A backsheet comprising a polyolefin-based functional layer facing the rear encapsulant.

Abstract

The present invention relates to a solar cell backsheet that includes a functional layer, and provides a backsheet that overcomes disadvantages such as curvature at the edges of the backsheet, relatively poor interlayer adhesion to adhesive layers, and the high oxygen permeability of polyethylene. [Solution] The functional layer includes a polyethylene alloy and a semi-crystalline polymer, such as polypropylene. The polyethylene alloy includes a copolymer containing an ethylene segment (-CH2-CH2-) selected from ethylene acrylate copolymer, ethylene-hexene copolymer, ethylene-octene copolymer, and ethylene-vinyl acetate copolymer. The functional layer further includes an inorganic filler selected from calcium carbonate, titanium dioxide, barium sulfate, mica, talc, kaolin, glass microbeads, and glass fiber. The present invention also relates to a photovoltaic module including the backsheet according to the present invention.

Description

Detailed Description of the Invention

[0001] The present invention relates to a backsheet for a solar cell module. In particular, the present invention relates to a backsheet comprising a polyolefin-based functional layer directly facing a rear encapsulant. The present invention also relates to a photovoltaic module comprising the backsheet.

[0002] Solar cells or photovoltaic modules are used to generate electrical energy from sunlight. Photovoltaic modules are an important source of renewable energy. In particular, they contain solar cells that emit electrons when exposed to sunlight. These solar cells, which are usually made of semiconductor materials that can be fragile, are typically encapsulated with a polymer material that protects them from physical impacts and scratches. Encapsulated solar cells are generally further protected by glass or another outer layer that is resistant to weathering, abrasion, or other physical insults.

[0003] Photovoltaic modules are traditionally mounted outdoors on rooftops or in wide-open spaces, where their exposure to sunlight is maximized. As sunlight intensity increases, the electrical output from a photovoltaic module also increases. However, the efficiency with which a photovoltaic module converts sunlight into electricity is typically only about 20%. The remaining approximately 80% of sunlight is reflected or absorbed by the module. The absorbed energy results in an increase in the module's operating temperature. Excess heat reduces the efficiency with which a photovoltaic module converts sunlight into electricity.

[0004] Solar cell modules have a front surface protective sheet placed on the side exposed to sunlight to protect the surface. This layer is, for example, a glass layer, which is a rigid outer layer that allows light energy to pass through and be converted into electricity while protecting the PV cells and electronics from the environment. Solar cell modules also have a solar cell rear surface protective sheet, called a backsheet, placed on the opposite side to protect the power-generating cells.

[0005] The fragile solar cells are further protected by the use of so-called encapsulants. The encapsulant is used to achieve adhesion between the solar cells, the front surface, and the rear surface or backsheet of the PV module. Suitable polymer materials for solar cell encapsulants typically have a combination of characteristics, such as high impact resistance, high permeation resistance, good ultraviolet (UV) resistance, good long-term thermal stability, adequate adhesion strength to glass and / or other rigid polymer sheets, high moisture resistance, and good long-term weathering resistance. Examples of encapsulants include ionomers, ethylene vinyl acetate (EVA), poly(vinyl acetal), polyvinyl butyral (PVB), thermoplastic polyurethane (TPU), polyvinyl chloride (PVC), metallocene-catalyzed linear low-density polyethylene, polyolefin block elastomers, poly(ethylene-co-methyl acrylate) and poly(ethylene-co-butyl acrylate), silicone elastomers, or epoxy resins. EVA is the most commonly used encapsulant material. EVA sheets are typically inserted between the solar cells and the top surface (called the front encapsulant) and between the solar cells and the back surface (called the back encapsulant).

[0006] The backsheet is a photovoltaic laminate that protects the PV module from UV, moisture, and weather while acting as an electrical insulator. The backsheet often contains several polymer layers that provide the above properties and minimize degradation in the long-term performance of the solar cell module. Each polymer layer has its own function in the backsheet. Typically, the backsheet includes a functional layer facing the cell, a structural reinforcing layer, a weatherproof layer, and an adhesive layer between the functional layer and the structural reinforcing layer and / or between the structural reinforcing layer and the weatherproof layer. Examples of polymers used in the above layers include polypropylene, polyvinyl chloride, polyesters such as PET or PBT, fluororesins such as PTFE or PVDF, and acrylic resins.

