Highly dispersible composite silver powder and method for preparing the same

Abstract

The application discloses a kind of high dispersibility composite silver powder and preparation method thereof, the high dispersibility composite silver powder, in silver powder 0.1-1% metal or non-metal element compound is added to silver powder quality, composite silver powder dispersibility is good, particle size is 1.0-1.8 μm, it is 5.5-6.5 g / cm 3 For preparing front electrode slurry can effectively improve the conversion efficiency of photovoltaic cell, in the process of front electrode sintering, the metal or non-metal in the high dispersibility composite silver powder can effectively dissolve silver, and uniformly precipitate silver grains at silver-silicon contact surface, form conductive channel, improve ohmic contact, reduce Rs series resistance, so as to improve the photoelectric conversion efficiency of crystalline silicon cell, and the overall efficiency is stable.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and specifically to a highly dispersed and highly concentrated silver powder for the silver paste of the front electrode of a photovoltaic crystalline silicon solar cell, and its preparation method. More particularly, it relates to a highly dispersed composite silver powder and its preparation method. Background Technology

[0002] Currently, the photovoltaic industry is experiencing explosive growth. As the photoelectric conversion efficiency of photovoltaic cells continues to improve, the power output of end-use modules is also constantly increasing. From the perspective of electrode materials, improving the conversion efficiency of photovoltaic cells involves two aspects: firstly, reducing the contact resistance of silver silicon to minimize the loss caused by the potential difference generated by crystalline silicon cells; and secondly, reducing the opening of the grid lines on the printing screen to reduce the shading area of ​​the grid lines, i.e., the larger the aspect ratio of the printed grid lines, the better.

[0003] Silver paste for the front electrode, used as the electrode material for the light-receiving surface of photovoltaic cells, is a key factor in improving the photoelectric conversion efficiency of photovoltaic cells. Traditional front electrode silver paste is made by mixing and rolling silver powder, glass powder, and organic carrier. However, due to the difference in specific gravity between glass powder and silver powder, the distribution of components in the silver paste is uneven. This results in varying degrees of corrosion of the battery substrate by the glass powder during the sintering process, leading to large fluctuations in the photoelectric conversion efficiency of the battery cells, and an overall low efficiency.

[0004] Current research includes, for example, Chinese patent application number 201110066153.2, "Highly Dispersible Nano-Silver and High-Performance Conductive Adhesive," which describes a high-performance conductive adhesive prepared by the following method: uniformly mixing epoxy resin curing agent and accelerator; uniformly mixing highly dispersed nano-silver with epoxy resin; and adding the mixture of epoxy resin curing agent and accelerator dropwise to the mixed components of highly dispersed nano-silver and epoxy resin being mixed at 10–25°C for 3–10 hours to obtain the high-performance conductive adhesive. The nano-silver of this invention can be fixed in epoxy resin and exhibits good dispersibility within it. Using it to prepare the conductive adhesive can fix the conductive network in the adhesive, improve conductivity, and avoid silver migration during use. This invention uses a combination of four epoxy resins with different functions, solving the defects of insufficient adhesive strength and shear strength in current conductive adhesives.

[0005] With the development of photovoltaic cell technology, the cost per kilowatt-hour is constantly decreasing. In order to improve the light-receiving surface of the front electrode, reduce the shading area, and reduce costs, the opening of the fine line printing screen for the front electrode is getting narrower and narrower, gradually changing from the current 15μm to 10μm. In order to meet the requirements of high-speed, fine grid printing, this places high demands on the dispersibility of silver powder. Summary of the Invention

[0006] To address the above requirements, this invention provides a highly dispersed composite silver powder and its preparation method. When the obtained highly dispersed composite silver powder is used to prepare the front electrode, it exhibits more uniform etching, silver melting, and silver deposition capabilities on the substrate, thereby improving the photoelectric conversion efficiency and stability of crystalline silicon solar cells. Using the highly dispersed composite silver powder obtained by this invention as the front silver paste, the photoelectric conversion efficiency is improved to 0.01-0.06%, mainly reflected in the increase in on-state voltage and the reduction in series resistance. Simultaneously, the proportion of high-efficiency wafers increases by 10.2%, and the welding pull strength is also improved.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] Silver powder is prepared using a wet process by adding a compound of a metallic or non-metallic element, equivalent to 0.5-1% of the silver powder's mass. By adjusting the reaction conditions, the metallic or non-metallic element either replaces the silver powder, coats it, or forms a uniform dispersion with it. The resulting highly dispersible composite silver powder has a particle size of D. 50 1.0-1.8 μm, tapped density 5.5-6.5 g / cm³ 3 .

