Title of Invention

SOLAR CELL ARRAY AND METHOD FOR CONNECTING A SOLAR CELL STRING

Abstract

The invention relates to a solar cell assembly comprising at least one first solar cell and at least one discrete protective diode (101) that is connected to the solar cell. The aim of the invention is to comprehensively protect a solar cell, a solar cell composite or a string of cells by means of one or more protective diodes, without resorting to the use of the material of the solar cells. To achieve this, in addition to a front and a rear contact (13, 15), the protective diode comprises an additional contact (14) that is placed at a distance from the front contact and is electrically connected to said contact via a p/n junction. A connector leads from the additional contact to a second solar cell, the latter in turn being connected to the first solar cell in a string.

Full Text

Description Solar Cell Array and Method for Connecting a Solar Cell String Tha method pertains to a solar cell array comprising of at least one solar cell with photoactive semiconductor layers running between front contact and back contact, as well as at least one discrete protective diode connected to the solar cell with a substrate made of semiconductor material of a first conductivity, in a layer formed on the surface region of the substrate or on the surface region of applied layer of second conductivity, a first metallic contact on the layer of the second conductivity and a second metallic contact arranged on the substrate, whereby connectors go out from the first and the second metallic contact for connecting the protective diodes. The invention further pertains to a method for connecting a solar cell string. The focus of semiconductor-solar cell-production, on account of the significantly higher degree of effectiveness in the conversion of sunlight into current, from the cost-effective silicon to III-V-semiconductor-solar cells (III = elements of the IIIrd group of the period system like Ga or In; V=elements of the Vth group of the period system like As or P) that are significantly costlier in material and production. In the corresponding solar cells production of the photoactive layers takes place in a cumbersome crystalline epitaxy by separating mostly a large number of different layers single-crystalline on a single crystalline germanium-disk (Ge-substrate wafer) that is comparatively much more expensive than silicon. This epitaxy wafer after layer separation contains all elements required for conversion of sunlight. After production they are then further processed into solar cells in usual photolithographic method used in semiconductor technology and etching, metallization- and anti-reflection damping etc. and ultimately cut-off from the wafer. By suitable choice of the layers and their composition of various III-V-materials, for different wavelengths of life different sensitive layer sequences are separated above one another and processed into so-called "multi-junction"-solar cells, which explains the high degree of effectiveness of a cell. The current state of application is triple cells, i.e. three sub-cells whereby two are made of epitactically grown III-V-material and the third one consists of the 2 actively mixed Ge-substrate. Generally nowadays III-V-solar cells are produced from round wafers (substrates) of 100 mm diameter (4"-wafer). A triple cell is a pre-time cells with three solar cells (3 cells (sub-cells) layered above one another and serially connected with different spectral sensitivity for enhancing the total effectiveness degree of triple cells; "multi-junction" cell: cell with several sub-cells). Suitable multi-junction solar cells in the form of triple cell could for example consist of a Ge- bottom-cell formed on the Ge-substrate, a GaInAs-centre cell and a GaInP top cell. The price of the epitaxy wafer is actually more than 20 times the price of a silicon wafer of the same size for producing silicon solar cells. On account of the high price of the starting material in the form of epitaxy wafer for producing III-V-solar cells, for reducing the wastage in the solar cell manufacturing process the number of processed steps are kept as low as possible in order to thereby avoid further cost increase in the end price of the cell. On account of the greater specific weight of III-V-compounds and germanium as compared to silicon (approx. factor 4) and the high transportation costs of satellites into space, the III-V- wafers are thinner than the usual ones in standard semiconductor technology (e.g. IC- production), whereby the failure risk in case of increase production complication is even more enhanced, especially as the Ge-substrates are much more brittle than Si-wafers. In order to keep the complication of joining to cells to strings (unit of serially connected solar cells to a desired working voltage on a panel; panel = Paneele; surface (wing) fitted with solar cell as indicated in satellite) as less as possible and at the same time not to get too short strings, as the working voltage of the modern III-V-cells is several times that of Si-cells, relatively large cells are desired. At the same time, the high price of the epitaxy wafer makes a desirable to use as much surface of the wafer as possible for the cells. Therefore, due to cost reasons cells of approx. 8 cm x 4 cm with two so-called cropped corner cells have become usual, whereby from a 4"-wafer two cells are obtained. By separating the corners a larger portion of the wafer surface can be used for the cell than in case of purely rectangular cells. In case of a qualitatively inadequate wafer edge of 2 mm width, a wafer of 100 mm diameter, one obtains a surface of 72.4 cm2. Two rectangular cells can attain a maximum surface of 3 6.79 cm x 6.79 cm = 46.1 cm2 (64%), whereas with two cells of 8 cm x 4 cm edge length with cropped corners of say 1.35 cm one obtains a surface of 60.34 cm2, so that 83% of the wafer face can be utilised. Due to reasons of geometry these cells do not completely fill up the surface of a panel: at the corners between the cells there remains a triangular surface not utilised for light conversion. In large-faced semiconductor diodes like the ones forming solar cells, high-ohm, local, small dimensioned electrical connections through the p/n junction of the semiconductor material (micro-short circuits) are often unavoidable, like e.g. through surface damages during production or especially in epitaxied p/n junctions as in III-V-solar cells through doping substance accumulations, e.g. in crystal damages (e.g. damages on account of slightly varying crystal screens). These micro-short circuits that do not or only very slightly reduce the function of the diodes as solar cells (p/n-junction in flow direction), could lead to destruction of the cell in the string during operation of the cell in locking direction. In case of locking p/n-junction the solar current can get pressed from the high string voltage U with the power N=Us.Is on account of the high-ohm micro-short circuits. This can locally lead to strong heating, un-doping and low ohm (strong degeneration of the semiconductor) and ultimately to destruction of the cell. Protection against the destruction can be effective by a so-called bypass or protection diode, i.e. an anti-parallel to the diode connected to the p/n-junction of the shadowed cell which is poled in flow direction when the p/n-junction of the cell locks and allows the current to pass at a voltage Ud that corresponds to the characteristic curve of this diode in flow direction with this current. The voltage Ur at the end of the string gets reduced due to the missing voltage Um of the cell and the flow voltage of the diode - Ud: Ur=Us - Um - Ud. In not shadowed condition of the cell the p/n-junction of the protective diode blocks the current flow through the same at a blocking voltage that merely conforms to the flow voltage of the allied solar cell. Usage of protective