Solar cell and solar cell assembly

Abstract

Solar cell assembly that includes at least first and second solar cells arranged adjacent each other to form a row. First electric contact pad of first solar cell is positioned adjacent to second electric contact pad of second solar cell and second electric contact pad of first solar cell is positioned adjacent to first electric contact pad of second solar cell. Interconnectors connect each first electric contact pad of first solar cell with adjacent second electric contact pad of second solar cell and each second electric contact pad of first solar cell with adjacent first electric contact pad of second solar cell. Each interconnector is sized so that, between adjacent cells, interconnector is below first electric contact pad. Cover glass is provided on a front surface of each solar cell, and each interconnector is provided with a cover member covering a front surface of interconnector.

Claims

1. A solar cell assembly including at least two interconnectable solar cells, wherein: each said at least two interconnectable solar cell comprising: a semiconductor substrate having a substrate front surface and a substrate rear surface; a first p-n-junction provided in the substrate close to and below the substrate front surface, the first p-n-junction separating the substrate into a substrate front portion having a first doping and a substrate rear portion having a second doping; a front layer comprising a further p-n-junction provided on the substrate front surface of the substrate, the further p-n-junction separating the front layer into a further front portion having the first doping and a further rear portion having the second doping, the further front portion being separated from the substrate front portion; at least one first electric contact being provided on a front side of the solar cell that is electrically connected to the further front portion; at least one second electric contact being provided on a rear side of the solar cell that is electrically connected to at least one contact point provided on the front side of the solar cell; the at least one contact point being placed on a bottom surface of a groove formed in the substrate that opens to the front side of the solar cell and which extends to the substrate rear portion; an electrical connection between the at least one second electric contact and the at least one contact point being provided by the substrate rear portion; and a cover glass being provided on a front surface of the front layer of each said solar cell, wherein each said cover glass is provided with cut-outs located at positions of the at least one contact point; the solar cell assembly comprising: the at least two solar cells arranged adjacent each other to form a row of solar cells, the at least two solar cells comprising at least a first and a second solar cell; first and second electric contact pads for respective first and second electric contacts for each solar cell, wherein a first electric contact pad of the first solar cell is positioned adjacent to a second electric contact pad of the second solar cell and a second electric contact pad of the first solar cell is positioned adjacent to a first electric contact pad of the second solar cell; and interconnectors being arranged to connect each first electric contact pad of the first solar cell with the adjacent second electric contact pad of the second solar cell and to connect each second electric contact pad of the first solar cell with the adjacent first electric contact pad of the second solar cell, wherein each interconnector is sized so that, between the adjacent first solar cell and the second solar cell, the interconnector is located below a height of the first electric contact pad and overlies or extends into an inter cell gap, wherein each interconnector is provided with a cover member covering a front surface of the interconnector, wherein the cover member is mounted to the interconnector with a flexible adhesive, and the cover member is a cover glass piece, and wherein the cover member and the cover glass comprise separate members that are separated from each other by a gap adapted to take up, along with the flexible adhesive, contraction of the inter cell gap.

2. The solar cell assembly according to claim 1, further comprising at least one intermediate layer comprising an intermediate p-n-junction provided between the substrate and the front layer, the intermediate p-n-junction separating the at least one intermediate layer into an intermediate front portion having the first doping and an intermediate rear portion having the second doping, the intermediate front portion being separated from the substrate front portion.

3. The solar cell assembly according to claim 1, wherein the groove is provided on and opens to a lateral side of the solar cell.

4. The solar cell assembly according to claim 1, further comprising at least one of: an antireflection coating at least partially provided on a front surface of the front layer; and the second electric contact pad being located at the at least one contact point on the bottom surface of the groove, the bottom surface having an antireflection coating at least partially around the at least one contact pad.

5. The solar cell assembly according to claim 1, wherein the solar cell is a III-V triple junction cell and the substrate is a Germanium wafer.

6. The solar cell assembly according to claim 1, wherein the cut-outs have a same size as the second electric contact pad forming the at least one contact point.

