Improved photovoltaic cell comprising a connection interface

Abstract

An electrical connection interface (20) comprising a silicon support (21) which has a front face (22) and a rear face (23) opposite the front face (22), wherein the front face (22) comprises a welded connection with a connector (30) intended to be connected to an electrical harness (10) and the rear face comprises an electrically conductive zone. A cell comprising such an interface (20). A photovoltaic module comprising such a cell.

Description

[0001] DESCRIPTION

[0002] TITLE

[0003] IMPROVED PHOTOVOLTAIC CELL INCLUDING A CONNECTION INTERFACE

[0004] TECHNICAL FIELD

[0005] The present invention relates to the field of photovoltaic modules, which comprise a set of photovoltaic cells (single junction, multi-junction) electrically connected to each other, and preferably photovoltaic cells based on monocrystalline silicon or multicrystalline silicon.

[0006] STATE OF THE PRIOR ART

[0007] A photovoltaic module is an assembly of photovoltaic cells arranged side by side between a first transparent layer forming a front face of the photovoltaic module and a second layer forming a rear face of the photovoltaic module.

[0008] The first layer forming the front face of the photovoltaic module is advantageously transparent to allow the photovoltaic cells to receive a luminous flux. It is traditionally made from a single glass plate, in particular tempered glass, with a thickness typically between fifty micrometers and five millimeters, conventionally of the order of three millimeters.

[0009] The second layer forming the rear face of the photovoltaic module can be made from glass, metal or plastic, among others. It is often formed by a polymer structure based on an electrically insulating polymer, for example of the polyethylene terephthalate (PET) or polyamide (PA) type, which can be protected by one or more layers based on fluorinated polymers, such as polyvinyl fluoride (PVF) or polyvinylidene fluoride (PVDF), and having a thickness of around 300 μm.The photovoltaic cells can be electrically connected to each other by front and rear electrical contact elements, called connecting conductors, and formed for example by strips of tinned copper, respectively arranged against the front faces (faces facing the front face of the photovoltaic module intended to receive a luminous flux) and rear faces (faces facing the rear face of the photovoltaic module) of each of the photovoltaic cells.

[0010] Furthermore, the photovoltaic cells, located between the first and second layers forming the front and rear faces of the photovoltaic module respectively, can be encapsulated. Conventionally, the chosen encapsulant corresponds to a polymer of the elastomer (or rubber) type, and can for example consist of the use of two layers (or films) of polyethylene vinyl acetate (EVA) between which the photovoltaic cells and the cell connecting conductors are arranged.

[0011] A classic example of a photovoltaic module 1 comprising photovoltaic cells 4 based on monocrystalline or multicrystalline silicon has thus been partially and schematically represented, respectively in section in Figure 1 and in exploded view in Figure 2.

[0012] As described above, the photovoltaic module 1 comprises a front face 2, generally made of transparent tempered glass with a thickness of approximately three millimeters, and a rear face 5, for example made of a polymer sheet, opaque or transparent, single-layer or multi-layer, having a Young's modulus greater than four hundred Mega Pascals at room temperature.

[0013] Between the front 2 and rear 5 faces of the photovoltaic module 1 are the photovoltaic cells 4, electrically connected to each other by connecting conductors 6 added by gluing using points of a first electrically conductive adhesive 90 to form chains 4.10 and 4.20 of photovoltaic cells 4 - also designated by the term "String" of photovoltaic cells 4. The chains 4.10 and 4.20 are immersed between two front 3a and rear 3b layers of encapsulating material, both forming an encapsulating assembly 3.

[0014] Furthermore, Figures 1 and 2 also show the junction box 7 of the photovoltaic module 1, intended to receive the wiring necessary for operating the module. Conventionally, this junction box 7 is made of plastic or rubber, and is completely waterproof. An electrical harness 10 comprising a first conductor 10.1 and a second conductor 10.2, generally made of silver, electrically connects the strings 4.10 and 4.20 to the junction box 7. The first conductor 10.1 connects, using points of a second electrically conductive adhesive 91, the start cell 4.11 of the string 4.10 and the start cell 4.21 of the string 4.20 to the junction box 7. The second conductor 10.2 connects, using points of adhesive 91, the end cell 4.12 of the string 4.10 and the end cell 4.22 of the string 4.20 to the junction box 7. The adhesive 91 is specific to the bonding of silicon to silver and is generally different from the adhesive 90.

