Multifunctional metasurface photovoltaic module cover plate and preparation method thereof

Abstract

This disclosure provides a multifunctional metasurface photovoltaic module cover plate and its preparation method, including the following steps: S1: micro-nano structure design; S2: photolithography substrate preparation; S3: structured mold preparation; S4: cover plate forming.

Description

Technical Field

[0001] This disclosure belongs to the field of solar cell fabrication technology, and relates to a multifunctional metasurface photovoltaic module cover plate and its fabrication method. Background Technology

[0002] Photovoltaic power generation, as a core component of renewable energy, plays a vital role in promoting the green transformation of the energy structure. The photovoltaic module cover, as a light-transmitting protective layer covering the surface of the battery cells, directly affects the power generation efficiency and service life of the photovoltaic system due to its optical performance, surface characteristics, and thermal management capabilities. Currently, photovoltaic module covers mainly use ultra-clear patterned glass, supplemented with anti-reflective coatings or hydrophobic coatings for surface modification. However, such covers face the following technical problems in practical applications: Firstly, there is the issue of light flux loss. Existing photovoltaic cover plates do not have a light-concentrating function. After incident sunlight is transmitted through the cover plate, it directly shines on the surface of the battery cell and cannot be effectively focused to the effective absorption area of ​​the cell. For photovoltaic cells with grid electrode shading and non-effective edge areas, a considerable portion of the incident light cannot be utilized by the light absorption layer, resulting in an inherent loss of light energy utilization.

[0003] Secondly, there is the issue of surface dust contamination. Photovoltaic modules operate outdoors for extended periods, causing atmospheric dust particles to gradually accumulate on the cover surface, forming a light scattering and absorption layer that significantly reduces light transmittance. Existing solutions primarily rely on periodic manual cleaning or the application of hydrophobic coatings. Manual cleaning is time-consuming, labor-intensive, and costly, while a single hydrophobic coating, although reducing dust adhesion, lacks passive self-cleaning capabilities and cannot effectively remove surface dust in light rain or dew.

[0004] Third, there is the issue of rising operating temperature. The photoelectric conversion efficiency of photovoltaic cells decreases as the temperature rises. Traditional cover materials have low emissivity in the mid-infrared band (especially in the atmospheric window of 8-13μm), making it difficult to effectively radiate the heat generated by the cell to the outer space. This results in the module operating temperature being higher than the ambient temperature, further exacerbating the efficiency loss.

[0005] In existing technologies, the solutions to the above problems are independent and conflict in terms of space and structure: optical concentrators (such as Fresnel lenses) are large in scale and difficult to integrate with the micro-nano structures on the cover plate surface; there are contradictions in material selection and film system design between radiative cooling coatings and anti-reflective coatings; and the micro-roughness required for hydrophobic self-cleaning is difficult to reconcile with the surface smoothness required for the concentrating structure. Due to these technical obstacles, no current technology can simultaneously achieve the synergistic integration of the three major functions of photovoltaic module cover plates: improved concentrating efficiency, self-cleaning, and radiative cooling, making it difficult to meet the comprehensive requirements of high-efficiency photovoltaic power generation systems for cover plate modules. Summary of the Invention

[0006] This disclosure provides a multifunctional metasurface photovoltaic module cover plate and its preparation method, which can effectively solve the above-mentioned problems.

[0007] This disclosure is implemented as follows: On the one hand, this disclosure provides a method for preparing a multifunctional metasurface photovoltaic module cover plate, including the following steps: S1: Micro-nano structure design: Based on the spectral response range and peak response range of solar cells, second-order zone plates are selected as the concentrating micro-nano structure; based on the materials of the photovoltaic module cover plate, hollow cylindrical arrays are selected as micro-nano structures that have both hydrophobic self-cleaning and radiative cooling functions. S2: Photolithography substrate fabrication: The designed micro-nano structure is processed by photolithography, and after development, a multifunctional metasurface photolithography substrate is obtained. S3: Structured mold preparation: The micro-nano structure of the photolithography substrate is transferred to the mold material to obtain the structured mold; S4: Cover plate forming: The micro-nano structure is transferred to the surface of the cover plate substrate through nanoimprinting process. After the transfer is completed, a hydrophobic nano-silica coating is applied to the surface and allowed to cure statically to obtain the multifunctional metasurface photovoltaic module cover plate. The second-order zone plate is disposed in the edge area of ​​the cover plate, and the hollow cylindrical array is disposed in the main surface area of ​​the cover plate. The second-order zone plate and the hollow cylindrical array do not overlap in the edge area.

