Screen segment printing process for improving electrical performance of Topcon battery piece

Abstract

The invention provides a silk screen section printing process for improving the electrical performance of a Topcon battery piece, and relates to the technical field of Topcon batteries. A silk screen section printing technology for improving the electrical performance of a Topcon battery piece comprises the following steps that front face main grid printing is carried out on a silicon wafer after silicon nitride deposition, and then primary drying is carried out; printing a main grid on the back surface of the silicon wafer after the primary drying, and then drying for the second time; printing a fine grid on the back surface of the silicon wafer after the secondary drying, and then drying for the third time; and printing a fine grid on the front surface of the silicon wafer dried for the third time, and sintering after silk-screen printing is completed. By adjusting the printing sequence of the silk screen section and printing and curing the front main grid in advance, the interference of the subsequent process on the front electrode is reduced, the contact stability between the front electrode and the silicon wafer is ensured, and the recombination loss is further reduced; meanwhile, the contact time of the back fine grid and a machine is shortened, and the abrasion degree of the back fine grid is reduced.

Description

Technical Field

[0001] The present application relates to the field of Topcon battery technology, and in particular to a screen segment printing process for improving the electrical performance of Topcon battery cells. Background Art

[0002] In the production of Topcon batteries, screen printing is a key process at the end. Generally speaking, the silicon wafer is first processed through multiple previous processes, such as texturing, diffusion, etc., before entering the screen printing stage. The conventional screen printing steps are usually as follows: back main grid → back fine grid → front main grid → front fine grid. High-temperature sintering allows a good ohmic contact to be formed between the electrode slurry and the silicon wafer, allowing the electrode to effectively collect and conduct carriers, and finally completing the screen printing process of the battery cell, obtaining a semi-finished Topcon battery cell with a basic electrode structure. Subsequently, it undergoes other processes such as testing to finally form a finished battery cell.

[0003] The existing printing sequence for the front busbar: 1. As the primary current collection channel, the three printing passes fail to achieve a close contact with the silicon wafer, increasing contact resistance. Furthermore, the front busbar paste does not have sufficient curing time, failing to maximize conductivity. 2. Regarding the stability of the front busbar, the front busbar is printed in three passes. The first and second steps increase interference with the front electrode, reducing contact stability between the front electrode and the silicon wafer, and thus increasing recombination losses.

[0004] Wear of the backside grid lines will cause the following electrical performance impacts: 1. Wear of the backside grid lines will destroy the good contact between them and the silicon wafer, increasing the contact resistance. According to Ohm's law, a greater voltage drop will be generated when current passes through, resulting in a lower open-circuit voltage of the battery, reducing the output voltage of the battery under no-load conditions, and affecting the overall performance of the battery; 2. Wear will cause the conductivity of the grid lines to decrease, reducing the efficiency of electron collection and transmission on the back side. Some electrons cannot be collected smoothly through the worn grid lines, thereby reducing the short-circuit current of the battery and reducing the maximum output current of the battery in the short-circuit state; 3. The reduction in open-circuit voltage and short-circuit current will directly lead to a decrease in fill factor. The fill factor is an important indicator for measuring the output characteristics of the battery. A decrease in its value means that the output power of the battery under actual working conditions is reduced and the photoelectric conversion efficiency is reduced. Summary of the Invention

[0005] The purpose of this application is to provide a screen segment printing process for improving the electrical performance of Topcon solar cells, which has the advantages of improving stability and reducing wear of the back-side fine grid.

[0006] In order to solve the above technical problems, the technical solutions adopted in this application are:

[0007] The present application provides a screen segment printing process for improving the electrical performance of Topcon solar cells, comprising the following steps:

[0008] S1. Printing a main grid on the front side of the silicon wafer after silicon nitride deposition, and then drying it once;

[0009] S2, printing the back main grid on the silicon wafer after the primary drying, and then performing secondary drying;

[0010] S3, printing fine grids on the back side of the silicon wafer after the second drying, and then drying it for the third time;

[0011] S4. Print fine grids on the front side of the silicon wafer after three dryings, and perform sintering after the screen printing is completed.

