Low-temperature base metal conductive paste and preparation method and application thereof

Abstract

The invention provides low-temperature base metal conductive paste and a preparation method and application thereof.The low-temperature base metal conductive paste comprises 86 wt%-90 wt% of a conductive phase, 3 wt%-6 wt% of resin, 0.1 wt%-0.5 wt% of a curing agent, 0.1 wt%-1 wt% of a dispersing agent, 0.1 wt%-3 wt% of an antioxidant, 0.8 wt%-1.4 wt% of an anti-settling agent and the balance solvent, the conductive phase comprises 30-60 wt% of first-class tin-coated copper powder, 10-30 wt% of second-class tin-coated copper powder and 30-60 wt% of pure copper powder, the first-class tin-coated copper powder is spheroidic and / or blocky and has an average particle size D1, the second-class tin-coated copper powder is flaky and has an average particle size D2, the pure copper powder has an average particle size D3, and D1 / D2 is larger than or equal to 0.5 and smaller than or equal to 1, and D1 / D3 is larger than or equal to 6 and smaller than or equal to 16.7. The tin-coated copper powder with different morphologies is matched according to a specific mass ratio and a specific particle size ratio and is further compounded with the pure copper powder according to a ratio, so that a conductive phase system with dense powder accumulation is formed, the electrode resistivity is reduced, metal silver does not need to be used, the dependence of conductive paste on a conductive network formed by silver powder is eliminated, and the remarkable cost reduction effect is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photovoltaic electronic devices, in particular to a low-temperature base metal conductive paste and a preparation method and application thereof. BACKGROUND

[0002] In the manufacture of photovoltaic electronic devices, conductive paste as a key material directly affects the quality and performance of the device. The traditional high-temperature sintering type conductive silver paste has a peak sintering temperature of more than 700 DEG C, and the production equipment has high load and high energy consumption. With the development of technology, new electronic devices such as hetero-junction with intrinsic thin-layer (HJT) cells have attracted widespread attention due to their high photoelectric conversion efficiency, good high-temperature characteristics, low process temperature, and low production cost (can reduce the thickness of silicon wafer).

[0003] However, HJT cells can only be cured and sintered at 200 DEG C-250 DEG C for a short time due to their material properties, which requires a conductive paste that supports low-temperature sintering. On the other hand, crystalline silicon cells such as Back Contact (BC) cells are also gradually developing towards low-temperature sintering for industrial upgrading to reduce costs and increase production.

[0004] Currently, the low-temperature sintering conductive paste on the market mainly uses silver powder as the conductive phase. However, silver is a precious metal with high cost and limited reserves, and its price fluctuates significantly, which significantly restricts the large-scale development of related industries. To reduce costs, existing technologies often use base metals such as nickel, copper, and aluminum to replace part of the silver powder to prepare low-temperature conductive paste, but there are still the following problems: 1) base metals are easily oxidized in the application process, and have poor conductivity; 2) existing low-temperature conductive paste cannot be free from the dependence on silver powder, and the proportion of base metal addition is limited, which cannot achieve the ideal cost reduction effect; 3) the conductivity of base metal powder is poorer than that of silver powder, and the packing density and dispersion uniformity of base metal paste designed by referring to the silver powder conductive system are not ideal, the contact between base metal powders is not good, which affects the continuity of the conductive network, and the performance of the electrode structure formed is poor. SUMMARY

[0005] To solve the above problems and meet the performance requirements of large-scale cost reduction and high conductivity efficiency of the conductive paste, a first aspect of the present application provides a low-temperature base metal conductive paste, comprising the following components in mass percentage: 86-90wt% of a conductive phase, 3-6wt% of a resin, 0.1-0.5wt% of a curing agent, 0.1-1wt% of a dispersant, 0.1-3wt% of an antioxidant, and 0.8-1.4wt% of an anti-settling agent, and the balance being a solvent, wherein the conductive phase comprises, based on the total mass of the conductive phase, 30-60wt% of a first type of tin-coated copper powder, 10-30wt% of a second type of tin-coated copper powder, and 30-60wt% of pure copper powder, the first type of tin-coated copper powder has a spherical shape and / or a block shape, an average particle size D1, the second type of tin-coated copper powder has a flaky shape, an average particle size D2, the pure copper powder has an average particle size D3, and satisfy: 0.5≤D1 / D2≤1, 6≤D1 / D3≤16.7.

[0006] In some optional embodiments, the average particle size D1 of the first type of tin-coated copper powder is 3-5μm, and the particle size range is 2.4-10.0μm; the average particle size D2 of the second type of tin-coated copper powder is 5-6μm, and the particle size range is 3-15μm.

[0007] In some optional embodiments, the pure copper powder has a spherical shape with a sphericity ≥90%, and an average particle size D3 of 0.3-0.5μm, and a particle size range of 0.1-0.8μm.

[0008] In some optional embodiments, the curing agent comprises a latent amine curing agent and / or a latent cation curing agent.

