Porous hollow spherical silver powder and preparation method and application thereof

Abstract

The invention belongs to the technical field of preparation of conductive materials. In particular to porous hollow spherical silver powder and a preparation method and application thereof, a BPOP-2 type COF material is creatively adopted as a configuration agent and a reducing agent for preparing the silver powder, configuration of the silver powder can be achieved in the reduction process of the silver powder, and the superfine porous hollow spherical silver powder can be obtained after the COF material is removed through sintering. The superfine porous hollow spherical silver powder is large in hollow rate, good in tap density, large in specific surface area, low in heat loss (650 DEG C), uniform in particle size distribution, excellent in printability, low in line breaking rate, good in printing line type and high in sintering activity, and has a remarkable effect of improving the efficiency of conductive silver paste. The whole technological process is simple and easy to control, and the product is excellent in comprehensive performance and stable in quality.

Description

Technical Field

[0001] The present invention relates to silver powder and its preparation method and application, and particularly to a porous hollow spherical silver powder and its preparation method and application; it belongs to the technical field of conductive material preparation. Background Art

[0002] Conductive silver paste, as a key material for crystalline silicon solar photovoltaic cells, mainly consists of three parts: silver powder, glass powder, and organic carrier. Silver powder is widely used in this field due to its excellent electrical conductivity. Its shape is mostly spherical (or quasi-spherical), and the particle size is tiny to meet the requirements of printing and electrical conductivity. Silver powder can form a high-quality ohmic contact with the surface of the silicon wafer, significantly improving the photoelectric conversion efficiency of solar cells. Glass powder acts as a binder in the silver paste. It can not only firmly adhere the silver powder to the surface of the silicon wafer but also etch the silicon nitride film on the surface of the silicon wafer, having a decisive impact on the ohmic contact performance of the silver paste. The organic carrier endows the silver paste with appropriate viscosity to ensure the smooth progress of the printing process. In the silver paste, the content of silver powder is extremely high (about 90%), and it plays a crucial role in the electrical conductivity and printing performance of the silver paste.

[0003] In recent years, the technology of crystalline silicon solar photovoltaic cells has developed rapidly, and the product update speed is extremely fast. From polycrystalline to single crystal, then to Perc and Perc-se technologies, and until the current popularization of N-type solar cell wafers, the product efficiency has increased from less than 10% initially to about 24% currently. This progress not only benefits from the continuous innovation of cell wafer technology but also is closely related to the continuous development of conductive silver paste. With the increase in the size of crystalline silicon cell wafers and the refinement of silver grid lines, the printing screen also tends to be high-density and fine-grid, which requires silver powder to have higher comprehensive performance. That is, silver powder needs to have high sintering activity, good printing performance, and perfect printing line pattern. As the line width of the printing screen continues to shrink, the particle size of silver powder also needs to be adjusted accordingly to ensure that the silver paste can smoothly pass through the mesh holes and be printed on the surface of the silicon wafer. Compared with solid silver powder, porous hollow silver powder has obvious advantages in printing line pattern and sintering shrinkage. Its aspect ratio is large, which helps to improve the current. Therefore, the research and preparation of ultra-fine porous hollow spherical silver powder have become the key direction to promote the performance improvement of silver powder. Summary of the Invention

[0004] In view of the problems in the prior art that the comprehensive performance of silver powder is poor, resulting in a high wire breakage rate, poor printing line type, and low photoelectric conversion efficiency of silicon solar conductive silver paste under narrow line width screen printing conditions, the present invention provides a porous hollow spherical silver powder, a preparation method thereof, and an application thereof. The silver salt is configured and reduced in a reduction dispersion system composed of a reducing COF material and a dispersant. The reducing COF material with a three-dimensional porous structure and an aldehyde group as a reducing group is innovatively introduced as a configurator and reducing agent for preparing silver powder, and then ultra-fine porous hollow spherical silver powder with a high hollowness ratio, a large specific surface area, and a uniform particle size distribution can be directly obtained by one-step reduction. The entire process flow is simple and easy to control, the comprehensive performance of the product is excellent, and the quality is stable.

[0005] To achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0006] According to the first embodiment of the present invention, a preparation method of a porous hollow spherical silver powder is provided, and the preparation method includes the following steps:

[0007] S1: Dissolve the silver salt in water (preferably deionized water or distilled water) to obtain a silver salt solution, and add the reducing COF material and the dispersant to water to obtain a reduction dispersion system. Then add the silver salt solution to the reduction dispersion system for reaction, and after the reaction is completed, perform solid-liquid separation treatment to obtain wet silver powder.

[0008] S2: Sinter the wet silver powder to obtain a porous hollow spherical silver powder.