[0012] Compared with the prior art, the embodiments of the present application have at least the following advantages or beneficial effects:

[0013] 1. In terms of optical performance:

[0014] ① As the primary current collection channel, prioritizing printing on the front busbar ensures closer contact with the silicon wafer, reducing contact resistance. Furthermore, curing the front busbar first allows for better alignment of the subsequently printed back busbar lines and front fine grid, minimizing misalignment and further reducing series resistance. Prioritizing printing and fully curing the front busbar allows for more efficient collection of photogenerated carriers, minimizing current loss and ultimately increasing short-circuit current (Isc).

[0015] ② Reducing backside fine grid wear reduces light reflection: After wear, the surface roughness of the backside grid lines decreases, which reduces the reflectivity of light on its surface. More light is absorbed and utilized by the silicon wafer, increasing the effective light absorption of the cell, improving the cell's photogenerated carrier generation rate, and thus improving the cell's short-circuit current and photoelectric conversion efficiency.

[0016] ③ Reduce the wear of the back-side fine grid and increase the scattering of light: Normal back-side grid lines can scatter the incident light to a certain extent, increase the propagation path of light in the silicon wafer, improve the light absorption efficiency, and thus more fully generate photogenerated carriers.

[0017] 2. Long-term stability:

[0018] ① Slowing down aging: Reducing backside grid line wear reduces changes in the battery's local electric field distribution. This reduces damage to the passivation layer on the silicon wafer surface during long-term use, slowing the battery's surface recombination rate. Furthermore, impurities and moisture easily accumulate at worn areas, leading to corrosion and other problems. Reducing backside wear extends the battery's lifespan and long-term stability.

[0019] ② Improved PID resistance: Reduces backside grid line wear and reduces the degree of change in the interface state between the backside grid line and the silicon wafer, thereby reducing the decline in the battery's PID (potential induced degradation) resistance. In actual applications, batteries are more susceptible to the PID effect, thereby improving output stability.

[0020] In summary, this application adjusts the printing order of the silk screen segments, prints and solidifies the front main grid in advance, reduces the interference of subsequent processes on the front electrode, ensures the contact stability between the front electrode and the silicon wafer, and further reduces the composite loss; at the same time, reduces the contact time between the back fine grid and the machine, thereby reducing the degree of wear of the back fine grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0022] Figure 1 This is a flow chart of the screen printing process according to an embodiment of the present application;

[0023] Figure 2 This is a flow chart of the screen printing process for the comparative example of this application;

[0024] Figure 3 This is a diagram showing the plasticity of the fine grid at the belt contact position on the back side of the silicon wafer produced in an embodiment of the present application;

[0025] Figure 4 This is a diagram showing the plasticity of the fine grid at the belt contact position on the back side of the silicon wafer produced as a comparative example of this application. DETAILED DESCRIPTION

[0026] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0027] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to specific embodiments.

[0028] A screen segment printing process for improving the electrical performance of Topcon solar cells includes the following steps:

[0029] S1. Printing a main grid on the front side of the silicon wafer after silicon nitride deposition, and then drying it once;

[0030] S2, printing the back main grid on the silicon wafer after the primary drying, and then performing secondary drying;

[0031] S3, printing fine grids on the back side of the silicon wafer after the second drying, and then drying it for the third time;

[0032] S4. Print fine grids on the front side of the silicon wafer after three dryings, and perform sintering after the screen printing is completed.

[0033] In some embodiments of the present application, the front main grid printing in the above-mentioned S1 step uses a 430 mesh 13 wire diameter 15 yarn 5 film 20 line width screen, a printing speed of 530 mm / s, an ink return speed of 1400 mm / s, a printing height offset of 2.2 mm, and a printing pressure of 60N.

