Narrow-linewidth porous silver powder for photovoltaics and method for preparing the same

Abstract

This invention discloses a narrow-linewidth porous silver powder for photovoltaic applications and its preparation method. The surface of the narrow-linewidth porous silver powder for photovoltaic applications has pores with a diameter of 10-150 nm. The D50 of the narrow-linewidth porous silver powder for photovoltaic applications is 1.0-1.5 μm, the particle size distribution Span is 0.7-1.0, and the tap density TD ≥ 6.0 g / cm³. 3 Its specific surface area is 0.45-0.55 m². 2 / g. This invention prepares the silver powder through seed-induced and rapid redox reactions. The product combines high sintering activity with low viscosity and printability, making it suitable for the narrow linewidth printing requirements of photovoltaic silver paste. This invention also provides modification schemes and industrial-scale preparation processes for the silver powder, with mild reaction conditions, low cost, and easy scale-up production.

Description

Technical Field

[0001] This invention belongs to the field of metal powder materials technology, specifically relating to a narrow-linewidth porous silver powder for photovoltaic applications and its preparation method. Background Technology

[0002] With the rapid development of the global photovoltaic industry, photovoltaic cells are iterating towards higher efficiency, narrower linewidths, and lower contact resistance, placing higher demands on conductive silver paste. Silver paste mainly consists of silver powder, glass frit, organic carriers, and additives. The morphology, particle size, density, specific surface area, and pore structure of the silver powder directly determine the paste's viscosity, printability, sintering properties, and conductivity. Narrow linewidth printing requires silver paste with lower viscosity and better rheological and thixotropic properties, while also requiring rapid sintering of the silver powder at low temperatures to form a dense conductive film, reducing contact resistance and series losses.

[0003] Existing silver powders are mostly spherical or near-spherical solid particles with a high specific surface area. After pulping, they have high oil absorption and viscosity, making them unsuitable for narrow linewidth printing. While some porous silver powders have improved sintering activity, they suffer from problems such as wide particle size distribution, low tap density, limited solid content, and loose conductive film. At the same time, traditional liquid-phase reduction methods are difficult to precisely control the surface nanopore structure, often resulting in defects such as particle agglomeration, uneven particle size, and poor batch stability, failing to simultaneously meet the dual requirements of high sintering activity and high printing performance.

[0004] To address the aforementioned contradictions, there is an urgent need to develop a silver powder with concentrated particle size, high tapping density, low specific surface area, and controllable nanopores to achieve compatibility between low-temperature, high-activity sintering and low-viscosity, excellent printing properties, thereby improving the overall performance of photovoltaic silver paste. This invention aims to provide a silver powder with controllable pore structure and its stable preparation method to fill the gaps in existing technologies. Summary of the Invention

[0005] This invention aims to solve the technical problems of existing photovoltaic silver powder, such as difficulty in balancing sintering activity and printing performance, difficulty in coordinating pore structure and particle size control, high slurry viscosity, and poor adaptability to narrow linewidth printing. It provides a porous silver powder for narrow linewidth photovoltaic applications, which is a silver powder with a special pore structure that achieves a balance between high sintering activity, low viscosity, high tap density, and excellent narrow linewidth printing performance.

[0006] The first aspect of the present invention provides a narrow-linewidth porous silver powder for photovoltaic applications, which has controllable nanopores on its surface, uniform particle size, high tap density, and low specific surface area.

[0007] The second aspect provides its preparation method, which uses seed-induced rapid reduction, and the process is stable and suitable for industrialization.

[0008] The first aspect of the present invention provides a narrow-linewidth porous silver powder for photovoltaic applications. The surface of the narrow-linewidth porous silver powder has pores with a diameter of 10-150 nm. The D50 of the narrow-linewidth porous silver powder is 1.0-1.5 μm, the particle size distribution (Span) is 0.7-1.0, and the tap density (TD) is ≥6.0 g / cm³. 3 Its specific surface area is 0.45-0.55 m². 2 / g.

[0009] The narrow-linewidth porous silver powder for photovoltaic applications of this invention has 10-150nm pores on its surface, which can reduce sintering temperature and improve sintering activity; its D50 is 1.0-1.5μm and its particle size distribution Span is 0.7-1.0, exhibiting excellent particle uniformity and making it suitable for narrow-linewidth, high-precision printing; its tap density TD ≥ 6.0g / cm³. 3 This results in a high solids content and low viscosity in the silver paste, leading to a dense conductive film after sintering; the specific surface area is controlled at 0.45-0.55 μm². 2 / g further reduces the viscosity of the slurry and improves printing performance, thereby achieving both high sintering activity and excellent narrow linewidth printability.

