Spherical silver powder for photovoltaic silver paste as well as preparation method and application of spherical silver powder

Abstract

The invention belongs to the technical field of solar photovoltaic panel conductive materials, and particularly relates to spherical silver powder for photovoltaic silver paste and a preparation method and application of the spherical silver powder. The preparation method of the spherical silver powder comprises the steps that (1) silver ions, a reducing agent and a dispersing agent are mixed and react to obtain reaction liquid, and polypropylene sodium salt (the molecular weight is 2000) is selected as the dispersing agent; and (2) centrifuging the reaction liquid to obtain a solid, and carrying out ball milling on the solid to obtain the spherical silver powder for the photovoltaic silver paste. The spherical silver powder is excellent in conductivity, and the resistivity can be as low as 7.4 mu omega.cm.

Description

Technical Field

[0001] The invention belongs to the technical field of conductive materials for solar photovoltaic panels, and specifically provides spherical silver powder for photovoltaic silver paste, a preparation method thereof, and an application thereof. Background Art

[0002] As the global consensus on high-quality development and sustainable development of renewable energy deepens, the photovoltaic industry, as a core area of ​​new energy, is experiencing rapid growth. Solar cells and photovoltaic silver pastes are key materials for photovoltaic modules, and their performance directly affects the photoelectric conversion efficiency. Silver powder, as the core conductive filler of photovoltaic silver paste, plays a decisive role in the conductivity, printability and electrical properties of the paste. The present invention belongs to the field of electronic conductive materials technology, and specifically relates to a technology for preparing high-purity, high-conductivity spherical silver powder by optimizing the use of dispersants and reaction conditions through a chemical reduction process. The product can be widely used in the fields of solar cell pastes, electronic devices, catalytic materials, and the like.

[0003] Currently, the preparation technologies for spherical silver powder mainly include three categories: chemical reduction, physical vapor deposition, and high-temperature melting. Among them, the chemical reduction method is a more commonly used method because it does not rely on high-energy heat sources or complex equipment (such as the high-maintenance equipment of the physical vapor deposition method, the high-energy heat source and inert gas protection of the plasma melting method), and the process cost is significantly lower than the latter two. However, the current chemical reduction method requires a dispersant to prevent agglomeration, and the amount of dispersant used is relatively large, resulting in the silver powder purity generally being less than 99.5%, seriously affecting conductivity. Summary of the Invention

[0004] In the present invention, a dispersant polypropylene sodium salt 2000 is screened out based on a chemical reduction method. The dispersant polypropylene sodium salt 2000 can reduce agglomeration and improve conductive performance when used in a relatively small amount (0.1wt%-0.2wt%).

[0005] In order to achieve the above object, the present invention can adopt the following technical solutions:

[0006] One aspect of the present invention provides a method for preparing spherical silver powder for photovoltaic silver paste, the preparation method comprising:

[0007] (1) silver ions, a reducing agent, and a dispersant are mixed to react to obtain a reaction solution, wherein the dispersant is polypropylene sodium salt, and the molecular weight of the polypropylene sodium salt is 2000;

[0008] (2) The reaction solution is centrifuged to obtain a solid, and the solid is ball-milled to obtain spherical silver powder for photovoltaic silver paste.

[0009] Preferably, in the above preparation method, the reducing agent is selected from one or more of ascorbic acid, sodium borohydride or hydrazine hydrate.

[0010] More preferably, in the above preparation method, the added amount of the dispersant is 0.1 wt%-0.2 wt% of the total mass of the silver ions and the reducing agent.

[0011] Preferably, in the above preparation method, the reaction solution is centrifuged and then washed and dried to obtain spherical silver powder for photovoltaic silver paste.

[0012] More preferably, in the above preparation method,

[0013] The cleaning process includes: 3 washes with deionized water, 2 washes with anhydrous ethanol, and 1 wash with acetone; centrifugation is performed after each wash; and / or

[0014] The drying process includes: drying at 40°C for 2 hours, drying at 60°C for 4 hours, and drying at 80°C for 6 hours.

[0015] Preferably, in the above preparation method, sieving is performed after ball milling, and the powder sieved out with a particle size of ≤1 nm is the spherical silver powder for photovoltaic silver paste.

