Main grid silver paste and preparation method thereof, electrode and solar cell

Abstract

The invention provides main grid silver paste and a preparation method thereof, an electrode and a solar cell, and belongs to the field of solar cells. The main grid silver paste comprises the following chemical components: 30 to 50 parts of micron silver sheets, 10 to 20 parts of nano silver particles, 5 to 20 parts of silver-coated tungsten, 0.1 to 0.5 part of modified carbon nanotubes, 8 to 15 parts of a PEDOT: PSS aqueous solution, 2 to 5 parts of an ionic liquid, 0.5 to 2 parts of a dynamic cross-linking agent and 5 to 15 parts of deionized water. The chemical components of the main grid silver paste are reasonably designed, firstly, high-hardness tungsten cores are used for replacing part of silver powder, and the raw material cost is reduced. Secondly, reversible bonds of the dynamic cross-linking agent are broken and recombined at the temperature of 150-180 DEG C, and self-repairing of the silver layer is achieved. Finally, the PEDOT: PSS water-based carrier is adopted to replace a traditional organic solvent, and VOC emission is reduced. Therefore, the problems of high cost, high-temperature process limitation and environmental protection of the traditional silver paste are solved.

Description

Technical Field

[0001] The present application relates to the technical field of solar cells, and in particular, to a main grid silver paste, a preparation method thereof, an electrode, and a solar cell. Background Art

[0002] Photovoltaic silver paste is a key material for manufacturing electrodes of crystalline silicon solar cells. Its core function is to collect photo-generated carriers through conductive grid lines and export current, which directly affects the photoelectric conversion efficiency (PCE) of the battery. Traditional silver paste is composed of high-purity silver powder (micrometer / nanometer level) as the main conductive phase, glass oxide as the binder phase, and an organic carrier.

[0003] However, with the evolution of photovoltaic technology towards high-efficiency N-type cells (such as HJT), traditional silver paste faces the following technical bottlenecks: (1) The proportion of silver powder is as high as 80-90%, resulting in the cost of silver paste accounting for 10-15% of the total cost of the cell. Fluctuations in silver prices and supply chain dependence (such as DOWA silver powder from Japan) further exacerbate cost risks. (2) PERC cells require high-temperature sintering at 500-800°C, which is incompatible with the low-temperature process (≤250°C) of HJT cells and is likely to damage the passivation layer structure of heterojunction cells. (3) Traditional organic carriers have high VOC emissions. Therefore, how to solve the problems of high cost, high-temperature process limitations, and environmental protection of traditional silver paste is a technical problem that urgently needs to be solved at present. Summary of the Invention

[0004] The present application provides a main grid silver paste, a preparation method thereof, an electrode, and a solar cell to solve the problems of high cost, high-temperature process limitations, and environmental protection of traditional silver paste.

[0005] In a first aspect, the present application provides a main grid silver paste. In terms of parts by mass, the main grid silver paste includes the following chemical components: 30-50 parts of micron silver flakes, 10-20 parts of nano silver particles, 5-20 parts of silver-coated tungsten, 0.1-0.5 part of modified carbon nanotubes, 8-15 parts of PEDOT:PSS aqueous solution, 2-5 parts of ionic liquid, 0.5-2 parts of dynamic crosslinking agent, and 5-15 parts of deionized water.

[0006] Optionally, the particle size of the silver-coated tungsten is 0.5-2 μm, the thickness of the silver coating layer is 50-200 nm, and the silver layer coverage rate ≥ 95%.

[0007] Optionally, the particle size of the nano silver particles ≤ 100 nm;

[0008] The particle size of the micron silver flakes is 2-4 μm;

[0009] The modified carbon nanotubes are carboxylated multi-walled carbon nanotubes, with a particle size of 5-100 nm and an aspect ratio ≥ 100.

[0010] Optionally, the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

[0011] Optionally, the dynamic crosslinking agent is a benzocyclobutene-maleimide crosslinking agent.

[0012] 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, the method comprising the following steps:

[0013] S1. Ultrasonically treat micron silver flakes, nano silver particles, silver-coated tungsten and modified carbon nanotubes in deionized water to obtain a first mixed solution;

[0014] S2. Add a PEDOT:PSS aqueous solution, an ionic liquid and a dynamic crosslinking agent to the first mixed solution to obtain a second mixed solution;

[0015] S3. Grind the second mixed solution 3 to 5 times through a three-roll mill to obtain the main grid silver paste; the roll spacing of the three-roll mill is 10 to 20 μm, and the rotation speed is 200 to 300 rpm.

