Low-temperature conductive paste and raw material composition thereof, and heterojunction cell electrode and manufacturing method therefor

Abstract

The present disclosure provides a low-temperature conductive paste and a raw material composition thereof, and a heterojunction cell electrode and a manufacturing method therefor. The raw material composition comprises the following components in percentage by mass: 2%-10% of a composite resin, 2%-4% of an organic solvent, 0.2%-1% of an auxiliary agent, and 85%-94% of conductive metal powder. The resin comprises a component A and a component B. The component A comprises a polyol and a blocked isocyanate. The component B comprises a curing agent and a resin. The present disclosure further provides a low-temperature conductive paste prepared from the raw material composition, a heterojunction cell electrode manufactured from the low-temperature conductive paste, a manufacturing method for the electrode, and a heterojunction cell manufactured from the electrode. The low-temperature conductive paste and the heterojunction cell electrode provided by the present disclosure have high conductivity and weather resistance.

Description

Low-temperature conductive paste and raw material composition thereof, heterojunction battery electrode and preparation method thereof

[0001] Related applications

[0002] This application claims priority to the Chinese invention patent application with application number 202410218709.2 filed on February 28, 2024, and cites the entire disclosure of the above patent application as part of this application. Technical Field

[0003] The present disclosure relates to the technical field of battery silver paste, and in particular to a low-temperature conductive paste and a raw material composition thereof, a heterojunction battery electrode and a preparation method thereof. Background Art

[0004] In recent years, the photovoltaic industry has experienced rapid growth, driven by technology-driven cost reduction and efficiency improvement. Heterojunction batteries (HJTs) boast a theoretical cell efficiency of up to 28.5%. Their high efficiency, simple process, excellent temperature characteristics, and low energy consumption make them the long-term trend in future battery technology development. However, HJTs currently have a low market share, primarily due to high manufacturing costs. Low-temperature conductive silver paste is a core auxiliary material for HJTs, accounting for approximately 50% of the non-silicon cost of the battery. Therefore, breakthroughs in low-cost, high-performance, low-temperature pastes are crucial for the industrialization of HJTs. The conductive phase of HJTs is primarily composed of precious metal silver powder, which accounts for over 98% of the total cost of the paste, making it the most significant factor influencing paste cost. Furthermore, limited silver reserves and prices mean limited potential for cost reduction, a factor that will inevitably constrain the future large-scale production of HJTs.

[0005] Low-temperature, low-silver pastes prepared by replacing silver powder with base metals can be used in heterojunction solar cells. The development of low-temperature, low-silver pastes is fully compatible with existing screen printing lines, simplifies the process, requires no additional investment, and significantly reduces paste costs, earning widespread industry recognition. However, due to the limitations of metal powder processing, these pastes suffer from uneven particle size distribution, poor printability, and are unable to meet the requirements of narrow line width printing. Furthermore, base metals are easily oxidized. Consequently, the overall performance of low-silver pastes is inferior to that of pure silver pastes. Summary of the Invention

[0006] In order to solve the above problems, the present disclosure aims to provide a low-temperature conductive paste and its raw material composition, a heterojunction battery electrode and its preparation method. The low-temperature conductive paste has high conductivity and weather resistance.

[0007] In order to achieve the above object, the present disclosure provides a raw material composition of a low-temperature conductive paste, which comprises 2%-10% of a composite resin, 2%-4% of an organic solvent, 0.2%-1% of an additive, and 85%-94% of a conductive metal powder, based on the total mass of the raw material composition as 100%.

[0008] Wherein, the composite resin comprises component A and component B;

[0009] Component A includes polyol and blocked isocyanate; component B includes curing agent and resin.

[0010] In the above raw material composition, the conductive metal powder includes a first metal powder and a second metal powder, the first metal powder has a D50 particle size of 3μm-4μm and a tap density of 3.5g / cc or more; the second metal powder has a D50 particle size of 0.8μm-1.5μm and a tap density of 4g / cc or more.

[0011] The first metal powder used in the present disclosure can improve the conductivity of the slurry, but too much of the first metal powder will lead to a decrease in the printability of the slurry and also affect the adhesion of the cured product; the second metal powder can improve the printability of the slurry, but will lead to an increase in the resistance and viscosity of the slurry, which will affect the efficiency of the heterojunction battery and limit its application. The present disclosure can make the conductive slurry have high conductivity, printability, battery efficiency and application prospects by controlling the ratio of the first metal powder and the second metal powder. In some specific embodiments, the mass ratio of the first metal powder to the second metal powder is 25:75-80:20, and can be further controlled to be 35:65-75:25. Specifically, the mass ratio of the first metal powder to the second metal powder can be specific values ​​such as 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, and ranges with any two of the above specific values ​​as endpoints.

[0012] Optionally, the mass ratio of the first metal powder to the second metal powder is 50-70:30-50. That is, the mass ratio of the first metal powder to the second metal powder is 50:50-70:30.

[0013] In the above raw material composition, the material of the conductive metal powder may include one or a combination of two or more of silver-coated copper powder, tin alloy powder, copper powder and silver powder. Specifically, the first metal powder may include one or a combination of two or more of silver-coated copper powder, tin alloy powder, copper powder and silver powder, and the second metal powder may include one or a combination of two or more of silver-coated copper powder, tin alloy powder, copper powder and silver powder. Among them, the tin alloy powder may specifically include one or a combination of two or more of tin-bismuth alloy, tin-nickel alloy, tin-copper alloy, tin-bismuth-silver alloy, tin-silver-copper alloy, etc. In some specific embodiments, the tin alloy powder may be selected from tin-bismuth-silver alloy. The materials of the first metal powder and the second metal powder may be the same or different.

