A high-strength photovoltaic solder for photovoltaic ribbon and its preparation method

Abstract

This invention discloses a high-strength photovoltaic solder for photovoltaic bonding strips and its preparation method, belonging to the field of energy-saving and environmental protection technology. The solder uses a Sn-Zn-Bi alloy as the matrix and achieves comprehensive performance enhancement by introducing a dual nano-reinforcing phase of multi-walled carbon nanotubes and nano-nickel particles. The preparation method includes steps such as matrix alloy melting, hydrothermal method, liquid-phase reduction method, ultrasonic dispersion, gas atomization powder preparation, silane coupling agent surface modification, flux compounding, and reflow soldering. The resulting solder exhibits excellent comprehensive performance, superior thermal fatigue resistance, and long-term reliability. This solder is suitable for interconnecting and welding the main grid, fine grid, and bonding strip of crystalline silicon photovoltaic cells, providing technical assurance for a photovoltaic module service life of over 25 years.

Description

Technical Field

[0001] This invention belongs to the field of energy conservation and environmental protection technology. Specifically, it relates to a high-strength photovoltaic solder for photovoltaic soldering strips and its preparation method. Background Technology

[0002] Photovoltaic power generation, as an important component of clean energy, has experienced rapid development in recent years. As the core component of a solar power system, the long-term reliability and conversion efficiency of photovoltaic modules directly affect the economic benefits and lifespan of the entire photovoltaic power plant. During the manufacturing process of photovoltaic modules, the welding quality between the solder ribbon and the solar cells is one of the key factors affecting module performance. The photovoltaic solder ribbon interconnects the main grid, fine grid, and busbar of the solar cells through solder joints, undertaking the dual functions of current transmission and mechanical support. Therefore, high-quality, high-reliability photovoltaic solder is of great significance for ensuring the long-term stable operation of the modules.

[0003] Traditional Sn-Pb solders have long dominated the fields of electronic packaging and photovoltaic manufacturing due to their excellent wettability, suitable melting point (approximately 183°C), and good mechanical properties. However, lead poses serious hazards to the environment and human health. With the implementation of environmental regulations such as the EU RoHS directive, the development of lead-free solders has become an inevitable trend in the industry. Currently, the most likely non-toxic alloys to replace Sn-Pb solders are Sn-based alloys, including Sn-Ag-Cu (SAC) series, Sn-Zn series, and Sn-Bi series. Although SAC solders have excellent performance, their main problems are a high melting point (217-227°C) and high cost. The addition of silver increases the cost of the solder by about 35% compared to traditional Sn-Pb solders. Sn-Zn solders have a melting point close to that of Sn-Pb eutectic alloys (approximately 198°C) and lower cost, but zinc is easily corroded in the solid state, reducing the corrosion resistance of the solder and limiting its widespread application. Sn-Bi solders have a low melting point (approximately 138°C), making them suitable for low-temperature soldering. However, excessive bismuth content can lead to increased solder joint brittleness, affecting reliability.

[0004] Photovoltaic modules face complex and harsh environmental conditions during outdoor use, including drastic temperature fluctuations (-40℃ to 85℃), ultraviolet radiation, damp heat aging, and mechanical stress. These environmental factors lead to multiple failure modes for photovoltaic solder joints: Soldering failure: Changes in temperature, mechanical, and electrical stress cause solder joint damage. Causes include incomplete soldering, over-soldering, insufficient tensile strength between the solder strip and silver paste, and insufficient soldering area. Incomplete soldering is mainly caused by factors such as excessively low soldering temperature, excessively short soldering time, and substandard quality of the cell silver paste. Thermal cycling fatigue failure: Under the alternating hot and cold thermal cycles, the mismatch in the coefficient of thermal expansion (CTE) between the cells, solder strip, and solder induces stress, leading to cracks, interface delamination, and even complete detachment of the solder joint. Studies have shown that after 200 thermal cycles (-40℃ to 85℃), the shear strength retention rate of the solder joint is often less than 80%, seriously affecting the long-term reliability of the module. Excessive growth of intermetallic compounds (IMC): During the soldering process, intermetallic compound layers such as Cu6Sn5 and Cu3Sn form at the interface between the solder and the cell's silver paste or copper solder strip. Excessive IMC layer thickness (>2μm) can lead to solder joint embrittlement, reducing mechanical strength and thermal fatigue resistance. Cell breakage due to mechanical stress: Thermal stress during soldering and mechanical loads during module use can cause cracks in the silicon wafer, expanding the cell failure area and reducing power output.

