Interconnection of solar cell modules

Abstract

A space-qualified solar cell assembly comprising a plurality of space-qualified solar cells mounted on a support, the support comprising a plurality of conductive vias extending from the top surface to the rear surface of the support. Each one of the pluralities of space-qualified solar cells is placed on the top surface with the first contact of a first polarity of the space-qualified solar cell electrically connected to the first conductive via. A second contact of a second polarity of each space-qualified solar cell can be connected to a second conductive via so that the first and second conductive portions form terminals of opposite conductivity type. The space-qualified solar cells on the module can be interconnected to form a string or an electrical series and/or parallel connection by suitably interconnecting the terminal pads of the vias on the back side of the module.

Claims

1. A method of manufacturing a solar array panel, comprising the steps of: providing a plurality of solar cell assemblies including at least a first solar cell assembly and a second solar cell assembly, each solar cell assembly comprising a support having a first side and an opposing second side, with a first conductive layer disposed on the first side of the support and a second conductive layer disposed on the second side of the support, and a plurality of solar cells mounted on the first side of the support; positioning the first solar cell assembly on a fixture; positioning the second solar cell assembly on the fixture so that the second solar cell assembly partially overlaps with the first solar cell assembly so that a first portion of the second conductive layer of the second solar cell assembly overlaps with a first portion of the first conductive layer of the first solar cell assembly; and bonding the first portion of the second conductive layer to the first portion of the first conductive layer, so as to establish a mechanical and electrical connection between the two conductive layers; and providing a serial electrical interconnection between the first and second solar cell assemblies.

2. A method as defined in claim 1, wherein the support is flexible and is composed of a poly (4,4-oxydiphenylene-pyromellitimide) material having a thickness between 25 and 100 microns.

3. A method as defined in claim 1, wherein each solar cell assembly comprises an array of discrete solar cells, each solar cell of the plurality of solar cells comprising a top surface including a contact of a first polarity type coupled to the first conductive layer and a rear surface including a contact of a second polarity type coupled to the second conductive layer.

4. A method as defined in claim 1, wherein the first portion of the first conductive layer is disposed on a first peripheral edge of the solar cell assembly, and the first portion of the second conductive layer is disposed on a second peripheral edge of the solar cell assembly opposite to the first edge.

5. A method as defined in claim 1, further comprising mounting the first and second interconnected solar cell assemblies on a panel.

6. A method as defined in claim 1, wherein the solar cells are mounted on the support in an automated manner by machine vision and a pick and place assembly tool.

7. A method as defined in claim 1, wherein the solar cells make up 95% or more of the total upper surface of the support.

8. A method as defined in claim 1, wherein the first conductive layer is an electrical bus interconnecting the bottom contacts of a subset of the solar cells on the solar cell assembly.

9. A method as defined in claim 1, further comprising providing a bypass diode electrically interconnecting the first conductive layer and the second conductive layer.

10. A method as defined in claim 9, wherein the solar cells and the bypass diode are located on the same side of the support

11. A method as defined in claim 1, further comprising bonding each solar cell to the first conductive layer by a conductive bonding material including an indium alloy.

12. A method as defined in claim 1, wherein each solar cell assembly has a substantially rectangular shape and a surface area in the range of 25 to 400 cm.sup.2.

13. A method as defined in claim 1, wherein the step of bonding the first portion of the second conductive layer to the first portion of the first conductive layer is performed using a conductive soldering or welding material.

14. A method as defined in claim 1, wherein the first and second solar cell assemblies are arranged in colinear planes, with a portion of the support of the first solar cell assembly is curved so as to overlap with a portion of the support of the second solar cell assembly.

15. A method as defined in claim 1, further comprising forming a plurality of first vias in the support extending from the first side of the support to the second side of the support, and providing a plurality of first conductive interconnects extending from the first side of the support to the second side of the support, each respective first interconnect making electrical contact with the contact of the first polarity type at the top surface of a respective solar cell and extending through a respective via to make electrical contact with the first conductive portion of the second conductive layer disposed on the second side of the support.

16. A method as defined in claim 15, further comprising forming a plurality of second vias in the support extending from the first side of the support to the second side of the support; a plurality of second conductive interconnects extending from the first side of the support to the second conductive portion of the first conductive layer, each respective interconnect making electrical contact with the contact of the second polarity type at the rear surface of a respective solar cell and extending through a respective one of the second vias to make electrical contact with a second conductive portion of the second conductive layer disposed on the second side of the support.

17. A method as defined in claim 16, wherein: each of the first interconnects includes conductive material in a respective one of the first vias and a wire connecting the conductive material in the respective one of the first vias to the contact of the first polarity on the top surface of a respective one of the solar cells; and each of the second interconnects includes conductive material in a respective one of the second vias and a wire connecting the conductive material in the respective one of the second vias to the contact of the second polarity on the rear surface of a respective one of the solar cells.

18. A method as defined in claim 1, wherein the solar cell assembly further comprises: a first terminal of the assembly of a first polarity type disposed on the second side of the support and connected to the first conductive layer; a second terminal of the assembly of a second polarity type disposed on the second side of the support and connected to the second conductive layer.

