Heterojunction low-temperature silver paste doped with graphene microemulsion and preparation method thereof

Abstract

The present invention relates to a heterojunction low-temperature silver paste doped with graphene microemulsion and a preparation method thereof, and belongs to the technical field of polymer-based conductive materials. The heterojunction low-temperature silver paste doped with graphene microemulsion of the present invention comprises: silver powder, graphene microemulsion, and organic carrier; the mass ratio of the silver powder, graphene microemulsion, and organic carrier is: 88-92:0.5-2:6-11.5; the graphene microemulsion is composed of 1-10% of graphene, 0.1-1% of coupling agent, and 89-98.9% of solvent by mass percentage; the silver powder comprises flaky silver powder and spherical silver powder. The heterojunction low-temperature silver paste provided by the present invention has been improved in terms of paste components, has well optimized the morphology of the grid line, has reduced the contact resistance of the electrode grid line, has improved the photoelectric conversion efficiency of the battery, can be well passed through screen printing, does not affect the printability of the low-temperature silver paste, and has broad application prospects.

Description

Technical Field

[0001] The invention relates to a graphene microemulsion-doped heterojunction low-temperature silver paste and a preparation method thereof, and belongs to the technical field of polymer-based conductive materials. Background Art

[0002] Heterojunction solar cells are a special PN junction formed by amorphous silicon and crystalline silicon materials. They are a type of N-type cells that deposit amorphous silicon thin films on crystalline silicon. Heterojunction cells were first developed by Japan's Sanyo Company in 1990. The laboratory efficiency of heterojunction cells has reached more than 26%, which is one step higher than the current mainstream PERC cells. At the same time, heterojunction cells can be superimposed with perovskite cells, IBC technology, etc. Therefore, heterojunction cells are the mainstream trend in the future.

[0003] The heterojunction cell has a double-sided symmetrical structure, in which a transparent conductive oxide film is deposited on the amorphous silicon thin layer on both sides, and then a conductive grid line is prepared on it. Due to the presence of the transparent conductive oxide film, the traditional high-temperature silver paste will cause great damage to it during the high-temperature sintering process. Therefore, the electrode grid line of the heterojunction cell is formed into an ohmic contact through low-temperature curing. The curing temperature is required to be lower than 220°C. The heterojunction low-temperature silver paste does not have glass powder sintering. It relies on the resin to connect the silver powder and the silver powder, the adhesion between the paste and the silicon wafer substrate, and plays the role of collecting carriers.

[0004] For heterojunction cells, it is crucial that the electrode grid lines have a good aspect ratio and high sintering density. Heterojunction low-temperature pastes only rely on resin to connect silver powder, and there is a certain gap in the electrode density after curing, resulting in high electrode grid line resistance. At the same time, the contact between the electrode grid line and the transparent conductive oxide film is poor. Optimizing the density of heterojunction electrode grid lines, reducing electrode grid line contact resistance, maintaining low line resistance, and improving the photoelectric conversion efficiency of the battery are also the focus of the current heterojunction silver paste development. Summary of the invention

[0005] The first object of the present invention is to provide a novel heterojunction low-temperature silver paste doped with graphene microemulsion.

[0006] To achieve the first object of the present invention, the heterojunction low-temperature silver paste doped with graphene microemulsion comprises: silver powder, graphene microemulsion, and organic carrier; the mass ratio of the silver powder, graphene microemulsion, and organic carrier is: 88-92:0.5-2:6-11.5;

[0007] The graphene microemulsion consists of 1-10% of graphene, 0.1-1% of coupling agent and 89-98.9% of solvent in terms of mass percentage;

[0008] The silver powder includes flaky silver powder and spherical silver powder.

[0009] If all flaky silver powder is used, the printability will be drastically reduced and poor, and a complete grid line cannot be formed. If all spherical silver powder is used, the resistance of the grid line formed by the conductive silver paste will increase sharply and the performance will be reduced. The combination of flaky silver powder and spherical silver powder has better printability and resistance.

