METHOD FOR PRODUCING SOLAR CELLS AND SOLAR CELL ASSEMBLIES

Abstract

A method for producing a mosaic solar cell assembly, comprising the steps of singulating a III-V compound circular semiconductor solar cell wafer having a wafer surface area into four discrete solar cell mosaic elements each substantially shaped as a quadrant of a circle; selecting a first and second solar cell mosaic element each having one curved edge in the shape of an arc of the circumference of the circular wafer from which the element was singulated, and three straight edges; and rearranging and positioning the first and second mosaic elements into a substantially rectangular mosaic assembly.

Claims

1. A method for producing a solar cell assembly, comprising the steps of: providing at least one III-V compound semiconductor circular solar cell wafer; chamfering each wafer along its circumferential edge into two diametrically opposed portions of the circumference of the wafer so as to produce a chamfered wafer having a circumference comprising at least first and second diametrically opposed curved edges representing the circumferential edge of the wafer; and a third and fourth straight chamfered edges which are sized so as to minimize the loss of usable wafer area; singulating each chamfered wafer through the center of the wafer into four quadrants to form a set of four mosaic elements; arranging only two of the mosaic elements directly adjacent to one another along a first axis, so that the first and second curved edges of each of the two mosaic elements are touching and adjacent one another and form a single row of mosaic elements, each of the two mosaic elements being aligned so as to have substantially the same height in a direction perpendicular to the first axis, the first mosaic element having a first edge parallel to the first axis and the second mosaic element having a second edge parallel to the first axis, the third and fourth edges being aligned in a direction perpendicular to the first axis, so as to form a substantially rectangular solar cell assembly, with the first edge of the first mosaic element forming a portion of one elongated side of the rectangular solar cell assembly, and the second edge of the second mosaic element forming a portion of the opposite elongated side of the rectangular solar cell assembly; and providing each of the first and second mosaic elements with a conductive interconnect, on one elongated side of the rectangular solar cell assembly, so that the first and second mosaic elements of the solar cell assembly can be electrically connected to corresponding electrical contacts on an adjacent solar cell assembly.

2. A method as defined in claim 1, further comprising mounting a single cover glass over both of the first and second mosaic elements.

3. A method as defined in claim 1, wherein the conductive interconnect comprises a first discrete conductive interconnect mounted on the first edge of the first mosaic element and a second discrete conductive interconnect mounted on the third chamfered edge of the second mosaic element.

4. A method as defined in claim 1, wherein the chamfered wafer includes two diametrically opposed and parallel straight line segments which are parallel to an axial line through the center of the wafer and which form the chamfered edge of each of the first and second mosaic elements.

5. A method as defined in claim 4, wherein the two diametrically opposed straight line segments have the same length.

6. A method as defined in claim 1, wherein the first and second mosaic elements are identical in size and shape.

7. A method as defined in claim 1, wherein the first and second mosaic elements are arranged and positioned with the straight chamfered edge on each mosaic element being positioned and aligned with the second edge of the other mosaic elements to form the solar cell assembly.

8. A method as defined in claim 2, wherein the first and second mosaic elements are mounted on a cover glass support forming a rectangular reference template with each mosaic element having the same height and arranged serially along the length of the rectangular template.

9. A method as defined in claim 1, wherein the one elongated side of the first solar cell assembly is disposed directly adjacent to the lower elongated side of a second solar cell assembly so that the conductive interconnect couples the first rectangular solar cell assembly in electrical series with the second solar cell assembly.

10. A method as defined in claim 1, wherein the chamfering of each circular solar cell wafer achieves greater than 90% wafer utilization.

11. A method as defined in claim 9, wherein the first and second solar cell assemblies are aligned so that the third and fourth edges of the first solar cell assembly align with the corresponding third and fourth edges of the second solar cell assembly.

12. A method as defined in claim 9, wherein the alignment of the first and second solar cell assemblies achieves a fill factor of 100% of a rectangular surface.

13. A method as defined in claim 9, wherein each of the first and second solar cell assemblies are identical in size and shape.

