A method for preparing a pn junction of a solar cell

Abstract

The application discloses a method for preparing a PN junction of a solar cell, which comprises the following steps: (1) pre-oxidizing a silicon wafer to form a silicon dioxide oxidation layer on the surface of the silicon wafer; (2) introducing a first carrier gas, oxygen and a second carrier gas carrying a phosphorus source into a diffusion device provided with the silicon wafer to perform low-temperature diffusion; (3) introducing the first carrier gas into the diffusion device to perform high-temperature propulsion; (4) cooling the diffusion device, and introducing the first carrier gas during the cooling process; the method further comprises the following steps: (5) introducing the first carrier gas and oxygen into the diffusion device to oxidize the silicon wafer; and (6) introducing the first carrier gas, oxygen and the second carrier gas carrying the phosphorus source into the diffusion device to supplement the second carrier gas carrying the phosphorus source. The application can improve the short-circuit current and open-circuit voltage under the premise of less influence on the fill factor, thereby improving the conversion efficiency of the solar cell.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology and relates to a method for preparing a PN junction in a solar cell. Background Technology

[0002] A solar cell is a device that directly converts light energy into electrical energy. Due to its cleanliness, lack of pollution, and inexhaustible supply, it has gradually become an important method of power generation. Its principle is to utilize the photovoltaic effect of a PN junction to convert light energy into electrical energy. The diffusion process is a crucial step in forming the PN junction, where N-type impurities are diffused onto a P-type substrate to form the PN junction, achieving contact between the P-type and N-type semiconductors.

[0003] Open-circuit voltage (Voc), short-circuit current (Isc), and fill factor (FF) are the three key parameters determining photoelectric conversion efficiency. Typically, surface doping can be reduced by directly decreasing the phosphorus oxychloride flux, thereby increasing the open-circuit voltage and short-circuit current. However, this also leads to a loss of fill factor. When the gains in open-circuit voltage and short-circuit current cannot compensate for the fill factor loss, the efficiency gains negatively, and the efficiency improvement method encounters a bottleneck. Current phosphorus diffusion methods have the following drawbacks: the PN junction depth and surface concentration are mutually constrained; due to the negative gain of the fill factor, the diffusion surface concentration cannot be further reduced, resulting in high surface recombination. Summary of the Invention

[0004] To address the aforementioned technical problems, the purpose of this invention is to provide a method for preparing a PN junction for a solar cell, which can further improve the short-circuit current and open-circuit voltage without affecting the fill factor or with minimal impact, thereby improving the conversion efficiency of the solar cell.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for fabricating a PN junction in a solar cell includes the following steps:

[0007] (1) Perform pre-oxidation on the silicon wafer to form a silicon dioxide oxide layer on the surface of the silicon wafer;

[0008] (2) A first carrier gas, oxygen and a second carrier gas carrying a phosphorus source are introduced into a diffusion device containing the silicon wafer to perform low-temperature diffusion;

[0009] (3) Introduce a first carrier gas into the diffusion device for high-temperature propulsion;

[0010] (4) The diffusion device is cooled down, and a first carrier gas is introduced during the cooling process;

[0011] The PN junction preparation method further includes the following steps:

[0012] (5) A first carrier gas and oxygen are introduced into the diffusion device to oxidize the silicon wafer;

[0013] (6) Introduce a first carrier gas, oxygen and a second carrier gas carrying a phosphorus source into the diffusion device to supplement the second carrier gas carrying the phosphorus source;

[0014] The temperature of the diffusion device in steps (5) and (6) is lower than the temperature of the diffusion device in step (3).

[0015] Preferably, in step (5), the temperature of the diffusion device is 790 to 810°C, for example, 790°C, 800°C or 810°C.

[0016] Preferably, in step (5), the oxygen flow rate is 100 to 300 sccm, for example, 100 sccm, 150 sccm, 200 sccm, 250 sccm or 300 sccm.

[0017] Preferably, in step (5), the flow rate of the first carrier gas is 1600 to 2000 sccm, for example, 1600 sccm, 1700 sccm, 1800 sccm, 1900 sccm or 2000 sccm.

[0018] Preferably, in step (5), the oxygen flow rate is 150 to 250 sccm, for example 150 sccm, 160 sccm, 170 sccm, 180 sccm, 190 sccm, 200 sccm, 210 sccm, 220 sccm, 230 sccm, 240 sccm or 250 sccm.

