NL2008838C2

NL2008838C2 - Polymer sheet.

Info

Publication number: NL2008838C2
Application number: NL2008838A
Authority: NL
Inventors: Johan Willy Declerck; Koen Hasaers; Kristof Proost
Original assignee: Novopolymers N V
Priority date: 2012-05-16
Filing date: 2012-05-16
Publication date: 2013-11-20

Description

POLYMER SHEET

The invention relates to a polymer sheet comprising a luminescence downshifting compound. Such compounds have the property that it can at least 5 partially absorb radiation having a certain wavelength and re-emit radiation at a longer wavelength than the wavelength of the absorbed radiation.

Such a polymer sheet is known from WO-A-2008/110567. This publication describes a polymer encapsulation sheet which is used to protect a photovoltaic cell and wherein the polymer encapsulation sheet comprises a luminescence 10 downshifting compound. This publication does not disclose any working examples. The specification does disclose a large list of possible luminescence downshifting compounds of which many are organic compounds.

Many organic compounds have favourable properties regarding their efficiency to absorb radiation in a certain wavelength and re-emit radiation at a higher 15 wavelength. A problem of applying such compounds is their stability. When a sheet comprising such organic compound is used in combination with a photovoltaic cell in a solar cell it is preferred that they remain stable during the life time of the solar cell.

The object of the present invention is to provide a polymer sheet comprising a luminescence downshifting compound, wherein the luminescence downshifting 20 compound retains its downshifting capability over a longer period of time.

This object is achieved by the following polymer sheet. Polymer sheet comprising multiple coextruded polymer layers, wherein at least one of these layers comprise a luminescence downshifting compound for at least partially absorbing radiation having a certain wavelength and re-emitting radiation at a longer 25 wavelength than the wavelength of the absorbed radiation.

Applicants found that by having separate polymer layers the stability of the luminescence downshifting compound as present in at least one layer can be improved.

The polymer sheet may have a first polymer layer comprising an UV 30 stabilizer additive and another polymer layer comprises the luminescence downshifting compound. In this manner the luminescence downshifting compound may be protected against UV radiation and UV induced degradation.

2

Preferably two or more layers of the polymer sheet comprise a luminescence downshifting compound. This allows that a layer comprising of luminescence downshifting compound or compounds which are less stable when exposed to radiation of a certain wavelength can be used in combination with a layer 5 comprising a luminescence downshifting compound which can convert by means of a Stoke shift the harmful radiation to a less harmful radiation. The above layout results in a more stable polymer sheet.

The invention further provides that UV sensible polymers, like for example ethylene vinyl acetate (EVA) can be used in combination with no or considerably less 10 UV stabilizer. In the prior art UV stabilizers are required to protect the polymer encapsulant sheet comprising EVA. The use of these stabilisers lowered the efficiency of a solar panel because the UV radiation is converted to heat by these UV stabilisers. By using a luminescent downshifting compound which can absorb radiation in the UV wavelength range and emit at a higher wavelength range the UV 15 light is converted into radiation which is less harmful for the polymer and which can be effectively used to generate electricity by means of the photovoltaic effect.

Unless stated otherwise, all percentages, parts, ratios, etc., are by weight. When an amount, concentration, or other value or parameter is given as either a range, preferred range or a list of upper preferable values and lower preferable 20 values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not 25 intended that the scope of the invention be limited to the specific values recited when defining a range.

When the term "about" is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end- point referred to.

30 As used herein, the terms "comprises," "comprising," "includes," "including," "containing," "characterized by," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such 3 process, method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive or and not to an exclusive or. The transitional phrase "consisting essentially of limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s) 5 of the claimed invention.

Where applicants have defined an invention or a portion thereof with an open-ended term such as "comprising," it should be readily understood that unless otherwise stated the description should be interpreted to also describe such an invention using the term "consisting essentially of.

10 Use of "a" or "an" are employed to describe elements and components of the invention. This is merely for convenience and to give a general sense of the invention. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

In describing certain polymers it should be understood that sometimes 15 applicants are referring to the polymers by the monomers used to produce them or the amounts of the monomers used to produce the polymers. While such a description may not include the specific nomenclature used to describe the final polymer or may not contain product-by-process terminology, any such reference to monomers and amounts should be interpreted to mean that the polymer comprises 20 those monomers (i.e. copolymerized units of those monomers) or that amount of the monomers, and the corresponding polymers and compositions thereof.

In describing and/or claiming this invention, the term "copolymer" is used to refer to polymers formed by copolymerization of two or more monomers. Such copolymers include dipolymers, terpolymers or higher order copolymers.

25 The “melt flow index”, further referred to as MFI herein, is a measure of the ease of flow of the melt of a thermoplastic polymer. It is defined as the mass of polymer, in grams, flowing in ten minutes through a capillary of a specific diameter and length by a pressure applied via prescribed alternative gravimetric weights for alternative prescribed temperatures, and is determined according to ASTM D1238. 30 It should be noted that where a polymer is formulated with a crosslinking mechanism that is initiated above a certain temperature, e.g. EVA copolyerms and peroxides, the rheology values employed herein refer to materials that are not, or only partially crosslinked. Once the crosllonking has been complete, e.g. in a photovoltaic module lamination process, the polymers that have crosslinked are no 4 longer considered as thermoplastic materials. Therefore, in so far as the specification refers to photovoltaic modules after lamination, the described properties refer to the polymers prior to the lamination process, also including the crosslinked polymers.

The term melting point as referred to herein refers to the transition from a 5 crystalline or semi-crystalline phase to a solid amorphous phase, also known as the crystalline melting temperature. The melting point of a polymer may be advantageously be determined by DSC. In the case of a block co-polymer, the term melting point herein refers to the temperature at which the higher melting block component will pass its glass transition temperature, thereby allowing the polymer to 10 melt and flow. The “extrusion temperature” refers to the temperature to which a polymer material is heated during extruded, by means of a heated extruder and/or heated die.

Where to the melting temperature of a certain layer is referred, due to the fact that the layers are essentially composed of polymer materials with additives or 15 optional other polymers only, this temperature will be largely determined by the melting temperature of the polymer material present in the layer. Accordingly, the melting temperature should be considered as the temperature of the polymer material present in the layer. The additives and/or optional polymers may be present in an amount of up to 25 wt%, based on the total weight of the main polymer in a 20 layer, provided that the inclusion of such additives and/or optional polymers does not adversely affect the melt flow index.

Preferably a luminescence downshifting compound is present in a first polymer layer, which luminescence downshifting compound has the property that it can absorb more radiation at a lower wavelength that the luminescence downshifting 25 compound present in a next layer. Thus the barrier layer will comprise luminescence downshifting compound or compounds which will absorb radiation at a lower wavelength than the luminescence downshifting compound(s) in the remaining polymer layer(s). This is advantageous because many organic compounds are sensitive to especially the shorter wavelength radiation. By filtering said shorter 30 wavelength radiation and re-emitting longer wavelength radiation a more stable polymer sheet is obtained. More preferably a first polymer layer, i.e. barrier layer, has the property that it can absorb at least partially UV radiation, suitably between 10 and 400 nm, and re-emit radiation at a higher wavelength. The luminescence downshifting compound(s) which absorb in this UV wavelength may be combined 5 with traditional UV stabilizers. It is preferred to limit the use of such classic stabilizers because they transform the absorbed UV radiation into thermal energy rather than re-emitting the radiation at the longer wavelengths. Thus a more efficient polymer sheet is obtained when such UV stabilizers are omitted or used in a low 5 concentration. The luminescence downshifting compound will then take over the protective function of the UV stabilizer.