[0009] In some optional embodiments, the antioxidant comprises one or more of a fat-soluble vitamin organic compound, an organic phosphate compound, an organic phosphine compound, an organic acid compound, an organic amine compound, and an inorganic salt compound.

[0010] In some optional embodiments, the antioxidant at least meets one of the following conditions:

[0011] a. The fat-soluble vitamin organic compound comprises one or more of vitamin A, vitamin C, and vitamin E;

[0012] b. The organic phosphate compound comprises Irgafos 168 phosphate and / or tris(nonylphenyl) phosphite; c. The organic phosphine compound comprises one or more of aminotri(methylene) phosphonic acid, ethylenediamine tetra(methylene) phosphonic acid, diethylenetriamine penta(methylene) phosphonic acid, and n-dodecyl phosphoric acid;

[0013] d. The organic acid compound includes one or more of acetic acid, formic acid, oxalic acid, sebacic acid, and adipic acid;

[0014] e. The organic amine compound includes oleylamine and / or cocoylamine;

[0015] f. The inorganic salt compound includes one or more of ammonium chloride, copper formate tetrahydrate, and copper naphthenate.

[0016] In some optional embodiments, the anti-settling agent includes one or more of polyamide wax, organic phosphate ester, and sodium carboxymethyl cellulose.

[0017] In some optional embodiments, the resin includes a mixture of epoxy resin, ethyl cellulose, and acrylic resin in a mass ratio of (70-80):(2-5):(15-22).

[0018] The dispersant includes one or more of DISPERBYK-111, 80, Solsperse 32500, DISPERBYK-102, DISPERBYK-180, 9900, and 66; and the solvent includes one or more of diethylene glycol butyl ether acetate, dimethyl carbonate, diethylene glycol butyl ether, and alcohol ester twelve.

[0019] A second aspect of the present application provides a preparation method of the low-temperature base metal conductive paste described in any one of the above, including the following steps:

[0020] S1: The antioxidant is placed in a heated container, the solvent and the resin are slowly added, the heating temperature is set to 60°C, and stirring is performed until the components are dissolved and fully mixed;

[0021] S2: The curing agent is added to the heated container, and stirring is performed until the components are fully mixed, and the obtained solution is clear and transparent;

[0022] S3: The anti-settling agent is added to the heated container, high-speed stirring is performed until the components are fully mixed, and the organic carrier is formed, which is then placed at room temperature for more than 8 hours for standby;

[0023] S4: The pure copper powder and the dispersant are weighed and added to the organic carrier, and uniform dispersion is performed to obtain a copper-containing paste;

[0024] S5: The second type of tin-coated copper powder is weighed and added to the copper-containing paste, and uniform dispersion is performed, and then the first type of tin-coated copper powder is added, and stirring and dispersion are continued to obtain the low-temperature base metal conductive paste.

[0025] The third aspect of the present application provides an application of the low-temperature base metal conductive paste or the low-temperature base metal conductive paste prepared by the preparation method described above, and the low-temperature base metal conductive paste is applied to heterojunction cells, back contact cells, PERC cells, TOPCon cells and flexible circuit boards.

[0026] The present application has at least the following technical effects:

[0027] 1) The first aspect of the present application provides a low-temperature base metal conductive paste. Different morphology tin-coated copper powders with specific mass ratio and particle size ratio are compounded, and further compounded with pure copper powder in proportion to form a low-temperature base metal conductive paste with oxidation resistance. The tin-coated copper powder is divided into a first type of tin-coated copper powder with a spherical and / or blocky morphology and a second type of tin-coated copper powder with a flaky morphology of pure copper powder. The average particle size D3 of the pure copper powder is significantly smaller than that of the tin-coated copper powder. Different morphology designs and different particle size combinations are carried out among the powders. The pure copper powder particles are the thinnest, and pre-dispersion is carried out to form a copper-containing paste. Then, the second type of tin-coated copper powder with a flaky morphology is added to form good contact with the pure copper powder and uniform dispersion. Finally, the first type of tin-coated copper powder with a spherical and / or blocky morphology is added, and mechanical stirring and / or grinding are carried out to fill the first type of tin-coated copper powder into the inter-particle pores of the second type of tin-coated copper powder. Finally, a tight packing is formed in the paste system, which enhances the density of the electrode formed by sintering, reduces the bulk resistance of the electrode, and the surface tin layer can still cover the copper powder surface after melting in the subsequent sintering process, continuing to play its anti-oxidation protection role and giving the paste system anti-oxidation performance. In addition, no silver metal powder is needed in the conductive phase system, which breaks the dependence of the conductive paste on silver metal powder to form a conductive network, achieving the ideal cost reduction effect. At the same time, the low-temperature base metal conductive paste can be adapted to a sintering process of 200-250°C, reducing production energy consumption and further enhancing economic benefits.

