Low-temperature alloy metallization and interconnection schemes for solar cells

Abstract

Embodiments relate to methods of connecting metallization components to a solar cell, and associated solar cells and solar modules. Some embodiments relate to a method of connecting metallization components to a solar cell. The method comprises contacting a first metallization component with a second metallization component at a connection location, and heating the first and second metallization components to locally form a eutectic mixture, comprising a first material and a second material, such that the eutectic mixture provides an electrically conductive bond between the first and second metallization components. Some embodiments relate to a solar cell comprising a first metallization component electrically connected to a second metallization component via a locally formed eutectic mixture comprising a first material and a second material. Some embodiments relate to a solar module comprising the solar cell.

Description

"Low- temperature alloy metallization and interconnection schemes for solar cells"Cross-Reference to Related Applications

[0001] The present application claims priority from Australian Provisional Patent Application No 2024902424 filed on 5 August 2024, the contents of which are incorporated herein by reference in their entirety.Technical Field

[0002] Embodiments relate to methods of connecting metallization components to a solar cell, and associated solar cells and solar modules.Background

[0003] Photovoltaic solar cells comprise metallization components to allow for the supply of electricity from the solar cell. Metals and alloys with low melting temperatures are used to connect metallization components together in the solar cell to avoid higher temperatures, which may damage the solar cell, but some of the more advantageous metals for this purpose are relatively rare or expensive.

[0004] It is desired to address or ameliorate one or more shortcomings or disadvantages associated with existing methods of connecting metallization components to a solar cell, or to at least provide a useful alternative.

[0005] Throughout this specification, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

[0006] Any discussion of documents, acts, materials, devices, articles or the like that has been included in the present specification is not to be taken as an admission thatany or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.Summary

[0007] Some embodiments relate to a method of connecting metallization components to a solar cell, the method comprising: contacting a first metallization component with a second metallization component at a connection location; and heating the first and second metallization components to locally form a eutectic mixture, comprising a first material and a second material, such that the eutectic mixture provides an electrically conductive bond between the first and second metallization components.

[0008] The term “eutectic mixture”, as used in the present disclosure, is intended to include any mixture of materials that exhibits eutectic behaviour, whether it comprises a perfectly eutectic composition or not. That is, meaning that the melting temperature of the eutectic mixture is lower than the melting temperature of either of the first and second materials in isolation.

[0009] In some embodiments, the first material is provided at the connection location without being metallically bonded to either of the first and second metallization components prior to the heating. For example, the first material may be provided in the form of a paste applied to the first or second metallization component at the connection location prior to the heating.

[0010] In some embodiments, the second metallization component comprises the second material prior to the heating. For example, the second metallization component may include a plated layer comprising the second material prior to the heating.

[0011] In some embodiments, the first and second materials are provided at the connection location without being metallically bonded to either of the first and second metallization components prior to the heating. For example, the first and second materials may be provided in the form of a paste applied to the first or second metallization component at the connection location prior to the heating.

[0012] In some embodiments, the first metallization component comprises the first material prior to the heating, and the second metallization component comprises the second material prior to the heating. For example, the first metallization component may include a plated layer comprising the first material prior to the heating, and the second metallization component may include a plated layer comprising the second material prior to the heating.

[0013] In some embodiments, each of the first and second metallization components comprises a component selected from a group including: a conductive finger; a busbar; a metal dash; a soldering tab; and an interconnection element for connecting the solar cell to another solar cell.

[0014] In some embodiments, the eutectic mixture is not present along at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of a length of at least one of the first and second metallization components.

[0015] In some embodiments, the first material or the second material comprises a material selected from a group comprising: tin, lead, bismuth, silver, nickel, germanium, indium, cadmium, copper.

[0016] In some embodiments, the heating is to a temperature of less than 300 degrees C, less than 250 degrees C, or less than 200 degrees C.

[0017] Some embodiments relate to a solar cell comprising a first metallization component electrically connected to a second metallization component via a locally formed eutectic mixture comprising a first material and a second material.

[0018] In some embodiments, the eutectic mixture is not present along at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of a length of at least one of the first and second metallization components.

[0019] In some embodiments, each of the first and second metallization components comprises a component selected from a group including: a conductive finger; a busbar; a metal dash; a soldering tab; and an interconnection element for connecting the solar cell to another solar cell.

[0020] In some embodiments, the first material or the second material comprises a material selected from a group comprising: tin, lead, bismuth, silver, nickel, germanium, indium, cadmium, copper.

[0021] Some embodiments relate to a solar module comprising one or more solar cells according to any one of the described embodiments.