[0014] According to specific embodiments of the present disclosure, the first metal powder and / or the second metal powder may include silver powder, a silver-coated copper powder, a tin alloy powder, a copper powder, or a combination of two or more thereof. Compared to using pure silver as the conductive metal powder or using a single base metal powder (such as silver-coated copper powder, tin alloy powder, or copper powder) as the conductive metal powder, using a combination of silver powder and an alkali metal powder as the first metal powder and / or the second metal powder can maintain the conductive metal powder's high conductivity while reducing costs.

[0015] Optionally, the first metal powder includes silver powder and silver-coated copper powder, and the second metal powder includes silver powder, silver-coated copper powder and tin alloy powder.

[0016] Most existing conductive pastes use silver powder as the conductive metal powder to produce pure silver paste. Some conductive pastes attempt to add base metals to the conductive metal powder instead of silver powder to produce low-silver pastes. However, the performance of existing low-silver pastes is significantly different from that of pure silver pastes. The present disclosure adds base metal powder (silver-coated copper powder, tin alloy powder, copper powder, etc.) to the conductive metal powder, and uses this conductive metal powder to compound with a novel organic system (composite resin) established in the present disclosure to form a low-silver low-temperature conductive paste for preparing heterojunction batteries. The synergistic effect between the conductive metal powder and the composite resin improves the conductivity, adhesion, weather resistance, and printability of the paste, thereby improving the overall performance of the heterojunction battery made with the paste while significantly reducing manufacturing costs.

[0017] In the above raw material composition, the mass proportion of silver powder in the conductive metal powder in the raw material composition can be less than or equal to 30%, that is, the above raw material composition can maintain better slurry properties when adding a small amount of silver powder (mass proportion is greater than 0% and less than or equal to 30%) or without adding silver powder (mass proportion is 0%). In some specific embodiments, the mass proportion of silver powder in the conductive metal powder in the raw material composition can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 25%, 30% and other specific values ​​and ranges with any two of the above specific values ​​as endpoints. For example, the mass proportion of silver powder in the conductive metal powder in the raw material composition can be 8%-30%.

[0018] Optionally, the silver powder in the conductive metal powder accounts for 8%-20% by mass in the raw material composition.

[0019] In the raw material composition, the conductive metal powder may be in the form of flakes, spheres, or dendrites, or a combination of two or more. The present disclosure does not limit the shape of the conductive metal powder. The shapes of the first and second metal powders may be the same or different.

[0020] In the above raw material composition, the weight content of the conductive metal powder in the raw material composition is generally 85%-94%, and specifically can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, and other specific values, as well as ranges with any two of the above specific values ​​as endpoints. Optionally, the weight content of the conductive metal powder in the raw material composition is 91%-93%.

[0021] Optionally, in the above raw material composition, when the first metal powder includes copper powder and / or tin alloy powder, the mass proportion of the copper powder and / or tin alloy powder in the raw material composition is less than or equal to 7%.

[0022] In the above-mentioned raw material composition, a low content of the composite resin in the raw material composition will result in poor adhesion between the composite resin and the substrate (such as the TCO layer); when the composite resin content is high, the low-temperature conductive paste has a high resistance and poor conductivity. The present disclosure controls the mass content of the composite resin in the raw material composition to 2%-10%, so that the paste can have both suitable adhesion and high conductivity. In some specific embodiments, the mass content of the composite resin in the raw material composition can be specific values ​​such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, and ranges with any two of the above specific values ​​as endpoints.

[0023] Optionally, the mass content of the composite resin in the raw material composition is 4%-6%.

[0024] Interpenetrating polymer networks (IPNs) are a unique class of polymer blends or polymer alloys formed by the interpenetration and entanglement of two or more polymers. They can form a stable combination of two polymers with very different properties or different functions, exhibiting excellent comprehensive performance and meeting the demand for product diversification.

[0025] The present invention adds a variety of resin components to the raw material components A and component B of the slurry to form a composite resin, utilizes synchronous IPN technology, and is synchronously cured to form an interpenetrating polymer network structure, which is easy to operate. Specifically, the molecular chains of the polyol in component A and the resin in component B are mutually penetrated and cross-linked in the form of chemical bonds to form an interpenetrating polymer network. The interpenetrating polymer network structure is introduced into the electrode material, which can effectively improve the mechanical strength and adhesion of the grid line, reduce the body resistance and contact resistance, and make it have high conductivity, welding tension and weather resistance. And after the components A and B in the composite resin are blended, the viscosity of the entire low-temperature conductive paste system can be reduced, which is helpful for the screen printing of the slurry, so that the slurry can be adapted to the narrow opening screen and improve the printing speed.

[0026] In the above raw material composition, the mass ratio of component A to component B can be 30-92:8-70. That is, based on 100% of the total mass of the composite resin, the composite resin generally comprises 30%-92% component A and 8%-70% component B. For example, the composite resin may comprise 55%-85% component A and 15%-45% component B. By controlling the ratio of component A to component B, good compatibility between the components can be ensured, and the resulting polymer network structure possesses both ideal conductivity and stability. In some specific embodiments, the mass proportion of component A in the composite resin can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92% and other specific values, as well as ranges with any two of the above specific values ​​as endpoints; the mass proportion of component B in the composite resin can be 8%, 9%, 10%, 11%, 15%, 17%, 20%, 25%, 30%, 33%, 35%, 40%, 42%, 45%, 50%, 55%, 60%, 65%, 70% and other specific values, as well as ranges with any two of the above specific values ​​as endpoints.

