WO2016180446A1

WO2016180446A1 - Method for screen printing on a substrate for the production of a solar cell, screen used in screen printing on a substrate for the production of a solar cell, and apparatus for screen printing on a substrate for the production of a solar cell

Info

Publication number: WO2016180446A1
Application number: PCT/EP2015/060231
Authority: WO
Inventors: Andrea Baccini; Tommaso Vercesi; Marco Galiazzo; Luigi De Santi
Original assignee: Applied Materials Italia S.R.L.
Priority date: 2015-05-08
Filing date: 2015-05-08
Publication date: 2016-11-17
Also published as: TW201701497A; EP3295488A1; TWI643356B; CN107534065A

Abstract

The present disclosure provides a method (100) for screen printing on a substrate (10) for the production of a solar cell. The method (100) includes printing of a first line pattern (210) on the substrate (10) in a first printing process using a screen (410), moving the substrate (10) away from the screen (410) and moving the substrate (10) back towards the screen (410), and printing of a second line pattern (220) over the first line pattern (210) in a second printing process using the screen (410).

Description

METHOD FOR SCREEN PRINTING ON A SUBSTRATE FOR THE PRODUCTION OF A SOLAR CELL, SCREEN USED IN SCREEN PRINTING ON A SUBSTRATE FOR THE PRODUCTION OF A SOLAR CELL, AND APPARATUS FOR SCREEN PRINTING ON A SUBSTRATE FOR THE

PRODUCTION OF A SOLAR CELL

FIELD

[0001] Embodiments of the present disclosure relate to a method for screen printing on a substrate for the production of a solar cell, a screen used in screen printing on a substrate for the production of a solar cell, and an apparatus for screen printing on a substrate for the production of a solar cell. Embodiments of the present disclosure particularly relate to methods and apparatuses for double printing of printing tracks, such as fingers, of a solar cell.

BACKGROUND [0002] Solar cells are photovoltaic (PV) devices that convert sunlight directly into electrical power. Within this field, it is known to produce solar cells on a substrate such as a crystalline silicon base by means of printing techniques, such as screen printing, achieving a structure of electrically conductive printing tracks on one or more surfaces of the solar cells. The printing tracks can subsequently be printed in a plurality of printing processes, for example, using a plurality of printing stations and screens. The printing tracks printed during the printing processes should be aligned with respect to each other in view of a quality of the manufactured solar cell. As an example, the alignment of the printing tracks with respect to each other can affect electrical characteristics, such as an output power, of the manufactured solar cell. [0003] Further, an apparatus for the manufacture of solar cells may have a plurality of process stations, such as the plurality of printing stations which are arranged along a transportation path along which the substrate is transported during the manufacturing process. Such an apparatus having a plurality of process stations consumes considerable space for installation. Further, the apparatuses generate costs, e.g., in regard to operation and maintenance.

[0004] In view of the above, new methods for screen printing on a substrate for the production of a solar cell, screens used in screen printing on a substrate for the production of a solar cell, and apparatuses for screen printing on a substrate for the production of a solar cell, that overcome at least some of the problems in the art are beneficial. In particular, the present disclosure aims at providing a method for screen printing on a substrate for the production of a solar cell that allows for an improved alignment of the printing tracks with respect to each other. Further, the present disclosure aims at providing an apparatus for screen printing on a substrate that has a reduced number of process stations.

SUMMARY [0005] In light of the above, a method for screen printing on a substrate for the production of a solar cell, a screen used in screen printing on a substrate for the production of a solar cell, and an apparatus for screen printing on a substrate for the production of a solar cell are provided. Further aspects, benefits, and features of the present disclosure are apparent from the claims, the description, and the accompanying drawings.

[0006] According to an aspect of the present disclosure, a method for screen printing on a substrate for the production of a solar cell is provided. The method includes printing of a first line pattern on the substrate in a first printing process using a screen, moving the substrate and the screen away from each other, moving the substrate and the screen back towards each other, and printing of a second line pattern over the first line pattern in a second printing process using the screen.

[0007] According to another aspect of the present disclosure, a method for screen printing on a substrate for the production of a solar cell is provided. The method includes printing of a first line pattern on the substrate in a first printing process using a screen, offsetting the substrate and the screen with respect to each other, and printing of a second line pattern over the first line pattern in a second printing process using the screen.

[0008] According to yet another aspect of the present disclosure, a screen used in screen printing on a substrate for the production of a solar cell is provided. The screen has at least one of a first screen pattern configured for the printing of fingers of the solar cell and a second screen pattern configured for the printing of busbars and/or one or more redundancy lines of the solar cell. The screen can be employed in the methods and apparatuses of the present disclosure. [0009] According to still another aspect of the present disclosure, an apparatus for screen printing on a substrate for the production of a solar cell is provided. The apparatus includes a screen configured for printing of a first line pattern and a second line pattern over the substrate, and a transport device configured for moving the substrate having the first line pattern printed thereon and the screen away from each other, and for moving the substrate and the screen back towards each other for printing of the second line pattern over the first line pattern.

[0010] According to an aspect of the present disclosure, an apparatus for screen printing on a substrate for the production of a solar cell is provided. The apparatus includes a screen configured for printing of a first line pattern and a second line pattern over the substrate, and a transport device configured for offsetting the substrate having the first line pattern printed thereon and the screen with respect to each other for printing of the second line pattern over the first line pattern.

[0011] Embodiments are also directed at apparatuses for carrying out the disclosed methods and include apparatus parts for performing each described method aspect. These method aspects may be performed by way of hardware components, a computer programmed by appropriate software, by any combination of the two or in any other manner. Furthermore, embodiments according to the disclosure are also directed at methods for operating the described apparatus. It includes method aspects for carrying out every function of the apparatus. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments. The accompanying drawings relate to embodiments of the disclosure and are described in the following:

FIG. 1 shows a flowchart of a method for screen printing on a substrate for the production of a solar cell according to embodiments described herein;

FIG. 2 shows a schematic view of a first line pattern and a second line pattern printed on a substrate according to embodiments described herein;

FIG. 3 shows a plan view of a solar cell manufactured using the method according to embodiments described herein;

FIG. 4 shows a schematic view of a screen used in a screen printing process for the manufacturing of solar cells according to embodiments described herein;

FIGs. 5(a) and (b) show schematic views of a positioning of a screen and a substrate in a first printing process and a second printing process according to embodiments described herein;

FIG. 6 shows a cross-sectional side-view of a finger on a substrate;

FIG. 7 shows a plan view of fingers and busbars of a solar cell according to embodiments described herein; FIG. 8 shows a graph illustrating an adjustment of printing parameters in a first printing process and a second printing process for the manufacture of solar cells according to embodiments described herein; FIG. 9 shows a schematic view of an apparatus for printing on a substrate for the production of a solar cell according to embodiments described herein; and

FIG. 10 shows a schematic view of an apparatus for printing on a substrate for the production of a solar cell according to further embodiments described herein.