[0009] Preferably, the preparation method further includes:

[0010] S3: Perform surface coating treatment on the porous hollow spherical silver powder with a coating solution, and after the coating is completed, sequentially perform drying treatment and optionally dispersion treatment to obtain a coated porous hollow spherical silver powder.

[0011] It should be noted that in the present invention, "optionally" means "perform" or "not perform".

[0012] Preferably, in step S1, the reducing COF material is prepared by a condensation reaction of tris(4-formylbiphenyl)amine with phenylenediamine or hydroquinone. Preferably, the phenylenediamine is p-phenylenediamine, o-phenylenediamine, and / or m-phenylenediamine, and the hydroquinone is p-hydroquinone, o-hydroquinone, and / or m-hydroquinone; further preferably, the phenylenediamine is p-phenylenediamine and / or m-phenylenediamine, and the hydroquinone is p-hydroquinone and / or m-hydroquinone. More preferably, the phenylenediamine is p-phenylenediamine, and the hydroquinone is p-hydroquinone.

[0013] Preferably, the condensation reaction is specifically as follows: tris(4-formylbiphenyl)amine and phenylenediamine (or dihydroxybenzene) are dissolved in an organic solvent (preferably absolute ethanol), an acid catalyst (preferably acetic acid) is added, and then the reaction is carried out at a temperature of 60-80 °C for 5-24 h (preferably at a temperature of 65-75 °C for 10-20 h). After the reaction is completed, the target product can be obtained through recrystallization treatment; the average molecular weight of the obtained product is 500-700 g / mol.

[0014] Preferably, in the condensation reaction, the molar ratio of tris(4-formylbiphenyl)amine to phenylenediamine or dihydroxybenzene during the reaction is 0.5-2:1, preferably 0.8-1.5:1. For example, it can be one of 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1.

[0015] Preferably, in the condensation reaction, the dosage of the acid catalyst is 0.01-0.3 times the molar dosage of tris(4-formylbiphenyl)amine, preferably 0.05-0.2 times.

[0016] Preferably, in step S1, the silver salt is silver nitrate.

[0017] Preferably, in step S1, the dispersant is one or more of polyvinylpyrrolidone, polyvinyl alcohol, and gelatin.

[0018] Preferably, in step S1, the concentration of the silver salt in the silver salt solution is 0.5-5 mol / L, preferably 1-3 mol / L. For example, the concentration can be one of 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L, 3.0 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L.

[0019] Preferably, in step S1, the mass concentration of the reducing COF material in the reduction dispersion system is 12-45%, preferably 20-35%. For example, the mass concentration can be one of 12%, 13%, 14%, 15%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%.

[0020] Preferably, in step S1, the mass concentration of the dispersant in the reduction dispersion system is 0.5-5%, preferably 1-3%. For example, the mass concentration is one of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.4%, 2.5%, 2.8%, 3.0%, 3.2%, 3.5%, 3.8%, 4.0%, 4.2%, 4.5%, 4.8%, 5%.

[0021] Preferably, the volume ratio of the silver salt solution to the reduction dispersion system is 1:1-10, preferably 1:2-8, and more preferably 1:3-6. For example, the volume ratio is one of 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10.

[0022] Preferably, in step S1, the reaction is a stirring reaction. The temperature of the stirring reaction is 20-60°C, preferably 25-50°C. The duration of the stirring reaction is 20-120 min, preferably 30-90 min. The stirring rate during the stirring reaction is 200-800 r / min, preferably 300-600 r / min.

[0023] Preferably, in step S1, the silver salt solution is added dropwise, and the dropping duration of the silver salt solution is 15-60 min, preferably 20-50 min.

[0024] Preferably, in step S2, the sintering treatment temperature is 150-500°C, preferably 200-400°C. The sintering treatment time is 0.5-5 h, preferably 1-3 h.

[0025] Preferably, in step S3, the coating solution includes a coating agent and a solvent. The coating agent is one or more of stearic acid, oleic acid, and amino silicone oil. The solvent is ethanol and / or isopropanol. Preferably, the mass concentration of the coating agent in the coating solution is 1-20%, preferably 5-15%, and more preferably 8-12%. For example, the concentration is one of 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%.

[0026] Preferably, in step S3, the drying treatment is drying at a temperature of 60-85°C for 1-12 h, preferably vacuum drying at a temperature of 65-80°C for 2-6 h.

[0027] Preferably, in step S3, the dispersion treatment is first carried out by airflow pulverization treatment, and then ultrasonic vibration sieving treatment is carried out.

[0028] According to the second embodiment of the present invention, a porous hollow spherical silver powder is provided:

[0029] A porous hollow spherical silver powder, which is prepared by the preparation method described in the first embodiment.

