Photovoltaic soldering strip and method for manufacturing the same

Abstract

The application discloses a kind of photovoltaic welding band and preparation method thereof, belong to photovoltaic material technical field.The method includes: in-situ chemical reduction preparation silver coating five silver nanometer reinforcing agent, silver nanoparticle uniform load forms core-shell structure;Ultrasonic-assisted smelting Sn-Bi-Ag-Cu quaternary solder master alloy;Copper band microetching forms Ra0.35-0.55 μm porous structure;Silane bridging hot-dip plating, control solder layer thickness 18-22 μm, staged cooling.Compared with prior art, the welding band tensile strength of the application is improved, the solder joint shear force is improved, the wet heat aging retention rate is in high position, the interface hole rate is reduced, the reliability and welding performance are significantly improved, and is suitable for high-efficiency photovoltaic module.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic materials technology, specifically, it relates to a photovoltaic solder ribbon and its preparation method. Background Technology

[0002] Photovoltaic solder ribbon, as a key material for interconnecting solar cells in photovoltaic modules, directly affects the module's electrical performance, mechanical reliability, and long-term power generation efficiency. With the rapid development of the photovoltaic industry, especially the widespread adoption of high-efficiency cell technologies such as PERC, TOPCon, and HJT, the requirements for solder ribbon performance are becoming increasingly stringent. Traditional photovoltaic solder ribbon typically consists of oxygen-free copper-based ribbon and Sn-Pb coated solder, connecting adjacent cells to form a series circuit for current collection and transmission. However, existing solder ribbon technologies have many defects that limit the power output and lifespan of photovoltaic modules.

[0003] First, traditional Sn-Pb solders pose significant environmental and health risks. Although Sn-Pb alloys have a low melting point (approximately 183℃) and good wettability, lead is highly toxic and its use is completely banned in the EU and other regions due to RoHS directives. Alternative lead-free solders, such as pure Sn or Sn-Ag-Cu (SAC), have melting points exceeding 220℃, resulting in high welding temperatures (>250℃). This easily causes thermal stress damage to the solar cells, leading to microcracks (hidden cracks), reducing the initial power of the module by 1-2W, and accelerating aging and degradation. In recent years, low-temperature Sn-Bi solders (melting point 138-150℃), such as Bi 52-58wt%, have emerged. However, the Bi phase is brittle and prone to segregation, resulting in uneven solder layers, high interfacial porosity (>5%), and a tensile strength of only 200-250MPa.

[0004] Secondly, thermomechanical fatigue is the primary mechanism of solder strip failure. During photovoltaic modules' service life, they undergo diurnal temperature cycling from -40℃ to 85℃ (IEC61215 standard TC test). The thermal expansion mismatch between the copper strip (CTE 17ppm / ℃), solder (CTE 20-25ppm / ℃), and silicon wafer (CTE 2.6ppm / ℃) induces the accumulation of shear stress and creep strain at the solder joints, leading to crack initiation, propagation, and fracture. Studies show that solder joint creep strain is the dominant damage form. After 1000 hours of damp heat aging (85℃ / 85%RH), the tensile strength retention rate drops to <80%, EL images show a darker main grid, and power degradation >3%. While thin solder strips (thickness <150μm) reduce series resistance (Rs <3mΩ) and increase fill factor (FF >80%), they have low yield strength (<250MPa), elongation <10%, uneven welding tensile force (<4N), and are prone to incomplete or over-soldering, resulting in localized whitening / blackening of the grid lines.

[0005] Secondly, weak adhesion at the copper-solder interface is another major challenge. Traditional micro-etching only creates a shallowly rough surface (Ra < 0.3 μm), resulting in poor solder wetting during soldering, leading to Kirkendall voids and poor corrosion resistance (corrosion rate > 10 μm after 48 hours of salt spray testing). Residual flux further corrodes the interface, accelerating IMC layer thickening (> 5 μm), increasing brittleness, and raising contact resistance (> 2 mΩ / cm). 2 In addition, the high resistivity of the solder strip (>3.5μΩ·cm) leads to current transmission loss, increasing the series resistance of fine grid line cells (MBB / SMBB) by 0.5-1mΩ and causing a power loss of 0.5-1W / p.

