A flexible solar cell front panel and its fabrication method

Abstract

This application discloses a flexible solar cell front panel and its fabrication method, comprising an outer weather-resistant film and an inner supporting base film, which are bonded together by an adhesive layer. The weather-resistant film has multiple equally spaced, parallel, isosceles triangular serrated stripes on both sides of its surface. A protective layer is formed on the surface of the serrated stripes by vacuum sputtering. The serrated stripes on both sides of the weather-resistant film are perpendicular to each other. The supporting base film includes a substrate layer, with an online coating layer on each side of the substrate layer. A barrier layer is sputtered to the outer side of the online coating layer. The weather-resistant film on the outer side of the front panel of this application, through the serrated stripes on its surface, increases the overall adhesion of the weather-resistant film and avoids the problem of easy delamination. The inner supporting base film provides support and protection as well as stronger barrier properties.

Description

Technical Field

[0001] This application belongs to the field of solar cell technology, and in particular relates to a flexible solar cell front panel and its preparation method. Background Technology

[0002] Flexible solar cells are a type of thin-film solar cell, boasting advanced technology, excellent performance, low cost, and wide applications. A key application area for flexible solar energy is building-integrated photovoltaics (BIPV), where they can be integrated into windows or roofs, exterior or interior walls. A typical solar photovoltaic module consists of a front panel, solar cells, encapsulation materials, and a backsheet. Solar photovoltaic modules are typically used outdoors, enduring wind, sun, rain, dust, and abrasion. Therefore, the performance requirements for the front panel, the light-receiving surface, are very high, necessitating high light transmittance, water resistance, UV resistance, and sufficient mechanical strength.

[0003] CN 108091715 A discloses a composite film for a solar cell front panel, comprising a support layer and a PVDF coating applied to the support layer. The PVDF coating is formed by spraying PVDF paint onto the surface of the support layer, and the support layer is made of transparent PMMA. CN 111391457 A discloses a front panel for a solar cell module, comprising several layers of sequentially stacked light-transmitting films, each of which is a fiber-reinforced thermoplastic composite film. The aforementioned layered front panels, in pursuit of light transmittance, primarily use PMMA substrates. After molding, the structure is fixed and difficult to bend, resulting in poor flexibility. The fixed structure of the solar cell front panel has limited sunlight utilization and cannot fully utilize oblique light. Furthermore, the anti-UV coating provided on the outermost side of the front panel in the aforementioned prior art is prone to peeling off, resulting in poor weather resistance.

[0004] CN 114447130 A discloses a high-transmittance flexible composite front panel and its preparation method. The high-transmittance flexible composite front panel includes a flexible front panel body, which is composed of a substrate layer, a frosted layer, and a moisture barrier layer. The substrate layer is a transparent modified ETFE film. The frosted layer is laminated to the air-facing surface of the substrate layer, and the moisture barrier layer is laminated to the air-repellent surface of the substrate layer. The substrate layer in this prior art uses a fluoroplastic film, which has poor water permeability and abrasion resistance, especially low surface energy, resulting in difficulties in lamination, weak adhesion, and easy delamination. Furthermore, due to the high market price of ETFE film, its use as a base support is costly, and its tendency to delaminate makes it a less than ideal choice.

[0005] CN 111933721 A discloses an anti-UV aging front panel for a flexible solar cell module. This prior art front panel actually protects the multi-layered coating structure on its surface, not the front panel itself. However, considering the high insulation requirements of flexible solar cells, multiple coating layers are insufficient to ensure the isolation of moisture and air. Moreover, the more coating layers there are, the weaker the bond between the layers becomes, making delamination more likely. Summary of the Invention

[0006] The technical problem to be solved by this application is to provide a flexible solar cell front panel and a method for its fabrication, so as to reduce or avoid the problems mentioned above.

[0007] To address the aforementioned technical problems, this application proposes a flexible solar cell front panel, comprising an outer weather-resistant film and an inner supporting base film, which are bonded together by an adhesive layer. The weather-resistant film is primarily composed of PVDF, and its two surfaces are formed with multiple equally spaced parallel serrated stripes of isosceles triangle cross-section. A protective layer is formed on the surface of the serrated stripes by vacuum sputtering. The serrated stripes on both sides of the weather-resistant film are perpendicular to each other. The supporting base film includes a substrate layer, with an online coating layer on each side. A barrier layer is sputtered onto the outer side of the online coating layer. The substrate layer includes an inner layer film facing the solar cell and an outer layer film away from the solar cell. The inner layer film has multiple equally spaced parallel inner prism structures of isosceles trapezoidal cross-section. A refractive layer is formed on the outer side of the inner prism structures by vacuum sputtering. The cavity between the outer layer film and the refractive layer is filled with the outer prism structure, and the outer layer film and the refractive layer are connected together by the outer prism structure.

[0008] Preferably, the base of the isosceles triangle of the sawtooth stripe has a length of 5-10 μm, a vertex angle of 45-135 degrees, a height of 5-10 μm, and a minimum gap between adjacent sawtooth stripes of 0-5 μm.

[0009] Preferably, the angle between the length direction of the serrated stripes and the four rectangular sides of the weather-resistant film is 45 degrees.

[0010] Preferably, the length of the lower base of the isosceles trapezoid of the cross-section of the inner prism structure is 20-30 μm, the lower base angle is 30-60 degrees, the height is 25-50 μm, and the minimum gap between adjacent inner prism structures is 50-100 μm.

[0011] Preferably, the online coating layer is formed by uniformly mixing acrylic resin, silica nanoparticles with a particle size of 5-10 nm, 1,4-dioxane, polyethylene oxide, and ethylene-vinyl acetate copolymer into a primer, and then curing it through online coating.

[0012] Preferably, the mass ratio of each component of the online coating layer (22) is 100: (10~15): (20~30): (10~15): (5~10).

