Double-cathode electrochemical cleaning method of monocrystalline silicon wafer for N-type TOPCon battery

Abstract

The invention relates to the technical field of solar cells, and particularly discloses a double-cathode electrochemical cleaning method of a monocrystalline silicon wafer for an N-type TOPCon cell. The double-cathode electrochemical cleaning method comprises the following steps: adding a strong alkali solution, an electrolyte and ultrapure water into an electrochemical tank body, and uniformly mixing to obtain a cleaning solution; and introducing air into the cleaning solution, turning on the first power supply, electrolyzing for 30-60 seconds, putting a silicon wafer to be cleaned, turning on the second power supply, cleaning for 10-120 seconds, turning off the second power supply, continuously cleaning for 10-20 seconds, turning off the first power supply, and finally carrying out acid pickling and water washing to obtain the clean silicon wafer. Through staged cooperative work of the double power supplies, a stepped cleaning gradient is formed, and by controlling the current density and the opening time of the two power supplies, the cleaning uniformity is ensured, the balance between the cleaning effect and the silicon wafer quality is optimized, deep cleaning is achieved on the premise that the silicon wafer is not damaged, and meanwhile the utilization rate of hydrogen peroxide is increased.

Description

Technical Field

[0001] The invention relates to the technical field of solar cells, and in particular to a double-cathode electrochemical cleaning method for a single-crystal silicon wafer for an N-type TOPCon cell. Background Art

[0002] In the field of solar cell technology, N-type TOPCon (Tunnel Oxide Passivated Contact) cells have gradually become an important direction for the development of the industry due to their advantages such as high conversion efficiency, low temperature coefficient and no light-induced degradation. As the key basic material of N-type TOPCon cells, the surface cleanliness of monocrystalline silicon wafers has a crucial impact on the performance and production yield of the cells.

[0003] Traditional single-crystal silicon wafer cleaning methods, such as simple chemical cleaning, can remove some surface pollutants, but the cleaning effect is limited for some metal impurities, organic residues and fine particles that are closely attached to the surface of the silicon wafer. In addition, the use of a large amount of chemicals cannot be avoided during chemical cleaning, especially hydrogen peroxide, a hazardous chemical with poor stability and not conducive to storage and transportation. Even if organic additives are used to reduce the amount of hydrogen peroxide used, the COD value of subsequent hazardous waste emissions will increase, making it difficult to meet the requirements of green manufacturing. In order to solve the pollution problem of chemical cleaning, researchers have proposed an electrochemical cleaning method. The current electrochemical cleaning method usually uses a single cathode, which has limitations in hydrogen peroxide utilization, cleaning uniformity and the ability to remove different types of pollutants. At the same time, there is also the problem of uneven current distribution that can easily cause over-etching of the silicon wafer surface, making it difficult to meet the increasingly stringent cleaning requirements for single-crystal silicon wafers for N-type TOPCon cells. Therefore, the development of an efficient, environmentally friendly cleaning method that can comprehensively improve the surface cleanliness of single-crystal silicon wafers without affecting battery performance has become a key issue that the industry needs to solve. Summary of the invention

[0004] In view of the problems of poor environmental protection, low cleaning efficiency, limited cleaning uniformity and limited ability to remove different pollutants in the existing single crystal silicon wafer cleaning methods, the present invention provides a double cathode electrochemical cleaning method for single crystal silicon wafers for N-type TOPCon cells. The present invention adopts an electrochemical double cathode cleaning method, and reduces oxygen in the air to ·OH with higher oxidation efficiency through a two-step electrochemical reduction method. Through its strong oxidizing property, different types of pollutants on the surface of the silicon wafer are quickly and efficiently removed, which not only greatly shortens the cleaning time, but also has a significantly better cleaning effect than the traditional method, truly achieving the goal of efficient, comprehensive and environmentally friendly silicon wafer cleaning, and has a high value for promotion and application.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0006] A double cathode electrochemical cleaning method for a single crystal silicon wafer for an N-type TOPCon cell comprises the following steps:

[0007] Adding strong alkaline solution, electrolyte and ultrapure water into the electrochemical cell body and mixing them evenly to obtain a cleaning solution;

[0008] Air is introduced into the cleaning solution, the first power source is turned on, and after electrolysis for 30s to 60s, a silicon wafer to be cleaned is placed, the second power source is turned on, cleaning is performed for 10s to 120s, the second power source is turned off, cleaning is continued for 10s to 20s, the first power source is turned off, and finally bubbling water washing is performed to obtain a clean silicon wafer;

[0009] Among them, the first power supply, the first anode and the first cathode constitute a first electrochemical circuit (first cathode area); the second power supply, the second anode and the second cathode constitute a second electrochemical circuit (second cathode area); the first electrochemical circuit and the second electrochemical circuit are arranged in the same electrochemical cell.

