Photovoltaic backsheet, its preparation method and application

Abstract

The present invention discloses a photovoltaic backsheet, a preparation method thereof and an application thereof. The photovoltaic backsheet at least comprises an adhesive layer, a core layer and a weather-resistant layer which are arranged in sequence from inside to outside, wherein the adhesive layer comprises 50-80 parts by mass of a heat-resistant polyamide, 5-20 parts by mass of a tackifying resin, 1-10 parts by mass of an ionomer, 1-30 parts by mass of a first filler, and 0.1-5 parts by mass of a first anti-aging agent; the core layer comprises 50-80 parts by mass of a first polypropylene, 5-20 parts by mass of a first modifier, 1-30 parts by mass of a second filler, and 0.1-5 parts by mass of a second anti-aging agent; the weather-resistant layer comprises 50-80 parts by mass of a second polypropylene, 5-20 parts by mass of a second modifier, 1-30 parts by mass of a third filler, 0-25 parts by mass of a polyamide, and 0.1-5 parts by mass of a third anti-aging agent. The photovoltaic backsheet has good heat resistance, weather resistance, adhesiveness and interlayer adhesion, and can greatly improve the heat resistance of the photovoltaic backsheet.

Description

Technical Field

[0001] The present invention belongs to the field of photovoltaic technology, and in particular, relates to a photovoltaic backplane and a preparation method and application thereof. Background Art

[0002] Solar energy has attracted widespread attention as a clean, pollution-free, and most abundant renewable energy. With the proposal of the "carbon peak and carbon neutrality" goals, the country will Europeanize its policies to optimize the industrial structure and energy structure, and clean energy will also usher in a larger market space. In the long-term outdoor environment of wind, rain, ultraviolet rays and other natural factors, the backplane of solar cells should use a backplane with excellent weather resistance and durability to protect the solar cells and extend their service life. At present, the mainstream solar cell backplanes in the market are still dominated by multi-layer composite structures, which are mainly divided into composite and coated types, both of which are based on polyester film (PET). The entire preparation process of the backplane is complicated, the operation cycle is long, and the production process is accompanied by the volatilization of organic solvents, which pollutes the environment. In addition, during long-term outdoor use, there is a problem of decreased interlayer adhesion, which is easy to cause interlayer separation and falling off, causing the backplane to lose its protective function.

[0003] In addition, under the pressure of cost, the size of battery modules on the market has begun to develop towards large size and high power, and the operating temperature of the modules will also rise. If individual battery cells have defects or are blocked by foreign objects, the power generation element will be converted into a load element, which will cause the local temperature of the module to be abnormally high, and then abnormal phenomena such as backplane bubbling and hot spots will occur. If the backplane is not heat-resistant enough, the backplane corresponding to the local high-temperature point may be burned through, resulting in packaging failure. However, there are few studies on solving the problem of backplane hot spots in related technologies. Therefore, improving the heat resistance of co-extruded backplanes is also an urgent problem to be solved. Summary of the invention

[0004] The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, one object of the present invention is to provide a photovoltaic backsheet and a preparation method and application thereof to improve the heat resistance, weather resistance, adhesion and interlayer adhesion of the photovoltaic backsheet.

[0005] In one aspect of the present invention, the present invention provides a photovoltaic backsheet. According to an embodiment of the present invention, the photovoltaic backsheet comprises at least a bonding layer, a core layer and a weather-resistant layer arranged in sequence from the inside to the outside, wherein:

[0006] The bonding layer comprises: 50-80 parts by mass of heat-resistant polyamide, 5-20 parts by mass of tackifying resin, 1-10 parts by mass of ion polymer, 1-30 parts by mass of first filler, and 0.1-5 parts by mass of first anti-aging agent;

[0007] The core layer comprises: 50-80 parts by mass of a first polypropylene, 5-20 parts by mass of a first modifier, 1-30 parts by mass of a second filler, and 0.1-5 parts by mass of a second anti-aging agent;

[0008] The weather-resistant layer comprises: 50-80 parts by mass of a second polypropylene, 5-20 parts by mass of a second modifier, 1-30 parts by mass of a third filler, 0-25 parts by weight of a polyamide, and 0.1-5 parts by mass of a third anti-aging agent;

[0009] Wherein, the first modifier and the second modifier each independently comprise at least one selected from polyethylene, an elastomer, and a compatibilizer.

[0010] The photovoltaic backsheet of the above embodiments of the present invention includes at least three layers of structure. The weather-resistant layer and the adhesive layer are located on two outer surfaces of the photovoltaic backsheet, and the core layer is located inside the photovoltaic backsheet. The weather-resistant layer is in direct contact with air, and the adhesive layer is bonded to the photovoltaic encapsulation hot melt adhesive film layer (usually an EVA layer). Among them, by selecting a heat-resistant polyamide as the main resin in the adhesive layer and modifying it with a tackifying resin and an ionomer, the obtained adhesive layer system can have good heat resistance and excellent adhesion to EVA. Thus, through the above structural design and selection of the composition of each layer, not only can the multi-layer co-extrusion of polyamide and polyolefin materials be realized, simplifying the preparation process and shortening the preparation cycle, but also the adhesion performance between each layer is excellent. At the same time, the problem of poor heat resistance of the photovoltaic backsheet can be solved, enabling the photovoltaic backsheet to have good heat resistance. In addition, the photovoltaic backsheet having the above structure and composition also has the advantages of good weather resistance, adhesiveness, and interlayer adhesion. The adhesive layer of the photovoltaic module made of this backsheet has no risk of melt flow within a certain temperature range, which can greatly improve the heat spot performance of the photovoltaic module and reduce the probability of failure of the photovoltaic module due to the backsheet reason.

[0011] In addition, the photovoltaic backsheet according to the above embodiments of the present invention may further have the following additional technical features:

[0012] In some embodiments of the present invention, the melting point of the heat-resistant polyamide is not lower than 180 °C.

[0013] In some embodiments of the present invention, the heat-resistant polyamide includes at least one selected from PA1010, PA11, PA1212, PA6, PA66, PA46, PA6T, and PA9T.

[0014] In some embodiments of the present invention, the tackifying resin includes a copolymer of ethylene and an acrylic resin.

[0015] In some embodiments of the present invention, the tackifying resin includes at least one selected from EVA resin, EMA resin, EAA resin, EEA resin, and EBA resin.

