Main grid silver paste based on copper alloy and preparation method thereof

Abstract

The invention provides main grid silver paste based on copper alloy and a preparation method thereof, and belongs to the field of conductive silver paste. The main grid silver paste comprises the following chemical components: 40 to 60 parts of silver powder, 5 to 10 parts of silver nanowires of which the surfaces are coated with thiol ligands, 5 to 20 parts of gradient silver-coated copper powder, 1.5 to 5.5 parts of glass materials, 20 to 30 parts of organic carriers, 0.5 to 1 part of multi-walled carbon nanotubes, 0.1 to 0.2 part of La2O3 and 0.1 to 0.3 part of VO2 nanoparticles. And 50% of pure silver is replaced by gradient silver-coated copper powder, so that the cost is reduced. The mercaptan-coated silver nanowires achieve conductivity enhancement through a small amount of materials through a high length-diameter ratio, and the use amount of precious metal is further reduced. Meanwhile, the micron silver powder provides a continuous conductive path, the silver nanowires are in bridge connection with particle gaps, a three-dimensional conductive network is formed, and the conductivity is improved. Therefore, the cost of the silver paste is reduced on the basis of ensuring the conductivity of the main grid silver paste.

Description

Technical Field

[0001] The present application relates to the technical field of conductive silver paste, and in particular to a copper alloy-based main grid silver paste and a preparation method thereof. Background Art

[0002] Main grid silver paste is the core material for the manufacture of photovoltaic cell electrodes. It is mainly used to collect and conduct photogenerated carriers, which directly affects the photoelectric conversion efficiency and reliability of the cell.

[0003] However, as photovoltaic technology evolves towards high-efficiency N-type cells (such as TOPCon), traditional silver paste faces the following technical bottlenecks: silver powder accounts for as much as 80-90%, resulting in silver paste costs accounting for 10-15% of the total cost of the cell. Silver price fluctuations and supply chain dependence (such as Japan's DOWA silver powder) further exacerbate cost risks. Therefore, how to reduce the cost of silver paste while ensuring the conductivity of the main grid silver paste. Summary of the invention

[0004] The present application provides a copper alloy-based main grid silver paste and a preparation method thereof to solve the following technical problem: how to reduce the cost of the silver paste while ensuring the conductivity of the main grid silver paste.

[0005] In the first aspect, the present application provides a copper alloy-based main grid silver paste, which includes the following chemical components by mass: 40 to 60 parts of silver powder, 5 to 10 parts of silver nanowires coated with thiol ligands on the surface, 5 to 20 parts of gradient silver-coated copper powder, 1.5 to 5.5 parts of glass material, 20 to 30 parts of organic carrier, 0.5 to 1 part of multi-walled carbon nanotubes, 0.1 to 0.2 parts of La2O3, and 0.1 to 0.3 parts of VO2 nanoparticles;

[0006] The silver layer of the gradient silver-coated copper powder is a gradient coating structure, the silver content of the inner layer is 30% to 50%, and the silver content of the outer layer is 80% to 90%.

[0007] Optionally, the organic carrier includes the following chemical components, measured in parts by mass: 50 to 70 parts of limonene, 10 to 30 parts of butyl carbitol acetate, 10 to 20 parts of pentaerythritol triacrylate, 1 to 3 parts of 2-hydroxy-2-methylpropiophenone, and 2 to 5 parts of polydimethylsiloxane.

[0008] Optionally, the silver nanowires with thiol ligands coated on the surface have a diameter of 20 to 50 nm and a length of 5 to 10 μm.

[0009] Optionally, in terms of mole percentage, the glass material consists of the following components: P2O5: 5-10 mol%, Bi2O3: 30-40 mol%, Na2O: 5-8 mol%, ZnO: 5-8 mol%, B2O3: 20-25 mol%, SiO2: 3-6 mol%, Al2O3: 1-3 mol%, V2O5: 8-12 mol%, MoO3: 2-5 mol%.

[0010] In a second aspect, the present application provides a method for preparing the main grid silver paste according to any one of the embodiments in the first aspect, and the method includes:

[0011] Ball-milling and mixing silver powder, gradient silver-coated copper core-shell powder, silver nanowires with a thiol ligand-coated surface, and multi-walled carbon nanotubes under nitrogen protection to obtain a mixed conductive phase;

[0012] Stirring and dispersing bismuth-based zinc borate composite glass powder and an organic carrier under vacuum conditions to obtain a carrier;

[0013] Adding the mixed conductive phase to the carrier, and then sequentially adding La2O3 and VO2 nanoparticles to obtain the main grid silver paste.

[0014] Optionally, the method for preparing the silver nanowires with a thiol ligand-coated surface includes:

[0015] Dissolving polyvinylpyrrolidone in ethylene glycol, and then adding silver nitrate to obtain a silver ion complex;

[0016] Under nitrogen protection, adding 1-decanethiol to the reaction system and heating to enable the thiol to bind to the silver surface through an Ag-S bond to obtain a mixed solution;

[0017] Centrifuging the mixed solution to remove free polyvinylpyrrolidone to obtain the silver nanowires with a thiol ligand-coated surface.

[0018] Optionally, the molecular weight of the polyvinylpyrrolidone is 58000-130000;

[0019] The molar concentration of the polyvinylpyrrolidone is 0.12-0.4 mol / L;

[0020] The molar concentration of the silver nitrate is 0.1-0.3 mol / L;

[0021] The molar concentration of the 1-decanethiol is 0.1-1 mmol / L;

[0022] The heating temperature is 150-180 °C, and the heating time is 1-3 h.

[0023] Optionally, the preparation method of the gradient silver-coated copper powder includes:

[0024] Sandblast the copper powder to form a rough surface structure, and then immerse it in a nitric acid solution for activation to obtain a porous copper core;

[0025] Immerse the porous copper core in a chemical plating solution of silver nitrate, ethylenediaminetetraacetic acid and glucose, and adjust the pH to deposit an initial silver layer on the surface of the porous copper core to obtain a first silver-coated copper;

[0026] Perform pulse electroplating on the first silver-coated copper in a mixed electrolyte of silver nitrate and copper sulfate, and gradually increase the silver content in the mixed electrolyte to obtain a second silver-coated copper;

[0027] Mix Ni nanoparticles and CeO2 and spray them onto the surface of the second silver-coated copper, and anneal under nitrogen protection to obtain gradient silver-coated copper powder.

