Radiative cooling film and method of making and using same

Abstract

The application relates to the field of refrigeration technology, and particularly relates to a radiative cooling film and a preparation method and application thereof. The preparation method of the radiative cooling film comprises the following steps: adopting a femtosecond laser to perform pattern processing on a single-crystal silicon substrate to prepare an intermediate body containing a groove array structure; adopting an etching liquid to perform etching processing on the intermediate body containing the groove array structure to form an inverted-pyramid-shaped array structure at the groove array structure, and to prepare a template containing the inverted-pyramid-shaped array structure; the etching liquid comprises the following components in terms of mass fraction: 2%-5% of a hydroxide, 30%-50% of an organic solvent and 45%-68% of water; a precursor liquid comprising a polymer and inorganic dielectric particles is applied to the template containing the inverted-pyramid-shaped array structure, and after solidification, forming and demolding, a radiative cooling film is prepared; the surface of the radiative cooling film has a pyramid-shaped array structure. The preparation method is simple in process, and the prepared radiative cooling film has excellent refrigeration performance.

Description

Technical Field

[0001] This application relates to the field of refrigeration technology, specifically to radiation-cooling films, their preparation methods, and applications. Background Technology

[0002] Radiative cooling, as a green and energy-saving technology that can achieve passive cooling without additional energy input, has broad application prospects in fields such as building energy conservation, outdoor equipment cooling, or thermal management of transportation facilities, and has become a research hotspot in the field of energy-saving materials.

[0003] Currently, radiation-cooling materials based on ordered photonic structures, such as one-dimensional and two-dimensional photonic crystals, heavily rely on a series of complex micro- and nano-fabrication techniques, including electron beam evaporation, photolithography, and reactive ion etching, resulting in cumbersome fabrication processes. Radiation-cooling materials based on random photonic structures, such as polymers, have simpler fabrication processes, but their cooling performance is weaker. Therefore, traditional methods for fabricating radiation-cooling films struggle to simultaneously achieve excellent cooling performance and simple fabrication processes. Summary of the Invention

[0004] Based on this, this application provides a radiation-cooling film, its preparation method, and its application. The preparation method of the radiation-cooling film provided in this application is simple and easy to industrialize, and the radiation-cooling film prepared by it has excellent cooling performance.

[0005] A first aspect of this application provides a method for preparing a radiation-cooling film, comprising the following steps:

[0006] A femtosecond laser was used to pattern a single-crystal silicon substrate to prepare an intermediate with a groove array structure.

[0007] An etching solution is used to etch the intermediate body containing the groove array structure to form an inverted pyramid array structure at the groove array structure, thereby preparing a template containing the inverted pyramid array structure; the etching solution comprises the following components by mass fraction: 2%~5% hydroxide, 30%~50% organic solvent and 45%~68% water;

[0008] A precursor liquid comprising polymer and inorganic dielectric particles is applied to a template containing an inverted pyramid array structure, cured and demolded to prepare the radiation cooling film; the surface of the radiation cooling film has a pyramid array structure.

[0009] In some embodiments, the step of patterning a single-crystal silicon substrate using a femtosecond laser includes:

[0010] A femtosecond laser with a center wavelength of 950nm~1050nm, a pulse width of 230fs~240fs, and a fundamental repetition frequency of 480kHz~520kHz is selected. A quarter-wave plate is configured in the femtosecond laser optical path, and the circularly polarized femtosecond laser is used as the processing light source.

[0011] A dual-stage pulse train processing method is adopted, in which a single pulse is split into a pulse train containing 1 to 5 sub-pulses. The repetition frequency between the sub-pulses is 35MHz to 45MHz. The sub-pulses are accumulated and processed using a laser with a repetition frequency of 480kHz to 520kHz. Each processing site on the single-crystal silicon substrate is cumulatively processed by 5 to 25 sub-pulses. The pulse energy of each sub-pulse is 3.64μJ to 60μJ, thus preparing the intermediate with the groove array structure.

[0012] In some embodiments, the single-crystal silicon substrate is <100> Crystal-oriented silicon wafers.

[0013] In some embodiments, the size of the grooves in the groove array structure of the intermediate body is 8μm~22μm.

[0014] In some embodiments, the hydroxide includes one or more of potassium hydroxide and tetramethylammonium hydroxide.

[0015] In some embodiments, the organic solvent includes one or more of methanol, ethanol, isopropanol, and acetone.

[0016] In some embodiments, the polymer includes one or more of polydimethylsiloxane, polyvinylidene fluoride, and polymethyl methacrylate.

[0017] In some embodiments, the inorganic dielectric particles include one or more of titanium dioxide, silicon nitride, zirconium dioxide, yttrium oxide, hexagonal boron nitride, barium sulfate, aluminum oxide, and magnesium oxide.

[0018] In some embodiments, the D50 particle size of the inorganic dielectric particles is 100 nm to 10 μm.

[0019] In some embodiments, the mass ratio of the polymer to the inorganic dielectric particles is (0.4~20):1.

[0020] A second aspect of this application provides a radiation-cooling film prepared by the preparation method described in the first aspect of this application, the radiation-cooling film comprising a substrate layer and a pyramid-shaped array structure disposed on at least one surface of the substrate layer, the radiation-cooling film comprising a polymer and inorganic dielectric particles dispersed in the polymer.

[0021] In some embodiments, the radiation cooling film is a one-piece molded structure.

[0022] In some embodiments, the distance between the centers of two adjacent pyramid structures in the pyramid array structure is 8µm to 30µm, and the distance is greater than or equal to the base dimension of each pyramid structure.

[0023] In some embodiments, the base dimension of each pyramid structure in the pyramid array structure is 8μm to 22μm.

[0024] In some embodiments, the ratio of the height of each pyramid structure to the base dimension of the pyramid structure is 0.7 to 0.71.

[0025] In some embodiments, the polymer includes one or more of polydimethylsiloxane, polyvinylidene fluoride, and polymethyl methacrylate.

[0026] In some embodiments, the inorganic dielectric particles include one or more of titanium dioxide, silicon nitride, zirconium dioxide, yttrium oxide, hexagonal boron nitride, barium sulfate, aluminum oxide, and magnesium oxide.

[0027] In some embodiments, the D50 particle size of the inorganic dielectric particles is 100 nm to 10 μm.

