DE202009006542U1 - Electrical contacting element for photovoltaic cells - Google Patents

Abstract

Electrical contacting element for photovoltaic cells, in particular solar cells, in which one or more electrically conductive wires, bare or with an electrically conductive coating on its outer side, on the photosensitive surface of the cell, in particular a wafer, are electrically conductive, characterized in that the cross-sectional profile of the wires (1) has a contiguous contour, one of which, over the surface of the solar cell (8) protruding part represents the cross-sectional profile of a polygon with oblique edges, in particular a triangle (2), whereas the other part (2a) arbitrarily designed is, in particular in the form of a triangle, quadrilateral, hemisphere or a hybrid form and wherein this part of the / of the wires on the cell or in particular in a corresponding groove / grooves (6) inserted in the cell and is electrically connected thereto.

Description

The The invention relates to an electrical contacting element for Photovoltaic cells, in particular solar cells, in which a or more electrically conductive wires, bare or with an electrically conductive coating on their Outside, on the photosensitive surface the cell, in particular a wafer, are conductively mounted.

solar cells have become key components of renewable energy sources established and take in their importance for energy production to. With them, light, usually sunlight, due to the photovoltaic effect converted into electrical energy. The usual Solar cells consist of semiconductor structures, so-called wafers, which are mostly built on the basis of silicon. In the preparation of become in printing technology current-conducting contact paths, so-called fingers, usually in the form of a metallic paste, applied. Metallic contact strips connect the individual fingers of a solar cell and several solar cells Solar modules with each other. This allows the current efficiency accordingly be increased.

After this the efficiency of the individual solar cell is quite low, namely about 14 to 17%, it is important to all the yield of converted To reduce energy-reducing influences. this concerns on the one hand the reduction of the electrical resistance of the wires and contacts and reducing the losses of irradiated Energy, in particular by shading.

Contacting elements of the type mentioned are already known, for example from the DE 102 39 845 C1 and from the publication of the Atomic Institute of the Vienna University of Technology "New methods for contacting solar cells", to be found on Google.

In the first mentioned document are on a semiconductor structure an electrically insulating, optically transparent film, one on top applied adhesive layer and on this several wires applied parallel to each other. These wires can have different cross-sectional contours without this however, in terms of their suitability for the given Purpose, in particular with regard to their shading of incident sunlight. These wires are parallel horizontal and crossing vertically on the semiconductor structure of Solar cell applied. Through the many wires is a clear shading of the incident sunlight on the semiconductor structure and thus a deterioration of the efficiency of the solar cell.

at the second mentioned publication is assumed by the well-known use of so-called "fingers", namely contact conductors on the semiconductor structures, the wafers. To improve the shading of sunlight on the fingers longitudinally soldered thin wires. Instead of these soldered wires is considered an alternative proposed to insert the fingers in grooves in the semiconductor structure. This also results in a reduction of shading. The scored However, improvement is relatively low in both cases.

The Invention has set itself the goal of the efficiency of a solar cell improve by reducing both the shading of the incident Sunlight as well as a reduction in electrical resistance should be achieved.

to Solution of the above object proposes the invention Therefore, before that the cross-sectional profile of the / the wires has a continuous contour, one of which, over the surface of the solar cell outstanding part, the Cross-sectional profile of a polygon with oblique edges, preferably one triangle, whereas the other part is arbitrary is designed, in particular the shape of a triangle, quadrilateral, hemisphere or a hybrid form, and wherein that part of the wire (s) on the cell or in particular in a corresponding groove / grooves used in the cell and is electrically connected thereto.

By This contour of the wire cross section is achieved by the protruding from the wafer triangular shape of the wire a direct Reflection of the incident sunlight takes place on the wafer and by the acute-angled formation of the triangle a significant proportion of incident sunlight, otherwise shaded by the wire would now be incident on the wafer and thus increases the optical efficiency. By the change of the angle of the apex of the triangle one can optimize this yield.

