Printing stencil and printing devices for forming conductor paths on a substrate and method for producing a metal contact structure of a photovoltaic cell

Abstract

The invention relates to a printing stencil (1) for forming conductor paths on a substrate. The printing stencil (1) has a plurality of recesses in the form of printing gaps (4) for forming the conductor paths. Each printing gap (4) of the plurality of printing gaps (4) has at least one print definition region (3) adjacent to the printing side and at least one printing medium supply region (2) adjacent to the squeegee side, wherein the volume of the print definition region (3) is smaller than the volume of the printing medium supply region. The invention also relates to a printing device for forming conductor paths on a substrate and a method for producing a metal contact structure of a photovoltaic solar cell.

Description

[0001] Printing stencil and pressing devices for forming conductor tracks on a substrate and method for producing a metallic contact structure of a photovoltaic solar cell

[0002] Description

[0003] The invention relates to a printing stencil 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 of a photovoltaic solar cell according to claim 13.

[0004] 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 form using a squeegee in order to apply the printing medium to the substrate. Typical screen printing forms have a screen printing mesh with a large number of elongated mesh elements, wherein the screen printing mesh is permeable to the printing medium. In order to structure the printing medium passing through the screen printing form, a printing stencil is arranged on the screen printing mesh, which has openings so that the printing medium only passes through the screen printing form in the region of the openings in the printing stencil, and thus a structure of printing medium predetermined by the openings in the printing stencil can be applied to the substrate.

[0005] For semiconductor components, and especially for photovoltaic solar cells, it is desirable to create narrow, rectilinear structures from the printing medium on the substrate, especially for forming narrow, rectilinear metallic contact elements, so-called contact fingers. To minimize shadowing from incident light, it is desirable to form particularly narrow, rectilinear structures. Therefore, it is necessary to avoid fluctuations in the cross-sectional area of ​​the structures during material deposition, since a decreasing cross-section results in efficiency losses due to increased conduction resistance.

[0006] A screen printing form for the formation of narrow, straight structures is known from DE 10 2019 122 126 A1.

[0007] There is a need to further optimize the printing forms in order to, on the one hand, form narrow, straight structures of printing medium on the substrate and, on the other hand, to provide a stable printing form that enables high throughput in production operations and yet a long durability and thus service life of the printing form.

[0008] This object is achieved by a printing stencil 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 of a photovoltaic solar cell according to claim 13. Advantageous embodiments can be found in the dependent claims.

[0009] The present invention is based on the recognition that the use of a printing stencil designed as a plate-shaped printing stencil is advantageous. However, to achieve sufficient stability, it is desirable to design the printing stencil with a sufficient thickness. This, however, has the disadvantage that the thickness of the printing gaps of the printing stencil increases in proportion to the thickness of the plate-shaped printing stencil. This can lead to disadvantages in the supply of the printing medium and / or in the uniform dispensing of the printing medium onto the substrate. According to the invention, these disadvantages are avoided by the printing gaps having a printing medium supply area and a print definition area:

[0010] The printing stencil according to the invention for forming conductor tracks on a substrate has a plurality of recesses in the form of printing gaps for forming the conductor tracks on the substrate. It is essential that the printing stencil is designed as a plate-shaped printing stencil. The printing stencil comprises a substrate side and a squeegee side opposite the substrate side. Each printing gap of the plurality of printing gaps has at least one print definition region adjacent to the printing side and at least one print medium feed region adjacent to the squeegee side, wherein the volume of the print definition region is smaller than the volume of the print medium feed region. The print medium feed region has a gap width that increases, preferably increases strictly monotonically, in the direction of the squeegee side.

[0011] It is also essential that the walls of the print definition area enclose a first opening angle which is smaller than a second opening angle enclosed by the walls of the print medium supply area and / or that the print definition area has a gap width which increases, preferably strictly monotonically increasing, in the direction of the substrate side.

[0012] The printing stencil according to the invention enables the formation of structures made of printing medium on the substrate through the printing gaps. A printing medium is applied through the printing definition area in the shape defined by the printing definition area. Applying structures with small dimensions requires correspondingly narrow printing gaps.