[0028] In some embodiments, the mass ratio of the polymer to the inorganic dielectric particles is (0.4~20):1.

[0029] A third aspect of this application provides the use of the radiative cooling film as described in any of the second aspects of this application in a passive radiative cooling device.

[0030] The method for preparing the radiation-cooling film provided in this application has at least the following advantages:

[0031] In the method for preparing the radiation-cooling film of this application, a femtosecond laser is used for patterning. This method does not rely on processing technologies such as photomasks, photolithography, or electron beam evaporation. The period, size, and other parameters of the groove array can be directly controlled by the femtosecond laser. This not only simplifies the patterning process but also improves the controllability and flexibility of the structure preparation.

[0032] Further wet etching of the intermediate containing the groove array structure using an etching solution optimizes the etching rate ratio between different crystal planes of single-crystal silicon, enabling precise exposure of the... <111> The crystal planes, in turn, form an inverted pyramid-shaped array structure at the groove array structure. A radiation-cooling film with a pyramid-shaped array structure on its surface is further prepared using a template containing the inverted pyramid-shaped array structure. This structure enhances the thermal radiation emission performance in the infrared band (especially the 8µm~14µm band). Meanwhile, the composite structure formed by the inorganic dielectric particles and polymers inside the film enhances the diffuse reflection of sunlight through multiple scattering effects, reducing solar radiation absorption. The synergistic effect of these two elements significantly improves the spectral selectivity of the film, thus endowing it with excellent radiation-cooling performance.

[0033] Therefore, the method for preparing the radiation cooling film provided in this application is simple and easy to industrialize, and the radiation cooling film prepared by it has excellent cooling performance. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the preparation method of the radiation cooling film in one example of this application.

[0035] Figure 2 This is a schematic diagram of the grooved array structure obtained after femtosecond laser treatment in step S10 and the inverted pyramid-shaped array structure formed after etching treatment in step S20.

[0036] Figure 3 This is a schematic diagram of the crystal planes of a single-crystal silicon substrate in one example of this application.

[0037] Figure 4 This is an electron microscope image of an inverted pyramid-shaped array structure formed on the surface of a single-crystal silicon substrate after step S20.

[0038] Figure 5 This is a cross-sectional view of a radiation-cooling film provided as an example of this application.

[0039] Figure 6 This is a schematic diagram of the structure of a radiation-cooling film provided as an example in this application.

[0040] Figure 7 This is a schematic diagram illustrating the pulse energy and damage threshold of a femtosecond laser, provided as an example of this application.

[0041] Figure 8 These are processing topography diagrams of the grooves formed by splitting a single pulse into different numbers of sub-pulses under the first-level pulse modulation of the Burst mode in Embodiments 4 to 7 and Embodiment 1 of this application.

[0042] Figure 9The images show the processing morphology of the grooves corresponding to different numbers of pulses during multi-pulse accumulation processing using a laser at a repetition frequency of 500 kHz in Examples 8-10, 1, and 11.

[0043] Figure 10 This is a microstructure diagram of the inverted pyramid structure formed on the surface of single-crystal silicon in Embodiment 12 of this application.

[0044] Figure 11 These are scanning electron microscope (SEM) images of templates with inverted pyramid array structures prepared in Examples 1 and 13 of this application, wherein (a) is an SEM image of the template with inverted pyramid array structure prepared in Example 1, and (b) is an SEM image of the template with inverted pyramid array structure prepared in Example 13.

[0045] Figure 12 These are scanning electron microscope (SEM) images of the templates with inverted pyramid array structures prepared in Embodiment 1 and Comparative Example 2 of this application. (a) is an SEM image of the template with inverted pyramid array structure prepared in Embodiment 1, and (b) is an SEM image of the template with inverted pyramid array structure prepared in Comparative Example 2.

[0046] Explanation of reference numerals in the attached figures

[0047] 10. Monocrystalline silicon substrate; 20. Radiation cooling film; 210. Substrate layer; 220. Pyramid array structure; 211. Polymer; 212. Inorganic dielectric particles. Detailed Implementation

[0048] The following detailed description, in conjunction with specific embodiments, provides a more complete and clear account of the radiation-cooling film, its preparation method, and its applications. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0049] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0050] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise stated or in case of conflict, the terms or phrases used herein have the following meanings:

[0052] In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more.

[0053] In this application, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only a non-exhaustive enumeration purpose and should be understood not to constitute a closed limitation on quantity.

[0054] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0055] In this application, terms such as "preferred," "better," "more suitable," and "ideal" are used only to describe implementation methods or embodiments with better effects, and should be understood not to constitute a limitation on the scope of protection of this application.

[0056] In this application, terms such as "further," "even more," and "particularly" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0057] Radiative cooling is a completely passive cooling mechanism that requires no additional external energy input, making it a green and energy-saving technology that reduces energy consumption. When the sky is clear, the atmosphere is essentially transparent to electromagnetic waves in the 8µm–14µm long-wave infrared range. This transparent window band largely coincides with the blackbody radiation spectrum of objects at Earth's surface temperature. Therefore, according to the second law of thermodynamics, heat can spontaneously flow from objects on Earth's surface (high-temperature objects) to outer space (low-temperature objects) through thermal radiation. Thus, if an object is positioned facing the sky and its surface emission spectrum is appropriately designed, it is possible to use the near-absolute-zero cosmic environment as a cold source to lower the object's temperature below ambient temperature. To achieve this, it is necessary to ensure that the cooling device has a high emissivity in the atmospheric window band of 8µm–14µm to radiate heat into space. Since the thermal radiation spectrum mainly depends on the temperature of the radiating body and the resonance of the material, the selection and construction of radiative cooling optical materials are needed to selectively modulate the thermal radiation wavelength to the atmospheric window band. On the other hand, the cooled object can also receive heat from the outside through other means. For example, in the solar radiation band with wavelengths of 0.3µm to 2.0µm, the energy input provided by the sun far exceeds the energy output power that radiative cooling can provide. Therefore, radiative cooling materials should have low absorptivity and high reflectivity in the solar radiation band.

