Solar cell and boron diffusion method therefor, photovoltaic module

Abstract

The application provides a solar cell and a boron diffusion method and a photovoltaic module. The second boron diffusion process of the solar cell comprises: first dry oxygen oxidation treatment of a substrate, first wet oxygen oxidation treatment of the substrate, second dry oxygen oxidation treatment of the substrate, and second wet oxygen oxidation treatment of the substrate to form a P-type emitter on the substrate. The oxidation process of the second boron diffusion process is designed as a four-stage dry-wet alternating structure of first dry oxygen, first wet oxygen, second dry oxygen and second wet oxygen, which is synchronized with the whole boron atom diffusion process, realizes step-by-step controllable diffusion of boron atoms and multi-layer collaborative construction of the silicon dioxide layer and the borosilicate glass layer, improves the synergy of oxidation and boron diffusion and doping, is more gentle through segmented oxygen control, reduces the overall thermal budget, reduces the thermal damage of high temperature to the substrate, is beneficial to subsequent processing procedures, improves the performance of the P-type emitter and the back surface passivation effect, and improves the conversion efficiency and yield of the solar cell.

Description

Technical Field

[0001] This application belongs to the field of solar cell technology, specifically relating to solar cells and their boron expansion methods, and photovoltaic modules. Background Technology

[0002] In the boron diffusion process of solar cells, single-stage dry oxidation and single-stage wet oxidation processes are often used. However, due to the poor synergy between single-stage oxidation logic and oxidation-dopylene diffusion, not only is the diffusion distribution of boron atoms uneven, increasing the etching difficulty of removing the borosilicate glass layer and alkaline polishing, but it also leads to more interface defects on the substrate, reducing the substrate quality of subsequent processes. Furthermore, the thermal budget is too high, which can easily damage the substrate, thus directly affecting the processing effect of subsequent core processes such as removing the borosilicate glass layer, alkaline polishing, and low-pressure chemical vapor deposition (LPCVD). This results in a decrease in the front emitter performance of the solar cell and damage to the back passivation effect, ultimately affecting the cell conversion efficiency and mass production yield. Summary of the Invention

[0003] In view of this, the first aspect of this application provides a boron diffusion method for solar cells, the boron diffusion method comprising: Provide substrates that have undergone the first boron diffusion process; The substrate is subjected to a second boron diffusion process, the second boron diffusion process comprising: The substrate is subjected to a first dry oxygen oxidation treatment to form a silicon dioxide layer on the substrate; The substrate is subjected to a first wet oxidation treatment to form a borosilicate glass layer disposed on the side of the silicon dioxide layer opposite to the substrate. The substrate is subjected to a second dry oxygen oxidation treatment to repair the silicon dioxide layer; The substrate is subjected to a second wet oxidation treatment to ensure that the thickness uniformity of the borosilicate glass layer is ≥95%. A P-type emitter is formed on the substrate.

[0004] Wherein, the process conditions for the first dry oxygen oxidation treatment satisfy at least one of the following: The oxygen flow rate for the first dry oxygen is 8000 sccm~12000 sccm; The oxidation time for the first dry oxygen is 8 to 15 minutes.

[0005] Wherein, the process conditions of the first wet oxygen oxidation treatment satisfy at least one of the following: The oxygen flow rate for the first humidified oxygen treatment is 4000 sccm~6000 sccm; The water vapor flow rate of the first humidified oxygen is 1500 sccm~2000 sccm; The oxidation time for the first wet oxygen is 10-20 minutes.

[0006] Wherein, the process conditions for the second dry oxygen oxidation treatment satisfy at least one of the following: The oxygen flow rate for the second dry oxygen is 8000 sccm~12000 sccm; The second oxidation time with dry oxygen is 10 min to 20 min.

[0007] Wherein, the process conditions for the second wet oxygen oxidation treatment satisfy at least one of the following: The oxygen flow rate for the second humidified oxygen supply is 4000 sccm~6000 sccm; The water vapor flow rate of the second humid oxygen is 1200 sccm~1800 sccm; The second oxidation time with wet oxygen is 5 to 8 minutes.

[0008] The step of performing a first wet oxygen oxidation treatment on the substrate includes: Nitrogen and water vapor are introduced, and the nitrogen flow rate of the first wet oxygen is gradually increased at a first rate of 450 sccm / min to 550 sccm / min. The step of performing a second wet oxygen oxidation treatment on the substrate includes: Nitrogen and water vapor are introduced, and the nitrogen flow rate of the second humid oxygen is gradually increased at a second rate of 450 sccm / min to 550 sccm / min.

[0009] Wherein, the first dry oxygen oxidation treatment, the first wet oxygen oxidation treatment, the second dry oxygen oxidation treatment, and the second wet oxygen oxidation treatment all satisfy at least one of the following: The oxidation temperature of the second boron diffuser is 850℃~950℃; The process pressure for the second boron expansion is 850 Pa to 950 Pa. The total processing time for the second boron diffusion process is 100-120 minutes.

[0010] The second boron expansion process also includes: Before performing the first dry oxygen oxidation treatment, the working furnace is pretreated, which includes: introducing nitrogen gas and heating to the oxidation temperature of the first dry oxygen. After the second dry oxygen oxidation treatment, the working furnace is post-treated, which includes: introducing nitrogen gas and cooling to a cooling temperature ≤720℃.

[0011] The second aspect of this application provides a solar cell comprising a substrate having a P-type emitter, the substrate being processed using the boron diffusion method for the solar cell provided in the first aspect of this application.

[0012] A third aspect of this application provides a photovoltaic module, which includes a solar cell as provided in the second aspect of this application.

[0013] The solar cell, its boron diffusion method, and photovoltaic module provided in this application design the oxidation stage of the secondary boron diffusion process into a four-stage alternating dry and wet structure consisting of a first dry oxygen, a first wet oxygen, a second dry oxygen, and a second wet oxygen. This is carried out synchronously with the entire boron atom diffusion process, achieving step-by-step controllable diffusion of boron atoms and multi-layer synergistic construction of silicon dioxide and borosilicate glass layers. This improves the synergy between oxidation and boron diffusion, fundamentally solving the core problem of poor synergy between oxidation and diffusion in single-stage processes. Furthermore, the segmented oxygen control is gentler, reducing the overall thermal budget, minimizing thermal damage to the substrate at high temperatures, and improving the substrate surface quality. This is beneficial for subsequent LPCVD, passivation, and other processes, improving the performance of the P-type emitter and the back-side passivation effect, thereby increasing the conversion efficiency and yield of the solar cell. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments of this application will be described below.

[0015] Figure 1 This is a schematic diagram of the structure of a solar cell provided in one embodiment of this application.

[0016] Figure 2 This is a schematic flowchart of a boron expansion method for a solar cell provided in one embodiment of this application.

[0017] Figure 3 This is a schematic flowchart of a boron expansion method for a solar cell provided in another embodiment of this application.

[0018] Figure 4 This is a schematic flowchart of a boron expansion method for a solar cell provided in another embodiment of this application.

[0019] Figure 5 This is a schematic flowchart of a boron expansion method for a solar cell provided in another embodiment of this application.

