Method for connecting a plurality of solar cells to form a solar cell string, solar cell string, and method for producing a solar module

Abstract

The invention relates to a method for connecting a plurality of solar cells (1) to form a solar cell string, comprising the following steps: a) providing a plurality of solar cells (1) each having a front face (5) and a rear face (6), b) providing a film (2) having embedded electrical conducting tracks (3), c) electrically connecting the front face (5) of one of the plurality of solar cells (1) to the rear face (6) of an adjacent of the plurality of solar cells (1) by means of the film (2) having the embedded electrical conducting tracks (3), in order to produce the solar cell string. The invention also relates to a solar cell string obtained by means of the method and to a method for producing a solar module by means of the solar cell string.

Description

[0001] Method for interconnecting several solar cells to form a solar cell string, solar cell string and method for producing a solar module

[0002] Description:

[0003] The invention relates to a method for interconnecting multiple solar cells to form a solar cell string, to a solar cell string, and to a method for producing a solar module. In particular, the invention relates to a method for interconnecting multiple solar cells to form a solar cell string using electrical conductors, to a solar cell string obtained by the method, and to a method for producing a solar module using the solar cell string.

[0004] It is common practice to interconnect solar cells using soldering. For this purpose, solar cells have dedicated areas, also called busbars, where the soldering takes place. Busbars are applied to the solar cells from expensive silver pastes during the solar cell manufacturing process, for example, by screen printing. Due to the placement tolerance of the cell connector connecting the solar cells, such as a wire in module construction, busbars have some areas that always cast shadows, even if the cell connector is perfectly aligned with the busbars. Poor alignment results in additional shadowing. This shadowing leads to power losses.

[0005] To create the interconnection, the cell connector, for example a round wire with a copper core and solder coating, is placed on the busbar using a soldering process and held in place on the solar cell with hold-down devices during soldering. After cooling, a solid connection is formed. However, poor alignment often occurs when placing the cell connector on the busbar. Alternatively, solder paste or an electrically conductive adhesive can be applied to the solar cell and then a cell connector can be placed on top and heated. The cell connector must also be aligned with the applied structures to minimize any shading it causes. A further disadvantage is that a larger amount of solder paste or adhesive has to be applied than necessary, which increases costs and causes shading.

[0006] In subsequent module construction, encapsulation materials such as ethylene vinyl acetate are used to create an optical connection between the front and rear glass or foil elements and the solar cell string created by interconnection. These encapsulation materials must be thick enough to enclose the cell connector and prevent damage from pressure. At the same time, the encapsulation materials absorb incident light, and the thicker they are, the more they absorb it. This leads to power losses. Furthermore, a compromise must be struck between shading and electrical losses due to cell connector resistance.

[0007] Furthermore, a solar module can produce

[0008] Temperature fluctuations, which cause different expansion coefficients between cell connector and solar cell materials, such as copper and silicon, and thus create stresses on the solder joint and the solar cell. In the long term, this can lead to solder joint failure and thus to significant performance losses.

[0009] EP 3 165 361 A1 further discloses a device such as a solar module comprising a polymer conductor film. The polymer conductor film comprises a polymer film with at least two adjacent zones and an elongated conductor. A first zone is sufficiently ductile and / or adhesive to fix the position of an elongated conductor on an outer side of the polymer film. A second zone adjacent to the first zone has a different degree of polymerization and / or crosslinking than the first zone. The elongated conductor is positioned on the surface of the first zone, which represents an outer side of the polymer film.

[0010] However, there is still a need to minimize the shadowing caused by cell connectors or conductors. Furthermore, it is desirable to provide more complex conductor structures that can also minimize shadowing.

[0011] It is an object of the present invention to provide a method for interconnecting a plurality of solar cells to form a solar cell string, a solar cell string and a method for producing a solar module, in which complex conductor shapes are possible and the least possible shading is achieved when interconnecting the solar cells.

[0012] According to the invention, this object is achieved by a method having the features of claim 1, a solar cell string having the features of claim 13, and a method having the features of claim 14. Advantageous further developments and modifications are specified in the subclaims.

