WO2010142272A2

WO2010142272A2 - Screen printing frame

Info

Publication number: WO2010142272A2
Application number: PCT/DE2010/000638
Authority: WO
Inventors: Mike Becker; Dietmar LÜTKE-NOTARP
Original assignee: Nb Technologies Gmbh
Priority date: 2009-06-09
Filing date: 2010-06-09
Publication date: 2010-12-16
Also published as: DE102009024877A1; CN201824658U; WO2010142272A3; DE202010007773U1

Abstract

The invention relates to a screen printing frame comprising a first layer with first cavities and a second layer with second cavities. The cavities are arranged in such a manner that a printing medium can be conveyed through one of the first cavities and from there through one of the second cavities to a substrate which can be placed beneath the second layer. Web elements are arranged in the first cavities and support elements are arranged in the second cavities, said web elements being joined to the support elements, and at least one web element has a height, together with a support element, which is equal to the height of the screen printing frame. One support element supports at least one web element which is arranged thereover and one of the web elements has a vertical cross-section which is different from the vertical cross-section of one of the support elements.

Description

screen printing forme

The invention relates to a screen printing form and a solar cell produced with the screen printing form.

In a solar cell having an n-doped layer, a p-doped layer and a pn junction layer, light incident on the n-doped layer causes an electric voltage to be generated between the n-doped layer and the p-doped layer, which generates an electrical current at a connected consumer. In order to be able to pick up the voltage, a metal plate is mounted on the side of the p-doped layer and metallic lines on the side of the n-doped layer. These metallic lines are usually on the one hand to fine metallic lines or so-called fingers, which are arranged for example parallel to each other. On the other hand, it is at least a relatively wide manifold, which is connected to the fingers, wherein by means of the manifold an electrical contact to a consumer can be made. The doped layers may also be present in a different order or number to form a solar cell. Regardless of the structure of the solar cell, an electrical contact is always required to connect a consumer can.

Such solar cells are known and work well. However, it has been observed that the fingers and manifolds have a cross-section that varies significantly along the length of the conduits. Since the electrical resistance of such a conduit depends to a considerable extent on the thinnest part of the conduit, there is a desire to be able to produce conduits with a smaller cross-sectional variation than heretofore.

The fingers and manifolds are required for the function of the solar cell. However, they have the disadvantage that they shade the arranged under the lines n-doped layer. Thus, only part of the surface of the solar cell is available for the conversion of light energy into electrical energy. The efficiency of a solar cell per unit area could be increased if it is possible to create fingers and busbars that shade a smaller area of the solar cell. However, the manifolds should not be made arbitrarily small, so that a good contact with metal leads is possible. Thus, there is a desire to provide a solar cell, which still allows a good electrical contact with low use of expensive electrically conductive materials, such as silver.

The fingers and manifolds can be made by screen printing, which is pushed through a screen printing die with narrow recesses for the fingers and wide recesses for the manifolds of electrically conductive material as a printing medium. Such a screen printing form can be formed by the use of etching technology. The disadvantage here is the large width difference between narrow recesses for the fingers and wide recesses for manifolds. Due to flow and field distributions, the etching rate is greater for a wide recess than for a narrow recess, so that different etching depths are achieved. If a broad recess is to be formed in a screen printing mold for a collecting line to be subsequently produced, it is not possible to form narrow recesses for later produced fingers with the same etching depth as in the wide recess in the same time or in the same etching step. In addition, the etching process is non-uniform with a wide recess in the width, because at the edge of the wide recess is etched deeper into the material due to a stronger flow of the etching liquid in the middle than in the middle.

Thus, it is an object of the invention to provide a screen printing plate for the production of narrow fingers and wide busbars of a solar cell, wherein narrow and wide recesses of the screen printing form can be formed by etching and thereby produce smaller variations in the etch depth and etching width than before. Furthermore, to be produced with the screen printing form finger and manifolds, which have a smaller cross-sectional variation than before and additionally shade a smaller area of the solar cell than previously customary. The screen printing form should be inexpensive and have a long life. Furthermore, it is an object of the invention that a solar cell with such a screen printing form can be produced.

