A front electrode paste for silicon solar cells and its preparation method

Abstract

The present invention belongs to the field of solar electrode printing, and specifically discloses a front electrode paste for silicon solar cells and a preparation method thereof. The raw materials for preparing the front electrode paste for silicon solar cells of the present invention include the following components in mass percentage: 80-90% of conductive silver powder, 6-10% of organic carrier, 4-6% of glass powder, 0-3% of aluminum powder, and 0-2% of other additives; the raw materials for preparing the organic carrier include the following components in mass percentage: 60-90% of organic solvent, 5-10% of organic resin, 1-5% of thixotropic agent, 1-5% of surfactant A, 1-5% of surfactant B, and 1-5% of nano polytetrafluoroethylene; the surfactant A is polyvinylpyrrolidone. The front electrode paste for silicon solar cells of the present invention has good printing performance, and there is no broken grid when printed with a 16μm line width screen, and the aspect ratio of the grid line is greater than 0.5.

Description

Technical Field

[0001] The present invention belongs to the field of solar electrode printing, and specifically relates to a front electrode paste for silicon solar cells and a preparation method thereof. Background Art

[0002] Under the background of the increasing global energy consumption, solar energy, which is widely available, easily accessible, and inexhaustible, is an important solution to alleviate energy demand. Solar cells are an important means of harvesting solar energy. Among them, silicon-based solar cells are the types of solar cells that have been widely used at present. After the photovoltaic effect occurs in the solar cell under light illumination, electrodes are required to collect and conduct the current, and the fabrication of electrodes is an important step in the production of solar cells. Currently, the commonly used electrode fabrication process is to screen-print the electrode paste onto the silicon wafer and then perform high-temperature sintering, so that the electrode paste corrodes the passivation layer on the surface of the silicon wafer and forms a good ohmic contact with the silicon wafer. The electrode paste usually consists of conductive phases such as silver powder and aluminum powder, an organic carrier, an inorganic glass powder, and other additives. Among them, the organic carrier plays an important role in the printability of the paste.

[0003] With the improvement of the battery fabrication process level, in order to reduce the loss of the battery conversion efficiency caused by electrode shading, it is necessary to further reduce the grid line opening width of the screen printing stencil and at the same time increase the aspect ratio of the grid lines, while ensuring the conductivity of the electrodes while reducing the electrode shading area, so as to obtain a higher battery conversion efficiency. Therefore, improving the printability of the electrode paste on the fine grid line stencil and increasing the aspect ratio of the grid lines are an important improvement direction for the front electrode paste of solar cells.

[0004] Existing front silver pastes for solar cells often add organic silicone oil and the like to improve the printing performance of the paste. For example, CN105679400A discloses a conductive silver paste for solar cells, which adds 0.1%-10% of silicone oil, including silicone oils substituted with different functional groups, to obtain better printing performance. Patent document CN114360767A discloses a positive silver paste for solar cells, which adds nano-sized spherical silica to improve the dispersion of silver powder, and at the same time adds silicone oils with different viscosities to improve the dispersion degree of silver powder and silica microspheres, so that the paste obtains better printing quality. However, it is difficult to completely remove the silicone oil during the sintering process, which will have a certain impact on the electrode performance, and the addition of silica will also cause an increase in the bulk resistance of the grid lines. Summary of the Invention

[0005] Aiming at the problems such as poor printing performance of the front electrode paste for silicon solar cells in the above-mentioned existing technologies, the present invention will provide a front electrode paste for silicon solar cells and a preparation method thereof.

[0006] To achieve the above object, the specific technical solutions include the following:

[0007] A front electrode paste for silicon solar cells, and the preparation raw materials of the front electrode paste for silicon solar cells include components with the following mass percentages: 80-90% of conductive silver powder, 6-10% of organic carrier, 4-6% of glass powder, 0-3% of aluminum powder, and 0-2% of other additives;

[0008] The preparation raw materials of the organic carrier include components with the following mass percentages: 60-90% of organic solvent, 5-10% of organic resin, 1-5% of thixotropic agent, 1-5% of surfactant A, 1-5% of surfactant B, and 1-5% of nano polytetrafluoroethylene; The surfactant A is polyvinylpyrrolidone; The conductive silver powder is at least one of spherical silver powder, flaky silver powder, and microcrystalline silver powder.

