Modified nickel powder, preparation method thereof, conductive silver-nickel paste and topcon solar cell

Abstract

The application discloses a modified nickel powder and a preparation method thereof, a conductive silver-nickel paste, and a TOPCon solar cell. The preparation method of the modified nickel powder comprises the following steps: demagnetizing treatment on the nickel powder; and surface coating treatment on the demagnetized nickel powder to obtain the modified nickel powder. The raw material composition of the conductive silver-nickel paste comprises, in percentage by weight, 60-90 wt% of silver powder, 2-30 wt% of the modified nickel powder, 1.2-4.5 wt% of glass powder, 1-5 wt% of organic resin, 1-10 wt% of organic solvent, 0.1-0.5 wt% of silicone oil, and 0.1-1 wt% of an additive. The application solves the problems of oxidation and magnetic agglomeration of the traditional nickel powder, improves the dispersion stability of the paste, reduces the contact resistance and the paste cost, and guarantees the conductivity and the adhesion.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solar cells, in particular to a modified nickel powder, a preparation method thereof, a conductive silver-nickel paste and a TOPCon solar cell. BACKGROUND

[0002] The photovoltaic conductive paste is the core material in the metallization process of solar cells, and its performance directly determines the conductivity efficiency and reliability of the cells. At present, in order to reduce the high cost of silver raw materials, the use of silver-nickel composite paste (partially replacing silver powder with nickel powder) has become one of the mainstream technical directions for realizing low silver in the industry. However, this scheme still faces a series of key technical bottlenecks in practical application:

[0003] Firstly, the nickel powder itself has inherent defects. Nickel powder is prone to oxidation during sintering, which leads to a significant increase in electrode grid line resistance, affecting the conversion efficiency of the cell. At the same time, nickel powder has ferromagnetic properties, and magnetic agglomeration between particles is easy to occur, causing uneven dispersion in the paste system, and further causing problems such as printing grid interruption and poor long-term printing stability, which seriously affect the production yield and electrode morphology.

[0004] Secondly, the existing silver-nickel paste formulation system lacks synergy. The traditional silver paste formulation has not been optimized for the characteristics of the modified nickel powder, and the interfacial compatibility between the nickel powder and the silver powder, glass powder and other components is poor, making it difficult to reduce costs while considering high conductivity, high adhesion and long-term weathering reliability.

[0005] Therefore, how to effectively suppress the oxidation and magnetic agglomeration of nickel powder, and stably and efficiently integrate it into the photovoltaic conductive paste system, to achieve the unity of cost, performance and reliability, has become the key to promoting the large-scale application of low-silver paste. SUMMARY

[0006] Therefore, the purpose of the present application is to provide a modified nickel powder, a preparation method thereof, a conductive silver-nickel paste and a TOPCon solar cell, aiming to solve the problems of oxidation and magnetic agglomeration of traditional nickel powder, improve the dispersion stability of the paste, reduce the contact resistance and the cost of the paste, and at the same time ensure the conductivity and adhesion.

[0007] A preparation method of a modified nickel powder, comprising the following steps:

[0008] The nickel powder is subjected to demagnetization treatment, and the demagnetized nickel powder is subjected to surface coating treatment to obtain a modified nickel powder.

[0009] Further, the demagnetization treatment includes at least one of heat demagnetization treatment, alternating current demagnetization treatment, mechanical vibration demagnetization treatment and chemical modification assisted demagnetization treatment.

[0010] Further, the demagnetization process comprises an alternating current demagnetization process, and the alternating current demagnetization process comprises the following steps:

[0011] The nickel powder is provided and subjected to a drying pretreatment;

[0012] The dried nickel powder is loaded into a non-magnetic container and arranged in the effective working area of the demagnetization coil at a set loading thickness;

[0013] An alternating magnetic field with a decreasing amplitude to zero is applied to the demagnetization coil for a set time to demagnetize the nickel powder;

[0014] The residual magnetic intensity of the nickel powder after demagnetization is detected, and when the residual magnetic intensity meets the preset magnetic intensity, it is transferred to the next process within a limited time.

[0015] Further, the specific conditions of the drying pretreatment include a drying temperature of 120-150°C, a vacuum degree of ≥-0.09MPa, and a drying time of 2-3h.

[0016] Further, the initial strength of the alternating magnetic field is 32-38 mT, the frequency is 50-60 Hz, and the amplitude decays to zero at a rate of 4-6 mT / min.

[0017] Further, the surface coating treatment comprises at least one of inorganic coating treatment and organic coating treatment.

[0018] Further, the surface coating treatment comprises inorganic coating treatment, and the inorganic coating treatment comprises at least one of oxide, nitride, and carbide coated on the surface of the demagnetized nickel powder.

[0019] Further, the nitride comprises at least one of boron nitride, nickel nitride, titanium nitride, aluminum nitride, silicon nitride, and zirconium nitride.

[0020] Further, the boron nitride comprises at least one of hexagonal boron nitride, cubic boron nitride, and rhombohedral boron nitride.

[0021] Further, the nitride is coated on the surface of the demagnetized nickel powder by a deposition process.

[0022] Further, the deposition process comprises a chemical vapor deposition process, and the chemical vapor deposition process comprises the following steps:

[0023] The demagnetized nickel powder is placed in a reactor, and after excluding air, an inert gas is filled to establish an inert protective atmosphere;

[0024] A precursor of the target nitride is added to the reactor, and the precursor is uniformly contacted with the nickel powder;

[0025] Under the inert protective atmosphere, the reaction system is warmed to the reaction temperature, and nitrogen source gas is introduced into the reaction system, so that the precursor and the nitrogen source gas chemically react on the surface of the nickel powder to form a nitride coating layer.

[0026] After the reaction is completed, the reaction system is cooled under the inert protective atmosphere, and the coated nickel powder is taken out.

[0027] Further, the warming rate is 8-10℃ / min, the reaction temperature is 350-750℃, the nitrogen source gas includes ammonia and / or nitrogen, the flow rate of the nitrogen source gas is 10-30mL / min, and the pressure in the reactor is 0.1-0.5MPa.

