Photovoltaic solder strip, preparation method thereof and photovoltaic module

Abstract

The invention discloses a photovoltaic solder strip, a preparation method thereof and a photovoltaic module. The photovoltaic solder strip comprises a conductive substrate, a first solder layer and a second solder layer from inside to outside, the first solder layer is made of tin-lead alloy, and the second solder layer is made of bismuth-containing alloy. The photovoltaic welding strip has the advantages of low cost, low-temperature welding performance, excellent mechanical property and long-term reliability.

Description

Technical Field

[0001] This invention belongs to the field of solar cells, specifically relating to a photovoltaic ribbon, its preparation method, and a photovoltaic module. Background Technology

[0002] Low-temperature solder ribbons (melting point <170℃) have broad application prospects in tunnel oxide passivated contact solar cells (TOPcon), heterojunction (HJT) cells, and back contact (BC) cell modules, representing a future upgrade direction for solder ribbons. Their solder layer is typically based on SnPbBi, SnBi, or SnBiAg systems. While Bi helps lower the solder melting point, during welding and long-term module service, Bi tends to segregate at the interface, forming brittle phases such as Bi phase or Bi-rich phase. This reduces the bond strength and long-term aging performance of the solder joint.

[0003] It is generally believed in the industry that the lower the Bi content in the solder layer, the better the mechanical properties and long-term reliability of the solder joint. For this reason, a series of bismuth-containing solder alloys with different Bi content have been developed, such as Sn43Pb43Bi14, Sn40Pb42Bi18, Sn37Pb42Bi21, Sn32Pb42Bi26, Sn27Pb41Bi32, Sn42Bi58, Sn42Bi57Ag1, Sn40.5Bi58Ag1.5, Sn46Bi52Ag2, etc. However, the reduction of Bi content will lead to an increase in the melting point of the solder, which limits the low-temperature application of the solder strip. In addition, the reduction of Bi content will lead to an increase in the amount of Sn used, which will increase the cost of the solder strip.

[0004] Existing technologies can improve solder joint bonding strength by adding trace elements or additives. Patent document CN116618885A discloses adding trace amounts of Cu, Sb, Ni, Ge, and Ce to the SnBiAg system for compounding. The trace amounts of Ce and Ni accumulate at the Bi-rich phase boundary, preventing the Bi-rich phase from segregating and growing, thus refining the grains and improving the mechanical properties of the solder joint. Simultaneously, it reduces Ag element loss, lowering costs. Patent document CN111088442B discloses adding boride (one or more of ZrB2, TiB2, CrB2, and MoB2) micro / nano particles to tin-bismuth solder, thereby improving the impact resistance and creep resistance of tin-bismuth when used as a low-temperature solder. However, adding trace elements increases the complexity of the solder system, potentially altering the alloy's surface tension, wettability, and fluidity, thereby reducing its solderability. This can lead to defects during the soldering process, such as voids or incomplete penetration; or it may cause other chemical reactions, such as the formation of intermetallic compounds, resulting in performance instability. Adding trace amounts of micro / nano additives may cause bulges in appearance or become stress concentration points. In addition, certain trace elements or micro / nano compounds may form electrical couples with the base alloy or other contact materials due to differences in electrochemical potential. In humid or electrolyte environments, these couples can easily accelerate electrochemical corrosion, thereby reducing the life of the solder joint.

[0005] Therefore, there is an urgent need to develop a photovoltaic welding strip that combines low cost, low-temperature welding performance, excellent mechanical properties, and long-term reliability. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention introduces a tin-lead alloy solder layer between the outer bismuth-containing alloy solder layer and the inner conductive substrate to prepare a photovoltaic solder ribbon. The photovoltaic solder ribbon of this invention improves the long-term reliability of the photovoltaic solder ribbon without significantly increasing material and processing costs, reducing low-temperature welding performance, or affecting mechanical properties.

[0007] Specifically, the present invention provides a photovoltaic solder ribbon, which includes, from the inside out, a conductive substrate, a first solder layer and a second solder layer; the first solder layer is made of a tin-lead alloy and the second solder layer is made of a bismuth-containing solder alloy.

