A welding method for improving the welding effect of interconnected welding wires and busbar-free solar cell piece grid lines

Abstract

The application relates to the field of solar cell manufacturing, and particularly discloses a welding method for improving the welding effect of interconnected welding wires and grid line welding of a main-grid-free solar cell, which comprises the following steps: S1, a cross position of a fine grid line of a cell and a welding wire is a to-be-processed area; S2, tin paste solder containing metal solder powder and acidic flux is coated on the to-be-processed area, the coating area of the tin paste solder completely covers the to-be-processed area, then drying is performed to make the tin paste solder adhere to the fine grid line; S3, the welding wire is placed on the tin paste solder of the fine grid line, then heating treatment is performed to form an electrical connection between the welding wire and the fine grid line; and S4, after welding is completed, film coating, lamination and curing are performed to obtain a main-grid-free cell assembly. The application has the characteristics of improving the welding firmness of the contact point of the welding wire and the fine grid line and improving the reliability of the solar cell.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of solar cell manufacturing, more particularly, it relates to a welding method for improving the welding effect of interconnecting solder wire and fine grid lines of a solar cell without main grid. BACKGROUND

[0002] As a new generation of high-efficiency photovoltaic technology, the solar cell without main grid realizes higher photoelectric conversion efficiency and lower manufacturing cost by canceling the traditional main grid lines and directly connecting the dense fine grid lines with the interconnecting solder wire. However, the welding quality between the interconnecting solder wire and the fine grid lines of the solar cell directly affects the reliability and power generation efficiency of the battery module, becoming a key bottleneck restricting the large-scale application of this technology.

[0003] Currently, the main packaging routes of the solar cell without main grid mainly include two categories: one is to lay the solder wire on the front and back surfaces of the cell sheet and cover the bearing film before heating and fixing the solder wire, and then form the cell string by connecting the positive and negative electrodes of the cell sheet, this method first contacts at the intersection of the auxiliary grid lines and the solder wire, and then melts the solder coating on the surface of the solder wire by infrared heating or hot pressing to form a weld at the intersection; the second is to fix the solder wire with tin coating on the predetermined position of the cell sheet by using UV glue, hot melt glue and other adhesives, so that the solder wire and the fine grid lines are perpendicular to each other, and the adhesive is cured, then the layout is stacked and heated and vacuum laminated to form a weld at the intersection of the solder wire and the fine grid lines.

[0004] However, the problem of the above method is that the welding firmness of the contact point between the solder wire and the fine grid lines is insufficient, and the soldering phenomenon is easy to occur, which seriously affects the service life and performance stability of the solar cell. SUMMARY

[0005] In order to improve the welding firmness of the contact point between the solder wire and the fine grid lines and improve the reliability of the solar cell, the present application provides a welding method for improving the welding effect of interconnecting solder wire and fine grid lines of a solar cell without main grid.

[0006] The present application provides a welding method for improving the welding effect of interconnecting solder wire and fine grid lines of a solar cell without main grid, which adopts the following technical scheme:

[0007] A welding method for improving the welding effect of interconnecting solder wire and fine grid lines of a solar cell without main grid, comprising the following steps:

[0008] S1, the intersection position of the fine grid lines and the solder wire on the cell sheet is a to-be-processed area;

[0009] S2, tin paste solder containing metal solder powder and acidic flux is coated on the to-be-processed area, the coating area of the tin paste solder completely covers the to-be-processed area, and then dried to make the tin paste solder stick to the fine grid lines;

[0010] S3, placing the solder wire on the tin paste solder of the fine grid line, and then heating to form an electrical connection between the solder wire and the fine grid line;

[0011] S4, after the welding is completed, film coating, lamination and curing are performed to obtain a main-grid-free battery assembly.

[0012] By adopting the technical scheme, in the present application, the solder paste is pre-coated at the intersection position of the fine grid line and the solder wire, the flux in the solder paste is melted first after heating, the surface of the fine grid line is cleaned, then the solder on the surface of the solder wire and the solder paste are melted together, the solder wire and the fine grid line are wrapped, and after cooling, an "alloy solder joint" is formed to stick the three together. The flux in the solder paste can not only reduce the surface tension of the solder, so that the molten solder can uniformly cover the fine grid line, but also help the solder on the surface of the solder wire to melt and form good wetting with the contacted fine grid line after melting, thereby obviously improving the welding firmness. Moreover, the acidic flux can have a certain dissolving effect on the oxide layer on the surface of the fine grid line and the solder wire, thereby reducing the contact resistance and forming a better electrical connection.

[0013] In addition, the solder in the solder paste can fill the small gap between the solder wire and the fine grid line after melting, form an intermetallic compound, and realize firm metallurgical bonding through atomic diffusion. Compared with the traditional direct welding, the resistivity is obviously reduced, and the welding reliability and product performance are improved.

[0014] Optionally, the solder paste in step S2 comprises metal solder powder and acidic flux, the metal solder powder comprises Sn-3Ag-1Bi-0.5Cu quaternary alloy solder powder and copper nanoparticles with a particle size of 40-80 nm, and the copper nanoparticles are 0.1-0.5 wt% of the addition amount of the quaternary alloy solder powder.

