A processing method of N-type TOPCon cell plated film defective pieces

Abstract

The application discloses a processing method for N-type TOPCon cell plated film defective pieces. The plated film defective pieces to be processed are put into a reaction tank, carbon tetrafluoride and oxygen electrolysis gas ionized by a high-frequency power supply are introduced into the closed reaction tank, and then reaction is carried out to obtain pretreated defective pieces; the pretreated defective pieces are subjected to subsequent pickling by a hydrofluoric acid solution and a mixed acid solution of hydrofluoric acid and hydrochloric acid, water washing, and drying to obtain recovered silicon pieces. The processing method for N-type TOPCon cell plated film defective pieces has strong applicability, is suitable for the recovery and processing of unqualified pieces caused by TOPCon front and back surface plating or front surface plating defects, and is also suitable for the processing of rework pieces or dirty bare silicon pieces before plating. On the premise of guaranteeing excellent performance of the recovered silicon pieces, the processing time is greatly shortened, the recovery efficiency is high, the method is suitable for industrialized production and application, the surface of the recovered silicon pieces is clean and bright, the appearance and performance of the recovered silicon pieces are normal, and the method has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and in particular to a method for processing defective N-type TOPCon solar cell wafers. Background Technology

[0002] In recent years, the increasingly strained energy and environmental issues have spurred the rapid development of the photovoltaic (PV) solar cell industry. Reducing production costs and improving the production efficiency of solar cells are currently the focus of research. TOPCon technology is currently the most advanced technology in the PV industry, and its main process flow is: texturing - boron diffusion - etching and polishing - LPCVD - phosphorus diffusion - cleaning - front alumina - front and back silicon nitride - printing and sintering. During the production of the front and back silicon nitride films in the TOPCon cell process, due to equipment and process issues, defective silicon nitride films (too thick, too thin, or with spots, etc.) are prone to occur. If substandard products are scrapped without rework, it will increase production costs. To recover the silicon wafers, rework and cleaning are necessary. Currently, the conventional cleaning method is to use hydrofluoric acid solution to etch and remove the substandard silicon nitride film thickness for reprocessing. Furthermore, to improve the removal rate of silicon nitride films, methods such as increasing the concentration of hydrofluoric acid or extending the cleaning time are commonly used. However, the quality of defective wafers varies greatly, with many reasons for non-compliance, including excessively thick or thin silicon nitride films, and even just spots. If the method of uniformly increasing the concentration of hydrofluoric acid solution or extending the cleaning time is used, it can easily lead to the scrapping of silicon wafers. Moreover, the process time is long, and the labor and chemical costs are high, resulting in persistently high production costs. Therefore, it is necessary to develop a processing method for silicon wafers suitable for various types of defective coatings to achieve the normal recycling and reuse of silicon wafers. Summary of the Invention

[0003] In view of the fact that the existing methods for processing defective N-type TOPCon battery wafers with poor coating are not effective for wafers with various quality problems, which can easily lead to the scrapping of silicon wafers, and the recycling process is time-consuming and costly, this invention provides a method for processing defective N-type TOPCon battery wafers with poor coating.

[0004] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0005] A method for processing defective N-type TOPCon battery coating sheets includes the following steps:

[0006] S1. Place the defective film to be treated into the reaction tank, and introduce the electrolytic gas of carbon tetrafluoride and oxygen after being ionized by a high-frequency power supply into the sealed reaction tank. React to obtain the pretreated defective film.

[0007] S2, the pre-treated defective sheet is immersed in hydrofluoric acid solution for pickling, and after pickling, it is washed with water to obtain the first pickled defective sheet.

[0008] S3, the first poorly pickled wafer is immersed in a mixed acid solution of hydrofluoric acid and hydrochloric acid for pickling. After pickling, it is washed with water and dried to obtain a recovered silicon wafer.

