The present invention relates to a solar cell array.
The present invention is in the field of so-called bifacial solar cells. Bifacial solar cells are solar cell, in which the front-side as well as the rear-side thereof can be used for power generation. Such solar cells are preferred to be used when the solar cell rear-side is illuminated by scattered light and therefore, the power is generated from scattered light.
PERC (Passivated Emitter and Rear Cell) refers to an innovative solar cell technology by which significantly higher efficiencies can be achieved. In a PERC-solar cell, the semiconductor body includes a structured passivation layer on the rear-side of the semiconductor body, which is provided for reducing recombination losses on the rear-side contact of the solar cell. The contact structure associated thereto is disposed on the passivation layer and locally contacts the rear-side surface of the semiconductor body via the contact openings present in the passivation layer.
The present invention relates to a solar cell array having such a bifacial PERC-solar cell topography, e.g. which is described in DE 20 2015 101 360 U1.
The rear-side contact structure is contacted via so-called cell-connector to the corresponding solder contacts. Therefore, the rear-side contacts can preferably be configured as Aluminum contacts, which is frequently applied as Aluminum-paste in a screen-printing process. However, the problem is that this Aluminum-paste has a low-adhesion to the rear-side passivation of PERC-solar cell, because Aluminum-paste should not include any abrasive glass frits, so that the rear-side passivation is not impaired. This low-adhesion of Aluminum-paste becomes noticeable, for example, in the so-called Ribbon pull-off test of the cell connector, in which during a pull-off test of the ribbon-like cell connector, sometimes unintentionally Aluminum-paste in the region of the current collecting rail is also removed. Thus, the adhesion of Aluminum-paste of the current collecting rail to the cell connector is greater than to the passivation layer. In the actual operation of the solar cell this might lead to that in case of mechanical loads, such as temperature fluctuations or snow and wind loads, crack formation occur in Aluminum contact of the current collecting rail or the surrounding contact fingers, because the cell connector and the solar cell or Aluminum contacts have different coefficients of expansion. The cracks in the contact fingers typically develop parallel to the current collecting rails.
Whereas in unifacial PERC-solar cells in such a case, the power transmission to the solder contact and subsequently to the cell connector is still ensured, because the rear-side Aluminum contact is completely configured and therefore, the current can still freely flow laterally, this is no longer really available in bifacial PERC-solar cells. There is always a risk in bifacial PERC-solar cells that in case of tearing off of the cell connector, the current collecting rail connected thereto and some of the contact fingers connected thereto are also torn off. But certain areas of the solar cell would thereby no longer be electrically connected and thus could no longer contribute—in particular continuously—in power generation.
This is a condition, which has to be avoided.
In the light of the above, the object underlying the present invention is to provide an improved bifacial PERC solar cell array.
In accordance with the invention, this object is accomplished by a solar cell array with the features of the claims 1 and 4.
Accordingly, it is provided:
The idea of the present invention is to configure the current collecting rails of the bifacial PERC solar cell array such that in case of tearing off of the cell connector and the corresponding underlying current collecting rails associated therewith, the function of the solar cell array is more or less completely preserved, so that a reliable power transmission of the contact fingers in the solder contacts is maintained.
According to a first aspect of the invention, this is realized in that the current collecting rail is configured wider in the middle than the cell connector. In this context, in the middle means that even after tearing-off, sections can be present in which the cell connector is wider than its underlying current collecting rail, however the sections in which the current collecting rail is wider than the corresponding cell connector, overall predominate. In case of tearing-off of the cell connector, in this case due to the middle greater width of the current collecting rail, a part of this current collecting rail would always remain and thus could also contribute in power transmission. The greater width of the rear-side current collecting rail in fact slightly reduces the efficiency of the bifacial solar cell, however this is taken into consideration by the enhanced reliability obtained thereby.
According to a second aspect of the invention, this is realized in that the current collecting rail is configured narrower than the cell connector and additional redundancy fingers are disposed more or less parallel to the current collecting rails. If in case of tearing-off of a cell connector, e.g. several contact fingers would be separated from the current collecting rail, the current flow could nevertheless be conducted to the solder contacts via these redundancy lines. The rear-side current collecting rails could thus be optimized with reference to the area thereof, with regard to the efficiency of the simultaneously higher reliability.
