Conductive silver paste and preparation method thereof

Abstract

The invention discloses conductive silver paste and a preparation method thereof. The conductive silver paste comprises the following components in parts by weight: 80-85 parts of silver powder; 1-5 parts of a quaternary ammonium salt polyion liquid containing an epoxy group; and 10-15 parts of an organic carrier. The epoxy group on the quaternary ammonium salt polyion liquid containing the epoxy group reacts with the resin to form a cross-linked network, so that a molecular chain of the polyion liquid is locked, ion permeation channels are reduced, and ion sites are firmly locked; chain segments of the polyion liquid are adsorbed on the surface of the silver powder through the interface adsorption effect of the polyion liquid, a compact interface layer is formed, and ions are prevented from being diffused to the outside; an epoxy group is subjected to a ring-opening reaction with a hydroxyl group on the surface of the silver powder and a functional group of a base material, so that silver particles form a more continuous conductive path, and a stable covalent bond is formed; quaternary ammonium salt cations neutralize negative charges on the surface of the silver powder, electrostatic repulsion between the silver powder is reduced, interface transmission resistance is reduced, and the internal binding force of the silver paste is improved.

Description

Technical Field

[0001] This invention belongs to the field of conductive silver paste preparation technology, specifically relating to a conductive silver paste and its preparation method. Background Technology

[0002] Currently, perovskite heterojunction tandem solar cells, as a novel solar energy technology, have become a research hotspot in the photovoltaic field due to their advantages such as high conversion efficiency and low power generation cost. Conductivity, as a core indicator of conductive silver paste, directly determines the photoelectric efficiency of the device. To improve the conductivity of the paste, existing technologies employ the method of adding ionic liquids to the conductive silver paste.

[0003] Ionic liquids, as a class of low-temperature molten salts composed of organic cations and inorganic or organic anions, exist in a liquid state at or near room temperature and possess unique chemical properties, such as high ionic conductivity, low volatility, good solubility, high thermal stability, and designability. Their high ionic conductivity promises to improve the overall conductivity of the paste; good solubility helps to better disperse silver powder and reduce agglomeration; their low volatility and stability will extend the paste's lifespan; and their designability will meet the needs of pastes in various fields. However, traditional ionic liquid molecules have strong fluidity and are prone to migration within the paste, even penetrating into the substrate, causing ion leakage. Ion leakage not only reduces conductivity but also corrodes the substrate, affecting the overall performance of the device.

[0004] Therefore, designing a conductive silver paste that simultaneously possesses high conductivity and prevents ion leakage has become a problem to be solved in this field. Summary of the Invention

[0005] To address the problems in the prior art, the present invention aims to provide a conductive silver paste and its preparation method.

[0006] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows: A conductive silver paste comprising the following components in parts by weight: 80-85 parts silver powder 1-5 parts of epoxy-containing quaternary ammonium salt polyionic liquid 10-15 parts of organic carrier Furthermore, the silver powder is made from silver-coated copper powder, flake silver powder, and nano-spherical silver powder.

[0007] Furthermore, the silver-coated copper powder has a particle size of 3-8 μm and a tap density of 5.6-6.2 g / cm³. 3 .

[0008] Furthermore, the flake-shaped silver powder has a particle size of 2-5 μm and a tap density of 3.7-6.2 g / cm³. 3 .

[0009] Furthermore, the diameter of the nanosphere silver powder is 20-80 nm.

[0010] Furthermore, the epoxy-containing quaternary ammonium salt polyionic liquid has the following structure: -R1- and -R4-: Linking groups, usually methylene chains or other organic segments, used to link quaternary ammonium salt cations and epoxy groups; R2 and R3: are usually alkyl or other substituents such as methyl (-CH3), ethyl (-CH2CH3); -CH(O)-CH2-CH2-: Characteristic chain segment unit formed after ring opening of the epoxy group; N + The quaternary ammonium salt cation center is covalently bonded to substituents R1, R2, R3, and R4, respectively, forming an sp... 3 The hybrid tetrahedral solid structure; the positive charge carried by N+ is the core charged unit of the polyionic liquid, and the corresponding equilibrium anion is X. - ; X - Balanced anions, commonly Cl- - ,Br - BF4 - and PF6 - These factors affect the solubility and conductivity of polyionic liquids. n: degree of aggregation, representing the number of repeating units, typically between tens and hundreds.