14. A method as defined in claim 9, wherein the first and second mosaic elements in each of the first and second solar cell assemblies are identical in size, shape, and positioning.

15. A method as defined in claim 3, wherein the interconnect is composed of a nickel-cobalt ferrons alloy material.

16. A method as defined in claim 1, wherein the singulation of the chamfered wafer into quadrants includes making a first cut through the wafer that bisects the dramatically opposed curved edges representing the circumferential edge of the wafer.

17. A method as defined in claim 16, wherein the singulation of the chamfered wafer into quadrants includes making a second cut through the wafer that bisects each of the third and fourth straight chamfered edges.

18. A method for producing a solar cell panel, comprising of the steps of: (a) fabricating a first “cell-interconnect-cover glass (CIC)” assembly by (i) providing at least one III-V compound semiconductor solar cell wafer; chamfering each wafer along its circumferential edge into at least two diametrically opposed portions of the circumference of the wafer so as to produce a chamfered wafer having a circumference comprising two diametrically opposed curved segments representing the circumferential edge of the wafer; (ii) singulating each chamfered wafer through the center of the wafer into only four quadrants to form a set of four mosaic elements; (iii) arranging only two of the mosaic elements directly adjacent to one another along a first axis, so that the two mosaic elements for a single row of mosaic elements, each of the two mosaic element being aligned so as to have substantially the same height in a direction perpendicular to the first axis, each of the two mosaic element having a first edge parallel to the first axis and a second edge parallel to the first axis, the first and second edges aligned in a direction perpendicular to the first axis, wherein the step of arranging the two mosaic elements along a first axis comprises positioning the two mosaic elements touching and adjacent to one another into a substantially rectangular solar cell assembly; so that a curved edge of the first mosaic element is placed adjacent to and touching against a curved edge of the second mosaic element, with the first edge of the first mosaic element and the first edge of the second mosaic element being aligned along a straight line and forming one elongated side of the rectangular solar cell assembly, and the second edge of the first mosaic element first edge of the second mosaic element being aligned along a straight line and forming the opposite elongated side of the rectangular solar cell assembly; (iv) providing each of the two mosaic elements with a single conductive interconnect at a respective first edge thereof, the conductor interconnects being aligned along a straight line so that each mosaic element of the solar cell assembly can be electrically connected to corresponding electrical contacts on an adjacent solar cell assembly; and (v) bonding the two mosaic elements to a first cover glass; (b) fabricating a second “cell-interconnect-cover glass (CIC)” assembly by performing steps (i) through (iv) above and bonding to the two mosaic elements in the second CIC to a second cover glass; (c) arranging the first and the second CIC assemblies one on top of the other so that the shorter edges of each of the CICs are aligned in a straight line, and the longer top edge of the first CIC is disposed adjacent to the longer bottom edge of the second CIC; and (d) coupling the interconnect disposed on the longer top edge of the first CIC with the lower long edge of the second CIC so as to make a series electrical circuit between the first and second CICs.

19. A method as defined in claim 19, further comprising (b) fabricating a third “cell-interconnect-cover glass (CIC)” assembly by performing steps (i) through (iv) in claim 19 and bonding to the two mosaic elements in the third CIC to a third cover glass; (c) arranging the second and the third CIC assembly directly adjacent to one another so that the shorter edges of each of the CICs are aligned in a straight line, and the longer top edge of the second CIC is disposed adjacent to the longer bottom edge of the third CIC; and (d) coupling the interconnect disposed on the longer top edge of the second CIC with the lower long edge of the third CIC so as to make a series electrical circuit between the first and second CICs.

