A room temperature storable low temperature cure conductive paste and method of making same

Abstract

The application relates to the fields of electronic material preparation and photovoltaics, and discloses a low-temperature curing conductive paste capable of being stored at room temperature and a preparation method thereof. The low-temperature curing conductive paste provided by the application comprises the following raw materials in percentage by mass: 90-95% of conductive metal powder, 1-5% of organic resin, 0.1-2% of a curing agent, 1-5% of a composite solvent and 0.1-2% of an additive; the composite solvent comprises at least two alcohol ether solvents; or the composite solvent comprises at least one alcohol ether solvent and at least one ester solvent; and the saturated vapor pressure of the alcohol ether solvent and the ester solvent at room temperature is independently 0.0005-0.4 mmHg. The low-temperature curing conductive paste prepared by the application has good conductivity and can be stably stored at room temperature.

Description

Technical Field

[0001] This invention relates to the fields of electronic material preparation and photovoltaics, specifically to a low-temperature curing conductive paste that can be stored at room temperature and its preparation method. Background Technology

[0002] Crystalline silicon heterojunction (HJT) solar cells, as a type of high-efficiency crystalline silicon solar cell, are widely regarded as one of the next-generation mainstream solar cell technologies due to their advantages such as high photoelectric conversion efficiency, low temperature coefficient, high bifaciality, and simple processing steps. However, the special structure of HJT cells requires that their fabrication process temperature not exceed 200℃, otherwise, the cell performance will degrade. Therefore, the metallization process of HJT cells typically employs low-temperature curing conductive pastes.

[0003] In the fabrication of high-junction thermoelectric cells (HJTs), the metallization process typically requires the conductive paste to cure within 8-10 minutes at temperatures below 200°C to form metal electrodes, while possessing good conductivity (volume resistivity ≤ 10 μΩ·cm) and excellent screen printing performance. Specifically, even if the opening size of the screen printing stencil is less than 20 μm, the paste must still pass through smoothly to avoid problems such as grid breaks or uneven height. Therefore, conductive pastes used for HJT battery metal electrodes often employ low-temperature curing systems. The principle is that the resin in the paste undergoes a cross-linking curing reaction at around 200°C, thereby firmly bonding the conductive metal powder to the surface of the cell to form electrodes. However, resins and curing agents that can cure rapidly below 200°C (8-10 minutes) usually also exhibit high curing reactivity at room temperature, leading to a spontaneous and slow cross-linking curing reaction during storage. This process directly causes a gradual increase in paste viscosity, significantly impacting its screen printing performance. Therefore, such slurries must be stored in a low-temperature environment of -30°C to -20°C to inhibit the curing tendency of resin and curing agent at room temperature and extend the shelf life of the slurry. However, this also places high demands on the transportation and use conditions of the slurry: (1) transportation must be carried out using cold chain vehicles with chemical transportation permits and capable of maintaining a constant temperature of -30°C; (2) the slurry must be thawed at room temperature for a long time before use, and the thawed slurry should not be refrozen and reused. These restrictions significantly increase the manufacturing cost of HJT batteries. The existing HJT battery conductive slurry solution that can achieve room temperature storage is to prepare the resin and curing agent separately and mix them before use. Although this method can achieve long-term room temperature storage of the slurry, it increases the complexity of the use process. In addition, most HJT battery manufacturers do not have the conditions to mechanically mix the two materials and need to purchase additional stirring equipment, which also increases production costs.

[0004] In summary, commonly used low-temperature curing conductive pastes have problems such as high volume resistivity and difficulty in achieving room temperature storage after preparation. These limitations in storage, transportation, and use remain one of the key factors restricting the cost reduction of HJT batteries. Summary of the Invention

[0005] This invention provides a low-temperature curing conductive paste that can be stored at room temperature and its preparation method, in order to solve the problem that the low-temperature conductive paste in the prior art has high volume resistivity and cannot be stored at room temperature.

