Boron diffusion method of solar cell and solar cell

Abstract

The invention discloses a boron diffusion method of a solar cell and the solar cell. The boron diffusion method comprises the following steps: forming a boron-doped layer for a cell substrate in an oxidation furnace tube to obtain a primarily-doped boron substrate, the boron-doped layer comprising a deep-junction boron diffusion layer and a borosilicate glass layer which are laminated from inside to outside; taking out the primarily-doped boron matrix from the oxidation furnace tube, and cooling the primarily-doped boron matrix until the cooled temperature is not higher than 200 DEG C; putting the cooled primarily-doped boron substrate into the preheated oxidation furnace tube again, and heating the primarily-doped boron substrate in an oxygen-free environment to activate non-active boron atoms in the boron-doped layer; and carrying out oxidation source absorption treatment on the deep-junction boron diffusion layer in the primarily-doped boron substrate, and redistributing boron atoms in the deep-junction boron diffusion layer. According to the boron diffusion method, the amount of active boron atoms contained in the surface of the deep-junction boron diffusion layer of the solar cell is increased, the boron doping concentration peak value in the deep-junction boron diffusion layer is reduced, the boron doping concentration distribution is relatively uniform, and the contact resistance between the metal electrode and the deep-junction boron diffusion layer is reduced.

Description

Technical Field

[0001] The present invention relates to a boron diffusion method for a solar cell and a solar cell. Background Art

[0002] Based on an N-type silicon wafer, fabricating a PN junction through boron diffusion treatment is one of the core processes in current crystalline silicon solar cell manufacturing. This boron diffusion treatment method directly affects the performance of the solar cell. Therefore, optimizing the boron diffusion treatment helps improve the performance of the solar cell.

[0003] Currently, in the boron diffusion treatment process, mainly after forming a boron source layer on the surface of the silicon wafer, high-temperature propulsion is carried out at a temperature above 900 °C to dope boron and diffuse it into the silicon wafer to form a boron diffusion layer, and then the temperature is continuously raised to above 1000 °C for oxidation and source absorption treatment of the boron diffusion layer. After oxidizing and absorbing the source for a period of time under high-temperature conditions, the temperature is lowered to below 800 °C, and at the same time, cooling oxidation is carried out to reduce the boron doping concentration. The existing treatment methods reduce the doping concentration on the surface of the boron diffusion layer, and have relatively little influence on the doping concentration inside the boron diffusion layer. Therefore, although the existing treatment methods can reduce carrier recombination by forming a relatively low doping concentration on the surface of the doped layer, the peak concentration inside the boron diffusion layer is still relatively large, resulting in a relatively high concentration difference between the surface and the inside of the boron diffusion layer, which is not conducive to the contact performance of the boron diffusion layer and leads to a relatively high contact resistance between the boron diffusion layer and the metal electrode. Summary of the Invention

[0004] In view of this, the present invention provides a boron diffusion method for a solar cell and a solar cell. Compared with the prior art, this boron diffusion method combines cooling and oxidation source absorption treatment to increase the amount of active boron atoms on the surface of the deep junction boron diffusion layer of the solar cell, and can reduce the peak value of the boron doping concentration in the deep junction boron diffusion layer, making the boron doping concentration distribution relatively uniform, so as to reduce the contact resistance between the metal electrode and the deep junction boron diffusion layer.

[0005] To solve the above technical problems, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a boron diffusion method for a solar cell, including:

[0007] Step 1: Form a boron-doped layer for the battery substrate in an oxidation furnace tube to obtain a preliminarily boron-doped substrate, where the boron-doped layer includes a deep junction boron diffusion layer and a boron-silicon glass layer stacked from the inside to the outside;

[0008] Step 2: Take out the preliminarily boron-doped substrate from the oxidation furnace tube and cool the preliminarily boron-doped substrate so that the temperature of the cooled preliminarily boron-doped substrate is not higher than 200 °C;

[0009] Step 3: Re-put the cooled initially boron-doped substrate back into the preheated oxidation furnace tube, and under an oxygen-free environment, raise the temperature of the initially boron-doped substrate to activate the inactive boron atoms in the boron-doped layer;

[0010] Step 4: Perform an oxidation and source-absorbing treatment on the boron-doped layer in the initially boron-doped substrate to redistribute the boron atoms in the deep junction boron diffusion layer.

[0011] In a second aspect, an embodiment of the present invention provides a solar cell, including: a deep junction boron diffusion layer formed by the boron diffusion method of the solar cell provided in the first aspect embodiment above.

[0012] The technical solution of the first aspect of the above invention has the following advantages or beneficial effects:

[0013] The technical solution provided by the embodiment of the present invention, after forming a boron-doped layer for the battery substrate to obtain an initially boron-doped substrate, first takes out the initially boron-doped substrate from the oxidation furnace tube and cools it to a temperature not higher than 200°C, and then re-puts the cooled initially boron-doped substrate back into the preheated oxidation furnace tube in an oxygen-free environment. The temperature difference formed between the cooled boron-doped substrate and the preheated oxidation furnace tube can, under the oxygen-free environment of the oxidation furnace tube, greatly activate the inactive boron atoms in the boron-doped layer. Based on the temperature difference formed between the cooled boron-doped substrate and the preheated oxidation furnace tube, further raising the temperature of the initially boron-doped substrate in an oxygen-free environment can further increase the activation amount and activity amount of boron atoms in the entire boron-doped layer (especially the deep junction boron diffusion layer). Subsequently, an oxidation and source-absorbing treatment is performed on the boron-doped layer to redistribute the boron atoms in the deep junction boron diffusion layer, that is, since the boron atoms are greatly activated, the boron atoms in the deep layer of the boron-doped layer migrate outward (i.e., the boron atoms migrate from the inside to the outside), reducing the peak concentration of boron atoms in the deep junction boron diffusion layer, and being able to reduce the concentration difference between the peak boron doping concentration in the inner layer of the finally formed deep junction boron diffusion layer and the boron doping concentration on the surface of the deep junction boron diffusion layer, making the doping concentration of the deep junction boron diffusion layer more uniform, effectively improving the contact performance between the deep junction boron diffusion layer and the metal electrode, and reducing the contact resistance between the deep junction boron diffusion layer and the metal electrode.

[0014] In addition, by combining the temperature difference formed between the cooled boron-doped substrate and the preheated oxidation furnace tube with further raising the temperature of the initially boron-doped substrate in an oxygen-free environment, the inactive boron atoms in the boron-doped layer are activated, reducing the risk of the occurrence of a dead layer (the dead layer is generally caused by the large presence of inactive boron atoms) on the surface of the deep junction boron diffusion layer, and can further push the boron atoms in an oxygen-free environment, that is, push the boron atoms in the boron-doped layer further towards the silicon substrate direction to increase the junction depth of the PN junction, further improving the contact performance between the deep junction boron diffusion layer and the metal electrode and reducing the contact resistance. Description of the Drawings

[0015] Figure 1 is a schematic diagram of the main process of the boron diffusion method for a solar cell provided by an embodiment of the present invention;

[0016] Figure 2 is a schematic diagram of the first structural change of a cell substrate processed by the boron diffusion method provided by an embodiment of the present invention;

[0017] Figure 3 is a schematic diagram of the second structural change of a cell substrate processed by the boron diffusion method provided by an embodiment of the present invention;

[0018] Figure 4A is a schematic diagram of the third structural change of a cell substrate processed by the boron diffusion method provided by an embodiment of the present invention;

[0019] Figure 4B is a schematic diagram of the fourth structural change of a cell substrate processed by the boron diffusion method provided by an embodiment of the present invention;

[0020] Figure 5 is a schematic diagram of the main process of the source doping stage provided by an embodiment of the present invention;

[0021] Figure 6 is a graph showing the change of the doping concentration of the boron diffusion layer with depth provided by Embodiment 1 and the comparative example of the present invention.

[0022] The reference numerals are as follows:

[0023] 10 - cell substrate; 10' - initially boron-doped substrate; 11 - crystalline silicon wafer; 12 - intrinsic silicon thin film layer; 13 - N+ region; 20 - boron-doped layer; 21 - deep junction boron diffusion layer; 22 - borosilicate glass layer; 21' - shallow junction boron diffusion layer; 22' - initial borosilicate glass layer; 30 - silicon oxide layer. Detailed implementation manners

[0024] In the prior art, the boron diffusion process mainly includes depositing a boron source layer by source deposition at a low temperature, and at a temperature higher than 900 °C, pushing boron atoms in the boron source layer into the crystalline silicon substrate / crystalline silicon wafer at a high temperature to form a boron diffusion layer. Subsequently, the temperature is raised to above 1000 °C, and oxidation and source absorption are carried out during the heating process and the subsequent constant temperature process. After oxidation and source absorption, the temperature is lowered to below 800 °C, and cooling oxidation is carried out simultaneously during the cooling process to reduce the diffusion concentration on the surface of the boron diffusion layer. Due to the long oxidation and source absorption time and large oxygen consumption in the prior art, the concentration of the P+ region formed after boron diffusion is relatively low. Although it can reduce the recombination in the PN junction region, at this time, the difference between the surface concentration and the peak concentration of the boron diffusion layer is relatively large, which is not conducive to the contact performance of the P+ region.

