Copper slurry, electrode, preparation method therefor, and use thereof

Abstract

The present application discloses a copper slurry, an electrode, a preparation method therefor, and a use thereof. The electrode comprises copper powder, the copper powder comprises copper nanoparticles and flaky copper powder, the copper nanoparticles include at least two connected primary copper nanoparticles, and adjacent primary copper nanoparticles are connected in a surface contact manner. According to the electrode of the present application, the copper nanoparticles formed by connecting two or more primary copper nanoparticles are used to fill a void region between large-sized flaky copper powder, so as to be in direct contact with the flaky copper powder, so that conductive channels between conductive particles are smoother; moreover, the filling of the copper nanoparticles makes the structure of the electrode more dense, significantly reducing the bulk resistance of the electrode, and achieving conductivity comparable to that of silver electrodes; the copper nanoparticles can also serve as an auxiliary binder after sintering and curing, which improves the adhesion between copper grid lines and a solar cell, thereby achieving firmer connection between the grid lines and the solar cell.

Description

A copper paste, electrode and preparation method and application thereof

[0001] Cross-reference to Related Applications

[0002] This application claims priority to the Chinese patent application No. 2024112458616, filed on September 5, 2024, entitled "A copper paste, electrode and preparation method and application thereof", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the field of solar cells, in particular to a copper paste, electrode and preparation method and application thereof. BACKGROUND

[0004] In recent years, with the continuous improvement of the photoelectric conversion efficiency of solar cells, its importance in solving energy shortage and environmental pollution is increasingly prominent, and it has important significance in promoting the development of green energy. Among them, the conductive paste, as an important component of solar cells, plays a crucial role in improving the efficiency of the battery. However, the conductive silver paste, as the mainstream of the market conductive paste, has led to high costs of solar cells, and if copper paste is used to replace silver paste as the grid line of solar cells, the cost will be greatly reduced.

[0005] The existing conductive copper paste adopts the traditional low-temperature curing mode, and the organic system (resin, curing agent, dispersing agent) is mixed with the conductive phase (copper powder) to obtain a mixture. Due to the difference in electrical conductivity between copper and silver, the electrical performance of the cured copper paste is poorer than that of the silver paste. SUMMARY

[0006] The present application aims to provide an electrode, which fills the gap area between the copper nanoparticles and the large-size flaky copper powder, so that the copper nanoparticles are in direct contact with the flaky copper powder, making the conductive channel between the conductive particles more unobstructed, and the filling of the copper nanoparticles makes the structure of the electrode more dense, greatly reducing the bulk resistance of the electrode, and the electrical conductivity is comparable to that of silver electrode.

[0007] The present application provides an electrode, which comprises copper nanoparticles and flaky copper powder, the copper nanoparticles comprise at least two primary copper nanoparticles connected in series, and the adjacent primary copper nanoparticles are connected in a face-to-face manner.

[0008] Further, the length median value of the copper nanoparticles is 150-700 nm, and the width median value of the copper nanoparticles is 40-400 nm.

[0009] Further, the copper nanoparticles are linear copper particles formed by at least two primary copper nanoparticles connected in series, and / or

[0010] The copper nanoparticles are connected by at least two primary copper nanoparticles connected at an angle to form 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.

[0011] Further, the electrode further comprises spherical copper powder.

[0012] Further, in the copper powder, the mass percentage of the copper nanoparticles is 0.5%-15%, the mass percentage of the flaky copper powder is 35%-60%, and the mass percentage of the spherical copper powder is 35%-60%.

[0013] Further, the median particle size of the spherical copper powder is 100 nm-500 nm.

[0014] 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; or

[0015] 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.

[0016] Further, the median diameter of the flaky copper powder is 2 μm-8 μm, and the median thickness is 100 nm-500 nm.

[0017] Further, the electrode comprises a main portion and a peripheral portion, the peripheral portion is located on both sides of the main portion, wherein the width of the peripheral portion on either side is not more than 5%-50% of the width of the main portion; the median particle size of the copper powder in the peripheral portion is smaller than the median particle size of the copper powder in the main portion.

[0018] Further, the copper powder in the peripheral portion comprises the copper nanoparticles, and the copper powder in the main portion comprises the flaky copper powder and the copper nanoparticles.

[0019] Further, the width of the main portion is 30-120 μm; or the width of the peripheral portion is 1-60 μm.

[0020] Further, the electrode is prepared by screen printing.

[0021] The application also provides a copper paste comprising copper powder, the copper powder comprising copper nanoparticles, flaky copper powder, and optionally spherical copper powder, the copper nanoparticles comprising at least two primary copper nanoparticles connected at an angle to form 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.

[0022] Further, the copper nanoparticles have a median value of length of 150-700 nm and a median value of width of 40-400 nm.

[0023] Further, the copper nanoparticles are linear copper particles formed by at least two primary copper nanoparticles connected in series, and / or

[0024] The copper nanoparticles 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 a side number of 5 or more, formed by at least two primary copper nanoparticles connected at an angle.

[0025] Further, the copper powder further comprises spherical copper powder, wherein the mass percentage of the copper nanoparticles is 0.5%-15%, the mass percentage of the flaky copper powder is 35%-60%, and the mass percentage of the spherical copper powder is 35%-60%.

[0026] Further, the flaky copper powder has a median value of diameter of 2-8 μm and a median value of thickness of 100-500 nm; or

[0027] The spherical copper powder has a median value of particle size of 100-500 nm.

[0028] Further, the flaky copper powder has a tap density of 4.4-5 g / ml, and the spherical copper powder has a tap density of 4.3-4.9 g / ml; or

[0029] The flaky copper powder has a specific surface area of 0.4-0.7 m 2 / g, and the spherical copper powder has a specific surface area of 2.5-3.0 m 2 / g.

[0030] Further, the copper paste further comprises a resin, a solvent, a curing agent, and an optional curing accelerator, wherein the weight fraction of the copper powder is 70-95 parts, the weight fraction of the resin is 5-15 parts, the weight fraction of the curing agent is 1-5 parts, the weight fraction of the solvent is 5-20 parts, and the weight fraction of the curing accelerator is 0-5 parts; or

[0031] The resin is selected from one or more than two of an epoxy resin, an acrylic resin, and a phenolic resin; or

[0032] The curing agent is selected from one or more than two of a tertiary amine, an isocyanate, an imidazole, a dicyandiamide, and an acid anhydride; or

[0033] The optional curing accelerator is a quaternary ammonium salt, an imidazole ester, an imidazolium salt, or a substituted urea; or

[0034] The solvent is selected from one or more of divalent acid ester (DBE), diethylene glycol butyl ether, diethylene glycol butyl ether acetate, terpineol, dipropylene glycol butyl ether, 2,2,4-trimethyl-1,3 pentanediol diisobutyrate, butyl acetate, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, diethylene glycol dimethyl ether, dimethyl formamide, N-methyl pyrrolidone, diacetone alcohol, dimethyl acetamide, gamma-butyrolactone, butyl carbitol, butyl carbitol acetate, ethyl carbitol, ethyl carbitol acetate, dihydroterpineol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dihydroterpinyl acetate, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether acetate.

[0035] The application also provides an electrode obtained by screen printing the aforementioned copper paste.