[0016] In some embodiments of the present invention, the main chain of the ionomer is a copolymer of ethylene and methacrylic acid, on which sodium ions and / or zinc ions are introduced.

[0017] In some embodiments of the present invention, the polyethylene includes at least one selected from high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene, and metallocene-catalyzed polyethylene.

[0018] In some embodiments of the present invention, the elastomer includes ethylene-α-olefin copolymer and / or propylene-α-olefin copolymer.

[0019] In some embodiments of the present invention, the compatibilizer includes at least one polyolefin polar group graft copolymer, the main chain of the graft copolymer includes at least one selected from polypropylene, ethylene-α-olefin copolymer, and propylene-α-olefin copolymer, and the polar group includes a group capable of forming a chemical bond with polyamide.

[0020] In some embodiments of the present invention, the first polypropylene and the second polypropylene independently include at least one selected from isotactic polypropylene, block polypropylene, and atactic polypropylene.

[0021] In some embodiments of the present invention, the first filler, the second filler, and the third filler independently include at least one selected from titanium dioxide, talc powder, calcium carbonate, aluminum oxide, aluminum silicate, magnesium silicate, diamond powder, aluminum hydroxide, silicon dioxide, mica powder, barium sulfate, diatomaceous earth, and pumice powder.

[0022] In some embodiments of the present invention, the first anti-aging agent, the second anti-aging agent, and the third anti-aging agent independently include at least one selected from antioxidants, ultraviolet absorbers, light stabilizers, acid absorbers, and free radical quenchers.

[0023] In some embodiments of the present invention, the first modifier includes the elastomer; and / or, the second modifier includes the elastomer and the compatibilizer.

[0024] In some embodiments of the present invention, the photovoltaic backsheet further includes: a first tackifying transition layer and / or a second tackifying transition layer, the first tackifying transition layer is disposed between the adhesive layer and the core layer, and the second tackifying transition layer is disposed between the core layer and the weather-resistant layer.

[0025] In some embodiments of the present invention, the first tackifying transition layer and the second tackifying transition layer each independently comprise at least one selected from polyethylene, ethylene copolymers, polypropylene, modified polypropylene, thermoplastic polyurethane, acrylic resin, and ABS resins; and / or, the first tackifying transition layer and the second tackifying transition layer each independently comprise a plurality of sub-transition layers.

[0026] In some embodiments of the present invention, the photovoltaic backsheet is obtained by one-step coextrusion molding.

[0027] In another aspect of the present invention, the present invention provides a method for preparing the above-mentioned photovoltaic backsheet. According to the embodiments of the present invention, the method comprises: (1) feeding the raw materials of the adhesive layer, the core layer, and the weather-resistant layer into different extruders; (2) simultaneously extruding the raw materials of each layer, and making the extruded product flow through a multi-layer coextrusion die head and cast onto a shaping roller for molding; (3) trimming and winding the molded sheet to obtain a coextruded photovoltaic backsheet. This method is obtained by one-step coextrusion molding, which not only has a simple process flow and a short production cycle, but also the prepared photovoltaic backsheet has good heat resistance, weather resistance, adhesiveness, and interlayer adhesion. Using it in photovoltaic modules can greatly improve the heat-spot resistance performance of the photovoltaic modules and reduce the probability of failure of the photovoltaic modules due to the backsheet.

[0028] In some embodiments of the present invention, in step (1), the raw materials of the adhesive layer, the first tackifying transition layer, the core layer, the second tackifying transition layer, and the weather-resistant layer are fed into different extruders.

[0029] In some embodiments of the present invention, in step (2), the extrusion temperature is 170 - 260 °C, and the rotational speed of the extrusion screw is 200 - 300 r / min.

[0030] In yet another aspect of the present invention, the present invention provides a photovoltaic module. According to the embodiments of the present invention, the photovoltaic module comprises: a photovoltaic front plate; a first hot melt adhesive film layer located on one side of the photovoltaic front plate; a battery cell located on the side of the first hot melt adhesive film layer away from the photovoltaic front plate; a second hot melt adhesive film layer located on the side of the battery cell away from the photovoltaic front plate; and a photovoltaic backsheet located on the side of the second hot melt adhesive film layer away from the photovoltaic front plate. Among them, the photovoltaic backsheet is the above-mentioned photovoltaic backsheet or the photovoltaic backsheet prepared by the above-mentioned method for preparing a photovoltaic backsheet. Thus, the photovoltaic module has all the features and advantages of the above-mentioned photovoltaic backsheet and the method for preparing the photovoltaic backsheet, which will not be elaborated here. Generally speaking, the photovoltaic module has good heat-spot resistance performance.

[0031] Additional aspects and advantages of the present invention will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0033] Figure 1 is a schematic structural diagram of a photovoltaic backsheet according to an embodiment of the present invention.

[0034] Figure 2 is a schematic structural diagram of a photovoltaic backsheet according to another embodiment of the present invention.

[0035] Figure 3 is a flowchart of a method for preparing a photovoltaic backsheet according to an embodiment of the present invention.

[0036] Figure 4 is a schematic structural diagram of a photovoltaic module according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings, in which the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0038] Currently, the solar cell backsheets disclosed in the related art all have various problems. For example, there is an extruded photovoltaic cell backsheet with a structure of a polyamide upper layer / a modified polyamide core layer / a polyamide lower layer. Although a certain amount of coupling agent is used in its inner layer (adhesive layer), it is impossible to know the bonding force stability of the polyamide and the EVA film after long-term aging, and polyamide materials are used in all three layers of this backsheet, resulting in a high cost. There is also a fluorine-free multi-layer co-extruded backsheet with a structure of a modified PA weather-resistant layer / a modified PET structural reinforcement layer / a modified PA adhesive layer. However, due to the use of a modified PA with a relatively low melting point, it is difficult to ensure the heat resistance of the backsheet, and the feasibility of the co-extrusion process of PET and PA is also in doubt. In addition, there is a polyolefin co-extruded backsheet with a polyolefin modified material as the core layer and the adhesive layer on the side of the film, but the heat resistance of this backsheet is poor.

