DE102011055148A1 - Solar module, has embedding polymer moistening passivation film such that set of wetting regions is formed, where portion of wetting regions is made of covering areas, in which passivation film is covered - Google Patents

Abstract

The module (14) has a back surface for polymerically forming a back encapsulation structure with an embedding polymer (12) that is located in contact with a metallic back electrode structure (11) of semiconductor wafer solar cells (10). The embedding polymer moistens a passivation film (17) such that a set of wetting regions is formed and the embedding polymer moistens the film in the regions. A portion of the wetting regions i.e. more than 50 percentages of the wetting regions, is made of covering areas, in which the passivation film is covered. An independent claim is also included for a method for manufacturing a solar module.

Description

The present invention relates to a solar module and a method for its production.

In particular, the present invention relates to a solar module having a front side and a back side having a plurality of semiconductor wafer solar cells. The plurality of semiconductor wafer solar cells are electrically connected to a solar cell string and each have a back side with a back surface. The back surface is surface-passivated by means of a dielectric passivation layer. On the passivation layer, a back-side electrode structure comprising sintered metal particles is arranged. The metallic backside electrode structure electrically contacts the semiconductor material of the semiconductor wafer via a plurality of local contact regions, wherein the contact regions are formed as openings of the passivation layer and occupy an overall electrical contact area of less than 5%, preferably less than 2%, of the backside surface. Furthermore, the solar module has a front side encapsulation element forming the front side of the solar module and a polymeric back side encapsulation structure forming the rear side of the solar module with an embedding polymer in contact with the metallic back side electrode structure of the semiconductor wafer solar cells. Usually, the front side encapsulation element, the back side encapsulation structure and the solar cell string are lamination laminated to ensure a stable bond.

For surface passivated-back side solar cells having a backside electrode structure of sintered metal particles, i. H. open-pored material, there is the problem that in the solar module production after lamination the adhesion of the back laminate laminate, i. H. the adhesion between backside encapsulation structure and semiconductor wafer solar cells is insufficient. The mechanical stability of the sintered metal pastes used to fabricate the backside electrode structure is insufficient to ensure a long term stable composite of the semiconductor wafer solar cell with the backside embedding polymer and the backside encapsulation element.

It is therefore an object of the present invention to provide a solar module which has a plurality of surface-passivated semiconductor wafer solar cells and a backside encapsulation structure suitable for forming a sufficiently long-term stable composite.

This object is achieved by a solar module according to claim 1 and a method for producing the solar module according to claim 10.

In the dependent claims advantageous embodiments are shown.

According to the invention, the embedding polymer wets the passivation layer such that wetting areas are formed in which the embedding polymer wets the passivation layer, and the proportion of wetting areas is more than 20%, preferably more than 35% and particularly preferably more than 50% with respect to areas which consist of Wetting areas and covering areas exist in which the passivation layer is covered by the back electrode structure.

For the purposes of the present invention, wetting areas are areas in which the embedding polymer wets the passivation layer microscopically. Cover regions in the present application are understood to mean regions in which the passivation layer is covered by the back-side electrode structure, but microscopically there is no contact between the metal particles and the passivation layer. The term "covered" thus means that the backside electrode structure does not cover the passivation layer, i. H. not wetted or contacted, but that there is at least one cavity between the backside electrode structure and passivation layer. The void is formed by the open-pore structure of the backside electrode structure and is not penetrated by the potting polymer such that the potting polymer wets the passivation layer. Ie. in the overlapping area, microscopically, neither the back surface electrode structure nor the embedding material is on the passivation layer, but the passivation layer is not exposed because the open-cell back side electrode structure is overlapped thereover.

The wetting may be realized by the potting polymer permeating the sponge-like open-pore backside electrode structure and / or by the potting polymer wetting the passivation layer in open areas where the backside electrode structure does not cover the passivation layer and where, therefore, the potting polymer does not penetrate the backside electrode structure due to its absence in order to contact the passivation layer and thus to wet it. Wetting areas within the meaning of the present invention can thus be formed outside the back-side electrode structure as usually macroscopic free areas or within the back-side electrode structure also as microscopic wetting areas.

Due to the wetting, which is sufficient in terms of its surface area, a break-off-resistant module bond between back-side encapsulation structure and semiconductor wafer solar cell is ensured. Even if the inherent stability of the sintered metal particles of the back surface electrode structure is insufficient, the back adhesion of the solar module is ensured by the contact of the encapsulation material with the passivation layer, particularly by the penetration of the back side electrode structure to the extent mentioned above.

In a preferred embodiment, the percentage of the metallic backside electrode structure is greater than 80% relative to the backside surface. Ie. the proportion of macroscopic areas of the backside surface in which no metal particles are present is less than 20%. Preferably, the percentage of the metallic back side electrode structure in relation to the back surface is more than 90%. More preferably, the percentage of the metallic backside electrode structure is greater than 95% relative to the backside surface. That is, the back surface electrode structure covers the back surface almost completely or completely. The wetting of the passivation layer with the embedding polymer is therefore preferably carried out by means of penetration of the backside electrode structure by the embedding polymer. For this purpose, it is necessary for the back-side electrode structure to be open-pore after sintering of the paste usually applied by screen printing or inkjet methods. The potting material penetrates the open pores of the backside electrode material during the lamination process and forms a network in the open pores of the backside electrode material. Preferably, the encapsulant polymer not only permeates but also covers the backside electrode material, so that the encapsulant polymer is also disposed on the backside electrode structure and the encapsulant polymer can form a uniform adhesion with a backside encapsulation member.