[0028] Further, the deposition treatment includes a physical adhesion treatment, the demagnetized nickel powder is mixed with the nitride in a dispersion medium, and after the dispersion treatment, the nitride is adhered to the surface of the nickel powder.

[0029] The application further provides a modified nickel powder prepared by the preparation method.

[0030] Further, the modified nickel powder has a core-shell structure, including a nickel core and a coating layer coated on the surface of the nickel core, the thickness of the coating layer is 5-30nm, and the residual magnetism intensity of the modified nickel powder is ≤0.05mT.

[0031] The application further provides a conductive silver-nickel paste, and the raw material composition of the conductive silver-nickel paste includes, by weight percentage, 60-90wt% of silver powder, 2-30wt% of the modified nickel powder, 1.2-4.5wt% of glass powder, 1-5wt% of organic resin, 1-10wt% of organic solvent, 0.1-0.5wt% of silicone oil, and 0.1-1wt% of additives; and the modified nickel powder is the modified nickel powder described above.

[0032] The application further provides a TOPCon solar cell, which includes an electrode, and the electrode is obtained by sintering after the electrode is printed on the surface of a cell sheet by using the conductive silver-nickel paste described above.

[0033] The beneficial effects of the present application are: by demagnetizing the nickel powder, the particle agglomeration caused by magnetic attraction is reduced, and the dispersion uniformity and storage stability of the nickel powder in the silver paste system are significantly improved; by surface coating treatment, a dense and stable coating layer is coated on the surface of the nickel powder, which can not only isolate oxygen from contacting the surface of the nickel powder and effectively inhibit the occurrence of oxidation reaction, but also act as an interface buffer medium between silver powder and nickel powder, which can adjust the silver-nickel interfacial tension, reduce the phase separation and micro-pore generation in the sintering process, reduce the interfacial contact resistance, realize the performance synergy of silver-nickel components, and improve the electrode conductivity continuity and structural stability; and the dense coating layer can effectively isolate the erosion of harsh environment such as humidity and heat on the nickel powder, inhibit the secondary oxidation and grain growth of the nickel powder, ensure the stable performance attenuation of the electrode in the service cycle of the photovoltaic module, and meet the long-term reliability requirements of high-efficiency photovoltaic cells. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0035] Figure 1 The oxidation morphology of the nickel powder of different sizes of the present application at room temperature and after sintering.

[0036] Figure 2 The 3D morphology diagram of the grid line after printing the paste of Example 1 (left) and Comparative Example 3 (right) for 4h. DETAILED DESCRIPTION

[0037] The present application provides a preparation method of modified nickel powder, comprising the following steps:

[0038] S1, demagnetizing the nickel powder; S2, surface coating treatment is performed on the demagnetized nickel powder to obtain modified nickel powder.

[0039] In the present embodiment, by demagnetizing the nickel powder, the particle agglomeration caused by magnetic attraction is reduced, and the dispersion uniformity and storage stability of the nickel powder in the silver paste system are significantly improved; by surface coating treatment, a dense and stable coating layer is coated on the surface of the nickel powder, which can not only isolate oxygen from contacting the surface of the nickel powder and effectively inhibit the occurrence of oxidation reaction, but also act as an interface buffer medium between silver powder and nickel powder, so as to adjust the silver-nickel interfacial tension, reduce the phase separation and micro-pore generation in the sintering process, reduce the interfacial contact resistance, realize the performance synergy of silver-nickel components, and improve the electrode conductivity continuity and structural stability; and the dense coating layer can effectively isolate the erosion of harsh environment such as humidity and heat on the nickel powder, inhibit the secondary oxidation and grain growth of the nickel powder, ensure the stable performance attenuation of the electrode in the service cycle of the photovoltaic module (25 years), and meet the long-term reliability requirements of high-efficiency photovoltaic cells.

[0040] In the present embodiment, by demagnetizing the nickel powder, the particle agglomeration caused by magnetic attraction is reduced, and the dispersion uniformity and storage stability of the nickel powder in the silver paste system are significantly improved; by surface coating treatment, a dense and stable coating layer is coated on the surface of the nickel powder, which can not only isolate oxygen from contacting the surface of the nickel powder and effectively inhibit the occurrence of oxidation reaction, but also act as an interface buffer medium between silver powder and nickel powder, so as to adjust the silver-nickel interfacial tension, reduce the phase separation and micro-pore generation in the sintering process, reduce the interfacial contact resistance, realize the performance synergy of silver-nickel components, and improve the electrode conductivity continuity and structural stability; and the dense coating layer can effectively isolate the erosion of harsh environment such as humidity and heat on the nickel powder, inhibit the secondary oxidation and grain growth of the nickel powder, ensure the stable performance attenuation of the electrode in the service cycle of the photovoltaic module (25 years), and meet the long-term reliability requirements of high-efficiency photovoltaic cells. 2 / g, and the tap density is 4-6 g / ml. In particular, the D50 of the modified nickel powder is 4-5 µm, the specific surface area is 0.4-0.6 m 2 / g, and the tap density is 5-6 g / ml, and the surface morphology is relatively smooth. If the size of the modified nickel powder is too small, the powder not only has poor oxidation resistance, but also increases the bulk resistance of the silver paste, thereby affecting the final cell efficiency. If the surface morphology of the modified nickel powder is not smooth, it will affect the mesh transparency during printing of the paste, resulting in paste grid breakage and low photoelectric conversion efficiency. The oxygen contents of nickel powders of different sizes at room temperature and after sintering are shown in Table 1. The oxygen content of the nickel powder with a D50 of 1.8 µm increases sharply from 0.42% to 9.75% after sintering, while the oxygen contents of the nickel powders with D50 of 4 µm and 5 µm are both maintained below 0.6% after sintering, and the oxidation resistance is significantly better. The oxidation morphologies of nickel powders of different sizes at room temperature and after sintering are shown in Table 1. Figure 1

[0041] Table 1 Oxygen contents of nickel powders of different sizes at room temperature and after sintering

[0042]

[0043] ​Further, the demagnetization treatment includes at least one of a thermal demagnetization treatment, an alternating current demagnetization treatment, a mechanical vibration demagnetization treatment, and a chemical modification assisted demagnetization treatment. Preferably, the demagnetization method is the alternating current demagnetization. The core benefit of using the alternating current demagnetization for the nickel powder lies in three aspects: complete demagnetization effect, small damage to the powder structure, and suitability for industrial continuous processing. Compared with the chemical demagnetization, the core advantages of using the alternating current demagnetization for the nickel powder lie in three aspects: no chemical pollution, no change in the powder properties, and strong controllability of the process.

