WO2013154897A1

WO2013154897A1 - Photovoltaic module backsheets and assemblies thereof

Info

Publication number: WO2013154897A1
Application number: PCT/US2013/035215
Authority: WO
Inventors: Nico REMS; Gert-Jan H. NIJHUIS
Original assignee: Lubrizol Advanced Materials, Inc.
Priority date: 2012-04-09
Filing date: 2013-04-04
Publication date: 2013-10-17
Also published as: TW201350540A

Abstract

The invention relates to photovoltaic module backsheets produced from at least one rigid thermoplastic polyurethane made by reacting at least one polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates. The invention also relates to an integrated photovoltaic module backsheet and photovoltaic encapsulant, wherein a photovoltaic encapsulant layer is present on the forward-facing surface of the backsheet. The invention also provides photovoltaic modules made with the described backsheets and integrated backsheet and photovoltaic encapsulant, as well as various methods and uses concerning the same.

Description

PHOTOVOLTAIC MODULE BACKSHEETS AND ASSEMBLIES THEREOF

Field of the Invention

[0001] The invention relates to photovoltaic module backsheets produced from at least one rigid thermoplastic polyurethane made by reacting at least one polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates. The invention also relates to an integrated photovoltaic module backsheet and photovoltaic encapsulant, wherein a photovoltaic encapsulant layer is present on the forward-facing surface of the backsheet. The invention also provides photovoltaic modules made with the described backsheets and integrated backsheet and photovoltaic encapsulant, as well as various methods and uses concerning the same.

Background of the Invention

[0002] Photovoltaic Energy is the converting of light into electrical energy, and is achieved through the use of semiconductors or photovoltaic solar cells. The cell assemblies are encapsulated into water tight modules for protection from moisture and impact. The resulting assembly is referred to as a solar panel or module. The principle components of a crystalline silicon photovoltaic module are the glass glazing, an encapsulant such as a cross-linked ethylene-vinyl acetate (EVA), the silicon wafers and associated wiring, a junction box and a protective backsheet.

[0003] Often such modules are produced by making a "sandwich" having the following layers stacked on top of each other: glass - encapsulant - wafers - encapsulant - backsheet. This sandwich can be laminated in a vacuum laminator or by autoclave. The sandwich is edge trimmed, framed, and a junction box is connected, completing the assembly.

[0004] The backsheets are necessary to provide the module mechanical protection, electrical insulation and corrosion protection. The backsheet must also exhibit good adhesion with the encapsulant, act as an effective oxygen and water barrier, show low shrinkage over time, and exhibit good weatherability resistance. A typical backsheet may have a thickness of around 350 micron. However, thickness can range from 275 micron up to 700 micron. [0005] Today backsheets are normally made as a laminated film composite, the most common being a trilayer structure of Tedlar®/Polyester/Tedlar®, also called TPT™. This structure allows the fluoropolymer to protect both sides of the polyester from photo-degradation. The Tedlar® film is tough, photostable, chemically resistant and unaffected by long term moisture exposure. It is also one of the few fluoropolymers that can be readily pigmented. Such TPT foil is suitable as backsheet because of its unique combination of useful properties like electrical insulation, no or low UV aging, dimensional stability at module lamination temperature (150°C), excellent adhesion to EVA adhesive films, at least if surface treated, and to sealants and limited water vapor permeability.

[0006] However, these TPT foils have several significant drawbacks. It is very expensive to produce as each layer must first be produced and then laminated in a separate step often with supplementary solvent based glues. TPT foil consists of halogenated material (Tedlar®) and hydrolysis sensitive materials (PET, PUR adhesives), which is a severe drawback for hot, humid, sunny climates. Thus, there exists a need for less costly materials that provide the same useful properties.

[0007] The present invention deals with improved photovoltaic module backsheets that address the issues with the current technology.

Summary of the Invention

[0008] The present invention deals with a photovoltaic module backsheet produced from at least one rigid thermoplastic polyurethane. Suitable rigid thermoplastic polyurethanes are made by reacting at least one polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates. In some embodiments, the rigid thermoplastic polyurethanes are made by reacting at least one polyisocyanate with at least one diol chain extender.

[0009] The invention provides for the described photovoltaic module backsheets where the rigid thermoplastic polyurethane has one or more of the following properties: (i) a Vicat softening point, as measured by ISO306/A50, of at least 140°C; (ii) a partial discharge, as measured by IEC 60664-1 , of greater than 1000 volts; (iii) a Shore D hardness of at least 70. [0010] The invention also provides an integrated photovoltaic module backsheet and photovoltaic encapsulant, wherein a photovoltaic encapsulant layer is present on the forward-facing surface of the backsheet. Suitable backsheets include any of those described herein. In some embodiments, the backsheet is produced from at least one rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates, which may also be referred to as polyols. In some embodiments, the photovoltaic encapsulant comprises at least one non-rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and one or more hydroxyl terminated polyether intermediates. In some embodiments, the backsheet is produced from at least one rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates and the photovoltaic encapsulant comprises at least one non-rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and one or more hydroxyl terminated polyether intermediates.

[0011] The invention also provides for a photovoltaic module comprising a backsheet produced from at least one rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates.

[0012] The invention also provides a photovoltaic module that has an integrated photovoltaic module backsheet and photovoltaic encapsulant, wherein a photovoltaic encapsulant layer is present on the forward-facing surface of the backsheet. The backsheet may be produced from at least one rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates. The photovoltaic encapsulant may comprise at least one non-rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and one or more hydroxyl terminated polyether intermediates. In some embodiments, these features can be combined and the backsheet may be produced from at least one rigid thermoplastic polyurethane and the photovoltaic encapsulant may comprise at least one non-rigid thermoplastic polyurethane.

[0013] The invention further provides for a method of producing a photovoltaic module backsheet produced from at least one at least one rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates wherein the method includes the step of: (i) extruding the rigid thermoplastic polyurethane to form the backsheet.

[0014] The invention also provides a method for producing an integrated photovoltaic module backsheet and photovoltaic encapsulant, wherein a photovoltaic encapsulant layer is present on the forward-facing surface of the backsheet. The method includes the steps of (i) laminating the photovoltaic encapsulant layer onto the forward-facing surface of the backsheet, or (ii) co- extruding the backsheet and photovoltaic encapsulant resulting in an integrated photovoltaic module backsheet and photovoltaic encapsulant with photovoltaic encapsulant layer present on the forward-facing surface of the backsheet. Here, as above, the backsheet may be produced from at least one rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates. The photovoltaic encapsulant may comprise at least one non-rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and one or more hydroxyl terminated polyether intermediates. The backsheet may be produced from at least one rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates and the photovoltaic encapsulant may comprise at least one non-rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and one or more hydroxyl terminated polyether intermediates.