[0008] On the other hand, this disclosure provides a multifunctional metasurface photovoltaic module cover plate, which is prepared using the above-described method for preparing a multifunctional metasurface photovoltaic module cover plate.

[0009] This disclosure provides a multifunctional metasurface photovoltaic module cover plate and its preparation method. By integrating a light-concentrating micro / nano structure and a self-cleaning / radiative cooling micro / nano structure on the same cover plate surface, the photovoltaic module can simultaneously achieve three major functions: light flux concentration, surface self-cleaning, and passive radiative cooling. This effectively improves the power generation efficiency of the photovoltaic module, reduces operation and maintenance costs, and extends the module's lifespan.

[0010] Compared with the prior art, this disclosure has the following beneficial effects: (1) By setting a second-order zone plate as a light-concentrating micro / nano structure in the edge region of the cover plate, the incident light can be effectively focused to the effective absorption region of the battery chip according to the spectral response characteristics of the solar cell. Experiments show that the output power of the GaAs battery using the cover plate disclosed in this invention can be increased by more than 10%, and the improvement is mainly reflected in the increase of short-circuit current density, proving that the light-concentrating structure can effectively improve the light utilization rate of the battery.

[0011] (2) Through the synergistic effect of hollow cylindrical array and hydrophobic nano SiO2 coating, the cover plate surface obtains superhydrophobic properties with a contact angle of 152°. Only a small amount of water (such as light rain or dew) is needed to effectively remove surface dust, greatly reducing the frequency of manual cleaning and maintenance costs.

[0012] (3) Through the micro-nano structure design of the hollow cylindrical array, the cover plate has a high mid-infrared emissivity in the 8-13 μm atmospheric window band, which can achieve passive radiation cooling. The measured cooling effect is better than that of ordinary glass cover plates, which is beneficial to improve photoelectric conversion efficiency and delay component aging.

[0013] (4) The light-concentrating structure, self-cleaning structure and radiation cooling structure are integrated on the same cover plate surface, without interfering with each other and working together, avoiding the compatibility problems of multiple independent solutions in space and structure in the existing technology. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a flowchart illustrating the fabrication process of the multifunctional metasurface structured mold in this embodiment of the present disclosure.

[0016] Figure 2 Image (a) is a scanning electron microscope image of the second-order zone plate structure in the multifunctional metasurface structured mold in the embodiments of this disclosure; Figure 2 Image (b) is a scanning electron microscope image of the hollow cylindrical array structure in the multifunctional metasurface structured mold in the embodiments of this disclosure.

[0017] Figure 3 This is a flowchart illustrating the fabrication process of a large-area multifunctional metasurface mold in an embodiment of this disclosure.

[0018] Figure 4 This is a photograph of the cover plate for the multifunctional metasurface photovoltaic module in the embodiments of this disclosure.

[0019] Figure 5 (a) is a scanning electron microscope image of the second-order zone plate structure in the cover plate of the multifunctional metasurface photovoltaic module, where (a1) is a local magnified view of the cross section, and (a2)-(a4) are local magnified views of different positions on the surface. Figure 5 (b) is a scanning electron microscope image of the cross-section of the hollow cylindrical array arranged at different heights in the cover plate of the multifunctional metasurface photovoltaic module.

[0020] Figure 6 This is a graph showing the relationship between the height of the hollow cylindrical array and the contact angle in an embodiment of this disclosure.

[0021] Figure 7 The diagram shows the test results of contact angle and roll angle of the hollow cylindrical array of equal height under different outer and inner diameter conditions in the embodiments of this disclosure.

[0022] Figure 8 The diagram shows the test results of contact angle and roll-off angle of hollow cylindrical arrays with different heights arranged in a cross pattern under different outer and inner diameter conditions in the embodiments of this disclosure.

[0023] Figure 9 This is a diagram showing the test results of the light-concentrating efficiency improvement performance of the cover plate of the multifunctional metasurface photovoltaic module in the embodiments of this disclosure.

[0024] Figure 10 This is a comparison chart of the self-cleaning performance test results of the multifunctional metasurface photovoltaic module cover plate and the ordinary glass cover plate in the embodiments of this disclosure.

[0025] Figure 11 This is a comparison chart of the 48-hour test results of the radiation cooling performance of the multifunctional metasurface photovoltaic module cover plate and the ordinary glass cover plate on the Topcon solar cells in the embodiments of this disclosure. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure. Therefore, the following detailed description of the embodiments of this disclosure provided in the accompanying drawings is not intended to limit the scope of the claimed disclosure, but merely represents selected embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0027] Example 1: Fabrication of a multifunctional metasurface photovoltaic module cover plate This embodiment provides a method for preparing a multifunctional metasurface photovoltaic module cover plate, including the following steps.

