A copper-based paste, a topcon cell and a preparation method thereof

Abstract

The application relates to the technical field of solar cells, in particular to a copper-based paste, a TOPCon cell and a preparation method thereof. The copper-based paste comprises: copper powder, which is densified in a sintering process as a main powder body to form an electrically conductive phase; a hydrogen storage material, which is used for releasing hydrogen elements in the sintering process to locally form a reducing atmosphere to prevent oxidation of the copper powder; the hydrogen storage material comprises a liquid hydrogen storage material; and an organic carrier, which provides fluidity and thixotropy for the paste. Compared with solid hydrogenated metal particles, the liquid hydrogen storage material can be more uniformly dispersed in the copper-based paste and can form a coating on the copper powder, so that the release of hydrogen elements in the copper-based paste is more uniform, thereby comprehensively inhibiting the oxidation of the copper powder. Meanwhile, the dehydrogenation amount of the liquid hydrogen storage material is much higher than that of the solid hydrogenated metal particles, and the release amount of hydrogen elements can be increased by several times under the same mass, thereby providing more sufficient oxidation protection for the copper powder.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solar cells, in particular to a copper-based paste, a TOPCon (Tunnel Oxide Passivated Contact) cell and a preparation method thereof. BACKGROUND

[0002] TOPCon is a selective contact structure formed by the combination of an ultra-thin tunnel oxide layer and a highly doped polysilicon. The TOPCon cell based on this structure is a high-efficiency passivated contact solar cell based on an N-type silicon substrate. The cell structure is as follows from top to bottom: an anti-reflection layer (silicon nitride), a passivation layer (aluminum oxide), P+ type monocrystalline silicon, N type monocrystalline silicon, a tunnel oxide layer (ultra-thin silicon oxide), N+ type polysilicon, and a passivation layer (silicon nitride). The traditional preparation method of the TOPCon cell is to use screen printing technology to print high-temperature silver paste on the front and back surfaces of the cell, and then to sinter the cell at a high temperature of 700-800℃. In this process, the glass powder in the high-temperature silver paste penetrates the anti-reflection layer and the passivation layer through chemical etching at high temperature, realizing Ohmic contact between the metal electrode and the silicon substrate, and finally forming a reliable silver / silicon conductive path. However, the silver consumption of this preparation method is as high as 10 mg / W. With the continuous rise of silver prices, the preparation cost of the TOPCon cell has increased significantly, which has put great pressure on the sustainable development of the industry. To address the problem of silver consumption cost, two alternative solutions have been explored in the industry: one is to use silver-coated copper materials to replace pure silver, and the other is to prepare copper grid lines through electroplating. However, the silver-coated copper solution has significant limitations. The sintering temperature needs to be strictly controlled. If it is too high, the silver shell of the silver-coated copper particles will fall off, and the exposed copper will be oxidized, which will seriously affect the performance of the cell, and this solution has not achieved complete silver elimination. The electroplated copper grid line solution faces the problems of complex process, high equipment investment, and environmental pollution caused by chemical reagents. If the silver paste is directly replaced by a copper-based paste, copper is easily oxidized at high temperatures, which will also seriously affect the performance of the cell. SUMMARY

[0003] The first aspect of the present application aims to provide a copper-based paste to solve the problem of easy oxidation of existing copper-based paste during sintering.

[0004] The second aspect of the present application aims to provide a TOPCon cell, and the copper-based conductive grid line of the TOPCon cell is prepared by the above-mentioned copper-based paste.

[0005] The third aspect of the present application aims to provide a preparation method of the above-mentioned TOPCon cell, which can solve the problems of complex preparation process, high cost and environmental pollution of the copper grid line of the TOPCon cell.

[0006] To achieve the above object, the present application provides the following technical solutions: a copper-based paste, comprising: copper powder, as a main powder, densified in a sintering process to form a conductive phase;

[0007] hydrogen storage material, for releasing hydrogen elements in the sintering process to form a reducing atmosphere in the gate line to prevent oxidation of the copper powder; the hydrogen storage material comprises a liquid hydrogen storage material;

[0008] organic carrier, providing rheological properties and thixotropy for the paste;

[0009] In the copper-based paste, the content of the copper powder is any value in the range of 60%-90% by mass percentage, the content of the organic carrier is any value in the range of 5%-30% by mass percentage, and the content of the hydrogen storage material is any value in the range of 0.1%-10% by mass percentage.