[0006] Existing improvement methods still have limitations. Adding Ge / Al microalloyed Sn-Bi solder refines the grains and suppresses Bi segregation, improving corrosion resistance, but the strengthening effect is limited (hardness <35HV), and the high-temperature creep rate remains high. Nanoparticle (such as TiO2, Ag) dispersion strengthening is widely reported, but it suffers from severe agglomeration (>10%), weak interfacial bonding, and uneven ultrasonic dispersion, resulting in an actual increase in solder joint strength of <10%. Surface treatments such as silane coupling are rarely used in solder ribbons, and cooling control is often crude (rate <20℃ / s), easily leading to stress concentration in the solder layer. Literature shows that solder ribbon failure accounts for more than 30% of outdoor module failures, with a high risk of premature aging (first-year degradation >2%). For example, after thin Sn-Bi solder ribbon TC200, the EL dark area rate increased by 20%, and the tensile strength decreased by 25%. To address these issues, a novel solder system needs to be developed: low-temperature melting, interface strengthening, and uniform nano-dispersion. Simultaneously, the copper strip structuring and graded cooling processes should be optimized to achieve high-reliability photovoltaic solder strips with solder joint strength >4.5N, aging retention rate >94%, and void ratio <2%. Traditional manufacturing processes also urgently need innovation. Vacuum melting neglects acoustic cavitation dispersion, uses a single etching solution, and lacks roughness control; hot-dip plating uses low-pressure air knives (<0.2MPa), resulting in thickness fluctuations >5μm. These factors lead to uneven solder layers, large performance fluctuations, and difficulties in large-scale production.

[0007] In summary, existing photovoltaic ribbons and their preparation methods have significant shortcomings in terms of environmental adaptability, mechanical durability, and process stability, and cannot meet the requirements of N-type high-efficiency cells (efficiency > 25%) and bifacial modules (double glass ratio > 50%), so innovative technical solutions are urgently needed. Summary of the Invention

[0008] To address the problems in existing photovoltaic soldering ribbons, such as high brittleness of the Bi phase, high interfacial void ratio (>5%), rapid thermomechanical fatigue failure (aging retention rate <80%), weak copper solder layer adhesion, and unstable welding tensile strength (<4N), this invention provides a high-reliability photovoltaic soldering ribbon and its preparation method.

[0009] The present invention adopts the following technical solution: A method for preparing photovoltaic solder ribbon, by mass, includes the following steps: (1) In-situ chemical reduction preparation of silver-coated tantalum pentoxide nano-reinforcing agent: Take 0.5-1 parts of tantalum pentoxide powder (CAS1314-61-0, purity ≥99%, D50≤50nm), add it to the aqueous solution of polyvinylpyrrolidone (CAS9003-39-8) to disperse it into a dispersion; slowly add silver nitrate (CAS7761-88-8) solution to the dispersion, and at the same time add ammonia (CAS1336-21-6, concentration 25wt%) to adjust the pH, and reduce the reaction so that the silver nanoparticles (average particle size 15-40nm) are uniformly loaded on the surface of tantalum pentoxide to obtain silver-coated tantalum pentoxide nano-reinforcing agent; (2) Ultrasonic-assisted melting preparation of nano-composite quaternary solder master alloy: Take tin ingot (CAS7440- 31-5), bismuth ingot (CAS7440-69-9), silver ingot (CAS7440-22-4) and copper ingot (CAS7440-50-8) are melted to obtain a quaternary alloy matrix; the silver coating tantalum pentoxide nano-reinforcer of step (1) is premixed with tin powder (D50 is 5-10μm), ball milled and then added to the melted quaternary alloy matrix for ultrasonic vibration, and cooled to cast ingot to obtain nanocomposite solder; (3) micro-nano structured pretreatment of copper strip surface: oxygen-free copper strip (CAS7440-50-8, thickness 0.1-0.2mm) is provided and after degreasing, it is immersed in micro-etching solution to form a porous copper strip; (4) silane bridging hot-dip plating: the porous copper strip of step (3) is immersed in flux bath to form a self-assembled monolayer, and then immersed in the nanocomposite solder of step (2) for hot-dip plating, controlling the thickness of the solder layer to 18-22μm, and then cooled in stages to obtain photovoltaic solder strip.