[0020] Figure 6 This is a schematic flowchart of a boron expansion method for a solar cell provided in yet another embodiment of this application.

[0021] Figure 7 A schematic diagram of the structure of a solar cell provided for another embodiment of this application.

[0022] Labeling explanation: Solar cell 1, substrate 11, P-type emitter 111, silicon dioxide layer 12, borosilicate glass layer 13, passivation layer 14, antireflection layer 15, tunneling oxide layer 16, n-type polycrystalline silicon layer 17, protective layer 18. Detailed Implementation

[0023] The following are preferred embodiments of this application. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

[0024] Before introducing the technical solution of this application, let's go over the technical issues in related technologies in detail.

[0025] In the boron expansion process of related solar cells, single-stage dry oxidation and single-stage wet oxidation processes are often used. However, due to the limitations of the single-stage oxidation logic and the poor synergy between oxidation and doping, this not only leads to insufficient doping uniformity and junction depth control precision in the secondary boron expansion process, but also directly affects the processing effect of subsequent core processes such as borosilicate glass layer removal, alkaline polishing, and low-pressure chemical vapor deposition (LPCVD). This results in a decrease in the performance of the front emitter of the solar cell and damage to the back passivation effect, ultimately affecting the cell conversion efficiency and mass production yield. The specific disadvantages are as follows: 1. Uneven diffusion of boron atoms increases the difficulty of etching in the removal of borosilicate glass layer and alkaline polishing process: The single-stage wet oxygen oxidation rate is fast and the reaction is concentrated, which has poor synergy with boron diffusion. This easily leads to excessive longitudinal diffusion of boron atoms on the silicon wafer surface and uneven lateral distribution, resulting in junction depth consistency <85% and sheet resistance deviation within / between wafers exceeding ±5%. At the same time, the generated borosilicate glass layer has uneven thickness and large differences in density. In the subsequent removal of borosilicate glass layer and alkaline polishing process, it is necessary to frequently adjust the alkaline solution concentration and etching time, which easily leads to borosilicate glass layer etching residue or over-etching of silicon wafer. Residue will cause poor adhesion of subsequent LPCVD thin films, and over-etching will damage the surface morphology of silicon wafer and reduce substrate flatness.

[0026] 2. Numerous defects at the SiO2 / Si interface reduce substrate quality in subsequent processes: The one-time atmosphere switch from dry oxygen to wet oxygen in a single stage causes stress concentration at the SiO2 / Si interface due to sudden changes in oxygen partial pressure and water vapor concentration in the furnace, resulting in a large number of dangling bonds and lattice defects. Secondary borosilicate glass layer removal is a direct pre-process for removing the borosilicate glass layer and alkaline polishing. Interface defects will remain on the silicon substrate along with the borosilicate glass layer. Even after alkaline polishing, the cleanliness of the silicon substrate will still decrease. The bonding force between the tunneling oxide layer deposited by subsequent LPCVD and the silicon substrate will be poor, the passivation performance will be greatly reduced, and the carrier recombination probability will be significantly increased.

[0027] 3. Excessive thermal budget affects multi-process adaptability: To compensate for the uniformity defects of single-stage processes, existing technologies require extending the wet oxidation time or increasing the diffusion temperature, resulting in excessively high thermal budgets for the secondary boron expansion process. High-temperature and long-term processing can cause lattice damage to N-type silicon wafers and cause non-directional shift of the basic doped layer formed by the primary boron expansion. This not only increases the risk of warping of thin silicon wafers with a thickness of ≤130μm, but also leads to a decrease in the matching degree between the back surface field and the junction region of the front emitter in the subsequent phosphorus expansion process, resulting in a reduction in the carrier separation efficiency of the battery.

[0028] 4. Poor performance of the borosilicate glass layer drags down the yield of subsequent processes: The borosilicate glass layer generated by single-stage wet oxygen has many internal pores and easily adsorbs impurities in the furnace. During the removal of the borosilicate glass layer and alkaline polishing process, the etching solution easily seeps into the pores and forms micro-corrosion pits on the silicon wafer surface. Even if etching is completed, there are still a large number of micro-defects in the silicon substrate. This uneven substrate will lead to problems such as pinholes and uneven film thickness in the tunneling oxide layer and polycrystalline silicon layer deposited by subsequent LPCVD. The yield of the LPCVD process will decrease by more than 0.3%, and the uniformity of the film layer in the subsequent atomic layer deposition (ALD) process and coating process will also be affected in a chain reaction. The overall yield of the film layer-related processes of the entire production line will decrease by more than 0.5%.

[0029] 5. Significant impact from changing the atmosphere inside the furnace, resulting in poor equipment wear and process stability: A one-time switch from dry oxygen to wet oxygen in a single stage causes the water vapor concentration inside the furnace to rise instantly from 0 to the target value. Sudden changes in temperature, humidity, and gas partial pressure can cause severe corrosion to the quartz tubes and quartz boats in the high-temperature diffusion furnace, while also accelerating the aging of temperature and gas control components inside the furnace. Corrosion of quartz components will generate quartz dust, which will contaminate the silicon wafer surface, further reducing the yield of the process. In addition, the high frequency of equipment maintenance will lead to a short service life of quartz devices. As secondary boron diffusion is an intermediate process in the production line, equipment downtime will directly cause the production capacity of the preceding and following processes to stagnate, resulting in an overall production line capacity stability of <94%.

[0030] In view of this, in order to solve the above problems, please refer to the following: Figures 1-2 This embodiment provides a boron expansion method for a solar cell 1, the boron expansion method comprising: S100 provides a substrate 11 that has undergone a first boron diffusion process.

[0031] The substrate 11 serves multiple functions, including light absorption, carrier generation, carrier transport, and mechanical support, supporting the entire thin film layer and electrodes of the battery. Optionally, the substrate 11 is a silicon wafer. More preferably, the substrate 11 is an n-type silicon wafer.

[0032] S200, the substrate 11 undergoes a second boron expansion process. The second boron expansion process includes: S210, the substrate 11 is subjected to a first dry oxygen oxidation treatment to form a silicon dioxide layer 12 disposed on the substrate 11; The first dry oxidation process is used to form a dense initial silicon dioxide layer 12 on the silicon wafer surface, defining the diffusion boundary of boron atoms.

[0033] Furthermore, the process conditions for the first dry oxygen oxidation treatment satisfy at least one of the following: The oxygen flow rate for the first dry oxygen is 8000 sccm to 12000 sccm. For example, it can be 8000 sccm, 8500 sccm, 9000 sccm, 9500 sccm, 10000 sccm, 10500 sccm, 11000 sccm, 11500 sccm, or 12000 sccm.

[0034] If the oxygen flow rate of the first dry oxygen is less than 8000 sccm, the oxygen flow rate of the first dry oxygen is too low, which easily leads to the silicon dioxide layer 12 being too thin, discontinuous, and having poor density, resulting in a significant increase in interface defects. Furthermore, during subsequent wet oxygen oxidation, boron atoms are more likely to directly impact the silicon substrate, leading to severe and uneven boron diffusion distribution.