[0022] In some embodiments, the first or second metallization component comprises an interconnection element connecting a first solar cell according to any one of the described embodiments to a second solar cell.

[0023] Some embodiments may comprise screen printing a tin-bismuth paste locally at connection points between metallization components and then heating to form the eutectic mixture and connect the metallization components.

[0024] Some embodiments may comprise locally plating (or printing) bismuth onto tin plated fingers (e.g., tin plated copper fingers) or solid tin fingers, at connection points, and then heating to form the eutectic mixture and connect the metallization components.Brief Description of Drawings

[0025] Embodiments will now be described, for illustrative purposes only, with reference to the drawings, in which:

[0026] Figure l is a schematic diagram of a conventional solar cell with metallization components;

[0027] Figure 2A is a plan view schematic diagram of a solar module comprising the solar cell of Figure 1;

[0028] Figure 2B is a side view schematic diagram of the solar module of Figure 2A;

[0029] Figure 3 A is a cross-section of a connection location illustrating the configuration of metallization components prior to heating and connection according to some embodiments of a connection method;

[0030] Figure 3B shows the metallization components of Figure 3A after heating and connection;

[0031] Figure 4A is a cross-section of a connection location illustrating the configuration of metallization components prior to heating and connection according to some embodiments of a connection method;

[0032] Figure 4B shows the metallization components of Figure 4A after heating and connection;

[0033] Figure 5A is a cross-section of a connection location illustrating the configuration of metallization components before heating and connection according to some embodiments of a connection method;

[0034] Figure 5B shows the metallization components of Figure 5 A after heating and connection; and

[0035] Figure 6 is a schematic diagram of a solar cell illustrating varying extents of connection materials at and near connection locations between metallization components according to various embodiments of the connection method.Description of Embodiments

[0036] The embodiments described herein relate to methods of manufacturing solar cells, particularly methods of connecting metallization components to a solar cell, and associated solar cells and solar modules.

[0037] The described connection methods may be applied in the manufacture of a wide variety of solar cells with different combinations and configurations of metallization components.

[0038] A general schematic diagram of solar cell metallization components is shown in Figure 1, for exemplary purposes only, but it will be understood that the described methods are equally suitable for the connection of other metallization components in other embodiments.

[0039] Referring to Figure 1, a photovoltaic solar cell 100 is shown according to some embodiments, illustrating a simple configuration of metallization components. The solar cell 100 comprises a semiconductor base 110 (e.g., doped silicon) configured to develop an electrical charge when illuminated by sunlight and a number of different metallization components configured to collect the charge and connect the solar cell to an electrical circuit to allow the generated charge to flow as electrical current.

[0040] The metallization components include fingers 120 which are connected to the base 110; busbars 130 which are connected to the fingers 120; and interconnection wires or ribbons 140, which are connected to the busbars 130. The ribbons 140 and busbars 130 may define any suitable form. For example, flat, round, corrugated, or any other suitable profile. In some embodiments, the ribbons 140 may be wider than the busbars 130.

[0041] Other metallization configurations and metallization components which may be connected using the described methods include: fingers, busbars, soldering tabs, metal dashes, ribbons, interconnection wires, multi-busbar configurations, super-multi-busbar configurations, busbar-less configurations with interconnection wires connected directly to fingers.

[0042] Referring to Figures 2A and 2B, a solar module 200 is shown for exemplary purposes, including a plurality of solar cells 100 connected together in a string. The solar module 200 comprises a frame 202 configured to support the solar cells 100, which are connected together by the interconnection wires 140 connecting the front side of each solar cell 100 to the back side of an adjacent solar cell 100, and ultimately to the external connection terminals of the solar module 200.

[0043] Again, this is a conventional arrangement, for illustrative purposes, and the described metallization connection methods may be applied to different solar cells arranged in a variety of different solar modules. For example, in some embodiments, the ribbons 140 may be connected to soldering tabs rather than busbars 130. In some embodiments, the ribbons 140 may be connected to contacts on back side of each of the adjacent solar cells, for example, in back-contact solar cells with contact points for both polarities on the rear surface of the cell.

[0044] Figures 3 to 5 show close up cross-sections of connections between metallization components illustrating a connection method according to various embodiments of the present disclosure.

[0045] With reference to Figures 3 to 5, a method of connecting metallization components to a solar cell can comprise: contacting a first metallization component 151 with a second metallization component 152 at a connection location and heating the first and second metallization components to locally form a eutectic mixture 160, comprising a first material 161 and a second material 162, such that the eutectic mixture 160 provides an electrically conductive bond between the first and second metallization components.

