Nickel powder for photovoltaic silver paste

Abstract

This invention discloses a nickel powder for photovoltaic silver paste, belonging to the field of conductive pastes. The nickel powder comprises an organic-inorganic hybrid coating structure consisting of a spherical nickel powder core, an inner oxide passivation layer, and an outer organic functional layer. The passivation layer is made of yttrium oxide, aluminum oxide, etc., with a thickness of 5-100 nm. The organic layer is composed of coupling agents such as silane and oleic acid, with a thickness of 30-150 nm. During preparation, the nickel powder is pretreated, then the oxide layer is deposited and sintered, and finally the organic functional layer is grafted. This invention provides a double-layer coating to form a relay-style antioxidant protection. The organic layer matches the silver paste carrier, eliminating dynamic sieving during printing and avoiding false printing. The oxide layer provides high-temperature protection against nickel oxidation, creating a low-resistance conductive interface. This nickel powder can replace up to 30 wt% of silver powder. The resulting silver paste exhibits superior battery conversion efficiency compared to pure silver paste, excellent printing stability, low resistivity, and a simple preparation process, significantly reducing the production cost of photovoltaic silver paste and making it suitable for large-scale production of photovoltaic cells.

Description

Technical Field

[0001] This invention relates to the field of conductive pastes, and more particularly to a nickel powder for photovoltaic silver paste. Background Technology

[0002] In recent years, the photovoltaic industry has experienced rapid development. As a core material for metallization of solar cells, silver paste has seen a significant increase in the proportion of non-silicon costs due to the continuously rising price of silver. Cost reduction and efficiency improvement have become core development trends in the industry. Using inexpensive nickel powder to partially replace silver powder in the preparation of silver-nickel conductive paste is a mainstream technical approach to reduce the cost of photovoltaic pastes. However, nickel powder itself faces three major technical challenges: easy oxidation at high temperatures, dynamic sieving effects during printing caused by differences in particle size and density compared to silver powder, and poor compatibility with organic carriers leading to agglomeration. These challenges severely restrict the electrical performance and long-term printing stability of silver-nickel pastes. Although existing patented technologies have explored nickel powder modification and silver-nickel paste formulations, many unavoidable technical defects still exist.

[0003] Patent CN119993604A improves oxidation resistance by increasing the nickel powder particle size through controlling the specific surface area and particle size of nickel powder, thus achieving a small-scale substitution of silver powder. However, this technology has significant limitations: on the one hand, increasing the nickel powder particle size reduces the screen permeability, and the continuous accumulation of nickel powder during long-term printing can easily lead to problems such as incomplete printing and battery efficiency degradation; on the other hand, nickel powder has high reactivity, and the proportion of nickel powder added can only be limited to within 10wt%. Exceeding this proportion, the resistivity of the paste increases sharply, the photoelectric conversion efficiency decreases significantly, the silver powder substitution rate is low, and the cost reduction effect is limited.

[0004] Patent CN120636896A discloses a multi-element nickel alloy powder conductive paste, which improves the oxidation resistance of nickel powder through alloying modification with elements such as chromium, molybdenum, and yttrium, and can achieve a certain proportion of silver powder replacement. However, the shortcomings of this technology are: the doping ratio of nickel alloy powder is limited, and it can only replace silver powder at a low ratio. Further increasing the amount of nickel alloy added will cause a significant decrease in the photoelectric conversion efficiency of the battery. It cannot achieve both a high replacement rate and high photoelectric performance, making it difficult to meet the large-scale cost reduction needs of the photovoltaic industry.

[0005] Patent CN121339425B proposes a demagnetization + nitride coating modified nickel powder technology to solve the problems of magneto-induced agglomeration and oxidation of nickel powder, which can increase the nickel powder addition amount to 20%. However, it suffers from the drawback of an extremely complex preparation process, requiring multiple special steps such as AC demagnetization and chemical vapor deposition, with stringent requirements on equipment and process parameters, resulting in high industrial production costs and difficulty in mass production. At the same time, this invention found that at the conventional addition ratios of 10% and 20%, the improvement in the photoelectric conversion efficiency of the battery under this existing technology is limited, with insufficient room for performance optimization, and the photoelectric conversion efficiency generally decreases after the addition of the modified nickel powder.

[0006] In summary, existing technologies suffer from limitations in nickel powder addition, efficiency degradation with high addition levels, complex preparation processes, and insufficient performance improvement. None of these technologies can simultaneously achieve the four core requirements of high nickel powder substitution ratio, excellent high-temperature oxidation resistance, stable long-term printability, and high photoelectric conversion efficiency. Therefore, developing a modified nickel powder and its preparation method that is simple to process, can significantly increase the amount of nickel powder added, and simultaneously considers the rheological properties of the paste, printing stability, and battery electrical performance has become a pressing technical challenge in this field. Summary of the Invention

[0007] Technical issues The nickel powder used in existing photovoltaic silver-nickel paste has technical problems such as easy oxidation at high temperatures, easy to produce false printing during dynamic sieving, poor compatibility with organic carriers, low nickel powder substitution ratio and cell photoelectric efficiency degradation at high addition levels, and complex conventional modification processes with limited improvement in photoelectric performance at low doping levels.

