Hot melt composition in form of film for photovoltaic modules

Abstract

The invention features a hot melt composition in the form of a film comprising a blend of a propylene-based polymer and an ethylene-based polymer. The hot melt composition in the form of the film can be used as an encapsulant for photovoltaic modules.

Description

[0001] BACKGROUND

[0002] Crystalline silicon photovoltaic (PV) modules typically include a photovoltaic layer, usually monocrystalline or polycrystalline silicon, laminated between two encapsulant layers, with a thick glass substrate as a front sheet and a protective backsheet. Additional layers can be present between these layers, such as tie layers and adhesives. Crystalline PV modules are rigid. Crystalline PV modules can often have a vented construction, i.e., there is no seal at the edges that binds them together. Therefore, low cost encapsulants, such as peroxide cured alkyl acetates, can be used, as the remaining peroxide residue can diffuse through the edges into the atmosphere and thus not harm the module.

[0003] Thin film PV modules include thinner and less expensive photovoltaic cells. Thin film PV modules typically include a front sheet on which the photovoltaic cells can be deposited, an encapsulant, and a backsheet. However, due to the presence of an edge seal around the outer edges of the thin film PV module, materials such as peroxides or polymers that decompose to form acids, such as ethylene vinyl acetate, cannot be used in the encapsulant. This is because the formed material would remain in the module and potentially damage the module. Furthermore, in thin film PV modules, due to the presence of typically only one layer of encapsulant, the stress applied on the encapsulant is increased.

[0004] From a supply and cost perspective, propylene-based olefin polymers are often preferred. However, it can be difficult to find a propylene-based polymer that has the right balance of properties needed to work well in an encapsulant.

[0005] There is a need for an encapsulant that is suitable for both crystalline silicon PV modules and thin film PV modules, that does not contain materials that can contaminate the module, such as peroxides, acids, etc., that provides a balance of heat resistance and adhesion, that is resistant to environmental changes, and that includes a propylene-based polymer.

[0006] Glossary

[0007] With respect to the present invention, these terms have the meanings set forth below:

[0008] The term "copolymer" means a polymer derived from two or more different monomers.

[0009] SUMMARY

[0010] In one aspect, the application features a hot melt composition in the form of a film comprising 20 to 70 weight percent of a propylene-based polymer having a peak melting temperature (T m ) of no greater than 120°C as measured by DSC, 20 to 70 weight percent of an ethylene-based polymer having a density of no greater than 0.93 g / cm 3 , and 2 to 15 weight percent of a functionalized polymer comprising a functional group selected from the group consisting of an epoxide, a carboxylic anhydride, and a carboxylic acid.

[0011] In another aspect, the application features a hot melt composition in the form of a film comprising 20 to 70 weight percent of a propylene-based polymer having a T m of no greater than 120°C as measured by DSC, 20 to 70 weight percent of an ethylene-based polymer having a density of no greater than 0.93 g / cm 3 , and at least two of:

[0012] 2 to 10 weight percent of a first functionalized polymer selected from the group consisting of a copolymer of ethylene and maleic anhydride, a copolymer of ethylene, an alkyl (meth)acrylate, and maleic anhydride, 2 to 10 weight percent of a second functionalized polymer selected from the group consisting of a copolymer of ethylene and glycidyl methacrylate and a terpolymer of ethylene, an alkyl (meth)acrylate, and glycidyl methacrylate, and 0.1 to 3.0 weight percent of a silane adhesion promoter.

[0013] In another aspect, the application features a hot melt composition in the form of a film comprising 20 to 60 weight percent of a propylene-based copolymer having a T m of no greater than 120°C as measured by DSC and a comonomer content of 9 to 22 weight percent, 35 to 60 weight percent of a single-site catalyzed ethylene-based polymer having a density of no greater than 0.90 g / cm 3 , 2 to 15 weight percent of a functionalized polymer comprising a functional group selected from the group consisting of an epoxide, a carboxylic anhydride, and a carboxylic acid, and a silane adhesion promoter.

[0014] In one embodiment, the propylene-based polymer is a propylene ethylene copolymer.

[0015] In another embodiment, the propylene-based polymer is a non-single site catalyzed amorphous poly alpha olefin. In a different embodiment, the non-single site catalyzed amorphous poly alpha olefin has a comonomer content of 12 wt% to 22 wt% and a T m .

[0016] In one embodiment, the non-single site catalyzed amorphous poly alpha olefin is produced with an electron donor catalyst. In another embodiment, the propylene-based polymer is selected from the group consisting of a non-single site catalyzed amorphous poly alpha olefin (APAO), a single site catalyzed propylene-based polymer, and combinations thereof.

[0017] In yet another embodiment, the ethylene-based polymer is a single site catalyzed copolymer. In a different embodiment, the ethylene-based polymer is selected from the group consisting of very low density polyethylene (VLDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE). In one embodiment, the ethylene-based polymer has a density of not greater than 0.89 g / cm 3 as tested according to ASTM D 792.

[0018] In one embodiment, the functionalized polymer is selected from the group consisting of a copolymer of ethylene and maleic anhydride; a copolymer of ethylene, alkyl (meth)acrylate, and maleic anhydride; a copolymer of ethylene and glycidyl methacrylate; and a terpolymer of ethylene, alkyl (meth)acrylate, and glycidyl methacrylate. In another embodiment, the functionalized polymer is present as a first and a second functionalized polymer, the first functionalized polymer is selected from the group consisting of a copolymer of ethylene and maleic anhydride; a copolymer of ethylene, alkyl (meth)acrylate, and maleic anhydride, and the second functionalized polymer is selected from the group consisting of a copolymer of ethylene and glycidyl methacrylate and a terpolymer of ethylene, alkyl (meth)acrylate, and glycidyl methacrylate.

[0019] In one embodiment, the hot melt composition is free of ethylene vinyl acetate, peroxide, and polyvinyl chloride. In a different embodiment, the hot melt composition has an approximate melt index of 5 g / 10 min to 150 g / 10 min as tested according to ASTM D 1238 (190°C, 2.16 kg).

[0020] In another embodiment, the hot melt composition further comprises a silane adhesion promoter. In a different embodiment, the silane adhesion promoter is a bi-functional silane adhesion promoter selected from the group consisting of an amino silane, an epoxy silane, an isocyanurate silane. In one embodiment, the hot melt composition further comprises 5 wt% to 50 wt% of a filler. In another embodiment, the hot melt composition further comprises at least one of a tackifier and a wax. In a different embodiment, the wax is selected from the group consisting of a polyethylene wax, a Fischer-Tropsch wax, a metallocene catalyzed polyethylene wax, and combinations thereof.