[0010] Further, a catalytic metal for promoting the release of hydrogen elements by the hydrogen storage material is further included;

[0011] In the copper-based paste, the content of the catalytic metal is 0.1%-3% by mass percentage.

[0012] Further, the liquid hydrogen storage material is any one or more of methylcyclohexane, dibenzyltoluene, perhydroethylcarbazole, and cyclohexane.

[0013] Further, the copper powder comprises first copper powder and second copper powder, the average particle size of the first copper powder is any value in the range of 1 µm-50 µm, the average particle size of the second copper powder is any value in the range of 10 nm-500 nm, the second copper powder is filled in the gaps of the first copper powder particles to improve the electrical conductivity of the conductive phase; the mass of the second copper powder is not more than 30% of the total amount of the copper powder.

[0014] Further, the organic carrier comprises a resin and an organic solvent; the resin is a conductive resin and / or a thermoplastic resin, and the organic solvent is a hydrocarbon compound with a boiling point not exceeding 300°C.

[0015] The present application also provides a TOPCon cell, comprising: a TOPCon cell piece and a copper-based conductive gate line;

[0016] A metal conductive seed layer is deposited on the TOPCon cell piece, and the copper-based conductive gate line is arranged on the TOPCon cell piece; the copper-based conductive gate line is prepared by printing and sintering from the above-mentioned copper-based paste.

[0017] The present application also provides a preparation method of the above-mentioned TOPCon cell, comprising the following steps:

[0018] Step S1, obtaining a TOPCon cell and depositing a metal conductive seed layer on the TOPCon cell;

[0019] Step S2, printing the copper-based paste on the metal conductive seed layer;

[0020] Step S3, performing a segmented sintering process on the TOPCon cell printed with the copper-based paste to form a copper-based conductive grid line on the TOPCon cell, thereby obtaining a TOPCon cell;

[0021] The segmented sintering process includes a low-temperature annealing stage and a medium-temperature sintering stage, which are used to gradually solidify the copper-based paste in stages to form a copper-based conductive grid line.

[0022] Further, the temperature range of the low-temperature annealing stage is 100-200 DEG C, which is used to remove the organic carrier and preliminary solidification;

[0023] The temperature range of the medium-temperature sintering stage is 300-500 DEG C, which is used to release hydrogen elements from the hydrogen storage material and densify the copper-based paste to form a copper-based conductive grid line.

[0024] Further, the deposition method of the metal conductive seed layer includes: opening the anti-reflection layer and the passivation layer on the TOPCon cell by laser process to form a laser opening on the TOPCon cell; and depositing a metal seed layer at the laser opening by chemical plating or electroplating process.

[0025] Further, the material of the metal seed layer is a base metal.

[0026] The copper-based paste provided by the present application introduces a liquid hydrogen storage material. Compared with solid hydrogenated metal particles, the liquid hydrogen storage material can be more uniformly dispersed in the copper-based paste and can form a coating on the copper powder, making the release of hydrogen elements in the copper-based paste more uniform, thereby enabling all-round inhibition of copper oxidation. At the same time, the dehydrogenation amount of the liquid hydrogen storage material is much higher than that of the solid hydrogenated metal particles, and the release amount of hydrogen elements can be increased by several times under the same mass, thereby providing more sufficient oxidation protection for the copper powder. The liquid hydrogen storage material can also inhibit copper oxidation while promoting densification between copper particles, thereby further reducing the line resistance and improving the conductivity of the copper grid line.

[0027] The copper-based paste provided by the present application significantly reduces the dehydrogenation temperature of the hydrogen storage material by introducing a catalytic metal, ensuring that it can effectively release hydrogen elements at a lower temperature, thereby significantly reducing the risk of copper powder oxidation during the heating process and as much as possible to completely inhibit the oxidation of copper powder.

[0028] The preparation method of the TOPCon cell provided in the present application first forms a laser opening on the surface of the TOPCon cell sheet through a laser process and deposits a metal seed layer to build a physical barrier to prevent copper from diffusing to the silicon substrate and avoid performance degradation of the cell; then copper-based paste is used to replace silver paste for printing and sintering to obtain copper-based conductive grid lines with comparable conductivity and stability to silver grid lines. The preparation method has low preparation cost, and compared with the electroplating copper process, it does not produce electroplating waste liquid during the preparation process, reducing environmental pollution, providing a sustainable development path for the TOPCon cell industry, and is expected to promote the comprehensive popularization of high-efficiency solar cells.

