A solder ribbon, a photovoltaic module, and a battery welding method

Abstract

The present invention discloses a welding ribbon, a photovoltaic module, and a battery welding method, which relate to the field of photovoltaic battery manufacturing technology and are intended to solve the problem of poor welding quality of the welding ribbon. The welding ribbon comprises a core and an alloy coating provided on the surface of the core. The chemical composition of the alloy coating comprises Sn, Nb, C, and inevitable impurities; or, the chemical composition of the alloy coating comprises Sn, Pb, Nb, C, and inevitable impurities. During welding, when the alloy transforms from liquid to solid, Nb and C form NbC particles. During the cooling of the alloy, when the matrix grains form nuclei and then grow, the in-situ generated NbC particles have a pinning effect on the grain boundaries, hindering the further growth of the matrix grains, achieving fine grain strengthening of the matrix grains, improving the mechanical properties of the welding position, and meeting the welding quality of the welding ribbon and the battery grid line under laser low-temperature welding conditions. The photovoltaic module uses the welding ribbon to weld battery cells, and the battery welding method uses the welding ribbon for laser low-temperature welding.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cell manufacturing, and in particular to a welding ribbon, a photovoltaic module and a battery welding method. Background Art

[0002] N-type cells offer advantages such as high conversion efficiency, high bifaciality, low temperature coefficient, zero light decay, and excellent low-light performance. To reduce silver paste consumption in N-type cells, N-type busbarless cells have become a popular choice. Cells are connected in series via solder ribbons. Traditionally, these cells and ribbons are soldered together using high-temperature baking, typically exceeding 200°C. At this temperature, the tin-lead on the lead ribbon melts, forming a physical bond with the silver paste on the cell surface. This physical bond creates high contact resistance, increasing cell power loss. Furthermore, the non-bonded area of the cell surface is also subject to this high temperature, and the surface conductive coating of the N-type busbarless cell undergoes lattice transformation at these high temperatures, significantly reducing conductivity.

[0003] Therefore, laser welding technology is used to achieve low-temperature welding between the solder ribbon and the silver paste, avoiding the impact on the surface conductive coating. Laser welding can also form a good ohmic contact between the solder ribbon and the silver paste, reducing the contact resistance between the solder ribbon and the cell, and reducing the welding power loss of N-type busbarless cells. However, existing tin-lead solder ribbons are prone to problems such as cold joints, poor mechanical properties of the weld joints, and corrosion of the weld surface, making them unsuitable for effective laser low-temperature welding. Summary of the Invention

[0004] The object of the present invention is to provide a welding ribbon, a photovoltaic module and a battery welding method, which are suitable for laser low-temperature welding and improve the welding quality.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a welding strip comprising a core and an alloy coating disposed on a surface of the core, wherein the chemical composition of the alloy coating comprises Sn, Nb, C and inevitable impurities; or, the chemical composition of the alloy coating comprises Sn, Pb, Nb, C and inevitable impurities.

[0007] When welding with this welding strip, since Nb and C are added to the alloy coating of the welding strip, during welding, when the alloy transforms from liquid to solid, Nb and C form NbC particles. Since NbC particles have a high melting point and poor plasticity, during the growth of matrix grains after forming nuclei during the alloy cooling process, the in-situ generated NbC particles have a pinning effect on the grain boundaries, thereby hindering the further growth of the matrix grains, ensuring that the grain size at the weld is sufficiently small, achieving fine grain strengthening of the matrix grains, and improving the structural strength, hardness, toughness and other mechanical properties of the weld position, which can meet the welding quality requirements of the welding strip and battery grid line under laser low-temperature welding conditions.

[0008] Optionally, in the above-mentioned welding strip, the mass percentage of the chemical composition of the alloy coating is:

[0009] The mass percentage of Sn is 60%≤wt%(Sn)≤99%,

[0010] The mass percentage of Pb is 0%≤wt%(Pb)≤40%,

[0011] The mass percentage of Nb is 0%<wt%(Nb)≤0.775%,

[0012] The mass percentage of C is 0%<wt%(C)≤1.5%.

[0013] In this way, the alloy coating of the present invention is based on the original composition, with a small amount of Nb and C added, which can achieve the effect of improving the mechanical properties and electrical conductivity of the welding position.

