Copper plating agent, preparation method of copper plating agent and application of copper plating agent in preparation of solar cell

Abstract

The invention provides a copper plating agent, a preparation method thereof and application of the copper plating agent in preparation of solar cells, and relates to the technical field of solar cells, and the copper plating agent comprises copper salt, a complexing agent, graphene quantum dots and rare earth oxide. The formula of the copper plating solution is improved, the nano material is introduced to improve the contact resistance performance, the graphene quantum dots are added to serve as a conductive enhancer to improve the contact resistance performance, the rare earth oxide is added, and the binding force of a plating layer and a matrix is enhanced through the lattice matching effect.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, in particular to a copper plating agent, a preparation method thereof and application in the preparation of solar cells. Background Art

[0002] Metallization is a key process in the manufacture of silicon solar cells. It's primarily used to create electrodes, forming ohmic contacts between the two ends of the PN junction and enabling current output. Screen printing is currently the most mature and common metallization process, but the high cost of the silver paste used has become a significant constraint on industry adoption. To reduce solar cell costs and improve cell efficiency, copper electroplating technology offers the greatest potential for cost reduction, as it eliminates the need for silver paste.

[0003] In the current copper manufacturing process of photovoltaic cells, conductive copper grid lines are mainly formed on the surface of silicon substrates by electroplating or chemical copper plating. The plating solution formula commonly used in the prior art usually contains copper sulfate (CuSO4), acidic additives (such as sulfuric acid), wetting agents (such as polyethylene glycol) and a small amount of chloride ions (Cl-). The process steps include substrate pretreatment, first preparing a seed layer to prevent copper diffusion, then electroplating copper as a conductive layer, and finally electroplating a protective layer, post-cleaning, etc. Specifically: At present, the industry mainly forms conductive grid lines on the surface of silicon substrates by electroplating copper, and its process includes:

[0004] Seed layer preparation: A thin layer of nickel is deposited on the surface of the silicon substrate as a barrier layer to prevent copper from diffusing into the PN junction. The copper electroplating process: Using an acidic sulfate bath (containing CuSO₄, H₂SO₄, Cl₁₄, etc.), direct current electroplating is performed at 50-60°C to form a copper conductive layer. Protective layer electroplating: Tin is plated on the surface of the copper layer to prevent oxidation, completing the electrode structure. However, the conductivity and uniformity of the copper grid lines produced using existing copper plating solutions are somewhat unstable, and both these aspects need to be further improved.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] One of the objectives of the present invention is to provide a copper plating agent that solves at least one of the technical problems existing in the prior art. The present invention improves the copper plating solution formula by introducing nanomaterials to improve contact resistance, adding graphene quantum dots as conductivity enhancers to improve contact resistance, and adding rare earth oxides to enhance the bonding between the coating and the substrate through the lattice matching effect.

[0007] A second object of the present invention is to provide a method for preparing a copper plating agent.

[0008] A third object of the present invention is to provide a copper plating agent or the use of the copper plating agent obtained by the above preparation method in the preparation of solar cells.

[0009] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0010] In a first aspect, the present invention provides a copper plating agent, the components of which include: copper salt, complexing agent, graphene quantum dots and rare earth oxide.

[0011] Further, the copper salt includes copper sulfate;

[0012] Preferably, the particle size of the graphene quantum dots is less than 5 nm;

[0013] Preferably, the rare earth oxide comprises cerium oxide.

[0014] Furthermore, the copper plating agent further comprises the following components: hydrochloric acid, a surfactant, a stabilizer, a brightener, an inhibitor and a pH adjuster;

[0015] Preferably, the surfactant includes one or more of oxyethylene fatty alcohol ether, alkylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester and polyoxyethylene lauryl ether;

[0016] Preferably, the stabilizer comprises a thiourea derivative and / or polydopamine;

[0017] Preferably, the brightener comprises one or more of sodium polydisulfide dipropane sulfonate, 2-mercaptobenzimidazole, and 2-mercaptobenzothiazole;

[0018] Preferably, the inhibitor comprises polyethylene glycol and / or benzotriazole;

[0019] Preferably, the pH adjuster comprises dilute sulfuric acid and / or methanesulfonic acid.

[0020] Furthermore, the components of the copper plating agent include: 200-250g / L copper salt, 0.3-0.5g / L graphene quantum dots, 0.1-0.2g / L rare earth oxide, 0.05-0.1ml / L hydrochloric acid, 0.1-0.5g / L surfactant, 3-8ml / L brightener, 3-5g / L polyethylene glycol, 3-5g / L benzotriazole, 60-80ml / L pH regulator and the balance water;

[0021] The copper plating agent further comprises a complexing agent; the complexing agent comprises at least one of hydroxyethylidene diphosphonic acid, copper pyrophosphate, sodium citrate and potassium sodium tartrate, or the complexing agent comprises any two of ethylenediamine, potassium tartrate, citric acid and disodium edetate; wherein the content of each complexing agent is independently 3-15 g / L.

[0022] In a second aspect, the present invention provides a method for preparing a copper plating agent, comprising: mixing formulated amounts of copper salt, complexing agent, graphene quantum dots and rare earth oxide to obtain the copper plating agent.

[0023] In a third aspect, the present invention provides a copper plating agent or use of the copper plating agent prepared by the preparation method in preparing solar cells.

[0024] In a fourth aspect, the present invention provides a solar cell, the preparation method of which includes: forming patterned grooves on the front and back sides of a silicon substrate of the solar cell, and then sequentially preparing a nickel layer, a copper layer and a tin layer in the patterned grooves; wherein, the copper plating agent or the copper plating agent prepared by the preparation method is used as an electroplating solution, and the copper layer is prepared by gradient pulse electroplating.

