Photovoltaic module backsheet including a polyolefin layer

Abstract

The present invention provides a solar cell module backsheet comprising a solar cell module backsheet comprising, in order, a functional layer and a weathering layer, wherein the backsheet does not comprise a fluorinated polymer; i) the functional layer comprises a blend of polyethylene and a polyethylene copolymer, wherein at least 50% by weight of the functional layer is polyethylene; and ii) the weathering layer comprises a first sublayer facing the functional layer and a second sublayer, wherein a) the first sublayer and the second sublayer each comprise at least 50% by weight of polypropylene; and b) the second sublayer has a minimum glass transition temperature (T g The present invention relates to a solar cell module back sheet having a structure comprising: The present invention also relates to a method for producing a backsheet according to the invention and a solar module comprising a backsheet according to the 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 in which each layer comprises at least 50% by weight of a polyolefin and does not contain a fluorinated polymer. The present invention also relates to a method for producing such a backsheet and a solar cell module comprising such a backsheet.

[0002] Solar modules are an important source of renewable energy. They comprise solar cells that release electrons when exposed to sunlight, thereby generating electricity. Solar cells are usually made of semiconducting materials, which can be brittle and are typically encapsulated in a polymer material that protects the solar cells from physical impact and scratches. Encapsulated solar cells are generally further protected on both sides by protective layers that are electrically insulating and resistant to weathering, abrasion, or other physical damage for the lifetime of the solar module.

[0003] Solar cell modules have a front protective sheet placed on the side where sunlight enters to protect the surface. This layer is, for example, a glass layer, which is a rigid outer layer that protects the solar cells and electronic devices from the environment while allowing light to pass through and be converted into electricity. Solar cell modules also have a solar cell rear protective sheet, called a backsheet, placed on the opposite side to protect the solar cells.

[0004] Backsheets are typically multilayer polymer sheets that protect PV modules from UV rays, moisture, and weather while also functioning as electrical insulators. They must provide protection from environmental conditions for periods exceeding 20 years. Therefore, they must be physically and chemically stable over such periods. Backsheets often contain several polymer layers to provide these properties and minimize degradation of the solar cell module's long-term performance. Each polymer layer has its own unique function in the backsheet. Backsheets typically include at least a functional layer facing the cells and a weathering layer facing away from the cells. Typical polymers used for these layers include polypropylene, polyvinyl chloride, polyesters such as PET or PBT, fluoropolymers such as PTFE or PVDF, and acrylics.

[0005] Recent developments in solar cell backsheets include the use of coextrusion to produce multilayer backsheets. This has the advantage of increasing interlayer strength and thereby reducing the likelihood of backsheet delamination. Coextrusion requires that the polymers of the multiple layers be sufficiently compatible for bonding and processable in the coextrusion equipment.

[0006] Another recent development in solar cell backsheets is the avoidance of fluorinated polymers. Fluorinated polymers, such as PVF and PVDF, are commonly used in solar cell backsheets because they have good barrier properties and protect module components from environmental conditions. However, fluorinated polymers cannot be recycled, which means that at the end of the solar cell module's lifespan, the fluorinated polymers are waste. Furthermore, fluorinated polymers can be decomposed or burned, releasing potentially harmful fluorinated compounds into the environment.

[0007] Fluorine-free coextruded backsheets have been described in the prior art. Polyamides provide a good barrier against weathering, especially damage caused by UV radiation. WO 2015103872 describes a solar module backsheet comprising a weathering layer containing a biaxially oriented polyamide or polyamide stabilized with a heat stabilizer and a UV stabilizer, and containing an inorganic material. WO 2018 / 087366 describes a solar module backsheet comprising a polyamide weathering layer. WO 2013 / 135349 describes a coextruded solar module backsheet comprising a polyamide layer and a thermoplastic polyolefin layer, such as a flexible polypropylene layer. The polyamide layer is present to improve mechanical integrity, provide an oxygen and CO2 barrier, and protect the thermoplastic polyolefin layer from corrosive decomposition products. US Patent Application Publication No. 20190181284 describes a three-layer solar module backsheet, in which the (outer) weathering layer comprises a polymer network plastic alloy obtained from crosslinking, preferably polyamide 12. EP Patent Application Publication No. 2617568 describes a solar module backsheet comprising three layers mainly comprising polyolefins.

