NL2008839C2 - Glass element. - Google Patents

Description

GLASS ELEMENT

The invention is directed to a glass element.

Glass elements are known to be used as cover of greenhouses. Sunlight 5 easily passes the glass roof of such a greenhouse and photosynthesis of at least one plant species takes place. But glass elements are also being used as a transparent and protective layer of a solar panel.

The present invention is directed to improve the efficiency of a light induced process such as but not limited to photosynthesis or power 10 generation by the means of the photovoltaic effect.

This aim is achieved by the following glass element. Glass element comprising two layers of glass, wherein a transparent polymer layer is present between the two layers of glass and wherein the polymer layer comprises a at least one luminescence downshifting compound adapted for at least partially 15 absorbing radiation having a certain wavelength and re-emitting radiation at a longer wavelength than the wavelength of the absorbed radiation.

Applicants found that when such a glass element is used as roof of a greenhouse the photosynthesis of at least one plant species can be enhanced because part of the shorter wavelength radiation is downshifted to a 20 wavelength more suited for photosynthesis. Thus more photosynthesis can take place at given sunlight intensity. Applicants also found that when such glass element is used as cover sheet of a photovoltaic system more power can be generated at a given sunlight intensity.

Another advantage is that the glass layers avoid water ingress towards 25 the polymer layer. Small amounts of water may negatively effect the stability of certain luminescence downshifting compounds, especially the organic luminescence downshifting compound. By using two layers of glass the luminescence downshifting compound as present in the polymer layer is effectively protected against water induced degradation. Further advantages 30 will be discussed when describing the preferred uses below.

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 values, this is to be understood as specifically disclosing all 2 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, 5 and all integers and fractions within the range. It is not 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.

10 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 15 not expressly listed or inherent to such 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) of the claimed 20 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.

25 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.

30 In describing certain polymers it should be understood that sometimes 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 3 such reference to monomers and amounts should be interpreted to mean that the polymer comprises those monomers (i.e. copolymerized units of those monomers) or that amount of the monomers, and the corresponding polymers and compositions thereof.

5 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.

The glass element comprises two layers of glass which sandwich a 10 transparent polymer layer. More than one polymer layer may be present. Suitably no non-transparent elements are present between the two glass layers which will reduce the transparency of visible light between 310 and 1400nm of the glass element as a whole by more than 5% preferably by more than 2%. This to achieve the most optimal transparency of the glass element. 15 Specifically it should be understood that no crystalline silica photovoltaic cells are present between the glass layers.

The polymer layer is preferably a material which may be applied to the glass layers by means of a thermal lamination process. Examples of suited polymers are ethylene vinyl acetate (EVA), polyvinylbutyral (PVB), , 20 polymethylmethacrylate (PMMA), alkylmethacrylate, alkylacrylate copolymers, such as for example polymethylmethacrylate poly-n-butylacrylate (PMMA--PnBA), elastomers, e.g. SEBS, SEPS, SIPS, polyurethanes, functionalized polyolefines, lonomers, 2-component polydimethylsiloxanes, thermoplast polydimethylsiloxane copolymers, or mixtures thereof. Preferably ethylene 25 vinyl acetate (EVA), polyvinylbutyral (PVB), silicone, polymethylmethacrylate(PMMA), alkylacrylate copolymers, such as for example polymethylmethacrylate poly-n-butylacrylate (PMMA-PnBA) are used. These polymers may be used in a thermal lamination process and are suited to provide a suitable matrix for the luminescence downshifting compound or 30 compounds.

Preferably the polymer is an ethylene/vinyl acetate copolymer (EVA copolymer) comprising of copolymerized units of ethylene and vinyl acetate. The EVA copolymer may have a melt flow rate (MFR) in the range of from 0.1 to 1000 g/10 minutes, preferably of from 0.3 to 300 g/10 minutes, yet more 4 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 35 wt% and even more 5 preferably between 25% up to 33 wt%.

The EVA copolymer may be a single EVA copolymer or a mixture of two or more different EVA copolymers. By different EVA copolymers is meant that the copolymers having different comonomer ratios, and/or the weight average molecular weight and/or molecular weight distribution may differ.