[0030] According to the third embodiment of the present invention, an application of a porous hollow spherical silver powder is provided:

[0031] An application of a porous hollow spherical silver powder or a porous hollow spherical silver powder prepared by the preparation method described in the first embodiment, applying the porous hollow spherical silver powder to the fields of conductive coatings, antibacterial materials and electromagnetic shielding, preferably used in conductive silver paste for solar cells.

[0032] In the present invention, the silver powder of the present invention is an ultrafine porous hollow spherical silver powder. Its ultrafine small particle size structure ensures excellent printability, while the porous hollow structure is beneficial to the excellent aspect ratio of printed line metallization. In order to realize the porous hollow structure of the silver powder, the COF material (BPOP-2 type) with a reducing group aldehyde group is innovatively introduced as a reducing agent and configurator for preparing the silver powder. Because it has a three-dimensional porous structure and strong adsorption, the silver powder formed after the reduction of silver salt will be wrapped around it. After high-temperature heat treatment in the later stage, the COF material in the silver powder escapes from it, and then a spherical or quasi-spherical structure with uniform particle size distribution, porous hollow, large hollow ratio, high specific surface area and excellent sintering performance can be formed.

[0033] In the present invention, the reducing COF material is a BPOP-2 type COF material formed by condensing tris(4-aminophenyl)amine as a monomer with p-phenylenediamine or hydroquinone. This COF material has a strong adsorption effect on other ions and has a three-dimensional porous structure. It will become the crystal nucleus of the silver powder during the process of reducing silver salt to form silver powder, so that the silver powder is wrapped around it, and then ultrafine porous spherical silver powder is formed. In addition, the pyrolysis temperature of this BPOP-2 type COF material is much lower than the melting point of silver, so it can be sintered and removed at a relatively low temperature, and will not affect the formed silver powder structure. Finally, a high-purity porous hollow spherical silver powder material with uniform particle size distribution, large hollow ratio, high specific surface area and excellent sintering performance is obtained.

[0034] In addition, it should be noted that the reducing COF material is prepared in-house. During the preparation process, the amount of tris(4-formylbiphenyl)amine used as a monomer is such that the molar amount of its aldehyde groups is in excess relative to the molar amount of the amino or hydroxyl groups of phenylenediamine or hydroquinone, that is, it is necessary to ensure that a considerable amount of unreacted aldehyde groups remain in the resulting reducing COF material, thereby ensuring that the reducing COF material has a network structure and good reducibility at the same time. In a preferred embodiment of the present invention, through research, it is found that in the condensation reaction, when the molar ratio of tris(4-formylbiphenyl)amine to aniline or phenol is between 0.5 and 2:1, the overall performance of the resulting reducing COF material is relatively good, and when the molar ratio of tris(4-formylbiphenyl)amine to aniline or phenol is between 0.8 and 1.5:1, the overall performance of the reducing COF material is basically optimal.

[0035] In the present invention, after the reducing COF material is prepared, a silver salt solution (i.e., silver nitrate solution) and a reduction dispersion system composed of the reducing COF material and a dispersant, namely water, are respectively prepared, and then the silver salt solution is added dropwise to the reduction dispersion system during stirring for reaction. Through continuous stirring, it is promoted that silver nitrate is quickly and uniformly dispersed in the reduction dispersion system, and agglomeration during the deposition of the silver powder formed by reduction in a local area is prevented, ensuring that the formed silver powder is uniformly deposited on the reducing COF material. After the addition of the silver salt solution is completed, stirring and reacting need to continue for a period of time to ensure the formation of a stable and uniform silver powder dispersion system. When the reaction is completed, the solid product is separated by suction filtration and washed 2 - 5 times with deionized water to remove residual impurities, and wet silver powder is obtained. Finally, the wet silver powder is sintered to remove impurities such as the reducing COF material and the remaining dispersant, the sintering temperature is controlled at 150 - 500 °C, and the sintering time is 0.5 - 5 hours to obtain high-purity ultrafine porous hollow spherical silver powder.

[0036] It should be noted that the inventors further found through experimental research and verification that during the reaction, the type and amount of the reducing COF material directly affect the hollowness ratio, specific surface area, tapped density, heat loss, particle size distribution and other properties of the porous hollow spherical silver powder. In a preferred embodiment of the present invention, when the reducing COF material is synthesized from tris(4-formylbiphenyl)amine and phenylenediamine or hydroquinone as raw materials, the configuration reduction effect of the resulting reducing COF material is the best, which is reflected in that the comprehensive performance of the resulting spherical silver powder is basically optimal: the hollowness ratio of the resulting porous hollow spherical silver powder can reach more than 95%, the specific surface area is significantly increased, the tapped density is more uniform, the heat loss is further reduced, the particle size distribution is more concentrated, and the overall performance is basically in an ideal state.