[0013] The electrical conductors embedded in the foil can have more complex shapes for electrically connecting solar cells. Furthermore, less shading can be achieved. Both of these factors lead to higher performance.

[0014] The invention relates to a method for interconnecting a plurality of solar cells to form a solar cell string, comprising the following steps: a) providing a plurality of solar cells, each having a front side and a back side, b) providing a film with embedded electrical conductor tracks, c) electrically interconnecting the front side of one of the plurality of solar cells with the back side of an adjacent one of the plurality of solar cells using the film with the embedded electrical conductor tracks, in order to produce the solar cell string. According to the invention, the electrical conductor tracks are embedded in the film. This makes it possible to use electrical conductor tracks with more complex shapes for the electrical interconnection of solar cells. In addition, less shading can be achieved. The film can be multi-layered. It is advantageous if the film is single-layered and consists of one material.

[0015] The term "film with embedded electrical conductor tracks" refers to a film that has recesses, such as grooves, into which the electrical conductor tracks are embedded, i.e., integrated. Preferably, the embedded electrical conductor tracks do not protrude from the film. Rather, the film is preferably designed to protrude relative to the embedded electrical conductor tracks or is designed to be flush with them.

[0016] The term “neighboring solar cell” means a solar cell that is adjacent to a first-mentioned solar cell in the solar cell string produced.

[0017] In a preferred embodiment, the film with embedded electrical conductor tracks provided in step b) is, in a first variant, one-piece, and the electrical conductor tracks are arranged in the film such that they extend from one surface of the film to another surface opposite this surface, wherein step c) applying the film with the embedded electrical conductor tracks to the front side of one solar cell and to the back side of the adjacent solar cell comprises the electrical wiring. During the wiring, the back side of one solar cell must be electrically connected to the front side of the adjacent solar cell, or vice versa. The film with the embedded electrical conductor tracks is guided from the back side of one solar cell to the front side of the adjacent solar cell, or vice versa.The electrical conductor tracks embedded in the film are therefore designed in such a way that they can make contact with the solar cell metallizations in the form of a front or rear electrode of the solar cells. The above embodiment achieves this in a simple manner by having recesses in the film into which the electrical conductor tracks are embedded.

[0018] In the first variant, the electrical conductor tracks embedded in the film are preferably formed as solid conductors, more preferably as wires. The electrical conductor tracks embedded in the film are preferably exposed in such a way that, when applied to the front or back of the adjacent solar cells, they make complete or essentially complete contact with them along their extension direction.

[0019] In a preferred embodiment, prior to step b), the electrical conductor tracks are embedded in the film in such a way that the electrical conductor tracks extend from one surface of the film to another surface opposite the surface, wherein the film thus produced with the embedded electrical conductor tracks is inserted in one piece in step c) according to the first variant.

[0020] In an alternatively preferred embodiment, the film provided in step b) with the embedded electrical conductor tracks comprises, in a second variant, several segments that are electrically interconnected or are interconnected in step c), wherein in step c), one of the segments is placed on the front side of one solar cell and the other segment is placed on the back side of the other solar cell. The segments can, but do not have to, be identical.

[0021] To provide the film according to the second variant, the film is preferably structured on one side before step b) so that it has grooves on one side. The film is structured, for example, in a roll-to-roll process using an embossing roller. The embossing is designed to create grooves that later exhibit advantageous optical properties. For example, the grooves have a triangular shape. Subsequently, the electrical conductor tracks are embedded in the grooves, for example, by selective electroplating, and the film is separated into the multiple segments. These two steps can be performed in any order.

[0022] Various materials and / or layers can be used to create the electrical conductor tracks embedded in the film according to the second variant. Preferably, a highly reflective material and a highly conductive material are used to embed the electrical conductor tracks in the film, and optionally an electrically conductive adhesive is embedded in the trenches. It is particularly advantageous if the electrical conductor tracks embedded in the film have the highest possible proportion of direct reflection so that they become optically transparent. A highly reflective material is suitable as a first layer, and then a highly conductive material such as copper is introduced into the trenches. In a further step, the film can be filled with the electrically conductive adhesive, for example in a roll-to-roll process.

