Screen printing screen for manufacturing a metallization grid for a photovoltaic cell

Abstract

Screen printing screen for manufacturing a metallization grid of a photovoltaic cell (C) using a screen printing squeegee (R), comprising: - a frame (1); - a perforated membrane (2), without wires, arranged inside the frame (1); comprising a surface area (20) intended to face the screen printing squeegee (R) and at least one underlying area (21) intended to face the photovoltaic cell (C); the surface area (20) is provided with a first series of oblong openings (200) each having a first width; said at least one underlying zone (21) is provided with a second series of oblong openings (210), each having a width strictly less than the first width; the second series of oblong openings (210) is aligned with the first series of oblong openings (200) of the surface zone (20); said at least one underlying zone (21) is made of a polymer material. Figure 1

Description

Title of the invention: Screen printing screen for manufacturing a metallization grid for a photovoltaic cell. Technical field

[0001] The invention relates to the technical field of screen printing screens.

[0002] The invention finds particular application in the manufacture of a metallization grid for a photovoltaic cell. State of the art

[0003] When designing a photovoltaic cell, a compromise must be found between the lowest possible resistance, denoted R, of the metal grid and the least possible shading caused by the presence of the metal grid on the photovoltaic cell. Consider the formula R = pL / S, where "p" is the resistivity of the metallic material, "L" is the length of the metal grid, and "S" is the cross-sectional area of ​​the metal grid. The design of the photovoltaic cell generally specifies the metallic material, and therefore "p", as well as the length "L". Thus, a person skilled in the art seeks a compromise on the cross-sectional area "S" of the metal grid, which must be large enough to obtain low resistance and small enough to obtain moderate shading. If we consider a rectangular cross-sectional area "S", the cross-sectional area is the product of the width, denoted "1", and the thickness, denoted "E", of the metal grid.We obtain the following formula: . IE Since shading is only affected by the width "1", a person skilled in the art seeks to minimize the width "1" and maximize the thickness "E" of the metal grid. In other words, a person skilled in the art seeks to manufacture the thinnest and thickest possible metal grids while maintaining the most uniform cross-section "S" possible.

[0004] In this regard, it is known in the prior art to use a mesh screen for silkscreen printing. Such a screen comprises a fine network of woven threads and a photosensitive emulsion for depositing an electrically conductive paste. The characteristics of the emulsion and the mesh, such as the size of the openings and the thread density, determine the resolution and thickness of the deposited conductive lines.

[0005] Such a prior art silkscreen is not entirely satisfactory insofar as the presence of a woven network is detrimental to the uniformity of the cross-section of the deposited conductive lines, which are susceptible to having holes and bumps. Furthermore, the presence of a woven network with Fine mesh tends to limit the flow rate and volume of the deposited electrically conductive paste, causing an increase in the operational time of the manufacturing process, and a restriction on the thickness of the deposited paste. Description of the invention

[0006] The invention aims to remedy, in whole or in part, the aforementioned drawbacks. To this end, the invention relates to a silkscreen for manufacturing a metallization grid for a photovoltaic cell using a silkscreen squeegee, comprising: - a frame; - a perforated membrane, without threads, arranged inside the frame; the perforated membrane comprising a surface area and at least one underlying area; the surface area being intended to face the screen printing squeegee, said at least one underlying area being intended to face the photovoltaic cell; the surface area is provided with a first series of oblong openings, each having a first width; said at least one underlying zone is provided with a second series of oblong openings, each having a width strictly less than the first width, the second series of oblong openings is aligned with the first series of oblong openings of the surface zone, said at least one underlying zone is made of a polymer material.

[0007] Thus, such a screen printing screen according to the invention makes it possible to improve the uniformity of the cross-section of the deposited conductive lines compared to the prior art, by eliminating the need for a network of woven threads. Indeed, the finest oblong openings (i.e., the smallest widths) are made in a polymer material in the underlying areas. Furthermore, the openings in the surface area and the openings in the underlying area(s) of the perforated membrane generate a funnel effect, allowing the formation of both thin and thick conductive lines with a higher flow rate of electrically conductive paste than that of the prior art.

