A method for preparing a photovoltaic ribbon alloy solder

Abstract

This invention relates to the field of tin-based composite solder preparation technology, specifically a method for preparing photovoltaic solder ribbon alloy solder. The alloy solder comprises 2.8–3.2% silver, 0.45–0.55% copper, 0.03–0.1% nickel-coated nano-alumina, 0.005–0.02% germanium, and the balance tin. After the tin block is melted, copper and silver particles are added, and the temperature is raised until the alloy is completely melted. After cooling, a Sn-Ge master alloy is added first, and then nickel-coated nano-alumina powder is slowly added to the melt by nitrogen blowing and ultrasonic coupling stirring. The melt is first heated and refined, and then cooled and allowed to stand to obtain the alloy solder melt. The copper strip is prepared into a photovoltaic solder ribbon by hot dipping. This invention improves the initial shear strength of the solder joint by synergizing nickel-coated nano-alumina and germanium, and the solder joint can maintain a high strength retention rate under thermal cycling and long-term high-temperature environment service, solving the problem of rapid decay of solder joint shear performance under harsh environment.

Description

Technical Field

[0001] This invention relates to the field of tin-based composite solder preparation technology, specifically a method for preparing photovoltaic solder ribbon alloy. Background Technology

[0002] Photovoltaic solder ribbon, also known as tin-plated copper ribbon or tin-coated copper ribbon, is a core welding material for connecting photovoltaic module cells, primarily used for current transmission and collection. It is classified into interconnect solder ribbon and bus solder ribbon according to its application, and its material consists of a copper substrate and a tin alloy coating. Currently, the two main methods for tin plating copper ribbon are hot-dip tinning and electroplating. Hot-dip tinning involves continuously immersing the copper ribbon in molten tin alloy, forming a coating through physical wetting and interfacial metallurgical bonding. Electroplating, on the other hand, uses electrolytic deposition to plate tin onto the surface of the copper ribbon.

[0003] Traditional SAC (tin-silver-copper) solder is the mainstream solder system for photovoltaic solder ribbons. However, photovoltaic modules installed in desert areas and Northeast China are subjected to high-temperature aging and high-low temperature cycling environments for a long time. As a result, the IMC at the solder joint interface is prone to rapid growth, leading to interface embrittlement and accelerated degradation of mechanical properties. This makes it difficult to meet the requirements of high stability and long lifespan of photovoltaic modules in harsh environments.

[0004] Existing technologies attempt to improve solder microstructure and inhibit IMC growth by adding nano-alumina particles alone. Specifically, SAC-XAl2O3 composite solder was prepared by powder metallurgy using Sn3.0Ag0.5Cu (SAC) as the matrix and Al2O3 nanoparticles as the reinforcing phase. The study found that after ball milling, Al2O3 particles were embedded in the surface of SAC solder powder and formed a tight bond with the solder powder. The addition of Al2O3 nanoparticles to the composite solder can refine the solder microstructure and inhibit IMC growth at the solder joint interface. Moreover, the refinement effect and inhibition effect are more significant with the increase of Al2O3 nanoparticles.

[0005] However, Al2O3 nanoparticles have high surface energy and are prone to agglomeration at high temperatures, resulting in uneven dispersion. Furthermore, Al2O3 nanoparticles are a typical ceramic material, and their interfacial reaction activity with tin alloy melt is weak, leading to poor wettability. Consequently, the solder joint shear strength is low and the reliability is insufficient.

[0006] Adding nano-alumina alone cannot stabilize the interface structure at the metallurgical level, and its effect on improving shear strength retention after high-temperature aging and thermal cycling is limited. Adding nickel or germanium alone is also difficult to simultaneously improve the initial shear strength and long-term service shear strength retention of the solder joint, and still cannot solve the technical problems of rapid decay of solder joint shear performance and poor thermal fatigue resistance under harsh environments. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for preparing a photovoltaic solder ribbon alloy, wherein the alloy solder comprises the following components in parts by weight percentage: 2.8–3.2% silver, 0.45–0.55% copper, 0.03–0.1% nickel-coated nano-alumina, 0.005–0.02% germanium, and the balance tin; the alloy solder preparation process includes the following steps: preparing a suspension: dissolving nickel nitrate hexahydrate in a mixed solvent prepared from anhydrous ethanol and deionized water, adding a dispersant, stirring evenly, then adding dried and activated nano-alumina, and ultrasonically dispersing for 20–40 min to form a uniform suspension.