[0010] Graphene is made into microemulsion by uniformly dispersing it in the solvent in the form of microemulsion. Directly mixing silver powder, graphene, coupling agent, solvent, organic carrier, etc. will cause the graphene sheets to be stacked and have poor performance.

[0011] In a specific embodiment, the particle size distribution of the flaky silver powder is D100≤1100nm, D50≤700nm, D10≥300nm, and the tap density is 5-6g / cm 3 , specific surface area 0.5~1.0m 2 / g; the particle size distribution of the spherical silver powder is D100≤900nm, D50≤600nm, D10≥200nm, and the tap density is 4.5~5.5g / cm 3 Specific surface area 0.6~0.8m 2 / g.

[0012] The specific surface area and density of silver have a great influence on the performance of silver paste. If the surface area of ​​silver powder is too large, it may not form silver paste, or the formed silver paste may be too dry and have too high viscosity to pass through the screen. If the surface area of ​​silver powder is too small, the viscosity of the formed silver paste is too low, and there will be problems with the linearity of the grid lines formed after screen printing. The grid lines are usually too wide and too low in height, which will increase the shading area, reduce the current, and reduce the electrical performance.

[0013] In a specific embodiment, the organic carrier includes a thermosetting resin, a curing agent, a solvent a, and an auxiliary agent; the thermosetting resin preferably includes at least one of bisphenol A resin, bisphenol F resin, polyester resin, phenolic resin, and acrylic resin; the curing agent is preferably a latent curing agent, and more preferably at least one of an imidazole curing agent, a polyamide curing agent, a methyl hexachloride curing agent, a methyl tetrachloride curing agent, and a blocked isocyanate; the solvent a is preferably at least one of diethylene glycol butyl ether acetate, tripropylene glycol methyl ether, alcohol resin 12, and pinene alcohol; the auxiliary agent is preferably at least one of a silane coupling agent and a dispersant;

[0014] The organic carrier includes a thermosetting resin, a curing agent, a solvent a, and an auxiliary agent in a mass ratio of 25-35:15-23:30-45:5-10; the curing agent is preferably composed of 13-20 parts by weight of a blocked isocyanate and 2-3 parts by weight of other curing agents.

[0015] In a specific embodiment, the graphene has an average particle size of 50 to 400 nm and a 3 to 5-layer flaky structure.

[0016] In a specific embodiment, the coupling agent is a silane coupling agent, preferably including at least one of methacryloxy silane, epoxy silane, amino functional silane, aminocarboxylate silane, aminopropyl silane, aryl silane or cationic silane.

[0017] In a specific embodiment, the solvent is at least one of butyl carbitol acetate, terpineol, terpineol, butyl carbitol, dimethyl glutarate or dimethyl adipate.

[0018] In a specific embodiment, the heterojunction low-temperature silver paste doped with graphene microemulsion is prepared by the following method:

[0019] S1: preparing graphene microemulsion: mixing and dispersing graphene, coupling agent and solvent uniformly, and emulsifying to obtain graphene microemulsion;

[0020] S2: preparing silver paste: mixing silver powder and organic carrier evenly until no obvious silver powder particles are left; and then mixing with graphene microemulsion evenly to obtain a uniform slurry;

[0021] S3: Slurry grinding: Grind the uniform slurry described in step S2 until the fineness of the slurry reaches less than 10 μm, thereby obtaining a heterojunction low-temperature silver paste doped with graphene microemulsion.

[0022] In a specific embodiment, the uniform dispersion in S1 is carried out by ultrasonic dispersion, the power of the ultrasound is preferably 500 to 1500 W, and the ultrasound time is 10 to 60 minutes; the emulsification is preferably carried out by an emulsifier for 10 to 60 seconds;

[0023] S2 The method for uniformly mixing the silver powder and the organic carrier is preferably stirring at a stirring speed of 500 to 1000 r / min for 1 to 2 hours; The method for uniformly mixing with the graphene microemulsion is stirring at a stirring speed of 500 to 1000 r / min for 30 to 60 minutes;

[0024] The grinding gap in S3 is preferably adjusted from large to small to 120 μm to 30 μm, and the roller is rolled 3 to 4 times for each gap.

