A flexible solar cell backsheet and a method for manufacturing the same

Abstract

The application discloses a flexible solar cell backboard and a preparation method thereof. The backboard comprises a base film, an adhesive layer and a weather-resistant film. The weather-resistant film comprises a PVDF film. A plurality of sawtooth stripes with isosceles triangle cross sections are arranged on the two side surfaces of the PVDF film in parallel at equal intervals. The base film comprises a base material layer. An in-line coating layer is arranged on each of the two side surfaces of the base material layer. A barrier layer is formed on the outer side of the in-line coating layer by sputtering. The base material layer comprises a transmission film and a heat-conducting film. A plurality of prism structures are arranged on the transmission film in parallel at equal intervals. The base material layer of the backboard is provided with the reflective prism structure with the physical structure, so that the light can be converged, and the heat dissipation area and the heat conduction efficiency are increased. In addition, the weather-resistant film is provided with the sawtooth stripes, so that the contact area with the adhesive is increased, the overall adhesion of the weather-resistant film is increased, the problem that the weather-resistant film is prone to delamination is avoided, and the weather-resistant film has excellent heat conduction performance and self-cleaning capacity.

Description

Technical Field

[0001] This application relates to a flexible solar cell backsheet and its fabrication method. Background Technology

[0002] Solar cell modules typically consist of a front panel, solar cells, encapsulation materials, and a backsheet. The solar cells are encapsulated between the front panel and the backsheet using encapsulation materials. 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 widely used in building-integrated photovoltaics (BIPV). The backsheet, as the encapsulation structure of the solar cell, plays a crucial role in extending the lifespan of the solar cell module. CN 101359695 A discloses a solar cell backsheet, including a substrate and a weather-resistant layer, the weather-resistant layer mainly composed of fluorinated resin. The technology of using fluorinated resin to form a weather-resistant film is described in the background section of CN 101582458 A, which mentions that a common backsheet structure is the TPT structure, where T usually refers to polyvinyl fluoride (PVF) film and P usually refers to polyethylene terephthalate (PET) film, i.e., a PVF / PET / PVF structure. The main function of PVF film is weather resistance, but it is expensive and has low surface energy, making it prone to delamination.

[0003] CN 114536906 A discloses a black photovoltaic backsheet, comprising a black layer, an inner coating layer, a support layer, and an outer layer arranged sequentially from the inside out. The black layer is positioned corresponding to the gaps between the photovoltaic module cells; the inner coating layer is white and used to reflect light; the support layer contains thermally conductive filler. In this prior art, the black layer primarily serves an aesthetic purpose, reflecting very little light, which is difficult to refract and utilize by the cells. The white inner coating layer inside the cells is the main surface reflecting light, and it is mainly made of white titanium dioxide and materials with poor thermal conductivity such as glass microspheres and resin. However, the particles like titanium dioxide and glass microspheres provide diffuse reflection, with a large amount of light actually absorbed by the inner coating layer. Furthermore, the inner coating layer has relatively poor thermal conductivity, resulting in low efficiency in transferring the absorbed heat to the support layer. Therefore, this prior art backsheet relies on the limited light-reflecting ability of the inner coating layer, has low efficiency in heat transfer to the support layer, and exhibits poor sealing properties.

[0004] CN 114156357 A discloses a flexible solar cell backsheet, comprising: a first grid layer, the first grid layer including weather-resistant resin, nano-sized filler A, isocyanate, and solvent; a second grid layer, the second grid including weather-resistant resin, nano-sized filler B, isocyanate, and solvent; an adhesive layer; a substrate layer; and a weather-resistant layer; wherein the particle size of nano-sized filler A is larger than that of nano-sized filler B. This prior art also utilizes nano-sized particles for reflection, which actually act as diffuse reflection. A large amount of light cannot be directly reflected back to the solar cell but is absorbed by the resin in the grid, and the absorbed heat is also difficult to conduct to the substrate layer. Summary of the Invention

[0005] The technical problem to be solved by this application is to provide a flexible solar cell backsheet and a method for its fabrication, so as to reduce or avoid the problems mentioned above.

[0006] To address the aforementioned technical problems, this application proposes a flexible solar cell backsheet, comprising a base film near the back of the solar cell and a weather-resistant film located outside the base film, wherein the weather-resistant film and the base film are bonded together by an adhesive layer; wherein, the weather-resistant film comprises a PVDF film, and multiple equally spaced parallel serrated stripes with an isosceles triangular cross-section are formed on both sides of the PVDF film; a white protective layer is formed on the surface of the serrated stripes facing the solar cell by vacuum sputtering, and a black protective layer is formed on the surface of the serrated stripes away from the solar cell by vacuum sputtering; the side of the PVDF film with the white protective layer is bonded with... A thermally conductive metal film is provided; the base film includes a substrate layer, each of the two sides of the substrate layer has an online coating layer, and a barrier layer is sputtered on the outer side of the online coating layer; the substrate layer includes a transmission film facing the solar cell and a thermally conductive film away from the solar cell, and a plurality of equally spaced parallel prism structures are formed on the transmission film. The prism structure consists of a body part with an isosceles triangle cross section and fins extending upward from the top of the body part. A metal reflective layer is formed on the outer side of the prism structure by vacuum sputtering. The recessed cavity between the thermally conductive film and the metal reflective layer is filled with thermally conductive adhesive, and the thermally conductive film and the metal reflective layer are connected as one unit by the thermally conductive adhesive.