[0029] The above description is only a summary of the technical solutions of the present application. In order to more clearly understand the technical means of the present application, and to implement the content of the description, the following will be described in detail with the preferred embodiments of the present application and with the aid of the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Reaction principle diagram when the copper-based paste of the present application is sintered;

[0031] Figure 2 Thermogravimetric analysis diagram when the copper-based paste of embodiment 1 of the present application is sintered;

[0032] Figure 3 Microstructure diagram of the copper-based conductive grid line shown in embodiment 2 of the present application;

[0033] Figure 4 Microstructure diagram of the copper-based conductive grid line shown in embodiment 3 of the present application;

[0034] Figure 5 Structure diagram of the TOPCon cell shown in embodiment 3 of the present application;

[0035] Figure 6 Structure diagram of the TOPCon cell shown in comparative example 1 of the present application;

[0036] REFERENCE NUMERALS:

[0037] 1, copper powder particles; 2, liquid mixture; 3, retained oxygen; 4, atmospheric oxygen; 5, surface oxide; 6, sintering neck; 7, nickel seed layer; 8, copper-based grid line; 9, silver grid line; 10, TOPCon cell sheet; 11, silicon nitride; 12, aluminum oxide; 13, P+-type monocrystalline silicon; 14, N-type monocrystalline silicon; 15, ultra-thin silicon oxide; 16, N+-type polycrystalline silicon. DETAILED DESCRIPTION

[0038] The technical solutions of the present application will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0039] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0040] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict.

[0041] The present application provides a copper-based paste, which comprises copper powder, hydrogen storage material and organic carrier. The copper powder is used as the main powder and gradually densifies to form a conductive phase during sintering. The hydrogen storage material is used to release hydrogen elements during sintering, form a reducing atmosphere in the grid lines, and have a reduction reaction with the oxygen elements on the surface of the copper powder, thereby effectively preventing the oxidation of the copper powder.

[0042] The hydrogen storage material can be selected from solid hydrogenated metal particles or liquid hydrogen storage material. The liquid hydrogen storage material can be selected from one or more of liquid hydrocarbons such as methylcyclohexane, dibenzyltoluene, perhydroethylcarbazole, cyclohexane, etc. When the liquid hydrogen storage material is used, the liquid hydrogen storage material is heated to a temperature above the boiling point of the liquid hydrogen storage material, and the liquid hydrogen storage material is vaporized to form a hydrogen atmosphere in the grid lines. Figure 1As shown, the liquid hydrogen storage material in the copper-based paste is mixed with the organic solvent to form a liquid mixture 2, which penetrates between the copper powder particles 1 and can adhere to the surface of the copper powder particles 1. During sintering, the hydrogen element can be released to remove the trapped oxygen 3 in the copper-based paste and reduce the surface oxide 5 on the surface of the copper powder particles 1, while also preventing the atmospheric oxygen 4 in the sintering atmosphere from oxidizing the copper powder, thereby inhibiting the oxidation of the copper powder. After sintering is completed, the liquid hydrogen storage material is completely converted into a gas and does not remain between the copper powder particles, thereby enabling more obvious sintering necks 6 to be formed between the copper powder particles 1. The hydrogenated metal particles can be selected from one or more of MgH2, CrH2, ZnH2, BaH2, CaH2, CuH, NiH, LiH, NaH, KH, and the like, and the particle size of the hydrogenated metal particles is not greater than the particle size of the copper powder. To ensure the conductivity of the copper-based conductive grid line or effectively inhibit the oxidation of the copper powder, CuH particles of the same metal element as the main powder are preferably used, or MgH2 powder with strong hydrogen storage capacity is used. However, if hydrogenated metal particles other than copper hydride particles are used as the hydrogen storage material, there may be a problem of balancing the effect of inhibiting the oxidation of the copper powder and its resistivity, i.e., when the amount of hydrogenated metal particles added is relatively large, the reducing atmosphere generated by the dehydrogenation reaction of the hydrogenated metal particles can more effectively inhibit the oxidation of the copper powder, but excessive metal particles remaining can form more conductive inclusions, resulting in a significant increase in the resistivity of the copper-based conductive grid line; conversely, if the amount of hydrogenated metal added is reduced to reduce the resistivity, the inhibiting effect on the oxidation of the copper powder will be weakened, especially in the early stage of high-temperature sintering, which can easily cause local oxidation, thereby damaging the conductivity of the grid line and the long-term reliability of the battery. In addition, the hydrogen storage material can also be a composite system of solid copper hydride particles and liquid hydrogen storage material. This composite system not only releases active hydrogen to remove oxygen elements and prevent the oxidation of the copper powder during sintering, but the copper particles formed by the decomposition of the copper hydride particles during sintering can also serve as additional conductive connection points, further improving the conductivity.