[0007] Backsheets comprising a polyolefin layer directly facing the back encapsulant are known in the art. These backsheets are disclosed, for example, in International Publication No. 2014083604. International Publication No. 2014083604 discloses a high-temperature, high-humidity resistant solar cell backsheet consisting of a weatherproof layer, a first connecting layer, a structural reinforcement layer, and a reflective layer. The reflective layer faces the cell and comprises polyethylene, a copolymer containing the ethylene chain segment -CH2-CH2-, a UV-resistant stabilizer, and a white inorganic pigment. The disadvantage of the described backsheet, which includes this reflective layer based on polyethylene and a copolymer containing the ethylene chain segment (-CH2-CH2-), is that it has poor integrity during lamination, resulting in excessive shrinkage, which can cause stress upon cooling after lamination, which can lead to curling at the edges of the backsheet. Furthermore, these backsheets exhibit relatively low interlayer adhesion to the adhesive layer attached to the structural reinforcement layer. Another disadvantage is the high oxygen permeability of polyethylene, which can lead to corrosion at the contacts in the PV module.

[0008] The object of the present invention is to overcome the above disadvantages.

[0009] The solar cell backsheet is provided with a functional layer facing the back encapsulant, wherein the functional layer comprises: , Po polyethylene alloy and Has a melting point above 140°C The objectives of the present invention are achieved in that it includes a semi-crystalline polymer.

[0010] It has been found that the integrity during lamination is increased, thus realizing reduced residual stress, and therefore achieving improved durability. Improved durability prevents the formation of surface planarity defects, such as curvature or waviness, and prevents the formation of microcrack growth in silicon cells and solder joints. It has also been found that the addition of a semi-crystalline polymer in the functional layer improves interlayer adhesion to the adhesive layer attached to the structural reinforcement layer. Surprisingly, the adhesion of the functional layer containing the semi-crystalline polymer to the backside encapsulant remains good.

[0011] During PV module lamination, a backsheet typically projects the PV module stack onto a belt in a laminator, with the AR-coated glass facing the belt. When pressure is applied to the stack at elevated temperatures, the backsheet is pressed against the belt, and the functional layer can therefore contact the belt. If the adhesion between the functional and structural layers is too low, portions of the functional layer will remain on the belt and contaminate the front side of the AR-coated glass in the next lamination cycle. Such contamination must be removed and can damage the AR coating during cleaning. Increasing adhesion between the structural and functional layers prevents this contamination, eliminating the need for cleaning and preventing the AR coating from being damaged.

[0012] The semi-crystalline polymer is preferably selected from the group consisting of polyolefins, polyamides, or polyesters.

[0013] Examples of semi-crystalline polyolefins are, for example, polyethylene, polypropylene homopolymers and copolymers, maleic anhydride grafted polypropylene and / or polybutylene, with polypropylene copolymers being most preferred.

[0014] In the case of polypropylene copolymers, propylene is the predominant monomer unit, which may contain other alpha-olefins such as ethylene and butene-1. These polypropylenes may be obtained using Ziegler-Natta or metallocene catalysts.

[0015] The term "semi-crystalline" is understood to mean that the polymer typically has a crystallinity in the range of 10-80%. Preferably, the crystallinity of the polymer is greater than 30%. Assessment of the crystallinity of a polymer is most easily accomplished using differential scanning calorimetry (DSC), which measures the heat flow to or from a sample as it is heated, cooled, or held at a constant temperature.

[0016] The Pyris6 DSC from PerkinElmer, for example, provides a means of measuring the percent crystallinity of thermoplastic materials. DSC measurements are well known in the art.

[0017] Regardless of how the degree of crystallinity of crystalline polypropylene is measured, it is the polymer's properties, as that term is used herein, that determine whether a given polymer is "semi-crystalline." The first property is the melting point. When semi-crystalline polypropylenes are prepared using Ziegler-Natta catalysts, they may have a melting point above 140°C. Preferably, the melting point is above 145°C, and most preferably, the melting point is between 150 and 170°C. The second determining property is the heat of fusion. When the polypropylene is a Ziegler-Natta derived polymer, it may have a heat of fusion of at least 100 joules / g, at least 115 joules / g, or at least 120 joules / g. The heat of fusion is determined using a differential scanning calorimeter and a method such as that described in ASTM D-3417-99, in which a 5-10 mg sample is heated and cooled at a rate of 10 degrees Celsius.