[0034] In some embodiments of the present application, the back main grid printing in the above-mentioned S2 step uses a 430 mesh 13 wire diameter 15 yarn 3.5 film 20 line width screen, a printing speed of 550 mm / s, an ink return speed of 1300 mm / s, a printing height offset of 2.0 mm, and a printing pressure of 50N.

[0035] In some embodiments of the present application, the back-side fine grid printing in the above-mentioned S3 step uses a 500 mesh 7 line diameter 10.5 yarn 3 film 11 line width screen, the printing speed is 550 mm / s, the ink return speed is 1300 mm / s, the printing height offset is 3.0 mm, and the printing pressure is 55N.

[0036] In some embodiments of the present application, the front fine grid printing in the above-mentioned S4 step uses a 500 mesh 7 wire diameter 9 yarn 4 film 10.5 line width screen, the printing speed is 550mm / s, the ink return speed is 1300mm / s, the printing height offset is 2.5mm, and the printing pressure is 60N.

[0037] In some embodiments of the present application, the printing paste for the front main grid and the back main grid is polymer CSP-M3M; the printing paste for the back fine grid is polymer CSP-N3P1; and the printing paste for the front fine grid is polymer CSP-N4TF.

[0038] In some embodiments of the present application, the drying process is specifically as follows: the preheating zone, the upper temperature zone to the upper seventh temperature zone, a total of 8 upper temperature zones, are 200℃, 280℃, 280℃, 280℃, 200℃, 200℃, and 200℃ respectively; the next temperature zone, a total of 1 lower temperature zone, is 200℃; the oven chain speed is 240mm / s.

[0039] In some embodiments of the present application, secondary drying is specifically performed as follows: the preheating zone, the upper temperature zone, the upper temperature zone, the upper temperature zone, the upper temperature zone, the upper temperature zone, the upper temperature zone, the upper temperature zone, the upper temperature zone, the upper temperature zone, the upper temperature zone, the lower ...

[0040] In some embodiments of the present application, three drying steps are performed: a preheating zone, the upper temperature zone through the upper temperature zone (eight upper temperature zones) at 180°C, 420°C, 420°C, 420°C, 420°C, 380°C, 380°C, and 380°C, respectively; and a lower temperature zone at 380°C. The oven chain speed is 240 mm / s.

[0041] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0042] Example

[0043] A screen segment printing process to improve the electrical performance of Topcon cells, such as Figure 1 As shown, the following steps are included:

[0044] S1. Print the busbar on the front side of the silicon wafer after silicon nitride deposition. The printing paste is polymer CSP-M3M. The front busbar is printed using a 430 mesh, 13 wire diameter, 15 yarn, 3.5 film, 20 line width screen. The printing speed is 530 mm / s, the ink return speed is 1400 mm / s, the printing height offset is 2.2 mm, the printing pressure is 60 N, the scraper height offset is 0.3 mm, the scraper printing delay is 0 ms, and the ink blade height offset is -0.2 mm. The ink knife return delay is 0ms, the printing start position is 45mm, and the printing end position is 268mm. After printing, the slurry is sent to an oven for drying. The specific drying process is as follows: preheating zone, upper temperature zone to upper seventh temperature zone, a total of 8 upper temperature zones are 200℃, 280℃, 280℃, 280℃, 280℃, 200℃, 200℃, 200℃; the next temperature zone, a total of 1 lower temperature zone is 200℃; the oven chain speed is 240mm / s.