[0043] In one embodiment, to further optimize the performance of the hydrogen storage material and ensure that it can effectively release hydrogen elements at a lower temperature, a catalytic metal can be introduced into the copper-based slurry. The catalytic metal is any one or more of platinum, nickel, copper, cobalt, iron, etc. Through this measure, the dehydrogenation temperature of the hydrogen storage material can be significantly reduced, the release of hydrogen elements under milder conditions can be promoted, and the temperature required for the subsequent sintering process can be effectively reduced, thereby significantly reducing the risk of oxidation of copper powder during the heating process, as much as possible to completely inhibit the oxidation of copper powder, and improving the production efficiency and energy utilization rate. The content of the catalytic metal in the copper-based slurry is 0.1%-3% by mass percentage. This proportion can ensure the significance of the catalytic effect, and can avoid the introduction of inclusions and other potential side effects caused by excessive addition.

[0044] In one embodiment, the copper powder at least includes first copper powder with an average particle size of 1 µm-50 µm. Since the contact between copper powder particles is more compact under the premise that the copper powder is not oxidized, the copper-based conductive grid line formed by sintering the copper-based slurry as raw material has better conductivity. Therefore, in order to make the copper-based conductive grid line obtained by sintering have a dense conductive network structure and significantly improve its conductivity, the copper powder can also include second copper powder with an average particle size of 10 nm-500 nm. The particle size of the second copper powder is significantly smaller than that of the first copper powder, so that the second copper powder fills the gaps between the first copper powder particles, thereby significantly improving the conductivity of the conductive phase. The mass of the second copper powder is not more than 30% of the total amount of the copper powder, so as to balance the rheology of the slurry and the conductivity after sintering. In some embodiments, copper hydride particles with a particle size significantly smaller than that of the first copper powder can also be selected as the second copper powder and added to the copper-based slurry, so as to fill the gaps between the first copper powder particles and release hydrogen elements during the sintering process to inhibit the oxidation of the copper powder.

[0045] The application also provides a TOPCon cell, which includes a TOPCon cell sheet and a copper-based conductive grid line disposed on the TOPCon cell sheet, and the copper-based conductive grid line is prepared by printing and sintering solidification of the above-mentioned copper-based slurry.

[0046] Since copper has high diffusivity, in the process of preparing and using the TOPCon cell, high temperature conditions will cause copper to diffuse into silicon, thereby causing the performance of the cell to decrease and the service life to be shortened, and there is a reliability risk. To inhibit the diffusion of copper into silicon, a metal conductive seed layer can be deposited on the TOPCon cell sheet before printing the copper-based conductive grid line on the TOPCon cell sheet.

[0047] The application also provides a preparation method of the above-mentioned TOPCon cell, which includes the following steps:

[0048] Step S1, obtaining a TOPCon cell and depositing a metal conductive seed layer with a relatively low price on the TOPCon cell, such as a metal seed layer with a material of one of nickel, titanium, aluminum, chromium, etc. In this application, the metal seed layer is preferably a nickel seed layer. The deposition method of the metal conductive seed layer includes: opening the anti-reflection layer and the passivation layer on the TOPCon cell by using a laser process, forming a laser opening on the TOPCon cell, and in this process, the opening size, depth and distribution need to be accurately controlled to minimize the impact on the photoelectric performance of the cell; and depositing a metal seed layer at the laser opening by using a chemical plating or electroplating process.

[0049] Step S2, first printing the above-mentioned copper-based paste on the deposited metal conductive seed layer, then placing the printed TOPCon cell into a sintering device for segmented sintering treatment, forming a copper-based conductive grid line on the TOPCon cell, and finally obtaining a TOPCon cell. The segmented sintering treatment includes a low-temperature annealing stage and a medium-temperature sintering stage, so that the copper-based paste is gradually solidified in stages to form a copper-based conductive grid line. The processing temperature of the low-temperature annealing stage is controlled in the range of 100-200℃, such as constant temperature conditions at 100℃, 120℃, 150℃, 175℃, etc. for low-temperature annealing treatment, which is used to remove the organic carrier and preliminary solidification, and to discharge the bubbles and stress between the copper powder particles. The processing temperature of the medium-temperature sintering stage is controlled in the range of 300-500℃, such as constant temperature conditions at 350℃, 425℃, 450℃, 500℃, etc. for medium-temperature sintering treatment, which is used to release hydrogen element by dehydrogenation of the hydrogen storage material to inhibit the oxidation of copper powder, to completely volatilize and remove the organic carrier, and to form a firm metallurgical bond and densification between the copper powder particles to form a copper-based conductive grid line.