diodes for the cells to prevent destruction of individual cells in the string with shadowing in the form of anti-parallel diodes electrically connected to the cells is actually known. For III-V-cells there exists as solution monolithic integrated protective diodes, i.e. diodes that are produced from similar elements like the cells already during production of the epitaxy directly on the wafer in mostly additional process steps and in additional technology steps 4 processed into such while produced into cells and are then also situated on the cells (refer to DE-A-3 826 721, US-A-2002/0179141). A basic disadvantage of these solutions is that the active surface of the cell gets reduced. The protective diodes are therefore generally selected as small as possible in their dimension. In this way their voltage during current flow and hence their power gets enhanced. This can lead to their destruction in the long run or - as the protective diode is part of the cell - lead to locally undesirable strong heating of the cell. As monolithic diodes required additional effort even at the wafer level, i.e. additional epitaxy layers and additional technological processes during production of the cells, these constitute an additional cost factor that is not negligible. As the monolithic diodes can only be made of screen-adapted III-V-material, only a very small freedom in choice of the type of diode (only III-V-diodes with high flow voltage) is possible. Therefore, a discrete diode that can be produced independent of the production of the cell and hence also offers more material freedom, should be preferred. This has the additional advantage of being selected and tested independent of the cell, so that a diode already damaged during production does not simultaneously mean an expensive unusable cell. Fixing discrete diodes on to the solar cells as alternative to the monolithic integrated protective diodes generally calls for additional effort on the part of manufacturers of solar panels while fixing. This applies particularly for rectangular solar cells that completely fill up the surface of the panel, so that for fixing the protective diodes one has to deviate into the third dimension (leads and diode below the cells). This means a high degree of effort and complication in the panel manufacture. Besides, the weight of the panel will increase on account of the additionally required long lead cable. From the document US-A-4, 481, 378 we can see a solar cell module with serially connected solar cells and protective diodes, whereby respectively one protective diode is respectively connected anti-parallel to one cell. The protective diodes are connected to adjacent cells with the back sides and arranged in the intermediate spaces between the solar cells. 5 According to the document US-B-6, 563, 289 a corner is cropped from an originally rectangular solar cell and connected as protective diode with opposite pole to the solar cell. A solar cell array according to the document US-B-6, 353, 176 comprises of solar cells with recessed corners into which protective diodes can be arranged. A solar cell array with current limiting protection according to US-B-6, 034, 322 comprises of rectangular cells with an inclined edge at one corner into which a triangular diode is arranged for protecting the solar cell. Only such connectors are used that allow a movement in the plane of the solar cells. According to the document US-A-2003/0029494 protective diodes are integrated in a solar cell string, whereby one connector leads from the front side of the protective diode to the back side of an adjacent solar cell that is connected with the front side of the solar cell to be protected serially in the string. The back side contact of the protective diode leads to the back side of the cell to be protected. It is the task of this invention to further develop a solar cell array of the type described above in such a way that to an adequate extent a solar cell or a solar cell bunch like string can be protected by one or more protective diodes, without having to compulsorily fall back on the materials of the solar cells themselves. Furthermore, a smooth connection between the protective diodes and the solar cells should be possible, whereby at the same time a huge increase in weight should be avoided. This task is fulfilled according to the invention, in that the second contact directly contacts the substrate of a protective diode and is arranged beside the first metallic contact at a distant to it and is connected to the first metallic contact electrically through a p/n-junction. The first or the second metallic contact can be connected with the back side of the second solar cell and the third metallic contact can be connected to the first solar cell. Also, the protective diode is connected through the first or second metallic contact anti-parallel to the first solar cell through the second solar cell. A solar cell array is suggested that comprises of a discrete of protective diode, which with respect to the front-side region is structured in such a way that apart from the n/p-or p/n- 6 junction of the protective diode a direct ohm contact is generated between the second metallic contact and the substrate of the protective diode, in order to on the one hand allow an electrically conductive connection between solar cells and on the other hand to connect the protective diode anti-parallel to the solar cell to be protected. According to the invention, the task of protecting a solar cell in the string is largely fulfilled by an anti-parallel connected discrete diode made of a semiconductor body of first conducting type (substrate), in which on the front side beside the first metallic contact on a semiconductor region of second conductivity type and at a distance from it on the semiconductor of the first conductivity type electrically separated by the p/n-junction a second metallic contact is foreseen that is electrically connected directly to the substrate. Depending on the type of solar cell and choice of conductivity type of the substrate of the diode, the back side of the solar cell to be protected can be electrically connected to the diode through the first or second contact by means of connectors, and to the second respective first metallic contact of the diode the back side of the cell to be protected is connected in the string directly to the subsequent cell, which on its part by means of the connector is electrically connected to the string for serial switching of the solar cells with the front side of the previous cell to be protected, whereby the diode in the group/bonding forms a protective diode arranged anti- parallel to the solar cells to be protected. In an extension it is foreseen that the first and second solar cell are connected through at least two protective diodes and a third metallic contact of one of the first protective diode is connected to the back contact of the second solar cell as well as to the second metallic contact of the second protective diode whose third metallic contact is connected to the front contact of the first solar cell. One thus obtains a simple connection of the solar cell among one another and at the same time connection of the protective diodes to the solar cell to be protected. On connecting to solar cells through two protective diodes one of the protective diodes can be resigned in such a way that the second metallic contact is connected to the first metallic contact and the surface region of second conductivity stretches below the first and the second metallic contact. In order to enable a simple connection of the connectors going out from the first and second protective diode and connecting these to one another, according to a further suggestion of the 7 invention it is foreseen that a connector going out from the second metallic contact of the first protective diode along with a connector going out from the second metallic contact of the second protective