Front fine grid slurry for printing narrow-linewidth steel plate and preparation method of front fine grid slurry

Abstract

The invention discloses front fine grid slurry for printing a narrow-linewidth steel plate and a preparation method of the front fine grid slurry, and belongs to the technical field of solar cells, and the front fine grid slurry comprises the following components in percentage by mass: 5.65-10.4% of an organic carrier; the organic carrier comprises 0.35%-0.9% of resin, 4.2%-8% of a solvent, 0.6%-1% of silicone oil and 0.5%-1.1% of an auxiliary agent; 85%-94% of silver powder; the resin is compounded by SEPS resin and CAB resin according to a certain proportion; the silver powder is formed by compounding high sintering activity silver powder A and smooth surface silver powder B, the D50 of the silver powder A is 1.30 [mu] m, the specific surface area of the silver powder A is 0.92 m / g, the D50 of the silver powder B is 1.60 [mu] m, the specific surface area of the silver powder B is 0.60 m / g, and the mass ratio of the silver powder A to the silver powder B is (2-4): 1; and 1%-3% of glass powder. According to the invention, the ink permeability, the shaping capability and the printing stability of the paste are improved by optimizing the components of the organic carrier, the proportion of the silver powder and an auxiliary agent system, and the aspect ratio of fine grid lines and the optimization of the battery efficiency are realized.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, specifically relating to a front-side fine grid paste for narrow linewidth steel plate printing and its preparation method, which is particularly suitable for high-precision printing scenarios with linewidth ≤15μm. Background Technology

[0002] In existing technologies, TOPCon cells have become the mainstream direction for high-efficiency crystalline silicon cells due to their high open-circuit voltage (Voc) and low recombination loss. These cells place extremely stringent requirements on the printing of the front electrode: extremely fine (<25μm), high-precision grid lines are needed to reduce light shading loss and increase current density, while also requiring good aspect ratio and flatness of the grid lines to improve the fill factor.

[0003] Currently, the screen printing apertures used for the front electrode of TOPCon have been continuously narrowed to within 10μm, posing a significant challenge to the printing of the paste. However, problems such as poor line flatness and difficulty in improving the aspect ratio still exist. Steel plate printing technology, due to its low printing pressure, precise aperture size, and absence of a mesh at the aperture, can achieve fine line printing with a large aspect ratio and high flatness (printing width <15μm), and is expected to reduce wet weight by 20% and improve efficiency by more than 0.05%, making it a highly promising direction for efficiency improvement. However, steel plates have lower tension and deformation capacity compared to screen printing, and the printing pressure is also lower. Existing organic systems adapted for screen printing often perform poorly on steel plates, exhibiting problems such as poor ink penetration, ink splatter, and insufficient shaping ability. Therefore, it is necessary to develop pastes adapted to steel plate printing technology. Summary of the Invention

[0004] The purpose of this invention is to provide a front-side fine grid paste for narrow linewidth steel plate printing and its preparation method, so as to overcome the above-mentioned technical problems. By optimizing the organic carrier composition, silver powder ratio and auxiliary agent system, the ink permeability, plasticity and printing stability of the paste are improved, thereby achieving high aspect ratio of fine grid lines and optimized battery efficiency.

[0005] The present invention solves the above-mentioned technical problems through the following technical solution: A fine grid paste for front-side printing on narrow linewidth steel plates is provided, comprising the following components by mass percentage: The organic carrier comprises 5.65%–10.4%; the organic carrier includes 0.35%–0.9% resin, 4.2%–8% solvent, 0.6%–1% silicone oil, and 0.5%–1.1% additives. The silver powder comprises 85%–94% silver powder; the silver powder is a compound of sintered active silver powder A and smooth surface silver powder B, wherein the D50 of silver powder A is 1.30 μm and the specific surface area is 0.92 m² / g, the D50 of silver powder B is 1.60 μm and the specific surface area is 0.60 m² / g, and the mass ratio of silver powder A to silver powder B is 2–4:1. The glass powder is the same as that used for the fine grid on the front side of TOPCon, with a particle size of 1.3-1.7μm and a proportion of 1% to 3%.