[0006] In a first aspect, the present invention provides a low-temperature curing conductive paste that can be stored at room temperature, comprising, by weight percentage, the following raw materials: 90-95% conductive metal powder, 1-5% organic resin, 0.1-2% curing agent, 1-5% composite solvent, and 0.1-2% additives; The organic resin includes epoxy resin, and the curing agent includes a first curing agent; the first curing agent includes one or more of BF3-piperidine complex, BF3-aniline complex, and AlCl3-pyridine complex. Alternatively, the organic resin may include phenolic resin, and the curing agent may include a second curing agent; the second curing agent may include one or more of benzyltriethylammonium chloride and p-toluenesulfonic acid pyridinium salt. Alternatively, the organic resin may include benzoxazine resin, and the curing agent may include a third curing agent; the third curing agent may include one or more of YbCl3-hexamethylphosphoric triamine and Sc(OTf)3-tributylamine complex; The composite solvent comprises at least two alcohol ether solvents; or the composite solvent comprises at least one alcohol ether solvent and at least one ester solvent; The saturated vapor pressures of the alcohol ether solvents and ester solvents at room temperature are independently 0.0005-0.4 mmHg.

[0007] In one optional embodiment, the epoxy resin includes at least one of E-12, E-20, E-42, and E-44; as the most widely used thermosetting resin with the most balanced comprehensive performance, it has excellent adhesive properties, outstanding mechanical strength, good process adaptability, and excellent chemical resistance. However, it also has certain disadvantages, such as high curing shrinkage and relatively limited heat resistance. The phenolic resin includes at least one of 638, 701, and 704; the phenolic resin is a classic thermosetting resin formed by the condensation of phenols and aldehydes, known for its excellent heat resistance, high rigidity, high hardness, chemical corrosion resistance, and excellent instantaneous high temperature resistance and flame retardant and ablation resistance. However, its disadvantages are relatively brittle, poor toughness, and the release of small molecules during the curing process, which can easily lead to pores and defects in the cured electrode.

[0008] In one optional embodiment, the benzoxazine resin includes at least one of JBZ-BA100N, JBZ-FA100N, JBZ-DP100N, and JBZ-OP100N; the benzoxazine resin is a novel high-performance thermosetting resin that is cured by ring-opening polymerization and has no small molecule release. It possesses near-zero volume shrinkage / expansion, excellent thermal stability and flame retardancy, and superior electrical properties, effectively compensating for the shortcomings of epoxy resins and phenolic resins in the aforementioned aspects.

[0009] In one optional embodiment, the silane coupling agent includes one or more of KH-550, KH-560, and KH-570; the silane coupling agent is mainly used in the slurry to improve the dispersibility and system stability of the conductive powder, and can significantly improve the adhesion between the metal electrode and the substrate after curing.

[0010] In one optional embodiment, the conductive metal powder comprises a first conductive metal powder and a second conductive metal powder; The first conductive metal powder includes flake-shaped silver powder, and the second conductive metal powder includes spherical conductive metal powder; Optionally, the second conductive metal powder includes at least one of a first spherical silver powder, a second spherical silver powder, and a spherical silver-coated copper powder.

[0011] In one optional embodiment, the room-temperature storable, low-temperature curing conductive paste satisfies at least one of the following conditions: (1) The median particle size D of the flake silver powder 50 2-5 μm; (2) The median particle size D of the spherical silver-coated copper powder 50 1-5 μm; (3) The median particle size D of the first spherical silver powder 50 The range is 200-800 nm; (4) The median particle size D of the second spherical silver powder 50 1-5 μm; (5) The mass ratio of the first conductive metal powder to the second conductive metal powder is (17-30): (60-75).

[0012] In one optional embodiment, the room-temperature storable, low-temperature curing conductive paste satisfies at least one of the following conditions: (1) The alcohol ether solvents include one or more of tripropylene glycol methyl ether, dipropylene glycol methyl ether, diethylene glycol dibutyl ether, and 1,3-propanediol monoethyl ether; (2) The ester solvents include one or more of ethylene glycol diacetate, diethyl sebacate and dibutyl phthalate.

