Cell connector for electronically contacting planar power sources, and use thereof

A cell connector (CC) for electrical contacting of planar current sources, the cell connector being able to be contacted electrically with the current source merely in regions. The cell connector thereby includes at least one electrically conductive layer which is configured as a transit region and via contact regions which constitute merely a fraction with respect to the total surface area of the transit region is contacted with the current source.

FIELD OF THE INVENTION

The present invention relates to a cell connector (CC) for electrical contacting of planar current sources, the cell connector being able to be contacted electrically with the current source merely in regions. A configuration of this type of this connector ensures that as little as possible mechanical stress occurs, for example during heating of the entire device.

BACKGROUND

For incorporation in modules, solar cells on a wafer basis are connected electrically in groups. The cell current must be guided from the cell surface to the cell edge and from there further to an adjacent cell. In most cases, the collection of partial currents from the cell surface and the transfer to the adjacent cell is effected by metallic cell connectors (CC). For contacting the CC, take-off points are provided in the cell surface or at the cell edge.

The conductive cross-section of the CC must be adequate for conducting through currents of several amperes (5-30) per cell with low losses. On the other hand, the CC should only introduce limited mechanical stresses into the contact points. Such mechanical stresses occur between adjacent contact points on individual cells and also on both sides of a bridged cell intermediate space. The mechanical stresses are caused by thermal expansion differences during production and operation of the modules and also deformation of the modules.

In the case of solar cells with contacts on both sides (BSCC), casting the front-side in shadow by the CC must be minimised in addition, this requirement not applying in the case of rear-side contact cells (RSCC).

In the case of BSCC, the cell-side take-off points are disposed on the front-side along straight lines and connected to continuous strips (busbars). On the rear-side a planar metallisation is normal. In the case of RSCC, the take-off points of both polarities are disposed on the rear-side either at the cell edge or in the cell surface. If they are situated at the cell edge, then the CC has no current-collecting function.

In the module production, planar cell connectors (CC) made of coated copper are used. In the case of BSCC, the cross-section thereof is constant and typically is approx. 2 mm×0.15 mm (FIG. 1). They are soldered respectively onto the front side over the entire length on the busbar of a cell and alternate via an offset portion backwards, to the rear-side of the neighbouring cell.

For RSCC with edge contacts, closed, curved or lozenge-shaped CC portions are used for bridging the cell intermediate space, said portions being connected to each other optionally (WO 2005 013 322, WO 2005 122 282).

In DE 43 30 282, U.S. Pat. No. 6,313,395 and JP 62 016 579, a stress-reducing portion in the CC is proposed at the transition between the cells. This embodiment produces high mechanical stress peaks in the CC without significantly lowering the stresses at the take-off points of the cell.

JP 11 312 820 describes a CC with a portion for reducing mechanical stresses in the region of the cells. These portions are configured as raised portions. Their effectiveness is limited because the encapsulation material penetrates underneath during the lamination process and this material subsequently hardens.

SUMMARY OF THE INVENTION

Starting from the state of the art, it is hence the object of the present invention to indicate a means for electrical connection of at least two current sources which, in comparison with the state of the art, ensures better reduction in mechanical stress at the take-off points of the current sources, without however having negative influences on the current conductivity.

According to the invention, a cell connector in a planar form for electrical contacting of at least two planar current sources is provided, which cell connector comprises at least one first electrically conductive layer which has at least one contact region for making contact in regions with each of the current sources, the non-contactable region forming a transit region for current conduction, whereina) the cross-section (B) of the cell connector in the at least one contact region is smaller in the main current direction than the maximum cross-section (A) of the cell connector in the main current direction and/orb) that at least the first conductive layer outwith the at least one contact region comprises at least one region, the course of which is not linear in the main current direction and which is subdivided by at least one oblong stamped-out division or opening into at least two strips which extend essentially parallel to the main current direction.

According to the invention, there is understood by a contact region the region at which the cell connector is connected to the current source. This can be effected for example by soldering, gluing or other connections which enable a current-conducting connection of the cell connector to the current source. With reference toFIG. 2there is understood by the cross-section of the cell connector the surface area which is produced by the section along the lines A or B1and B2. This sectional surface area hence also depends upon the thickness (i.e. the dimensioning in the drawing plane ofFIG. 2).