[0015] There are also so-called heterojunction photovoltaic cells 8 which are likely to degrade more quickly at temperature, particularly during the interconnection steps. Such cells have improved solar efficiencies compared to other crystalline silicon cells. A module comprising such cells is shown in Figure 3.

[0016] It is also known to produce chains 9 of cells 4 by replacing the connecting conductors 6 between the cells 8 by a partial covering of the cells 8 in the manner of roof tiles. This technology is called "tiling" or "shingle" and is shown in Figures 4 and 5. The cells 8 are connected to each other by gluing using adhesive strips 90 to form chains - here a first chain 8.10 and a second chain 8.20. The first chain 8.10 comprises a start cell 8.11 and an end cell 8.12 connected by intermediate cells 8.13 - here three in number. The second chain 8.20 comprises a start cell 8.21 and an end cell 8.22 connected by intermediate cells 8.23 ​​- here three in number. The other arrangements (front panel 2, encapsulant 3, rear panel 5, junction box 7, harness 10) of module 1 remain identical.For space applications, the design of the photovoltaic modules 1 described above must be modified so that the modules withstand the specific thermal cycling of objects in low Earth orbit, namely a change from -120 degrees centigrade to +120 degrees centigrade over a time interval of one and a half hours. Under these conditions, the failure of the photovoltaic module 1 is caused by the degradation of the adhesive 91 at the connections of the start cells 8.11, 8.21 and end cells 8.12, 8.22 with the harness 10.

[0017] SUBJECT OF THE INVENTION

[0018] The invention aims to improve the durability of a photovoltaic module for space or stratospheric applications.

[0019] STATEMENT OF THE INVENTION

[0020] For this purpose, an electrical connection interface is provided comprising a silicon support which has a front face and a rear face opposite the front face, in which the front face comprises a solder connection with a connector intended to be connected to an electrical harness, and the rear face comprises an electrically conductive zone.

[0021] For the purposes of this application, "welded connection" means any connection resulting in at least partial melting of the support and / or the connector, and / or of a bonding filler metal.

[0022] According to other particular, non-exclusive and optional embodiments of the invention:

[0023] The connector includes at least one relaxation loop.

[0024] The front and / or back face is at least partially metallized.

[0025] The invention also relates to a photovoltaic cell for tile installation comprising a connection interface as described above and in which the silicon support comprises a first N-doped layer and a second P-doped layer, the first layer and the second layer being separated by a space charge zone. Advantageously:

[0026] The connection area extends over a fraction of the surface, the underlying area of ​​which is isolated from the rest of the space charge area, preferably by etching.

[0027] The first layer of the underlying area includes a portion that is N-doped.

[0028] The second layer includes a space charge region.

[0029] The third layer includes a third portion which is P-doped.

[0030] Etching makes it possible to isolate these first two layers at the connection zone from the rest of the PN junction.

[0031] An electrical shunt connects the front and rear sides.

[0032] The cell is of the heterojunction type.

[0033] The invention also relates to a photovoltaic module comprising a connection interface and / or a cell as described above.

[0034] Other characteristics and advantages of the invention will appear on reading the following description of a particular non-limiting embodiment of the invention.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Reference will be made to the attached figures, including:

[0037] Figure 1 is a schematic cross-sectional representation of a known photovoltaic module; Figure 2 is an exploded perspective schematic representation of a known photovoltaic module; Figure 3 is an exploded perspective schematic representation of a known photovoltaic module with heterojunction cells; Figure 4 is an exploded perspective schematic representation of a known photovoltaic module with heterojunction cells arranged in a tiled pattern; Figure 5 is a schematic cross-sectional representation of the photovoltaic module of Figure 4; Figure 6 is a partial perspective schematic representation of a photovoltaic module according to a first embodiment of the invention; Figure 7 is a partial perspective schematic representation of a connection interface according to a first embodiment of the invention;Figure 8 is a schematic sectional representation of a first step of implementing the connection interface of Figure 7; Figure 9 is a schematic sectional representation of a second step of implementing the connection interface of Figure 7; Figure 10 is a schematic sectional representation of a third step of implementing the connection interface of Figure 7; Figure 11 is a schematic sectional representation of a string of photovoltaic cells according to a second embodiment of the invention; Figure 12 is a schematic perspective representation of a photovoltaic cell according to a third embodiment of the invention; Figure 13 is a schematic perspective representation of a photovoltaic cell according to a fourth embodiment of the invention;Figure 14 is a schematic perspective representation of a photovoltaic cell according to a fifth embodiment of the invention; Figure 15 is a schematic perspective representation of a photovoltaic cell according to a sixth embodiment of the invention; Figure 16 is a schematic perspective representation of a string of photovoltaic cells according to a seventh embodiment of the invention; Figure 17 is a schematic perspective representation of a string of photovoltaic cells according to an eighth embodiment of the invention. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS;