[0008] The silkscreen according to the invention may include one or more of the following characteristics.

[0009] According to one feature of the invention, the perforated membrane comprises at least two underlying zones; the first width of the oblong openings of the first series and the widths of the oblong openings of the second series follow a strictly decreasing function from the surface zone to said at least two underlying zones.

[0010] Thus, one advantage provided is to obtain a progressive funnel effect which makes it possible to effectively reduce the risks of clogging of the perforated membrane with an electrically conductive paste, and thereby improve the flow rate of electrically conductive paste passing through the perforated membrane.

[0011] According to a feature of the invention, the strictly decreasing function is linear.

[0012] Thus, it has been found that a linear variation leads to greater efficiency of the flow rate of electrically conductive paste under operating conditions.

[0013] According to a feature of the invention, the strictly decreasing function has a slope between 12% and 15% in absolute value.

[0014] Thus, an advantage provided by such a linear variation is to maximize the efficiency of the flow rate of electrically conductive paste under operating conditions.

[0015] According to one feature of the invention, the surface area is made of a metallic material so as to form a metallic strip.

[0016] Thus, one advantage provided is to improve the mechanical strength of the silkscreen.

[0017] According to a feature of the invention, the first width of the oblong openings of the first series with which the surface area is provided is between 50 pm and 250 pm.

[0018] According to a feature of the invention, the surface area is made of a polymer material.

[0019] Thus, one advantage provided is the ability to form openings by laser ablation with a smaller width than for a metallic surface area.

[0020] According to a feature of the invention, the first width of the oblong openings of the first series with which the surface area is provided is between 24 pm and 50 pm.

[0021] According to one feature of the invention, the surface area and said at least one underlying area are monobloc so as to form a single-layer membrane.

[0022] Thus, one advantage provided is to improve the mechanical strength of the screen printing screen.

[0023] According to one feature of the invention, the polymer material is chosen from polyethylene terephthalate, polyethylene, polyimide, polyurethane, polyvinyl chloride, polypropylene, polytetrafluoroethylene, polymethyl methacrylate, polystyrene.

[0024] Thus, an advantage provided by such polymer materials is their resistance to wear that may be caused by repeated friction with a screen printing squeegee.

[0025] According to a feature of the invention: - the width, noted 1, of the oblong openings of the second series of said at least one underlying zone is greater than 24 pm; - said at least one underlying zone has a thickness, denoted e, satisfying: 1.5^½ <2.5.

[0026] Thus, an advantage provided by such a thickness is to obtain a satisfactory mechanical strength, adapted to the width of the oblong openings.

[0027] According to a feature of the invention: - the width, noted 1, of the oblong openings of the second series of said at least one underlying zone is less than 24 pm; - said at least one underlying zone has a thickness, denoted e, satisfying: 3<; / e<3.5.

[0028] Thus, an advantage provided by such a thickness is to obtain a satisfactory mechanical strength, adapted to the width of the oblong openings.

[0029] According to one feature of the invention, the screen printing screen comprises a screen printing fabric, preferably made of polyester, mounted stretched between the frame and the perforated membrane.

[0030] Thus, one advantage provided is to obtain a trampoline effect which improves the efficiency of the transfer of the electrically conductive paste in terms of homogeneity.

[0031] The invention also relates to a method for manufacturing a metallization grid for a photovoltaic cell, comprising the successive steps: a) using a photovoltaic cell; b) arrange a silkscreen according to the invention above the photovoltaic cell so that said at least one underlying area faces the photovoltaic cell; c) apply an electrically conductive paste to the surface area of ​​the perforated membrane; d) use a squeegee to spread the electrically conductive paste into the first set of oblong openings so as to deposit the electrically conductive paste onto the photovoltaic cell via the second set of oblong openings; e) remove the silkscreen; f) place the photovoltaic cell on which the electrically conductive paste is deposited in a suitable oven to dry and harden the electrically conductive paste.