[0008] During use, solar modules can experience large temperature fluctuations between day and night, and also between summer and winter. Daily temperature cycles are particularly pronounced in desert climates, where solar farms are often located due to high solar radiation and a lack of land competition for agriculture or other purposes. These temperature cycles over a wide temperature range can lead to cracking of the backsheet and other defects, such as discoloration (e.g., yellowing of white backsheets) and distortion. Cracking, in particular, can lead to two problems: reduced electrical insulation and reduced water resistance, both of which increase the likelihood of electrical failure, either directly or through corrosion.

[0009] Cracking has been observed in two locations in particular on prior art backsheets. First, cracking typically occurs in the weathering layer directly above the tabbing or metal wire present on the solar cell. The tabbed area is metallic and raised. Second, cracking typically occurs in the weathering layer adjacent to the slits cut into the backsheet to allow electrical conduction from the solar cell to the junction box.

[0010] The object of the present invention is to overcome the above-mentioned drawbacks, and in particular to reduce cracking of the backsheet above the metal tabs and adjacent to slits cut in the backsheet.

[0011] The present inventors have surprisingly found that co-extruded solar module backsheets can be produced that each comprise a majority of polyolefin-containing layers, avoiding the use of fluorinated polymers, and that have good resistance to cracking after being subjected to high and low temperature cycling.

[0012] Therefore, the present invention provides a solar cell module backsheet including a functional layer and a weather-resistant layer, The backsheet does not contain fluorinated polymers, i) the functional layer comprises a blend of polyethylene and a polyethylene copolymer, wherein at least 50% by weight of the functional layer is polyethylene; and ii) the weathering layer includes a first sublayer facing the functional layer and a second sublayer; a) the first sublayer and the second sublayer each comprise at least 50% by weight of polypropylene; and b) the second sublayer has a minimum glass transition temperature (T g ) The present invention provides a solar cell module back sheet characterized by the above-mentioned.

[0013] Furthermore, the present invention provides i) feeding the functional layer composition, the first sublayer composition, the second sublayer composition, and, if present, the third sublayer composition into a multilayer film coextrusion apparatus; and ii) melting and co-extruding the composition in a multilayer film co-extrusion apparatus onto a solar module backsheet in the following order: functional layer, first sublayer, second sublayer, and, if present, third sublayer. The present invention provides a method for manufacturing a solar cell module backsheet, comprising:

[0014] The present invention further provides a solar cell module comprising a solar module backsheet as defined herein.

[0015] As used herein, the term polyolefin includes copolymers of olefins in which at least 70% of the monomers are olefinic, for example, the term polyethylene includes copolymers of ethylene in which at least 70% of the monomers are polyethylene, and the term polypropylene includes copolymers of propylene in which at least 70% of the monomers are polypropylene.

[0016] As used herein, wt % refers to the weight percent of a particular polymer relative to the weight of the layer in which the polymer is present.

[0017] The polypropylene used in any of the layers of the present invention can be homopolypropylene, copolypropylene, block copolypropylene, or a blend thereof. Suitable comonomers include α-polyolefins such as 1-butene, 1-hexene, 1-octene, and combinations thereof. The polypropylene copolymer preferably contains at least 75% of monomer units derived from propene, more preferably at least 85% of monomer units, and even more preferably at least 95% of monomer units. The polypropylene can be linear or branched.

[0018] The polyethylene used in any of the layers of the present invention can be homopolyethylene, copolyethylene, block copolyethylene, or a blend thereof. Suitable comonomers include α-polyolefins such as 1-butene, 1-hexene, 1-octene, and combinations thereof. The polyethylene copolymer preferably contains at least 75% of the monomer units derived from ethene, more preferably at least 85% of the monomer units, and even more preferably at least 95% of the monomer units. The polyethylene can be linear or branched.

[0019] The weathering layer is disposed on one side of the backsheet, which, when used in a solar cell module, is exposed to air and the opposite side is adjacent to the solar cell encapsulant and faces the solar cell.