DETAILED DESCRIPTION OF EMBODIMENTS

[0013] Reference will now be made in detail to the various embodiments of the disclosure, one or more examples of which are illustrated in the figures. Within the following description of the drawings, the same reference numbers refer to same components. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation of the disclosure and is not meant as a limitation of the disclosure. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the description includes such modifications and variations.

[0014] In the manufacture of solar cells, double printing can be used to print line patterns on top of each other. As an example, a second line pattern is superimposed on top of a first line pattern to form fingers of the solar cell. Double printing may allow for a reduced finger width and an increased finger thickness. The printing of the first line pattern and the printing of the second line pattern can be performed in two different printing stations using two different screens. As an example, a first printing station is used to print the first line pattern for forming a first layer of the fingers. A second printing station is used to print the second line pattern for forming a second layer of the fingers on top of the first layer.

[0015] The double printing processes may use a plurality of screens, such as a first screen used in the printing of the first line pattern and a second screen used in the printing of the second line pattern. The first screen and the second screen can mismatch, for example, due to deformations of the screens and/or manufacturing tolerances of the screens. The positioning of the second line pattern with respect to the first line pattern may be inaccurate, and a quality of the manufactured solar cell can be reduced. Further, a first alignment process of the substrate and the screen with respect to each other can be performed prior to the printing of the first line pattern. Additionally, a second alignment process can be performed prior to the printing of the second line pattern. The alignment processes can be conducted using, for example, a double vision system, one for the printing of the first line pattern and another one for the printing of the second line pattern. Providing the double vision system complicates system architecture of the apparatus for manufacturing of the solar cells. Further, costs, such as manufacturing costs and maintenance costs are increased.

[0016] The present disclosure provides a method for screen printing on a substrate for the production of a solar cell that uses only one single screen for the double printing process. In particular, after the printing of the first line pattern, the substrate and the screen are moved with respect to each other, e.g., for drying of the first line pattern. The substrate and the screen are positioned with respect to each other and the second line pattern is superimposed on the first line pattern using the same screen as in the printing of the first line pattern.

[0017] As an example, after the printing of the first line pattern, the substrate and the screen are moved away from each other, e.g., for drying of the first line pattern. The substrate and the screen are then moved back towards each other and the second line pattern is superimposed on the first line pattern using the same screen as in the printing of the first line pattern. In a further example, after the printing of the first line pattern, the substrate and the screen can be offset with respect to each other and the second line pattern is superimposed on the first line pattern using the same screen as in the printing of the first line pattern. [0018] Using the same screen avoids the above-explained drawbacks with respect to the mismatch of and the deformation of the screen and/or manufacturing tolerances of the screen. The positioning of the second line pattern with respect to the first line pattern can be accurate, which is particularly beneficial for thin fingers. A quality of the manufactured solar cell can be improved. Further, in some embodiments, an alignment of the substrate and the screen with respect to each other prior to the printing of the second line pattern may be omitted. No double vision system for the second printing has to be provided and the system architecture of the apparatus for the manufacture of the solar cells can be simplified. Moreover, an amount of printing paste can be reduced using the methods and apparatuses according to the embodiments described herein.

[0019] FIG. 1 shows a flowchart of a method 100 for screen printing on a substrate for the production of a solar cell according to embodiments described herein. FIG. 2 shows a schematic view of a first line pattern 210 and a second line pattern 220 printed on the substrate 10 according to embodiments described herein. [0020] The method includes in block 110 a printing of the first line pattern 210 on the substrate 10 in a first printing process using a screen. In block 120, the substrate 10 and the screen are moved away from each other, and, afterwards, the substrate 10 and the screen are moved back towards each other. The second line pattern 220 is printed over the first line pattern 210 in a second printing process in block 130 using the screen. As an example, the first line pattern 210 can be a first layer of fingers and/or busbars of the solar cell. The second line pattern 220 can be a second layer of the fingers and/or busbars. The first line pattern 210 can be printed directly on the substrate 10. A printing material used in the printing of the first line pattern 210 and the second line pattern 220 may include, or be, silver. According to some embodiments, which can be combined with other embodiments described herein, the printing material can be selected from the group consisting of silver, aluminum, copper, tin, nickel, silicon based pastes, and any combination thereof.

[0021] Using the same screen for the double printing is particularly beneficial for printing of thin fingers of a solar cell. As an example, a width 230 of the fingers formed by the first line pattern 210 and the second line pattern 220 superimposed on the first line pattern 210 can be less than 100 micrometers, specifically less than 80 micrometers, and more specifically less than 60 micrometers. A thickness 240 of the fingers formed by the first line pattern 210 and the second line pattern 220 superimposed on the first line pattern 210 can be more than 15 micrometers, specifically more than 20 micrometers, and more specifically more than 30 micrometers. [0022] When reference is made to the term "over", e.g., the second line pattern 220 being over the first line pattern 210, it is understood that, starting from the substrate 10, the first line pattern 210 is printed over the substrate 10, and the second line pattern 220, printed after the first line pattern 210, is thus over the first line pattern 210 and over the substrate 10. In other words, the term "over" is used to define an order of printed patterns or layers, wherein the starting point is the substrate 10. This is irrespective of whether the solar cell is depicted upside down or not.

[0023] According to some implementations, the second line pattern 220 is superimposed on (or congruent with) the first line pattern 210. As an example, the second line pattern 220 is not printed on the substrate 10 but is completely printed on top of the first line pattern 210. In other implementations, the second line pattern 220 is partially superimposed on the first line pattern 210. Examples for the partially superimposed line patterns are explained with reference to FIG. 7.

[0024] According to some embodiments, which can be combined with other embodiments described herein, the screen may include at least one of a net, a printing mask, a sheet, a metal sheet, a plastic sheet, a plate, a metal plate, and a plastic plate. In some implementations, the screen defines a screen pattern or features corresponding to a structure to be printed on the substrate 10, wherein the screen pattern or features may include at least one of holes, slots, incisions or other apertures. In some embodiments, a printing device such as a squeegee contacts the screen, wherein the printing device urges material to be printed onto the substrate 10 through the screen, and particularly through the apertures defining, for example, the first line pattern 210 and the second line pattern 220.

[0025] In some implementations, the screen has a first screen pattern configured for the printing of fingers of the solar cell and a second screen pattern configured for the printing of busbars of the solar cell. The first screen pattern and the second screen pattern can be used to subsequently print the first line pattern and the second line pattern. According to some embodiments, the screen has a third screen pattern configured for printing of one or more redundancy lines of the solar cell.

[0026] The substrate 10 according to the embodiments described herein may include at least one of a conductive material, particularly with silicon or aluminum, a plate, a wafer, a foil, a semiconductor wafer, a solar cell wafer, a silicon solar cell waver, or a green-tape circuit board, which can particularly be used to form solar cells.

[0027] Moving the substrate 10 and the screen away from each other can be understood as a spatial and/or physical separation of the substrate 10 and the screen after the first printing process. As an example, the substrate 10 and the screen can be spatially separated to have a distance therebetween of, for example, one or more millimeters or one or more centimeters. Separating the substrate 10 and the screen after the first printing process can prevent that the substrate 10 and the screen adhere to each other after the first printing process, e.g., due to a drying of the first line pattern 210 printed on the substrate 10.