19. A method of manufacturing a solar array panel, comprising the steps of: providing a roll of polyimide material; providing conductive traces on and attaching electronic components to the upper surface of the roll; providing a plurality of solar cell assemblies on the roll; cutting the roll into at least a first solar cell assembly and a second solar cell assembly, each solar cell assembly comprising a portion of the roll forming a support having a first side and an opposing second side, with a first conductive layer disposed on the first side of the support and a second conductive layer disposed on the second side of the support, and a plurality of solar cells mounted on the first side of the support; automatically placing the second solar cell assembly over a portion of the first solar cell assembly so that the second solar cell assembly partially overlaps with the first solar cell assembly such that a portion of the second conductive layer of the second solar cell assembly contacts and overlaps with a portion of the first conductive layer of the first solar cell assembly; and bonding the portion of the second conductive layer to the portion of the first conductive layer, so as to establish a mechanical and electrical connection between the two conductive layers on the first and second solar cell assemblies respectively.

20. A solar cell array panel comprising: a flexible support having a first side and an opposing second side, with a first conductive layer disposed on the first side of the flexible support, with a first conductive layer disposed on the first side of the support and a second conductive layer disposed on the second side of the support; a plurality of solar cell assemblies including a first solar cell assembly and a second solar cell assembly, each solar cell assembly comprising a plurality of solar cells mounted on a first and a second flexible support respectively; a plurality of solar cells mounted on the first side of the support wherein a contact of first polarity of the solar cell assembly is coupled to the first conductive layer and a contact of second polarity of the solar cell assembly is coupled to the second conductive layer; the second solar cell assembly on the substrate so that a portion of the second solar cell assembly partially overlaps with the first solar cell assembly so that a portion of the second conductive layer of the second solar cell assembly overlaps with a portion of the first conductive layer of the first solar cell assembly and makes electrical contact thereto; and the portion of the second conductive layer being bonded to the portion of the first conductive layer so as to establish a mechanical and electrical connection between the two conductive layers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0127] To complete the description and in order to provide for a better understanding of the disclosure, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the disclosure, which should not be interpreted as restricting the scope of the disclosure, but just as examples of how the disclosure can be carried out. The drawings comprise the following figures:

[0128] FIG. 1A is a perspective view of a support that can be used for fabricating a module according to the present disclosure depicting metallization over the top and bottom surfaces;

[0129] FIG. 1B is a perspective view of the support of FIG. 1A after a step of forming a plurality of grooves in the bottom metal layer of the support in a first embodiment;

[0130] FIG. 1C is a perspective view of the support of FIG. 1A after a step of forming a plurality of spaced apart metal pads in the top metal layer of the support in a first embodiment;

[0131] FIG. 1D is a cross-sectional view of the support of FIG. 1C through the 1D-1D plane shown in FIG. 1C;

[0132] FIG. 1E is an enlarged perspective view of one of the metal pads on the support as shown in FIG. 1C;

[0133] FIG. 1F is a perspective view of the bottom of the support as shown in FIG. 1B after fabrication of two rows of vias;

[0134] FIG. 1G is a perspective view of a solar cell;

[0135] FIG. 1H is a perspective view of a solar cell mounted on the support;

[0136] FIG. 2A is a top perspective view of the support in a second embodiment in which only the bottom surface is metallized;

[0137] FIG. 2B is a top perspective view of the support of FIG. 2A in which two rows of vias have been fabricated;

[0138] FIG. 2C is a top perspective view of the support of FIG. 2B after metallization of the vias;

[0139] FIG. 2D is a bottom perspective view of the support of FIG. 2C depicting an embodiment of metallization of the bottom surface similar to that of FIG. 1B;

[0140] FIG. 2E is a top perspective view of a portion of the support of FIG. 2B after which two rows of solar cells have been mounted;

[0141] FIG. 2F is an enlarged perspective view of one of the solar cells in FIG. 2E mounted on the support;

[0142] FIG. 2G is a perspective view of a portion of the support of another embodiment in which an adhesive patch is applied to the surface of the support where a solar cell is to be attached;

[0143] FIG. 2H is a perspective view of the embodiment of FIG. 2G after bonding a solar cell to the support;

[0144] FIG. 2I is a perspective view of the solar cell of FIG. 2H after connection of a first interconnect to a pad on one via;

[0145] FIG. 3A is a top perspective view of the module with an array of solar cells mounted on the surface;

[0146] FIG. 3B is a top perspective view of the module of FIG. 3A after attachment of the interconnects;

[0147] FIG. 3C is a bottom plan view of the module of FIG. 3A depicting the location of the vias with respect to the array of solar cells on the top surface of the module, as depicted in dashed lines;

[0148] FIG. 4A is a schematic diagram of the one row of the components of the module;

[0149] FIG. 4B is a schematic diagram of a solar cell showing contacts of two polarities;

[0150] FIG. 4C is a schematic diagram of an array of solar cells as seen from the back side of the support;

[0151] FIG. 4D is a plan view of the array of FIG. 4C with all of the solar cells connected in parallel;