[0020] The weathering layer of the present invention comprises a first sublayer and a second sublayer, in order, each of which comprises at least 50% by weight of polypropylene. The first sublayer faces toward the functional layer, and the second sublayer faces away from the functional layer. The sublayers of the weathering layer may comprise a blend of polypropylene and an alternative polymer. The alternative polymer may be polyethylene, polyamide, or polyester. Preferably, the alternative polymer, when present, is polyethylene.

[0021] Preferably, the weathering layer comprises a first sublayer, a second sublayer, and a third sublayer, in that order, with the third sublayer comprising at least 50% by weight of polypropylene. Accordingly, the weathering layer of the present invention preferably comprises a first sublayer, a second sublayer, and a third sublayer, in that order, with each of the first sublayer, the second sublayer, and the third sublayer comprising at least 50% by weight of polypropylene. The first sublayer faces toward the functional layer, and the third sublayer faces away from the functional layer. The sublayers of the weathering layer may comprise a blend of polypropylene and an alternative polymer. The alternative polymer may be polyethylene, polyamide, or polyester. Preferably, the alternative polymer, when present, is polyethylene.

[0022] Typically, each sub-layer of the weathering layer comprises at least 60% by weight polypropylene, more preferably at least 70% by weight polypropylene. Typically, each sub-layer of the weathering layer comprises at most 98% by weight polypropylene. Preferably, each sub-layer of the weathering layer comprises at most 90% by weight polypropylene, more preferably at most 80% by weight polypropylene.

[0023] Typically, the first and third sublayers each contain 70 to 90% by weight of polypropylene, and preferably, the first and third sublayers each contain 75 to 85% by weight of polypropylene.

[0024] Preferably, the polypropylene of the weathering layer sub-layer is a polypropylene-polyethylene copolymer.

[0025] Typically, the compositions of the first and third sublayers are similar. For example, the polymer compositions of the first and third sublayers are typically the same. Typically, the first and third sublayers differ only in the type and / or amount of additives present in the layers. For example, the amount of inorganic filler or titanium dioxide in the two sublayers may differ. The third sublayer may contain a lower weight percent of inorganic filler than the first sublayer. The third sublayer may contain a higher weight percent of titanium dioxide than the first sublayer. However, typically, the first and third sublayers have the same chemical composition.

[0026] Preferably, the second sublayer has a minimum glass transition temperature (T g ) that is at least 20°C lower than the minimum glass transition temperature (T g Preferably, the second sublayer has a minimum glass transition temperature (T g ) that is at least 20°C lower than the minimum glass transition temperature (T g More preferably, the second sublayer has a minimum glass transition temperature (T g ) that is at least 20°C lower than the minimum glass transition temperature (T gTypically, the second sublayer has a glass transition temperature (T ) lower than the lowest glass transition temperature (T ) of each of the first and third sublayers. g ) has a minimum glass transition temperature that is at least 30°C lower than that of

[0027] In one embodiment, the solar cell module backsheet comprises, in order, a functional layer and a weathering layer, wherein the backsheet does not comprise a fluorinated polymer and is characterized by: i) the functional layer comprises a blend of polyethylene and a polyethylene copolymer, wherein at least 50% by weight of the functional layer is polyethylene; and ii) the weathering layer comprises a first sublayer, a second sublayer, and a third sublayer, in that order; a) each of the first sublayer, the second sublayer, and the third sublayer comprises at least 50% by weight polypropylene; and b) The second sublayer has a glass transition temperature (T ) lower than the lowest glass transition temperature (T ) of each of the first and third sublayers. g ) that is at least 20°C lower than the minimum glass transition temperature (T g )

[0028] The second sublayer has a minimum glass transition temperature (T g Preferably, the second sublayer has a minimum glass transition temperature of less than -50°C. More preferably, the second sublayer has a minimum glass transition temperature of less than -60°C.

[0029] Typically, the second sublayer comprises a blend of polypropylene and a polyolefin elastomer. Typically, the second sublayer comprises 10% to 50% by weight of the polyolefin elastomer. Preferably, the second sublayer comprises 20% to 40% by weight of the polyolefin elastomer. More preferably, the connecting layer comprises 25% to 35% by weight of the polyolefin elastomer. The polyolefin elastomer is a blend of the first and third sublayers. g Compared to the T of the second sublayer, g This contributes to lowering

[0030] Without wishing to be bound by any theory, the inventors believe that low T g It is believed that the presence of the sublayer having a minimum glass transition temperature (T) of less than -40°C provides some flexibility to the backsheet at low temperatures. This can reduce the stress intensity within the backsheet by allowing movement of the weathering layer during thermal cycling. For example, it can allow relative movement between the first and third sublayers. This effect is due to the fact that the second sublayer has a minimum glass transition temperature (T) of less than -40°C. g ), this is particularly noticeable when the TC200 test described below is used, in which the minimum temperature reached is -40°C.