[0037] In the present invention, as a preferred technical solution of the present invention, the obtained ultrafine porous hollow spherical silver powder is further subjected to surface coating treatment with a coating agent, and after the coating treatment, it is dried to obtain the coated porous hollow spherical silver powder. The coating treatment prevents the oxidation of the porous hollow spherical silver powder during long-term exposure, improves the stability of the porous hollow spherical silver powder, and also further improves the optical effect of the porous hollow spherical silver powder.

[0038] In the present invention, through a specific process and by selecting a specific configurational reducing agent, the obtained porous hollow spherical silver powder not only has excellent optical properties but also exhibits excellent chemical stability. Specifically, the obtained porous hollow spherical silver powder has a minimum hollowness of greater than 80%, a specific surface area of 0.38 - 0.6 m 2 / g, a tapped density of 5.2 - 5.8 g / cm 3 , a thermal loss (at 650 °C) of 0.1 - 0.8%, and a particle size distribution of D10 ≤ 0.6 μm, D50 ≤ 1.0 μm, and D90 ≤ 2.0 μm. It has high sintering activity (the sintering temperature is 5 - 10 degrees lower than the reference), and the photoelectric conversion efficiency is increased by 0.18 - 0.32% compared to the reference. It has excellent printability, a low wire break rate, a good printed line shape, high sintering activity, and significantly improves the efficiency of conductive silver paste.

[0039] Compared with the prior art, the technical solution provided by the present invention has the following beneficial technical effects:

[0040] 1. The present invention creatively uses the BPOP-2 type COF material as the configurant and reducing agent for preparing silver powder, which can realize the configuration of silver powder during the reduction process of silver powder, and after simply removing the COF material through a sintering process, ultrafine porous hollow spherical silver powder can be obtained. It has the advantages of a short overall process, convenient operation, high production efficiency, and stable product quality.

[0041] 2. The present invention optimizes the process mechanism, pre-adjusts a suitable reduction dispersion system according to the dosage of silver salt, which is conducive to obtaining porous hollow spherical silver powder with expected structural and performance indicators, making the obtained porous hollow spherical silver powder have excellent sphericity and porosity, improving the conductive performance and antibacterial effect, being applicable to high-performance solar cell conductive silver paste, and significantly improving the photoelectric conversion efficiency.

[0042] 3. The porous hollow spherical silver powder prepared by the present invention has significantly improved conductivity, antibacterial property, and electromagnetic shielding property. Especially in the application of solar cell conductive silver paste, it significantly improves the battery efficiency and stability. The prepared submicron hollow silver powder has high sintering activity, and the photoelectric conversion efficiency is increased by 0.18 - 0.32% compared to solid silver powder, and it has good printability and basically no wire breakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is the scanning electron microscope image of the porous hollow spherical silver powder obtained in Example 5 of the present invention.

[0044] Figure 2 This is the scanning electron microscope image of the solid spherical silver powder obtained in Comparative Example 1.

[0045] Figure 3 This is the printed linear contour diagram of the conductive silver paste prepared using the porous hollow spherical silver powder obtained in Example 5.

[0046] Figure 4 This is the printed linear contour diagram of the conductive silver paste prepared using the solid spherical silver powder obtained in Comparative Example 1. Detailed implementation manners

[0047] The technical solutions of the present invention will be illustrated by examples below. The scope of protection claimed by the present invention includes but is not limited to the following examples.

[0048] Example 1

[0049] Preparation of reducing COF material I: Dissolve 1 mol of tris(4 - aldehyde biphenyl)amine and 1 mol of o - phenylenediamine in absolute ethanol, then add 0.1 mol of acetic acid, and then react at 60 °C for 12 h. After the reaction is completed, perform recrystallization to obtain reducing COF material I with an average molecular weight of about 550 g / mol.

[0050] Preparation of silver nitrate solution: Dissolve silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L;

[0051] Preparation of reduction dispersion system: Add reducing COF material I and polyvinylpyrrolidone to deionized water to obtain a reduction dispersion system with a mass concentration of 25% of reducing COF material I and a mass concentration of 1% of polyvinylpyrrolidone.

[0052] First, measure 3 L of the reduction dispersion system and place it in a stirring reactor; then, under the conditions of a temperature of 25 °C and a stirring rate of 450 r / min, slowly drip 1 L of the silver nitrate solution into the reduction dispersion system, and control the dripping rate of the silver nitrate solution so that the time required for the complete addition of the silver nitrate solution to the reduction dispersion system is 30 min; after the silver nitrate solution is dripped, continue to stir and react for 30 min; after the reaction is completed, turn off the stirring and temperature control equipment, filter the reaction system by suction, and wash it 3 times with deionized water to obtain wet silver powder; finally, heat - treat the wet silver powder in a sintering furnace at 200 °C for 1 h to obtain porous hollow spherical silver powder.