[0011] Furthermore, the organic carrier includes a resin, a solvent, and additives; The resin is selected from one or a combination of epoxy resin, acrylic resin, polyester, and polyurethane. The solvent includes one or a combination of alcohols, esters, and ethers; The additives include one or a combination of several of the following: dispersants, coupling agents, curing agents, and thixotropic agents.

[0012] Furthermore, the dispersant is one or a mixture of several of sodium polyacrylate, sodium citrate, BYK-164, BYK-9076, and ethyl cellulose; The coupling agent is one or a combination of two of the following: organosilicon coupling agents and titanate coupling agents; The curing agent includes a cationic curing agent or an anionic curing agent. The cationic curing agent is a boron trifluoride-ethylamine complex or an amine-blocked hexafluoroantimonate. The anionic curing agent is a tertiary amine curing agent or an imidazole curing agent. The tertiary amine curing agent is one or a combination of several of o-hydroxybenzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, triethylamine, and triethanolamine. The imidazole curing agent is one or a combination of several of 2-methylimidazole, 2-ethyl-4-methylimidazole, and 2-phenylimidazole. The thixotropic agent is sodium polyamide.

[0013] This invention also discloses a method for preparing conductive silver paste, comprising the following steps: S1) Preparation of epoxy-containing quaternary ammonium salt polyionic liquids: A halogenated hydrocarbon containing an epoxy group and a tertiary amine are added to ethanol or water and stirred at 0-5°C. After the reaction is completed, the polymer monomer is obtained by recrystallization from acetone and vacuum drying. The obtained polymer monomer product is dissolved in ethanol to prepare a monomer solution. An initiator is added to carry out a polymerization reaction to form a polymer solution. The pH of the polymer solution is adjusted to neutral, unreacted monomers are washed away, centrifuged, and dried to obtain a white solid polyionic liquid. S2) Preparation of organic carriers: The resin, solvent, and additives are mixed and stirred evenly to obtain an organic carrier. S3) Add the white solid polyionic liquid obtained in step S1 to the organic support obtained in step S2, stir at room temperature for 1-3 hours to fully dissolve and disperse, and obtain the support liquid; S4) Add the carrier liquid to the silver powder, stir evenly to obtain a semi-finished silver paste, and grind it with a three-roll mill according to the gap between the fast rollers until the fineness of the silver paste reaches below 10µm. After the silver paste is rolled, it is packaged and stored at low temperature to obtain the desired conductive silver paste product.

[0014] Furthermore, in step S4, a three-roll mill is used to grind the silver paste with a fast roller gap of 90µm-60µm, a medium roller gap of 60µm-30µm, and a slow roller gap of 30µm-20µm. Each pair of gaps is ground 2-3 times until the fineness of the silver paste reaches below 10µm.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Inhibit ion leakage: The epoxy groups on the epoxy-containing quaternary ammonium salt polyionic liquid react with the resin to form a cross-linked network, which further locks the polyionic liquid molecular chain, reduces ion permeation channels, and firmly locks the ion sites; the interfacial adsorption of the polyionic liquid causes its chain segments to adsorb on the surface of silver powder, forming a dense interfacial layer that hinders the diffusion of ions to the outside. 2. Enhanced conductivity of silver paste: Epoxy groups can undergo ring-opening reactions with hydroxyl groups on the surface of silver powder and functional groups of the substrate, reducing silver powder agglomeration and allowing silver particles to form more continuous conductive pathways; Quaternary ammonium salt cations can neutralize the negative charges generated on the surface of silver powder due to oxidation and impurity adsorption, reducing electrostatic repulsion between silver powder particles, making particle contact tighter, and reducing contact resistance caused by physical gaps; The ionic conductivity of polyionic liquids can fill the insulating areas between silver powder particles, synergistically reducing contact resistance; 3. Enhance the adhesion of silver paste to the substrate: The epoxy groups react with the groups on the substrate surface to form stable covalent bonds; the epoxy groups can react with the hydroxyl groups on the surface of silver powder to form a cross-linking network, which firmly fixes the silver powder particles in the system; the quaternary ammonium salt cations are tightly bound to the slightly negatively charged surface of silver powder through electrostatic adsorption, which prevents the silver powder from separating from the resin matrix and enhances the internal bonding force of the silver paste. At the same time, the entanglement of polymer chains further enhances the tightness of the bonding of the components inside the silver paste. Detailed Implementation

