DE102010020974A1 - Method for manufacturing solar cells utilized for supplying power to e.g. stationary apparatus, involves performing splitting process on wafer by exerting pressure vertically and evenly on wafer from top to bottom of wafer by knife - Google Patents

Abstract

The method involves executing wedge-shaped cutting of a predetermined pattern parallel to easily cleavable crystal orientation surfaces of a crystalline wafer with a splitting knife at slight pressing force. A splitting process is performed on the crystalline wafer based on impressions formed on the wafer by exerting pressure vertically and evenly on the wafer from top to bottom of the wafer. A cleavage crack is produced in the crystalline wafer, where the splitting process is performed until a workpiece is broken from the wafer along a predetermined separation line. The crystalline wafer is a pseudo-quadratic solar cell wafer (100).

Description

The present invention relates to a method for producing special solar cells from a wafer according to the preamble of claim 1, as well as by means of the method produced special solar cell according to claim 8.

State of the art

Special solar cells such. B. Concentrating photovoltaic (CPV) solar cell chips typically include a high-power solar cell chip packaged on a cooling element. The solar cell chips are usually made from a wafer, which usually comprises a great many identical rectangular solar cell chips. After the completion of the wafer, the chips are separated from the wafer. The singulation of the chips takes place i. d. R. by means of a diamond saw or laser cutting. The individual chips then typically have edge lengths of 1 to 10 mm.

These Vereizelungsprozesse are relatively easy to implement, but have the major disadvantage that arise on the entire edge length crystal defects that affect the functionality of the solar cell massively. It is known that the disturbed crystal areas z. B. to remove by etching the lateral solar cell edges and thus to reduce the local short circuits at the p-n junction. However, this requires an additional complex and costly process step. Considering area losses due to saw cut and wafer edge, hardly more than 60% of the losses due to cutting losses can be used as active solar cell surface.

For cell sizes less than 2 mm, the usable area decreases even more drastically due to cut losses. Overall, the processes mentioned above are time consuming, material-consuming and expensive.

Other cost-effective solutions with high wafer utilization are not yet known.

It is also known that even small application-oriented solar cells, such as solar cells for mobile applications, are cut out of so-called solar cell fractures by means of laser cutting. However, these solar cells have, due to thermal processing, massive damage to the processing edge layers. The efficiency of such solar cells usually decreases by 30%.

task

It is therefore the object of the present invention to provide a method for separating special solar cells from a wafer, which enables material-saving and cost-effective production processes of application-oriented solar cells.

This object is achieved according to the invention by the features specified in claim 1 and in claim 2 and 8 for the production of special solar cells. Further embodiments of the invention are the subject of dependent claims.

The inventive method for separating and producing special solar cells is particularly applicable for those devices that both as Konzenrator solar cells or solar cells in energy self-sufficient products and power supply systems that provide for the direct conversion of solar energy into electrical energy, as well as for photo elements for energy supply in the Microelectronics and exposure technology. These include in particular photo-semiconductor, photoresistor, photodiode cell, phototransistor.

An essential idea of the invention is that a simple cleavage of the crystals is possible due to the fragility of the warfer. Overall, it is generally known that silicon wafers are very brittle and break easily. Since the cracks in the crystalline wafer usually occur along the crystal orientation, the present invention takes advantage of this fact.

The wafer ( 100 ) is inventively mitels a wedge-shaped blade ( 400a - 400 b ) exactly and quickly long since a desired cutting line ( 103 ) mechanically split with a slight pressing force. The splitting process takes place after pressing in, ( 2a ) ie, a splitting knife ( 400 ) exerts vertical and uniform pressure on the entire wafer from top to bottom, resulting in a continuous gap crack ( 2 B ) in the wafer. The tool does not pass through the wafer completely, but only so far until the workpiece along the intended or predetermined parting line ( 103 ) breaks.

The break points are preferably carried out automatically by a fitted with a splitting knife pneumatic or electrically driven servo presses. The pressing process is then applied uniformly according to the invention on the entire surface of the wafer until the wafer breaks straight.

Optionally, the breakages z. B. also be produced by hand press or manually.

In the splitting process, it should be ensured that the pad a plane, non-slip and easy forms flexible surface. As preferred are preferred documents made of plastic, hard rubber, cork.

The splitting knife ( 400 ) is made of metal, plastic or glass and is longer than the wafer to be split. The slit cutting tip ( 400a - 400 b ) then preferably has an angle of 30 ° to 110 °.

The separation process is preferably carried out by relative movement of wafer and blade: this may be a movement of the wafer table or the gap cutting tip with respect to the wafer.

