Anti-reflection radiation cooling composite film and preparation and application thereof

Abstract

The invention discloses an anti-reflection radiation cooling composite film as well as preparation and application thereof. The composite film comprises a substrate layer and a microarray structure arranged on the substrate layer, a SiO2 layer is deposited on the microarray structure, a magnesium fluoride layer is deposited on the SiO2 layer, and the microarray structure is formed by arranging pyramid-shaped point units according to a rectangular dot matrix pattern. The method comprises the following steps of: preparing an inverted pyramid array structure on a silicon wafer substrate plated with silicon nitride by adopting technologies such as photoetching, dry etching and wet etching to form a concave die; a PDMS film with a positive pyramid array structure is formed by using a soft nanoimprint technology, and a silicon dioxide layer and a magnesium fluoride layer are sequentially deposited on the surface of the positive pyramid array structure, so that the anti-reflection radiation cooling composite film with excellent visible light transmission performance and radiation cooling performance and stable mechanical performance can be simply, conveniently and efficiently obtained. The method can be widely applied to photovoltaic power generation assemblies, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to a radiation-cooling composite film and its preparation method, and more particularly to an anti-reflective radiation-cooling composite film, its preparation and application. Background Technology

[0002] A solar cell module is a device that uses semiconductor materials to absorb solar energy and directly convert it into electrical energy through the photovoltaic effect. Currently, there are various types of solar cells, such as silicon-based solar cells, gallium arsenide solar cells, copper indium gallium selenide solar cells, perovskite solar cells, and organic solar cells. However, regardless of the type of solar cell, only a portion of the incident photons (corresponding to approximately 20% of solar energy) can be converted into electrical energy during operation. The remaining solar radiation is converted into waste heat, causing the temperature of the solar cell to rise. For example, when the operating temperature of a silicon-based solar cell increases by 1°C, its efficiency will decrease by 0.45%. At temperatures approaching 60°C, the efficiency of solar cells may drop to only 2-3%, significantly lower than their theoretical limit. Next-generation photovoltaic cells, perovskite solar cells, have even stricter temperature requirements; to rapidly commercialize them, it is necessary to find effective methods to reduce the operating temperature of solar cells.

[0003] Existing technologies have explored various methods for cooling solar cells, including air cooling, water spraying, water immersion, heat pipes, radiators, and secondary heat recovery to utilize waste heat generated by photovoltaic thermal systems. While these methods can cool solar cells to some extent, they either inevitably increase additional energy consumption or waste additional resources and pollute the environment, increasing the operating costs of photovoltaic power generation. Therefore, there is an urgent need to develop an environmentally friendly and energy-free method for cooling solar cells.

[0004] Passive radiative cooling can passively reduce the surface temperature of objects without consuming any energy. It transfers heat to the cold space through thermal radiation, constituting a truly eco-friendly and innovative cooling technology. Existing research has designed silicon photonic crystals for high-performance solar cells, cooling the solar cells via radiative cooling, and experimental results have demonstrated its ability to improve solar cell efficiency.

[0005] Ideally, a radiative cooler for cooling solar cells should transmit most visible light and radiate heat through an atmospheric window. However, existing radiative coolers cannot simultaneously achieve both high transmittance in the visible light band and high emissivity through the atmospheric window for radiative cooling. For example, Chinese patent CN111718584A discloses a radiative cooling film with 95% reflectivity in the solar band and 96% emissivity in the atmospheric window band, achieving a temperature up to 10°C lower than the surrounding environment under illumination. This demonstrates that to achieve high radiative cooling, the film must possess both high emissivity (i.e., high emissivity) and a visible light reflectivity as high as 95%. However, extremely high visible light reflectivity means that visible light cannot penetrate the film. When this film is applied to the surface of a solar cell, visible light cannot pass through and reach the solar cell, preventing the solar cell from converting light energy into electrical energy. Therefore, existing radiative cooling films cannot meet the application requirements of simultaneously achieving high visible light transmittance and high emissivity through the atmospheric window. Summary of the Invention

[0006] Objectives of this invention: The objective of this invention is to provide an anti-reflective radiation-cooling composite thin film, solving the problem of how to achieve both high visible light transmittance and high atmospheric emissivity in the composite thin film. A second objective is to propose a method for preparing the anti-reflective radiation-cooling composite thin film, addressing the problem of how to prepare such a film. A third objective is to propose an application of the anti-reflective radiation-cooling composite thin film in the fabrication of photovoltaic power generation modules, addressing the problem of how to improve the efficiency of solar cells.