[0025] Furthermore, the time of the gradient pulse electroplating is 1.5-5 min; the temperature of the gradient pulse electroplating is 30-50° C.;

[0026] Preferably, the gradient pulse electroplating includes: a first electroplating stage, a second electroplating stage and a third electroplating stage;

[0027] Preferably, the pulse frequencies of the first electroplating stage, the second electroplating stage and the third electroplating stage decrease gradually;

[0028] Preferably, the frequency of the first electroplating stage is 9-11 kHz, and the duty cycle is 15%-25%; the frequency of the second electroplating stage is 0.5-1.5 kHz, and the duty cycle is 45%-55%; the frequency of the third electroplating stage is 80-120 Hz, and the duty cycle is 75%-85%;

[0029] Preferably, the electroplating time of the first electroplating stage is 10%-20% of the total gradient pulse electroplating time; the electroplating time of the second electroplating stage is 60%-80% of the total gradient pulse electroplating time; the electroplating time of the third electroplating stage is 10%-20% of the total gradient pulse electroplating time;

[0030] Preferably, the gradient pulse electroplating process further comprises: reverse pulse assisted processing; the reverse pulse assisted processing comprises: applying a microsecond anodic pulse during the cathode pulse interval; the reverse pulse assisted processing time is 3-5% of the total gradient pulse electroplating time;

[0031] Preferably, the thickness of the copper layer is 9 to 12 μm;

[0032] Preferably, the nickel layer is prepared by constant current electroplating, pulse electroplating, constant current light induced electroplating, pulse light induced electroplating or chemical plating; the thickness of the nickel layer is 0.1 to 2 μm;

[0033] Preferably, the tin layer is prepared by constant current electroplating, pulse electroplating, constant current light induced electroplating, pulse light induced electroplating or chemical plating; the thickness of the tin layer is 1 to 2 μm;

[0034] Preferably, a pulse device is provided during chemical tinning, and the current density of the pulse current is 1A / dm 2 ~15A / dm 2 .

[0035] Furthermore, the width of the patterned groove is 10 to 50 μm; the depth of the patterned groove is 80 to 100 nm;

[0036] Preferably, the solar cell silicon substrate after the grooves are sequentially subjected to acid washing, drying and annealing treatments;

[0037] Preferably, the pickling temperature is 25-38°C; the pickling time is 5-50s;

[0038] Preferably, the annealing temperature is 750-800°C.

[0039] Furthermore, after the annealing and before the nickel layer is formed, the cell is edge-sealed;

[0040] Preferably, UV glue is used to seal the edges of the cell; the components of the UV glue include: modified acrylate resin, nano-silicon dioxide and fluorocarbon compound; the viscosity of the UV glue is 100-1000 cP;

[0041] Preferably, the main components of UV glue include but are not limited to modified acrylic resin, nano-silicon dioxide and fluorocarbon compounds, with a viscosity of 100-1000 cP;

[0042] Preferably, after the glue is applied, the cell is pre-cured and finally cured in sequence; the UV irradiation intensity of the pre-curing is 70-90mW / cm 2 The pre-curing time is 2-10s; the final curing UV intensity is 300-500mW / cm 2 ; The final curing time is 5-30s;

[0043] Preferably, the glue coating thickness is 5-20 μm, and the glue coating width is 10-20 μm.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] The copper plating agent provided by the present invention uses copper salt as the main salt to provide copper ions. A complexing agent is added to the formula to improve the stability of the plating solution and achieve nano-scale uniform deposition. Graphene quantum dots and rare earth oxides are also added to the formula. The graphene quantum dots serve as a conductivity enhancer to reduce contact resistance. In addition, the high specific surface area and edge active sites of the graphene quantum dots can adsorb copper ions, reducing deposition activation energy, which is beneficial to lowering the copper plating temperature, reducing energy consumption, and delaying the decomposition of additives. The rare earth oxide enhances the bonding strength between the coating and the substrate through the lattice matching effect. DETAILED DESCRIPTION

[0046] Unless otherwise defined herein, scientific and technical terms used in conjunction with the present invention shall have the meanings commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear; however, in the event of any potential ambiguity, the definitions provided herein take precedence over any dictionary or external definitions. In this application, the use of "or" means "and / or" unless otherwise stated. In addition, the use of the term "including" and other forms is non-limiting.

[0047] The technical solutions of the present invention are described clearly and completely below with reference to the embodiments. It is obvious that the embodiments described are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0048] A first aspect of the present invention provides a copper plating agent, the components of which include: copper salt, complexing agent, graphene quantum dots and rare earth oxide.

[0049] In some preferred embodiments, the copper salt includes copper sulfate (CuSO4·5H2O).

[0050] Preferably, the particle size of the graphene quantum dots is less than 5 nm.

[0051] In the present invention, it serves as a conductive enhancer to reduce contact resistance.

[0052] Preferably, the rare earth oxide comprises cerium oxide.

[0053] In the present invention, the bonding force between the coating and the substrate is enhanced through the lattice matching effect.

[0054] In some preferred embodiments, the copper plating agent further comprises the following components: hydrochloric acid, a surfactant, a stabilizer, a brightener, an inhibitor, and a pH adjuster;

[0055] Preferably, the surfactant includes one or more of oxyethylene fatty alcohol ether, alkylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester and polyoxyethylene lauryl ether.

[0056] In the present invention, a surfactant is used to improve the wettability of the plating solution, and hydrochloric acid is used to provide chloride ions to enhance the complexing ability of copper ions.

[0057] Preferably, the stabilizer comprises a thiourea derivative (such as N-methylthiourea) and / or polydopamine.

[0058] In the present invention, the stabilizer is used to selectively accelerate bottom deposition, inhibit side reactions and extend the life of the plating solution.

[0059] Preferably, the brightener includes one or more of sodium polydipropylene sulfonate, 2-mercaptobenzimidazole, and 2-mercaptobenzothiazole.

[0060] In the present invention, a brightener is used to regulate the reduction rate of copper ions, thereby achieving a smooth and dense coating.

[0061] Preferably, the inhibitor comprises polyethylene glycol and / or benzotriazole.

[0062] In the present invention, polyethylene glycol and benzotriazole are used in combination, which has a synergistic effect, inhibits excessive surface deposition, and is conducive to achieving a high aspect ratio copper grid line.

[0063] Preferably, the pH adjuster comprises dilute sulfuric acid and / or methanesulfonic acid (MSA).