[0027] In the component A of the above-mentioned raw material composition, the polyol comprises one or more combinations of polycaprolactone diol, polyoxypropylene diol, polyoxypropylene-ethylene oxide diol, polytetramethylene glycol, polypropylene triol, polyether triol, oxalic acid polyester diol, aromatic polyester polyol, polymer polyester polyol, polycarbonate diol, castor oil derivative polyol, and palm oil polyol. Alternatively, the polyol may comprise one or more combinations of polycaprolactone diol, polyoxypropylene-ethylene oxide diol polycarbonate diol. In some specific embodiments, the molecular weight of the polyol may be 500-1500.

[0028] In some embodiments, the polyol may include a combination of polycaprolactone diol, polypropylene triol, aromatic polyester polyol, polycarbonate diol, and polyether triol.

[0029] In the raw material composition, the blocked isocyanate includes one or a combination of two or more of hexamethyl diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate. Alternatively, the blocked isocyanate includes hexamethyl diisocyanate and / or isophorone diisocyanate.

[0030] In the above raw material composition, the blocking agent used for the blocked isocyanate includes one or a combination of two or more of phenol, caprolactam, diethyl malonate, butanone oxime, acetylacetone, methyl ethyl oxime, diethylene glycol monomethyl ether, and nonylphenol.

[0031] In the above raw material composition, the deblocking temperature of the blocked isocyanate is 80°C-180°C, for example, it can be 80°C, 90°C, 100°C, 11°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0032] In the above raw material composition, in component A, the mass ratio of the polyol to the blocked isocyanate is generally controlled to be 1:1-1:2, for example, it can be 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, and other specific values, as well as ranges with any two of the above specific values ​​as endpoints. Optionally, the mass ratio of the polyol to the blocked isocyanate is 1:1.25-1:1.9.

[0033] In the raw material composition, the glass transition temperature of the resin in component B is generally 70°C or higher, and can be further controlled to be 75°C or higher, 80°C or higher, 85°C or higher, or 90°C or higher. The glass transition temperature of the resin in component B can be 90°C or higher.

[0034] In the above raw material composition, the resin in component B includes a thermosetting resin and / or a thermoplastic resin, for example, a thermosetting resin having a glass transition temperature of 70°C or higher and / or a thermoplastic resin having a high glass transition temperature of 70°C or higher. Specifically, the resin in component B may include one or a combination of two or more of unsaturated polyester resin, melamine formaldehyde resin, phenolic resin, furan resin, acrylic resin, epoxy resin, polybutadiene resin, silicone resin, urea-formaldehyde resin, and the like.

[0035] In the above raw material composition, the acrylic resin may specifically include one or a combination of two or more of epoxy acrylic resin, polyester modified acrylic resin, and polyurethane modified acrylic resin.

[0036] In the raw material composition, the epoxy resin may specifically include one or a combination of two or more of a novolac epoxy resin, an alicyclic epoxy resin, and a polyurethane-modified epoxy resin. The number average molecular weight of the epoxy acrylic resin may be 1000-2500.

[0037] Optionally, the resin in component B is an epoxy resin and / or an acrylic resin. More preferably, the epoxy resin includes a novolac epoxy resin and / or an alicyclic epoxy resin; and the acrylic resin includes an epoxy acrylic resin and / or a polyester-modified acrylic resin.

[0038] In some specific embodiments, the resin in component B includes one or a combination of two or more of epoxy acrylic resin, polyester-modified epoxy acrylic resin, phenolic epoxy resin, and alicyclic epoxy resin.

[0039] In the above raw material composition, the curing agent in component B may include a blocked cationic curing agent. Specifically, the blocked cationic curing agent may include a blocked antimonate thermally initiated cationic curing agent and / or a blocked phosphate thermally initiated cationic curing agent.

[0040] In some specific embodiments, the curing agent in component B includes a combination of a blocked antimonate thermally triggered cationic curing agent and a blocked phosphate thermally triggered cationic curing agent; wherein the mass ratio of the blocked antimonate thermally triggered cationic curing agent to the blocked phosphate thermally triggered cationic curing agent can be 1:1-7:3.

[0041] In the above raw material composition, in component B, the mass ratio of the resin to the curing agent can be controlled to be 1:0.02-0.1, for example, 1:0.02, 1:0.025, 1:0.03, 1:0.035, 1:0.04, 1:0.045, 1:0.05, 1:0.055, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1 and other specific values, as well as ranges with any two of the above specific values ​​as endpoints.

[0042] In the above raw material composition, the mass ratio of the polyol in component A to the resin in component B is 5:1-1:4, for example, specific values ​​such as 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:4, and ranges having any two of the above specific values ​​as endpoints. The mass ratio of the polyol in component A to the resin in component B can be further controlled to be 2:1-1:4.

[0043] In the above raw material composition, the organic solvent may specifically include one or a combination of two or more of diethylene glycol butyl ether, diethylene glycol butyl ether acetate, dimethyl adipate, terpineol, dibasic acid ester (DBE), butyl acetate, and ethylene glycol ethyl ether acetate. Alternatively, the organic solvent includes diethylene glycol butyl ether acetate and / or dimethyl adipate.

