Wire-based metallization and stringing of solar cells

Abstract

This article describes a wire-based metallization and stringing technology for solar cells, as well as the resulting solar cells, modules and devices. In a certain example, a substrate has a surface. A plurality of N-type and P-type semiconductor regions are disposed in or on the surface of the substrate. A conductive contact structure is disposed on the plurality of N-type and P-type semiconductor regions. The conductive contact structure includes a plurality of conductive wires, each of the plurality of conductive wires being substantially directly and continuously bonded to a corresponding one of the N-type and P-type semiconductor regions.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Provisional Application No. 62 / 649,985, filed earlier on March 29, 2018, the entire contents of which are hereby incorporated by reference herein. Technical Field

[0003] Embodiments of the present disclosure relate to the field of renewable energy, and more particularly, include wire-based metallization and stringing techniques for solar cells and resulting solar cells, modules, and devices. Background Art

[0004] Photovoltaic cells (often referred to as solar cells) are well-known devices for converting solar radiation directly into electrical energy. Generally speaking, solar cells are manufactured on semiconductor wafers or substrates using semiconductor processing techniques to form pn junctions near the surface of the substrate. Solar radiation that impinges on the substrate surface and enters the substrate forms electron and hole pairs in the bulk of the substrate. The electron and hole pairs migrate to p-doped and n-doped regions in the substrate, thereby generating a voltage difference between the doped regions. The doped regions are connected to conductive regions on the solar cell to direct current from the cell to an external circuit coupled thereto.

[0005] Electrical conversion efficiency is an important characteristic of solar cells because it is directly related to the ability of the solar cell to generate electricity; higher efficiency provides added value to the end customer; and, all other things being equal, higher efficiency also reduces the manufacturing cost per watt. Likewise, simplified manufacturing methods offer the opportunity to reduce manufacturing costs by reducing the unit cost of production. Therefore, techniques for improving solar cell efficiency and techniques for simplifying the manufacture of solar cells are generally needed. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1A A plan view of the back side of a solar cell with wire-based metallization according to a certain embodiment of the present disclosure is shown.

[0007] Figure 1B Shown with Figure 1A A cross-sectional view corresponding to a solar cell.

[0008] Figure 2A Cross-sectional views of (a) a conventional bonding wire and (b) a compressed wire are shown according to certain embodiments of the present disclosure.

[0009] Figure 2B (c) a cross-sectional view and (d) a cross-sectional view of a compressed wire according to an embodiment of the present disclosure

[0010] (b) Plan view of the compressed wire.

[0011] Figure 3 Included is a schematic diagram illustrating the concept of compression bonding a wire to a solar cell surface according to a certain embodiment of the present disclosure.

[0012] FIG. 4A to FIG. 4C A plan view showing various stages in a method of metallization and stringing of a back-contact solar cell according to an embodiment of the present disclosure is shown.

[0013] Figure 5 A solar cell string according to a certain embodiment of the present disclosure is shown.

[0014] Fig. 6A is an image of an area between two solar cell portions and a corresponding pictorial plan view of two such solar cells according to a certain embodiment of the present disclosure.

[0015] Figure 6B and Figure 6C are images showing the surface texture of a smooth round wire before bonding and a wire with microgrooves after bonding, respectively, according to a certain embodiment of the present disclosure.

[0016] Fig.6D An inter-cell interconnection of two adjacent cells according to a certain embodiment of the present disclosure is shown.

[0017] Fig. 7A A plan view of the back side of a solar cell with wire-based metallization according to a certain embodiment of the present disclosure is shown.

[0018] Figure 7B Shown with Fig. 7A A cross-sectional view corresponding to a solar cell.

[0019] Figure 8 is a graph of solar cell efficiency (%) of a solar cell with conductive lines compressed to the silicon surface without an intermediate M1 layer and a solar cell with conductive lines compressed to the silicon surface and an intermediate M1 layer in a fishbone pattern according to a certain embodiment of the present disclosure.

[0020] Fig. 9 Plan views of (a) an entire solar cell and (b) a portion of the cell are shown with an M1 layer having conductive lines and a fishbone pattern according to certain embodiments of the present disclosure.

[0021] Fig.10 Detailed description is given of cross-sectional views of (a) a solar cell before a bus bar is folded and (b) a solar cell after the bus bar is folded according to a certain embodiment of the present disclosure.

[0022] Fig.11A and Fig. 11BPlan views of stages in a metallization method for a solar cell and for coupling the solar cell according to a certain embodiment of the present disclosure are shown.

[0023] Fig. 12A Schematic diagrams of (a) a bond head and (b) a wire path through the bond head according to certain embodiments of the present disclosure are shown.

[0024] Fig. 12B A cross-sectional view of a bonding head of a tool for bonding a wire to a solar cell according to a certain embodiment of the present disclosure is shown, wherein the cross section is taken along a plane parallel to a wire guiding groove and the center of the groove.

[0025] Fig. 12C A bottom view of a bond head of a tool for bonding a wire to a solar cell is shown according to a certain embodiment of the present disclosure.

[0026] Fig.12D A possible back surface of a bond head according to a certain embodiment of the present disclosure is shown.

[0027] Fig.13 is a schematic diagram showing side and top views of a tool system incorporating an ultrasonic bonder and a wire guide according to a certain embodiment of the present disclosure.

[0028] Fig.14 is a schematic diagram showing side and top views of a tool system with separate ultrasonic bonders and wire guides according to certain embodiments of the present disclosure.

[0029] FIG. 15A to FIG. 15D An example semiconductor substrate manufactured using the methods, approaches, or apparatus described herein is shown according to some embodiments.

[0030] Fig.16A and Fig. 16B Cross-sectional and plan views of various arrangements of wire-based metallization of a solar cell according to a certain embodiment of the present disclosure are shown. DETAILED DESCRIPTION

[0031] The following specific embodiments are merely exemplary in nature and are not intended to limit the application and use of these embodiments or such embodiments. As used herein, the word "exemplary" means "used as an example, instance or illustration". Any embodiment described herein as exemplary is not necessarily preferred or advantageous over other embodiments. In addition, it is not intended to be bound by any express or implied theory presented in the aforementioned technical field, background technology, invention content or the following specific embodiments.

[0032] References to "one embodiment" or "an embodiment" are not necessarily to the same embodiment. The particular features, structures, or characteristics may be combined in any suitable manner consistent with the present disclosure.

[0033] Terminology. The following paragraphs provide definitions and / or context for terms found in this disclosure (including the appended claims):

[0034] "Comprising" is an open term and does not exclude other structures or steps.

[0035] "Configured to" refers to a structure by indicating a device, such as a unit or component, including a structure that performs one or more tasks during operation, and such structure is configured to perform the task even if the device is not currently in operation (e.g., not turned on / activated). A device "configured to" perform one or more tasks is expressly intended not to invoke the interpretation of 35 U.S.C. §112(f), paragraph 6, as a method or step plus function.

[0036] The terms "first", "second", etc. are used as labels for the nouns that follow them and do not imply any type of order (e.g., spatial, temporal, logical, etc.). For example, referring to a "first" solar cell does not necessarily mean that the solar cell is in a certain sequence; rather, the term "first" is used to distinguish the solar cell from another solar cell (e.g., a "second" solar cell).

[0037] Unless expressly stated otherwise, "coupled" means that an element, feature, structure, or node is or can be joined or communicated with another element / node / feature, either directly or indirectly, and not necessarily directly mechanically.

[0038] "Prevent" describes reducing, diminishing, minimizing, or effectively or physically eliminating something, such as completely avoiding an outcome, consequence, or future state.

[0039] "Doped regions", "semiconductor regions" and similar terms describe semiconductor regions disposed in, on, over, or above a substrate. Such regions may have N-type conductivity or P-type conductivity, and the doping concentration may vary. Such regions may refer to multiple regions, such as a first doped region, a second doped region, a first semiconductor region, a second semiconductor region, etc. These regions may be formed from polysilicon on the substrate or as part of the substrate itself.

[0040] "Thin dielectric layer", "tunneling dielectric layer", "dielectric layer", "thin dielectric material" or intermediate layer / material refers to a material located on a semiconductor region, between a substrate and another semiconductor layer, or between doped regions or semiconductor regions on or within a substrate. In a certain embodiment, the thin dielectric layer can be a tunneling oxide layer or nitride layer having a thickness of about 2 nanometers or less. The thin dielectric layer can be referred to as a very thin dielectric layer through which electrical conduction can be achieved. The conduction can be due to quantum tunneling and / or the presence of smaller regions that are directly physically connected through thin points in the dielectric layer. Exemplary materials include silicon oxide, silicon dioxide, silicon nitride, and other dielectric materials.

[0041] An "intermediate layer" or "insulating layer" describes a layer that provides electrical insulation, passivation, and blocks light reflectivity. The intermediate layer can be multiple layers, such as a stack of intermediate layers. In some cases, the insulating layer can be interchanged with a tunneling dielectric layer, while in other cases, the insulating layer is a masking layer or an "anti-reflective coating" (ARC layer). Exemplary materials include silicon nitride, silicon oxynitride, silicon dioxide, aluminum oxide, amorphous silicon, polycrystalline silicon, molybdenum oxide, tungsten oxide, indium tin oxide, tin oxide, vanadium oxide, titanium oxide, silicon carbide, and other materials. In a certain example, the intermediate layer can include a material that can act as a moisture barrier. Additionally, for example, the insulating material can be a passivation layer of a solar cell.

