A solar cell backsheet and its preparation method

Abstract

This application discloses a solar cell backsheet and its fabrication method, comprising a base film, an adhesive layer, and a weather-resistant film. The base film includes a substrate layer, with an online coating layer on each of its two surfaces. A barrier layer is sputtered onto the outer side of the online coating layer. The substrate layer includes a transmission film and a thermally conductive film. Multiple equally spaced parallel prism structures are formed on the transmission film. A metal reflective layer is formed on the outer side of the prism structures by vacuum sputtering. A thermally conductive adhesive is filled in the recessed cavity between the thermally conductive film and the metal reflective layer, and the thermally conductive film and the metal reflective layer are bonded together by the thermally conductive adhesive. The solar cell backsheet of this application, by setting a substrate layer with a physically structured reflective prism structure, not only concentrates 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 increases the heat dissipation area and thermal conductivity. Furthermore, the base film also possesses excellent barrier properties due to the inclusion of a barrier layer.

Description

Technical Field

[0001] This application relates to a solar cell backsheet and a method for preparing the same. Background Technology

[0002] 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.

[0003] CN 114156357 A discloses a 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

[0004] The technical problem to be solved by this application is to provide a solar cell backsheet and a method for its fabrication, so as to reduce or avoid the problems mentioned above.

[0005] To address the aforementioned technical problems, this application proposes a 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 base film comprises a substrate layer, each of the two sides of the substrate layer having an online coating layer, and a barrier layer is sputtered to form the outer side of the online coating layer; the substrate layer comprises a transmission film facing the solar cell and a thermally conductive film away from the solar cell, wherein a plurality of equally spaced parallel prism structures are formed on the transmission film, each prism structure consisting 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 being formed on the outer side of the prism structure by vacuum sputtering, and a thermally conductive adhesive filling the recessed cavity between the thermally conductive film and the metal reflective layer, wherein the thermally conductive film and the metal reflective layer are bonded together by the thermally conductive adhesive.

[0006] 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; the mass ratio of each component of the online coating layer is 100:(10-15):(20-30):(10-15):(5-10).

[0007] Preferably, the barrier layer is made of silicon dioxide and has a thickness of 200 nm.

[0008] Preferably, the metal reflective layer is formed by sputtering metallic silver.

[0009] Preferably, the prism structure is made of UV-curable acrylic resin.

[0010] Preferably, the transmission film is made of PET with a visible light transmittance of greater than 85%.

[0011] 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.

[0012] Preferably, the height of the fins is 15-50 μm and the thickness is 2-10 μm.

[0013] Preferably, the thermally conductive film is made of PET with added thermally conductive filler.

[0014] Preferably, the thermally conductive adhesive is made of a thermosetting resin with added thermally conductive filler.

[0015] Preferably, the thermally conductive filler is boron nitride.

[0016] Furthermore, this application also proposes a method for preparing the aforementioned solar cell backsheet, including a base film preparation step and a bonding step between the base film and a 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, wherein the prism structure has a cross-section The system consists of an isosceles triangular body and fins extending upward from the top of the body. A metal reflective layer is formed on the prism structure by vacuum sputtering. Thermally conductive adhesive is filled into a recessed cavity on the outside of the metal reflective layer, and a thermally conductive film is bonded to the outside of the metal reflective layer and the filled thermally conductive adhesive, on the side away from the solar cell. 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.

[0017] Preferably, the thermally conductive adhesive filling is flush with the top of the metal reflective layer.

[0018] 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.

[0019] 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.

[0020] The solar cell backsheet of this application, by incorporating a substrate layer with a physically structured reflective prism, not only concentrates light but also increases the reflective area. The metal reflective layer on the back of the reflective prism structure not only reflects light but also increases the heat dissipation area and thermal conductivity. Furthermore, the base film possesses excellent barrier properties through the inclusion of a barrier layer. Attached Figure Description

[0021] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of this application.

[0022] Figure 1 The diagram shown is a cross-sectional schematic of a solar cell backsheet according to a specific embodiment of this application.

[0023] Figure 2 The diagram shown is a cross-sectional schematic of a base film that can be used in the backsheet of a solar cell according to a specific embodiment of this application.

[0024] Figure 3 The diagram shown is a cross-sectional schematic of a base film that can be used in the backsheet of a solar cell according to another specific embodiment of this application.