[0039] To this end, in one aspect of the present invention, the present invention provides a photovoltaic backsheet. According to an embodiment of the present invention, the photovoltaic backsheet 100 at least includes an adhesive layer 110, a core layer 120, and a weather-resistant layer 130 arranged in sequence from the inside out. Among them, the adhesive layer 110 includes: 50-80 parts by mass of heat-resistant polyamide, 5-20 parts by mass of tackifying resin, 1-10 parts by mass of ionomer, 1-30 parts by mass of the first filler, 0.1-5 parts by mass of the first anti-aging agent; the core layer 120 includes: 50-80 parts by mass of the first polypropylene, 5-20 parts by mass of the first modifier, 1-30 parts by mass of the second filler, 0.1-5 parts by mass of the second anti-aging agent; the weather-resistant layer 130 includes: 50-80 parts by mass of the second polypropylene, 5-20 parts by mass of the second modifier, 1-30 parts by mass of the third filler, 0-25 parts by weight of polyamide, 0.1-5 parts by mass of the third anti-aging agent; wherein, the first modifier and the second modifier each independently include at least one selected from polyethylene, elastomer, and compatibilizer. The photovoltaic backsheet includes at least three layers of structure. The weather-resistant layer and the adhesive layer are located on the two outer surfaces of the photovoltaic backsheet, and the core layer is located inside the photovoltaic backsheet. The weather-resistant layer is in direct contact with the air, and the adhesive layer is bonded to the photovoltaic encapsulation hot melt adhesive film layer (usually an EVA layer). Among them, in the adhesive layer, by selecting heat-resistant polyamide as the main resin and modifying it with tackifying resin and ionomer, the obtained adhesive layer system can have good heat resistance and excellent bonding performance with EVA. Thus, through the above structural design and the selection of the composition of each layer, not only can the multi-layer co-extrusion of polyamide and polyolefin materials be realized, simplifying the preparation process and shortening the preparation cycle, but also the bonding performance between each layer is excellent, and at the same time, the problem of poor heat resistance of the photovoltaic backsheet can be solved, enabling the photovoltaic backsheet to have good heat resistance. In addition, the photovoltaic backsheet with the above structure and composition also has the advantages of good weather resistance, adhesiveness, and interlayer bonding force. The adhesive layer of the photovoltaic module backsheet made of this backsheet has no risk of melt flow within a certain temperature range, which can greatly improve the heat spot resistance of the photovoltaic module and reduce the probability of failure of the photovoltaic module due to the backsheet reason. It should be noted that in the present invention, in the "arranged in sequence from the inside out", "inside" refers to the side of the photovoltaic backsheet close to the photovoltaic module cell, and "outside" refers to the side of the photovoltaic backsheet far from the photovoltaic module cell. The following refers to Figures 1 - 2 A detailed description will be given to the photovoltaic backsheet 100 of the above embodiment of the present invention.

[0040] Adhesive layer 110

[0041] According to an embodiment of the present invention, the formulation of the adhesive layer 110 includes: 50 - 80 parts by mass of a heat-resistant polyamide (such as 55, 60, 65, 70, or 75 parts by mass, etc.), 5 - 20 parts by mass of a tackifying resin (such as 6, 8, 10, 12, 15, or 18 parts by mass, etc.), 1 - 10 parts by mass of an ionomer (such as 2, 4, 6, or 8 parts by mass, etc.), 1 - 30 parts by mass of a first filler (such as 3, 6, 9, 12, 15, 18, 21, 24, or 27 parts by mass, etc.), 0.1 - 5 parts by mass of a first anti-aging agent (such as 0.5, 1, 2, 3, or 4 parts by mass, etc.). Preferably, the total mass fraction of each component in the adhesive layer formulation can be 100 parts by weight. In the present invention, the melting point of the heat-resistant polyamide is not lower than 180 °C. The adhesive layer 110 uses polyamide as the main resin. Among them, nylon is a polymer containing an amide bond (-CONH-) in the main chain, has a relatively high melting point compared to polyolefins, and has good comprehensive mechanical properties. In the present invention, by selecting a polyamide resin with a melting point not lower than 180 °C and controlling the proportion of the polyamide resin with a melting point not lower than 180 °C in the adhesive layer to be the above-mentioned ratio, preferably not less than 50 wt%, the excellent heat resistance of the adhesive layer can be ensured. In addition, it can be understood that the type of heat-resistant polyamide in the present invention is not particularly limited, and those skilled in the art can select according to actual needs. For example, the heat-resistant polyamide can include but is not limited to at least one of PA1010 (polydodecanedioyl dodecamethylenediamine), PA11 (polyundecanamide), PA1212 (polydodecanedioyl dodecamethylenediamine), PA6 (nylon 6), PA66 (nylon 66, i.e., polyhexamethylene adipamide), PA46 (polyhexamethylene succinamide), PA6T (hexamethylene terephthalamide), PA9T (poly-1,9-nonylene terephthalamide).

[0042] According to an embodiment of the present invention, a tackifying resin is further added to the formulation of the adhesive layer 110. The tackifying resin may preferably be composed of a copolymer of ethylene and acrylic resin. Such a tackifying resin is a polymer with thermoplasticity and extremely high adhesiveness, which can be compatible with all olefin polymers. There is chain segment entanglement at the interface of the EVA melt during the lamination process, which can ensure the bonding performance with the EVA encapsulation film. In addition, the inventors also found that if the addition amount of the tackifying resin in the adhesive layer formulation is too small, it is difficult for the adhesive layer to achieve the standard bonding force with EVA, while if its addition amount is too high, it will cause an increase in the overall cost of the photovoltaic backsheet. By controlling the proportion of the tackifying resin in the adhesive layer formulation as described above, not only can the excellent bonding performance between the adhesive layer and EVA be ensured, but also the production cost can be controlled at a relatively low level. Preferably, the mass proportion of the tackifying resin in the adhesive layer formulation can be 5wt%-20wt%, such as 10wt% or 15wt%. In addition, it can be understood that the specific type of the tackifying resin in the present invention is not particularly limited, and those skilled in the art can select according to actual needs. For example, it may include but is not limited to at least one of EVA resin, EMA resin (ethylene-methyl acrylate copolymer), EAA resin (ethylene-acrylic acid copolymer), EEA resin (ethylene-ethyl acrylate copolymer), and EBA resin (ethylene-butyl acrylate).