[0058] Early radiative cooling materials primarily used naturally occurring or chemically synthesized materials, such as white pigments, polymer films, and silicon monoxide films. While these cooling devices could exhibit some selective emission characteristics in the atmospheric window wavelength range, their emissivity was insufficient, limiting their practical cooling performance. Furthermore, due to the lack of precise design and efficient modulation of the reflection and emission spectra, these devices generally could only operate at night, requiring avoidance of energy input from solar radiation. In recent years, the development of micro-nano optics has provided new ideas for the design of daytime radiative cooling materials. When the dielectric particle size is comparable to the wavelength of sunlight, resonant scattering occurs; when the structural period matches the wavelength, a photonic bandgap effect is induced, thereby achieving a spectrally selective structure that generates strong interactions with specific spectra. Therefore, in the field of radiative cooling technology, the current mainstream technical solutions can be mainly divided into two categories: radiative cooling materials based on ordered photonic structures and radiative cooling materials based on random photonic structures.

[0059] Radiation-cooling materials based on ordered photonic structures, such as one-dimensional photonic crystals, two-dimensional photonic crystals, and metasurfaces, can achieve precise spectral control through accurate periodic structure design, thus obtaining excellent spectral selectivity and superior cooling performance. However, the preparation of these materials relies on a series of complex micro-nano fabrication techniques, such as electron beam evaporation, photolithography, and reactive ion etching. These processes are not only cumbersome and expensive, but also inefficient, making large-scale, low-cost production and widespread application difficult, greatly limiting their practical applications.

[0060] Radiation-cooling materials based on random photonic structures, such as polymer-based thin films, primarily utilize the infrared emission properties of the polymer matrix itself to achieve radiation cooling. While these materials are relatively simple to fabricate, their cooling performance is relatively low. Furthermore, although methods have been found to effectively improve radiation performance by constructing microstructures on the material surface, how to synergistically design surface and internal structures, and how to fabricate these surface microstructures in a low-cost and controllable manner, remain significant challenges.

[0061] Based on this, such as Figures 1-6 As shown, the first aspect of this application provides a method for preparing a radiation-cooling film, comprising the following steps:

[0062] S10: A femtosecond laser is used to pattern a single-crystal silicon substrate to prepare an intermediate with a groove array structure.

[0063] S20: The intermediate body containing the groove array structure is etched using an etching solution to form an inverted pyramid array structure at the groove array structure, thus preparing a template containing the inverted pyramid array structure.

[0064] S30: A precursor liquid comprising polymer and inorganic dielectric particles is applied to a template containing an inverted pyramid array structure, cured and demolded to prepare a radiation cooling film; the surface of the radiation cooling film has a pyramid array structure.

[0065] In the method for preparing the radiation-cooling film of this application, a femtosecond laser is used for patterning. This method does not rely on processing technologies such as photomasks, photolithography, or electron beam evaporation. The period, size, and other parameters of the groove array can be directly controlled by the femtosecond laser. This not only simplifies the patterning process but also improves the controllability and flexibility of the structure preparation.

[0066] Further wet etching of the intermediate body containing the groove array structure using an etching solution can precisely expose the... <111> The crystal planes, in turn, form an inverted pyramid-shaped array structure at the groove array structure. A radiation-cooling film with a pyramid-shaped array structure on its surface is further prepared using a template containing the inverted pyramid-shaped array structure. This structure enhances the thermal radiation emission performance in the infrared band (especially the 8µm~14µm band). Meanwhile, the composite structure formed by the inorganic dielectric particles and polymers inside the film enhances the diffuse reflection of sunlight through multiple scattering effects, reducing solar radiation absorption. The synergistic effect of these two elements significantly improves the spectral selectivity of the film, thus endowing it with excellent radiation-cooling performance.

[0067] Therefore, the method for preparing the radiation cooling film provided in this application is simple and easy to industrialize, and the radiation cooling film prepared by it has excellent cooling performance.

[0068] In some examples, in step S10, the femtosecond laser is used in a circularly polarized light combined with a dual-stage pulse train processing method. The dual-stage pulse train processing method includes: using the laser's Burst mode to split a single pulse into a pulse train containing 1 to 5 sub-pulses, with a repetition frequency of 35MHz to 45MHz between the sub-pulses, and using the laser's repetition frequency of 480kHz to 520kHz to accumulate the sub-pulses for processing, with each processing site on the single-crystal silicon substrate receiving a cumulative 5 to 25 sub-pulses.

[0069] This application employs a circularly polarized light combined with a two-stage pulse train processing method. Through precise temporal distribution of laser energy, it effectively solves the problems of edge chipping and heat-affected zone diffusion caused by excessively high single-pulse peak power. For example... Figure 7 As shown, because the femtosecond laser beam exhibits a Gaussian distribution in space, when the single pulse energy is too high (black curve), there are many areas in its beam cross-section that exceed the material damage threshold (black dashed line), and the excess energy in the central region, far exceeding the threshold, will be converted into heat and diffuse outwards, leading to an increase in the heat-affected zone. However, by using the circularly polarized light combined with the dual-stage pulse train processing method in this application, the pulse energy (blue curve) is slightly higher than the damage threshold, thereby enabling precise control of the ablation depth of the single-crystal silicon substrate.

[0070] Furthermore, in some examples, step S10, the step of patterning the single-crystal silicon substrate using a femtosecond laser, includes:

[0071] A femtosecond laser with a center wavelength of 950nm~1050nm, a pulse width of 230fs~240fs, and a fundamental repetition frequency of 480kHz~520kHz is selected. A quarter-wave plate is configured in the femtosecond laser optical path, and the circularly polarized femtosecond laser is used as the processing light source.

[0072] A dual-stage pulse train processing method is adopted, in which a single pulse is split into a pulse train containing 1 to 5 sub-pulses. The repetition frequency between the sub-pulses is 35MHz to 45MHz. The sub-pulses are accumulated and processed using a laser with a repetition frequency of 480kHz to 520kHz. Each processing site on the single-crystal silicon substrate is cumulatively processed by 5 to 25 sub-pulses. The pulse energy of each sub-pulse is 3.64μJ to 60μJ, thus preparing an intermediate with a groove array structure.