[0050] Compared with the traditional electroplating deposition of copper grid line on the TOPCon cell with a metal seed layer, the preparation method provided by the present application is simple to operate, does not need to use expensive equipment, and has significantly lower equipment investment cost and preparation cost. More importantly, the preparation method does not produce electroplating waste liquid which pollutes the environment, effectively reduces the pollution to the environment, and provides a sustainable development path for the TOPCon cell industry.

[0051] Example 1

[0052] Preparation of copper-based paste: 80 g of copper powder with an average particle size of 3 pm, 5 g of methylcyclohexane, 7.5 g of bisphenol A epoxy resin and 7.5 g of diethylene glycol monobutyl ether were weighed and added into a homogenizer. After stirring at a speed of 1500 rad / s for 90 s, a copper-based paste mixture was obtained. The copper-based paste mixture was transferred into a three-roll mill for uniform mixing to obtain a copper-based paste. An appropriate amount of the copper-based paste was taken as a sample, and the mass and mass change rate of the copper-based paste with temperature were analyzed by thermogravimetric method (TG) and differential thermogravimetric method (DTG). The thermogravimetric curve (TG curve and DTG curve) was recorded and plotted, and the related results are shown in FIG. 1. As can be seen from the obtained curve, in the temperature range of 0-500°C, the copper-based paste first showed a gradually decreasing trend with the increase of temperature, corresponding to the vaporization and decomposition of organic solvents and resins. When the temperature reached about 350°C, the mass decreased to the lowest, and then began to slowly increase, corresponding to the phenomenon that part of the copper powder particles were oxidized. When the temperature reached about 400°C, the mass began to decrease again, corresponding to the reduction reaction caused by the dehydrogenation of methylcyclohexane. Therefore, the copper-based paste undergoes a series of complex chemical changes such as decomposition, oxidation and reduction during the sintering process. In the middle of the temperature rise, the copper-based paste undergoes an oxidation process, which causes the copper powder particles to be oxidized to a certain extent, but then the copper powder is reduced due to the dehydrogenation of methylcyclohexane. Figure 2

[0053] Step S1, a TOPCon cell is obtained, a laser process is used to open the anti-reflection layer and the passivation layer on the TOPCon cell, and a laser opening is formed on the TOPCon cell. Then, a chemical plating process is used to deposit a nickel metal seed layer at the laser opening.

[0054] Step S2, the above-mentioned copper-based paste is first printed on the metal conductive seed layer, and then the printed TOPCon cell is placed in a sintering equipment for segmented sintering treatment. The segmented sintering treatment process includes: first, low-temperature annealing at a temperature of 180°C for 5 min to remove the organic carrier in the copper-based paste, then the temperature is increased to 400°C and kept for 5 min to perform medium-temperature sintering of the copper-based paste for bonding and curing, to form a copper-based conductive grid line on the TOPCon cell, and finally a TOPCon cell is obtained.

[0055] Example 2

[0056] Preparation of copper-based paste: 75 g of first copper powder with an average particle size of 3 pm, 10 g of hydrogenous cuprous powder with an average particle size of 500 nm, 7.5 g of bisphenol A epoxy resin and 7.5 g of diethylene glycol monobutyl ether were weighed and added into a homogenizer. After stirring at a speed of 1500 rad / s for 90 s, a copper-based paste mixture was obtained. The copper-based paste mixture was transferred into a three-roll mill for uniform mixing to obtain a copper-based paste. ​

[0057] Step S1, obtain a TOPCon cell, open the anti-reflection layer and the passivation layer on the TOPCon cell by a laser process, and form a laser opening on the TOPCon cell; then, deposit a nickel seed layer at the laser opening by a chemical plating process.

[0058] Step S2, first print the above-mentioned copper-based paste on the metal conductive seed layer, then place the printed TOPCon cell into a sintering device for segmented sintering treatment; the segmented sintering treatment process includes: first, low-temperature annealing at a temperature of 180°C for 5 min to remove the organic carrier in the copper-based paste, then increase the temperature to 400°C and keep for 5 min to perform medium-temperature sintering of the copper-based paste for bonding and curing, to form a copper-based conductive grid line on the TOPCon cell, as shown in Figure 3 , which is a microstructure schematic diagram of the copper-based conductive grid line, and finally obtain a TOPCon cell.

