Screen printing device and printing method for silver-coated copper photovoltaic cell piece

Abstract

The application discloses a kind of for silver copper photovoltaic cell piece screen printing device and printing method, device includes slurry storage and detection unit, screen printing unit, cell piece conveying and protection unit, method is based on the device corresponding operation of execution.The device realizes homogeneous storage of slurry by tank, electrode is equipped for detection in discharge pipe, controller applies low-frequency alternating excitation current to detect slurry resistivity, three-way valve linkage realizes qualified feed, unqualified shunt;Conveying protection unit is pre-dried cell piece by heating rod, realizes printing whole process low-oxygen protection by three-cavity alternating on-off structure cooperation micro-negative pressure, inert gas conveying.Compared with prior art, the beneficial effects of the present application are that: silver shell damage, copper oxidation and other defects of slurry can be accurately identified, unqualified products are intercepted in advance, copper core oxidation problem is completely solved, cell piece rejection rate is reduced, electrode conductivity is improved, and the demand of photovoltaic cell piece large-scale production is met.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic cell manufacturing technology, specifically relating to a screen printing device and printing method for silver-coated copper photovoltaic cells. Background Technology

[0002] In the production of photovoltaic cells, screen printing is a core step in electrode preparation. The quality of the electrode paste directly determines the power generation efficiency, reliability, and production cost of the cell. To reduce production costs and improve efficiency, the widely used pure silver electrode paste is gradually being replaced by silver-coated copper composite paste. Silver-coated copper paste uses copper as the core and silver as the outer layer, thus maintaining good conductivity while significantly reducing electrode preparation costs due to the low cost of copper.

[0003] Typically, the thickness of the silver casing is only 50 to 200 nanometers, making it relatively fragile and easily damaged during screen printing due to mechanical pressure or friction, resulting in the exposure of the copper core. Furthermore, copper is chemically reactive and readily oxidizes in ambient conditions of room temperature, oxygen, and high humidity, forming copper oxide. Copper oxide is almost non-conductive, which leads to a sharp increase in electrode resistance, poor ohmic contact, and ultimately affects the power generation efficiency of the photovoltaic cell, or even causes cell failure.

[0004] In existing technologies, most paste quality inspection methods are offline sampling methods, which can only be inspected after the fact and cannot reflect the paste status in real time. This method can easily lead to substandard paste flowing into the printing process, causing the cells to be scrapped. In addition, there are also online inspection methods such as spectral detection or simple two-electrode resistance detection. The former requires a complex optical structure, has high detection costs, and is easily affected by external interference; the latter is affected by electrode polarization effects, has large errors, and cannot accurately identify key defects such as silver shell damage, copper oxidation, and paste delamination, making it difficult to meet the needs of online continuous inspection.

[0005] Therefore, in response to the above-mentioned technical problems, it is necessary to provide a screen printing apparatus and printing method for silver-clad copper photovoltaic cells.

[0006] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide a screen printing apparatus and method for silver-clad copper photovoltaic cells, which can solve the technical problems mentioned in the background art.

[0008] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0009] A screen printing device for silver-coated copper photovoltaic cells includes a screen printing main unit, a mixing mechanism, multiple sets of detection electrodes, and a three-way valve. The mixing mechanism includes a tank containing silver-coated copper paste. A stirring rod is mounted on the tank. A motor for driving the stirring rod is fixedly connected to the upper end of the tank. A discharge pipe is fixedly connected to the lower end of the tank, with one end of the discharge pipe connected to the screen printing main unit. Multiple sets of detection electrodes are mounted on the discharge pipe. Each set of detection electrodes includes a first electrode for applying an excitation current to the silver-coated copper paste in the discharge pipe and a second electrode for collecting voltage signals across the paste. Both the first and second electrodes are connected to a controller. The three-way valve is mounted on the discharge pipe and has a discharge pipe and a feed pipe. One end of the feed pipe is connected to the screen printing main unit, and the discharge pipe is used to connect to a waste tank.

[0010] In one or more embodiments of the present invention, the first conveying mechanism includes a first housing, and a plurality of first conveyor belts for conveying photovoltaic cells are installed inside the first housing. Two partitions are installed on the first housing, and the partitions divide the screen printing device into a feeding end, a feeding buffer chamber and a printing chamber. When the feeding end and the feeding buffer chamber are connected, the feeding buffer chamber and the printing chamber are not connected. When the feeding end and the feeding buffer chamber are not connected, the feeding buffer chamber and the printing chamber are connected.