[0042] "Substrate" may refer to, but is not limited to, a semiconductor substrate such as silicon, specifically, such as a single crystal silicon substrate, a polycrystalline silicon substrate, a wafer, a silicon wafer, and other semiconductor substrates for solar cells. In a certain example, such substrates may be used in microelectronic devices, photovoltaic cells or solar cells, diodes, photodiodes, printed circuit boards, and other devices. These terms are used interchangeably herein.

[0043] "About" or "approximately." As used herein, with respect to recited values, including, for example, integers, fractions, and / or percentages, the term "about" or "approximately" generally means that the recited value encompasses a range of values ​​(e.g., + / - 5% to 10% of the recited value) that one of ordinary skill in the art would consider equivalent to the recited value (e.g., performing substantially the same function, acting in substantially the same manner and / or having substantially the same results).

[0044] In addition, certain terms may be used in the following description for reference purposes only, and thus these terms are not intended to be limiting. For example, terms such as "upper," "lower," "above," and "below" refer to directions provided for reference in the accompanying drawings. Terms such as "front," "back," "rear," "side," "outside," and "inside" describe the orientation and / or position of certain portions of a component within a consistent but arbitrary reference system, which orientation and / or position can be clearly understood by reference to the text describing the component in question and the associated drawings. Such terms may include the words specifically mentioned above, their derivatives, and words of similar meaning.

[0045] Wire-based metallization and serial connection techniques for solar cells and the resulting solar cells, modules, and devices are described herein. In the following description, many specific details such as specific process flow operations are set forth in order to provide a thorough understanding of the embodiments of the present disclosure. It will be apparent to those skilled in the art that embodiments of the present disclosure may be practiced without these specific details. In other examples, well-known manufacturing techniques, such as lithography and patterning techniques, are not described in detail to avoid unnecessarily obscuring the embodiments of the present disclosure. In addition, it should be understood that the various embodiments shown in the figures are exemplary displays and are not necessarily drawn to scale.

[0046] The present invention discloses a solar cell. In one embodiment, a substrate has a back surface and an opposite light receiving surface. A plurality of semiconductor regions are arranged in or on the back surface of the substrate. A semiconductor contact structure is arranged on these semiconductor regions. The semiconductor contact structure includes a plurality of conductive wires, each of which is substantially directly and continuously bonded to a corresponding one of the semiconductor regions. In one embodiment, each of the plurality of conductive wires may be bonded to one of the semiconductor regions through a metal layer. In a certain example, the metal layer may be a metal seed layer. In a certain embodiment, each of the plurality of conductive wires may be an uncoated conductive wire. In one example, the conductive contact structure may include one uncoated conductive wire or a plurality of uncoated conductive wires.

[0047] In addition, a solar cell string is disclosed herein. In one embodiment, a solar cell string includes a plurality of solar cells, such as back contact solar cells or front contact solar cells. Each of the plurality of back contact solar cells includes a P-type doped diffusion region and an N-type doped diffusion region. A plurality of conductive wires are arranged above the back surface of each of the plurality of solar cells, wherein each of the plurality of conductive wires is substantially parallel to the P-type doped diffusion region and the N-type doped diffusion region of each of the plurality of solar cells. In a region between each adjacent pair of cells of the plurality of solar cells, every other conductive wire of the plurality of conductive wires is cut. The portion of the uncut conductive wire has a different cross-sectional profile in a region between each adjacent pair of cells of the plurality of solar cells compared to the portion of the uncut conductive wire bonded to the solar cell.

[0048] This document also discloses a method for making a solar cell string. In one embodiment, an electrical coupling method of solar cells involves arranging conductive wires neatly on the back side of adjacent solar cells. The arranged conductive wires are substantially parallel to the P-type doped diffusion region and the N-type doped diffusion region of the solar cell. The method involves directly bonding the conductive wires to the P-type doped diffusion region and the N-type doped diffusion region on the back side of each of the solar cells using thermocompression bonding, ultrasonic bonding, or thermosonic bonding.

[0049] This document also discloses an electrical coupling system for solar cells. In one embodiment, a system includes a wire support for aligning a conductive wire substantially parallel to a P-type doped diffusion region and an N-type doped diffusion region of each of the solar cells. The system also includes a bonding head for bonding a wire to the P-type doped diffusion region and the N-type doped diffusion region on the back side of each of the solar cells. The system also includes a cutter for cutting the wire.

[0050] Thus, one or more embodiments described in this document are directed to metallization and stringing techniques. According to various embodiments, wires can be used to string back-contact solar cells together instead of patterned cell interconnects. The wires can also be used as metallization structures to collect current flowing through the cells, and these wires are either metallized themselves or used as the metallization structure together with the first-level metallization structure on the solar cell.

[0051] To provide background information, the technology for connecting back-contact solar cells in series can be different from the technology for connecting front-contact cells in series. Prior art connecting solar cells in series can involve the use of metal ribbons that run from the back of one cell to the front of the next cell. In other words, between two cells, a ribbon can run from the bottom of one cell and across the top of another adjacent cell (such as the next cell). Running from the front of a cell to its back can cause manufacturing challenges (e.g., difficulty in alignment, etc.).

[0052] In one example involving a back-contact cell, the metal finger electrodes of each polarity (N and P) can be connected to a single bus bar at the edge of the cell. Then, soldering can be performed from the "P bus bar" (e.g., the bus bar connected to the metal finger electrodes of a given P-type region) of one cell to the "N bus bar" (e.g., the bus bar connected to the metal finger electrodes of a given N-type region) of the next solar cell to form the cell interconnect. The spacing used for these bus bars on the solar cell reduces the overall efficiency of the solar cell. Moreover, the process of forming the metal finger electrodes and bus bars on the cell can be costly.

[0053] According to various embodiments, instead of using a bus bar to collect the current running through each cell, a continuous conductive wire is used to directly connect each finger electrode (e.g., a P-type doped diffusion region or an N-type doped diffusion region) of one cell to the corresponding finger electrode (e.g., a finger electrode of opposite polarity) of the next cell. First, the wires are attached to some or all of the cells in a whole string of cells (e.g., a continuous string) to short-circuit each pair of solar cells. Then, one of every other wires between the two cells is cut to restore independent P and N electrodes. For example, the P and N electrodes are each independent but connected back and forth if every other wire is not cut. Every other wire connects the P electrode of the first cell to the N electrode of the second cell. The other wires connect the N electrode of the first cell to the P electrode of the second cell. If one of the two sets of wires is not cut, the pair of cells will be short-circuited. Therefore, by cutting one of the two sets of wires between a given pair of cells, the independent P and N electrodes can be restored.

[0054] It should be understood that it is generally necessary to improve the metallization method for forming the conductive contacts of solar cells. Compared with some metallization methods (e.g., electroplating conductive contacts on solar cells), other techniques may include bonding conductive foil and / or conductive wires to semiconductor substrates (e.g., silicon substrates). Such methods may require a large number of wires to be loaded and reloaded into bonding tools, which may be particularly challenging for settings and processes. The technology described herein provides methods and equipment for placing, aligning and bonding conductive wires and semiconductor substrates in solar cell metallization and / or series connection processes. Various embodiments are provided throughout this article.

[0055] Figure 1A and Figure 1B A plan view of the back side of a solar cell with wire-based metallization according to an embodiment of the present disclosure and a corresponding cross-sectional view are respectively shown.

[0056] refer to Figure 1A and Figure 1B , a portion 100 of a solar cell includes a substrate 102 having a back surface 104 and an opposite light receiving surface 106. In or on the back surface 104 of the substrate 102, a plurality of N-type and P-type semiconductor regions are provided (108 shows such a region). A conductive contact structure is provided on the plurality of N-type semiconductor regions and P-type semiconductor regions 108. The conductive contact structure includes a plurality of conductive wires (110 shows one conductive wire). Each conductive wire 110 is substantially directly and continuously bonded to the solar cell. It should be understood that in some embodiments, a continuous bonding or substantially continuous bonding arrangement is described with respect to exposed silicon. In a particular embodiment, a large portion of the semiconductor (e.g., polysilicon) is covered by a dielectric (e.g., a bottom anti-reflective coating layer), so the wire is directly in contact with the semiconductor only at periodic openings in the dielectric, but does so continuously or substantially continuously. In some embodiments, these openings are also continuous, for example, in contrast to non-periodic openings in the dielectric. In a certain embodiment, each conductive wire 110 can be an uncoated conductive wire. In one example, the conductive contact structure can include an uncoated conductive line or a plurality of uncoated conductive lines.

[0057] In one embodiment, each of the plurality of conductive lines 110 is parallel to the first direction 112, forming a one-dimensional layout of the metallization layer of the portion 100 of the solar cell. FIG. 4A to FIG. 4C and Figure 5 Examples of this are described in more detail.

