Printing stencil and printing device for forming conductor tracks on substrate, and method for producing metal contact structure of photovoltaic solar cell

Abstract

The invention relates to a printing template (1) for forming conductor tracks on a substrate. The printing template (1) has a plurality of notches in the form of printing gaps (4) for forming conductor tracks on the substrate. Each printing gap (4) of the plurality of printing gaps (4) has at least one printing defining region (3) adjoining the printing side and at least one printing medium supply region (2) adjoining the squeegee side, the volume of the printing defining region (3) being smaller than the volume of the printing medium supply region. The invention further relates to a printing device for forming a conductor track on a substrate and to a method for producing a metal contact structure for a photovoltaic solar cell.

Description

[0001] The invention relates to a printing template for forming conductor tracks on a substrate according to claim 1 , a printing device for forming conductor tracks on a substrate according to claim 12 , and a method for producing a metallic contact structure for a photovoltaic solar cell according to claim 13 .

[0002] In order to apply a printing medium, in particular a screen printing paste, to a substrate, it is known to press the printing medium through a screen printing die by means of a doctor blade so as to apply the printing medium to the substrate. Conventional screen printing dies have a screen printing mesh having a plurality of elongated mesh elements, which is permeable to the printing medium. In order to structure the printing medium passing through the screen printing die, a printing template is arranged on the screen printing mesh, which has openings, so that the printing medium passes through the screen printing die only in the region of the openings of the printing template, and thus a structure consisting of the printing medium, which is defined by the openings of the printing template, can be applied to the substrate.

[0003] For semiconductor components and in particular for photovoltaic solar cells, it is desirable to produce narrow, rectilinear structures on a substrate from a printed medium, in particular in order to form narrow, rectilinear metal contact elements, so-called contact fingers. In order to keep the shading of incident light low, it is desirable to form particularly narrow, rectilinear structures. Therefore, there is a requirement to avoid fluctuations in the cross-sectional area of ​​the structures when applying the material, since a reduced cross section would lead to efficiency losses due to increased line resistance.

[0004] DE 10 2019 122 126 A1 discloses a screen printing mold for forming narrow, linear structures.

[0005] There is a need to further optimize the printing mold in order to, on the one hand, form a narrow, rectilinear structure from the printing medium on the substrate and, on the other hand, to provide a stable printing mold which achieves high productivity in the manufacturing operation and still achieves a high durability of the printing mold and thus a long service life thereof.

[0006] This object is achieved by a printing template for forming conductor tracks on a substrate according to claim 1, a printing device for forming conductor tracks on a substrate according to claim 12, and a method for producing a metallic contact structure for a photovoltaic solar cell according to claim 13. Advantageous embodiments are given in the dependent claims.

[0007] The invention is based on the recognition that it is advantageous to use a printing template that is designed as a plate-shaped printing template. However, in order to achieve sufficient stability, it is desirable that the printing template is designed to have a sufficient thickness. However, this has the disadvantage that the thickness of the printing gap of the printing template also increases according to the thickness of the plate-shaped printing template. This results in disadvantages in the supply of the print medium and / or in the uniform output of the print medium to the substrate. According to the invention, these disadvantages are avoided in that the printing gap has a print medium supply area and a print limiting area.

[0008] The printing template according to the invention for forming conductor tracks on a substrate has a plurality of recesses in the form of printing gaps for forming conductor tracks on the substrate.

[0009] It is important here that the printing template is designed as a plate-shaped printing template. The printing template comprises a base side and a scraper side opposite the base side. Each of the plurality of printing gaps has at least one printing-limited area adjacent to the printing side and at least one print medium supply area adjacent to the scraper side, the volume of the printing-limited area being smaller than the volume of the print medium supply area. The print medium supply area has a gap width that increases in the direction of the scraper side, preferably strictly monotonically.

[0010] It is also important that the walls of the print defined area form a first angle which is smaller than a second angle formed by the walls of the print medium supply area and / or that the print defined area has an increasing, preferably strictly monotonically increasing, gap width towards the substrate side.

