WO2010054908A1

WO2010054908A1 - Production of solar cell modules

Info

Publication number: WO2010054908A1
Application number: PCT/EP2009/063441
Authority: WO
Inventors: Peter Battenhausen; Ernst Becker; Klaus Schultes; Sven Strohkark
Original assignee: Evonik Röhm Gmbh
Priority date: 2008-11-13
Filing date: 2009-10-15
Publication date: 2010-05-20
Also published as: DE102008043707A1; TW201031704A

Abstract

The invention relates to the use of a) at least one polyalkyl(meth)acrylate and b) at least one compound of the common formula of formula (I), where R is an optionally substituted alkyl, cycloalkyl, aralkyl or aryl group and the ring A may comprise further substituents, for the production of solar cell modules, particularly for the production of light concentrators for solar cell modules.

Description

Production of solar cell modules

The present invention relates to the production of solar cell modules and the corresponding solar cell modules.

STATE OF THE ART

A solar cell or photovoltaic cell is an electrical component that converts the radiation energy contained in the light, especially in sunlight, directly into electrical energy. The physical basis of the transformation is the photovoltaic effect, which is a special case of the internal photoelectric effect.

Fig. 3 is a schematic cross section showing the basic structure of a solar cell module. In Fig. 3, 501 denotes a photovoltaic element, 502 a solidifying agent, 503 a disc, and 504 a rear wall. Sunlight is irradiated on the photosensitive surface of the photovoltaic element 501 by penetrating the disk 503 and the solidifying agent 502, and is converted into electric energy. The generated current is output from output terminals (not shown).

The photovoltaic element can not withstand extreme external conditions because it is easily corroded and very fragile. It must therefore be covered and protected by a suitable material. In most cases, this is accomplished by placing the photovoltaic element between a transparent weather-resistant sheet, such as a glass sheet, using a suitable solidifying agent. a glass sheet, and a back wall having excellent moisture resistance and a high electrical resistance and laminated.

As solidifying agents for solar cells, polyvinyl butyral and ethylene-vinyl acetate copolymers (EVA) are often used. In particular, crosslinkable EVA Compositions excellent properties, such as a good heat resistance, high weather resistance, high transparency and cost efficiency.

The solar cell module is said to have a high durability because it is to be used outside for a long time. Consequently, the solidifying agent u. a. have an excellent weather resistance and a high heat resistance. However, light-induced and / or thermally-induced degradation of the solidifying agent and, as a result, yellowing of the solidifying agent and / or peeling off of the photovoltaic element are frequently observed when the module is left for a long time, e.g. ten years, used outside. The yellow discoloration of the solidifying agent leads to a decrease in the usable portion of the incident light and consequently to a lower electrical power. On the other hand, peeling off of the photovoltaic element allows the penetration of moisture, which can lead to corrosion of the photovoltaic element itself or of metallic parts in the solar cell module and also results in a deterioration of the solar cell module performance.

Although the commonly used EVAs per se are good solidifying agents, they are gradually degraded by hydrolysis and / or pyrolysis. Over time, heat or moisture releases acetic acid. This leads to a yellow discoloration of the solidifying agent, a decrease in the mechanical strength and a decrease in the adhesive strength of the solidifying agent. Furthermore, the liberated acetic acid acts as a catalyst and accelerates the degradation in addition. In addition, there is a problem that the photovoltaic element and / or other metal parts in the solar cell module are corroded by the acetic acid.

To solve these problems, European patent application EP 1 065 731 A2 proposes the use of a solar cell module comprising a photovoltaic element and a polymeric solidifying agent, wherein the polymeric solidifying agent comprises Ethylene-acrylic ester-acrylic acid terpolymer, an ethylene-acrylic ester-maleic anhydride terpolymer, an ethylene-methacrylic ester-acrylic ester terpolymer, an ethylene-acrylic acid ester-methacrylic acid terpolymer, an ethylene-methacrylic acid ester-methacrylic acid terpolymer, and / or an ethylene-methacrylic acid ester -Maleinsäureanhydrid terpolymer should contain. However, both the weatherability and the effectiveness of such solar cell modules is limited.

From the prior art, the improvement of the weather resistance of acrylic molding compositions by the use of suitable UV absorbers is known.

For example, German Patent DE 18 01 221 B1 teaches the use of compounds of the formula (I)

as a UV absorber for polymers. The remainder should be arranged in the m- or p-position to the already existing group on the ring A. Furthermore, ring A may be substituted by one or more halogen atoms, alkyl or methoxy groups. The radical R is an optionally substituted alkyl, cycloalkyl, aralkyl or aryl radical.

The use in polyacrylates is mentioned as an option. However, references to the use of the molding compositions for the production of solar cell modules are not to be found in the document.