Detailed Description of the Invention

[0015] Various preferred features and embodiments will be described below by way of non-limiting illustration. The Photovoltaic Modules and Backsheets Thereo f

[0016] The invention provides for a photovoltaic module backsheet produced from at least one rigid thermoplastic polyurethane (TPU) made by reacting at least one polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates. The rigid TPU used to make the photovoltaic module backsheet may be any of the rigid TPU described below. The invention also provides for a photovoltaic module made with the described backsheets. The invention further provides methods of making and using the described photovoltaic modules and photovoltaic module backsheets.

[0017] The invention provides for an integrated photovoltaic module encapsulant layer and backsheet, where a second, or lower, encapsulant layer is combined with a photovoltaic module backsheet, to provide an integrated layer the improves the photovoltaic module construction process by reducing the number of spate layers involved that have to be assembled. The invention also provides for a photovoltaic module made with the described integrated encapsulant backsheets. The invention further provides methods of making and using the described photovoltaic modules and integrated encapsulant backsheets.

[0018] The term "photovoltaic devices", also referred to herein as photovoltaic modules, can convert solar energy or other suitable sources of photons into electricity. Photovoltaic modules broadly include amorphous silicon, monocrystalline silicon, multicrystalline silicon, near-multicrystalline silicon, geometric multicrystalline silicon, cadmium telluride, copper indium gallium (di)selenide, and/or other suitable photovoltaic materials. Photovoltaic modules may be generally rigid and/or generally flexible, depending on construction techniques and/or fabrication materials. Examples of photovoltaic modules include solar panels, solar modules, and/or solar arrays.

[0019] The term "solar energy" broadly refers to any suitable portion of the electromagnetic spectrum, including for example, infrared light, visible light, and/or ultraviolet light. Solar energy can come from any suitable source, such as a star, and in particular the Sun. [0020] According to one embodiment, this invention can include a photovoltaic device for converting solar energy into electricity. The photovoltaic device can include a transparent layer for receiving solar energy also referred to as a transparent superstrate or frontsheet, and at least one photovoltaic cell disposed below the transparent layer. The photovoltaic device can include a backsheet disposed below the at least one photovoltaic cell. The photovoltaic device can include an encapsulant bonding together and/or laminating the transparent layer, the at least one photovoltaic cell, an optional thin film substrate (also referred to as a polymeric mat), and the backsheet, where the encapsulant consists of an upper layer and a lower layer surrounding the layers to be encapsulated, typically the least one photovoltaic cell and the optional thin film substrate when present, with the frontsheet then present on the outside upper layer of encapsulant and the backsheet present on the outside lower layer of encapsulant.

[0021] The term "transparent layer" broadly refers to a material capable of passing and/or transmitting at least a portion of incoming radiation from the electromagnetic spectrum. According to one embodiment, the transparent layer can pass at least about 60 percent of solar energy contacting a surface of the transparent layer, at least about 80 percent of solar energy contacting a surface of the transparent layer, at least about 90 percent of solar energy contacting a surface of the transparent layer, and/or the like. The transparent layer may include any suitable coatings and/or additives, such as antireflection coatings, ultraviolet filtering additives, and/or the like. The transparent layer may include any suitable size, shape, and/or material. According to one embodiment, the transparent layer includes polycarbonate, poly(methyl methacrylate), fluoropolymers (for example, (ethylene-tetrafluoroethylene) fluorocopolymer, fluorinated ethylene propylene copolymer, (ethylene chlorotrifluoroethylene) fluorocopolymer) glass, and/or the like. The transparent layer can be rigid and/or flexible, for example. Desirably, the transparent layer includes a surface of the photovoltaic device that can receive solar energy, such as at least generally oriented towards the Sun.

[0022] The term "photovoltaic cell" broadly refers to any suitable apparatus for converting photons into electrical power, such as silicon solar cells and/or the like. Photovoltaic cells can be arranged in any suitable configuration, such as in parallel and/or in series to produce a desired voltage level and/or a desired current flow. The photovoltaic device may include any suitable number of photovoltaic cells, such as at least about 1 , at least about 10, at least about 36, at least about 72, at least about 144, at least about 250, at least about 500, and/or the like.

[0023] The term "backsheet" can broadly refer to compounds or materials useful for at least a portion of a layer or a cover on a side opposite the transparent layer of the photovoltaic device. Often the backsheet may be a sheet, a film, and/or a membrane. It can be flexible and/or rigid and can include any suitable material. The backsheet may have suitable dielectric properties, such as, for example, to prevent short circuiting and/or allow reliable operation of a photovoltaic device. The backsheet may also provide protection or resistance to water or moisture ingress into the photovoltaic device. In the present invention, the backsheet is made from certain rigid thermoplastic polyurethanes and provides benefits over the more general backsheets currently in use.

[0024] The term "encapsulant" broadly refers to compounds or materials useful for laminating, fusing, adhering, adjoining, gluing, sealing, caulking, bonding, melting, joining, and/or the like at least a portion of components of a photovoltaic device. The encapsulant may bond or laminate the transparent layer, the at least one photovoltaic cell, the optional thin film substrate (also referred to as a polymeric mat), the backsheet, and/or the like into a generally unitary apparatus. The encapsulant may include any suitable materials or compounds, such as ethylene vinyl acetate copolymers, ethylene methyl acetate copolymers, ethylene butyl acetate copolymers, ethylene propylene diene terpolymers, silicones, polyurethanes, thermoplastic olefins, ionomers, acrylics, polyvinyl butyrals, and/or the like. Optionally, the encapsulant may include an adhesion promoter, such as a silane material.

[0025] The photovoltaic devices of the invention may include any suitable layers and/or arrangements of encapsulant materials. For example, a single encapsulant layer may provide sufficient lamination for the entire photovoltaic device including the transparent layer, the at least one photovoltaic cell, the backsheet, and/or the like. Desirably, but not necessarily, the encapsulant material flows around and/or through materials during the lamination process, such as may allow the encapsulant to contact regions between materials where the solid sheet of encapsulant was not present before lamination.

[0026] In the alternative, a first sheet of encapsulant may be disposed between the transparent layer and the at least one photovoltaic cell, and a second sheet of encapsulant may be disposed between the polymeric mat and the backsheet. Other configurations and/or locations of the encapsulant layers for the photovoltaic device are within the scope of this invention.

[0027] The term "bonding" as used herein may broadly refer to joining or securing, such as with physical forces, chemical forces, mechanical forces, and/or like. Suitable chemical forces may include strong forces and/or weak forces, such as ionic bonds, covalent bonds, hydrogen bonds, van der Waals forces, and/or the like. According to one embodiment, bonding includes a suitable amount of cross-linking between functional groups, such as silane molecules of an adhesion promoter.