[0036] The application also provides a method for preparing the aforementioned copper paste, comprising the following steps:

[0037] Preparation of copper nanoparticles;

[0038] Mixing of the copper nanoparticles with flaky copper powder, spherical copper powder, resin, solvent, curing agent, and optional curing accelerator to obtain the copper paste;

[0039] The copper nanoparticles comprise at least two primary copper nanoparticles connected in a face-to-face manner.

[0040] The application also provides a solar cell comprising the aforementioned electrode, which is in contact with the surface of the solar cell.

[0041] Further, the copper nanoparticles are contained in the vicinity of the contact interface.

[0042] Further, the surface of the solar cell has a textured structure, and the electrode is located on the upper portion of the textured structure of the solar cell.

[0043] Further, in the main body of the electrode, the volume content of the nanoscale copper powder in the vicinity of the contact interface is greater than that in other regions of the electrode.

[0044] Further, the surface of the flaky copper powder is attached to the surface of the electrode in a substantially horizontal state.

[0045] Further, the flaky copper powder is arranged in a direction forming an angle α with the surface of the electrode, where 0°≤α≤50°.

[0046] Further, the area of the flaky copper powder attached to the surface of the electrode in orthographic projection on the surface of the electrode accounts for 30%-65% of the surface area of the electrode.

[0047] The electrode and copper paste described in the present application, by using copper nanoparticles connected by two or more primary copper nanoparticles, filling in the gap area between large size flaky copper powder, wherein the copper nanoparticles have a three-dimensional unequal diameter shape, which is conducive to the copper nanoparticles matching the various shaped gaps formed between multiple flaky copper powders, and the surface has more contact points with flaky copper powder and other copper nanoparticles, which can increase the contact area between flaky copper powder and copper nanoparticles and between copper particles, increase the conductive path between various conductive copper powders, and the filling of copper nanoparticles makes the structure of the electrode more dense, greatly reducing the bulk resistance of the electrode, which is comparable to the conductivity of the electrode prepared by silver paste; the copper nanoparticles can also act as an auxiliary adhesive after sintering and curing, improving the adhesion of the copper paste to the solar cell, making the connection between the electrode and the solar cell more secure. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 is a scanning electron microscope image of the electrode prepared in Example 1-1.

[0049] Figure 2 is a scanning electron microscope image of the electrode prepared in Example 1-1.

[0050] Figure 3 is a scanning electron microscope image of the electrode prepared in Example 2-1.

[0051] Figure 4 is a scanning electron microscope image of the electrode provided by the present application.

[0052] Figure 5 is a scanning electron microscope image of the electrode provided by the present application.

[0053] Figure 6 is a scanning electron microscope image of the electrode provided by the present application.

[0054] 1 - electrode main part, 2 - electrode peripheral part, 3 - cell sheet surface without electrode coverage. DETAILED DESCRIPTION

[0055] The exemplary embodiments of the present application are described below, including various details of the embodiments of the present application to help understanding, which should be considered only as exemplary. Therefore, those of ordinary skill in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present application. Also, in order to be clear and concise, the description below omits the description of well-known functions and structures.

[0056] The application provides an electrode comprising copper nanoparticles and flaky copper powder, wherein the copper nanoparticles, which can also be referred to as nano-copper particles, refer to copper particles of nanometer size, specifically copper particles of nanometer size in any one direction, comprising at least two primary copper nanoparticles connected by face contact.

[0057] In this application, the face contact connection 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 primary copper nanoparticle. In this application, the face contact connection between the two primary copper nanoparticles can be detected or observed by, for example, SEM or TEM.

[0058] In this application, the copper nanoparticles fill the gap between the flaky copper powder and directly contact the flaky copper powder, so that the conductive channel between the conductive particles is more unobstructed, and the filling of the copper nanoparticles makes the electrode structure more compact, greatly reducing the bulk resistance of the electrode and keeping the conductivity of the electrode at the same level as that of the silver electrode.

[0059] In this application, the length median value of the copper nanoparticles is 150 nm-700 nm, and the width median value of the copper nanoparticles is 40 nm-400 nm.

[0060] Specifically, the length median value of the copper nanoparticles can be any value between 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, 520 nm, 550 nm, 580 nm, 600 nm, 620 nm, 650 nm, 680 nm, 700 nm.

[0061] Specifically, the width median value of the copper nanoparticles can be any value between 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 260 nm, 280 nm, 300 nm, 320 nm, 340 nm, 360 nm, 380 nm, 400 nm.

[0062] In this article, the test method of the median value of length and the median value of width of copper nanoparticles: the measurement is made by SEM (scanning electron microscope), 10 different areas of the test sample are photographed, a total of 10 photos are taken, then the size of any 10 copper nanoparticles observed in each photo is measured along the length direction, and then the median value of a total of 100 nanoparticles is calculated, which is the median value of length. In the same way, the size is measured along the width direction, and then the median value is calculated, which is the median value of width. 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 selected photographing area or number of copper nanoparticles based on the actual situation. For a copper nanoparticle, the length direction is the direction corresponding to the longest length, and the width direction is the direction corresponding to the narrowest width in the remaining cross section except the contact surface in any cross section of the particle. The size of various copper particles in the copper paste is also measured by SEM to obtain the median value. The median values of the following flaky copper powder and spherical copper powder are measured by this method.

[0063] In this application, the copper nanoparticles are linear copper particles formed by at least two connected primary copper nanoparticles; the copper nanoparticles can also be 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 (polygonal copper particles with more than 5 sides can be pentagonal copper particles, hexagonal copper particles, heptagonal copper particles, etc.), preferably linear copper particles. In this article, two or more of linear copper particles, 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 can exist in the same electrode, for example, in some embodiments, the electrode has linear copper particles, L-shaped copper particles, V-shaped copper particles, U-shaped copper particles, triangular copper particles. In some embodiments, the electrode has linear copper particles, L-shaped copper particles, V-shaped copper particles, U-shaped copper particles, quadrilateral copper particles. In some embodiments, the electrode has linear copper particles, L-shaped copper particles, V-shaped copper particles, U-shaped copper particles, pentagonal copper particles. In some embodiments, the electrode has linear copper particles, V-shaped copper particles, U-shaped copper particles, triangular copper particles. In some embodiments, the electrode has linear copper particles, L-shaped copper particles, V-shaped copper particles, U-shaped copper particles, triangular copper particles, and quadrilateral copper particles.

[0064] The copper nanoparticles described in the present application have a three-dimensional unequal-diameter shape, which is conducive to the copper nanoparticles matching various shapes of gaps formed between the sheet-shaped copper powders, thereby effectively reducing the gaps formed by the sheet-shaped copper powders and increasing the conductive paths between the copper powders. In particular, for linear, L-shaped, and V-shaped copper particles, they have more contact points with the sheet-shaped copper powders and other copper nanoparticles in the length direction than spherical copper particles, which can increase the contact area between the sheet-shaped copper powders and the copper nanoparticles and between the copper nanoparticles, increase the conductive paths between the copper powders, and increase the conductivity of the copper paste after the copper paste becomes an electrode. For triangular, quadrilateral, and polygonal copper particles, the end portions thereof have multiple protrusions formed by smaller primary copper nanoparticles, which serve as bridges for electron conduction between the sheet-shaped copper powders and can also increase the conductivity of the electrode.