[0016] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0017] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0018] On one hand, the present invention discloses a conductive silver paste comprising the following components in parts by weight: 80-85 parts silver powder 1-5 parts of epoxy-containing quaternary ammonium salt polyionic liquid 10-15 parts of organic carrier.

[0019] In some implementations, silver powder, as the main component of conductive silver paste, plays a crucial role in the paste's conductivity. The silver powder is made from silver-coated copper powder, flake silver powder, and nanosphere silver powder. The combination of flake and nanosphere silver powder increases the contact area of ​​the silver powder, thereby improving conductivity.

[0020] In some specific embodiments, the silver-coated copper powder has a particle size of 3-8 μm and a tap density of 5.6-6.2 g / cm³. 3 It has excellent fluidity and is easy to print.

[0021] In some specific embodiments, the flake silver powder has a particle size of 2-5 μm and a tap density of 3.7-6.2 g / cm³. 3 It serves to thicken the mixture.

[0022] In some specific embodiments, the diameter of the nanosphere silver powder is 20-80nm, which has a large specific surface area and high activation energy. It can be melted at 100-120℃ as a low melting point metal powder to wet the surface of silver-coated copper powder and flake silver powder, making the contact between conductive particles denser. In addition, it greatly improves the contact between silver powder and substrate, avoiding the problem of poor conductivity caused by the main bonding between silver powders with resin.

[0023] In some embodiments, epoxy-containing quaternary ammonium salt polyionic liquids have the following structures: -R1- and -R4-: Linking groups, usually methylene chains or other organic segments, used to link quaternary ammonium salt cations and epoxy groups; R2 and R3: are usually alkyl or other substituents such as methyl (-CH3), ethyl (-CH2CH3); -CH(O)-CH2-CH2-: Characteristic chain segment unit formed after ring opening of the epoxy group; N + The quaternary ammonium salt cation center is covalently bonded to substituents R1, R2, R3, and R4, respectively, forming an sp... 3 The hybrid tetrahedral solid structure; the positive charge carried by N+ is the core charged unit of the polyionic liquid, and the corresponding equilibrium anion is X. - ; X - Balanced anions, commonly Cl- - ,Br - BF4 - and PF6 - These factors affect the solubility and conductivity of polyionic liquids. n: degree of aggregation, representing the number of repeating units, typically between tens and hundreds.

[0024] Epoxy-containing quaternary ammonium salt polyionic liquids have a long-chain polymer network structure and a large molecular weight. This network not only serves as an ion channel to improve conductivity, but also locks its own ions through steric hindrance. At the same time, during the curing process, the epoxy groups can undergo cross-linking reactions with the hydroxyl groups on the surface of silver powder and the resin. The resulting three-dimensional cross-linked structure can fix the ions and ensure conduction with the help of quaternary ammonium salt ions, which meets the core requirements of conductive silver paste.

[0025] In some embodiments, the organic carrier mainly includes resins, solvents, and additives.

[0026] In some specific embodiments, the resin can be epoxy resin, acrylic resin, polyester, polyurethane, etc., accounting for 3.8%-7.8% of the total mass of the silver paste, and its main function is to disperse and bind the silver powder.

[0027] In some specific embodiments, the solvent includes alcohols, esters, ethers, etc., accounting for 2.9%-6.9% of the total mass of the silver paste, and is mainly used to dissolve resins and additives, and adjust the viscosity of the paste, etc.

