Solar cell bsg cleaning method and topcon cell preparation method

Abstract

The application discloses a solar cell BSG cleaning method and a TOPcon cell preparation method. The cleaning method comprises the following steps: performing groove type pickling on a silicon wafer after boron diffusion by using HF with a first concentration in a groove, so as to clean the BSG layer on the surface of the silicon wafer; performing water washing and drying on the silicon wafer; and performing chain type pickling on the dried silicon wafer by using HF with a second concentration, so as to clean the remaining BSG layer on the back surface and the side surface of the silicon wafer. According to the technical scheme disclosed by the application, the groove type pickling and the chain type pickling are used to clean the BSG layer. Since only part of the BSG layer remains on the back surface and the side surface of the silicon wafer after the groove type pickling, the cleaning of the BSG layer is easier after the groove type pickling, so that when the chain type pickling is used for cleaning, the remaining BSG layer on the back surface and the side surface can be cleaned without high-concentration HF, and the BSG layer removal effect can be improved. Even if the horizontal position of the roller is slightly abnormal during the chain type pickling, the effect of removing the remaining BSG layer is not affected, and the consumption of HF is reduced.

Description

Technical Field

[0001] This application relates to the field of TOPcon cell fabrication technology, and more specifically, to a method for cleaning BSG in solar cells and a method for fabricating TOPcon cells. Background Technology

[0002] In the N-type TOPcon cell structure, the PN junction on the front side of the cell is created by doping with a boron source. High-efficiency solar cells require emitters with low surface concentrations. During the boron diffusion process, an inactive boron-rich layer is inevitably formed. At the same time, in order to protect the front side of the cell from damage in subsequent processes, a long oxidation time is required to form a BSG (borosilicate glass) layer. The BSG layer is relatively thick and difficult to process.

[0003] Currently, in the fabrication of N-type TOPcon batteries, the BSG layer is removed using a one-step chain roller acid washing process. However, due to the thickness of the BSG layer, the chain roller acid washing process requires a high HF concentration, typically 55%-65%. Producing high-concentration HF places stringent demands on equipment and the environment. Furthermore, the one-step chain roller HF acid washing process does not remove the BSG layer evenly, resulting in poor removal efficiency, and issues with roller levelness can lead to increased HF consumption at high concentrations.

[0004] In summary, how to reduce the concentration of HF used to remove BSG while improving the BSG removal effect is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the purpose of this application is to provide a method for cleaning BSG in solar cells and a method for preparing TOPcon cells, which can both reduce the concentration of HF used to remove BSG and improve the BSG removal effect.

[0006] To achieve the above objectives, this application provides the following technical solution:

[0007] A method for cleaning BSG in solar cells, comprising:

[0008] The silicon wafer after boron diffusion is subjected to a tank-type acid pickling using HF of the first concentration in the tank to clean the BSG layer on the surface of the silicon wafer.

[0009] The silicon wafers after tank pickling are then washed with water and dried.

[0010] The dried silicon wafer is subjected to a chain pickling process using HF of a second concentration to clean the remaining BSG layer on the back and sides of the silicon wafer.

[0011] Preferably, the first concentration is less than the second concentration.

[0012] Preferably, the first concentration is 5%-10%, and the second concentration is 20%-25%.

[0013] Preferably, before performing a chain pickling process on the dried silicon wafer using HF of a second concentration to clean the remaining BSG layer on the back and sides of the silicon wafer, the method further includes:

[0014] The reflectance at multiple sampling points on the surface of the dried silicon wafer was measured.

[0015] Determine whether the reflectance at each sampling point is within the set reflectance range;

[0016] If the reflectivity at a sampling point is lower than the minimum value within the set reflectivity range, then return to the step of using HF of the first concentration in the tank to perform tank acid washing on the boron-diffused silicon wafer to clean the BSG layer on the surface of the silicon wafer.

[0017] If the reflectance at each of the sampling points is within the set reflectance range, then the step of using HF of the second concentration to perform chain acid washing on the dried silicon wafer to clean the remaining BSG layer on the back and sides of the silicon wafer is performed.

[0018] Preferably, the time length of the tank pickling is 180s±10s, the process parameters of the chain pickling are (3.6m±0.5m) / min, and the temperature of both the tank pickling and the chain pickling is 18℃-25℃.

[0019] Preferably, the tank further contains HCl, and when using the first concentration of HF contained in the tank to perform tank-type acid pickling on the boron-diffused silicon wafer, the process further includes:

[0020] The silicon wafer was cleaned using HCl;

[0021] And / or, when chain-washing the dried silicon wafer with HF of a second concentration, the process further includes:

[0022] The silicon wafer was cleaned using HCl.