[0064] In the present invention, the pH regulator can maintain the pH value of the plating solution at 2.5-3.5, and methanesulfonic acid replaces part of the sulfuric acid, thereby reducing the risk of corrosion to the silicon substrate.

[0065] In some preferred embodiments, the components of the copper plating agent include: 200-250g / L copper salt, 0.3-0.5g / L graphene quantum dots, 0.1-0.2g / L rare earth oxide, 0.05-0.1ml / L hydrochloric acid, 0.1-0.5g / L surfactant, 1-3g / L thiourea derivative, 1-3g / L polydopamine, 3-8ml / L brightener, 3-5g / L polyethylene glycol, 3-5g / L benzotriazole, 60-80ml / L pH regulator and the balance water.

[0066] Wherein, in the copper plating agent, the addition amount of copper salt is 200-250g / L, for example, it can be 200g / L, 210g / L, 220g / L, 230g / L, 240g / L, 250g / L, etc.;

[0067] Wherein, the addition amount of graphene quantum dots in the copper plating agent is 0.3-0.5 g / L, for example, 0.3 g / L, 0.4 g / L, 0.5 g / L, etc.;

[0068] Wherein, the addition amount of rare earth oxide in the copper plating agent is 0.1-0.2 g / L, for example, it can be 0.1 g / L, 0.15 g / L, 0.2 g / L, etc.;

[0069] Wherein, in the copper plating agent, the amount of hydrochloric acid added is 0.05-0.1 ml / L, for example, it can be 0.05 ml / L, 0.075 ml / L, 0.1 ml / L, etc.;

[0070] Wherein, in the copper plating agent, the addition amount of the surfactant is 0.1-0.5 g / L, for example, it can be 0.1 g / L, 0.3 g / L, 0.5 g / L, etc.;

[0071] Wherein, in the copper plating agent, the addition amount of the thiourea derivative is 1-3 g / L, for example, 1 g / L, 2 g / L, 3 g / L, etc.;

[0072] Wherein, the amount of polydopamine added to the copper plating agent is 1-3 g / L, for example, 1 g / L, 2 g / L, 3 g / L, etc.;

[0073] Wherein, in the copper plating agent, the addition amount of the brightener is 3-8 ml / L, for example, 3 ml / L, 5.5 ml / L, 8 ml / L, etc.;

[0074] Wherein, the amount of polyethylene glycol added to the copper plating agent is 3-5 g / L, for example, 3 g / L, 4 g / L, 5 g / L, etc.;

[0075] Wherein, in the copper plating agent, the addition amount of benzotriazole is 3-5 g / L, for example, 3 g / L, 4 g / L, 5 g / L, etc.;

[0076] Wherein, the addition amount of the pH adjuster in the copper plating agent is 60-80 ml / L, for example, it can be 60 ml / L, 70 ml / L, 80 ml / L, etc.

[0077] The copper plating agent also includes a complexing agent as a component; the complexing agent includes at least one of hydroxyethylidene diphosphonic acid, copper pyrophosphate, sodium citrate and potassium sodium tartrate, or the complexing agent includes any two of ethylenediamine, potassium tartrate, citric acid and disodium edetate; wherein the content of each complexing agent is independently 3-15 g / L, for example, 3 g / L, 5 g / L, 7 g / L, 9 g / L, 11 g / L, 13 g / L, 15 g / L, etc.

[0078] Optionally, the combination of the complexing agents is 5-10 g / L of ethylenediamine and 5-10 g / L of potassium tartrate, or the combination of the complexing agents is 5-10 g / L of citric acid and 5-10 g / L of disodium ethylenediaminetetraacetate.

[0079] In the present invention, the complexing agent can enhance the complexing ability of chloride ions. When the complexing agent composite system is used, the stability of the plating solution can be further improved, and nano-level uniform deposition can be achieved.

[0080] Further preferably, the components of the copper plating agent include:

[0081] 200-250g / L copper salt, composite complexing agent (ethylenediamine 5-10g / L + potassium tartrate 5-10g / L, or, citric acid 5-10g / L + disodium ethylenediaminetetraacetic acid 5-10g / L), 0.3-0.5g / L graphene quantum dots, 0.1-0.2g / L rare earth oxide, 0.05-0.1ml / L hydrochloric acid, 0.1-0.5g / L surfactant, stabilizer (1-3g / L thiourea derivative, 1-3g / L polydopamine), 3-8ml / L brightener (specifically sodium polydisulfide dipropane sulfonate), inhibitor (polyethylene glycol 3-5g / L, benzotriazole 3-5g / L), 60-80ml / L pH adjuster (dilute sulfuric acid and methanesulfonic acid, the volume ratio of the two is 1:1) and the balance water.

[0082] A second aspect of the present invention provides a method for preparing a copper plating agent, comprising: mixing formulated amounts of copper salt, a complexing agent, graphene quantum dots, and rare earth oxides to obtain the copper plating agent.

[0083] The copper plating agent provided by the present invention significantly improves adhesion and extends the life of the plating solution by adding a stabilizer and a trace amount of rare earth elements; adopts a dual complexing agent system and pulse electroplating to promote uniform deposition, and the high specific surface area and edge active sites of graphene quantum dots can adsorb copper ions, reducing deposition activation energy, which is beneficial to lowering the copper plating temperature, reducing energy consumption, and delaying the decomposition of additives.

[0084] A third aspect of the present invention provides a copper plating agent or use of the copper plating agent prepared by the preparation method in preparing solar cells.

[0085] A fourth aspect of the present invention provides a solar cell, the preparation method of which comprises: forming patterned grooves on the front and back sides of a silicon substrate of the solar cell, and then sequentially preparing a nickel layer, a copper layer, and a tin layer in the patterned grooves; wherein, the copper plating agent or the copper plating agent prepared by the preparation method is used as an electroplating solution, and the copper layer is prepared by gradient pulse electroplating.