[0044] The specific steps of the alternating current demagnetization treatment include:

[0045] S11, raw material preparation step: providing the nickel powder and performing drying pretreatment thereon; that is, selecting a photovoltaic nickel powder (nickel content ≥ 99.5%) with a D50 of 2-6 μm, drying the same at a drying temperature of 120-150 °C and a vacuum degree of ≥-0.09 MPa for 2-3 h, and cooling to room temperature for standby;

[0046] S12, loading and arrangement step: loading the dried nickel powder into a non-magnetic container (polytetrafluoroethylene or ceramic sealed container), and arranging the same in the effective working area of the demagnetization coil with a set loading thickness (2-4 cm) and at a distance of ≤3 cm from the center of the adjustable alternating current demagnetization coil (coil inner diameter 30-50 cm, number of turns 500-800 turns);

[0047] S13, demagnetization treatment step: applying an alternating magnetic field with a decreasing amplitude to zero to the demagnetization coil, and maintaining the same for a set time (5-8 min) to demagnetize the nickel powder; wherein the initial magnetic field strength is set to 32-38 mT, the frequency is 50-60 Hz, the amplitude decreases to 0 mT at a uniform rate of 4-6 mT / min, and no external magnetic field interference is maintained throughout the process;

[0048] S14, quality verification and transfer step: detecting the residual magnetic intensity of the demagnetized nickel powder (using a gauss meter with a precision of 0.01 mT to detect three points on the nickel powder), and when the residual magnetic intensity meets the preset magnetic intensity (residual magnetism ≤ 0.05 mT), transferring the same to the next process within a limited time (≤30 min).

[0049] Further, the surface coating treatment includes at least one of inorganic coating treatment and organic coating treatment. The inorganic coating treatment obtains demagnetization-inorganic coating modified nickel powder, and the organic coating treatment obtains demagnetization-organic coating modified nickel powder.

[0050] The organic coating treatment includes at least one of fatty acid, nitrogen-containing heterocycle, high molecular polymer, and coupling agent coated on the surface of the demagnetized nickel powder. The preparation method of the organic coating modified nickel powder includes physical coating method (mechanical mixing method, melting coating method) and chemical coating method (in-situ polymerization coating method, coordination / integration coating method, sol-gel coating method).

[0051] Preferably, the surface coating treatment is an inorganic coating treatment. The inorganic coating treatment includes at least one of oxides, nitrides, and carbides coated on the surface of the demagnetized nickel powder. Preferably, the inorganic material in the inorganic coating treatment is a nitride. The nitride (such as BN, TiN, AlN, Si3N4) coated nickel powder has high hardness and excellent thermal / electrical conductivity, mechanical wear resistance, and impact resistance, which are superior to oxides; has strong bonding force with the nickel powder matrix, good uniformity of coating, and is not easy to peel off; has outstanding high-temperature resistance, strong chemical stability, and excellent oxidation resistance.

[0052] Further, the nitride includes at least one of boron nitride, nickel nitride, titanium nitride, aluminum nitride, silicon nitride, and zirconium nitride. Preferably, the nitride is one or more than two of boron nitride, aluminum nitride, and silicon nitride.

[0053] Further, the boron nitride includes at least one of hexagonal boron nitride, cubic boron nitride, and rhombohedral boron nitride. Preferably, the boron nitride is hexagonal boron nitride. Hexagonal boron nitride has a layered structure, has excellent layered coating ability, and itself is a diamagnetic material without magnetic enhancement effect, can limit nickel powder particles through the layered structure, weaken the magnetic interaction of the particles, has excellent demagnetization effect, and can form a tight coating layer with the nickel powder, and the preparation process is also more flexible.

[0054] Further, the nitride is coated on the surface of the demagnetized nickel powder through a deposition treatment.

[0055] Further, the deposition treatment includes a chemical vapor deposition treatment, and the chemical vapor deposition treatment includes the following steps:

[0056] S21, a reaction environment preparation step: placing the demagnetized nickel powder in a reactor (vacuum reaction kettle), filling inert gas (nitrogen) after excluding air (vacuuming to ≥-0.095 MPa) to establish an inert protective atmosphere; wherein, the purity of the nitrogen gas is ≥99.99%, and the nitrogen gas is replaced for 3 times (each time is kept at 0.1 MPa and is placed for 5 min), and the oxygen and moisture in the kettle are completely excluded;

[0057] S22, a precursor introduction and mixing step: adding a precursor of a target nitride (corresponding to a target coated nitride, such as isopropyl alcohol aluminum and tetraethyl orthosilicate) into the reactor, and making the precursor uniformly contact with the nickel powder;

[0058] S23, chemical vapor deposition reaction step: under the inert protective atmosphere, the reaction system is warmed to the reaction temperature, and nitrogen source gas is introduced into the reaction system, so that the precursor and the nitrogen source gas chemically react on the surface of the nickel powder (heat preservation reaction for 1.5-5h), to form a nitride coating layer; that is, the temperature is increased to 350-750℃ (the specific temperature is adjusted according to the selected nitride) at a temperature increase rate of 8-10℃ / min, high-purity nitrogen source gas (ammonia, nitrogen or a mixed gas thereof, purity ≥99.99%) is introduced, the gas flow rate is controlled to be 10-30mL / min, and the pressure in the kettle is controlled to be 0.1-0.5MPa;

[0059] S24, product post-treatment step: after the reaction is completed, the reaction system is cooled (cooled to below 100℃ at a rate of 5-8℃ / min) under an inert protective atmosphere (nitrogen is introduced), and the coated nickel powder is taken out.