[0010] Narrow linewidth printing requires silver paste to have high resolution, uniform lines, no broken lines, and no ink buildup. Therefore, the silver powder must have a highly concentrated and uniform particle size distribution to avoid large particles scratching the screen and clogging the mesh; low specific surface area and low oil absorption make the paste viscosity low and thixotropic to be suitable for fine line transfer.

[0011] Narrow linewidth photovoltaic printing technology places more stringent and special requirements on conductive silver powder: on the one hand, the silver powder is required to have high sintering activity in order to achieve low-temperature rapid sintering and form a dense conductive film; on the other hand, the silver powder is required to have excellent printing performance in order to meet the printing requirements of narrow linewidth, high precision, and no line breaks.

[0012] To simultaneously meet the above requirements, the present invention specifies the structure of the silver powder: the surface of the silver powder has pores with a diameter of 10-150 nm, the D50 of the narrow-linewidth photovoltaic porous silver powder is 1.0-1.5 μm, the particle size distribution Span is 0.7-1.0, and the tap density TD ≥ 6.0 g / cm³. 3 Its specific surface area is 0.45-0.55 m². 2 / g, to achieve high solids content, low viscosity, and good printing leveling properties.

[0013] The aforementioned structural limitations are determined by the specific requirements of narrow linewidth photovoltaic applications. The parameters are synergistic and inseparable, working together to make silver powder suitable for the field of narrow linewidth photovoltaic silver paste.

[0014] According to some embodiments of the present invention, the number of porous silver powder for narrow linewidth photovoltaic applications is ≥20% under a 20,000x scanning electron microscope.

[0015] Under a 20,000x scanning electron microscope, the number of porous silver powder for narrow-linewidth photovoltaic applications is ≥20%, ensuring that the silver powder has a stable and sufficient porous structure. This allows the silver powder to soften uniformly and form sintering necks simultaneously during the sintering process, avoiding problems such as uneven sintering and poor contact caused by insufficient porous particle ratio. This further improves the sintering consistency and conductivity reliability of the silver powder, ensuring that narrow-linewidth photovoltaic silver paste can still form a dense, continuous, and low-resistance conductive path even under low-temperature sintering.

[0016] According to some embodiments of the present invention, the surface pore diameter of the narrow linewidth photovoltaic porous silver powder is 10–100 nm.

[0017] According to some embodiments of the present invention, the surface pore diameter of the narrow linewidth photovoltaic porous silver powder is any value among 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, and 100nm, such as 50nm, or any range formed by both, such as 30nm to 70nm.

[0018] By controlling the surface pores within the fine range of 10-100nm, the softening temperature of silver powder during sintering can be significantly reduced, sintering necks can be formed quickly, and high sintering activity can be guaranteed. At the same time, problems such as insufficient silver powder strength, decreased tap density, and broken lines in the paste printing caused by excessively large pore sizes can be avoided. This achieves the best balance between sintering activity and powder physical properties, making the silver paste more stable and better in both narrow linewidth printing and low-temperature sintering scenarios.

[0019] A second aspect of the present invention provides a method for preparing narrow-linewidth porous silver powder for photovoltaic applications according to the first aspect of the present invention, comprising the following steps: (1) Prepare silver nitrate solution, seed solution, and base solution containing reducing agent respectively; (2) Add the seed solution to the silver nitrate solution and the base solution respectively, adjust the pH of the base solution, and then add the silver nitrate solution to the base solution to carry out the redox reaction; (3) After adding a coating agent to the solution in step (2) for coating, the solution is washed, dehydrated, dried and crushed to obtain the narrow linewidth porous silver powder for photovoltaic use.

