WO2009030409A2

WO2009030409A2 - Method for producing a solar cell

Info

Publication number: WO2009030409A2
Application number: PCT/EP2008/007008
Authority: WO
Inventors: Klaus Metzner
Original assignee: Manz Automation Ag
Priority date: 2007-08-29
Filing date: 2008-08-27
Publication date: 2009-03-12
Also published as: DE102007041057A1; KR20100054820A; WO2009030409A3; KR101138097B1; CN101803034A; EP2193548A2

Abstract

The invention relates to a method for producing a solar cell (10, 11) in which the solar cell (10, 11) is printed in multiple process steps using the screen printing method. In a first printing process, the solar cell (10, 11) is disposed in a first orientation relative to the printing direction (18) of a doctor and, in a second printing process, the solar cell is disposed in a different orientation relative to the printing direction. In this manner, the solar cell (10, 11) is always optimally aligned for printing oblong structures.

Description

Process for producing a solar cell

Description :

The invention relates to a method for producing a solar cell, in which the solar cell is printed by the screen printing method in a plurality of production steps.

It is known to print both the back and the front of solar cells during their production by screen printing. In the prior art, the solar cell to be printed and the printing direction have a fixed, unchangeable, relative orientation to one another.

Two types of printing units are currently used in screen printing technology: flat screen printing units and rotary screen printing units. As a printing direction is generally referred to in flat screen printing units, the direction of movement of the doctor over the print material. In rotary screen printing units, the printing direction is defined by the transport direction of the print material.

An important criterion in screen printing is the detachment of the screen from the print product after the squeegee has passed over the screen: the so-called screen bounce. The following version explains the relationships with a flat screen printing unit, which basically apply to rotary screen printing units.

Since the printing pastes are highly viscous liquids, strong adhesion forces, which initially hold the screen after the squeegee has traveled over a point to be printed, on the printed material (solar cell). The detachment is made possible by the relatively strong tension of the sieve. The sieve jump, however, requires a certain amount of time which depends on various printing parameters (paste, screen texture, printed image). The time required for the Siebabsprung is an important factor, since the printed matter must not be moved until it is done safely. This is another reason why it is customary today to move the screen upwards (away from the print material) before the further transport of the print material, which promotes the screen skip. The Siebabsprung turns out to be difficult whenever a printed image on the entire width of the object without interruption to print, such as the full-area backside printing or the busbars, or the fingers in solar cells. Individual interruptions of the printing structure, such. For example, the many individual fingers when printing the solar cell front side simplify the Siebabsprung when they are printed in Rakelbewegungsrichtung.

The printing of the busbars and the fingers for the front side contact, so the printing of the solar cell front side, technically represents the biggest challenge. The positioning of the solar cell for alignment of the printing screen and the Rakelbewegungsrichtung is therefore optimally chosen for this process step as far as possible. This means that the fingers of the solar cell front side are printed in the direction of movement of the doctor blade. However, the busbars on the back side of the solar cell are aligned transversely to the fingers of the solar cell front side. Thus, if the solar cell is aligned so that optimum printing of the Solar cell front is possible, this also means that because of the rigid arrangement of the doctor blade movement to the solar cell, the printing of the solar cell rear side takes place under poor conditions, since the full width of the solar module without interruption must be printed across the Rakelbewegungs- 5 direction. The sieve jump is the most difficult here and must be ensured by appropriate process settings.

One possible solution is to implement a wait. However, this lo extends the printing cycle. Alternatively or additionally, the screen can be moved to the end of the print. This also prolongs the printing cycle. Furthermore, it is conceivable to increase the wire tension. However, this shortens the life of the sieve.

It is therefore an object of the present invention to provide a method with which the printing cycle can be shortened and the service life of the screen can be increased.