[0011] In one or more embodiments of the present invention, a gantry frame matching the partition is mounted on the first housing, and a cylinder matching the partition is mounted on the gantry frame, with the output end of the cylinder fixedly connected to the partition.

[0012] In one or more embodiments of the present invention, a first connection port is installed at one end of the second conveying mechanism, a second connection port matching the feed buffer chamber is installed on the partition, a gas recovery pipe is installed between the first connection port and the second connection port, an exhaust pipe is installed on the gas recovery pipe, valves are installed on both the gas recovery pipe and the exhaust pipe, and an air pump is installed on the gas recovery pipe.

[0013] In one or more embodiments of the present invention, the first conveying mechanism is equipped with an inert gas conveying pipe that matches the printing cavity.

[0014] In one or more embodiments of the present invention, a negative pressure pipe matching the feed buffer chamber is installed at the lower end of the first housing, and a negative pressure pump is installed at one end of the negative pressure pipe.

[0015] In one or more embodiments of the present invention, a heating rod for drying photovoltaic cells is installed inside the second conveying mechanism.

[0016] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0017] The screen printing method for silver-clad copper photovoltaic cells includes the following steps:

[0018] S1. The silver-coated copper paste is placed in a sealed tank and continuously homogenized and stirred. The stirred silver-coated copper paste is then conveyed in a directional manner through a sealed discharge pipe with a constant cross-sectional size.

[0019] S2. A low-frequency AC excitation current is applied to the silver-coated copper paste flowing in the discharge pipe through a pair of excitation electrodes and a second detection electrode arranged on the inner wall of the discharge pipe. The real-time voltage drop signal of the paste between the two electrodes is collected simultaneously. The real-time resistivity of the silver-coated copper paste is calculated based on the voltage drop signal to complete the online judgment of the paste quality.

[0020] S3. Based on the online judgment result of the paste quality, switch the paste delivery path through the three-way valve; when the paste is judged to be qualified, the silver-coated copper paste is delivered to the screen printing host; when the paste is judged to be unqualified, the silver-coated copper paste is diverted and discharged to the waste pool.

[0021] S4. Place the photovoltaic cells to be printed in a sealed conveying environment for low-temperature pre-drying treatment to remove the water vapor adsorbed on the surface of the cells.

[0022] S5. The pre-dried photovoltaic cells are transported to a sealed conveying channel consisting of an alternately open and closed feed end, a feed buffer chamber, and a printing chamber. By controlling the open and closed states of adjacent chambers, the photovoltaic cells are sent into the printing station of the printing chamber, which is completely isolated from the outside world. Under the protection of inert gas, the silver-coated copper electrode is screen printed on the surface of the photovoltaic cells by the screen printing host.

[0023] S6. The photovoltaic cells are printed in a printing chamber with inert gas continuously introduced to achieve low oxygen protection for the printed wet grid lines on the surface of the photovoltaic cells, and then the photovoltaic cells are transported to the subsequent curing and sintering process.

[0024] In one or more embodiments of the present invention, in step S2, the first excitation electrode and the second detection electrode are arranged in pairs on the upper and lower inner walls of the discharge pipe along the slurry flow direction, and the detection surfaces of the two electrodes are flush with the inner wall of the discharge pipe. In step S3, when the real-time resistivity is within the preset qualified threshold range, the slurry is determined to be qualified; when the real-time resistivity exceeds the upper limit of the preset qualified threshold, the slurry is determined to be unqualified, corresponding to defects such as silver shell damage, copper core oxidation, and stratification sedimentation in the slurry.

[0025] In one or more embodiments of the present invention, in step S6, nitrogen gas is continuously introduced into the printing chamber as an inert gas to keep the oxygen concentration in the printing chamber below 100 ppm, thereby providing low-oxygen protection for the printed wet grid lines throughout the process.

[0026] Compared with the prior art, the beneficial effects of the present invention are: to realize online paste detection, to reflect the paste status in real time, and to divert the paste before it enters the printing process, thereby avoiding the situation where low-quality paste leads to the scrapping of photovoltaic cells after printing is completed;

[0027] By setting up detection electrodes, in-situ, continuous, and full-process online real-time detection can be completed during the paste delivery process. The quality of each section of paste flowing through can be fully inspected before the paste enters the screen printing host, with no blind spots and avoiding the risk of missed detection in sampling inspection. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the structure of a screen printing apparatus for silver-coated copper photovoltaic cells according to an embodiment of the present invention. Figure 1 ;

[0030] Figure 2 This is a schematic diagram of the structure of a screen printing apparatus for silver-coated copper photovoltaic cells according to an embodiment of the present invention. Figure 2 ;