[0015] By adopting the technical scheme, in the present application, the metal solder powder is a mixture of alloy solder powder and copper nanoparticles. The nano-copper particles have a large specific surface area and high surface activity, can quickly diffuse to the solder joint interface during welding, rapidly react with the surrounding metal atoms to form firm chemical bonds, and enhance the bonding force of the solder joint. At the same time, the nano-copper particles fill the pores in the solder joint to reduce the defects of the solder joint and improve the density of the solder joint, thereby improving the firmness of the welding. In addition, the melting point of the nano-copper particles is lower than that of the micron-level quaternary alloy solder powder, which can preferentially melt to form a "liquid bridge" during heating, promote the metallurgical bonding of the solder and the fine grid line, and form intermetallic compounds with silver in the grid line and zinc in the solder. The intermetallic compounds are distributed in layers or needles and embedded in the interface between the solder and the grid line, thereby obviously improving the welding firmness.

[0016] The addition of Bi element in the quaternary alloy solder powder can reduce the alloy melting point, realize low-temperature welding, reduce the thermal damage to the battery, and at the same time, Bi can improve the flowability of the alloy powder, so that the solder can better fill the gap between the welding wire and the fine grid line, and improve the welding firmness.

[0017] Optionally, the flux in the tin paste solder in step S2 comprises the following raw materials by weight:

[0018] Rosin derivative 25-40 parts, ammonium fluoride 1-3 parts, nano titanium dioxide particles 1-5 parts, citric acid 3-8 parts, phosphoric acid 1-3 parts, benzotriazole 0.5-2 parts, and cerium oxide 0.1-0.5 parts, and mixed solvent 20-30 parts.

[0019] By adopting the above technical scheme, the flux takes rosin derivative as the main material to provide basic wettability, reduce the surface tension of the molten solder, and enhance the wettability, which helps the solder to penetrate into the fine grid line after melting, improves the wettability, and improves the welding effect; citric acid as a relatively mild organic acid can remove the oxides on the surface of the metal during the welding process, and at the same time, will not cause excessive corrosion to the battery sheet, phosphoric acid has strong acidity and can more effectively remove stubborn oxide layers, the synergistic effect of the two acids improves the flux effect, and ammonium fluoride has weak acid corrosion effect on one hand to avoid damaging the battery sheet substrate, on the other hand, ammonium fluoride can remove stubborn oxide layers at high temperature, and nano titanium dioxide can accelerate the flow of molten solder through surface plasmon effect to improve the infiltration speed and effect, and it can enhance the mechanical strength of the welding point, inhibit the excessive growth of intermetallic compound layer, and improve the thermal fatigue life, the addition of cerium oxide can improve the flowability and wettability of the droplet, improve the welding quality, reduce the defects such as no cavity or crack in the welding point, and the welding point is uniform and dense, and the rare earth element in the cerium oxide can reduce the surface tension of the liquid solder through adsorption effect, and form Ce-Sn intermetallic compound with the base metal to improve the interface bonding energy, so that the welding tension between the fine grid line and the welding wire is stronger, and the welding is more firm.

[0020] Optionally, the rosin derivative is maleic rosin prepared by modifying rosin with maleic anhydride.

[0021] By adopting the above technical scheme, when maleic rosin is selected, maleic rosin contains three carboxyl groups which can react with metal oxides to generate metal rosin salt soluble in rosin, thereby removing the oxide layer, and after melting, an isolation layer is formed on the solder to avoid secondary oxidation during welding, and by reducing the surface tension of the molten solder, the wettability of the solder to the fine grid line is enhanced, the welding point between the fine grid line and the welding wire is uniform and dense, and the welding quality is improved.

[0022] Optionally, the maleic rosin is added after modification treatment, and the modification treatment comprises the following steps:

[0023] Maleic rosin was dissolved in butyl acetate, hydroxyethyl acrylate and glycidyl methacrylate were added, and after mixing, hydroquinone and triethylamine were added. After mixing evenly, the mixture was heated to 140-160℃ and reacted for 3-5 hours. After washing with water, the mixture was concentrated and dried to obtain modified rosin.

[0024] By adopting the above technical solution, the maleic rosin molecule contains conjugated double bonds and carboxyl groups, but lacks highly reactive functional groups. It is necessary to improve the flux performance through chemical grafting. In this application, hydroxyethyl acrylate contains hydroxyl groups and double bond groups, and glycidyl methacrylate contains epoxy groups and double bond groups. Using maleic rosin as the matrix, hydroxyethyl acrylate and glycidyl methacrylate are used as functional monomers to polymerize with maleic rosin, introducing hydroxyl and epoxy groups into the maleic rosin molecular chain. The introduced hydroxyl functional groups can form hydrogen bonds or coordination bonds with the metal oxides on the surface of the welding wire, enhancing wettability and promoting the spread of molten solder. The introduction of epoxy groups reacts with the carboxyl groups of maleic rosin to form a rosin derivative with a ternary epoxy structure. At the welding temperature, the epoxy groups form metal complexes with the metal on the surface of the welding wire, and they also crosslink with hydroxyl groups or hydroxyl groups on the metal surface at the welding temperature to form a three-dimensional network structure. This significantly improves the bonding force of the solder joint and enhances the welding reliability of the fine grid lines and the welding wire.