[0013] In one optional embodiment, when the organic resin is an epoxy resin, the composite solvent includes at least two of tripropylene glycol methyl ether, dipropylene glycol methyl ether, diethylene glycol dibutyl ether, and 1,3-propanediol monoethyl ether. In one optional embodiment, when the organic resin is a phenolic resin, the composite solvent includes at least one alcohol ether solvent and at least one ester solvent; In one optional embodiment, when the organic resin is a benzoxazine resin, the composite solvent includes at least one alcohol ether solvent and at least one ester solvent.

[0014] In one alternative embodiment, the additives include thixotropic agents, dispersants, and coupling agents.

[0015] In one optional embodiment, the mass ratio of the thixotropic agent, dispersant, and coupling agent is (0.1-0.5):(0.1-0.4):(0.1-0.3).

[0016] In one alternative embodiment, the thixotropic agent includes one or more of ethyl cellulose and polyamide wax.

[0017] In one alternative embodiment, the dispersant includes one or more of sodium dodecyl sulfate and polyacrylamide.

[0018] In one alternative embodiment, the coupling agent comprises a silane coupling agent.

[0019] Secondly, the present invention provides a method for preparing the low-temperature curing conductive paste that can be stored at room temperature, comprising the following steps: S1. Mix the composite solvent with organic resin, curing agent and additives to obtain a composite organic carrier; S2. The conductive metal powder and the composite organic carrier obtained in S1 are mixed and then ground to obtain the low-temperature curing conductive slurry.

[0020] The technical solution of this invention has the following advantages: 1. The present invention provides a low-temperature curing conductive paste, comprising, by weight percentage, the following raw materials: 90-95% conductive metal powder, 1-5% organic resin, 0.1-2% curing agent, 1-5% composite solvent, and 0.1-2% additives; wherein the organic resin includes epoxy resin, and the curing agent includes a first curing agent; the first curing agent includes one or more of BF3-piperidine complex, BF3-aniline complex, and AlCl3-pyridine complex; or, the organic resin includes phenolic resin, and the curing agent includes a second curing agent; the second... The curing agent includes one or more of benzyltriethylammonium chloride and p-toluenesulfonic acid pyridinium salt; or, the organic resin includes benzoxazine resin, and the curing agent includes a third curing agent; the third curing agent includes one or more of YbCl3-hexamethylphosphoric triamine and Sc(OTf)3-tributylamine complex; the composite solvent includes at least two alcohol ether solvents; or the composite solvent includes at least one alcohol ether solvent and at least one ester solvent; the saturated vapor pressure of the alcohol ether solvent and the ester solvent at room temperature is independently 0.0005-0.4 mmHg.

[0021] Among them, BF3-piperidine complex, BF3-aniline complex, and AlCl3-pyridine complex are heat-latent epoxy resin curing agents, which are extremely stable at room temperature and hardly react with epoxy resin. However, under heating conditions of 50~120°C, they decompose and release active Lewis acids, thereby catalyzing the rapid curing of epoxy resin. Benzyltriethylammonium chloride and p-toluenesulfonic acid pyridine salt need to be heated to 100~140°C to decompose and produce protic acids or amines to initiate the curing of phenolic resin, thus avoiding reaction at room temperature. YbCl3-hexamethylphosphoric triamine and Sc(OTf)3-tributylamine complex also remain stable at room temperature, but can release highly active cationic catalysts when heated to 140°C, initiating the curing reaction of benzoxazine resin. The acid strength and reactivity of this type of curing agent can be finely adjusted by the central metal ion and organic base ligand, thereby enabling precise control of the onset temperature and reaction rate of the benzoxazine resin curing reaction over a wide range. This allows the resin system to meet the dual requirements of ultra-long storage period and rapid curing under mild curing conditions without the release of small molecules.