The luminescence downshifting compound may be an organic or inorganic luminescent compound, which are capable of partially absorbing radiation having a certain wavelength and re-emitting radiation at a longer wavelength than the 10 wavelength of the absorbed radiation. Such compounds are known and for example described by Efthymios Klampaftis, David Ross, Keith R. McIntosh, Bryce S. Richards, Enhancing the performance of a solar cell via luminescent down-shifting of incident spectrum, a review, Solar Energy Materials & Solar Cells 93 (2009) 1182-1194. At least some of the luminescence downshifting compounds are preferably 15 organic compounds because the advantages of the invention apply especially to this group of compounds.

Suitable organic luminescence downshifting compound are for example laser dyes. The following compounds, of which some are also used as a laser dye, may find application as an organic luminescence downshifting compound: Rhodamine, for 20 example 5-carboxytetramethylrhodamine, Rhodamine 6G, Rhodamine B, Rubrene, aluminium tris-([delta]-hydroxyquinoline (Alq3), N,N'-diphenyl-N,N'-bis-(3-methylphenyl)-1 ,1 '-biphenyl-4-4'-diamine (TPD), bis-(8-hydroxyquinoline)-chlorogallium (Gaq2CI); a perylene carbonic acid or a derivative thereof; a naphthalene carbonic acid or a derivative thereof; a violanthrone or an iso-25 violanthrone or a derivative thereof. Examples of organic luminescence downshifting compound are Quinine, Fluorescien, sulforhodamine, ,5-Bis(5-tert-butyl-2-enzoxazolyl)thiophene, Nile Blue.

Other examples of suitable organic luminescence downshifting compounds are Coumarin dyes, for example 7-Diethylaminocoumarin-3-carboxylic acid hydrazide 30 (DCCH), 7-Diethylaminocoumarin-3-carboxylic acid succinimidyl ester, 7-

Methoxycoumarin-3-carboxylic acid succinimidyl ester, 7-Hydroxycoumarin-3-carboxylic acid succinimidyl ester, 7-Diethylamino-3-((((2-iodoacetamido)ethyl)amino)carbonyl)coumarin (IDCC), 7-Diethylamino-3-((((2-maleimidyl)ethyl)amino)carbonyl)coumarin (MDCC), 7-Dimethylamino-4- 6 methylcoumarin-3-isothiocyanate (DACITC), N-(7-Dimethylamino-4-methylcoumarin- 3-yl)maleimide (DACM), N-(7-Dimethylamino-4-methylcoumarin-3-yl)iodoacetamide (DACIA), 7-Diethylamino-3-(4'-maleimidylphenyl)-4-methylcoumarin (CPM), 7-Diethylamino-3-((4'-(iodoacetyl)amino)phenyl)-4-methylcoumarin (DCIA), 7-5 Dimethylaminocoumarin-4-acetic acid (DMACA) and 7-Dimethylaminocoumarin-4-acetic acid succinimidyl ester (DMACASE).

Other examples of suitable organic luminescence downshifting compounds are perylene dyes, for example N, N'- Bis(2,6-diisopropylphenyl)perylene-3,4:9,10-tetracarbonic acid diimide, N,N'-Bis(2,6- dimethylphenyl)perylene-3,4:9,10-10 tetracarbonic acid diimide, N,N'-Bis(7- tridecyl)perylene-3,4:9,10-tetracarbonic acid diimide, N,N'-Bis(2,6-diisopropylphenyl)- 1,6,7,12-tetra(4-tert.-octylphenoxy)perylene-3,4:9,10-tetracarbonic acid diimide, N, N'- Bis(2,6-diisopropylphenyl)-1,6,7,12-tetraphenoxyperylene-3,4:9,10-tetracarbonic acid diimide, N,N'-Bis(2,6-diisopropylphenyl)-1,6- and -1,7-bis(4-tert- octylphenoxy)perylene-3,4:9,10-15 tetracarbonic acid diimide, N,N'-Bis(2,6- diisopropylphenyl)-1,6- and -1,7-bis(2,6-diisopropylphenoxy)-perylene-3,4:9,10- tetracarbonic acid diimide, N-(2,6-diisopropylphenyl)perylene-3,4-dicarbonic acid imide, N-(2,6-diisopropylphenyl)-9-phenoxyperylene-3,4-dicarbon acid imide, N-(2,6- diisopropylphenyl)-9-(2,6-diisopropylphenoxy)perylene-3,4-dicarbonic acid imide, N- (2,6-diisopropylphenyl)-9-20 cyanoperylene-3,4-dicarbonic acid imide, N-(7-tridecyl)-9- phen-oxyperylene-3,4-dicarbonic acid imide, perylene-3,9- and -3,10-dicarbonic acid diisobutyl-ester, 4,10-dicyanoperylene-3,9- and 4,9-dicyanoperylene-3,10-dicarbonic acid diisobutyl-ester and perylene-3,9- and -3,10-dicarbonic acid di(2,6- diisopropylphenyl)amide.

Perylene dyes usually absorb radiation in the wavelength region of 360 to 630 25 nm and re-emit between 470 to 750 nm. Besides perylene dyes, other fluorescent dyes having similar structures may be employed, such as dyes on the basis of violanthrones and/or iso-violanthrones, such as the structures disclosed in EP-A-073 007. As a preferred example of well suited compounds are alkoxylated violanthrones and/or iso-violanthrones, such as 6,15-didodecyloxyisoviolanthronedion-(9,18).

30 Other examples of suitable organic luminescence downshifting compounds are naphthalene type compounds. These dyes typically exhibit an absorption within the UV range at wavelengths of about 300 to 420 nm and exhibit an emission range at about 380 to 520 nm. Examples of naphthalene type compounds are the naphthalene carbonic acid derivatives, for example naphthalene 1,8:4,5-tetracarbonic 7 acid diimides, and especially naphthalene-1,8-dicarbonic acid imides, most preferably 4,5-dialkoxynaphthalene-1,8-dicarbonic acid monoimides and 4-phenoxynaphthalene-1,8-dicarbonic acid monoimides. Other naphthalene type compounds are for example 5 N-(2-ethylhexyl)-4,5-dimethoxynaphthalene-1,8-dicarbonic acid imide, N- (2,6-diisopropyl-phenyl)-4,5-dimethoxynaphthalene-1,8-dicarbonic acid imide, N-(7- tridecyl)-4,5-dimethoxy-naphthalene-1,8 dicarbonic acid imide, N-(2,6- diisopropylphenyl)-4,5-diphenoxynaphthalene-1,8-dicarbonic acid imide and N, N'- Bis(2,6-diisopropylphenyl)-1,8:4,5-naphthalene tetracarbonic acid diimide.

10 Other examples are Lumogen F Yellow 083, Lumogen F Orange 240, Lumogen F Red 300 and Lumogen F Violet 570 as obtainable from BASF.

For example the following organic luminescence downshifting compounds are capable of absorbing (excitation wavelength) at 300 to 360 nm and have an emission spectrum with a maximum around 365 up to 400 Nm: diphenyloxazole (2,5-15 diphenyloxazol 1,4-Di[2-(5-phenyloxazolyl)benzene, 4,4'-diphenylstilbene, 3,5,3"",5""-tetra-t-butyl-p-quinquephenyl. These compounds can be obtained for example from Synthon Chemicals GmbH and Luminescence Technology Corp.