[0008] In one or more embodiments, the maximum melting point of the tin-lead alloy is 183-190°C.

[0009] In one or more embodiments, the maximum melting point of the bismuth-containing solder alloy is 138-167°C.

[0010] In one or more embodiments, the melting point of the tin-lead alloy is higher than that of the bismuth-containing solder alloy.

[0011] In one or more embodiments, the mass fraction of Sn in the first solder layer is 60wt%-63wt%, and the mass fraction of Pb is 37wt%-40wt%; preferably, the material of the first solder layer is Sn60Pb40 or Sn63Pb37.

[0012] In one or more embodiments, the thickness of the second solder layer is 5-15 μm.

[0013] In one or more embodiments, the material of the second solder layer is a tin-lead-bismuth alloy, a tin-bismuth alloy, or a tin-bismuth-silver alloy; preferably, in the tin-lead-bismuth alloy, the mass fraction of Sn is 27wt%-43wt%, the mass fraction of Pb is 41wt%-43wt%, and the mass fraction of Bi is 14wt%-32wt%; in the tin-bismuth alloy, the mass fraction of Sn is 41wt%-43wt%, and the mass fraction of Bi is 57wt%-59wt%; in the tin-bismuth-silver alloy, the mass fraction of Sn is 40.5%. The mass fraction of Bi is 52wt%-58wt%, and the mass fraction of Ag is 1wt%-2wt%. Preferably, the material of the second solder layer is selected from Sn43Pb43Bi14, Sn40Pb42Bi18, Sn37Pb42Bi21, Sn32Pb42Bi26, Sn27Pb41Bi32, Sn42Bi58, Sn42Bi57Ag1, Sn40.5Bi58Ag1.5, and Sn46Bi52Ag2.

[0014] In one or more embodiments, the conductive substrate is made of copper with a copper content of ≥99.97%.

[0015] In one or more embodiments, the cross-sectional shape of the conductive substrate is selected from one of the following: circular, square, rectangular, triangular, trapezoidal, and elliptical.

[0016] This invention provides a method for preparing the photovoltaic ribbon described herein, the method comprising the following steps:

[0017] (1) A photovoltaic ribbon intermediate with a first solder layer is prepared by sequentially coating the conductive substrate with flux and then with tin-lead alloy liquid.

[0018] (2) The photovoltaic ribbon intermediate is coated with flux and then coated with bismuth-containing solder alloy liquid in sequence to obtain a photovoltaic ribbon with a second solder layer.

[0019] The method for preparing photovoltaic ribbon of the present invention further includes: drawing and rolling the raw material of the conductive substrate, annealing, and water cooling to obtain the conductive substrate; preferably, the annealing is short-circuit annealing or induction annealing.

[0020] The method for preparing photovoltaic solder ribbon of the present invention further includes: coating with bismuth-containing solder alloy liquid and then cooling with air duct.

[0021] In one or more embodiments, in step (1), the tin-lead alloy liquid is coated by hot-dip plating or electroplating, preferably hot-dip plating; more preferably, the hot-dip plating temperature is 190-250°C.

[0022] In one or more embodiments, in step (2), the coating method of the bismuth-containing solder alloy liquid is hot-dip plating or electroplating, preferably hot-dip plating; more preferably, the hot-dip plating temperature is 143-177°C, which is 5-15°C higher than the maximum melting point of the bismuth-containing solder alloy.

[0023] The present invention provides a method for preparing a photovoltaic module, the method comprising welding solar cells using the photovoltaic solder ribbon described in the present invention. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a photovoltaic solder strip according to some embodiments of the present invention.

[0025] Figure 1 In the diagram, 1 represents the conductive substrate, 2 represents the first solder layer, and 3 represents the second solder layer. Detailed Implementation

[0026] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used herein are explained and defined in general terms below. Unless otherwise specified, all technical and scientific terms used herein have the common meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0027] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0028] In this document, the terms “contains,” “includes,” “containing,” and similar terms encompass the meanings of “basically composed of” and “composed of.” For example, when this document discloses “A contains B and C,” “A is basically composed of B and C” and “A is composed of B and C” should be considered as having been disclosed in this document.