WO 2008/025738 describes the use of a composition containing two UV absorbers for the protection of organic substrates, in particular of organic polymers, against degradation due to environmental influences, such as yellowing, loss of transparency and gloss reduction. Benzylidenebismalonate of above formula (I), in particular Hostavin® B-CAP, a substituted in para-position Benzylidenbismalonat of formula (I) without further substituents with R = ethyl, are used in this context as a UV absorber.

The use of the composition for ethylene alkyl acrylate copolymers, ethylene alkyl methacrylate copolymers and ethylene acrylic acid copolymers is mentioned as a possibility. However, references to the use of the molding compositions for the production of solar cell modules are not to be found in the document.

US 6,433,044 B1 discloses a methyl methacrylate resin composition comprising methyl methacrylate resin and a 2- (1-arylalkylidene) -malonic acid ester in an amount ranging from 0.0005 to 0.1 parts by weight per 100 parts by weight of methyl methacrylate resin ,

The resin composition is intended to be used in particular for the production of light guides. However, references to the use of the molding compositions for the production of solar cell modules are not to be found in the document.

JP 2005-298748 A provides moldings of a methacrylic resin which preferably comprises 100 parts by weight of methacrylic resin comprising 60-100% by weight of meth-methacrylate units and 0-40% by weight of other copolymerizable vinyl monomer units, and 0.005-0.15% by weight % 2- (2-hydroxy-4-n-octyloxyphenyl) -4,6-bis (2,4-dimethylphenyl) -1, 3,5-thazine and / or 2-hydroxy-4-octyloxybenzophenone. The moldings are said to have a marked barrier to UV rays and to exhibit a transparency of at most 20% at 340 nm and a transparency of at least 70% at 380 nm, measured on moldings having a thickness in the range of 0.5 to 5 mm.

The moldings are to be used in particular as lighting covers. However, references to the use of the molded parts for the production of solar cell modules can not be found in the publication. SUMMARY OF THE INVENTION

It is therefore an object of the present invention to identify ways to reduce the power loss of a solar cell during long-term use outdoors, especially at high temperature and / or high humidity. For this purpose, in particular, ways were sought to achieve excellent weather resistance, the highest possible heat resistance and the greatest possible light transmittance and the lowest possible water absorption. Furthermore, the lowest possible release of corrosion-promoting substances, in particular of acids, and the strongest possible adhesion to the various basic elements of a solar cell module were desired.

These and other non-specific tasks, which arise from the contexts discussed in the introduction, however, in a manner lying close are achieved by the use of a molding compound having all the features of the present patent claim 1. The dependent claims on claim 1 describe particularly useful variants of the invention. Furthermore, the corresponding solar cell modules are placed under protection.

In that a) at least one polyalkyl (meth) acrylate and b) at least one compound of the general formula of the formula (I)

in which R is an optionally substituted alkyl, cycloalkyl, aralkyl or aryl radical and the ring A may have further substituents, for the production of solar cell modules, in particular for the production of light concentrators for solar cell modules, succeeds in not easily foreseeable way, a performance degradation of a solar cell for long-term use outdoors, especially at high temperature and / or high humidity to prevent as possible. In particular, excellent weatherability, very high heat resistance, and very high light transmittance, and extremely low water absorption are achieved. Furthermore, no corrosion-promoting substances are released even in long-term outdoor use and it is achieved a very strong adhesion to the various basic elements of a solar cell module.

The solution presented here allows the efficient use of "usable" light in the visible wavelength range, while effectively absorbing other wavelength ranges, especially in the UV range, which can not be used to generate electricity, which increases the weatherability of the solar cell modules Furthermore, the absorption prevents a disadvantageous heating of the light collectors without having to use cooling elements for this purpose, the life of the solar cell modules is extended and their overall performance and effectiveness are increased.

The procedure according to the invention gives rise in particular to the following advantages:

A solar cell module having excellent weather resistance, heat resistance and moisture resistance is made available. No peeling occurs even if the module is exposed to outdoor conditions for a long time. Furthermore, the weather resistance is improved because no acid is released even at high temperatures and high humidity. Since no corrosion of the photovoltaic element by acid occurs, stable long-term performance of the solar cell is maintained. Furthermore, materials are used whose weatherability, heat resistance and moisture resistance are outstanding and which have excellent light transmission, which enables the production of very good solar cell modules.

DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic cross section of a preferred solar cell module according to the present invention.

Figs. 2a and 2b are schematic cross sections showing the basic structure of a photovoltaic element which is preferably used in the solar cell module of Fig. 1 and a plan view of the photosensitive surface of the photovoltaic element, respectively.

