EP2286463A2

EP2286463A2 - Photovoltaic modules containing plasticized interlayer films having a high volume resistance and good penetration resistance

Info

Publication number: EP2286463A2
Application number: EP09742148A
Authority: EP
Inventors: Uwe Keller
Original assignee: Kuraray Europe GmbH
Current assignee: Kuraray Europe GmbH
Priority date: 2008-05-08
Filing date: 2009-05-08
Publication date: 2011-02-23
Also published as: JP2011520278A; WO2009135930A2; WO2009135930A3; US20110056555A1; DE102008001654A1; CN102017185A

Abstract

The invention relates to the use of plasticized, polyvinyl acetal-based films which comprise more than 10 ppm metal ions selected from the group including alkaline earth metals, zinc and aluminum and less than 150 ppm alkali metal ions, for producing photovoltaic modules. The films preferably have an electrical volume resistance of more than 1E11 ohm*cm in an ambient environment of 85% RH/23°C. The photovoltaic modules can be used as façade components, roof surfaces, conservatory covers, noise protection walls, balcony or breastwork elements or as components of window surfaces.

Description

Description Photovoltaic modules containing plasticized interlayer films with high

Volume resistance and good penetration resistance Technical field

The invention relates to the production of photovoltaic modules using plasticized films based on polyvinyl acetal with increased volume resistance and good penetration resistance

State of the art

Photovoltaic modules consist of a photosensitive semiconductor layer, which is provided to protect against external influences with a transparent cover. As a photosensitive semiconductor layer, monocrystalline solar cells or polycrystalline, thin semiconductor layers can be used on a support. Thin-film solar modules consist of a photosensitive semiconductor layer deposited on a substrate such as a substrate. a transparent plate or a flexible carrier sheet e.g. by vapor deposition, vapor deposition, sputtering or wet deposition is applied.

Both systems are often placed between a sheet of glass and a rigid, rear cover plate, e.g. laminated from glass or plastics using a transparent adhesive.

The transparent adhesive must completely enclose the photosensitive semiconductor layer and its electrical connection lines, be UV-stable and insensitive to moisture and be completely bubble-free after the lamination process.

Curing resins or crosslinkable systems based on ethylene-vinyl acetate (EVA) are frequently used as transparent adhesives, as disclosed, for example, in DE 41 22 721 C1 or DE 41 28 766 A1. These adhesive systems can be set in the uncured state so low viscosity that they surround the solar cell units bubble-free. After adding a hardener or crosslinking agent, a mechanically resistant adhesive layer is obtained. A disadvantage of these adhesive systems is that during the curing process often aggressive substances such as acids are released, which can destroy the photosensitive semiconductor layers, in particular thin-film modules. In addition, some casting resins tend after some years to blistering or delamination by UV radiation.

An alternative to thermosetting adhesive systems is the use of plasticized films based on polyvinyl acetals, such as polyvinyl butyral (PVB) known from the manufacture of laminated glass. The solar cell units are covered with one or more PVB films and bonded under elevated pressure and temperature with the desired covering materials into a laminate.

Process for the production of solar modules by means of PVB films are z. Example by DE 40 26 165 C2, DE 42 278 60 A1, DE 29 237 70 C2, DE 35 38 986 C2 or US 4,321,418 known. The use of PVB films in solar modules as composite safety glazings is e.g. in DE 20 302 045 U 1, EP 1617487 A1, and DE 35 389 86 C2. However, these documents contain no information about the mechanical, chemical and electrical properties of the PVB films used.

In particular, the electrical properties of the films are becoming increasingly important with increasing performance of the photosensitive semiconductor layers and the global distribution of solar modules. Charge losses or even short circuits of the semiconductor layer must be avoided even under extreme weather conditions such as tropical temperatures, high humidity or strong UV radiation over the entire life of the module. Photovoltaic modules are subjected to a multitude of tests according to IEC 61215 (damp heat test, wet leakage current test) in order to reduce the leakage currents of the modules.

