Preparation method of conductive paste for solar cell

Abstract

The invention discloses a preparation method of conductive paste for a solar cell, and relates to the technical field of solar cell preparation. The preparation method comprises the following steps: adding a copper source, a surfactant, a dispersant and a brightness modifier into a solvent to obtain a first mixed solution; adding a reducing agent and a chelating agent into a solvent to obtain a second mixed solution; the first mixed solution and the second mixed solution are mixed according to the preset volume ratio, a third mixed solution is obtained, and seed copper powder with the preset mass fraction is added into the third mixed solution; the third mixed solution after the reaction is sequentially subjected to sedimentation cooling treatment, centrifugal treatment, drying treatment and grinding treatment, micron-sized copper powder is prepared, a conductive silver layer is deposited on the surface of the micron-sized copper powder through chemical reduction reaction, silver-coated copper powder is prepared, and the conductive paste is prepared through the silver-coated copper powder. The micron-sized copper powder prepared through the method can meet the high target size interval yield, the preparation cost is low, and the process compatibility is high.

Description

Technical Field

[0001] This invention relates to the field of solar cell fabrication technology, and more specifically to a method for preparing a conductive paste for solar cells. Background Technology

[0002] With the rapid development of the photovoltaic industry, the market demand for conductive pastes for solar cells continues to grow. Silver powder has always been the main conductive material in photovoltaic pastes due to its excellent conductivity, but the high price of silver keeps the cost of pastes high. To reduce costs while maintaining good conductivity, silver-coated copper powder, with its core-shell structure of inexpensive copper as the core and a silver coating on the surface, has become an ideal material to replace pure silver powder and has broad application prospects in the field of photovoltaic pastes.

[0003] The performance of silver-coated copper powder largely depends on the particle size and morphology of the core copper powder. Photovoltaic pastes have extremely stringent requirements for copper powder: the particle size distribution needs to be highly concentrated, typically requiring a D50 between 3 and 5 μm, a D10 greater than 2 μm, and a D90 not exceeding 8 μm. Excessively fine particles can lead to unstable silver coating, unstable paste viscosity, and deteriorated printing performance; excessively coarse particles affect the ink permeability and grid line formation ability of the paste. Therefore, obtaining micron-sized copper powder with a concentrated particle size distribution is crucial for preparing high-performance conductive pastes.

[0004] Currently, the mainstream method for preparing copper powder in industry is the physical method, including physical vapor deposition and atomization. Although this type of method has the advantages of high yield, high purity and good sphericity, the randomness of nucleation and growth during the preparation process results in a wide particle size distribution of the copper powder. It is difficult to obtain the narrow distribution copper powder that meets the requirements of photovoltaic paste, so a large amount of copper powder needs to be removed by sieving, resulting in reduced yield and increased production costs.

[0005] To address these issues, existing technologies often employ methods such as mechanical sieving, ball milling modification, or chemical hydrothermal treatment for particle size control. However, mechanical sieving struggles to fundamentally improve particle size distribution, ball milling introduces impurities and offers limited particle size control, while hydrothermal methods, though effective, require high temperature and pressure, resulting in complex processes and high energy consumption. Furthermore, existing chemical reduction methods typically use copper ions as starting materials, making it difficult to efficiently re-regulate and utilize existing physical copper powders. Simultaneously, current technologies often directly mix reducing agents and chelating agents in the design of reduction and complexation systems, leading to coupling between the reduction and complexation control processes. This makes precise control of copper ion release and reduction difficult, easily resulting in transient nucleation and particle agglomeration. Moreover, there are shortcomings in the synergistic regulation of dispersants and other functional components, hindering precise control of the reaction process. Summary of the Invention

[0006] One objective of this invention is to provide a method for preparing conductive paste for solar cells, thereby solving the technical problems in the prior art where the physical method for preparing copper powder has a wide particle size distribution, making it difficult to obtain a high proportion of narrow particle size distribution copper powder that meets the requirements of photovoltaic paste, resulting in low material yield, low resource utilization, and high production costs.

[0007] Another objective of this invention is to obtain copper powder materials with concentrated particle size distribution, uniform morphology, and dense structure.

[0008] According to the purpose of this invention, a method for preparing a conductive paste for solar cells is provided, comprising the following steps: A copper source, surfactant, dispersant, and brightening modifier are added to a solvent, and the mixture is stirred to obtain a first mixed solution. A reducing agent and a chelating agent are added to the solvent, and the mixture is stirred to obtain a second mixed solution. The first mixed solution and the second mixed solution are mixed at a preset volume ratio to obtain a third mixed solution. A preset mass fraction of seed copper powder is added to the third mixed solution to carry out a seed-induced chemical reduction reaction under preset reaction conditions. The particle size D50 of the seed copper powder is any value between 1 μm and 2 μm. After the reaction, the third mixed solution was subjected to sedimentation and cooling treatment, centrifugation treatment, drying treatment and grinding treatment in sequence to prepare micron-sized copper powder with a particle size D50 of 3μm-5μm, a particle size D10 greater than 2μm and a particle size D90 less than or equal to 8μm. A conductive silver layer is deposited on the surface of micron-sized copper powder using a chemical reduction reaction to prepare silver-coated copper powder, and the conductive paste is prepared using the silver-coated copper powder; wherein, The mass fraction of the brightening modifier in the first mixed solution is any value between 5wt% and 10wt%, the mass fraction of the chelating agent in the second mixed solution is any value between 15wt% and 30wt%, and the preset mass fraction is any value between 4wt% and 8wt%.

[0009] Optionally, the reaction temperature of the preset reaction conditions is any value between 60℃ and 90℃, and the reaction time is any value between 1h and 5h.

