A photovoltaic conductive paste

Abstract

The application discloses a kind of photovoltaic conductive paste, belongs to conductive paste technical field.The paste includes silver powder, metal silicide, nano silicon powder, glass powder, organic auxiliary agent and organic carrier, silver powder is compounded with sintered active silver powder and smooth surface silver powder, metal silicide is selected from two and above combinations in TiSi2 And NiSi2 And / or CoSi2, organic carrier contains rosin resin antioxidant component.The application is compounded by titanium and nickel / cobalt silicide, cooperates with the antioxidation protection of nano silicon powder and rosin resin, effectively reduces the contact resistance of paste and silicon wafer, inhibits interface carrier recombination, widens sintering process window.The obtained paste is suitable for screen printing, and after sintering, it is in good contact with silicon substrate, can significantly improve the photoelectric conversion efficiency of high-efficiency photovoltaic cells such as TOPCon, and the comprehensive performance is better than that of traditional conductive paste, suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of conductive pastes, and specifically relates to a photovoltaic conductive paste. Background Technology

[0002] Tunnel oxide passivating contact (TOPCon) cells and back contact (BC) cells are currently the mainstream technologies for photovoltaic cells. Improving the conversion efficiency of solar cells is a goal that the industry has been pursuing. Among them, photovoltaic conductive paste is one of the key materials affecting the conversion efficiency of solar cells. Conductive paste contains glass powder, conductive powder, and organic carrier. During the sintering process of conductive paste, the glass powder erodes the passivation layer, thereby allowing the conductive powder in the conductive paste to form contact with the silicon wafer under the passivation layer after sintering. The quality of the contact between the paste and the silicon wafer after sintering directly affects the conversion efficiency of the cell. How to achieve lower contact resistance while maintaining a low carrier recombination rate is a significant challenge for N-type TOPCon back-side sub-busbar conductive silver paste and BC cell silver paste, and is also the key to improving cell efficiency.

[0003] In the existing technology, the relevant disclosed solutions mainly have similar technical routes, but they all have obvious limitations: First, patent CN 116565059 A discloses a solar cell back electrode structure, which adopts a four-layer stacked structure of seed metal silicide layer + seed metal oxide thin layer + mixed conductive layer + outer metal layer in the local open film area of ​​passivation layer. The seed metal silicide is selected from one or more layers of molybdenum silicide, nickel silicide and titanium silicide. The silicide and oxide thin layer are formed in situ through two heat treatments to improve contact stability and reduce metal recombination loss. However, this scheme is a vacuum deposition / annealing thin film process route, which relies on complex processes such as seed layer sputtering, laser film opening, and high-temperature oxidation annealing, and is completely different from the conventional screen printing conductive paste system. Its core technology lies in the in-situ self-assembly to form an oxide insulating barrier layer and multilayer electrodes, rather than using silicide powder as a functional filler to optimize the silver paste formula. This is fundamentally different from the technical idea, implementation path, and application scenarios of this invention based on paste component control. Furthermore, this invention has also found that the improvement effect of molybdenum silicide in paste is not good.

[0004] Secondly, patent CN 120977642 A discloses a solar conductive silver paste, which adds nickel silicide and / or cobalt silicide powder to a silver powder, glass powder, and organic carrier system. This improves the silver-silicon contact quality and reduces the amount of silver powder used, preferably using a NiSi2 and CoSi2 composite to achieve lattice matching and interface optimization. However, this solution is limited to combinations of nickel-based and cobalt-based silicides and does not involve titanium silicide components. Furthermore, in the experiments of this invention, the effect of simply using a nickel silicide + cobalt silicide composite on improving photoelectric conversion efficiency (ETA) still needs improvement, making it difficult to meet the contact performance and higher performance requirements of high-efficiency batteries.

[0005] In summary, existing silicide-related metallization technologies either involve complex electrode structures due to thin-film deposition, which are incompatible with paste systems, or are limited to nickel / cobalt silicide composite silver pastes, offering limited performance improvements. Therefore, the industry urgently needs a conductive paste technology that is compatible with screen printing, has simpler formulation control, and superior contact performance. This technology, through a novel silicide composite system, can simultaneously reduce contact resistance and suppress interfacial recombination, further breaking through the metallization bottleneck of high-efficiency crystalline silicon solar cells. Summary of the Invention

[0006] Existing silicide electrode technology is complex and incompatible with paste systems. Using only a silver paste made from nickel silicide and cobalt silicide can only improve performance to a limited extent.

