High-stability low-temperature curing type copper paste as well as preparation method and application thereof

Abstract

The invention relates to the technical field of conductive materials, in particular to high-stability low-temperature curing type copper paste and a preparation method and application thereof. Comprising the following raw materials in percentage by mass: 85%-92% of double-coated nano copper powder, 6%-12% of an organic solvent system and 0.1%-4% of thermosetting resin, the molecular weight of the thermosetting resin is (5-7) * 10 < 5 >. The copper paste provided by the technical scheme of the invention is good in oxidation resistance and easy to store, the adhesion strength and the conductivity are not obviously changed along with time within the storage period, the difficulty that pure copper paste is difficult to apply to a heterojunction battery is effectively solved, and the problem that the copper paste is poor in oxidation resistance is solved. In addition, the copper paste provided by the invention can realize double-sided metallization on a heterojunction cell under a low-temperature condition, and a grid line formed by printing and curing the low-temperature curing type copper paste has good adhesiveness on an ITO (Indium Tin Oxide) conductive film layer on the surface of a heterojunction.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive materials, and particularly relates to a highly stable low-temperature curable copper paste and a preparation method and application thereof. Background Art

[0002] With the rise of the photovoltaic industry, crystalline silicon solar cells have shown great development potential. Among them, silicon heterojunction (HJT) solar cells, which have the advantages of high theoretical conversion efficiency, low temperature coefficient, and bifacial power generation, have become the development direction of the next generation of high-efficiency photovoltaic power generation.

[0003] The introduction of the amorphous silicon passivation structure in HJT cells usually limits the metallization and annealing temperatures to 180 - 230 °C. In order to reduce the volume resistivity of the paste, the silver powder addition amount of low-temperature silver paste usually needs to reach more than 90%, which makes the cost of low-temperature paste too high and is not conducive to the large-scale promotion of heterojunction solar cells.

[0004] Therefore, the photovoltaic industry is committed to improving and optimizing the metallization process to reduce silver consumption. Among them, replacing precious metal silver with low-cost metal copper is an effective way to reduce costs and achieve large-scale production, showing great development potential. Copper has good electrical conductivity, second only to silver, and at the same time, its price is much lower than that of silver. Therefore, low-cost and well-conductive nano-copper paste is expected to replace the existing low-temperature curable silver paste technology. However, copper paste has the problems of being easily oxidized, the oxide being non-conductive, and difficult to store. Therefore, the present invention is proposed. Summary of the Invention

[0005] The first object of the present invention is to provide a highly stable low-temperature curable copper paste, which has stable performance, is not easily oxidized, and is easy to store. The second object of the present invention is to provide a preparation method and application of the copper paste.

[0006] The present invention provides a highly stable low-temperature curable copper paste, which comprises the following raw materials in mass percentage: 85% - 92% of double-coated nano copper powder, 6% - 12% of an organic solvent system, and 0.1% - 4% of a thermosetting resin; the molecular weight of the thermosetting resin is (5 - 7) × 10 5 . More preferably, it comprises 90% of double-coated nano copper powder, 6% - 10% of an organic solvent system, and 0.1% - 2% of bisphenol A epoxy resin, or 87% of double-coated nano copper powder, 8% - 12% of an organic solvent system, and 0.1% - 4% of polyurethane-modified epoxy resin.

[0007] Preferably, the coating agent used for the double-coated nano copper powder comprises copper metal-organic decomposition ink and pyrrolidone compounds; the pyrrolidone compounds include one or more of N-vinylpyrrolidone, α-pyrrolidone, acetamide pyrrolidone, and crosslinked polyvinylpyrrolidone.

[0008] Preferably, the copper metal-organic decomposition ink is prepared by the following method: uniformly mixing a metal copper precursor, absolute ethanol, and a complexing agent, and stirring at room temperature to obtain;

[0009] Wherein the metal copper precursor includes one or more of copper formate tetrahydrate, copper acetate, and copper nitrate; the complexing agent includes one or more of 3-(diethylamino)-1,2-propanediol, 1,2-propanediamine, N,N-dimethylformamide, isooctylamine, 2-amino-2-methyl-propanol, and n-octylamine. More preferably, the metal copper precursor is copper formate tetrahydrate, and the complexing agent is a mixture of isooctylamine and 2-amino-2-methyl-propanol.