[0031] Figure 3 This is a cross-sectional view of a screen printing apparatus for silver-clad copper photovoltaic cells according to an embodiment of the present invention. Figure 1 ;

[0032] Figure 4 This is a cross-sectional view of a screen printing apparatus for silver-clad copper photovoltaic cells according to an embodiment of the present invention. Figure 2 ;

[0033] Figure 5 This is a schematic diagram of the installation of the detection electrode in one embodiment of the present invention;

[0034] Figure 6 This is a cross-sectional view of the mixing mechanism in one embodiment of the present invention;

[0035] Figure 7 This is a main flowchart of a screen printing method for silver-coated copper photovoltaic cells according to an embodiment of the present invention;

[0036] Figure 8 This is a flowchart of paste detection and diversion control in a screen printing method for silver-clad copper photovoltaic cells according to an embodiment of the present invention.

[0037] Figure 9 This is a flowchart of a screen printing method for silver-coated copper photovoltaic cells, specifically a low-oxygen printing and protection process for the cells, according to an embodiment of the present invention.

[0038] Explanation of key figure labels:

[0039] 1. Screen printing main unit; 2. First conveying mechanism; 3. First housing; 4. First conveyor belt; 5. Partition; 6. Feeding end; 7. Feeding buffer chamber; 8. Printing chamber; 9. Gantry frame; 10. Cylinder; 11. Second conveying mechanism; 12. Second housing; 13. Second conveyor belt; 14. Heating rod; 15. First connection port; 16. Second connection port; 17. Gas recovery pipe; 18. Exhaust pipe; 19. Valve; 20. Negative pressure pipe; 21. Negative pressure pump; 22. Mixing mechanism; 23. Tank; 24. Stirring rod; 25. Motor; 26. Feeding port; 27. Discharge pipe; 28. Detection electrode; 29. ​​Electrical connection wire; 30. Controller; 31. Three-way valve; 32. Discharge pipe; 33. Feeding pipe. Detailed Implementation

[0040] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0041] like Figures 1-4 As shown, the screen printing device for silver-coated copper photovoltaic cells in one embodiment of the present invention includes three major functional modules: a paste storage and detection unit, a screen printing unit, and a cell conveying and protection unit. It can realize online accurate detection of silver-coated copper paste, early interception of defective products, and low-oxygen protection throughout the printing process, thus meeting the quality requirements of large-scale production of photovoltaic cells.

[0042] The screen printing unit is the printing execution mechanism for silver-clad copper electrodes, used to complete the screen printing of silver-clad copper electrodes on the surface of photovoltaic cells. Its core is the screen printing host 1. The printing station of the screen printing host 1 is set between the cell conveying and the printing of the protection unit, and can complete precise and stable electrode printing on the photovoltaic cells conveyed to the designated station.

[0043] The paste storage and testing unit is connected to the screen printing unit, and the paste in the paste storage and testing unit is used to supply the screen printing unit to complete the printing operation. In this embodiment, the paste storage and testing unit is the core module for realizing source quality control before printing, mainly for the sealed and homogeneous storage of silver-plated copper paste, online real-time quality detection, and precise diversion and interception of unqualified paste.

[0044] The slurry storage and testing unit includes a mixing mechanism 22 for the sealed storage and homogenization of the silver-coated copper slurry, preventing performance inconsistencies caused by slurry stratification and sedimentation from the source. The mixing mechanism 22 includes a sealed tank 23. The top of the tank 23 is provided with an inlet 26 for replenishing the silver-coated copper slurry. A motor 25 is fixed at the center of the top of the tank 23. The output shaft of the motor 25 extends into the tank 23 and is fixedly connected to a stirring rod 24, which can drive the stirring rod 24 to rotate continuously inside the tank 23, performing homogenization treatment on the silver-coated copper slurry stored inside throughout the process, ensuring stable slurry performance.

[0045] The bottom of the tank 23 is connected to a sealed discharge pipe 27 for conveying paste to the screen printing unit. The discharge pipe 27 is equipped with multiple sets of detection electrodes for online detection of paste quality, which can identify core defects of silver-coated copper paste such as silver shell damage, copper oxidation, and stratification sedimentation in real time.

