TOPCon solar cell and preparation method thereof

Abstract

The invention relates to the technical field of solar cells, and discloses a TOPCon solar cell and a preparation method thereof, and the method comprises the following steps: (1) carrying out the silk-screen printing of a first conductive paste on the back surface of a semi-finished battery piece, and carrying out the sintering processing, and obtaining a first back surface grid line electrode; the first conductive paste comprises silver powder, first silver-copper-nickel alloy powder, glass powder and an organic carrier; and (2) performing silk-screen printing on the surface of the first back grid line electrode by using second conductive paste, and performing curing treatment to obtain a second back grid line electrode, thereby obtaining the TOPCon solar cell, and the second conductive paste comprises modified copper powder, a resin binder, a curing agent and an organic solvent. According to the invention, the two conductive pastes with specific components are combined with the silk-screen printing technology to respectively prepare the back grid line electrodes, the preparation method which is simple in process and green and environment-friendly is provided, and the solar cell which is excellent in electrical property and low in manufacturing cost is obtained.

Description

Technical Field

[0001] This invention relates to the field of solar cells, specifically to a TOPCon solar cell and its fabrication method. Background Technology

[0002] TOPCon (Tunnel Oxide Passivated Contact) solar cells are an advanced type of crystalline silicon solar cell. Due to their advantages such as ultra-high photoelectric conversion efficiency, high open-circuit voltage (Voc) and fill factor (FF), low degradation performance, excellent temperature coefficient and high bifaciality, they are considered to be one of the most promising and commercially valuable next-generation high-efficiency crystalline silicon cells after the mainstream PERC (Passivated Emitter and Back Contact) solar cells, and are also a popular cell technology in the photovoltaic industry.

[0003] The photovoltaic industry is currently facing severe challenges. Demand for photovoltaic installations is insufficient, while the entire industry chain, including silicon materials, wafers, cells, and modules, suffers from severe overcapacity. Furthermore, the front and back grid electrodes of TOPCon solar cells are typically made using silver paste, and the continuous rise in silver prices has further increased the manufacturing cost of solar cells. Maintaining a cost advantage has become a key factor for existing companies to compete in the market and survive. To reduce the manufacturing cost of solar cells, existing companies are increasingly using base metals to replace silver in the paste. Among these, copper, aluminum, and nickel have received widespread attention due to their excellent electrical conductivity.

[0004] However, the application of copper, aluminum, and nickel in solar cells also has unresolved drawbacks, making it difficult to effectively guarantee the excellent electrical performance of solar cells during application. Aluminum diffuses rapidly in silicon, easily leading to a significant decrease in the open-circuit voltage of crystalline silicon cells. Copper and nickel are easily oxidized at high temperatures, severely limiting their application in crystalline silicon cells. Furthermore, copper and nickel electrodes are typically prepared using electroplating processes; however, electroplating is a complex process, and the patterning stage generates organic wastewater, causing environmental pollution. Summary of the Invention

[0005] In view of this, the present invention aims to provide a TOPCon solar cell and its preparation method to solve the problem that the prior art cannot simultaneously achieve excellent electrical performance and low manufacturing cost, as well as the defects of the prior art that the back grid electrode is made using a complex process and easily generates waste that pollutes the environment.

[0006] In a first aspect, the present invention provides a method for preparing a TOPCon solar cell, comprising the following steps: (1) A first back grid electrode is prepared by screen printing on the back of a semi-finished battery cell using a first conductive paste and then sintering. The first conductive paste includes silver powder, a first silver-copper-nickel alloy powder, glass powder and an organic carrier. (2) A second conductive paste is used to screen print on the surface of the first back grid electrode away from the semi-finished cell, and then cured to obtain the second back grid electrode, thus obtaining the TOPCon solar cell; the second conductive paste includes modified copper powder, resin binder, curing agent and organic solvent.

[0007] In one alternative embodiment, based on the total mass of the first conductive paste, the first conductive paste satisfies at least one of the following conditions: (a1) The mass content of the silver powder is 70wt%~80wt%.

[0008] (a2) The mass content of the first silver-copper-nickel alloy powder is 10wt%~20wt%.

[0009] (a3) The mass content of the glass powder is 1.5wt%~5wt%.

[0010] (a4) The organic carrier has a mass content of 5wt% to 15wt%.

[0011] Optionally, the first conductive paste is prepared by mixing and rolling silver powder, a first silver-copper-nickel alloy powder, glass powder and an organic carrier in the specified amounts.

[0012] The present invention does not specifically limit the rolling equipment used in the preparation of the first conductive paste, and those skilled in the art can choose according to their needs. Exemplarily, but not limitingly, the rolling equipment includes a three-roll mill.

[0013] Optionally, the glass powder includes the main components PbO, SiO2, Bi2O3, TeO2, ZnO, V2O5, and B2O3.

[0014] Optionally, the glass powder may further include alkali metal compounds and / or alkaline earth metal compounds.

[0015] Optionally, the alkali metal compound includes at least one of Li2O, Li2O2, Na2O, Na2O2, NaO2, K2O, K2O2, KO2, Rb2O, RbO2, Cs2O, and CsO2.

[0016] Optionally, the alkaline earth metal compound includes at least one of BeO, MgO, CaO, CaO2, SrO, SrO2, BaO, and BaO2.