[0025] In addition, through research, it is found that since the oxidation and source absorption process has a small promoting effect when the temperature is below 950°C, the generated oxide layer targets source absorption on the P-region surface at this time, has little influence on the peak concentration, and will result in the surface concentration being much lower than the peak concentration. However, since a surface dead layer is likely to appear on the surface of the boron diffusion layer (the surface dead layer means that there are non-active boron atoms on the surface of the boron diffusion layer that cannot form effective contact with the metal electrode), both the too-low surface concentration and the surface dead layer will affect the contact performance between the paste and the PN junction in the subsequent battery. Therefore, a method for reducing the gap between the P+ region surface concentration and the peak concentration is needed to improve the battery contact, increase the fill factor of the battery, and ultimately enhance the conversion efficiency of the battery. Based on this, the embodiments of the present invention provide an improved boron diffusion method for a solar cell.

[0026] Among them, Figure 1 FIG. shows a schematic main process diagram of the boron diffusion method for a solar cell provided by an embodiment of the present invention.

[0027] The embodiments of the present invention provide a boron diffusion method for a solar cell. As Figure 1 shown, the boron diffusion method for this solar cell may include the following steps:

[0028] Step S101: Form a boron-doped layer 20 for the battery substrate 10 in an oxidation furnace tube to obtain a preliminarily boron-doped substrate 10'. The boron-doped layer 20 includes a deep-junction boron diffusion layer 21 and a borosilicate glass layer 22 stacked from the inside to the outside.

[0029] Among them, the battery substrate 10 may be a crystalline silicon wafer 11, or may be the general term for the crystalline silicon wafer 11 and the functional layers formed thereon. Exemplarily, as Figure 2 shown, the battery substrate 10 is a crystalline silicon wafer 11; as Figure 3 shown, the battery substrate 10 is the general term for the crystalline silicon wafer 11 and the intrinsic silicon thin film layer 12 laminated on one main surface of the battery substrate 10; as Figure 4A shown, the battery substrate 10 is the general term for the crystalline silicon wafer 11 and the N+ regions 13 arranged at intervals on one main surface of the crystalline silicon wafer 11; in addition, as Figure 4B shown, the battery substrate 10 may also be the general term for the crystalline silicon wafer 11 and the intrinsic silicon thin film layer 12 and the N+ regions 13 alternately and spacedly arranged on one main surface of the crystalline silicon wafer 11. It should be noted that Figure 2 , Figure 3 , Figure 4A and Figure 4B are only exemplary structures, and any other structure for boron diffusion implemented based on the technical solutions provided by the embodiments of the present invention is within the scope of its protection.

[0030] In addition, the above battery substrate 10 is generally formed based on an N-type silicon substrate to form a PN junction through the technical solutions provided by the embodiments of the present invention.

[0031] Specifically, as Figure 2 and Figure 4A shown, the boron-doped layer 20 can be directly formed on the crystalline silicon wafer 11, that is, boron atoms are pushed into the crystalline silicon wafer 11 to a certain depth to form a deep junction boron diffusion layer 21, and a borosilicate glass layer 22 is formed on the side of the deep junction boron diffusion layer 21 away from the crystalline silicon wafer 11 (i.e., the outside of the deep junction boron diffusion layer 21). Then, the boron-doped layer 20 includes the deep junction boron diffusion layer 21 formed by diffusing boron atoms on the crystalline silicon wafer 11 and the borosilicate glass layer 22 formed on the outside of the deep junction boron diffusion layer 21. In addition, as Figure 3 and Figure 4B shown, the boron-doped layer 20 may include a deep junction boron diffusion layer 21 formed based on the intrinsic silicon thin film 12 laminated on the surface of the crystalline silicon wafer 11 (i.e., boron atoms are doped into a part or all of the intrinsic silicon thin film 12 to form the deep junction boron diffusion layer 21) and a borosilicate glass layer 22 formed on the outside of the deep junction boron diffusion layer 21. Among them, the borosilicate glass layer 22 refers to the mixture formed by the remaining components after boron diffusion and silicon oxide. Specifically, the borosilicate glass layer 22 generally contains silicon oxide, boron oxide and boron atoms.

[0032] Regardless of which structure the boron-doped layer 20 is formed on, as Figure 5 shown, the specific implementation method of this step S101 may include the following steps:

[0033] Step S1011: Form a first silicon oxide layer 30 for the battery substrate 10.

[0034] There are various formation methods for this step.

[0035] Exemplarily, as Figure 2 shown, this step can directly form a first silicon oxide layer 30 on one main surface of the crystalline silicon wafer 11.

[0036] In addition, it can also be as Figure 3 shown, this step forms an intrinsic silicon thin film layer 12 on one main surface of the crystalline silicon wafer 11 (i.e., obtaining the battery substrate 10); and a first silicon oxide layer 30 is formed on the side of the intrinsic silicon thin film layer 12 away from the crystalline silicon wafer 11.

[0037] It can also be as Figure 4A shown, N+ regions 13 arranged at intervals are formed on one main surface of the crystalline silicon wafer 11 (i.e., obtaining the battery substrate 10); a first silicon oxide layer 30 is formed on the region of the crystalline silicon wafer 11 adjacent to the N+ regions 13, and there is an interval region 14 between the first silicon oxide layer 30 and the adjacent N+ regions 13. For this Figure 4AThe structure of the formed first silicon oxide layer 30 is shown. The first silicon oxide layer 30 can be formed synchronously on the outer sides of the N+ region 13 and the spacer region 14, and then the first silicon oxide layer 30 formed on the N+ region 13 and the spacer region 14 is removed by laser etching to obtain Figure 4A the relative relationship among the N+ region 13, the first silicon oxide layer 30, and the spacer region 14 as shown. Additionally, for Figure 4A the structure of the formed first silicon oxide layer 30 shown, it is also possible to form the first silicon oxide layer 30 on the basis of covering a mask on the N+ region 13 and the spacer region 14, and then removing the mask to obtain Figure 4A the structure of the formed first silicon oxide layer 30 shown.

[0038] It is also possible, as Figure 4B shown, to form spaced-apart N+ regions 13 on one main surface of the crystalline silicon wafer 11; form an intrinsic silicon thin film layer 12 in the region adjacent to the N+ region 13 on the crystalline silicon wafer 11, with a spacer region 14 (i.e., obtaining the cell substrate 10) between the intrinsic silicon thin film layer 12 and its adjacent N+ region 13; and form a first silicon oxide layer 30 on the side of the intrinsic silicon thin film layer 12 away from the crystalline silicon wafer 11. For the Figure 4B structure of the formed first silicon oxide layer 30 shown, the first silicon oxide layer 30 can be formed synchronously on the outer sides of the N+ region 13 and the spacer region 14, and then the first silicon oxide layer 30 formed on the N+ region 13 and the spacer region 14 is removed by laser etching to obtain Figure 4B the relative relationship among the N+ region 13, the first silicon oxide layer 30, the intrinsic silicon thin film layer 12, and the spacer region 14 as shown. Additionally, for Figure 4B the structure of the formed first silicon oxide layer 30 shown, it is also possible to form the first silicon oxide layer 30 on the basis of covering a mask on the N+ region 13 and the spacer region 14, and then removing the mask to obtain Figure 4B the structure of the formed first silicon oxide layer 30 shown. It should be noted that other functional layers such as a passivation layer can be contained in the spacer region 14, as long as electrical isolation between the N+ region 13 and the newly formed P+ region can be ensured.

[0039] It should be noted that Figure 4A the formed spaced-apart N+ regions 13 can be formed by existing technologies. Figure 4B The formed alternately arranged N+ regions 13 and intrinsic silicon thin film layers 12 can be formed by existing technologies, which will not be elaborated here. Additionally, the N+ region 13 can be a tunneling oxide layer and an N-type doped polysilicon layer stacked from the inside to the outside.

[0040] That is to say, for battery substrates 10 with different structures, in this step S101, by forming a first silicon oxide layer 30 on the battery substrate 10; sequentially doping boron atoms into the first silicon oxide layer 30 through multiple source gas supply processes to form a shallow junction boron diffusion layer 21' and an initial borosilicate glass layer 22' stacked from the inside to the outside; and under an oxygen-free environment, raising the temperature to promote the boron atoms in the shallow junction boron diffusion layer 21' and the boron atoms in the initial borosilicate glass layer 22', so as to form a deep junction boron diffusion layer 21 and a borosilicate glass layer 22 on the battery substrate 10. Among them, the deep junction boron diffusion layer 21 is formed by the boron atoms in the initial borosilicate glass layer 22' and the boron atoms in the shallow junction boron diffusion layer 21' entering the crystalline silicon wafer 11 or the intrinsic silicon thin film layer 12 on the surface of the crystalline silicon wafer 11 after the temperature is raised and promoted. After this step of treatment, the boron atom concentration in the borosilicate glass layer 22 decreases.

[0041] Specifically, the process of forming the first silicon oxide layer 30 in this step S1011 may include:

[0042] First, in the diffusion equipment preparation stage, that is, preheating the oxidation furnace tube to 830°C - 850°C, evacuating the oxidation furnace tube, and at the same time introducing nitrogen with a flow rate of 3000scm - 7000scm into the oxidation furnace tube to make the environment inside the oxidation furnace tube an oxygen-free environment; among them, the preheating of the oxidation furnace tube can also be adjusted according to the working parameters of the oxidation furnace tube itself. Generally, the preheating temperature is not lower than the standby temperature of the oxidation furnace tube. For example, the preheating temperature in this preheating process can be 830°C, 835°C, 840°C, 845°C, 850°C, etc.; the nitrogen flow rate introduced in this preheating process can be 3000scm, 3500scm, 4000scm, 4500scm, 4800scm, 5000scm, 5500scm, 6000scm, 6500scm, 7000scm, etc.;

[0043] Second, in the boat loading stage, send the quartz boat carrying the battery substrate 10 into the oxidation furnace tube, control the furnace tube temperature to be maintained at 830°C - 850°C, and maintain for 8min - 15min, so that the battery substrate 10 is heated to 830°C - 850°C. Among them, the furnace tube temperature can be 830°C, 835°C, 840°C, 845°C, 850°C, etc.; the maintenance time can be 8min, 10min, 12min, 15min, etc.