[0025] Optionally, in the process of modifying maleic rosin, the mass ratio between hydroxyethyl acrylate and glycidyl methacrylate is 1:(0.8-1), the amount of butyl acetate added is 2-3 times the mass of maleic rosin, and the amount of hydroxyethyl acrylate added is 10-20 wt% of maleic rosin.

[0026] The amount of hydroquinone added is 0.1-0.5 wt% of the amount of maleic rosin added, and the amount of triethylamine added is 1-3 wt% of the amount of maleic rosin added.

[0027] By adopting the above technical solution, hydroquinone is used as a polymerization inhibitor to reduce the self-polymerization between hydroxyethyl acrylate and glycidyl methacrylate, and triethylamine is used as a catalyst.

[0028] Optionally, the mixed solvent is composed of ethanol, isopropanol, hexafluoroisopropanol and butyl acetate in a mass ratio of 1:(0.8-1.2):(0.2-0.4):(2-3).

[0029] By adopting the above technical solution, the addition of hexafluoroisopropanol can directly promote the ring-opening reaction of epoxy groups by providing hydrogen bonds to activate CO bonds, thereby promoting the ring-opening cross-linking of epoxy groups with hydroxyl groups, etc., without the need for additional catalysts.

[0030] Optionally, the solder paste applied to the core area of ​​the area to be processed in step S2 includes metal solder powder and acidic flux in a mass ratio of 85-95:5-15.

[0031] The tin paste solder applied to the peripheral region of the to-be-processed area in step S2 comprises metal solder powder and acidic flux in a mass ratio of 70-80:20-30, and the first 70-80% of the radius of the to-be-processed area is the core region, and the remaining part is the peripheral region.

[0032] By adopting the technical scheme, high-solder-content tin paste solder is applied to the core region of the intersection area of the welding wire and the fine grid line, to ensure the welding strength, and low-solder-content and high-flux-content tin paste solder is applied to the peripheral edge region, to form a flux buffer zone and prevent solder overflow during welding from affecting the electrochemical performance.

[0033] Optionally, after the welding wire is placed on the tin paste solder of the fine grid line in step S3, heating treatment is performed by infrared or a hot press, and the heating temperature is 150-180 DEG C.

[0034] Optionally, the surface of the welding strip is provided with a groove for embedding the fine grid, and the groove surface is in a circular arc or polygonal shape.

[0035] By adopting the technical scheme, the fine grid line can be embedded in the groove, and the tin paste solder forms an alloy layer to enhance the welding bonding force, and the groove surface is arranged to avoid stress concentration.

[0036] Optionally, the surface of the welding strip is provided with a groove for embedding the fine grid, and the groove surface is in a circular arc or polygonal shape.

[0037] By adopting the technical scheme, the surface of the copper material welding strip is provided with a low-temperature alloy coating, which can reduce the welding temperature and reduce the damage of thermal stress to the thinned battery.

[0038] In summary, the present application has the following beneficial effects:

[0039] 1、In the application, the solder paste solder is pre-coated at the intersection position of the battery piece fine grid line and the welding wire. After heating, the flux in the solder paste solder is melted first, cleaning the surface of the fine grid line, then the solder on the surface of the welding wire and the solder paste solder are melted together, wrapping the welding wire and the fine grid line, and after cooling, forming an "alloy solder joint", sticking the three together. The flux in the solder paste solder not only can reduce the surface tension of the solder, so that the molten solder can uniformly cover the fine grid line, which helps the molten solder on the surface of the welding wire to infiltrate the contacted fine grid line and form effective welding, significantly improving the welding firmness, but also the acidic flux can have a certain dissolving effect on the oxidation layer on the surface of the fine grid line and the welding wire, reducing the contact resistance, and can form better power connection; 2、In the application, the metal solder powder is a mixture of alloy solder powder and copper nanoparticles. The nano copper particles have a large specific surface area and high surface activity, which can quickly diffuse to the solder joint interface during welding, rapidly react with the surrounding metal atoms to form a strong chemical bond, and enhance the solder joint bonding force. At the same time, the nano copper particles fill the pores in the solder joint, reducing solder joint defects and improving solder joint density, thereby improving the firmness of the solder joint. At the same time, the melting point of the nano copper particles is lower than that of the micron-sized four-element alloy solder powder, which preferentially melts to form a "liquid bridge" during heating, promoting metallurgical bonding between the solder and the fine grid line, and forming intermetallic compounds between the silver in the grid line and the zinc in the solder. The intermetallic compounds are distributed in layers or needles and embedded in the interface between the solder and the grid line, which significantly improves the welding firmness.