[0058] One or more embodiments described herein provide a technique for bonding (thermocompression or thermosonication and compression) a metal wire (such as an aluminum wire) to a solar cell. In a certain embodiment, the metal wire is allowed or caused to flow away or stretch away from a bonding interface (such as a silicon bonding interface). When the metal wire is stretched, the existing surface oxide cracks to expose unreacted metal (e.g., a fresh aluminum surface), which will easily bond to the features of the solar cell. It should be understood that in some embodiments, aluminum wires are preferred because they can be subjected to thermocompression bonding in the range of about 300 to 450 degrees Celsius or at lower temperatures when ultrasonic energy is included. In a certain specific example, the bonding temperature may include about 350 degrees Celsius. In contrast, copper wires may need to be heated to a substantially higher temperature for thermocompression bonding, and therefore, when cooled after bonding to a silicon substrate, may cause the silicon substrate to bend. It should also be understood that excessive bending of the copper wire may be caused by the fact that the yield strength of copper is higher than that of pure aluminum. When cooled, both aluminum and copper will shrink to drive the wafer to bend, but the extent of shrinkage of aluminum is limited by the low yield strength. Many aluminum alloys have a higher yield strength (e.g., AL6061 is 241 MPA), while the yield strength of pure aluminum is 11 MPA. Therefore, in some embodiments, pure or substantially pure aluminum wire is used to form the metallization layer of the silicon-based solar cell to achieve low bending. In a certain example, the aluminum wire does not include any additional coating or layer. However, in other embodiments, copper wire is used to form the metallization layer of the silicon-based solar cell.

[0059] According to one or more embodiments of the present disclosure, the conductive wire has a non-circular or slightly flattened cross-section due to a compression bonding process such as a thermocompression bonding process or a thermosonic or ultrasonic bonding process. As a comparative example, Figure 2A Cross-sectional views of (a) a conventional bonding wire and (b) a compressed wire are shown according to certain embodiments of the present disclosure.

[0060] refer to Figure 2A , a conventional bonding wire comprises a wire 200 bonded to a silicon feature 206 such as a substrate or an emitter layer via a solderable layer 202 and / or a conductive adhesive or solder 204. The wire 200 maintains a substantially circular shape. In contrast, the wire 200 of FIG. Figure 2A In part (b), a compression bond wire (such as a thermal compression wire) includes a wire 250 directly bonded to (i.e., in direct contact with) a silicon feature 252 such as a substrate or an emitter layer. The wire 250 has a flat shape and has extended flat upper and lower surfaces and curved side surfaces. In one embodiment, the "flat" wire shape is a flat circular shape, such as Figure 2AIn other embodiments, the starting wire has a square, rectangular, triangular, pseudo-square or pseudo-triangular shape, and the resulting compressed wire is a flattened version of the corresponding shape. In still other embodiments, a triangular cross-section can be made after bonding, so that the initially used round wire ends up with a rectangular or triangular shape with a flat bottom to match the surface contour of the wafer. In one embodiment, Figure 2A The conductor 250 of part (b) does not include an additional layer or coating, for example, Figure 2A In contrast to the conductor 200 of part (a), the conductor includes an additional solderable layer 202.

[0061] According to one or more embodiments of the present disclosure, due to compression bonding such as a thermocompression bonding process or a thermosonic or ultrasonic bonding process, the conductive wire is in direct contact with the silicon portion of the solar cell, but there is a small gap between the bonding surfaces. As an example, Figure 2B A (c) cross-sectional view and a (d) plan view of a compressed wire according to a certain embodiment of the present disclosure are shown.

[0062] refer to Figure 2B , a compression bond wire (such as a thermal compression wire) includes a wire 250 that is directly bonded to (i.e., in direct contact with) a silicon feature 252 such as a substrate or an emitter layer. Even though there may be voids, oxides, surface contaminants, or coatings on the silicon (shown as dark areas) on the order of several microns between the bonding surfaces, the wire 250 is considered to be directly and substantially continuously bonded to the silicon feature 252. In a certain embodiment, the bulk material of the wire 252 is within 2 microns of the bulk material of the silicon feature 252 because no solder, flux, adhesive, polymer, or solderable layer is used for bonding.

[0063] refer to Figure 2B 2, which is a plan view of a wire 250 bonded to a silicon region 252. The wire has a substantially flat surface along the center of the wire. In one embodiment, the wire 250 is continuously bonded to the silicon over a length, for example, greater than 10 mm, as opposed to point bonding produced by a spot welding process. In another embodiment, closely spaced periodic regions of the wire 250 have greater compression (due to periodic increases in downward force) to enhance adhesion.

[0064] Figure 3 Included is a schematic diagram illustrating the concept of compression bonding a wire to a solar cell surface according to a certain embodiment of the present disclosure.

[0065] refer to Figure 3In part (a), a wafer 302 is supported by a chuck 300 (e.g., a graphite vacuum chuck maintained at a temperature in the range of, for example, about 400 to 450 degrees Celsius, such as 420 degrees Celsius). As the wafer 302 moves in the direction of the arrow, the conductive wire 304 is compressed against the surface of the wafer 302. The compression may involve oxide decomposition 306 and may be achieved using a pre-aligner 308. A fixed slide 310 applies pressure to the conductive wire 304 and, in some embodiments, may be maintained at substantially the same temperature as the chuck 300.

[0066] refer to Figure 3 , the incoming wire 352 is positioned on the surface of a substrate 354 supported by a chuck 350. The chuck 350 moves in the direction of the incoming page and pushes the wire 352 toward a fixed slotted bond head slider 356. After bonding, the substrate 354 has a heat-compressed wire 352' disposed thereon. In one embodiment, the incoming wire is circular, but the slot in the bond head is triangular or rectangular or trapezoidal, thereby forcing the resulting metal finger electrodes to take on that shape, similar to an extrusion process, as shown. In one particular embodiment, the triangular finger electrodes are beneficial for light capture, especially in double-sided applications.

[0067] FIG. 4A to FIG. 4C A plan view showing various stages in a method of metallization and stringing of a back-contact solar cell according to an embodiment of the present disclosure is shown.

[0068] Figure 4A A back view of adjacent solar cells 402 to be connected in series is shown, including alternating P-type doped diffusion regions 404 and N-type doped diffusion regions 406. In one such embodiment, each of the plurality of solar cells 402 is substantially rectangular, and the P-type doped diffusion regions 404 and the N-type doped diffusion regions 406 are substantially parallel to the edges 401, 403 of the solar cell 402. The substantially rectangular solar cells may be, for example, square or another rectangular shape, and may have standard corners, cut corners, or rounded corners. Figure 4A As shown, since the end of one side (e.g., side 403) of the solar cell 402 is a P-finger electrode and the opposite side (e.g., side 401) is an N-finger electrode, the solar cell 402 is asymmetric. The asymmetric solar cells can then be placed along the cell string in alternating orientations, such as Figure 4A The design of the asymmetric solar cell, together with the alternating orientation along the string of cells, makes it possible to use wires parallel to the edges 401, 403 of the solar cells, because the P finger electrodes on one of the solar cells are directly opposite to the N finger electrodes of the adjacent solar cell, as described below in conjunction with Figure 4C This is explained.

[0069] refer to Figure 4B , a method of metallization and serial connection includes attaching a non-conductive shield, tape or paint strip 408 to the back of adjacent solar cells 402. When viewed from the front, the non-conductive shield, tape or paint strip 408 can be used to hide the wires. Therefore, the non-conductive shield covers the exposed portion of the wires between each adjacent pair of solar cells. Therefore, according to various embodiments, the non-conductive shield, tape or paint strip 408 includes a substantially opaque material that is sufficient to shield the wires when viewed from the front. The non-conductive shield, tape or paint strip 408 can also help align the solar cells and / or fix the solar cells 402 together. The non-conductive shield, tape or paint strip 408 can include materials such as polypropylene or polyethylene, and can also include an adhesive layer such as acrylate. The non-conductive shield, tape or paint strip 408 with an adhesive layer can be beneficial to help align. Although the non-conductive shield, tape or paint strip 408 may be beneficial for the above reasons, other embodiments do not include a non-conductive shield (e.g., the non-conductive shield 408 may be optional).

[0070] refer to Figure 4C , the method of metallization and serial connection includes aligning conductive wires 410 over the back sides of adjacent solar cells 402. In one embodiment, the conductive wires 410 are aligned substantially parallel to the P-type doped diffusion regions 404 and the N-type doped diffusion regions 406 of the solar cells 402. The cross-sectional shape of the conductive wires 410 may be circular, flat, slightly flat, or other shapes. Circular conductive wires may be beneficial because they may be curled or wound. In another embodiment involving the arrangement and placement of circular conductive wires, the conductive wires may be flattened before or during bonding the conductive wires to the back sides of each of the solar cells.

[0071] The conductive wires include a conductive material (e.g., a metal such as aluminum, copper, or another suitable conductive material), with or without a coating such as tin, silver, or nickel. In one embodiment, no organic solderability preservative is used on the conductive wires. In another embodiment, an organic solderability preservative is used on the conductive wires. Figure 4CIn the illustrated embodiment, the number of wires is equal to (or substantially equal to) the number of diffusion regions of each of the plurality of solar cells. In one example, the number of wires may be approximately between 5 and 15 wires, between 10 and 20 wires, between 15 and 25 wires, between 20 and 30 wires, between 25 and 35 wires, between 30 and 40 wires, between 35 and 45 wires, between 40 and 50 wires, or greater than 50 wires. In one such embodiment, a single wire is aligned over each of the P-type doped diffusion region 404 and the N-type doped diffusion region 406 of the solar cell 402. According to one embodiment, each of the wires 410 is approximately centered over one of the P-type doped diffusion region 404 and the N-type doped diffusion region 406 of the solar cell 402. As Figure 4C As shown, the conductive lines 410 may be aligned such that they are substantially parallel to the edges 401 , 403 of the plurality of solar cells 402 .