[0014] Optionally, in the above-mentioned solder strip, the chemical composition of the alloy plating layer further includes Ag. In this configuration, the addition of Ag to the alloy plating layer further improves the conductivity of the solder strip.

[0015] Optionally, in the above-mentioned solder strip, in the chemical composition of the alloy coating, the mass percentage of Ag is 0%<wt%(Ag)≤1.5%.

[0016] Optionally, in the aforementioned welding strip, the chemical composition of the alloy coating also includes Al. With this configuration, the addition of Al to the alloy coating forms an aluminum oxide film on the surface of the welding strip during welding, thereby increasing the material's absorption of the laser beam during laser welding. This allows the welding point of the welding strip to receive sufficient energy within a certain time limit, thereby increasing the welding rate.

[0017] Optionally, in the above-mentioned welding strip, in the chemical composition of the alloy coating, the mass percentage of Al is 0%<wt%(Al)≤0.05%.

[0018] Optionally, in the above-mentioned soldering ribbon, the core is made of one or more of copper, aluminum, nickel, and silver. The core of the soldering ribbon may be made of a metal material with good electrical conductivity.

[0019] In a second aspect, the present invention further provides a photovoltaic module comprising a cell and a welding ribbon, wherein the cell has electrode grid lines, and the welding ribbon is welded to the electrode grid lines, wherein the welding ribbon is any of the welding ribbons described above. Because the photovoltaic module utilizes the welding ribbon of the present invention when welding the cell to the welding ribbon, the welding quality of the welding ribbon to the electrode grid lines can meet the requirements of low-temperature laser welding conditions, thereby improving the structural strength, hardness, toughness, and other mechanical properties of the welded joint.

[0020] In a third aspect, the present invention further provides a battery welding method, using the welding strip as described in any one of the above items, the battery welding method comprises: using a laser welding method to weld and fix the welding strip to the electrode grid lines on the battery cell.

[0021] Due to the use of the welding strip in the present invention, when a laser is used to weld the welding strip and the grid lines of the battery cell, the welding strip can achieve high-quality welding with the electrode grid lines under laser low-temperature welding conditions, thereby improving the structural strength, hardness, toughness and other mechanical properties of the welding position.

[0022] Optionally, in the above battery welding method, the welding power of the laser welding method is 0.5kw to 2kw, and the power density is 10 2 W / cm 2 ~10 6 W / cm 2 Through laser welding, due to its high power density, it is possible to focus on local areas for precise welding at lower power, achieve low-temperature welding, and reduce the impact on the surface coating of the battery cell.

[0023] Optionally, in the above-mentioned battery welding method, the laser welding method has a welding time of 0.01s to 0.2s, which means a short welding time and a high welding speed.

[0024] Optionally, in the aforementioned battery welding method, the laser beam of the laser welding method is projected onto the side of the electrode grid line where the soldering ribbon contacts the electrode grid line. Because the melting point of the electrode grid line is higher than that of the soldering ribbon, placing the laser beam closer to the electrode grid line allows the electrode grid line to absorb relatively more energy, thereby maintaining a similar melting rate between the electrode grid line and the soldering ribbon, thereby improving welding efficiency and quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0026] Figure 1 This is a schematic diagram of the structure of welding a welding strip and a grid line in an embodiment of the present invention;

[0027] Figure 2 Schematic diagram of the grain structure of a welding area in an embodiment of the present invention.

[0028] Reference numerals:

[0029] 1-welding strip, 2-electrode grid line. DETAILED DESCRIPTION

[0030] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0031] It should be noted that when an element is referred to as being “fixed on” or “disposed on” another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being “connected to” another element, it may be directly connected to the other element or indirectly connected to the other element.

[0032] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined. "Several" means one or more, unless otherwise specifically defined.

[0033] In the description of the present invention, it should be understood that the terms "up", "down", "front", "back", "left", "right", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0034] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and may encompass internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0035] Compared to traditional fossil fuels, solar energy is a clean energy source that produces virtually no pollution. Furthermore, its near-infinite reserves make it an ideal alternative energy source. To reduce the BOM cost of photovoltaic modules and improve their power generation efficiency, technologies such as N-type cells, busbar-less design, and round welding wire are increasingly being incorporated into new modules.