[0023] Preferably, the dried silicon wafer is subjected to chain pickling using HF of a second concentration, including:

[0024] The dried silicon wafers are subjected to chain pickling using HF of the second concentration placed in the pickling tank.

[0025] Preferably, the dried silicon wafer is subjected to chain pickling using HF of the second concentration disposed in the pickling tank, comprising:

[0026] The dried silicon wafer is subjected to a single chain pickling process using HF of the second concentration set in the first pickling tank.

[0027] The silicon wafer after the first chain pickling is subjected to a second chain pickling using HF of the second concentration, which is set in the second pickling tank.

[0028] Preferably, after performing a chain pickling process on the dried silicon wafer using HF of a second concentration to clean the remaining BSG layer on the back and sides of the silicon wafer, the process further includes:

[0029] The silicon wafers after chain pickling are washed with water and dried.

[0030] Preferably, when performing a chain pickling process on the dried silicon wafer using HF of a second concentration to clean the remaining BSG layer on the back and sides of the silicon wafer, the process further includes:

[0031] The boron-rich layer on the back and sides of the silicon wafer is cleaned using HF of the second concentration.

[0032] A method for fabricating an N-type TOPcon battery, comprising:

[0033] Texturing is performed on an N-type silicon wafer to create a pyramidal textured surface on the wafer surface;

[0034] Boron diffusion is performed on the pyramidal textured surface of the silicon wafer;

[0035] The BSG layer on the surface of the boron-diffused silicon wafer is cleaned using the solar cell BSG cleaning method described in any of the above-mentioned methods.

[0036] The back side of the silicon wafer is polished, and a passivation contact layer is prepared on the polished back side of the silicon wafer;

[0037] The silicon wafer is subjected to a winding cleaning process to prepare an aluminum oxide film and a silicon oxynitride film on the front side of the silicon wafer.

[0038] A silicon nitride thin film is prepared on the back side of the silicon wafer;

[0039] Electrodes are fabricated on the front and back sides of the silicon wafer.

[0040] This application provides a method for cleaning BSG in solar cells and a method for fabricating TOPcon cells. The method for cleaning BSG in solar cells includes: using HF of a first concentration in a tank to perform a tank-type acid washing on a boron-diffused silicon wafer to clean the BSG layer on the surface of the silicon wafer; washing and drying the silicon wafer after tank-type acid washing; and using HF of a second concentration to perform a chain-type acid washing on the dried silicon wafer to clean the remaining BSG layer on the back and sides of the silicon wafer.

[0041] The technical solution disclosed in this application utilizes a tank filled with HF of a first concentration to perform a tank-type acid pickling on the boron-diffused silicon wafer. This tank-type acid pickling removes a portion of the BSG layer from the surface of the silicon wafer. The pickled silicon wafer is then washed with water and dried to avoid affecting subsequent chain-type acid pickling. Afterward, a second concentration of HF is used to perform a chain-type acid pickling on the dried silicon wafer to remove the remaining BSG layer from the back and sides of the wafer. Since the tank-type acid pickling involves placing the silicon wafer in HF, it eliminates the need for high-concentration HF to clean part of the BSG layer. Furthermore, the tank-type acid pickling method ensures a more uniform surface of the remaining BSG layer and minimizes significant variations in the thickness of the BSG layer within the wafer, thereby improving the BSG layer removal efficiency. Since only a portion of the BSG layer remains on the back and sides of the silicon wafer after tank pickling, it is easier to clean the BSG after tank pickling. Therefore, when using chain pickling, high-concentration HF is not required to clean the remaining BSG layer on the back and sides of the silicon wafer, and the BSG layer removal effect can be improved. Furthermore, based on the combination of tank pickling and chain pickling, even if the roller level is slightly abnormal during chain pickling, it will not affect the removal of the remaining BSG layer. Therefore, HF consumption can be reduced, and the later maintenance costs of the equipment can be decreased. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0043] Figure 1 A flowchart of a solar cell BSG cleaning method provided in this application embodiment;

[0044] Figure 2 This is a flowchart illustrating a method for fabricating an N-type TOPcon battery, as provided in an embodiment of this application. Detailed Implementation

[0045] In the fabrication of N-type TOPcon batteries, the resulting BSG layer is relatively thick. The chain roller acid washing process requires a high HF concentration, typically around 65%, and demands precise tank and roller levels. Incomplete removal of the BSG layer on the back side is a common problem, increasing workshop costs. Furthermore, the production of high-concentration HF places stringent requirements on equipment and the environment.