[0046] like Figure 5 As shown, each set of detection electrodes includes a first excitation electrode for applying excitation current to the silver-coated copper paste in the discharge pipe 27, and a second detection electrode for collecting voltage signals across the paste. The detection surfaces of both electrodes are flush with the inner wall of the discharge pipe 27 to avoid interfering with the stable flow of the paste. Both the first excitation electrode and the second detection electrode are electrically connected to the controller 30 via electrical connection line 29. The controller 30 has a built-in AC constant current source, signal amplification module, and data processing module, which can output a stable low-frequency AC excitation current to the first excitation electrode and simultaneously receive the voltage signal collected by the second detection electrode, calculate the resistivity of the paste in real time, and complete the online judgment of the paste quality.

[0047] Specifically, the discharge pipe 27 is a constant-thickness flow channel with a constant cross-sectional dimension, and the cross-sectional area S of the slurry flowing within the channel remains constant. The first excitation electrode and the second detection electrode of each group are arranged in pairs on the upper and lower relative inner walls of the flow channel along the slurry flow direction. The center distance L between the two electrodes is fixed, and the electrode detection surface is completely flush with the inner wall of the flow channel, without protrusions or steps, which ensures both stable and non-stagnant slurry flow and a constant slurry conductive length between the two electrodes.

[0048] According to the formulas for conductivity (R=U / I) and resistivity (ρ=R×S / L), when the electrode spacing (L) and the cross-sectional area of ​​the slurry flow are fixed, the resistivity (ρ) of the slurry is strictly linearly proportional to the resistance (R). The resistance (R) is only related to the voltage drop (U) across the slurry and the excitation current (I). Therefore, the true resistivity of the slurry can be accurately calculated by detecting the voltage signal; this value is determined solely by the conductivity of the silver-coated copper slurry itself.

[0049] Furthermore, the controller 30 incorporates a high-precision AC constant current source that continuously outputs a constant low-frequency AC sinusoidal signal with a frequency of 1kHz and an amplitude of 5mA to the first excitation electrode. This constant current is then injected without loss into the silver-coated copper paste within the flow channel, forming a stable current loop through the paste between the first excitation electrode and the second detection electrode. The primary purpose is to completely eliminate electrode polarization effects and the risk of paste electrolysis: if DC excitation is used, conductive particles in the silver-coated copper paste will undergo directional migration under a DC electric field, and a double-layer polarization capacitance will form at the electrode-paste interface, leading to a significant deviation in the measured voltage, with errors exceeding 20%. The 1kHz low-frequency AC signal, however, keeps the polarization capacitance at the electrode interface in a low-impedance state, completely canceling out the polarization effect and preventing paste electrolysis and electrode corrosion, thus ensuring the stability and accuracy of long-term online detection.

[0050] When a constant current flows through the copper-plated silver paste between the first excitation electrode and the second detection electrode, according to Ohm's law U=I×R, a real-time voltage drop proportional to the paste's own resistance will form between the two electrodes. Here, I is the constant, known value of the excitation current, R is the real-time resistance of the paste between the two electrodes, and U is the real-time voltage drop formed between the two electrodes.

[0051] With the pre-fixed structural parameters, the conductive length L and the cross-sectional area S of the slurry between the two electrodes are fixed values. Therefore, the resistivity ρ of the slurry has a strict linear relationship with the detected voltage drop U. The change in the voltage signal directly and uniquely reflects the change in the conductivity of the slurry itself.

[0052] A three-way valve 31 for switching the slurry path is installed at the end of the discharge pipe 27. This valve allows for precise control of the supply of qualified slurry and the directional diversion of unqualified slurry based on slurry quality testing results. The three ports of the three-way valve 31 are connected to the discharge pipe 27, the feed pipe 33, and the discharge pipe 32, respectively. The end of the feed pipe 33 is connected to the slurry inlet of the screen printing unit, and the end of the discharge pipe 32 is connected to an external waste pool. The control terminal of the three-way valve 31 is electrically connected to the controller 30, allowing for real-time path switching based on the slurry quality judgment results from the controller 30.

[0053] When the real-time resistivity is within the qualified threshold range, the paste is deemed qualified, corresponding to an intact, unoxidized, and uniformly dispersed silver shell. The controller 30 controls the three-way valve 31 to switch to the feed pipe 33 channel, and the paste is normally supplied to the screen printing host 1.

[0054] When the real-time resistivity exceeds the upper limit of the qualified threshold, the paste is judged to be unqualified, which corresponds to defects such as silver shell damage, copper core oxidation, and paste stratification and sedimentation. The controller 30 controls the three-way valve 31 to switch to the discharge pipe 32 channel, and the unqualified paste is discharged into the waste pool to avoid flowing into the printing process and causing the battery cells to be scrapped.