The backside electrode structure has open pores in the embodiment described above before contacting with the potting polymer. In lamination of the semiconductor wafer solar cell with the encapsulant polymer and the backside encapsulant, the encapsulant polymer penetrates and fills the open pores so that the network of open pores forms an embedding polymer network upon lamination. The open pores are interconnected in a variety of ways such that the backside electrode structure has a porous metal network or skeleton penetrated by the potting polymer and completely filled under appropriate conditions. That is, the semiconductor wafer solar cell has as a layer a metal network and an embedding polymer network, which may still have open pores in the layer. Preferably, the proportion of open pores in the layer is low. In this way, a layer is obtained which has two respective cohesive networks, which in combination provides good adhesion of the composite semiconductor wafer solar cell / embedding polymer / Rückseitenverkapselungselement and a good conductivity, wherein the optimized long-term stable adhesion by the sufficient in terms of their area ratio wetting the passivation layer is ensured with the embedding polymer.

In a preferred embodiment, the lamination has been carried out in such a way that there is a layer of embedding polymer on the layer which has the two above-mentioned networks, so that a whole-area adhesion between embedding polymer and back-side encapsulation element is realized. The solar module therefore has, in addition to possible other layers on the back side, the layer sequence backside encapsulation element / optional embedding polymer / network of embedding polymer and network of metal / passivation layer.

Preferably, the resistivity of the backside electrode structure is ≦ 10 × 10 ^-7 ohm.cm, more preferably ≦ 7 × 10 ^-7 ohm.cm, more preferably ≦ 5 × 10 ^-7 ohm.cm. This ensures a sufficiently good conductivity for the desired efficiency of these cells.

In a preferred embodiment, the backside electrode structure has a varying layer thickness with adhesion regions having lower layer thicknesses of less than 30 microns, preferably less than 25 microns, more preferably less than 20 microns, even more preferably less than 15 microns compared to the other regions. The lower layer thickness of the adhesion regions results in these adhesion regions after the lamination process being more likely to penetrate the porous metal structure and to microscopically wet the underlying passivation layer with the embedding polymer than in the remaining regions of the backside electrode structure with a greater layer thickness. Finally, the adhesion regions described above represent a possibility of realizing an anchoring region, referred to as wetting regions in the context of this invention, between back-side electrode structure and passivation layer. Likewise, an open area represents a wetting area, because in the open area the embedding polymer can directly wet the passivation layer without to penetrate an open porous metal matrix would be required.

Preferably, the area ratio of wetting areas in which the embedding polymer wets the passivation layer compared to the area ratio of areas where the embedding polymer does not wet the passivation layer decreases as the layer thickness of the backside electrode structure increases. If the backside electrode structure has a smaller layer thickness, it may be more easily penetrated by the potting material. When the film thickness of the back surface electrode structure becomes zero, there is a free space.

In a preferred embodiment, the embedding polymer is crosslinked. Crosslinking links the embedding polymer into a three-dimensional network. The crosslinked potting polymer has advantageous properties that prevent peeling of the passivation layer and the backside electrode structure. For example, a crosslinked polymer has higher viscosity, lower solubility, and higher melting point compared to the uncrosslinked polymer.

Preferably, the passivation layer is constructed as a thin-film stack.

The thin-film stack has at least one passivation layer applied directly to the semiconductor material. Optionally, one or more further layers may be on the first one. As a preferred variant of a passivation layer constructed as a thin-film stack, the thin-film stack has, as the uppermost layer, an adhesion promoter layer. The topmost layer is the layer on which the backside metal electrode structure or, in the case of lamination, the embedding material is arranged. If the primer layer is wetted with the embedding material and thus contacted, forms a particularly good adhesion. Due to the contact of the embedding material with the uppermost layer of the passivation layer stack, sufficient adhesion of the overall composite of solar cell / embedding material / backside encapsulation element to be produced is ensured. Alternatively, the thin-film stack has as the uppermost layer a conductive layer. As an alternative, the thin-film stack has, as the uppermost layer, a dielectric layer such as, for example, a silicon nitride or silicon oxynitride layer.

As embedding material z. As ethylene vinyl acetate (EVA), polyolefins, polyvinyl butyral (PVB), thermoplastic polyurethane (TPU), silicones suitable. Preferably, EVA is used. Ethylene vinyl acetate has good adhesion to passivation layers such as silicon nitride or silicon oxynitride and also has good adhesion to a backside encapsulant such as glass or a plastic film.

In a preferred embodiment, the backside surface of the semiconductor wafer solar cells has free areas to an area fraction of less than 20%, preferably less than 10%, more preferably less than 5%, in which the passivation layer is not covered by the backside electrode structure. That is, the wetting of the passivation layer with the embedding polymer is realized mainly by permeating the back surface electrode structure with the embedding polymer. This is advantageous because good current conduction properties can be achieved in almost the entire surface area of the passivation layer.