Fig. 3 is a schematic cross section of a conventional solar cell.

reference numeral

FIG. 1

101 photovoltaic element

102 solidifying agent

103 disc

104 solidifying agent

105 rear wall

FIG. 2a

201 conductive substrate

202 reflective layer

203 photoactive semiconductor layer

204 transparent conductive layer

205 collecting electrode 206a alligator clip 206b alligator clip

207 conductive, adhesive paste

208 conductive paste or solder

FIG. 2b

201 conductive substrate

202 reflective layer

203 photoactive semiconductor layer

204 transparent conductive layer

205 Collecting electrode 206a Alligator clip 206b Alligator clip

207 conductive, adhesive pastes

FIG. 3

501 photovoltaic element

502 solidifying agent

503 disc

504 rear wall

DETAILED DESCRIPTION OF THE INVENTION

In the context of the present invention, a) at least one polyalkyl (meth) acrylate and b) at least one compound of the general formula of the formula (I) are used for the production of solar cell modules. These components may together in a composition, for. B. in a mixture in a molding composition, for producing a common element, such as. As a molding, the solar cell module can be used. But it is also possible that they are each used separately for the production of various individual elements of a solar cell module.

The polyalkyl (meth) acrylate can be used individually or in a mixture of several different polyalkyl (meth) acrylates. Furthermore, the polyalkyl (meth) acrylate may also be in the form of a copolymer.

In the context of the present invention, homopolymers and copolymers of C 1 -C 18 -alkyl (meth) acrylates, advantageously of C 1 -C 10 -alkyl (meth) acrylates, in particular of C 1 -C ₄ -alkyl (meth) acrylate polymers, which may still be present thereof may contain various monomer units, more preferably.

The notation (meth) acrylate here means both methacrylate, such as. As methyl methacrylate, ethyl methacrylate, etc., as well as acrylate, such as. As methyl acrylate, ethyl acrylate, etc., as well as mixtures of both monomers.

The use of copolymers containing 70 wt .-% to 99 wt .-%, in particular 70 wt .-% to 90 wt .-%, Ci-Cio-alkyl (meth) acrylates, has proven particularly useful. Preferred C 1 -C 10 -alkyl methacrylates include methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, Heptyl methacrylate, octyl methacrylate, isooctyl methacrylate and ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate and cycloalkyl methacrylates such as cyclohexyl methacrylate, isobornyl methacrylate or ethylcyclohexl methacrylate. Preferred C 1-8 -alkyl acrylates include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, isooctyl acrylate, nonyl acrylate, decyl acrylate and ethylhexyl acrylate, as well as cycloalkyl acrylates such as cyclohexyl acrylate, isobornyl acrylate or Ethycyclohexlacrylat.

Very particularly preferred copolymers comprise 80% by weight to 99% by weight of methyl methacrylate (MMA) units and 1% by weight to 20% by weight, preferably 1% by weight to 5% by weight, of do-alkyl acrylate units, especially methyl acrylate, ethyl acrylate, and / or butyl acrylate units. The use of the polymethyl methacrylate available from Rohm GmbH PLEXIGLAS ^® 7N has proven itself in this context in particular.

The polyalkyl (meth) acrylate can be prepared by polymerization methods known per se, free radical polymerization processes, in particular, bulk, solution, suspension and emulsion polymerization processes being particularly preferred. Particularly suitable for this purpose initiators include in particular azo compounds, such as 2,2'-azobis (isobutyronitrile) or 2,2'-azobis (2,4-dimethylvaleronitrile), redox systems, such as the combination of tertiary amines with peroxides or Nathium disulfite and persulfates of potassium, sodium or ammonium or preferably peroxides (cf., for example, H. Rauch-Puntigam, Th. Völker, "Acrylic and Methacrylic Compounds", Springer, Heidelberg, 1967 or Kirk-Othmer, Encyclopedia of Chemical Technology, Vol 1, pp. 386ff, J. Wiley, New York, 1978). Examples of particularly suitable peroxide polymerization initiators are dilauroyl peroxide, tert-butyl peroctoate, tert-butyl phesononanoate, dicyclohexyl peroxydicarbonate, dibenzoyl peroxide and 2,2-bis (tert-butylperoxy) butane. It is also preferable to carry out the polymerization with a mixture of different polymerization initiators having a different half-life, for example Dilauroyl peroxide and 2,2-bis- (tert-butylperoxy) -butane to keep the radical flow constant during the course of the polymerization and at different polymerization temperatures. The amounts of polymerization initiator used are generally from 0.01% by weight to 2% by weight, based on the monomer mixture.

The polymerization can be carried out both continuously and batchwise. After polymerization, the polymer is removed via conventional isolation and separation steps, such. As filtration, coagulation and spray drying, won.