[0011] The printing template according to the invention makes it possible to form structures consisting of a printing medium on a substrate through a printing gap. The printing medium is applied by printing defined areas in a shape defined by the printing defined areas. Applying structures with small dimensions requires a narrow and elongated printing gap corresponding to said dimensions.

[0012] In the prior art, in printing dies for screen printing, the printing gap has vertically extending side walls. If such a printing gap is small in size and therefore has a small width in previously known printing dies, there is the problem that the printing medium cannot be replenished in sufficient quantities. In order to overcome this problem, the printing templates according to the prior art should be made as thin as possible. However, thin printing templates lead to reduced durability and therefore have to be frequently replaced during production operations and / or require a supporting structure, such as a screen printing mesh, on which the printing template is arranged.

[0013] In the printing template according to the invention, the print medium supply area has a larger volume than the print limit area. This allows the use of printing templates with a greater thickness and thus a greater stability compared to the prior art, since an increased print medium flow to the print medium limit area is achieved due to the greater volume of the print medium supply area. Due to the greater stability, in the printing template according to the invention, it is thus also possible to dispense with support structures, in particular screen printing meshes, in the region of the print gap.

[0014] The printing medium supply region of the printing template according to the invention has an increasing, preferably strictly monotonically increasing, gap width in the direction of the squeegee side, thereby facilitating the supply of printing medium on the squeegee side.

[0015] Furthermore, in the printing template according to the present invention, advantageously, the increased gap width prevents the printing medium from depositing.

[0016] The printing template according to the invention is particularly suitable for forming a metal contact structure of a photovoltaic solar cell. Such a contact structure of the solar cell, in particular the contact fingers, is usually designed as a straight line. Therefore, it is advantageous if each of the plurality of printing gaps is designed as a straight line printing gap.

[0017] It is within the scope of the invention that the first angle formed by the wall of the print-limited area and the second angle formed by the wall of the print medium supply area have the same orientation. In this case, the print-limited area also has a gap width that increases in the direction of the scraper side, preferably strictly monotonically. In this case, the first angle is smaller than the second angle in order to achieve a large volume in the print medium supply area and to achieve a precise definition of the narrow and elongated printing structure in the print-limited area.

[0018] Therefore, in an advantageous embodiment, the printing template has:

[0019] The opening angle of the printing defined area is smaller than that of the printing medium supply area, in particular, it has an opening angle that is 10° smaller, preferably 20° smaller, in particular 30° smaller than that of the printing medium supply area.

[0020] It is also within the scope of the invention that the first angle has an orientation opposite to the second angle. In this advantageous embodiment, the print-limited area has a gap width that increases in the direction of the substrate side, preferably strictly monotonically. This also enables an exact definition of the structure to be printed.

[0021] In this case, the printed defined area has an opening angle of greater than 30°, preferably greater than 40°, particularly preferably greater than 60°.

[0022] This embodiment has the advantage that, on the one hand, a large supply flow of printing medium can be achieved in the printing medium supply area and, on the other hand, a precise definition of the structures to be printed is facilitated.

[0023] In one embodiment, an advantageous configuration results in that the printing template has a thickness of more than 50 μm, in particular more than 100 μm, preferably more than 500 μm.

[0024] The advantage of this design is that the stability increases with increasing thickness of the template.

[0025] In one embodiment, an advantageous configuration results in that the printed defined area has a thickness of less than 250 μm, in particular less than 50 μm, preferably less than 25 μm.

[0026] The advantage of this configuration is that it allows the structures formed on the print medium to have a target height of less than 250 μm, in particular less than 50 μm, preferably less than 25 μm.

[0027] In one embodiment, an advantageous configuration results in that the template body consists of a material selected from the group consisting of glass, silicon and stainless steel, preferably glass.

[0028] Different from conventional materials, when using said material, particularly using glass, the advantage is that glass has higher scratch resistance. In addition, glass has a high elastic modulus and also has less thermal expansion.

[0029] In one embodiment, an advantageous configuration results in that the width of each of the plurality of printing nips at the end of the print-defined area facing the squeegee is less than 50 μm, in particular less than 25 μm, preferably less than 15 μm.

[0030] An advantage of this embodiment is that the flow properties of the printing medium are decisively influenced thereby, as a result of which the geometry of the printed structures has a high degree of uniformity.