7. The solar cell assembly according to claim 1, wherein the interconnectors are formed in a U-shaped or a W-shaped configuration, wherein at least one free end of the interconnector extending from a connection to one of the first or second electric contact pad is bent upwardly away from the one first or second electric contact pad and spaced from a sidewall of the groove, and wherein each interconnector comprises a plurality of grid fingers, each of which is contacted separately to the associated electric contact pad.

8. A solar cell assembly of at least three interconnectable solar cells, wherein: each said at least three interconnectable solar cell comprising: a semiconductor substrate having a substrate front surface and a substrate rear surface; a first p-n-junction provided in the substrate close to and below the substrate front surface, the first p-n-junction separating the substrate into a substrate front portion having a first doping and a substrate rear portion having a second doping; a front layer comprising a further p-n-junction provided on the substrate front surface of the substrate, the further p-n-junction separating the front layer into a further front portion having the first doping and a further rear portion having the second doping, the further front portion being separated from the substrate front portion; at least one first electric contact being provided on a front side of the solar cell that is electrically connected to the further front portion; at least one second electric contact being provided on a rear side of the solar cell that is electrically connected to at least one contact point provided on the front side of the solar cell; the at least one contact point being placed on a bottom surface of a groove formed in the substrate that opens to the front side of the solar cell and which extends to the substrate rear portion; an electrical connection between the at least one second electric contact and the at least one contact point being provided by the substrate rear portion; and a cover glass being provided on a front surface of the front layer of each said solar cell, wherein each said cover glass is provided with cut-outs located at positions of the at least one contact point; the solar cell assembly comprising: the at least three interconnectable solar cells being arranged to form an array of solar cells; first and second electric contacts pads for respective first and second electric contacts for each of the at least three solar cells, wherein a first electric contact pad of one solar cell is positioned adjacent to a second electric contact pad of another solar cell and a second electric contact pad of the one solar cell is positioned adjacent to a first electric contact pad of the another solar cell; interconnectors being arranged to connect each first electric contact pad of the one solar cell with the adjacent second electric contact pad of the another solar cell and to connect each second electric contact pad of the one solar cell with the adjacent first electric contact pad of the another solar cell, wherein each interconnector is sized so that, between the adjacent one solar cell and the another solar cell, the interconnector is located below a height of the first electric contact pad and overlies or extends into an inter cell gap, wherein each interconnector is provided with a cover member covering a front surface of the interconnector, wherein each cover member is mounted to each interconnector with a flexible adhesive, and each respective cover member is a cover glass piece, and wherein the cover member and the cover glass comprise separate members that are separated from each other by a gap adapted to take up, along with the flexible adhesive, contraction of the inter cell gap.

9. The solar cell assembly according to claim 8, further comprising at least one intermediate layer comprising an intermediate p-n-junction provided between the substrate and the front layer, the intermediate p-n-junction separating the at least one intermediate layer into an intermediate front portion having the first doping and an intermediate rear portion having the second doping, the intermediate front portion being separated from the substrate front portion.

10. The solar cell assembly according to claim 8, wherein the groove is provided on and opens to a lateral side of the solar cell.

11. The solar cell assembly according to claim 8, further comprising at least one of: an antireflection coating at least partially provided on a front surface of the front layer; and the second electric contact pad being located at the at least one contact point on the bottom surface of the groove, the bottom surface having an antireflection coating at least partially around the at least one contact pad.

12. The solar cell assembly according to claim 8, wherein the solar cell is a III-V triple junction cell and the substrate is a Germanium wafer.

13. The solar cell assembly according to claim 8, wherein the cut-outs have a same size as the second electric contact pad forming the at least one contact point.

