Conductive paste for heterojunction solar cells and preparation method thereof

Abstract

The present invention provides a conductive paste for heterojunction solar cells and a preparation method thereof, belonging to the field of conductive pastes. The present invention introduces spherical nanosilver, silver nanowires and silver nanosheets, and utilizes a three-dimensional conductive network formed by three metal morphologies to significantly improve the conductivity of the paste, and maintains high stability in long-term use through synergistic effects to avoid the decline of conductive performance; carbon nanotubes are modified by mixed acid and coupling agents to improve dispersibility and enhance interfacial bonding, thereby improving the conductivity and mechanical strength of the paste; graphene utilizes the introduction of thiol groups to improve dispersibility and compatibility, and restores conductivity through sodium borohydride reduction; silver-coated silicon carbide is used as a filler to improve conductivity and retain silicon carbide hardness, enhance the wear resistance of the paste, and extend the service life; the synergistic effects of modified carbon nanotubes, modified graphene and silver-coated silicon carbide enable the paste to exhibit excellent performance in terms of conductivity, thermal stability and mechanical strength.

Description

Technical Field

[0001] The invention belongs to the technical field of conductive pastes and relates to a conductive paste for a heterojunction solar cell and a preparation method thereof. Background Art

[0002] Conductive paste is a functional material widely used in many fields, especially in electronic devices, energy storage devices, coatings, solar cells and other fields. As a composite material, conductive paste is usually composed of components such as conductive fillers, polymer matrix, solvents and surfactants. Through the careful combination and synergistic effect of these components, the conductive paste can exert excellent electrical conductivity while ensuring good fluidity and coating performance, thereby achieving efficient current conduction. The excellent properties of the paste make it an indispensable basic material in electronic devices, especially in various fields that require conductive functions. For example, in printed circuits, flexible electronic devices and battery manufacturing, conductive paste is an indispensable and important component.

[0003] Conductive paste plays a vital role in the manufacturing process of solar cells. Especially for heterojunction solar cells, conductive paste is not only a material for forming electrodes, but its quality directly affects the photoelectric conversion efficiency, stability and production cost of the cell. The high efficiency performance of heterojunction solar cells depends on the excellent conductivity, adhesion and film-forming ability of the conductive paste. The core function of the conductive paste is to ensure that the current can be collected and conducted efficiently, so the selection of the paste is crucial to the overall efficiency of the cell. Generally speaking, an ideal conductive paste should have the following characteristics: good conductivity to ensure efficient current conduction; excellent adhesion to ensure a firm bond between the electrode layer and the substrate; appropriate viscosity to ensure that the paste can be evenly coated; good printability and fluidity to form a uniform and stable electrode layer on the cell surface.

[0004] However, although conductive paste plays an important role in many applications, existing conductive pastes still have some shortcomings. The conductive fillers in the paste often have problems with poor dispersion and uniformity. The agglomeration of fillers will lead to uneven current conduction paths, ultimately affecting the current collection efficiency of the battery. This poor dispersion problem not only reduces battery efficiency, but may also lead to increased manufacturing costs. Summary of the invention

[0005] In view of the above problems, the object of the present invention is to provide a conductive paste for heterojunction solar cells and a preparation method thereof. The present invention introduces spherical nanosilver, silver nanowires and silver nanosheets as the main conductive particles to form a three-dimensional conductive network to improve the overall conductivity of the paste; modified carbon nanotubes are used as fillers, and after being treated with mixed acid and coupling agent, their dispersibility is improved and the interface bonding force with other components is enhanced, thereby improving the conductivity and mechanical strength of the paste; graphene is modified to improve its hydrophobicity and chemical inertness, and its dispersibility is improved and its compatibility with other components is enhanced after adding thiol groups. Sodium borohydride is used to reduce some of the oxygen-containing functional groups of graphene, effectively restoring its conductivity while maintaining excellent dispersibility and interface compatibility. Silver-coated silicon carbide not only improves the conductivity of the paste, but also retains the hardness of silicon carbide and enhances the wear resistance of the paste, especially in long-term use, effectively reducing the damage of the conductive network and extending the service life of the battery. Through the synergistic effect of carbon nanotubes, graphene and silver-coated silicon carbide, the conductive paste of the present invention exhibits excellent comprehensive performance in terms of conductivity, thermal stability and mechanical strength.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a conductive paste for a heterojunction solar cell, the method for preparing a conductive paste for a heterojunction solar cell comprising:

[0008] S1: adding carbon nanotubes to a mixed acid, ultrasonically treating at a first temperature, centrifuging, washing, and vacuum drying at a first temperature to obtain carboxylated carbon nanotubes; preparing an ethanol aqueous solution and adding a silane coupling agent KH550, adjusting the pH with glacial acetic acid to obtain a coupling agent solution, adding the carboxylated carbon nanotubes to the coupling agent solution to obtain a reaction solution A, refluxing under nitrogen protection to obtain a reaction solution B, filtering and washing to obtain wet-modified carbon nanotubes, and vacuum drying to obtain modified carbon nanotubes;

[0009] S2: Mix graphite with concentrated sulfuric acid, add potassium persulfate and phosphorus pentoxide in an ice bath and pre-oxidize, cool to room temperature, add potassium permanganate to obtain reaction solution C, stir to react to obtain reaction solution D, pour it into deionized water and add hydrogen peroxide solution until the solution turns golden yellow, centrifuge, wash, and dry to obtain graphene; prepare a graphene dispersion, ultrasonically disperse, add 3-mercaptopropylamine under continuous stirring, use dilute hydrochloric acid to adjust the pH to obtain reaction solution E, react at a second temperature, centrifuge, wash to obtain pre-modified graphene, add sodium borohydride solution to the pre-modified graphene dispersion for reduction reaction, adjust the pH with ammonia water, centrifuge, wash, and dry to obtain modified graphene;

[0010] S3: Silicon carbide is mixed with potassium hydroxide solution and activated, filtered, washed and dried to obtain activated silicon carbide; ammonia water is added dropwise to the nitrate solution under stirring to obtain a complex liquid, the activated silicon carbide is added to the complex liquid to obtain a mixed liquid, glucose solution is added in portions to obtain a reaction liquid G, reacted under nitrogen protection, filtered, washed and dried to obtain silver-coated silicon carbide.

[0011] S4: prepare a mixed solvent of ethylene glycol / isopropanol / deionized water, add a surfactant to obtain a first dispersion, add modified carbon nanotubes, modified graphene, and silver-coated silicon carbide in sequence, ultrasonically disperse to obtain a second dispersion, add conductive particles, and high-speed shear to obtain a conductive slurry for heterojunction solar cells.