[0017] Optionally, based on the total mass of the organic carrier, the organic carrier comprises a surfactant at a mass content of 1 wt% to 5 wt%, a polymeric binder at a mass content of 1 wt% to 10 wt%, a thixotropic agent at a mass content of 1 wt% to 10 wt%, and the balance being an organic solvent. The surfactant includes at least one of sodium linoleate, hydroxyethyl acrylate, fatty acid glycerides, sodium oleate, and lecithin; the polymeric binder includes at least one of ethyl cellulose, hydroxyethyl cellulose, hydrogenated rosin resin, phenolic resin, acrylic resin, and polyvinyl butyral; the thixotropic agent includes at least one of hydrogenated castor oil, polyamide wax, polyacrylate, fumed silica, and organobentonite. The organic solvent includes at least one of butyl carbitol, butyl carbitol acetate, dodecayl alcohol, and terpineol.

[0018] In one optional embodiment, the particle size D50 of the first silver-copper-nickel alloy powder is 300nm~800nm.

[0019] In one optional embodiment, the first silver-copper-nickel alloy powder includes a first silver element, the mass of which accounts for more than 80 wt% of the total mass of the first silver-copper-nickel alloy powder.

[0020] In one optional embodiment, the first silver-copper-nickel alloy powder further includes a first copper element and a first nickel element, wherein the mass ratio of the first copper element to the first nickel element is (1~5):1.

[0021] In one alternative embodiment, based on the total mass of the second conductive paste, the second conductive paste satisfies at least one of the following conditions: (b1) The modified copper powder has a mass content of 85wt%~92wt%.

[0022] (b2) The mass content of the resin adhesive is 1wt%~5wt%.

[0023] (b3) The curing agent has a mass content of 1wt% to 5wt%.

[0024] (b4) The organic solvent has a mass content of 5wt% to 10wt%.

[0025] Optionally, the second conductive paste is prepared by rolling a mixture of modified copper powder, resin binder, curing agent and organic solvent in the specified amounts.

[0026] The present invention does not specifically limit the rolling equipment used in the preparation of the second conductive paste, and those skilled in the art can choose according to their needs. Exemplarily, but not limitingly, the rolling equipment includes a three-roll mill.

[0027] It should be noted that the present invention does not specifically limit the timing and order of preparation of the first conductive paste and the second conductive paste, and those skilled in the art can choose according to their needs. Exemplarily, but not limitingly, the first conductive paste can be prepared first, and then the second conductive paste can be prepared; or, the second conductive paste can be prepared first, and then the first conductive paste can be prepared; or, the first conductive paste and the second conductive paste can be prepared simultaneously.

[0028] Optionally, in the second conductive paste, the resin binder includes at least one of epoxy resin, phenolic resin, acrylic resin, and hydrogenated rosin resin.

[0029] Optionally, in the second conductive paste, the curing agent includes at least one of ethylenediamine, phthalic anhydride, dicyandiamide, and boron trifluoride amine complex.

[0030] Optionally, in the second conductive paste, the organic solvent includes at least one of diethylene glycol monobutyl ether, diethylene glycol butyl ether acetate, propylene glycol methyl ether acetate, and alcohol ester twelve.

[0031] In one optional embodiment, the preparation process of the modified copper powder includes: acid washing of copper powder to obtain pretreated copper powder, then mixing the pretreated copper powder with a second silver-copper-nickel alloy powder, and then drying it to obtain the modified copper powder.

[0032] It should be noted that the present invention does not specifically limit the timing of the preparation of modified copper powder, and those skilled in the art can choose according to their needs.

[0033] Optionally, the pickling reagent used in the pickling treatment includes at least one of formic acid, sulfuric acid, oxalic acid, and hypophosphoric acid.

[0034] Optionally, the concentration of the pickling reagent used in the pickling treatment is 5wt%~15wt%.

[0035] Preferably, in the preparation process of the modified copper powder, the mass ratio of the copper powder to the second silver-copper-nickel alloy powder is (5~10):1.

[0036] Preferably, the second silver-copper-nickel alloy powder includes a second silver element, a second copper element, and a second nickel element, wherein the mass of the second silver element accounts for more than 80 wt% of the total mass of the second silver-copper-nickel alloy powder, and the mass ratio of the second copper element to the second nickel element is (1~5):1.

[0037] Preferably, the particle size D50 of the second silver-copper-nickel alloy powder is 300nm~800nm.

[0038] In one optional embodiment, the copper powder includes a first copper powder particle, a second copper powder particle, and a third copper powder particle.

[0039] Preferably, the copper powder satisfies at least one of the following conditions: (c1) The first copper powder particles are spherical nanoparticles with a particle size D50 of 150nm~500nm.

[0040] (c2) Based on the total mass of the copper powder, the mass content of the first copper powder particles is 20wt%~50wt%.

[0041] (c3) The second copper powder particles are spherical micron particles with a particle size D50 of 1µm to 3µm.

[0042] (c4) Based on the total mass of the copper powder, the mass content of the second copper powder particles is 30wt%~60wt%.

[0043] (c5) The third copper powder particles are dendritic particles with a particle size D50 of 1µm to 3µm.

[0044] (c6) Based on the total mass of the copper powder, the mass content of the third copper powder particles is 5wt%~20wt%.

[0045] It should be noted that, in this invention, "dendritic particles" refers to particles with a branched structure extending from a common vertex, and the "particle size" of "dendritic particles" refers to the length between the two farthest ends of the dendritic particle.

[0046] In one alternative embodiment, the fineness of the first conductive paste is <5µm.

[0047] In one alternative embodiment, the fineness of the second conductive paste is <10µm.

[0048] In one optional embodiment, the mass ratio of the first conductive paste to the second conductive paste is 1:(1~3).