[0010] Optionally, the stirring speed for the seed-induced chemical reduction reaction is any value between 80 rpm / min and 90 rpm / min.

[0011] Optionally, the chelating agent is at least one of ethylenediamine, ethylenediaminetetraacetic acid, or citric acid.

[0012] Optionally, the brightening modifier is at least one of polyethylene glycol, polyethyleneimine, 2,2'-bipyridine, o-phenanthroline, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and polyacrylic acid.

[0013] Optionally, the preset volume ratio is any value between 2:1 and 3:1.

[0014] Optionally, the copper source is at least one of copper sulfate pentahydrate, anhydrous copper sulfate, copper nitrate hexahydrate, or copper nitrate.

[0015] Optionally, the dispersant is a mixture of polyvinylpyrrolidone and β-cyclodextrin, wherein the mass ratio of polyvinylpyrrolidone to β-cyclodextrin is any value of (10-1):1.

[0016] Optionally, the settling and cooling treatment time is any value between 6h and 24h, the drying treatment temperature is any value between 50℃ and 80℃, and the drying time is any value between 2h and 8h.

[0017] Optionally, the reducing agent is at least one of sodium hypophosphite, ascorbic acid, hydrazine hydrate, or formaldehyde, and the mass ratio of the reducing agent to the solvent is 1:(4-10).

[0018] This invention organically combines the construction of a copper source system, a reduction system, seed-induced chemical reduction growth, and post-processing when preparing conductive paste for solar cells. By synergistically controlling multiple parameters such as the content of brightening modifier, chelating agent, seed copper powder addition ratio, and reaction temperature, copper ions preferentially and selectively deposit on the surface of the seed copper powder during the reduction process. This suppresses disordered nucleation while achieving controlled particle growth. Overall, it achieves synergistic unity in controlling the interface state, regulating deposition behavior, and unifying the particle growth process of micron-sized copper powder. This facilitates the subsequent preparation of silver-coated copper powder with regular particle morphology, concentrated particle size distribution, good dispersibility, stable paste viscosity, excellent printing performance, high grid line formation consistency, and stable conductivity through chemical reduction reactions, thereby improving the conductivity of the conductive paste prepared using silver-coated copper powder. This allows the initial copper powder with a particle size of 1μm-2μm to grow uniformly and narrow its particle size distribution during the growth process, ultimately obtaining micron-sized copper powder with a particle size D50 of 3μm-5μm, a D10 greater than 2μm, and a D90 less than or equal to 8μm, which can meet the requirements of photovoltaic paste for particle size concentration and printability.

[0019] Furthermore, in this invention, the preset volume ratio of the first mixed solution and the second mixed solution is any value between 2:1 and 3:1. That is, when the proportion of the first mixed solution is appropriately dominant, it is beneficial to maintain a sufficient supply of copper ions and the driving force for deposition on the seed surface, promoting preferential growth. When the proportion of the second mixed solution is controlled, it can avoid excessive chelation leading to reaction inhibition or homogeneous nucleation caused by excessive reducing agent. Therefore, through synergistic regulation within this volume ratio range, a dynamic balance of the complexation-reduction process is achieved, enabling copper ions to be deposited in an orderly and stable manner on the seed surface, inhibiting particle agglomeration and abnormal growth, thereby obtaining copper powder material with concentrated particle size distribution, uniform morphology, and dense structure.

[0020] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0021] The following sections will describe some specific embodiments of the invention in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings: Figure 1 This is a schematic flowchart of a method for preparing conductive paste for solar cells according to an embodiment of the present invention; Figure 2 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Example 1 of the present invention; Figure 3 This is a particle size distribution diagram of the micron-sized copper powder prepared according to Example 1 of the present invention; Figure 4 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Example 2 of the present invention; Figure 5 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 1 of the present invention; Figure 6 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 2 of the present invention; Figure 7 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 3 of the present invention; Figure 8 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 4 of the present invention; Figure 9 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 5 of the present invention; Figure 10 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 6 of the present invention; Figure 11This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 7 of the present invention; Figure 12 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 8 of the present invention; Figure 13 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 9 of the present invention; Figure 14 This is a scanning electron microscope image of micron-sized copper powder prepared according to Comparative Example 10 of the present invention; Figure 15 This is a particle size distribution diagram of micron-sized copper powder prepared according to Comparative Example 10 of the present invention; Figure 16 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 11 of the present invention. Detailed Implementation

[0022] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0023] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0024] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0025] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0026] Figure 1 This is a schematic flowchart of a method for preparing conductive paste for solar cells according to an embodiment of the present invention.

[0027] like Figure 1 As shown, the present invention provides a method for preparing a conductive paste for solar cells, comprising the following steps: Step S100: Add copper source, surfactant, dispersant and brightening modifier to solvent, stir and treat to obtain first mixed solution; Step S200: Add the reducing agent and chelating agent to the solvent, and stir to obtain a second mixed solution; Step S300: Mix the first mixed solution and the second mixed solution according to a preset volume ratio to obtain a third mixed solution, and add a preset mass fraction of seed copper powder to the third mixed solution to carry out a seed-induced chemical reduction reaction under preset reaction conditions. The particle size D50 of the seed copper powder is any value between 1μm and 2μm. Step S400: After the reaction, the third mixed solution is subjected to sedimentation and cooling treatment, centrifugation treatment, drying treatment and grinding treatment in sequence to prepare micron-sized copper powder with particle size D50 of 3μm-5μm, particle size D10 greater than 2μm and particle size D90 less than or equal to 8μm. Step S500: A conductive silver layer is deposited on the surface of micron-sized copper powder using a chemical reduction reaction to prepare silver-coated copper powder, and a conductive paste is prepared using the silver-coated copper powder; wherein, the mass fraction of the brightening modifier in the first mixed solution is any value between 5wt% and 10wt%, the mass fraction of the chelating agent in the second mixed solution is any value between 15wt% and 30wt%, and the preset mass fraction is any value between 4wt% and 8wt%. Here, the mass fraction of the brightening modifier in the first mixed solution can be 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%, or any other value between 5wt% and 10wt%, the mass fraction of the chelating agent in the second mixed solution can be 15wt%, 20wt%, 25wt%, or 30wt%, or any other value between 15wt% and 30wt%, and the preset mass fraction of the added seed copper powder can be 4wt%, 5wt%, 6wt%, 7wt%, or 8wt%, or any other value between 4wt% and 8wt%.