[0020] This invention employs a stepwise seed crystal addition, rapid redox reaction, and mild post-treatment preparation method. The seed crystals induce uniform nucleation and directional growth of silver particles, and with the help of dispersants, the silver powder exhibits a concentrated particle size distribution, good particle dispersibility, and is less prone to agglomeration. By adding seed crystals separately to the silver nitrate solution and the base solution and precisely controlling the pH, a uniformly distributed nanoporous structure can be stably generated, ensuring that the silver powder possesses both high sintering activity and low specific surface area. Subsequent coating and mild crushing processes protect the porous structure from damage, while further improving the dispersibility and batch stability of the silver powder. This method features mild process conditions, conventional equipment, controllable parameters, and good repeatability, making it suitable for large-scale industrial production and capable of stably preparing high-performance porous silver powder that meets the requirements of narrow linewidth photovoltaic printing.

[0021] According to some embodiments of the present invention, in step (1), the concentration of the silver nitrate solution is 10~20%wt.

[0022] According to some embodiments of the present invention, in step (1), the concentration of the silver nitrate solution is any value among 10%wt, 11%wt, 12%wt, 13%wt, 14%wt, 15%wt, 16%wt, 17%wt, 18%wt, 19%wt, and 20%wt, such as 15%wt, or any range formed by both, such as 12%wt to 18%wt.

[0023] Controlling the concentration of silver nitrate solution to 10-20 wt% ensures a suitable concentration of silver ions, which can meet the high-efficiency output requirements of industrial production while avoiding excessively high concentrations that lead to excessively rapid reactions, particle agglomeration, uneven particle size, and uncontrolled pore structure. At the same time, it can prevent problems such as low reaction efficiency, insufficient yield, and high energy consumption caused by excessively low concentrations. This ensures that the reduction reaction is stable and controllable, nucleation and growth are uniform, and porous silver powder with particle size, morphology, and pore structure that meet the requirements is obtained stably.

[0024] According to some embodiments of the present invention, in the base solution containing the reducing agent, the amount of the reducing agent added is 53.0~55.0%wt of silver nitrate.

[0025] According to some embodiments of the present invention, in the base liquid containing the reducing agent, the amount of reducing agent added is any one of the following values ​​of silver nitrate mass fraction: 53.0%wt, 53.5%wt, 54.0%wt, 54.5%wt, and 55.0%wt, such as 54.0%wt, or any range formed by both, such as 53.5%wt to 54.5%wt.

[0026] By controlling the amount of reducing agent in the base solution within the above-mentioned range, it is possible to ensure that silver ions are fully and stably reduced, avoiding incomplete reduction of silver ions and low product purity due to insufficient reducing agent. At the same time, it can prevent problems such as excessive reaction, particle agglomeration, widening of particle size distribution, and difficulty in controlling pore structure caused by excessive reducing agent. This ensures that the reduction reaction rate is moderate and nucleation and growth are synchronous and stable, thereby obtaining target silver powder with uniform particle size, good dispersibility, and regular pore structure.

[0027] According to some embodiments of the present invention, in step (1), the method for preparing the seed solution includes: adding a superdispersant to a silver nitrate solution with a concentration of 0.05~0.10 mol / L and stirring until uniform, wherein the mass of the superdispersant is 0.01wt%~0.1wt% of the mass of silver nitrate in the silver nitrate solution; then adding a reducing agent solution with a concentration of 0.06~0.20 mol / L, wherein the molar concentration ratio of silver nitrate to reducing agent is 1:(1.2~2.0); mixing until uniform to obtain the seed solution.

[0028] According to some embodiments of the present invention, the superdispersant includes at least one selected from polyvinyl alcohol, polyethylene glycol, polyacryl alcohol, polycarboxylate, and polyurethane.

[0029] According to some embodiments of the present invention, in step (2), by volume, 1 part of silver nitrate solution with a concentration of 10~20wt% is set to 400L, 1 part of base liquid containing reducing agent is set to 450L, and 1 part of seed solution is set to 1L; 0.5~1.5 parts of seed solution are added to each part of silver nitrate solution and 0.5~1.5 parts of seed solution are added to each part of base liquid.

[0030] According to some embodiments of the present invention, in step (2), the pH of the base solution is adjusted to be controlled between 0.5 and 1.5.

[0031] By controlling the amount of seed crystals added within this range, the number of nuclei and the growth rate of silver powder can be precisely controlled, so that the nucleation and growth of silver particles can be balanced, ensuring that the silver powder has a concentrated particle size distribution and good particle uniformity. At the same time, it can stably induce the formation of a uniform and appropriate amount of nanoporous structure, avoiding the problems of insufficient nucleation and fewer pores due to too low a seed crystal ratio, or particle refinement, increased specific surface area, and increased viscosity due to too high a seed crystal ratio. Thus, it can stably prepare narrow-linewidth porous silver powder for photovoltaics that has high sintering activity, low viscosity, and excellent printability.