[0053] Example 2

[0054] Preparation of Reductive COF Material II: Dissolve 1 mol of tris(4 - aldehyde biphenyl)amine and 1 mol of p - phenylenediamine in absolute ethanol, then add 0.1 mol of acetic acid, and then react at 60 °C for 12 h. After the reaction is completed, perform recrystallization to obtain reductive COF Material II with an average molecular weight of about 550 g / mol.

[0055] Preparation of silver nitrate solution: Dissolve silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L;

[0056] Preparation of reduction dispersion system: Add reductive COF Material II and polyvinylpyrrolidone to deionized water to obtain a reduction dispersion system with a mass concentration of 25% of reductive COF Material II and a mass concentration of 1% of polyvinylpyrrolidone.

[0057] First, measure 3 L of the reduction dispersion system and place it in a stirring reactor; then, at a temperature of 25 °C and a stirring rate of 450 r / min, drip 1 L of the silver nitrate solution into the reduction dispersion system, and control the dripping rate of the silver nitrate solution so that the total time required for the silver nitrate solution to be completely added to the reduction dispersion system is 30 min; after the silver nitrate solution is dripped, continue to stir and react for 30 min; after the reaction is completed, turn off the stirring and temperature control equipment, filter the reaction system by suction, and wash it 3 times with deionized water to obtain wet silver powder; finally, heat - treat the wet silver powder in a sintering furnace at 200 °C for 1 h to obtain porous hollow - spherical silver powder.

[0058] Example 3

[0059] Preparation of Reductive COF Material III: Dissolve 1 mol of tris(4 - aldehyde biphenyl)amine and 1 mol of m - phenylenediamine in absolute ethanol, then add 0.1 mol of acetic acid, and then react at 60 °C for 12 h. After the reaction is completed, perform recrystallization to obtain reductive COF Material III with an average molecular weight of about 550 g / mol.

[0060] Preparation of silver nitrate solution: Dissolve silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L;

[0061] Preparation of reduction dispersion system: Add reductive COF Material III and polyvinylpyrrolidone to deionized water to obtain a reduction dispersion system with a mass concentration of 25% of reductive COF Material III and a mass concentration of 1% of polyvinylpyrrolidone.

[0062] First, measure 3 L of the reduction dispersion system and place it in a stirring reactor; then, under the conditions of a temperature of 25 °C and a stirring rate of 450 r / min, slowly add 1 L of silver nitrate solution to the reduction dispersion system, and control the dropping rate of the silver nitrate solution so that the time taken for the complete addition of the silver nitrate solution to the reduction dispersion system is 30 min; after the addition of the silver nitrate solution, continue stirring and reacting for 30 min; after the reaction is completed, turn off the stirring and temperature control equipment, perform suction filtration on the reaction system, and wash it 3 times with deionized water to obtain wet silver powder; finally, heat-treat the wet silver powder in a sintering furnace at a temperature of 200 °C for 1 h to obtain porous hollow spherical silver powder.

[0063] Example 4

[0064] Preparation of reducing COF material IV: Dissolve 1 mol of tris(4-formylbiphenyl)amine and 1 mol of catechol in absolute ethanol, then add 0.1 mol of acetic acid, and then react at a temperature of 60 °C for 12 h. After the reaction is completed, perform recrystallization to obtain reducing COF material IV with an average molecular weight of about 570 g / mol.

[0065] Preparation of silver nitrate solution: Dissolve silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L;

[0066] Preparation of reduction dispersion system: Add reducing COF material IV and polyvinylpyrrolidone to deionized water to obtain a reduction dispersion system with a mass concentration of reducing COF material IV of 25% and a mass concentration of polyvinylpyrrolidone of 1%.

[0067] First, measure 3 L of the reduction dispersion system and place it in a stirring reactor; then, under the conditions of a temperature of 25 °C and a stirring rate of 450 r / min, slowly add 1 L of silver nitrate solution to the reduction dispersion system, and control the dropping rate of the silver nitrate solution so that the time taken for the complete addition of the silver nitrate solution to the reduction dispersion system is 30 min; after the addition of the silver nitrate solution, continue stirring and reacting for 30 min; after the reaction is completed, turn off the stirring and temperature control equipment, perform suction filtration on the reaction system, and wash it 3 times with deionized water to obtain wet silver powder; finally, heat-treat the wet silver powder in a sintering furnace at a temperature of 200 °C for 1 h to obtain porous hollow spherical silver powder.