[0073] Understandably, each processing point corresponds to a groove in the groove array structure. Furthermore, the transmitted light intensity can be continuously adjusted by changing the angle of the half-wave plate in a precision rotating power attenuation system, allowing the sub-pulse energy reaching the surface of the monocrystalline silicon substrate to range from 3.64 μJ to 60 μJ. As an example, the monocrystalline silicon substrate is... <100> Crystal-oriented silicon wafer. For example, the pulse energy of the sub-pulse includes, but is not limited to, 3.64 μJ, 3.8 μJ, 4 μJ, 4.2 μJ, 4.3 μJ, 4.4 μJ, 4.45 μJ, 4.46 μJ, 4.47 μJ, 4.48 μJ, 4.5 μJ, 5 μJ, 8 μJ, 10 μJ, 15 μJ, 20 μJ, 25 μJ, 30 μJ, 40 μJ, 50 μJ, or 60 μJ, or a range formed by any two of the above point values ​​as endpoint values.

[0074] Figure 2 This diagram illustrates the grooved array structure obtained after femtosecond laser treatment in step S10 and the inverted pyramid-shaped array structure formed after etching in step S20. On the surface of a single-crystal silicon substrate 10, a maskless patterning process is performed using a femtosecond laser. During this process, a controlled displacement stage can fabricate a periodically arranged grooved array structure on the surface of the single-crystal silicon substrate 10. Furthermore, the grooved array structure formed after femtosecond laser treatment modifies the single-crystal silicon substrate, thus providing an induction region for subsequent etching. The circularly polarized light combined with a dual-pulse train processing method ensures the isotropy of the grooved array structure, eliminating groove shape distortion and improving morphology. This provides a foundation for obtaining a template with a highly consistent inverted pyramid-shaped array structure.

[0075] In some examples, the size of the grooves in the intermediate containing the groove array structure is 8 μm to 22 μm. In this application, "groove size" refers to the maximum width of the grooves along the periodic arrangement. This application found that, through the femtosecond laser in step S10, and with the synergy of the sub-pulse energy of 3.64 μJ to 60 μJ, the size of the grooves in the groove array structure can be continuously adjusted from 8 μm to 22 μm. Further, the size of the grooves in the groove array structure is 8 μm to 10 μm. This application found that the size of the grooves in the groove array structure of 8 μm to 10 μm can reduce the flat area between adjacent structures in the micro-geometry to reduce reflection loss, while producing excellent spectral coupling effect with the mid-infrared band (8 μm to 14 μm) emitted by the target, enhancing the thermal radiation emission capability of the material, and thus giving the radiation cooling film an extremely excellent cooling effect.

[0076] In some examples, in step S10, where a femtosecond laser is used to pattern the single-crystal silicon substrate, the center-to-center distance between two adjacent processing sites is set to 8 μm to 30 μm. Further, in step S10, where a femtosecond laser is used to pattern the single-crystal silicon substrate, the center-to-center distance between two adjacent processing sites is set to 8 μm to 22 μm. Even further, in the step of patterning the single-crystal silicon substrate using a femtosecond laser, the center-to-center distance between two adjacent processing sites is set to 8 μm to 10 μm.

[0077] Furthermore, the single-crystal silicon substrate 10 is <100> Crystal-oriented silicon wafers. In some examples, the etching solution comprises the following components by mass fraction: 2%–5% hydroxide, 30%–50% organic solvent, and 45%–68% water. As an example, the mass fraction of hydroxide in the etching solution includes, but is not limited to, 2%, 3%, 4%, or 5%, or any two of the above values ​​as endpoints. The mass fraction of organic solvent includes, but is not limited to, 30%, 35%, 40%, 42%, 43%, 44%, 45%, 48%, or 50%, or any two of the above values ​​as endpoints. The mass fraction of water includes, but is not limited to, 45%, 48%, 50%, 52%, 53%, 54%, 55%, 56%, 58%, 60%, 65%, or 68%, or any two of the above values ​​as endpoints.

[0078] In some of these examples, the hydroxide includes one or more of potassium hydroxide and tetramethylammonium hydroxide.

[0079] In some of these examples, the organic solvent includes one or more of methanol, ethanol, isopropanol, and acetone.

[0080] Further, in step S20, the step of etching the intermediate containing the groove array structure with an etching solution includes: immersing the intermediate containing the groove array structure in the etching solution for wet etching. Further, the etching temperature is 60℃~75℃, and the etching time is 15min~25min. As an example, the etching temperature includes, but is not limited to, 60℃, 63℃, 65℃, 66℃, 68℃, 70℃, 73℃, or 75℃, or any two of the above values ​​as endpoints within a range.

[0081] This application reveals that when the aforementioned etching solution is used to etch an intermediate containing a groove array structure, the etching solution exhibits different etching rates on different crystal planes of a single-crystal silicon substrate. For example... Figure 3As shown, the single-crystal silicon substrate has <100> Crystal facets <110> Crystal planes and <111> Crystal plane, the above etching solution on <111> The etching rate of the crystal plane is the slowest; therefore, the etching process of the etching solution will begin from the femtosecond laser-modified region, and its effect on… <110> The crystal plane has a low etching rate and can be etched along the slowest etching path. <111> The crystal planes automatically terminate, thus forming a regular, clearly defined inverted pyramid-shaped array structure on the surface of the single-crystal silicon substrate without a mask. Further, the electron microscope image of the inverted pyramid-shaped array structure formed on the surface of the single-crystal silicon substrate after step S20 is shown below. Figure 4 As shown in the electron microscope image, the inverted pyramid-shaped array structure is regular and has clear boundaries. If a traditional alkaline solution is used, it will cause a "cross-shaped" distortion at the edges of the resulting inverted pyramid-shaped array structure.

[0082] In some of these examples, in step S30, the polymer includes one or more of polydimethylsiloxane, polyvinylidene fluoride, and polymethyl methacrylate.

[0083] In some of these examples, in step S30, the inorganic dielectric particles include one or more of titanium dioxide, silicon nitride, zirconium dioxide, yttrium oxide, hexagonal boron nitride, barium sulfate, aluminum oxide, and magnesium oxide.

[0084] Preferably, the inorganic dielectric particles include one or more of yttrium oxide and hexagonal boron nitride.

[0085] In some of these examples, in step S30, the D50 particle size of the inorganic dielectric particles is 100 nm to 10 μm.

[0086] In some examples, in step S30, the mass ratio of polymer to inorganic dielectric particles is (0.4~20):1. As examples, the mass ratio of polymer to inorganic dielectric particles includes, but is not limited to, 0.4:1, 0.42:1, 0.43:1, 0.45:1, 0.5:1, 0.6:1, 0.65:1, 0.66:1, 0.67:1, 0.68:1, 0.7:1, 0.8:1, 1:1, 1.1:1, 1.5:1, 3:1, 5:1, 10:1, 15:1, or 20:1, or any two of the above values ​​as endpoints within a range.