[0010] Preferably, the organic solvent system includes raw materials in the following mass percentages: 0.3%-2% of a leveling agent, 0.1%-0.5% of an antioxidant, and the rest is a solvent. More preferably, it includes 1% of a leveling agent, 0.2% of an antioxidant, and 98.8% of a solvent. Among them, the leveling agent is used to improve the fluidity of copper powder during the preparation and printing of copper paste to ensure sufficient contact between copper particles and the ITO (Indium Tin Oxides) layer, and the antioxidant is used to prevent oxidation on the surface of copper powder and inhibit the formation of oxides in the subsequent process of copper paste.

[0011] Preferably, the leveling agent is one or more of polyether silicone copolymer, vinyl-terminated dimethyl vinyl-terminated dimethyl polysiloxane (CAS No.: 68083-19-2), cetyl docosanoate (CAS No.: 42233-11-4); the antioxidant is a radical inhibitor; the solvent is an alcohol organic compound.

[0012] Preferably, the antioxidant is one or more of N-methyl-N-hydroxyethyl-p-toluidine, p-phenylenediamine, butanone oxime (CAS No.: 96-29-7), and formamide (CAS No.: 75-12-7); the solvent is one or more of alcohol organic compounds and their compounds that have good solubility in resin, have a certain temperature gradient during volatilization, and have a monomer carbon number of 2-6; more preferably, the solvent is one or more of polyethylene glycol, n-butanol, isobutanol, neopentyl alcohol, and cyclohexanemethanol.

[0013] Preferably, the thermosetting resin is one or more of acrylic resin, epoxy resin, and alkyd resin.

[0014] The second aspect of the present invention provides a preparation method of the above-mentioned high-stability low-temperature curing copper paste, including the following steps:

[0015] S1. Mix nano copper powder with hypochlorous acid or hypophosphorous acid, ultrasonicate, centrifuge to remove the supernatant, add alcohol and ultrasonically oscillate, and centrifuge to remove the supernatant to obtain pretreated copper powder;

[0016] S2. Mix the pretreated copper powder with the copper metal-organic decomposition ink, centrifuge to remove the supernatant, complete the first coating, and refrigerate at low temperature.

[0017] S3. Mix the copper powder obtained in step S2 with a pyrrolidone compound, sonicate, centrifuge to remove the supernatant, and complete the second coating.

[0018] S4. Mix the copper powder obtained in step S3 with an ethanol solution, sonicate, centrifuge to remove the supernatant, evacuate and introduce nitrogen to obtain double-coated nano copper powder.

[0019] S5. Mix the organic solvent system and the thermosetting resin evenly, then add the double-coated nano copper powder and mix evenly to obtain a low-temperature curable copper paste.

[0020] Preferably, the shape of the nano copper powder in step S1 is spherical and / or flaky; the particle size of the nano copper powder is 450 - 3000 nm; more preferably, the particle size of the nano copper powder is 500 - 2000 nm, and more preferably 500 nm, 800 nm, 1000 nm, 1500 nm, 1800 nm, 2000 nm.

[0021] Preferably, the mass ratio of the double-coated nano copper powder, the organic solvent system, and the thermosetting resin in step S5 is (85 - 92):(6 - 12):(0.1 - 4); more preferably, the mass ratio of the double-coated nano copper powder, the organic solvent system, and the thermosetting resin is 90:8:2 or 87:9:4.

[0022] The third aspect of the present invention provides an application of the above high-stability low-temperature curable copper paste or the low-temperature curable copper paste obtained by the above preparation method in the double-sided metallization of heterojunction solar cells.

[0023] Preferably, the surface of the heterojunction solar cell has an ITO conductive film, and a conductive paste is printed on the surface of the ITO conductive film to form grid lines, and the grid lines are formed by low-temperature drying using the above low-temperature curable copper paste.

[0024] Select a typical industrialized cell size of M2 (156 mm × 156 mm).

[0025] The application of the above high-stability low-temperature curable copper paste in the double-sided metallization of heterojunction solar cells is as follows:

[0026] (1) Ultrasonically wash the heterojunction cell to be prepared with grid lines in absolute ethanol to remove impurities on its surface, and dry in a vacuum drying oven to remove absolute ethanol.