[0006] Further, the resin comprises the following components: styrene-ethylene-propylene-styrene block copolymer (SEPS) resin and cellulose acetate butyrate (CAB) resin; by mass percentage of the slurry, the styrene-ethylene-propylene-styrene block copolymer resin is 0.3% to 0.6%, the cellulose acetate butyrate resin is 0.1% to 0.3%, and the mass ratio of the styrene-ethylene-propylene-styrene block copolymer resin to the cellulose acetate butyrate resin is 5:1 to 12:1.

[0007] Further, the solvent includes diethylene glycol butyl ether acetate, dodecyl alcohol ester, diethylene glycol dibutyl ether, benzyl benzoate, and ethylene glycol butyl ether benzoate, in the following percentages by slurry mass: diethylene glycol butyl ether acetate: 1.4%–2%; dodecyl alcohol ester: 0.6%–1.4%; diethylene glycol dibutyl ether: 0.6%–1.4%; benzyl benzoate: 1.2%–2%; ethylene glycol butyl ether benzoate: 0.4%–1.2%.

[0008] Furthermore, the silicone oil is one or more of polydimethylsiloxanes selected from 50cst, 100cst, and 350cst.

[0009] Furthermore, the additives include a dispersant and a thixotropic agent, wherein the dispersant is lauryl alcohol polyoxyethylene ether, accounting for 0.1% to 0.3% of the slurry mass; and the thixotropic agent is activated polyamide wax, accounting for 0.3% to 0.9% of the slurry mass.

[0010] Furthermore, the optimal mass ratio of silver powder A to silver powder B is 3:1.

[0011] This invention also provides a method for preparing a front-side fine grid paste suitable for narrow linewidth steel plate printing, characterized by comprising the following steps: (1) The resin and solvent are mixed in proportion, heated in a water bath at 50-70°C and dispersed at high speed for 2 hours to obtain an organic carrier; (2) Then, silver powder, glass powder and organic carrier are mixed in proportion, premixed by mixing a mixer at a speed of 500-800 rpm for 30 minutes, and then repeatedly ground by a three-roll mill 3-5 times until the particle size distribution is uniform.

[0012] The three-roll mill has a roller spacing of 0.01 to 0.05 mm and a vacuum filtration pore size of ≤2 μm.

[0013] This invention optimizes the printability of printing paste by adjusting the resin ratio. The SEPS resin is a non-polar triblock polymer with good flexibility and strong thixotropy, which imparts good ink permeability and thixotropy to the paste, making it suitable for low-pressure printing. The cellulose acetate butyrate resin is a flexible, low-molecular-weight polar resin that acts as a binder and support for the organic and metallic phases, providing cohesion and plasticity to the paste, reducing ink splatter during printing, and improving long-term printing stability. This invention combines SEPS resin and low-molecular-weight cellulose acetate butyrate, not only leveraging their respective properties to adapt the paste to stencil printing, but also allowing for adjustable paste flowability and viscosity to match different screen parameters.

[0014] This invention has demonstrated through numerous experiments that the optimal addition ratio of SEPS resin as the main resin is 0.3% to 0.6%, and the optimal addition ratio of cellulose acetate butyrate as the auxiliary resin is 0.1% to 0.3%. If the proportion of SEPS resin is too low, the ink will be difficult to penetrate during stencil printing, and the printing grid will easily break. If the proportion of cellulose acetate butyrate is too low, the ink will easily splatter during stencil printing, resulting in poor plasticity.

[0015] This invention achieves a balance between ink penetration and plasticity of the printing paste by optimizing the viscosity and ratio of silicone oil. During printing, due to its low surface energy, the silicone oil precipitates onto the surface of the paste, aiding in demolding and thus improving undesirable effects such as incomplete printing, as well as the line shape and aspect ratio of the printed grid lines.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention provides a paste that is well adapted to steel plate printing and can obtain better grid line profiles. Experiments show that the paste can achieve fine grid lines with a line width of 13μm and a height of 7.7μm, while ensuring printing stability and achieving a good aspect ratio. This invention provides a solution for electrode materials of high-efficiency crystalline silicon cells that combines performance and cost advantages. This invention, by designing an organic carrier with high ink permeability and thixotropy, and using hollow silver powder with a high specific surface area, gives the paste excellent adaptability to steel plate printing.