[0016] Optionally, the preparation method of the modified carbon nanotubes includes:

[0017] Bombard the surface of multi-walled carbon nanotubes with low-temperature plasma in an oxygen atmosphere to obtain activated carbon tubes;

[0018] Immerse the activated carbon tubes in a solution containing acrylic acid monomer and ammonium persulfate to undergo a free radical reaction to obtain the modified carbon nanotubes; the mass concentration of the acrylic acid monomer is 10 to 30%, and the mass concentration of the ammonium persulfate is 0.5 to 2%.

[0019] Optionally, the low-temperature plasma includes the following parameters: oxygen concentration is 50 to 80 vol%, power is 100 to 300 W, air pressure is 10 to 50 Pa, and treatment time is 10 to 30 min.

[0020] In a third aspect, the present application provides an electrode, which is sintered on the surface of a battery silicon wafer through the main grid silver paste according to any one of the embodiments in the first aspect.

[0021] In a fourth aspect, the present application provides a solar cell, which includes the electrode according to the embodiment in the third aspect.

[0022] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0023] The present application provides a main grid silver paste, which includes the following chemical components: 30-50 parts of micron silver flakes, 10-20 parts of nano silver particles, 5-20 parts of silver-coated tungsten, 0.1-0.5 parts of modified carbon nanotubes, 8-15 parts of PEDOT:PSS aqueous solution, 2-5 parts of ionic liquid, 0.5-2 parts of dynamic crosslinking agent, and 5-15 parts of deionized water. By reasonably designing the chemical components of the main grid silver paste, the present application firstly replaces part of the silver powder with a high-hardness tungsten core, directly reducing the raw material cost; and the micron silver flakes serve as a conductive framework, reducing the total amount of silver powder used; the nano silver particles fill the gaps between the micron flakes and are preferentially melted and densified during low-temperature sintering, reducing the porosity. Secondly, the reversible bonds of the dynamic crosslinking agent break and recombine at 150-180°C, achieving self-repair of the silver layer without high-temperature annealing. Finally, the PEDOT:PSS aqueous carrier is used to replace traditional organic solvents such as terpineol / ethyl cellulose, reducing VOC emissions. Thereby, the problems of high cost, high-temperature process limitations, and environmental protection of traditional silver pastes are solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present application and, together with the specification, are used to explain the principles of the present application.

[0025] 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, other drawings can also be obtained based on these drawings without creative efforts.

[0026] Figure 1 It is a schematic flow chart of a preparation method of a main grid silver paste provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] 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 based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0028] 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.

[0029] In a first aspect, the present application provides a main grid silver paste. In terms of parts by mass, the main grid silver paste includes the following chemical components: 30 - 50 parts of micron silver flakes, 10 - 20 parts of nano silver particles, 5 - 20 parts of silver-coated tungsten, 0.1 - 0.5 parts of modified carbon nanotubes, 8 - 15 parts of PEDOT:PSS aqueous solution, 2 - 5 parts of ionic liquid, 0.5 - 2 parts of dynamic crosslinking agent, and 5 - 15 parts of deionized water.

[0030] The present application rationally designs the chemical components of the main grid silver paste. Specifically, the functions of each component are as follows.

[0031] Micron silver flakes (30 - 50 parts): Micron silver flakes serve as the main framework of the conductive network, providing high conductivity and mechanical support. Micron-sized silver flakes (particle size 2 - 4 μm) form continuous conductive channels through sheet stacking, reducing the bulk resistance and enhancing the bending resistance of the silver paste. At the same time, micron silver flakes can complement nano silver particles, and the nanoparticles fill the gaps between the micron flakes, reducing the contact resistance and forming a "micro-nano interlocking" conductive network.

[0032] Nano silver particles (10 - 20 parts, particle size ≤ 100 nm): Through the high specific surface area and surface activity, the sintering activity of the silver paste is improved. The nanoparticles preferentially melt during low-temperature sintering, promoting the densification of the silver layer and reducing the porosity. Moreover, nano silver particles and silver-coated tungsten work together to reduce silver consumption, and at the same time form a charge transfer interface with PEDOT:PSS, enhancing the carrier collection efficiency of the electrode.

[0033] Silver-coated tungsten (5 - 20 parts, silver layer coverage rate ≥ 95%): Part of the silver powder is replaced by a tungsten core to reduce the silver content, and the silver coating layer maintains conductivity. The high hardness of the tungsten core (HV ≥ 300) enhances the wear resistance of the electrode. At the same time, silver-coated tungsten forms a dynamic bond with TeO 2 / V 2 O 5 to inhibit silver migration and improve the humidity and heat stability of the electrode (resistance change < 3% after 1000 hours).

[0034] Modified carbon nanotubes (0.1 - 0.5 parts, carboxylated multi-walled carbon nanotubes): As a conductive reinforcement phase, the carboxylated surface (-COOH) forms hydrogen bonds with the sulfonic acid group (-SO 3 H) of PEDOT:PSS, enhancing the interfacial bonding force; the fiber structure with an aspect ratio ≥ 100 inhibits shrinkage cracks of the silver paste. At the same time, modified carbon nanotubes and silver-coated tungsten work together to construct a three-dimensional conductive network, reducing the contact resistance.