[0044] Finally, in the pre-oxidation stage, control the furnace tube temperature to be maintained at 830°C - 850°C, switch the nitrogen gas transported to the oxidation furnace tube to oxygen, the oxygen flow rate introduced into the oxidation furnace tube is 8000sccm - 15000sccm, and the pre-oxidation time is 1min - 10min, and the thickness of the first silicon oxide layer 30 formed is 5nm - 30nm.

[0045] Exemplarily, in the pre-oxidation stage, the furnace tube temperature is maintained at 830°C, 835°C, 840°C, 845°C, 850°C, etc.; the oxygen flow rate is 8000 sccm, 8500 sccm, 9000 sccm, 10000 sccm, 11000 sccm, 12000 sccm, 13000 sccm, 14000 sccm, 15000 sccm, etc. Also, for example, the time of the pre-oxidation stage can be 1 min, 2 min, 3 min, 4 min, 5 min, 7 min, 9 min, 10 min, etc. In addition, the thickness of the first silicon oxide layer 30 formed in the pre-oxidation stage can be 5 nm, 6 nm, 7 nm, 10 nm, 15 nm, 20 nm, 25 nm, 28 nm, 30 nm, etc. That is, after the battery substrate 10 is heated up and the temperature is maintained at 830°C to 850°C, oxygen is passed to the battery substrate 10 to form the first silicon oxide layer 30, ensuring the uniformity of the first silicon oxide layer 30.

[0046] By forming the first silicon oxide layer 30 on the battery substrate 10, on the one hand, it can serve as a buffer layer for subsequent diffusion. During the subsequent source passing process, a large amount of boron oxide and boron atoms are enriched in the first silicon oxide layer 30, which can prevent a large amount of boron oxide and boron atoms from directly impacting the silicon substrate, reducing the damage to the silicon substrate during the diffusion process; on the other hand, the first silicon oxide layer 30 can also effectively control the depth of the subsequent formed deep junction boron diffusion layer 21, thereby effectively controlling the junction depth of the formed PN junction to reduce carrier recombination, which helps to improve the performance of the subsequent formed solar cell.

[0047] Step S1012: Sequentially dope the first silicon oxide layer 30 with boron atoms through multiple source passing processes to form a shallow junction boron diffusion layer 21' and an initial borosilicate glass layer 22' stacked from the inside to the outside.

[0048] Step S1013: In an oxygen-free environment, heat up to promote the boron atoms in the shallow junction boron diffusion layer 21' and the boron atoms in the initial borosilicate glass layer 22' to form a deep junction boron diffusion layer 21 and a borosilicate glass layer 22 on the battery substrate 10. It should be noted that the borosilicate glass layer 22 is formed after the initial borosilicate glass layer 22' is promoted by heating.

[0049] Regarding the above step S1012, as Figure 5 shown, its specific implementation manner may include the following steps:

[0050] Step S1012-1: Introduce oxygen, boron source gas, boron-carrying nitrogen gas, and furnace door nitrogen gas into the oxidation furnace tube. Control the pressure inside the oxidation furnace tube to be 100 mbar to 300 mbar, the temperature inside the oxidation furnace tube to be 830 °C to 850 °C, and the duration to be 2 min to 3 min. Among them, the flow rate of oxygen is 400 sccm to 600 sccm; the flow rate of boron source gas is 100 sccm to 400 sccm; the flow rate of boron-carrying nitrogen gas is 3000 sccm to 4000 sccm; the flow rate of furnace door nitrogen gas is 300 sccm to 700 sccm; restore the inside of the oxidation furnace tube to a nitrogen atmosphere and purge the oxidation furnace tube; the temperature does not change between the source introduction and the purge.

[0051] Among them, the furnace door nitrogen gas generally refers to the nitrogen gas purging the furnace door of the oxidation furnace. This nitrogen gas generally remains in the furnace door area and is used to disperse the boron source gas to avoid the accumulation of the boron source gas in the furnace door area.

[0052] Among them, the boron source generally selects BCl3. Introducing boron-carrying nitrogen gas can avoid the blockage of the gas pipeline by BCl3.

[0053] The pressure inside the oxidation furnace tube controlled in this step can be 100 mbar, 150 mbar, 180 mbar, 200 mbar, 220 mbar, 250 mbar, 280 mbar, or 300 mbar, etc. In addition, the temperature of the oxidation furnace used in this step can be 830 °C, 835 °C, 840 °C, 845 °C, or 850 °C, etc.; the duration of this step can be 2 min, 2.5 min, or 3 min, etc.; the flow rate of oxygen in this step can be 400 sccm, 450 sccm, 500 sccm, 550 sccm, or 600 sccm, etc.; the flow rate of boron source gas in this step can be 100 sccm, 150 sccm, 300 sccm, 350 sccm, or 400 sccm, etc.; the flow rate of boron-carrying nitrogen gas in this step can be 3000 sccm, 3500 sccm, or 4000 sccm, etc.; in addition, the flow rate of furnace door nitrogen gas can be 300 sccm, 400 sccm, 500 sccm, 600 sccm, or 700 sccm, etc.

[0054] Step S1012-2: Introduce oxygen, boron source gas, boron-carrying nitrogen gas, and furnace door nitrogen gas into the oxidation furnace tube. Control the pressure inside the oxidation furnace tube to be 100 mbar to 300 mbar, the temperature inside the oxidation furnace tube to be 830 °C to 850 °C, and the duration to be 2 min to 3 min. Among them, the flow rate of oxygen is 400 sccm to 600 sccm; the flow rate of boron source gas is 100 sccm to 400 sccm; the flow rate of boron-carrying nitrogen gas is 3000 sccm to 4000 sccm; the flow rate of furnace door nitrogen gas is 300 sccm to 700 sccm; restore the inside of the oxidation furnace tube to a nitrogen atmosphere and purge the oxidation furnace tube; the temperature does not change between the source introduction and the purge.

[0055] The pressure inside the oxidation furnace tube controlled in this step can be 100 mbar, 150 mbar, 180 mbar, 200 mbar, 220 mbar, 250 mbar, 280 mbar, 300 mbar, etc. Additionally, the temperature of the oxidation furnace used in this step can be 830 °C, 835 °C, 840 °C, 845 °C, 850 °C, etc.; the duration of this step can be 2 min, 2.5 min, 3 min, etc.; the flow rate of oxygen in this step can be 400 sccm, 450 sccm, 500 sccm, 550 sccm, 600 sccm, etc.; the flow rate of the boron source gas in this step can be 100 sccm, 150 sccm, 300 sccm, 350 sccm, 400 sccm, etc.; the flow rate of boron-carrying nitrogen gas in this step can be 3000 sccm, 3500 sccm, 4000 sccm, etc.; additionally, the flow rate of nitrogen gas at the furnace door can be 300 sccm, 400 sccm, 500 sccm, 600 sccm, 700 sccm, etc.

[0056] Step S1012 - 3: Introduce oxygen, boron source gas, boron-carrying nitrogen gas, and nitrogen gas at the furnace door into the oxidation furnace tube, control the pressure inside the oxidation furnace tube to be 100 mbar to 300 mbar, the temperature inside the oxidation furnace tube to be 830 °C to 850 °C, and the duration to be 2 min to 3 min. Among them, the flow rate of oxygen is 400 sccm to 600 sccm; the flow rate of the boron source gas is 100 sccm to 400 sccm; the flow rate of boron-carrying nitrogen gas is 3000 sccm to 4000 sccm; the flow rate of nitrogen gas at the furnace door is 300 sccm to 700 sccm; restore the inside of the oxidation furnace tube to a nitrogen atmosphere to purge the oxidation furnace tube, and the temperature does not change between the source introduction and the purging.

[0057] The pressure inside the oxidation furnace tube controlled in this step can be 100 mbar, 150 mbar, 180 mbar, 200 mbar, 220 mbar, 250 mbar, 280 mbar, 300 mbar, etc. Additionally, the temperature of the oxidation furnace used in this step can be 830 °C, 835 °C, 840 °C, 845 °C, 850 °C, etc.; the duration of this step can be 2 min, 2.5 min, 3 min, etc.; the flow rate of oxygen in this step can be 400 sccm, 450 sccm, 500 sccm, 550 sccm, 600 sccm, etc.; the flow rate of the boron source gas in this step can be 100 sccm, 150 sccm, 300 sccm, 350 sccm, 400 sccm, etc.; the flow rate of boron-carrying nitrogen gas in this step can be 3000 sccm, 3500 sccm, 4000 sccm, etc.; additionally, the flow rate of nitrogen gas at the furnace door can be 300 sccm, 400 sccm, 500 sccm, 600 sccm, 700 sccm, etc.

[0058] During the above three boron source introduction processes, the boron source introduction conditions can be controlled to be the same for each time, or different. It should be noted that after each boron source introduction is completed, the inside of the oxidation furnace tube needs to be restored to a nitrogen atmosphere first, that is, after purging the oxidation furnace tube with nitrogen, the next boron source introduction can be carried out to avoid excessive accumulation of boron source in the oxidation furnace tube due to too long single boron source introduction time, resulting in too much boron entering the battery substrate 10. Therefore, through three boron source introductions and restoring the inside of the oxidation furnace tube to a nitrogen atmosphere after each boron source introduction is completed, the doping concentration of boron doping can be guaranteed, and the formation of a too deep PN junction can be avoided.