The present invention likewise provides a method for producing a solar module having a front side and a rear side, comprising the following steps: providing a plurality of semiconductor wafer solar cells which are electrically connected to form a solar cell string and each have a rear side with a rear side surface, wherein the backside surface is surface-passivated by a dielectric passivation layer, and the backside electrode structure comprises a sintered metal particle electrically contacting the semiconductor material of the semiconductor wafer via a plurality of local contact regions, wherein the contact regions are formed as openings of the passivation layer and collectively an electric Contact area of less than 5%, preferably less than 2%, occupy the back surface and lamination to form the back side of the solar module forming a polymeric backside encapsulation structure with an embedding polymer on the backside of the solar cells such that the encapsulant polymer is in contact with the metallic backside electrode structure of the semiconductor wafer solar cells. The method is characterized in that lamination parameters such as contact pressure and temporal temperature profile are adjusted so that the embedding polymer wets the passivation layer such that wetting areas are formed in which the embedding polymer wets the passivation layer, and the proportion of wetting areas is more than 20%, preferably more is greater than 35% and more preferably greater than 50% with respect to areas consisting of wetting areas and coverage areas where the passivation layer is covered by the backside electrode structure.

The semiconductor wafer solar cell is provided in a preferred embodiment such that the backside electrode structure has a varying layer thickness. This can be achieved by applying the back-side electrode structure by screen printing in the form of a plurality of fingers at a small distance on the passivation layer. After the subsequent firing, the fingers are no longer spaced, but back electrode sections having smaller layer thickness are formed between the fingers than at the back side electrode structure finger sections. As the backside electrode material, a metal paste, preferably an aluminum paste such as Ferro CN 53-200, commercially available from the manufacturer Ferro (Cleveland, USA) is used. As back-end electrode structure, all metal pastes are suitable which form an open porosity after firing. Alternatively, the varying layer thickness z. B. also be generated by multiple printing.

The embedding polymer at least partially penetrates the back-side electrode structure as far as the passivation layer and wets it. This can be achieved by applying the embedding polymer as a solid, for example in the form of a film, to the backside electrode structure and subjecting it to a temporal temperature profile. For example, the embedding polymer is heated to a first temperature at which the embedding polymer has a lower viscosity than at room temperature. Due to the lower viscosity at the first temperature, the embedding polymer at least partially penetrates the backside electrode structure to wet the passivation layer. Subsequently, when in the form of a thermoplastic, the embedding polymer is cooled to a second temperature, the viscosity increasing such that the thermoplastic loses its fluidity to penetrate the backside electrode structure. For example, when the embedding polymer is ethylene vinyl acetate, it is heated to a higher second temperature after being heated to the first lower viscosity temperature, where it forms a higher viscosity because of the onset of crosslinking than at the first temperature.

In a preferred embodiment, the temporal temperature profile comprises heating to a first temperature at which the embedding polymer has a lower viscosity than at room temperature, and heating to a second temperature at which the embedding polymer has a higher viscosity than at the first temperature.

The heating to the first temperature is preferably carried out under reduced pressure, i. H. a vacuum or vacuum pressure technique is used when the embedding polymer is to penetrate into open pores of the backside electrode structure. By means of these techniques filling resistances such as narrow pore necks can be overcome.

As a result of the embedding polymer having a lower viscosity at the first temperature than at room temperature, the embedding polymer during lamination penetrates into open areas and / or open pores of the backside electrode structure and wets the passivation layer. When heated to the second temperature, the viscosity of the embedding polymer is increased, so that the embedding polymer can no longer run out of the free areas and / or pores. Preferably, gelation and / or crosslinking of the embedding polymer takes place at the second temperature. Caked embedding polymer has such a viscosity that it does not leak out of the free areas and / or pores. Crosslinking links the embedding polymer into a three-dimensional network. The crosslinking alters the properties of the embedding polymer. The crosslinked encapsulant polymer has a higher viscosity, lower solubility, and higher melting point than the uncrosslinked encapsulant polymer.

An example of an encapsulating polymer having a lower viscosity at room temperature than at room temperature and a higher viscosity at the second temperature than at the first temperature is ethylene vinyl acetate. Examples of ethyl vinyl acetate polymer as embedding are PHOTOCAP ^® products such as PHOTOCAP ^® FC280P / UF, the STR ^® Specialized Technology Resources, Inc. (Enfield, United States) are commercially available. The embedding polymer may contain crosslinking agent but is otherwise applied as a film to the semiconductor wafer solar cell as much as possible to prevent voids such as bubbles or cracks by, for example, evaporating substances and to achieve uniform coating and penetration of the backside electrode structure.

The temporal temperature profile is preferably adjusted such that the embedding polymer wets more than 25%, preferably more than 30% and particularly preferably more than 50% of the passivation layer at the first temperature and crosslinks the embedding polymer at the second temperature. In that the embedding polymer has a lower viscosity at room temperature than at room temperature, the embedding polymer at the first temperature may be the one Penetrate the backside electrode structure and wet the passivation layer. At the second temperature, the viscosity of the embedding polymer is increased such that it can not reverse the penetration of the backside electrode structure, but the penetration of the backside electrode material remains stable and is maintained for a long period of time.

In a preferred embodiment, the first temperature is in a range of 70 to 115 ° C, preferably 80 to 100 ° C, more preferably 90 to 100 ° C, and the second temperature is in a range of 130 to 230 ° C, preferably 130 to 200 ° C, more preferably 140 to 170 ° C. In particular, when the embedding polymer is ethylene-vinyl acetate, the embedding polymer has a lower viscosity at the first temperature range than at room temperature and a higher viscosity at the second temperature range than at the first temperature range.