The adjustment of the chain lengths of the polymers or copolymers can be carried out by polymerization of the monomer or monomer mixture in the presence of molecular weight regulators, in particular of the known mercaptans, for example n-butyl mercaptan, n-dodecyl mercaptan, 2-mercaptoethanol or 2-ethylhexyl thioglycolate, pentaerythritol tetrathioglycolate; wherein the molecular weight regulator generally in amounts of 0.05 wt .-% to 5 wt .-% based on the monomer or monomer mixture, preferably in amounts of 0.1 wt .-% to 2 wt .-%, and particularly preferably in amounts from 0.2% by weight to 1% by weight, based on the monomer or monomer mixture (cf., for example, H. Rauch-Puntigam, Th. Völker, "Acrylic and Methacrylic Compounds", Springer, Heidelberg, 1967 Houben-Weyl, Methods of Organic Chemistry, Vol. XIV / 1, page 66, Georg Thieme, Heidelberg, 1961 or Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 1, pp. 296ff, J. Wiley, New York, 1978 ). Particular preference is given to using n-dodecylmercaptan as molecular weight regulator.

In the context of the present invention, at least one compound of the general formula of the formula (I) is furthermore used to prepare the solar cell modules

in which R is an optionally substituted alkyl, cycloalkyl, aralkyl or aryl radical and the ring A may have further substituents.

The radicals R may be the same or different.

Suitable radicals R are especially methyl, ethyl, propyl, dodecyl, cyclohexyl, benzyl, phenyl and optionally substituted by halogen, alkyl and alkoxy phenyl radicals. Particular preference is given to alkyl groups having 1 to 18 carbon atoms and cycloalkyl groups having 1 to 18 carbon atoms, in particular radicals having 1 to 8 carbon atoms, preferably having 1 to 4 carbon atoms, in particular methyl groups and ethyl groups. Ethyl groups are most preferred.

Suitable substituents for A are, for example, halogen or alkyl. In a particularly preferred variant of the invention, the ring has no further substituents except hydrogen.

Preferred compounds of the framework of the formula (I) are those of the formula (II)

and the formula

wherein the radicals R 'have the same meaning as before and preferably represent a non-substituted alkyl radical having 1-20 carbon atoms, a cyclohexyl, benzyl or phenyl radical. Particular preference is given to compounds of the formula (II) in which R ', in each case independently of one another, is ethyl, n-dodecyl, cyclohexyl, benzyl or phenyl, in particular ethyl.

The compounds of the formula (I) can be prepared, for example, by condensation of dialdehydes of the formula (IV)

wherein the ring A may optionally have further substituents, with malonic esters of the formula (V)

O O

Il

ROC-CH ₂ -COR

(Behavior.

Suitable aldehydes of the formula (IV) are, in particular, terephthalaldehyde, isophthalaldehyde, 2-chloroterephthalaldehyde, 2-fluoroterephthalaldehyde, 2-methylterephthalaldehyde, 2,2-dichloroterephthalaldehyde, 2,5-dichloroterephthalaldehyde, 2,5-diethylterephthalaldehyde, tetramethylterephthalaldehyde, 2,5- Dimethoxyterephthalaldehyde, 4-methoxyisophthalaldehyde, 5-methylisophthalaldehyde and tetramethylisophthalaldehyde.

Suitable malonic acid esters of the formula (V) are in particular diethyl malonate, dodecyl malonate, dibenzyl malonate, dimethyl malonate, methyl malonate, diethyl malonate, methyl malonate, malonyl dipropylate, malonic acid di- (3-chloropropyl) ester, diisopropyl malonate, dibutyl malonate, malonic acid di-sec di-butyl ester, diisobutyl malonate, malonic acid di-tert-butyl ester, malonic acid dipentyl ester, diisyl malonate, dioctyl malonate, dinonyl malonate, malonic acid dodecyl ester, dodecyl malonate, dioctadecyl malonic acid ester and methyl malonate.

In the context of the present invention, it may be helpful to additionally use adjuvants which are well known to the person skilled in the art. Preference is given to external lubricants, antioxidants, flame retardants, other UV stabilizers, flow aids, metal additives for shielding electromagnetic radiation, antistatic agents, mold release agents, dyes, pigments, adhesion promoters, weathering inhibitors, plasticizers, fillers and the like.

In a particularly preferred embodiment of the present invention, at least one hindered amine is used, thereby further improving the weather resistance. Yellow discoloration or degradation of materials exposed to outdoor conditions for a long time can be further reduced.

Particularly preferred hindered amines include dimethyl succinate 1 - (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperazine polycondensate, poly [{6- (1,1,3,3-tetramethylbutyl) amino] 1, 3,5-triazine-2,4, -diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-piperedyl) imino} ], N, N'-bis (3 aminopropyl) ethylenediannine-2,4-bis [N-butyl-N- (1,2,6,6-pentanoethyl-4-piperidyl) amino] -6-chloro-1,3,5-triazine condensate, bis ( 2,2,6,6-tetramethyl-4-piperidyl) sebacate and 2- (3,5-di-t-4-hydroxybenzyl) -2-n-butylmalonate bis (1,2,2,6,6-pentamethyl 4-piperidyl).