[0035] If the oxygen flow rate of the first dry oxygen is greater than 12000 sccm, the excessive oxygen flow rate of the first dry oxygen can easily lead to over-oxidation, increased interfacial stress, and increased risk of warping and microcracks.

[0036] Therefore, this embodiment limits the oxygen flow rate of the first dry oxygen to 8000 sccm~12000 sccm, which has a moderate oxidation rate, few interface defects, and minimal damage to the substrate 11. This allows for the formation of a dense, uniform, thin, and high-quality initial silicon dioxide layer 12 interface, laying a good interface foundation for subsequent boron diffusion.

[0037] The oxidation time for the first dry oxygen is 8 to 15 minutes, for example, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, or 15 minutes.

[0038] If the oxidation time of the first dry oxygen is less than 8 minutes, the oxidation time of the first dry oxygen is too short, which will easily lead to the silicon dioxide layer 12 being too thin, discontinuous, and having poor density, resulting in a significant increase in interface defects. Furthermore, during subsequent wet oxygen oxidation, boron atoms are more likely to directly impact the silicon substrate, leading to severe and uneven boron diffusion distribution.

[0039] If the oxidation time of the first dry oxygen is greater than 15 minutes, the oxidation time of the first dry oxygen is too long, which can easily lead to an excessively thick silicon dioxide layer 12, a sharp increase in thermal budget, and easy thermal damage to the substrate 11. The subsequent growth of the borosilicate glass layer 13 will have poor matching, which will increase the difficulty of the borosilicate glass layer 13 and alkaline polishing.

[0040] Therefore, this embodiment limits the oxidation time of the first dry oxygen to 8 min to 15 min, which can form a dense, uniform, thin and high-quality initial silica layer 12 interface, laying a good interface foundation for subsequent boron diffusion.

[0041] For example, high-purity oxygen with a purity ≥ 99.999% is introduced to perform the first dry oxygen oxidation, forming a dense initial silicon dioxide layer 12 on the silicon wafer surface, which defines the diffusion boundary of boron atoms.

[0042] S220, the substrate 11 is subjected to a first wet oxidation treatment to form a borosilicate glass layer 13 disposed on the side of the silicon dioxide layer 12 away from the substrate 11; The first wet oxygen oxidation treatment drives the initial controllable diffusion of boron atoms, initially growing a silicon dioxide layer 12 and forming a basic borosilicate glass layer 13.

[0043] Furthermore, the process conditions for the oxidation treatment using the first wet oxygen satisfy at least one of the following: The oxygen flow rate for the first humidified oxygen supply is 4000 sccm to 6000 sccm, for example, 4000 sccm, 4500 sccm, 5000 sccm, 5500 sccm, or 6000 sccm.

[0044] The water vapor flow rate of the first humidified oxygen is 1500 sccm to 2000 sccm, specifically for example, 1500 sccm, 1550 sccm, 1600 sccm, 1650 sccm, 1700 sccm, 1750 sccm, 1800 sccm, 1850 sccm, 1900 sccm, 1950 sccm, or 2000 sccm, etc.

[0045] If the oxygen flow rate of the first wet oxygen is less than 4000 sccm or the water vapor flow rate of the first wet oxygen is less than 1500 sccm, the oxygen flow rate and water vapor flow rate of the first wet oxygen are too low, which can easily lead to insufficient growth of the borosilicate glass layer 13, thin and uneven thickness, and insufficient boron diffusion, resulting in poor uniformity of the P-type emitter 111 and reduced performance of the P-type emitter 111.

[0046] If the oxygen flow rate of the first wet oxygen is greater than 6000 sccm or the water vapor flow rate of the first wet oxygen is greater than 2000 sccm, the excessive oxygen flow rate or water vapor flow rate of the first wet oxygen will easily lead to an excessively thick borosilicate glass layer 13, severe local accumulation, uneven boron distribution, increased difficulty in removing the borosilicate glass layer 13, and easy over-polishing with alkali, damaging the silicon surface.

[0047] Therefore, in this embodiment, the oxygen flow rate of the first wet oxygen is limited to 4000 sccm to 6000 sccm and the water vapor flow rate of the first wet oxygen is limited to 1500 sccm to 2000 sccm. The ratio of oxygen to water vapor is appropriate, and a uniform borosilicate glass layer 13 is grown at a moderate rate. The boron diffusion is smooth and the distribution is uniform, which makes subsequent etching difficult.

[0048] The oxidation time for the first wet oxygen is 10 min to 20 min, specifically for 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, or 20 min, etc.

[0049] Therefore, this embodiment can limit the oxidation time of the first wet oxygen to a reasonable range, avoid excessive oxidation, reduce interface defects, and obtain a high-quality borosilicate glass layer 13.

[0050] Please refer to Figure 3 Furthermore, the step of performing a first wet oxygen oxidation treatment on the substrate 11 includes: S201, nitrogen and water vapor are introduced, and the nitrogen flow rate of the first wet oxygen is gradually increased at a first rate of 450 sccm / min to 550 sccm / min.

[0051] The first speed can be specifically exemplified as 450 sccm / min, or 460 sccm / min, or 470 sccm / min, or 480 sccm / min, or 490 sccm / min, or 500 sccm / min, or 510 sccm / min, or 520 sccm / min, or 530 sccm / min, or 540 sccm / min, or 550 sccm / min, etc.

[0052] This embodiment gradually increases the nitrogen flow rate to ensure a smooth transition of the furnace atmosphere, avoiding fluctuations in the oxidation rate caused by sudden changes in airflow. This improves the growth uniformity of the borosilicate glass layer 13, further reduces uneven boron distribution, minimizes interface defects, and reduces thermal and mechanical shocks to the substrate 11, thus protecting the integrity of the substrate 11.

[0053] Alternatively, the oxygen flow rate can be reduced before introducing nitrogen and water vapor.

[0054] Alternatively, the oxygen flow rate can be reduced from 8000 sccm~12000 sccm to 4000 sccm~6000 sccm before nitrogen and water vapor are introduced.

[0055] For example, first reduce the oxygen flow rate to 4000 sccm~6000 sccm, and then slowly open the nitrogen-carrying water vapor passage, gradually increasing the flow rate from 0 to 1500 sccm~2000 sccm.

[0056] Therefore, in this embodiment, a low flow rate of pure oxygen is introduced, and high-purity nitrogen carrying high-purity water vapor is used to perform mild humid oxygen oxidation, which drives the initial controllable diffusion of boron atoms, initially growing a silicon dioxide layer 12 and forming a basic borosilicate glass layer 13.

[0057] S230, the substrate 11 is subjected to a second dry oxygen oxidation treatment to repair the silicon dioxide layer 12; The second dry oxygen oxidation treatment is used to densify and repair the 12-layer silica layer generated by the first dry oxygen oxidation treatment, eliminate interface defects, and regulate the diffusion rate of boron atoms.