[0017] (2) This invention uses a blend of non-polar elastomer resin and low molecular weight polar resin to give the paste high thixotropy, good ink penetration and shaping ability; at the same time, by optimizing the ratio of the two resins, the printability and grid line aspect ratio of the paste are improved.

[0018] (3) By adjusting the grade and amount of the release agent, the present invention takes into account both the release ability and the shaping ability of the slurry, and achieves the optimization of the grid line shape.

[0019] (4) This invention achieves the effect of optimizing grid line shaping ability by adjusting the specific surface area and proportion of silver powder and adjusting the viscosity and thixotropy of the slurry; in addition, the optimization of the sintering activity of silver powder can achieve a balanced performance of contact and opening pressure, thereby increasing the cell efficiency by 0.08% compared with the unoptimized version. Detailed Implementation

[0020] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0021] Slurry preparation: The resin, solvent, silicone oil, and additives were weighed according to the formula ratio, and dispersed in a water bath at 60°C and 1000 rpm for 2 hours to obtain an organic carrier. The silver powder, glass powder and organic carrier are weighed and mixed according to the formula ratio. They are premixed by a mixing mixer at a speed of 600 rpm for 30 minutes. Then, they are repeatedly ground by a three-roll mill three times until the particle size distribution is uniform. The silver powder A used has a D50 of 1.30 μm and a specific surface area of ​​0.92 m² / g, while the silver powder B has a D50 of 1.60 μm and a specific surface area of ​​0.60 m² / g. The three-roll mill used has a roller gap of 0.03 mm and a vacuum filtration aperture of 2 μm.

[0022] Viscosity testing: A 15g sample of slurry was taken, and the average viscosity of the slurry was determined using a Brookfield DV2 viscometer and a rotor SC-14 at 25℃ and 50 rpm / min.

[0023] Printing experiment: The conductive paste used in the examples and comparative examples was printed onto the front side of the solar cell. The printability testing screen used was a fully open steel screen: 10μm linewidth opening, total thickness 25μm, and thickness at the opening 14μm. The weight of the solar cell before and after printing was measured to obtain the wet weight of the front-side grid.

[0024] Electrical performance testing: The printed solar cells are dried in a belt sintering furnace and sintered at 800°C. The cell efficiency is tested using a HALMIV tester, and the poor printing and broken grids of the positive fine grid lines are detected using an electroluminescence (EL) device.

[0025] Linearity test: The surface morphology of the grid lines was photographed using a Keyence 3D laser microscope, and the average height and width of the grid lines were measured to obtain the aspect ratio of the grid lines. Example

[0026] Conductive pastes S1-S3 were obtained according to the formulation in Table 1 and the preparation method described above. Their viscosity, printability, and aspect ratio were measured, and the results are shown in the table below.

[0027] Table 1 shows that the viscosity of the slurry gradually increases with the increase of CAB resin content. Conversely, the wet weight of the slurry gradually increases with the increase of SEPS content from 50% to 100%. Unlike screen printing, which relies on normal force to expel the slurry through the screen, stencil printing uses lower printing pressure, requiring the slurry to have stronger flowability after shearing to fill the openings in the stencil, as well as better release properties to achieve ink penetration. CAB resin molecules contain numerous hydrogen bonds, which can form an intermolecular hydrogen bond network with hydrogen-bonded solvents and thixotropic agents, enhancing the system's cohesion. SEPS is a non-polar elastomer structure; its weak polarity results in low slurry cohesion, while its elastomer structure makes the slurry more flexible and enhances its thixotropy. Therefore, increasing the SEPS resin content can improve ink penetration, reduce printed grid breaks, and increase wet weight. Slurries with high CAB content have excessively strong cohesion and poor ink penetration. Furthermore, due to the high surface energy of CAB resin, printing it onto solar cells can cause grid line widening, resulting in a low aspect ratio of the slurry. However, the low viscosity and surface energy of pure SEPS resin paste lead to widened printing lines, rough edges, and ink splatter. A paste with optimal aspect ratio and moderate viscosity is obtained when the ratio of SEPS resin to CAB resin is 5:1.