[0043] According to an embodiment of the present invention, an ionomer is further added to the formulation of the adhesive layer 110. Among them, the ionomer preferably has a copolymer of ethylene and methacrylic acid as the main chain, and sodium ions and / or zinc ions are introduced thereon. The inventors found that the ionic polymer has excellent melt strength, toughness, and ultraviolet resistance. After adding it, not only can the strength and uniformity of the overall film formation of the adhesive layer be improved, but also the common moisture absorption effect in the polyamide component can be significantly weakened. If its addition amount is too small, it cannot achieve the purpose of increasing strength and uniformity, while if its addition amount is too large, it will bring about an increase in cost. By controlling the proportion of the ionomer in the adhesive layer formulation as described above, both the good overall strength and uniformity of the adhesive layer can be ensured, and it is also beneficial to reduce the production cost. Preferably, the mass proportion of the ionomer in the adhesive layer formulation can be 1-10wt%.

[0044] According to an embodiment of the present invention, the type of the first filler used in the formulation of the adhesive layer 100 is not particularly limited, and those skilled in the art can select according to actual needs. For example, the first filler may include at least one selected from titanium dioxide, talc powder, calcium carbonate, aluminum oxide, aluminum silicate, magnesium silicate, diamond powder, aluminum hydroxide, silicon dioxide, mica powder, barium sulfate, diatomaceous earth, and pumice powder. The inventors have found that incorporating a small amount of the first filler into the adhesive layer can improve the reflection effect of the adhesive layer. However, if the amount of the filler incorporated is too small, its dispersion in the film layer is less, and a high reflection effect cannot be achieved. Increasing the amount of the filler within a certain addition range can improve the reflectivity of the film layer. However, if its incorporation amount is too high, such as higher than 30 wt%, it will reduce the mechanical strength and adhesive effect of the adhesive layer, and at the same time increase the manufacturing cost. In the present invention, by controlling the first filler to be the above proportion in the adhesive layer formulation, a good reflection effect can be achieved for the adhesive layer without affecting the mechanical strength and adhesive performance of the adhesive layer, thereby being more conducive to improving the light utilization rate and efficiency of the photovoltaic module.

[0045] According to an embodiment of the present invention, adding a certain amount of anti-aging agent to the adhesive layer formulation can delay the aging of the adhesive layer, extend the action time of the adhesive layer and the protective effect of the photovoltaic backsheet on the photovoltaic module. Among them, the composition of the first anti-aging agent in the present invention is not particularly limited, and those skilled in the art can select according to actual needs. For example, the first anti-aging agent may include at least one selected from antioxidants, ultraviolet absorbers, light stabilizers, acid absorbers and radical quenchers. In addition, it can be understood that the types of antioxidants, ultraviolet absorbers, light stabilizers, acid absorbers and radical quenchers in the present invention are not particularly limited, and those skilled in the art can select according to actual needs. For example, the antioxidant may be at least one selected from hindered phenol antioxidants, phosphite antioxidants and thioester antioxidants, and preferably may be pentaerythritol [β-(3’,5’-di-tert-butyl-4’-hydroxyphenyl)propionate] and tris(2,4-di-tert-butylphenyl) phosphite; for another example, the acid absorber may be calcium stearate, which is used to eliminate halogens present in polypropylene; the radical quencher may be a hindered amine radical quencher; in addition, the preferred ultraviolet absorber may be 2-hydroxy-4-n-octyloxybenzophenone, and the preferred light stabilizer may be bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate. More preferably, the light stabilizer can be used in combination with the ultraviolet absorber. The inventors have found that the combination of the two can achieve the best effect that cannot be achieved by using the ultraviolet absorber alone, can more effectively prevent the yellowing of the material and block the loss of physical properties, inhibit or weaken the photo-degradation effect, and improve the light aging resistance performance. Further, the inventors have also found that if the dosage of the anti-aging agent in the adhesive layer formulation is less than 0.1 part by mass, the expected anti-aging effect cannot be achieved; and when the amount of the anti-aging agent reaches a certain amount (such as 5 parts by mass), the anti-aging effect of the adhesive layer will not continue to increase due to the increase in the content of the anti-aging agent. On the contrary, it will affect the stretchability of the material and the bonding performance with EVA. By controlling the first anti-aging agent in the adhesive layer formulation to be the above-mentioned proportion in the present invention, the adhesive layer can have a better anti-aging effect without affecting the stretchability and adhesiveness of the material.

[0046] Core layer 120

[0047] According to an embodiment of the present invention, the formulation of the core layer 120 includes: 50 - 80 parts by mass of a first polypropylene (for example, it can be 55, 60, 65, 70 or 75 parts by mass, etc.), 5 - 20 parts by mass of a first modifier (for example, it can be 6, 8, 10, 12, 15 or 18 parts by mass, etc.), 1 - 30 parts by mass of a second filler (for example, it can be 3, 6, 9, 12, 15, 18, 21, 24 or 27 parts by mass, etc.), 0.1 - 5 parts by mass of a second anti-aging agent (for example, it can be 0.5, 1, 2, 3 or 4 parts by mass, etc.). Preferably, the total mass fraction of each component in the core layer formulation can be 100 parts by weight. In the present invention, the main resin of the core layer is polypropylene, which is inexpensive and has excellent mechanical properties. It can be used as the overall support layer of the backplane, and its melting point is higher than the lamination temperature, so it will not be crushed during lamination, and can maximize the insulation penetration (DTI) of the backplane. It can be understood that the type of the first polypropylene in the present invention is not particularly limited, and those skilled in the art can select according to actual needs. For example, the first polypropylene can include one or more selected from isotactic polypropylene, block polypropylene, and atactic polypropylene.