[0007] Preferably, the serrated stripes on both sides of the PVDF film are arranged perpendicularly to each other; the angle between the length direction of the serrated stripes and the four rectangular sides of the PVDF film is 45 degrees.

[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 isosceles triangle of the body part of the prism structure has a base length of 20-30 μm, a vertex angle of 45-135 degrees, a height of 25-50 μm, and a minimum gap between adjacent prism structures of 0-50 μm.

[0010] Preferably, the height of the fins is 15-50 μm and the thickness is 2-10 μm.

[0011] Furthermore, this application also proposes a method for preparing the aforementioned flexible solar cell backsheet, including a base film preparation step, a weather-resistant film preparation and arrangement step, and a bonding step between the base film and the weather-resistant film; wherein, the base film preparation step includes: providing a transmission film facing the solar cell side, and forming an online coating and a barrier layer on one side surface; providing a thermally conductive film away from the solar cell side, and forming an online coating and a barrier layer on one side surface; and curing a plurality of equally spaced parallel prism structures on the side of the transmission film where the online coating and barrier layer are not formed. The mirror structure consists of a body portion with an isosceles triangular cross-section and fins extending upward from the top of the body portion. A metal reflective layer is formed on the prism structure by vacuum sputtering. Thermally conductive adhesive is filled into the recessed cavity outside the metal reflective layer, and a thermally conductive film away from the solar cell is bonded to the outside of the metal reflective layer and the filled thermally conductive adhesive. The side of the thermally conductive film that does not form the online coating layer and the barrier layer is bonded to the metal reflective layer. The thermally conductive adhesive is cured by heating, and the thermally conductive film and the metal reflective layer are connected together by the thermally conductive adhesive to obtain the base film.

[0012] Preferably, the method further includes the following steps: using PET chips as raw materials for preparing PET film, obtaining a single-layer thick sheet through melt extrusion, preheating and then longitudinally stretching it into a film, and after longitudinal stretching, using a coating machine to online coat a mixture of components constituting the online coating layer of this application on one side of the film, and then stretching it laterally, shaping, cooling and winding it up, thereby forming an online coating layer on the surface of the film, and then sputtering a barrier layer composed of silicon dioxide on the outside of the online coating layer, thereby obtaining a transmission film with an online coating layer and a barrier layer.

[0013] Preferably, the method further includes the following steps: using PET chips and -wt% thermally conductive filler particles as raw materials for preparing PET film, obtaining a single-layer thick sheet through melt extrusion, preheating and then longitudinally stretching it into a film, and after longitudinal stretching, using a coating machine to online coat a mixture of components constituting the online coating layer of this application on one side of the film, and then stretching it laterally, shaping, cooling and winding it to form an online coating layer on the surface of the film, and then sputtering a barrier layer composed of silicon dioxide on the outside of the online coating layer to obtain a thermally conductive film with an online coating layer and a barrier layer.

[0014] Preferably, the preparation steps of the weather-resistant film include: providing a PVDF film; forming multiple equally spaced parallel serrated stripes with isosceles triangle cross-sections on both sides of the PVDF film by hot pressing; forming a white protective layer on one side of the serrated stripes by vacuum sputtering, and forming a black protective layer on the other side of the serrated stripes by vacuum sputtering; and bonding a thermally conductive metal film to the side with the white protective layer, thereby forming the weather-resistant film.

[0015] 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.

[0016] The backplate of this application, by setting a substrate layer with a reflective prism structure, can not only concentrate light but also increase the heat dissipation area and thermal conductivity. In addition, the weather-resistant film, with its serrated stripes, can increase the contact area with the adhesive, thereby increasing the overall adhesion of the weather-resistant film and avoiding the problem of easy delamination. It also has excellent thermal conductivity and self-cleaning ability. Attached Figure Description

[0017] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of this application.

[0018] Figure 1 The diagram shown is a cross-sectional schematic of a flexible solar cell backsheet according to a specific embodiment of this application.

[0019] Figure 2 The diagram shown is a cross-sectional schematic of a weather-resistant film that can be used in the backsheet of a flexible solar cell according to a specific embodiment of this application.

[0020] Figure 3 The diagram shown is a structural schematic of a PVDF film for a weather-resistant film used as a backsheet of a flexible solar cell according to a specific embodiment of this application.

[0021] Figure 4 The diagram shown is a cross-sectional schematic of a base film that can be used in the backsheet of a flexible solar cell according to a specific embodiment of this application.

[0022] Figure 5 The diagram shown is a cross-sectional schematic of a weather-resistant film that can be used in the backsheet of a flexible solar cell according to another specific embodiment of this application.

[0023] Figure 6 The diagram shown is an exploded perspective view of the base film of a flexible solar cell backsheet that can be used in this application, according to yet another specific embodiment of this application.

[0024] Figure 7 The diagram shown is a partially enlarged schematic of a base film of a flexible solar cell backsheet according to 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 1 As shown, this application proposes a flexible solar cell backsheet, including a base film 100 near the back of the solar cell (not shown) and a weather-resistant film 200 located on the outer side of the base film 100. The weather-resistant film 200 and the base film 100 are bonded together by an adhesive layer 300. In a specific embodiment, the total thickness of the backsheet is approximately 170-332 μm; the thickness of the base film 100 is approximately 120-250 μm; the thickness of the weather-resistant film 200 is approximately 45-72 μm; and the thickness of the adhesive layer 300 is approximately 5-10 μm.