[0046] Therefore, this application provides a method for cleaning BSG in solar cells and a method for preparing TOPcon cells, which can both reduce the concentration of HF used to remove BSG and improve the BSG removal effect.

[0047] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0048] See Figure 1 The diagram illustrates a flowchart of a solar cell BSG cleaning method provided in this application embodiment. The solar cell BSG cleaning method provided in this application embodiment may include:

[0049] S11: Use the first concentration of HF in the tank to perform tank-type acid washing on the boron-diffused silicon wafer to clean the BSG layer on the surface of the silicon wafer.

[0050] In this application, after boron diffusion is performed on a silicon wafer (specifically, an N-type silicon wafer used to fabricate N-type TOPcon cells, where a BSG layer forms on the wafer surface after boron diffusion), the boron-diffused silicon wafer can be placed in a tank (specifically, the back side of the silicon wafer can be in contact with HF of a first concentration), the tank containing HF of a first concentration. That is, the boron-diffused silicon wafer can be placed in a tank containing HF of a first concentration to clean the BSG layer on the surface of the boron-diffused silicon wafer using the HF of the first concentration in the tank. Here, the silicon wafer surface refers to the surface where the BSG layer is formed, specifically the back, side, and front sides. Due to the tank-type acid washing process...

[0051] Furthermore, during tank pickling, the thickness of the BSG layer removed can be controlled by adjusting the pickling time. Considering that a certain thickness of BSG layer needs to be retained on the front side of the silicon wafer, a portion of the BSG layer on the silicon wafer surface can be removed by tank pickling. Specifically, the tank cleaning can be stopped once the thickness of the remaining BSG layer on the front side of the silicon wafer meets the fabrication requirements of N-type TOPcon cells. In other words, tank pickling can remove a certain thickness of BSG layer from the silicon wafer surface, resulting in a relatively thin remaining BSG layer. In addition, since tank pickling involves immersing the silicon wafer in HF of a first concentration for BSG layer cleaning, a high concentration of HF is not required (i.e., the first concentration is relatively low), and the cleaning of the BSG layer is more uniform. The remaining BSG layer surface is also more uniform, and there is no significant difference in BSG thickness within the same surface. In other words, tank pickling can improve the cleaning quality of the BSG layer.

[0052] As shown above, tank-type pickling makes it easier to control the BSG thickness and the uniformity of BSG layer removal, and the process is simple. Traditional pickling machines can be used, resulting in lower costs.

[0053] S12: Wash and dry the silicon wafers after the tank pickling process.

[0054] After the BSG layer on the surface of the silicon wafer is subjected to tank pickling, that is, after step S11, the silicon wafer after tank pickling can be washed with water to remove the surface complex (the complex is generated by the reaction of HF and BSG layer) and residual HF, thereby avoiding the impact on subsequent processes.

[0055] In the process of rinsing the silicon wafers after tank-type pickling, two tanks can be set up. For distinction, the tank containing the highest concentration of HF can be designated as Tank 1 (i.e., Tank 1 is the pickling tank), and the two rinsing tanks can be designated as Tanks 2 and 3 (i.e., Tanks 2 and 3 are both rinsing tanks). Both Tanks 2 and 3 contain DI water (deionized water). The pickled silicon wafers can be sequentially immersed in Tanks 2 and 3 to effectively clean the complexes and residual HF on the wafer surface using the DI water in Tanks 2 and 3. The total rinsing time in Tanks 2 and 3 can be 120 seconds (the time can be evenly distributed between Tanks 2 and 3, or more time can be allocated to Tank 2 or Tank 3, depending on actual needs). Of course, the rinsing time can also be modified according to actual conditions.

[0056] After the silicon wafers are rinsed with water following the acid pickling process, they can be dried to remove residual moisture from the surface, thus preventing any impact on subsequent processes. This drying can also be carried out in a drying tank (referred to as tank number 4, i.e., tank number 4 is the drying tank). The drying temperature can be 75℃-85℃ (i.e., the process operating conditions for tank number 4 are 75℃-85℃), and the drying time can be 300 seconds. Of course, the drying temperature and time can be modified according to actual conditions.

[0057] As can be seen from the above, the tank pickling machine and process steps are connected in series. The specific process steps are: tank pickling - water washing 1 - water washing 2 - drying.

[0058] S13: Use HF of the second concentration to perform chain pickling on the dried silicon wafer to clean the remaining BSG layer on the back and sides of the silicon wafer.