[0008] Technical solution To address the aforementioned problems, this invention provides a modified nickel powder with an organic-inorganic hybrid coating layer for conductive pastes and its preparation method. This nickel powder, through a specifically designed organic-inorganic hybrid multilayer coating structure, exhibits differentiated functions at multiple process stages of the paste system, simultaneously possessing high-temperature oxidation resistance, high compatibility with silver paste organic carriers, and long-term stability against dynamic sieving in screen printing. While ensuring the electrical properties and long-term printability of the paste, the nickel metal addition ratio can be increased to 30 wt%.

[0009] To achieve the above-mentioned technical effects, the present invention provides a nickel powder for photovoltaic silver paste, wherein the nickel powder for photovoltaic silver paste is composed of spherical nickel powder and an organic-inorganic hybrid composite coating layer covering its surface; the organic-inorganic hybrid composite coating layer includes an inner oxide passivation layer and an outer organic functional layer.

[0010] Furthermore, the particle size range of the spherical nickel powder is 0.5-8.0 μm.

[0011] Furthermore, the spherical nickel powder can be elemental nickel or a nickel alloy.

[0012] Furthermore, the inner oxide passivation layer is composed of one or more of yttrium oxide, aluminum oxide, zirconium oxide, silicon oxide, and titanium oxide, with a coating thickness of 5-100 nm, which forms a dense physical barrier during the high-temperature sintering stage (760-850℃) to inhibit nickel core oxidation.

[0013] Specifically, the inner oxide passivation layer is composed of yttrium oxide, silicon oxide and titanium oxide, aluminum oxide, or zirconium oxide.

[0014] Specifically, when the inner oxide passivation layer is silicon oxide and titanium oxide, the molar ratio of SiO2 to TiO2 is 2~4:1.

[0015] Furthermore, the inner oxide passivation layer has a coating thickness of 20-50 nm.

[0016] Furthermore, the outer organic functional layer is composed of molecules containing two or more functional groups including hydroxyl, carboxyl, amino, epoxy and long-chain alkyl groups, specifically composed of one or more of silane coupling agents, oleic acid, titanate coupling agents and phosphate coupling agents, which are covalently grafted onto the surface of the inner oxide passivation layer.

[0017] Furthermore, the coating thickness of the outer organic functional layer is 30-150 nm.

[0018] Specifically, the outer organic functional layer is composed of a silane coupling agent and oleic acid, or a long-chain silane coupling agent, or a titanate coupling agent and oleic acid, or a phosphate coupling agent.

[0019] Specifically, the silane coupling agents are KH-550 and / or KH-560.

[0020] Specifically, the long-chain silane coupling agent is dodecyltrimethoxysilane.

[0021] Specifically, the titanate coupling agent is GR-101 titanate coupling agent, named isopropyl dioleoyloxy (dioctyl phosphate oxy) titanate.

[0022] Specifically, the phosphate coupling agent is AC-IAM phosphate coupling agent, named phosphate bistitanium ester coupling agent, with the molecular formula C. 27 H 62 O 13 Ti2.

[0023] Furthermore, the inner oxide passivation layer and the outer organic functional layer are connected by covalent chemical bonds to form a hybrid interface; the covalent bond between the inner oxide passivation layer and the outer organic functional layer is selected from at least one of Si-OM bond, Ti-OM bond, and POM bond, where M represents the metal element of the inner oxide layer.

[0024] Specifically, when the inner oxide passivation layer is yttrium oxide, the outer organic functional layer is composed of KH-550 and / or KH-560, and oleic acid.

[0025] Specifically, when the inner oxide passivation layer is silicon oxide and / or titanium oxide, the outer organic functional layer is composed of dodecyltrimethoxysilane.

[0026] Specifically, when the inner oxide passivation layer is zirconium oxide, the outer organic functional layer is composed of titanate coupling agent and oleic acid.

[0027] Specifically, when the inner oxide passivation layer is aluminum oxide, the outer organic functional layer is composed of a phosphate ester coupling agent.

[0028] Furthermore, when the outer organic functional layer is composed of KH-550 and oleic acid, the mass ratio of KH-550 to oleic acid is 1:1~2.

[0029] Furthermore, when the outer organic functional layer is composed of titanate coupling agent and oleic acid, the mass ratio of titanate coupling agent to oleic acid is 1~2:1.

[0030] The present invention also provides a method for preparing the above-mentioned nickel powder for photovoltaic silver paste, comprising the following steps: S1. Take nickel powder and heat treat it, then clean it, then soak it in an acid solution to remove the surface oxide layer and expose the active sites, then wash it with water until neutral and dry it. S2. Disperse the dried nickel powder in ethanol, then add the precursor solution to obtain mixed system 1, heat the reaction, and then filter to retain the solid. S3. The obtained solid is sintered at high temperature under a protective atmosphere to obtain nickel powder coated with an oxide passivation layer. S4. Take the nickel powder coated with oxide passivation layer and disperse it in ethanol, then add organic functional modification liquid to obtain mixed system 2. Heat the mixture to react, then filter to retain the solid and dry it to obtain nickel powder for photovoltaic silver paste.

[0031] Furthermore, in step S1, the heat treatment temperature is 200~300℃ and the time is 0.5~2 hours.

[0032] Furthermore, in step S1, the acid solution is a hydrochloric acid aqueous solution with a concentration of 0.1~1 M, and the soaking time is 5~20 minutes.