[0072] Reference again Figure 4C , the conductive wires 410 may be aligned by a variety of mechanisms. For example, in one embodiment, aligning the conductive wires 410 over the back surfaces of adjacent solar cells 402 involves the use of a grooved roller or bonding head. Instead of or in addition to a grooved roller or bonding head, other mechanisms may be used to align the conductive wires 410 over the P-type doped diffusion regions 404 and the N-type doped diffusion regions 406 of the solar cells 402. For example, according to one embodiment, a reed or other suitable mechanism may be used to align and guide the conductive wires. According to a certain embodiment, when aligning the conductive wires on a solar cell other than the first, the fact that the conductive wires are bonded to the first solar cell may help align the conductive wires on subsequent solar cells.

[0073] After the conductive wires 410 are aligned, they are bonded to the back side of the solar cell 402, i.e., the P-type doped diffusion region 404 and the N-type doped diffusion region 406 of the solar cell 402, for example, using a thermocompression bonding or ultrasonic bonding method as described herein. Figure 4C According to one embodiment, the metallization and serial connection method includes cutting off every other wire in the wires 410 between each adjacent pair of solar cells 402. Figure 4CAs shown, the wire 410 at the cutting position 412 is cut so that all the wires connected to the P-type diffusion region on one side of the solar cell 402 and all the wires connected to the N-type diffusion region on the opposite side of the solar cell are cut. Before the wire 410 at the cutting position 412 is cut, the pair of solar cells is short-circuited. Cutting the wire 410 allows the solar cells to be electrically coupled to collect current from the solar cell string. Cutting the wire 410 at the cutting position 412 may involve any wire cutting technique. For example, the wire 410 at the cutting position 412 may be cut with a laser or a blade. Although FIG. 4A to FIG. 4C Only two solar cells are shown, but a solar cell string may include any number of solar cells connected in series (eg, two or more solar cells connected in series). The process is continuous, as solar cell strings of any length may be made.

[0074] In another embodiment, conduction in the diffusion region occurs perpendicular to the direction of the wire (e.g., a one-dimensional grid of p- and n-regions has a superimposed one-dimensional grid of wires bonded perpendicularly thereto, but where a single wire only contacts either the n-region or the p-region, as controlled by an opening in the dielectric).

[0075] Figure 5 An example of a solar cell string according to a certain embodiment of the present disclosure is shown. Figure 5 The solar cell string 500A shown includes a plurality of solar cells 502 electrically coupled together in series. The solar cell string 500A has two end solar cells 501, and an inner solar cell 503 connected in series between the two end solar cells 501. Each of the two end solar cells 501 is electrically coupled with a bus bar 514. At each of the end solar cells 501, every other wire of the wire is coupled with a bus bar 514 to only one of the two electrodes of the end solar cell, that is, either a P-type doped diffusion region 504 or an N-type doped diffusion region 506. In one embodiment, to couple every other wire of the wires of the end solar cells 501 with the bus bar 514, all wires at each end of the string may be cut first, and only wires used for the P-type doped diffusion region or the N-type doped diffusion region may be connected. Alternatively, all wires used for the end solar cells 501 may be connected to the bus bar 514 first, and then every other wire may be cut.

[0076] Only the end solar cells 501 are connected to the bus bar 514, which is in contrast to other stringing techniques, which may involve attaching one or more bus bars to each solar cell according to some embodiments. The bus bar 514 may couple the solar cell string 500A to another solar cell string (e.g., solar cell string 500B) or to another circuit (e.g., a circuit outside the module passing through a junction box).

[0077] like Figure 5 As shown, in one embodiment, a given tangent segment is to electrically couple at most two solar cells in series, wherein the P-type doped diffusion region of one of the two solar cells is connected to the N-type doped diffusion region of the other solar cell. However, other embodiments may include more than two solar cells coupled together by a given tangent segment. For example, if the solar cells are connected in parallel, it is possible to connect more than two cells by a given tangent segment. Also, as shown in FIG. Figure 5 As shown, in one embodiment, the tangent segment that electrically couples the end solar cell 501 to the bus bar 514 couples a single solar cell to the bus bar 514. However, as described above, in various embodiments of parallel solar cells, a given tangent segment can connect more than one solar cell to the bus bar. Therefore, a solar cell string can be formed with multiple wires 510 by aligning and bonding these wires over the P-type doped diffusion region and the N-type doped diffusion region of each of the solar cells, and then cutting off some of the wires to achieve the desired stringed solar cell configuration.

[0078] Therefore, according to one or more embodiments of the present disclosure, a string connection method provides a structure with compressed wires, wherein every second wire between the wafer and the bus bar at the end is cut. It should be understood that the portion of the compressed wire between the solar cells is not compressed. In one embodiment, the wire that is not cut between the solar cells has a different cross-section on the solar cell than between the solar cells. As an example, Fig. 6A is an image of an area between two solar cell portions and a corresponding pictorial plan view of two such solar cells according to a certain embodiment of the present disclosure.

[0079] refer to Fig. 6A, the solar cells 602 include wires 600 located thereon and therebetween. In one such embodiment, every other wire 600 between the cells 602 is cut. For the wires that are not cut, the wires 600 have a substantially circular cross-section between the solar cells 602 and a flat circular cross-sectional profile on the solar cells 602, wherein the wires 600 have been compressed (e.g., thermally compressed or ultrasonically compressed) to the solar cells 602. In a certain embodiment, each wire 600 has a surface with microgrooves 604 along the length of the wire 600, as shown. In one such embodiment, the microgrooves 604 are formed in the wires 600 by wire guides during the process of guiding the wires 600 to align with the cells 602.

[0080] It should be understood that the microgrooves 604 can be formed by a series connection and / or bonding process. As an example, Figure 6B and Figure 6C 6 and 7 respectively show the surface texture of a smooth round wire 620 before bonding and a wire 622 with microgrooves after bonding according to certain embodiments of the present disclosure. The microgrooves of the wire 622 may be formed as part of the wire bonding process to the battery.

[0081] Reference again Fig. 6A , two interconnected cells may each have an associated bus bar. As an example, Fig.6D An inter-cell interconnection of two adjacent cells according to a certain embodiment of the present disclosure is shown.

[0082] refer to Fig.6D , the first half solar cell portion 630 is interconnected to the second half solar cell portion 632 by wire 634. In one embodiment, wire 634 includes a stress relief feature between cells 630 and 632, where every second wire is cut and the wire is bent in the plane of cells 630 and 632. Fig. 6A As depicted, according to a certain embodiment of the present disclosure, portions of the wire 634 between the cell portions 630 and 632 are substantially round and smooth, while those portions of the wire 634 are flattened to some extent and have microgrooves formed therein. In a certain embodiment, as depicted, each of the half solar cell portions 630 and 632 has an associated bus bar 636.

[0083] In another aspect, the wire is not compressed directly to the silicon surface, but rather to a metal seed layer on the silicon surface. Fig. 7A and Figure 7B A plan view of the back side of a solar cell with wire-based metallization according to a certain embodiment of the present disclosure is shown, along with a corresponding cross-sectional view.

[0084] refer to Fig. 7A and Figure 7B , a portion 700 of a solar cell includes a substrate 702 having a back surface 704 and an opposite light receiving surface 706. In or on the back surface 704 of the substrate 702, a plurality of N-type and P-type semiconductor regions are provided (708 shows such a region). A conductive contact structure is provided on the plurality of N-type and P-type semiconductor regions 708. The conductive contact structure includes a plurality of conductive wires (710 shows one conductive wire). Each conductive wire 710 is bonded to a bonding point of the solar cell. Each of the plurality of conductive wires 710 is parallel to a first direction 712, forming a one-dimensional layout of the metallization layer of the portion 700 of the solar cell.

[0085] In one embodiment, if Fig. 7A and Figure 7B As depicted, the conductive contact structure also includes a metal seed layer 714 (e.g., M1 layer) disposed between the plurality of N-type and P-type semiconductor regions 708 and the plurality of conductive wires 710. In some embodiments including the metal seed layer 714, the conductive wires may be soldered or welded (e.g., with a laser) to the metal seed layer 714. In a certain embodiment, the metal seed layer 714 is an aluminum seed layer. In one such embodiment, the aluminum layer has a thickness of approximately between 50 and 150 nanometers, between 100 and 200 nanometers, between 150 and 250 nanometers, between 200 and 300 nanometers, between 250 and 350 nanometers, between 300 and 400 nanometers, between 350 and 450 nanometers, or between 400 and 500 nanometers, and contains greater than approximately 97% aluminum and approximately 0 to 2% silicon. In other embodiments, the metal seed layer 714 contains a metal such as, but not limited to, nickel, silver, cobalt, titanium, or tungsten.