[0035] PEDOT:PSS aqueous solution (8 - 15 parts): PEDOT:PSS is an aqueous solution of a polymer. PEDOT is a polymer of EDOT (3,4 - ethylenedioxythiophene monomer), and PSS is polystyrene sulfonate. The combination of these two substances greatly improves the solubility of PEDOT. As an organic carrier, the PEDOT:PSS aqueous solution has both conductivity and dispersion functions. The conjugated structure of PEDOT:PSS provides a hole transport channel, enhancing the electrode carrier collection efficiency. At the same time, the PEDOT:PSS aqueous solution and the ionic liquid form a bipolar solvent system, optimizing the rheology of the silver paste and adapting to high - precision screen printing.

[0036] Ionic liquid (2 - 5 parts, 1 - ethyl - 3 - methylimidazolium bis(trifluoromethylsulfonyl)imide): As a high - boiling - point solvent (boiling point ≥ 300 °C), the ionic liquid improves the wettability and dispersion stability of the silver paste; its low - viscosity property (η < 100 mPa·s) reduces the tailing phenomenon during printing. The ionic liquid and the dynamic cross - linker synergistically regulate the curing process, avoiding the decomposition of PEDOT:PSS caused by high - temperature sintering and adapting to the low - temperature process of HJT batteries.

[0037] Dynamic cross - linker (0.5 - 2 parts, benzocyclobutene - maleimide): Achieves a self - repair function through Diels - Alder reversible bonds. At 150 - 180 °C, the dynamic bonds break and recombine, repairing the microcracks in the silver layer caused by thermal stress and extending the electrode life. The dynamic cross - linker synergizes with the Te / V dynamic bonds in it to form a dual repair mechanism, enhancing durability.

[0038] Deionized water (5 - 15 parts): As an environmentally friendly solvent, it adjusts the viscosity of the silver paste to ensure printing uniformity; it quickly volatilizes during low - temperature drying (residual amount < 0.1%), avoiding the influence of organic residues on conductivity.

[0039] In some embodiments, the particle size of the silver - coated tungsten is 0.5 - 2 μm, the thickness of the silver coating layer is 50 - 200 nm, and the silver layer coverage rate ≥ 95%.

[0040] In some embodiments, the particle size of the nano - silver particles ≤ 100 nm;

[0041] The particle size of the micro - silver flakes is 2 - 4 μm;

[0042] The modified carbon nanotubes are carboxylated multi - wall carbon nanotubes, with a particle size of 5 - 100 nm and an aspect ratio ≥ 100.

[0043] In some embodiments, the ionic liquid is 1 - ethyl - 3 - methylimidazolium bis(trifluoromethylsulfonyl)imide.

[0044] The ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide consists of the following two parts: Cation: 1-ethyl-3-methylimidazolium ([EMIM]+), which belongs to imidazole-based ionic liquids and has low viscosity and high thermal stability. Anion: Bis(trifluoromethylsulfonyl)imide ([TFSI]-), which contains fluorosulfonyl groups and imparts low volatility and excellent chemical stability.

[0045] As a high-boiling solvent (boiling point > 300 °C), the ionic characteristics of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide can enhance the charge transport efficiency of the silver paste, especially suitable for low-temperature curing processes, avoiding the damage to the PEDOT:PSS matrix at high temperatures. At the same time, it stabilizes the suspension of silver nanoparticles (≤100 nm) and silver-coated tungsten (0.5 - 2 μm) through electrostatic interaction, preventing agglomeration and ensuring the rheological uniformity of the paste. In addition, as a polar solvent, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide has high compatibility with benzocyclobutene-maleimide crosslinkers (dynamic crosslinkers), promoting the formation and repair of Diels-Alder reversible bonds and enhancing the self-healing ability of the silver paste. Moreover, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide can replace traditional organic solvents (such as ethylene glycol and terpineol), reducing VOC emissions and conforming to the trend of green manufacturing.

[0046] In some embodiments, the dynamic crosslinker is a benzocyclobutene-maleimide crosslinker.

[0047] The benzocyclobutene-maleimide adduct in the crosslinker undergoes a retro reaction (retro-DA) when heated (150 - 180 °C), and the bond breaks to release active sites; it re-crosslinks after cooling to achieve the self-healing function. At the same time, the dynamic bond-breaking temperature of the crosslinker (Td = 150 - 180 °C) matches the low-temperature curing process of the silver paste (180 - 210 °C), avoiding the damage to the PEDOT:PSS conductive polymer network during high-temperature sintering. In addition, the maleimide group in the crosslinker can form coordination bonds with the surface oxides of silver particles (such as AgO), enhancing the adhesion between the silver layer and the silicon substrate.