[0010] Preferably, in step (1), the particle size D50 of the tantalum pentoxide powder is 20-40 nm, the amount of polyvinylpyrrolidone added is 1.2-1.8% of the mass of tantalum pentoxide, and the mass percentage concentration of the polyvinylpyrrolidone aqueous solution is 1-2%; the dispersion method in step (1) is ultrasonic dispersion, with a time of 30-60 min, a frequency of 20-40 kHz, and a power of 250-400 W; the concentration of the silver nitrate solution in step (1) is 0.05-0.2 mol / L. The mass ratio between silver and tantalum pentoxide powder in step (1) is 1:4-1:6; the concentration of ammonia in step (1) is 20-30wt%; the pH adjusted in step (1) is 9-11; the conditions for the reduction reaction in step (1) are as follows: the reduction reaction is carried out at 300-500r / min for 6-10h under room temperature and light-protected conditions, and argon gas is used for protection throughout the reduction reaction; the thickness of the silver coating of the silver-coated tantalum pentoxide nano-reinforcer obtained in step (1) is 5-15nm.

[0011] Preferably, the mass percentages of tin ingot, bismuth ingot, silver ingot, and copper ingot in step (2) are as follows: Bi 40-60%, Ag 0.1-0.6%, Cu 0.1-1.0%, and the balance being Sn; the melting equipment in step (2) is a vacuum induction melting furnace, and the melting temperature is 200-250℃; the mass ratio between the silver-coated tantalum pentoxide nano-reinforcement agent and tin powder in step (2) is 1:(10-20); the ball milling parameters in step (2) are as follows: a planetary ball mill is used under argon protection, using ZrO2 balls, φ5mm, with a ball-to-material ratio of 10:1, a rotation speed of 200-600r / min, and a time of 1-2h; the ultrasonic vibration parameters in step (2) are as follows: the ultrasonic amplitude transformer is made of titanium alloy, with an end face amplitude ≥35μm, an applied frequency of 20-30kHz, and a power density of 450-550W / cm². 2 Ultrasonic vibration for 30-45 minutes.

[0012] Preferably, the thickness of the oxygen-free copper strip in step (3) is 0.1-0.2 mm; the parameters for degreasing in step (3) are as follows: the solution is anhydrous ethanol, the ultrasonic frequency is 40 kHz, the ultrasonic power is 300-600 W, the ultrasonic temperature is 35-45 ℃, and the ultrasonic time is 8-12 min; the composition of the micro-etching solution in step (3) is as follows: the mass fraction of sulfuric acid is 10-15%, the mass fraction of hydrogen peroxide is 5-7%, the mass fraction of phosphoric acid is 0.1-0.6%, the mass fraction of ethylene glycol monobutyl ether (CAS111-76-2) is 0.06-0.12%, and the remainder is deionized water; the parameters for immersion in step (3) are as follows: the temperature is 38-42 ℃, and the time is 8-12 s; (3) The roughness of the porous copper strip is Ra0.35-0.55μm; the porous copper strip in step (3) is also treated by water washing and nitrogen drying. The parameters of water washing are as follows: First stage: high pressure spray, nozzle pressure 0.3-0.5MPa, spray angle 45°, temperature 40-50℃, time 20-30s; Second stage: nitrogen micro-bubbling flow rate 1-2L / min, temperature 30-40℃, time 30-45s; Third stage: pure deionized water spray, pressure 0.2-0.3MPa, room temperature, time 20-30s, and final rinsing; The parameters of nitrogen drying are as follows: drying under high purity nitrogen, air pressure 0.3-0.5MPa, air temperature 50-70℃.

[0013] Preferably, the flux composition in step (4) is as follows: adipic acid (CAS124-04-9) 2.5-3.5%, succinic acid (CAS110-15-6) 1.2-1.8%, 3-aminopropyltriethoxysilane (CAS919-30-2) 1.5-2.5%, fluorocarbon surfactant (CAS2991-51-7) 0.06-0.09%, with the balance being isopropanol (CAS67-63-0).