[0027] (2) The low-temperature curable copper paste is evenly printed on the upper surface of the heterojunction cell obtained in step (1) through a screen printing machine using a specific grid line pattern on the screen plate.

[0028] (3) The heterojunction cell obtained in step (2) is placed in a drying oven and dried at 60 - 100 °C for 10 - 30 min.

[0029] (4) The dried cell in step (3) is inverted and the lower surface grid lines are printed again using screen printing.

[0030] (5) The heterojunction cell obtained in step (4) is placed in the drying oven again, dried at 60 - 100 °C for 10 - 30 min under an inert atmosphere, and then heated at a rate of 5 - 25 °C / min to 200 °C and held for 70 - 110 min under an inert atmosphere condition. The copper paste is cured to form grid lines, and a double-sided metallized structure of the heterojunction cell is obtained.

[0031] In summary, the present invention has the following advantages:

[0032] The high-stability low-temperature curable copper paste provided by the technical solution of the present invention has good antioxidant performance, is easy to store, and the adhesion strength and conductivity do not change significantly with time within the storage period. It effectively solves the difficulty of applying pure copper paste to heterojunction cells and overcomes the problem of poor antioxidant performance of copper paste. In addition, the high-stability low-temperature curable copper paste provided by the present invention can achieve double-sided metallization on heterojunction cells under low-temperature conditions, and the grid lines formed by printing and curing of this low-temperature curable copper paste have good adhesion to the ITO conductive film layer on the heterojunction surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1 It is a schematic diagram of the preparation process of the low-temperature curable copper paste provided by the present invention;

[0035] Figure 2 It is a schematic diagram of the preparation process of the double-coated nano copper powder provided by the present invention;

[0036] Figure 3 It is a schematic diagram after printing and curing of the low-temperature curable copper paste in Example 1 of the present invention;

[0037] Figure 4Schematic diagram of the welding tensile force measurement method for the low-temperature curing copper paste in Embodiment 1 of the present invention;

[0038] Figure 5 Variation diagram of the volume resistivity of the low-temperature curing copper paste with the curing temperature and curing time in Embodiment 1 of the present invention;

[0039] Figure 6 Variation diagram of the volume resistivity and welding tensile force of the low-temperature curing copper paste with the storage time within the storage validity period in Embodiment 1 of the present invention. Detailed implementation manners

[0040] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0041] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present invention.

[0042] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the described features. In the description of the present invention, "a plurality" means two or more, unless otherwise specifically defined. In addition, the terms "mounted", "connected", and "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0043] Embodiment 1

[0044] A highly stable low-temperature curing copper paste, which is composed of raw materials with the following mass percentages: 90% of double-coated nano copper powder, 8% of organic solvent system, and 2% of bisphenol A epoxy resin (purchased from Dow Chemical Company, model DER383, viscosity 9000 - 10500 cps).

[0045] Among them, the coating agents used for the double-coated nano copper powder are copper metal-organic decomposition ink (Cu MOD ink) and cross-linked polyvinylpyrrolidone. The Cu MOD ink is prepared by the following method: copper formate tetrahydrate, absolute ethanol, and a complexing agent (the complexing agent is isooctylamine and 2-amino-2-methyl-propanol, and the molar ratio of the two is 1:1) are mixed evenly and magnetically stirred at room temperature for 30 minutes. The mass percentage of copper formate tetrahydrate added is 12%, the mass percentage of absolute ethanol is 80%, and the mass percentage of the complexing agent is 8%.

[0046] The organic solvent system is composed of raw materials with the following mass percentages: 1% of polyether silicone copolymer (purchased from Sichuan Ruikaibang Chemical Materials Co., Ltd., model RianPont 2506), 0.1% of p-phenylenediamine, 0.1% of N-methyl-N-hydroxyethyl-p-toluidine, and 98.8% of a mixture of polyethylene glycol and isobutanol (the molar ratio of polyethylene glycol and isobutanol in the mixture is 1:1).

[0047] The preparation method of the above-mentioned highly stable low-temperature immobilized copper paste is as Figure 1 shown, and the specific process is as follows:

[0048] S1. Mix the nano copper powder with hypophosphorous acid, ultrasonicate for 30 min, centrifuge to remove the supernatant, add alcohol and ultrasonically vibrate, then centrifuge to remove the supernatant to obtain pretreated copper powder; the shape of the nano copper powder is spherical, and the particle size is 800 nm.