[0007] Technical solution: The present invention provides an anti-reflective radiation cooling composite film, comprising a substrate layer and a microarray structure disposed on the substrate layer. A SiO2 layer is deposited on the microarray structure, and a magnesium fluoride layer is deposited on the SiO2 layer. The microarray structure is composed of pyramid-shaped dot units arranged in a rectangular dot matrix pattern.

[0008] Preferably, the base side length of the pyramid-shaped dot unit is 5-9 μm, and the period of the rectangular dot matrix pattern is 8-12 μm.

[0009] The second aspect of this invention discloses a method for preparing the above-mentioned anti-reflective radiation cooling composite thin film, comprising the following steps:

[0010] (1) A rectangular lattice structure is prepared by etching on a silicon wafer coated with silicon nitride to obtain a rectangular lattice structure substrate with silicon nitride as a mask.

[0011] (2) The second substrate is obtained by wet etching of the rectangular lattice structure substrate;

[0012] (3) The second substrate is etched by inductively coupled plasma to obtain the third substrate;

[0013] (4) The third substrate is subjected to oxygen plasma treatment, and then subjected to low surface energy treatment to obtain the concave mold;

[0014] (5) The imprinting adhesive is laid on the die, and a base film with a microarray structure is obtained by soft nanoimprinting.

[0015] (6) A SiO2 layer is deposited on the microarray structure of the base film to obtain the first composite film;

[0016] (7) Magnesium fluoride is deposited on the SiO2 layer of the first composite film to obtain an anti-reflective radiation cooling composite film.

[0017] Preferably, in step (1), the method for etching and preparing a rectangular lattice structure on a silicon wafer coated with silicon nitride is as follows:

[0018] S1. A silicon wafer coated with silicon nitride is processed using the HMDS process to obtain a pretreated silicon wafer substrate;

[0019] S2. Photoresist is coated on a pretreated silicon wafer substrate and then photolithography is performed to obtain a photolithographic substrate. The photolithographic substrate is then developed and cleaned in a developing solution to obtain a dry etched substrate.

[0020] S3. The dry etching substrate is etched using an inductively coupled plasma etching process, and then the photoresist is removed by cleaning to obtain a rectangular dot matrix structure substrate with silicon nitride as a mask.

[0021] In S1, the silicon nitride deposition process on the silicon wafer is low-pressure chemical vapor deposition, and the silicon nitride film thickness is 100±5 nm. The silicon substrate is preferably a p-doped n-type single-sided polished silicon wafer with a crystal orientation of [missing information]. <100> Resistivity 1-10 Ωcm -2 The thickness is 500±0.3μm.

[0022] In S2, the photoresist is a conventional positive photoresist, preferably S1813, to transfer the mask pattern onto the photoresist via ultraviolet exposure. The preferred method for coating the photoresist onto the pretreated silicon substrate is spin coating, with a photoresist volume of 2-4 mL; a spin coating speed of 3000-5000 rpm; a coating time of 55-65 s; and a coating thickness of 1.1-1.5 μm. The preferred pre-baking temperature after photoresist coating is 110-120℃, and the preferred pre-baking time is 50-70 s. The photomask period is 8-12 μm, with a rectangular structure of 5-9 μm sides, and the photolithography time is 1-2 s. The development and cleaning time is 45-50 s.

[0023] In this invention, when using inductively coupled plasma etching (ICP-C) to sequentially etch photoresist residue and silicon nitride on a dry-etched substrate, the unexposed photoresist on the silicon nitride surface serves as a mask. The gas used for etching the photoresist residue is a mixture of O2 and CHF3 with a volume ratio of 1:5-7, while the etching gas used for etching the silicon nitride is a mixture of O2 and CF4. This configuration facilitates thorough etching of each layer.

[0024] In S3, the method for cleaning and removing photoresist is as follows: reagent immersion and ultrasonic treatment. The photoresist is dissolved by reagent immersion, and ultrasonic treatment is used to promote the detachment of photoresist from the silicon nitride film surface. The immersion reagent can be at least one of acetone and N-methylpyrrolidone; the ultrasonic treatment time is 4-6 minutes; finally, in order to remove residual acetone on the substrate surface, the substrate is ultrasonically cleaned with deionized water, and this process is repeated three times.

[0025] Preferably, in step (2), the wet etching method is as follows: the rectangular lattice structure substrate with silicon nitride as a mask is immersed in a mixed solution of isopropanol, potassium hydroxide and water, and etched at 75-85°C for 20-180 min. The volume ratio of isopropanol to water in the mixed solution is 4-6:10-14, and the final concentration of potassium hydroxide is 10-15 mol / L.

