Laser shooting mask for interconnecting photovoltaic cells

Abstract

The invention relates to a laser firing mask (20m) for a laser welding unit (20) of a laser welding interconnection device for photovoltaic cells (4) to form at least one string of photovoltaic cells (4) interconnected by connecting conductors (6), characterized in that it comprises a plurality of laser firing points (22) through which at least one laser shot is capable of being performed for the local fusion welding of at least one connecting conductor (6) positioned on the front face (4a) or the rear face (4b) of at least one photovoltaic cell (4), each laser firing point (22) being hollow and having a conical opening (22o). Figure for the abstract: Figure 1

Description

Title of the invention: Laser firing mask for the interconnection of photovoltaic cells. TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the general field of photovoltaic modules, which comprise a set of photovoltaic cells electrically connected to each other, and preferably so-called "crystalline" photovoltaic cells, that is to say, which are based on monocrystalline or multicrystalline silicon, III-V materials, thin films (CIGS, CdTe, perovskites, etc.) or any combination of these different materials.

[0002] In particular, it relates to tandem type photovoltaic cells combining silicon and a perovskite material, homojunction or heterojunction photovoltaic cells based on monocrystalline silicon (c-Si) and / or multicrystalline silicon (mc-Si), photovoltaic cells comprising at least one material among amorphous silicon (a-Si), microcrystalline silicon (pC-Si), cadmium telluride (CdTe), copper-indium selenide (CIS), copper-indium / gallium diselenide (CIGS), and perovskites, among others.

[0003] More specifically, the invention relates to the field of interconnecting photovoltaic cells which allows the formation of chains or series (or "strings" in English) of photovoltaic cells, and it relates in particular to the equipment and processes used during the welding carried out for the interconnection.

[0004] It thus relates to the field of photovoltaic modules used for space applications, but also for terrestrial applications, and also for applications such as electronic mobility, balloons or drones, among others. More generally, the invention applies to photovoltaic applications for which the issue of interconnecting photovoltaic cells is relevant.

[0005] The invention thus relates to a laser firing mask for the interconnection of photovoltaic cells, a laser welding unit comprising such a mask, as well as a method of interconnecting photovoltaic cells implemented by means of such a laser welding unit. STATE OF THE ART

[0006] A terrestrial photovoltaic module is typically made up of photovoltaic cells electrically connected to each other, generally in series, and encapsulated in a stack of polymer and / or glass materials. This stack protects the photovoltaic cells from the external environment, such as rain, wind, snow, humidity, etc. ultraviolet radiation, radiation, thermal shocks, among others, while retaining the photoelectric conversion function.

[0007] Thus, classically, a terrestrial photovoltaic module forms a stack comprising successively: a rear protection element called "backsheet" in English, transparent or not, such as for example a glass plate or a polymer film; a first encapsulating polymer film; photovoltaic cells electrically connected to each other, typically by interconnectors, most often tinned copper strips; a second encapsulating polymer film; a front protection element called "frontsheet" in English, transparent, such as for example a glass plate or a polymer film.

[0008] The front protective element is designed to transmit solar radiation to the photovoltaic cells to generate electricity, while protecting them from environmental stresses. This stack is then bonded together during a hot lamination step, typically between 100 and 150°C, to melt the encapsulating films and cause the polymers to cross-link, resulting in the formation of a solid encapsulating envelope for the photovoltaic cells bonded to the front and rear protective elements.

[0009] The interconnection of photovoltaic cells is necessary to extract the electrical current generated by the cells while limiting resistance. It must be resilient to maintain performance and prevent potentially catastrophic incidents, such as fires. The article "A review of interconnection technologies for improved crystalline silicon solar cell photovoltaic module assembly," Musa T. Zarmai et al., School of Engineering, Faculty of Science and Engineering, University of Wolverhampton, Applied Energy 154, 173-182, September 15, 2015, presents, for example, various known approaches to interconnecting photovoltaic cells in the field of terrestrial photovoltaics.