[0065] The linear copper particle is defined as a string-shaped structure, and multiple connected primary copper nanoparticles are arranged in sequence and face-to-face contact and extend in the length direction. For example, when the linear copper particle is composed of two primary copper nanoparticles, it is gourd-shaped or peanut-shaped.

[0066] The angle bending connection refers to that multiple connected primary copper nanoparticles are sequentially connected in face-to-face contact, and the extension directions of two connected primary copper nanoparticles among the three sequentially connected primary copper nanoparticles (primary copper nanoparticle A, primary copper nanoparticle B, and primary copper nanoparticle C) 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.

[0067] In the copper nanoparticles, the number of primary copper nanoparticles can be 2, 3, 4, 5, or more, and multiple primary copper nanoparticles are sequentially connected together.

[0068] In some embodiments, the primary copper nanoparticles are single-crystal phase nano-copper particles, and the surfaces thereof are smooth.

[0069] In some embodiments, the primary copper nanoparticles are spherical or polyhedral, and the polyhedral can be hexahedral, octahedral, or the like.

[0070] In some embodiments, the primary copper nanoparticles are copper elements or copper-containing alloys. From the perspective of improving the oxidation resistance of copper, the copper-containing alloys can be copper-silver alloys, copper-nickel alloys, copper-aluminum alloys, copper-tin alloys, or the like.

[0071] The median particle size of the primary copper nanoparticles is 40 nm to 400 nm, in some embodiments, the median particle size of the primary copper nanoparticles is 40 nm to 300 nm, in some embodiments, the median particle size of the primary copper nanoparticles is 50 nm to 200 nm, in some embodiments, the median particle size of the primary copper nanoparticles is 60 nm to 100 nm.

[0072] In particular, the median particle size of the primary copper nanoparticles can be any value between 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 260 nm, 280 nm, 300 nm, 320 nm, 340 nm, 380 nm, 400 nm.

[0073] In the present application, the electrode further comprises a spherical copper powder.

[0074] In the present application, the flaky copper powder refers to a ratio of length to width (diameter / thickness) greater than or equal to 2 in an image observed by a scanning electron microscope. The ratio of the longest diameter to the shortest diameter of the flaky copper powder is 1 to 10. The spherical copper powder refers to a ratio of length to width (diameter / thickness) less than 2 in an image observed by a scanning electron microscope.

[0075] In some embodiments, in the copper powder, the mass percentage of the copper nanoparticles is 0.5% to 15%, the mass percentage of the flaky copper powder is 35% to 60%, and the mass percentage of the spherical copper powder is 35% to 60%.

[0076] In particular, in the copper powder, the mass percentage of the copper nanoparticles can be any value between 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%.

[0077] In particular, in the copper powder, the mass percentage of the flaky copper powder can be any value between 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%.

[0078] Specifically, the mass percentage of the spherical copper powder in the copper powder can be any value between 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%.

[0079] Further, the flaky copper powder has a median value of diameter of 2 μm-8 μm and a median value of thickness of 100 nm-500 nm. The spherical copper powder has a median value of particle size of 100 nm-500 nm.

[0080] Specifically, the flaky copper powder has a median value of diameter of 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm.

[0081] Specifically, the flaky copper powder has a median value of thickness of 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm.

[0082] Specifically, the spherical copper powder has a median value of particle size of 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm.

[0083] In this context, the copper nanoparticles 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. By matching the shape and / or mass of the flaky copper powder, the spherical copper powder and the copper nanoparticles, the copper particles of various particle sizes and shapes are tightly packed, and the conductive channels between the conductive particles are more unobstructed.

[0084] In this application, 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.

[0085] 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, 5 g / ml.

[0086] 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, 4.9 g / ml.

[0087] 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.

[0088] Specifically, the specific surface area of the spherical copper powder can be any value between 2.5 m 2 / g, 2.55 m 2 / g, 2.60 m 2 / g, 2.65 m 2 / g, 2.70 m 2 / g, 2.75 m 2 / g, 2.80 m 2 / g, 2.85 m 2 / g, 2.90 m 2 / g, 2.95 m 2 / g, 3.0 m 2 / g.

[0089] In this article, the tap density, i.e. the bulk density of the powder after vibration, refers to the density of the powder after the container is vibrated to destroy the voids in the powder and the powder is in a tightly packed state. The flowability and void ratio 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 BT-301.

[0090] 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.

[0091] In the present application, the electrode comprises a main body portion and a peripheral portion, the peripheral portion is located on both sides of the main body portion, wherein the width of the peripheral portion on any one side is not more than 5%-50% of the width of the main body portion; the median value of the particle size of the copper powder in the peripheral portion is smaller than the median value of the particle size of the copper powder in the main body portion.

[0092] In some embodiments, the main body portion and the peripheral portion have the same extension direction, the peripheral portion comprises a first peripheral portion and a second peripheral portion, the first peripheral portion and the second peripheral portion are respectively located on both sides of the main body portion and symmetrically arranged with the extension direction of the main body portion as the axis of symmetry.

[0093] In some embodiments, the copper powder in the peripheral portion comprises copper nanoparticles, and the copper powder in the main body portion comprises copper nanoparticles and flaky copper powder.

[0094] In some embodiments, the copper powder in the peripheral portion comprises copper nanoparticles and spherical copper powder, and the copper powder in the main body portion comprises copper nanoparticles, flaky copper powder and spherical copper powder.

[0095] In the present application, the method for measuring the width of the main body portion of the electrode is not limited, and the skilled person in the art can make a routine selection based on the actual needs, for example, the width of the main body portion of the electrode can be measured by SEM, for example, the width of the bottom of the copper electrode in a certain area within the SEM measurement field of view 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 electrode.

[0096] In the present application, the width of the peripheral portion of the electrode is not limited, and the skilled person in the art can measure it by a routine method in the art, for example, the width of the peripheral portion of the electrode can be measured by SEM; for example, the height of the copper powder covered by the main body portion and the peripheral portion of the electrode has a significant difference, and the particle size of the copper powder in the two areas also has a significant difference, so the dividing line between the main body portion and the peripheral portion of the copper electrode can be found by SEM, the dividing line is used as the starting line of the peripheral portion, 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 electrode is located is defined as the width of the peripheral portion, and 10 measurement positions are randomly selected for measurement on a test sample of an electrode.

[0097] For example, the width of the peripheral portion on either side is no more than 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc. of the width of the main body portion. FIG. 1 is a copper electrode according to the embodiments of the present application, wherein 1 is the main body portion of the electrode, 2 is the peripheral portion of the electrode, and 3 is the surface of the battery sheet without electrode coverage. The width of the peripheral portion on either side is no more than 5%-50% of the width of the main body portion.

[0098] FIG. 2 is an electron microscope image of the diffusion of copper paste. 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.

[0099] The electrode according to the embodiments of the present application has a peripheral portion with a certain width on both sides of the main body portion of the electrode, and the median value of the particle size of the copper powder in the peripheral portion is smaller than the median value of the particle size of the copper powder in the main body portion. Thus, a dense structure can be formed in the peripheral portion, the contact area between the electrode and the surface of the battery is increased, the adhesion of the electrode is improved, water and oxygen are prevented from penetrating into the main body portion from the interface between the electrode and the bottom battery and oxidizing the copper powder in the main body portion, thereby reducing the bulk resistance of the electrode and the contact resistance between the electrode and the battery. Meanwhile, the width of the peripheral portion on either side is no more than 5%-50% of the width of the main body portion, which can ensure that the electrode has a relatively low bulk resistivity and contact resistance, and also ensure that the electrode has a relatively small shading rate to light.