[0009] A method for preparing highly dispersible composite silver powder includes the following steps:

[0010] S1: Prepare a silver nitrate solution with a concentration of 0.1-2.5 mol / L in mixing tank I, and disperse it at high speed with a dispersion speed of 1200-1800 r / min for 30 min;

[0011] A metal compound is added during the high-speed dispersion and stirring of a silver nitrate solution to obtain a silver nitrate solution containing the metal compound. The amount of the added metal compound is 0.5-1% of the mass of the highly dispersible composite silver powder prepared.

[0012] The metal compound is selected from PbO. 2、 One of Pb₂O₃, Pb₃O₄, Pb(NO₃)₂, and Pb(CH₃COO)₂;

[0013] S2: Prepare the reducing agent solution in mixing tank II and disperse it at high speed. The dispersion and stirring speed is 1200-1800 r / min, and the stirring is carried out for 30 min. Adjust the pH of the reducing solution to 7-9.

[0014] The reducing agent is one of sodium citrate, NaBH4, polyacrylamide, glucose, formaldehyde, ascorbic acid, hydrazine hydrate, and triethanolamine. After being prepared into a reducing agent solution, its concentration and amount added can fully reduce silver nitrate.

[0015] S3: Prepare a dispersant solution with a concentration of 0.5-2 M in the mixing tank III, and disperse it at high speed with a stirring speed of 1200-1800 r / min for 30 min;

[0016] The dispersant is one of polyvinylpyrrolidone, polyacrylamide, citric acid, gum arabic, gelatin, polyvinyl alcohol, sodium dodecyl sulfonate, and polyethylene glycol;

[0017] S4: Add all the reducing agent solution treated in S2 and the dispersant solution treated in S3 into the reactor and mix them thoroughly.

[0018] S5: Add the silver nitrate solution containing the metal compound obtained in S1 to the reaction vessel in S4, and complete the addition within 5-10 minutes. React at 30-50 °C for 10 minutes, and use high-speed dispersion and stirring at a speed of 1200-1800 r / min for 20 minutes. Filter and wash the mixed solution after the reaction to obtain the composite silver powder semi-finished product.

[0019] S6: Add additives to the composite silver powder semi-finished product obtained in S5, disperse, dry, and air-dry to obtain highly dispersible composite silver powder. The amount of additives is 0.1-1% of the mass of the highly dispersible composite silver powder obtained.

[0020] The additive is one of PVA, polyethylene glycol-400, fatty acids, oleic acid, oleylamine, stearic acid amine, palmitic acid, palmitic acid amine, castor oil, and hydrogenated castor oil;

[0021] The highly dispersible composite silver powder exhibits good dispersibility and has a particle size of D. 50 1.0-1.8 μm, tapped density 5.5-6.5 g / cm³ 3 .

[0022] In this invention:

[0023] The optimal concentration of the silver nitrate solution in step S1 is 0.5-2 mol / L, which can prepare highly dispersed composite silver powder with a particle size suitable for use in photovoltaic front electrode silver paste.

[0024] The metal compound mentioned in step S1 is selected from compounds that are soluble in water and form a uniform dispersion in aqueous solution, preferably Pb(CH3COO)2.

[0025] In step S2, the pH of the reducing solution is preferably adjusted to 7-8. The reagents for adjusting the pH are NaOH, KOH, and ammonia, with ammonia being the preferred method for pH adjustment.

[0026] This invention also relates to a highly dispersible composite silver powder, obtained by the above-described method for preparing highly dispersible composite silver powder. The highly dispersible composite silver powder exhibits good dispersibility and has a particle size of D. 50 1.0-1.8μm, tapped density 5.5-6.5g / cm³ 3 .

[0027] This invention also relates to the application of the aforementioned highly dispersed composite silver powder for preparing front electrodes, which can effectively improve the conversion efficiency of photovoltaic cells. Using the highly dispersed composite silver powder obtained by this invention as a front silver paste, the photoelectric conversion efficiency is increased to 0.01-0.06%, mainly reflected in the improvement of the opening voltage and the reduction of the series resistance. At the same time, the proportion of high-efficiency wafers is increased by 10.2%, and the welding pull force is also improved.

[0028] When applied to the preparation of positive silver paste, during the sintering process of the front electrode, the metal or non-metal in this highly dispersed composite silver powder can effectively dissolve silver and uniformly precipitate silver grains at the silver-silicon contact surface, forming a conductive channel, improving ohmic contact, and reducing Rs series resistance, thereby improving the photoelectric conversion efficiency of crystalline silicon cells and ensuring overall efficiency stability.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. The highly dispersed composite silver powder of the present invention can effectively dissolve silver in the metal or non-metal during the sintering process of the front electrode, and uniformly precipitate silver grains on the silver-silicon contact surface to form a conductive channel, improve ohmic contact, reduce Rs series resistance, thereby improving the photoelectric conversion efficiency of crystalline silicon cells.