[0016] In another aspect, the present invention provides spherical silver powder for photovoltaic silver paste, which is prepared by the above preparation method.

[0017] In another aspect, the present invention provides a photovoltaic front silver paste, which includes the above-mentioned spherical silver powder for photovoltaic silver paste.

[0018] Another aspect of the present invention provides a photovoltaic cell comprising the photovoltaic front silver paste of the present invention.

[0019] The beneficial effects of the present invention include: the silver powder prepared by the preparation method of the spherical silver powder for photovoltaic silver paste provided by the present invention has excellent electrical conductivity and the resistivity can be as low as 7.4 μΩ·cm. DETAILED DESCRIPTION

[0020] The examples are provided to better illustrate the present invention, but are not intended to limit the present invention to the examples. Therefore, non-essential improvements and adjustments to the embodiments made by those skilled in the art based on the above-mentioned invention still fall within the scope of protection of the present invention.

[0021] The terms used herein are only used to describe specific embodiments and are not intended to limit the present disclosure. Unless the context has a significantly different meaning, expressions in the singular include expressions in the plural. As used herein, it should be understood that terms such as "include", "have", "comprise" and the like are intended to indicate the presence of features, numbers, operations, components, parts, elements, materials or combinations. The terms of the present invention are disclosed in the specification and are not intended to exclude the possibility that one or more other features, numbers, operations, components, parts, elements, materials or combinations thereof may exist or may be added. As used herein, " / " may be interpreted as "and" or "or", depending on the circumstances.

[0022] In a first aspect, an embodiment of the present invention provides a method for preparing spherical silver powder for photovoltaic silver paste, the preparation method comprising:

[0023] (1) silver ions, a reducing agent, and a dispersant are mixed to react to obtain a reaction solution, wherein the dispersant is polypropylene sodium salt, and the molecular weight of the polypropylene sodium salt is 2000;

[0024] (2) The reaction solution is centrifuged to obtain a solid, and the solid is ball-milled to obtain spherical silver powder for photovoltaic silver paste.

[0025] It should be noted that polypropylene sodium salt 2000 was selected as a dispersant in the present invention, which can reduce agglomeration and improve conductivity even with a relatively low dosage (0.1wt%-0.2wt%). Its effect is superior to other dispersants, such as polyethylene glycol (PEG) 1000, polyvinyl pyrrolidone (PVP), or sodium dodecyl sulfate (SDS). It should be understood that the reaction solution obtained by the mixed reaction of silver ions, reducing agent, and dispersant is reacted in a solution environment, and the medium of the solution environment is preferably deionized water.

[0026] In some specific examples, in the above preparation method, the reducing agent is selected from one or more of ascorbic acid, sodium borohydride or hydrazine hydrate.

[0027] It should be noted that the reducing agent in the present invention is well known in the art, such as one or more of ascorbic acid, sodium borohydride, or hydrazine hydrate. Among them, ascorbic acid is preferred. The resistivity of the silver powder prepared using ascorbic acid as a reducing agent is lower than that of the silver powder prepared using sodium borohydride or hydrazine hydrate as a reducing agent.

[0028] In some specific examples, in the above preparation method, the amount of the dispersant added is 0.1 wt%-0.2 wt% of the total mass of the silver ions and the reducing agent.

[0029] It should be noted that polypropylene sodium salt 2000 is selected as a dispersant in the present invention, which can reduce agglomeration and improve conductive properties when used in a relatively small amount (0.1wt%-0.2wt%).

[0030] In some specific examples, in the above preparation method, the reaction solution is centrifuged and then washed and dried to obtain spherical silver powder for photovoltaic silver paste.

[0031] It should be noted that in the present invention, the reaction solution can be preferentially centrifuged and then washed and dried to increase the purity of the spherical silver powder. In addition, washing and drying are conventional operations in the art and have no special meaning.

[0032] In some specific examples, in the above preparation method,

[0033] The cleaning process includes: 3 washes with deionized water, 2 washes with anhydrous ethanol, and 1 wash with acetone; centrifugation is performed after each wash; and / or

[0034] The drying process includes: drying at 40°C for 2 hours, drying at 60°C for 4 hours, and drying at 80°C for 6 hours.