[0152] FIG. 4E is a plan view of the array of FIG. 4C with all of the solar cells connected in series;

[0153] FIG. 4F is a plan view of the array of FIG. 4C with some solar cells connected in series, and some in parallel;

[0154] FIG. 4G is a bottom plan view of the module showing the location of the solar cells on the top surface, as depicted in dashed line;

[0155] FIG. 4H is a bottom plan view of the module of FIG. 4G, further depicting the location of the vias with respect to the array of solar cells on the top surface of the module, as depicted in dashed lines;

[0156] FIG. 4I is a bottom plan view of the module of FIG. 4H with the solar cells connected in parallel;

[0157] FIG. 5 is a cross-sectional view of a III-V compound semiconductor solar cell that may be implemented on the module according to the present disclosure;

[0158] FIG. 6A is a cross-sectional view of two adjacent solar cells mounted on the module of FIG. 3A through the 6A-6A plane;

[0159] FIG. 6B is a cross-sectional view of the two solar cells of FIG. 3B through the 6B-6B plane after an interconnect has been attached to the top contact of the solar cell on the left, and the contact pad of the adjacent via;

[0160] FIG. 6C is a cross sectional view of the two solar cells of FIG. 3B through the 6C-6C plane after an interconnect has been attached to the bottom contact of another solar cell, and the contact pad of the adjacent via;

[0161] FIG. 7 depicts a wafer with a large number of small solar cells scribed and ready to be detached from the wafer;

[0162] FIG. 8 is a highly simplified perspective view of a space vehicle incorporating an array in which the deployable solar cell panel incorporates the interconnected solar cell module assemblies according to the present disclosure; and

[0163] FIG. 9 is a highly simplified perspective view of a space vehicle incorporating an array in which the deployable solar cell panel incorporates the interconnected solar cell module assemblies according to the present disclosure.

[0164] FIG. 10A is a schematic cross-sectional view of a first solar cell module of FIG. 6A mounted on a panel or supporting substrate during the first step of a panel assembly process;

[0165] FIG. 10B is a schematic cross-sectional view of a second solar cell module of FIG. 6A positioned and about to be coupled with the first solar cell module during the second step of a panel assembly process;

[0166] FIG. 10C is a schematic cross-sectional view of the second solar cell module shown in FIG. 7B being coupled with the first solar cell module shown in FIG. 7A during the third step of a panel assembly process; and

[0167] FIG. 10D is a schematic cross-sectional view of the second solar cell module shown in FIG. 7C being mounted on the panel or supporting substrate during the fourth step of a panel assembly process.

DETAILED DESCRIPTION

[0168] Details of the present disclosure will now be described including exemplary aspects and embodiments thereof. Referring to the drawings and the following description, like reference numbers are used to identify like or functionally similar elements, and are intended to illustrate major features of exemplary embodiments in a highly simplified diagrammatic manner.

[0169] Moreover, the drawings are not intended to depict every feature of the actual embodiment nor the relative dimensions of the depicted elements, and are not drawn to scale.

[0170] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases in one embodiment or in an embodiment in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0171] The present disclosure provides a process for the design and fabrication of a modular solar cell subassembly, and the interconnection of solar cells in the subassembly utilizing different interconnection elements and routing techniques.

[0172] FIG. 1A illustrates an example of a support 100 that can be used in an embodiment of the disclosure in the fabrication of the modular subassembly. The support comprises an insulating support layer 101 and a conductive metal layer 102 arranged on a top surface of the support layer 101 and a conductive metal layer 103 arranged on a bottom surface of the support layer 101. In some embodiments of the disclosure, the metal layer 102 is a copper layer, having a thickness in the range of from 1 m and up to 50 m. In some embodiments of the disclosure, the support layer 101 is a KAPTON sheet. The chemical name for KAPTON is poly (4,4-oxydiphenylene-pyromellitimide). A polyimide film sheet or layer may also be used. Preferably the metal layer is attached to the support layer in an adhesive-less manner, to limit outgassing when used in a space environment. In some embodiments of the disclosure the support layer can have a thickness in the range of 1 mil (25.4 m) to 4 mil (101.6 m). In some embodiments of the disclosure, a support can be provided comprising KAPTON, or another suitable support material, on both sides of the metal film 102, with cut-outs for the attachment of solar cells and interconnects to the metal film. In some embodiments of the disclosure, the metal film layer 103 at the bottom surface of the support is of the same material and has the same or a similar thickness as the metal film layer 102 at the top surface of the support. In some embodiments, the two metal film layers are of different materials and/or have different thicknesses.

[0173] Although the support 100 is depicted in FIG. 1A as the size and shape of the ultimate module, which may be a square, rectangular or another geometrically shaped element ranging from 1 inch to 6 inches on a side, the support 100 may be fabricated out of a roll or larger support material such as a polymide film. Such material may be automatically processed and cut to produce the individual support 100 depicted in FIG. 1A, or subsequently depicted processed structures. A description of such fabrication processes goes beyond the scope of the present disclosure, but is described in the related applications.