[0008] Preparation of nickel-coated nano-alumina powder: Adjust the pH of the suspension to 8.5-9.5, stir at 50-60℃ for 2 hours to allow nickel ions to precipitate uniformly and coat the surface of alumina particles in the form of nickel hydroxide. Then, transfer the suspension to a high-pressure reactor, add a reducing agent, and keep it at 160-180℃ for 3-4 hours under a N2 protective atmosphere to reduce nickel hydroxide to metallic nickel. Cool, centrifuge at 6000-10000 rpm for 8-15 minutes, wash three times alternately with anhydrous ethanol and deionized water, vacuum dry at 70-80℃ for 10-12 hours, and grind through a 150-300 mesh sieve to obtain nickel-coated nano-alumina powder.

[0009] Preparation of alloy solder: High-purity tin blocks are placed in a graphite crucible and heated to 260-280°C under a N2 protective atmosphere until the tin blocks are completely melted. Then, copper and silver granules are added, the temperature is raised to 300-310°C, and the mixture is stirred for 10-15 minutes until the alloy is completely melted. The temperature of the melt is lowered to 280-290°C, Sn-Ge master alloy is added, and the mixture is stirred at 200 rpm for 5-10 minutes. Nickel-coated nano-alumina powder is slowly added to the melt using nitrogen blowing and ultrasonic coupling stirring. The melt is then heated to 310-320°C and refined for 5-10 minutes to remove gases and inclusions. The temperature is then lowered to 290-300°C, surface slag is skimmed off, and the mixture is allowed to stand for 5-10 minutes to obtain the alloy solder melt.

[0010] Preferably, the mixed solvent is prepared by anhydrous ethanol and deionized water in a volume ratio of (4-6):1, the concentration of nickel nitrate hexahydrate is 20-40 g / L, the mass ratio of nickel nitrate hexahydrate to nano alumina is 5:(4-6), and the mass ratio of nickel to nano alumina is 1:(4-6).

[0011] Preferably, the dispersant is one of PVP-K30, sodium polyacrylate, and PVA, and the concentration of the dispersant is 0.3 to 1.2 g / L.

[0012] Preferably, the reducing agent is one of ethylene glycol, glucose, and ascorbic acid.

[0013] Preferably, when the reducing agent is ethylene glycol, the amount of reducing agent added is equal to the volume of the suspension.

[0014] Preferably, when the reducing agent is glucose or ascorbic acid, the concentration added is 10-40 g / L.

[0015] Preferably, the preparation process of the Sn-Ge master alloy is as follows: high-purity tin blocks and germanium granules are put into a graphite crucible and heated to 330-370°C to melt. Under a N2 protective atmosphere, the mixture is stirred at 300-400 rpm for 8-15 minutes to fully dissolve Ge in the Sn melt. After casting and cooling, the mixture is crushed to obtain the Sn-Ge master alloy.

[0016] Preferably, the Sn-Ge master alloy contains 85-95 parts by weight of Sn and 5-15 parts by weight of Ge.

[0017] Preferably, the drying and activation conditions for the nano-alumina are drying and activation at 100-120°C for 1.5-3 hours.

[0018] Preferably, the nitrogen injection flow rate is 0.5–1 g / min; the ultrasonic frequency is 20–30 kHz; the ultrasonic power is 300–500 W; and the stirring speed is 400–500 rpm.

[0019] The present invention has at least one of the following technical effects: 1. The present invention improves the initial shear strength of the solder joint by coordinating nickel-coated nano-alumina with germanium, and the solder joint can maintain a high strength retention rate under extreme environments, such as thermal cycling and long-term high-temperature service, thus solving the problem of rapid decay of the shear performance of the solder joint under harsh environments.

[0020] 2. The nickel shell of nickel-coated nano-alumina forms a strong metallurgical bond with the tin alloy. The resulting fine-grained (Cu, Ni)6Sn5 phase can inhibit the columnar growth of IMC. The nano-alumina particles, as an inorganic reinforcing phase, improve the density of the solder matrix and simultaneously enhance the mechanical properties of the solder joint interface and the matrix. Ge preferentially segregates at the Cu-Sn interface to form an atomic barrier layer, reducing the interdiffusion rate of Cu and Sn atoms, thereby inhibiting IMC growth from the root and ensuring the mechanical stability of the solder joint during long-term service.