[0035] It should be noted that the cleaning and drying methods in the present invention may preferably be the above-mentioned cleaning and drying methods, which can significantly improve the purity of the spherical silver powder and improve the electrical properties.

[0036] In some specific examples, in the above preparation method, ball milling is followed by screening, and the powder with a particle size of ≤1 nm is spherical silver powder for photovoltaic silver paste.

[0037] It should be noted that in the present invention, the powder with a diameter of preferably ≤1 nm is the spherical silver powder for photovoltaic silver paste, and its conductive performance is slightly better than the spherical silver powder for photovoltaic silver paste that has not been screened.

[0038] In a second aspect, an embodiment of the present invention provides a spherical silver powder for photovoltaic silver paste, which is prepared by the above-mentioned preparation method.

[0039] It should be noted that the spherical silver powder for photovoltaic silver paste prepared by the preparation method of the present invention has excellent electrical conductivity, and the resistivity can be as low as 7.4 μΩ·cm.

[0040] In a third aspect, an embodiment of the present invention provides a photovoltaic front silver paste, which includes the above-mentioned spherical silver powder for photovoltaic silver paste.

[0041] It should be noted that the spherical silver powder used in the photovoltaic silver paste of the present invention can be prepared into photovoltaic front silver paste. The preparation method is well known in the art, and those skilled in the art can select it according to specific needs.

[0042] In a fourth aspect, an embodiment of the present invention provides a photovoltaic cell comprising the photovoltaic front silver paste of the present invention.

[0043] It should be noted that the photovoltaic front silver paste in the present invention can be coated on the surface of a TOPCOn cell to prepare a photovoltaic cell, and then to prepare a photovoltaic cell.

[0044] In order to better understand the present invention, the content of the present invention is further explained below with reference to specific examples, but the content of the present invention is not limited to the following examples.

[0045] Preparation Example

[0046] Example 1

[0047] (1) dissolving silver nitrate in deionized water to prepare a silver nitrate solution with a concentration of 1 mol / L; dissolving ascorbic acid in deionized water to prepare an ascorbic acid solution with a concentration of 1 mol / L;

[0048] (2) Heat the silver nitrate solution and ascorbic acid solution to 60°C respectively;

[0049] (3) During the stirring process, 1 L of ascorbic acid solution was slowly added to 1 L of silver nitrate solution; then, 0.1 wt % of polypropylene sodium salt (molecular weight 2000) was added during the reaction, and the pH was adjusted to 3 with HNO 3 , and the reaction was carried out to obtain a reaction solution;

[0050] (4) separating the reaction solution by centrifugal separation equipment to obtain silver powder at a centrifugal speed of 10,000 r / min for 20 min;

[0051] (5) After centrifugation, the silver powder was washed several times with deionized water to remove impurities and dispersant remaining on the surface; the washing process included: 3 times with deionized water (50°C, solid-liquid ratio 1:5) → 2 times with anhydrous ethanol (solid-liquid ratio 1:3) → 1 time with acetone (solid-liquid ratio 1:2), and centrifugation was performed after each washing (10,000 r / min, 20 min);

[0052] (6) Dry the cleaned silver powder in a vacuum drying oven (vacuum degree -0.098 MPa) to remove moisture. The drying process is: 40°C (2 h) → 60°C (4 h) → 80°C (6 h);

[0053] (7) The dried silver powder is processed using a ball mill to obtain spherical silver powder; wherein the diameter ratio of the grinding balls is 1:2:4, the rotation speed is 170 rpm / min, and the ball-to-material ratio is 20:1.

[0054] (8) Spherical silver powder is screened out using a screening device to obtain spherical silver powder with a particle size of ≤1 nm.

[0055] Example 2

[0056] Example 2 is substantially the same as Example 1. The difference between Example 2 and Example 1 is that step (8) is not performed in Example 2. The other steps are the same as Example 1, and spherical silver powder is prepared.

[0057] Example 3

[0058] Example 3 is substantially the same as Example 1. The difference between Example 3 and Example 1 is that the reducing agent in Example 3 is different from that in Example 1, that is, sodium borohydride (NaBH4) is used in Example 3 to replace the ascorbic acid in Example 1. The other steps are the same as in Example 1, and spherical silver powder is prepared.