[0033] Furthermore, in step S2, the precursor in the precursor solution is one or more of yttrium isopropoxide, TEOS, tetrabutyl titanate, zirconium isopropoxide, and aluminum isopropoxide.

[0034] Specifically, in step S2, the precursor in the precursor solution is yttrium isopropoxide, or TEOS and tetrabutyl titanate, or zirconium isopropoxide, or aluminum isopropoxide.

[0035] Specifically, when the precursor in the precursor solution in step S2 is yttrium isopropoxide, zirconium isopropoxide, or aluminum isopropoxide, the pH of the solution is acidic, specifically 3 to 4.5.

[0036] Specifically, when the precursor in the precursor solution in step S2 is TEOS and tetrabutyl titanate, the pH of the solution is alkaline, specifically 8~10.

[0037] Furthermore, in step S2, the nickel powder concentration in the mixing system 1 is 150~250 g / L.

[0038] Furthermore, in step S2, the precursor concentration in the mixed system 1 is 5~15 g / L.

[0039] Furthermore, in step S2, the mass ratio of nickel powder to precursor in the mixed system 1 is 15~25:1.

[0040] Specifically, when the precursor in the precursor solution in step S2 is TEOS and tetrabutyl titanate, the mass ratio of TEOS to tetrabutyl titanate is 1~3:1.

[0041] Furthermore, in step S2, the heating temperature is 50~60℃ and the heating time is 2~5 hours.

[0042] Furthermore, in step S3, the protective gas is a chemically inert gas such as nitrogen or argon.

[0043] Furthermore, in step S3, the high-temperature sintering temperature is 450~600℃, and the time is 1~5 h.

[0044] Furthermore, the organic functional modification components of the organic functional modification liquid in step S4 include one or more of silane coupling agents, oleic acid, titanate coupling agents, and phosphate coupling agents.

[0045] Specifically, when the precursor is yttrium isopropoxide, the organic functional modification solution contains silane coupling agents (KH-550 and / or KH-560) and oleic acid.

[0046] Specifically, when the precursor is TEOS and tetrabutyl titanate, the organic functional modification solution contains dodecyltrimethoxysilane.

[0047] Specifically, when the precursor is zirconium isopropoxide, the organic functional modification solution contains titanate coupling agent and oleic acid.

[0048] Specifically, when the precursor is aluminum isopropoxide, the organic functional modification solution contains a phosphate coupling agent.

[0049] Specifically, when the organic functional modification solution contains silane coupling agents (KH-550 and / or KH-560), oleic acid, titanate coupling agents, and phosphate coupling agents, the pH of the organic functional modification solution is acidic, specifically 2 to 5.

[0050] Furthermore, in step S4, the concentration of nickel powder coated with oxide passivation layer in mixed system 2 is 200~300 g / L.

[0051] Furthermore, in step S4, the concentration of the organic functional modification component in the mixed system 2 is 5~20 g / L.

[0052] Furthermore, in step S4, the heating temperature for the heating reaction is 50~60℃, and the heating time is 2~5 hours.

[0053] Furthermore, in step S4, the drying process can be either air drying or heat drying.

[0054] The nickel powder for photovoltaic silver paste provided by this invention can be applied in the field of photovoltaic silver paste. Adding the nickel powder for photovoltaic silver paste to photovoltaic silver paste can replace the use of silver powder, and can replace up to 35 wt% of silver powder without causing a decrease in battery performance.

[0055] This invention provides a silver paste containing nickel powder for photovoltaic silver paste, wherein the silver paste contains ≤35wt% nickel powder for photovoltaic silver paste.

[0056] Specifically, in the aforementioned silver paste containing nickel powder for photovoltaic silver paste, the composition of the silver paste is 85-90 wt% conductive phase, 4.5-5 wt% organic carrier, 2.5-3 wt% glass powder, 0.1-0.3 wt% dispersant, and the balance being solvent.

[0057] Furthermore, the conductive phase is composed of silver powder and nickel powder for photovoltaic silver paste, wherein the proportion of nickel powder for photovoltaic silver paste is ≤35wt%.

[0058] Specifically, the proportion of nickel powder used in photovoltaic silver paste in the conductive phase is ≤30wt%.

[0059] Specifically, the conductive phase contains 95-70 wt% silver powder and 5-30 wt% nickel powder for photovoltaic silver paste.

[0060] Furthermore, the silver powder is spherical silver powder with a D50 of 1~1.5μm.

[0061] Furthermore, the organic carrier is composed of 40-60% resin and 40-60% solvent; the resin is composed of 25-50% ethyl cellulose, 20-40% polyvinyl butyral, 15-45% acrylic acid and 5-25% epoxy resin; the solvent is composed of 30-50% diethylene glycol butyl ether acetate, 15-40% butyl carbitol acetate, 10-30% dodecayl alcohol ester and 5-20% dimethyl phthalate.

[0062] Furthermore, the glass powder is composed of 30-50% PbO, 25-45% TeO2, 9-19% BiO3, 5-10% SiO2, 0.5-4% transition metals, and 0.1-0.4% Ag2O, 0.05-0.15% CuO and 0.05-0.25% ZnO; the transition metals include one or more of zinc powder, chromium powder and yttrium powder.

[0063] Furthermore, the dispersant is one or more of BYK-110, BYK-111, AD-374M, AKM-0531, ED120 and ED403.