[0005] To improve the performance of lead-free solders, researchers have conducted extensive research. Adding trace elements (such as In, Ga, and Ni) can improve solder wettability and interfacial reactions, but the effects are limited. In recent years, nano-reinforcement technology has provided a new approach to improving solder performance. Introducing appropriate nanoparticles into the solder can improve the wettability of the molten solder on the base material surface, refine the solder joint structure, inhibit the growth of intermetallic compounds at the interface, and effectively improve the reliability of the solder joint. However, existing research on nano-reinforced solders mainly focuses on the field of electronic packaging, with relatively little research on nanocomposite solders for photovoltaic ribbon applications. Existing technologies have the following shortcomings: Poor nanoparticle dispersion: Nanoparticles tend to agglomerate in the solder matrix, making it difficult to form a uniform distribution, resulting in unstable reinforcement effects. Difficulty in balancing wettability and strength: Lowering the melting point often comes at the cost of sacrificing mechanical strength, while increasing strength may worsen wettability, making it difficult to achieve comprehensive performance optimization. Insufficient thermal cycling reliability: Existing lead-free solders experience rapid performance degradation under thermal cycling conditions, making it difficult to meet the requirements of photovoltaic modules with a service life of over 25 years. The preparation process is complex: the introduction of nanoparticles increases the complexity of the process, and how to achieve uniform dispersion and stable composite of nano-reinforced phases is a technical challenge.

[0006] Therefore, developing a nano-reinforced photovoltaic solder that combines low melting point, high strength, excellent wettability, and long-term reliability is of great practical significance and application value for improving the performance of photovoltaic modules, reducing manufacturing costs, and extending service life. Summary of the Invention

[0007] To address the following issues with existing lead-free photovoltaic solders: Current lead-free solders face challenges in performance optimization: SAC-based solders, while possessing excellent mechanical properties, have high melting points (217-227℃) and poor wettability; Sn-Bi-based solders have low melting points, but excessive bismuth content leads to increased solder joint brittleness and insufficient mechanical strength; Sn-Zn-based solders, while exhibiting good tensile strength, suffer from deteriorated wettability due to zinc's easy oxidation, making complete oxide film removal difficult even with flux. Lowering the melting point often comes at the cost of sacrificing mechanical strength, while increasing strength may worsen wettability, making comprehensive performance optimization difficult. Nanoparticles are prone to agglomeration in the solder matrix, a core challenge in nanomaterial applications. Due to their large specific surface area and high surface energy, nanoparticles readily aggregate during preparation, storage, and processing through van der Waals forces, electrostatic forces, and magnetic forces. High nanoparticle content further induces agglomeration, resulting in uneven solder structure and unstable reinforcement effects. While traditional mechanical stirring and dispersion methods can break up agglomerates, the particles may re-agglomerate after being discharged from the disperser because the interparticle forces remain unchanged. The stability of the solder interface depends on the thickness control of the IMC layer. An IMC layer that is too thin (<0.3-0.5μm) leads to insufficient bonding strength, while one that is too thick (>2μm) causes interface cracking due to increased brittleness, severely affecting solder joint reliability. The ideal IMC layer thickness should be controlled between 0.5-1.5μm. However, current technologies struggle to precisely control the IMC layer growth rate, especially during thermal cycling and long-term aging, where IMC phases such as Cu6Sn5 and Cu3Sn continue to grow, leading to solder joint performance degradation. Photovoltaic modules must withstand severe temperature fluctuations from -40℃ to 85℃ and a service life of over 25 years in outdoor environments. Existing lead-free solders exhibit rapid performance degradation under thermal cycling conditions; after 200 thermal cycles, the shear strength retention rate of solder joints often falls below 80%, severely impacting the long-term reliability of the modules. Thermal cycling fatigue failure primarily stems from stress induced by the mismatch in the coefficient of thermal expansion (CTE) between the solder, solar cell, and solder strip, leading to solder joint cracks, interfacial delamination, and even complete detachment. The introduction of nanoparticles increases process complexity; achieving uniform dispersion and stable composite formation of nano-reinforcing phases remains a technical challenge. While nano-sized Sn-Ag-Cu particle solders can lower sintering temperatures, their preparation process is complex and costly. Composite solders formed by nanoparticle doping often have higher melting points than traditional solders, causing welding process mismatches and limiting practical applications.

[0008] The present invention adopts the following technical solution: a method for preparing high-strength photovoltaic solder for photovoltaic soldering ribbon, comprising the following steps by weight: (1) taking 45-65 parts of tin powder (CAS No.: 7440-31-5, particle size 15-25μm), 8-12 parts of zinc powder (CAS No.: 7440-66-6, particle size 10-20μm), 3-7 parts of bismuth powder (CAS No.: 7440-69-9, particle size 8-15μm), and 0.2-0.5 parts of nano silver powder (particle size 100-200nm) and mixing them evenly, and then melting them to obtain a nanocomposite matrix alloy; (2) selecting citric acid (CAS No.: 77-92-9), urea (CAS No.: 57-13-6), nickel nitrate hexahydrate (CAS No.: 13478-00-7) and deionized water in a mass ratio of (8-15):(4-10) (1-5): (80-120) are mixed, and after hydrothermal reaction, they are centrifuged and dried to obtain multi-walled carbon nanotubes. Then, 0.01-0.05 parts of multi-walled carbon nanotubes and 0.2-0.8 parts of nano-nickel particles are added to anhydrous ethanol at 30-60 times the mass of nano-nickel particles and ultrasonically dispersed to obtain a nano-reinforced phase dispersion. (3) The nano-reinforced phase dispersion obtained in step (2) is added to the nano-composite matrix alloy obtained in step (1) and mechanically stirred and mixed. Then, nano-composite solder powder is obtained by gas atomization. (4) The nano-composite solder powder obtained in step (3) is immersed in the modification liquid for surface modification to obtain surface-modified nano-composite solder powder. (5) The surface-modified nano-composite solder powder obtained in step (4) is stirred and mixed with composite flux at a mass ratio of (85-95): (8-15) to obtain high-strength photovoltaic solder.