[0018] When the semi-crystalline polypropylene is obtained by using a metallocene catalyst, the polypropylene has a melting point of at least about 158°C and a heat of fusion of at least 90 Joules / g. For Ziegler-Natta derived polypropylenes, the crystalline characteristics of the metallocene-catalyzed polypropylene can also be assessed using DSC. Examples of semi-crystalline polypropylenes useful in the present invention are ATOFINA™, BP™ Accpro 9346, BASELLADSTIF™ HA722J, Sinopec K8003, and SUNOCO™ PPF-050-HC.

[0019] The functional layer contains at least 5 wt% semi-crystalline polymer, preferably at least 10 wt% semi-crystalline polymer, based on the total weight of polymer in the functional layer, and more preferably 10-49 wt% semi-crystalline polymer, based on the total weight of polymer in the functional layer.

[0020] The polyethylene (PE) alloy or blend in the functional layer of the present invention preferably comprises polyethylene and "polar" polyethylene. Polar polyethylene refers to ethylene copolymerized with a polar comonomer selected from, for example, vinyl acetate, acrylic acid esters and methacrylic acid esters, such as methyl acrylate, ethyl acrylate, butyl acrylate, or ethylhexyl acrylate. Preferably, the polyethylene (PE) alloy is a blend of polyethylene and an ethylene-methacrylate copolymer and / or an ethylene-vinyl acetate copolymer.

[0021] Semicrystalline polyamides have high dimensional stability under heat, lower water absorption, improved resistance to hydrolysis, and increased dimensional stability under the action of moisture. Low moisture absorption also ensures good electrical insulation in high humidity environments. Examples of semicrystalline polyamides include polyamide 6; polyamide 6.6; polyamide 4.6; polyamide 4.10; polyamide 6.10; polyamide 6.12; polyamide 6.14; polyamide 6.13; polyamide 6.15; polyamide 6.16; polyamide 11; polyamide 12; polyamide 10; polyamide 9.12; polyamide 9.13; polyamide 9.14; polyamide 9.15; polyamide 6.16; polyamide 10.10; polyamide 10.12; polyamide 10.13; polyamide 10.14; polyamide 12.10; polyamide 12.12; polyamide 12.13; polyamide 12.14.Adipamide polyethylene terephthalate, polyethylene terephthalate azelaic acid amide, polyethylene sebacic acid amide, polyethylene terephthalate twelve diamide, adipic adipamide / terephthalic adipamide copolyamide, adipamide terephthalate / isophthalate copolymerized adipamide amide, m-xylene polyadipates amide, terephthalic adipamide / terephthalic acid methyl glutaramide glutaramido), adipic adipamide / terephthalate adipamide / isophthalate copolyamide adipamide, polycaprolactam-terephthalate adipamide, polyamide 12, and any mixtures thereof. Preferred polyamides with limited moisture absorption are selected, such as polyamides 11, 12, or 4, 10;

[0022] Examples of semicrystalline polyesters are poly(trans-1,4-cyclohexylenealkanedicarboxylates), such as poly(trans-1,4-cyclohexylene succinate) and poly(trans-1,4-cyclohexylene adipate), poly(cis or trans-1,4-cyclohexanedimethylene), alkanedicarboxylates, such as poly(cis1,4-cyclohexanedimethylene)oxalate and poly(cis1,4-cyclohexanedimethylene)succinate, poly(alkylene terephthalates), such as poly(cis-1,4-cyclohexanedimethylene)oxalate and poly(cis1,4-cyclohexanedimethylene)succinate, poly(alkylene terephthalates), such as poly(cis-1,4-cyclohexylene alkanedicarboxylate), poly(cis-1,4-cyclohexanedimethylene)oxalate and poly(cis1,4-cyclohexanedimethylene)succinate, poly(alkylene terephthalates), such as poly(cis-1,4-cyclohexylene alkanedicarboxylate), poly(cis-1,4-cyclohexanedimethylene)oxalate and poly(cis1,4-cyclohexanedimethylene)succinate, poly(alkylene terephthalates), such as poly(cis-1,4-cyclohexylene alkanedicarboxylate), poly(cis-1,4-cyclohexylene alkanedicarboxylate), poly(cis-1,4-cyclohexanedimethylene)oxalate and poly(cis-1,4-cyclohexanedimethylene)succinate, ... polyethylene terephthalate and polytetramethylene terephthalate, poly(alkylene isophthalates), such as polyethylene isophthalate and polytetramethylene isophthalate, poly(p-phenylene alkane dicarboxylates), such as poly(p-phenylene glutarate) and poly(p-phenylene adipate), poly(p-xylene oxalate), poly(o-xylene oxalate), poly(p-phenylene dialkylene terephthalates), such as poly(p-phenylenedimethylene terephthalate) and poly(p-phenylene -di-1,4-butylene terephthalate), poly(alkylene-1,2-ethylenedioxy-4,4'-dibenzoates), for example, poly(ethylene-1,2-ethylenedioxy-4,4'-dibenzoate), poly(tetramethylene-1,2-ethylenedioxy-4,4'-dibenzoate) and poly(hexamethylene-1,2-ethylenedioxy-4,4'-dibenzoate), poly(alkylene-4,4'-dibenzoates), for example, poly(pentamethylene-4,4'-dibenzoate), poly(hexamethylene-4,4'-dibenzoate), and poly(decamethylene-4,4'-dibenzoate), poly(alkylene-2,6-naphthalenedicarboxylates), such as poly(ethylene-2,6-naphthalenedicarboxylate), poly(trimethylene-2,6-naphthalenedicarboxylate) and poly(tetramethylene-2,6-naphthalenedicarboxylate), and poly(alkylenesulfonyl-4,4'-dibenzoates), such as poly(octamethylenesulfonyl-4,4'-dibenzoate) and poly-(decamethylenesulfonyl-4,4'-dibenzoate).A preferred polyester is a poly(alkylene terephthalate), such as polyethylene terephthalate (PET) or polybutylene terephthalate (PBT).