[0014] Preferably, the parameters for hot-dip galvanizing in step (4) are as follows: high-pressure hot nitrogen air knife, air pressure 0.25-0.35MPa, air temperature 230-250℃, slit 0.3mm; the parameters for staged cooling in step (4) are as follows: first zone: nitrogen cooling rate 25-35℃ / s to 90℃, nitrogen flow rate 15-25m / s; second zone: water cooling to room temperature, water temperature 10-20℃.

[0015] Preferably, the parameters for cooling the ingot in step (2) are as follows: First stage: cooling to 150°C at 8-15°C / min for 7-10 min; Second stage: cooling from 150°C to 100°C at 15-25°C / min for 2-3 min; Third stage: naturally cooling from below 100°C to room temperature for 30-60 min.

[0016] Preferably, the silver nitrate solution is added at a rate of 0.5-1 mL / min in step (1). After the reaction, the centrifugation and washing are performed using magnetic separation. The centrifugation speed is 8000-10000 r / min (preferably 9000 r / min), the time is 5-15 min (preferably 10 min), and the temperature is 4℃. The magnet used for magnetic separation is a neodymium iron boron permanent magnet with a surface magnetic field strength ≥0.4T to ensure that the silver loading uniformity is >95%.

[0017] A photovoltaic solder ribbon, wherein the photovoltaic solder ribbon is obtained by the preparation method described above.

[0018] Compared to existing technologies, this invention achieves a leap in solder ribbon performance through innovations such as silver-coated Ta2O5 nano-reinforcing agents, ultrasonic dispersion, micro / nano-structured copper strips, and silane bridging. Tensile strength is increased by over 20% (285MPa vs. 240MPa), solder joint shear force is increased by 25% (4.82N vs. 3.8N), aging retention reaches 94% (compared to <80% in conventional methods), and void ratio is reduced to 1.8% (compared to >5% in conventional methods). In-situ reduction synthesis of core-shell Ag@Ta2O5 nano-reinforcing agents: Traditional nanoparticles (such as TiO2 and ZrO2) are prone to agglomeration (>10%) and uneven loading. This invention pioneers a Tollens reduction mechanism to in-situ load AgNPs (15-40nm) onto the Ta2O5 surface, forming a core-shell structure with a silver layer thickness of 5-15nm and a loading uniformity >95%. Mechanism: The Ag shell improves the interfacial compatibility with the Sn-Bi phase (reducing the interfacial energy by 20%), the Ta2O5 core provides high modulus (E=280GPa), and the Orowan strengthening mechanism pins dislocations, increasing the yield strength by 34%. Simultaneously, Ag catalyzes and inhibits oxidation, and PVP stabilizes the dispersion, preventing secondary agglomeration. Compared to pure Ta2O5, this structure reduces the wetting angle to 10.4° and achieves a spreading rate of 83%. Ultrasonic assistance and pre-ball milling ensure uniform dispersion and improve microstructure stability: Existing melting processes neglect dispersion kinetics. This invention utilizes pre-ball milling (tin powder coating, D50 2-5μm) and acoustic cavitation (25kHz, 510W / cm²) to achieve uniform dispersion. 2 A uniform distribution of 0.3-0.7 wt% reinforcing agent (without agglomeration) was achieved within 38 minutes. Mechanism: Cavitation bubble collapse generates local high pressure (>100 MPa) and microjets (>100 m / s), breaking up agglomerated clusters; β-Sn grains are refined (area reduced by 50%), eutectic layer lamellar spacing is reduced, and the Hall-Petch effect increases hardness by 38 HV; Bi segregation is suppressed, and creep rate is reduced. Results: Tensile strength increased by 34%, and ductility increased by 115%, far exceeding that of unreinforced Sn-Bi-Ag. Multi-level micro-etching and silane self-assembly achieve chemical metallurgical bonding at the copper solder interface: Traditional etching results in Ra < 0.3 μm and weak adhesion. This invention uses an H2SO4-H2O2-H3PO4-ethylene glycol ether solution (40℃, 10s) to form a 200-500 nm porous structure (Ra 0.45 μm), increasing mechanical intercalation by 3 times. KH550 silane (1.5-2.5 wt%, pH 4) self-assembles a monolayer, forming Cu-O-Si-Sn bridges with a chemical bonding energy > 200 kJ / mol. Mechanism: Silane hydrolysis-condensation anchors the copper surface; amino-coupled solder Sn increases wetting force by 5.34 mN; Kirkendall voids (uneven Cu / Sn diffusion) are suppressed; the IMC layer is stabilized (Cu6Sn5 < 3 μm), and the contact resistance is reduced to < 1 mΩ / cm. 2The porosity at the interface after aging is 1.8%. High-pressure air knife and staged cooling precisely control the microscopic residual stress of the weld layer: Traditional cooling rates are <20℃ / s, resulting in stress concentration. The air knife of this invention (0.3MPa, 240℃) controls the thickness to a uniform 20μm. Nitrogen cooling (30℃ / s, up to 90℃) and water cooling (overall 50℃ / s) form fine equiaxed crystals (d<5μm). Mechanism: Rapid cooling inhibits columnar crystal growth and reduces thermal gradient stress; nano-reinforcement enriches grain boundaries, dispersed phase pinning inhibits recrystallization, and improves creep resistance (activation energy Q increases by 15%). Results: Fatigue life is extended by 2 times, and the resistance to damp heat is excellent. Summary of advantages and performance verification: The welding strip of this invention has a melting point of 142℃, which is suitable for low-temperature welding (<200℃), avoiding battery heat loss; comprehensive performance: microhardness 38HV, corrosion resistance <2μm / 1000h. The implementation examples demonstrate superior performance compared to the comparative examples (without enhancement / no ultrasonic treatment), comply with IEC61215 standards, are suitable for HJT / TOPCon modules, increase module power by >0.5W / p, and reduce degradation by <0.4% / year. This innovative approach integrates nano-metallurgy, surface engineering, and process optimization, filling the gap in low-temperature, high-reliability solder strips and possessing significant industrialization potential. Attached Figure Description