[0028] 2) The second aspect of the present application provides a preparation method of a low-temperature base metal conductive paste, which is used to prepare the low-temperature base metal conductive paste described in any of the above. The prepared low-temperature base metal conductive paste does not need to add silver metal powder, which maximally reduces the cost of raw materials, and the different morphology tin-coated copper powders are compounded with pure copper powder in a specific mass ratio and particle size ratio. The obtained conductive paste has a dense packing between the powders in the conductive phase system, a significantly reduced electrode bulk resistivity, and is suitable for a low-temperature sintering process. The molten tin continuously plays an anti-oxidation role, the electrode contact structure formed by sintering has good density, low resistivity and good electrical performance.

[0029] 3) The third aspect of the present application provides an application of the low-temperature base metal conductive paste. The low-temperature base metal conductive paste described in any one of the above can be applied to the heterojunction cell, the back contact cell, the PERC cell, the TOPCon cell and the flexible circuit board and the like. Through the collocation of the tin-coated copper powder and the pure copper powder, the purpose of reducing the paste body resistance and improving the paste oxidation resistance is achieved. The sintering forms the electrode contact structure with good density and low resistivity, thereby guaranteeing the electrical performance of the photovoltaic electronic device. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the description of the embodiments of the present application will be briefly introduced.

[0031] Figure 1 is a SEM scanning diagram of a cross section of a metal grid line formed after screen printing and sintering of the low-temperature base metal conductive paste provided by the present application, which is magnified by 3000 times;

[0032] Figure 2 is a SEM scanning diagram of a cross section of a metal grid line formed after screen printing and sintering of another optional low-temperature base metal conductive paste provided by the present application, which is magnified by 4000 times;

[0033] Figure 3 is a SEM scanning diagram of a cross section of a metal grid line formed after screen printing and sintering of another optional low-temperature base metal conductive paste provided by the present application, which is magnified by 10,000 times. DETAILED DESCRIPTION

[0034] The embodiments of the present application will be described in detail below, which are only used to explain the present application and cannot be understood as a limitation of the present application.

[0035] In the description of the embodiments of the present application, it should be noted that all the ranges disclosed in the present application should be understood as including any and all sub-ranges falling within the range. For example, the stated range "86-90wt%" should be considered to include any and all sub-ranges starting with a minimum value of 86wt% or more and ending with a maximum value of 90wt% or less, for example, 86-89wt%, or 88-90wt%. At the same time, all the ranges disclosed in the present application should be considered to include the end points of the range, unless otherwise explicitly stated. For example, the range "3-5μm" or "3μm to 5μm" or "between 3μm and 5μm" should be considered to include the end points 3μm and 5μm.

[0036] In this paper, unless otherwise specified, the proportion refers to the mass ratio, and the percentage refers to the mass percentage.

[0037] Herein, all possible combinations between technical features in various embodiments or examples are not described in order to simplify the description. Therefore, as long as there is no contradiction in the combination of technical features, various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered as the scope described in the specification.

[0038] In the field of photovoltaic electronic devices, the use of base metals instead of silver for conductive superposition low-temperature sintering can reduce the generation cost of photovoltaic devices in terms of raw material cost and sintering energy consumption, and is an important research direction for future photovoltaic devices. However, base metals such as nickel, copper and aluminum are easily oxidized during sintering, affecting the conductivity, and the powder bulk density of base metal powder is poor, affecting the continuity of the conductive network, resulting in poor performance of the electrode structure. Based on this, the present application explores the technical scheme of low-temperature base metal conductive paste with zero addition of silver powder, which can significantly reduce the cost of conductive paste and battery while achieving the same battery conversion efficiency as 30wt% silver content conductive silver paste.

[0039] Based on this, a low-temperature base metal conductive paste, the conductive paste comprises the following components in mass percentage: 86-90wt% of conductive phase, 3-6wt% of resin, 0.1-0.5wt% of curing agent, 0.1-1wt% of dispersant, 0.1-3wt% of antioxidant and 0.8-1.4wt% of anti-settling agent, and the balance is solvent, wherein, based on the total mass of the conductive phase, the conductive phase comprises 30-60wt% of first type tin-coated copper powder, 10-30wt% of second type tin-coated copper powder and 30-60wt% of pure copper powder, the morphology of the first type tin-coated copper powder is spherical and / or blocky, the average particle size is D1, the morphology of the second type tin-coated copper powder is flaky, the average particle size is D2, the average particle size of the pure copper powder is D3, and 0.5≤D1 / D2≤1, 6≤D1 / D3≤16 are satisfied.