[0028] Moving the substrate 10 and the screen back towards each other can be understood as a positioning of the substrate 10 with respect to the screen so that the second printing process for forming of the second line pattern 220 can be performed. As an example, the substrate 10 can be positioned below the screen so that the second printing process can be performed. In some implementations, a relative position of the substrate 10 and the screen with respect to each other is substantially the same or identical during the first printing process and the second printing process. Using substantially the same or identical relative position for the first printing process and the second printing process allows for an alignment of the first line pattern 210 and the second line pattern 220 with respect to each other. As an example, no additional alignment process is performed prior to printing of the second line pattern 220 using, e.g., a vision system. However, the present disclosure is not limited thereto and, according to some embodiments, an alignment process can be performed prior to the printing of the second line pattern 220. [0029] The term "substantially the same or identical" relates to a substantially the same or identical relative orientation of the substrate 10 and the screen in the first printing process and the second printing process, wherein a deviation within a tolerance range from an exact same or identical orientation is still considered as "substantially the same or identical". The tolerance range can be, for example, plus/minus 50 micrometers in any direction (e.g., the direction parallel to a lengthwise extension of lines of the first line pattern 210), and specifically plus/minus 1 micrometer in any direction.

[0030] According to some embodiments, which can be combined with other embodiments described herein, one or more further processes of the solar cell manufacturing process can be performed between the first printing process and the second printing process. As an example, the one or more further processes of the solar cell manufacturing process can be performed during and/or between the moving of the substrate 10 and the screen away from each other and the moving of the substrate 10 and the screen back towards each other. In some implementations, the first line pattern 210 can be dried between the first printing process and the second printing process. During the drying process, for example a solvent can be removed from the first line pattern 210.

[0031] According to some embodiments, which can be combined with other embodiments described herein, the method 100 includes at least one of a drying of the first line pattern 210 after the printing of the first line pattern 210 and a drying of the second line pattern 220 after the printing of the second line pattern 220. As an example, the drying of the first line pattern 210 can be performed during and/or between the moving of the substrate 10 and the screen away from each other and the moving of the substrate 10 and the screen back towards each other. The drying of the second line pattern 220 after the printing of the second line pattern 220 can be performed after the second printing process. For the drying of the second line pattern 220, the substrate 10 and the screen can be moved away from each other again. In some implementations, the substrate 10 can be moved to a drying station including, for example, an oven to dry the first line pattern 210 and/or the second line pattern 220. [0032] In some implementations, the drying of at least one of the first line pattern 210 and the second line pattern 220 includes at least one of conductive heating, convective heating, irradiation heating, and any combination thereof. As an example, the drying of at least one of the first line pattern 210 and the second line pattern 220 includes at least one of laser heating and heating using a heater included in a substrate support. This will be explained in more detail with reference to FIGs. 9 and 10. According to some embodiments, a drying time of the first line pattern 210 and/or the second line pattern 220 is at least 1 s. As an example, a drying time of the first line pattern 210 and/or the second line pattern 220 is in a range of 1 to 20 s, specifically in a range of 1 to 10 s, and more specifically in a range of 5 to 10 s. In some implementations, the drying of the second line pattern 220 can be omitted. [0033] Moving the substrate 10 and the screen with respect to each other, such as moving the substrate 10 and the screen away from each other and moving the substrate 10 and the screen back towards each other may involve a relative movement of the substrate 10 and the screen. As an example, the substrate 10 could be moved while the screen is kept stationary, or the screen could be moved while the substrate 10 is kept stationary. In other examples, both the substrate 10 and the screen are moved, for example, simultaneously or sequentially.

[0034] In some implementations, moving the substrate 10 and the screen away from each other and moving the substrate 10 and the screen back towards each other includes a moving of the substrate 10 away from the screen and moving the substrate 10 back towards the screen using, for example, transport device. The screen can be stationary while the substrate 10 is moved. As an example, the first printing process and the second printing process can be performed in the same printing station. The printing station can have the screen that is in a stationary position. The substrate 10 can be moved to, and from, the printing station using, for example, the transport device. [0035] According to some embodiments, which can be combined with other embodiments described herein, the transport device can include at least one of a rotary table and a moveable substrate support. In some implementations, moving the substrate 10 away from the screen and moving the substrate 10 back to the screen includes at least one of a rotating of the rotary table and a moving of the moveable substrate support. Examples for the transport device and the moving of the substrate 10 are given with reference to FIGs. 9 and 10. [0036] According to further implementations, moving the substrate 10 and the screen away from each other and moving the substrate 10 and the screen back towards each other includes moving the screen away from the substrate 10 and moving the screen back towards the substrate 10. As an example, the first printing process and the second printing process are performed in different printing stations such as a first printing station for the first printing process and a second printing station for a second printing process. The screen and the substrate 10 can be moved from the first printing station to the second printing station. One or more further processes of the solar cell manufacturing process can be performed during and/or between the moving of the substrate 10 from the first printing station to the second printing station. As an example, a drying process can be performed to remove solvent from the first line pattern 210.

[0037] According to some embodiments, which can be combined with other embodiments described herein, the method 100 further includes an alignment of the substrate 10 with respect to the screen prior to the printing of the first line pattern 210. In some implementations, the aligning of the substrate 10 with respect to the screen can be performed only prior to the first printing process, and can be omitted prior to the second printing process. As an example, the relative position of the substrate 10 and the screen with respect to each other can be substantially the same or identical during the first printing process and the second printing process. Using the same relative positions for the first printing process and the second printing process allows for an alignment of the first line pattern and the second line pattern with respect to each other. No additional alignment process has to be performed prior to second printing process.

[0038] In some embodiments, the alignment of the substrate 10 with respect to the screen prior to the printing of the first line pattern 210 can use, for example, a vision system including one or more cameras. According to some embodiments, the method further includes an alignment of the substrate 10 with respect to the screen prior to the printing of the second line pattern 220. In other embodiments, no alignment of the substrate 10 with respect to the screen prior to the printing of the second line pattern 220 is performed. At least one of the alignment processes prior to the printing of the first line pattern 210 and the second line pattern 220 can use a camera that is configured to take a picture of the substrate 10. A processing device can evaluate a position of the substrate 10 with respect to, for example, at least one of the substrate support, a printing device and the screen. The processing device can adjust a positon of at least one of the substrate 10, the substrate support, and the screen so as to adjust the relative positon of the substrate 10 and the screen. [0039] According to embodiments described herein, the method for screen printing on a substrate for the production of a solar cell can be conducted by means of computer programs, software, computer software products and the interrelated controllers, which can have a CPU, a memory, a user interface, and input and output means being in communication with the corresponding components of the apparatus for processing a large area substrate.

[0040] The embodiments of the present disclosure can be used for printing of line patterns on a front surface of the solar cell. However, the present disclosure is not limited thereto, and the embodiments of the present disclosure can be used for printing line patterns on at least one of a front surface and a back surface of the solar cell using the same screen. As an example, the methods and apparatuses can be employed in a manufacturing process of bifacial solar cells.