[0013] In addition, this application also proposes a method for preparing a flexible solar cell front panel, including a weather-resistant film preparation step, a supporting base film preparation step, and a bonding step between the supporting base film and the weather-resistant film; wherein, the weather-resistant film preparation step includes: providing a PVDF film mainly composed of PVDF; forming multiple equally spaced parallel serrated stripes with isosceles triangle cross-sections on both sides of the PVDF film by hot pressing; and forming a protective layer on the serrated stripes by vacuum sputtering, thereby forming a weather-resistant film.

[0014] Preferably, the specific steps for forming the serrated stripes are as follows: using two rollers with patterns matching the shape of the serrated stripes placed vertically opposite each other, passing the heated PVDF film between the two rollers, and then air-cooling or water-cooling the PVDF film to obtain the cured serrated stripes on the PVDF film; the length directions of the patterns matching the shape of the serrated stripes on the surfaces of the two rollers placed vertically opposite each other are perpendicular to each other; the direction of the patterns on the surfaces of the two rollers forms a 45-degree angle with the direction of the PVDF film's movement.

[0015] Preferably, the preparation steps of the supporting base film include: using PET chips as raw materials for preparing PET film, obtaining a single-layer thick sheet through melt extrusion, preheating and longitudinally stretching into a film, then passing it through a coating machine to online coat a mixture of components constituting the online coating layer on one side of the film, followed by transverse stretching, shaping, cooling, and winding, thereby forming an online coating layer on the film surface, and then sputtering a barrier layer composed of silicon dioxide on the outside of the online coating layer, thereby obtaining an inner layer film and an outer layer film with an online coating layer and a barrier layer for later use; on the side of the inner layer film where the online coating layer and the barrier layer have not been formed, curing to form multiple equally spaced parallel cross-sections. An inner prism structure with an oval shape is formed; a refractive layer is formed on the inner prism structure by vacuum sputtering; ultraviolet-curable acrylic resin is filled in the recessed cavity on the outside of the refractive layer, and an outer film away from the solar cell is bonded to the outside of the refractive layer and the filled ultraviolet-curable acrylic resin; the side of the outer film that does not form the online coating layer and the barrier layer is bonded to the refractive layer; ultraviolet light is irradiated through the barrier layer side of the outer film to cure the filled ultraviolet-curable acrylic resin to form the outer prism structure; while the outer prism structure is curing, the outer film and the refractive layer are connected together through the outer prism structure to obtain the base film.

[0016] Preferably, the bonding step of the supporting base film and the weather-resistant film includes: bonding one side of the outer layer of the supporting base film to the weather-resistant film as a whole through an adhesive layer.

[0017] The weather-resistant film on the outer side of the front panel of this application increases its overall adhesion through the serrated stripes on its surface, avoiding the problem of easy delamination. The inner supporting base film provides support and protection as well as stronger barrier properties. The substrate layer of the supporting base film improves the utilization rate of sunlight by setting a refractive layer between the inner and outer prismatic structures. Attached Figure Description

[0018] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of this application.

[0019] Figure 1 The diagram shown is a cross-sectional schematic of the front panel of a flexible solar cell according to a specific embodiment of this application.

[0020] Figure 2 The diagram shown is a cross-sectional schematic of a weather-resistant film that can be used in the front panel of a flexible solar cell according to another specific embodiment of this application.

[0021] Figure 3 The diagram shown is a structural schematic of a weather-resistant film that can be used in the front panel of a flexible solar cell according to yet another specific embodiment of this application.

[0022] Figure 4 The diagram shown is a schematic representation of a specific structure of a support base film for a flexible solar cell front panel according to a specific embodiment of this application.

[0023] Figure 5 The diagram shown is a structural schematic of a support base film for a flexible solar cell front panel according to another specific embodiment of this application.

[0024] Figure 6 The diagram shown is an exploded perspective view of the substrate layer of a support base film for a flexible solar cell front panel according to yet another specific embodiment of this application. Detailed Implementation

[0025] To provide a clearer understanding of the technical features, objectives, and effects of this application, specific embodiments are now described with reference to the accompanying drawings. Identical components are denoted by the same reference numerals.

[0026] like Figure 1As shown, this application proposes a flexible solar cell front panel, including an outer weather-resistant film 100 and an inner supporting base film 200, which are bonded together by an adhesive layer 300. In a specific embodiment, the total thickness of the front panel is approximately 125-240 μm; the thickness of the weather-resistant film 100 is approximately 20-30 μm; the thickness of the supporting base film 200 is approximately 100-200 μm; and the thickness of the adhesive layer 300 is approximately 5-10 μm.

[0027] The main functions of the weather-resistant film 100 on the outermost side of the front panel are reinforcement, weather resistance, UV resistance, moisture protection, low dielectric constant, and high breakdown voltage. Preferably, a PVDF film with a thickness of 20-30μm can be used as the weather-resistant film 100. For example, a commercially available PVDF film with a thickness of 20-30μm can be used, or PVDF raw material particles with a mass content of greater than or equal to 90% can be used, with the addition of ultraviolet absorbers, wear-resistant fillers, etc., and formed by melt co-extrusion and biaxial stretching.

[0028] The support base film 200 is adjacent to the circuit side of the solar panel. In addition to providing stronger support and protection, it also needs to provide stronger barrier properties to protect the internal circuitry.

[0029] The adhesive layer 300 can be made of conventional EVA adhesive or UV-cured adhesive.

[0030] The following provides a more detailed description of a weather-resistant film for the front panel of a flexible solar cell according to this application.