[0031] 2. The method for preparing highly dispersible composite silver powder according to the present invention involves adding a selected water-soluble metal compound into a reaction vessel. During the chemical reaction of the silver powder, the compound can be uniformly deposited on the surface of the silver powder or uniformly distributed in the silver powder, resulting in highly dispersible composite silver powder with good dispersibility. Attached Figure Description

[0032] Figure 1 This is a scanning electron microscope image of the highly dispersed composite silver powder prepared in Example 1 of the present invention (metal ions are distributed in small particle form).

[0033] Figure 2 This is a scanning electron microscope image of the highly dispersed composite silver powder prepared in Example 2 of the present invention (metal ions are distributed in small particles, with some directly attached to the surface of the silver powder). Detailed Implementation

[0034] The present invention is further described in detail below through embodiments, but these embodiments should not be considered as limitations on the present invention. Unless otherwise specified, the raw materials and equipment used in the embodiments of this application were purchased commercially, and the methods in the embodiments, unless otherwise specified, are conventional methods in the art.

[0035] Example:

[0036] A method for preparing highly dispersible composite silver powder:

[0037] A highly dispersible composite silver powder was prepared using the following ratios and process parameters, and the relevant parameters of the highly dispersible composite silver powder were tested. The ratios and processes for preparing a highly dispersible composite silver powder are shown in Table 1.

[0038] Table 1: Preparation process of highly dispersible composite silver powder in Examples 1-3:

[0039]

[0040] Table 2: Physical parameters of the highly dispersed composite silver powders prepared in Examples 1-3:

[0041]

[0042] Table 2 combined Figure 1 and Figure 2 This indicates that the highly dispersed composite silver powder prepared in Examples 1-3 has a narrow overall particle size distribution, with a maximum particle size D. 50 <1.8μm, D 100 <5μm, good dispersibility.

[0043] Figure 1 This is a scanning electron microscope image of the highly dispersed composite silver powder prepared in Example 1 (metal ions are distributed in small particle form).

[0044] Figure 2 This is a scanning electron microscope image of the highly dispersed composite silver powder prepared in Example 2 (metal ions are distributed in small particles, with some directly attached to the surface of the silver powder).

[0045] The highly dispersed composite silver powder in Table 2 was used to prepare the front electrode silver paste, which was then screen-printed onto the front of a P-type monocrystalline PERC cell. After drying and sintering, the photoelectric conversion efficiency and adhesion were tested. The test results are shown in Table 3.

[0046] Table 3. Viscosity, electrical properties, and adhesion data of silver paste:

[0047]

[0048] Where, Uoc: open-circuit voltage; Isc: short-circuit current; Rsh: parallel resistance; Rs: series resistance; FF: fill factor; Eff: conversion efficiency; F: average pull force.

[0049] Comparative Example 1:

[0050] The difference between Comparative Example 1 and Example 1 is that Cu(CH3COO)2 was used instead of Pb(CH3COO)2, otherwise the same as Example 1.

[0051] The obtained composite silver powder has a particle size of D. 50 2.5 μm, tapped value 6.2 g / cm 3 ;

[0052] The results show that Pb(CH3COO)2 is crucial because it contains lead ions. Replacing Pb(CH3COO)2 with other metal compounds will result in coarser silver powder particles and a finer slurry. Example 1 added Pb(CH3COO). 2， When composite silver powder is made into a paste, the fineness is less than 5μm, the photoelectric conversion efficiency is increased by 0.03%, and the welding pull value is large. However, when other metal compounds are used to make pastes, the photoelectric conversion efficiency is low and the welding pull value is small.

[0053] Comparative Example 2:

[0054] The difference between Comparative Example 2 and Example 1 is that the amount of metal added is 0.2%, otherwise it is the same as Example 1.

[0055] The obtained composite silver powder has a particle size of D. 50 2.9 μm, tapped value 6.5 g / cm 3 ;

[0056] The results show that the amount of metal added is crucial. Less metal is not necessarily better. If the amount of metal added is less than 0.5%, it will result in the silver powder paste having a large fineness, low welding tensile strength, and low photoelectric conversion efficiency.

[0057] Comparative Example 3:

[0058] The difference between Comparative Example 3 and Example 1 is that the amount of metal added is 1.2%, otherwise it is the same as Example 1.

[0059] The obtained composite silver powder has a particle size of D. 50 0.95μm, tapped value 5.2 g / cm 3 ;

[0060] The results show that the amount of metal added is crucial, and more metal is not necessarily better. With an addition of 1.2% metal, the photoelectric conversion efficiency of the silver powder paste increased by 0.02%, mainly reflected in the improvement of the opening voltage and the reduction of the series resistance, but the fineness of the paste and the welding tensile strength were also reduced.