[0028] Table 1. Formulations and test data for S1-S3

[0029] Example 2:

[0030] Conductive pastes S4-S7 were obtained according to the formula in Table 2 and the preparation method described above. Their viscosity, printability and aspect ratio were measured, and the results are shown in the table below.

[0031] Table 2 shows that as the molecular weight of the silicone oil gradually increases, the viscosity of the paste increases, the wet weight of the printed lines decreases, and the linewidth of the grid lines narrows. This is because silicone oil, as a lubricating release agent, has better compatibility with organic systems at lower molecular weights, primarily acting as an internal lubricant, reducing internal friction between molecular chains and between the carrier and the silver powder, thus improving the fluidity of the paste. Silicone oils with higher molecular weights have poorer compatibility with organic carriers and tend to precipitate on the surface of the paste, acting as an external lubricant, which is beneficial for the release and shaping ability of the paste. However, stencil printing requires high fluidity of the paste during printing; excessively high molecular weight silicone oil will weaken the fluidity of the paste, causing severe grid breakage. Silicone oil with a viscosity of 100 cSt can achieve a balance between printability and shaping ability, obtaining the best aspect ratio.

[0032] With increasing silicone oil dosage, the viscosity and wet weight of the slurry increased slightly. However, with insufficient silicone oil, the slurry's release ability was insufficient, making it difficult to achieve high line heights and causing issues such as ink splatter. Increasing the silicone oil dosage to 0.9% resulted in the best aspect ratio performance without significantly increasing the wet weight. However, excessive silicone oil dosage could lead to excessive sintering residues of organic matter, affecting cell performance; therefore, the silicone oil dosage was not further increased.

[0033] Table 2 Formulations and Test Data for S4-S7

[0034] Example 3:

[0035] Conductive pastes S8-S10 were obtained according to the formula in Table 3 and the preparation method described above. Their viscosity, printability and aspect ratio were measured, and the results are shown in the table below.

[0036] Table 3 shows that the combination of the two silver powders significantly affects the printability and electrical performance of the paste. As the amount of high-specific-surface-area, high-activity silver powder A increases, the viscosity and shaping ability of the paste are further enhanced. The paste made with silver powder A alone has excessive viscosity, affecting its flowability and ink penetration, leading to dense grid breaks. While the smoother, larger-particle-size silver powder B has poor shaping ability, it improves the flowability of the paste. Using the two in a 3:1 ratio yields printed grid lines with an aspect ratio of 59.7%. Due to the high aspect ratio of the fine grid lines, the light-shielding area of ​​the solar cell is reduced, which is beneficial for optimizing the short-circuit circuit (Isc) and fill factor (FF). Simultaneously, the different sintering activities of the two silver powders affect the temperature window for glass etching and silver-silicon contact. The high-activity powder achieves a higher open-circuit voltage (Voc), while the low-activity powder achieves better silver-silicon contact. This also affects the efficiency performance of the solar cell. Taking both factors into account, a 3:1 ratio of silver powder A to B can balance printability and efficiency, resulting in a 0.08% improvement compared to the unoptimized version.

[0037] Table 3 Formulations and Test Data for S8-S10

[0038] Extensive experiments have shown that the conductive paste of the present invention, by weight, comprises: 0.3%–0.6% SEPS resin; 0.1%–0.3% CAB resin; 0.6%–0.9% silicone oil with a viscosity of 100 cst; 1.6%–2.4% diethylene glycol butyl ether acetate; 0.6%–1.4% dodecyl alcohol ester; 0.6%–1.4% diethylene glycol dibutyl ether; 0.4%–1.2% ethylene glycol butyl ether ester; 1.2%–2.0% benzyl benzoate; 0.3%–0.9% polyamide wax; 0.2% lauryl alcohol polyoxyethylene ether; 50%–80% high specific surface area, high activity silver powder A; 10%–40% low specific surface area, large particle size silver powder B; and 1%–3% glass powder.