[0045] S2. After the silicon wafer has been dried once, it is conveyed by a belt and then printed with the back main grid. The printing paste is polymer CSP-M3M. The back main grid is printed using a 430 mesh 13 wire diameter 15 yarn 3.5 film 20 line width screen. The printing speed is 550mm / s, the ink return speed is 1300mm / s, the printing height offset is 2.0mm, the printing pressure is 50N, the scraper height offset is 0.7mm, the scraper printing delay is 0ms, the ink knife height offset is -0.3mm, the ink knife ink return delay is 0ms, the printing start position is 45mm, and the printing end position is 270mm. After printing, the slurry is sent to the second oven for secondary drying. The secondary drying is specifically as follows: the preheating zone, the upper temperature zone to the upper seventh temperature zone, a total of 8 upper temperature zones, are 200℃, 280℃, 280℃, 280℃, 250℃, 250℃, and 250℃ respectively; the next temperature zone, a total of 1 lower temperature zone, is 200℃. The oven chain speed is 240 mm / s.

[0046] S3. The silicon wafer after secondary drying is conveyed by a belt and then printed with a fine grid on the back side. The printing paste is polymer CSP-N3P1. The fine grid on the back side is printed using a 500 mesh 7 wire diameter 10.5 yarn 3 film 11 line width screen. The printing speed is 550mm / s, the ink return speed is 1300mm / s, the printing height offset is 3.0mm, the printing pressure is 55N, the scraper height offset is 0.1mm, the scraper printing delay is 0ms, the ink knife height offset is 0.1mm, the ink knife ink return delay is 0ms, the printing start position is 25mm, and the printing end position is 263mm. After printing, the slurry is sent to three ovens for three dryings. The three dryings are specifically as follows: preheating zone, upper temperature zone to upper seventh temperature zone, a total of 8 upper temperature zones, which are 180℃, 420℃, 420℃, 420℃, 420℃, 380℃, 380℃, and 380℃ respectively; the next temperature zone, a total of 1 lower temperature zone, is 380℃. The oven chain speed is 240 mm / s.

[0047] S4. The silicon wafers after three dryings are conveyed by a belt and then printed with fine grids on the front side. The printing paste is polymer CSP-N4TF. The fine grids on the front side are printed with a 500 mesh, 7 wire diameter, 9 yarn, 4 film, and 10.5 line width screen. The printing speed is 550 mm / s, the ink return speed is 1300 mm / s, the printing height offset is 2.5 mm, the printing pressure is 60 N, the scraper height offset is 1.5 mm, the scraper printing delay is 0 ms, the ink knife height offset is 0.5 mm, the ink knife ink return delay is 0 ms, the printing start position is 28 mm, and the printing end position is 260 mm. After the screen printing is completed, the wafers are sent to a sintering furnace for sintering.

[0048] Comparative Example

[0049] The difference between this comparative example and the embodiment is only the printing order, the process parameters and raw materials are the same. Figure 2 As shown, specifically:

[0050] S1. Print the backside busbar on the silicon wafer after silicon nitride deposition. The printing paste is polymer CSP-M3M. The backside busbar printing adopts a 430 mesh 13 wire diameter 15 yarn 3.5 film 20 line width screen. The printing speed is 550mm / s, the ink return speed is 1300mm / s, the printing height offset is 2.0mm, the printing pressure is 50N, the scraper height offset is 0.7mm, the scraper printing delay is 0ms, and the ink blade height offset is -0.3mm. The ink knife return delay is 0ms, the printing start position is 45mm, and the printing end position is 270mm; after printing, the slurry is sent to an oven for drying; the specific drying process is: preheating zone, upper temperature zone to upper seventh temperature zone, a total of 8 upper temperature zones are 200℃, 280℃, 280℃, 280℃, 280℃, 200℃, 200℃, 200℃; the next temperature zone, a total of 1 lower temperature zone is 200℃; the oven chain speed is 240mm / s.