[0059] Example 3

[0060] Preparation of copper-based paste: weigh 70 g of first copper powder with an average particle size of 3 µm, 10 g of second copper powder with an average particle size of 500 nm, 5 g of methylcyclohexane, 7.5 g of bisphenol A epoxy resin, and 7.5 g of diethylene glycol monobutyl ether into a homogenizer, stir at a speed of 1500 rad / s for 90 s to obtain a copper-based paste mixture; transfer the copper-based paste mixture to a three-roll machine for uniform mixing to obtain a copper-based paste.

[0061] Prepare a copper-based conductive grid line on the TOPCon cell 10 by the same preparation method as in Example 2, as shown in Figure 4 , which is a microstructure schematic diagram of the copper-based conductive grid line, wherein the TOPCon cell 10 includes, from top to bottom, silicon nitride 11, aluminum oxide 12, P+ type monocrystalline silicon 13, N type monocrystalline silicon 14, ultra-thin silicon oxide 15, N+ type polycrystalline silicon 16, and silicon nitride 11. First, deposit a nickel seed layer 7 on the TOPCon cell 10, then deposit a copper-based grid line, and finally obtain a TOPCon cell; as shown in Figure 5 , which is a structure schematic diagram of the TOPCon cell.

[0062] Example 4

[0063] Preparation of copper-based paste: 70 g of first copper powder with an average particle size of 3 pm, 10 g of second copper powder with an average particle size of 500 nm, 5 g of methylcyclohexane, 0.5 g of nickel, 7.5 g of bisphenol A epoxy resin and 7.5 g of diethylene glycol monobutyl ether are weighed into a homogenizer, and after stirring at a speed of 1500 rad / s for 90 s, a copper-based paste mixture is obtained; the copper-based paste mixture is transferred to a three-roll machine for uniform mixing to obtain a copper-based paste. The nickel acts as a catalyst to further reduce the dehydrogenation temperature of the liquid hydrogen storage material, so that it releases hydrogen elements at a lower temperature.

[0064] Step S1, obtain a TOPCon cell, use a laser process to open the anti-reflection layer and the passivation layer on the TOPCon cell, and form a laser opening on the TOPCon cell; then, use a chemical plating process to deposit a nickel seed layer at the laser opening.

[0065] Step S2, first print the above copper-based paste on the metal conductive seed layer, and then place the printed TOPCon cell in a sintering device for segmented sintering treatment; the segmented sintering treatment process includes: first, low-temperature annealing at a temperature of 150°C for 5 min to remove the organic carrier in the copper-based paste, then increasing the temperature to 330°C and keeping it for 5 min to perform medium-temperature sintering of the copper-based paste to bond and cure, forming a copper-based conductive grid line on the TOPCon cell, and finally obtaining a TOPCon cell.

[0066] Example 5

[0067] Preparation of copper-based paste: 65 g of first copper powder with an average particle size of 3 pm, 15 g of second copper powder with an average particle size of 350 nm, 5 g of dibenzyltoluene, 7.5 g of bisphenol A epoxy resin and 7.5 g of diethylene glycol monobutyl ether are weighed into a homogenizer, and after stirring at a speed of 1500 rad / s for 90 s, a copper-based paste mixture is obtained; the copper-based paste mixture is transferred to a three-roll machine for uniform mixing to obtain a copper-based paste.

[0068] Step S1, obtain a TOPCon cell, use a laser process to open the anti-reflection layer and the passivation layer on the TOPCon cell, and form a laser opening on the TOPCon cell; then, use a chemical plating process to deposit a nickel seed layer at the laser opening.

[0069] Step S2, first print the above-mentioned copper-based paste on the metal conductive seed layer, then put the printed TOPCon cell into the sintering equipment for segmented sintering treatment; the segmented sintering treatment process includes: first low-temperature annealing at 180℃ for 5min to remove the organic carrier in the copper-based paste, then increase the temperature to 350℃ and keep for 5min to perform medium-temperature sintering of the copper-based paste for bonding and curing, to form a copper-based conductive grid line on the TOPCon cell, and finally obtain a TOPCon cell.

[0070] Comparative Example 1

[0071] Form a silver grid line 9 on the TOPCon cell 10 by high-temperature silver paste sintering, and finally obtain a commonly used TOPCon cell on the market, such as Figure 6 As shown in the structure schematic diagram of the commonly used TOPCon cell on the market.