[0010] For terrestrial photovoltaic modules, interconnectors are typically copper ribbons or wires with a silver (Ag) or tin (Sn) coating. In the vast majority of cases, the electrical connection between the ribbons / wires and the cells is achieved without melting the base metals, by brazing with a filler metal, which allows for good ohmic contact at temperatures below 400°C. In an interconnection device using brazing, the ribbons or wires are generally placed on the front and rear faces of the photovoltaic cells, and then the front and rear faces are simultaneously brazed by heating to prevent bowing. A ribbon / wire retaining mask on the photovoltaic cells can be used to maintain contact between the ribbons / wires and metal pads, particularly silver pads.

[0011] In the space sector, brazing is not recommended for interconnection. Indeed, at space operating temperatures below -40°C, tin changes from its [3] form to its a form, and this change is accompanied by a volume modification and embrittlement of the material with the presence of cracks (embrittlement). This phenomenon is called "tin plague".

[0012] Another approach, valid for both terrestrial and space applications, involves using a weld, with or without filler metal, which involves melting the base metals, particularly silver, copper, and aluminum. For low temperatures, on the order of 100°C, conductive adhesives, often composed of metallic particles, particularly silver, in a polymer matrix, can be used. For locally high temperatures, for example, above 600°C, typically around 1085°C for copper, 962°C for silver, and 660°C for aluminum, a weld without filler metal can be performed.Thus, it may be necessary to reach temperatures that are too high and incompatible with the use of certain categories of photovoltaic cells, such as silicon heterojunction photovoltaic cells, which require a manufacturing and processing temperature below 200°C, or tandem type cells, which require a manufacturing and processing temperature below 150°C, when heating is global as in brazing interconnection processes.

[0013] There is therefore a need to obtain a localized energy input in order to reach the high temperatures required by the welding.

[0014] The interconnection is critical due to its essential function of current transmission. It must withstand expansions related to environmental stresses during manufacturing, particularly during welding, or during the operation of the photovoltaic module, for example during eclipses in Earth orbits, despite differences in coefficients of thermal expansion (or CTE). Thus, obtaining an optimal solution for localized heating should make it possible to limit the effects of CTE. Description of the invention

[0015] The invention aims to remedy at least partially the needs mentioned above and the disadvantages relating to the achievements of the prior art.

[0016] In particular, the invention aims to enable the interconnection of photovoltaic cells while maintaining excellent ohmic conductivity between the cells regardless of the applied deformations, whether mechanical or thermomechanical.

[0017] It aims in particular to allow interconnection by welding for multiple types of photovoltaic cells, without temperature constraints, while allowing welding on both sides of the photovoltaic cells.

[0018] It also aims to allow the contact between connecting conductors and a photovoltaic cell to be maintained in position during laser welding, while ensuring the efficiency and accuracy of the laser shot.

[0019] The invention thus relates, according to one of its aspects, to a laser firing mask for a laser welding unit of a laser welding interconnection device of photovoltaic cells to form at least one chain of photovoltaic cells interconnected by connecting conductors, characterized in that it comprises a plurality of laser firing pins through which at least one laser shot is suitable for local fusion welding, or localized fusion, of at least one connecting conductor positioned on the front or rear face of at least one photovoltaic cell, each laser firing pin being hollow and having a conical opening.

[0020] The laser shooting mask according to the invention may further include one or more of the following characteristics taken individually or in any possible technical combinations.

[0021] Each laser firing pin may comprise a first laser firing inlet end, a main body, and a second support end. The first laser firing inlet end may comprise the conical-shaped opening.

[0022] Furthermore, the laser firing mask may include a laser firing pin mounting plate on which the laser firing pins are fixed at intervals between them, particularly at their first laser firing input end. The first laser firing input end of each laser firing pin may pass through the mounting plate.