[0032] Thus, such a process according to the invention makes it possible to manufacture a fine and thick metallization grid with a more uniform section than in the prior art, and this for an operational time shorter than that of the prior art.

[0033] Definitions

[0034] - By "membrane", we mean a structure designed to allow the passage of a electrically conductive paste within it. Under operating conditions, the membrane separates the photovoltaic cell from the screen printing squeegee.

[0035] - By "superficial zone", we mean an upper part of the membrane which is oriented towards the screen printing squeegee in working order.

[0036] - By "underlying zone", we mean a zone of the membrane located below the surface area, oriented towards the photovoltaic cell under operating conditions.

[0037] - By "oblong", we mean that the openings of the first and second series Each dimension has a length greater than its width. The terms "length" and "width" refer to a horizontal plane under conditions of use. The term "thickness" refers to a dimension along a vertical axis under conditions of use.

[0038] - The term "aligned" used in the expression "the second series of openings" "Oblong openings are aligned with the first series of oblong openings in the surface area" means that each opening in the second series is aligned with an opening in the first series along a vertical axis in use. More precisely, the center of each opening in the second series is aligned with the center of an opening in the first series along a vertical axis in use.

[0039] - The term "linear" is understood within the usual tolerances related to the conditions experimental manufacturing, and not perfectly in the mathematical sense of the term.

[0040] - By "metal strip" is meant a plate (or strip) of thin metal.

[0041] - The values ​​X and Y expressed using the expressions "between X and Y" or "inclusive" between X and Y" are included in the defined range of values.

[0042] - By "monobloc", it is understood that the surface area and the underlying area or the underlying areas are made from a single piece of the same material, without assembly.

[0043] - By "monolayer membrane", it is meant that the membrane is made from a single layer of the same polymer material. Brief description of the drawings

[0044] Other features and advantages will become apparent in the detailed description of different embodiments of the invention, the description being accompanied by examples and references to the accompanying drawings.

[0045] [Fig. 1] is a schematic cross-sectional view illustrating a silkscreen according to the invention in the presence of a silkscreen squeegee and a substrate comprising photovoltaic cells. This figure illustrates an embodiment with an area superficial of the perforated membrane forming a metallic strip and with an underlying area of ​​polymer material.

[0046] [Fig. 2] is a schematic cross-sectional view illustrating a silkscreen according to the invention in the presence of a silkscreen squeegee and a substrate comprising photovoltaic cells. This figure illustrates an embodiment with a perforated surface area of ​​the membrane made of a first polymer material and with an underlying area made of a second polymer material different from the first polymer material.

[0047] [Fig.3] is a schematic view analogous to [Fig.2] in the presence of a screen printing fabric mounted stretched between the frame and the perforated membrane.

[0048] [Fig.4] is a schematic view analogous to [Fig.2] where the second polymer is identical to the first polymer. The surface area and the underlying area are monolithic so that the perforated membrane forms a monolayer.

[0049] [Fig.5] is a schematic view analogous to [Fig.4] in the presence of a screen printing fabric mounted stretched between the frame and the perforated membrane.

[0050] [Fig. 6] is a schematic cross-sectional view illustrating a silkscreen according to the invention in the absence of a silkscreen squeegee and a substrate comprising photovoltaic cells. This figure illustrates an embodiment with a perforated surface area of ​​the membrane forming a metal strip and with two underlying areas made of different polymer materials.

[0051] [Fig. 7] is a schematic cross-sectional view illustrating a silkscreen according to the invention in the absence of a silkscreen squeegee and a substrate comprising photovoltaic cells. This figure illustrates an embodiment with a perforated surface area of ​​the membrane made of a polymer material and with two underlying areas made of a polymer material. The polymer material is different for each of the underlying areas and for the surface area.

[0052] [Fig.8] is a schematic view analogous to [Fig.7] in the presence of a screen printing fabric mounted stretched between the frame and the perforated membrane.