[0010] Compared with the prior art, the dual cathode electrochemical cleaning method for single crystal silicon wafers for N-type TOPCon cells provided by the present invention firstly uses an electrochemical oxygen reduction method to selectively cause oxygen to undergo a two-electron oxygen reduction reaction in the first cathode region to generate hydrogen peroxide, and then causes the hydrogen peroxide to react non-selectively in the second cathode region to generate ·OH, and utilizes ·OH and hydrogen peroxide that does not react in time to efficiently oxidize the surface of the silicon wafer, and further reacts with an alkaline solution to achieve the purpose of fully cleaning and removing pollutants on the surface of the silicon wafer; through the staged synergistic effect of the first power supply and the second power supply, a step-type cleaning gradient is formed, and the electrolysis time of the first power supply and the second power supply is controlled, and the ratio of hydrogen peroxide to ·OH is controlled to achieve the regulation of the oxidizing property of the cleaning solution. In this process, the precise oxidizing property regulation enables the cleaning solution to both strongly remove different types of pollutants on the surface of the silicon wafer and not damage the crystal structure of the single crystal silicon wafer due to excessive oxidizing property, thereby ensuring that the electrical properties, optical properties and mechanical properties of the silicon wafer are not affected, and laying a solid foundation for the subsequent high-quality preparation of N-type TOPCon cells.

[0011] Compared with traditional chemical cleaning methods, the dual-cathode electrochemical cleaning method provided by the present invention can save the use of a large amount of chemicals and reduce the discharge of chemical reagents. At the same time, it also effectively improves the utilization rate of hydrogen peroxide. It is an efficient, green and environmentally friendly method for cleaning single crystal silicon wafers. It can meet the strict requirements for cleaning single crystal silicon wafers in different application scenarios and has wide applicability and promotion value.

[0012] The chemical reaction occurring in the first cathode region of the dual cathode electrochemical reduction system of the present invention is mainly: O2+2e - +2H + →H2O2 or O2+2e -+2H2O→H2O2+2OH - ; In the second cathode region, OH and Mn are generated non-selectively. + +H2O2+xH + →Mm + +H2O+·OH or H2O2+2e - →2·OH. The surface of the silicon wafer is oxidized by ·OH and hydrogen peroxide that has not reacted in time, and the chemical reactions that may occur during the further reaction with the alkali solution include the reactions shown in Formulas 1 to 6:

[0013] H2O2+·OH→·OOH+H2O 1

[0014] ·OH+·OH→H2O2 2

[0015] 2·OH+Si→SiO2+H2O 3

[0016] 2H2O2+Si→SiO2+H2O 4

[0017] OR+·OH→CO2+H2O+small molecule inorganic matter 5

[0018] OR+H2O2→CO2+H2O+small molecule inorganic matter 6

[0019] Among them, reaction formula 3 and formula 4 are the process of silicon wafer surface oxidation, through which particles on the silicon wafer surface can be removed, and as the oxide is subsequently washed away, the metal ions coated in the oxide can be removed. Reaction formula 5 and formula 6 are the reactions of washing away the organic matter on the silicon wafer surface and diffusing into the cleaning solution, mainly formula 6.

[0020] In the above cleaning process, the first power supply is first turned on to reduce oxygen to hydrogen peroxide, and then the second power supply is turned on to react hydrogen peroxide to generate ·OH. The ratio of hydrogen peroxide to ·OH is controlled by controlling the opening time of the second power supply, so that the cleaning solution has moderate oxidizing properties, and the adverse effects on the performance of the silicon wafer are minimized while ensuring that different types of pollutants on the surface of the silicon wafer are fully removed; the second power supply opening stage is the stage of organic matter removal and rapid oxidation of the damaged layer on the surface of the silicon wafer. After the second power supply is turned off, the cleaning is continued for 10s to 20s under the condition that the first power supply is turned on. The first power supply continues to act in this stage, and its mild electrolytic characteristics are used to further remove the residual fine impurities, and at the same time, the surface of the silicon wafer after the second power supply acts is finely repaired and adjusted. This synergistic effect not only ensures the thorough removal of various types of pollution on the surface of the silicon wafer, but also effectively promotes the improvement of the surface flatness of the silicon wafer by precisely controlling the cleaning time and power supply parameters. During the entire cleaning process, damage to the silicon wafer caused by excessive cleaning is avoided, and the crystal structure integrity and surface quality of the silicon wafer are guaranteed, thereby meeting the high quality requirements of the N-type TOPCon battery for silicon wafers.