[0086] It should be understood that there can be different approaches to including the M1 layer: (1) M1 is constructed by etching after bonding the wires. In this case, M1 is actually an intermediate layer and is constructed by etching after bonding the wires (where the wires are used to protect the underlying metal seed layer). In this case, the M1 layer can be very thin because it only serves to improve bonding and no separate seed patterning step is required except for a very short etch after placing the wires. However, since the collection between the wires is in the semiconductor or in the polysilicon, a relatively large number of wires may be required (although, as described below, the polysilicon and doped regions can be interdigitated to allow the use of an intermediate number of wires). In another approach (2), M1 is designed for collection between wires, which is compatible with an interdigitated pattern or a pattern in which the M1 layer is parallel to the wires but wider than the wires. In one embodiment, a larger number of collection wires allows M1 to be relatively thin. In some examples, the number of conductors may be between 5 and 15 conductors, between 10 and 20 conductors, between 15 and 25 conductors, between 20 and 30 conductors, between 25 and 35 conductors, between 30 and 40 conductors, between 35 and 45 conductors, between 40 and 50 conductors, or greater than 50 conductors.

[0087] Figure 8 is a graph 800 of solar cell efficiency (%) for a solar cell with conductive lines compressed to the silicon surface without an intervening M1 layer and a solar cell with conductive lines compressed to the silicon surface and an intervening M1 layer in a fishbone pattern according to certain embodiments of the present disclosure. Fig. 9 Plan views of (a) an entire solar cell and (b) a portion of the cell are shown with an M1 layer having conductive lines and a fishbone (interdigitated finger electrodes) pattern according to certain embodiments of the present disclosure.

[0088] refer to Fig. 9 , the solar cell includes a seed layer (M1 layer) 902 having a fishbone pattern. A plurality of such fishbone patterns are interlaced with each other. Conductive wires 900 extend parallel to the longitudinal direction of each fishbone pattern of the M1 layer. In a particular embodiment, the spacing of the wires 900 is approximately 1.0 to 1.5 mm, such as 1.2 mm. The M1 layer may be on a larger silicon emitter region 904, such as on a polycrystalline silicon region. Grooves 906 may be formed between such polycrystalline silicon regions. As shown in graph 800, this arrangement provides an efficient solar cell. In other embodiments, a continuous polycrystalline silicon layer or region is used. In another embodiment, the M1 layer is excluded and the polycrystalline silicon emitter layer has a fishbone pattern, effectively providing a seedless fishbone pattern.

[0089] According to one or more embodiments of the present disclosure, folded busbars are implemented by using wire-based metallization. As an example, Fig.10 Detailed description is given of cross-sectional views of (a) a solar cell before a bus bar is folded and (b) a solar cell after the bus bar is folded according to a certain embodiment of the present disclosure.

[0090] refer to Fig.10 In part (a), solar cells 1002 have wire metallization 1000 thereon and the solar cells 1002 are connected in series. Busbars 1004 are included at the ends of the wire metallization 1000. Fig.10 In part (b), the bus bar 1004 is folded over the footprint of the solar cell 1002. As shown, an insulator feature 1006 may be included to isolate the folded portion of the wire metallization 1000 from the wire metallization 1000 on the solar cell 1002.

[0091] Thus, wire-based metallization enables the manufacture of busbars that are folded back into the back cell to reduce the size of the overall module, thereby increasing the efficiency of the module. An insulator is placed between the busbar and the back of the cell to prevent short circuits. In another embodiment, rather than folding the wires back onto the busbars, a conductive member with a patterned insulator is used that allows connection to alternating wires (thus only those wires that are connected to the n wire at one end). In this approach or folding method, the conductive members at the ends of each of the two cells can be connected together by a separate interconnect, or the wires can be terminated at one end of each cell (using a folded member or insulator) and then directly connected to the adjacent cell using a wire that extends beyond the edge of the adjacent cell.

[0092] According to one or more embodiments of the present disclosure, a bond head is used for wire-based metallization, where each wire is aligned and compressed by a heated bond head. The bond head can be fixed to the heated bond head, and the bond head can be maintained at a fixed distance (e.g., about 5 to 50 microns) above the wafer. Using the bond head enables precise control of wire placement on the wafer so that the wire is aligned with the corresponding emitter finger electrode.

[0093] In one embodiment, a solar cell may have a bus bar on one end of the solar cell and a wire metallization extending outward from the other end. In a certain embodiment, the wire metallization on the other end may be electrically connected to a bus bar of another solar cell. In one example, the wire metallization of a solar cell may be located on or in contact with a bus bar of another solar cell. Multiple solar cells may be connected in this manner to form a solar cell string (e.g., two or more solar cells may be connected in series by placing a metallization on one end of one solar cell and in contact with a bus bar at one end of another solar cell).

[0094] In one exemplary bonding scheme, Fig.11A and Fig. 11B Plan views of stages in a metallization method for a solar cell and for coupling the solar cell according to a certain embodiment of the present disclosure are shown.

[0095] refer to Fig.11A , the conductive wire 1110 can be placed 1142 in the bonding head 1132. In addition, a method for bonding the conductive wire 1110 to the semiconductor substrate ( Fig. 11B 1120). In certain embodiments, the conductive wire 1110 may include a conductive material (e.g., a metal such as aluminum, copper, or another suitable conductive material, with or without a coating such as tin, silver, nickel, or an organic solderability preservative). In one embodiment, the conductive wire 1110 may be unrolled from a delivery unit 1101 and then placed 1142 in a bonding head 1132. In some embodiments, the box 1101 may alternatively represent a wire guide, where the wire guide 1101 may be used to align the conductive wire 1110 into the bonding head 1132. In certain examples, the wire guide 1101 may include wires dispensed from a plurality of grooves, wherein the grooves allow the conductive wire 1110 to be aligned into the bonding head 1132.

[0096] Referring to 11B, according to some embodiments, the conductive wire 1110 may be aligned 1144 over the semiconductor substrate 1120. In one embodiment, the semiconductor substrate 1120 is a solar cell. In a certain embodiment, the bond head 1132 may include a plurality of openings. In a certain example, the plurality of openings may allow the conductive wire to be aligned 1144 over the semiconductor substrate 1120. In a certain embodiment, the bond head 1132 may align the conductive wire 1110 with the semiconductor substrate 1120. In one embodiment, the bond head 1132 allows the conductive wire 1110 to be placed over the semiconductor substrate 1120. In some embodiments, components of the bond head 1132 may include stainless steel, ceramic, or graphite.

[0097] Reference again Fig. 11B According to some embodiments, the conductive wire 1110 can be bonded to the semiconductor substrate 1120. In one embodiment, a bonding head 1132 can be used to bond the conductive wire 1110 to the semiconductor substrate 1120. In one embodiment, the bonding head 1132 can implement thermal compression bonding. In one embodiment, the bonding head 1132 can bond the conductive wire 1110 from the first position 1143 to the second position 1145 along the bonding path 1147. In one example, as Fig.11A As depicted, a continuous length of conductive wire 1110 may be placed 1142 from first delivery unit 1101 into bonding head 1132. After conductive wire 1110 is placed into bonding head 1132, reference is made to Fig. 11B , the conductive wire 1110 can be placed into the wire clamping unit 1103, wherein both the conveying unit 1101 and the wire clamping unit 1103 can hold the conductive wire in place during bonding. After the conductive wire 1110 is placed into the wire clamping unit 1103, the conductive wire 1110 can be bonded to the semiconductor substrate 1120 along the bonding path 1147. In one embodiment, the bonding head 1132 prevents lateral movement 1149 of the conductive wire 1110 during bonding 1147. In one example, the bonding head 1132 can prevent the conductive wire 1110 from moving during the bonding process and / or prevent the conductive wire from being misaligned during the bonding process. Fig. 11B As shown, in one example, lateral movement 1149 can be perpendicular to bonding movement and / or path 1147 .

[0098] Fig. 12A Schematic diagrams of (a) a bond head and (b) a wire path through the bond head according to certain embodiments of the present disclosure are shown.

[0099] refer to Fig. 12A In part (a), the bonding head 1200 includes an opening 1202 therein for accommodating each wire. Fig. 12A In part (b), the wire path 1226 includes an entry slot 1220 and an exit slot 1222. A compression zone 1224 is between the entry slot 1220 and the exit slot 1222. In a certain embodiment, the entry slot 1220 has a diameter slightly wider than the diameter of the wire, the compression zone, and the exit slot. The depth of the compression slot 1222 is less than the diameter of the wire, so that the surface of the wire protrudes below the bond head 1200. Due to the rigidity of the wire, and possibly also due to the presence of a pre-aligner or slotted guide adjacent to the bond head, the wire is held in the loaded slot so that the wire is supported by the pre-aligner and extends from the pre-aligner to the slot of the bond head. It should be understood that in some embodiments, even after the wire is cut, due to the rigidity of the wire, the wire will remain in the slot. In a certain embodiment, the bond head 1200 is composed of a material having non-stick properties (e.g., graphite, polished steel with a hard coating (TiN, TiCr, TiAIN, CrN, etc.) or polished ceramic (such as stabilized zirconia)).

