Copper grid line and use

Abstract

Provided in the present application are a copper grid line and the use. The copper grid line comprises a grid line body portion and a grid line peripheral portion, wherein the grid line peripheral portion is located on both sides of the grid line body portion, and the width of the grid line peripheral portion on either side does not exceed 15%-50% of the width of the grid line body portion; the median particle size of a copper powder in the grid line peripheral portion is less than the median particle size of a copper powder in the grid line body portion. Since a dense structure can be formed at the grid line peripheral portion, the contact area between the copper grid line and the surface of a cell is increased, and the adhesion of the copper grid line is improved, such that moisture and oxygen are prevented from penetrating through the interface between the copper grid line and the underlying cell to oxidize the copper powder in the body portion of the copper grid line, thereby reducing the bulk resistivity of the grid line and the contact resistance between the grid line and the cell.

Description

Copper grid lines and uses

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 2024112442872, filed on September 5, 2024, entitled “Copper grid lines and uses” and Chinese Patent Application No. 2024112458279, filed on September 5, 2024, entitled “An electrode and its preparation method and application”, the contents of which are incorporated herein by reference in their entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of solar cells, in particular to a copper grid line and uses. BACKGROUND

[0004] Silver is used in large quantities in solar cells. Silver is a precious metal, and its proven reserves are small, so finding a substitute for silver has great strategic significance.

[0005] Among all the metals currently available, copper is the most promising substitute metal. Copper has basically comparable electrical conductivity to silver, but its price is only one hundredth of silver. The biggest disadvantage of copper compared to silver is its high activity, which can easily oxidize or corrode, resulting in a decrease in its electrical conductivity, especially at the micro-nano scale. Therefore, it is of great significance to develop copper grid lines with high electrical conductivity. SUMMARY

[0006] Based on the technical problems existing in the related art, the present application provides a copper grid line and uses, which is prepared by using copper paste, so that the copper paste can diffuse onto the main grid line, increase the contact area, and reduce the contact resistivity.

[0007] The specific technical solutions of the present application are as follows:

[0008] The present application provides a copper grid line, which comprises a grid line main body part and a grid line peripheral part, the grid line peripheral part is located on both sides of the grid line main body part, wherein the width of any one side of the grid line peripheral part is not more than 15-50% of the width of the grid line main body part; the median value of the particle size of the copper powder of the grid line peripheral part is smaller than the median value of the particle size of the copper powder of the grid line main body part.

[0009] Further, the width of the copper grid line main body part is 30-120 microns.

[0010] Further, the width of the copper grid line peripheral part is 10-60 microns, and / or the height of the copper grid line peripheral part is 0.05-2.5 microns.

[0011] Further, the height of the copper grid line main body part is 10-25 microns.

[0012] Further, the copper grid line comprises nanoscale spherical copper powder and micrometer scale flaky copper powder, the median value of particle size of the spherical copper powder is 100-700 nm, the median value of diameter of the flaky copper powder is 2-8 μm, and the median value of thickness of the flaky copper powder is 100 nm-500 nm.

[0013] Further, the mass percentage of the micrometer scale flaky copper powder in the copper powder is 40-70%, and the mass percentage of the nanoscale spherical copper powder in the copper powder is 30-60%.

[0014] Further, the copper grid line comprises nanoscale spherical copper powder and micrometer scale flaky copper powder, and the peripheral portion of the grid line comprises only nanoscale spherical copper powder.

[0015] Further, the copper grid line is prepared by screen printing.

[0016] Further, the copper grid line comprises nanoscale spherical copper powder and micrometer scale flaky copper powder, and the surface of the flaky copper powder is attached to the surface of the copper grid line in a substantially horizontal state.

[0017] Further, the flaky copper powder is arranged in a direction with an angle α with the surface of the copper grid line, 0°≤α≤45°.

[0018] Further, the area of the flaky copper powder attached to the surface of the copper grid line in the orthographic projection of the surface of the copper grid line accounts for 30%-70% of the surface area of the copper grid line.

[0019] The application also provides a solar cell comprising the aforementioned copper grid line.

[0020] Further, the surface of the solar cell has a textured structure, and the copper grid line is located on the upper portion of the textured structure of the solar cell.

[0021] Further, the height of the peripheral portion of the copper grid line is 0.05-2.5 μm.

[0022] The copper grid line described in the application is provided with a peripheral portion with a certain width on both sides of the main body portion of the grid line, and the median value of particle size of the copper powder in the peripheral portion is smaller than the median value of particle size of the copper powder in the main body portion of the grid line, so that a dense structure can be formed in the peripheral portion of the grid line, the contact area between the copper grid line and the surface of the cell is increased, the adhesion of the copper grid line is improved, water and oxygen are prevented from penetrating from the interface between the copper grid line and the bottom cell and oxidizing the copper powder in the main body portion of the grid line, so that the volume resistivity of the grid line and the contact resistance between the grid line and the cell are reduced. Meanwhile, the width of the peripheral portion on either side of the grid line is not more than 15%-50% of the width of the main body portion of the grid line, so that the copper grid line has a relatively low volume resistivity and contact resistance, and the copper grid line has a relatively small shading rate for light.

[0023] The copper grid line described in the present application has a resistivity of less than 25 μΩ·cm, a contact resistivity of no more than 1 mΩcm2, and an efficiency comparable to that of silver paste. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a schematic diagram of the copper grid line of the present application.