[0174] In some embodiments, the support 100 may be cut to a different geometric shape, e.g. triangular, hexagonal, octagonal, or with irregular or non-linear edges, with one or more legs or extensions that support other electronic components or conductive traces that attach to the support.

[0175] FIG. 1B is a perspective view of the support 100 of FIG. 1A after a step of forming a plurality of grooves in the bottom metal layer 103 of the support in a first embodiment. FIG. 1B illustrates the support 100 of FIG. 1A after a step in which a portion of the metal layer 103 has been removed, by for example etching or laser scribing, whereby channels or grooves 192 are formed traversing the metal layer 103, separating it into at least a plurality of strips 107, 108, extending in parallel and in some embodiments connected to each other at a terminal 190, 191 respectively on opposing peripheral edges of the support 100.

[0176] In another embodiment, the grooves etc. are V-shaped or triangular, and so are the strips such as depicted in FIGS. 2B and 3C of parent application Ser. No. 14/719,111. The use of this kind of strips the width of which increases along the strip when moving from the free end of the strip to the end where the strip is connected to the terminals 190, 191, is that when in use and with solar cells arranged in a row along the strip 180, current will flow in one direction, and current will be lowest towards the free end of the strip (where the current corresponds to the one produced by one solar cell), and higher towards the end where the strip connects to the terminal 190, 191 (where the current is the sum of the currents produced by the solar cells arranged on the strip). Thus, the need for a sufficient cross section of conductive material is higher towards the end where the strip mates with the terminals 190, 191. Thus, the increasing width corresponds to an optimization of the use of conductive material, which can be important especially for space applications.

[0177] FIGS. 1C and 1D show the support of FIG. 1A after a step of forming a plurality of spaced apart metal pads 110-117, 810-817 in the top metal layer 102 of the support, for example by etching or laser scribing, creating channels or grooves 120-126 and 150-156. FIG. 1E shows an enlarged perspective view of one of the metal pads 111, placed adjacent to two vias 303 and 304. Further vias 301, 305, 315 are shown in FIG. 1C.

[0178] FIG. 1F is a perspective view of the bottom of the support as shown in FIG. 1B after fabrication of two rows of vias 301, 303,315 and 302, 304 . . . , 306, respectively. These vias can be used to connect solar cells placed on the metal pads 110-117, to the strips formed in the bottom metal layer 103. The vias can be filled with conductive material, or be used to accommodate for example an interconnecting wire. When the vias are filled with a conductive material, interconnects such as wires can be electrically connected to the top and bottom surfaces or contact pads of the vias and to respective contacts on the solar cells, so as to establish electrical connection between the electrical contacts on the solar cells and the bottom metal layer 103.

[0179] FIG. 1G is a perspective view of a solar cell 201 with a top surface having a contact pad 201 corresponding to a contact of a first polarity type, a bottom surface with a metal layer 251 corresponding to a contact of a second polarity type. A cut-out 250 provides access to the contact of the second polarity type from above.

[0180] FIG. 1H is a perspective view of a solar cell 201 mounted on the support, adjacent to a via 301. The solar cell c a n in this embodiment be placed on one of the metallic contact pads 110-117 shown in FIG. 1C.

[0181] FIG. 2A is a top perspective view of the support 100 in a second embodiment in which only the bottom surface is metallized, so that the support layer 101 features a conductive layer 103 on only one of its two sides.

[0182] FIG. 2B is a perspective view of the support of FIG. 2A after the next process step of providing vias 301, 303, . . . 315 in a first row, and 302, 304, . . . 316 in a second row, extending into or through the support 100 according to the present disclosure. The vias can be provided using any suitable means.

[0183] FIG. 2C is a perspective view of the support of FIG. 2B illustrates in the first embodiment how the vias 301, . . . 315 and 302, . . . 316 may be plated with metal so as to form a conductive path from the bottom metal layer 103 to the top surface of the support.

[0184] FIG. 2D is a bottom perspective view of the support of FIG. 2C in first embodiment and illustrates how the vias traverse the body 101 and emerge at the bottom surface thereof and stop at the top of the metal film strips 107 and 108. (Only the first two rows of vias 301, . . . 315 and 302, . . . 316 are shown for simplicity).

[0185] FIG. 2E is a perspective view of the support of FIG. 2C after the next process step of mounting a plurality of solar cells 810, 811, . . . 817 on a first row along the top surface of the support according to the present disclosure.

[0186] FIG. 2F is an enlarged perspective view of a single solar cell. Each solar cell has a top surface in which a contact pad of a first polarity (in the enlarged depiction represented by 210 for solar cell 207), such as a cathode contact pad, is provided. Two vias 301 and 302 are shown, adjacent to the solar cell.

[0187] FIG. 2G is a perspective view of a portion of the support of another embodiment in which an adhesive patch 401 is applied to the surface of the support where a solar cell is to be attached; the adhesive patch 401 can be used to adhere a solar cell to the support. Two vias 303 and 304 are shown.

