METHOD FOR PRODUCING SOLAR CELLS AND SOLAR CELL ASSEMBLIES

Abstract

Solar cells are obtained by singulating a non-rectangular solar cell wafer into a plurality of solar cells, in one embodiment a first solar cell having a surface area corresponding to at least 60% of the wafer surface area but less than 90% of the wafer surface area, and at least two second solar cells each having a surface area of less than 10% of the wafer surface area. Such a first solar cell can be connected in parallel with a plurality of the second solar cells, to establish a substantially rectangular subassembly, and such subassemblies can be combined into a larger solar cell assembly, which may be mounted on a support including other electrical components on the backside thereof, and attached to a small satellite (e.g., CubeSat) exterior surface, or deployable wing.

Claims

1. A method for producing solar cells, comprising the step of dividing a non-rectangular solar cell wafer having a wafer surface area into a plurality of solar cells, the plurality of solar cells comprising one first solar cell and at least two second solar cells, each second solar cell having a surface area of less than 10% of the wafer surface area, characterized in that the first solar cell has a surface area corresponding to at least 70% of the wafer surface area but less than 90% of the wafer surface area.

2. The method of claim 1, wherein the first solar cell has a surface area of more than 75% of the wafer surface area.

3. The method of claim 2, wherein the first solar cell has a surface area of more than 80% of the wafer surface area.

4. The method of claim 1, wherein each of the second solar cells has a surface area of less than 8% of the wafer surface area.

5. The method of claim 4, wherein each of the second solar cells has a surface area of less than 5% of the wafer surface area,

6. The method of claim 1, wherein the first solar cell has a substantially polygonal shape with more than four sides.

7. The method of claim 6, wherein the first solar cell has a substantially octagonal shape.

8. A method of claim 1, wherein the first solar cell has a length and a width, the length being larger than the width.

9. A method of claim 1, wherein the second solar cells have a substantially polygonal shape.

10. A method of claim 1, wherein the wafer is divided into not more than five solar cells.

11. A method of claim 1, wherein the solar cell wafer is a multifunction III-V compound semiconductor solar cell wafer.

12. A solar assembly comprising: a support; and a plurality of solar cells mounted on the support, wherein a first set of the plurality of the solar cells have a first size and a second set of the plurality of solar cells have a second size different from the first size.

13. A solar cell assembly as defined in claim 12, wherein the plurality of solar cells are singulated from a solar cell wafer including first solar cells each having a surface area corresponding to at least 60% of the wafer surface area but less than 90% of the wafer surface area and a plurality of second solar cells each having a surface area of less than 10% of the wafer surface area; the solar cells being mounted on the support and forming an array of subassemblies, each subassembly having a substantially rectangular shape, each subassembly comprising one of the first solar cells and a plurality of the second solar cells, connected in parallel.

14. A solar cell assembly as defined in claim 13, a plurality of substantially rectangular subassemblies, each subassembly comprising a first solar cell having a non-rectangular shape and a surface area having a first size, and a plurality of second solar cells each having a surface area of less than a second size, the second size being less than of the first size, the first and the second solar cells of each subassembly being electrically interconnected in parallel.

15. The solar cell assembly of claim 12, wherein the second size is less than 1/10 of the first size.

16. The solar cell assembly of claim 12, wherein each solar cell in the first set of the plurality of solar cells has a substantially polygonal shape with more than four sides.

17. The solar cell assembly of claim 13, wherein each solar cell of the first set of solar cells has a length and a width, the length being larger than the width, and each solar cell in the second set of solar cells has a substantially triangular or polygonal shape.

18. A solar cell assembly as defined in claim 12, wherein the support has a fronst side on which the solar cells are mounted, and a backside including one or more of the following electronic or electrical components: bypass diodes, blocking diodes, bleed resistors, temperature sensors, end terminations, and terminal outputs.

19. A solar cell assembly as defined in claim 12, wherein the support is sized to mount on a single CubeSat body panel.

20. A space vehicle including a photovoltaic array panel, in which the panel comprises a plurality of solar cells including at least one solar cell having a first geometric configuration and at least one solar cell having a second geometric configuration, the second geometric configuration being different from the first geometric configuration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] 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:

[0069] FIG. 1 schematically illustrates a prior art arrangement for producing a closely packed solar cell array out of square solar cells obtained from a circular solar cell wafer.

