Copper paste and preparation method thereof, and HBC solar cell metallization method

Abstract

The invention relates to a conductive material containing metal or alloy and a method specially suitable for manufacturing an HBC solar cell, in particular to copper paste, a preparation method thereof and an HBC solar cell metallization method, and aims to solve the problems that the production cost is high, the cost is low and the like due to the fact that copper powder is coated with silver or tin in an existing raw material for preparing a grid line. And pure copper powder is easy to oxidize in the air, so that the conductivity is reduced, and the grid line is poor in adhesive force and easy to fall off. The copper paste comprises copper powder and tin powder, and the copper powder is pure copper powder without a coating layer on the surface; the problem that direct silk-screen printing copper paste is poor in adhesive force is solved by constructing the transition layer, and due to the fact that silver and a coating layer are not adopted, the metallization cost of the HBC solar cell can be remarkably reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a conductive material containing metal or alloy, a method specially suitable for manufacturing HBC solar cells, and in particular to a copper paste and a preparation method thereof, and a HBC solar cell metallization method. BACKGROUND

[0002] Heterojunction back contact (HBC) solar cells have higher conversion efficiency and are considered as the next generation mainstream technology, and the metal electrode is a key step in the production of HBC solar cells. However, the low-temperature silver paste currently used in HBC solar cells has high consumption and high price, resulting in high manufacturing cost, which hinders the marketization of HBC solar cells.

[0003] Chinese patents CN114055007A and CN114055008A introduce two kinds of solder powder, metal powder and their preparation methods related to solder paste, which are used to improve the efficiency and reduce the cost of solar cells.

[0004] Among them, CN114055007A discloses a solder powder containing silver and / or tin coated copper powder, pure tin powder, pure bismuth powder and pure indium powder. The particle size and coating thickness of this solder powder are different, and the solder paste made therefrom has better conductivity and thermal conductivity than pure copper after solidification, and the melting point is 155 degrees. This solder paste is particularly suitable for solar cell fine grid line printing, can replace silver paste, reduce the breakpoint and series resistance, improve the conversion efficiency, and thus reduce the cost.

[0005] Among them, CN114055008A introduces a metal powder containing silver plated copper powder and tin powder for preparing ultra-fine solder paste. The solder paste described in this patent can effectively reduce the grid line width and shading loss in solar cell applications, thereby improving the conversion efficiency of solar cells and reducing the metallization cost. This method can more economically prepare solder paste and facilitate industrialization and application.

[0006] The copper powder in the above-mentioned solder powder is coated with silver and / or tin, and the copper powder in the above-mentioned metal powder is coated with silver. Since silver has a high cost, the process of preparing silver or tin coated copper powder involves additional processing steps, and chemical waste that must be treated may be generated during the coating process, resulting in increased production cost.

[0007] If copper powder is not coated with silver or tin, the following problems will be encountered:

[0008] (1) Oxidation problem: copper powder is easily oxidized in air, which will affect the soldering performance of the solder paste and the long-term stability of the grid line, and the use of silver or tin coated copper powder can protect the copper powder from oxidation to some extent;

[0009] (2) The adhesion is weakened: the binding force between copper and transparent conductive oxide (TCO) film is poor, so the grid lines are prone to falling off. SUMMARY

[0010] The present application aims to solve the problems of the prior art, i.e. the use of silver or tin-coated copper powder as raw material for preparing grid lines results in high production cost, the use of pure copper powder is prone to oxidation in air, which leads to poor conductivity and poor adhesion of the grid lines, and provides a copper paste, a preparation method thereof and a HBC solar cell metallization method.

[0011] To solve the problems of the prior art, the present application provides the following technical solutions:

[0012] A copper paste, characterized in that it comprises metal powder, organic acid flux, plasticizing agent and viscosity regulator.

[0013] The metal powder is composed of copper powder and tin powder.

[0014] The mass percentage of the copper powder in the metal powder is 50-80wt%, the copper powder is spherical or quasi-spherical pure copper powder, and the average particle size is 5-15 microns.

[0015] The tin powder is pure tin powder or tin alloy powder, the tin powder is spherical, and the particle size is 3-15 microns, and the tin alloy powder comprises tin and one or more of bismuth, lead and indium.