[0100] In some embodiments, the width of the main body portion of the electrode is not limited by the present application, and the width of the main body portion of the copper electrode commonly used in the art can be used. The width of the main body portion of the electrode is 30-120 microns. In some embodiments, the width of the peripheral portion of the electrode is 1-60 microns.

[0101] For example, the width of the main body portion of the electrode can be 30 microns, 40 microns, 50 microns, 60 microns, 70 microns, 80 microns, 90 microns, 100 microns, 110 microns, 120 microns, etc.

[0102] For example, the width of the peripheral portion of the electrode can be 1 micron, 5 microns, 10 microns, 15 microns, 20 microns, 30 microns, 40 microns, 50 microns, 60 microns, etc.

[0103] In some embodiments, the height of the main body portion of the electrode is 10-25 microns.

[0104] In the present application, the height of the electrode body part refers to the vertical height at the center point of the bottom edge of the electrode cross section, which is measured by SEM (scanning electron microscope). The vertical height at the center point of the bottom edge of the electrode cross section is measured at any 20 positions of the test sample, and then the average value is calculated, which is the height of the electrode body part. It is also 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 number of selected measurement positions of the electrode based on the actual situation.

[0105] In the present application, the height of the electrode body part, the width of the peripheral part and the width of the body part are set within the above three numerical ranges. The obtained copper electrode can not only have a firm contact with the solar cell, but also reduce the resistivity and improve the current collection efficiency, and also can reduce the use cost of the copper electrode.

[0106] In the present application, the electrode is prepared by screen printing.

[0107] In the present application, the method of screen printing is not limited, and those skilled in the art can use conventional methods in the art to screen print the copper paste. For example, the width of the electrode peripheral part and the width and height of the electrode body part can be achieved by controlling the printing pressure, doctor blade hardness, doctor blade angle, paste solvent type and solvent usage amount, etc. Those skilled in the art can obtain the desired result by conventional optimization of these process conditions.

[0108] The present application also provides a copper paste, which comprises copper powder, the copper powder comprises copper nanoparticles, flaky copper powder and optional spherical copper powder, the copper nanoparticles comprise at least two primary copper nanoparticles connected by face contact.

[0109] The median value of the length of the copper nanoparticles is 150-700 nm, in some embodiments, the median value of the length of the copper nanoparticles is 150-500 nm, in some embodiments, the median value of the length of the copper nanoparticles is 150-400 nm; the median value of the width of the copper nanoparticles is 40-400 nm, in some embodiments, the median value of the width of the copper nanoparticles is 40-200 nm, in some embodiments, the median value of the width of the copper nanoparticles is 40-100 nm.

[0110] In the present application, optional means that it can exist or not exist, for example, in one embodiment, a copper paste of the present application includes copper powder, the copper powder includes copper nanoparticles, flaky copper powder; in another embodiment, a copper paste of the present application includes copper powder, the copper powder includes copper nanoparticles, flaky copper powder and spherical copper powder.

[0111] In the present application, the description of copper nanoparticles, flaky copper powder and spherical copper powder in the copper paste in terms of morphology, size, mass content, tap density and specific surface area can refer to the description of copper nanoparticles, flaky copper powder and spherical copper powder in the aforementioned electrode.

[0112] In this paper, the gap area between the copper nanoparticles, flaky copper powder and spherical copper powder is filled, and the copper nanoparticles are in direct contact with the flaky copper powder and the spherical copper powder. By matching the shape and mass of the flaky copper powder, the spherical copper powder and the copper nanoparticles, the copper particles of various particle sizes and shapes are tightly packed, and the conductive channels between the conductive particles are more unobstructed.

[0113] In this paper, the surface of the flaky copper powder and the spherical copper powder is coated with an antioxidant. By coating the surface of the copper powder with an antioxidant, the copper powder in the copper paste is less likely to be oxidized. The method of forming an antioxidant layer is a conventional method, for example, using an antioxidant in a solution to treat the flaky copper powder or the spherical copper powder after pickling, so that the antioxidant is coated on the copper powder.

[0114] The antioxidant is selected from one or more of the group consisting of fatty acid, amine, phosphoric acid, mercaptan and polymer compounds. The fatty acid compound can include but is not limited to linear or branched C6-C22 saturated fatty acid or unsaturated fatty acid, and these fatty acid compounds can be used alone or in combination with two or more; the amine compound can include but is not limited to linear or branched C6-C22 fatty amine, and these amine compounds can be used alone or in combination with two or more. In addition, the phosphoric acid compound can include but is not limited to phosphorous acid and its ester or salt, hypophosphorous acid and its ester or salt; the mercaptan compound can include but is not limited to ethanethiol, methanethiol, propanethiol, butanethiol, mercaptoethanol, etc. The polymer compound can include but is not limited to polyvinylpyrrolidone, polyvinyl butyral, carboxymethyl cellulose and / or polyacrylic acid.

[0115] In the present application, the copper paste further comprises resin, solvent, curing agent and optional curing agent accelerator, the weight fraction of the copper powder is 70-95 parts, the weight fraction of the resin is 5-15 parts, the weight fraction of the solvent is 5-20 parts, the weight fraction of the curing agent is 1-5 parts, and the weight fraction of the curing accelerator is 0-5 parts. Specifically, in the copper paste, the weight fraction of the copper powder can be any value between 70 parts, 72 parts, 74 parts, 76 parts, 78 parts, 80 parts, 82 parts, 84 parts, 86 parts, 88 parts, 90 parts, 92 parts, 94 parts and 95 parts.

[0116] Specifically, in the copper paste, the weight fraction of the resin can be any value between 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 2 parts, 13 parts, 14 parts and 15 parts.

[0117] Specifically, in the copper paste, the weight fraction of the solvent can be any value between 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 2 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts and 20 parts.

[0118] Specifically, in the copper paste, the weight fraction of the curing agent can be any value between 1 part, 2 parts, 3 parts, 4 parts and 5 parts.

[0119] Specifically, in the copper paste, the weight fraction of the curing agent accelerator can be any value between 0 part, 1 part, 2 parts, 3 parts, 4 parts and 5 parts.

[0120] Specifically, the resin is selected from one or more than two of epoxy resin, acrylic resin and phenolic resin, and preferably is epoxy resin.

[0121] Further, the epoxy resin is thermosetting resin, and is selected from one or more than two 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 type epoxy resin, polyol glycidyl ether type epoxy resin and polybasic acid glycidyl ester type epoxy resin; preferably is bisphenol A type epoxy resin or bisphenol F epoxy resin.

[0122] Specifically, the curing agent is selected from one or more than two of tertiary amine, isocyanate, imidazole, dicyandiamide and acid anhydride curing agent; preferably is tertiary amine; further, the tertiary amine is triethanolamine.

[0123] Further, the isocyanate is selected from one or more than two of Trixene BI 7982 (blocked isocyanate based on HDI), MF-K60X (blocked polyisocyanate HDI curing agent), ketoxime-terminated isocyanate, hexanethiol-terminated hexamethylene diisocyanate, dodecanethiol-terminated diphenyl diisocyanate.