[0040] It should be noted that the first type of tin-coated copper powder can be a single powder with a spherical morphology, a single powder with a blocky morphology, or a mixed powder with a spherical and blocky morphology. Overall, the first type of tin-coated copper powder is relatively dense, has fewer surface defects, is easier to disperse, and has better flowability. The densification characteristics can also help reduce the bulk resistance of the electrode structure. In addition, the tin coating melts and adheres to each other during sintering, which is beneficial for the sintering of the conductive paste. The second type of tin-coated copper powder has a flaky morphology and a relatively flat surface, which has a large contact area and thus good contact performance. The subsequent paste can provide good surface contact, resulting in excellent bulk resistance. However, there is a large steric hindrance effect between the powders, which has poor packing density and forms a large number of voids. The average particle size of pure copper powder is orders of magnitude different from that of tin-coated copper powder, and it also has good electrical conductivity. The combination of the three can first pre-disperse the pure copper powder with the smallest particle size, which can maximize the prevention of particle agglomeration under the action of dispersants and anti-settling agents. Then, the second type of tin-coated copper powder with a flaky morphology is added to form good contact with the pure copper powder and to disperse uniformly. Finally, the first type of tin-coated copper powder with a spherical and / or blocky morphology is added, and mechanical stirring and / or three-roll refining is used to fill the first type of tin-coated copper powder into the pores between the second type of tin-coated copper powder. This can form a compact packing in the paste system, enhance the density of the sintered electrode, and reduce the bulk resistance of the electrode. In the subsequent sintering process, the surface tin layer can still cover the copper powder after melting, continuing to play its role in protecting against oxidation and giving the paste system antioxidant properties.

[0041] In addition, no silver metal is needed in the conductive phase system, which eliminates the dependence of the conductive paste on silver metal powder to form a conductive network, achieving optimal cost reduction. At the same time, the low-temperature base metal conductive paste can be adapted to a sintering process at 200-250°C, reducing production energy consumption and further enhancing economic benefits.

[0042] In the specific implementation process, the aforementioned low-temperature base metal conductive paste is screen printed and sintered to form a grid line structure. The cross-section of the grid line is characterized by a scanning electron microscope, as shown in Figures 1-3 It can be seen that the powder has high packing density. Further TLM testing of the grid line structure shows that the line resistance and contact resistance performance of the grid line are excellent, indicating that the oxidation of the base metal powder is controlled during sintering, and the electrode resistivity is also improved.

[0043] In this application, the sum of the components in the conductive paste is 100%.

[0044] Further, the first type of tin-coated copper powder has an average particle size D1 of 3-5 μm and a particle size range of 2.4-10.0 μm; and the second type of tin-coated copper powder has an average particle size D2 of 5-6 μm and a particle size range of 3-15 μm.

[0045] Further, the pure copper powder has a spherical shape with a sphericity of ≥ 90%, and an average particle size D3 of 0.3-0.5 μm and a particle size range of 0.1-0.8 μm.

[0046] In some embodiments, the curing agent includes a latent amine curing agent and / or a latent cation curing agent.

[0047] Specifically, the curing agent can be 4,4'-diaminodiphenyl sulfone or diphenyl-(4-phenylthio) phenyl sulfonium hexafluoroantimonate, or a mixture of 4,4'-diaminodiphenyl sulfone and diphenyl-(4-phenylthio) phenyl sulfonium hexafluoroantimonate at a certain ratio, for example, the ratio can be 2:8.

[0048] In some embodiments, the antioxidant includes one or more of a fat-soluble vitamin organic compound, an organic phosphate compound, an organic phosphine compound, an organic acid compound, an organic amine compound, and an inorganic salt compound.

[0049] The fat-soluble vitamin organic compound includes one or more of vitamin A, vitamin C, and vitamin E.

[0050] The organic phosphate compound includes Irgafos 168 phosphate and / or tris(nonylphenyl) phosphite.

[0051] The organic phosphine compound includes one or more of aminotri(methylene) phosphonic acid, ethylenediamine tetra(methylene) phosphonic acid, diethylenetriamine penta(methylene) phosphonic acid, and n-dodecyl phosphonic acid.

[0052] The organic acid compound includes one or more of acetic acid, formic acid, oxalic acid, sebacic acid, and adipic acid.

[0053] The organic amine compound includes oleyl amine and / or cocoyl amine.

[0054] The inorganic salt compound includes one or more of ammonium chloride, copper formate tetrahydrate, and copper naphthenate.

[0055] For example, the fat-soluble vitamin organic compounds can play the reduction characteristics with the oxidized pure copper powder in the sintering solidification process, and part of the oxidized pure copper powder is reduced to copper element; and the organic phosphate compounds, the organic phosphine compounds, and the organic amine compounds can decompose to produce reducing atmosphere such as H2, NH3, and CO in the solidification process, which can not only consume the oxygen in the sintering atmosphere, but also reduce part of the oxidized copper; the organic acid can remove the surface impurities and organic matters of the metal powder in the conductive phase, and improve the sintering density; and the inorganic salt compound can be decomposed to produce copper element or reducing atmosphere, and reduce the influence of the oxidation of copper.

[0056] It should be noted that the Irgafos 168 phosphate is the salted Irgafos 168, and the Irgafos 168 is a product sold by BASF Company, and the core chemical composition includes: tris (2, 4-di-tert-butylphenyl) phosphite.