[0064] Furthermore, the solvent is one or more selected from diethylene glycol butyl ether acetate, butyl carbitol acetate, dodecyl alcohol ester, and dimethyl phthalate.

[0065] The silver paste containing nickel powder for photovoltaic silver paste provided by the present invention can be used in the field of solar cells, including as a back paste coated on TOPCon cells.

[0066] Beneficial effects 1. Synergistic effect of high temperature anti-oxidation: The organic-inorganic double coating forms a "relay protection". The outer organic layer decomposes and consumes interfacial oxygen in the early stage of sintering, while the inner oxide passivation layer forms a dense physical barrier to block oxygen, which greatly reduces the weight gain of nickel powder due to high temperature oxidation and solves the problem of easy oxidation of nickel powder at high temperature.

[0067] 2. Good compatibility of the paste, eliminating the defects of dynamic screening in printing: The outer organic functional layer regulates the surface polarity of nickel powder, which is highly compatible with the organic carrier of silver paste. The thixotropic properties of the paste are close to those of pure silver paste. The nickel powder ratio fluctuates very little during continuous long-term printing, and there will be no false printing of grid lines. The long-term printing stability is excellent.

[0068] 3. Excellent conductivity and improved battery photoelectric efficiency: After sintering, a silver-oxide transition layer-nickel gradient conductive network is formed, with low interfacial contact resistance; nickel powder can replace up to 30wt% of silver powder, resulting in a higher battery conversion efficiency than pure silver paste, while maintaining excellent levels of open-circuit voltage, short-circuit current, and fill factor.

[0069] 4. Cost reduction and suitability for industrial mass production: The use of inexpensive nickel powder to replace high-priced silver powder in a large proportion significantly reduces the cost of photovoltaic silver paste raw materials; the entire preparation process is simple, requiring no complex special equipment, and has low production difficulty and manufacturing cost, making it suitable for large-scale industrial application of TOPCon photovoltaic cells. Attached Figure Description

[0070] Figure 1 A schematic diagram of the sandwich structure of organic-inorganic hybrid coated nickel powder.

[0071] Figure 2This is a SEM image of raw nickel powder.

[0072] Figure 3 SEM image of nickel powder coated on the inner layer of Y2O3.

[0073] Figure 4 SEM image of organic-inorganic hybrid coated nickel powder covalently grafted with Y2O3 inner layer + KH-550-oleic acid outer layer.

[0074] Figure 5 The electrode grid morphology of the battery cell in Example 1 and Comparative Example 1 is shown in the initial stage of printing and 24 hours after printing. Detailed Implementation

[0075] The silver powder used in the following examples and comparative examples is spherical silver powder with a particle size D50 of 1.3 μm.

[0076] The nickel powder used is elemental nickel, and the powder morphology is spherical with a particle size D50 of 1.5~4.2μm.

[0077] The organic carrier used consists of 50% resin and 50% solvent; the resin consists of 40% ethyl cellulose, 20% polyvinyl butyral, 15% acrylic acid and 25% epoxy resin; the solvent consists of 40% diethylene glycol butyl ether acetate, 40% butyl carbitol acetate, 15% dodecayl alcohol ester and 5% dimethyl phthalate.

[0078] The glass powder used consists of 50% PbO, 28% TeO2, 14% BiO3, 6% SiO2, 1.65% yttrium powder, 0.2% Ag2O, 0.05% CuO, and 0.1% ZnO.

[0079] The dispersant used was BYK-110.

[0080] The solvent used is diethylene glycol butyl ether acetate.

[0081] Unless otherwise specified above, all other raw materials are ordinary commercially available raw materials.

[0082] Example 1 Example 1 provides a TOPCon battery back slurry: The back-side slurry comprises: 90 wt% conductive phase; 4.7 wt% organic carrier; 2.8 wt% glass powder; 0.2 wt% dispersant; and the balance being solvent. The 90 wt% conductive phase includes 60 wt% silver powder and 30 wt% modified nickel powder. The modified nickel powder consists of a Y₂O₃ inner layer and a KH-550-oleic acid outer layer, with an oxide layer thickness of approximately 30 nm and an organic layer thickness of 80-100 nm.

[0083] The specific preparation steps of the modified nickel powder are as follows: Step 1: Nickel powder pretreatment and Y2O3 coating S11. Take 100 g of nickel powder, heat treat at 250℃ for 0.5 h, cool and place in anhydrous ethanol for ultrasonic cleaning for 15 min, filter, and repeat twice. S12. Immerse the cleaned nickel powder in 0.5 M dilute hydrochloric acid and stir for 10 min to remove the surface oxide layer and expose the active sites; S13. Wash with deionized water until neutral, and dry in a vacuum oven at 60℃ for 2 hours for later use; S14. Disperse the dried nickel powder in 500 mL of anhydrous ethanol and ultrasonically disperse for 30 min; S15. Dissolve 5 g of yttrium isopropoxide in a mixture of 20 mL of anhydrous ethanol and 2 mL of deionized water, and stir until homogeneous to obtain a yttrium isopropoxide solution. S16. Slowly add yttrium isopropoxide solution while stirring continuously, adjust the pH to 4.5 with dilute acetic acid, and heat to 70°C; S17. After stirring the reaction for 3 h, stop the reaction, allow it to cool naturally, filter it, and wash it 3 times with anhydrous ethanol. S18. Place the powder in a tube furnace, heat it to 500℃ at 5℃ / min under nitrogen protection, hold it at that temperature for 2 h, and then cool it naturally to obtain nickel powder with Y2O3 inner layer coating.

