Copper paste and preparation method therefor, electrode and preparation method therefor, and solar cell

Abstract

The present application provides a copper paste for a solar cell and a preparation method therefor, an electrode and a preparation method therefor, and a solar cell. The copper paste comprises copper powder and a solvent, wherein when the copper paste is heated under a nitrogen atmosphere at a rate of 10°C / min, the measured weight loss percentage satisfies at least one of the following conditions: the weight loss upon being heated from 25°C to 150-170°C accounts for 35-55% of the total weight of the solvent; the weight loss upon being heated from 25°C to 120-140°C accounts for 20-40% of the total weight of the solvent; or the weight loss upon being heated from 25°C to 80-110°C accounts for 10-25% of the total weight of the solvent. According to the present application, the copper paste can be cured at a low temperature of between 25°C and 220°C, the curing cost is low, and the resulting grid lines have a high crosslinking density, a high strength, and a strong tensile force.

Description

Copper paste and its preparation method, electrodes and their preparation method, and solar cells

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese application No. 2025100464292, filed on January 10, 2025, entitled "Copper paste and method for preparation thereof, electrode and method for preparation thereof and solar cell", the contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of solar cell technology, specifically to copper paste for solar cells and methods for preparing the same, electrodes and methods for preparing the same, and solar cells. Background Technology

[0004] With the advancement of technology, the demand for solar cells is increasing daily. However, the copper paste used in solar cells relies heavily on silver, and as is well known, silver, as a precious metal, has limited global reserves. As a major producer of solar cells, my country imports a large amount of silver annually, facing risks of supply chain disruptions and price fluctuations. Therefore, finding alternatives to silver in solar cells has significant strategic value. Among many metals, copper stands out as the most promising alternative due to its similar electrical conductivity to silver and its price being only one-eightieth that of silver.

[0005] In the process of fabricating solar cells, the weight loss process of the printed paste when it transforms from a liquid state to a solid grid line has a significant impact on the quality of the grid line. Summary of the Invention

[0006] To address the aforementioned technical problems, in a first aspect of this application, a copper paste for solar cells is provided, comprising copper powder and a solvent, wherein the weight loss percentage of the copper paste, measured when heated at a rate of 10°C / min under a nitrogen atmosphere, satisfies at least one of the following conditions:

[0007] The weight loss when heated from 25℃ to 150℃-170℃ accounts for 35%-55% of the total weight of the solvent;

[0008] The weight loss when heated from 25°C to 120°C-140°C is 20%-40% of the total weight of the solvent; or the weight loss when heated from 25°C to 80°C-110°C is 10-25% of the total weight of the solvent.

[0009] Optionally, the weight loss percentage of the copper paste measured when heated at a rate of 10°C / min under a nitrogen atmosphere meets the following condition: the weight loss when heated from 25°C to 190°C-220°C accounts for 85%-100% of the total weight of the solvent.

[0010] Optionally, the weight loss of the copper paste when heated from 25°C to 30°C at a rate of 10°C / min under a nitrogen atmosphere is less than 0.01%.

[0011] Optionally, the weight loss rate measured when the copper paste is heated at a rate of 10°C / min under a nitrogen atmosphere satisfies at least one of the following conditions:

[0012] The weight loss rate when heated from 25°C to 80°C-110°C is 5% to 20% of the weight loss rate when heated from 25°C to 400°C.

[0013] The weight loss rate when heated from 25°C to 120°C-140°C is 10% to 25% of the weight loss rate when heated from 25°C to 400°C.

[0014] The weight loss rate when heated from 25°C to 150°C-170°C is 20% to 40% of the weight loss rate when heated from 25°C to 400°C.

[0015] The weight loss rate when heated from 25°C to 190°C-220°C is 55% to 75% of the weight loss rate when heated from 25°C to 400°C; or,

[0016] The weight loss rate when heated from 25°C to 80°C-110°C is 10% to 30% of the weight loss rate when heated from 25°C to 190°C-220°C.

[0017] Optionally, in the TG-DSC curve of the copper paste heated from 25°C to 400°C, the TG-DSC curve exhibits an endothermic peak between 170°C and 210°C.

[0018] Optionally, at a shear rate of 200 s -1 Under the specified measurement conditions, the viscosity of the copper paste was measured to be in the range of 1 Pa·s to 25 Pa·s.

[0019] Optionally, in the copper paste, the weight percentage of copper powder is between 80% and 95%, and the weight percentage of solvent is between 2% and 8%.

[0020] Optionally, the solvent includes a first solvent and a second solvent, wherein the boiling point of the second solvent differs from that of the first solvent by more than 60°C.

[0021] Optionally, the boiling point of the first solvent is between 100°C and 200°C, and the boiling point of the second solvent is between 180°C and 300°C.

[0022] Optionally, the first solvent is selected from at least one of the following components: ester solvents, ether solvents, ketone solvents, and alcohol solvents; the second solvent is selected from at least one of the following components: ether solvents and ester solvents.

[0023] Optionally, the mass ratio of the first solvent to the second solvent is any value between 2:1 and 1:1.

[0024] Optionally, the copper powder includes spherical copper powder and / or flake copper powder.

[0025] Optionally, the copper paste may further include a resin, a curing agent, and an optional curing accelerator.

[0026] In a second aspect of this application, a method for preparing the copper paste for solar cells described above is provided, the method comprising the steps of: providing copper powder; and uniformly mixing and grinding the copper powder, solvent, resin, curing agent and optional curing accelerator.

[0027] In a third aspect of this application, an electrode for a solar cell is provided, which is prepared from the copper paste used in solar cells as described above.

[0028] In a fourth aspect of this application, a method for preparing an electrode for a solar cell is provided, the method using the copper paste for solar cells as described above, wherein the method includes the steps of: printing the pre-prepared copper paste onto a solar cell; and heating the solar cell with the printed copper paste to cure the copper paste.

[0029] Optionally, the method further includes the following steps: performing the printing at a temperature in the range of 25°C to 35°C; and curing the copper paste by holding it at a temperature in the range of 100°C to 250°C for a curing period of time, wherein the curing period of time is in the range of 10 min to 120 min.

[0030] In a fifth aspect of this application, a solar cell is provided, the solar cell comprising the electrodes of the aforementioned solar cell.

[0031] Optionally, the solar cell is selected from any one of BC cells, HJT cells, and perovskite / crystalline silicon tandem cells.

[0032] According to this application, by controlling the weight loss ratio of copper paste at different temperatures within the range of 25°C to 220°C, multiple processes of volatile component volatilization and copper powder aggregation can be balanced, the tightness of the connection between copper powders and the connection strength between copper powder and substrate can be strengthened, and delamination, voids and cracks can be avoided when copper paste forms grid lines. This allows the copper paste to achieve low-temperature curing between 25°C and 220°C, resulting in high-quality copper grid lines.