[0028] Optionally, the concentration of silver nitrate in the chemical plating solution is 5-10 g / L, the concentration of ethylenediaminetetraacetic acid is 20-30 g / L, the concentration of glucose is 10-15 g / L, the pH value is adjusted to 10-11, and the reaction temperature is 45-55 °C;

[0029] The initial Ag + / Cu 2+ concentration ratio in the mixed electrolyte is 10:1;

[0030] The duty cycle of the pulse electroplating is 50%, the frequency is 100 Hz, and the time is 60 min;

[0031] The mass ratio of the Ni nanoparticles to CeO2 is 1:1, and the spraying thickness is 50-100 nm;

[0032] The annealing temperature is 300-400 °C, and the annealing holding time is 1-2 h.

[0033] Optionally, the gradually increasing the silver content in the mixed electrolyte includes:

[0034] At 0-30 min, continuously supply an AgNO3 concentrate with a concentration of 200 g / L at a constant rate, and the supply rate is 0.5 mL / min to adjust the Ag + / Cu 2+ concentration ratio to 10:1;

[0035] At 30-60 min, adjust the supply rate of the AgNO3 concentrate to 2 mL / min to adjust the Ag + / Cu 2+ concentration ratio to 20:1.

[0036] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0037] The present application provides a main grid silver paste based on copper alloy. On the one hand, by replacing 50% of pure silver with gradient silver-coated copper powder, the cost is reduced. The thiol-coated silver nanowires achieve enhanced conductivity with a small amount of material through a high aspect ratio, further reducing the usage of precious metals. On the other hand, the micron silver powder provides a continuous conduction path, and the silver nanowires bridge the particle gaps to form a three-dimensional conductive network, improving the conductivity. The gradient silver-coated copper powder ensures conductivity through a high silver content in the outer layer, reduces the cost with a copper core in the inner layer, has a perfect match in the thermal expansion coefficient with the silicon substrate, and reduces the interface stress. The VO2 nanoparticles adjust the local resistance using the phase change at 68°C, significantly reducing the hot spot effect and extending the battery life. Thus, while ensuring the conductivity of the main grid silver paste, the cost of the silver paste is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0040] Figure 1 It is a schematic flowchart of a preparation method of a main grid silver paste provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present application belong to the scope of protection of the present application.

[0042] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, and equipment used in the present application can be obtained through market purchases or can be prepared by existing methods.

[0043] In the first aspect, the present application provides a main grid silver paste based on copper alloy. In parts by mass, the main grid silver paste includes the following chemical components: 40-60 parts of silver powder, 5-10 parts of silver nanowires with a thiol ligand-coated surface, 5-20 parts of gradient silver-coated copper powder, 1.5-5.5 parts of glass material, 20-30 parts of organic carrier, 0.5-1 part of multi-walled carbon nanotubes, 0.1-0.2 part of La2O3, and 0.1-0.3 part of VO2 nanoparticles;

[0044] The silver layer of the gradient silver-coated copper powder is a gradient coating structure, with the silver content in the inner layer being 30%-50% and the silver content in the outer layer being 80%-90%.

[0045] Silver powder (40-60 parts): As the main conductive phase, it provides high conductivity and accounts for more than 70% of the conductive performance of the paste. A continuous conductive path is formed through the close packing of micron-sized silver particles (D50 = 1-5 μm), reducing the contact resistance. At the same time, it forms a "point-line" composite conductive network with thiol-coated silver nanowires. The nanowires bridge the gaps between silver particles, reducing the percolation threshold. The silver layer (85% Ag in the outer layer) in the gradient silver-coated copper powder forms a seamless interface with the silver powder, reducing the grain boundary resistance.

[0046] Silver nanowires with a thiol ligand-coated surface (5-10 parts, diameter 20-50 nm, length 5-10 μm): The aspect ratio of the nanowires > 100, forming a three-dimensional conductive framework in the paste and enhancing the stretchability of the flexible electrode. Thiol (such as 1-decanethiol) coats the silver surface through Ag-S bonds, inhibiting silver oxidation. At the same time, the terminal group (-SH) of the thiol binds to the oxygen vacancies of La2O3, enhancing the interfacial binding force. Collaborating with VO2 nanoparticles, it adjusts the local resistance through phase change, reducing the hot spot effect.

[0047] Gradient silver-coated copper powder (5-20 parts): The copper core replaces pure silver, reducing the cost by 30-50%. At the same time, the high silver content (85%) in the outer layer ensures conductivity. The gradient distribution of the silver layer (30% Ag in the inner layer → 85% Ag in the outer layer) reduces the thermal expansion difference with the silicon substrate. The Ni-CeO2 spray coating (thickness 50-100 nm) inhibits the diffusion of copper to the surface and, together with La2O3, enhances the high-temperature oxidation resistance. It reacts with MoO3 in the glass material to form a Mo-Ag interfacial phase, reducing the contact resistance.

[0048] Glass material: Bi2O3 (30-40 mol%) + V2O5 (8-12 mol%) reduces the softening point and adapts to the TOPCon cell process. The molten glass penetrates the pores of the silver layer, forming a mechanical anchoring structure.

[0049] Organic carrier (20-30 parts): The organic carrier and the glass material volatilize synergistically during sintering, avoiding electrode contamination.

[0050] Multi-walled carbon nanotubes (0.5-1 part): One-dimensional structure runs through the gaps between silver particles, increasing the density of the conductive network. It increases tensile strength and adapts to the bending requirements of flexible batteries. At the same time, the surface functional groups (-COOH) and La2O3 3+ Coordination, inhibition of carbon tube agglomeration, and dispersion uniformity.

[0051] La2O3 (0.1-0.2 parts): La 3+ It absorbs oxygen vacancies on the surface of copper core to inhibit the migration of copper ions. At the same time, it forms LaAlO3 phase with Al2O3 in glass to improve high temperature stability.

[0052] VO2 nanoparticles: semiconductor-metal phase transition regulates local resistance and reduces hot spot effect.

[0053] In some embodiments, the organic carrier includes the following chemical components, measured by mass: 50 to 70 parts of limonene, 10 to 30 parts of butyl carbitol acetate, 10 to 20 parts of pentaerythritol triacrylate, 1 to 3 parts of 2-hydroxy-2-methylpropiophenone, and 2 to 5 parts of polydimethylsiloxane.

[0054] Limonene (50-70 parts): Replaces traditional toxic solvents such as terpineol, reduces VOC emissions by more than 50%, complies with RoHS standards, and reduces environmental hazards. The medium boiling point property balances the volatilization rate during the printing process, avoiding printing defects (such as pinholes and cracks) caused by too fast drying of the slurry. Provides a low-polarity environment to promote the uniform dispersion of conductive phases such as silver powder and nanowires.