[0023] Furthermore, the second support end may include a support collar adapted to hold in place at least one connecting conductor in contact with the front or rear face of said at least one photovoltaic cell. The support collar may be adapted to bear against said at least one connecting conductor on either side. The second support end may include a circular opening.

[0024] The main body of each laser firing pin may include elastic return means, in particular a spring, allowing movement of the second support end relative to the first input end of the laser firing and exerting pressure against at least one bonding conductor in contact with the front face or the rear face of said at least one photovoltaic cell.

[0025] Furthermore, the laser firing pins can be regularly spaced and separated by a spacing distance greater than or equal to 10 mm. The laser firing pins can be arranged in a plurality of rows. The number of rows can be greater than or equal to the number of busbars in a Photovoltaic cell. The number of laser firing pins per row can be greater than or equal to 10.

[0026] Furthermore, according to another aspect of the invention, a laser welding unit for a laser welding interconnection device for photovoltaic cells to form at least one string of photovoltaic cells interconnected by connecting conductors, characterized in that it comprises:

[0027] - a laser head configured to perform at least one laser shot for local fusion, or localized melting of at least one connecting conductor positioned on the front or rear face of at least one photovoltaic cell,

[0028] - a laser firing mask as defined above, through which the laser head is capable of performing said at least one laser shot, the laser shooting mask being configured to hold said at least one connecting conductor in position against the front or rear face of said at least one photovoltaic cell.

[0029] The first distance Dl, between the end of the laser head generating a laser shot and the center of said at least one photovoltaic cell, and the second distance D2, between the center 4c of said at least one photovoltaic cell 4 and a laser firing pin 22 of the laser firing mask 20m, define a cone angle a such that tan(a) = D1 / D2, which corresponds to the angle between the base and the apothem of the cone of the conical aperture.

[0030] Furthermore, the laser head of the laser welding unit can be mounted in translation relative to a first frame of the laser welding unit, in particular mounted in translation along a first horizontal axis, in translation along a second horizontal axis and in translation along a third vertical axis, the first, second and third axes being the axes of a three-axis frame.

[0031] Furthermore, the invention also relates, according to another of its aspects, to a device for interconnecting photovoltaic cells by laser welding to form at least one chain of photovoltaic cells interconnected by linking conductors, characterized in that it comprises a laser welding unit as defined above.

[0032] The laser welding interconnection device may include a conveying unit, in particular a belt conveyor or conveyor belt, on which said at least one string of photovoltaic cells is formed and on which said at least one photovoltaic cell is intended to be conveyed after laser welding carried out on the front and rear faces of said at least one photovoltaic cell.

[0033] The laser welding unit may include at least a first vision system enabling the laser head to be positioned according to a predetermined position.

[0034] The interconnection device may further include:

[0035] - a photovoltaic cell stacking unit,

[0036] - a gripping unit, in particular a gripping robot, of said at least one cell photovoltaic from the stacking unit for transport to a drop-off area at the laser welding unit.

[0037] The socket unit may include means for gripping said at least one photovoltaic cell, in particular in the form of suction cups for sucking said at least one photovoltaic cell.

[0038] In addition, the gripping unit may include a second vision system allowing the gripping means to be positioned according to a predetermined position.

[0039] The interconnection device may also include a unit for routing connecting conductors to a deposit area at the laser welding unit.

[0040] Furthermore, the invention also relates, according to another of its aspects, to a method of interconnecting by laser welding photovoltaic cells interconnected by linking conductors, implemented by means of a laser welding unit as defined above.

