BC battery boron diffusion method, BC battery and preparation method of BC battery

Abstract

The invention relates to a BC battery boron diffusion method, a BC battery and a preparation method of the BC battery, and the BC battery boron diffusion method comprises the following steps: feeding a quartz boat with a silicon wafer into a quartz furnace tube, controlling the temperature of the quartz furnace tube to a standby temperature, and carrying out leakage detection; controlling the temperature of the quartz furnace tube to rise to a deposition temperature, and sequentially carrying out pre-oxidation treatment and deposition treatment on the silicon wafer; controlling the temperature of the quartz furnace tube to rise to a propelling temperature, and carrying out propelling treatment on the silicon wafer; controlling the temperature of the quartz furnace tube to rise to an oxidation temperature, and carrying out constant-temperature oxidation treatment on the silicon wafer; and after the quartz furnace tube is controlled to be cooled to the boat-out temperature, back-pressure boat-out is carried out. By reducing the temperature and time of an oxidation high-temperature area after boron diffusion, a tunnel junction required by BC route boron diffusion is formed, one part of the surface boron-rich concentration forms a BSG layer through oxidation segregation and is reduced, and the other part forms secondary distribution through high-temperature junction pushing, so that the surface boron-rich concentration is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic cells, and in particular to a BC cell boron diffusion method and a BC cell and a preparation method thereof. Background Art

[0002] The concept of back-contact photovoltaic cells (BC) was first proposed by Schwartz and Lammert in 1975. Its core feature is that both the PN junction and the metal contact surface are located on the back of the solar cell. As a platform technology, BC can be combined with existing technologies such as PERC, TOPCon, HJT and perovskite to break through the efficiency bottleneck of a single technology route and achieve efficiency breakthroughs. Among them, TBC is a process route that combines TOPCon and BC. TOPCon has an excellent passivation contact structure that can increase the open circuit voltage. BC has excellent short-circuit gain because there is no grid line blocking the front. The combination of TOPCon and BC can provide solar cells with both high open circuit voltage and high short circuit current, with an efficiency limit of up to 29.1%.

[0003] Since TBC is an upgraded version of TOPCon, the difficulties of some processes of TOPCon will also be brought into the TBC route. Among them, the damage of the furnace tube in the boron expansion process and the damage of the quartz device are major difficulties of boron expansion; the service life of conventional quartz furnace tubes is 3-4 months. The main reasons include: 1. The borosilicate glass layer formed on the surface of the quartz parts during the boron diffusion process has a different thermal stress coefficient from the silica quartz parts, resulting in different expansion coefficients; 2. The oxidation temperature after boron diffusion is too high, resulting in an increase in the deformation of the furnace tube, especially the large temperature difference at the furnace mouth and furnace tail, which further reduces the service life of the furnace tube. At present, the oxidation temperature after boron expansion is as high as 1000-1050℃, and the high temperature time is 1-1.8h. The main function is to react the boron-rich layer on the surface of the silicon wafer to form a borosilicate glass layer, especially the front expansion area, which is convenient for post-process cleaning. However, long-term high temperature not only consumes electricity costs, but also easily causes a large loss of quartz devices. Directly lowering the oxidation temperature to increase the life of the furnace tube will make it difficult to clean the back expansion. Summary of the invention

[0004] Based on this, the purpose of the present invention is to provide a BC battery boron diffusion method and a BC battery and a preparation method thereof. By reducing the temperature and time of the high-temperature oxidation zone after boron diffusion, the tunnel junction required for boron diffusion of the BC route is formed, and the surface boron-rich concentration is partially reduced by oxidation segregation to form a BSG layer, and partially reduced by high-temperature push junction to form a secondary distribution.

[0005] The present invention provides a BC battery boron diffusion method, which comprises the following steps: S11. The quartz boat with silicon wafers is sent into the quartz furnace tube, the quartz furnace tube is controlled to heat up to the standby temperature and leak detection; S12. Controlling the quartz furnace tube to heat up to the deposition temperature, and sequentially performing pre-oxidation treatment and deposition treatment on the silicon wafer; S13. Controlling the temperature of the quartz furnace tube to the advancement temperature to advance the silicon wafer; S14. Controlling the temperature of the quartz furnace tube to the oxidation temperature, and performing a constant temperature oxidation treatment on the silicon wafer; S15. After controlling the temperature of the quartz furnace tube to the boat exit temperature, the quartz furnace tube is pressurized to exit the boat.