[0009] As a preferred embodiment of the present invention, the conductive silver powder is a mixture of conductive silver powders with different average particle sizes.

[0010] As a preferred embodiment of the present invention, the conductive silver powder is spherical silver powder, and the spherical silver powder includes spherical silver powder A with an average particle size D50 of 0.1-1 μm and spherical silver powder B with an average particle size D50 of 0.5-5 μm;

[0011] The tapped density of the spherical silver powder A > 2.0 g / cm 3 , and the tapped density of the spherical silver powder B > 4.0 g / cm 3 .

[0012] As a further preferred embodiment of the present invention, the average particle size D50 of the conductive silver powder B is 1-3 μm.

[0013] The combination of two different particle size silver powders in the present invention reduces the porosity after silver powder sintering, making the grid line have a lower bulk resistance.

[0014] As a preferred embodiment of the present invention, among the spherical silver powders of the conductive silver powder, the mass percentage of spherical silver powder A is 50-80%, and the mass percentage of spherical silver powder B is 20-50%.

[0015] As a further preferred embodiment of the present invention, among the spherical silver powders of the conductive silver powder, the mass percentage of spherical silver powder A is 60%, and the mass percentage of spherical silver powder B is 40%.

[0016] The combination of spherical silver powders with different sizes can improve the contact between silver powders, reduce the porosity after silver powder sintering, and ensure that the grid line has a lower bulk resistance.

[0017] As a preferred embodiment of the present invention, the raw materials for preparing the organic carrier include components with the following mass percentages: 81-84% organic solvent, 9% organic resin, 3% surfactant A, 2% surfactant B, 2% thixotropic agent, and 3% nano polytetrafluoroethylene.

[0018] As a preferred embodiment of the present invention, the raw materials for preparing the front electrode paste of the silicon solar cell include components with the following mass percentages: 80.8% conductive silver powder, 3% aluminum powder, 6% glass powder, 10% organic carrier, and 0.2% additive.

[0019] In the present invention, polyvinylpyrrolidone can improve the wetting ability of the paste to the silicon wafer, improve the adhesion between the paste and the silicon wafer, improve the printing quality of the paste, and at the same time make the line type more plump and improve the aspect ratio of the grid line. In addition, the nitrogen element in polyvinylpyrrolidone can dope the residual carbon components after sintering, enhance its conductivity, and reduce its impact on the conductivity of the electrode.

[0020] Polytetrafluoroethylene has the characteristics of low friction coefficient and solvent resistance, can improve the dispersion of silver powder in the silver paste, enhance the lubricity and permeability of the paste during the printing process, plays a role in improving the printing performance of the paste, and reduces the occurrence of broken grids and void printing; and polytetrafluoroethylene can be removed during the sintering process, without the defect that its residue affects the electrode performance when adding silicone oil as a lubricant.

[0021] As a preferred embodiment of the present invention, the nano polytetrafluoroethylene model is 3M TF9027Z, and the primary particle size is 120nm.

[0022] As a preferred embodiment of the present invention, the surfactant B includes at least one of Tween 85, Tween 80, Tween 60, and Span 60.

[0023] The surfactant can be selected from Tween 85, Tween 80, and Tween 60, which plays a role in assisting the dissolution of polyvinylpyrrolidone and adjusting the surface tension of the paste.

[0024] In the present invention, when polyvinylpyrrolidone and Tween 80 are added synergistically, while the aspect ratio of the grid line printed by the electrode paste can be synergistically improved, the sheet resistance of the grid line also decreases to a certain extent. When only one of them is added alone, the effect is not as good as when both are added simultaneously.

[0025] As a preferred embodiment of the present invention, the preparation method of the organic carrier includes the following steps: first dissolve the organic resin in the organic solvent to obtain a resin solution; then add surfactant A, surfactant B, thixotropic agent, and nano polytetrafluoroethylene to the resin solution, and activate it under stirring to finally obtain the organic carrier.

[0026] As a preferred embodiment of the present invention, in the preparation method of the organic carrier, the dissolution temperature of the organic resin is 70 - 100 °C, the activation temperature is 50 - 70 °C, and the activation time is 30 - 60 min.