[0007] To address the aforementioned technical problems, this invention proposes a photovoltaic conductive paste and its preparation method. This conductive paste can effectively improve the silver-silicon contact quality to enhance the photoelectric conversion efficiency of solar cells.

[0008] The photovoltaic conductive paste provided by the present invention comprises silver powder, metal silicide, nano-silicon powder, glass powder, organic additives and organic carrier.

[0009] Furthermore, the photovoltaic conductive paste, by mass parts, is composed of 80-90 parts silver powder, 0.5-5 parts metal silicide, 0.05-0.5 parts nano silicon powder, 2.5-5 parts glass powder, 5-10 parts organic carrier, 0.1-0.5 parts dispersant and 0.2-0.5 parts silicone oil.

[0010] Furthermore, the photovoltaic conductive paste, by mass parts, is composed of 80-90 parts silver powder, 2-4 parts metal silicide, 0.1-0.3 parts nano silicon powder, 2.5-3 parts glass powder, 5-10 parts organic carrier, 0.1-0.5 parts dispersant and 0.2-0.5 parts silicone oil.

[0011] Furthermore, the silver powder has a D50 of 1~2μm and a specific surface area of ​​0.4~2m². 2 / g.

[0012] Furthermore, the silver powder is a blend of spherical silver powder A and spherical silver powder B; the D50 of silver powder A is 1.2~1.6μm, and the specific surface area is 0.5~1m². 2 / g, the D50 of silver powder B is 1.4~1.8μm, and the specific surface area is 0.4~0.8m². 2 / g, the mass ratio of silver powder A to silver powder B is 1~4:1.

[0013] Furthermore, the metal silicide is TiSi2, NiSi2, CoSi2, or any combination thereof.

[0014] Furthermore, the metal silicide is a combination of TiSi2 and NiSi2, or a combination of TiSi2 and CoSi2, or a combination of TiSi2, NiSi2 and CoSi2.

[0015] Furthermore, the metal silicide is a combination of TiSi2 and NiSi2 in a mass ratio of 1~1.5:1~1.5.

[0016] Furthermore, the metal silicide is a combination of TiSi2 and CoSi2 in a mass ratio of 1~1.5:1~1.5.

[0017] Furthermore, the metal silicide is TiSi2, NiSi2 and CoSi2, in a combination of TiSi2 and NiSi2 in a mass ratio of 1~1.5:1~1.5 and TiSi2 and CoSi2 in a mass ratio of 1~1.5:1~1.5.

[0018] Furthermore, the particle size of the metal silicide is 0.2-2 micrometers.

[0019] Furthermore, the particle size of the nano-silicon powder is 0.2-0.5 micrometers.

[0020] Furthermore, the glass powder comprises 30-50 mol% TeO2, 15-30 mol% PbO2, 5-15 mol% Bi2O3, 10-35 mol% Li2O, and 5-30 mol% of at least two oxides selected from SiO2, Na2O, K2O, SrO, CaO, ZnO, MoO3, WO3, and Cu2O.

[0021] Furthermore, the organic additives include dispersants and silicone oils.

[0022] Furthermore, the organic carrier includes organic solvents, organic resins, and additives.

[0023] Furthermore, the organic solvent includes one or more of diethylene glycol butyl ether acetate, dodecyl alcohol ester, hexadecyl alcohol ester, benzyl benzoate, and dimethyl phthalate.

[0024] Furthermore, the organic resin includes one or more of polyvinyl butyral (PVB), ethyl cellulose, cellulose acetate butyrate, epoxy resin, polyester resin, polyacrylic acid resin, rosin resin, and modified resins thereof, such as rosin glycerol ester resin, maleic rosin ester resin, and pentaerythritol hydrogenated rosin ester.

[0025] Furthermore, the additives include dispersants (e.g., TDO) and thixotropic agents (e.g., polyamide wax powder).