[0012] As a preferred technical solution of the present invention, in step S1, the volume ratio of sulfuric acid to nitric acid in the mixed acid is 1-2:1, for example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0013] In some optional embodiments, the mass ratio of the carbon nanotubes to the mixed acid is 1:10-15, for example, it can be 1:10.0, 1:10.5, 1:11.0, 1:11.5, 1:12.0, 1:12.5, 1:13.0, 1:13.5, 1:14.0, 1:14.5 or 1:15.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0014] In some optional embodiments, the first temperature is 50-60°C, for example, it can be 50.0°C, 51.0°C, 52.0°C, 53.0°C, 54.0°C, 55.0°C, 56.0°C, 57.0°C, 58.0°C, 59.0°C or 60.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] In some optional embodiments, the time of ultrasound at the first temperature is 1-2h, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] In some optional embodiments, the vacuum drying time at the first temperature is 6-8h, for example, it can be 6.0h, 6.2h, 6.4h, 6.6h, 6.8h, 7.0h, 7.2h, 7.4h, 7.6h, 7.8h or 8.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] In some optional embodiments, the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 95:5-99:1, for example, it can be 95:5, 96:4, 97:3, 98:2, 99:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] In some optional embodiments, the silane coupling agent is silane coupling agent KH550, and the mass fraction of the silane coupling agent KH550 in the ethanol aqueous solution is 4-5wt.%, for example, it can be 4.0wt.%, 4.1wt.%, 4.2wt.%, 4.3wt.%, 4.4wt.%, 4.5wt.%, 4.6wt.%, 4.7wt.%, 4.8wt.%, 4.9wt.% or 5.0wt.%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] In some optional embodiments, the mass fraction of the glacial acetic acid is 1-2wt.%, for example, it can be 1.0wt.%, 1.1wt.%, 1.2wt.%, 1.3wt.%, 1.4wt.%, 1.5wt.%, 1.6wt.%, 1.7wt.%, 1.8wt.%, 1.9wt.% or 2.0wt.%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] In some optional embodiments, the pH is adjusted to 4-5 using glacial acetic acid, for example, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9 or 5.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] In some optional embodiments, the mass ratio of the carboxylated carbon nanotubes to the coupling agent solution is 1:25-30, for example, it can be 1:25.0, 1:25.5, 1:26.0, 1:26.5, 1:27.0, 1:27.5, 1:28.0, 1:28.5, 1:29.0, 1:29.5 or 1:30.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] In some optional embodiments, the reflux temperature of the reaction liquid A under nitrogen protection is 55-65°C, for example, it can be 55.0°C, 56.0°C, 57.0°C, 58.0°C, 59.0°C, 60.0°C, 61.0°C, 62.0°C, 63.0°C, 64.0°C or 65.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] In some optional embodiments, the reflux time of the reaction liquid A under nitrogen protection is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] In some optional embodiments, the vacuum drying temperature of the wet-modified carbon nanotubes is 60-70°C, for example, it can be 60.0°C, 61.0°C, 62.0°C, 63.0°C, 64.0°C, 65.0°C, 66.0°C, 67.0°C, 68.0°C, 69.0°C or 70.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] As a preferred technical solution of the present invention, in step S2, the mass ratio of graphite to concentrated sulfuric acid is 1:15-20, for example, it can be 1:15.0, 1:15.5, 1:16.0, 1:16.5, 1:17.0, 1:17.5, 1:18.0, 1:18.5, 1:19.0, 1:19.5 or 1:20.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] In some optional embodiments, the mass ratio of potassium persulfate to phosphorus pentoxide is 1-2:1, for example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2.0:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] In some optional embodiments, the mass ratio of the mixture of potassium persulfate and phosphorus pentoxide to graphite is 1-2:1, for example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] In some optional embodiments, the pre-oxidation temperature is 75-85°C, for example, it can be 75.0°C, 76.0°C, 77.0°C, 78.0°C, 79.0°C, 80.0°C, 81.0°C, 82.0°C, 83.0°C, 84.0°C or 85.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In some optional embodiments, the pre-oxidation time is 4-5h, for example, it can be 4.0h, 4.1h, 4.2h, 4.3h, 4.4h, 4.5h, 4.6h, 4.7h, 4.8h, 4.9h or 5.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] In some optional embodiments, the mass ratio of potassium permanganate to graphite is 3-4:1, for example, it can be 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1, 4:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] In some optional embodiments, the stirring reaction temperature of the reaction liquid C is 30-40°C, for example, it can be 30.0°C, 31.0°C, 32.0°C, 33.0°C, 34.0°C, 35.0°C, 36.0°C, 37.0°C, 38.0°C, 39.0°C or 40.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] In some optional embodiments, the stirring reaction time of the reaction liquid C is 12-14h, for example, it can be 12.0h, 12.2h, 12.4h, 12.6h, 12.8h, 13.0h, 13.2h, 13.4h, 13.6h, 13.8h or 14.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] In some optional embodiments, the volume ratio of the reaction liquid D to deionized water is 1:10-15, for example, it can be 1:10.0, 1:10.5, 1:11.0, 1:11.5, 1:12.0, 1:12.5, 1:13.0, 1:13.5, 1:14.0, 1:14.5 or 1:15.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] In some optional embodiments, the mass fraction of the hydrogen peroxide solution is 15-20%, for example, it can be 15.0%, 15.5%, 16.0%, 16.5%, 17.0%, 17.5%, 18.0%, 18.5%, 19.0%, 19.5% or 20.0%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] In some optional embodiments, the concentration of the graphene dispersion is 1.8-2.2 mg / mL, for example, it can be 1.80 mg / mL, 1.84 mg / mL, 1.88 mg / mL, 1.92 mg / mL, 1.96 mg / mL, 2.00 mg / mL, 2.04 mg / mL, 2.08 mg / mL, 2.12 mg / mL, 2.16 mg / mL, 2.20 mg / mL, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] In some optional embodiments, the power of ultrasonic dispersion of the graphene dispersion is 200-300 W, for example, it can be 200 W, 210 W, 220 W, 230 W, 240 W, 250 W, 260 W, 270 W, 280 W, 290 W or 300 W, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] In some optional embodiments, the ultrasonic dispersion time of the graphene dispersion is 20-30 min, for example, it can be 20.0 min, 21.0 min, 22.0 min, 23.0 min, 24.0 min, 25.0 min, 26.0 min, 27.0 min, 28.0 min, 29.0 min or 30.0 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] In some optional embodiments, the molar ratio of graphene to 3-mercaptopropylamine is 1:3.5-4.5, for example, it can be 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, 1:4.0, 1:4.1, 1:4.2, 1:4.3, 1:4.4 or 1:4.5, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In some optional embodiments, the concentration of the dilute hydrochloric acid is 0.1-0.5M, for example, it can be 0.1M, 0.15M, 0.2M, 0.25M, 0.3M, 0.35M, 0.4M, 0.45M or 0.5M, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] In some optional embodiments, the pH is adjusted to 4-5 using dilute hydrochloric acid, for example, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9 or 5.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] In some optional embodiments, the second temperature is 55-65°C, for example, it can be 55.0°C, 56.0°C, 57.0°C, 58.0°C, 59.0°C, 60.0°C, 61.0°C, 62.0°C, 63.0°C, 64.0°C or 65.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0042] In some optional embodiments, the reaction time of the reaction liquid E at the second temperature is 3-4h, for example, it can be 3.0h, 3.1h, 3.2h, 3.3h, 3.4h, 3.5h, 3.6h, 3.7h, 3.8h, 3.9h or 4.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] In some optional embodiments, the concentration of the pre-modified graphene dispersion is 1-2 mg / mL, for example, it can be 1.0 mg / mL, 1.1 mg / mL, 1.2 mg / mL, 1.3 mg / mL, 1.4 mg / mL, 1.5 mg / mL, 1.6 mg / mL, 1.7 mg / mL, 1.8 mg / mL, 1.9 mg / mL or 2.0 mg / mL, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0044] In some optional embodiments, the concentration of the sodium borohydride solution is 0.08-0.12M, for example, it can be 0.08M, 0.084M, 0.088M, 0.092M, 0.096M, 0.1M, 0.104M, 0.108M, 0.112M, 0.116M or 0.12M, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0045] In some optional embodiments, the mass ratio of sodium borohydride to pre-modified graphene is 3.5-4.5:1, for example, it can be 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1, 4.0:1, 4.1:1, 4.2:1, 4.3:1, 4.4:1 or 4.5:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] In some optional embodiments, the temperature of the reduction reaction is 50-60°C, for example, it can be 50.0°C, 51.0°C, 52.0°C, 53.0°C, 54.0°C, 55.0°C, 56.0°C, 57.0°C, 58.0°C, 59.0°C or 60.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] In some optional embodiments, the reduction reaction time is 4-5h, for example, it can be 4.0h, 4.1h, 4.2h, 4.3h, 4.4h, 4.5h, 4.6h, 4.7h, 4.8h, 4.9h or 5.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] In some optional embodiments, the concentration of the ammonia water is 0.5-1.5M, for example, it can be 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1.0M, 1.1M, 1.2M, 1.3M, 1.4M or 1.5M, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] In some optional embodiments, the pH is adjusted to 10-11 with aqueous ammonia, for example, 10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9 or 11.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0050] As a preferred technical solution of the present invention, in step S3, the concentration of the potassium hydroxide solution is 2-3M, for example, it can be 2.0M, 2.1M, 2.2M, 2.3M, 2.4M, 2.5M, 2.6M, 2.7M, 2.8M, 2.9M or 3.0M, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0051] In some optional embodiments, the mass ratio of silicon carbide to potassium hydroxide solution is 1:15-20, for example, it can be 1:15.0, 1:15.5, 1:16.0, 1:16.5, 1:17.0, 1:17.5, 1:18.0, 1:18.5, 1:19.0, 1:19.5 or 1:20.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] In some optional embodiments, the activation temperature is 75-85°C, for example, it can be 75.0°C, 76.0°C, 77.0°C, 78.0°C, 79.0°C, 80.0°C, 81.0°C, 82.0°C, 83.0°C, 84.0°C or 85.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0053] In some optional embodiments, the activation time is 1-2h, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0054] In some optional embodiments, the concentration of silver nitrate is 0.1-0.2M, for example, it can be 0.1M, 0.11M, 0.12M, 0.13M, 0.14M, 0.15M, 0.16M, 0.17M, 0.18M, ​​0.19M or 0.2M, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0055] In some optional embodiments, the concentration of ammonia water is 25-28%, for example, it can be 25.0%, 25.3%, 25.6%, 25.9%, 26.2%, 26.5%, 26.8%, 27.1%, 27.4%, 27.7%, 28.0%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0056] In some optional embodiments, the amount of ammonia water is 1.2-1.5 times the volume of the silver nitrate solution, for example, it can be 1.2 times, 1.23 times, 1.26 times, 1.29 times, 1.32 times, 1.35 times, 1.38 times, 1.41 times, 1.44 times, 1.47 times, or 1.5 times, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0057] In some optional embodiments, the content of silver ions in the mixed solution is 15-16% of the mass of activated silicon carbide, for example, it can be 15.0%, 15.1%, 15.2%, 15.3%, 15.4%, 15.5%, 15.6%, 15.7%, 15.8%, 15.9% or 16.0%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0058] In some optional embodiments, the concentration of the glucose solution is 0.1-0.2M, for example, it can be 0.1M, 0.11M, 0.12M, 0.13M, 0.14M, 0.15M, 0.16M, 0.17M, 0.18M, ​​0.19M or 0.2M, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0059] In some optional embodiments, the interval time for adding glucose is 10-15 min, for example, it can be 10.0 min, 10.5 min, 11.0 min, 11.5 min, 12.0 min, 12.5 min, 13.0 min, 13.5 min, 14.0 min, 14.5 min or 15.0 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0060] In some optional embodiments, the molar ratio of glucose to silver ions is 1.8-2.2:1, for example, it can be 1.8:1, 1.84:1, 1.88:1, 1.92:1, 1.96:1, 2.0:1, 2.04:1, 2.08:1, 2.12:1, 2.16:1, 2.2:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0061] In some optional embodiments, the reaction temperature of the reaction liquid G under nitrogen protection is 60-70°C, for example, it can be 60.0°C, 61.0°C, 62.0°C, 63.0°C, 64.0°C, 65.0°C, 66.0°C, 67.0°C, 68.0°C, 69.0°C or 70.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0062] In some optional embodiments, the reaction time of the reaction liquid G under nitrogen protection is 40-60 min, for example, it can be 40.0 min, 42.0 min, 44.0 min, 46.0 min, 48.0 min, 50.0 min, 52.0 min, 54.0 min, 56.0 min, 58.0 min, 60.0 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0063] As a preferred technical solution of the present invention, in step S4, the volume ratio of ethylene glycol, isopropanol and deionized water in the ethylene glycol / isopropanol / deionized water mixed solvent is 3-4:2:1, for example, it can be 3.0:2:1, 3.1:2:1, 3.2:2:1, 3.3:2:1, 3.4:2:1, 3.5:2:1, 3.6:2:1, 3.7:2:1, 3.8:2:1, 3.9:2:1 or 4.0:2:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0064] In some optional embodiments, the power of the ultrasonic dispersion is 400-500 W, for example, it can be 400 W, 410 W, 420 W, 430 W, 440 W, 450 W, 460 W, 470 W, 480 W, 490 W or 500 W, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0065] In some optional embodiments, the ultrasonic dispersion time is 20-30 min, for example, it can be 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min or 30 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0066] In some optional embodiments, the rotation speed of the high-speed shearing is 7500-8500rpm, for example, it can be 7500rpm, 7600rpm, 7700rpm, 7800rpm, 7900rpm, 8000rpm, 8100rpm, 8200rpm, 8300rpm, 8400rpm or 8500rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0067] In some optional embodiments, the high-speed shearing time is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0068] In a second aspect, the present invention provides a conductive paste for a heterojunction solar cell, wherein the conductive paste for a heterojunction solar cell comprises the following components in parts by weight:

[0069] 0.7-0.9 parts of modified carbon nanotubes;

[0070] 1.4-1.8 parts of modified graphene;

[0071] Silver coated silicon carbide 1-1.5 parts;

[0072] Conductive particles 75-85 parts;

[0073] 5-7 parts of surfactant;

[0074] 35-45 parts of mixed solvent;

[0075] Among them, the mass proportion of spherical nanosilver in the conductive particles is 45-50 parts, the mass proportion of silver nanowires is 15-17 parts, and the mass proportion of silver nanosheets is 15-18 parts.

[0076] In some optional examples, the mass proportion of modified carbon nanotubes is 0.7-0.9 parts, for example, it can be 0.7 parts, 0.72 parts, 0.74 parts, 0.76 parts, 0.78 parts, 0.8 parts, 0.82 parts, 0.84 parts, 0.86 parts, 0.88 parts or 0.9 parts, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0077] In some optional examples, the mass fraction of modified graphene is 1.4-1.8 parts, for example, it can be 1.4 parts, 1.44 parts, 1.48 parts, 1.52 parts, 1.56 parts, 1.6 parts, 1.64 parts, 1.68 parts, 1.72 parts, 1.76 parts or 1.8 parts, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0078] In some optional examples, the mass proportion of silver-coated silicon carbide is 1-1.5 parts, for example, it can be 1 part, 1.05 parts, 1.1 parts, 1.15 parts, 1.2 parts, 1.25 parts, 1.3 parts, 1.35 parts, 1.4 parts, 1.45 parts or 1.5 parts, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0079] In some optional examples, the mass fraction of the conductive particles is 75-85 parts, for example, it can be 75 parts, 76 parts, 77 parts, 78 parts, 79 parts, 80 parts, 81 parts, 82 parts, 83 parts, 84 parts or 85 parts, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0080] In some optional embodiments, the mass proportion of the surfactant is 5-7 parts, for example, it can be 5 parts, 5.2 parts, 5.4 parts, 5.6 parts, 5.8 parts, 6 parts, 6.2 parts, 6.4 parts, 6.6 parts, 6.8 parts or 7 parts, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0081] In some optional embodiments, the mass proportion of the mixed solvent is 35-45 parts, for example, it can be 35 parts, 36 parts, 37 parts, 38 parts, 39 parts, 40 parts, 41 parts, 42 parts, 43 parts, 44 parts or 45 parts, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0082] In some optional examples, the mass fraction of spherical nanosilver in the conductive particles is 45-50 parts, for example, it can be 45 parts, 45.5 parts, 46 parts, 46.5 parts, 47 parts, 47.5 parts, 48 ​​parts, 48.5 parts, 49 parts, 49.5 parts or 50 parts, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0083] In some optional examples, the mass fraction of silver nanowires in the conductive particles is 15-17 parts, for example, it can be 15 parts, 15.2 parts, 15.4 parts, 15.6 parts, 15.8 parts, 16 parts, 16.2 parts, 16.4 parts, 16.6 parts, 16.8 parts or 17 parts, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0084] In some optional examples, the mass fraction of silver nanosheets in the conductive particles is 15-18 parts, for example, it can be 15 parts, 15.3 parts, 15.6 parts, 15.9 parts, 16 parts, 16.3 parts, 16.6 parts, 16.9 parts, 17 parts, 17.3 parts, 17.6 parts, 17.9 parts or 18 parts, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0085] The present invention introduces spherical nanosilver, silver nanowires and silver nanosheets as the main conductive particles, and uses a three-dimensional conductive network formed by three metal materials with different morphologies to significantly improve the overall conductivity of the slurry. At the same time, the synergistic effect between the three can maintain the high stability of the slurry during long-term use and avoid the decline of conductive performance. Carbon nanotubes are used as fillers, and the mixed modification of mixed acid and coupling agent not only improves the dispersibility, but also enhances the interfacial bonding force between it and other components, thereby improving the conductive performance and mechanical strength of the slurry. Graphene is modified by hydrophobicity and chemical inertness, and its dispersibility and compatibility with other components are improved by the introduction of thiol groups, and the conductivity is restored by removing some oxygen-containing functional groups through sodium borohydride reduction, ensuring the high conductivity and excellent dispersibility of graphene. Silver-coated silicon carbide is used as a filler, which not only improves the conductivity of the slurry, but also retains the hardness of silicon carbide, improves the wear resistance of the slurry, and effectively reduces the damage of the conductive network and prolongs the battery life, especially in long-term use. Through the synergistic effect of modified carbon nanotubes, graphene and silver-coated silicon carbide, the paste exhibits excellent comprehensive properties in conductivity, thermal stability and mechanical strength.

[0086] In the present invention, three types of metals with morphologies, namely spherical nanosilver, silver nanowires and silver nanosheets, are selected as the main conductive particles. Spherical nanosilver has a smaller particle size and a larger specific surface area, and can provide an effective electron conduction path. The spherical morphology makes it easy for nanosilver to disperse in the slurry, reducing the aggregation phenomenon, and the spherical structure is easier to disperse in the solvent, reducing the risk of agglomeration, thereby maintaining the uniformity of the slurry; the silver nanowire has a one-dimensional structure, and the length is usually much larger than the diameter, which can form a long-range conductive path and has very good electronic conductivity. The length of the silver nanowire enables it to connect other conductive particles in the slurry through a network effect to form a stable conductive path, thereby improving the overall conductivity of the conductive slurry. Through the long-range connection of the silver nanowire, the connection between the conductive particles in the slurry is closer, thereby enhancing the overall stability of the conductive network; the silver nanosheet has a two-dimensional structure, and the larger surface contact area can effectively promote electronic conduction and enhance the binding force with other particles. The two-dimensional structure of silver nanosheets enables them to form a larger contact area with spherical nanosilver and silver nanowires in the slurry, thereby enhancing the formation and stability of the conductive network, and can further optimize the conductive properties of the slurry by combining with other conductive particles.

[0087] There is also a synergistic enhancement effect between these three silver nanomaterials with different morphologies: spherical nanosilver provides better dispersibility, can fill the gaps in the slurry, and provide a basic conductive path; silver nanowires form long-range conductive paths, connecting multiple conductive particles through their ductility, thereby building a stable conductive network; silver nanosheets increase the surface contact area of ​​conductive particles, allowing other particles to better combine, enhancing the stability of the conductive network and overall conductivity.

[0088] The introduction of silver nanowires and silver nanosheets not only improves the conductivity, but also improves the mechanical strength and stability of the slurry. The long-range connection of silver nanowires in the slurry can effectively improve the toughness of the conductive network and avoid the breakage or failure of the conductive network due to external forces during use; the two-dimensional structure of silver nanosheets helps to improve the structural stability of the slurry and reduce the sedimentation or agglomeration of conductive materials; because spherical nanosilver has good dispersibility, it can help silver nanowires and silver nanosheets maintain uniform distribution in the slurry, prevent the agglomeration of large particles, and ensure the fluidity and uniformity of the slurry.

[0089] Through the synergistic effect of spherical silver nanowires, silver nanosheets, the conductive properties of the conductive paste are effectively enhanced, and the formed three-dimensional conductive network greatly improves the overall conductivity of the paste; at the same time, due to the multi-morphological structure of these materials, the conductive paste can maintain a high stability during long-term use, especially in high temperature or high humidity environments, and can effectively avoid the decline of conductive properties.