[0029] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0030] Unless otherwise specified, percentages refer to mass percentages and proportions refer to mass ratios in this article.

[0031] In this document, when describing embodiments or examples, it should be understood that it is not intended to limit the invention to those embodiments or examples. Rather, all alternatives, modifications, and equivalents of the methods and materials described herein are covered within the scope defined by this invention.

[0032] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0033] This invention provides a photovoltaic solder ribbon, which comprises, from the inside out, a conductive substrate, a first solder layer, and a second solder layer. In some embodiments, the inner surface of the first solder layer is in contact with the conductive substrate, and the outer surface of the first solder layer is in contact with the second solder layer, such as... Figure 1 As shown. In this invention, the material of the first solder layer can be a tin-lead alloy; preferably, the mass fraction of Sn can be 60wt%-63wt%, and the mass fraction of Pb can be 37wt%-40wt%; more preferably, the material of the first solder layer can be Sn60Pb40 or Sn63Pb37. The first solder layer (i.e., the tin-lead solder layer) introduced in this invention does not melt, ensuring that the outermost low-temperature solder layer has sufficient thickness and will not reduce the welding effect; the introduced first solder layer reduces the overall Bi content of the photovoltaic solder ribbon, weakening the segregation, precipitation, and growth of Bi phase and Bi-rich phase and other hard and brittle phases during welding and long-term service of the photovoltaic module, which is beneficial to improving the solder joint strength and improving the long-term reliability of the module; the introduced first solder layer has a high melting point and good corrosion resistance, which improves the corrosion resistance and hot spot resistance of the photovoltaic solder ribbon; the introduced first solder layer blocks the leaching of Cu substrate in the hot dipping process of Bi-containing solder, which is beneficial to reducing the loss of Bi-containing solder melt and reducing the number of solder dross cleaning times.

[0034] In this invention, the material of the second solder layer can be a bismuth-containing solder alloy; preferably, the material of the second solder layer can be a tin-lead-bismuth alloy, a tin-bismuth alloy, or a tin-bismuth-silver alloy. Preferably, in the tin-lead-bismuth alloy, the mass fraction of Sn can be 27wt%-43wt%, the mass fraction of Pb can be 41wt%-43wt%, and the mass fraction of Bi can be 14wt%-32wt%; in the tin-bismuth alloy, the mass fraction of Sn can be 41wt%-43wt%, and the mass fraction of Bi can be 57wt%-59wt%; in the tin-bismuth-silver alloy, the mass fraction of Sn can be 40.5wt%-46wt%, and the mass fraction of Bi can be... The mass fraction of Ag can be 1 wt% to 2 wt%, with a mass fraction of 52 wt% to 58 wt%. More preferably, the material of the second solder layer can be selected from Sn43Pb43Bi14, Sn40Pb42Bi18, Sn37Pb42Bi21, Sn32Pb42Bi26, Sn27Pb41Bi32, Sn42Bi58, Sn42Bi57Ag1, Sn40.5Bi58Ag1.5, and Sn46Bi52Ag2.

[0035] In the solder composition of this invention, the melting point is mostly within a range. The minimum melting point corresponding to a solder component represents the solder just beginning to melt, and the maximum melting point corresponding to a solder component represents the solder component completely transforming into a liquid phase. Table 1 shows the melting points of the solder components corresponding to the first solder layer and the second solder layer in some embodiments of this invention.

[0036] Table 1: Melting points of solder components corresponding to the first and second solder layers

[0037]

[0038] In this invention, the maximum melting point of the tin-lead alloy is 183-190℃, for example, 183℃, 184℃, 185℃, 186℃, 187℃, 188℃, 189℃, and 190℃.

[0039] In this invention, the maximum melting point of the bismuth-containing solder alloy is 138-167℃, for example 138℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, and 167℃.