10 Accordingly the EVA copolymer may also comprise copolymers that have the same comonomer ratios, but different MFR due to having different molecular weight distribution.

In a preferred embodiment, the EVA copolymers advantageously comprise further monomers other than ethylene and vinyl acetate, such as 15 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 propyl, butyl, pentyl, and hexyl groups.

Exemplary alkyl acrylates include, but are not limited to, methyl acrylate, ethyl acrylate, /-butyl acrylate, and n-butyl acrylate. The polarity of the alkyl 20 acrylate comonomer may be manipulated by changing the relative amount and identity of the alkyl group present in the comonomer. Similarly, a C1-C6 alkyl methacrylate comonomer may be used as a comonomer. Such comonomers include methyl methacrylate, ethyl methacrylate, i-butyl methacrylate, and n-butyl methacrylate.

25 The EVA compositions used in the materials according to the invention may further comprise one or more other optional polymers, such as, for example, polyolefins including ethylene homopolymers, propylene homopolymers, additional ethylene copolymers, and propylene copolymers; ethylene (meth)acrylic copolymers. The optional polymers may be present in 30 an amount of up to about 25 wt%, based on the total weight of the EVA copolymer, provided that the inclusion of such optional polymers does not adversely affect the desirable performance characteristics of the EVA copolymer, such as the transparency, melt flow index, pigment dispersion and/or adhesion properties.

5

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, UV 5 absorbers, UV stabilizers, dispersants, surfactants, chelating agents, coupling agents, reinforcement additives, such as glass fiber, fillers and the like.

If luminescence downshifting compound or compounds are used which absorb radiation in the UV wavelength less UV stabilizers or even no UV stabilizers can be comprised in the polymer layer. The luminescence 10 downshifting compound will then take over the protective function of the UV stabilizer.

Silane coupling agents may be added to the EVA copolymer to improve its adhesive strength. Useful illustrative silane coupling agents include [gamma]-chloropropylmethoxysilane, vinylmethoxysilane, vinyltriethoxysilane, 15 vinyltris([beta]- methoxyethoxy)silane,[gamma]-vinylbenzylpropylmethoxy-silane, N-[beta]-(N- vinylbenzylaminoethyl)-[gamma]-aminopropyl-trimethoxysilane, [gamma]- methacryloxypropyltriethoxysilane, [gamma]-methacryloxypropyltrimethoxysilane, [gamma]-methacryloxypropyltriethoxysilane, vinyltriacetoxysilane, v-20 glycidoxypropyltrimethoxysilane, [gamma]-glycidoxypropyltriethoxysilane, [beta]-(3,4- epoxycyclohexyl)ethylthmethoxysilane, vinylthchlorosilane, [gamma]-mercaptopropylmethoxysilane, [gamma]-aminopropyltriethoxysilane, N-[beta]-(aminoethyl)-[gamma]- aminopropyltrinethoxysilane, and/or mixtures of two or more thereof.

25 The silane coupling agents are preferably incorporated in the polymer layer at a level of about 0.01 to about 5 wt%, or more preferably about 0.05 to about 1 wt%, based on the total weight of the EVA copolymer.

The glass layer may sodium free glass, for example aluminosilicate or borosilicate glass. For large volume production it is preferred to use a soda 30 lime glass or borosilicate glass. The soda lime glass may comprise between 67-75% by weight Si02, between 10-20% by weight; Na20, between 5-15% by weight CaO, between 0-7% by weight MgO, between 0-5% by weight Al203;between 0-5% by weight K2O, between 0-1.5% by weight U2O and 6 between 0-1 %, by weight BaO. Other elements like Cerium and/or Antimony are also typical in high transmission glass and do influence the transparency at low wavelengths. Such a glass will suitably have a transparency of higher than 90%. Suitably the glass has been subjected to a thermally toughening 5 treatment.

Preferably at least one of the glass layers has a thickness of between 0.1 and 3.2 mm. The total thickness of the glass element is suitably less than 5 mm. The glass layer facing the incoming radiation is preferably between 0.1 and 4 mm in order to provide enough thickness to avoid damage due to hail 10 and the like. The glass layer through which the downshifted radiation passes may be thinner, suitably between 0.1 and 2 mm. The glass layer may for example be float glass or roll glass.