For example the following organic luminescence downshifting compounds are capable of re-emitting the incoming radiation emission towards 400 - 460 Nm: 2,5-20 thiopenediylbis(5-tert-butyl-1,3-benzoxale).

For example the following organic luminescence downshifting compounds are capable of re-emitting the incoming radiation emission towards 560nm: hostasole 3G naphtalimide (Clariant), Lumogen F Yellow 083 (BASF), Rhodamine 110 (Lambdachrome 5700).

25 For example the following organic luminescence downshifting compounds are capable of re-emitting the incoming radiation emission towards 580-640nm: hostazole GG thioxanthene benzanthione (Clariant), - Lumogen F Red 300 (BASF), benzoic rhodamine 6G ethylaminoxanthene (Lambdachrome 5900),

For example the following organic luminescence downshifting compounds are 30 capable of re-emitting the incoming radiation emission towards 640-680nm: cretsyl purple diaminobenzole, Sublforhodamine B (Lambdachrome LC6200),

For example the following organic luminescence downshifting compounds are capable of re-emitting the incoming radiation emission towards 700-1 OOOnm: 8

Rhodamine 800 (Sigma), Pyridine 2 (Lambdachrome LC7600), DOTC, HITC (Lambdachrome LC7880), Styril 9 (Lambdachrome LC8400).

Suitable inorganic luminescent compounds are semiconducting quantum dot materials and nanoparticles comprising Sm3+, Cr3+, ZnSe, Eu2+ and Tb3+ and 5 nanoparticles comprising ZnO; ZnS doped with Mg, Cu, and/or F; CdSe; CdS; Ti02; Zr3+, Zi“4+; and/or Eu3+, Sm3+, or Tb3+ doped YPO4. A common characteristic of these materials is that they are capable of exhibiting fluorescence. The nanoscale particles may be made by any suitable process, for example by the process as disclosed in US7384680. They may have an average diameter of less than 75 nm, 10 more in particular they may have a size of between 3 and 50 nm as determined using Transmission electron microscopy (TEM). Possible Europium complexes suitable as luminescent compounds are [Eu((3-diketonate)3-(DPEPO)] as described by Omar Moudam etal, Chem. Commun., 2009, 6649-6651 by the Royal Society of Chemistry 2009.

15 Another example of a suitable inorganic luminescent compound are moleculair sives comprising oligo atomic metal clusters include clusters ranging from 1 to 100 atoms of the following metals (sub nanometer size), Si, Cu, Ag, Au, Ni, Pd, Pt, Rh,

Co and Ir or alloys thereof such as Ag/Cu, Au/Ni etc. The moluculair sieves are selected from the group consisting of zeolites, porous oxides, 20 silicoaluminophosphates, aluminophosphates, gallophosphates, zincophophates, titanosilicates and aluminosilicates, or mixtures thereof. In a particular embodiment of present invention the molecular sieves of present invention are selected from among large pore zeolites from the group consisting of MCM-22, ferrierite, faujastites X and Y. The molecular sieves in another embodiment of present invention are materials 25 selected from the group consisting of zeolite 3 A, Zeolite 13X, Zeolite 4A, Zeolite 5 A and ZKF. Preferably the oligo atomic metal clusters are oligo atomic silver molecules containing 1 to 100 atoms. Illustrative examples of such molecular sieve based downshifting compounds are described in WO-A-2009006708, which publication is hereby incorporated by reference.

30 The concentration of the luminescence downshifting compound in the polymer layer will depend on the chosen luminescence downshifting compound. Some compounds are more effective and will require a lower concentration in the polymer 9 layer and some compounds will require a higher concentration because they are less efficient in absorbing and re-emitting radiation.

The polymer layer may comprise at least one luminescence downshifting compound. The polymer layer may comprise a single luminescence downshifting 5 compound or more than one luminescence downshifting compound. If more than one luminescence downshifting compounds are present it is preferred that compounds are combined which absorb radiation at a different wavelength and re-emit radiation at a different longer wavelength. In this manner a so-called luminescence downshifting "cascade" may be obtained, wherein radiation re-emitted by one 10 compound is absorbed by a next compound. Such a cascade is also referred to as a Photon-Absorption-Emitting Chain (PAEC).

More preferably the polymer sheet comprises the following coextruded polymer layers: a first polymer layer (a) comprises a luminescence downshifting compound for 15 absorbing radiation at between 280 to 400 nm and re-emitting radiation at between 400 to 550 nm, another polymer layer (b) comprises a luminescence downshifting compound for absorbing radiation at between 360 to 470 nm and re-emitting radiation at between 410 to 670 nm, and 20 another polymer layer (c) comprises a luminescence downshifting compound for absorbing radiation at between 360 to 570 nm and re-emitting radiation at between 410 to 750 nm.

One or more luminescence downshifting compounds may be present in one of the above layers. Additional layers may be present in the polymer sheet, wherein the 25 additional layers may also comprise luminescence downshifting compounds or other additives.

Examples of suitable luminescence downshifting compounds for layer (a) are 2,5- diphenyloxazol (PPO diphenyloxazole), 4,4'-Diphenylstilbene (DPS), 1,4-Di[2-(5-phenyloxazolyl)benzene (POPOP), 3,5,3"",5""-Tetra-t-butyl-p-quinquephenyl (QUI P-30 quinqaphenyl), 1,8-ANS (1-Anilinonaphthalene-8-sulfonic acid), 1-

Anilinonaphthalene-8-sulfonic acid (1,8-ANS), 6,8-Difluoro-7-hydroxy-4-methylcoumarin pH 9.0, 7-Amino-4-methylcoumarin pH 7.0, 7-Hydroxy-4-methylcoumarin, 7-Hydroxy-4-methylcoumarin pH 9.0, Alexa 350, BFP (Blue Fluorescent Protein), Cascade Yellow, Cascade Yellow antibody conjugate pH 8.0, 10

Coumarin, Dansyl Cadaverine, Dansyl Cadaverine, MeOH, DAPI, DAPI-DNA, Dapoxyl (2-aminoethyl) sulphonamide, DyLight 350, Fura-2 Ca2+, Fura-2, high Ca, Fura-2, no Ca, Hoechst 33258, Hoechst 33258-DNA, Hoechst 33342, lndo-1, Ca free, LysoSensor Yellow pH 3.0, LysoSensor Yellow pH 9.0, Marina Blue, Sapphire, 5 and/or SBFI-Na+ .

Examples of suitable luminescence downshifting compounds for layer (b) are: 7-Diethylaminocoumarin-3-carboxylic acid hydrazide (DCCH), 7-Diethylaminocoumarin-3-carboxylic acid succinimidyl ester, 7-Methoxycoumarin-3-carboxylic acid succinimidyl ester, 7-Hydroxycoumarin-3-carboxylic acid succinimidyl 10 ester, 7-Diethylamino-3-((((2-iodoacetamido)ethyl)amino)carbonyl)coumarin (IDCC), 7-Diethylamino-3-((((2-maleimidyl)ethyl)amino)carbonyl)coumarin (MDCC), 7-Dimethylamino-4-methylcoumarin-3-isothiocyanate (DACITC), N-(7-Dimethylamino- 4-methylcoumarin-3-yl)maleimide (DACM), N-(7-Dimethylamino-4-methylcoumarin-3-yl)iodoacetamide (DACIA), 7-Diethylamino-3-(4'-maleimidylphenyl)-4-15 methylcoumarin (CPM), 7-Diethylamino-3-((4'-(iodoacetyl)amino)phenyl)-4-methylcoumarin (DCIA), 7-Dimethylaminocoumarin-4-acetic acid (DMACA), 7-Dimethylaminocoumarin-4-acetic acid succinimidyl ester (DMACASE), Acridine Orange, Alexa 430, Alexa Fluor 430 antibody conjugate pH 7.2, Auramine O, Di-8 ANEPPS, Di-8-ANEPPS-lipid, FM 1^3, FM 1-43 lipid, Fura Red Ca2+, Fura Red, 20 high Ca, Fura Red, low Ca, Lucifer Yellow and/or CH, SYPRO Ruby (CAS 260546-55-2).