[0084] Step 2: Organic functional layer grafting S21. Take 50 g of nickel powder coated with the inner layer of Y2O3, redisperse it in 200 mL of anhydrous ethanol, and ultrasonically disperse it for 15 min; S22. Preparation of organic functional modification solution: Dissolve 1.5 g KH-550 and 2.4 g oleic acid in a mixture of 50 mL anhydrous ethanol and 2 mL deionized water, adjust the pH to 4.8 with dilute acetic acid, and stir for 30 min to hydrolyze. S23. Slowly add the organic functional modification solution dropwise into the nickel powder dispersion, heat to 55℃, and stir the reaction for 1.5 h; S24. After the reaction is complete, filter the solution and wash it three times with anhydrous ethanol and deionized water in sequence. S25. Dry in a vacuum oven at 60℃ for 2 hours, and pass through a 500-mesh sieve to obtain organic-inorganic hybrid coated nickel powder covalently grafted with Y2O3 inner layer + KH-550-oleic acid outer layer.

[0085] Example 2 Example 2 provides a TOPCon battery back slurry, which differs from Example 1 only in that: The modified nickel powder is replaced by an equal amount (30wt%) of nickel powder coated with an inner layer of SiO2-TiO2 composite oxide and an outer layer of long-chain silane. The inner oxide passivation layer of the modified nickel powder is prepared using TEOS and tetrabutyl titanate as dual precursors to form the SiO2-TiO2 composite oxide layer. The outer organic functional layer is grafted with a C12 long-chain silane coupling agent (dodecyltrimethoxysilane). The SiO2:TiO2 molar ratio is 3:1, the total oxide layer thickness is about 40 nm, and the organic layer thickness is 60-90 nm.

[0086] The specific preparation steps of the modified nickel powder are as follows: Step 1: Nickel powder pretreatment and SiO2-TiO2 coating S11. Take 100 g of nickel powder, heat treat at 250℃ for 0.5 h, cool and place in anhydrous ethanol for ultrasonic cleaning for 15 min, filter, and repeat twice. S12. Immerse the cleaned nickel powder in 0.5 M dilute hydrochloric acid and stir for 10 min to remove the surface oxide layer and expose the active sites; S13. Wash with deionized water until neutral, and dry in a vacuum oven at 60℃ for 2 hours for later use; S14. Disperse the dried nickel powder in 500 mL of anhydrous ethanol and ultrasonically disperse for 30 min; S15. Dissolve 3.3 g TEOS and 1.7 g tetrabutyl titanate in 20 mL of anhydrous ethanol and stir until homogeneous to obtain TEOS solution and tetrabutyl titanate solution respectively. S16. Slowly add TEOS solution and tetrabutyl titanate solution while stirring continuously, adjust the pH to 9.0 with dilute ammonia solution, and heat to 60℃; S17. After stirring the reaction for 3 h, stop the reaction, allow it to cool naturally, filter it, and wash it 3 times with anhydrous ethanol. S18. Place the powder in a tube furnace, heat it to 650℃ at 5℃ / min under nitrogen protection, hold it at that temperature for 2 h, and then cool it naturally to obtain SiO2-TiO2 inner layer coated nickel powder.

[0087] Step 2: Organic functional layer grafting S21. Take 50 g of nickel powder coated with the inner layer of SiO2-TiO2, redisperse it in 200 mL of anhydrous ethanol, and ultrasonically disperse it for 15 min; S22. Preparation of organic functional modification solution: Dissolve 1.5 g of dodecyltrimethoxysilane in 50 mL of anhydrous ethanol and stir for 30 min to dissolve; S23. Slowly add the organic functional modification solution dropwise into the nickel powder dispersion, heat to 55℃, and stir the reaction for 1.5 h; S24. After the reaction is complete, filter the solution and wash it three times with anhydrous ethanol and deionized water in sequence. S25. Dry in a vacuum oven at 60℃ for 2 hours, and pass through a 500-mesh sieve to obtain organic-inorganic hybrid coated nickel powder with an inner layer of SiO2-TiO2 composite oxide and an outer layer of long-chain silane covalently grafted.

[0088] Example 3 Example 3 provides a TOPCon battery back slurry, which differs from Example 1 only in that: The modified nickel powder is replaced by an equal amount (30wt%) of nickel powder coated with an inner layer of ZrO2 and an outer layer of oleic acid-titanium ester composite. The inner oxide passivation layer of the modified nickel powder is prepared by using zirconium isopropoxide precursor to form the ZrO2 layer, and the outer organic functional layer is prepared by using oleic acid and GR-101 titanate coupling agent (mass ratio 1:1). The thickness of the ZrO2 layer is about 30 nm, and the thickness of the organic layer is 80-110 nm.