[0026] In some embodiments, the volume ratio of isopropanol to water is preferably 5:12, the final concentration of potassium hydroxide is 12.6 mol / L, and the wet etching time is preferably 130-150 min.

[0027] Preferably, in step (3), the inductively coupled plasma etching method is as follows: using a mixture of O2 and CF4 gas with a volume ratio of 1:8-12 as the etching gas to etch and remove the silicon nitride layer on the second substrate.

[0028] Preferably, in step (4), the low surface energy treatment method is as follows: in a vacuum system, the third substrate after oxygen plasma treatment is treated with perfluoroalkylchlorosilane at 70-90°C for 5-10 hours.

[0029] In step (4), the third substrate is subjected to oxygen plasma treatment using an ICP-RIE etching apparatus. The oxygen flow rate is 9-11 sccm, the Bias RF Power is 35-45W, and the pretreatment time is 50-70s. Performing oxygen plasma treatment before low surface energy treatment can introduce hydroxyl groups on the surface of the third substrate, which facilitates the subsequent bonding of perfluoroalkyl chlorosilanes.

[0030] In some embodiments, the vacuum level of the vacuum system is 10 during low surface energy processing. -3Torr; the perfluoroalkylchlorosilane is 1H,1H,2H,2H-perfluorodecyltrichlorosilane; the low surface energy treatment temperature is 80-85℃; the low surface energy treatment time is 6-8h. These parameters are beneficial for the vaporization of perfluoroalkylchlorosilane and promote the bonding of perfluoroalkylchlorosilane vapor with hydroxyl groups on the third substrate surface after oxygen plasma treatment.

[0031] Preferably, in step (5), the soft nanoimprinting method is as follows:

[0032] The imprinting adhesive is evenly spread on the concave mold, and air bubbles are removed under vacuum for at least 1 hour. Then it is cured at 70-90℃ for 2-6 hours. After demolding, a base film with a microarray structure is obtained. The imprinting adhesive is made of at least one of polydimethylsiloxane, polytetrafluoroethylene, polyvinyl chloride, and acrylate.

[0033] In some embodiments, the imprinting adhesive is made of polydimethylsiloxane (PDMS), with a coating weight of 3.5 g; the coating thickness is 590-610 μm, more preferably 600 μm; and the vacuum degree under vacuum conditions is 10. -3 Torr is used to remove air bubbles from the imprinted adhesive layer and to smooth the adhesive layer. The time for removing air bubbles is 2 hours. The preferred curing temperature of the adhesive layer is 80°C, and the preferred curing time is 4 hours.

[0034] Preferably, in step (6), the method for depositing the SiO2 layer is as follows: after the substrate film with the microarray structure is pretreated with oxygen plasma, a SiO2 layer with a thickness of 50-100nm is deposited on the microarray structure of the substrate film by chemical vapor deposition at a rate of 0.1-1nm / s; the deposition temperature is 30-40℃.

[0035] In some embodiments, an oxygen plasma pretreatment is performed using an inductively coupled plasma etching process, with pure O2 as the etching gas, to form a base film with a thin oxide layer and a hydrophilic surface, so that silicon dioxide can be deposited more easily on its surface.

[0036] In step (7), the method for depositing magnesium fluoride is as follows: using magnetron sputtering deposition, magnesium fluoride with a thickness of 100-140 nm is deposited on the SiO2 layer surface of the first composite film at a rate of 0.1-0.7 nm / s to obtain an anti-reflective radiation cooling composite film.

[0037] The third aspect of this invention discloses the application of the above-mentioned anti-reflective radiation cooling composite film in the preparation of photovoltaic modules.

[0038] This invention uses polydimethylsiloxane (PDMS) as a soft nanoimprint substrate material because it has high transmittance in the visible light band and a refractive index of 1.4 (glass has a refractive index of 1.5, so PDMS has a certain anti-reflection effect). At the same time, it has high emissivity in the atmospheric window band and is easy to expand. It can play a certain role in anti-reflection radiation cooling for perovskite solar cells with glass substrates. Furthermore, by combining micro-nano processing technology with coating technology, a stable composite film with high transmittance in the visible light and high emissivity in the atmospheric window is prepared using a simple operation method and low cost. Moreover, this composite film is scalable and can be used for large-scale industrial production.