[0041] The process may include the following steps:

[0042] - position the laser welding mask against the front face or the face at the rear of at least one photovoltaic cell, each laser firing pin being supported on either side of a connecting conductor,

[0043] - to perform a plurality of laser shots through the laser firing pins for welding by local fusion, or localized fusion, of the connecting conductors positioned on the front or rear face of said at least one photovoltaic cell. BRIEF DESCRIPTION OF THE FIGURES

[0044] Other advantages, purposes and special features of the invention will become apparent from the following non-limiting description of at least one embodiment of the present invention, with reference to the accompanying figures, in which: • Figure [1] shows, in partial perspective view, an example of a laser welding unit according to the invention for a laser welding interconnection device for photovoltaic cells, • Fig. 2 shows a detailed view of Fig. 1, allowing visualization of the laser welding mask positioned against connecting conductors on the front face of a photovoltaic cell. • [Fig.3] represents a detailed view of a laser firing pin of the laser welding mask of [Fig.2], • Figure [Fig. 4] illustrates in cross-section, schematically and partially, the laser firing mask according to the invention, • Figure 5 illustrates the principle of determining the conical angle of the laser firing pins of the laser welding mask according to the invention, and • [Fig.6] schematically illustrates the conical angle at the conical opening of a laser firing pin of the laser welding mask according to the invention.

[0045] Throughout these figures, identical references may designate identical or analogous elements.

[0046] Furthermore, the different parts shown in the figures are not necessarily to a uniform scale, in order to make the figures more legible. DETAILED DESCRIPTION OF THE INVENTION

[0047] It should be noted that the terms "vertical" and "horizontal" are to be understood here in their usual sense, and in particular with regard to the positioning of a string of photovoltaic cells 4 extending in a horizontal direction. Furthermore, a so-called "vertical" axis is orthogonal to a so-called "horizontal" axis. In addition, the expression "moving in translation along an axis" can also mean here "moving in translation parallel to an axis".

[0048] With reference to Figures 1 to 6, we will now describe an example of the embodiment of a 20m laser firing mask and a laser welding unit 20 for a laser welding interconnection device, enabling the interconnection of several photovoltaic cells 4 to form a string, by welding involving local melting of the pure metal(s) at high temperatures, in particular above 600°C, applicable to photovoltaic cells 4 that cannot withstand excessively high temperatures, in particular above 200°C. The success of this local melting can depend in particular on the intensity, duration, and efficiency of the laser beam. It can, in particular, allow welding on a predetermined surface on either side of a connecting conductor, for example, a surface on the order of 100 µm x 100 µm.

[0049] The laser welding unit 20 enables laser welding of the linking conductors 6, typically ribbons or interconnecting wires, to the front face 4a, and the rear face 4b, of the photovoltaic cells 4 to form a string of photovoltaic cells 4.

[0050] As seen in [Fig.1], the laser welding unit 20 comprises a laser head 20t configured to perform one or more laser shots TL (see figures 4 and 5) in the direction of the photovoltaic cell 4. In this way, a local or localized melting of the connecting conductors 6 positioned on the front face 4a of the photovoltaic cell 4 is achieved.

[0051] The TL laser shots are performed by the 20t laser head through a 20m laser shooting mask which allows both the holding in position of the connecting conductors 6 against the front face 4a of the photovoltaic cell 4 and, by means of laser firing pins 22 through which the laser shots TL pass, the laser welding in a localized manner.

[0052] In addition, the laser welding unit 20 includes a first vision system 20v allowing the laser head 20t to be correctly positioned in relation to the photovoltaic cell 4, here two first vision systems 20v, on either side of the laser head 20t, each comprising a camera.

[0053] Advantageously, the laser head 20t of the laser welding unit 20 is mounted in translation along the three axes X, Y, Z of a three-axis frame relative to a frame 20b of the laser welding unit 20.

[0054] In particular, the laser head 20t is translationally movable about a first horizontal axis X relative to a first horizontal frame 20bx, translationally movable about a second horizontal axis Y relative to a second horizontal frame 20by, and translationally movable about a third vertical axis Z relative to a third vertical frame 20bz. Motors can be provided at the ends of each of the first 20bx, second 20by, and third 20bz frames to move the laser head 20t.

[0055] As seen in Figures 2, 3 and 4, the 20m laser shooting mask has laser shooting pins 22, also called holding pins, through which the laser shots TL are made for the local or localized fusion welding of the connecting conductors 6 positioned on the front face 4a of the photovoltaic cell 4.