Advantageous configurations and improvements result from the further subordinate claims and from the description with reference to the figures of the drawing.
In a preferred configuration, the current collecting rail is wider than the cell connector over the entire length thereof, thus not only partially. Therefore, the current collecting rail is particularly wider than the cell connector even in the region outside the solder contacts.
In a preferred configuration, at least one redundancy finger per solar cell is provided. A Redundancy finger, which is occasionally also referred to as Redundancy line or Redundancy collecting rail, denotes an electrically conductive contact structure, which electrically interconnects several contact fingers, preferably all contact fingers of a solar cell and which is also configured to conduct current to a solder contact in addition or complementary to the current collecting rails during the operation of the solar cell. Hence, such a redundancy finger kind of forms a redundant current collecting rail, however without—such as the current collecting rail—electrically being contacted via solder contacts and to be directly connected to the cell connectors via these solder contacts. These redundancy fingers additionally improve the reliability of the solar cell array.
In a preferred configuration, the current collecting rail is flared at least in the region of the solder contacts. In particular, it is advantageous if the lateral width of the current collecting rail continuously increases along the longitudinal direction thereof to one such flared solder contact. This takes into account of the higher current density in the region of the solder contact. Moreover, this measure reduces the shadowing losses there as well as the material consumption for the current collecting rail there, due to the narrower current collecting rail outside the solder contact.
In a preferred configuration, the current collecting rails are constantly wide along the entire longitudinal direction thereof, thus also in the region of the solder contacts.
In a preferred configuration, the redundancy finger is disposed at least partially along the longitudinal direction of the current collecting rail thereof. Preferably, the redundancy finger is disposed completely parallel to the current collecting rail and thus does not directly contact the corresponding collecting rail, but only indirectly contacts via the contact fingers.
In a preferred configuration, several redundancy fingers per solar cell are provided, which extend substantially parallel to each other. As a result, the reliability is additionally enhanced and the power-losses are reduced. Moreover, in this way, the area of redundancy fingers and current collecting rails can be optimized with regards to the efficiency at simultaneously higher reliability.
In a preferred configuration, a redundancy finger includes at least one inter connecting section through which the redundancy finger is electrically connected to the current collecting rail.
Preferably, this redundancy finger in the region of the solder contact is electrically connected to the current collecting rail. In case of the failure or tearing off of one or more contact fingers, it is nevertheless ensured by this direct contact that the current collected by these contact fingers, however contributes to power generation through the redundancy fingers. Preferably, the redundancy finger in the region of the interconnection leads radially, i.e. directly towards the current collecting rail or the solder contact thereof. It is particularly preferred if the redundancy finger is led in the region of the interconnection in an arch, i.e. curved with respect to the current collecting rail or the solder contact thereof. In this way, the redundancy finger can include a large number of contact fingers.
In a preferred configuration, at least one redundancy finger is provided, which is disposed between a current collecting rail and a cell border of a respective solar cell. In this case, the failure or tearing-off of the connection of contact finger to the current collecting rail would be most serious, because the current could be collected thereby through another adjoining current collecting rail. This is effectively prevented by means of the redundancy fingers.
In a preferred configuration, the current collecting rail includes several solder contacts along the longitudinal direction thereof, for electrically contacting the cell connectors. As a result, the current densities along the current collecting rails are uniformly divided and power-losses reduced.
In a preferred configuration, at least one current collecting rail is at least partially omitted and/or interrupted between two solder contacts. In addition, the redundancy finger is therefore configured and disposed so as to take over the current transmission to the solder contacts at least partially, particularly completely.
Current collecting rails consisting of Aluminum can be produced particularly inexpensively, for example by means of an Aluminum-paste. However, Aluminum has a low adhesion on the passivation. The present invention now particularly effectively counteracts these low adhesion characteristics. Therefore, the present invention is particularly advantageous in current collecting rails consisting of Aluminum or an Aluminum containing alloy.