[0031] For weather-resistant films 100, some existing weather-resistant films use PVDF (polyvinylidene fluoride) coatings, while others use fluoroplastic films. The main component of PVDF coatings is adhesive resin, and the PVDF content is limited, resulting in inferior weather resistance compared to weather-resistant films primarily composed of PVDF. However, PVDF weather-resistant films suffer from low surface energy and insufficient adhesion, leading to easy delamination. Furthermore, their outer surface is not wear-resistant and easily attracts dust.

[0032] In view of this, this application proposes a weather-resistant film 100 that can be used in the front panel of the flexible solar cell of this application, such as... Figure 2-3 As shown, the weather-resistant film 100 in this specific embodiment is preferably composed of PVDF as the main component, wherein the mass content of PVDF in the weather-resistant film is greater than or equal to 90%, and ultraviolet light absorbers, wear-resistant fillers, etc. can be added to improve its performance.

[0033] Furthermore, as shown in the figure, multiple equally spaced parallel sawtooth stripes 11 with cross-sections of isosceles triangles are formed on both sides of the weathering film 100. The sawtooth stripes on both sides of the weathering film 100 are identical. The size of the weathering film 100 shown in the figure has been enlarged for easier observation and understanding. The actual size of the sawtooth stripes is relatively small, with only very small, barely perceptible texture on the surface, and does not affect the overall light transmittance of the weathering film 100. In one specific embodiment, the maximum thickness of the weathering film 100 is 20-30 μm.

[0034] Existing PVDF weather-resistant films have low surface energy and insufficient adhesion, leading to a tendency to delaminate when bonded to the supporting base film 200 using adhesives. To overcome this problem, this application forms serrated stripes 11 on the surface of the weather-resistant film 100. The serrated stripes 11 increase the contact area with the adhesive layer 300. For example, when the apex angle of the isosceles trapezoid of the serrated stripes 11 is 60 degrees, the serrated stripes 11 can double the surface area, thereby increasing the overall adhesion of the weather-resistant film 100 and preventing the problem of easy delamination.

[0035] It should be noted that improving the overall adhesion of the weather-resistant film 100 actually only requires setting serrated stripes 11 on the inner side of the weather-resistant film 100. However, since the stripes are very small and difficult to observe, in order to facilitate assembly operations, the inventors chose to form the same serrated stripes 11 on both sides of the weather-resistant film 100 simultaneously, so that film coating operations can be performed on both sides, thereby increasing the applicability of the weather-resistant film. The inventors believed that the serrated stripes 11 originally located on the outer side did not seem to have any intended function. However, in actual laying experiments, it was found that if the scale of the serrated stripes 11 formed on the surface of the weather-resistant film 100 is smaller than a certain range, it can play a self-cleaning role, reducing the adhesion of dust to the surface of the weather-resistant film 100, and rainwater can easily wash away the attached dust. For example, in a specific embodiment, preferably, the isosceles triangle of the serrated stripe 11 has a base length of 5-10 μm, a vertex angle of 45-135 degrees, a height of 5-10 μm, and a minimum gap between adjacent serrated stripes 11 of 0-5 μm. Forming the same serrated stripes on both sides of the weather-resistant film 100 can not only reduce manufacturing costs, but also, by selecting serrated stripes within this size range, achieve better adhesion on the inner side and create excellent dust resistance on the outer side.

[0036] Furthermore, when the same sawtooth stripes 11 are formed on both sides, the sawtooth stripes 11 may reflect sunlight, reducing the utilization rate of the solar cells. For example, after flexible solar cells are integrated into a building, their orientation cannot be adjusted. When the sun's deflection angle is exactly perpendicular to one side of the sawtooth stripe 11 surface, some light will be reflected back by that surface. Of course, this can be avoided by adjusting the installation angle of the sawtooth stripes 11 during installation, but this requires very high installation standards and is difficult to implement in practice. To avoid the problem of reduced sunlight utilization due to improper installation angles on both sides of the sawtooth stripes 11, this application proposes a special design in which the sawtooth stripes 11 on both sides of the weather-resistant film 100 are set perpendicular to each other, thereby avoiding the problem of simultaneous reflection on both sides reducing sunlight utilization.

[0037] Furthermore, the serrated stripes 11 on the surface of the weather-resistant film 100 of this application can cause incident light to converge towards the center of the serrated stripes, allowing the tilt angle of the light to be deflected to a certain extent towards a direction as perpendicular as possible to the solar cell, thereby improving the utilization rate of sunlight in the tilted state. In addition, since the serrated stripes on both sides of the weather-resistant film are arranged perpendicularly to each other, they can play a certain role in correcting the direction of light in different directions, and can modulate the direction of light under different changes in solar altitude angle after installation.

[0038] Furthermore, to improve the adhesion of the weather-resistant film 100 and prevent delamination, this application selects the angle between the length direction of the serrated stripes 11 and the four rectangular sides of the weather-resistant film 100 to be 45 degrees, such as... Figure 3 As shown. Generally, solar panels are designed in a rectangular shape with four perpendicular sides. If the length direction of the sawtooth stripes 11 is perpendicular to one pair of rectangular sides of the weather-resistant film 100, then the other pair of rectangular sides will be parallel to the length direction of the sawtooth stripes 11. Since the stiffness of the sawtooth stripes 11 is different in the length and width directions, their expansion rates are also different, which can cause the pair of rectangular sides of the weather-resistant film 100 to warp and delaminate easily. In this application, the direction of the sawtooth stripes 11 is turned to form a 45-degree angle with the four rectangular sides. Therefore, the proportion of stiffness differences in different directions caused by the sawtooth stripes 11 spreading to the four rectangular sides will tend to be averaged, thus avoiding the delamination problem of the weather-resistant film 100 caused by the setting of the sawtooth stripes 11, and further improving the structural performance of the weather-resistant film 100.