[0021] It should be noted that the dual cathode electrochemical cleaning method provided by the present invention can replace the pre-cleaning and post-cleaning process of any process in the production process of N-type TOPCon batteries, such as the pre-cleaning and post-cleaning before texturing, the pre-cleaning and post-cleaning of BSG removal and alkali polishing processes, and the pre-cleaning and post-cleaning of PSG removal processes, which can all adopt the dual cathode electrochemical cleaning method provided by the present invention. As long as the conventional alkali + hydrogen peroxide cleaning process in the traditional N-type TOPCon battery can be replaced by the dual cathode electrochemical cleaning process provided by the present invention.

[0022] As a specific embodiment of the present invention, the first cathode and the second cathode may be made of carbon felt or graphite felt. The first anode and the second anode may be made of platinum electrode or graphite electrode.

[0023] As a specific embodiment of the present invention, an insulating partition is provided between the first cathode and the second cathode to prevent the first cathode and the second cathode from directly contacting each other. A plurality of pores are provided on the insulating partition to allow ·OH and hydrogen peroxide to pass freely. Specifically, the insulating partition is a PT partition.

[0024] Furthermore, the current density of the first power source is 10 mA / cm 2 ~20mA / cm 2 .

[0025] Furthermore, the current density of the second power supply is 20 mA / cm 2 ~100mA / cm 2 .

[0026] The dual-power dual-cathode design can promote the oxygen reduction reaction and the further conversion of hydrogen peroxide into ·OH reaction to accelerate in the forward direction, and by controlling the current density, improve the oxygen reduction efficiency and the utilization rate of hydrogen peroxide. At the same time, it can also ensure that the cleaning degree of each area on the silicon wafer surface is consistent, avoiding the occurrence of incomplete cleaning or over-cleaning problems.

[0027] The above-mentioned preferred current density can not only ensure the cleaning effect, but also avoid damage to the crystal structure of the silicon wafer, thereby ensuring the surface quality of the silicon wafer and meeting the high quality requirements of the N-type TOPCon battery for the silicon wafer.

[0028] Further, if the electrochemical cleaning process is a pre-cleaning process, the second preset time is 60s to 120s; if the electrochemical cleaning process is a post-cleaning process, the second preset time is 10s to 60s.

[0029] Furthermore, the air flow rate is 20 mL / min to 100 mL / min.

[0030] Furthermore, the concentration of the strong alkaline solution is 47wt% to 49wt%.

[0031] Furthermore, the strong alkaline solution is a potassium hydroxide solution or a sodium hydroxide solution.

[0032] As a specific embodiment of the present invention, the ratio of the strong alkali solution to ultrapure water can be conventionally adjusted according to the cleaning requirements of different processes. Specifically, if the electrochemical cleaning process is a pre-cleaning or post-cleaning process for alkali texturing, the volume ratio of the strong alkali solution to ultrapure water is (5-15): (600-700). If the electrochemical cleaning process is a pre-cleaning and post-cleaning process for BSG removal and alkali polishing, the volume ratio of the strong alkali solution to ultrapure water is (2-5): (400-500). If the electrochemical cleaning process is a pre-cleaning or post-cleaning process for PSG removal and surface cleaning, the volume ratio of the strong alkali solution to ultrapure water is (5-15): (400-500).

[0033] Furthermore, the temperature of the strong alkaline solution is 20°C to 30°C, and the temperature of the ultrapure water is 50°C to 80°C.

[0034] Furthermore, the electrolyte is anhydrous sodium sulfate or anhydrous potassium sulfate; and the concentration of the electrolyte in the cleaning solution is 0.04 mol / L to 0.06 mol / L.

[0035] It should be noted that the pickling is a conventional cleaning process using a hydrofluoric acid solution in the art, and specific cleaning parameters can be selected from the pickling process of the existing process.