[0025] Figure 2 is a schematic diagram of the peripheral portion of the copper grid line of the present application.

[0026] Figure 3 is a schematic diagram of the surface of the copper grid line of the present application.

[0027] Figure 4 is a scanning electron microscope image of spherical copper powder placed in air.

[0028] Figure 5 is a scanning electron microscope image of flaky copper powder placed in air.

[0029] Figure 6 is a scanning electron microscope image of a portion of the surface of the copper grid line of the present application. DETAILED DESCRIPTION

[0030] The present application will be described in detail below with reference to the embodiments described. Although specific embodiments of the present application are shown, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present application can be more thoroughly understood and so that the scope of the present application can be conveyed to those skilled in the art.

[0031] It should be noted that certain terms are used throughout the specification and claims which refer to particular components. As one skilled in the art will appreciate, the terms used can be substituted with other terms that have the same meaning. Without limitation, the detailed description herein has not been limited to division based on terminology that can vary from one implementation to another implementation. As used throughout the specification and claims, "comprising" or "including" is to be construed as meaning "including but not limited to." The subsequent description is provided as a preferred embodiment of the present application, but is intended to be illustrative of the general principles of the present application and is not intended to limit the scope of the present application. The scope of the present application is defined by the appended claims.

[0032] The present application provides a copper grid line, comprising a grid line main portion and a grid line peripheral portion, the grid line peripheral portion being located on both sides of the grid line main portion, wherein the width of any one of the grid line peripheral portions is no more than 15%-50% of the width of the grid line main portion; the median value of the particle size of the copper powder of the grid line peripheral portion is less than the median value of the particle size of the copper powder of the grid line main portion.

[0033] In the present application, the determination method of the width of the main body portion of the gate line is not limited in the present application, and the skilled in the art can make a routine selection based on the actual needs, for example, the width of the main body portion of the gate line can be measured by SEM, for example, the width of the copper gate line at the bottom of a certain area in the SEM measurement field is measured, and the average value is calculated by continuously measuring 10 areas, so as to obtain the width of the main body portion of the gate line.

[0034] In the present application, the main body portion of the gate line has a significant difference in the height covered by the copper powder in the area where the peripheral portion of the gate line is located, and there is a significant difference in the particle size of the copper powder in the peripheral portion of the gate line, wherein the area with high copper powder coverage and large copper powder particle size is the main body portion of the gate line, and the portion extending to both sides with the main body portion of the gate line as the boundary is the peripheral portion of the gate line.

[0035] In the present application, the determination method of the width of the peripheral portion of the gate line is not limited in the present application, and the skilled in the art can determine it by the routine method in the art, for example, the width of the peripheral portion of the gate line can be measured by SEM; for example, because the height covered by the copper powder in the area where the main body portion and the peripheral portion of the gate line are located has a significant difference, and the particle size of the copper powder in the two areas has a significant difference, the boundary between the main body portion and the peripheral portion of the copper gate line can be found by SEM, and the boundary is used as the starting line of the peripheral portion of the gate line, the center of the area with a copper powder projection area ratio of 30%-40% per square centimeter is used as the end point of the measurement, and the vertical distance between the starting point and the end point relative to the straight line where the gate line is located is defined as the width of the peripheral portion of the gate line, and 10 measurement positions are randomly selected for measurement on a test sample of a gate line. For example, the width of the peripheral portion of the gate line on either side does not exceed 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc. of the width of the main body portion of the gate line.

[0036] FIG. 1 is a copper gate line in the specific embodiment of the present application, wherein 1 is the main body portion of the gate line, 2 is the peripheral portion of the gate line, and 3 is the portion of the gate line that is not diffused, wherein the width of the peripheral portion of the gate line on either side does not exceed 15%-50% of the width of the main body portion of the gate line.

[0037] FIG. 2 is an electron microscope image of the peripheral portion of the copper gate line, and the block diagram in FIG. 2 shows the schematic diagram of the diffusion of the copper powder in the copper paste into the pyramid suede structure, as can be seen from FIG. 2, the copper powder in the copper paste diffuses into the pyramid suede structure to form a dense structure.

[0038] In some embodiments, the width of the copper grid line body portion is 30-120 microns. In some embodiments, the width of the copper grid line peripheral portion is 10-60 microns. For example, the width of the copper grid line body portion can be 30 microns, 35 microns, 40 microns, 45 microns, 50 microns, 55 microns, 60 microns, 65 microns, 70 microns, 75 microns, 80 microns, 85 microns, 90 microns, 95 microns, 100 microns, 105 microns, 110 microns, 115 microns, 120 microns, etc.

[0039] For example, the width of the copper grid line peripheral portion can be 10 microns, 15 microns, 20 microns, 25 microns, 30 microns, 35 microns, 40 microns, 45 microns, 50 microns, 55 microns, 60 microns, etc.

[0040] In some embodiments, the height of the copper grid line body portion is 10-25 microns. In some embodiments, the height of the copper grid line peripheral portion is 0.05-2.5 microns.

[0041] In the present application, for the height of the copper grid line body portion, it refers to the vertical height at the center point of the bottom edge of the cross section of the copper grid line, which is measured by SEM (scanning electron microscope), and the vertical height at the center point of the bottom edge of the cross section of the grid line at any 20 positions in the test sample is measured, and then the average value is obtained, which is the height of the copper grid line body portion. Those skilled in the art can also understand that the above method is only exemplary, and those skilled in the art can appropriately reduce or increase the number of selected measurement positions of the copper grid line based on the actual situation.