[0019] Figure 1 This is the infrared spectrum of the silver-coated tantalum pentoxide nano-reinforcer prepared in Example 1.

[0020] Figure 2 This is a sample image of the nanocomposite quaternary solder master alloy prepared in Example 1.

[0021] Figure 3 This is a sample image of the photovoltaic ribbon prepared in Example 1. Detailed Implementation

[0022] 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).

[0023] Example 1

[0024] The method for preparing the photovoltaic ribbon in this embodiment includes the following steps: (1) In-situ chemical reduction preparation of silver-coated tantalum pentoxide nano-reinforcement: Take 10.0g of tantalum pentoxide powder (CAS1314-61-0, purity ≥99.9%, D50=30nm), add 1000g of polyvinylpyrrolidone (CAS9003-39-8) aqueous solution (PVP mass concentration 1.5wt%, i.e., PVP 15.0g), disperse in an ultrasonic cleaner (power 300W, frequency 40kHz) for 45min to obtain a uniform dispersion. Add silver nitrate (CAS7761-88-8) solution (0.1mol / L) to the dispersion at a rate of 0.8mL / min, with a silver to tantalum pentoxide mass ratio of 1:5 (i.e., silver nitrate solution contains Ag 2.0g), and simultaneously add 25wt% ammonia water to adjust the pH to 10.0. The entire reaction was carried out at room temperature (25±2℃), in the dark, and under continuous high-purity argon gas (flow rate 2L / min) protection, with stirring using a magnetic stirrer (500rpm) for 8 hours. After the reaction, the mixture was centrifuged at 8000r / min for 10min, washed three times with deionized water and once with anhydrous ethanol, and then vacuum dried at 60℃ for 12 hours to obtain a silver-coated tantalum pentoxide nano-reinforcement (silver layer thickness 10nm, loading uniformity ≥96%, core-shell structure). Its infrared spectrum is shown below. Figure 1 As shown. (2) Preparation of nano-composite quaternary solder master alloy by ultrasonic-assisted melting: Take 5400g of tin ingot, 5200g of bismuth ingot, 40g of silver ingot, and 60g of copper ingot (total mass 10700g), and put them into a vacuum induction melting furnace (medium frequency power 50kW) according to Bi 52%, Ag 0.4%, Cu 0.6% and the balance Sn. Melt and stir evenly at 230℃ to obtain quaternary alloy matrix. 10.0g of nano-reinforcing agent obtained in step (1) and 150.0g of micron-sized tin powder (D50=8μm, purity 99.95%) at a mass ratio of 1:15 in an argon-protected planetary ball mill (ZrO2 ball φ5mm, ball-to-material ratio 10:1, speed 400r / min) for 1.5h to obtain coated intermediate alloy particles (D50≈3.5μm). The coated particles were added to the molten matrix, and a titanium alloy ultrasonic amplitude transformer (end-face amplitude 40μm) was inserted. A frequency of 25kHz and a power density of 500W / cm² were applied. 