[0051] S2. The silicon wafer after the primary drying is conveyed by a belt and then printed with a fine grid on the back side. The printing paste is polymer CSP-N3P1. The fine grid on the back side is printed using a 500 mesh 7 wire diameter 10.5 yarn 3 film 11 line width screen. The printing speed is 550mm / s, the ink return speed is 1300mm / s, the printing height offset is 3.0mm, the printing pressure is 55N, the scraper height offset is 0.1mm, the scraper printing delay is 0ms, the ink knife height offset is 0.1mm, the ink knife ink return delay is 0ms, the printing start position is 25mm, and the printing end position is 263mm. After printing, the slurry is sent to the second oven for secondary drying. The secondary drying is specifically as follows: the preheating zone, the upper temperature zone to the upper seventh temperature zone, a total of 8 upper temperature zones, are 200℃, 280℃, 280℃, 280℃, 280℃, 250℃, 250℃, and 250℃ respectively; the next temperature zone, a total of 1 lower temperature zone, is 200℃. The oven chain speed is 240 mm / s.

[0052] S3. The silicon wafer after secondary drying is conveyed by belt and then printed with the main grid on the front side. The printing paste is polymer CSP-M3M. The main grid is printed with a 430 mesh 13 wire diameter 15 yarn 3.5 film 20 line width screen. The printing speed is 530mm / s, the ink return speed is 1400mm / s, the printing height offset is 2.2mm, the printing pressure is 60N, the scraper height offset is 0.3mm, the scraper printing delay is 0ms, the ink knife height offset is -0.2mm, the ink knife ink return delay is 0ms, the printing start position is 45mm, and the printing end position is 268mm. After printing, the slurry is sent to three ovens for three drying. The three drying processes are as follows: preheating zone, upper temperature zone to upper seventh temperature zone, a total of 8 upper temperature zones, which are 180℃, 420℃, 420℃, 420℃, 420℃, 380℃, 380℃, and 380℃ respectively; the next temperature zone, a total of 1 lower temperature zone, is 380℃. The oven chain speed is 240 mm / s.

[0053] S4. The silicon wafers after three dryings are conveyed by a belt and then printed with fine grids on the front side. The printing paste is polymer CSP-N4TF. The fine grids on the front side are printed with a 500 mesh, 7 wire diameter, 9 yarn, 4 film, and 10.5 line width screen. The printing speed is 550 mm / s, the ink return speed is 1300 mm / s, the printing height offset is 2.5 mm, the printing pressure is 60 N, the scraper height offset is 1.5 mm, the scraper printing delay is 0 ms, the ink knife height offset is 0.5 mm, the ink knife ink return delay is 0 ms, the printing start position is 28 mm, and the printing end position is 260 mm. After the screen printing is completed, the wafers are sent to a sintering furnace for sintering.

[0054] Experimental example

[0055] 1. Comparison of the plasticity of the fine grid at the belt contact position on the back side of the silicon wafer produced in the embodiment and the comparative example (3D microscope observation) Figure 3 (Example) and Figure 4 (Comparative Example) Figure 3 and Figure 4 As can be seen from the figure, compared to the comparative printing sequence, the front main grid, as the main current collection channel, is printed in the first pass ahead of the front main grid, ensuring closer contact with the silicon wafer and reducing contact resistance. At the same time, the front main grid slurry has more time to cure, ensuring maximum conductivity. Finally, the contact time between the back main grid and the belt is reduced, thereby reducing wear, increasing the overall line height by 0.6μm and improving line flatness.

[0056] 2. The electrical performance parameters of the silicon wafers processed by the embodiment and the comparative example are compared, as shown in Table 1.

[0057] Table 1

[0058]

[0059]

[0060] As can be seen in Table 1, the new printing sequence in this application exhibits significantly higher electrical performance than the conventional printing sequence in the comparative example, primarily in the form of a 4.6 mA higher current Isc and a 0.014% gain in conversion efficiency Eta. This is due to the fact that the front main grid is printed and cured in advance, allowing the fine grid to form a better connection with the main grid, reducing losses during current collection. Furthermore, the surface roughness of the back grid lines after wear is reduced, lowering the reflectivity of light on their surface. This increases the effective light absorption of the battery, improves the photogenerated carrier generation rate of the battery, and thus improves the battery's short-circuit current and photoelectric conversion efficiency.