[0048] According to an embodiment of the present invention, a first modifier is added to the core layer formulation to modify the first polypropylene, so as to improve the low-temperature resistance, electrical insulation performance, compatibility, or bonding performance with adjacent layers of the first polypropylene. Among them, in the present invention, the first modifier includes at least one selected from polyethylene, elastomer, and compatibilizer. By adding a small amount of polyethylene to the core layer, the low-temperature resistance and electrical insulation performance of the polypropylene material can be improved, and the price of polyethylene is cheap, which is also beneficial to reducing the production cost; it can be understood that the specific type of polyethylene used as the modifier in the present invention is not particularly limited, and those skilled in the art can select according to actual needs. For example, polyethylene can include at least one selected from high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene, and metallocene-catalyzed polyethylene. Among them, ultra-high molecular weight polyethylene refers to polyethylene with a molecular weight of more than 1 million. In addition, the elastomer can be an α-olefin copolymer, for example, it can include ethylene-α-olefin copolymer and / or propylene-α-olefin copolymer. The inventors found that using the above elastomer can increase the compatibility between the core layer polypropylene and the polyethylene material, and at the same time can increase the bonding performance between the core layer and the adjacent layer. However, the elastomer has a low softening point and poor heat resistance, and the addition amount should not be too high, otherwise it will affect the heat resistance of the core layer, and further affect the dielectric breakdown (DTI) of the backplane. It is preferably controlled that the content of the α-olefin copolymer in the formulation is below 20 wt%, so that not only can the system have good compatibility, and there will be no phenomenon of self-phase separation or insufficient cohesion, but also the heat resistance and dielectric breakdown of the backplane will not be affected. Furthermore, the compatibilizer can include at least one polyolefin polar group graft copolymer. The main chain of the graft copolymer can include at least one selected from polypropylene, ethylene-α-olefin copolymer, and propylene-α-olefin copolymer. The polar group includes a group that can form a chemical bond with polyamide, for example, it can include at least one selected from acid anhydride, acid, epoxide, silane, and isocyanate. Among them, adding a compatibilizer to the core layer can not only improve the compatibility between polypropylene and polyamide, but also using the compatibilizer and polyolefin elastomer together can simultaneously improve the low-temperature performance and heat-aging resistance of the system. Preferably, the first modifier includes an elastomer, whereby the compatibility and bonding performance between the core layer and the adjacent layer can be further ensured.

[0049] According to an embodiment of the present invention, a second filler and a second anti-aging agent are further added to the core layer formulation. The type of the second filler in the core layer formulation is not particularly limited, and those skilled in the art can select according to actual needs. For example, the optional range and specific selection of the second filler can be the same as those of the first filler, and the composition of the second filler can be the same as or different from that of the first filler, which will not be elaborated here one by one. The inventor found that adding a small amount of the second filler to the core layer can also improve the reflectivity. However, if the addition amount is too high, it will also reduce the mechanical strength of the core layer and its bonding effect with the adjacent layer, and at the same time increase the manufacturing cost. In the present invention, by controlling the second filler to be the above-mentioned proportion in the core layer formulation, the core layer can achieve a better reflection effect without affecting the mechanical strength of the core layer and the bonding performance with the adjacent layer, thus being more conducive to improving the light utilization rate and efficiency of the photovoltaic module; preferably, since the core layer is located inside the backsheet and does not directly participate in reflection, on the premise of considering cost, the content of the second filler can not exceed 20 parts by mass. In addition, adding a second anti-aging agent to the core layer formulation can also delay the aging of the core layer. The composition of the second anti-aging agent used for the core layer is not particularly limited, and those skilled in the art can select according to actual needs. For example, the optional range and specific selection of the second anti-aging agent can be the same as those of the first anti-aging agent, and the composition of the second anti-aging agent can be the same as or different from that of the first anti-aging agent, which will not be elaborated here one by one. Further, the inventor also found that if the dosage of the anti-aging agent in the core layer formulation is less than 0.1 part by mass, the expected anti-aging effect cannot be achieved; when the amount of the anti-aging agent reaches a certain amount (such as 5 parts by mass), the anti-aging effect of the core layer will not continue to increase due to the increase in the content of the anti-aging agent. On the contrary, it will affect the stretchability of the material and the bonding performance with the adjacent layer. In the present invention, by controlling the second anti-aging agent to be the above-mentioned proportion in the core layer formulation, the core layer can have a better anti-aging effect without affecting the stretchability of the material and the bonding property with the adjacent layer.

[0050] Weather-resistant layer 130

[0051] According to an embodiment of the present invention, the formulation of the weather-resistant layer 130 includes: 50 - 80 parts by mass of a second polypropylene (for example, it can be 55, 60, 65, 70, or 75 parts by mass, etc.), 5 - 20 parts by mass of a second modifier (for example, it can be 6, 8, 10, 12, 15, or 18 parts by mass, etc.), 1 - 30 parts by mass of a third filler (for example, it can be 3, 6, 9, 12, 15, 18, 21, 24, or 27 parts by mass, etc.), 0 - 25 parts by weight of polyamide (for example, it can be 3, 6, 9, 12, 15, 18, 21, or 24 parts by mass, etc.), and 0.1 - 5 parts by mass of a third anti-aging agent (for example, it can be 0.5, 1, 2, 3, or 4 parts by mass, etc.). Preferably, the total mass parts of each component in the weather-resistant layer formulation can be 100 parts by weight. In the present invention, the main resin of the weather-resistant layer is also polypropylene, and it can be modified by adding a small amount of polyamide to improve the weather resistance and wear resistance of the weather-resistant layer. Among them, selecting polypropylene as the main resin of the weather-resistant layer can further ensure that the photovoltaic backsheet prepared by the co-extrusion process will not be crushed during the lamination process. It can be understood that the type of the second polypropylene in the present invention is not particularly limited either, and those skilled in the art can select according to actual needs. For example, the second polypropylene can include one or more selected from isotactic polypropylene, block polypropylene, and atactic polypropylene. In addition, the types of the second polypropylene and the first polypropylene can be the same or different.

[0052] According to an embodiment of the present invention, the polyamide in the weather-resistant layer can be obtained by polycondensation of a dibasic acid and a diamine. Among them, the polyamide has good compatibility with polypropylene, and has excellent weather resistance and low price. Using it in the weather-resistant layer is beneficial to forming a layer structure with better weather resistance and also helps to reduce the manufacturing cost of the photovoltaic backsheet. Further, the inventors also found that when the content of polyamide in the weather-resistant layer is too high, it is not conducive to forming a good bond between the weather-resistant layer and the core layer. In the present invention, by controlling the proportion of polyamide in the weather-resistant layer formulation to be no more than 25 parts by mass, it can not only ensure good bonding performance between the weather-resistant layer and the core layer, but also be beneficial to forming a better layer structure.