[0060] Further, the deposition treatment includes a physical adhesion treatment, in which the demagnetized nickel powder and the nitride (such as h-BN nanosheet) are mixed in a dispersion medium, and the nitride is adhered to the surface of the nickel powder after dispersion treatment.

[0061] The application provides a modified nickel powder prepared by the preparation method.

[0062] Further, the modified nickel powder has a core-shell structure, including a nickel core and a coating layer coated on the surface of the nickel core, the thickness of the coating layer is 5-30nm, and the residual magnetism intensity of the modified nickel powder is ≤0.05mT.

[0063] The application provides a conductive silver-nickel paste, and the raw material composition of the conductive silver-nickel paste includes, in percentage by weight, 60-90wt% of silver powder, 2-30wt% of modified nickel powder, 1.2-4.5wt% of glass powder, 1-5wt% of organic resin, 1-10wt% of organic solvent, 0.1-0.5wt% of silicone oil and 0.1-1wt% of auxiliary agent; the modified nickel powder is the modified nickel powder described above.

[0064] The silver powder is high-tap single-dispersion spherical silver powder, the particle size D50 of the silver powder is 1.0-2.5μm, the specific surface area is 0.3-0.5m 2 / g, and the tap density is 5.5-6.0g / ml.

[0065] The organic resin includes one or two or more of polyvinyl butylal, phenolic resin, acrylic resin, hydroxypropyl methylcellulose, ethyl cellulose, cellulose acetate butyrate, polyvinyl butylal ester, rosin resin and poly-alpha-methylstyrene.

[0066] The organic solvent includes any one or two or more of dimethyl phthalate, dimethyl adipate, diethylene glycol butyl ether acetate, terpineol, diethylene glycol monobutyl ether, ethylene glycol phenyl ether acetate, alcohol ester twelve, dimethyl adipate, alcohol ester sixteen, isopropyl alcohol, benzyl benzoate, glyceryl triacetate, and tripropylene glycol butyl ether;

[0067] The silicone oil includes at least one of dimethyl polysiloxane, polymethylhydroxysiloxane, and polymethyl ethoxy silicone oil;

[0068] The auxiliary agent includes at least one of fatty acid polyoxyethylene ether, tallow acryl diamine oleate, silane coupling agent, titanate coupling agent, polyamide wax, lecithin, oleic acid, polyvinylpyrrolidone, and polyethylene glycol;

[0069] The glass powder is prepared from mixed raw materials via melting, cooling and ball milling; the mixed raw materials are composed of the following components in percentage by weight: lead oxide 35.3%-46.31%, silicon oxide 5.38%-13.2%, lithium oxide 2.64%-4.16%, zinc oxide 1.85%-3.5%, sodium oxide 1.22%-1.76%, magnesium oxide 0.43%-2.61%, calcium oxide 0.35%-1.57%, tellurium oxide 0-30.53%, barium oxide 0-21.72%, boron oxide 0-19.55%, tungsten oxide 0-9.65%, and copper oxide 0-0.53%.

[0070] The application further provides a preparation method of the conductive silver-nickel paste.

[0071] Step one, the silver powder, modified nickel powder, glass powder, organic resin, organic solvent, dispersant and thixotropic agent are added into a reaction device and mixed;

[0072] Step two, stirring is performed to uniformly wet the materials;

[0073] Step three, three-roll mill grinding is performed, the grinding interval is 10-120 mu m, and the grinding rotation speed is 50-400 r / min, so that the paste with a FOG squeegee fineness tester fineness less than 5 mu m is finally obtained.

[0074] In the step two, the stirring time can be, for example, 45 minutes.

[0075] The application provides a TOPCon solar cell, which includes an electrode, and the electrode is obtained by sintering after being printed on the surface of a cell sheet via the conductive silver-nickel paste.

[0076] The application has the following beneficial effects:

[0077] 1. Solve the problem of traditional nickel powder magnetic agglomeration: through alternating current demagnetization, the residual magnetism of nickel powder is reduced to below 0.05 mT, eliminating the particle agglomeration caused by magnetic force, and significantly improving the dispersion uniformity and storage stability of nickel powder in silver paste system.

[0078] 2. Solve the core problem of traditional nickel powder easy oxidation and poor silver-nickel interface compatibility: a dense and stable coating layer (such as nitride) is coated on the surface of nickel powder, which can not only isolate oxygen from contacting the surface of nickel powder and effectively inhibit the oxidation reaction, but also act as an interface buffer medium between silver powder and nickel powder, which can adjust the silver-nickel interfacial tension, reduce phase separation and micro-pore generation during sintering process, reduce the interfacial contact resistance, realize the performance synergy of silver-nickel components, and improve the electrode conductivity continuity and structural stability.

[0079] 3. Achieve the synergistic optimization of silver paste cost and performance: the modified nickel powder has excellent conductivity and anti-aging performance, which can greatly increase the replacement ratio of nickel powder in silver paste, significantly reduce the amount of silver powder and the cost of paste production, and at the same time avoid the problem of conductivity and adhesion decay in traditional low-silver solution, achieving the performance balance of "low cost, high conductivity and high adhesion".

[0080] 4. Improve the long-term reliability of silver-nickel paste: the dense nitride coating layer can effectively isolate the corrosion of nickel powder by harsh environment such as humidity and heat, inhibit the secondary oxidation and grain growth of nickel powder, ensure the stable performance decay of electrode in photovoltaic module (25 years) service cycle, and meet the long-term reliability requirements of high-efficiency photovoltaic cells.