[0070] FIG. 2 schematically illustrates how circular solar cells packed to obtain a maximum packing factor imply a staggered arrangement of solar cells in an array of solar cells, or a solar cell assembly.

[0071] FIG. 3 schematically illustrates another prior art arrangement, based on the use of square solar cell with cropped corners obtained from a circular wafer.

[0072] FIG. 4A schematically illustrates how a substantially circular solar cell wafer can be divided into one relatively large first solar cell and a plurality of relatively small solar cells, it accordance with one embodiment of the disclosure.

[0073] FIG. 4B schematically illustrates how the solar cells obtained in accordance with FIG. 4A can be combined into a subassembly of rectangular shape, with a high packing factor.

[0074] FIG. 5A schematically illustrates how a substantially circular solar cell wafer can be divided into one relatively large first solar cell and a plurality of relatively small solar cells, in accordance with another embodiment of the disclosure.

[0075] FIG. 5B schematically illustrates how the solar cells obtained in accordance with FIG. 5A can be combined into a subassembly of rectangular shape, with a high packing factor.

[0076] FIG. 6 schematically illustrates a solar cell assembly comprising a plurality of solar cell subassemblies, in accordance with an embodiment of the disclosure.

[0077] FIG. 7 schematically illustrates the relation between panel power density and cost per watt for different solar cell arrangements.

[0078] FIGS. 8A-8C schematically illustrate three further embodiments of the disclosure.

[0079] FIG. 9 is a graph schematically illustrating the relationship between packing factor and use of wafer surface, in relation to some embodiments of the disclosure.

[0080] FIG. 10 is a perspective view of a CubeSat space vehicle incorporating one embodiment of a solar cell assembly according to the present disclosure.

DETAILED DESCRIPTION

[0081] FIG. 4A schematically illustrates how 4 circular wafer 100 can be subdivided into one relatively large first solar cell 101, in this case having an octagonal shape, and a plurality of relatively small second solar cells 110, each having a substantially triangular shape. FIG. 4B schematically illustrates how the first solar cell 101 and four of the second solar cells 110 can be arranged to form a rectangular subassembly 140, in which the first solar cell 101 and the second solar cells 110 are connected in parallel, by interconnects 120 and 130. Interconnects 130 are arranged for further interconnecting the subassembly in series with another subassembly when forming a solar cell assembly out of the subassemblies. It is clear from FIGS. 4A and 4B that a high wafer utilization is achieved (as wafer material outside the first octagonal solar cell 101 is used for making the further, second, solar cells), and that a subassembly 140 with high packing factor is achieved, namely, with 100% (or close to 100%) packing factor. The rectangular shape of the subassembly 140 makes the subassembly suitable for the manufacture of a solar cell assembly featuring a likewise high packing factor, also known as panel packing factor.

[0082] FIG. 5A schematically illustrates another embodiment of the disclosure, in which a circular wafer is subdivided into one relatively large first solar cell 201 having a length larger than its width and with an octagonal shape, and four relatively small second solar cells 210 and 220, two of which are slightly larger than the other two. That is, it is not necessary that all of the second solar cells have the same size or shape. FIG. 5B schematically illustrates how the first solar will 201 and the second solar cells 210 and 220 can be arranged to form a rectangular subassembly 250, in which the first solar cell 201 and the second solar cells 210 and 220 are connected in parallel, by interconnects 230 and 240. Interconnects 240 are arranged for further interconnecting the subassembly in series with another subassembly. It is clear from FIGS. 5A and 5B that also in this embodiment a high wafer utilization is achieved (as wafer material outside the first octagonal solar cell 201 is used for making the further, second, solar cells), while a subassembly 250 with high packing factor is achieved, namely, with 100% (or close to 100%) packing factor. Also here the rectangular shape of the subassembly 250 makes the subassembly suitable for the manufacture of a solar cell assembly featuring a likewise high packing factor.

[0083] FIG. 6 schematically illustrates a solar cell assembly 300 or solar array panel comprising a matrix of solar cell subassemblies 250 as per the embodiment illustrated in FIG. 5B. As schematically illustrated in FIG. 6, due to the rectangular shape of the subassemblies 250, also the combination of such subassemblies can feature a high packing factor of 100% or close to 100%.