[0053] According to an embodiment of the present invention, a second modifier is added to the weather-resistant layer formulation to modify the second polypropylene, so as to improve the low-temperature resistance, electrical insulation property, compatibility, or adhesion property with an adjacent layer of the first polypropylene, etc. In the present invention, the role played by the second modifier in the weather-resistant layer is the same as that played by the first modifier in the core layer. The second modifier may also include at least one selected from polyethylene, elastomer, and compatibilizer. Among them, by adding a small amount of polyethylene to the weather-resistant layer, the low-temperature resistance and electrical insulation property of the polypropylene material can be improved. Adding an elastomer to the weather-resistant layer can increase the compatibility between the polypropylene in the weather-resistant layer and the polyethylene material, and at the same time can increase the adhesion property between the weather-resistant layer and the core layer. However, the elastomer has a low softening point and poor heat resistance, and the addition amount should not be too high, otherwise it will affect the heat resistance of the weather-resistant layer, and further affect the dielectric breakdown (DTI) of the backsheet. Adding a compatibilizer to the weather-resistant layer can not only improve the compatibility between polypropylene and polyamide, but also improve the low-temperature property and heat-resistant oxygen property of the system when the compatibilizer and polyolefin elastomer are used together. Preferably, the second modifier may simultaneously include a compatibilizer and a polyolefin elastomer, and their contents in the weather-resistant layer formulation may not be higher than 20 wt%, which is more conducive to ensuring the compatibility, low-temperature property, and heat-resistant oxygen property of the system. It should be noted that the optional range and specific selection of polyethylene, elastomer, and compatibilizer may also be the same as those of the first modifier, which will not be elaborated here one by one. Specifically, the composition of the second modifier may be the same as or different from that of the first modifier.

[0054] According to an embodiment of the present invention, a third filler and a third anti-aging agent are further added to the weather-resistant layer formula, wherein the type of the third filler in the weather-resistant layer formula is not particularly limited, and those skilled in the art can select it according to actual needs. For example, the optional range and specific selection of the third filler can be the same as the first filler, and the composition of the third filler can be the same as or different from that of the first filler, which will not be described one by one here. The inventors have found that adding a small amount of the third filler to the weather-resistant layer can also improve the reflectivity, but if the amount added is too high, it will also reduce the mechanical strength of the weather-resistant layer and its bonding effect with the core layer, while increasing the manufacturing cost. In the present invention, by controlling the third filler in the weather-resistant layer formula to the above-mentioned proportion, a better reflection effect can be achieved without affecting the mechanical strength of the weather-resistant layer and the bonding performance with the core layer, thereby being more conducive to improving the light utilization and efficiency of the photovoltaic module. In addition, the aging of the weather-resistant layer can also be delayed by adding a third anti-aging agent to the weather-resistant layer formula, wherein the composition of the third anti-aging agent used for the weather-resistant layer is not particularly limited, and those skilled in the art can select it according to actual needs. For example, the optional range and specific selection of the third anti-aging agent can be the same as the first anti-aging agent, and the composition of the third anti-aging agent can be the same as or different from that of the first anti-aging agent, which will not be described one by one here. Furthermore, the inventors also found that if the amount of the anti-aging agent in the weather-resistant layer formula is less than 0.1 parts by mass, the expected anti-aging effect will not be achieved; and when the amount of the anti-aging agent reaches a certain amount (such as 5 parts by mass), the anti-aging effect of the weather-resistant layer will not continue to increase due to the increase in the content of the anti-aging agent, but on the contrary, it will affect the elasticity of the material and the bonding performance with the core layer. In the present invention, by controlling the third anti-aging agent in the weather-resistant layer formula to the above proportion, the weather-resistant layer can have a better anti-aging effect without affecting the elasticity of the material and the bonding performance with the core layer.

[0055] According to an embodiment of the present invention, referring to Figure 2As shown, the photovoltaic backsheet 100 may further include: a first tackifying transition layer 140 and / or a second tackifying transition layer 150. Among them, the first tackifying transition layer 140 may be provided between the adhesive layer 110 and the core layer 120, and the second tackifying transition layer 150 may be provided between the core layer 120 and the weather-resistant layer 130. In the present invention, the first tackifying transition layer and the second tackifying transition layer are provided to increase the bonding performance between adjacent layers. Among them, the raw material formula of the first tackifying transition layer 140 may be an intermediate component of the adhesive layer and the core layer, and the raw material formula of the second tackifying transition layer 150 may be an intermediate component of the weather-resistant layer and the core layer. The main materials of the two may be selected according to the specific composition of the adjacent layers to be bonded together. For example, the formula materials of the first tackifying transition layer 140 and the second tackifying transition layer 150 may each independently include at least one selected from polyethylene, ethylene copolymers, polypropylene, modified polypropylene, thermoplastic polyurethane, acrylic resin, and ABS resin system, which can further contribute to improving the bonding performance between adjacent layers. In addition, the specific structures of the first tackifying transition layer 140 and the second tackifying transition layer 150 are not particularly limited, and those skilled in the art can select according to actual needs. For example, the first tackifying transition layer 140 and the second tackifying transition layer 150 may each independently be a single-layer structure or may each independently include multiple sub-transition layers, as long as a good tackifying effect can be achieved.

[0056] According to an embodiment of the present invention, the photovoltaic backsheet 100 can be obtained by a coextrusion process in one step. Specifically, the raw materials of each layer can be formed into a final product by a coextrusion process. The temperature of the coextrusion process can be 170 - 260 °C, and each layer is extruded through a different extruder. The rotation speed of the extrusion screw in the coextrusion process can be 200 - 300 r / min. The materials of each layer are cast onto a shaping roller through a multi-layer coextrusion die head, and the coextruded photovoltaic backsheet is prepared after trimming and winding. This process is not only simple but also has a short production cycle, which is more conducive to reducing production costs.

[0057] In another aspect of the present invention, the present invention proposes a method for preparing the above-mentioned photovoltaic backsheet. According to an embodiment of the present invention, the method includes: (1) supplying the raw materials of the adhesive layer, the core layer, and the weather-resistant layer into different extruders; (2) simultaneously extruding the raw materials of each layer, so that the extruded product is cast onto a shaping roller through a multi-layer coextrusion die head for shaping; (3) trimming and winding the shaped plate to obtain a coextruded photovoltaic backsheet. This method is obtained by a coextrusion process in one step. It not only has a simple process flow and a short production cycle, but also the prepared photovoltaic backsheet has good heat resistance, weather resistance, adhesiveness, and interlayer bonding force. Using it in a photovoltaic module can greatly improve the heat spot performance of the photovoltaic module and reduce the probability of failure of the photovoltaic module due to the backsheet.