Examples of suitable luminescence downshifting compounds for layer (c) are the above compounds illustrated for layer (b) and rhodamine 110, Rhodamine 6G ethylaminoxanthene benzoique (obtainable from Lambdachrome), Alexa Fluor 647 25 R-phycoerythrin streptavidin pH 7.2, Ethidium Bromide, Ethidium homodimer,

Ethidium homodimer-1-DNA, FM 4-64, FM 4-64, 2% CHAPS, Nile Red-lipid and/or Propidium Iodide.

An example of another possible cascade may comprise a first luminescence downshifting compound with an absorption range located at approximately 280 nm 30 tot 365 nm and with an emission range located at approximately 380 nm to 430 nm. An example of a suitable luminescence downshifting compound is 3,5,3"",5""-tetra-t-butyl-p-quinquephenyl, known to have a maximum absorption at approximately 310 nm and a maximum emission at approximately 390 nm. This luminescence downshifting compound may be added at a concentration of for example around 33% 11 of the total content of luminescence downshifting compounds in the polymer layer. A second luminescence downshifting compound with an absorption range located at approximately 335 to 450 nm and with an emission range located at approximately 410 up to 550 nm. An example of a suitable luminescence downshifting compound is 5 2,3,5,6-1 H,4H- tetrahydroquinolizino-[9,9a, 1 -gh]-coumarin, with a maximum excitation wavelength at approximately 396 nm and a maximum emission wavelength at approximately 490 nm in a concentration of for example around 33% of the total content of luminescence downshifting compounds in the polymer layer. A third luminescence downshifting compound of the cascade may have an absorption range 10 located at approximately 450 nm tot 550 nm and with an emission range located at 560 nm till 700 nm. An example of a suitable luminescence downshifting compound is 1-amino-2-methylantraquinone with a maximum absorption around 450 nm and a maximum emission at approximately 600 nm in a concentration of for example around 33% of the total content of luminescence downshifting compounds in the 15 polymer layer.

The total concentration of the down conversion blend in the polymer matrix depends on the thickness of the film as the efficient down conversion is function of the amount of molecules the incident light will encounter per volume. A polymer layer of approximately 400 to 450 microns may for example be doped with the constituting 20 luminescence downshifting compounds in the range of 200 up to 1000 ppm. A suitable polymer layer of 450 microns with a good balance of UV blocking and transmission was for example obtained at a concentration of the constituting luminescence downshifting compounds of approximately 500 ppm in the final polymer layer.

25 The polymer material of the different polymer layers of the polymer sheet may be ethylene vinyl acetate (EVA), polyvinylbutyral (PVB), polymethylmethacrylate(PMMA), alkylmethacrylate, alkylacrylate copolymers, such as for example polymethacrylate poly-n-butylacrylate (PMMA-PnBA), elastomers, e.g. SEBS, SEPS, SIPS, polyurethanes, functionalized polyolefines, lonomers, 30 thermoplast polydimethylsiloxane copolymers, or mixtures thereof. Preferably ethylene vinyl acetate (EVA), polyvinylbutyral (PVB), silicone, polymethylmethacrylate(PMMA), alkylacrylate copolymers, such as for example polymethacrylate poly-n-butylacrylate (PMMA-PnBA) are used. Preferably, at least one of the polymer layers is composed of an ethylene vinyl acetate polymer. These 12 polymers are advantageous because they provide a suitable matrix for the luminescence downshifting compound or compounds. Furthermore the resulting sheet can be easily used in a thermal lamination process to make an end product comprising the polymer sheet. Other possible polymers are polymethylmethacrylate 5 (PMMA), polyvinylbutyral (PVB), polyvinylidene fluoride (PVDF), polycarbonate (PC), polyurethane, silicone or mixtures thereof.

Preferably the polymer is an ethylene/vinyl acetate copolymer (EVA) comprising copolymerized units of ethylene and vinyl acetate. The EVA may have a melt flow rate (MFR) in the range of from 0.1 to 1000 g/10 minutes, preferably of from 10 0.3 to 300 g/10 minutes, yet more preferably of from 0.5 to 50 g/10 minutes, as determined in accordance with ASTM D1238 at 190°C and 2.16 kg.

Preferably the ethylene vinyl acetate has an acetate content of between 12 and 45 wt%, more preferably between 20 and 40 wt% and even more preferably between 25% up to 40 wt%.

15 The EVA may be a single EVA or a mixture of two or more different EVA

polymers. By different EVA polymers is meant that the copolymers having different comonomer ratios, and/or the weight average molecular weight and/or molecular weight distribution may differ. Accordingly the EVA polymer may also comprise polymers that have the same comonomer ratios, but different MFR due to having 20 different molecular weight distribution.

In a preferred embodiment, the EVA polymers advantageously comprise further monomers other than ethylene and vinyl acetate, such as alkyl acrylates, whereby the alkyl moiety of the alkyl acrylate may contain 1 -6 or 1 -4 carbon atoms, and may be selected from methyl groups, ethyl groups, and branched or unbranched 25 propyl, butyl, pentyl, and hexyl groups.

The EVA copolymers used herein may also contain other additives known within the art. The additives may include processing aids, flow enhancing additives, lubricants, dyes, flame retardants, impact modifiers, nucleating agents, anti-blocking agents such as silica, thermal stabilizers, dispersants, surfactants, chelating agents, 30 coupling agents, reinforcement additives, such as glass fiber, fillers and the like.

The polymer layers comprising of ethylene-vinyl acetate copolymer preferably comprise of one or more organic peroxides, which enables to crosslink the ethylene-vinyl acetate copolymer, thereby increasing the adhesion strength, humidity resistance and penetration resistance, while maintaining a high transparency, if so 13 desired. Any organic peroxides that are decomposed at a temperature of at least 110°C to generate radicals may advantageously be employed as the above-mentioned organic peroxide. The organic peroxide or combination of peroxides are generally selected in the consideration of film-forming temperature, conditions for 5 preparing the composition, curing (bonding) temperature, heat resistance of body to be bonded and storage stability.According to a preferred embodiment of the subject invention, the peroxide is chosen such that it does essentially no decompose the resin processing temperature, in particular during coextrusion and/or a further extrusion and pelletizing step, while is only activated at the solar cell formation 10 temperature or lamination temperature. “Essentially not decomposing” according to the present invention refers to a half-life of at least 0.1 to 1 hours at the coextrusion temperature. Examples of the organic peroxides include 2,5-dimethylhexane-2,5-dihydroperoxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 3-di-tert-butylperoxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(2-ethylhaxanoylperoxy)hexane, 2,5-dimethyl-15 2,5-di(tert-butylperoxy)hexane, tert-butylcumylperoxide, [alpha],[alpha]'-bis(tert-butylperoxyisopropyl)benzene, [alpha],[alpha]'-bis(tert- butylperoxy)diisopropylbenzene, n-butyl-4,4-bis(tert-butylperoxy)butane, 2,2-bis(tert-butylperoxy)butane, 1,1 -bis(tert-butylperoxy)cyclohexane, 1,1 -bis(tert-butylperoxy)- 3,3,5-trimethylcyclohexane, tert-butylperoxybenzoate, benzoyl peroxide, and 1,1-di 20 (tert-hexylperoxy)-3,3,5-trimethylcyclohexane. Of these, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane, and 1,1-di (tert-hexylperoxy)-3,3,5-trimethylcyclohexane are particularly preferred. The content of the organic peroxide in the film layers is preferably in the range of 0.1 to 5 parts by weight, more preferably in the range of 0.2 to 1.8 parts by weight based on 100 parts by weight of 25 ethylene-vinyl acetate copolymer.