These objects are achieved by the subject matter of the independent claims. Advantageous developments of the invention are the subject of the dependent claims. The object to provide a screen printing form is achieved by a screen printing form, which has a first layer with first recesses and a second layer with second recesses, wherein the recesses are arranged so that a pressure medium through one of the first recesses and from there through a the second recesses can be conveyed to a substrate which can be placed under the second layer, web elements being provided in the first recesses and support elements being provided in the second recesses, the web elements being connected to the support elements, and at least one web element and a support element having a height together, which is equal to the Siebdruckformhöhe, wherein a support member supports at least one web element arranged above it, wherein a vertical cross-section of one of the web elements is not equal to a vertical cross-section of one of the support elements.

Such a screen printing form thus has recesses with web elements and support elements, which reduce the passage area for a printing medium. This allows the production of a manifold, which has less pressure medium than a manifold, which is made with a screen printing form, the recesses having no web elements and support elements. Since a web member and a support member, which may be integral, together have the same height as the screen printing mold, no print medium can reach the position of the support member, whereby a negative pressure is prevented. This point is on the substrate, which may be the surface of a solar cell, thus not provided with the printing medium, so that at this point radiating light reaches the substrate or the solar cell and no shading occurs. Thus, a higher efficiency of a solar cell can be achieved.

The support elements form at a wide recess for a wide manifold a mechanical support, which reduces bending of the screen printing form by a drawn at the top of the stencil doctor. By means of the support elements thus the bending stiffness of the screen printing mold is increased overall. Furthermore, a lower elasticity of the screen printing form can thus be achieved so that when the squeegee moves along on the upper side of the screen printing form, it is stretched less. This has the consequence that the screen printing form according to the invention achieves a longer service life than previous stencils. In the preparation of the screen printing plate according to the invention by etching, the support points also form flow obstructions, so that compared to narrow recesses for the production of fingers no significantly stronger flow for the etching liquid can arise. The etching speeds in the narrow recesses for the fingers to be produced later in comparison to the wide recesses in which web elements and support elements are present thus hardly differ, so that in the screen printing form an etching depth and etching width can be achieved with relatively small variations. This also causes a homogeneous etching and fingers and manifolds with low cross-sectional variation are possible.

According to the invention, furthermore, a vertical cross section of one of the web elements is unequal to a vertical cross section of one of the support elements. This can be attached to the substrate arbitrary structures. The function of the support and recess on the substrate is thus independent of the opening size or web geometry in the first layer of the screen printing form. The first layer and the second layer of the screen printing form can thus have very different geometries relative to each other. According to a preferred embodiment of the invention, the first or second recess has a width of at least 30 micrometers. Furthermore, the web elements or support elements have at least a width of 10 micrometers, preferably less than 20 micrometers. Thus, the above advantages can be achieved particularly well. Such small dimensions can also be produced relatively inexpensively by etching technique, when compared to screen printing forms comprising woven metallic filaments.

It is advantageous if the support elements each have a round, hexagonal or rectangular cross-section. This can be easily produced by means of etching technology. The support elements may be arranged at regular or irregular intervals from each other, the arrangement at regular intervals allows a homogeneous bending stiffness on the entire surface.

If the web elements have a distance of 30 to 100 micrometers from one another, fine lines can be achieved with a printing medium to be conveyed through the recesses. According to one embodiment of the invention, the surfaces of the recess and the web elements or support elements are provided with a coating. The coating reduces the passage area for the print medium and allows even narrower line widths, so that lines with even less pressure medium can be produced.

Preferably, the coating has a thickness that is at least 5% of the smallest cross-sectional width of the first or second recess.