[0025] The second object of the present invention is to provide a method for preparing the above-mentioned heterojunction low-temperature silver paste doped with graphene microemulsion.

[0026] To achieve the second object of the present invention, the method comprises:

[0027] S1: preparing graphene microemulsion: mixing and dispersing graphene, coupling agent and solvent uniformly, and emulsifying to obtain graphene microemulsion;

[0028] S2: preparing silver paste: mixing silver powder and organic carrier evenly until no obvious silver powder particles are left; and then mixing with graphene microemulsion evenly to obtain a uniform slurry;

[0029] S3: Slurry grinding: Grind the uniform slurry described in step S2 until the fineness of the slurry reaches less than 10 μm, thereby obtaining a heterojunction low-temperature silver paste doped with graphene microemulsion.

[0030] In a specific embodiment, the method further comprises S4: slurry storage: storing the heterojunction low-temperature silver slurry doped with graphene microemulsion obtained in S3 in a refrigerator at -5 to 5°C;

[0031] S1: The uniform dispersion is carried out by ultrasonic dispersion, the power of the ultrasound is preferably 500-1500W, and the ultrasound time is 10-60 minutes; the emulsification is preferably carried out by an emulsifier for 10-60 seconds;

[0032] S2 The method for uniformly mixing the silver powder and the organic carrier is preferably stirring at a stirring speed of 500 to 1000 r / min for 1 to 2 hours; The method for uniformly mixing with the graphene microemulsion is stirring at a stirring speed of 500 to 1000 r / min for 30 to 60 minutes;

[0033] The grinding gap in S3 is preferably adjusted from large to small to 120 μm to 30 μm, and the roller is rolled 3 to 4 times for each gap.

[0034] Beneficial effects:

[0035] The preparation method of the heterojunction low-temperature silver paste provided by the present invention improves the paste components, optimizes the morphology of the grid lines, reduces the contact resistance of the electrode grid lines, improves the photoelectric conversion efficiency of the battery, and has broad application prospects.

[0036] The heterojunction low-temperature silver paste doped with the graphene microemulsion of the present invention can be well screen-printed without affecting the printability of the low-temperature silver paste. DETAILED DESCRIPTION

[0037] To achieve the first object of the present invention, the heterojunction low-temperature silver paste doped with graphene microemulsion comprises: silver powder, graphene microemulsion, and organic carrier; the mass ratio of the silver powder, graphene microemulsion, and organic carrier is: 88-92:0.5-2:6-11.5;

[0038] The graphene microemulsion consists of 1-10% of graphene, 0.1-1% of coupling agent and 89-98.9% of solvent in terms of mass percentage;

[0039] The silver powder includes flaky silver powder and spherical silver powder.

[0040] If all flaky silver powder is used, the printability will be drastically reduced and poor, and a complete grid line cannot be formed. If all spherical silver powder is used, the resistance of the grid line formed by the conductive silver paste will increase sharply and the performance will be reduced. The combination of flaky silver powder and spherical silver powder has better printability and resistance.

[0041] Graphene is made into microemulsion by uniformly dispersing it in the solvent in the form of microemulsion. Directly mixing silver powder, graphene, coupling agent, solvent, organic carrier, etc. will cause the graphene sheets to be stacked and have poor performance.

[0042] In a specific embodiment, the particle size distribution of the flaky silver powder is D100≤1100nm, D50≤700nm, D10≥300nm, and the tap density is 5-6g / cm 3 , specific surface area 0.5~1.0m 2 / g; the particle size distribution of the spherical silver powder is D100≤900nm, D50≤600nm, D10≥200nm, and the tap density is 4.5~5.5g / cm 3 , specific surface area 0.6~0.8m 2 / g.