[0028] The photovoltaic device may meet and/or exceed any suitable industry standard and/or test, such as for safety, reliability, performance, and/or the like. According to one embodiment, the photovoltaic device can have no dielectric breakdown or surface tracking when measured according to a dielectric withstand test as defined in IEC 61730 (part 2, 2004 edition) under a minimum of 6000 volts. Optionally, and/or alternatively, the photovoltaic device can have a measured wet insulation resistance times an area of the photovoltaic device at least above 40 megaohms meter squared when measured at 1000 volts as defined in IEC 61215 (2005 edition). The entire teachings of IEC 61730 (part 2, 2004 edition) and IEC 61215 (2005 edition) are hereby incorporated by reference into this specification. IEC refers to the International Electrotechnical Commission with a Central Office in Geneva Switzerland. According to one embodiment, the photovoltaic device can have a wet insulation resistance tested at 1000 volts of at least 40 megaohms meter squared after aging for about 1000 hours under about 85 degrees Celsius and about 85 percent relative humidity as defined in IEC 61215 (2005 edition). According to one embodiment, the photovoltaic device can have a suitable cut resistance and/or puncture resistance. Particularly, the photovoltaic device can pass the Cut Susceptibility Test, MST 12, as defined in IEC 61730 part 2, section 10.3.

[0029] According to one embodiment, this invention may include a process for making a photovoltaic device. The process may include the step of providing a transparent layer, and the step of placing a first sheet of encapsulant over at least a portion of the transparent layer. The process may include the step of placing at least one photovoltaic cell over the first sheet of encapsulant material. The process may include the step of placing an optional thin film substrate, also referred to as a polymer mat, over the at least one photovoltaic cell. The process may include the step of placing a second sheet of encapsulant over the at least one photovoltaic cell (or the thin film substrate when present), and the step of placing the described backsheet over the second sheet of encapsulant material. The process may include the step of laminating the photovoltaic device for a sufficient time and/or a sufficient temperature for sufficient bonding of the first sheet and/or the second sheet to the other materials.

[0030] According to another embodiment, the process may include the step of providing a transparent layer, and the step of placing a first sheet of encapsulant over at least a portion of the transparent layer. The process may include the step of placing at least one photovoltaic cell over the first sheet of encapsulant material, and then optionally a thin film substrate. The process may include the step of placing an integrated encapsulant and backsheet over the at least one photovoltaic cell (or the thin film substrate when present), where the integrated encapsulant and backsheet includes a second sheet of encapsulant and a backsheet pre-laminated or co-extruded to form an integrated layer such as to reduce a number of layers used during fabrication. The process may include the step of laminating the photovoltaic device for a sufficient time and/or a sufficient temperature for sufficient bonding of the first sheet and/or the second sheet to the other materials.

[0031] In some embodiments, the integrated photovoltaic module backsheet and photovoltaic encapsulant is oriented such that the photovoltaic encapsulant layer is present on the forward-facing surface, or upper surface, of the backsheet. That is, the surface of the backsheet that faces the interior of the photovoltaic module, opposite of the surface that forms the exterior of the back of the photovoltaic module. In some embodiments, the backsheet is produced from one or more of the rigid thermoplastic polyurethane described herein and may be integrated with any conventional encapsulant, for example, EVA resins such as Elvax® commercially available from DuPont™, and polyvinyl butyral polymers such as PV5200 and PV5300 encapsulant sheets also commercially available from DuPont™. In other embodiments, the photovoltaic encapsulant includes one or more non-rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and one or more hydroxyl terminated polyether intermediates, and may be integrated with any conventional backsheet. In still other embodiments, the backsheet is produced from one or more of the rigid thermoplastic polyurethane described herein and the photovoltaic encapsulant includes one or more non-rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and one or more hydroxyl terminated polyether intermediates.

[0032] In embodiments where the integrated photovoltaic module backsheet and photovoltaic encapsulant has a non-rigid thermoplastic polyurethane encapsulant integrated with any backsheet, the backsheet may be produced from one or more of the following materials: ethyl ene-vinyl acetate copolymers (EVA), thermoplastic elastomers (TPE), thermoplastic polyurethanes (TPU), polyvinyl fluoride polymers (PVF), polyvinylidene fluoride polymers (PVDF), polyethylene terephthalate polymers (PET), ethylene propylene diene monomer -based polymers (EPDM), epoxy resins with dicyandiamide curing agents, polyimides, polyesters, hybrid epoxy polyesters, cyanate esters, acrylics, or combinations thereof. Additional examples of more conventional backsheet materials include polyvinyl fluoride (PVF) films, such as Tedlar® films, and polyester films, such as Mylar®, Melinex®, and Teijin® Tetoron® polyester films, all commercially available from DuPont™.

[0033] In some embodiments, the backsheet is substantially free of, or even completely free of, polyamides.

[0034] In some embodiments, the photovoltaic modules of the invention include the following materials, layered and/or assembled in the following order: (a) the described backsheet; (b) an adhesive layer and/or backside pottant layer and/or first encapsulant layer; (c) a least one solar cell; (d) a transparent pottant layer and/or an adhesive layer and/or second encapsulant layer; and (e) a transparent superstrate layer, which may also be referred to as a frontsheet. The adhesive layer, pottant layer, and transparent superstrate layer are other well-known components of typical photovoltaic modules and may be used herein as defined in Michelle Poliskie, Solar Module Packaging, CRC Press, 2011, especially beginning at section 2.2 on page 22, the entire contents of said Poliskie book are incorporated by reference. In some embodiments, the photovoltaic modules of the invention include the following materials, layered and/or assembled in the following order: (a) the described backsheet; (b) a first encapsulant layer; (c) a least one solar cell; (d) a second encapsulant layer; and (e) a transparent superstrate layer.

[0035] In some embodiments, the photovoltaic modules of the invention include the following materials, layered and/or assembled in the following order: (a) the described integrated photovoltaic module backsheet and photovoltaic encapsulant; (b) a least one solar cell; (c) a second encapsulant layer; and (d) a transparent superstrate layer or frontsheet.

[0036] The invention also provides a method for producing the described photovoltaic module backsheet, wherein the method includes the step of: (i) extruding the rigid thermoplastic polyurethane to form the backsheet. Any of the rigid thermoplastic polyurethanes described herein may be used in these methods.

[0037] The invention also provides methods for producing the described integrated photovoltaic module backsheet and photovoltaic encapsulant, wherein the method includes the steps of (i) laminating the photovoltaic encapsulant layer onto the forward-facing surface of the backsheet, or (ii) co-extruding the backsheet and photovoltaic encapsulant resulting in an integrated photovoltaic module backsheet and photovoltaic encapsulant with photovoltaic encapsulant layer present on the forward-facing surface of the backsheet. Any of the rigid thermoplastic polyurethanes and non-rigid thermoplastic polyurethanes described herein may be used in these methods. Any of the backsheet materials and encapsulant materials described herein may be used in these methods. The Rigid Thermoplastic Polvurethane

[0038] The backsheets of the invention may be produced from at least one rigid thermoplastic polyurethane (TPU). Such rigid TPU are made by reacting a polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates. In some embodiments, the rigid TPU of the invention are made by reacting a polyisocyanate with at least one diol chain extender.