[0058] According to an embodiment of the present invention, when it is necessary to provide a tackifying transition layer between the adhesive layer and the core layer and between the core layer and the weather-resistant layer, the raw materials of the adhesive layer, the first tackifying transition layer, the core layer, the second tackifying transition layer, and the weather-resistant layer can also be supplied to different extruders, and then co-extruded to prepare the photovoltaic backsheet. It should be noted that the raw materials of the adhesive layer, the core layer, the weather-resistant layer, the first tackifying transition layer, and the second tackifying transition layer can all be selected according to the predetermined formula composition or materials described above, and will not be elaborated here one by one.

[0059] According to an embodiment of the present invention, the temperature of the co-extrusion process can be 170 - 260 °C, and the rotation speed of the extrusion screw can be 200 - 300 r / min. The inventors found that when the temperature of the co-extrusion process is too low, the materials for forming the photovoltaic backsheet cannot be sufficiently melt-blended, and a co-extruded film layer cannot be formed; while when the temperature of the co-extrusion process is too high, the melt fluidity of the materials for forming the photovoltaic backsheet will be too high, which is not conducive to forming a co-extruded film layer or the obtained co-extruded film layer shows an interpenetrating phenomenon between layers, and cannot meet the use requirements of the photovoltaic backsheet; in addition, too large or too small rotation speed of the extrusion screw is not conducive to forming an appropriate thickness of the photovoltaic backsheet. In the present invention, by controlling the co-extrusion process within the above parameter range, it is not only more conducive to obtaining a photovoltaic backsheet with a good layered structure, but also can obtain a more appropriate backsheet thickness, which can meet the requirements of the photovoltaic backsheet for protecting the photovoltaic module and weather resistance, etc., and at the same time avoid waste of raw materials.

[0060] It should be noted that the features and effects described for the above photovoltaic backsheet also apply to the method for preparing the photovoltaic backsheet, and will not be elaborated here one by one.

[0061] In another aspect of the present invention, the present invention provides a photovoltaic module. According to an embodiment of the present invention, as shown in Figure 4 , the photovoltaic module includes: a photovoltaic front plate 500, a first hot melt adhesive film layer 400, a battery cell 300, a second hot melt adhesive film layer 200, and a photovoltaic backsheet 100. Among them, the first hot melt adhesive film layer 400 is located on one side of the photovoltaic front plate 500; the battery cell 300 is located on the side of the first hot melt adhesive film layer 400 away from the photovoltaic front plate 500; the second hot melt adhesive film layer 200 is located on the side of the battery cell 300 away from the photovoltaic front plate 500; the photovoltaic backsheet 100 is located on the side of the second hot melt adhesive film layer 200 away from the photovoltaic front plate 500. Among them, the photovoltaic backsheet 100 is the above-mentioned photovoltaic backsheet or the photovoltaic backsheet prepared by the above method for preparing the photovoltaic backsheet. The photovoltaic front plate can be a transparent plate, such as photovoltaic glass, etc. The second hot melt adhesive film layer can be an EVA adhesive layer, etc. Thus, the photovoltaic module has all the features and advantages of the foregoing photovoltaic backsheet and the method for preparing the photovoltaic backsheet, and will not be elaborated here one by one. Generally speaking, the photovoltaic module has good hot spot resistance performance.

[0062] The solutions of the present application will be described below through specific embodiments (the dosages in the following formulations are all in parts by mass). It should be noted that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those without specific technologies or conditions noted in the embodiments, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For reagents or instruments without the manufacturer noted, they are all conventional products that can be obtained through commercial purchase.

[0063] Examples 1-4 and Comparative Examples 1-4

[0064] Among them, the structures of the photovoltaic backsheets in Examples 1-4 and Comparative Examples 1-4 are all three-layer structures of an adhesive layer, a core layer, and a weather-resistant layer. Moreover, the formulations of the core layer and the weather-resistant layer in Examples 1-4 and Comparative Examples 1-4 are the same, as shown in Table 1 in detail; the formulations of the adhesive layer in Examples 1-4 and Comparative Examples 1-4 are shown in Table 2 in detail.

[0065] Examples 1-4 and Comparative Examples 1-4 mainly vary in the formulation of the heat-resistant adhesive layer, and through relevant tests, it is verified that the co-extruded backsheet of the present invention has excellent performance in terms of heat resistance, adhesion to EVA, interlayer adhesion fastness, and aging resistance. The test results are shown in Table 3 in detail.

[0066] Table 1 Formulations of the core layer and the weather-resistant layer in Examples 1-4 and Comparative Examples 1-4

[0067]

[0068] Table 2 Formulations of the photovoltaic backsheets in Examples 1-4 and Comparative Examples 1-4

[0069]

[0070] Among them, in Table 1 and Table 2, the filler compositions in the adhesive layer, the core layer, and the weather-resistant layer are the same, and they are all titanium dioxide, talcum powder, and calcium carbonate with a mass ratio of 1:1:1; in the adhesive layer, the core layer, and the weather-resistant layer, the anti-aging agent compositions used are the same, and they are all antioxidant, ultraviolet absorber, and light stabilizer with a mass ratio of 1:1:2. In Comparative Example 1, the formulation composition of the modified polyolefin is: 30 parts by mass of polyethylene, 50 parts by mass of polypropylene, 10 parts by mass of elastomer, 2 parts by mass of anti-aging agent composition, and 8 parts by mass of filler.

[0071] According to the formulations in Table 1 and Table 2, the compositions of each layer of the photovoltaic backsheets in Examples 1-4 and Comparative Examples 1-4 were respectively mixed and then added to an extruder, melted in the extruder screw, and extruded through a T-die (casting method) to prepare a solar cell backsheet with a three-layer structure. Corona treatment was carried out on the heat-resistant adhesive layer as needed to obtain a backsheet for solar cell modules. Then, its performance was tested. The heat-resistant adhesive layer was separately subjected to film coating to prepare a single-layer film for heat resistance performance testing. All the test results are as follows:

[0072] Table 3 Test Results of Photovoltaic Backsheets of Examples 1-4 and Comparative Examples 1-4

[0073]

[0074] Among them, the performance test methods on which Table 3 is based are as follows:

[0075] 1) Heat-resistant Adhesive Layer Load Deformation Test: Vertically suspend the heat-resistant adhesive layer sample film in a 180 °C forced-air oven, fix a 100 g weight at the lower end of the film, and observe the deformation of the film after 1 h.

