the thin film has omnidirectional high emissivity independent of angle, which limits its application to radiation-cooling in the horizontal direction. Second, the patent document does not explicitly mention how to improve the transmittance of the thin film in the visible light band, which is crucial for achieving radiation-cooling on transparent surfaces.

[0005] WO2023284350A1 improves the preparation method of radiation-cooling thin films by adding periodic micro-nano structures to the surface of polymer films to control the absorption and radiation characteristics of radiation-cooling thin films in the visible and infrared light bands. The thin film proposed in this patent document also has the characteristic of omnidirectional high emissivity, which limits its radiation-cooling performance when used in building facades.

[0006] Currently, radiative cooling technology has been widely applied in building energy conservation, automobiles, solar cell cooling, outdoor equipment heat dissipation, agricultural greenhouses, tents, umbrellas, textiles, and other fields. Among the commercially available radiative cooling products, radiative cooling films have a relatively high market share. In use, the radiative cooling film is typically attached to the outer surface of the object to be cooled, such as the exterior walls or roof of a building, to achieve a cooling effect. However, since most building surfaces are facades, the radiative cooling effect of existing radiative cooling films used on building facades still needs further improvement.

[0007] Currently, transparent radiative cooling materials designed for upward-facing windows already possess excellent cooling performance. However, developing directional transparent radiative cooling materials suitable for building facade windows remains highly challenging. Therefore, developing transparent directional radiative cooling materials is crucial for improving the energy efficiency of windows. Summary of the Invention

[0008] To address the problem of poor cooling effect of existing transparent radiative cooling materials when used for cooling building facade windows, this invention proposes a method for preparing a transparent directional radiative cooling material, which has the advantage of improving the radiative cooling effect of building facade glass.

[0009] The objective of this invention can be achieved through the following technical solutions:

[0010] The first aspect of the present invention provides a transparent directional radiation cooling material, which is assembled from a sawtooth grating film with an infrared reflective layer deposited on it and an impedance matching layer filled with a sawtooth structure.

[0011] The transparent directional radiation cooling material satisfies the following:

[0012] The infrared reflective layer is a transparent metal oxide layer;

[0013] Average transmittance in the visible light band ≥65%;

[0014] The average emissivity difference between the high-emission side and the low-emission side in the mid-infrared band is ≥40%.

[0015] Furthermore, when the transparent directional radiative cooling material is placed vertically, it can reflect the thermal radiation energy of the high-temperature ground or environment, effectively improving the radiative cooling performance of the facade windows.

[0016] Furthermore, the thickness of the transparent directional radiation cooling material is 0.05-3 mm.

[0017] Furthermore, the thickness of the infrared reflective layer is 50-500 nm, preferably 300 nm;

[0018] The sawtooth period of the polymer sawtooth grating film is 10-300μm, the sawtooth base angle α is 10°-60°, and the base angle β is 10°-60°.

[0019] The transparent metal oxide layer is indium tin oxide or aluminum-doped zinc oxide.

[0020] Furthermore, the infrared reflective layer is prepared by a directional deposition process, wherein the transparent metal oxide layer forms a continuous cover layer on the inclined surface of the sawtooth grating in the sawtooth grating film, while exhibiting a discontinuous distribution on the vertical surface of the sawtooth of the sawtooth grating film.

[0021] When the sawtooth grating film is placed vertically, the vertical surface of the sawtooth in the polymer sawtooth grating film faces the sky, resulting in high emission characteristics in the direction facing the sky; the beveled surface of the transparent metal oxide surface of the sawtooth in the sawtooth grating film faces the ground, resulting in low emissivity characteristics in the direction facing the ground.

[0022] That is, when the film is placed vertically, the mid-infrared high-emissivity polymer side of the serration faces the sky, resulting in high emission characteristics in the direction facing the sky, while the transparent metal oxide side of the serration faces the ground, resulting in low mid-infrared emissivity characteristics in the direction facing the ground.

[0023] Furthermore, the material of the sawtooth grating is selected from at least one of polydimethylsiloxane, polymethyl methacrylate, polyvinyl alcohol, polyurethane, polycarbonate, polyethylene terephthalate, and polypropylene.