[0009] Compared to existing technologies, the method for processing defective N-type TOPCon solar cells provided by this invention uses fluorine atom active groups generated by the ionization of carbon tetrafluoride and oxygen using a high-frequency power supply to etch silicon nitride on the defective wafers. The fluorine atom active groups have high reactivity with silicon nitride and a fast reaction rate, which can treat defective wafers with different quality problems, effectively removing silicon nitride spots or excessively thick or thin silicon nitride films on the defective wafers, significantly shortening the processing time. The subsequent two specific acid washes improve the cleanliness and flatness of the silicon wafer surface, prevent significant thinning of the silicon wafer, reduce the amount of waste silicon wafers during the recycling process, and the entire process is simple, highly controllable, and can greatly improve the efficiency of silicon wafer recycling. The TOPCon solar cells made from the recycled silicon wafers can maintain excellent photoelectric conversion efficiency, reduce the production cost of TOPCon cells, and have high application value.

[0010] Preferably, step S1 specifically involves: placing the defective wafer to be treated into the reaction tank, evacuating the reaction tank to 50-120 Pa, introducing carbon tetrafluoride and oxygen into the reaction tank, and after the pressure inside the chamber stabilizes, starting the radio frequency power supply to ionize the carbon tetrafluoride and oxygen for reaction. After the reaction is completed, introducing inert gas into the reaction tank to remove residual reaction gas, closing the vacuum, introducing inert gas again until it is balanced with the pressure outside the reaction tank, and then taking out the silicon wafer.

[0011] Furthermore, in conjunction with the above, in step S1, the flow rate of carbon tetrafluoride is 150-250 mL / min, and the flow rate of oxygen is 50-100 mL / min.

[0012] Preferably, in step S1, the frequency of the high-frequency power supply is 13.56MHz and the power is 500-800W.

[0013] Preferably, in step S1, the reaction temperature is 20-40℃ and the reaction time is 5-8 min.

[0014] Optimized process conditions can increase the amount of fluorine atom active groups generated, increase the reaction rate between fluorine atom active groups and silicon nitride, and improve processing efficiency.

[0015] It should be noted that carbon tetrafluoride and oxygen react under high-frequency power ionization as follows:

[0016] CF4→CF3 * +CF2 * +CF * +F *

[0017] CF X * +O2→COF x ↑+CO↑+CO2↑

[0018] O2+COF x →CO2+F *

[0019] Si3N4+F * →SiF4↑+N2↑

[0020] Carbon tetrafluoride and oxygen are ionized by a high-frequency power supply to generate fluorine atom active free radicals. The fluorine atom free radicals react with silicon nitride to generate silicon tetrafluoride gas and nitrogen gas. The generated gas is extracted from the reaction tank by a vacuum system, so no impurities remain on the surface of the silicon wafer. This also helps to shorten the subsequent acid washing time and greatly improves the efficiency of silicon wafer recycling.

[0021] In one embodiment of the present invention, in step S1, the reaction tank includes a reaction tank body, an ionization chamber that is sealed and connected to the reaction tank body, and an ionization assembly disposed on the ionization chamber.

[0022] The ionization component includes a coil, a radio frequency (RF) connection line, and an RF power supply; the coil is arranged around the periphery of the ionization chamber, and the RF power supply is connected to the coil via the RF connection line.

[0023] Furthermore, in conjunction with the above, the reaction tank is also equipped with a flow equalization plate for diverting the electrolytic gas and controlling the direction of the electrolytic gas entering the reaction tank.

[0024] Equalizing plates are installed at the bottom and four side walls of the reaction tank to divert the electrolytic gas, which helps the electrolytic gas to fully contact the poorly coated wafers, allowing the electrolytic gas to fully etch the silicon nitride and improve the cleanliness of the recovered silicon wafers.

[0025] Furthermore, in conjunction with the above, the ionization chamber is provided with an air inlet, which is connected to the gas supply pipelines for carbon tetrachloride and oxygen.

[0026] In one embodiment of the present invention, the reaction tank is further provided with a vacuum system, wherein the inlet of the vacuum system and the inlet of the gas supply pipeline are respectively located on opposite side walls inside the reaction tank. Positioning the vacuum system on the opposite side of the gas supply pipeline increases the contact time between the electrolytic gas and the defective wafer, thus ensuring sufficient etching of the silicon nitride on the defective wafer.

[0027] In one specific implementation, the vacuum system is a vacuum pump.

[0028] Preferably, in step S2, the mass concentration of the hydrofluoric acid solution is 5%-6%.