[0049] In one optional embodiment, the semi-finished solar cell in step (1) is prepared by texturing, boron expansion, alkaline polishing, back POLY (back side polycrystalline silicon thin film preparation), RCA (wet chemical cleaning process for silicon wafers), and front and back coating processes.

[0050] In one optional embodiment, before screen printing the first conductive paste, step (1) also involves screen printing and drying the back grid paste on the back side of the semi-finished battery cell.

[0051] In this invention, the source of the back grid paste is not specifically limited, and those skilled in the art can choose it as needed. Exemplarily, and not limitingly, the back grid paste can be commercially available.

[0052] In an alternative embodiment, step (1) involves drying the first conductive paste after screen printing.

[0053] In an optional embodiment, after screen printing the first conductive paste in step (1), screen printing and drying processes are performed on the front side of the semi-finished battery cell for the front main grid paste and the front fine grid silver paste in sequence, and then the sintering process is performed.

[0054] In this invention, the source of the front main grid paste and the front fine grid silver paste is not specifically limited, and those skilled in the art can choose according to their needs. Exemplarily, and not limitingly, the front main grid paste and the front fine grid silver paste can be commercially available.

[0055] In one optional embodiment, the sintering temperature in step (1) is 700°C to 750°C.

[0056] In one optional embodiment, the curing temperature in step (2) is 200°C to 300°C.

[0057] In one alternative embodiment, laser sintering is performed after the curing process described in step (2).

[0058] Secondly, the present invention also provides a TOPCon solar cell, which is prepared using the TOPCon solar cell preparation method described in the first aspect.

[0059] The technical solution of this invention has the following advantages: 1. The present invention provides a method for preparing a TOPCon solar cell, comprising the following steps: (1) screen printing a first conductive paste on the back of a semi-finished cell, and then preparing a first back grid electrode after sintering; the first conductive paste comprises silver powder, a first silver-copper-nickel alloy powder, glass powder and an organic carrier; (2) screen printing a second conductive paste on the surface of the first back grid electrode away from the semi-finished cell, and then preparing a second back grid electrode after curing, thereby obtaining the TOPCon solar cell; the second conductive paste comprises modified copper powder, resin binder, curing agent and organic solvent. This invention uses a two-stage screen printing process to fabricate the back grid electrode. First, a first conductive paste is screen-printed and sintered, followed by a second conductive paste screen-printed and cured. The first conductive paste contains a silver seed layer formed by combining silver powder with a first silver-copper-nickel alloy powder, glass powder, and an organic carrier. After sintering, the silver seed layer serves as the first back grid electrode, resulting in good ohmic contact between the first back grid electrode and the crystalline silicon solar cell. The second conductive paste contains a copper paste formed by combining modified copper powder with a resin binder, curing agent, and organic solvent, replacing the original structure which consisted entirely of silver paste. This reduces the manufacturing cost of the solar cell, while the superior conductivity of the copper paste ensures that the prepared back grid electrode has a low electrode resistance, thus guaranteeing excellent electrical performance of the resulting TOPCon solar cell. On the other hand, the first silver-copper-nickel alloy powder introduced into the first conductive paste of this invention partially replaces the silver powder, which can further reduce the battery manufacturing cost. Secondly, since the silver-copper-nickel alloy has a low melting point, it can effectively reduce the sintering temperature during the preparation of the back grid electrode, ensuring the excellent electrical performance of the resulting TOPCon solar cell while further reducing the energy consumption and cost of battery manufacturing. Furthermore, the silver-copper-nickel alloy powder in the first conductive paste after sintering can act as a bridge between the silver seed layer electrode and the subsequent screen-printed second conductive paste, ensuring good contact between the silver seed layer electrode inside the back grid electrode of the final TOPCon solar cell and the copper layer electrode that serves as the second back grid electrode, thereby improving the performance of the TOPCon solar cell. In addition, the paste coating method used in the TOPCon solar cell preparation process of this invention is screen printing, which eliminates the electroplating process used in the preparation of the back grid electrode, making the preparation process simpler and effectively preventing the pollution of the environment by organic wastewater generated in the patterning stage of the electroplating process, thus making the manufacturing process of TOPCon solar cells more green and environmentally friendly.

[0060] 2. The present invention provides a process for preparing modified copper powder, comprising: acid washing copper powder to obtain pretreated copper powder; then, mixing the pretreated copper powder with a second silver-copper-nickel alloy powder, and drying the mixture to obtain the modified copper powder. In this invention, acid-washed copper powder is thoroughly mixed with the second silver-copper-nickel alloy powder and then dried to obtain modified copper powder. The surface of the copper powder particles in the modified copper powder forms silver-copper-nickel alloy contact points, which can synergistically interact with the first silver-copper-nickel alloy in the first back grid electrode, jointly serving as a bridging medium between the first and second back grid electrodes in the TOPCon solar cell, further reducing the contact resistance between the two back grid electrodes. Furthermore, the silver-copper-nickel alloy contact points formed on the surface of the copper powder particles in the modified copper powder can effectively isolate the copper powder from direct contact with the external environment, preventing oxidation of the copper powder during preparation or use, thereby ensuring the superior conductivity of the second back grid electrode.