[0027] The adhesive layer 300 can be made using conventional EVA adhesive or UV-curable adhesive. The weather-resistant film on the outer side of the flexible solar cell backsheet provides good resistance to environmental erosion. The weather-resistant film 200 can be made from PVDF film, for example, commercially available PVDF film with a thickness of 20-30μm, or PVDF raw material particles with a mass content of ≥90%, with the addition of UV absorbers, wear-resistant fillers, etc., formed by melt co-extrusion and biaxial stretching.

[0028] Furthermore, since the fluorinated films used as weather-resistant films in the prior art are expensive and suffer from problems such as low surface energy, insufficient adhesion, and easy delamination, this application proposes a weather-resistant film 200 that can be used in the flexible solar cell backsheet of this application, such as... Figure 2-3 As shown, the weather-resistant film 200 of this application includes a PVDF film 201. Multiple equally spaced parallel serrated stripes 211 with an isosceles triangle cross section are formed on both sides of the PVDF film 201. A white protective layer 212 is formed on the surface of the serrated stripes 211 facing the solar cell by vacuum sputtering, and a black protective layer 213 is formed on the surface of the serrated stripes 211 away from the solar cell by vacuum sputtering.

[0029] The PVDF membrane 201 contains PVDF with a mass content of ≥90%. To improve its performance, ultraviolet absorbers, wear-resistant fillers, etc., can be added. Preferably, the serrated stripes 211 formed on both sides of the PVDF membrane 201 are identical. The dimensions of the weather-resistant membrane 200 shown in the figure have been enlarged for easier observation and understanding; the actual serrated stripes 211 are relatively small, with only barely perceptible textures on the surface. In one specific embodiment, the maximum thickness of the PVDF membrane 201 is 20-30 μm.

[0030] Existing PVDF weather-resistant films suffer from low surface energy and insufficient adhesion, leading to a tendency to delaminate. To overcome this technical problem, this application forms serrated stripes 211 on the surface of the PVDF film 201. The serrated stripes 211 increase the contact area with the adhesive 203 (which will be described in further detail later). For example, when the apex angle of the isosceles trapezoid of the serrated stripes 211 is 60 degrees, the serrated stripes 211 can double the surface area, thereby increasing the overall adhesion of the PVDF film 201 and preventing the weather-resistant film from easily delaminating.

[0031] It should be noted that improving the overall adhesion of the weather-resistant film 200 actually only requires setting serrated stripes 211 on the inner side of the PVDF film 201. However, since the stripes are very small and difficult to observe, the inventors chose to form the same serrated stripes 211 on both sides of the PVDF film 201 simultaneously for ease of assembly, so that film coating can be performed on both sides, thus increasing the applicability of the weather-resistant film 200. The inventors believed that the serrated stripes 211 originally located on the outer side did not seem to have any function. However, in actual laying experiments, it was found that if the scale of the serrated stripes 211 formed on the surface of the PVDF film 201 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 200, and rainwater can easily wash away the attached dust. For example, in a specific embodiment, the isosceles triangle of the serrated stripes 211 preferably 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 211 of 0-5 μm. Forming identical serrated stripes 211 on both sides of the PVDF film 201 not only reduces manufacturing costs, but also allows for better adhesion on the inner side and excellent dust resistance on the outer side by selecting serrated stripes 211 within this size range. Furthermore, the serrated stripes 211 on the outer side further increase the surface area, thereby increasing the heat dissipation area and improving the overall heat dissipation performance of the weather-resistant film.

[0032] Furthermore, to improve the adhesion of the PVDF film 201 and prevent delamination, this application selects the angle between the length direction of the serrated stripes 211 and the four rectangular sides of the weather-resistant film 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 211 is perpendicular to one pair of rectangular sides of the weather-resistant film 200, then the other pair of rectangular sides will be parallel to the length direction of the sawtooth stripes 211. Since the stiffness of the sawtooth stripes 211 is different in the length and width directions, their expansion rates are also different, which can cause one pair of rectangular sides of the weather-resistant film 200 to warp and delaminate. In this application, the direction of the sawtooth stripes 211 is turned at a 45-degree angle to the four rectangular sides. The proportion of stiffness differences in different directions caused by the sawtooth stripes 211 spreading to the four rectangular sides will tend to be averaged, thus avoiding the delamination problem of the weather-resistant film 200 caused by the sawtooth stripes 211, and further improving the structural performance of the weather-resistant film 200.

[0033] Furthermore, if the same serrated stripes 211 are formed on both sides, and the serrated stripes 211 on both sides are oriented in the same direction (i.e., the length directions of the serrated stripes 211 on both sides are parallel), the different thermal expansion rates on both sides will be concentrated in the same direction, which may lead to stress concentration and delamination. To avoid the delamination problem caused by the serrated stripes 211 on both sides being oriented in the same direction, this application further proposes a special design in which the serrated stripes 211 on both sides of the PVDF film 201 are arranged perpendicular to each other, thereby avoiding the problem of delamination caused by the simultaneous formation of a bias in one direction.

[0034] Furthermore, to avoid the problem that the excessively thick backsheets of existing technologies are difficult to apply to flexible solar cells with higher flexibility requirements, this application forms a white protective layer 212 and a black protective layer 213 on the PVDF film with a serrated stripe structure via vacuum sputtering. Since the bonding strength of the sputtered layer formed by vacuum sputtering is much greater than that of adhesive bonding, a very thin protective layer can achieve the protective function. For example, the white protective layer 212 can be made of titanium dioxide; the black protective layer 213 can be made of silicon carbide. Preferably, the thicknesses of the white protective layer 212 and the black protective layer 213 are 1-3 μm, respectively.

