A supporting substrate film for the front panel of a solar cell and its preparation method

Abstract

This application discloses a support base film for a solar cell front panel and its preparation method, including 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 with isosceles trapezoidal cross-sections. 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 as a single unit through the outer prism structure. By setting a refractive layer between the inner and outer prism structures, this application allows tilted light rays to converge towards the center of the prism structure through the trapezoidal edges, thus deflecting the tilt angle of the light rays to a direction as perpendicular as possible to the solar cell, thereby improving the utilization rate of sunlight.

Description

Technical Field

[0001] This application belongs to the field of solar cell technology, and in particular relates to a thin film substrate that can be used in solar cells, and especially to a support base film for the front panel of a solar cell and its preparation method. Background Technology

[0002] Solar energy, as an inexhaustible, safe, and pollution-free energy source, is widely used. Currently, widely used solar cells include crystalline silicon solar cells and thin-film solar cells. Flexible solar cells, a type of thin-film solar cell, are technologically advanced, have excellent performance, low cost, and wide applications. An important application area for flexible solar energy is building-integrated photovoltaics (BIPV), which can be integrated into windows or roofs, exterior walls or interior walls. To prevent damage and corrosion from moisture, ultraviolet radiation, and other environmental factors in practical applications, solar cells must be encapsulated and protected, forming photovoltaic modules. A photovoltaic module typically consists of a front panel, solar cells, encapsulation material, and a back panel. The solar cells are encapsulated between the front panel and the back panel using the encapsulation material.

[0003] CN 108091715 A discloses a composite film for a solar cell front panel, including 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 UV-resistant 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. Summary of the Invention

[0004] The technical problem to be solved by this application is to provide a supporting base film for the front panel of a solar cell and a method for preparing the same, so as to reduce or avoid the problems mentioned above.

[0005] To address the aforementioned technical problems, this application proposes a supporting base film for a solar cell front panel, comprising 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 with isosceles trapezoidal cross-sections. A refractive layer is formed on the outer side of the inner prism structures by vacuum sputtering. The recessed 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 as a single unit through the outer prism structure.

[0006] Preferably, the refractive indices of both the inner and outer prism structures are less than the refractive index of the refractive layer.

[0007] Preferably, the inner prism structure is made of UV-curable acrylic resin with added UV-excited phosphor.

[0008] Preferably, the refractive layer is composed of Nb2O5 with a refractive index of 2.01 to 2.48.

[0009] Preferably, the mass percentage of the ultraviolet-excited phosphor in the inner prism structure is 3% to 5%.

[0010] Preferably, the outer prism structure is made of UV-curable acrylic resin.

[0011] Preferably, the inner and outer membranes are made of PET with a visible light transmittance of greater than 85%.

[0012] Preferably, the refractive index of the inner prism structure is 1.6-1.7.

[0013] Preferably, the refractive index of the outer prism structure is 1.4-1.6.

[0014] In addition, this application also proposes a method for preparing a support base film for a solar cell front panel, comprising the following steps: providing an inner layer film facing the side of the solar cell; curing a plurality of equally spaced parallel inner prism structures with isosceles trapezoidal cross sections on the inner layer film; forming a refractive layer on the inner prism structure by vacuum sputtering; filling the recessed cavity outside the refractive layer with ultraviolet-curable acrylic resin, and attaching an outer layer film away from the solar cell to the outside of the refractive layer and the filled ultraviolet-curable acrylic resin; irradiating the outer layer film with ultraviolet light to cure the filled ultraviolet-curable acrylic resin to form an outer prism structure, wherein the outer layer film and the refractive layer are connected as one unit through the outer prism structure while the outer prism structure is curing.

[0015] This application, by setting a refractive layer between the inner and outer prism structures, allows tilted light rays to converge towards the center of the prism structure through the trapezoidal edges. This deflects the angle of the light rays to a direction as perpendicular as possible to the solar cell, thereby improving the utilization rate of sunlight. Furthermore, by adding ultraviolet-excited phosphors to the inner prism structure, the converged ultraviolet light can be converted into long-wavelength visible light, further enhancing the utilization rate of sunlight. Attached Figure Description

[0016] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of this application.