20. A solar cell assembly comprising: a first mosaic element and a second mosaic element each singulated as a quadrant of a circle cut from a III-V compound semiconductor circular solar cell wafer; the first mosaic element being chamfered along its circumferential edge into a first straight chamfered edge which is sized so as to minimize the loss of usable wafer area and disposed adjacent to the circumferential edge; and having a second straight edge having a length equal to the radius of the circular wafer adjacent to the other end of the circumferential edge, and a third straight edge adjacent to and orthogonal to the first straight chamfered edge; the first and second mosaic elements being arranged directly adjacent to one another along a first axis, so that the first and second curved edges of each of the two mosaic elements are touching and adjacent one another and form a single row of mosaic elements, each of the two mosaic element being aligned so as to have substantially the same height in a direction perpendicular to the first axis, the first mosaic element having a first edge parallel to the first axis and the second mosaic element having a second edge parallel to the first axis, the third and fourth edges being aligned in a direction perpendicular to the first axis, so as to form a substantially rectangular solar cell assembly, with the first edge of the mosaic element forming a portion of one elongated side of the rectangular solar cell assembly, and the second edge of the second mosaic element forming a portion of the opposite elongated side of the rectangular solar cell assembly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] 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:

[0078] FIG. 1A illustrates a circular solar cell wafer from which three solar cells according to the present disclosure are scribed;

[0079] FIG. 1B illustrates a CIC assembly according to a first embodiment of the present disclosure utilizing the three solar cells of FIG. 1A;

[0080] FIG. 2A illustrates a circular solar cell wafer from which eight solar cells are scribed;

[0081] FIG. 2B illustrates a CIC assembly according to a second embodiment of the present disclosure utilizing the eight solar cells of FIG. 2A;

[0082] FIG. 2C illustrates a CIC assembly similar to FIG. 1B using a single piece interconnect;

[0083] FIG. 2D illustrates a CIC assembly similar to FIG. 2B using a single piece interconnect;

[0084] FIG. 2E illustrates a CIC assembly derived from solar cells utilizing a plurality of wafers, and a single piece interconnect;

[0085] FIG. 3A schematically illustrates a circular solar cell wafer from which four solar cells are scribed, in accordance with a second embodiment of the disclosure;

[0086] FIG. 3B schematically illustrates the assembly of a first unit cell from the wafer of FIG. 3A;

[0087] FIG. 3C schematically illustrates the assembly of a second unit cell from the wafer of FIG. 3A;

[0088] FIG. 3D schematically illustrates a circular solar cell wafer from which four solar cells are scribed, in accordance with another embodiment of the disclosure;

[0089] FIG. 3E schematically illustrates the assembly of another embodiment of a unit cell utilizing four mosaic elements based on a quadrant of the wafer;

[0090] FIG. 3F schematically illustrates the assembly of another embodiment of a unit cell utilizing three mosaic elements based on using two quadrants of the wafer, and a semicircle from the wafer;

[0091] FIG. 3G schematically illustrates the assembly of another embodiment of a unit cell utilizing three mosaic elements based on using two quadrants of the wafer, and a semicircle from the wafer;

[0092] FIG. 4 is a cross-sectional view of the two adjacent CICs through the 4-4 plane shown in FIG. 3C; and

[0093] FIG. 5 is a graph which depicts the relation between the packing factor and the wafer utilization or amount of used wafer surface area for a given wafer for two mosaic assemblies according to the present disclosure, compared to a typical assembly with a 1-fer or 2-fer.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0094] Details of the present invention 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. 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.

[0095] A variety of different features of mosaic solar cell assemblies are disclosed in the related applications noted above. Some, many or all of such features may be included in the structures and fabrication processes associated with the solar cell assemblies of the present disclosure.

[0096] Figure TA illustrates a circular solar cell wafer 100 from which three mosaic solar cell elements 101, 102, and 103 according to the present disclosure are scribed. In the depicted embodiment, the wafer 100 is a four-inch (or 100 mm diameter) wafer, and the area of the mosaic elements 101, and 102/103 are 50.63 cm.sup.2 and 8.40 cm.sup.2 respectively.

[0097] FIG. 1B illustrates a portion of the CIC assembly 108 according to a first embodiment of the present disclosure utilizing the three mosaic solar cell elements of FIG. TA arranged into a rectangular reference template, with individual discrete interconnects 104, 105, 106 and 107 attached to the top edge of each of the mosaic solar cell element.