[0089] The specific preparation steps of the modified nickel powder are as follows: Step 1: Nickel powder pretreatment and inner ZrO2 coating S11. Take 100 g of nickel powder, heat treat at 250℃ for 0.5 h, cool and place in anhydrous ethanol for ultrasonic cleaning for 15 min, filter, and repeat twice. S12. Immerse the cleaned nickel powder in 0.5 M dilute hydrochloric acid and stir for 10 min to remove the surface oxide layer and expose the active sites; S13. Wash with deionized water until neutral, and dry in a vacuum oven at 60℃ for 2 hours for later use; S14. Disperse the dried nickel powder in 500 mL of anhydrous ethanol and ultrasonically disperse for 30 min; S15. Dissolve 5 g of zirconium isopropoxide in a mixture of 20 mL of anhydrous ethanol and 0.5 mL of deionized water, adjust the pH to 3.0 with dilute acetic acid, and stir until homogeneous to obtain a zirconium isopropoxide solution. S16. Slowly add zirconium isopropoxide solution while stirring continuously, and heat to 50°C; S17. After stirring the reaction for 3 h, stop the reaction, allow it to cool naturally, filter it, and wash it 3 times with anhydrous ethanol. S18. Place the powder in a tube furnace, heat it to 500℃ at 5℃ / min under nitrogen protection, hold it at that temperature for 2 h, and then cool it naturally to obtain ZrO2 inner layer coated nickel powder.

[0090] Step 2: Grafting of the outer organic functional layer S21. Take 50 g of nickel powder with ZrO2 inner layer, redisperse it in 200 mL of anhydrous ethanol, and ultrasonically disperse it for 15 min; S22. Preparation of organic functional modification solution: Dissolve 1.2 g oleic acid and 1.2 g titanate coupling agent in a mixture of 50 mL anhydrous ethanol and 0.5 mL deionized water, adjust the pH to 3.0 with dilute acetic acid, and stir for 30 min to hydrolyze. S23. Slowly add the organic functional modification solution dropwise into the nickel powder dispersion, heat to 55℃, and stir the reaction for 1.5 h; S24. After the reaction is complete, filter the solution and wash it three times with anhydrous ethanol and deionized water in sequence. S25. Dry in a vacuum oven at 60℃ for 2 hours, and pass through a 500-mesh sieve to obtain organic-inorganic hybrid coated nickel powder with a ZrO2 inner layer and an oleic acid-titanium ester composite outer layer covalently grafted.

[0091] Example 4 Example 4 provides a TOPCon battery back slurry, which differs from Example 1 only in that: The modified nickel powder is replaced by an equal amount (30wt%) of nickel powder coated with an inner layer of Al2O3 and an outer layer of phosphate ester. The inner oxide passivation layer of the modified nickel powder is prepared by using aluminum isopropoxide precursor to form an Al2O3 layer, and the outer organic functional layer is grafted with AC-IAM phosphate ester coupling agent. The thickness of the Al2O3 layer is about 20nm, and the thickness of the organic layer is 35-70nm.

[0092] The specific preparation steps of the modified nickel powder are as follows: Step 1: Nickel powder pretreatment and Al2O3 coating S11. Take 100 g of nickel powder, heat treat at 250℃ for 0.5 h, cool and place in anhydrous ethanol for ultrasonic cleaning for 15 min, filter, and repeat twice. S12. Immerse the cleaned nickel powder in 0.5 M dilute hydrochloric acid and stir for 10 min to remove the surface oxide layer and expose the active sites; S13. Wash with deionized water until neutral, and dry in a vacuum oven at 60℃ for 2 hours for later use; S14. Disperse the dried nickel powder in 500 mL of anhydrous ethanol and ultrasonically disperse for 30 min; S15. Dissolve 5 g of aluminum isopropoxide in a mixture of 20 mL of anhydrous ethanol and 1.0 mL of deionized water, adjust the pH to 4.0 with dilute acetic acid, and stir until homogeneous to obtain an aluminum isopropoxide solution. S16. Slowly add aluminum isopropoxide solution and heat to 80°C; S17. After stirring the reaction for 3 h, stop the reaction, allow it to cool naturally, filter it, and wash it 3 times with anhydrous ethanol. S18. Place the powder in a tube furnace, heat it to 600℃ at 5℃ / min under nitrogen protection, hold it at that temperature for 3 h, and then cool it naturally to obtain Al2O3 coated nickel powder.

[0093] Step 2: Organic functional layer grafting S21. Take 50 g of Al2O3-coated nickel powder, redisperse it in 200 mL of anhydrous ethanol, and ultrasonically disperse it for 15 min; S22. Preparation of organic functional modification solution: Dissolve 1.0 g of phosphate coupling agent in a mixture of 50 mL of anhydrous ethanol and 2 mL of deionized water, and adjust the pH to 2.0 with dilute acetic acid; S23. Slowly add the organic functional modification solution dropwise into the nickel powder dispersion, heat to 55℃, and stir the reaction for 1.5 h; S24. After the reaction is complete, filter the solution and wash it three times with anhydrous ethanol and deionized water in sequence. S25. Dry in a vacuum oven at 60℃ for 2 hours, and pass through a 500-mesh sieve to obtain organic-inorganic hybrid coated nickel powder with an inner layer of Al2O3 and an outer layer of phosphate ester covalently grafted.

[0094] Example 5 Example 5 provides a TOPCon battery back slurry, which differs from Example 1 only in that: The 90wt% conductive phase was adjusted to include 70wt% silver powder and 20wt% modified nickel powder, wherein the modified nickel powder is nickel powder coated with Y2O3 inner layer + KH-550-oleic acid outer layer.