[0016] Further, the organic acid flux is composed of one or more of citric acid, salicylic acid, sulfosalicylic acid, succinic acid and aminosulfonic acid; the plasticizing agent is composed of one or more of hydrogenated castor oil, castor oil monoethanolamide, ethyl cellulose, acrylic resin, ethylene glycol propyl ether, butyl oleate, diethylene glycol monobutyl ether acetate or polyamide wax; and the viscosity regulator comprises one or more of epoxy resin, phenolic resin, bisphenol epoxy resin and phenolic cyanate.

[0017] Further, the organic acid flux is sulfosalicylic acid; the plasticizing agent is ethyl cellulose or ethylene glycol propyl ether; and the viscosity regulator is bisphenol epoxy resin.

[0018] Further, the mass percentage of the copper powder in the metal powder is 50wt%, the copper powder is spherical pure copper powder, and the particle size is 10 microns.

[0019] The tin powder is pure tin powder, and the particle size is 10 microns.

[0020] Meanwhile, the present application also provides a preparation method of the copper paste, which utilizes the above-mentioned copper paste, and is characterized by the following steps.

[0021] Step 1, mix the metal powder under inert gas protection to obtain mixture A;

[0022] Step 2, mix the organic acid flux, plasticizing agent and viscosity regulator to obtain mixture B;

[0023] Step 3, mix mixture A with mixture B under inert gas protection to obtain copper paste; the mass percentage of mixture B in the copper paste is greater than or equal to 5% and less than or equal to 10%.

[0024] Further, in step 3, the mass percentage of mixture B in the copper paste is 8%.

[0025] The application provides a HBC solar cell metallization method, which is characterized by comprising the following steps:

[0026] Step 1, setting a transition layer on the TCO film of the HBC solar cell substrate to be metallized;

[0027] Step 2, setting copper paste grid lines on the transition layer in step 1 at the preset electrode grid line positions by screen printing using the copper paste in claim 5, and heating and curing the copper paste grid lines;

[0028] Step 3, etching the transition layer in the area where the copper paste grid lines are not set to complete the metallization of the HBC solar cell.

[0029] Further, in step 1, the transition layer is a metal thin film made by PVD, which is composed of one or more of copper, nickel, titanium, tungsten and magnesium, and has a thickness of 20-100 nanometers.

[0030] Further, in step 2, the heating and curing conditions of the copper paste grid lines are as follows: vacuum or inert atmosphere, temperature 150-250℃, heating time 1-10 seconds; the vacuum is 0.1Mpa-0.02Mpa, and the inert atmosphere is nitrogen or argon.

[0031] Compared with the prior art, the application has the following beneficial effects:

[0032] (1) The copper paste of the application comprises copper powder and tin powder, and the copper powder is pure copper powder without a surface coating layer; the copper paste grid lines can be prepared by screen printing using the application, and since silver and a coating layer are not used, the metallization cost of the HBC solar cell can be significantly reduced.

[0033] (2) The application discloses a HBC solar cell metallization method, which constructs a transition layer on a HBC solar cell substrate, improves the binding force between a copper paste grid line and a TCO film, and guarantees good contact between the two; in addition, during a heating and curing process, tin powder is melted, and copper powder is deposited downward due to the fact that the density of the copper powder is greater than that of the tin powder, so that only tin exists on the surface of the copper paste grid line, and the tin powder wraps the copper powder after curing, thereby protecting the copper powder from being oxidized.

[0034] (3) The application discloses a HBC solar cell metallization method, the resistivity of the prepared copper paste grid line is 8x10 -6 Ωcm or below, and has high stability in air (the body resistivity does not change obviously after being stored in air for 1 month), although the resistance value of the copper grid line prepared from pure copper paste can reach 6x10 -6 Ωcm or below, the copper grid line is easily oxidized in air and needs to be plated with tin or silver on the surface.