[0059] Example 4

[0060] Example 4 is substantially the same as Example 1. The difference between Example 4 and Example 1 is that the reducing agent in Example 4 is different from that in Example 1, that is, hydrazine hydrate (N2H4H2O) is used in Example 4 to replace the ascorbic acid in Example 1. The other steps are the same as in Example 1, and spherical silver powder is prepared.

[0061] Example 5

[0062] Example 5 is substantially the same as Example 1, and the difference between Example 5 and Example 1 is that the amount of dispersant added in Example 5 is different from that in Example 1, and the amount of dispersant added in Example 5 (sodium salt of polypropylene (molecular weight of 2000)) is 0.2 wt%.

[0063] Comparative Example 1

[0064] Comparative Example 1 is substantially the same as Example 1, except that the dispersant in Comparative Example 1 is different from that in Example 1, that is, polyethylene glycol (PEG) (molecular weight 1000) is used in Comparative Example 1 to replace polypropylene sodium salt (molecular weight 2000) in Example 1. Other steps are the same as in Example 1 to prepare spherical silver powder.

[0065] Comparative Example 2

[0066] Comparative Example 2 is substantially the same as Example 1. The difference between Comparative Example 2 and Example 1 is that the dispersant in Comparative Example 2 is different from that in Example 1, that is, polyvinylpyrrolidone (PVP) is used in Comparative Example 2 to replace the sodium salt of polypropylene (molecular weight of 2000) in Example 1. Other conditions are the same as in Example 1 to prepare spherical silver powder.

[0067] Comparative Example 3

[0068] Comparative Example 3 is substantially the same as Example 1. The difference between Comparative Example 3 and Example 1 is that the dispersant in Comparative Example 2 is different from that in Example 1, that is, sodium lauryl sulfate (SDS) is used in Comparative Example 3 to replace the sodium salt of polypropylene (molecular weight of 2000) in Example 1. Other conditions are the same as in Example 1 to prepare spherical silver powder.

[0069] Comparative Example 4

[0070] Comparative Example 4 is substantially the same as Example 1. The difference between Comparative Example 4 and Example 1 is that the dispersant in Comparative Example 2 is different from that in Example 1, that is, sodium polypropylene salt (molecular weight of 1500) is used in Comparative Example 3 to replace sodium polypropylene salt (molecular weight of 2000) in Example 1. Other conditions are the same as in Example 1 to prepare spherical silver powder.

[0071] Comparative Example 5

[0072] Comparative Example 5 is substantially the same as Example 1. The difference between Comparative Example 5 and Example 1 is that the dispersant in Comparative Example 2 is different from that in Example 1, that is, sodium polypropylene salt (molecular weight 3000) is used in Comparative Example 5 to replace sodium polypropylene salt (molecular weight 2000) in Example 1. Other steps are the same as in Example 1 to prepare spherical silver powder.

[0073] Conductivity test

[0074] In the following test, the preparation method of photovoltaic silver paste includes: mixing conductive silver paste and dopant, and stirring and mixing by a disperser to obtain photovoltaic silver paste; wherein the conductive silver paste includes: 45 parts by weight of spherical silver powder, 8 parts by weight of bisphenol A epoxy resin, 2 parts by weight of imidazole curing agent and 10 parts by weight of DBE solvent; the dopant includes: phosphorus oxide with an average particle size of 100 nm and metal indium particles with an average particle size of 100 nm; the mass of phosphorus oxide is 0.5% of the mass of the conductive silver paste, and the mass of the metal indium particles is 0.5% of the mass of the conductive silver paste.

[0075] The spherical silver powders prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were used to prepare different photovoltaic silver pastes according to the above-described photovoltaic silver paste preparation method. The pastes were then printed on the surface of TOPCon cells and dried and cured at 200°C for 30 minutes. The resistivity and ohmic contact properties of the silver powders prepared in Examples and Comparative Examples were tested using an ST2285C benchtop four-probe tester. The resistivity values ​​obtained are shown in Table 1 below.