[0095] Example 6 Example 5 provides a TOPCon battery back slurry, which differs from Example 1 only in that: The 90wt% conductive phase was adjusted to include 80wt% silver powder and 10wt% modified nickel powder, wherein the modified nickel powder is nickel powder coated with Y2O3 inner layer + KH-550-oleic acid outer layer.

[0096] Comparative Example 1 Comparative Example 1 provides a TOPCon battery back slurry, which differs from Example 1 in that: The modified nickel powder was adjusted from a Y2O3 inner layer + KH-550-oleic acid outer layer coated nickel powder to an equal amount (30wt%) of Y2O3 inner layer coated nickel powder.

[0097] Comparative Example 2 Comparative Example 2 provides a TOPCon battery back slurry, which differs from Example 1 in that: The modified nickel powder was changed from Y2O3 inner layer + KH-550 outer layer coated nickel powder to an equal amount (30wt%) of KH-550-oleic acid outer layer coated nickel powder.

[0098] The specific preparation steps for the KH-550 outer layer coated with nickel powder are as follows: S1. Take 50 g of nickel powder, disperse it in 200 mL of anhydrous ethanol, and ultrasonically disperse it for 15 min; S2. Preparation of organic functional modification solution: Dissolve 1.5 g KH-550.2.4 g oleic acid in a mixture of 50 mL anhydrous ethanol and 2 mL deionized water, adjust the pH to 4.8 with dilute acetic acid, and stir for 30 min to hydrolyze; S3. Slowly add the hydrolysate dropwise into the nickel powder dispersion, heat to 55℃, and stir the reaction for 1.5 h; S4. After the reaction is complete, filter the solution and wash it three times with anhydrous ethanol and deionized water, respectively. S5. Dry in a vacuum oven at 60℃ for 2 hours, then pass through a 500-mesh sieve to obtain KH-550-oleic acid-coated nickel powder.

[0099] Comparative Example 3 Comparative Example 3 provides a TOPCon battery back slurry, which differs from Example 1 in that: The 90wt% conductive phase was adjusted to 90wt% silver powder.

[0100] Silicon solar cells were prepared using the conductive pastes provided in Examples 1-6 and Comparative Examples 1-3.

[0101] Using screen printing technology, the conductive pastes provided in Examples 1-6 and Comparative Examples 1-3 were printed onto silicon wafer substrates to form solar cells. The solar cells were dried in a belt drying oven and then sintered in a chain sintering furnace at 760-850°C. After sintering, they were cooled to form silicon crystal solar cells.

[0102] After screen printing and sintering, the cross-section of the metal grid lines in Examples 1-6 approximates a Gaussian distribution. The linewidth is controlled at approximately 25 μm, and the line height at approximately 4.6 μm.

[0103] The conversion efficiency, open-circuit voltage, short-circuit current, and fill factor of the silicon solar cells prepared in Examples 1-6 and Comparative Examples 1-3 were tested using an IV tester. The IV data were based on Comparative Example 3 (pure silver paste), and the differences in various indicators between each example and Comparative Example 3 were used to characterize the results. Here, ΔEff represents the difference in conversion efficiency, ΔUoc represents the difference in open-circuit voltage, ΔIsc represents the difference in short-circuit current, and ΔFF represents the difference in fill factor. The bulk resistivity and contact resistance were tested using a TLM contact resistance meter, where ρ represents the bulk resistivity and Rc represents the contact resistance value. The actual test results of the electrical performance of the silicon solar cell prepared in Comparative Example 3, including conversion efficiency, open-circuit voltage, short-circuit current, fill factor, bulk resistivity, and contact resistance, are shown in Table 1 below. Table 1. Electrical performance test results for Comparative Example 3

[0104] The electrical performance test results of Examples 1-6 and Comparative Examples 1-4 are shown in Table 2 below: Table 2. Electrical performance test results of Examples 1-6 and Comparative Examples 1-3

[0105] As can be seen from Table 2: Experimental data from Examples 1-4 and Comparative Example 3 show that the modified nickel powder with inorganic-organic hybrid coating exhibits significant improvements in both electrical properties and long-term printability. In Example 1, the double-layer organic coating and the Y2O3 inorganic barrier layer work synergistically to form a high-density barrier. During sintering, the outer organic layer undergoes uniform carbonization, forming a nano-carbon network in situ on the Y2O3 surface. The resulting carbon coating effectively protects the structural integrity of the Y2O3 layer. The Y2O3 layer segregates towards the nickel particle surface, forming a stable interface phase with the nickel matrix, significantly inhibiting oxygen diffusion into the nickel interior, and constructing a continuous low-resistance conductive path from the nickel core → Y2O3 → carbon network → silver phase. The amino groups introduced by KH-550 form chemical bonds with the carrier, and the van der Waals forces between the oleic acid hydrocarbon chains and the organic carrier are enhanced, giving the nickel powder surface an overall hydrophobic-organophilic characteristic. This enhances the bonding strength between the nickel powder and the organic carrier, making it less prone to separation of the nickel powder from the organic phase during repeated printing, thus effectively improving the long-term printability of the paste. The mechanism of action of the modified nickel powder in Examples 2-4 is similar to that in Example 1.