[0035] The white protective layer 212 provides excellent light reflection, reflecting as much light transmitted from the front of the solar cell back to the solar cell as possible, thus improving light conversion efficiency. Furthermore, since the white protective layer 212 is integrally sputtered onto the surface of the serrated stripes 211, an additional white polyethylene film layer is unnecessary, simplifying the structure of the weather-resistant film 200 and reducing the film thickness.

[0036] The black protective layer 213 is also a very thin sputtered layer, which can be used to improve wear resistance and enhance the weather-resistant film 200's ability to resist wind and sand erosion. In addition, the black protective layer 213 has better thermal radiation capabilities, facilitating the rapid dissipation of heat absorbed by the backsheet to reduce the temperature of the solar cell module. Simultaneously, the sputtering method improves adhesion while reducing additional film layers, thus lowering thickness and cost.

[0037] Furthermore, to further improve the heat dissipation capacity of the backplate, this application adheres a thermally conductive metal film 202 to one side of the PVDF film 201 with the white protective layer 212. For example, the thermally conductive metal film 202 can be bonded to the PVDF film 201 as a single unit using a suitable adhesive 203. Through the thermally conductive metal film 202, the heat absorbed by the backplate can be conducted to the PVDF film 201, and the heat can be efficiently radiated away through the increased surface area of ​​the serrated stripes on the outer side. In a specific embodiment, the thermally conductive metal film 202 can be made of aluminum foil with a thickness of 8-16 μm, and the adhesive 203 can be commercially available EVA adhesive or acrylic adhesive with a maximum thickness of 15-20 μm.

[0038] Examples 1-6

[0039] The weather-resistant film for the flexible solar cell backsheet used in this application was prepared according to the parameters in the table below.

[0040]

[0041]

[0042] In Examples 1-3, the angle between the serrated stripes and the rectangular sides of the weather-resistant film is 45 degrees. In Examples 4-6, the angle between the serrated stripes and the rectangular sides 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. The white protective layer is composed of titanium dioxide; the black protective layer is composed of silicon carbide.

[0043] Comparative Examples 1-6

[0044] Comparative Examples 1-6 used PVDF films without serrated stripes, and bonded thermally conductive metal films as weather-resistant films, with the following parameters. In both Examples 1-6 and Comparative Examples 1-6, EVA adhesive was used, and aluminum foil was used as the thermally conductive metal film.

[0045] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 PVDF film thickness (μm) 20 22 24 26 28 30 Maximum adhesive thickness (μm) 15 16 17 18 19 20 Thermally conductive metal film thickness (μm) 8 10 12 12 14 16

[0046] The weather-resistant films of Examples 1-6 and Comparative Examples 1-6 were respectively bonded to the surface of a 188μm PET base film. The parameter performance of each example of the weather-resistant film was measured and compared as follows.

[0047]

[0048]

[0049] As can be seen from the performance parameter comparison of the above embodiments, the weather-resistant film for flexible solar cell backsheets of this application, even with serrated stripes, can significantly improve adhesion performance and avoid delamination, has excellent thermal conductivity, increases the contact angle of the outer surface, improves self-cleaning ability, and has excellent dust resistance.

[0050] The base film on the inner side of the backsheet of a flexible solar cell possesses excellent insulation and mechanical properties. In existing technologies, the base film in the backsheet typically only serves a simple supporting function; the reflection of transmitted light and heat transfer require the use of other coatings, which involve complex processes and unstable coating structures, making them prone to aging and delamination under prolonged heating.

[0051] Therefore, this application proposes an improved base film for the flexible solar cell backsheet used in this application. In one specific embodiment of this application, the base film 100 can be made of PET film, which 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, the process characteristics require stronger barrier properties to protect the internal circuitry, thus placing high demands on the backsheet, typically requiring a barrier property of 10. - 3 g / m 2 • Day level. The common approach to enhancing barrier properties is to increase the thickness of the material, which increases the material cost, increases the unit weight, and reduces the material's flexibility. Excessively thick material can also cause slippage and leakage when the edges of the sheet are bent.

[0052] In view of this, Figure 4 In one specific embodiment of the base film 100 shown, the base film 100 includes a substrate layer 101, with an online coating layer 102 on each of its two side surfaces. A barrier layer 103 is sputtered onto the outer side of the online coating layer 102. The thickness of the substrate layer 101 is approximately 120-250 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 103, the barrier properties of the substrate layer 101 can be improved without increasing the thickness of the substrate layer 101, thus improving the adaptability of flexible solar cells. In order to improve surface smoothness and enhance the adhesion of the barrier layer 103, it is preferable to perform an online coating process on both sides of the substrate layer 101 before sputtering to form the barrier layer 103, forming an online coating layer 102 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 101 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 102 can be applied to the thick sheet before or during the stretching of the polyester film constituting the substrate layer 101. 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 102.

[0056] In one specific embodiment, the online coating layer 102 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 102 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 188μm biaxially oriented PET film, and then a barrier layer composed of silicon dioxide was sputtered on the outside of the online coating layer.