[0022] The low-temperature curing conductive paste provided by this invention is suitable for the metallization process of HJT batteries. This application uses a composite solvent system with a low vapor pressure (0.0005-0.4 mmHg) at room temperature, ensuring slow evaporation and stable viscosity during storage, thus guaranteeing smooth printing. In HJT battery production, the metallization process typically requires continuous screen printing, and a single container of paste may last up to a day. If the organic solvent evaporates too quickly, the paste viscosity will increase significantly, severely affecting its screen printing performance. The composite low vapor pressure solvent system used in this invention effectively avoids this problem. Furthermore, during the heat curing stage, the composite low vapor pressure solvent evaporates smoothly and exhibits excellent leveling properties, which is beneficial for forming a smooth and dense metal electrode. In contrast, pastes using a single solvent system tend to evaporate too quickly when heated to the solvent's boiling point, causing defects such as "skinning," pinholes, and poor leveling. Simultaneously, this composite low vapor pressure solvent does not easily evaporate during storage, which helps maintain the stability of the paste ratio and achieve long-term storage. Traditional volatile pastes not only require strict sealing to prevent evaporation, but their formulations are also more prone to change.

[0023] Furthermore, the curing agent introduced in this invention is a heat-latent curing agent, which effectively inhibits the curing reaction between the resin and the curing agent in the slurry at room temperature, achieving stable storage at room temperature. Simultaneously, it releases a catalyst during heating to accelerate resin curing, allowing the slurry to cure rapidly in a short time. The slurry solution proposed in this invention not only reduces the dependence of low-temperature conductive slurries on freezing conditions during transportation and storage, avoiding the thawing process before and after use of low-temperature cured conductive slurries, but also helps improve the production efficiency of HJT batteries and further control costs.

[0024] 2. The composite conductive metal powder comprises a first conductive metal powder and a second conductive metal powder; the first conductive metal powder comprises flake silver powder, and the second conductive metal powder comprises spherical conductive metal powder.

[0025] The composite conductive metal powder provided by this invention includes a first conductive metal powder comprising flake silver powder, which has good lateral conductivity, and a second conductive metal powder having good flowability due to the presence of spherical particles, while filling the gaps generated by the accumulation of the first conductive metal powder, making the electrode more compact. The composite conductive metal powder formed by combining the first conductive metal powder and the second conductive metal powder has better screen printing properties, higher density, and better conductivity. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a graph showing the viscosity of the low-temperature curing conductive paste prepared in Examples 1-3 and Comparative Example 1 of the present invention as a function of storage time at room temperature; Detailed Implementation The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0028] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0029] The sources of raw materials used in the verification ratios of the embodiments provided in this invention are as follows: Epoxy resin, model E12, manufacturer: Nan Ya Electronic Materials (Kunshan) Co., Ltd. Phenolic resin, model 638, manufacturer: Nan Ya Electronic Materials (Kunshan) Co., Ltd. Benzoxazine resin, model JBZ-BA100N, manufacturer: JFE Chemical Co., Ltd. Silane coupling agent, model KH-550, manufacturer: Jiangxi Chenguang New Materials; BF3-piperidine complex, CAS No.: 592-39-2, purity: 98%, manufacturer: Wuhan Yuqing Jiaheng Pharmaceutical Co., Ltd.; Tripropylene glycol methyl ether, CAS No.: 25498-49-1, purity >93% (GC), manufacturer: Shanghai Aladdin Biochemical Technology Co., Ltd.; Dipropylene glycol methyl ether, CAS No.: 34590-94-8, purity: 98%, manufacturer: Shanghai Maclean Biochemical Technology Co., Ltd.; Diethylene glycol dibutyl ether, CAS No.: 112-73-2, purity: 99%, manufacturer: Shanghai Maclean Biochemical Technology Co., Ltd.; Diethyl sebacate, CAS No.: 110-40-7, purity: 98%, manufacturer: Shanghai Maclean Biochemical Technology Co., Ltd.; 1,3-Propanediol monoethyl ether, CAS No.: 111-35-3, purity: 97%, manufacturer: Shanghai Maclean Biochemical Technology Co., Ltd.; Dibutyl phthalate, CAS No.: 84-74-2, purity >98.5%, manufacturer: Shanghai Maclean Biochemical Technology Co., Ltd. Butylcarbidol, CAS No.: 112-34-5, purity: 99%, manufacturer: Shanghai Maclean Biochemical Technology Co., Ltd.; Desmodur® BL 1265, manufactured by Bayer Group; Polyacrylamide, CAS No.: 9003-05-8, nonionic, molecular weight: 5 million, manufacturer: Shanghai Maclean Biochemical Technology Co., Ltd.