[0009] Preferably, the parameters for the melting treatment in step (1) are as follows: melting treatment at 350-450℃ for 20-40 minutes under inert atmosphere protection, with a rotation speed of 300-500 rpm.

[0010] Preferably, the inert atmosphere in step (1) is nitrogen or argon.

[0011] Preferably, the parameters for the hydrothermal reaction in step (2) are as follows: the reaction is carried out in a hydrothermal reactor at 160-200℃ for 8-16 hours; the parameters for centrifugation in step (2) are as follows: 8000-12000 rpm for 15-25 minutes; the parameters for drying in step (2) are as follows: vacuum drying at 80-120℃ for 6-12 hours; the parameters for multi-walled carbon nanotubes in step (2) are as follows: outer diameter of 10-30 nm, length of 5-15 μm, and number of wall layers of 8-20; and modified single-walled carbon nanotubes with a mass of 1-2 times the urea are added during the hydrothermal reaction. The preparation method of carbon nanotubes is as follows: Melamine is dissolved in 10 times its weight of deionized water and stirred at 65-70℃ for 1-2 hours until completely dissolved. Then, 0.2-0.4 times the weight of melamine, single-walled carbon nanotubes (CAS No.: 308068-56-6) and 0.1-0.3 times the weight of melamine, triethylenetetramine disulfide (CAS No.: 25291-67-2) are added. After heating to 90℃, the mixture is placed in a tube furnace and heated to 850℃ at 5℃ / min under a nitrogen atmosphere. The temperature is maintained for 6-8 hours and then naturally cooled to room temperature.

[0012] Preferably, the preparation method of the nano-nickel particles in step (2) is as follows: a 0.1-0.3 mol / L nickel sulfate solution (CAS No.: 10101-97-0) and a 0.2-0.5 mol / L sodium borohydride solution (CAS No.: 16940-66-2) are reacted at 30-50℃ for 1-3 hours at a mass ratio of (1-4):1. Polyvinylpyrrolidone (CAS No.: 9003-39-8, molecular weight 40000-60000) is added during the process as... The amount of dispersant, polyvinylpyrrolidone, is 0.5-2 times the mass of nickel sulfate. After the reaction is completed, centrifuge at 10000-15000 rpm for 20-30 min, then wash with anhydrous ethanol 3-5 times, and vacuum dry at 60-100℃ for 8-15 h to obtain nano-nickel particles with a particle size of 40-80 nm. The parameters of ultrasonic dispersion in step (2) are as follows: ultrasonic power 400-800W, frequency 20-40kHz, temperature 40-55℃, and time 20-40 min.

[0013] Preferably, the mechanical stirring parameters in step (3) are as follows: mixing at 350-600 rpm for 25-45 min at 300-400℃; the gas atomization parameters in step (3) are as follows: atomization pressure 2-5 MPa, atomization gas is nitrogen, atomization time is 40-60 min; and the particle size of the nanocomposite solder powder in step (3) is 20-45 μm.

[0014] Preferably, in step (4), the modification solution is 0.5-2 parts of 3-aminopropyltriethoxysilane (CAS No.: 919-30-2) or γ-methacryloyloxypropyltrimethoxysilane (CAS No.: 2530-85-0) dissolved in 80-150 parts of 75-85% ethanol solution, and the pH is adjusted to 4.5-6.5; the surface modification parameters in step (4) are as follows: stir at 200-400 rpm for 2-6 h at 25-45℃, and vacuum dry at 60-90℃ for 4-8 h.

[0015] Preferably, the preparation method of the composite flux in step (5) is as follows: take 8-15 parts of rosin (CAS No.: 8050-09-7), 25-40 parts of anhydrous ethanol, 1-5 parts of diethanolamine (CAS No.: 111-42-2), and 2-8 parts of polyethylene glycol-400 (CAS No.: 25322-68-3) and mix them to obtain the flux.

[0016] Preferably, the mixing parameters in step (5) are as follows: mix at 80-150 rpm for 15-30 min in a planetary mixer.

[0017] A high-strength photovoltaic solder for photovoltaic ribbons is obtained by the preparation method described above.