[0028] (1) Design of micro / nano structures for improving light concentration efficiency This embodiment utilizes the diffraction and focusing properties of a second-order zone plate (FZP) to design a focused micro / nano structure for enhanced light concentration. During the design process, parameters such as the focal length and focusing wavelength of the FZP must be determined to meet practical application requirements.

[0029] The spectral response range of mainstream commercial solar cells (such as GaAs and crystalline silicon cells) is 0.4-1.1 μm, with peak spectral response in the 0.8-0.9 μm band. This embodiment uses a second-order (phase-type) zone plate, whose theoretical diffraction efficiency can reach approximately 41%, ensuring high light concentration utilization while simplifying the processing technology. To match the peak response of the aforementioned cells and consider the processing accuracy and module thickness requirements of the laser direct-writing equipment, this embodiment designs the concentration wavelength... λ =0.8μm, focal length f =3mm second-order zone plate.

[0030] According to the diffraction principle of FZP, the distance from the focal point P to each half-wave zone is... According to the Pythagorean theorem, FZP is the first... n The outer ring radius of each band With focal length The following relationship must be satisfied: (1) The radius of each ring of the zone plate can be calculated by simplifying the equation by taking the square root on both sides. : (2) For example, λ =0.8μm, f Substituting 3mm into formula (2), the radius of the first ring, r1 ≈ 0.2mm, can be calculated, and the radii of subsequent rings can be deduced accordingly. Those skilled in the art can determine the specific location of each ring based on the above formula, without needing to list them one by one.

[0031] (2) Design of micro / nano structures with both hydrophobic self-cleaning and radiative cooling properties When designing micro / nanostructures that combine hydrophobic self-cleaning and radiative cooling, surface wettability and mid-infrared emissivity performance must be comprehensively considered. Based on wetting theory, the micro / nanostructure should place the droplet in a Cassie-Baxter composite wetting state to achieve a superhydrophobic self-cleaning effect. Simultaneously, the structural dimensions need to be optimized to enhance radiative cooling capacity in the 8-13 μm atmospheric window band. This disclosure uses a periodic height hollow cylinder array (PHHCA) as the core structure, with each unit being a hollow cylinder. By adjusting the height, outer diameter, and inner diameter parameters, hydrophobic performance and radiative cooling requirements are balanced. The array period (i.e., center-to-center distance) between adjacent hollow cylinders is set according to the outer diameter of the hollow cylinder. To ensure a stable Cassie-Baxter composite wetting state on the cover surface for a superhydrophobic self-cleaning effect, this disclosure does not fix a single value for the center-to-center distance but controls the net distance between the opposing sidewalls of adjacent hollow cylinders to be 2.8-3.2 μm. This net spacing, matched with the height of the hollow cylinder, effectively traps an air layer, keeping the droplets in a Cassie-Baxter state on the structure surface, thus achieving a superhydrophobic self-cleaning effect. In other words, as the outer diameter of the hollow cylinder changes, the array period (center distance) adaptively adjusts to always maintain the aforementioned net spacing within the range of 2.8-3.2 μm.

[0032] Experiments have verified that, under the same height, outer diameter / side length, and array period, the hydrophobic properties of solid cylindrical arrays and solid square column arrays are significantly lower than those of the hollow cylindrical array disclosed in this invention. In particular, the droplet roll-off angle on the surface of the hollow cylindrical array is significantly lower than that of the comparative arrays, making droplets more likely to roll off. While reducing the outer diameter and spacing of the aforementioned solid column structures to the nanometer scale (keeping the height and spacing-to-outer diameter ratio constant) achieves a hydrophobic effect comparable to that of the hollow cylindrical array disclosed in this invention, the resulting structural stability is significantly worsened. Therefore, the hollow cylindrical array of this invention can achieve superior hydrophobic performance under the same structural dimensions, or achieve higher structural stability and fabrication feasibility under the same hydrophobic performance conditions.