[0061] 3. In order to ensure the excellent conductivity of the second back grid electrode formed by the second conductive paste, the present invention selects three types of copper powder particles when preparing the modified copper powder in the second conductive paste. Among them, spherical nano copper powder particles with a particle size D50 of 150nm~500nm can fill the pores of spherical micron copper powder particles with a particle size D50 of 1µm~3µm, ensuring close contact between copper powder particles. Furthermore, dendritic copper powder particles of a specific size are introduced to maximize the connection between copper powder particles, increase the connection channels inside the second back grid electrode in the resulting battery, and fully ensure the excellent conductivity of the second back grid electrode. Detailed Implementation

[0062] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0063] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0064] In one specific embodiment, the semi-finished solar cell is prepared by texturing, boron diffusion, alkaline polishing, back-side POLY (back-side preparation of polycrystalline silicon thin film), RCA (wet chemical cleaning process for silicon wafers), and front and back coating processes. The specific preparation process includes the following steps: (i) Texturing the silicon substrate.

[0065] (ii) Boron diffusion treatment is performed on the front side of the texturized silicon substrate to prepare a PN junction.

[0066] (iii) The back side of the boron-diffused silicon substrate is subjected to alkaline polishing.

[0067] (iv) A tunneling silicon oxide layer and a doped polysilicon (Poly-Si) layer are prepared on the back side of the silicon substrate after alkaline polishing.

[0068] (v) Remove the polysilicon layer from the silicon substrate by wrapping and clean the surface of the silicon substrate.

[0069] (vi) The front and back sides of the silicon substrate are coated to form an aluminum oxide-silicon nitride stacked antireflection film on the front side of the cell and a silicon nitride passivation film on the back side to obtain a semi-finished cell.

[0070] The back grid paste used in the following embodiments is commercially available and comes from Nantong Tiansheng New Energy Co., Ltd., with the model number BA703.

[0071] The front grid paste used in the following embodiments is commercially available and comes from Nantong Tiansheng New Energy Co., Ltd., with the model number BA703.

[0072] The front fine grid silver paste involved in the following embodiments is commercially available from Changzhou Juhe New Material Co., Ltd., and its model number is CSP-N3TF.

[0073] The specific composition of the glass powder used in the preparation of the first conductive paste in the following embodiments is as follows: based on a total mass of 100wt% of glass powder, the glass powder includes 28wt% PbO, 10wt% SiO2, 15wt% Bi2O3, 25wt% TeO2, 5wt% ZnO, 3wt% V2O5, 5wt% B2O3, and 9wt% Li2O.

[0074] The specific composition of the organic carrier used in the preparation of the first conductive paste in the following examples is as follows: based on a total mass of 100wt% of the organic carrier, the organic carrier includes 5wt% of mono-fatty acid glycerides, 10wt% of acrylic resin, 5wt% of polyamide wax, 25wt% of butyl carbitol, 25wt% of butyl carbitol acetate, and 30wt% of dodecyl alcohol ester.

[0075] Example 1 This embodiment provides a method for fabricating a TOPCon solar cell, including the following steps: S1. Take 70g of silver powder, 20g of first silver-copper-nickel alloy powder, 1.5g of glass powder and 8.5g of organic carrier, mix them, and then roll them using a three-roll mill to obtain a first conductive slurry with a fineness <5µm. The particle size D50 of the first silver-copper-nickel alloy powder is 300nm, and the mass ratio of silver, copper, and nickel in the first silver-copper-nickel alloy is 80:10:10.

[0076] S2. Take spherical nano copper powder particles with a particle size D50 of 150nm, spherical micron copper powder particles with a particle size D50 of 1µm, and dendritic copper powder particles with a particle size D50 of 1µm and mix them as copper powder. The mass ratio of spherical nano copper powder particles, spherical micron copper powder particles and dendritic copper powder particles is 50:30:20.

[0077] The copper powder was cleaned with 5wt% formic acid to obtain pretreated copper powder. Then, the pretreated copper powder was thoroughly mixed with a second silver-copper-nickel alloy powder and dried to obtain modified copper powder. The particle size D50 of the second silver-copper-nickel alloy powder was 300 nm, the mass ratio of silver, copper, and nickel in the second silver-copper-nickel alloy was 80:10:10, and the mass ratio of copper powder to the second silver-copper-nickel alloy powder was 5:1.

[0078] S3. Take 85g of the modified copper powder prepared in step S2, 2.5g of acrylic resin binder, 2.5g of dicyandiamide curing agent, 5g of diethylene glycol monobutyl ether and 5g of diethylene glycol butyl ether acetate, mix them, and roll them through a three-roll mill to obtain a second conductive slurry with a fineness of <10µm.

[0079] S4. The semi-finished battery cells prepared through texturing, boron expansion, alkaline polishing, back POLY, RCA, front and back coating processes are put into the screen printing process. The back grid paste is screen printed on the back of the semi-finished battery cells. After the first drying, the first conductive paste obtained in step S1 is screen printed on the back of the semi-finished battery cells after the back grid paste is printed. Then, after the second drying, the battery process cell I is obtained.

[0080] S5. In the battery process wafer I obtained in step S4, the front side of the battery cell is first screen-printed with the front main grid paste. After the third drying, the fine grid silver paste is screen-printed on the front side of the battery cell after the front main grid paste is printed. Then, it is sintered at 700°C to obtain battery process wafer II. In this case, the first conductive paste screen-printed in step S4 forms the first back grid line electrode on the back side of the battery cell.