[0029] Preferably, in step S2, the pickling temperature is 20-40℃ and the time is 3-5 minutes.

[0030] Preferably, in step S2, the water washing temperature is 20-40℃ and the time is 5-8 minutes.

[0031] Preferably, in step S3, the mass concentration of hydrofluoric acid in the mixed acid solution is 4.5%-5%, and the mass concentration of hydrochloric acid is 4.5%-5%.

[0032] Preferably, in step S3, the pickling temperature is 20-40℃ and the time is 5-8 minutes.

[0033] Preferably, in step S3, the water washing temperature is 20-40℃ and the time is 5-8 minutes.

[0034] For example, in steps S2 and S3, the water washing process can also be combined with bubbling treatment, using nitrogen gas for bubbling to improve the water washing effect.

[0035] Preferably, in step S3, the drying is carried out by nitrogen blowing, the drying temperature is 70-80℃, and the drying time is 5-8 minutes.

[0036] The method for processing defective N-type TOPCon battery wafers provided by this invention has strong applicability. It is not only applicable to the recycling and processing of defective wafers caused by poor coating on the front and back sides of TOPCon or poor coating on the front side, but also applicable to the processing of rework wafers or dirty bare silicon wafers before coating. While ensuring the excellent performance of the recycled silicon wafers, it greatly shortens the process time, has high recycling efficiency, is suitable for industrial production applications, and the recycled silicon wafers have a clean and bright surface, normal appearance and performance, and have broad application prospects. Attached Figure Description

[0037] Figure 1 This is a three-dimensional structural diagram of the reaction tank in an embodiment of the present invention;

[0038] Figure 2 This is a top view of the reaction tank in an embodiment of the present invention;

[0039] Figure 3 This is a schematic diagram illustrating the working principle of the reaction tank in an embodiment of the present invention;

[0040] Figure 4 This is a schematic diagram of the processing flow for defective coated sheets in an embodiment of the present invention;

[0041] In the figure, 100 is the reaction tank, 101 is the ionization chamber, 102 is the coil, 103 is the radio frequency power supply, 104 is the radio frequency connection line, 105 is the silicon wafer to be processed, 106 is the flow equalizer, 107 is the vacuum pump, 108 is the vacuum pipeline, and 109 is the filter.

[0042] B1, Carbon tetrafluoride flow meter; B2, Oxygen flow meter; D1, Main valve; D2, Pre-extraction valve; D3, Main extraction valve; D4, Carbon tetrafluoride valve; D5, Oxygen valve; D6, Nitrogen dilution valve; D7, Nitrogen valve; D8, Nitrogen charging valve; D9, High-purity nitrogen check valve 1; D10, High-purity nitrogen check valve 2; D11, First pressure regulating valve; D12, Second pressure regulating valve; D13, Third pressure regulating valve; A2, Electronic actuator;

[0043] a. Carbon tetrafluoride, b. Oxygen, c. High-purity nitrogen 1, d. High-purity nitrogen 2, e. Compressed air. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0045] To better illustrate the present invention, further examples are provided below.

[0046] See Figures 1-4 The reaction tanks used in the following embodiments will now be described.

[0047] See Figure 1 The reaction tank includes a reaction tank body 100, an ionization chamber 101 that is sealed and connected to the reaction tank body 100, and an ionization assembly disposed on the ionization chamber.

[0048] The ionization component includes a coil 102, a radio frequency connection line 104, and a radio frequency power supply 103. The coil 102 is arranged around the periphery of the ionization chamber 101, and the radio frequency power supply 103 is connected to the coil 102 through the radio frequency connection line 104.

[0049] As one specific implementation method, see [link / reference]. Figure 2 The reaction tank 100 is provided with a flow equalization plate 106 for diverting the electrolytic gas entering the reaction tank 100.

[0050] As one specific implementation method, see [link / reference]. Figure 2The reaction tank also includes a vacuum pump 107 and a vacuum pipeline 108 for connecting the vacuum pump 107 and the reaction tank 100. The vacuum pump 107 is used to control the vacuum environment inside the reaction tank 100 and to extract the residual gas from the reaction tank 100 after the etching reaction is completed.