[0059] After the silicon wafer is dried, it can be subjected to chain pickling (i.e. chain roller pickling) using HF of a second concentration to clean the remaining BSG layer on the back and sides of the silicon wafer.

[0060] Since the BSG layer remaining on the back and sides of the silicon wafer is relatively thin after tank pickling, compared with the existing method of cleaning the BSG layer by simply using chain pickling, this application can greatly reduce the concentration of HF used in chain pickling by first performing tank pickling and then chain pickling, thereby reducing the requirements of HF production on equipment and environment.

[0061] Adding a tank-type pickling process before chain pickling reduces the required HF concentration and improves BSG layer removal. Furthermore, tank pickling achieves thinner BSG layers on the back and sides, resulting in a more uniform remaining BSG layer and less significant variations in thickness within the wafer. Even slight leveling issues with the chain pickling rollers do not affect the removal of residual BSG, further reducing machine maintenance costs and HF consumption. Regarding HF consumption, a single chain pickling cycle (i.e., using only chain pickling) consumes 6000L of HF per 1.2 million wafers using the current solution change cycle. Adding tank pickling increases the cycle life to 240,000 wafers, and chain pickling to 1.2 million wafers. By adjusting the initial formula and automatic replenishment parameters, combining tank pickling with chain pickling reduces cycle HF consumption to 3600L, a 40% decrease, significantly reducing chemical consumption. In other words, tank pickling makes it easier to control BSG layer thickness, reducing overall HF consumption by approximately 40%, and greatly lowering factory chemical costs.

[0062] The electrical performance of N-type TOPcon batteries prepared by BSG layer cleaning through tank pickling and chain pickling is no different from that of N-type TOPcon batteries prepared by one-step chain pickling.

[0063] The technical solution disclosed in this application utilizes a tank filled with HF of a first concentration to perform a tank-type acid pickling on the boron-diffused silicon wafer. This tank-type acid pickling removes a portion of the BSG layer from the surface of the silicon wafer. The pickled silicon wafer is then washed with water and dried to avoid affecting subsequent chain-type acid pickling. Afterward, a second concentration of HF is used to perform a chain-type acid pickling on the dried silicon wafer to remove the remaining BSG layer from the back and sides of the wafer. Since the tank-type acid pickling involves placing the silicon wafer in HF, it eliminates the need for high-concentration HF to clean part of the BSG layer. Furthermore, the tank-type acid pickling method ensures a more uniform surface of the remaining BSG layer and minimizes significant variations in the thickness of the BSG layer within the wafer, thereby improving the BSG layer removal efficiency. Since only a portion of the BSG layer remains on the back and sides of the silicon wafer after tank pickling, it is easier to clean the BSG after tank pickling. Therefore, when using chain pickling, high-concentration HF is not required to clean the remaining BSG layer on the back and sides of the silicon wafer, and the BSG layer removal effect can be improved. Furthermore, based on the combination of tank pickling and chain pickling, even if the roller level is slightly abnormal during chain pickling, it will not affect the removal of the remaining BSG layer. Therefore, HF consumption can be reduced, and the later maintenance costs of the equipment can be decreased.

[0064] This application provides a method for cleaning BSG in a solar cell, wherein the first concentration is less than the second concentration.

[0065] Since this application uses a process of first tank pickling and then chain pickling to clean and remove the BSG layer, and the tank pickling only removes part of the BSG layer on the surface of the silicon wafer, the concentration of HF used in the tank pickling can be less than the concentration of HF used in the chain pickling (i.e., the first concentration is less than the second concentration). Furthermore, the concentration of HF used in both the tank pickling and the chain pickling is less than the concentration of HF used in the existing chain roller pickling.

[0066] This application provides a method for cleaning BSG in solar cells, wherein the first concentration is 5%-10% and the second concentration is 20%-25%.

[0067] In this application, the first concentration is specifically 5%-10% (including the endpoint value), that is, the HF concentration of the tank pickling is 5%-10%, and the second concentration is specifically 20%-25% (including the endpoint value), that is, the HF concentration of the chain pickling is 20%-25%.

[0068] Tank-type pickling uses 5%-10% HF to remove a certain thickness of BSG layer, resulting in a more uniform surface of the remaining BSG layer and no significant thickness variation within the wafer. Chain-type pickling, using 20%-25% HF, removes the remaining BSG layer. Compared to existing chain-type pickling methods that require approximately 65% ​​HF for BSG layer cleaning, the chain-type pickling process in this application reduces HF consumption by approximately 40%.