Preferably the polymer layer comprises two or suitably 2-12 coextruded polymer layers, wherein two or more polymer layers comprise a luminescence downshifting compound. Such a multi-layer is made by simultaneously coextruding and orienting a film composed of the different layers.

30 The polymers used for the different layers may be different provided that the difference in Melt Flow Index of the polymers at the conditions of coextruding is less than 4 points and preferably less than 2 points. If different polymers having a different MFI at for example a standard condition are combined it is preferred to adjust the extrusion temperature of the different polymers such that the MFI at the conditions of 14 coextruding are within the above described ranges. A polymer sheet having at least 3 layers will comprise of two outer layers and at least one inner layer. Preferably the melt flow index of the inner polymer layer at the extrusion temperature of inner polymer layer is equal to or in the range of from -2 to plus 2 MFI points to the MFI of 5 the outer layers at the extrusion temperature or temperatures of the outer layers layers. Preferably the MFI of an inner polymer layer differs in a range of from 0.5 to 10 from the MFI of an outer polymer layer or both outer polymer layers at a temperature TL, wherein TL is the lamination temperature of a vacuum lamination process to prepare a solar panels comprising the polymer sheet according to the 10 invention. Typical temperatures for the lamination are in the range of from 135 to 165 °C, preferably 145 to 155 °C.

Preferably one or both outer polymer layers have a melting point T1 which at least 10 °C below the melting point T2 of at least one of the inner polymer layers. Preferably, the melting point T1 is between 10 and 50 °C lower than the melting point 15 T2, more preferably between 10 and 35 °C lower. Applicants found that shrinkage of the poymer sheet at lamination conditions can be significantly lower when such a high melting inner polymer layer is part of the polymer sheet. More preferably the MFI of both outer layers are higher than the MFI of at least one inner polymer layer as measured at the lamination temperature. Applicants found that such a polymer sheet 20 may advantageously be used to make a solar panel in a thermal lamination process wherein the silicon cells are sufficiently encapsulated by the outer layer of the polymer sheet while at the same time no or very reduced shrinkage occurs. This is advantageous because less or no annealing of the polymer sheet will then be required when preparing the polymer sheet. Shrinkage of the polymer sheet is to be 25 avoided or reduced in order to avoid that the sheet damages the vulnerable silicon photovoltaic cells when laminating a solar panel. Applicants found that for a preferred combination of polymer materials for the layers of the polymer sheet the lamination temperature as applied, when the polymer sheet is combined with for example a photovoltaic cell, is higher than the temperature at which the inner layer is extruded, 30 when preparing the polymer sheet, and wherein the temperature at which the inner layer is extruded, when preparing the polymer sheet, is in turn higher than the temperature at which at least one of the outer layers is extruded, when preparing the polymer sheet.

15

Suitably the above described inner polymer layer comprises of an optionally hydrogenated polystyrene block copolymer with butadiene, isoprene and/or butylenes/ethylene copolymers, for example SIS, SBS and/or SEBS; a polymethacrylate polyacrylate block copolymer, a polyolefin, a polyolefine copolymer 5 or terpolymer, or an olefin copolymer or terpolymer, with copolymerizable functionalised monomers such as methacyrylic acid (ionomer). Examples are a poly methyl metacrylate n-butylacrylate block copolymer, as disclosed in WO2012057079, and commercially available as “Kurarity” from Kuraray Corp. A further example comprises a polyolefin, preferably a polyethylene or polypropylene, such as an LDPE 10 type. Polyolefins, such as polyethylene and polypropylene suitable for the inner sub layer include high density polyethylene, medium density polyethylene, low density polyethylene, linear low density polyethylene, metallocene-derived low density polyethylene homopolypropylene, and polypropylene co-polymer.

Coextrusion is well known process to the skilled person and utilizes two or more 15 extruders to melt and deliver a steady volumetric throughput of different viscous polymers to a single extrusion head (die) which will extrude the materials in the desired sheet like form. The layer thicknesses may be controlled by the relative speeds and sizes of the individual extruders delivering the polymeric materials.

It may be preferable to add additives to at least one of the outer layers of the 20 polymer sheet which improve the adhesive strength of the polymer sheet to glass. In some applications the polymer sheet is applied directly onto a glass layer and a good adhesive property of the polymer sheet will then be required. If the polymer sheet is applied between two layers of glass it is preferred that both outer layers of the polymer sheet have good adhesive strengths to glass. Possible additives are silane 25 coupling agents may be added to the EVA copolymer to improve its adhesive strength with the glass layer or layers. Useful illustrative silane coupling agents include [gamma]-chloropropylmethoxysilane, vinylmethoxysilane, vinyltriethoxysilane, vinyltris([beta]- methoxyethoxy)silane,[gamma]-vinylbenzylpropylmethoxysilane, N-[beta]-(N- vinylbenzylaminoethyl)-[gamma]-aminopropyltrimethoxysilane, [gamma]-30 methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, Y- glycidoxypropyltrimethoxysilane, [gamma]-glycidoxypropyltriethoxysilane, [beta]-(3,4-epoxycyclohexyl)ethylthmethoxysilane, methacryloxypropyltriethoxysilane, vinylthchlorosilane, methacryloxypropyltrimethoxysilane, [gamma]-mercapto- 16 propylmethoxysilane, [gamma]-aminopropyltriethoxysilane, N-[beta]-(aminoethyl)-[gamma]- aminopropyltrinethoxysilane, and/or mixtures of two or more thereof.

The silane coupling agents are preferably incorporated in the relevant polymer layer. For a polymer layer comprising of the an ethylene vinyl acetate 5 polymer the silane coupling agents are preferably incorporated at a level of 0.01 to about 5 wt%, or more preferably 0.05 to about 1 wt%, based on the total weight of the polymer.

The polymer sheet according to the invention is especially suited to convert the shorter wavelength radiation of sunlight to longer wavelength radiation having a 10 wavelength range in which photovoltaic cells convert radiation into electricity more effectively. The invention is thus also directed to the use of the polymer sheet according to the invention for enhancing the performance of a photovoltaic cell by luminescent down-shifting of sunlight.

The polymer sheet according to the invention is preferably used as part of a 15 solar panel comprising a photovoltaic cell. The photovoltaic cell may comprise at least one of the following materials: CdS, CdTe; Si, preferably p-doped Si or crystalline Si or amorphous Si or multicrystalline Si; InP; GaAs; Cu2S; Copper Indium Gallium Diselenide (CIGS). A solar panel may be prepared by stacking the different layers of glass, the polymer sheet according to the invention, the photovoltaic cell, 20 additional encapsulant layer or layers and a backsheet layer and subjecting the formed stack to a lamination process step.