[0039] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0040] 1. This invention utilizes photolithography, dry etching, and wet etching techniques to fabricate an inverted pyramid array structure on a silicon wafer substrate with a silicon nitride thin film, forming a nanoimprint template. Then, using soft nanoimprinting technology, the inverted pyramid array structure on the nanoimprint template is copied onto a PDMS thin film to obtain a PDMS thin film with a positive pyramid array structure. Next, a silicon dioxide thin film is deposited on the surface of the PDMS thin film using plasma-enhanced chemical vapor deposition technology. Finally, magnesium fluoride is deposited onto the silicon dioxide surface using magnetron sputtering coating technology, thus obtaining a composite thin film with anti-reflective radiation cooling in a simple and efficient manner.

[0041] 2. This invention has the advantages of simple operation, low cost, scalability, and easy mass production, and has broad application prospects in photovoltaic power generation and energy-saving windows. Based on the method provided by this invention, the transmittance and emissivity of the composite thin film can be simply and efficiently controlled by process parameters such as wet etching time, plasma-enhanced chemical vapor deposition, and magnetron sputtering coating. The composite thin film prepared by this invention has a transmittance of up to 99.18% in the visible light band and an emissivity of 97.71% in the atmospheric window band, making it suitable for photovoltaic power generation devices. Attached Figure Description

[0042] Figure 1 This is a flowchart of the preparation method of the present invention;

[0043] Figure 2 SEM image of the anti-reflective radiation cooling composite film prepared in Example 1;

[0044] Figure 3 SEM image of the anti-reflective radiation cooling composite film prepared in Example 2;

[0045] Figure 4 SEM image of the anti-reflective radiation cooling composite film prepared in Example 3;

[0046] Figure 5 These are the test results of the visible light transmittance and atmospheric window emissivity of this invention;

[0047] Figure 6 The results are the performance test results of the composite films prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0048] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0049] Example 1: Figure 1 As shown, a method for preparing an anti-reflective radiation cooling composite thin film based on micro / nano fabrication is as follows:

[0050] (1) A rectangular lattice structure is prepared by etching on a silicon wafer coated with silicon nitride, as follows:

[0051] Silicon nitride films were prepared on silicon substrates using low-pressure chemical vapor deposition (LPCVD). The silicon nitride film thickness was 100 ± 5 nm. The silicon substrate was a p-doped n-type single-sided polished silicon wafer with the following crystal orientation: <100> Resistivity 1-10 Ωcm -2 The thickness is 500±0.3μm. Under vacuum conditions, the silicon wafer coated with silicon nitride is baked at 160℃ for 10min in a chamber; then hexamethyldisilazane (HMDS) vapor is introduced, and the substrate is held in the HMDS vapor atmosphere for 120s to allow the HMDS vapor to undergo a full silanization reaction on the hot substrate surface, thus obtaining the pretreated silicon wafer substrate;

[0052] 3 mL of S1813 photoresist was spin-coated onto a pretreated silicon wafer substrate at a spin speed of 4000 rpm for 60 s, resulting in a coating thickness of approximately 1.3-1.4 μm. The preferred pre-baking temperature after photoresist coating was 115 °C, and the preferred pre-baking time was 60 s. Photolithography was then performed on the photomask with a period of 10 μm and a structure of rectangular units with a side length of 5 μm. The photolithography time was 1.7 s. The mask pattern was transferred onto the photoresist by ultraviolet exposure to obtain a photolithographic substrate. The photolithographic substrate was then developed and cleaned in a developer for 47 s to obtain a dry-etched substrate.

[0053] Inductively coupled plasma etching (ICP-RIE) was used to etch photoresist residue from a dry-etched substrate. The process employed an ICP-RIE equipment with a 1:6 volume ratio of O2 to CHF3 as the etching gas. The gas flow rate was set to 14 sccm, the bias RF power to 40 W, and the pretreatment time to 60 s. The photoresist was then dissolved by immersion in acetone, followed by ultrasonic treatment at 90% power for 5 min to promote its detachment from the silicon nitride film surface. Finally, the substrate was ultrasonically cleaned with deionized water three times to remove residual acetone, resulting in a rectangular lattice structure substrate with silicon nitride as a mask.

[0054] (2) A rectangular lattice structure substrate with silicon nitride as a mask was immersed in a mixed solution of isopropanol, potassium hydroxide, and water, and etched at 80°C for 140 min to obtain a second substrate. The volume ratio of isopropanol to water in the mixed solution was 5:12, and the final concentration of potassium hydroxide was 12.6 mol / L.