[0072] Comparative Example 2

[0073] Preparation of copper-based paste: 70g of first copper powder with an average particle size of 3µm, 10g of second copper powder with an average particle size of 500nm, 7.5g of bisphenol A epoxy resin and 7.5g of diethylene glycol monobutyl ether are weighed and added to a homogenizer, after stirring at a speed of 1500rad / s for 90s, a copper-based paste mixture is obtained; the copper-based paste mixture is transferred to a three-roll machine for uniform mixing to obtain a copper-based paste.

[0074] Preparation of copper-based conductive grid line on TOPCon cell using the same preparation method as in Example 1, and finally obtain a TOPCon cell.

[0075] The resistivity of the copper-based conductive grid line prepared in the above-mentioned Examples 1-5 and the resistivity of the copper-based conductive grid line prepared in Comparative Example 2 are detected by four-probe method respectively. Among them, the four probes are arranged in a straight line and at equal intervals, the outer two probes apply a suitable constant current I, and the inner two probes are used to detect the voltage V; the resistivity is calculated by the formula ρ=(V / I) S / L, S is the cross-sectional area of the grid line, and L is the length of the measured grid line. The test results are shown in Table 1.

[0076] Table 1. Comparison of line resistance of copper-based conductive grid line in the examples and comparative examples of the present application.

[0077]

[0078] As shown in Table 1, the line resistances of the copper-based conductive grid lines prepared in Examples 1-5 are all significantly lower than that of the copper-based conductive grid line prepared in Comparative Example 2. This comparison strongly demonstrates that the introduction of the hydrogen storage material into the copper-based paste can effectively inhibit the oxidation process of the copper powder, thereby significantly improving the conductive performance of the copper-based conductive grid line obtained by sintering. The line resistances of the copper-based conductive grid lines prepared in Examples 3-5 are significantly lower than those of the copper-based conductive grid lines prepared in Examples 1 and 2, thereby demonstrating that the use of the liquid hydrogen storage material to prepare the copper-based paste can better inhibit the oxidation of the copper powder during sintering, thereby obtaining better conductive performance. As shown in Figs. 2 and 3, the microstructure of the copper-based conductive grid line prepared in Example 2 is compared with that of the copper-based conductive grid line prepared in Example 3. As shown in Figs. 2 and 3, the surface of the copper particles in Example 3 is smoother, and the oxide layer on the surface thereof is significantly less than that in Example 2. This microstructure feature also provides strong evidence for the aforementioned conclusion that the use of the liquid hydrogen storage material to prepare the copper-based paste can better inhibit the oxidation of the copper powder. Figure 3 、 Figure 4 As shown in Figs. 2 and 3, the microstructure of the copper-based conductive grid line prepared in Example 2 is compared with that of the copper-based conductive grid line prepared in Example 3. As shown in Figs. 2 and 3, the surface of the copper particles in Example 3 is smoother, and the oxide layer on the surface thereof is significantly less than that in Example 2. This microstructure feature also provides strong evidence for the aforementioned conclusion that the use of the liquid hydrogen storage material to prepare the copper-based paste can better inhibit the oxidation of the copper powder.

[0079] As shown in Figs. 2 and 3, the microstructure of the copper-based conductive grid line prepared in Example 2 is compared with that of the copper-based conductive grid line prepared in Example 3. As shown in Figs. 2 and 3, the surface of the copper particles in Example 3 is smoother, and the oxide layer on the surface thereof is significantly less than that in Example 2. This microstructure feature also provides strong evidence for the aforementioned conclusion that the use of the liquid hydrogen storage material to prepare the copper-based paste can better inhibit the oxidation of the copper powder.

[0080] The electrical properties of the TOPCon cell obtained in Example 3 and the TOPCon cell in Comparative Example 1 were detected, that is, the current-voltage (I-V) curve was measured under AM1.5G spectrum according to IEC60904-1 standard, and the detection results are shown in Table 2.

[0081] Table 2. Comparison of electrical parameters of the TOPCon cell obtained in Example 3 and the conventional cell in Comparative Example 1.