[0017] Figure 1 The diagram shown is a structural schematic of a support base film for a solar cell front panel according to a specific embodiment of this application.

[0018] Figure 2 The diagram shown is an exploded perspective view of a support base film for a solar cell front panel according to another specific embodiment of this application. Detailed Implementation

[0019] 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.

[0020] As described in the background section, a typical solar photovoltaic module consists of a front panel, solar cells, encapsulation materials, and a backsheet. The front panel of a typical crystalline silicon solar cell is made of transparent glass, resulting in a heavy structure that is difficult to maintain. An important application area for flexible solar cells is building-integrated photovoltaics (BIPV), where they can be integrated into windows or roofs, exterior or interior walls. Therefore, the front panel must be easy to install while possessing light transmittance and insulation properties similar to transparent glass front panels.

[0021] Front panels made of plastic composite materials are lightweight, impact-resistant, and highly flexible, and have gained a significant market share in high-end solar cells, especially flexible solar cells. However, for mainstream CI(G)S flexible solar cells, the manufacturing process requires stronger barrier properties to protect the internal circuitry, thus placing high demands on the front panel, back panel, and even encapsulation materials. Typically, a barrier property of 10 is required. -3 The 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.

[0022] The prior art CN 108091715 A cited in the background section describes a front panel with a multi-layer structure, in which a PMMA substrate serves as the supporting base film, covered by a PVDF coating. To achieve multiple functions such as water resistance, weather resistance, UV resistance, puncture resistance, and mechanical damage resistance, the front panel typically employs a multi-layered film structure, utilizing different structures to achieve different functions. The supporting base film, as the fundamental structural component of the front panel, needs to provide excellent insulation, water resistance, mechanical properties, and dimensional stability.

[0023] In view of this, such as Figure 1-2 As shown, this application proposes a support base film 10 for the front panel of a solar cell. Unlike traditional single-layer transparent support base films, the support base film 10 of this application includes an inner layer film 1 facing the solar cell (not shown in the figure) and an outer layer film 2 away from the solar cell. The inner layer film 1 has a plurality of equally spaced parallel inner prism structures 3 with an isosceles trapezoidal cross section. A refractive layer 4 is formed on the outside of the inner prism structure 3 by vacuum sputtering. The recessed 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.

[0024] 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.

[0025] 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, and its refractive index is preferably 1.4-1.6. 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, and its refractive index is preferably 1.4-1.6.

[0026] 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 the supporting base film of this application, an inner prism structure and an outer prism structure are set and formed, 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 in 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.

[0027] Regarding the principle of light-gathering using prism structures, 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 gain 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 two fields 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. However, in the field of solar cells, issues such as sealing and waterproofing must be considered, making it impossible to allow air within the supporting substrate. Therefore, when applying a 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.

[0028] Furthermore, since the supporting substrate film in solar cells needs to be airtight, different interface materials need to be integrated in the absence of air, while also considering manufacturing costs. While using two prism structures with different refractive indices is feasible, it's difficult to find two materials with similar transmittance and significantly different refractive indices, considering light transmittance. Moreover, significant differences in processing techniques between two materials with such different properties can lead to substantial cost drawbacks, and the need for specialized equipment compatibility further complicates matters, making this impractical in real-world applications.

[0029] 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.

[0030] 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. Preferably, the mass percentage of the UV-excited phosphor in the inner prism structure 3 is 3% to 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.

[0031] 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%, 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 solar cells.

[0032] 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 supporting base film. 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.

[0033] The method for preparing the supporting substrate film for the front panel of a solar cell according to this application is further described in detail below with reference to the accompanying drawings. Specifically, the preparation method of this application includes the following steps:

[0034] First, an inner layer film 1 is provided facing the side of the solar cell. This inner layer film 1 can be a 40-60 μm biaxially oriented PET film with a visible light transmittance of 85%-95%.

[0035] Then, multiple equally spaced, parallel inner prism structures 3 with isosceles trapezoidal cross-sections are cured on the inner film 1. 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 irradiation 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.