[0027] As a further preferred embodiment of the present invention, the dissolution temperature of the organic resin is 80 °C, the activation temperature is 60 °C, and the activation time is 40 min.

[0028] As a preferred embodiment of the present invention, the other additive is a dispersant, and the dispersant is BYK110; the organic solvents in the organic carrier include at least one of lauryl alcohol phthalate, butyl carbitol, butyl carbitol acetate, terpineol, tributyl acetylcitrate, diethylene glycol monoethyl ether acetate, dipropylene glycol methyl ether acetate, dimethyl adipate, diethylene glycol monomethyl ether, diethylene glycol dibutyl ether, tripropylene glycol butyl ether, dimethyl adipate, and diethyl adipate.

[0029] As a further preferred embodiment of the present invention, the organic solvents are dimethyl adipate, dimethyl adipate, and diethylene glycol monoethyl ether acetate, and the mass ratio of dimethyl adipate: dimethyl adipate: diethylene glycol monoethyl ether acetate = dimethyl adipate: dimethyl adipate: diethylene glycol monoethyl ether acetate = (1 - 2):1:(2 - 3).

[0030] As a further preferred embodiment of the present invention, the mass ratio of dimethyl adipate: dimethyl adipate: diethylene glycol monoethyl ether acetate = 2:1:2.6.

[0031] As a preferred embodiment of the present invention, the organic resin in the organic carrier includes at least one of ethyl cellulose, acrylic resin, and polyvinyl butyral resin; the thixotropic agent in the organic carrier includes at least one of modified polyamide wax and hydrogenated castor oil.

[0032] As a further preferred embodiment of the present invention, the organic resin is ethyl cellulose and polyvinyl butyral resin, and the mass ratio of ethyl cellulose and polyvinyl butyral resin is 1:(2 - 3).

[0033] As a further preferred embodiment of the present invention, the organic resin is ethyl cellulose and polyvinyl butyral resin, and the mass ratio of ethyl cellulose and polyvinyl butyral resin is 1:2.

[0034] The thixotropic agent is composed of one or several of modified polyamide wax or hydrogenated castor oil, and plays a role in adjusting the thixotropy of the slurry.

[0035] As a further preferred embodiment of the present invention, the thixotropic agent is Disparlon 6500.

[0036] The dispersant can be selected from the commonly used dispersants in the art, preferably BYK110, which plays the role of dispersing the powder, adjusting the viscosity, and stabilizing the carrier.

[0037] The present invention also provides a preparation method of a positive electrode paste for a silicon solar cell, comprising the following steps: First, mix the raw materials, then perform pre-dispersion until the powder is completely wetted by the organic carrier and uniformly dispersed, and then perform grinding until the fineness of the paste is less than 10 microns, and finally obtain the positive electrode paste for the silicon solar cell.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The positive electrode paste for the silicon solar cell of the present invention has good printing performance, and there is no broken grid when printed with a 16μm line width screen, and the aspect ratio of the grid line is greater than 0.5.

[0040] (2) In the present invention, nano-level polytetrafluoroethylene micropowder is added, which improves the dispersion of silver powder in the paste and enhances the printing performance of the paste.

[0041] (3) In the present invention, polyvinylpyrrolidone is added, which can act synergistically with other surfactants to improve the wettability between the paste and the silicon wafer, improve the printing quality of the paste, and at the same time increase the aspect ratio of the grid line.

[0042] (4) The positive electrode paste for the silicon solar cell of the present invention uses a combination of two different average particle size silver powders, which reduces the porosity after sintering of the silver powder and makes the grid line have a lower bulk resistance. Specific embodiments

[0043] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below through specific comparative examples and examples.

[0044] Examples 1-6

[0045] (1) The preparation method of the organic carrier includes the following steps: Weigh the organic solvents according to the formula (mass percentage) in Table 1 and mix them, heat to 80°C and add the organic resin in batches under stirring, stir until all the organic resin is dissolved to obtain a homogeneous and transparent resin solution; then add surfactant A, thixotropic agent, surfactant B and nano-polytetrafluoroethylene to the resin solution in sequence, and stir and activate at high speed at 60°C for 40 minutes to obtain the organic carriers of Examples 1-6.