[0043] The specific surface area and density of silver have a great influence on the performance of silver paste. If the surface area of ​​silver powder is too large, it may not form silver paste, or the formed silver paste may be too dry and have too high viscosity to pass through the screen. If the surface area of ​​silver powder is too small, the viscosity of the formed silver paste is too low, and there will be problems with the linearity of the grid lines formed after screen printing. The grid lines are usually too wide and too low in height, which will increase the shading area, reduce the current, and reduce the electrical performance.

[0044] In a specific embodiment, the organic carrier includes a thermosetting resin, a curing agent, a solvent a, and an auxiliary agent; the thermosetting resin preferably includes at least one of bisphenol A resin, bisphenol F resin, polyester resin, phenolic resin, and acrylic resin; the curing agent is preferably a latent curing agent, and more preferably at least one of an imidazole curing agent, a polyamide curing agent, a methyl hexachloride curing agent, a methyl tetrachloride curing agent, and a blocked isocyanate; the solvent a is preferably at least one of diethylene glycol butyl ether acetate, tripropylene glycol methyl ether, alcohol resin 12, and pinene alcohol; the auxiliary agent is preferably at least one of a silane coupling agent and a dispersant;

[0045] The organic carrier includes a thermosetting resin, a curing agent, a solvent a, and an auxiliary agent in a mass ratio of 25-35:15-23:30-45:5-10; the curing agent is preferably composed of 13-20 parts by weight of a blocked isocyanate and 2-3 parts by weight of other curing agents.

[0046] In a specific embodiment, the graphene has an average particle size of 50 to 400 nm and a 3 to 5-layer flaky structure.

[0047] In a specific embodiment, the coupling agent is a silane coupling agent, preferably including at least one of methacryloxy silane, epoxy silane, amino functional silane, aminocarboxylate silane, aminopropyl silane, aryl silane or cationic silane.

[0048] In a specific embodiment, the solvent is at least one of butyl carbitol acetate, terpineol, terpineol, butyl carbitol, dimethyl glutarate or dimethyl adipate.

[0049] In a specific embodiment, the heterojunction low-temperature silver paste doped with graphene microemulsion is prepared by the following method:

[0050] S1: preparing graphene microemulsion: mixing and dispersing graphene, coupling agent and solvent uniformly, and emulsifying to obtain graphene microemulsion;

[0051] S2: preparing silver paste: mixing silver powder and organic carrier evenly until no obvious silver powder particles are left; and then mixing with graphene microemulsion evenly to obtain a uniform slurry;

[0052] S3: Slurry grinding: Grind the uniform slurry described in step S2 until the fineness of the slurry reaches less than 10 μm, thereby obtaining a heterojunction low-temperature silver paste doped with graphene microemulsion.

[0053] In a specific embodiment, the uniform dispersion in S1 is carried out by ultrasonic dispersion, the power of the ultrasound is preferably 500 to 1500 W, and the ultrasound time is 10 to 60 minutes; the emulsification is preferably carried out by an emulsifier for 10 to 60 seconds;

[0054] S2 The method for uniformly mixing the silver powder and the organic carrier is preferably stirring at a stirring speed of 500 to 1000 r / min for 1 to 2 hours; The method for uniformly mixing with the graphene microemulsion is stirring at a stirring speed of 500 to 1000 r / min for 30 to 60 minutes;

[0055] The grinding gap in S3 is preferably adjusted from large to small to 120 μm to 30 μm, and the roller is rolled 3 to 4 times for each gap.

[0056] The second object of the present invention is to provide a method for preparing the above-mentioned heterojunction low-temperature silver paste doped with graphene microemulsion.

