WO2018142261A1

WO2018142261A1 - Solar cell with improved electrodes and solar module composed of such cells

Info

Publication number: WO2018142261A1
Application number: PCT/IB2018/050520
Authority: WO
Inventors: Zoltán ÁDÁM; Zsolt VADADI
Original assignee: Ecosolifer Invest Ag
Priority date: 2017-01-31
Filing date: 2018-01-29
Publication date: 2018-08-09
Also published as: HUP1700044A2

Abstract

A solar cell for photovoltaic modules having a front and a rear side, that comprises a plurality of parallel spaced first electrodes (2, 2a, 2b, 2c) and second electrodes (3, 3a, 3b) extending substantially normal to the first electrodes (2, 2a, 2b, 2c), and the first and second electrodes (2, 3) are electrically interconnected at mutually formed junctions, wherein the second electrodes (3, 3a, 3b) are formed as spaced electrode pairs being aligned along the whole cell (1) and at least of a group of the first electrodes (2, 2a, 2b) terminates at their junctions with the second electrodes (3, 3a, 3b), wherein the first and second electrodes (2,3) cover substantially the whole front side, and in the aligned spaces formed between the pairs of said second electrodes (3, 3a, 3b) respective connection wires (4) are placed and connected both mechanically and electrically to the two adjacent second electrodes (3a, 3b), and the connection wires (4) extend at least along substantially across the whole cell.

Description

Solar cell with improved electrodes and solar module composed of such cells

The invention relates to a solar cell for photovoltaic modules having a front and a rear side that comprises a plurality of parallel spaced first electrodes and second electrodes extending substantially normal to the first electrodes and the first and second electrodes are electrically interconnected at mutually formed junctions.

The invention also relates to a solar module built of such solar cells.

Generating electrical energy by direct converting the sunlight to electricity using photovoltaic devices has been invented and well industrialized in the recent decades. Moreover, several types and structures of photovoltaic cells have been developed as well as photovoltaic module structures and designs. The combination of different photovoltaic cell types and photovoltaic module designs are possible that provide a wide range of direct applications.

In most of the applied solutions the photovoltaic cell comprises a semiconductor single (or multi-) junction based on mono- or multi-crystalline silicon, in some cases using amorphous silicon or other thin-film semiconducting material as embedded in the p-n junction. Most commonly one of the surfaces of such structures is covered by a light transparent conductive oxide such as indium-tin-oxide or zinc-oxide or a similar material. The other side is either plated by metal layer such as aluminum or it is covered in similar way as the other side. Finally, both surfaces are prepared with a mesh of electrically conductive electrodes, which have the role of collecting the electric energy generated by the photovoltaic cell.

In practical applications a plurality of photovoltaic cells are assembled to form a photovoltaic module by embedding the serially connected photovoltaic cells between polymeric encapsulating materials (such as polyethylene-acetate or polyolefin or silicone or similar) and covered either or from both sides by a glass plate or from one side a glass plate and at the other side by a polymeric sheet (usually non-transparent).

In the assembly process of photovoltaic modules one of the most sensitive and costly process is the connection of the constituting photovoltaic cells in series to form a module. In a widely used method for assuring a series connection between photovoltaic cells as described in US 8,975, 506 B2 relatively wide parallel conductive stripes (usually 3 stripes per side) with a width of 0,5-2 mm are provided on the surface of the photovoltaic cell which are also called as bus bar electrodes and they received current from a plurality of transversely directed much thinner spaced finger electrodes having a width between 0,05 and 0,1 mm which collect charges from the adjacent surface areas. Respective wiring members are separately connected to each of the bus bars and they extend over the edges of their associated cell and where they are slightly bent in their plane (height) to extend along the lower side (which is opposite of the side of the incident light) of the adjacent cell which side has a similar structure. The wiring members of the last cell in a column are coupled to separate connecting members which interconnect all wiring members of the last cells in a row and they are connected to the respective terminals of the module.