[0038] With reference to Figure 6, an electrical connection interface 20 comprises a silicon support 21 which has a front face 22 and a rear face 23 opposite the front face 22. The support 21 is here rectangular in shape and has two large edges 24.1 and 24.2 of great length L24 substantially equal to the width 18 of a cell 8 - here a cell of size M2 of one hundred and fifty-six millimeters on each side. The faces are metallized - here with silver - to a thickness of ten microns by screen printing. As visible in Figure 7, the screen printing on the front face 22 is carried out so as to define a front metallized welding zone 25 and leave free a front non-metallized zone 26. The screen printing on the rear face 23 is carried out so as to define a rear metallized bonding zone 27 and leave free a rear non-metallized zone 28. The metallized areas 25 and 27 extend respectively along the edges 24.1 and 24.2 in a "head-to-tail" configuration.Symmetrically, the non-metallized areas 26 and 28 extend respectively along the edges 24.2 and 24.1 in a "head-to-tail" configuration. The areas 25 and 26 are separated by a front boundary 29.1. The areas 27 and 28 are separated by a rear boundary 29.2.

[0039] A first end 31 of a silver connector 30 is attached by PRGW (Parallel Gap Resistance Welding) type welding to the zone 25. The second end 32 of the connector 30 is connected by welding to the conductor 10.1.

[0040] As seen in Figures 6 and 7, the connector 30 comprises a relaxation loop 33. A relaxation loop designates a portion of the conductor which comprises an inflection point on either side of which the tangents to the neutral fiber of the conductor are not parallel. Such a loop allows thermomechanical relaxation, that is to say that it totally or partially absorbs the parasitic forces which could be induced on the connector by temperature gradients or external mechanical forces.

[0041] The implementation of the interface 20 will now be described in connection with figures 8 to 11. According to a first step, the interface 20 is positioned between the conductor 10.1 of the harness 10 and the start cell 8.11 so that the bonding zone 27 of the interface 20 faces the front face 8.112 of the cell 8.11. In this configuration, the rear boundary 29.2 is substantially in line with the free edge of the cell 8.11b (figure 8).

[0042] According to a second step, a bead of adhesive 90 is deposited on the front face 8.112 near a free edge 8.111 of the cell 8.11 (figure 9). The interface 20 is then moved so as to bring the bead of adhesive 90 into contact with the bonding zone 27 of the interface 20. The end 32 of the connector 30 is then welded to the conductor 10.1 (figure 10).

[0043] After bonding the end cell 8.12 to the conductor 10.2 and encapsulating the cell string 8 thus produced, a photovoltaic module 1 is obtained having improved durability under spatial conditions. Indeed, the welding connections which connect the conductor 10.1 to the welding zone 25 of the interface 20 are notoriously resistant to spatial conditions. Finally, the adhesive connection 90 between the bonding zone 27 of the interface 20 and the start cell 8.11 is also resistant to spatial conditions.

[0044] Elements identical or analogous to those previously described will bear a numerical reference identical to this one in the following description of the second, third, fourth, fifth, sixth, seventh and eighth embodiments of the invention.

[0045] According to a second embodiment shown in Figure 11, in parallel with the operations of connecting the conductor 10.1 to the start cell 8.11, the connection of the conductor 10.2 to the end cell 8.12 is carried out by means of a second interface 40 identical to the interface 20. The installation method is identical to that described with reference to the interface 20.