[0028] In this embodiment, the method for preparing conductive paste for solar cells firstly involves preparing a first mixed solution containing a copper source, surfactant, dispersant, and brightening modifier, and a second mixed solution containing a reducing agent and a chelating agent. Then, the first and second mixed solutions are mixed uniformly according to a preset volume ratio to obtain a third mixed solution. Seed copper powder with a preset mass fraction and a particle size D50 of any value between 1 μm and 2 μm is added to the third mixed solution to perform a seed-induced chemical reduction reaction under preset reaction conditions to prepare micron-sized copper powder with increased particle size. Subsequently, after sedimentation cooling, centrifugation, drying, and grinding treatments, micron-sized copper powder with a particle size D50 of 3 μm-5 μm, a particle size D10 greater than 2 μm, and a particle size D90 less than or equal to 8 μm is obtained. Then, a conductive silver layer is deposited on the surface of the micron-sized copper powder using a chemical reduction reaction to prepare silver-coated copper powder, and the conductive paste is prepared using the silver-coated copper powder.

[0029] In this embodiment, when preparing conductive paste for solar cells, the construction of the copper source system, the construction of the reduction system, the seed-induced chemical reduction growth, and the post-processing are organically combined. By synergistically controlling multiple parameters such as the content of brightening modifier, chelating agent, seed copper powder addition ratio, and reaction temperature, copper ions preferentially and selectively deposit on the surface of seed copper powder during the reduction process. While suppressing disordered nucleation, controlled particle growth is achieved. This results in the overall synergistic unification of the interface state control, deposition behavior regulation, and particle growth process of micron-sized copper powder. This facilitates the subsequent preparation of silver-coated copper paste powder with regular particle morphology, concentrated particle size distribution, good dispersibility, stable paste viscosity, excellent printing performance, high grid line formation consistency, and stable conductivity using chemical reduction reaction, thereby improving the conductivity of conductive paste prepared using silver-coated copper powder. This allows the initial copper powder with a particle size of 1μm-2μm to grow uniformly and narrow its particle size distribution during the growth process, ultimately obtaining micron-sized copper powder with a particle size D50 of 3μm-5μm, a D10 greater than 2μm, and a D90 less than or equal to 8μm, which can meet the requirements of photovoltaic paste for particle size concentration and printability.

[0030] Meanwhile, compared to the problems of wide particle size distribution and low yield due to sieving required for physical methods to prepare micron-sized copper powder, as well as the problems of complex processes, high energy consumption and difficulty in directly utilizing physical copper powder resources, this embodiment can achieve active control of particle size distribution through seed-induced growth without changing the source of physical copper powder. This not only increases the proportion of copper powder in the target particle size range, but also has the advantages of mild process conditions, strong controllability and suitability for large-scale implementation, thereby achieving comprehensive optimization of particle size distribution, surface morphology and structural stability.

[0031] It should be noted that while physical methods for preparing copper powder offer advantages such as high yield and purity, their particle size distribution is typically wide, making it difficult to meet the requirements of photovoltaic pastes for copper powder particle size concentration. Chemical reduction or electroless plating methods are mostly used to directly generate copper particles or form a metal layer on the substrate surface, focusing on the deposition reaction itself and film quality control. For further copper deposition on the surface of copper seeds, the presence of oxide layers, contaminants, or surface defects often leads to insufficient interfacial bonding, uneven deposition, localized stress concentration, and decreased structural stability. Furthermore, new nucleation behaviors may occur during deposition, complicating the particle size distribution. Therefore, achieving stable, uniform, and controllable further growth on existing copper powder to avoid uneven deposition or deterioration of particle size distribution presents significant uncertainties. This makes it difficult for those skilled in the art to directly formulate such technical concepts based on existing technologies, and a clear technical path is lacking for effective control of particle size distribution.

[0032] Furthermore, the introduction of copper seeds into a copper-containing chemical reduction system leads to deposition behavior influenced by a combination of factors, including seed surface state, reduction rate, complexation equilibrium, solution composition, and synergistic effects among various additives. Deviations in any of these factors can result in new homogeneous nucleation, particle agglomeration, or uneven deposition, further deteriorating the particle size distribution. Simultaneously, to achieve preferential copper growth on the seed surface and suppress disordered deposition, precise matching of the types, amounts, and ratios of surfactants, dispersants, brightening modifiers, and chelating agents is required, along with systematic control of reaction conditions to maintain a dynamic balance between the deposition process and particle dispersion. This necessitates synergistic optimization across multiple aspects, including comprehensive interface control, reaction kinetics, and particle growth behavior. Achieving this relies on a finely coupled multi-parameter control process, exhibiting high uncertainty and technical complexity, making it difficult to obtain directly through conventional process optimization or limited experiments.

