Highly conductive silver / graphene composite solute and preparation method thereof

Abstract

The application belongs to the technical field of electronic materials, and particularly relates to a high-conductivity silver / graphene composite solute and a preparation method thereof. The method comprises the following steps: acidizing graphene to obtain an acidized graphene dispersion liquid; mixing the acidized graphene dispersion liquid with a formaldehyde solution to perform an aldehyde reaction, and obtaining an aldehyde graphene dispersion liquid; mixing the aldehyde graphene dispersion liquid with a silver-ammonia solution to perform a silver mirror reaction, and obtaining a silver / graphene composite solute. The graphene is subjected to acidization and aldehyde treatment, and then is subjected to a silver mirror reaction with a silver-ammonia solution to form a silver / graphene composite solute. A small amount of the prepared silver / graphene composite solute is added to commercial silver paste, which not only optimizes the conductive path of the silver paste, but also effectively reduces the porosity problem in the sintering process, thereby significantly enhancing the electron transmission performance, greatly improving the conductivity of the silver paste, and finally promoting the solar cell to achieve higher photoelectric conversion efficiency.

Description

Technical Field

[0001] This invention belongs to the field of electronic materials technology, specifically relating to a highly conductive silver / graphene composite solute and its preparation method. Background Technology

[0002] With increasing energy demand, the depletion of fossil fuels, and environmental issues, clean and renewable energy sources are becoming central. Solar energy, especially crystalline silicon solar cells, is becoming a key alternative to traditional energy sources due to its high efficiency and reduced cost. In the structure of a crystalline silicon solar cell, the front metal electrode plays a crucial role, primarily in efficiently collecting and extracting photogenerated electrons, thereby improving the cell's current output and conversion efficiency.

[0003] Silver is widely used in the front-side metal electrode paste of crystalline silicon solar cells due to its high conductivity and good oxidation resistance. Conductive silver paste consists of a conductive phase (silver powder), a binder phase, and an organic carrier. The binder phase accounts for 1%–4%, the conductive phase is silver powder (80%–90%), and the organic carrier accounts for approximately 8%. The binder phase is responsible for etching the silicon nitride layer on the silicon surface and ensuring strong contact between the silver grid lines and the cell surface. The organic carrier is responsible for adjusting the paste viscosity and maintaining a good aspect ratio. The silver powder determines the conductivity of the paste and is its main component. Generally, the silver paste is applied to the silicon wafer surface via screen printing. During sintering, the binder phase etches the silicon wafer, and the silver powder thermally shrinks to form strong silver grid lines. Silver powder goes through three stages during sintering: (1) bonding stage, where silver powder particles form a metallurgical bond and conductivity is enhanced; (2) sintering neck growth stage, where the distance between particles is reduced, pores are reduced, and density and strength are increased; (3) closed-pore spheroidization stage, where pores are closed, shrinkage is slowed down, and finally dense and high-strength silver electrode grid lines are formed.

[0004] However, in the actual sintering process, many factors can cause discontinuities in the conductive paths of the silver grid lines, ultimately affecting the conductivity. For example, (1) uneven distribution of silver particles or incomplete particle contact can lead to gaps in the conductive paths; (2) bubbles are generated when the binder phase and organic phase volatilize and are not completely discharged, forming pores; (3) incomplete sintering or excessive etching of the binder phase can lead to poor bonding of silver particles; (4) the sintering activity of silver powder is low, and it cannot be completely fused, forming discontinuous conductive paths. Therefore, although the design and development of commercial silver paste is currently quite active, its conductivity has not been significantly improved, and it is still not possible to enable crystalline silicon solar cells to have higher photoelectric conversion efficiency. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a highly conductive silver / graphene composite solute and its preparation method. Graphene is acidified and aldehyde-treated, then reacted with a silver ammonia solution via a silver mirror reaction to form a silver / graphene composite solute. This solute is then added in small amounts to commercial silver paste to significantly improve the conductivity of the paste, thereby promoting higher photoelectric conversion efficiency in solar cells.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0007] On one hand, the present invention provides a method for preparing a highly conductive silver / graphene composite solute, comprising the following steps:

[0008] S1. Acidification treatment of graphene to obtain acidified graphene dispersion.

[0009] S2. The acidified graphene dispersion is mixed with formaldehyde solution to carry out an aldehyde reaction, thereby obtaining an aldehyde-based graphene dispersion.

[0010] S3. Mix the aldehyde graphene dispersion and the silver ammonia solution, and carry out the silver mirror reaction to obtain the silver / graphene composite solute.