According to one embodiment of the invention, the coating has a contact angle with water in a range of 0 ° to 90 °. A contact angle is the angle formed by a drop of liquid on the surface of a solid to this surface. At a contact angle in the range of 0 ° to 90 °, the liquid or pasty pressure medium thus forms a relatively good interaction with the surface of the coating, so that a large part of the

Pressure medium adhered in the thus coated recesses when the screen printing form is removed from the substrate to be printed. In this way, a homogeneous layer thickness can be printed without too much material is printed from the recesses of the top with on the substrate.

According to another embodiment of the invention, the coating has a contact angle to water in a range of greater than 90 ° to 150 °, it forms only a small interaction of the pressure medium to the surface of the coating. The pressure medium can be conveyed into the recess with less resistance. In addition, after pressing the printing medium and removing the screen printing form from the substrate, the printing medium remaining in the recess can be removed with little effort. In the recesses introduced printing medium remains only a small proportion in the recesses when the screen printing form is removed from the substrate. The result is a job with a height that can be equal to the height of the screen printing form.

According to a further embodiment, at least one support element extends from one side of the second recess to the opposite side of the second recess and divides the second recess into at least two segments. This can be a Establish a manifold, which has two line segments and is interrupted, so that no continuous power transport is possible. In this way, expensive metallic printing medium can be saved. Nevertheless, the function of the collecting line is ensured if subsequently an additional metal strip bridges the two line segments, wherein the metal strip is connected in parallel with the interrupted bus line.

The invention further relates to a solar cell which is produced with a screen printing form as described above.

Further advantages and features of the invention will be explained with reference to the following figures, in which:

Fig. 1 shows a first cross section of a first embodiment of the invention

Screen printing form; Fig. 2 is a second cross section of the first embodiment of the invention

Screen printing form;

Fig. 3 is a plan view of the first embodiment of the screen printing form according to the invention;

Fig. 4 is a plan view of a second embodiment of the invention

Screen printing form; 5 shows a first plan view of a substrate produced by means of the screen printing form according to the invention; 6 shows a second plan view of a substrate produced by means of the screen printing form according to the invention; Fig. 7 shows a cross section of a third embodiment of the invention

Screen printing form;

8 shows a horizontal section of the third embodiment of the screen printing form according to the invention;

Fig. 9 is a plan view of the third embodiment of the invention

Screen printing form; Fig. 10 is a plan view of a substrate made by the screen printing form of the present invention; Fig. 11 is a cross-section of a fourth embodiment of the invention

Screen printing form; and FIG. 12 is a side view of a substrate, which by means of the fourth

Embodiment of the screen form is provided with a pressure medium.

Several views of a first embodiment of the screen printing form according to the invention are shown in FIGS. Fig. 3 shows a plan view of the screen printing form 100, wherein in Fig. 1 is a cross section along the dash-dotted line designated A-B and in Fig. 2 is a cross section along the designated C-D dot-dash line. The screen printing form 100 has a first layer 1, which is referred to below as a network layer 1. Along the upper side of the net layer 1, a printing medium can be conveyed into a first recess 2 with a doctor, not shown. In the first recess 2 web elements 3 are arranged, which are distributed with a regular, net-like structure in the first recess 2, see Fig. 3. Below the network layer 1, a second layer 4, hereinafter referred to as stencil layer 4, present at This Ausführungsforrn is integrally formed with the network layer 1. The stencil sheet 4 has a second recess 5, in which support elements 6 are provided.

As can be seen from FIG. 1, the web elements 3 are connected to the support elements 6 and formed in one piece. The height of a web element 3 and an associated support element 6 is equal to the height 7 of the screen printing form 100. If a doctor along the top of the net layer 1 moves sideways and a pressure medium transported in the recesses 2 and 3, reduce the support elements 6 a deflection of the screen printing form 100 perpendicular to the doctor blade movement, since the support elements 6 are supported on the arranged under the stencil sheet 4 to be printed substrate.