US 5,084,107 describes a different method in which a plurality of thin (with a diameter of around 50 micron) wires are coated by a conductive adhesive material and placed across a surface of the solar cell and they are pressed against the surface under elevated temperature that bonds the wires to the surface and provides electrical connection therewith. The ends of the high number of coated thin wires are then cut. The patent is silent on the way how these coated wires are assembled into a solar module. In US 5,759,291 the coated metallic wires are attached to the surface of the solar cell by the adhesive coating as in the previous document or the connection is made in spaced discrete spots and the ends of the wires are interconnected by one or more bus bars extending normal to the wires. The bus bars were formed either on the light incident side of the cell surface in central regions or in the edges of the rear surfaces.

In the last few years a new way of connection method has been introduced wherein the series connection of photovoltaic cells is done by plated copper wires, however the coupling of these wires to the surface of the photovoltaic cell is made without the use of the previously applied wide conductive stripes but this task has been made by using a transparent polymeric foil provided with an adhesive material on one side and secondly by soldering the copper wires to narrow electrically conductive electrodes provided on the surface of the photovoltaic cells (so called fingers) as described in US 7,432,438. The adhesion assures electrical connection between the photovoltaic cell and the plated copper wires. The increased number and the associated reduced overall cross-section of the plated copper have eliminated the use of wide conductive stripes on the surface of the photovoltaic cell, whereby the loss caused by the shading effect has got decreased.

This recent connection technology has several advantages compared to those using wide conductive stripes including the elimination of the costs and manufacturing expenses connected with using wide conductive stripes and the reduction of electrical losses arising from the longer paths that the generated charges had to make along the surface of the photovoltaic cell to reach the nearest conductive electrode, since the increased number and density of the plated copper wires has reduced this path length and furthermore the electrical losses coming from the potential adhesion failures have also been reduced because the number of connection points has been substantially increased by the higher number of the thin plated copper wires.

Nevertheless, the presence of the transparent polymeric foil as the primary adhering element has resulted in negative effects of this technology. Firstly, the transparency loss (shadowing effect) of the presence of a polymeric foil that necessarily covers the whole surface of the photovoltaic cell has decreased the final electrical output of such photovoltaic modules. Secondly, the polymeric foil's light-induced degradation has an adverse effect on the long-term performance of the photovoltaic module. In third, the electrical connection of the cells takes place in a later step of the manufacturing process of the photovoltaic module and during the lamination process the plated copper wire must fulfill requirement of low temperature soldering. This feature narrows the range of usable plating materials, naturally having higher material cost. As fourth point, the cost of the transparent polymeric foil itself and the required additional manufacturing step where plated copper wires are adhered to the transparent polymeric foil have necessarily increased the production costs.

The object of the present invention is to provide an optimized overall manufacturing technology for forming a solarcell and a solar module of a plurality of solar cells, in which the shadowing effect is reduced to an acceptable level, the collection of charge carriers is efficient and wherein there is no need for using separate bus bars or collection electrodes as the collection wires can be directly used for the series connection of the individual cells therefore the solar module can be assembled with minimum costs and steps. The invention is based on the recognition that a new connection technology for collecting the generated charge carriers is required which can be directly utilized also for the series connection of the individual solar cells where the advantages of technology using wider conductive stripes are partially kept, while the negative features of the technology not using wide connection stripes are eliminated or remarkably lowered, so that an increased number of plated copper wires is used that have a reduced width which is higher than the size of the thin finger electrodes collecting the charge carriers from the cell surface, wherein the positioning and fixing of the wires are substantially facilitated by a novel layout of the electrodes provided on the surface of the cells, in which there is no need of using any transparent polymeric foil with their listed drawbacks and bus bars or connection electrodes that take valuable space and their use is connected with additional manufacturing steps and cost.