[0046] (2) Preparation of the front electrode paste for silicon solar cells: The organic carriers of Examples 1 to 6 above were formulated according to the recipe in Table 2 and other components were proportioned by weight. After mixing the raw materials, they were pre-dispersed using a planetary disperser until the powder was completely wetted by the organic carrier. After uniform dispersion, they were ground using a three-roll mill until the fineness of the paste was less than 10 microns, and the front electrode pastes for silicon solar cells of Examples 1 to 6 were prepared respectively.

[0047] Example 7

[0048] (1) The preparation method of the organic carrier includes the following steps: Weigh the organic solvents respectively according to the recipe (mass percentage) in Table 1 and mix them. Add the organic resin in batches under heating and stirring, and stir at 70 °C until all the organic resin is dissolved to obtain a homogeneous and transparent resin solution; then add surfactant A, thixotropic agent, surfactant B and nano-polytetrafluoroethylene to the resin solution in sequence, and stir and activate at high speed at 50 °C for 30 minutes to obtain the organic carrier.

[0049] (2) The preparation method of the front electrode paste for silicon solar cells is the same as that of Example 1.

[0050] Example 8

[0051] (1) The preparation method of the organic carrier includes the following steps: Weigh the organic solvents respectively according to the recipe (mass percentage) in Table 1 and mix them. Add the organic resin in batches under heating and stirring, and stir at 100 °C until all the organic resin is dissolved to obtain a homogeneous and transparent resin solution; then add surfactant A, thixotropic agent, surfactant B and nano-polytetrafluoroethylene to the resin solution in sequence, and stir and activate at high speed at 70 °C for 60 minutes to obtain the organic carrier.

[0052] (2) The preparation method of the front electrode paste for silicon solar cells is the same as that of Example 1.

[0053] Comparative Examples 1 to 3

[0054] (1) The preparation method of the organic carrier includes the following steps: Weigh the organic solvents respectively according to the recipe (mass percentage) in Table 1 and mix them. Add the organic resin in batches under heating and stirring, and stir at 80 °C until all the organic resin is dissolved to obtain a homogeneous and transparent resin solution; then add other raw materials to the resin solution, and stir and activate at high speed at 60 °C for 40 minutes to obtain the organic carriers of Comparative Examples 1 to 3.

[0055] (2) Preparation of the front electrode paste for silicon solar cells: The organic carriers of Comparative Examples 1-3 were formulated with other components according to the recipes in Table 2 by weight ratio. After mixing the raw materials, they were pre-dispersed using a planetary disperser until the powder was completely wetted by the organic carrier. After uniform dispersion, they were ground using a three-roll mill until the fineness of the paste was less than 10 μm, and the front electrode pastes for silicon solar cells of Comparative Examples 1-3 were prepared respectively.

[0056] Table 1 Recipes of the organic carriers of Examples 1-8 and Comparative Examples 1-3

[0057]

[0058]

[0059] Table 2 Recipes of the front electrode pastes for silicon solar cells of Examples 1-8 and Comparative Examples 1-3

[0060]

[0061] Among them, the average particle size D50 of spherical silver powder A is 0.1 - 1 μm, and the tapped density of spherical silver powder A > 2.0 g / cm 3 , the average particle size D50 of spherical silver powder B is 0.5 - 5 μm, and the tapped density of spherical silver powder B > 4.0 g / cm 3 ; Polyvinylpyrrolidone is purchased from Ashland Group, USA, with the model K30; Nano polytetrafluoroethylene is 3M TF9027Z, and the primary particle size is 120 nm.

[0062] The front electrode pastes for silicon solar cells prepared in Examples 1-6 and Comparative Examples 1-3 were printed on the front surface of n-type TOPCon cell wafers using a 16-μm line-width screen plate for testing. The aspect ratio of the grid lines and the appearance of the grid lines were measured using a 3D microscope, and the electrical properties were tested using an IV tester. The number of broken grids was counted after detection using an electroluminescence detector. The specific results are shown in Table 3.