[0046] In Figures 3 to 5, the first metallization component 151 is illustrated as a busbar, and the second metallization component 152 is illustrated as an interconnection wire. However, as previously discussed, the first and second metallization components may comprise any combination of various different metallization components, which may be connected to each other by an electrically conductive bond, in any suitable metallization configuration for a solar cell.

[0047] In the context of the present disclosure, a eutectic mixture, which may also be considered a eutectic system, is a mixture of at least two materials that has a melting point lower than that of each of the two materials separately (in isolation). The lowest possible melting point over all of the mixing ratios of the constituents is called the eutectic temperature, and the corresponding mixing ratio is the eutectic composition. On a phase diagram, the eutectic temperature is seen as the eutectic point at the eutectic composition.

[0048] The composition of the eutectic mixture is not necessarily at the eutectic point or eutectic composition (though it may be in some embodiments), but the eutectic mixture may comprise a non-eutectic composition (i.e., not purely eutectic) and still exhibit eutectic behaviour with the melting temperature of the eutectic mixture being lower than that of each of the first and second materials separately, i.e., having a lower melting temperature than either of the first and second materials in isolation.

[0049] Non-eutectic compositions have different melting temperatures for their different constituents since one component's lattice will melt at a lower temperature than the other's. Conversely, as a non-eutectic composition cools down, each of its components solidify (form a lattice) at a different temperature, until the entire mass is solid.

[0050] Eutectic alloys have two or more materials and have a eutectic composition. When a non-eutectic alloy solidifies (i.e., a eutectic mixture with non-eutectic composition), its components solidify at different temperatures, exhibiting a plastic melting range. Conversely, when a well-mixed, eutectic alloy with a perfectly eutecticcomposition melts, it does so at a single, sharp temperature. The various phase transformations that occur during the solidification of a particular alloy composition can be understood by drawing a vertical line from the liquid phase to the solid phase on the phase diagram for that alloy.

[0051] The term “eutectic mixture”, as used in the present disclosure, is intended to include any mixture of materials that exhibits eutectic behaviour, whether it comprises a perfectly eutectic composition or not. Examples of suitable materials and combinations of materials to form suitable eutectic mixtures are set out further below.

[0052] In each of the embodiments described below, the first and second materials 161, 162 are heated until they combine to form a eutectic mixture 160 which connects the metallization components 151, 152 together. In some embodiments, the resulting connection may comprise a first region (or zone) comprising the first material 161, a second region (or zone) comprising the second material 162, and a third region (or zone) comprising the eutectic mixture 160. This melting point of the third region (the eutectic mixture 160) being lower than the melting temperature of the first region (the first material 161) and lower than the melting temperature of the second region (the second material).

[0053] In some embodiments, the eutectic mixture 160 may be substantially homogenous in the composition of the first and second materials 161, 162. In some embodiments, the eutectic mixture 160 (in the third region), may be non-homogenous. The composition of the eutectic mixture 160 may vary in concentration depending on the degree of mixing between the first and second materials 161, 162. For example, the eutectic mixture 160 may comprise a concentration gradient varying from a region of a relatively higher concentration of the first material 161, through a transition region, to a region of a relatively higher concentration of the second material 162.

[0054] In some embodiments, the eutectic mixture 160 may comprise additional components, such as a third material, or further additional materials.

[0055] Referring to Figures 3A and 3B, one example configuration of the first and second metallization components and first and second materials is shown according to some embodiments. Figure 3 A shows the configuration prior to heating, and Figure 3B shows the connection after heating to form the eutectic mixture 160.

[0056] As shown in Figure 3 A, the first material 161 is provided at the connection location without being metallically bonded to either of the first and second metallization components prior to the heating. For example, the first material may be provided in the form of a paste applied to the first or second metallization component at the connection location prior to the heating.

[0057] The first material 161 could be provided at the location according to any suitable method, including screen printing, inkjet printing, dispensing, rotary printing, pattern transfer printing, plating, or thermal evaporation, for example.

[0058] In this embodiment, the second metallization component 152 comprises the second material 162 prior to the heating. For example, the second metallization component 152 may include a plated layer comprising the second material 151 prior to the heating, as shown in Figure 3 A.

[0059] In other embodiments, the bulk of the second metallization component 152 may comprise the second material 162 prior to heating. The second metallization component 152 may be entirely formed of the second material 162 (e.g., tin fingers), or may comprise an alloy comprising the second material 162.

[0060] When the metallization components 151, 152 are heated to a sufficient temperature, the first and second materials 161, 162 combine to form the eutectic mixture 160 as shown in Figure 3B. After heating, the eutectic mixture 160 solidifies to bond the first and second metallization components 151, 152 to each other, and create an electrically conductive connection between the metallization components 151, 152.