By utilizing said recognition a solar cell for photovoltaic modules has been provided of substantially flat design having a front side receiving incident light and a rear side opposite to the front side that comprises electrodes collecting charge carriers formed at the rear side, the cell comprises a plurality of parallel spaced first electrodes and second electrodes extending substantially normal to the first electrodes provided at least on the front side, and the first and second electrodes are electrically interconnected at mutually formed junctions, and according to the invention the second electrodes are formed as spaced electrode pairs being aligned along the whole cell and at least of a group of the first electrodes terminates at their junctions with the second electrodes, wherein the first and second electrodes constitute a mesh on the front surface of the cell covering substantially the whole front side and the number of said second electrode pairs is higher than three in a cell, and in the aligned spaces formed between the pairs of said second electrodes respective connection wires are placed and connected both mechanically and electrically to the two adjacent second electrodes, and the connection wires extend at least along substantially across the whole cell.

In a preferred embodiment the first electrodes are thin conductive stripes being between about 10 and 50 microns in size.

It is preferred if the second electrodes are thin conductive stripes being between about 10 and 100 microns in size. The fitting of the connection wires is preferred if the connection wires have size in the range of the width (w) of the gap between the pairs of second electrodes.

In a preferred embodiment, the first electrodes are arranged in parallel groups, wherein only the electrodes of discrete groups terminate at contact junctions with the second electrodes and the first electrodes of the remaining groups extend along substantially the whole width of the cell and contact all of the connection wires where their paths cross each other.

From the point of view of manufacturing and assembly costs it is preferred if the rear side of the cell has identical electrodes as on the front side.

In a preferable embodiment, the connection wires are substantially and at most twice longer than the size of the cell and extend out at one of its sides.

From the point of view of manufacturing it is preferred if the connection wires are coupled to the second electrodes by soldering or by using an electrically conductive adhesive.

From the solar cells a solar module can be made which is composed of a plurality of solar cells according to the previously described designs, wherein the connection wires that extend out from the front side of a first cell are lead to the rear side of the adjacent cell and connected to the electrodes on the rear side, and the connection wires on the front side of the second cell are connected to the rear side of the third cell and the cells in the module are connected in this way electrically in series with each other.

In a preferred embodiment, each of the cells in the solar module have the same electrode structure on both of their sides, and the connection wires of the front side of the respective cells constitute the connection wires on the rear side of the next adjacent cell.

The invention will now be described in connection with preferred embodiments thereof, in which reference will be made to the accompanying drawings. In the drawing:

Fig. 1 shows the top view of a first embodiment of a solar cell;

Fig. 2 is a similar view to Fig. 1 showing a second embodiment;

Fig. 3 shows the embodiment of Fig. 1 with the connection wires 4 placed;

Fig. 4 is an enlarged cross sectional detail with distorted scale before the placement of the connection wires; Fig. 5 is a view similar to Fig. 4 showing the cross section after the placement of the connection wire 4; and

Fig. 6 is a simplified illustration how adjacent cells are connected in series.

Fig. 1 is a plan view of a first embodiment of a rectangular photovoltaic cell 1 designed according to the present invention which is a semiconductor single- (or multi-) junction structure on the basis of mono- or multi-crystalline silicon, in some cases using amorphous silicon or other thin-film semiconducting material as embedded in the p-n junction. The light incident (front) surface of the cell 1 is covered by a light transparent conductive oxide layer (such as indium-tin-oxide or zinc-oxide or similar material). The other rear side can have a similar conductive layer or it can have a metal layer (such as aluminum or copper) or it can be provided by a conductive foil as well. The task of the conductive cover on the rear side is to collect and lead out the charge carriers. Light transparency is not a requirement at the rear side.

On the front surface of the photovoltaic cell 1 an array of electrically conductive first electrodes 2a and 2b are provided which are often referred also to as finger electrodes, wherein pairs of the electrodes 2a and 2b are aligned in a line so that between the neighboring edges of the pairs of the first electrodes 2a and 2b a uniform space is provided which form respective vertical columns. In the embodiment shown in Fig. 1 the electrodes 2b in the central region of the cell 1 have typically double length relative to that of the electrodes 2a which are arranged at the two edge regions and extend almost till the respective sides of the cell. In Fig. 1 the electrodes 2a, 2b extend in horizontal direction leaving a uniform spacing in vertical direction so that set of the aligned electrodes 2a and 2b substantially covers the full area between the outlines of the photovoltaic cell 1. This means that all points on the surface are at most as far from an electrode 2a or 2b which corresponds to the half of the space between the electrodes, i.e. the charge carriers do not have to travel a long distance to reach the closest one of the first electrodes 2a, 2b which together are referred to as first electrodes 2.