Alternatively, the temporal temperature profile comprises heating to a first temperature at which the embedding polymer has a lower viscosity than at room temperature, and cooling to a second temperature at which the embedding polymer has a higher viscosity than at the first temperature. This temporal temperature profile is suitable, for example, if the embedding polymer is a thermoplastic. Polyolefins, polyvinyl butyral (PVB), thermoplastic polyurethane (TPU) and silicones are, for example, thermoplastic. The first temperature is selected according to the material properties of the embedding polymer used, while room temperature is selected as the second temperature. That is, the embedding polymer is heated to the first temperature where it has a lower viscosity than room temperature and is deformable to penetrate the backside electrode structure and wet the passivation layer, and then cooled or allowed to cool to room temperature, so that the encapsulating polymer is no longer deformable and the penetration of the back electrode structure can not be undone.

Further alternatively, the embedding polymer may be selected to have sufficient viscosity to penetrate the backside electrode structure and wet the passivation layer as it is applied thereto, and cure in air or by addition of a hardener. Examples of such embedding polymers are silicones, for example as 2K components.

In the case of lamination, the contact pressure is preferably set in the range from 50,000 Pa to 100,000 Pa. In this setting, a vacuum is created which helps the embedding polymer to penetrate the open pores of the backside electrode structure by helping to overcome filling resistances such as narrow pore necks. The greater the negative pressure, the better the filling resistances are overcome. On the other hand, a negative pressure can also lead to cracks and / or defects of the back side electrode structure. For the purposes of the present invention, the contact pressure results from the difference between the laminating vacuum and the pressure in the pressure chamber.

Alternatively, in the lamination, the contact pressure is set in the range of 100,000 Pa to 300,000 Pa. In this setting, an overpressure is created which forces the embedding polymer into the open pores of the backside electrode structure. The overpressure helps to overcome filling resistances that are generated by the open-pored structure. Again, the greater the overpressure, the better the filling resistances are overcome. However, over-pressure can also lead to cracks and / or imperfections in the backside electrode structure. Therefore, it may also be advantageous to perform the lamination at ambient pressure or near ambient pressure.

Further advantages and properties of the solar module will be explained with reference to the preferred embodiments described below.

It shows:

1 schematically a sectional view oriented in the plane of a semiconductor wafer solar cell through its backside electrode structure, wherein the backside electrode structure is completely penetrated by an embedding polymer;

2 schematically a partial cross-sectional view of a solar module according to the invention;

3 schematically a partial cross-sectional view of another solar module according to the invention;

4 schematically a partial cross-sectional view of another solar module according to the invention;

5 schematically a method for producing the solar module according to the invention;

6 schematically another method for producing the solar module according to the invention; and

7 schematically another method for producing the solar module according to the invention.

1 schematically shows one in the plane of a semiconductor wafer solar cell 10 oriented sectional view through the back electrode structure 11 wherein the backside electrode structure 11 in the entire area of an embedding polymer 12 is permeated. The semiconductor wafer solar cell 10 is part of the solar module according to the invention. The embedding polymer 12 that has good adhesion between the semiconductor solar cell 10 and a backside encapsulation element (which is disclosed in US Pat 1 not shown), penetrates the back side electrode structure 11 from open-pore sintered metal particles. The sintered metal particles of the back surface electrode structure 11 are shown here schematically black. In the open pores is the embedding polymer 12 stored, which is shown here in white. It is emphasized that here a model and therefore purely exemplary periodically formed distribution of metal particles and open pores is shown. In microscopic reality usually no such regular structures will be found.

The embedding polymer 12 Penetrates the open pores of the backside electrode structure 11 such that it forms wetting areas in which there is the passivation layer (not shown here) of the semiconductor wafer solar cell 10 wetted. Wetting means that the embedding material 12 the backside electrode structure 11 penetrates to the underlying passivation layer and over the open pores of the backside electrode structure 11 when viewed microscopically, it makes contact with the passivation layer. The proportion of wetting areas relative to wetting areas and coverage areas in which the embedding polymer 12 the passivation layer 17 not wetted and the backside electrode structure 11 the passivation layer 17 not contacted, but covered, is more than 25%. How out 1 can be seen, over the entire back surface area both a conductive structure by means of the back electrode structure 11 as well as an adhesive structure interwoven with the conductive structure by means of the embedding polymer 12 will be realized. By virtue of the conductive structure and the adhesive structure extending along the backside surface in common, both a stable bond between the semiconductor wafer solar cell 10 and the backside encapsulation element (not shown here) as well as a semiconductor wafer solar cell 10 be provided with good electrical properties.

2 schematically shows a partial cross-sectional view of a solar module according to the invention 14 , The solar module 14 includes a plurality of semiconductor wafer solar cells 10 of which a part is shown here. The semiconductor wafer solar cell 10 has a semiconductor wafer 16 , one on the semiconductor wafer 16 arranged passivation layer 17 and one on the passivation layer 17 arranged backside electrode structure 11 (shown in black here). The backside electrode structure 11 contacts the semiconductor material of the semiconductor wafer 16 via a plurality of local contact areas (not shown here) electrically, wherein the contact areas as openings of the passivation layer 17 are formed. The electrical contact area occupies less than 5% of the back surface. The backside electrode structure 11 is from an embedding polymer 12 (here shown in white) completely penetrated so that wetting areas are formed in which the embedding polymer 12 wets the passivation layer. The proportion of wetting areas is more than 25% with respect to areas consisting of the wetting areas as well as covering areas in which the backside electrode structure 11 the passivation layer 17 covered. On the layer containing the back side electrode structure 11 and the embedding polymer 12 includes, is a Rückseitenverkapselungselement 19 disposed between the backside electrode structure 11 and the backside encapsulation element 19 typically consist of areas where the embedding polymer 12 not from back side electrode structure 11 is permeated. Due to the fact that the embedding polymer 12 the passivation layer 17 wetted and the backside electrode structure 11 penetrates and the Rückseitenverkapselungselement 19 contacted, becomes a stable bond between the semiconductor wafer solar cell 10 and the backside encapsulation element 19 guaranteed. Furthermore, the solar module 14 a front encapsulation material 15 on top of that on the semiconductor wafer 16 is arranged. The front encapsulation material 15 includes, for example, a layer of ethylene vinyl acetate and a glass sheet.