[0040] In this invention, the melting point of the tin-lead alloy can be higher than that of the bismuth-containing solder alloy. The outer layer of the photovoltaic solder ribbon of this invention has a layered design. The inner tin-lead alloy has a high melting point, and the corresponding first solder layer plays a role in copper-based protection and bismuth reduction. The outer bismuth-containing solder alloy has a low melting point, and the corresponding second solder layer plays a welding role. The welding temperature is controlled between the melting points of the inner and outer solder layers, so that only the outer solder melts and achieves metallization bonding with the photovoltaic cell, without reducing the welding effect.

[0041] In this invention, the thickness of the first solder layer can be 1-5μm, for example 1μm, 2μm, 3μm, 4μm, 5μm.

[0042] In this invention, the thickness of the second solder layer can be 5-15μm, for example 5μm, 7μm, 9μm, 11μm, 13μm, 15μm.

[0043] In this invention, the cross-sectional shape of the conductive substrate can be selected from one of the following: circle, square, rectangle, triangle, trapezoid, and ellipse.

[0044] In this invention, the conductive substrate can be made of copper, such as TU1 oxygen-free copper with a copper content ≥99.97%.

[0045] This invention provides a method for preparing photovoltaic solder ribbon, the method comprising the following steps:

[0046] (1) A photovoltaic ribbon intermediate with a first solder layer is prepared by sequentially coating the conductive substrate with flux and then with tin-lead alloy liquid.

[0047] (2) The photovoltaic ribbon intermediate is coated with flux and then coated with bismuth-containing solder alloy liquid in sequence to obtain a photovoltaic ribbon with a second solder layer.

[0048] During hot-dip coating of this invention, the flux is almost completely decomposed or evaporated due to the high temperature, and the trace residue formed on the copper base will enter the solder slag as the solder ribbon moves and the molten solder flows.

[0049] The method for preparing photovoltaic ribbon of the present invention further includes: drawing and rolling the raw material of the conductive substrate, annealing, and water cooling to obtain the conductive substrate; preferably, the annealing can be short-circuit annealing or induction annealing.

[0050] The method for preparing photovoltaic solder ribbon of the present invention further includes: coating with bismuth-containing solder alloy liquid and then cooling with air duct.

[0051] In step (1), the coating method of the tin-lead alloy liquid can be hot-dip plating or electroplating, preferably hot-dip plating.

[0052] In step (1), the hot-dip galvanizing temperature can be 190-250℃, for example 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃.

[0053] In step (2), the coating method of the bismuth-containing solder alloy liquid is hot-dip plating or electroplating, preferably hot-dip plating.

[0054] In step (2), the hot-dip plating temperature can be 143-177℃, which can be 5-15℃ higher than the maximum melting point of the bismuth-containing solder alloy, for example, 5℃, 6℃, 7℃, 8℃, 9℃, 10℃, 11℃, 12℃, 13℃, 14℃, 15℃.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] (1) The outer layer of the photovoltaic solder ribbon of the present invention has a layered design. The inner high-melting-point layer plays the role of copper-based protection and Bi reduction, while the outer low-melting-point solder plays the role of welding. The welding temperature is controlled between the melting points of the inner and outer solders. Only the outer solder melts and achieves metallization with the photovoltaic cell, without reducing the welding effect.

[0057] (2) The present invention reduces the overall Bi content in the solder layer, weakens the segregation, precipitation and growth of hard and brittle phases such as Bi phase and Bi-rich phase during welding and long-term service of photovoltaic modules, which is beneficial to improving the strength of solder joints and improving the long-term reliability of modules.

[0058] (2) The tin-lead solder layer of the present invention has a high melting point and good corrosion resistance, which improves the corrosion resistance and hot spot resistance of the composite solder layer solder strip;

[0059] (4) In the production of solder ribbon, during the hot-dip coating process of Bi-containing solder, the pre-coated tin-lead solder layer blocks the leaching of Cu substrate, which helps to reduce the loss of Bi-containing solder melt and reduce the number of times tin dross cleaning is required.

[0060] The present invention will be described below by way of specific embodiments. It should be understood that these embodiments are merely illustrative and are not intended to limit the scope of the invention. The methods, reagents, and materials used in the embodiments are conventional methods, reagents, and materials in the art, unless otherwise stated. The raw material compounds in the embodiments are all commercially available.