[0024] Furthermore, the material of the impedance matching layer is selected from at least one of polyethylene, polypropylene, and butene-styrene thermoplastic elastomer.

[0025] A second aspect of the present invention provides a method for preparing the transparent directional radiation cooling material as described above, comprising the following steps:

[0026] S1. Dissolve the visible light transparent mid-infrared high-emission polymer in the first solvent to form solution A;

[0027] S2. Pour solution A into the sawtooth template and solidify it. Demold the solution to obtain a sawtooth grating film.

[0028] S3. The sawtooth grating film is placed at an angle, and an infrared reflective layer is directionally deposited on the sawtooth grating film;

[0029] S4. Dissolve the infrared transparent polymer in a second solvent to form solution B;

[0030] S5. Solution B is cast onto a sawtooth grating film covered with a reflective layer and cured to form an impedance matching layer, thus obtaining a transparent directional radiation cooling material.

[0031] Further, in S1, the mass ratio of the visible light transparent mid-infrared high-emission polymer to the first solvent forming solution A is (0.1~1):1, and in one embodiment of the present invention, it is preferably 0.175:1;

[0032] The visible-light transparent mid-infrared high-emission polymer is selected from at least one of polydimethylsiloxane, polymethyl methacrylate, polyvinyl alcohol, polyurethane, polycarbonate, polyethylene terephthalate, and polypropylene, preferably polyvinyl alcohol (PVA).

[0033] The first solvent is selected from at least one of water, tetrahydrofuran, chloroform, toluene, cyclohexane, n-hexane, toluene, and xylene. In one embodiment of the present invention, water is preferred.

[0034] Furthermore, in S3, the method for directional deposition of the infrared reflective layer is selected from magnetron sputtering, electron beam evaporation, and thermal evaporation.

[0035] Furthermore, directional deposition refers to the process of depositing transparent metal oxides in a specific direction on a sawtooth grating film by controlling deposition conditions (such as angle and gas pressure) during the preparation of the infrared reflective layer. Specifically, the polymer sawtooth grating film is fixed on a sample stage and tilted at a certain angle. Then, a vapor phase deposition method (such as magnetron sputtering, electron beam evaporation, or thermal evaporation) is used to sputter transparent metal oxides onto the polymer sawtooth grating film in a specific direction. Due to the angle control and physical shielding effect during the deposition process, the transparent metal oxides form a continuous capping layer on the inclined surface of the sawtooth grating, while exhibiting a discontinuous distribution on the vertical surface of the sawtooth. This results in the film having different reflection and transmission characteristics of infrared light in different directions, thereby achieving the effect of directional radiative cooling.

[0036] Further, in S4, the second solvent is selected from at least one of cyclohexane, tetrahydrofuran, chloroform, toluene, cyclohexane, n-hexane, ethyl acetate, butyl acetate, xylene, toluene, and carbon tetrachloride.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1) This invention proposes a method for preparing a transparent directional radiative cooling material. This radiative cooling material exhibits high transmittance in the visible light band and asymmetric directional high emissivity in the infrared band. It can improve the radiative cooling effect of transparent building envelopes, compensating for the insufficient cooling performance caused by the omnidirectional high emissivity of traditional glass in building facades, and effectively reducing the increased cooling energy consumption due to the absorption of ambient heat radiation during hot seasons. This invention provides a new method for the design of radiative cooling windows, with potential economic and social benefits.

[0039] 2) This invention addresses the shortcomings of existing technologies by preparing a transparent infrared asymmetric directional radiation cooling material through casting and thin film directional deposition. When this transparent directional radiation cooling material is used for windows on building facades, it can improve the cooling effect of the windows. Attached Figure Description

[0040] Figure 1 A photograph of a transparent directional radiation cooling material;

[0041] Figure 2SEM images of the surface and cross-section of a transparent directional radiation cooling material;

[0042] Figure 3 Visible light transmittance spectrum of a transparent directional radiation cooling material;

[0043] Figure 4 The average emissivity of a transparent directional radiation cooling material at different incident angles;