[0044] In the above raw material composition, the mass content of the organic solvent in the raw material composition is generally 2%-4%, for example, it can be 2%, 2.5%, 3%, 3.5%, 4% and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0045] In the above raw material composition, the auxiliary agent includes one or a combination of two or more of a chain extender, a coupling agent, an antioxidant, and a defoaming agent.

[0046] In the above raw material composition, the chain extender may include one or a combination of two or more of 3,5-diethyltoluenediamine, 4,4-methylenedianiline, 1,4-bis-sec-butylaminobenzene, 4,4-bis-sec-butylaminodiphenylmethane, ethylene glycol bis-2-aminoethyl ether, and diethylene glycol bis(2-aminopropyl) ether. Alternatively, the chain extender includes ethylene glycol bis-2-aminoethyl ether.

[0047] In the above raw material composition, the coupling agent may include one or a combination of two or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, bistriethanolamine diisopropyl titanate, and neoalkoxytris(p-aminophenoxy) zirconate. Alternatively, the coupling agent includes γ-aminopropyltrimethoxysilane and / or bistriethanolamine diisopropyl titanate.

[0048] In the above raw material composition, the antioxidant may include one or a combination of two or more of 2,6-di-tert-butyl-p-cresol, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, N,N'-hexamethylenebis-3(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxyphenyl)isocyanate, 4-hydroxydodecanoic acid anilide, tris(nonylphenyl)phosphite, and tris(2,4-di-tert-butylphenyl)phosphite. Alternatively, the antioxidant includes 1,3,5-tris(3,5-di-tert-butyl-4-hydroxyphenyl)isocyanate.

[0049] In the above raw material composition, the defoaming agent may include a copolymer of ethylene oxide and propylene oxide.

[0050] In the above raw material composition, the mass content of the auxiliary agent in the raw material composition is generally 0.2%-1%, for example, it can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% and other specific values, as well as a range with any two of the above specific values ​​as endpoints.

[0051] This disclosure also provides a low-temperature conductive paste, which is prepared by mixing the above-mentioned raw material composition. The low-temperature conductive paste provided by this disclosure has low volume resistivity and contact resistivity. The paste has low viscosity, good printability, and is compatible with 17μm screen openings. Furthermore, the low-temperature conductive paste has improved tensile strength, resulting in high reliability.

[0052] In some specific embodiments, the preparation method of the low-temperature conductive paste may include mixing and grinding the above raw material composition to obtain the low-temperature conductive paste. More specifically, the preparation method may include stirring the composite resin, additives, and solvent in the above raw material composition at 25°C for 1-3 hours at a stirring rate of 1000-1500 r / min, then adding conductive metal powder and stirring, and then grinding and dispersing the mixture using a three-roll mill to obtain the low-temperature conductive paste.

[0053] The present disclosure also provides a method for preparing a heterojunction battery electrode, the method comprising:

[0054] The low-temperature conductive paste is printed, dried and cured to obtain the electrode material.

[0055] In the above-mentioned electrode preparation method, the curing process may include staged curing and / or constant temperature curing. Staged curing can eliminate internal stress, prevent implosion, and facilitate cross-linking between components A and B to form an interpenetrating polymer network structure, thereby improving the electrical and mechanical properties of the low-temperature conductive paste.

[0056] In some specific embodiments, the staged curing process includes: increasing the temperature from the first temperature to the second temperature in 5-12 stages, with each temperature stage being held for 1-5 minutes, wherein the first temperature is any temperature between 160-170°C and the second temperature is 210°C. Furthermore, the staged curing temperature (i.e., the staged curing process) also includes decreasing the temperature from the second temperature to the first temperature in 5-12 stages, with each temperature stage being held for 1-5 minutes.

[0057] That is, in some specific embodiments, the staged curing process may include: heating from the first temperature to the second temperature in 5-12 stages, with the holding time of each temperature stage being 1 min-5 min; then cooling from the second temperature to the first temperature in 5-12 stages, with the holding time of each temperature stage being 1 min-5 min; wherein the first temperature is any one temperature between 160-170°C, and the second temperature is 210°C.

[0058] According to specific embodiments of the present disclosure, during the staged curing, the temperature differences between each stage can be the same or different. For example, in a case where the first temperature is 170°C, the second temperature is 210°C, and the temperature is increased in four stages, the same temperature difference between each stage can be: 170-180°C for the first stage, 180-190°C for the second stage, 190-200°C for the third stage, and 200-210°C for the fourth stage. Different temperature differences between each stage can be: 170-185°C for the first stage, 185-190°C for the second stage, 190-205°C for the third stage, and 205-210°C for the fourth stage.

[0059] According to a specific embodiment of the present disclosure, the staged curing process may be performed in a tunnel furnace.

[0060] In the above-mentioned method for preparing the electrode, the constant temperature curing temperature may be 180-220° C., and the constant temperature curing time may be 5 min-30 min, for example, 8 min-20 min.

[0061] In the above-mentioned method for preparing the electrode, the curing process may also include pretreatment first and then staged curing to obtain the electrode material.

[0062] In the above-mentioned electrode preparation method, the pretreatment is a pre-curing process, which can cross-link part of the composite resin, control the heat of the cured product, help form the IPN network, and shorten the curing time. The pretreatment can specifically include UV light curing.

[0063] In the above-mentioned method for preparing the electrode, the temperature of the pretreatment (UV light curing) may be 80° C.-160° C., and the time of the pretreatment (UV light curing) may be 20 s-120 s.