[0006] As a further improvement of the above solution of the present invention, in step S14, the oxidation temperature is 900-980°C.

[0007] As a further improvement of the above solution of the present invention, in step S14, the isothermal oxidation treatment is carried out at a pressure of 600-950 mbar, with an oxygen flow rate of 5000-20000 sccm, for 1000-3000 s.

[0008] As a further improvement of the above solution of the present invention, in step S11, the standby temperature is 750-820°C.

[0009] As a further improvement of the above solution of the present invention, in step S12, the deposition temperature is 780-870°C; And / or, in step S12, the pre-oxidation treatment is carried out at a pressure of 100-400 mbar by introducing oxygen with a flow rate of 300-2000 sccm and nitrogen with a flow rate of 300-3000 sccm.

[0010] As a further improvement of the above solution of the present invention, in step S13, the advancing temperature is 850-950°C; And / or, in step S13, the pushing treatment is carried out at a pressure of 200-400 mbar and a flow rate of 2000-5000 sccm of nitrogen.

[0011] The present invention also provides a method for preparing a BC battery, which comprises the following steps: S21. The silicon wafer is cleaned for the first time and double-sided polished; S22. The silicon wafer is subjected to a deposition process to sequentially form a tunneling oxide layer and an amorphous silicon poly layer on the back of the silicon wafer; S23. Performing the BC cell boron diffusion method as described above on the silicon wafer to form a P+ emitter and a BSG protective layer on the back of the silicon wafer; S24. Performing a first laser treatment on the silicon wafer to pattern the back side of the silicon wafer; S25. Cleaning the silicon wafer for a second time; S26. Performing a deposition process on the silicon wafer to sequentially form a tunneling oxide layer 2 and an amorphous silicon poly layer 2 on the back of the silicon wafer; S27. Diffusion of phosphorus on the silicon wafer to form an N+ layer; S28. performing a second laser treatment on the silicon wafer to pattern the back side of the silicon wafer; S29. The silicon wafer is cleaned for the third time to remove the B / PSG and polysilicon on the front and edge of the silicon wafer, and the GAP area on the back of the silicon wafer and the P / BSG on the back are removed by a slot machine; S210. Performing a deposition process on the silicon wafer to sequentially form an aluminum oxide layer and a silicon nitride layer on both sides of the silicon wafer; S211. Screen printing is performed on the back side of the silicon wafer, followed by sintering to produce a BC battery.

[0012] As a further improvement of the above solution of the present invention, in step S29, the third cleaning includes the following steps: S291. Loading the silicon wafer to a chain-type PSG cleaning machine, pouring water on the back of the silicon wafer to form a water mask; S292. The front side of the silicon wafer is in contact with an acid polishing solution to remove the amorphous silicon and B / PSG layer at the front side and edge of the silicon wafer; S293. The silicon wafers are driven by the chain machine to enter the water spray device and the drying device in sequence, and then enter the trough machine after drying.

[0013] As a further improvement of the above scheme of the present invention, in step S292, the acid polishing solution contains the following components in volume percentage: 10-20% HF, 30%-55% HNO3, 5%-15% H2SO4, and 30-50% H2O.

[0014] The present invention also provides a BC battery, which is prepared by the preparation method as described above.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention forms the tunnel junction required for boron diffusion of the BC route by reducing the temperature and time of the high-temperature oxidation zone after boron diffusion. A part of the surface boron-rich concentration is reduced by oxidation segregation to form a BSG layer, and a part is reduced by high-temperature pushing junction to form a secondary distribution. In the subsequent cleaning process, the front side and edge plating are polished by wet method, which reduces the risk of tunnel junction breakdown and improves the passivation effect of the tunnel layer, thereby improving the battery efficiency and yield.