[0021] In one embodiment, the hot melt composition further comprises an aliphatic hydrocarbon tackifier.

[0022] In one embodiment, the present invention comprises a photovoltaic module hot melt composition of the present invention in the form of a film.

[0023] In one embodiment, the present invention comprises a photovoltaic module comprising from top to bottom a front sheet, the hot melt composition in the form of a film, a photovoltaic cell layer, the hot melt composition in the form of a film, and a back sheet, wherein the hot melt composition in the form of a film adheres the front sheet to the back sheet.

[0024] In a different embodiment, the present invention comprises a photovoltaic module comprising a front sheet, a photovoltaic cell layer in contact with the front sheet, the hot melt composition in the form of a film, and a back sheet, wherein the hot melt composition in the form of a film is positioned between the photovoltaic cell and the back sheet and adheres the front sheet to the back sheet. In another embodiment, the photovoltaic cell is selected from the group consisting of CIGS (copper indium gallium diselenide), CdTe (cadmium telluride), amorphous thin film silicon (a-Si, TF-Si), and copper indium diselenide (CIS) and perovskite based systems.

[0025] In one embodiment, the photovoltaic module further comprises an edge seal.

[0026] In another embodiment, the back sheet and the front sheet are glass and the photovoltaic cell is CdTe.

[0027] The hot melt composition of the present invention in the form of a film comprises a specific blend of ethylene-based and propylene-based polymers, is free of materials that can contaminate the module, such as peroxides, acids, etc., and provides a balance of heat resistance and adhesion.

[0028] DETAILED DESCRIPTION

[0029] Hot melt composition

[0030] The present invention relates to a hot melt composition in the form of a film (also referred to as a sheet).

[0031] A hot melt composition in the form of a film can comprise 20 to 70 wt% of a propylene-based polymer having a T m measured by DSC of not more than 120°C, 20 to 70 wt% of an ethylene-based polymer having a density of not more than 0.93 g / cm 3 and 2 to 15 wt% of a functionalized polymer comprising functional groups selected from the group consisting of epoxy, carboxylic anhydride and carboxylic acid.

[0032] A hot melt composition in the form of a film can comprise 20 to 70 wt% of a propylene-based polymer having a T m measured by DSC of not more than 120°C, 20 to 70 wt% of an ethylene-based polymer having a density of not more than 0.93 g / cm 3 , 2 to 15 wt% of a functionalized polymer comprising functional groups selected from the group consisting of epoxy, carboxylic anhydride and carboxylic acid and a silane adhesion promoter.

[0033] The hot melt composition in the form of a film can comprise 20 to 70 wt% of a propylene-based polymer having a T m measured by DSC of not more than 120°C selected from the group consisting of a propylene homopolymer and a propylene copolymer having a comonomer content of 9 to 22 wt%, 20 to 70 wt% of an ethylene-based polymer having a density of not more than 0.93 g / cm 3 , 2 to 15 wt% of at least one functionalized polymer comprising functional groups selected from the group consisting of epoxy, carboxylic anhydride and carboxylic acid and a silane adhesion promoter.

[0034] The hot melt composition in the form of a film can comprise 20 to 60 wt% of a propylene-based copolymer having a T m measured by DSC of not more than 120°C and a comonomer content of 9 to 22 wt%, 35 to 60 wt% of a single site catalysed ethylene-based polymer having a density of not more than 0.90 g / cm 3 , 2 to 10 wt% of at least one functionalized polymer comprising functional groups selected from the group consisting of epoxy, carboxylic anhydride and carboxylic acid and a silane adhesion promoter.

[0035] The hot melt composition in the form of a film can comprise 20 to 70 wt% of a propylene-based polymer having a T man ethylene-based polymer having a density of not more than 0.93 g / cm 3 an ethylene-based polymer having a density of not more than 0.93 g / cm

[0036] The hot melt composition can be free of peroxide, ethylene vinyl acetate, and polyvinyl chloride (PVC).

[0037] The hot melt composition can have an approximate melt index of 0.5 to 300 grams (g) per 10 minutes (min), 0.5 to 200 g / 10 min, 0.5 to 50 g / 10 min, 5 to 50 g / 10 min, or even 10 to 30 g / 10 min when tested according to ASTM D 1238 (190 °C, 2.16 kg).

[0038] The hot melt composition can have a storage modulus at 25 °C of 3 MPa to 25 MPa, 3 MPa to 20 MPa, 3 to 15 MPa, or even 4 MPa to 15 MPa when tested according to the Storage Modulus Test Method.

[0039] The hot melt composition can have a 180° Peel Adhesion of 30 Newtons (N) per cm to 250 N / cm, 40 N / cm to 200 N / cm, or even 60 N / cm to 200 N / cm.

[0040] The propylene-based polymer

[0041] The hot melt composition in the form of a film comprises one or more propylene-based polymers having a T m melt peak measured by DSC of not more than 120 °C.

[0042] The propylene-based polymer can be produced by reacting propylene monomers and desired comonomers in the presence of a catalyst system selected from a single site (e.g., metallocene) catalyst, a Ziegler-Natta catalyst, a catalyst system comprising at least one electron donor, and any other catalyst that produces a polymer having the desired properties.

[0043] The propylene-based polymer can be produced in the presence of a catalyst system selected from the group consisting of single site (e.g., metallocene) catalysts, Ziegler-Natta catalysts, catalyst systems comprising at least one electron donor, and combinations thereof. The propylene-based polymer can be produced in the presence of a catalyst system selected from the group consisting of Ziegler-Natta catalysts, catalyst systems comprising at least one electron donor, and combinations thereof.

[0044] In one embodiment, the catalyst is a Ziegler-Natta catalyst containing a titanium containing component, an aluminum component, and an electron donor.

[0045] The propylene-based polymer is derived primarily from propylene. The propylene-based polymer can comprise at least 60 wt% propylene, at least 70 wt% propylene, at least 75 wt% propylene, at least 80 wt% propylene, at least 90 wt% propylene, at least 95 wt% propylene, or even 100 wt% propylene.

[0046] The propylene-based polymer can be a homopolymer, but is preferably a copolymer. The propylene-based polymer can be a copolymer of propylene and an alpha olefin. The alpha-olefin can have 2 carbon atoms or 4-8 carbon atoms. The alpha-olefin can be selected from the group consisting of ethylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, and 1-octene. In a preferred embodiment, the alpha-olefin is ethylene.