[0035] (4) The application discloses a HBC solar cell metallization method, which constructs a transition layer, thereby significantly improving the tensile force of the prepared copper paste grid line (the tensile force of the copper paste grid line can reach 1.5 N / cm2 or above as tested by a tensile force machine), and avoids the phenomenon that the grid line has poor adhesion and is easily peeled off. DETAILED DESCRIPTION

[0036] The application will be further described below in combination with exemplary embodiments.

[0037] The application discloses a copper paste, which comprises metal powder, organic acid flux, plasticizing agent and viscosity regulator.

[0038] The metal powder is composed of copper powder and tin powder, and serves as a main conductive component of the copper paste.

[0039] The mass percentage of the copper powder in the metal powder is 50-80 wt%, the copper powder is spherical or quasi-spherical pure copper powder, and the average particle size is 5-15 microns; the quasi-spherical shape is a spherical shape with inconsistent particle sizes.

[0040] The tin powder is pure tin powder or tin alloy powder, the tin powder is spherical, and the particle size is 5-15 microns; the tin alloy powder comprises tin and one or more of bismuth, lead and indium.

[0041] The organic acid flux is used to help welding between the metal powders during a heat treatment process, promotes the combination of metal particles by removing the oxide layers on the surfaces of the metals and reducing the surface tension between the metals; the organic acid flux is composed of one or more of citric acid, salicylic acid, sulfosalicylic acid, succinic acid and aminosulfonic acid, and is preferably sulfosalicylic acid.

[0042] The plasticizing agent is used to improve the printing performance of the copper paste, so that the copper paste can maintain a proper shape during the printing process to form an accurate grid pattern; the plasticizing agent is composed of one or more of hydrogenated castor oil, castor oil monoethanolamide, ethyl cellulose, acrylic resin, ethylene glycol propyl ether, butyl oleate, diethylene glycol monobutyl ether acetate or polyamide wax, and is preferably ethyl cellulose and ethylene glycol propyl ether.

[0043] The viscosity adjusting agent is used to adjust the fluidity and consistency of the copper paste during the printing process; the viscosity adjusting agent includes one or more of epoxy resin, phenolic resin, bisphenol epoxy resin and phenolic cyanate, and is preferably bisphenol epoxy resin.

[0044] The application discloses a preparation method of a copper paste.

[0045] Step 1: uniformly mixing metal powder under the protection of inert gas to obtain mixture A;

[0046] Step 2: uniformly mixing organic acid flux, plasticizing agent and viscosity adjusting agent to obtain mixture B;

[0047] Step 3: uniformly mixing mixture A and mixture B under the protection of inert gas to obtain the copper paste; the mass percentage of the mixture B in the copper paste is greater than or equal to 5% and less than or equal to 10%.

[0048] The application discloses a HBC solar cell metallization method.

[0049] Step 1: arranging a transition layer on a TCO film of a HBC solar cell substrate to be metallized;

[0050] The transition layer is a metal thin film made by physical vapor deposition (PVD) and is composed of one or more of copper, nickel, titanium, tungsten and magnesium, and has a thickness of 20-100 nanometers; the main function of the transition layer is to connect the copper paste grid line and the TCO film, because the binding force between the copper paste grid line and the TCO film is poor, direct printing has the risk of falling off, and the transition layer made by the PVD process has good binding force with the copper paste grid line and the TCO film, and can ensure good contact between the two;

[0051] Step 2: arranging a copper paste grid line on the transition layer in step 1 by using the above-mentioned copper paste through silk screen printing, and heating and curing the copper paste grid line;

[0052] The heating and curing conditions of the copper paste grid line are as follows: vacuum or inert atmosphere, temperature 150-250 DEG C, heating time 1-10 seconds; the vacuum is 0.1 Mpa-0.02 Mpa, and the inert atmosphere is nitrogen or argon;

[0053] Step 3, etching the transition layer in the area without copper paste grid line to complete the metallization of HBC solar cell;

[0054] Specifically, the wet etching technology can be used to remove the transition layer in the area without copper paste grid line. The wet chemical etching process uses the transition layer made by PVD and the copper paste composition is different. The transition layer is selectively removed, that is, the copper paste is used as a hard mask to protect the transition layer. The area without copper paste protection is etched. Therefore, according to the type of copper paste, a suitable etching liquid composition needs to be selected.