[0039] The rigid TPU may also be described as a high hardness TPU, that is having a Shore D hardness of about 80, 81 , 82, 83 or greater, and in some embodiments about 83.5 and or even about 85, as measured according to ASTM D- 2240.

[0040] The rigid and/or high hardness TPU may be made by reacting a polyisocyanate with a short chain diol (i.e., chain extender), and optionally less than about 5, 4, 3, 2, or 1 weight percent of polyol (i.e., hydroxyl terminated intermediate). In some embodiments, the TPU is even substantially free of any polyol. Thus, the TPU has at least 95%, 96%, 97%, 98% or 99% weight hard segment, and in some embodiments even 100% hard segment.

[0041] Suitable chain extenders to make the TPU include relatively small polyhydroxy compounds, for example, lower aliphatic or short chain glycols having from 2 up to about 20 or in some cases from 2 up to about 12 carbon atoms. Suitable examples include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1 ,4-butanediol (BDO), 1 ,6-hexanediol (HDO), 1 ,3-butanediol, 1 ,5-pentanediol, neopentylglycol, 1 ,4-cyclohexanedimethanol (CHDM), 2,2-bis[4- (2-hydroxyethoxy) phenyljpropane (HEPP) and hydroxyethyl resorcinol (HER), and the like, as well as mixtures thereof. In some embodiments, the chain extenders are 1 ,4-butanediol and 1 ,6-hexanediol. Other glycols, such as aromatic glycols could be used, but in some embodiments the TPUs of the invention are not made using such materials.

[0042] In some embodiments, the chain extender used to prepare the TPU is substantially free of, or even completely free of, 1 ,6-hexanediol. In some embodiments, the chain extender used to prepare the TPU includes a cyclic chain extender. Suitable examples include CHDM, HEPP, HER, and combinations thereof. In some embodiments, the chain extender used to prepare the TPU includes an aromatic cyclic chain extender, for example, HEPP, HER, or a combination thereof. In some embodiments, the chain extender used to prepare the TPU includes an aliphatic cyclic chain extender, for example, CHDM. In some embodiments, the chain extender used to prepare the TPU is substantially free of, or even completely free of aromatic chain extenders, for example, aromatic cyclic chain extenders.

[0043] Suitable polyisocyanates to make the rigid TPU include aromatic diisocyanates such as 4,4 ^'-methyl en ebis-(phenyl isocyanate) (MDI), m-xylene diisocyanate (XDI), phenylene- l,4-diisocyanate, naphthalene- 1,5-diisocyanate, and toluene diisocyanate (TDI); as well as aliphatic diisocyanates such as isophorone diisocyanate (IPDI), 1 ,4-cyclohexyl diisocyanate (CHDI), decane-1 , 10- diisocyanate, and dicyclohexylmethane-4,4 ^'-diisocyanate (H12MDI).

[0044] Mixtures of two or more polyisocyanates may be used. In some embodiments, the polyisocyanate is MDI and/or H12MDI. In some embodiments, particularly when referring to the TPU of the backsheets described below, the polyisocyanate may include MDI. In some embodiments, particularly when referring to the TPU of the encapsulants described below, the polyisocyanate may include H12MDI.

[0045] Suitable polyols (hydroxyl terminated intermediates), when present, include one or more hydroxyl terminated polyesters, one or more hydroxyl terminated polyethers, one or more hydroxyl terminated polycarbonates or mixtures thereof.

[0046] Suitable hydroxyl terminated polyester intermediates include linear polyesters having a number average molecular weight (Mn) of from about 500 to about 10,000, from about 700 to about 5,000, or from about 700 to about 4,000, and generally have an acid number generally less than 1.3 or less than 0.8. The molecular weight is determined by assay of the terminal functional groups and is related to the number average molecular weight. The polyester intermediates may be produced by (1) an esterification reaction of one or more glycols with one or more dicarboxylic acids or anhydrides or (2) by transesterification reaction, i.e., the reaction of one or more glycols with esters of dicarboxylic acids. Mole ratios generally in excess of more than one mole of glycol to acid are preferred so as to obtain linear chains having a preponderance of terminal hydroxyl groups. Suitable polyester intermediates also include various lactones such as polycaprolactone typically made from ε-caprolactone and a bifunctional initiator such as diethylene glycol. The dicarboxylic acids of the desired polyester can be aliphatic, cycloaliphatic, aromatic, or combinations thereof. Suitable dicarboxylic acids which may be used alone or in mixtures generally have a total of from 4 to 15 carbon atoms and include: succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, dodecanedioic, isophthalic, terephthalic, cyclohexane dicarboxylic, and the like. Anhydrides of the above dicarboxylic acids such as phthalic anhydride, tetrahydrophthalic anhydride, or the like, can also be used. Adipic acid is a preferred acid. The glycols which are reacted to form a desirable polyester intermediate can be aliphatic, aromatic, or combinations thereof, including any of the glycol described above in the chain extender section, and have a total of from 2 to 20 or from 2 to 12 carbon atoms. Suitable examples include ethylene glycol, 1 ,2- propanediol, 1 ,3 -propanediol, 1 ,3-butanediol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,6- hexanediol, 2,2-dimethyl- 1 ,3 -propanediol, 1 ,4-cyclohexanedimethanol, decamethylene glycol, dodecamethylene glycol, and mixtures thereof.

[0047] Suitable hydroxyl terminated polyether intermediates include polyether polyols derived from a diol or polyol having a total of from 2 to 15 carbon atoms, in some embodiments an alkyl diol or glycol which is reacted with an ether comprising an alkylene oxide having from 2 to 6 carbon atoms, typically ethylene oxide or propylene oxide or mixtures thereof. For example, hydroxyl functional polyether can be produced by first reacting propylene glycol with propylene oxide followed by subsequent reaction with ethylene oxide. Primary hydroxyl groups resulting from ethylene oxide are more reactive than secondary hydroxyl groups and thus are preferred. Useful commercial polyether polyols include poly( ethylene glycol) comprising ethylene oxide reacted with ethylene glycol, poly(propylene glycol) comprising propylene oxide reacted with propylene glycol, poly(tetramethylene glycol) comprising water reacted with tetrahydrofuran (PTMEG). In some embodiments, the polyether intermediate includes PTMEG. Suitable polyether polyols also include polyamide adducts of an alkylene oxide and can include, for example, ethylenediamine adduct comprising the reaction product of ethylenediamine and propylene oxide, diethylenetriamine adduct comprising the reaction product of diethylenetriamine with propylene oxide, and similar polyamide type polyether polyols. Copolyethers can also be utilized in the current invention. Typical copolyethers include the reaction product of THF and ethylene oxide or THF and propylene oxide. These are available from BASF as Poly THF B, a block copolymer, and poly THF R, a random copolymer. The various polyether intermediates generally have a number average molecular weight (Mn) as determined by assay of the terminal functional groups which is an average molecular weight greater than about 700, such as from about 700 to about 10,000, from about 1000 to about 5000, or from about 1000 to about 2500. A particular desirable polyether intermediate is a blend of two or more different molecular weight polyethers, such as a blend of 2000 M_n and 1000 M_n PTMEG.