[0055] Butyl carbitol acetate (10-30 parts): forms an azeotropic system with limonene, prolongs the open time of the slurry, and is suitable for high-precision screen printing. The plasticizing effect reduces the glass transition temperature (Tg) of the slurry and improves the flexibility of the uncured slurry after printing. The polar ester group (-COO-) enhances the wettability of silver powder and glass materials, with a contact angle of ≤10°, and reduces the printing porosity.

[0056] Pentaerythritol triacrylate (10-20 parts): Contains four acrylate functional groups, quickly crosslinks under UV irradiation (wavelength 365nm) (curing time ≤ 10 seconds), forming a three-dimensional network structure. High crosslinking density, high hardness after curing. Curing shrinkage ≤ 1%, reducing the thermal stress difference with the silicon substrate.

[0057] 2-Hydroxy-2-methylpropiophenone (1-3 parts): absorbs UV light (absorption peaks 245nm, 280nm), generates active free radicals, triggers the polymerization of acrylate monomers. At the same time, it avoids interface contamination caused by unreacted monomers. The decomposition temperature is ≥200℃, which is suitable for TOPCon battery sintering process and has no thermal decomposition by-products.

[0058] Polydimethylsiloxane (PDMS, 2 - 5 parts): The thixotropic index (TI) is adjusted to 1.5 - 2.0. The low viscosity during printing ensures high resolution, and the high viscosity during standing inhibits sedimentation.

[0059] In some embodiments, the diameter of the silver nanowires with a thiol ligand surface coating is 20 - 50 nm, and the length is 5 - 10 μm.

[0060] In some embodiments, in terms of mole percentage, the glass material consists of the following components: P2O5: 5 - 10 mol%, Bi2O3: 30 - 40 mol%, Na2O: 5 - 8 mol%, ZnO: 5 - 8 mol%, B2O3: 20 - 25 mol%, SiO2: 3 - 6 mol%, Al2O3: 1 - 3 mol%, V2O5: 8 - 12 mol%, MoO3: 2 - 5 mol%.

[0061] The functions of each component of the glass material are as follows:

[0062] Bi2O3 (30 - 40 mol%): Bi2O3 is a strong flux, and its high content can reduce the glass softening point. At the same time, the high polarizability of Bi 3+ promotes the wetting of the glass melt to the silver / copper electrode, reducing the interfacial pores. In addition, the Bi - O bond provides weak conductivity, inhibiting the increase of the electrode contact resistance.

[0063] B2O3 (20 - 25 mol%): The B - O bond forms a three - dimensional network structure, endowing the glass with basic stability. At the same time, B2O3 can reduce the melt viscosity and improve the low - temperature fluidity. Collaborating with Bi2O3, it matches the thermal expansion coefficient of the silicon substrate.

[0064] V2O5 (8 - 12 mol%): The V - O bond energy is low, further reducing the softening point. At the same time, V 5+ inhibits the oxidation of copper ions and reduces the risk of electrode contact failure.

[0065] Na2O (5 - 8 mol%): Na + breaks the B - O and Bi - O bonds, reducing the glass transition temperature. At the same time, the migration of Na + improves the melt ion exchange ability and optimizes the sintering densification.

[0066] ZnO (5 - 8 mol%): Zn 2+ fills the network voids and enhances the resistance to water erosion. At the same time, it can adjust the thermal expansion difference between the glass and the silicon wafer, reducing the interfacial stress cracks.

[0067] MoO3 (2 - 5 mol%): Mo 6+Hinder the crystallization tendency of components such as Bi2O3 and maintain an amorphous structure. Meanwhile, the Mo-O bond enhances the chemical bonding between the glass and the silver layer.

[0068] P2O5 (5 - 10 mol%): The P-O bond and the B-O bond form a co-constructed network to enhance the mechanical strength of the glass. Meanwhile, the phosphate network is more easily depolymerized at high temperatures, promoting melting and spreading at 250 °C.

[0069] SiO2 (3 - 6 mol%): A small amount of SiO2 improves chemical durability, while an excessive amount increases the softening point. Meanwhile, the Si-O bond reacts with the hydroxyl groups on the surface of the silicon wafer to reduce interface recombination losses.

[0070] Al2O3 (1 - 3 mol%): Al 3+ Fill the network voids and reduce the internal defects of the glass. Meanwhile, inhibit the phase separation of Bi2O3 at high temperatures and improve the thermal cycle stability.

[0071] Thus, Bi2O3 + V2O5 + Na2O forms a low melting point core, B2O3 + P2O5 provides fluidity, and MoO3 inhibits crystallization. Meanwhile, ZnO + SiO2 regulates thermal expansion, Al2O3 enhances durability, and MoO3 optimizes electrode bonding. V2O5 inhibits oxidation, and Bi2O3 optimizes conductivity.

[0072] Figure 1 It is a schematic flow diagram of a preparation method of a main grid silver paste provided by an embodiment of the present application.

[0073] In a second aspect, the present application provides a preparation method of the main grid silver paste according to any one of the embodiments in the first aspect, and the method includes:

[0074] S1. Ball-mill and mix silver powder, gradient silver-coated copper core-shell powder, silver nanowires surface-coated with thiol ligands, and multi-walled carbon nanotubes under nitrogen protection to obtain a mixed conductive phase;

[0075] S2. Stir and disperse bismuth-based zinc borate composite glass powder and an organic carrier under vacuum conditions to obtain a carrier;

[0076] S3. Add the mixed conductive phase to the carrier, and then sequentially add La2O3 and VO2 nanoparticles to obtain the main grid silver paste.

[0077] In some embodiments, the preparation method of the silver nanowires surface-coated with thiol ligands includes:

[0078] Dissolve polyvinylpyrrolidone in ethylene glycol, and then add silver nitrate to obtain a silver ion complex;

[0079] Under nitrogen protection, 1-decanethiol was added to the reaction system and heated to allow the thiol to bind to the silver surface through Ag-S bonds, obtaining a mixed solution;

[0080] The mixed solution was centrifuged to remove free polyvinylpyrrolidone, obtaining the silver nanowires with a thiol ligand-coated surface.

[0081] In some embodiments, the molecular weight of the polyvinylpyrrolidone is 58,000 - 130,000;

[0082] The molar concentration of the polyvinylpyrrolidone is 0.12 - 0.4 mol / L;

[0083] The molar concentration of the silver nitrate is 0.1 - 0.3 mol / L;

[0084] The molar concentration of the 1-decanethiol is 0.1 - 1 mmol / L;

[0085] The temperature of the heating is 150 - 180 °C, and the time of the heating is 1 - 3 h.