14. The solar cell assembly according to claim 8, wherein the interconnectors are formed in a U-shaped or a W-shaped configuration, wherein at least one free end of the interconnector extending from a connection to one of the first or second electric contact pad is bent upwardly away from the one first or second electric contact pad and spaced from a sidewall of the groove, and wherein each interconnector comprises a plurality of grid fingers, each of which is contacted separately to the associated electric contact pad.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

(2) FIG. 1 shows a cross sectional view through a prior art triple junction solar cell;

(3) FIG. 2 shows a top view on a layout of a front side grid on the solar cell;

(4) FIG. 3 shows a prior art example of interconnecting individual cells into a photovoltaic assembly for space use;

(5) FIG. 4 shows a cross sectional view through a solar cell according to the invention;

(6) FIG. 5 shows a top view on the solar cell of FIG. 4 and on a cover glass therefore;

(7) FIG. 6 shows a detailed cross sectional view through the solar cell of FIG. 4 at a contact location with a welding tool;

(8) FIG. 7 shows examples of interconnector shapes of a solar cell array according to the invention;

(9) FIG. 8 shows an ion erosion protected interconnector in a solar cell array according to the invention;

(10) FIG. 9 shows an example of grounding conductively coated cover glasses;

(11) FIG. 10 is an illustration of a cell repair process for a solar cell assembly possible in conjunction with solar cell according to the invention;

(12) FIG. 11 shows an example of an automated string manufacturing process for a solar cell assembly according to the invention; and

(13) FIG. 12 shows a one step integration process for a solar cell assembly according to the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(14) The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

(15) The solar cell C shown in FIG. 4 is made of a semiconductor substrate 4 having a front surface 4 and a rear surface 4. A first p-n-junction 3 is provided in the substrate 4 close to the front surface 4 thereof. The p-n-junction 3 separates the substrate into a front portion having a first doping n and a rear portion having a second doping p.

(16) FIG. 4 illustrates the proposed technique of a solar cell C according to this invention to establish a contact point 304 of a rear side contact 8 on the cell front side. The contact point 304 is electrically connected via a rear portion 303 of the substrate 4 to the rear side contact 8 by exploiting the high conductivity of the Germanium substrate 4. The drawing is not to scale and the solar cell C shown in FIG. 4 serves illustration purposes only. The invention is in no way limited to this particular cell type or geometry. Features of the solar cell C according to the invention which resemble features of the prior art solar cell shown in FIGS. 1 and 2 have been allotted the same reference numerals and for their description reference is made to the description of FIGS. 1 and 2.

(17) A front layer 1 comprising a p-n-junction 1 is provided on the front surface of the substrate 4, wherein the p-n-junction separates the front layer 1 into a front portion having the first doping n and a rear portion having the second doping p. The front layer's front portion is separated from the substrate front portion 306.

(18) An intermediate layer 2 comprising a p-n-junction 2 is provided between said substrate 4 and said front layer 1. The p-n-junction separates the intermediate layer 2 into a front portion having the first doping n and a rear portion having the second doping p. The intermediate layer's front portion is separated from the substrate front portion.

(19) First electric contacts 9 are provided on the front side C of the solar cell C in the form of grid fingers and are electrically connected to the front portion of the front layer 1. These grid finger contacts are connected to a plurality of contact pads 10 which are disposed on a lateral side of the front surface of the solar cell C.

(20) Second electric contact pads 304 forming the contact points 304 are provided so that they are accessible from the front side C of the solar cell C as will be described below. These second electric contact pads 304 are electrically connected to the rear portion 303 of the substrate 4. The second electric contact pads 304 are placed on the bottom surface of a groove 305 which opens to the front side C of the solar cell C and which extends to the rear portion 303 of the substrate 4. Groove 305 opens also to lateral side 7 of cell C.

(21) To provide the contact groove 305 for the second, rear side contact pad 304 the epitaxy is etched at 301 to about 10 m, whereas the width of the groove 305 forming a contact pad area 302 for the contact pad 304 of contact point 304 is a one hundred times as large. The height 7 of the remaining wafer is in the order of 100 m.

(22) The first element of this invention involves an efficient way to establish an independent (+) contact point 304 at the location 300 on the cell front side C as well, next to the () contact pad 10 already present there. In other words, the contact which is in the prior art present on the cell rear side is moved to the front side C. This is achieved as shown in FIG. 4 by relying on the conductivity of the p doped Germanium wafer 4 itself. It has to be noted that the polarity of the contacts and the associated doping (p or n) in FIG. 4 just serves as an example. Opposite polarities are of course feasible as well.