It is hence essential to the invention that the cell connector is connected merely at points to the current source.

The connection between two contact points of the CC is weakened according to the invention with respect to the modulus of elasticityby cross-sectional thinning (FIG. 2,3,4,5,6,7) orby cross-sectional segmentation (FIG. 8,9,10).

Such an embodiment of a means for electrical connection of current sources, relative to the state of the art, offers the following advantages:

current sources, for example solar cells, CC and contact points are stressed less by mechanical stresses.

module producers can manufacture thinner current sources and make connections with higher-melting, lead-free soldering, hence saving costs and protecting the environment or fulfilling corresponding conditions.

by configuring the CC with a variable cross-section, also conductive material can be saved.

The maximum cross-section (A) is thereby advantageously dimensioned such that the total current flowing between the current sources with a maximum electrical load can flow without a heat load which damages the cell connector. Hence the cross-section depends directly upon the type or the dimensioning of the current sources which are used. In the case where the current source is a solar cell, the dimensioning of the cross-section hence depends for example upon the useful surface area or the power of the solar cell. For smaller solar cells, a small cross-section in fact suffices here, whilst a correspondingly large cross-section must be chosen in the case of more powerful solar cells.

Furthermore, it is advantageous if the cross-section of the at least one region is dimensioned such that the total current flowing between the current sources with a maximum electrical load can flow without a heat load which damages the cell connector.

In a first preferred embodiment, at least the first layer thereby has at least one opening for texturing, which abuts against the respective contact region. This leads to a further increase in flexibility of the cell connector. The texturing can thereby be effected via the normal methods known from the state of the art, for example etching, punching or milling. The cell connector hence retains high flexibility relative to the current source so that, for example with mechanical expansion (in particular if the current source and the material of the cell connector have different coefficients of heat expansion), a reduction in the otherwise occurring mechanical stress is ensured. The openings are thereby not restricted to a particular geometrical shape, but preferably they have however an essentially square, rectangular, lozenge-shaped oval and/or circular configuration. The total surface area of the at least one opening relative to the total surface area of the first layer thereby has preferably a ratio of 0.1 to 0.75, preferably 0.1 to 0.5, particularly preferred between 0.2 and 0.4.

Furthermore, it is preferred if the number of openings corresponds to the number of contact regions7, i.e. that an opening9is assigned to each contact region7, the contact region and the respective openings being in the immediate vicinity of each other. An embodiment of this type is shown for example inFIG. 2where an opening is disposed on respectively one side of each contact region.

As an alternative hereto, it is likewise favourable if at least two openings are assigned to each contact region, in particular two openings which are disposed respectively on an oppositely-situated side of the contact region. An embodiment of this type is reproduced inFIG. 3where each contact region is flanked or surrounded on both oppositely-situated sides by respectively one opening9.

A further preferred alternative or additional embodiment provides that the cell connector has an increasing and/or reducing cross-section in the current direction. Embodiments of this type are reproduced for example inFIGS. 4 and 5. In the embodiment as represented inFIG. 4, the cross-section of the cell connector in the region of the contact regions7increases constantly starting from the edge region towards the centre (B1to B4) and reaches its maximum (cross-section A) in the centre between the current sources to be connected. Of course this advantageous embodiment, according to which the cross-section varies, can also be combined with the previously discussed embodiments, according to which at least the first surface area of the cell connector3has texturing. An embodiment of this type is represented for example inFIG. 5.

As a further preferred embodiment of the cell connector, the latter can be configured in such a manner that a second layer which conducts current is disposed on the side of the first layer which is orientated away from the current source, said second layer having a contact for making contact in regions with the first layer. Hence a further increase in current throughput and mechanical strength can be effected whilst avoiding mechanical stresses. The contacting of both layers can thereby be effected via soldered contacts. Analogously, further layers can likewise be applied on the second layer and/or on each further layer. It is thereby favourable if the contact regions of the first layer for the current source and the contact regions between first and second layer—as represented inFIGS. 6a,6band7—are offset relative to each other.