diode protrudes above the front side of the first and second solar cell or their cover glasses and are joined outside the cover glasses preferably by welding or soldering. Irrespective of whether the solar cells are connected through one or more protective diodes a suggestion of the invention foresees that the first solar cell and/or the second solar cell in top view has a rectangular shape with sloping corners and the at least one protective diode runs in the region of one of the sloping corners. In this way one obtains an optimum utilisation of the panel surface, whereby simultaneously a simple switching/connection of protective diodes and solar cells is possible. It is particularly foreseen that several solar cells connected into a string are connected through corresponding protective diodes. In each sloping corner one protective diode can be arranged. Protective diodes and solar cells lie in this case in one plane. According to the invention it is suggested that the protective diode has a triangular geometric shape in top view. It is particularly foreseen that the protective diode has the geometrical shape of a triangular column. In a solar cell with quadratic surface with bevelled corners and an edge position of 8 cm, before the corners are removed the protective diode should have a basic face F of preferably approximately 0.7 cm2≤F ≤ 1 cm2, particularly approximately 0.8 cm2≤F ≤ 0.9 cm2. The invention further pertains to a method for switching/connecting a solar cell string that is characterised by the following process steps: - Arrangement of the solar cells with the backside on a base support; - Connection of front side contacts of the solar cells with first connectors; - Fixing of one or more transparent covers on the front side of the solar cells; - Turning of the solar cells; - Connecting the first and second solar cells to a string through the first connectors; 8 - Fixing of protective diodes in the free spaces between the solar cells; - Connecting the protective diodes with the solar cells; and - Connecting the thus created string to a base support. Before fixing the protective diodes adjacent solar cells are connected in series through the first connectors. In an extension it is foreseen that protective diodes are arranged with their backside contacts, i.e. third metallic contacts in the front side region of the solar cells and adjacent solar cells are connected in series through respectively one protective diode with simultaneous anti-parallel connection of the protective diode to one of the adjacent solar cells. The following process steps are foreseen: a) Arrangement of the solar cells with the backside on a base support; b) Fixing of protective diodes in the free spaces between the diodes; c) Connecting front side contacts of the solar cells to the second contacts (backside contacts) of the protective diodes running front-sided in the string; d) Fixing of one or more transparent covers on the front sides of the solar cells; e) Turning the solar cells; f) Connecting the first and third contacts (front contacts) of the protective diodes running back-sided in the string with back-sided contacts of adjacent solar cells; and g) Connecting the thus created strings to a support base. The string can be turned before connecting to the base support. The invention further foresees that two protective diodes are arranged between two adjacent solar cells, out of which one protective diode with its backside contact (third metallic contact) and the other protective diode with its front side contact (first and second metallic contact) are arranged in the front side region of the solar cells. The adjacent solar cells are connected in series through the two protective diodes and the protective diodes are connected/switched through contacts running in the region of the backsides of the solar cells. Second connectors that are connected outside the solar cell strings can go out from contacts of the protective diodes running in the region of the backsides of the solar cells. 9 The invention also suggests a diode with a substrate made of semiconductor material of a first conductivity, a layer formed in the surface region of the substrate or a layer of second conductivity applied on the surface region, a first metallic contact on the layer of second conductivity and a second metallic contact near the first metallic contact at a distance from it and electrically insulated and connected through a p/n-junction, which is directly contacted with the substrate of the protective diode, for using as protective diode in a solar cell array. The p/n-junction in the protective diode can be replaced by a Schottky contact. Further details, advantages and features of the invention can be obtained not only from the claims describing these features - individually and/or in combination - but also from the following description and the design forms given in the drawing. The following are shown: Fig. 1 A first design form of a protective diode; Fig. 2 A further protective diode; Fig. 3 An alternative design form of a protective diode given in Fig. 1 with current circulation; Fig. 4 A principle depiction of two solar cells with bevelled corners produced from a semiconductor wafer; Fig. 5 A solar cell string in cross-section and in cut-out, Fig. 6 A cross-section through a panel with solar cells connected through protective diodes; Fig. 7 Rear-view of a cut-out of a string with protective diodes of different geometrical shapes; Fig. 8 A further design form of a panel in cut-out with solar cells connected through protective diodes; Fig. 9 Light incidence side cut-out of a string connected by protective diodes; Fig. 10 The depiction as shown in Fig. 9, however from the rear side; Fig. 11A principle depiction of a solar cell with bevelled corners; Fig. 12 A solar cell with bevelled corners and protective diodes arranged in them; Fig. 13 A cross-section to a panel with solar cells respectively connected through two protective diodes; 9 10 Fig. 14 An extension of the solar cell connections through protective diodes as shown in Fig. 13; Fig. 15 A principle depiction of a first process for connecting/switching solar cells. On the basis of design examples given in the figures the shape of discrete protective diodes for solar cells and their integration into a solar cell string or panel is described in more details below. Same elements are denoted by same reference signs or corresponding reference signs. Fig. 1 shows a protective diode 101 as per the invention in a first design form, which is made of a semiconductor material like silicon, germanium or a material from the IIIrd and Vth group of the period system like GaS or GaP or GalnAs or GalnP. The main body, i.e. the substrate 11 can be doped p-conductive. In a surface region, namely in the region of the front side of the protective diode 101a n-doped region 12 is designed up to the surface, which along with the substrate 11 forms a good backward blocking n-/p-junction (n-up-diode), that is the actual protective diode. As indicated clearly in the depiction in fig. 1, the n-doped region stretches only over a portion of the top side of the substrate 11. The n-doped region is covered in the outside by a metallic contact 13. This is designated as first contact. Along the backside stretches an electrically conductive contact 15 with the conductivity of the substrate 11 and is in ohm contact with it. This contact is designated as third contact. At a distance to the first contact 13 an electrically insulated from it a further metallic contact 14 is applied on the top side of the substrate 11, i.e. outside the n-doped region 12; this contact has an ohm contact with the substrate 11. This contact is designated as second contact. Through the electrically conductive first and second contacts 13, 14 on the front side of the protective diode 101 and the back contact 15 (third contact) solar cells are connected in the manner described below. A further protective diode 102 can be seen in fig. 2. Here the n-doped surface region 12 stretches mostly along the entire top side. The n-doped region 12 is then covered by the first metallic contact 13. Otherwise the protective diode 102 structure-wise corresponds to the protective diode 101. 