[0087] Further, in step S30, the preparation step of the precursor liquid includes: mixing the polymer and inorganic dielectric particles in a solvent, and then preparing the precursor liquid after ultrasonic treatment and mechanical stirring.

[0088] Furthermore, the mass-to-volume ratio of the polymer to the solvent is (0.9~1.1):1. For example, the solvent includes, but is not limited to, toluene and n-hexane.

[0089] A second aspect of this application provides a radiation-cooling film prepared by the method of the first aspect of this application. See also Figure 5 and Figure 6 The radiation-cooling film 20 includes a substrate layer 210 and a pyramidal array structure 220 disposed on at least one surface of the substrate layer 210. The radiation-cooling film 20 includes a polymer 211 and inorganic dielectric particles 212 dispersed in the polymer 211.

[0090] In some examples, the radiation-cooling film 20 is a one-piece structure. A precursor liquid, including polymers and inorganic dielectric particles, is cured and demolded on a template containing an inverted pyramid array structure using surface imprinting technology. This allows the pyramid array structure in the template to be accurately replicated onto the surface of the radiation-cooling film 20, forming a one-piece structure.

[0091] In some examples, the distance between the centers of two adjacent pyramid structures in the pyramid array structure is 8 μm to 30 μm. This distance is greater than or equal to the base dimension of each pyramid structure. Further, the distance between the centers of two adjacent pyramid structures in the pyramid array structure is 8 μm to 22 μm. Even further, the distance between the centers of two adjacent pyramid structures in the pyramid array structure is 8 μm to 10 μm.

[0092] In some examples, the base dimension of each pyramid in the pyramid array structure is 8 μm to 22 μm. Further, the base dimension of each pyramid in the pyramid array structure is 8 μm to 10 μm. This application has found that a base dimension of 8 μm to 10 μm for the pyramid structure can produce an excellent spectral coupling effect with the mid-infrared band (8 μm to 14 μm) emitted by the target, enhancing the thermal radiation emission capability of the material and thus endowing the radiation-cooling film with excellent cooling effect.

[0093] In some examples, the ratio of the height of each pyramid to the base dimension of the pyramid array structure is 0.7 to 0.71. Further, due to the fixed crystal plane angle of silicon, the ratio of the height of each pyramid to the base dimension of the pyramid structure is 0.707.

[0094] In some of these examples, the polymer includes one or more of polydimethylsiloxane, polyvinylidene fluoride, and polymethyl methacrylate.

[0095] In some of these examples, the inorganic dielectric particles include one or more of titanium dioxide, silicon nitride, zirconium dioxide, yttrium oxide, hexagonal boron nitride, barium sulfate, aluminum oxide, and magnesium oxide.

[0096] In some of these examples, the D50 particle size of the inorganic dielectric particles is 100 nm to 10 μm.

[0097] In some of these examples, the mass ratio of polymer to inorganic dielectric particles is (0.4~20):1.

[0098] The radiation-cooling film 20 provided by this patent achieves dual modulation of the solar spectrum and thermal radiation spectrum through the synergistic interaction of polymers, inorganic dielectric particles, and a pyramidal array structure, resulting in a radiation-cooling film 20 with excellent cooling performance. Furthermore, the aforementioned radiation-cooling film 20 possesses excellent flexibility, allowing it to conform to surfaces of varying curvatures. It can be widely applied in various scenarios such as building energy conservation, transportation facilities, and thermal management of outdoor equipment, demonstrating strong adaptability to different applications.

[0099] A third aspect of this application provides the use of the radiative cooling film as described in any of the second aspects of this application in a passive radiative cooling device.

[0100] Alternatively, passive radiant cooling equipment may include, but is not limited to, building energy-saving equipment, outdoor equipment cooling equipment, or transportation facility thermal management equipment.

[0101] The following specific embodiments illustrate this application in detail. It should also be understood that the following embodiments are only for further explanation of this application and should not be construed as limiting the scope of protection of this application. Any non-essential improvements and adjustments made by those skilled in the art based on the above content of this application fall within the scope of protection of this application. The specific process parameters, etc., in the following embodiments are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the range based on the description herein, and are not necessarily limited to the specific values ​​in the embodiments below.

[0102] Example 1

[0103] Example 1 provides a radiation cooling film 20 and its preparation method.

[0104] See Figure 5 and Figure 6 The radiation-cooling film 20 comprises a polymer 211 (PDMS) and inorganic dielectric particles 212 (yttrium oxide, 1 μm in diameter) in a mass ratio of 2:3, with the inorganic dielectric particles 212 dispersed in the polymer 211. Structurally, the radiation-cooling film 20 includes a substrate layer 210 and a pyramid-shaped array structure 220 disposed on one surface of the substrate layer 210. The thickness of the substrate layer 210 is 500 μm. In the pyramid-shaped array structure, the distance between the centers of two adjacent pyramid structures is 8 μm, the base dimension of each pyramid structure is 8 μm, and the height of the pyramid structure is 5.656 μm.

[0105] The preparation steps of the radiation cooling film 20 are as follows:

[0106] (1) A femtosecond laser is used to pattern a single-crystal silicon substrate. The femtosecond laser has a center wavelength of 1030 nm, a pulse width of 236 fs, and a basic repetition frequency of 500 kHz. A quarter-wave plate is configured in the femtosecond laser optical path, and a circularly polarized femtosecond laser is used as the processing light source. The Burst pulse train mode in the laser is enabled, and a two-stage pulse train processing method is adopted. The single pulse is split into a pulse train containing 5 sub-pulses. The repetition frequency between the sub-pulses is 40 MHz. The sub-pulses are accumulated using the 500 kHz repetition frequency of the laser. Each processing site of the single-crystal silicon substrate is cumulatively processed by 20 sub-pulses. The pulse energy of each sub-pulse is 4.46 μJ. The center distance between two adjacent processing sites is set to 8 μm to prepare an intermediate with a groove array structure.

[0107] (2) The intermediate containing the groove array structure is immersed in the etching solution for wet etching to form an inverted pyramid array structure at the groove array structure, thus preparing a template containing the inverted pyramid array structure. The etching solution includes the following components by mass fraction: 3% hydroxide (potassium hydroxide), 43% organic solvent (methanol) and 54% water. The etching temperature is 65℃ and the etching time is 20min.