[0081] S6. The second conductive paste prepared in step S3 is screen-printed on the surface of the first back grid electrode of the cell process piece II, away from the semi-finished cell. Then, the resulting product is placed in a curing oven and cured at 200°C to obtain cell process piece III. Finally, cell process piece III is laser-sintered to obtain a TOPCon solar cell. The mass ratio of the first conductive paste screen-printed in step S4 to the second conductive paste screen-printed in step S6 is 1:3. Specifically, the wet weight (i.e., printing weight) of the first conductive silver paste screen-printed in step S4 is 15 mg, and the wet weight of the second conductive paste screen-printed in step S6 is 45 mg.

[0082] Example 2 This embodiment provides a method for fabricating a TOPCon solar cell, including the following steps: S1. Take 80g of silver powder, 10g of first silver-copper-nickel alloy powder, 5g of glass powder and 5g of organic carrier, mix them, and then roll them using a three-roll mill to obtain a first conductive slurry with a fineness <5µm. Among them, the particle size D50 of the first silver-copper-nickel alloy powder is 800nm, and the mass ratio of silver, copper and nickel in the first silver-copper-nickel alloy is 88:10:2.

[0083] S2. Take spherical nano copper powder particles with a particle size D50 of 300nm, spherical micron copper powder particles with a particle size D50 of 3µm, and dendritic copper powder particles with a particle size D50 of 3µm and mix them as copper powder. The mass ratio of spherical nano copper powder particles, spherical micron copper powder particles and dendritic copper powder particles is 20:60:20.

[0084] The copper powder was cleaned with 15wt% formic acid to obtain pretreated copper powder. Then, the pretreated copper powder was thoroughly mixed with a second silver-copper-nickel alloy powder and dried to obtain modified copper powder. The particle size D50 of the second silver-copper-nickel alloy powder was 800 nm, the mass ratio of silver, copper, and nickel in the second silver-copper-nickel alloy was 88:10:2, and the mass ratio of copper powder to the second silver-copper-nickel alloy powder was 10:1.

[0085] S3. Take 92g of the modified copper powder prepared in step S2, 1g of epoxy resin binder, 1g of ethylenediamine curing agent, 3g of diethylene glycol monobutyl ether and 3g of diethylene glycol butyl ether acetate, mix them, and roll them through a three-roll mill to obtain a second conductive paste with a fineness of <10µm.

[0086] S4. The semi-finished battery cells prepared through texturing, boron expansion, alkaline polishing, back POLY, RCA, front and back coating processes are put into the screen printing process. The back grid paste is screen printed on the back of the semi-finished battery cells. After the first drying, the first conductive paste obtained in step S1 is screen printed on the back of the semi-finished battery cells after the back grid paste is printed. Then, after the second drying, the battery process cell I is obtained.

[0087] S5. In the battery process wafer I obtained in step S4, the front side of the battery cell is first screen-printed with the front main grid paste. After the third drying, the fine grid silver paste is screen-printed on the front side of the battery cell after the front main grid paste is printed. Then, it is sintered at 750°C to obtain battery process wafer II. In this case, the first conductive paste screen-printed in step S4 forms the first back grid line electrode on the back side of the battery cell.

[0088] S6. The second conductive paste prepared in step S3 is screen-printed on the surface of the first back grid electrode of the cell process wafer II, away from the semi-finished cell. Then, the resulting product is placed in a curing oven and cured at 300°C to obtain cell process wafer III. Finally, cell process wafer III is laser-sintered to obtain a TOPCon solar cell. The mass ratio of the first conductive paste screen-printed in step S4 to the second conductive paste screen-printed in step S6 is 1:1. Specifically, the wet weight (i.e., printing weight) of the first conductive silver paste screen-printed in step S4 is 15 mg, and the wet weight of the second conductive paste screen-printed in step S6 is 15 mg.

[0089] Example 3 This embodiment provides a method for fabricating a TOPCon solar cell, including the following steps: S1. Take spherical nano copper powder particles with a particle size D50 of 500nm, spherical micron copper powder particles with a particle size D50 of 3µm, and dendritic copper powder particles with a particle size D50 of 3µm and mix them as copper powder. The mass ratio of spherical nano copper powder particles, spherical micron copper powder particles and dendritic copper powder particles is 50:45:5.

[0090] The copper powder was cleaned with 15wt% formic acid to obtain pretreated copper powder. Then, the pretreated copper powder was thoroughly mixed with a second silver-copper-nickel alloy powder and dried to obtain modified copper powder. The particle size D50 of the second silver-copper-nickel alloy powder was 300 nm, the mass ratio of silver, copper, and nickel in the second silver-copper-nickel alloy was 88:10:2, and the mass ratio of copper powder to the second silver-copper-nickel alloy powder was 10:1.

[0091] S2. Take 85g of the modified copper powder prepared in step S1, 5g of acrylic resin binder, 5g of dicyandiamide curing agent, 2.5g of diethylene glycol monobutyl ether and 2.5g of diethylene glycol butyl ether acetate, mix them, and roll them with a three-roll mill to obtain a second conductive slurry with a fineness of <10µm.

[0092] S3. Mix 73.5g of silver powder, 10g of first silver-copper-nickel alloy powder, 1.5g of glass powder, and 15g of organic carrier, then roll the mixture using a three-roll mill to obtain a first conductive slurry with a fineness <5µm. The particle size D50 of the first silver-copper-nickel alloy powder is 300nm, and the mass ratio of silver, copper, and nickel in the first silver-copper-nickel alloy is 88:10:2.

[0093] S4. The semi-finished battery cells prepared through texturing, boron expansion, alkaline polishing, back POLY, RCA, front and back coating processes are put into the screen printing process. The back grid paste is screen printed on the back of the semi-finished battery cells. After the first drying, the first conductive paste obtained in step S3 is screen printed on the back of the semi-finished battery cells after the back grid paste is printed. Then, after the second drying, the battery process cell I is obtained.