[0041] FIG. 3 shows a plan view of a solar cell 300 manufactured using the method according to embodiments described herein.

[0042] The solar cell 300 includes a plurality of fingers 310 and two or more busbars 320. In the solar cell 300, light is absorbed and causes charge carriers to flow along the fingers 310 to the busbars 320, which may serve as endpoints for connections between individual solar cells 300 in a solar cell module. According to some implementations, the solar cell 300 can include one or more redundancy lines 330. The one or more redundancy lines 330 can be provided at edge portions of the substrate 10 connecting end portions of the fingers 310. The redundancy lines 330 can provide a bypass for the charge carriers flowing along the fingers 310, e.g., when there is an (electrical) interruption or breakage in a finger 310.

[0043] In some implementations, the first line pattern and the second line pattern provide at least one of the fingers 310, the busbars 320, and the one or more redundancy lines 330. As an example, at least one of the first line pattern and the second line pattern includes two or more line sub-patterns, wherein the two or more line sub-patterns are selected from the group consisting of: fingers of the solar cell, busbars of the solar cell, finger redundancy lines of the solar cell, and any combination thereof. [0044] According to some embodiments, the fingers 310, the busbars 320, and the one or more redundancy lines 330 can be printed using only one screen. The fingers 310, the busbars 320, and the one or more redundancy lines 330 can be printed in the first printing process and the second printing process in, for example, the same printing station. According to some embodiments, which can be combined with other embodiments described herein, the first line pattern can form a first layer of the fingers 310, and optionally a first layer of the busbars 320 and/or the one or more redundancy lines 330. The second line pattern can form a second layer of the fingers 310, and optionally a second layer of the busbars 320 and/or the one or more redundancy lines 330. As an example, a first layer of the fingers 310, the busbars 320, and the one or more redundancy lines 330 is printed on the substrate 10 in the first printing process. A second layer of the fingers 310, the busbars 320, and the one or more redundancy lines 330 is printed on the first layer in the second printing process.

[0045] In some implementations, the fingers 310 are formed by the first line pattern and the second line pattern printed over the first line pattern. The busbars 320 can be formed by the first line pattern and/or the second line pattern. In other words, the busbars 320 can be printed in the first printing process, the second printing process, or in both printing processes. The one or more redundancy lines 330 can be formed by the first line pattern and/or the second line pattern. In other words, the one or more redundancy lines 330 can be printed in the first printing process, the second printing process, or in both printing processes.

[0046] As an example, in some implementations, the first printing process includes the printing of the first line pattern having fingers 310, busbars 320, and one or more redundancy lines 330 of the solar cell, wherein at least the one or more redundancy lines 330 are not printed in the second printing process. Such a selective printing process can be provided using, for example, an adjustment of one or more print parameters as explained with reference to FIG. 8. [0047] Using the same screen and optionally only one printing station for printing of the fingers 310, the busbars 320, and the one or more redundancy lines 330 allows for reducing the number of printing stations. A throughput of the system can be increased, in particular since only two printing processes are used for printing of the fingers 310, the busbars 320, and the one or more redundancy lines 330.

[0048] FIG. 4 shows a schematic view of a screen 410 configured for a screen printing process for the manufacture of solar cells according to embodiments described herein. The screen can be configured for printing of the fingers, the busbars, and the one or more redundancy lines shown in the example of FIG. 3. [0049] According to some embodiments, which could be combined with other embodiments described herein, the screen 410 defines a screen pattern 420 or features corresponding to a structure (e.g., the first line pattern and the second line pattern) to be printed on the substrate. The screen pattern 420 or features may include at least one of holes, slots, incisions or other apertures. The screen pattern 420 defines the first line pattern and the second line pattern that are to be printed on the substrate in the first printing process and the second printing process, respectively. The example of FIG. 4 shows a plurality of parallel apertures 430 that provide the first line pattern and the second line pattern. A printing device such as a squeegee contacts the screen and moves along a printing direction 425. The printing device urges material to be printed onto the substrate 10 through the screen 410, and particularly through the screen pattern 420. The material may include silver.

[0050] In some implementations, the screen 410 has a first screen pattern configured for printing of fingers of the solar cell and a second screen pattern configured for printing of busbars of the solar cell. In some embodiments, the screen 410 has a third screen pattern configured for printing of one or more redundancy lines of the solar cell. The first screen pattern, the second screen pattern and optionally the third screen pattern can be used to subsequently print the first line pattern and the second line pattern.

[0051] In some implementations, a net or mesh can be provided in at least some of the apertures 430 of the pattern screen 420, e.g., in the plurality of parallel apertures 430 that provide the first line pattern and the second line pattern. The net or mesh can be provided by a plurality of first wires 442 extending in a first direction and a plurality of second wires 444 extending in a second direction. The net or mesh can be a woven net or mesh of wires. The plurality of first wires 442 and the plurality of second wires 444 can have a diameter in a range of 10 to 30 micrometers, and specifically in a range of 15 to 20 micrometers. The plurality of first wires 442 and the plurality of second wires 444 define a plurality of openings 446 therebetween. The openings can have a size (e.g., an average diameter) in a range of 1 to 500 micrometers, specifically in a range of 10 to 150 micrometers, and more specifically in a range of 15 to 100 micrometers. As an example, the size can be about 60 micrometers. [0052] In some implementations, the first direction of the first wires 442 and the second direction of the second wires 444 can be different. As an example, the first direction and the second direction can be substantially perpendicular to each other. The term "substantially perpendicular" relates to a substantially perpendicular orientation e.g. of the first direction and the second direction, wherein a deviation of a few degrees, e.g. up to 10° or even up to 15°, from an exact perpendicular orientation is still considered as "substantially perpendicular".

[0053] In some implementations, the first direction and the second direction can be inclined with respect to a lengthwise extension of the apertures 430 of the screen pattern 420, e.g., with respect to a lengthwise extension of first lines of the first line pattern and/or second lines of the second line pattern. As an example, the first direction and the second direction can be inclined with respect to a lengthwise extension of the apertures 430 of the pattern 420 by an angle in a range of about 20 degrees to about 60 degrees. As an example, the first direction and the second direction can be inclined by about 22.5 degrees, about 30 degrees, or about 45 degrees, as shown in the example of FIG. 4. [0054] FIGs. 5(a) and (b) show schematic views of a positioning of a screen 410 and a substrate 10 in a first printing process and a second printing process according to embodiments described herein.

[0055] During use of the screen 410 in a screen printing process, the screen may be locally clogged by printing material. As an example, referring to FIG. 4, one or more of the openings 446 in the net or mesh provided in the apertures 430 of the screen pattern 420 can be clogged by dried printing material. Clogged screen portions can result in an interruption of the pattern printed on the substrate 10, such as the first line pattern and the second line pattern. As an example, the clogged screen portions can result in interruptions in the line patterns that prevent a current from flowing through the interrupted lines.