[0028] In some specific embodiments, the additives mainly include dispersants, coupling agents, curing agents, thixotropic agents, etc., accounting for 2%-6% of the total mass of the silver paste. The dispersant mainly serves to prevent silver powder agglomeration; the dispersant is one or a mixture of several selected from sodium polyacrylate, sodium citrate, BYK-164, BYK-9076, and ethyl cellulose. The coupling agent mainly enhances the bonding force between the silver powder and the resin; the coupling agent is one or a combination of two selected from organosilicon coupling agents and titanate coupling agents, with KH550 being the preferred organosilicon coupling agent. The curing agent primarily enables the resin in the silver paste to undergo a cross-linking reaction. Curing agents include cationic and anionic curing agents. Cationic curing agents are mainly boron trifluoride-ethylamine complexes or amine-blocked hexafluoroantimonate. Anionic curing agents are mainly tertiary amine curing agents and imidazole curing agents. Tertiary amine curing agents are one or a combination of several of o-hydroxybenzyl dimethylamine (DMP-10), 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), triethylamine, and triethanolamine. Imidazole curing agents are one or a combination of several of 2-methylimidazole, 2-ethyl-4-methylimidazole, and 2-phenylimidazole. Thixotropic agents are mainly used to adjust the rheological properties of the paste, and sodium polyamide is preferred.

[0029] On the other hand, the present invention also discloses a method for preparing conductive silver paste, comprising the following steps: S1) Preparation of epoxy-containing quaternary ammonium salt polyionic liquids: A halogenated hydrocarbon containing an epoxy group (such as epichlorohydrin, epibromopropane, etc.) and a tertiary amine (such as trimethylamine, triethylamine, pyridine, etc.) are added to ethanol or water at a molar ratio of 1:1.1~1.2. The mixture is stirred and reacted at 0-5℃ for 4-6 hours. After the reaction, the product is recrystallized from acetone and dried under vacuum to obtain the polymer monomer. The obtained polymer monomer product is dissolved in ethanol to prepare a 30-40 wt% monomer solution. An initiator with a molar amount of 0.03-0.04 times the monomer is added, and polymerization is carried out at room temperature for 8-12 hours to form a polymer solution. The polymer solution is adjusted to neutral by adding NaHCO3, etc., and washed 2-3 times with diethyl ether to remove unreacted monomer. After centrifugation, the product is dried in a vacuum oven at 40-60℃ to obtain a white solid polyionic liquid. S2) Preparation of organic carriers: The resin, solvent, and additives are mixed and stirred evenly to obtain an organic carrier. S3) Add the white solid polyionic liquid obtained in step S1 to the organic support obtained in step S2, stir at room temperature for 1-3 hours to fully dissolve and disperse, and obtain the support liquid; S4) Add the carrier liquid to the silver powder and stir evenly to obtain a semi-finished silver paste. Then, use a three-roll mill to grind the silver paste with a fast roller gap of 90µm-60µm, a medium roller gap of 60µm-30µm, and a slow roller gap of 30µm-20µm. Grind each pair of gaps 2-3 times until the fineness of the silver paste reaches below 10µm. After the silver paste is rolled, package it and store it at a low temperature to obtain the desired conductive silver paste product.

[0030] Example 1 A conductive silver paste comprising the following components in parts by weight: 85 parts silver powder 1 part of epoxy-containing quaternary ammonium salt polyionic liquid 14.7 portions of organic carrier.

[0031] In this embodiment, silver powder, as the main component of the conductive silver paste, plays a crucial role in the conductivity of the paste. The silver powder is composed of 40 parts of silver-coated copper powder, 35 parts of flake silver powder, and 10 parts of nano-spherical silver powder. The combination of flake silver powder and nano-spherical silver powder can increase the contact area of ​​the silver powder and improve the conductivity.

[0032] The silver-coated copper powder has a particle size of 4 μm and a tap density of 5.8 g / cm³. 3 It has excellent fluidity and is easy to print.

[0033] The flake-shaped silver powder has a particle size of 4 μm and a tap density of 4.8 g / cm³. 3 It serves to thicken the mixture.