[0031] In one embodiment, another advantageous design is obtained, wherein the width of each of the multiple printing gaps at the end of the printing defined area facing the substrate side is less than 50 μm, in particular less than 25 μm, preferably less than 15 μm, and / or in the range of 15 μm to 25 μm.

[0032] An advantage of this embodiment is that the flow properties of the printing medium are decisively influenced thereby, as a result of which the geometry of the printed structures has a high degree of uniformity.

[0033] A further advantageous embodiment results in that the width of each of the plurality of printing nips at the end of the print medium supply area facing the doctor blade is greater than 15 μm, in particular greater than 25 μm, preferably greater than 50 μm.

[0034] In this embodiment, it is advantageous that sufficient printing medium is thus supplied. In addition, the width of the printing gap at the end facing the scraper side is important for the volume formed in the printing medium supply area. This volume forms the printing medium reservoir, from which the replenishing medium is provided.

[0035] In one embodiment, a further advantageous configuration results in that the print medium supply area ends directly on the scraper side and the print definition area ends directly on the substrate side, in particular the print medium supply area and the print definition area adjoin one another.

[0036] A further advantageous embodiment results in one embodiment in which the print delimiting area tapers in the direction of the squeegee side and the print medium supply area is open in the direction of the squeegee side.

[0037] In this embodiment, which is similar to an hourglass in outline, it is advantageous that this design forms a volume open to the substrate. This volume makes it possible to accommodate print medium supplied by replenishing the print medium and, as in the previously described embodiment, to output a larger amount of print medium to the substrate.

[0038] In addition, the present invention is also aimed at providing a printing mold, a printing device and a method for forming a conductor track on a substrate.

[0039] The printing mold according to the invention comprises a printing template according to the invention, wherein the printing template is arranged in a frame, preferably under tensile stress.

[0040] The arrangement in a frame has the advantage that the tensioned printing template is stable due to the tensile stress but is nevertheless arranged on the frame with little flexibility.

[0041] An advantageous embodiment of the printing mold according to the invention results in that no supporting structure, in particular no mesh-like supporting structure, in particular no screen printing mesh, is formed at the opening of the printing gap.

[0042] In conventional screen printing dies, a support material, in particular a mesh-like support material with a certain mesh size, is provided over the entire surface of the template. However, it is disadvantageous that, in particular for screen printing meshes, a support material must be used for very small structures, the threads of which have a diameter that is significantly smaller than the structure to be printed. Such a support material results in a low stability and poor dimensional stability of the printing template. These disadvantages are avoided by omitting the support structure when using a plate-like printing template. In this embodiment, the support material can be omitted because the stability of the printing template does not have to be achieved by a mesh-like support material, because the printing template can be designed, as described above, to have a sufficient thickness for achieving the inherent stability of the printing template.

[0043] A printing medium, in particular a screen printing paste, is applied to a substrate by means of a printing device according to the invention, comprising a printing template according to the invention, in particular a preferred embodiment of the printing template, and at least one scraper, by means of which the printing medium is applied to the substrate through the printing template.

[0044] The printing device according to the invention makes it possible to form structures, in particular linear structures, on a substrate from a printing medium through the printing nip of the printing template using a printing template having high durability.

[0045] The method for manufacturing a metal contact structure for a photovoltaic solar cell according to the present invention comprises the following steps:

[0046] - applying the printing medium onto the squeegee side of the printing template,

[0047] Printing the print medium with at least one squeegee through the printing nip of a printing template in order to apply the print medium structure to the solar cell substrate on the substrate side of the printing template opposite the squeegee side.

[0048] It is important here that the printing template is designed as a plate-shaped printing template having a substrate side and a scraper side opposite the substrate side, and

[0049] Each of the plurality of printing gaps has at least one printing defined area adjacent to the printing side and at least one printing medium supply area adjacent to the scraper side, the volume of the printing defined area being smaller than the volume of the printing medium supply area,

[0050] The print medium supply region has a gap width which increases in the direction of the scraper side, preferably strictly monotonically.