[0056] According to some embodiments, which can be combined with other embodiments described herein, a first relative orientation of the substrate 10 with respect to the screen in the first printing process (FIG. 5(a)) and a second relative orientation of the substrate 10 with respect to the screen in the second printing process (FIG. 5(b)) can be different. As an example, the first relative orientation and the second relative orientation can be offset (indicated with reference numeral 530) from each other.

[0057] As an example, according to a further aspect of the present disclosure, a method for screen printing on a substrate for the production of a solar cell is provided. The method includes printing of a first line pattern on the substrate 10 in a first printing process using a screen 410, offsetting the substrate 10 and the screen 410 with respect to each other, and printing of a second line pattern over the first line pattern in a second printing process using the (same) screen 410. As used throughout the present disclosure, the terms "offsetting" and "offset" can also be understood in the sense of "shifted" or "displaced".

[0058] Interruptions in the printed line pattern can be reduced or even avoided by offsetting (shifting, displacing) the substrate 10 and the screen 410 with respect to each other after the first printing process and before the second printing process. As an example, when a screen portion is clogged by (dried) printing material, an interruption can be present in the first line pattern printed in the first printing process. When the same screen portion is still clogged during the second printing process, the second line pattern may also have an interruption. However, this interruption in the second line pattern will be offset with respect to the interruption in the first line pattern. In other words, the second line pattern provides a bridge over the interruption in the first line pattern, and no interruption is present in the printed line pattern, e.g., in a finger of the solar cell. This can increase an efficiency of the manufactured solar cell. [0059] Further, offsetting the substrate 10 and the screen 410 with respect to each other between the printing processes can provide for a reduction of a number of cleaning processes for the screen 410, since possible interruptions in the first line pattern can be cured (bridged) by the second line pattern, and vice versa. A downtime for, e.g., maintenance of the apparatus for manufacture of the solar cells can be reduced and production yield can be increased.

[0060] In some implementations, the offset (indicated with reference numeral "520" in FIG. 5) is in a direction substantially parallel to a first lengthwise extension of one or more first lines of the first line pattern. The one or more first lines can be fingers of the solar cell. As an example, the offset is substantially parallel to a lengthwise extension of the fingers of the solar cell. The term "substantially parallel" relates to a substantially parallel orientation e.g. of the offset direction and the lengthwise extension of the fingers, wherein a deviation of a few degrees, e.g. up to 10° or even up to 15°, from an exact parallel orientation is still considered as "substantially parallel". The term "lengthwise extension" is to be understood as an extension of the lines of the first line pattern (and the second line pattern) in a direction of the length of the lines. The length of the lines refers to the longer dimension of the lines, wherein the width of the lines refers to the shorter dimension of the lines.

[0061] According to some embodiments, which can be combined with other embodiments described herein, the offset can be provided by a movement of the substrate 10 and the screen 410 with respect to each other in a plane substantially parallel to a surface of the substrate 10 on which the first line pattern and the second line pattern are to be printed. In some implementations, the offset is provided by a linear movement of the substrate 10 and the screen 410 with respect to each other. The linear movement can be substantially parallel or substantially perpendicular to the first lengthwise extension of the one or more first lines of the first line pattern. As an example, the offset is provided by a linear movement of the substrate 10 and/or the screen 410 substantially parallel to the lengthwise extension of the fingers of the solar cell. [0062] According to further embodiments, the offset is provided by a two-dimensional movement of the substrate 10 and the screen 410 with respect to each other. The two- dimensional movement can be a movement in a plane substantially parallel to a surface of the substrate 10 on which the first line pattern and the second line pattern are to be printed. As an example, the offset is provided by a two-dimensional movement of the substrate 10 and/or the screen 410 with movement components substantially parallel and perpendicular to the first lengthwise extension of the one or more first lines of the first line pattern.

[0063] In some implementations, the offset (e.g., an amount of displacement as indicated with reference numeral "530") is in a range of 10 to 1000 micrometers, specifically in the range of 10 to 500 micrometers, and more specifically in the range of 100 to 200 micrometers. As an example, the offset 430 can be at least 10 micrometers, and specifically at least 50 micrometers.

[0064] In some implementations, offsetting the substrate 10 and the screen 410 with respect to each other includes a moving of the substrate 10 using, for example, a transport device. Examples for the transport device and the moving of the substrate 10 are given with reference to FIGs. 9 and 10. The screen 410 can be stationary while the substrate 10 is moved. As an example, the first printing process and the second printing process can be performed in the same printing station. The printing station can have the screen 410 that is in a stationary position. The substrate 10 can be moved to provide the offset using, for example, a moveable substrate support on which the substrate 10 is positioned.

[0065] In other implementations, offsetting the substrate 10 and the screen 410 with respect to each other includes a moving of the screen 410. The substrate 10 can be stationary while the screen 410 is moved using, for example, an actuator such as a linear motor. As an example, the first printing process and the second printing process can be performed in the same printing station. The printing station can have the screen 410 that is moveably provided therein.

[0066] According to some embodiments, which can be combined with other embodiments described herein, one or more further processes of the solar cell manufacturing process can be performed between the first printing process and the second printing process, as it is described with reference to FIG. 1. As an example, the one or more further processes of the solar cell manufacturing process can be performed before or after the offsetting of the substrate 10 and the screen 410 with respect to each other. In some implementations, the first line pattern can be dried between the first printing process and the second printing process. The second line pattern can optionally be dried after the second printing process. During the drying process, for example a solvent can be removed from the first line pattern 210. In some implementations, the drying of at least one of the first line pattern and the second line pattern includes at least one of laser heating and heating using a heater included in a substrate support. According to some embodiments, a drying time of the first line pattern and/or the second line pattern is at least 1 s. As an example, a drying time of the first line pattern and/or the second line pattern is in a range of 1 to 20 s, specifically in a range of 1 to 10 s, and more specifically in a range of 5 to 10 s.

[0067] FIG. 6 shows a cross-sectional side-view of a line of the first line pattern printed on the substrate 10. The line can be a finger 310 of a solar cell. [0068] The lines of the first line pattern printed in the first printing process can have a varying thickness. As an example, the thickness of the lines of the first line pattern can vary approximately sinusoidal. The varying thickness can result from the structure of the screen, and particularly from the mesh or net provided in the apertures as illustrated in FIG. 4. As an example, the line of the first line pattern can have maxima 610 and minima 620. The maxima 610 and minima 620 can have a periodicity 630.