[0033] The above and other objects, advantages and features of this application will become more apparent to those skilled in the art from the following detailed description of specific embodiments of this application in conjunction with the accompanying drawings. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the specific embodiments or related technologies of this application, the accompanying drawings used in the description of the specific embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0035] Figure 1 shows the weight loss rate curve of a copper paste according to an embodiment of the present application at different temperatures;

[0036] Figure 2 is a schematic diagram showing the thermogravimetric-differential scanning calorimetry (TG-DSC) curves of a copper paste according to an embodiment of the present application at 25°C-100°C;

[0037] Figure 3 is a schematic diagram showing the TG-DSC curve of a copper paste according to an embodiment of the present application at 25°C-130°C;

[0038] Figure 4 is a schematic diagram showing the TG-DSC curve of a copper paste according to an embodiment of the present application at 25°C-160°C;

[0039] Figure 5 is a schematic diagram showing the TG-DSC curve of a copper paste according to an embodiment of the present application at 25°C-190°C;

[0040] Figure 6 is a schematic diagram showing the TG-DSC curve of a copper paste according to an embodiment of the present application at 25°C-200°C;

[0041] Figure 7 is a schematic diagram showing the TG-DSC curves of a copper paste according to an embodiment of this application at temperatures ranging from 25°C to 400°C; and

[0042] Figure 8 is a schematic diagram showing the DSC curve of a copper paste according to an embodiment of the present application at 25°C-400°C. Detailed Implementation

[0043] The exemplary embodiments of this application will now be described in more detail with reference to the accompanying drawings. The description of the exemplary embodiments is merely illustrative and is by no means a limitation of this application or its application or use. Furthermore, the dimensions and proportions of the components in the drawings are merely schematic and do not strictly correspond to actual products.

[0044] Although copper has conductivity comparable to silver and is relatively inexpensive, its high reactivity leads to easy oxidation and corrosion, especially at the micro- and nanoscale. Oxidation is exacerbated at high temperatures, resulting in a sharp decline in the electrical properties of the oxidized copper paste. Furthermore, to ensure good conductivity during copper electrode fabrication, the copper powder content needs to be increased. However, as the copper powder content increases, the viscosity of the copper paste also increases, reducing screen printing operability and affecting the precise formation of electrode patterns. Therefore, balancing the content of copper powder and the dispersion medium is crucial for preparing high-performance copper pastes.

[0045] In a first aspect of this application, a copper paste for solar cells is provided, the copper paste comprising copper powder and a solvent, wherein the weight loss percentage measured when the copper paste is heated at a rate of 10°C / min under a nitrogen atmosphere satisfies at least one of the following conditions:

[0046] The weight loss when heated from 25℃ to 150℃-170℃ accounts for 35%-55% of the total weight of the solvent;

[0047] The weight loss when heated from 25°C to 120°C-140°C accounts for 20%-40% of the total solvent weight; or,

[0048] The weight loss when heated from 25°C to 80°C-110°C accounts for 10-25% of the total weight of the solvent.

[0049] For example, the weight loss of copper paste when heated from 25°C to 150°C-170°C at a rate of 10°C / min under a nitrogen atmosphere can be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, or 55% of the total solvent weight. The temperature range of 150°C-170°C here applies to the following description of this temperature range.

[0050] For example, the weight loss of copper paste when heated from 25°C to 120°C-140°C at a rate of 10°C / min under a nitrogen atmosphere can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, or 40% of the total solvent weight. The temperature range of 120°C-140°C here applies to the following description of this temperature range.

[0051] For example, the weight loss of copper paste when heated from 25°C to 80°C-110°C at a rate of 10°C / min under a nitrogen atmosphere can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, or 25% of the total solvent weight. The temperature range of 80°C-110°C here applies to the following description of this temperature range.

[0052] In this application, the weight loss ratio refers to the ratio of the weight lost by the copper paste after heating to the total weight of the solvent in the copper paste before heating. Solvent refers to the liquid component used to disperse copper powder in the copper paste and / or dissolve organic binders (e.g., organic resins) in the copper paste. Before measuring the total weight of the solvent, the total weight of the copper paste can be weighed first, then the solvent can be separated from the copper paste, and finally the weights of the remaining solid and liquid phases can be weighed to calculate the total weight of the solvent. The solvent separation method can be distillation under pressure, cryogenic cooling, solvent extraction, gas-phase extraction, evaporation, or a combination of multiple separation methods, or other conventional methods in the art.

[0053] The weight loss percentage was obtained using the TG-DSC test method. The prepared copper paste was ground using a three-roll mill, followed by centrifugal stirring to ensure the homogeneity and consistency of the material, thus producing the copper paste to be tested. It should be noted that the test environment was controlled within a nitrogen atmosphere, with the nitrogen flow rate set to 30 ml / min or another value to prevent oxidation and other side reactions from interfering with the test results. The testing instrument used was a TG-DSC coupled device, which can simultaneously measure thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). During the test, the heating rate was set to 10℃ / min, and the initial temperature was set to 25℃ to gradually observe the weight change and thermal property data of the sample as it was heated at different temperatures from room temperature.

[0054] The heating methods for different temperature ranges during the test are as follows: heating from 25℃ to 30℃ at a rate of 10℃ / min, and holding at 30℃ for 60±10min; or heating from 25℃ to 80℃-110℃, and holding for 30±5min; or heating from 25℃ to 120℃-140℃, and holding for 30±5min; or heating from 25℃ to 150℃-170℃, and holding for 30±5min; or heating from 25℃ to 190℃-220℃, and holding for 30±5min; or heating from 25℃ to 400℃, and holding at 400℃ for 60±10min.

[0055] The temperature range of 80℃-110℃ can be 80℃, or 85℃, or 90℃, or 95℃, or 100℃, or 105℃, or 110℃, or any value between any two of the above.

[0056] The temperature range of 120℃-140℃ can be 120℃, or 125℃, or 130℃, or 135℃, or 140℃, or any value between any two of the above.

[0057] The temperature range of 150℃-170℃ can refer to 150℃, or 155℃, or 160℃, or 165℃, or 170℃, or any value between any two of the above.

[0058] The temperature range of 190℃-220℃ can refer to 190℃, or 195℃, or 200℃, or 205℃, or 210℃, or 215℃, or 220℃, or any value between any two of the above.

[0059] Most of the solvent in the copper paste of this application gradually evaporates during the heating process from 25℃ to 220℃. Therefore, the weight loss during the heating process from 25℃ to 220℃ in the TG-DSC test is mainly due to the evaporation of solvents and other components. Thus, controlling the weight loss ratio to meet at least one of the aforementioned conditions can balance the evaporation process of volatile components with the aggregation process between copper powders, enhancing the tightness of the connection between copper powders and the bonding strength between copper powders and the substrate, and preventing delamination, voids, and cracks when the copper paste solidifies to form grid lines. If the weight loss is too rapid, the volatile components will evaporate quickly during the thermal curing process, forming voids, which will affect the density and mechanical stability of the grid lines. If the weight loss is too slow, the formed grid lines will be difficult to achieve the required aspect ratio, increasing the resistivity of the grid lines.