[0108] (3) The polymer (PDMS precursor and crosslinking agent, 40% by mass) and inorganic dielectric particles (yttrium oxide, 1 μm in diameter, 60% by mass) are mixed in a solvent (n-hexane). After ultrasonic treatment and mechanical stirring, a precursor liquid is prepared. The precursor liquid is solidified and molded on a template with an inverted pyramid array structure using surface imprinting technology and then demolded to prepare a radiation cooling film 20.

[0109] Example 2

[0110] Radiation cooling film 20: It is basically the same as that in Example 1, except that the radiation cooling film 20 in Example 2 includes polymer 211 (polydimethylsiloxane) and inorganic dielectric particles 212 (yttrium oxide, particle size 1 micrometer) in a mass ratio of 3:7, with the inorganic dielectric particles 212 dispersed in polymer 211.

[0111] The preparation steps of the radiation cooling film 20 are basically the same as those in Example 1, the main difference being that step (3) in Example 2 is different from that in Example 1. Step (3) in Example 2 is as follows:

[0112] (3) The polymer (30% by mass) and inorganic dielectric particles (1 μm by mass) were mixed in a solvent (n-hexane). After ultrasonic treatment and mechanical stirring, a precursor liquid was prepared. The precursor liquid was solidified and molded on a template with an inverted pyramid array structure using surface imprinting technology and then demolded to prepare a radiation cooling film 20.

[0113] Example 3

[0114] Radiation-cooling film 20: It is basically the same as that in Example 1, except that the radiation-cooling film 20 in Example 3 includes polymer 211 (polydimethylsiloxane) and inorganic dielectric particles 212 (hexagonal boron nitride with an average particle size of 1 micrometer) in a mass ratio of 1:1. The inorganic dielectric particles 212 are dispersed in polymer 211.

[0115] The preparation steps of the radiation cooling film 20 are basically the same as those in Example 1, the main difference being that step (3) in Example 3 is different from that in Example 1. Step (3) in Example 3 is as follows:

[0116] (3) The polymer (PDMS precursor and crosslinking agent, 50% by mass) and inorganic dielectric particles (hexagonal boron nitride, 1 μm in diameter, 50% by mass) are mixed in a solvent (n-hexane). After ultrasonic treatment and mechanical stirring, a precursor liquid is prepared. The precursor liquid is solidified and molded on a template with an inverted pyramid array structure using surface imprinting technology and then demolded to prepare a radiation cooling film 20.

[0117] Examples 4 to 7

[0118] Examples 4 to 7 provide a radiation cooling film 20 and its preparation method.

[0119] Radiation-cooling film 20: Same as in Example 1.

[0120] The preparation steps of the radiation cooling film 20 are basically the same as those in Example 1. The main difference is that in step (1) of Example 4, the single pulse is split into a pulse train containing one sub-pulse. In step (1) of Example 5, the single pulse is split into a pulse train containing two sub-pulses. In step (1) of Example 6, the single pulse is split into a pulse train containing three sub-pulses. In step (1) of Example 7, the single pulse is split into a pulse train containing four sub-pulses.

[0121] Examples 4-7 and Example 1 show the machining morphology of the grooves formed by splitting a single pulse into different numbers of sub-pulses under the first-level pulse modulation in Burst mode, as shown in the following figures. Figure 8As shown. Among them, Burst=1 corresponds to Example 4, Burst=2 corresponds to Example 5, Burst=3 corresponds to Example 6, Burst=4 corresponds to Example 7, and Burst=5 corresponds to Example 1.

[0122] Depend on Figure 8 As can be seen, Embodiments 4-7 and Embodiment 1 of this application introduce the Burst mode of a femtosecond laser. While maintaining a constant total energy for a single trigger, the original high-energy single pulse is split in the time domain into a pulse train containing 1-5 sub-pulses, with a repetition frequency of 40MHz between the sub-pulses. Through energy segmentation, the peak power of a single sub-pulse is reduced, making its intensity distribution closer to the material's damage threshold (e.g., ...). Figure 7 (As shown by the black dashed line in the middle). This soft ablation mechanism ensures material removal while minimizing excess energy used to generate a thermal effect, thereby significantly improving the sharpness of the aperture edge and suppressing the heat-affected zone. The radiation-cooling films prepared in Examples 4-7, similar to those in Example 1, all achieve good cooling effects.

[0123] Examples 8 to 11

[0124] Examples 8 to 11 provide a radiation cooling film 20 and its preparation method.

[0125] Radiation-cooling film 20: Same as in Example 1.

[0126] The preparation steps of the radiation cooling film 20 are basically the same as those in Example 1. The main difference is that in step (1) of Example 8, each processing site of the monocrystalline silicon substrate is subjected to a total of 5 sub-pulses. In step (1) of Example 9, each processing site of the monocrystalline silicon substrate is subjected to a total of 10 sub-pulses. In step (1) of Example 10, each processing site of the monocrystalline silicon substrate is subjected to a total of 15 sub-pulses. In step (1) of Example 11, each processing site of the monocrystalline silicon substrate is subjected to a total of 25 sub-pulses.

[0127] In Examples 8-10, Example 1, and Example 11, multi-pulse accumulation machining was performed using a laser with a repetition frequency of 500 kHz. The machining morphology of the grooves corresponding to different pulse numbers is shown in the figures below. Figure 9 As shown. By Figure 9 It is evident that by utilizing the high-frequency accumulation effect of low-energy subpulses, not only can surface quality be improved, but also micron-level precise control of microstructure depth can be achieved through pulse counting.

[0128] Example 12

[0129] Example 12 provides a method for preparing an intermediate template for comparison. Steps (1) and (2) of Example 12 are basically the same as those of Example 1, the main difference being that the polarization state of the femtosecond laser in step (1) of Example 12 is different from that in Example 1. Steps (1) and (2) of Example 12 are as follows:

[0130] (1) A femtosecond laser was used to pattern a single-crystal silicon substrate. A quarter-wave plate was not configured in the femtosecond laser optical path, and the linearly polarized femtosecond laser was used directly as the processing light source. All other processing parameters (wavelength, pulse width, repetition frequency, bi-stage pulse train mode and energy, etc.) were kept the same as in Example 1.