[0042] For the measurement of the height of the grid line peripheral portion, the present application does not make any limitation, and those skilled in the art can determine it by the conventional method in the art, which is measured by SEM (scanning electron microscope), for example, after the test area of the grid line peripheral portion is determined according to the foregoing method, the thickness of the grid line peripheral portion at any 10 positions in the test area is measured, i.e. the height of the grid line peripheral portion. Those skilled in the art can also understand that the above method is only exemplary, and those skilled in the art can appropriately reduce or increase the number of selected measurement positions of the copper grid line based on the actual situation.

[0043] For example, the height of the copper grid line body portion can be 10 microns, 11 microns, 12 microns, 13 microns, 14 microns, 15 microns, 16 microns, 17 microns, 18 microns, 19 microns, 20 microns, 21 microns, 22 microns, 23 microns, 24 microns, 25 microns, etc.

[0044] For example, the height of the copper grid line peripheral portion can be 0.05 microns, 0.1 microns, 0.3 microns, 0.5 microns, 0.7 microns, 0.9 microns, 1 micron, 1.2 microns, 1.4 microns, 1.6 microns, 1.8 microns, 2.0 microns, 2.2 microns, 2.5 microns.

[0045] The application sets the height of the main portion of the copper grid line, the width of the peripheral portion, and the width of the main portion within the above three numerical ranges, so that the obtained copper grid line can have firm contact with the solar cell, reduce the resistivity and improve the current collection efficiency, have a small light blocking rate, and reduce the use cost of the copper grid line.

[0046] In some embodiments, the copper grid line contains micron-level flaky copper powder and nanometer-level spherical copper powder, the median value of the particle size of the spherical copper powder is 100-700 nm, the median value of the diameter of the flaky copper powder is 2-8 microns, and the median value of the thickness of the flaky copper powder is 100-500 nm.

[0047] For example, the median value of the particle size of the spherical copper powder can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, etc.

[0048] The median value of the diameter of the flaky copper powder can be 2 microns, 3 microns, 4 microns, 5 microns, 6 microns, 7 microns, 8 microns, etc.

[0049] The median value of the thickness of the flaky copper powder can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, etc.

[0050] In this article, the median value refers to the particle size corresponding to the cumulative volume percentage of 50% of a sample. Its physical meaning is that the particles with a particle size greater than it account for 50%, and the particles with a particle size less than it also account for 50%.

[0051] In the present application, the method for determining the median value of the particle size of copper powder is not limited, and the method in the art can be used for determination, for example, the median value can be measured by SEM (scanning electron microscope); for example, 10 different areas in the test sample are photographed, then the size of 10 flaky copper powders observed in each photo is measured along the horizontal plane, and then the median value is calculated, which is the median value of the diameter, and the size is measured along the vertical plane, and then the median value is calculated, which is the median value of the thickness. For 10 spherical copper powders observed in each photo, the diameter is measured, and the median value is calculated, which is the median value of the particle size of the spherical copper powder. Both the flaky copper powder and the spherical copper powder are measured by this method.

[0052] In some embodiments, the micrometer flaky copper powder accounts for 40-70% by mass percentage in the copper powder, and the nanometer spherical copper powder accounts for 30-60% by mass percentage in the copper powder.

[0053] For example, the micrometer flaky copper powder can account for 40%, 45%, 50%, 55%, 60%, 65%, 70% or the like by mass percentage in the copper powder; and the nanometer spherical copper powder accounts for 30%, 35%, 40%, 45%, 50%, 55%, 60% or the like by mass percentage in the copper powder.

[0054] In the present application, the particle size of the flaky copper powder is large, the contact area between the flaky copper powders is large, and the conductivity is good; the particle size of the spherical copper powder is small, and the spherical copper powder can be better filled into the gap of the pyramid velvet surface, so as to reduce the contact resistance. Therefore, by controlling the size and / or mass ratio of the flaky copper powder and the spherical copper powder, the bulk resistivity and the contact resistance of the gate line can be in a small range.

[0055] In some embodiments, the copper gate line comprises nanometer spherical copper powder and micrometer flaky copper powder, and the peripheral part of the gate line comprises only nanometer spherical copper powder. In some embodiments, the copper gate line is prepared by screen printing.

[0056] In the present application, the method of screen printing is not limited, and the copper paste can be screen printed by using the method in the art. For example, the width of the peripheral part of the gate line and the width and height of the main body part of the gate line can be realized by controlling the printing pressure, the hardness of the doctor blade, the angle of the doctor blade and the like, and the skilled person in the art can obtain the desired result by optimizing the process conditions.

[0057] In some embodiments, the copper gate line comprises nanometer spherical copper powder and micrometer flaky copper powder, and the surface of the flaky copper powder is attached to the surface of the copper gate line in a substantially horizontal state. As can be seen from FIG. 3, the flaky copper powder is attached to the surface of the copper gate line in a substantially horizontal state, and the surface of the copper gate line refers to the tangent line of the surface of the copper gate line at the intersection of the flaky copper powder and the electrode.

[0058] In the copper grid line of the present application, the flaky copper powder with better oxidation resistance is attached to the surface of the copper grid line in a near-horizontal or horizontal state to improve the oxidation resistance of the copper grid line as a whole when placed in air and reduce the resistivity of the copper grid line.