[0060] During the heating process of copper paste, the solvent composition, boiling point, heating rate, or the type and concentration of other organic components in the paste can be controlled to allow the solvent in the copper paste to gradually evaporate during heating at 25℃-220℃. It is understood that the selection of multiple parameters in the above heating process can be adjusted for different copper paste systems, and this application does not specifically limit this. In some embodiments, the weight loss percentage measured when the copper paste is heated at a rate of 10℃ / minute under a nitrogen atmosphere meets the following condition: the weight loss when heated from 25℃ to 190℃-220℃ accounts for 85%-100% of the total solvent weight.

[0061] For example, the weight loss of copper paste when heated from 25°C to 190°C-220°C at a rate of 10°C / min under a nitrogen atmosphere can be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% of the total solvent weight. The temperature range of 190°C-220°C here applies to the aforementioned description of this temperature range and will not be repeated here.

[0062] In some embodiments, the weight loss rate of the copper paste when heated from 25°C to 30°C at a rate of 10°C / min under a nitrogen atmosphere is less than 0.01%. In this application, weight loss rate refers to the ratio of the weight lost by the copper paste during heating to the total weight of the copper paste before heating. This low weight loss rate indicates that the copper paste is very stable within the temperature range of 25°C-35°C, with almost no mass loss due to temperature changes, ensuring excellent printability of the copper paste at 25°C-35°C and improving the consistency and reliability of the paste during the printing process.

[0063] In some embodiments, the weight loss measured when the copper paste is heated and cured at a rate of 10°C / min under a nitrogen atmosphere satisfies at least one of the following conditions: the weight loss when heated from 25°C to 80°C-110°C is 5% to 20% of the weight loss when heated from 25°C to 400°C; the weight loss when heated from 25°C to 120°C-140°C is 10% to 25% of the weight loss when heated from 25°C to 400°C; from 2... The weight loss rate when heated from 5°C to 150°C-170°C is 20% to 40% of the weight loss rate when heated from 25°C to 400°C; the weight loss rate when heated from 25°C to 190°C-220°C is 55% to 75% of the weight loss rate when heated from 25°C to 400°C; and the weight loss rate when heated from 25°C to 80°C-110°C is 10% to 30% of the weight loss rate when heated from 25°C to 190°C-220°C.

[0064] For example, the weight loss rate of copper paste when heated from 25°C to 80°C-110°C at a rate of 10°C / min under a nitrogen atmosphere can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20% of the weight loss rate when heated from 25°C to 400°C, or any value between any two of the above.

[0065] For example, the weight loss rate of copper paste when heated from 25°C to 120°C-140°C at a rate of 10°C / min in a nitrogen atmosphere can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, or 25%, or any value between the two above, which is the weight loss rate when heated from 25°C to 400°C.

[0066] For example, the weight loss rate of copper paste when heated from 25°C to 150°C-170°C at a rate of 10°C / min in a nitrogen atmosphere can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, or 40%, or any value between any two of the above, which is the weight loss rate when heated from 25°C to 400°C.

[0067] For example, the weight loss rate of copper paste when heated from 25°C to 190°C-220°C at a rate of 10°C / min under a nitrogen atmosphere can be 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, or 75%, or any value between any two of the above, which is the weight loss rate when heated from 25°C to 400°C.

[0068] For example, the weight loss rate of copper paste when heated from 25°C to 80°C-110°C at a rate of 10°C / min under a nitrogen atmosphere can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%, or any value between the two above, which is the weight loss rate when heated from 25°C to 190°C-220°C.

[0069] The aforementioned weight loss rate and the aforementioned weight loss percentage were measured using the same testing method, namely the TG-DSC test method, which will not be elaborated further here.

[0070] In the TG-DSC test of the copper paste of this application, the weight loss of the copper paste after maintaining it at 400°C for 60 minutes is mainly due to the carbonization and decomposition of other non-volatile components in the copper paste, such as organic resins, at high temperatures. That is, the carbonization and decomposition temperature of the non-volatile components is higher than that of the volatile components. Therefore, by controlling the weight loss rate to meet at least one of the aforementioned conditions, the carbonization and decomposition of the non-volatile organic components in the copper paste can be avoided during the solvent evaporation process. This separates the solvent evaporation process from the carbonization and decomposition process of the non-volatile organic components, thereby not affecting the aggregation and fusion process of the copper powder, enhancing the tightness of the connection between copper powders and the connection strength between copper powders and the substrate, and preventing delamination, voids, and cracks when the copper paste solidifies to form grid lines.

[0071] In some embodiments, in the TG-DSC curves of the copper paste heated from 25°C to 400°C, an endothermic peak is observed between 170°C and 210°C. When the copper paste is heated to 170°C-210°C, an endothermic peak is generated due to the curing reaction of the copper paste. That is, the curing temperature range of the copper paste in this application overlaps with the volatilization temperature range of volatile components such as solvents. This results in better shape retention of the grid lines formed from printing to completion of curing, enabling the formed grid lines to achieve the required aspect ratio and reducing the resistivity and contact resistance of the grid lines.

[0072] In some embodiments, the copper paste according to this application is subjected to a shear rate of 200 s. -1 Under the specified measurement conditions, the viscosity of the copper paste is within the range of 1 Pa·s to 25 Pa·s. Specifically, in some embodiments, the measured viscosity of the copper paste is within the range of 1 Pa·s to 15 Pa·s. During the test, the copper paste is evenly spread on the test platform, and the test temperature is controlled using a constant temperature bath to maintain the temperature of the copper paste at 25℃ ± 0.5℃. The test parameters are controlled at a shear rate of 200 s⁻¹.-1 The viscosity η of the slurry at that time was measured using a rotational rheometer.

[0073] For example, at a shear rate of 200 s -1 Under the specified measurement conditions, the viscosity of the copper paste is 1 Pa·s, or 3 Pa·s, 5 Pa·s, 7 Pa·s, 9 Pa·s, 11 Pa·s, 13 Pa·s, 15 Pa·s, 17 Pa·s, 19 Pa·s, 21 Pa·s, 23 Pa·s, 25 Pa·s, or any value between the two.

[0074] It should be understood that in order to ensure good fluidity and printability of the copper paste during printing, the viscosity value of the copper paste needs to be maintained within a relatively low range. According to the copper paste of this application, by precisely controlling the rheological properties of the paste, especially the viscosity, the printability of the copper paste can be significantly improved, thereby optimizing the screen printing process and improving the performance and yield of solar cells.