[0032] According to some embodiments of the present invention, in step (2), the pH of the base solution is adjusted to be controlled between 0.5 and 1.5.

[0033] According to some embodiments of the present invention, in step (2), the pH of the base solution is adjusted to any value among 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, and 1.5, such as 1.0, or any range formed by both, such as 0.8 to 1.2.

[0034] Controlling the pH of the base solution within this strongly acidic range can stabilize the reduction reaction system, inhibit premature hydrolysis and abnormal nucleation of silver ions, and ensure that the reduction reaction proceeds only in a directional and uniform manner under seed induction. At the same time, it can effectively improve particle dispersibility, prevent agglomeration, and ensure that the silver powder has a concentrated particle size, regular morphology, and uniform and controllable nanopores. This pH range can also make the reaction rate mild and moderate, avoiding problems such as particle size fluctuations and abnormal pore structure caused by uncontrolled reaction, and significantly improving the batch stability and performance consistency of the product.

[0035] According to some embodiments of the present invention, in step (3), the coating agent includes at least one of stearic acid, lauric acid, gelatin and gum arabic.

[0036] According to some embodiments of the present invention, in step (3), the amount of coating agent added is 0.15-0.25 wt% of the mass of silver nitrate.

[0037] According to some embodiments of the present invention, in step (3), the amount of coating agent added is any one of 0.15wt%, 0.17wt%, 0.19wt%, 0.21wt%, 0.23wt%, or 0.25wt% of the mass of silver nitrate, such as 0.20wt%, or any range formed by both, such as 0.18wt% to 0.22wt%.

[0038] By controlling the amount of coating agent within this range, a uniform, thin, and complete coating layer can be formed on the surface of silver powder particles. This effectively prevents particle agglomeration, improves dispersibility and storage stability, and avoids the increase in specific surface area of ​​silver powder, increase in paste viscosity, and decrease in sintering activity caused by excessive coating agent. At the same time, it can protect the surface nanoporous structure from being damaged, so that the silver powder can maintain high dispersion and high stability while still having excellent printing performance and sintering activity, ensuring the stable and reliable overall performance of narrow linewidth photovoltaic silver paste.

[0039] According to some embodiments of the present invention, in step (3), the coating time is 10~20 min.

[0040] According to some embodiments of the present invention, in step (3), the covering time is any value among 10min, 11min, 12min, 13min, 14min, 15min, 16min, 17min, 18min, 19min, and 20min, such as 15min, or any range formed by both, such as 12min to 18min.

[0041] This coating time ensures that the coating agent is fully adsorbed and uniformly film-formed on the surface of the silver powder particles, achieving stable dispersion and anti-agglomeration effects. Too short a time will result in incomplete coating and easy particle agglomeration, while too long a time will easily lead to coating agent redundancy, increased slurry viscosity, and reduced sintering activity. Controlling the time to 10-20 minutes can balance coating integrity and production efficiency, maintaining the advantages of low viscosity and high sintering activity of silver powder while protecting the nanoporous structure, making it suitable for continuous industrial production.

[0042] According to some embodiments of the present invention, in step (3), the drying temperature is 60~70°C.

[0043] According to some embodiments of the present invention, in step (3), the drying temperature is any value among 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, and 70°C, such as 65°C, or any range formed by both, such as 62°C to 68°C.

[0044] According to some embodiments of the present invention, in step (3), the drying time is 2 to 6 hours.

[0045] According to some embodiments of the present invention, in step (3), the drying time is any value of 2h, 3h, 4h, 5h, 6h, such as 4h, or a range of any two, such as 3h~5h.

[0046] According to some embodiments of the present invention, in step (3), the crushing pressure is 0.4~0.8MPa.

[0047] According to some embodiments of the present invention, in step (3), the crushing pressure is any value among 0.4MPa, 0.5MPa, 0.6MPa, 0.7MPa, and 0.8MPa, such as 0.6MPa, or a range of any two, such as 0.5MPa to 0.7MPa. Attached Figure Description

[0048] Figure 1 This is one of the microscopic morphology images of the silver powder in Example 1.

