A silver paste, its preparation method and application

Abstract

This invention relates to a silver paste, its preparation method, and its application. The silver paste comprises a composite material, glass powder, and an organic carrier, wherein the raw materials of the composite material include silver powder and graphite emulsion. The silver paste of this invention can improve the problem of silver migration, thereby improving the performance of solar cells.

Description

Technical Field

[0001] This invention relates to fields such as solar energy, and specifically to a silver paste, its preparation method, and its application. Background Technology

[0002] Conductive silver paste is a crucial raw material in the manufacture of solar photovoltaic cells, and its characteristics and applications directly affect the conductivity, energy conversion efficiency, and reliability of the solar cells. Conductive silver paste mainly consists of conductive silver powder, inorganic binder glass frit, organic carrier, and trace additives to improve cell performance. Conductive silver paste is used on both the front and back sides of solar photovoltaic cells. The front conductive silver paste is used to create the conductive paths within the cell. Especially in polycrystalline silicon cells, conductive silver paste is used to connect the metal mesh between the cells, forming the current guide and distribution. The back conductive silver paste typically serves as the back contact layer. This layer facilitates the flow of current from the back of the cell to the back electrode, improving the cell's conductivity.

[0003] Conductive silver paste typically requires stable and reliable silver-silicon ohmic contacts to ensure smooth current flow between the silver electrode and the silicon substrate. High conductivity is also crucial to provide a low-resistance conductive path and improve battery energy conversion efficiency. Furthermore, low cost is essential to reduce production costs while maintaining performance, thus improving economic efficiency. Good solderability, adhesion, and printability are also necessary to ensure good performance during printing and other processes. Silver powder is the main component of conductive silver paste. However, silver migration is a concern. While increasing the amount of silver powder can improve conductivity, excessive powder can lead to agglomeration, limiting conductivity and significantly increasing the cost of the conductive silver paste.

[0004] Therefore, as a key component of electrode materials, it is of great significance to develop high-performance conductive silver paste that also takes cost into account. Summary of the Invention

[0005] In view of the deficiencies in the existing technology, the purpose of this invention is to provide a silver paste, its preparation method and application. The silver paste of this invention can improve the problem of silver migration, thereby improving the electrical performance of solar cells.

[0006] To achieve the above objectives, the first aspect of the present invention provides a silver paste comprising a composite material, glass powder, and an organic carrier, wherein the raw materials of the composite material include silver powder and graphite emulsion.

[0007] Based on the above technical solution, the preparation method of the composite material includes: mixing silver powder and graphite emulsion and drying. In this invention, this preparation method can form a carbon-coated silver composite material structure, thereby overcoming the problem of silver migration and improving conductivity and stability.

[0008] Based on the above technical solution, the formulation of graphite emulsion may include, but is not limited to: by weight percentage, the graphite emulsion contains 9-11% graphite, 1-2% dispersant, 2-4% binder, 1-2% ammonia, 0.8-1.8% thickener, and 81-85% water.

[0009] Based on the above technical solution, the dispersant is selected from one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl alcohol, and gum arabic.

[0010] Based on the above technical solution, the binder is selected from silica sol.

[0011] Based on the above technical solution, the thickener is selected from carboxymethyl cellulose.

[0012] Based on the above technical solution, the weight ratio of silver powder to graphite emulsion is 1:0.2-0.5. For example, but not limited to: the weight ratio of silver powder to graphite emulsion is 1:0.2-0.5, 1:0.3-0.5, 1:0.4-0.5, 1:0.2-0.4, 1:0.3-0.4, etc.

[0013] Based on the above technical solution, the particle size of the silver powder is 0.5-5μm. The particle size of the silver powder may be, for example but not limited to, 0.5-5μm, 1-5μm, 1.5-5μm, 2-5μm, 2.5-5μm, 3-5μm, 3.5-5μm, 4-5μm, 4.5-5μm, 0.5-4μm, 1-4μm, 1.5-4μm, 2-4μm, 2.5-4μm, 3-4μm, 3.5-4μm, 0.5-3μm, 1-3μm, 1.5-3μm, 2-3μm, 2.5-3μm, etc.

[0014] Based on the above technical solution, the drying conditions include: a temperature of 60-100℃ and a time of 2-10 hours. In this invention, the drying temperature can be, but is not limited to, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, etc.

[0015] Based on the above technical solution, with the total weight of silver paste as the benchmark, the content of composite material is 50-85% by weight, the content of glass powder is 2-5% by weight, and the content of organic carrier is 14-45% by weight.