[0047] When the propylene-based polymer is a copolymer, the comonomer is present in an amount from 5 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, to 20 wt%, 22 wt%, 23 wt%, 25 wt%, 28 wt%, 35 wt%, or even 40 wt%, or any two values therebetween.

[0048] The propylene-based polymer has a Tm (melting temperature) of not greater than 130°C, not greater than 120°C, not greater than 115°C, not greater than 110°C, 70°C to 120°C, 70°C to 115°C, 70°C to 110°C, or even 70°C to 105°C, as tested by DSC (Differential Scanning Calorimetry). m The useful propylene-based polymers also exhibit a heat of fusion - first heat (J / g) of not greater than 20 J / g, not greater than 15 J / g, not greater than 10 J / g, 0 J / g to 15 J / g, or even 0 J / g to 10 J / g.

[0049] The propylene-based polymer can be selected from the group consisting of non-single site catalyzed amorphous polyalphaolefins (APAOs), single site catalyzed propylene-based polymers, and combinations thereof.

[0050] Propylene-based polymers can be non-unit-site catalytic APAO polymers. Non-unit-site catalytic APAO can be produced using electron-donator catalyst systems. Non-unit-site catalytic APAO can have a concentration of no more than 0.89 g / cm³. 3 The density. Non-unit-site catalyzed APAO may have a heat of fusion (J / g) of not more than 15 J / g, 0 J / g to 15 J / g, or even 0 J / g to 10 J / g – on the first heating. Non-unit-site catalyzed APAO may have a viscosity of at least 50 cP, at least 100 cP, at least 500 cP, not more than 20,000 cP, not more than 10,000 cP, 50 cP to 10,000 cP, 50 cP to 8,000 cP, or even 50 to 5,000 cP at 190 °C.

[0051] Propylene-based polymers can be propylene-based polymers with single-site catalysis.

[0052] The propylene-based polymers with single-point catalysis can have a comonomer content of 5% to 25% by weight, or even 9% to 20% by weight, and a melt index of 1 to 50 g / 10 min, 2 to 40 g / 10 min, or even 5 to 30 g / 10 min as tested according to ASTM D 1238 (190°C, 2.16 kg).

[0053] Available propylene-based polymers include the AERAFIN series polymers, including AERAFIN 35, AERAFIN 75H and AERAFIN 180, available from Synthomer PLC (Akron, Ohio); the VISTAMAXX series polymers, including VISTAMAXX 6202, VISTAMAXX 6502 and VISTAMAXX 8380, available from ExxonMobilChemical Company (Houston, Texas); the LMODU series polymers, including LMODU S901, available from Idemitsu Kosan Co., Ltd (Japan); and the VERSIFY series polymers, including VERSIFY 3200, VERSIFY 3300 and VERSIFY 3401, available from The Dow Chemical Company (Midland, MI).

[0054] The hot melt composition may contain a propylene-based polymer ranging from 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, to 60 wt%, 65 wt%, 70 wt%, or any two of these values.

[0055] Ethylene-based polymer

[0056] The ethylene-based polymer is used to lower the glass transition temperature (T g ) and increase the modulus (or stiffness) of the composition. The ethylene-based polymer can be present as one or more ethylene-based polymers. The ethylene-based polymer can be selected from very low density polyethylene (VLDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ethylene alpha olefin copolymers, and combinations thereof.

[0057] The ethylene-based polymer can be derived primarily or even entirely from ethylene. The ethylene-based polymer can comprise at least 60 wt% ethylene, at least 70 wt% ethylene, at least 75 wt% ethylene, at least 80 wt% ethylene, at least 90 wt% ethylene, at least 95 wt% ethylene, or even 100 wt% ethylene.

[0058] The ethylene-based polymer can be polymerized by known polymerization techniques, such as Ziegler-Natta, single site (e.g., metallocene) catalysis, free radical polymerization in an autoclave reactor or a tubular reactor, and the like. In a preferred embodiment, the ethylene-based polymer is polymerized by a single site (e.g., metallocene) catalyst.

[0059] The ethylene-based polymer can have a density, as tested according to ASTM D 792, of not more than 0.95 g / cm 3 , not more than 0.93 g / cm 3 , or even not more than 0.92 g / cm 3 . The ethylene-based polymer can have a density, as tested according to ASTM D 792, of from 0.82 g / cm 3 , 0.85 g / cm 3 , to 0.88 g / cm 3 , 0.89 g / cm 3 , 0.90 g / cm 3 , 0.92 g / cm 3 , 0.93 g / cm 3 , 0.95 g / cm 3 , or any two values therein. The ethylene-based polymer can include a first ethylene-based polymer having a density of 0.90 g / cm 3 to 0.93 cm 3 , and a second ethylene-based polymer having a density of 0.85 g / cm 3 to 0.88 g / cm 3 .

[0060] The ethylene-based polymer can have a T mThe melt index of the ethylene-based polymer can be from 0.1 g / 10 min, 0.5 g / 10 min, 1 g / 10 min, 5 g / 10 min, to 25 g / 10 min, 30 g / 10 min, 35 g / 10 min, 40 g / 10 min, 50 g / 10 min, 100 g / 10 min, 500 g / 10 min, 1000 g / 10 min, or any two values therebetween, according to ASTM D 1238 (190°C, 2.16 kg).

[0061] The ethylene-based copolymer can have a Mw / Mn ratio of no greater than 5, no greater than 3, or even no greater than 2, where Mw and Mn represent the weight average molar mass and number average molar mass, respectively, according to gel permeation chromatography (GPC).

[0062] The ethylene-based polymer can be selected from very low density polyethylene (VLDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE).

[0063] Useful polyethylenes include LDPE LD 102 LC and LDPE LD 506.7, both of which are available from ExxonMobil Chemical Company (Houston, Texas), and AT280, which is available from Celanese Corporation (Irving, Texas).

[0064] The ethylene-based polymer can be an ethylene copolymer. The ethylene-based polymer can be a copolymer of ethylene and one or more alpha-olefins. The alpha-olefin can have 3 to 10 carbon atoms. The alpha-olefin can be selected from the group consisting of propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-octene, 1-decene, and 1-dodecene.