[0106] The experimental data from Example 1 and Comparative Example 1 show that the inner oxide passivation layer acts as an antioxidant barrier during the high-temperature sintering stage, effectively inhibiting nickel powder oxidation and ensuring the electrical properties of the paste. However, during long-term printing, issues such as incomplete printing have occurred. Figure 2 As shown, in Comparative Example 1, the proportion of nickel powder on the electrode grid line increased significantly after 24 hours of printing, while in Example 1, the proportion of nickel powder on the electrode grid line remained basically unchanged.

[0107] The experimental data from Example 1 and Comparative Example 2 show that the outer organic functional layer effectively resists the cumulative increase in nickel ratio caused by the dynamic sieving effect, ensuring long-term printing stability. However, the lack of protection from the inner passivation layer leads to severe nickel powder oxidation, and the volume resistivity increases by about 2.5 times compared to pure silver, which has a significant impact on electrical performance.

[0108] Using the baseline conversion efficiency of 26.746% for pure silver paste in Example 3 as a reference, the conversion efficiencies of all examples were higher than this baseline value. Specifically, Example 1 had a conversion efficiency of 26.926%, Example 2 26.846%, Example 3 26.896%, Example 4 26.786%, Example 5 26.966%, and Example 6 26.986%, all above 26.75%, which is superior to existing technologies. This confirms that the organic-inorganic hybrid coating structure of the present invention can stably maintain or even improve the photoelectric conversion efficiency of the battery while achieving a high proportion of silver powder substitution.

[0109] In summary, by rationally designing the inner passivation layer and the outer organic functional layer of modified nickel powder, the oxidation degree of modified nickel powder during the metallization sintering process can be reduced. At the same time, the rheological behavior of modified nickel powder can be made more consistent with that of silver powder, thereby improving the electrical properties and long-term printability of the conductive paste. This makes its electrical performance comparable to that of pure silver conductive paste, while significantly reducing the paste cost and improving economic efficiency.

[0110] 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 nickel powder for photovoltaic silver paste, characterized in that, The nickel powder for photovoltaic silver paste is composed of spherical nickel powder and an organic-inorganic hybrid composite coating layer covering its surface; the organic-inorganic hybrid composite coating layer includes an inner oxide passivation layer and an outer organic functional layer; The inner oxide passivation layer is composed of one or more of yttrium oxide, aluminum oxide, zirconium oxide, silicon oxide, and titanium oxide, with a coating thickness of 5-100 nm. The outer organic functional layer is composed of one or more of silane coupling agents, oleic acid, titanate coupling agents, and phosphate coupling agents, with a coating thickness of 30-150 nm.

2. The nickel powder for photovoltaic silver paste according to claim 1, characterized in that, The spherical nickel powder has a particle size range of 0.5-8.0 μm and is elemental nickel or a nickel alloy.

3. The nickel powder for photovoltaic silver paste according to claim 1, characterized in that, When the inner oxide passivation layer is yttrium oxide, the outer organic functional layer is composed of KH-550 and / or KH-560 and oleic acid.

4. The nickel powder for photovoltaic silver paste according to claim 1, characterized in that, When the inner oxide passivation layer is silicon oxide and / or titanium oxide, the outer organic functional layer is composed of dodecyltrimethoxysilane.

5. The nickel powder for photovoltaic silver paste according to claim 1, characterized in that, When the inner oxide passivation layer is zirconium oxide, the outer organic functional layer is composed of titanate coupling agent and oleic acid.

6. The nickel powder for photovoltaic silver paste according to claim 1, characterized in that, When the inner oxide passivation layer is aluminum oxide, the outer organic functional layer is composed of a phosphate ester coupling agent.

7. The method for preparing nickel powder for photovoltaic silver paste according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Take nickel powder, heat treat it, then clean it, then soak it in an acid solution, then wash it with water until neutral, and dry it. S2. Disperse the dried nickel powder in ethanol, then add the precursor solution to obtain mixed system 1, heat the reaction, and then filter to retain the solid. The precursor in the precursor solution is one or more of yttrium isopropoxide, TEOS, tetrabutyl titanate, zirconium isopropoxide, and aluminum isopropoxide; S3. The obtained solid is sintered at high temperature under a protective atmosphere to obtain nickel powder coated with an oxide passivation layer. S4. Take the nickel powder coated with oxide passivation layer and disperse it in ethanol, then add organic functional modification liquid to obtain mixed system 2, heat the reaction, filter to retain the solid, and dry to obtain nickel powder for photovoltaic silver paste; the organic functional modification components of the organic functional modification liquid include one or more of silane coupling agent, oleic acid, titanate coupling agent, and phosphate coupling agent.

8. The preparation method according to claim 7, characterized in that, In step S2, the concentration of nickel powder in the mixed system 1 is 150~250 g / L; the concentration of precursor is 5~15 g / L; and the mass ratio of nickel powder to precursor is 15~25:

1.

9. The preparation method according to claim 7, characterized in that, In step S4, the concentration of nickel powder coated with oxide passivation layer in mixed system 2 is 200~300 g / L; the concentration of organic functional modification component is 5~20 g / L.

10. A silver paste containing nickel powder for photovoltaic silver paste according to any one of claims 1 to 6, characterized in that, The silver paste is composed of 85-90 wt% conductive phase, 4.5-5 wt% organic carrier, 2.5-3 wt% glass powder, 0.1-0.3 wt% dispersant, and the balance being solvent; the conductive phase contains 95-70 wt% silver powder, and the photovoltaic silver paste according to any one of claims 1-6 contains 5-30 wt% nickel powder.

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