[0011] It should be noted that after the silver mirror reaction, the reaction solution needs to be washed and centrifuged multiple times before drying to finally obtain a silver / graphene composite solute powder. This invention involves acidifying and aldehyde-treating graphene, followed by a silver mirror reaction with a silver ammonia solution to form a silver / graphene composite solute. The main structure of the silver / graphene composite solute is irregular silver flakes attached to graphene sheets. When a small amount of the composite solute is added to the silver paste, during sintering, the silver flakes and silver particles come into contact and form a tight bond. This contact provides an effective additional conductive path. Furthermore, by increasing the contact area, the silver flakes improve the interconnectivity between silver powder particles, reducing potential aggregation during sintering and allowing for a more uniform distribution of silver particles. This reduces porosity in the silver grid lines and improves conductivity. In addition, graphene has extremely high conductivity, and its two-dimensional structure provides a wide range of conductive paths. Through its excellent electron mobility, graphene can effectively compensate for any gaps or incomplete connections between silver particles. The combination of graphene and silver not only enhances the conductivity of silver but also further improves the conductive pathways in the silver grid lines through its own conductive network, acting as a bridge and reducing the resistance to electron transport. It is this network effect that significantly improves conductivity.

[0012] In a specific embodiment, the concentration of the acidified graphene dispersion is 2 mg / mL to 20 mg / mL.

[0013] In a specific embodiment, during the acidification process, a nitric acid solution with a mass concentration of 2% to 20% is added to the graphene, and the graphene is then subjected to ultrasonic treatment. The ultrasonic power is 80W to 200W, the temperature is 20℃ to 30℃, and the time is 0.5h to 2h. The concentration of the acidified graphene dispersion is 2mg / mL to 20mg / mL.

[0014] It should be noted that this invention introduces oxygen-containing functional groups, such as carboxyl and hydroxyl groups, onto the graphene surface through acidification. The purpose of introducing these functional groups is to impart a certain negative charge to the graphene. Through electrostatic adsorption, these groups combine with positively charged silver ions. In the subsequent aldehyde reaction, formaldehyde can reduce these silver ions to elemental silver. Furthermore, the nitric acid solution used in this invention has a low concentration, resulting in a milder degree of acidification and oxidation of the graphene. This slight introduction of functional groups increases the hydrophilicity of the graphene, making the subsequent reaction more uniform, while avoiding severe acidification that could exacerbate graphene defects and reduce its conductivity.

[0015] After the acidification treatment, the acidified graphene was washed with deionized water and centrifuged until neutral to obtain an acidified graphene dispersion.

[0016] In a specific embodiment, the volume ratio of the acidified graphene dispersion to the formaldehyde solution is 1:1 to 5.

[0017] In a specific embodiment, during the aldehyde reaction, the mass concentration of the formaldehyde solution is 1% to 5%, and the aldehyde reaction is carried out by ultrasound with a power of 80W to 200W, a temperature of 20℃ to 30℃, and a time of 0.2h to 2h.

[0018] It should be noted that the present invention uses formaldehyde to aldehyde-treated acidified graphene. On the one hand, oxygen-containing functional groups, such as carboxyl and hydroxyl groups, combine with silver ions, and formaldehyde can act as a reducing agent to reduce them to form elemental silver. On the other hand, after aldehyde treatment, aldehyde sites can be added to the surface of graphene. These reducing aldehyde groups can react with silver ions in silver ammonia solution to form elemental silver, further increasing the amount of elemental silver.

[0019] In a specific embodiment, the volume ratio of the aldehyde graphene dispersion to the silver ammonia solution is 1:1.5 to 3.

[0020] It should be noted that the silver ammonia solution used in this invention is obtained by adding silver nitrate solution dropwise to ammonia water under stirring conditions until the precipitate in the solution completely disappears and the solution becomes transparent.

[0021] In a specific embodiment, the concentration of the silver ammonia solution is 50 mg / mL to 500 mg / mL, and the silver mirror reaction is carried out under stirring conditions at 20 to 50°C for 0.1 h to 1 h.

[0022] It should be noted that this invention uses aldehyde-based graphene as a catalyst, reducing agent, and carrier to reduce silver ions in ammoniacal silver solution to elemental silver, which then gradually aggregates to form silver nanoparticles. The graphene surface provides a good substrate for the formation and deposition of silver nanoparticles. The silver nanoparticles further aggregate to form irregular silver flakes, which adhere to the graphene flakes, ultimately forming a silver / graphene composite solute. When a small amount of the composite solute is added to the silver paste, during sintering, the silver flakes and silver particles come into contact with each other and form a tight bond. This contact provides an effective additional conductive path. Furthermore, by increasing the contact area, the silver flakes improve the interconnectivity between silver powder particles, reduce the aggregation phenomenon that may occur during sintering, and allow the silver particles to be distributed more uniformly, thereby reducing the porosity in the silver grid lines and improving conductivity.