[0016] Based on the above technical solution, the glass powder is selected from one or more of borosilicate glass powder, alkali metal glass powder, ultra-white rolled glass powder, and ultra-white float glass powder. In this invention, for example, but not limited to, based on the total weight of the glass powder, the content of SiO2 is 30-60% by weight, the content of PbO is 25-40% by weight, the content of Al2O3 is 0.1-3% by weight, the content of Na2O is 5-20% by weight, the content of K2O is 0.1-1% by weight, the content of MgO is 1-6% by weight, the content of CaO is 6-12% by weight, the content of MoO2 is 0-1% by weight, and the content of SnO2 is 0-1% by weight.

[0017] Based on the above technical solution, the organic carrier includes a solvent and optional additives.

[0018] Based on the above technical solution, the solvent is selected from one or more of diethylene glycol butyl ether acetate, dimethyl glutarate, dimethyl succinate, and dimethyl adipate.

[0019] Based on the above technical solution, the additive is selected from one or more of dispersants, leveling agents, thixotropic agents, coupling agents, and defoamers. In this invention, the dispersant, leveling agent, thixotropic agent, coupling agent, and defoamer can be conventional options in the art. For example, the dispersant can be BYK-W980, etc.; the coupling agent can be a silane coupling agent, etc.; the leveling agent can be castor oil, etc.; and the defoamer can be dimethyl silicone oil, etc. In this invention, the amount of additive added, based on the total weight of the silver paste, can be 0-0.5% by weight. For example, but not limited to, 0.1% by weight, 0.2% by weight, 0.3% by weight, 0.4% by weight, 0.5% by weight, etc.

[0020] Based on the above technical solution, the silver paste is a conductive silver paste for the front side of a solar cell.

[0021] A second aspect of the present invention provides a method for preparing the above-mentioned silver paste, comprising: mixing silver powder, a composite material, and an organic carrier. The mixing may, but is not limited to, rolling and dispersing in a three-roll mill to achieve uniform dispersion.

[0022] The third aspect of the present invention provides the application of the above-described silver paste in solar cells.

[0023] The beneficial effects of this invention are:

[0024] Silver migration is indeed a significant concern, especially in applications such as solar cells, where silver, as a primary material in conductive silver paste, has a particularly pronounced impact. Migration can lead to a decline in the electrical performance and weakened adhesion of solar cells. This invention employs a graphite emulsion to coat silver, forming a carbon-coated silver composite material. The carbon material serves as a protective layer, coated on the surface of the silver. The carbon material possesses excellent stability and barrier properties, effectively preventing the migration of silver ions, thereby extending the lifespan of solar cells and improving the electrical performance, adhesion, and aging resistance of solar cells prepared with silver paste. Moreover, the graphite emulsion used in this invention is low-cost, reducing the overall cost of silver paste. Detailed Implementation

[0025] In the following technical description, for ease of explanation, numerous details are used to provide a full understanding of the disclosed embodiments. However, one or more embodiments may still be practiced without these details. In other instances, well-known structures and apparatuses may be shown in a simplified manner for the sake of illustration.

[0026] The terms "first," "second," etc., used in the specification and claims of this disclosure and in the above embodiments are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate for the embodiments of this disclosure described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0027] The following are examples. In the following examples and comparative examples, all raw materials used were commercially available.

[0028] Preparation Example 1

[0029] Preparation of graphite emulsion:

[0030] 11% by weight of graphite was mixed with 1.5% by weight of ammonia and degelatinated using a grinding mill equipped with steel balls for 1 hour. Then, 1.5% by weight of polyvinylpyrrolidone, 3% by weight of silica sol, 10% by weight of carboxymethyl cellulose, and 82% by weight of water were added and mixed, stirred for 1 hour, and after stirring evenly, an electromagnet was fixed to remove iron. The sample was placed for 10 hours and then shaken on a shaking machine for 1 hour to obtain graphite emulsion.

[0031] Preparation Example 2

[0032] Preparation of glass powder:

[0033] 50 wt% SiO2, 30 wt% PbO, 1 wt% Al2O3, 10 wt% Na2O, 0.5 wt% K2O, 2.5 wt% MgO, and 6 wt% CaO are thoroughly mixed to obtain glass powder.

[0034] Example 1

[0035] Step 1: The particle size D 50 1 μm silver powder was mixed with the graphite emulsion obtained in Preparation Example 1 at a weight ratio of 1:0.2, stirred for 1 hour, and dried at 80°C for 4 hours to obtain the composite material.

[0036] Step 2: Mix 80 wt% of the composite material prepared in Step 1, 3 wt% of glass powder (obtained in Preparation Example 2), 16.6 wt% of diethylene glycol butyl ether acetate, 0.2 wt% of castor oil leveling agent, and 0.2 wt% of dispersant BYK-W980. Disperse the slurry evenly using ultrasonic dispersion and a three-roll mill to obtain silver paste.