[0016] 2. The present invention greatly reduces the temperature of oxidation after boron expansion, increases the service life of the furnace and thermocouples, and extends the life cycle; reduces the risk of damage and deformation of furnace tubes and quartz boats, reduces the cost of furnace tube wear, and extends the life of quartz devices; reduces the time of oxidation after boron expansion, increases the capacity of the process, and increases the overall capacity by 40%, reducing the purchase cost of the machine; reduces the downtime rate of the machine and reduces the maintenance cost of the process; the battery conversion efficiency of the present invention is 0.05% higher than that of the boron expansion high-temperature oxidation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 1 is an ECV curve diagram of constant temperature oxidation in the boron diffusion step in the embodiments of the present invention and the comparative example. DETAILED DESCRIPTION

[0018] For ease of understanding of the present invention, the present invention will be described more fully below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0020] Example This embodiment provides a BC battery, and the preparation method thereof includes the following steps: S1. First cleaning: The original silicon wafer (using an N-type original silicon wafer with a size of 183mm*210mm, a thickness of 150μm, and a resistivity of 0.4-1.6Ω·cm) is double-sided polished using a NaOH alkaline solution.

[0021] S2. First poly: A tunnel oxide layer and an amorphous silicon poly layer are formed on the back of the silicon wafer by low-pressure chemical vapor deposition (LPCVD) or PECVD.

[0022] S3. Boron diffusion: Boron is doped into the amorphous silicon poly layer 1 on the back of the silicon wafer by boron diffusion to form a P+ emitter; a BSG protective layer is then prepared by oxidation, and boron atoms are condensed and redistributed. In this embodiment, the boron diffusion specifically includes the following nine steps S31-S39.

[0023] S31. Put the silicon wafer into the boat and heat it up: put the silicon wafer with the tunnel oxide layer 1 and the amorphous silicon poly layer 1 into the quartz boat, and then send the quartz boat into the quartz furnace tube. The standby temperature of the quartz furnace tube is set to 750-820℃.

[0024] S32. Pumping and leak detection: Under low pressure 20-200mbar, the airflow is set to 0, and leak detection is performed at standby temperature to ensure the sealing of the furnace tube and guarantee the stability of the subsequent process.

[0025] S33. Pre-oxidation: Raise the pressure to 100-400mbar, introduce oxygen with a flow rate of 300-2000sccm and nitrogen with a flow rate of 300-3000sccm into the quartz furnace tube to form an oxidizing environment, raise the temperature to 780-870℃, and form an oxide layer on the surface of the silicon wafer to play a role in getting rid of impurities and provide conditions for subsequent reactions.

[0026] S34. Deposition: BCL3 gas with a flow rate of 90-180sccm, oxygen gas with a flow rate of 300-1000sccm, and nitrogen gas with a flow rate of 1000-5000sccm are introduced into a quartz furnace tube with a pressure of 100-400mbar to perform deposition at a deposition temperature of 780-870°C to form a boron-rich layer; in this embodiment, the deposition step can be completed in multiple steps.

[0027] S35. Purge: introduce nitrogen gas with a flow rate of 1000-4000 sccm for purge, blow the waste gas generated during the deposition process out of the furnace tube, and provide a heating time buffer for subsequent deposition or advancement; in this embodiment, the purge step is performed multiple times.

[0028] S36. Push: Back pressure to 200-400mbar, introduce nitrogen with a flow rate of 2000-5000sccm, raise the temperature to 850-950℃, increase the temperature to initially push the boron impurities, form a preliminary tunneling junction, and initially crystallize the amorphous silicon poly layer formed by LPCVD or PECVD.

[0029] S37. Constant temperature oxidation: increase the pressure to 500-950mbar, increase the temperature to 900-980℃, introduce oxygen with a flow rate of 5000-20000sccm, control the oxygen introduction time to be 1000-3000s, and perform constant temperature oxidation. The effects of constant temperature oxidation include: 1. Through the different segregation coefficients of silicon dioxide and silicon, the boron-rich concentration on the shallow surface is reduced by segregation, a BSG layer is formed on the surface of the silicon wafer, and the front and edge are cleaned by a wet segment chain; 2. The high-concentration boron on the shallow surface is pushed deep into the silicon wafer, and a secondary push distribution is performed in the poly layer, so that the overall boron concentration of the tunnel junction tends to be consistent, forming the required tunnel junction type; 3. The amorphous silicon poly layer formed by LPCVD or PECVD is crystallized for the second time. In this embodiment, the constant temperature oxidation step can be divided into multiple steps, and the total oxidation time of the multiple steps is controlled to be 1000-3000s.

[0030] S38. Cooling: Cool the quartz furnace tube to 650-850°C, introduce sufficient oxygen, nitrogen or a mixture of nitrogen and oxygen, and the cooling time is 1100-2500s. After this step, the thickness of the oxide layer mask is controlled to be 10-80nm.