2 After ultrasonic vibration for 40 minutes, the ingot was cooled and cast to obtain a nano-composite quaternary solder master alloy (melting point 142℃) with a nano-reinforcing agent mass fraction of 0.5 wt%. Figure 2As shown. (3) Pretreatment of copper strip surface micro-nano structure: Take oxygen-free copper strip with a thickness of 0.15mm (width 10mm), after ultrasonic degreasing with ethanol, continuously pass it through micro-etching solution (sulfuric acid 12wt%, hydrogen peroxide 6wt%, phosphoric acid 0.45wt%, ethylene glycol monobutyl ether 0.09wt%, balance deionized water), temperature 40℃, treatment for 10s, to form a structure with Ra=0.45μm and multi-level pores (diameter 200~500nm). Wash with water and blow dry with nitrogen. (4) Silane bridging hot-dip plating coating: flux formula (mass g): adipic acid 30g, succinic acid 15g, 3-aminopropyltriethoxysilane 20g, fluorocarbon surfactant 0.8g, isopropanol 934.2g, solid content 6.5wt%, pH=4.0. Step (3) The copper strip passes through the flux bath at a speed of 2 m / min (forming a silane self-assembled monolayer), and immediately enters the nanocomposite solder bath for hot-dip plating in step (2). Then, the solder layer thickness is controlled to 20 μm using a high-pressure hot nitrogen air knife (air pressure 0.3 MPa, air temperature 240℃, slit 0.3 mm). Staged cooling: First, it enters the -5~5℃ nitrogen cooling zone (flow rate 20 m / s, cooling rate 30℃ / s, to 90℃), then water-cooled (water temperature 15℃, overall cooling rate 45℃ / s) to room temperature to obtain the photovoltaic solder strip, such as... Figure 3 As shown.

[0025] Examples 1-12 and Comparative Examples 1-12

[0026] To verify the range of key parameters and the effects of components, Examples 1-12 and Comparative Examples 1-12 were designed. Except for the difference parameters explicitly listed in the table, all other parameters are identical to those in Example 1. All units of mass are grams (g). Furthermore, Examples 10, 11, and 12 were set up for verification in parallel groups. Generally, Examples 2-12 and the Comparative Examples below only list the difference parameters; the rest are the same as in Example 1.

[0027] Table 1: Preparation parameters of silver-coated tantalum pentoxide nano-reinforcement in step (1)

[0028]

[0029]

[0030] Table 2: Step (2) Quaternary solder master alloy and reinforcing agent addition parameters

[0031]

[0032]

[0033] Table 3: Micro-etching parameters for step (3)

[0034]

[0035] Table 4: Flux and Hot-Dip Plating Parameters for Step (4)

[0036]

[0037] Test methods (all examples / comparative examples adopted the following unified standard): Tensile strength: GB / T228.1-2021, electronic universal testing machine (Instron 5967), gauge length 50 mm, speed 5 mm / min. Solder joint shear force: IEC62757-1, shear speed 10 mm / min, average value of 10 solder joints tested. Retention rate of damp heat aging: IEC61215-2021, tensile strength retention rate after 2000 h at 85℃ / 85%RH. Interface porosity: X-ray micro-CT (Zeiss Xradia 510), 3D reconstructed volume percentage. Solder layer thickness: metallographic microscope, Image-ProPlus software, 10-point average.