11 In practice, for improving the properties of the protective diodes 101, 102 insulation layers and/or passivasion and/or metallization can be applied on the semiconductor or the semiconductor layers 11, 12 or even on parts of the metallic contacts 13, 14, 15. The dimensioning protective diodes 101, 102 is ideally selected in such a way that these are arranged in a string in regions that are not covered by solar cells, that are preferably designed as cropped corner cells, i.e. solar cells with bevelled or cropped corners. The protective diodes 101, 102 should be arranged in the distant corners of the solar cells particularly in the region of solar cells partitioned from one another, in order to connect/switch the solar cells in the manner described below. Instead of protective diodes 101, 102 with n/p-junction, as n-up-diodes, even protective diodes with crossed doping can be used for corresponding doped solar cells. In this case the doping is crossed, i.e. p - n and n - p. Fig. 3 shows a further design form of a protective diode 20 as per the invention that in principle corresponds to the protective diode 101. Area wise, in the protective diode 20 the p/n-junction can first be produced on one side of the surface covering the entire area. As example, one can mention diffusion or ion-implantation of a suitable doping substance or epitactic separation of layers and subsequent removal (etching out) of a portion of the doped region 22 opposite to the substrate 21. The protective diode 20 shown in fig. 3 is one such diode of the type p-up, where a metallic contact 23 is applied on the p-conducting layer 22 as the first contact. At a distance from it and electrically insulated from it an ohm contact to the n-conducting substrate 21, the second metallic 24 is arranged. Along the back side of the substrate 21 stretches the third metallic contact 25 or back contact. On the basis of the protective diode 20 it should be clear that protective diodes of the above described type, i.e. protective diodes 101, 102 and 20, particularly those shown in fig. 1 and fig. 3 can be advantageously used in various applications. For this, the electrical circuit (StKr) including possible terminal points K1, K2, K3, K4 and the elements electrically active in the interior are shown, i.e. the diodes (P (p-up)), the resistances R1 and R3 that run between the terminals K1 and K2 or K4 and K3, as well as the resistance R4, which in the design example runs horizontally through the n-conducting substrate 21, and the resistance R2 that prevails in the backside contact 25 (third contact). 12 A rough estimation of the maximum voltage loss ∆V in the diode 20 in addition to the voltage drop at the p/n-junction on account of the voltage loss in the inner resistances R1 to R4 for an assumed current of I = J A can be calculated from ∆V = R . I with R = [(R1+R2+R3). R4]/[ R1+R2+R3+R4]. The estimation was conducted in such a way that the calculation resistance are always greater than they would actually be in reality and the voltage loss would accordingly be lesser in reality. As calculation example one can take a diode that corresponds to the diode 101 and is produced from 20 mΩcm Si-substrate (p1 = 2E-2Ωcm). The shape corresponds to that in fig. 6, the surface of the diode 101 is F1 = 1 cm2, p-(14) and n-(13) region is respectively Fn = Fp = 0.5 cm2, where the double face of the diode bottom side is not taken into account. The thickness of the diode 101 is D1 = 150 urn = 0.015 cm, the length of the separating edge B1 between the contacts 13 and 14 is B1 = 1.2 cm, its distance S1 is S1 = 100 µm (0.01 cm), the thickness B2 of metallization (p2 = 1.6E-6Ωcm) from Ag: B2 = 10 µm (0.001 cm), the distance A1 between the connectors 40a and 40b is A1 = 0.5 cm. The estimation is done with the help of the formula for calculation of resistances from specific resistance p and external geometry of the resistance, that is length L and cross section F : R = p . length L/cross section F. For R1 and R3 (vertical resistance in the substrate 21) the following estimation is valid: p1 = 2E-2Ωcm silicon for both R1 and R2 we have: area F = Fp (14) = Fn (13 = 0.5 cm2, length L = D1 =0.015 cm R1=R3 = 1.5E-4Ω For R2 in contact metal made of Ag: thickness D2 = 10 µm (0.001 cm), p = 1.6 E-6 Ωcm F can be calculated from F = D2 . B1 = 0.0006 cm . 1.2 cm = 7.2 E-4 cm2, Length L = Al = 0.5 cm R2 = 6.6 E-4Ω For R4 (horizontal resistance in the substrate): pl= 2E-2Ωcm silicon F determines itself from the thickness Dl and Bl to F = Dl . Bl = 1.2 cm, Length L = A1 =0.01 cm R4=1.1E-2Ω 13 The voltage loss AV = R . 1: ∆V = [(R1+R2+R3)*R4]/[ R1+R2+R3+R4]* ∆V = 0.88 E-3V = 0.88 mV. In practice, this voltage drop can be made even lesser. As in the case of application of a silicon diode the voltage drop at the p/n-junction is approx. 0.68 V (680 mV), therefore the voltage drop on the inner resistances of the protective diode make only a very small additional contribution. On the basis of the following explanations the use of protective diodes as per the invention is explained in more details under consideration of standard connecting techniques of solar cells. The design of a solar cell 30 favoured now a days with cropped corners 32 made of III-V- material and on the base of an epitaxy wafer of 31 to 100 mm diameter is schematically shown in fig. 4 from the light incidence side. The metal current collecting bars 33 with the contact faces 34 for fixing the electrical serial connections (connectors) between the cells 30 in the string lie on the shorter side of both longer sides limited by both cropped corners 32 that immediately bordered against the cells connected serially in the string. For almost optimum utilization of the wafer face the edge lengths a, b, c of the cell 30 are for example a = 8 cm, b = 4 cm and c = 1.35 cm. In this case, on the string plane at an angle of 45° between the edges b and c there remains a triangular face not used for converting light with edges of lengths Ld = approx. 0.95 cm/0.95 cm/1.35 cm, i.e. a face of Fd = approx. 0.9 cm2. Fig. 5 shows in cross-section and in cut-out purely schematically a possible connecting type from cell to cell and cell to diode, whereby the last mentioned corresponds to the type shown in fig. 2. For the sake of clarity the current flow diagram has also been drawn in and is marked with 4b7. The solar cells 30a 30b are once of the triple type, where for example on a germanium substrate a Ge bottom cell and on it a GalnAs centre cell and finally a GaInP top cell are applied which are separated by tunnel diodes. To this extent however, reference is made to 14 known solar cell types. The solar cells themselves are fixed by a sticker 4b6 on a base 4b5. On the light incidence side the solar cells 30a, 30b and hence also the protective diodes 102 are covered over a sticker 4b3a, 4b3b by means of a cover glass 4b2a, 4b2b. In the design example the topmost semiconductor layer of the cells 30a, 30b is n-conducting (n-up-cells) without any restriction to the principle of the invention. In a usual production method of strings for panels that exercise the function of the carrier 4b5, first the connectors 4bl are fixed on the light incidence side (front side) of the solar cells 30a, 30b to the front side contact faces 34. Then the cover glass 4b2a is fixed with the help of a sticker 4b3a. In this condition the solar cell is also denoted as CIC (connector integrated cell) or SCA (solar cell assembly). The solar cells are then turned around for connecting into a string, so that the backside lies on top. Then the connectors 4b1 are electrically connected to the back side of the bordering cell by welding or