[0031] S39. Press back out of the boat.

[0032] S4. First laser: The back of the silicon wafer after boron expansion is patterned by laser to modify the boron-doped polysilicon layer in the laser gate line area.

[0033] S5. Second cleaning: Use a slot machine to remove the boron-doped polysilicon layer in the GAP area on the back of the silicon wafer.

[0034] S6. Second Poly: Form a tunnel oxide layer 2 and an amorphous silicon poly layer 2 on the back of the silicon wafer through low-pressure chemical vapor deposition LPCVD or PECVD.

[0035] S7. Phosphorus diffusion: Place the silicon wafer into a phosphorus diffusion furnace to deposit doped phosphorus atoms to form an N+ layer.

[0036] S8. Second laser: The back of the silicon wafer is patterned by laser to modify the phosphorus-doped polysilicon layer in the laser grid line area.

[0037] S9. Third cleaning: remove the B / PSG on the front and edge of the silicon wafer by a B / P removal chain machine, and remove the GAP area and P / BSG on the back of the silicon wafer by a texturing machine. In this embodiment, removing the B / PSG and polysilicon on the front and edge of the silicon wafer by a chain machine specifically includes three steps S91-S93.

[0038] S91. Load the silicon wafer horizontally to the chain B / P removal chain machine, and sprinkle water on the back of the silicon wafer as a mask to prevent over-engraving; S92. The front side of the silicon wafer contacts the acid polishing liquid, in which: the initial amount of HF is 30-58L, accounting for 10-20% by volume; the initial amount of HNO3 is 80-160L, accounting for 30%-55% by volume of HNO3; the initial amount of H2SO4 is 15-45L, accounting for 5%-15% by volume of H2SO4; the initial amount of H2O is 80-150L, ​​accounting for 30-50% by volume of H2O; the chain acid polishing removes the amorphous silicon and B / PSG layer on the front and edge of the silicon wafer through chemical corrosion, and the back is protected by a water film; S93. The silicon wafers follow the rollers into the water spray device and drying device in turn, and then enter the texturing machine after drying.

[0039] S10.ALD: Aluminum oxide film (AlOx) is deposited on both sides of the silicon wafer by atomic layer deposition (ALD); S11. Front and back film: Silicon nitride (SiNx) thin film is deposited on both sides of the silicon wafer by PECVD; S12. Screen printing: Screen printing is used to make interdigitated metal electrodes on the back side; S13. Laser induced sintering to produce BC battery.

[0040] Comparative Example This comparative example proposes a BC battery, and its preparation method comprises the following steps: S1. First cleaning: The original silicon wafer (using an N-type original silicon wafer with a size of 183mm*210mm, a thickness of 150μm, and a resistivity of 0.4-1.6Ω·cm) is double-sided polished using a NaOH alkaline solution.

[0041] S2. First poly: A tunnel oxide layer and an amorphous silicon poly layer are formed on the back of the silicon wafer by low-pressure chemical vapor deposition (LPCVD) or PECVD.

[0042] S3. Boron diffusion: Boron is doped into the amorphous silicon poly layer on the back of the silicon wafer by boron diffusion to form a P+ emitter; a BSG protective layer is then prepared by oxidation, and boron atoms are condensed and redistributed. In this comparative example, the boron diffusion specifically includes the following nine steps S31-S39.

[0043] S31. Put the silicon wafer into the boat and heat it up: put the silicon wafer with the tunnel oxide layer 1 and the amorphous silicon poly layer 1 into the quartz boat, and then send the quartz boat into the quartz furnace tube. The standby temperature of the quartz furnace tube is set to 750-820℃, and the temperature is increased to reduce the temperature difference when the furnace door is opened.

[0044] S32. Pumping and leak detection: Under low pressure 20-200mbar, the airflow is set to 0, and leak detection is performed at standby temperature to ensure the sealing of the furnace tube and guarantee the stability of the subsequent process.

[0045] S33. Pre-oxidation: Raise the pressure to 100-400 mbar, introduce oxygen with a flow rate of 300-2000 sccm and nitrogen with a flow rate of 300-3000 into the quartz furnace tube to form an oxidizing environment, raise the temperature to 780-870°C, and form an oxide layer on the surface of the silicon wafer.