[0040] 3、In the application, Bi element is added to the four-element alloy solder powder, which can reduce the alloy melting point, realize low-temperature welding, and reduce the thermal damage to the battery. At the same time, Bi can improve the flowability of the alloy powder in the alloy, making the solder better fill the gap between the welding wire and the fine grid line, and improving the firmness of the welding. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a schematic diagram of the position of the solder paste solder before the welding wire is heated and welded in the application;

[0042] Figure 2 is a schematic diagram of the state of the solder paste solder, welding wire and fine grid line before the welding wire is heated and welded in Example 1 of the application;

[0043] Figure 3 is a schematic diagram of the state of the solder paste solder, welding wire and fine grid line after the welding wire is heated and welded in Example 1 of the application. DETAILED DESCRIPTION

[0044] The application will be further described in detail below in conjunction with the examples. It is particularly pointed out that: in the following examples, the specific conditions are not specified, and the conventional conditions or the conditions recommended by the manufacturer are used. The raw materials used in the following examples can be obtained from ordinary market sources unless otherwise specified.

[0045] The percentages in the following examples are mass percentages unless otherwise specified.

[0046] The solder wire in the present application is a tin-coated copper ribbon, that is, a copper material is used as the interconnection ribbon, and a tin-lead-bismuth alloy coating is coated thereon, the tin-lead-bismuth alloy coating has a composition of 65Sn34Pb4Bi, and the single-sided coating thickness is 0.01 mm. The coating is coated by a solder ribbon calendering tin coating machine.

[0047] The Sn-3Ag-1Bi-0.5Cu quaternary alloy solder powder is prepared by an atomization powdering process using 3wt% Ag elements, 1wt% Bi elements, and 0.5wt% Cu elements, and the balance of Sn elements. The particle size of the Sn-3Ag-1Bi-0.5Cu quaternary alloy solder powder is 20-30μm.

[0048] The maleic rosin in the present application can be obtained from the market or prepared by modification using a method commonly used in the art. In the following examples, the maleic rosin is prepared by the following method:

[0049] The rosin is heated to 160℃, maleic anhydride is added, the amount of maleic anhydride added is 15wt% of the amount of rosin added, the temperature is raised to 190℃, and maleic rosin with an acid value of 210 is prepared after 3h of reaction.

[0050] Example 1

[0051] A soldering method for improving the soldering effect of interconnection solder wire and grid line of a main grid-free solar cell, comprising the following steps:

[0052] S1, combination Figure 1 The position where the fine grid line of the cell piece intersects with the solder wire is the to-be-processed area, specifically, the solder wire is placed horizontally, the fine grid line is placed vertically, and the intersection point is the to-be-processed area, which is also the soldering point;

[0053] S2, specifically comprising the following steps:

[0054] S2-1, preparation of tin paste solder:

[0055] 2g of ammonium fluoride, 5g of citric acid, 2g of phosphoric acid, and 25g of a mixed solvent are mixed, stirred at 40℃ until completely dissolved, then 1g of benzotriazole is added, stirred at 60℃ for 40min, then 30g of rosin derivative is added, the rosin derivative is added in 3 times with an interval of 15min each time, after the addition is completed, continue to stir for 1h, finally add 3g of nano titanium dioxide particles and 0.3g of cerium oxide, ultrasonic dispersion at 60℃ for 40min (ultrasonic power 400W), after cooling, grind to obtain the flux; wherein the mixed solvent is a mixture of ethanol, isopropyl alcohol, hexafluoroisopropyl alcohol, and butyl acetate in a mass ratio of 1:1:0.3:2.5;

[0056] The Sn-3Ag-1Bi-0.5Cu quaternary alloy solder powder and copper nanoparticles (purity 99.9%) with a particle size of 40-80 nm are ball-milled to prepare a metal solder powder, and the copper nanoparticles are 0.2wt% of the added amount of the quaternary alloy solder powder;

[0057] Then the above prepared metal solder powder and flux are vacuum stirred in a mass ratio of 90:10 to obtain a solder paste;

[0058] S2-2, the tin paste solder obtained above is coated on the to-be-processed area at the intersection of the fine grid line and the welding wire by screen printing, the coating area of the tin paste solder completely covers the to-be-processed area, and the coating thickness is 30μm, then the tin paste solder is dried at 80℃ after coating to adhere to the fine grid line;

[0059] S3, referring to Figure 2 and Figure 3 , the welding wire is placed on the tin paste solder of the fine grid line, and then infrared heating treatment is performed by using a near-infrared heating lamp, the heating temperature is 160℃, the flux in the tin paste solder is melted first, the surface of the fine grid line is cleaned, then the tin paste solder on the surface of the welding wire is melted, the copper tape and the fine grid line are wrapped, and after cooling, an "alloy welding point" is formed, an electrical connection is formed between the welding wire and the fine grid line;

[0060] S4, after the welding is completed, IFC direct film coating process is performed, an EVA film coating material with a thickness of 0.5mm is covered on the battery piece, then the battery piece with the film is put into a laminating equipment for laminating operation, the laminating temperature is 150℃, the pressure is 0.1MPa, and the time is 10min, so that the film coating material is bonded and solidified between the surface of the battery piece and the welding wire, and a no-main-grid battery assembly is prepared.