The optimal photovoltaic performance of a PV cell will be different for each type of PV cell and thus the degree of conversion required by the luminescent downconversion compounds may be different for different PV cells. Preferably the 25 polymer layer comprising a luminescence downshifting compound of the polymer sheet which is most spaced away from the photovoltaic cell comprises a luminescence downshifting compound which has the property that it can absorb at least partially UV radiation (between 10 and 400 nm) and re-emit radiation at a higher wavelength.

30 The invention is also directed to a solar panel comprising the polymer sheet according to the invention and a photovoltaic cell. Preferably the polymer layer comprising a luminescence downshifting compound which is most spaced away from the photovoltaic cell comprises a luminescence downshifting compound for at least partially absorbing UV radiation and re-emitting radiation at a higher wavelength.

17

Such a solar panel preferably has a layer sequence of a glass layer, the polymer sheet, a photovolataic cell, an encapsulant layer and a back sheet. The encapsulant layer may be a state of the art encapsulant layer, for example a thermally curable polymer layers such as the earlier described EVA copolymer. The photovoltaic cell is 5 suitably a crystalline silicon cell, CdTe, aSi, micromorph Si or Tandem junction aSi. The backsheet may be a hard polymer, such as for example a layer of PET or more preferably a glass layer. When thin film photovoltaic cells are used, or example CIGS and CIS type cells, the solar cell panel may comprise a glass top layer, the polymer sheet of the present invention, the thin film photovoltaic cell and a rigid support, such 10 as for example glass.

Preferably the glass layer facing the incoming radiation has a thickness of between 1.5 and 4 mm and wherein the glass layer used as back sheet has a thickness of 1.5 and 4 mm and wherein the total thickness of the solar panel is less than 9 mm. The glass layer may for example be float glass or roll glass. The glass 15 may optionally be thermally treated. Suitable thermally toughened thin glass sheets glass layers having such a thickness may be obtained from for example Saint Gobain Glass. The glass layer may sodium free glass, for example aluminosilicate or borosilicate glass. For large volume production it is preferred to use a soda lime glass or borosilicate glass. The soda lime glass may comprise between 67-75% by weight 20 Si02, between 10-20% by weight; Na20, between 5-15% by weight CaO, between 0-7% by weight MgO, between 0-5% by weight AI2O3; between 0-5% by weight K2O, between 0-1.5% by weight U2O and between 0-1 %, by weight BaO. Such a glass will suitably have a transparency of higher than 90%. Suitably the glass has been subjected to a thermally toughening treatment.

25 The surface of the glass layer, especially the surface not facing the polymer sheet and facing the incoming radiation is coated with a suitable anti-reflection layer. The anti-reflective layer will limit the radiation which reflects at the glass surface. Limiting this reflection will increase the radiation passing the glass element which will as a result enhance the efficiency of the glass element to transmit radiation.

30 Preferably the coating is applied to one glass layer, namely the glass layer which will in use face the incoming radiation, i.e. sunlight. The side facing the polymer sheet may optionally be provided with such a coating. A suitable anti-reflection coating will comprise of a layer of porous silica. The porous silica may be applied by a sol-gel 18 process as for example described in US-B-7767253. The porous silica may comprise of solid silica particles present in a silica based binder. Such a coating is obtainable from DSM, The Netherlands, as Khepri Coat™. Processes to prepare glass layers having an anti-reflective coating are for example described in WO-A-2004104113 5 and WO-A-2010100285.

The glass surface facing the incoming radiation may also have an embossed structure to capture incoming radiation more effectively, as for example described in W02005111670.

A solar panel as described above may be obtained by subjecting a stack 10 comprising the following layers: a glass layer (a), a polymer sheet according to the invention (b), a layer (c) comprising a photovoltaic cell, a polymer encapsulant layer (d); and 15 a glass layer (e), to a thermal lamination at an elevated lamination temperature.

The lamination temperature may be between 115 and 175 °C and wherein the environment of the stack preferably has a pressure of less than 30 mBar, more preferably less than 1 mBar. In this process the stack is preferably present in a 20 vacuum laminator and pressure bonded under conversion heating at a temperature in the range of from of 115 to 175°C, preferably 140 to 165°C, most preferably from 145 to 155°C. The laminate is preferably also subjected to degassing. The compression lamination pressure preferably is in the range of from of 0.1 to 1.5 kg/cm2. The lamination time typically is in the range of from 5 to 15 minutes. This 25 heating enables for example the ethylene-vinyl acetate copolymer contained in the polymer sheet according to the invention and in the encapsulant layer to crosslink, whereby the photovoltaic cell, the polymer sheet and the encapsulant layer are strongly adhered to seal the photovoltaic cell and obtain the solar panel.

Applicants have found that when the MFI at the lamination temperature is 30 different between outer sub layers and an inner layer even less shrinkage occurs.

The invention is thus also directed to a preferred process of manufacture of the solar panel wherein the first and/or second polymer encapsulant layer is comprised of 3 or more multiple coextruded thermoplast polymer sub-layers comprising two outer sublayers and at least one inner sub-layer and wherein at the lamination temperature the 19 MFI of the inner sub-layer differs in a range of from 0.5 to 10 points from the MFI of one or both of the outer sub-layers of the same layer.

Even more preferred process of manufacture is wherein the polymer sheet according to the invention is comprised of 3 or more multiple coextruded thermoplast 5 polymer sub-layers comprising two outer sub-layers and at least one inner sub-layer, wherein the multiple coextruded thermoplast polymer layer is obtained by co-extrusion of different polymer materials which polymer materials are extruded at an extrusion temperature for each sub-layer so chosen that the largest difference in melt flow index of the polymers of the sub-layers at the extrusion temperature as 10 applied for each sub-layer is lower than 5 MFI points, preferably lower than 3 MFI points, wherein the lamination temperature TL is higher than the extrusion temperature TC of an inner sub-layer and wherein the temperature TC is higher than the extrusion temperature TA 15 of an outer sub-layer and/or TB of the other outer sub-layer.

Claims

1. Polymeervel dat meerdere co-geëxtrudeerde polymeerlagen omvat, waarbij ten minste 5 één van deze lagen een luminescente "downshiftende" verbinding omvat voor het tenminste gedeeltelijk absorberen van straling met een bepaalde golflengte, en het opnieuw uitzenden van straling met een langere golflengte dan de golflengte van de geabsorbeerde straling.A polymer sheet comprising a plurality of co-extruded polymer layers, wherein at least one of these layers comprises a luminescent "downshifting" connection for at least partially absorbing radiation with a certain wavelength, and retransmitting radiation with a longer wavelength than the wavelength of the absorbed radiation.

2. Polymeervel volgens conclusie 1, waarbij twee of meer lagen van het polymeervel een luminescente "downshiftende" verbinding omvatten.The polymer sheet of claim 1, wherein two or more layers of the polymer sheet comprise a luminescent "downshifting" compound.