[0075] In some embodiments, the copper powder in the copper paste comprises between 80% and 95% by weight, and the solvent comprises between 2% and 8% by weight. With the solvent weight percentage within this range, the weight loss of the copper paste during heat curing is less than 8%, meaning the amount of volatiles is small. This minimizes the impact on the integrity of the bond between copper powders during the curing process, resulting in sufficient bonding strength and preventing delamination, voids, and cracks caused by excessive weight loss when the copper paste is cured into grid lines.

[0076] In some embodiments, the solvent includes a first solvent and a second solvent, wherein the boiling point of the second solvent differs from that of the first solvent by more than 60°C. During the curing process, the difference in boiling point between the second solvent and the first solvent means that the evaporation rates of the first solvent and the second solvent are different. By controlling the gradient evaporation of the first solvent and the second solvent, it is not only ensured that the binder, such as the resin, can be fully fused and bonded at a high concentration, but also that the copper powder in the copper paste achieves tight aggregation with the help of the binder.

[0077] In some embodiments, the boiling point of the first solvent is between 100°C and 200°C, and the boiling point of the second solvent is between 180°C and 300°C. According to this application, by selecting mixed solvents with different boiling points and adjusting the ratio of the first and second solvents, the combined use of low-boiling-point and high-boiling-point solvents facilitates the formation of a slurry with the aforementioned weight loss properties. This not only ensures excellent printability of the slurry at temperatures between 25°C and 35°C, but also enables low-temperature curing between 25°C and 220°C. During the curing process, by controlling the evaporation rates of the first and second solvents, the binder, such as the resin, reacts at a high concentration, resulting in a high density, high strength, and strong tensile strength of the resulting grid lines.

[0078] For example, the boiling point of the first solvent may be 100°C, or 110°C, or 120°C, or 130°C, or 140°C, or 150°C, or 160°C, or 170°C, or 180°C, or 190°C, or 200°C, or 210°C, or 220°C, or any value between any two of the above.

[0079] For example, the boiling point of the second solvent may be 180°C, or 190°C, or 200°C, or 210°C, or 220°C, or 230°C, or 240°C, or 250°C, or 260°C, or 270°C, or 280°C, or 290°C, or 300°C, or any value between any two of the above.

[0080] In this application, the first solvent may be selected from at least one of the following components: ester solvents, ether solvents, ketone solvents, and alcohol solvents. Specifically, the first solvent may include at least one of the following low-boiling-point solvents: sec-amyl acetate, cyclohexanone, amyl propionate, isopropyl lactate, pentanol, hexanol, heptanol, octanol, butyl acetate, diethyl carbonate, sec-amyl alcohol, ethylene glycol, propylene glycol, ethylene glycol monoethyl ether, methyl pentanol, ethylene glycol monomethyl ether, ethylene glycol butyl ether, ethylene glycol diethyl ether, ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, 4-heptanone, ethylene glycol monoisopropyl ether, amyl acetate, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol propyl ether, dipropylene glycol butyl ether, dipropylene glycol ether, ethylene glycol dimethyl ether, tripropylene glycol methyl ether, tripropylene glycol dimethyl ether, etc. It should be noted that the first solvent is not limited to the solvent types listed above; that is, the first solvent can also be selected from other types of low-boiling-point solvents.

[0081] Furthermore, the second solvent may be selected from at least one of the following components: ether solvents and ester solvents. Specifically, the second solvent may include at least one of the following solvents: diethylene glycol monobutyl ether, diethylene glycol acetate, diethylene glycol butyl ether acetate, ethylene glycol carbonate, propylene glycol carbonate, tributyl borate, triphenyl phosphate, tricresyl phosphate, divalent esters (DBE), etc. It should be noted that the second solvent is not limited to the solvent types listed above; that is, the second solvent may also be selected from other types of solvents that meet the boiling point requirements required by this application.

[0082] In some embodiments, the mass ratio of the first solvent to the second solvent is any value between 2:1 and 1:1, that is, the mass ratio of the first solvent to the second solvent is greater than or equal to 1:1 and less than or equal to 2:1. This configuration allows for adjustment of the composition and content of the solvent portion, altering the viscosity, volatility, thixotropy, and other properties of the copper paste. This results in higher fluidity of the paste during printing, increasing the aspect ratio of the grid lines and improving the cell's conversion efficiency, while simultaneously preventing delamination, voids, and cracks during the copper paste curing process to form the grid lines. Furthermore, it allows for control of the weight loss rate of the copper paste at different temperatures during curing, and enables the copper paste to effectively diffuse to the base of the pyramid. It should be noted that in the microstructure of a solar cell, the base region of the pyramid structure plays a crucial role in charge collection and transport. The diffusion of the copper paste to the base of the pyramid increases the contact area between the grid lines and the pyramid structure, significantly reducing the resistivity of the grid lines.

[0083] For example, the mass ratio of the first solvent to the second solvent can be 1:1, or 1.1:1, or 1.2:1, or 1.3:1, or 1.4:1, or 1.5:1, or 1.6:1, or 1.7:1, or 1.8:1, or 1.9:1, or 2:1, or any value between any two of the above.

[0084] In some embodiments, the copper powder in the copper paste includes spherical copper powder and / or flake copper powder. It should be noted that flake copper powder refers to copper powder with an aspect ratio (shortest diameter / thickness) of not less than 2 in an image observed under a scanning microscope, and the ratio of the longest diameter to the shortest diameter of the flake copper powder is any value between 1 and 5; while spherical copper powder refers to copper powder with an aspect ratio of less than 2 in an image observed under a scanning microscope.

[0085] In some embodiments, the copper powder in the copper paste includes spherical copper powder and flake copper powder, with the weight percentage of flake copper powder being 35%-60% and the weight percentage of spherical copper powder being 40%-65%. For example, the weight percentage of flake copper powder can be 35%, 40%, 45%, 50%, 55%, or 60%, or any value between any two of the above; correspondingly, the weight percentage of spherical copper powder can be 65%, 60%, 55%, 50%, 45%, or 40%, or any value between any two of the above.

[0086] In some embodiments, the median diameter of the flake-shaped copper powder is 2μm-8μm, and the median thickness is 100nm-500nm; the median particle size of the spherical copper powder is 100nm-500nm. The median diameter of the flake-shaped copper powder or the median particle size of the spherical copper powder is measured using a laser particle size analyzer or a SEM (Self-Electron Microscope), and the median thickness of the flake-shaped copper powder is measured using a SEM.

[0087] For example, the median diameter of the flake copper powder can be any value between 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, and 8μm.

[0088] For example, the median thickness of the flake copper powder can be any value between 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm, 320nm, 350nm, 380nm, 400nm, 420nm, 450nm, 480nm, and 500nm.

[0089] For example, the median particle size of spherical copper powder can be any value between 100nm, 120nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm, 320nm, 350nm, 380nm, 400nm, 420nm, 450nm, 480nm, and 500nm.