[0057] In some embodiments, the anti-settling agent includes one or more of polyamide wax, organic phosphate, sodium carboxymethyl cellulose, and RHEOBYK-410.

[0058] The RHEOBYK-410 is a product sold by BYK Company in Germany.

[0059] In some embodiments, the resin includes a mixture of epoxy resin, ethyl cellulose, and acrylic resin in a mass ratio of (70-80):(2-5):(15-22).

[0060] The dispersant includes one or more of DISPERBYK-111, 80, Solsperse 32500, DISPERBYK-102, DISPERBYK-180, 9900, and 66; and the solvent includes one or more of diethylene glycol butyl ether acetate, dimethyl carbonate, diethylene glycol butyl ether, and alcohol ester twelve.

[0061] The DISPERBYK-111, the DISPERBYK-102, and the DISPERBYK-180 are products sold by BYK Company in Germany, 80 is a known emulsifier, the Solsperse 32500 is a product sold by Lubrizol Company, 9900, and 66 are products sold by Walker Company.

[0062] The second aspect of the present application provides a preparation method of the low-temperature base metal conductive paste as described in any one of the preceding aspects, including the following steps:

[0063] S1: Put the antioxidant into a heating container, slowly add the solvent and the resin, set the heating temperature to 60°C, stir until the components are dissolved and fully mixed;

[0064] S2: Put the curing agent into the heating container, stir until the components are fully mixed, and the resulting solution is clear and transparent;

[0065] S3: Put the anti-settling agent into the heating container, stir at high speed until the components are fully mixed, form the organic carrier, and stand at room temperature for more than 8 hours for standby;

[0066] S4: Weigh the pure copper powder and the dispersing agent, and add them to the organic carrier to obtain a copper-containing paste;

[0067] S5: Weigh the second type of tin-coated copper powder, add it to the copper-containing paste, and then add the first type of tin-coated copper powder after uniform dispersion, continue to stir and disperse to obtain the low-temperature base metal conductive paste.

[0068] In this application, room temperature is generally defined as 25°C according to the conventional interpretation.

[0069] The low-temperature base metal conductive paste prepared by the preparation method of the present application does not need to add silver metal powder, which maximally reduces the cost of raw materials, and the different morphologies of tin-coated copper powder are matched with the pure copper powder according to a specific mass ratio and particle size ratio. The resulting conductive paste has a compact stacking between the powder materials of the conductive phase system, the resistivity of the electrode body is significantly reduced, and it is suitable for low-temperature sintering process. The molten tin continuously plays the role of oxidation resistance, and the electrode contact structure formed by sintering has good density, low resistivity, and good electrical performance.

[0070] The third aspect of the present application provides an application of a low-temperature base metal conductive paste. The low-temperature base metal conductive paste described in any one of the above can be applied to heterojunction cells, back contact cells, PERC cells, TOPCon cells, and flexible circuit boards. By matching tin-coated copper powder with pure copper powder, the purpose of reducing the resistivity of the paste body and improving the oxidation resistance of the paste is achieved. The electrode contact structure formed by sintering has good density, low resistivity, and good electrical performance of photovoltaic electronic devices.

[0071] The following examples further illustrate the present application.

[0072] Unless otherwise specified, the reagents and materials used in the following examples and comparative examples are commercially available.

[0073] The resin used in the examples and comparative examples is a mixture of epoxy resin, ethyl cellulose, and acrylic resin with a mass ratio of 80:3:17;

[0074] The antioxidant used in the examples and comparative examples is vitamin C;

[0075] The curing agent used in the examples and comparative examples is a mixture of 4,4'-diaminodiphenyl sulfone and diphenyl-(4-phenylthio)phenyl sulfonium hexafluoroantimonate in a mass ratio of 2:8.

[0076] The solvent used in the examples and comparative examples is a mixture of diethylene glycol butyl ether acetate: dimethyl carbonate: diethylene glycol butyl ether in a mass ratio of 60:20:20.

[0077] Example 1

[0078] Example 1 provides a method for preparing a low-temperature base metal conductive paste, comprising the following steps:

[0079] S1: Put 15g of the antioxidant into a heated container, set the heating temperature to 60°C, slowly add 42g of the solvent and 60g of the resin, and mechanically stir at 80rpm for 45min to fully mix the components;

[0080] S2: Add 3g of the curing agent to the heated container, mechanically stir at 80rpm for 30min until the components are fully mixed, and the obtained solution is clear and transparent;

[0081] S3: Add 13g of the anti-settling agent to the heated container, stir at 120rpm for 30min until the components are fully mixed, form 133g of the organic carrier, and stand at room temperature for more than 8h for standby;

[0082] S4: Weigh 364g of the pure copper powder and 5g of the dispersant BYK-111, add them to 133g of the organic carrier, and mechanically stir at 60rpm for 10min to uniformly disperse to obtain a copper-containing paste;

[0083] S5: Weigh 173.8g of the second type of tin-coated copper powder, add it to the copper-containing paste, mechanically stir at 60rpm for 5min, then add 364g of the first type of tin-coated copper powder, and mechanically stir at 100rpm for 20min to obtain the low-temperature base metal conductive paste.