Furthermore, the use of Silanhaftvermittlern or organic titanium compound has proven particularly useful, whereby the adhesion to inorganic materials is further improved.

Suitable silane coupling agents include vinyltrichlorosilane, vinyltris (β-methoxyethoxy) silane, vinyltriethoxysilane, vinyltrimethoxysilane, Y-methacryloxypropylthmethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrinnethoxysilane, N-.beta.-amino (aminoethyl) -γ-aminopropylmethyldimethoxysilane, .gamma.-aminopropylthethoxysilane, N-phenyl-.gamma.-aminopropyltrimethoxysilane, .gamma.-mercaptopropyltrimethoxysilane, and .alpha.-chloropropylmethoxysilane.

The relative proportions of the polyalkyl (meth) acrylate and the compound of the general formula (I) can in principle be chosen freely.

Appropriately, they are present in a common molding material. Particularly preferred molding compositions comprise, in each case based on their total weight, a) 90% by weight to 99.99% by weight of polyalkyl (meth) acrylate and b) 0.01% by weight to 0.4% by weight of compound the general formula (I).

The incorporation of the compounds into a common molding composition can be carried out by the processes known from the literature, for example by mixing with the polymer before further processing at a higher temperature, by adding it to the melt of the polymer or by adding it to suspended or dissolved polymer during its processing. If appropriate, they can also already be added to the starting materials for the preparation of the polymer and also lose their weight in Presence of other conventional light and heat stabilizers, oxidizing and reducing agents and the like does not improve their absorbency.

A particularly preferred for the purposes of the present invention, the molding composition has a softening temperature of not less than 80 ⁰ C (Vicat softening point VSP (ISO 306-B50)). It is therefore particularly suitable as a solidifying agent for solar cell modules, since it does not begin to creep, even if the module is exposed to high temperatures in use.

Also particularly advantageous are molding compositions which have a comparatively high total light transmittance and thus prevent, in particular in the application of the molding compound as solidification agent in solar cell modules, a power loss of the solar cell, which could be due to optical loss of the solidifying agent. Over the wavelength range from 400 nm to less than 500 nm, the total light transmittance is preferably at least 90%. Over the wavelength range from 500 nm to less than 1000 nm, the total light transmittance is preferably at least 80% (measurement using the spectral photometer Lambda 19 from Perkin Elmer).

Furthermore, molding compounds are also advantageous, which have a discharge resistance of 1 to 500 kΩ xx ccmm ²² for the avoidance of the leakage of the solar cell due to short-circuits, as far as possible.

Molding compounds which contain the constituents mentioned are particularly suitable as solidifying agents for solar cell modules. Furthermore, they are preferably used for the production of so-called light concentrators. These are components that concentrate light with high efficiency on the smallest possible area, thus achieving high irradiance. It is not necessary to create an image of the light source. For the purposes of the present invention, particularly advantageous light concentrators are converging lenses that collect light incident in parallel and focus it in the focal plane. In particular, the light incident parallel to the optical axis is focused at the focal point.

Compound lenses may be biconvex (arched on both sides), plano-convex (1 side plan, 1 side convex) or concave-convex (1 side arched inside, 1 side arched outward, the convex side being preferably more curved than the concave one) , Conveying lenses which are particularly preferred according to the invention comprise at least one convex region, plano-convex structures having proven to be particularly advantageous.

In the context of a particularly preferred embodiment of the present invention, the light concentrators have the structure of a Fresnel lens. This is an optical lens that generally results in weight and volume reduction due to the design principle used, which is particularly noticeable for large short focal length lenses.

The reduction of the volume occurs in the Fresnel lens by a division into annular areas. In each of these areas, the thickness is reduced so that the lens receives a series of annular steps. Since light is only refracted at the surface of the lens, the angle of refraction does not depend on the thickness but only on the angle between the two surfaces of a lens. Therefore, the lens retains its focal length, although the image quality is degraded by the step structure. In the context of a first particularly preferred embodiment of the present invention, rotationally symmetrical lenses with a Fresnel structure to the optical axis are used. They focus the light in one direction to a point.

In another particularly preferred embodiment of the present invention, Fresnel-type linear lenses are used which focus the light in a plane. Incidentally, the solar cell module may have a structure known per se. It preferably comprises at least one photovoltaic element, which is expediently inserted and laminated between a pane and a rear wall, wherein the pane and the rear wall are in each case advantageously fastened to the photovoltaic element with a solidifying agent. In this case, the solar cell module, in particular the pane, the rear wall and / or the solidifying agent, preferably comprises the components used according to the invention, ie the polyalkyl (meth) acrylate and the compound of general formula (I).

Within the scope of a further very particularly preferred embodiment of the present invention, the solar cell module a) comprises at least one photovoltaic element, b) at least one light concentrator containing at least one polyalkyl (meth) acrylate, and c) at least one transparent pane containing at least one compound of the general formula of the formula (I)

A particularly advantageous structure of a solar cell module will be described below with occasional reference to the figures Fig. 1 to Fig. 2B.