[0069] Please refer to Table 1 for details, which shows the process parameters for tank pickling and chain pickling:

[0070] Table 1. Process parameters for tank pickling and chain pickling

[0071]

[0072] The pre-pickling process (i.e., tank pickling) uses 5%-10% HF, which can effectively remove a small amount of BSG, thereby matching the chain pickling process, so that the post-pickling process (i.e., chain pickling) can effectively remove the BSG residue on the back side with 20%-25% HF. It should be noted that (1) if the HF concentration of the tank pickling is low and the HF concentration of the chain pickling remains unchanged, the tank pickling will not remove enough BSG, resulting in the chain pickling not completely removing BSG, which will lead to batch defects; (2) if the HF concentration of the tank pickling is normal and the chain pickling concentration is reduced, the BSG after the chain pickling will not be completely removed, which will lead to batch defects; (3) if the concentrations of the tank pickling and the chain pickling decrease at the same time, the back reflectivity of the tank pickling will be low, the BSG layer will be thick, the chain pickling will not remove the residual BSG, which will lead to batch defects.

[0073] Through the above process, the BSG layer thickness can be reduced from 80nm to 20nm-30nm by tank pickling. This reduction in BSG layer thickness allows the subsequent BSG removal process to use approximately 20% HF to remove the BSG layer from the back and sides.

[0074] The BSG cleaning method for solar cells provided in this application embodiment may further include, before performing a chain acid wash on the dried silicon wafer using HF of a second concentration to clean the remaining BSG layer on the back and sides of the silicon wafer:

[0075] Measure the reflectance at multiple sampling points on the surface of the dried silicon wafer;

[0076] Determine whether the reflectance at each sampling point is within the set reflectance range;

[0077] If the reflectivity at a sampling point is lower than the minimum value of the set reflectivity range, then return to the step of using the first concentration of HF in the tank to perform tank acid washing on the boron-diffused silicon wafer to clean the BSG layer on the surface of the silicon wafer.

[0078] If the reflectance at each sampling point is within the set reflectance range, then the process of chain acid washing of the dried silicon wafer with HF of the second concentration is performed to clean the remaining BSG layer on the back and sides of the silicon wafer.

[0079] In this application, before using a second concentration of HF to perform a chain-like acid pickling on the dried silicon wafer to clean the remaining BSG layer on the back and sides of the wafer, the reflectance at multiple sampling points on the surface of the dried silicon wafer can be measured (specifically, the reflectance at multiple sampling points on the back side can be measured). Higher reflectance indicates a thinner BSG layer, and lower reflectance indicates a thicker BSG layer. Then, it can be determined whether the reflectance at each sampling point is within a set reflectance range. Specifically, the set reflectance range can be 5%-8% (this reflectance is well-matched to the chain-like acid pickling process). Of course, the set reflectance range can be adjusted based on experiments, etc.

[0080] If the reflectance at a sampling point is lower than the minimum value of the set reflectance range, it indicates that the remaining BSG layer after the tank acid pickling is relatively thick. In this case, the process of using the first concentration of HF in the tank to perform tank acid pickling on the boron-diffused silicon wafer to clean the BSG layer on the surface of the silicon wafer can be repeated to clean and remove the BSG layer, thereby reducing the thickness of the BSG layer and improving the BSG layer removal effect.

[0081] If the reflectance at all sampling points is within the set reflectance range, it indicates that the BSG layer can be well matched with the chain pickling process. Therefore, the step of using HF of the second concentration to perform chain pickling on the dried silicon wafer can be performed to clean the remaining BSG layer on the back and sides of the silicon wafer, so as to effectively remove the remaining BSG layer on the back and sides.

[0082] If the reflectivity at a sampling point exceeds the maximum value of the set reflectivity range, it indicates that the BSG layer is relatively thin. In this case, a chain acid washing process using a second concentration of HF can be performed on the dried silicon wafer to clean the remaining BSG layer on the back and sides of the wafer, thus removing the thinner BSG layer. Alternatively, an alarm can be issued so that relevant personnel can be promptly notified of the thin BSG layer, allowing for adjustment of the tank acid washing time to improve the performance of the final N-type TOPcon cell.

[0083] The present application provides a solar cell BSG cleaning method, wherein the tank pickling time is 180s±10s, the chain pickling process parameters are (3.6m±0.5m) / min, and the temperature of both tank pickling and chain pickling is 18℃-25℃.

[0084] In this application, the time length of the tank pickling can be 180s±10s (180s is better), and the process parameters of the chain pickling can be (3.6m±0.5m) / min (3.6m / min is better) in order to improve the BSG layer removal effect.