[0051] See Figure 3 and Figure 4 The processing procedure for defective coated sheets in the embodiments of the present invention will be described.

[0052] The silicon wafer 105 to be processed is placed into the reaction tank 100. The vacuum pump 107 is started. First, the pre-evacuation valve D2 is opened for pre-evacuation, and then the main evacuation valve D3 is opened. The opening and closing of the pre-evacuation valve D2 and the main evacuation valve D3 are controlled by the electronic actuator A2 through the introduction of compressed air e. Vacuum is evacuated until the vacuum pressure in the reaction tank 100 is maintained at 50-120 Pa. Then, the carbon tetrafluoride flow meter B1 and the carbon tetrafluoride valve D4 are opened, and the oxygen flow meter B2 and the oxygen valve D5 are opened simultaneously to introduce carbon tetrafluoride a and oxygen b into the reaction tank. After the chamber pressure stabilizes, the radio frequency power supply 103 is started to make the carbon tetrafluoride a and oxygen b into the reaction tank. Fluorinated carbon a and oxygen b generate fluorine atom active free radicals that react with the silicon nitride film. At the start of the reaction, the nitrogen dilution valve D6 is opened to dilute the reaction gas in the reaction tank and then promptly extract it from the reaction tank through the vacuum pump 107. After the reaction is completed, the nitrogen valve D7 is opened to introduce high-purity nitrogen c1 into the reaction tank. The residual reaction gas in the reaction tank 100 is filtered through the filter 109 and then extracted from the reaction tank 100. The vacuum pump 107 is turned off, and the nitrogen filling valve D8 is opened to introduce high-purity nitrogen d2 into the reaction tank 100 again until the pressure inside and outside the chamber is balanced. Then the tank cover is opened and the silicon wafer is taken out.

[0053] Example 1

[0054] This invention provides a method for processing defective N-type TOPCon battery coating sheets, comprising the following steps:

[0055] S1. Place the defective wafer to be treated into the reaction tank, evacuate the reaction tank to 50-80 Pa, and introduce carbon tetrafluoride and oxygen into the reaction tank at a flow rate of 200 mL / min and a flow rate of 80 mL / min. After the pressure in the chamber stabilizes, start the radio frequency power supply to ionize the carbon tetrafluoride and oxygen. The frequency of the high-frequency power supply is 13.56 MHz and the power is 700 W. After ionizing fluorine atom free radicals and reacting with silicon nitride for 7 min, introduce inert gas into the reaction tank to remove residual reaction gas, close the vacuum, and introduce inert gas again until the pressure is balanced with that outside the reaction tank. Then take out the silicon wafer.

[0056] S2, the pre-treated defective sheet is immersed in a 5.5% hydrofluoric acid solution for pickling at 30°C for 4 minutes. After pickling, it is washed with water at 30°C for 6 minutes to obtain the first pickled defective sheet.

[0057] S3, the first defective pickled wafer is immersed in a mixed acid solution of hydrofluoric acid and hydrochloric acid for pickling. The mass concentration of hydrofluoric acid is 4.8% and the mass concentration of hydrochloric acid is 4.8%. The pickling temperature is 30°C and the pickling time is 6 minutes. After pickling, it is washed with water at 30°C for 6 minutes. It is then dried with nitrogen gas at a temperature of 75°C to obtain the recovered silicon wafer.

[0058] Example 2

[0059] This invention provides a method for processing defective N-type TOPCon battery coating sheets, comprising the following steps:

[0060] S1. Place the defective wafer to be treated into the reaction tank, evacuate the reaction tank to 90-110 Pa, and introduce carbon tetrafluoride and oxygen into the reaction tank at a flow rate of 150 mL / min and a flow rate of 50 mL / min. After the pressure in the chamber stabilizes, start the radio frequency power supply to ionize the carbon tetrafluoride and oxygen. The frequency of the high-frequency power supply is 13.56 MHz and the power is 500 W. After ionizing fluorine atom free radicals and reacting with silicon nitride for 5 min, introduce inert gas into the reaction tank to remove residual reaction gas, close the vacuum, and introduce inert gas again until the pressure is balanced with that outside the reaction tank. Then take out the silicon wafer.