[0086] High molecular weight PVP has a stronger chain entanglement ability, selectively adsorbs on the {100} crystal plane of silver crystals through carbonyl oxygen (C=O), inhibits lateral growth, promotes one-dimensional extension along the {111} crystal plane, and forms nanowires instead of particles. Subsequently, PVP forms a stable complex with Ag + through a coordination bond, controls the Ag + release rate, and avoids explosive nucleation. Thiol (-SH) competes with PVP for adsorption on the silver surface. The higher the thiol concentration, the denser the coating layer. High temperature (≥150 °C) activates the reducibility of ethylene glycol to reduce Ag + to Ag 0 nanowires. Finally, the nanowires (high density) and free PVP (low density) are separated by differential sedimentation.

[0087] In some embodiments, the preparation method of the gradient silver-coated copper powder includes:

[0088] The copper powder was sandblasted to form a rough surface structure and then immersed in a nitric acid solution for activation to obtain a porous copper core;

[0089] The porous copper core was immersed in an electroless plating solution of silver nitrate, ethylenediaminetetraacetic acid and glucose, and the pH was adjusted to deposit an initial silver layer on the surface of the porous copper core, obtaining a first silver-coated copper;

[0090] The first silver-coated copper was subjected to pulse electroplating in a mixed electrolyte of silver nitrate and copper sulfate, and the silver content in the mixed electrolyte was gradually increased to obtain a second silver-coated copper;

[0091] Mix Ni nanoparticles with CeO₂ and spray them onto the surface of the second silver-coated copper, and anneal under nitrogen protection to obtain gradient silver-coated copper powder.

[0092] In some embodiments, the concentration of silver nitrate in the electroless plating solution is 5 - 10 g / L, the concentration of ethylenediaminetetraacetic acid is 20 - 30 g / L, the concentration of glucose is 10 - 15 g / L, the pH value is adjusted to 10 - 11, and the reaction temperature is 45 - 55 °C;

[0093] The initial Ag + / Cu 2+ concentration ratio of silver nitrate to copper sulfate in the mixed electrolyte is 10:1;

[0094] The duty cycle of the pulse electroplating is 50%, the frequency is 100 Hz, and the time is 60 min;

[0095] The mass ratio of the Ni nanoparticles to CeO₂ is 1:1, and the spraying thickness is 50 - 100 nm;

[0096] The annealing temperature is 300 - 400 °C, and the annealing holding time is 1 - 2 h.

[0097] In some embodiments, the step of gradually increasing the silver content in the mixed electrolyte includes:

[0098] In the range of 0 - 30 min, a concentrated AgNO₃ solution with a concentration of 200 g / L is replenished at a constant rate of 0.5 mL / min to adjust the Ag + / Cu 2+ concentration ratio to 10:1;

[0099] In the range of 30 - 60 min, the replenishment rate of the concentrated AgNO₃ solution is adjusted to 2 mL / min to adjust the Ag + / Cu 2+ concentration ratio to 20:1.

[0100] First, by using 50 - 100 μm alumina sand grains, the surface roughness of the copper powder is increased, the specific surface area is enlarged, and the adhesion of the subsequent silver layer is enhanced. Through nitric acid activation, micron-sized pores are formed on the copper surface by corrosion, and the silver ion adsorption efficiency is improved.

[0101] Second, during the electroless silver plating process, the plating solution formula is reasonably designed: silver nitrate (5 - 10 g / L): provides Ag + , too low concentration results in discontinuous plating layer, and too high concentration causes particle aggregation. EDTA (20 - 30 g / L): complexes Ag + to form [Ag(EDTA)] 3-, Stabilize the plating solution (stability ≥ 24 h) to inhibit spontaneous reduction. Glucose (10 - 15 g / L): reducing agent, which reduces Ag + to Ag 0 under alkaline conditions (pH 10 - 11). The reaction temperature is 45 - 55 °C to balance the reaction rate and the compactness of the coating (coverage rate ≥ 95%).

[0102] Thirdly, during pulse electroplating (in a mixed electrolyte of silver nitrate - copper sulfate), the initial Ag + / Cu 2+ concentration ratio is 10:1. The high Ag + concentration ensures the rapid deposition of the initial silver layer (thickness 50 - 100 nm), covering the micropores on the surface of the copper core to prevent copper diffusion. Pulse parameters (duty cycle 50%, frequency 100 Hz, time 60 min). Duty cycle 50%: The on - off cycle balances the deposition rate and the compactness of the coating, reducing dendrite growth. Frequency 100 Hz: High - frequency pulses refine the grains and reduce the surface roughness. 0 - 30 min (0.5 mL / min): Slowly supply AgNO3 (200 g / L) at a low speed, and the Ag + / Cu 2+ maintains 10:1, forming a dense inner - layer silver (Ag content 30%). 30 - 60 min (2 mL / min): Rapidly supply to increase the Ag + / Cu 2+ to 20:1, accelerating the deposition of the outer - layer silver (Ag content 85%) to achieve a gradient structure.

[0103] Finally, Ni - CeO2 spraying and annealing. Ni nanoparticles enhance the interfacial bonding between the silver layer and the copper core through metallic bonding. CeO2 nanoparticles fill the micropores in the silver layer to inhibit high - temperature oxidation.

[0104] In summary, the main - grid silver paste and its preparation method provided by the embodiments of the present application have the following core advantages:

[0105] (1) High - performance conductive network design: Micron - sized silver powder (40 - 60 parts) provides a continuous conduction path, silver nanowires (5 - 10 parts) bridge the particle gaps to form a three - dimensional conductive network, and the conductivity is increased by more than 20%. Gradient silver - coated copper powder (5 - 20 parts) ensures conductivity through a high silver content (85%) in the outer layer, and the inner - layer copper core reduces costs. The coefficient of thermal expansion perfectly matches that of the silicon substrate, reducing interfacial stress. VO2 nanoparticles (0.1 - 0.3 parts) adjust the local resistance using the phase change at 68 °C, with a temperature difference ≤ 3 °C, significantly reducing the hot - spot effect and extending the battery life.

[0106] (2) Low cost and resource conservation: Gradient silver-coated copper powder replaces 50% of pure silver, reducing costs by 30 - 50%. At the same time, the thickness of the silver layer (50 - 100 nm) is precisely controlled by pulse electroplating to avoid waste of silver resources. Thiol-coated silver nanowires achieve enhanced conductivity with a small amount of material through a high aspect ratio (>100), further reducing the usage of precious metals.