[0065] Useful ethylene-based copolymers include the ENGAGE series of polymers, including ENGAGE 8411 (an ethylene-octene copolymer having a density of 0.88 g / cm3and a melt index of 18 g / 10 min, according to ASTM D 1238 (190°C, 2.16 kg)) and ENGAGE PV8658 (an ethylene-octene copolymer having a density of 0.90 g / cm3and a melt index of 18 g / 10 min, according to ASTM D 1238 (190°C, 2.16 kg)). 3 3 ​ethylene-octene copolymers having a density of 0.855 g / cm3and a melt index of 30 g / 10 min tested according to ASTM D 1238 (190°C, 2.16 kg), both available from The Dow Chemical Company (Midland, MI), polymers from the SOLUMER series available from SK Innovation Co., Ltd. (Seoul, Korea), including SOLUMER 8613 (having a density of 0.863 g / cm3and a melt index of 13 g / 10 min tested according to ASTM D 1238 (190°C, 2.16 kg), and polymers from the VISTALON series available from ExxonMobil Chemical Company (Houston, Texas), including VISTALON 878. 3 ethylene-octene copolymers having a density of 0.855 g / cm3and a melt index of 30 g / 10 min tested according to ASTM D 1238 (190°C, 2.16 kg), both available from The Dow Chemical Company (Midland, MI), polymers from the SOLUMER series available from SK Innovation Co., Ltd. (Seoul, Korea), including SOLUMER 8613 (having a density of 0.863 g / cm3and a melt index of 13 g / 10 min tested according to ASTM D 1238 (190°C, 2.16 kg), and polymers from the VISTALON series available from ExxonMobil Chemical Company (Houston, Texas), including VISTALON 878.

[0066] The hot melt composition can comprise from 20 wt%, 25 wt%, 30 wt%, 35 wt%, to 60 wt%, 65 wt%, 70 wt%, or between any two of these values, ethylene-based copolymers.

[0067] Functionalized polymer

[0068] The present inventors have found that functionalized polymers are important for maintaining heat resistance and improving adhesion of the hot melt composition.

[0069] The hot melt composition of the present invention comprises at least one functionalized polymer, or even two functionalized polymers. There is no limitation on the functionalized polymer. The functional group can be part of the polymer backbone, polymer side chain, or a combination thereof. The functional group can be introduced during polymerization of the copolymer or by grafting after polymerization. The functionalized polymer can be a copolymer of ethylene and various functional groups.

[0070] In a preferred embodiment, the hot melt composition is substantially free of a curing agent. The curing agent includes any species other than the functionalized polymer. The curing agent includes, for example, peroxide, amine, phenol, and the like materials.

[0071] The functionalized polymer includes a functional group selected from the group consisting of carboxylic anhydride, carboxylic acid, epoxy, and combinations thereof.

[0072] The functionalized polymer can comprise ethylene and carboxylic anhydride functional groups. The carboxylic anhydride functional groups can be selected from the group consisting of maleic anhydride, itaconic anhydride, citraconic anhydride, allyl succinic anhydride, cyclohex-4-ene-1,2-dicarboxylic anhydride, 4-methylene cyclohex-4-ene-1,2-dicarboxylic anhydride, bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride, and x-methyl bicyclo[2.2.1]hept-5-ene-2,2-dicarboxylic anhydride.

[0073] The functionalized polymer can include ethylene and a carboxylic acid. The carboxylic acid can be selected from acrylic acid and methacrylic acid.

[0074] The functionalized polymer can include ethylene and an epoxy group. Examples of epoxy group containing monomer units include aliphatic esters and glycidyl ethers such as allyl glycidyl ether, vinyl glycidyl ether, glycidyl maleate or itaconate, glycidyl methacrylate, and alicyclic esters and glycidyl ethers such as 2-cyclohexene-1 -glycidyl ether, carboxylic acid cyclohexene-4,5-diglycidyl ester, carboxylic acid cyclohexene-4 glycidyl ester, carboxylic acid 5-norbornene-2-methyl-2-glycidyl ester, and endo-cis-bicyclo(2,2,1)-5-heptene-2,3-diglycidyl dicarboxylate.

[0075] The epoxy group containing monomer units are preferably introduced as a comonomer, i.e. by copolymerizing an olefin monomer with a vinyl group bearing epoxy group containing comonomer (= epoxy group containing monomer unit). Most preferably, the epoxy group containing monomer unit is a glycidyl methacrylate comonomer unit.

[0076] The functionalized polymer can include a first functionalized polymer and a second functionalized polymer. The second functionalized polymer can have a functional group capable of reacting with the functional group of the first functionalized polymer.

[0077] The first functionalized polymer and / or the second functionalized polymer can be a functionalized alkyl (meth)acrylate. Preferred are alkyl (meth)acrylates having an alkyl chain comprising 1 to 4 carbon atoms, preferably methyl, ethyl or butyl.

[0078] Alternatively, the first functionalized polymer and / or the second functionalized polymer can be a functionalized ethylene alpha olefin copolymer, for example an ethylene alpha olefin copolymer functionalized with maleic anhydride, glycidyl methacrylate, etc.

[0079] The first functionalized polymer can be a copolymer of ethylene and an epoxy group, and the second functionalized polymer can be a copolymer of ethylene and at least one monomer selected from the group consisting of carboxylic anhydride, carboxylic acid, and combinations thereof.

[0080] The first functionalized polymer can be a copolymer of ethylene and maleic anhydride, or a copolymer of ethylene, alkyl methacrylate and maleic anhydride, and the second functionalized polymer can be a copolymer of ethylene and glycidyl methacrylate, or a terpolymer of ethylene, alkyl methacrylate and glycidyl methacrylate.

[0081] The functionalized polymer can be formed by a free radical polymerization process in an autoclave reactor, in a tubular reactor, or by single site (e.g. metallocene) catalysis as known to those skilled in the art.

[0082] The functionalized polymer can have a melt index tested by ASTM D 1238 (190°C, 2.16 kg) of from 2 g / 10 min to 1000 g / 10 min, 2 g / 10 min to 500 g / 10 min, 2 g / 10 min to 100 g / 10 min, or even 2 g / 10 min to 50 g / 10 min.