[0018] This invention introduces a dual nano-reinforcing phase of multi-walled carbon nanotubes (MWCNTs) and nickel nanoparticles (Ni-NPs), employs an optimized Sn-Zn-Bi matrix alloy formulation and innovative preparation process, to obtain a high-strength photovoltaic solder with superior comprehensive performance. Compared with existing technologies, it has the following significant advantages: shear strength ≥80MPa, tensile strength ≥95MPa, elongation ≥15%, microhardness ≥25HV, and comprehensive mechanical properties significantly superior to traditional lead-free solders. The introduction of carbon nanotubes increases the material's elastic modulus by 16-22% and tensile strength by 37-56%, without significantly reducing ductility. This is mainly attributed to the following synergistic reinforcement mechanism: load transfer effect: MWCNTs have a tensile strength as high as 63GPa and an elastic modulus of about 1TPa. Their high aspect ratio (length 5-15μm, outer diameter 10-30nm) enables them to efficiently bear and transfer stress, significantly reinforcing the matrix even at an ultra-low concentration of 0.043wt%. Bridging effect: Carbon nanotubes form a three-dimensional network structure in the solder matrix, acting as nanobridges to hinder crack propagation, significantly improving the fracture toughness of the material and increasing the energy required for crack propagation by 44%. Precipitation strengthening: Nano-nickel particles react with Sn to form Ni3Sn4 nano-precipitates (50-200nm in size), which pin dislocation movement through the Orowan mechanism, significantly improving the material strength. Grain refinement: Nanoparticles act as heterogeneous nucleation cores, promoting grain refinement and improving strength through the Hall-Petch effect. The thickness of the intermetallic compound (IMC) layer is precisely controlled within 1.5μm, which is 15-30% less than that of traditional solders, significantly improving the reliability of the solder joint. Key technological breakthroughs include: Formation of Ni3Sn4 phase: Nano-nickel particles preferentially react with Sn to form (Cu,Ni)6Sn5 and Ni3Sn4 phases, inhibiting the excessive growth of brittle IMCs such as Cu6Sn5 and Cu3Sn. Studies have shown that Ni3Sn4 is more stable and has a slower growth rate than Cu6Sn5, which is beneficial for long-term reliability. Interface reaction regulation: Ni-NPs consume Sn atoms at the interface, reducing the driving force of the interface reaction and decreasing the growth rate of the IMC layer by 20-35%. Morphology optimization: The IMC layer transforms from the traditional scallop-shaped coarse grains to a fine, uniform granular or needle-like structure, effectively reducing stress concentration. Thermal aging stability: During aging at 200℃, the Ni3Sn4 phase remains stable, avoiding solder joint embrittlement caused by excessive growth of the Cu3Sn layer. After 200 thermal cycles from -40℃ to 85℃, the shear strength retention rate of the solder joint is ≥80%, and after 1000 hours of humid heat aging at 85℃ / 85%RH, the resistance growth rate is <5%, far exceeding the performance indicators of existing lead-free solders. The core mechanisms for improved reliability include: Coefficient of thermal expansion (CTE) matching optimization: The addition of Bi adjusts the CTE of the solder, reducing the thermal stress mismatch between the solder joint and the substrate, and reducing the initiation of thermal fatigue cracks.Grain stability: The pinning effect of Ni3Sn4 nano-precipitates and MWCNTs inhibits grain growth, with a grain size growth rate of <10% and strength retention of ≥85% after 500 hours of thermal aging at 150℃. Crack resistance: The bridging effect and energy absorption capacity of carbon nanotubes significantly improve the fatigue resistance of the solder joints, increasing thermal cycle life by 2-3 times. Oxidation resistance: Nitrogen atmosphere protection and the synergistic effect of Zn-Bi improve the stability of the surface oxide film, preventing performance degradation caused by interfacial oxidation. Resistivity <15μΩ·cm, conductivity ≥12%IACS, thermal conductivity ≥50W / (m·K), meeting the requirements of high-efficiency current transmission and heat dissipation of photovoltaic modules. Performance improvement mechanisms include: Ag nanoparticles enhance conductivity: The addition of nano-silver (0.2-0.5 parts) forms a highly conductive pathway, reducing contact resistance. CNTs conductive network: The high conductivity of multi-walled carbon nanotubes (up to 10). 6The S / m and three-dimensional network structure provide additional electron transport paths. IMC layer thickness control: The resistivity of Ni3Sn4 phase is lower than that of Cu6Sn5, and a thin IMC layer reduces interfacial resistance. Porosity reduction: The porosity of the weld joint is controlled within 3%, reducing current transport barriers and Joule heat loss. Contact angle is reduced to 30-40°, wetting rate is increased by 35-50%, spreading area is increased by 20-30%, and weld quality is significantly improved. Key factors for improved wettability include: Bi reducing surface tension: The addition of Bi (3-7 parts) reduces the surface tension of the melt from about 500 mN / m to below 400 mN / m, promoting wetting. CNTs reducing interfacial energy: The distribution of carbon nanotubes at the solid-liquid interface reduces the interfacial free energy and improves wetting kinetics. Nitrogen atmosphere deoxidation: Welding under nitrogen protection allows the existing oxide layer to dissolve at a lower temperature, improving wettability. Flux Optimization: Diethanolamine in the composite flux acts as an activator, effectively removing surface oxides; polyethylene glycol-400 adjusts rheological properties, keeping the viscosity controlled between 150-350 Pa·s. The melting temperature range is 180-230℃ (liquidite 215-230℃, solidus 180-195℃), approximately 20-40℃ lower than SAC-based solders (217-227℃), making it suitable for low-temperature soldering processes and reducing thermal damage to silicon wafers. Process advantages include: Reduced energy consumption: Low-temperature soldering reduces energy consumption by 15-25%, meeting energy conservation and environmental protection requirements. Strong equipment compatibility: Suitable for various equipment such as infrared reflow ovens, hot air reflow ovens, and laser reflow ovens, requiring no modification to existing production lines. Short soldering time: Maintaining the peak temperature in the reflow zone for 15-25 seconds achieves sufficient wetting and interfacial reaction, improving production efficiency. Uniform dispersion and long-term stability of the nano-reinforced phase are achieved through hydrothermal preparation of MWCNTs, liquid-phase reduction preparation of Ni-NPs, ultrasonic dispersion (power 400-800W), and surface modification with silane coupling agents. Key technical features include: High ultrasonic dispersion efficiency: The localized high temperature, high pressure, and microjets generated by ultrasonic cavitation weaken the van der Waals forces between nanoparticles, increasing dispersion efficiency by 60-80%. Surface modification to prevent agglomeration: APTES or KH-570 forms a 2-10nm modified layer on the particle surface, preventing agglomeration through chemical bonding and steric hindrance, reducing surface energy to 25-35mN / m. PVP dispersant role: PVP (molecular weight 40000-60000) coats the nano-nickel particles, providing electrostatic repulsion and steric hindrance, inhibiting agglomeration. Rapid atomization and solidification: Cooling rate 10³-10 5K / s, fixing the distribution of nanoparticles and preventing segregation during solidification. Suitable for interconnecting the main grid and fine grid of crystalline silicon photovoltaic cells (monocrystalline or polycrystalline silicon) with tin-plated or silver-plated copper solder strips. It can be used in the manufacture of conventional photovoltaic modules, bifacial photovoltaic modules, shingled modules, and heterojunction (HJT) photovoltaic modules. Application advantages include: Compatibility with multiple substrates: exhibits good wettability and bonding strength to various metal substrates such as Cu, Ni, and Ag. Wide range of welding process parameters: welding temperature 240-280℃, time 10-30 seconds, adaptable to different module manufacturing process requirements. Long-term stable service: meets the 25+ year service life requirement of photovoltaic modules, maintaining stable performance in outdoor environments. Completely lead-free formula, compliant with EU RoHS directives and other environmental regulations, posing no harm to the environment or human health. Environmental advantages include: Free of toxic heavy metals: contains no toxic elements such as Pb, Cd, and Hg, posing no environmental pollution risk during production and use. Recyclable: Sn, Zn, Bi, and Ag are all recyclable metals, conforming to the concept of a circular economy. Low flux residue: Components such as rosin and diethanolamine in the composite flux are low-toxicity materials, with minimal environmental impact from residues. Compared to SAC-based solders, costs are reduced by approximately 20-30%, the process is simple and reliable, and easy to industrialize. Economic advantages include: Low Ag usage: The amount of nano-Ag added is only 2-5 parts, far lower than traditional solders such as SAC305 (3%), reducing material costs. Zn-Bi synergistic cost reduction: Zn and Bi are much cheaper than Ag, significantly reducing costs while maintaining performance. High production efficiency: High gas atomization powder production efficiency, simple surface modification process, and a 15-20% reduction in the overall production cycle. High yield: Solder joint porosity <3%, precise control of IMC layer thickness, and a welding yield rate exceeding 98%.