[0061] Example 1

[0062] (1) A conductive substrate is obtained by drawing, rolling and short-circuiting copper strips. The conductive substrate has a circular cross-section and a diameter of φ0.18mm.

[0063] (2) A photovoltaic ribbon intermediate with a first solder layer of Sn60Pb40 with a single-sided thickness of 5μm is prepared by coating the conductive substrate with flux, hot-dip plating with Sn60Pb40 alloy liquid, and cooling with air duct. The hot-dip plating temperature is 220℃.

[0064] (3) The photovoltaic ribbon intermediate is coated with flux, hot-dip coated with Sn43Pb43Bi14 alloy liquid, and cooled with air duct to obtain a photovoltaic ribbon with a Sn43Pb43Bi14 second solder layer with a single-sided thickness of 5μm, wherein the hot-dip coating temperature is 177℃.

[0065] Example 2

[0066] (1) A conductive substrate is obtained by drawing, rolling and short-circuiting copper strips. The conductive substrate has a circular cross-section and a diameter of φ0.18mm.

[0067] (2) A photovoltaic ribbon intermediate with a first solder layer of Sn63Pb37 with a single-sided thickness of 5μm is prepared by coating the conductive substrate with flux, hot-dip plating with Sn63Pb37 alloy liquid, and cooling with air duct. The hot-dip plating temperature is 220℃.

[0068] (3) The photovoltaic ribbon intermediate is coated with flux, hot-dip coated with Sn32Pb42Bi26 alloy liquid, and cooled with air duct to obtain a photovoltaic ribbon with a Sn32Pb42Bi26 second solder layer with a single-sided thickness of 5μm, wherein the hot-dip coating temperature is 155℃.

[0069] Example 3

[0070] (1) A conductive substrate is obtained by drawing, rolling and short-circuiting copper strips. The conductive substrate has a circular cross-section and a diameter of φ0.18mm.

[0071] (2) A photovoltaic ribbon intermediate with a first solder layer of Sn60Pb40 with a single-sided thickness of 5μm is prepared by coating the conductive substrate with flux, hot-dip plating with Sn60Pb40 alloy liquid, and cooling with air duct. The hot-dip plating temperature is 220℃.

[0072] (3) The photovoltaic ribbon intermediate is coated with flux, hot-dip coated with Sn42Bi58 alloy liquid, and cooled with air duct to obtain a photovoltaic ribbon with a single-sided thickness of 5μm of Sn42Bi58 second solder layer, wherein the hot-dip coating temperature is 150℃.

[0073] Example 4

[0074] (1) A conductive substrate is obtained by drawing, rolling and short-circuiting copper strips. The conductive substrate has a circular cross-section and a diameter of φ0.18mm.

[0075] (2) A photovoltaic ribbon intermediate with a first solder layer of Sn60Pb40 with a single-sided thickness of 5μm is prepared by coating the conductive substrate with flux, hot-dip plating with Sn60Pb40 alloy liquid, and cooling with air duct. The hot-dip plating temperature is 220℃.

[0076] (3) The photovoltaic ribbon intermediate is coated with flux, hot-dip coated with Sn42Bi57Ag1 alloy liquid, and cooled with air duct to obtain a photovoltaic ribbon with a single-sided thickness of 5μm of Sn42Bi57Ag1 second solder layer, wherein the hot-dip coating temperature is 152℃.

[0077] Comparative Example 1

[0078] (1) A conductive substrate is obtained by drawing, rolling and short-circuiting copper strips. The conductive substrate has a circular cross-section and a diameter of φ0.18mm.

[0079] (2) The photovoltaic ribbon precursor is coated with flux, hot-dip coated with Sn43Pb43Bi14 alloy liquid, and cooled with air duct to obtain a conventional low-temperature photovoltaic ribbon with a Sn43Pb43Bi14 solder layer with a single-sided thickness of 10μm. The hot-dip coating temperature is 177℃.

[0080] Comparative Example 2

[0081] (1) A conductive substrate is obtained by drawing, rolling and short-circuiting copper strips. The conductive substrate has a circular cross-section and a diameter of φ0.18mm.