Perpendicular to the horizontally extending and aligned first electrodes 2 and along the columns formed by the edges of the first electrodes vertically extending conductive second electrodes 3a and 3b are provided that interconnect the edges of the first electrodes 2a, 2b and define the border lines of the aforementioned columns which have a narrow spacing (width) which ranges between about 0,1 to 1,0 mm. The electrodes 3a and 3b are referred to together as second electrodes 3. The junctions or connection point of the first and second electrodes 2 and 3 are all electrically connected. I n the embodiment shown in Fig. 1 six pairs of the second electrodes 3a and 3b are formed.

The first and second electrodes 2 and 3 can be provided in a number of ways, e.g. as described in the previously cited prior art. There are a number of ways how the first and second electrodes can be arranged therefore the example in Fig. 1 serves one possibility only. FIG. 2 shows a further preferred design of the first and second electrodes which differ from the first embodiment in that several vertically spaced groups of horizontally extending first electrodes 2c extend across the whole width of the cell 1 i.e. they are not separated by the column electrodes. In Fig. 2 three of such groups were used. Both above and under the horizontal areas formed by the full electrodes a similar array of the first electrodes 2a and 2b are provided as shown in Fig. 1, wherein a horizontal line comprises the first electrodes 2a at the edges with typically half length and typically double sized first electrodes 2b between them and spaced from one another in the same ways as shown in Fig. 1. Respective vertical second electrodes 3c, 3d interconnect the ends of the first electrodes 2a and 2b in the associated regions, which are only as long as the height of the region. The second electrodes in this embodiment are aligned in vertical direction.

From the point of view of the present invention it is important that the surface of the cell 1 is practically covered by the electrodes 2, 3 and on the first hand any point of the cell is at most only by about the half spacing away from the closest one of the electrodes and on the other hand a sufficient number of spaced pairs of the aligned vertical second electrodes are provided. In this way the surface of the cell 1 comprises a mesh of the first and second electrodes 2, 3.

The first and second electrodes 2 and 3 can be made by a number of ways, e.g. as described in the previously cited prior art, however a preferred method is the deposition of thin metal (e.g. silver or copper) stripes by a technology similar to printing i.e. all electrodes are provided in a single step, and the electrical connection is automatically provided where a vertical column crosses the end of a horizontal electrode. Owing to the fact that the distance of the points of the cell 1 are close to one of the electrodes, they can be made with a comparatively small width, being preferably in the range of 10 to 50. With such a small width the electrodes 2, 3 have a negligibly low shadow effect.

Fig. 3 shows the cell 1 after respective connection wires 4 (preferably made of copper) have been placed in the vertical gaps (columns) formed between the second electrodes 3c, 3d that contact and interconnect the full length electrodes 2c as well. It is preferred if the connection wires 4 extend beyond the end of the cell 1 at one side which has a substantial length that can be almost as long as the full height of the cell 1 in the direction of the wires 4. The reason is simple: if both surfaces of the cell is designed in the same way as shown in either Fig. 1 or 2, then the extending part of the wires 4 can be lead and connected to the similar columns of the lower (rear) side of the next cell in the module which cares for the easy series connection of adjacent cells. Of course, if the rear sides of the cells are covered with a metal or conductive foil, the wires 4 have to be sufficiently long to be connected to such a foil. From the point of view of manufacturing cost and using a uniform technology, the identical design of both cell surfaces is preferred.

Referring now to Fig. 4 which shows the enlarged cross section of a portion of the cell 1 (with a distorted scale in both directions) before the placement of the connection wires 4. The right end of the first electrode 2b show is connected to the second elect- rode 3b and the left end of the first electrode 2a is connected to the second electrode 3a. In the drawing the second electrodes 3a, 3b are slightly higher and wider than the first electrodes 2a, 2b. Between the two spaced vertical second electrodes 3a, 3b the space has a width w which substantially corresponds to the size of the connection wires 4. The height of the connection wire 4 is higher than that of the second electrodes 3. The lower face of the cell 1 has a similar design.