[0124] Specifically, the solvent is selected from one or more than two of divalent acid ester (DBE), diethylene glycol butyl ether, diethylene glycol butyl ether acetate, terpineol, dipropylene glycol butyl ether, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, butyl acetate, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, diethylene glycol dimethyl ether, dimethyl formamide, N-methyl pyrrolidone, diacetone alcohol, dimethyl acetamide, gamma-butyrolactone, butyl carbitol, butyl carbitol acetate, ethyl carbitol, ethyl carbitol acetate, dihydroterpineol, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dihydroterpinyl acetate, diethylene glycol monoethyl ether acetate, and diethylene glycol monobutyl ether acetate.

[0125] Specifically, the curing accelerator can catalyze the curing of the resin, reduce the curing temperature, and shorten the curing time. The curing accelerator is selected from one of quaternary ammonium salts, imidazole esters or imidazolium salts, and substituted ureas. Specifically, the quaternary ammonium salt can be benzyl triethyl ammonium chloride, and the substituted urea 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-methylimidazole urea, etc. The imidazole and its ester or imidazolium salt can be imidazole sulfonate, imidazole phosphate, or imidazole acetate, such as imidazole dibutyl phosphate, 1-ethyl-3-methyl imidazole acetate, 1-ethyl-3-methyl imidazolium methane sulfonate, 1-cyanoethyl-2-undecyl imidazolium based on trimellitic acid ester, 2-methyl imidazolium based on isocyanurate, 2-ethyl-4-methyl imidazolium based on tetraphenyl borate, and 2-ethyl-1,4-dimethyl imidazolium based on tetraphenyl borate.

[0126] In the present application, the copper nanoparticles can improve the rheological properties of the paste, improve the smoothness and uniformity during printing, and have a high surface area, so that they have more contact points with other ingredients (such as resin, solvent, etc.) in the paste, which helps to improve the dispersibility and wettability of the powder in the paste, thus ensuring good printability of the paste.

[0127] The present application also provides a preparation method of the above-mentioned copper paste, comprising the following steps:

[0128] Step one: preparation of copper nanoparticles:

[0129] After mixing the copper salt, the reducing agent, the dispersing agent and the solvent, the mixture is gradually heated to a reaction temperature of 50-100°C, preferably 60-80°C, at a rate of 20-40°C / hour under a nitrogen atmosphere, and the reaction is carried out at the reaction temperature for 2-15 hours, preferably 5-10 hours.

[0130] The copper salt is a monovalent or divalent organic copper salt or inorganic copper salt, which can be selected from one or more of copper sulfate, anhydrous copper sulfate, copper carboxylate (copper formate, copper acetate, copper lactate, copper oxalate, copper tartrate, copper oleate, copper glycolate, copper oleate, copper stearate, copper myristate, copper citrate), copper chloride and copper bromide.

[0131] The reducing agent is selected from at least one of sodium borohydride, hypophosphorous acid, sodium hypophosphite, sodium phosphite, dimethylamine borane, amine borane, ascorbic acid, hydrazine hydrate, formic acid, oleylamine, formaldehyde. Preferably, sodium borohydride or ascorbic acid is used.

[0132] The dispersing agent can use a compound having adsorbability to the primary copper nanoparticles. For example, a high molecular compound such as polyvinyl alcohol, polyacrylic acid, polyvinyl pyrrolidone, hydroxypropyl cellulose, propyl cellulose, ethyl cellulose, etc., a chelating compound such as ethylenediaminetetraacetic acid, iminodiacetic acid long chain amine (e.g., C6-C16 alkyl amine such as hexyl amine, octyl amine, nonyl amine, decyl amine, undecyl amine, dodecyl amine, tridecyl amine, tetradecyl amine, pentadecyl amine, hexadecyl amine, trioctyl amine, dodecyl dimethyl amine), etc. can be used. Preferably, polyvinyl pyrrolidone or polyacrylic acid is used.

[0133] The solvent is selected from one or more of divalent acid ester (DBE), diethylene glycol butyl ether, diethylene glycol butyl ether acetate, terpineol, dipropylene glycol butyl ether and 2,2,4-trimethyl-1,3 pentanediol diisobutyrate, butyl acetate, ethylene glycol monomethyl ether and propylene glycol monomethyl ether.

[0134] The molar ratio of the copper salt to the reducing agent is (1-2):(1-5).

[0135] In some embodiments, the molar ratio of the copper salt to the reducing agent is 1:(1-5), for example, it can be 1:1, 1:2, 1:3, 1:4, 1:5, 2:1, 2:3, 2:4, 2:5.

[0136] Step two: mixing the copper nanoparticles with flaky copper powder, optional spherical copper powder, resin, solvent, curing agent and optional curing agent accelerator to obtain a copper paste.

[0137] The median value of the length of the copper nanoparticles is 150-700 nm, and the median value of the width of the copper nanoparticles is 40-400 nm.

[0138] The ratio and weight percentage of the copper nanoparticles, flaky copper powder, optional spherical copper powder, resin, solvent, curing agent and optional curing agent promoter in step two can refer to the ratio and weight percentage of the copper nanoparticles, flaky copper powder, spherical copper powder, resin, solvent, curing agent and curing agent promoter in the aforementioned copper paste.

[0139] The present application also provides another kind of copper paste, which comprises 70-95 parts by weight of copper powder, 5-15 parts by weight of resin, 1-5 parts by weight of curing agent, 1-3 parts by weight of reducing agent, 1-5 parts by weight of copper salt, 5-20 parts by weight of solvent and 0-5 parts by weight of curing promoter.

[0140] The copper powder comprises flaky copper powder and further comprises spherical copper powder, wherein the mass percentage of the flaky copper powder is 35%-60% and the mass percentage of the spherical copper powder is 35%-60%.

[0141] The parameters of the flaky copper powder and the spherical copper powder in the copper paste of the present application can refer to the aforementioned description.

[0142] The types of the resin, curing agent, solvent and curing promoter in the copper paste of the present application can refer to the types of the resin, curing agent, solvent and curing promoter in the aforementioned copper paste.

[0143] The reducing agent is selected from at least one of hypophosphorous acid, sodium phosphite, hypophosphite salt (such as sodium hypophosphite, potassium hypophosphite, calcium hypophosphite, magnesium hypophosphite), dimethylamine borane, amine borane, glucose, hydrazine hydrate, formic acid, ethylene glycol, oleylamine, formaldehyde and ammonia. Hypophosphorous acid, hypophosphite salt and formic acid are preferably used. The copper salt is a monovalent or divalent organic copper salt or inorganic copper salt, which can be selected from one or more than two of copper sulfate, anhydrous copper sulfate, copper carboxylate (copper formate, copper acetate, copper propionate, copper butyrate, copper lactate, copper oxalate, copper glycolate, copper stearate, copper myristate), copper chloride and copper bromide, and is preferably copper formate or copper citrate.

[0144] Through the combination of the reducing agent and the copper salt, the copper salt is reduced to copper nanoparticles by the reducing agent when the paste is heated and cured. Through the selection of the copper salt and the reducing agent and the control of the reduction process such as curing temperature and curing time, the reduction process is simultaneously carried out with the resin curing process of the paste, so that the space between the flaky powder and / or the spherical powder filled with the reducing agent and the copper salt becomes the reaction space of the reducing agent and the copper salt, and further forms the copper nanoparticles of the shape of the present application, and at the same time the copper nanoparticles connect the flaky copper powder and the spherical copper powder, improving the conductivity of the copper powder.