[0033] In this embodiment, a copper source, surfactant, dispersant, and brightening modifier are introduced into the first mixed solution. By pre-constructing a stable and dispersed copper ion environment, copper ions are uniformly distributed in the system. The surfactant regulates the interfacial wettability between the copper seed and the solution, reducing interfacial energy. The dispersant inhibits the aggregation of copper source particles, ensuring system homogeneity. The brightening modifier regulates the growth orientation and surface morphology of copper crystals during subsequent deposition. The synergistic effect of these multiple components provides a uniform reaction basis for copper ions during subsequent reduction, providing conditions for selective deposition and controllable particle size growth from the outset.

[0034] In this embodiment, the chelating agent is placed in the second mixed solution and together with the reducing agent to construct a complexation-reduction system. This avoids excessive complexation of the chelating agent with copper ions in the copper source during the first mixing stage, which would limit the reactivity. Thus, when the second mixed solution is mixed with the first mixed solution, the complexation regulation and reduction reaction are triggered simultaneously, allowing copper ions to preferentially deposit on the surface of the seed copper powder under controlled conditions. This is beneficial for achieving precise control of particle size distribution and stability of the deposition process.

[0035] In step S300, the first mixed solution and the second mixed solution are mixed in proportion to couple the interface control system and the reaction driving system at the same time. Through the synergistic effect of chelation control, reduction kinetics and interface energy control, controllable deposition and uniform growth of copper ions on the seed surface are achieved, instead of new homogeneous nucleation in the solution. This significantly reduces the dispersion of particle size distribution, avoids uncontrolled reaction rate and local deposition anomalies, thereby achieving narrowing of particle size distribution and stable formation of particle structure.

[0036] In other embodiments, changing the order of the above components or the mixing method may cause the complexation regulation and reduction reaction to lose their synergistic relationship, thereby leading to problems such as uncontrolled reaction, increased homogeneous nucleation or uneven deposition, making it difficult to achieve precise control over the particle size distribution and surface morphology of micron-sized copper powder.

[0037] In this embodiment, by introducing seed copper powder with a particle size D50 of 1μm-2μm, copper ions in the system preferentially deposit on the existing copper surface under the dual driving forces of thermodynamics and kinetics, achieving seed-induced growth. This mechanism can effectively reduce the probability of new nucleus generation, transforming the particle growth process from multinucleated random nucleation to directional growth, thereby achieving ordered enlargement and narrowing of particle size distribution. Here, the particle size D50 of the seed copper powder can be 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, or 2μm, or any other value within the 1μm-2μm range.

[0038] In this embodiment, by synergistically controlling multiple parameters such as the amount of brightening modifier, chelating agent, seed copper powder, and reaction conditions, a coupling relationship is formed between interface control, reaction kinetics, and particle growth behavior. Specifically, the brightening modifier controls the crystal growth direction and surface smoothness, the chelating agent controls the copper ion release rate and reduction reaction rhythm, and the seed copper powder controls the nucleation site and growth path. The interaction of these multiple parameters transforms the deposition process from single-reaction control to multi-factor synergistic control, thereby achieving precise control over particle size distribution and ultimately obtaining micron-sized copper powder with a uniform particle size distribution suitable for photovoltaic paste systems.

[0039] In this embodiment, unreacted and abnormal particles are further removed through post-processing steps such as sedimentation cooling, centrifugal separation, drying, and grinding. The morphology of the particles is optimized so that the final copper powder particle size is concentrated in the range of D50 of 3μm-5μm, while controlling D10 to be greater than 2μm and D90 to be less than or equal to 8μm. This significantly improves the consistency and flowability of the particle size, avoids the screen clogging problem caused by sheet-like or excessively large particles, and meets the requirements of conductive paste for screen printing performance.

[0040] In this embodiment, the solvent is a mixed solution of ethylene glycol and deionized water, with a mass ratio of ethylene glycol to deionized water of any value between 5:(1-20). Specifically, the mass ratio of ethylene glycol to deionized water can be 5:1, 5:5, 5:10, 5:15, or 5:20, or any other value between 5:(1-20). In this embodiment, ethylene glycol, as a high-boiling-point solvent with strong reducing and complexing abilities, can participate in the gentle reduction of copper ions during the reaction process. By increasing the viscosity of the system, it reduces the ion diffusion rate, thereby inhibiting instantaneous nucleation and promoting directional deposition on the seed surface. Deionized water, as a polar solvent, is beneficial for the full dissolution and uniform dispersion of copper salt and related components. Furthermore, by adjusting the solution polarity and ion migration ability, it can influence the reduction reaction rate and crystal nucleation behavior. By adjusting the relative content of ethylene glycol and deionized water within the stated ratio range, a synergistic match can be achieved between the system's viscosity, reducing power, and solubility / mass transfer performance. This avoids homogeneous nucleation or particle agglomeration caused by excessively rapid reduction rates, as well as incomplete reactions due to limited diffusion. Therefore, under the synergistic effect of this solvent system, controllable growth of copper on the seed surface can be achieved while ensuring reaction uniformity, resulting in copper powder materials with concentrated particle size distribution, regular morphology, and dense structure.

[0041] In a further embodiment, the preset reaction conditions include a reaction temperature of any value between 60℃ and 90℃, and a reaction time of any value between 1h and 5h. Specifically, the preset reaction temperature can be 60℃, 70℃, 80℃, or 90℃, or any other value between 60℃ and 90℃, and the reaction time can be 1h, 2h, 3h, 4h, or 5h, or any other value between 1h and 5h. In this embodiment, by controlling the reaction temperature within the range of 60℃-90℃ and the reaction time within the range of 1h-5h, a synergistic regulatory relationship is formed between the reduction kinetics, complexation equilibrium, and crystal growth rate of the reaction system. This ensures sufficient reaction while avoiding the adverse effects caused by excessively fast or slow reaction rates. Specifically, the reaction temperature within the above range is beneficial for increasing the reduction reaction rate and promoting the orderly deposition of copper on the seed surface, while the reasonable setting of the reaction time allows copper ions to continuously and uniformly deposit and grow within a relatively stable reaction window, thereby suppressing stress concentration caused by excessively rapid local deposition and particle size unevenness caused by insufficient reaction. Therefore, under the synergistic effect of temperature and time, the growth process of copper particles is transformed from reaction kinetic control to diffusion and interface regulation synergistic control, thereby obtaining micron-sized copper powder with concentrated particle size distribution, uniform morphology and stable structure, and improving its fluidity and printability in photovoltaic paste applications.