[0059] Example 7 Example 8 Example 9 Example 10 Example 11 acrylic resin 100 100 100 100 100 Silica nanoparticles 10 11.5 12.5 13.5 15 1,4-Dioxane 20 22 25 28 30 Polyethylene oxide 10 12 13 14 15 Ethylene-vinyl acetate copolymer 5 6 7.5 8 10 Online coating thickness (nm) 100 150 200 250 300 Barrier layer thickness (nm) 200 200 200 200 200

[0060] As a comparison, a 200 nm thick barrier layer of silicon dioxide was directly sputtered onto each of the two surfaces of a 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 shown, this application proposes another specific embodiment of a base film that can be used in the flexible solar cell backsheet of this application, and... Figure 4 Similar to the illustrated embodiment, the base film 100 in this embodiment also includes a substrate layer 101, with an online coating layer 102 on each of its two surfaces. A barrier layer 103 is sputtered onto the outer side of the online coating layer 102. (Similar to...) Figure 2 The difference between this embodiment and the previous one is that the substrate layer 101 in this embodiment is a multilayer thin film composite structure, while the remaining online coating layer 102 and barrier layer 103 can have the same structure and composition as in the previous embodiment. The following is a detailed description of the substrate layer 101 of the multilayer composite structure in this embodiment.

[0062] like Figure 5-7 As shown, the substrate layer 101 in this embodiment includes a transmission film 1 facing the solar cell and a thermally conductive film 2 away from the solar cell. The transmission film 1 has a plurality of equally spaced parallel prism structures 3 formed on it. Each prism structure 3 consists of a body portion 31 with an isosceles triangular cross-section and fins 32 extending upward from the top of the body portion 31 (see details). Figure 7 A metal reflective layer 4 is formed on the outside of the prism structure 3 by vacuum sputtering. The recessed cavity between the thermally conductive film 2 and the metal reflective layer 4 is filled with thermally conductive adhesive 5. The thermally conductive film 2 and the metal reflective layer 4 are connected as one unit by the thermally conductive adhesive 5. Figure 3 To make it clearer, the thickness of the fin 32 has been enlarged. The actual thickness is very small, and it is basically concentrated at the vertex of the body part 31, without significantly altering the triangular cross-sectional shape of the body part 31.

[0063] The substrate layer 101 of this application adopts a multi-layer composite structure. A physical reflective prism structure is set between the two integrally structured films (transmissive film 1 and thermally conductive film 2), which can converge and reflect light from different angles. The angled reflective surface not only converges light but also increases the reflective area. The metal reflective layer on the back of the reflective prism structure not only has a reflective function but also a thermal conductive function. As the reflective surface is bent, the reflective surface increases in size, which not only increases the reflectivity but also increases the heat dissipation area. In addition, to further increase the heat dissipation area, fins are extended from the top of the prism structure body. By forming a metal reflective layer on the surface of the fins, the fins with the attached metal reflective layer become heat sinks, further increasing the heat dissipation area and thermal conductivity.

[0064] The transmissive film 1 can be made of PET with a light transmittance greater than 85%, and the thermally conductive film 2 can be made of PET with added thermally conductive fillers. The double-layer PET film can provide excellent insulation, water resistance, mechanical properties, and dimensional stability. The transmissive film 1 and the thermally conductive film 2 encapsulate the central prism structure. The metal reflective layer 4 sputtered on the back of the prism structure isolates the outer heat dissipation structure. The bent metal reflective layer 4 elongates the isolation channel, thereby enhancing water resistance and airtightness.

[0065] In one specific embodiment, the prism structure 3 is made of UV-curable acrylic resin. The metal reflective layer 4 can be formed by sputtering metallic silver, which has excellent reflective and thermal conductivity properties. The thermally conductive adhesive 5 can be made of UV-curable acrylic resin with added thermally conductive fillers, or, to avoid the thermally conductive fillers affecting light transmittance and resulting in poor UV curing effect, the thermally conductive adhesive 5 is preferably made of thermosetting resin with added thermally conductive fillers.

[0066] Solar panels are typically fixed in orientation after installation, making their efficiency highly dependent on the direction of sunlight. While direct sunlight generally provides the highest efficiency, it is short-lived, and for a significant portion of the time, the sunlight is directed at an angle. In this application, a prism structure is incorporated into the substrate layer 101. Light entering the prism structure is reflected by the outer metallic reflective layer on the angled triangular sides. The reflected light gradually converges towards the base of the triangle and ultimately reflects back in a direction as perpendicular as possible to the solar cell. Therefore, even angled light can be gathered and reflected for utilization, thus improving sunlight utilization. Furthermore, for flexible solar cells installed on rooftops, prisms with stripes pointing north-south are more efficient, improving the utilization of east-west facing light in the morning and evening. For flexible solar cells installed on vertical walls, prisms with stripes pointing east-west are more efficient, enhancing the utilization of light angled from the top onto the wall during the strongest midday sunlight.

[0067] Examples 12-14

[0068] The substrate layer for the base film that can be used in the flexible solar cell backsheet of this application is prepared according to the parameters in the table below.

[0069]

[0070] Comparative Examples 12-14

[0071] Comparative Examples 12-14 used a single-layer PET film as the base film and the white coating of the second grid layer, as specified in CN 114156357 A, as the reflective coating. The relevant reflective parameters are as follows.

[0072] Comparative Example 12 Comparative Example 13 Comparative Example 14 PET film thickness (μm) 250 250 250 Reflective coating thickness μm 15 10 1

[0073] The parameter performance of each embodiment is compared as follows.