[0055] A second conveying mechanism 11 and a first conveying mechanism 2 are sequentially connected along the direction of solar cell conveying. The second conveying mechanism 11 is used for pre-drying and sealing the solar cells to be printed, which can remove moisture adsorbed on the surface of the solar cells in advance and reduce the risk of oxidation during subsequent printing. It includes a sealed second housing 12. A second conveyor belt 13 for conveying the photovoltaic solar cells to be printed is installed inside the second housing 12. Multiple sets of heating rods 14 are installed on the top of the inner wall of the second housing 12 to perform low-temperature pre-drying treatment on the solar cells during the conveying process. The discharge end of the second housing 12 is provided with a first connection port 15 for sealed communication with the first conveying mechanism 2.

[0056] The first conveying mechanism 2 is used for the zoned sealed conveying of solar cells and for isolating and protecting the printing process. Through a multi-cavity alternating on / off structure, it achieves complete isolation between the printing process and the outside air. It includes a sealed first housing 3. Inside the first housing 3 is a first conveyor belt 4 for conveying photovoltaic solar cells. Two vertically movable partitions 5 are installed at intervals along the conveying direction of the solar cells on the inner wall of the first housing 3. The two partitions 5 sequentially divide the internal channel of the first housing 3 along the conveying direction into a feeding end 6, a feeding buffer chamber 7, and a printing chamber 8. The printing station of the screen printing host 1 is located within the printing chamber 8, which also serves as a discharge protection chamber and is connected to the subsequent curing and sintering process.

[0057] The top of the first housing 3 is fixed with a gantry frame 9 corresponding to each of the two partitions 5. Each gantry frame 9 is fixed with a cylinder 10. The output shaft of the cylinder 10 is vertically downward and fixedly connected to the top of the corresponding partition 5, which can drive the partition 5 to move up and down, realizing the on / off control of adjacent cavities: when the partition 5 near the feeding end 6 rises and the partition 5 near the printing cavity 8 falls, the feeding end 6 is connected to the feeding buffer cavity 7, and the feeding buffer cavity 7 is isolated from the printing cavity 8. When the partition 5 near the feeding end 6 falls and the partition 5 near the printing cavity 8 rises, the feeding end 6 is isolated from the feeding buffer cavity 7, and the feeding buffer cavity 7 is connected to the printing cavity 8.

[0058] A second connection port 16 is provided on the side wall of the feed end 6. The second connection port 16 is connected to the first connection port 15 of the second conveying mechanism 11 through a gas recovery pipe 17. An air pump and a valve 19 are installed on the gas recovery pipe 17. An exhaust pipe 18 is also connected to the side wall of the gas recovery pipe 17. A valve 19 is also installed on the exhaust pipe 18, which can realize the recovery and reuse of gas inside the cavity and the discharge of waste gas. Due to the presence of the heating rod 14, the gas recovered through the gas recovery pipe 17 has a certain temperature. When the photovoltaic cells enter the feeding buffer chamber 7, warm inert gas rushes into the feeding buffer chamber 7 to dry the photovoltaic cells inside. At the same time, a negative pressure pipe 20 is installed at the bottom of the feeding buffer chamber 7, and a negative pressure pump 21 is connected to the end of the negative pressure pipe 20. This can perform a slight negative pressure treatment on the feeding buffer chamber 7, allowing warm inert gas to enter and simultaneously expel moisture, reducing the oxygen content in the feeding buffer chamber 7, and even expelling all the oxygen. After the oxygen content reaches the standard, the feeding buffer chamber 7 is connected to the printing chamber 8, and the feeding end 6 is isolated from the feeding buffer chamber 7.

[0059] The printing chamber 8 is equipped with an inert gas delivery pipe on its side wall, which can continuously introduce inert gas into the printing chamber 8 to form a stable low-oxygen protective atmosphere.

[0060] In this embodiment, the working process of the silver-coated copper photovoltaic cell screen printing device is as follows: the silver-coated copper paste is fed into the tank 23 through the feed port 26. The motor 25 drives the stirring rod 24 to rotate continuously, homogenizing and stirring the paste to ensure stable paste performance. Driven by the delivery pump, the paste flows along the discharge pipe 27. When it flows through the detection area of ​​the detection electrode 28, the controller 30 applies a low-frequency AC excitation current to the paste through the first excitation electrode, and at the same time collects the voltage signal across the paste through the second detection electrode to calculate the resistivity of the paste in real time. If the resistivity of the paste is within the preset qualified threshold range, the controller 30 determines that the paste is qualified and controls the three-way valve 31 to switch to the feed pipe 33 passage. The paste is then fed into the screen printing host 1 through the feed pipe 33 for electrode printing. If the resistivity of the paste exceeds the preset qualified threshold, the controller 30 determines that the paste has defects such as silver shell damage, copper oxidation or stratification sedimentation, and controls the three-way valve 31 to switch to the discharge pipe 32 passage. The unqualified paste is discharged into the waste pool through the discharge pipe 32 to avoid flowing into the printing process and causing the battery cells to be scrapped.