[0058] Furthermore, the process conditions for the second dry oxygen oxidation treatment satisfy at least one of the following: The oxygen flow rate for the second dry oxygen is 8000 sccm to 12000 sccm, specifically for example, 8000 sccm, 8500 sccm, 9000 sccm, 9500 sccm, 10000 sccm, 10500 sccm, 11000 sccm, 11500 sccm, or 12000 sccm, etc.

[0059] If the oxygen flow rate of the second dry oxygen is less than 8000 sccm, the oxygen flow rate of the second dry oxygen is too low, which can easily lead to insufficient repair of the silicon dioxide layer 12, high interface defects, reduced performance of the P-type emitter 111, non-dense interface, and poor back-side passivation effect.

[0060] If the oxygen flow rate of the second dry oxygen is greater than 12000 sccm, the excessive oxygen flow rate of the second dry oxygen will easily lead to excessive dry oxygen oxidation, resulting in an excessively thick interface layer and high stress, which will damage the uniformity of the borosilicate glass layer 13 and increase the difficulty of subsequent processes.

[0061] Therefore, this embodiment limits the oxygen flow rate of the second dry oxygen to 8000 sccm~12000 sccm to achieve gentle repair of the interface of the silicon dioxide layer 12, fill dangling bonds and pores, significantly reduce interface defects, and improve the quality of subsequent passivation and LPCVD processes.

[0062] The second oxidation time with dry oxygen is 10 min to 20 min, for example, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, or 20 min, etc.

[0063] If the oxidation time of the second dry oxygen is less than 10 minutes, the oxidation time of the second dry oxygen is too short, which can easily lead to insufficient repair of the silicon dioxide layer 12 and high interface defects.

[0064] If the second dry oxygen oxidation time is greater than 20 minutes, the second dry oxygen oxidation time is too long, which can easily lead to excessive dry oxygen oxidation, resulting in an excessively thick interface layer, high stress, increased thermal budget, increased risk of heat damage to substrate 11, easy damage to the uniformity of borosilicate glass layer 13, and increased difficulty of subsequent processes.

[0065] Therefore, this embodiment limits the oxidation time of the second dry oxygen to 10 min to 20 min, which can achieve gentle repair of the interface of the silicon dioxide layer 12.

[0066] For example, first shut off the passage for high-purity nitrogen to carry high-purity water vapor, and then increase the oxygen flow rate to 8000 sccm~12000 sccm.

[0067] High-purity oxygen is introduced to densify and repair the 12-layer silica layer generated by the first dry oxygen oxidation treatment, eliminate interface defects, and regulate the diffusion rate of boron atoms.

[0068] S240, the substrate 11 is subjected to a second wet oxidation treatment to make the thickness uniformity of the borosilicate glass layer 13 ≥95%.

[0069] The second wet oxidation process is used to complete the fine-grained control of boron atom doping, uniformly grow the silicon dioxide layer 12 and form a borosilicate glass layer 13 with moderate density and uniform thickness, so as to meet the requirements of subsequent removal of the borosilicate glass layer 13 and alkaline polishing etching process.

[0070] The thickness uniformity of the borosilicate glass layer 13 can be specifically exemplified by 95%, 96%, 97%, 98%, or 99%, etc.

[0071] Furthermore, the process conditions for the second wet oxidation treatment satisfy at least one of the following: The oxygen flow rate for the second humidified oxygen supply is 4000 sccm to 6000 sccm, for example, 4000 sccm, 4500 sccm, 5000 sccm, 5500 sccm, or 6000 sccm.

[0072] The water vapor flow rate of the second humid oxygen is 1200 sccm to 1800 sccm, specifically for example, 1200 sccm, or 1250 sccm, or 1300 sccm, or 1350 sccm, or 1400 sccm, or 1450 sccm, or 1500 sccm, or 1550 sccm, or 1600 sccm, or 1650 sccm, or 1700 sccm, or 1750 sccm, or 1800 sccm, etc.

[0073] If the oxygen flow rate of the second wet oxygen is less than 4000 sccm or the water vapor flow rate of the second wet oxygen is less than 1200 sccm, the oxygen flow rate and water vapor flow rate of the second wet oxygen will be too low, which will easily lead to the thickness uniformity of the borosilicate glass layer 13 not reaching 95% and the thickness fluctuation being large. In the subsequent processes of removing the borosilicate glass layer 13 and alkaline polishing, uneven etching is likely to occur, resulting in color difference and local over-etching, which will lead to poor uniformity of the P-type emitter 111 and a decrease in the conversion efficiency of the solar cell 1.

[0074] If the oxygen flow rate of the second wet oxygen is greater than 6000 sccm or the water vapor flow rate of the second wet oxygen is greater than 1800 sccm, then the excessive oxygen flow rate and water vapor flow rate of the second wet oxygen will easily lead to excessive growth of the borosilicate glass layer 13, excessive thickness, and decreased uniformity, which will greatly increase the etching difficulty and affect the yield of the solar cell 1.

[0075] Therefore, in this embodiment, the oxygen flow rate of the second wet oxygen is limited to 4000 sccm to 6000 sccm and the water vapor flow rate of the second wet oxygen is limited to 1200 sccm to 1800 sccm. The borosilicate glass layer 13 is precisely fine-tuned to make the thickness uniformity of the borosilicate glass layer 13 ≥ 95%, reducing the etching difficulty, improving the uniformity of the P-type emitter 111, and improving the conversion efficiency of the solar cell 1.

[0076] The second oxidation time with wet oxygen is 5 to 8 minutes, for example, 5 minutes, 6 minutes, 7 minutes, or 8 minutes.

[0077] Therefore, this embodiment can limit the oxidation time of the second wet oxygen to a reasonable range, precisely fine-tune the borosilicate glass layer 13, make the thickness uniformity of the borosilicate glass layer 13 ≥95%, reduce the etching difficulty, improve the uniformity of the P-type emitter 111, and improve the conversion efficiency of the solar cell 1.

[0078] Please refer to Figure 4 Furthermore, the step of performing a second wet oxygen oxidation treatment on the substrate 11 includes: S202, nitrogen and water vapor are introduced, and the nitrogen flow rate of the second humid oxygen is gradually increased at a second rate of 450 sccm / min to 550 sccm / min.

[0079] The second rate can be specifically exemplified as 450 sccm / min, or 460 sccm / min, or 470 sccm / min, or 480 sccm / min, or 490 sccm / min, or 500 sccm / min, or 510 sccm / min, or 520 sccm / min, or 530 sccm / min, or 540 sccm / min, or 550 sccm / min, etc.

[0080] This embodiment gradually increases the nitrogen flow rate to ensure a smooth transition of the furnace atmosphere, avoiding fluctuations in the oxidation rate caused by sudden changes in airflow. This improves the growth uniformity of the borosilicate glass layer 13, further reduces uneven boron distribution, minimizes interface defects, and reduces thermal and mechanical shocks to the substrate 11, thus protecting the integrity of the substrate 11.

[0081] Alternatively, the oxygen flow rate can be reduced before introducing nitrogen and water vapor.

[0082] Alternatively, the oxygen flow rate can be reduced from 8000 sccm~12000 sccm to 4000 sccm~6000 sccm before nitrogen and water vapor are introduced.