[0013] In the printing forms used in prior art screen printing, the printing gaps have vertically running side walls. If these printing gaps are small, and thus the printing gaps in previously known printing forms are narrow, the problem arises that the printing medium cannot be fed in sufficient quantities. To counteract this problem, the printing stencils are manufactured as thin as possible in the prior art. However, thin printing stencils lead to reduced durability and therefore must be replaced frequently in production and / or require support structures such as a screen printing mesh on which the printing stencil is mounted.

[0014] In the printing stencil according to the invention, the printing medium supply area has a larger volume than the print definition area. This allows the use of printing stencils with greater thickness and thus greater stability compared to the prior art, since the larger volume of the printing medium supply area enables an increased flow of printing medium to the printing medium definition area. Due to the greater stability, the printing stencil according to the invention also eliminates the need for supporting structures in the area of ​​the printing gap, in particular a screen printing mesh.

[0015] The printing medium feed area of ​​the printing stencil according to the invention has a gap width that increases toward the squeegee side, preferably strictly monotonically. This facilitates the feeding of printing medium on the squeegee side.

[0016] A further advantage of the printing stencil according to the invention is that the increasing gap width prevents the printing medium from settling.

[0017] The printing stencil according to the invention is particularly suitable for forming metallic contact structures of a photovoltaic solar cell. Such contact structures, in particular the contact fingers of such solar cells, are typically linear. Advantageously, the printing gaps of the plurality of printing gaps are therefore designed as linear printing gaps.

[0018] It is within the scope of the invention that a first opening angle, which is formed by the walls of the print definition area, and a second opening angle, which is formed by the walls of the print medium supply area, have the same orientation. In this case, the print definition area also has a gap width that increases toward the doctor blade side, preferably increasing strictly monotonically. However, the first opening angle is smaller than the second opening angle in this case in order to enable a large volume in the print medium supply area and precise definition of the narrow print structures in the print definition area.

[0019] In an advantageous embodiment, the printing stencil therefore has a printing definition area whose opening angle is smaller than the printing medium supply area, in particular an opening angle that is 10°, preferably 20°, in particular 30° smaller.

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

[0021] In this case, the opening angle of the pressure definition area is advantageously greater than 30°, preferably greater than 40°, particularly preferably greater than 60°.

[0022] The advantage of this embodiment is that, on the one hand, a high inflow of printing medium in the printing medium supply area and, on the other hand, a precise definition of the structure to be printed is promoted.

[0023] An advantageous embodiment results in an embodiment wherein the printing stencil has a thickness greater than 50 pm, in particular greater than 100 pm, preferably greater than 500 pm.

[0024] An advantage of this design is that stability increases with the stencil thickness.

[0025] An advantageous embodiment results in an embodiment wherein the pressure definition region has a thickness of less than 250 pm, in particular less than 50 pm, preferably less than 25 pm.

[0026] An advantage of this design is that the targeted height of the structure formed from the pressure medium of less than 250 pm, in particular less than 50 pm, preferably less than 25 pm, can be achieved.

[0027] An advantageous embodiment results in an embodiment in which the stencil body is made of one of the following materials: glass, silicon, or stainless steel, preferably glass. The advantages of using these materials, particularly glass, compared to conventional materials, are based on its increased scratch resistance. Furthermore, glass has a high modulus of elasticity and lower thermal expansion.

[0028] An advantageous embodiment results in an embodiment wherein the width of each printing gap of the plurality of printing gaps at the end of the printing definition area facing the doctor blade side is less than 50 pm, in particular less than 25 pm, preferably less than 15 pm.

[0029] The advantage of this embodiment is that the flow behavior of the printing medium is significantly influenced, whereby the geometry of the printed structures has a high degree of homogeneity.

[0030] A further advantageous embodiment results in an embodiment wherein the width of each printing gap of the plurality of printing gaps at the end of the printing definition region facing the substrate side is less than 50 pm, in particular less than 25 pm, preferably less than 15 pm and / or lies in the range 15 pm to 25 pm.

[0031] The advantage of this embodiment is that the flow behavior of the printing medium is significantly influenced, whereby the geometry of the printed structures has a high degree of homogeneity.