[0039] To improve the weather-resistant membrane 100's ability to resist wind and sand erosion, in another specific embodiment of this application, a protective layer 12 is formed on the surface of the serrated stripes 11 on the surface of the weather-resistant membrane 100 by vacuum sputtering. Preferably, the protective layer 12 is made of silicon dioxide and has a thickness of 1-3 μm.

[0040] Examples 1-6

[0041] The weather-resistant film was prepared according to the parameters in the table below (the detailed preparation method will be explained in more detail below).

[0042]

[0043] In Examples 1-3, the angle between the serrated stripes and the rectangular side of the weather-resistant film is 45 degrees. In Examples 4-6, the angle between the serrated stripes and the rectangular side of the weather-resistant film is 0 / 90 degrees, that is, the angle between the serrated stripes and one pair of rectangular sides is 0 degrees, and the angle with the other pair of rectangular sides is 90 degrees.

[0044] Comparative Examples 1-6

[0045] Comparative Examples 1-6 used PVDF films without serrated stripes as weather-resistant films, with the following parameters:

[0046]

[0047] The weather-resistant films of Examples 1-6 and Comparative Examples 1-6 were respectively bonded to the surface of a 188μm PET support base film. The parameter performance of each example of the weather-resistant film was measured and compared as follows.

[0048]

[0049] As can be seen from the performance parameter comparison of the above embodiments, the weather-resistant film that can be used in the flexible solar cell front panel of this application can significantly improve the adhesion performance and avoid delamination when it has serrated stripes. At the same time, it can improve the light transmittance of tilted light, increase the contact angle of the outer surface, improve the self-cleaning ability, and have excellent dust adsorption resistance.

[0050] The supporting base film of the flexible solar cell front panel of this application will be described in further detail below.

[0051] like Figure 1 As shown, the supporting base film 200 can be made of PET film with a visible light transmittance greater than 85%, and can be a single-layer or multi-layer structure formed by biaxial stretching. PET film can provide excellent insulation, water resistance, mechanical properties, and dimensional stability. However, for solar cells, especially for mainstream CI(G)S flexible solar cells, their manufacturing process requires stronger barrier properties to protect the internal circuitry, thus placing high demands on the front panel, typically requiring a barrier property of 10. -3The g / m²·day level is a common approach to enhance barrier properties by increasing material thickness, which increases material cost, increases unit weight, and reduces material flexibility. Excessive thickness also leads to slippage and leakage when the edges of the substrate are bent. Current domestic encapsulation technologies struggle to achieve the required barrier properties. Even in Japan, with its advanced encapsulation technology, flexible solar cells have not yet reached mass production levels, resulting in high costs for commercially available flexible solar cells. Furthermore, their actual lifespan is slightly shorter than that of crystalline silicon solar cells due to limitations in the encapsulation process.

[0052] In view of this, Figure 4 In one specific embodiment of the support base film 200 shown, the support base film 200 includes a substrate layer 21, with an in-line coating layer 22 on each of its two side surfaces. A barrier layer 23 is sputtered to the outer side of the in-line coating layer 22. The thickness of the substrate layer 21 is approximately 100-200 μm, and it can be made of a single-layer 188 μm biaxially oriented PET film, or it can be made of a multilayer film composite (this will be described in further detail below). The barrier layer 23 is preferably made of silicon dioxide and has a thickness of 200 nm.

[0053] By setting the barrier layer 23, the barrier properties of the substrate layer 21 can be improved without increasing the thickness of the substrate layer 21, thus improving the adaptability of flexible solar cells. In order to improve the surface smoothness and enhance the adhesion of the barrier layer 23, it is preferable to perform an online coating process on both sides of the substrate layer 21 before sputtering to form the barrier layer 23, forming an online coating layer 22 with a preferred thickness of 0.1-0.3 μm on each side.

[0054] Online coating allows chemicals to be applied directly to the substrate layer 21 during the production process using an online coating machine. Online coating can be formed directly in the later stages of the substrate layer production process without the need to re-unroll the roll material. The coating is uniform, fast, efficient, and low-cost.

[0055] In one specific embodiment, the primer liquid constituting the online coating layer 22 can be applied to the thick sheet before or during the stretching of the polyester film constituting the substrate layer 21. Then, as the thick sheet is stretched into a film of the required thickness, the primer liquid coated on its surface becomes thinner as it is stretched, and is cured together with the high temperature during the stretching process to form the online coating layer 22.

[0056] In one specific embodiment, the online coating layer 22 is formed by uniformly mixing acrylic resin, silica nanoparticles with a particle size of 5-10 nm, 1,4-dioxane, polyethylene oxide, and ethylene-vinyl acetate copolymer into a primer, and then curing it through online coating.

[0057] Specifically, the mass ratio of each component in the online coating layer 22 is as follows: acrylic resin: silica nanoparticles: 1,4-dioxane: polyethylene oxide: ethylene-vinyl acetate copolymer = 100:(10~15):(20~30):(10~15):(5~10). The ethylene-vinyl acetate copolymer can be Evaflex 550 from Mitsui Chemicals, Inc. of Japan, containing 14% vinyl acetate polymer by mass.

[0058] According to the raw material weight ratio in the table below, online coating layers were prepared on both sides of a single-layer 188μm biaxially oriented PET film. Then, a barrier layer composed of silicon dioxide was sputtered onto the outside of the online coating layer.

[0059]

[0060] In comparison, a 200 nm thick barrier layer of silicon dioxide was sputtered onto each of the two surfaces of a single 188 μm biaxially oriented PET film as a comparative example. Measurements showed that the 180-degree peel strength (N / 25 mm) of the barrier layers in Examples 7-11 was increased by 34.5%, 36.2%, 35.1%, 34.8%, and 36.1% respectively compared to the comparative examples.