[0044] Figure 5 The temperature of the transparent directional radiative cooling material and glass tested when placed vertically outdoors at noon;

[0045] Figure 6 A schematic diagram of a transparent directional radiation cooling material. Detailed Implementation

[0046] Overall, this invention relates to a transparent directional radiative cooling material and its preparation method. The radiative cooling material is assembled from a polymer sawtooth grating with an infrared reflective layer deposited in a specific direction and an impedance matching layer filled with sawtooth structures. The transparent directional radiative cooling material has a transmittance of over 65% in the visible light spectrum and an asymmetric directional high emissivity in the mid-infrared band. When placed vertically, the transparent radiative cooling material can reflect the thermal radiation energy from the high-temperature ground or environment, effectively improving the radiative cooling performance of facade windows. Addressing the problem of insufficient cooling performance of traditional transparent radiative cooling materials used in facade windows, this invention provides a method for controlling the thermal radiation direction of the transparent radiative cooling material, which can improve the energy-saving effect of facade windows.

[0047] In a specific implementation, the transparent directional radiation cooling material of the present invention is assembled from a sawtooth grating with an infrared reflective layer deposited in a specific direction and an impedance matching layer filled with a sawtooth structure.

[0048] In specific implementation, the thickness of the transparent directional radiation cooling material is 0.05-3mm.

[0049] In specific implementation, the visible light transmittance of the transparent directional radiation cooling material is not less than 65%, and the average emissivity difference between the high-emissivity side and the low-emissivity side in the mid-infrared band is ≥40%.

[0050] Another objective of this invention is to disclose the above-mentioned transparent directional radiation cooling material and its preparation method, comprising the following steps:

[0051] a) Mix the visible light transparent mid-infrared high-emission polymer and solvent A in a certain mass ratio, and stir thoroughly until the visible light transparent mid-infrared high-emission polymer is completely dissolved to form solution A;

[0052] b) The solution A is cast onto the sawtooth grating template and cured under certain conditions; after the solution A has completely cured, the cured and demolded polymer film is peeled off from the sawtooth grating template to obtain the polymer sawtooth grating film.

[0053] c) The polymer sawtooth grating film is fixed on a sample stage and tilted at a certain angle. A transparent metal oxide of a certain thickness is sputtered onto the polymer sawtooth grating film in a specific direction using a vapor deposition method. After deposition, a transparent metal oxide / polymer sawtooth grating film is obtained.

[0054] d) Mix the visible-infrared transparent polymer used for the impedance matching layer and solvent B in a certain mass ratio, and stir thoroughly until the visible-infrared transparent polymer is completely dissolved to form solution B;

[0055] e) Cast the solution B onto the transparent metal oxide / polymer sawtooth grating film obtained in step c), and cure the solution B under certain conditions; after the solution B has completely cured, the transparent directional radiation cooling material is obtained.

[0056] In specific implementation, the mass ratio of the visible light transparent mid-infrared high-emission polymer and solvent A in step a) is (0.1~1):1.

[0057] In specific implementation, the visible light transparent mid-infrared high-emission polymer mentioned in step a) can be materials such as polydimethylsiloxane, polymethyl methacrylate, polyvinyl alcohol, polyurethane, polycarbonate, polyethylene terephthalate, and polypropylene.

[0058] In specific implementation, solvent A mentioned in step a) is used to dissolve the visible-light transparent mid-infrared high-emission polymer. The solvent can be one or a combination of multiple solvents such as water, tetrahydrofuran, chloroform, toluene, cyclohexane, n-hexane, toluene, and xylene.

[0059] In specific implementation, the sawtooth period of the sawtooth grating template mentioned in step b) is 10-300 μm, see [reference]. Figure 6 The base angle α of the serration is 10°-60°, and the base angle β is 10°-60°.

[0060] In practice, the vapor deposition method described in step c) can be magnetron sputtering, electron beam evaporation, or thermal evaporation.

[0061] In specific implementation, the transparent metal oxide mentioned in step c) can be materials such as indium tin oxide (ITO) and aluminum-doped zinc oxide (AZO).