[0036] Furthermore, the water washing temperature is 23° C. to 27° C., and the water washing time is 60s to 90s.

[0037] It should be noted that new liquid medicine needs to be replaced every 600 to 700 batches (about 720 tablets per batch) to ensure the cleaning effect.

[0038] The dual-cathode electrochemical cleaning method for single-crystal silicon wafers for N-type TOPCon cells provided by the present invention forms a stepped cleaning gradient by means of the coordinated work of dual power supplies in stages, and ensures cleaning uniformity by controlling the current density and the opening time of the two power supplies, optimizes the balance between the cleaning effect and the quality of the silicon wafer, and achieves deep cleaning without damaging the silicon wafer. The entire cleaning process is completed in the same electrochemical cell body, and only the power supply and time need to be controlled, the operation is simple, and the production efficiency is greatly improved. In addition, the entire cleaning process does not require the use of a large amount of hazardous chemicals or the addition of organic additives, thereby reducing the use and discharge of chemical agents, meeting the requirements of sustainable development, and being conducive to further promoting the development of green cleaning technology, with high practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The schematic diagram of the structure of the double cathode electrochemical cleaning tank used in the embodiment of the present invention; wherein: ① first anode; ② first power supply; ③ first cathode; ④ middle partition; ⑤ second cathode; ⑥ second power supply; ⑦ second anode;

[0040] Figure 2 The zeta diagrams of the tower base on the back side of the silicon wafer obtained in step S306 of Application Example 1 and Comparative Application Example 1, wherein (a) is Application Example 1, and (b) is Comparative Application Example 1;

[0041] Figure 3 The zeta diagrams of the silicon wafer side tower base obtained in step S508 of Application Example 1 and Comparative Application Example 1, where (a) is Application Example 1, and (b) is Comparative Application Example 1. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0043] In order to better illustrate the present invention, further examples are given below.

[0044] The schematic diagram of the structure of the dual cathode electrochemical cleaning tank used in the following examples is as follows: Figure 1 As shown. The dual cathode electrochemical cleaning tank comprises ① a first anode, ② a first power supply, ③ a first cathode, ④ a middle partition, ⑤ a second cathode, ⑥ a second power supply, and ⑦ a second anode. The first anode, the first power supply, and the first cathode form a first cathode region; the second anode, the second power supply, and the second cathode form a second cathode region; a perforated insulating partition is provided between the first cathode and the second cathode to prevent the first cathode and the second cathode from directly contacting each other.

[0045] Specifically, the first cathode and the second cathode are carbon felt or graphite felt; the first anode and the second anode can be platinum electrodes or graphite electrodes; and the insulating separator is a PT separator.

[0046] In the following examples, room temperature refers to 25±2°C.

[0047] Example 1

[0048] This embodiment provides a double cathode electrochemical cleaning method for a single crystal silicon wafer for an N-type TOPCon cell, comprising the following steps:

[0049] S1, at room temperature, 10 L of 48 wt% sodium hydroxide solution, anhydrous sodium sulfate and 650 L of ultrapure water preheated to 65° C. are added to a double cathode electrochemical cell in sequence to obtain a cleaning solution; wherein the concentration of anhydrous sodium sulfate in the cleaning solution is 0.05 mol / L;

[0050] S2, introduce air into the double cathode electrochemical cell through the gas pipeline, the gas flow rate is 60mL / min, and the oxygen concentration in the system is detected by the oxygen detector probe. When the oxygen concentration is ≥3%, the aeration is stopped, and when the oxygen concentration is <1%, the aeration device is turned on;

[0051] S3, turn on the first power supply and control the current density to 15mA / cm 2 , maintain for 50s, use a robot to grab the flower basket to load (6 baskets at a time, 120 pieces per basket), open the double cathode electrochemical tank cover, and the robot puts the material, 3 baskets in the first cathode area and the second cathode area, close the tank cover, and turn on the second power supply at the same time, controlling the current density to 60mA / cm 2 , clean for 90 seconds, turn off the second power supply, and continue cleaning for 15 seconds;

[0052] S4, transfer the flower basket to a water tank and wash it with bubbling water at room temperature for 80 seconds to obtain a clean silicon wafer.