[0059] Further, the flaky copper powder is arranged in a direction with an angle a with the surface of the copper grid line, 0°≤a≤45°. FIG. 3 is a schematic diagram of the surface of the copper grid line. As can be seen from FIG. 3, a is the angle of inclination of the flaky copper powder on the surface of the copper grid line relative to the surface of the copper grid line. Here, a is 32.7°.

[0060] In the present application, the angle a is measured by SEM (scanning electron microscope). A flaky copper powder in the field of view is selected, and the midpoint of the intersection line between the horizontal plane of the flaky copper powder and the surface of the copper grid line is selected to draw a tangent line of the surface of the copper grid line. An angle a is obtained by calculating the angle between the horizontal plane of the flaky copper powder and the tangent line. More than 10 flaky copper powders in different regions of the test sample are measured by the same method, and the average value of all measured angles a is calculated. It can also be understood by those skilled in the art that the above method is only exemplary, and those skilled in the art can appropriately reduce or increase the selected photographing area or number of test samples based on actual conditions.

[0061] In some embodiments, 0°≤a≤40°.

[0062] In some embodiments, 0°≤a≤35°.

[0063] In some embodiments, 0°≤a≤30°.

[0064] In some embodiments, 0°≤a≤25°.

[0065] In some embodiments, 5°≤a≤40°.

[0066] In some embodiments, 5°≤a≤35°.

[0067] In some embodiments, 5°≤a≤30°.

[0068] In some embodiments, 5°≤a≤25°.

[0069] Specifically, a can be 45°, 42°, 40°, 38°, 35°, 32°, 30°, 28°, 25°, 22°, 20°, 18°, 15°, 12°, 10°, 8°, 5°, etc.

[0070] Further, the area of the orthographic projection of the flaky copper powder attached to the surface of the copper grid line on the surface of the copper grid line accounts for 30%-70% of the surface area of the copper grid line.

[0071] In the copper grid line of the present application, the shape difference between the flaky powder and the spherical powder can be further utilized to control the surface area ratio of the flaky copper powder on the surface of the copper grid line, thereby improving the adhesion of the flaky copper powder on the surface and ensuring a high copper powder filling rate of the copper grid line, and further reducing the resistivity of the copper grid line.

[0072] In this application, the area of the flaky copper powder on the surface of the copper grid line is measured by SEM (scanning electron microscope). The surface area of the copper grid line is measured by a 3D microscope. The shape and size of the copper grid line are measured by a 3D microscope, and then the surface area is calculated. The cross section of the copper grid line is generally trapezoidal or trapezoidal-like. The upper base a, the lower base b and the height h of the trapezoid are measured, and the length l of the copper grid line is measured. The surface area of the copper grid line is calculated by the following formula:

[0073] Specifically, the area of the flaky copper powder on the surface of the copper grid line can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.

[0074] In this application, the copper paste is not limited, as long as the copper paste is used to obtain the above-mentioned copper grid line by screen printing.

[0075] For example, the copper paste comprises micro-nano copper powder, high molecular resin, solvent, curing agent and dispersant. In some embodiments, the micro-nano copper powder comprises micron-level flaky copper powder and nano-level spherical copper powder,

[0076] The median value of the micron-level flaky copper powder is 2-8 μm, and the median value of the nano-level spherical copper powder is 100-700 nm.

[0077] In this application, in order to remove the oxygen-containing substances on the surface of the original copper powder and improve its oxidation resistance, the copper powder is treated by a surface passivation agent. In this application, the method for surface treatment of the powder is not limited, and those skilled in the art can use conventional methods in the art to treat the copper powder. For example, the copper powder can be treated by the following method: after pickling, the copper powder is dispersed in alcohol again, a passivation agent is added and stirred, and then the passivation agent pretreated copper powder is obtained after separation and drying. Further, the passivation agent is selected from one or more of saturated / unsaturated fatty acids containing 8-18 carbons, silane coupling agent, PVP, and mercaptans.

[0078] In some embodiments, the microscale flaky copper powder is 40-70% by mass percentage in the copper powder, and the nanoscale spherical copper powder is 30-60% by mass percentage in the copper powder.

[0079] For example, the microscale flaky copper powder can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc. by mass percentage in the copper powder.

[0080] The nanoscale spherical copper powder can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc.

[0081] In some embodiments, the copper powder is 87-93% by mass percentage in the copper paste, the dispersant is 1-5%, the high-molecular resin is 2-4%, the solvent is 3-6%, and the curing agent is 0.2-0.4%.

[0082] For example, the copper powder can be 87%, 88%, 89%, 90%, 91%, 92%, 93%, etc. by mass percentage in the copper paste.

[0083] The dispersant can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

[0084] The high-molecular resin can be 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.6%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, etc.

[0085] The solvent can be 3%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6%, etc.

[0086] The curing agent can be 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, etc.

[0087] The types of the high-molecular resin, the solvent, and the curing agent are not limited in the present application, and a person skilled in the art can make a routine selection based on the needs, for example, the high-molecular resin can be one or a combination of two of epoxy resin, polyurethane resin, polyester resin, and phenolic resin.

[0088] The solvent can be one or a combination of two of ethylene glycol butyl ether, ethylene glycol dimethyl ether, dipropylene glycol butyl ether, isophorone, and diethylene glycol butyl ether.

[0089] The curing agent can be one of latent imidazole, boron trifluoride ethylamine, and disubstituted urea.