[0061] Referring to Figures 4 A and 4B, another example configuration of the first and second metallization components and first and second materials is shown according to some embodiments. Figure 4A shows the configuration prior to heating, and Figure 4B shows the connection after heating to form the eutectic mixture 160.

[0062] In this embodiment, the first and second materials 161, 162 are provided at the connection location without being metallically bonded to either of the first and second metallization components prior to the heating. For example, the first and second materials 161, 162 may be provided in the form of a paste applied to the first or second metallization component at the connection location prior to the heating.

[0063] The paste may comprise solid particles of the first and second materials 161, 162 provided in a carrier substance, such that the paste can be applied to the first or second metallization components 151, 152 and temporarily remain in position, as shown in Figure 4A, until the metallization components are heated so that the first and second materials 161, 162 combine to form the eutectic mixture 160 and form an electrically conductive bond between the metallization components 151, 152, as shown in Figure 4B. The paste may comprise a carrier substance to carry the solid particles of the first and second materials 161, 162. For example, the carrier substance may comprise a flux and / or various anti-oxidation components.

[0064] Referring to Figures 5 A and 5B, another example configuration of the first and second metallization components and first and second materials is shown according to some embodiments. Figure 5A shows the configuration prior to heating, and Figure 5B shows the connection after heating to form the eutectic mixture 160.

[0065] In this embodiment, the first metallization component 151 comprises the first material 161 prior to the heating, and the second metallization component 152 comprises the second material 162 prior to the heating.

[0066] As discussed above, the first and second metallization components 151, 152 may comprise the respective first and second materials 161, 162 as part or whole of abulk material of the metallization components, or alternatively in the form of a coating or plating.

[0067] The first metallization component 151 may include a plated layer comprising the first material 161 prior to the heating, and the second metallization component 152 may include a plated layer comprising the second material 162 prior to the heating, as shown in Figure 5A.

[0068] When the first and second metallization components 151, 152 are heated to a sufficient temperature, the first and second materials 161, 162 combine to form the eutectic mixture 160, as shown in Figure 5 A, to create an electrically conductive bond between the first and second metallization components 151, 152.

[0069] The method of locally forming a eutectic mixture at the connection location with the first and second materials means that the first and second materials do not necessarily need to be provided along an entire length of each metallization component.

[0070] Therefore, in some embodiments, the eutectic mixture may only be formed at or near the connection location.

[0071] In some embodiments, the eutectic mixture is not present along at least 50% of a length of at least one of the first and second metallization components. In some embodiments, the eutectic mixture is not present along at least 60%, at least 70%, at least 80%, at least 90%, or at least 95% of a length of at least one of the first and second metallization components.

[0072] This may provide an advantage in reducing the usage of rare or expensive materials to form the eutectic mixture.

[0073] In embodiments where rare or expensive materials are used to form the eutectic mixture, the extent to which use of the materials can be minimised depends on the number of connections required for each metallization component, as well as theprecision that can be achieved in locating the first and second materials at the connection location (depending on the manufacturing technique) and the amount of material required to provide a sufficiently durable bond between the metallization components.

[0074] Referring to Figure 6, a solar cell metallization configuration is shown for illustrative purposes with two busbars 130 connected to different numbers of fingers 120. The extent of the eutectic mixture around each connection location 170 is indicated by the rectangular boxes 172. This is to illustrate the usage of materials in the eutectic mixture for different manufacturing scenarios, for example only.

[0075] One busbar 130 is connected to fewer fingers 120, so there are fewer connection locations along the length of the busbar 130, but the extent of the eutectic mixture around each connection location is relatively larger.

[0076] The other busbar 130 is connected to more fingers 120, so there are more connection locations along the length of the busbar 130, but the extent of the eutectic mixture is limited to be relatively nearer to the connection location.

[0077] In some embodiments, the extent of the eutectic mixture 172 may be extended to a relatively large soldering tab to provide a larger connection area for connecting ribbons, for example. In some embodiments, the soldering tabs may comprise a wider part of a busbar, and the eutectic mixture 172 may be formed on or in combination with the soldering tab.

[0078] The metallization components may be provided with any suitable dimensions for various solar cell designs. For example, the busbar may have a width of approximately 60pm, and the soldering tabs may be approximately 500pm wide and 800pm long. In some embodiments, a width of the soldering tabs may be in the range of 100pm to 1000pm, 200pm to 800pm, 300pm to 600pm or about 500pm, for example. In some embodiments, a length of the soldering tabs may be in the range of200pm to 2000pm, 500pm to 1500pm, 400pm to 1200pm or about 800pm, for example.