[0042] In a further embodiment, the stirring speed for the seed-induced chemical reduction reaction is any value between 80 rpm / min and 90 rpm / min. Specifically, the stirring speed can be 80 rpm / min, 82 rpm / min, 84 rpm / min, 86 rpm / min, 88 rpm / min, or 90 rpm / min, or any other value between 80 rpm / min and 90 rpm / min. This allows for a synergistic regulatory relationship between the mass transfer process, reaction kinetics, and particle growth behavior, thereby achieving stable transport of copper ions to the surface of the copper powder in the seeds and promoting uniform deposition. Specifically, the stirring speed within the aforementioned range can, on the one hand, improve the macroscopic and microscopic mixing uniformity of the system, reduce local concentration gradients, and avoid homogeneous nucleation and particle agglomeration caused by local enrichment of copper ions. On the other hand, it avoids shear damage to the deposited copper layer or secondary collisions and agglomeration between particles due to excessive stirring intensity, thus maintaining a stable growth environment on the seed surface while ensuring the reaction proceeds fully. Therefore, under the coordinated control of stirring speed, the mass transfer process and deposition reaction process in the system are kept in dynamic equilibrium, which promotes the preferential growth of copper on the seed surface and inhibits disordered deposition behavior, thereby obtaining micron-sized copper powder with concentrated particle size distribution, dense surface structure and uniform morphology.

[0043] In a further embodiment, the chelating agent is at least one of ethylenediamine, ethylenediaminetetraacetic acid, or citric acid. Different structural types of chelating agents form stable coordination with copper ions, thereby synergistically regulating the release rate of copper ions and the reduction reaction process. Specifically, the chelating agent complexes copper ions through a multidentate coordination structure, maintaining a low and stable concentration of freely distributed copper ions in the system, effectively suppressing the instantaneous reduction behavior and homogeneous nucleation tendency of copper ions. Simultaneously, different types of chelating agents differ in coordination ability, complexation stability, and dissociation rate, and can be selected or combined according to reaction requirements to adjust the complexation strength and release rhythm of copper ions, thereby achieving precise control of the reduction reaction rate. Therefore, under the chelation regulation, copper ions preferentially and selectively deposit on the surface of the seed copper powder, avoiding particle agglomeration or uneven deposition due to local supersaturation, thereby achieving narrowing of particle size distribution and uniformity of particle morphology, and improving the structural stability of the obtained copper powder and its applicability in photovoltaic pastes.

[0044] In a further embodiment, the brightening modifier is at least one of polyethylene glycol, polyethyleneimine, 2,2'-bipyridine, o-phenanthroline, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and polyacrylic acid. By introducing organic molecules or surface-active components with different structural characteristics into the reaction system, the coordination environment of copper ions, crystal growth orientation, and interfacial energy are synergistically regulated, thereby achieving precise control of the copper deposition process. Specifically, the coordination molecules in the brightening modifier, such as polyethyleneimine, 2,2'-bipyridine, and o-phenanthroline, can form stable coordination structures with copper ions, reduce the transient activity of free copper ions, inhibit non-directional nucleation, and guide the crystal to preferentially grow along specific crystal planes. Surfactants, such as hexadecyltrimethylammonium bromide and sodium dodecyl sulfate, can adsorb on the particle surface and regulate interfacial tension, improving the dispersibility of particles in solution and preventing particle aggregation. Meanwhile, polymers, such as polyethylene glycol and polyacrylic acid, can further suppress the abnormal growth of coarse grains through steric hindrance and selective coverage of growth sites.

[0045] In a further embodiment, the preset volume ratio is any value between 2:1 and 3:1, meaning the volume ratio of the first mixed solution and the second mixed solution can be 2:1, 2.2:1, 2.4:1, 2.6:1, 2.8:1, or 3:1, or any other value between 2:1 and 3:1. In this embodiment, the first mixed solution typically provides the copper source and seed-inducing reaction environment, while the chelating agent and reducing agent in the second mixed solution work synergistically to regulate the effective concentration and release rate of copper ions. By setting a reasonable volume ratio, the chelation regulation capacity and reduction capacity in the system are matched. That is, when the proportion of the first mixed solution is appropriately dominant, it is beneficial to maintain sufficient copper ion supply and seed surface deposition driving force, promoting preferential growth. When the proportion of the second mixed solution is controlled, it can avoid excessive chelation leading to reaction inhibition or homogeneous nucleation caused by excessive reducing agent. Therefore, by utilizing the synergistic regulation within the aforementioned preset volume ratio range, a dynamic balance of the complexation-reduction process is achieved, enabling copper ions to be deposited in an orderly and stable manner on the seed surface, inhibiting particle aggregation and abnormal growth, thereby obtaining copper powder materials with concentrated particle size distribution, uniform morphology, and dense structure.