[0061] S2, the pre-treated defective sheet is immersed in a 5% hydrofluoric acid solution for pickling at 20°C for 5 minutes. After pickling, it is washed with water at 20°C for 8 minutes to obtain the first pickled defective sheet.

[0062] S3, the first poorly pickled wafer is immersed in a mixed acid solution of hydrofluoric acid and hydrochloric acid for pickling. The mass concentration of hydrofluoric acid is 4.5% and the mass concentration of hydrochloric acid is 4.5%. The pickling temperature is 40°C and the pickling time is 5 minutes. After pickling, it is washed with water at 40°C for 5 minutes. It is then dried with nitrogen gas at 80°C to obtain the recovered silicon wafer.

[0063] Example 3

[0064] This invention provides a method for processing defective N-type TOPCon battery coating sheets, comprising the following steps:

[0065] S1. Place the defective wafer to be treated into the reaction tank, evacuate the reaction tank to 80-100 Pa, and introduce carbon tetrafluoride and oxygen into the reaction tank at a flow rate of 250 mL / min and a flow rate of 100 mL / min. After the pressure in the chamber stabilizes, start the radio frequency power supply to ionize the carbon tetrafluoride and oxygen. The frequency of the high-frequency power supply is 13.56 MHz and the power is 800 W. After ionizing fluorine atom free radicals and reacting with silicon nitride for 8 min, introduce inert gas into the reaction tank to remove residual reaction gas, close the vacuum, and introduce inert gas again until the pressure is balanced with that outside the reaction tank. Then take out the silicon wafer.

[0066] S2, the pre-treated defective sheet is immersed in a 6% hydrofluoric acid solution for pickling at 40°C for 3 minutes. After pickling, it is washed with water at 40°C for 5 minutes to obtain the first pickled defective sheet.

[0067] S3, the first poorly pickled wafer is immersed in a mixed acid solution of hydrofluoric acid and hydrochloric acid for pickling. The mass concentration of hydrofluoric acid is 5%, the mass concentration of hydrochloric acid is 5%, the pickling temperature is 20°C, and the pickling time is 8 minutes. After pickling, it is washed with water at 20°C for 8 minutes. It is then dried with nitrogen gas at a temperature of 70°C to obtain a recovered silicon wafer.

[0068] Comparative Example 1

[0069] This comparative example provides a method for processing defective N-type TOPCon battery coating sheets, including the following steps:

[0070] S1. Take the defective film to be treated and put it into a 9% hydrofluoric acid aqueous solution and soak it at room temperature for 30 minutes.

[0071] S2, after soaking, the defective tablets are placed in a cleaning tank containing deionized water for 10 minutes.

[0072] S3. Place the cleaned defective sheet into the ultrasonic tank for ultrasonic cleaning. Use a mixed acid solution of hydrofluoric acid and hydrochloric acid for ultrasonic cleaning. The mass concentration of HF is 7% and the mass concentration of HCl is 6%. The ultrasonic temperature is controlled at 80-90℃ and the cleaning time is 15min.

[0073] S4. Place the defective wafer after ultrasonic cleaning into a cleaning tank containing deionized water for 10 minutes.

[0074] S5, compressed air drying, drying temperature controlled at 70-80℃, yields recycled silicon wafers.

[0075] TOPCon solar cells were fabricated using recycled silicon wafers obtained in Example 1 and Comparative Example 1 according to conventional processes. The open-circuit voltage, short-circuit current, and fill factor of the solar cells were measured using an IV analyzer, and the cell conversion efficiency was calculated. The results are shown in Table 1. The testing standard was 60904-1-2020. Three groups of recycled silicon wafers were used for testing: G1, G2, and G3. Group G1 used silicon wafers from Comparative Example 1, while groups G2 and G3 used silicon wafers from Example 1.

[0076] Table 1

[0077] G1 0.692 12.708 81.97 21.762 G2 0.701 13.014 82.05 22.598 G3 0.697 13.110 82.10 22.648

[0078] According to statistics, the silicon wafers recovered by the method for processing defective N-type TOPCon battery wafers provided by this invention can reach a pass rate of 96%, while the pass rate of recovered silicon wafers in Comparative Example 1 is only 78%.