[0145] In the present application, the surface of the flaky copper powder and the spherical copper powder is coated with an antioxidant, and the types and effects of the antioxidant can refer to the aforementioned description.

[0146] The application also provides a preparation method of the aforementioned copper paste, comprising the following steps:

[0147] Providing copper powder (the copper powder includes flaky copper powder and spherical copper powder);

[0148] Mixing the flaky copper powder, the spherical copper powder, the copper salt, the reducing agent, the resin, the solvent, the curing agent and the curing agent promoter to form the copper paste.

[0149] Specifically, 70-95 parts by weight of the copper powder (wherein the parts by weight of the flaky copper powder is 35-60, and the parts by weight of the spherical copper powder is 35-60), 5-15 parts by weight of the resin, 1-5 parts by weight of the curing agent, 1-3 parts by weight of the reducing agent, 1-5 parts by weight of the copper salt, 5-20 parts by weight of the solvent and 1-5 parts by weight of the curing promoter are mixed and grinded through a three-roll grinder.

[0150] The types and sizes of the flaky copper powder, the spherical copper powder, the copper salt, the reducing agent, the resin, the solvent, the curing agent and the curing agent promoter in the preparation method can refer to the description in the aforementioned copper paste.

[0151] The application also provides an electrode, wherein the electrode is prepared by the aforementioned copper paste.

[0152] The application also provides a preparation method of the aforementioned electrode, comprising the following steps:

[0153] The aforementioned copper paste is heated and cured in a nitrogen atmosphere to obtain the electrode. The curing temperature is 100-200°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc., and the curing time is 10-60 minutes, for example, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, etc.

[0154] The application also provides a preparation method of the aforementioned electrode, comprising the following steps: the copper paste prepared in advance is screen printed on a battery sheet (for example, HJT / HBC), the grid line width is 40-120 μm, and then the copper paste is heated and cured in a nitrogen oven, the curing temperature is generally 100-200°C, and the curing time is 10-60 minutes, so as to form an electrode grid line, and the electrode grid line can be characterized by SEM.

[0155] The application also provides a solar cell, wherein the solar cell comprises the aforementioned electrode, and the electrode and the surface of the solar cell have a contact interface.

[0156] In the present application, the region near the contact interface refers to the region 3 microns above the contact interface; the electrode body portion has the same meaning as the electrode body portion in the aforementioned electrode.

[0157] Further, the copper nanoparticles are contained in the region near the contact interface, the surface of the copper nanoparticles in the present application has more contact points, which can further increase the contact area of the electrode and the surface of the solar cell, reduce the contact resistance of the electrode, and improve the current collection capability of the solar cell.

[0158] The surface of the solar cell has a textured structure, and the electrode is located on the upper portion of the textured structure of the solar cell.

[0159] In some embodiments, the solar cell has a textured structure for light trapping to increase the solar radiation collection effect. The textured structure is a surface with regular or irregular shape for scattering incident light and reducing the amount of light reflected back from the surface of the solar cell, which can be a pyramid structure.

[0160] When the electrode contacts the pyramid textured structure of the solar cell, the contact interface is located on the surface of the textured structure, and the region near the contact interface refers to the region 3 microns above the base of the pyramid textured structure.

[0161] In some embodiments, in the electrode body portion, the volume content of the nanoscale copper powder in the region near the contact interface is greater than the volume content in other regions of the electrode.

[0162] In the present application, by controlling the volume content of the nanoscale copper powder in the region near the contact interface to be greater than the volume content in other regions of the electrode, the normal projection area of the nanoscale copper powder on the contact interface is greater than the normal projection area of the micrometer-scale flaky copper powder on the contact interface, the nanoscale copper powder has a larger specific surface area and surface activity than the micrometer-scale flaky copper powder, the adhesion of the electrode to the surface of the solar cell is enhanced, the contact resistance of the electrode is reduced, and the current collection capability of the solar cell is improved.

[0163] In the present application, the nanoscale copper powder refers to copper particles with a particle size distribution of 1-800 nm, which can include copper nanoparticles and / or nanosphere powder.

[0164] In some embodiments, the surface of the flaky copper powder is attached to the surface of the electrode in a substantially horizontal state.

[0165] In the present application, the electrode surface refers to the tangent of the electrode surface at the intersection of the flaky copper powder and the electrode.

[0166] In the present application, flaky copper powder with better oxidation resistance is used to adhere to the surface of the electrode in a near-horizontal or horizontal state, thereby improving the oxidation resistance of the electrode as a whole when placed in air and reducing the resistivity of the electrode.

[0167] Further, the flaky copper powder is arranged in a direction with an angle a with the surface of the electrode, 0°≤a≤50°. As can be seen from FIG. 6, a is the angle of inclination of the flaky copper powder on the surface of the electrode relative to the surface of the electrode.

[0168] In this context, 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 electrode is selected to draw a tangent to the surface of the electrode, and the angle between the horizontal plane of the flaky copper powder and the tangent is obtained to obtain an angle a. According to the same method, more than 10 flaky copper powders in different regions of the test sample are measured for the angle a, and the average value of all measured angles a is calculated. 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 test sample areas or quantities based on actual conditions.

[0169] In some embodiments, 0°≤a≤40°.

[0170] In some embodiments, 0°≤a≤35°.

[0171] In some embodiments, 0°≤a≤30°.

[0172] In some embodiments, 0°≤a≤25°.

[0173] In some embodiments, 5°≤a≤40°.

[0174] In some embodiments, 5°≤a≤35°.

[0175] In some embodiments, 5°≤a≤30°.

[0176] In some embodiments, 5°≤a≤25°.

[0177] Specifically, a can be 50°, 45°, 42°, 40°, 38°, 35°, 32°, 30°, 28°, 25°, 22°, 20°, 18°, 15°, 12°, 10°, 8°, 5°, etc.

[0178] Further, the area of the orthographic projection of the flaky copper powder on the surface of the electrode on the surface of the electrode accounts for 30%-65% of the surface area of the electrode.

[0179] In the present application, the difference in shape between flaky and spherical powders can be further utilized to control the proportion of the surface area of flaky copper powder on the electrode surface, thereby improving the adhesion of flaky powder on the surface and ensuring a high copper powder filling rate of the electrode, and further reducing the resistivity of the electrode.

[0180] The area of the flaky copper powder on the electrode surface is measured by SEM (scanning electron microscope). The electrode surface area is measured by a 3D microscope, which measures the shape and size of the electrode and then calculates the surface area. For example, when the electrode is a grid line of a solar cell, the cross section of the electrode is trapezoidal or trapezoidal-like, the cross section is perpendicular to the extension direction of the electrode, the upper base a, the lower base b and the height h of the trapezoid are measured, and the length l of the electrode is measured, and the surface area of the electrode is calculated by the following formula:

[0181] Specifically, the proportion of the area of the flaky copper powder on the electrode surface to the electrode surface area can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, etc.

[0182] Further, the solar cell is selected from one of a BC cell, an HJT cell and a perovskite / silicon stacked cell.

[0183] In some embodiments, the solar cell is a crystalline silicon cell, and there is a conductive barrier layer between the electrode and the crystalline silicon cell.