FIG. 2 shows a cross section of the screen printing form 100 along the dot-dash line indicated by CD in FIG. 3. The web elements 3 in the first recess 2 can be seen, however, no support element 6 is shown in this cross section. The second recess 5 thus has no support element 6 at this location, so that a pressure medium can reach the second recess 5 through the first recess 2 and forms a pressure line on the substrate arranged below the screen printing form 100, which width corresponds to the width of the second recess 5 equivalent. The web elements 3 can thus be suppressed, the web elements 3 increase the stability of the network layer 1. However, support elements 6 are provided in the second recess 5, which are supported on the substrate, can reach no pressure medium at these support points, so that at these locations a negative pressure is prevented and the printing medium on the substrate is not present. This additionally causes a saving of pressure medium, which is usually a relatively expensive metallic and conductive material such as silver in a solar cell.

The width 8 of the first recess 2 is at least 30 micrometers, wherein the width of a web element 3 is at least 10 micrometers. In Fig. 1 and Fig. 3 are

Support elements 6 shown having a circular horizontal cross-section. As can be seen from FIG. 3, the support elements 6 can be located below a web element 3 and thus reduce the deflection of the first recess 2 or of the screen printing form 100. The support elements 6 can also be arranged at intersections of the web elements 3, see for example FIGS second embodiment of the

Screen printing form 100 in FIG. 4, which also has a support element with an elliptical cross section. In this case, a regular arrangement of the support elements 6 is advantageous in view of a low deflection of the screen printing form.

FIG. 5 shows a printed image on a substrate 9. The applied printing medium 10 has at the locations where the circular support elements 6 are arranged in the screen printing mold 100, recesses 11. There is no printing medium 10 is present, so that in a metallic and electrically conductive printing medium 10, an electric current in the area around the Recesses 11 is passed around. The recesses can also be hexagonal or rectangular, see reference numerals 12, 13 and 14 in FIG. 6. Recesses with a hexagonal cross-section are advantageous for optimum area utilization. The rectangular recess 14 causes an electric current in the printing medium 10 to be interrupted. The associated support element is then designed such that it extends from one side of the second recess 5 to the opposite side of the second recess 5 and the second recess is divided into two segments, see FIGS. 7 to 9 The pressure medium 10 forms a recess 30 to the recess In the embodiment shown in Fig. 6, this line is straight. However, it is also possible that this boundary line 30 is curved. In a honeycomb-shaped recess, the boundary line 30 is rectilinear only in sections. FIG. 9 shows a plan view of a third embodiment of the screen printing form 100, wherein FIG. 7 shows the cross section along the dot-dash line indicated by EF in FIG. A rectangular support element 6 is arranged under a first recess 2, the support element 6 extending from one side of the second recess 5 to the opposite other side of the second recess. The second recess 5 is completely traversed at this point by a support member 6, so that a pressed through the first recess 2 through the pressure medium can not reach the substrate at this point. The second recess 5 is thus divided into a first segment 15 and a second segment 16, see FIG. 8. Only in these two segments 15 and 16 can the printing medium reach the substrate.