It is known that the electrical resistance of PVB films drops steeply with increasing moisture content, which strongly favors the occurrence of leakage currents in photovoltaic modules. In the edge region of the photovoltaic module, the films are open as encapsulating material to the environment and exposed to environmental conditions such as high ambient humidity. As a result, the water content of the films in the edge region can increase sharply and values up to Equilibrium moisture content (about 3% by weight). The increased water content in the edge region of the film greatly reduces their electrical resistance in this area. Although the water content decreases again towards the center of the film, the photosensitive semiconductor layers can not be laid as far as the edge area of the film or module in order to avoid leakage currents. This reduces the area occupancy and thus the current efficiency of the module.

Solar cells, in particular photosensitive semiconductor layers of thin-film solar modules, e.g. based on CIS (Copper / indium / (di) selenite) or

Copper / indium / gallium / sulphide / selenite (CIGS) or the thin conductive layers (TCO) are chemically susceptible to corrosion, so the encapsulant must be chemically inert and free from aggressive chemicals Additives such as crosslinkers, crosslinkers or primers, and the presence of water, alkali metal ions or traces of acid should be avoided.

Although the plastics commonly used in photovoltaic modules are generally known as electrically good insulating materials, however, have Restleitfähigkeiten, which are as a rule due to impurities such as water, ionic catalyst residues or salts. In particular, the interaction of ionic impurities with diffusing water, which is always to be expected in the case of ambient humidities typical for use, has a considerable share in the residual conductivity.

For this reason, it seems obvious that in the case of adhesive film for photovoltaic modules, the salt content should be as low as possible. In the usual polyvinyl butyral (PVB) films, which are often used for the production of laminated safety glass, the salt content of the film depends firstly on the salt content of the PVB polymer, which from the manufacturing process depending on the quality of the washing process used there, salts of Mineral acids such as NaCl, KCl, NaNO ₃ , KNO ₃ , Na ₂ SO ₄ or K ₂ SO ₄ typically in amounts between 20-300 ppm. On the other hand, alkali and alkaline earth metal salts are often added to the usual PVB films as so-called anti-adhesion agents to increase the penetration resistance of the glass / film / glass composites in amounts of about 20-500 ppm. These salts are required to set a sufficiently low level of adhesion of the film to the glass. If a photovoltaic module produced with PVB film is therefore also to have the safety properties of a laminated safety glass in addition to high power generation, for example because the module is part of a glass façade, the problem arises that the anti-adhesive agent combinations and quantities normally used to reduce adhesion impair the electrical resistance can also increase the corrosion of the semiconductor layers.

The safety properties of a glass component on laminated glass are generally considered to be sufficient if the component in the pendulum impact test according to EN 12600 at least Class 3B for which a 50 kg double tire pendulum from a height of 190 mm is levitated against the glass , If the pendulum does not break through the glass component or if there is no large opening and no Sharp-edged splinters detach, the test is passed. In the commonly used adhesion-reduced PVB film in thickness of 0.76 mm, laminated glass also has the pendulum impact test at significantly greater deflection heights, in particular 1200 mm, which then achieves the highest resistance class 1 B. If, for example, a photovoltaic module is to be integrated into a building façade as a glass component and thereby meet the usual high demands on the fracture safety of a laminated safety glass, the PVB film should have a not too high adhesion to the glass or the adjacent functional layers.

Technical task

Object of the present invention was therefore, plasticizer-containing films based on polyvinyl acetal with high volume resistance and provide good penetration resistance in conjunction with glass layers for the manufacture of photovoltaic modules.

Technical solution

It has been found that by a PVB film with an addition of e.g. Alkaline earth salts and at the same time a low content of alkali metal salts can be obtained photovoltaic modules with sufficient penetration properties. In addition, the volume resistivity of the films based on plasticized polyvinyl acetals is further increased and their corrosiveness to semiconductor layers is reduced.