The glass may optionally be thermally treated. Because of the polymer, layer breakage of the glass element will not result in dangerously 15 large glass pieces but instead the glass element will remain, although fractured, as one piece. This property of the glass element would make the use of non-thermally treated glass, or at least one layer of non-thermally treated glass possible. Suitable thermally toughened thin glass sheets having such a thickness may be obtained from for example Saint Gobain Glass, AGC, 20 PPG, and Ducatt

The use of these thin glass layers is advantageous because the total thickness of the glass element will then also be thin. A glass element may be obtained having the thickness of a typical glass. The advantage of the glass element of the present invention as compared to a glass plate of the same 25 dimensions is that radiation will pass the glass element having a defined and desired wavelength and that the glass element is safer that a single glass layer. This because in case of breakage of the glass layer the polymer layer will hold together the resulting broken glass pieces.

The surface of the glass element, especially the surface not facing the 30 polymer layer 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. Preferably the coating is applied to one glass layer, namely the glass layer 7 which will in use face the incoming radiation, i.e. direct or diffuse sunlight. The side facing the polymer layer 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 process as for example described in 5 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 and WO-A-2010100285.

10 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.

The luminescence downshifting compound may be an organic or inorganic luminescent compound, which are capable of partially absorbing 15 radiation having a certain wavelength and re-emitting radiation at a longer wavelength than the 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 20 Energy Materials & Solar Cells 93 (2009) 1182-1194.

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 example 5-carboxytetramethylrhodamine, Rhodamine6G, 25 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-violanthrone or a derivative thereof. Examples of 30 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 (DCCH), 7-Diethylaminocoumarin-3-carboxylic acid 8 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-4-5 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), 7-10 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, N1- Bis(2,6-diisopropylphenyl)perylene-3,4:9,10-tetracarbonic acid diimide, N,N'-Bis(2,6-15 dimethylphenyl)perylene-3,4:9,10-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(2,6-20 diisopropylphenyl)-1,6- and -1,7-bis(4-tert- octylphenoxy)perylene-3,4:9,10-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-(2,6-25 diisopropylphenyl)-9-(2,6-diisopropylphenoxy)perylene-3,4-dicarbonic acid imide, N- (2,6-diisopropylphenyl)-9-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 -30 3,10-dicarbonic acid di(2,6- diisopropylphenyl)amide.

Perylene dyes usually absorb radiation in the wavelength region of 360 to 630 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 9 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).

Other examples of suitable organic luminescence downshifting 5 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 acid diimides, and especially naphthalene-10 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 N-(2-ethylhexyl)-4,5-dimethoxynaphthalene-1,8-dicarbonic acid imide, N- (2,6-diisopropyl-phenyl)-4,5-dimethoxynaphthalene-1,8-dicarbonic acid 15 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 20 diimide.

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 25 nm and have an emission spectrum with a maximum around 365 up to 400 nm: diphenyloxazole (2,5- 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.

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

For example the following organic luminescence downshifting compounds are capable of re-emitting the incoming radiation emission 10 towards 560nm: hostasole 3G naphtalimide (Clariant), Lumogen F Yellow 083 (BASF), Rhodamine 110 (Lambdachrome 5700).

For example the following organic luminescence downshifting compounds are capable of re-emitting the incoming radiation emission 5 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 capable of re-emitting the incoming radiation emission 10 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: Rhodamine 800 (Sigma), Pyridine 2 (Lambdachrome 15 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 nanoparticles comprising ZnO; ZnS doped with Mg, Cu, and/or F; 20 CdSe; CdS; Ti02; Zr3+, Zr4+; 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, more in particular they may have a size 25 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 et al, Chem. Commun., 2009, 6649-6651 by the Royal Society of Chemistry 2009.

30 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 11 etc. The moluculair sieves are selected from the group consisting of zeolites, porous oxides, silicoaluminophosphates, aluminophosphates, gallophosphates, zincophophates, titanosilicates and aluminosilicates, or mixtures thereof. In a particular embodiment of present invention the 5 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 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 10 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.