[0019] Preferably, the PN junction preparation method further includes the following steps:

[0020] (7) The diffusion device is cooled down, and a first carrier gas is introduced during the cooling process;

[0021] (8) Introduce a first carrier gas, oxygen and a second carrier gas carrying a phosphorus source into the diffusion device to supplement the second carrier gas carrying the phosphorus source;

[0022] In step (8), the flow rate of the second carrier gas carrying the phosphorus source is greater than that in step (6).

[0023] Preferably, in step (6), the flow rate of the second carrier gas carrying the phosphorus source is 125-145 sccm, more preferably 130-140 sccm, for example 130 sccm, 132 sccm, 134 sccm, 136 sccm, 138 sccm and 140 sccm.

[0024] In step (8), the flow rate of the second carrier gas carrying the phosphorus source is 160-180 sccm, more preferably 165-175 sccm, for example 165 sccm, 167 sccm, 169 sccm, 170 sccm, 171 sccm, 173 sccm, or 175 sccm.

[0025] Preferably, the flow rate of the second carrier gas carrying the phosphorus source in step (2) is less than the flow rate of the second carrier gas carrying the phosphorus source in step (6) or (8).

[0026] More preferably, in step (6), the diffusion equipment is cooled at a temperature of 790–810°C. During the cooling process, a first carrier gas, oxygen, and a second carrier gas carrying a phosphorus source are introduced. The flow rate of the first carrier gas is 1100–1300 sccm, the flow rate of oxygen is 650–850 sccm, the flow rate of phosphorus oxychloride is 125–145 sccm, and the reaction time is 220–260 s. In step (8), the diffusion equipment is cooled at a temperature of 770–790°C. During the cooling process, a first carrier gas, oxygen, and a second carrier gas carrying a phosphorus source are introduced. The flow rate of the first carrier gas is 1300–1700 sccm, the flow rate of oxygen is 450–650 sccm, the flow rate of phosphorus oxychloride is 160–180 sccm, and the reaction time is 340–380 s.

[0027] Preferably, the PN junction preparation method further includes performing the following steps after supplementing with a second carrier gas carrying a phosphorus source:

[0028] (9) The diffusion equipment is filled with a first carrier gas and oxygen to perform post-oxidation on the silicon wafer;

[0029] (10) The diffusion device is annealed by introducing a first carrier gas and oxygen.

[0030] Preferably, in step (9), post-oxidation is performed at a temperature of 700–770°C in the diffusion equipment, with a first carrier gas flow rate of 1000–1400 sccm and an oxygen flow rate of 600–1000 sccm. More preferably, in step (9), the temperature of the diffusion equipment is 720–750°C, further 730–740°C, specifically 735°C. More preferably, in step (9), the carrier gas flow rate is 1100–1300 sccm, for example 1100 sccm, 1150 sccm, 1200 sccm, 1250 sccm, or 1300 sccm. More preferably, in step (9), the oxygen flow rate is 700–900 sccm, for example 700 sccm, 750 sccm, 800 sccm, 850 sccm, or 900 sccm.

[0031] Preferably, in step (10), the temperature of the diffusion device is 770–790°C, the pressure is atmospheric pressure, the first carrier gas flow rate is 2000–4000 sccm, the oxygen flow rate is 1000–2000 sccm, and the time is 1100–1300 s. More preferably, the temperature of the diffusion device in step (10) is 775–785°C. More preferably, the carrier gas flow rate in step (10) is 2500–3500 sccm, for example, 2500 sccm, 2800 sccm, 3000 sccm, 3200 sccm, or 3500 sccm. More preferably, the oxygen flow rate in step (10) is 1200–1800 sccm, for example, 1200 sccm, 1400 sccm, 1500 sccm, 1600 sccm, or 1800 sccm.

[0032] Preferably, steps (1) to (6) and (9) are carried out under a vacuum pressure of 90 to 110 mbar.

[0033] Preferably, the first carrier gas and the second carrier gas are nitrogen or inert gases.

[0034] Preferably, the silicon wafer is placed inside the furnace tube of the diffusion equipment.