(23) Over a sufficiently large area 302, e.g. 81.2 mm.sup.2, the entire epitaxy is etched away to form the groove 305 of a height 301 down to the p doped rear portion 303 of the Germanium substrate 4. The same etch processes used to establish the mesa groove 6 at the cell edge or to isolate the integrated diode can be applied here as well. The metal contact pad 304 is then deposited on the p doped rear portion 303 of the Germanium substrate 4 and serves as a contact pad for an external cell connector.

(24) Typically the same ohmic contact pad system is used for the cell front side contact 9 and contact pad 10 (interfacing for example to the n doped Ga(In)As based cap layer) as for a cell rear side contact 8 (interfacing to the p doped Germanium). Therefore both front side contacts can also be deposited in on step on the cell front side. The Germanium substrate in state of the art triple junction cells is fairly highly doped, resulting in specific resistances in the 10 mcm range (Ref.: C. G. Zimmermann, Journal of Applied Physics, 100, 023714, 2006). Assuming a thickness of the Germanium wafer of 140 m and three (+) contact pads 304 with an area of 7 mm.sup.2 each, the resistance R of this current path through the Germanium wafer equates to
R=10 mmcm*140 m/(3*7 mm.sup.2)=0.7 m.

(25) With typical cell currents around 0.5 A, this results in a negligible voltage loss below 1 mV. The high conductivity of the Germanium substrate is thus exploited to establish (+) front side contact points 304 for the rear contact 8 on the cell as the main feature of this design.

(26) Other approaches of the prior art, for example for Si solar cells with a Si wafer of much higher resistance, require an additional conductive member at the cell edge to establish the front side contacts. Most notably this is suggested in U.S. Pat. No. 3,527,619 A. Although the cell emitter including the p-n-junction is etched away in this prior art approach as well, the sole purpose of this etching is to avoid the necessity for an additional insulating layer between the wrapped around conductive surface and the cell edge; without this etching the cell would be short circuited at the cell edge in this prior art approach.

(27) The rear side metallization at rear side contact 8, which is typically equally thick as the front side metallization at front side contact 9 to ensure the same properties at the contact pad location, might be in addition reduced in thickness, depending on the amount of additional ohmic losses tolerable. The antireflection coating 12 in the (+) contact area 302 is optional.

(28) With respect to the spatial arrangement of the (+) contact pad location, there is complete flexibility. In a non-rectangular cell, e.g. a cell with cropped corners, the cropped corner region can be a preferred location of the contact pads or welding pads. At these locations the possibility exists to use part of the circular wafer region unsuitable as solar cell itself for the contact pad and thus minimize the loss in additional cell area.

(29) In FIG. 5 a spatial arrangement of the additional (+) contacts 400, 401 on the cell front side together with an adapted layout of a cover glass 403 is shown.

(30) A more conventional placement of the (+) contacts 400 for a 84 cm.sup.2 sized triple junction cell with flute () contact pads 10 and an integrated diode 102 is illustrated in FIG. 5. For interconnection of the diode of the neighboring cell, a fourth (+) contact 401 is required. Assuming that 10 mm.sup.2 of active cell area are etched away for a 7 mm.sup.2 contact pad, which ensures sufficient distance of the contact pad metal to the open p-n-junctions, 1.3% of the cell area is lost due to the placement of the (+) contacts on the cell front side. Of course the horizontal collecting gridline 100 has to be shaped around (see at 402) the contact pad required for the optional diode contact 401.

(31) The cover glass 403 is adapted for this top contact solar cell design such that this cell is still compatible with the state of the art sequential manufacturing flow. As already outlined in the description of the prior art, the cells have to be protected by a cover glass to survive the radiation environment in space. For example in the geostationary orbit characterized by a high dose of low energy protons a cell would suffer severe damage within weeks if even the smallest cell area were to be left uncovered. Therefore the entire active cell area as well as the integrated diode has to be covered up to the very edge in the top contact solar cells when the cells are designated for space use. This requirement, however, does not apply to the (+) contacts on the front. Since no active cell area is present at these locations, these can remain completely uncovered.