[0059] In addition, after the above three boron source introductions, the boron atoms doped in the first silicon oxide layer 30 can be made more uniform. It should be noted that the above three boron source introductions do not form three boron-silicate glass layers in the first silicon oxide layer 30. Instead, after the first boron source introduction, when boron atoms enter the first silicon oxide layer 30 to form a boron-silicate glass layer, during the second boron source introduction process, boron atoms enter the boron-silicate glass layer formed by the first boron source introduction, changing the boron atom concentration and boron atom distribution in the boron-silicate glass layer. Further, during the third boron source introduction process, boron atoms enter the boron-silicate glass layer formed by the second boron source introduction, further improving the boron atom concentration and boron atom distribution in the boron-silicate glass layer, so that during the subsequent temperature increase to promote boron atoms, while reducing the lateral diffusion of boron atoms, the distribution uniformity of the deep junction boron diffusion layer 21 in the lateral direction (the direction parallel to the main surface of the battery substrate 10) can be improved, and the doping concentration difference of the deep junction boron diffusion layer 21 in the thickness direction of the battery substrate 10 can be reduced.

[0060] Further, as Figure 5 shown, the specific implementation manner of the above step S1013 may include: step S1013-1: Raise the temperature of the oxidation furnace tube to 880 °C to 920 °C, and control the nitrogen flow rate into the oxidation furnace tube to be 2000 sccm to 4000 sccm; the pressure inside the oxidation furnace tube is 100 mbar to 300 mbar, and the duration is 5 min to 15 min to promote boron atoms to form a deep junction boron diffusion layer 21.

[0061] Exemplarily, in this step S1013-1, the temperature of the oxidation furnace tube can be raised to 880 °C, 890 °C, 900 °C, 910 °C, 920 °C, etc. The nitrogen flow rate introduced into the oxidation furnace tube in this step S1013-1 can be 2000 sccm, 2200 sccm, 2500 sccm, 2800 sccm, 3000 sccm, 4000 sccm, etc. Additionally, the pressure inside the oxidation furnace tube in this step S1013-1 can be 100 mbar, 140 mbar, 150 mbar, 170 mbar, 200 mbar, 230 mbar, 250 mbar, 280 mbar, 300 mbar, etc.

[0062] By raising the temperature of the oxidation furnace tube and in a nitrogen atmosphere, boron atoms can be pushed towards the Figure 2 or Figure 4A shown crystalline silicon wafer 11 or Figure 3 or Figure 4B shown intrinsic silicon thin film layer 12, that is, boron atoms enter the crystalline silicon wafer 11 or the intrinsic silicon thin film layer 12 to form a deep junction boron diffusion layer 21, and the boron atom concentration in the borosilicate glass layer 22 decreases. Compared with an oxygen atmosphere, this nitrogen atmosphere helps the boron atoms to be pushed towards the crystalline silicon wafer 11 or the intrinsic silicon thin film layer 12, thereby obtaining an initially boron-doped substrate 10' as exemplarily shown in Figure 2 , Figure 3 , Figure 4A and Figure 4B Exemplarily shown.

[0063] Step S102: Take out the initially boron-doped substrate 10' from the oxidation furnace tube and cool the initially boron-doped substrate 10' so that the temperature of the initially boron-doped substrate 10' after cooling is not higher than 200 °C.

[0064] For example, in this step, the initially boron-doped substrate 10' can be cooled to 200 °C, 180 °C, 150 °C, 120 °C, 100 °C, 80 °C, 70 °C, 50 °C, 30 °C, 20 °C, 15 °C, etc.

[0065] Specifically, in this step, the oxidation furnace tube can be first cooled to the standby temperature, and nitrogen gas is introduced into the oxidation furnace tube at a flow rate of 20,000 sccm to 30,000 sccm for a duration of 10 min to 15 min. The preliminarily boron-doped substrate 10' is taken out of the oxidation furnace tube. Preferably, the preliminarily boron-doped substrate 10' is cooled to room temperature. For example, the flow rate of the nitrogen gas introduced in this step can be 20,000 sccm, 25,000 sccm, 28,000 sccm, or 30,000 sccm, etc. The duration can be 10 min, 12 min, 13 min, or 15 min, etc. Through this process, the pressure inside the oxidation furnace tube reaches the atmospheric pressure to facilitate taking out the preliminarily boron-doped substrate 10' from the oxidation furnace tube. Additionally, it can be understood that the room temperature in the above-mentioned cooling of the preliminarily boron-doped substrate 10' to room temperature is generally the ambient temperature of 10°C to 30°C. Exemplarily, the room temperature can be 10°C, 15°C, 20°C, 25°C, or 30°C, etc.

[0066] Step S103: Put the cooled preliminarily boron-doped substrate 10' back into the preheated oxidation furnace tube, and under an oxygen-free environment, heat up the preliminarily boron-doped substrate 10' to activate the inactive boron atoms in the boron-doped layer 20.

[0067] For this step, its specific implementation manner can include: putting the cooled preliminarily boron-doped substrate 10' back into the oxidation furnace tube with a preheating temperature reaching 870°C to 900°C; with a nitrogen gas flow rate of 2,000 sccm to 3,000 sccm, heating up the oxidation furnace tube to 950°C to 1,050°C and maintaining the temperature for a duration of 5 min to 8 min, and controlling the pressure inside the furnace tube to be 100 mbar to 200 mbar. For example, the preset temperature can be 870°C, 880°C, 890°C, or 900°C, etc. The preheating temperature is generally higher than the standby temperature of the oxidation furnace tube. Also, for example, the flow rate of the nitrogen gas introduced in this step can be 2,000 sccm, 2,400 sccm, 2,500 sccm, 2,800 sccm, or 3,000 sccm, etc. In this step, after the cooled preliminarily boron-doped substrate 10' is stabilized at 870°C to 900°C, the temperature of the oxidation furnace tube is further increased. For example, the temperature of the oxidation furnace tube can be increased to 950°C, 980°C, 1,000°C, 1,020°C, or 1,050°C, etc.

[0068] This step S103 works in conjunction with the above-mentioned step S102. First, the initially boron-doped substrate 10' with the boron-doped layer 20 formed in step S101 is cooled to 200 °C or below. Then, the initially boron-doped substrate 10' at 200 °C or below is placed back into the preheated oxidation furnace tube. Due to the temperature difference between the initially boron-doped substrate 10' and the preheated oxidation furnace tube, in an oxygen-free environment, this temperature difference can effectively activate the inactive boron atoms in the boron-doped layer 20. And in the oxygen-free environment, further increasing the temperature of the initially boron-doped substrate 10' can further activate the inactive boron atoms. The activated inactive boron atoms result in more active boron atoms, and the active boron atoms are more likely to migrate. Therefore, based on steps S102 and S103, subsequently, through the oxidation and gettering treatment, the boron atoms in the region with a relatively high doping concentration of the deep-junction boron diffusion layer 21 in the boron-doped layer 20 can be migrated to the outside, which helps to reduce the peak doping concentration in the deep-junction boron diffusion layer 21 and reduce the content of inactive boron atoms on the surface of the deep-junction boron diffusion layer 21, so as to reduce the risk of the formation of a dead layer on the surface of the deep-junction boron diffusion layer 21.

[0069] Step S104: Perform an oxidation and gettering treatment on the boron-doped layer 20 in the initially boron-doped substrate 10' to redistribute the boron atoms in the deep-junction boron diffusion layer 21.

[0070] Specifically, the specific process of implementing the oxidation and gettering treatment in this step S104: Oxygen is introduced into the oxidation furnace tube at a flow rate of 20000 sccm to 26000 sccm to form a second silicon oxide layer, and the oxidation and gettering treatment of the boron-doped layer 20 is carried out based on the second silicon oxide layer. The conditions for the oxidation and gettering treatment include: the temperature of the oxidation furnace tube is 1000 °C to 1050 °C, the pressure of the oxidation furnace tube is 800 mbar to 900 mbar, and the duration is 60 min to 150 min. Among them, in this step, nitrogen can be switched to oxygen after the temperature is raised to 1000 °C to 1050 °C, or nitrogen can be directly switched to oxygen during the heating process. No matter which method is used, this step introduces oxygen in a high-temperature environment. That is to say, compared with the conventional boron diffusion process, the technical solution provided by the embodiment of the present invention omits the heating and oxidation gettering process.

[0071] For the parameters controlled in step S104, exemplarily, the oxygen flow rate can be 20000 sccm, 21000 sccm, 23000 sccm, 24000 sccm, 25000 sccm, 26000 sccm, etc. The temperature of the oxidation furnace controlled in this step can be 1000 °C, 1020 °C, 1040 °C, 1050 °C, etc. Additionally, the pressure of the oxidation furnace tube in this step can be 800 mbar, 820 mbar, 840 mbar, 850 mbar, 870 mbar, 890 mbar, 900 mbar, etc. The duration of the oxidation and boron source absorption in this step can be 60 min, 65 min, 70 min, 75 min, 80 min, 90 min, 100 min, 120 min, 150 min, etc. Since the above-mentioned step S102 and step S103 cooperate to activate the inactive boron atoms, this step S104 cooperates with step S102 and step S103, making it easier for boron atoms to migrate to the second silicon oxide layer. Compared with the prior art, the duration of the oxidation and boron source absorption in this step S104 is shorter, which can effectively reduce the energy consumption in the production of solar cells.