[0048] Figure 1 It is a schematic flow chart of a preparation method of a main grid silver paste provided by an embodiment of the present application.

[0049] As Figure 1 shown, in the 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 the following steps:

[0050] S1. Ultrasonically treat micron silver flakes, silver nanoparticles, silver-coated tungsten, and modified carbon nanotubes in deionized water to obtain a first mixed solution;

[0051] Ultrasonic dispersion is used to uniformly mix the micron silver flakes, nanosilver particles, silver-coated tungsten and modified carbon nanotubes to avoid agglomeration and ensure uniform distribution of the conductive network.

[0052] S2, adding PEDOT:PSS aqueous solution, ionic liquid and dynamic crosslinking agent to the first mixed solution to obtain a second mixed solution;

[0053] S3, grinding the second mixed solution through a three-roll grinder for 3 to 5 times to obtain the main grid silver paste; the roller spacing of the three-roll grinder is 10 to 20 μm, and the rotation speed is 200 to 300 rpm.

[0054] The particles are further refined and evenly dispersed through high shear force to ensure that the slurry viscosity and rheology are suitable for screen printing. The roller gap (10-20μm) and rotation speed (200-300rpm) control the grinding accuracy to avoid excessive damage to the nanostructure. Multiple grinding (3-5 times) can improve the uniformity of the slurry and reduce the risk of broken screens during printing.

[0055] In some embodiments, the method for preparing the modified carbon nanotubes comprises:

[0056] In an oxygen atmosphere, the surface of multi-walled carbon nanotubes is bombarded by low-temperature plasma to obtain activated carbon nanotubes; the low-temperature plasma includes the following parameters: oxygen concentration of 50-80 vol%, power of 100-300 W, gas pressure of 10-50 Pa, and treatment time of 10-30 min;

[0057] The activated carbon tube is immersed in a solution containing acrylic acid monomer and ammonium persulfate to generate a free radical reaction to obtain the modified carbon nanotube; the mass concentration of the acrylic acid monomer is 10-30%, and the mass concentration of the ammonium persulfate is 0.5-2%.

[0058] In an oxygen atmosphere, plasma bombards the surface of multi-walled carbon nanotubes to introduce oxygen-containing functional groups (such as hydroxyl and carboxyl groups), enhance surface activity, and provide sites for subsequent grafting reactions. At the same time, through the grafting modification of acrylic acid monomers, carbon nanotubes are given hydrophilicity and their dispersibility in the slurry is improved; the carboxylic acid group can also form a chemical bond with the surface of silver particles to enhance the interface bonding strength, and as an initiator, promote the free radical polymerization reaction of acrylic acid monomers on the surface of carbon tubes.

[0059] In a third aspect, the present application provides an electrode, which is formed by sintering the main grid silver paste described in any one of the embodiments in the first aspect on the surface of a battery silicon wafer.

[0060] The highly conductive electrode formed after the main grid silver paste is sintered is responsible for collecting photogenerated carriers and conducting current through the main grid, reducing the series resistance and improving the battery conversion efficiency.

[0061] Fourthly, the present application provides a solar cell, which includes the electrode described in the embodiment of the third aspect.

[0062] The battery using this electrode has lower contact resistance and higher fill factor (FF), and is suitable for HJT batteries.

[0063] In summary, the main grid silver paste provided by the present application forms a high-performance electrode through multi-scale silver particles (micrometer + nanometer), cost reduction by silver-coated tungsten, and enhanced conductivity by modified carbon nanotubes. Specifically, the advantages are as follows:

[0064] (1) Low-cost and silver consumption reduction innovation: Replacing part of the silver powder with tungsten core (HV≥300), the silver layer coverage rate ≥95%, significantly reducing the silver usage while maintaining conductivity, meeting the industry trend of cost reduction. It is estimated that silver-coated tungsten can reduce the silver consumption by about 15% - 30%, adapting to the cost reduction demand of domestic photovoltaic silver paste. At the same time, the micro silver flakes (30 - 50 parts) and nano silver particles (10 - 20 parts) form a "micro-nano interlocking" structure, and the nano particles fill the gaps between the micro flakes, reducing the porosity and sintering temperature, further reducing energy consumption and silver consumption. In addition, through the Diels-Alder bond and TeO 2 / V 2 O 5 dynamic bond coordination, reducing the usage amount and lowering the formulation cost.

[0065] (2) High conductivity and interface optimization: The micro silver flakes provide a framework support, the nano silver particles enhance the sintering density, and the modified carbon nanotubes (aspect ratio ≥100) and silver-coated tungsten cooperate to form a three-dimensional conductive path, reducing the contact resistance. At the same time, the carboxylated carbon nanotubes (-COOH) and the sulfonic acid group (-SO 3 H) of PEDOT:PSS form hydrogen bonds, enhancing the interfacial binding force and improving the carrier collection efficiency.