[0090] In some embodiments, the dispersant can be an ester and / or alcohol, wherein the ester dispersant is selected from one or more of dibasic acid ester (DBE), diethylene glycol butyl ether acetate, ethylene glycol butyl ether acetate, triethyl phosphate, and triethyl phosphite; the alcohol dispersant is selected from one or more of ethylene glycol, 1,2-propanediol, glycerol, pentaerythritol, polyethylene glycol 400, polyethylene glycol 600, polypropylene glycol 400, and polypropylene glycol 600, and the dispersant is preferably a mixture of ester and alcohol. In some embodiments, the mass ratio of the ester compound and the alcohol compound is 1:1-4.

[0091] For example, the mass ratio of the ester compound and the alcohol compound (m 酯类化合物 : m 醇类化合物 ) can be 1:1, 1:2, 1:3, 1:4, etc.

[0092] By using a mixture of ester and alcohol as the dispersant, the dispersibility of the copper powder can be increased, and the small-particle-size nano copper powder can be dispersed to the peripheral part of the grid line, located at the bottom of the pyramid of the solar cell surface, so as to increase the contact area of the copper grid line and the ITO or TCO of the cell surface, and reduce the contact resistance. Therefore, the diffusion width of the peripheral part of the grid line can be controlled by adjusting the type of the dispersant.

[0093] The application provides a solar cell comprising the copper grid line described in any one of the above. In some embodiments, the solar cell is provided with a surface structure having a light-trapping effect for increasing the effect of collecting solar radiation. The surface structure is a surface having a regular or irregular shape for scattering incident light and reducing the amount of light reflected back from the surface of the solar cell, and can be a pyramid structure.

[0094] The copper grid line is located at the upper part of the pyramid structure of the solar cell.

[0095] In the present application, the pyramid is a TCO layer. The pyramid structure is in an inverted triangular structure, and only the powder with a small enough particle size can be tightly filled. The flaky copper powder and the spherical copper powder are matched in size and shape, and are tightly stacked in the main part of the grid line. When printing, only the nano spherical copper powder with a small particle size can be diffused to the peripheral part of the grid line and tightly filled to the bottom of the pyramid structure, while the flaky copper powder is mostly blocked outside the pyramid structure, so as to obtain a good contact resistance.

[0096] Further, the height of the copper grid line peripheral portion on the surface of the solar cell is 0.05-2.5 microns. If the height of the copper grid line peripheral portion is too large, the bulk resistance of the grid line will increase, and if the height of the copper grid line peripheral portion is too small, the adhesion of the copper grid line to the solar cell cannot be effectively increased, and a good contact resistance cannot be obtained. In this context, when the copper grid line is in contact with the solar cell surface introducing a pyramid-shaped textured structure, the nano-spherical copper powder with a smaller particle size will fill the bottom of the pyramid, and the height of the copper grid line peripheral portion is measured from the lowest point of the copper powder filling the bottom of the pyramid.

[0097] In some embodiments, the solar cell is selected from one of a BC cell, an HJT cell, and a perovskite / silicon tandem cell.

[0098] In this application, the perovskite / silicon tandem cell refers to a silicon-perovskite tandem solar cell, in which the silicon cell can be an HJT cell, etc. It uses a composite material as a light absorption layer, mainly composed of perovskite material and silicon material. This material has the characteristics of high absorption rate and high conversion efficiency, and can convert sunlight into electrical energy.

[0099] The BC cell refers to a back contact cell, which sets the PN junction and metal contact on the back of the solar cell, and the front of the cell uses SiNx / SiOx double-layer anti-reflective passivation film without metal electrode shielding, maximizes the use of incident light, reduces optical loss, brings more effective generating area, has high conversion efficiency, and is more beautiful in appearance.

[0100] The HJT cell is a new type of solar cell technology, which is called silicon heterojunction solar cell.

[0101] In this application, the copper grid line (i.e. copper electrode) contains copper powder with different diameters and shapes. The specific surface area of spherical copper powder is large and the surface activity is high, but the oxidation resistance is weaker. In comparison, the oxidation resistance of flaky copper powder is stronger. As can be seen from FIGS. 4-5, after the spherical copper powder and the flaky copper powder are placed in the air for a period of time, an oxide layer is formed on the surface of the spherical copper powder, while the surface of the flaky copper powder hardly changes (FIG. 4a is the initial morphology of the spherical copper powder, FIG. 4b is the morphology after being placed for a period of time, FIG. 5a is the initial morphology of the flaky copper powder, and FIG. 5b is the morphology after being placed for a period of time). In order to obtain a copper grid line with excellent electrical performance, the particle size, shape and amount of copper powder need to be adjusted to improve the filling rate of copper powder in the copper grid line and ensure high oxidation resistance.

[0102] Therefore, the application further provides another copper grid line, wherein the copper grid line comprises flaky copper powder and spherical copper powder, and the surface of the flaky copper powder is attached to the surface of the copper grid line in a substantially horizontal state. As shown in FIG. 6, the flaky copper powder is attached to the surface of the copper grid line in a substantially horizontal state, and the surface of the copper grid line here refers to the tangent of the surface of the copper grid line at the intersection of the flaky copper powder and the copper grid line.

[0103] In the copper grid line of the application, the flaky copper powder with better oxidation resistance is attached to the surface of the copper grid line in a substantially horizontal state or a horizontal state, so as to improve the oxidation resistance of the copper grid line as a whole when placed in air and reduce the resistivity of the copper grid line.