FIG. 10 shows a plan view of a substrate produced by means of the screen printing form 100 according to the invention. The substrate, in this case a solar cell 23, is printed by means of a printing medium 10 with a printed first metallic line 17 having a width 18 and a second metallic line 19 having a width 20. The first metallic line 17 is a relatively narrow line that can act as a finger on a solar cell. The second metallic conduit 19 is a relatively wide conduit which electrically contacts the first metallic conduits 17 and acts as a manifold. In the solar cell 23 shown in FIG. 10, the second metallic line 19 has circular recesses 11 and rectangular recesses 13. Further, a recess 21 is provided, which interrupts the second metallic line 19. This is also achieved with the recesses 22. The printing medium 10 is then applied in a round, rectangular or hexagonal geometry so that the surrounding area forms the recess. The recess may then be referred to as a "negative", with the print medium 10 forming the "positive". It is possible that the recesses 21 and 22 occupy a large area, so that only smaller areas are covered with a pressure medium 10. These may be sufficient to attach a low-cost metallic strip bridging the second metallic line so that the expensive material for the second metallic line can be saved. FIG. 11 shows a cross section of a fourth embodiment of the screen printing form 100 according to the invention. The surfaces of the first recess 2 and the second recess 5 and the web elements 3 and support elements 6 are provided with a coating 24. The coating reduces the passage area for the printing medium 10, so that even narrower lines can be produced on a substrate 9. FIG. 12 shows a side view of the substrate 9, which is provided with the printing medium 10 by means of the fourth embodiment of the screen printing form. However, the metallic line 25 from the printing medium 10 is shown extending slightly in width in this illustration. The coating has a thickness that is at least 5% of the smallest cross-sectional width of the passage opening 26 of the first recess 2 or second

Recess 5 is. In the limiting case, it can also close the passage opening 26, so that no pressure medium can pass through it. By using such a coating, even smaller passage openings can be achieved than has hitherto been possible with the production technology for producing a passage opening. If the coating is a non-stick coating, can be very narrow

Passage widths of Durchtrittsöffiiung 26 the print medium well in the direction of the substrate 9 reach.

The screen printing form 100 with the first layer 1 as a mesh layer and the second layer 4 as a stencil layer may be integrally formed. The two layers 1 and 4 are then defined only by the depth of the recesses 2 and 5. However, it is also possible that the first layer 1 and second layer 4 are formed of two parts, which consist of the same or different materials. The screen printing form may consist of a stainless steel foil, from which the mesh layer 2 and stencil layer 4 are worked out by means of chemical etching. In a preferred embodiment, the mesh layer has a film which has the first recesses 2 and is combined with a stencil layer 4 and firmly joined, which has been worked out of photosensitive emulsion based on polyvinyl alcohol, a capillary film or a solid resist, or by means of structured electroplating , preferably by means of nickel.

Claims

claims

A screen-printing form, which has a first layer with first recesses and a second layer with second recesses, wherein the recesses are arranged so that a printing medium can be placed through one of the first recesses and from there through one of the second recesses to a position that can be placed under the second layer Substrate is conveyed, wherein in the first recesses web elements and in the second recesses support elements are provided, wherein the web elements are connected to the support elements, and at least one web element together with a support member has a height which is equal to the Siebdruckformenhöhe, wherein a support element at least supports a web element arranged above it, wherein a vertical cross section of one of the web elements is unequal to a vertical cross section of one of the support elements.

2. Screen printing form according to claim 1, wherein the first or second recess a

Width of at least 30 microns owns.

3. Screen printing form according to one of the preceding claims, wherein the web elements or support elements have at least a width of 10 micrometers.

4. Screen printing form according to one of the preceding claims, wherein the web elements or support elements have a maximum width of 20 microns.

5. Screen printing form according to one of the preceding claims, wherein the support elements each have a round, hexagonal or rectangular cross-section.

6. Screen printing form according to one of the preceding claims, wherein the web elements have a distance of 30 to 100 micrometers to each other.

7. Screen printing form according to one of the preceding claims, wherein the surfaces of the

Recesses and the web elements or support elements are provided with a coating.

A screen printing form according to claim 7, wherein the coating has a thickness which is at least 5% of the smallest cross-sectional width of the first or second recess.

A screen printing form according to claim 8, wherein the coating has a contact angle with water in a range of 0 ° to 90 °.

10. A screen printing form according to claim 8, wherein the coating has a contact angle with respect to water in a range of greater than 90 ° to 150 °.

11. Screen printing form according to one of the preceding claims, wherein at least one support element extends from one side of the second recess to the opposite side of the second recess and divides the second recess into at least two segments.

12. Solar cell, which is produced with a screen printing form according to one of the preceding claims.