[0046] In a further embodiment, the copper source is at least one of copper sulfate pentahydrate, anhydrous copper sulfate, copper nitrate hexahydrate, or copper nitrate. Sulfate or nitrate copper sources exhibit good solubility in a water / ethylene glycol mixed solvent, enabling uniform dispersion of copper ions and avoiding non-uniform deposition caused by local concentration fluctuations. Simultaneously, different anions regulate the coordination environment of copper ions and the ionic strength of the solution, influencing the complexation equilibrium and reduction kinetics of copper ions to a certain extent, thus facilitating control of the reduction reaction rate and inhibiting homogeneous nucleation. Furthermore, the presence of water of crystallization in copper sulfate pentahydrate and copper nitrate hexahydrate can regulate the local polarity and mass transfer behavior of the system during dissolution, resulting in a smoother release of copper ions, which is beneficial for stable deposition on the surface of the seed copper powder.

[0047] In a further embodiment, the dispersant is a mixture of polyvinylpyrrolidone (PVP) and β-cyclodextrin, with a mass ratio of PPVP to β-cyclodextrin of any value within (10⁻¹):1. Specifically, the mass ratio of PPVP to β-cyclodextrin can be 10:1, 8:1, 6:1, 4:1, 2:1, or 1:1, or any other value within (10⁻¹):1, allowing the system to achieve a synergistic effect in dispersion stability, interface regulation, and particle growth behavior. PPVP possesses good solubility and a high molecular chain structure, enabling it to adsorb onto the surface of copper particles through steric hindrance, effectively inhibiting direct contact and aggregation between particles. It also selectively covers crystal growth sites during deposition, thereby limiting abnormal growth. β-cyclodextrin, with its unique cavity structure and molecular recognition ability, can regulate the distribution of copper ions or related organic molecules in the solution through inclusion, improving the microscopic uniformity of the system and influencing complexation equilibrium and mass transfer processes to a certain extent. By working together within the aforementioned ratio range, the dispersion stability of the system can be improved and the risk of particle agglomeration can be reduced. On the other hand, it helps to regulate the migration and deposition behavior of copper ions on the seed surface, thereby achieving uniform particle growth and inhibiting disordered nucleation.

[0048] In this embodiment, the mass ratio of copper source, dispersant and solvent is any value in 1:(0.4-2):(2.3-5), that is, the mass ratio of copper source, dispersant and solvent can be 1:0.4:2.3, 1:0.5:2.3, 1:1:2.3, 1:1.5:2.3, 1:2:2.3, 1:0.4:3, 1:0.4:4 or 1:0.4:5, or any other value in 1:(0.4-2):(2.3-5), to achieve a synergistic match between copper ion supply, system dispersion stability and solution mass transfer performance, thereby promoting uniform deposition and growth of copper on the seed surface while inhibiting particle agglomeration and disordered nucleation, and thus obtaining copper powder with concentrated particle size distribution and stable morphology.

[0049] In a further embodiment, the settling and cooling treatment time is any value between 6h and 24h, the drying treatment temperature is any value between 50℃ and 80℃, and the drying time is any value between 2h and 8h. That is, the settling and cooling treatment time can be 6h, 10h, 15h, 20h, or 24h, or any other value between 6h and 24h; the drying treatment temperature can be 50℃, 60℃, 70℃, or 80℃, or any other value between 50℃ and 80℃; and the drying time can be 2h, 4h, 6h, or 8h, or any other value between 2h and 8h, so that a synergistic regulatory relationship is formed between the particle classification and settling, structure stabilization, and solvent removal processes. In particular, appropriately extending the settling and cooling time is beneficial for the full stratification and stable precipitation of particles of different sizes, reducing the entrainment of fine particles and improving the concentration of particle size distribution. Under the conditions of mild drying temperature and reasonable drying time, particle agglomeration, surface structure damage or internal stress caused by rapid volatilization or excessive temperature can be avoided, thereby ensuring that the powder is fully dried while maintaining its original morphology and structural stability.

[0050] In a further embodiment, the reducing agent is at least one of sodium hypophosphite, ascorbic acid, hydrazine hydrate, or formaldehyde, and the mass ratio of the reducing agent to the solvent is 1:(4-10), that is, the mass ratio of the reducing agent to the solvent can be 1:4, 1:5, or 1:10, or any other value within the range of 1:(4-10). In this embodiment, different reducing agents differ in terms of reducing strength and reaction rate, which can achieve a mild or relatively rapid reduction process according to the system requirements. By controlling the ratio of the reducing agent to the solvent, the effective concentration and release rate of the reducing agent can be further adjusted, thereby avoiding homogeneous nucleation caused by an excessively fast reduction reaction or insufficient deposition caused by an excessively slow reduction reaction.

[0051] The technical solution of this application will be further described below with reference to specific embodiments.

[0052] Example 1 The preparation method of conductive paste for solar cells includes the following steps: Step S100: Weigh 100g of copper nitrate hexahydrate as the copper source, add 100g of polyethylene glycol as the dispersant, add 8g of polyacrylic acid as the brightening modifier, and add it to a solvent with a mass ratio of ethylene glycol to deionized water of 1:8 until the total mass is 550g. Stir at 60℃ for 2h to obtain the first mixed solution. Step S200: Weigh 50g of ascorbic acid as a reducing agent, add a solvent with a mass ratio of ethylene glycol to deionized water of 1:8, add 96g of ethylenediamine to a total mass of 450g, and stir at 60℃ for 1h to obtain a second mixed solution; Step S300: The first mixed solution and the second mixed solution are mixed at a preset volume ratio of 2.3:1 to obtain a third mixed solution. 6 wt% of a preset mass fraction of seed copper powder is added to the third mixed solution, and the mixture is reacted at 85°C for 1.5 h to carry out a seed-induced chemical reduction reaction. The particle size D50 of the seed copper powder is 1.8 μm and the particle size D10 is 1.0 μm. Step S400: The third mixed solution after the reaction was subjected to sedimentation and cooling treatment, centrifugation treatment, drying treatment and grinding treatment for 24 hours in sequence. The drying treatment temperature was 50℃ and the drying time was 6 hours to prepare micron-sized copper powder with a particle size D50 of 4.5 μm, a particle size D10 of 2.5 μm and a particle size D90 of 7.8 μm, and the yield in the target range reached 80%. Step S500: Add the above-mentioned micron-sized copper powder to a silver ammonia solution and sonicate at 52°C for 25 minutes to deposit a conductive silver layer on the surface of the micron-sized copper powder using a chemical reduction reaction, thereby preparing silver-coated copper powder. Conductive paste is then prepared using the silver-coated copper powder. The silver ammonia solution is prepared by adding 9.3g of silver nitrate to 190mL of deionized water and mixing thoroughly, and then adding 5mL of 95wt% nitric acid solution.