[0064] The preparation method provided by the present disclosure can utilize the process of light pre-curing and segmented curing, and promote the simultaneous polymerization, cross-linking, and mutual penetration of the various components of the composite resin during the curing process by uniformly increasing the temperature, thereby promoting the formation of an interpenetrating polymer network of the composite resin. The resulting slurry can be in close contact with the substrate (such as the TCO layer), and the resistivity and tensile force after the slurry is cured are effectively reduced, and the slurry performance is significantly improved. Through the combination of UV pre-curing and segmented curing processes, the formation of an interpenetrating polymer network can be promoted during the slurry curing process, thereby improving the performance of the slurry.

[0065] The present disclosure also provides a heterojunction battery electrode, which is obtained by the above-mentioned preparation method. The heterojunction battery electrode provided by the present disclosure has high conductivity and photoelectric conversion efficiency.

[0066] The present disclosure also provides a heterojunction battery (HJT battery) made from the aforementioned heterojunction battery electrodes. By controlling the composition of the conductive metal powder and constructing a composite resin system, base metal powders such as silver-coated copper powder, tin alloy powder, and copper powder can be incorporated as raw materials. This allows the resulting battery to have higher overall performance while significantly reducing manufacturing costs.

[0067] The beneficial effects of the present disclosure include:

[0068] 1. The low-temperature conductive paste raw material composition provided in the present disclosure can utilize synchronous IPN technology to introduce polyurethane-based interpenetrating network polymers into the paste, which can effectively improve the conductivity, weather resistance and printability of the paste.

[0069] 2. The polyurethane-based interpenetrating network structure and the conductive metal powder formed by the raw material composition form a synergistic effect. First, the interpenetrating network structure improves the conductivity of the composite resin. At the same time, the rational ratio of the metal powder and the polyurethane-based interpenetrating network structure in the conductive paste promotes the mechanical strength and stability of the electrode after the paste is cured, with low volume resistivity and good ohmic contact with the ITO.

[0070] The low-temperature conductive paste obtained from the above raw material composition has reduced viscosity and improved printability, and can be applied to screens with narrow mesh openings (such as 17 μm openings).

[0071] 3. Using the disclosed low-temperature conductive paste to prepare electrodes can reduce the bulk and contact resistivity of the electrodes, improve their conductivity and tensile strength, and enhance battery reliability and photoelectric conversion efficiency. Heterojunction batteries prepared using these electrodes exhibit high conductivity and weather resistance, high stability, and resistance to oxidative corrosion, improving heterojunction battery efficiency and reducing heterojunction battery costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0073] FIG1 is a DSC curve of the cured composite resins of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0074] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present disclosure, the technical solution of the present disclosure is now described in detail below, but it should not be understood as limiting the scope of implementation of the present disclosure.

[0075] Examples 1 to 11 and 14, Comparative Examples 1 to 3

[0076] Examples 1 to 11 and 14, and Comparative Examples 1 to 3 respectively provide a low-temperature conductive paste, wherein the raw material composition of the conductive paste includes a first metal powder, a second metal powder, component A, component B, a solvent, and an additive;

[0077] The solvents and additives used in the above examples and comparative examples are the same. In parts by mass, the solvents and additives are composed as follows:

[0078] Solvent: 1.5 parts of diethylene glycol butyl ether acetate, 0.5 parts of dimethyl adipate;

[0079] Additives: 0.3 parts of ethylene glycol bis-2-aminoethyl ether, 0.1 parts of γ-aminopropyltrimethoxysilane, 0.2 parts of bistriethanolamine diisopropyl titanate, 0.3 parts of 1,3,5-tris(3,5-di-tert-butyl-4-hydroxyphenyl) isocyanate, and 0.1 parts of 2,6-di-tert-butyl-p-cresol.

[0080] The compositions of the first metal powder, the second metal powder, the component A and the component B in the raw material compositions of Examples 1 to 11 and Comparative Examples 1 to 3 are summarized in Tables 1 and 2. Among them, Table 1 lists in detail the specific ingredients and ratios of component A and component B of Preparation Examples 1 to 8. The proportions of polyols 1 to 5 and the corresponding blocked isocyanates contained in component A of each preparation example are different. Resins 1 to 4 contained in component B in each preparation example are all resins with a glass transition temperature above 70°C, and the proportions used are different. Therefore, the corresponding amount of curing agent is also different. In summary, in Preparation Examples 1-6, the ratios of component A polyol and component B resin used are 2:1, 1:1, 1:2, 4:1, 5:1 and 1:4, respectively. Preparation Example 7 does not contain component B, and Preparation Example 8 does not contain component A.

[0081] Table 1 (Unit: parts by mass)

[0082] In Table 1, the blocking agent of blocked isocyanate 1 is diethyl malonate, and the deblocking temperature is 120°C; the blocking agent of blocked isocyanate 2 is ethylene glycol ethyl ether, and the deblocking temperature is 160°C.

[0083] Table 2 (Unit: parts by mass)

[0084] In each embodiment of Table 2, the total weight of the pure silver powder contained in the first metal powder and the second metal powder (metal powder 1+metal powder 5) is no more than 20 parts.