[0034] The nanosphere silver powder has a diameter of 50nm, a large specific surface area and a high activation energy. It can be melted at 100-120℃ as a low melting point metal powder to wet the surface of silver-coated copper powder and flake silver powder, making the contact between conductive particles denser. In addition, it greatly improves the contact between silver powder and substrate, avoiding the problem of poor conductivity caused by the main bonding between silver powders with resin.

[0035] Epoxy-containing quaternary ammonium salt polyionic liquids have a long-chain polymer network structure and a large molecular weight. This network not only serves as an ion channel to improve conductivity, but also locks its own ions through steric hindrance. At the same time, during the curing process, the epoxy groups can undergo cross-linking reactions with the hydroxyl groups on the surface of silver powder and the resin. The resulting three-dimensional cross-linked structure can fix the ions and ensure conduction with the help of quaternary ammonium salt ions, which meets the core requirements of conductive silver paste.

[0036] The organic carrier comprises 5.8 parts resin, 4.9 parts solvent, and 4 parts additives. The resin includes 2.5 parts bisphenol F epoxy resin, 1.8 parts bisphenol A epoxy resin, and 1.5 parts polyurethane resin, and its main function is to disperse and bind the silver powder.

[0037] The solvents include 2.4 parts of diethylene glycol butyl ether acetate and 2.5 parts of dioctyl phthalate, which are mainly used to dissolve resins and additives and adjust the viscosity of slurry.

[0038] Additives include dispersants, coupling agents, curing agents, and thixotropic agents.

[0039] The dispersant mainly serves to prevent silver powder from agglomerating, and 0.6 parts of BYK-164 are used.

[0040] The coupling agent mainly enhances the bonding force between silver powder and resin, including 0.8 parts of organosilicon coupling agent and 1 part of titanate coupling agent. The organosilicon coupling agent is KH550.

[0041] The curing agent mainly enables the resin in the silver paste to undergo a cross-linking reaction. The curing agent includes a cationic curing agent, and the cationic curing agent is 0.8 parts of boron trifluoride-monoethylamine complex.

[0042] Thixotropic agents are mainly used to adjust the rheological properties of slurries, and 0.8 parts of sodium polyamide are used.

[0043] A method for preparing conductive silver paste includes the following steps: S1) Preparation of epoxy-containing quaternary ammonium salt polyionic liquids: Epichlorohydrin and trimethylamine were added to ethanol at a molar ratio of 1:1.2 and reacted under low temperature (0°C) with stirring for 4 hours. After the reaction was completed, the polymer monomer was obtained by recrystallization from acetone and vacuum drying. The obtained polymer monomer product was dissolved in ethanol to prepare a 30 wt% monomer solution, and an initiator with a molar amount of 0.03 times the monomer was added. The polymer solution was stirred at room temperature for 8 hours to form a polymer solution. NaHCO3 was added to the polymer solution to adjust the pH to neutral. Unreacted monomers were removed by washing three times with diethyl ether. After centrifugation, the solution was dried in a vacuum oven at 50°C for 24 hours to obtain a white solid polyionic liquid poly(2,3-epoxypropyltrimethylammonium chloride). S2) Preparation of organic carriers: Mix 5.8 parts of resin, 4.9 parts of solvent, and 4 parts of additive until homogeneous to obtain an organic carrier; S3) Add the white solid polyionic liquid obtained in step S1 to the organic support obtained in step S2, stir at room temperature for 1 hour to fully dissolve and disperse, and obtain the support liquid; S4) Add the carrier liquid to the silver powder and stir evenly to obtain a semi-finished silver paste. Then, use a three-roll mill to grind the silver paste with a fast roller gap of 90µm-60µm, a medium roller gap of 60µm-30µm, and a slow roller gap of 30µm-20µm. Grind each pair of gaps twice until the fineness of the silver paste reaches below 10µm. After the silver paste is rolled, package it and store it at a low temperature to obtain the desired conductive silver paste product.

[0044] Example 2 The difference between this embodiment and Embodiment 1 is that in this embodiment, poly(2,3-epoxypropyltriethylammonium chloride) is used instead of poly(2,3-epoxypropyltrimethylammonium chloride) in Embodiment 1.