By the other part of the contour of the cross section of the wire (s), which is embedded in the groove / grooves of the cell (wafer), the Size of the total electrical resistance of the / Wires are set. You can see the resistance of this Partly smaller by enlargement of the cross section and can also do the triangle with the same total resistance make smaller, with the result that the shading is less is and the optical efficiency of the arrangement increases. To this Way one can by varying the cross sections of triangle and other part of the overall efficiency or else affect the efficiencies of the parts.

For the purposes of the invention, you can also there by that the / the wires protrude at least with their triangular contour from the surface of the cell, namely possibly also a little more, the irradiation reflection of the sunlight and thus affect the efficiency.

A expedient development of the invention sees suggest that the triangular contour above the cell is isosceles is.

at Direct, vertical (vertical) incidence of light would be Angle at the apex of less than 90 ° advantageous for direct reflection on the solar cell surface. However, all other angles are possible, too in the case of angles over 90 ° of lower efficiency.

In Further development of the invention may be expedient be that the cross-sectional profile of the / the wires represents a trapezium by the triangle tip through a small Surface is replaced. This may be for purposes of soliciting be favorable from crossing wires. Furthermore the groove depth can then be kept lower.

For the wires according to the invention is a good one electrical conductivity important. It is preferred Metals such as copper, silver, gold, aluminum, tin, zinc or nickel and their alloys used. Possible in the sense the invention also copper-plated steel wires and copper-clad aluminum wires.

In preferred development of the invention are the wires with an electrically conductive, metal solderable or adhesive coating provided from the metals Tin, lead, zinc silver, gold, nickel, platinum, palladium and theirs Alloys can exist. But it is also possible eutectic To use alloys of the type Sn43 / Bi57 or Sn42 / Bi58 or one Alloy based on tin / indium.

A very interesting coating is the alloy SnBiAgCu, in which the copper content of Cu is well above the amount of normalized, natural impurity limits, ie the Trace elements, d. H. about 0.5 to 1%.

Further can in the context of the invention, a multiple coating ver used become.

The Practical application of the invention provides that several Wires parallel in horizontal and vertical direction arranged on a cell and contacted at the respective crossing point and that these wires are also the connection between several cells (solar cell modules) produce. At very many wires in horizontal and vertical direction also plays a minor improvement in efficiency in a wire already a not negligible role.

in the Following is the invention with reference to the drawing in several Embodiments explained in more detail become.

It demonstrate:

1 the cross section of a wire according to the invention in the form of a standing on the top quadrangle;

2 the cross section of a wire whose upper part the contour of a triangle whose lower part has the contour of a rectangle;

3 the cross section of a wire, the lower part. has the contour of a hemisphere;

4 the cross section of a wire whose lower part has the contour of a trapezoid

5 the cross section of a currently used round wire with incident and reflected light rays;

6 the cross section of a square wire according to the invention with incident and reflected light rays;

7 a schematic representation of the top of a cell with intersecting wires.

In 1 is a wire 1 in cross section 2 shown, the contour of which has the shape of a quadrilateral, a rhombus placed on top. The connecting line AB of the outer peaks of the upper triangle simultaneously represents the surface of a cell 8th in which the wire is 1 with its lower part 2a is used. The pages 3 of the triangle are designated in detail with a, b, c and d. The pages 3 of the triangle are covered with an electrically conductive, metallic solderable or adhesive coating 4 provided, which also has a good reflection behavior. The lower part 2a of the square wire is with its side surfaces c and d in a groove 6 the cell 8th used and conductively connected by soldering or gluing or otherwise connecting to this.

In the 2 . 3 and 4 are different cross-sectional contours of the lower part 2a of the wire 1 shown. These contours are the shape of the grooves 6 matched in the cell and can be chosen according to the size of the requirements in terms of electrical resistance.

In 5 Is a round wire 5 shown in cross-section, in the vertically incident light rays and their reflection are shown. Such round wires are commonly used for solar cells and it can be seen from the drawing that the shading is great for the incident from above sunlight; the area corresponds to the diameter of the wire. Only a few rays of light, like L4, are from the surface of the wire 5 on the surface of the cell 8th reflected. A deterioration of the optical yield results from the running coating 4 when soldering the wire on the cell 8th , In addition, in round wires an increase in the diameter to reduce the electrical resistance has an immediate effect on the increasing shading and thus on the optical efficiency. These problems with round wires were occasion for the realization of the invention.