[0019] In summary, this invention, through innovative material design, breakthroughs in process technology, and comprehensive performance optimization, successfully solves the technical challenges of existing lead-free photovoltaic solders in terms of mechanical strength, wettability, thermal cycling reliability, and nanoparticle dispersion. It provides important technical support for the high-quality manufacturing and long-term stable operation of photovoltaic modules and is of great significance to promoting the sustainable development of the photovoltaic industry. Attached Figure Description

[0020] Figure 1 This is a scanning electron microscope image of the nano-reinforced phase dispersion prepared in Example 1.

[0021] Figure 2 This is a sample image of the nano-reinforced phase dispersion prepared in Example 1.

[0022] Figure 3 This is the infrared spectrum of the nano-reinforced phase dispersion prepared in Example 1. Detailed Implementation

[0023] The present invention will now be described in detail through specific embodiments. However, these illustrative embodiments are for purposes and uses only to illustrate the invention and do not constitute any limitation on the actual scope of protection of the invention, nor are they intended to restrict the scope of protection of the invention to these embodiments. For parameter ranges not mentioned, intermediate values ​​are selected. Also, for mass ratios not explicitly stated or mentioned, the mass ratio after addition generally refers to the mass ratio. Furthermore, in the present invention, the unit of mass is grams (g).