The maximum conducting cross-section (A) is defined here such that it represents the sum of the layer thicknesses of the first layer3, the second layer4including the contact5disposed between the layers. In the region of the contacting of the first layer with the current source in which no contacting between the two layers3and4is present, the entire cell connector1hence has a smaller cross-section since here no contact5is applied in fact between the layers3and4. Of course both the layer3and the layer4and also any further layer can have the texturings represented inFIGS. 2 and 3, these structurings being configured then in such a manner that for example the layer3is perforated in the direction of the layer4; on the other hand, it is conceivable here also that the layers3and/or4have a corresponding varying cross-section (as represented inFIG. 4). Of course also combinations of the previously mentioned possibilities are indicated, as represented inFIG. 5.

As a further preferred embodiment, it is provided that the oblong openings12have a channel-shaped, arcuate, undulating, at least approximately sinusoidal, S-shaped and/or lamellar configuration. As a result, at least the first conductive layer of the CC is divided into a plurality of quasi-parallel regions or strips extending in the main current direction, said regions or strips being separated from each other physically by the openings perpendicular to the main current direction. With reference toFIGS. 8 to 10, these openings can be configured in such a manner that they are disposed for example between the solar cells, these openings here being able to extend essentially parallel to each other and being able to have a curved configuration. As an alternative hereto, also arcuate embodiments, corresponding to the mode of representation ofFIG. 10, are conceivable. As a common feature, these structures have however a loose arrangement of a plurality of conductive strips via which an efficient reduction in mechanical stress can be effected. It is hereby important that these loose elements have no connection to each other. Furthermore, it is thereby favourable if the cross-section of the CC according toFIG. 8has, in the region of the contact7, a smaller cross-section B than the maximum cross-section A.

It is in particular advantageous hereby if the at least one region has at least two, preferably 2 to 50, further preferred 3 to 25, particularly preferred 4 to 15, oblong stamped-out openings for texturing.

For the optional further layers, this advantageous embodiment can of course likewise apply. There should be understood thereby that structures which are textured for mechanical stress reduction (for example channels, recesses or openings which can have a channel-shaped, linear and/or lamellar configuration) are introduced into the respective layer in the region between two current sources. Hence the mechanical flexibility of the transit layer between two current sources is significantly increased. The width of the opening is preferably between 10 μm and 1000 μm, preferably between 50 μm and 300 μm.

Furthermore, it can be advantageous if at least the first conductive layer3outwith the at least one contact region7comprises at least two regions11and11′ which have at least one oblong stamped-out opening12for texturing, the course of which is not linear in the main current direction6, the regions11and11′ being connected via a region13which is configured without an opening. An embodiment of this type is represented inFIG. 10.

The region13hereby has a larger cross-section in the main current direction6than corresponds to the sum of the cross-sections of region11and also of the contact regions7. It is ensured by the region13that as large as possible currents can flow between the two current sources.

Furthermore, it is advantageous in particular in the case of elongated CC portions (e.g. from 5 mm) if the contact region is configured such that the ratio of contact surface area to the total surface area of the conductive first layer is less than 0.2, preferably less than 0.1. There is understood thereby by the contact surface area the surface area which the contact region has in cross-section. With reference to the Figures, this is the surface area which constitutes the projection of the contact region7on the layer3. This definition also applies to the intermediate contacts5. There is understood by the total surface area of the first layer the entire surface area of one side of the layer3on which the respective contact5or7is applied.

In an alternative embodiment, it is however likewise possible that the contact region is configured such that the ratio of contact surface area to total surface area of the conductive first layer is between 0.1 and 0.85, preferably between 0.3 and 0.7, particularly preferred between 0.4 and 0.6.

It is thereby favourable if at least 2, preferably 3 to 10, contact regions per current source are present. These contact regions are then configured in particular such that their respective contact surface area with respect to the total surface area of the conductive first layer, in particular with elongated CC portions, is small. Due to the presence of a plurality of contacts, a synergetic effect comprising mechanical stability and flexibility is produced, which enables a significant reduction in stress. Furthermore, it is thereby preferred if the contact regions are at a regular spacing relative to each other. There should be understood thereby regular one- and two-dimensional patterns and/or arrangements, for example in linear, square, hexagonal and/or lozenge-shaped arrangement. An alternative embodiment provides that the cell connector is configured such that only one contact region per current source is present. This contact region then preferably has a larger contact surface area with respect to the total surface area of the first conductive layer.