Based on 6 representing the cross-sectional contour of the 1 has, the invention will now be explained with its advantages. An acute-angled quadrangle on the tip 1 , a rhombus, is beginning with its lateral tips A and B and ending with its lower tip D, into the groove 6 in a cell 8th used. The side surfaces c and d are with their coating 4 with the groove 6 soldered or otherwise connected.

It can be seen from the figure that the sun rays L1, L2, L3 incident vertically from above impinge on the side surfaces a and b of the triangle at different locations and are reflected onto the cell. Thus, although the line AB is covered by the wire, a large part of the sun's rays incident on this route is used by pointing at the cell 8th be reflected. By changing the angle at the tip C, the amount of incident sunlight can be optimized.

In 7 a practical embodiment of a solar cell is shown schematically. It can be seen that many wires 1 in horizontal and vertical direction on a cell 8th strained and possibly in grooves 6 pressed in and soldered. At junctions 10 they are contacted with each other, preferably soldered. The projecting beyond the solar cell wire ends are connected to such a top, bottom or side, adjacent cell, so that a so-called solar module is formed. The series and parallel connection of many solar cells gives the desired total voltage and total current of the solar module.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• - DE 10239845 C1 [0004]

Claims (12)

Electrical contacting element for photovoltaic cells, in particular solar cells, in which one or more electrically conductive wires, bare or with an electrically conductive coating on its outer side, on the photosensitive surface of the cell, in particular a wafer, are electrically conductive, characterized in that the cross-sectional profile of the wires ( 1 ) has a contiguous contour, one of which, over the surface of the solar cell ( 8th ) protruding part of the cross-sectional profile of a polygon with oblique edges, in particular a triangle ( 2 ), whereas the other part ( 2a ), in particular has the shape of a triangle, quadrilateral, hemisphere or a mixed shape and wherein this part of the / the wires on the cell or in particular in a corresponding groove / grooves ( 6 ) is inserted in the cell and electrically connected thereto. Electrical contacting element according to claim 1, characterized in that the wires ( 1 ) at least with its triangular contour from the surface of the cell ( 8th protrude). Electrical contacting element according to claim 1, characterized in that the triangle isosceles is. Electrical contacting element according to claim 1, characterized in that the electrical wire (s) ( 1 ) has the cross-sectional profile of a trapezoid by the triangle tip is replaced by a small area. Electrical contacting element according to claim 1, characterized in that the electrical wires alternatively made of copper, tin, zinc, silver, gold, aluminum or Nickel and their alloys exist. Electrical contacting element according to claim 1 characterized in that the electrical wires alternatively made of copper-plated steel wires or copper clad Consist of aluminum wires. Electrical contacting element according to claim 1, characterized in that the electrical (1) Wires with an electrically conductive, metallic are provided with solderable or adhesive coating, in particular of the metals tin, zinc silver, gold, Nickel platinum palladium and their alloys. Electrical contacting element according to claim 7, characterized in that the coating on the Base of the alloy tin / bismuth, preferably from the eutectic Alloy Sn43 / Bi57 with melting point 139 ° C or nearly identical commercially available alloy Sn42 / Bi58. Electrical contacting element according to claim 7, characterized in that as an alloy coating Sn, Bi, Ag, Cu is provided, whose adjusted Cu content significantly above the normalized natural impurity limits (trace elements) lies. Electrical contacting element according to claim 7, characterized in that as an alloy coating is based on tin / indium. Electrical contacting element according to one of Claims 7, 8, 9, 10 characterized in that a plurality Coatings on top of each other on the wires are applied. Electrical contacting element according to claim 1, characterized in that a plurality of wires ( 1 ) arranged parallel in horizontal and vertical direction on a cell (wafer) and at the respective crossing point ( 10 ) are contacted and that these wires make the connection between several cells (solar cell module).