[0094] S5. In the battery process wafer I obtained in step S4, the front side of the battery cell is first screen-printed with the front main grid paste. After the third drying, the fine grid silver paste is screen-printed on the front side of the battery cell after the front main grid paste is printed. Then, it is sintered at 750°C to obtain battery process wafer II. In this case, the first conductive paste screen-printed in step S4 forms the first back grid line electrode on the back side of the battery cell.

[0095] S6. The second conductive paste prepared in step S2 is screen-printed on the surface of the first back grid electrode of the cell process wafer II, away from the semi-finished cell. Then, the resulting product is placed in a curing oven and cured at 300°C to obtain cell process wafer III. Finally, cell process wafer III is laser-sintered to obtain a TOPCon solar cell. The mass ratio of the first conductive paste screen-printed in step S4 to the second conductive paste screen-printed in step S6 is 1:2. Specifically, the wet weight (i.e., printing weight) of the first conductive silver paste screen-printed in step S4 is 15 mg, and the wet weight of the second conductive paste screen-printed in step S6 is 30 mg.

[0096] Example 4 The only difference between this embodiment and Embodiment 1 is that, in the preparation of the first conductive paste in step S1, the mass of silver powder added is 60g, the mass of the first silver-copper-nickel alloy powder is 20g, the mass of glass powder is 5g, and the mass of the organic carrier is 15g. All other contents are the same as in Embodiment 1.

[0097] Example 5 The only difference between this embodiment and Embodiment 1 is that, in the preparation of the first conductive paste in step S1, the mass of silver powder added is 82g, the mass of the first silver-copper-nickel alloy powder is 10g, the mass of glass powder is 1.5g, and the mass of the organic carrier is 6.5g. All other contents are the same as in Embodiment 1.

[0098] Example 6 The only difference between this embodiment and Embodiment 1 is that, in the preparation of the first conductive paste in step S1, the mass of silver powder added is 75g, the mass of the first silver-copper-nickel alloy powder is 5g, the mass of glass powder is 5g, and the mass of the organic carrier is 15g. All other contents are the same as in Embodiment 1.

[0099] Example 7 The only difference between this embodiment and Embodiment 1 is that, in the preparation of the first conductive paste in step S1, the mass of silver powder added is 70g, the mass of the first silver-copper-nickel alloy powder is 23.5g, the mass of glass powder is 1.5g, and the mass of the organic carrier is 5g. All other contents are the same as in Embodiment 1.

[0100] Example 8 The only difference between this embodiment and Embodiment 1 is that the mass ratio of silver, copper, and nickel in the first silver-copper-nickel alloy powder used in step S1 and the second silver-copper-nickel alloy powder used in step S2 is 70:15:15. All other aspects are the same as in Embodiment 1.

[0101] Example 9 The only difference between this embodiment and Embodiment 1 is that, in the preparation of the modified copper powder in step S2, the mass ratio of copper powder to the second silver-copper-nickel alloy powder is adjusted to 3:1. All other aspects are the same as in Embodiment 1.

[0102] Example 10 The only difference between this embodiment and Embodiment 1 is that, in the preparation of the modified copper powder in step S2, the mass ratio of copper powder to the second silver-copper-nickel alloy powder is adjusted to 12:1. All other aspects are the same as in Embodiment 1.

[0103] Example 11 The only difference between this embodiment and Embodiment 1 is that in the preparation of the modified copper powder in step S2, only formic acid is used to clean the copper powder, while the addition of the second silver-copper-nickel alloy powder is omitted. All other aspects are the same as in Embodiment 1.

[0104] Example 12 The only difference between this embodiment and Embodiment 1 is that in step S2, the dendritic copper powder particles used to prepare the modified copper powder are replaced with an equal mass of spherical copper powder particles with a particle size D50 of 1µm, and the addition of the dendritic copper powder particles is omitted. All other aspects are the same as in Embodiment 1.

[0105] Example 13 The only difference between this embodiment and Example 1 is that, in the copper powder used to prepare the modified copper powder in step S2, the addition of spherical nano-copper powder particles with a particle size D50 of 150 nm is omitted, and the mass of the omitted spherical nano-copper powder particles is allocated to the two according to the mass ratio of spherical micron-sized copper powder particles and dendritic copper powder particles in the original formula. All other contents are the same as in Example 1.

[0106] Example 14 The only difference between this embodiment and Example 1 is that, in the copper powder used to prepare the modified copper powder in step S2, the addition of spherical micron copper powder particles with a particle size D50 of 1µm is omitted, and the mass of the omitted spherical micron copper powder particles is allocated to the two according to the mass ratio of spherical nano copper powder particles and dendritic copper powder particles in the original formula. All other contents are the same as in Example 1.

[0107] Comparative Example 1 The only difference between this comparative example and Example 1 is that the addition of the first silver-copper-nickel alloy powder is omitted in the first conductive paste of step S1, and the second conductive paste only includes 90g of silver powder, 1.5g of glass powder, and 8.5g of organic carrier mixed together. All other contents are the same as in Example 1.

[0108] Comparative Example 2 The only difference between this comparative example and Example 1 is that in step S3, the modified copper powder in the second conductive paste is replaced with an equal mass of copper powder, and no modification treatment is performed on the copper powder. All other contents are the same as in Example 1.