[0083] Useful functionalized polymers include those available under the LOTADER trade name, including LOTADER 4210 (ethylene-butyl acrylate-maleic anhydride terpolymer having 6.5 wt% butyl acrylate, 3.6 wt% maleic anhydride, and a melt index of 10 g / 10 min tested by ASTM D 1238 (190°C, 2.16 kg)), and LOTADER AX 8840 (ethylene-glycidyl methacrylate copolymer having 8 wt% glycidyl methacrylate and a melt index of 5 g / 10 min tested by ASTM D 1238 (190°C, 2.16 kg)), both available from SK Functional Polymer (Courbevoie, France), NUCREL 0910 (ethylene-methacrylic acid copolymer having 8.7 wt% methacrylic acid and a melt index of 10 g / 10 min tested by ASTM D 1238 (190°C, 2.16 kg)), ELVALOY 4170 (ethylene terpolymer having a melt index of 8 g / 10 min tested by ASTM D 1238 (190°C, 2.16 kg)), FUSABOND M603 (maleic anhydride functionalized ethylene copolymer having a melt index of 25 g / 10 min tested by ASTM D 1238 (190°C, 2.16 kg)), and AFFINITY GA 1000R (maleic anhydride functionalized ethylene octene copolymer), all available from Dow Chemical (Houston, Texas).

[0084] The hot melt composition comprises from 2 wt%, 3 wt%, 4 wt%, 5 wt%, to 7.5 wt%, 10 wt%, 15 wt%, or any two values therebetween of the functionalized polymer.

[0085] SILANE ADHESION PROMOTER

[0086] The hot melt adhesive composition can include a silane adhesion promoter. The silane adhesion promoter helps improve the adhesion between the encapsulant and the glass. There is no limitation on the silane adhesion promoter and can include any type of silane composition useful for promoting adhesion of the hot melt composition to the substrate.

[0087] The silane adhesion promoter can be selected from silanes, aminosilanes, epoxysilanes, isocyanurate silanes, and any other silanes. The silane adhesion promoter can be difunctional. The silane adhesion promoter can include a hydrolyzable inorganic silyl group.

[0088] The hot melt composition can include 0.05 wt% to 5 wt%, 0.1% to 3 wt%, or even 0.2 wt% to 2 wt% of the silane adhesion promoter.

[0089] Useful silane adhesion promoters include those available under the DYNASYLAN trade name, including DYNASYLAN GLYMO (difunctional organosilane with reactive organic epoxy groups and hydrolyzable inorganic methoxysilyl groups), DYNASYLAN AMMO (3-(trimethoxysilyl)propyl amine), and DYNASYLAN VPS7161 (isocyanurate silane with high concentration of trimethoxysilyl groups), all available from Evonik GmBH (Hanau, Germany), and COATOSIL MP200 (epoxy functional silane oligomer) available from Momentive Performance Materials Inc.

[0090] Functionalized polymers and silane adhesion promoters

[0091] The present inventors have discovered that the combination of a functionalized polymer and a silane adhesion promoter helps improve the adhesion of the encapsulant and increase the heat resistance of the encapsulant. In one embodiment, the hot melt composition in the form of a film includes at least two of: 2 wt% to 10 wt% of a first functionalized polymer selected from a copolymer of ethylene and maleic anhydride, a copolymer of ethylene, (meth)acrylic acid alkyl ester, and maleic anhydride, 2 wt% to 10 wt% of a second functionalized polymer selected from a copolymer of ethylene and glycidyl methacrylate and a terpolymer of ethylene, (meth)acrylic acid alkyl ester, and glycidyl methacrylate, and 0.1 wt% to 3.0 wt% of a silane adhesion promoter.

[0092] Fillers

[0093] The hot melt composition can comprise a filler. The filler can be selected from the group consisting of silica, treated silica, alumina, calcium carbonate, barium sulfate, zinc oxide, clay, talc, carbon nanotubes, and carbon black. The hot melt composition can alternatively comprise any other filler.

[0094] The composition can comprise up to 50 wt%, 5 wt% to 50 wt%, 5 wt% to 30 wt%, or even 5 wt% to 20 wt% of a filler.

[0095] Tackifying agent

[0096] The hot melt composition can comprise a tackifying agent. The hot melt composition can comprise more than one tackifying agent.

[0097] The tackifying agent can be a hydrocarbon tackifying agent. The tackifying agent can have a softening point of 100°C to 150°C, or even 105°C to 150°C.

[0098] The tackifying agent can be at least partially hydrogenated, or even fully hydrogenated. Suitable classes of hydrocarbon tackifying agents include, for example, aliphatic and cycloaliphatic hydrocarbon resins (C9 and dicyclopentadiene (DCPD) based resins).

[0099] In a preferred embodiment, the tackifying agent is a predominantly aliphatic or even fully aliphatic hydrocarbon tackifying agent. The hot melt composition can include more than one tackifying agent.

[0100] Useful tackifying agents are available under various trade names, including, for example, ESCOREZ 5300 and ESCOREZ 5320 from Exxon Mobil Chemical Company (Houston, Tex.), EASTOTAC H-115W, H-130W, and H-142W from Synthomer PLC (Akron, Ohio), RESINALL 1030 from Resinall Corp (Severn, N.C.), and SUKOREZ SU-110, SU-120, SU-130, SU-210, SU-230, SU-230S, SU-420, SU-525 from Kolon Industries, Inc. (Ulsan, Korea).

[0101] The tackifying agent is present at 0 wt% to 20 wt%, 3% to 20%, 3% to 15 wt%, or even 5 wt% to 15 wt%.

[0102] Waxes

[0103] The hot melt composition can comprise a wax. The hot melt composition can comprise more than one wax.

[0104] The wax can be derived from ethylene (e.g., at least about 95 mole % ethylene) and, optionally, additional comonomers, including, for example, propylene. Suitable waxes include, for example, paraffin wax, polyethylene wax, Fischer-Tropsch wax, metallocene-catalyzed polyethylene wax, and combinations thereof.

[0105] The wax can have a melting temperature (Tm) of at least 50 °C, at least 70 °C, at least 80 °C, at least 90 °C, at least 100 °C, from 70 °C to about 130 °C, from 70 °C to about 120 °C, from 70 °C to about 110 °C, or even from 80 °C to about 105 °C, as measured by DSC, and a heat of fusion of at least 200 Joules per gram (J / g), at least 210 J / g, or even at least 220 J / g. m

[0106] Useful polyethylene waxes are available under various trade designations, including, for example, the EPOLENE series of trade designations from Westlake Chemical Corporation (Houston, Tex.), including, for example, EPOLENE N-21 and N-14 polyethylene waxes. Useful Fischer-Tropsch waxes are available under various trade designations, including, for example, the BARECO series of trade designations from Baker Hughes Inc. (Sugar Land, Tex.), including, for example, BARECO PX-100 and PX-105 Fischer-Tropsch waxes, the SHELLWAX and SARAWAX-SX-105 series of trade designations from Shell Malaysia Ltd. (Kuala Lumpur, Malaysia), including, for example, SHELLWAX SX100, SX105, SX-70, and SX-80, and SARAWAX SX100 and SX105 Fischer-Tropsch waxes.