[0076] Table 1 Resistivity of Examples and Comparative Examples

[0077] Example / Comparative Example Resistivity (μΩ·cm) Example 1 7.4 Example 2 8.4 Example 3 7.9 Example 4 8.0 Example 5 7.6 Comparative Example 1 15.6 Comparative Example 2 18.3 Comparative Example 3 14.7 Comparative Example 4 15.2 Comparative Example 5 14.3

[0078] It can be seen from Table 1 above that the resistivity of Examples 1 to 4 is significantly lower than that of Comparative Examples 1 to 5. Specifically:

[0079] First, by comparing Example 1 with Comparative Examples 1 to Comparative Examples 3, it can be seen that the resistivity of the silver powders prepared with different dispersants is significantly different. The resistivity of the silver powder prepared by using sodium polypropylene (molecular weight 2000) as a dispersant in the present invention is significantly lower than the resistivity of the silver powders prepared with polyethylene glycol (PEG) 1000, polyvinyl pyrrolidone (PVP) and sodium dodecyl sulfate (SDS);

[0080] Secondly, by comparing Example 1 with Comparative Examples 4 to 5, it can be seen that the resistivity of silver powder prepared from sodium polypropylene salts with different molecular weights is different. If the molecular weight is too small, the electrostatic repulsion and steric hindrance between the particles are insufficient, the silver powder particles are easily agglomerated due to van der Waals forces, and the uniformity and long-term stability of the dispersion system are reduced; if the molecular weight is too large, the viscosity in the solution is high, which may hinder its uniform diffusion and adsorption on the surface of the silver powder particles, resulting in uneven dispersion; therefore, in the present invention, sodium polypropylene salt with a molecular weight of 2000 is selected.

[0081] Third, by comparing Example 1 with Example 2, it can be seen that the conductivity of the spherical silver powder with a particle size of ≤1 nm is slightly better than that of the spherical silver powder without particle size screening;

[0082] Fourthly, by comparing Example 1 with Examples 3 to 4, it can be seen that the conductivity of silver powder prepared with different reducing agents is also different. In the present invention, ascorbic acid is the preferred reducing agent, followed by sodium borohydride, and then hydrazine hydrate.

[0083] Fifth, by comparing Example 1 with Example 5, it can be seen that the silver powder prepared when the dispersant dosage in the present invention is 0.1 wt %-0.2 wt % can improve the conductive performance.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be covered by the scope of the claims of the present invention.

Claims

1. A method for preparing spherical silver powder for photovoltaic silver paste, characterized in that: include: (1) silver ions, a reducing agent, and a dispersant are mixed to react to obtain a reaction solution, wherein the dispersant is polypropylene sodium salt, and the molecular weight of the polypropylene sodium salt is 2000; (2) The reaction solution is centrifuged to obtain a solid, and the solid is ball-milled to obtain spherical silver powder for photovoltaic silver paste.

2. The preparation method according to claim 1, characterized in that The reducing agent is selected from one or more of ascorbic acid, sodium borohydride or hydrazine hydrate.

3. The preparation method according to claim 1 or 2, characterized in that The added amount of the dispersant is 0.1wt%-0.2wt% of the total mass of the silver ions and the reducing agent.

4. The preparation method according to claim 1 or 2, characterized in that The reaction solution is centrifuged, washed, and dried to obtain spherical silver powder for photovoltaic silver paste.

5. The preparation method according to claim 4, characterized in that The cleaning process includes: 3 washes with deionized water, 2 washes with anhydrous ethanol, and 1 wash with acetone; centrifugation is performed after each wash; and / or The drying process includes: drying at 40°C for 2 hours, drying at 60°C for 4 hours, and drying at 80°C for 6 hours.

6. The preparation method according to claim 1, 2 or 5, characterized in that: After ball milling, the powder is screened out and the powder with a particle size of ≤1nm is the spherical silver powder for photovoltaic silver paste.

7. Spherical silver powder for photovoltaic silver paste, characterized in that: Prepared by the preparation method according to any one of claims 1 to 6.

8. Photovoltaic front silver paste, characterized in that: Including the spherical silver powder for photovoltaic silver paste as described in claim 7.

9. Photovoltaic cell, characterized in that: Including the photovoltaic front silver paste as described in claim 8.