[0049] Figure 2 This is the second microscopic morphology image of the silver powder in Example 1.

[0050] Figure 3 This is one of the microscopic morphology images of the silver powder in Example 2.

[0051] Figure 4 This is the second microscopic morphology image of the silver powder in Example 2.

[0052] Figure 5 This is one of the microscopic morphology images of the silver powder in Comparative Example 1.

[0053] Figure 6 This is the second microscopic morphology image of the silver powder in Comparative Example 1.

[0054] Figure 7 This is one of the microscopic morphology images of the silver powder in Comparative Example 2.

[0055] Figure 8 This is the second microscopic morphology image of the silver powder in Comparative Example 2.

[0056] Figure 9 This is the microstructure of the silver powder after sintering in Example 1.

[0057] Figure 10 This is the microstructure of the silver powder after sintering in Example 2.

[0058] Figure 11 The microstructure of the silver powder after sintering in Comparative Example 2 is shown. Detailed Implementation

[0059] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0060] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0061] Unless otherwise specified, "room temperature" in this invention means 25℃±5℃.

[0062] Unless otherwise specified, "about" in this invention means that the allowable error is within ±2%.

[0063] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0064] Example 1 A narrow-linewidth porous silver powder for photovoltaic applications was prepared by the following method: Preparation of silver nitrate solution: Dissolve silver nitrate crystals in 400L of pure water to prepare a solution with a concentration of 15%wt. The conductivity of the pure water should be ≤1µm / cm. The temperature after dissolution should be controlled at 25-35℃.

[0065] Seed crystal preparation: Prepare 0.5L of silver nitrate solution with a concentration of 0.05mol / L and 0.5L of vitamin C reducing agent solution with a concentration of 0.06mol / L respectively; add polyvinyl alcohol superdispersant (0.1% of the mass of silver) to the silver nitrate solution, stir evenly, and then mix with the reducing agent solution. The total volume after mixing is 1L, which is 1 part of seed crystal solution.

[0066] Preparation of the base solution: Add 450L of pure water to the reactor, and then add the reducing agent vitamin C, wherein the mass fraction of vitamin C is 54.0wt% of the mass of silver nitrate in the first step; maintain a constant stirring speed between 180-260r / min for 30 minutes, and control the temperature at 25-35℃.

[0067] Redox reaction: Before the reaction, seed solution is added to both the silver nitrate solution and the base solution. 0.5 parts of seed solution are added to each part (by mass) of silver nitrate solution and base solution. After stirring for 2 minutes, the pH of the base solution is adjusted to 1.0. Finally, the prepared silver nitrate solution is added evenly to the reactor within 30 seconds. During the reaction, the stirring speed is maintained at a constant value between 180-260 r / min. After the addition is completed, the relevant valves are closed.

[0068] After the feeding is completed, add stearic acid coating agent (0.2% of the total mass of silver nitrate) to coat it. Keep the stirring speed constant during the process and control the coating time to 10-20 minutes.

[0069] Silver powder cleaning: The silver powder from the reactor is fed into a centrifuge or dehydrator for cleaning and dehydration to obtain wet silver powder with a moisture content of 10-25%.

[0070] Silver powder drying: Place the dehydrated silver powder on a tray and put it into an oven. The drying temperature is controlled at 60-70℃ and the drying time is 4 hours.

[0071] Silver powder crushing: The dried silver powder is subjected to airflow crushing with a crushing pressure of 0.4-0.8 MPa to obtain silver powder that meets the technical requirements.

[0072] Example 2 A narrow-linewidth porous silver powder for photovoltaic applications was prepared by the following method: Preparation of silver nitrate solution: Dissolve silver nitrate crystals in 400L of pure water to prepare a solution with a concentration of 15%wt. The conductivity of the pure water should be ≤1µm / cm. The temperature after dissolution should be controlled at 25-35℃.

[0073] Seed crystal preparation: Prepare 0.5 L of 0.08 mol / L silver nitrate solution and 0.5 L of 0.12 mol / L vitamin C reducing agent solution. Add polyvinyl alcohol superdispersant to the silver nitrate solution at 0.5% of the silver mass, stir well, and then mix with the reducing agent solution. The total volume after mixing is 1 L, which is one part of seed crystal solution. Prepare two parts of seed crystal solution according to the above ratio.