Presentation of the invention

The present invention therefore relates to photovoltaic modules comprising a laminate of a) a transparent front cover b) one or more photosensitive semiconductor layers c) at least one plasticizer-containing polyvinyl acetal-based film and d) a back cover wherein the plasticizer-containing polyvinyl acetal-based Film c) has more than 10 ppm of metal ions selected from the group of alkaline earth metals, zinc and aluminum and less than 150 ppm of alkali metal ions.

When using several different metal ions, said concentrations refer to the respective sums of the individual concentrations, i. E. to the total concentrations of alkali metal ions or polyvalent metal ions.

Preferably, the film used according to the invention c) contains more than 15 ppm, preferably more than 20 ppm, preferably more than 30 ppm, preferably more than 50 ppm, preferably more than 75 ppm, preferably more than 100 ppm, preferably more than 125 ppm and more preferably more than 150 ppm ions of the alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra), zinc or aluminum. On the other hand, in order to avoid undesired clouding of the film, not more than 1000 ppm of said polyvalent metals should be present. At the same time, the content of alkali metal ions (Li, Na, K, Rb, Cs, Fr) in the plasticizer-containing polyvinyl acetal-based film should be as low as possible. In particular, the film contains less than 100 ppm, preferably less than 75 ppm, preferably less than 50 ppm, preferably less than 25 ppm, preferably less than 15 ppm, preferably less than 10 ppm and more preferably less than 5 ppm alkali metal ions.

The respective alkaline earth metal, zinc, aluminum or the

Alkali metal ions are added to the film mixture in the form of the salts of mono- or polyvalent inorganic or mono- or polyvalent organic acids. Examples of counterions are e.g. Salts of organic carboxylic acids such as formates, acetates, trifluoroacetates, propionates, butyrates, benzoates, 2-ethylhexanoates, etc., preferably carboxylic acids having less than 10 C atoms, preferably less than 8, preferably less than 6, preferably less than 4 and especially preferably be used with less than 3 C-atoms. Examples of inorganic counterions are chlorides, nitrates, sulfates, phosphates.

Preferably, the films used in the invention in a

Ambient humidity of 85% RH at 23 ° C a resistivity of at least 1E + 11 ohms * cm, preferably at least 5E + 11 ohms * cm, 1E + 12 ohms ^* cm, 5E + 12 ohms ^* cm, 1E + 13 , 5E + 13 ohms ^* cm or 1E + 14 ohms * cm.

For the preparation of polyvinyl acetal polyvinyl alcohol is dissolved in water and acetalized with an aldehyde such as butyraldehyde with the addition of an acid catalyst. The precipitated polyvinyl acetal is separated, washed neutral, optionally suspended in an alkaline aqueous medium, then washed neutral again and dried.

The acid used for the acetalization must be neutralized again after the reaction. A low level of alkali metal ions can be achieved inter alia in the synthesis of the polyvinyl acetal by dispensing with the sodium or potassium hydroxides or carbonates usually used to neutralize the catalyst or by thoroughly washing the polyvinyl acetal obtained in the acetalization become. As an alternative to the bases NaOH or KOH, the catalyst acid can be neutralized from the acetalization step, for example by blowing in carbon dioxide or ethylene oxide.

The polyvinyl alcohol content of the polyvinyl acetal can be adjusted by the amount of aldehyde used in the acetalization.

It is also possible to acetalize with others or more

Aldehydes having 2-10 carbon atoms (e.g., valeraldehyde).

The films based on plasticized polyvinyl acetal preferably contain uncrosslinked polyvinyl butyral (PVB), which is obtained by acetalization of polyvinyl alcohol with butyraldehyde.

The use of crosslinked polyvinyl acetals, in particular crosslinked polyvinyl butyral (PVB) is also possible. Suitable crosslinked polyvinyl acetals are e.g. in EP 1527107 B1 and WO 2004/063231 A1 (thermal self-crosslinking of polyvinyl acetals containing carboxyl groups), EP 1606325 A1 (polyvinyl acetals crosslinked with polyaldehydes) and WO 03/020776 A1 (polyvinyl acetals crosslinked with glyoxylic acid). The disclosure of these patent applications is fully incorporated by reference.