In a preferred configuration, the solder contacts include a solderable metal. Preferably, the solderable metal is Silver or an alloy including Silver.
Advantageously, the current collecting rails and/or redundancy fingers and/or contact fingers are applied on the solar cell at least partially, particularly completely by means of a screen-printing process and/or an extrusion printing process and/or Ink-jet process and/or Plating process. The use of such processes has proven as particularly efficient and inexpensive.
In a preferred configuration, at least one redundancy finger includes a width increasing towards the solder contacts.
The above configurations and improvements can be randomly combined with each other, wherever appropriate. Further possible configurations, improvements and implementations of the invention also include combinations not explicitly mentioned previously or described in the following with reference to the features of the exemplary embodiments. In particular, the skilled person may also therefore add individual aspects as improvements or additions to the respective basic form of the present invention.
The present invention is explained in more details in the following with the help of exemplary embodiments listed in the schematic figures of the drawings. Therefore, these show:
The accompanying drawings shall impart a broad understanding of the embodiments of the invention. They illustrate embodiments and serve in conjunction with the description of the explanation of principles and concepts of the invention. Other embodiments and many of the advantages mentioned result in view of the drawings. The elements of the drawings are not necessarily shown to scale with respect to each other.
In the figures of the drawing, same, functionally same and similarly working elements, features and components are respectively provided with the same reference numerals, unless explained otherwise.
A semiconductor body, for example consisting of monocrystalline Silicon is indicated by reference numeral 10. The p-doped semiconductor body 10 includes a front-side 11 and a rear-side 12.
An n-doped front-side emitter 13 is introduced on the front-side 11 in the semiconductor body 10, on which an amorphous Silicon nitride layer 14 is applied as an anti-reflection coating. Further, a front-side contact arrangement 15 is provided on the front-side 11. The front-side contact arrangement 15 includes a plurality of current collecting rails, cell connectors and contact fingers, not represented in more details. The front-side contact arrangement 15 is connected to the front-side emitter 13 through the openings 16 in Silicon nitride layer 14. For an excellent electrical connection, the front-side emitter 13 includes highly doped n-contacts 17 in the region under the openings 16.
An extensive passivation layer 18 is applied on the semiconductor body 10 on the rear-side 12. This passivation layer 18 is provided for reducing the recombination losses on the rear-side contact of the solar cell. Aluminum-contact structure 19 associated therewith is applied on the passivation layer 18 and locally contacts the rear-side surface 12a of the semiconductor body, in which it extends up to the surface 12a through the contact openings 20 present in the passivation layer 18. This Aluminum-contact structure 19 includes a plurality of current collecting rails, cell connectors, contact fingers, etc. not represented in more details here, the exact arrangement of which is explained in more details in the following with the help of
For the sake of clarity, the exact configuration of the emitter structures and the like are not represented in more details in
An Aluminum-contact structure is provided on the rear-side of the semiconductor body, which includes the current collecting rails 30 and contact fingers 31 in a manner known per se.
The contact fingers 31 are disposed substantially parallel to each other in the example shown and form a direct metal-semiconductor contact with the rear-side surface of the semiconductor body. These contact fingers 31 are used for absorbing charge carriers, which are generated in the semiconductor body because of the photovoltaic effect by the incident light.
Each of the contact fingers 31 is electrically connected to at least one current collecting rail 30. These current collecting rails 30, which are often also referred to as Busbar and are generally also disposed parallel to each other, are contacted with the rear-side surface of the semiconductor body in the example shown. However, it is also possible to open the passivation layer under the current collecting rails, so that these are directly connected to the rear-side surface of the semiconductor body via a metal-semiconductor contact and are thus likewise used for absorbing the charge carriers from the semiconductor body. The current collecting rails 30 absorb the charge current absorbed via the different contact fingers 31. The current collecting rails 30 and contact fingers 31 are thus used for collecting and combining the charge carriers generated in the semiconductor body 10.