[0061] The above test results show that the printing sequence adjusted in this application has a significant improvement on the overall photoelectric conversion efficiency.

[0062] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

Claims

1. A screen segment printing process for improving the electrical performance of Topcon cells, characterized in that: The following steps are involved: S1, printing the main grid on the front side of the silicon wafer after silicon nitride deposition, and then drying it once; S2, printing the back main grid on the silicon wafer after the primary drying, and then performing secondary drying; S3, printing fine grids on the back side of the silicon wafer after the second drying, and then drying it for a third time; S4. Print fine grids on the front side of the silicon wafer after three dryings, and perform sintering after the screen printing is completed.

2. A screen segment printing process for improving the electrical performance of Topcon cells according to claim 1, characterized in that: In the step S1 , the front main grid printing adopts a 430 mesh 13 wire diameter 15 yarn 5 film 20 line width screen, a printing speed of 530 mm / s, an ink return speed of 1400 mm / s, a printing height offset of 2.2 mm, and a printing pressure of 60 N.

3. The screen segment printing process for improving the electrical performance of Topcon cells according to claim 1, characterized in that: The back main grid printing in step S2 uses a 430 mesh 13 wire diameter 15 yarn 3.5 film 20 line width screen, a printing speed of 550 mm / s, an ink return speed of 1300 mm / s, a printing height offset of 2.0 mm, and a printing pressure of 50N.

4. The screen segment printing process for improving the electrical performance of Topcon cells according to claim 1, characterized in that: The back fine grid printing in step S3 uses a 500 mesh, 7 line diameter, 10.5 yarn, 3 film, and 11 line width screen, with a printing speed of 550 mm / s, an ink return speed of 1300 mm / s, a printing height offset of 3.0 mm, and a printing pressure of 55N.

5. The screen segment printing process for improving the electrical performance of Topcon cells according to claim 1, characterized in that: The front fine grid printing in step S4 uses a 500 mesh, 7 wire diameter, 9 yarn, 4 film, 10.5 line width screen, with a printing speed of 550 mm / s, an ink return speed of 1300 mm / s, a printing height offset of 2.5 mm, and a printing pressure of 60N.

6. The screen segment printing process for improving the electrical performance of Topcon cells according to claim 1, characterized in that: The printing paste for the front main grid and the back main grid is polymerized CSP-M3M; the printing paste for the back fine grid is polymerized CSP-N3P1; and the printing paste for the front fine grid is polymerized CSP-N4TF.

7. The screen segment printing process for improving the electrical performance of Topcon cells according to claim 1, characterized in that: The specific one-time drying is: the preheating zone, the upper temperature zone to the upper seventh temperature zone, a total of 8 upper temperature zones are 200℃, 280℃, 280℃, 280℃, 280℃, 200℃, 200℃, and 200℃ respectively; the next temperature zone, a total of 1 lower temperature zone is 200℃; the oven chain speed is 240mm / s.

8. The screen segment printing process for improving the electrical performance of Topcon cells according to claim 7, characterized in that: The secondary drying is specifically as follows: the preheating zone, the upper temperature zone to the upper seventh temperature zone, a total of 8 upper temperature zones, are 200℃, 280℃, 280℃, 280℃, 280℃, 250℃, 250℃, and 250℃ respectively; the next temperature zone, a total of 1 lower temperature zone, is 200℃; the oven chain speed is 240mm / s.

9. The screen segment printing process for improving the electrical performance of Topcon cells according to claim 8, characterized in that: The three drying steps are as follows: preheating zone, upper temperature zone to upper seventh temperature zone, a total of 8 upper temperature zones are 180℃, 420℃, 420℃, 420℃, 420℃, 380℃, 380℃, 380℃; the next temperature zone, a total of 1 lower temperature zone is 380℃; the oven chain speed is 240mm / s.

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