[0061] Furthermore, such as Figure 5 As described above, this application presents a schematic diagram of the structure of a supporting base film for a flexible solar cell front panel that can be used in this application, according to another specific embodiment. Figure 4 Similar to the illustrated embodiment, the support base film 200 in this embodiment also includes a substrate layer 21. Each of the two surfaces of the substrate layer 21 has an online coating layer 22, and a barrier layer 23 is sputtered onto the outer side of the online coating layer 22. Similar to... Figure 4 The difference between this embodiment and the previous one is that the substrate layer 21 is a multilayer thin film composite structure, while the remaining online coating layer 22 and barrier layer 23 can have the same structure and composition as in the previous embodiment. The following is a detailed description of the substrate layer 21 of the multilayer composite structure in this embodiment.

[0062] like Figure 5-6 As shown, the substrate layer 21 of this embodiment includes an inner layer film 1 facing the solar cell (not shown) and an outer layer film 2 away from the solar cell. The inner layer film 1 has a plurality of parallel inner prism structures 3 with equal intervals and isosceles trapezoidal cross sections. A refractive layer 4 is formed on the outside of the inner prism structure 3 by vacuum sputtering. The cavity between the outer layer film 2 and the refractive layer 4 is filled with an outer prism structure 5. The outer layer film 2 and the refractive layer 4 are connected as one unit through the outer prism structure 5.

[0063] The inner film 1 and the outer film 2 can be made of PET with a visible light transmittance greater than 85%. The double-layer PET film can provide excellent insulation, water resistance, mechanical properties, and dimensional stability. Two nested prismatic structures are formed between the inner film 1 and the outer film 2, and the two prismatic structures are separated by a sputtered refractive layer 4, which elongates the channel between the two prismatic structures and enhances water resistance and airtightness.

[0064] In one specific embodiment, the refractive indices of both the inner prism structure 3 and the outer prism structure 5 are lower than the refractive index of the refractive layer 4. For example, the refractive layer 4 can be composed of Nb₂O₅ with a refractive index of 2.01 to 2.48. The outer prism structure 5 can be made of UV-curable acrylic resin, with a preferred refractive index of 1.4-1.6 (a small amount of high-refractive-index particles can be added as needed to adjust the overall refractive index, such as 1%-5% lead fluoride nanoparticles). The inner prism structure 3 can be made of the same material as the outer prism structure 5, that is, it can be made of UV-curable acrylic resin, with a preferred refractive index of 1.4-1.6 (again, a small amount of high-refractive-index particles can be added as needed to adjust the overall refractive index, such as 1%-5% lead fluoride nanoparticles).

[0065] As mentioned earlier, since flexible solar cells can be integrated into windows, roofs, exterior walls, or interior walls, their orientation is fixed and cannot be adjusted once installed. Therefore, the efficiency of flexible solar cells is greatly affected by the direction of sunlight. Generally speaking, direct sunlight has the highest efficiency, but the duration is very short, and the direction of sunlight is tilted for a large part of the time. In this application, the substrate layer 21 is provided and formed with an inner prism structure and an outer prism structure, with a refractive layer between them. When light shines at an angle on the trapezoidal side of the prism structure, due to the difference in the angle of illumination and refractive index, the light entering the inner prism structure will converge towards the center of the prism structure. This allows the tilt angle of the light to be deflected to a certain extent towards a direction as perpendicular as possible to the solar cell, thereby improving the utilization rate of sunlight. In addition, for flexible solar cells laid on roofs, the prism structure with the stripes pointing north and south is more efficient, which can improve the utilization rate of east and west-facing light in the morning and evening. For flexible solar cells laid on vertical walls, the prism structure with the stripes pointing east and west is more efficient, which can improve the utilization rate of light that shines on the wall at an angle from the top during the strongest midday sunlight.

[0066] Regarding the prism structure and the aforementioned sawtooth stripe light-gathering principle, the inventors drew inspiration from the prism film technology used in backlight panels of liquid crystal displays (LCDs). Since the applicant's field has involved years of research and development in LCDs, the inventors were able to draw inspiration from the vastly different field of LCDs. However, this inspiration should not be considered obvious to those skilled in the art of solar cells, as the fields of solar cells and LCDs differ significantly. For example, in LCDs, light refraction only requires refraction from air into the prism; the refractive index difference between air and the prism is substantial, thus eliminating the need for an additional refractive layer. In the solar cell field of this application, however, considerations such as sealing and waterproofing are necessary, making it impossible to contain air in the substrate layer 21. Therefore, when applying the prism structure to solar cells, the material layers do not exhibit a significant difference in refractive index. Applying the prism film technology from LCD backlight panels to solar cells cannot directly achieve the light-gathering effect.

[0067] Furthermore, since the substrate layer 21 in the field of solar cells needs to be airtight, in the absence of air, it is necessary to consider using different interface materials to form a single unit, while also taking into account manufacturing costs. While using two prism structures with different refractive indices is feasible, considering light transmittance, it is difficult to find two materials with similar light transmittance but significantly different refractive indices. Moreover, significant differences in processing technology between two materials with significantly different properties can lead to substantial cost drawbacks, and the compatibility with specialized equipment must also be considered, making this impractical in real-world applications.

[0068] Therefore, the two-layer prism structure in this application can be made of materials with the same or similar properties. For example, it can be prepared using UV-cured acrylic resin commonly used in prism films for liquid crystal display backplanes. The processing technology for the two-layer prism structure is the same, and it can be formed using the same UV curing equipment. Moreover, the light transmittance and refractive index of the two layers are the same or similar, making it easy to select materials with a suitable refractive index range to prepare the refractive layer. In addition, it should be emphasized that since solar cells need to maintain a relatively high light transmittance, it is difficult to change the refractive index of the bulk material by adding a high-refractive-index material to the two-layer prism structure. This is because the increased difference between the refractive index of the added high-refractive-index material and the refractive index of the bulk material will cause refractive index mismatch defects, leading to a decrease in the light transmittance of the material.