[0084] FIG. 7 is a schematic diagram in which the cost per watt for the solar cell corresponds to the horizontal axis, and the panel power density corresponds to the vertical axis. Case A corresponds to the case suggested in FIG. 2, when circular solar cells are used, with no loss of wafer material. This provides for a low cost per watt when the cell is considered, but also for a relatively low packing factor and thus a relatively low power density when the entire assembly or panel is considered. Case B corresponds to the case suggested in FIG. 1, where perfectly rectangular solar cells are cut out of a substantially circular wafer. The waste of wafer material implies a relatively high cost per watt, but the high packing factor (about 100%) that can be achieved provides for a high panel power density. On the other hand, case C corresponds to the use of composite subassemblies in accordance with the principles of the present disclosure, where the reduced waste implies a lower cost per watt than case B but a higher cost per watt than case A (due to the fact that there is still some waste of wafer material and additionally a cost of interconnection of the first and second solar cells), whereas the same high panel power density can be obtained as in case B.

[0085] FIG. 8A illustrates a further embodiment of the disclosure. Also in this embodiment the first cell 810 has an octagonal configuration, and two second cells 811, 812 of triangular shape are cut out of the substantially circular wafer 800. The illustrated arrangement is estimated to provide for a packing factor of about 99%. However, it is clear that there is a substantial waste of wafer surface, which tends to increase the cost of the solar cell assembly.

[0086] The embodiment of FIG. 8B also features a first cell 810 having an octagonal layout, and four second sells, two larger ones 820, 821 and two smaller ones 822, 823. The estimated packing factor is 97%, that is, slightly less than the one of the embodiment of FIG. 8A, but the embodiment of FIG. 8B instead provides for a more efficient use of the material of the wafer 800, which contributes to a reduced cost in terms of the cost of the wafer material needed to provide a solar cell assembly with a given surface of solar cell material.

[0087] The embodiment of FIG. 8C makes even more efficient use of the wafer material. Also here, a first cell 830 having an octagonal shape is cut out of a substantially circular wafer 800, and two second cells 831, 832 are provided, each including a curved portion, substantially following the edge of the circular wafer. The embodiment of FIG. 8C visibly provides for an efficient use of wafer surface, thereby contributing to a reduced cost of the solar cell assembly in what regards the cost corresponding to wafer material. However, this has to be balanced against a lower packing factor, in this case estimated to be in the order of 89%.

[0088] FIG. 9 schematically illustrates how the relation between the packing factor and the amount of used wafer surface area for a given wafer can be enhanced by implementing different embodiments of the disclosure. The horizontal axis represents the aggregate solar cell area, that is, the area of the wafer surface that is actually used for producing the corresponding solar cell subassembly, and the vertical axis represents the packing factor. The indicated numbers are not intended to represent a preferred embodiment, but are just indicated to simplify the understanding of the disclosure.

[0089] In the illustrated embodiment the diameter of the solar cell wafer is assumed to be a standard 100 mm. The total surface area of such a wafer is 78.5 square centimeters. Since normal fabrication processes exclude usage of a small portion of the edge of the wafer, the actual usable surface area to be singulated into individual solar cells is typically in the range of 70 to 75 square centimeters. The x-axis of FIG. 9 represents the aggregate solar cell area of such a wafer implemented under various singulation scenarios covered by the present disclosure, and third 70 to 73 square centimeters are tabulated on the far right end of the x-axis, corresponding to the maximum useable surface area.

[0090] The y-axis of FIG. 9 represents the packing factor or percentage of coverage of the local array area by the assembled pattern of singulated solar cells.

