Preparation method of superfine silver powder for photovoltaic cell silver paste

Abstract

The invention provides a preparation method of superfine silver powder for photovoltaic cell silver paste, the preparation raw materials comprise an oxidizing agent, a reducing agent, a dispersing agent and a pH regulator, and the method comprises the following steps: preparing a reducing agent solution containing the pH regulator, placing the reducing agent solution in an oil bath environment, and rapidly stirring for a period of time to obtain the superfine silver powder for the photovoltaic cell silver paste. And then, an oxidizing agent solution added with a dispersing agent solid is dropwise added into the mixture for a reduction reaction, the reacted solution is rapidly cooled through a room-temperature water bath, and superfine silver powder particles are obtained through centrifugation. The method has the advantages that the glucose which is low in cost, rich in raw material, mild in reducing capacity and environmentally friendly is selected as a green reducing agent, the waste liquid treatment cost and toxicity are reduced, the toxic reducing agent in chemical synthesis can be fully replaced, and by adjusting the molar ratio of the glucose to the oxidizing agent and the dosage of the pH adjusting agent, the waste liquid treatment cost is lowered. The particle size and the dispersity of the metal powder can be effectively controlled in the production process, and finally the micron-sized superfine silver powder particles with the uniform particle size and the controllable shape can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of photovoltaic silver powder preparation, and in particular to a method for preparing ultrafine silver powder for photovoltaic cell silver paste. Background Art

[0002] Ultrafine silver powder is a micron-sized silver powder. It has become one of the indispensable raw materials for photovoltaic solar cells, especially the silver paste on the front of solar cells, because of its excellent surface activity, electrical conductivity, large specific surface area and catalytic performance. my country's photovoltaic industry is developing rapidly, and it also puts forward higher requirements for ultrafine silver powder used in photovoltaic silver paste. So far, the ultrafine silver powder used in the photovoltaic field mainly includes spherical silver powder and flaky silver powder, and its morphology and structure can directly affect the printing performance and stacking quality of the silver paste. In order to ensure the final printing effect of the silver paste, ultrafine silver powder with a particle size of less than 5μm is usually selected in the production process. The precise control of this process can be achieved by regulating the nucleus formation and growth process in the liquid phase reduction method.

[0003] With the continuous innovation of photovoltaic technology and the need for cost control, how to design process parameters and select suitable reducing agents to prepare silver powder within the required particle size range has become the focus of research for those skilled in the art. Summary of the invention

[0004] In order to solve the problems of high cost, poor dispersibility and uneven silver powder particle size in the prior art, the present invention aims to provide an ultrafine silver powder with low production cost, good dispersibility and efficient preparation of micron-sized particle size and a preparation method thereof.

[0005] In order to achieve the above objectives, the present invention adopts the following technical solutions:

[0006] As a further improvement of the present invention, in preparing the oxidant solution, the oxidant is any one of silver nitrate or silver sulfate.

[0007] As a further improvement of the present invention, in preparing the oxidant solution, the dispersant is one or more of polyvinyl pyrrolidone K30, Tween 80, polyethylene glycol 4000 or polyvinyl alcohol.

[0008] As a further improvement of the present invention, in preparing the oxidant solution, the amount of the dispersant is 0.01 to 2 times the amount of the oxidant.

[0009] As a further improvement of the present invention, in preparing the reducing agent solution, the reducing agent is one or more of vitamin C, hydrazine hydrate, glucose or trisodium citrate.

[0010] As a further improvement of the present invention, in preparing the reducing agent solution, the molar ratio between the reducing agent and the oxidizing agent is (0.1-2.5):1.

[0011] As a further improvement of the present invention, in the preparation of the reducing agent solution, the pH adjuster is any one of ammonia water, ammonium bicarbonate, ammonium carbonate, sodium bicarbonate, sodium carbonate or sodium hydroxide.

[0012] As a further improvement of the present invention, in preparing the reducing agent solution, the molar ratio between the pH regulator and the reducing agent is (0.1-2.5):1.

[0013] In the present invention, the "solutions" are all prepared with deionized water, and the reaction temperature in the entire silver powder preparation process is room temperature except for oil bath and drying.