According to the invention, this object is achieved in a particularly simple and surprising manner by a method of the type mentioned above in which the solar cell and the printing direction are aligned for at least one first printing operation in a first orientation to each other and in at least one further printing operation in another Orientation aligned with each other. The solar cell 25 is thus arranged for at least one first printing operation in a first orientation to the doctor movement direction of a doctoring or transport direction of the solar cell and in at least one further printing operation in a different orientation to the doctor movement direction of a doctor blade or the transport direction of the solar cell. This dimensional measure ensures that the solar cell is optimally aligned with the direction of doctor movement or transport direction for each printing operation, in particular is aligned to print elongated structures, so that the disadvantages described above can be largely avoided at Siebabsprung. This means that the printing screens are subjected to less stress and thus a higher service life of the printing screen is achieved. In addition, the printing cycle is shortened considerably. The productivity of the plant on which the process is carried out is increasing. In addition, the quality of the individual printing processes increases. The advantages of this new method apply to flat screen printing units in the same way as for rotary screen printing units.

In a particularly preferred variant of the method it can be provided that the solar cell to be printed is rotated by 90 ° before at least one printing operation. As a result, the solar cell is brought in a different orientation to the doctor blade movement direction or transport direction in comparison to the preceding printing operation. Thus, elongated structures arranged perpendicular to previously imprinted structures may be applied in the same blade advance direction as the elongate structures applied in the previous printing operation. In principle, it would also be conceivable, instead of rotating the solar cell by 90 °, to change the direction of movement of the doctor blade by 90 ° or to use a second doctor blade with an offset by 90 ° movement direction. In any case, the solar cell according to the invention for two different printing operations on different orientations with respect to a blade movement direction or transport direction.

A further optimization with respect to the screening jump results if at least some elongate structures in the printing direction, that is to say the direction of movement of a doctor blade or transport direction of the solar cell, are printed in each printing operation. In a variant of the method can be provided that in a first printing busbars (busbars) in particular with a printing paste, z. B. silver paste, are printed on the solar cell back, wherein the printing direction in the direction of the extension of aufzudruckenden

5 busbars runs. This variant of the method represents the exact opposite of the known prior art, where the bus bars on the solar cell rear side are aligned transversely to the blade movement direction, whereby the above-mentioned disadvantages arise in Siebabsprung. In a flat screen printing unit, this means that the squeegee is moved during printing in the direction of the extent of the busbars to be printed on.

Furthermore, it can be provided that in a second printing process, the solar cell rear side in particular with a printing paste, for. B. aluminum paste, is printed, wherein the printing direction runs in the direction of extension i5 of previously printed on busbars. For a flat screen printing unit, this means that the squeegee is moved in the direction of extension of previously printed busbars. This means that the first and second printing process, with the orientation of the solar cell remaining the same, with respect to the doctoring direction or transport direction of the cell,

20 which corresponds to the printing direction to be performed.

Advantageously, in a third printing operation, busbars and fingers are in particular provided with a printing paste, e.g. As silver paste, printed on the solar cell front side, the printing direction in the direction of Er-

25 extension of the fingers to be printed passes. In a flat screen printing unit, this means that the squeegee is moved during printing in the direction of the extension of the fingers to be printed. This ensures that the very thin fingers are imprinted with optimum accuracy and run without interruption. It is also conceivable

3o first the solar cell front side and then the solar cell back to print. In this case, the solar cells would have to after the Printing the solar cell front side are reoriented with respect to the Rakelbewegungsrichtung. The terms "first, second and third printing" can therefore refer to a chronological sequence of the printing processes, but need not.

Particular advantages arise when the solar cell is detected with a gripper before at least one printing operation and is aligned with respect to the printing direction. In this case, in particular a Bemoulli gripper can be used. Preferably, the solar cell is rotated by 90 ° by the gripper before the third printing process in which the solar cell front side is printed.

The productivity of a plant in which the process is carried out can be increased if, in at least one printing operation, several solar cells are printed simultaneously. Preferably, several solar cells are printed simultaneously in all printing processes. This means that several solar cells, in particular by a Bernoulli gripper, are reoriented before at least one printing operation.

The scope of the invention also includes a screen printing machine with a gripper, in particular a Bernoulli gripper for carrying out the method. The screen printing machine may have a flat screen printing unit in which the printing direction corresponds to the doctor blade movement direction, or a rotary screen printing unit in which the printing direction corresponds to the transport direction of the printed matter (solar cell).