[0023] In a specific embodiment, the method for preparing graphene includes the following steps:

[0024] Using graphite as raw material, graphite is dispersed in a mixed solvent to form a graphite dispersion. Graphene dispersion is obtained by liquid-phase ultrasonic exfoliation. After washing, centrifugation, and drying, graphene is obtained.

[0025] In a specific embodiment, the concentration of the graphite dispersion is 5 mg / mL to 50 mg / mL, the mixed solvent is a mixed solution formed by water and ethanol, the volume ratio of water to ethanol is 1 to 10:1, and during the liquid phase ultrasonic exfoliation process, the ultrasonic power is 180 W to 720 W, the temperature is 20 °C to 30 °C, and the time is 12 h to 48 h.

[0026] It should be noted that this invention uses graphite as raw material and prepares graphene through liquid-phase ultrasonic exfoliation. By leveraging the interaction between the mixed solvent molecules and the graphite layers, the van der Waals forces between the graphite layers are reduced, allowing the graphite to be uniformly dispersed in the mixed solvent. The combination of the mechanical action of ultrasound and the chemical action of solvent molecules effectively overcomes the van der Waals forces between the graphite layers, achieving efficient exfoliation and preparation of graphene with lower costs and a simpler process. Besides liquid-phase ultrasonic exfoliation, other methods such as chemical vapor deposition and redox reactions can also be used, but these have higher costs and more complex processes.

[0027] On the other hand, this invention also provides a highly conductive silver / graphene composite solute, prepared using the above method. The highly conductive silver / graphene composite solute provided by this invention, when added in small amounts to commercial silver paste, not only improves the conductive path of the silver paste and reduces porosity issues during sintering, but also enhances electron transport performance, providing an innovative and efficient solution for solar cell materials.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] This invention involves acidifying and aldehyde-modifying graphene, followed by a silver mirror reaction with a silver ammonia solution to form a silver / graphene composite solute. The main structure of the silver / graphene composite solute is irregular silver flakes attached to graphene sheets. When a small amount of the composite solute is added to silver paste, during sintering, the silver flakes and silver particles come into contact and form a tight bond. This contact provides an effective additional conductive path. Furthermore, the increased contact area of ​​the silver flakes improves the interconnectivity between silver powder particles, reduces potential aggregation during sintering, and allows for a more uniform distribution of silver particles, thereby reducing porosity in the silver grid lines and improving conductivity. Additionally, graphene possesses extremely high conductivity, and its two-dimensional structure provides extensive conductive paths. Through its superior electron mobility, graphene can effectively compensate for any gaps or incomplete connections between silver particles. The combination of graphene and silver not only enhances the conductivity of silver, but also further improves the conductive pathways in the silver grid lines through its own conductive network, playing a bridging role and reducing the resistance to electron transport. It is this conductive network effect that significantly improves conductivity. Attached Figure Description

[0030] Figure 1 Scanning electron microscope image of the silver / graphene composite solute prepared in Example 1 of this invention.

[0031] Figure 2 Scanning electron microscope image of the silver / graphene composite solute prepared in Example 2 of this invention.

[0032] Figure 3 Scanning electron microscope image of the silver / graphene composite solute prepared in Example 3 of this invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0035] The following specific examples will provide further explanation.

[0036] Example 1

[0037] A method for preparing a highly conductive silver / graphene composite solute includes the following steps:

[0038] S1. Preparation of graphene: Prepare 80 mL of a water / ethanol mixed solution with a volume ratio of 6:1, disperse 800 mg of graphite powder into the mixed solution, sonicate for 48 hours at a power of 720 W and a temperature of 20 °C, wash and centrifuge multiple times, and then dry to obtain graphene powder.

[0039] S2. Preparation of acidified graphene dispersion: Prepare 4 mL of 2% dilute nitric acid solution, disperse 20 mg of graphene powder obtained in S1 in the dilute nitric acid solution, sonicate for 1 h at 120 W and 20 °C, wash with deionized water and centrifuge until neutral to obtain acidified graphene dispersion.

[0040] S3. Preparation of aldehyde-based graphene dispersion: Prepare 2 mL of 1% formaldehyde solution and mix it with 2 mL of acidified graphene dispersion obtained by L2. Sonicate for 0.75 h at 120 W and 20 °C to obtain aldehyde-based graphene dispersion.