[0188] FIG. 2H is a perspective view of the embodiment of FIG. 2G after bonding a solar cell to the support. The solar cell features a top contact with contact pad 210 corresponding to a contact of a first polarity type, and a conductive layer 251 at the bottom of the solar cell, corresponding to a contact of a second polarity type. This conductive layer 251 is placed on the adhesive patch 401. Access to the conductive layer 251 from above is provided for by the recess or cut-out 250.

[0189] FIG. 2I is a perspective view of the solar cell of FIG. 2H after connection of a first interconnect 450 to electrically connect the contact pad 210 to the conductive material filling via 303, thereby establishing contact between the contact pad 210 and the conductive portion 108 (see FIG. 2D) on the other side of the support.

[0190] FIG. 3A is a top perspective view of the module with an array of solar cells 200-207, 500-507, 810-817 mounted on the surface of the first side of the support. In the enlarged portion, a contact 207a of the first polarity type and two contacts 207b, 507b of the second polarity type of are shown in relation to two solar cells 207, 507.

[0191] FIG. 3B is a top perspective view of the module of FIG. 3A after attachment of three interconnects 451, 452 and 453, two of them attached to the contacts 207b, 507b of the second polarity type and one of them attached to the contact of the first polarity type 207a, in order to electrically connect these contacts to the respective conductive portions on the other side of the support, through the vias.

[0192] FIG. 3C is a bottom plan view of the module of FIG. 3A depicting the location of the vias 309-316 with respect to the array of solar cells 814-817 on the top surface of the module, as depicted in dashed lines. Each solar cell is arranged to be electrically connected to two of said vias, so that, for example, a contact of the second polarity type of solar cell 814 is connected to via 309, and the contact of the first polarity type of solar cell 814 is connected to via 310. In this way, the contacts of different solar cells can be electrically interconnected, in parallel or in series, through the vias and through the conductive portions 107 and 108 on the bottom side of the support (cf. for example FIG. 2D).

[0193] FIG. 4A is a schematic diagram of one row of the components of the module. A plurality of solar cells 200 are connected in parallel between two bus bars 107 and 108, corresponding to the second and to the first conductive portions, respectively, and with a bypass diode 350 common to the plurality of solar cells. Each solar cell is a multijunction solar cell.

[0194] Bypass diodes are frequently used for each solar cell in solar cell arrays comprising a plurality of series connected solar cells or groups of solar cells. One reason for this is that if one of the solar cells or groups of solar cells is shaded or damaged, current produced by other solar cells, such as by unshaded or undamaged solar cells or groups of solar cells, can flow through the by-pass diode and thus avoid the high resistance of the shaded or damaged solar cell or group of solar cells. Placing the by-pass diodes at the cropped corners of the solar cells can be an efficient solution as it makes use of a space that is not used for converting solar energy into electrical energy. As a solar cell array or solar panel often includes a large number of solar cells, and often a correspondingly large number of bypass diodes, the efficient use of the area at the cropped corners of individual solar cells adds up and can represent an important enhancement of the efficient use of space in the overall solar cell assembly.

[0195] In addition to the bypass diodes, a solar cell array or panel also incorporates a blocking diode that functions to prevent reverse currents during the time when the output voltage from a solar cell or a group of series connected solar cells is low, for example, in the absence of sun. Generally, only one blocking diode is provided for each set or string of series connected solar cells, and the blocking diode is connected in series with this string of solar cells. Often, since a panel includes a relatively large amount of solar cells that are connected in series, a relatively substantial blocking diode is required, in terms of size and electrical capacity. The blocking diode is generally connected to the string of solar cells at the end of the string. As the blocking diode is generally only present at the end of the string, not much attention has been paid to the way in which it is shaped and connected, as this has not been considered to be of major relevance for the over-all efficiency of the solar cell assembly. Standard diode components have been used.

[0196] FIG. 4B is a schematic diagram of a solar cell showing contacts of two polarities, for example, a contact of a first polarity type (henceforth: N contact) and a contact of a second polarity type (henceforth: P contact). This kind of solar cells can be arranged in an array, as schematically shown in FIG. 4C. Now, using the backplane of the support, these solar cells can be interconnected in different ways, for example, as shown in FIGS. 4D-4F.

[0197] FIG. 4D is a plan view of the array of FIG. 4C with all of the solar cells connected in parallel. This can be achieved, for example, by connecting the P contacts of the solar cells through one of the conductive portions 107 or 108, and the N contacts of all of the solar cells to another one of the conductive portions 108 or 107, through vias in the support, as previously explained.

[0198] FIG. 4E is a plan view of the array of FIG. 4C with all of the solar cells connected in series. Also, this can be carried out using, for example, conductive portions or traces at a rear surface of the support to interconnect a P contact of one solar cell with an N contact of a following solar cell, in a string of solar cells, etc. In other embodiments, at least part of the interconnections between P contacts and N contacts can be carried out directly using interconnects, without using the vias in the support.