When splitting the wafer, it is preferable to ensure that the orientation of the break points ( 103 ) with respect to the crystal structure of the workpiece is preferably chosen so that they are parallel to crystal surfaces ( 300 ), which are usually easily split. Another crystal orientation can also be chosen, but is not so cheap.

The fractures can be generated either on the front or back of the wafer. However, the rear side is particularly preferred.

In the case of ( 100 ) -oriented silicon wafer, the break points are preferably parallel or perpendicular to a ( 100) Orientation flat, wherein rectangular solar cell chips are generated. When using a ( 111 Hexagonal semiconductor wafers can also be made hexagonal semiconductor chips. The break points in this case run at an angle of 30 ° and 90 ° with respect to one ( 110 ) -Kennzeichnungsflat. The breaking edges of the individual chips run in this case in the direction of slightly refractive ( 111 ) Crystal faces.

In principle, it is not urgently required that the break points always run parallel to the easily fissile crystal surfaces. For example, the ( 111 ) -oriented wafers in squares ( 151 ) or rectangles ( 153 ). On this occasion, it is preferable to first select the ones that are harder to split ( 110 ) Edges parallel to the orientation flat and then to the perpendicular ( 111 ) Edges split.

The breakage of the wafer has the significant advantage that less crystal defects occur on the side surfaces of the solar cells compared to costly diamond sawing or laser cutting. In addition, it is not absolutely necessary to post-process the side surfaces of the solar cell chips after the separation to eliminate the local short circuits. Since the individual layers are separated relatively cleanly, an additional process step is saved.

A further preferred embodiment of the invention provides that during the usual coating process of the solar cell wafer with metal-containing contact paste, in addition a plurality of conductor tracks ( 101 - 101b ) are applied. A continuous pathway passing through the wafer is then split among several isolated solar cells. ( 2 B - 3a )

The additional printed conductors are printed vertically / horizontally or diagonally as a silver grid and printed conductors on the front and back, preferably parallel to the direction of the respective crystal orientation of a wafer and then baked.

In a preferred variant of the invention, the image of the contacts on the back side of the wafer is offset by half the width to the front contacts ( 5 . 6 ). In this way, the electrical interconnection of the smallest solar cells is facilitated.

This manufacturing process is achieved by a simple change in the printed image of the screen. As a result of this conversion, completely new and application-oriented concepts of special solar cells (in ordinary wafer production lines) can be 3a ) getting produced.

According to a preferred embodiment of the invention, a film, preferably an adhesive film, is applied to the wafer before the singulation of the solar cells, and in this state the wafer is broken. For manual splitting, an adherent film with an orientation grid ( 102 ) intended. After breaking, the individual solar cells directly from the film for further processing, such. B. for soldering or packaging, be picked.

A further advantageous embodiment of the present invention is that in this case also locally or mechanically damaged wafers can be used. These break cells are usually fully intact but useless solar cells, which are treated as a waste product due to local damage. Thanks to this process, there will be less production waste and more reusability of wafers.

The invention likewise provides a special solar cell with an active surface area suitable for the direct conversion of solar energy into electrical energy, which can be produced by the method described above.

embodiment

Preferred embodiments of the invention are explained below with reference to the accompanying figures.

It shows:

1 a representation of a 156 × 156 mm pseudo-square solar cell wafer ( 100 ) with metallic contacts ( 101 ) (an image of the electrically conductive grid has been rejected) and with the displayed ( 111 Level) of the crystal orientation. ( 300 )

2 a wafer ( 100 ) with several printed electrical contacts ( 101 ) and orientation grid film according to the invention ( 102 ) for manual processing, with predetermined breaking points ( 103 )

2a a wafer ( 100 ) with applied grid foil ( 102 ) and exemplary distribution of 20 mm × 20 mm special solar cells on the wafer. Furthermore, an embodiment of the splitting process by a splitting blade ( 400 ) parallel to the crystal orientation ( 300 ).

2 B split wafer ( 100 ) after the splitting process, with newly generated strips ( 150 ) including 9 special solar cells with an edge length of 20 mm ( 150a ). According to this illustration, it can be clearly seen how the contacts according to the invention uniformly distribute themselves to the newly produced special solar cells. The total number of 20 × 20 mm solar cells is in this case 50 Piece. Such solar cell sizes are particularly suitable for the power supply of stationary or mobile devices.

3 a wafer ( 100 ) with several diagonally printed electrical contacts ( 100b ), and a grid foil ( 102 ) for manual processing, with predetermined breaking points. Diagonal contacts according to the invention, which are applied parallel to the crystal orientation lines, have the decisive advantage that this can be divided into two adjacent solar cells. ( 3b )

3a Wafer ( 100 ) with applied raster foil ( 102 ) with predetermined breaking points ( 103 ) with possible number of 220 pieces of 10 × 10 mm of spinal solar cells. In this example, it becomes clear that with such an arrangement and low waste, as many new concepts of special solar cells can arise, which are then particularly suitable for the production of concentrator modules (CPV). Such cost-effective special solar cells with an edge length of for example 1 mm to 5 mm, can then be used for power supply in microelectronics.