[0046] According to a third embodiment shown in Figure 12, the interface 20 is integrated into the photovoltaic cell 8 to form an optimized photovoltaic cell 50. The cell 50 then comprises a silicon support 51 which has a front face 52 and a rear face 53. The cell 50 is of substantially rectangular shape comprising two small edges 54.1 and 54.2. The support 51 comprises a first N-doped layer 51.1 (with phosphorus) and a second P-doped layer 51.2 (with boron), the first layer 51.1 and the second layer 51.2 are separated by a space charge zone 51.3 in order to form a heterojunction cell.

[0047] The front face 52 comprises a silver-plated soldering area 55 and a silver-plated soldering area 56. The rear face 53 comprises a silver-plated soldering area 57. The areas 56 and 57 extend along the edge 54.2. The area 55 extends along the edge 54.1. The area 56 may be continuous or discontinuous and occupies an area of ​​0.1 to 10 percent of the total area of ​​the cell 50, preferably 0.5 to 5 percent of the total area of ​​the cell 50.

[0048] In order to protect the layers 51.1, 51.2 and the space charge zone 51.3 from thermal degradation during welding operations on the welding zones 55, 56 and 57, the portions of the layers 51.1, 51.2 and 51.3 located directly above the welding zones 55, 56 and 57 may be modified, in addition to a possible adaptation of the welding parameters.

[0049] Thus, and according to a fourth embodiment shown in Figure 13, an insulating segment 60 produced by etching and which extends from the front face 52 of the cell 50 to pass through the layer 51.1, the PN space charge zone 51.3 and extend into the layer 51.2. The segment 60 then extends beyond the space charge zone 51.3. This segment 60 defines a first portion 61 of the layer 51.3 which is isolated from the rest of the layer 51.3. The portion 61 extends, here, substantially directly above the zone 56.

[0050] According to a fifth embodiment shown in Figure 14, the layer 51.1 comprises a second portion 62 which is P-doped. The second layer 51.2 comprises, for its part, a third portion 63 which is N-doped. The portions 62 and 63 extend, here, respectively substantially directly above the zones 56 and 55. According to a sixth embodiment shown in Figure 15, the cell 50 comprises an electrical shunt 64 connecting the front face 52 and the rear face 53. This shunt 64 ideally takes the form of a metal braid whose ends 64.1 and 64.2 are respectively connected by soldering to the zones 56 and 57.

[0051] According to a seventh embodiment shown in Figure 16, optimized cells 50 can be integrated into the cell chain 8.10 to replace the start cells 8.11 and end cells 8.12 as shown in Figure 16. The cell chain 8.10 then comprises a first optimized start cell 50.11, three intermediate cells 8.13 and a second optimized end cell 50.12. A connector 30.11 is soldered onto the area 55.11 of the optimized cell 50.11 to connect it to the conductor 10.1. The area 56.11 of the optimized cell 50.11 is connected to the rear face of a cell 8.13 by gluing with adhesive 90. The intermediate cells 8.13 are arranged in a tiled pattern and connected to each other by gluing with adhesive 90. The area 57.12 of the optimized cell 50.12 is connected to the front face of a cell 8.13 by gluing with adhesive 90. A connector 30.12 is soldered to the area 56.12 of the optimized cell 50.12 to connect it to the conductor 10.2.

[0052] According to an eighth embodiment shown in Figure 17, the cell chain 8.10 is entirely produced by assembling optimized cells 50. The cell chain 8.10 then comprises a first optimized cell 50.11 at the start, three intermediate cells 50.13 and a second optimized cell 50.12 at the end. A connector 30.11 is soldered onto the area 55.11 of the optimized cell 50.11 to connect it to the conductor 10.1. The area 56.11 of the optimized cell 50.11 is connected to the rear face of a cell 50.13 by gluing with adhesive 90. The intermediate cells 50.13 are arranged in a tiled pattern and connected to each other by gluing with adhesive 90. The area 57.12 of the optimized cell 50.12 is connected to the front face of a cell 50.13 by gluing with adhesive 90. A connector 30.12 is soldered to the area 56.12 of the optimized cell 50.12 to connect it to the conductor 10.2.According to a preferred embodiment applicable to the embodiments of Figures 6 to 12, the interface 20 is preferably non-photoactive. This means that it is not designed to generate an electric current under the effect of light radiation. For this purpose, it advantageously consists of a silicon wafer doped according to a single type of conductivity, either P or N. Unlike photovoltaic cells, this wafer does not include a PN junction.