[0026] Specifically, the organic carrier is composed of a first organic carrier and a second organic carrier; the mass ratio of the two is 2~5:1.

[0027] Specifically, the first organic carrier is composed of 15-25 wt% organic solvent, 70-80 wt% thickening organic resin, and 3-8 wt% additives.

[0028] Specifically, the organic solvent includes one or more of diethylene glycol butyl ether acetate, dodecyl alcohol ester, hexadecyl alcohol ester, benzyl benzoate, and dimethyl phthalate.

[0029] Specifically, the tackifying organic resin includes polyvinyl butyral (PVB), ethyl cellulose, cellulose acetate butyrate, epoxy resin, polyester resin, polyacrylic acid resin, and any combination thereof.

[0030] Specifically, the additives include dispersants (e.g., TDO) and thixotropic agents (e.g., polyamide wax powder).

[0031] Specifically, the second organic carrier is composed of 40-60 wt% organic solvent and 40-60 wt% antioxidant resin.

[0032] Specifically, the organic solvent includes one or more of diethylene glycol butyl ether acetate, dodecyl alcohol ester, hexadecyl alcohol ester, benzyl benzoate, and dimethyl phthalate.

[0033] Specifically, the antioxidant resin includes rosin resin and its modified resins, such as rosin glycerol ester resin, maleic rosin ester resin, and pentaerythritol hydrogenated rosin ester.

[0034] The application of the photovoltaic conductive paste provided by this invention in solar cells.

[0035] Furthermore, the application includes printing the aforementioned photovoltaic conductive paste onto the back of a silicon wafer substrate to form a solar cell.

[0036] TiSi2 is a relatively stable silicide with low resistivity. At the silicon interface, it can form a good TiSi2 / Si contact with silicon, and its Schottky barrier height is relatively moderate compared to p-type and n-type silicon, enabling good ohmic contacts. NiSi2 and CoSi2 have minimal lattice mismatch with silicon, allowing for perfect epitaxial contacts with low interface defect density, achieving excellent Schottky barrier height tuning, especially for n-type silicon, where they can form low-resistance ohmic contacts. During sintering, these silicide particles aggregate at the interface between the silver electrode and the silicon substrate, providing a low-resistance path for current transport between silver and silicon, significantly reducing contact resistance. Furthermore, the excellent barrier tuning effect of metal silicides and the silicon substrate effectively reduces contact resistance and improves minority carrier lifetime through interface passivation, thus increasing battery conversion efficiency.

[0037] The combined application of TiSi2 and NiSi2 / CoSi2 further optimizes contact quality, reduces recombination, and improves open-circuit voltage and current. TiSi2 has stronger reduction reactivity to remove insulating oxide layers, which are either native oxide layers on the silicon surface or formed during the sintering process. TiSi2 opens conductive channels, and NiSi2 / CoSi2 forms an ideal lattice-matched contact interface on the silicon surface, fundamentally reducing the Schottky barrier resistance. At the same time, the defect density at the contact interface is low, and the open-circuit voltage is improved.

[0038] Furthermore, the present invention uses nano-silica as an inorganic antioxidant, which can protect metal silicides from oxidation or minimize oxidation during high-temperature sintering, thus broadening the process window.

[0039] Finally, this invention incorporates rosin resin as part of the organic carrier. The acidic groups of rosin resin can effectively bind to the powder surface, forming a coating film on the silver powder, silver-silicon alloy powder, and silicon powder in the slurry, isolating them from oxygen in the air and reducing oxidation during storage and processing. Furthermore, rosin resins decompose during the initial stage of high-temperature sintering, generating a reducing atmosphere that protects the inorganic powders from oxidation. Therefore, the introduction of rosin resin provides excellent protection for TiSi2, NiSi2, and CoSi2 powders, further preventing oxidation during sintering and allowing them to better improve contact quality. This results in increased open-circuit voltage and fill factor, thereby improving conversion efficiency.