[0199] FIG. 4F is a plan view of the array of FIG. 4C with some solar cells connected in series, and some in parallel. In some embodiments, this can be achieved by connecting a set of solar cells in series electrically connecting the P contact of one solar cell to the N contact of the next solar cell forming a string of solar cells, and thereafter connecting a plurality of said strings in parallel, by connecting the N contact of the first solar cell in each string to one of the conductive portions 107 or 108 (cf. FIG. 2D) on the rear surface of the support, and the P contact of the last solar cell in each string to another conductive portion 108 or 107 of the support, through the respective vias in the support.

[0200] FIG. 4G is a bottom plan view of the module showing the location of the solar cells 204-207, 504-507 on the top surface, as depicted in dashed lines.

[0201] FIG. 4H is a bottom plan view of the module of FIG. 4G, further depicting the location of the vias with respect to the array of solar cells on the top surface of the module, as depicted in dashed lines. For example, via P11 is associated to the contact of the second polarity type of solar cell 207, and via N11 is associated to the contact of the first polarity type of solar cell 207; via P21 is associated to the contact of the second polarity type of solar cell 507, and via N21 is associated to the contact of the first polarity type of solar cell; etc. Here, associated means that the via is used, in one way or another, to electrically connect the corresponding contact to a conductive portion at the bottom side of the support.

[0202] FIG. 4I is a bottom plan view of the module of FIG. 4H with the solar cells connected in parallel; this is achieved by interconnecting, on the one hand, all of the vias associated to the contacts of the first polarity type using a first conductive portion 108 on the bottom side of the support, and, on the other hand, all of the vias associated to the contacts of the second polarity type using a second conductive portion 107 on the bottom side of the support. Further, bypass diode 350 has been depicted in FIG. 4I. Thus, it can easily be understood how by using vias as described and appropriately designing the conductive portions on the bottom side of the support, for example, by removing selected portions of an original conductive layer 103, the desired interconnection of the solar cells mounted on the front side of the support can be achieved, using the vias. In some embodiments, in addition to the interconnection of solar cells using the backplane (the conductive portions on the bottom side of the support), solar cells can also be interconnected, for example, in series, by using interconnects directly interconnecting solar cells on the front side of the support.

[0203] FIG. 5 is a cross-sectional view of a III-V compound semiconductor solar cell that may be implemented on the module according to the present disclosure. In the Figure, each dashed line indicates the active region junction between a base layer and emitter layer of a subcell.

[0204] As shown in the illustrated example of FIG. 5, the bottom subcell 901 includes a substrate 912 formed of p-type germanium (Ge) which also serves as a base layer. A contact pad 911 formed on the bottom of base layer 912 provides electrical contact to the multijunction solar cell 901. The bottom subcell 901 further includes, for example, a highly doped n-type Ge emitter layer 914, and an n-type indium gallium arsenide (InGaAs) nucleation layer 916. The nucleation layer is deposited over the base layer 912, and the emitter layer is formed in the substrate by diffusion of deposits into the Ge substrate, thereby forming the n-type Ge layer 914. Heavily doped p-type aluminum gallium arsenide (AlGaAs) and heavily doped n-type gallium arsenide (GaAs) tunneling junction layers 918, 917 may be deposited over the nucleation layer 916 to provide a low resistance pathway between the bottom and middle subcells.

[0205] In the illustrated example of FIG. 5, the middle subcell 902 includes a highly doped p-type aluminum gallium arsenide (AlGaAs) back surface field (BSF) layer 920, a p-type InGaAs base layer 922, a highly doped n-type indium gallium phosphide (InGaP.sub.2) emitter layer 924 and a highly doped n-type indium aluminum phosphide (AlInP.sub.2) or indium gallium phosphide (GaInP) window layer 926. The InGaAs base layer 922 of the middle subcell 902 can include, for example, approximately 1.5% In. Other compositions may be used as well. The base layer 922 is formed over the BSF layer 920 after the BSF layer is deposited over the tunneling junction layers 918 of the bottom subcell 904.

[0206] The BSF layer 920 is provided to reduce the recombination loss in the middle subcell 907. The BSF layer 920 drives minority carriers from a highly doped region near the back surface to minimize the effect of recombination loss. Thus, the BSF layer 920 reduces recombination loss at the backside of the solar cell and thereby reduces recombination at the base layer/BSF layer interface. The window layer 926 is deposited on the emitter layer 924 of the middle subcell 902. The window layer 926 in the middle subcell 902 also helps reduce the recombination loss and improves passivation of the cell surface of the underlying junctions. Before depositing the layers of the top cell 903, heavily doped n-type InGaP and p-type AlGaAs tunneling junction layers 927, 928 may be deposited over the middle subcell B.

[0207] In the illustrated example, the top subcell 903 includes a highly doped p-type indium gallium aluminum phosphide (InGaAlP) BSF layer 930, a p-type InGaP2 base layer 932, a highly doped n-type InGaP.sub.2 emitter layer 934 and a highly doped n-type InAlP2 window layer 936. The base layer 932 of the top subcell 903 is deposited over the BSF layer 930 after the BSF layer 930 is formed over the tunneling junction layers 928 of the middle subcell 907. The window layer 936 is deposited over the emitter layer 934 of the top subcell after the emitter layer 934 is formed over the base layer 932. A cap or contact layer 938 may be deposited and patterned into separate contact regions over the window layer 936 of the top subcell 903. The cap or contact layer 938 serves as an electrical contact from the top subcell 903 to metal grid layer 940. The doped cap or contact layer 938 can be a semiconductor layer such as, for example, a GaAs or InGaAs layer.