[0086] In some preferred embodiments, the time of the gradient pulse electroplating is 1.5-5 min, for example, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, etc.; the temperature of the gradient pulse electroplating is 30-50° C., for example, 30° C., 40° C., 50° C., etc.;

[0087] Preferably, the gradient pulse electroplating includes: a first electroplating stage, a second electroplating stage and a third electroplating stage;

[0088] Preferably, the pulse frequencies of the first electroplating stage, the second electroplating stage and the third electroplating stage decrease gradually;

[0089] Preferably, the frequency of the first electroplating stage is 9-11kHz, for example, 9kHz, 10kHz, 11kHz, etc., and the duty cycle is 15%-25%, for example, 15%, 20%, 25%, etc., to suppress dendrites and promote uniform adsorption of graphene quantum dots; the frequency of the second electroplating stage is 0.5-1.5kHz, for example, 0.5kHz, 1kHz, 1.5kHz, etc., and the duty cycle is 45%-55%, for example, 45%, 50%, 55%, etc., to increase the deposition rate; the frequency of the third electroplating stage is 80-120Hz, for example, 80Hz, 100Hz, 120Hz, etc., and the duty cycle is 75%-85%, for example, 75%, 80%, 85%, etc., to release internal stress and form a dense coating;

[0090] Preferably, the electroplating time of the first electroplating stage is 10%-20% of the total gradient pulse electroplating time, for example, it can be 10%, 15%, 20%, etc.; the electroplating time of the second electroplating stage is 60%-80% of the total gradient pulse electroplating time, for example, it can be 60%, 70%, 80%, etc.; the electroplating time of the third electroplating stage is 10%-20% of the total gradient pulse electroplating time, for example, it can be 10%, 15%, 20%, etc.

[0091] In the present invention, by adjusting the pulse electroplating parameters, the graphene quantum dots are uniformly distributed, and can be uniformly co-deposited with copper, thereby improving the reliability of the gate line. The above three-level pulse is a cathode pulse.

[0092] Preferably, the gradient pulse electroplating process further comprises:

[0093] Reverse pulse assist: Microsecond anodic pulses are applied between cathodic pulses to remove loose deposits and improve coating smoothness. The reverse pulse assist duration is 3-5% of the total gradient pulse plating time, for example, 3%, 4%, 5%, etc.

[0094] Preferably, the thickness of the copper layer is 9 to 12 μm, for example, 9 μm, 10 μm, 11 μm, 12 μm, etc.

[0095] Preferably, the nickel layer is prepared by constant current electroplating, pulse electroplating, constant current light induced electroplating, pulse light induced electroplating, or chemical plating; the thickness of the nickel layer is 0.1 to 2 μm, for example, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, etc.;

[0096] Preferably, the nickel-plated battery cell is washed with deionized water and dried; then pickled for 70-90 seconds, for example, 70 seconds, 80 seconds, 90 seconds, etc., with the pickling solution being 15-20% sulfuric acid solution, for example, 15%, 17.5%, 20%, etc.

[0097] Preferably, the tin layer is prepared by constant current electroplating, pulse electroplating, constant current light induced electroplating, pulse light induced electroplating, or chemical plating; the thickness of the tin layer is 1 to 2 μm, for example, 1 μm, 1.5 μm, 2 μm, etc.;

[0098] Preferably, a pulse device is provided during chemical tinning, and the current density of the pulse current is 1A / dm 2 ~15A / dm 2 , for example, it can be 1A / dm 2 , 5A / dm 2 、10A / dm 2 、15A / dm 2 wait.

[0099] In some preferred embodiments, the width of the patterned groove is 10 to 50 μm, for example, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, etc.; the depth of the patterned groove is 80 to 100 nm, for example, 80 nm, 90 nm, 100 nm, etc.;

[0100] Preferably, the solar cell silicon substrate after the grooves are sequentially subjected to acid washing, drying and annealing treatments;

[0101] Preferably, the pickling solution used for pickling contains hydrofluoric acid, and the amount of hydrofluoric acid added is 10 to 20 mL / L, for example, 10 mL / L, 15 mL / L, 20 mL / L, etc.;

[0102] Preferably, the pickling temperature is 25-38° C.; the pickling time is 5-50 s, for example, 5 s, 10 s, 15 s, 20 s, 25 s, 30 s, 35 s, 40 s, 45 s, 50 s, etc.;

[0103] Preferably, the annealing temperature is 750-800°C, for example, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, etc.

[0104] In some preferred embodiments, after the annealing and before the nickel layer is formed, the cell is edge-sealed;

[0105] Preferably, UV glue is used to seal the edges of the cell; the components of the UV glue include but are not limited to modified acrylic resin, nano-silicon dioxide and fluorocarbon compounds; the viscosity of the UV glue is 100-1000 cP;

[0106] Preferably, the main components of UV glue include but are not limited to modified acrylic resin, nano-silicon dioxide and fluorocarbon compounds, with a viscosity of 100-1000 cP;

[0107] Preferably, after the glue is applied, the cell is pre-cured and finally cured in sequence; the UV irradiation intensity of the pre-curing is 70-90mW / cm 2 , for example, it can be 70mW / cm 2 , 80mW / cm 2 , 90mW / cm 2 The pre-curing time is 2-10s, for example, 2s, 6s, 10s, etc.; the final curing UV intensity is 300-500mW / cm 2 , for example, it can be 300mW / cm 2 , 400mW / cm 2 , 500mW / cm 2 The final curing time is 5-30s, for example, 5s, 10s, 15s, 20s, 25s, 30s, etc.;

[0108] Preferably, the glue coating thickness is 5-20 μm, for example, 5 μm, 10 μm, 15 μm, 20 μm, etc.; the glue coating width is 10-20 μm, for example, 10 μm, 15 μm, 20 μm, etc.

[0109] In the prior art, during the electroplating process, metal often deposits on the sides of the cell due to the lack of a passivation film, which is in a conductive state. This leads to severe edge leakage and reduced parallel resistance of the cell. The present invention improves the process to solve the problem of plating on the cell edges and ensures parallel resistance.

[0110] Furthermore, the copper plating agent formulation of the present invention achieves significant improvements in coating performance through the synergistic effects of its components and innovative electroplating methods, particularly achieving unexpected technical results in terms of contact resistance, bonding strength, and uniformity. The following details the two aspects of component synergy and process innovation:

[0111] 1. Component synergistic mechanism

[0112] 1. Synergy between nanomaterials and complex systems: Graphene quantum dots (<5nm): embedded in the copper plating as a conductive network skeleton, reducing the interface potential barrier and electron scattering through the quantum confinement effect, thereby reducing contact resistance.