[0014] The method for preparing the ultrafine silver powder for photovoltaic cell silver paste comprises the following steps: (1) preparing an oxidant solution: weigh a certain amount of silver nitrate or silver sulfate solid, dissolve it in deionized water, stir it thoroughly to prepare an oxidant solution, add an appropriate amount of one or more of polyvinyl pyrrolidone K30, Tween 80, polyethylene glycol 4000 or polyvinyl alcohol, and keep the metal ion concentration in the oxidant solution at 0.01-5 mol / L; (2) preparing a reducing agent solution: adding weighed vitamin C, hydrazine hydrate, glucose or trisodium citrate to deionized water, stirring and dissolving the mixture, and adding an appropriate amount of ammonia water, ammonium bicarbonate, ammonium carbonate, sodium bicarbonate, sodium carbonate or sodium hydroxide to the deionized water, wherein the volume of the reducing agent solution is 0.1 to 5 times the volume of the oxidizing agent solution; (3) Solution mixing: First, place the reducing agent solution in a 40-100°C oil bath and stir rapidly for 5-60 minutes, then add the oxidizing agent solution dropwise at a certain rate, with the addition time controlled within 5-20 minutes, and stir the reaction for a period of time; (4) Post-treatment: After stirring, the mixed solution is quickly placed in a water bath at room temperature to cool down for 1 to 60 minutes; (5) Filtration and drying: After the reaction is completed, the solution is centrifuged and filtered, ultrasonically cleaned, and finally dried to obtain micron silver metal powder with good dispersion.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The method for preparing ultrafine silver powder for photovoltaic cell silver paste provided by the present invention helps to evenly disperse the formed micron-sized silver powder seeds by adding an appropriate amount of dispersant to the oxidant solution in advance, so that the silver reduced later can evenly grow on this basis to obtain silver powder particles with uniform particle size; 2. The method for preparing ultrafine silver powder for photovoltaic cell silver paste provided by the present invention can make the reactants undergo reduction reaction under appropriate conditions by adding an appropriate amount of pH regulator to the reducing agent solution in advance and heating it in an oil bath, which helps to improve the conversion rate of the reaction, shorten the reaction time, and increase the yield; 3. The method for preparing ultrafine silver powder for photovoltaic cell silver paste provided by the present invention can effectively control the morphology and crystallinity of the powder and ensure the quality of the metal powder by rapidly cooling the solution in a room temperature water bath; 4. The method for preparing ultrafine silver powder for photovoltaic cell silver paste provided by the present invention uses glucose, which is cheap, easily available and highly renewable, as a reducing agent, is environmentally friendly, reduces the cost and toxicity of treating waste liquid, can effectively replace the use of reducing agents that are harmful to the human body in industrial production, meets the requirements of green production in industrialization, and is suitable for mass production; 5. The method for preparing ultrafine silver powder for photovoltaic cell silver paste provided by the present invention has a simple preparation process, does not require a high vacuum environment, has low cost, mild reaction conditions, stable output, and good economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a scanning electron microscope image of the silver powder prepared in Comparative Example 1 of the present invention.

[0017] Figure 2 It is the UV-visible spectrum of the silver powder prepared in Comparative Example 2 of the present invention.

[0018] Figure 3 It is a scanning electron microscope image of the silver powder prepared in Comparative Example 2 of the present invention.

[0019] Figure 4 It is a scanning electron microscope image of the silver powder prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0020] The present invention is described in detail below in conjunction with specific implementation cases, but the present invention is not limited to these embodiments. It should be noted that, under the premise of no conflict, the embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0021] The terms "including" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0022] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources, wherein silver nitrate, glucose, sodium hydroxide and polyvinylpyrrolidone K30 were all of analytical grade.

[0023] In the present invention, a German ZEISS Sigma 300 scanning electron microscope is used to detect the microscopic morphology of the silver powder, and a UH5300 spectrophotometer is used to characterize the prepared micron silver particle dispersion.

[0024] The present application provides a method for preparing ultrafine silver powder for photovoltaic cell silver paste, comprising the following raw materials: an oxidant, a reducing agent, a dispersant and a pH regulator.

[0025] Preferably, in the preparation of the oxidant solution, the oxidant is silver nitrate, and the metal ion concentration in the oxidant solution is 0.01-2 mol / L.

[0026] Preferably, in the preparation of the oxidant solution, the dispersant is polyvinyl pyrrolidone K30, and its amount is 1 to 1.5 times the amount of the oxidant.

[0027] Preferably, in the preparation of the reducing agent solution, the reducing agent is glucose, and the molar ratio between the reducing agent and the oxidant is (1-2):1.

[0028] Preferably, in the preparation of the reducing agent solution, the pH adjuster is sodium hydroxide, and the molar ratio between the pH adjuster and the reducing agent is (1-2):1.

[0029] Preferably, during solution mixing, the oil bath temperature is 60-80° C., the stirring time is 10-40 min, and the feeding time is controlled at 5-15 min.