[0208] After the cap or contact layer 938 is deposited, the grid lines 940 are formed. The grid lines 940 are deposited via evaporation and lithographically patterned and deposited over the cap or contact layer 938. The mask is subsequently lifted off to form the finished metal grid lines 940 as depicted in the Figure, and the portion of the cap layer that has not been metallized is removed, exposing the surface of the window layer 936.

[0209] As more fully described in U.S. patent application Ser. No. 12/218,582 filed Jul. 18, 2008, hereby incorporated by reference, the grid lines 940 are preferably composed of Ti/Au/Ag/Au, although other suitable materials may be used as well.

[0210] During the formation of the metal contact layer 940 deposited over the p+ semiconductor contact layer 938, and during subsequent processing steps, the semiconductor body and its associated metal layers and bonded structures will go through various heating and cooling processes, which may put stress on the surface of the semiconductor body. Accordingly, it is desirable to closely match the coefficient of thermal expansion of the associated layers or structures to that of the semiconductor body, while still maintaining appropriate electrical conductivity and structural properties of the layers or structures. Thus, in some embodiments, the metal contact layer 940 is selected to have a coefficient of thermal expansion (CTE) substantially similar to that of the adjacent semiconductor material. In relative terms, the CTE may be within a range of 0 to 15 ppm per degree Kelvin different from that of the adjacent semiconductor material. In the case of the specific semiconductor materials described above, in absolute terms, a suitable coefficient of thermal expansion of layer 940 would range from 5 to 7 ppm per degree Kelvin. A variety of metallic compositions and multilayer structures including the element molybdenum would satisfy such criteria. In some embodiments, the layer 940 would preferably include the sequence of metal layers Ti/Au/Mo/Ag/Au, Ti/Au/Mo/Ag, or Ti/Mo/Ag, where the thickness ratios of each layer in the sequence are adjusted to minimize the CTE mismatch to GaAs. Other suitable sequences and material compositions may be used in lieu of those disclosed above.

[0211] FIG. 6A is a cross-sectional view of the support of FIG. 3A through the 6A-6A plane shown in FIG. 3A, and shows the corresponding part of the assembly prior to incorporation of the wire including the channel 105a and the via 147.

[0212] FIG. 6B is a cross-sectional view of the support of FIG. 3A through the 6B-6B plane shown in FIG. 3A and illustrates the same part of the assembly after incorporation of the wire 453 in a first embodiment. Here, it can be seen how the wire 453 interconnects the contact pad 207a and the metal filling the via 147. A first end 453a of the wire is wire bonded to the contact pad 207a, and a second end 453b of the wire is wire bonded to the metal material filling the via 147, which in turn is connected to the bottom metal layer 103.

[0213] FIG. 6C is a cross-sectional view of the support of FIG. 3A through the 6C-6C plane shown in FIG. 3A and illustrates the same part of the assembly after incorporation of the wire 452 in a first embodiment. Here, it can be seen how the wire 452 interconnects the bottom metal layer 510 of the solar cell 507 and the metal layer 103 on the bottom surface of the support 101, through the via 147a.

[0214] As schematically shown in FIG. 7, obtaining individual solar cells by dividing a substantially circular solar cell wafer 200A into a large number of small solar cells 201, such as solar cells having areas of less than 5 cm.sup.2 or less than 1 cm.sup.2, enhances wafer utilization. Also, it is possible to discard solar cells from defective regions.

[0215] FIG. 8 is a highly simplified perspective view of a space vehicle 10000 incorporating a solar cell array 2000 in the form of a deployable flexible sheet including a flexible substrate 2001 on which solar cell modules 1000 and 1001 according to the present disclosure are placed. The sheet may wrap around a mandrel 20042 prior to being deployed in space with the aid of rollers 2002, 2003. The space vehicle 10000 includes a payload 10003 which is powered by the array of solar cell assemblies 2000.

[0216] FIG. 9 is a highly simplified perspective view of a space vehicle 10000 incorporating a solar cell array 2000 of FIG. 8 as the deployable flexible sheet 2001 is being deployed.