[0023] The functional layer according to the present invention may further contain inorganic fillers and other additives. Examples of inorganic fillers include calcium carbonate, titanium dioxide, barium sulfate, mica, talc, kaolin, ZnO, ZnS, glass microbeads, and glass fiber. When such fillers are used, the functional layer contains 0.05 to 20 wt. % of the filler, based on the total weight of the polymer in the functional layer. Preferably, the functional layer contains 5 to 15 wt. % of the filler, based on the total weight of the polymer in the functional layer. Examples of additives are selected from UV stabilizers, UV absorbers, antioxidants, heat stabilizers, and / or hydrolysis stabilizers. When such stabilizers are used, the functional layer contains 0.05 to 10 wt. % of the additive, based on the total weight of the polymer in the functional layer, more preferably up to 5 wt. %.

[0024] White pigments, such as TiO2, ZnO, or ZnS, can be added to the functional layer to increase the backscattering of sunlight, resulting in increased efficiency of the solar module. Black pigments, such as carbon black, can also be added for aesthetic reasons.

[0025] The solar backsheet according to the present invention may further comprise other layers, such as a structural reinforcement layer and / or a weathering layer. The structural reinforcement layer and / or the weathering layer may further comprise an inorganic filler or additive as mentioned in the above paragraph.

[0026] The solar backsheet according to the present invention may further comprise an adhesive layer disposed between the functional layer and the structural reinforcing layer and / or between the structural reinforcing layer and the weather-resistant layer. The adhesive layer may comprise, for example, a maleic anhydride-grafted polyolefin, such as maleic anhydride-grafted polyethylene or maleic anhydride-grafted polypropylene, an ethylene-acrylic acid copolymer, or an ethylene-acrylic acid ester-maleic anhydride terpolymer. Preferably, the adhesive layer comprises a maleic anhydride-grafted polyolefin, such as maleic anhydride-grafted polyethylene or maleic anhydride-grafted polypropylene.

[0027] The weather resistant layer may comprise, for example, a polyamide or a fluororesin such as PTFE or PVDF. The polyamide may, for example, be selected from one or more of the following materials: Polyamide 6, Polyamide 6,6; Polyamide 4,6; Polyamide 4,10; Polyamide 6,10; Polyamide 6,12; Polyamide 6,14; Polyamide 6,13; Polyamide 6,15; Polyamide 6,16; Polyamide 11; Polyamide 12, Polyamide 10, Polyamide 9,12, Polyamide 9,13, Polyamide 9,14, Polyamide 9,15, Polyamide 6,16, Polyamide 10,10, Polyamide 10,12, Polyamide 10,13, Polyamide 10,14, Polyamide 12,10, Polyamide 12,12, Polyamide 12,13, Polyamide 12,14, Adipic adipamide / terephthalic adipamide copolyamide, Terephthalic adipamide / isophthalic adipamide copolyamide copolyamide), poly(adipic acid meta-dimethylbenzamide), terephthalic adipamide / terephthalic 2-methylglutaramide, adipic adipamide / terephthalic adipamide / isophthalic adipamide copolyamide, and polycaprolactam-terephthalic adipamide. The weathering layer may further comprise titanium dioxide or barium sulfate, UV stabilizers, and heat stabilizers.