[0061] Example 2

[0062] A welding method for improving the welding effect of interconnected welding wires and no-main-grid solar cell grid lines, comprising the following steps:

[0063] S1, finding the intersection position of the fine grid line of the battery piece and the welding wire as the to-be-processed area, specifically, the welding wire is placed horizontally, the fine grid line is placed vertically, and the intersection point is the to-be-processed area, which is also the welding point;

[0064] S2, specifically comprising the following steps:

[0065] S2-1, preparing a tin paste solder:

[0066] Mixing 1 g of ammonium fluoride, 3 g of citric acid, 1 g of phosphoric acid and 20 g of mixed solvent, stirring at 40℃ until completely dissolved, then adding 0.5 g of benzotriazole, stirring at 60℃ for 40 min, then adding 25 g of rosin derivative, stirring the rosin derivative at 80℃, adding in 3 times with 15 min interval each time, after adding, continue stirring for 1 h, finally add 1 g of nano titanium dioxide particles and 0.1 g of cerium oxide, ultrasonic dispersion at 60℃ for 40 min (ultrasonic power 400W), after cooling, grinding to obtain the flux;

[0067] The mixed solvent is a mixture of ethanol, isopropyl alcohol, hexafluoroisopropyl alcohol and butyl acetate with a mass ratio of 1:0.8:0.2:2;

[0068] The Sn-3Ag-1Bi-0.5Cu quaternary alloy solder powder and copper nanoparticles (purity 99.9%) with a particle size of 40-80 nm are ball-milled to prepare a metal solder powder, and the copper nanoparticles are 0.1wt% of the added amount of the quaternary alloy solder powder;

[0069] Then the metal solder powder prepared above is vacuum stirred with the flux according to a mass ratio of 85:15 to obtain a tin paste solder;

[0070] S2-2, the tin paste solder obtained above is coated on the to-be-processed area at the intersection of the fine grid line and the welding wire by screen printing, the coating area of the tin paste solder completely covers the to-be-processed area, and the coating thickness is 30μm, then the tin paste solder is dried at 80℃ after coating to adhere to the fine grid line;

[0071] S3, the welding wire is placed on the tin paste solder of the fine grid line, and then infrared heating treatment is performed by using a near-infrared heating lamp, the heating temperature is 150℃, the flux in the tin paste solder is melted first to clean the surface of the fine grid line, then the tin paste solder on the surface of the welding wire is melted to wrap the copper tape and the fine grid line, and after cooling, an "alloy welding point" is formed, and an electrical connection is formed between the welding wire and the fine grid line;

[0072] S4, after the welding is completed, IFC direct film coating process is performed, an EVA film coating material with a thickness of 0.5mm is covered on the battery piece, then the battery piece with the film coating is put into a laminating equipment for laminating operation, the laminating temperature is 150℃, the pressure is 0.1MPa, and the time is 10min, so that the film coating material is bonded and solidified with the surface of the battery piece and the welding wire, and a main-grid-free battery assembly is prepared.

[0073] Example 3

[0074] A welding method for improving the welding effect of interconnected welding wires and main-grid-free solar cell grid lines, comprising the following steps:

[0075] S1, find the position of the intersection of the fine grid line of the battery piece and the welding wire as the to-be-processed area, specifically, the welding wire is placed horizontally, the fine grid line is placed vertically, and the intersection point is the to-be-processed area, which is also the welding point;

[0076] S2, specifically comprising the following steps:

[0077] S2-1, preparing the tin paste solder:

[0078] Mix 3g of ammonium fluoride, 8g of citric acid, 3g of phosphoric acid and 30g of mixed solvent, stir at 40℃ until completely dissolved, then add 2g of benzotriazole, stir at 60℃ for 40min, then add 40g of rosin derivative, stir the rosin derivative at 80℃, add in 3 times with 15min interval each time, continue stirring for 1h after adding, finally add 5g of nano titanium dioxide particles and 0.5g of cerium oxide, ultrasonic dispersion at 60℃ for 40min (ultrasonic power 400W), grind after cooling to obtain the flux; wherein the mixed solvent is a mixture of ethanol, isopropyl alcohol, hexafluoroisopropyl alcohol and butyl acetate with a mass ratio of 1:1.2:0.4:3;

[0079] Sn-3Ag-1Bi-0.5Cu quaternary alloy solder powder and copper nanoparticles (purity 99.9%) with a particle size of 40-80nm are ball-milled to prepare the metal solder powder, and the copper nanoparticles are 0.5wt% of the added amount of the quaternary alloy solder powder;

[0080] Then the above prepared metal solder powder and the flux are vacuum stirred according to a mass ratio of 95:5 to obtain the tin paste solder;