shouldering, in the design example the neighbouring cell 30b. At this point of time fixing of a diode 102 as per the invention takes shape very easily, i.e. in the design example a n-up-diode for a n-up-solar cell 30a in a cropped corner of the cell 30a - or in each cropped corner a corresponding diode 102 as per the invention - of the same type, however mirror-symmetric in design. Thus on the p-conducting type, i.e. in the shown case of the n-up-diode on the metallic contact 15, the p-contact, a connector 40b corresponding to the connector 4b1 is fixed and a second connector 40a is fixed on the metallic contact 13 covering the n-conducting region 12, the diode 102 is inserted in one of the cropped corners in order to create electrically conducting connections on the one hand between the back side of the cell 30b and the metallic contact 15 of the protective diode 102 and, on the other hand, between the contact 13 and the back contact of the solar cell 30a through the connector 40a (see current diagram 4b7). On using a p-up-diode the contact 13 and 15 can be switched. The diode 102 can similarly be provided with a sticker 4b3b with a cover glass 4b2b, or the cover glass 4b2a of the cell 30a is designed so big that the diode 102 can be directly pasted in an electrically connected in the above described method. The further sequence of panel creation by applying the string with the help of a sticker 4b6 on the base 4b5 is not tangibly influenced by installing the protective diode 102. 15 For a p-up-cell with principally the same design as in fig. 5, for example, a diode 102 with corresponding opposite doping can be used in the same manner. The use of the diode 101 (fig. 1) can be made even simpler as fixing of connectors on the diode 101 before introducing into the string array is not necessary, as one can see from fig. 6. Fig. 6 shows purely schematically a cross-section through a possible connecting method of cell 30a to cell 30b and the cells 30a, 30b with the protective diode 101. Here too the current flow diagram 4b7 has been drawn in for the sake of clarity. Instead of the diode 101 as shown in fig. 1 also a diode 20 shown in fig. 3 can be installed without deviating from the principle of the invention. The same holds good for the other design examples. The solar cells 30a, 30b are once like those describe in the context of fig. 5, so that reference can be made to the concern designs. Consequently these are, without any restriction to the invention, solar cells 30a, 30b of the type n-up. In the standard production process of string for panels first the connectors 4bl are fixed on the light incidence side of the solar cells 30a, 30b to the front contact 34, then the cover glass 4b2a is fixed with the help of the sticker 4b3, the corresponding solar cells 30a, 30b called CICs are turned around for connecting into a string, so that the back side shows upwards, so that then the connectors 4b1 can be electrically connected to the respective neighbouring cell by welding or shouldering, that is in the design example with the cell 30b. Simultaneously - as already explained - the protective diode 101 is installed which corresponding to the n-up-cell is a n-up-diode and connected anti-parallel. Fixing the protective diode 101 takes place in one of the cropped corners of the cell 30a. If required, a corresponding protective diode can be fixed in each cropped corner, whereby the design is mirror-symmetric. Fixing is even simpler as compared to the shape in fig. 5, as after inserting the diode 101 into the array of the cells 30a, 30b lying beside one another only the connectors 40a and 40b between the metallic layer stretching along the n-doped layer 12 or the first metallic contact 13 with the back side of the solar cell 30a and the electrically conducting second contact 14 running directly on the p-conducting substrate 11 with the back side of the solar cell 30b has to be connected like between the cells. Here too the diode 101 can be provided with the cover glass 4b2b through a sticker 4b3b or the cover glass of the cell 4b2a 16 is designed large enough to directly paste the diode 101 and electrically connected in this manner. The further process sequence of panel creation as well as fixing of the string with the help of another sticker 4b6 on the base is not effective by the installation of the diode 101. The above described process with the significance processed step is shown once again purely as a principle in fig. 15. For a p-up-cell with principally the same design as shown in fig. 6, a diode corresponding in one in fig. 1 can be used with the limitation that the substrate is n-conducting and the doped surface layer is p-conducting. There is further the possibility of connecting the protective diode 101 between the first solar cell 30a and the second solar cell 30b in such a way that the first contact 13 is connected with the back side contact of the second solar cell 30b and the second contact 14 is connected with the back side of the first solar cell 30a. For corresponding connection the p-/n-junction must be accordingly re-doped. Fig. 7 shows in cut-out two part views of a string of cells 30a, 30b with protective diodes 101, viewed from the back side, which are connected to a string. The cell strings are different to the extent that the designs of the connections between the protective diode 101 and the solar cells 30a or solar cells 30b vary from one another. Fig. 8 gives a preferred extension and utilization of the protective diodes as per the invention, which is not only connected anti-parallel to a solar cell but also at the same time serves as a part of the connection between cells bordering one another. The simplified panel production can be obtained from the fig. 8 to 10 and 16, whereby similarly - without any general limitation - the solar cells 50a, 50b to be connected are of the type n-up-cell. Here too protective diode 101 or 20 - ideally in mirror-symmetric design - are used for connecting successive solar cells 50a, 50b, as one can directly see from fig. 9 and 10. A protective diode 101 is respectively electrically connected in a bevelled corner of the solar cell 50a before fixing the common cover glass 5a2 with the help of a sticker 5al by a connector 5a3 in such a way, that the front side of the cell 50a is connected with the bottom side of the diode 101, i.e. 17 the third contact 15 or 25 as shown in fig. 1, running along the front side of the solar cells 50a, 50b to be connected to the string. For this, in the design of the cell 50a contact faces 5a are designed on the edge region of the cropped corner that are connected to the current collecting bars 5a7. The solar cell 50a with protective diode 101 or 20 is then connected by fixing a connector 40a between the second metallic contact 14 or 24 directly contacted with the substrate 11 of the protective diode 101 or 20 and back side of the cell 50b and by fixing a connector 40b between the first electrically conducting contact 13 or 23 arranged on the p- doped layer 12 and the back side of the solar cell 50a and integrated in the string. Further fixing on the panel corresponds to the already given explanations. Fig. 8 is the current diagram 5a4 with the relevant diode and resistances. The connector 40b - as one can see from the process sequence in fig. 16 - can also be fixed before fixing the common cover glass 5a2 between the back side of the cell 50a and the contact 13 of the diode 101. In Fig. 16 one can purely see the principle of the process sequence for connecting the protective diode 101 - and correspondingly the protective diode 20 - with the solar cells 50a, 50b or anti-parallel to the solar cell 50a. Thus the protective diodes 101 are first arranged in the "free" corners of the solar cells 50a, 50b and the front contacts of the first solar cells 50a and the second solar cells 50b are respectively connected with the third contacts of protective diodes 101, generally referred to as back