[0048] Suitable hydroxyl terminated polycarbonates include those prepared by reacting a glycol with a carbonate. U.S. Patent No. 4, 131 ,731 is hereby incorporated by reference for its disclosure of hydroxyl terminated polycarbonates and their preparation. Such polycarbonates are linear and have terminal hydroxyl groups with essential exclusion of other terminal groups. The essential reactants are glycols and carbonates. Suitable glycols are selected from cycloaliphatic and aliphatic diols containing 4 to 40, and or even 4 to 12 carbon atoms, and from polyoxyalkylene glycols containing 2 to 20 alkoxy groups per molecular with each alkoxy group containing 2 to 4 carbon atoms. Diols suitable for use in the present invention include aliphatic diols containing 4 to 12 carbon atoms such as butanediol-1 ,4, pentanediol-1 ,4, neopentyl glycol, hexanediol-1 ,6, 2,2,4- trimethylhexanediol-1 ,6, decanediol-1, 10, hydrogenated dilinoleylglycol, hydrogenated dioleylglycol; and cycloaliphatic diols such as cyclohexanediol-1,3, dimethylolcyclohexane-1 ,4, cyclohexanediol-1 ,4, dimethylolcyclohexane-1 ,3, 1 ,4- endomethylene-2-hydroxy-5-hydroxymethyl cyclohexane, and polyalkylene glycols. The diols used in the reaction may be a single diol or a mixture of diols depending on the properties desired in the finished product. Polycarbonate intermediates which are hydroxyl terminated are generally those known to the art and in the literature. Suitable carbonates are selected from alkylene carbonates composed of a 5 to 7 member ring. Suitable carbonates for use herein include ethylene carbonate, trim ethylene carbonate, tetram ethylene carbonate, 1 ,2- propylene carbonate, 1 ,2-butylene carbonate, 2,3-butylene carbonate, 1 ,2-ethylene carbonate, 1 ,3-pentylene carbonate, 1 ,4-pentylene carbonate, 2,3-pentylene carbonate, and 2,4-pentylene carbonate. Also, suitable herein are dialkylcarbonates, cycloaliphatic carbonates, and diarylcarbonates. The dialkylcarbonates can contain 2 to 5 carbon atoms in each alkyl group and specific examples thereof are diethylcarbonate and dipropylcarbonate. Cycloaliphatic carbonates, especially dicycloaliphatic carbonates, can contain 4 to 7 carbon atoms in each cyclic structure, and there can be one or two of such structures. When one group is cycloaliphatic, the other can be either alkyl or aryl. On the other hand, if one group is aryl, the other can be alkyl or cycloaliphatic. Examples of suitable diarylcarbonates, which can contain 6 to 20 carbon atoms in each aryl group, are diphenylcarbonate, ditolylcarbonate, and dinaphthylcarbonate.

[0049] In some embodiments, the rigid TPU is made by reacting the polyisocyanate shown above with the chain extender, without any polyol being present. If polyols are used, they should be used in small amounts of less than about 5 weight percent of the total TPU weight. If used, the polyols, also known as hydroxyl terminated intermediates, are used in very small amounts as stated above to increase processability and impact strength. The polyols which can be used are any of the normal polyols used in making TPU polymers. These include hydroxyl terminated polyesters, hydroxyl terminated polyethers, hydroxyl terminated poly(ester-ether), and hydroxyl terminated polycarbonates.

[0050] The level of polyisocyanate, preferably diisocyanate, used is the equivalent weight of diisocyanate to the equivalent weight of hydroxyl containing components (i.e., hydroxyl terminated intermediate, if used, and the chain extender glycol). The ratio of equivalent weight of polyisocyanate to hydroxyl containing components may be from about 0.95 to about 1.10, or from about 0.96 to about 1.02, or even from about 0.97 to about 1.005.

[0051] The reactants to make the rigid TPU may be reacted together in a "one shot" polymerization process wherein all of the components, including reactants are added together simultaneously or substantially simultaneously to a heated extruder and reacted to form the TPU polymer. The reaction temperature utilizing urethane catalyst are generally from about 175°C to about 245°C, and in some embodiments from about 180°C to about 220°C. The equivalent ratio of the diisocyanate to the total equivalents of the hydroxyl terminated intermediate and the diol chain extender is generally from about 0.95 to about 1.05, desirably from about 0.97 to about 1.03, or from about 0.98 to about 1.01.

[0052] Various additives can be added to the TPU as is known in the art, such as stabilizers, impact modifiers, and various process aids, which are described in greater detail below.

[0053] Suitable rigid TPU are available commercially as Isoplast^® available from Lubrizol Advanced Materials, Inc. of Cleveland, Ohio, U.S.A.

[0054] In some embodiments, the rigid TPU suitable for use in the invention have one or more of the following properties: (i) a Vicat softening point, as measured by ISO306/A50, of at least 140°C; (ii) a partial discharge, as measured by IEC 60664-1 , of greater than 1000 volts; (iii) a Shore D hardness of at least 70. In some embodiments, the rigid TPU has all of these properties. In some embodiments, the rigid TPU has a Shore D hardness of at least 75, 80, or 81 , or at least 82, 83 or 83.5.

[0055] In some embodiments, the rigid TPU of the invention includes a rigid aliphatic TPU composition prepared from: (a) one or more aliphatic polyisocyanates; and (b) one or more cyclic aliphatic diol chain extenders; and optionally (c) one or more cyclic aliphatic polyols. In some embodiments, the rigid TPU of the invention is substantially free of, or even completely free of, rigid aromatic TPU.

[0056] In some embodiments, the rigid TPU of the invention includes a rigid aromatic TPU composition prepared from: (a) one or more aromatic polyisocyanates; and (b) one or more cyclic aliphatic and/or aromatic diol chain extenders; and optionally (c) one or more cyclic aliphatic and/or aromatic polyols. In some embodiments, the rigid TPU of the invention is substantially free of, or even completely free of, rigid aliphatic TPU.

[0057] In any of these embodiments, the mole ratio of (a) isocyanate functional groups to (b) hydroxyl functional groups in the rigid TPU, expressed as the mole ratio (a):(b), is between 0.95 : 1 to 1.07: 1 , or from 0.95 : 1 to 1.10: 1 , or from 0.96: 1 to 1.02: 1 , or from 0.97: 1 to 1.005 : 1. These ratios may also be expressed as ranges, for example, a ratio of from 0.95 to 1.10 may also be expressed herein as a ratio of 0.95 : 1 to 1.10: 1.