[0068] Example 5

[0069] Preparation of reducing COF material V: Dissolve 1 mol of tris(4-formylbiphenyl)amine and 1 mol of hydroquinone in absolute ethanol, then add 0.1 mol of acetic acid, and then react at a temperature of 60 °C for 12 h. After the reaction is completed, perform recrystallization to obtain reducing COF material V with an average molecular weight of about 570 g / mol.

[0070] Preparation of silver nitrate solution: Dissolve silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L;

[0071] Preparation of reduction dispersion system: Add reducing COF material V and polyvinylpyrrolidone to deionized water to obtain a reduction dispersion system with a mass concentration of 25% of reducing COF material V and a mass concentration of 1% of polyvinylpyrrolidone.

[0072] First, measure 3 L of the reduction dispersion system and place it in a stirring reactor; then, under the conditions of a temperature of 25 °C and a stirring rate of 450 r / min, slowly add 1 L of the silver nitrate solution to the reduction dispersion system, controlling the dropping rate of the silver nitrate solution so that the total time taken for the complete addition of the silver nitrate solution to the reduction dispersion system is 30 min; after the addition of the silver nitrate solution, continue stirring and reacting for 30 min; after the reaction is completed, turn off the stirring and temperature control equipment, perform suction filtration on the reaction system, and wash it 3 times with deionized water to obtain wet silver powder; finally, heat-treat the wet silver powder in a sintering furnace at 200 °C for 1 h to obtain porous hollow spherical silver powder.

[0073] Example 6

[0074] Preparation of reducing COF material VI: Dissolve 1 mol of tris(4-formylbiphenyl)amine and 1 mol of resorcinol in absolute ethanol, then add 0.1 mol of acetic acid, and then react at 60 °C for 12 h. After the reaction is completed, perform recrystallization to obtain reducing COF material V with an average molecular weight of about 570 g / mol.

[0075] Preparation of silver nitrate solution: Dissolve silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L;

[0076] Preparation of reduction dispersion system: Add reducing COF material VI and polyvinylpyrrolidone to deionized water to obtain a reduction dispersion system with a mass concentration of 25% of reducing COF material VI and a mass concentration of 1% of polyvinylpyrrolidone.

[0077] First, measure 3 L of the reduction dispersion system and place it in a stirring reactor; then, under the conditions of a temperature of 25 °C and a stirring rate of 450 r / min, slowly add 1 L of the silver nitrate solution to the reduction dispersion system, controlling the dropping rate of the silver nitrate solution so that the total time taken for the complete addition of the silver nitrate solution to the reduction dispersion system is 30 min; after the addition of the silver nitrate solution, continue stirring and reacting for 30 min; after the reaction is completed, turn off the stirring and temperature control equipment, perform suction filtration on the reaction system, and wash it 3 times with deionized water to obtain wet silver powder; finally, heat-treat the wet silver powder in a sintering furnace at 200 °C for 1 h to obtain porous hollow spherical silver powder.

[0078] Example 7

[0079] Repeat Example 2, except that the molar ratio of tris(4-formylbiphenyl)amine to p-phenylenediamine is 1.5:1.

[0080] Example 8

[0081] Repeat Example 2, except that the molar ratio of tris(4-formylbiphenyl)amine to p-phenylenediamine is 0.8:1.

[0082] Example 9

[0083] Repeat Example 2, except that the obtained porous hollow spherical silver powder is subjected to surface coating treatment. The coating agent is an isopropanol solution of stearic acid with a concentration of 8%. After the coating treatment is completed, it is baked in a vacuum drying oven at 70 °C for 4 h. Then, it is subjected to crushing treatment using an air flow crusher, and then ultrasonically vibrated and sieved (400-mesh sieve) to obtain the coated porous hollow spherical silver powder.

[0084] Example 10

[0085] Repeat Example 2, except that the obtained porous hollow spherical silver powder is subjected to surface coating treatment. The coating agent is an isopropanol solution of oleic acid with a concentration of 10%. After the coating treatment is completed, it is baked in a vacuum drying oven at 75 °C for 3.5 h. Then, it is subjected to crushing treatment using an air flow crusher, and then ultrasonically vibrated and sieved (400-mesh sieve) to obtain the coated porous hollow spherical silver powder.

[0086] Example 11

[0087] Repeat Example 2, except that the temperature during the stirring reaction is 30 °C and the stirring rate is 400 r / min.

[0088] Example 12

[0089] Repeat Example 2, except that the sintering temperature is 240 °C and the sintering duration is 1.5 h.

[0090] Example 13

[0091] Repeat Example 2, except that the time taken for the complete addition of the silver nitrate solution to the reduction dispersion system is 40 min.