[0107] (3) Process adaptability: In the Bi2O3-based glass material (1.5 - 5.5 parts), Bi2O3 (30 - 40 mol%) and V2O5 (8 - 12 mol%) synergistically reduce the softening point to adapt to the sintering process of TOPCon cells. The molten glass penetrates the pores of the silver layer to form a mechanical anchoring structure, reducing the contact resistance and improving the adhesion.

[0108] (4) High-reliability interface and antioxidant property: During the spraying and annealing of Ni-CeO2, Ni nanoparticles enhance the bonding of the silver layer, and CeO2 fills the pores, improving the antioxidant property. La2O3 (0.1 - 0.2 parts) passivates the oxygen vacancies of the copper core, inhibits copper diffusion, and improves the high-temperature stability.

[0109] (5) Environmental protection and process compatibility: Limonene (organic carrier) replaces traditional terpineol, reducing VOC emissions by 50% and meeting the RoHS standard. The UV curing process (pentaerythritol triacrylate) enables low-temperature and rapid curing, reducing energy consumption. Multi-walled carbon nanotubes (0.5 - 1 part) and PDMS synergistically enhance the flexibility of the slurry to meet the requirements of flexible photovoltaic modules.

[0110] (6) Process innovation and precise control: Pulse electroplating (duty cycle 50%, frequency 100 Hz) combined with an Ag + concentration gradient (10:1 → 20:1) achieves a continuous gradient distribution of the silver layer, avoiding interface defects. The staged replenishment of AgNO3 (0.5 → 2 mL / min) optimizes the deposition rate, and the density of the outer silver layer is increased by 30%. At the same time, thiol-coated silver nanowires (1-decanethiol) inhibit oxidation, synergistically enhance the interface bonding with La2O3, and improve the electrical conductivity stability.

[0111] The following further elaborates on this application in combination with specific embodiments. It should be understood that these embodiments are only used to illustrate this application and not to limit the scope of this application. The experimental methods without specific conditions noted in the following embodiments are generally determined according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0112] Example 1

[0113] A main grid silver paste based on copper alloy, by mass, the main grid silver paste includes the following chemical components: spherical silver powder (20 - 100μm) 50 parts, silver nanowires with thiol ligand surface coating 8 parts, gradient silver-coated copper powder 10 parts, glass material 2 parts, organic carrier 25 parts, multi-walled carbon nanotubes (CAS No.: 308068-56-6) 1 part, La2O3 0.2 part, VO2 nanoparticles (model: SS-V50, CAS: 12036-21-4) 0.3 part.

[0114] Among them, by mass, the organic carrier includes the following chemical components: limonene 60 parts, butyl carbitol acetate 20 parts, pentaerythritol triacrylate 15 parts, 2-hydroxy-2-methylpropiophenone 2 parts, polydimethylsiloxane 3 parts.

[0115] The diameter of the silver nanowires with thiol ligand surface coating is 20 - 50nm, and the length is 5 - 10μm.

[0116] By mole percentage, the glass material is composed of the following components: P2O5: 7mol%, Bi2O3: 36mol%, Na2O: 7mol%, ZnO: 7mol%, B2O3: 22mol%, SiO2: 4mol%, Al2O3: 3mol%, V2O5: 10mol%, MoO3: 4mol%.

[0117] Based on the above main grid silver paste, this embodiment also provides a preparation method of the main grid silver paste, the method includes:

[0118] S11. Ball mill and mix silver powder, gradient silver-coated copper core-shell powder, silver nanowires with thiol ligand surface coating and multi-walled carbon nanotubes under nitrogen protection to obtain a mixed conductive phase;

[0119] Among them, the preparation method of the silver nanowires with thiol ligand surface coating includes: dissolving polyvinylpyrrolidone in ethylene glycol, then adding silver nitrate to obtain a silver ion complex; under nitrogen protection, adding 1-decanethiol to the reaction system and heating to make the thiol bind to the silver surface through Ag-S bonds to obtain a mixed solution; centrifuging the mixed solution to remove free polyvinylpyrrolidone to obtain the silver nanowires with thiol ligand surface coating. The molecular weight of the polyvinylpyrrolidone is 60000 - 80000; the molar concentration of the polyvinylpyrrolidone is 0.3mol / L; the molar concentration of the silver nitrate is 0.2mol / L; the molar concentration of the 1-decanethiol is 0.5mmol / L; the heating temperature is 160°C, and the heating time is 2h.

[0120] The preparation method of the gradient silver-coated copper powder includes: sandblasting copper powder to form a rough surface structure, and then immersing it in a nitric acid solution for activation to obtain a porous copper core; soaking the porous copper core in a chemical plating solution of silver nitrate, ethylenediaminetetraacetic acid and glucose, and adjusting the pH to deposit an initial silver layer on the surface of the porous copper core to obtain the first silver-coated copper; performing pulse electroplating on the first silver-coated copper in a mixed electrolyte of silver nitrate and copper sulfate, and gradually increasing the silver content in the mixed electrolyte to obtain the second silver-coated copper; mixing Ni nanoparticles and CeO2 and spraying them onto the surface of the second silver-coated copper, and annealing under nitrogen protection to obtain the gradient silver-coated copper powder. The concentration of silver nitrate in the chemical plating solution is 8 g / L, the concentration of ethylenediaminetetraacetic acid is 25 g / L, the concentration of glucose is 12 g / L, the pH value is adjusted to 10.5, and the reaction temperature is 55 °C; the initial Ag + / Cu 2+ concentration ratio in the mixed electrolyte is 10:1; the duty cycle of the pulse electroplating is 50%, the frequency is 100 Hz, and the time is 60 min; the mass ratio of the Ni nanoparticles to CeO2 is 1:1, and the spraying thickness is 80 nm; the annealing temperature is 350 °C, and the annealing holding time is 1.5 h. The step of gradually increasing the silver content in the mixed electrolyte includes: in the range of 0 - 30 min, continuously supplying an AgNO3 concentrate with a concentration of 200 g / L at a constant rate, and the supply rate is 0.5 mL / min to adjust the Ag + / Cu 2+ concentration ratio to 10:1; in the range of 30 - 60 min, adjusting the supply rate of the AgNO3 concentrate to 2 mL / min to adjust the Ag + / Cu 2+ concentration ratio to 20:1.

[0121] S21. Stir and disperse the bismuth-based zinc borate composite glass powder and the organic carrier under vacuum conditions to obtain a carrier;

[0122] S31. Add the mixed conductive phase to the carrier, and then sequentially add La2O3 and VO2 nanoparticles to obtain the main grid silver paste.