[0063] Table 3 Test results of the front electrode pastes for silicon solar cells

[0064]

[0065] As can be seen from the test results in Table 3, after adding nano-polytetrafluoroethylene micro-powder, the number of broken grids printed by the electrode paste of the present invention has decreased significantly, indicating that nano-polytetrafluoroethylene micro-powder can improve the printability of the electrode paste. When polyvinylpyrrolidone and Tween 80 are added synergistically, while the aspect ratio of the grid lines printed by the electrode paste can be synergistically increased, the bulk resistance of the grid lines also decreases to a certain extent. When only one of them is added alone, the effect is not as good as when both are added simultaneously. The main function of polyvinylpyrrolidone is to reduce the line width and increase the aspect ratio of the grid lines, while Tween 80 can improve the overall printing performance of the paste and reduce the broken grids. Compared with other surfactants, the effects of Tween 60 and Span 60 are not as good as that of Tween 80.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A front electrode paste for a silicon solar cell, characterized in that, The raw materials for preparing the front electrode paste of the silicon solar cell include components with the following mass percentages: 80-90% of conductive silver powder, 6-10% of organic carrier, 4-6% of glass powder, 3% of aluminum powder, and 0-2% of other additives; The raw materials for preparing the organic carrier include components with the following mass percentages: 60-90% of organic solvent, 5-10% of organic resin, 1-5% of thixotropic agent, 1-5% of surfactant A, 1-5% of surfactant B, and 1-5% of nano polytetrafluoroethylene; Surfactant A is polyvinylpyrrolidone; Surfactant B includes at least one of Tween 85, Tween 80, and Tween 60; The conductive silver powder is spherical silver powder, and the spherical silver powder includes spherical silver powder A with an average particle size D50 of 0.1-1 μm and spherical silver powder B with an average particle size D50 of 0.5-5 μm; The tapped density of the spherical silver powder A > 2.0 g / cm 3 , and the tapped density of the spherical silver powder B > 4.0 g / cm 3 ; Among the spherical silver powders of the conductive silver powder, the mass percentage of spherical silver powder A is 50-80%, and the mass percentage of spherical silver powder B is 20-50%.

2. The front electrode paste for silicon solar cells according to claim 1, characterized in that, The raw materials for preparing the organic carrier include components with the following mass percentages: 81% of organic solvent, 9% of organic resin, 3% of surfactant A, 2% of surfactant B, 2% of thixotropic agent, and 3% of nano polytetrafluoroethylene.

3. The front electrode paste for a silicon solar cell according to claim 1, characterized in that, The preparation method of the organic carrier includes the following steps: First, dissolve the organic resin in the organic solvent to obtain a resin solution; Then add surfactant A, surfactant B, thixotropic agent, and nano polytetrafluoroethylene to the resin solution, and carry out activation under stirring to finally obtain the organic carrier.

4. The front electrode paste for silicon solar cells according to claim 3, characterized in that, In the preparation method of the organic carrier, the dissolution temperature of the organic resin is 70-100 °C, the activation temperature is 50-70 °C, and the activation time is 30-60 min.

5. The front electrode paste for a silicon solar cell according to claim 1, characterized in that The other additive is a dispersant, and the dispersant is BYK110; The organic solvent in the organic carrier includes at least one of lauryl alcohol ester, butyl carbitol, butyl carbitol acetate, terpineol, tributyl acetylcitrate, diethylene glycol monoethyl ether acetate, dipropylene glycol methyl ether acetate, dimethyl adipate, diethylene glycol monomethyl ether, diethylene glycol dibutyl ether, tripropylene glycol butyl ether, dimethyl adipate, and diethyl adipate.

6. The front electrode paste for silicon solar cells according to claim 1, wherein The organic resin in the organic carrier includes at least one of ethyl cellulose, acrylic resin, and polyvinyl butyral resin; The thixotropic agent in the organic carrier includes at least one of modified polyamide wax and hydrogenated castor oil.

7. The preparation method of the front electrode paste for the silicon solar cell according to any one of claims 1 to 6, characterized in that It includes the following steps: First, mix the raw materials, then carry out pre-dispersion until the powder is completely wetted by the organic carrier and uniformly dispersed, and then carry out grinding until the fineness of the paste is less than 10 microns, and finally prepare the front electrode paste of the silicon solar cell.

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