[0079] The silicon wafers recovered in Examples 2-3 can achieve technical effects that are basically equivalent to those in Example 1.

[0080] In summary, the method for processing defective N-type TOPCon battery wafers provided by this invention can effectively remove the silicon nitride film from the defective wafers. The recovered silicon wafers have a clean and bright surface, normal appearance and performance, ensuring the excellent performance of the recovered silicon wafers. Moreover, the processing efficiency is high and the qualification rate of the recovered silicon wafers is high. It is a green and environmentally friendly new method with high promotion and application value.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for processing defective N-type TOPCon battery coating sheets, characterized in that, Includes the following steps: S1. Place the defective film to be treated into the reaction tank, and introduce the electrolytic gas of carbon tetrafluoride and oxygen after being ionized by a high-frequency power supply into the sealed reaction tank. React to obtain the pretreated defective film. S2, the pre-treated defective sheet is immersed in hydrofluoric acid solution for pickling, and after pickling, it is washed with water to obtain the first pickled defective sheet; the mass concentration of the hydrofluoric acid solution is 5%-6%, the pickling temperature is 20-40℃, and the time is 3-5min. S3, the first poorly pickled wafer is immersed in a mixed acid solution of hydrofluoric acid and hydrochloric acid for pickling. After pickling, it is washed with water and dried to obtain a recycled silicon wafer. The mass concentration of hydrofluoric acid in the mixed acid solution is 4.5%-5%, and the mass concentration of hydrochloric acid is 4.5%-5%; the pickling temperature is 20-40℃, and the time is 5-8 minutes.

2. The method for processing defective N-type TOPCon battery coating sheets as described in claim 1, characterized in that, Step S1 is as follows: Place the defective wafer to be treated into the reaction tank, evacuate the reaction tank to 50-120 Pa, introduce carbon tetrafluoride and oxygen into the reaction tank, and after the pressure in the chamber stabilizes, start the radio frequency power supply to ionize the carbon tetrafluoride and oxygen to react. After the reaction is completed, introduce inert gas into the reaction tank to remove residual reaction gas, close the vacuum, introduce inert gas again until it is balanced with the pressure outside the reaction tank, and take out the silicon wafer.

3. The method for processing defective N-type TOPCon battery coating sheets as described in claim 1 or 2, characterized in that, In step S1, the flow rate of carbon tetrafluoride is 150-250 mL / min, and the flow rate of oxygen is 50-100 mL / min; and / or In step S1, the frequency of the high-frequency power supply is 13.56MHz, and the power is 500-800W; and / or In step S1, the reaction temperature is 20-40℃ and the reaction time is 5-8 min.

4. The method for processing defective N-type TOPCon battery coating sheets as described in claim 1 or 2, characterized in that, In step S1, the reaction tank includes a reaction tank body, an ionization chamber that is sealed and connected to the reaction tank body, and an ionization assembly disposed on the ionization chamber. The ionization component includes a coil, a radio frequency (RF) connection line, and an RF power supply; the coil is arranged around the periphery of the ionization chamber, and the RF power supply is connected to the coil via the RF connection line.

5. The method for processing defective N-type TOPCon battery coating sheets as described in claim 4, characterized in that, The reaction tank is also equipped with a flow equalization plate, which is used to divert the electrolytic gas and control the direction of the electrolytic gas entering the reaction tank.

6. The method for processing defective N-type TOPCon battery coating sheets as described in claim 4, characterized in that, The ionization chamber is provided with an air inlet, which is connected to the gas supply pipelines for carbon tetrachloride and oxygen.

7. The method for processing defective N-type TOPCon battery coating sheets as described in claim 1, characterized in that, In step S2, the water washing temperature is 20-40℃ and the time is 5-8 minutes.

8. The method for processing defective N-type TOPCon battery coating sheets as described in claim 1, characterized in that, In step S3, the water washing temperature is 20-40℃ and the time is 5-8 minutes.

9. The method for processing defective N-type TOPCon battery coating sheets as described in claim 1, characterized in that, In step S3, the drying is carried out by nitrogen blowing, the drying temperature is 70-80℃, and the drying time is 5-8 minutes.

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