[0041] S3. Preparation of silver / graphene composite solute: Under magnetic stirring, 6 mL of 50 mg / mL silver nitrate solution was added dropwise to 3% ammonia water until the precipitate in the solution completely disappeared and the solution became transparent, thus obtaining a silver ammonia solution. Under magnetic stirring, aldehyde graphene dispersion was added dropwise to the silver ammonia solution, and a silver mirror reaction was carried out at 40°C for 0.25 h. After multiple washings and centrifugation, the solution was dried to obtain silver / graphene composite solute powder.

[0042] Example 2

[0043] A method for preparing a highly conductive silver / graphene composite solute includes the following steps:

[0044] S1. Preparation of graphene: Prepare 80 mL of a water / ethanol mixed solution with a volume ratio of 3:1, disperse 800 mg of graphite powder into the mixed solution, sonicate for 48 hours at a power of 720 W and a temperature of 20 °C, wash and centrifuge multiple times, and then dry to obtain graphene powder.

[0045] S2. Preparation of acidified graphene dispersion: Prepare 4 mL of 10% dilute nitric acid solution, disperse 40 mg of graphene powder obtained in S1 in the dilute nitric acid solution, sonicate for 1 h at 120 W and 20 °C, wash with deionized water and centrifuge until neutral to obtain acidified graphene dispersion.

[0046] S3. Preparation of aldehyde-based graphene dispersion: Prepare 5 mL of 3% formaldehyde solution and mix it with 2 mL of acidified graphene dispersion obtained by L2. Sonicate for 0.75 h at 120 W and 20 °C to obtain aldehyde-based graphene dispersion.

[0047] S3. Preparation of silver / graphene composite solute: Under magnetic stirring, 6 mL of 100 mg / mL silver nitrate solution was added dropwise to 3% ammonia water until the precipitate in the solution completely disappeared and the solution became transparent, thus obtaining a silver ammonia solution; under magnetic stirring, aldehyde graphene dispersion was added dropwise to the silver ammonia solution, and a silver mirror reaction was carried out at 40 °C for 0.25 h. After multiple washings and centrifugation, the solution was dried to obtain silver / graphene composite solute powder.

[0048] Example 3

[0049] A method for preparing a highly conductive silver / graphene composite solute includes the following steps:

[0050] S1. Preparation of graphene: Prepare 80 mL of a water / ethanol mixed solution with a volume ratio of 9:1, disperse 800 mg of graphite powder into the mixed solution, sonicate for 48 hours at a power of 720 W and a temperature of 20 °C, wash and centrifuge multiple times, and then dry to obtain graphene powder.

[0051] S2. Preparation of acidified graphene dispersion: Prepare 4 mL of 20% dilute nitric acid solution, disperse 80 mg of graphene powder obtained in S1 in the dilute nitric acid solution, sonicate for 1 h at 120 W and 20 °C, wash with deionized water and centrifuge until neutral to obtain acidified graphene dispersion.

[0052] S3. Preparation of aldehyde-based graphene dispersion: Prepare 10 mL of 5% formaldehyde solution and mix it with 2 mL of acidified graphene dispersion obtained by L2. Sonicate for 0.75 h at 120 W and 20 °C to obtain aldehyde-based graphene dispersion.

[0053] S3. Preparation of silver / graphene composite solute: Under magnetic stirring, 6 mL of 500 mg / mL silver nitrate solution was added dropwise to 3% ammonia water until the precipitate in the solution completely disappeared and the solution became transparent, thus obtaining a silver ammonia solution; under magnetic stirring, aldehyde graphene dispersion was added dropwise to the silver ammonia solution, and a silver mirror reaction was carried out at 40 °C for 0.25 h. After multiple washings and centrifugation, the solution was dried to obtain silver / graphene composite solute powder.

[0054] The structure and properties of the silver / graphene composite solutes prepared in Examples 1 to 3 were tested, and the results are as follows:

[0055] Figure 1 Scanning electron microscope image of the silver / graphene composite solute prepared in Example 1 of this invention. Figure 2 This is a scanning electron microscope image of the silver / graphene composite solute prepared in Example 1 of the present invention. Figure 3 This is a scanning electron microscope (SEM) image of the silver / graphene composite solute prepared in Example 3 of this invention. Figures 1 to 3 As shown, the three composite solutes prepared in Examples 1 to 3 have similar microstructures, all consisting of tiny, irregular silver flakes adsorbed on the surface of graphene sheets, and a relatively large amount of elemental silver. Graphene primarily acts as a carrier, providing numerous sites for the reduction of silver ions to elemental silver. The synthesis of these irregular silver flakes lays the foundation for the formation of conductive pathways between the silver flakes and silver nanoparticles during subsequent sintering.