[0056] Specifically, each laser firing pin 22 is hollow. It comprises a first laser firing inlet end 22a, a main body 22c, and a second support end 22p. The first laser firing inlet end 22a advantageously has a conical opening, this type of opening ensuring that the laser firing TL correctly reaches the area to be welded, namely the connecting conductor 6 in contact with the photovoltaic cell 4.

[0057] Furthermore, the 20m laser shooting mask includes a mounting plate 23, or frame, for securing the laser firing pins 22, and to which the laser firing pins 22 are fixed at intervals. Specifically, the laser firing pins 22 are fixed to the mounting plate 23 at their first laser firing inlet end 22a, which passes through the mounting plate 23. Advantageously, this mounting plate 23, via the laser firing pins 22, provides point rather than surface support to limit the risk of breakage of the photovoltaic cells 4.

[0058] The pressure is thus exerted by means of the second support end 22p of each laser firing pin 22 which has a support collar, suitable for holding the connecting conductor 6 in contact with the front face 4a of the photovoltaic cell 4.

[0059] The support collar advantageously rests on either side of the connecting conductor 6 and has a circular opening.

[0060] Furthermore, the pressure exerted by the laser firing pins 22 can be defined by means of elastic return means 22r, in particular springs 22r, schematically shown in [Fig. 4], at the level of the main body 22c of each laser firing pin 22. These springs 22r allow the movement of the second support end 22p relative to the first input end of the laser firing pin 22a, as schematically shown by the arrow FR in [Fig. 3], and the exertion of pressure against the connecting conductor 6 in contact with the front face 4a of the photovoltaic cell 4. The second support end 22p may have a hole with a diameter of approximately 100 pm in contact with the photovoltaic cell 4.

[0061] Furthermore, as can be seen in [Fig. 2], the laser firing pins 22 are advantageously spaced regularly from each other, according to a regular grid, and separated by a spacing distance De of approximately 10 mm. The laser firing pins 22 are arranged in rows of laser firing pins. The number of rows can be greater than or equal to the number of busbars of the photovoltaic cell 4. The number of laser firing pins 22 per row can be on the order of 10.

[0062] Figures 5 and 6 further illustrate the first distance Dl, between the end of the laser head 20t generating a laser shot TL and the center 4c of the photovoltaic cell 4, and the second distance D2, between the center 4c of the photovoltaic cell 4 and a laser shooting pin 22 of the laser shooting mask 20m, here for example located at the end of the laser shooting mask 20m.

[0063] These first D1 and second D2 distances define a cone angle a such that tan(a) = D1 / D2, which corresponds to the angle between the base and the apothem of the cone of the conical opening 22o, as seen in [Fig.6].

[0064] The first Dl and second D2 distances are thus linked together so that the laser shot TL can strike the laser firing pin 22 furthest from the center 4c of the photovoltaic cell 4. Preferably, it is appropriate to maximize this cone angle a rather than increase the size of the conical opening 22o in order to ensure better retention of the connecting conductor 6 on the laser firing pin 22.

[0065] The laser welding interconnection method using the laser welding unit 20 described above can then be implemented by positioning the laser welding mask 20m against the front face 4a or the rear face 4b of a photovoltaic cell 4, each laser firing pin 22 being supported on either side of a connecting conductor 6, and then by carrying out a plurality of laser shots TL through the laser firing pins 22 for local or localized fusion welding. connecting conductors 6 positioned on the front face 4a or the rear face 4b of the photovoltaic cell 4.

[0066] Of course, the invention is not limited to the embodiments just described. Various modifications can be made to them by a person skilled in the art.

Claims

Demands

1. Laser firing mask (20m) for a laser welding unit (20) of a laser welding interconnection device for photovoltaic cells (4) to form at least one string of photovoltaic cells (4) interconnected by connecting conductors (6), characterized in that it comprises a plurality of laser firing pins (22) through which at least one laser firing is capable of being carried out for the local fusion welding of at least one connecting conductor (6) positioned on the front face (4a) or the rear face (4b) of at least one photovoltaic cell (4), each laser firing pin (22) being hollow and comprising a conical opening (22o).