[0069] In another improved embodiment, the inner prism structure 3 can be made of UV-curable acrylic resin with added UV-excited phosphor, preferably with a refractive index of 1.6-1.7 (a small amount of high-refractive-index microparticles can be added as needed to adjust the overall refractive index, such as 1%-5% lead fluoride nanoparticles). Preferably, the mass percentage of the UV-excited phosphor in the inner prism structure 3 is 3%~5%. In this embodiment, adding an appropriate amount of commercially available UV-excited phosphor can spectrally modulate the UV light focused into the inner prism structure, converting harmful UV light into longer-wavelength visible light, thereby achieving effective UV radiation protection and improved light utilization efficiency.

[0070] It should be noted that commonly used UV-excited phosphors on the market typically emit red light and are generally one or a mixture of silicate, aluminate, nitride, and fluoride phosphor materials. This application preferably uses UV-excited phosphor materials made of fluoride phosphors. The advantage is that the refractive index of fluoride phosphor materials is slightly higher than that of UV-curable acrylic resins. Therefore, with a small addition of 3%-5% (by mass), the light transmittance of the original prism structure prepared by UV-curable acrylic resin can be maintained. If the refractive index of the phosphor material differs significantly from that of the bulk material, the light transmittance in the visible light range will be weakened, which is detrimental to the light conversion of the solar cell. Furthermore, a small amount of high-refractive-index microparticles can be added as needed to adjust the overall refractive index, for example, adding 1%-5% (by mass) of lead fluoride nanoparticles.

[0071] This improved embodiment, by adding ultraviolet-excited phosphor to the inner prism structure 3, can further convert the ultraviolet light in the converged light into long-wavelength visible light usable by the solar panel, based on the light convergence of the prism structure. This can further improve light utilization and reduce the damage of ultraviolet light to the solar panel. Of course, adding ultraviolet-excited phosphor will reduce the overall light transmittance of the substrate layer 21. Therefore, it is not recommended to add ultraviolet-excited phosphor to the outer prism structure 5 as well. Since the ultraviolet-excited phosphor added to the inner prism structure 3 can convert the converged light, it can offset the impact on light transmittance to some extent. Therefore, this improved embodiment is a compromise solution, achieving a higher solar energy utilization rate at a lower cost, while effectively preventing ultraviolet light damage to the solar panel.

[0072] Examples 6-11

[0073] The substrate layer for preparing the support base film for the front panel of a flexible solar cell is prepared according to the parameters in the table below.

[0074]

[0075]

[0076] Comparative Examples 12-14

[0077] Comparative Examples 12-14 used a single-layer PET film as the substrate layer, with the following parameters:

[0078]

[0079] The parameter performance of each embodiment is compared as follows:

[0080]

[0081]

[0082] As can be seen from the performance parameter comparison of the above embodiments, the insulation, light transmittance, mechanical properties, ultraviolet light blocking properties, and dimensional stability of the substrate layer for the front panel of flexible solar cells in this application are significantly improved, while the ultraviolet light transmittance of the improved example with added phosphor is significantly reduced.

[0083] The method for fabricating the front panel of the flexible solar cell of this application will be further described in detail below with reference to the accompanying drawings.

[0084] As previously described, the flexible solar cell front panel of this application includes an outer weather-resistant film 100 and an inner supporting base film 200, which are bonded together by an adhesive layer 300. The weather-resistant film 100 is mainly composed of PVDF, and multiple equally spaced parallel serrated stripes 11 with isosceles triangular cross-sections are formed on both sides of the weather-resistant film 100. A protective layer 12 is formed on the surface of the serrated stripes 11 by vacuum sputtering, and the serrated stripes 11 on both sides of the weather-resistant film 100 are arranged perpendicularly to each other. The supporting base film 200 includes a substrate layer 21, and each side of the substrate layer 21 has an online coating layer 22. A barrier layer 23 is sputtered to the outside of the online coating layer 22. The substrate layer 21 includes an inner layer film 1 facing the solar cell and an outer layer film 2 away from the solar cell. The inner layer film 1 has multiple equally spaced, parallel inner prism structures 3 with isosceles trapezoidal cross-sections. A refractive layer 4 is formed on the outer side of the inner prism structures 3 by vacuum sputtering. The cavity between the outer layer film 2 and the refractive layer 4 is filled with an outer prism structure 5. The outer layer film 2 and the refractive layer 4 are connected as a single unit through the outer prism structure 5. To save costs and reduce processing steps, the preparation method of this application uses PET films of the same thickness as the inner layer film 1 and the outer layer film 2.

[0085] Furthermore, the preparation method of this application includes the steps of preparing the weather-resistant film 100, the preparation step of the supporting base film 200, and the bonding step of the supporting base film 200 and the weather-resistant film 100.

[0086] The preparation steps of the weather-resistant film 100 include:

[0087] First, a PVDF membrane mainly composed of PVDF is provided. This PVDF membrane can be a commercially available PVDF membrane with a thickness of 20-30μm, or it can be formed by melt co-extrusion and biaxial stretching of PVDF raw material particles with a mass content of ≥90%, with the addition of ultraviolet absorbers, wear-resistant fillers, etc.

[0088] Then, multiple equally spaced parallel serrated stripes 11 with isosceles triangular cross-sections are formed on both sides of the PVDF film by hot pressing. For example, two rollers with patterns matching the shape of the serrated stripes can be used, one above the other, to pass the heated PVDF film between the two rollers, and then the PVDF film is air-cooled or water-cooled to obtain the cured serrated stripes 11 on the PVDF film. The length directions of the patterns matching the shape of the serrated stripes on the surfaces of the two rollers are perpendicular to each other, thus forming mutually perpendicular serrated stripes 11 on both sides of the PVDF film. For example, if the pattern direction on the surfaces of the two rollers forms a 45-degree angle with the direction of the PVDF film's movement, serrated stripes 11 at a 45-degree angle to the four rectangular sides of the weather-resistant film can be formed.