[0084] The average particle size of the first type of tin-coated copper powder is 3.4μm, the particle size range is 2.4-10.0μm, the powder morphology is spherical and blocky; the average particle size of the second type of tin-coated copper powder is 5.2μm, the particle size range is 3-15μm, and the powder morphology is flaky; the average particle size of the pure copper powder is 0.37μm, the particle size range is 0.1-0.8μm, and the powder morphology is spherical with a sphericity of ≥90%.

[0085] The components of the low temperature base metal conductive paste in Example 1 are: 86.72wt% of conductive phase, 5.77wt% of resin, 0.29wt% of curing agent, 0.48wt% of dispersant, 1.44wt% of antioxidant, 1.25wt% of anti-settling agent, 4.05wt% of solvent; the conductive phase comprises 40.36wt% of pure copper powder, 40.36wt% of the first type of tin-coated copper powder and 19.28wt% of the second type of tin-coated copper powder.

[0086] Example 2

[0087] Example 2 provides a low temperature base metal conductive paste, which is only different from Example 1 in that: the conductive phase comprises 60wt% of pure copper powder, 10wt% of the second type of tin-coated copper powder and 30wt% of the first type of tin-coated copper powder.

[0088] Example 3

[0089] Example 3 provides a low temperature base metal conductive paste, which is only different from Example 1 in that: 88.43wt% of conductive phase, 3.88wt% of resin, 0.20wt% of curing agent, 0.55wt% of dispersant, 1.6wt% of antioxidant, 1.12wt% of anti-settling agent, 4.22wt% of solvent; the conductive phase comprises 40.36wt% of pure copper powder, 40.36wt% of the first type of tin-coated copper powder and 19.28wt% of the second type of tin-coated copper powder.

[0090] Comparative Example 1

[0091] Comparative Example 1 provides a low temperature base metal conductive paste, which is only different from Example 1 in that: the conductive phase is 100wt% of pure copper powder.

[0092] Comparative Example 2

[0093] Comparative Example 2 provides a low temperature base metal conductive paste, which is only different from Example 1 in that: the conductive phase is 100wt% of the first type of tin-coated copper powder.

[0094] Comparative Example 3

[0095] Comparative Example 3 provides a low temperature base metal conductive paste, which is only different from Example 1 in that: the conductive phase comprises 80wt% of the first type of tin-coated copper powder and 20wt% of the second type of tin-coated copper powder.

[0096] Comparative Example 4

[0097] Comparative Example 4 provides a low temperature base metal conductive paste, which is only different from Example 1 in that: the flaky second type of tin-coated copper powder is replaced by flaky pure copper powder; the flaky pure copper powder has an average particle size of 5.2μm and a particle size range of 3-15μm.

[0098] Comparative Example 5

[0099] Comparative Example 5 provides a low-temperature base metal conductive paste, which is different from Example 1 only in that: 92.85wt% of the conductive phase, 3.3wt% of the resin, 0.16wt% of the curing agent, 0.5wt% of the dispersant, 0.52wt% of the anti-settling agent, 2.67wt% of the solvent; the conductive phase includes 78wt% of silver content of 12% silver-coated copper powder and 22wt% of pure silver powder, the average particle size of the silver-coated copper powder is 5μm, the particle size range is 3.1-8.5μm, and the sphericity is ≥95%; the average particle size of the pure silver powder is 0.3μm, the particle size range is 0.2-0.4μm, and the sphericity is ≥90%.

[0100] The low-temperature base metal conductive paste provided by Examples 1-3 and Comparative Examples 1-5 is used to prepare silicon wafer solar cell pieces.

[0101] The low-temperature base metal conductive paste provided by Examples 1-3 and Comparative Examples 1-5 is printed on the back of the HJT cell piece using a screen printing technique, and the front is printed using a conventional low-temperature pure silver paste to form a cell piece. The cell piece is dried in a belt drying furnace, and then sintered at 210-230℃ in a belt sintering furnace. After sintering and cooling, an HJT solar cell is formed. After screen printing and sintering, the cross section of the metal grid line of Examples 1-3 is close to a Gaussian distribution, as shown in Figure 1 The cross section SEM of the grid line of the cell piece corresponding to Example 1 is obtained by laser back cutting, and it can be seen from the figure that the grid line after curing is dense and accumulated. The line width is controlled at about 45μm, and the line height is about 12μm.