[0123] Example 2

[0124] A main grid silver paste based on a copper alloy, in parts by mass, the main grid silver paste includes the following chemical components: spherical silver powder (20 - 100 μm) 40 parts, silver nanowires coated with thiol ligands 5 parts, gradient silver-coated copper powder 5 parts, glass material 1.5 parts, organic carrier 20 parts, multi-walled carbon nanotubes (CAS No.: 308068-56-6) 0.5 part, La2O3 0.1 part, VO2 nanoparticles (model: SS-V50, CAS: 12036-21-4) 0.1 part.

[0125] Among them, by mass parts, the organic carrier includes the following chemical components: 50 parts of limonene, 10 parts of butyl carbitol acetate, 10 parts of pentaerythritol triacrylate, 1 part of 2-hydroxy-2-methylpropiophenone, and 2 parts of polydimethylsiloxane.

[0126] The diameter of the silver nanowires with a thiol ligand-coated surface is 20 - 50 nm, and the length is 5 - 10 μm.

[0127] By mole percentage, the glass material is composed of the following components: P2O5: 10 mol%, Bi2O3: 40 mol%, Na2O: 8 mol%, ZnO: 8 mol%, B2O3: 20 mol%, SiO2: 3 mol%, Al2O3: 1 mol%, V2O5: 8 mol%, MoO3: 2 mol%.

[0128] Based on the above main grid silver paste, this embodiment also provides a preparation method for the main grid silver paste, and the method includes:

[0129] S11. Ball-milling and mixing silver powder, gradient silver-coated copper core-shell powder, silver nanowires with a thiol ligand-coated surface, and multi-walled carbon nanotubes under nitrogen protection to obtain a mixed conductive phase;

[0130] Among them, the preparation method of the silver nanowires with a thiol ligand-coated surface includes: dissolving polyvinylpyrrolidone in ethylene glycol, and then adding silver nitrate to obtain a silver ion complex; under nitrogen protection, adding 1-decanethiol to the reaction system and heating to enable the thiol to bind to the silver surface through the Ag-S bond to obtain a mixed solution; centrifuging the mixed solution to remove the free polyvinylpyrrolidone to obtain the silver nanowires with a thiol ligand-coated surface. The molecular weight of the polyvinylpyrrolidone is 60000 - 90000; the molar concentration of the polyvinylpyrrolidone is 0.12 mol / L; the molar concentration of the silver nitrate is 0.1 mol / L; the molar concentration of the 1-decanethiol is 0.1 mmol / L; the heating temperature is 150 °C, and the heating time is 3 h.

[0131] The preparation method of the gradient silver-coated copper powder includes: sandblasting copper powder to form a rough surface structure, and then immersing it in a nitric acid solution for activation to obtain a porous copper core; soaking the porous copper core in a chemical plating solution of silver nitrate, ethylenediaminetetraacetic acid and glucose, and adjusting the pH to deposit an initial silver layer on the surface of the porous copper core to obtain a first silver-coated copper; performing pulse electroplating on the first silver-coated copper in a mixed electrolyte of silver nitrate and copper sulfate, and gradually increasing the silver content in the mixed electrolyte to obtain a second silver-coated copper; mixing Ni nanoparticles and CeO2 and spraying them onto the surface of the second silver-coated copper, and annealing under nitrogen protection to obtain the gradient silver-coated copper powder. The concentration of silver nitrate in the chemical plating solution is 5 g / L, the concentration of ethylenediaminetetraacetic acid is 20 g / L, the concentration of glucose is 10 g / L, the pH value is adjusted to 10, and the reaction temperature is 45 °C; the initial Ag + / Cu 2+ concentration ratio in the mixed electrolyte is 10:1; the duty cycle of the pulse electroplating is 50%, the frequency is 100 Hz, and the time is 60 min; the mass ratio of the Ni nanoparticles to CeO2 is 1:1, and the spraying thickness is 50 nm; the annealing temperature is 300 °C, and the annealing holding time is 2 h. The step of gradually increasing the silver content in the mixed electrolyte includes: in the range of 0 - 30 min, continuously supplying an AgNO3 concentrate with a concentration of 200 g / L at a constant rate, and the supply rate is 0.5 mL / min to adjust the Ag + / Cu 2+ concentration ratio to 10:1; in the range of 30 - 60 min, adjusting the supply rate of the AgNO3 concentrate to 2 mL / min to adjust the Ag + / Cu 2+ concentration ratio to 20:1.

[0132] S21. Stir and disperse the bismuth-based zinc borate composite glass powder and the organic carrier under vacuum conditions to obtain a carrier;

[0133] S31. Add the mixed conductive phase to the carrier, and then sequentially add La2O3 and VO2 nanoparticles to obtain the main grid silver paste.

[0134] Example 3

[0135] A main grid silver paste based on copper alloy, in parts by mass, the main grid silver paste includes the following chemical components: spherical silver powder (20 - 100 μm) 60 parts, silver nanowires coated with thiol ligands 10 parts, gradient silver-coated copper powder 20 parts, glass material 5.5 parts, organic carrier 30 parts, multi-walled carbon nanotubes (CAS No.: 308068-56-6) 0.5 - 1 part, La2O3 0.2 part, VO2 nanoparticles (model: SS-V50, CAS: 12036-21-4) 0.3 part.

[0136] Among them, in parts by mass, the organic carrier includes the following chemical components: 70 parts of limonene, 30 parts of butyl carbitol acetate, 20 parts of pentaerythritol triacrylate, 3 parts of 2-hydroxy-2-methylpropiophenone, and 5 parts of polydimethylsiloxane.

[0137] The diameter of the silver nanowires with a thiol ligand surface coating is 20 - 50 nm, and the length is 5 - 10 μm.

[0138] In terms of mole percentage, the glass material consists of the following components: P2O5: 6 mol%, Bi2O3: 32 mol%, Na2O: 6 mol%, ZnO: 5 mol%, B2O3: 25 mol%, SiO2: 6 mol%, Al2O3: 3 mol%, V2O5: 12 mol%, MoO3: 5 mol%.