[0081] Example and comparative example analysis

[0082] The following examples are prepared according to the following preparation process: alternating current demagnetization-nitride coating modified nickel powder preparation process:

[0083] Alternating current demagnetization pretreatment

[0084] S11. Select D50: 2-6 μm photovoltaic nickel powder (nickel content ≥ 99.5%), dry at 120-150 ℃, vacuum degree ≥-0.09 MPa for 2-3 h, and cool to room temperature for standby;

[0085] S12. Put the nickel powder into a polytetrafluoroethylene or ceramic sealed container (loading thickness 2-4 cm), place it in the center of the adjustable alternating current demagnetization coil (coil inner diameter 30-50 cm, number of turns 500-800 turns), and the distance between the container and the coil is ≤3 cm;

[0086] S13. Set the initial magnetic field strength to 32-38 mT, frequency to 50-60 Hz, and reduce to 0 mT at a uniform rate of 4-6 mT / min, for 5-8 min, and keep the whole process free from external magnetic field interference;

[0087] S14. Use a gauss meter with an accuracy of 0.01 mT to detect the upper, middle, and lower three points on the nickel powder, ensuring that the residual magnetism is ≤0.05 mT, and seal and transfer to the coating process within 30 min.

[0088] Nitride coating using chemical vapor deposition processing method

[0089] S21, Pre-preparation: Transfer the demagnetized qualified nickel powder to the vacuum reaction kettle, evacuate to ≥-0.095 MPa, and introduce nitrogen gas with a purity of ≥99.99% for replacement 3 times (each time maintain 0.1 MPa and stand for 5 min), and completely exclude oxygen and moisture in the kettle.

[0090] S22, Add selected nitride precursor (corresponding to the target coated nitride, such as aluminum isopropylate, silicon nitride) to the reaction kettle, start the stirring device to uniformly mix the nickel powder and the precursor;

[0091] S23, heat to 350-750℃ at a rate of 8-10℃ / min (the specific temperature is adjusted according to the selected nitride), introduce high-purity nitrogen source gas (ammonia, nitrogen or its mixture, purity ≥99.99%), control the gas flow rate to be 10-30 mL / min, and the pressure in the kettle to be 0.1-0.5 MPa; heat for 1.5-5 h, so that the nitrogen source and the precursor react on the surface of the nickel powder to form a dense nitride coating layer;

[0092] S24, After the reaction is completed, keep the nitrogen atmosphere, cool to below 100℃ at a rate of 5-8℃ / min, and take out the nickel powder.

[0093] Nitride coating using physical adhesion processing method

[0094] S31, Place the demagnetized nickel powder in a mixing container;

[0095] S32, Add selected nitride (such as h-BN nanosheet) and dispersion medium (anhydrous ethanol solution and polyvinylpyrrolidone) to the mixing container, disperse the treatment to coat the nitride on the surface of the nickel powder, and form a dense nitride coating layer.

[0096] To specifically illustrate the feasible solutions of the surface coating treatment, the application provides various embodiments based on different nitride materials and corresponding deposition technologies. For example, chemical vapor deposition method can be used, isopropyl alcohol aluminum or tetraethyl orthosilicate is used as a precursor, an aluminum nitride (AlN) or silicon nitride (Si3N4) coating layer is respectively formed on the surface of the nickel powder under a specific mass ratio (for example, the mass ratio of the precursor to the nickel powder ranges from 1:4 to 1:9). Physical adhesion method can also be used, hexagonal boron nitride (h-BN) nanosheets are uniformly mixed with the nickel powder in a dispersing medium at a specific mass ratio (for example, the mass ratio of the h-BN nanosheets to the nickel powder is 1:10) to make the h-BN nanosheets adhere to the surface of the nickel powder to form a coating layer. The above methods can all prepare modified nickel powder with a dense coating layer and low residual magnetism, and the specific process parameters can be adjusted within a reasonable range according to the properties of the target nitride, as shown in Table 2.

[0097] Table 2: Proportion of nitride material components and adding method

[0098]

[0099] Preparation of glass powder:

[0100] The glass powder of the following examples and comparative examples is prepared from mixed raw materials via melting, cooling and ball milling; the mixed raw materials are composed of the following components in percentage by weight: lead oxide 35.3%-46.31%, silicon oxide 5.38%-13.2%, lithium oxide 2.64%-4.16%, zinc oxide 1.85%-3.5%, sodium oxide 1.22%-1.76%, magnesium oxide 0.43%-2.61%, calcium oxide 0.35%-1.57%, tellurium oxide 0-30.53%, barium oxide 0-21.72%, boron oxide 0-19.55%, tungsten oxide 0-9.65%, and copper oxide 0-0.53%; the glass powder used in the following examples is prepared according to the composition range and preparation method described above, and the specific oxide proportion can be adjusted within the disclosed range to achieve the purpose of the application.

[0101] The specific preparation steps of the glass powder are as follows: the raw materials are weighed according to the proportion, mixed to obtain a mixture; the mixture is melted at 1250-1300℃ for 1.5h, quenched to obtain glass fragments; the glass fragments are placed in a 20L vertical ball mill, 15kg of zirconia balls with a diameter of 5-10mm are added, 2kg of deionized water and oleic acid are added, and the mixture is stirred at a speed of 250r / min for 8h to obtain a glass slurry; the glass slurry is sieved and dried to obtain glass powder with a particle size of 2-5μm.

[0102] The conductive silver-nickel paste described in Examples 1-7 and Comparative Examples 1-3 below is prepared by using the modified nickel powder and glass powder prepared by the foregoing method and prepared according to the following steps:

[0103] Step one, add silver powder, modified nickel powder, glass powder, organic resin, organic solvent, dispersant and thixotropic agent into the reaction device and mix;

[0104] Step two, stir to make each material evenly wet;

[0105] Step three, three-roll mill grinding, grinding distance is 10-120 pm, grinding speed is 50-400 r / min, finally get the slurry with FOG squeegee fineness tester fineness less than 5 pm.

[0106] In some embodiments, the time for stirring in step two may be, for example, 45 minutes.