[0023] In a preferred embodiment, a plurality of embedded electrical conductor tracks extend in each segment in a direction of extension, and one of the embedded electrical conductor tracks extends in a direction transverse, preferably perpendicular, to the direction of extension, in order to represent a wiring region for interconnection with a further wiring region of a further segment. The electrical conductor track, which extends in a direction transverse to the direction of extension, can be segmented. This allows film regions to be located between the conductor track segments, which can be glued together. The connection of the film regions can be achieved, for example, by means of pressure and / or temperature.

[0024] In a preferred embodiment, the segments are preferably interconnected to form a film. For this purpose, the segments with the embedded electrical conductors are placed on top of one another in such a way that their interconnection areas lie on top of one another. The segments are then electrically connected, for example, using pressure and / or temperature to create a composite. The resulting composite is then interconnected with neighboring solar cells. If the interconnection areas cause significant shading, they can be arranged on the side of the solar cell string facing away from the light incidence side during the interconnection of neighboring solar cells.

[0025] In an alternative process variant, the segments are preferably not connected to the solar cells before interconnection. Instead, the solar cells and the segments are preferably placed one after the other and only then connected. Preferably, one of the several solar cells is positioned, then a segment is positioned next to it, followed by another segment being placed on the positioned solar cell and another solar cell on the positioned segment. The composite created in this way is preferably glued together. The composite is preferably further electrically connected to one another using temperature and, if necessary, pressure. The temperature bonds the film to the solar cells and presses the embedded electrical conductor tracks against the front and back electrodes of the solar cells, creating a press contact.If an electrically conductive adhesive is used between the electrical tracks and the solar cells, it is activated by the temperature and creates an electrical connection between the electrical tracks and the front and back electrodes.

[0026] The temperature required for electrical interconnection is preferably below 220°C, which is typically used in a soldering process. This significantly reduces thermal stress. The process is ideal for temperature-sensitive solar cells.

[0027] Preferably, the foil with the embedded electrical conductor tracks is attached to the front and back sides of adjacent solar cells using an electrically conductive adhesive. This easily establishes an electrical connection to the solar cell metallization in the form of its front and back electrodes.

[0028] Preferably, step c) is carried out using heat and / or pressure. This effectively implements the electrical interconnection.

[0029] The electrical conductors embedded in the film are preferably designed such that light incident perpendicularly to them is completely coupled into the solar module upon integration of the solar cell string. In a preferred embodiment, the cross-section of the electrical conductors embedded in the film is triangular. This effectively achieves this coupling. Since the electrical conductors embedded in the film are effectively optically transparent, a large number of conductors can be used. This, in turn, reduces the electrical losses of the front-side electrodes of the solar cells, e.g., in the form of solar cell fingers, since shorter paths need to be covered.

[0030] Preferably, the electrical conductor tracks embedded in the film each have a ratio of height (Y) to width (X) in the range Y / X >0.19.

[0031] The plurality of solar cells can each be configured as a solar cell having a front electrode and / or busbars and a rear electrode. Step c) then preferably comprises electrically connecting the electrical conductor tracks embedded in the film to the front electrode and / or the busbars of one of the plurality of solar cells and the rear electrode of the adjacent solar cell.

[0032] For the purposes of this invention, the term "solar cell" refers to a semiconductor structure that has a photovoltaically active junction, in particular a pn junction, and is intended, in a final state, for use in converting sunlight into electrical energy. For the solar cell feature to be fulfilled, it is not necessary for the semiconductor structure to have all the structural features of a fully processed solar cell. For example, metallized electrode structures may still be missing. This means that even a partially processed semiconductor structure with a photovoltaically active junction, in particular a pn junction, fulfills the feature of a "solar cell" within the meaning of the present invention.

[0033] In a preferred embodiment, the plurality of solar cells are each busbarless, front-side electrodeless, and / or back-side electrodeless. These solar cells are more efficient due to the reduced shading. There is neither shading nor recombination losses due to busbars or solder pads. Therefore, the performance is comparatively high. In particular, the film with the embedded electrical conductor tracks can replace finger electrodes. Preferably, the plurality of solar cells are busbarless and front-side electrodeless. Step c) then preferably comprises electrically connecting the electrical conductor tracks embedded in the film to a doped layer, which forms a front side of one of the plurality of solar cells over part or all of its surface, and to the back side electrode of the adjacent solar cell, wherein the film with the embedded electrical conductor tracks acts not only as a cell connector, but also as the front side electrode of one of the solar cells.