[0090] The present invention introduces carbon nanotubes as fillers for conductive pastes. Carbon nanotubes are an ideal conductive filler due to their excellent nanostructure characteristics. In the structure of carbon nanotubes, carbon atoms are arranged in a hexagonal shape to form a tubular structure with a high aspect ratio. This dimensional characteristic enables them to have significant electron transmission capabilities in the conductive network. Due to the unique π-π conjugated structure of carbon nanotubes, they exhibit excellent performance in terms of electrical conductivity and can effectively improve the current transmission capacity of the conductive paste. In addition, the one-dimensional nanostructure of carbon nanotubes has a high degree of structural stability and can form a conductive skeleton in the paste system, providing an efficient transmission path for electrons in the paste, thereby improving the transmission efficiency and conductivity of electrons.

[0091] However, despite the outstanding advantages of carbon nanotubes in terms of electrical conductivity and mechanical properties, they also face some challenges in practical applications. First, the chemical inertness and hydrophobicity of carbon nanotubes make it difficult to disperse well in polar solvents, and they easily agglomerate to form large lumps, resulting in poor uniformity and stability of the slurry. Secondly, there is a lack of sufficient active functional groups on its surface, resulting in weak interfacial bonding with other materials, which limits its wide application in composite materials. Therefore, it is necessary to modify the surface of carbon nanotubes to improve its dispersibility in different solvents, improve its compatibility with other components, and enhance its interfacial bonding with other materials in the slurry.

[0092] The present invention adopts a mixed acid oxidation method to modify the surface of carbon nanotubes. Mixed acid oxidation destroys the carbon-carbon double bonds on the surface of carbon nanotubes through the action of a strong oxidant, introduces oxidation defects, and generates oxygen-containing polar functional groups such as carboxyl and hydroxyl. These polar groups significantly improve the hydrophilicity of carbon nanotubes, allowing them to be better dispersed in aqueous or polar solvents, thereby avoiding agglomeration. In addition, functional groups such as carboxyl also provide chemically active sites for subsequent coupling reactions, thereby enhancing the interfacial bonding between carbon nanotubes and other materials.

[0093] In the modification process, the present invention uses a silane coupling agent KH550, which undergoes a condensation reaction with the carboxyl group introduced on the surface of the carbon nanotube through the amino group to form an amide bond. This chemical reaction enhances the chemical activity of the carbon nanotube surface and further improves its binding force with other components. In addition, the siloxane groups in KH550 can be hydrolyzed in an aqueous environment to generate silanols, which are further cross-linked with other silanol groups through a condensation reaction to form a stable silicon oxide cross-linked structure. This cross-linking reaction not only enhances the interfacial binding force between the modified carbon nanotubes and other components, but also gives the carbon nanotubes and other components of the slurry stronger chemical compatibility and mechanical strength. Through silanization modification, the dispersibility of the carbon nanotubes is significantly improved, so that the uniformity of the slurry is improved, material agglomeration and sedimentation problems are avoided, and the long-term stability of the slurry during use is ensured.

[0094] The modified carbon nanotubes effectively improve the conductive properties of the conductive paste through improved dispersibility and enhanced interface bonding. The stable conductive network formed by the modified carbon nanotubes in the paste allows electrons to be transferred more efficiently in the paste, thereby improving the overall conductive properties; the modified carbon nanotubes form a strong interface bonding force through chemical crosslinking with other components, which enhances the mechanical strength of the paste, making the conductive paste more stable during application and able to withstand greater mechanical stress without being prone to cracking or breaking; the modified carbon nanotubes not only improve the fluidity and coatability of the paste, but also improve the stability during processing, making the handling, coating and application of the paste easier and more efficient.

[0095] The present invention introduces graphene as a filler for conductive slurry. Graphene is a two-dimensional material composed of a single layer of carbon atoms arranged in a honeycomb lattice. Its unique structure and excellent performance make it have great potential for application in conductive materials. The high mechanical strength and excellent thermal stability of graphene make it an ideal material that can remain stable in extreme environments. At the same time, the π-π conjugated electronic structure of graphene gives it very high conductivity, which can effectively improve the current conduction efficiency in the conductive slurry. In addition, the two-dimensional sheet structure of graphene not only provides a huge specific surface area, but also can form a wider contact area with other components in the slurry system, thereby further enhancing the conductive performance of the slurry.

[0096] Although graphene has excellent electrical conductivity and structural characteristics, it has some shortcomings in practical applications. The original graphene has strong hydrophobicity and high chemical inertness, which makes it poorly dispersible in solvents and easily aggregates into larger aggregates, resulting in its inability to effectively play its conductive role. In addition, the lack of sufficient active functional groups on the surface of graphene makes its interaction with other materials weak, limiting its application in composite materials.

[0097] The present invention oxidizes graphite by the Hummers method. The Hummers method uses a strong oxidant such as potassium permanganate to treat graphite in concentrated sulfuric acid, peels off the graphite layer by oxidation, and introduces oxygen-containing functional groups such as hydroxyl, carboxyl and epoxy groups. This oxidation process can not only expand the interlayer spacing of graphite, making it easier to disperse, but also these oxygen-containing groups can serve as chemically active sites, providing a basis for subsequent surface functionalization. The introduction of oxygen-containing groups improves the hydrophilicity of graphene, allowing it to be more evenly dispersed in aqueous or polar solvents. Through Hummers oxidation and thiol treatment, the dispersibility and interfacial compatibility of graphene are significantly improved, which enables graphene to form a more uniform and stable conductive network in the slurry.

[0098] Although the dispersibility of graphene oxide is improved, the oxygen-containing functional groups introduced during the oxidation process may affect the conductivity of graphene, so further modification is required to restore its conductive properties. To this end, the present invention uses 3-mercaptopropylamine to thiolate graphene oxide. The thiol group not only has strong chemical activity and can form chemical bonds with metal ions and other substances to enhance the interaction between graphene and other components, but also has good electrical conductivity, which can further improve the conductivity of the modified graphene.

[0099] Through thiolation, the surface of graphene is further functionalized, which not only improves the dispersion of graphene and avoids agglomeration, but also improves the chemical compatibility between graphene and other components, thereby enhancing the conductivity of the conductive paste. Moreover, thiol itself has good conductivity. Graphene treated with thiol can form a more stable conductive network in the paste, effectively improving the current collection efficiency and conductivity, while enhancing the stability of the paste and extending its service life.

[0100] At the same time, the present invention uses sodium borohydride as a reducing agent to perform a reduction treatment on graphene oxide. Through the reduction reaction, sodium borohydride can remove some oxygen-containing functional groups, restore the π-π conjugated structure of graphene, and then restore its conductivity. This process not only improves the electronic conductivity of graphene, but also enables it to play a better role in the conductive slurry, providing a more efficient electron transmission channel.

[0101] The synergistic effect between the two modification methods is as follows: thiol modification improves the dispersibility and interface affinity of graphene by introducing thiol groups, allowing it to be evenly dispersed in the solvent and form a strong interface bond with other materials. Good dispersibility and interface compatibility can promote the stability of the conductive network and reduce the agglomeration of graphene in the slurry; sodium borohydride also restores the π-π conjugated structure of graphene, improves the conductivity of graphene, restores its original high conductivity, and ensures the conductive performance of the slurry in practical applications; thiol modification ensures the dispersibility and interface compatibility of graphene, while reduction treatment ensures the high conductivity of graphene, thereby enhancing the comprehensive advantages of graphene as a conductive filler.

[0102] The present invention introduces silicon carbide as a filler, mainly based on its mechanical and thermal performance advantages in conductive pastes. Silicon carbide is a material with high hardness, high thermal conductivity and excellent chemical stability, and has a wide range of application potential. Silicon carbide can improve the hardness, wear resistance and thermal stability of the material in conductive pastes, so that the paste can maintain good performance in high temperature or harsh environment in practical applications. However, a major disadvantage of silicon carbide is its low conductivity, which limits its wide application in conductive pastes.

[0103] In order to solve this problem, the present invention coats the surface of silicon carbide with silver, so that silicon carbide obtains high electrical conductivity while retaining its excellent properties such as mechanical strength and thermal conductivity. Silver has excellent electrical conductivity. By coating with a silver layer, the electrical conductivity of silicon carbide can be effectively improved, so that it plays a vital role in the conductive paste. In addition, the silver coating has another important role, which is to enhance the compatibility of silicon carbide with other materials and provide a more stable conductive network in the paste, especially in the process of combining with other conductive materials such as silver nanowires, silver nanosheets, etc., which can further optimize the conductive performance.

[0104] The silver coating can also effectively prevent the migration and oxidation of silver ions, which is crucial to the long-term stability of the conductive paste. Under high temperature, humidity or extreme conditions, metal particles may oxidize or migrate, resulting in decreased conductivity and degradation of the paste performance. Silver-coated silicon carbide not only avoids direct exposure of silver, but also prevents silver from migrating in the paste, thereby improving the stability and durability of the paste and extending the service life of the paste in batteries or other electronic devices.

[0105] First, the present invention uses potassium hydroxide solution to alkaline activate silicon carbide. In this process, potassium hydroxide reacts with the surface of silicon carbide to form hydroxyl groups and other active sites. These active sites can provide important chemical reaction sites for subsequent silver ion complexation and deposition, thereby improving the deposition efficiency and uniformity of silver ions. This step helps to improve the surface affinity of silicon carbide and provides a better basis for silver coating.