3. Polymeervel volgens conclusie 2, waarbij een luminescente "downshiftende" verbinding aanwezig is in een eerste polymeerlaag, waarbij de luminescente "downshiftende" 15 verbinding meer straling kan absorberen met een lagere golflengte dan de luminescente "downshiftende" verbinding die aanwezig is in een volgende laag.3. Polymer sheet according to claim 2, wherein a luminescent "downshifting" compound is present in a first polymer layer, wherein the luminescent "downshifting" compound can absorb more radiation with a lower wavelength than the luminescent "downshifting" compound present in a subsequent low.

4. Polymeervel volgens conclusie 3, waarbij de eerste polymeerlaag een luminescente "downshiftende" verbinding omvat voor het tenminste gedeeltelijk absorberen van UV 20 straling en het opnieuw uitzenden van straling met een hogere golflengte.4. Polymer sheet according to claim 3, wherein the first polymer layer comprises a luminescent "downshifting" connection for at least partially absorbing UV radiation and retransmitting radiation with a higher wavelength.

5. Polymeervel volgens conclusie 4, waarbij een eerste polymeerlaag een luminescente "downshiftende" verbinding omvat voor het absorberen van straling met een golflengte die gelegen is tussen 280 en 400 nm, en het opnieuw uitzenden van straling met een 25 golflengte die gelegen is tussen 405 en 550 nm, waarbij een andere polymeerlaag een luminescente "downshiftende" verbinding omvat voor het absorberen van straling met een golflengte die gelegen is tussen 360 en 470 nm, en het opnieuw uitzenden van straling met een golflengte die gelegen is tussen 410 en 670 nm, en waarbij een andere polymeerlaag een luminescente "downshiftende" verbinding omvat voor het absorberen van straling met een golflengte die gelegen is tussen 360 en 570 nm, en het opnieuw uitzenden van straling met een golflengte die gelegen is tussen 410 en 750 nm. 55. Polymer sheet according to claim 4, wherein a first polymer layer comprises a luminescent "downshifting" connection for absorbing radiation with a wavelength that is between 280 and 400 nm, and retransmitting radiation with a wavelength that is between 405 and 550 nm, wherein another polymer layer comprises a luminescent "downshifting" compound for absorbing radiation with a wavelength that is between 360 and 470 nm, and retransmitting radiation with a wavelength that is between 410 and 670 nm, and wherein another polymer layer comprises a luminescent "downshifting" compound for absorbing radiation with a wavelength that is between 360 and 570 nm, and retransmitting radiation with a wavelength that is between 410 and 750 nm. 5

6. Polymeerlaag volgens één der conclusies 1-5, waarbij ten minste één van de polymeerlagen gevormd is uit ethyleenvinylacetaat (EVA), polyvinylbutyral (PVB), polymethylmethacrylaat (PMMA), alkylmethacrylaat, alkylacrylaat co-polymeren, polyurethanen, gefunctionaliseerde polyolefinen, ionomeren, tweecomponenten 10 polydimethylsiloxanen, thermoplastische co-polymeren van polydimethylsiloxanen, dan wel uit mengsels daarvan.Polymer layer according to any of claims 1-5, wherein at least one of the polymer layers is formed from ethylene vinyl acetate (EVA), polyvinyl butyral (PVB), polymethyl methacrylate (PMMA), alkyl methacrylate, alkyl acrylate copolymers, polyurethanes, functionalized polyolefins, ionomers, two-component polydimethylsiloxanes, thermoplastic copolymers of polydimethylsiloxanes, or from mixtures thereof.

7. Polymeerlaag volgens conclusie 6, waarbij ten minste één van de polymeerlagen gevormd is uit ethyleenvinylacetaat (EVA), polyvinylbutyral (PVB), siliconen, 15 polymetylmethacrylaat (PMMA), of alkylacrylaat co-polymeren.7. Polymer layer according to claim 6, wherein at least one of the polymer layers is formed from ethylene vinyl acetate (EVA), polyvinyl butyral (PVB), silicones, polymetyl methacrylate (PMMA), or alkyl acrylate copolymers.

8. Polymeerlaag volgens conclusie 7, waarbij ten minste één van de polymeerlagen gevormd is uit een ethyleenvinylacetaatpolymeer.A polymer layer according to claim 7, wherein at least one of the polymer layers is formed from an ethylene vinyl acetate polymer.

9. Polymeervel volgens conclusie 8, waarbij het ethyleenvinylacetaat een acetaatgehalte bezit van 12% tot 45% op gewichtsbasis.The polymer sheet of claim 8, wherein the ethylene vinyl acetate has an acetate content of 12% to 45% by weight.

10. Polymeervel volgens conclusie 9, waarbij de luminescente "downshiftende" verbindingen aanwezig zijn in meerdere co-geëxtrudeerde lagen van een 25 ethyleenvinylacetaatpolymeer met een acetaatgehalte van 12% tot 45% op gewichtsbasis.10. Polymer sheet according to claim 9, wherein the luminescent "downshifting" compounds are present in a plurality of co-extruded layers of an ethylene vinyl acetate polymer with an acetate content of 12% to 45% by weight.

11. Polymeervel volgens één der conclusies 1-10, waarbij ten minste één van de buitenste polymeerlagen een silaanbindend middel omvat. 30The polymer sheet of any one of claims 1-10, wherein at least one of the outer polymer layers comprises a silane binding agent. 30

12. Polymeervel volgens één der conclusies 1-11, waarbij het vel twee buitenste polymeerlagen omvat en ten minste één binnenste polymeerlaag, en waarbij een buitenste polymeerlaag of de beide buitenste polymeerlagen een smeltpunt Tl vertonen dat tenminste 10°C lager ligt dan het smeltpunt T2 van ten minste één binnenste 5 polymeerlaag.A polymer sheet according to any one of claims 1-11, wherein the sheet comprises two outer polymer layers and at least one inner polymer layer, and wherein an outer polymer layer or both outer polymer layers have a melting point T1 that is at least 10 ° C lower than the melting point T2 of at least one inner polymer layer.

13. Polymeervel volgens conclusie 12, waarbij het smeltpunt Tl tussen 10 en 100°C lager is gelegen dan het smeltpunt T2.The polymer sheet of claim 12, wherein the melting point T1 is between 10 and 100 ° C lower than the melting point T2.

14. Polymeervel volgens één der conclusies 12-13, waarbij het polymeervel bekomen wordt door middel van een co-extrusie van verschillende polymere materialen, waarbij deze polymere materialen geëxtrudeerd worden bij een extrusietemperatuur die voor elke sublaag op een zodanige wijze gekozen is dat het grootste verschil in smeltindex van de polymeren van de sublagen bij de extrusietemperatuur, zoals deze wordt toegepast voor 15 elke sublaag, kleiner is dan 3 MFI-punten.A polymer sheet according to any of claims 12-13, wherein the polymer sheet is obtained by co-extrusion of different polymeric materials, said polymeric materials being extruded at an extrusion temperature selected for each sublayer in such a way that the largest difference in melt index of the polymers of the sublayers at the extrusion temperature, as applied for each sublayer, is less than 3 MFI points.

15. Polymeervel volgens één der conclusies 12-13, waarbij de binnenste polymeerlaag een eventueel gehydrogeneerde polystyreen blok-co-polymeer is met butadieen, isopreen en/of butyleen/ethyleen co-polymeren (SIS, SBS, en/of SEBS); een polymethacrylaat 20 polyacrylaat blok-co-polymeer, een polyolefine, een polyolefine co-polymeer of ter- polymeer, of een olefine co-polymeer of ter-polymeer, met co-polymeriseerbare gefunctionaliseerde monomeren zoals methacrylzuur (ionomeer).The polymer sheet according to any of claims 12-13, wherein the inner polymer layer is an optionally hydrogenated polystyrene block copolymer with butadiene, isoprene and / or butylene / ethylene copolymers (SIS, SBS, and / or SEBS); a polymethacrylate, polyacrylate block copolymer, a polyolefin, a polyolefin copolymer or terpolymer, or an olefin copolymer or terpolymer, with copolymerizable functionalized monomers such as methacrylic acid (ionomer).