[0032] A further advantageous embodiment results in an embodiment wherein the width of each printing gap of the plurality of printing gaps at the end of the printing medium supply region facing the doctor blade side is greater than 15 pm, in particular greater than 25 pm, preferably greater than 50 pm.

[0033] The advantage of this embodiment is that sufficient printing medium is supplied. The width of the printing gap at the end facing the squeegee side is also crucial for the volume formed in the printing medium supply area. This volume represents a printing medium reservoir from which the medium feed is fed. A further advantageous refinement results from an embodiment in which the printing medium supply area terminates directly at the squeegee side and the print definition area terminates directly at the substrate side, in particular in which the printing medium supply area and the print definition area are adjacent to one another.

[0034] A further advantageous embodiment results in an embodiment wherein the print definition area tapers in the direction of the squeegee side and the print medium supply area opens in the direction of the squeegee side.

[0035] An advantage of this design, which resembles an hourglass in profile, is that it creates an open volume facing the substrate. This volume allows the print medium to be absorbed by the print medium feed and, as in the previously mentioned embodiments, to be dispensed onto the substrate in a larger amount.

[0036] Furthermore, it is an object of the invention to propose a printing form, a printing device and a method for forming conductor tracks on a substrate.

[0037] A printing form according to the invention comprises a printing stencil according to the invention, wherein the printing stencil is arranged in a frame, preferably under tensile stress.

[0038] The advantage of mounting in a frame is that the clamped printing stencil is stable due to tensile stress, but still has a slight flexibility on the frame.

[0039] An advantageous embodiment of a printing form according to the invention results in an embodiment wherein no support structures, in particular no net-like support structures, are formed at the openings of the printing gaps, and in particular no screen printing mesh is arranged. In conventional screen printing forms, a support material, in particular a net-like support material which has a mesh size, is arranged over the entire surface of the stencil. A disadvantage, however, particularly with screen mesh, is that for very small structures, a support material must be used which has wires with a diameter which is essentially smaller than the structure to be printed. These support materials lead to lower stability and poorer dimensional accuracy of the printing stencil. The disadvantages described are prevented by omitting the support structure when using the plate-shaped printing stencil.A carrier material can be dispensed with in this embodiment, since the stability of the printing stencil does not have to be achieved by net-like carrier structures, since the printing stencil can be designed with a thickness sufficient for the inherent stability of the printing stencil, as previously explained.

[0040] The printing medium, in particular a screen printing paste, is applied to a substrate using a printing device according to the invention. The printing device comprises a printing stencil according to the invention, in particular a preferred embodiment thereof, and at least one squeegee. The squeegee applies the printing medium through the printing form to the substrate.

[0041] The printing device according to the invention enables structures, in particular rectilinear structures, of printing medium to be formed on the substrate by means of the printing gaps of the printing stencil when using a printing stencil with high durability.

[0042] The method according to the invention for producing a metallic contact structure of a photovoltaic solar cell comprises the following process steps:

[0043] Applying printing medium to a squeegee side of a printing stencil. Printing the printing medium through printing gaps of the printing stencil by means of at least one squeegee in order to apply a printing medium structure to a solar cell substrate on a substrate side of the printing stencil opposite the squeegee side. What is important here is that the printing stencil is designed as a plate-shaped printing stencil, with a substrate side and a squeegee side opposite the substrate side, and that each printing gap of the plurality of printing gaps has at least one print definition region adjacent to the printing side and at least one print medium supply region adjacent to the squeegee side, wherein the volume of the print definition region is smaller than the volume of the print medium supply region, and the print medium supply region has a gap width that increases, preferably strictly monotonically increasing, in the direction of the squeegee side.

[0044] It is also essential that the walls of the print definition area enclose a first opening angle which is smaller than a second opening angle enclosed by the walls of the print medium supply area and / or that the print definition area has a gap width which increases, preferably strictly monotonically increasing, in the direction of the substrate side.

[0045] The method according to the invention enables structures, particularly linear structures, to be formed from the printing medium on the substrate through the printing gaps of the printing stencil. A printing medium is applied through the printing definition area in the shape defined by the printing definition area.