[0072] In addition, although the duration of the oxidation and boron source absorption in this step S104 is shorter, due to the activation of the inactive boron atoms in the boron-doped layer 20 by the above-mentioned step S103, this step S104 can further effectively improve the boron atom migration ability. Under the short-time oxidation and boron source absorption in this step, the boron atoms in the peak region of the deep junction boron diffusion layer 21 can migrate to reduce the peak value of the doping concentration of the boron atoms in the deep junction boron diffusion layer 21 and make the distribution of the boron atoms in the deep junction boron diffusion layer 21 more uniform.

[0073] Furthermore, by cooperating with the above-mentioned step S103 and step S104, during the oxidation source absorption process, oxygen is introduced at a temperature of 950°C or above, which can not only further promote the junction depth of the deep junction boron diffusion layer 21, but also can condense the active boron atoms in the area with relatively high doping concentration into the second silicon oxide layer, thereby reducing the peak concentration of boron doping in the deep junction boron diffusion layer 21. In summary, the technical solution provided by the present invention is to form a boron-doped layer 20 for the battery substrate 10 to obtain a primary boron-doped substrate 10', and then first cool the primary boron-doped substrate 10' to a temperature not higher than 200°C, and then put the cooled primary boron-doped substrate 10' back into the preheated oxidation furnace tube. The temperature difference formed between the cooled primary boron-doped substrate 10' and the preheated oxidation furnace tube can activate a large number of inactive boron atoms in an oxygen-free environment. On the basis of the temperature difference formed between the cooled primary boron-doped substrate 10' and the preheated oxidation furnace tube, the primary boron-doped substrate 10' is further heated in an oxygen-free environment, which can further increase the activation amount of boron atoms and the activation of boron atoms. The deep junction boron diffusion layer 21 included in the boron doping layer 20 is subsequently subjected to an oxidation source absorption treatment. Since a large number of boron atoms are activated, the boron atoms in the inner layer of the deep junction boron diffusion layer 21 migrate to the surface of the deep junction boron diffusion layer 21, and the boron atoms in the deep junction boron diffusion layer 21 migrate outward, thereby reducing the peak concentration of boron atoms in the deep junction boron diffusion layer 21, and reducing the concentration difference between the peak boron doping concentration of the inner layer of the deep junction boron diffusion layer 21 and the boron doping concentration on the surface of the deep junction boron diffusion layer 21, thereby making the doping concentration of the deep junction boron diffusion layer 21 more uniform, effectively improving the contact performance between the deep junction boron diffusion layer 21 and the metal electrode, and reducing the contact resistance between the deep junction boron diffusion layer 21 and the metal electrode. That is, the boron diffusion method provided in the embodiment of the present invention activates the inactive boron atoms in the deep junction boron diffusion layer 21 by re-regulating the heating and cooling process and by means of the high temperature difference, so that the boron atoms in the deep junction boron diffusion layer 21 can migrate outward more, reduce the peak value of the boron doping concentration in the deep junction boron diffusion layer 21, and improve the uniformity of the distribution of boron atoms in the deep junction boron diffusion layer 21. In addition, by means of the high temperature difference, the inactive boron atoms on the surface of the deep junction boron diffusion layer 21 are activated to reduce the risk of a dead layer (the dead layer is mainly caused by inactive boron atoms) on the surface of the deep junction boron diffusion layer 21, so as to achieve the purpose of improving the contact performance between the deep junction boron diffusion layer 21 and the metal electrode and reducing the contact resistance between the deep junction boron diffusion layer 21 and the metal electrode.

[0074] Since the entire boron diffusion method mainly uses the oxidation furnace tube commonly used in the current solar cell production process as the process equipment, on the basis of the original process production, the heating and cooling processes and the coordination between heating and cooling are adjusted. All the oxidations in the heating process and the cooling process in the existing oxidation process are cancelled, the influence of low-temperature oxidation on the surface concentration is reduced, the process controllability is improved, which is beneficial to the industrialization of the boron diffusion method. Moreover, no new equipment is required in the whole process, and the oxygen consumption can be reduced, the cost of boron diffusion can be effectively controlled, and it is suitable for mass production and promotion.

[0075] In addition, the temperature difference formed between the initially boron-doped substrate 10' cooled and the preheated oxidation furnace tube is combined with further heating the initially boron-doped substrate 10' in an oxygen-free environment, which can activate the boron atoms in the deep junction boron diffusion layer 21 and the borosilicate glass layer 22, and can further promote the boron atoms in the oxygen-free environment to increase the junction depth of the PN junction and further improve the contact performance between the deep junction boron diffusion layer 21 and the metal electrode.

[0076] Further, after the deep junction boron diffusion layer 21 and the borosilicate glass layer 22 stacked from the inside to the outside are formed for the battery substrate 10 in the above step S101, the initially boron-doped substrate 10' is cooled to a temperature not higher than 200 °C through step S102, and then the cooled initially boron-doped substrate 10' is heated again through step S103 to activate the inactive boron atoms in the boron-doped layer 20, and then it enters step S104 for oxidation and source absorption treatment. Since after the deep junction boron diffusion layer 21 and the borosilicate glass layer 22 (i.e., boron diffusion) are formed, the cooling and heating processes are experienced in the middle before the oxidation and source absorption are carried out, which separates the boron diffusion from the oxidation and source absorption completely. The cooling and heating processes are experienced in the middle, which is more beneficial to activating the boron atoms in the boron-doped layer 20 (especially the deep junction boron diffusion layer 21).

[0077] In addition, compared with the prior art, the technical solution provided by the embodiment of the present invention cancels the oxygen oxidation in the heating process and the oxygen oxidation in the cooling process during the oxidation and source absorption process, reduces the oxygen consumption, and is beneficial to cost control.

[0078] Further, for the technical solution provided by the embodiment of the present invention, before the oxidation and source absorption, cooling is carried out first and then heating, which will not cause too high boron doping concentration in the PN junction region and will not cause boron atom recombination. By cooling first and then heating, more is to activate the boron atoms on the dead layer surface of the deep junction boron diffusion layer 21, which is beneficial to activating the inactive boron atoms on the surface of the deep junction boron diffusion layer 21, reducing the dead layer on the surface of the deep junction boron diffusion layer 21 (the dead layer is mainly formed due to the existence of a large number of inactive boron atoms), reducing the contact resistance, and reducing the difficulty of the subsequent cleaning process (the dead layer is relatively difficult to clean).

[0079] Further, as Figure 1 shown, after the above step S104, it may further include:

[0080] Step S105: Under an anaerobic environment, cool down the oxidation furnace tube to the standby temperature, and restore the pressure of the oxidation furnace tube to the atmospheric pressure, with a duration of 40 min to 50 min. For example, the duration of this step can be 40 min, 45 min, or 50 min, etc. The anaerobic environment of this step can be achieved by nitrogen or other inert gases. It should be noted that after the oxidation and source absorption are completed at a temperature of 1000°C to 1050°C of the oxidation furnace tube in the above step S104, step S105 is entered, the oxygen used for oxidation and source absorption is switched to nitrogen or other inert gases, and the product with the deep junction boron diffusion layer 21 is cooled down under an anaerobic environment. That is to say, the technical solution provided by the embodiment of the present invention omits the process of cooling and oxidation source absorption. More specifically, the technical solution provided by the embodiment of the present invention only performs oxidation source absorption treatment under a high-temperature environment, omitting the processes of heating and oxidation source absorption and cooling and oxidation source absorption. Exemplarily, nitrogen is introduced to restore the pressure of the oxidation furnace tube to the atmospheric pressure, and the flow rate of the introduced nitrogen can be selected according to requirements. It should be noted that this duration refers to the time counted from the start of introducing nitrogen and the start of cooling the oxidation furnace tube. This step S105 cools down the solar cell with a boron-doped layer 20 under an anaerobic environment. Compared with the prior art of cooling and oxidizing for further oxidation source absorption in an oxygen environment, this step cools down the boron-doped layer 20 under an anaerobic environment, which can effectively reduce the fluctuation of the doping concentration of the surface active boron atoms in the deep junction boron diffusion layer 21 of the boron-doped layer 20. Therefore, during the cooling process, the doping concentration of the surface active boron atoms in the deep junction boron diffusion layer 21 can continuously maintain a relatively high doping concentration (compared with the surface concentration of the boron diffusion layer prepared by the existing conventional process), which is beneficial to improving the contact performance of the deep junction boron diffusion layer 21 and reducing the contact resistance between the deep junction boron diffusion layer 21 and the metal electrode. Thereby effectively improving the fill factor and open-circuit voltage of the solar cell and enhancing the efficiency of the cell.

[0081] In addition, compared with the surface concentration of the boron diffusion layer prepared by the existing conventional process, the technical solution provided by the embodiment of the present invention, on the one hand, activates the non-active boron atoms in the boron-doped layer by the temperature difference formed between the cooled boron-doped substrate and the preheated oxidation furnace tube and the heating of the initially boron-doped substrate under an anaerobic environment, and on the other hand, effectively reduces the fluctuation of the doping concentration of the surface active boron atoms in the deep junction boron diffusion layer 21 of the boron-doped layer 20 during the cooling process under an anaerobic environment after high-temperature oxidation source absorption, which is beneficial to further increasing the doping concentration of the surface active boron atoms in the deep junction boron diffusion layer 21.