[0058] In some embodiments, the rigid TPU of the invention is prepared from: (a) one or more aromatic polyisocyanates that includes methylene diphenyl diisocyanate; and (b) one or more cyclic aliphatic diol chain extenders that includes 1 ,4-cyclohexanedimethanol (CHDM). In some of these embodiments, the mole ratio of (a) isocyanate functional groups to (b) hydroxyl functional groups in the rigid TPU, expressed as the mole ratio (a):(b), is between 0.95 : 1 to 1.07: 1 , or from 0.95 : 1 to 1.10: 1 , or from 0.96: 1 to 1.02: 1 , or from 0.97: 1 to 1.005 : 1. These ratios may also be expressed as ranges, for example a ratio of from 0.95 to 1.10 may also be expressed herein as a ratio of 0.95 : 1 to 1.10: 1.

[0059] In some embodiments, the rigid TPU is made from materials that are substantially free of, or even completely free of, cyclic polyols (where the polyol is a separate optional component from the chain extender). In some embodiments, the rigid TPU is made from materials that are substantially free of, or even completely free of, any polyols (where the polyol is separate optional component from the chain extender).

[0060] In some embodiments, the weight ratio of (a), the one or more aromatic polyisocyanates, to (b), the one or more cyclic aliphatic and/or aromatic diol chain extenders, present in the reaction to produce the rigid TPU, expressed as the weight ratio (a):(b) is from 1 : 1.5 to 1 :2 or from 1 : 1.7 to 1 : 1.8 or even above 1 : 1.75.

[0061] Any of the rigid TPU described above may also include one or more additives. These additives may be present with the components that react to form the rigid TPU, or these additives may be added to the rigid TPU after it has been prepared. Suitable additives include pigments, UV stabilizers, UV absorbers, antioxidants, lubricity agents, heat stabilizers, hydrolysis stabilizers, cross-linking activators, flame retardants, layered silicates, fillers, colorants, reinforcing agents, adhesion mediators, impact strength modifiers, antimicrobials, and of course any combination thereof.

[0062] Suitable pigments include white pigments such as titanium dioxide or zinc oxide, as well as black pigments such as carbon black. In some embodiments, particularly with regard to the backsheets described below, the TPU includes at least one pigment. In some embodiments, particularly with regard to the encapsulants described below, the TPU is substantially free of, or even completely free of, any pigments.

[0063] Suitable impact strength modifiers include carbonyl modified polyolefins and acrylic impact modifiers, for example, PARALOID™ EXL materials commercially available from Dow®. When present the impact modifier may make up from 1 to 20 percent by weight of the TPU, or from 5 to 15, or from 5 to 10 percent by weight of the TPU.

[0064] In some embodiments, the rigid TPU of the invention may be blended with other materials, for example, with polyamides. In other embodiments, the rigid TPU of the invention is substantially free of, or even completely free of, polyamides. By substantially free of it is meant that the overall TPU composition, or even the backsheet made from the TPU, contains no more than 5 percent by weight polyamide materials, or even no more than 4, 3, 2, 1 , or 0.5 percent by weight polyamide materials.

[0065] In some embodiments, the rigid TPU of the invention is a rigid aromatic TPU that is a rigid TPU containing aromatic groups in the backbone of the TPU. In some embodiments, the rigid TPU of the invention is a rigid aliphatic TPU that is a rigid TPU that does not contain any aromatic groups in the backbone of the TPU. In some embodiments, the rigid TPU of the invention is a rigid cyclic aliphatic TPU that is a rigid TPU that does not contain any aromatic groups in the backbone of the TPU but which does contain cyclic non-aromatic groups in the backbone of the TPU.

The Non-Rigid Thermoplastic Polvurethane

[0066] In some embodiments of the invention, the encapsulant includes one or more non-rigid thermoplastic polyurethanes (TPU). Such non-rigid TPU are made by reacting a polyisocyanate with at least one diol chain extender, and one or more hydroxyl terminated polyether intermediates.

[0067] Suitable polyisocyanates for use in making the non-rigid TPU include any of those described above in the rigid TPU section. Suitable diol chain extenders suitable for making the non-rigid TPU include any of those described above in the rigid TPU section. Suitable hydroxyl terminated polyether intermediates include any of those described above in the rigid TPU section.

[0068] In some embodiments, the non-rigid TPU includes a TPU made from (i) a diisocyanates that includes 4,4 ^'-methyl enebis-(phenyl isocyanate) (MDI), m-xylene diisocyanate (XDI), dicyclohexylmethane-4,4^'-diisocyanate (H12MDI), or some combination thereof; (ii) a chain extender that includes ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1 ,4-butanediol, 1 ,6-hexanediol, 1 ,3- butanediol, 1 ,5-pentanediol, neopentylglycol, or some combination thereof; and (iii) a polyether polyols that includes poly( ethylene glycol) comprising ethylene oxide reacted with ethylene glycol, poly(propylene glycol) comprising propylene oxide reacted with propylene glycol, poly(tetramethylene glycol) comprising water reacted with tetrahydrofuran (PTMEG). In some embodiments, the encapsulant includes a non-rigid TPU made from (i) MDI, (ii) 1,4-butanediol, 1 ,6-hexanediol, or a combination thereof, and (iii) PTMEG. In some embodiments, the encapsulant includes a non-rigid TPU made from (i) H12MDI, (ii) 1 ,4-butanediol, 1 ,6- hexanediol, or a combination thereof, and (iii) PTMEG.

[0069] In some embodiments, the non-rigid thermoplastic polyurethane of the photovoltaic encapsulant has one or more of the following properties: (i) a haze value, as measured by ASTM D1003 of less than 0.5 percent, or less than 0.4, 0.35, 0.3 percent, or from 0.0 or 0.01 up to 0.3; (ii) a transmission value, as measured by ASTM D1003 of at least 80 percent, or at least 85, or even 90 percent, or from 85 to 95 or 85 to 90 percent; (iii) a yellowness index, as measured by ASTM D 1925 , or less than 1 ; and (iv) a refractive index, as measured by ASTM D542-95, from 1.4 to 1.6, or from 1.45 to 1.55 , or of about 1.5.

[0070] The non-rigid TPU may be made by the same methods and processes described for the rigid TPU above, and in some embodiments may include one or more additional additives and/or be blended with one or more other polymeric materials. Suitable additional additives include any of those described above. Suitable polymeric materials include any of those described above, especially those described as alternative encapsulant materials.

[0071] It is known that some of the materials described above may interact in the final formulation, so that the components of the final formulation may be different from those that are initially added. For instance, metal ions (of, e.g., a detergent) can migrate to other acidic or anionic sites of other molecules. The products formed thereby, including the products formed upon employing the composition of the present invention in its intended use, may not be susceptible of easy description. Nevertheless, all such modifications and reaction products are included within the scope of the present invention; the present invention encompasses the composition prepared by admixing the components described above.