[0081] S2-2, the tin paste solder obtained above is coated on the to-be-processed area at the intersection of the fine grid line and the welding wire by silk screen printing, the coating area of the tin paste solder completely covers the to-be-processed area, and the coating thickness is 30μm, then the tin paste solder is dried at 90℃ after coating to make the tin paste solder stick to the fine grid line;

[0082] S3, place the welding wire on the tin paste solder of the fine grid line, then use a near-infrared heating lamp for infrared heating treatment, the heating temperature is 180℃, the flux in the tin paste solder is melted first to clean the surface of the fine grid line, then the tin paste solder on the surface of the welding wire is melted to wrap the copper strip and the fine grid line, and a "alloy welding point" is formed after cooling, an electrical connection is formed between the welding wire and the fine grid line;

[0083] S4, after the welding is completed, the IFC direct film coating process is carried out, the EVA film coating material with a thickness of 0.5mm is covered on the battery piece, then the battery piece with the film coating is put into the laminating equipment for laminating operation, the laminating temperature is 150℃, the pressure is 0.1MPa, and the time is 10min, so that the film coating material is bonded and solidified with the surface of the battery piece and the welding wire, and a main grid-free battery assembly is prepared.

[0084] Example 4

[0085] A welding method for improving the welding effect of interconnection welding wire and grid line of a solar cell without a main grid, which is performed according to the method in Example 1, with the difference that:

[0086] The maleic rosin in the flux in step S2 is added after modification treatment, and the modification treatment includes the following steps:

[0087] The maleic rosin is dissolved in butyl acetate, hydroxyethyl acrylate and glycidyl methacrylate are added, hydroquinone and triethylamine are added after mixing, and the mixture is uniformly mixed and heated to 150℃, and then washed with water, concentrated and dried after reacting for 4h to obtain modified rosin;

[0088] The mass ratio of hydroxyethyl acrylate and glycidyl methacrylate is 1:0.9, the amount of butyl acetate added is 2.5 times the mass of the maleic rosin, the amount of hydroxyethyl acrylate added is 15wt% of the maleic rosin, the amount of hydroquinone added is 0.3wt% of the amount of maleic rosin added, and the amount of triethylamine added is 2wt% of the amount of maleic rosin added.

[0089] Example 5

[0090] A welding method for improving the welding effect of interconnection welding wire and grid line of a solar cell without a main grid, which is performed according to the method in Example 1, with the difference that:

[0091] The maleic rosin in the flux in step S2 is added after modification treatment, and the modification treatment includes the following steps:

[0092] The maleic rosin is dissolved in butyl acetate, hydroxyethyl acrylate and glycidyl methacrylate are added, hydroquinone and triethylamine are added after mixing, and the mixture is uniformly mixed and heated to 140℃, and then washed with water, concentrated and dried after reacting for 5h to obtain modified rosin;

[0093] The mass ratio of hydroxyethyl acrylate and glycidyl methacrylate is 1:0.8, the amount of butyl acetate added is 2 times the mass of the maleic rosin, the amount of hydroxyethyl acrylate added is 10wt% of the maleic rosin, the amount of hydroquinone added is 0.1wt% of the amount of maleic rosin added, and the amount of triethylamine added is 1wt% of the amount of maleic rosin added.

[0094] Example 6

[0095] A welding method for improving the welding effect of interconnection welding wire and grid line of a solar cell without a main grid, which is performed according to the method in Example 1, with the difference that:

[0096] The maleic rosin in the flux in step S2 is added after modification treatment, and the modification treatment includes the following steps:

[0097] Dissolve the maleic rosin in butyl acetate, add hydroxyethyl acrylate and glycidyl methacrylate, after mixing, add hydroquinone and triethylamine, mix evenly, then heat to 160℃, react for 3h, then wash with water, concentrate, dry to obtain the modified rosin; wherein the mass ratio of hydroxyethyl acrylate and glycidyl methacrylate is 1:1, the amount of butyl acetate added is 3 times the mass of maleic rosin, the amount of hydroxyethyl acrylate added is 20wt% of the maleic rosin, the amount of hydroquinone added is 0.5wt% of the maleic rosin, and the amount of triethylamine added is 3wt% of the maleic rosin.

[0098] Example 7

[0099] A welding method for improving the welding effect of interconnecting welding wires and grid line welding of solar cell pieces without main grid, which is carried out according to the method in Example 1, except that the rosin derivative is hydrogenated rosin.

[0100] Example 8

[0101] A welding method for improving the welding effect of interconnecting welding wires and grid line welding of solar cell pieces without main grid, which is carried out according to the method in Example 1, except that,

[0102] After obtaining the metal solder powder and the flux in step S2-1, the metal solder powder and the flux are vacuum stirred at a mass ratio of 90:1 to obtain a first solder paste, and the metal solder powder and the flux are vacuum stirred at a mass ratio of 75:25 to obtain a second solder paste;

[0103] The specific operation in step S2-2 is that the first solder paste is screen printed on the core area of the to-be-processed area at the intersection point of the fine grid line and the welding wire, and the second solder paste is screen printed on the peripheral area, the center point of the intersection of the fine grid line and the welding wire in the to-be-processed area is taken as the center, and the first 70% of the area with a radius of the to-be-processed area is the core area, and the remaining part is the peripheral area.