[0030] Example 1 This embodiment provides a low-temperature curing conductive paste that can be stored at room temperature, comprising the following components by weight percentage: 90% conductive metal powder (of which, 20% is first spherical silver powder (median particle size D)). 50 300 nm), 30% flake silver powder (median particle size D) 50 (4 μm) and 40% second spherical silver powder (median particle size D) 50 The composition includes 2 μm, 3% epoxy resin (E-12), 2% BF3-piperidine complex, 4% composite solvent (2% tripropylene glycol methyl ether (saturated vapor pressure of 0.03 mmHg at 25℃), 1% dipropylene glycol methyl ether (saturated vapor pressure of 0.4 mmHg at 25℃) and 1% diethylene glycol dibutyl ether (saturated vapor pressure of 0.0274 mmHg at 25℃)) and 1% additives (including 0.3% thixotropic agent (ethyl cellulose), 0.4% dispersant (polyacrylamide) and 0.3% silane coupling agent (KH-550)).

[0031] This embodiment provides a method for preparing a low-temperature curing conductive paste that can be stored at room temperature, including the following steps: S1. Tripropylene glycol methyl ether, dipropylene glycol methyl ether, and diethylene glycol dibutyl ether are mixed evenly in a mass ratio of 2:1:1. The mixing method is stirring at 100 rpm for 5 minutes to obtain the mixed composite solvent.

[0032] The composite solvent, epoxy resin, BF3-piperidine complex, ethyl cellulose, polyacrylamide, and silane coupling agent (KH-550) were mixed in a mass ratio of 4:3:2:0.3:0.4:0.3 and stirred at 80°C for 4 hours at a stirring speed of 100 rpm. After the mixture became homogeneous and clear, the composite organic carrier was obtained.

[0033] S2. The median particle size D50 The first spherical silver powder is 300nm in diameter, with a median particle size D. 50 Two spherical silver powders and flake silver powders with a diameter of 2 μm were weighed at a mass ratio of 2:4:3 and mixed in a mixer for 4 hours. After uniform mixing, the conductive metal powder and composite organic carrier were mixed using a high-speed dispersing mixer (mass ratio of conductive metal powder to composite organic carrier was 90:10) at a speed of 400 rpm for 30 minutes to obtain a mixed slurry. The mixed slurry was then ground using a three-roll mill until the fineness of the slurry was ≤7 μm to obtain the low-temperature curing conductive slurry.

[0034] The prepared low-temperature curing conductive paste was tested and found to have a volume resistivity of 9 μΩ. The viscosity was measured at cm, and the change in viscosity with storage time at room temperature was tested. The results are as follows: Figure 1 As shown.

[0035] Example 2 This embodiment provides a low-temperature curing conductive paste that can be stored at room temperature, comprising the following components by weight percentage: 95% conductive metal powder (20% first spherical silver powder (median particle size D)). 50 (300 nm), 20% flake silver powder (median particle size D) 50 (4 μm) and 55% spherical silver-coated copper powder (median particle size D) 50 The composition includes 2 μm), 1.5% phenolic resin (638), 0.7% p-toluenesulfonic acid pyridine salt, 2.5% composite solvent (1% tripropylene glycol methyl ether (saturated vapor pressure of 0.03 mmHg at 25℃), 1% dipropylene glycol methyl ether (saturated vapor pressure of 0.4 mmHg at 25℃) and 0.5% diethyl sebacate (saturated vapor pressure of 0.000544 mmHg at 25℃)) and 0.3% additives (including 0.1% thixotropic agent (polyamide wax), 0.1% dispersant (sodium dodecyl sulfate) and 0.1% silane coupling agent (KH-550)).

[0036] This embodiment provides a method for preparing a low-temperature curing conductive paste that can be stored at room temperature, including the following steps: S1. Tripropylene glycol methyl ether, dipropylene glycol methyl ether, and diethyl sebacate are mixed evenly in a mass ratio of 2:2:1. The mixing method is stirring at a speed of 150 rpm. After stirring at room temperature for 5 minutes, a mixed composite solvent is obtained. The composite solvent, phenolic resin, pyridinium p-toluenesulfonate, polyamide wax, sodium dodecyl sulfate, and silane coupling agent (KH-550) were mixed in a mass ratio of 2.5:1.5:0.7:0.1:0.1:0.1 and stirred at 90°C for 3 hours at a stirring speed of 50 rpm. After the mixture became homogeneous and clear, the composite organic carrier was obtained.