[0109] Comparative Example 3 The only difference between this comparative example and Example 1 is that the preparation of the first conductive paste in step S1 and the screen printing process of the first conductive paste in step S4 are omitted. The mass of the omitted first conductive paste is replaced with an equal mass of second conductive paste, which, together with the original second conductive paste in step S6, is screen printed on the back of the semi-finished battery cell after the back grid paste has been printed. All other contents are the same as in Example 1.

[0110] The cell efficiency of the TOPCon solar cells prepared by the methods provided in Examples 1-14 and Comparative Examples 1-3 was tested using an IV meter. The test conditions were: temperature 25°C and light intensity 1000 W / m². 2The atmospheric quality was AM1.5, and the test results included photoelectric conversion efficiency (Eta), open circuit voltage (Voc), short circuit current (Isc), fill factor (FF), parallel resistance (Rshunt), and series resistance (Rser).

[0111] The test results are shown in Table 1.

[0112] Table 1 Test results of battery electrical performance

[0113] As shown in Table 1, the TOPCon solar cells prepared using the method of this invention exhibit high photoelectric conversion efficiency, high open-circuit voltage and fill factor, and low series resistance. This demonstrates that the solar cells prepared by this invention using a combination of a first conductive paste and a second conductive paste with specific compositions and a screen printing process achieve excellent electrical performance. Furthermore, the addition of the second conductive paste and the first silver-copper-nickel alloy powder to partially replace silver metal reduces the manufacturing cost of the solar cells. Additionally, the screen printing process employed is simple and environmentally friendly.

[0114] Comparative Example 1 omits the addition of the first silver-copper-nickel alloy powder to the first conductive paste. The resulting TOPCon solar cell mainly exhibits a decrease in photoelectric conversion efficiency, a lower fill factor (FF), and a larger series resistance. This is because the first conductive paste does not contain the silver-copper-nickel alloy, and without the silver-copper-nickel alloy as a bridging medium, the contact between the first back grid line electrode and the second back grid line electrode deteriorates, thereby leading to a decrease in the electrical performance of the solar cell.

[0115] In Comparative Example 2, the modified copper powder in the second conductive paste was replaced with untreated copper powder. The resulting TOPCon solar cell mainly exhibited a decrease in photoelectric conversion efficiency, a decrease in fill factor, and an increase in series resistance. This is because the copper powder was directly added, leaving the surface of the copper powder exposed. During preparation and use, the copper powder is prone to oxidation at high temperatures, which leads to a decrease in the conductivity of the second back grid electrode. Furthermore, the copper powder surface lacks silver-copper-nickel alloy contact points, and the lack of silver-copper-nickel alloy as a bridging medium further worsens the contact between the first and second back grid electrodes.

[0116] Comparative Example 3 omitted the screen printing process for the first conductive paste. The resulting TOPCon solar cell exhibited extremely low photoelectric conversion efficiency and fill factor, and a significant increase in series resistance. This was because the silver seed layer paste was not printed, and the silicon nitride oxide layer could not be etched through, resulting in the inability to form an effective ohmic contact, which led to poor cell contact and a significant decrease in electrical performance.

[0117] Examples 4-5 adjusted the mass content of silver powder in the first conductive paste. If the mass content of silver powder is too low, it will lead to a reduction in the effective conductive particles in the paste, resulting in an increase in the series resistance of the battery and a decrease in the photoelectric conversion efficiency and fill factor of the battery. If the mass content of silver powder is too high, it will lead to an excessively high viscosity of the paste, a deterioration in the electrode profile, and uneven electrode resistance, thereby increasing the series resistance and decreasing the photoelectric conversion efficiency and fill factor of the battery.

[0118] Examples 6-7 adjusted the mass content of the first silver-copper-nickel alloy powder in the first conductive paste. If the mass content of the first silver-copper-nickel alloy powder is too low, it will lead to poor contact between the first back grid line electrode and the second back grid line electrode, an increase in the series resistance of the battery, and a decrease in the photoelectric conversion efficiency and fill factor of the battery. If the mass content of the first silver-copper-nickel alloy powder is too high, it will lead to poor electrode conductivity, an increase in series resistance, and a decrease in the photoelectric performance of the battery.

[0119] Example 8 adjusted the mass ratio of silver, copper and nickel in the first silver-copper-nickel alloy powder and the second silver-copper-nickel alloy powder. If the mass ratio of silver in the silver-copper-nickel alloy powder is too low, it will lead to poor electrode conductivity, increased series resistance, and slightly lower photoelectric conversion efficiency and fill factor of the battery.

[0120] In Examples 9-10, the mass ratio of copper powder to second silver-copper-nickel alloy powder was adjusted during the preparation of modified copper powder. If the mass ratio is too low and the amount of second silver-copper-nickel alloy powder added is relatively too high, the electrode conductivity will deteriorate, the series resistance of the solar cell will increase, and the photoelectric conversion efficiency and fill factor of the cell will decrease. If the mass ratio is too high and the amount of second silver-copper-nickel alloy powder added is relatively too low, the first back grid electrode and the second back grid electrode will have poor contact, thereby increasing the series resistance of the obtained solar cell and decreasing the photoelectric conversion efficiency and fill factor.

[0121] Example 11 omitted the addition of the second silver-copper-nickel alloy powder to the modified copper powder. Although acid washing was performed, the surface of the copper powder was still exposed and prone to oxidation, which led to a decrease in the conductivity of the second back grid electrode. The modified copper powder without the silver-copper-nickel alloy powder treatment lacked the silver-copper-nickel alloy as a bridging medium, which resulted in poor contact between the first and second back grid electrodes, leading to an increase in the series resistance of the solar cell and a decrease in both photoelectric conversion efficiency and fill factor.