[0055] Embodiment one

[0056] The embodiment discloses a copper paste, which comprises metal powder, organic acid flux, plasticizing agent and viscosity regulator.

[0057] The metal powder is composed of copper powder and tin powder; the mass percentage of the copper powder in the metal powder is 50wt%; the copper powder is spherical pure copper powder with a particle size of 10 microns; and the tin powder is spherical pure tin powder with a particle size of 10 microns.

[0058] The organic acid flux is sulfosalicylic acid.

[0059] The plasticizing agent is ethylene glycol propyl ether.

[0060] The viscosity regulator is bisphenol epoxy resin.

[0061] The content of the organic matter accounts for 8% of the total mass.

[0062] The embodiment discloses a preparation method of a copper paste, which utilizes the above-mentioned copper paste and comprises the following steps:

[0063] Step 1, under the protection of inert gas, uniformly mixing the metal powder to obtain mixture A;

[0064] Step 2, uniformly mixing the organic acid flux, plasticizing agent and viscosity regulator to obtain mixture B;

[0065] Step 3, under the protection of inert gas, uniformly mixing mixture A and mixture B to obtain the copper paste; the mass percentage of mixture B in the copper paste is 8%.

[0066] The embodiment discloses a metallization method of HBC solar cell, which comprises the following steps:

[0067] Step 1, setting a transition layer on the TCO film of the HBC solar cell substrate to be metallized;

[0068] The transition layer is composed of copper and has a thickness of 100 nanometers; in other embodiments, the thickness can be adaptively adjusted in the range of 20-100 nanometers;

[0069] Step 2, the copper paste grid lines are set on the transition layer in the electrode grid line position by screen printing using the copper paste, and the copper paste grid lines are heated and cured.

[0070] The conditions for heating and curing the copper paste grid lines are: under the condition of a vacuum degree of 0.1 Mpa, a temperature of 250 DEG C, and a heating time of 8 seconds; in other embodiments, the vacuum degree can be adaptively adjusted in the range of 0.1 Mpa-0.02 Mpa.

[0071] Step 3, etching the transition layer in the area where the copper paste grid lines are not set, to complete the metallization of the HBC solar cell.

[0072] Embodiment Two

[0073] The embodiment discloses a copper paste, which comprises metal powder, organic acid flux, plasticizing agent, and viscosity regulator.

[0074] The metal powder is composed of copper powder and tin powder; the mass percentage of the copper powder in the metal powder is 80wt%; the copper powder is spherical pure copper powder with a particle size of 10 microns; and the tin powder is spherical tin-lead alloy powder with a particle size of 5 microns. In other embodiments, tin-bismuth alloy powder or tin-indium alloy powder can also be used.

[0075] The organic acid flux is succinic acid and sulfamic acid.

[0076] The plasticizing agent is ethyl cellulose.

[0077] The viscosity regulator is bisphenol epoxy resin and epoxy resin.

[0078] The embodiment discloses a metallization method for an HBC solar cell, and the mass percentage of the mixture B in the copper paste in step 3 is 5%; in other embodiments, the mass percentage of the mixture B in the copper paste can be adaptively adjusted in the range of [5%, 10%]; and the remaining settings are the same as those in Embodiment One.

[0079] The embodiment discloses a metallization method for an HBC solar cell, in step 1, the transition layer is composed of copper and nickel, and has a thickness of 50 nanometers; in step 2, the conditions for heating and curing the copper paste grid lines are: under the condition of nitrogen, a temperature of 190 DEG C, and a heating time of 10 seconds; in other embodiments, the nitrogen can be replaced by argon; and the remaining settings are the same as those in Embodiment One.

[0080] Embodiment Three

[0081] The embodiment discloses a copper paste, which comprises metal powder, organic acid flux, plasticizing agent, and viscosity regulator.

[0082] The metal powder is composed of copper powder and tin powder; the mass percentage of the copper powder in the metal powder is 70wt%, the copper powder is quasi-spherical pure copper powder with an average particle size of 8 microns; and the tin powder is spherical tin-lead alloy powder with a particle size of 7 microns.

[0083] The organic acid flux is citric acid.