3 schematically shows a partial cross-sectional view of another solar module according to the invention 14 , Just like in 2 , is partially a semiconductor wafer solar cell 10 the plurality of semiconductor wafer solar cells 10 shown, wherein the semiconductor wafer solar cell 10 a semiconductor wafer 16 , one on the semiconductor wafer 16 arranged passivation layer 17 and one on the passivation layer 17 arranged backside electrode structure 11 (shown black here). The backside electrode structure 11 contacts the semiconductor material of the semiconductor wafer 16 via a plurality of local contact areas electrically, wherein the contact areas as openings (not shown here) of the passivation layer 17 are formed, wherein the electrical contact area less than 5% of Rear surface occupies. Furthermore, the solar module 14 a front encapsulation element 15 on top of that on the semiconductor wafer 16 is arranged. Unlike the in 2 shown solar module 14 puts in the 3 shown back side electrode structure 11 no continuous layer on the passivation layer 17 but has areas 20 hereinafter referred to as outdoor areas 20 be designated. The outdoor areas 20 make prior to contacting the semiconductor wafer solar cell 10 Areas where the passivation layer 17 exposed and not from the open-pored backside electrode structure 11 is covered. After contacting the semiconductor wafer solar cell 10 with the embedding polymer 12 (shown here in white) wets the embedding polymer 12 the passivation layer 17 on the one hand in the outdoor areas 20 and, on the other hand, by penetrating the open-celled backside electrode structure 11 so that wetting areas are formed. Overall, the proportion of wetting areas is more than 25% with respect to the combination of coverage areas and coverage areas in which the backside electrode structure 11 the passivation layer 17 covered. The embedding polymer 12 is so on or with the back side electrode structure 11 arranged that between the back side electrode structure 11 and a backside encapsulation element 19 the embedding polymer 12 located.

4 schematically shows a partial cross-sectional view of another solar module according to the invention 14 , As in the previous ones 2 and 3 has the solar module 14 a plurality of semiconductor wafer solar cells 10 some of which are shown here. The semiconductor wafer solar cell 10 has a semiconductor wafer 16 , one on the semiconductor wafer 16 arranged passivation layer 17 and one on the passivation layer 17 arranged backside electrode structure 11 (shown in black here). The backside electrode structure 11 contacts the semiconductor material of the semiconductor wafer 16 via a plurality of local contact areas (not shown here) electrically, wherein the contact areas as openings of the passivation layer 17 are formed, wherein the electrical contact area occupies less than 5% of the back surface. Furthermore, the solar module 14 a front encapsulation material 15 on top of that on the semiconductor wafer 16 is arranged. Unlike the in 2 and 3 shown solar module 14 , indicates the solar module 14 according to 4 a backside electrode structure 11 with varying layer thickness. The varying layer thickness results in a different degree of penetration of the backside electrode structure 11 with an embedding polymer 12 reached. In non-detention areas 21 has the embedding polymer 12 the backside electrode structure is not or only slightly penetrated so that the backside electrode structure 11 the passivation layer 17 covered or contacted, but in non-detention areas 21 the passivation layer 17 not from the embedding polymer 12 is wetted. In these non-detention areas 21 are the pores of the backside electrode structure 11 in the area of the boundary layer to the passivation layer 17 mostly not with embedding polymer 12 filled and thus form so-called microscopically covered areas. This is in the 4 thereby clarifying that the metal particles in the non-stick areas 21 are shown as gray and not as black dots.

In detention areas 22 Penetrates the embedding polymer 12 the backside electrode structure 11 up to the passivation layer 17 and is therefore in a position microscopically seen in wetting the passivation layer 17 to wet. The area fraction of wetting areas in which the embedding polymer 12 the passivation layer 17 compared with the area ratio of wetting areas and coverage areas in which the backside electrode structure 11 the passivation layer 17 covered, increases with increasing layer thickness of the back side electrode structure 11 from. The embedding polymer 12 can areas of the backside electrode structure 11 compared with other areas of the backside electrode structure 11 have a lower layer thickness, penetrate faster and better. The embedding polymer 12 is also such on the backside electrode structure 11 arranged that between the back side electrode structure 11 and a backside encapsulation element 19 the embedding polymer 12 so as to provide full-surface adhesion to the backside encapsulation element 19 to enable.