[0102] For the prepared cell, Examples 1-3 are denoted as SC1-3, and Comparative Examples 1-5 are denoted as C1-5; the electrical properties of the cell are tested using an I-V tester, and the contact resistance and line resistance are tested using a TLM contact resistance meter. The test data of the conversion efficiency, short-circuit current, fill factor, line resistance and contact resistance of the HJT cell pieces prepared by the above examples and comparative examples are shown in Table 1, wherein Eta refers to the conversion efficiency value, Isc refers to the short-circuit current value, FF refers to the fill factor value, Rb refers to the line resistance value, and Rc refers to the contact resistance value. The test results are shown in Table 1 as follows:

[0103] Table 1-Electrical property test of Examples 1-3 and Comparative Examples 1-5

[0104] Eta (%) Isc (A) FF (%) Rb (ohm) Rc (ohm) Example 1 25.26 8.715 85.34 2.84 0.78 Example 2 25.18 8.714 85.07 3.16 0.56 Example 3 25.23 8.715 85.28 2.94 0.62 Comparative Example 1 22.06 8.717 81.34 4.27 1.33 Comparative Example 2 25.08 8.714 84.88 2.41 1.28 Comparative Example 3 25.14 8.716 84.99 2.07 1.53 Comparative Example 4 24.35 8.716 83.26 3.69 0.83 Comparative Example 5 25.23 8.716 85.36 2.18 1.05

[0105] As can be seen from Table 1:

[0106] As can be seen from the experimental data of SC1-3 and C1-5, SC1 performs best, as shown in Figure 2 andFigure 3 The SEM cross-section scanning image shows that the tin-coated copper powder and pure copper powder designed in the application can make the powder in the slurry have excellent bulk density and lower bulk resistance and contact resistance. The small particle size of the color in the figure corresponds to the pure copper powder, the large particle ball is the first type of tin-coated copper powder, and the irregular particle corresponds to the second type of tin-coated copper powder. The three types of powders form a hierarchical filling effect, have high bulk density, and the surface tin layer of the flaky tin-coated copper powder is melted to bond the surrounding pure copper powder and spherical tin-coated copper powder, forming sintering and improving the contact performance.

[0107] According to the experimental data of SC1 and C5, the first type of tin-coated copper powder, the second type of tin-coated copper powder, and the pure copper powder in SC1 form the most compact packing. During the printing and curing process of the slurry, the tin on the surface of the tin-coated copper powder melts to form sintering and covers the surface of the copper powder (see Figure 3 ), and continues to play its antioxidant protection role. At the same time, the flaky morphology of the second type of tin-coated copper powder has good surface contact characteristics, and the large particle size of the first type of tin-coated copper powder has good conductivity, so that the slurry after printing and curing has good line resistance and contact resistance.

[0108] According to the experimental data of SC2 and SC1, the conversion efficiency Eta of SC2 is 0.08% lower than that of SC1. Increasing the proportion of pure copper powder and reducing the proportion of tin-coated copper powder reduces the sintering activity and antioxidant ability of the slurry after curing, increases the line resistance, and significantly reduces the contact resistance.

[0109] According to the experimental data of SC3, the content of the conductive phase is increased without changing the proportion of metal powders in the conductive phase, the proportion of resin, curing agent, and anti-settling agent is reduced, and the proportion of dispersant, antioxidant, and solvent is increased. The conversion efficiency Eta of the slurry after printing and curing is slightly lower than that of SC1 by 0.03%. The main reason is that the amount of resin polymer material in the slurry after curing is reduced, more antioxidant is required to protect the copper powder, the line resistance of the slurry increases slightly, and the contact resistance decreases.

[0110] According to the experimental data of C1-4, the conductive phase in C1 uses pure copper powder, the powder particle size is small, the bulk density is low, the powder has no tin layer protection during the curing process, the antioxidant ability is weak, but the contact resistance is low, which shows the important role of pure copper powder in forming a conductive network. C4 uses pure copper powder with a particle size and morphology similar to the second type of tin-coated copper powder in SC1 instead of the second type of tin-coated copper powder in SC1. The conversion efficiency Eta of C4 is 0.091% lower than that of SC1, which shows that under the premise of compact powder packing, the lack of antioxidant protection of the tin layer increases the line resistance and contact resistance of the slurry. The slurry C2-3 uses tin-coated copper powder and does not use nano copper powder. Due to the good conductivity of the first type and the second type of tin-coated copper powder, the line resistance of the slurry after curing is significantly reduced, but the contact resistance increases significantly.

[0111] From the above test data, it can be seen that by using tin-coated copper powder and pure copper powder in combination, with a ratio of: the first type of tin-coated copper powder with a spherical and block morphology 30-60wt%, the second type of tin-coated copper powder with a flaky morphology 10-30wt%; pure copper powder 30-60wt%; 0.1-0.5wt% of a curing agent, 0.1-1wt% of a dispersing agent, 0.1-3wt% of an antioxidant, 0.8-1.4wt% of an anti-settling agent, and the balance being a solvent, the low-temperature base metal conductive paste prepared has a total silver content of 29.12% in the conductive paste under the premise of not containing silver, the experimental data can be flat with the conductive paste of C5, has obvious performance advantages and cost advantages.