[0113] It works synergistically with a double complexing agent system (such as ethylenediamine + potassium tartrate): the complexing agent preferentially adsorbs on the graphene surface, regulates the directional deposition of copper ions on its edge, avoids the agglomeration of nanomaterials, and achieves uniform dispersion at the nanoscale.

[0114] 2. Lattice matching between rare earth oxides and stabilizers

[0115] Cerium oxide (CeO2): Its structure has a lattice constant match with the silicon substrate crystal plane, and the coating adhesion is enhanced through the epitaxial growth mechanism.

[0116] Together with the polydopamine stabilizer, it selectively adsorbs on defect sites of the silicon substrate to inhibit the abnormal nucleation of copper.

[0117] 3. Dynamic balance between inhibitors and brighteners

[0118] Benzotriazole + PEG:

[0119] During the cathode stage of pulse electroplating, it is adsorbed in the high current density area to inhibit dendrite growth; during the anode reverse pulse stage, it is partially desorbed to avoid excessive inhibition and a decrease in deposition rate.

[0120] Synergistically with sodium polydisulfide dipropane sulfonate brightener: the brightener preferentially occupies the grain boundary position, while the inhibitor covers the crystal surface, forming a "grain boundary-crystal surface" differentiated regulation to obtain a mirror-grade coating.

[0121] 4. Corrosion inhibition by pH adjusters and surfactants

[0122] Methanesulfonic acid (MSA) replaces part of sulfuric acid:

[0123] The organic anions of MSA form a monomolecular protective layer on the silicon surface, reducing the acid etching rate.

[0124] Compounded with oxyethylene fatty alcohol ether surfactant: dynamically reduce interfacial tension.

[0125] 2. Electroplating process: gradient pulse electroplating technology

[0126] High frequency-medium frequency-low frequency three-stage control:

[0127] First electroplating stage (preferably 10kHz): High-frequency pulses force copper ions to preferentially nucleate on the surface of graphene quantum dots, forming a dense bottom layer; high frequency promotes the vertical alignment of graphene quantum dots to the substrate, building a three-dimensional conductive network and improving mechanical strength;

[0128] Second electroplating stage (preferably 1kHz): medium-frequency pulses expand the thickness of the diffusion layer to achieve rapid bulk filling;

[0129] The third electroplating stage (preferably 100 Hz): low-frequency pulses promote lattice rearrangement, release internal stress, and promote the deposition of graphene quantum dots in the horizontal direction to form a layered structure and enhance conductivity.

[0130] The present invention comprehensively improves the conductivity, uniformity, adhesion and plating solution stability of photovoltaic cell electrodes through formula improvement, process optimization and equipment parameter adjustment, while solving technical problems such as leakage at the edges of electroplated cell sheets.

[0131] The present invention is further described below by way of examples. Unless otherwise specified, the materials in the examples were prepared according to existing methods or directly purchased from the market.

[0132] Example 1

[0133] This embodiment provides a copper plating agent, including the following components:

[0134] 225g / L CuSO4·5H2O, composite complexing agent (7.5g / L ethylenediamine and 7.5g / L potassium tartrate), 0.4g / L graphene quantum dots (particle size <5nm), 0.15g / L rare earth oxide (specifically cerium oxide), 0.075ml / L hydrochloric acid, 0.3g / L surfactant (specifically oxyethylene fatty alcohol ether), stabilizer (2g / L N-methylthiourea, 2g / L amino polydopamine), 5.5ml / L brightener (specifically sodium polydisulfide dipropylene glycol sulfonate), inhibitor (4g / L polyethylene glycol, 4g / L benzotriazole), 70ml / L pH adjuster (dilute sulfuric acid and methanesulfonic acid, the volume ratio is 1:1) and the balance is water.

[0135] Example 2

[0136] This embodiment provides a copper plating agent, including the following components:

[0137] 200g / L CuSO4·5H2O, composite complexing agent (5g / L ethylenediamine and 10g / L potassium tartrate), 0.3g / L graphene quantum dots (particle size <5nm), 0.2g / L rare earth oxide (specifically cerium oxide), 0.05ml / L hydrochloric acid, 0.5g / L surfactant (specifically oxyethylene fatty alcohol ether), stabilizer (1g / L N-methylthiourea, 3g / L amino polydopamine), 3ml / L brightener (specifically sodium polydisulfide dipropane sulfonate), inhibitor (3g / L polyethylene glycol, 5g / L benzotriazole), 60ml / L pH adjuster (dilute sulfuric acid and methanesulfonic acid, the volume ratio is 1:1) and the balance is water.

[0138] Example 3

[0139] This embodiment provides a copper plating agent, including the following components:

[0140] 250g / L CuSO4·5H2O, composite complexing agent (10g / L ethylenediamine and 5g / L potassium tartrate), 0.5g / L graphene quantum dots (particle size <5nm), 0.1g / L rare earth oxide (specifically cerium oxide), 0.1ml / L hydrochloric acid, 0.1g / L surfactant (specifically oxyethylene fatty alcohol ether), stabilizer (3g / L N-methylthiourea, 1g / L amino polydopamine), 8ml / L brightener (specifically sodium polydisulfide dipropane sulfonate), inhibitor (5g / L polyethylene glycol, 3g / L benzotriazole), 80ml / L pH adjuster (dilute sulfuric acid and methanesulfonic acid, the volume ratio is 1:1) and the balance is water.

[0141] Example 4

[0142] This embodiment provides a copper plating agent, including the following components:

[0143] 150g / L CuSO4·5H2O, composite complexing agent (4g / L ethylenediamine and 11g / L potassium tartrate), 0.2g / L graphene quantum dots (particle size <5nm), 0.3g / L rare earth oxide (specifically cerium oxide), 0.04ml / L hydrochloric acid, 0.6g / L surfactant (specifically oxyethylene fatty alcohol ether), stabilizer (0.5g / L N-methylthiourea, 4g / L amino polydopamine), 2ml / L brightener (specifically sodium polydisulfide dipropylene glycol sulfonate), inhibitor (6g / L polyethylene glycol, 2g / L benzotriazole), 90ml / L pH adjuster (dilute sulfuric acid and methanesulfonic acid, the volume ratio is 1:1) and the balance is water.