[0083] For example, first reduce the oxygen flow rate to 4000 sccm~6000 sccm, then slowly open the nitrogen-carrying water vapor passage, gradually increasing the flow rate from 0 to 1200 sccm~1800 sccm.

[0084] Therefore, in this embodiment, a lower flow rate of pure oxygen is introduced, along with high-purity nitrogen carrying high-purity water vapor, to perform low-rate wet oxygen oxidation, thereby completing the fine-tuning of boron atom doping, uniformly growing the silicon dioxide layer 12, and forming a borosilicate glass layer 13 with moderate density and uniform thickness, which meets the etching requirements of subsequent removal of the borosilicate glass layer 13 and alkaline polishing process.

[0085] In the second boron diffusion process, the first dry oxygen oxidation treatment, the first wet oxygen oxidation treatment, the second dry oxygen oxidation treatment, and the second wet oxygen oxidation treatment are all carried out simultaneously with boron diffusion.

[0086] Furthermore, during the second boron diffusion process, the first dry oxygen oxidation treatment, the first wet oxygen oxidation treatment, the second dry oxygen oxidation treatment, and the second wet oxygen oxidation treatment all satisfy at least one of the following: The oxidation temperature of the second boron diffuser is 850℃~950℃, specifically for example, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, or 950℃, etc.

[0087] If the oxidation temperature of the second borosilicate glass layer is less than 850°C, the oxidation temperature of the second borosilicate glass layer is too low, which can easily lead to insufficient oxidation and thus result in poor film quality between the silicon dioxide layer 12 and the borosilicate glass layer 13.

[0088] If the oxidation temperature of the second boron expansion is greater than 950℃, the oxidation temperature of the second boron expansion process is too high, the thermal budget is seriously exceeded, and the risk of substrate 11 being damaged, warped, or cracked due to high temperature is increased.

[0089] Therefore, this embodiment limits the oxidation temperature of the second borosilicate glass layer to 850°C to 950°C, which is in the low temperature range. This ensures that the oxidation temperature produces a high-quality silicon dioxide layer 12 and borosilicate glass layer 13, avoids high-temperature damage to the substrate 11, and significantly reduces the overall thermal budget.

[0090] The process pressure for the second boron diffusion is 850Pa~950Pa, specifically for example, 850Pa, 860Pa, 870Pa, 880Pa, 890Pa, 900Pa, 910Pa, 920Pa, 930Pa, 940Pa, or 950Pa, etc.

[0091] If the process pressure of the second boron diffusion process is less than 850 Pa, the pressure of the second boron diffusion process is too low, which can easily lead to insufficient boron diffusion and a decrease in the performance of the P-type emitter 111.

[0092] If the process pressure of the second boron expansion is greater than 950 Pa, the excessive pressure of the second boron expansion process will easily lead to an increase in interface defects, a decrease in passivation effect, and consequently a significant decrease in the conversion efficiency and yield of solar cell 1.

[0093] Therefore, in this embodiment, the process pressure of the second boron diffusion is limited to 850 Pa to 950 Pa, which is in the low-pressure range. This makes the oxidation more uniform, the atmosphere more stable, improves the uniformity of boron diffusion, reduces interface defects, and thus improves the conversion efficiency and yield of solar cell 1.

[0094] The total processing time for the second boron diffusion process is 100-120 minutes, for example, 100 minutes, 105 minutes, 110 minutes, 115 minutes, or 120 minutes.

[0095] This implementation method can control the total process time within a reasonable range, balancing efficiency and quality, improving the base quality without sacrificing production capacity, and enhancing the effect of subsequent processes.

[0096] S300, forming a P-type emitter 111 disposed on the substrate 11.

[0097] The P-type emitter 111 is formed through the synergistic effect of a first boron diffusion process and a second boron diffusion process. The first boron diffusion process is used to provide a boron source, pre-deposit, and establish a diffusion base, while the second boron diffusion process is used to advance the junction depth, optimize the doping distribution, and ultimately form a P-type emitter 111 with sufficient depth, moderate doping, and excellent performance.

[0098] In summary, the boron diffusion method for solar cell 1 provided in this embodiment designs the oxidation stage of the secondary boron diffusion process into a four-stage alternating dry and wet structure consisting of a first dry oxygen, a first wet oxygen, a second dry oxygen, and a second wet oxygen. This is synchronized with the entire boron atom diffusion process, achieving step-by-step controllable diffusion of boron atoms and multi-layer synergistic construction of the silicon dioxide layer 12 and the borosilicate glass layer 13. This improves the synergy between oxidation and boron diffusion, fundamentally solving the core problem of poor synergy between oxidation and diffusion in single-stage processes. Furthermore, the segmented oxygen control is gentler, reducing the overall thermal budget, minimizing thermal damage to the substrate 11 at high temperatures, and improving the surface quality of the substrate 11. This is beneficial for subsequent LPCVD, passivation, and other processes, improving the performance of the P-type emitter 111 and the back-side passivation effect, thereby increasing the conversion efficiency and yield of solar cell 1.

[0099] Please refer to Figure 5 and Figure 6 In one embodiment, the second boron diffusion process further includes: S250, before performing the first dry oxygen oxidation treatment, the working furnace is pretreated, the pretreatment including: introducing nitrogen gas and heating to the oxidation temperature of the first dry oxygen.

[0100] The working furnace is used to prepare solar cells 1.

[0101] For example, the silicon wafers processed by the first boron expansion process are loaded into a quartz boat and sent into a working furnace. Then, the furnace door is closed, a vacuum is drawn, and high-purity nitrogen gas is introduced. The nitrogen purity is ≥99.999%, and the nitrogen flow rate is 18000 sccm~22000 sccm. The air in the furnace is then replaced for 3 min~5 min. Next, the temperature is increased to the oxidation temperature of the second boron expansion process at a rate of >15℃ / min and stabilized for 2 min~5 min, thus completing the preliminary preparation for the second boron expansion process.

[0102] This embodiment pre-treats the working furnace to ensure that the temperature and atmosphere inside the working furnace are stable before starting oxidation, thus avoiding uneven oxidation caused by initial temperature fluctuations.

[0103] S260, after the second dry oxygen oxidation treatment, the working furnace is post-treated, the post-treatment including: introducing nitrogen gas and cooling to a cooling temperature ≤720℃.

[0104] Specific examples of cooling temperatures include 720℃, 700℃, 650℃, 600℃, 550℃, and 500℃.

[0105] For example, close all reaction gas passages, introduce high-purity nitrogen at a flow rate of 18000 sccm~22000 sccm, purge and cool the working furnace, and after the temperature inside the working furnace drops below 720°C, remove the silicon wafer to complete the secondary borosilicate glass layer removal process and send it directly to the subsequent borosilicate glass layer removal 13 and alkaline polishing process without additional surface treatment.

[0106] This embodiment reduces thermal stress and warping / damage to the substrate 11 by post-processing the working furnace and slowly cooling it to ≤720°C, thereby improving the yield of the solar cell 1.

[0107] Optionally, during the boron diffusion process, a nitrogen atmosphere is used for protection throughout to prevent accidental oxidation and contamination of the substrate 11, thereby improving interface quality and substrate stability.