[0035] Preferably, the PN junction preparation method is implemented as follows:

[0036] (1) Place the silicon wafer into the furnace tube of the diffusion equipment, and form a silicon dioxide oxide layer on the surface of the silicon wafer at a furnace tube temperature of 790-800℃. Set the vacuum pressure to 90-110 mbar, and introduce a first carrier gas and oxygen into the furnace tube. The flow rate of the first carrier gas is 1300-1700 sccm, the flow rate of oxygen is 400-600 sccm, and the duration is 230-270 s.

[0037] (2) Temperature is the same as in step (1), low-temperature diffusion. First carrier gas, oxygen, and phosphorus oxychloride are introduced into the furnace tube. The flow rate of the first carrier gas is 1200–1500 sccm, the flow rate of oxygen is 400–600 sccm, and the flow rate of phosphorus oxychloride is maintained at 100 sccm. The reaction time is 80–100 s. After raising the temperature of each zone by 5–15°C, the reaction continues for 250–300 s.

[0038] (3) High-temperature propulsion is carried out under the condition that the furnace tube temperature is 820-870℃. During this process, the first carrier gas is introduced into the furnace tube, the flow rate of the first carrier gas is 1800-2200 sccm, and the reaction time is 900-1100s;

[0039] (4) Cool down the furnace tube at a temperature of 790-810℃. During this process, the first carrier gas is introduced into the furnace tube. The flow rate of the first carrier gas is 1800-2200 sccm and the reaction time is 400-500s.

[0040] (5) Under the condition that the furnace tube temperature is 790-810℃, the temperature is reduced and oxidation continues. During this process, the first carrier gas and oxygen are introduced into the furnace tube. The flow rate of the first carrier gas is 1600-2000 sccm, the flow rate of oxygen is 150-250 sccm, and the reaction time is 350-450 s.

[0041] (6) At a furnace tube temperature of 790–810°C, the temperature is lowered and a second carrier gas carrying the phosphorus source is added. During this process, the first carrier gas, oxygen, and phosphorus oxychloride are introduced into the furnace tube. The flow rate of the first carrier gas is 1100–1300 sccm, the flow rate of oxygen is 650–850 sccm, the flow rate of phosphorus oxychloride is 125–145 sccm, and the reaction time is 220–260 s.

[0042] (7) Cool down the furnace tube at a temperature of 770-790℃. During this process, the first carrier gas is introduced into the furnace tube at a flow rate of 1800-2200 sccm and a reaction time of 340-380 s.

[0043] (8) At a furnace tube temperature of 770–790°C, the temperature is lowered and a second carrier gas carrying the phosphorus source is added. During this process, the first carrier gas, oxygen, and phosphorus oxychloride are introduced into the furnace tube. The flow rate of the first carrier gas is 1300–1700 sccm, the flow rate of oxygen is 450–650 sccm, the flow rate of phosphorus oxychloride is 160–180 sccm, and the reaction time is 340–380 s.

[0044] (9) Post-oxidation is performed at a furnace tube temperature of 700-770℃. A first carrier gas and oxygen are introduced into the furnace tube. The flow rate of the first carrier gas is 1000-1400 sccm, and the flow rate of oxygen is 600-1000 sccm.

[0045] (10) Annealing and impurity removal are performed at a furnace tube temperature of 770-790℃. The pressure is atmospheric pressure. The first carrier gas and oxygen are introduced into the furnace tube. The flow rate of the first carrier gas is 2000-4000 sccm, the flow rate of oxygen is 1000-2000 sccm, and the time is 1100-1300 s.

[0046] Preferably, steps (1) to (9) are carried out under a vacuum pressure of 90 to 110 mbar.

[0047] The present invention adopts the above solution, which has the following advantages compared with the prior art:

[0048] The method for preparing the PN junction of the solar cell of the present invention involves introducing carrier gas and oxygen into a diffusion device after power supply, high temperature and constant temperature propulsion to cool and oxidize the silicon wafer, and then replenishing the phosphorus source after oxidation. During the cooling oxidation process, silicon dioxide is generated on the surface of the silicon wafer as a masking layer, which reduces the near-surface phosphorus concentration of the silicon wafer without affecting the fill factor or with minimal impact, reduces the recombination of charge carriers on the silicon wafer surface, and further improves the short-circuit current and open-circuit voltage, thereby improving the overall conversion efficiency of the solar cell. Attached Figure Description

[0049] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is a process flow diagram of a method for fabricating a PN junction in a solar cell according to an embodiment of the present invention;

[0051] Figure 2 This is a schematic diagram comparing the PN junction curves of embodiments and comparative examples of the present invention. Detailed Implementation

[0052] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more readily understood by those skilled in the art. It should be noted that the description of these embodiments is for the purpose of aiding understanding the present invention, but does not constitute a limitation thereof.