[0089] Subsequently, a protective layer 12 is formed on the serrated stripes 11 by vacuum sputtering. For example, a silicon dioxide layer with a thickness of 1-3 μm can be formed on the serrated stripes 11 by vacuum sputtering. Since the thickness of the formed protective layer 12 is relatively very thin, Figure 3 The protective layer 12 is not shown in the text. Figure 2 The protective layer 12 in the image has also been enlarged for easier understanding.

[0090] The preparation steps of the supporting base film 200 include:

[0091] First, PET chips are used as the raw material for preparing PET film. A single-layer sheet is obtained through melt extrusion, preheated, and then longitudinally stretched into a film. After longitudinal stretching, a mixture of components constituting the online coating layer of this application is online coated on one side of the film using a coating machine. Then, the film is transversely stretched, shaped, cooled, and wound up, thereby forming an online coating layer 22 on the film surface. A barrier layer 23 composed of silicon dioxide is then sputtered to form on the outer side of the online coating layer 22, thus obtaining an inner layer film 1 and an outer layer film 2 with the online coating layer 22 and the barrier layer 23 for later use. The thickness of the inner layer film 1 and the outer layer film 2 is preferably 40-60 μm, and the visible light transmittance is 85%-95%.

[0092] Then, on the side of the inner film 1 where the online coating layer 22 and the barrier layer 23 are not formed, a plurality of equally spaced parallel inner prism structures 3 with isosceles trapezoidal cross-sections are cured to form. For example, a roller with a pattern matching the shape of the inner prism structure can be used. UV-curable acrylic resin is applied to the roller, and the inner film 1 is pressed and rolled along the roller surface, while the UV-curable acrylic resin is pressed onto the inner film 1 according to the shape of the inner prism structure. Then, the UV-curable acrylic resin is cured by irradiating with UV light, thereby forming the inner prism structure 3 of the desired shape on the inner film 1. The refractive index of the formed inner prism structure 3 is 1.4-1.6. Alternatively, in another embodiment, UV-curable acrylic resin with added UV-excited phosphor can be used to form the inner prism structure 3 using the same process, with a refractive index of 1.6-1.7. The length of the lower base of the isosceles trapezoidal cross section of the formed inner prism structure 3 is 20-30 μm, the lower base angle is 30-60 degrees, the height is 25-50 μm, and the minimum gap between adjacent inner prism structures 3 is 50-100 μm.

[0093] Subsequently, a refractive layer 4 is formed on the inner prism structure 3 by vacuum sputtering. For example, a layer of Nb₂O₅ with a thickness of 0.5-2 μm and a refractive index of 2.01-2.48 can be formed on the inner prism structure 3 by vacuum sputtering. Since the thickness of the formed refractive layer 4 is relatively very thin, Figure 4 The refractive layer 4 is not shown in the image. Figure 3The refractive layer 4 in the image has also been magnified for easier understanding. It should be noted that the refractive layer 4 primarily provides interface refraction, ensuring light transmittance while also providing a certain degree of isolation. Furthermore, because the inner prism structure 3 protrudes from the surface of the inner film 1 during sputtering, the thickness of the refractive layer 4 formed on the surface of the inner prism structure 3 is slightly thicker, while the refractive layer 4 formed on the surface of the inner film 1 located between the inner prism structures 3 is slightly thinner. This refractive layer 4 on the surface of the inner film 1 does not contribute to light convergence; it primarily serves an isolation function, and its 0.5-2 μm thickness does not affect light transmittance.

[0094] Next, UV-curable acrylic resin is filled into the recessed cavity on the outer side of the refractive layer 4. An outer film 2, located away from the solar cell, is then bonded to the outer side of the refractive layer 4 and the filled UV-curable acrylic resin. The side of the outer film 2 without the online coating layer 22 and the barrier layer 23 is bonded to the refractive layer 4. Preferably, while filling the recessed cavity on the outer side of the refractive layer 4 with UV-curable acrylic resin, the resin outside the top of the refractive layer 4 is scraped off with a scraper, making the filled UV-curable acrylic resin flush with the top of the refractive layer 4. This eliminates gaps and ensures a stronger bond between the bonded layers. Because the refractive layer 4 is relatively thin, the thickness of the filled UV-curable acrylic resin is almost equal to the thickness of the inner prism structure 3.

[0095] Then, ultraviolet light is irradiated through one side of the barrier layer 23 of the outer film 2 to cure the filled ultraviolet light curing acrylic resin to form the outer prism structure 5. While the outer prism structure 5 is curing, the outer film 2 and the refractive layer 4 are connected together through the outer prism structure 5 to obtain the support base film 200.

[0096] The bonding steps of the support base film 200 and the weather-resistant film 100 include: bonding one side of the outer layer 2 of the support base film 200 to the weather-resistant film 100 as a whole through the adhesive layer 300.

[0097] Those skilled in the art should understand that although this application is described by way of multiple embodiments, not every embodiment contains only one independent technical solution. This description is merely for clarity, and those skilled in the art should understand the specification as a whole and consider the technical solutions involved in each embodiment as being able to be combined with each other to form different embodiments to understand the scope of protection of this application.

[0098] The above description is merely an illustrative embodiment of this application and is not intended to limit the scope of this application. Any equivalent changes, modifications, and combinations made by those skilled in the art without departing from the concept and principles of this application shall fall within the scope of protection of this application.