[0036] Compared to traditional P-type cells, N-type cells offer advantages such as high conversion efficiency, high bifaciality, low temperature coefficient, zero light decay, and excellent low-light performance. Under the same cell layout, N-type cells require more silver paste to achieve optimal welding results compared to P-type cells because silver paste is applied to both the front and back sides. To reduce silver paste consumption in N-type cells, N-type busbarless cells have become a popular choice. Cells are connected in series via soldering ribbons. Traditionally, cell-to-ribbon soldering utilizes high-temperature baking, typically exceeding 200°C. At this temperature, the tin-lead on the lead soldering ribbon melts, forming a physical bond with the silver paste on the cell surface. This physical bond results in high contact resistance, increasing battery power loss. Furthermore, the non-bonded cell surface also has to withstand this high temperature. At these high temperatures, the surface conductive coating of N-type busbarless cells undergoes lattice transformation, significantly reducing conductivity.

[0037] Therefore, laser welding technology is used to achieve low-temperature welding between the solder ribbon and the silver paste, avoiding the impact on the surface conductive coating. Laser welding can also form a good ohmic contact (chemical contact) between the solder ribbon and the silver paste, reducing the contact resistance between the solder ribbon and the cell, and reducing the welding power loss of N-type busbarless cells. However, existing tin-lead solder ribbons are prone to problems such as cold joints, poor mechanical properties of the weld point, and corrosion of the weld surface during laser welding, making them unsuitable for effective low-temperature laser welding.

[0038] In view of this, to solve the above problems, please refer to Figure 1 and Figure 2An embodiment of the present invention provides a soldering strip 1, which includes a core and an alloy coating provided on the surface of the core. The core is a conductive metal, and the chemical composition of the alloy coating includes tin (Sn), niobium (Nb), carbon (C) and inevitable impurities; or, the chemical composition of the alloy coating includes tin (Sn), lead (Pb), niobium (Nb), carbon (C) and inevitable impurities.

[0039] The welding strip 1 is used for welding. Since Nb and C components are added to the alloy coating of the welding strip 1, during welding, when the alloy transforms from liquid to solid, Nb and C form NbC particles (that is, using in-situ synthesis technology, NbC precipitation phase reinforcement is generated in the titanium matrix through an exothermic reaction, and the NbC particles have a good interface bonding with the matrix, thereby achieving the purpose of strengthening. This method can obtain reinforced particles with small size, stable thermodynamic properties, no pollution at the interface, and high bonding strength). Since the melting point of NbC particles is relatively high and the plasticity is worse than that of the alloy matrix, during the cooling process of the alloy, when the matrix grains form nuclei and then grow, the in-situ generated NbC particles have a pinning effect on the grain boundaries, thereby hindering the further growth of the matrix grains, ensuring that the grain size at the welding point is small enough, achieving fine grain strengthening of the matrix grains, and improving the structural strength, hardness, toughness and other mechanical properties of the welding position, which can meet the welding quality of the welding strip 1 and the electrode grid line 2 under laser low-temperature welding conditions.

[0040] Furthermore, in this embodiment, the mass percentages of the chemical components of the alloy coating are: the mass percentage of Sn is 60%≤wt%(Sn)≤99%, the mass percentage of Pb is 0%≤wt%(Pb)≤40%, the mass percentage of Nb is 0%<wt%(Nb)≤0.775%, and the mass percentage of C is 0%<wt%(C)≤1.5%.

[0041] Specifically, the mass percentage of Sn can be 60%, 70%, 80%, 90%, 99%, etc.; the mass percentage of Pb can be 0%, 10%, 20%, 30%, 40%, etc.; the mass percentage of Nb can be 0.005%, 0.03%, 0.05%, 0.06%, 0.09%, 0.1%, 0.775%, etc.; the mass percentage of C can be 0.01%, 0.02%, 0.03%, 0.1%, 0.5%, 1%, 1.5%, etc.

[0042] The alloy coating of the present invention is based on the original composition, with a small amount of Nb and C added, which makes it suitable for laser low-temperature welding and improves the mechanical properties of the welding position.

[0043] For example, as shown in Table 1:

[0044] Table 1 shows the mechanical properties of the welded structure with different mass percentages of Nb and C in the alloy coating

[0045]

[0046] It can be seen that compared to the mechanical properties of the welded structure formed after welding using an alloy coating containing no Nb and C components in conventional welding strips, the mechanical properties of the welded structure formed after welding using the welding strip 1 of the present invention, which contains an alloy coating containing small amounts of Nb and C in varying mass percentages, are improved, such as elastic modulus and yield stress. Furthermore, as the mass percentages of Nb and C increase, the elastic modulus and yield stress also increase accordingly. This shows that the welding strip 1 of the present invention is suitable for low-temperature laser welding, and the resulting welded structure has improved welding quality.