[0038] Table 5: Performance Test Results (Units: MPa, N, %, %)

[0039]

[0040] Results Analysis and Mechanism Elucidation: Examples 1-12, with parameter adjustments within the specified range, all achieved tensile strength ≥286 MPa, shear force ≥4.58 N, retention rate ≥94.3%, and porosity ≤1.9%, far exceeding existing technologies. Comparative Example 1 (No Reinforcing Agent): Without Orowan strengthening and interface pinning, the grains are coarse, resulting in a strength of only 238.6 MPa and a porosity of 6.8%. Comparative Example 2 (Physically Mixed Ag Powder): Without core-shell structure, Ag agglomerates, resulting in poor wettability and a shear force of only 3.88 N. Comparative Example 3 (Excessively Thick Silver Layer 1:3): An excessively thick Ag layer leads to increased interfacial brittleness, with a retention rate of only 82.6%. Comparative Example 5 (No Pre-ball Milling): Reinforcing agent agglomerates, with a dispersion <70%, resulting in a significant decrease in strength. Comparative Example 8 (No Silane and No Staged Cooling): No chemical bonding at the interface + high residual stress, resulting in a porosity of 9.5% and a retention rate of 74.2%. Comparative Example 10 (low air knife pressure): The weld layer thickness fluctuated by ±8μm, resulting in stress concentration and decreased performance, but still better than no process optimization. Examples 2 and 3, using endpoint values, still showed satisfactory performance, demonstrating a wide process window. When the parameters in the comparative examples deviated significantly from or lacked key components, performance deteriorated substantially, consistent with scientific principles.

[0041] 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 photovoltaic solder ribbon, characterized in that, The steps, by weight, are as follows: (1) Take 0.5-1 parts of tantalum pentoxide powder and add it to a polyvinylpyrrolidone aqueous solution to disperse it into a dispersion; slowly add silver nitrate solution to the dispersion and add ammonia water to adjust the pH, and reduce the reaction to obtain silver-coated tantalum pentoxide nano-reinforcing agent; (2) Take tin ingot, bismuth ingot, silver ingot and copper ingot and melt them to obtain a quaternary alloy matrix; premix the silver-coated tantalum pentoxide nano-reinforcing agent from step (1) with tin powder, ball mill it and add it to the melted quaternary alloy matrix for ultrasonic vibration, cool and cast the ingot to obtain nano-composite solder; (3) Provide oxygen-free copper strip and after degreasing, immerse it in a micro-etching solution to form a porous copper strip; (4) the porous structure of step (3) The structural copper strip is immersed in a flux bath to form a self-assembled monolayer, and then immersed in the nanocomposite solder of step (2) for hot-dip plating, controlling the solder layer thickness to 18-22 μm. After graded cooling, a photovoltaic solder strip is obtained. In step (1), the particle size D50 of tantalum pentoxide powder is 20-40 nm, the amount of polyvinylpyrrolidone added is 1.2-1.8% of the mass of tantalum pentoxide, and the mass percentage concentration of polyvinylpyrrolidone aqueous solution is 1-2%. In step (1), the dispersion method is ultrasonic dispersion, the time is 30-60 min, the frequency is 20-40 kHz, and the power is 250-400 W. In step (1), the concentration of silver nitrate solution is 0.05-0.2%. mol / L; the mass ratio between silver and tantalum pentoxide powder in step (1) is 1:4-1:6; the concentration of ammonia in step (1) is 20-30wt%; the pH adjusted in step (1) is 9-11; the conditions for the reduction reaction in step (1) are as follows: the reduction reaction is carried out at 300-500r / min for 6-10h under light-protected conditions at room temperature, and argon gas is used for protection throughout the reduction reaction; the thickness of the silver coating of the silver-coated tantalum pentoxide nano-reinforcing agent obtained in step (1) is 5-15nm; the mass percentages of tin ingot, bismuth ingot, silver ingot and copper ingot in step (2) are as follows: Bi 40-60%, Ag 0.1-0.6%, Cu 0.1 -1.0% and the balance is Sn; the melting equipment in step (2) is a vacuum induction melting furnace, and the melting temperature is 200-250℃; the mass ratio between the silver-coated tantalum pentoxide nano-reinforcer and tin powder in step (2) is 1:(10-20); the parameters of ball milling in step (2) are as follows: a planetary ball mill is used under argon protection, using ZrO2 balls, φ5mm, ball-to-material ratio of 10:1, with a rotation speed of 200-600r / min and a time of 1-2h; the parameters of ultrasonic vibration in step (2) are as follows: the ultrasonic amplitude transformer is made of titanium alloy, the end face amplitude is ≥35μm, the applied frequency is 20-30kHz, and the power density is 450-550W / cm 2 Ultrasonic vibration for 30-45 minutes.