[0107] Example 1

[0108] The conductive silver-nickel paste is made of the following raw materials by weight:

[0109] Silver powder (D50 is 1.0-2.5 pm): 78.5%;

[0110] Modified nickel powder (D50 is 4-5 pm): AC demagnetization-hexagonal boron nitride coated modified nickel powder 10%;

[0111] Glass powder: 2.5%;

[0112] Organic resin: ethyl cellulose (Dow STD-4) 1%, polyvinyl butyral resin (Kuraray B60H) 0.5%;

[0113] Auxiliary agent: oleic acid 0.3%, polyamide wax 0.2%;

[0114] Silicone oil: polydimethylsiloxane (viscosity 100 mPa·s) 0.5%;

[0115] Solvent: benzyl benzoate 1.2%, diethylene glycol butyl ether acetate 4.3%, alcohol ester twelve 1%.

[0116] Example 2

[0117] The conductive silver-nickel paste is made of the following raw materials by weight:

[0118] Silver powder (D50 is 1.0-2.5 pm): 78.5%;

[0119] Modified nickel powder (D50 is 4-5 pm): AC demagnetization-silicon nitride coated modified nickel powder 10%;

[0120] Glass powder: 2.5%;

[0121] Organic resin: ethyl cellulose (Dow STD-4) 1%, polyvinyl butyral resin (Kuraray B60H) 0.5%;

[0122] Auxiliary: oleic acid 0.3%, polyamide wax 0.2%;

[0123] Silicone oil: dimethicone (viscosity 100 mPa·s) 0.5%;

[0124] Solvent: benzyl benzoate 1.2%, diethylene glycol butyl ether acetate 4.3%, alcohol ester twelve 1%.

[0125] Example 3

[0126] The conductive silver nickel paste is made of the following raw materials in parts by weight:

[0127] Silver powder (D50 1.0-2.5 μm): 78.5%;

[0128] Modified nickel powder (D50 4-5 μm): AC demagnetization-aluminum nitride coated modified nickel powder 10%;

[0129] Glass powder: 2.5%;

[0130] Organic resin: ethyl cellulose (Dow STD-4) 1%, polyvinyl butyral resin (Kuraray B60H) 0.5%;

[0131] Auxiliary: oleic acid 0.3%, polyamide wax 0.2%;

[0132] Silicone oil: dimethicone (viscosity 100 mPa·s) 0.5%;

[0133] Solvent: benzyl benzoate 1.2%, diethylene glycol butyl ether acetate 4.3%, alcohol ester twelve 1%.

[0134] Example 4

[0135] The conductive silver nickel paste is made of the following raw materials in parts by weight:

[0136] Silver powder (D50 1.0-2.5 μm): 73.4%;

[0137] Modified nickel powder (D50 4-5 μm): AC demagnetization-hexagonal boron nitride coated modified nickel powder 15%;

[0138] Glass powder: 2.6%;

[0139] Organic resin: ethyl cellulose (Dow STD-4) 1%, polyvinyl butyral resin (Kuraray B60H) 0.5%;

[0140] Auxiliary: oleic acid 0.3%, polyamide wax 0.2%;

[0141] Silicone oil: dimethicone (viscosity 100 mPa-s) 0.5%;

[0142] Solvent: benzyl benzoate 1.2%, diethylene glycol butyl ether acetate 4.3%, alcohol ester twelve 1%.

[0143] Example 5

[0144] The conductive silver nickel paste was made from the following raw materials in parts by weight:

[0145] Silver powder (D50 1.0-2.5 pm): 68.3%;

[0146] Modified nickel powder (D50 4-5 pm): AC demagnetization-hexagonal boron nitride coated modified nickel powder 20%;

[0147] Glass powder: 2.7%;

[0148] Organic resin: ethyl cellulose (Dow STD-4) 1%, polyvinyl butyral resin (Kuraray B60H) 0.5%;

[0149] Auxiliary agent: oleic acid 0.3%, polyamide wax 0.2%;

[0150] Silicone oil: dimethicone (viscosity 100 mPa-s) 0.5%;

[0151] Solvent: benzyl benzoate 1.2%, diethylene glycol butyl ether acetate 4.3%, alcohol ester twelve 1%.

[0152] Example 6

[0153] The conductive silver nickel paste was made from the following raw materials in parts by weight:

[0154] Silver powder (D50 1.0-2.5 pm): 73.5%;

[0155] Modified nickel powder (D50 4-5 pm): AC demagnetization-hexagonal boron nitride coated modified nickel powder 15%;

[0156] Glass powder: 2.5%;

[0157] Organic resin: ethyl cellulose (Dow STD-4) 1%, polyvinyl butyral resin (Kuraray B60H) 0.5%;

[0158] Auxiliary agent: oleic acid 0.3%, polyamide wax 0.2%;

[0159] Silicone oil: dimethicone (viscosity 100 mPa-s) 0.5%;

[0160] Solvent: benzyl benzoate 1.2%, diethylene glycol butyl ether acetate 4.3%, alcohol ester twelve 1%.

[0161] Example 7

[0162] The conductive silver nickel paste was made from the following raw materials in parts by weight:

[0163] Silver powder (D50 1.0-2.5 pm): 68.5%;

[0164] Modified nickel powder (D50 4-5 pm): AC demagnetization-hexagonal boron nitride coated modified nickel powder 20%;

[0165] Glass powder: 2.5%;

[0166] Organic resin: ethyl cellulose (Dow STD-4) 1%, polyvinyl butyral resin (Kuraray B60H) 0.5%;

[0167] Auxiliary agent: oleic acid 0.3%, polyamide wax 0.2%;

[0168] Silicone oil: dimethicone (viscosity 100 mPa-s) 0.5%;

[0169] Solvent: benzyl benzoate 1.2%, diethylene glycol butyl ether acetate 4.3%, alcohol ester twelve 1%.