[0056] Since the silver / graphene composite solutes prepared in Examples 1 to 3 have similar structures and essentially the same properties, the silver / graphene composite solute powder prepared in Example 2 was used in commercial silver paste to illustrate the improvement of the conductivity of commercial silver paste by the prepared silver / graphene composite solute. The commercial silver paste was purchased from Shanghai Mifang Electronics Technology Co., Ltd., and the paste model was BASE-CD01. This silver paste was prepared by mixing silver powder and resin filler, and the solid content was 64±3%. The specific steps included: diluting the BASE-CD01 commercial silver paste with a small amount of anhydrous ethanol, then adding the silver / graphene composite solute powder prepared in Example 2 to the commercial silver paste. The amounts of the silver / graphene composite solute powder prepared in Example 2 were 1 wt%, 1.5 wt%, and 2 wt% of the commercial silver paste mass, respectively. The mixture was stirred evenly and allowed to stand until the anhydrous ethanol completely evaporated, resulting in three composite silver pastes.

[0057] Commercial silver paste and the three composite silver pastes prepared above were printed onto a polyimide film using direct writing printing to form two sets of silver grid lines. The resistance and cross-sectional area of ​​the two sets of silver grid lines were measured using a four-probe tester and a profilometer, respectively. The measurement results are shown in Table 1.

[0058] Table 1. Test results of conductivity properties of commercial silver paste and three composite silver pastes

[0059]

[0060] As shown in Table 1, after adding 1 wt%, 1.5 wt%, and 2 wt% of the silver / graphene composite solute prepared in Example 2 to commercial silver paste, the conductivity of the composite paste increased by 20.6%, 31.3%, and 41.5%, respectively, compared to the commercial silver paste. It can be seen that the conductivity of the composite paste increases with the increase in the amount of silver / graphene composite solute added.

[0061] In summary, compared to commercial silver paste, the silver / graphene composite solute provided by this invention has the great potential to significantly improve the conductivity of commercial silver paste, which can further promote the photoelectric conversion efficiency of crystalline silicon solar cells and lay the foundation for the rapid development of the solar energy field.

[0062] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0063] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A composite silver paste, characterized in that, The composite silver paste is a composite of commercial silver paste and silver / graphene composite solute. The amount of silver / graphene composite solute used is 1 wt%, 1.5 wt%, or 2 wt% of the mass of commercial silver paste. The preparation method of silver / graphene composite solute includes the following steps: Graphene was acidified to obtain an acidified graphene dispersion. During the acidification process, a nitric acid solution with a mass concentration of 2% to 20% is added to the graphene, and the graphene is acidified by ultrasound. The ultrasound power is 80W to 200W, the temperature is 20℃ to 30℃, and the time is 0.5h to 2h. The concentration of the acidified graphene dispersion is 2mg / mL to 20mg / mL. The acidified graphene dispersion was mixed with formaldehyde solution to carry out an aldehyde reaction, thereby obtaining an aldehyde-treated graphene dispersion; the volume ratio of the acidified graphene dispersion to the formaldehyde solution was 1:1 to 5. The formaldehyde solution has a mass concentration of 1% to 5%, and the aldehyde reaction is carried out by ultrasound. The ultrasonic power is 80W to 200W, the temperature is 20℃ to 30℃, and the time is 0.2h to 2h. Aldehyde-based graphene dispersion and silver ammonia solution were mixed and subjected to a silver mirror reaction to obtain a silver / graphene composite solute; the volume ratio of aldehyde-based graphene dispersion to silver ammonia solution was 1:1.5–3. The concentration of the silver ammonia solution was 50 mg / mL to 500 mg / mL, and the silver mirror reaction was carried out under stirring conditions at 20℃ to 50℃ for 0.1 h to 1 h. The commercial silver paste was purchased from Shanghai Mifang Electronic Technology Co., Ltd., and the paste model is BASE-CD01.

2. The composite silver paste according to claim 1, characterized in that, The preparation method of graphene includes the following steps: Using graphite as raw material, graphite is dispersed in a mixed solvent to form a graphite dispersion. Graphene dispersion is obtained by liquid-phase ultrasonic exfoliation. After washing, centrifugation, and drying, graphene is obtained.

3. The composite silver paste according to claim 2, characterized in that, The concentration of the graphite dispersion was 5 mg / mL to 50 mg / mL. The mixed solvent was a mixed solution of water and ethanol with a volume ratio of 1 to 10:

1. During the liquid phase ultrasonic exfoliation process, the ultrasonic power was 180 W to 720 W, the temperature was 20 °C to 30 °C, and the time was 12 h to 48 h.

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