The solar cell module according to the invention preferably comprises a photovoltaic element 101, a disk 103 covering the front side of the photovoltaic element 101, a first solidifying agent 102 between the photovoltaic element 101 and the disk 103, a rear wall 105 covering the rear side 104 of the photovoltaic element 101 Photovoltaic element 101 covered and a second solidification agent 104 between the photovoltaic element 101 and the rear wall 105th

The photovoltaic element preferably comprises a photoactive semiconductor layer on a conductive substrate as a first electrode for light conversion and a transparent conductive layer as a second electrode formed thereon.

The conductive substrate in this context preferably comprises stainless steel, thereby further improving the adhesion strength of the solidifying agent to the substrate.

A collecting electrode containing copper and / or silver as an ingredient is preferably formed on the photosensitive side of the photovoltaic element, and a polyalkyl (meth) acrylate which preferably contains at least one compound of the formula (I) preferably contacts the collecting electrode brought.

The photosensitive surface of the photovoltaic element is favorably covered with a polyalkyl (meth) acrylate preferably containing at least one compound of the formula (I), and then preferably a thin fluoride polymer film is disposed as the outermost layer thereon.

The first solidifying agent 102 is intended to protect the photovoltaic element 101 from external exposure by covering unevenness of the photosensitive surface of the photovoltaic element 101. Furthermore, it also serves to bind the disk 103 to the photovoltaic element 101. Therefore, it should have high weather resistance, high adhesion and high heat resistance in addition to high transparency. Furthermore, it should show a low water absorption and release no acid. In order to satisfy these desires, a polyalkyl (meth) acrylate is preferably used as the first solidifying agent which preferably contains at least one compound of the formula (I). In order to minimize a reduction in the amount of light that reaches the photovoltaic element 101, the light transmittance of the first solidifying agent 102 in the visible wavelength range of 400 nm to 800 nm is preferably at least 80%, more preferably at least 90% in the wavelength range from 400 nm to less than 500 nm (Measurement using the spectral photometer Lambda 19 from the company Perkin Elmer). Furthermore, it preferably has a refractive index of 1, 1 - 2.0, advantageously 1, 1 - 1, 6, to facilitate the incidence of light from air (measurement according to ISO 489).

The second solidification agent 104 is used to protect the photovoltaic element 101 from external influences by covering unevenness on the back surface of the photovoltaic element 101. Furthermore, it also serves to bind the rear wall 105 to the photovoltaic element 101. Therefore, the second solidifying agent such as the first solidifying agent should have high weather resistance, high adhesion and high heat resistance. It is therefore preferable to use a polyalkyl (meth) acrylate which preferably contains at least one compound of the formula (I) as a second solidifying agent. Preferably, the same material is used for both the first solidifying agent and the second solidifying agent. However, since the transparency is optional, if necessary, a filler such as an organic oxide may be added to the second solidifying agent to further improve the weatherability and the mechanical properties, or a pigment may be added to color it.

As photovoltaic element 101, known elements, in particular monocrystalline silicon cells, multicrystalline silicon cells, amorphous silicon and microcrystalline silicon are preferably used, as they are also used in thin-film silicon cells. Furthermore, copper-indium-selenide and semiconductor compounds are particularly suitable. A schematic block diagram of a preferred photovoltaic element is shown in Figs. 2a and 2b. Fig. 2a is a schematic cross-sectional view of a photovoltaic element, whereas Fig. 2b is a schematic plan view of a photovoltaic element. In these figures, numeral 201 denotes a conductive substrate, 202 a reflective layer on the back surface, 203 a photoactive semiconductor layer, 204 a transparent conductive layer, 205 a collector electrode, 206a and 206b alligator clips, and 207 and 208 conductive, adhesive or conductive pastes.

The conductive substrate 201 serves not only as a substrate of the photovoltaic element but also as a second electrode. The material of the conductive substrate 201 preferably comprises silicon, tantalum, molybdenum, tungsten, stainless steel, aluminum, copper, titanium, a carbon foil, a leaded steel plate, a resin film and / or ceramic having a conductive layer thereon.

On the conductive substrate 201, a metal layer, a metal oxide layer or both is preferably provided as a reflective layer 202 on the back side. The metal layer preferably comprises Ti, Cr, Mo, B, Al, Ag and / or Ni, whereas the metal oxide layer preferably contains ZnO, TiO 2 and SnO 2. The metal layer and the metal oxide layer are suitably formed by vapor deposition by heating or by electron beam or by sputtering.