[0051] It is also important that the walls of the print defined area form a first angle which is smaller than a second angle formed by the walls of the print medium supply area and / or that the print defined area has a gap width which increases, preferably strictly monotonically, in the direction of the substrate side.

[0052] The method according to the invention makes it possible to form structures, in particular linear structures, on a substrate from a printing medium through the printing gap of a printing template.The printing medium is applied through the printing defined area in a shape defined by the printing defined area.

[0053] Furthermore, the aforementioned objectives are also achieved by the use according to the invention of a printing template for forming metallic conductor tracks of a photovoltaic solar cell, preferably on the front side of the photovoltaic solar cell facing the light incidence.

[0054] In particular, the so-called LIDE (laser induced deep etching) method is suitable for producing the printing template according to the invention. This method can produce the printing gap and the defined opening angle, as is necessary for the template according to the invention. This method is described in WO 2018 / 162385 A1. It is particularly advantageous here if the printing template consists of glass.

[0055] It is within the scope of the invention that the printing device is designed in a manner known per se and has a movement unit known per se for moving the doctor blade and a supply unit for supplying printing medium to the doctor blade side.

[0056] It is also within the scope of the invention that the printing template has, in addition to the plurality of printing gaps, further printing gaps or indentations which have a different structural design. In particular, it is within the scope of the invention that one or more printing gaps are provided with a greater width in order to connect the contact fingers produced by the plurality of printing gaps via connections, so-called busbars.

[0057] The volume of the print medium supply area is preferably defined by the wall of the printing gap within the print medium supply area and by the scraper side of the printing template, in particular the scraper side of the printing template as a planar continuation. Preferably, the volume is also defined in the direction of the substrate side by the print limit area.

[0058] The volume of the print defined area is preferably defined by the wall of the print gap within the print defined area and by the base side of the printing template, in particular the base side of the printing template as a planar continuation. Preferably, the volume is also defined by the print medium supply area in the direction of the scraper side.

[0059] The plurality of printing gaps of the printing template according to the invention preferably has at least 5, particularly preferably at least 10, and even more preferably at least 15 printing gaps.

[0060] Further preferred features and embodiments are described below with reference to examples and drawings. Figure 1 and Figure 2 Embodiments of the printing gap of the printing template according to the invention are respectively shown. Figure 3 An embodiment of a printing template according to the invention is shown. Figure 4 An embodiment of a printing apparatus according to the present invention is shown.

[0061] The drawings show schematic, not true to scale illustrations. The same reference numerals in the figures designate the same or identically acting elements.

[0062] exist Figure 1 , an exemplary embodiment of a printing template according to the invention is shown in a sectional view, wherein a detail of a printing template with printing gaps is shown. The printing template continues in the same way to the right and to the left. In the present case, the printing template has a total of 19 printing gaps arranged in parallel and having the same geometry.

[0063] The plate-shaped printing template 1 has an opening with an opening angle β on the scraper side R located at the top in the figure. The printing template 1 has an opening with an opening angle α on the base side S located at the bottom in the figure. The opening angle β on the scraper side is greater than the opening angle α on the base side. Both opening angles are oriented identically.

[0064] In this embodiment, the printing medium supply area 2 is formed by a volume defined by the printing template upper side on the squeegee side and the opening side edges of the channel wall of the opening defined by the opening angle β.

[0065] In this exemplary embodiment, the print defined area 3 is formed by the volume delimited by the substrate-side printing template underside S and the opening side edges of the opening of the printing gap defined by the opening angle α.

[0066] The print medium supply area 2 thus ends directly on the squeegee side. In contrast, the print definition area 3 ends directly on the substrate side.

[0067] In this arrangement, the print medium supply area and the print limit area are directly adjacent to each other. In this embodiment, the height H2 of the print medium supply area is selected to be greater than the height H3 of the print limit area. In addition, the volume of the print medium supply area 2 is greater than the volume of the print limit area 3, which is advantageously achieved by being able to replenish sufficient print medium.

[0068] The printing template according to the present invention is Figure 2The embodiment shown in FIG. 1 is shown in a sectional view, wherein a portion of a printing template with printing gaps is shown. The printing template continues in the same way to the right and to the left. In the present case, overall, the printing template has a total of 19 printing gaps arranged in parallel and having the same geometry.