In the context of the present invention, terpolymers of hydrolyzed vinyl acetate / ethylene copolymers can also be used as the polyvinyl alcohol. These compounds are typically hydrolyzed to greater than 98 mole percent and contain from 1 to 10 weight percent ethylene based units (e.g., "Exceval" type from Kuraray Europe GmbH).

As polyvinyl alcohol, hydrolyzed copolymers of vinyl acetate and at least one further ethylenically unsaturated monomer can also be used within the scope of the present invention.

The polyvinyl alcohols can be used in the context of the present invention purely or as a mixture of polyvinyl alcohols with different degree of polymerization or degree of hydrolysis.

Polyvinyl acetals still contain in addition to the acetal units

Vinyl acetate and vinyl alcohol resulting units. The polyvinyl acetals used according to the invention preferably have a polyvinyl alcohol content of less than 22% by weight, 20% by weight or 18 % By weight, less than 16% by weight or 15% by weight and in particular less than 14% by weight. A polyvinyl alcohol content of 12% by weight should not be exceeded.

The polyvinyl acetate content of the invention used

Polyvinyl acetal is preferably less than 5% by weight, less than 3% by weight or less than 1% by weight, particularly preferably less than 0.75% by weight, very preferably less than 0.5% by weight and in particular less than 0.25% by weight. ,

From the polyvinyl alcohol content and the residual acetate content, the degree of acetalization can be determined by calculation.

Preferably, the films have a plasticizer content of at most 40% by weight, 35% by weight, 32% by weight, 30% by weight, 28% by weight, 26% by weight, 24% by weight, 22% by weight. , 20 wt.%, 18 wt.%, 16 wt.%, Wherein a plasticizer content of 15 wt.% For reasons of processability of the film should not be exceeded (in each case based on the total film formulation). Inventive films or photovoltaic modules may contain one or more plasticizers.

Basically suitable plasticizers for the films used according to the invention are one or more compounds selected from the following groups:

Esters of polyhydric aliphatic or aromatic acids, e.g. Dialkyladipates such as Dihexyladipat, Dioctyladipat, Hexylcyclohexyladipat, mixtures of heptyl and nonyl adipates, Diisononyladipat, heptylnonyl adipate and esters of adipic acid with cycloaliphatic or ether-containing ester alcohols, dialkyl sebacates such as dibutyl sebacate and esters of sebacic acid with cycloaliphatic or ether-containing ester alcohols, esters of phthalic acid such as butyl benzyl phthalate or bis-2-butoxyethyl phthalate

- esters or ethers of polyhydric aliphatic or aromatic alcohols or Oligoetherglykolen with one or more unbranched or branched aliphatic or aromatic substituents, such as esters of di-, tri- or tetraglycols with linear or branched aliphatic or cycloaliphatic carboxylic acids; As examples of the latter group can serve Diethylene glycol bis (2-ethylhexanoate), triethylene glycol bis (2-ethylhexanoate), tri-ethylene glycol bis (2-ethylbu-ta-no-ate),

Tetraethylene glycol bis-n-heptanoate, triethylene glycol bis-n-heptanoate, triethylene glycol bis-n-hexanoate, tetraethylene glycol dimethyl ether and / or Dipropylenglykolbenzoat

Phosphates with aliphatic or aromatic ester alcohols, e.g. Tris (2-ethylhexyl) phosphate (TOF), triethyl phosphate, diphenyl-2-ethylhexyl phosphate, and / or tricresyl phosphate

- Esters of citric acid, succinic acid and / or fumaric acid. Suitable as a plasticizer for the inventively used