[0082]

[0083] As shown in Table 2, the electrical properties of the TOPCon cell prepared by the preparation method provided in the present application are equivalent to those of the commonly used TOPCon cell on the market, and even slightly better than those of the commonly used TOPCon cell on the market. Specifically, the TOPCon cell prepared in Example 3 has improved energy conversion efficiency (Eta), open circuit voltage (Voc), and fill factor (FF), and the series resistance (Rs) is also reduced, while the short-circuit current (Isc) remains at a level similar to that of the commonly used TOPCon cell on the market. These data also fully show that the TOPCon cell prepared by the preparation method provided in the present application can replace the conventional TOPCon cell using silver conductive grid lines. More importantly, the TOPCon cell preparation scheme provided in the present application realizes silver-free, significantly reduces the dependence of the TOPCon cell on silver materials, thereby greatly reducing the preparation cost, effectively addressing the challenge of the rapid increase in the manufacturing cost of the TOPCon cell due to the continuous rise in silver prices, and providing a more economical and efficient solution for the industry.

[0084] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but as long as the combinations of the technical features do not contradict each other, they should be considered within the scope of the present disclosure.

[0085] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the scope of protection of the present application should be subject to the appended claims.

Claims

1. A copper-based paste, characterized in that, Copper-based slurry includes: copper powder, which is densified during sintering to form a conductive phase; A hydrogen storage material is used to release hydrogen during sintering and to create a reducing atmosphere locally to prevent the oxidation of copper powder; the hydrogen storage material is a liquid hydrogen storage material. Organic carriers provide fluidity and thixotropy to the slurry; By mass percentage, the copper-based slurry contains copper powder at any value between 60% and 90%, organic carrier at any value between 5% and 30%, and hydrogen storage material at any value between 0.1% and 10%. It also includes a catalytic metal for promoting the release of hydrogen from the hydrogen storage material, wherein the catalytic metal is any one or more of platinum, nickel, copper, cobalt, and iron; In the copper-based slurry, the content of the catalytic metal is 0.1%-3% by mass percentage.

2. The copper-based paste as described in claim 1, characterized in that, The liquid hydrogen storage material is any one or more of methylcyclohexane, dibenzyltoluene, perhydrogenated ethylcarbazole, and cyclohexane.

3. The copper-based paste as described in claim 2, characterized in that, The copper powder includes a first copper powder and a second copper powder. The average particle size of the first copper powder is any value between 1µm and 50µm, and the average particle size of the second copper powder is any value between 10nm and 500nm. The second copper powder fills the gaps between the first copper powder particles to improve the conductivity of the conductive phase. The mass of the second copper powder does not exceed 30% of the total amount of copper powder.

4. The copper-based paste as described in claim 2, characterized in that, The organic carrier includes a resin and an organic solvent; the resin is a conductive resin and / or a thermoplastic resin, and the organic solvent is a hydrocarbon with a boiling point not exceeding 300°C.

5. A TOPCon battery, characterized in that, include: TOPCon solar cells and copper-based conductive grid lines; A metal conductive seed layer is deposited on the TOPCon solar cell, and the copper-based conductive grid lines are disposed on the TOPCon solar cell; the copper-based conductive grid lines are prepared by printing and sintering the copper-based paste according to any one of claims 1-4.

6. The method for preparing the TOPCon battery according to claim 5, characterized in that, Includes the following steps: Step S1: Obtain TOPCon solar cells and deposit a metal conductive seed layer on the TOPCon solar cells; Step S2: Print the copper-based paste onto the metal conductive seed layer; Step S3: Perform segmented sintering on the TOPCon battery cell printed with the copper-based paste to form copper-based conductive grid lines on the TOPCon battery cell, thereby obtaining a TOPCon battery. The segmented sintering process includes a low-temperature annealing stage and a medium-temperature sintering stage, which are used to gradually solidify the copper-based slurry in stages to form copper-based conductive grid lines.

7. The method for preparing a TOPCon battery as described in claim 6, characterized in that, The temperature range of the low-temperature annealing stage is 100℃-200℃, which is used to remove the organic carrier and perform preliminary curing. The temperature range of the intermediate-temperature sintering stage is 300℃-500℃, which is used to dehydrogenate the hydrogen storage material to release hydrogen and to densify the copper-based slurry to form copper-based conductive grid lines.

8. The method for preparing a TOPCon battery as described in claim 6, characterized in that, The deposition method of the metal conductive seed layer includes: using a laser process to open the antireflection layer and passivation layer on the TOPCon solar cell to form a laser opening on the TOPCon solar cell; and using a chemical plating or electroplating process to deposit a metal seed layer at the laser opening.

9. The method for preparing a TOPCon battery as described in claim 8, characterized in that, The material of the metal seed layer is a base metal.

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