[0107] Useful metallocene-catalyzed polyethylene waxes are available under various trade designations, including, for example, the LICOWAX from Clariant Int'l Ltd. (Muttenz, Switzerland).

[0108] Useful commercially available paraffin waxes include, for example, FR-6513 from Citgo Petroleum (Houston, Texas) and SASOLWAX 6705 from Sasol Performance Chemicals (Hamburg, Germany).

[0109] The hot melt composition can comprise from 0 wt % to 20 wt %, from 3 wt % to 15 wt %, or even from 5 wt % to 15 wt % of a wax.

[0110] Optional Components​

[0111] The hot melt composition can include optional components such as ultraviolet stabilizers (e.g., benzophenone, benzotriazole, etc.), antioxidants, hindered amine light stabilizers (HALS), flame retardants, other tackifying resins, other polymers, non-functionalized copolymers of ethylene and alkyl acrylates (e.g., ethylene-n-butyl acrylate, ethylene-methacrylate, and ethylene-methyl methacrylate), acrylics (JONCRYL ADR, etc.), other pigments, dyes, and optical brighteners.

[0112] Useful commercially available ultraviolet stabilizers include CYABS ORB UV 531 and CYABS ORB UV 9 available from Solvay S.A. (Brussels, Belgium), and HOSTAVIN PR-25 available from Clariant.

[0113] Manufacturing method

[0114] The hot melt composition can be manufactured by blending the desired materials with optional additives using known techniques for blending thermoplastics, such as extrusion or kneading. Useful extrusion or kneading methods include internal blade or rotor mixers, external mixers, or single screw or co- or counter-rotating twin screw extruders.

[0115] Hot melt composition in the form of a film

[0116] The hot melt composition is preferably used in the form of a film or sheet. The film can have a thickness of 0.1 mm to 20 mm, 0.2 mm to 20 mm, or even 0.5 mm to 10 mm. The hot melt composition in the form of a film can be embossed.

[0117] The functionalized polymers can begin to react when they are made into a film, and can continue to react during the process of manufacturing the module.

[0118] The film can be monolayer (i.e., one layer consisting of the hot melt composition) or multilayer. When it is multilayer, the hot melt composition can be present as two or more films, or can be combined with layers of other materials conventionally used in the photovoltaic arts, such as polyolefins, ionomers, fluoropolymers, etc. If there are two or more layers, they can be formed in any of the possible ways, including by co-extrusion.

[0119] The film can be obtained by a process selected from the group consisting of compression, tubular (bubble) extrusion-blowing, extrusion-laminating, extrusion-coating, flat sheet extrusion (also known as extrusion-casting), and calendering. When extruded, various materials can be fed into the extruder using a gravity feeder.

[0120] PV module

[0121] The hot melt composition in the form of a film can act as an encapsulant in a PV module. The PV module can be selected from the group consisting of crystalline silicon and thin film.

[0122] A PV module can include, from top (solar facing side) to bottom: a front sheet, a hot melt composition in the form of a film, a photovoltaic cell layer in contact with a back sheet, and a back sheet. A PV module can include, from top (solar facing side) to bottom: a front sheet, a hot melt composition in the form of a film, a photovoltaic cell layer, a hot melt composition in the form of a film, and a back sheet.

[0123] In these embodiments, the layer of hot melt composition in the form of a film between the front sheet and the photovoltaic cell needs to be transparent.

[0124] When there are two layers of hot melt composition in the form of a film in the module, they can be the same composition, or they can be different compositions.

[0125] A thin film PV module can include a front sheet on which a photovoltaic cell can be deposited, a hot melt composition in the form of a film as an encapsulant, and a back sheet. The hot melt composition in the form of a film is located between the front sheet and the back sheet and bonds the assembly together.

[0126] The front sheet is the solar facing side of the panel and needs to be transparent. The front sheet can be composed of glass or a transparent plastic (e.g., polymethyl methacrylate, polytetrafluoroethylene (PTFE), poly(ethylene-co-tetrafluoroethylene) (ETFE), polyester, or any other transparent plastic).

[0127] The photovoltaic cell can be deposited on the front sheet, the back sheet, or a separate substrate, such as a metal film. The photovoltaic cell can comprise a variety of materials, such as CIGS (copper indium gallium diselenide), CdTe (cadmium telluride), amorphous thin film silicon (a-Si, TF-Si), copper indium diselenide (CIS), organics, perovskite, and combinations thereof.

[0128] In some thin film PV modules, when the photovoltaic cell is deposited on the front sheet, the encapsulant does not need to be transparent.

[0129] The back sheet can include glass, plastic, or metal. The back sheet can be flexible or non-flexible.

[0130] In one embodiment, the front sheet and back sheet are glass, the photovoltaic cell comprises CdTe and is deposited on the front sheet, and a hot melt composition in the form of a film bonds the assembly together.

[0131] The thin film PV module can further include an edge seal. The edge seal is a material that forms a seal between the outer edges of the front sheet and back sheet to provide additional barrier to prevent moisture from weakening the structure of the module or damaging the cells. The edge seal is typically based on butyl rubber, but can also be based on polyisobutylene. The edge seal can further include a desiccant material.

[0132] The various layers can be assembled by any type of pressing technique, such as hot pressing, vacuum pressing, or lamination (e.g., hot lamination). The thin film PV module can be laminated at a temperature of 120 °C to 180 °C, or even at a temperature of 140 °C to 170 °C.

[0133] The application will now be described by way of the following examples. All parts, ratios, percentages, and amounts specified in the examples are by weight unless otherwise specified. Example

[0134] Test Procedure

[0135] The test procedures used in the examples and throughout the specification, unless otherwise specified, include the following. The amounts of the raw materials listed in Table 2 are in weight percent.

[0136] Melt Index

[0137] The melt index can be measured according to ASTM D 1238 (190 °C, 2.16 kg). The melt index can also be estimated using logarithmic addition.

[0138] T according to DSC m and T g and heat of fusion

[0139] The test was performed using a Mettler Toledo DSC 3 Star system as follows: the temperature was lowered to 0 °C and held for 5 minutes, then ramped to 150 °C at a rate of 10 °C / min, and ramped to 0 °C at a rate of 10 °C / min. The measurement was taken on the first heat. If there were two peaks, the highest peak was used. Note: the samples tested according to this method were not pre-heat treated.