[0034] The invention further relates to a solar cell string obtained by a method according to one of the embodiments described above.

[0035] The electrical conductor tracks that are in electrical contact with the front side of one solar cell can be designed differently than the electrical conductor tracks that are in electrical contact with the back side of the adjacent solar cell; the number of electrical conductor tracks can also vary. Furthermore, relief loops can be incorporated into the electrical conductor tracks so that the voltage from solar cell to solar cell is reduced. The invention further relates to a method for producing a solar module, comprising

[0036] Providing the solar cell string described above, placing a front-side encapsulation element on a light-incident side of the solar cell string and a back-side encapsulation element on a side of the solar cell string facing away from the light-incident side to obtain a sandwich-like structure, and

[0037] Laminating the sandwich-like structure.

[0038] Since the electrical conductors are already embedded in the film, an encapsulating material such as EVA is not required. Alternatively, a comparatively thin encapsulating material, e.g., <500 μm, can be used. This comparatively thin encapsulating material is more transparent than a thicker one, resulting in higher solar module performance. In addition, encapsulating materials with different properties can be used, offering advantages in reliability, cost, and optical coupling.

[0039] The method may further comprise producing a cross-connection, i.e., a series connection from solar cell string to solar cell string using a film with embedded electrical conductor tracks, which is produced as described above for the method for producing a solar cell string. In this case, the electrical conductor tracks can run on the sides of the solar cells facing away from the light incidence side, so that a higher packing density can be achieved. This increases the solar module efficiency.

[0040] Further features and advantages of the invention are described in connection with preferred embodiments, which are explained in more detail with the aid of the following figures.

[0041] Shown are: Fig. 1 a partial cross-sectional view of a solar cell string according to the invention;

[0042] Fig. 2 is a partial plan view of the solar cell string shown in Fig. 1;

[0043] Fig. 3 is a partial side view of a solar cell string according to the invention;

[0044] Fig. 4 is a partial perspective view of the solar cell string shown in Fig. 3;

[0045] Fig. 5 is a further partial perspective view of the solar cell string shown in Fig. 3;

[0046] Fig. 6a to 6g each show a step for producing a film with embedded electrical conductor tracks;

[0047] Fig. 7 is a cross-sectional view of the solar cell string shown in Fig. 6g.

[0048] Fig. 1 shows a partial cross-sectional view of a solar cell string according to the invention. The solar cell string has a plurality of solar cells 1 with a front side 5 and a back side 6, one of which is visible in Fig. 1. Arranged on a surface 4, in this case the front side 5 of the solar cell 1, is a film 2 with embedded electrical conductor tracks 3, one of which is shown. The electrical conductor track 3 has a triangular shape. The front side 5 is a light incident side of the solar cell 1. During operation, light rays 10 also strike the electrical conductor track 3 embedded in the film 2, wherein shading by this is relatively minimal, as shown.

[0049] Fig. 2 shows a partial top view of the solar cell string shown in Fig. 1. The film 2 is arranged on the surface 4 of the front side 5 of the solar cell 1 and is transparent. The electrical conductor track 3 is arranged on a partial area of ​​the surface 4.

[0050] Fig. 3 shows a partial side view of a solar cell string according to the invention. The solar cell string has a plurality of solar cells 1 with surfaces 4, each forming a front side 5 and a back side 6 of the solar cells 1. Furthermore, the solar cell string has a one-piece film 2 with embedded electrical conductor tracks 3. The electrical conductor tracks 3 are arranged in the film 2 such that they extend from one surface 21 of the film 2 to another surface 22 opposite the surface 21, so that the electrical interconnection is created by applying the film 2 with the embedded electrical conductor tracks 3 to the front side 5 of one solar cell 1 and to the back side 6 of the adjacent solar cell 1.