Further features and advantages of the invention will become apparent from the following detailed description of embodiments of the invention with reference to the figures of the drawing, which shows details essential to the invention, and from the claims. The features shown there are not necessarily to scale and thus represented provides that the features of the invention can be made clearly visible. The various features may be implemented individually for themselves or for a plurality of combinations in variants of the invention.

In the schematic drawing embodiments of the invention are illustrated and explained in more detail in the following description.

Show it:

Figure 1 is a plan view of the back of two solar cells after a first printing operation.

FIG. 2 shows a plan view of the back side of two solar cells after a second printing process; FIG. and

Fig. 3 is a plan view of the front of the solar cells after a third printing operation.

In the figure 1, two solar cells 10, 11 are shown, with the rear side 12, 13 is visible. The solar cells 10, 11 have on their back side 12, 13 in each case by screen printing simultaneously printed in a first printing so-called busbars 14 to 17. The printing direction, ie the direction of blade movement in flat screen printing units or the transport direction in rotary screen printing units, is indicated by the arrow 18. This means that the busbars 14 to 17 were printed in the printing direction 18. This facilitates the sieve jump. Busbars 14 to 17 were created by printing a silver paste. FIG. 2 shows the solar cells 10, 11, on which in turn an aluminum paste 19, 20 was printed at the same time. The printing direction is again indicated by an arrow 21. This means that the printing direction 18, 21 and orientation of the solar cells 10, 11 were the same in both printing processes.

FIG. 3 shows a plan view of the front side 25, 26 of the solar cells 10, 11. The solar cells 10, 11 are rotated relative to the illustrations of Figures 1 and 2 by 90 °. This could fingers 27, 28 are applied in the printing direction 29 in a third printing process, wherein the printed as a silver paste fingers 27, 28 are offset from the busbars 14 to 17 of the solar cell rear side by 90 °. The busbars 30, 31 of the front sides 25, 26 were also printed transversely to the printing direction 29 in the third printing process. The printing directions 18, 21, 29 are therefore the same for all printing processes. However, the orientation of the solar cells 10, 11 with respect to the printing direction 29 has been changed for the printing of the solar cell front side 25, 26.

Claims

Patent claims

1. A method for producing a solar cell (10, 11), wherein the solar cell (10, 11) is printed in several manufacturing steps in Sieblo printing process, characterized in that the

Solar cell (10, 11) and the printing direction (18, 21, 29) are aligned for at least a first printing operation in a first orientation to each other and in at least one further printing operation in a different orientation to each other out.

2. The method according to claim 1, characterized in that the solar cell to be printed (10, 11) is rotated by at least one printing operation by 90 °.

20

3. The method according to claim 1 or 2, characterized in that in each printing at least some elongated structures in the printing direction (18, 21, 29) are printed.

25 4. The method according to any one of the preceding claims, characterized in that in a first printing busbars (busbars (14 to 17)) on the solar cell rear side (12, 13) are printed, wherein the printing direction in the direction of the extension of the busbars to be printed (14 to 17).

30

5. The method according to any one of the preceding claims, characterized in that in a second printing process, the solar cell rear side (12, 13) is printed, wherein the printing direction in the direction of extension of previously printed busbars (14

5 to 17).

6. The method according to any one of the preceding claims, characterized in that in a third printing operation busbars and fingers (27, 28) on the solar cell front side (25, 26) imprinted lo, wherein the printing direction in the direction of extension of the aufzudruckenden fingers (27, 28) runs.

7. The method according to any one of the preceding claims, characterized in that before at least one printing process, the i5 solar cell (10, 11) is detected with a gripper and with respect to the

Printing direction (18, 21, 29) is aligned.

8. The method according to any one of the preceding claims, characterized in that in at least one printing process several So-

20 larzellen (10, 11) are printed simultaneously.

9. screen printing machine with a gripper for carrying out the method according to any one of the preceding claims.

25 10. A system according to claim 9, characterized in that the printing unit is a flat screen printing unit, wherein the printing direction of the blade movement direction corresponds.

11. Plant according to claim 9, characterized in that the printing unit is a rotary screen printing unit, wherein the printing direction corresponds to the transport direction of the solar cell.