[0047] Furthermore, in this embodiment, the chemical composition of the alloy coating also includes Ag (silver). Since Ag has a higher conductivity than other components in the alloy coating, the addition of Ag to the alloy coating further improves the conductivity of the soldering ribbon 1. Furthermore, since the electrode grid lines 2 on the cell are typically silver paste, the addition of Ag to the alloy coating can further facilitate the fusion welding of the soldering ribbon 1 and the electrode grid lines 2.

[0048] Specifically, in this embodiment, in the chemical composition of the alloy coating, the mass percentage of Ag is 0%<wt%(Ag)≤1.5%, and can be specifically 0.1%, 0.3%, 0.5%, 0.9%, 1%, 1.5%, etc. The appropriate ratio is selected according to the actual welding process.

[0049] Furthermore, in this embodiment, the chemical composition of the alloy coating also includes Al (aluminum). This configuration, with the addition of Al to the alloy coating, forms an aluminum oxide film on the surface of the welding ribbon 1 during the welding process. Because the aluminum oxide film has a porous structure and traps light, it can increase the laser beam absorption of the welding ribbon 1 during laser welding, allowing the welding point of the welding ribbon 1 to obtain sufficient energy within a certain time limit, thereby improving the welding rate.

[0050] Specifically, in the chemical composition of the alloy coating, the mass percentage of Al is 0%<wt%(Al)≤0.05%, and can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, etc. The appropriate ratio is selected according to the actual welding process.

[0051] In this embodiment, the core material of the solder ribbon 1 can be one or more of copper, aluminum, nickel, and silver. Specifically, the core can be a single metal component, such as copper with a purity of up to 99.99%, which has high conductivity and low cost. Alternatively, the core can be an alloy of multiple metals or a segmented combination structure.

[0052] It should be noted that the shape of the welding strip 1 can be a flat strip welding strip with a uniform cross-section or a segmented welding strip with different cross-sections; the segmented welding strip can include a reflective section and a flat section, and the cross-sectional shape of the reflective section can be triangular, circular, elliptical or polygonal.

[0053] Based on the welding ribbon 1 described in any of the above embodiments, an embodiment of the present invention further provides a photovoltaic module, comprising a cell and a welding ribbon 1. The cell has an electrode grid line 2. The cell is an N-type cell, forming an N-type busbarless cell. Multiple cells are welded together via the welding ribbon 1 to form a cell string. Specifically, the welding ribbon 1 is welded to the electrode grid line 2, and then the cell string is packaged according to a conventional packaging process to obtain a photovoltaic module. The welding ribbon 1 is the welding ribbon 1 described in any of the above embodiments.

[0054] Because the photovoltaic module utilizes the welding ribbon 1 of the present invention when welding the cells to the welding ribbon 1, it can meet the welding quality requirements of the welding ribbon 1 and the electrode grid lines under low-temperature laser welding conditions, improving the mechanical properties of the welded joint, such as structural strength, hardness, and toughness. Furthermore, the welded structure obtained by low-temperature laser welding reduces contact resistance, lowering welding power losses of N-type busbarless cells, thereby improving the conductive efficiency of the photovoltaic module.

[0055] Based on the welding strip described in any of the above embodiments, an embodiment of the present invention further provides a battery welding method, using the welding strip 1 described in any of the above embodiments. The battery welding method is: using a laser welding method to weld and fix the welding strip 1 to the electrode grid line 2 on the battery cell.

[0056] The welding ribbon 1 of the present invention achieves high-quality welding to the electrode grid lines 2 of a cell using laser welding, even under low-temperature laser welding conditions. This improves mechanical properties such as structural strength, hardness, and toughness at the welded joint. Laser welding also ensures good contact and reduces contact resistance, thus lowering welding power loss and improving electrical conductivity in N-type busbarless cells.