Slides are one or more compounds selected from the group consisting of di-2-ethylhexyl sebacate (DOS), di-2-ethylhexyl adipate (DOA), dihexyl adipate (DHA), dibutyl sebacate (DBS), triethylene glycol bis-n-heptanoate (3G7), Tetraethylene glycol bis-n-heptanoate (4G7), triethylene glycol bis-2-ethylhexanoate (3GO or 3G8) tetraethylene glycol bis-n-2-ethylhexanoate (4GO or 4G8) di-2-butoxy-ethyl adipate (DBEA ), Di-2-butoxyethoxyethyl adipate (DBEEA) di-2-butoxyethyl sebacate (DBES), di-2-ethylhexyl phthalate (DOP), di-isononyl phthalate (DINP) triethylene glycol bis-isononanoate, triethylene glycol bis-2-propylhexanoate, tris ( 2-ethylhexyl) phosphate (TOF), 1, 2-cyclohexanedicarboxylic acid diisononyl ester (DINCH) and Dipropylenglykolbenzoat.

Plasticizers whose polarity expressed by the formula 100 × O / (C + H) is less than or equal to 9.4 are particularly suitable as plasticizers for the films used according to the invention, where O, C and H are the number of oxygen atoms. , Carbon and hydrogen atoms in each molecule. The following table shows plasticizers which can be used according to the invention and their polarity values according to the formula 100 × O / (C + H).

[0038]

Table 1

Name polarity value

Furthermore, the ion mobility which is possibly dependent on the water content of the film and thus the specific resistance can be influenced by the addition of silica, in particular pyrogenic SiO ₂ . The plasticizer-containing films based on polyvinyl acetal preferably contain 0.001 to 15% by weight, preferably 0.01 to 10% by weight and in particular 2 to 5% by weight of SiO ₂ .

Furthermore, the films of the invention may additionally contain conventional additives, such as oxidation stabilizers, UV stabilizers, dyes, pigments and anti-adhesive.

The basic preparation and composition of films based on polyvinyl acetals is z. In EP 185 863 B1, EP 1 118 258 B1, WO 02/102591 A1. EP 1 118 258 B1 or EP 387 148 B1.

The photovoltaic modules are produced by laminating the transparent front cover a), the photosensitive semiconductor layers b) and the rear cover d) by means of at least one plasticizer-containing film based on polyvinyl acetal c) with fusion of the films, so that a bubble-free and schlierenfreier Inclusion of the photosensitive semiconductor layer is obtained.

In this variant of the photovoltaic modules according to the invention, the photosensitive semiconductor layers are embedded between two films c) and thus bonded to the covers a) and d).

The thickness of the plasticized polyvinyl acetal based

Foils are usually 0.38, 0.51, 0.76, 1.14, 1.52 or 2.28 mm. Particularly in the case of thin-film solar modules, the photosensitive semiconductor layer is applied directly to a support (for example by vapor deposition, vapor deposition, sputtering or wet deposition). An encapsulation of the photosensitive semiconductor layer is not possible here.

In a variant of the photovoltaic modules according to the invention, the photosensitive semiconductor layers are applied to the cover d) (for example by vapor deposition, vapor deposition, sputtering or wet deposition) and bonded to the transparent front cover a) by at least one film c).

In another variant, the photosensitive semiconductor layers are applied to the transparent front cover a) and glued by at least one film c) with the rear cover d).

In general, in thin-film modules, the photosensitive

Semiconductor layer applied over the entire surface of the carrier i. to the edge of the carrier. Subsequently, part of the photosensitive semiconductor layer is removed again at the edge, so that for isolation purposes, a semiconductor-free edge region remains (so-called edge deletion). Due to the high resistance values of the film used according to the invention, this edge region can be very narrow, preferably below 3 cm, especially below 2 cm and in particular below 1 cm.

[0049] Films used according to the invention fill during the

Laminierprozesses the existing on the photosensitive semiconductor layers or their electrical connections cavities.