[0106] Next, silver nitrate and ammonia water are used to react to generate a silver-ammine complex. The silver-ammine complex has strong stability and solubility and is easy to disperse evenly in the solution. With glucose as a reducing agent, the silver-ammine complex is reduced to elemental silver in the reduction reaction, thereby forming a uniform silver coating on the surface of silicon carbide. Glucose not only provides electrons as a reducing agent to promote the reduction of silver ions to elemental silver, but also controls the deposition rate of silver, avoids the agglomeration of silver particles, and ensures the uniformity of the silver coating.

[0107] Silver-coated silicon carbide not only provides good conductivity, but also maintains the excellent mechanical strength, thermal stability and chemical stability of silicon carbide, which makes it more widely used and durable in conductive pastes. The silver coating can effectively conduct current, and due to its chemical stability, it can ensure that the performance of the paste remains unchanged during long-term use or in harsh environments. In addition, while improving conductivity, silver-coated silicon carbide retains the hardness of silicon carbide, which can improve the wear resistance of the paste, especially during long-term battery use, it can effectively reduce the damage to the conductive network and extend the service life of the battery.

[0108] The introduction of silver-coated silicon carbide filler can improve the mechanical properties and thermal stability of the slurry while improving the conductivity. It provides a more solid conductive skeleton for the conductive slurry, effectively improves the conductive network stability of the slurry, and ensures the stable collection and conduction of current during use. At the same time, since silver-coated silicon carbide has good dispersibility, its uniform distribution in the slurry can further improve the processability of the slurry and reduce the agglomeration of the filler.

[0109] At the same time, there is a significant synergistic enhancement effect between modified carbon nanotubes, modified graphene and silver-coated silicon carbide, which can significantly improve the comprehensive performance of the conductive paste. Specifically, carbon nanotubes provide a one-dimensional conductive network. Its high aspect ratio and excellent electron transmission ability enable it to form an efficient electron channel in the paste, playing a role in rapid conduction. At the same time, graphene provides a rich conductive path through its two-dimensional sheet structure. The π-π conjugated electronic structure and high conductivity of graphene can effectively promote the rapid transmission of electrons and enhance the connectivity of the conductive network together with carbon nanotubes. Finally, silver-coated silicon carbide, as a three-dimensional filler, provides a wider range of conductive contact points and stable conductive support. Its silver coating can effectively improve the conductive performance and maintain the thermal and chemical stability of silicon carbide, providing the paste with reliability under extreme conditions. The interaction between the three makes the paste not only significantly improved in conductivity, but also exhibits excellent comprehensive performance in thermal stability and mechanical strength.

[0110] In addition, the carbon nanotubes and modified graphene modified by silanization have good dispersibility and can be evenly distributed in the slurry system. This uniform distribution is crucial to the processability and final performance of the slurry, and can effectively avoid the decrease in conductivity caused by filler agglomeration. At the same time, the modified carbon nanotubes and modified graphene can form good chemical compatibility with other components due to the improvement of surface chemical properties, further enhancing the synergy between the components in the slurry. This synergy not only allows the conductive fillers to be closely combined, but also promotes the conductive network stability and mechanical strength of the slurry, ensuring the long-term stability and high-efficiency conductive performance of the slurry under different environments.

[0111] Compared with the prior art, the present invention has the following beneficial effects:

[0112] (1) Spherical nanosilver, silver nanowires and silver nanosheets are selected as the main conductive particles. The three-dimensional conductive network formed by the three metal materials with different morphologies greatly improves the overall conductivity of the paste. The synergistic effect of the three can also enable the conductive paste to maintain a high stability during long-term use, effectively avoiding the decline of conductive performance;

[0113] (2) Carbon nanotubes modified by mixed acid and coupling agent are introduced as fillers. The modified carbon nanotubes effectively improve the conductive properties of the conductive paste through improved dispersibility and enhanced interfacial bonding strength. They also form strong interfacial bonding strength with other components through chemical cross-linking, thereby enhancing the mechanical strength of the paste.

[0114] (3) Graphene was used as a filler and its hydrophobicity and chemical inertness were modified. The dispersion of graphene was improved by introducing thiol groups, thereby enhancing its compatibility with other components. Sodium borohydride was used as a reducing agent to remove some oxygen-containing functional groups and restore its conductivity, which not only ensured the dispersion and interface compatibility of graphene, but also ensured the high conductivity of graphene.

[0115] (4) Silver-coated silicon carbide is introduced as a filler. Silver-coated silicon carbide improves conductivity while retaining the hardness of silicon carbide, which can improve the wear resistance of the slurry. Especially during long-term battery use, it can effectively reduce the damage to the conductive network and extend the service life of the battery.

[0116] (5) The combination of modified carbon nanotubes, modified graphene and silver-coated silicon carbide and the interaction between the three materials not only significantly improve the conductivity of the slurry, but also show excellent comprehensive performance in thermal stability and mechanical strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0117] Figure 1 A flow chart of a method for preparing a conductive paste for a heterojunction solar cell provided in Example 1 of the present invention;

[0118] Figure 2 The square resistance values ​​of the conductive pastes for heterojunction solar cells provided in Examples 1-4 and Comparative Examples 1-6 of the present invention. DETAILED DESCRIPTION

[0119] The technical solution of the present invention is described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific embodiments of the present invention, which are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limitations on the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments recorded herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments recorded herein.

[0120] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products without further purification.

[0121] Example 1

[0122] like Figure 1 As shown, this embodiment provides a conductive paste for a heterojunction solar cell and a preparation method thereof, wherein the conductive paste for a heterojunction solar cell comprises the following components in parts by weight:

[0123] 0.8 parts of modified carbon nanotubes;

[0124] 1.7 parts of modified graphene;

[0125] Silver-coated silicon carbide 1.4 parts;

[0126] Conductive particles 79 parts;

[0127] 7 parts of surfactant;

[0128] 42 parts of mixed solvent;

[0129] Among them, the mass parts of spherical nanosilver in the conductive particles are 47 parts, the mass parts of silver nanowires are 17 parts, and the mass parts of silver nanosheets are 15 parts.

[0130] The preparation method specifically comprises the following steps:

[0131] S1: adding carbon nanotubes to mixed acid, wherein the volume ratio of sulfuric acid to nitric acid in the mixed acid is 1:1, and the mass ratio of carbon nanotubes to the mixed acid is 1:12, ultrasonically treating at a first temperature of 55°C for 1.5h, centrifuging, washing, and vacuum drying at the first temperature for 8h to obtain carboxylated carbon nanotubes; preparing an ethanol aqueous solution and adding a silane coupling agent KH550, wherein the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 95:5, and the mass fraction of the silane coupling agent KH550 in the ethanol aqueous solution is 4.5wt.%, using glacial acetic acid with a mass fraction of 2wt.% to adjust the pH to 4.6 to obtain a coupling agent solution, adding the carboxylated carbon nanotubes to the coupling agent solution to obtain a reaction solution A, wherein the mass ratio of the carboxylated carbon nanotubes to the coupling agent solution is 1:27, refluxing at 60°C under nitrogen protection for 2.6h to obtain a reaction solution B, filtering and washing to obtain wet-modified carbon nanotubes, and vacuum drying at 65°C to obtain modified carbon nanotubes;

[0132] S2: Graphite was mixed with concentrated sulfuric acid at a mass ratio of 1:18, potassium persulfate and phosphorus pentoxide were added under an ice bath and pre-oxidized, the mass ratio of potassium sulfate to phosphorus pentoxide was 1.5:1, the mass ratio of the mixture of potassium persulfate and phosphorus pentoxide to graphite was 1:1, the pre-oxidation temperature was 80°C, and the pre-oxidation time was 4 hours. After cooling to room temperature, potassium permanganate was added at a mass ratio of 3.6:1 to graphite to obtain reaction solution C, and the reaction was stirred at 35°C for 13 hours to obtain reaction solution D, which was poured into deionized water and a 15% mass fraction of hydrogen peroxide solution was added until the solution turned golden yellow, wherein the volume ratio of reaction solution D to deionized water was 1:12, and graphene was obtained after centrifugation, washing, and drying; the concentration was 2 mg / mL A graphene dispersion is prepared by ultrasonic dispersion at a power of 260 W for 25 min, 3-mercaptopropylamine is added under continuous stirring, wherein the molar ratio of graphene to 3-mercaptopropylamine is 1:4, 0.2 M dilute hydrochloric acid is used to adjust the pH to 4 to obtain a reaction solution E, reacting at a second temperature of 60° C. for 3.8 h, centrifuging and washing to obtain pre-modified graphene, adding a 0.08 M sodium borohydride solution to the pre-modified graphene dispersion at a concentration of 2 mg / mL for reduction reaction, wherein the mass ratio of sodium borohydride to pre-modified graphene is 3.5:1, the temperature of the reduction reaction is 55° C., and the time is 4.7 h, the pH is adjusted to 10 with 1 M ammonia water, centrifuging, washing, and drying to obtain modified graphene;

[0133] S3: Silicon carbide and 2M potassium hydroxide solution are mixed in a mass ratio of 1:18 and activated at 80°C for 2h, filtered, washed and dried to obtain activated silicon carbide; 0.15M nitrate solution is added dropwise with stirring to 25% ammonia water until the precipitate is completely dissolved to obtain a complex solution, wherein the amount of ammonia water is 1.5 times the volume of the silver nitrate solution, activated silicon carbide is added to the complex solution to obtain a mixed solution, wherein the content of silver ions in the mixed solution is 15% of the mass of the activated silicon carbide, 0.2M glucose solution is added in batches to obtain reaction solution G, wherein the interval time for adding glucose is 15min, and the molar ratio of glucose to silver ions is 1.8:1, and the reaction is carried out at 66°C for 50min under nitrogen protection, filtered, washed and dried to obtain silver-coated silicon carbide.