[0074]

[0075] The test was conducted in accordance with GJB 5023.1A-2012, Test Methods for Reflectivity and Emissivity of Materials and Coatings.

[0076]

[0077] As can be seen from the performance parameter comparison of the above embodiments, the mechanical properties, reflectivity, peeling performance, thermal conductivity, etc. of the substrate layer of the flexible solar cell backsheet of this application are significantly improved.

[0078] The method for fabricating the flexible solar cell backsheet of this application will be further described in detail below with reference to the accompanying drawings. As mentioned above, the flexible solar cell backsheet of this application includes a base film 100 near the back of the solar cell and a weather-resistant film 200 located on the outer side of the base film 100. The weather-resistant film 200 and the base film 100 are bonded together by an adhesive layer 300. The base film 100 includes a substrate layer 101, and each of the two sides of the substrate layer 101 has an online coating layer 102. A barrier layer 103 is sputtered to the outer side of the online coating layer 102. The substrate layer 101 includes a transmission film 1 facing the solar cell and a thermally conductive film 2 away from the solar cell. Multiple equally spaced parallel prism structures 3 are formed on the transmission film 1. Each prism structure 3 consists of a body portion 31 with an isosceles triangular cross section and fins 32 extending upward from the top of the body portion 31. A metal reflective layer 4 is formed on the outside of the prism structure 3 by vacuum sputtering. The recessed cavity between the thermally conductive film 2 and the metal reflective layer 4 is filled with thermally conductive adhesive 5. The thermally conductive film 2 and the metal reflective layer 4 are connected as one unit by the thermally conductive adhesive 5. The weather-resistant film 200 may include a PVDF film 201. The two sides of the PVDF film 201 are formed with a plurality of equally spaced parallel sawtooth stripes 211 with an isosceles triangle cross section. The surface of the sawtooth stripes 211 facing the solar cell is formed with a white protective layer 212 by vacuum sputtering, and the surface of the sawtooth stripes 211 away from the solar cell is formed with a black protective layer 213 by vacuum sputtering. A thermally conductive metal film 202 is bonded to the side of the PVDF film 201 with the white protective layer 212.

[0079] Furthermore, the preparation method of this application includes the preparation steps of the base film 100, the preparation steps of the weather-resistant film 200, and the bonding steps of the base film 100 and the weather-resistant film 200.

[0080] The preparation steps of the base film 100 include:

[0081] First, a transmission film 1 facing the side of the solar cell is provided, and an online coating 102 and a barrier layer 103 are formed on one side surface. In one specific embodiment, PET chips are used as raw materials for preparing PET films. A single-layer thick sheet is obtained by melt extrusion, preheated, and then longitudinally stretched into a film. After longitudinal stretching, a mixture of the 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 laterally stretched, shaped, cooled, and wound up, thereby forming an online coating layer 102 on the surface of the film. Then, a barrier layer 103 made of silicon dioxide is sputtered to form on the outside of the online coating layer 102, thereby obtaining a transmission film 1 with an online coating layer 102 and a barrier layer 103 for later use. The thickness of the transmission film 1 is preferably 40-60 μm, and the visible light transmittance is 85%-95%.

[0082] Simultaneously, regardless of the order, a thermally conductive film 2 is provided on the side away from the solar cell, and an online coating 102 and a barrier layer 103 are formed on one side of its surface. In one specific embodiment, PET chips and 5-10 wt% thermally conductive filler particles are used as raw materials to prepare PET film. A single-layer thick sheet is obtained by melt extrusion, preheated, and then longitudinally stretched into a film. After longitudinal stretching, a mixture of the components constituting the online coating layer of this application is online coated on one side of the film using a coating machine. Then, it is stretched laterally, shaped, cooled, and wound up, thereby forming an online coating layer 102 on the surface of the film. Then, a barrier layer 103 composed of silicon dioxide is sputtered to form on the outside of the online coating layer 102, thereby obtaining a thermally conductive film 2 with an online coating layer 102 and a barrier layer 103 for later use. In one specific embodiment, the thermally conductive filler can be one of boron nitride, graphite, and graphene, or a mixture thereof, preferably boron nitride.

[0083] Then, on the side of the transmission film 1 where the online coating layer 102 and the barrier layer 103 are not formed, a plurality of equally spaced parallel prism structures 3 are cured to form. Each prism structure 3 consists of a body portion 31 with an isosceles triangular cross-section and fins 32 extending upwards from the top of the body portion 31. For example, a roller with a pattern matching the shape of the prism structure can be used. UV-curable acrylic resin is applied to the roller, and the transmission film 1 is pressed and rolled along the roller surface, simultaneously pressing the UV-curable acrylic resin onto the transmission film 1 according to the shape of the prism structure. Then, UV-curable acrylic resin is cured by irradiation with UV light, thereby forming the desired shape of the prism structure 3 on the transmission film 1. The length of the base of the isosceles triangle of the body portion 31 of the formed prism structure 3 is 20-30 μm, the apex angle is 60-120 degrees, the height is 25-50 μm, and the minimum gap between adjacent prism structures 3 is 0-50 μm. The height of fin 32 is 15-50μm and the thickness is 2-10μm.

[0084] Subsequently, a metallic reflective layer 4 is formed on the prism structure 3 by vacuum sputtering. For example, a layer of metallic silver with a thickness of 2-10 μm can be formed on the prism structure 3 by vacuum sputtering. Since the thickness of the formed metallic reflective layer 4 is relatively very thin, Figure 2 and 3 The metal reflective layer 4 is not shown in the figure.