Fig. 5 is similar to Fig. 4 and it illustrates the connection of the wires 4 to the electrodes 3a, 3b. The junctions formed between the connection wires 4 and the two laterally positioned adjacent second electrodes 3a, 3b can be made by known electric charge carrying connection methods, like using soldering, conductive pasting. In any way the connection is provided by using a connection material 5 that is preferably a solder or a conductive adhesive paste. In Fig. 5 the wire has a flat elliptical cross section but it can have a circular or rectangular one as well. There are known methods for the full or partial coating of the wires 4 with either a soldering or a conductive adhesive material. In both cases the connection is done by applying heat and pressure for a predetermined period of time. Of these methods soldering is one preferred technology, wherein the solder material has preferably low melting temperature. The connection material 5 can be positioned prior to the placement of the connection wires 4 e.g. not only by a prior coating of the wires 4 but also by applying an electrically conductive hot melting ribbon or liquid paste that assures both electric and physical connection between the connection wire 4 and the electrodes 3.

The suggested arrangement of the connection wires 4 has a number of advantages over the bus bars used in prior art technologies. The shallow groove formed between the two spaced second electrodes 3a, 3b provides both a nest and lateral support for the wire 4 placed between them as well as the soldering or connection will be more definite as the connection material 5 contacts the wire 4 along a large surface and has lateral support at both sides. Owing to this property the electrical resistance between the connection wires 4 and the electrodes 3 will be minimum, and this increases efficiency.

A further advantage is obtained that the connection wires 4 can be much less in size than in case of prior art designs. With the suggested design it is not true anymore that the resistive losses will increase if the size of the wires is less than 0,5 mm. In preferred embodiments of the present invention the connection wires 4 can be as thin as even 0,1 mm, but in any case a size of 0,2 mm is sufficient. The reduction of the size of the connection wires decreases shadow losses even if the number of the wires 4 used for a cell 1 is higher than in prior designs, as the overall surface area taken by the wires is still smaller.

The use of wires 4 in the preferred range around 0,1 -0,3 mm does not mean that the design of the present invention is not useful or preferred even if the diameter or size of the wires 4 are increased over the mentioned range, since the smaller contact resistance, the better mechanical connection of the wires to the electrodes are advantages than do not disappear with increasing wire size.

A further preferred property of the present invention lies in that the use of longer wires 4 than the size of the cell eliminates the need of using separate bus bars and connection members which has the purpose of connecting adjacent cells in series. Fig. 6 is a simplified schematic illustration how the different cells can be connected in series to form a photovoltaic solar module 10, also with distorted scale in vertical direction. Assuming that the cell 1 was the first in a series of adjacent cells three cells 1, 6 and 7 are shown on which respective sets of connection wires 4, 8 and 9 are provided. The upper surfaces of the cells 1, 6, 7 are exposed to the incident light, but the cells are made in a symmetrical way i.e. both their front and rear surfaces has the same electrode structure as shown in Figs. 1 or 2. The connection wires 4 extend over the side of the first celll and they are slightly inclined in direction and continue their ways to the lower or rear face of the second cell 6. Of course, the placement of the wires to tally with the column requires the use of appropriate tools, e.g. a large plate with grooves that correspond in size and direction with the columns and the wires are placed first on such plates, and at the same phase (or in a separate second phase) to the bottom of the second cell 6, and the application of the required pressure and heat connects the wires 4 both to the upper surface of the first cell 1 and the lower or rear surface of the second cell 6 which is positioned with a minimum gap beside the cell 1. Similarly, the wires 8 are placed on the front (top) side of the second cell 6 and positioned under the third cell 7 to contact the rear surface of the third cell 7. The wires 9 of the third cell 7 continue to and fixed the rear side of the next cell (not shown). The wires 4 of the first cell 1 and those of the last cell (not shown) are interconnected by respective bus bars and these constitute the terminals of the module 10. Of course, during the assembly the cells in the module should be mechanically fixed and it should be ensured that the wires are not exposed to mechanical forces.