[0057] To achieve the second object of the present invention, the method comprises:

[0058] S1: preparing graphene microemulsion: mixing and dispersing graphene, coupling agent and solvent uniformly, and emulsifying to obtain graphene microemulsion;

[0059] S2: preparing silver paste: mixing silver powder and organic carrier evenly until no obvious silver powder particles are left; and then mixing with graphene microemulsion evenly to obtain a uniform slurry;

[0060] S3: Slurry grinding: Grind the uniform slurry described in step S2 until the fineness of the slurry reaches less than 10 μm, thereby obtaining a heterojunction low-temperature silver paste doped with graphene microemulsion.

[0061] In a specific embodiment, the method further comprises S4: slurry storage: storing the heterojunction low-temperature silver slurry doped with graphene microemulsion obtained in S3 in a refrigerator at -5 to 5°C;

[0062] S1: The uniform dispersion is carried out by ultrasonic dispersion, the power of the ultrasound is preferably 500-1500W, and the ultrasound time is 10-60 minutes; the emulsification is preferably carried out by an emulsifier for 10-60 seconds;

[0063] S2 The method for uniformly mixing the silver powder and the organic carrier is preferably stirring at a stirring speed of 500 to 1000 r / min for 1 to 2 hours; The method for uniformly mixing with the graphene microemulsion is stirring at a stirring speed of 500 to 1000 r / min for 30 to 60 minutes;

[0064] The grinding gap in S3 is preferably adjusted from large to small to 120 μm to 30 μm, and the roller is rolled 3 to 4 times for each gap.

[0065] The specific implementation modes of the present invention are further described below in conjunction with embodiments, but the present invention is not limited to the scope of the embodiments.

[0066] Example 1

[0067] A heterojunction low-temperature silver paste doped with a graphene microemulsion is prepared from 91 parts of a combined silver powder, 8 parts of an organic carrier (preparation of the organic carrier: bisphenol A resin, blocked isocyanate, diethylene glycol butyl ether acetate solvent, 2014FG latent modified polyamide curing agent, and dispersant BYK333 auxiliary agent are mixed in a mass ratio of 30:16.25:43.7:2.5:7.5), and 1 part of a graphene microemulsion per 100 parts by mass; wherein the combined silver powder comprises 40.95 parts of flaky silver powder (the flaky silver powder used in Example 1 has a D100 of 15, a D50 of 6.6, a D10 of 2, a tap density of 4.5, and a specific surface area of ​​0.27) and 50.05 parts of spherical silver powder (the spherical silver powder used in Example 1 has a D100 of 3.99, a D50 of 1.62, a D10 of 2, a tap density of 4.5, and a specific surface area of ​​0.27). 1.08, tap density 6.29, specific surface area 0.41); the graphene microemulsion is composed of 0.05 parts of graphene with an average particle size of 100nm and a three-layer flaky structure, 0.01 parts of methacryloyloxy silane coupling agent, and 0.94 parts of diethylene glycol acetate solvent.

[0068] Example 2

[0069] A heterojunction low-temperature silver paste doped with a graphene microemulsion is prepared from 91 parts of a combined silver powder, 7 parts of an organic carrier (preparation of the organic carrier: bisphenol A resin, blocked isocyanate, diethylene glycol butyl ether acetate solvent, 2014FG latent modified polyamide curing agent, and dispersant BYK333 auxiliary agent are mixed in a mass ratio of 30:16.25:43.7:2.5:7.5), and 2 parts of a graphene microemulsion per 100 parts by mass; wherein the combined silver powder is composed of 40.95 parts of flaky silver powder (the flaky silver powder used in Example 2 has a D100 of 15, a D50 of 6.6, a D10 of 2, a tap density of 4.5, and a specific surface area of ​​0.27) and 50.05 parts of spherical silver powder (the spherical silver powder used in Example 2 has a D100 of 3.99, a D50 of 1.62, a D10 of 2, and a tap density of 4.5 and a specific surface area of ​​0.27). 1.08, tap density 6.29, specific surface area 0.41); the graphene microemulsion consists of 0.1 parts of graphene with an average particle size of 100nm and a three-layer lamellar structure, 0.02 parts of methacryloyloxy silane coupling agent, and 1.88 parts of diethylene glycol acetate solvent.