[0091] In FIG. 9, the curve 905 schematically represents different relations between packing factor and used amount of wafer surface that can be obtained by singulating or dicing solar cells out of a substantially circular wafer. As shown, generally, increased packing factor implies a less efficient use of wafer surface. The region 904 schematically represents how it is possible to expand beyond the boundaries of that basic curve 905 by implementing different embodiments of the disclosure, thereby enhancing the relationship between packing factor and used wafer surface area. In an exemplary embodiment, a very high packing factor combined with a reasonably efficient use of wafer surface area is represented at 901, which corresponds to the embodiment of FIG. 8A. 902 represents the embodiment of FIG. 8B. Here, the packing factor is not as good as in the case of the embodiment of FIG. 8A, but the use of wafer surface area has been improved. 903 represents the embodiment FIG. 8C, featuring a rather efficient use of wafer surface area but at the cost of a further reduced packing factor. Thus, FIG. 9 illustrates how different embodiments can be used to optimize the efficiency in terms of packing factor and use of wafer surface area. Thus, a person implementing the disclosure can choose an adequate embodiment depending on the importance of packing factor on one hand (for example, the importance of a high packing factor is greater when the power/weight ratio of the assembly is of great concern, such as in space applications), and efficient use of wafer material on the other (the importance of an efficient use of wafer material increases with the cost of the wafer material), in a given situation, subject to the constraint of limiting the number of singulated solar cells from a single wafer.

[0092] FIG. 10 illustrates a miniature satellite or CubeSat 350 according to the present disclosure. Solar assemblies as taught in the present disclosure, and in the related applications noted above may be mounted on supports 301, 302 which are then mounted on the CubeSat 350. CubeSats 350 are a type of miniaturized satellites or nanosatellite. A typical CubeSat is a 10 cm10 cm10 cm cube, thus having a volume of one liter. CubeSats can be attached to one another in strings or blocks to provide functionalities and capabilities that would not otherwise be practically available in a single CubeSat. FIG. 10 for example illustrates three individual CubeSats 351, 352, 353 forming a 3-unit CubeSat 350. For example, one CubeSat can be used to store a deployable photovoltaic array to supply power necessary for other attached. CubeSats to perform their functions. Reference may be made to U.S. patent application Ser. No. 14/921,238 filed. Oct. 23, 2015, herein incorporated by reference, depicting an embodiment of such a deployable solar cell array.

[0093] The solar cell assemblies described herein above can be particularly advantageous for attaching to a CubeSat. For example, the solar cell assembly can be attached directly to the surface of the support 301, 302 which are then mounted directly on the CubeSat without a need for a frame (e.g., an aluminum or honeycomb frame). Further, the solar cell supports 301, 302 can be composed of a light weight flexible support (e.g., a Kapton or other polyimide support) or a rigid and non-flexible support. The polyimide sheets as either a continuous layer or a patterned layer designed for a particular application. The base or backplane of the unit is typically a space qualified or qualifiable material (e.g., Kapton, polyester, polyimide, Aramid, Pyralux) that is lightweight, flexible, and reliable in space applications, Kapton is a poly (4,4-oxydiphenylene-pyromellitimide) material.

[0094] The different embodiments for attaching and bonding the solar cell assemblies to the support 301, 302 are described in U.S. patent application Ser. No. 14/795,461 filed Jul. 9, 2015. As noted therein, a pressure sensitive adhesive (PSA) layer or pattern may be applied.

[0095] In FIG. 10, we illustrate a panel 301 with an array of nine solar cell assemblies 310, 311, 312, etc. The solar cell assemblies 310, 311, 312 are depicted as substantially square and equally sized in the Figure to illustrate one embodiment. In another embodiment, solar cell assemblies 310 and 311 are of a first size or configuration, and solar cell assembly 312 is of a second size or configuration different from the first size or configuration. Other combinations or configurations, such as depicted in the present disclosure, may also be employed.

[0096] The packing factor referred to in this document is generally the local packing factor, which in many embodiments can differ from the overall packing factor of the solar cell assembly, for example due to a lower local packing factor in correspondence with the edges of the assembly (for example, due to the size and/or shape of the assembly), and/or due to the presence of other components on the solar cell assembly.

[0097] Another aspect of the present disclosure is to provide a suitable base or backplane support 301, 302 for the variety of solar cell assemblies described above to be mounted on CubeSat panel or extensible wing.

[0098] The backplane 301, 302 may be a sheet or may be patterned to it a specific application, such as a standard CubeSat at body panel, or to fit snugly around panel features such as hold-down release mechanisms or hinges. The backplane 301, 302 may contain no components or design features or may have certain features such as metal traces to allow it to interface, mechanically, electrically, or otherwise, to other modules or interconnections, terminal outputs, or related satellite features or components.