The concentration of the luminescence downshifting compound in the polymer layer will depend on the chosen luminescence downshifting 15 compound. Some compounds are more effective and will require a lower concentration in the polymer 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 20 compound. The polymer layer may comprise a single luminescence downshifting compound. Preferably the polymer layer comprises two or more different luminescence downshifting compounds, wherein the compounds are chosen to form a cascade. The cascade is defined in that a compound in the cascade reemits radiation in a wavelength range at which a next compound 25 absorbs radiation. Such a cascade is also referred to as a Photon-Absorption-Emitting Chain (PAEC).

An example of a possible cascade may comprise a first luminescence downshifting compound with an absorption range located at approximately 280 nm tot 365 nm and with an emission range located at approximately 380 30 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% of the total content of 12 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 5 downshifting compound is 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 10 downshifting compound of the cascade may have an absorption range 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 15 concentration of for example around 33% of the total content of luminescence downshifting compounds in the 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 20 volume. A polymer layer of approximately 400 to 450 microns may for example be doped with the constituting 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 25 downshifting compounds of approximately 500 ppm in the final polymer layer.

More than one layer of polymer may be present between the two layers of glass. In a preferred embodiment two or more layers of polymer are present, wherein each layer comprises a different luminescence downshifting compound or a different mixture of luminescence downshifting compound.

30 This will result in that each polymer layer will be able to absorb radiation at a different wavelength and re-emitting radiation at a different longer wavelength as compared to the next polymer layer. Preferably a combination of luminescence downshifting compounds are used which result in the above referred to luminescence downshifting "cascade". More preferably the polymer 13 layers comprise luminescence downshifting compounds able to absorb radiation at a first wavelength and re-emitting radiation at a second longer wavelength, wherein the first and second wavelength at which radiation is absorbed and re-emitted increases per polymer layer in the main direction of 5 incoming radiation. The polymer layers are preferably stacked in and immobilsed such that the luminescence downshifting compounds remain in their respective layer in the final glass element.

Preferably the polymer layer comprises two or more, suitably 2-12 coextruded polymer sub-layers. Such a multi-layer is preferably made by 10 simultaneously coextruding and orienting a film composed of the different sublayers. The polymers used for the different sub-layers may be different provided that the difference in Melt Flow Index of the polymers at the conditions of coextruding is less than 5 points and preferably less than 3 points. If different polymers having a very different MFI at standard conditions 15 are combined it is preferred to adjust the extrusion temperature of the polymers such that the MFI at the conditions of coextruding are within the above described ranges.

Coextrusion is well known process to the skilled person and utilizes two or more extruders to melt and deliver a steady volumetric throughput of 20 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.

The different polymer sub-layers of the polymer layer may comprise 25 different additives and/or different luminescence downshifting compounds.

This is advantageous because combinations of additives and/or luminescence downshifting compounds can be used which are not optimal compatible with another. Further one may chose a polymer for a sub-layer which is better compatible with an additive or certain luminescence downshifting compound 30 than a polymer chosen for another sub-layer.

Suitably the two outer sub-layers facing the glass layers comprise a silane coupling agent, wherein the silane coupling agent may be as described above. One of the outer sub-layers or a next sub-layer may comprise a luminescence downshifting compound which can absorb, at least partially, UV

14 radiation, suitably between 10 and 400 nm, and re-emit radiation at a higher wavelength, optionally by means of a cascade. The presence of such compounds is advantageous because it enables one to use UV radiation sensible luminescence downshifting compound or compounds in a next or 5 further sub-layer. When the polymer is EVA a further advantage is apparent. EVA is typically protected by UV stabilisers. The invention provides for that no or considerably less UV stabilizer is required. The use of these UV stabilisers reduces the efficiency of transmitting radiation, because instead of transmitting UV radiation UV radiation is converted to heat. By using a 10 luminescent downshifting compound which can absorb radiation in the UV wavelength range and emit at a higher wavelength range the UV light is converted into radiation which is less harmful for the polymer. Thus radiation is allowed to pass the glass element. By shifting the wavelength to a longer wavelength the quality of the radiation which passes the glass element may 15 further be improved. This is especially favorable when the glass element is used in combination with a photovoltaic cell in a process to generate electricity.