[0061] During the screen printing process, after the battery cell enters the feeding end 6, the cylinder 10 drives the two partitions 5 to move, so that the feeding end 6 is connected to the feeding buffer chamber 7 and the feeding buffer chamber 7 is isolated from the printing chamber 8. The battery cell is sent into the printing station of the printing chamber 8 through the first conveyor belt 4. The screen printing host 1 is started and the silver-coated copper electrode is printed on the surface of the battery cell.

[0062] Nitrogen gas is continuously introduced into the printing chamber 8 through an inert gas delivery pipe, keeping the oxygen concentration inside the chamber below 100 ppm, thus providing low-oxygen protection for the printed wet grid lines throughout the entire process. The protected solar cells are then discharged through the outlet end of the printing chamber 8 and directly enter the subsequent curing and sintering process, completing the entire screen printing process.

[0063] like Figures 7-9 As shown, a screen printing method for silver-clad copper photovoltaic cells according to an embodiment of the present invention includes the following steps:

[0064] S1. The silver-coated copper paste is fed into the sealed tank 23 of the mixing mechanism 22 through the feed port 26. The stirring rod 24 is driven by the motor 25 to rotate continuously, so as to homogenize and stir the silver-coated copper paste in the tank 23 throughout the process, avoid the slurry stratification and sedimentation, and ensure the stability of the slurry performance. The stirred silver-coated copper paste is then conveyed in a direction through the sealed discharge pipe 27 with a constant cross-sectional size under the drive of the delivery pump.

[0065] S2. When the silver-coated copper paste flows through the detection area on the discharge pipe 27, a stable low-frequency AC excitation current is output to the first excitation electrode by the AC constant current source built into the controller 30 through the first excitation electrode and the second detection electrode arranged in pairs on the inner wall of the discharge pipe 27. The first excitation electrode injects a constant current into the silver-coated copper paste in the discharge pipe 27 to form a stable current loop. At the same time, the real-time voltage drop signal of the paste between the two electrodes is collected by the second detection electrode. After the voltage signal is processed by the signal amplification module and data processing module built into the controller 30, the real-time resistivity of the silver-coated copper paste is calculated based on Ohm's law and resistivity formula, thus completing the online judgment of the paste quality.

[0066] The first excitation electrode and the second detection electrode are arranged in pairs on the upper and lower inner walls of the discharge pipe 27 along the slurry flow direction. The detection surfaces of the two electrodes are flush with the inner wall of the discharge pipe 27, without protrusions or steps, which ensures stable and unrestricted slurry flow and a constant slurry conductivity length between the two electrodes.

[0067] S3, the controller 30 sends a control signal to the three-way valve 31 based on the online judgment result of the slurry quality, and switches the slurry conveying path through the three-way valve 31:

[0068] When the real-time resistivity is within the preset qualified threshold range, the paste is judged to be qualified, corresponding to the silver shell being intact, free from oxidation, and uniformly dispersed. The controller 30 controls the three-way valve 31 to switch to the feed pipe 33 passage, and the silver-coated copper paste is normally transported to the screen printing host 1 through the feed pipe 33 for subsequent electrode printing.

[0069] When the real-time resistivity exceeds the upper limit of the preset qualified threshold, the paste is judged to be unqualified. The corresponding paste has defects such as silver shell damage, copper core oxidation, and stratification sedimentation. The controller 30 controls the three-way valve 31 to switch to the discharge pipe 32 channel. The unqualified paste is diverted through the discharge pipe 32 to the external waste pool to avoid flowing into the printing process and causing the battery cells to be scrapped.

[0070] S4. The photovoltaic cells to be printed are fed into the sealed second housing 12 of the second conveying mechanism 11 and conveyed directionally by the second conveyor belt 13. During the conveying process, the photovoltaic cells are pre-dried at low temperature by multiple sets of heating rods 14 on the top of the inner wall of the second housing 12 to remove the water vapor adsorbed on the surface of the cells in advance and reduce the risk of oxidation in the subsequent printing process.