[0085] The 3.6 m / min speed is consistent with the one-step chain pickling process. Due to the simplicity of the process, the traditional tank pickling machine can be used, resulting in lower costs.

[0086] Furthermore, the temperature for both tank pickling and chain pickling can be 18℃-25℃, allowing HF to achieve better BSG cleaning and removal effects.

[0087] This application provides a solar cell BSG cleaning method, in which the tank further contains HCl. When using HF of a first concentration contained in the tank to perform tank-type acid washing on the boron-diffused silicon wafer, the method may further include:

[0088] Using HCl to clean silicon wafers;

[0089] And / or, when chain-washing the dried silicon wafers with a second concentration of HF, it may also include:

[0090] HCL is used to clean silicon wafers.

[0091] In this application, in addition to containing HF of a first concentration, the tank may also contain HCl. The concentration of HCl in the tank may be lower than a third concentration, which can be set based on experiments and experience; specifically, the third concentration may be 1%. Based on the foregoing, when using the HF of the first concentration in the tank to perform tank-type acid pickling on boron-diffused silicon wafers, the HCl in the tank can also be used to clean the silicon wafers to remove metal ions from the surface, thereby improving the cleaning effect.

[0092] In addition to chain-type acid washing of the dried silicon wafers using a second concentration of HF, HCl can also be used to clean the silicon wafers. The concentration of HCl used in this case can be lower than that of the third concentration. This method achieves the simultaneous removal of the remaining BSG layer on the silicon wafer surface and the removal of metal ions from the silicon wafer surface using HCl, thereby improving the silicon wafer cleaning effect.

[0093] Both tank pickling and chain pickling can include HCl cleaning, or HCl cleaning can be performed in one of the pickling processes in tank pickling or chain pickling to reduce cleaning costs.

[0094] This application provides a solar cell BSG cleaning method, which uses a second concentration of HF to perform a chain acid washing on the dried silicon wafer, and may include:

[0095] The dried silicon wafers are subjected to chain pickling using HF of a second concentration placed in the pickling tank.

[0096] In this application, when using a second concentration of HF to perform chain pickling on the dried silicon wafer, specifically, a second concentration of HF set in an pickling tank can be used to perform chain pickling on the dried silicon wafer. Specifically, the chain rollers can carry the silicon wafer through the pickling tank, and the second concentration of HF in the pickling tank can be sprayed onto the silicon wafer to pickle the sides and back of the silicon wafer to remove the BSG layer.

[0097] Chain pickling in a pickling tank allows HF to flow into the tank, enabling its reuse and recycling while ensuring safety.

[0098] This application provides a solar cell BSG cleaning method, which uses HF of a second concentration placed in an acid washing tank to perform a chain acid washing on the dried silicon wafer, and may include:

[0099] The dried silicon wafers are subjected to a single chain pickling process using HF of a second concentration set in the first pickling tank.

[0100] The silicon wafers after the first chain pickling were subjected to a second chain pickling using HF of a second concentration set in the second pickling tank.

[0101] In this application, when using HF of a second concentration set in the pickling tank to perform chain pickling on the dried silicon wafer, specifically, the dried silicon wafer can be subjected to a first chain pickling using HF of a second concentration set in the first pickling tank, and then the dried silicon wafer can be subjected to a second chain pickling using HF of a second concentration set in the second pickling tank, so as to improve the removal effect of the remaining BSG layer on the back and sides through two chain pickling processes.

[0102] The BSG cleaning method for solar cells provided in this application embodiment, after using HF of a second concentration to perform chain acid washing on the dried silicon wafer to clean the remaining BSG layer on the back and sides of the silicon wafer, may further include:

[0103] The silicon wafers after chain pickling are washed with water and dried.

[0104] In this application, after chain-washing the dried silicon wafer with HF of a second concentration to clean the remaining BSG layer on the back and sides of the wafer, the chain-washed silicon wafer can be washed with water. Specifically, a water bath can be used to wash the chain-washed silicon wafer. That is, after chain-washing the dried silicon wafer with HF of a second concentration, the chain-washed silicon wafer can be input into a water bath for washing to remove the back complex and acid residue, thereby avoiding any impact on subsequent fabrication processes.

[0105] After the silicon wafers undergo chain pickling and subsequent water washing, they can be dried to remove surface moisture. Specifically, a drying tank can be used to dry the wafers. This prevents surface moisture from affecting subsequent fabrication processes.

[0106] The BSG cleaning method for solar cells provided in this application embodiment, when using HF of a second concentration to perform chain acid washing on the dried silicon wafer to clean the remaining BSG layer on the back and sides of the silicon wafer, may further include:

[0107] The boron-rich layer on the back and sides of the silicon wafer is cleaned using HF of a second concentration.