As explained above UV stabilizer are preferably avoided and instead a suitable luminescent downshifting compound is comprised in the polymer layer. Optionally UV stabilizer may be present, for example when a solar 20 panel does not comprise luminescent downshifting compounds, or in small quantities. Examples of typical UV stabilizer, which cannot be considered to be luminescent downshifting compounds, are benzotriazoles, hydroxybenzo-phenones, hydroxyphenyl triazines, esters of substituted and unsubstituted benzoic acids, and the like and mixtures thereof. The EVA copolymer may 25 contain any effective amount of UV stabilizer. When UV stabilizer are typically utilized, the EVA copolymer contains at least about 0.05 wt%, and up to about 10 wt%, more preferably up to about 5 wt%, and most preferably up to about 1 wt%, of UV stabilizer, based on the total weight of the EVA copolymer. When a luminescent downshifting compound which can absorb UV radiation is 30 comprised in the polymer layer the content of UV stabilizer is suitably less than 0.05 wt%.

Preferably a cascade of luminescence downshifting compounds is present in at least one of the coextruded polymer sub-layers, wherein the one 15 or more different luminescence downshifting compounds present in a first layer will absorb radiation at a lower wavelength that the or more different luminescence downshifting compounds present in a next layer. The compounds forming the cascade may be present in one or more of the sub-5 layers of the polymer layer.

The glass element may be used for various applications wherein it is desired to filter radiation having a short wavelength and being transparent for radiation having a longer wavelength. A preferred use is wherein the glass element is used for changing the properties of sun light and wherein the thus 10 obtained adapted sunlight as it has passed the glass element is used to grow plants or more generally wherein the adapted sunlight is used in a photosynthesis process. The invention is also directed to a building, like a green house, having a roof comprising a glass element according to the invention.

15 Another preferred use of the glass element is for changing the properties of sun light in a process of generating electricity. More preferably the process for generating electricity involves a photovoltaic cell (photovoltaic cell) which is capable of generating an electrical current using the adapted sun light. The photovoltaic cell is suitably positioned near of adjacent the glass element, 20 suitably fixed to the glass element. Many photovoltaic cells have a poor spectral response to the shorter wavelengths, for example the radiation in the UV range. By absorbing radiation in the shorter wavelength area and reemitting at the longer wavelength, optionally by means of a cascade as described above, it is possible to effectively make use of the energy 25 comprised in the radiation having these shorter wavelength in the form of radiation having a higher wavelength at which the photovoltaic cell have their optimal photovoltaic performance. The optimal photovoltaic performance of a photovoltaic cell will be different for each type of photovoltaic cell. Indeed, different Internal Quantum Efficiency (IQE) plots are obtained over a 30 wavelength range from 300 up to 1100 for cSi screen printed cells, depending on the type of cSi cell, the surface texture and cell surface treatment.

The glass layer between de polymer layer comprising the luminescence downshifting compound and the photovoltaic cell will provide a barrier against compounds being transported from the polymer layer to the photovoltaic cell 16 or from the photovoltaic cell to the polymer layer. A solar panel will be used for many years and during its lifetime luminescence downshifting compounds or other additives present in the polymer layer may decompose into fragments which may be harmful for the photovoltaic cell. Examples of such elements or 5 compounds are amines, chlorides, sodium and sulphur containing compounds. The glass layer will avoid that such compounds can migrate and reach the photovoltaic cell and thus provide a longer lifetime of the photovoltaic cell itself. The glass element thus provides the use of organic luminescence downshifting compounds, which may decompose into these harmful 10 fragments, in combination with a photovoltaic cell. Furthermore compounds may migrate from the photovoltaic cell towards the polymer layer which may result in degradation of the polymer and/or the luminescence downshifting compounds. The glass layer effectively avoids such migration.

The photovoltaic cell may comprise at least one of the following 15 materials: CdS, CdTe; Si, preferably p-doped Si or crystalline Si or amorphous Si or multicrystalline Si or multiple junction Si; InP; GaAs; Cu2S; Copper Indium Gallium Diselenide (CIGS). A solar panel may be prepared by stacking the different layers of the glass element and the photovoltaic cell, additional encapsulant layer or layers and a backsheet layer and subjecting the formed 20 stack to a lamination process step. In this manner the glass element is formed simultaneously with the formation of the solar cell itself.