[0046] The object mentioned at the outset is further achieved by an inventive use of a printing stencil according to the invention for forming metallic conductor tracks of a photovoltaic solar cell, preferably on a front side of the photovoltaic solar cell facing the incidence of light.

[0047] The so-called LIDE (Laser Induced Deep Etching) process is particularly suitable for producing the printing stencil according to the invention. This process can be used to create the printing gaps and the defined opening angles required for the stencil according to the invention. One such process is described in WO 2018 / 162385 A1. It is particularly advantageous to form the printing stencil from glass. It is within the scope of the invention that the printing device is constructed in a manner known per se and has known movement units for moving the squeegee and feed units for feeding printing medium to the squeegee side.

[0048] It is also within the scope of the invention for the printing stencil to have, in addition to the described plurality of printing gaps, further printing gaps or recesses that have different structural configurations. In particular, it is within the scope of the invention to provide one or more printing gaps with a greater width in order to connect the contact fingers created by the plurality of printing gaps via a connector, the so-called busbar.

[0049] The volume of the printing medium supply area is preferably limited by the walls of the printing gap in the area of ​​the printing medium supply area and by the squeegee side of the printing stencil, in particular the squeegee side of the printing stencil that continues as a flat surface. Preferably, the volume is further limited toward the substrate side by the print definition area.

[0050] The volume of the print definition area is preferably delimited by the walls of the printing gap in the area of ​​the print definition area and by the substrate side of the printing stencil, in particular the substrate side of the printing stencil that continues as a flat surface. Preferably, the volume is further delimited toward the squeegee side by the printing medium supply area.

[0051] The plurality of printing columns of the printing stencil according to the invention preferably has at least 5, particularly preferably at least 10, further preferably at least 15 printing columns.

[0052] Further preferred features and embodiments are explained below with reference to exemplary embodiments and figures. Figures 1 and 2 each show an exemplary embodiment of a printing gap of the printing stencil according to the invention. Figure 3 shows an exemplary embodiment of a printing stencil according to the invention. Figure 4 shows an exemplary embodiment of a printing device according to the invention. The figures are schematic representations, not to scale. The same reference numerals in the figures denote the same or identically functioning elements.

[0053] The exemplary embodiment of a printing stencil according to the invention shown in Figure 1 is shown in a sectional view, depicting a partial section of the printing stencil with a printing gap. The printing stencil continues to the right and left in the same way. In total, the printing stencil in this case has 19 parallel printing gaps with the same geometry.

[0054] The plate-shaped printing stencil 1 has an opening with an opening angle β on a squeegee side R, which is located at the top in the figures. The printing stencil 1 has an opening with an opening angle α on a substrate side S, which is located at the bottom in the figures. The squeegee-side opening angle β is larger than the substrate-side opening angle α. Both opening angles are oriented in the same direction.

[0055] In this embodiment, a printing medium supply area 2 is formed over a volume which is limited by the squeegee-side printing stencil top side and the opening flanks of the channel walls of the opening defined by the opening angle ß.

[0056] In this embodiment, a print definition area 3 is formed over a volume which is limited by the substrate-side printing stencil underside S and the opening flanks of the opening of the printing gap defined by the opening angle a

[0057] The print medium feed area 2 thus directly adjoins the squeegee side. The print definition area 3, on the other hand, directly adjoins the substrate side.

[0058] In this arrangement, the print medium supply area and the print definition area are adjacent to one another. In this exemplary embodiment, the height of the print medium supply area H2 is selected to be greater than the height of the print definition area H3. Furthermore, the volume of the print medium supply area 2 is larger than the volume of the print definition area 3, thus ensuring that sufficient print medium can be supplied.

[0059] The exemplary embodiment of a printing stencil according to the invention shown in Figure 2 is shown in a sectional view, depicting a partial section of the printing stencil with a printing gap. The printing stencil continues to the right and left in the same way. In total, the printing stencil in this case has 19 parallel printing gaps with the same geometry.