[0098] FIG. 2A illustrates a circular solar cell wafer in a second embodiment from which four mosaic solar cell elements are scribed; including two identical upper and lower solar cells 207, 208; two right and left solar cells 201, 202; and four center solar cells 203, 204, 205, 206. In a four inch (100 mm) wafer, the center mosaic solar cell elements are rectangular in shape with dimensions of 15 mm×60 mm, or each having an area of 9 cm.sup.2.

[0099] FIG. 2B illustrates a portion of a CIC assembly 210 according to a second embodiment of the present disclosure utilizing the eight mosaic solar cell elements of FIG. 2A. Individual interconnects 251 are provided along the upper edge depicted in the Figure making electrical contact with the top surface of each of the mosaic elements 207, 201, 203, 204, 205, 206, 202 and 208.

[0100] FIG. 2C illustrates a portion of CIC assembly 220 similar to FIG. 1B using a single piece interconnect 252 making contact with each of the mosaic elements 207, 215, and 208.

[0101] FIG. 2D illustrates a portion of a CIC assembly 230 similar to FIG. 2B using a single piece interconnect 253 making contact with each of the mosaic elements 207, 201, 203, 204, 205, 206, 202 and 208.

[0102] FIG. 2E illustrates a portion of a CIC assembly derived from solar cells utilizing a plurality of wafers, and a single piece interconnect 254 making contact with each of the mosaic elements 207, 201, 203, 204, 207, 201, 205, 206, 211, 212, 202 and 208. (The cover glass of the CIC is omitted from FIGS. 1B and 2B through 2E for simplicity).

[0103] FIG. 3A schematically illustrates how, in accordance with an embodiment of the disclosure, a substantially circular solar cell wafer 300 is divided into four sectors (in the figure, the sectors are quadrants), thus producing four solar cells 301, 302, 303 and 304, in which 301 and 303 each have a curved edge 316 and 317 respectively, corresponding to the arc portion of the circumference of the circular wafer 300, and three substantially straight edges 310, 311 and 312A/312B and 313A/313B, and 314A/314B; 315A/315B respectively extending at a right angle (90 degrees). These solar cells can be packed to form a solar cell assembly 320 or 330 as illustrated in FIGS. 3B and 3C, that is, in accordance with a pattern formed by an array of equal rectangles or “unit cells” A (as shown in FIGS. 3B and 3C), these rectangles being arranged adjacent to each other forming an array.

[0104] Each rectangle 350 or 360 encompasses two solar cells 301, 303 or 302, 304 respectively, fitting efficiently into the area of the rectangle or unit cell as shown in FIGS. 3B and 3C respectively. These unit cells can fill a rectangular panel or surface with a fill factor of 100%. Thus, the fill factor of the solar cells on the panel, that is, the fill factor of the solar cells 301, 303 and 302, 304 in the entire solar cell array, will be the same as the fill factor of the solar cells 301, 33 and 302, 304 in the unit cell.

[0105] The sequence of steps for fabricating the CIC or mosaic solar cell assembly comprises the steps of: providing a circular solar cell wafer 300; chamfering at least one diametrically opposed pair of sides 310 and 311 of the wafer along two spaced apart portions of the circumference; cutting the wafer into four quadrants 301, 302, 303 and 304 to form mosaic elements; providing a cover glass support (cover glass 981 shown in FIG. 4); rearranging and positioning at least two mosaic elements adjacent to one another into a substantially rectangular mosaic assembly shown in FIG. 3B or FIG. 3C; providing a metal interconnect 341, 342 or 343, 344 to each of the mosaic elements so that the mosaic elements may be electrically connected to an adjacent mosaic assembly (CIC 800 shown in FIG. 4); and bonding the cover glass support 981 to the top of the mosaic assembly.

[0106] It has been found that the use of solar cells shaped substantially as quadrants of a circle can at least sometimes be an appropriate solution, taking into account how the quadrants can fit into a rectangular unit cell with a fill factor of about 90% or greater, that is, with a rather high fill factor.