[0053] [Fig.9] is a schematic view analogous to [Fig.7] where the polymer material is identical for each of the underlying zones and for the surface zone. The surface zone and the two underlying zones are monolithic so that the perforated membrane forms a monolayer.

[0054] [Fig. 10] is a schematic view analogous to [Fig.9] in the presence of a screen printing fabric mounted stretched between the frame and the perforated membrane.

[0055] It should be noted that the drawings described above are schematic and not to scale for the sake of legibility and to simplify their understanding. For example, the step effects between the width of the openings in the surface area and the width of the openings in the underlying area (or areas) are accentuated on The drawings are compared to reality. For example, in the case of laser ablation, step widths are generally less than 1 µm. Cuts are made along a vertical axis under operating conditions. Detailed description of the implementation methods

[0056] Identical elements or elements performing the same function shall bear the same references for the different embodiments, for the sake of simplification.

[0057] An object of the invention is a silkscreen for manufacturing a metallization grid for a photovoltaic cell C using a silkscreen squeegee R, comprising: - a frame 1; - a perforated membrane 2, without wires, arranged inside the frame 1; the perforated membrane 2 comprising a surface area 20 and at least one underlying area 21; the surface area 20 being intended to face the screen printing squeegee R, said at least one underlying area 21 being intended to face the photovoltaic cell C; the surface area 20 is equipped with a first series of oblong openings 200 each having a first width; said at least one underlying zone 21 is provided with a second series of oblong openings 210 each having a width strictly less than the first width, the second series of oblong openings 210 is aligned with the first series of oblong openings 200 of the surface zone 20, said at least one underlying zone 21 is made of a polymer material.

[0058] Frame

[0059] The frame 1 is advantageously made of a metallic material, preferably aluminium or an alloy comprising aluminium.

[0060] The screen printing screen advantageously comprises a screen printing fabric 3, preferably made of polyester, mounted taut between the frame 1 and the perforated membrane 2. The screen printing fabric 3 is advantageously fixed under the frame 1, for example by gluing.

[0061] Perforated membrane

[0062] The perforated membrane 2 is free of threads.

[0063] The perforated membrane 2 is arranged inside the frame 1. The perforated membrane 2 is advantageously fixed under the frame 1, for example by gluing. In the presence of a screen-printing fabric 3, the perforated membrane 2 is advantageously fixed under the screen-printing fabric 3, for example by gluing.

[0064] Surface area

[0065] The perforated membrane 2 includes a surface area 20 intended to face the screen printing squeegee R under conditions of use.

[0066] The surface area 20 is provided with a first series of oblong openings 200, each having a first width. By way of non-limiting example, the first series of oblong openings 200 can be obtained by laser ablation.

[0067] According to a first embodiment, the surface area 20 is made of a metallic material so as to form a metal strip. The first width is then advantageously between 50 µm and 250 µm, for example 200 µm. By way of non-limiting example, the metallic material may be stainless steel. The metal strip may have a thickness between 10 µm and 50 µm, for example 30 µm.

[0068] According to a second embodiment, the surface area 20 is made of a polymer material. The first width is then advantageously between 24 µm and 50 µm. The polymer material is advantageously chosen from polyethylene terephthalate, polyethylene, polyimide, polyurethane, polyvinyl chloride, polypropylene, polytetrafluoroethylene, polymethyl methacrylate, and polystyrene. The surface area may have a thickness between 10 µm and 40 µm.

[0069] Underlying area(s)

[0070] The perforated membrane 2 has at least one area 21 underlying the surface area 20. The area 21 or the areas 21 are intended to face the photovoltaic cell C under operating conditions.