[0025] Figure 4 The diagram shown is an exploded perspective view of a base film of a solar cell backsheet that can be used in this application, according to yet another specific embodiment of this application.

[0026] Figure 5 The diagram shown is a partially enlarged schematic of a base film of a solar cell backsheet according to another specific embodiment of this application. Detailed Implementation

[0027] 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.

[0028] like Figure 1 As shown, this application proposes a 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.

[0029] The adhesive layer 300 can be made of conventional EVA adhesive or UV-curable adhesive. The weather-resistant film 200 is preferably made of 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., and formed by melt co-extrusion followed by biaxial stretching.

[0030] The weather-resistant film on the outer side of a solar cell backsheet provides excellent resistance to environmental corrosion, while the base film on the inner side possesses good insulation and mechanical properties. In the prior art backsheets cited in the background section, the base film only serves a simple supporting function; the reflection of transmitted light and heat transfer require other coatings, which involve complex processes and unstable coating structures, making them prone to aging and delamination under prolonged heating.

[0031] 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 / m2·day level. The usual 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.

[0032] In view of this, Figure 2 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] Example 1 Example 2 Example 3 Example 4 Example 5 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

[0040] 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 1-5 was increased by 34.5%, 36.2%, 35.1%, 34.8%, and 36.1% respectively compared to the comparative examples.

[0041] Furthermore, such as Figure 3 As shown, this application proposes another specific embodiment of a base film that can be used in the backsheet of the solar cell of this application, and... Figure 2Similar 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.

[0042] like Figure 3-5 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 3 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] The method for preparing the solar cell backsheet of this application will be further described in detail below with reference to the accompanying drawings. As mentioned above, the 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.

[0048] Furthermore, the preparation method of this application includes a step of preparing a base film 100, and a step of bonding the base film 100 and the weather-resistant film 200. The step of preparing the base film 100 includes:

[0049] 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%.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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).

[0055] 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 single unit via an adhesive layer 300. The weather-resistant film 200 can be composed of a PVDF film with PVDF as the main component. This PVDF film can be a commercially available PVDF film with a thickness of 20-30 μm, or it can be formed by melt co-extrusion and biaxial stretching of PVDF raw material particles with a mass content of ≥90%, adding ultraviolet absorbers, wear-resistant fillers, etc.

[0056] Examples 6-8

[0057] The substrate layer for preparing the base film that can be used in the backsheet of the solar cell of this application is prepared according to the parameters in the table below.

[0058]

[0059]

[0060] Comparative Examples 6-8

[0061] Comparative Examples 6-8 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.

[0062] Comparative Example 6 Comparative Example 7 Comparative Example 8 PET film thickness (μm) 250 250 250 Reflective coating thickness μm 15 10 1

[0063] The parameter performance of each embodiment is compared as follows.

[0064]

[0065] The test was conducted in accordance with GJB 5023.1A-2012, Test Methods for Reflectivity and Emissivity of Materials and Coatings.

[0066]

[0067] 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 used for solar cell backsheets in this application are significantly improved.

[0068] 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.

[0069] 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 solar cell backsheet, comprising a base film (100) near the back of a 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 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 on the outside 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 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).

2. The backplate as described in claim 1, characterized in that, 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 base coat, and then curing it through online coating. The mass ratio of each component of the online coating layer (102) is 100:(10-15):(20-30):(10-15):(5-10).

3. The backplate as described in claim 1, characterized in that, The barrier layer (103) is made of silicon dioxide and has a thickness of 200 nm.

4. The backplate as described in claim 1, characterized in that, The metal reflective layer (4) is formed by sputtering metallic silver.

5. 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.

6. 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.

7. A method for preparing a solar cell backsheet as described in any one of claims 1-6, comprising a step of preparing a base film (100), and a step of bonding the base film (100) and a weather-resistant film (200); wherein, The preparation steps of the base film (100) include: A transmissive film (1) is provided facing one side of the solar cell, and an in-line coating (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 (102) and a barrier layer (103) are formed on one side of the surface thereon; 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).

8. The preparation method according to claim 7, characterized in that, The thermally conductive adhesive (5) is flush with the top of the metal reflective layer (4).

9. The preparation method according to claim 7 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 of this application 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).

10. The preparation method according to claim 7 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 then longitudinally stretching into a film, and after longitudinal stretching, using a coating machine to online coat a mixture of the components constituting the online coating layer of this application 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).

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