[0084] The plasticizing agent is hydrogenated castor oil and ethyl cellulose.

[0085] The viscosity regulator is phenolic cyanate.

[0086] The embodiment discloses a HBC solar cell metallization method, and the mass percentage of the mixture B in the copper paste is 8% in step 3; in other embodiments, the mass percentage of the mixture B in the copper paste can be adaptively adjusted in the range of [5%, 10%]. The remaining settings are the same as those in the first embodiment.

[0087] The embodiment discloses a HBC solar cell metallization method, and in step 1, the transition layer is composed of copper and nickel, and the thickness is 80 nanometers; in step 2, the conditions for heating and curing the copper paste grid line are as follows: under the condition of nitrogen, the temperature is 200 DEG C, and the heating time is 10 seconds; in other embodiments, the nitrogen can be replaced by argon; the remaining settings are the same as those in the first embodiment.

Claims

1. A copper paste, characterized in that: Includes metal powder, organic acid flux, plasticizer, and viscosity modifier; The metal powder is composed of copper powder and tin powder; The copper powder has a mass percentage of 50-80 wt% in the metal powder, and the copper powder is spherical or quasi-spherical pure copper powder with an average particle size of 5-15 micrometers. The tin powder is pure tin powder or tin alloy powder. The tin powder is spherical with a particle size of 3-15 micrometers. The tin alloy powder includes tin, as well as one or more of bismuth, lead, and indium.

2. The copper paste according to claim 1, characterized in that: The organic acid flux is composed of one or more of citric acid, salicylic acid, sulfosalicylic acid, succinic acid, and aminosulfonic acid; the plasticizer is composed of one or more of hydrogenated castor oil, castor oil monoethanolamide, ethyl cellulose, acrylic resin, ethylene glycol propyl ether, butyl oleate, diethylene glycol monobutyl ether acetate, or polyamide wax; the viscosity modifier includes one or more of epoxy resin, phenolic resin, bisphenol epoxy resin, and phenolic cyanate.

3. The copper paste according to claim 2, characterized in that: The organic acid flux is sulfosalicylic acid; the plasticizer is ethyl cellulose or ethylene glycol propyl ether; and the viscosity modifier is bisphenol epoxy resin.

4. A copper paste according to any one of claims 1 to 3, characterized in that: The copper powder has a mass percentage of 50 wt% in the metal powder, and the copper powder is spherical pure copper powder with a particle size of 10 micrometers. The tin powder is pure tin powder with a particle size of 10 micrometers.

5. A method for preparing copper paste, using the copper paste material according to claim 1, characterized in that, Includes the following steps: Step 1: Under the protection of an inert gas, the metal powder is mixed to obtain mixture A; Step 2: Mix the organic acid flux, plasticizer, and viscosity modifier to obtain mixture B; Step 3: Under inert gas protection, mix mixture A and mixture B to obtain copper paste; the mass percentage of mixture B in the copper paste is greater than or equal to 5% and less than or equal to 10%.

6. The method for preparing copper paste according to claim 5, characterized in that: In step 3, the mass percentage of mixture B in the copper paste is 8%.

7. A method for metallizing HBC solar cells, characterized in that, Includes the following steps: Step 1: Set a transition layer on the TCO film of the HBC solar cell substrate to be metallized; Step 2: In step 1, the electrode grid lines on the transition layer are pre-set at the positions described in claim 5 using the copper paste, and then the copper paste grid lines are heated and cured. Step 3: Etch the transition layer in the area where no copper paste grid lines are set to complete the metallization of the HBC solar cell.

8. The method for metallizing HBC solar cells according to claim 7, characterized in that: In step 1, the transition layer is a metal thin film produced by PVD, which is composed of one or more of copper, nickel, titanium, tungsten, and magnesium, and has a thickness of 20-100 nanometers.

9. A method for metallizing HBC solar cells according to claim 7 or 8, characterized in that: In step 2, the conditions for heating and curing the copper paste grid are: vacuum or in an inert atmosphere, temperature 150-250℃, heating time 1-10 seconds; the vacuum is a vacuum degree of 0.1Mpa-0.02Mpa, and the inert atmosphere is nitrogen or argon.