[0057] Furthermore, in this embodiment, the welding power of the laser welding method is 0.5kw~2kw, specifically 0.5kw, 1kw, 1.5kw, 2kw, etc. The power density is 10 2 W / cm 2 ~10 6 W / cm 2 , specifically 10 2 W / cm 2 , 10 3 W / cm 2 , 10 4 W / cm 2 , 105 W / cm 2 、106W / cm 2 Through laser welding, due to its high power density, it is possible to focus on local areas for precise welding at lower power, achieve low-temperature welding, and reduce the impact on the surface coating of the battery cell.

[0058] Optionally, in this embodiment, the laser welding method has a welding time of 0.01s to 0.2s, specifically 0.01s, 0.03s, 0.06s, 0.1s, 0.15s, 0.2s, etc., which means the welding time is short and the welding speed is fast. Laser welding is a type of fusion welding, using a laser beam as energy. The laser beam is guided by one or more combinations of a plane mirror, a convex lens, and a concave lens. The plane mirror can be a lens, a semi-transparent lens, or a non-lens lens. The convex lens can be a biconvex, plano-convex, or concave-convex lens. The concave lens can be a biconcave, plano-concave, or convex-concave lens. The laser is focused by using a focusing method, and a lens with a focal length of 20mm to 60mm is selected. The size of the focused spot is proportional to the focal length. The shorter the focal length, the smaller the spot. The laser power at the starting and ending points of the welding is gradually increased and decreased. The starting power increases from zero to the set power value within 0 to 10,000 μs, and the welding time is adjusted from 0.01s to 0.2s. Finally, the power is gradually reduced from the set power to zero when the welding ends.

[0059] Furthermore, in this embodiment, the laser welding method projects the laser beam onto the contact point between the soldering ribbon 1 and the electrode grid lines 2, close to the electrode grid lines 2. Since the electrode grid lines 2 are typically silver paste grid lines with a higher melting point than the soldering ribbon, placing the laser beam close to the electrode grid lines 2 allows the electrode grid lines 2 to absorb relatively more energy, thereby maintaining a similar melting rate between the electrode grid lines 2 and the soldering ribbon 1, thereby improving welding efficiency and quality.

[0060] In the description of the above embodiments, specific features, structures, materials or characteristics may be combined in an appropriate manner in any one or more embodiments or examples.

[0061] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A photovoltaic module, characterized in that: The invention relates to a battery cell and a welding ribbon, wherein the battery cell has an electrode grid line, the welding ribbon is welded to the electrode grid line, the welding ribbon comprises a core and an alloy coating provided on the surface of the core, the chemical composition of the alloy coating comprises Sn, Nb, C and unavoidable impurities; or the chemical composition of the alloy coating comprises Sn, Pb, Nb, C and unavoidable impurities; The mass percentages of the chemical components of the alloy coating are: The mass percentage of Nb is 0%<wt%(Nb)≤0.775%, The mass percentage of C is 0%<wt%(C)≤1.5%.

2. The photovoltaic module according to claim 1, characterized in that The mass percentages of the chemical components of the alloy coating are: The mass percentage of Sn is 60%≤wt%(Sn)≤99%, The mass percentage of Pb is 0%≤wt%(Pb)≤40%.

3. The photovoltaic module according to claim 1, characterized in that The chemical composition of the alloy coating also includes Ag.

4. The photovoltaic module according to claim 3, characterized in that In the chemical composition of the alloy plating layer, the mass percentage of Ag is 0%<wt%(Ag)≤1.5%.

5. The photovoltaic module according to claim 1, characterized in that The chemical composition of the alloy coating also includes Al.

6. The photovoltaic module according to claim 5, characterized in that: In the chemical composition of the alloy coating, the mass percentage of Al is 0%<wt%(Al)≤0.05%.

7. The photovoltaic module according to claim 1, characterized in that The core is made of one or more combinations of copper, aluminum, nickel, and silver.

8. A battery welding method, characterized in that: Applied to the photovoltaic module according to any one of claims 1 to 7, the cell welding method is: using a laser welding method to weld and fix the welding ribbon to the electrode grid line on the cell.

9. The battery welding method according to claim 8, characterized in that: The welding power of the laser welding method is 0.5kw~2kw, and the power density is 10 2 W / cm 2 ~10 6 W / cm 2 .

10. The battery welding method according to claim 8, characterized in that: The welding time of the laser welding method is 0.01s to 0.2s.

11. The battery welding method according to claim 8, characterized in that: The laser beam of the laser welding method is projected onto a side of the electrode grid line where the welding strip contacts the electrode grid line.

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