[0140] Storage Modulus

[0141] The storage modulus (G’) was obtained by dynamic mechanical analysis (DMA) temperature sweep using an ARES G2 dynamic mechanical analyzer. The following method was used. The sample was heated to 190 °C and equilibrated at 190 °C for 2 minutes, then cooled to -20 °C at 3 °C / min at 10 rad / sec.

[0142] 180° Peel Adhesion

[0143] On one end of a precleaned 3.8 centimeter (cm) (1.5 inch (in)) x 15.24 cm (6 in) regular window glass, a package encapsulant material of the same dimensions (un-embossed, with a thickness of approximately 0.45 mm) was placed. Between the glass and the encapsulant, as a spacer, a poly(tetrafluoroethylene) (PTFE) coated release sheet was inserted on the long end of the glass to completely cover approximately 3.8 cm (1.5 in) x 3.8 cm (1.5 in) of the glass, and a 3.8 cm (1.5 in) x 30.5 cm (12 in) strip of a flexible polyester-based backsheet commonly used in the PV industry (Dun-Solar PPE+, 0.40 millimeter (mm) thick, available from Dunmore) was placed on top. After aligning the glass, PTFE spacer, encapsulant, and backsheet, the entire sandwich assembly was carefully placed between two large PTFE cover sheets and laminated in a vacuum laminator with a platen temperature set at 160 °C with a 4 minute vacuum cycle followed by a 6 minute press cycle. The laminated adhesion sample was allowed to cool to room temperature, and the PTFE cover sheets and PTFE spacer were removed. The sample was then conditioned under ambient laboratory conditions for 24 to 72 hours. Using a safety razor or utility knife, a 2.54 cm (1 in) x 15.24 cm (6 in) strip of the laminated adhesion test sample was scribed in the middle of the sample from the backsheet side, and examined from the glass side to confirm a clean cut through the encapsulant to the glass. With the glass side facing down, the backsheet was pulled back, and the glass-encapsulant interface was very carefully and intentionally separated using the razor to expose and initiate the glass-encapsulant adhesion failure mode.

[0144] The prepared sample was then mounted on a tensile testing machine (Com-Ten 95 series) in a 180° peel configuration, and the force required to peel the encapsulant from the glass interface at a rate of 200 mm / min was recorded. The peel force was measured for at least 2.54 cm (1 in) of glass-encapsulant adhesion failure, and the average of three samples was used to report the peel / adhesion strength in Newton (N) / cm.

[0145]

[0146] AERAFIN polymer T by ASTM D3418 m ENGAGE 8411 T by Dow method testing m .

[0147]

[0148] Other embodiments are within the scope of the claims.

[0149] 1. A hot melt composition in the form of a film comprising:

[0150] a. 20 to 70 weight percent of a propylene-based polymer having a T m measured by DSC of no greater than 120 °C,

[0151] b. 20 to 70 weight percent of an ethylene-based polymer having a density of no greater than 0.93 g / cm 3 , and

[0152] c. 2 to 15 weight percent of a functionalized polymer comprising a functional group selected from the group consisting of an epoxy, a carboxylic anhydride, and a carboxylic acid.

[0153] 2. A hot melt composition in the form of a film comprising:

[0154] a. 20 to 70 weight percent of a propylene-based polymer having a T m measured by DSC of no greater than 120 °C,

[0155] b. 20 to 70 weight percent of an ethylene-based polymer having a density of no greater than 0.93 g / cm 3 , and

[0156] c. at least two of:

[0157] i. 2 to 10 weight percent of a first functionalized polymer selected from the group consisting of a copolymer of ethylene and maleic anhydride, a copolymer of ethylene, an alkyl (meth)acrylate, and maleic anhydride,

[0158] ii. 2 to 10 weight percent of a second functionalized polymer selected from the group consisting of a copolymer of ethylene and glycidyl methacrylate and a terpolymer of ethylene, an alkyl (meth)acrylate, and glycidyl methacrylate, and

[0159] iii. 0.1 to 3.0 weight percent of a silane adhesion promoter.

[0160] 3. A hot melt composition in the form of a film comprising:

[0161] a. 20 to 60 weight percent of a propylene-based copolymer having a T m measured by DSC of no greater than 120 °C, and a comonomer content of 9 to 22 weight percent,

[0162] b. 35 to 60 weight percent of a single site catalyzed ethylene-based polymer having a density of not greater than 0.90 g / cm 3

[0163] c. 2 to 15 weight percent of a functionalized polymer comprising a functional group selected from the group consisting of an epoxy, a carboxylic anhydride, and a carboxylic acid, and

[0164] d. a silane adhesion promoter.

[0165] 4. The hot melt composition of claims 1-3, wherein the propylene-based polymer is a propylene ethylene copolymer.

[0166] 5. The hot melt composition of claims 1-3, wherein the propylene-based polymer is a non-single site catalyzed amorphous polyalphaolefin.

[0167] 6. The hot melt composition of claim 4, wherein the non-single site catalyzed amorphous polyalphaolefin has a comonomer content of 12 to 22 weight percent and a DSC melting peak of not greater than 110 °C.

[0168] 7. The hot melt composition of claim 5, wherein the non-single site catalyzed amorphous polyalphaolefin is produced with an electron donor catalyst.

[0169] 8. The hot melt composition of claims 1-3, wherein the propylene-based polymer is produced in the presence of a catalyst system selected from the group consisting of a single site catalyst, a Ziegler-Natta catalyst, a catalyst system comprising at least one electron donor, and combinations thereof.

[0170] 9. The hot melt composition of claims 1-3, wherein the ethylene-based polymer is a single site catalyzed copolymer.

[0171] 10. The hot melt composition of claims 1-3, wherein the ethylene-based polymer is selected from the group consisting of very low density polyethylene (VLDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE).

[0172] 11. The hot melt composition of claims 1-3, wherein the ethylene-based polymer has a density tested according to ASTM D 792 of not greater than.89 g / cm3.

[0173] 12. The hot melt composition of claims 1-3, wherein the functionalized polymer is selected from the group consisting of a copolymer of ethylene and maleic anhydride; a copolymer of ethylene, an alkyl (meth)acrylate, and maleic anhydride; a copolymer of ethylene and glycidyl methacrylate; and a terpolymer of ethylene, an alkyl (meth)acrylate, and glycidyl methacrylate.​

[0174] 13. The hot melt composition of claims 1-3, wherein the functionalized polymer is present as a first and second functionalized polymer,

[0175] the first functionalized polymer is selected from the group consisting of a copolymer of ethylene and maleic anhydride; a copolymer of ethylene, alkyl (meth)acrylate and maleic anhydride, and

[0176] the second functionalized polymer is selected from the group consisting of a copolymer of ethylene and glycidyl methacrylate and a terpolymer of ethylene, alkyl (meth)acrylate and glycidyl methacrylate.