[0055] (3) The second substrate is processed by inductively coupled plasma etching process. The etching gas is a mixture of O2 and CF4 with a volume ratio of 1:10. The other process parameters are the same as in step (1). The silicon nitride layer on the second substrate is removed by etching to obtain the third substrate.

[0056] (4) The third substrate was subjected to oxygen plasma treatment using an ICP-RIE etching system. The oxygen flow rate was 10 sccm, the bias RF power was 40 W, and the pretreatment time was 60 s. The oxygen plasma-treated third substrate was then placed under a vacuum of 10... -3 In Torr's vacuum system, a low surface energy treatment with 1H,1H,2H,2H-perfluorodecyltrichlorosilane at 80°C for 7 hours was used to obtain a concave mold.

[0057] (5) Spread 3.5g of polydimethylsiloxane (PDMS) evenly on the concave mold to a thickness of 600μm, and then apply it under a vacuum of 10. -3 The air bubbles were removed under vacuum for 2 hours, and then cured at 80°C for 4 hours. After demolding, a base film with a microarray structure was obtained.

[0058] (6) Oxygen plasma pretreatment of the substrate film with microarray structure was performed using inductively coupled plasma etching (ICP-RIE) equipment. The etching gas was pure O2, the oxygen flow rate was set to 15 sccm, the BiasRF Power was 40 W, and the pretreatment time was 60 s. After oxygen plasma pretreatment, a 75 nm thick SiO2 layer was deposited on the microarray structure of the substrate film at a rate of 0.5 nm / s using chemical vapor deposition at 35 °C to obtain the first composite film.

[0059] (7) Deposition of magnesium fluoride layer using magnetron sputtering coating machine: When the vacuum degree of the coating machine chamber reaches 10 -4 At Pa, the deposition process begins. A 120 nm thick layer of magnesium fluoride is deposited on the surface of the SiO2 layer of the first composite film at a rate of 0.4 nm / s, resulting in an anti-reflective radiation cooling composite film. Its SEM image is shown below. Figure 2 As shown. By Figure 2 It can be seen that a microarray structure composed of pyramid-shaped dot units arranged in a rectangular dot matrix pattern is formed on the PDMS substrate layer.

[0060] Example 2: A method for preparing an anti-reflective radiation cooling composite thin film based on micro / nano fabrication is as follows:

[0061] (1) A rectangular lattice structure is prepared by etching on a silicon wafer coated with silicon nitride, as follows:

[0062] The silicon wafer coated with silicon nitride was the same as in Example 1. Under vacuum conditions, the silicon wafer coated with silicon nitride was baked at 150°C for 5 minutes in a chamber; then hexamethyldisilazane (HMDS) vapor was introduced, and the substrate was kept in the HMDS vapor atmosphere for 120 seconds to obtain the pretreated silicon wafer substrate.

[0063] 2 mL of S1813 photoresist was spin-coated onto a pretreated silicon wafer substrate at a spin speed of 3000 rpm. The coating time was 55 s, and the coating thickness was 1.1-1.2 μm. The preferred pre-baking temperature of the substrate after photoresist coating was 110 °C, and the preferred pre-baking time was 50 s. Photolithography was then performed. The photomask had a period of 10 μm and a structure of rectangular units with a side length of 5 μm. The photolithography time was 1 s. The mask pattern was transferred onto the photoresist by ultraviolet exposure to obtain a photolithographic substrate. The photolithographic substrate was then developed and cleaned in a developer for 45 s to obtain a dry etched substrate.

[0064] The photoresist residue in the dry-etched substrate was etched using the same inductively coupled plasma etching process as in Example 1, with the etching gas being a mixture of O2 and CHF3 in a volume ratio of 1:6. The photoresist was then dissolved by immersion in N-methylpyrrolidone, and ultrasonic treatment for 4 minutes was used to promote its detachment from the silicon nitride film surface. Finally, the substrate was ultrasonically cleaned with deionized water, repeated three times, to remove residual N-methylpyrrolidone from the substrate surface, resulting in a rectangular lattice structure substrate with silicon nitride as a mask.

[0065] (2) A rectangular lattice structure substrate with silicon nitride as a mask was immersed in a mixed solution of isopropanol, potassium hydroxide, and water, and etched at 75°C for 20 min to obtain a second substrate. The volume ratio of isopropanol to water in the mixed solution was 4:10, and the final concentration of potassium hydroxide was 10 mol / L.

[0066] (3) The second substrate was etched using the same inductively coupled plasma process as in Example 1. The etching gas was a mixture of O2 and CF4 with a volume ratio of 1:8. The silicon nitride layer on the second substrate was removed by etching to obtain the third substrate.