[0021] 3. Ge preferentially oxidizes at high temperatures to form a dense GeO2 film, which can prevent Sn from being further oxidized and block external oxygen from penetrating to the solder joint interface, thus avoiding the decrease in bonding strength caused by interface oxidation and further improving the thermal fatigue resistance of the solder joint. Attached Figure Description

[0022] Figure 1 This is a scanning electron microscope image of the nickel-coated nano-alumina powder prepared in Example 1.

[0023] Figure 2This is an IMC morphology diagram of the solder joint corresponding to the solder prepared in Example 1.

[0024] Figure 3 This is an IMC morphology image of the solder joint corresponding to the solder prepared in Example 1 after aging at 150°C for 500 hours. Detailed Implementation

[0025] 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 limit the scope of protection of the invention to these embodiments. All equivalent transformations or simple substitutions made based on the substantive content of this application should fall within the scope of protection of this application. For parameter ranges not mentioned, intermediate values ​​are selected. Furthermore, for mass percentages or weight percentages not explicitly stated or mentioned, they generally refer to the final concentration after addition.

[0026] The singular forms “for,” “or,” “a,” “any,” and “the” used in this application are intended to include the plural forms unless the context clearly indicates otherwise.

[0027] Example 1.

[0028] Preparation of suspension: Prepare a mixed solvent by mixing 40 mL of anhydrous ethanol and 10 mL of deionized water. Dissolve 1 g of nickel nitrate hexahydrate in the mixed solvent, add 0.04 g of PVP-K30, stir evenly, then add 1 g of dried and activated nano-alumina, and ultrasonically disperse for 30 min to form a uniform suspension. Nano-alumina with a particle size of 30-50 nm needs to be dried and activated at 110℃ for 2 h.

[0029] Preparation of nickel-coated nano-alumina powder: The pH of the suspension was adjusted to 9, and the mixture was stirred at 55℃ for 2 hours to allow nickel ions to precipitate uniformly and coat the surface of the alumina particles as nickel hydroxide. The suspension was then transferred to a high-pressure reactor, and an equal volume of ethylene glycol was added. Under a nitrogen atmosphere, the mixture was heated at 160℃ for 4 hours to reduce the nickel hydroxide to metallic nickel. After cooling, the mixture was centrifuged at 8000 rpm for 10 minutes, washed three times alternately with anhydrous ethanol and deionized water, vacuum dried at 80℃ for 10 hours, and then ground through a 200-mesh sieve to obtain nickel-coated nano-alumina powder. The nickel shell thickness of this powder was 10-15 nm. Figure 1 The scanning electron microscope image is shown.

[0030] Nano-alumina is a ceramic oxide with polar hydroxyl groups on its surface. It has poor chemical compatibility and is difficult to wet with non-polar, low-surface-energy tin alloy melts, resulting in low bonding strength. However, after being encapsulated with a nickel shell, the nickel shell and the tin alloy melt are both metallically bonded, resulting in excellent compatibility with the tin melt and significantly improving wettability and interfacial bonding. Furthermore, the metallic nickel shell can react in situ with tin to generate intermetallic compounds such as Ni3Sn4 and (Cu,Ni)6Sn5, which transforms the weak physical bond between nano-alumina and the tin alloy into a strong metallurgical bond between Ni and Sn. The Ni3Sn4 and (Cu,Ni)6Sn5 phases act as inorganic reinforcing phases to increase the density of the solder joint matrix and directly improve the initial shear strength.

[0031] Furthermore, the nickel shell prevents the nano-alumina particles from directly contacting each other. The surface energy of the nickel shell is much lower than that of the nano-alumina, thus reducing the adsorption force between the nano-alumina particles. This solves the problem of easy agglomeration and poor dispersion of pure nano-alumina, ensuring a uniform distribution of the reinforced structure and stabilizing the shear performance of the solder joint. Meanwhile, the nickel element reacts in situ with tin to generate a fine-grained (Cu,Ni)6Sn5 phase, which replaces the traditional single Cu6Sn5 phase. This inhibits the columnar growth of IMC from a metallurgical perspective, slows down interfacial catalysis under high temperature and thermal cycling conditions, and delays the decay of shear strength.