[0031] Each sub-layer of the weathering layer typically contains a UV stabilizer, typically a hindered amine light stabilizer.

[0032] Each sublayer of the weathering layer typically contains one or more antioxidants. Typically, each sublayer contains 0.1 to 5 wt. % of antioxidant. Preferably, each sublayer contains 0.2 to 4 wt. % of antioxidant, for example, 0.75 wt. %, 1.0 wt. %, 1.5 wt. %, 2.0 wt. %, or 3.0 wt. % of antioxidant.

[0033] Suitable primary antioxidants include phenolic antioxidants or aromatic amine antioxidants. The primary antioxidant is a radical scavenger. It is typically a phenolic antioxidant. Preferably, the primary antioxidant is a phenolic antioxidant, such as benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-octadecyl ester; 2,5,7,8-tetramethyl-2-(4',8',12'-trimethyl-tridecyl)-chroman-6-ol; N,N'-hexamethylenebis(3,5-di-t-butyl-4-hydroxyhydrocinnamamide); ethylene bis(oxyethylene)bis(3-t-butyl-4-hydroxy-5-methylhydrocinnamate); hexamethylene bis(3,5-di-t-butyl-4-hydroxycinnamate); phenol, 4,4',4''''-[(2,4,6-trimethyl-1,3,5-benzenetriyl)-tris-(methylene)]-tris-2,6-bis(1,1-dimethylethyl)-; bis-[3,3-bis-(4'-hydroxyphenyl)-2,6-bis(1,1-dimethylethyl)]- tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate; 3,9-bis(2-(3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane; 1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5 triazine-2,4,6-(1H,3H,5H)-trione; and tetrakis[methylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate)]methane 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionic acid ester with 1,3,5-tris(2-hydroxyethyl)isocyanurate.

[0034] Suitable secondary antioxidants include trivalent phosphorus-containing antioxidants or thioether-containing antioxidants.Secondary antioxidants are typically hydroperoxide decomposers.They are typically thioether-containing antioxidants.Preferably, the secondary antioxidant is a thioether antioxidant, and is selected from dilauryl thiodipropionate; distearyl thiodipropionate; pentaerythrityl tetrakis(β-lauryl thiopropionate); and propanoic acid, 3,3'-thiobis-, 1,1'-dimethyl ester, polymers containing 1,4-cyclohexanedimethanol, octadecyl ester.

[0035] Each sub-layer of the weathering layer may contain one or more additional additives in addition to the UV stabilizer, primary antioxidant, and secondary antioxidant. Examples of additives include UV absorbers, heat stabilizers, and / or hydrolysis stabilizers. When such additional additives are used, each sub-layer of the weathering layer contains 0.05 to 10 wt. % of the additive, more preferably 5 wt. %.

[0036] Each sublayer of the weathering layer according to the present invention may further contain an inorganic filler. Examples of these inorganic fillers include calcium carbonate, titanium dioxide, barium sulfate, mica, talc, kaolin, ZnO, ZnS, glass microbeads, and glass fiber. When such a filler is used, each sublayer of the weathering layer contains 0.05 to 20 wt. % of the filler, based on the total weight of the sublayer.

[0037] Each sub-layer of the weathering layer according to the present invention may further comprise a white pigment, such as TiO2, ZnO, or ZnS, which is typically added to increase the backscattering of sunlight and improve the efficiency of the solar module. Each sub-layer of the weathering layer according to the present invention may further comprise a black pigment, such as carbon black, which is typically added for aesthetic reasons.

[0038] The weather-resistant layer typically has a thickness of 100 to 500 μm. Preferably, the weather-resistant layer has a thickness of 100 to 400 μm. More preferably, the weather-resistant layer has a thickness of 150 to 300 μm, and even more preferably, 200 to 250 μm.