[0071] The underlying zone 21 or zones 21 are made of a polymer material. The polymer material is advantageously selected from polyethylene terephthalate, polyethylene, polyimide, polyurethane, polyvinyl chloride, polypropylene, polytetrafluoroethylene, polymethyl methacrylate, and polystyrene. When the surface zone 20 is made of a polymer material, the surface zone 20 and the underlying zone(s) 21 are advantageously one-piece so as to form a single-layer membrane 2. However, different polymer materials may be used for the surface zone 20 and for the underlying zone 21 or zones 21.

[0072] The underlying zone 21, or each underlying zone 21, is provided with a second series of oblong apertures 210 aligned with the first series of oblong apertures 200. Each oblong aperture 210 in the second series has a width strictly less than the width of the first. By way of non-limiting example, the second series or series of oblong apertures 210 can be obtained by laser ablation.

[0073] In the case where the perforated membrane 2 has at least two zones 21 underlying the surface zone 20, the first width of the oblong openings 200 of the first series and the widths of the oblong openings 210 of the second series advantageously follow a strictly decreasing function from the surface zone 20 to the aforementioned at least two underlying zones 21. The strictly decreasing function is advantageously linear. The strictly decreasing function advantageously has a slope between 12% and 15% in absolute value.

[0074] According to a first embodiment: - the width, noted "1", of the oblong 210 openings of the second series of the underlying zone 21 or of the underlying zones 21 is greater than 24 pm; - the underlying zone 21 or the underlying zones 21 each have a thickness, denoted e, satisfying: 1.5 < l / e < 2.5.

[0075] By way of non-limiting example, the width "1" may be between 24 pm and 50 pm and the thickness of the underlying zone 21 or zones 21 may be between 10 pm and 40 pm.

[0076] According to a second embodiment: - the width, noted "1", of the oblong 210 openings of the second series of the underlying zone 21 or of the underlying zones 21 is less than 24 pm; - the underlying zone 21 or the underlying zones 21 each have a thickness, denoted e, satisfying: 3^ l / e 3.5.

[0077] By way of non-limiting example, the width "1" may be between 10 pm and 20 pm and the thickness of the underlying zone 21 or zones 21 may be between 3 pm and 8 pm.

[0078] An object of the invention is a method for manufacturing a metallization grid of a C photovoltaic cell, comprising the successive steps: a) use a C photovoltaic cell; b) arrange a silkscreen according to the invention above the photovoltaic cell C so that said at least one underlying area 21 faces the photovoltaic cell C; c) apply an electrically conductive paste to the surface area 20 of the perforated membrane 2; d) use a squeegee R to spread the electrically conductive paste in the first set of oblong openings 200 so as to deposit the electrically conductive paste onto the photovoltaic cell C via the second set of oblong openings 210; e) remove the silkscreen; f) place the photovoltaic cell C on which the electrically conductive paste is deposited in a suitable oven to dry and harden the electrically conductive paste.

[0079] Step a)

[0080] Any type of C photovoltaic cell requiring a metallization grid for charge carrier collection can be used in step a).

[0081] Step b)

[0082] A substrate containing the photovoltaic C cells can be placed on a printing table equipped with substrate support means. The silkscreen is arranged above the substrate so as to ensure alignment between the photovoltaic C cells (i.e., the areas where the metallization grid is formed) and the oblong openings 210 of the second series of the perforated membrane 2. To achieve this, cameras and / or optical sensors are advantageously provided to obtain precise alignment.

[0083] Step c)

[0084] By way of non-limiting examples, the electrically conductive paste applied in step c) may mainly comprise silver particles with a content between 90% and 95%, or may mainly comprise a mixture of silver particles and particles of another metallic material, preferably selected from copper, aluminum, and tin.

[0085] Step d)

[0086] The squeegee R is used to push the electrically conductive paste through the oblong openings 200 of the first set until it reaches the oblong openings 210 of the second set. The squeegee R has a blade with a shape adapted (generally beveled) to ensure uniform application of the electrically conductive paste.

[0087] Step e)

[0088] Step e) is carried out taking care not to damage the electrically conductive lines laid.

[0089] Step f)

[0090] By way of non-limiting example, step f) can be carried out at a temperature of around 200°C for a duration of between 5 minutes and 20 minutes.