[0122] Examples 12-14 lack the addition of one of the three types of copper powder particles. Example 12 lacks dendritic copper powder particles, and the copper powder particles are only in point contact between spherical particles, which reduces the number of connection channels, resulting in a decrease in the conductivity of the second back grid electrode and a decrease in the photoelectric performance of the obtained solar cell. Examples 13 and 14 lack the addition of spherical nano copper powder particles and spherical micro copper powder particles, respectively. The contact between the spherical copper powder particles is not tight enough, which also leads to a decrease in the conductivity of the second back grid electrode, resulting in a decrease in the photoelectric conversion efficiency and fill factor of the obtained solar cell and an increase in the series resistance.

[0123] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for fabricating a TOPCon solar cell, characterized in that, Includes the following steps: (1) A first back grid electrode is prepared by screen printing on the back of a semi-finished battery cell using a first conductive paste and then sintering. The first conductive paste includes silver powder, a first silver-copper-nickel alloy powder, glass powder and an organic carrier. (2) A second conductive paste is used to screen print on the surface of the first back grid electrode away from the semi-finished cell, and then cured to obtain the second back grid electrode, thus obtaining the TOPCon solar cell; the second conductive paste includes modified copper powder, resin binder, curing agent and organic solvent.

2. The method for preparing a TOPCon solar cell according to claim 1, characterized in that, Based on the total mass of the first conductive paste, the first conductive paste satisfies at least one of the following conditions: (a1) The silver powder has a mass content of 70wt%~80wt%; (a2) The mass content of the first silver-copper-nickel alloy powder is 10wt%~20wt%; (a3) The mass content of the glass powder is 1.5wt%~5wt%; (a4) The organic carrier has a mass content of 5wt% to 15wt%.

3. The method for preparing a TOPCon solar cell according to claim 1 or 2, characterized in that, The particle size D50 of the first silver-copper-nickel alloy powder is 300nm~800nm; And / or, the first silver-copper-nickel alloy powder includes a first silver element, the mass of which accounts for more than 80 wt% of the total mass of the first silver-copper-nickel alloy powder; And / or, the first silver-copper-nickel alloy powder further includes a first copper element and a first nickel element, wherein the mass ratio of the first copper element to the first nickel element is (1~5):

1.

4. The method for preparing a TOPCon solar cell according to any one of claims 1 to 3, characterized in that, Based on the total mass of the second conductive paste, the second conductive paste satisfies at least one of the following conditions: (b1) The modified copper powder has a mass content of 85wt%~92wt%; (b2) The resin adhesive has a mass content of 1wt%~5wt%; (b3) The curing agent has a mass content of 1wt%~5wt%; (b4) The organic solvent has a mass content of 5wt% to 10wt%.

5. The method for preparing a TOPCon solar cell according to any one of claims 1 to 4, characterized in that, The preparation process of the modified copper powder includes: acid washing of copper powder to obtain pretreated copper powder, then mixing the pretreated copper powder with a second silver-copper-nickel alloy powder, and then drying it to obtain the modified copper powder. Preferably, in the preparation process of the modified copper powder, the mass ratio of the copper powder to the second silver-copper-nickel alloy powder is (5~10):1; Preferably, the second silver-copper-nickel alloy powder includes a second silver element, a second copper element, and a second nickel element, wherein the mass of the second silver element accounts for more than 80 wt% of the total mass of the second silver-copper-nickel alloy powder, and the mass ratio of the second copper element to the second nickel element is (1~5):1; Preferably, the particle size D50 of the second silver-copper-nickel alloy powder is 300nm~800nm.

6. The method for preparing a TOPCon solar cell according to claim 5, characterized in that, The copper powder includes first copper powder particles, second copper powder particles, and third copper powder particles.

7. The method for preparing a TOPCon solar cell according to claim 6, characterized in that, The copper powder satisfies at least one of the following conditions: (c1) The first copper powder particles are spherical nanoparticles with a particle size D50 of 150nm~500nm; (c2) Based on the total mass of the copper powder, the mass content of the first copper powder particles is 20wt%~50wt%; (c3) The second copper powder particles are spherical micron particles with a particle size D50 of 1µm to 3µm; (c4) Based on the total mass of the copper powder, the mass content of the second copper powder particles is 30wt%~60wt%; (c5) The third copper powder particles are dendritic particles with a particle size D50 of 1µm to 3µm; (c6) Based on the total mass of the copper powder, the mass content of the third copper powder particles is 5wt%-20wt%.

8. The method for preparing a TOPCon solar cell according to any one of claims 1 to 7, characterized in that, The fineness of the first conductive paste is <5µm; And / or, the fineness of the second conductive paste is <10µm; And / or, the mass ratio of the first conductive paste to the second conductive paste is 1:(1~3).

9. The method for preparing a TOPCon solar cell according to any one of claims 1 to 8, characterized in that, The semi-finished battery cells in step (1) are prepared by texturing, boron diffusion, alkaline polishing, back POLY, RCA, front and back coating processes; And / or, the sintering temperature in step (1) is 700℃~750℃; And / or, the curing temperature in step (2) is 200℃~300℃; And / or, after the curing process described in step (2), laser sintering is also performed.

10. A TOPCon solar cell, characterized in that, The TOPCon solar cell is prepared using the method described in any one of claims 1 to 9.

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