(32) So the basic cover glass layout in conjunction with the top contact cell design is identical to the standard cover glass geometry with additional cut-outs 404 matching exactly the location and size of the (+) contact pads 400, 401.

(33) In FIG. 6 an enlarged detailed cross-sectional view through the solar cell is shown wherein the cover glass at a (+) contact location is illustrated. The cover glass 403 overlooks at 405 the active cell area 406 completely and thus ensures complete protection of the active cell from particle radiation. Similar as in the standard manufacturing flow outlined before, interconnectors are attached to the () contacts first. Then the cover glass 403 is bonded with transparent silicone adhesive 208. The cut-outs 404 leave ample space around the (+) contact pads, e.g. for welding electrodes 407 such that the (+) interconnector 408 welding can be performed after cover glass bonding.

(34) In this way, the top or front contact cell and subsequently the top or front contact solar cell cover glass unit (CIC) is compatible with the state of the art manufacturing flow and allows for a range of design, measurement and manufacturing features of the photovoltaic assembly (PVA) that are also part of the present invention.

(35) FIG. 7 shows examples of interconnector shapes adapted to the front contact solar cell according to this invention. It is to be noted that the dimensions are not to scale: the cell to cell distance 501 is typically 5-10 times as large as the cell height 502.

(36) Since the contact pads 304 and 10 of two adjacent cells are roughly on equal height, merely differing by the height of the epitaxy 500 that was etched away for the (+) contact, no S-shaped interconnector loop is required anymore. The shape of the thermal expansion loop can be rather confined to the space that is defined by the inter cell gap 501 (i.e. the distance between two adjacent cells in a string configuration) and the height of the cell 502. Examples for proposed shapes are a U-shaped interconnector geometry 503 or a W-shaped interconnector geometry 504 as shown in FIG. 7. Other shapes are possible which are all characterized by the fact that they have no element above the height of the solar cell 502 at all. In this way the cell to cell interconnector 503, 504 is completely protected from mechanical damage, like bending, during all solar array manufacturing and cleaning steps. This is an important advantage, since several interconnector concepts use fairly soft and thin metal foils, which are capable of surviving a large number of thermal cycles if their designed shape remains undistorted. Accidental changes in shape introduce stress concentration points that dramatically reduce the lifetime of the interconnector. The completely protected shape according to this invention thus has the potential of being able to use some shape sensitive interconnector materials for mission requiring a high number of thermal cycles.

(37) Care has to be taken that the end 505 of the interconnector 503, 504 does not come in contact with the open p-n-junctions 506 of the cell. Therefore the end of the interconnector can be optionally bend upwards by 90 (as shown at 507) which mitigates any possibility for it to touch the p-n-junctions 506, since the interconnector is stopped by the cover glass 403 and is thus distant from the side wall of groove 500 which accommodates contact 304 like in the example of FIG. 4.

(38) It is immediately obvious to persons skilled in the art that with this solar cell assembly design, individual solar cells as well as individual diodes can be easily measured electrically even in higher assembly stages, e.g. within a string or on a photovoltaic assembly, by placing measurement electrodes on the appropriate (+) contacts on two adjacent cells. In contrast, this is not possible in the standard prior art design where all front side contacts are covered and the rear side contacts are not accessible.

(39) An even more important consideration is the interaction of the solar cells in a solar array with energetic ions emitted by ion thrusters used for example for attitude control of the satellite. Typically Xenon ions with energies around 100 eV are incident on the inner panels of the solar cells. The tolerance of an array to such conditions is determined above all by the erosion occurring on the solar cell interconnectors. Interruption of those separates the electrical network and results in the loss of entire strings. By confining the interconnector to the inter cell gap as outlined above, the view factor to the Xenon ions is greatly reduced and thus the critical dose of Xenon ions resulting in an unacceptable erosion of material by sputtering is increased.