[0033] The multifunctional metasurface photovoltaic module cover plate disclosed herein adopts a partitioned, non-overlapping integrated design in its structural spatial layout: a second-order zone plate, as a light-concentrating micro / nano structure, is set in the edge region of the cover plate, with its focal point corresponding to the effective photosensitive area of ​​the photovoltaic cell chip below; a hollow cylindrical array, as a micro / nano structure with both self-cleaning and radiative cooling functions, covers the main surface area of ​​the cover plate (including the central area directly above the cell chip), and does not overlap with the second-order zone plate in the edge region. Specifically, as shown... Figure 4As shown, the second-order zone plate is located around the perimeter of the cover plate, forming a surrounding focusing structure; the hollow cylindrical array is located in the central region, forming a clear transition zone on the inner edge of the zone plate. This spatially separated layout ensures that the precise phase modulation of the incident light by the second-order zone plate is not interfered with by the surface roughness, and allows the hollow cylindrical array to fully utilize its superhydrophobic self-cleaning and mid-infrared radiation cooling effects in the main working area of ​​the battery chip. The focusing function of the second-order zone plate relies on the precise phase modulation of the incident light wavefront by its annular structure, which can effectively utilize the light energy around the battery chip, increasing power generation without increasing the battery chip area. The two structures have no overlapping parts and do not affect each other. This design achieves the coexistence and synergistic enhancement of three functions on the same cover plate through the coordinated arrangement of spatial partitioning and matching of feature dimensions: on the one hand, the spatial partitioning scheme, with the zone plate located at the edge and the hollow cylinder at the center, avoids the mutual occupation of planar positions by the two micro / nano structures; on the other hand, the zone plate rings (micrometer-level spacing) and the hollow cylinder (submicrometer-level outer diameter) are located at different spatial frequency scales, and there is no interference between them in terms of structural dimensions. Thus, the three functions of improving light concentration efficiency, self-cleaning, and radiative cooling can work collaboratively and independently on the same cover plate surface.

[0034] (3) Preparation of multifunctional metasurface molds The fabrication process of multifunctional metasurface structured molds is as follows: Figure 1 As shown. First, a micro / nano structure containing a second-order zone plate pattern and a hollow cylindrical array pattern is fabricated onto the substrate surface in a single step using a laser direct writing device. Then, the substrate is successively immersed in propylene glycol methyl ether acetate (PGMEA) for 20 min and cleaned in isopropanol (IPA) for 10 min to remove photoresist, resulting in a photolithographic substrate with both micro / nano structure relief patterns. Next, polydimethylsiloxane (PDMS) prepolymer and a curing agent (e.g., a commercially available PDMS-compatible curing agent) are thoroughly mixed at a weight ratio of 10:1 and allowed to stand for 2 h until all air bubbles are removed. The PDMS mixture is then drop-coated onto the surface of the photolithographic substrate and cured in an oven at 90°C for 2 h. After curing, the PDMS layer is manually peeled off from the surface of the photolithographic substrate to obtain a multifunctional metasurface structured mold (see [link to product description]). Figure 2 In some implementations, the cover plate corresponds to the size of a single photovoltaic cell chip.

[0035] like Figure 2As shown, a second-order zone plate is disposed on the edge region of the mold, and a hollow cylindrical array is disposed on the surface region of the mold. The two micro-nano structures are located in different spatial positions on the mold. This spatial layout corresponds to the actual structure of the photovoltaic module: the edge region of the mold where the second-order zone plate is located corresponds to the edge position around the cell chip in the photovoltaic module after the cover plate is packaged, and is used to focus the incident light onto the surface of the cell chip. In some embodiments, the edge region of the mold where the second-order zone plate is located corresponds spatially to the orthographic projection of the grid line shading area and the surrounding non-effective area of ​​the photovoltaic cell. The surface region of the mold where the hollow cylindrical array is located corresponds to the central region directly above the cell chip after the cover plate is packaged, and is used to form a superhydrophobic self-cleaning and radiative cooling functional layer on the surface of the cover plate. Thus, by setting two micro-nano structures in different regions of the mold, the corresponding functional structures can be simultaneously formed at the corresponding positions on the surface of the cover plate in a single nanoimprinting process, without the need for multiple overprinting or step-by-step processing.

[0036] This disclosure achieves simultaneous photolithography and nanoimprint transfer of two functional structures by designing the annular structure of a second-order zone plate and the subwavelength periodic structure of a hollow cylindrical array on the same photolithography pattern. This process route avoids the complex process of multiple overlay alignments, ensures that the integrity of the zone plate's phase distribution is not disrupted by random scattering structures, and realizes the process integration and functional synergy of three functions—focusing efficiency enhancement, self-cleaning, and radiative cooling—on a single cover plate.

[0037] When a large-area mold is required, a splicing process can be used to expand the aforementioned small-area mold to the required size. The process is as follows: Figure 3 As shown.