[0108] In this application, when using HF of a second concentration to perform chain pickling on the dried silicon wafer to clean the remaining BSG layer on the back and sides of the silicon wafer, the second concentration of HF can also be used to clean the boron-rich layer (the boron-rich layer is located below the BSG layer, i.e., close to the silicon wafer side) on the back and sides of the silicon wafer, so as to reduce the boron-rich layer and improve the conversion efficiency of the prepared solar cell (specifically, improve the solar cell efficiency by more than 0.05%).

[0109] This application also provides a method for fabricating an N-type TOPcon battery. See [link to relevant documentation]. Figure 2 It illustrates a flowchart of an N-type TOPcon battery fabrication method provided in an embodiment of this application, which may include:

[0110] Texturing is performed on N-type silicon wafers to create a pyramidal textured surface on the wafer surface;

[0111] Boron diffusion is performed on the pyramidal textured surface of a silicon wafer;

[0112] The BSG layer on the surface of the boron-diffused silicon wafer is cleaned using any of the above-mentioned solar cell BSG cleaning methods.

[0113] The back side of the silicon wafer is polished, and a passivation contact layer is prepared on the back side of the polished silicon wafer;

[0114] A silicon wafer is cleaned by winding plating, and an aluminum oxide film and a silicon oxynitride film are prepared on the front side of the silicon wafer.

[0115] A silicon nitride thin film is prepared on the back side of a silicon wafer;

[0116] Electrodes are fabricated on the front and back sides of a silicon wafer.

[0117] The method for fabricating an N-type TOPcon battery provided in this application embodiment may include:

[0118] 1) Select an N-type single crystal silicon wafer with a (100) crystal orientation and a resistivity of 1.2 Ω·cm.

[0119] 2) An anisotropic etching method using alkaline texturing is used to prepare (111) crystal orientation pyramid textured surfaces on silicon wafers.

[0120] 3) A uniform emitter is prepared on the textured silicon wafer using a boron furnace tube method, with a front sheet resistance of 100Ω. At the same time, a BSG layer and an oxide layer are grown on the front and back sides.

[0121] 4) Use a tank with 5% HF to remove the oxide layer on the front and back sides and part of the BSG layer on the front and back sides (and sides). After washing with water to remove surface complexes and acid residues, dry in a drying tank for 300 seconds.

[0122] 5) Use a chain-type 20% concentration HF to remove the remaining BSG layer on the back (and sides), wash away the complexes and acid residues with water, and then dry in a drying tank. That is, any of the above-mentioned solar cell BSG cleaning methods can be used to clean the BSG layer on the surface of the boron-diffused silicon wafer. Specifically, 4) and 5) can be used in any of the above-mentioned solar cell BSG cleaning methods.

[0123] 6) The back pyramid tip was removed using an anisotropic etching method with alkaline polishing (i.e., polishing the back of the silicon wafer). The conditions used were: NaOH concentration of 2.5%, polishing additive concentration of 0.8%, solution temperature of 62℃, and time of 180s. After polishing the back of the silicon wafer, the silicon wafer was washed with water (to remove the alkaline solution on the surface of the silicon wafer), and then cleaned with alkali + hydrogen peroxide (to remove organic residues on the surface of the silicon wafer). After that, the silicon wafer was washed with water (to remove alkali and hydrogen peroxide from the surface of the silicon wafer), and then the silicon wafer was washed with mixed acid (HF + HCl, to (1) neutralize the alkaline residue; (2) form hydrophobic bonds; (3) remove metal ions from the surface of the silicon wafer using HCl). After that, the silicon wafer was washed with water and then dried. The dried silicon wafer can proceed to the next process, that is, to prepare a passivation contact layer on the back of the silicon wafer.

[0124] 7) A passivation contact layer is fabricated on the back side of an N-type silicon wafer using an LPCVD furnace tube method. This layer includes a tunneling oxide layer and a doped polysilicon layer. The thickness of the tunneling oxide layer is 1.2 nm, and the thickness of the phosphorus-doped polysilicon layer is 120 nm. During the process, a wrap-around coating is formed around the perimeter and edges of the silicon wafer.

[0125] 8) The polysilicon layer around the perimeter and edges was removed using an alkaline etching method. The conditions were: NaOH concentration of 4%, temperature of 58°C, and etching time of 120 seconds. After the process, the polysilicon layer around the perimeter and edges was completely removed.