[0032] 0.9g of high-purity tin block and 0.1g of germanium granules were added to a graphite crucible and heated to 350℃ to melt. Under a N2 protective atmosphere, the mixture was stirred at 400rpm for 8min to fully dissolve Ge in the Sn melt. After casting and cooling, the mixture was crushed to obtain the Sn-Ge master alloy.

[0033] Pure Ge particles do not melt and are difficult to dissolve in SAC solder. However, in the Sn-Ge master alloy, Ge is pre-dissolved into the Sn matrix in the form of interstitial solid solution. When added to the tin alloy melt, it can be dispersed instantly and avoids local high concentrations of Ge. At high temperatures, Ge is preferentially oxidized to form a dense GeO2 film, which can prevent Sn from being further oxidized. Furthermore, Ge agglomerates at the Cu-Sn interface, hindering the interdiffusion of Cu and Sn atoms and effectively reducing the IMC growth rate.

[0034] 96.42g of high-purity tin ingot was placed in a graphite crucible and heated to 270℃ under a N2 protective atmosphere until the tin ingot was completely melted. Then, 0.5g of copper granules and 3g of silver granules were added, the temperature was raised to 300℃, and the mixture was stirred for 15 minutes until the alloy was completely melted. The temperature of the melt was lowered to 290℃, and 0.05g of Sn-Ge master alloy with a Ge content of 10% was added. The mixture was stirred at 200 rpm for 10 minutes. 0.03g of nickel-coated nano-alumina powder was taken and slowly added to the melt using nitrogen blowing and ultrasonic coupling stirring. The nitrogen blowing flow rate was 0.5g / min, the ultrasonic frequency was 20kHz, the ultrasonic power was 500W, and the stirring speed was 400 rpm. The melt was then heated to 320℃ and refined for 5 minutes to remove gas and inclusions. The temperature was then lowered to 295℃, the surface slag was skimmed off, and the mixture was allowed to stand for 8 minutes to obtain the alloy solder melt.

[0035] Example 2.

[0036] The difference from Example 1 is that the amount of nano-alumina added is 0.8g, the thickness of the nickel shell of the nickel-coated nano-alumina powder is 8-12nm, and the rest of the preparation method is the same as that in Example 1.

[0037] Example 3.

[0038] The difference from Example 1 is that the amount of nano-alumina added is 1.2g, the thickness of the nickel shell of the nickel-coated nano-alumina powder is 12-18nm, and the rest of the preparation method is the same as that in Example 1.

[0039] Example 4.

[0040] The difference from Example 1 is that the amount of nickel-coated nano-alumina powder used is 0.07g, with the remainder being tin, and the rest of the preparation method is the same as in Example 1.

[0041] Example 5.

[0042] The difference from Example 1 is that the amount of nickel-coated nano-alumina powder used is 0.1g, with the remainder being tin, and the rest of the preparation method is the same as in Example 1.

[0043] Example 6.

[0044] The difference from Example 1 is that the amount of Sn-Ge master alloy with a Ge content of 10% added is 0.2g, with the balance being tin, and the rest of the preparation method is the same as in Example 1.

[0045] Example 7.

[0046] The difference from Example 4 is that the amount of Sn-Ge master alloy with a Ge content of 10% added is 0.2g, with the balance being tin, and the rest of the preparation method is the same as in Example 4.

[0047] Example 8.

[0048] The difference from Example 5 is that the amount of Sn-Ge master alloy with a Ge content of 10% added is 0.2g, with the balance being tin, and the rest of the preparation method is the same as in Example 5.

[0049] Example 9.

[0050] The difference from Example 2 is that the amount of nickel-coated nano-alumina powder used is 0.07g, with the remainder being tin, and the rest of the preparation method is the same as in Example 2.

[0051] Example 10.

[0052] The difference from Example 2 is that the amount of Sn-Ge master alloy with a Ge content of 10% added is 0.2g, with the balance being tin, and the rest of the preparation method is the same as in Example 2.

[0053] Example 11.

[0054] The difference from Example 1 is that the reducing agent is glucose, the amount of glucose added is 3g, and the rest of the preparation method is the same as in Example 1.

[0055] Comparative example.

[0056] Comparative Example 1.