[0085] The first metal powder and the second metal powder include silver powder, silver-coated copper powder, copper powder, and tin alloy powder (specifically tin-bismuth-silver alloy powder), respectively. The parameters of the various metal powders are as follows:

[0086] Metal powder 1 (silver powder): D50 of 3-4 μm, tap density of not less than 3.5 g / cc;

[0087] Metal powder 2 (silver-coated copper powder): D50 of 3-4 μm, tap density of not less than 3.5 g / cc;

[0088] Metal powder 3 (copper powder): D50 of 3-4 μm, tap density of not less than 3.5 g / cc;

[0089] Metal powder 4 (tin alloy powder): D50 of 3-4 μm and tap density of not less than 3.5 g / cc;

[0090] Metal powder 5 (silver powder): D50 of 0.8-1.5 μm, tap density of not less than 4 g / cc;

[0091] Metal powder 6 (silver-coated copper powder): D50 of 0.8-1.5 μm, tap density of not less than 4 g / cc;

[0092] Metal powder 7 (copper powder): D50 of 0.8-1.5 μm, tap density of not less than 4 g / cc;

[0093] Metal powder 8 (tin alloy powder): D50 is 0.8-1.5 μm, and tap density is not less than 4 g / cc.

[0094] Heterojunction battery electrodes were prepared using the compositions of Examples 1 to 11 and 14, and Comparative Examples 1 to 3, respectively. The preparation methods included:

[0095] 1. Mix component A, component B, solvent and additives, stir at a stirring speed of 1000-1500 r / min at 25°C for 1-3 hours, then add the first metal powder and the second metal powder, grind and disperse on a three-roll mill for 6 times to obtain a low-temperature conductive paste;

[0096] 2. The low-temperature conductive paste is UV cured at 120°C for 30 seconds, and then segmented cured. During the curing process, the temperature is raised from 170°C to 210°C, with each temperature rising interval being 10°C and each temperature rising interval being maintained for 1 minute; then the temperature is lowered from 210°C to 170°C, with each temperature falling interval being 10°C and each temperature falling interval being maintained for 1 minute, completing segmented curing to obtain the electrode material;

[0097] The staged curing process is carried out in a tunnel oven. The curing process is as follows: 170°C-180°C for 1 minute, 180°C-190°C for 1 minute, 190°C-200°C for 1 minute, and 200°C-210°C for 1 minute; then 210°C-200°C for 1 minute, 200°C-190°C for 1 minute, 190°C-180°C for 1 minute, and 180°C-170°C for 1 minute. The total curing time is 8 minutes.

[0098] Example 12

[0099] This embodiment provides a heterojunction battery electrode. The preparation method of this electrode is similar to the electrode preparation method of Example 2, except that the electrode preparation method of this embodiment omits the UV curing process and only performs segmented curing.

[0100] Example 13

[0101] This embodiment provides a heterojunction battery electrode, and the preparation method of the electrode is similar to the electrode preparation method of Example 2, except that: the electrode preparation method of this embodiment replaces the segmented curing process with constant temperature curing, and the constant temperature curing conditions are 220°C and 20 minutes.

[0102] Test Example 1

[0103] This test example provides the performance test results of the low-temperature conductive pastes prepared in the above embodiments and comparative examples.

[0104] The test method is as follows:

[0105] 1. Viscosity

[0106] The viscosity test was performed using a Brookfield viscometer at a speed of 10 rpm and the viscosity value was measured for 4 minutes.

[0107] 2. Resistivity test

[0108] A four-probe ohmmeter was used to measure the resistance at both ends of the sintered electrode body.

[0109] 3. Ohmic contact resistance test

[0110] The low-temperature conductive paste is screen-printed on the heterojunction cell and then dried and solidified, and the contact resistance is measured using a contact resistance device.

[0111] 4. Welding tensile test

[0112] Use copper-based lead-tin soldering strip, solder at 350℃, and use a universal material testing machine to pull it off at a constant speed of 180° to test the average tensile force.

[0113] 5. Electrical performance test

[0114] Solar simulator, 25°C, M1.5 spectrum, 1.000KW / m 2 .

[0115] The test results are shown in Table 3.

[0116] Table 3

[0117] In Table 3, “commercial pure silver” is the HC series pure silver paste produced by Suzhou Jingyin New Material Technology Co., Ltd. instead of the low-temperature conductive silver paste in the above examples and comparative examples, and the test is carried out according to the above method.

[0118] It can be seen from Table 3 that the composite resin of Comparative Example 1 does not contain component B, and the composite resin of Comparative Example 2 does not contain component A; the conductive metal powder of Comparative Example 3 contains only the first metal powder and does not contain the second metal powder.

[0119] It can be seen from Comparative Example 3 and Examples 10 and 11 that after compounding the first metal powder and the second metal powder, the resistivity of the prepared heterojunction battery decreases and the photoelectric conversion performance improves.

[0120] Preferably, when the first metal powder includes copper powder and / or tin alloy powder, the mass proportion of copper powder and / or tin alloy powder in the raw material composition is less than or equal to 7%. This is to further improve the mechanical properties and photoelectric conversion performance of the heterojunction battery. The conductive metal powder of Example 5 contains both silver powder and base metal powder (silver powder, silver-coated copper powder, tin alloy powder), while the conductive metal powder of Example 14 contains only silver powder. It can be seen from Examples 5 and 14 that compared with heterojunction batteries made with pure silver powder as the conductive metal powder, the resistivity and contact resistance of heterojunction batteries made with conductive metal powders formed by combining base metals such as silver-coated copper powder, tin alloy powder, and pure copper powder with silver powder are reduced, and the welding tensile force is improved, indicating that the conductive performance of low-silver low-temperature conductive paste is at least comparable to that of pure silver low-temperature conductive paste, and in some aspects of performance, low-silver conductive paste is even higher than pure silver conductive paste. This result shows that by replacing part of the silver powder in the conductive metal powder with base metals, the cost can be greatly reduced while maintaining the performance of the heterojunction battery.