[0045] The preparation steps of poly(2,3-epoxypropyltriethylammonium chloride) polyionic liquid are as follows: In a 250 mL three-necked round-bottom flask, 100 mL of anhydrous ethanol was added. The mixture was cooled in an ice-salt bath. Then, 1 mol and 81 mL of epichlorohydrin and 1.2 mol and 167 mL of triethylamine were added sequentially. The mixture was stirred for 4 h. After the reaction was complete, the product was rotary evaporated to obtain a pale yellow oily solid. 300 mL of acetone was added to the crude product, and the mixture was stirred in an ice bath to induce crystallization. The precipitated solid was collected by vacuum filtration. The solid was washed three times with 50 mL of cold acetone to further remove impurities. The resulting pale yellow solid was dried in a vacuum oven at 50 °C to obtain the GTEA monomer. Weigh 30g of GTEA monomer and place it in a 100mL single-necked flask. Add 70g of anhydrous ethanol to prepare a 30wt% monomer solution. While stirring continuously at room temperature, add the initiator (…). (monomers and ( The molar ratio of the initiator to the polymer solution was 1:0.03, and the reaction was continued for 8 hours. After the reaction was completed, a small amount of solid NaHCO3 was added to the polymer solution to adjust the pH of the reaction system to neutral to quench the initiator. The polymer solution was poured into stirred diethyl ether (about 500 mL), at which point the polymer precipitated. The supernatant was discarded, and this washing operation was repeated 3 times. After centrifuging the polymer, the resulting white solid was dried in a vacuum oven at 50 °C to obtain the final product, poly(2,3-epoxypropyltriethylammonium chloride) polyionic liquid.

[0046] The remaining steps are the same as in Example 1.

[0047] Example 3 The difference between this embodiment and Example 1 is that in this embodiment, poly(epoxypropylbenzyldimethylammonium chloride) is used instead of poly(2,3-epoxypropyltrimethylammonium chloride) in Example 1.

[0048] The preparation steps of poly(glycidylbenzyldimethylammonium chloride) polyionic liquid are as follows: At 0 °C, 1 mol of epichlorohydrin and 1.2 mol of N,N-dimethylbenzylamine were added to 100 mL of anhydrous ethanol and stirred for 4 h. After the reaction was complete, a pale yellow oil was obtained by rotary evaporation. The crude product was transferred to a beaker, cooled in an ice bath, and stirred. 300 mL of acetone was added, and the mixture was stirred and ground until a solid precipitated. The solid was filtered and washed with 50 mL of cold acetone to thoroughly remove residual raw materials and organic impurities. The obtained solid was dried in a vacuum drying oven at 50 °C to obtain purified epichlorohydrin benzyl dimethyl ammonium chloride monomer. Weigh 30 g of glycidylbenzyldimethylammonium chloride monomer and place it in a 100 mL single-necked flask. Add 70 g of anhydrous ethanol, stir to dissolve, and prepare a 30 wt% solution. Slowly add (…) while stirring at room temperature. (monomers and ( The molar ratio of the polymers was 1:0.03, and the reaction was continued with stirring at room temperature for 8 hours. After the reaction was complete, a small amount of solid NaHCO3 was slowly added to the viscous polymer solution to adjust the pH of the reaction system to neutral. The neutralized polymer solution was then slowly poured into a large amount of diethyl ether, and the polymer precipitated out as a fibrous or flocculent precipitate. The polymer was allowed to settle, and the supernatant was discarded. 100 mL of fresh diethyl ether was added to the precipitated polymer, and the mixture was shaken and washed. After settling, the diethyl ether was discarded. After several washes, the polymer was centrifuged, and the supernatant was discarded to obtain a pale yellow solid polymer. This solid polymer was dried in a vacuum oven at 50°C for 24 hours to obtain the final product, poly(epoxypropylbenzyl dimethyl ammonium chloride) polyionic liquid.

[0049] The remaining steps are the same as in Example 1. Comparative Example 1 In this comparative example, a small molecule ionic liquid (1-ethyl-3-methylimidazolium nitrate) was used instead of poly(2,3-epoxypropyltrimethylammonium chloride) in Example 1, and the rest was the same as in Example 1.