However it is likewise possible that the current sources have take-off points merely at the edge. In this case, the CC bridges above all the intermediate space of adjacent current sources, this intermediate space11being made flexible by lamellar structuring (FIG. 8). As a result, the same advantages are produced as in the previously mentioned embodiments.

Furthermore, it is preferred if the at least one contact region which is present per current source is disposed in the edge region of the cell connector. There is understood thereby that the contact regions are disposed essentially on the outermost points of the CC.

Alternatively, it is however equally possible that the at least one contact region which is present per current source is disposed transversely relative to the current direction essentially in the centre in the cell connector.

It is likewise possible that an insulating layer is disposed between the first layer and the current sources and/or between the first and second layer and/or between the respectively further layers, the insulating layer being perforated respectively by the contact regions.

With respect to the dimensions thereof, the cell connector is configured such that it has a strip-like structure, i.e. has a thickness in the range of several μm to several 100 μm and a width in the range of several mm. The dimensions are thereby not restricted to a particular dimension but preferably the layer thickness of the at least one first and/or each further layer, independently of each other, is between 10 μm and 300 μm, preferably between 20 μm and 100 μm.

The width of the at least one first and/or each further layer, independently of each other, is between 0.5 mm and 50 mm, preferably between 1 mm and 10 mm.

With respect to the materials from which the cell connector is formed, the means is not subject according to the invention to any restriction, merely that the material must be selected from conductive materials with low resistance. Preferably, the components of the cell connector are however selected from the group comprising copper, aluminium and/or silver.

The planar current source is thereby preferably a solar cell and/or fuel cell.

It is thereby irrelevant how the cell connector is used for connection of the planar current sources. For example, the means can be applied as front-, rear-side- and/or side contact on the current source. The current sources can be wired to each other by the means in parallel and/or in series. The means can thereby also connect a front- to a rear-side contact, for example of a solar cell, so that it has a step-like structure.

The present invention is explained in more detail with reference to the accompanying Figures without wishing to restrict the invention to the special embodiments represented there.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a cell connector as is known from the state of the art. The cell connector is thereby configured as a continuous copper strip and, in the region of the contact to the current source, is connected continuously to the latter. Hence there is no possibility of reducing mechanical stresses which occur.

InFIG. 2, a CC1which has a textured single-layer structure is represented. The textured regions9thereby represent openings which here have a quasi-rectangular configuration. In the case of rear-side contact cells, the CC1is not casting a shadow so that the layer3can be configured widely to increase the conductivity. The layer3improves the conductance of the collected current and can have an additional insulating layer towards the cell. The current collection and guidance is effected from the solar cell2via the contact regions7and the layer3. Only the contact points7are connected to the current source2. This contacting7can be effected for example via soldered contacts. Of course another further conductive layer can be applied here also on the first layer3(at the top in the image plane) by means of soldered contacts5. It is hereby essential to the invention that the cross-section of the cell connector1which is produced by a section along the line A represented inFIG. 2is greater than the cross-section which is produced by a section of the cell connector along the lines B1and B2. Hence the cross-sectional surface area in the contact region is less than the maximum cross-sectional surface area of the cell connector1. As a result, excellent flexibility is achieved.

As represented inFIG. 3, the texturing9can also be effected such that a single-layer structure results, in which the contact regions7can also be disposed between two texturings9. This leads to improved flexibility of the CC1. Otherwise the same embodiments as forFIG. 2apply. The Figures represent plan views on the respective CC1. As mentioned already inFIG. 2, the cross-section here which is produced along the line B1and B2and B2′ inFIG. 3, i.e. the cross-sectional surface area of the contact region7, is also smaller than the maximum cross-section of the cell connector1. As a result of the fact that the openings are applied respectively in pairs on the contact region7, a further increase in flexibility of the cell connector1is provided.