[0039] The conductive paste of the present invention preferably comprises 0.5% SEPS resin, 0.1% CAB resin, 1.6%–2.4% diethylene glycol butyl ether acetate, 0.6%–1.4% dodecyl alcohol ester, 0.6%–1.4% diethylene glycol dibutyl ether, 0.4%–1.2% ethylene glycol butyl ether benzoate, 1.2%–2.0% benzyl benzoate, 0.3%–0.9% polyamide wax, 0.2% lauryl alcohol polyoxyethylene ether, 0.9% polydimethylsiloxane with a viscosity of 100, 67.5% high specific surface area and high activity silver powder A, 22.5% low specific surface area and large particle size silver powder B, and 1%–3% glass powder.

[0040] 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 the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred comparative examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

[0041] The proportions provided above are not intended to limit the scope of this invention, nor are the described steps intended to limit the order of their execution. Any obvious modifications made to this invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims of this invention.

Claims

1. A fine grid paste for front-side printing on narrow linewidth steel plates, characterized in that, The slurry comprises the following components by mass percentage: The organic carrier comprises 5.65%–10.4%; the organic carrier includes 0.35%–0.9% resin, 4.2%–8% solvent, 0.6%–1% silicone oil, and 0.5%–1.1% additives. The silver powder comprises 85%–94% silver powder; the silver powder is a compound of sintered active silver powder A and smooth surface silver powder B, wherein the D50 of silver powder A is 1.30 μm and the specific surface area is 0.92 m² / g, the D50 of silver powder B is 1.60 μm and the specific surface area is 0.60 m² / g, and the mass ratio of silver powder A to silver powder B is 2–4:

1. The glass powder is 1% to 3%; the glass powder has a particle size of 1.3-1.7 μm.

2. The slurry according to claim 1, characterized in that, The resin includes styrene-ethylene-propylene-styrene block copolymer resin and cellulose acetate butyrate resin. By mass percentage of the slurry, the styrene-ethylene-propylene-styrene block copolymer resin is 0.3% to 0.6%, the CAB resin is 0.1% to 0.3%, and the mass ratio of styrene-ethylene-propylene-styrene block copolymer resin to cellulose acetate butyrate resin is 5:1 to 12:

1.

3. The slurry according to claim 1, characterized in that, The solvents include diethylene glycol butyl ether acetate, dodecyl alcohol ester, diethylene glycol dibutyl ether, benzyl benzoate, and ethylene glycol butyl ether benzoate, in the following percentages by mass of the slurry: diethylene glycol butyl ether acetate 1.4%–2%; dodecyl alcohol ester 0.6%–1.4%; diethylene glycol dibutyl ether 0.6%–1.4%; benzyl benzoate 1.2%–2%; and ethylene glycol butyl ether benzoate 0.4%–1.2%.

4. The slurry according to claim 1, characterized in that, The silicone oil is one or more of polydimethylsiloxanes selected from 50cst, 100cst, and 350cst.

5. The slurry according to claim 1, characterized in that, The additives include a dispersant and a thixotropic agent. The dispersant is lauryl alcohol polyoxyethylene ether, accounting for 0.1% to 0.3% of the slurry mass; the thixotropic agent is activated polyamide wax, accounting for 0.3% to 0.9% of the slurry mass.

6. The slurry according to claim 1, characterized in that, The mass ratio of silver powder A to silver powder B is 3:

1.

7. A method for preparing the slurry according to any one of claims 1 to 6, characterized in that, Includes the following steps: (1) The organic carrier is prepared by adding resin, solvent, silicone oil and additives in a water bath and mixing them in proportion, heating at 50-70°C and dispersing at 1000 rpm for 2 hours. (2) Then, silver powder, glass powder and organic carrier are mixed in proportion, premixed by mixing a mixer at a speed of 500-800 rpm for 30 minutes, and then repeatedly ground by a three-roll mill 3-5 times until the particle size distribution is uniform.

8. The method for preparing the slurry according to claim 7, characterized in that, The three-roll mill has a roller gap of 0.01 to 0.05 mm and a vacuum filtration pore size of ≤2 μm.

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