[0039] A functional layer is disposed on one side of the backsheet. When used in a solar module, this layer is adjacent to the solar cell encapsulant and faces the solar cell. One function of the backsheet functional layer is to adhere to the encapsulant. Another function is to reflect light back to the solar cell.

[0040] The functional layer of the present invention comprises at least 50% by weight of a polyolefin. The functional layer comprises a blend of polyethylene and a polyethylene copolymer.

[0041] Typically, the functional layer comprises at least 50% by weight of polyethylene. Preferably, the functional layer comprises at least 60% by weight of polyethylene, more preferably at least 70% by weight, even more preferably at least 80% by weight, or even at least 90% by weight of polyethylene. The weathering layer comprises up to 98% by weight of polyethylene. Preferably, the weathering layer comprises up to 95% by weight of polyethylene, more preferably at least 92% by weight, or even 90% by weight of polyethylene.

[0042] Typically, the functional layer contains 1 to 30 wt. % polypropylene. Preferably, the functional layer contains 5 to 15 wt. % polypropylene. The polypropylene serves to increase the heat resistance of the functional layer, thus reducing delamination or thermal shrinkage at high operating temperatures.

[0043] Preferably, the functional layer comprises a ternary blend of polypropylene, polyethylene and a polyethylene copolymer. Preferably, the polyethylene is linear low density polyethylene.

[0044] Typically, the polyethylene copolymer is an ethylene acrylate copolymer, preferably an ethylene methacrylate copolymer, such as DuPont's Elvaloy AC 1820. Typically, the functional layer further comprises a vinyl acetate copolymer.

[0045] Typically, the ethylene methacrylate polymer is present in an amount of 1 to 40% by weight, preferably 20 to 30% by weight. The ethylene methacrylate copolymer serves to enhance adhesion between the functional layer and the EVA encapsulant.

[0046] Typically, the functional layer comprises a UV stabilizer, a primary antioxidant, a secondary antioxidant, a UV absorber, a heat stabilizer and / or a hydrolysis stabilizer, an inorganic filler or pigment as defined above with respect to the weathering layer.

[0047] The functional layer typically has a thickness of 10 to 50 μm. Preferably, the functional layer has a thickness of 20 to 40 μm, more preferably 25 to 30 μm. The functional layer typically has a thickness less than 20% of the thickness of the solar cell module backsheet. Preferably, the functional layer has a thickness less than 15% of the thickness of the solar cell module backsheet. More preferably, the functional layer has a thickness less than 10% or even less than 5% of the thickness of the solar cell backsheet. The solar cell module backsheet typically has a thickness of 150 to 500 μm. Preferably, the solar cell module backsheet has a thickness of 200 to 400 μm, more preferably 250 to 350 μm, for example, about 300 μm.

[0048] The solar cell backsheet of the present invention may include layers other than the functional layer and the weather-resistant layer. For example, the backsheet may further include a connecting layer disposed between the functional layer and the weather-resistant layer. When present, the connecting layer typically includes polyethylene. More preferably, the connecting layer includes a polyethylene copolymer.

[0049] Typically, the connecting layer comprises at least 50% by weight of polyethylene. Preferably, the connecting layer comprises at least 60% by weight of polyethylene, more preferably at least 70% by weight, even more preferably at least 80% by weight of polyethylene, or even at least 90% by weight of polyethylene. The connecting layer comprises up to 98% by weight of polyethylene. Preferably, the connecting layer comprises up to 95% by weight of polyethylene, more preferably at least 92% by weight of polyethylene, or even 90% by weight of polyethylene.

[0050] The tie 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, an ethylene acrylic acid terpolymer, or an ethylene-acrylic acid ester-maleic anhydride terpolymer.

[0051] The tie layer preferably comprises a polyethylene-polypropylene block copolymer. More preferably, the tie layer comprises a polyethylene-polypropylene block copolymer with a polyolefin blend. Preferably, the polypropylene is ungrafted.

[0052] The connecting layer may include a modifier. For example, the connecting layer may include a polyolefin elastomer. The connecting layer typically includes up to 30% by weight of the polyolefin elastomer. Preferably, the connecting layer includes 10 to 20% by weight of the polyolefin elastomer. More preferably, the connecting layer includes about 25% by weight of the polyolefin elastomer.