[0060] The plate-shaped printing stencil 1 has an opening with an opening angle β on a squeegee side R, which is located at the top in the figures. The printing stencil 1 has an opening with an opening angle α on a substrate side S, which is located at the bottom in the figures. The squeegee-side opening angle β is larger than the substrate-side opening angle α. Both opening angles are oriented in opposite directions. As a result, the two areas form an hourglass shape.

[0061] In this embodiment, a printing medium supply area 2 is formed over a volume which is limited by the squeegee-side printing stencil top side and the opening flanks of the channel walls of the opening defined by the opening angle ß.

[0062] In this embodiment, a print definition area 3 is formed over a volume which is limited by the substrate-side printing stencil underside S and the opening flanks of the opening of the printing gap defined by the opening angle a.

[0063] The print medium feed area 2 thus directly adjoins the squeegee side. The print definition area 3, on the other hand, directly adjoins the substrate side.

[0064] In this arrangement, the print medium supply area 2 and the print definition area 3 are adjacent to one another. In this embodiment, the height of the print medium supply area H2 is selected to be greater than the height of the print definition area H3. Furthermore, the volume of the print medium supply area 2 is larger than the volume of the print definition area 3, thus ensuring that sufficient print medium can be supplied.

[0065] Figure 3 shows a top view of an embodiment of a printing stencil 1 according to the invention. The printing stencil 1 is square and has 19 parallel printing gaps with the same geometry. In this embodiment, the printing gaps 4 are arranged parallel to one another and parallel to an edge of the printing stencil 2. The printing gaps 4 enable the creation of rectilinear structures of printing medium on the substrate. These structures represent metallic contact elements.

[0066] The top view shown in Figure 3 also corresponds to the top view of the embodiments shown in Figures 1 and 2.

[0067] Figure 4 schematically illustrates an embodiment of a printing device according to the invention. The printing device comprises a printing forme formed from a printing stencil 1 according to the embodiment shown in Figure 1 and a frame 5. The printing stencil 1 is arranged in the frame 5. The printing forme with printing stencil 1 and frame 5 thus represents an embodiment of a printing forme according to the invention which has no support structures, in particular no screen printing mesh, at the openings of the printing gaps 4.

[0068] A squeegee 6 is arranged above the printing form on a movement unit 7. The movement unit 7 and the frame 5 are arranged on a mounting of the printing device (not shown), which also has a support for a substrate 8. The substrate 8 represents a precursor of a silicon solar cell, to which metallic contact fingers 10 are to be applied. By means of a printing medium supply unit (also not shown) of the printing device, a printing paste 9 containing metal particles is applied to the upper squeegee side of the printing stencil 1.

[0069] By means of the movement unit 7, the squeegee 6 is moved over the printing stencil 1 and thereby the printing paste 9 is pressed through the printing gap 4 of the printing stencil 1 onto the substrate 8, so that printing paste is applied to the substrate 8 in the form of thin, parallel, rectilinear contact fingers 10.

[0070] Figure 4 shows a schematic representation. In a real configuration, the printing stencil 1 typically bends slightly in the area of ​​the squeegee 6 toward the substrate 8.