[0046] S34. Deposition: BCL3 gas with a flow rate of 90-180 sccm, oxygen gas with a flow rate of 300-2000 sccm, and nitrogen gas with a flow rate of 1000-5000 sccm are introduced into a quartz furnace tube with a pressure of 100-400 mbar to perform deposition at a deposition temperature of 780-870°C to form a boron-rich layer.

[0047] S35. Purge: introduce nitrogen gas with a flow rate of 1000-4000sccm for purge, blow the waste gas generated during the deposition process out of the furnace tube, and provide a heating time buffer for subsequent deposition or advancement.

[0048] S36. Push: Back pressure to 200-400mbar, introduce nitrogen with a flow rate of 2000-5000sccm, raise the temperature to 850-950℃, increase the temperature to initially push the boron impurities, form a preliminary tunneling junction, and initially crystallize the amorphous silicon poly layer formed by LPCVD or PECVD.

[0049] S37. Constant temperature oxidation: increase the pressure to 600-800 mbar, increase the temperature to 1000-1050°C, introduce oxygen at a flow rate of 8000-25000 sccm, control the oxygen introduction time to 3000-6000 s, and perform constant temperature oxidation.

[0050] S38. Cooling: Cool the quartz furnace tube to 650-850°C, introduce sufficient oxygen, nitrogen or a mixture of nitrogen and oxygen, and the cooling time is 1500-2500s. After this step, the thickness of the oxide layer mask is controlled to be 80-150nm; S39. Press back out of the boat.

[0051] S4. First laser: The back of the silicon wafer after boron expansion is patterned by laser to modify the boron-doped polysilicon layer in the laser gate line area.

[0052] S5. Second cleaning: Use a BSG removal chain machine to remove the BSG on the front and edge, and use a slot-type alkaline polishing machine to remove the P-poly plated on the front and side and the boron-doped polysilicon layer in the GAP area on the back of the silicon wafer.

[0053] S6. Second Poly: Form a tunnel oxide layer 2 and an amorphous silicon poly layer 2 on the back of the silicon wafer through low-pressure chemical vapor deposition LPCVD or PECVD.

[0054] S7. Phosphorus diffusion: Place the silicon wafer into a phosphorus diffusion furnace to deposit doped phosphorus atoms to form an N+ layer.

[0055] S8. Second laser: Use laser to pattern the back of the silicon wafer and modify the phosphorus-doped polysilicon layer in the laser gate area; Function: Facilitate the third cleaning to remove the phosphorus-doped polysilicon layer in the GAP area.

[0056] S9. The third cleaning: Remove the PSG on the front and edge through the PSG removal chain machine. Conventional PSG uses 40-100L of HF for the initial dosage, accounting for 10-20% by volume, and 300-400L of water for the initial dosage, accounting for 80-90% by volume; through texturing, the phosphorus-doped polysilicon exposed after the second laser treatment is removed by the front / side wrapping phosphorus-doped polysilicon, and the anisotropic corrosion characteristics of silicon are used. The second is to corrode to form a pyramid velvet surface to increase light absorption. The pyramid velvet structure is formed through the texturing process, which is conducive to light absorption.

[0057] S10.ALD: Aluminum oxide film (AlOx) is deposited on both sides of the silicon wafer by atomic layer deposition (ALD); S11. Front and back film: Silicon nitride (SiNx) thin film is deposited on both sides of the silicon wafer by PECVD; S12. Screen printing: Screen printing is used to make interdigitated metal electrodes on the back side; S13. Laser induced sintering to produce BC battery.

[0058] Figure 1 The ECV test curves of the low-temperature oxidation process after boron expansion in the embodiment and the high-temperature oxidation process after boron expansion in the comparative example are shown in FIG. Figure 1 It can be seen that the doping concentration range of the embodiment is 1E^19-7E^20, and the junction depth range is 0.12-0.4um, which shows that the lower oxidation temperature can reduce the risk of boron doping tunneling through the tunneling oxide layer, reduce the probability of internal expansion, and thus improve the passivation effect. It can be seen from the comparative data that high-temperature oxidation causes the tunneling passivation layer to be destroyed, and the overall efficiency is reduced.

[0059] The BC cells prepared in the embodiment and the comparative example were tested by an IV tester under the following test conditions: light intensity: the solar light intensity under AM1.5G conditions should be 1000W / m², that is, the light intensity is 100MW / cm; temperature: the temperature of the photovoltaic cell is 25°C. The test results are shown in Table 1.