[0074] Preparation of the base solution: Add 450L of pure water to the reactor, and then add vitamin C, wherein the mass fraction of vitamin C is 54.0wt% of the mass of silver nitrate in the first step; maintain a constant stirring speed between 180-260r / min for 30 minutes, and control the temperature at 25-35℃.

[0075] Redox reaction: Before the reaction, seed solution was added to both the silver nitrate solution and the base solution, with 0.5 parts seed solution added to the silver nitrate solution and 1.5 parts seed solution added to the base solution. After stirring for 2 minutes, the pH of the base solution was adjusted to 1.0. Finally, the prepared silver nitrate solution was uniformly added to the reactor within 30 seconds. During the process, the stirring speed was maintained at a constant value between 180-260 r / min. After the addition was completed, the relevant valves were closed.

[0076] After the feeding is completed, add stearic acid as a coating agent at 0.2% of the total mass of silver nitrate to coat the material. Keep the stirring speed constant during the process and control the coating time at 15 minutes.

[0077] Silver powder cleaning: The silver powder from the reactor is fed into a centrifuge or dehydrator for cleaning and dehydration to obtain wet silver powder with a moisture content of 20%.

[0078] Silver powder drying: Place the dehydrated silver powder on a tray and put it into an oven. The drying temperature is controlled at 65℃ and the drying time is 4 hours.

[0079] Silver powder crushing: The dried silver powder is subjected to airflow crushing with a crushing pressure of 0.6 MPa to obtain silver powder that meets the technical requirements.

[0080] Example 3 A narrow-linewidth porous silver powder for photovoltaic applications was prepared by the following method: Preparation of silver nitrate solution: Dissolve silver nitrate crystals in 400L of pure water to prepare a solution with a concentration of 15%wt. The conductivity of the pure water should be ≤1µm / cm. The temperature after dissolution should be controlled at 25-35℃.

[0081] Seed crystal preparation: Prepare 0.5 L of 0.10 mol / L silver nitrate solution and 0.5 L of 0.20 mol / L vitamin C reducing agent solution. Add polyvinyl alcohol superdispersant to the silver nitrate solution at an amount of 1.0% of the silver mass, stir well, and then mix with the reducing agent solution. The total volume after mixing is 1 L, which is 1 part of seed crystal solution. Prepare a total of 2.5 parts of seed crystal solution according to the above ratio.

[0082] Preparation of the base solution: Add 450L of pure water to the reactor, and then add the reducing agent, wherein the mass fraction of the reducing agent is 54.0wt% of the mass of silver nitrate in the first step; maintain a constant stirring speed between 180-260r / min for 30 minutes, and control the temperature at 25-35℃.

[0083] Redox reaction: Before the reaction, seed solution was added to both the silver nitrate solution and the base solution, with 1.5 parts seed solution added to the silver nitrate solution and 1 part seed solution added to the base solution. After stirring for 2 minutes, the pH of the base solution was adjusted to 1.0. Finally, the prepared silver nitrate solution was uniformly added to the reactor within 30 seconds. During the process, the stirring speed was maintained at a constant value between 180-260 r / min. After the addition was completed, the relevant valves were closed.

[0084] After the feeding is completed, add stearic acid as a coating agent at 0.2% of the total mass of silver nitrate to coat the material. Keep the stirring speed constant during the process and control the coating time at 10-20 minutes.

[0085] Silver powder cleaning: The silver powder from the reactor is fed into a centrifuge or dehydrator for cleaning and dehydration to obtain wet silver powder with a moisture content of 10-25%.

[0086] Silver powder drying: Place the dehydrated silver powder on a tray and put it into an oven. The drying temperature is controlled at 60-70℃ and the drying time is 4 hours.

[0087] Silver powder crushing: The dried silver powder is subjected to airflow crushing with a crushing pressure of 0.6 MPa to obtain silver powder that meets the technical requirements.

[0088] Comparative Example 1 The difference from Example 2 is that no superdispersant is added when preparing the seed crystals.

[0089] Comparative Example 2 The difference from Example 2 is that 0.3 parts of seed solution were added to both the silver nitrate solution and the base solution.

[0090] Comparative Example 3 The difference from Example 2 is that 0.5 parts of seed solution are added to the silver nitrate solution, and 2.0 parts of seed solution are added to the base solution.