[0131] (2) The intermediate containing the groove array structure is immersed in the etching solution for wet etching treatment, with parameters consistent with those in Example 1.

[0132] Due to the significant anisotropy of femtosecond laser ablation, the near-field response induced by the linearly polarized laser in Example 12 caused the energy spatial distribution to partially lose its circular symmetry. Experiments revealed that some of the initial ablation holes created in this step were stretched along the polarization direction. After undergoing the anisotropic wet etching in step (2), this initial morphological defect was further amplified, ultimately leading to a partially asymmetrical distortion of the inverted pyramid structure formed on the single-crystal silicon surface.

[0133] At this point, the microstructure diagram of the inverted pyramid structure formed on the surface of the single crystal silicon in Example 12 is as follows: Figure 10 As shown. By Figure 10 It is evident that some of the inverted pyramid structures on the surface of single-crystal silicon exhibit defects such as asymmetry and irregularity, which results in a slightly inferior radiation cooling film compared to that of Example 1.

[0134] Therefore, the comparison between Example 1 and Example 12 verifies the necessity of using circularly polarized light in the embodiments of this application to ensure the high symmetry and roundness of the microstructure in all directions.

[0135] Example 13

[0136] Example 13 provides a method for preparing a radiation-cooling film for comparison. Example 13 is basically the same as Example 1, the main difference being that in step (1) of Example 13, the center-to-center distance between two adjacent processing sites (micropores) is set to 12 μm. This center-to-center distance is 8 μm higher than the base dimension of each pyramid structure.

[0137] The dense arrangement of microstructures on the surface of the radiation-cooling film in Example 1 maximizes the multiple scattering effect. In Example 13, because the set scanning interval (12 μm) is greater than the base dimension of each pyramid structure (8 μm), adjacent inverted pyramid structures in Example 13 were not fully connected after step (2). The scanning electron microscope image of the template containing the inverted pyramid array structure formed in Example 13 at this time is shown below. Figure 11 As shown in (b). A scanning electron microscope image of the template containing the inverted pyramid array structure formed in Example 1 is shown below. Figure 11 As shown in (a).

[0138] Depend on Figure 11 As can be seen, the template formed in Example 13 retains a wide and continuous planar platform area between the inverted pyramid units. The resulting radiation-cooling film will have a large number of flat areas on its surface, which will slightly weaken the material's light-trapping ability. Therefore, the cooling effect of the radiation-cooling film in Example 13 is slightly worse than that in Example 1.

[0139] Comparative Example 1

[0140] Comparative Example 1 provides a radiation cooling film and its preparation method.

[0141] The preparation steps of the radiation cooling film 20 are as follows:

[0142] (1) A femtosecond laser is used to pattern a single-crystal silicon substrate. The femtosecond laser has a center wavelength of 1030 nm, a pulse width of 236 fs, and a basic repetition frequency of 500 kHz. A quarter-wave plate is configured in the femtosecond laser optical path, and a circularly polarized femtosecond laser is used as the processing light source. The Burst pulse train mode in the laser is enabled, and a two-stage pulse train processing method is adopted to split a single pulse into a pulse train containing 5 sub-pulses. The repetition frequency between the sub-pulses is 40 MHz. The sub-pulses are accumulated using the laser's 500 kHz repetition frequency. Each processing site on the single-crystal silicon substrate is cumulatively processed by 20 sub-pulses. The pulse energy of each sub-pulse is 4.46 μJ. An intermediate with a groove array structure is prepared.

[0143] (2) The polymer (PDMS precursor and crosslinking agent, 40% by mass) and inorganic dielectric particles (yttrium oxide, 1 μm in diameter, 60% by mass) are mixed in a solvent (n-hexane). After ultrasonic treatment and mechanical stirring, a precursor liquid is prepared. The precursor liquid is solidified and molded on a template containing a groove array structure of intermediate body using surface imprinting technology and then demolded to prepare a radiation cooling film.

[0144] Comparative Example 2

[0145] Comparative Example 2 provides a method for preparing an intermediate template for comparison. The preparation steps of the intermediate template provided in Comparative Example 2 are basically the same as steps (1) and (2) of Example 1, the main difference being that the etching solution used in Comparative Example 2 is different from that in Example 1. Steps (1) and (2) of Comparative Example 2 are as follows:

[0146] (1) A single-crystal silicon substrate was patterned using a femtosecond laser to prepare an intermediate with a groove array structure (parameters are the same as in Example 1).

[0147] (2) The intermediate containing the groove array structure was immersed in the etching solution for wet etching. A 30% potassium hydroxide aqueous solution (without organic solvent) was used as the etching solution, the etching temperature was 65℃ and the etching time was 20min.

[0148] In Comparative Example 2, due to the use of high-concentration soda ash solution as the etching solution, severe over-etching occurred on the surface of the single-crystal silicon, preventing the formation of a regular inverted pyramid structure, and resulting in obvious distortion and damage at the edges. Furthermore, because the single-crystal silicon surface obtained by etching in step (2) was extremely irregular, it could not be used as a template for subsequent coating and imprinting of the precursor solution. Therefore, Comparative Example 2 could not produce a radiation-cooling film with a regular pyramidal array structure on its surface.

[0149] Figure 12 These are scanning electron microscope (SEM) images of the templates containing inverted pyramid array structures prepared in Embodiment 1 and Comparative Example 2 of this application. Image (a) is the SEM image of the template containing the inverted pyramid array structure prepared in Embodiment 1, and image (b) is the SEM image of the template containing the inverted pyramid array structure prepared in Comparative Example 2. Figure 12 As shown in Figure (b), Comparative Example 2 used a traditional 20%–40% high-concentration soda ash solution (without added organic solvents). Due to the excessively rapid etching rate and lack of selective adjustment for specific crystal planes, severe over-etching occurred in the femtosecond laser-induced region, resulting in damage and distortion at the edges of the pyramid structure. Because the etching result was extremely irregular, it could not be used as a template for subsequent polymer imprinting, thus failing to produce the corresponding radiation-cooling film for optical testing. In contrast, [the following text appears to be incomplete and requires further context: "by..."] Figure 12 As shown in Figure (a), this application uses a composite etching solution of low-concentration hydroxide and organic solvent (such as 2%~5% potassium hydroxide and 30%~50% methanol) to precisely control the etching of different crystal planes (especially...). <100> and <110> The etching rate ratio of the crystal plane allows the etching to proceed along the crystal plane. <111> The crystal planes terminated automatically and perfectly, resulting in a clearly defined and extremely regular inverted pyramid array template, which was a necessary prerequisite for the subsequent successful replication of a high-optical-performance radiation-cooling film.