[0070] Comparative Example 1

[0071] A heterojunction low-temperature silver paste, comprising, by weight, 91 parts of a combined silver powder and 9 parts of an organic carrier (preparation of the organic carrier: bisphenol A resin, blocked isocyanate, diethylene glycol butyl ether acetate solvent, 2014FG latent modified polyamide curing agent, and dispersant BYK333 auxiliary agent are mixed in a weight ratio of 30:16.25:43.7:2.5:7.5); wherein the combined silver powder comprises 40.95 parts of flaky silver powder (the flaky silver powder used in comparative example 1 has a D100 of 15, a D50 of 6.6, a D10 of 2, a tap density of 4.5, and a specific surface area of ​​0.27) and 50.05 parts of spherical silver powder (the spherical silver powder used in comparative example 1 has a D100 of 3.99, a D50 of 1.62, a D10 of 1.08, a tap density of 6.29, and a specific surface area of ​​0.41);

[0072] Comparative Example 2

[0073] A heterojunction low-temperature silver paste, which comprises, by weight, 90 parts of a combined silver powder and 10 parts of an organic carrier (preparation of the organic carrier: bisphenol A resin, blocked isocyanate, diethylene glycol butyl ether acetate solvent, 2014FG latent modified polyamide curing agent, and dispersant BYK333 auxiliary agent are mixed in a weight ratio of 30:16.25:43.7:2.5:7.5 for every 100 parts); wherein the combined silver powder comprises 40.5 parts of flaky silver powder (the flaky silver powder used in comparative example 1 has a specific D100 of 15, a D50 of 6.6, a D10 of 2, a tap density of 4.5, and a specific surface area of ​​0.27) and 49.5 parts of spherical silver powder (the spherical silver powder used in comparative example 2 has a D100 of 3.99, a D50 of 1.62, a D10 of 1.08, a tap density of 6.29, and a specific surface area of ​​0.41);

[0074] The preparation process of Example 1-2 and Comparative Example 1-2 is as follows based on the above raw material specifications and formulas:

[0075] S1 (Comparative Example 1-2 does not have this step): prepare graphene microemulsion: add graphene and coupling agent to a solvent, and disperse by ultrasound at an ultrasonic power of 1000 W for 0.5 hours until the graphene is uniformly dispersed in the solvent, and then emulsify by an emulsifier for 30 seconds to obtain a graphene microemulsion;

[0076] S2: Preparation of silver paste: weigh a combination of silver powder consisting of flaky silver powder and spherical silver powder, add it to an organic carrier, pour it into a reactor, stir at a speed of 800 r / min, and stir for 1 hour until there are no obvious silver powder particles; then add graphene microemulsion, stir at a speed of 800 r / min, and stir for 0.5 hour until a uniform slurry is obtained.

[0077] S3: Slurry grinding: Grind the slurry stirred evenly in step S2, and adjust the grinding gap from large to small to 120 μm to 30 μm (Example 1-2 and Comparative Example 1-2 are 120 μm, 60 μm, and 30 μm), and roll each gap 3 to 4 times, including 4 times for 120 μm, 3 times for 60 μm, and 3 times for 30 μm, to achieve a sufficient grinding effect, until the fineness of the slurry reaches less than 10 μm, that is, the slurry is obtained;

[0078] S4: Slurry storage: Store the final product in a refrigerator at -5-5℃.

[0079] The specific contents of the components in the above examples and the properties of the prepared heterojunction low-temperature silver paste are shown in the following table:

[0080] Table 1 Components and properties of Examples 1-2 and Comparative Examples 1-2

[0081]

[0082] The slurry sample prepared by the present invention is deposited on a heterojunction cell by screen printing, cured at a low temperature of 150° C. for 10 minutes, and then cured at <220° C. for 30 minutes.