[0049] S2. Put 1 part of the pretreated copper powder obtained in step S1 and 5 parts of copper metal-organic decomposition ink into a planetary mixer and mix for 20 min, then transfer to a centrifuge and centrifuge at 3000 r / min for 10 min to remove the supernatant to complete the first coating, and refrigerate at -20 °C for 12 h;

[0050] S3. Mix 1 part of the copper powder obtained in step S2 with 3 parts of cross-linked polyvinylpyrrolidone, ultrasonicate for 20 min, centrifuge to remove the supernatant to complete the second coating;

[0051] S4. Mix the copper powder obtained in step S3 with an ethanol solution, ultrasonicate for 10 min, wash off the excess cross-linked polyvinylpyrrolidone and other free reagents, centrifuge to remove the supernatant, place it in a vacuum chamber, evacuate and introduce nitrogen for 30 min to obtain double-coated nano copper powder (the preparation process of the double-coated nano copper powder is as Figure 2 shown);

[0052] S5. Mix the organic solvent system and bisphenol A epoxy resin, stir them evenly at room temperature at 300 r / min with a magnetic stirrer for 40 min, then add the double-coated nano copper powder obtained in step S4 and mix them evenly, and stir them in a planetary mixer filled with nitrogen for 30 min to obtain a low-temperature curing copper slurry.

[0053] The low-temperature curing copper paste prepared above is applied to the double-sided metallization of heterojunction solar cells. The process diagram is shown in Figure 3 As shown, the upper and lower surfaces of the heterojunction battery are indium tin oxide conductive films (ITO), and the battery cell specification is selected as M2 (156mm×156mm). The specific steps are as follows:

[0054] (1) The heterojunction cell with the gate line to be prepared is ultrasonically cleaned in anhydrous ethanol for 2 minutes to remove impurities on the surface, and then dried in a vacuum drying oven at 60° C. for 3 minutes to remove the anhydrous ethanol;

[0055] (2) using a screen printing machine to uniformly print the low-temperature curing copper paste on the upper surface of the heterojunction solar cell obtained in step (1) through a specific grid line pattern on the screen;

[0056] (3) placing the heterojunction cell obtained in step (2) in a drying furnace and drying at 80° C. for 10 min under an inert gas;

[0057] (4) Inverting the solar cell obtained in step (3) after printing the copper paste grid lines on the upper surface and drying it, and screen printing the grid lines on the lower surface again;

[0058] (5) The heterojunction battery cell obtained in step (4) is placed in a drying furnace again, dried at 80° C. for 10 min under an inert atmosphere, and then heated to 200° C. at a rate of 20° C. / min and kept warm for 90 min. The low-temperature copper paste is solidified to form grid lines, thereby obtaining a double-sided metallization structure of the heterojunction battery.

[0059] The copper paste prepared in this example was tested for performance:

[0060] 1. Volume resistivity test, the specific process is as follows:

[0061] 1. Stir the copper paste thoroughly, use a customized screen to print a sample strip on the crystalline silicon blue film, with a length of 3-7cm, a width of 3-7mm, and a thickness of 30-50μm, and dry and cure according to the process conditions, such as Figure 3 shown.

[0062] 2. Use two sets of probes of the multimeter (Kelvin / four-wire method test) to respectively place them at both ends of the copper paste, and read the resistance reading of the multimeter, recorded as R.

[0063] 3. Measure the width W (accurate to 0.01 mm) and thickness h (accurate to 0.01 μm) of the cured paste. The cross-sectional area is S = W × h.

[0064] 4. Calculate the volume resistivity ρ = RS / L, and take the average value of three splines.

[0065] II. Adhesion test, as Figure 4 shown, the specific process is as follows:

[0066] 1. Stir the paste thoroughly and use a screen printing machine to print the main grid electrode on the crystalline silicon blue film. It is recommended that the length is not less than 15 cm, the width is 0.4 - 1 mm, and the thickness is 11 - 15 μm. Dry and cure according to the process conditions.

[0067] 2. Immerse the solder tape in the flux for 5 - 15 min, take it out and air dry at room temperature.

[0068] 3. Preheat the crystalline silicon solar cell to be welded to 50 ± 5 °C. Use a temperature-controlled soldering iron to weld the solder tape to the cured electrode, and the welding time does not exceed 30 s.