16. Polymeervel volgens één der conclusies 12-15, waarbij ten minste één van de buitenste 25 lagen een ethyleenvinylacetaat co-polymeer omvat. 1 Polymeervel volgens conclusie 16, waarbij het ethyleenvinylacetaat een acetaatgehalte bezit van meer dan 18% op gewichtsbasis.16. Polymer sheet according to any of claims 12-15, wherein at least one of the outer layers comprises an ethylene vinyl acetate copolymer. A polymer sheet according to claim 16, wherein the ethylene vinyl acetate has an acetate content of more than 18% by weight.

18. Gebruik van het polymeervel volgens één der conclusies 1-17, voor het verbeteren van de prestatie van een fotovoltaïsche cel door het luminescent "downshiften" van zonlicht.Use of the polymer sheet according to any one of claims 1-17, for improving the performance of a photovoltaic cell by the luminescent "downshifting" of sunlight.

19. Zonnepaneel, een polymeervel volgens één der conclusies 1-17, en een fotovoltaïsche 5 cel omvattende.19. Solar panel, comprising a polymer sheet according to any one of claims 1-17, and a photovoltaic cell.

20. Zonnepaneel volgens conclusie 19, waarbij de polymeerlaag die een luminescente "downshiftende" verbinding omvat en die het verst van de fotovoltaïsche cel gelegen is, een luminescente "downshiftende" verbinding omvat voor het tenminste gedeeltelijk 10 absorberen van UV straling en het opnieuw uitzenden van straling met een langere golflengte.20. Solar panel according to claim 19, wherein the polymer layer comprising a luminescent "downshifting" connection and which is furthest from the photovoltaic cell comprises a luminescent "downshifting" connection for at least partially absorbing UV radiation and retransmitting UV radiation. radiation with a longer wavelength.

21. Zonnepaneel volgens één der conclusies 19-20-15, waarbij het paneel een opeenvolging van lagen bezit die overeenstemt met een glazen laag, het polymeervel, een 15 fotovoltaïsche cel, een omhullende laag, en een achterste laag.21. Solar panel as claimed in any of the claims 19-20-15, wherein the panel has a sequence of layers corresponding to a glass layer, the polymer sheet, a photovoltaic cell, an envelope layer, and a rear layer.

22. Zonnepaneel volgens conclusie 21, waarbij de achterste laag een glazen laag is.The solar panel of claim 21, wherein the rear layer is a glass layer.

23. Zonnepaneel volgens conclusie 17, waarbij de glazen laag die gericht is naar de 20 invallende straling, een dikte heeft die gelegen is tussen 1,4 en 4 mm, waarbij de glazen laag die gebruikt wordt als achterste laag, een dikte heeft die gelegen is tussen 1,5 en 4 mm, en waarbij de totale dikte van het zonnepaneel kleiner is dan 9 mm.23. Solar panel according to claim 17, wherein the glass layer that is directed to the incident radiation has a thickness that is between 1.4 and 4 mm, the glass layer that is used as a rear layer has a thickness that is located is between 1.5 and 4 mm, and where the total thickness of the solar panel is less than 9 mm.

24. Zonnepaneel volgens één der conclusies 21-23, waarbij de glazen laag die gericht is 25 naar de invallende straling, is voorzien van een anti-weerkaatsende coating.24. Solar panel as claimed in any of the claims 21-23, wherein the glass layer that is directed to the incident radiation is provided with an anti-reflective coating.

25. Werkwijze voor de vervaardiging van een zonnepaneel, door een stapel met de volgende opeenvolging van lagen: een glazen laag (a), 30 een polymeervel volgens één der conclusies 1-17 (b), een laag (c) die een fotovoltaïsche cel omvat, een polymere omhullende laag (d); en een glazen laag (e) te onderwerpen aan een thermische laminatie bij een hogere laminatietemperatuur. 525. Method for the manufacture of a solar panel, by a stack having the following sequence of layers: a glass layer (a), a polymer sheet according to any one of claims 1-17 (b), a layer (c) comprising a photovoltaic cell comprises a polymeric envelope layer (d); and subjecting a glass layer (e) to thermal lamination at a higher lamination temperature. 5

26. Werkwijze volgens conclusie 25, waarbij het polymeervel drie of meer meervoudig co-geëxtrudeerde thermoplastische polymere sublagen omvat met twee buitenste sublagen en ten minste één binnenste sublaag, en waarbij, bij de laminatietemperatuur, het verschil tussen de MFI van de binnenste sublaag en de MFI van één van de, of van beide 10 sublagen van dezelfde laag gelegen is in een bereik van 0,5 tot 10 punten.The method of claim 25, wherein the polymer sheet comprises three or more multiply co-extruded thermoplastic polymeric sublayers with two outer sublayers and at least one inner sublayer, and wherein, at the lamination temperature, the difference between the MFI of the inner sublayer and the MFI of one or both of the 10 sub-layers of the same layer is in a range of 0.5 to 10 points.

27. Werkwijze volgens één der conclusies 15-26, waarbij het polymeervel (b) drie of meer meervoudig co-geëxtrudeerde thermoplastische polymere sublagen omvat met twee buitenste sublagen en ten minste één binnenste sublaag, 15 waarbij het polymeervel (b) wordt bekomen door co-extrusie van verschillende polymere materialen, waarbij deze polymere materialen geëxtrudeerd worden bij een extrusietemperatuur die voor elke sublaag op een zodanige wijze gekozen is dat het grootste verschil in smeltindex van de polymeren van de sublagen bij de extrusietemperatuur, zoals deze wordt toegepast voor elke sublaag, kleiner is dan 5 20 MFI-punten, waarbij de laminatietemperatuur TL hoger ligt dan de extrusietemperatuur TC van een binnenste sublaag, en waarbij de temperatuur TC hoger is dan de extrusietemperatuur TA van een buitenste sublaag en/of TB van de andere buitenste sublaag. 2527. A method according to any one of claims 15-26, wherein the polymer sheet (b) comprises three or more multiply co-extruded thermoplastic polymeric sublayers with two outer sublayers and at least one inner sublayer, wherein the polymer sheet (b) is obtained by co -extrusion of various polymeric materials, these polymeric materials being extruded at an extrusion temperature selected for each sublayer in such a way that the largest difference in melt index of the polymers of the sublayers at the extrusion temperature, as applied for each sublayer, is less than 5 MFI points, wherein the lamination temperature TL is higher than the extrusion temperature TC of an inner sublayer, and wherein the temperature TC is higher than the extrusion temperature TA of an outer sublayer and / or TB of the other outer sublayer. 25

28. Werkwijze volgens één der conclusies 25-27, waarbij de laminatietemperatuur gelegen is tussen 115 en 175°C, en waarbij in de omgeving van de stapel een druk heerst die kleiner is dan 30 mbar.A method according to any one of claims 25-27, wherein the laminating temperature is between 115 and 175 ° C, and wherein a pressure prevailing in the vicinity of the stack is less than 30 mbar.