[0066] (3) Stability: The flaky stacking structure of the micro silver flakes (particle size 2 - 4μm) enhances the anti-bending property, and the high hardness of the tungsten core (HV≥300) improves the wear resistance of the electrode, which is suitable for flexible components and harsh outdoor environments.

[0067] (4) Adapt to the technological iteration of N-type batteries: Suitable for the main grid electrode of HJT batteries, the PEDOT:PSS aqueous solution (8 - 15 parts) enhances the adhesion to the silicon nitride layer of the silicon substrate, forming a stable Ag-Si ohmic contact. At the same time, the dynamic cross-linking agent optimizes the sintering temperature, meeting the low-temperature process requirements of HJT and avoiding the risk of hydrogen escape from the amorphous silicon thin film. In addition, the design of low contact resistance and high fill factor (FF≥85%) adapts to high-efficiency N-type batteries and can improve the conversion efficiency.

[0068] (5) Environmental protection and process optimization: Use PEDOT:PSS aqueous solution and ionic liquid (2-5 parts) to replace organic solvents, reduce VOC emissions, and conform to the trend of green manufacturing. At the same time, ultrasonic treatment combined with three-roll grinding (roll spacing 10-20 μm, rotation speed 200-300 rpm) realizes uniform dispersion of nanoparticles and reduces the risk of broken grids. In addition, the plasma activation and acrylic grafting process of modified carbon nanotubes improve their dispersion stability in the slurry.

[0069] Thus, the main grid silver paste of this application realizes multiple advantages of low cost, high conductivity, high stability, and compatibility with N-type batteries through a composite conductive system (micro / nano silver + silver-coated tungsten + carbon nanotubes) and an environmentally friendly aqueous formula, meeting the technical requirements of the photovoltaic industry for high-efficiency silver paste.

[0070] 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 usually determined according to industry standards. If there is no corresponding industry standard, they are carried out according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0071] Example 1

[0072] This example provides a main grid silver paste, which includes the following chemical components by mass:

[0073] Micro silver flakes: 30 parts (particle size 2 μm, Zhongke Keyou);

[0074] Nano silver particles: 10 parts (particle size 80 nm, Zhongke Keyou);

[0075] Silver-coated tungsten: 5 parts (particle size 0.5 μm, silver layer thickness 50 nm, coverage rate 95%, model: AgW70);

[0076] Modified carbon nanotubes: 0.1 part (carboxylated multi-walled carbon nanotubes, particle size 5 nm, aspect ratio 100);

[0077] PEDOT:PSS aqueous solution: 8 parts (model: Clevios PH1000);

[0078] Ionic liquid: 2 parts (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, CAS No.: 174899-82-2);

[0079] Dynamic cross-linking agent: 0.5 part (benzocyclobutene-maleimide cross-linking agent);

[0080] Deionized water: 15 parts.

[0081] Based on the above main grid silver paste, this embodiment also provides a preparation method of the main grid silver paste, which includes the following steps:

[0082] S1. Ultrasonically treat micron silver flakes, nano silver particles, silver-coated tungsten, and modified carbon nanotubes in deionized water to obtain a first mixed solution;

[0083] Among them, the preparation method of the modified carbon nanotubes includes: bombarding the surface of multi-walled carbon nanotubes with low-temperature plasma in an oxygen atmosphere to obtain activated carbon tubes; the low-temperature plasma includes the following parameters: oxygen concentration is 50 vol%, power is 100 W, air pressure is 10 Pa, and treatment time is 30 min; immerse the activated carbon tubes in a solution containing acrylic acid monomer and ammonium persulfate to undergo a free radical reaction to obtain the modified carbon nanotubes; the mass concentration of the acrylic acid monomer is 10%, and the mass concentration of the ammonium persulfate is 0.5%.

[0084] S2. Add PEDOT:PSS aqueous solution, ionic liquid, and dynamic cross-linking agent to the first mixed solution to obtain a second mixed solution;

[0085] Among them, the dynamic cross-linking agent is a benzocyclobutene-maleimide cross-linking agent, and its preparation method includes the following steps:

[0086] Under nitrogen protection, dissolve benzocyclobutene (1 mol) and maleimide (1 mol) in toluene (200 mL), stir and mix evenly. Then heat to 150 °C and reflux for 6 hours. After the reaction is completed, cool to room temperature, and remove toluene by vacuum distillation to obtain a pale yellow solid crude product. Recrystallize the crude product with a mixed solvent of ethyl acetate / n-hexane (volume ratio 1:3), filter and dry. Obtain a white crystal-like benzocyclobutene-maleimide cross-linking agent.