[0069] The present disclosure can provide for a smoothening of the thickness of the lines of the first line pattern by applying the offset as described with reference to FIGs. 5(a) and (b). The second line pattern printed on the first line pattern can have a similar thickness variation. According to some embodiments, which can be combined with other embodiments described herein, the offset can be selected such that the thickness variation in the second line pattern at least partially compensates the thickness variation in the first line pattern. As an example, a minimum of the second line pattern is positioned on top of a maximum of the first line pattern, and a maximum of the second line pattern is positioned on top of a minimum of the first line pattern. [0070] In some implementations, the offset can be selected based on the periodicity 630 of the thickness variation. As an example, the offset can correspond to the periodicity 630 of the thickness variation of the first line pattern. According to some embodiments, the periodicity 630 of the first line pattern can be measured, for example, in-situ between the first printing process and the second printing process. The offset can then be determined based on the measurement result. In other embodiments, the periodicity 630 of the first line pattern can be previously measured in a calibration measurement or can be estimated. The so determined periodicity can then be used to apply a predetermined offset for the second printing process. [0071] FIG. 7 shows a plan view of a first line pattern and a second line pattern printed on a substrate 10 according to embodiments described herein. The first line pattern and the second line pattern can form fingers 310 and busbars 320 of the solar cell. A printing device such as a squeegee can contact the screen and move along a printing direction 340 for printing of the first line pattern and the second line pattern. [0072] The busbar 320 of the solar cell includes a first portion 322 printed in the first printing process and a second portion 324 printed in the second printing process. In other words, the busbars can be printed in a two-step process, wherein the first portion 322, which may be a first half of the busbar, is printed in the first printing process, and the second portion 324, which may be a second half of the busbar, is printed in the second printing process. The first portion 322 and the second portion 324 can be printed on a surface of the substrate 10 adjacent to each other. In other words, the first portion 322 and the second portion 324 are not printed on top of each other. The first portion 322 and the second portion 324 can contact each other. As an example, the second portion 324 can partially overlap the first portion 322. [0073] According to some embodiments, which can be combined with other embodiments described herein, the first printing process includes the printing of the first line pattern having fingers 310 and the first portion 322 of the busbars 320, and the second printing process includes the printing of the second line pattern having the fingers 310 and the second portion 324 of the busbars. The first portion 322 of the busbars 320 and the second portions 324 of the busbars 324 can be adjacent to each other on the substrate. The first portion 322 and the second portion 324 can contact each other to provide an electrical contact between the first portion 322 and the second portion 324. Optionally, the first portion 322 and the second portion 324 can partially overlap each other to further improve the electrical contact between the first portion 322 and the second portion 324. [0074] The first portion 322 and the second portion 324 can have a lengthwise extension in a direction substantially perpendicular to printing direction 340. As an example, the first portion 322 and the second portion 324 can have a lengthwise extension in a direction substantially perpendicular to the lengthwise extension of the fingers 310. Likewise, the first portion 322 and the second portion 324 can have a widthwise extension in a direction substantially parallel to the printing direction 340. A first width of the first portion 322 and a second width of the second portion 324 can be substantially the same. The term "substantially the same" relates to a substantially the same width of the first portion 322 and the second portion 324, wherein a deviation within a tolerance range from an exact same width is still considered as "substantially the same". The tolerance range can be, for example, plus/minus 50 micrometers in the widthwise direction of the busbar, and specifically plus/minus 10 micrometers in the widthwise direction of the busbar. In other examples, the width of the first portion 322 and the width of the second portion 324 can be different.

[0075] In some implementations, the offset between the first relative orientation and the second relative orientation can correspond to the width of the first portion 322. As an example, the offset between the first relative orientation and the second relative orientation can correspond to a half of a width of the busbar 320. According to some embodiments, the offset is in a range of 250 to 1500 micrometers, specifically in the range of 500 to 1000 micrometer, and more specifically about 750 micrometers. As an example, an offset of about 750 micrometers may result in busbars 320 having a width of about 1500 micrometers.

[0076] Printing the busbars 320 widthwise in a two-step process allows to use the offset for a reduction of, for example, interruptions in the lines of the line patterns and/or a thickness variation of the line patterns without printing of redundant busbars or "blind" busbars or lines on the substrate. Further, an aspect ratio of the busbars 320 can be improved. A separate printing station for printing of the busbars 320 can be omitted, and a number of printing stations can be reduced.

[0077] FIG. 8 shows a graph illustrating an adjustment of printing parameters in a first printing process and a second printing process for the manufacture of solar cells according to embodiments described herein. The x-axis denotes a positon of a printing device with respect to the screen and/or the substrate. The x-direction can also be referred to as "printing direction". The y-axis denotes a printing parameter applied during the first printing process (upper graph in FIG. 8) and in the second printing process (lower graph in FIG. 8). The printing parameter can be a pressure P that the printing device, such as a squeegee, applies to the screen and/or the substrate.

[0078] According to some embodiments, which could be combined with other embodiments described herein, variations (e.g., real-time variations during printing) of one or more print parameters are provided. In some implementations, the one or more print parameters include at least one of an angle of the squeegee with respect to the screen, a moving speed of the squeegee with respect to the screen, and a pressure or force of the squeegee acting on the screen, the substrate and/or the substrate support. By controlling or adjusting at least one of said print parameters before or during the printing, different printing conditions for instance in different screen regions can be provided. As an example, at least one print parameter of the one or more print parameters can be controlled such that printing material is printed on (or transferred to) the substrate or no printing material is printed on (or transferred to) the substrate.

[0079] According to some embodiments, which could be combined with other embodiments described herein, the pressure of the squeegee acting on the screen can be adjusted by controlling a distance (snap off) of the squeegee with respect to the screen. As an example, the squeegee may be moveable in a direction perpendicular to the screen. According to some embodiments, which can be combined with other embodiments described herein, the distance of the squeegee with respect to the screen can be changed from about +20 mm to about -50 mm, and particularly from about +5 mm to about -35 mm, wherein a surface of the screen is positioned at 0 mm when it is not deformed, e.g., due to a contact of the squeegee with said screen. As an example, when the squeegee is positioned at +5 mm, the screen is pushed down towards the substrate (or deformed) 5 mm, wherein, when the squeegee is positioned at - 35 mm, it is positioned at a distance of 35 mm from the screen.

[0080] In some implementations, the one or more print parameters in the first printing process are selected such that that printing material is printed on (or transferred to) the substrate in substantially the complete region of the screen where the screen patterns for the printing of the first line pattern are provided. In other words, substantially the complete first line pattern as defined by the screen pattern(s) is printed on the substrate. As an example, a pressure P of the squeegee acting on the screen is kept above a printing level so that printing material is transferred to the substrate through the screen. The pressure can be substantially constant, as exemplarily illustrated in the upper graph of FIG. 8 (indicated with "P0"). Reference numeral 810 denotes positions of the redundancy lines shown, for example, in FIG. 3.

[0081] The one or more print parameters in the second printing process are selected such that the printing material is printed on (or transferred to) the substrate in a selected region of the screen. In other words, only a portion of the second line pattern as defined by the screen pattern(s) is printed on the substrate. As an example, a pressure P of the squeegee acting on the screen is kept above a printing level in a region of the fingers and the busbars of the solar cell, and is kept below the printing level in a region of the one or more redundancy lines. The fingers and the busbars have a double-layer structure. The redundancy lines can only have one single layer printed in the first printing process.

[0082] Printing the line patterns using an adjustment of at least one print parameter of the one or more print parameters allows for use of the offset to reduce, for example, interruptions in the lines of the line patterns and/or a thickness variation of the line patterns without printing double redundancy lines.