[0060] Table 1

[0061] It can be seen from Table 1 that the efficiency of the low temperature oxidation method (900-980°C) of the embodiment is 0.05% higher than that of the high temperature oxidation method (1000-1050°C) of the comparative example.

[0062] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0063] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A BC battery boron diffusion method, characterized in that: It includes the following steps: S11. The quartz boat with silicon wafers is sent into the quartz furnace tube, the quartz furnace tube is controlled to heat up to the standby temperature and leak detection; S12. Controlling the quartz furnace tube to heat up to the deposition temperature, and sequentially performing pre-oxidation treatment and deposition treatment on the silicon wafer; S13. Controlling the temperature of the quartz furnace tube to the advancement temperature to advance the silicon wafer; S14. Controlling the temperature of the quartz furnace tube to the oxidation temperature, and performing a constant temperature oxidation treatment on the silicon wafer; S15. After controlling the temperature of the quartz furnace tube to the boat exit temperature, the quartz furnace tube is pressurized to exit the boat.

2. The BC battery boron diffusion method according to claim 1, characterized in that: In step S14, the oxidation temperature is 900-980°C.

3. The BC battery boron diffusion method according to claim 1, characterized in that: In step S14, the isothermal oxidation treatment is carried out at a pressure of 600-950 mbar, with oxygen gas at a flow rate of 5000-20000 sccm, for 1000-3000 seconds.

4. The BC battery boron diffusion method according to claim 1, characterized in that: In step S11, the standby temperature is 750-820°C.

5. The BC battery boron diffusion method according to claim 1, characterized in that: In step S12, the deposition temperature is 780-870°C; And / or, in step S12, the pre-oxidation treatment is carried out at a pressure of 100-400 mbar by introducing oxygen with a flow rate of 300-2000 sccm and nitrogen with a flow rate of 300-3000 sccm.

6. The BC battery boron diffusion method according to claim 1, characterized in that: In step S13, the advancing temperature is 850-950°C; And / or, in step S13, the pushing treatment is carried out at a pressure of 200-400 mbar and a flow rate of 2000-5000 sccm of nitrogen.

7. A method for preparing a BC battery, characterized in that: It includes the following steps: S21. The silicon wafer is cleaned for the first time and double-sided polished; S22. The silicon wafer is subjected to a deposition process to sequentially form a tunneling oxide layer and an amorphous silicon poly layer on the back of the silicon wafer; S23. Performing the boron diffusion method according to any one of claims 1 to 6 on the silicon wafer to form a P+ emitter and a BSG protection layer on the back side of the silicon wafer; S24. Performing a first laser treatment on the silicon wafer to pattern the back side of the silicon wafer; S25. Cleaning the silicon wafer for a second time; S26. Performing a deposition process on the silicon wafer to sequentially form a tunneling oxide layer 2 and an amorphous silicon poly layer 2 on the back of the silicon wafer; S27. Diffusion of phosphorus on the silicon wafer to form an N+ layer; S28. performing a second laser treatment on the silicon wafer to pattern the back side of the silicon wafer; S29. The silicon wafer is cleaned for the third time to remove the B / PSG and polysilicon on the front and edge of the silicon wafer, and the GAP area on the back of the silicon wafer and the P / BSG on the back are removed by a slot machine; S210. Performing a deposition process on the silicon wafer to sequentially form an aluminum oxide layer and a silicon nitride layer on both sides of the silicon wafer; S211. Screen printing is performed on the back side of the silicon wafer, followed by sintering to produce a BC battery.

8. The method for preparing a BC battery according to claim 7, characterized in that: In step S29, the third cleaning comprises the following steps: S291. Loading the silicon wafer to a chain-type PSG cleaning machine, pouring water on the back of the silicon wafer to form a water mask; S292. The front side of the silicon wafer is in contact with an acid polishing solution to remove the amorphous silicon and B / PSG layer at the front side and edge of the silicon wafer; S293. The silicon wafers are driven by the chain machine to enter the water spray device and the drying device in sequence, and then enter the trough machine after drying.

9. The method for preparing a BC battery according to claim 8, characterized in that: In step S292, the acid polishing solution contains the following components in volume percentage: 10-20% HF, 30%-55% HNO3, 5%-15% H2SO4, and 30-50% H2O.

10. A BC battery, characterized in that: It is prepared by the preparation method described in any one of claims 7 to 9.

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