[0100] Fig. 12B A cross-sectional view of a bonding head of a tool for bonding a wire to a solar cell according to a certain embodiment of the present disclosure is shown, wherein the cross section is taken along a plane parallel to a wire guiding groove and the center of the groove. Fig. 12C A bottom view of a bond head of a tool for bonding a wire to a solar cell is shown according to a certain embodiment of the present disclosure.

[0101] refer to Fig. 12B, the bonding head 1230 includes one or more grooves 1232 for guiding one or more corresponding wires 1235. A steel holding wire 1234 may be included. A bonding surface 1236 provides a location for performing bonding to the solar cell. A recess 1238 may be included as a location for including a wire cutter, for example. Reference Fig. 12C , showing the guide wire 1235 passing through the bond head 1230 to the bonding surface 1236.

[0102] Fig.12D A possible back surface of a bond head according to an embodiment of the present disclosure is shown. Fig.12D , the back of the bonding head 1200 has a horizontal flat area for cutting 1240 of the wire 1242 ( Fig. 12A portion (a)), or having an edge for cutting 1250 of wire 1252.

[0103] According to one or more embodiments of the present disclosure, wire-based metallization of solar cells is achieved by ultrasonically welding the wires to the solar cells. To provide background information, a large portion of the manufacturing cost of solar cells, particularly interdigitated back contact (IBC) cells, is generated during the metallization process. Metallization typically includes applying a metal seed layer, electroplating or bonding a thick metal layer to the metal seed layer, and then performing one or more process operations to pattern the metal seed layer and / or the thick metal layer to form a desired pattern. By bonding the wires directly to the cell, one or more of the above operations can be eliminated. However, achieving high-quality bonding between aluminum and silicon typically requires low vacuum, high temperature, or both. To address one or more of the above problems, one or more embodiments described herein relate to an ultrasonic welding technique that applies aligned aluminum wires directly to a silicon wafer or silicon nitride coating without the need for a metal seed layer or the high temperatures and pressures required for thermocompression bonding.

[0104] To provide further background information, ultrasonic bonding of metal foil to wafers typically involves the use of a knurled surface attached to an ultrasonic horn that clamps the foil and vibrates it against the surface to be bonded, which is pressed against an anvil. Such knurling is typically very rough and has the potential to pierce very thin wires and damage the underlying surface. By using grooves rather than a knurled surface (i.e., essentially a 1D groove pattern rather than a 2D groove pattern), the wire can be clamped and aligned with features on the wafer for bonding without damaging the wire. In one specific embodiment, this approach enables ultrasonic bonding of aluminum directly to a silicon wafer.

[0105] Fig.13 is a schematic diagram showing side and top views of a tool system 1300 incorporating an ultrasonic bonder and a wire guide according to a certain embodiment of the present disclosure.

[0106] refer to Fig.13 , the wire 1310A is wrapped around an ultrasonic horn 1304, which is coupled to a power source or transducer and a rotary motor 1302. The ultrasonic horn 1304 has a groove / notch that is shallower than the diameter of the wire 1310A and can be rectangular (as shown) or other shapes. This arrangement limits the lateral position of the wire 1310A, but still allows these wires to be pressed onto the surface of the wafer 1306. At the location where metallization should begin, the wire 1310A in the horn 1304 is aligned with the desired surface features near the edge of the wafer 1306. The wire 1310A is ultrasonically bonded by a very short (e.g., <2s, even <0.2s) ultrasonic welding process. The ultrasonic horn / wire guide 1304 is then pulled / rolled across the wafer 1306, where continuous or periodic welds secure the wire in place to provide a bonded wire portion 1310B.

[0107] In one embodiment, the above process can bond dissimilar metals (e.g., copper and aluminum) that would otherwise not adhere to each other during the electroplating process and would rapidly diffuse into each other during the thermocompression bonding process. Heat can be applied (e.g., from a heating plate) to improve adhesion and / or contact resistance. The wire guiding and bonding functions can also be separated by using a wire guide (with a channel to constrain the wire) adjacent to the cylindrical ultrasonic horn 1304, which bonds the wire to the wafer at the location where the wire leaves the guide. In other embodiments, wires embedded in a polymer matrix can be used to simplify the handling of the wires (e.g., a single wire grid can be used instead of 300+ individual wires as input). In one embodiment, for example, ultrasonic agitation can remove any polymer coating from the wire before bonding the wire to the substrate (possibly with different power / pressure / amplitude settings).

[0108] Fig.14 is a schematic diagram showing side and top views of a tool system 1400 with separate ultrasonic bonders and wire guides according to certain embodiments of the present disclosure.

[0109] refer to Fig.14, using a separate wire guide 1452 to guide the wire 1410A from the spool 1408, the wire guide having a channel to constrain the wire 1410A in the lateral dimension. Bonding is accomplished by periodic (or continuous) ultrasonic vibrations from a long, narrow horn 1404, which is not required to guide the wire 1410A, but only to clamp the wire with a knurled surface (e.g., features significantly smaller than the diameter of the wire). Heat from a heating plate 1450 may also be applied along with ultrasonic agitation to assist in bonding. Depending on the feasible bond width, the ultrasonic horn 1404 may be a single cylinder or more than one cylinder / wheel. The process provides a bonded wire portion 1410B on a substrate 1406, which may be supported on a heating plate 1450.

[0110] FIG. 15A to FIG. 15D An exemplary semiconductor substrate manufactured using the methods, methods or apparatus described herein according to some embodiments is shown. In a certain embodiment, the semiconductor substrate is a solar cell 1520a, 1520b, 1520c, 1520d. In a certain embodiment, the solar cell 1520a, 1520b, 1520c, 1520d may include a silicon substrate 1525. In some embodiments, the silicon substrate 1525 may be cleaned, polished, planarized and / or thinned or otherwise processed. In a certain embodiment, the semiconductor substrate 1525 may be a single crystal silicon substrate or a multicrystalline silicon substrate. In a certain embodiment, the silicon substrate 1525 may be an N-type silicon substrate or a P-type silicon substrate. In a certain example, the semiconductor substrate may be a single crystal silicon substrate, such as a bulk single crystal N-type doped silicon substrate. In a certain embodiment, the solar cell 1520a, 1520b, 1520c, 1520d may have a front side 1502 and a back side 1504, wherein the front side 1502 is opposite to the back side 1504. In one embodiment, the front side 1502 may be referred to as a light receiving surface 1502, and the back side 1504 may be referred to as a back surface 1504. In a certain embodiment, the solar cells 1520a, 1520b, 1520c, 1520d may include a first doped region 1521 and a second doped region 1522. In a certain embodiment, the first doped region may be a P-type doped region (e.g., doped with boron), and the second doped region may be an N-type doped region (e.g., doped with phosphorus). In a certain embodiment, the solar cells 1520a, 1520b, 1520c, 1520d may include an anti-reflective coating (ARC) 1528 located on the front side 1502 of the solar cell. In some embodiments, the solar cells 1520a, 1520b, 1520c, 1520d may include an anti-reflective coating (ARC) 1526.

[0111] refer to Fig.15A, according to some embodiments, an exemplary back-contact solar cell is manufactured using the methods, means or apparatus described herein. The back-contact solar cell 1520a may include a first doped region 1521 and a second doped region 1522 disposed on the back side 1504 of the solar cell 1520a. In a certain embodiment, the conductive wires 1511, 1512 may be bonded to the first doped region 1521 and the second doped region 1522 on the back side 1504. In a certain example, the first doped region and / or the second doped region may include a polysilicon region. In one example, the first doped region 1521 and the second doped region 1522 are separated by a lightly doped region 1579 therebetween, for example, wherein the doping concentration of the lightly doped region may be substantially less than that of the first doped region 1521 and the second doped region 1522. In a certain embodiment, a thin oxide layer 1573 (e.g., a tunnel oxide layer) may be disposed between the first doped region 1521 and the second doped region 1522 and the substrate 1525. The first doped region 1521 and the second doped region 1522 may alternatively be located in the substrate 1525. The first doped region 1521 and the second doped region 1522 may have a separation region formed therebetween. In one example, trenches are formed between the first doped region 1521 and the second doped region 1522, and the trenches partially extend into the substrate. The trenches may be replaced by an intrinsic or lightly doped semiconductor region.

[0112] refer to Fig. 15B , according to some embodiments, an exemplary front-contact solar cell is manufactured using the methods, means, or apparatus described herein. The front-contact solar cell 1520b may include a first doped region 1521 disposed on the back side 1504 of the solar cell 1520b. In a certain example, a second doped region 1522 may be disposed on the front side 1502 of the solar cell 1520b. Although one example of the second doped region 1522 is shown, one or more of the second doped regions 1522 may be used. In a certain embodiment, conductive wires 1511, 1512 may be bonded to the first doped region 1521 and the second doped region 1522 on the front and back sides 1504 of the solar cell 1520b. The second doped region 1522 may be offset from the first doped region 1521, as shown. The second doped region 1522 may be aligned with the first doped region 1521, for example, vertically aligned.