[0071] Reference symbol list

[0072] 1 printing template

[0073] 2 Print media feed area

[0074] 3 Pressure definition area

[0075] 4 printing gap

[0076] 5 frames

[0077] 6 squeegees

[0078] 7 movement units

[0079] 8 Substrat

[0080] 9 Printing paste

[0081] 10 contact fingers

[0082] R Squeegee side

[0083] S substrate side a, ß opening angle

Claims

Claims: A printing stencil (1) for forming conductor tracks on a substrate, wherein the printing stencil (1) has a plurality of recesses in the form of printing slots (4) for forming the conductor tracks on the substrate, characterized in that the printing stencil (1) is designed as a plate-shaped printing stencil (1) with a substrate side (S) and a doctor blade side (R) opposite the substrate side (S), and that each printing slot (4) of the plurality of printing slots (4) has at least one printing definition area (3) adjacent to the printing side and at least one printing medium supply area (2) adjacent to the doctor blade side (R), wherein the volume of the printing definition area (3) is smaller than the volume of the printing medium supply area (2), and the printing medium supply area (2) has a slot width that increases in the direction of the doctor blade side (R), preferably in a strictly monotonically increasing manner.and the walls of the pressure definition area (3) enclose a first opening angle (a) which is smaller than a second opening angle (β) enclosed by the walls of the pressure medium supply area (2) and / or the pressure definition area (3) has a gap width that increases towards the substrate side (S), preferably in a strictly monotonically increasing manner. A printing stencil (1) according to claim 1, characterized in that the walls of the pressure definition area (3) enclose an opening angle (a) that is 10°, preferably 20°, in particular 30° smaller than that of the walls of the pressure medium supply area (2). A printing stencil (1) according to any of the preceding claims, characterized in that the printing stencil has a thickness of 50 pm, in particular greater than 100 pm, preferably greater than 500 pm. A printing stencil (1) according to any of the preceding claims, characterized in that the print definition area (3) has a thickness of less than 250 pm, in particular less than 50 pm, preferably less than 25 pm. A printing stencil (1) according to any of the preceding claims, characterized in that the stencil body is made of one of the materials glass, stainless steel, or silicon, preferably glass. A printing stencil (1) according to any of the preceding claims, characterized in that the width of each printing gap (4) of the plurality of printing gaps (4) at the end of the print definition area (3) facing the squeegee side (R) is less than 50 pm, in particular less than 25 pm, preferably less than 15 pm.A printing template (1) according to one of the preceding claims, characterized in that the width of each printing gap (4) of the plurality of printing gaps (4) at the end of the pressure definition area (3) facing the substrate side (S) is less than 50 pm, in particular less than 25 pm, preferably less than 15 pm and / or is in the range of 15 pm to 25 pm. A printing template (1) according to one of the preceding claims, characterized in that the width of each printing gap (4) of the plurality of printing gaps (4) at the end of the pressure medium supply area (2) facing the doctor blade side (R) is greater than 15 pm, in particular greater than 25 pm, preferably greater than 50 pm. Printing stencil (1) according to one of the preceding claims, characterized in that the printing medium supply area (2) terminates directly at the squeegee side (R) and the printing definition area (3) terminates directly at the substrate side (S), in particular that the printing medium supply area (2) and the printing definition area (3) adjoin each other. Printing form with a printing stencil (1) according to one of the preceding claims, wherein the printing stencil is arranged in a frame, preferably under tensile tension. Printing form according to claim 10, characterized in that no support structures, in particular no mesh-like support structures, are formed at the openings of the printing gap (4), and in particular no screen printing mesh is arranged.Printing device for forming conductive tracks on a substrate, comprising a printing stencil (1) according to one of the preceding claims, and at least one squeegee, wherein the screen printing device is configured to apply the printing medium through the screen printing stencil onto the substrate by means of the squeegee. Method for producing a metallic contact structure of a photovoltaic solar cell, comprising the process steps. - Applying printing medium to a squeegee side (R) of a printing stencil (1 ) - Printing the printing medium through printing gaps (4) of the printing stencil (1) by means of at least one squeegee in order to apply a printing medium structure to a solar cell substrate on a substrate side (S) of the printing stencil opposite the squeegee side (R), characterized in that that the printing stencil (1 ) is designed as a plate-shaped printing stencil (1 ), with a substrate side (S) and a doctor blade side (R) opposite the substrate side (S), and that each printing gap (4) of the plurality of printing gaps (4) has at least one printing definition area (3) adjacent to the printing side and at least one printing medium supply area (2) adjacent to the doctor blade side (R), wherein the volume of the printing definition area (3) is smaller than the volume of the printing medium supply area (2), the printing medium supply area (2) has a gap width that increases in the direction of the doctor blade side (R), preferably in a strictly monotonically increasing manner, and the walls of the printing definition area (3) enclose a first opening angle (a) which is smaller than a second opening angle (β) enclosed by the walls of the printing medium supply area (2), and / or the printing definition area (3) has a gap width that increases in the direction of the substrate side (S).preferably having a strictly monotonically increasing gap width. Use of a printing stencil (1) according to one of the preceding claims 1 to 9 for forming metallic conductor tracks of a photovoltaic solar cell, preferably on a front side of the photovoltaic solar cell facing the incident light.

Images