[0085] Next, thermally conductive adhesive 5 is filled into the recessed cavity on the outer side of the metal reflective layer 4, and the thermally conductive film 2 is bonded to the outer side of the metal reflective layer 4 and the filled thermally conductive adhesive 5; wherein the side of the thermally conductive film 2 that does not form the online coating layer 102 and the barrier layer 103 is bonded to the metal reflective layer 4. Preferably, while filling the recessed cavity on the outer side of the metal reflective layer 4 with thermally conductive adhesive 5, the thermally conductive adhesive outside the top of the metal reflective layer 4 is scraped off with a scraper, so that the filled thermally conductive adhesive 5 is flush with the top of the metal reflective layer 4, to eliminate gaps and ensure a stronger bond between the bonded layers, such as... Figure 3 As shown.

[0086] Finally, the thermally conductive adhesive 5 is cured. Simultaneously, the thermally conductive film 2 and the metal reflective layer 4 are bonded together using the thermally conductive adhesive 5, thereby obtaining the base film 100. In one specific embodiment, as mentioned above, the thermally conductive adhesive 5 can be made of UV-curable acrylic resin with added thermally conductive filler. Therefore, during curing, the thermally conductive adhesive 5 can be cured by irradiating the thermally conductive film 2 with ultraviolet light. Alternatively, since both the thermally conductive film 2 and the thermally conductive adhesive 5 contain thermally conductive filler, considering the light transmittance issue, it is preferable that the thermally conductive adhesive 5 is made of thermosetting resin with added thermally conductive filler. Therefore, during curing, the thermally conductive adhesive 5 is cured by heating. The thermally conductive adhesive 5 can be any commercially available adhesive resin with thermal conductivity, or thermally conductive filler can be purchased and added to an existing adhesive resin to prepare the thermally conductive adhesive. In one specific embodiment, the thermally conductive filler can be one of boron nitride, graphite, and graphene, or a mixture thereof, preferably boron nitride. The thermally conductive adhesive 5 is preferably a thermosetting resin with a thermal conductivity of 20-25 W / (m·K).

[0087] The preparation steps of the weather-resistant film 200 include:

[0088] First, a PVDF membrane 201 is provided. This PVDF membrane 201 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.

[0089] Then, a plurality of equally spaced, parallel serrated stripes 211 with isosceles triangular cross-sections are formed on both sides of the PVDF film 201 by hot pressing. For example, two rollers with patterns matching the shape of the serrated stripes, positioned vertically opposite each other, can be used. The heated PVDF film 201 is passed between the two rollers, and then the PVDF film 201 is air-cooled or water-cooled to obtain the cured serrated stripes 211 on the PVDF film 201. The length directions of the patterns matching the shape of the serrated stripes on the surfaces of the two vertically opposite rollers are perpendicular to each other, thus forming mutually perpendicular serrated stripes 211 on both sides of the PVDF film 201. For example, if the pattern direction on the surfaces of the two rollers forms a 45-degree angle with the direction of travel of the PVDF film 201, serrated stripes 11 forming a 45-degree angle with the four rectangular sides of the weather-resistant film 200 can be formed.

[0090] Subsequently, a white protective layer 212 is formed on one side of the serrated stripe 211 by vacuum sputtering, and a black protective layer 213 is formed on the other side of the serrated stripe 211 by vacuum sputtering. For example, a layer of titanium dioxide with a thickness of 1-3 μm can be formed on one side of the serrated stripe 211 by vacuum sputtering to form the white protective layer 212; and a layer of silicon carbide with a thickness of 1-3 μm can be formed on the other side of the serrated stripe 211 by vacuum sputtering to form the black protective layer 213. Since the thickness of the formed protective layer is relatively very thin, Figure 3 The protective layer is not shown in the image, and at the same time, Figure 2 The protective layers 212 and 213 in the image have also been enlarged for easier understanding.

[0091] Finally, a thermally conductive metal film 202 is adhered to the side with the white protective layer 212 to form the weather-resistant film 200. For example, a layer of acrylic adhesive with a thickness of 15-20 μm can be coated on the side with the white protective layer 212, the surface can be smoothed, and then an 8-16 μm layer of aluminum foil can be adhered as the thermally conductive metal film 202 to prepare the weather-resistant film 200.

[0092] The bonding steps of the base film 100 and the weather-resistant film 200 include: bonding one side of the thermally conductive film 2 of the base film 100 to the weather-resistant film 200 as a whole through the adhesive layer 300.

[0093] 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.

[0094] 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 backsheet, comprising a base film (100) near the back of the solar cell and a weather-resistant film (200) located outside the base film (100), wherein the weather-resistant film (200) and the base film (100) are bonded together by an adhesive layer (300); characterized in that, The weather-resistant film (200) includes a PVDF film (201). Multiple equally spaced, parallel serrated stripes (211) with isosceles triangular cross-sections are formed on both sides of the PVDF film (201). A white protective layer (212) is formed on the surface of the serrated stripes (211) facing the solar cell by vacuum sputtering, and a black protective layer (213) is formed on the surface of the serrated stripes (211) away from the solar cell by vacuum sputtering. A thermally conductive metal film (202) is adhered to the side of the PVDF film (201) with the white protective layer (212). The base film (100) includes a substrate layer (101), and each side of the substrate layer (101) has an online coating layer (102). A barrier layer (103) is sputtered on the outer side of the online coating layer (102); the substrate layer (101) includes a transmission film (1) facing the solar cell and a thermally conductive film (2) away from the solar cell. Multiple prism structures (3) are formed on the transmission film (1) in parallel at equal intervals. The prism structure (3) consists of a body part (31) with an isosceles triangle cross section and fins (32) extending upward from the top of the body part (31). A metal reflective layer (4) is formed on the outer side of the prism structure (3) by vacuum sputtering. The recessed cavity between the thermally conductive film (2) and the metal reflective layer (4) is filled with thermally conductive adhesive (5). The thermally conductive film (2) and the metal reflective layer (4) are connected as one unit by the thermally conductive adhesive (5).