[0091] Comparative Example 4 The difference from Example 2 is that 2 parts of seed solution are added to the silver nitrate solution, and 0.5 parts of seed solution are added to the base solution.

[0092] The parameter differences between Examples 1-3 and Comparative Examples 1-4 are shown in Table 1 below.

[0093] Table 1

[0094] The properties of the silver powders prepared in Examples 1-3 and Comparative Examples 1-4 were measured.

[0095] 1. Particle size, specific surface area, and tap density tests: The particle size, specific surface area, and tap density of the silver powders prepared in Examples 1-3 and Comparative Examples 1-4 were measured using a laser particle size analyzer, a specific surface area analyzer, and a tap density analyzer, respectively.

[0096] 2. Viscosity test The silver powders obtained in Examples 1-3 and Comparative Examples 1-4 were mixed with organic resin, glass powder, and other components to form conductive silver paste. The viscosity of the silver paste was tested using a rheometer.

[0097] The results are shown in Table 2.

[0098] Table 2

[0099] As shown in Table 2, the silver powders prepared in Examples 1-3 of this invention have a D50 of 1.247-1.440 μm, a particle size distribution Span of 0.75-0.79, and a tap density TD ≥ 6.0 g / cm³. 3 The specific surface area (BET) is 0.48–0.53 m². 2 / g, the silver paste viscosity is 46.2~48.9mPa·s, it has high sintering activity, and all indicators meet the requirements of narrow linewidth photovoltaic silver powder.

[0100] The silver powders in Comparative Examples 1 to 4 have a wider particle size distribution, lower tap density, higher specific surface area, significantly increased slurry viscosity, and significantly worse sintering activity, which cannot meet the application requirements.

[0101] Compared with the comparative example, the embodiments of the present invention have significant advantages in terms of particle size uniformity, tap density, slurry viscosity, and sintering activity.

[0102] This invention demonstrates that by controlling key process conditions such as seed ratio, superdispersant, reaction pH, and coating parameters, it is possible to stably prepare narrow-linewidth porous silver powder for photovoltaic applications with concentrated particle size distribution, high tap density, low specific surface area, low viscosity, and high sintering activity. The reasonable selection of key process parameters is a necessary condition for obtaining the above-mentioned excellent properties. The lack of or deviation from these process conditions will lead to a significant decrease in the overall performance of the silver powder.

[0103] 3. Sintering activity determination Sintering activity test: 1g of silver powder was placed on a ceramic plate, evenly spread, and sintered at 300℃. Its appearance morphology was then observed using a scanning electron microscope.

[0104] Figure 1 and Figure 2 This is a microscopic morphology image of the silver powder in Example 1. It can be seen that the pore size is 43-99 nm, and the proportion of silver powder particles with pores is 53.7%, indicating good dispersion of the silver powder and that the proportion of porous particles is as expected.

[0105] Figure 3 and Figure 4 This is a microscopic morphology image of the silver powder in Example 2. It can be seen that the pore size is 52-57 nm, and the proportion of silver powder particles with pores is 52%, indicating good silver powder dispersion and that the proportion of porous particles is as expected.

[0106] Figure 5 and Figure 6 This is a microscopic morphology image of the silver powder in Comparative Example 1. It can be seen that, in the absence of a superdispersant, the material agglomerates.

[0107] Figure 7 and Figure 8 This is a microscopic morphology diagram of the silver powder in Comparative Example 2. It can be seen that the proportion of porous silver powder particles is only 6.5%, the amount of seed crystals is reduced, the particle size is relatively large, and the proportion of silver powder particles with voids is decreasing.

[0108] Figure 9 This is the microstructure of the silver powder after sintering in Example 1.

[0109] Figure 10 This is the microstructure of the silver powder after sintering in Example 2.

[0110] Figure 11 The microstructure of the silver powder after sintering in Comparative Example 2 is shown.

[0111] from Figures 9 to 11 As can be seen, after sintering in Examples 1 and 2, SEM showed that the silver powder had softened at the sintering temperature, and sintering necks appeared between the particles, indicating dense sintering and high sintering activity. In contrast, the silver powder particles in the comparative example had not softened yet, and only some points between the particles softened to form contact, indicating weak sintering activity.