[0184] The diffusion of copper ions into the crystalline silicon cell can have a negative impact on the performance of the cell. Copper ions can affect the properties of the PN junction of the crystalline silicon cell, causing dark point leakage (dark leakage) and open circuit voltage drop of the cell. This will result in a decrease in the overall efficiency and performance of the cell. In some embodiments, the conductive barrier layer can be an oxide (such as aluminum oxide and other metal transparent conductive oxides), a metal nitride (such as titanium nitride), or a metal (such as silver), graphene, which has good barrier properties. These conductive barrier layers can also be suitable conductive polymer films or other materials that can effectively prevent the diffusion of copper ions into the silicon.

[0185] In some embodiments, the conductive barrier layer has a thickness of 5-500 nm, for example, it can be any value between 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm.

[0186] Examples

[0187] The experimental methods used in the following examples are conventional methods unless otherwise specified.

[0188] The materials, reagents, etc. used in the following examples can be obtained commercially unless otherwise specified.

[0189] Example 1-1

[0190] The preparation method of the electrode of the present example comprises the following steps:

[0191] Step one: Preparation of copper nanoparticles: mix ascorbic acid, polyvinylpyrrolidone and ethanol to prepare a reducing agent solution, then drop the ethanol solution of copper citrate into the reducing agent solution, gradually heat to 70°C (reaction temperature) under nitrogen protection, the heating rate is 20°C / hour, after 5 hours of reaction, separate and purify to obtain copper nanoparticles, which are formed by the face contact connection of two or more primary copper nanoparticles.

[0192] Step two: mix 1 part by weight of the above-prepared copper nanoparticles with a solution of 50 parts by weight of flaky copper powder, 40 parts by weight of spherical copper powder, 2 parts by weight of hydrogenated bisphenol A type epoxy resin, 1.5 parts by weight of imidazole dibutyl phosphate, 1.5 parts by weight of blocked isocyanate and 5 parts by weight of diethylene glycol butyl ether solvent, and grind through a three-roll grinder to obtain a copper paste.

[0193] Step three: screen print the copper paste on a solar cell sheet to form a grid line with a width of 70μm, and then heat and cure in a nitrogen oven at a curing temperature of 190°C to obtain an electrode grid line. The microstructure of the obtained grid line is observed by scanning electron microscope, as shown in Figure 3. As can be seen from Figure 3, the electrode grid line contains copper nanoparticles, flaky copper powder and spherical copper powder, wherein the copper nanoparticles are formed by the face contact connection of two or more primary copper nanoparticles, and contain linear copper particles, V-shaped copper particles and polygonal copper particles, and the copper nanoparticles are distributed between the large particle flaky copper powder and the spherical copper powder; in the region near the contact interface of the pyramid suede structure (the region above 5 microns from the bottom of the tower), the content of the nanoscale copper powder accounts for the majority, and the volume content of the nanoscale copper powder in the region near the contact interface of the pyramid suede structure is greater than that in other regions of the electrode.

[0194] The copper paste is cured into a copper film by screen printing through a screen, and the sheet resistance R (mΩ) of the copper film is tested by a four-probe sheet resistance meter, and the film thickness t (μm) is measured by a screw micrometer, and the resistivity p = R x t / 10.

[0195] The parameters of the electrode grid line and the copper paste are shown in Table 1.

[0196] The electrode of Example 1-2-Example 1-3 is different from the electrode of Example 1-1 in that the parameters of the flaky copper powder, the spherical copper powder, and the copper nanoparticles are all different, and other parameters are the same. The specific parameters are shown in Table 1.

[0197] The electrode of Example 1-4 is different from the electrode of Example 1-1 in that the parameters of the flaky copper powder are different, and other parameters are the same. The specific parameters are shown in Table 1.

[0198] The electrode of Example 1-5 is different from the electrode of Example 1-1 in that the parameters of the spherical copper powder are different, and other parameters are the same. The specific parameters are shown in Table 1.

[0199] The electrode of Comparative Example 1-1 is different from the electrode of Example 1-1 in that the parameters of the copper nanoparticles are different, and other parameters are the same. The specific parameters are shown in Table 1.

[0200] The electrode of Comparative Example 1-2 is different from the electrode of Example 1-1 in that there is no flaky copper powder, and other parameters are the same. The specific parameters are shown in Table 1.

[0201] Table 1 shows the parameters of each example and comparative example

[0202] Summary: As can be seen from Table 1, the copper paste described in the present application, and the copper nanoparticles in the present application fill the gap 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. Compared with irregular copper nanoparticles with larger particle size formed by aggregation, the copper nanoparticles in the present application make the conductive channel between the conductive particles more unobstructed, and the filling of the copper nanoparticles makes the grid line structure prepared from the copper paste more dense, greatly reducing the bulk resistance of the grid line.

[0203] Example 2-1

[0204] The preparation method of the copper paste of the present example is as follows:

[0205] 50 parts by weight of flaky copper powder and 40 parts by weight of spherical copper powder, 5 parts by weight of hydrogenated bisphenol A type epoxy resin as a resin, 1.5 parts by weight of imidazole dibutyl phosphate as a curing accelerator, 1.5 parts by weight of blocked isocyanate as a curing agent, 1 part by weight of formic acid as a reducing agent, 1 part by weight of copper oxalate as a copper salt, and 5 parts by weight of diethylene glycol butyl ether solvent are provided; after the above materials are prepared in a certain proportion, the copper paste is prepared by a three-roll mill.

[0206] The prepared copper paste was printed on the battery sheet by screen printing, the grid line width was 70 μm, and then the electrode grid line was obtained by heating and curing in a nitrogen oven at a curing temperature of 190 °C. The microstructure of the obtained grid line was observed by scanning electron microscope, as shown in Figures 4-5. As shown in Figure 4, the electrode grid line contains copper nanoparticles, flaky copper powder and spherical copper powder, wherein the copper nanoparticles are formed by the fusion connection of two or more primary copper nanoparticles, and contain linear copper particles, V-shaped copper particles and polygonal copper particles, and the copper nanoparticles are distributed between the large particle flaky copper powder and the spherical copper powder. As shown in Figure 5, the surface of the flaky copper powder is attached to the electrode surface in a substantially horizontal state.

[0207] The copper paste was cured into a copper film by screen printing with a screen, and the square resistance R (mΩ) of the copper film was tested by a four-probe square resistance meter, and the film thickness t (μm) was measured by a screw micrometer, and the resistivity p = R x t / 10. The parameters of the electrode grid line are shown in Table 2.

[0208] Example 2-2 and Example 2-3 are different from the electrode of Example 2-1 in that the parameters of the flaky copper powder, the spherical copper powder and the copper nanoparticles are different, and the other parameters are the same. The specific parameters are shown in Table 2.

[0209] Example 2-4 is different from the electrode of Example 2-1 in that the parameters of the flaky copper powder are different, the reducing agent in the preparation process of the copper nanoparticles is different, and the other parameters are the same. The specific parameters are shown in Table 2.

[0210] Example 2-5 is different from the electrode of Example 2-1 in that the parameters of the spherical copper powder are different, and the other parameters are the same. The specific parameters are shown in Table 2.

[0211] Example 2-6 is different from the electrode of Example 2-1 in that no spherical copper powder is added, and the other parameters are the same. The specific parameters are shown in Table 2.