The photoactive semiconductor layer 203 serves to perform the photoelectric conversion. Matehals preferred in this context are pn junction polycrystalline silicon, amorphous silicon pin junction types, microcrystalline silicon pin junction types, and semiconductor compounds, particularly CuInSe ₂ , CuInS ₂ , GaAs, CdS / Cu ₂ S, CdS / CdTe, CdS / lnP and CdTe / Cu ₂ Te. The use of pin junction types made of amorphous silicon is particularly preferred. The preparation of the photoactive semiconductor layer is preferably carried out by forming molten silicon into a film, or by heat treatment of amorphous silicon in the case of polycrystalline silicon, by plasma gas phase deposition using a silane gas as the starting material in the case of amorphous silicon and microcrystalline silicon, and by ion plating, ion beam deposition , Vacuum evaporation, sputtering or electroplating in the case of a semiconductor compound.

The transparent conductive layer 204 serves as the upper electrode of the solar cell. It preferably comprises In ₂ O ₃ , SnO ₂ , In ₂ O ₃ -SnO ₂ (ITO), ZnO, TiO ₂ , Cd ₂ SnO _4, or a crystalline semiconductor layer doped with a large concentration of impurities. It can be formed by resistance heating vapor deposition, sputtering, spraying, vapor deposition or by diffusion of impurities.

Incidentally, in the photovoltaic element on which the transparent conductive layer 204 has been formed, the conductive substrate and the transparent conductive layer may partially due to the unevenness of the surface of the conductive substrate 201 and / or the non-uniformity at the time of formation of the photoactive Semiconductor layer be shorted. In this case, there is a large current loss proportional to the output voltage. That is, the leakage resistance (shunt resistance) is low. Therefore, it is desirable to eliminate the short circuits and to subject the photovoltaic element to a defect-removing treatment after the formation of the transparent conductive layer. Such a treatment is described in detail in US Pat. No. 4,729,970. By this treatment, the shunt resistance of the photovoltaic element is set to 1 - 500 kΩ · cm ² , preferably 10 - 500 kΩ · cm ² .

On the transparent conductive layer 204, the collecting electrode (grid) can be formed. It preferably has the form of a grid, a comb, a line or the like to effectively collect the electric current. Preferred examples of the material constituting the collecting electrode 205 are Ti, Cr, Mo, W, Al, Ag, Ni, Cu, Sn or a conductive paste called silver paste.

The collecting electrode 205 is preferably formed by sputtering using a mask pattern, by resistance heating, by vapor deposition, by a method comprising the steps of forming a metal film over the entire layer by gas deposition and removing unnecessary portions of the film by etching, by a method in which one forms a lattice electron pattern by photochemical vapor deposition by a method comprising the steps of forming a negative lattice electrode marking pattern and plating the patterned surface by a method of printing a conductive paste by a method which is used to solder metal wires onto a printed conductive paste. As the conductive paste, there is preferably used a binder polymer in which silver, gold, copper, nickel, carbon or the like is dispersed in the form of a fine powder. The binder polymer preferably includes polyester resins, ethoxy resins, acrylic resins, alkyd resins, polyvinyl acetate resins, rubbers, urethane resins, and / or phenolic resins.

Finally, alligator clips 206 are preferably attached to conductive substrate 201 and collector electrode 205, respectively, for tapping the electromotive force. The attachment of the tapping clips 206 to the conductive substrate is preferably accomplished by placing a metal body, such as a metal body. a copper nose is attached to the conductive substrate by spot welding or soldering, while the attachment of the pickup ends to the collecting electrode is preferably accomplished by electrically connecting a metal body to the collecting electrode by means of a conductive paste or solder 207 and 208.

The photovoltaic elements are connected either in series or in parallel according to the desired voltage or current. Furthermore, the voltage can or amperage can be controlled by inserting the photovoltaic elements into an insulating substrate.

The pane 103 in FIG. 1 should have the highest possible weather resistance, the best possible dirt-repellent effect and the greatest possible mechanical strength, since it is the outermost layer of the solar cell module. Furthermore, it should ensure the long-term reliability of the solar cell module in outdoor use. Discs that may be suitably used for the purposes of the present invention include (reinforced) glass sheets and fluoride polymer films. As the glass sheet, a glass sheet having high light transmittance is preferably used. Suitable fluoride polymer films include, in particular, ethylene tetrafluoride-ethylene copolymer (ETFE), polyvinyl fluoride resin (PVF), polyvinylidene fluoride resin (PVDF), tetrafluoroethylene resin (TFE), ethylene tetrafluoride-propylene hexafluoride copolymer (FEP), and chlorotrifluoroethylene (CTFE). The polyvinylidene fluoride resin is particularly suitable in terms of weatherability, while the ethylene tetrafluoride-ethylene copolymer is particularly advantageous in the combination of weatherability and mechanical strength. In order to improve the adhesion between the fluoride polymer film and the solidifying agent, it is desirable to subject the film to a corona treatment or a plasma treatment. Furthermore, stretched film is also preferably used to further improve the mechanical strength.