[0038] First, a clean glass substrate is prepared, and a small amount of UV-curable adhesive is dropped onto it. Then, a small-area structured PDMS mold is gently pressed onto the UV adhesive surface and cured under UV light for 2 minutes. After peeling off the PDMS mold, a UV adhesive substrate with micro / nano structures is obtained on the glass substrate. This process is repeated to prepare multiple UV adhesive substrates. Subsequently, multiple UV adhesive substrates are assembled and spliced ​​together in the same plane to form a large-area splicing mother plate. The surface of the splicing mother plate is subjected to silanization treatment (e.g., fumigation in a vacuum dryer with trimethylchlorosilane or perfluorodecyltrichlorosilane for 2-4 hours) to reduce surface energy and facilitate subsequent demolding. Finally, a mixture of PDMS prepolymer and curing agent is cast onto the silanized splicing mother plate surface and cured under the aforementioned curing conditions (90°C, 2 hours). After curing, the large-area PDMS layer is completely peeled off to obtain a large-area integrated multifunctional metasurface mold. The above splicing process allows small-area molds to be expanded to any required size (such as the standard size of photovoltaic modules), effectively solving the problem of limited processing area of ​​photolithography equipment and meeting the needs of industrial-scale manufacturing. Furthermore, due to the integral casting process, the micro-nano structures at the splicing seams transition continuously, without affecting the final performance of the cover plate.

[0039] (4) Fabrication of multifunctional metasurface photovoltaic module cover plate Epoxy resin and curing agent (e.g., commercially available epoxy resin-compatible curing agent) were thoroughly mixed at a weight ratio of 3:1 and allowed to stand for 30 minutes until all air bubbles in the epoxy resin disappeared. The epoxy resin was then drop-coated onto the center of a clean glass substrate. A multifunctional metasurface mold was then placed over the epoxy resin surface, and light pressure was applied to evenly spread the epoxy resin between the mold and the glass substrate. Excess epoxy resin was scraped off around the edges. After the epoxy resin had fully cured at room temperature, the multifunctional metasurface mold was peeled off. Subsequently, a commercially available hydrophobic nano-SiO2 coating was applied to the surface of the cured epoxy resin cover plate and allowed to stand for 24 hours to fully cure, ultimately yielding the multifunctional metasurface photovoltaic module cover plate (see [link to product description]). Figure 4 ).

[0040] Scanning electron microscope (SEM) images of the second-order zone plate structure in the cover plate of a multifunctional metasurface photovoltaic module, as shown below. Figure 5 As shown in (a), the SEM image of the hollow cylindrical array structure with periodic height is as follows: Figure 5 As shown in (b), at the microscale, the micro-nano structures on the surface of the multifunctional metasurface photovoltaic module cover plate are arranged regularly without any significant loss.

[0041] Example 2 (Preparation of a multifunctional metasurface photovoltaic module cover plate based on a nickel-based metal mold) To address the problem that polymer molds (such as PDMS molds) have limited mechanical strength and are easily damaged during repeated imprinting, this embodiment provides a preparation method that uses a nickel-based metal mold as an alternative.

[0042] (1) Preparation of nickel-based metal molds First, following the steps of Example 1, a micro-nano structure containing both a second-order zone plate pattern and a hollow cylindrical array pattern is fabricated on a substrate using a laser direct writing device. After development, a multifunctional metasurface photolithography substrate is obtained.

[0043] Subsequently, the photolithographic substrate was placed in a thermal evaporation apparatus to deposit a 100 nm thick nickel film on its surface, serving as a conductive seed layer for the subsequent electroforming process. The nickel-plated photolithographic substrate was used as the cathode, and a high-purity nickel target as the anode, both immersed in an electroforming solution containing nickel sulfate and nickel chloride for electroforming. After electroforming, the nickel layer was peeled off the surface of the photolithographic substrate, yielding a nickel-based metal mold with high mechanical strength.

[0044] (2) Replication of cover plate structure Epoxy resin and curing agent were thoroughly mixed at a weight ratio of 3:1 and allowed to stand for 30 minutes to remove air bubbles. The epoxy resin was then drop-coated onto the center of a clean glass substrate. A nickel-based metal mold was placed over the epoxy resin surface, and light pressure was applied to evenly spread the epoxy resin between the mold and the glass substrate. Excess resin overflowing from the edges was scraped off. After the epoxy resin had fully cured at room temperature, the nickel-based metal mold was peeled off, revealing an epoxy resin cover plate with a micro / nanostructure pattern on the glass substrate surface.