[0024] Example 1

[0025] The preparation method of high-strength photovoltaic solder for photovoltaic solder ribbon includes the following steps: (1) Take 55g of tin powder (CAS No.: 7440-31-5, particle size 20μm), 10g of zinc powder (CAS No.: 7440-66-6, particle size 15μm), 5g of bismuth powder (CAS No.: 7440-69-9, particle size 12μm), and 0.4g of nano silver powder and mix them evenly. Melt them at 400℃ for 30min under nitrogen inert atmosphere protection, while maintaining a rotation speed of 400rpm to obtain a nanocomposite matrix alloy. (2) Citric acid (CAS No.: 77-92-9), urea (CAS No.: 57-13-6), nickel nitrate hexahydrate (CAS No.: 13478-00-7), and deionized water were mixed in a mass ratio of 11.5:7:3:100 and placed in a hydrothermal reactor. After reacting at 180℃ for 12 h, the mixture was centrifuged at 10000 rpm for 20 min and vacuum dried at 100℃ for 9 h to obtain multi-walled carbon nanotubes with an outer diameter of 20 nm, a length of 10 μm, and 14 wall layers. The hydrothermal reaction... The following modified single-walled carbon nanotubes (1.5 times the mass of urea) were also added during the process: Melamine was dissolved in 10 times its mass of deionized water and stirred at 68°C for 1.5 hours until completely dissolved. Then, 0.3 times the mass of melamine was added to the single-walled carbon nanotubes (CAS No.: 308068-56-6) and 0.2 times the mass of melamine was added to the triethylenetetramine disulfide (CAS No.: 25291-67-2). After heating to 90°C, the mixture was placed in a tube furnace and heated at a rate of 5°C / min under a nitrogen atmosphere. The temperature was raised to 850℃ and maintained for 6-8 hours, then naturally cooled to room temperature. The preparation method for nano-nickel particles is as follows: a 0.2 mol / L nickel sulfate solution (CAS No.: 10101-97-0) and a 0.35 mol / L sodium borohydride solution (CAS No.: 16940-66-2) were reacted at 40℃ for 2 hours at a mass ratio of 4:1. Polyvinylpyrrolidone (CAS No.: 9003-39-8, molecular weight 50000) was added as a dispersant during the reaction. The polyvinylpyrrolidone... The amount of nickel used was 1.25 times the mass of nickel sulfate. After the reaction, the mixture was centrifuged at 12500 rpm for 25 min, then washed four times with anhydrous ethanol, and vacuum dried at 80℃ for 12 h to obtain nickel nanoparticles with a particle size of 60 nm. Next, 0.03 g of multi-walled carbon nanotubes and 0.5 g of nickel nanoparticles were added to 45 times the volume of anhydrous ethanol containing the nickel nanoparticles. The mixture was then ultrasonically dispersed at 600 W, 30 kHz, 47.5℃ for 30 min to obtain a nano-reinforced phase dispersion. Figure 1 and Figure 2 and Figure 3As shown. (3) Add the nano-reinforcing phase dispersion obtained in step (2) to the nano-composite matrix alloy obtained in step (1), and mechanically stir at 350°C and 475 rpm for 35 min. Then, use gas atomization method with atomization pressure of 3.5 MPa, atomization gas of nitrogen, and atomization time of 50 min to obtain nano-composite solder powder with a particle size of 32.5 μm. (4) Immerse the nano-composite solder powder obtained in step (3) in a modification solution for surface modification. The modification solution is 1.25 parts of 3-aminopropyltriethoxysilane (CAS No.: 919-30-2) dissolved in 115 parts of 80% ethanol solution, and the pH is adjusted to 5.5. The surface modification parameters are as follows: stir at 300 rpm for 4 h at 35°C, and vacuum dry at 75°C for 6 h to obtain surface-modified nano-composite solder powder. (5) The surface-modified nanocomposite solder powder obtained in step (4) is mixed with the composite flux at a mass ratio of 90:11.5. The composite flux is prepared as follows: 11.5g of rosin (CAS No.: 8050-09-7), 32.5g of anhydrous ethanol, 3g of diethanolamine (CAS No.: 111-42-2), and 5g of polyethylene glycol-400 (CAS No.: 25322-68-3) are mixed to obtain the high-strength photovoltaic solder. The mixture is stirred in a planetary mixer at a speed of 115rpm for 22.5min. (6) Reflow soldering and curing: The high-strength photovoltaic solder paste obtained in step (5) is coated on the surface of the photovoltaic cell (coating thickness 85μm), and soldered in an infrared reflow oven. A four-temperature zone reflow curve is adopted: the preheating zone temperature is 140℃ and held for 60s, the activation zone temperature is 180℃ and held for 47.5s, the reflow zone peak temperature is 260℃ and held for 20s, and the cooling zone is cooled to room temperature at a rate of 10℃ / s. The entire reflow process is carried out under the protection of nitrogen atmosphere with purity ≥99.999%, oxygen content <50ppm, and moisture content <20ppm to obtain a high-strength photovoltaic solder strip joint; the shear strength of the welded joint is ≥80MPa, the tensile strength is ≥95MPa, the elongation is ≥15%, the thickness of the intermetallic compound (IMC) layer at the joint interface is <1.5μm, the porosity of the solder joint is <3%, and the resistivity is <15μΩ·cm. This solder is suitable for interconnecting the main grid and fine grid of crystalline silicon photovoltaic cells (monocrystalline silicon or polycrystalline silicon) with tin-plated copper solder or silver-plated copper solder. The welding temperature is 260℃ and the welding time is 20s. The resulting high-strength photovoltaic solder joint has high mechanical strength, excellent thermal fatigue resistance and long-term reliability. After 200 thermal cycles from -40℃ to 85℃, the shear strength retention rate of the solder joint is ≥80%, and the resistance growth rate is <5% after 1000 hours of humid heat aging at 85℃ / 85%RH. It is suitable for the manufacture of conventional photovoltaic modules, bifacial photovoltaic modules, shingled modules and heterojunction (HJT) photovoltaic modules.