[0037] Example 2

[0038] Step 1: The particle size D 50 1 μm silver powder was mixed with the graphite emulsion obtained in Preparation Example 1 at a weight ratio of 1:0.5, stirred for 1 hour, and dried at 80°C for 4 hours to obtain the composite material.

[0039] Step 2: Mix 80 wt% of the composite material prepared in Step 1, 3 wt% of glass powder (obtained in Preparation Example 2), 16.6 wt% of diethylene glycol butyl ether acetate, 0.2 wt% of castor oil leveling agent, and 0.2 wt% of dispersant BYK-W980. Disperse the slurry evenly using ultrasonic dispersion and a three-roll mill to obtain silver paste.

[0040] Example 3

[0041] Step 1: The particle size D 50 Silver powder with a thickness of 3 μm was mixed with the graphite emulsion obtained in Preparation Example 1 at a weight ratio of 1:0.2, stirred for 1 hour, and dried at 80°C for 4 hours to obtain the composite material.

[0042] Step 2: Mix 80 wt% of the composite material prepared in Step 1, 3 wt% of glass powder (obtained in Preparation Example 2), 16.6 wt% of diethylene glycol butyl ether acetate, 0.2 wt% of castor oil leveling agent, and 0.2 wt% of dispersant BYK-W980. Disperse the slurry evenly using ultrasonic dispersion and a three-roll mill to obtain silver paste.

[0043] Example 4

[0044] Step 1: The particle size D 50 1 μm silver powder was mixed with the graphite emulsion obtained in Preparation Example 1 at a weight ratio of 1:0.2, stirred for 1 hour, and dried at 60°C for 8 hours to obtain the composite material.

[0045] Step 2: Mix 85% by weight of the composite material prepared in Step 1, 2% by weight of glass powder (obtained in Preparation Example 2), 12.6% by weight of diethylene glycol butyl ether acetate, 0.2% by weight of castor oil leveling agent, and 0.2% by weight of dispersant BYK-W980. Disperse the slurry evenly using ultrasonic dispersion and three-roll milling to obtain silver paste.

[0046] Example 5

[0047] Step 1: The particle size D 50 1 μm silver powder was mixed with the graphite emulsion obtained in Preparation Example 1 at a weight ratio of 1:0.8, stirred for 1 hour, and dried at 80°C for 4 hours to obtain the composite material.

[0048] Step 2: Mix 80 wt% of the composite material prepared in Step 1, 3 wt% of glass powder (obtained in Preparation Example 2), 16.6 wt% of diethylene glycol butyl ether acetate, 0.2 wt% of castor oil leveling agent, and 0.2 wt% of dispersant BYK-W980. Disperse the slurry evenly using ultrasonic dispersion and a three-roll mill to obtain silver paste.

[0049] Example 6

[0050] The method is the same as in Example 1, except that the silver powder and graphite emulsion are mixed but not dried, i.e.:

[0051] Step 1: The particle size D 50 Silver powder with a particle size of 1 μm was mixed with the graphite emulsion obtained in Preparation Example 1 at a weight ratio of 1:0.2 to obtain a composite material.

[0052] Step 2: Mix 80 wt% of the composite material prepared in Step 1, 3 wt% of glass powder (obtained in Preparation Example 2), 16.6 wt% of diethylene glycol butyl ether acetate, 0.2 wt% of castor oil leveling agent, and 0.2 wt% of dispersant BYK-W980. Disperse the slurry evenly using ultrasonic dispersion and a three-roll mill to obtain silver paste.

[0053] Comparative Example 1

[0054] 80% by weight of particle size D 50 The silver paste was prepared by mixing 1 μm silver powder, 3 wt% glass powder (obtained in Preparation Example 2), 16.6 wt% diethylene glycol butyl ether acetate, 0.2 wt% castor oil leveling agent, and 0.2 wt% dispersant BYK-W980, and by ultrasonic dispersion and three-roll mill mixing to uniformly disperse the slurry.

[0055] Test case

[0056] Performance testing: The resistivity, contact resistivity, peel strength and aging performance of the electrodes prepared with conductive silver paste in the examples and comparative examples were tested respectively. The results are shown in Table 1.

[0057] (1) Resistivity Testing Method: The conductive pastes of the examples and comparative examples were screen-printed and coated onto N-type TOPCon solar blue films, and vacuum dried at room temperature for 3 hours. They were then cured using circulating hot air at 200°C for 30 minutes to obtain fine-wire electrodes. The resistance of the fine-wire electrodes was measured using an AEMC 6240 micro-resistivity meter, and the width and length of the filaments were measured using a WI-5000 interferometric coaxial three-dimensional stereomicroscope. The pattern specifications of the formed fine-wire electrodes were as follows: the width of the middle line segment was 40 μm, the length was 9 cm, and the contact pads at the head and tail were 2 mm × 2 mm. The line resistance was measured by four-terminal sensing between the contact pads. The measured resistance was normalized by the grid line length and multiplied by the cross-sectional area (measured using an α-step profiler) to obtain the resistivity of the grid lines. Each resistivity dataset was obtained by averaging the values ​​measured for four different grid lines.