[0053] like Figure 1 As shown, the process flow of the PN junction fabrication method for the solar cell of the present invention is as follows: pre-oxidation → primary power supply → secondary power supply → heating-driven → isothermal-driven → cooling → cooling oxidation → primary power replenishment → cooling → secondary power replenishment → post-oxidation → annealing and gettering. The phased implementation of heating-driven, isothermal-driven, and cooling-driven processes is beneficial to the uniformity of sheet resistance, significantly improving the intra-wafer and inter-wafer uniformity of the resulting silicon wafer sheet resistance, reducing recombination centers, and thus increasing on-state voltage and efficiency.

[0054] The specific implementation of this PN junction preparation method is as follows:

[0055] (1) Place the silicon wafer into the furnace tube of the diffusion equipment and form a silicon dioxide oxide layer on the surface of the silicon wafer at a furnace tube temperature of 790-800℃. Set the vacuum pressure to 90-110 mbar and introduce nitrogen (first carrier gas) and oxygen into the furnace tube. The nitrogen flow rate is 1300-1700 sccm and the oxygen flow rate is 400-600 sccm for 230-270 s.

[0056] (2) Temperature is the same as in step (1), and low-temperature diffusion is carried out. During this process, nitrogen (first carrier gas), oxygen and phosphorus oxychloride are introduced into the furnace tube. The flow rate of nitrogen is 1200-1500 sccm, the flow rate of oxygen is 400-600 sccm, and the flow rate of phosphorus oxychloride is 100 sccm. The reaction time is 80-100 s, which is the first source introduction. After raising the temperature of each temperature zone by 5-15℃, the reaction continues for 250-300 s, which is the second source introduction.

[0057] Phosphorus oxychloride decomposes at high temperatures (>600℃) to form phosphorus pentachloride, which then reacts with silicon at a diffusion temperature to form silicon dioxide and phosphorus atoms. The resulting phosphorus pentachloride is difficult to decompose and corrodes silicon, damaging the surface of the silicon wafer. However, in the presence of oxygen, phosphorus pentachloride further decomposes into phosphorus pentoxide, releasing chlorine gas. The resulting phosphorus pentoxide then reacts with silicon to form silicon dioxide and phosphorus atoms. Therefore, to promote the complete decomposition of phosphorus oxychloride and avoid its corrosive effect on the silicon wafer surface during phosphorus diffusion, oxygen must be introduced simultaneously with nitrogen. In the presence of oxygen, phosphorus oxychloride reacts with oxygen to form phosphorus pentoxide and chlorine gas. The phosphorus pentoxide produced by the decomposition of phosphorus oxychloride deposits on the silicon wafer surface. The phosphorus pentoxide reacts with silicon to form silicon dioxide and phosphorus atoms, forming a phosphorus-silicon glass layer on the silicon wafer surface. The phosphorus atoms then diffuse into the silicon.

[0058] The second source is at a higher temperature than the first, and a relatively high concentration of phosphorus source is deposited on the phosphorus-silicon glass deposited in the first stage to prepare for subsequent high-temperature propulsion.

[0059] (3) High-temperature propulsion is carried out at a furnace tube temperature of 820-870℃ to accelerate the diffusion of phosphorus atoms on the silicon wafer surface so that they can enter the N-type part as much as possible. During this process, nitrogen gas (first carrier gas) is introduced into the furnace tube at a flow rate of 1800-2200 sccm and a reaction time of 900-1100 s.

[0060] (4) Cooling is carried out at a furnace tube temperature of 790-810℃. During this process, nitrogen gas (first carrier gas) is introduced into the furnace tube at a flow rate of 1800-2200 sccm and a reaction time of 400-500 s.

[0061] (5) Under the condition of furnace tube temperature of 790-810℃, the temperature is further reduced and oxidation is carried out to generate silicon dioxide. During this process, nitrogen (first carrier gas) and oxygen are introduced into the furnace tube. The nitrogen flow rate is 1600-2000 sccm, the oxygen flow rate is 150-250 sccm, and the reaction time is 350-450 s. The silicon dioxide here acts as a mask, which effectively reduces the surface phosphorus concentration, reduces surface recombination, and increases the short-circuit current and open-circuit voltage during subsequent source replenishment, thereby improving the conversion efficiency of the solar cell.