[0170] Comparative Example 1

[0171] The conductive silver paste was made from the following raw materials in parts by weight:

[0172] Silver powder (D50 1.0-2.5 pm): 88.5%;

[0173] Glass powder: 2.5%;

[0174] Organic resin: ethyl cellulose (Dow STD-4) 1%, polyvinyl butyral resin (Kuraray B60H) 0.5%;

[0175] Auxiliary agent: oleic acid 0.3%, polyamide wax 0.2%;

[0176] Silicone oil: dimethicone (viscosity 100 mPa-s) 0.5%;

[0177] Solvent: benzyl benzoate 1.2%, diethylene glycol butyl ether acetate 4.3%, alcohol ester twelve 1%.

[0178] Comparative Example 2

[0179] The conductive silver paste was made from the following raw materials in parts by weight:

[0180] Silver powder (D50 1.0-2.5 pm): 78.5%;

[0181] Modified nickel powder (D50: 4-5 pm): 10% of nickel powder;

[0182] Glass powder: 2.5%;

[0183] Organic resin: ethyl cellulose (Dow STD-4) 1%, polyvinyl butyral resin (Kuraray B60H) 0.5%;

[0184] Auxiliary agent: oleic acid 0.3%, polyamide wax 0.2%;

[0185] Silicone oil: dimethicone (viscosity 100 mPa-s) 0.5%;

[0186] Solvent: benzyl benzoate 1.2%, diethylene glycol butyl ether acetate 4.3%, alcohol ester twelve 1%.

[0187] Comparative Example 3

[0188] The conductive silver paste was made from the following raw materials in parts by weight:

[0189] Silver powder (D50: 1.0-2.5 pm): 78.5%;

[0190] Modified nickel powder (D50: 4-5 pm): 10% of hexagonal boron nitride coated modified nickel powder (not demagnetized, directly coated on the surface according to the above method);

[0191] Glass powder: 2.5%;

[0192] Organic resin: ethyl cellulose (Dow STD-4) 1%, polyvinyl butyral resin (Kuraray B60H) 0.5%;

[0193] Auxiliary agent: oleic acid 0.3%, polyamide wax 0.2%;

[0194] Silicone oil: dimethicone (viscosity 100 mPa-s) 0.5%;

[0195] Solvent: benzyl benzoate 1.2%, diethylene glycol butyl ether acetate 4.3%, alcohol ester twelve 1%.

[0196] The paste of Examples 1 to 7 and Comparative Examples 1 to 3 was taken as a sample, and each sample was printed on the same substrate for related property testing, and the testing process was as follows:

[0197] 1. Contact resistance: after printing a specific pattern on the TOPcon cell sheet with the paste and drying and curing, a laser cutting machine was used to cut the printed pattern area to size; a contact resistance device was used to measure the contact resistance.

[0198] 2. Viscosity test: 15-20 g of the sample slurry was taken, and the average viscosity value of the slurry was measured using a Brookfield DV2 viscosity tester and a rotor SC-14 under the measurement conditions of 25°C / rotation speed 10 rpm / 60 seconds.

[0199] 3. Resistivity test: The resistance between the two electrodes was tested using a four-probe ohmmeter.

[0200] 4. 3D topography test: The surface grid line topography of the slurry was tested using a Keyence 3D topography tester.

[0201] 5. Printability test: The conductive slurry in the above examples and comparative examples was printed onto the back of a silicon wafer by screen printing technology. The screen printing detection screen used had the following specifications: no knot multi-opening screen, 600 mesh, 7 pm wire diameter, total thickness 12-13 pm, and openings of 11 pm, 10 pm, and 9 pm, respectively. The battery piece was dried in an infrared drying oven, and then the slurry printability was observed by the naked eye and optical microscope to determine whether there were broken grids and ghost prints.

[0202] Table 3. Test performance table of each example and comparative example

[0203]

[0204] According to Table 3 above, it can be seen from Examples 1-3 and Comparative Example 1 that when the modified nickel powder is "AC demagnetization-hexagonal boron nitride coating" and the addition ratio is 10%, the difference in photoelectric conversion efficiency between the silver-nickel slurry and the pure silver slurry is only 0.02% (Example 1 vs. Comparative Example 1). This is because the hexagonal boron nitride is tightly bonded to the interface of the nickel powder, can form a uniform and dense coating layer, and has excellent chemical stability and thermal stability, which is suitable for the production and application environment of photovoltaic slurry. Silicon nitride is a ferromagnetic compatible material, which cannot weaken the magnetism of nickel powder after coating, and its ceramic phase hardness is too high, the interface bonding force with nickel powder is weak, the coating layer is easy to fall off, and it also increases the overall brittleness of the powder. Although aluminum nitride is a diamagnetic material, it cannot effectively demagnetize the nickel powder, and has poor interface compatibility with the nickel powder, making it difficult to form a uniform coating layer, and it is also easy to hydrolyze in a humid environment, leading to oxidation of the surface of the nickel powder and damage to the performance of the powder. Therefore, the efficiencies of Examples 2 and 3 are significantly different from that of the pure silver slurry.

[0205] It can be seen from the comparison of Example 1 with Comparative Examples 3 and 2 that if the nickel powder is not demagnetized, it will be disturbed by the magnetic field (Comparative Example 3), leading to powder agglomeration and poor slurry dispersibility, thereby affecting the printing of the slurry. From the comparison of Example 1 with Comparative Example 2, it can be seen that if the nickel powder is not coated, the surface of the nickel powder is not smooth, and the interface compatibility with the silver powder is poor, making it difficult to form a uniform coating layer, and the silver-nickel slurry has poor dispersibility and printability. Figure 2The difference between the two slurries can be clearly seen (the black large particles in the figure are nickel powder), and the nickel powder in Example 1 is subjected to degaussing treatment. After the slurry is printed for 4 hours, the nickel powder does not appear to be a large agglomeration and accumulation in the grid line. Compared with Comparative Example 3, the nickel powder particles agglomerate and accumulate on the screen as the printing time increases, so that the nickel powder in the grid line increases, and finally leads to a decrease in efficiency over time and a decrease in printing. If the nickel powder is not modified by coating (Comparative Example 2), not only is the oxidation resistance poor, but the nickel powder is prone to agglomeration, resulting in poor electrical performance and poor printing.