[0144] Example 5

[0145] This embodiment provides a copper plating agent, including the following components:

[0146] 300g / L CuSO4·5H2O, composite complexing agent (11g / L ethylenediamine and 4g / L potassium tartrate), 0.6g / L graphene quantum dots (particle size <5nm), 0.05g / L rare earth oxide (specifically cerium oxide), 0.2ml / L hydrochloric acid, 0.05g / L surfactant (specifically oxyethylene fatty alcohol ether), stabilizer (4g / L N-methylthiourea, 0.5g / L amino polydopamine), 9ml / L brightener (specifically sodium polydisulfide dipropane sulfonate), inhibitor (2g / L polyethylene glycol, 6g / L benzotriazole), 50ml / L pH adjuster (dilute sulfuric acid and methanesulfonic acid, the volume ratio is 1:1) and the balance is water.

[0147] Example 6

[0148] This embodiment provides a copper plating agent, which is different from Example 1 in that 7.5 g / L potassium tartrate is used as a complexing agent; the rest is the same as Example 1.

[0149] Example 7

[0150] This embodiment provides a copper plating agent, which differs from Example 1 in that a complexing agent is a combination of 7.5 g / L potassium tartrate and 7.5 g / L disodium ethylenediaminetetraacetate; the rest is the same as Example 1.

[0151] Example 8

[0152] This embodiment provides a copper plating agent, which is different from Example 1 in that the stabilizer does not contain amino polydopamine; the rest is the same as Example 1.

[0153] Example 9

[0154] This embodiment provides a copper plating agent, which is different from the embodiment 1 in that the inhibitor does not contain benzotriazole; the rest is the same as the embodiment 1.

[0155] Example 10

[0156] This embodiment provides a copper plating agent, which is different from the embodiment 1 in that the pH regulator does not contain methanesulfonic acid; the rest is the same as the embodiment 1.

[0157] Examples 11-20

[0158] Examples 11-20 provide a solar cell, each using the copper plating agent of Examples 1-10. The preparation process of the solar cell is as follows:

[0159] Step 1: Providing a solar cell silicon substrate, and forming patterned grooves on the front and back sides of the solar cell silicon substrate in sequence by laser film cutting, wherein the patterned grooves have a width of 30 μm and a depth of 90 nm;

[0160] Step 2: The opened film portion of the solar cell is pickled and dried; the pickled and dried cell is then subjected to high-temperature annealing at 780°C, a conveyor speed of 4m / min, and nitrogen as a protective gas. The pickling solution contains hydrofluoric acid at a rate of 15mL / L; the pickling solution is at a temperature of 35°C; and the silicon substrate is allowed to float in the pickling solution for 30 seconds.

[0161] Step 3: After the repair, seal the edges of the cell with UV glue.

[0162] Among them, the main components of UV glue include modified acrylic resin, nano-silica and fluorocarbon compounds, with a viscosity of 800cP; after coating, it is pre-cured (80mW / cm 2 , 6s) and final curing (400mW / cm 2 , 20s); glue thickness 15μm, width 15μm;

[0163] Step 4: The coated cell is nickel-plated on both sides by constant current electroplating; the thickness of the nickel plating layer is 1 μm; the nickel-plated cell is washed with deionized water and dried; and then pickled for 80 seconds with a 20% sulfuric acid solution.

[0164] Step 5: Examples 11-20 respectively use the copper plating agent formulas in Examples 1-10 to prepare copper plating agents, and the preparation process is: the formula amounts of copper sulfate, hydrochloric acid, complexing agent, surfactant, stabilizer, brightener, inhibitor, pH regulator, graphene quantum dots, rare earth oxides and other raw materials are fully mixed and used (it should be noted that the copper plating agent formulas in some embodiments do not contain certain components, and the configuration is based on the formula in the actual Examples 1-10); the copper plating temperature is 40 ° C, the electroplating time is 4 min; the copper plating agent is used as the electroplating solution, and the copper plating adopts a gradient pulse electroplating process. The process is as follows (the operation is: using a suction cup to adsorb the battery cell, and then the side of the battery cell to be copper-plated is contacted with the electroplating solution, and then electroplating is carried out. The specific operation mode of pulse electroplating is a technology well known to those skilled in the art and will not be repeated here). The specific parameters in the process are:

[0165] Stage 1 (high frequency, 15% plating time): 10kHz, 20% duty cycle;

[0166] Stage 2 (medium frequency, 70% plating time): 1kHz, 50% duty cycle;

[0167] Stage 3 (low frequency, 15% plating time): 100 Hz, 80% duty cycle;

[0168] Among them, reverse pulse assistance was used (4% of the plating time): microsecond anodic pulses were applied between cathodic pulses;

[0169] The thickness of the copper plating layer is 10um;

[0170] Step 6: Double-sided tinning by chemical plating; chemical tinning is equipped with a pulse device, and the current density of the pulse current is 8A / dm 2 ;The thickness of the tin plating layer is 1.5um;

[0171] Step 7: The tinned cell is washed with deionized water and dried to obtain a solar cell.

[0172] Example 21

[0173] This embodiment provides a solar cell, which uses the copper plating agent in Example 1. The difference between the preparation process of the solar cell and that of Example 11 is as follows:

[0174] In step 5, copper plating adopts gradient pulse electroplating process, and the process is as follows:

[0175] Stage 1 (high frequency, 10% plating time): 9kHz, 15% duty cycle;

[0176] Stage 2 (medium frequency, 80% plating time): 1.5kHz, 55% duty cycle;

[0177] Stage 3 (low frequency, 10% plating time): 80 Hz, 75% duty cycle;

[0178] Among them, reverse pulse assistance (3% plating time) was used: microsecond anodic pulses were applied between cathodic pulses;

[0179] The remaining steps are consistent with Example 11.