5 schematically shows a method for producing the solar module according to the invention. The method comprises the steps of providing a plurality of semiconductor wafer solar cells 51 and lamination 52 , The step 51 comprises providing a plurality of semiconductor wafer solar cells electrically connected to a solar cell string and each having a backside with a backside surface, the backside surface being surface passivated by a dielectric passivation layer, and a backside electrode structure comprising sintered metal particles disposed on the passivation layer; metallic backside electrode structure electrically contacts the semiconductor material of the semiconductor wafer via a plurality of local contact regions, wherein the contact regions are formed as openings of the passivation layer and occupy an overall electrical contact area of less than 5%, preferably less than 2%, of the backside surface. The semiconductor wafer solar cells continue to have Front side encapsulation element, which is arranged on the semiconductor wafer. The front encapsulant may comprise an encapsulating polymer and a glass, glass or plastic film used in the step described below 52 also be subjected to a lamination process. The step 52 includes lamination of a polymeric backside encapsulation structure forming the back side of the solar module with an encapsulant polymer on the back side of the solar cells so that the encapsulant polymer is in contact with the metallic backside electrode structure of the semiconductor wafer solar cells so that the encapsulant polymer after lamination 52 Wetting areas in which the embedding polymer wets the passivation layer such that the proportion of wetting areas is more than 25% preferably more than 30% and particularly preferably more than 50% with respect to wetting areas and coverage areas in which the backside electrode structure covers the passivation layer. Possibly. For example, lamination parameters such as contact pressure and temperature over time are adjusted to achieve the above degree of wetting. The lamination parameters depend on the embedding polymer used in the backside encapsulation structure. For example, if the embedding polymer is silicone, the lamination may 52 be carried out at room temperature and atmospheric pressure. Possibly. a silicone is used to which a hardener is added. The material of the encapsulant polymer of the backside encapsulation structure may be the same as or different from the material of the encapsulant polymer of the front encapsulation structure. They are preferably the same.

6 schematically shows a further method for producing the solar module according to the invention. In this exemplary case, EVA is used as the embedding material. The method comprises the steps of providing a plurality of semiconductor wafer solar cells 51 , Arranging a backside encapsulation structure 52a , Heating to a first temperature 52b and heating to a second temperature 52c , The step 51 is the same as in the process of 5 , Its explanation is therefore to the comments too 5 directed. In step 52a For example, the backside encapsulation structure is arranged on the back surface of the plurality of semiconductor wafer solar cells so as to cover them over the entire area. In step 52a The plurality of semiconductor wafer solar cells and back side encapsulation structure are heated to a first temperature. In particular, when the embedding polymer is ethylene vinyl acetate, the first temperature is in a range of 70 to 115 ° C. In this range, the embedding polymer has a lower viscosity than at room temperature and can easily penetrate the backside electrode structure and form wetting areas to the extent desired. Subsequently, step 52c in which the plurality of semiconductor wafer solar cells and the backside encapsulation structure are heated to a second temperature. In particular, when the embedding polymer is ethylene vinyl acetate, the second temperature is in a range of 130 to 230 ° C. In this temperature range, the embedding polymer has a higher viscosity than at the first temperature and cures so as to prevent it from coming out of the backside electrode structure. Overall, one will stable bond between solar cell, embedding polymer and Rückseitenverkapselungselement achieved. The steps 52b and 52c are carried out in a laminator such as Meier ICO-Laminator-28-18 from Caerus Systems, LLC (Milford, USA), in which in addition to the temperature profile and the contact pressure is set. The contact pressure in the pressure chamber of the laminator is, for example, 100,000 Pa to 300,000 Pa (gauge pressure). However, the contact pressure in the pressure chamber of the laminator can also be, for example, 50,000 Pa (negative pressure relative to ambient) up to 100,000 Pa (ambient pressure).

7 schematically shows a further method for producing the solar module according to the invention. In this exemplary case, a thermoplastic is used as the embedding material. The method comprises the steps of providing a plurality of semiconductor wafer solar cells 51 , Arranging a backside encapsulation structure 52a , Heating to a first temperature 52b and cooling to a second temperature 52d , The step 51 is the same as in the process of 5 , Its explanation is therefore to the comments too 5 directed. In step 52a For example, the backside encapsulation structure is arranged on the back surface of the plurality of semiconductor wafer solar cells so as to cover them over the entire area. In step 52a The plurality of semiconductor wafer solar cells and back side encapsulation structure are heated to a first temperature. The first temperature is selected such that the encapsulant polymer has a lower viscosity than at room temperature and is malleable such that the encapsulant polymer can readily penetrate the backside electrode structure and form wetting areas to the extent desired. Subsequently, step 52d in which the plurality of semiconductor wafer solar cells and the backside encapsulation structure are actively or passively cooled to a second temperature. The second temperature is chosen so that the embedding polymer has a higher viscosity than at the first temperature and is no longer deformable. Ideally, the second temperature is room temperature. As a result of the temperature profile, the embedding polymer hardens in such a way that it prevents it from emerging from the back-side electrode structure. Overall, a stable bond between the solar cell, embedding polymer and Rückseitenverkapselungselement is achieved. The step 52b is carried out in a laminator, in which in addition to the temperature profile and the contact pressure is set. The contact pressure in the pressure chamber of the laminator is, for example, 100,000 Pa to 300,000 Pa (gauge pressure). The step 52d can be realized by removing the solar module from the laminator and leaving it at room temperature.