[0062] In specific implementation, the thickness in step c) is 50-500nm.

[0063] In specific implementation, the visible-infrared transparent polymer used as the impedance matching layer in step d) can be materials such as polyethylene, polypropylene, and butene-styrene thermoplastic elastomer.

[0064] In specific implementation, solvent B mentioned in step e) is used to dissolve the visible-infrared transparent polymer. The organic solvent may be one or a combination of multiple solvents such as cyclohexane, tetrahydrofuran, chloroform, toluene, cyclohexane, n-hexane, ethyl acetate, butyl acetate, xylene, toluene, and carbon tetrachloride.

[0065] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Any preparation methods, materials, structures, or compositional ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0066] Example 1

[0067] This embodiment modulates the optical properties of a radiation-cooling thin film in the visible and infrared bands by designing a periodic sawtooth micro / nano structure on the surface of a polymer film. Specifically, the periodic sawtooth structure, with its unique geometry, interacts with light waves in the visible and infrared bands, thereby modulating the light waves. This structural design, based on the principles of light scattering and geometric optics, ensures high transmittance of visible light while exhibiting directional high emissivity in the mid-infrared band. This allows the thin film to more effectively dissipate heat into outer space via thermal radiation when used for facade radiation cooling, thus improving the facade radiation cooling efficiency.

[0068] This embodiment prepares a transparent directional radiation cooling material, including the following steps:

[0069] a) Polyvinyl alcohol (PVA) was completely dissolved in water and stirred at 80°C for 2 hours to obtain a 15wt% PVA aqueous solution A;

[0070] b) Cast 2 mL of the PVA aqueous solution A from step a) onto a 2.5*5 cm sawtooth grating template, wherein the sawtooth period of the template is 31 μm and the two bottom angles of the sawtooth are 69° and 21° respectively; after drying at room temperature for 24 hours, peel off the PVA to obtain the PVA sawtooth grating film A.

[0071] c) Fix the PVA sawtooth grating film A obtained in step b) onto the sample stage of magnetron sputtering and place it at a 30° angle. Deposit a 300 nm thick ITO layer on the sample surface by magnetron sputtering at 60 W RF and 0.4 Pa. After sputtering, the ITO / PVA sawtooth grating film A is obtained.

[0072] d) Completely dissolve SEBS in cyclohexane and stir for 2 hours to obtain a 5 wt% SEBS solution A;

[0073] e) Cast 1 mL of the SEBS solution A obtained in step d) onto the ITO / PVA sawtooth grating film A obtained in step c), and dry it at room temperature without forced convection for 24 hours, waiting for the cyclohexane in the SEBS solution A to completely evaporate, to obtain a transparent directional radiation cooling material.

[0074] Physical examples of transparent directional radiation cooling materials Figure 1 As shown.

[0075] In this invention, the infrared reflective layer is prepared by a directional deposition process, wherein the transparent metal oxide layer forms a continuous cover layer on the inclined surface of the sawtooth grating in the sawtooth grating film, while exhibiting a discontinuous distribution on the vertical surface of the sawtooth of the sawtooth grating film.

[0076] See Figure 6 When the film is placed vertically, the mid-infrared high-emissivity polymer side of the serration faces the sky, thus exhibiting high emissivity in the sky-facing direction; while the transparent metal oxide side of the serration faces the ground, thus exhibiting mid-infrared low emissivity in the ground-facing direction.

[0077] Traditional planar radiative cooling films typically employ a single polymer material or a uniform coating on the surface. This structure cannot control the direction of emitted thermal radiation; it cannot effectively reflect thermal radiation from the ground below to reduce heat absorption, nor can it, like this invention, emit thermal radiation only towards the sky to increase heat radiation. In contrast, this invention uses a directional deposition process to prepare a transparent metal oxide layer on a sawtooth grating film, forming a continuous cover layer on the inclined surface and discontinuously distributed on the vertical surface. It utilizes the difference in mid-infrared optical properties of the materials on both sides of the sawtooth structure to control the directionality of thermal radiation, exhibiting unique optical performance and superior facade cooling effect, effectively solving the problem of limited cooling performance of traditional planar films used on facades.