[0090] In some embodiments, the tap density of the flake copper powder is 4.4–5.2 g / ml, and the tap density of the spherical copper powder is 4.3–4.9 g / ml; the specific surface area of ​​the flake copper powder is 0.4–0.7 m². 2 / g, the specific surface area of ​​spherical copper powder is 0.5~3.0m². 2 / g.

[0091] For example, the tap density of flake copper powder can be any value between 4.4 g / ml, 4.5 g / ml, 4.6 g / ml, 4.7 g / ml, 4.8 g / ml, 4.9 g / ml, 5 g / ml, 5.1 g / ml, and 5.2 g / ml.

[0092] For example, the tap density of spherical copper powder can be any value between 4.3 g / ml, 4.4 g / ml, 4.5 g / ml, 4.6 g / ml, 4.7 g / ml, 4.8 g / ml, and 4.9 g / ml.

[0093] For example, the specific surface area of ​​flake copper powder can be 0.4 m². 2 / g, 0.45m 2 / g, 0.5m 2 / g, 0.55m 2 / g, 0.6m 2 / g, 0.65m 2 / g, 0.7m 2 Any value between / g.

[0094] For example, the specific surface area of ​​spherical copper powder can be 0.5 m². 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g、m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g, 2.0m 2 / g、2.1m 2 / g, 2.2m 2 / g, 2.3m 2 / g, 2.4m 2 / g, 2.5m 2 / g, 2.60m 2 / g, 2.70m 2 / g, 2.80m 2 / g, 2.90m 2 / g, 3.0m 2 Any value between / g.

[0095] It should be noted that tapped density, or bulk density of powder after compaction, refers to the density of powder after it has been packed into a specific container and the container has been vibrated to break down the voids in the powder, resulting in a tightly packed state. Measuring tapped density can determine the flowability and porosity of the powder. Tapped density can be calculated by measuring the volume after 1000 vibrations using a BT-301 vibrator. Specific surface area refers to the surface area per unit mass of a porous solid material, and its commonly used unit is m². 2 / g, the specific surface area can be tested by conventional methods, such as GB / T 13390-2008 Determination of Specific Surface Area of ​​Metal Powders.

[0096] In this application, the unique physicochemical properties of copper powder in different forms are fully considered. By combining flake copper powder and spherical copper powder in terms of shape and / or quality, copper particles of various sizes and shapes are densely packed, making the conductive channels between conductive particles smoother.

[0097] In some embodiments, the copper paste also includes a resin, a curing agent, and an optional curing accelerator.

[0098] Optionally, the resin is selected from at least one of epoxy resin, phenolic resin, acrylic resin, and polyester resin. Further, the epoxy resin is a thermosetting resin selected from at least one of bisphenol A type epoxy resin, bisphenol F epoxy resin, hydrogenated bisphenol A type epoxy resin, polyurethane modified epoxy resin, dimer acid modified epoxy resin, siloxane modified epoxy resin, phenolic epoxy resin, polyol glycidyl ether type epoxy resin, and polyacid glycidyl ester type epoxy resin.

[0099] Optionally, the curing agent may be selected from at least one of dicyandiamide curing agents, tertiary amine curing agents, isocyanates, imidazole curing agents, acid anhydride curing agents, and latent imidazole curing agents. For example, it may be selected from at least one of blocked isocyanates, phenyl imidazoles, maleic anhydride, hexahydromethylphthalic anhydride, disubstituted urea, MF-K60X (blocked polyisocyanate HDI curing agent), ketoxime-terminated isocyanates, hexamethylene diisocyanate-terminated hexamethylene diisocyanate-terminated and dodecyl mercaptan-terminated diphenyl diisocyanate-terminated.

[0100] Curing accelerators can catalyze the curing of resins, lower the curing temperature, and shorten the curing time. The copper paste of this application may or may not contain a curing accelerator. The curing accelerator can be selected from quaternary ammonium salts, imidazole esters, imidazole onium salts, and substituted ureas. Specifically, quaternary ammonium salts can be benzyltriethylammonium chloride, etc., and substituted ureas can be N-p-chlorophenyl-N,N'-dimethylurea, N-(3,4-dichlorophenyl)-N,N'-dimethylurea, N-(3-phenyl)-N,N'-dimethylurea, N-(4-phenyl)-N,N'-dimethylurea, 2-methylimidazolium urea, etc.; imidazoles and their derivatives... Esters or imidazodium salts can be alkylimidazoles, imidazosulfonates / salts, imidazophosphates / salts, or imidazoacetic acid esters / salts, such as dibutyl imidazophosphate, 1-ethyl-3-methylimidazolate, 1-ethyl-3-methylimidazodium methanesulfonate, trimellitate 1-cyanoethyl-2-undecapidazodium, isocyanurate 2-methylimidazodium, tetraphenylboronic acid 2-ethyl-4-methylimidazodium, and tetraphenylboronic acid 2-ethyl-1,4-dimethylimidazodium.

[0101] In some embodiments, the copper paste contains 80% to 95% copper powder by weight, 2% to 8% solvent by weight, 1% to 15% resin by weight, and 1% to 5% curing agent by weight.

[0102] Optionally, in some embodiments, the copper paste may also include other additives, such as thixotropic agents.

[0103] This application also provides a method for preparing the aforementioned copper paste for solar cells, the method comprising the steps of:

[0104] Copper powder is provided;

[0105] Copper powder, solvent, resin, curing agent and optional curing accelerator are uniformly mixed and ground to make the copper paste meet one or more of the aforementioned conditions.

[0106] The method for preparing copper paste in this application is simple and easy to implement. By controlling the weight loss rate of the paste, grid lines with high crosslinking density, high strength, and high tensile strength can be obtained.

[0107] This application also provides an electrode for a solar cell, which is prepared from the aforementioned copper paste used in solar cells.

[0108] This application also provides a method for preparing the aforementioned electrode of a solar cell, the method using the aforementioned copper paste for solar cells, wherein the method includes the following steps: printing a pre-prepared copper paste onto a solar cell; heating the solar cell with the printed copper paste to solidify the copper paste.

[0109] In some embodiments, printing is performed at a temperature ranging from 25°C to 35°C. For example, a pre-prepared copper paste is screen-printed onto the solar cell at the aforementioned temperature. The copper paste is then cured by holding it at a temperature ranging from 100°C to 250°C for a curing period, wherein the curing period is between 10 minutes and 120 minutes. For example, the curing temperature can be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C, or any value between any two of the above. The curing time can be any value between 10 min and 120 min, for example, it can be 10 min, or 20 min, or 30 min, or 40 min, or 50 min, or 60 min, or 70 min, or 80 min, or 90 min, or 100 min, or 110 min, or 120 min, or any value between any two of the above.