[0083] FIG. 9 shows a schematic view of an apparatus 900 for screen printing on a substrate for the production of a solar cell according to embodiments described herein.

[0084] The apparatus 900 includes a screen configured for printing of a first line pattern and a second line pattern on the substrate, and a transport device configured for moving the substrate having the first line pattern printed thereon and the first screen with respect to each other. As an example, the transport device is configured for moving the substrate having the first line pattern printed thereon and the first screen away from each other, and for moving the substrate and the first screen back towards each other for printing of the second line pattern over the first line pattern. In a further example, the transport device is configured for offsetting the substrate having the first line pattern printed thereon and the screen with respect to each other for printing of the second line pattern over the first line pattern.

[0085] In some implementations, the apparatus 900 includes a plurality of process stations, such as a printing station 910, a drying station 920, and one or more further process stations 930 such as at least one of another printing station, an inspection station and another drying station. The screen is provided in the printing station 910. The drying station 920 can be configured for drying the first line pattern and/or the second line pattern printed on the substrate in the printing station 910. The drying station 920 can, for example, include an oven. The one or more further process stations can include another printing station configured for, e.g., printing of the busbars on the substrate having the fingers printed thereon. The inspection station can be configured for a quality control of the line patterns printed on the substrate. As an example, the inspection system can include a vision system including one or more cameras. As an example, a camera can take a picture of the substrate or portions of the substrate having the line patterns printed thereon. A processing device can determine a position of the line patterns or portions of the line patterns with respect to, for example, features (e.g., an edge) of the substrate and/or each other. The processing device can determine a quality of the printed line pattern and optionally determine whether the substrate is to be dumped or not.

[0086] The transport device is configured for moving the substrate between at least some of the process stations. As an example, the transport device is configured for moving the substrate from the printing station 910 to the drying station 920 (indicated with arrow 940) for a drying of the first line pattern. The transport device is configured for moving the substrate from the drying station 920 back towards the printing station 910 (indicated with arrow 950) for printing of the second line pattern. The transport device can further be configured for moving the substrate from the printing station 910 to the one or more further process stations 930 (indicated with arrow 960) for, e.g., at least one of a quality control, a further printing and/or a further drying process.

[0087] According to some embodiments, which can be combined with other embodiments described herein, the printing station 910 can be a first printing station configured for printing the first line pattern and the one or more further process stations 930 can include a second printing station configured for printing the second line pattern. The transport device can be configured for movement of the screen between the first printing station and the second printing station. As an example, the first line pattern can be printed on the substrate in the first printing station and the screen can be moved to the second printing station. Optionally, the transport device can be further configured for moving the substrate to the drying station 920 for a drying of the first line pattern and for moving the substrate to the second printing station for printing of the second line pattern on top of the first line pattern. [0088] According to some embodiments, which could be combined with other embodiments described herein, the substrate is positioned on a substrate support, such as a moveable substrate support ("shuttle"). In some embodiments, the substrate support may include a nest or other support, on which the substrate can be placed for screen printing. For printing of the line patterns, the printing device such as the squeegee may move along the printing direction with respect to the substrate support.

[0089] FIG. 10 shows a schematic view of an apparatus for screen printing on a substrate for the production of a solar cell according to further embodiments described herein.

[0090] According to some embodiments, which could be combined with other embodiments described herein, the transport device includes at least one of a rotary table and a moveable substrate support. The apparatus shown in the example of FIG. 10 has a rotary table 1000. In some implementations, the substrate is positioned on a substrate support, such as a moveable substrate support ("shuttle"), which can be attached to the rotary table 1000. In other implementations, the rotary table 1000 has the substrate support. As an example, the rotary table 1000 can provide a support surface on which the substrate can be positioned.

[0091] The apparatus having the transport device, such as the rotary table 1000, according to the present disclosure can be part of a serial production line and can be configured to manufacture solar cells. In some implementations, the apparatus can at least have a printing station, a solar cell flipper, a centering device and a testing station where solar light is simulated by a light source or lamp to determine electrical characteristics of the manufactured solar cell. In some implementations, a vision system for alignment of the substrate 10 prior to the second printing process can be omitted since the substrate 10 remains in the substantially same position during the rotation of the rotary table 1000 and can be kept in position by, for example, a vacuum or other holding techniques.

[0092] FIG. 10 shows an exemplary apparatus for screen printing on a substrate for the production of a solar cell having the rotary table 1000 and a printing station 910 according to embodiments described herein. According to some embodiments, the apparatus includes an input device 3100 configured for transferring the substrate 10 to the rotary table 1000, an alignment device 3300 configured for aligning the substrate 10 before transferring of the substrate 10 to the rotary table 1000, and an output device 3200 configured for receiving the substrate 10 having the first line pattern and the second line pattern printed thereon from the rotary table 1000.

[0093] As illustrated, the input device 3100 can have an incoming conveyor. The incoming conveyor can have one or more first conveyor belts. For example the incoming conveyor may include two first conveyor belts 3150 arranged in parallel, for example, at a distance of between 5 cm and 15 cm from each other. The output device 3200 can be configured to receive the substrate 10 having the first line pattern and the second line pattern printed thereon from the rotary table 1000. The output device 3200 can have an outgoing conveyor. The outgoing conveyor can have one or more second conveyor belts. For example the outgoing conveyor may include two second conveyor belts 3250 arranged in parallel, for example, at a distance to each other of between 5 cm and 15 cm. The input device 3100 and the output device 3200 may be automated substrate handling devices that are part of a larger production line. [0094] According to some embodiments, the apparatus includes the alignment device 3300 configured for aligning the substrate 10 before the transfer of the substrate 10 to the rotary table 1000. As an example, an inspection system (not shown) can be provided at the input device 3100 or the alignment device 3300. The inspection system can be configured for determining a position of the substrate 10, e.g., on the conveyor belts 3150. The alignment device 3300 can be configured to align a position of the substrate 10 based on data received from the inspection system.

[0095] The apparatus includes the printing station 910 having the screen positioned therein. The printing station 910 can extend over the rotary table 1000. Printing of the first line pattern and/or the second line pattern can be done while the substrate 10 is provided at a printing position 2.

[0096] The rotary table 1000 can be rotatable around a rotation axis 1050. As an example, the rotary table 1000 can be configured to be rotatable around the rotation axis 1050 at least between a substrate receiving position 1 and the printing position 2. According to embodiments, the rotary table 1000 is configured to be rotatable between the substrate receiving position 1, the printing position 2, and at least one of a substrate discharge position 3 and a substrate dump position 4.

[0097] The rotary table 1000 is configured to rotate and transport substrates 10 along an orbit as defined by the rotary table's rotational movement, e.g., around the rotation axis 1050. The rotary table 1000 may be rotated in order to move the substrates 10 positioned on the rotary table 1000 or a substrate support (e.g., moveable substrate support or shuttle) attached to the rotary table 1000 according to a clockwise or anticlockwise rotation. The rotary table 1000 can be configured to accelerate to a maximum rotational speed and then to decelerate the movement again to halt the rotary table 1000 again.