[0026] The resulting high-strength photovoltaic solder has the following physical parameters: shear strength of 92.5 MPa and tensile strength of 102.3 MPa.

[0027] The specific parameters for Examples 2-8 and Comparative Examples 1-8 are listed in the following tables. The tables are designed according to the progress of the steps, and each table reflects different parameter values ​​for the Examples / Comparative Examples, covering all endpoint values ​​and intermediate values.

[0028] Table 1: Parameters of step (1)

[0029]

[0030] Table 2: Parameters of step (1) (continued, comparative example)

[0031]

[0032] Table 3: Parameter 1 of step (2) (Hydrothermal reaction part)

[0033]

[0034] Table 4: Parameter 2 of step (2) (Nickel nanoparticle preparation part)

[0035]

[0036] Table 5: Parameter 3 of step (2) (continued, comparative example)

[0037]

[0038] Table 6: Parameters of step (2) Part 4 (continued, comparative example, nickel nanoparticles)

[0039]

[0040] Table 7: Parameters of step (3)

[0041]

[0042] Table 8: Parameters of step (3) (continued, comparative example)

[0043]

[0044] Table 9: Parameters of step (4)

[0045]

[0046] Table 10: Parameters of step (4) (continued, comparative example)

[0047]

[0048] Table 11: Parameter 1 of step (5) (Composite flux preparation part)

[0049]

[0050] Table 12: Parameter 2 of step (5) (continued, comparative example)

[0051]

[0052] Table 13: Parameters of step (6)

[0053]

[0054] Table 14: Parameter 2 of step (6) (continued, comparative example)

[0055]

[0056] To verify the performance of the high-strength photovoltaic solder for photovoltaic ribbons described in this invention, multi-dimensional tests were conducted on the products prepared in Examples 1-8 and Comparative Examples 1-8. The tests included mechanical properties (shear strength MPa, tensile strength MPa, elongation %), interfacial properties (IMC layer thickness μm, solder porosity %), resistivity μΩ·cm, and reliability (shear strength retention %) after 200 thermal cycles and resistivity growth %) after 1000 hours of damp heat aging. The test methods are as follows: Mechanical property testing: Shear strength, tensile strength, and elongation were tested using a universal testing machine (model: Instron 5567) according to GB / T11363-2008 standard. Sample size: Standard sample of solder ribbon joint; test speed: 10 mm / min. Interfacial property testing: IMC layer thickness was measured using a scanning electron microscope (SEM, model: Hitachi S-4800); porosity was evaluated using an optical microscope (model: Olympus BX51); and resistivity was measured using the four-probe method (model: Keithley 2400). Reliability testing: Shear strength retention rate was tested after 200 thermal cycles from -40℃ to 85℃ according to IEC61215 standard; resistance growth rate was measured after 1000 hours of humid heat aging at 85℃ / 85%RH.

[0057] Table 15: Test Results 1 (Mechanical and Interface Properties)

[0058]

[0059] Table 16: Test Results 2 (Reliability)

[0060]

[0061] Table 17: Test Results 3 (Comparative Example, Mechanical Properties and Interface Properties)

[0062]

[0063] Table 18: Test Results Four (Comparative Example, Reliability)

[0064]

[0065] The test results show that the shear strength of the products in the examples is 90.7-94.2 MPa, the thermal cycling retention rate is 83.9-87.2%, and the resistance growth rate is 2.8-3.8%, demonstrating excellent performance. In contrast, the comparative examples show a significant decrease in performance due to missing components or parameter deviations (e.g., shear strength drops to 69.9-73.1 MPa, and the resistance growth rate increases to 7.5-8.6%). This proves the superiority of the preparation method of this invention.

[0066] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection defined by the claims submitted herein.