[0110] This application also provides a solar cell comprising the electrodes of the aforementioned solar cell, wherein the surface of the solar cell has a textured structure, and the electrodes of the solar cell are located on the upper part of the textured structure of the solar cell.

[0111] Optionally, the solar cell is selected from any of BC cells, HJT cells, and perovskite / crystalline silicon tandem cells. In some embodiments, the solar cell is a crystalline silicon cell, and a conductive barrier layer exists between the electrodes of the solar cell and the crystalline silicon cell.

[0112] It should be noted that the preparation methods of copper paste, the electrodes of solar cells and their preparation methods, and the copper paste of solar cells have the same or similar beneficial effects, and the relevant parts between the two can be referred to each other. To avoid repetition, they will not be elaborated here.

[0113] The present application will be further explained below with reference to specific embodiments.

[0114] Example 1

[0115] The following materials are provided: 34 parts by weight of flake copper powder (median diameter 5 μm, median thickness 200 nm) and 51 parts by weight of spherical copper powder (median particle size 200 nm), 7 parts by weight of hydrogenated bisphenol A type epoxy resin as resin, 1 part by weight of heptadecanidazole and 1.5 parts by weight of blocked isocyanate as curing agent, and 5.5 parts by weight of 4-heptanone and diethylene glycol acetate (mass ratio 1.5:1) as solvent. After the above materials are prepared in the specified proportions, they are ground into copper paste by a three-roll mill.

[0116] Example 2

[0117] The following materials are provided: 38 parts by weight of flake copper powder (median diameter 5 μm, median thickness 200 nm) and 57 parts by weight of spherical copper powder (median particle size 200 nm), 1 part by weight of hydrogenated bisphenol A type epoxy resin as resin, 0.5 parts by weight of heptadecanidazole and 0.5 parts by weight of blocked isocyanate as curing agent, and 3 parts by weight of pentanol and diethylene glycol monobutyl ether (mass ratio 2:1) as solvent. After the above materials are prepared in the specified proportions, they are ground into copper paste by a three-roll mill.

[0118] Example 3

[0119] The following materials are provided: 38 parts by weight of flake copper powder (median diameter 5 μm, median thickness 200 nm) and 57 parts by weight of spherical copper powder (median particle size 200 nm), 1 part by weight of hydrogenated bisphenol A type epoxy resin as resin, 0.5 parts by weight of heptadecanidazole and 0.5 parts by weight of blocked isocyanate as curing agent, and 3 parts by weight of 4-heptanone and diethylene glycol acetate (mass ratio 2:1) as solvent. After the above materials are prepared in the specified proportions, they are ground into copper paste by a three-roll mill.

[0120] Example 4

[0121] The following materials are provided: 38 parts by weight of flake copper powder (median diameter 5 μm, median thickness 200 nm) and 57 parts by weight of spherical copper powder (median particle size 200 nm), 1 part by weight of hydrogenated bisphenol A type epoxy resin as resin, 0.5 parts by weight of heptadecanidazole and 0.5 parts by weight of blocked isocyanate as curing agent, and 3 parts by weight of ethylene glycol diethyl ether and triphenyl phosphate (mass ratio 2:1) as solvent. After the above materials are prepared in the specified proportions, they are ground into copper paste by a three-roll mill.

[0122] Example 5

[0123] The following materials are provided: 34 parts by weight of flake copper powder (median diameter 5 μm, median thickness 200 nm) and 51 parts by weight of spherical copper powder (median particle size 200 nm), 7 parts by weight of hydrogenated bisphenol A type epoxy resin as resin, 1 part by weight of heptadecanidazole and 1.5 parts by weight of blocked isocyanate as curing agent, and 5.5 parts by weight of pentanol and diethylene glycol monobutyl ether (mass ratio 1.5:1) as solvent. After the above materials are prepared in the specified proportions, they are ground into copper paste by a three-roll mill.

[0124] Example 6

[0125] The following materials are provided: 34 parts by weight of flake copper powder (median diameter 5 μm, median thickness 200 nm) and 51 parts by weight of spherical copper powder (median particle size 200 nm), 7 parts by weight of hydrogenated bisphenol A type epoxy resin as resin, 1 part by weight of heptadecanidazole and 1.5 parts by weight of blocked isocyanate as curing agent, and 5.5 parts by weight of ethylene glycol diethyl ether and triphenyl phosphate (mass ratio 1.5:1) as solvent. After the above materials are prepared in the specified proportions, they are ground into copper paste by a three-roll mill.

[0126] Example 7

[0127] The following materials are provided: 32 parts by weight of flake copper powder (median diameter 5 μm, median thickness 200 nm) and 48 parts by weight of spherical copper powder (median particle size 200 nm), 8 parts by weight of hydrogenated bisphenol A type epoxy resin as resin, 2 parts by weight of heptadecanidazole and 3 parts by weight of blocked isocyanate as curing agent, and 7 parts by weight of pentanol and diethylene glycol monobutyl ether (mass ratio 1:1) as solvent; after the above materials are prepared in proportion, they are ground into copper paste by a three-roll mill.

[0128] Example 8

[0129] The following materials are provided: 32 parts by weight of flake copper powder (median diameter 5 μm, median thickness 200 nm) and 48 parts by weight of spherical copper powder (median particle size 200 nm), 8 parts by weight of hydrogenated bisphenol A type epoxy resin as resin, 2 parts by weight of heptadecanidazole as curing accelerator, 3 parts by weight of blocked isocyanate as curing agent, and 7 parts by weight of 4-heptanone and diethylene glycol acetate (mass ratio 1:1) as solvent; after the above materials are prepared in proportion, they are ground into copper paste by a three-roll mill.

[0130] Example 9

[0131] The following materials are provided: 32 parts by weight of flake copper powder (median diameter 5 μm, median thickness 200 nm) and 48 parts by weight of spherical copper powder (median particle size 200 nm), 8 parts by weight of hydrogenated bisphenol A type epoxy resin as resin, 2 parts by weight of heptadecanidazole and 3 parts by weight of blocked isocyanate as curing agent, and 7 parts by weight of ethylene glycol diethyl ether and triphenyl phosphate (mass ratio 1:1) as solvent. After the above materials are prepared in the specified proportions, they are ground into copper paste by a three-roll mill.

[0132] Comparative Example 1

[0133] The following materials are provided: 34 parts by weight of flake copper powder (median diameter 5 μm, median thickness 200 nm) and 51 parts by weight of spherical copper powder (median particle size 200 nm), 7 parts by weight of hydrogenated bisphenol A type epoxy resin as resin, 1 part by weight of heptadecanidazole and 1.5 parts by weight of blocked isocyanate as curing agent, and 5.5 parts by weight of pentanol as solvent; after the above materials are prepared in proportion, they are ground into copper paste by a three-roll mill.