[0134] S4: prepare a mixed solvent of ethylene glycol / isopropanol / deionized water, wherein the volume ratio of ethylene glycol, isopropanol and deionized water is 3.5:2:1, add polyvinyl pyrrolidone to obtain a first dispersion, add modified carbon nanotubes, modified graphene and silver-coated silicon carbide in sequence, and ultrasonically disperse at a power of 400 W for 20 min to obtain a second dispersion, add conductive particles, and high-speed shear at a rotation speed of 8000 rpm for 2.5 h to obtain a conductive slurry for heterojunction solar cells.

[0135] Example 2

[0136] This embodiment provides a conductive paste for a heterojunction solar cell and a preparation method thereof, wherein the conductive paste for a heterojunction solar cell comprises the following components in parts by weight:

[0137] 0.84 parts of modified carbon nanotubes;

[0138] 1.6 parts of modified graphene;

[0139] Silver-coated silicon carbide 1.3 parts;

[0140] 82 parts of conductive particles;

[0141] 6.5 parts of surfactant;

[0142] 40 parts of mixed solvent;

[0143] Among them, the mass parts of spherical nanosilver in the conductive particles are 49 parts, the mass parts of silver nanowires are 16 parts, and the mass parts of silver nanosheets are 17 parts.

[0144] The preparation method specifically comprises the following steps:

[0145] S1: adding carbon nanotubes to a mixed acid, wherein the volume ratio of sulfuric acid to nitric acid in the mixed acid is 2:1, and the mass ratio of carbon nanotubes to the mixed acid is 1:15, subjecting the mixture to ultrasonic treatment at a first temperature of 50°C for 1 hour, centrifuging, washing, and vacuum drying at the first temperature for 6 hours to obtain carboxylated carbon nanotubes; preparing an ethanol aqueous solution and adding a silane coupling agent KH550, wherein the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 96:4, and the mass fraction of the silane coupling agent KH550 in the ethanol aqueous solution is 4wt.%, using glacial acetic acid with a mass fraction of 1.5wt.% to adjust the pH to 4 to obtain a coupling agent solution, adding the carboxylated carbon nanotubes to the coupling agent solution to obtain a reaction solution A, wherein the mass ratio of the carboxylated carbon nanotubes to the coupling agent solution is 1:30, refluxing at 63°C for 3 hours under nitrogen protection to obtain a reaction solution B, filtering and washing to obtain wet-modified carbon nanotubes, and vacuum drying at 68°C to obtain modified carbon nanotubes;

[0146] S2: Graphite was mixed with concentrated sulfuric acid at a mass ratio of 1:15, potassium persulfate and phosphorus pentoxide were added under an ice bath and pre-oxidized, the mass ratio of potassium sulfate to phosphorus pentoxide was 1.8:1, the mass ratio of the mixture of potassium persulfate and phosphorus pentoxide to graphite was 2:1, the pre-oxidation temperature was 75°C, and the pre-oxidation time was 4.5h. After cooling to room temperature, potassium permanganate was added at a mass ratio of 4:1 to graphite to obtain reaction solution C, and the reaction was stirred at 40°C for 12h to obtain reaction solution D, which was poured into deionized water and a hydrogen peroxide solution with a mass fraction of 18.6% was added until the solution turned golden yellow, wherein the volume ratio of reaction solution D to deionized water was 1:10, and graphene was obtained after centrifugation, washing, and drying; the configuration concentration was 1.8mg / mL A graphene dispersion is prepared by ultrasonic dispersion at a power of 280 W for 20 min, 3-mercaptopropylamine is added under continuous stirring, wherein the molar ratio of graphene to 3-mercaptopropylamine is 1:3.5, 0.4 M dilute hydrochloric acid is used to adjust the pH to 4.5 to obtain a reaction solution E, reacting at a second temperature of 65° C. for 3 h, centrifuging and washing to obtain pre-modified graphene, adding a 0.1 M sodium borohydride solution to the pre-modified graphene dispersion at a concentration of 1.5 mg / mL for reduction reaction, wherein the mass ratio of sodium borohydride to pre-modified graphene is 4.5:1, the temperature of the reduction reaction is 58° C., and the time is 4 h, adjusting the pH to 10.5 with 1.2 M ammonia water, centrifuging, washing, and drying to obtain modified graphene;

[0147] S3: Silicon carbide and 3M potassium hydroxide solution are mixed in a mass ratio of 1:15 and activated at 85°C for 1h, filtered, washed and dried to obtain activated silicon carbide; 0.17M nitrate solution is added dropwise with stirring to 26% ammonia water until the precipitate is completely dissolved to obtain a complex solution, wherein the amount of ammonia water is 1.4 times the volume of the silver nitrate solution, activated silicon carbide is added to the complex solution to obtain a mixed solution, wherein the content of silver ions in the mixed solution is 15.8% of the mass of activated silicon carbide, 0.1M glucose solution is added in batches to obtain reaction solution G, wherein the interval time for adding glucose is 10min, and the molar ratio of glucose to silver ions is 1.9:1, and the reaction is carried out at 60°C for 40min under nitrogen protection, filtered, washed and dried to obtain silver-coated silicon carbide.

[0148] S4: prepare a mixed solvent of ethylene glycol / isopropanol / deionized water, wherein the volume ratio of ethylene glycol, isopropanol and deionized water is 4:2:1, add sodium dodecylbenzene sulfonate to obtain a first dispersion, add modified carbon nanotubes, modified graphene and silver-coated silicon carbide in sequence, and ultrasonically disperse at a power of 480 W for 27 min to obtain a second dispersion, add conductive particles, and high-speed shear at a rotation speed of 8500 rpm for 2 h to obtain a conductive slurry for heterojunction solar cells.

[0149] Example 3

[0150] This embodiment provides a conductive paste for a heterojunction solar cell and a preparation method thereof, wherein the conductive paste for a heterojunction solar cell comprises the following components in parts by weight:

[0151] 0.7 parts of modified carbon nanotubes;

[0152] 1.4 parts of modified graphene;

[0153] 1 part of silver-coated silicon carbide;

[0154] Conductive particles 78 parts;

[0155] 5 parts of surfactant;

[0156] 35 parts of mixed solvent;

[0157] Among them, the mass proportion of spherical nanosilver in the conductive particles is 45 parts, the mass proportion of silver nanowires is 15 parts, and the mass proportion of silver nanosheets is 18 parts.

[0158] The preparation method specifically comprises the following steps:

[0159] S1: adding carbon nanotubes to mixed acid, wherein the volume ratio of sulfuric acid to nitric acid in the mixed acid is 1.5:1, and the mass ratio of carbon nanotubes to the mixed acid is 1:10, ultrasonically treating at a first temperature of 58°C for 2h, centrifuging, washing, and vacuum drying at the first temperature for 7h to obtain carboxylated carbon nanotubes; preparing an ethanol aqueous solution and adding a silane coupling agent KH550, wherein the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 97:3, and the mass fraction of the silane coupling agent KH550 in the ethanol aqueous solution is 5wt.%, using glacial acetic acid with a mass fraction of 1wt.% to adjust the pH to 5 to obtain a coupling agent solution, adding the carboxylated carbon nanotubes to the coupling agent solution to obtain a reaction solution A, the mass ratio of the carboxylated carbon nanotubes to the coupling agent solution is 1:25, refluxing at 65°C for 2h under nitrogen protection to obtain a reaction solution B, filtering and washing to obtain wet-modified carbon nanotubes, and vacuum drying at 70°C to obtain modified carbon nanotubes;

[0160] S2: Graphite was mixed with concentrated sulfuric acid at a mass ratio of 1:20, potassium persulfate and phosphorus pentoxide were added under an ice bath and pre-oxidized, the mass ratio of potassium sulfate to phosphorus pentoxide was 1:1, the mass ratio of the mixture of potassium persulfate and phosphorus pentoxide to graphite was 1.6:1, the pre-oxidation temperature was 85°C, and the pre-oxidation time was 4.8h. After cooling to room temperature, potassium permanganate was added at a mass ratio of 3:1 to graphite to obtain reaction solution C, and the reaction was stirred at 30°C for 14h to obtain reaction solution D, which was poured into deionized water and a 17.5% mass fraction of hydrogen peroxide solution was added until the solution was golden yellow, wherein the volume ratio of reaction solution D to deionized water was 1:15, and graphene was obtained after centrifugation, washing, and drying; the concentration was 2.2mg / mL of graphene dispersion, ultrasonically disperse for 30 min at a power of 200 W, add 3-mercaptopropylamine under continuous stirring, wherein the molar ratio of graphene to 3-mercaptopropylamine is 1:4.5, use 0.1M dilute hydrochloric acid to adjust the pH to 5 to obtain reaction solution E, react at a second temperature of 55°C for 4h, centrifuge and wash to obtain pre-modified graphene, add 0.12M sodium borohydride solution to the pre-modified graphene dispersion with a concentration of 1 mg / mL to carry out reduction reaction, wherein the mass ratio of sodium borohydride to pre-modified graphene is 4:1, the temperature of the reduction reaction is 50°C, and the time is 5h, adjust the pH to 10.4 with 0.5M ammonia water, centrifuge, wash, and dry to obtain modified graphene;

[0161] S3: Silicon carbide and 2.5M potassium hydroxide solution are mixed in a mass ratio of 1:17 and activated at 82°C for 1.4h, filtered, washed and dried to obtain activated silicon carbide; 0.1M nitrate solution is added dropwise with stirring to 27% ammonia water until the precipitate is completely dissolved to obtain a complex solution, wherein the amount of ammonia water is 1.3 times the volume of the silver nitrate solution, activated silicon carbide is added to the complex solution to obtain a mixed solution, wherein the content of silver ions in the mixed solution is 16% of the mass of the activated silicon carbide, 0.15M glucose solution is added in portions to obtain reaction solution G, wherein the interval time for adding glucose is 12min, and the molar ratio of glucose to silver ions is 2:1, and the reaction is carried out at 68°C for 55min under nitrogen protection, filtered, washed and dried to obtain silver-coated silicon carbide.