Examples

[0072] The invention will be further illustrated by the following examples. While the Examples are provided to illustrate the invention, they are not intended to limit it. Example Set A

[0073] A set of backsheet examples is prepared by extruding a rigid thermoplastic polyurethane (TPU) composition into a form, resulting in a TPU backsheet for a photovoltaic module. The following table shows the TPU composition that is used in each sample backsheet. Table 1 - Backsheet Examples

Example Set B

[0074] A set of photovoltaic modules is prepared using the backsheet examples of Example Set A. The modules are assembled, by layering a transparent frontsheet (also referred to as a transparent superstrate), a front encapsulant layer (also referred to as the upper or first encapsulant layer), a photovoltaic metallization layer, a back encapsulant layer (also referred to as the lower or second encapsulant layer), and the specified backsheet. These modules are identified as Examples B-1 to B-12, with B-1 using the A-1 backsheet and B-2, B-3, B-4, B-5, B-6, B-7, B-8, B-9, B-10, B-l l , and B-12 using backsheets A-2, A-3, A-4, A-5, A-6, A-7, A-8, A- 9, A-10, A-l l , and A-12 respectively.

[0075] Another set of photovoltaic modules is prepared using the backsheet examples of Example Set A. The modules are assembled, by layering a transparent frontsheet (also referred to as a transparent superstrate), a front encapsulant layer (also referred to as the upper or first encapsulant layer), a photovoltaic metallization layer, a thin film substrate (also referred to as a polymeric mat), a back encapsulant layer (also referred to as the lower or second encapsulant layer), and the specified backsheet. These modules are identified as Examples B-101 to B- 1 12, with B-101 using the A-1 integrated encapsulant and backsheet and B-102 to B-1 12 each using the corresponding integrated encapsulant and backsheet from A-2 to A-12. Example Set C

[0076] A set of integrated encapsulant and backsheet examples is prepared by co-extruding an encapsulant with a backsheet material into a form, resulting in an integrated encapsulant and backsheet for a photovoltaic module. The following table shows the encapsulant and backsheet materials used for each example.

Table 2 - Integrated Backsheet Examples

Example Backsheet Description Encapsulant Description

C-l the A-l backsheet material Elvax® ethylene -vinyl acetate (EVA) resin

C-2 the A-2 backsheet material same as C-l's encapsulant

C-3 the A-7 backsheet material same as C-l's encapsulant

C-4 the A- 8 backsheet material same as C-l's encapsulant

C-5 the A-l backsheet material PV5200 polyvinyl butyral polymer sheet.

C-6 the A-2 backsheet material same as C-5's encapsulant

C-7 the A-7 backsheet material same as C-5's encapsulant

C-8 the A- 8 backsheet material same as C-5's encapsulant

C-9 An ethylene -vinyl acetate made via one shot polymerization (OSP)

copolymers (EVA) from dicyclohexylmethane-4,4 '-diiscynate

(H12MDI), 1,6-hexanediol (HDO), and poly(tetramethylene glycol) (PTMEG)

C-10 same as C-9's backsheet made via OSP from H12MDI, HDO,

ethylene glycol (EG), PTMEG

C-ll same as C-9's backsheet made via OSP from H12MDI, 1,4- butanediol (BDO), PTMEG

C-12 same as C-9's backsheet made via OSP from H12MDI, BDO, EG,

PTMEG

C-13 same as C-9's backsheet made via OSP from 4,4'-methylenebis- (phenyl isocyanate) (MDI), HDO, PTMEG

C-14 same as C-9's backsheet made via OSP from MDI, HDO, ethylene

glycol (EG), PTMEG

C-15 same as C-9's backsheet made via OSP from MDI, 1,4-butanediol

(BDO), PTMEG

C-16 same as C-9's backsheet made via OSP from MDI, BDO, EG,

PTMEG

C-17 Tedlar® polyvinyl fluoride (PVF) same as C-9's encapsulant

C-18 same as C-17's backsheet same as C-10's encapsulant

C-19 same as C-17's backsheet same as C-ll's encapsulant

C-20 same as C-17's backsheet same as C-12's encapsulant

C-21 same as C-17's backsheet same as C-13's encapsulant

C-22 same as C-17's backsheet same as C-14's encapsulant

C-23 same as C-17's backsheet same as C-15's encapsulant

C-24 same as C-17's backsheet same as C-16's encapsulant

C-25 same as C-l's backsheet same as C-9's encapsulant

C-26 same as C-2's backsheet same as C-9's encapsulant

C-27 same as C-3's backsheet same as C-9's encapsulant

C-28 same as C-4's backsheet same as C-9's encapsulant

C-29 same as C-l's backsheet same as C-10's encapsulant

C-30 same as C-2's backsheet same as C-10's encapsulant

C-31 same as C-3's backsheet same as C-10's encapsulant

C-32 same as C-4's backsheet same as C-10's encapsulant Example Set D

[0077] A set of photovoltaic modules is prepared using the integrated encapsulant and backsheet examples of Example Set C. The modules are assembled, by layering a transparent frontsheet (also referred to as a transparent superstrate), a front encapsulant layer (also referred to as the upper or first encapsulant layer), a photovoltaic metallization layer, and the specified integrated encapsulant and backsheet. These modules are identified as Examples D-l to D-32, with D-l using the C-l integrated encapsulant and backsheet and D-2 to D-32 each using the corresponding integrated encapsulant and backsheet from C-2 to C-32.

[0078] Another set of photovoltaic modules is prepared using the backsheet examples of Example Set C. The modules are assembled, by layering a transparent frontsheet (also referred to as a transparent superstrate), a front encapsulant layer (also referred to as the upper or first encapsulant layer), a photovoltaic metallization layer, a thin film substrate (also referred to as a polymeric mat), and the specified integrated encapsulant and backsheet. These modules are identified as Examples D-l 01 to D-132, with D-101 using the C-l integrated encapsulant and backsheet and D-102 to D-132 each using the corresponding integrated encapsulant and backsheet from C-2 to C-32.

[0079] Each of the documents referred to above is incorporated herein by reference. Except in the Examples, or where otherwise explicitly indicated, all numerical quantities in this description specifying amounts of materials, reaction conditions, molecular weights, number of carbon atoms, and the like, are to be understood as modified by the word "about." Except where otherwise indicated, all numerical quantities in the description specifying amounts or ratios of materials are on a weight basis. Unless otherwise indicated, each chemical or composition referred to herein should be interpreted as being a commercial grade material which may contain the isomers, byproducts, derivatives, and other such materials which are normally understood to be present in the commercial grade. However, the amount of each chemical component is presented exclusive of any solvent or diluent oil, which may be customarily present in the commercial material, unless otherwise indicated. It is to be understood that the upper and lower amount, range, and ratio limits set forth herein may be independently combined. Similarly, the ranges and amounts for each element of the invention can be used together with ranges or amounts for any of the other elements. As used herein, the expression "consisting essentially of permits the inclusion of substances that do not materially affect the basic and novel characteristics of the composition under consideration.