Claims

1. A method for preparing a high strength photovoltaic solder for photovoltaic ribbon, characterized by: The method comprises the following steps in terms of weight parts: (1) uniformly mixing 45-65 parts of tin powder, 8-12 parts of zinc powder, 3-7 parts of bismuth powder and 0.2-0.5 parts of nano silver powder, and then performing melting treatment to obtain a nano composite matrix alloy; (2) mixing citric acid, urea, nickel nitrate hexahydrate and deionized water according to a mass ratio of (8-15):(4-10):(1-5):(80-120), and then performing hydrothermal reaction, centrifugation and drying to obtain multi-walled carbon nanotubes; then 0.01-0.05 parts of the multi-walled carbon nanotubes and 0.2-0.8 parts of nano nickel particles are added into anhydrous ethanol with a mass of 30-60 times that of the nano nickel particles, and then ultrasonic dispersion treatment is performed to obtain a nano reinforcing phase dispersion liquid; (3) adding the nano reinforcing phase dispersion liquid obtained in step (2) into the nano composite matrix alloy obtained in step (1), and then performing mechanical stirring and mixing; then a nano composite solder powder is obtained by using a gas atomization method; (4) immersing the nano composite solder powder obtained in step (3) into a modification liquid to perform surface modification, and then a surface-modified nano composite solder powder is obtained; (5) stirring and mixing the surface-modified nano composite solder powder obtained in step (4) and a composite flux according to a mass ratio of (85-95):(8-15) to obtain a high-strength photovoltaic solder; the multi-walled carbon nanotubes in step (2) have the following parameters: an outer diameter of 10-30 nm, a length of 5-15 μm and 8-20 wall layers; the nano nickel particles in step (2) are prepared by the following method: a nickel sulfate solution with a concentration of 0.1-0.3 mol / L and a sodium borohydride solution with a concentration of 0.2-0.5 mol / L are mixed according to a mass ratio of (1-4):1 at 30-50 °C for 1-3 h, polyvinylpyrrolidone is added as a dispersant during the reaction, the amount of the polyvinylpyrrolidone is 0.5-2 times that of the nickel sulfate, after the reaction, centrifugal separation is performed at 10000-15000 rpm for 20-30 min, then the nano nickel particles are washed with anhydrous ethanol for 3-5 times, and vacuum drying is performed at 60-100 °C for 8-15 h to obtain nano nickel particles with a particle size of 40-80 nm; the ultrasonic dispersion parameters in step (2) are as follows: an ultrasonic power of 400-800 W, a frequency of 20-40 kHz, a temperature of 40-55 °C and a time of 20-40 min.

2. The method for preparing high-strength photovoltaic solder for photovoltaic ribbons according to claim 1, characterized in that: The melting treatment parameters in step (1) are as follows: melting treatment is performed at 350-450 °C for 20-40 min under the protection of an inert atmosphere, and the rotation speed is 300-500 rpm.

3. The method of claim 2, wherein the high strength photovoltaic solder for photovoltaic ribbon is prepared by: The inert atmosphere in step (1) is nitrogen or argon.

4. The method of claim 1, wherein the high strength photovoltaic solder for photovoltaic ribbon is prepared by: The parameters of the hydrothermal reaction in step (2) are as follows: being placed in a hydrothermal reaction kettle and reacting at 160-200℃ for 8-16h; the parameters of the centrifugation in step (2) are as follows: 8000-12000rpm, 15-25min; the parameters of the drying in step (2) are as follows: 80-120℃ vacuum drying for 6-12h; wherein the modified single-walled carbon nanotubes are added in an amount of 1-2 times the mass of urea during the hydrothermal reaction, and the preparation method is as follows: dissolving melamine in deionized water in an amount of 10 times the mass of melamine, stirring at 65-70℃ for 1-2h until completely dissolved, then adding single-walled carbon nanotubes in an amount of 0.2-0.4 times the mass of melamine and diethylene triamine disulfate in an amount of 0.1-0.3 times the mass of melamine, heating to 90℃, then placing in a tube furnace, heating to 850℃ at 5℃ / min under a nitrogen atmosphere, maintaining for 6-8h, and then naturally cooling to room temperature.

5. The method for preparing high-strength photovoltaic solder for photovoltaic ribbons according to claim 1, characterized in that: The parameters of the mechanical stirring in step (3) are as follows: 300-400℃, 350-600rpm for 25-45min; the parameters of the gas atomization method in step (3) are as follows: atomization pressure 2-5MPa, atomization gas is nitrogen, atomization time is 40-60min; the particle size of the nanocomposite solder powder in step (3) is 20-45μm.

6. The method of claim 1, wherein the high strength photovoltaic solder for photovoltaic ribbon is prepared by: The modified liquid in step (4) is 0.5-2 parts of 3-aminopropyl triethoxysilane or γ-methacryloyloxypropyl trimethoxysilane dissolved in 80-150 parts of an ethanol solution with a mass fraction of 75-85%, and the pH is adjusted to 4.5-6.5; the parameters of the surface modification in step (4) are as follows: stirring at 25-45℃, 200-400rpm for 2-6h, and vacuum drying at 60-90℃ for 4-8h.

7. The method for preparing high-strength photovoltaic solder for photovoltaic ribbons according to claim 1, characterized in that: The preparation method of the composite flux in step (5) is as follows: mixing 8-15 parts of rosin, 25-40 parts of anhydrous ethanol, 1-5 parts of diethanolamine, and 2-8 parts of polyethylene glycol-400, and the mixture is obtained.

8. The method of claim 1, wherein the high strength photovoltaic solder for photovoltaic ribbon is prepared by: The parameters of the stirring and mixing in step (5) are as follows: mixing in a planetary mixer at a speed of 80-150rpm for 15-30min.

9. A high strength photovoltaic solder for photovoltaic ribbon, characterized by, The high-strength photovoltaic solder for photovoltaic solder strips is obtained by the preparation method of any one of claims 1-8.

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