2. Mask (20m) according to claim 1, in which each laser firing pin (22) comprises a first laser firing inlet end (22a), a main body (22c) and a second support end (22p), the first laser firing inlet end (22a) comprising in particular the conical-shaped opening (22o).

3. Mask (20m) according to claim 2, wherein the laser shooting mask (20m) comprises a laser firing pin (23) mounting plate (22) on which the laser firing pins (22) are fixed at intervals between them, in particular at their first laser firing entry end (22a), the first laser firing entry end (22a) of each laser firing pin (22) passing in particular through the mounting plate (23).

4. Mask (20m) according to claim 2 or 3, wherein the second support end (22p) has a support collar, suitable for holding in place at least one connecting conductor (6) in contact with the front face (4a) or the rear face (4b) of said at least one photovoltaic cell (4), the support collar being suitable for bearing on either side of said at least one connecting conductor (6), the second support end (22p) having in particular a circular opening.

5. Mask (20m) according to any one of claims 2 to 4, wherein the main body (22c) of each laser firing pin (22) comprises elastic return means (22r), in particular a spring, allowing movement of the second support end (22p) relative to the first laser firing input end (22a) and the exertion of pressure against at least one connecting conductor (6) in contact with the front face (4a) or the rear face (4b) of said at least one photovoltaic cell (4).

6. Mask (20m) according to any one of the preceding claims, wherein the laser firing pins (22) are regularly spaced from each other and separated by a spacing distance (De) greater than or equal to 10 mm.

7. A laser welding unit (20) of a laser welding interconnection device for photovoltaic cells (4) to form at least one string of photovoltaic cells (4) interconnected by connecting conductors (6), characterized in that it comprises: - a laser head (20t) configured to perform at least one laser shot for the local fusion of at least one connecting conductor (6) positioned on the front face (4a) or the rear face (4b) of at least one photovoltaic cell (4), - a laser firing mask (20m) according to any one of the preceding claims, through which the laser head (20t) is capable of performing said at least one laser shot, the laser firing mask (20m) being configured to hold said at least one connecting conductor (6) in position against the front face (4a) or the rear face (4b) of said at least one photovoltaic cell (4).

8. Laser welding unit (20) according to claim 7, wherein the first distance D1, between the end of the laser head (20t) generating a laser shot (TL) and the center (4c) of said at least one photovoltaic cell (4), and the second distance D2, between the center (4c) of said at least one photovoltaic cell (4) and a laser shooting pin (22) of the laser shooting mask (20m), define a cone angle a such that tan(a) = D1 / D2, which corresponds to the angle between the base and the apothem of the cone of the conical aperture (22o).

9. Laser welding unit (20) according to claim 7 or 8, wherein the laser head (20t) of the laser welding unit (20) is mounted in translation relative to a first frame (20b) of the laser welding unit (20), in particular mounted in translation about a first horizontal axis (Xo), in translation about a second horizontal axis (Yo) and in translation about a third vertical axis (Zo), the first (Xo), second (Yo) and third (Zo) axes being the axes of a three-axis frame.

10. Method for interconnecting photovoltaic cells (4) by laser welding to form at least one cell string photovoltaics (4) interconnected by connecting conductors (6), implemented by means of a laser welding unit (20) according to any one of claims 7 to 9.

11. A method according to claim 10, wherein the method comprises the following steps: - positioning the laser firing mask (20m) against the front face (4a) or the rear face (4b) of at least one photovoltaic cell (4), each laser firing pin (22) being supported on either side of a connecting conductor (6), - performing a plurality of laser firings (TL) through the laser firing pins (22) for the local fusion welding of the connecting conductors (6) positioned on the front face (4a) or the rear face (4b) of said at least one photovoltaic cell (4).

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