[0150] Test: The spectral response of the radiation cooling film in the above embodiment was tested. In the field of radiation cooling, due to the different climate conditions in different regions, the cooling effect is generally not compared. Instead, the core optical indicators recognized in the field of radiation cooling can be used: reflectivity in the solar spectrum band (0.3~2.0 μm) and emissivity in the atmospheric window band (8~14 μm).

[0151] The testing standards / conditions were as follows: Reflectance in the solar spectral band (0.3–2.0 μm) was measured using a UV-Vis-NIR spectrophotometer (equipped with an integrating sphere); emissivity in the atmospheric window band (8–14 μm) was measured using a Fourier transform infrared spectrometer. Weighted average solar reflectance. Defined as: Where λ is the wavelength of light, in μm; I sun (λ) represents solar spectral irradiance, measured in W / m². -2 μm -1 , ρ sun (λ) represents the solar spectral reflectance.

[0152] Atmospheric window mean emissivity Defined as: Where λ is the wavelength of light, in μm; Emissivity in the long-wave infrared spectrum. Weighted average solar reflectivity. and average emissivity of atmospheric window The test values ​​are shown in Table 1.

[0153] Table 1

[0154]

[0155] As shown in Table 1, the radiation-cooling film provided in this application embodiment possesses both high solar weighted average reflectivity and atmospheric window average emissivity. A higher solar weighted average reflectivity means the radiation-cooling film has a stronger ability to reflect sunlight, absorbs less solar heat, and is more conducive to achieving radiation cooling. A higher atmospheric window average emissivity means the radiation-cooling film has a stronger infrared radiation capability, higher heat dissipation efficiency, and a more significant cooling effect.

[0156] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0157] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a radiation-cooling film, characterized in that, Includes the following steps: A femtosecond laser was used to pattern a single-crystal silicon substrate to prepare an intermediate with a groove array structure. An etching solution is used to etch the intermediate body containing the groove array structure to form an inverted pyramid array structure at the groove array structure, thereby preparing a template containing the inverted pyramid array structure; the etching solution comprises the following components by mass fraction: 2%~5% hydroxide, 30%~50% organic solvent and 45%~68% water; A precursor liquid comprising polymer and inorganic dielectric particles is applied to a template containing an inverted pyramid array structure, cured and demolded to prepare the radiation cooling film; the surface of the radiation cooling film has a pyramid array structure.

2. The method for preparing the radiation-cooling film according to claim 1, characterized in that, The steps for patterning a single-crystal silicon substrate using a femtosecond laser include: A femtosecond laser with a center wavelength of 950nm~1050nm, a pulse width of 230fs~240fs, and a fundamental repetition frequency of 480kHz~520kHz is selected. A quarter-wave plate is configured in the femtosecond laser optical path, and the circularly polarized femtosecond laser is used as the processing light source. A dual-stage pulse train processing method is adopted, in which a single pulse is split into a pulse train containing 1 to 5 sub-pulses. The repetition frequency between the sub-pulses is 35MHz to 45MHz. The sub-pulses are accumulated and processed using a laser with a repetition frequency of 480kHz to 520kHz. Each processing site on the single-crystal silicon substrate is cumulatively processed by 5 to 25 sub-pulses. The pulse energy of each sub-pulse is 3.64μJ to 60μJ, thus preparing the intermediate with the groove array structure.

3. The method for preparing the radiation-cooling film according to claim 1 or 2, characterized in that, The single-crystal silicon substrate is <100> Crystal-oriented silicon wafers; and / or, In the intermediate body containing the groove array structure, the size of the grooves in the groove array structure is 8μm~22μm.

4. The method for preparing the radiation-cooling film according to claim 1 or 2, characterized in that, The hydroxide includes one or more of potassium hydroxide and tetramethylammonium hydroxide.

5. The method for preparing the radiation-cooling film according to claim 1 or 2, characterized in that, The organic solvent includes one or more of methanol, ethanol, isopropanol, and acetone.

6. The method for preparing the radiation-cooling film according to claim 1 or 2, characterized in that, The polymer comprises one or more of polydimethylsiloxane, polyvinylidene fluoride, and polymethyl methacrylate; and / or, The inorganic dielectric particles include one or more of titanium dioxide, silicon nitride, zirconium dioxide, yttrium oxide, hexagonal boron nitride, barium sulfate, aluminum oxide, and magnesium oxide; and / or, The inorganic dielectric particles have a D50 particle size of 100 nm to 10 μm; and / or, The mass ratio of the polymer to the inorganic dielectric particles is (0.4~20):

1.

7. A radiation-cooling film prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The radiation-cooling film includes a substrate layer and a pyramid-shaped array structure disposed on at least one surface of the substrate layer. The radiation-cooling film includes a polymer and inorganic dielectric particles dispersed in the polymer.

8. The radiation-cooling film according to claim 7, characterized in that, The radiation cooling film is a one-piece molded structure; and / or, In the pyramid-shaped array structure, the distance between the centers of two adjacent pyramid structures is 8μm to 30μm, and this distance is greater than or equal to the base dimension of each pyramid structure; and / or, In the pyramid-shaped array structure, the base dimension of each pyramid structure is 8μm~22μm; and / or, In the pyramid-shaped array structure, the ratio of the height of each pyramid structure to the base dimension of the pyramid structure is 0.7 to 0.

71.

9. The radiation-cooling film according to claim 7 or 8, characterized in that, The polymer comprises one or more of polydimethylsiloxane, polyvinylidene fluoride, and polymethyl methacrylate; and / or, The inorganic dielectric particles include one or more of titanium dioxide, silicon nitride, zirconium dioxide, yttrium oxide, hexagonal boron nitride, barium sulfate, aluminum oxide, and magnesium oxide; and / or, The inorganic dielectric particles have a D50 particle size of 100 nm to 10 μm; and / or, The mass ratio of the polymer to the inorganic dielectric particles is (0.4~20):

1.

10. The application of the radiation cooling film as described in any one of claims 7 to 9 in a passive radiation cooling device.

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