[0104] Example 9

[0105] A welding method for improving the welding effect of interconnecting welding wires and grid line welding of solar cell pieces without main grid, which is carried out according to the method in Example 1, except that,

[0106] After obtaining the metal solder powder and the flux in step S2-1, the metal solder powder and the flux are vacuum stirred at a mass ratio of 95:5 to obtain a first solder paste, and the metal solder powder and the flux are vacuum stirred at a mass ratio of 70:30 to obtain a second solder paste;

[0107] The specific operation in step S2-2 is that the first solder paste is applied to the core area of the to-be-processed area at the intersection of the fine grid line and the welding wire by silk-screen printing, and the second solder paste is applied to the peripheral area. The intersection center of the fine grid line and the welding wire in the to-be-processed area is the center, and the first 80% of the area with the radius of the to-be-processed area is the core area, and the remaining part is the peripheral area.

[0108] Example 10

[0109] A welding method for improving the welding effect of interconnection welding wire and grid line of a solar cell without a main grid, which is performed according to the method in Example 1, except that a groove for embedding the fine grid is arranged on the surface of the welding strip, and the groove surface is in the shape of a circular arc.

[0110] Example 11

[0111] A welding method for improving the welding effect of interconnection welding wire and grid line of a solar cell without a main grid, which is performed according to the method in Example 1, except that the Sn-3Ag-1Bi-0.5Cu quaternary alloy solder powder in the metal solder powder is replaced by an equal amount of Sn-3Ag-0.5Cu ternary alloy solder powder.

[0112] Example 12

[0113] A welding method for improving the welding effect of interconnection welding wire and grid line of a solar cell without a main grid, which is performed according to the method in Example 1, except that no copper nanoparticles are added to the metal solder powder.

[0114] Example 13

[0115] A welding method for improving the welding effect of interconnection welding wire and grid line of a solar cell without a main grid, which is performed according to the method in Example 1, except that no cerium oxide is added to the flux in step S2.

[0116] Example 14

[0117] A welding method for improving the welding effect of interconnection welding wire and grid line of a solar cell without a main grid, which is performed according to the method in Example 1, except that no nano-titanium dioxide particles are added to the flux in step S2.

[0118] Comparative Example 1

[0119] A welding method for improving the welding effect of interconnection welding wire and grid line of a solar cell without a main grid, which comprises the following steps:

[0120] S1, laying a welding wire on the fine grid line of a cell, with the welding wire placed horizontally and the fine grid line placed vertically;

[0121] S2, after the laying of the solder wire, IFC direct film coating process is carried out, the EVA film coating material with a thickness of 0.5 mm is covered on the battery piece, near-infrared heating lamp is used for infrared heating treatment to fix the solder wire, the heating temperature is 160℃, then the battery piece which has been coated is put into the laminating equipment to carry out laminating operation, the laminating temperature is 150℃, the pressure is 0.1 MPa, the time is 10 min, so that the coating material is bonded and solidified with the surface of the battery piece and the solder wire, and the no-main-grid battery assembly is prepared.

[0122] Performance detection

[0123] The soldering of the solder wire and the fine grid line is carried out according to the method in the above examples and comparative examples, after the soldering is completed, the pulling force tester is used to apply pulling force to the soldering point, until the solder wire is pulled out from the fine grid line or the soldering point is broken, the soldering pulling force result is counted, the detection result is shown in Table 1. In addition, the virtual welding rate of the no-main-grid battery assembly prepared in the examples and comparative examples is detected and counted, and the maximum output power attenuation rate of the prepared no-main-grid battery assembly after TC200 (thermal cycle test) test is counted, the result is shown in Table 1.

[0124] Table 1:

[0125]

[0126]

[0127] Table 1 (continued):

[0128]

[0129] In combination with the detection results in Table 1, the soldering tensile force of the soldering joint between the fine grid line and the solder wire is high, the virtual soldering rate of the battery assembly is low, and the maximum output power decay rate after the TC200 test is low, which has good soldering reliability. In combination with the detection results of Examples 4-6, the soldering tensile force can be further improved and the virtual soldering rate can be further reduced after the maleic rosin is modified. In combination with the detection results of Example 7, when the hydrogenated rosin is selected as the rosin derivative in the flux, the effect is lower than that of the maleic rosin in Example 1, the soldering tensile force is lower, the virtual soldering rate is higher, and the maximum output power decay rate after the TC200 test is also higher. In combination with the detection results of Examples 8-9, when different proportions of the tin paste solder are coated at the intersection of the fine grid line and the solder wire, the soldering tensile force is high, the solder overflow can be reduced, unnecessary accumulation of the solder in the non-soldering area can be avoided, and the generation of holes and defects can be reduced. Therefore, it can be seen that the maximum output power decay rate after the TC200 test is further reduced in Examples 8-9, and the high solder content in the core area in Examples 8-9 ensures the soldering strength, and the high flux content in the peripheral area promotes the wetting and spreading of the solder, which helps to reduce the virtual soldering rate.