[0053] Example 2 The difference between Example 2 and Example 1 is only in step S200, where the mass fraction of ethylene glycol in the solvent is 62wt%, and 56g of ethylenediamine is added to bring the total mass to 250g. The mixture is stirred at 60°C for 1h to obtain the second mixed solution.

[0054] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that no chelating agent was added to the second mixed solution.

[0055] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the added chelating agent has a mass fraction of 5 wt%.

[0056] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that the added chelating agent has a mass fraction of 8 wt%.

[0057] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that the mass fraction of the seed copper powder is 10 wt%.

[0058] Comparative Example 5 The only difference between Comparative Example 5 and Example 1 is that the mass fraction of the seed copper powder is 2 wt%.

[0059] Comparative Example 6 The only difference between Comparative Example 6 and Example 1 is that the particle size D50 of the seed copper powder is 0.5 μm.

[0060] Comparative Example 7 The only difference between Comparative Example 7 and Example 1 is that the particle size D50 of the seed copper powder is 3 μm.

[0061] Comparative Example 8 The only difference between Comparative Example 8 and Example 2 is that the mass fraction of the brightening modifier in the first mixed solution is 2 wt%.

[0062] Comparative Example 9 The only difference between Comparative Example 9 and Example 2 is that the mass fraction of the brightening modifier in the first mixed solution is 15 wt%.

[0063] Comparative Example 10 The difference between Comparative Example 10 and Example 1 is that the micron-sized copper powder was purchased, with the grade name Brofos-Cu-W01 and CAS number 7440-50-8.

[0064] Comparative Example 11 The difference between Comparative Example 11 and Example 1 is in step S300, where 6 wt% of a preset mass fraction of seed copper powder is added to the third mixed solution to react at 95°C for 6 hours to prepare micron-sized copper powder.

[0065] Figure 2 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Example 1 of the present invention. Figure 3 This is a particle size distribution diagram of the micron-sized copper powder prepared according to Example 1 of the present invention. Figure 4 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Example 2 of the present invention. Figure 5 Here is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 1 of this invention. Figure 6 Here is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 2 of this invention. Figure 7 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 3 of the present invention. Figure 8 Here is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 4 of this invention. Figure 9 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 5 of the present invention. Figure 10 Here is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 6 of this invention. Figure 11 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 7 of the present invention. Figure 12 Here is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 8 of this invention. Figure 13 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 9 of the present invention. Figure 14 Here is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 10 of the present invention. Figure 15This is a particle size distribution diagram of the micron-sized copper powder prepared according to Comparative Example 10 of the present invention. Figure 16 This is a scanning electron microscope image of the micron-sized copper powder prepared according to Comparative Example 11 of the present invention.

[0066] First, the micron-sized copper powders prepared in Examples 1-2 and Comparative Examples 1-11 were subjected to scanning electron microscopy and particle size (D50, D10, and D90) tests, as shown in Table 1. Figures 2 to 16 The test results are shown.

[0067] Table 1. Particle size test results of micron-sized copper powders obtained in Examples 1-2 and Comparative Examples 1-11

[0068] According to Table 1 and Figure 2-4 The test results show that the micron-sized copper powders prepared in Examples 1 and 2 exhibit significant advantages in terms of particle size distribution and yield within the target range. Specifically, Example 1 has a D50 of 4.5 μm, a D10 of 2.5 μm, and a D90 of 7.8 μm, while Example 2 has a D50 of 5.6 μm, a D10 of 4.5 μm, and a D90 of 6.6 μm. Both meet the stringent requirements of photovoltaic pastes for copper powder particle size distribution, and the yields within the target range reach 80% and 90%, respectively, significantly higher than the comparative examples. This demonstrates that this application, through seed-induced chemical reduction and multi-parameter synergistic regulation, can effectively achieve uniform particle growth and significantly increase the proportion of narrow-particle-size copper powder.

[0069] As shown in Table 1 and Figures 5 to 7 As shown in Comparative Examples 1-3, the setting and content of the chelating agent have a significant impact on the particle size distribution. When no chelating agent is added (Comparative Example 1) or the chelating agent content is too low (Comparative Examples 2-3), although the D50 is still within a certain range, the yield in the target range decreases significantly (75%, 70%, 64%), indicating that the copper ions in the system lack effective complexation regulation, leading to instability in the reduction process and easy occurrence of local nucleation and particle size distribution dispersion. In contrast, by controlling the chelating agent content within a reasonable range in the examples, the activity of copper ions can be effectively adjusted to achieve uniform deposition and growth, thereby improving the concentration of particle size distribution.

[0070] like Figure 8 and Figure 9As shown in the table and in conjunction with Comparative Examples 4-5 in Table 1, the addition ratio of seed copper powder also has a significant impact on the final particle size distribution. When the seed addition amount is too high (10wt%) or too low (2wt%), the D90 of the obtained micron-sized copper powder increases to 8.9μm and 9.9μm, respectively, and the yield of the target range decreases to 76% and 65%, indicating that too much or too little seed will disrupt the balance of the deposition process, resulting in uneven particle growth. In Examples 1 and 2, by controlling the seed addition ratio within a reasonable range, copper ions are evenly distributed and deposited on the seed surface, thereby obtaining a more concentrated particle size distribution.