[0053] Example 2

[0054] This embodiment provides a double cathode electrochemical cleaning method for a single crystal silicon wafer for an N-type TOPCon cell, comprising the following steps:

[0055] S1, at room temperature, 4 L of 49 wt% sodium hydroxide solution, anhydrous sodium sulfate and 450 L of ultrapure water preheated to 50° C. are added to a double cathode electrochemical cell in sequence to obtain a cleaning solution; wherein the concentration of anhydrous sodium sulfate in the cleaning solution is 0.06 mol / L;

[0056] S2, introduce air into the double cathode electrochemical cell through the gas pipeline, the gas flow rate is 20mL / min, and the oxygen concentration in the system is detected by the oxygen detector probe. When the oxygen concentration is ≥3%, the aeration is stopped, and when the oxygen concentration is <1%, the aeration device is turned on;

[0057] S3, turn on the first power supply and control the current density to 10mA / cm 2 , maintain for 60s, use a robot to grab the flower basket to load (6 baskets at a time, 120 pieces per basket), open the double cathode electrochemical tank cover, and the robot puts the material, 3 baskets in the first cathode area and 3 baskets in the second cathode area, close the tank cover, and turn on the second power supply at the same time, controlling the current density to 100mA / cm 2 , clean for 60 seconds, turn off the second power supply, and continue cleaning for 10 seconds;

[0058] S4, transfer the flower basket to a water tank and wash it with bubbling water at room temperature for 60 seconds to obtain a clean silicon wafer.

[0059] Example 3

[0060] This embodiment provides a double cathode electrochemical cleaning method for a single crystal silicon wafer for an N-type TOPCon cell, comprising the following steps:

[0061] S1, at room temperature, 10 L of 47 wt% sodium hydroxide solution, anhydrous sodium sulfate and 450 L of ultrapure water preheated to 80° C. are added to a double cathode electrochemical cell in sequence to obtain a cleaning solution; wherein the concentration of anhydrous sodium sulfate in the cleaning solution is 0.04 mol / L;

[0062] S2, introduce air into the double cathode electrochemical cell through the gas pipeline, the gas flow rate is 100mL / min, and the oxygen concentration in the system is detected by the oxygen detector probe. When the oxygen concentration is ≥3%, the aeration is stopped, and when the oxygen concentration is <1%, the aeration device is turned on;

[0063] S3, turn on the first power supply and control the current density to 20mA / cm 2 , maintain for 30s, use a robot to grab the flower basket to load (6 baskets at a time, 120 pieces per basket), open the double cathode electrochemical tank cover, and the robot puts the material, 3 baskets in the first cathode area and the second cathode area, close the tank cover, and turn on the second power supply at the same time, controlling the current density to 20mA / cm 2 , clean for 120 seconds, turn off the second power supply, and continue cleaning for 20 seconds;

[0064] S4, transfer the flower basket to a water tank and wash with bubbling water at room temperature for 90 seconds to obtain a clean silicon wafer.

[0065] Application Examples

[0066] The following provides an application example of the above dual cathode electrochemical cleaning process in the production process of N-type single crystal TOPCon cells. The preparation of the N-type single crystal TOPCon cell specifically includes the following steps:

[0067] 1. Velvet making

[0068] S101, pre-cleaning: same as in Example 1;

[0069] S102, alkali texturing, temperature 80℃, texturing time 8min;

[0070] S103, bubbling water washing in a water tank at room temperature for 80 seconds;

[0071] S104, post-cleaning: same as in Example 1;

[0072] S105, bubbling water washing in a water tank at room temperature for 80 seconds;

[0073] S106, after acid washing (650L pure water + 75L hydrofluoric acid, washing at room temperature for 120s), water washing (bubbling water washing at room temperature for 80s), slow pulling and drying, a silicon wafer with a velvet surface is obtained;

[0074] 2. Boron Diffusion

[0075] 3. Remove BSG and alkali polishing

[0076] S301, chain BSG removal, temperature 25°C, belt speed 4.3m / min;

[0077] S302, pre-cleaning: same as in Example 2;

[0078] S303, alkali polishing, temperature 70°C, alkali cleaning time 10 min;

[0079] S304, bubbling water at room temperature in the sink for 80 seconds;

[0080] S305, post-cleaning: same as in Example 2;

[0081] S306, after acid washing (450 pure water + 55L hydrofluoric acid, washing at room temperature for 120s), water washing (bubbling water washing at room temperature for 80s), slow pulling and drying, a silicon wafer with a relatively flat back surface is obtained;