[0121] As can be seen from Table 3, various indicators (especially conductivity and photoelectric conversion efficiency) of Examples 1 to 7 and Examples 12 to 14 are superior to those of Comparative Examples 1 and 2. This indicates that, compared to adding a single-component resin, adding a two-component composite resin to the raw materials can synergize with the low-silver conductive metal powder (conductive metal powder containing non-pure silver powder) to better improve the slurry's adhesion, conductivity, weather resistance, and photoelectric conversion capacity.

[0122] Comparing Comparative Example 3 with Example 2, it can be seen that when the composite resin, additives, solvent, and the total amount of conductive metal powder are the same, compared with Comparative Example 3 where only the first metal powder is added as the conductive metal powder, Example 2 improves the conductivity and photoelectric conversion efficiency of the heterojunction battery by compounding the first metal powder and the second metal powder with different particle sizes and tap densities to form the conductive metal powder.

[0123] Comparing the test results of each embodiment with the test results of commercial silver paste, it can be seen that the performance of the low-temperature conductive silver paste provided by the embodiments of the present disclosure is at least equivalent to that of the commercial silver paste as a whole. This result shows that the present disclosure can significantly reduce the cost (all or part of the silver powder is replaced by base metal) while ensuring the performance of the low-temperature conductive silver paste at a high level by introducing a composite resin organic system and adjusting the composition of the conductive metal powder.

[0124] Compared to Examples 12 and 13, the low-temperature conductive paste of Example 2 showed significant improvements in resistivity, tensile strength, and photoelectric conversion efficiency. This result demonstrates that the raw material composition provided in this disclosure, prepared through a pre-curing and staged curing process, can promote slurry curing and thereby improve the performance of heterojunction cells.

[0125] Furthermore, it can be seen from the test results of Examples 1 to 6 and 7 to 13 in Table 3 that the performance of the heterojunction battery can be further improved by adjusting the composition of the composite resin and the composition of the conductive metal powder.

[0126] Furthermore, a comparison of the test results of Examples 1 to 6 in Table 3 shows that the photoelectric conversion efficiency of the above examples all reached above 25%, with Examples 1, 2, 6, and 3 achieving higher photoelectric conversion efficiencies than Examples 4 and 5. This result demonstrates that, given the same conductive metal powder composition, a higher photoelectric conversion effect can be achieved by controlling the mass ratio of the polyol in component A to the resin in component B within a range of 5:1 to 1:4. Further adjusting the mass ratio of the polyol in component A to the resin in component B (e.g., controlling it to 2:1 to 1:4) can further increase the photoelectric conversion efficiency of the battery (above 25.5%).

[0127] Test Example 2

[0128] Component A and component B in Example 1 were mixed and then cured. The curing method was the same as that in Example 1, specifically: UV curing was performed at 120°C for 30 seconds, and then segmented curing was performed: heating from 170°C to 210°C, with each heating interval being 10°C and each heating interval being maintained for 1 minute; then cooling from 210°C to 170°C, with each cooling interval being 10°C and each cooling interval being maintained for 1 minute to complete segmented curing.

[0129] The resin of component B in Comparative Example 1 and the curing agent were mixed and then cured. The curing process was the same as that in Example 1.

[0130] The cured composite resins of Example 1 and Comparative Example 1 were subjected to DSC testing using a DSC-350L differential scanning calorimeter at a heating rate of 10 K / min. The results are shown in Figure 1. It can be seen that the cured composite resin product produced a significant endothermic peak during heating, corresponding to a glass transition temperature of 75°C. This demonstrates that the composite resin components A and B in Example 1 form an IPN structure after simultaneous curing following blending. The cured composite resin of Comparative Example 1 does not exhibit this structure.

[0131] In summary, the blending of composite resin components A and B is beneficial to improving the printability of low-temperature conductive paste. The IPN interpenetrating network structure formed after curing is beneficial to the electrical properties and welding tension of low-silver-containing paste, and can improve the conductivity of low-silver-containing paste, thereby reducing the paste cost and improving the photoelectric conversion efficiency of heterojunction batteries.

Claims

1. A raw material composition for a low-temperature conductive paste, comprising, based on the total mass of the raw material composition as 100%, 2%-10% of a composite resin, 2%-4% of an organic solvent, 0.2%-1% of an additive, and 85%-94% of a conductive metal powder; in, The composite resin includes component A and component B; The component A comprises polyol and blocked isocyanate; the component B comprises resin and curing agent.

2. The raw material composition according to claim 1, wherein The conductive metal powder includes a first metal powder and a second metal powder, wherein the D50 particle size of the first metal powder is 3 μm-4 μm and the tap density of the first metal powder is greater than 3.5 g / cc; the D50 particle size of the second metal powder is 0.8 μm-1.5 μm and the tap density of the second metal powder is greater than 4 g / cc; Preferably, the mass ratio of the first metal powder to the second metal powder is 25:75-80:20; More preferably, the mass ratio of the first metal powder to the second metal powder is 35:65-75:

25.