[0069] The plate-shaped printing template 1 has an opening with an opening angle β on the scraper side R located at the top in the figure. The printing template 1 has an opening with an opening angle α on the base side S located at the bottom in the figure. The opening angle β on the scraper side is greater than the opening angle α on the base side. The two opening angles are oriented in opposite directions. As a result, the two areas are configured in an hourglass shape.

[0070] In this embodiment, the printing medium supply area 2 is formed by a volume defined by the printing template upper side on the squeegee side and the opening side edges of the channel wall of the opening defined by the opening angle β.

[0071] In this exemplary embodiment, the print defined area 3 is formed by the volume delimited by the substrate-side printing template underside S and the opening side edges of the opening of the printing gap defined by the opening angle α.

[0072] The print medium supply area 2 thus ends directly on the squeegee side. In contrast, the print definition area 3 ends directly on the substrate side.

[0073] In this arrangement, the print medium supply area 2 and the print limit area 3 are adjacent to each other. In this embodiment, the height H2 of the print medium supply area is selected to be greater than the height H3 of the print limit area. In addition, the volume of the print medium supply area 2 is greater than the volume of the print limit area 3, which is advantageously achieved by being able to replenish sufficient print medium.

[0074] exist Figure 3 1 shows an embodiment of a printing template 1 according to the invention in a top view. The printing template 1 is designed to be square and the current printing template 1 has 19 parallel printing gaps, which have the same geometric structure. In this embodiment, the printing gaps 4 are arranged parallel to each other and parallel to the edge of the printing template 2. The printing gaps 4 make it possible to produce linear structures composed of printing medium on the substrate. These structures constitute metal contact elements.

[0075] Figure 3 The top view shown in FIG. Figure 1 and Figure 2 A top view of the embodiment shown in FIG.

[0076] exist Figure 4 Schematically shows an embodiment of a printing device according to the present invention. The printing device has a printing mold, which is composed of a Figure 1The embodiment shown in FIG. 1 is composed of a printing template 1 and a frame 5. The printing template 1 is arranged in the frame 5. The printing mold with the printing template 1 and the frame 5 thus constitutes an embodiment of a printing mold according to the invention, which has no supporting structure at the opening of the printing gap 4, in particular no printing screen cloth.

[0077] Above the printing template, a squeegee 6 is arranged on a moving unit 7. The moving unit 7 and the frame 5 are arranged on a support (not shown) of the printing device, which also has a mount for a substrate 8. The substrate 8 is a precursor of a silicon solar cell, on which metallic contact fingers 10 are to be applied. A printing paste 9 containing metal particles is applied to the upper squeegee side of the printing template 1 by a printing medium supply unit (not shown) of the printing device.

[0078] The squeegee 6 is moved over the printing template 1 by the movement unit 7 and thereby presses the printing paste 9 through the printing nip 4 of the printing template 1 onto the substrate 8 , so that the printing paste is applied to the substrate 8 in the form of thin, parallel, linear contact fingers 10 .

[0079] Figure 4 In a real design, the printing template 1 is usually slightly curved in the region of the squeegee 6 in the direction of the substrate 8 .

[0080] Reference numerals list

[0081] 1 Printing template

[0082] 2 Printing media supply area

[0083] 3 Printing limited area

[0084] 4 Printing gap

[0085] 5 Framework

[0086] 6 Scraper

[0087] 7 Motion Unit

[0088] 8 Base

[0089] 9 Printing paste

[0090] 10 Contact finger

[0091] R Scraper side

[0092] S basal side

[0093] α, β opening angle

Claims

1. A printing template (1) for forming conductor tracks on a substrate, the printing template (1) having a plurality of recesses in the form of printing gaps (4) for forming conductor tracks on the substrate, It is characterized in that The printing template (1) is configured as a plate-shaped printing template (1), the printing template (1) having a base side (S) and a scraper side (R) opposite to the base side (S), and Each of the plurality of printing gaps (4) has at least one printing defined area (3) adjacent to the printing side and at least one printing medium supply area (2) adjacent to the scraper side (R), the volume of the printing defined area (3) being smaller than the volume of the printing medium supply area (2), The printing medium supply area (2) has a gap width which increases in the direction of the scraper side (R), preferably strictly monotonically, and - the wall of the printing limiting area (3) forms a first angle (α), which is smaller than a second angle (β) formed by the wall of the printing medium supply area (2), and / or The printed defined area (3) has a gap width which increases in the direction of the substrate side (S), preferably strictly monotonically.