[0134] Comparative Example 2

[0135] The following materials are provided: 34 parts by weight of flake copper powder (median diameter 5 μm, median thickness 200 nm) and 51 parts by weight of spherical copper powder (median particle size 200 nm), 7 parts by weight of hydrogenated bisphenol A type epoxy resin as resin, 1 part by weight of heptadecanidazole and 1.5 parts by weight of blocked isocyanate as curing agent, and 5.5 parts by weight of diethylene glycol monobutyl ether as solvent; after the above materials are prepared in proportion, they are ground into copper paste by a three-roll mill.

[0136] The component contents of the copper pastes according to the embodiments and comparative examples of this application are shown in Table 1.

[0137] Table 1

[0138] Figure 1 shows the weight loss rate curves of the copper paste according to Embodiment 1 of this application at different temperatures. As shown in Figure 1, when the copper paste according to this application is heated from 25°C to 30°C at a rate of 10°C / min under a nitrogen atmosphere and held at 30°C for 60 min, the measured weight loss rate of the copper paste is less than 0.01%. This test result significantly demonstrates that the components in the copper paste remain stable within the printing ambient temperature range of 25°C to 35°C, without significant volatilization or decomposition. This excellent stability means that the physical and chemical properties of the paste do not change significantly during the printing process, thus ensuring the continuity and consistency of the printing process. Specifically, due to the stability of the paste, its viscosity remains constant during the printing process, which is crucial for maintaining printing quality. Furthermore, since the electrical properties of the paste are unaffected within this temperature range, this further ensures the conductivity and performance stability of the printed electrodes, which is essential for the normal operation and long-term reliability of solar cells. This demonstrates the excellent stability of the copper paste within a temperature range of 25℃ to 35℃, with no significant volatilization or decomposition. This ensures both constant viscosity and electrical properties during printing, and guarantees consistency and superior performance in multi-sheet printing. As temperature increases, the weight loss rate gradually increases, with a significant increase above 200℃. The weight loss rate curves of the copper paste in this application at different temperatures are described in more detail below with reference to Figures 2 to 8.

[0139] Figure 2 shows the TG-DSC curves of the copper paste according to Example 1 of this application at 25°C-100°C. During this test, the copper paste was heated from 25°C to 100°C at a rate of 10°C / min under a nitrogen atmosphere and held at 100°C for 30 minutes. The copper paste solidified, and the measured weight loss rate was 1%, meaning the weight of the copper paste decreased to 99% of its original weight, representing 18.2% of the total solvent weight. Furthermore, while the TG curve showed weight loss characteristics, the DSC curve showed endothermic characteristics. During the heating process from 25°C to 100°C, the volatile components in the copper paste gradually evaporated and detached from the paste due to endothermic absorption, resulting in both the weight loss characteristics of the TG curve and the endothermic characteristics of the DSC curve.

[0140] Figure 3 shows the TG-DSC curves of the copper paste according to Example 1 of this application at 25°C-130°C. In this application, when the copper paste according to this application is heated from 25°C to 130°C at a rate of 10°C / min under a nitrogen atmosphere and held at 130°C for 30 min, the copper paste begins to solidify. The measured weight loss rate of the copper paste is 1.6%, and the weight lost accounts for 29% of the total weight of the solvent. In addition, while the TG curve shows weight loss characteristics, the DSC curve shows endothermic characteristics. During the heating process from 25°C to 130°C, the volatile components in the copper paste gradually volatilize and detach from the paste due to endothermic reaction. Under the test conditions of 130°C, the weight loss rate shown on the TG curve and the heat flow rate shown on the DSC curve are significantly higher than those under the test conditions of 100°C.

[0141] Figure 4 shows the TG-DSC curves of the copper paste according to Example 1 of this application at 25°C-160°C. In this application, the copper paste according to this application was heated from 25°C to 160°C at a rate of 10°C / min under a nitrogen atmosphere and held at 160°C for 30 min. The copper paste solidified, and the measured weight loss rate was 2.4%, representing 43.6% of the total solvent weight. Furthermore, while the TG curve showed weight loss characteristics, the DSC curve showed endothermic characteristics. During the heating process from 25°C to 160°C, the volatile components in the copper paste gradually volatilized and detached from the paste due to endothermic absorption. Under the test condition of 160°C, the weight loss rate shown in the TG curve and the heat flow rate shown in the DSC curve significantly increased further.

[0142] Figure 5 shows the TG-DSC curves of the copper paste according to Example 1 of this application at 25°C-190°C. In this application, when the copper paste according to this application was heated from 25°C to 190°C at a rate of 10°C / min under a nitrogen atmosphere and held at 190°C for 30 min, the copper paste solidified. The measured weight loss rate of the copper paste was 5.1%, and the weight lost accounted for 92.7% of the total weight of the solvent. In addition, while the TG curve showed weight loss characteristics, the DSC curve showed endothermic characteristics. During the heating process from 25°C to 190°C, the volatile components in the copper paste gradually volatilized and detached from the paste due to endothermic reaction. Under the test conditions of 190°C, the weight loss rate shown on the TG curve and the heat flow rate shown on the DSC curve were significantly increased further.

[0143] Figure 6 shows the TG-DSC curves of the copper paste according to Example 1 of this application at 25°C-200°C. In this application, when the copper paste according to this application is heated from 25°C to 200°C at a rate of 10°C / min under a nitrogen atmosphere and held at 200°C for 30 min, the TG-DSC curve shows an endothermic heat flow peak, indicating that the copper paste has solidified. The measured weight loss rate of the copper paste is 5.5%, which represents 100% of the solvent weight. Furthermore, while the TG curve shows weight loss characteristics, the DSC curve shows endothermic characteristics. During the heating process from 25°C to 200°C, the volatile components in the copper paste gradually volatilize and detach from the paste due to endothermic absorption. Under the test condition of 200°C, the weight loss rate shown on the TG curve and the heat flow rate shown on the DSC curve are significantly increased further.

[0144] Figure 7 shows the TG-DSC curves of a copper paste according to an embodiment of this application from 25°C to 400°C. In this application, when the copper paste according to this application is heated from 25°C to 400°C at a rate of 10°C / min under a nitrogen atmosphere and held at 400°C for 60 min, the copper paste solidifies. The measured weight loss rate of the copper paste is 9%, mainly due to the carbonization and decomposition of the resin at high temperature, resulting in a rapid change in the mass of the copper paste. Furthermore, while the TG curve shows weight loss characteristics, the DSC curve generally shows endothermic characteristics because during the heating process from 25°C to 400°C, the volatile components in the copper paste gradually volatilize and detach from the paste due to endothermic absorption. Simultaneously, as shown in Figure 8, due to the cross-linking and curing reaction of the resin, a weak upward exothermic peak exists in the DSC curve between 170°C and 210°C.