[0091] The invention is not limited to the embodiments described. A person skilled in the art is able to consider their technically operative combinations, and to substitute equivalents for them.

Claims

Demands

1. A silkscreen for manufacturing a metallization grid for a photovoltaic cell (C) using a silkscreen squeegee (R), comprising: - a frame (1); - a perforated membrane (2), without wires, arranged inside the frame (1); the perforated membrane (2) comprising a surface area (20) and at least one underlying area (21); the surface area (20) being intended to face the silkscreen squeegee (R), said at least one underlying area (21) being intended to face the photovoltaic cell (C); the surface area (20) is provided with a first series of oblong openings (200), each having a first width;said at least one underlying zone (21) is provided with a second series of oblong openings (210) each having a width strictly less than the first width, the second series of oblong openings (210) is aligned with the first series of oblong openings (200) of the surface zone (20), said at least one underlying zone (21) is made of a polymer material.;

2. Screen printing screen according to claim 1, wherein the perforated membrane (2) has at least two underlying zones (21); the first width of the oblong openings (200) of the first series and the widths of the oblong openings (210) of the second series follow a strictly decreasing function from the surface zone (20) to said at least two underlying zones (21).

3. Screen printing screen according to claim 2, wherein the strictly decreasing function is linear.

4. Screen printing screen according to claim 3, wherein the strictly decreasing function has a slope between 12% and 15% in absolute value.

5. Screen printing screen according to any one of claims 1 to 4, wherein the surface area (20) is made of a metallic material so as to form a metallic strip.

6. Screen printing screen according to claim 5, wherein the first width of the oblong openings (200) of the first series with which the surface area (20) is provided is between 50 pm and 250 pm.

7. Screen printing screen according to any one of claims 1 to 4, wherein the surface area (20) is made of a polymer material.

8. Screen printing screen according to claim 7, wherein the first width of the oblong openings (200) of the first series with which the surface area (20) is provided is between 24 pm and 50 pm.

9. Screen printing screen according to claim 7 or 8, wherein the surface area (20) and said at least one underlying area (21) are monolithic so as to form a single-layer membrane (2).

10. Screen printing screen according to any one of claims 1 to 9, wherein the polymer material is selected from polyethylene terephthalate, polyethylene, polyimide, polyurethane, polyvinyl chloride, polypropylene, polytetrafluoroethylene, polymethyl methacrylate, polystyrene.

11. A silkscreen according to any one of claims 1 to 10, wherein: - the width, denoted 1, of the oblong openings (210) of the second series of said at least one underlying zone (21) is greater than 24 pm; - said at least one underlying zone (21) has a thickness, denoted e, satisfying: 1.5 < < 2.

5.

12. Screen printing screen according to any one of claims 1 to 10, wherein: - the width, denoted 1, of the oblong openings (210) of the second series of said at least one underlying zone (21) is less than 24 pm; - said at least one underlying zone (21) has a thickness, denoted e, satisfying: 3 < l / e <3.

5.

13. Screen printing screen according to any one of claims 1 to 12, comprising a screen printing fabric (3), preferably made of polyester, mounted stretched between the frame (1) and the perforated membrane (2).

14. A method for manufacturing a metallization grid for a photovoltaic cell (C), comprising the successive steps: a) using a photovoltaic cell (C); b) arranging a silkscreen according to any one of claims 1 to 13 above the photovoltaic cell (C) such that said at least one underlying zone (21) faces the photovoltaic cell (C); c) apply an electrically conductive paste to the surface area (20) of the perforated membrane (2); d) use a squeegee (R) to spread the electrically conductive paste into the first set of oblong openings (200) so as to deposit the electrically conductive paste onto the photovoltaic cell (C) via the second set of oblong openings (210); e) remove the silkscreen; f) place the photovoltaic cell (C) on which the electrically conductive paste is deposited in an oven suitable for drying and hardening the electrically conductive paste.