[0113] Fig. 15CAn exemplary front contact solar cell manufactured using the methods, means or apparatus described herein according to some embodiments is shown. The front contact solar cell 1520c may include a first doped region 1521 disposed on the back side 1504 of the solar cell 1520c. Conductive contact structures 1511, 1512 may be formed on the front side 1502 and the back side 1504 of the solar cell 1520c, respectively, by wire bonding techniques, wherein the conductive contact structures 1511, 1512 include thermally compressed wires or wire portions on the first doped region 1521 and the second doped region 1522. The first doped region 1521 and the second doped region 1522 may include amorphous silicon regions. The solar cell 1520d may include an intermediate layer (e.g., an anti-reflective layer coating ARC) 1526 on the front side 1502 of the solar cell 1520c. The solar cell 1520c may include a back intermediate layer (e.g., a back anti-reflective coating BARC) 1526 on the back side 1504 of the solar cell 1520c. A thin oxide layer 1530 may be disposed between the first doping region 1521 and the substrate 1525 .

[0114] Fig.15D Another exemplary front contact solar cell manufactured using the methods, means or apparatus described herein according to some embodiments is shown. The solar cell 1520d may include first doped regions 1521A, 1521B disposed on the back side 1504 of the solar cell 1520d. In a certain example, the second doped regions 1522A, 1522B may be disposed on the front side 1502 of the solar cell 1520d. In a certain embodiment, conductive contact structures 1511, 1512 may be formed on the front side and back side 1504 of the solar cell 1520d, respectively, by wire bonding technology, wherein the conductive contact structures 1511, 1512 include thermally compressed wires or wire portions on the first doped regions 1521A, 1521B and the second doped regions 1522A, 1522B. The first doped regions 1521A, 1521B may include doped polysilicon regions. The solar cell 1520d may include an intermediate layer (e.g., an anti-reflective coating ARC) 1528 on the front side 1502 of the solar cell 1520d. The solar cell 1520d may include a back intermediate layer (eg, a back anti-reflective coating (BARC)) 1526 on the back side 1504 of the solar cell 1520d.

[0115] refer to FIG. 15A to FIG. 15DIn one embodiment, the methods described herein may be applied to front contact solar cells and / or back contact solar cells. In a certain example, the conductive wire 1510 may be aligned and bonded to the doped regions 1521, 1522 on either or both of the front side 1502 and the back side 1504 of the solar cell. In one example, the conductive wire 1510 may be bonded to a single face, for example, the back side 1504 or the front side 1502. In a certain embodiment, the conductive wire and / or the conductive contact structure 1511, 1512 may have a square, rectangular, semi-square, and / or semi-rectangular shape due to the bonding techniques described herein (e.g., thermocompression bonding). In some examples, the conductive wire and / or the conductive contact structure 1511, 1512 may have a partially rounded surface and / or a semi-circular surface due to the bonding techniques described herein (e.g., thermocompression bonding).

[0116] According to one or more embodiments of the present disclosure, strain relief structures and interconnects are described. As an example, Fig.16A and Fig. 16B Cross-sectional and plan views of various arrangements of wire-based metallization of a solar cell according to a certain embodiment of the present disclosure are shown.

[0117] refer to Fig.16A In part (a), the solar cell 1600 includes an emitter region 1602 having a wire 1604 coupled thereto. Fig.16A In part (b), a wire 1604 having excess length is provided, which is then bent to form an out-of-plane stress relief feature 1606. The bend 1606 can be toward or away from the glass, or both. In one embodiment, the bend 1606 is less than the distance between the back of the cell and the glass or backsheet of the solar panel. In a certain embodiment, 1606 does not include a sharp feature. The bend 1606 can allow the bend to withstand any thermal expansion / contraction or mechanical stresses, rather than going directly into the weld / solder joint.

[0118] refer to Fig.16A The portion (c) includes epoxy or a rigid body 1608 to prevent force transfer to the A1 wire and battery connection. In one embodiment, an epoxy or coating is adhered to the wire and battery on one or both sides of the battery-to-battery gap. This arrangement can transfer any stress in the wire to a location away from the solder / weld bond and diffuse it to the battery. This arrangement can also add robustness to portions of the wire that can be thinned or work hardened by the battery bonding process.

[0119] refer to Fig.16AIn section (d), the inter-battery bus 1610 is offset (in plane) relative to the on-battery wire 1604 and extends perpendicular to the on-battery wire 1604. This arrangement can relieve stress by not having a continuous wire that is the length of two batteries. In addition, this arrangement can increase redundancy because a broken wire does not necessarily cause power loss of two batteries. The inter-battery bus 1610 can be connected to each wire (as depicted in the figure), or every other wire.

[0120] refer to Fig.16A In section (e), a single bend stress relief feature 1610 is in a plane relative to the wires 1604 on the battery. In this example, a single bend stress relief feature 1610 is made for all wires. This arrangement can relieve stress by not having a continuous straight line the length of two batteries. It should be understood that this arrangement can avoid sharp features, may require additional wire length, and the batteries move together during bending.

[0121] refer to Fig. 16B In section (f), the double bend stress relief feature 1610 is in a plane relative to the wire 1604 on the battery. This arrangement can relieve stress by not having a continuous straight line the length of two batteries. It should be understood that this arrangement can avoid sharp features, may require additional wire length, and the batteries move together during bending. The double bend stress relief feature 1610 can be made for each wire, or every other wire (as depicted in the figure).

[0122] refer to Fig. 16B In section (g), a single bend stress relief feature 1610 is in a plane relative to the wire 1604 on the battery. In this example, a single bend stress relief feature 1610 is made for every other wire. This arrangement can relieve stress by not having a continuous straight line with the length of two batteries. It should be understood that this arrangement can avoid sharp features, may require additional wire length, and the batteries move together during bending.

[0123] Although certain materials are specifically described with reference to the above embodiments, in such embodiments, other materials may be easily substituted for some of the materials, and these embodiments remain within the spirit and scope of the embodiments of the present disclosure. For example, in a certain embodiment, a substrate of a different material, such as a substrate of a III-V material, may be used in place of a silicon substrate. In addition, although primarily reference is made to a back-contact solar cell arrangement, it should be understood that the methods described herein may also be applied to front-contact electrode solar cells. In other embodiments, the above methods may be applicable to the manufacture of things other than solar cells. For example, the manufacture of light emitting diodes (LEDs) may benefit from the methods described herein.

[0124] Thus, wire-based metallization and stringing techniques for solar cells and resulting solar cells, modules, and devices have been disclosed.

[0125] Although specific embodiments have been described above, even if only a single embodiment is described with respect to a particular feature, these embodiments are not intended to limit the scope of the present disclosure. Unless otherwise specified, the examples of features provided in the present disclosure are intended to be illustrative rather than restrictive. The above description is intended to cover those alternatives, modifications, and equivalents that will be apparent to those skilled in the art that have the beneficial effects of the present disclosure.

[0126] The scope of the present disclosure includes any feature or combination of features disclosed herein (expressly or implicitly), or any generalization thereof, whether or not it mitigates any or all of the problems addressed herein. Accordingly, new claims may be made for any such combination of features during the examination process of the present application (or an application claiming priority thereto). In particular, with reference to the appended claims, features from dependent claims may be combined with those of the independent claims, and features from corresponding independent claims may be combined in any appropriate manner, and not just in the specific forms enumerated in the appended claims.

[0127] The following embodiments relate to further embodiments. The various features of the different embodiments can be combined in various ways with some features included and other features excluded to suit various different applications.

[0128] Example 1

[0129] A solar cell includes a substrate having a surface. A plurality of N-type and P-type semiconductor regions are disposed in or on the surface of the substrate. A conductive contact structure is disposed on the plurality of N-type and P-type semiconductor regions, the conductive contact structure including a plurality of conductive wires, each of the plurality of conductive wires being substantially directly and continuously bonded to a corresponding one of the N-type and P-type semiconductor regions.

[0130] Example 2

[0131] According to the solar cell of exemplary embodiment 1, each of the plurality of conductive lines is parallel along a certain direction to form a one-dimensional layout of the conductive contact structure.

[0132] Example 3

[0133] The solar cell according to example embodiment 1 or 2, wherein each of the plurality of conductive lines has a flat circular profile.

[0134] Example 4

[0135] The solar cell according to example embodiment 1, 2 or 3, wherein each of the plurality of conductive lines has a micro-grooved surface along the length of the conductive line.

[0136] Example 5

[0137] The solar cell according to example embodiment 1, 2, 3 or 4, wherein the substrate is substantially rectangular, and wherein the plurality of N-type and P-type semiconductor regions and the plurality of conductive lines are substantially parallel to an edge of each of the substrate.

[0138] Example 6

[0139] The solar cell according to example embodiment 1, 2, 3, 4 or 5, wherein the plurality of N-type and P-type semiconductor regions are disposed in a back surface of the substrate, the back surface being opposite to an opposite light receiving surface of the substrate.

[0140] Example 7

[0141] The solar cell according to example embodiment 1, 2, 3, 4 or 5, wherein the plurality of N-type and P-type semiconductor regions are disposed over a back surface of the substrate, the back surface being opposite to an opposite light receiving surface of the substrate.

[0142] Example 8

[0143] A solar cell includes a substrate having a surface. A plurality of N-type and P-type semiconductor regions are disposed in or on the surface of the substrate. A conductive contact structure is disposed on the plurality of N-type and P-type semiconductor regions, the conductive contact structure including a plurality of uncoated conductive wires, each of the plurality of uncoated conductive wires being directly bonded to a corresponding one of the N-type and P-type semiconductor regions.