The advantages of the present invention have been mentioned, but further benefits come from the fact that the finger or first electrodes 2 are smaller than in the prior art because they are closer to the respective sources of the generated charge carriers and they have to travel shorter paths to reach the closest one of the electrodes. This further reduces the shadowing effect. A further advantage comes from the simpler and easier technology used, the elimination of the space, costs and problem how the adjacent cells should be connected in series, whereby simpler and comparatively cheaper solar modules can be manufactured.

Claims

Claims:

1. A solar cell for photovoltaic modules of substantially flat design having a front side receiving incident light and a rear side opposite to the front side that comprises electrodes collecting charge carriers formed at the rear side, said cell (1) comprising a plurality of parallel spaced first electrodes (2, 2a, 2b, 2c) and second electrodes (3, 3a, 3b) extending substantially normal to the first electrodes (2, 2a, 2b, 2c) provided at least on the front side, and the first and second electrodes (2, 3) are electrically interconnected at mutually formed junctions, characterized in that said second electrodes (3, 3a, 3b) are formed as spaced electrode pairs being aligned along the whole cell (1) and at least of a group of the first electrodes (2, 2a, 2b) terminates at their junctions with the second electrodes (3, 3a, 3b), wherein the first and second electrodes (2,3) constitute a mesh on the front surface of the cell (1) covering substantially the whole front side and the number of said second electrode pairs (3) is higher than three in a cell, and in the aligned spaces formed between the pairs of said second electrodes (3, 3a, 3b) respective connection wires (4) are placed and connected both mechanically and electrically to the two adjacent second electrodes (3a, 3b), and the connection wires (4) extend at least along substantially across the whole cell.

2. The solar cell as claimed in claim 1, characterized in that said first electrodes (2, 2a, 2b, 2c) are thin conductive stripes being between about 10 and 50 microns in size.

3. The solar cell as claimed in claims 1 or 2, characterized in that said second electrodes (3, 3a, 3b) are thin conductive stripes being between about 10 and 100 microns in size.

4. The solar cell as claimed in any of the claims 1 to 3, characterized in that the connection wires (4) have size in the range of the width (w) of the gap between said pairs of second electrodes (3, 3a, 3b).

5. The solar cell as claimed in any of the claims 1 to 4, characterized in that said first electrodes (2, 2a, 2b, 2c) are arranged in parallel groups, wherein only the electrodes of discrete groups terminate at contact junctions with the second electrodes (3, 3a, 3b) and the first electrodes (2c) of the remaining groups extend along substantially the whole width of the cell (1) and contact all of the connection wires (4) where their paths cross each other.

6. The solar cell as claimed in any of the claims 1 to 5, characterized in that the rear sides of the cell (1) has identical electrodes as on the front side.

7. The solar cell as claimed in any of the claims 1 to 6, characterized in that the connection wires (4) are substantially longer but at most twice longer than the size of the cell (1) and extend out at one of its sides.

8. The solar cell as claimed in any of the claims 1 to 6, characterized in that the connection wires (4) are coupled to the second electrodes (3, 3a, 3b) by soldering or by using an electrically conductive adhesive,

9. A solar module composed of a plurality of solar cells according to claims 7 or 8, characterized in that the connection wires (4) that extend out from the front side of a first cell (1) are lead to the rear side of the adjacent cell (6) and connected to the electrodes on the rear side, and the connection wires (8) on the front side of the second cell (6) are connected to the rear side of the third cell (7) and the cells (1, 6, 7) in the module are connected in this way electrically in series with each other.

10. The solar module as claimed in claim 9, characterized in that each of the cells (1, 6, 7) in the solar module have the same electrode structure on both of its sides, and the connection wires (4, 8, 9) of the front side of the respective cells constitute the connection wires on the rear side of the next adjacent cells.