[0104] Further, the flaky copper powder is arranged in a direction with an angle a with the surface of the copper grid line, and 0°≤a≤45°. As shown in FIG. 3, a is the inclination angle of the flaky copper powder on the surface of the copper grid line relative to the surface of the copper grid line.

[0105] In some embodiments, 0°≤a≤40°.

[0106] In some embodiments, 0°≤a≤35°.

[0107] In some embodiments, 0°≤a≤30°.

[0108] In some embodiments, 0°≤a≤25°.

[0109] In some embodiments, 5°≤a≤40°.

[0110] In some embodiments, 5°≤a≤35°.

[0111] In some embodiments, 5°≤a≤30°.

[0112] In some embodiments, 5°≤a≤25°.

[0113] Specifically, a can be 45°, 42°, 40°, 38°, 35°, 32°, 30°, 28°, 25°, 22°, 20°, 18°, 15°, 12°, 10°, 8°, 5°, etc.

[0114] Further, the area of the orthographic projection of the flaky copper powder attached to the surface of the copper grid line on the surface of the copper grid line accounts for 30%-70% of the surface area of the copper grid line.

[0115] In the copper grid line of the application, the difference in shape between the flaky copper powder and the spherical copper powder is further utilized to control the surface area ratio of the flaky copper powder on the surface of the copper grid line, so as to improve the firmness of the flaky copper powder attached to the surface and ensure that the copper grid line has a high copper powder filling rate, thereby further reducing the resistivity of the copper grid line.

[0116] Further, the mass ratio of the flaky copper powder to the spherical copper powder is (0.7-2):1.

[0117] Further, the flaky copper powder has a thickness median value of 100-500 nm and a diameter median value of 1-10 μm.

[0118] Further, the spherical copper powder has a particle size median value of 100-500 nm.

[0119] Further, the tap density of the flaky copper powder is 4.4-5 g / ml, and the tap density of the spherical copper powder is 4.3-4.9 g / ml. The specific surface area of the flaky copper powder is 0.4-0.7 m 2 / g, and the specific surface area of the spherical copper powder is 2.5-3.0 m 2 / g.

[0120] Specifically, the tap density of the flaky 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, and 5 g / ml.

[0121] Specifically, the tap density of the 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.

[0122] Specifically, the specific surface area of the flaky copper powder can be any value between 0.4 m 2 / g, 0.45 m 2 / g, 0.5 m 2 / g, 0.55 m 2 / g, 0.6 m 2 / g, 0.65 m 2 / g, 0.7 m 2 / g.

[0123] Specifically, the specific surface area of the spherical copper powder can be any value between 2.5 m 2 / g, 2.51 m 2 / g, 2.52 m 2 / g, 2.53 m 2 / g, 2.54 m 2 / g, 2.55 m 2 / g, 2.56 m 2 / g, 2.57 m 2 / g, 2.58 m 2 / g, 2.59 m 2 / g, and 3.0 m 2 / g.

[0124] In the present text, the tap density, i.e. the bulk density of the powder after tapping, refers to the density of the powder after the powder is filled into a specific container and the container is vibrated, thereby destroying the voids in the powder and making the powder in a tightly packed state. The flowability and porosity of the powder can be determined by measuring the tap density, which can be calculated by measuring the volume after 1000 times of vibration using a BT-301.

[0125] The specific surface area refers to the surface area per unit mass of a porous solid substance. The commonly used unit is square meters per gram. It can be tested by conventional methods, for example, by using GB / T 13390-2008 Metal Powder Specific Surface Area Test Method.

[0126] Further, the cross section of the copper grid line is trapezoidal or trapezoidal-like, which is the cross section perpendicular to the extension direction of the copper grid line.

[0127] Further, the copper grid line is prepared by screen printing.

[0128] Further, the copper grid line further comprises nano-copper particles, and the nano-copper particles comprise at least two primary copper nanoparticles connected in series, and the adjacent primary copper nanoparticles are connected in a face contact manner.

[0129] In the present text, the face contact connection manner refers to that there are at least two connection points between the two adjacent primary copper nanoparticles or there is an overlapping part between the two adjacent primary copper nanoparticles, and the maximum distance of the two connection points or the intersection arc length of the overlapping part accounts for at least 10% of the diameter of any one of the primary copper nanoparticles. In the present application, the face contact connection between the two primary copper nanoparticles can be detected or observed by, for example, SEM or TEM.

[0130] In the present application, the nano-copper particles fill the gap area between the flaky copper powder and the spherical copper powder, and are in direct contact with the flaky copper powder and the spherical copper powder, so that the conductive channel between the conductive particles is more unobstructed, and the filling of the nano-copper particles makes the copper grid line structure more dense, greatly reducing the bulk resistance of the copper grid line and keeping the conductivity of the silver grid line.

[0131] Further, the nano-copper particles are linear copper particles formed by at least two primary copper nanoparticles connected in series, and / or the nano-copper particles are L-shaped copper particles, V-shaped copper particles, U-shaped copper particles, triangular copper particles, quadrilateral copper particles, W-shaped copper particles, or polygonal copper particles with more than 5 sides, which are formed by at least two primary copper nanoparticles connected in series at a certain angle.