[0053] Typically, the tie layer comprises a UV stabilizer, a primary antioxidant, a secondary antioxidant, a UV absorber, a heat stabilizer and / or a hydrolysis stabilizer, an inorganic filler or pigment as defined above for the weathering layer.

[0054] The connecting layer typically has a thickness of 10 to 50 μm, preferably 20 to 40 μm, more preferably 25 to 30 μm.

[0055] Polymeric materials suitable for solar cell encapsulation typically have a combination of properties, such as high impact resistance, high penetration 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. EVA sheets are typically inserted between the solar cell and the top surface (called the front encapsulant) and between the solar cell and the back surface (called the rear encapsulant).

[0056] The present invention provides a solar cell module comprising a solar cell backsheet as defined herein, the solar cell module comprising at least the following layers, in order of location from the front surface facing the sun to the rear surface facing away from the sun: (1) a transparent window (representing the front sheet), (2) a front encapsulant, (3) a solar cell layer, (4) a rear encapsulant, and (5) a backsheet according to the present invention.

[0057] The front sheet is typically either a glass plate or, in the case of flexible modules, a polymer sheet with high optical transparency.

[0058] The present invention further relates to a method for manufacturing a solar cell module backsheet, the preferred method comprising the steps of: i) feeding a functional layer composition, a tie layer composition, a first sublayer composition, a second sublayer composition, and a third sublayer composition into a multilayer film coextrusion apparatus; and ii) melting the composition and co-extruding it onto a solar module backsheet in the following order in a multilayer film co-extrusion device: functional layer, connecting layer, first sublayer, second sublayer, third sublayer.

[0059] The invention will now be demonstrated by a series of examples and comparative experiments.

[0060] Example Method for manufacturing a solar cell backsheet: The materials for the first, second, and third sublayers of the weathering layer, the connecting layer, and the functional layer were each pelletized in an extruder to obtain plastic pellets for each layer. The pellets for each layer were added to multiple inputs of a multi-layer extruder (HRPC-1000, manufactured by Tianjin Hengrui Plastic Machinery Co., Ltd.), melt-extruded at 230°C, passed through an adapter and die, cooled by a cooling roller, and molded to produce a multi-layer backsheet. The layers were, in order, the functional layer, the connecting layer, and the weathering layer. When the weathering layer contained multiple sublayers, the first sublayer was adjacent to the connecting layer, and the second sublayer was located between the first and third sublayers. The compositions of the different layers of the multi-layer backsheet are shown in Table 1.

[0061] [Table 1]

[0062] Method for manufacturing a solar module: Module stacks were fabricated by laminating the following in the specified order: a sheet of solar glass (1644 x 985 mm) SM manufactured by FSG, a sheet of EVA encapsulant (1644 x 985 x 0.45 mm) F406P manufactured by Hangzhou First, a string of solar cells, a second sheet of EVA encapsulant (1644 x 985 x 0.45 mm) F806P manufactured by Hangzhou First, and a solar cell backsheet (1654 x 995 mm). First, slits were cut into the backsheet for electrical contact. The stack was assembled in an SM Innotech Profilam 21-10 solar module laminator equipped with an additional oil circulation system and pin lift system. The lamination protocol was 300 seconds of ejection and melting; 60 seconds of pressure ramp-up time; 600 seconds of pressing / curing time at 800 mbar; and 60 seconds of pressure release time. A sealant was attached to the junction box, and an aluminum frame was fixed to form a solar cell module.

[0063] measurement The glass transition temperature (T g ) was measured by differential scanning calorimetry. A heating rate of 10 K / min was used. In Example 1, the T g is approximately -20°C, and the T of the second sublayer g In Example 2, the T of the first sublayer was approximately -60°C. g is approximately -20°C, and the T of the second sublayer g was about -60°C.