[0112] Based on the above microscopic morphology characterization, it can be seen that the superdispersant determines the particle dispersion, and its absence directly leads to agglomeration. The seed crystal addition ratio determines the proportion of porous particles and particle size uniformity; if the ratio is too low, there will be insufficient pores and performance degradation. Sufficient and appropriately sized nanopores are a core prerequisite for high sintering activity. Examples 1 and 2, through seed crystal induction, superdispersant regulation, and reasonable coating, achieved a silver powder structure with uniform pores, a satisfactory proportion, and good dispersibility, ultimately exhibiting low viscosity and high sintering activity, perfectly matching the requirements of narrow linewidth photovoltaic silver paste; the comparative examples, due to the lack of key process control, did not meet the standards in terms of morphology and sintering performance.

[0113] It should be noted that the narrow linewidth porous silver powder for photovoltaics of the present invention refers to narrow linewidth printing with a linewidth of 4~8μm.

[0114] The present invention has been described in detail above with reference to the embodiments. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A porous silver powder for narrow-linewidth photovoltaic applications, characterized in that, The narrow-linewidth porous silver powder for photovoltaic applications has pores with a diameter of 10-150 nm on its surface. The D50 of the narrow-linewidth porous silver powder for photovoltaic applications is 1.0-1.5 μm, the particle size distribution span is 0.7-1.0, and the tap density TD ≥ 6.0 g / cm³. 3 Its specific surface area is 0.45-0.55 m². 2 / g.

2. The narrow-linewidth porous silver powder for photovoltaic applications according to claim 1, characterized in that, The narrow-linewidth porous silver powder for photovoltaics has ≥20% pores under a 20,000x scanning electron microscope.

3. The narrow-linewidth porous silver powder for photovoltaic applications according to claim 1, characterized in that, The surface pore diameter of the narrow-linewidth porous silver powder for photovoltaics is 10–100 nm.

4. A method for preparing narrow-linewidth porous silver powder for photovoltaic applications as described in any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Prepare silver nitrate solution, seed solution, and base solution containing reducing agent respectively; (2) Add the seed solution to the silver nitrate solution and the base solution respectively, adjust the pH of the base solution, and then add the silver nitrate solution to the base solution to carry out the redox reaction; (3) After adding a coating agent to the solution in step (2) for coating, the solution is washed, dehydrated, dried and crushed to obtain the narrow linewidth porous silver powder for photovoltaic use.

5. The method according to claim 4, characterized in that, In step (1), the concentration of the silver nitrate solution is 10~20%wt; and / or, in the base solution containing the reducing agent, the amount of reducing agent added is 53.0~55.0%wt of the mass fraction of silver nitrate.

6. The method according to claim 4, characterized in that, In step (1), the method for preparing the seed solution includes: adding a superdispersant to a silver nitrate solution with a concentration of 0.05~0.10 mol / L and stirring until homogeneous, wherein the mass of the superdispersant is 0.01wt%~0.1wt% of the mass of silver nitrate in the silver nitrate solution; then adding a reducing agent solution with a concentration of 0.06~0.20 mol / L, wherein the molar concentration ratio of silver nitrate to reducing agent is 1:(1.2~2.0); mixing until homogeneous to obtain the seed solution.

7. The method according to claim 6, characterized in that, The superdispersant includes at least one of polyvinyl alcohol, polyethylene glycol, polyacryl alcohol, polycarboxylate, and polyurethane.

8. The method according to claim 4, characterized in that, In step (2), by volume, 1 part of silver nitrate solution with a concentration of 10~20wt% is set to 400L, 1 part of the base solution containing reducing agent is set to 450L, and 1 part of seed solution is set to 1L; 0.5~1.5 parts of seed solution are added to each part of silver nitrate solution, and 0.5~1.5 parts of seed solution are added to each part of base solution; and / or, in step (2), the pH of the base solution is adjusted to be controlled between 0.5 and 1.

5.

9. The method according to claim 4, characterized in that, In step (3), the coating agent includes at least one of stearic acid, lauric acid, gelatin and gum arabic; and / or, in step (3), the amount of coating agent added is 0.15-0.25 wt% of the mass of silver nitrate.

10. The method according to claim 4, characterized in that, In step (3), the coating time is 10~20 min; and / or, in step (3), the drying temperature is 60~70℃; and / or, in step (3), the drying time is 2~6 h; and / or, in step (3), the crushing pressure is 0.4~0.8 MPa.

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