[0082] Further, after the above step S105, it may further include: removing the borosilicate glass layer after the oxidation and boron source absorption treatment. This removal process can be directly completed by using existing processes for removing the borosilicate glass layer, such as wet etching, laser etching, etc. It can be understood that during the oxidation and boron source absorption treatment in the above step S104, the formed second silicon oxide layer will absorb boron atoms to form a new borosilicate glass layer, and this new borosilicate glass layer is located outside the original borosilicate glass layer 22. This step will remove both the original borosilicate glass layer 22 and the newly formed borosilicate glass layer, etc. In short, all the borosilicate glass layers formed after the oxidation and boron source absorption treatment are removed.

[0083] In addition, the junction depth of the PN junction formed by the technical solution provided by the above embodiment is generally 1μm - 1.3μm. For example, the junction depth can be 1μm, 1.1μm, 1.2μm, or 1.3μm, etc. The junction depth of the PN junction formed by this technical solution is beneficial to form a stable contact with the metal electrode and can effectively reduce the risk of metal electrode detachment. Moreover, the junction depth of the PN junction formed by this technical solution can minimize carrier recombination as much as possible, which helps to improve the efficiency and performance of the solar cell.

[0084] Further, an embodiment of the present invention also provides a solar cell. This solar cell includes: a deep junction boron diffusion layer 21 formed based on the boron diffusion method of the solar cell provided by the above embodiment. Among them, the deep junction boron diffusion layer 21 can be in direct contact with the crystalline silicon wafer 11 of the solar cell. The deep junction boron diffusion layer 21 can be formed by doping on the surface of the crystalline silicon wafer 11, or the deep junction boron diffusion layer 21 can also be doped in the intrinsic silicon thin film layer 12 on the crystalline silicon wafer 11.

[0085] The following uses two specific embodiments to detail the boron diffusion method of the solar cell provided by the embodiment of the present invention.

[0086] Embodiment 1:

[0087] Step A1, Equipment preparation stage, the set temperature in the oxidation furnace tube is 850°C, and the flow rate of nitrogen is 5000 scm.

[0088] Step B1, Boat loading stage, send the quartz boat carrying the crystalline silicon wafer into the furnace tube, the running time is 12 min, and the temperature in the furnace tube is set to 850°C.

[0089] Step C1, Vacuum pumping stage, the furnace tube is pumped to a certain vacuum degree by a vacuum pump.

[0090] Step D1, Pre-oxidation stage, the temperature in the furnace tube is maintained at 850°C, control the oxygen flow rate to be 10000 sccm, and the pre-oxidation duration is 4 min to form a first silicon oxide layer on the surface of the silicon wafer.

[0091] Step E1, the first source introduction stage: The temperature inside the furnace tube is 850 °C, the oxygen flow rate is 400 sccm, the boron source flow rate is 120 sccm, the nitrogen flow rate carrying the boron source is 3000 sccm, the furnace door nitrogen flow rate is 300 sccm, and the duration is 2 min. After the source introduction is completed, the furnace tube is purged with purging nitrogen at a flow rate of 200 sccm and furnace door nitrogen at a flow rate of 1000 sccm for 2 min. During the source introduction process, the pressure inside the furnace tube is maintained at 220 mbar.

[0092] Step F1, the second source introduction stage: The temperature inside the furnace tube is controlled at 850 °C, the oxygen flow rate is 400 sccm, the boron source flow rate is 120 sccm, the nitrogen flow rate carrying the boron source is 3000 sccm, the furnace door nitrogen flow rate is 300 sccm, and the duration is 2 min. After the source introduction is completed, the furnace tube is purged with purging nitrogen at a flow rate of 200 sccm and 1000 sccm of furnace door nitrogen for 2 min. During the source introduction process, the pressure inside the furnace tube is maintained at 220 mbar.

[0093] Step G1, the third source introduction stage: The temperature inside the furnace tube is controlled at 850 °C, the oxygen flow rate is 400 sccm, the boron source flow rate is 120 sccm, the nitrogen flow rate carrying the boron source is 3000 sccm, the furnace door nitrogen flow rate is 300 sccm, and the duration is 2 min. After the source introduction is completed, the furnace tube is purged with purging nitrogen at a flow rate of 200 sccm and 1000 sccm of furnace door nitrogen for 2 min. During the source introduction process, the pressure inside the furnace tube is maintained at 220 mbar. Through three times of source introduction, a boron source layer is deposited on the surface of the first silicon oxide layer to form a shallow junction boron diffusion layer 21' and an initial borosilicate glass layer 22' on the battery substrate 10.

[0094] Step H1, the heating and advancing stage: The temperature of the furnace tube is increased from 850 °C to 890 °C, nitrogen is introduced into the oxidation furnace tube, the nitrogen flow rate is 3500 sccm, the pressure inside the oxidation furnace tube is maintained at 220 mbar, and the duration is 5 min to obtain the initially boron-doped substrate 10'.

[0095] Step I1, the furnace tube cooling and boat removal cooling stage: The temperature of the furnace tube is reduced to 790 °C, the nitrogen flow rate is adjusted to 20000 sccm, the pressure of the furnace tube is restored to atmospheric pressure, the quartz boat is pushed out of the furnace tube, and the boron diffusion process ends. The initially boron-doped substrate on the quartz boat is cooled to about 100 °C.

[0096] Step J1, the boat loading and heating stage: During the boat loading stage, the temperature of the furnace tube gradually rises to 880 °C. After the temperature of the furnace tube stabilizes at 880 °C, the initially boron-doped substrate is stabilized at 880 °C. After the furnace tube is evacuated and leak-tested, the pressure reaches 200 mbar, the temperature is increased to 950 °C, and the nitrogen flow rate is controlled at 2000 sccm. The temperature of 950 °C lasts for 5 min.

[0097] Step K1, Oxidation and Source Absorption Stage: After the temperature of the furnace tube rises and is maintained at 1050 °C, nitrogen is switched to oxygen at a constant temperature of 1050 °C, and oxidation and source absorption are carried out under the condition that the oxygen flow rate is 20000 sccm. The entire oxidation and source absorption duration is 100 min.

[0098] Step L1, Cooling and Gas Filling Stage: The temperature of the furnace tube is reduced to 790 °C, nitrogen is filled into the furnace tube at a flow rate of 20000 sccm, the pump pressure reaches 1000 MPa, and the quartz boat is pushed out of the furnace tube, ending the process.

[0099] Example 2:

[0100] Step A2, Equipment Preparation Stage: The set temperature inside the oxidation furnace tube is 850 °C, and the nitrogen flow rate is 5000 sccm.

[0101] Step B2, Boat Loading Stage: The quartz boat carrying the silicon wafer is sent into the furnace tube, and the running time is 12 min. The temperature inside the furnace tube is set at 850 °C.

[0102] Step C2, Vacuum Pumping Stage: The furnace tube is pumped to a certain vacuum degree by a vacuum pump.

[0103] Step D2, Pre-oxidation Stage: The temperature inside the furnace tube is maintained at 850 °C, the oxygen flow rate is controlled at 10000 sccm, and the pre-oxidation duration is 4 min to form a first silicon oxide layer on the surface of the silicon wafer.

[0104] Step E2, First Source Introduction Stage: The temperature inside the furnace tube is 850 °C, the oxygen flow rate is 400 sccm, the boron source flow rate is 120 sccm, the nitrogen flow rate carrying the boron source is 3000 sccm, and the furnace door nitrogen flow rate is 300 sccm, with a duration of 2 min. After the source introduction is completed, the furnace tube is purged for 2 min with purging nitrogen at a flow rate of 200 sccm and furnace door nitrogen at a flow rate of 1000 sccm. The pressure inside the furnace tube is maintained at 220 mbar during the source introduction process.

[0105] Step F2, Second Source Introduction Stage: The temperature inside the furnace tube is controlled at 850 °C, the oxygen flow rate is 400 sccm, the boron source flow rate is 120 sccm, the nitrogen flow rate carrying the boron source is 3000 sccm, and the furnace door nitrogen flow rate is 300 sccm, with a duration of 2 min. After the source introduction is completed, the furnace tube is purged for 2 min with purging nitrogen at a flow rate of 200 sccm and 1000 sccm furnace door nitrogen. The pressure inside the furnace tube is maintained at 220 mbar during the source introduction process.

[0106] Step G2, the third boron source introduction stage: The temperature inside the furnace tube is controlled at 850 °C, the flow rate of oxygen is 400 sccm, the flow rate of boron source is 120 sccm, the flow rate of nitrogen carrying the boron source is 3000 sccm, the flow rate of nitrogen at the furnace door is 300 sccm, and the duration is 2 min. After the boron source introduction is completed, the furnace tube is purged with purging nitrogen at a flow rate of 200 sccm and furnace door nitrogen at a flow rate of 1000 sccm for 2 min. During the boron source introduction process, the pressure inside the furnace tube is maintained at 220 mbar. Through three times of boron source introduction, a boron source layer is deposited on the surface of the first silicon oxide layer to form a shallow junction boron diffusion layer 21' and an initial boron-silicon glass layer 22' on the battery substrate 10.

[0107] Step H2, the temperature increase and promotion stage: The temperature of the furnace tube is increased from 850 °C to 900 °C, nitrogen is introduced into the oxidation furnace tube, the flow rate of nitrogen is 3500 sccm, and the duration is 5 min to obtain the initially boron-doped substrate 10'.

[0108] Step I2, the furnace tube cooling and boat removal and cooling stage: The temperature of the furnace tube is reduced to 790 °C, the flow rate of nitrogen is 20000 sccm, the pressure of the furnace tube is restored to atmospheric pressure, the quartz boat is pushed out of the furnace tube, the boron diffusion process ends, and the initially boron-doped substrate on the quartz boat is cooled to about 100 °C.