[0030] Preferably, in the post-treatment, the cooling time is 5 to 30 minutes.

[0031] Preferably, a method for preparing ultrafine silver powder for photovoltaic cell silver paste comprises the following steps: (1) Preparation of oxidant solution: Weigh a certain amount of silver nitrate solid and dissolve it in deionized water and stir thoroughly to prepare the oxidant solution. Add an appropriate amount of polyvinyl pyrrolidone K30, which is 1 to 1.5 times the amount of the oxidant, and keep the metal ion concentration in the oxidant solution at 0.01 to 2 mol / L; (2) Prepare reducing agent solution: weigh a certain amount of glucose at a molar ratio of (1-2):1 to silver nitrate, add it to deionized water and stir to dissolve, wherein the volume of reducing agent solution is 0.1-5 times the volume of oxidizing agent solution, and add an appropriate amount of sodium hydroxide at a molar ratio of (1-2):1 to glucose; (3) Solution mixing: First, place the reducing agent solution in a 60-80°C oil bath and stir rapidly for 10-40 minutes, then add the oxidizing agent solution dropwise at a certain rate, with the addition time controlled at 5-15 minutes, and stir the reaction for a period of time; (4) Post-treatment: After stirring, the mixed solution is quickly placed in a water bath at room temperature to cool for 5 to 30 minutes; (5) Filtration and drying: After the reaction is completed, the solution is centrifuged and filtered, ultrasonically cleaned, and finally dried to obtain micron silver metal powder with good dispersion.

[0032] [Example 1] A method for preparing ultrafine silver powder for photovoltaic cell silver paste comprises the following steps:

[0033] Prepare the oxidant solution: weigh a certain amount of silver nitrate solid and dissolve it in deionized water and stir it thoroughly to prepare the oxidant solution, keep the metal ion concentration in the oxidant solution at 0.05 mol / L, and add polyvinyl pyrrolidone K30, the amount of which is 1.5 times the amount of the oxidant.

[0034] Prepare reducing agent solution: weigh a certain amount of glucose at a molar ratio of 1.5:1 with silver nitrate, add it into deionized water and stir to dissolve, and add sodium hydroxide at a molar ratio of 2:1 with glucose, wherein the volume of reducing agent solution is the same as that of oxidant solution.

[0035] Solution mixing: first place the reducing agent solution in a 70°C oil bath and stir rapidly for 30 minutes, then add the oxidizing agent solution dropwise at a certain rate, control the addition time at 5-15 minutes, and stir the reaction for a period of time.

[0036] Post-treatment: After stirring, the mixed solution was quickly placed in a water bath at room temperature to cool for 10 minutes.

[0037] Filtration and drying: After the reaction is completed, the solution is centrifuged and filtered, ultrasonically cleaned, and finally dried to obtain nano silver metal powder with good dispersion.

[0038] [Example 2] A method for preparing ultrafine silver powder for photovoltaic cell silver paste is different from Example 1 in that the molar ratio of sodium hydroxide to glucose in the preparation of the reducing agent solution is 1.5:1. The rest is substantially the same as Example 1 and will not be described again.

[0039] [Comparative Example 1] A method for preparing ultrafine silver powder for photovoltaic cell silver paste is different from Example 2 in that the molar ratio of glucose to silver nitrate in the preparation of the reducing agent solution is 1:1. The rest is substantially the same as Example 2 and will not be described again.

[0040] The scanning electron microscope image of the silver powder prepared in this comparative example shows that the micron-sized silver powder prepared under this condition is unevenly distributed, has a low yield, irregular particle shape, and a wide particle size distribution range of 0.1-1 μm.

[0041] [Comparative Example 2] A method for preparing ultrafine silver powder for photovoltaic cell silver paste is different from Example 2 in that the molar ratio of glucose to silver nitrate in the preparation of the reducing agent solution is 0.67:1. The rest is substantially the same as Example 2 and will not be described again.

[0042] The UV-visible spectrum of the silver powder prepared in this comparative example shows that the UV characteristic peak of the metal particles is stable, and the product is determined to be nanosilver. The corresponding scanning electron microscope image shows that the prepared micron-level silver powder is distributed in a quasi-spherical shape, and the silver particles are all in a monodispersed form. The average particle size of the silver powder prepared in this comparative example is about 0.1 μm. The yield, dispersibility and uniformity of the silver powder prepared under this condition are improved, and it is suitable for preparing ultrafine silver powder for photovoltaic cell silver paste.