[0180] Example 22

[0181] This embodiment provides a solar cell, which uses the copper plating agent in Example 1. The difference between the preparation process of the solar cell and that of Example 11 is as follows:

[0182] In step 5, copper plating adopts gradient pulse electroplating process, and the process is as follows:

[0183] Stage 1 (high frequency, 20% plating time): 11kHz, 25% duty cycle;

[0184] Stage 2 (medium frequency, 60% plating time): 0.5kHz, 45% duty cycle;

[0185] Stage 3 (low frequency, 20% plating time): 120 Hz, 85% duty cycle;

[0186] Among them, reverse pulse assistance (5% plating time) was used: microsecond anodic pulses were applied between cathodic pulses;

[0187] The remaining steps are consistent with Example 11.

[0188] Example 23

[0189] This embodiment provides a solar cell, which uses the copper plating agent in Example 1. The difference between the preparation process of the solar cell and that of Example 11 is as follows:

[0190] In step 5, copper plating adopts gradient pulse electroplating process, and the process is as follows:

[0191] Stage 1 (high frequency, 3% plating time): 8kHz, 10% duty cycle;

[0192] Stage 2 (medium frequency, 90% plating time): 2kHz, 60% duty cycle;

[0193] Stage 3 (low frequency, 7% plating time): 70 Hz, 70% duty cycle;

[0194] Among them, reverse pulse assistance (2% plating time) was used: microsecond anodic pulses were applied between cathodic pulses;

[0195] The remaining steps are consistent with Example 11.

[0196] Example 24

[0197] This embodiment provides a solar cell, which uses the copper plating agent in Example 1. The difference between the preparation process of the solar cell and that of Example 11 is as follows:

[0198] In step 5, copper plating adopts gradient pulse electroplating process, and the process is as follows:

[0199] Stage 1 (high frequency, 25% plating time): 12kHz, 30% duty cycle;

[0200] Stage 2 (medium frequency, 50% plating time): 0.3kHz, 40% duty cycle;

[0201] Stage 3 (low frequency, 25% plating time): 150 Hz, 90% duty cycle;

[0202] Among them, reverse pulse assistance (6% plating time) was used: microsecond anodic pulses were applied between cathodic pulses;

[0203] The remaining steps are consistent with Example 11.

[0204] Example 25

[0205] This embodiment provides a solar cell, which uses the copper plating agent in Example 1. The difference between the preparation process of the solar cell and that of Example 11 is as follows:

[0206] In step 5, copper plating adopts gradient pulse electroplating process, and the process is as follows:

[0207] Stage 1 (low frequency, 15% plating time): 100 Hz, 80% duty cycle;

[0208] Stage 2 (medium frequency, 70% plating time): 1kHz, 50% duty cycle;

[0209] Stage 3 (high frequency, 15% plating time): 10kHz, 20% duty cycle;

[0210] The remaining steps are consistent with Example 11.

[0211] Example 26

[0212] This embodiment provides a solar cell, which uses the copper plating agent in Example 1. The difference between the preparation process of the solar cell and Example 11 is that in step 5, reverse pulse auxiliary treatment is not performed; the remaining steps are consistent with Example 11.

[0213] Example 27

[0214] This embodiment provides a solar cell, which uses the copper plating agent in Example 1. The difference between the preparation process of the solar cell and Example 11 is that step 3 is not performed, that is, UV glue is not used to seal the edges of the solar cell; the remaining steps are consistent with Example 11.

[0215] Comparative Example 1

[0216] This comparative example provides a copper plating agent, which differs from Example 1 in that it does not contain graphene quantum dots; the rest is consistent with Example 1.

[0217] Comparative Example 2

[0218] This comparative example provides a copper plating agent, which differs from Example 1 in that it does not contain a complexing agent; the rest is the same as Example 1.

[0219] Comparative Example 3

[0220] This comparative example provides a copper plating agent, which differs from Example 1 in that it does not contain rare earth oxides; the rest is the same as Example 1.

[0221] Comparative Examples 4-6

[0222] Comparative Examples 4-6 provide a solar cell, which uses the copper plating agents in Comparative Examples 1-3 respectively. The preparation process of the solar cell is consistent with that of Example 11.

[0223] Comparative Example 7

[0224] This comparative example provides a solar cell, which differs from Example 11 in that, in step 5, non-gradient pulse plating is used, and the parameters are as follows:

[0225] The pulse frequency is 1 kHz, the duty cycle is 50%, and the plating time is 4 min;

[0226] The remaining steps are consistent with Example 11.

[0227] Test Case

[0228] Test samples: The solar cells prepared in Examples 11-27 and Comparative Examples 4-7 were used as samples for testing.

[0229] Test method:

[0230] (1) Electrical performance test: Offline solar IV tester;

[0231] (2) Welding tension under low temperature conditions: tensile force meter;

[0232] (3) Grid line uniformity: Use a nine-square grid to measure the grid line aspect ratio in different areas and calculate its variance. The smaller the value, the more stable the aspect ratio.

[0233] (4) Resistance test: Use a probe resistance tester.

[0234] The test results are shown in Table 1.

[0235] Table 1

[0236]

[0237]

[0238] As can be seen from the data in Table 1, through Example 11 and Examples 14-20, and Comparative Examples 4-6, it can be seen that the copper plating agent provided by the present invention uses specific components and is within the specific component range, which can improve the comprehensive performance of the battery; at the same time, through Example 11 and Examples 23-27, and Comparative Example 7, it can be seen that the battery preparation method provided by the present invention has more excellent effects under specific process parameters; the present invention improves the contact resistance performance by introducing nanomaterials, increases graphene quantum dots, and improves the contact resistance performance as a conductive enhancer, and adds rare earth oxides to enhance the bonding strength between the coating and the substrate. A double complexing agent system (such as ethylenediamine + potassium tartrate) achieves nanoscale uniform dispersion and promotes the enhancement of grid line uniformity and bonding strength. Methanesulfonic acid (MSA) replaces part of sulfuric acid, reduces the acid etching rate of the silicon surface, and can improve battery efficiency; improves the electroplating process, gradient pulse electroplating technology, promotes preferential nucleation on the surface of graphene quantum dots, forms a dense bottom layer, improves mechanical strength, and enhances conductivity.