[0112] Although the embodiments of the present embodiment have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, replacements and variations can be made to these embodiments without departing from the principles and purposes of the present embodiment, and the scope of the present embodiment is defined by the claims and their equivalents.

Claims

1. A low-temperature base metal conductive paste, characterized in that, The conductive paste comprises the following components by mass percentage: 86-90 wt% conductive phase, 3-6 wt% resin, 0.1-0.5 wt% curing agent, 0.1-1 wt% dispersant, 0.1-3 wt% antioxidant, and 0.8-1.4 wt% anti-settling agent, with the balance being solvent. The conductive phase, by total mass, comprises 30-60 wt% first-type tin-coated copper powder, 10-30 wt% second-type tin-coated copper powder, and 30-60 wt% pure copper powder. The first-type tin-coated copper powder has a spherical and / or blocky morphology with an average particle size of D1. The second-type tin-coated copper powder has a flake-like morphology with an average particle size of D2. The pure copper powder has an average particle size of D3, and satisfies the following conditions: 0.5 ≤ D1 / D2 ≤ 1, 6 ≤ D1 / D3 ≤ 16.

7.

2. The low-temperature base metal conductive paste according to claim 1, characterized in that, The average particle size D1 of the first type of tin-coated copper powder is 3-5 μm, and the particle size range is 2.4-10.0 μm; the average particle size D2 of the second type of tin-coated copper powder is 5-6 μm, and the particle size range is 3-15 μm.

3. The low-temperature base metal conductive paste according to claim 1, characterized in that, The pure copper powder has a morphology of sphericity ≥90% and an average particle size D3 of 0.3-0.5 μm, with a particle size range of 0.1-0.8 μm.

4. The low-temperature base metal conductive paste according to claim 1, characterized in that, The curing agent includes latent amine curing agents and / or latent cationic curing agents.

5. The low-temperature base metal conductive paste according to claim 1, characterized in that, The antioxidants include one or more of the following: fat-soluble vitamin-like organic compounds, organophosphate compounds, organophosphorus compounds, organic acid compounds, organic amine compounds, and inorganic salt compounds.

6. The low-temperature base metal conductive paste according to claim 5, characterized in that, The antioxidant must meet at least one of the following conditions: a. The fat-soluble vitamin-like organic compounds include one or more of vitamin A, vitamin C, and vitamin E; b. The organophosphate compounds include Irgafos 168 phosphate and / or tris(nonylphenyl) phosphite; c. The organophosphorus compound includes one or more of aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, and n-dodecyl phosphoric acid; d. The organic acid compounds include one or more of acetic acid, formic acid, oxalic acid, sebacic acid, and adipic acid; e. The organic amine compounds include oleylamine and / or cocoylamine; f. The inorganic salt compound includes one or more of ammonium chloride, copper formate tetrahydrate, and copper oleate.

7. The low-temperature base metal conductive paste according to claim 1, characterized in that, The anti-settling agent includes one or more of the following: polyamide wax, organophosphate ester, and sodium carboxymethyl cellulose.

8. The low-temperature base metal conductive paste according to claim 1, characterized in that, The resin comprises a mixture of epoxy resin, ethyl cellulose, and acrylic resin in a mass ratio of (70-80):(2-5):(15-22); the dispersant comprises DISPERBYK-111, 80. Solsperse 32500, DISPERBYK-102, DISPERBYK-180, 9900 and One or more of 66; the solvent includes one or more of diethylene glycol butyl ether acetate, dimethyl ester, diethylene glycol butyl ether and 12-ol ester.

9. A method for preparing a low-temperature base metal conductive paste as described in any one of claims 1-8, characterized in that, Includes the following steps: S1: Place the antioxidant in a heating container, slowly add the solvent and the resin, set the heating temperature to 60°C, and stir until all components are dissolved and fully mixed; S2: Add the curing agent into the heating container and stir until all components are fully mixed and the resulting solution is clear and transparent; S3: Add the anti-settling agent into the heating container, stir at high speed until all components are fully mixed to form the organic carrier, and let stand at room temperature for more than 8 hours for later use. S4: Weigh the pure copper powder and the dispersant, add them to the organic carrier, and disperse them evenly to obtain a copper-containing paste; S5: Weigh the second type of tin-coated copper powder, add it to the copper-containing paste, disperse it evenly, then add the first type of tin-coated copper powder, and continue stirring and dispersing to obtain the low-temperature base metal conductive paste.

10. An application of a low-temperature base metal conductive paste, characterized in that, The low-temperature base metal conductive paste is the low-temperature base metal conductive paste according to any one of claims 1-8 or the low-temperature base metal conductive paste prepared according to the preparation method of claim 9. The low-temperature base metal conductive paste is applied to heterojunction cells, back contact cells, PERC cells, TOPCon cells and flexible circuit boards.

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