[0062] (6) Cool down and replenish phosphorus source at a furnace tube temperature of 790-810℃. During this process, nitrogen (first carrier gas), oxygen and phosphorus oxychloride are introduced into the furnace tube. The flow rate of nitrogen is 1100-1300 sccm, the flow rate of oxygen is 650-850 sccm, the flow rate of phosphorus oxychloride is 125-145 sccm, and the reaction time is 220-260 s.

[0063] (7) Cool down the furnace tube at a temperature of 770-790℃. During this process, nitrogen gas (first carrier gas) is introduced into the furnace tube at a flow rate of 1800-2200 sccm and a reaction time of 340-380s.

[0064] (8) Cool down and replenish phosphorus source at a furnace tube temperature of 770-790℃. During this process, nitrogen (first carrier gas), oxygen and phosphorus oxychloride are introduced into the furnace tube. The flow rate of nitrogen is 1300-1700 sccm, the flow rate of oxygen is 450-650 sccm, the flow rate of phosphorus oxychloride is 160-180 sccm, and the reaction time is 340-380 s.

[0065] (9) Post-oxidation is performed at a furnace tube temperature of 700-770℃. Nitrogen (first carrier gas) and oxygen are introduced into the furnace tube at a flow rate of 1000-1400 sccm and a flow rate of 600-1000 sccm.

[0066] (10) Annealing and getter absorption are performed at a furnace tube temperature of 770–790℃ to improve the quality of the PN junction formed by diffusion doping. At atmospheric pressure, nitrogen (the first carrier gas) and oxygen are introduced into the furnace tube at a flow rate of 2000–4000 sccm and a flow rate of 1000–2000 sccm for 1100–1300 s. The slow backpressure from a small flow rate of nitrogen, combined with a large flow rate of oxygen, effectively achieves annealing and getter absorption, thereby increasing the short-circuit current and open-circuit voltage.

[0067] In steps (1) to (10) above, phosphorus oxychloride is carried by a second carrier gas (specifically nitrogen gas), and the phosphorus oxychloride flow rate is specifically the flow rate of the second carrier gas carrying phosphorus oxychloride.

[0068] Example 1

[0069] For details of the diffusion process on the silicon wafer in this embodiment, please refer to Table 1 below.

[0070] Table 1

[0071]

[0072] Comparative Example

[0073] For details of the diffusion process of the comparative silicon wafer, please refer to Table 2 below.

[0074] Table 2

[0075]

[0076] For a comparison of phosphorus concentration distribution between the silicon wafers prepared in Example 1 and the comparative example, see [link to example]. Figure 2 . Figure 2 In the diagram, the horizontal axis represents the PN junction depth, and the vertical axis represents the phosphorus concentration. (From...) Figure 2 It can be seen that when the junction depth is in the near-surface range (0–0.03 μm), the phosphorus concentration of the silicon wafer prepared in Example 1 is lower than that of the silicon wafer prepared in the comparative example. As the junction depth increases, i.e., when the junction depth is in the range of 0.1–0.5 μm, the phosphorus concentration of the silicon wafer prepared in Example 1 is higher than that of the silicon wafer in the comparative example, making the sheet resistance of the silicon wafer in Example 1 and the sheet resistance of the silicon wafer in the comparative example approximately the same. Reducing the near-surface phosphorus concentration can reduce surface recombination.

[0077] Battery performance comparison

[0078] The silicon wafers obtained in Example 1 and the comparative example were selected and fabricated into solar cells. The performance of the solar cells was tested, and the test results are shown in Table 3.

[0079] Table 3

[0080] Open circuit voltage / V Short circuit current / A Fill factor / % Conversion efficiency Example 1 0.6817 10.1692 81.03 22.453 Comparative Example 0.6802 10.1597 81.05 22.386

[0081] As shown in Table 3, the fill factor of Example 1 is slightly lower than that of the comparative example, but the gains in short-circuit current and open-circuit voltage can compensate for this, without causing a negative gain. Conversely, the solar cell using the silicon wafer prepared in Example 1 has a smaller impact on the fill factor when the open-circuit voltage and short-circuit current are increased, thus further improving the overall conversion efficiency of the solar cell.