[0045] (3) Surface functionalization treatment Commercial hydrophobic nano-SiO2 coating was coated onto the surface of the cured epoxy resin cover plate and allowed to stand at room temperature for 24 hours to fully cure, ultimately yielding a multifunctional metasurface photovoltaic module cover plate.

[0046] Example 3 (Structural parameter design of hollow cylindrical array) This embodiment uses the method described in Embodiment 1 to prepare a multifunctional metasurface photovoltaic module cover plate, and optimizes the structural parameters of the hollow cylindrical array with periodic height in the cover plate to clarify the influence of each parameter on surface wettability and mid-infrared emissivity, providing a basis for obtaining the best comprehensive performance.

[0047] Height (H): The contact angle of a droplet on the cover plate surface was determined using the seated drop method on a contact angle measuring instrument. The test liquid was deionized water, the droplet volume was 5 μL, and the test was conducted at room temperature. Five different locations were measured for each sample, and the average value was taken.

[0048] Each set of cover plates used for testing employed an array of hollow cylinders of equal height. Each array had an outer diameter of 6 μm and an inner diameter of 3 μm, with a net distance of 3 μm between the opposing sidewalls of adjacent hollow cylinders (the center-to-center distance between adjacent hollow cylinders was 15 μm). For contact angle test results of the hollow cylindrical arrays at different heights, please refer to [reference needed]. Figure 6 As shown, when the height of the hollow cylinder is less than 9 μm, due to the low surface roughness, the droplet is easily in the Wenzel state on the surface of the structure, resulting in a low contact angle; when the height reaches 9 μm or more, the droplet transforms into the Cassie-Baxter state, and the contact angle stabilizes at around 145°.

[0049] Based on the experimental results above, the height was set to 9-19 μm. This height (~10 μm) is on the same order of magnitude as the mid-infrared wavelength, which can effectively enhance the emissivity in the 8-13 μm band, thereby achieving a radiative cooling effect.

[0050] Outer diameter (R) and inner diameter (r): The roll-off angle was measured using the same contact angle measuring instrument. During the test, the sample stage was slowly tilted, and the critical angle between the sample stage and the horizontal plane at the instant the droplet began to roll was recorded. The test liquid was deionized water, the droplet volume was 5 μL, and the test was conducted at room temperature. Five different locations were measured for each sample, and the average value was taken.

[0051] Group 1: Each group of cover plates used for testing employed an array of hollow cylinders of equal height, with each array having a height of 13 μm and a net distance of 3 μm between the opposing sidewalls of adjacent hollow cylinders. For the roll angle test results of the hollow cylinder arrays with different outer and inner diameters, please refer to [reference needed]. Figure 7 As shown.

[0052] The second group: Each group of cover plates used for testing consisted of hollow cylindrical arrays arranged in a staggered pattern at different heights. The height of each array was a combination of high hollow cylinders (H=15 μm) and low hollow cylinders (h=10 μm), with a net distance of 3 μm between the opposing sidewalls of adjacent hollow cylinders. For the roll angle test results of the hollow cylindrical arrays with different outer and inner diameters, please refer to [reference needed]. Figure 8 As shown.

[0053] from Figure 7 and 8 It can be seen that the dimensions of both the outer and inner diameters affect air capture capability, and the combination of the outer and inner diameters needs to be controlled to maintain the Cassie-Baxter configuration. From Figure 7 It can be seen that when the outer diameter is 6 μm, the droplet maintains the Cassie-Baxter state on the structure surface only when the inner diameter is 3 μm. When the inner diameter increases to 3.5 μm and 4 μm, the droplet transforms into the Wenzel state. From Figure 8 It can be seen that, compared with the array of hollow cylinders of equal height, the hollow cylinders of different heights arranged in a cross pattern introduce additional surface roughness on the basis of the original periodic array. Not only is the contact angle improved to a certain extent, reaching 152.1°, but the roll-off angle is also optimized more significantly, reaching 21.5°.

[0054] Example 4: Performance Testing of Multifunctional Metasurface Photovoltaic Module Cover Plate This embodiment tests the light-gathering efficiency, self-cleaning performance, and radiative cooling performance of the multifunctional metasurface photovoltaic module cover plate prepared using the method described in Embodiment 1. Specifically, the micro / nano structure of the multifunctional metasurface photovoltaic module cover plate is as follows: the light-gathering micro / nano structure uses a second-order zone plate with a light-gathering wavelength of λ=0.8 μm and a focal length of f=3 mm; the self-cleaning and radiative cooling micro / nano structure uses a hollow cylindrical array, which is composed of hollow cylinders of different heights arranged in a staggered pattern. The high hollow cylinders have a height H=15 μm, and the low hollow cylinders have a height h=10 μm. Each hollow cylinder has an outer diameter R=5 μm and an inner diameter r=3 μm. The net distance between the opposite sidewalls of adjacent hollow cylinders is 3 μm (the center distance between adjacent hollow cylinders is 13 μm).