In order to conduct the charge carriers so collected and also to enable an interconnection of different solar cells, the so-called cell connectors 32 are provided, which are often referred to as series connectors. These cell connector 32, which are typically not a component of the actual solar cell, but of the solar module, are at least partially disposed on the current collecting rails 30 and firmly bonded to these. For example, these cell connectors 32 can be soldered, bonded or pressed on the respective current collecting rail 30 for a firm bonding.
The current collecting rails 30 include at least one solder contact 33 for providing a defined electrical contact. Therefore, the cell connectors 32 on the solder contact 33 are electrically connected to the respective current collecting rail 30 via a solder joint 34.
In the example shown, the cell connectors 32 are disposed along the same longitudinal direction X of the current collecting rails 30 and directly above the current collecting rails 30. On the other hand, the contact fingers 31 are oriented orthogonally to the current collecting rails 30 along the direction Y in the example shown.
Each contact finger 31 has a width 31 and a distance Al from an adjoining contact finger 1G. In accordance with the invention, width D2 of the current collecting rail 30 along the entire longitudinal direction X in the example shown, is greater than width B3 of a cell connector 33 disposed thereon.
Comparatively inexpensive materials such as Aluminum, Nickel and the like, or comparatively highly conductive materials such as Silver can be used as the material for the contact fingers 31 and current collecting rails 30. Preferably, a good solderable material, such as Silver or a suitable Silver alloy is used as solder joint 34.
The contact fingers 31 and current collecting rails 30 are normally manufactured by a strip-shaped conducting paste, e.g. Aluminum conductive paste applied in the screen-printing process and sintering of this applied conductive paste. Alternatively, an extrusion process can also be used. The cell connectors 32 are generally applied by selective soldering in the region of the solder joint 34 on the current collecting rail 30.
In the example of
In the example of
B4 denotes the width of a redundancy finger 35. The redundancy fingers 35 can be of constant or even variable width, e.g. a width B4 (not shown here) increasing towards the solder contacts 33.
In the example of
In the example shown of
Another exemplary embodiment, not shown here, provides that the current collecting rails 35 are completely interrupted or are at least omitted. The current collecting function is predominantly or even completely taken over by the redundancy fingers 35.
Although, the present invention was fully described above with the help of preferred exemplary embodiments, they are not restricted to these, but can be modified in many ways.
In the examples shown, the different contact fingers as well as the different current collecting rails and/or redundancy fingers extend parallel to each other, however this is not absolutely necessary. Also, in the example shown, the current collecting rails are disposed perpendicular to the respective contact fingers, which is also not absolutely necessary.
In particular, the invention is also not restricted to the materials mentioned, though at times they are advantageous, such as the use of Aluminum.
In the same manner, the present invention is also not restricted to the use of p or n-conductive semiconductor materials or p or n-type of solar cells. It goes without saying that by appropriate variation, other conductive types and dopant concentrations can also be used.
The manufacturing process indicated are also used only for explaining the advantages during the manufacture, however the invention is not restricted to these.
In the context of the present invention, above and below means away from the respective surface of the semiconductor body or towards the respective surface of the semiconductor body. The widths and distance data refer to the projection of the respective top-view.
10 Semiconductor body
11 Front-side
11
a Front-side surface
12 Rear-side
12
a Rear-side surface
13 Rear-side emitter
14 Silicon nitride layer, Antireflection coating
15 Rear-side contact arrangement
16 Opening
17 Contact
18 Passivation layer
19 (Aluminum) contact structure
20 Contact opening
21 Solar cell array with bifacial PERC solar cells
30 Current collecting rails, Busbar
30
a Flared area of the current collecting rail
30
b Region of the current collecting rail
31 Contact finger
32 Cell connector, Series connector
33 Solder contact
34 Solder joint
35 Redundancy finger
35
a Section of the redundancy finger
X Longitudinal direction
Y Direction (orthogonal to the longitudinal direction)
A1 Distance of adjoining contact finger
B1 Width of a contact finger
B2 Width of a current collecting rail
B2a Flared width of a current collecting rail
B3 Width of a cell connector
B4 Width of a redundancy finger
Number | Date | Country | Kind |
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202015004065.9 | Jun 2015 | DE | national |