[0069] 4. Clamp the specimen on a tensile testing machine and uniformly pull the solder tape along the 180° direction at a speed of 100 - 300 mm / min, record the average tensile force in the relatively stable interval of the tensile force value, take the average tensile force as the breaking tensile force, and take the average value of three splines.

[0070] After testing, the low-temperature curable copper paste prepared in this example can be stored for more than six months at -20 °C. During the storage period, the adhesion strength and conductivity do not change significantly with time. The resistivity and welding tensile force (adhesion strength) of the low-temperature curable copper paste change with the storage time as Figure 6 shown. As can be seen from Figure 6 , within the six-month storage period, the resistivity of this copper paste remains at a relatively low level, and the welding tensile force > 1.5 N. It effectively solves the difficulty of applying pure copper paste to heterojunction batteries and overcomes the problems of poor oxidation resistance and insufficient conductivity of copper paste.

[0071] As Figure 5 shown, the resistivity of the low-temperature curable copper paste prepared in this example decreases to 7.71 μΩ·cm under the process conditions of curing at 200 °C for 90 minutes. Then, with the extension of time and the increase of temperature, the resistivity shows an increasing trend.

[0072] The low-temperature curable copper paste provided in this example can achieve grid line curing on heterojunction batteries at 200 °C; moreover, the grid lines formed by printing and curing this low-temperature curable copper paste have good adhesion and printing formability on the ITO conductive film layer on the surface of the heterojunction.

[0073] Example 2

[0074] A highly stable low-temperature curing copper paste, which is composed of raw materials with the following mass percentages: 87% of double-coated nano copper powder, 9% of organic solvent system, and 4% of polyurethane-modified epoxy resin (purchased from Dow Chemical Company, model DER791, viscosity about 3000 - 5000 cps @ 25°C).

[0075] Among them, the coating agents used for the double-coated nano copper powder are copper metal-organic decomposition ink and cross-linked polyvinylpyrrolidone, and the preparation of the copper metal-organic decomposition ink is the same as that in Example 1.

[0076] The organic solvent is composed of raw materials with the following mass percentages: 2% of cetyl docosanoate, 0.1% of butanone oxime, 0.1% of formamide, and 97.8% of cyclohexane methanol.

[0077] The preparation method of the above highly stable low-temperature curing copper paste is basically the same as that in Example 1. The difference is that in this example, the nano copper powder in step S1 is a mixture of sheet-shaped and spherical shapes, where the mass fraction of the sheet-shaped is 70% and the particle size is 1500 nm; the mass fraction of the spherical is 30% and the particle size is 500 nm.

[0078] Apply the low-temperature curing copper paste prepared above to the double-sided metallization of heterojunction solar cells, and the curing process is the same as that in Example 1.

[0079] After use testing, under the optimal process conditions of curing the low-temperature curing copper paste prepared in this example at 200°C for 60 minutes, through volume resistivity testing, the initial average resistivity is 34.12 μΩ·cm, and it is stored at -20°C for six months, and the adhesion strength and conductivity decrease by ≤20%, and the adhesion strength and conductivity do not change significantly with time during the storage period.

[0080] Comparative Example

[0081] A low-temperature curing copper paste, the technical solution in this example is basically the same as that in Example 1. The difference is that: the Cu MOD ink coating in Example 1 is replaced with a mixed solution coating of copper formate and ethanol, and the mass percentage of copper formate in the mixed solution is 12% and the mass percentage of ethanol is 88%, that is, the Cu MOD ink in step S2 is replaced with a mixed solution of copper formate and ethanol during preparation.

[0082] The low-temperature curing copper paste prepared in this comparative example is tested for volume resistivity. The initial resistivity is 560 μΩ·cm, and precipitates appear after being stored at -20°C for three months, and the resistivity ≥ 1×10 6 μΩ·cm, the conductivity is poor, and the volume conductivity drops sharply with the storage time.