[0082] 4. LPCVD

[0083] 5. PSG removal and surface cleaning

[0084] S501, chain PSG removal, temperature 25°C, belt speed 4.3m / min;

[0085] S502, alkali washing to remove the plating, temperature 65℃, time 300s;

[0086] S503, bubbling water washing in a water tank at room temperature for 80 seconds;

[0087] S504, pre-cleaning: same as in Example 3;

[0088] S505, pickling, HF solution cleaning at room temperature for 90s;

[0089] S506, bubbling water washing in a water tank at room temperature for 80 seconds;

[0090] S507, post-cleaning: same as in Example 3;

[0091] S508, acid washing (450 pure water + 55L hydrofluoric acid, room temperature washing for 120s), water washing (room temperature bubbling water washing for 80s), slow pulling and drying to obtain a silicon wafer with a clean surface;

[0092] 6. ALD process

[0093] 7. PECVD process

[0094] 8. Screen printing, sintering, light injection, LECO, testing and sorting to obtain qualified N-type single crystal TOPCon cells.

[0095] Except for the pre-cleaning and post-cleaning processes, the other processes are conventional processes in the art, and the process parameters can be selected from conventional parameters in the prior art, and the present invention does not make special limitations.

[0096] Comparative application example 1

[0097] This comparative example provides an application example of a traditional alkaline + hydrogen peroxide cleaning process in the production process of N-type single crystal TOPCon cells:

[0098] The only difference between this comparative application example and application example 1 is that the pre-cleaning and post-cleaning processes are replaced by: placing the silicon wafer in a cleaning solution of alkali + hydrogen peroxide, soaking and cleaning at 60°C for 150 seconds; the cleaning solution composition is: 650L ultrapure water + 10L 48% sodium hydroxide solution + 45L hydrogen peroxide. The remaining processes and parameter controls are exactly the same as those in application example 1, and will not be repeated here.

[0099] The average reflectivity of the silicon wafer produced by the texturing process of Application Example 1 is 9.8%, which is 10.58% lower than the average reflectivity of the silicon wafer produced by the texturing process of Application Example 1.

[0100] The zeta diagram of the silicon wafer back side tower base obtained in step S306 in application example 1 and comparative application example 2 is as follows: Figure 2 As shown, the average size of the pyramid base of Application Example 1 is 9.53 μm, and the average size of the pyramid base of Comparative Application Example 1 is 10.17 μm. The reflectivity of the silicon wafer obtained in step S305 of Application Example 1 is 43.07%, and the reflectivity of the silicon wafer obtained in step S305 of Comparative Application Example 1 is 41.06%.

[0101] The side tower base zeta diagram of the silicon wafer obtained in step S508 in Application Example 1 and Comparative Application Example 2 is as follows: Figure 3 As shown in the figure, it can be seen that the average size of the side tower base of Application Example 1 is 12.19 μm, and the average size of the side tower base of Comparative Application 1 is 14.93 μm.

[0102] After the entire process of Application Example 1, the average weight loss of silicon wafers is 0.28g, while that of Comparative Application Example 1 is 0.3g. On average, for every 500 batches of silicon wafers (720 wafers per batch), Application Example 1 can save 500-750L of hydrogen peroxide compared with the traditional alkali + hydrogen peroxide process in Comparative Application Example 1.

[0103] The conversion efficiency of the TOPCon cell of Application Example 1 is 26.15%, while that of Comparative Application Example 1 is 26.05%.

[0104] Comparative Application Example 2

[0105] This comparative example provides an application example of a single cathode electrochemical cleaning process in the production process of N-type single crystal TOPCon cells:

[0106] The only difference between this comparative application example and application example 1 is that the pre-cleaning and post-cleaning processes are replaced by the following processes:

[0107] S1, at room temperature, 10 L of 48 wt% sodium hydroxide solution, anhydrous sodium sulfate and 650 L of ultrapure water preheated to 65° C. are added to a double cathode electrochemical cell in sequence to obtain a cleaning solution; wherein the concentration of anhydrous sodium sulfate in the cleaning solution is 0.5 mol / L;

[0108] S2, introduce air into the double cathode electrochemical cell through the gas pipeline, the gas flow rate is 60mL / min, and the oxygen concentration in the system is detected by the oxygen detector probe. When the oxygen concentration is ≥3%, the aeration is stopped, and when the oxygen concentration is <1%, the aeration device is turned on;

[0109] S3, use a robot to grab the flower basket to load (6 baskets at a time, 120 pieces per basket), open the electrochemical tank cover, put the material by the robot, close the tank cover, turn on the power, and control the current density to 40mA / cm 2 , maintain for 140 seconds;

[0110] S4, transfer the flower basket to a water tank and wash it with bubbling water at room temperature for 80 seconds to obtain a clean silicon wafer.