Further advantages and properties of the solar module will be explained with reference to the example described below, which, however, is not intended to limit the present invention.

example

A plurality of semiconductor wafer solar cells (6 "cells with 3 busbars) with a front encapsulation element and surface passivated back have been provided. The uppermost layer of the side of the passivation layer facing away from the semiconductor wafer material is a silicon nitride layer having a refractive index of 2-2.1 at 633 nm. The Ferro CN 53-200 metal paste, which is commercially available from Ferro (Cleveland, USA), was applied to the silicon nitride layer with a layer thickness of <20 μm in a screen printing process. The particle size distribution of the metal paste is determined by means of grindometers (according to DIN 53 203 respectively. DIN EN 21 524 and ISO 1524 ). The particle sizes were greater than or equal to 12 μm (10 streaks) and greater than or equal to 20 μm (3 streaks). The metal paste was screen printed on the silicon nitride layer. The screen (400 threads / inch, 18 μm diameter) was used at a 45 ° wrap angle. The thickness of the metal paste emulsion above the screen was 15 μm. After applying the metal paste to the silicon nitride layer, the semiconductor wafer solar cells were fired in a fiery oven for 1.24 degree hours (degrees Celsius per hour) at temperatures above 400 ° C. On the silicon nitride layer, after firing, an open-pore back electrode structure was arranged. Ready-to-use semiconductor wafer solar cells were now finished.

The back of the semiconductor wafer solar cells was treated with a ethylene-vinyl acetate film as an embedding polymer (commercially available PHOTOCAP FC280P / UF, the (STR ^® Specialized Technology Resources, Inc. Enfield, USA) is) coated. The ethylene vinyl acetate film used has the following properties: a tensile strength of 18.5 (2684) MPa (PSI), a stretching effect of 700%, a 10% flexural modulus of 14.8 (2150) MPa (PSI), a hardness of 80 / 22 Shore A / D, an optical transmission of 93%, a refractive index of 1.482, a dielectric strength of 1400 V / mil, a volume resistivity of 5 x 10 ¹⁴ ohms / cm, a UV cut-off wavelength of 360 nm, and adhesion Glass of 70-88 N / 10 mm. On the ethylene vinyl acetate layer Icosolar AAA 3554 of the manufacturer Isovoltaic (Lebring, Austria) was arranged as Rückseitenverkapselungselement. The back-coated semiconductor wafer solar cells were placed in a Meier ICO Laminator-28-18 from Caerus Systems, LLC (Milford, USA). The laminator was brought to a temperature of 145 ° C and evacuated twice for 4 min., So that the laminator chamber and lid were evacuated. The lid was then vented to 80,000 Pa in 1 minute. The condition was maintained for another 7 min. Subsequently, the laminator chamber and lid were ventilated. The lid was removed and the solar module was removed from the laminator chamber and allowed to stand at room temperature.

To test the adhesion of the backside encapsulation structure to the laminated solar cells of a solar module according to the invention, the following tear test was carried out on at least one predetermined test strip.

To test the adhesion, the tensile testing machine Z 10 from Coesfeld (Dortmund, Germany) was used. The at least one test strip was torn off at an angle of about 180 °. The tensile tester had the following settings: speed: 100 mm / min, travel distance: 300 mm and breaking strength threshold: ΔF = 200. The force threshold was set to 0.1 N at the beginning of the recording, force limit (abort of the measurement) was on 95 N is set. The solar module was placed in the tensile testing machine and tightened so that the at least one test strip could just be demolished. The pull wire of the tensile tester was placed straight and centered on the test strip and the tensile test measurement was started. The measurement was discontinued if the test strip breaks and / or if the test strip is completely torn off at <300 nm. The at least one test strip was photographed after the tear-off test.

It has been found that in the solar modules according to the invention, in which the embedding polymer wets the passivation layer such that wetting areas are formed in which the embedding polymer wets the passivation layer, and the proportion of wetting areas more than 25%, preferably more than 30% and especially Preferably, more than 50% with respect to areas consisting of wetting areas and coverage areas in which the passivation layer is covered by the backside electrode structure, the crack area is not within the backside electrode structure but located in the semiconductor wafer substrate. Thus, such behavior of a solar module with solar cells having a screen-printed backside metallization is an indication that the penetration of the backside metallization by the embedding polymer has been done so as to ensure long-term stable adhesion.

LIST OF REFERENCE NUMBERS

10

Semiconductor wafer solar cell

11

Backside electrode structure

12

embedding polymer

14

solar module

15

Frontseitenverkapselungselement

16

Semiconductor wafer

17

passivation

19

Rückseitenverkapselungselement

20

outdoor Space

21

Non-stick region

22

adhesion area

51

Provision of a plurality of semiconductor wafer solar cells

52

lamination

52a

Arranging a backside encapsulation structure

52b

Heating up to a first temperature

52c

Heating up to a second temperature

52d

Cool to a second temperature

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• DIN 53 203 [0054]
• DIN EN 21 524 [0054]
• ISO 1524 [0054]

Claims (15)