[0132] The nano-copper particles in the present application have a three-dimensional unequal-diameter shape, which is conducive to matching various shapes of gaps formed between the plurality of sheet-shaped copper powders, thereby effectively reducing the gaps formed by the sheet-shaped copper powders and increasing the conductive path between the copper powders. Especially for the linear, L-shaped, and V-shaped copper particles, compared with the spherical copper particles, they have more contact points with the sheet-shaped copper powders and other nano-copper particles in the length direction, which can increase the contact area between the sheet-shaped copper powders and the nano-copper particles and between the sheet-shaped copper powders and the copper particles, increase the conductive path between the copper powders, and increase the conductivity of the copper paste after the copper paste becomes a copper gate line. For the triangular, quadrilateral, and polygonal copper particles, the end portion has a plurality of protrusions formed by smaller copper nanoparticles, which become a bridge for electronic conduction between the sheet-shaped copper powders, and also increase the conductivity of the copper gate line.

[0133] The linear copper particle is defined as a string-shaped structure, and a plurality of connected primary copper nanoparticles are arranged in sequence and contact in the length direction, for example, when the linear copper particle is composed of two primary copper nanoparticles, it is a gourd-shaped or peanut-shaped structure.

[0134] The bending connection at a certain angle means that a plurality of connected primary copper nanoparticles are connected in sequence and contact, and the extension directions of two connected primary copper nanoparticles among the three primary copper nanoparticles (copper nanoparticle A, copper nanoparticle B, and copper nanoparticle C) connected in sequence at a certain position are different from the extension directions of the other two connected primary copper nanoparticles, and have a certain angle, that is, the extension direction after the connection of the primary copper nanoparticle A and the primary copper nanoparticle B is different from the extension direction after the connection of the primary copper nanoparticle B and the primary copper nanoparticle C, and has a certain angle.

[0135] In the nano-copper particle, the number of primary copper nanoparticles can be 2, 3, 4, 5, or more, and a plurality of primary copper nanoparticles are connected in sequence.

[0136] The present application provides another solar cell, which comprises the copper gate line according to any one of the above.

[0137] Embodiment

[0138] The materials used in the test and the test method are generally and / or specifically described in the present application. In the following examples, % means wt%, that is, weight percentage, unless otherwise specified. If the manufacturer of the reagent or instrument is not specified, it is a conventional reagent product that can be obtained by purchase.

[0139] Example 1

[0140] (1) 2 g of a mixed resin of epoxy resin and 1 g of phenol resin were added to 5 g of DBE solvent, and mixed by stirring at room temperature, and then filtered through a 500-mesh screen to remove impurities, to obtain a high-molecular resin solution.

[0141] (2) 0.5 g of a dispersant, polyethylene glycol 400, and 0.5 g of a dispersant, triethyl phosphate, were added to the high-molecular resin solution, and stirred and dispersed uniformly, and then 0.3 g of a latent imidazole was added as a curing agent to the solution and dispersed uniformly, and then 45 g of nanometer spherical copper powder (median particle size 200 nm) and 45 g of micron flake copper powder (median diameter 2 μm, thickness 100 nm) were pre-mixed in a planetary mixer to obtain a pre-mix.

[0142] (3) The pre-mix was ground by high-speed shearing in a three-roll mill to obtain a low-temperature conductive copper paste, and the copper paste was filtered through a 400-mesh screen to remove impurities and large particles, and then vacuum defoaming was performed to obtain a copper paste.

[0143] The copper paste obtained in Example 1 was screen-printed onto a cell sheet to prepare a grid line, and the grid line was photographed by SEM, and is shown in FIGS. 1, 2 and 3, respectively. In FIG. 1, 1 is the main body of the grid line, 2 is the peripheral portion of the grid line, and 3 is the portion of the grid line to which diffusion has not occurred. From the cross-section of the grid line, it can be seen that the peripheral portion of the grid line has spherical copper powder having a smaller particle size than the main body of the grid line, and the median particle size is less than 200 nm. From FIG. 2, it can be seen that the copper powder in the copper paste is distributed on the tower of the cell sheet to form a dense structure. From FIG. 3, it can be seen that the flake copper powder has an angle of 32.7° with the surface of the copper grid line, and it can be observed that the flake copper powder is attached to the surface of the grid line in a substantially horizontal state. The contact resistivity of the grid line and the cell sheet was measured using a TLM contact resistance tester commonly used in the art, and the contact resistivity was free from the influence of the line width, spacing and ITO sheet resistance of the grid line. The results are shown in Table 1, and Table 1 also shows the width and height of the main body of the grid line and the width of the peripheral portion of the grid line on one side.

[0144] Example 2

[0145] Example 2 and Example 1 differ in that 3 g of polyethylene glycol 400 and 1 g of a dispersant, diethylene glycol butyl ether acetate, were used to prepare the copper paste, and the grid line was prepared in the same manner as in Example 1, and the cell rate and contact resistivity, the width and height of the main body of the grid line and the width of the peripheral portion of the grid line on one side were measured.

[0146] Example 3

[0147] Example 3 and Example 1 differ in that the median value of the diameter of the microparticle-shaped copper powder is 10 μm, and the grid line is prepared in the same manner as Example 1, and the battery rate and the contact resistance rate, the width and height of the main body portion of the grid line, and the width of the one-side grid line peripheral portion are measured.

[0148] Example 4

[0149] Example 4 and Example 1 differ in that the median value of the particle diameter of the nanosphere-shaped copper powder is 900 nm, and the grid line is prepared in the same manner as Example 1, and the battery rate and the contact resistance rate, the width and height of the main body portion of the grid line, and the width of the one-side grid line peripheral portion are measured.