[0028] The structural reinforcement layer may comprise, for example, an engineering plastic such as polypropylene or a blend of polypropylene or modified polypropylene, a polyester such as PET or a polyamide as described above.

[0029] The backsheet of the present invention, which includes a structural reinforcement layer and / or a weather-resistant layer and / or an adhesive layer, may further include inorganic fillers and other additives. Examples of fillers and additives and possible amounts are described above.

[0030] The solar backsheet according to the present invention can be prepared using a multi-layer co-extrusion process, which includes the steps of compounding the individual formulations of the functional layer and other layers, such as the structural reinforcement layer and / or the weathering layer and / or the adhesive layer, including inorganic fillers, additives and stabilizers, followed by extrusion of the different layers and laminating them together.

[0031] Alternatively, the solar backsheet according to the present invention can also be produced by the following method: The first method includes the following steps: (1) pelletizing the all-weather layer material, adhesive layer material, structural reinforcement layer material, and functional layer material in an extruder, respectively, to obtain all-weather layer plastic particles, adhesive layer plastic particles, structural reinforcement layer plastic particles, and functional layer plastic particles; and (2) fusing and co-extruding the all-weather layer plastic particles, adhesive layer plastic particles, structural reinforcement layer plastic particles, and functional layer plastic particles prepared in step (1) into a multilayer coextruded film.

[0032] Another method includes the following steps: (1) pelletizing the adhesive layer material, the structural reinforcement layer material, and the functional layer material in an extruder, respectively, to obtain adhesive layer plastic particles, structural reinforcement layer plastic particles, and functional layer plastic particles; and (2) fusing and co-extruding the adhesive layer plastic particles, structural reinforcement layer plastic particles, and functional layer plastic particles prepared in step (1) through an extruder, and extrusion laminating a co-extruded multilayer film onto the all-weather layer.

[0033] The backsheet can also be obtained by extruding separate layers of the backsheet and laminating the layers together with an adhesive, for example an epoxy, acrylate or polyurethane adhesive.

[0034] The present invention also relates to a photovoltaic module comprising a solar backsheet according to the present invention. The photovoltaic module (abbreviated as PV module) comprises at least the following layers in order of location from the front sun-facing side to the back non-sun-facing side: (1) a transparent pane (representing the front sheet), (2) a front encapsulant, (3) a solar cell layer, (4) a back encapsulant, and (5) a backsheet according to the present invention.

[0035] The front sheet is typically a glass plate or, in the case of flexible modules, a layer from a fluorinated polymer, such as ETFE (ethylene tetrafluoroethylene) or PVDF (polyvinylidene fluoride).

[0036] The present invention further relates to a process for preparing such a solar cell module, the process comprising (a) providing an assembly comprising one or more polymer layers as described above, and (b) laminating the assembly to form a solar cell module. The lamination step of the process may be performed by subjecting the assembly to heat and optionally vacuum or pressure.

[0037] The invention will now be illustrated by a series of examples and comparative experiments.

[0038] [Example] The method for manufacturing the lower solar backplate includes the following steps: The materials for the weathering-resistant layer, adhesive layer, structural reinforcing layer and functional layer are each pelletized by an extruder to obtain plastic pellets.

[0039] The backsheet is prepared by a multi-layer co-extrusion process, in which the pellets of each layer are added to multiple extruders, melt-extruded at high temperature, passed through an adapter and a die, cooled by a cooling roller, and shaped to produce a multi-layer backsheet. The compositions of different layers in the multi-layer backsheet are shown in Table 1.

[0040] [measurement] The peel strength between the functional layer and the structural reinforcing layer, and between the functional layer and EVA as an encapsulant, is measured.

[0041] Aging is measured: appearance after 48 hours of aging in a HAST high pressure accelerated aging tester (121°C, 100% humidity).

[0042] Appearance and yellowing are measured after aging under 120 KWH UV light.

[0043] The results of these measurements for the multilayer backsheets of Comparative Examples I and II, and Examples 1-5, are shown in Table 2.

[0044] [Comparative Example I (CE-I)] PVDF fluoropolymer is used as the weathering-resistant layer, and a blend of maleic anhydride-grafted polypropylene and EMA (ethylene methyl acrylate) polymer is used as the adhesive layer, which can bond both the fluoropolymer and the maleic anhydride-grafted polypropylene. No semi-crystalline polymer is used as the functional layer.