[0139] Based on the above-mentioned main grid silver paste, this embodiment also provides a preparation method for the main grid silver paste, and the method includes:

[0140] S11. Ball-mill and mix silver powder, gradient silver-coated copper core-shell powder, silver nanowires with a thiol ligand surface coating, and multi-walled carbon nanotubes under nitrogen protection to obtain a mixed conductive phase;

[0141] Among them, the preparation method of the silver nanowires with a thiol ligand surface coating includes: dissolving polyvinylpyrrolidone in ethylene glycol, and then adding silver nitrate to obtain a silver ion complex; under nitrogen protection, adding 1-decanethiol to the reaction system and heating to enable the thiol to bind to the silver surface through the Ag-S bond to obtain a mixed solution; centrifuging the mixed solution to remove free polyvinylpyrrolidone to obtain the silver nanowires with a thiol ligand surface coating. The molecular weight of the polyvinylpyrrolidone is 60,000 - 80,000; the molar concentration of the polyvinylpyrrolidone is 0.4 mol / L; the molar concentration of the silver nitrate is 0.3 mol / L; the molar concentration of the 1-decanethiol is 1 mmol / L; the heating temperature is 180 °C, and the heating time is 1 h.

[0142] The preparation method of the gradient silver-coated copper powder includes: sandblasting copper powder to form a rough surface structure, then immersing it in a nitric acid solution for activation to obtain a porous copper core; soaking the porous copper core in a chemical plating solution of silver nitrate, ethylenediaminetetraacetic acid and glucose, and adjusting the pH to deposit an initial silver layer on the surface of the porous copper core to obtain the first silver-coated copper; performing pulse electroplating on the first silver-coated copper in a mixed electrolyte of silver nitrate and copper sulfate, and gradually increasing the silver content in the mixed electrolyte to obtain the second silver-coated copper; mixing Ni nanoparticles and CeO2 and spraying them onto the surface of the second silver-coated copper, and annealing under nitrogen protection to obtain the gradient silver-coated copper powder. The concentration of silver nitrate in the chemical plating solution is 10 g / L, the concentration of ethylenediaminetetraacetic acid is 30 g / L, the concentration of glucose is 15 g / L, the pH value is adjusted to 11, and the reaction temperature is 55 °C; the initial Ag + / Cu 2+ concentration ratio in the mixed electrolyte is 10:1; the duty cycle of the pulse electroplating is 50%, the frequency is 100 Hz, and the time is 60 min; the mass ratio of the Ni nanoparticles and CeO2 is 1:1, and the spraying thickness is 100 nm; the annealing temperature is 400 °C, and the annealing holding time is 1 h. The step of gradually increasing the silver content in the mixed electrolyte includes: in the range of 0 - 30 min, continuously supplying an AgNO3 concentrate with a concentration of 200 g / L at a constant rate, and the supply rate is 0.5 mL / min to adjust the Ag + / Cu 2+ concentration ratio to 10:1; in the range of 30 - 60 min, adjusting the supply rate of the AgNO3 concentrate to 2 mL / min to adjust the Ag + / Cu 2+ concentration ratio to 20:1.

[0143] S21. Stir and disperse the bismuth-based zinc borate composite glass powder and the organic carrier under vacuum conditions to obtain a carrier;

[0144] S31. Add the mixed conductive phase to the carrier, and then sequentially add La2O3 and VO2 nanoparticles to obtain the main grid silver paste.

[0145] Comparative Example 1

[0146] Based on the disclosure of Example 1, this comparative example is modified as follows:

[0147] Silver nanowires coated with thiol ligands are not added to the silver paste.

[0148] Comparative Example 2

[0149] Based on the disclosure of Example 1, this comparative example is modified as follows:

[0150] No gradient silver-coated copper powder is added to the silver paste.

[0151] Comparative Example 3

[0152] Based on what is disclosed in Example 1, the following modifications are made in this comparative example:

[0153] No multi-walled carbon nanotubes are added to the silver paste.

[0154] Comparative Example 4

[0155] Based on what is disclosed in Example 1, the following modifications are made in this comparative example:

[0156] No La2O3 is added to the silver paste.

[0157] Comparative Example 5

[0158] Based on what is disclosed in Example 1, the following modifications are made in this comparative example:

[0159] No VO2 nanoparticles are added to the silver paste.

[0160] The main grid silver pastes of Examples 1 to 3 and Comparative Examples 1 to 5 are subjected to performance measurements, and the results are shown in Table 1. The specific performance measurement methods are as follows:

[0161] Resistivity: The conductivity is measured by the four-probe method.

[0162] Bonding strength: The peeling strength of the silver paste and the substrate (silicon wafer) is tested by a tensile testing machine.

[0163] Antioxidant property: The weight loss at high temperature is tested by a thermogravimetric analyzer (TGA).

[0164] Film thickness uniformity: The thickness of the printed grid lines is observed by an electron microscope or a laser particle size analyzer.

[0165] Thermal stability: The resistance change rate (ΔR) after high-temperature cycling.

[0166] Table 1 Performance of the main grid silver pastes of Examples 1 to 3 and Comparative Examples 1 to 5

[0167]

[0168]

[0169] As can be seen from Table 1, the resistivity of the silver pastes of Examples 1 to 3 is 3.5 - 4.1 μΩ·cm, the bonding strength is 18 - 20 MPa, and the film thickness uniformity is ±0.3 μm.

[0170] In Comparative Example 1, there are no silver nanowires with a thiol ligand coating. The silver nanowires (20 - 50 nm in diameter, 5 - 10 μm in length) form a three-dimensional conductive network through their high aspect ratio, replacing part of the spherical silver powder and reducing the contact resistance of the electron transport path. After its absence, the conductive network becomes discontinuous and the resistivity increases. Meanwhile, the silver nanowires play a "skeleton" role during the printing process, enhancing the rheological properties of the slurry. Its absence leads to uneven slurry fluidity and increased film thickness fluctuations.

[0171] In Comparative Example 2, there are no gradient silver-coated copper powders. The gradient silver-coated copper powders (Ni / CeO2 coating + pulse electroplating) reduce the silver usage through a core-shell structure. Meanwhile, the silver layer gradient design (Ag + / Cu 2+ concentration ratio from 10:1 to 20:1) ensures high surface conductivity. After its absence, pure silver powder needs to be used, resulting in increased costs and increased resistivity. The Ni / CeO2 coating (annealed at 400 °C) of the gradient silver-coated copper inhibits the oxidation of the copper core. After its absence, the exposure of copper leads to increased oxidation at high temperatures.

[0172] In Comparative Example 3, there are no multi-walled carbon nanotubes. The multi-walled carbon nanotubes enhance the mechanical interlock between the slurry and the substrate through their high specific surface area. After its absence, the bonding strength decreases. Meanwhile, the thermal conductivity of the carbon nanotubes can disperse local hot spots. After its absence, silver particles agglomerate at high temperatures and the resistivity fluctuations intensify.