[0217] Thus, an assembly of a plurality of solar cells connected in parallel is obtained, and this kind of assembly can be used as a subassembly or module, together with more subassemblies or modules of the same kind, to form a larger assembly, such as a solar array panel, including strings of series connected assemblies. For example, the present disclosure describes a space-qualified solar cell assembly designed for operation at AM0 and at a 1 MeV electron equivalent fluence of at least 510.sup.14 e/cm.sup.2, the assembly comprising III-V compound semiconductor multijunction space-qualified solar cells including at least three subcells, including a ceria doped borosilicate glass supporting member that is 3 to 6 mils in thickness attached to each space-qualified solar cell with a transparent adhesive, wherein a combination of compositions and band gaps of the subcells is designed to maximize efficiency of the space-qualified solar cells at a predetermined time, after initial deployment when the space-qualified solar cells are deployed in space at AM0 and at an operational temperature in the range of 40 to 70 degrees Centigrade, the predetermined time being at least five years and referred to as the end-of-life (EOL), the space-qualified solar cell assembly comprising: a support comprising a first side and an opposing second side; a first conductive layer comprising first and second spaced-apart conductive portions disposed on the second side of the support; a plurality of space-qualified solar cells mounted on the first side of the support, each space-qualified solar cell of the plurality of space-qualified solar cells comprising a top surface including a contact of a first polarity type, and a rear surface including a contact of a second polarity type; a plurality of first vias in the support extending from the first side of the support to the second side of the support; a plurality of second vias in the support extending from the first side of the support to the second side of the support; a plurality of first conductive interconnects extending from the first side of the support to the first conductive portion of the first conductive layer, each respective interconnect making electrical contact with the contact of the first polarity type of a respective space-qualified solar cell and extending through a respective one of the first vias to make electrical contact with the first conductive portion of the first conductive layer disposed on the second side of the support; a plurality of second conductive interconnects extending from the first side of the support to the second conductive portion of the first conductive layer, each respective interconnect making electrical contact with the contact of the second polarity type of a respective space-qualified solar cell and extending through a respective one of the second vias to make electrical contact with the second conductive portion of the first conductive layer disposed on the second side of the support; and a first terminal of the module of a first polarity type disposed on the second side of the support and connected to the first conductive portion of the first conductive layer; and a second terminal of the module of a second polarity type disposed on the second side of the support and connected to the second conductive portion of the first conductive layer.

[0218] The figures are only intended to schematically show embodiments of the disclosure. In practice, the spatial distribution will mostly differ: solar cells are to be packed relatively close to each other and arranged to occupy most of the surface of the assembly, so as to contribute to an efficient space utilization from a W/m.sup.2 perspective.

[0219] FIG. 10A is a schematic cross-sectional view of a first solar cell module or assembly 1000 of the type described above, mounted on a panel or supporting substrate 500 during the first step of a panel assembly process. An adhesive layer 501 is present on the top surface of the substrate 500 for attaching the assembly 1000 to the substrate 500. An interconnection pad 550, for example, of a conductive materialsuch as for example an indium alloythat can be fused to bond two conductive layers to each other, is played adjacent to an edge of the assembly 1000, on top of the first conductive layer 102 and, more specifically, on the second terminal part of the first lateral conductive layer.

[0220] FIG. 10B schematically illustrates how a second solar cell assembly 1001, of the same type as the first solar cell assembly 1000, is being transferred to a position partially overlapping with the first solar cell assembly 1000, by a schematically illustrated pick-and-place apparatus 502.

[0221] FIG. 10C schematically illustrates a third step of the process, with the second solar cell module 1001 coupled with the first solar cell module 1000. It can be seen how the second solar cell module 1001 and the first solar cell module partially overlap with each other: more specifically, the second solar cell module 1001 is placed on top of a portion of the first conductive layer 102 of the first solar cell module 1000 that is free from solar cells, that is, a portion that corresponds to the second terminal described above.

[0222] FIG. 10D schematically illustrates the first and the second solar cell modules arranged on the supporting substrate after a fourth step of a panel assembly process. Here, a major portion of the second solar cell assembly 1001 has been aligned with the first solar cell assembly 1000 and glued to the supporting substrate 500 by the adhesive layer 501. The first terminal of the second solar cell assembly 1001 has been bonded to the second terminal of the first solar cell assembly 1000.

[0223] It is to be noted that the terms front, back, top, bottom, over, on, under, and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the disclosure described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.

[0224] Furthermore, those skilled in the art will recognize that boundaries between the above described operations are merely illustrative. The multiple units/operations may be combined into a single unit/operation, a single unit/operation may be distributed in additional units/operations, and units/operations may be operated at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular unit/operation, and the order of operations may be altered in various other embodiments.

[0225] In the claims, the word comprising or having does not exclude the presence of other elements or steps than those listed in a claim. The terms a or an, as used herein, are defined as one or more than one. Also, the use of introductory phrases such as at least one and one or more in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles a or an limits any particular claim containing such introduced claim element to disclosures containing only one such element, even when the claim includes the introductory phrases one or more or at least one and indefinite articles such as a or an. The same holds true for the use of definite articles. Unless stated otherwise, terms such as first and second are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage.

[0226] The present disclosure can be embodied in various ways. The above described orders of the steps for the methods are only intended to be illustrative, and the steps of the methods of the present disclosure are not limited to the above specifically described orders unless otherwise specifically stated. Note that the embodiments of the present disclosure can be freely combined with each other without departing from the spirit and scope of the disclosure.

[0227] Although some specific embodiments of the present disclosure have been demonstrated in detail with examples, it should be understood by a person skilled in the art that the above examples are only intended to be illustrative but not to limit the scope of the present disclosure. It should be understood that the above embodiments can be modified without departing from the scope and spirit of the present disclosure which are to be defined by the attached claims.