[0036] 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 2 The refractive layer 4 is not shown in the image. Figure 1The 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.

[0037] Next, UV-curable acrylic resin is filled into the recessed cavity on the outer side of the refractive layer 4, and an outer layer film 2, located away from the solar cell, is bonded to the outer side of the refractive layer 4 and the filled UV-curable acrylic resin. This outer layer film 2 can be a 40-60 μm biaxially oriented PET film with a visible light transmittance of 85%-95%. 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, thus eliminating gaps and ensuring a stronger bond between the bonded layers. Because the thickness of the refractive layer 4 is relatively very thin, the thickness of the filled UV-curable acrylic resin is almost equal to the thickness of the inner prism structure 3.

[0038] Finally, ultraviolet light is irradiated through 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 as one unit through the outer prism structure 5.

[0039] Examples 1-6

[0040] The supporting base film for the front panel of a solar cell is prepared according to the parameters in the table below.

[0041]

[0042]

[0043]

[0044] Comparative Examples 7-9

[0045] Comparative Examples 7-9 used a single-layer PET film as the supporting base film, with the following parameters.

[0046]

[0047] The parameter performance of each embodiment is compared as follows.

[0048]

[0049]

[0050] 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 supporting base film for the front panel of solar cells in this application are significantly improved, while the ultraviolet light transmittance of the improved example with added phosphor is significantly reduced.

[0051] 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.

[0052] 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 support base film for a front sheet of a solar cell, comprising an inner layer film (1) on a side facing a solar cell piece and an outer layer film (2) on a side away from the solar cell piece, characterized in that, The inner layer film (1) is provided with a plurality of inner layer prism structures (3) with isosceles trapezoidal cross section arranged in parallel at equal intervals, a refractive layer (4) is formed on the outer side of the inner layer prism structures (3) by vacuum sputtering, the recessed cavities between the outer layer film (2) and the refractive layer (4) are filled with outer layer prism structures (5), and the outer layer film (2) and the refractive layer (4) are connected into an integrated whole through the outer layer prism structures (5); the refractive indexes of the inner layer prism structures (3) and the outer layer prism structures (5) are all less than the refractive index of the refractive layer (4).

2. The support base film according to claim 1, wherein The inner layer prism structures (3) are made of ultraviolet light curing acrylic resin added with ultraviolet light excited fluorescent powder.

3. The support base film according to claim 1, wherein The refractive layer (4) is composed of Nb2O5 with a refractive index of 2.01-2.

48.

4. The support base film according to claim 2, wherein The mass percentage of the ultraviolet light excited fluorescent powder in the inner layer prism structures (3) is 3%-5%.

5. The support base film according to claim 1, wherein The outer layer prism structures (5) are made of ultraviolet light curing acrylic resin.

6. The support base film according to claim 1, wherein The inner layer film (1) and the outer layer film (2) are made of PET with visible light transmittance greater than 85%.

7. The support base film according to claim 1, wherein The refractive index of the inner layer prism structures (3) is 1.6-1.

7.

8. The support base film according to claim 1, wherein The refractive index of the outer layer prism structures (5) is 1.4-1.

6.

9. A method for preparing a support base film for a front plate of a solar cell according to any one of claims 1-8, comprising the following steps: providing an inner layer film (1) facing one side of a solar cell piece; solidifying a plurality of inner layer prism structures (3) with isosceles trapezoidal cross section arranged in parallel at equal intervals on the inner layer film (1); forming a refractive layer (4) on the inner layer prism structures (3) by vacuum sputtering; filling ultraviolet light curing acrylic resin in the recessed cavities on the outer side of the refractive layer (4), and adhering an outer layer film (2) away from the side of the solar cell piece on the outer side of the refractive layer (4) and the filled ultraviolet light curing acrylic resin; illuminating ultraviolet light through the outer layer film (2) to solidify the filled ultraviolet light curing acrylic resin into outer layer prism structures (5), and simultaneously connecting the outer layer film (2) and the refractive layer (4) into an integrated whole through the outer layer prism structures (5).

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