contact. A separate protective diode 101 is allocated to each first and second solar cell 50a, 50b. For this a first connector 5a3 is used. The connector 40b can also be already fitted at this point of time. Then a cover glass 5a2 is pasted respectively on a solar cell with this connected protective diode, the created units are turned around and then - if it has not happened partially already - the first and second contacts 13, 14 of protective diodes 101 are connected or welded with first and second solar cells in order to connect the solar cells serially to a string while simultaneously integrating the protective diodes. After turning the thus created string it is pasted on a panel in the usual manner. An estimation of the additional voltage drop between the cells 50a and 50b on account of using the protective diode in the manner shown as example can be obtained for this example again from Fig. 3. Here the current flows from terminal point K2 to K4. The current will flow 18 through serial resistances R2 + R3 (the resistances R3 + R4 lie parallel and at best reduce the total resistance), the voltage drop for current flow I = IA will therefore be maximum ∆V = (R2+R3) .1 = (6.6E-4 +1.5E-4). IA = 8.1E-4 V = 0.81 mV and will be lower in practice. The tendency towards larger solar cells makes the introduction of solar cells with the main axes of approx 8 cm . 8cm always more probable. Then one cell is produced per 4-inch-wafer, so that the reduction in total complication becomes particularly significant and hence use of discrete protective diodes that are easy to integrate becomes important. Fig. 11 shows a possible design of such a solar cell 60 with altogether 4 cropped corners 62. Corresponding solar cells 60 can be connected according to the procedure already explained with one or two protective diodes of suitable design with neighbouring cells. With the help of a special design of a solar cell 70 as shown in Fig. 12, in which the current collecting bar 73 is connected electrically conductive with all four contact faces 7 laid in the region of the fringes or edges of the cropped corners 76, four diodes l0al, 10a2, l0bl, 10b2 can protect the cell 70 and the connection to the previous cell 70a - following cell 70b - can take place according to the explanations in the context of Fig. 8 only along the backside. This results in an inner connection of all cells with the protective diodes as per the invention and outer connections among one another with the protective diodes as per the invention. Thus Fig. 13 shows purely in principle a cross-section through a panel with cells 70 that respectively have four cropped corners. The connection of the cells among one another takes place through so called outer connectors 711 on the backside of the SCA 75 (SCA = solar cell assembly = solar cell 70 and connected diode l0al, 10a2, l0bl, 10b2 on the front side (light incidence side) provided with a common cover glass 77 by means of the sticker 78) with the help of the protective diodes l0al, 10a2, l0bl, 10b2 that are connected by so called inner connectors 76 (within the SCAs) to the cell. As diodes l0bl and 10b2 one can use the diodes as shown in Fig. 2 as well as protective diodes of opposite conductivity corresponding to those in Fig. 1 and 3, as the second contact 14 of the diode according to Fig. 1 is not required for attaching a connector and the face of the first contact 13 can take up the entire surface of the front side for reducing the electrical resistance in the diode. 19 A variant of the outer connector is schematically shown in Fig. 14. As there is no danger of short circuit on the sides of the diodes l0al and those adjacent to it with opposite conductivity of the type as shown in Fig. 1 and 2, one half of the outer connector can be guided over the side of the cover glass 77 onto the front side of the CIC in order to establish an electrical connection by welding or soldering (see arrow). The advantage of this technology lies in the fact that till shortly before the final production of the panel the SCA can be measured and in case of defects a repair can be carried out relatively easily, e.g. replacement of a SCA. Such a connector also offers the possibility of connecting the front side of the cover glass 77 against electrostatic charging with the cell. One can see especially from Fig. 7, 9, 10 and 12 that the protective diodes 20, 101 in top view have a triangular geometrical shape, preferably a shape with right angle and equally long arms/shanks. Other geometrical shapes are similarly possible. Irrespective of that the protective diodes fill up the free spaces between the solar cells created by the cropped corners. 20 Patent Claims 1. Solar cell array comprising of at least one solar cell (30a, 50a, 60, 70) with photoactive semiconductor layers running between front and back contact (34), as well as at least one discrete protective diode (101, 20, l0al, 10b2, 10b3) with a substrate made of semiconductor material of first conductivity, in a layer (12) forming a surface region of the substrate or on the surface region of an applied layer (22) of second conductivity, a first metallic contact (13, 23) on the layer of second conductivity and a second metallic contact (14, 24) arranged on the substrate, whereby connectors (5a3, 4b7, 40a, 40b, 40c) go out from the first and second metallic contact for connecting the protective diode, having the distinctive feature that the second contact (14, 24) directly contacts the substrate (11, 21) of the protective diode (121, l0al, 10b2, 10b3) and is beside the first metallic contact (13, 23) and arranged at a distance to it and is connected electrically with the first metallic contact through a p/n-junction. 2. Solar cell array as per claim 1, having the distinctive feature that on the side of the substrate (11, 21) lie opposite with respect to the first and second contact (13, 23; 14, 24) a third metallic contact (15, 25) is arranged on it. 3. Solar cell array as per claim 2, having the distinctive feature that the third metallic contact is connected to the first solar cell (30a, 50a, 60, 70) or to a second solar cell (30b, 50b, 70b). 4. Solar cell array as per claim 1, having the distinctive feature that the connectors going out from the first and second metallic contact (13, 23, 24; 14, 24) join the first solar cell (30a, 50a, 60, 70)with a second solar cell (30b, 50b, 70b). 5. Solar cell as per claim 3 or 4, having the distinctive feature that 12 the second metallic contact (14, 24) is connected to the backside of the second solar cell (30b, 50b, 70b) and the third metallic contact (15, 25) is connected to the front side of the solar cell (30a, 50a, 70) and vice versa. 6. Solar cell array as per at least claim 4, having the distinctive feature that the protective diode (101) is connected through the second metallic contact (14) anti- parallel to the first solar cell (30a) through the second solar cell (30b). 7. Solar cell array as per at least claim 4, having the distinctive feature that the protective diode (101) is connected through the second metallic contact (13) anti- parallel to the first solar cell (30a) through the second solar cell (30b). 8. Solar cell array as per at least claim 2, having the distinctive feature that the first and the second solar cell (70, 70b) are connected through at least two protective diodes (l0al, 10b2) and the third metallic contact (711) of the first protective diode (10b2) is connected to the back contact of the second solar cell (70b) as well as to the second metallic contact of the second protective diode (l0al) whose third metallic contact is connected to the front contact of the first solar cell (70) (Fig. 13, 14). 9. Solar cell array as per claim 8, having the distinctive feature that a connector (200) going out from the third metallic contact of the first protective diode (10b2) is connected with the connector (202) going out from the second metallic contact of the second protective diode (l0al) protrudes above the front side of the first and second solar cell (70, 70b) or their cover glasses (75a, 75c) and are connected outside the cover glasses preferably by welding or soldering (Fig. 14). 