[0082] (2) The photovoltaic ribbon precursor is coated with flux, hot-dip coated with Sn32Pb42Bi26 alloy liquid, and cooled with air duct to obtain a conventional low-temperature photovoltaic ribbon with a Sn32Pb42Bi26 solder layer with a single-sided thickness of 10μm. The hot-dip coating temperature is 177℃.

[0083] Comparative Example 3

[0084] (1) A conductive substrate is obtained by drawing, rolling and short-circuiting copper strips. The conductive substrate has a circular cross-section and a diameter of φ0.18mm.

[0085] (2) The photovoltaic ribbon precursor is coated with flux, hot-dip coated with Sn42Bi58 alloy liquid, and cooled with air duct to obtain a conventional low-temperature photovoltaic ribbon with a Sn42Bi58 solder layer with a single-sided thickness of 10μm. The hot-dip coating temperature is 150℃.

[0086] Comparative Example 4

[0087] (1) A conductive substrate is obtained by drawing, rolling and short-circuiting copper strips. The conductive substrate has a circular cross-section and a diameter of φ0.18mm.

[0088] (2) The photovoltaic ribbon precursor is coated with flux, hot-dip coated with Sn42Bi57Ag1 alloy liquid, and cooled with air duct to obtain a conventional low-temperature photovoltaic ribbon with a Sn42Bi57Ag1 solder layer with a single-sided thickness of 10μm. The hot-dip coating temperature is 152℃.

[0089] Test case

[0090] (1) Welding tensile test

[0091] The welding tensile strength standard for the welding strip and the solar cell is generally determined by the enterprise, typically ranging from 0.3 to 0.8 N. Qualified multi-busbar (MBB) solar cells and the photovoltaic welding strips prepared in Examples 1-4 and Comparative Examples 1-4 are connected by string welding on an automatic string welding machine. The welded solar cells are fixed to a tensile testing machine using tooling. A clamp connected to a tensile sensor is used to clamp the end of the welding strip. The photovoltaic welding strip is pulled horizontally at 180°, and the peak value is recorded. The average of the peak tensile strengths is taken as the welding tensile strength; the higher the average peak tensile strength, the better the welding effect. The welding tensile strength test results of the photovoltaic welding strips prepared in Examples 1-4 and Comparative Examples 1-4 are shown in Table 2.

[0092] (2) Corrosion resistance test

[0093] Generally, the resistance of photovoltaic (PV) ribbons depends on the copper substrate and is not significantly affected by the coating composition or thickness. Changes in the resistance of PV ribbons are primarily due to changes in the resistance of the copper substrate. Therefore, the corrosion resistance of PV ribbons can be determined by the rate of change in resistivity before and after the corrosion resistance test. The corrosion resistance test was conducted using a neutral salt spray test according to GB / T 10125. Three PV ribbons each from Examples 1-4 and Comparative Examples 1-4, each 200 mm in length, were used to test the initial resistivity and take the average value ρ0. After 48 hours of salt spray testing, 2 cm was cut off from both ends of the PV ribbons from Examples 1-4 and Comparative Examples 1-4, and the resistivity was tested again and taken as the average value ρ1. The rate of change in resistivity was then calculated. The smaller the rate of change in resistivity, the better the corrosion resistance of the PV ribbon. The corrosion resistance test results of the PV ribbons from Examples 1-4 and Comparative Examples 1-4 are shown in Table 2.

[0094] (3) Long-term reliability testing

[0095] The photovoltaic ribbons prepared in Examples 1-4 and Comparative Examples 1-4 were used to fabricate standard modules. Thermal cycling tests (TC300) and hot spot + reverse current tests were conducted according to IEC 61215 and IEC 61730. The power of the standard modules before and after the tests was measured, and the power attenuation ratio of the standard modules was calculated. This yielded the TC300 power attenuation and hot spot + reverse current power attenuation test results. A smaller attenuation ratio indicates better long-term reliability. The TC300 power attenuation and hot spot + reverse current power attenuation test results of the photovoltaic ribbons prepared in Examples 1-4 and Comparative Examples 1-4 are shown in Table 2.