[0067] (4) The third substrate was subjected to oxygen plasma treatment using an ICP-RIE etching system. The oxygen flow rate was 9 sccm, the Bias RF Power was 35 W, and the pretreatment time was 50 s. The oxygen plasma-treated third substrate was then placed under a vacuum of 10... -3 In Torr's vacuum system, a low surface energy treatment with 1H,1H,2H,2H-perfluorodecyltrichlorosilane at 85°C for 6 hours was used to obtain a concave mold.

[0068] (5) Spread 3.5g of polydimethylsiloxane (PDMS) evenly on the concave mold to a thickness of 590μm, and then apply it under a vacuum of 10. -3 The air bubbles were removed under vacuum for 2 hours, and then cured at 70°C for 6 hours. After demolding, a base film with a microarray structure was obtained.

[0069] (6) The substrate film with the microarray structure was pretreated with oxygen plasma using the same inductively coupled plasma etching process as in Example 1, and the etching gas was pure O2. Subsequently, a SiO2 layer with a thickness of 50 nm was deposited on the microarray structure of the substrate film at a rate of 0.1 nm / s using chemical vapor deposition at 30 °C to obtain the first composite film;

[0070] (7) Magnesium fluoride with a thickness of 100 nm was deposited on the SiO2 layer surface of the first composite film at a rate of 0.1 nm / s using magnetron sputtering to obtain an anti-reflective radiation cooling composite film. Its SEM image is shown below. Figure 3 As shown.

[0071] Example 3: A method for preparing an anti-reflective radiation cooling composite thin film based on micro / nano fabrication is as follows:

[0072] (1) A rectangular lattice structure is prepared by etching on a silicon wafer coated with silicon nitride, as follows:

[0073] The silicon wafer coated with silicon nitride was the same as in Example 1. Under vacuum conditions, the silicon wafer coated with silicon nitride was baked at 140°C for 6 minutes in a chamber; then hexamethyldisilazane (HMDS) vapor was introduced, and the substrate was kept in the HMDS vapor atmosphere for 80 seconds to obtain the pretreated silicon wafer substrate.

[0074] 4 mL of S1813 photoresist was spin-coated onto a pretreated silicon wafer substrate at a spin speed of 5000 rpm. The coating time was 65 s, and the coating thickness was approximately 1.4-1.5 μm. The preferred pre-baking temperature after photoresist coating was 120 °C, and the preferred pre-baking time was 70 s. Photolithography was then performed. The photomask had a period of 10 μm and a structure of rectangular units with a side length of 5 μm. The photolithography time was 2 s. The mask pattern was transferred onto the photoresist by ultraviolet exposure to obtain a photolithographic substrate. The photolithographic substrate was then developed and cleaned in a developer for 50 s to obtain a dry-etched substrate.

[0075] The photoresist residue in the dry-etched substrate was etched using the same inductively coupled plasma etching process as in Example 1, with the etching gas being a mixture of O2 and CHF3 in a volume ratio of 1:6. The photoresist was then dissolved by immersion in acetone, and ultrasonic treatment for 6 minutes was used to promote its detachment from the silicon nitride film surface. Finally, the substrate was ultrasonically cleaned with deionized water, repeated three times to remove residual acetone from the substrate surface, resulting in a rectangular lattice structure substrate with silicon nitride as a mask.

[0076] (2) A rectangular lattice structure substrate with silicon nitride as a mask was immersed in a mixed solution of isopropanol, potassium hydroxide, and water, and etched at 85°C for 80 min to obtain a second substrate. The volume ratio of isopropanol to water in the mixed solution was 6:14, and the final concentration of potassium hydroxide was 15 mol / L.

[0077] (3) The second substrate was etched using the same inductively coupled plasma process as in Example 1. The etching gas was a mixture of O2 and CF4 with a volume ratio of 1:12. The silicon nitride layer on the second substrate was removed by etching to obtain the third substrate.

[0078] (4) The third substrate was subjected to oxygen plasma treatment using an ICP-RIE etching system. The oxygen flow rate was 11 sccm, the bias RF power was 45 W, and the pretreatment time was 70 s. The oxygen plasma-treated third substrate was then placed under a vacuum of 10... -3 In Torr's vacuum system, a low surface energy treatment with 1H,1H,2H,2H-perfluorodecyltrichlorosilane at 83°C for 8 hours was used to obtain a concave mold.