[0057] The difference from Example 4 is that the nickel-coated nano-alumina powder is replaced with an equal mass of nickel, while the rest of the preparation method is the same as in Example 4.

[0058] Comparative Example 2.

[0059] The difference from Example 4 is that the nickel-coated nano-alumina powder is replaced with an equal mass of nano-alumina, while the rest of the preparation method is the same as in Example 4.

[0060] Comparative Example 3.

[0061] The difference from Example 4 is that nickel-coated nano-alumina is not added; only Sn-Ge master alloy is added. The rest of the preparation method is the same as in Example 4.

[0062] Comparative Example 4.

[0063] The difference from Example 4 is that Sn-Ge master alloy is not added, only nickel-coated nano-alumina is added, and the rest of the preparation method is the same as in Example 4.

[0064] The alloy solder melt prepared in the above embodiments and comparative examples was maintained at 300°C and continuously stirred under a N2 protective atmosphere. The copper strip sample, which had undergone alkali washing, water washing, acid washing, fluxing, and drying, was immersed in the alloy solder melt for static hot-dip plating. The immersion lasted for 25 seconds to allow the alloy solder to fully coat the surface of the copper strip. Then, the copper strip sample was removed, excess solder was removed from the surface, and it was allowed to cool naturally to room temperature to obtain a tin-plated copper strip with a tin alloy coating on the surface, which is a photovoltaic solder strip.

[0065] The coating thickness of the prepared photovoltaic ribbon was measured, and the initial shear strength of the solder joint was measured and recorded as follows: The shear strength after thermal cycling and high-temperature aging was tested and recorded as follows: , The shear strength retention rate after thermal cycling and high-temperature aging was analyzed. The strength retention rate (%) = (strength after test / initial strength) × 100%. The results are shown in Table 1 below. The temperature range of thermal cycling is -40℃ to 85℃, and the high-temperature aging is aging at 150℃ for 500h.

[0066] Table 1. Coating Thickness and Solder Joint Shear Strength

[0067]

[0068] As can be seen from Examples 1-3, when only the proportion of nano-alumina in the nickel-plated nano-alumina powder is increased, the shear strength of the solder joint and the strength retention rate after extreme environmental treatment both increase slightly and steadily.

[0069] The comparison of Examples 1, 4 and 5 shows that the higher the amount of nickel-coated nano alumina powder added, the higher the initial shear strength and the higher the strength retention rate after thermal cycling and high-temperature aging. Specifically, the strength retention rate after thermal cycling increased from 80% to 83.7%, and the strength retention rate after high-temperature aging increased from 78.6% to 82.5%.

[0070] Comparing Example 6 with Example 1, Example 7 with Example 4, and Example 8 with Example 5, it is shown that increasing the amount of Ge added improves the oxidation resistance of the solder joint at high temperatures and significantly increases the strength retention rate of the solder joint.

[0071] Comparing Examples 1-10 with Comparative Examples 1-4, it can be seen that adding a single element (nickel, nano-alumina, germanium) results in lower shear strength of the solder joints compared to adding nickel-coated nano-alumina powder combined with germanium in this invention. The strength retention rate after high-temperature aging or thermal cycling is also weaker than that of this invention. This indicates that nickel-coated nano-alumina powder combined with germanium can simultaneously achieve high initial shear strength and excellent long-term shear reliability. Under extreme environments, the strength decay of photovoltaic cells is slower and the lifespan is longer.

[0072] like Figure 2 As shown, after shear strength testing of the corresponding solder joints of the photovoltaic solder ribbon prepared in Example 1, the morphology of the IMC at the solder joint interface was observed. It can be seen that there is no obvious peeling or crack at the solder joint interface. Due to the formation of the (Cu,Ni)6Sn5 phase, the IMC layer has a wavy fine-grained structure rather than a coarsened columnar structure, indicating that nickel-coated nano-alumina effectively inhibits the columnar growth of IMC.

[0073] like Figure 3 As shown, after aging the corresponding solder joints of the photovoltaic solder ribbon prepared in Example 1 at 150°C for 500 hours, the IMC morphology at the interface of the sheared solder joints was observed again. It can be seen that the thickness of the IMC layer did not increase significantly, indicating that the addition of germanium hindered the interdiffusion of Cu and Sn atoms, effectively reduced the IMC growth rate, and ensured the mechanical stability of the solder joints during long-term service. Furthermore, the interface was free of pores and microcracks after high-temperature treatment, indicating that nickel-coated nano-alumina improved the interfacial bonding strength, so that the shear strength would not decrease significantly under high-temperature aging.