[0107] FIG. 3B schematically illustrates the assembly of a first embodiment of a mosaic assembly 320 from the wafer of FIG. 3A using the mosaic elements 301 and 303. Interconnects 341 and 342 are provided and mounted to the top surface of mosaic elements 303 and 301 respectively along edges 315B and 312A respectively to make electrical contact with a bus bar (not shown) on the top surface thereof.

[0108] FIG. 3C schematically illustrates the assembly of a second embodiment of a mosaic assembly 330 from the wafer of FIG. 3A using the mosaic elements 302 and 304. Interconnects 343 and 344 are provided and mounted to the top surface of mosaic elements 302 and 303 respectively to make electrical contact with a bus bar (not shown) on the top surface thereof.

[0109] FIG. 3D schematically illustrates a circular solar cell wafer 350 from which four solar cell mosaic elements 360, 361, 362 and 363 are scribed, in accordance with another embodiment of the disclosure.

[0110] FIG. 3E schematically illustrates the assembly of a third embodiment of a mosaic assembly 370 from the wafer of FIG. 3D using the mosaic elements 371, 372, 373, and 374. Interconnects 375 are provided and mounted to the top surface of each of the mosaic elements 371, 372, 373 and 374 respectively to make electrical contact with a bus bar (not shown) on the top surface thereof.

[0111] FIG. 3F schematically illustrates the assembly of a fourth embodiment of a mosaic assembly 380 from the wafer of FIG. 3D using the mosaic elements 381, 382, and 383. Interconnects 385 are provided and mounted to the top surface of mosaic elements 381, 382, and 383 respectively to make electrical contact with a bus bar (not shown) on the top surface thereof.

[0112] FIG. 3G schematically illustrates the assembly of a fifth embodiment of a mosaic assembly 390 from the wafer of FIG. 3D using the mosaic elements 391, 392 and 393. Interconnects 395 are provided and mounted to the top surface of mosaic elements 391, 392 and 393 respectively to make electrical contact with a bus bar (not shown) on the top surface thereof.

[0113] FIG. 4 is a cross-sectional view of the CICs of FIG. 3C after the next process step of alignment of the CIC 700 with the edge of an adjacent CIC 800, in the process of fabricating an interconnected array or string of solar cells. Several strings may then be arranged in parallel to form an array. The solar cell of similar CIC 800 includes layers 811, 812 through 836, 838, and 840 similar to layers 911, 912, . . . through 936, 938, and 940 respectively of a solar cell of CIC 700. A cover glass 881 is attached by adhesive 880 to the solar cell 800 similar to that of the cover glass 981 in solar cell 300. The composition of the solar cell layers are described more fully in the related applications incorporated herein by reference.

[0114] FIG. 5 is a graph which depicts the relation between the packing factor and the wafer utilization or amount of used wafer surface area for a given wafer for two mosaic assemblies according to the present disclosure, compared to a typical assembly with a 1-fer or 2-fer solar cell (labelled “Rectangular Limit”). The circular references refer to the assemblies of FIG. 3B or 3C, while the square references refer to the assemblies of FIG. 2B, 2C, 2D or 2E.

[0115] 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.

[0116] In this specification, the term “solar cell” or “solar cell mosaic element” refers to a solar cell, or simply “mosaic element”, that is an integral portion of a solar cell wafer, rather than a solar cell made up of a plurality of interconnected portions.

[0117] References to rows and columns of an array do not imply any specific orientation of the rows and columns, for example, rows are not necessarily oriented horizontally and columns are not necessarily orientated vertically. Rather, the references to rows and columns refer to solar cells arranged in a more or less regular pattern, wherein groups of solar cells can be identified in which the solar cells are arranged after each other. A group of solar cells in which the solar cells are arranged after each other in one direction can be considered a column, and a group of solar cells in which the solar cells are arranged after each other in a different direction can be regarded a column.

[0118] 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.

[0119] The disclosure is 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.