A preferred photovoltaic cell is a thin film cadmium telluride (CdTe) photovoltaic cell. This type of photovoltaic cell shows an optimal photovoltaic effect at a wavelength of between 500 and 800 nm. By combining such a PV 25 cell with the glass element according to the invention it is found possible to more effectively make use of the lower wavelength radiation of sunlight. The one or more luminescence downshifting compounds present in the glass element will absorb the lower wavelength radiation and reemit at the above wavelength range at which the CdTe photovoltaic cell exhibits maximum IQE. 30 Preferably a luminescence downshifting compound or compounds or a cascade of luminescence downshifting compounds will be present in the polymer layer of the glass element which will absorb radiation at a wavelength below 500 nm and reemit radiation at a wavelength between 500 and 800 nm.

17

Preferably the earlier described luminescence downshifting cascade is present in the glass element.

The invention is thus also directed to a CdTe photovoltaic solar cell comprising the glass element according to the invention, (a) a transparent 5 electrode layer, (b) an n-type semiconductor layer, (c) an absorber, cadmium telluride (CdTe), and (d) a back contact. Layers (a)-(d) are deposited sequentially on the glass element according the invention. The glass element preferably is provided with the above described anti reflective coating at one side and with the above layers at its opposite side. Preferably the glass layer 10 provided with the anti-reflective coating is thicker than the glass layer facing the layers (a)-(d).

The transparent electrode layer (a) may for example be comprised of tin oxide (Sn02) or a doped tin oxide, for example fluorine-, zinc or cadmium doped tin oxed, indium-tin oxide (ITO), zinc oxide (ZnO), and cadmium 15 stannate (Cd2Sn04). For example, the buffer layer 205 may be formed to a thickness of up to about 1.5 microns or about 0.8-1.5 microns and may include ZnO and Sn02 in about a one to two (1:2) stoichiometric ratio. Preferably tin oxide is used.

The n-type semiconductor layer (b) may be CdS, Sn02, CdO, ZnO, 20 AnSe, GaN, In202, CdSnO, ZnS, CdZnS or other suitable n-type semiconductor material and preferably CdS. Layer (b) may be formed by chemical bath deposition or by sputtering and may have a thickness from about 0.01 to about 0.1 pm.

The cadmium terruride (CdTe) layer (c) may be applied by screen 25 printing, spraying, close-spaced sublimation, electro-deposition, vapor transport deposition, sputtering, and evaporation.

The back contact layer may be any suitable conductive material and combinations thereof. For example, suitable materials include materials including, but not limited to, graphite, metallic silver, nickel, copper, aluminum, 30 titanium, palladium, chrome, molybdenum alloys of metallic silver, nickel, copper, aluminum, titanium, palladium, chrome, and molybdenum and any combination thereof. Suitably the back contact layer (d) is a combination of graphite, nickel and aluminium alloys.

18

The layers (a)-(d) may be encapsulated by a further glass layer (e). Encapsulating glass layer (e) may be a rigid structure suitable for use with the CdTe photovoltaic cell. The encapsulating glass layer (e) may be the same material as the glass used in the glass element or may be different. In addition 5 encapsulating glass layer (e) may include openings or structures to permit wiring and/or connection to the CdTe photovoltaic cell.

Applying the above layers to the glass element according to the invention to obtain the preferred CdTe photovoltaic solar cell may be performed by the numerous methods known in the art. Examples of such 10 methods and variations in the different layers are described in US-A- 2011/0308593, EP-A-2430648, US-A-2012073649, US-A-2011259424 and the like.

The glass element may also be combined with wafer-based photovoltaic cells based on monocrystalline silicon (c-Si), poly- or multi-crystalline silicon 15 (poly-Si or mc-Si) and ribbon silicon. Preferably the solar cell comprising such a wafer-based PV cell will comprise the glass element according to the invention as front facing in use the incoming radiation, a polymer layer, a layer comprising a wafer-based PV cell and a back sheet layer.