[0206] As can be seen from Examples 4-7, when the proportion of nickel increases, the content of glass powder needs to be increased (e.g., Examples 4-5) to reduce the loss of efficiency. Thus, it can be concluded that there is a certain synergistic relationship between nickel powder and glass powder. The core mechanism of adjusting the content of glass powder when the proportion of nickel increases includes: supplementing glass powder to compensate for the performance defects of the slurry caused by the physical and chemical properties of the nickel powder; the wettability of the nickel powder is much worse than that of the silver powder, and more liquid phase formed by the melting of the glass powder can spread on the interface between the nickel powder and the silicon wafer and fill the gap between the particles, thereby improving the density of the electrode layer; the sintering activation energy of the nickel powder is higher, and the additional glass powder can act as a sintering aid to reduce the sintering temperature of the system, providing a mass transfer channel for the diffusion and rearrangement of nickel powder particles, and promoting sintering densification; at the same time, more glass powder can fully etch the SiNx passivation layer on the surface of the silicon wafer to form an effective contact channel, and also form a low-melting-point eutectic phase with the surface of the nickel powder, thereby inhibiting the formation of nickel-silicon high-resistance phases and ensuring the contact performance of the electrode. The efficiency of Examples 6-7 (increased nickel powder and no increased glass powder) decreases slightly, further verifying the necessity of "supplementing glass powder when the proportion of nickel increases".

[0207] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A conductive silver-nickel paste, characterized in that, The conductive silver-nickel paste, by weight percentage, comprises: 60-90 wt% silver powder, 2-30 wt% modified nickel powder, 1.2-4.5 wt% glass powder, 1-5 wt% organic resin, 1-10 wt% organic solvent, 0.1-0.5 wt% silicone oil, and 0.1-1 wt% additives; the modified nickel powder is prepared by the following steps: The nickel powder is demagnetized; the demagnetized nickel powder is then surface coated to obtain modified nickel powder.

2. The conductive silver-nickel paste as described in claim 1, characterized in that, The demagnetizing treatment includes at least one of the following: dethermal demagnetizing treatment, AC demagnetizing treatment, mechanical vibration demagnetizing treatment, and chemical modification-assisted demagnetizing treatment.

3. The conductive silver-nickel paste as described in claim 1, characterized in that, The demagnetization process includes an AC demagnetization process, the specific steps of which include: Provide nickel powder and perform a drying pretreatment on it; The dried nickel powder is loaded into a non-magnetic container and arranged in the effective working area of ​​the demagnetizing coil with a set loading thickness. An alternating magnetic field with an amplitude decreasing to zero is applied to the demagnetizing coil and maintained for a set time to demagnetize the nickel powder; The residual magnetic strength of the nickel powder after demagnetization is detected. Once the residual magnetic strength meets the preset magnetic strength, it is transferred to the next process within a limited time.

4. The conductive silver-nickel paste as described in claim 3, characterized in that, The specific conditions for the drying pretreatment include: drying temperature 120-150℃, vacuum degree ≥-0.09MPa, and drying time 2-3h.

5. The conductive silver-nickel paste as described in claim 3, characterized in that, The initial strength of the alternating magnetic field is 32-38 mT, the frequency is 50-60 Hz, and it decays to zero at a rate of 4-6 mT / min.

6. The conductive silver-nickel paste as described in claim 1, characterized in that, The surface coating treatment includes at least one of inorganic coating treatment and organic coating treatment.

7. The conductive silver-nickel paste as described in claim 1, characterized in that, The surface coating treatment includes an inorganic coating treatment, wherein at least one of oxides, nitrides, and carbides is coated onto the surface of the demagnetized nickel powder.

8. The conductive silver-nickel paste as described in claim 7, characterized in that, The nitrides include at least one of boron nitride, nickel nitride, titanium nitride, aluminum nitride, silicon nitride, and zirconium nitride.

9. The conductive silver-nickel paste as described in claim 8, characterized in that, The boron nitride includes at least one of hexagonal boron nitride, cubic boron nitride, and rhombohedral boron nitride.

10. The conductive silver-nickel paste as described in claim 7, characterized in that, The nitride is deposited onto the surface of the demagnetized nickel powder.

11. The conductive silver-nickel paste as described in claim 10, characterized in that, The deposition process includes chemical vapor deposition, which includes the following steps: The demagnetized nickel powder is placed in a reactor, and after the air is removed, an inert gas is introduced to establish an inert protective atmosphere. A precursor of the target nitride is added to the reactor, and the precursor is brought into uniform contact with nickel powder. Under the inert protective atmosphere, the reaction system is heated to the reaction temperature, and nitrogen source gas is introduced into the reaction system so that the precursor and nitrogen source gas react chemically on the surface of nickel powder to form a nitride coating layer. After the reaction is complete, the reaction system is cooled under an inert protective atmosphere, and the coated nickel powder is removed.

12. The conductive silver-nickel paste as described in claim 11, characterized in that, The heating rate is 8-10℃ / min, the reaction temperature is 350-750℃; the nitrogen source gas includes ammonia and / or nitrogen, the flow rate of the nitrogen source gas is 10-30mL / min, and the pressure inside the reactor is 0.1-0.5MPa.

13. The conductive silver-nickel paste as described in claim 10, characterized in that, The deposition process includes a physical adhesion process, in which demagnetized nickel powder and nitride are mixed in a dispersion medium and then dispersed to allow the nitride to adhere to the surface of the nickel powder.

14. The conductive silver-nickel paste as described in claim 1, characterized in that, The modified nickel powder has a core-shell structure, including a nickel core and a coating layer covering the surface of the nickel core. The thickness of the coating layer is 5-30 nm, and the remanence of the modified nickel powder is ≤0.05 mT.

15. A TOPCon solar cell, characterized in that, The electrode is obtained by printing a conductive silver-nickel paste as described in any one of claims 1-14 onto the surface of the battery cell and then sintering it.

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