[0079] The first and second materials 161, 162 may comprise any suitable materials, i.e., any suitable materials which combine to form a eutectic mixture (displaying eutectic behaviour with a melting temperature lower than that of the components in isolation). For example, any suitable combination of the following materials: tin (Sn), lead (Pb), bismuth (Bi), silver (Ag), nickel (Ni), germanium (Ge), indium (In), cadmium (Cd), copper (Cu), such as, Ag-Cu-Sn, Sn-Ag, Sn-Pb, Sn-Cu, any combination of Sn, Ag, Pb, Bi, In, Cd, or any other suitable combination of materials.

[0080] Some embodiments may comprise screen printing a tin-bismuth paste locally at connection points between metallization components and then heating to form the eutectic mixture and connect the metallization components.

[0081] Some embodiments may comprise locally plating (or printing) bismuth onto tin plated fingers (e.g., tin plated copper fingers) or solid tin fingers, at connection points, and then heating to form the eutectic mixture and connect the metallization components.

[0082] The first and second materials 161, 162 may be heated to the melting point of the eutectic mixture to be formed for a sufficient duration to allow the first and second materials 161, 162 to melt together to form the eutectic mixture. For example, the melting temperature of the eutectic mixture may be less than 300°C, less than 250°C, or less than 200°C.

[0083] It will be appreciated by persons skilled in the art that numerous variations and / or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

Claims

CLAIMS:

1. A method of connecting metallization components to a solar cell, the method comprising: contacting a first metallization component with a second metallization component at a connection location; and heating the first and second metallization components to locally form a eutectic mixture, comprising a first material and a second material, such that the eutectic mixture provides an electrically conductive bond between the first and second metallization components.

2. The method of claim 1, wherein the first material is provided at the connection location without being metallically bonded to either of the first and second metallization components prior to the heating.

3. The method of claim 2, wherein the first material is provided in the form of a paste applied to the first or second metallization component at the connection location prior to the heating.

4. The method of claim 2 or 3, wherein the second metallization component comprises the second material prior to the heating.

5. The method of claim 4, wherein the second metallization component includes a plated layer comprising the second material prior to the heating.

6. The method of claim 1, wherein the first and second materials are provided at the connection location without being metallically bonded to either of the first and second metallization components prior to the heating.

7. The method of claim 6, wherein the first and second materials are provided in the form of a paste applied to the first or second metallization component at the connection location prior to the heating.

8. The method of claim 1, wherein the first metallization component comprises the first material prior to the heating, and wherein the second metallization component comprises the second material prior to the heating.

9. The method of claim 8, wherein the first metallization component includes a plated layer comprising the first material prior to the heating, and wherein the second metallization component includes a plated layer comprising the second material prior to the heating.

10. The method of any one of claims 1 to 9, wherein each of the first and second metallization components comprises a component selected from a group including: a conductive finger; a busbar; a metal dash; a soldering tab; and an interconnection element for connecting the solar cell to another solar cell.

11. The method of any one of claims 1 to 10, wherein the eutectic mixture is not present along at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of a length of at least one of the first and second metallization components.

12. The method of any one of claims 1 to 11, wherein the first material or the second material comprises a material selected from a group comprising: tin, lead, bismuth, silver, nickel, germanium, indium, cadmium, copper.

13. The method of any one of claims 1 to 12, wherein the heating is to a temperature of less than 300 degrees C, less than 250 degrees C, or less than 200 degrees C.

14. A solar cell comprising a first metallization component electrically connected to a second metallization component via a locally formed eutectic mixture comprising a first material and a second material.

15. The solar cell of claim 14, wherein the eutectic mixture is not present along at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% of a length of at least one of the first and second metallization component.

16. The solar cell of claim 14 or 15, wherein each of the first and second metallization components comprises a component selected from a group including: a conductive finger; a busbar; a metal dash; a soldering tab; and an interconnection element for connecting the solar cell to another solar cell.

17. The solar cell of any one of claims 14 to 16, wherein the first material or the second material comprises a material selected from a group comprising: tin, lead, bismuth, silver, nickel, germanium, indium, cadmium, copper.

18. A solar module comprising one or more solar cells according to any one of claims 14 to 17.

19. The solar module of claim 18, wherein the first or second metallization component comprises an interconnection element connecting a first solar cell according to any one of claims 14 to 16 to a second solar cell.

20. A method or apparatus comprising any two or more of the features, steps, components, compositions, or structures described herein.

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