[0098] In some implementations, a rotation angle between adjacent positions, such as the substrate receiving position 1 and the printing position 2, can be about 90°. As an example, the rotary table 1000 can be rotated by 90° for moving the substrate 10 from the substrate receiving position 1 to the printing position 2. Likewise, the rotary table 1000 can be rotated by 90° for moving the substrate 10 from the printing position 2 to the substrate discharge position 3.

[0099] According to some embodiments, a rotation time of the rotary table 1000 between adjacent positions can be in the range of 400 to 500 ms, and can specifically be about 450 ms. As an example, a rotation time of the rotary table 1000 between the substrate receiving position 1 and the printing position 2 can be in the range of 400 to 500 ms, and can specifically be about 450 ms. The term "rotation time" can refer to a time that it takes for the rotary table 1000 to move the substrate 10 from a positon, e.g., the substrate receiving position 1, to an adjacent position, e.g., the printing positon 2. [00100] According to some embodiments, which can be combined with other embodiments described herein, the rotary table 1000 includes a drive or a motor configured for rotating the rotary table 1000 around the rotation axis 1050. As an example, the drive or motor can be a direct drive configured to directly drive the rotation axis 1050. In other examples, the drive or motor can include a transmission device, such as a belt, for transmitting the rotation provided by the drive or motor to the rotation axis 1050.

[00101] According to some embodiments, which can be combined with other embodiments described herein, one or more further processes of the solar cell manufacturing process can be performed during and/or between the rotating of the rotary table 1000. In some implementations, the substrate 10 having the first line pattern printed thereon can be rotated by about 360 degrees starting from the printing station 910. In other words, the substrate 10 is moved away from the printing station 910 and is then moved back to the printing station 910 by the rotation of the rotary table 1000 around the rotation axis 1050. During the rotation of the rotary table 100 the first line pattern and/or the second line pattern can be dried.

[00102] In some implementations, the apparatus includes at least one heater selected from the group consisting of a laser heater and an electrical heater. The heater can be included in the substrate support such as the moveable substrate support ("shuttle") that can be attached to the rotary table 1000. In other implementations, the heater can be included in the rotary table 1000, e.g., when the substrate is positioned on a support surface provided by the rotary table 1000.

[00103] According to some embodiments, which can be combined with other embodiments described herein, in a single process station, the following aspects can be performed. Loading the substrate (cell). Performing the first printing process (e.g., only finger). During rotation of the rotary table 1000, drying the first line pattern can employ at least one of conductive heating, convective heating, irradiation heating, and any combination thereof. As an example, drying the first line pattern can include at least one of laser heating and a heater integrated in the substrate support (nest). After the drying process, the substrate comes back on the printing station for the second printing process. Performing the second printing process (e.g., only finger). The substrate is heated a second time and unloaded. The substrate moves to a second printing station for (only) busbar deposition.

[00104] The present disclosure provides methods and apparatuses for screen printing on a substrate for the production of a solar cell that only use one single screen for the double printing process. In particular, after the printing of the first line pattern, the substrate and the screen are moved with respect to each other, e.g., for drying of the first line pattern. The substrate and the screen are positioned with respect to each other and the second line pattern is superimposed on the first line pattern using the same screen as in the printing of the first line pattern.

[00105] Using the same screen avoids drawbacks with respect to the mismatch of and the deformation of the screen and/or manufacturing tolerances of the screen. The positioning of the second line pattern with respect to the first line pattern can be accurate, what is particularly beneficial for thin fingers. The quality of the manufactured solar cell can be improved. Further, an alignment of the substrate and the screen with respect to each other prior to printing of the second line pattern may be omitted. No double vision system for the second printing has to be provided and the system architecture of the apparatus for the manufacture of the solar cells can be simplified. Moreover, an amount of printing paste can be reduced using the methods and apparatuses according to the embodiments described herein. [00106] While the foregoing is directed to embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. Method for screen printing on a substrate for the production of a solar cell, comprising: printing a first line pattern on the substrate in a first printing process using a screen; moving the substrate and the screen away from each other, and moving the substrate and the screen back towards each other; and printing a second line pattern over the first line pattern in a second printing process using the screen.

2. The method of claim 1, further including at least one of: drying of the first line pattern after the printing of the first line pattern; and drying of the second line pattern after the printing of the second line pattern, wherein the drying of the first line pattern is performed during and/or between the moving of the substrate and the screen away from each other and the moving of the substrate and the screen back towards each other.

3. The method of claim 1 or 2, wherein moving the substrate and the screen away from each other and moving the substrate and the screen back towards each other includes: moving the substrate away from the screen and moving the substrate back towards the screen.

4. The method of claim 3, wherein moving the substrate away from the screen and moving the substrate back towards the screen includes at least one of a rotating of a rotary table and a moving of a moveable substrate support.

5. The method of one of claims 1 to 4, wherein moving the substrate and the screen away from each other and moving the substrate and the screen back towards each other includes a moving of the screen.

6. The method of any one of claims 1 to 5, wherein the first printing process and the second printing process are performed in the same printing station.

7. The method of any one of claims 1 to 6, wherein at least one of the first line pattern and the second line pattern includes two or more line sub-patterns, wherein the two or more line sub-patterns are selected from the group consisting of: fingers of the solar cell, busbars of the solar cell, finger redundancy lines of the solar cell, and any combination thereof.

8. The method of claim 7, wherein the first printing process includes the printing of the first line pattern having fingers, busbars, and one or more redundancy lines of the solar cell, and wherein at least the one or more redundancy lines are not printed in the second printing process.

9. The method of claim 7 or 8, wherein the first printing process includes the printing of the first line pattern having fingers and a first portion of the busbars, wherein the second printing process includes the printing of the second line pattern having the fingers and a second portion of the busbars, and wherein the first portion of the busbars and the second portions of the busbars are adjacent to each other on the substrate.

10. The method of any one of claims 1 to 9, wherein a first relative orientation of the substrate with respect to the screen in the first printing process and a second relative orientation of the substrate with respect to the screen in the second printing process are different.

11. The method of claim 10, wherein the first relative orientation and the second relative orientation are offset from each other.

12. The method of claim 11, wherein the offset is in a direction parallel to a first lengthwise extension of one or more first lines of the first line pattern.

13. Screen for use in the method of any one of claims 1 to 12, wherein the screen has at least one of a first screen pattern configured for the printing of fingers of the solar cell and a second screen pattern configured for the printing of busbars and/or one or more redundancy lines of the solar cell.

14. Apparatus for screen printing on a substrate for the production of a solar cell, comprising: a screen configured for printing of a first line pattern and a second line pattern over the substrate; and a transport device configured for moving the substrate, having the first line pattern printed thereon, and the screen away from each other, and for moving the substrate and the screen back towards each other for the printing of the second line pattern over the first line pattern.

15. The apparatus of claim 14, wherein the transport device includes at least one of a rotary table and a moveable substrate support.