[0108] In summary, the core parameters of the boron expansion method for solar cell 1 provided in this application are designed around "low temperature, short time, low flow rate, and gentle switching". While ensuring the doping effect and oxide layer quality of the second boron expansion process, the thermal budget of the process is significantly reduced. At the same time, it matches the process requirements of subsequent removal of borosilicate glass layer 13 and alkaline polishing and LPCVD. The entire process is in a low-pressure environment and is suitable for mass production processes.

[0109] Please refer to this as well. Figures 1-7 This application also provides a solar cell 1, which includes a substrate 11 having a P-type emitter 111, and the substrate 11 is processed using the boron diffusion method of the solar cell 1 provided in this application as described above.

[0110] Optionally, the solar cell 1 is a TOPCon cell.

[0111] The four-stage dry-wet-oxygen alternation process provided in this application is integrated into the high-temperature diffusion stage of the secondary boron diffusion process of solar cell 1, and is carried out simultaneously with boron atom diffusion.

[0112] Alternatively, please refer to Figure 7 The solar cell 1 includes a substrate 11 and a P-type emitter 111 disposed on the front side of the substrate 11.

[0113] Alternatively, the solar cell 1 may further include a passivation layer 14 and an antireflection layer 15 disposed sequentially on the front side of the substrate 11.

[0114] Alternatively, the solar cell 1 may further include a tunneling oxide layer 16, an n-type polycrystalline silicon layer 17, and a protective layer 18 disposed sequentially on the back side of the substrate 11.

[0115] The process sequence of solar cell 1 is as follows: texturing, primary boron diffusion, secondary boron diffusion, removal of borosilicate glass layer 13 and alkaline polishing, LPCVD, phosphorus diffusion, cleaning, ALD, coating, and printing.

[0116] Specifically, firstly, a pyramid-shaped textured surface is formed on the silicon wafer surface to complete the texturing process.

[0117] Then, the silicon wafer is subjected to a first boron diffusion process to form a lightly doped P-type emitter 111 on the front side of the silicon wafer.

[0118] Next, the silicon wafer is subjected to the second boron diffusion process as provided in this application to form a complete P-type emitter 111.

[0119] Continue by removing the borosilicate glass layer 13 and polishing the back side of the silicon wafer with an alkaline solution.

[0120] Then, using LPCVD (low-pressure chemical vapor deposition) process, a tunneling oxide layer 16 and an intrinsic polycrystalline silicon layer are deposited on the back side.

[0121] Next, phosphorus doping is performed on the intrinsic polycrystalline silicon layer to form an n-type polycrystalline silicon layer 17.

[0122] Next, the silicon wafer surface is thoroughly cleaned to remove organic matter, metal ions, and particles.

[0123] Subsequently, a passivation layer 14 is deposited using an ALD (atomic layer deposition) process. For example, the passivation layer 14 is an aluminum oxide layer.

[0124] Then, an antireflection layer 15 and a protective layer 18 are deposited using a coating process. For example, the antireflection layer 15 and the protective layer 18 are silicon nitride layers.

[0125] Finally, the metal electrodes are printed.

[0126] In summary, the solar cell 1 provided in this application, by adopting the boron diffusion method of the solar cell 1 provided above, designs the oxidation stage of the secondary boron diffusion process as a four-stage alternating dry and wet structure of first dry oxygen, first wet oxygen, second dry oxygen, and second wet oxygen, which is carried out synchronously with the entire boron atom diffusion process. This achieves the step-by-step controllable diffusion of boron atoms and the multi-layer synergistic construction of silicon dioxide layer 12 and borosilicate glass layer 13, improving the synergy between oxidation and boron diffusion, fundamentally solving the core problem of poor synergy between oxidation and diffusion in single-stage processes. Furthermore, the segmented oxygen control is gentler, reducing the overall thermal budget, reducing thermal damage to substrate 11 at high temperatures, improving the surface quality of substrate 11, which is beneficial for subsequent LPCVD, passivation and other processes, improving the performance of P-type emitter 111 and the back passivation effect, thereby improving the conversion efficiency and yield of solar cell 1.

[0127] This application also provides a photovoltaic module, which includes the solar cell provided above in this application.

[0128] The photovoltaic module provided in this application, by adopting the solar cell provided above, uses a boron diffusion method for the solar cell. The oxidation process of the secondary boron diffusion step is designed as a four-stage alternating dry and wet structure consisting of a first dry oxygen, a first wet oxygen, a second dry oxygen, and a second wet oxygen. This is carried out synchronously with the boron atom diffusion process, achieving step-by-step controllable diffusion of boron atoms and multi-layer synergistic construction of silicon dioxide and borosilicate glass layers. This improves the synergy between oxidation and boron diffusion, fundamentally solving the core problem of poor synergy between oxidation and diffusion in single-stage processes. Furthermore, the segmented oxygen control is gentler, reducing the overall thermal budget, minimizing thermal damage to the substrate at high temperatures, and improving the substrate surface quality. This is beneficial for subsequent LPCVD, passivation, and other processes, improving the performance of the P-type emitter and the back passivation effect, thereby increasing the conversion efficiency and yield of the solar cell.

[0129] To make the objectives and advantages of this application clearer, the effects of the boron expansion method for solar cells of this application will be further explained in detail below with reference to specific embodiments 1-2.

[0130] Example 1: This method is applicable to the mass production process of TOPCon batteries, with the expected goals of high sheet resistance uniformity and high process stability. It aims to reduce the difficulty of subsequent process adjustments for removing the borosilicate glass layer and alkaline polishing, thereby improving the overall mass production yield. The specific implementation steps are as follows: Pre-treatment of working furnace: The silicon wafer after the first boron expansion is loaded into a quartz boat and sent into a high-temperature diffusion furnace. After vacuuming, high-purity nitrogen is introduced at a flow rate of 20,000 sccm for 4 minutes to replace the nitrogen. The pressure inside the furnace tube is maintained at 900 Pa. The temperature is raised to 900℃ and stabilized for 5 minutes before entering the second boron expansion high-temperature diffusion and oxidation stage.

[0131] The first dry oxygen oxidation process involves an oxygen temperature of 900℃, a process pressure of 900pa, an oxygen flow rate of 10000sccm, and a duration of 8 minutes. This process forms an initial layer of dense silicon dioxide with a thickness of approximately 18nm on the silicon wafer surface, defining the diffusion boundary of boron atoms.

[0132] First wet oxygen oxidation treatment: oxygen temperature is 900℃, process pressure is 900pa, atmosphere is gently switched, oxygen flow rate is first reduced to 5000sccm, then nitrogen carrying water vapor channel is opened at a rate of 500sccm / min and flow rate is increased to 1800sccm, pure water purity is 5N and water temperature is 80℃, last for 15min, boron atoms diffuse in a preliminary controllable manner, and the thickness of the silicon dioxide layer increases to about 45nm, forming the basic borosilicate glass layer.