(40) A further protection is possible, as illustrated in FIG. 8, by bonding of an additional cover glass piece 600 by e.g. silicone adhesive 601 on the open (+) contact pads 304 after the interconnector 503 has been attached. This cover glass piece extends into the inter cell gap 501 and protects the interconnector 503 below from the energetic ions. The contraction of the inter cell gap 501 due to operating temperatures in orbit above the manufacturing temperature of the array is taken up by the flexible cover glass adhesive 601 and a gap 603 on the inner end of the (+) contact.

(41) Since the attachment point 604 of interconnector 503 and contact pad 304, e.g, the weld spot, is located underneath the cover glass, the electrically relevant portion of the interconnector is protected. Due to the small dimensions of this additional cover glass piece, which is understood to cover the entire width of the interconnector, e.g. 82 mm, the bonding process is most convenient if it is performed in an automated way.

(42) In some solar array designs the front side of the cover glass has to be equipped with a conductive coating 700 as shown in FIG. 9. In state of the art cover glass designs, this conductive coating is connected to a metalized region on the cover glass side 701. The cell design of this inventive example provides a very easy grounding method of these cover glasses, if the metalized region is positioned in the cut-outs of the cover glass around the (+) contacts. Basis is the interconnector with the 90 bend 702 described with respect to FIG. 7. The upright portion 703 is connected to the metalized cover glass edge 701 by a conductive silicone adhesive 704, like the one available under the trade names NuSil CV2646 or NuSil CV1500.

(43) The interconnector is usually not composed of a continuous sheet, but rather consists of individual grid fingers 705, which are contacted separately at a contact position 706 to the contact pad for redundancy reasons. In the area of the 90 bend 707, the interconnector becomes continuous again in the proposed design, before ending again in individual fingers 708. The space between the individual fingers 709 in the upright part of the interconnector finger allows the conductive adhesive to contact the metalized glass, whereas the continuous part in the area of the 90 bend 707 prevents the adhesive from touching and thus shorting the open p-n-junctions 506.

(44) The solar cell assembly design with the (+) contacts on the front has in addition the advantage of providing a better repair method in case a solar cell has to be replaced within a string of solar cells due to cell damage. The solar cells in a string are bonded with silicone adhesive 800 to the carbon fiber support structure 801. In case of damage to one solar cell 802, this cell has to be removed and replaced by a new one. In the prior art this is can only be achieved by welding the interconnectors of the replacement solar cell to the interconnectors of the two neighboring solar cells of the solar cell assembly. While this repair method is still compatible with the new design, the top contact solar cell has the possibility of an improved repair method in which the interconnector is not affected by the repair process at all. This has the advantage, in contrast to the prior art, that its fatigue behavior is not changed.

(45) This repair process which is enabled by the inventive design of the solar cells and solar cell assemblies is illustrated in FIG. 10. The interconnector 803 is removed from the (+) contact of the cell 804 to the left by separating the original contact section 604 from the contact pad 304 as is shown at 805. Care is taken in this case, that the contact pad 304 is not damaged, i.e. that all damage is contained in the interconnector 803 which is not required anymore. Once a new solar cell has been bonded to the structure instead of solar cell 802, its interconnector is again welded to the contact pad 304 of cell 804 at a slightly offset location 806.

(46) The interconnector 807 to the solar cell 808 to the right is removed in a similar fashion from the contact pad 304 of cell 802 as is shown at 809. In this case, however, care is taken during separating the original contact section 604 to contain all damage in the contact pad 304 and not in the interconnector 807. Once the new solar cell has been bonded at the location of solar cell 802, the interconnector 807 is welded to the contact pad 304 of the replacement cell at a slightly offset location 810.

(47) In this way, the electrically active part of the left hand side interconnector 803 and the right hand side interconnector 807 remain completely unaffected by the repair process. The only prerequisite of this repair method is that silicone adhesive 800 is present underneath the location of the respective contact pads of solar cell 802 and solar cell 804 to support the cell during the contacting (e.g. welding) operation.

(48) As outlined previously, the interconnection of single CICs into a string is hard to fully automate in the prior art, since the CICs have to be turned upside down and the interconnectors have to be placed at the respective rear side positions. In the frame of the present invention, the CICs can be placed directly onto a suitable positioning plate 900, on which the exact cell positions are marked by appropriate grooves 901 or similar fixations.