[0078] The periodic micro / nanostructure proposed in this invention can alter the propagation path of mid-infrared light within a thin film, while allowing visible light to pass through without being reflected or absorbed. When placed vertically, the film's high visible light transmittance ensures adequate lighting inside the building, while simultaneously transferring heat through thermal radiation towards the sky, thereby reducing surface temperature. This light modulation is based on the principles of light scattering and geometric optics, achieving precise modulation of multiple wavelengths of light by controlling the size, shape, and arrangement of the micro / nanostructure.

[0079] At the fabrication process level, some existing technologies employ complex three-dimensional micro / nano structures to enhance radiative cooling effects. However, these structures often rely on precise photolithography or etching processes, resulting in high fabrication costs, complex processes, and difficulties in large-scale production. This invention, through a sawtooth grating design combined with directional deposition technology, simplifies the fabrication process, reduces production costs, and is more conducive to large-scale industrial applications while achieving efficient control of infrared light. The innovation of this invention lies in achieving, or even surpassing, the cooling performance of complex micro / nano structure materials with a relatively simple structure and highly operable process, providing a more advantageous solution for the popularization and application of radiative cooling technology.

[0080] Experimental Example 1

[0081] This experiment tested the microstructure and optical properties of the transparent directional radiation cooling material prepared in Example 1.

[0082] a) Characterizing the microstructure of transparent directional radiation cooling materials:

[0083] The microstructure of the transparent directional radiation-cooling material was observed using field emission scanning electron microscopy, such as... Figure 2 As shown, the surface of the transparent directional radiation cooling material is very smooth, and the serrated structure can be clearly seen in the cross-section;

[0084] b) Test the transmittance of the transparent directional radiation cooling material in the visible light band:

[0085] The transmittance spectrum of the transparent directional radiocooling material in the visible light wavelength range of 300–800 nm was measured using a UV-Vis-NIR spectrophotometer (Lambda 1050, PerkinElmer). Figure 3 As shown, the average visible light transmittance of the transparent directional radiation cooling material is 83%.

[0086] c) Testing the mid-infrared emissivity of the transparent directional radiation cooling material at different incident angles:

[0087] The average emissivity of the transparent directional radiation-cooling material in the wavelength range of 6–20 μm was measured using an integrating sphere Fourier transform infrared (FTIR) spectrometer (Nicolet 6700, Thermo Scientific). Figure 4 As shown, the average emissivity of the transparent directional radiation cooling material is 0.86 in the positive incident angle direction and 0.36 in the negative incident angle direction.

[0088] The above tests show that the transparent directional radiation cooling material has high transmittance in the visible light band and asymmetric high directional emissivity in the mid-infrared band. This indicates that when the transparent directional radiation cooling material is used in facade windows, it can perform radiation cooling in the direction facing the sky, reducing heat radiation from the ground and the environment.

[0089] d) Testing the radiative cooling performance of transparent directional radiative cooling materials:

[0090] Temperature tests of the radiative cooling performance were conducted using two 10×10×5 cm acrylic measuring chambers, each with a solar reflective film on the outside. A transparent directional radiative cooling material and glass were placed in the windows of the two chambers, respectively, with the glass serving as a control. Both materials were placed on polystyrene foam supports inside the measuring chambers, 1 cm away from the windows. The measuring chambers were placed vertically. The temperature of the samples was recorded during the test using thermocouples with a temperature uncertainty of 0.1 °C. The test results showed that during the midday period, the average ground temperature reached 58.3 °C, and the transparent directional radiative cooling material was on average 1.4 °C cooler than the glass. This indicates that the prepared transparent directional radiative cooling material exhibits excellent radiative cooling performance when placed vertically.

[0091] The directional radiation cooling principle of this invention is based on the scattering and interference effects of light. The periodic micro / nano structure enhances the emissivity of the thin film in the infrared band, enabling it to more effectively absorb ambient heat and dissipate it into outer space via infrared radiation, thus achieving a cooling effect. Simultaneously, this structure reduces the reflectivity of the thin film in the visible light band and increases its transmittance, allowing the film to absorb more solar radiation heat under sunlight during the day, further enhancing its cooling power. This innovative design allows the radiation-cooling thin film of this invention to significantly improve cooling efficiency while maintaining high light transmittance, solving the problem of poor cooling performance in existing technologies.