[0050] The pastes from the examples and comparative examples were screen-printed onto the surface of perovskite heterojunction tandem solar cell substrates and cured in a 120°C oven for 20 minutes. The resistivity, contact resistance, tensile strength of the grid lines, and ion leakage of the paste were tested. The test results are shown in Table 1. The test methods are as follows: 1. Resistivity Test: A four-probe ohmmeter is used to test the resistance between the two ends of the electrodes. A resistance meter is used to test the resistance between two points on the grid line, and a 3D microscope is used to test the width and height of the grid line. The resistivity value can be calculated according to the resistivity formula: Resistivity = Resistance / Main grid width × Main grid height.

[0051] 2. Ion leakage test: This invention uses an "immersion-ion chromatography" method to test ion leakage performance, and the specific steps are as follows: Test sample preparation: The cured silver paste electrode was cut into 1cm×1cm square samples, the surface was wiped with anhydrous ethanol, and then vacuum dried for 2 hours to remove residual solvent. The samples were then weighed accurately (recorded as m1).

[0052] Immersion extraction: The sample was completely immersed in 50 mL of deionized water (the water was ultrapure water with a resistivity ≥18.2 MΩ•cm) and statically soaked in a constant temperature water bath at 25℃ for 1000 h. During this period, the solution was prevented from evaporating and deionized water was added periodically to maintain a constant volume.

[0053] Ion detection: Take 20 mL of the soaking aqueous solution and detect chloride ions using an ion chromatograph (equipped with an anion exchange column, eluent is a mixed solution of 20 mmol / L Na2CO3 and 10 mmol / L NaHCO3, flow rate 1.0 mL / min). Chloride ions are derived from the equilibrium anions of polyionic liquids or small molecule ionic liquids. (C , unit mg / L)

[0054] Leakage calculation: Ion leakage (Q) is calculated using the following formula: Q = (c×V) / (m1×S), where V is the volume of the immersion liquid (L) and S is the sample surface area (cm²). 2 The calculation results are expressed in μg / cm³. 2 This indicates that the smaller the value, the weaker the ion leakage.

[0055] Parallel validation: Three parallel samples are set up for each group of samples, and the average value of the test results is taken as the final data to ensure that the test error is ≤5%.

[0056] 3. Welding tensile test: Conductive silver paste is printed onto the silicon wafer by screen printing, cured at low temperature to form a conductive silver grid, solder ribbon is welded onto the conductive silver grid, and the tensile strength of the silver electrode is tested using a tensile testing machine.

[0057] 4. Contact resistance: After printing specific patterns of perovskite heterojunction tandem cell silver paste onto a silicon wafer by screen printing and drying and curing, the contact resistance between the cured electrode and the substrate can be detected by using the four-probe method.

[0058] Table 1 As shown in Table 1, Comparative Example 1, which added small molecule ionic liquid, exhibited higher resistivity, higher contact resistance, lower welding pull, and higher ion migration. In contrast, Examples 1-3, after adding epoxy-containing quaternary ammonium salt polyionic liquid, showed a significant decrease in resistivity and contact resistance, a significant increase in welding pull, and a decrease in ion migration. This demonstrates that epoxy-containing quaternary ammonium salt polyionic liquid can significantly improve the conductivity and adhesion of silver paste, effectively prevent ion leakage, and effectively enhance the overall performance of silver paste, thus solving the ion leakage problem of small molecule ionic liquid.

[0059] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0060] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A conductive silver paste, characterized in that, The components include the following parts by weight: 80-85 parts silver powder 1-5 parts of epoxy-containing quaternary ammonium salt polyionic liquid 10-15 parts of organic carrier.

2. The conductive silver paste according to claim 1, characterized in that, The silver powder is made from silver-coated copper powder, flake silver powder, and nano-spherical silver powder.

3. The conductive silver paste according to claim 2, characterized in that, The silver-coated copper powder has a particle size of 3-8 μm and a tap density of 5.6-6.2 g / cm³. 3 .