Claims

1. A flexible solar cell front panel, comprising an outer weather-resistant film (100) and an inner supporting base film (200), wherein the weather-resistant film (100) and the supporting base film (200) are bonded together by an adhesive layer (300); characterized in that, The weather-resistant film (100) is mainly composed of PVDF. Multiple equally spaced, parallel serrated stripes (11) with isosceles triangular cross-sections are formed on both sides of the weather-resistant film (100). A protective layer (12) is formed on the surface of the serrated stripes (11) by vacuum sputtering. The serrated stripes (11) on both sides of the weather-resistant film (100) are arranged perpendicularly to each other. The supporting base film (200) includes a substrate layer (21). Each side of the substrate layer (21) has an online coating layer (22). A barrier layer (23) is sputtered onto the outer side of the online coating layer (22). The substrate layer (21)... The device includes an inner layer film (1) facing the solar cell and an outer layer film (2) away from the solar cell. Multiple inner prism structures (3) with isosceles trapezoidal cross sections are formed on the inner layer film (1) in parallel with equal intervals. A refractive layer (4) is formed on the outside of the inner prism structure (3) by vacuum sputtering. The cavity between the outer layer film (2) and the refractive layer (4) is filled with an outer prism structure (5). The outer layer film (2) and the refractive layer (4) are connected as one unit through the outer prism structure (5). The refractive indices of the inner prism structure (3) and the outer prism structure (5) are both less than the refractive index of the refractive layer (4).

2. The front panel as described in claim 1, characterized in that, The isosceles triangle of the sawtooth stripe (11) has a base length of 5-10 μm, a vertex angle of 45-135 degrees, a height of 5-10 μm, and a minimum gap between adjacent sawtooth stripes (11) of 0-5 μm.

3. The front panel as described in claim 1, characterized in that, The angle between the length direction of the serrated stripes (11) and the four rectangular sides of the weather-resistant film (100) is 45 degrees.

4. The front panel as described in claim 1, characterized in that, The length of the lower base of the isosceles trapezoid of the cross section of the inner prism structure (3) is 20-30 μm, the lower base angle is 30-60 degrees, the height is 25-50 μm, and the minimum gap between adjacent inner prism structures (3) is 50-100 μm.

5. The front panel as described in claim 1, characterized in that, The online coating layer (22) is formed by uniformly mixing acrylic resin, silica nanoparticles with a particle size of 5-10 nm, 1,4-dioxane, polyethylene oxide, and ethylene-vinyl acetate copolymer into a primer, and then curing it through online coating.

6. The front panel as described in claim 5, characterized in that, The mass ratio of each component of the online coating layer (22) is as follows: acrylic resin: silica nanoparticles: 1,4-dioxane: polyethylene oxide: ethylene-vinyl acetate copolymer is 100: (10~15): (20~30): (10~15): (5~10).

7. A method for preparing a flexible solar cell front panel as described in any one of claims 1-6, comprising a step of preparing a weather-resistant film (100), a step of preparing a supporting base film (200), and a step of bonding the supporting base film (200) and the weather-resistant film (100); wherein, The preparation steps of the weather-resistant film (100) include: Provide a PVDF membrane mainly composed of PVDF; Multiple equally spaced parallel sawtooth stripes with an isosceles triangle cross section are formed on both sides of the PVDF film by hot pressing (11). A protective layer (12) is formed on the serrated stripes (11) by vacuum sputtering, thereby forming a weather-resistant film (100).

8. The method as described in claim 7, characterized in that, The specific steps for forming the sawtooth stripes (11) are as follows: two rollers with patterns matching the shape of the sawtooth stripes (11) are placed vertically opposite each other. The heated PVDF film is passed between the two rollers, and then the PVDF film is cooled by air or water to obtain the cured sawtooth stripes (11) on the PVDF film. The length direction of the patterns matching the shape of the sawtooth stripes on the surfaces of the two rollers is perpendicular to each other. The pattern direction on the surfaces of the two rollers forms a 45-degree angle with the direction of the PVDF film's movement.

9. The method as described in claim 8, characterized in that, The preparation steps of the supporting base film (200) include: Using PET chips as raw material for preparing PET film, a single-layer thick sheet is obtained by melt extrusion. After preheating, it is stretched longitudinally into a film. After longitudinal stretching, a mixture of components constituting the online coating layer is coated on one side of the film by a coating machine. Then, it is stretched laterally, shaped, cooled, and wound up to form an online coating layer (22) on the surface of the film. Then, a barrier layer (23) composed of silicon dioxide is sputtered on the outside of the online coating layer (22) to obtain an inner film (1) and an outer film (2) with an online coating layer (22) and a barrier layer (23) for later use. On the side of the inner membrane (1) where the online coating layer (22) and the barrier layer (23) are not formed, multiple inner prism structures (3) with isosceles trapezoidal cross sections are cured and arranged in parallel at equal intervals. A refractive layer (4) is formed on the inner prism structure (3) by vacuum sputtering. The recessed cavity on the outside of the refractive layer (4) is filled with UV-curable acrylic resin, and an outer film (2) on the side away from the solar cell is attached to the outside of the refractive layer (4) and the filled UV-curable acrylic resin; wherein the outer film (2) is attached to the side of the refractive layer (4) where the online coating layer (22) and the barrier layer (23) are not formed. Ultraviolet light is irradiated through one side of the barrier layer (23) of the outer membrane (2) to cure the filled ultraviolet light curing acrylic resin to form an outer prism structure (5). While the outer prism structure (5) is curing, the outer membrane (2) and the refractive layer (4) are connected together through the outer prism structure (5) to prepare the base film (200).

10. The method as described in claim 8, characterized in that, The bonding steps of the support base film (200) and the weather-resistant film (100) include: bonding one side of the outer layer film (2) of the support base film (200) to the weather-resistant film (100) as a whole through the adhesive layer (300).

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