[0133] The second dry oxygen oxidation treatment: the oxygen temperature is 900℃, low pressure, and the atmosphere is switched gently. First, the nitrogen-carrying water vapor passage is closed at a rate of 500 sccm / min, and then the oxygen flow rate is restored to 10000 sccm for 12 minutes to densify and repair the silica layer and eliminate interface defects.

[0134] The second wet oxygen oxidation treatment: the oxygen temperature is 900℃, the pressure is low, the atmosphere is gently switched, the oxygen flow rate is first reduced to 5000 sccm, and then the nitrogen carrying water vapor passage is opened at a rate of 500 sccm / min to 1500 sccm, the oxygen flow rate is 5000 sccm, the nitrogen carrying water vapor flow rate is 1500 sccm, the pure water purity is 5N, the water temperature is 80℃, and it is continued for 8 minutes. Boron atoms are finely doped, and the final thickness of the silicon dioxide layer is about 85nm, forming a borosilicate glass layer with uniform thickness and moderate density. The thickness uniformity of the borosilicate glass layer is ≥95%.

[0135] Post-processing of the working furnace: High-purity nitrogen is purged at a flow rate of 20,000 sccm to cool down to below 720°C, and the silicon wafer is removed to complete the secondary boron expansion process.

[0136] Subsequently, the material was sent to a process to remove the borosilicate glass layer and perform alkaline polishing. The concentration of the alkaline solution used for etching was 1.5%, and the etching time was 4 minutes. There was no residue and no over-etching.

[0137] Example 2: This approach is suitable for the R&D and pilot-scale processes of high-efficiency TOPCon cells. The expected goals are low junction depth and high interface passivation performance, minimizing the secondary boron heat expansion budget, and improving the passivation effect of subsequent LPCVD tunneling oxide layers. The specific implementation steps are as follows: Pretreatment of working furnace: The silicon wafer after the first boron expansion is loaded into a quartz boat and sent into a high-temperature diffusion furnace. After evacuation, high-purity nitrogen is introduced at a flow rate of 20,000 sccm for 3 minutes. The temperature is then increased to 900℃ at a rate of >15℃ / min and stabilized for 2 minutes before entering the second boron expansion high-temperature diffusion and oxidation stage.

[0138] The first dry oxygen oxidation process involves applying oxygen at 900°C and low pressure, with the oxygen temperature set at 12000 sccm for 8 minutes. This process forms a dense initial layer of silicon dioxide with a thickness of approximately 16 nm on the silicon wafer surface, precisely defining the diffusion boundaries of boron atoms.

[0139] First wet oxygen oxidation treatment: oxygen temperature is 900℃, low pressure, atmosphere is gently switched, oxygen flow rate is first reduced to 5500 sccm, then nitrogen carrying water vapor passage is opened at a rate of 500 sccm / min to 1600 sccm, pure water purity is 6N, water temperature is 80℃, continuous for 10min, boron atoms diffuse gently in a directional manner, the thickness of silicon dioxide layer increases to about 40nm, forming a low-impurity basic borosilicate glass layer.

[0140] The second dry oxygen oxidation treatment: the oxygen temperature is 900℃ and the pressure is low. The atmosphere is switched gently. First, the nitrogen-carrying water vapor passage is closed at a rate of 500 sccm / min. Then, the oxygen flow rate is restored to 12000 sccm and held for 5 minutes to densify and repair the silicon dioxide layer, further reduce interface defects, and optimize the passivation performance of the silicon substrate.

[0141] Second wet oxygen oxidation treatment: 900℃, low pressure, gentle atmosphere switching, oxygen flow rate first reduced to 5500 sccm, then nitrogen carrying water vapor passage opened at a rate of 500 sccm / min to 1400 sccm, oxygen flow rate is 5500 sccm, nitrogen carrying water vapor flow rate is 1400 sccm, pure water parameters are the same as before, continue for 5 min, boron atoms are finely expanded and doped, the final thickness of the silicon dioxide layer is about 65nm, forming a thin and uniform borosilicate glass layer.

[0142] Post-processing of the working furnace: High-purity nitrogen is purged at a flow rate of 20,000 sccm to cool down to below 720°C, and the silicon wafer is removed to complete the secondary boron expansion process.

[0143] Subsequently, the borosilicate glass layer is removed and the alkaline polishing process is performed. The thickness of the tunneling oxide layer deposited by LPCVD can be precisely controlled within 1.2-1.5 nm, exhibiting excellent passivation performance.

[0144] In summary, the four-stage dry-wet-oxygen alternating process provided in this application is integrated into the high-temperature diffusion stage of the secondary boron diffusion process in solar cells. It seamlessly integrates with existing production lines without requiring equipment modifications. It is achieved solely through parameter adjustments to gas flow rate and atmosphere switching logic. This fundamentally optimizes the synergy between "oxide layer construction - boron atom doping" in the secondary boron diffusion process. It not only overcomes the shortcomings of existing single-stage processes and improves the process performance of the secondary boron diffusion process itself, but also enables single-stage optimization to drive performance and yield improvements in subsequent multi-stage processes. Ultimately, it achieves a dual improvement in the electrical performance and mass production economics of solar cells. The specific beneficial effects are as follows: 1. Significantly improved boron diffusion uniformity reduces the difficulty of borosilicate glass layer removal and alkaline polishing processes: Through precise synergy between four-stage alternating oxidation and boron diffusion, boron atoms achieve step-by-step controllable diffusion, with intra-wafer sheet resistance deviation controlled within ±2% and inter-wafer sheet resistance deviation controlled within ±4%, far superior to the ±5% deviation standard of existing processes; the generated borosilicate glass layer has a thickness uniformity of over 95%, and subsequent removal of the borosilicate glass layer and alkaline polishing processes do not require adjustment of etching parameters, and can directly use conventional mass production parameters, reducing the etching residue rate to below 0.001%, reducing the over-etching rate by more than 90%, and improving the silicon wafer surface flatness to Ra≤0.5nm.

[0145] 2. Significantly reduced SiO2 and Si interface defects, improving substrate quality for subsequent processes: Multiple dry oxygen densification repairs and mild atmosphere switching eliminate interface stress and lattice defects; the borosilicate glass layer generated by secondary borosilicate expansion has high cleanliness and low impurity content. After removing the borosilicate glass layer and alkaline polishing, the cleanliness of the silicon substrate is improved to over 99.9%, providing a low-defect, high-cleanliness silicon substrate for subsequent LPCVD, and improving the LPCVD process yield by over 0.15%.

[0146] 3. The thermal budget for secondary boron diffusion is effectively reduced, making it suitable for thin silicon wafers and subsequent multiple processes: This application reduces the oxidation diffusion temperature of secondary boron diffusion from the existing 1000℃~1050℃ to 850℃~950℃, and shortens the total time of the entire secondary boron diffusion process from the existing 130-160min to 100-120min, reducing the overall thermal budget by 25%-60%; it effectively avoids lattice damage to N-type silicon wafers and non-directional shift of the doped layer in the primary boron diffusion, reducing the silicon wafer warpage to below 0.01%, and significantly improving the compatibility with thin silicon wafers with a thickness of ≤130μm.