[0082] The diffusion process for PN junction fabrication in this embodiment proposes a solution to overcome the efficiency gain limitation imposed by the fill factor, based on existing diffusion processes. As can be seen from the above embodiments and comparative examples, the method of this invention improves the silicon wafer diffusion process steps by continuing to cool and oxidize after cooling in step (4), thereby reducing the surface phosphorus concentration, decreasing carrier recombination on the silicon wafer surface, increasing short-circuit current and open-circuit voltage, and having a smaller impact on the fill factor, thus improving the overall conversion efficiency of the solar cell.

[0083] The above embodiments are merely illustrative of the technical concept and features of the present invention, and are preferred embodiments. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and they should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made according to the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a PN junction of a solar cell, comprising the following steps: (1) pre-oxidizing a silicon wafer to form a silicon dioxide layer on the surface of the silicon wafer; (2) introducing a first carrier gas, oxygen and a second carrier gas carrying a phosphorus source into a diffusion device in which the silicon wafer is placed, and performing low-temperature diffusion; (3) introducing the first carrier gas into the diffusion device, and performing high-temperature pushing; (4) cooling the diffusion device, and introducing the first carrier gas during the cooling process; characterized in that The method for preparing the PN junction further comprises the following steps: (5) introducing the first carrier gas and oxygen into the diffusion device to oxidize the silicon wafer; (6) introducing the first carrier gas, oxygen and the second carrier gas carrying the phosphorus source into the diffusion device to supplement the second carrier gas carrying the phosphorus source; The temperature of the diffusion device in steps (5) and (6) is lower than the temperature of the diffusion device in step (3). In step (2), nitrogen, oxygen and phosphorus oxychloride are introduced into the furnace tube of the diffusion device, and under the same temperature conditions as in step (1), a first source is reacted for 80-100 seconds; then the temperature of each temperature zone is increased by 5-15°C, and a second source is continuously reacted for 250-300 seconds. Step (5) is performed before the second carrier gas carrying the phosphorus source is supplemented; in step (5), nitrogen and oxygen are introduced into the furnace tube at a furnace tube temperature of 790-810°C, the nitrogen flow rate is 1600-2000 sccm, the oxygen flow rate is 150-250 sccm, and the reaction time is 350-450 seconds to form a silicon dioxide mask on the surface of the silicon wafer; in step (6), nitrogen with a flow rate of 1100-1300 sccm, oxygen with a flow rate of 650-850 sccm and phosphorus oxychloride with a flow rate of 125-145 sccm are introduced into the furnace tube at a furnace tube temperature of 790-810°C, and the reaction time is 220-260 seconds. After step (6), step (7) is further included: cooling at a furnace tube temperature of 770-790°C, and introducing nitrogen into the furnace tube at a nitrogen flow rate of 1800-2200 sccm, and the reaction time is 340-380 seconds. After step (7), a post-oxidation step is further included, which comprises introducing nitrogen and oxygen into the furnace tube, the nitrogen flow rate is 1000-1400 sccm, and the oxygen flow rate is 600-1000 sccm.

2. The method of claim 1, wherein the step of forming the PN junction is performed by implanting the dopant into the substrate. The method for preparing the PN junction further comprises the following step: (8) introducing the first carrier gas, oxygen and the second carrier gas carrying the phosphorus source into the diffusion device to supplement the second carrier gas carrying the phosphorus source; In step (8), the flow rate of the second carrier gas carrying the phosphorus source is greater than the flow rate of the second carrier gas carrying the phosphorus source in step (6).

3. The method of claim 2, wherein the step of forming the PN junction is performed by implanting the dopant into the substrate. In step (8), the flow rate of the second carrier gas carrying the phosphorus source is 160-180 sccm.

4. The method of claim 3, wherein the step of forming the PN junction is performed by implanting the dopant into the substrate. The flow rate of the second carrier gas carrying the phosphorus source in step (2) is less than the flow rate of the second carrier gas carrying the phosphorus source in step (6) or (8).