[0109] Step J2, the boat entry and temperature increase stage: During the boat entry stage, the temperature of the furnace tube is gradually stabilized at 890 °C. After the temperature of the furnace tube is stabilized at 890 °C, the quartz boat carrying the initially boron-doped substrate is re-introduced into the furnace tube. After vacuum pumping and leak detection, the temperature is increased to 1000 °C, and the flow rate of nitrogen is controlled at 2000 sccm, and the duration is 8 min.

[0110] Step K2, the oxidation and boron source absorption stage: The temperature of the furnace tube is maintained at 1000 °C. Under the condition that the flow rate of oxygen is 20000 sccm, the oxidation and boron source absorption is continued at a constant temperature of 1000 °C, and the entire oxidation and boron source absorption duration is 100 min.

[0111] Step L2, the temperature decrease and nitrogen filling stage: The temperature of the furnace tube is reduced to 790 °C, and nitrogen is filled into the furnace tube at a flow rate of 20000 sccm. When the pump pressure reaches atmospheric pressure, the quartz boat is pushed out of the furnace tube, and the process ends.

[0112] Comparative Example 1:

[0113] Step A3, the equipment preparation stage: The set temperature inside the furnace tube is 850 °C, and the flow rate of nitrogen is 5000 scm.

[0114] Step B3, the boat loading stage: The quartz boat carrying the crystalline silicon wafer is sent into the furnace tube, and the running time is 12 min. The temperature inside the furnace tube is set at 850 °C.

[0115] Step C3, evacuation stage: The furnace tube is evacuated by a vacuum pump to a certain vacuum degree.

[0116] Step D3, pre-oxidation stage: The temperature inside the furnace tube is raised to 850 °C, the oxygen flow rate is 10000 sccm, and the oxidation duration is 4 min to form a first silicon oxide layer on the surface of the silicon wafer.

[0117] Step E3, first source injection stage: The temperature inside the furnace tube is 850 °C, the oxygen flow rate is 400 sccm, the boron source flow rate is 120 sccm, the nitrogen flow rate carrying the boron source is 3000 sccm, and the furnace door nitrogen flow rate is 300 sccm, with a duration of 2 min. After the source injection is completed, the furnace tube is purged with purging nitrogen at a flow rate of 200 sccm and furnace door nitrogen at a flow rate of 1000 sccm for 2 min.

[0118] Step F3, second source injection stage: The temperature inside the furnace tube is 850 °C, the oxygen flow rate is 400 sccm, the boron source flow rate is 120 sccm, the nitrogen flow rate carrying the boron source is 3000 sccm, and the furnace door nitrogen flow rate is 300 sccm, with a duration of 2 min. After the source injection is completed, the furnace tube is purged with purging nitrogen at a flow rate of 200 sccm and furnace door nitrogen at a flow rate of 1000 sccm for 2 min.

[0119] Step G3, third source injection stage: The temperature inside the furnace tube is 850 °C, the oxygen flow rate is 400 sccm, the boron source flow rate is 120 sccm, the nitrogen flow rate carrying the boron source is 3000 sccm, and the furnace door nitrogen flow rate is 300 sccm, with a duration of 2 min. After the source injection is completed, the furnace tube is purged with purging nitrogen at a flow rate of 200 sccm and furnace door nitrogen at a flow rate of 1000 sccm for 2 min.

[0120] Step H3, temperature increase and advancement stage: The furnace tube temperature is raised from 850 °C to 900 °C, and the furnace door nitrogen flow rate is 3500 sccm, with a duration of 5 min.

[0121] Step I3, furnace tube cooling stage: The furnace tube temperature is lowered to 790 °C, the nitrogen flow rate is 20000 sccm, and the furnace tube pressure returns to atmospheric pressure, ending the boron diffusion process.

[0122] Step J3, oxidation and temperature increase stage: Directly take the product at about 790 °C after the boron diffusion process in Step I3 into the oxidation and temperature increase stage. In an oxygen atmosphere, the furnace tube temperature gradually stabilizes to 890 °C during the boat loading stage.

[0123] Step K3, Oxidation and Source Absorption Stage: Under the condition that the oxygen flow rate is 20,000 sccm, the furnace tube temperature is raised and then maintained at 1000 °C, and oxidation and source absorption continue at a constant temperature. The entire oxidation and source absorption duration is 100 min.

[0124] Step L3, Cooling and Oxidation Stage: Under the condition that the oxygen flow rate is 20,000 sccm, the furnace tube temperature is gradually reduced to 800 °C, and oxidation and source absorption continue during the cooling process. The entire oxidation and source absorption duration is 50 min.

[0125] Step M3, Cooling and Gas Filling Stage: The furnace tube temperature is reduced to 790 °C, nitrogen gas with a flow rate of 20,000 sccm is filled, the pump pressure reaches atmospheric pressure, and the quartz boat is pushed out of the furnace tube, and the process ends.

[0126] Comparative Example 2:

[0127] The processing procedures and parameters of steps A3 (Equipment Preparation Stage), B3 (Boat Placing Stage), C3 (Vacuum Pumping Stage), D3 (Pre-oxidation Stage), E3 (First Source Feeding Stage), F3 (Second Source Feeding Stage), G3 (Third Source Feeding Stage), L3 (Cooling and Oxidation Stage), and M3 (Cooling and Gas Filling Stage) of this Comparative Example 2 are exactly the same as those of Comparative Example 1, and will not be elaborated here. The steps where Comparative Example 2 differs from Comparative Example 1: The furnace tube temperature in the heating and advancing stage of step H3 of Comparative Example 1 is increased from 850 °C to 970 °C, and the other parameters of this step are the same as those of Comparative Example 1. Further, this Comparative Example 2 omits steps I3 (Furnace Tube Cooling Stage) and J3 (Oxidation and Heating Stage) of Comparative Example 1, and directly enters step K3 from step H3. After directly entering step K3 from step H3 in Comparative Example 2, the temperature of step K3 is controlled to be stable at 1050 °C, and the oxidation and source absorption time is also 100 min.

[0128] The main differences in the processes between the above-mentioned Example 1 and Example 2 and Comparative Example 1 are that in Example 1 and Example 2 provided by the present invention, in the furnace tube cooling and boat taking out and cooling stage, the battery substrate is cooled to a relatively low temperature (about 100 °C), and in the subsequent boat entering and heating stage, the battery substrate is heated in an oxygen-free environment. After the heating in the oxygen-free environment is completed, it enters the oxidation and source absorption stage. After the oxidation and source absorption stage is completed, it directly enters the cooling and gas filling stage, omitting the cooling and oxidation stage (that is, Example 1 and Example 2 directly enter the cooling and gas filling stage from the oxidation and source absorption stage). The difference is that in the comparative example, there is no cooling involved in the furnace tube cooling stage, and in the oxidation and heating stage after the furnace tube cooling stage, it is directly oxidized and heated (that is, the product after the boron diffusion process in step I3 directly enters the oxidation and heating stage at about 790 °C), and there is also a cooling and oxidation stage (step L3) between the oxidation and source absorption stage (step K3) and the cooling and gas filling stage (step M3).

[0129] By detecting the passivation effects and electrical properties of solar cells with deep junction boron diffusion layers produced in Example 1, solar cells with boron diffusion layers produced in Example 2, solar cells with boron diffusion layers produced in Comparative Example 1, and solar cells with boron diffusion layers produced in Comparative Example 2, the test results show that in the case where the processing procedures in Example 1 and Example 2 are exactly the same and only the processing parameters are slightly different, the test results of Example 1 and Example 2 do not differ much, indicating that the technical solutions provided in the embodiments of the present invention can be regulated within a certain range by controlling parameters (such as parameters in the temperature rise and advancement stage, parameters in the boat entry and temperature rise stage, and parameters in the oxidation and source absorption stage). Therefore, the technical solutions provided in the embodiments of the present invention have a certain process operability window, which is helpful for product industrialization and process promotion. Since the detection results of Example 1 and Example 2 are similar, the detection results of Example 1, Comparative Example 1, and Comparative Example 2 are further explained below. The detection results of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Table 1 below.

[0130] Table 1

[0131]

[0132] Among them, Lifetime in Table 1 represents the hole carrier lifetime in the silicon wafer after boron diffusion. The higher the carrier lifetime, the more conducive the battery is to the transmission of carriers; J0 represents the recombination current density, which represents the degree of carrier recombination in the battery. The higher the recombination degree, the greater the current density and the lower the battery efficiency; Est_Bulk_Lifetime_ represents the bulk lifetime of the battery. The greater the bulk lifetime of the battery, the smaller the recombination probability in the PN junction region and the easier it is to improve the battery lifetime; iVoc represents the dark open-circuit voltage. The greater this dark open-circuit voltage, the better the passivation effect of the P+ region of the battery and the greater the potential for the battery to reach a higher open-circuit voltage.

[0133] It can be seen from the detection results of the hole carrier lifetime, recombination current density, bulk lifetime, and dark open-circuit voltage of Example 1, Comparative Example 1, and Comparative Example 2 in Table 1 above that the solar cells processed by the technical solutions proposed in the present invention can effectively improve the carrier lifetime, bulk lifetime, and dark open-circuit voltage of the battery, and can significantly reduce the recombination current density of the battery, which is beneficial to reducing the recombination in the PN junction region of the battery and thus can improve the battery efficiency.

[0134] Furthermore, the sheet resistance and sheet resistance uniformity of the products produced in Example 1, Comparative Example 1, and Comparative Example 2 are tested, and the test results are shown in Table 2 below.