[0040] This invention patent reduces the contact resistance between the slurry and silicon solar cells by adding a combination of titanium-based and nickel / cobalt-based silicides to the slurry, while maintaining a low interfacial recombination rate, thereby improving the cell conversion efficiency to over 26.85%. Simultaneously, nano-silicon powder is used as a high-temperature sintering antioxidant, combined with rosin resin in the organic carrier, to coat the metal silicides in the slurry, further protecting them from oxidation during storage and sintering. The combined application of these compounds broadens the application window of the slurry, achieving the goal of improved efficiency. Detailed Implementation

[0041] In the examples, silver powder A is spherical silver powder of type S700-4, purchased from Suzhou Yinrui Optoelectronic Materials Co., Ltd.; silver powder B is spherical silver powder of type 152-16, purchased from Shandong Jianbang Colloidal Materials Co., Ltd. Unless otherwise specified, all reagents and materials used in the following examples and comparative examples are commercially available.

[0042] Examples 1-13 A method for preparing a photovoltaic conductive paste includes the following steps: S1. The preparation of organic carriers is divided into the first organic carrier and the second organic carrier: First organic carrier: Weigh out 5% CAB381-2, 5% G1652, 6% PVB-16HH and 5% STD-4 by mass percentage as the resin component; weigh out 28% diethylene glycol butyl ether acetate, 10% dodecyl alcohol ester, 16% hexadecyl alcohol ester, 15% benzyl benzoate and 5% dimethyl phthalate as the organic solvent component; and weigh out 5% polyamide wax as the thixotropic agent. After mixing the resin, organic solvent and thixotropic agent, set the speed to 2000 rpm and stir and disperse at room temperature for 2 hours. Then raise the temperature to 80℃, stir at 2000 rpm for 2 hours to obtain the first organic carrier.

[0043] Second organic carrier: Weigh 25% alcohol ester dodecyl and 25% diethylene glycol butyl ether acetate as organic solvents, and 50% Foralyn 110 hydrogenated rosin ester resin by mass percentage. Mix the resin and organic solvent, set the speed to 2000 rpm, stir and disperse at room temperature for 2 hours, then raise the temperature to 80℃, stir at 2000 rpm for 2 hours to obtain the second organic carrier. S2. Preparation of silver powder: Silver powder A and silver powder B are mixed together.

[0044] S3. Preparation of glass powder: Weigh out 40% TeO2, 25% PbO, 7% Bi2O3, 3% SiO2, 5% WO3, and 5% ZnO using a molar percentage meter. Weigh out 5% Na₂CO₃ and 10% Li₂CO₃, mix them thoroughly, add them to an alumina crucible, place it in a muffle furnace, heat to 1000℃, and hold for 30 minutes. After 40 minutes, the molten glass is poured into deionized water, quenched, dried, and ball-milled to produce a D50 of less than 2μm and a Dmax of less than 7μm; the glass powder has a Tg of less than 350℃ and a melting point of no more than 800℃.

[0045] S4. Preparation of slurry: Silver powder, glass powder, organic carrier, nano-silicon powder, dispersant and silicone oil are mixed in proportion (see Table 1 below, calculated by mass parts, unit is parts), premixed by mixing with a mixer at a speed of 500 rpm for 30 minutes, and then repeatedly ground by a three-roll mill 3 times until the particle size distribution is uniform and the fineness is ≤5 microns.

[0046] Comparative Example 1 Weigh out 6.3 parts organic carrier I, 2 parts organic carrier II, 2.7 parts glass powder, 44.4 parts silver powder A, 44.0 parts silver powder B, 0.2 parts dispersant (TDO), and 0.4 parts dimethyl silicone oil (50CS) by mass percentage. Then mix the silver powder, glass powder, organic carrier, dispersant, and dimethyl silicone oil, premix them using a mixing mixer at 500 rpm for 30 minutes, and then repeatedly grind them three times using a three-roll mill until the particle size distribution is uniform and the fineness is ≤5 microns.

[0047] Comparative Example 2 The TiSi2 was replaced with an equal amount of MoSi2 according to the formulation of Example 7, and the slurry was prepared according to the preparation process of Example 1.

[0048] Table 1

[0049] Using screen printing technology, the above paste was printed onto the back of the silicon wafer substrate to form a solar cell. The solar cell used was a TOPCON solar cell with a size of 210*183. The solar cell was dried in a belt drying oven, and then sintered in a belt sintering furnace at 760~820℃, followed by laser sintering. After sintering, it was cooled to form a silicon crystal solar cell. The performance was then tested, and the test results are shown in Table 2 below.