Solar module ( 14 ) having the front side and a rear side, the following features: a plurality of semiconductor wafer solar cells ( 10 ) which are electrically connected to form a solar cell string and each have a rear side with a rear side surface, wherein the rear side surface by means of a dielectric passivation layer ( 17 ) is surface-passivated, and on the passivation layer ( 17 ) a backside electrode structure comprising sintered metal particles ( 11 ) and the metallic back side electrode structure ( 11 ) the semiconductor material of the semiconductor wafer ( 16 ) electrically contacted via a plurality of local contact areas, wherein the contact areas as openings of the passivation layer ( 17 ) are formed and occupy an overall electrical contact area of less than 5%, preferably less than 2%, of the rear side surface, • a front side encapsulation element forming the front side of the solar module ( 15 ) and • a polymer backside encapsulation structure forming the rear side of the solar module with an embedding polymer ( 12 ) in contact with the metallic back side electrode structure ( 11 ) of the semiconductor wafer solar cells ( 10 ), characterized in that the embedding polymer ( 12 ) the passivation layer ( 17 ) so that wetting areas are formed in which the embedding polymer ( 12 ) the passivation layer ( 17 ), and the proportion of wetting areas is more than 20%, preferably more than 35% and particularly preferably more than 50% in relation to areas consisting of wetting areas and coverage areas, in which the passivation layer ( 17 ) from the backside electrode structure ( 11 ) is covered. Solar module ( 14 ) according to claim 1, characterized in that the percentage of the metallic back-side electrode structure ( 11 ) is greater than 80%, preferably greater than 90%, more preferably greater than 95% relative to the back surface. Solar module ( 14 ) according to claim 1 or 2, characterized in that the resistivity of the back side electrode structure ( 11 ) ≦ 10 × 10 ^-7 ohm.cm, preferably ≦ 7 × 10 ^-7 ohm.cm, more preferably ≦ 5 × 10 ^-7 ohm.cm. Solar module ( 14 ) according to one of the preceding claims, characterized in that the back side electrode structure ( 11 ) a varying layer thickness with adhesion areas ( 22 ) compared to the other areas ( 21 ) have lower layer thicknesses of less than 30 μm, preferably less than 25 μm, more preferably less than 20 μm, even more preferably less than 15 μm. Solar module ( 14 ) according to claim 4, characterized in that the area fraction of wetting areas in which the embedding polymer ( 12 ) the passivation layer ( 17 ) compared with the area fraction of areas in which the embedding polymer ( 12 ) the passivation layer ( 17 ) not wetted, with increasing layer thickness of the back side electrode structure ( 11 ) decreases. Solar module ( 14 ) according to any one of the preceding claims, characterized in that the embedding polymer ( 12 ) is networked. Solar module ( 14 ) according to one of the preceding claims, characterized in that the passivation layer ( 17 ) is constructed as a thin-film stack. Solar module ( 14 ) according to one of the preceding claims, characterized in that the thin-film stack has as topmost layer a bonding agent layer and / or a conductive layer. Solar module ( 14 ) according to one of the preceding claims, characterized in that the backside surface of the semiconductor wafer solar cells ( 10 ) Outdoor areas ( 20 ) to an area fraction of less than 20%, preferably less than 10%, more preferably less than 5%, in which the passivation layer ( 17 ) not from the backside electrode structure ( 11 ) is covered. Method for producing a solar module ( 14 ) with a front side and a back side comprising the following steps: 51 ) a plurality of semiconductor wafer solar cells ( 10 ) which are electrically connected to form a solar cell string and each have a rear side with a rear side surface, wherein the rear side surface by means of a dielectric passivation layer ( 17 ) is surface-passivated, and on the passivation layer ( 17 ) a backside electrode structure comprising sintered metal particles ( 11 ) and the metallic back side electrode structure ( 11 ) the semiconductor material of the semiconductor wafer ( 16 ) electrically contacted via a plurality of local contact areas, wherein the contact areas as openings of the passivation layer ( 17 ) and have an overall electrical contact area of less than 5%, preferably less than 2%, of the back surface and 52 ) one the back of the solar module ( 14 ) forming polymer back side encapsulation structure with an embedding polymer ( 12 ) on the back of the solar cells ( 10 ), so that the embedding polymer ( 12 ) in contact with the metallic backside electrode structure ( 11 ) of the semiconductor wafer solar cells ( 10 ), characterized in that Lamination parameters such as contact pressure, temporal temperature profile and laminating chamber pressure can be set such that the embedding polymer ( 12 ) the passivation layer ( 17 ) are wetted such that wetting areas are formed in which the embedding polymer ( 12 ) the passivation layer ( 17 ), and the proportion of wetting areas is more than 20%, preferably more than 35% and particularly preferably more than 50% in relation to areas consisting of wetting areas and coverage areas, in which the passivation layer ( 17 ) from the backside electrode structure ( 11 ) is covered. A method according to claim 10, characterized in that the temporal temperature profile, a heating to a first temperature ( 52a ), in which the embedding polymer ( 12 ) has a lower viscosity than at room temperature, and heating to a second temperature ( 52b ), in which the embedding polymer ( 12 ) has a higher viscosity than at the first temperature. A method according to claim 10 or 11, characterized in that the temporal temperature profile is adjusted such that the embedding polymer ( 12 ) at the first temperature more than 25%, preferably more than 30% and more preferably more than 50% of the passivation layer ( 17 ) and the embedding polymer ( 12 ) at the second temperature. Method according to one of the preceding claims 11 or 12, characterized in that the first temperature in a range of 70 to 115 ° C, preferably 80 to 100 ° C, more preferably 90 to 100 ° C, and the second temperature in a range of 130 to 230 ° C, preferably 130 to 200 ° C, more preferably 140 to 170 ° C, is located. Method according to one of the preceding claims 10 to 13, characterized in that in the lamination ( 52 ) the contact pressure in the range of 50,000 Pa to 100,000 Pa is set. Method according to one of the preceding claims 10 to 13, characterized in that in the lamination ( 52 ) the contact pressure in the range of 100,000 Pa to 300,000 Pa is set.

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