[0126] 9) A passivated aluminum oxide layer is prepared on the front side of the silicon wafer using a plate-type on-film deposition method to reduce surface recombination.

[0127] 10) A front-side silicon oxynitride thin film was prepared using PECVD. The front-side silicon oxynitride thin film had a thickness of 85 nm and a refractive index of 2.0 as an anti-reflection passivation agent.

[0128] 11) A silicon nitride thin film on the back side was prepared using PECVD. The back side silicon nitride film had a thickness of 75 nm and a refractive index of 2.2, serving as an anti-reflection passivation agent.

[0129] 12) Metal electrodes are prepared on both sides of the silicon wafer using a screen printing and overlay sintering method.

[0130] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that the elements inherent in a process, method, article, or apparatus that includes a list of elements are included. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Additionally, portions of the technical solutions provided in the embodiments of this application that are consistent with the implementation principles of corresponding technical solutions in the prior art have not been described in detail to avoid excessive elaboration.

[0131] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for cleaning BSG in solar cells, characterized in that, include: The silicon wafer after boron diffusion is subjected to a tank-type acid pickling using HF of the first concentration in the tank to clean the BSG layer on the surface of the silicon wafer. The first concentration is 5%-10%; The silicon wafers after tank pickling are then washed with water and dried. The reflectance at multiple sampling points on the surface of the dried silicon wafer was measured. Determine whether the reflectance at each sampling point is within the set reflectance range; If the reflectivity at a sampling point is lower than the minimum value within the set reflectivity range, then return to the step of using HF of the first concentration in the tank to perform tank acid washing on the boron-diffused silicon wafer to clean the BSG layer on the surface of the silicon wafer. If the reflectance at each of the sampling points is within the set reflectance range, then a chain acid washing process is performed on the dried silicon wafer using HF of a second concentration to clean the remaining BSG layer on the back and sides of the silicon wafer; the second concentration is 20%-25%.

2. The solar cell BSG cleaning method according to claim 1, characterized in that, The time length of the tank pickling is 180s±10s, the process parameters of the chain pickling are (3.6m±0.5m) / min, and the temperature of both the tank pickling and the chain pickling is 18℃-25℃.

3. The solar cell BSG cleaning method according to claim 1, characterized in that, The tank also contains HCl, and when using the first concentration of HF contained in the tank to perform tank-type acid washing on the boron-diffused silicon wafer, the process further includes: The silicon wafer was cleaned using HCl; And / or, when chain-washing the dried silicon wafer with HF of a second concentration, the process further includes: The silicon wafer was cleaned using HCl.

4. The solar cell BSG cleaning method according to claim 1, characterized in that, The dried silicon wafers are subjected to a chain pickling process using HF of a second concentration, including: The dried silicon wafers are subjected to chain pickling using HF of the second concentration placed in the pickling tank.

5. The solar cell BSG cleaning method according to claim 4, characterized in that, The dried silicon wafer is subjected to chain pickling using HF of the second concentration placed in an acid pickling tank, including: The dried silicon wafer is subjected to a single chain pickling process using HF of the second concentration set in the first pickling tank. The silicon wafer after the first chain pickling is subjected to a second chain pickling using HF of the second concentration, which is set in the second pickling tank.

6. The solar cell BSG cleaning method according to claim 1, characterized in that, After performing a chain pickling process on the dried silicon wafer using HF of a second concentration to clean the remaining BSG layer on the back and sides of the silicon wafer, the process further includes: The silicon wafers after chain pickling are washed with water and dried.

7. The solar cell BSG cleaning method according to claim 1, characterized in that, When performing a chain acid pickling process on the dried silicon wafer using HF of a second concentration to clean the remaining BSG layer on the back and sides of the silicon wafer, the process further includes: The boron-rich layer on the back and sides of the silicon wafer is cleaned using HF of the second concentration.

8. A method for preparing an N-type TOPcon battery, characterized in that, include: Texturing is performed on an N-type silicon wafer to create a pyramidal textured surface on the wafer surface; Boron diffusion is performed on the pyramidal textured surface of the silicon wafer; The BSG layer on the surface of the boron-diffused silicon wafer is cleaned using the solar cell BSG cleaning method as described in any one of claims 1 to 7. The back side of the silicon wafer is polished, and a passivation contact layer is prepared on the polished back side of the silicon wafer; The silicon wafer is subjected to a winding cleaning process to prepare an aluminum oxide film and a silicon oxynitride film on the front side of the silicon wafer. A silicon nitride thin film is prepared on the back side of the silicon wafer; Electrodes are fabricated on the front and back sides of the silicon wafer.

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