FIG. 4shows an embodiment with a varying cross-section of the CC1. In this plan view, the contact region7is hence not directly visible and characterised by the hatched region. As a result of the contacting merely at points, higher mechanical flexibility is produced, whilst the increasing cross-section of the CC1towards the region between the current sources2and2′ ensures that improved current conduction of the current accumulated over the entirety of the contacts7is provided. The cell connector1represented inFIG. 4is now distinguished in that, starting from the edge region, the cross-section thereof increases constantly (this corresponds to the cross-sectional surface areas which are produced by the section of the cell connector along the lines B1, B2, B3and B4). The CC1reaches its maximum cross-sectional region in the bridging region between two solar cells2and2′. This increase in cross-section is effected in that the current flow in the current direction, i.e. between the two cells2and2′, accumulates over the four contacts7and hence is increased. Due to the increasing cross-section in the current direction, it is now ensured that efficient current conduction is ensured.

A CC1with a varying cross-section is however possible also in an embodiment represented inFIG. 5in which a texturing9of the layer3is present in addition. The embodiments forFIG. 2andFIG. 3apply. Hence this embodiment is a combination of the increasing cross-section ofFIG. 6and of the embodiment of the contact portions according toFIG. 4. In this embodiment, it is also constantly ensured that the cross-sectional surface area in the contact regions7(characterised by the sum of the section surface areas along the lines B1and B2or B1and B2′) is always smaller than the maximum cross-section, e.g. along the line A.

FIGS. 6aand6bshow a CC1which comprises two layers3,4.FIG. 6athereby shows the structure of a CC1comprising two layers, whilstFIG. 6brepresents the electrical contacting of the CC1to a solar cell2. The arrow6marks the current direction. The two layers3,4are connected to each other, e.g. soldered or glued conductively, only in portions5. The contacting7to the solar cell is effected likewise in portions via the layer3of the CC1which is orientated towards the cell. The connection points5and7are thereby mutually offset. The contact regions7are connected to the CC1via a smaller cross-section than corresponds to its maximum, electrically conductive cross-section. The maximum conductive cross-section hereby represents the sum of the layer thicknesses3and4and also of the contacts5; the smaller cross-section of the contact region7is in contrast defined only by the two layer thicknesses3and4. If such a multilayer CC1is provided with a shoulder8(FIG. 7), as is required for series wiring of solar cells, a reduced danger of rupture exists upon expansion because a smaller preloading of the loose bond at the bent edges is produced.

FIG. 8shows an embodiment, by way of example, of a multi-divided, indirect course in lamellar form12of the CC1which connects two adjacent RSCC with edge contacts. By dividing the connection cross-section into lamellar structures, which were produced by S-shaped incisions in the part11of the CC1which bridges the two solar cells2and2′, the flexural rigidity of such arcuate connection pieces drops significantly, a transition from rigid to loose bond is achieved. In a CC1with a material thickness of for example 100 μm, gap widths below 100 μm can be produced. Such a course can also be provided in any differently configured CC1for reducing the mechanical stress, for example in rectangular form as represented inFIG. 9. Also in the embodiment represented inFIG. 8, the CC1is distinguished in that its cross-section along the line B which extends in the contact region is smaller than its maximum cross-section (characterised by the line A). Of course, also multilayer structures are conceivable here, also the contacting in the case of a plurality of layers requiring here to be effected merely at points.

InFIG. 10, a cell connector1for connecting solar cells (2,2′) is represented, said cell connector having take-off points7in the edge region. The layer3is thereby contacted in pairs via the contact regions7to the solar cells (2,2′) and has textured regions11and11′ which have lamellar openings12and are attached to a connection piece13which carries a plurality of contact pairs. The current flows perpendicular6to the connection piece13. This embodiment is distinguished in that the regions11and11′, which contact the connection piece13on both sides, are textured or structured by a plurality of arcuate openings, as a result of which a loose bond of a plurality of conductor strands is produced. It is thereby characterising that these conductor strands are not connected to each other so that these conductor strands have extremely high flexibility relative to each other. Such an arrangement enables an exceptionally efficient reduction or lowering of mechanical stresses.