[0037] S2. Weigh the first spherical silver powder, flake silver powder, and spherical silver-coated copper powder at a mass ratio of 4:4:11, and mix them in a mixer for 4 hours. After uniform mixing, use a high-speed dispersing mixer to mix the above conductive metal powder and composite organic carrier (mass ratio of conductive metal powder to composite organic carrier is 90:10). The preferred stirring speed is 450 rpm, and the stirring time is 60 min to obtain a mixed slurry. Then, grind the mixed slurry using a three-roll mill until the fineness of the slurry is ≤7μm to obtain the low-temperature curing conductive slurry.

[0038] The prepared low-temperature curing conductive paste was tested and found to have a volume resistivity of 8.5 μΩ. The viscosity was measured at cm, and the change in viscosity with storage time at room temperature was tested. The results are as follows: Figure 1 As shown.

[0039] Example 3 This embodiment provides a low-temperature curing conductive paste that can be stored at room temperature, comprising the following components by weight percentage: 92% composite conductive metal powder (15% first spherical silver powder (median particle size D)). 50 (300nm), 17% flake silver powder (median particle size D) 50 (4 μm) and 60% spherical silver-coated copper powder (median particle size D) 50 The composition includes 2 μm, 1% epoxy resin, 1% benzoxazine resin (JBZ-BA100N), 0.5% BF3-aniline complex, 0.5% YbCl3-hexamethylphosphoric triamine, 2.5% composite solvent (1% dipropylene glycol methyl ether (saturated vapor pressure of 0.4 mmHg at 25℃), 1% 1,3-propanediol monoethyl ether (saturated vapor pressure of 0.0105 mmHg at 25℃) and 0.5% dibutyl phthalate (saturated vapor pressure of 0.04 mmHg at 25℃)) and 1% additives (including 0.5% thixotropic agent (polyamide wax), 0.3% dispersant (sodium dodecyl sulfate) and 0.2% silane coupling agent (KH-550)).

[0040] This embodiment provides a method for preparing a low-temperature curing conductive paste that can be stored at room temperature, including the following steps: S1. Dipropylene glycol methyl ether, 1,3-propanediol monoethyl ether, and dibutyl phthalate were mixed evenly at a mass ratio of 2:2:1. The mixing method was stirring at 150 rpm. After stirring at room temperature for 5 minutes, a mixed composite solvent was obtained. The composite solvent, epoxy resin, benzoxazine resin, BF3-aniline complex, YbCl3-hexamethylphosphoric triamine, polyamide wax, sodium dodecyl sulfate, and silane coupling agent (KH-550) were mixed in a mass ratio of 25:10:10:5:5:5:3:2 and stirred at 90°C for 3 hours at a stirring speed of 50 rpm. After the mixture became homogeneous and clear, the composite organic carrier was obtained.

[0041] S2. Weigh the first spherical silver powder, flake silver powder, and spherical silver-coated copper powder at a mass ratio of 15:17:60, and mix them in a mixer for 4 hours. After uniform mixing, use a high-speed dispersing mixer to mix the above conductive metal powder and composite organic carrier (mass ratio of conductive metal powder to composite organic carrier is 90:10). The preferred stirring speed is 450 rpm, and the stirring time is 60 min. Then, grind the mixed slurry using a three-roll mill until the fineness of the slurry is ≤7μm to obtain the low-temperature curing conductive slurry.

[0042] The prepared low-temperature curing conductive paste was tested and found to have a volume resistivity of 9.5 μΩ. The viscosity was measured at cm, and the change in viscosity with storage time at room temperature was tested. The results are as follows: Figure 1 As shown.

[0043] Comparative Example 1 This comparative example provides a low-temperature curing conductive paste and its preparation method. The only difference from Example 2 is that the curing agent used is a conventional curing agent (Desmodur® BL 1265), and the other steps are the same as in Example 2.