[0212] Comparative Example 2-1 is different from the electrode of Example 2-1 in that the parameters of the copper nanoparticles are different, and the other parameters are the same. The specific parameters are shown in Table 2.

[0213] Comparative Example 2-2 is different from the electrode of Example 2-1 in that no flaky copper powder is added and the parameters of the copper nanoparticles are different, and the other parameters are the same. The specific parameters are shown in Table 2.

[0214] Table 2 shows the parameters of each example and comparative example

[0215] Summary: As can be seen from Table 2, the copper paste described in the present application, by the combination of reducing agent and copper salt, makes the copper salt reduced to the copper nanoparticles of the present application by the reducing agent when the paste is heated and solidified, thus filling the voids between the flaky and / or spherical powders, directly contacting the flaky copper powder and the spherical copper powder, relative to the spherical copper nanoparticles of similar particle size, the copper nanoparticles of the present application make the conductive channels between the conductive particles more unobstructed, and the filling of the copper nanoparticles makes the grid line structure prepared from the copper paste more dense, greatly reducing the bulk resistance of the grid line.

[0216] Although the embodiments of the present application are described above, the present application is not limited to the specific embodiments and application fields described above, and the specific embodiments described above are merely illustrative, instructive, and not limiting. A person of ordinary skill in the art can make many forms under the inspiration of the present specification and without departing from the scope protected by the claims of the present application, and these all belong to the protection of the present application.

Claims

1. An electrode, wherein, The copper nanoparticles include at least two primary copper nanoparticles connected by face contact.

2. The electrode of claim 1, wherein, The copper nanoparticles have a median length of 150-700 nm and a median width of 40-400 nm.

3. The electrode of claim 1, wherein, The copper nanoparticles are linear copper particles formed by at least two primary copper nanoparticles connected, and / or The copper nanoparticles 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, formed by at least two primary copper nanoparticles connected at an angle.

4. The electrode of claim 1, wherein, The electrode further includes spherical copper powder.

5. The electrode of claim 4, wherein, In the copper powder, the mass percentage of the copper nanoparticles is 0.5-15%, the mass percentage of the flaky copper powder is 35-60%, and the mass percentage of the spherical copper powder is 35-60%.

6. The electrode of claim 4, wherein, The spherical copper powder has a median particle size of 100-500 nm.

7. The electrode of claim 4, wherein, The flaky copper powder has a tap density of 4.4-5 g / ml, and the spherical copper powder has a tap density of 4.3-4.9 g / ml; or 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.

8. The electrode of claim 1, wherein, The flaky copper powder has a median diameter of 2-8 μm and a median thickness of 100-500 nm.

9. The electrode of claim 1, wherein, The electrode includes a main body portion and a peripheral portion on both sides of the main body portion, wherein the width of the peripheral portion on either side is not more than 5-50% of the width of the main body portion; and the median particle size of the copper powder in the peripheral portion is smaller than the median particle size of the copper powder in the main body portion.

10. The electrode of claim 9, wherein, The copper powder in the peripheral portion includes the copper nanoparticles, and the copper powder in the main body portion includes the flaky copper powder and the copper nanoparticles.

11. The electrode of claim 9, wherein, The width of the main body portion is 30-120 μm, and / or the width of the peripheral portion is 1-60 μm.

12. The electrode according to any one of claims 1 to 11, wherein, The electrode is prepared by screen printing.

13. A copper paste, wherein, The copper powder includes copper nanoparticles, flaky copper powder, and optionally spherical copper powder, wherein the copper nanoparticles include at least two primary copper nanoparticles connected by face contact.

14. The copper paste of claim 13, wherein, The copper nanoparticles have a median length of 150-700 nm and a median width of 40-400 nm.

15. The copper paste of claim 13, wherein, The copper nanoparticles are linear copper particles formed by at least two primary copper nanoparticles connected, and / or The copper nanoparticles 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, formed by at least two primary copper nanoparticles connected at an angle.

16. The copper paste of claim 13, wherein, The copper powder further includes spherical copper powder, and in the copper powder, the mass percentage of the copper nanoparticles is 0.5-15%, the mass percentage of the flaky copper powder is 35-60%, and the mass percentage of the spherical copper powder is 35-60%.

17. The copper paste of claim 16, wherein, The flaky copper powder has a median diameter of 2-8 μm and a median thickness of 100-500 nm; or The median value of the particle size of the spherical copper powder is 100-500 nm.

18. The copper paste of claim 16, wherein, 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; or 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.

19. The copper paste of any one of claims 13-18, wherein, The copper paste further comprises resin, solvent, curing agent and optional curing accelerator, the weight fraction of the copper powder is 70-95 parts, the weight fraction of the resin is 5-15 parts, the weight fraction of the curing agent is 1-5 parts, the weight fraction of the solvent is 5-20 parts, and the weight fraction of the curing accelerator is 0-5 parts; or The resin is selected from one or more than two of epoxy resin, acrylic resin and phenolic resin; or The curing agent is selected from one or more than two of tertiary amine, isocyanate, imidazole, dicyandiamide and acid anhydride curing agent; or The optional curing accelerator is quaternary ammonium salt, imidazole ester, imidazolium salt or substituted urea; or The solvent is selected from one or more than two of divalent acid ester (DBE), diethylene glycol butyl ether, diethylene glycol butyl ether acetate, terpineol, dipropylene glycol butyl ether, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, butyl acetate, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, diethylene glycol dimethyl ether, dimethylformamide, N-methylpyrrolidone, diacetone alcohol, dimethylacetamide, γ-butyrolactone, butyl carbitol, butyl carbitol acetate, ethyl carbitol, ethyl carbitol acetate, dihydromenthols, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, dihydroterpine acetate, diethylene glycol monoethyl ether acetate and diethylene glycol monobutyl ether acetate.

20. An electrode, wherein, The electrode is obtained by screen printing the copper paste of any one of claims 13-19.

21. A method of preparing the copper paste of any one of claims 13-19, wherein, The method comprises the following steps: Preparation of copper nanoparticles; Mixing of the copper nanoparticles with flaky copper powder, spherical copper powder, resin, solvent, curing agent and optional curing accelerator to obtain copper paste; The copper nanoparticles comprise at least two primary copper nanoparticles connected in a face-to-face manner.

22. A solar cell, wherein, The electrode of any one of claims 1-12 or 20 is in contact with the surface of the solar cell.

23. The solar cell of claim 22, comprising the copper nanoparticles in a region near the contact interface.

24. The solar cell of any of claims 22-23, wherein, The surface of the solar cell has a textured structure, and the electrode is located on the upper portion of the textured structure of the solar cell.

25. The solar cell of any of claims 22-23, wherein, In the main body portion of the electrode, the volume content of the nanoscale copper powder in the region near the contact interface is greater than that in other regions of the electrode.

26. The solar cell of claim 22, wherein, The surface of the flaky copper powder adheres to the surface of the electrode in a substantially horizontal state.

27. The solar cell of claim 26, wherein, The flaky copper powder is arranged in a direction forming an angle α with the surface of the electrode, where 0°≤α≤50°.

28. The solar cell of claim 26, wherein, The area of the flaky copper powder adhering to the surface of the electrode in the orthographic projection of the surface of the electrode accounts for 30%-65% of the surface area of the electrode.

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