[0162] S4: prepare a mixed solvent of ethylene glycol / isopropanol / deionized water, wherein the volume ratio of ethylene glycol, isopropanol and deionized water is 3:2:1, add polyethylene glycol-4000 to obtain a first dispersion, add modified carbon nanotubes, modified graphene and silver-coated silicon carbide in sequence, and ultrasonically disperse at a power of 450 W for 30 min to obtain a second dispersion, add conductive particles, and high-speed shear at a rotation speed of 8200 rpm for 2.2 h to obtain a conductive slurry for heterojunction solar cells.

[0163] Example 4

[0164] This embodiment provides a conductive paste for a heterojunction solar cell and a preparation method thereof, wherein the conductive paste for a heterojunction solar cell comprises the following components in parts by weight:

[0165] 0.9 parts of modified carbon nanotubes;

[0166] 1.8 parts of modified graphene;

[0167] Silver-coated silicon carbide 1.5 parts;

[0168] 83 parts of conductive particles;

[0169] 6 parts of surfactant;

[0170] 45 parts of mixed solvent;

[0171] Among them, the mass proportion of spherical nanosilver in the conductive particles is 50 parts, the mass proportion of silver nanowires is 16.5 parts, and the mass proportion of silver nanosheets is 16.5 parts.

[0172] The preparation method specifically comprises the following steps:

[0173] S1: adding carbon nanotubes to a mixed acid, wherein the volume ratio of sulfuric acid to nitric acid in the mixed acid is 1.7:1, and the mass ratio of carbon nanotubes to the mixed acid is 1:13, ultrasonically treating at a first temperature of 60°C for 1.8h, centrifuging, washing, and vacuum drying at the first temperature for 7.4h to obtain carboxylated carbon nanotubes; preparing an ethanol aqueous solution and adding a silane coupling agent KH550, wherein the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 98:2, and the mass fraction of the silane coupling agent KH550 in the ethanol aqueous solution is 4.8wt.%, using glacial acetic acid with a mass fraction of 1.8wt.% to adjust the pH to 4.7 to obtain a coupling agent solution, adding the carboxylated carbon nanotubes to the coupling agent solution to obtain a reaction solution A, wherein the mass ratio of the carboxylated carbon nanotubes to the coupling agent solution is 1:28, refluxing at 55°C under nitrogen protection for 2.8h to obtain a reaction solution B, filtering and washing to obtain wet-modified carbon nanotubes, and vacuum drying at 60°C to obtain modified carbon nanotubes;

[0174] S2: Graphite was mixed with concentrated sulfuric acid at a mass ratio of 1:17, potassium persulfate and phosphorus pentoxide were added in an ice bath and pre-oxidized, the mass ratio of potassium sulfate to phosphorus pentoxide was 2:1, the mass ratio of the mixture of potassium persulfate and phosphorus pentoxide to graphite was 1.7:1, the pre-oxidation temperature was 83°C, and the pre-oxidation time was 5h. After cooling to room temperature, potassium permanganate was added at a mass ratio of 3.9:1 to graphite to obtain reaction solution C, and the reaction was stirred at 37°C for 13.6h to obtain reaction solution D, which was poured into deionized water and a 20% mass fraction of hydrogen peroxide solution was added until the solution turned golden yellow, wherein the volume ratio of reaction solution D to deionized water was 1:13, and graphene was obtained after centrifugation, washing, and drying; a graphite solution with a concentration of 2.1mg / mL was prepared. A graphene dispersion is ultrasonically dispersed at a power of 300 W for 28 minutes, 3-mercaptopropylamine is added under continuous stirring, wherein the molar ratio of graphene to 3-mercaptopropylamine is 1:4.2, 0.5M dilute hydrochloric acid is used to adjust the pH to 4.8 to obtain a reaction solution E, reacting at a second temperature of 63° C. for 3.5 hours, centrifuging and washing to obtain pre-modified graphene, adding a 0.11M sodium borohydride solution to the pre-modified graphene dispersion having a concentration of 1.7 mg / mL for reduction reaction, wherein the mass ratio of sodium borohydride to pre-modified graphene is 4.2:1, the temperature of the reduction reaction is 60° C., and the time is 4.4 hours, adjusting the pH to 11 with 1.5M ammonia water, centrifuging, washing, and drying to obtain modified graphene;

[0175] S3: Silicon carbide is mixed with a 2.8M potassium hydroxide solution in a mass ratio of 1:20 and activated at 75°C for 1.7h, filtered, washed and dried to obtain activated silicon carbide; 0.2M nitrate solution is added dropwise with stirring to 28% ammonia water until the precipitate is completely dissolved to obtain a complex solution, wherein the amount of ammonia water is 1.2 times the volume of the silver nitrate solution, activated silicon carbide is added to the complex solution to obtain a mixed solution, wherein the content of silver ions in the mixed solution is 15.5% of the mass of the activated silicon carbide, 0.18M glucose solution is added in portions to obtain reaction solution G, wherein the interval time for adding glucose is 14min, and the molar ratio of glucose to silver ions is 2.2:1, and the reaction is carried out at 70°C for 60min under nitrogen protection, filtered, washed and dried to obtain silver-coated silicon carbide.

[0176] S4: prepare a mixed solvent of ethylene glycol / isopropanol / deionized water, wherein the volume ratio of ethylene glycol, isopropanol and deionized water is 3.3:2:1, add polyvinyl pyrrolidone and sodium dodecylbenzene sulfonate to obtain a first dispersion, add modified carbon nanotubes, modified graphene and silver-coated silicon carbide in sequence, and ultrasonically disperse at a power of 500 W for 29 minutes to obtain a second dispersion, add conductive particles, and high-speed shear at a rotation speed of 7500 rpm for 3 hours to obtain a conductive slurry for heterojunction solar cells.

[0177] Comparative Example 1

[0178] This comparative example provides a conductive paste for heterojunction solar cells, which is different from Example 1 in that in step S1, the mass ratio of carbon nanotubes to mixed acid is 1:20, and other operating steps and process parameters are exactly the same as those in Example 1.

[0179] Comparative Example 2

[0180] This comparative example provides a conductive paste for heterojunction solar cells, which is different from Example 1 in that in step S1, the mass ratio of carbon nanotubes to mixed acid is 1:5, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0181] Comparative Example 3

[0182] This comparative example provides a conductive paste for heterojunction solar cells, which is different from Example 1 in that in step S2, the molar ratio of graphene to 3-mercaptopropylamine is 1:8, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0183] Comparative Example 4

[0184] This comparative example provides a conductive paste for heterojunction solar cells, which is different from Example 1 in that in step S2, the molar ratio of graphene to 3-mercaptopropylamine is 1:1, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0185] Comparative Example 5

[0186] This comparative example provides a conductive paste for a heterojunction solar cell, which is different from Example 1 in that in step S2, the mass ratio of sodium borohydride to pre-modified graphene is 6:1, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0187] Comparative Example 6

[0188] This comparative example provides a conductive paste for a heterojunction solar cell, which is different from Example 1 in that in step S2, the mass ratio of sodium borohydride to pre-modified graphene is 1:1, and the other operating steps and process parameters are exactly the same as those in Example 1.

[0189] The performance test of the conductive paste for heterojunction solar cells of the above-mentioned Examples 1-4 and Comparative Examples 1-6 was carried out, and the specific process is as follows:

[0190] Resistivity test: the conductive paste is screen-printed on the substrate, dried at 150°C for 20 minutes, and the conductivity of the paste is tested with a four-probe resistance meter. The lower the square resistance value, the stronger the conductivity;

[0191] The test results are as follows Figure 2 shown.

[0192] Depend on Figure 2 It can be seen that the conductive paste for heterojunction solar cells prepared in Examples 1-4 provided by the present invention has good conductive properties. From the test results of Example 1 and Comparative Examples 1 and 2, it can be seen that the mixed acid can perform an oxidation reaction on the surface of the carbon nanotubes. When the amount of the mixed acid used is too much, the surface of the carbon nanotubes is over-oxidized, and too many oxygen-containing functional groups are formed, resulting in instability of the surface of the carbon nanotubes, which leads to uneven dispersion in the conductive paste, thereby affecting the conductive properties; when the amount of the mixed acid used is insufficient, the surface of the carbon nanotubes is not fully oxidized, and the surface modification is not obvious. It is difficult to disperse well in the conductive paste, forming large agglomerates, resulting in a decrease in the performance of the paste.