[0044] The prepared low-temperature curing conductive paste was tested and found to have a volume resistivity of 12 μΩ. The viscosity was measured at cm, and the change in viscosity with storage time at room temperature was tested. The results are as follows: Figure 1 As shown.

[0045] Comparative Example 2 This comparative example provides a low-temperature curing conductive paste and its preparation method. The only difference from Example 2 is that the composite solvent is replaced with butyl carbitol (saturated vapor pressure at 25°C is 0.76 mmHg), and the remaining steps are the same as in Example 2.

[0046] The prepared low-temperature curing conductive paste was tested and found to have a volume resistivity of 15 μΩ. The viscosity was measured at cm, and the change in viscosity with storage time at room temperature was tested. The results are as follows: Figure 1 As shown.

[0047] Comparative Example 3 This comparative example provides a low-temperature curing conductive paste and its preparation method. The only difference from Example 2 is that the composite solvent is replaced with tripropylene glycol methyl ether, and the remaining steps are the same as in Example 2.

[0048] The prepared low-temperature curing conductive paste was tested and found to have a volume resistivity of 13.5 μΩ. The viscosity was measured at cm, and the change in viscosity with storage time at room temperature was tested. The results are as follows: Figure 1 As shown.

[0049] Test Example 1 The low-temperature curing conductive pastes prepared in Examples 1-3 and Comparative Examples 1-3 were screen-printed onto glass slides to form 1×6cm plates. 2 The electrode pattern was then placed in an oven at 200℃ for 8 minutes to cure, thus obtaining the metal electrode. The sheet resistance of the metal electrode was measured using a four-probe sheet resistance meter, and the film thickness was measured using a step tester (Veeco Dektak 150, Bruker). The final volume resistivity ρ was obtained by multiplying the two measurements, and the results are shown in Table 1.

[0050] After the prepared slurry was allowed to stand at room temperature for 2 hours, its viscosity was tested using a viscometer (BROOKFIELD DV-Ⅱ+) with a No. 14 rotor at a rotation speed of 10 rpm. The rotational shear viscosity of the sample at each rotation speed for 2 minutes was recorded using the single-point averaging method. The test results are shown in [Figure number missing]. Figure 1 .

[0051] When the viscosity of the paste exceeds 350 Pa·s, the screen printing characteristics of the paste become very poor. The printed grid electrodes will exhibit phenomena such as grid breakage and large height fluctuations (hump phenomenon), which will greatly reduce the conductivity of the grid electrodes and reduce the conversion efficiency of the solar cell.

[0052] Table 1. Comparison of the bulk resistivity of the conductive pastes prepared in Examples 1-3 and Comparative Examples 1-3

[0053] Table 1 shows the volume resistivity test results of the low-temperature curing conductive pastes prepared in Examples 1-3 and Comparative Examples 1-3 after curing. It can be seen that the volume resistivity of the pastes in Examples 1-3 of this invention is lower than that in Comparative Examples 1-3, indicating that the low-temperature curing conductive pastes prepared in this invention have superior conductivity after curing. Furthermore, from... Figure 1It can be seen that, under room temperature storage conditions, the viscosity of the slurries in Examples 1-3 changed little with time, and the highest viscosity after 5 months of storage did not exceed 335 Pa·s. In contrast, Comparative Example 1 used a conventional curing agent instead of the heat-latent curing agent provided by this invention (the other components and proportions were the same). Its slurry viscosity began to increase after 2 months of storage, reaching 370 Pa·s after 5 months, indicating that the conventional curing agent had undergone a slow cross-linking reaction with the resin during storage. Comparative Example 2 used a conventional organic solvent instead of the low vapor pressure solvent (the other components and proportions were the same). Its slurry viscosity was high from the beginning of storage and gradually increased from the initial storage period, reaching 420 Pa·s after 5 months. This indicates that the conventional solvent is easy to volatilize when stored at room temperature, and has the most significant negative impact on the storage stability of the slurry. Comparative Example 3 used only a single low vapor pressure solvent (the other parameters remained unchanged). Its slurry viscosity remained stable during storage, and was close to the viscosity of the slurry using a composite low vapor pressure solvent, but the volume resistivity was higher. This may be due to uneven solvent evaporation during the curing process, which caused defects such as "peeling" and voids in the electrodes, thereby reducing conductivity. The above results show that the low-temperature curing conductive paste provided by the present invention not only achieves excellent conductivity but also has good long-term storage stability at room temperature.