2. The printing template (1) according to claim 1, It is characterized in that The wall of the print definition area (3) forms an opening angle (α) that is 10° smaller, preferably 20° smaller, and in particular 30° smaller than the wall of the print medium supply area (2).

3. The printing template (1) according to any one of the preceding claims, It is characterized in that The printing template has a thickness of 50 μm, in particular greater than 100 μm, preferably greater than 500 μm.

4. The printing template (1) according to any one of the preceding claims, It is characterized in that The printed defined area (3) has a thickness of less than 250 μm, in particular less than 50 μm, preferably less than 25 μm.

5. The printing template (1) according to any one of the preceding claims, It is characterized in that The template body is made of one of glass, stainless steel and silicon, preferably glass.

6. The printing template (1) according to any one of the preceding claims, It is characterized in that The width of each printing gap (4) of the plurality of printing gaps (4) at the end of the printing defined area (3) facing the scraper side (R) is less than 50 μm, in particular less than 25 μm, preferably less than 15 μm.

7. The printing template (1) according to any one of the preceding claims, It is characterized in that The width of each printing gap (4) of the plurality of printing gaps (4) at the end of the printing defined area (3) facing the substrate side (S) is less than 50 μm, in particular less than 25 μm, preferably less than 15 μm, and / or in the range of 15 μm to 25 μm.

8. The printing template (1) according to any one of the preceding claims, It is characterized in that The width of each printing gap (4) of the plurality of printing gaps (4) at the end of the printing medium supply area (2) facing the scraper side (R) is greater than 15 μm, in particular greater than 25 μm, preferably greater than 50 μm.

9. The printing template (1) according to any one of the preceding claims, It is characterized in that The print medium supply area (2) ends directly at the scraper side (R), and the print definition area (3) ends directly at the substrate side (S), in particular, the print medium supply area (2) and the print definition area (3) are adjacent to each other.

10. Printing mold, Having a printing template (1) according to any one of the preceding claims, The printing template is arranged in a frame, preferably under tensile stress.

11. The printing mold according to claim 10, It is characterized in that No supporting structure, in particular no mesh-like supporting structure, and in particular no screen printing mesh is provided at the opening of the printing gap (4).

12. Printing equipment for forming conductor tracks on substrates, The screen printing device has a printing template (1) according to any one of the above claims and at least one scraper, the screen printing device being configured to apply a printing medium through the screen printing template onto the substrate by means of the scraper.

13. A method for producing a metal contact structure for a photovoltaic solar cell, The method has the following steps: - applying the printing medium onto the squeegee side (R) of the printing template (1), - printing the printing medium by means of at least one squeegee through the printing gap (4) of the printing template (1) in order to apply the printed medium structure to the solar cell substrate on the substrate side (S) of the printing template opposite the squeegee side (R), It is characterized in that The printing template (1) is configured as a plate-shaped printing template (1), the printing template (1) having a base side (S) and a scraper side (R) opposite to the base side (S), and Each of the plurality of printing gaps (4) has at least one printing defined area (3) adjacent to the printing side and at least one printing medium supply area (2) adjacent to the scraper side (R), the volume of the printing defined area (3) being smaller than the volume of the printing medium supply area (2), The printing medium supply area (2) has a gap width which increases in the direction of the scraper side (R), preferably strictly monotonically, and - the wall of the printing limiting area (3) forms a first angle (α), which is smaller than a second angle (β) formed by the wall of the printing medium supply area (2), and / or The printed defined area (3) has a gap width which increases in the direction of the substrate side (S), preferably strictly monotonically.

14. Use of a printing template (1) according to any one of claims 1 to 9 for forming metallic conductor tracks of photovoltaic solar cells, preferably on the front side of the photovoltaic solar cell facing the incidence of light.

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