[0130] In combination with the detection results of Example 10, the recess for embedding the fine grid line is provided on the surface of the solder wire, which further improves the soldering tensile force and reduces the virtual soldering rate. The provision of the recess can enhance the contact area and bonding force between the solder wire and the fine grid line. In combination with the detection results of Example 1 and Example 11, the ternary alloy solder powder is used in Example 11 without adding Bi element, which has lower soldering tensile force than that of Example 1. In Example 12, the soldering tensile force is also lower than that of Example 1 without adding copper nanoparticles, which can enhance the bonding force of the solder joint during soldering. In combination with the detection results of Example 13 and Example 14, the soldering tensile force is lower and the maximum output power decay rate after the TC200 test is higher when the cerium oxide or nano-titanium dioxide particles are not added in the flux, which helps to improve the wettability of the solder and reduce the contact resistance.

[0131] In combination with the detection results of Example 1 and Comparative Example 1, the pre-coated tin paste solder process is not used, and the film fixing lamination operation is directly performed, which has low soldering pressure, high virtual soldering rate, and high maximum output power decay rate after the TC200 test.

[0132] The specific embodiments are only an explanation of the present application, which is not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, which is protected by the patent law as long as it is within the scope of the claims of the present application.

Claims

1. A welding method for improving the welding effect of interconnect wires and grid lines of gridless solar cells, characterized in that, Includes the following steps: S1. The area where the fine grid lines of the battery cell intersect with the welding wire is the area to be processed; S2. Apply solder paste containing metal solder powder and acid flux to the area to be treated. The solder paste completely covers the area to be treated and then dries so that the solder paste adheres to the fine grid lines. S3. Place the solder wire on the solder paste of the fine grid line, and then heat it to form an electrical connection between the solder wire and the fine grid line; S4. After welding, the membrane is coated and laminated for curing to obtain a gridless battery module. The flux in the solder paste in step S2 includes the following raw materials in parts by weight: The mixture contains 25-40 parts of rosin derivatives, 1-3 parts of ammonium fluoride, 1-5 parts of nano-titanium dioxide particles, 3-8 parts of citric acid, 1-3 parts of phosphoric acid, 0.5-2 parts of benzotriazole, 0.1-0.5 parts of cerium oxide, and 20-30 parts of mixed solvent. The rosin derivative is selected from maleic rosin obtained by modifying rosin with maleic anhydride, and the maleic rosin is added after modification treatment, which includes the following steps: Maleic rosin was dissolved in butyl acetate, hydroxyethyl acrylate and glycidyl methacrylate were added, and after mixing, hydroquinone and triethylamine were added. After mixing evenly, the temperature was raised to 140-160℃, and the reaction was carried out for 3-5 hours. After washing with water, the mixture was concentrated and dried to obtain modified rosin. The solder paste applied to the core area of ​​the area to be processed in step S2 consists of metal solder powder and acidic flux in a mass ratio of 85-95:5-15. The solder paste applied to the outer area of ​​the area to be processed in step S2 consists of metal solder powder and acidic flux in a mass ratio of 70-80:20-30. The first 70-80% of the radius of the area to be processed is the core area, and the remaining part is the outer area.

2. The welding method for improving the welding effect of interconnect wires and grid lines of gridless solar cells according to claim 1, characterized in that: The solder paste in step S2 includes metal solder powder and acidic flux. The metal solder powder includes Sn-3Ag-1Bi-0.5Cu quaternary alloy solder powder and copper nanoparticles with a particle size of 40-80nm, and the copper nanoparticles are added at 0.1-0.5wt% of the quaternary alloy solder powder.

3. The welding method for improving the welding effect of interconnect wires and grid lines of gridless solar cells according to claim 1, characterized in that: In the modification process of maleic rosin, the mass ratio of hydroxyethyl acrylate to glycidyl methacrylate is 1:(0.8-1), the amount of butyl acetate added is 2-3 times the mass of maleic rosin, and the amount of hydroxyethyl acrylate added is 10-20 wt% of maleic rosin. The amount of hydroquinone added is 0.1-0.5 wt% of the amount of maleic rosin added, and the amount of triethylamine added is 1-3 wt% of the amount of maleic rosin added.

4. The welding method for improving the welding effect of interconnecting wires and grid lines of gridless solar cells according to claim 1, characterized in that: The mixed solvent is composed of ethanol, isopropanol, hexafluoroisopropanol and butyl acetate in a mass ratio of 1:(0.8-1.2):(0.2-0.4):(2-3).

5. The welding method for improving the welding effect of interconnect wires and grid lines of gridless solar cells according to claim 1, characterized in that: The surface of the welding wire is provided with grooves for embedding fine grids, and the groove surfaces are circular or polygonal.

6. The welding method for improving the welding effect of interconnect wires and grid lines of gridless solar cells according to claim 1, characterized in that: The surface of the welding wire is coated with a tin-lead-bismuth low-temperature alloy.

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