10. Solar cell array as per claim 1 or 4, having the distinctive feature that the first solar cell (30a, 50a, 70) and/or the second solar cell (30b, 50b, 70b) in top view has a rectangular shape with bevelled corners and the at least one protective diode (101, 20, l0al, 10b2, 10b3) runs in the region of one of the bevelled corners. 11. Solar cell array as per claim 10, having the distinctive feature that several solar cells connected into a string are connected through protective diodes (101, 20, l0al, 10b2, 10b3) arranged in the region of the bevelled corners. 12. Solar cell array as per claim 10 or 11, having the distinctive feature that the protective diode (101, 20, l0al, 10b2, 10b3) in top view has a triangular geometrical shape. 13. Solar cell array as per claim 10 or 11 having the distinctive feature that the protective diode (101, 20, l0al, 10b2, 10b3) has the geometrical shape of a triangular column. 14. Solar cell array as per claim 1 or 12, having the distinctive feature that the protective diode (101, 20, l0al, 10b2, 10b3) has a basic surface F of preferably approximately 0.7 cm2 ≤ F ≤ 1 cm2, particularly approximately 0.8 cm2 ≤ F ≤ 0.9 cm2. 15. Solar cell array as per claim 10, having the distinctive feature that preferably in each bevelled corner of the first and/or second solar cell (30a, 50a, 70; 30b, 50b, 70b) a protective diode (101, 20, l0al, 10b2, 10b3) is arranged. 16. Solar cell array as per claim 1, having the distinctive feature that the first conductivity is n-conductive and the second conductivity is p-conductive or vice versa. 23 17. Solar cell array as per claim 1, having the distinctive feature that the first solar cell (30a, 50a, 70) and/or the second solar cell (30b, 50b, 70b) is a triple cell with preferably a Ge-bottom cell, preferably a GaInAs-centre cell and preferably a GalnP-top cell. 18. Solar cell array as per claim 1 or 2, having the distinctive feature that two solar cells (70, 70b) arranged beside one another are connected through two protective diodes (l0al, 10b2); the solar cells are solar cell front sided n-conductive; one of the protective diodes (10b2) is front sided p-conductive in the layer of second conductivity; and the other protective diode (l0al) is back sided n-conductive in the layer of second conductivity and has a third metallic contact (Fig. 13). 19. Solar cell array as per claim 8, having the distinctive feature that the back side contact of the first protective diode (10b2) is connected to the back side of the second solar cell (70b) as well as to the second metallic contact of the second protective diode (l0al); the third metallic contact of the second protective diode running front sided in the string is connected to the front contact of the first solar cell (70); and the first metallic contact of the second protective diode running back sided in the string is connected to the back side of the first solar cell (Fig. 14). 20. Solar cell array as per claim 8 having the distinctive feature that in solar cells with p/n-junction the first protective diode has a n/p-junction and the second protective diode has a p/n-junction. 21. Method for connecting a solar cell string using protective diodes as per at least one of the previous claims having the features of the following process steps: 24 - Arrangement of the solar cells with the backside on a base support; - Connection of front side contacts of the solar cells with first connectors; - Fixing of one or more transparent covers on the front side of the solar cells; - Turning of the solar cells; - Connecting the first and second solar cells to a string through the first connectors; - Fixing of protective diodes in the free spaces between the solar cells; - Connecting the protective diodes with the solar cells; and - Connecting the thus created string to a base support (Fig. 6). 22. Method for connecting a solar cell string using protective diodes as per at least one of the previous claims having the features of the following process steps: - Arrangement of the solar cells with the backside on a base support; - Fixing of protective diodes in the free spaces between the diodes; - Connecting front side contacts of the solar cells to the third contacts (backside contacts) of the protective diodes running front-sided in the string; - Connecting front sided contacts of the solar cells with first connectors; - Fixing of one or more transparent covers on the front sides of the solar cells and the protective diodes; - Connecting the first and second contacts (front contacts) of the protective diodes running back-sided in the string with back-sided contacts of adjacent solar cells; -Turning the solar cells; and - Connecting the thus created strings to a support base (Fig. 8). 23. Method as per claim 19, having the distinctive feature that protective diodes are arranged with their third contacts in the front side region of the solar cells and adjacent solar cells are connected in series through at least respectively one protective diode with simultaneous anti-parallel connections of the protective diode to one of the adjacent solar cells (Fig. 6). 24. Method as per claim 1, having the distinctive feature that two protective diodes are arranged between two adjacent solar cells, out of which one protective diode is arranged with its third contact and the other protective diode with 25 its first and second contact in the front side region of the solar cells, and the adjacent solar cells are connected in series through the two protective diodes and the protective diodes are connected/switched through contacts running in the region of the back sides of the solar cells (Fig. 13). 25. Method as per claim 21, having the distinctive feature that two connectors (200, 202)go out from the contacts of the protective diodes (l0al, 10b2) running in the region of the back sides of the solar cells (70, 70b), which are connected outside the solar cell strings in their front side region (Fig. 14). 26. Diode (101, 20, l0al, 10b2, 10b3) with a substrate (11, 21) made of semiconductor material of first conductivity, a layer (12, 22) formed in the surface region of the substrate or a layer of second conductivity applied on the surface region, a first metallic contact (13, 23) on the layer of second conductivity and a second metallic contact (14, 24) beside the first metallic contact and at a distance from it and electrically insulated and connected through a p/n-junction, which is directly contacted with the substrate of the protective diode, for using as protective diode in a solar cell array. 27. Diode as per claim 26, having the distinctive feature that a third metallic contact (15, 25) is arranged on the side of the substrate (11,21) lying opposite with respect to the first and second metallic contact (13, 23; 14, 24). 28. Diode as per claim 26, having the distinctive feature that the p/n-junction in the protective diode is replaced by a Schottky contact. Dated this 11th day of APRIL 2007 The invention relates to a solar cell assembly comprising at least one first solar cell and at least one discrete protective diode (101) that is connected to the solar cell. The aim of the invention is to comprehensively protect a solar cell, a solar cell composite or a string of cells by means of one or more protective diodes, without resorting to the use of the material of the solar cells. To achieve this, in addition to a front and a rear contact (13, 15), the protective diode comprises an additional contact (14) that is placed at a distance from the front contact and is electrically connected to said contact via a p/n junction. A connector leads from the additional contact to a second solar cell, the latter in turn being connected to the first solar cell in a string.