2. The backplate as described in claim 1, characterized in that, The serrated stripes (211) on both sides of the PVDF membrane (201) are arranged perpendicularly to each other; the length direction of the serrated stripes (211) forms an angle of 45 degrees with the four rectangular sides of the PVDF membrane (201).

3. The backplate as described in claim 1, characterized in that, The isosceles triangle of the sawtooth stripe (211) 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 (211) of 0-5 μm.

4. The backplate as described in claim 1, characterized in that, The isosceles triangle of the body part (31) of the prism structure (3) has a base length of 20-30μm, a vertex angle of 45-135 degrees, a height of 25-50μm, and a minimum gap between adjacent prism structures (3) of 0-50μm.

5. The backplate as described in claim 1, characterized in that, The height of the fin (32) is 15-50 μm and the thickness is 2-10 μm.

6. A method for preparing a flexible solar cell backsheet as described in any one of claims 1-5, comprising a step of preparing a base film (100), a step of preparing a weather-resistant film (200), and a step of bonding the base film (100) and the weather-resistant film (200); wherein, The preparation steps of the base film (100) include: A transmissive film (1) facing one side of the solar cell is provided, and an online coating layer (102) and a barrier layer (103) are formed on one side surface of the solar cell. A thermally conductive film (2) is provided on the side away from the solar cell, and an online coating layer (102) and a barrier layer (103) are formed on one side of the film. On the side of the transmission film (1) where the online coating layer (102) and the barrier layer (103) are not formed, a plurality of equally spaced parallel prism structures (3) are cured and formed. The prism structure (3) consists of a body part (31) with an isosceles triangle cross section and fins (32) extending upward from the top of the body part (31). A metal reflective layer (4) is formed on the prism structure (3) by vacuum sputtering; Thermally conductive adhesive (5) is filled into the recessed cavity on the outside of the metal reflective layer (4), and a thermally conductive film (2) on the side away from the solar cell is attached to the outside of the metal reflective layer (4) and the filled thermally conductive adhesive (5); wherein the side of the thermally conductive film (2) without the online coating layer (102) and the barrier layer (103) is attached to the metal reflective layer (4); The thermally conductive adhesive (5) is cured by heating, and the thermally conductive film (2) and the metal reflective layer (4) are connected together by the thermally conductive adhesive (5) to obtain the base film (100).

7. The preparation method according to claim 6 further includes the following steps: using PET chips as raw materials for preparing PET film, obtaining a single-layer thick sheet by melt extrusion, preheating and then longitudinally stretching into a film, and after longitudinal stretching, using a coating machine to online coat a mixture of components constituting the online coating layer on one side of the film, and then stretching laterally, shaping, cooling and winding, thereby forming an online coating layer (102) on the surface of the film, and then sputtering a barrier layer (103) composed of silicon dioxide on the outside of the online coating layer (102), thereby obtaining a transmission film (1) with an online coating layer (102) and a barrier layer (103).

8. The preparation method according to claim 6 further includes the following steps: using PET chips and 5-10 wt% thermally conductive filler particles as raw materials for preparing PET film, obtaining a single-layer thick sheet by melt extrusion, preheating and longitudinally stretching into a film, and after longitudinal stretching, using a coating machine to online coat a mixture of components constituting the online coating layer on one side of the film, and then stretching laterally, shaping, cooling and winding, thereby forming an online coating layer (102) on the surface of the film, and then sputtering a barrier layer (103) composed of silicon dioxide on the outside of the online coating layer (102), thereby obtaining a thermally conductive film (2) with an online coating layer (102) and a barrier layer (103).

9. The preparation method according to claim 6, characterized in that, The preparation steps of the weather-resistant film (200) include: providing a layer of PVDF film (201); Multiple equally spaced parallel sawtooth stripes (211) with isosceles triangle cross sections are formed on both sides of the PVDF film (201) by hot pressing. A white protective layer (212) is formed on the serrated stripe (211) on one side by vacuum sputtering, and a black protective layer (213) is formed on the serrated stripe (211) on the other side by vacuum sputtering. A thermally conductive metal film (202) is adhered to one side of the white protective layer (212) to form the weather-resistant film.

10. The preparation method according to claim 9, characterized in that, The specific steps for forming the sawtooth stripes (211) are as follows: using two rollers with patterns matching the shape of the sawtooth stripes (211) placed vertically opposite each other, passing the heated PVDF film (201) between the two rollers, and then air-cooling or water-cooling the PVDF film to obtain the cured sawtooth stripes (211) on the PVDF film; the length direction of the patterns matching the shape of the sawtooth stripes on the surfaces of the two rollers placed vertically opposite each other 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.

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