3. The raw material composition according to claim 2, wherein The first metal powder includes one or a combination of two or more of silver-coated copper powder, copper powder, tin alloy powder, and silver powder; the second metal powder includes one or a combination of two or more of silver-coated copper powder, copper powder, tin alloy powder, and silver powder; Preferably, the tin alloy powder comprises one or a combination of two or more of tin-bismuth alloy, tin-nickel alloy, tin-copper alloy, tin-bismuth-silver alloy, and tin-silver-copper alloy; Preferably, the mass proportion of the silver powder in the conductive metal powder in the raw material composition is less than or equal to 30%; More preferably, the silver powder in the conductive metal powder accounts for 8%-30% by mass in the raw material composition.

4. The raw material composition according to claim 1, wherein Based on the total mass of the composite resin being 100%, the composite resin comprises 30%-92% of component A and 8%-70% of component B; Preferably, the composite resin comprises 55%-85% of component A and 15%-45% of component B; Preferably, the mass ratio of the polyol in component A to the resin in component B is 5:1-1:4, more preferably 2:1-1:

4.

5. The raw material composition according to claim 1, wherein The polyol includes one or a combination of two or more of polycaprolactone diol, polyoxypropylene diol, polyoxypropylene-ethylene oxide diol, polytetramethylene glycol, polypropylene triol, polyether triol, oxalic acid polyester diol, aromatic polyester polyol, polymer polyester polyol, polycarbonate diol, castor oil derivative polyol, and palm oil polyol; Preferably, the molecular weight of the polyol is 500-1500.

6. The raw material composition according to claim 1, wherein The blocked isocyanate includes one or a combination of two or more of hexamethyl diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate; Preferably, the blocking agent used for the blocked isocyanate includes one or a combination of two or more of phenol, caprolactam, diethyl malonate, butanone oxime, acetylacetone, methyl ethyl oxime, diethylene glycol monomethyl ether, and nonylphenol; Preferably, the deblocking temperature of the blocked isocyanate is 80°C-180°C.

7. The raw material composition according to claim 1, wherein In component A, the mass ratio of the polyol to the blocked isocyanate is 1:1-1:

2.

8. The raw material composition according to claim 1, wherein In the component B, the resin includes a thermosetting resin and / or a thermoplastic resin; The curing agent in the component B includes a blocked cationic curing agent; preferably, the blocked cationic curing agent includes a blocked antimonate thermally initiated cationic curing agent and / or a blocked phosphate thermally initiated cationic curing agent; Preferably, the glass transition temperature of the resin is above 70°C, more preferably above 90°C; More preferably, the resin comprises one or a combination of two or more of unsaturated polyester resin, melamine formaldehyde resin, phenolic resin, furan resin, acrylic resin, epoxy resin, polybutadiene resin, silicone resin, and urea-formaldehyde resin; Further preferably, the acrylic resin includes one or a combination of two or more of epoxy acrylic resin, polyester modified acrylic resin, and polyurethane modified acrylic resin; More preferably, the epoxy resin comprises one or a combination of two or more of a novolac epoxy resin, an alicyclic epoxy resin, and a polyurethane-modified epoxy resin; More preferably, the number average molecular weight of the epoxy acrylic resin is 1000-2500.

9. The raw material composition according to claim 1, wherein In component B, the mass ratio of the resin to the curing agent is 1:0.02-1:0.

1.

10. The raw material composition according to claim 1, wherein The auxiliary agent includes one or a combination of two or more of a chain extender, a coupling agent, an antioxidant, and a defoaming agent; Preferably, the chain extender comprises one or a combination of two or more of 3,5-diethyltoluenediamine, 4,4-methylenedianiline, 1,4-bis-sec-butylaminobenzene, 4,4-bis-sec-butylaminodiphenylmethane, ethylene glycol bis-2-aminoethyl ether, and diethylene glycol bis-(2-aminopropyl) ether; Preferably, the coupling agent includes one or a combination of two or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane, bistriethanolamine diisopropyl titanate, and neoalkoxytris(p-aminophenoxy) zirconate; Preferably, the antioxidant includes one or a combination of two or more of 2,6-di-tert-butyl-p-cresol, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, N,N'-hexamethylenebis-3(3,5-di-tert-butyl-4-hydroxyphenyl)propionamide, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxyphenyl)isocyanate, 4-hydroxydodecanoic acid anilide, tris(nonylphenyl)phosphite, and tris(2,4-di-tert-butylphenyl)phosphite; Preferably, the defoaming agent comprises a copolymer of ethylene oxide and propylene oxide.

11. A low-temperature conductive paste, which is prepared by mixing the raw material composition according to any one of claims 1 to 10.

12. A method for preparing a heterojunction battery electrode, the method comprising: The conductive paste according to claim 11 is printed, dried, and cured to obtain an electrode material; Preferably, the curing process includes staged curing and / or constant temperature curing, and the staged curing process includes: heating from a first temperature to a second temperature in 5-12 stages, with each stage temperature being held for 1 min-5 min, wherein the first temperature is any one of 160-170° C., and the second temperature is 210° C.; More preferably, the staged curing process further comprises lowering the temperature from the second temperature to the first temperature in 5-12 stages, with each temperature being maintained for 1 min to 5 min; Preferably, the constant temperature curing temperature is 180-220° C., and the constant temperature curing time is 5 min-30 min, more preferably 8 min-20 min.

13. The preparation method according to claim 12, wherein The curing process includes pretreatment and then staged curing. Preferably, the pretreatment is UV light curing, the temperature of the UV light curing is 80° C.-160° C., and the time of the pretreatment is 20s-120s.

14. A heterojunction battery electrode, obtained by the preparation method according to claim 12 or 13.

15. A heterojunction battery made of the heterojunction battery electrode according to claim 14.

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