[0079] (5) Spread 3.5g of polydimethylsiloxane (PDMS) evenly on the concave mold to a thickness of 610μm, and then apply it under a vacuum of 10. -3 The air bubbles were removed under vacuum for 1 hour, and then cured at 90°C for 2 hours. After demolding, a base film with a microarray structure was obtained.

[0080] (6) The substrate film with the microarray structure was pretreated with oxygen plasma using the same inductively coupled plasma etching process as in Example 1, and the etching gas was pure O2. Subsequently, a 100nm thick SiO2 layer was deposited on the microarray structure of the substrate film at a rate of 1nm / s using chemical vapor deposition at 40°C to obtain the first composite film;

[0081] (7) Magnesium fluoride with a thickness of 140 nm was deposited on the SiO2 layer surface of the first composite film at a rate of 0.7 nm / s using magnetron sputtering to obtain an anti-reflective radiation cooling composite film. Its SEM image is shown below. Figure 4 As shown.

[0082] Comparative Example 1: Everything else is the same as in Example 1, except that:

[0083] By replacing SiO2 with TiO2, a TiO2 layer is deposited.

[0084] Comparative Example 2: Everything else is the same as in Example 1, except that:

[0085] The photomask structure is a rectangular unit with a side length of 3μm, and the wet etching time is 15min.

[0086] Comparative Example 3: Everything else is the same as in Example 1, except that:

[0087] The photomask has a period of 13μm and a structure of rectangular units with a side length of 11μm. The wet etching time is 30min.

[0088] The performance of the anti-reflective radiation cooling composite films obtained in Examples 1-3 was tested, and the results are as follows: Figure 5 As shown, Figure 5 The left image shows the transmittance test results, and the right image shows the emissivity test results. Figure 5 In the figure, 5μm represents Example 2, 7μm represents Example 3, and 9μm represents Example 1. Figure 5 This invention demonstrates that it can achieve a transmittance of 99.18% in the visible light band and an emissivity of 97.71% in the atmospheric window band.

[0089] The composite films prepared in Example 1 and Comparative Example 1 were subjected to performance tests, and the results are as follows: Figure 6 As shown, Figure 6 The left image shows the transmittance test results, and the right image shows the emissivity test results. Figure 6 The results show that when the SiO2 layer is replaced with the TiO2 layer, the transmittance of the composite film in the visible light band is significantly reduced. Therefore, the improvement of the transmittance performance of the composite film depends on a specific non-metallic oxide layer.

[0090] The average light transmittance in the 400-700 nm wavelength range and the emissivity in the atmospheric window wavelength range of the composite films prepared in Example 1, Comparative Example 2, and Comparative Example 3 were tested, and the results are as follows:

[0091] Table 1. Test results of transmittance performance of different composite films in the visible light band.

[0092] Group Transmission rate (%) Emittance (%) Example 1 99.18 97.71 Comparative Example 2 88.12 93.49 Comparative Example 3 90.20 93.04

[0093] As shown in Table 1, the improved transmittance of the composite film also depends on the specific structural parameters of the pyramid-shaped dot units in the microarray structure. When the base side of the pyramid-shaped dot units is too long or too short, it will cause incorrect refraction or reflection of the incident visible light, which will lead to a significant reduction in the visible light transmittance of the composite film.

[0094] The nanoimprinting die prepared in this invention can be reused multiple times. The overall preparation method has the advantages of simple operation, low cost, and scalable production. The final anti-reflective radiation cooling composite film has stable mechanical properties, hydrophobicity, and wear resistance. It can be applied in photovoltaic devices such as perovskite solar cells and organic solar cells, as well as energy-saving windows, with broad application prospects.

[0095] This invention utilizes photolithography, dry etching, and wet etching techniques to fabricate an inverted pyramid array structure on a silicon wafer substrate coated with silicon nitride, forming a nanoimprint template. Then, using soft nanoimprinting technology, the inverted pyramid array structure on the nanoimprint template is replicated into a PDMS imprint adhesive layer, forming a PDMS film with a positive pyramid array structure. A layer of silicon dioxide is then deposited using plasma-enhanced chemical vapor deposition (PECVD), followed by a layer of magnesium fluoride deposition using magnetron sputtering. This simple and efficient method yields a high-performance, mechanically stable, anti-reflective radiation cooling composite film. The fabrication method provided by this invention offers advantages such as simple operation, low cost, scalability, and easy mass production. By controlling the process parameters, the performance of the composite film can be easily and efficiently controlled, showing broad application prospects in photovoltaic power generation and energy-saving windows.