[0064] The solar cell modules were subjected to a thermal cycle test. 3 Tests were performed in accordance with IEC 61215:2016, test MQT11, using a 7018 apparatus. Temperature cycling was performed from -40°C to +85°C with a 10-minute dwell time at each temperature. For the TC200, 200 cycles were performed. For the TC400 and TC600, 400 and 600 cycles were performed, respectively. The results are shown in Table 2. [Table 2]

[0065] The backsheets of Examples 1 and 2 did not show visible cracks in the outer layer above the tabbing or adjacent to the slit edge after TC200, TC400, or (for Example 1) TC600. Conversely, Comparative Example 1 showed cracks through the weathering layer at both of these locations after TC200. Comparative Example 2 showed cracks through the weathering layer above the tabbing after TC400. This indicates an improvement by using a weathering layer comprising three sublayers, the second sublayer being able to withstand temperatures below -40°C. g and T of the first and third sublayers g T 40°C lower than g It has.

Claims

1. A solar cell module backsheet including a functional layer and a weather-resistant layer, the solar cell module backsheet does not contain a fluorinated polymer, the functional layer comprises a blend of polyethylene and a polyethylene copolymer, at least 50% by weight of the functional layer being polyethylene; and the weathering layer includes a first sublayer facing the functional layer and a second sublayer; the first sublayer and the second sublayer each comprise at least 50% by weight polypropylene; and The second sublayer has a minimum glass transition temperature (T ｇ ) having a minimum glass transition temperature (T g ) that is at least 20° C. lower than the minimum glass transition temperature (T g ) of said first sublayer. A solar cell module backsheet characterized by:

2. 2. The solar cell module backsheet of claim 1, wherein the weathering layer comprises, in order, the first sublayer, the second sublayer, and a third sublayer, and the third sublayer comprises at least 50% by weight of polypropylene.

3. The second sublayer has a minimum glass transition temperature (T ｇ ) at least 20° C. lower than the minimum glass transition temperature (T ｇ 3. The solar cell module backsheet according to claim 2, wherein

4. 4. The solar cell module backsheet of claim 3, wherein each of the first sublayer and the third sublayer comprises 70% to 90% by weight of polypropylene.

5. The solar cell module backsheet according to any one of claims 2 to 4, wherein the first sub-layer and the third sub-layer have the same chemical composition.

6. The solar cell module backsheet according to any one of claims 1 to 5, wherein the second sub-layer comprises a blend of polypropylene and a polyolefin elastomer.

7. The solar cell module backsheet according to any one of claims 1 to 6, wherein the second sublayer comprises 20% to 40% by weight of a polyolefin elastomer.

8. The solar cell module backsheet according to any one of claims 1 to 7, further comprising a connection layer disposed between the functional layer and the weather-resistant layer.

9. The solar cell module backsheet according to any one of claims 1 to 8, wherein the functional layer comprises a ternary blend of polypropylene, polyethylene and a polyethylene copolymer.

10. 10. The solar cell module backsheet of claim 9, wherein the polyethylene copolymer is an ethylene methacrylate copolymer.

11. The solar cell module backsheet according to any one of claims 1 to 10, wherein the functional layer has a thickness of 10 to 50 µm.

12. The solar cell module backsheet according to any one of claims 1 to 11, wherein the weather-resistant layer has a thickness of 100 to 500 µm.

13. A solar cell module comprising a solar cell module backsheet as defined in any one of claims 1 to 12.

14. A method for producing a multilayer film, comprising: feeding a functional layer composition, a first sublayer composition, a second sublayer composition, and, if present, a third sublayer composition, into a multilayer film coextrusion apparatus; and melting the functional layer composition, the first sublayer composition, the second sublayer composition, and, if present, the third sublayer composition in the multilayer film coextrusion apparatus and co-extruding them onto a solar module backsheet in the order of functional layer, first sublayer, second sublayer, and, if present, third sublayer; A method for manufacturing a solar module backsheet as defined in any one of claims 1 to 12, comprising:

15. A method for producing a multilayer film, comprising: feeding a functional layer composition, a connecting layer composition, a first sublayer composition, a second sublayer composition, and a third sublayer composition into a multilayer film coextrusion apparatus; and melting the functional layer composition, the connecting layer composition, the first sublayer composition, the second sublayer composition, and the third sublayer composition in the multilayer film coextrusion device, and co-extruding them onto a solar cell module backsheet in the order of functional layer, connecting layer, first sublayer, second sublayer, and third sublayer; A method for manufacturing a solar module backsheet as defined in any one of claims 1 to 12, comprising:

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