[0111] The remaining processes and parameter controls are exactly the same as those in Application Example 1 and will not be described again here.

[0112] The qualified rate (including appearance, reflectivity, etc.) of the TOPCon cell in Application Example 1 is 97.42%, while the qualified rate of the conventional alkaline + hydrogen peroxide cleaning in Comparative Application Example 1 is 96.51%, and the qualified rate of the one-step electrochemical cleaning process in Comparative Application Example 2 is 95.59%. Moreover, compared with the one-step electrochemical cleaning method in Comparative Application Example 2, the utilization rate of hydrogen peroxide in Application Example 1 is higher, saving 1% to 2% of the power loss.

[0113] Application Example 1 can also adopt the pre-cleaning process of Examples 2 to 3, and the post-cleaning process of Examples 5 to 6, and can achieve basically equivalent technical effects.

[0114] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A double cathode electrochemical cleaning method for single crystal silicon wafers for N-type TOPCon cells, characterized in that: The following steps are involved: Adding strong alkaline solution, electrolyte and ultrapure water into the electrochemical cell body and mixing them evenly to obtain a cleaning solution; Air is introduced into the cleaning solution, the first power source is turned on, and after electrolysis for 30s to 60s, a silicon wafer to be cleaned is placed, the second power source is turned on, cleaning is performed for 10s to 120s, the second power source is turned off, cleaning is continued for 10s to 20s, the first power source is turned off, and finally pickling and water washing are performed to obtain a clean silicon wafer; The first power source, the first anode and the first cathode form a first electrochemical circuit; the second power source, the second anode and the second cathode form a second electrochemical circuit; the first electrochemical circuit and the second electrochemical circuit are arranged in the same electrochemical cell.

2. The double cathode electrochemical cleaning method for single crystal silicon wafers for N-type TOPCon cells according to claim 1, characterized in that: The current density of the first power source is 10 mA / cm 2 ~20mA / cm 2 .

3. The double cathode electrochemical cleaning method for single crystal silicon wafers for N-type TOPCon cells according to claim 1, characterized in that: The current density of the second power source is 20 mA / cm 2 ~100mA / cm 2 .

4. The double cathode electrochemical cleaning method for single crystal silicon wafers for N-type TOPCon cells according to claim 3, characterized in that: If the electrochemical cleaning process is a pre-cleaning process, the second preset time is 60s to 120s; if the electrochemical cleaning process is a post-cleaning process, the second preset time is 10s to 60s.

5. The double cathode electrochemical cleaning method for single crystal silicon wafers for N-type TOPCon cells according to claim 1, characterized in that: The air flow rate is 20 mL / min to 100 mL / min.

6. The double cathode electrochemical cleaning method for single crystal silicon wafers for N-type TOPCon cells according to claim 1, characterized in that: The concentration of the strong alkali solution is 47 wt % to 49 wt %.

7. The double cathode electrochemical cleaning method for single crystal silicon wafers for N-type TOPCon cells according to claim 6, characterized in that: The strong alkaline solution is a potassium hydroxide solution or a sodium hydroxide solution.

8. The double cathode electrochemical cleaning method for single crystal silicon wafers for N-type TOPCon cells according to claim 6, characterized in that: The temperature of the strong alkaline solution is 20°C to 30°C, and the temperature of the ultrapure water is 50°C to 80°C.

9. The double cathode electrochemical cleaning method for single crystal silicon wafers for N-type TOPCon cells according to claim 1, characterized in that: The electrolyte is anhydrous sodium sulfate or anhydrous potassium sulfate; the concentration of the electrolyte in the cleaning solution is 0.04 mol / L to 0.06 mol / L.

10. The double cathode electrochemical cleaning method for single crystal silicon wafers for N-type TOPCon cells according to claim 1, characterized in that: The water washing temperature is 23° C. to 27° C., and the water washing time is 60s to 90s.

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