5. The method of claim 3, wherein the step of forming the PN junction is performed by implanting the dopant into the substrate. In step (8), the temperature of the diffusion device is decreased to 770-790 DEG C, and the first carrier gas, oxygen and the second carrier gas carrying the phosphorus source are introduced during the temperature decreasing process, the flow rate of the first carrier gas is 1300-1700 sccm, the flow rate of oxygen is 450-650 sccm, the flow rate of phosphorus oxychloride is 160-180 sccm, and the reaction time is 340-380 s.

6. The method of claim 2 to 5, wherein After step (8), the post-oxidation step (9) and the following step (10) are sequentially performed. The first carrier gas and oxygen are introduced into the diffusion device for annealing.

7. The method of claim 6, wherein the step of forming the PN junction is performed by implanting the dopant into the substrate. In the post-oxidation step (9), the temperature of the diffusion device is 700-770 DEG C, and in step (10), the temperature of the diffusion device is 770-790 DEG C, the pressure is normal pressure, the flow rate of the first carrier gas is 2000-4000 sccm, the flow rate of oxygen is 1000-2000 sccm, and the time is 1100-1300 s; and / or, steps (1) to (6) and (9) are performed under a vacuum pressure of 90-110 mbar.

8. The method of claim 1, wherein the step of forming the PN junction is performed by a process selected from the group consisting of diffusion, ion implantation, epitaxy, and combinations thereof. The PN junction preparation method is specifically implemented as follows: (1) the silicon wafer is placed in the furnace tube of the diffusion device, the temperature of the furnace tube is 790-800 DEG C, the vacuum pressure is set to 90-110 mbar, the first carrier gas and oxygen are introduced into the furnace tube, the flow rate of the first carrier gas is 1300-1700 sccm, the flow rate of oxygen is 400-600 sccm, and the duration is 230-270 s; (2) the temperature is the same as that in step (1), the first carrier gas, oxygen and phosphorus oxychloride are introduced into the furnace tube, the flow rate of the first carrier gas is 1200-1500 sccm, the flow rate of oxygen is 400-600 sccm, the flow rate of phosphorus oxychloride is continuously 100 sccm, the reaction time is 80-100 s, and after the temperature of each temperature zone is increased by 5-15 DEG C, the reaction is continued for 250-300 s; (3) the temperature of the furnace tube is 820-870 DEG C, and the first carrier gas is introduced into the furnace tube during the process, the flow rate of the first carrier gas is 1800-2200 sccm, and the reaction time is 900-1100 s; (4) the temperature of the furnace tube is decreased to 790-810 DEG C, and the first carrier gas is introduced into the furnace tube during the process, the flow rate of the first carrier gas is 1800-2200 sccm, and the reaction time is 400-500 s; (5) the temperature of the furnace tube is decreased to 790-810 DEG C, and the first carrier gas and oxygen are introduced into the furnace tube during the process, the flow rate of the first carrier gas is 1600-2000 sccm, the flow rate of oxygen is 150-250 sccm, and the reaction time is 350-450 s; (6) the temperature of the furnace tube is decreased to 790-810 DEG C, and the first carrier gas, oxygen and phosphorus oxychloride are introduced into the furnace tube during the process, the flow rate of the first carrier gas is 1100-1300 sccm, the flow rate of oxygen is 650-850 sccm, the flow rate of phosphorus oxychloride is 125-145 sccm, and the reaction time is 220-260 s; (7) under the condition of furnace tube temperature 770~790℃, cooling down, in this process, the first carrier gas is introduced into the furnace tube, the first carrier gas flow rate is 1800~2200sccm, and the reaction time is 340~380s; (8) under the condition of furnace tube temperature 770~790℃, cooling down and supplementing the second carrier gas carrying the phosphorus source, in this process, the first carrier gas, oxygen and phosphorus oxychloride are introduced into the furnace tube, the first carrier gas flow rate is 1300~1700sccm, the oxygen flow rate is 450~650sccm, the phosphorus oxychloride flow rate is 160~180sccm, and the reaction time is 340~380s; (9) under the condition of furnace tube temperature 700~770℃, the first carrier gas and oxygen are introduced into the furnace tube, the first carrier gas flow rate is 1000~1400sccm, and the oxygen flow rate is 600~1000sccm; (10) under the condition of furnace tube temperature 770~790℃ and normal pressure, the first carrier gas and oxygen are introduced into the furnace tube, the first carrier gas flow rate is 2000~4000sccm, the oxygen flow rate is 1000~2000sccm, and the time is 1100~1300s.

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