3b a representation of a predetermined breaking point ( 103 ), which runs through the middle of the longitudinal axis of an electrical contact.

4 Embodiment of the splitting tool (for manual processing) made of trasparent acrylic glass with two different wedge-shaped gap cutting, which have a preferred angle. ( 400a - 90 °) and ( 400 b - 60 °)

5 Front and back of the wafer with with according to the invention offset metallic contacts. This ensures that at the opposite breaking edge of the special solar cell, an electrical contact ( 200 ), which will facilitate a later Verschaltug the smallest cells.

6 an enlargement of the previous illustration ( 200 ).

LIST OF REFERENCE NUMBERS

100

Wafer 156 mm × 156 mm

100a

Wafer 156 mm × 156 mm (back)

101

Metallic contacts

101

Variety of electrical contacts (vertical)

101b

Variety of electrical contacts (diagonal)

101c

Variety of electrical contacts from the back (diagonal)

102

Adhesive grid foil with predetermined breaking points

103

Predetermined breaking points

150

Strip with 9 pieces of special solar cells

151a

Rough-shaped (square) 20 mm × 20 mm special solar cell

152

Special solar cell in the form of a triangle (no waste)

153

Various embodiments of the spinal cell solar cells (marked in red)

154

Special solar cell in the form of a triangle (no waste)

200

Offset of the contact on the back

300

Crystal orientation ( 111 Level)

400

splitting knife

400a

Wedge-shaped cutting tip at an angle of 90 °

400b

Wedge-shaped cutting tip at an angle of 60 °

500

pressing force

Claims (10)

Process for the production of special solar cells from a crystalline wafer by means of a mechanical splitting process, which is carried out by a splitting knife ( 400 ) with a wedge-shaped cutting edge ( 400a - 400 b ) is carried out in a predetermined pattern parallel to the easily cleavable crystal orientation surfaces of the respective wafer with a slight pressing force. The splitting process takes place after pressing in, ( 2a ) ie, a splitting knife ( 400 ) exerts vertical and uniform pressure on the entire wafer from top to bottom, resulting in a continuous gap crack ( 2 B ) in the wafer. The tool does not pass through the wafer completely, but only so far until the workpiece along the intended or predetermined parting line ( 103 ) breaks. A method according to claim 1, characterized in that during the normal production process of crystalline solar cells, the printed image is changed in the screen such that at the front and back of the wafer a plurality of parallel to the line of the crystal orientation of the wafer extending electrical contacts ( 101 - 101b ), the number of which is parallel to each other at the front and back, wherein the number of electrical traces is on each side between 4 and 80 pieces. Depending on the application, the width of the metallic interconnects ranges from 0.6 mm to 2.2 mm, and the number of grid lines (grid) is accordingly between 67 and 91, depending on the cell size. A method according to claim 2, characterized in that at the back of the wafer a plurality of electrical conductor tracks is applied, which are offset in such a way that the break points arise exactly in the middle of the longitudinal axis of an electrical conductor track ( 200 ), so that at least two special solar cells produced in this way share this trace. ( 3b . 5 . 6 ) A method according to claim 1, characterized in that in the case of different directions of crystal orientation and the metallic contact on the wafer, rugeartige, rectangular and / or square solar cells ( 151 ), wherein the conductor tracks run in the middle, through the longitudinal axis of the solar cell. Method according to claim 1, characterized in that the splitting knife ( 400 ) made of metal, plastic or glass, and has a cutting tip at an angle between 30-110. A method according to claim 1, characterized in that the fractures preferably automatically by a with a splitting blade ( 400 ) equipped pneumatic or electrically driven servo presses in relative motion of the wafer and the cutting edge, are produced on the front or back of the wafer. Optionally, the break points are also produced by means of a hand press and movable clamping device with prefabricated guideways for the splitting knife, or manually using a grid foil. A method according to claim 1, characterized in that prior to the separation of the solar cells, a film, preferably an adhesive film is applied to the wafer and in this state, the wafer is broken. For manual splitting, an adherent foil with a given grid ( 102 ) glued. Method according to the preceding claims, characterized in that the method according to the invention solar cells with an edge length between 1 mm and 50 mm, and a total area of 1 mm × to 2500 mm ² are produced. A method according to claim 1, characterized in that the mentioned in claim 1, the mechanical gap method for singulating integrated circuits (chips) is applied from a wafer.

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