[0053] Furthermore, the interface has a length strictly less than that of the photovoltaic cells to which it is welded. More specifically, this length is preferably less than half the length of the photovoltaic cell. This reduced dimension allows the interface to minimize the space occupied at the end of the chain while remaining large enough to provide a welding zone and a bonding zone on both sides.

[0054] Choosing a material such as P- or N-doped silicon to form the interface offers several advantages. In addition to its compatibility with the manufacturing process of photovoltaic cells and modules, it ensures increased mechanical and electrical robustness at the interface. In addition, the absence of photoactivity ensures that the interface does not disrupt the operation of adjacent cells.

[0055] These features are particularly relevant in the embodiments of Figures 6 to 12, where it can be seen that the interface is positioned between the conductors and the photovoltaic cells at the beginning and end of the string. Its role is to ensure a reliable connection while supporting the conditions of use in demanding environments, such as space applications.

[0056] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0057] In particular, although here the front and rear faces of the interface support are metallized, the invention also applies to a support metallized on one side only. This is turned over depending on whether it is intended to be connected to a cell at the start or end of the chain; although here the metallization is carried out by screen printing to obtain a thickness of ten microns, the invention also applies to other metallization processes such as for example high-speed projection (HVOF) to obtain thicknesses preferably between ten and thirty microns, the metallization material being able to be freely chosen from different conductive metals such as for example aluminum or copper; although here the silver screen printing is carried out so as to define a welding zone and a bonding zone, the invention also applies to an interface of which one or two faces are fully metallized, the bonding being carried out on the metallization;although here the connector is attached by PGRW welding to the metallized area, the invention also applies to other types of heat-welded connection such as for example brazing, TIG welding, with or without filler metal; although here the N doping is carried out using Phosphorus, the invention also applies to other materials such as for example Arsenic; although here the P doping is carried out using Boron, the invention also applies to other materials such as for example Gallium; although here the rear face comprises a metallized area, the invention also applies to other types of electrically conductive area such as for example an area comprising an electrical connector.;

Claims

CLAIMS 1. Photovoltaic cell (50) for tile installation comprising an electrical connection interface (20) comprising a silicon support (21) which has a front face (22) and a rear face (23) opposite the front face (22), in which the front face (22) comprises a solder connection with a connector (30) intended to be connected to an electrical harness (10) and the rear face (23) comprises an electrically conductive zone (27), in which the silicon support (51) comprises a first N-doped layer (51.1) and a second P-doped layer (51.2), the first layer (51.1) and the second layer (51.2) being separated by a PN space charge zone (51.3), in which the PN space charge zone (51.3) comprises a first portion (61) of PN space charge zone (51.3) which is isolated from the rest of the space charge zone PN (51.3), preferably by engraving.

2. Photovoltaic cell (50) according to claim 1, wherein the first layer (51.1) comprises a second portion (62) which is P-doped.

3. Photovoltaic cell (50) according to any one of the preceding claims, in which the second layer (51.2) comprises a third portion (63) which is N-doped.

4. Photovoltaic cell (50) according to any one of the preceding claims, comprising an electrical shunt (64) connecting the front face (52) and the rear face (53).

5. Photovoltaic cell (50) according to any one of the preceding claims, the cell (50) being of the heterojunction type.

6. Photovoltaic cell (50) according to any one of the preceding claims, wherein the connector (30) comprises at least one relaxation loop (33).

7. Photovoltaic cell (50) according to any one of the preceding claims, in which the front face (22) and / or the rear face (23) is at least partially metallized.

8. Photovoltaic module (1) comprising a plurality of photovoltaic cells as well as a connection interface (20) according to any one of claims 1 to 3 and / or the plurality of photovoltaic cells comprising at least one cell (50) according to any one of claims 4 to 8.

9. Photovoltaic module (1) according to claim 8, wherein the front face is connected by gluing to a photovoltaic cell of the plurality of cells.

10. Photovoltaic module (1) according to claim 8 or 9, wherein the rear face is connected by gluing to a photovoltaic cell of the plurality of cells.

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