[0150] Example 5

[0151] Example 5 and Example 1 differ in that the amount of the nanosphere-shaped copper powder is 18 g, and the amount of the microparticle-shaped copper powder is 72 g, and the copper paste is prepared, and the grid line is prepared in the same manner as Example 1, and the battery rate and the contact resistance rate, the width and height of the main body portion of the grid line, and the width of the one-side grid line peripheral portion are measured.

[0152] Example 6

[0153] Example 6 and Example 1 differ in that the amount of the nanosphere-shaped copper powder is 27 g, and the amount of the microparticle-shaped copper powder is 63 g, and the copper paste is prepared, and the grid line is prepared in the same manner as Example 1, and the battery rate and the contact resistance rate, the width and height of the main body portion of the grid line, and the width of the one-side grid line peripheral portion are measured.

[0154] Example 7

[0155] Example 7 and Example 1 differ in that the median value of the diameter of the microparticle-shaped copper powder is 8 μm, and the grid line is prepared in the same manner as Example 1, and the battery rate and the contact resistance rate, the width and height of the main body portion of the grid line, and the width of the one-side grid line peripheral portion are measured.

[0156] Example 8

[0157] Example 8 and Example 1 differ in that the median value of the particle diameter of the nanosphere-shaped copper powder is 700 nm, and the grid line is prepared in the same manner as Example 1, and the battery rate and the contact resistance rate, the width and height of the main body portion of the grid line, and the width of the one-side grid line peripheral portion are measured.

[0158] Comparative Example 1

[0159] Comparative Example 1 and Example 1 differ in that Comparative Example 1 uses only polyethylene glycol 400 to prepare the copper paste, and the grid line is prepared in the same manner as Example 1, and the battery rate and the contact resistance rate, the width and height of the main body portion of the grid line, and the width of the one-side grid line peripheral portion are measured.

[0160] Comparative Example 2

[0161] Comparative Example 2 and Example 1 differ in that Comparative Example 2 uses only spherical copper powder to prepare the copper paste, and the grid lines are prepared in the same manner as Example 1, and the battery rate and contact resistance rate, the grid line main body portion width and height, and the one side grid line peripheral portion width are measured.

[0162] Table 1

[0163] As can be seen from the above table, when the width of the one side grid line peripheral portion is not more than 15% to 50% of the width of the grid line main body portion, the resistance rate and the contact resistance rate of the copper grid line are both low.

[0164] The above description is merely preferred embodiments of the present application, but not a limitation to the present application. Any modification, equivalent, and improvement made without departing from the spirit and scope of the present application shall fall within the protection scope of the present application.

Claims

1. A copper grid line, comprising a grid line main body portion and a grid line peripheral portion, the grid line peripheral portion being located on both sides of the grid line main body portion, wherein the width of any one of the grid line peripheral portions is not more than 15%-50% of the width of the grid line main body portion; the median value of the particle size of the copper powder in the grid line peripheral portion is less than the median value of the particle size of the copper powder in the grid line main body portion.

2. The copper grid line of claim 1, wherein, The width of the grid line main body portion is 30-120 microns.

3. The copper grid line of claim 2, wherein, The width of the grid line peripheral portion is 10-60 microns, and / or the height of the grid line peripheral portion is 0.05-2.5 microns.

4. The copper grid line of claim 1, wherein, The height of the grid line main body portion is 10-25 microns.

5. The copper grid line of claim 1, wherein, The copper grid line comprises nanoscale spherical copper powder and micrometer scale flaky copper powder, the median value of the particle size of the spherical copper powder is 100-700 nm, the median value of the diameter of the flaky copper powder is 2-8 microns, and the median value of the thickness of the flaky copper powder is 100-500 nm.

6. The copper grid line of claim 5, wherein, The micrometer scale flaky copper powder accounts for 40-70% by mass percentage in the copper powder, and the nanoscale spherical copper powder accounts for 30-60% by mass percentage in the copper powder. 7.The copper grid line according to any one of claims 1-6, comprising nanoscale spherical copper powder and micrometer scale flaky copper powder, and the grid line peripheral portion only comprises nanoscale spherical copper powder.

8. The copper power plane of any of claims 1-6, wherein, The copper grid line is prepared by screen printing.

9. The copper power plane of any of claims 1-6, wherein, The copper grid line comprises nanoscale spherical copper powder and micrometer scale flaky copper powder, and the surface of the flaky copper powder is attached to the surface of the copper grid line in a substantially horizontal state.

10. The copper grid line of claim 8, wherein, The flaky copper powder is arranged in a direction with an angle of α with the surface of the copper grid line, wherein 0°≤α≤45°.

11. The copper grid line of claim 8, wherein, The area of the normal projection of the flaky copper powder attached to the surface of the copper grid line on the surface of the copper grid line accounts for 30%-70% of the surface area of the copper grid line.

12. The copper grid line of claim 1, wherein, The copper grid line further comprises nanometer copper particles, the nanometer copper particles comprising at least two primary copper nanoparticles connected in a surface contact manner. 13.A solar cell, comprising the copper grid line according to any one of claims 1-11.

14. The solar cell of claim 13, wherein, The surface of the solar cell has a textured structure, and the copper grid line is located on the upper portion of the textured structure of the solar cell.

15. The solar cell of claim 13, wherein, The height of the grid line peripheral portion is 0.05-2.5 microns.

Images