[0055] (1) Testing of light concentration efficiency For areas of 25 mm 2 and 100 mm 2 For square GaAs solar cells, second-order zone plate concentrator arrays matching the effective area of ​​the cell were designed, and corresponding multifunctional metasurface photovoltaic module cover plates were fabricated. Specifically, for an effective area of ​​25 mm²... 2 For a GaAs cell with an effective area of ​​100, the diameter of the corresponding second-order zone plate concentrator array is 5 mm (denoted as 5 mm ESFZP); for a GaAs cell with an effective area of ​​100, the diameter of the corresponding second-order zone plate concentrator array is 10 mm (denoted as 10 mm ESFZP).

[0056] Under AM1.5G standard illumination conditions, JV tests were performed on two different sizes of square GaAs cells using the aforementioned cover plate. During the test, the center of the zone plate array on the cover plate was aligned with the center of the cell to ensure that the converging light spot completely covered the effective absorption area of ​​the cell. The test results are as follows: Figure 9 As shown. The multifunctional metasurface photovoltaic module cover plate allows for a 25 mm... 2 and 100 mm 2The output power of GaAs cells increased by 18.25% and 10.34%, respectively. Notably, the short-circuit current density of GaAs cells was significantly improved compared to the open-circuit voltage. This is because when light intensity increases, more photons are absorbed by the solar cell, generating more electron-hole pairs, which in turn increases the photocurrent.

[0057] (2) Self-cleaning performance test Please refer to Figure 10 The multifunctional metasurface photovoltaic module cover plate and a regular glass cover plate were placed at a 30° angle to simulate the actual installation conditions of the photovoltaic module, and their self-cleaning capabilities when covered with dust were tested. The regular glass cover plate and the cover plate in this embodiment used glass substrates of the same material and thickness. After uniformly sprinkling simulated dust on the cover plate surface, approximately 50 μL of water droplets were used to rinse the cover plate surface, and the dust removal was observed. The dust adhered firmly to the glass cover plate surface, but on the surface of the multifunctional metasurface photovoltaic module cover plate in this embodiment, the dust was quickly carried away by the passing water droplets. The contact angle of the cover plate surface with water reached 152°, while that of the glass cover plate was 49°. Compared to the glass cover plate, the cover plate in this embodiment only requires a small amount of water (such as light rain or dew) to effectively remove surface dust. Furthermore, since raindrops often carry a small amount of dust, when the surface moisture of the glass cover plate evaporates, the dust in the raindrops will adhere to its surface; in contrast, water droplets are unlikely to remain on the surface of the cover plate in this embodiment, effectively avoiding secondary pollution.

[0058] (3) Radiative cooling performance test Actual tests were conducted on a self-cooling photovoltaic module (SCPVM) consisting of Topcon solar cells and the aforementioned multifunctional metasurface photovoltaic module cover plate, a photovoltaic module (CSPVM) consisting of Topcon solar cells and a regular glass cover plate, and a Topcon cell without a cover plate. The 48-hour test results for SCPVM, CSPVM, and Topcon cells are as follows: Figure 11 As shown in the figure. The battery temperature is obtained in real time by thermocouple sensors attached to the surface of the photovoltaic module backsheet. The sensors are arranged at positions corresponding to the battery cells, and the temperature data is continuously recorded by a data acquisition device.

[0059] During clear days, the background radiation temperature is approximately -24°C to -30°C, and the solar irradiance is approximately 1064 W / m². 2 .

[0060] During the sunny period of the second day (from 10:00 AM to 2:00 PM), the glass cover reduced the battery temperature by 6.03°C, while the multifunctional metasurface photovoltaic module cover performed even better, achieving a temperature reduction of 8.19°C.

[0061] Comparing the test results during the two sunny days, compared to the Topcon cells without a cover, the cooling effect of both the cover plate and the glass cover plate on the multifunctional metasurface photovoltaic module remained stable without significant fluctuations. During the cloudy period of the second day (3 PM to 7 PM), the cooling effect of both was significantly weakened due to the decrease in atmospheric window transmittance caused by increased cloud cover. This trend indicates that the decrease in cell temperature is mainly attributed to the radiative cooling mechanism of the cover plate.