[0071] S5. The pre-dried photovoltaic cells are conveyed into the sealed first housing 3 of the first conveying mechanism 2 and fed into a sealed conveying channel composed of an alternately open and closed feed end 6, a feed buffer chamber 7, and a printing chamber 8. The photovoltaic cells undergo air removal and drying in the feed buffer chamber 7. When the feed buffer chamber 7 and the printing chamber 8 are connected, oxygen will not enter the printing chamber 8. The photovoltaic cells are printed in the printing chamber 8 and then conveyed from the printing chamber 8 to the next process via the second conveying mechanism 11.

[0072] S6. Nitrogen gas is continuously introduced into the printing chamber 8 as an inert gas to keep the oxygen concentration in the printing chamber 8 below 100ppm, so as to provide low oxygen protection for the printed wet grid lines on the surface of the photovoltaic cell throughout the process. After the protection is completed, the photovoltaic cell is sent out through the discharge end of the printing chamber 8 and directly transported to the subsequent curing and sintering process to complete the entire screen printing process of the silver-coated copper photovoltaic cell.

[0073] The beneficial effects of the screen printing apparatus and method for silver-clad copper photovoltaic cells in the above embodiments include at least the following:

[0074] Through a constant-thickness discharge pipe 27 with a constant cross-sectional dimension, and paired detection electrodes 28 arranged along the flow direction of the slurry on the inner wall of the discharge pipe 27, a strict linear correspondence between the resistivity of the slurry and the detection voltage is established with a fixed electrode center spacing and a constant flow cross-sectional area of ​​the slurry in the discharge pipe 27. This allows for accurate calculation of the true conductivity of the silver-coated copper slurry. Through a controller 30 electrically connected to the detection electrodes 28 via an electrical connection line 29, a built-in high-precision AC constant current source outputs a low-frequency AC constant current excitation with a frequency of 1kHz and an amplitude of 5mA. This completely eliminates the electrode polarization effect and slurry electrolysis risk of traditional DC detection, accurately identifying defects in the silver-coated copper slurry that affect electrode performance, such as silver shell damage, copper core oxidation, and stratification sedimentation.

[0075] The sealed tank 23 of the mixing mechanism 22, together with the stirring rod 24 driven by the motor 25 at the top of the tank 23 and the feed inlet 26 set at the top of the tank 23, realizes the full-process sealed homogeneous storage and continuous stirring of the silver-coated copper paste. This avoids the problem of stratification and sedimentation during long-term storage and transportation of the paste from the source, and ensures the long-term uniformity and stability of the paste's electrical conductivity and rheological properties.

[0076] By using detection electrodes 28 arranged in pairs on the inner wall of the discharge pipe 27, in-situ, continuous, and full-process online real-time detection is completed during the slurry transportation process. This allows for full quality inspection of each section of slurry flowing through the machine before it enters the screen printing host 1, eliminating blind spots and avoiding the risk of missed detections in sampling inspections. In conjunction with a three-way valve 31 that is linked in real-time with the detection results of the controller 30, the transportation path can be switched in milliseconds based on the slurry quality judgment results: qualified slurry is normally supplied to the screen printing host 1 via the feed pipe 33, while unqualified slurry is directly diverted to the waste pool via the discharge pipe 32. This achieves pre-interception, preventing unqualified products from flowing into the next process, fundamentally eliminating batch scrapping of battery cells due to defects such as silver shell damage, copper oxidation, and slurry stratification. This significantly reduces production material losses and rework costs for defective products, and significantly improves the yield of battery cell production.

[0077] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0078] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A screen printing apparatus for silver-clad copper photovoltaic cells, characterized in that, include: Screen printing main unit; A mixing mechanism includes a tank containing silver-plated copper paste, a stirring rod mounted on the tank, a motor for driving the stirring rod to rotate fixedly connected to the upper end of the tank, and a discharge pipe fixedly connected to the lower end of the tank, one end of which is connected to the screen printing host. Multiple sets of detection electrodes are installed on the discharge pipe. Each set of detection electrodes includes a first electrode for applying an excitation current to the silver-coated copper paste in the discharge pipe and a second electrode for collecting voltage signals at both ends of the paste. Both the first and second electrodes are connected to the controller. A three-way valve is installed on the discharge pipe. The three-way valve is equipped with a discharge pipe and a feed pipe. One end of the feed pipe is connected to the screen printing host, and the discharge pipe is used to connect to the waste pool.