[0087] S3. Grind the second mixed solution 3 to 5 times with a three-roll mill to obtain the main grid silver paste; the roll spacing of the three-roll mill is 10 μm and the rotation speed is 200 rpm.

[0088] Example 2

[0089] This embodiment provides a main grid silver paste, and in terms of mass parts, the main grid silver paste includes the following chemical components:

[0090] Micron silver flakes: 40 parts (particle size 3 μm, Zhongke Keyou);

[0091] Nano silver particles: 15 parts (particle size 50 nm, Zhongke Keyou);

[0092] Silver-coated tungsten: 12 parts (particle size 1.2 μm, silver layer thickness 120 nm, coverage rate 97%, model: AgW70);

[0093] Modified carbon nanotubes: 0.3 parts (carboxylated multi-walled carbon nanotubes, particle size 50 nm, aspect ratio 200);

[0094] PEDOT:PSS aqueous solution: 12 parts (model: Clevios PH1000);

[0095] Ionic liquid: 3.5 parts (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, CAS No.: 174899-82-2);

[0096] Dynamic crosslinking agent: 1.2 parts (benzocyclobutene-maleimide crosslinking agent);

[0097] Deionized water: 10 parts.

[0098] Based on the above main grid silver paste, this embodiment also provides a preparation method of the main grid silver paste, including the following steps:

[0099] S1. Ultrasonically treat micron silver flakes, nano silver particles, silver-coated tungsten and modified carbon nanotubes in deionized water to obtain a first mixed solution;

[0100] Among them, the preparation method of the modified carbon nanotubes includes: bombarding the surface of multi-walled carbon nanotubes with low-temperature plasma in an oxygen atmosphere to obtain activated carbon tubes; the low-temperature plasma includes the following parameters: oxygen concentration is 60 vol%, power is 200 W, air pressure is 30 Pa, and treatment time is 20 min; Immerse the activated carbon tubes in a solution containing acrylic monomer and ammonium persulfate to undergo a free radical reaction to obtain the modified carbon nanotubes; the mass concentration of the acrylic monomer is 20%, and the mass concentration of the ammonium persulfate is 1%.

[0101] S2. Add the PEDOT:PSS aqueous solution, ionic liquid and dynamic crosslinking agent to the first mixed solution to obtain a second mixed solution;

[0102] Among them, the dynamic crosslinking agent is a benzocyclobutene-maleimide crosslinking agent, and the preparation method includes the following steps:

[0103] Under nitrogen protection, dissolve benzocyclobutene (1 mol) and maleimide (1 mol) in toluene (200 mL), stir and mix evenly. Then heat to 150 °C and reflux for 6 hours. After the reaction is completed, cool to room temperature and remove toluene by vacuum distillation to obtain a pale yellow solid crude product. Recrystallize the crude product with a mixed solvent of ethyl acetate / n-hexane (volume ratio 1:3), filter and dry. Obtain a white crystal-like benzocyclobutene-maleimide crosslinking agent.

[0104] S3. Grind the second mixture 4 times through a three-roll mill to obtain the main grid silver paste; the roll spacing of the three-roll mill is 20 μm and the rotation speed is 300 rpm.

[0105] Example 3

[0106] This example provides a main grid silver paste. In terms of parts by mass, the main grid silver paste includes the following chemical components:

[0107] Micro silver flakes: 50 parts (particle size 4 μm, Zhongke Keyou);

[0108] Nanometer silver particles: 20 parts (particle size 100 nm, Zhongke Keyou);

[0109] Silver-coated tungsten: 20 parts (particle size 2 μm, silver layer thickness 200 nm, coverage rate 99%, model: AgW70);

[0110] Modified carbon nanotubes: 0.5 part (carboxylated multi-walled carbon nanotubes, particle size 100 nm, aspect ratio 300);

[0111] PEDOT:PSS aqueous solution: 15 parts (model: Clevios PH1000);

[0112] Ionic liquid: 5 parts (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, CAS No.: 174899-82-2)

[0113] Dynamic crosslinking agent: 2 parts (benzocyclobutene-maleimide crosslinking agent)

[0114] Deionized water: 5 parts.

[0115] Based on the above main grid silver paste, this example also provides a preparation method of the main grid silver paste, including the following steps:

[0116] S1. Ultrasonically treat micro silver flakes, nanometer silver particles, silver-coated tungsten and modified carbon nanotubes in deionized water to obtain a first mixture;

[0117] Among them, the preparation method of the modified carbon nanotubes includes: bombarding the surface of multi-walled carbon nanotubes through low-temperature plasma in an oxygen atmosphere to obtain activated carbon tubes; the low-temperature plasma includes the following parameters: oxygen concentration is 80 vol%, power is 300 W, air pressure is 50 Pa, and treatment time is 10 min; immerse the activated carbon tubes in a solution containing acrylic acid monomer and ammonium persulfate to undergo a free radical reaction to obtain the modified carbon nanotubes; the mass concentration of the acrylic acid monomer is 30%, and the mass concentration of the ammonium persulfate is 2%.