2. The method for preparing photovoltaic solder ribbon according to claim 1, characterized in that, The thickness of the oxygen-free copper strip in step (3) is 0.1-0.2 mm; the degreasing parameters in step (3) are as follows: the solution is anhydrous ethanol, the ultrasonic frequency is 40 kHz, the ultrasonic power is 300-600 W, the ultrasonic temperature is 35-45 ℃, and the ultrasonic time is 8-12 min; the composition of the micro-etching solution in step (3) is as follows: the mass fraction of sulfuric acid is 10-15%, the mass fraction of hydrogen peroxide is 5-7%, the mass fraction of phosphoric acid is 0.1-0.6%, the mass fraction of ethylene glycol monobutyl ether is 0.06-0.12%, and the balance is deionized water; the immersion parameters in step (3) are as follows: the temperature is 38-42 ℃, and the time is 8-12 s; the porous structure in step (3) The roughness of the copper strip is Ra0.35-0.55μm; in step (3), the porous copper strip is also treated by water washing and nitrogen drying. The parameters of water washing are as follows: First stage: high pressure spray, nozzle pressure 0.3-0.5MPa, spray angle 45°, temperature 40-50℃, time 20-30s; Second stage: nitrogen micro-bubbling flow rate 1-2L / min, temperature 30-40℃, time 30-45s; Third stage: pure deionized water spray, pressure 0.2-0.3MPa, room temperature, time 20-30s, and final rinsing; The parameters of nitrogen drying are as follows: drying under high purity nitrogen, air pressure 0.3-0.5MPa, air temperature 50-70℃.

3. The method for preparing photovoltaic solder ribbon according to claim 1, characterized in that, The flux composition in step (4) is as follows: adipic acid 2.5-3.5%, succinic acid 1.2-1.8%, 3-aminopropyltriethoxysilane 1.5-2.5%, fluorocarbon surfactant 0.06-0.09%, and the balance is isopropanol.

4. The method for preparing photovoltaic solder ribbon according to claim 1, characterized in that, The parameters for hot-dip galvanizing in step (4) are as follows: high-pressure hot nitrogen air knife, air pressure 0.25-0.35MPa, air temperature 230-250℃, slit 0.3mm; the parameters for staged cooling in step (4) are as follows: first zone: nitrogen cooling rate 25-35℃ / s to 90℃, nitrogen flow rate 15-25m / s; second zone: water cooling to room temperature, water temperature 10-20℃.

5. The method for preparing photovoltaic solder ribbon according to claim 1, characterized in that, The parameters for cooling the ingot in step (2) are as follows: First stage: cool to 150℃ at 8-15℃ / min for 7-10 min; Second stage: cool from 150℃ to 100℃ at 15-25℃ / min for 2-3 min; Third stage: cool naturally from below 100℃ to room temperature for 30-60 min.

6. The method for preparing photovoltaic solder ribbon according to claim 1, characterized in that, In step (1), the silver nitrate solution is added at a rate of 0.5-1 mL / min.

7. A photovoltaic welding strip, characterized in that: The photovoltaic ribbon is obtained by the method for preparing the photovoltaic ribbon according to any one of claims 1-6.

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