[0050] Table 2

[0051] As can be seen from the test data in Table 2, the embodiments of the present invention are significantly better than comparative examples 1 and 2 in terms of key indicators such as conductivity, contact resistance, adhesion, sintering window and photoelectric conversion efficiency.

[0052] The comparison between Examples 1 and 2 mainly shows that the addition of nano-silicon powder plays an important role in preventing the oxidation of metal silicides during high-temperature sintering and improving performance. The comparison between Examples 5 and 6 and Example 1 highlights that the amount of nano-silicon powder added should not be too high; therefore, an addition atmosphere of 0.05~0.2% can achieve the maximum protective effect and performance improvement.

[0053] The comparison between Examples 3 and 4 and Examples 1, 2 and Comparative Example 1 mainly demonstrates the role of TiSi2 in this invention. It can improve ohmic contact, enhance battery conversion efficiency, and has a certain effect in the addition range of 0.5 to 5.

[0054] Examples 7 and 8 exhibit the best overall performance, with Eta reaching over 26.85. Compared with Examples 1, 9, and 10, these are the optimal implementation schemes of the present invention, demonstrating that the combination of TiSi2 and NiSi2 / CoSi2 can further improve contact quality, reduce contact recombination, and enhance battery conversion efficiency.

[0055] The comparison between Example 11 and Example 2 shows that the addition of rosin resin plays a certain role in enabling TiSi2 / NiSi2 to exert its effect and reducing the oxidation of TiSi2 / NiSi2 during the sintering process.

[0056] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A photovoltaic conductive paste, characterized in that, The photovoltaic conductive paste, by mass parts, consists of 80-90 parts silver powder, 0.5-5 parts metal silicide, 0.05-0.5 parts nano silicon powder, 2.5-5 parts glass powder, 5-10 parts organic carrier, 0.1-0.5 parts dispersant, and 0.2-0.5 parts silicone oil; The metal silicide is a combination of TiSi2 and CoSi2 in a mass ratio of 1~1.5:1~1.5, or the metal silicide is a combination of TiSi2 and NiSi2 in a mass ratio of 1~1.5:1~1.5, or the metal silicide is a combination of TiSi2, NiSi2 and CoSi2 in a mass ratio of 1~1.5:1~1.5 for TiSi2 and NiSi2 and a mass ratio of 1~1.5:1~1.5 for TiSi2 and CoSi2. The glass powder is 30-50 mol% of TeO2, 15-30 mol% of PbO2, 5-15 mol% of Bi2O3, 10-35 mol% of Li2O, and 5-30 mol% of at least two oxides selected from SiO2, Na2O, K2O, SrO, CaO, ZnO, MoO3, WO3 and Cu2O. The organic carrier is composed of a first organic carrier and a second organic carrier; the mass ratio of the two is 2~5:1; the first organic carrier is composed of 15~25wt% organic solvent, 70~80wt% thickening organic resin, and 3~8wt% additives; The second organic carrier is composed of 40-60 wt% organic solvent and 40-60 wt% antioxidant resin; the antioxidant resin includes rosin resin and its modified resins such as rosin glycerol ester resin, maleic rosin ester resin, and pentaerythritol hydrogenated rosin ester.

2. The photovoltaic conductive paste according to claim 1, characterized in that, The photovoltaic conductive paste, by mass, consists of 80-90 parts silver powder, 2-4 parts metal silicide, 0.1-0.3 parts nano silicon powder, 2.5-3 parts glass powder, 5-10 parts organic carrier, 0.1-0.5 parts dispersant, and 0.2-0.5 parts silicone oil.

3. The photovoltaic conductive paste according to claim 1, characterized in that, The particle size of the metal silicide is 0.2-2 micrometers.

4. The photovoltaic conductive paste according to claim 1, characterized in that, The nano-silicon powder has a particle size of 0.2-0.5 micrometers.

5. The application of the photovoltaic conductive paste according to any one of claims 1 to 4 in solar cells.

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