[0173] In Comparative Example 4, there is no La2O3. La2O3, as a glass phase modifier (Bi-Zn-B glass system), reduces the glass softening point and inhibits the silver / silicon interface reaction (such as Ag-Si alloying). After its absence, a high-resistance layer forms at the interface and the thermal stability decreases. La2O3 combines with free oxygen at high temperatures to form a La-O stable phase. After its absence, silver oxidation intensifies.

[0174] In Comparative Example 5, there are no VO2 nanoparticles. VO2 has a phase change characteristic (68 °C semiconductor-metal transition), which can adjust the thermal expansion coefficient of the slurry. After its absence, the thermal stress mismatch between the silver layer and the substrate occurs during high-temperature cycling, resulting in cracks. VO2 forms a V-O passivation layer at high temperatures to inhibit silver oxidation. After its absence, the TGA weight loss rate doubles.

[0175] The various embodiments of the present application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be construed as a rigid limitation on the scope of the present application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, and this applies regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0176] In addition, in the description of the specification of the present application, the terms "comprising", "including", etc. mean "including but not limited to". In this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0177] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather will conform to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A main grid silver paste based on copper alloy, characterized in that, In parts by mass, the main grid silver paste comprises the following chemical components: 40 - 60 parts of silver powder, 5 - 10 parts of silver nanowires with a thiol ligand surface coating, 5 - 20 parts of gradient silver-coated copper powder, 1.5 - 5.5 parts of glass material, 20 - 30 parts of organic carrier, 0.5 - 1 part of multi-walled carbon nanotubes, 0.1 - 0.2 parts of La2O3, and 0.1 - 0.3 parts of VO2 nanoparticles; The silver layer of the gradient silver-coated copper powder is a gradient coating structure, with the inner silver content being 30% - 50% and the outer silver content being 80% - 90%.

2. The main grid silver paste according to claim 1, wherein In parts by mass, the organic carrier comprises the following chemical components: 50 - 70 parts of limonene, 10 - 30 parts of butyl carbitol acetate, 10 - 20 parts of pentaerythritol triacrylate, 1 - 3 parts of 2-hydroxy-2-methylpropiophenone, and 2 - 5 parts of polydimethylsiloxane.

3. The main grid silver paste according to claim 1, wherein The diameter of the silver nanowires with a thiol ligand surface coating is 20 - 50 nm, and the length is 5 - 10 μm.

4. The main grid silver paste according to claim 1, characterized in that In mole percentage, the glass material is composed of the following components: P2O5: 5 - 10 mol%, Bi2O3: 30 - 40 mol%, Na2O: 5 - 8 mol%, ZnO: 5 - 8 mol%, B2O3: 20 - 25 mol%, SiO2: 3 - 6 mol%, Al2O3: 1 - 3 mol%, V2O5: 8 - 12 mol%, MoO3: 2 - 5 mol%.

5. A method for preparing the main grid silver paste according to any one of claims 1 to 4, characterized in that, The method includes: Ball-milling and mixing silver powder, gradient silver-coated copper core-shell powder, silver nanowires with a thiol ligand surface coating, and multi-walled carbon nanotubes under nitrogen protection to obtain a mixed conductive phase; Stirring and dispersing bismuth-based zinc-boron composite glass powder and an organic carrier under vacuum conditions to obtain a carrier; Adding the mixed conductive phase to the carrier, and then sequentially adding La2O3 and VO2 nanoparticles to obtain the main grid silver paste.

6. The method according to claim 5, wherein The preparation method of the silver nanowires with a thiol ligand surface coating includes: Dissolving polyvinylpyrrolidone in ethylene glycol, and then adding silver nitrate to obtain a silver ion complex; Under nitrogen protection, adding 1-decanethiol to the reaction system and heating to enable the thiol to bind to the silver surface through Ag-S bonds to obtain a mixed solution; Centrifuging the mixed solution to remove free polyvinylpyrrolidone to obtain the silver nanowires with a thiol ligand surface coating.

7. The method according to claim 6, characterized in that, The molecular weight of the polyvinylpyrrolidone is 58000 - 130000; The molar concentration of the polyvinylpyrrolidone is 0.12 - 0.4 mol / L; The molar concentration of the silver nitrate is 0.1 - 0.3 mol / L; The molar concentration of the 1-decanethiol is 0.1 - 1 mmol / L; The heating temperature is 150 - 180 °C, and the heating time is 1 - 3 h.

8. The method according to claim 5, characterized in that, The preparation method of the gradient silver-coated copper powder includes: Sandblasting copper powder to form a rough surface structure, and then immersing it in a nitric acid solution for activation to obtain a porous copper core; Soaking the porous copper core in an electroless plating solution of silver nitrate, ethylenediaminetetraacetic acid, and glucose, and adjusting the pH to deposit an initial silver layer on the surface of the porous copper core to obtain a first silver-coated copper; The first silver-coated copper is subjected to pulse electroplating in a mixed electrolyte of silver nitrate and copper sulfate, and the silver content in the mixed electrolyte is gradually increased to obtain a second silver-coated copper; Ni nanoparticles and CeO2 are mixed and sprayed onto the surface of the second silver-coated copper, and annealing is carried out under nitrogen protection to obtain gradient silver-coated copper powder.

9. The method according to claim 8, characterized in that The concentration of silver nitrate in the electroless plating solution is 5-10 g / L, the concentration of ethylenediaminetetraacetic acid is 20-30 g / L, the concentration of glucose is 10-15 g / L, the pH value is adjusted to 10-11, and the reaction temperature is 45-55 °C; The initial Ag + / Cu 2+ concentration ratio of silver nitrate to copper sulfate in the mixed electrolyte is 10:1; The duty cycle of the pulse electroplating is 50%, the frequency is 100 Hz, and the time is 60 min; The mass ratio of the Ni nanoparticles to CeO2 is 1:1, and the spraying thickness is 50-100 nm; The annealing temperature is 300-400 °C, and the holding time of the annealing is 1-2 h.

10. The method according to claim 8, wherein The gradual increase in the silver content in the mixed electrolyte includes: From 0 to 30 minutes, a concentrated AgNO3 solution with a concentration of 200 g / L was replenished at a constant rate of 0.5 mL / min to adjust the Ag + / Cu 2+ concentration ratio to 10:1; Within 30 to 60 minutes, adjust the replenishment rate of the AgNO3 concentrate to 2 mL / min to adjust the Ag + / Cu 2+ concentration ratio to 20:1.

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