[0239] The present invention comprehensively improves the conductivity, uniformity, adhesion and plating solution stability of photovoltaic cell electrodes through formula improvement, process optimization and equipment parameter adjustment, while solving technical problems such as leakage at the edges of electroplated cell sheets.

[0240] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A copper plating agent, characterized in that The components include copper salt, complexing agent, graphene quantum dots and rare earth oxide.

2. The copper plating agent according to claim 1, characterized in that The copper salt includes copper sulfate; Preferably, the particle size of the graphene quantum dots is less than 5 nm; Preferably, the rare earth oxide comprises cerium oxide.

3. The copper plating agent according to claim 1, characterized in that The copper plating agent further comprises the following components: hydrochloric acid, a surfactant, a stabilizer, a brightener, an inhibitor and a pH regulator; Preferably, the surfactant includes one or more of oxyethylene fatty alcohol ether, alkylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester and polyoxyethylene lauryl ether; Preferably, the stabilizer comprises a thiourea derivative and / or polydopamine; Preferably, the brightener comprises one or more of sodium polydisulfide dipropane sulfonate, 2-mercaptobenzimidazole, and 2-mercaptobenzothiazole; Preferably, the inhibitor comprises polyethylene glycol and / or benzotriazole; Preferably, the pH adjuster comprises dilute sulfuric acid and / or methanesulfonic acid.

4. The copper plating agent according to claim 3, characterized in that The copper plating agent comprises: 200-250 g / L copper salt, 0.3-0.5 g / L graphene quantum dots, 0.1-0.2 g / L rare earth oxide, 0.05-0.1 ml / L hydrochloric acid, 0.1-0.5 g / L surfactant, 1-3 g / L thiourea derivative, 1-3 g / L polydopamine, 3-8 ml / L brightener, 3-5 g / L polyethylene glycol, 3-5 g / L benzotriazole, 60-80 ml / L pH regulator and the balance water; The copper plating agent further comprises a complexing agent; the complexing agent comprises at least one of hydroxyethylidene diphosphonic acid, copper pyrophosphate, sodium citrate and potassium sodium tartrate, or the complexing agent comprises any two of ethylenediamine, potassium tartrate, citric acid and disodium edetate; wherein the content of each complexing agent is independently 3-15 g / L.

5. The method for preparing the copper plating agent according to any one of claims 1 to 4, wherein: include: The copper plating agent is obtained by mixing the copper salt, the complexing agent, the graphene quantum dots and the rare earth oxide in the formulated amounts.

6. Use of the copper plating agent according to any one of claims 1 to 4 or the copper plating agent prepared by the preparation method according to claim 5 in the preparation of solar cells.

7. A solar cell, characterized in that: The preparation method comprises: forming patterned grooves on the front and back sides of a solar cell silicon substrate, and then sequentially preparing a nickel layer, a copper layer, and a tin layer in the patterned grooves; wherein the copper plating agent described in any one of claims 1 to 4 or the copper plating agent prepared by the preparation method described in claim 5 is used as an electroplating solution, and the copper layer is prepared by gradient pulse electroplating.

8. The solar cell according to claim 7, characterized in that The time of the gradient pulse electroplating is 1.5-5 minutes; the temperature of the gradient pulse electroplating is 30-50°C; Preferably, the gradient pulse electroplating includes: a first electroplating stage, a second electroplating stage and a third electroplating stage; Preferably, the pulse frequencies of the first electroplating stage, the second electroplating stage and the third electroplating stage decrease gradually; Preferably, the frequency of the first electroplating stage is 9-11 kHz, and the duty cycle is 15%-25%; the frequency of the second electroplating stage is 0.5-1.5 kHz, and the duty cycle is 45%-55%; the frequency of the third electroplating stage is 80-120 Hz, and the duty cycle is 75%-85%; Preferably, the electroplating time of the first electroplating stage is 10%-20% of the total gradient pulse electroplating time; the electroplating time of the second electroplating stage is 60%-80% of the total gradient pulse electroplating time; the electroplating time of the third electroplating stage is 10%-20% of the total gradient pulse electroplating time; Preferably, the gradient pulse electroplating process further comprises: reverse pulse assisted processing; the reverse pulse assisted processing comprises: applying a microsecond anodic pulse during the cathode pulse interval; the reverse pulse assisted processing time is 3-5% of the total gradient pulse electroplating time; Preferably, the thickness of the copper layer is 9 to 12 μm; Preferably, the nickel layer is prepared by constant current electroplating, pulse electroplating, constant current light induced electroplating, pulse light induced electroplating or chemical plating; the thickness of the nickel layer is 0.1 to 2 μm; Preferably, the tin layer is prepared by constant current electroplating, pulse electroplating, constant current light induced electroplating, pulse light induced electroplating or chemical plating; the thickness of the tin layer is 1 to 2 μm; Preferably, a pulse device is provided during chemical tinning, and the current density of the pulse current is 1A / dm 2 ~15A / dm 2 .

9. The solar cell according to claim 7, wherein: The width of the patterned groove is 10 to 50 μm; the depth of the patterned groove is 80 to 100 nm; Preferably, the solar cell silicon substrate after the grooves are sequentially subjected to acid washing, drying and annealing treatments; Preferably, the pickling temperature is 25-38°C; the pickling time is 5-50s; Preferably, the annealing temperature is 750-800°C.

10. The solar cell according to claim 9, characterized in that After the annealing and before the nickel layer is formed, the battery cell is edge-sealed; Preferably, UV glue is used to seal the edges of the cell; the components of the UV glue include: modified acrylate resin, nano-silicon dioxide and fluorocarbon compound; the viscosity of the UV glue is 100-1000 cP; Preferably, after the glue is applied, the cell is pre-cured and finally cured in sequence; the UV irradiation intensity of the pre-curing is 70-90mW / cm 2 The pre-curing time is 2-10s; the final curing UV intensity is 300-500mW / cm 2 ; The final curing time is 5-30s; Preferably, the glue coating thickness is 5-20 μm, and the glue coating width is 10-20 μm.

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