[0071] like Figure 10 and Figure 11 As shown in Table 1, and in conjunction with Comparative Examples 6-7, it can be seen that the initial particle size of the seed copper powder has a significant impact on particle growth behavior. When the seed particle size is too small (0.5 μm) or too large (3 μm), the D50 of the resulting micron-sized copper powder is significantly larger, and the D90 increases to 13.4 μm (Comparative Example 7). The yields in the target range decrease to 74% and 62%, respectively, indicating that deviations from the reasonable seed particle size range lead to a mismatch in growth rates, which in turn causes a deterioration in particle size distribution. In contrast, the seed copper powder with a D50 of 1.8 μm selected in Example 1 is beneficial for achieving uniform scale-up growth and narrowing the particle size distribution.

[0072] like Figure 12 and Figure 13 As shown in Table 1, and in conjunction with Comparative Examples 8-9, it can be seen that the content of the brightening modifier has a regulatory effect on the particle morphology and particle size distribution. When its content is too low (2wt%) or too high (15wt%), the D90 reaches 11.3μm and 12.4μm, respectively, and the yield in the target range is significantly reduced. This indicates that insufficient or excessive brightening modifier will destroy the orderliness of crystal growth, leading to abnormal particle growth or agglomeration. In the examples, by reasonably controlling its content, the crystal growth behavior can be effectively regulated, and micron-sized copper powder with smooth surface and uniform particle size can be obtained.

[0073] like Figures 14 to 16 As shown in Table 1, Comparative Examples 10 and 11 represent micron-sized copper powder obtained by physical and hydrothermal processing methods, respectively. Their target range yields are only 50% and 53%, which are significantly lower than those of Examples 1 and 2 of this application, indicating that traditional methods are difficult to achieve effective concentration of particle size distribution.

[0074] In summary, this application, by constructing a seed-induced chemical reduction system and synergistically regulating multiple parameters, can not only significantly improve the concentration of particle size distribution but also increase the yield of micron-sized copper powder within the target particle size range. This allows for the reuse of seed copper powder prepared by physical methods that does not conform to the target range, further reducing the preparation cost of conductive paste.

[0075] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0076] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a conductive paste for solar cells, characterized in that, Includes the following steps: A copper source, surfactant, dispersant, and brightening modifier are added to a solvent, and the mixture is stirred to obtain a first mixed solution. A reducing agent and a chelating agent are added to the solvent, and the mixture is stirred to obtain a second mixed solution. The first mixed solution and the second mixed solution are mixed at a preset volume ratio to obtain a third mixed solution. A preset mass fraction of seed copper powder is added to the third mixed solution to carry out a seed-induced chemical reduction reaction under preset reaction conditions. The particle size D50 of the seed copper powder is any value between 1 μm and 2 μm. After the reaction, the third mixed solution was subjected to sedimentation and cooling treatment, centrifugation treatment, drying treatment and grinding treatment in sequence to prepare micron-sized copper powder with a particle size D50 of 3μm-5μm, a particle size D10 greater than 2μm and a particle size D90 less than or equal to 8μm. A conductive silver layer is deposited on the surface of micron-sized copper powder using a chemical reduction reaction to prepare silver-coated copper powder, and the conductive paste is prepared using the silver-coated copper powder; wherein, The mass fraction of the brightening modifier in the first mixed solution is any value between 5wt% and 10wt%, the mass fraction of the chelating agent in the second mixed solution is any value between 15wt% and 30wt%, and the preset mass fraction is any value between 4wt% and 8wt%.

2. The method for preparing conductive paste for solar cells according to claim 1, characterized in that, The preset reaction conditions are: a reaction temperature of any value between 60℃ and 90℃, and a reaction time of any value between 1h and 5h.

3. The method for preparing conductive paste for solar cells according to claim 2, characterized in that, The stirring speed for the seed-induced chemical reduction reaction is any value between 80 rpm / min and 90 rpm / min.

4. The method for preparing conductive paste for solar cells according to claim 3, characterized in that, The chelating agent is at least one of ethylenediamine, ethylenediaminetetraacetic acid, or citric acid.

5. The method for preparing conductive paste for solar cells according to claim 4, characterized in that, The brightening modifier is at least one of polyethylene glycol, polyethyleneimine, 2,2'-bipyridine, o-phenanthroline, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and polyacrylic acid.

6. The method for preparing conductive paste for solar cells according to claim 5, characterized in that, The preset volume ratio is any value between 2:1 and 3:

1.

7. The method for preparing the conductive paste for solar cells according to any one of claims 1-6, characterized in that, The copper source is at least one of copper sulfate pentahydrate, anhydrous copper sulfate, copper nitrate hexahydrate, or copper nitrate.

8. The method for preparing conductive paste for solar cells according to claim 7, characterized in that, The dispersant is a mixture of polyvinylpyrrolidone and β-cyclodextrin, wherein the mass ratio of polyvinylpyrrolidone to β-cyclodextrin is any value of (10-1):

1.

9. The method for preparing conductive paste for solar cells according to claim 8, characterized in that, The settling and cooling treatment time is any value between 6h and 24h, the drying treatment temperature is any value between 50℃ and 80℃, and the drying time is any value between 2h and 8h.

10. The method for preparing conductive paste for solar cells according to claim 9, characterized in that, The reducing agent is at least one of sodium hypophosphite, ascorbic acid, hydrazine hydrate, or formaldehyde, and the mass ratio of the reducing agent to the solvent is 1:(4-10).

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