[0083] The present invention uses Cu MOD ink to achieve the first layer of coating. During the curing process, the ink thermally decomposes between copper particles to form new nano-copper particles, which improves the particle stacking density and enhances the contact and conductive effect between copper particles and between copper particles and the ITO layer. The second layer of coating is achieved with pyrrolidone compounds to ensure the stability of the Cu MOD ink coating and isolate air, thereby realizing the self-reduction property of nano-copper powder. The prepared low-temperature curing copper paste has good antioxidant performance, and its adhesion strength and conductivity do not change significantly over time during the storage period, effectively solving the difficulty of applying pure copper paste to heterojunction batteries and overcoming the problems of poor antioxidant performance and insufficient conductivity of copper paste. In addition, the low-temperature curing copper paste provided by the present invention can achieve the preparation of grid lines on heterojunction batteries under low-temperature conditions; moreover, the grid lines formed by printing and curing the low-temperature curing copper paste have good adhesion to the ITO conductive film layer on the surface of the heterojunction.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-stability, low-temperature curing copper paste, characterized in that: The invention comprises the following raw materials in percentage by weight: 85%-92% of double-coated nano copper powder, 6%-12% of organic solvent system, and 0.1%-4% of thermosetting resin; the molecular weight of the thermosetting resin is (5-7)×10 5 .

2. The high stability and low temperature curing copper paste according to claim 1, characterized in that: The coating agent used in the double-coated nano copper powder includes copper metal organic decomposition ink and pyrrolidone compounds; the pyrrolidone compounds include one or more of N-vinyl pyrrolidone, α-pyrrolidone, acetamide pyrrolidone, and cross-linked polyvinyl pyrrolidone.

3. The high stability and low temperature curing copper paste according to claim 2, characterized in that: The copper metal organic decomposition ink is prepared by the following method: a metal copper precursor, anhydrous ethanol and a complexing agent are uniformly mixed and stirred at room temperature; The metallic copper precursor includes one or more of copper formate tetrahydrate, copper acetate, and copper nitrate; the complexing agent includes one or more of 3-(diethylamino)-1,2-propylene glycol, 1,2-propylenediamine, N,N-dimethylformamide, isooctylamine, 2-amino-2-methyl-propanol, and n-octylamine.

4. The high stability and low temperature curing copper paste according to claim 1, characterized in that: The organic solvent system comprises the following raw materials in percentage by mass: 0.3%-2% of a leveling agent, 0.1%-0.5% of an antioxidant, and the rest being a solvent.

5. The high stability and low temperature curing copper paste according to claim 4, characterized in that: The leveling agent is one or more of polyether siloxane copolymer, vinyl-terminated dimethyl polysiloxane, and hexadecyl behenate; the antioxidant is a free radical inhibitor; and the solvent is an alcohol organic substance.

6. The high stability and low temperature curing copper paste according to claim 5, characterized in that: The antioxidant is one or more of N-methyl-N-hydroxyethyl p-toluidine, p-phenylenediamine, butanone oxime, and formamide; the solvent is one or more of polyethylene glycol, n-butanol, isobutanol, neopentyl alcohol, and cyclohexamethylenetetramine.

7. The high stability and low temperature curing copper paste according to claim 1, characterized in that: The thermosetting resin is one or more of acrylic resin, epoxy resin and alkyd resin.

8. A method for preparing the high-stability, low-temperature curing copper paste according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Mixing nano copper powder with hypochlorous acid or hypophosphorous acid, ultrasonicating, centrifuging to remove supernatant, adding alcohol for ultrasonic shaking, centrifuging to remove supernatant, and obtaining pretreated copper powder; S2, mixing the pretreated copper powder with the copper metal organic decomposition ink, removing the supernatant by centrifugation, completing the first coating, and refrigerating at low temperature; S3, mixing the copper powder obtained in step S2 with the pyrrolidone compound, ultrasonicating, and centrifuging to remove the supernatant to complete the second coating; S4, mixing the copper powder obtained in step S3 with the ethanol solution, ultrasonicating, centrifuging to remove the supernatant, and vacuuming and introducing nitrogen to obtain double-coated nano copper powder; S5. Evenly mix the organic solvent system and the thermosetting resin, and then add the double-coated nano copper powder and mix evenly to obtain a low-temperature curing copper paste.

9. The preparation method according to claim 8, characterized in that: The shape of the nano copper powder in step S1 is spherical or / and flake; the particle size of the nano copper powder is 450-3000nm.

10. Use of the low-temperature curing copper paste according to any one of claims 1 to 7 in double-sided metallization of heterojunction solar cells.

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