[0092] Example 14

[0093] Repeat Example 2, except that the reducing COF material IV and polyvinylpyrrolidone are added to deionized water to obtain a reduction dispersion system with a mass concentration of the reducing COF material IV of 20% and a mass concentration of polyvinylpyrrolidone of 1.2%.

[0094] Comparative Example 1

[0095] Preparation of silver nitrate solution: Dissolve silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 2 mol / L;

[0096] Preparation of reduction dispersion system: Add citric acid and polyvinylpyrrolidone to deionized water to obtain a reduction dispersion system with an ascorbic acid concentration of 0.67 mol / L and a polyvinylpyrrolidone concentration of 0.17 mol / L.

[0097] First, measure 3 L of the reduction dispersion system and place it in a stirring reactor; then, at a temperature of 25 °C and a stirring rate of 450 r / min, slowly drip 1 L of the silver nitrate solution into the reduction dispersion system, and control the dripping rate of the silver nitrate solution so that the total time required for the complete addition of the silver nitrate solution to the reduction dispersion system is 30 min; after the addition of the silver nitrate solution, continue stirring and reacting for 30 min; after the reaction is completed, turn off the stirring and temperature control equipment, perform suction filtration on the reaction system, and wash it 3 times with deionized water. Finally, bake it in a vacuum drying oven at 75 °C for 4 h to obtain solid spherical silver powder.

[0098] The porous hollow spherical silver powders prepared in Examples 1 - 8 and the solid spherical silver powder prepared in Comparative Example 1 were tested, and the test results are shown in the following table:

[0099]

[0100] In the present invention, the specific surface area and tapped density were tested according to the provisions of GB / T 1774 - 2009, the thermal loss was tested according to GB / T 5150, the particle size distribution was tested according to GB / T 19077 - 2016, and the hollowness was calculated by observing with a scanning electron microscope.

[0101] Application examples

[0102] The porous hollow spherical silver powders prepared in Examples 1 - 8 and the solid spherical silver powder prepared in Comparative Example 1 were respectively formulated into conductive silver pastes at the same ratio: the silver powder content was 90%, the glass powder content was 2%, and the organic carrier content was 8%. After the paste was stirred evenly, it was rolled 5 times with a three-roll mill to make the fineness of the paste meet the standard (≤6 μm). By adjusting the viscosity of the organic carrier, the viscosity of each paste was controlled to be basically the same. Each paste was printed on a Perc-se silicon wafer with a narrow linewidth screen printing plate. After the solar cell was sintered in a sintering furnace and the temperature dropped to room temperature, the electrical performance data was tested. Among them, the organic carrier was composed of 3% ethyl cellulose, 2% polyamide wax thixotropic agent, 4% dispersant TDO, and 91% mixed solvent (ethyl acetate: butyl carbitol = 2:1).

[0103] The electrical performance data and printing conditions of each silver powder are shown in the following table:

[0104]

[0105] As can be seen from the above table, the paste made from the porous hollow spherical silver powder in Examples 1-8 of the present invention has an efficiency improvement of 0.18-0.32% compared to the paste made from the solid silver powder in Comparative Example 1, which is a significant improvement on crystalline silicon solar photovoltaic wafers. The paste made from the porous hollow spherical silver powder in Examples 1-8 has basically no broken lines during printing, which is significantly less than the paste made from the solid silver powder in Comparative Example 1. This is mainly due to the smaller particle size of the porous hollow spherical silver powder, which is beneficial for printing, and the paste prepared has a higher fill factor. In addition, the Isc (short-circuit current) of the paste made from the porous hollow spherical silver powder in Examples 1-8 is significantly improved compared to the paste made from the solid silver powder in Comparative Example 1, which benefits from the porous hollow structure of the silver powder.

[0106] In the embodiments of the present invention, the sources of some substances are as follows: tris(4-formylbiphenyl)amine is purchased from Beijing Huawei RuiKe Chemical Co., Ltd.; o-phenylenediamine, p-phenylenediamine, and m-phenylenediamine are all purchased from Nanjing Jirui Chemical Co., Ltd.; catechol, hydroquinone, and resorcinol are all purchased from Langfang Qianyao Technology Co., Ltd.; oleic acid is purchased from Shanghai Lishen Chemical Industry, with a purity of 99.5%. Stearic acid is provided by Guangzhou Gongxin Chemical Industry, with a purity of 98.8%. Isopropyl alcohol is purchased from Shandong Qilu Chemical Industry, with a purity of 99.7%. The experimental water is deionized water, with a purity reaching 99.9%. Citric acid is purchased from Jiangsu Suhua Group, with a purity of 99.5%. Polyvinylpyrrolidone (CAS: 9003-39-8) is purchased from Gongbik New Material Technology Co., Ltd., PVP-K25, with a number average molecular weight of 32000, resin content (wt%) > 95, viscosity (mps.s-25°C / 5% ap) 1.7-2.1, pH 3.0-7.0, K value 22.4-27.0, and purity 99.3%. Polyvinyl alcohol is purchased from Anhui Longyang Environmental Protection Technology Co., Ltd. Anhydrous ethanol, with a purity of 99.9%, is purchased from Hunan Xianghua Biotechnology Co., Ltd. Acetic acid, with a purity of 99.9%, is purchased from Jinan Chengyi Jia Chemical Technology Co., Ltd. Each raw material has undergone strict quality inspections to ensure the accuracy and reliability of the experimental results.