[0083] By comparing Example 1, Example 2 and Comparative Example 1, the performance is significantly improved by doping with graphene microemulsion, the contact resistance is reduced, the line resistance is not significantly increased, and the photoelectric conversion efficiency is improved. As can be seen from Example 1 and Comparative Example 2, by doping with graphene microemulsion and connecting the gaps between silver powders, the amount of silver powder used can be appropriately reduced. In summary, the heterojunction low-temperature silver paste obtained by the present invention can effectively reduce the line resistance and contact resistance of the electrode grid line, and improve the photoelectric conversion efficiency of the heterojunction solar cell.

Claims

1. Heterojunction low-temperature silver paste doped with graphene microemulsion, characterized in that: The heterojunction low-temperature silver paste doped with graphene microemulsion comprises: silver powder, graphene microemulsion, and organic carrier; the mass ratio of the silver powder, graphene microemulsion, and organic carrier is: 88-92:0.5-2:6-11.5; The graphene microemulsion consists of 1-10% of graphene, 0.1-1% of coupling agent and 89-98.9% of solvent in terms of mass percentage; The silver powder includes flaky silver powder and spherical silver powder; The particle size distribution of the flaky silver powder is D100≤1100nm, D50≤700nm, D10≥300nm, and the tap density is 5-6g / cm 3 , specific surface area 0.5~1.0m 2 / g; the particle size distribution of the spherical silver powder is D100≤900nm, D50≤600nm, D10≥200nm, and the tap density is 4.5~5.5g / cm 3 , specific surface area 0.6~0.8m 2 / g; The organic carrier comprises a thermosetting resin, a curing agent, a solvent a, and an auxiliary agent; the thermosetting resin comprises at least one of bisphenol A resin, bisphenol F resin, polyester resin, phenolic resin, and acrylic resin; the curing agent is a latent curing agent; the solvent a is at least one of diethylene glycol butyl ether acetate, tripropylene glycol methyl ether, alcohol resin 12, and pinene alcohol; the auxiliary agent is at least one of a silane coupling agent and a dispersant; The organic carrier comprises a thermosetting resin, a curing agent, a solvent a and an auxiliary agent in a mass ratio of 25 to 35:15 to 23:30 to 45:5 to 10.

2. The heterojunction low-temperature silver paste doped with graphene microemulsion according to claim 1, characterized in that: The curing agent is at least one of an imidazole curing agent, a polyamide curing agent, a methyl hexacarboxylic anhydride curing agent, a methyl tetracarboxylic anhydride curing agent, and a blocked isocyanate.

3. The heterojunction low-temperature silver paste doped with graphene microemulsion according to claim 1, characterized in that: The curing agent is composed of 13 to 20 parts by weight of blocked isocyanate and 2 to 3 parts by weight of other curing agents.

4. The heterojunction low-temperature silver paste doped with graphene microemulsion according to claim 1 or 2, characterized in that: The graphene has an average particle size of 50 to 400 nm and a 3 to 5-layer flake structure.

5. The heterojunction low-temperature silver paste doped with graphene microemulsion according to claim 1 or 2, characterized in that: The coupling agent is a silane coupling agent.

6. The graphene microemulsion-doped heterojunction low-temperature silver paste according to claim 5, characterized in that: The silane coupling agent includes at least one of methacryloxysilane, epoxysilane, aminofunctional silane, aminocarboxylate silane, aminopropylsilane, arylsilane or cationic silane.

7. The heterojunction low-temperature silver paste doped with graphene microemulsion according to claim 1 or 2, characterized in that: The solvent is at least one of butyl carbitol acetate, terpineol, alcohol 12, butyl carbitol, dimethyl glutarate or dimethyl adipate.