[0058] (2) Contact resistivity test method: The conductive pastes of the examples and comparative examples were screen-printed and coated onto N-type TOPCon solar blue films, and vacuum dried at room temperature for 3 hours. Then, they were cured at 200°C using circulating hot air for 50 minutes to obtain fine-line electrodes. The electrode pattern consisted of five linear electrodes with a line width of 0.5 mm and a length of 50 mm, with a line spacing of 3 mm. The resistance between the line electrodes with different spacings was then measured using an AEMC 6240 microresistivity meter, and the distance was calculated using the transmission line model (TLM) method to obtain the contact resistivity (Rt) with the substrate. c ).

[0059] (3) Peel strength test method: The conductive pastes of the examples and comparative examples were screen-printed and coated onto N-type TOPCon solar blue films, and vacuum dried at room temperature for 3 hours. Then, they were cured using circulating hot air at 200°C for 50 minutes to obtain fine-wire electrodes. The electrode pattern was obtained by screen printing. The test electrode pattern was 5cm long and 2mm wide, and then a 1mm wide tin-plated copper strip was soldered onto the test electrode. The substrate was fixed on a tension gauge platform to test the peel strength. The tension gauge type was an NLB-□100 electronic push-pull pressure gauge. The test conditions were to peel the solder strip at a speed of 60mm / min at a 180° angle and obtain the tensile force value, recorded once per second. The obtained tension is the average value of a 5cm long electrode.

[0060] (4) Test method for aging resistance: 200 cycles of hot and cold cycling to test the decay of photoelectric conversion efficiency. Aging resistance (decay%) = (initial photoelectric conversion efficiency - photoelectric conversion efficiency after 200 cycles of hot and cold cycling) ÷ initial photoelectric conversion efficiency × 100%.

[0061] Table 1

[0062]

[0063] As can be seen from the table above, the silver paste for solar cells prepared using the formula of this invention can significantly reduce resistivity and contact resistivity; the resistivity can be reduced from 9.3 × 10⁻⁶. -6 Ω·cm decreased to 5.9×10 -6 Ω·cm, contact resistivity can range from 3.6Ω·cm 2 Decrease by 0.70×10 -6 Ω·cm. It can also improve peel strength and aging resistance.

[0064] This application is not limited to the embodiments described above, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

[0065] In this application, each embodiment may focus on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other.

Claims

1. A silver paste comprising a composite material, glass powder, and an organic carrier, wherein, The raw materials of the composite material include silver powder and graphite emulsion; wherein the weight ratio of silver powder to graphite emulsion is 1:0.2-0.5; the preparation method of the composite material includes: mixing silver powder and graphite emulsion and drying. The graphite emulsion contains, by weight percentage, 9-11% graphite, 1-2% dispersant, 2-4% binder, 1-2% ammonia, 0.8-1.8% thickener, and 81-85% water. Based on the total weight of the silver paste, the content of composite materials is 50-85% by weight, the content of glass powder is 2-5% by weight, and the content of organic carrier is 14-45% by weight.

2. The silver paste according to claim 1, characterized in that, The dispersant is selected from one or more of sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl alcohol, and gum arabic.

3. The silver paste according to claim 1, characterized in that, The binder is selected from silica sol.

4. The silver paste according to claim 1, characterized in that, The thickener is selected from carboxymethyl cellulose.

5. The silver paste according to claim 1, characterized in that, The silver powder has a particle size of 0.5-5 μm.

6. The silver paste according to claim 1, characterized in that, The drying conditions include a temperature of 60-100℃ and a time of 2-10 hours.

7. The silver paste according to claim 1, characterized in that, The glass powder is selected from one or more of borosilicate glass powder, alkali metal glass powder, ultra-white rolled glass powder, and ultra-white float glass powder.

8. The silver paste according to claim 1, characterized in that, The organic carrier includes a solvent and optional additives.

9. The silver paste according to claim 8, characterized in that, The solvent is selected from one or more of diethylene glycol butyl ether acetate, dimethyl glutarate, dimethyl succinate, and dimethyl adipate.

10. The silver paste according to claim 8, characterized in that, The additive is selected from one or more of dispersants, leveling agents, thixotropic agents, coupling agents, and defoamers.

11. The silver paste according to any one of claims 1-10, characterized in that, The silver paste is a conductive silver paste used on the front side of a solar cell.

12. A method for preparing silver paste according to any one of claims 1-11, comprising: Glass powder, composite materials, and organic carriers are mixed.

13. The use of the silver paste according to any one of claims 1-11 in a solar cell.

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