Documents:

01270-kolnp-2007-abstract.pdf

01270-kolnp-2007-claims.pdf

01270-kolnp-2007-correspondence others 1.1.pdf

01270-kolnp-2007-correspondence others 1.2.pdf

01270-kolnp-2007-correspondence others 1.3.pdf

01270-kolnp-2007-correspondence others.pdf

01270-kolnp-2007-description complete.pdf

01270-kolnp-2007-drawings.pdf

01270-kolnp-2007-form 1.pdf

01270-kolnp-2007-form 18.pdf

01270-kolnp-2007-form 2.pdf

01270-kolnp-2007-form 3.pdf

01270-kolnp-2007-form 5.pdf

01270-kolnp-2007-gpa.pdf

01270-kolnp-2007-international exm report.pdf

01270-kolnp-2007-international publication.pdf

01270-kolnp-2007-international search report.pdf

01270-kolnp-2007-pct others.pdf

01270-kolnp-2007-pct request.pdf

01270-kolnp-2007-priority document.pdf

1270-KOLNP-2007-(02-01-2014)-ABSTRACT.pdf

1270-KOLNP-2007-(02-01-2014)-ANNEXURE TO FORM 3.pdf

1270-KOLNP-2007-(02-01-2014)-CLAIMS.pdf

1270-KOLNP-2007-(02-01-2014)-CORRESPONDENCE.pdf

1270-KOLNP-2007-(02-01-2014)-DESCRIPTION (COMPLETE).pdf

1270-KOLNP-2007-(02-01-2014)-DRAWINGS.pdf

1270-KOLNP-2007-(02-01-2014)-FORM-1.pdf

1270-KOLNP-2007-(02-01-2014)-FORM-2.pdf

1270-KOLNP-2007-(02-01-2014)-FORM-5.pdf

1270-KOLNP-2007-(02-01-2014)-OTHERS.pdf

1270-KOLNP-2007-(02-01-2014)-PETITION UNDER RULE 137.pdf

1270-KOLNP-2007-(11-05-2012)-PETITION UNDER RULE 137.pdf

1270-KOLNP-2007-CORRESPONDENCE 1.1.pdf

abstract-01270-kolnp-2007.jpg