[0144] Example 9

[0145] According to the solar cell of exemplary embodiment 8, each of the plurality of uncoated conductive lines is parallel along a certain direction to form a one-dimensional layout of the conductive contact structure.

[0146] Example 10

[0147] The solar cell according to example embodiment 8 or 9, wherein each of the plurality of uncoated conductive wires has a flat circular profile.

[0148] Example 11

[0149] The solar cell according to example embodiment 8, 9 or 10, wherein each uncoated conductive line of the plurality of uncoated conductive lines has a micro-grooved surface along the length of the uncoated conductive line.

[0150] Example 12

[0151] The solar cell of example embodiments 8, 9, 10 or 11, wherein the substrate is substantially rectangular, and wherein the plurality of N-type and P-type semiconductor regions and the plurality of uncoated conductive lines are substantially parallel to an edge of each of the substrates.

[0152] Example 13

[0153] The solar cell according to example embodiment 8, 9, 10, 11 or 12, wherein the plurality of N-type and P-type semiconductor regions are disposed in a back surface of the substrate, the back surface being opposite to an opposite light receiving surface of the substrate.

[0154] Example 14

[0155] The solar cell according to example embodiment 8, 9, 10, 11 or 12, wherein the plurality of N-type and P-type semiconductor regions are disposed over a back surface of the substrate, the back surface being opposite to an opposite light receiving surface of the substrate.

[0156] Example 15

[0157] A solar cell includes a substrate having a surface. A plurality of N-type and P-type semiconductor regions are disposed in or on the surface of the substrate. A conductive contact structure is disposed on the plurality of N-type and P-type semiconductor regions, the conductive contact structure including a plurality of uncoated conductive wires, each of the plurality of uncoated conductive wires being bonded to a corresponding one of the N-type and P-type semiconductor regions through a metal layer.

[0158] Example 16

[0159] According to example embodiment 15, the solar cell, wherein the metal layer is a metal seed layer.

[0160] Example 17

[0161] According to the solar cell of example embodiment 15 or 16, each of the plurality of uncoated conductive lines is parallel along a certain direction to form a one-dimensional layout of the conductive contact structure.

[0162] Example 18

[0163] The solar cell according to example embodiment 15, 16 or 17, wherein each of the plurality of uncoated conductive lines has a flat circular profile.

[0164] Example 19

[0165] The solar cell according to example embodiment 15, 16, 17 or 18, wherein each uncoated conductive line of the plurality of uncoated conductive lines has a microgrooved surface along the length of the uncoated conductive line.

[0166] Example 20

[0167] The solar cell of example embodiments 15, 16, 17, 18 or 19, wherein the substrate is substantially rectangular, and wherein the plurality of N-type and P-type semiconductor regions and the plurality of uncoated conductive lines are substantially parallel to an edge of each of the substrates.

[0168] Example 21

[0169] A solar cell string includes a plurality of back-contact solar cells, wherein each of the plurality of back-contact solar cells includes a P-type doped diffusion region and an N-type doped diffusion region. A plurality of conductive wires are disposed over a back surface of each of the plurality of solar cells, wherein each of the plurality of conductive wires is substantially parallel to the P-type doped diffusion region and the N-type doped diffusion region of each of the plurality of solar cells. Every other conductive wire of the plurality of conductive wires is cut in a region between each adjacent pair of cells in the plurality of solar cells, and wherein a portion of the uncut wire has a different cross-sectional profile in the region between each adjacent pair of cells in the plurality of solar cells than a portion of the uncut wire bonded to the solar cell.

[0170] Example 22

[0171] The solar cell string according to example embodiment 21, wherein the portion of the uncut wire has a circular cross-sectional profile in the region between each adjacent pair of cells in the plurality of solar cells, and the portion of the uncut wire bonded to the solar cell has a flat circular profile.

[0172] Example 23

[0173] The solar cell string according to example embodiment 21 or 22, wherein each of the plurality of solar cells is substantially rectangular, and wherein the P-type doped diffusion region, the N-type doped diffusion region, and the plurality of conductive lines are substantially parallel to a first edge of each of the plurality of solar cells.

[0174] Example 24

[0175] A solar cell string according to example embodiments 21, 22 or 23, wherein a given tangent segment of the plurality of conductive lines electrically couples at most two solar cells together in series, wherein a P-type doped diffusion region of one of the two solar cells is connected to an N-type doped diffusion region of the other of the two solar cells.

[0176] Example 25

[0177] The solar cell string according to example embodiment 21, 22, 23 or 24 further comprises a conductive bus bar at an end of the solar cell string, wherein the conductive bus bar is folded over a back of one of the solar cells.

[0178] Example 26

[0179] A method of electrically coupling solar cells includes aligning a conductive wire over the backside of adjacent solar cells, wherein the conductive wire is aligned substantially parallel to a P-type doped diffusion region and an N-type doped diffusion region of the solar cell. The method further includes directly bonding the conductive wire to the backside of each of the solar cells using thermocompression bonding, ultrasonic bonding, or thermosonic bonding over the P-type doped diffusion region and the N-type doped diffusion region. The method further includes cutting every other conductive wire of the plurality of conductive wires between each adjacent pair of cells in the solar cell.

[0180] Example 27

[0181] A system for electrically coupling solar cells includes a wire support for aligning a conductive wire substantially parallel to a P-type doped diffusion region and an N-type doped diffusion region of each of the solar cells. The system also includes a bonding head for bonding the conductive wire to the P-type doped diffusion region and the N-type doped diffusion region on the back side of each of the solar cells. The system also includes a cutter for severing the conductive wire.

[0182] Example 28

[0183] A system according to exemplary embodiment 27, wherein the bonding head applies pressure to the conductive wires, wherein the bonding head includes corresponding grooves or side walls to ensure that each conductive wire cannot move laterally during the bonding, thereby maintaining alignment with a corresponding one of the P-type doped diffusion region and the N-type doped diffusion region.

Claims

1. A solar cell comprising: a substrate having a surface; a plurality of N-type and P-type semiconductor regions disposed in or above the surface of the substrate; A conductive contact structure, the conductive contact structure is disposed on the plurality of N-type and P-type semiconductor regions, the conductive contact structure comprises a plurality of conductive wires, each of the plurality of conductive wires is bonded to a corresponding one of the plurality of N-type and P-type semiconductor regions through a metal seed layer in a fishbone pattern in the middle; wherein the conductive wires of the plurality of conductive wires have a first portion and a second portion, wherein the first portion of the conductive wires has a substantially flat cross-section along the length of the conductive wires above the solar cells, and wherein the second portion of the conductive wires has a substantially circular cross-section between the solar cells, each conductive wire having a surface having microgrooves along the length of the conductive wire; and wherein the second portion is the portion where the solar cell is interconnected with another solar cell. 2 . The solar cell according to claim 1 , wherein each of the plurality of conductive lines is parallel along a direction to form a one-dimensional layout of the conductive contact structure.

3. The solar cell of claim 1, wherein the substrate is substantially rectangular, and wherein the plurality of N-type and P-type semiconductor regions and the plurality of conductive lines are substantially parallel to an edge of each of the substrate. 4 . The solar cell of claim 1 , wherein the plurality of N-type and P-type semiconductor regions are disposed in a back surface of the substrate, the back surface being opposite to an opposite light-receiving surface of the substrate. 5 . The solar cell of claim 1 , wherein the plurality of N-type and P-type semiconductor regions are disposed over a back surface of the substrate, the back surface being opposite to an opposite light-receiving surface of the substrate.

6. A solar cell comprising: a substrate having a surface; a plurality of N-type and P-type semiconductor regions disposed in or above the surface of the substrate; A conductive contact structure, the conductive contact structure is disposed on the plurality of N-type and P-type semiconductor regions, the conductive contact structure comprising a plurality of uncoated conductive wires, each of the plurality of uncoated conductive wires being bonded to a corresponding one of the N-type and P-type semiconductor regions through a metal seed layer in a middle fishbone pattern; wherein the conductive wires of the plurality of conductive wires have a first portion and a second portion, wherein the first portion of the conductive wires has a substantially flat cross-section along the length of the conductive wires above the solar cells, and wherein the second portion of the conductive wires has a substantially circular cross-section between the solar cells, each conductive wire having a surface having microgrooves along the length of the conductive wire; and wherein the second portion is the portion where the solar cell is interconnected with another solar cell. 7 . The solar cell according to claim 6 , wherein each of the plurality of uncoated conductive lines is parallel along a direction to form a one-dimensional layout of the conductive contact structure.

8. The solar cell of claim 6, wherein the substrate is substantially rectangular, and wherein the plurality of N-type and P-type semiconductor regions and the plurality of uncoated conductive lines are substantially parallel to an edge of each of the substrate. 9 . The solar cell of claim 6 , wherein the plurality of N-type and P-type semiconductor regions are disposed in a back surface of the substrate, the back surface being opposite to an opposite light-receiving surface of the substrate. 10 . The solar cell of claim 6 , wherein the plurality of N-type and P-type semiconductor regions are disposed over a back surface of the substrate, the back surface being opposite to an opposite light-receiving surface of the substrate.

Images