8. The graphene microemulsion-doped heterojunction low-temperature silver paste according to claim 1 or 2, characterized in that: The heterojunction low-temperature silver paste doped with graphene microemulsion is prepared by the following method: S1: preparing graphene microemulsion: mixing and dispersing graphene, coupling agent and solvent uniformly, and emulsifying to obtain graphene microemulsion; S2: preparing silver paste: mixing silver powder and organic carrier evenly until no obvious silver powder particles are left; and then mixing with graphene microemulsion evenly to obtain a uniform slurry; S3: Slurry grinding: Grind the uniform slurry described in step S2 until the fineness of the slurry reaches less than 10 μm, thereby obtaining a heterojunction low-temperature silver paste doped with graphene microemulsion.

9. The heterojunction low-temperature silver paste doped with graphene microemulsion according to claim 8, characterized in that: S1 The uniform dispersion is carried out by ultrasonic dispersion.

10. The graphene microemulsion-doped heterojunction low-temperature silver paste according to claim 9, characterized in that: The power of the ultrasound in S1 is 500 to 1500 W, and the time of the ultrasound is 10 to 60 minutes.

11. The graphene microemulsion-doped heterojunction low-temperature silver paste according to claim 9, characterized in that: The emulsification in S1 is performed by using an emulsifier for 10 to 60 seconds.

12. The graphene microemulsion-doped heterojunction low-temperature silver paste according to claim 9, characterized in that: S2: The method for uniformly mixing the silver powder and the organic carrier is stirring at a stirring speed of 500 to 1000 r / min for 1 to 2 hours; the method for uniformly mixing with the graphene microemulsion is stirring at a stirring speed of 500 to 1000 r / min for 30 to 60 minutes.

13. The heterojunction low-temperature silver paste doped with graphene microemulsion according to claim 9, characterized in that: The grinding gap in S3 is adjusted from large to small to 120 μm to 30 μm, and each gap is rolled 3 to 4 times.

14. The method for preparing the heterojunction low-temperature silver paste doped with graphene microemulsion according to any one of claims 1 to 13, characterized in that: The method comprises: S1: preparing graphene microemulsion: mixing and dispersing graphene, coupling agent and solvent uniformly, and emulsifying to obtain graphene microemulsion; S2: preparing silver paste: mixing silver powder and organic carrier evenly until no obvious silver powder particles are left; and then mixing with graphene microemulsion evenly to obtain a uniform slurry; S3: Slurry grinding: Grind the uniform slurry described in step S2 until the fineness of the slurry reaches less than 10 μm, thereby obtaining a heterojunction low-temperature silver paste doped with graphene microemulsion.

15. The method for preparing the heterojunction low-temperature silver paste doped with graphene microemulsion according to claim 13, characterized in that: The method further comprises S4: slurry storage: storing the heterojunction low-temperature silver slurry doped with graphene microemulsion obtained in S3 in a refrigerator at -5 to 5°C; S1 The uniform dispersion is carried out by ultrasonic dispersion.

16. The method for preparing the heterojunction low-temperature silver paste doped with graphene microemulsion according to claim 15, characterized in that: The power of the ultrasound in S1 is 500 to 1500 W, and the time of the ultrasound is 10 to 60 minutes.

17. The method for preparing the heterojunction low-temperature silver paste doped with graphene microemulsion according to claim 15, characterized in that: The emulsification in S1 is performed by using an emulsifier for 10 to 60 seconds.

18. The method for preparing the heterojunction low-temperature silver paste doped with graphene microemulsion according to claim 15, characterized in that: S2: The method for uniformly mixing the silver powder and the organic carrier is stirring at a stirring speed of 500 to 1000 r / min for 1 to 2 hours; the method for uniformly mixing with the graphene microemulsion is stirring at a stirring speed of 500 to 1000 r / min for 30 to 60 minutes.

19. The method for preparing the heterojunction low-temperature silver paste doped with graphene microemulsion according to claim 15, characterized in that: The grinding gap in S3 is adjusted from large to small to 120 μm to 30 μm, and each gap is rolled 3 to 4 times.

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