The back sheet layer may be a multilayered film, typically comprising at 20 least three layers which may be prepared from different polymeric materials.

The back sheet layer preferably comprises a so-called white reflector. The presence of a white reflector is advantageous because it will reflect radiation to the photovoltaic cell and thus improve the efficiency of the cell.

Possible backsheet layers comprise fluoropolymer layers. Instead of a 25 fluoropolymer layer a second glass sheet may be provided at the back of the solar cell. This will provide a solar cell which has a glass front and backside. The glass layer for use as backside will preferably have a thickness of less than 3 mm. The glass layers may be as described above. The use of a glass front and backside is advantageous because it provides a structural strength 30 to the panel such that no aluminium frame is necessary. The glass backside will also provide an absolute barrier towards water ingress and the like which is advantageous for extending the life time of the panel. The use of the glass layer will make it possible to avoid the use of a back sheet comprising a fluoropolymer.

19

The glass element according to the invention may be prepared by subjecting a stack of a first glass layer, the polymer layer and the second glass layer is made to a thermal lamination process. In such a process the polymer layer will become more fluid and connect to the glass layers while 5 any gas is forced away from the stack by applying a vacuum.

Claims (19)

An element comprising two layers of glass, wherein a transparent polymer layer is present between the two layers of glass, and wherein the polymer layer comprises at least one luminescent "downshifting" connection for at least partially absorbing radiation of a certain wavelength, and the retransmitting radiation with a longer wavelength than the wavelength of the absorbed radiation. The element of claim 1, wherein the polymer is 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 polydoxides, polydimiles, polydimiles is mixtures thereof. 15 The element of claim 2, wherein the polymer is ethylene vinyl acetate (EVA), polyvinyl butyral (PVB), silicone, polymetyl methacrylate (PMMA), or alkyl acrylate copolymers. The element of claim 2, wherein the polymer is an ethylene vinyl acetate with an acetate content of 12% to 45% by weight. The element of any one of claims 1-4, wherein the glass of the glass layers is a borosilicate glass or a sodium lime glass. 25 The element of any one of claims 1-5, wherein the total thickness of the glass element is less than 5 mm. 7. Element as claimed in any of the claims 1-6, wherein at least one of the glass layers has a thickness that is between 0.1 and 2 mm. The element of claim 7, wherein one of the glass layers has a thickness that is between 0.1 and 4 mm, while the other glass layer has a thickness that is between 0.1 and 2 mm. 5 The element of any one of claims 1-8, wherein at least one glass layer has a surface that is not directed towards the polymer layer and that is covered with an anti-reflective coating. The element of any one of claims 1-9, wherein at least one glass layer has a relief surface that is not facing the polymer layer. 11. Element as claimed in any of the claims 1-10, wherein the polymer layer comprises two or more different luminescent "downshifting" connections, wherein the connections are selected in such a way that they form a cascade, and wherein the cascade is defined by a connection in the cascade re-emits radiation in a wavelength range in which the following compound absorbs radiation. The element of any one of claims 1-11, wherein the polymer layer comprises at least two co-extruded polymer layers, and wherein the one or more different luminescent "downshifting" compounds present in a first layer will absorb radiation with a wavelength that is lower than the one or more luminescent "downshifting" connections that are present in a subsequent layer. 25 The element of claim 12, wherein the two outer layers facing the glass layers comprise a silane binding agent. 14. Use of the element according to any of claims 1-13, for changing the properties of sunlight in a method for growing plants. Use of the element according to any of claims 1-13, for changing the properties of sunlight in a method for generating electricity. A building with a roof comprising an element according to any one of claims 1-13. A photovoltaic module comprising a layer which in turn comprises a photovoltaic cell, as well as a cover layer comprising the element according to any one of claims 1-13. The photovoltaic module of claim 17, wherein the photovoltaic cell is a thin film cadmium telluride photovoltaic cell. A photovoltaic solar cell comprising the glass element according to any one of claims 1-13, as well as (a) a transparent electrode layer, (b) a semiconductor layer of the n-15 type, (c) a cadmium telluride-absorbing layer, and ( d) a contact layer.