The transparent front cover is usually made of glass or PMMA. The rear cover of the photovoltaic module according to the invention may consist of glass, plastic or metal or their composites, wherein at least one of the carrier may be transparent. It is also possible to use one or both covers as composite glazing (ie as a laminate of at least two glass panes and at least one PVB foil) or as insulating glazing with a gas gap. Of course, that too Combination of these measures possible.

The photosensitive semiconductor layers used in the modules need not possess any special properties. Mono-, polycrystalline or amorphous systems can be used.

For lamination of the laminate thus obtained, the

Those skilled in the art process with and without previous production of a pre-bond can be used.

So-called autoclave processes are carried out at an elevated pressure of about 10 to 15 bar and temperatures of 130 to 145 ° C for about 2 hours. Vacuum bag or vacuum ring method, for example, according to EP 1 235 683 B1 operate at about 200 mbar and 130 to 145 ⁰ C.

Preferably, for the preparation of the inventive

Photovoltaic modules used vacuum laminators. These consist of a heatable and evacuable chamber, in which composite glazing can be laminated within 30 - 60 minutes. Reduced pressures of 0.01 to 300 mbar and temperatures of 100 to 200 ⁰ C, in particular 130 - 160 ⁰ C have proven in practice.

Alternatively, a laminated as described above laminated body between at least one pair of rollers at a temperature of 60 to 150 ° C are pressed into a module according to the invention. Systems of this type are known for the production of laminated glazing and usually have at least one heating tunnel before or after the first press shop in systems with two pressing plants.

Industrial Applicability

The invention further provides for the use of plasticized polyvinyl acetal-based films c) containing more than 10 ppm metal ions selected from the group of alkaline earth metals, zinc and aluminum and less than 150 ppm alkali metal ions or with the preferred embodiments mentioned Production of photovoltaic modules.

Photovoltaic modules according to the invention can be used as a facade component,

Roof areas, conservatory cover, soundproof wall, balcony or Parapet element or used as part of window surfaces.

Measurement Methods:

The measurement of the volume resistivity of the film is carried out according to DIN IEC 60093 at a defined temperature and ambient humidity (23 ° C and 85% rl_F) after the film has been conditioned for at least 24 hours under these conditions. To carry out the measurement, a plate electrode Type 302 132 from Fetronic GmbH and an ohmmeter ISO-Digi 5 kV from Amprobe were used. The test voltage was 2.5kV, the waiting time after application of the test voltage to the value acquisition 60 sec. To ensure adequate contact between the flat plates of the measuring electrode and the film, their surface roughness R _z should not be greater than 10 mm when measured according to DIN EN ISO 4287, ie, if necessary, the original surface of the PVB film before the resistance measurement by thermal embossing be smoothed.

The polyvinyl alcohol and polyvinyl alcohol acetate content of

Polyvinyl acetals were determined according to ASTM D 1396-92. The analysis of the metal ion content was carried out by atomic absorption spectroscopy (AAS). The water or moisture content of the films is determined by the Karl Fischer method.

The pendulum impact test is carried out in accordance with EN 12600; the result is given in the classification of this standard.

The adhesion of the film to the glass is given in "punch values" in each case based on the fire or tin side of the glass.

The haze is determined by the Haze value in% according to ASTM 1003 D on a smooth film.

To assess the adhesion of a PVB film is the

Compression shear test based on DE 197 56 274 A1 performed on a glass / glass laminate without solar cell. For the preparation of the test specimens, the PVB film to be tested is placed between two flat silicate glass panes of the format 300 mm × 300 mm with a thickness of 2 mm, vented in a Vorverbundofen calender rolls to a glass pre-composite and then in an autoclave at a pressure of 12 bar and at a temperature of 140 ° C within a total of 90 min. pressed into a flat laminated safety glass. From the laminated safety glass thus produced, 10 samples measuring 25.4 mm × 25.4 mm are cut. These are clamped at an angle of 45 ° in a test apparatus according to DE 197 56 274 A1, wherein the depth of the recesses is about 2/3 of the respective glass thickness. The upper half is subjected to a steadily increasing, exactly vertically downward force until it shears within the test body, ie the laminated safety glass panes to be tested.