Claims

What is claimed is:

1. A photovoltaic module backsheet produced from at least one rigid thermoplastic polyurethane made by reacting at least one polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates.

2. The photovoltaic module backsheet of claim 1 wherein the rigid thermoplastic polyurethane has one or more of the following properties: (i) a Vicat softening point, as measured by ISO306/A50, of at least 140°C; (ii) a partial discharge, as measured by IEC 60664-1, of greater than 1000 volts; (iii) a Shore D hardness of at least 70.

3. The photovoltaic module backsheet of any preceding claim wherein the rigid thermoplastic polyurethane comprises a rigid aliphatic thermoplastic polyurethane composition prepared from: (a) one or more aliphatic polyisocyanates; and (b) one or more cyclic aliphatic diol chain extenders; and optionally (c) one or more cyclic aliphatic polyols.

4. The photovoltaic module backsheet of claims 1 or 2 wherein the rigid thermoplastic polyurethane comprises a rigid aromatic thermoplastic polyurethane composition prepared from: (a) one or more aromatic polyisocyanates; and (b) one or more cyclic aliphatic and/or aromatic diol chain extenders; and optionally (c) one or more cyclic aliphatic and/or aromatic polyols.

5. The photovoltaic module backsheet of any preceding claim wherein the mole ratio of isocyanate functional groups to hydroxyl functional groups in the rigid thermoplastic polyurethane is between 0.95 to 1.07.

6. The photovoltaic module backsheet of claims 1 , 2, or 4 wherein the rigid thermoplastic polyurethane is prepared from: (a) one or more aromatic polyisocyanates comprising methylene diphenyl diisocyanate; and (b) one or more cyclic diol chain extenders having aliphatic hydroxyl groups comprising 1 ,4- cyclohexanedimethanol (CHDM), 2,2-bis[4-(2-hydroxyethoxy)phenyl]propane (HEPP) and hydroxyethyl resorcinol (HER), or some combination thereof.

7. The photovoltaic module backsheet of any preceding claim wherein the rigid thermoplastic polyurethane contains at least one additive, selected from the group consisting of white pigments, black pigments, UV stabilizers, UV absorbers, antioxidants, lubricity agents, heat stabilizers, hydrolysis stabilizers, cross-linking activators, flame retardants, layered silicates, fillers, colorants, reinforcing agents, adhesion mediators, impact strength modifiers, and antimicrobials.

8. The photovoltaic module backsheet of any preceding claim wherein the rigid thermoplastic polyurethane contains a white pigment comprising titanium dioxide or zinc oxide, or a black pigment comprising carbon black.

9. An integrated photovoltaic module backsheet and photovoltaic encapsulant, wherein a photovoltaic encapsulant layer is present on the forward-facing surface of the backsheet;

wherein (i) the backsheet is produced from at least one rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates; or (ii) the photovoltaic encapsulant comprises at least one non-rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and one or more hydroxyl terminated polyether intermediates; or (iii) both (i) and (ii).

10. The integrated photovoltaic module backsheet and photovoltaic encapsulant of claim 9 wherein the backsheet is produced from at least one rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates.

1 1. The integrated photovoltaic module backsheet and photovoltaic encapsulant of claim 10 wherein the thermoplastic polyurethane has one or more of the following properties: (i) a Vicat softening point, as measured by ISO306/A50, of at least 140°C; (ii) a partial discharge, as measured by IEC 60664-1 , of greater than 1000 volts; (iii) a Shore D hardness of at least 70.

12. The integrated photovoltaic module backsheet and photovoltaic encapsulant of claim 9 wherein the photovoltaic encapsulant comprises at least one non-rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and one or more hydroxyl terminated polyether intermediates.

13. The integrated photovoltaic module backsheet and photovoltaic encapsulant of claim 9 wherein the non-rigid thermoplastic polyurethane of the photovoltaic encapsulant has one or more of the following properties: (i) a haze value, as measured by ASTM D1003 of less than 0.5 percent, (ii) a transmission value, as measured by ASTM D1003 of at least 80 percent, (iii) a yellowness index, as measured by ASTM D1925, or less than 1 , and (iv) a refractive index, as measured by ASTM D542-95, from 1.4 to 1.6.

14. The integrated photovoltaic module backsheet and photovoltaic encapsulant of claim 12 wherein the backsheet is produced from one or more: ethylene-vinyl acetate copolymers (EVA), thermoplastic elastomers (TPE), thermoplastic polyurethanes (TPU), polyvinyl fluoride polymers (PVF), polyvinylidene fluoride polymers (PVDF), polyethylene terephthalate polymers (PET), ethylene propylene diene monomer-based polymers (EPDM), epoxy resins with dicyandiamide curing agents, polyimides, polyesters, hybrid epoxy polyesters, cyanate esters, acrylics, or combinations thereof.

15. A photovoltaic module comprising a backsheet produced from at least one rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates.

16. The photovoltaic module of claim 14 comprising:

(a) said backsheet,

(b) an adhesive layer and/or backside pottant layer and/or first encapsulant layer,

(c) a least one solar cell,

(d) a transparent pottant layer and/or an adhesive layer and/or second encapsulant layer; and

(e) a transparent superstrate layer;

forming a photovoltaic module.

17. A photovoltaic module comprising an integrated photovoltaic module backsheet and photovoltaic encapsulant, wherein a photovoltaic encapsulant layer is present on the forward-facing surface of the backsheet; and

18. The photovoltaic module comprising an integrated photovoltaic module backsheet and photovoltaic encapsulant of claim 14 comprising:

(a) said integrated photovoltaic module backsheet and photovoltaic encapsulant,

(b) a least one solar cell,

(c) a second encapsulant layer; and

(d) a transparent superstrate layer; forming a photovoltaic module.

19. A method for producing a photovoltaic module backsheet produced from at least one at least one rigid thermoplastic polyurethane made by reacting a polyisocyanate with at least one diol chain extender, and optionally one or more hydroxyl terminated intermediates wherein the method includes the step of:

(i) extruding the rigid thermoplastic polyurethane to form the backsheet.

20. A method for producing an integrated photovoltaic module backsheet and photovoltaic encapsulant, wherein a photovoltaic encapsulant layer is present on the forward-facing surface of the backsheet; and

wherein the method includes the steps of (i) laminating the photovoltaic encapsulant layer onto the forward-facing surface of the backsheet, or (ii) co- extruding the backsheet and photovoltaic encapsulant resulting in an integrated photovoltaic module backsheet and photovoltaic encapsulant with photovoltaic encapsulant layer present on the forward-facing surface of the backsheet; and