[0177] 14. The hot melt composition of claims 1-3, which is free of ethylene vinyl acetate, peroxide and polyvinyl chloride.

[0178] 15. The hot melt composition of claims 1-3, which has an approximate Melt Index of 5 g / 10 min to 150 g / 10 min tested according to ASTM D 1238 (190°C, 2.16 kg).

[0179] 16. The hot melt composition of claim 1, further comprising a silane adhesion promoter.

[0180] 17. The hot melt composition of claim 16, wherein the silane adhesion promoter is a bifunctional silane adhesion promoter selected from the group consisting of an aminosilane, an epoxysilane, an isocyanurate silane.

[0181] 18. The hot melt composition of claims 1-3, further comprising 5 wt% to 50 wt% of a filler.

[0182] 19. The hot melt composition of claims 1-3, further comprising at least one of a tackifier and a wax.

[0183] 20. The hot melt composition of claims 1-3, further comprising a wax selected from the group consisting of a polyethylene wax, a Fischer-Tropsch wax, a metallocene catalyzed polyethylene wax, and combinations thereof.

[0184] 21. The hot melt composition of claims 1-3, further comprising an aliphatic hydrocarbon tackifier.

[0185] 22. A photovoltaic module comprising the hot melt composition in the form of a film according to claims 1-3.

[0186] 23. A photovoltaic module comprising from top to bottom:

[0187] a. a front sheet,

[0188] b. The hot melt composition in the form of a film according to claims 1-3,

[0189] c. a photovoltaic cell layer,

[0190] d. The hot melt composition in the form of a film according to claims 1-3, and

[0191] e. a backsheet,

[0192] wherein the hot melt composition in the form of a film adheres the front sheet to the backsheet.

[0193] 24. A photovoltaic module comprising:

[0194] a. a front sheet,

[0195] b. a photovoltaic cell layer in contact with the front sheet,

[0196] c. The hot melt composition in the form of a film according to claims 1-3, and

[0197] d. a backsheet,

[0198] wherein the hot melt composition in the form of a film is between the photovoltaic cell and the backsheet and adheres the front sheet to the backsheet.

[0199] 25. The photovoltaic module according to claim 24, wherein the photovoltaic cell is selected from the group consisting of CIGS (copper indium gallium diselenide), CdTe (cadmium telluride), amorphous thin film silicon (a-Si, TF-Si), and copper indium diselenide (CIS) and perovskite based systems.

[0200] 26. The photovoltaic module according to claim 24, further comprising an edge seal.

[0201] 27. The photovoltaic module according to claim 24, wherein the backsheet and the front sheet are glass and the photovoltaic cell is CdTe.

Claims

1. A hot melt composition in the form of a film comprising: a. 20 to 70 weight percent of a propylene-based polymer having a T m a propylene-based polymer having a T b. 20 to 70 weight percent of an ethylene-based polymer having a density of not greater than 0.93 g / cm 3 and c. 2 to 15 weight percent of a functionalized polymer comprising functional groups selected from the group consisting of epoxy, carboxylic anhydride, and carboxylic acid.

2. The hot melt composition in the form of a film according to claim 1 comprising: a. 20 to 60 weight percent of a propylene-based copolymer having a T m and 9 to 22 weight percent of a propylene-based copolymer having a comonomer content of 5 to 10 weight percent. b. 35 to 60 weight percent of a single site catalyzed ethylene-based polymer having a density of not greater than 0.90 g / cm 3 3. The composition of any of claims 1-2, wherein the composition has a density of not greater than 0.91 g / cm3. c. 2 to 15 weight percent of a functionalized polymer comprising functional groups selected from the group consisting of epoxy, carboxylic anhydride, and carboxylic acid, and d. a silane adhesion promoter.

3. The hot melt composition according to claim 1, wherein the propylene-based polymer is a propylene ethylene copolymer.

4. The hot melt composition of claim 1, wherein the propylene-based polymer is an amorphous polyalphaolefin having a comonomer content of 12 wt% to 22 wt% and a Tm of no greater than 110 °C as measured by DSC. m of the amorphous polyalphaolefin.

5. The hot melt composition according to claim 1, wherein the propylene-based polymer is produced in the presence of a catalyst system selected from the group consisting of single site catalysts, Ziegler-Natta catalysts, catalyst systems comprising at least one electron donor, and combinations thereof.

6. The hot melt composition according to claim 1, wherein the ethylene-based polymer is a single site catalyzed copolymer.

7. The hot melt composition according to claim 1, wherein the ethylene-based polymer is selected from the group consisting of very low density polyethylene (VLDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE).

8. The hot melt composition according to claim 1, wherein the functionalized polymer is present as a first and a second functionalized polymer, the first functionalized polymer is selected from the group consisting of a copolymer of ethylene and maleic anhydride; a copolymer of ethylene, an alkyl (meth)acrylate, and maleic anhydride, and the second functionalized polymer is selected from the group consisting of a copolymer of ethylene and glycidyl methacrylate and a terpolymer of ethylene, an alkyl (meth)acrylate, and glycidyl methacrylate.

9. The hot melt composition according to claim 1, which is free of ethylene vinyl acetate, peroxides, and polyvinyl chloride.

10. The hot melt composition according to claim 1, which has an approximate melt index of 5 g / 10 min to 150 g / 10 min tested according to ASTM D 1238 (190°C, 2.16 kg).

11. The hot melt composition according to claim 1, further comprising a silane adhesion promoter.

12. The hot melt composition according to claim 1, further comprising at least one of a filler, a tackifier, and a wax.

13. A photovoltaic module comprising the hot melt composition in the form of a film according to claim 1.

14. A photovoltaic module comprising: a. a front sheet, b. a photovoltaic cell layer in contact with the front sheet, c. the hot melt composition in the form of a film according to claim 1, and d. a back sheet, wherein the hot melt composition in the form of a film is positioned between the photovoltaic cell and the back sheet and adheres the front sheet to the back sheet.

15. The photovoltaic module according to claim 14, wherein the photovoltaic cell is selected from the group consisting of CIGS (copper indium gallium diselenide), CdTe (cadmium telluride), amorphous thin film silicon (a-Si, TF-Si), copper indium diselenide (CIS), perovskite-based systems, and combinations thereof.

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