[0074] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0075] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A method for preparing a photovoltaic solder ribbon alloy, characterized in that, The alloy solder comprises the following components in parts by weight percentage: 2.8–3.2% silver, 0.45–0.55% copper, 0.03–0.1% nickel-coated nano-alumina, 0.005–0.02% germanium, and balance tin; The alloy solder preparation process includes the following steps: Preparation of suspension: Dissolve nickel nitrate hexahydrate in a mixed solvent of anhydrous ethanol and deionized water, add dispersant, stir evenly, then add dried and activated nano-alumina, and ultrasonically disperse for 20-40 minutes to form a uniform suspension. Preparation of nickel-coated nano-alumina powder: Adjust the pH of the suspension to 8.5-9.5, stir at 50-60℃ for 2h, then transfer the suspension to a high-pressure reactor, add a reducing agent, keep warm at 160-180℃ for 3-4h under N2 protective atmosphere, cool, centrifuge, wash, vacuum dry at 70-80℃ for 10-12h, grind and sieve to obtain nickel-coated nano-alumina powder; Preparation of alloy solder: High-purity tin blocks are placed in a graphite crucible and heated to 260-280°C under a N2 protective atmosphere until the tin blocks are completely melted. Then, copper and silver granules are added, the temperature is raised to 300-310°C, and the mixture is stirred for 10-15 minutes until the alloy is completely melted. The temperature of the melt is lowered to 280-290°C, Sn-Ge master alloy is added, and the mixture is stirred at 200 rpm for 5-10 minutes. Nickel-coated nano-alumina powder is slowly added to the melt using nitrogen blowing and ultrasonic coupling stirring. The melt is then heated to 310-320°C and refined for 5-10 minutes. The temperature is then lowered to 290-300°C, the surface slag is skimmed off, and the melt is allowed to stand for 5-10 minutes to obtain the alloy solder melt. The preparation process of the Sn-Ge master alloy is as follows: High-purity tin blocks and germanium granules are placed in a graphite crucible and heated to 330–370°C to melt. Under a N2 protective atmosphere, the mixture is stirred at 300–400 rpm for 8–15 minutes to fully dissolve Ge in the Sn melt. After casting and cooling, the mixture is crushed to obtain the Sn-Ge master alloy.

2. The method for preparing a photovoltaic solder ribbon alloy according to claim 1, characterized in that: The mixed solvent is prepared by anhydrous ethanol and deionized water in a volume ratio of (4-6):1, the concentration of nickel nitrate hexahydrate is 20-40 g / L, and the mass ratio of nickel nitrate hexahydrate to nano alumina is 5:(4-6).

3. The method for preparing a photovoltaic solder ribbon alloy according to claim 1, characterized in that: The dispersant is one of PVP-K30, sodium polyacrylate, and PVA, and the concentration of the dispersant is 0.3 to 1.2 g / L.

4. The method for preparing a photovoltaic solder ribbon alloy according to claim 1, characterized in that: The reducing agent is one of ethylene glycol, glucose, and ascorbic acid.

5. The method for preparing a photovoltaic solder ribbon alloy according to claim 4, characterized in that: When the reducing agent is ethylene glycol, the amount of reducing agent added is equal to the volume of the suspension.

6. The method for preparing a photovoltaic solder ribbon alloy according to claim 4, characterized in that: When the reducing agent is glucose or ascorbic acid, the concentration added is 10-40 g / L.

7. The method for preparing a photovoltaic solder ribbon alloy according to claim 1, characterized in that: The Sn-Ge master alloy contains 85-95 parts by weight of Sn and 5-15 parts by weight of Ge.

8. The method for preparing a photovoltaic solder ribbon alloy according to claim 1, characterized in that: The drying and activation conditions for the nano-alumina are: drying and activation at 100–120°C for 1.5–3 hours.

9. The method for preparing a photovoltaic solder ribbon alloy according to claim 1, characterized in that: The flow rate of nitrogen injection is 0.5–1 g / min; the ultrasonic frequency is 20–30 kHz; the ultrasonic power is 300–500 W; and the stirring speed is 400–500 rpm.

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