Claims

1. A method for preparing porous hollow spherical silver powder, characterized in that: The preparation method comprises the following steps: S1: dissolving a silver salt in water to obtain a silver salt solution, adding a reducing COF material and a dispersant into the water to obtain a reducing dispersion system; then adding the silver salt solution into the reducing dispersion system to react, and after the reaction is completed, performing solid-liquid separation to obtain wet silver powder; S2: Sintering the wet silver powder to obtain porous hollow spherical silver powder; Preferably, the preparation method further comprises: S3: using a coating liquid to coat the surface of the porous hollow spherical silver powder, and after coating, sequentially performing drying treatment and optionally breaking up treatment to obtain coated porous hollow spherical silver powder.

2. The preparation method according to claim 1, characterized in that: In step S1, the reducing COF material is prepared by condensing tris(4-formylbiphenyl)amine with phenylenediamine or hydroquinone; preferably, the phenylenediamine is p-phenylenediamine, o-phenylenediamine and / or m-phenylenediamine, and the hydroquinone is catechol, pyrocatechol and / or resorcinol; Preferably, the condensation reaction is specifically as follows: dissolving tris(4-formylbiphenyl)amine and phenylenediamine (or hydroquinone) in an organic solvent (preferably anhydrous ethanol), adding an acid catalyst (preferably acetic acid), and then reacting at a temperature of 60-80°C for 5-24h (preferably at a temperature of 65-75°C for 10-20h), and after the reaction is completed, the target product can be obtained by recrystallization; the average molecular weight of the obtained product is 500-700g / mol; preferably, the molar ratio of tris(4-formylbiphenyl)amine to aniline or phenol during the reaction is 0.5-2:1, preferably 0.8-1.5:

1.

3. The preparation method according to claim 1, characterized in that: In step S1, the silver salt is silver nitrate; and / or In step S1, the dispersant is one or more of polyvinyl pyrrolidone, polyvinyl alcohol, and gelatin.

4. The preparation method according to any one of claims 1 to 3, characterized in that: In step S1, the concentration of silver salt in the silver salt solution is 0.5-5 mol / L, preferably 1-3 mol / L; the mass concentration of the reducing COF material in the reducing dispersion system is 12-45%, preferably 20-35%; The mass concentration of the dispersant in the reducing dispersion system is 0.5-5%, preferably 1-3%; Preferably, the volume ratio of the silver salt solution to the reducing dispersion system is 1:1-10, preferably 1:2-8.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In step S1, the reaction is a stirring reaction; the temperature of the stirring reaction is 20-60° C., preferably 25-50° C.; the duration of the stirring reaction is 20-120 min, preferably 30-90 min; the stirring rate during the stirring reaction is 200-800 r / min, preferably 300-600 r / min; Preferably, the silver salt solution is added dropwise, and the duration of the silver salt solution addition dropwise is 15 to 60 minutes, preferably 20 to 50 minutes.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In step S2, the sintering temperature is 150-500°C, preferably 200-400°C; the sintering time is 0.5-5h, preferably 1-3h.

7. The preparation method according to any one of claims 1 to 6, characterized in that: In step S3, the coating liquid includes a coating agent and a solvent; the coating agent is one or more of stearic acid, oleic acid, and amino silicone oil; the solvent is ethanol and / or isopropanol; preferably, the mass concentration of the coating agent in the coating liquid is 1-20%, preferably 5-15%.

8. The preparation method according to any one of claims 1 to 7, characterized in that: In step S3, the drying process is drying at a temperature of 60-85° C. for 1-12 hours, preferably vacuum drying at a temperature of 65-80° C. for 2-6 hours; and / or In step S3, the breaking up process is firstly air flow crushing process and then ultrasonic vibration screening process.

9. A porous hollow spherical silver powder, characterized in that: The porous hollow spherical silver powder is prepared according to the preparation method according to any one of claims 1-8.

10. A porous hollow spherical silver powder or a use of the porous hollow spherical silver powder prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The porous hollow spherical silver powder is applied to the fields of conductive coatings, antibacterial materials and electromagnetic shielding, and is preferably used in conductive silver paste for solar cells.

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