[0054] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A low-temperature curing conductive paste that can be stored at room temperature, characterized in that, By weight percentage, it includes the following raw materials: 90-95% conductive metal powder, 1-5% organic resin, 0.1-2% curing agent, 1-5% composite solvent, and 0.1-2% additives; The organic resin includes epoxy resin, and the curing agent includes a first curing agent; the first curing agent includes one or more of BF3-piperidine complex, BF3-aniline complex, and AlCl3-pyridine complex. Alternatively, the organic resin may include phenolic resin, and the curing agent may include a second curing agent; the second curing agent may include one or more of benzyltriethylammonium chloride and p-toluenesulfonic acid pyridinium salt. Alternatively, the organic resin may include benzoxazine resin, and the curing agent may include a third curing agent; the third curing agent may include one or more of YbCl3-hexamethylphosphoric triamine and Sc(OTf)3-tributylamine complex; The composite solvent comprises at least two alcohol ether solvents; or the composite solvent comprises at least one alcohol ether solvent and at least one ester solvent; The saturated vapor pressures of the alcohol ether solvents and ester solvents at room temperature are independently 0.0005-0.4 mmHg.

2. The low-temperature curing conductive paste that can be stored at room temperature according to claim 1, characterized in that, The conductive metal powder comprises a first conductive metal powder and a second conductive metal powder; The first conductive metal powder includes flake-shaped silver powder, and the second conductive metal powder includes spherical conductive metal powder; Optionally, the second conductive metal powder includes at least one of a first spherical silver powder, a second spherical silver powder, and a spherical silver-coated copper powder.

3. The low-temperature curing conductive paste that can be stored at room temperature according to claim 2, characterized in that, At least one of the following conditions must be met: (1) The median particle size D of the flake silver powder 50 2-5 μm; (2) The median particle size D of the spherical silver-coated copper powder 50 1-5 μm; (3) The median particle size D of the first spherical silver powder 50 The range is 200-800 nm; (4) The median particle size D of the second spherical silver powder 50 1-5 μm; (5) The mass ratio of the first conductive metal powder to the second conductive metal powder is (17-30): (60-75).

4. The low-temperature curing conductive paste that can be stored at room temperature according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The alcohol ether solvents include one or more of tripropylene glycol methyl ether, dipropylene glycol methyl ether, diethylene glycol dibutyl ether, and 1,3-propanediol monoethyl ether; (2) The ester solvents include one or more of ethylene glycol diacetate, diethyl sebacate and dibutyl phthalate.

5. The low-temperature curing conductive paste that can be stored at room temperature according to claim 1, characterized in that, The additives include thixotropic agents, dispersants, and coupling agents.

6. The low-temperature curing conductive paste that can be stored at room temperature according to claim 5, characterized in that, The mass ratio of the thixotropic agent, dispersant, and coupling agent is (0.1-0.5):(0.1-0.4):(0.1-0.3).

7. The low-temperature curing conductive paste that can be stored at room temperature according to claim 5, characterized in that, The thixotropic agent includes one or more of ethyl cellulose and polyamide wax.

8. The low-temperature curing conductive paste that can be stored at room temperature according to claim 5, characterized in that, The dispersant includes one or more of sodium dodecyl sulfate and polyacrylamide.

9. The low-temperature curing conductive paste that can be stored at room temperature according to claim 5, characterized in that, The coupling agent includes a silane coupling agent.

10. A method for preparing a low-temperature curing conductive paste that can be stored at room temperature according to any one of claims 1-9, characterized in that, Includes the following steps: S1. Mix the composite solvent with organic resin, curing agent and additives to obtain a composite organic carrier; S2. The conductive metal powder and the composite organic carrier obtained in S1 are mixed and then ground to obtain the low-temperature curing conductive slurry.

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