The test parameters are as follows:

[0065]

Table 2

For each test specimen, the force exerted during shearing is linearly averaged by ten equal specimens. As far as reference is made in the following examples and the claims to the mean compression shear test value, this means this mean of 10 measurements. For the rest, reference is made to DE 197 56 274 A1.

Examples Sheets of thickness 0.76 mm were prepared with the mixtures of the composition listed in the following table and examined for their electrical resistance and their adhesion to glass and the pendulum impact resistance of laminated glass with the structure 5 mm float glass / foil / 5 mm float glass ,

The amounts given in Table 3 and 4 are given in wt.%, Based on the sum PVB and plasticizer. 3G8 stands for triethylene glycol bis-2-ethylhexanoate, AEROSIL 130 and TINUVIN 328 are commercial products of Evonik Degussa GmbH or CIBA. The volume resistivity according to DIN IEC 60093 is indicated on a film conditioned in ohms at 23 ° C./85% RH (as described above).

The PVB was a high-viscosity polyvinyl butyral having a viscosity 60-90 mPas (measured according to DIN53015 as a 5% solution in ethanol (with 5% water) at 20 ⁰ C) and a PVA content of 20.0 wt.%, The content thereof of Na ions by thorough washing below 3 ppm.

It has been found that films having the salt concentration according to the invention have a high specific resistance with good penetration resistance of the glass / foil / glass laminates produced therewith. Films of this type are suitable for photovoltaic applications. A further improvement of the resistivity could be achieved by adding SiO ₂ .

[0071]

Table 3

72]

Table 4

Claims

claims

A photovoltaic module comprising a laminate of a) a transparent front cover b) one or more photosensitive semiconductor layers c) at least one plasticizer-containing polyvinyl acetal-based film and d) a rear cover, characterized in that the plasticized polyvinyl acetal-based film c) more having 10 ppm metal ions selected from the group of alkaline earth metals, zinc and aluminum and less than 150 ppm of alkali metal ions.

2. Photovoltaic module according to claim 1, characterized in that the plasticizer-containing polyvinyl acetal-based films c) have a plasticizer content of at most 40% by weight.

3. Photovoltaic module according to claim 1 or 2, characterized in that the plasticizer-containing, based on polyvinyl acetal films c) have an electrical contact resistance of more than 1 E11 ohm * cm in an ambient climate of 85% RH / 23 ° C.

4. Photovoltaic module according to one of claims 1 to 3, characterized in that the polyvinyl acetal has a polyvinyl acetate content of less than 5 wt.%.

5. Photovoltaic module according to one of claims 1 to 4, characterized in that as plasticizer one or more compounds are used whose polarity, expressed by the formula 100 x O / (C + H) is less than or equal to 9.4, wherein O, C and H stands for the number of oxygen, carbon and hydrogen atoms in the respective molecule.

6. Photovoltaic module according to one of claims 1 to 5, characterized in that the polyvinyl acetal has a polyvinyl alcohol content of less than 22 wt.%.

7. Photovoltaic module according to one of claims 1 to 6, characterized in that the plasticizer-containing, based on polyvinyl acetal film c) 0.001 to 15 wt.% SiO ₂ .

8. Photovoltaic module according to one of claims 1 to 7, characterized in that one or more photosensitive semiconductor layers b) on a transparent front cover a) or a rear cover d) are applied and glued together by at least one plasticizer-containing, based on polyvinyl acetal film c).

9. Use of plasticized polyvinyl acetal based films containing more than 10 ppm metal ions selected from the group of alkaline earth metals, zinc and aluminum and less than 150 ppm alkali metal ions for the manufacture of photovoltaic modules.

10. Use of photovoltaic modules according to one of claims 1 to 8 as a facade component, roof surfaces, conservatory cover, sound insulation wall, balcony or parapet or as part of windows.