4. The conductive silver paste according to claim 2, characterized in that, The flake-shaped silver powder has a particle size of 2-5 μm and a tap density of 3.7-6.2 g / cm³. 3 .

5. The conductive silver paste according to claim 2, characterized in that, The diameter of the nanosphere silver powder is 20-80 nm.

6. The conductive silver paste according to claim 1, characterized in that, The epoxy-containing quaternary ammonium salt polyionic liquid has the following structure: -R1- and -R4-: Linking groups used to connect quaternary ammonium salt cations and epoxy groups; R2 and R3: Indicate alkyl or other substituents; -CH(O)-CH2-CH2-: Characteristic chain segment unit formed after ring opening of the epoxy group; N + The quaternary ammonium salt cation center is covalently bonded to substituents R1, R2, R3, and R4, respectively, forming an sp... 3 Hybrid tetrahedral solid configuration; N + The positive charge it carries is the core charged unit of the polyionic liquid, and the corresponding equilibrium anion is X. - ; X - Balanced anions affect the solubility and conductivity of polyionic liquids; n: degree of aggregation, representing the number of repeating units.

7. The conductive silver paste according to claim 1, characterized in that, The organic carrier includes resin, solvent, and additives; The resin is selected from one or a combination of epoxy resin, acrylic resin, polyester, and polyurethane. The solvent includes one or a combination of alcohols, esters, and ethers; The additives include one or a combination of several of the following: dispersants, coupling agents, curing agents, and thixotropic agents.

8. The conductive silver paste according to claim 7, characterized in that, The dispersant is one or a mixture of several of the following: sodium polyacrylate, sodium citrate, BYK-164, BYK-9076, and ethyl cellulose. The coupling agent is one or a combination of two of the following: organosilicon coupling agents and titanate coupling agents; The curing agent includes a cationic curing agent or anionic curing agent. The cationic curing agent is a boron trifluoride-ethylamine complex or an amine-blocked hexafluoroantimonate. The anionic curing agent is a tertiary amine curing agent or an imidazole curing agent. The tertiary amine curing agent is one or a combination of several of o-hydroxybenzyldimethylamine, 2,4,6-tris(dimethylaminomethyl)phenol, triethylamine, and triethanolamine. The imidazole curing agent is one or a combination of several of 2-methylimidazole, 2-ethyl-4-methylimidazole, and 2-phenylimidazole. The thixotropic agent is sodium polyamide.

9. A method for preparing conductive silver paste, characterized in that, Includes the following steps: S1) Preparation of epoxy-containing quaternary ammonium salt polyionic liquids: A halogenated hydrocarbon containing an epoxy group and a tertiary amine are added to ethanol or water and stirred at 0-5°C. After the reaction is completed, the polymer monomer is obtained by recrystallization from acetone and vacuum drying. The obtained polymer monomer product is dissolved in ethanol to prepare a monomer solution. An initiator is added to carry out a polymerization reaction to form a polymer solution. The pH of the polymer solution is adjusted to neutral, unreacted monomers are washed away, centrifuged, and dried to obtain a white solid polyionic liquid. S2) Preparation of organic carriers: The resin, solvent, and additives are mixed and stirred evenly to obtain an organic carrier. S3) Add the white solid polyionic liquid obtained in step S1 to the organic support obtained in step S2, stir at room temperature for 1-3 hours to fully dissolve and disperse, and obtain the support liquid; S4) Add the carrier liquid to the silver powder, stir evenly to obtain a semi-finished silver paste, and grind it with a three-roll mill according to the gap between the fast rollers until the fineness of the silver paste reaches below 10µm. After the silver paste is rolled, it is packaged and stored at low temperature to obtain the desired conductive silver paste product.

10. The method for preparing a conductive silver paste according to claim 9, characterized in that, In step S4, a three-roll mill is used to grind the silver paste with a fast roller gap of 90µm-60µm, a medium roller gap of 60µm-30µm, and a slow roller gap of 30µm-20µm. Each pair of gaps is ground 2-3 times until the fineness of the silver paste reaches below 10µm.

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