[0045] [Comparative Example II (CE-II)] Nylon 12 (PA12) polymer is used as the weathering resistant layer, maleic anhydride grafted polypropylene is used as the adhesive layer, and no semi-crystalline polymer is added to the functional layer.

[0046] [Examples 1 to 4] A semi-crystalline polymer, such as polypropylene or maleic anhydride grafted polypropylene, is added to the functional layer in Examples 1-4, respectively.

[0047] [Table 1] TIFF0007753181000002.tif103147

[0048] In Table 1, each layer is a multi-component layer, and the proportion of each component is in parts by weight.

[0049] Elvaloy AC1224 is a copolymer of ethylene and methyl acrylate from DuPont.

[0050] [Table 2]

[0051] It can be seen from the data in Table 2 that adding 5 to 15 parts of polypropylene (PP) to the functional layer significantly improved adhesion between the functional layer and the structural reinforcement layer, while slightly reducing adhesion between the functional layer and the EVA encapsulation layer. The adhesion between the functional layer and the structural reinforcement layer increased with the addition of 10 parts by weight of polypropylene (PP) and 15 parts by weight of maleic anhydride-grafted polypropylene (MPP). From the HAST and UV aging resistance test results, it can be seen that the addition of polypropylene or maleic anhydride-grafted polypropylene in the functional layer did not have much effect on hydrolysis resistance and UV aging resistance.

[0052] As can be seen from Tables 1 and 2, the adhesion between the functional layer and the structural reinforcement layer in the backsheets of Examples 1 to 4 is significantly improved relative to the adhesion of the backsheets of Comparative Examples I and II. Furthermore, the peel strength to the sealing layer can also be maintained at a good level, and there are no shortcomings in terms of the adhesion between the backsheet layers and the adhesion to the sealing layer, which means that the overall durability of the backsheet is improved.

Claims

1. A solar cell backsheet comprising a functional layer facing a back encapsulant, the functional layer comprising a blend of a polyethylene alloy and at least 5 wt. %, based on the total weight of polymers in the functional layer, of a semi-crystalline polymer having a melting point above 140°C selected from a polypropylene homopolymer or copolymer; A solar cell backsheet, wherein the backsheet further comprises a structural reinforcement layer, the structural reinforcement layer comprising a layer selected from the group consisting of polypropylene, modified polypropylene, maleic anhydride grafted polypropylene, or blends thereof.

2. 10. The solar cell backsheet of claim 1, wherein the functional layer comprises at least 10 wt% of semi-crystalline polymer, based on the total weight of the polymer in the functional layer.

3. 3. The solar cell backsheet according to claim 1 or 2, wherein said copolymer of polypropylene is selected from polypropylene random, polypropylene block copolymer or maleic anhydride grafted polypropylene.

4. The polyethylene alloy has an ethylene segment (—CH ２ -CH ２ 10. The solar cell backsheet of claim 1, comprising a copolymer containing .alpha.-.

5. The ethylene segment (—CH ２ -CH ２ 5. The solar cell backsheet of claim 4, wherein the copolymer containing (-) is selected from one or more of an ethylene acrylate copolymer, an ethylene methacrylate copolymer, an ethylene-hexene copolymer, an ethylene-octene copolymer, or an ethylene-vinyl acetate copolymer.

6. The solar cell backsheet of claim 5 , wherein the copolymer comprises an ethylene acrylate copolymer.

7. The solar cell backsheet according to any one of claims 1 to 6, wherein the functional layer further comprises an inorganic filler.

8. 8. The solar cell backsheet of claim 7, wherein the inorganic filler is selected from one of calcium carbonate, titanium dioxide, barium sulfate, mica, talc, kaolin, glass microbeads, and glass fiber.

9. The solar cell backsheet according to any one of claims 1 to 8, further comprising a weather-resistant layer and / or an adhesive layer.

10. The solar cell backsheet according to claim 9 , wherein the weather-resistant layer comprises a fluororesin or a polyamide.

11. 10. The solar cell backsheet of claim 9, wherein the adhesive layer comprises a maleic anhydride-grafted polyolefin.

12. The solar cell backsheet according to any one of claims 9 to 11, wherein the structural reinforcement layer and / or the weather-resistant layer and / or the adhesive layer further comprises an inorganic filler.

13. A photovoltaic module comprising a backsheet according to any one of claims 1 to 12.

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