Claims

1. A composite thin film for cooling under anti-reflective radiation, characterized in that, It includes a substrate layer and a microarray structure disposed on the substrate layer. A SiO2 layer is deposited on the microarray structure, and a magnesium fluoride layer is deposited on the SiO2 layer. The microarray structure is composed of pyramid-shaped point units arranged in a rectangular lattice pattern.

2. The anti-reflective radiation cooling composite film according to claim 1, characterized in that, The base side length of the pyramid-shaped dot unit is 5-9 μm, and the period of the rectangular dot matrix pattern is 8-12 μm.

3. The method for preparing the anti-reflective radiation cooling composite thin film according to claim 1, characterized in that, Includes the following steps: (1) A rectangular lattice structure is prepared by etching on a silicon wafer coated with silicon nitride to obtain a rectangular lattice structure substrate with silicon nitride as a mask. (2) The second substrate is obtained by wet etching of the rectangular lattice structure substrate; (3) The second substrate is etched by inductively coupled plasma to obtain the third substrate; (4) The third substrate is subjected to oxygen plasma treatment, and then subjected to low surface energy treatment to obtain the concave mold; (5) The imprinting adhesive is laid on the die, and a base film with a microarray structure is obtained by soft nanoimprinting. (6) A SiO2 layer is deposited on the microarray structure of the base film to obtain the first composite film; (7) Magnesium fluoride is deposited on the SiO2 layer of the first composite film to obtain an anti-reflective radiation cooling composite film.

4. The method for preparing the anti-reflective radiation cooling composite thin film according to claim 3, characterized in that, In step (1), the method for etching a rectangular lattice structure on a silicon wafer coated with silicon nitride is as follows: S1. A silicon wafer coated with silicon nitride is processed using the HMDS process to obtain a pretreated silicon wafer substrate; S2. Photoresist is coated on a pretreated silicon wafer substrate and then photolithography is performed to obtain a photolithographic substrate. The photolithographic substrate is then developed and cleaned in a developing solution to obtain a dry etched substrate. S3. The dry etching substrate is etched using an inductively coupled plasma etching process, and then the photoresist is removed by cleaning to obtain a rectangular dot matrix structure substrate with silicon nitride as a mask.

5. The method for preparing the anti-reflective radiation cooling composite thin film according to claim 3, characterized in that, In step (2), the wet etching method is as follows: A rectangular lattice structure substrate with silicon nitride as a mask is immersed in a mixed solution of isopropanol, potassium hydroxide and water, and etched at 75-85℃ for 20-180 min. The volume ratio of isopropanol to water in the mixed solution is 4-6:10-14, and the final concentration of potassium hydroxide is 10-15 mol / L.

6. The method for preparing the anti-reflective radiation cooling composite thin film according to claim 3, characterized in that, In step (3), the inductively coupled plasma etching method is as follows: A mixture of O2 and CF4 in a volume ratio of 1:8-12 was used as the etching gas to etch and remove the silicon nitride layer on the second substrate.

7. The method for preparing the anti-reflective radiation cooling composite thin film according to claim 3, characterized in that, In step (4), the method for treating low surface energy is as follows: In a vacuum system, the third substrate after oxygen plasma treatment is treated with perfluoroalkylchlorosilane for 5-10 hours at 70-90°C.

8. The method for preparing the anti-reflective radiation cooling composite thin film according to claim 3, characterized in that, In step (5), the soft nanoimprinting method is as follows: The imprinting adhesive is evenly spread on the concave mold, and air bubbles are removed under vacuum for at least 1 hour. Then it is cured at 70-90℃ for 2-6 hours. After demolding, a base film with a microarray structure is obtained. The imprinting adhesive is made of at least one of polydimethylsiloxane, polytetrafluoroethylene, polyvinyl chloride, and acrylate.

9. The method for preparing the anti-reflective radiation cooling composite thin film according to claim 3, characterized in that, In step (6), the method for depositing the SiO2 layer is as follows: after the substrate film with microarray structure is pretreated with oxygen plasma, a SiO2 layer with a thickness of 50-100nm is deposited on the microarray structure of the substrate film by chemical vapor deposition at a rate of 0.1-1nm / s. In step (7), the method for depositing magnesium fluoride is as follows: using magnetron sputtering deposition, magnesium fluoride with a thickness of 100-140 nm is deposited on the SiO2 layer surface of the first composite film at a rate of 0.1-0.7 nm / s to obtain an anti-reflective radiation cooling composite film.

10. The application of the anti-reflective radiation cooling composite thin film according to claim 1 or 2 in the preparation of photovoltaic modules.

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