[0193] From the test results of Example 1, Comparative Examples 3 and 4, it can be seen that the introduction of 3-mercaptopropylamine to modify graphene oxide can not only form chemical bonds with metal ions and other substances, enhance the interaction between graphene and other components, but also further improve the conductivity of graphene. However, when the usage of 3-mercaptopropylamine is too high, the graphene surface will be over-modified. Although the thiol group helps to enhance the hydrophilicity of graphene and the interfacial compatibility with other materials, too many thiol groups may also cause aggregation and interaction between functional groups, resulting in crowding or aggregation on the graphene surface, thereby affecting the conductive properties; if the usage is too low, the number of thiol functional groups on the graphene surface will be insufficient, resulting in poor interfacial compatibility between graphene and other components, affecting the uniformity and conductive properties of the slurry.

[0194] From the test results of Example 1 and Comparative Examples 5 and 6, it can be seen that sodium borohydride is a strong reducing agent used to reduce the oxidized functional groups on graphene to restore its conductivity. When sodium borohydride is excessive, it will lead to excessive reduction of the oxidized functional groups on the surface of graphene, thereby destroying the structure of graphene. At the same time, excessive reduction will also lead to structural instability of graphene, defects, and even dissociation or fragmentation of graphene sheets, reducing its overall electronic conductivity; when the amount of sodium borohydride used is too low, the oxidized functional groups on graphene are still retained in large quantities, and these functional groups will increase the hydrophilicity of graphene, reduce its compatibility with other components, and also hinder the conductivity of graphene, thereby affecting the performance of the conductive paste.

[0195] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a conductive paste for a heterojunction solar cell, characterized in that: The preparation method comprises: S1: adding carbon nanotubes to a mixed acid, ultrasonically treating at a first temperature, centrifuging, washing, and vacuum drying at a first temperature to obtain carboxylated carbon nanotubes; preparing an ethanol aqueous solution and adding a silane coupling agent, adjusting the pH with glacial acetic acid to obtain a coupling agent solution, adding the carboxylated carbon nanotubes to the coupling agent solution to obtain a reaction solution A, refluxing under nitrogen protection to obtain a reaction solution B, filtering and washing to obtain wet-modified carbon nanotubes, and vacuum drying to obtain modified carbon nanotubes; S2: Mix graphite with concentrated sulfuric acid, add potassium persulfate and phosphorus pentoxide in an ice bath and pre-oxidize, cool to room temperature, add potassium permanganate to obtain reaction solution C, stir to react to obtain reaction solution D, pour it into deionized water and add hydrogen peroxide solution until the solution turns golden yellow, centrifuge, wash, and dry to obtain graphene; prepare a graphene dispersion, ultrasonically disperse, add 3-mercaptopropylamine under continuous stirring, use dilute hydrochloric acid to adjust the pH to obtain reaction solution E, react at a second temperature, centrifuge, wash to obtain pre-modified graphene, add sodium borohydride solution to the pre-modified graphene dispersion for reduction reaction, adjust the pH with ammonia water, centrifuge, wash, and dry to obtain modified graphene; S3: mixing silicon carbide with potassium hydroxide solution and activating it, filtering, washing and drying to obtain activated silicon carbide; adding ammonia water dropwise to the nitrate solution under stirring to obtain a complex solution, adding the activated silicon carbide to the complex solution to obtain a mixed solution, adding glucose solution in portions to obtain a reaction solution G, reacting under nitrogen protection, filtering, washing and drying to obtain silver-coated silicon carbide; S4: prepare a mixed solvent of ethylene glycol / isopropanol / deionized water, add a surfactant to obtain a first dispersion, add modified carbon nanotubes, modified graphene, and silver-coated silicon carbide in sequence, ultrasonically disperse to obtain a second dispersion, add conductive particles, and high-speed shear to obtain a conductive slurry for heterojunction solar cells.

2. The method for preparing a conductive paste for heterojunction solar cells according to claim 1, characterized in that: In S1: The volume ratio of sulfuric acid to nitric acid in the mixed acid is 1-2:1; The mass ratio of the carbon nanotubes to the mixed acid is 1:10-15; The first temperature is 50-60°C; The ultrasonic time at the first temperature is 1-2h; The vacuum drying time at the first temperature is 6-8h; The volume ratio of ethanol to deionized water in the ethanol aqueous solution is 95:5-99:1; The silane coupling agent is silane coupling agent KH550, and the mass fraction of silane coupling agent KH550 in the ethanol aqueous solution is 4-5wt.%.

3. The method for preparing a conductive paste for a heterojunction solar cell according to claim 1, characterized in that: In S1: The mass fraction of the glacial acetic acid is 1-2wt.%; The pH value is adjusted to 4-5 using glacial acetic acid; The mass ratio of the carboxylated carbon nanotubes to the coupling agent solution is 1:25-30; The reflux temperature of the reaction solution A under nitrogen protection is 55-65°C; The reaction solution A is refluxed under nitrogen protection for 2-3 hours; The vacuum drying temperature of the wet modified carbon nanotubes is 60-70°C.

4. The method for preparing a conductive paste for a heterojunction solar cell according to claim 1, characterized in that: In S2: The mass ratio of graphite to concentrated sulfuric acid is 1:15-20; The mass ratio of potassium persulfate to phosphorus pentoxide is 1-2:1; The mass ratio of the mixture of potassium persulfate and phosphorus pentoxide to graphite is 1-2:1; The pre-oxidation temperature is 75-85°C; The pre-oxidation time is 4-5h; The mass ratio of potassium permanganate to graphite is 3-4:1; The stirring reaction temperature of the reaction solution C is 30-40°C; The stirring reaction time of the reaction solution C is 12-14 hours.

5. The method for preparing a conductive paste for a heterojunction solar cell according to claim 1, characterized in that: In S2: The volume ratio of the reaction solution D to deionized water is 1:10-15; The mass fraction of the hydrogen peroxide solution is 15-20%; The concentration of the graphene dispersion is 1.8-2.2 mg / mL; The power of ultrasonic dispersion of the graphene dispersion is 200-300W; The ultrasonic dispersion time of the graphene dispersion is 20-30 minutes; The molar ratio of graphene to 3-mercaptopropylamine is 1:3.5-4.5; The concentration of the dilute hydrochloric acid is 0.1-0.5M; The pH is adjusted to 4-5 using dilute hydrochloric acid.

6. The method for preparing a conductive paste for a heterojunction solar cell according to claim 1, characterized in that: In S2: The second temperature is 55-65°C; The reaction time of the reaction solution E at the second temperature is 3-4h; The concentration of the pre-modified graphene dispersion is 1-2 mg / mL; The concentration of the sodium borohydride solution is 0.08-0.12M; The mass ratio of sodium borohydride to pre-modified graphene is 3.5-4.5:1; The temperature of the reduction reaction is 50-60°C; The reduction reaction time is 4-5h; The concentration of the ammonia water is 0.5-1.5M; The pH is adjusted to 10-11 with aqueous ammonia.

7. The method for preparing a conductive paste for a heterojunction solar cell according to claim 1, characterized in that: In S3: The concentration of the potassium hydroxide solution is 2-3M; The mass ratio of silicon carbide to potassium hydroxide solution is 1:15-20; The activation temperature is 75-85°C; The activation time is 1-2h; The silver nitrate concentration is 0.1-0.2M; The ammonia concentration is 25-28%; The amount of ammonia water used is 1.2-1.5 times the volume of the silver nitrate solution.

8. The method for preparing a conductive paste for a heterojunction solar cell according to claim 1, characterized in that: In S3: The content of silver ions in the mixed solution is 15-16% of the mass of activated silicon carbide; The concentration of the glucose solution is 0.1-0.2M; The glucose addition interval is 10-15min; The molar ratio of glucose to silver ions is 1.8-2.2:1; The reaction temperature of the reaction liquid G under nitrogen protection is 60-70°C; The reaction time of the reaction liquid G under nitrogen protection is 40-60 minutes.

9. The method for preparing a conductive paste for a heterojunction solar cell according to claim 1, characterized in that: In S4: The volume ratio of ethylene glycol, isopropanol and deionized water in the ethylene glycol / isopropanol / deionized water mixed solvent is 3-4:2:1; The surfactant is any one of polyvinyl pyrrolidone, sodium dodecylbenzene sulfonate, and polyethylene glycol-4000, or a combination of at least two thereof; The power of the ultrasonic dispersion is 400-500W; The ultrasonic dispersion time is 20-30min; The conductive particles include spherical nanosilver, silver nanowires and silver nanosheets; The rotation speed of the high-speed shearing is 7500-8500rpm; The high-speed shearing time is 2-3h.

10. A conductive paste for heterojunction solar cells prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The conductive paste for heterojunction solar cells comprises the following components in parts by weight: 0.7-0.9 parts of modified carbon nanotubes; 1.4-1.8 parts of modified graphene; Silver coated silicon carbide 1-1.5 parts; Conductive particles 75-85 parts; 5-7 parts of surfactant; 35-45 parts of mixed solvent; Among them, the mass proportion of spherical nanosilver in the conductive particles is 45-50 parts, the mass proportion of silver nanowires is 15-17 parts, and the mass proportion of silver nanosheets is 15-18 parts.

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