[0061] Results analysis:

[0062] 1. When the selected water-soluble metal compound is added to the reaction vessel, it can be uniformly deposited on the surface of the silver powder or uniformly distributed in the silver powder during the chemical reaction of the silver powder. The highly dispersible composite silver powder has good dispersibility.

[0063] 2. Using the highly dispersible composite silver powder obtained in this invention as the positive silver paste enables the front electrode to effectively and uniformly etch the passivation layers of silicon nitride and aluminum oxide during the sintering process, ensuring high on-state voltage and high short-current while providing good adhesion.

[0064] 3. Using the highly dispersible composite silver powder obtained by this invention as positive silver paste, the photoelectric conversion efficiency is improved to 0.01-0.06%, mainly reflected in the improvement of opening voltage and the reduction of series resistance. At the same time, the proportion of high-efficiency wafers is increased by 10.2%, and the welding pull force is also improved.

[0065] 4. By comparing the basic performance of the embodiments and the comparative examples, the fineness, efficiency and tensile strength of the embodiments are improved to varying degrees compared with the comparative examples.

[0066] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a high dispersibility composite silver powder, characterized by: It comprises the following steps: S1: configuring silver nitrate solution with concentration of 0.1-2.5 mol / L in ingredient kettle I, and carrying out high-speed dispersion stirring, the dispersion speed is 1200-1800 r / min, and stirring for 30 min; adding metal compound during high-speed dispersion stirring of silver nitrate solution to obtain silver nitrate solution containing metal compound, the amount of added metal compound is 0.5-1% of the mass of prepared high-dispersion composite silver powder; the metal compound is selected from one of Pb(NO3)2 and Pb(CH3COO)2; S2: configuring reducing agent solution in ingredient kettle II, and carrying out high-speed dispersion stirring, the dispersion stirring speed is 1200-1800 r / min, and stirring for 30 min, and the pH of the reducing solution is adjusted to 7-9; the reducing agent is one of sodium citrate, NaBH4, polyacrylamide, glucose, formaldehyde, ascorbic acid, hydrazine hydrate and triethanolamine, and after being configured into reducing agent solution, the concentration and the adding amount thereof can sufficiently reduce silver nitrate; S3: configuring dispersant solution with solution concentration of 0.5-2 M in ingredient kettle III, and carrying out high-speed dispersion, the dispersion stirring speed is 1200-1800 r / min, and stirring for 30 min; the dispersant is one of polyvinylpyrrolidone, polyacrylamide, citric acid, gum arabic, gelatin, polyvinyl alcohol, sodium dodecyl sulfonate and polyethylene glycol; S4: adding the reducing agent solution treated in S2 and the dispersant solution treated in S3 into a reaction kettle and mixing uniformly; S5: adding the silver nitrate solution containing metal compound obtained in S1 into the reaction kettle in S4, controlling the adding to be completed within 5-10 min, reacting for 10 min at 30-50 ℃, and carrying out high-speed dispersion stirring, the dispersion stirring speed is 1200-1800 r / min, and stirring for 20 min, filtering and cleaning the mixed solution after reaction to obtain composite silver powder semi-product; S6: adding additive to the composite silver powder semi-product obtained in S5 to carry out dispersion, drying and airflow to obtain high-dispersion composite silver powder, the amount of additive is 0.1-1% of the mass of obtained high-dispersion composite silver powder; the additive is one of PVA, polyethylene glycol-400, fatty acid, oleic acid, oleylamine, stearic acid amine, palmitic acid, palmitic acid amine, castor oil and hydrogenated castor oil; The high-dispersibility composite silver powder has good dispersibility, and the particle size D 50 1.0-1.8μm, and the tap density is 5.5-6.5 g / cm 3 .

2. The method for preparing a highly dispersible composite silver powder according to claim 1, characterized in that: the concentration of the silver nitrate solution in step S1 is 0.5-2 mol / L.

3. The method for preparing a highly dispersible composite silver powder according to claim 1, characterized in that: the metal compound in step S1 is selected from Pb(CH3COO)2.

4. The method for preparing a highly dispersible composite silver powder according to claim 1, characterized in that: In step S2, the pH of the reducing solution is adjusted to 7-8, and the reagent for adjusting the pH value is NaOH, KOH or ammonia water.

5. A highly dispersible, composite silver powder, characterized by: The high-dispersibility composite silver powder is prepared by the method of any one of claims 1-4, and has good dispersibility, a particle size of D 50 1.0-1.8 μm, and a tap density of 5.5-6.5 g / cm 3 .

6. The use of a highly dispersible composite silver powder according to claim 5, characterized in that: It is used for preparation of positive electrode or positive silver paste.

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