(49) As illustrated in FIG. 11, a CIC 902 is laterally positioned. The next CIC 903 in a solar cell array of string form is automatically placed (arrow 904) at its position which simultaneously places its interconnectors 905 at the correct welding pad position 906 of the CIC 902. Merely the diode interconnector 907 of CIC 902 has to be temporarily moved out of the way (arrow 908) during the placement of CIC 903. This can be accomplished easily by compressed air (nozzle 909) or any other device that bends the diode interconnector 907 upwards. The contacting of the CICs e.g. by welding with welding electrodes 910, can then also be performed automatically.

(50) The welding electrodes 910 can in addition serve to fine adjust the interconnector positions automatically (arrow 911) with the help of a camera based technique (machine vision). The positioning foil is then placed on top of the string and the further solar cell array manufacturing process continues.

(51) Finally the top contact solar cell opens up the possibility to integrate the solar cell array in one step by an automated manufacturing sequence directly on a support structure 1000, e.g. the carbon fiber/honeycomb panel as shown in FIG. 12.

(52) In this manufacturing flow, silicone adhesive is first applied on the rear side of the individual solar cells 1001, preferably by a dispense technique with dispenser 1002. This technique together with room temperature vulcanizing silicone adhesives (RTVs) which are typically used in solar arrays for space, is hard to apply on larger panels, since the viscosity of the adhesive changes with time and leads to vastly different adhesive conditions during lay down of the first compared to the last string on an large area solar array panel. Applied to single solar cells, however, these problems do not arise.

(53) The adhesive pattern 1003 can have any shape, however, an advantageous requirement here is that adhesive is present underneath all front side contact pad locations 1004. The solar cells 1001 are turned upside down and automatically placed onto the structure 1000, and a suitable device, e.g. a metal stamp 1005, cures the adhesive underneath by applying pressure as well as temperature. Typical conditions are T<100 C., for less than 1 min and pressures of less than one bar.

(54) As soon as there are two solar cells present on the panel, the interconnectors 1006 are placed between the solar cells and welded, e.g. by welding electrodes 1007, to the contact pads. Finally the cover glasses 1008 are bonded to the cells, again after the adhesive has been applied onto it, e.g. with a dispenser 1009. The adhesive can thus be applied by a dispense technique as well, however, it has to be applied as continuous layer in the active region of the solar cell and has to be free of voids in order to minimize transmission losses. In particular this manufacturing method allows covering a plurality of cells 1010 at once with the same, large area cover glass.

(55) Optionally, only the adhesive spots 1004 underneath the front side contact pads can be cured first. The interconnection 1006 to the nearest neighbor solar cells is performed subsequently. By placing a contact probe on two front side contact pads of opposite polarity, a check of the mechanical and electrical integrity of the solar cell and the diode is performed, e.g. by electroluminescence imaging and light I-V measurement. Only then the remaining adhesive 1003 is cured thereafter. This has the advantage that the cell can be easier removed in case damage to the cell has been detected, e.g. caused by the welding operation.

(56) The present invention thus provides a top contact solar cell. The provision of an electrical contact, originally in the prior art present on the cell rear side, is placed on the cell front side. This inventive technique is suitable for all multi-junction solar cells, having several p-n-junctions stacked on top of each other and a bottom junction of sufficient mechanical stability and conductivity. The rear side contact is established by etching away on a localized area all p-n-junctions, including the emitter of the bottom p-n-junction. The basis of the bottom cell is then equipped with an ohmic contact and establishes a conductive path between cell rear side and front side.

(57) The top contact solar cell can be equipped with a cover glass having cut outs around the contacts of the rear side doping provided on the front side of the cell. With these solar cells with integrated cover and interconnectors a solar cell assembly can be manufactured in a manufacturing process which is compatible with the photovoltaic assembly manufacturing processes of the prior arts that existing machinery can be used also with the solar cells according to the invention.

(58) Reference numerals in the claims and in the description are provided only for better understanding the invention and shall not limit the scope of the invention which is defined by the claims only.

(59) It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.