[0118] S2. Add the PEDOT:PSS aqueous solution, ionic liquid, and dynamic crosslinking agent to the first mixture to obtain a second mixture;

[0119] Among them, the dynamic crosslinking agent is a benzocyclobutene-maleimide crosslinking agent, and its preparation method includes the following steps:

[0120] Under nitrogen protection, dissolve benzocyclobutene (1 mol) and maleimide (1 mol) in toluene (200 mL), stir and mix evenly. Then heat to 150 °C and reflux for 6 hours. After the reaction is completed, cool to room temperature, and remove toluene by vacuum distillation to obtain a crude product of pale yellow solid. Recrystallize the crude product with a mixed solvent of ethyl acetate / n-hexane (volume ratio 1:3), filter and dry. Obtain a white crystal-like benzocyclobutene-maleimide crosslinking agent.

[0121] S3. Grind the second mixture 5 times through a three-roll mill to obtain the main grid silver paste; the roll spacing of the three-roll mill is 20 μm and the rotation speed is 200 rpm.

[0122] Comparative Example 1

[0123] On the basis of what is disclosed in Example 2, this example makes the following changes:

[0124] Do not add nano silver particles to the main grid silver paste.

[0125] Comparative Example 2

[0126] On the basis of what is disclosed in Example 2, this example makes the following changes:

[0127] Do not add modified carbon nanotubes to the main grid silver paste.

[0128] Comparative Example 3

[0129] On the basis of what is disclosed in Example 2, this example makes the following changes:

[0130] Do not add the PEDOT:PSS aqueous solution to the main grid silver paste.

[0131] Comparative Example 4

[0132] On the basis of what is disclosed in Example 2, this example makes the following changes:

[0133] Do not add ionic liquid to the main grid silver paste.

[0134] Comparative Example 5

[0135] On the basis of what is disclosed in Example 2, this example makes the following changes:

[0136] Do not add dynamic crosslinking agent to the main grid silver paste.

[0137] The performance of the main grid silver pastes obtained in Examples 1 to 3 and Comparative Examples 1 to 5 was measured, and the results are shown in Tables 1 and 2. The specific measurement methods are as follows:

[0138] Sheet resistance (Rsh): The resistance of the cured silver layer was measured by the four-probe method, and the average value of 5 points was taken. The measurement standard is GB / T 1551-2009.

[0139] Welding tensile force (F): The peel strength between the silver layer and the silicon substrate was measured using a tensile testing machine (such as Instron 3365) at a speed of 1 mm / s. The measurement standard is GB / T 2790-2008.

[0140] Porosity (P): SEM image analysis (such as Hitachi SU8010), and the proportion of the pore area was calculated by selecting 5 regions. The measurement standard is ASTM E2109.

[0141] Self-healing efficiency (η): After damp heat aging (85°C / 85% RH, 1000 h), the change rate of the sheet resistance before and after aging was compared: η = (Rsh_initial - Rsh_aging) / Rsh_initial × 100%. The measurement standard is IEC 61215.

[0142] Resistance to damp heat aging (ΔR): After damp heat aging (85°C / 85% RH, 1000 h), the resistance change rate: ΔR = (Rsh_aging - Rsh_initial) / Rsh_initial × 100%. The measurement standard is IEC 61215.

[0143] Table 1 Performance of the main grid silver pastes in Examples 1 to 3

[0144] Group Sheet Resistance (mΩ / sq) Welding Tensile Strength (N / mm) Porosity (%) Self-healing Efficiency (%) ΔR of Damp Heat Aging (%) Example 1 4.2 3.4 8.9 82.5 9.1 Example 2 2.6 3.9 5.2 92.4 4.2 Example 3 1.5 4.2 3.1 97.2 1.4

[0145] As can be seen from Table 1, in this application, through multi-component collaborative design (nano-silver / micro-silver interlocking, dynamic bond self-healing, carbon nanotube reinforcement), the conductivity, mechanical strength, and environmental stability of the silver paste were systematically optimized.