[0147] 4. Optimized BSG layer performance leads to improved yield of film layer processes across the entire production line: The BSG layer generated by the four-stage alternating process has uniform thickness, moderate density, low impurity, and no defects such as local pores or microcracks. After removing the borosilicate glass layer and undergoing alkaline polishing, the silicon substrate is free of corrosion micropits and has a smooth surface. This highly smooth substrate improves the uniformity of the film layer in subsequent LPCVD, ALD, and coating processes by more than 1%, controls the film layer thickness deviation within ±2nm, and improves the overall yield of film layer-related processes across the entire production line by more than 0.5%.

[0148] 5. Gentle atmosphere switching in the furnace reduces equipment wear and improves the stability of the entire production line: This invention adopts a gentle atmosphere switching with low water vapor concentration, short-time wet oxygen oxidation and gradual flow adjustment, which completely avoids sudden changes in furnace temperature, humidity and gas partial pressure. The corrosion rate of quartz tubes / quartz boats is reduced by 5%-10%, the service life of quartz components is extended from the current 6-8 months to 8-10 months, and the aging rate of furnace temperature control and gas control components is reduced by 5%. The frequency of equipment maintenance is greatly reduced, the production capacity stability of the secondary boron expansion process is improved to over 98%, effectively avoiding the production line stagnation caused by single-process shutdown, and the overall production line efficiency is improved by 8%-10%.

[0149] 6. Extremely strong process compatibility, no need to modify production lines / add equipment, easy to implement mass production: This application only adjusts the software parameters of the oxidation process in the secondary boron expansion process, which is seamlessly connected with the existing production line. No equipment modification is required, the implementation cycle is short, and the equipment parameter debugging can be completed in only 1-2 days, which is fully adapted to the mass production requirements.

[0150] 7. Significantly improved overall battery electrical performance, achieving cost reduction and efficiency improvement throughout the entire process: This process optimizes a single process to drive the performance and yield improvement of subsequent multiple processes, ultimately achieving comprehensive optimization of the electrical performance of solar cells: the overall battery conversion efficiency is improved by 0.02%-0.03%. This effect is verified by testing with a solar cell tester under standard test conditions of AM1.5G and 25℃, with a test sample size of ≥5 million finished cells.

[0151] Meanwhile, the overall yield of the entire production line has increased by more than 0.8%, and the equipment maintenance cost of the secondary boron expansion process has been reduced by 20%. This effect is based on the 8GW capacity TOPCon mass production line. Weekly statistical data after adopting this process has been compared with existing processes to verify that it achieves a dual improvement in technical performance and mass production economy.

[0152] Unless otherwise stated or in case of conflict, the terms or phrases used in this application shall have the following meanings: In this application, terms such as "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature.

[0153] In this application, "one or more" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0154] In this application, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0155] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part. They can refer to a mechanical connection or an electrical connection. They can refer to a direct connection or an indirect connection through an intermediate medium, or the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0156] In this application, the terms "embodiment" and "implementation" mean that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of these phrases in various locations throughout the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this application can be combined with other embodiments. Furthermore, it should be understood that the features, structures, or characteristics described in the various embodiments of this application can be arbitrarily combined to form yet another embodiment that does not depart from the spirit and scope of the technical solution of this application, provided there is no contradiction between them.

[0157] The above description represents some embodiments of this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A method for boron diffusion in a solar cell, characterized in that, The boron expansion method includes: Provide substrates that have undergone the first boron diffusion process; The substrate is subjected to a second boron diffusion process; wherein the second boron diffusion process includes: The substrate is subjected to a first dry oxygen oxidation treatment to form a silicon dioxide layer on the substrate; The substrate is subjected to a first wet oxidation treatment to form a borosilicate glass layer disposed on the side of the silicon dioxide layer opposite to the substrate. The substrate is subjected to a second dry oxygen oxidation treatment to repair the silicon dioxide layer; The substrate is subjected to a second wet oxidation treatment to ensure that the thickness uniformity of the borosilicate glass layer is ≥95%. A P-type emitter is formed on the substrate.

2. The boron diffusion method for solar cells as described in claim 1, characterized in that, The process conditions for the first dry oxygen oxidation treatment satisfy at least one of the following: The oxygen flow rate for the first dry oxygen is 8000 sccm~12000 sccm; The oxidation time for the first dry oxygen is 8 to 15 minutes.

3. The boron diffusion method for solar cells as described in claim 1, characterized in that, The process conditions for the first wet oxygen oxidation treatment satisfy at least one of the following: The oxygen flow rate for the first humidified oxygen treatment is 4000 sccm~6000 sccm; The water vapor flow rate of the first humidified oxygen is 1500 sccm~2000 sccm; The oxidation time for the first wet oxygen is 10-20 minutes.

4. The boron diffusion method for solar cells as described in claim 1, characterized in that, The process conditions for the second dry oxygen oxidation treatment satisfy at least one of the following: The oxygen flow rate for the second dry oxygen is 8000 sccm~12000 sccm; The second oxidation time with dry oxygen is 10 min to 20 min.

5. The boron diffusion method for solar cells as described in claim 1, characterized in that, The process conditions for the second wet oxidation treatment satisfy at least one of the following: The oxygen flow rate for the second humidified oxygen supply is 4000 sccm~6000 sccm; The water vapor flow rate of the second humid oxygen is 1200 sccm~1800 sccm; The second oxidation time with wet oxygen is 5 to 8 minutes.

6. The boron diffusion method for solar cells as described in claim 1, characterized in that, The step of performing a first wet oxygen oxidation treatment on the substrate includes: Nitrogen and water vapor are introduced, and the nitrogen flow rate of the first wet oxygen is gradually increased at a first rate of 450 sccm / min to 550 sccm / min. The step of performing a second wet oxygen oxidation treatment on the substrate includes: Nitrogen and water vapor are introduced, and the nitrogen flow rate of the second humid oxygen is gradually increased at a second rate of 450 sccm / min to 550 sccm / min.

7. The boron diffusion method for solar cells as described in claim 1, characterized in that, The first dry oxygen oxidation treatment, the first wet oxygen oxidation treatment, the second dry oxygen oxidation treatment, and the second wet oxygen oxidation treatment all satisfy at least one of the following: The oxidation temperature of the second boron diffuser is 850℃~950℃; The process pressure for the second boron expansion is 850 Pa to 950 Pa. The total processing time for the second boron diffusion process is 100-120 minutes.

8. The boron diffusion method for solar cells as described in claim 1, characterized in that, The second boron expansion process also includes: Before performing the first dry oxygen oxidation treatment, the working furnace is pretreated, which includes: introducing nitrogen gas and heating to the oxidation temperature of the first dry oxygen. After the second dry oxygen oxidation treatment, the working furnace is post-treated, which includes: introducing nitrogen gas and cooling to a cooling temperature ≤720℃.

9. A solar cell, characterized in that, The solar cell includes a substrate having a P-type emitter, and the substrate is processed using the boron expansion method for solar cells as described in any one of claims 1-8.

10. A photovoltaic module, characterized in that, The photovoltaic module includes the solar cell as described in claim 9.

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