[0062] The above results indicate that the three functions can work collaboratively on the same cover plate surface without interfering with each other. Specifically, the focusing wavelength of the second-order zone plate... λ The 0.8 μm diameter matches the peak spectral response of commercial solar cells (0.8-0.9 μm), ensuring maximum concentration efficiency. The height of the hollow cylindrical array (~10 μm) matches the atmospheric window wavelength (8-13 μm), ensuring radiative cooling. Simultaneously, the annular structure of the second-order zone plate (annular spacing on the order of micrometers) and the outer diameter of the hollow cylindrical array (on the order of micrometers) are on the same scale, allowing them to coexist on the cover plate surface without structural conflict. Furthermore, concentration efficiency improvement experiments show that the hollow cylindrical array achieves superhydrophobic self-cleaning and radiative cooling of the cell temperature without substantially affecting the concentration performance of the second-order zone plate. This synergistic design solves the technical challenge of spatial and structural incompatibility of multiple functions in existing technologies.

[0063] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A method for preparing a multifunctional metasurface photovoltaic module cover plate, characterized in that, Includes the following steps: S1: Micro-nano structure design: Based on the spectral response range and peak response range of solar cells, a second-order zone plate is selected as the concentrating micro-nano structure; Based on the materials of the photovoltaic module cover plate, hollow cylindrical arrays were selected as micro-nano structures that combine hydrophobic self-cleaning and radiation cooling functions. S2: Photolithography substrate fabrication: The designed micro-nano structure is processed by photolithography, and after development, a multifunctional metasurface photolithography substrate is obtained. S3: Structured mold preparation: The micro-nano structure of the photolithography substrate is transferred to the mold material to obtain the structured mold; S4: Cover plate forming: The micro-nano structure is transferred to the surface of the cover plate substrate through nanoimprinting process. After the transfer is completed, a hydrophobic nano-silica coating is applied to the surface and allowed to cure statically to obtain the multifunctional metasurface photovoltaic module cover plate. The second-order zone plate is disposed in the edge area of ​​the cover plate, and the hollow cylindrical array is disposed in the main surface area of ​​the cover plate. The second-order zone plate and the hollow cylindrical array do not overlap in the edge area.

2. The method for preparing the multifunctional metasurface photovoltaic module cover plate according to claim 1, characterized in that, In step S1, the focusing wavelength of the second-order zone plate is 0.8 μm and the focal length is 3 mm.

3. The method for preparing the multifunctional metasurface photovoltaic module cover plate according to claim 1, characterized in that, In step S1, the height of the hollow cylinders in the hollow cylinder array is 9-19 μm; The hollow cylinder has an outer diameter of 5 μm and an inner diameter of 2-3 μm, or an outer diameter of 6 μm and an inner diameter of 3 μm. The net distance between the opposite sidewalls of adjacent hollow cylinders is 2.8-3.2 μm.

4. The method for preparing the multifunctional metasurface photovoltaic module cover plate according to claim 1, characterized in that, The hollow cylinder array is composed of hollow cylinders of different heights arranged in a cross pattern, including a first hollow cylinder with a height of 15 μm and a second hollow cylinder with a height of 10 μm; The hollow cylinder has an outer diameter of 5-7 μm and an inner diameter of 2-5 μm, and the difference between the outer diameter and the inner diameter is 2-3 μm. The net distance between the opposite sidewalls of adjacent hollow cylinders is 2.8-3.2 μm.

5. The method for preparing the multifunctional metasurface photovoltaic module cover plate according to claim 1, characterized in that, In step S4, the cover plate includes a glass substrate and an epoxy resin layer formed on the glass substrate.

6. The method according to claim 1, characterized in that, In step S3, the mold material is polydimethylsiloxane or UV-curable adhesive. The micro-nano structure is transferred to the mold material by nano-transfer printing to obtain a structured soft mold.

7. The method according to claim 1, characterized in that, In step S3, the mold material is a metal material. The micro-nano structure is transferred to the metal material by one or a combination of vapor deposition, electroplating or chemical plating to obtain a structured metal hard mold.

8. The method for preparing the multifunctional metasurface photovoltaic module cover plate according to claim 1, characterized in that, Between steps S3 and S4, there is also a large-area mold splicing step: multiple structured UV-curable adhesive molds are combined and spliced, and after silanization treatment, polydimethylsiloxane is used for casting and peeling to obtain a large-area multifunctional metasurface mold.

9. A multifunctional metasurface photovoltaic module cover plate, characterized in that, It is prepared by the method described in any one of claims 1-8.

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