[0076] 2) Adhesion Force Test with the Glue Film: Conduct the test in accordance with "T / CPIA 0015-2019".

[0077] 3) Adhesion Fastness Test between the Adhesive Layer and the Core Layer: After preparing the backsheet, peel off the adhesive layer and the core layer of the backsheet, and then conduct the test according to item 6.7 in "GB / T 31034-2014", using a universal tensile testing machine of model ETM-104B for the test.

[0078] Results and Conclusions: By comparing the contents in Tables 1-3, it can be seen that the photovoltaic backsheets of the above embodiments of the present invention have good heat resistance and heat deformation resistance, and have good bonding performance, and can meet the usage requirements of photovoltaic modules.

[0079] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0080] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

Claims

1. A photovoltaic backsheet, characterized in that, It at least includes an adhesive layer, a core layer, and a weather-resistant layer arranged in sequence from inside to outside, where: The adhesive layer includes: 50-80 parts by mass of heat-resistant polyamide, 5-20 parts by mass of tackifying resin, 1-10 parts by mass of ionomer, 1-30 parts by mass of the first filler, 0.1-5 parts by mass of the first anti-aging agent; The core layer includes: 50-80 parts by mass of the first polypropylene, 5-20 parts by mass of the first modifier, 1-30 parts by mass of the second filler, 0.1-5 parts by mass of the second anti-aging agent; The weather-resistant layer includes: 50-80 parts by mass of the second polypropylene, 5-20 parts by mass of the second modifier, 1-30 parts by mass of the third filler, 0-25 parts by weight of polyamide, 0.1-5 parts by mass of the third anti-aging agent; Wherein, the first modifier and the second modifier are each independently selected from at least one of polyethylene, elastomer, and compatibilizer; The heat-resistant polyamide is selected from at least one of PA1010, PA11, PA1212, PA6, PA66, PA46, PA6T, and PA9T; The tackifying resin is selected from at least one of copolymers of ethylene and acrylic resin, EVA resin, EMA resin, EAA resin, EEA resin, and EBA resin; The main chain of the ionomer is a copolymer of ethylene and methacrylic acid, and sodium ions and / or zinc ions are introduced thereon; The polyethylene is selected from at least one of high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, ultra-high molecular weight polyethylene, and metallocene-catalyzed polyethylene; The elastomer is selected from ethylene-α-olefin copolymer and / or propylene-α-olefin copolymer; The compatibilizer is selected from at least one polyolefin polar group graft copolymer, the main chain of the graft copolymer is selected from at least one of polypropylene, ethylene-α-olefin copolymer, and propylene-α-olefin copolymer, and the polar group is a group capable of forming a chemical bond with polyamide, selected from at least one of acid anhydride, acid, epoxide, silane, and isocyanate.

2. The photovoltaic backsheet according to claim 1, wherein The melting point of the heat-resistant polyamide is not lower than 180 °C.

3. The photovoltaic backsheet according to claim 1, wherein Meet at least one of the following conditions: The first polypropylene and the second polypropylene are each independently selected from at least one of isotactic polypropylene, block polypropylene, and atactic polypropylene; The first filler, the second filler, and the third filler are each independently selected from at least one of titanium dioxide, talc powder, calcium carbonate, aluminum trioxide, aluminum silicate, magnesium silicate, diamond powder, aluminum hydroxide, silicon dioxide, mica powder, barium sulfate, diatomaceous earth, and pumice powder; The first anti-aging agent, the second anti-aging agent, and the third anti-aging agent are each independently selected from at least one of antioxidant, ultraviolet absorber, light stabilizer, acid absorber, and free radical quencher.

4. The photovoltaic backsheet according to claim 3, characterized in that, The first modifier includes the elastomer; and / or, the second modifier includes the elastomer and the compatibilizer.

5. The photovoltaic backsheet according to any one of claims 1 to 4, characterized in that, Further includes: The first tackifying transition layer and / or the second tackifying transition layer, wherein the first tackifying transition layer is disposed between the adhesive layer and the core layer, and the second tackifying transition layer is disposed between the core layer and the weather-resistant layer.

6. The photovoltaic backsheet according to claim 5, characterized in that, The first tackifying transition layer and the second tackifying transition layer each independently include at least one selected from the group consisting of polyethylene, ethylene copolymers, polypropylene, modified polypropylene, thermoplastic polyurethane, acrylic resin, and ABS resins; and / or, The first tackifying transition layer and the second tackifying transition layer each independently include a plurality of sub-transition layers.

7. The photovoltaic backplane according to claim 1, characterized in that, The photovoltaic backsheet is obtained by one-time forming using a co-extrusion process.

8. A method for preparing the photovoltaic backsheet according to any one of claims 1 to 7, characterized in that, Comprising: (1) Supplying the raw materials of the adhesive layer, the core layer, and the weather-resistant layer to different extruders; (2) Extruding the raw materials of each layer simultaneously, and causing the extruded product to flow through a multi-layer co-extrusion die head and cast onto a shaping roller to form; (3) Trimming and winding the formed sheet to obtain a co-extruded photovoltaic backsheet.

9. The method according to claim 8, characterized in that, In step (1), the raw materials of the adhesive layer, the first tackifying transition layer, the core layer, the second tackifying transition layer, and the weather-resistant layer are supplied to different extruders; Optionally, in step (2), the extrusion temperature is 170~260 °C, and the extrusion screw speed is 200~300 r / min.

10. A photovoltaic module, characterized in that, Comprising: A photovoltaic front plate; A first hot melt adhesive film layer, which is located on one side of the photovoltaic front plate; A solar cell, which is located on the side of the first hot melt adhesive film layer away from the photovoltaic front plate; A second hot melt adhesive film layer, which is located on the side of the solar cell away from the photovoltaic front plate; A photovoltaic backsheet, which is located on the side of the second hot melt adhesive film layer away from the photovoltaic front plate, wherein, the photovoltaic backsheet is the photovoltaic backsheet according to any one of claims 1~7 or the photovoltaic backsheet prepared by the method according to any one of claims 8~9.

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