[0092] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A transparent directional radiative cooling material, characterized in that, The transparent directional radiation cooling material is assembled from a sawtooth grating film with an infrared reflective layer and an impedance matching layer filled with a sawtooth structure. The infrared reflective layer is a transparent metal oxide layer; The sawtooth period of the sawtooth grating film is 10-300μm, the sawtooth base angle α is 10°-60°, and the base angle β is 10°-60°; The infrared reflective layer is prepared by a directional deposition process, wherein the transparent metal oxide layer forms a continuous cover layer on the inclined surface of the sawtooth grating in the sawtooth grating film, while exhibiting a discontinuous distribution on the vertical surface of the sawtooth grating film. The transparent directional radiation cooling material satisfies the following: Average transmittance in the visible light band ≥65%; The average emissivity difference between the high-emission side and the low-emission side in the mid-infrared band is ≥40%.

2. The transparent directional radiation cooling material according to claim 1, characterized in that, The thickness of the transparent directional radiation cooling material is 0.05-3 mm.

3. The transparent directional radiation cooling material according to claim 1, characterized in that, The thickness of the infrared reflective layer is 50-500 nm; The transparent metal oxide layer is indium tin oxide or aluminum-doped zinc oxide.

4. The transparent directional radiation cooling material according to claim 3, characterized in that, When the sawtooth grating film is placed vertically, the sawtooth surface without the infrared reflective layer faces the sky, resulting in high emissivity in the skyward direction. The sawtooth surface with the infrared reflective layer deposited in the sawtooth grating film faces the ground, resulting in low mid-infrared emissivity in the groundward direction.

5. The transparent directional radiation cooling material according to claim 1, characterized in that, The material of the sawtooth grating is selected from at least one of polydimethylsiloxane, polymethyl methacrylate, polyvinyl alcohol, polyurethane, polycarbonate, polyethylene terephthalate, and polypropylene.

6. The transparent directional radiation cooling material according to claim 1, characterized in that, The impedance matching layer is made of at least one of polyethylene, polypropylene, and butene-styrene thermoplastic elastomer.

7. A method for preparing a transparent directional radiation cooling material as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Dissolve the visible light transparent mid-infrared high-emission polymer in the first solvent to form solution A; S2. Pour solution A into the sawtooth template and solidify it. Demold the solution to obtain a sawtooth grating film. S3. The sawtooth grating film is placed at an angle, and an infrared reflective layer is directionally deposited on the sawtooth grating film; S4. Dissolve the infrared transparent polymer in a second solvent to form solution B; S5. Solution B is cast onto a sawtooth grating film covered with a reflective layer and cured to form an impedance matching layer, thus obtaining a transparent directional radiation cooling material.

8. The method for preparing a transparent directional radiation cooling material according to claim 7, characterized in that, In S1, the mass ratio of the visible light transparent mid-infrared high-emission polymer to the first solvent forming solution A is (0.1~1):1; The visible light transparent mid-infrared high-emission polymer is selected from at least one of polydimethylsiloxane, polymethyl methacrylate, polyvinyl alcohol, polyurethane, polycarbonate, polyethylene terephthalate, and polypropylene. The first solvent is selected from at least one of water, tetrahydrofuran, chloroform, cyclohexane, n-hexane, toluene, and xylene.

9. The method for preparing a transparent directional radiation cooling material according to claim 7, characterized in that, In S3, the method for directional deposition of the infrared reflective layer is selected from magnetron sputtering, electron beam evaporation, and thermal evaporation.

10. The method for preparing a transparent directional radiation cooling material according to claim 7, characterized in that, In S4, the second solvent is selected from at least one of cyclohexane, tetrahydrofuran, chloroform, toluene, cyclohexane, n-hexane, ethyl acetate, butyl acetate, xylene, and carbon tetrachloride.

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