2. The screen printing apparatus for silver-clad copper photovoltaic cells according to claim 1, characterized in that, The first conveying mechanism includes a first housing, inside which are installed a plurality of first conveyor belts for conveying photovoltaic cells. Two partitions are installed on the first housing, which divide the screen printing device into a feeding end, a feeding buffer chamber and a printing chamber. When the feed end and the feed buffer chamber are connected, the feed buffer chamber and the printing chamber are not connected; When the feed end and the feed buffer chamber are not connected, the feed buffer chamber and the printing chamber are connected.

3. The screen printing apparatus for silver-clad copper photovoltaic cells according to claim 2, characterized in that, The first housing is equipped with a gantry frame that matches the partition, and a cylinder that matches the partition is mounted on the gantry frame. The output end of the cylinder is fixedly connected to the partition.

4. The screen printing apparatus for silver-clad copper photovoltaic cells according to claim 3, characterized in that, One end of the second conveying mechanism is equipped with a first connection port, and the partition is equipped with a second connection port that matches the feed buffer chamber. A gas recovery pipe is installed between the first connection port and the second connection port. An exhaust pipe is installed on the gas recovery pipe. Valves are installed on both the gas recovery pipe and the exhaust pipe. An air pump is installed on the gas recovery pipe.

5. The screen printing apparatus for silver-clad copper photovoltaic cells according to claim 4, characterized in that, The first conveying mechanism is equipped with an inert gas conveying pipe that matches the printing cavity.

6. The screen printing apparatus for silver-clad copper photovoltaic cells according to any one of claims 2 to 5, characterized in that, The lower end of the first housing is equipped with a negative pressure pipe that matches the feed buffer chamber, and a negative pressure pump is installed at one end of the negative pressure pipe.

7. The screen printing apparatus for silver-clad copper photovoltaic cells according to claim 1, characterized in that, The second conveying mechanism is equipped with heating rods for drying photovoltaic cells.

8. A method for screen printing silver-clad copper photovoltaic cells, characterized in that, Includes the following steps: S1. The silver-coated copper paste is placed in a sealed tank and continuously homogenized and stirred. The stirred silver-coated copper paste is then conveyed in a directional manner through a sealed discharge pipe with a constant cross-sectional size. S2. A low-frequency AC excitation current is applied to the silver-coated copper paste flowing in the discharge pipe through a pair of excitation electrodes and a second detection electrode arranged on the inner wall of the discharge pipe. The real-time voltage drop signal of the paste between the two electrodes is collected simultaneously. The real-time resistivity of the silver-coated copper paste is calculated based on the voltage drop signal to complete the online judgment of the paste quality. S3. Based on the online judgment result of the paste quality, switch the paste delivery path through the three-way valve; when the paste is judged to be qualified, the silver-coated copper paste is delivered to the screen printing host; when the paste is judged to be unqualified, the silver-coated copper paste is diverted and discharged to the waste pool. S4. Place the photovoltaic cells to be printed in a sealed conveying environment for low-temperature pre-drying treatment to remove the water vapor adsorbed on the surface of the cells. S5. The pre-dried photovoltaic cells are transported to a sealed conveying channel consisting of an alternately open and closed feed end, a feed buffer chamber, and a printing chamber. By controlling the open and closed states of adjacent chambers, the photovoltaic cells are sent into the printing station of the printing chamber, which is completely isolated from the outside world. Under the protection of inert gas, the silver-coated copper electrode is screen printed on the surface of the photovoltaic cells by the screen printing host. S6. The photovoltaic cells are printed in a printing chamber with inert gas continuously introduced to achieve low oxygen protection for the printed wet grid lines on the surface of the photovoltaic cells, and then the photovoltaic cells are transported to the subsequent curing and sintering process.

9. The screen printing method for silver-clad copper photovoltaic cells according to claim 8, characterized in that, In step S2, the first excitation electrode and the second detection electrode are arranged in pairs on the upper and lower inner walls of the discharge pipe along the slurry flow direction, and the detection surfaces of the two electrodes are flush with the inner wall of the discharge pipe. In step S3, when the real-time resistivity is within the preset qualified threshold range, the slurry is deemed qualified; when the real-time resistivity exceeds the upper limit of the preset qualified threshold, the slurry is deemed unqualified, and the corresponding slurry has defects such as silver shell damage, copper core oxidation, and stratification sedimentation.

10. The screen printing method for silver-clad copper photovoltaic cells according to claim 9, characterized in that, In step S6, nitrogen gas is continuously introduced into the printing chamber as an inert gas to keep the oxygen concentration in the printing chamber below 100 ppm, thus providing low-oxygen protection for the printed wet grid lines throughout the process.

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