[0096] Table 2: Performance test results of photovoltaic ribbons prepared in Examples 1-4 and Comparative Examples 1-4

[0097]

Claims

1. A photovoltaic welding strip, characterized in that, The photovoltaic solder ribbon includes, from the inside out, a conductive substrate, a first solder layer, and a second solder layer; the first solder layer is made of a tin-lead alloy, and the second solder layer is made of a bismuth-containing solder alloy.

2. The photovoltaic welding strip as described in claim 1, characterized in that, The method has one or more of the following characteristics: The maximum melting point of the tin-lead alloy is 183-190℃; The maximum melting point of the bismuth-containing solder alloy is 138-167℃; The melting point of the tin-lead alloy is higher than that of the bismuth-containing solder alloy.

3. The photovoltaic welding strip as described in claim 1, characterized in that, The thickness of the first solder layer is 1-5 μm; and / or In the first solder layer, the mass fraction of Sn is 60wt%-63wt%, and the mass fraction of Pb is 37wt%-40wt%; preferably, the material of the first solder layer is Sn60Pb40 or Sn63Pb37.

4. The photovoltaic welding strip as described in claim 1, characterized in that, The thickness of the second solder layer is 5-15 μm.

5. The photovoltaic welding strip as described in claim 1, characterized in that, The material of the second solder layer is a tin-lead-bismuth alloy, a tin-bismuth alloy, or a tin-bismuth-silver alloy. Preferably, in the tin-lead-bismuth alloy, the mass fraction of Sn is 27wt%-43wt%, the mass fraction of Pb is 41wt%-43wt%, and the mass fraction of Bi is 14wt%-32wt%; in the tin-bismuth alloy, the mass fraction of Sn is 41wt%-43wt%, and the mass fraction of Bi is 57wt%-59wt%; in the tin-bismuth-silver alloy, the mass fraction of Sn is 40.5wt%-46wt%, the mass fraction of Bi is 52wt%-58wt%, and the mass fraction of Ag is 1wt%-2wt%. Preferably, the material of the second solder layer is selected from one of Sn43Pb43Bi14, Sn40Pb42Bi18, Sn37Pb42Bi21, Sn32Pb42Bi26, Sn27Pb41Bi32, Sn42Bi58, Sn42Bi57Ag1, Sn40.5Bi58Ag1.5, and Sn46Bi52Ag2.

6. The photovoltaic welding strip as described in claim 1, characterized in that, The conductive substrate is made of copper, with a copper content preferably ≥99.97wt%.

7. The photovoltaic welding strip as described in claim 1, characterized in that, The cross-sectional shape of the conductive substrate is selected from one of the following: circular, square, rectangular, triangular, trapezoidal, and elliptical.

8. A method for preparing the photovoltaic ribbon according to any one of claims 1-7, characterized in that, The method includes the following steps: (1) A photovoltaic ribbon intermediate with a first solder layer is prepared by sequentially coating the conductive substrate with flux and then with tin-lead alloy liquid. (2) The photovoltaic ribbon intermediate is coated with flux and then coated with bismuth-containing solder alloy liquid in sequence to obtain a photovoltaic ribbon with a second solder layer.

9. The preparation method according to claim 8, characterized in that, The method has one or more of the following characteristics: The method further includes: drawing and rolling the raw material of the conductive substrate, annealing, and water cooling to obtain the conductive substrate; preferably, the annealing is short-circuit annealing or induction annealing; the method further includes: coating with bismuth-containing solder alloy liquid and then cooling with air duct; In step (1), the coating method of the tin-lead alloy liquid is hot-dip plating or electroplating, preferably hot-dip plating; more preferably, the hot-dip plating temperature is 190-250℃. In step (2), the coating method of the bismuth-containing solder alloy liquid is hot-dip plating or electroplating; preferably hot-dip plating; more preferably, the hot-dip plating temperature is 143-177℃, which is 5-15℃ higher than the maximum melting point of the bismuth-containing solder alloy.

10. A method for preparing a photovoltaic module, characterized in that, The method includes welding solar cells using photovoltaic solder ribbons as described in any one of claims 1-7.

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