[0146] Table 2 Performance of the main grid silver pastes in Comparative Examples 1 to 5

[0147] Group Sheet Resistance (mΩ / sq) Welding Tensile Strength (N / mm) Porosity (%) Self-healing Efficiency (%) ΔR of Damp Heat Aging (%) Comparative Example 1 7.2 2.6 13.8 67.8 16.8 Comparative Example 2 5.1 2.2 11.8 72.3 11.2 Comparative Example 3 8.9 1.6 17.9 55.6 22.9 Comparative Example 4 8.5 2.6 8.9 66.9 15.1 Comparative Example 5 4.1 3.7 6.9 -- 8.4

[0148] As can be seen from Table 2, the absence of silver nanoparticles in Comparative Example 1 leads to a decrease in sintering activity, the voids between the micron-sized silver flakes are not filled, the conductive network is discontinuous, the porosity increases, and the self-healing ability is limited. In Comparative Example 2, the absence of carbon nanotubes weakens the three-dimensional support of the conductive network, the mechanical strength of the silver layer decreases, the crack resistance is poor, and the interfacial bonding force decreases. In Comparative Example 3, the carrier transport channel of PEDOT:PSS is lost, the conductivity drops suddenly, and the poor dispersion stability causes the silver particles to agglomerate. In Comparative Example 4, the absence of ionic liquid results in poor wettability of the silver paste, decreased printing uniformity, uneven dispersion of the dynamic cross-linking agent, and reduced self-healing efficiency. In Comparative Example 5, the absence of dynamic bonds makes the silver layer unable to self-heal, the cracks expand after hydrothermal aging, and the resistance increases significantly.

[0149] Therefore, the silver nanoparticles reduce the porosity by filling the gaps between the micron-sized silver flakes and simultaneously enhance the sintering activity. The carboxylated carbon nanotubes are combined with PEDOT:PSS through hydrogen bonds to enhance the interfacial strength and inhibit crack propagation. The self-healing ability of the Diels-Alder dynamic bonds directly determines the durability of the silver layer. The wettability and dispersion stability of the ionic liquid are the key to printing accuracy.

[0150] 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 description of the range has specifically disclosed all possible sub-ranges and the individual values within that range. For example, it should be considered that the description of the range 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 the individual numbers within the range, such as 1, 2, 3, 4, 5, and 6, 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.

[0151] 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 article, 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.

[0152] 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 to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A main grid silver paste, characterized in that: The main grid silver paste includes the following chemical components in parts by mass: 30 to 50 parts of micron silver flakes, 10 to 20 parts of nano silver particles, 5 to 20 parts of silver-coated tungsten, 0.1 to 0.5 parts of modified carbon nanotubes, 8 to 15 parts of PEDOT:PSS aqueous solution, 2 to 5 parts of ionic liquid, 0.5 to 2 parts of dynamic crosslinking agent, and 5 to 15 parts of deionized water.

2. The main grid silver paste according to claim 1, characterized in that: The particle size of the silver-coated tungsten is 0.5-2 μm, the thickness of the silver coating layer is 50-200 nm, and the coverage rate of the silver layer is ≥95%.

3. The main grid silver paste according to claim 1, characterized in that: The particle size of the nano silver particles is ≤100 nm; The particle size of the micron silver flakes is 2 to 4 μm; The modified carbon nanotubes are carboxylated multi-walled carbon nanotubes with a particle size of 5 to 100 nm and an aspect ratio of ≥100.

4. The main grid silver paste according to claim 1, characterized in that: The ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

5. The main grid silver paste according to claim 1, characterized in that: The dynamic crosslinking agent is a benzocyclobutene-maleimide crosslinking agent.

6. A method for preparing a main grid silver paste according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: S1, subjecting micron silver flakes, nanosilver particles, silver-coated tungsten and modified carbon nanotubes to ultrasonic treatment in deionized water to obtain a first mixed solution; S2, adding PEDOT:PSS aqueous solution, ionic liquid and dynamic crosslinking agent to the first mixed solution to obtain a second mixed solution; S3, grinding the second mixed solution through a three-roll grinder for 3 to 5 times to obtain the main grid silver paste; the roller spacing of the three-roll grinder is 10 to 20 μm, and the rotation speed is 200 to 300 rpm.

7. The method for preparing a main grid silver paste according to claim 6, characterized in that: The preparation method of the modified carbon nanotubes comprises: In an oxygen atmosphere, the surface of multi-walled carbon nanotubes is bombarded by low-temperature plasma to obtain activated carbon nanotubes; The activated carbon tube is immersed in a solution containing acrylic acid monomer and ammonium persulfate to generate a free radical reaction to obtain the modified carbon nanotube; the mass concentration of the acrylic acid monomer is 10-30%, and the mass concentration of the ammonium persulfate is 0.5-2%.

8. The method for preparing a main grid silver paste according to claim 7, characterized in that: The low-temperature plasma includes the following parameters: oxygen concentration is 50-80 vol%, power is 100-300 W, gas pressure is 10-50 Pa, and processing time is 10-30 min.

9. An electrode, characterized in that: The electrode is formed by sintering the main grid silver paste described in any one of claims 1 to 5 on the surface of the battery silicon wafer.

10. A solar cell, characterized in that: The solar cell comprises the electrode according to claim 9.

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