[0051] Fig. 4 shows a partial perspective view of the solar cell string shown in Fig. 3 along the line IV-IV. The electrical conductor tracks 3 are embedded triangularly into the surface (not shown) so that they do not protrude, while the surface 22 is free of conductor tracks.

[0052] Fig. 5 shows another perspective partial view of the solar cell string shown in Fig. 3 along the line VV. The electrical conductor tracks 3 are embedded triangularly into the surface 22 so that they do not protrude, while the opposite surface (not shown) is free of conductor tracks.

[0053] 6a to 6g each show a step for producing a film with embedded electrical conductor tracks. Fig. 6a shows a step in which a film 2, which is shown in a partial cross-sectional view, is structured on one side so that it has trenches 7 on one side. Fig. 6b shows a step in which electrical conductor tracks 3 are embedded in the trenches 7 of the film 2 shown in the partial cross-sectional view so that they are triangular, wherein a highly reflective material (not shown) and a highly conductive material (not shown) can be embedded in each case for embedding the electrical conductor tracks 3 in the film. In step 6c it is shown that an electrically conductive adhesive 8 is further embedded in the trenches 7 on the electrical conductor tracks 3 in the film 2 shown in the partial cross-sectional view.In step 6d, a plan view of the film 2 is shown, which has three segments 2a, 2b, 2c that can be separated by cutting along cutting regions 11. In each of the segments 2a, 2b, 2c, a plurality of the embedded electrical conductor tracks 3 extend in a direction of extension E, and one of the embedded electrical conductor tracks 3 extends in a direction perpendicular to the direction of extension E in order to represent a wiring region for interconnecting with a further wiring region of a further segment 2a, 2b, 2c. In step 6e, the two segments 2a, 2b are shown in plan view, which have been separated by cutting, wherein the segment 2b is smaller than in FIG.6d is rotated by 180°, as indicated by an arrow, so that the electrical conductor tracks 3 of segment 2a and the electrical conductor tracks 3 of the segment point towards each other, wherein the electrical conductor tracks 3 of segment 2b are actually not visible in this figure and are therefore shown in dashed lines. Fig. 6f shows a step in plan view of the segments 2a, 2b, in which the interconnection areas of the two segments 2a, 2b are electrically interconnected using temperature and, if necessary, pressure, wherein the electrical conductor tracks 3 of segment 2b are actually not visible in this figure and are therefore shown in dashed lines. Fig. 6g shows a step in which a solar cell 1 is electrically interconnected with one of the segments 2a, 2b, wherein the resulting solar cell string is shown in plan view and wherein the electrical conductor tracks 3 of segment 2b are actually not visible in this figure and are therefore shown in dashed lines.The back side (not shown) of one solar cell 1 is electrically connected to the segment 2a, while a surface 4 of the front side 5 of the adjacent solar cell 1 is electrically connected to the segment 2b.

[0054] Fig. 7 shows a cross-sectional view of the solar cell string shown in Fig. 6g. The surface 4 of the rear side 6 of one solar cell 1 is electrically connected to the electrical conductor tracks 3 of segment 2a, while the surface 4 of the front side 5 of the adjacent solar cell 1 is electrically connected to the electrical conductor tracks 3 of segment 2b. Furthermore, the interconnection regions 3b of the two segments 2a, 2b are electrically interconnected.

[0055] In a variant of the method shown in Fig. 6a to 6g, the segments 2a, 2b can not be connected to the solar cells 1 prior to interconnection in order to create the solar cell string shown in Fig. 6g, 7. Alternatively, the solar cells 1 and the segments 2a, 2b can be deposited one after the other and only then connected. To do this, one of the several solar cells 1 is positioned, then the segment 2b is positioned next to it, followed by the segment 2a being placed on the positioned solar cell 1 and another solar cell 1 being placed on the positioned segment 2b. The composite is preferably glued and electrically connected using temperature and, if necessary, pressure.