[0043] [Comparative Example 3] A method for preparing ultrafine silver powder for photovoltaic cell silver paste is different from Example 2 in that the molar ratio of glucose to silver nitrate in the preparation of the reducing agent solution is 0.5:1. The rest is substantially the same as Example 2 and will not be described again.

[0044] The scanning electron microscope image of the silver powder prepared in this comparative example shows that the uniformity of the micron-sized silver powder prepared under this condition is lower than that of comparative example 2, and there is a certain degree of agglomeration between the silver particles, and the particle size distribution range is 0.2~0.5μm.

[0045]

In summary

[0046] In the process of preparing silver powder, the present invention can effectively control the particle size of the silver powder by controlling the amount of the reducing agent and the pH adjusting agent, thereby ensuring that the silver powder can undergo directional growth under the condition of a suitable pH value and maintain good sphericity. According to the method for preparing ultrafine silver powder for photovoltaic cell silver paste in the present invention, the average particle size of the prepared quasi-spherical silver powder particles is about 0.1 μm, the particle size distribution is concentrated, and the dispersibility is good. Comprehensive evaluation shows that when glucose is used as the reducing agent and the molar ratio with silver nitrate is 0.67:1, the prepared silver powder particles have the best performance, the best sphericity, a smoother surface morphology, and higher dispersibility, which can meet the requirements of industrial mass production of spherical silver powder.

[0047] The above contents are only embodiments of the present invention and are only used to illustrate the implementation scheme of the present invention. The protection scope of the present application is not limited by these specific embodiments, but is determined by the claims of the present application. Those skilled in the art can modify the technical solutions in the present invention, and any modification, equivalent replacement, improvement, etc. made within the technical ideas and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing ultrafine silver powder for photovoltaic cell silver paste, characterized in that: The preparation method of the silver powder comprises the following steps: (1) preparing an oxidant solution: weigh a certain amount of silver nitrate or silver sulfate solid, dissolve it in deionized water, stir it thoroughly to prepare an oxidant solution, add an appropriate amount of one or more of polyvinyl pyrrolidone K30, Tween 80, polyethylene glycol 4000 or polyvinyl alcohol, and keep the metal ion concentration in the oxidant solution at 0.01-5 mol / L; (2) preparing a reducing agent solution: adding weighed vitamin C, hydrazine hydrate, glucose or trisodium citrate to deionized water, stirring and dissolving the mixture, and adding an appropriate amount of ammonia water, ammonium bicarbonate, ammonium carbonate, sodium bicarbonate, sodium carbonate or sodium hydroxide to the deionized water, wherein the volume of the reducing agent solution is 0.1 to 5 times the volume of the oxidizing agent solution; (3) Solution mixing: First, place the reducing agent solution in a 40-100°C oil bath and stir rapidly for 5-60 minutes, then add the oxidizing agent solution dropwise at a certain rate, with the addition time controlled within 5-20 minutes, and stir the reaction for a period of time; (4) Post-treatment: After stirring, the mixed solution is quickly placed in a water bath at room temperature to cool down for 1 to 60 minutes; (5) Filtration and drying: After the reaction is completed, the solution is centrifuged and filtered, ultrasonically cleaned, and finally dried to obtain micron silver metal powder with good dispersion.

2. The method for preparing ultrafine silver powder for photovoltaic cell silver paste according to claim 1, characterized in that: The oxidant is any one of silver nitrate or silver sulfate.

3. The method for preparing ultrafine silver powder for photovoltaic cell silver paste according to claim 1, characterized in that: The reducing agent is one or more of vitamin C, hydrazine hydrate, glucose or trisodium citrate, and the molar ratio between the reducing agent and the oxidant is (0.1-2.5):

1.

4. The method for preparing ultrafine silver powder for photovoltaic cell silver paste according to claim 1, characterized in that: The dispersant is one or more of polyvinyl pyrrolidone K30, Tween 80, polyethylene glycol 4000 or polyvinyl alcohol, and the amount of the added dispersant is 0.01 to 2 times the amount of the oxidant.

5. The method for preparing ultrafine silver powder for photovoltaic cell silver paste according to claim 1, characterized in that: The pH adjuster is any one of ammonia water, ammonium bicarbonate, ammonium carbonate, sodium bicarbonate, sodium carbonate or sodium hydroxide, and the molar ratio between the pH adjuster and the reducing agent is (0.1-2.5):

1.

6. A method for preparing ultrafine silver powder for photovoltaic cell silver paste, characterized in that: The raw materials required for preparation include an oxidant, a reducing agent, a dispersant and a pH regulator.

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