Within the scope of a particularly preferred embodiment of the present invention, the disc comprises at least one polyalkyl (meth) acrylate, which preferably also contains at least one compound of the formula (I),

The disk is furthermore preferably a light concentrator which concentrates light with high efficiency on the photovoltaic element, ie achieves a high irradiance. Particularly preferred are converging lenses that collect parallel incident light and focus in the focal plane. In particular, the light incident parallel to the optical axis is focused at the focal point. The converging lenses may be biconvex, plano-convex or concavo-convex. However, plano-convex structures are particularly preferred. Furthermore, the disk preferably has the structure of a Fresnel lens.

The rear wall 105 is for electrical insulation between the photovoltaic element 101 and the environment and for improving the weatherability and acts as a reinforcing material. It is preferably formed of a material which ensures sufficient electrical insulating properties, has excellent long term durability, can withstand thermal expansion and thermal contraction, and is flexible. Particularly suitable materials for these purposes include nylon films, polyethylene terephthalate (PET) films, and polyvinyl fluoride films. When moisture resistance is required, it is preferred to use aluminum-laminated polyvinyl fluoride films, aluminum-coated PET films, silica-coated PET films. Furthermore, the fire resistance of the module can be improved by using a foil-laminated galvanized iron foil or a frost-free steel foil as the back wall.

Within the scope of a particularly preferred embodiment of the present invention, the rear wall comprises at least one polyalkyl (meth) acrylate which preferably also contains at least one compound of the formula (I).

A supporting plate may be mounted on the outer surface of the backplane to further enhance the mechanical strength of the solar cell module or to prevent buckling and sagging of the backplane due to temperature changes. Particularly preferred back panels are sheets of frost-free steel, plastic sheets and sheets of FRP (fiber reinforced plastic). Furthermore, a building material may be attached to the rear window.

The production of such a solar cell module can be carried out in a manner known per se. However, a procedure which is described below is particularly expedient. In order to cover the photovoltaic element with the solidifying agent, it is preferable to use a method of thermally melting the solidifying agent and extruding it through a slit to form a film which is then thermally fixed to the element. The solidifying agent film is preferably introduced between the element and the disk and solidified between the element and the back wall and then.

For carrying out the thermal solidification, known methods such as e.g. Vacuum lamination and roll lamination can be used.

The solar cell module according to the invention preferably has an operating temperature of up to 80 ⁰ C or higher, in particular at high temperatures, the heat-resistant effect of the molding composition of the invention, which preferably contains the ingredients of the invention can be effectively used.

Claims

1. Use of a) at least one polyalkyl (meth) acrylate and b) at least one compound of the general formula of the formula (I)

in which R is an optionally substituted alkyl, cycloalkyl, aralkyl or aryl radical and the ring A may have further substituents for the preparation of solar cell modules.

2. Use according to claim 1, characterized in that the molding composition contains at least one Ci-Ci ₈ alkyl (meth) acrylate homopolymer or copolymer.

3. Use according to claim 2, characterized in that the molding composition contains at least one copolymer, the 80 wt .-% to 99 wt .-% of methyl methacrylate units and 1 wt .-% to 20 wt .-% of d-Cio-alkyl acrylate - includes units.

4. Use according to claim 3, characterized in that the copolymer comprises methyl acrylate and / or ethyl acrylate units.

5. Use according to at least one of the preceding claims, characterized in that in formula (I) the radicals R are acyl groups having 1 to 18 carbon atoms or cycloalkyl groups 1 to 18 carbon atoms.

6. Use according to claim 5, characterized in that in formula (I) the radicals R are alkyl groups having 1 to 8 carbon atoms.

7. Use according to claim 6, characterized in that in formula (I) the radicals R are ethyl.

8. Use according to at least one of the preceding claims, characterized in that the molding composition contains at least one compound of the general formula of the formula (II)

wherein R ', each independently, is ethyl, n-dodecyl, cyclohexyl, benzyl or phenyl.

9. Solar cell module comprising moldings comprising a) at least one polyalkyl (meth) acrylate and b) at least one compound of the general formula of the formula (I)

10. Solar cell module according to claim 9, characterized in that the molded part is a light concentrator.

11. Solar cell module according to claim 10, characterized in that the molded part is a converging lens.

12. Solar cell module according to claim 11, characterized in that the convergent lens comprises a convex portion.

13. Solar cell module according to claim 12, characterized in that the convergent lens has a plano-convex structure.

14. Solar cell module according to claim 13, characterized in that the convergent lens is a Fresnel lens.

15. Solar cell module according to at least one of claims 10 to 14, characterized in that it further comprises a photovoltaic element.

16. A solar cell module comprising a) at least one photovoltaic element, b) at least one convergent lens containing at least one polyalkyl (meth) acrylate, and c) at least one transparent pane containing at least one compound of the general formula of the formula (I)