[0145] Test Implementation Examples

[0146] Resistivity testing method: The copper paste is screen printed using a screen printing plate and then heated and cured in a nitrogen oven at 200℃ for 20 minutes to form a copper film. The sheet resistance R (mΩ) is measured using a four-probe sheet resistance meter, and the film thickness t (μm) is measured using a micrometer. The resistivity ρ = R × t / 10.

[0147] Contact resistivity method: The contact resistivity between the grid lines and the solar cells is tested using a TLM contact resistance tester commonly used in this field.

[0148] Tensile testing method: The paste is printed onto the solar cell, with 9 ribbons printed and 1 mm wide. It is then cured in a nitrogen oven at 200℃ for 20 minutes. One end of the solder ribbon is welded to the main grid surface, and the other end is fixed to a tensile testing machine. When the solder ribbon or grid line peels off, the breaking tensile force is recorded in N / cm². 2 .

[0149] Viscosity testing method: The copper paste is evenly spread on the test platform. The test temperature is controlled by a constant temperature bath, maintaining the temperature of the copper paste at 25℃±0.5℃. The test parameters are controlled at a shear rate of 200s. -1 The viscosity η of the slurry at that time was measured using a rotational rheometer.

[0150] The test results of the copper pastes according to the embodiments and comparative examples of this application are shown in Table 2.

[0151] Table 2

[0152] As shown in Table 2 above, the copper paste of this application exhibits excellent printability at temperatures between 25°C and 35°C because the weight loss ratio relative to the total solvent weight can be controlled at different temperatures. This balances the processes of volatile component evaporation, resin fusion, and copper powder aggregation, enhancing the tightness of the connection between copper powder particles and the bonding strength between the copper powder and the substrate. Consequently, the paste can achieve low-temperature curing between 100°C and 220°C, resulting in grid lines with low resistivity, low contact resistance, and high tensile strength. Since the weight loss rate of the copper paste during low-temperature curing is within 5.5%, the integrity of the copper powder connections is minimally affected during curing, resulting in lower resistivity.

[0153] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "one example," "some embodiments," or "preferred embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0154] The embodiments of this application have been described in detail above. However, aspects of this application are not limited to the embodiments described above. Various modifications and substitutions can be applied to the above embodiments without departing from the scope of this application.

Claims

1. A copper paste for use in solar cells, wherein, The copper paste comprises copper powder and a solvent, wherein the weight loss percentage of the copper paste measured when heated at a rate of 10°C / min under a nitrogen atmosphere satisfies at least one of the following conditions: The weight loss when heated from 25℃ to 150℃-170℃ accounts for 35%-55% of the total weight of the solvent; The weight loss when heated from 25°C to 120°C-140°C accounts for 20%-40% of the total solvent weight; or, The weight loss when heated from 25°C to 80°C-110°C accounts for 10-25% of the total weight of the solvent.

2. The copper paste for solar cells according to claim 1, wherein, The weight loss percentage of the copper paste measured when heated at a rate of 10°C / min under a nitrogen atmosphere meets the following condition: the weight loss when heated from 25°C to 190°C-220°C accounts for 85%-100% of the total weight of the solvent.

3. The copper paste for solar cells according to claim 1, wherein, The weight loss of the copper paste is less than 0.01% when heated from 25°C to 30°C at a rate of 10°C / min under a nitrogen atmosphere.

4. The copper paste for solar cells according to any one of claims 1-3, wherein, The weight loss rate of the copper paste measured when heated at a rate of 10°C / min under a nitrogen atmosphere satisfies at least one of the following conditions: The weight loss rate when heated from 25°C to 80°C-110°C is 5% to 20% of the weight loss rate when heated from 25°C to 400°C. The weight loss rate when heated from 25°C to 120°C-140°C is 10% to 25% of the weight loss rate when heated from 25°C to 400°C. The weight loss rate when heated from 25°C to 150°C-170°C is 20% to 40% of the weight loss rate when heated from 25°C to 400°C. The weight loss rate when heated from 25°C to 190°C-220°C is 55% to 75% of the weight loss rate when heated from 25°C to 400°C; or, The weight loss rate when heated from 25°C to 80°C-110°C is 10% to 30% of the weight loss rate when heated from 25°C to 190°C-220°C.

5. The copper paste for solar cells according to any one of claims 1-4, wherein, In the TG-DSC curve of the copper paste heated from 25°C to 400°C, an endothermic peak is observed between 170°C and 210°C.

6. The copper paste for solar cells according to any one of claims 1-4, wherein, At a shear rate of 200 s -1 Under the specified measurement conditions, the viscosity of the copper paste is between 1 Pa·s and 25 Pa·s.

7. The copper paste for solar cells according to any one of claims 1-4, wherein, In the copper paste, the weight percentage of copper powder is between 80% and 95%, and the weight percentage of solvent is between 2% and 8%.

8. The copper paste for solar cells according to claim 7, wherein, The solvent includes a first solvent and a second solvent, wherein the boiling point of the second solvent differs from that of the first solvent by more than 60°C.

9. The copper paste for solar cells according to claim 8, wherein, The boiling point of the first solvent is between 100°C and 200°C, and the boiling point of the second solvent is between 180°C and 300°C.

10. The copper paste for solar cells according to claim 8, wherein, The first solvent is selected from at least one of the following components: ester solvents, ether solvents, ketone solvents, and alcohol solvents; the second solvent is selected from at least one of the following components: ether solvents and ester solvents.

11. The copper paste for solar cells according to claim 8, wherein, The mass ratio of the first solvent to the second solvent is any value between 2:1 and 1:

1.

12. The copper paste for solar cells according to any one of claims 1-4, wherein, The copper powder includes spherical copper powder and / or flake copper powder.

13. The copper paste for solar cells according to any one of claims 1-12, wherein, The copper paste also includes resin, curing agent, and optional curing accelerator.

14. A method for preparing a copper paste for solar cells according to any one of claims 1-13, wherein, The method includes the following steps: Copper powder is provided; as well as The copper powder, solvent, resin, curing agent, and optional curing accelerator are uniformly mixed and then ground.

15. An electrode for a solar cell, wherein, The electrodes of the solar cell are prepared from the copper paste for solar cells according to any one of claims 1-13.

16. A method for fabricating electrodes for a solar cell, wherein, The method uses the copper paste for solar cells according to any one of claims 1-13, wherein the method comprises the following steps: The pre-prepared copper paste is printed onto the battery cell; and The battery cell printed with the copper paste is heated to solidify the copper paste.

17. The method according to claim 16, wherein, The method further includes the following steps: The printing is performed at a temperature ranging from 25°C to 35°C; and The copper paste is cured by holding it at a temperature in the range of 100°C to 250°C for a curing period of time, wherein the curing period is in the range of 10 min to 120 min.

18. A solar cell comprising the electrodes of the solar cell of claim 15.

19. The solar cell according to claim 18, wherein the solar cell is selected from any one of BC cells, HJT cells, and perovskite / crystalline silicon tandem cells.

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