[0056] List of reference symbols:

[0057] 1 solar cell

[0058] 2 Slide 2a, 2b, 2c each segment

[0059] 3 electrical conductor track

[0060] 3a Busbar

[0061] 3b Wiring area

[0062] 4 Surface 5 Front

[0063] 6 Back

[0064] 7 ditch

[0065] 8 glue

[0066] 10 Light beam 11 Cutting area

[0067] 21 Surface

[0068] 22 additional surfaces

Claims

Patent claims:

1. A method for interconnecting a plurality of solar cells (1) to form a solar cell string, comprising the following steps: a) providing a plurality of solar cells (1), each having a front side (5) and a back side (6), b) providing a film (2) with embedded electrical conductor tracks (3), c) electrically interconnecting the front side (5) of one of the plurality of solar cells (1) with the back side (6) of an adjacent one of the plurality of solar cells (1) using the film (2) with the embedded electrical conductor tracks (3) to produce the solar cell string.

2. Method according to claim 1, characterized in that the film (2) provided in step b) with embedded electrical conductor tracks (3) is in a first variant in one piece and the electrical conductor tracks (3) are arranged in the film (2) in such a way that they extend from one surface (21) of the film (2) to a further surface (22) opposite the surface (21), wherein step c) of applying the film (2) with the embedded electrical conductor tracks (3) to the front side (5) of one solar cell (1) and to the back side (6) of the adjacent solar cell (1) comprises the electrical wiring.

3. Method according to claim 2, characterized in that the electrical conductor tracks (3) embedded in the film (2) are designed as solid conductors, preferably as wires.

4. Method according to one of claims 1 to 3, characterized in that before step b) an embedding of the electrical conductor tracks (3) in the film (2) is carried out in such a way that the electrical conductor tracks (3) extend from a surface (21) of the film (2) to a further surface (22) opposite the surface (21) and that the film (2) thus produced with the embedded electrical conductor tracks (3) is inserted in one piece in step c).

5. The method according to claim 1, characterized in that the film (2) provided in step b) with the embedded electrical conductor tracks (3) in a second variant has a plurality of segments (2a, 2b) which are electrically interconnected or are interconnected in step c), wherein in step c) one of the segments (2b) is placed on the front side (5) of one solar cell (1) and the other segment (2a) is placed on the back side (6) of the other solar cell (1).

6. The method according to claim 5, characterized in that before step b) the film (2) is structured on one side so that it has trenches (7) on one side, the electrical conductor tracks (3) are embedded in the trenches (7) and the film (2) is separated into the plurality of segments (2a, 2b, 2c).

7. Method according to claim 6, characterized in that for embedding the electrical conductor tracks (3) in the film, a highly reflective material and a highly conductive material and optionally an electrically conductive adhesive (8) are embedded in the trenches (7).

8. Method according to one of claims 5 to 7, characterized in that in the segments (2a, 2b, 2c) a plurality of the embedded electrical conductor tracks (3) extend in an extension direction (E) and one of the embedded electrical conductor tracks (3) extends in a direction transverse, preferably perpendicular to the extension direction (E), in order to form a To represent an interconnection area for interconnecting with a further interconnection area of ​​a further segment (2a, 2b, 2c).

9. Method according to one of the preceding claims, characterized in that step c) is carried out using heat and / or pressure.

10. Method according to one of the preceding claims, characterized in that a cross section of the electrical conductor tracks (3) embedded in the film (2) is triangular.

11. Method according to one of the preceding claims, characterized in that the electrical conductor tracks (3) embedded in the film (2) each have a ratio of height (Y) to width (X) in the range of Y:X >0.

19.

12. Method according to one of the preceding claims, characterized in that the plurality of solar cells (1) are each busbarless, front-side electrodeless and / or back-side electrodeless.

13. Solar cell string obtained by a process according to any one of the preceding claims.

14. A method for producing a solar module, comprising Providing a solar cell string according to claim 13, placing a front-side encapsulation element on a light-incident side of the solar cell string and a back-side encapsulation element on a side of the solar cell string facing away from the light-incident side to obtain a sandwich-like structure, and laminating the sandwich-like structure.

15. The method according to claim 14, characterized in that a plurality of solar cell strings are provided, which are subjected to a series connection from solar cell string to solar cell string using a film with embedded electrical conductor tracks.

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