[0099] The backplane 301, 302 may be blank or may incorporate metallization applied through additive or subtractive processes that would enable or facilitate interconnection of solar cells into series and parallel arrangements, provide for the incorporation of bypass diodes, blocking diodes, bleed resistors, temperature sensors, and other applicable components 330 commonly incorporated into space solar arrays including end terminations, terminal outputs, or related features to interconnect the solar cells, cover glass interconnected cells (CICs), strings, or circuits on the backplane to other photovoltaic modules, to other panels, or to the satellite.

[0100] The backplane 301, 302 may incorporate or he joined with single-sided, or dual-sided pressure sensitive adhesive (PSA) on one or on both sides of the backplane. Frontside PSA may allow solar cells, CICs, or other components to be bonded or mounted onto the backplane 301, 302. Backside PSA may allow the backplane, which can be supporting solar cells, CICs, or other components, to be adhered to a solar panel that may be made of a rigid or flexible material, may be on a deployable wing for a satellite, or may be body-mounted to a satellite, as is the case for CubeSats, for example.

[0101] This backplane structure 301, 302 can enable the solar module to be self-adhesive through removal of a release liner or other protective film on one or both sides of the PSA-backplane followed by application of the module to the surface to which it is to be bonded.

[0102] The solar cells, CICs, and/or other components 310, 311, 312 to be incorporated into the module may be pre-assembled into free-standing assemblies, strings, or circuits, then bonded onto the backplane, by using frontside PSA or using some other adhesive material such as a silicone, which is commonly used in space solar panel manufacturing today, or by using solder, epoxy, or some similar material that can also provide electrical connection between the components and the backplane 301, 302 in the case that the backplane 301, 302 is metallized to support the function and/or interconnection of the components or modules. The assemblies, strings, or circuits can be subassemblies that may be assembled manually, or may be assembled in an automated fashion, in whole or in part, by one production machine, or by multiple production machines, and assembled onto, incorporated into, or combined with the backplane in a manual or an automated fashion.

[0103] Alternatively, the solar cells, CICs, and/or other components 310, 311, 312 to be incorporated into the module may be assembled, individually or as part of sub-assemblies, directly onto the backplane 301, 302, using similar methods to those described herein. The resulting assemblies, strings, or circuits made directly on the backplane 301, 302 may be assembled manually, or may be assembled in an automated fashion, in whole or in part, by one production machine or by multiple production machines.

[0104] The solar cells and other components 310, 311, 312 assembled into/onto the module may be of one uniform form factor (shape and size), or may be multiple and/or include a variety of form factors, and may be assembled with one uniform inter-component spacing, or a multiple and/or a variety of intra-components spacings as needed to best achieve the required specifications for the module, as taught by the present disclosure.

[0105] The components 310, 311, 312 may be interconnected by one uniform method, or by multiple and/or a variety of methods (e.g., wiring, interconnects, metal traces, wire/ribbon bonding, solder) as needed to achieve the performance, reliability, and/or other desired characteristics or required specifications for the module.

[0106] The completed module may optionally be coated, manually or by machine, with any of a variety of materials, including but not limited to transparent silicones, adhesives, conductive or insulating grouting between cells and/or other components, coverglass or other materials, as needed to achieve the performance, reliability, and/or other desired characteristics or required specifications for the module.

[0107] The CubeSat modules 351, 352, 353 may be any size or shape as needed to achieve the performance, reliability, and/or other desired characteristics or required specifications for the satellite or space vehicle. This means that a module can constitute an entire solar circuit or a partial circuit, can be connected in series or parallel to other module(s) to meet certain required performance specifications, such as an optical element 354.

[0108] In some embodiments, the module is envisioned to be consistent with the so-called CubeSat standard, such that CubeSat manufacturers and/or integrators can apply self-adhesive solar modules directly to their body mounted or deployable CubeSat panels.

[0109] In another embodiment, the module is envisioned to be one building block of a larger integrated unit in which solar panel or array manufacturers and/or integrators apply multiple self-adhesive solar modules directly to their body mounted or deployable solar panels, or rigid or flexible solar array structures. In this embodiment, the module can optionally be custom-designed to maximize utilization of the rigid or flexible solar panel and/or array structure to optimize power output, minimize mass, or otherwise meet certain required performance specifications.

[0110] In this text, the term comprises and its derivations (such as comprising, etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc.

[0111] The disclosure is obviously not limited to the specific embodiment(s) described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the disclosure as defined in the claims.