[0135] Table 2

[0136]

[0137] Among them, the average sheet resistance in Table 2 is obtained by using the four-probe method to separately measure the sheet resistance and contact resistivity at multiple positions of multiple products produced in Example 1 (or Comparative Example 1 or Comparative Example 2), and calculating the average value of the sheet resistance at multiple positions of multiple products produced in Example 1 (or Comparative Example 1 or Comparative Example 2), which is the average sheet resistance; this average sheet resistance can reflect the contact between the PN junction region and the metal electrode and the difficulty of the lateral transport of carriers. Among them, the larger the sheet resistance value, the more difficult it is for the printing paste to match the contact with the PN junction region and the worse the contact between the metal electrode and the PN junction; the larger the sheet resistance value, the more difficult the lateral transport of carriers, which will reduce the fill factor of the battery. Further, by calculating the ratio between the minimum sheet resistance value and the maximum sheet resistance value, the sheet resistance uniformity index of the sheet resistance at multiple positions of multiple products produced in Example 1 (or Comparative Example 1 or Comparative Example 2) is calculated (as shown in the following calculation formula (1)), and this sheet resistance uniformity index can represent the sheet resistance uniformity. The larger the value of the sheet resistance uniformity index, the more uneven the diffusion of the boron diffusion process on the silicon wafer, which will cause the imbalance of carriers and serious carrier recombination in local areas, seriously affecting the carrier transport of the battery.

[0138] Sheet resistance uniformity index (UI) = R s,min ÷R s,max ×100% (1)

[0139] Among them, R s，min represents the minimum sheet resistance value among the sheet resistances at multiple positions of multiple products; R s，max represents the maximum sheet resistance value among the sheet resistances at multiple positions of multiple products.

[0140] The contact resistivity in Table 2 represents the contact resistance per unit area between two contacting bodies, and the contact resistivity is calculated based on the current used in the four-probe test method, the voltage generated by the product, and the area of the region to which the four-probe test method is applied (as shown in the following calculation formula (2)). This contact resistivity directly affects the conductivity of the contact point, and the smaller the contact resistivity, the better the contact performance.

[0141] Contact resistivity (r) = U÷(I×S) (2)

[0142] Among them, U represents the voltage generated by the product; I represents the current applied to the product; S represents the area of the region where the four-probe test method acts.

[0143] It can be clearly seen from the average sheet resistance, sheet resistance uniformity index, and contact resistivity in Table 2 that the average sheet resistance, sheet resistance uniformity index, and contact resistivity of Example 1 are significantly lower than those of Comparative Example 1 and Comparative Example 2. This shows that the technical solution provided by the embodiments of the present invention can significantly reduce the sheet resistance of solar cells, help improve the contact performance between the metal electrode and the PN junction region, reduce the contact resistance between the metal electrode and the PN junction region, and can also improve the sheet resistance uniformity, enhance the uniformity and balance of the carrier transport ability, and reduce carrier recombination. Moreover, the technical solution provided by the embodiments of the present invention reduces the sheet resistance uniformity index (i.e., improves the sheet resistance uniformity), which is beneficial to improving the uniformity of the photoelectric conversion efficiency of solar cells, enabling the photoelectric conversion efficiency of each region of the solar cell to be basically consistent, thereby improving the photoelectric conversion efficiency of the photovoltaic module prepared from the solar cell.

[0144] Furthermore, for the solar cells with the deep junction boron diffusion layer 21 produced in Example 1, the solar cells with the boron diffusion layer produced in Comparative Example 1, and the solar cells with the boron diffusion layer produced in Comparative Example 2, the cell performance (open circuit voltage Voc, fill factor FF, and photoelectric conversion efficiency Eta) was respectively tested. Among them, the fill factor FF is the ratio of the product of the current and voltage at the maximum output power of the cell to the product of the current and open circuit voltage when the cell is short-circuited. The test results are shown in Table 3 below.

[0145] Table 3

[0146] Group Voc (mV) FF (%) Eta (%) Example 1 723 84.73 24.96 Comparative Example 1 719 83.24 24.669 Comparative Example 2 719 81.79 24.019

[0147] It can be clearly seen from Table 3 that the deep junction boron diffusion layer 21 prepared by the technical solution provided by the embodiments of the present invention is beneficial to improving the open circuit voltage, fill factor, and photoelectric conversion efficiency of solar cells.

[0148] Furthermore, the doping concentration of the boron diffusion layers of Example 1, Example 2, Comparative Example 1, and Comparative Example 2 was detected with respect to the change with depth (this depth gradually increases from the surface of the deep junction boron diffusion layer 21 towards the silicon substrate direction, that is, the surface depth of the deep junction boron diffusion layer 21 is 0). Since the change of the doping concentration with depth in Example 1 and Example 2 is similar, for the sake of clearly showing the differences between the examples and Comparative Example 1 and Comparative Example 2, the detection results of Example 1 and the detection results of Comparative Example 1 and Comparative Example 2 are taken as examples for comparison and description, as Figure 6 shown.

[0149] From Figure 6It can be clearly seen that, from the surface of the boron diffusion layer of Comparative Example 1 and Comparative Example 2 inward, the boron doping concentration first increases from low to high (appearing a doping concentration peak), and the boron doping concentration on the surface of the boron diffusion layer is significantly lower than the doping concentration peak. After that, as the depth increases, the boron doping concentration gradually decreases, and a doping concentration peak appears in a relatively deep region in Comparative Example 2. Compared with Comparative Example 1 and Comparative Example 2, the doping concentration on the surface of the deep junction boron diffusion layer 21 formed in Example 1 is significantly increased, and the concentration difference between the doping concentration peak and the surface doping concentration of the deep junction boron diffusion layer 21 formed in Example 1 is reduced, so that the boron doping concentration distribution in the entire deep junction boron diffusion layer 21 is more uniform, and the doping concentration inside the deep junction boron diffusion layer 21 is significantly reduced, which helps to reduce the contact resistance of the battery and improve the battery efficiency. The Figure 6 Combined with the doping concentration vs. depth curves given and the test results in Table 1, Table 2 and Table 3 above, it shows that compared with the boron diffusion layer prepared by the conventional preparation process, the technical solution provided by the embodiments of the present invention can increase the doping concentration on the surface of the deep junction boron diffusion layer 21, reduce the concentration difference between the doping concentration peak and the surface doping concentration of the deep junction boron diffusion layer 21, and by controlling the doping concentration on the surface of the deep junction boron diffusion layer 21 and the concentration difference between the doping concentration peak and the surface doping concentration of the deep junction boron diffusion layer, it helps to reduce the sheet resistance, contact resistance, contact resistivity of the solar cell, and improve the carrier lifetime, cell body lifetime, passivation effect of the P+ region of the cell and cell performance (such as open circuit voltage, fill factor and photoelectric conversion efficiency, etc.).

[0150] It is found that in the oxidation and source absorption treatment, continuously introducing oxygen during the cooling process and continuously introducing oxygen during the heating process will not affect the peak concentration of boron doping in the deep junction boron diffusion layer 21, but will cause the surface doping concentration of the PN junction to decrease, and will also affect the contact between the metal electrode and the PN junction, increasing the contact resistance and reducing the fill factor. Both Comparative Example 1 and Comparative Example 2 have this defect. In addition, as in Comparative Example 1, after the heating is advanced, only the furnace tube temperature is lowered to a relatively high temperature, then oxidation heating is carried out, and after the oxidation and source absorption are completed, cooling oxidation is continued during the cooling process, resulting in too high sheet resistance of the PN junction and the PN junction not being able to meet the carrier transport.

[0151] The introduction provided in the above steps is only used to help understand the method, structure and core idea of the present invention. For those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A boron diffusion method for a solar cell, characterized in that, Comprising: Step 1: Form a boron-doped layer (20) for the battery substrate (10) in the oxidation furnace tube to obtain a preliminarily boron-doped substrate (10'), wherein the boron-doped layer (20) comprises a deep junction boron diffusion layer (21) and a borosilicate glass layer (22) stacked from the inside to the outside; Step 2: Take out the preliminarily boron-doped substrate (10') from the oxidation furnace tube, cool the preliminarily boron-doped substrate (10'), and make the temperature of the cooled preliminarily boron-doped substrate (10') not higher than 200°C; Step 3: Put the cooled preliminarily boron-doped substrate (10') back into the preheated oxidation furnace tube, and under an oxygen-free environment, raise the temperature of the preliminarily boron-doped substrate (10') to activate the non-active boron atoms in the boron-doped layer (20); Step 4: Perform an oxidation and source-absorbing treatment on the boron-doped layer (20) in the preliminarily boron-doped substrate (10') to redistribute the boron atoms in the deep junction boron diffusion layer (21).

2. The boron diffusion method of the solar cell according to claim 1, characterized in that Step 1 includes: Step 11: Form a first silicon oxide layer (30) for the battery substrate (10); Step 12: Dope boron atoms into the first silicon oxide layer (30) through multiple source-introducing treatments in sequence to form a shallow junction boron diffusion layer (21') and an initial borosilicate glass layer (22') stacked from the inside to the outside; Step S13: Under an oxygen-free environment, raise the temperature to push the boron atoms in the shallow junction boron diffusion layer (21') and the boron atoms in the initial borosilicate glass layer (22') to form the deep junction boron diffusion layer (21) and the borosilicate glass layer (22) on the battery substrate (10).

3. The boron diffusion method for a solar cell according to claim 2, wherein the battery substrate (10) comprises a crystalline silicon wafer (11), and Step 11 includes: directly forming a first silicon oxide layer (30) on one main surface of the crystalline silicon wafer (11); Or, the battery substrate (10) comprises a crystalline silicon wafer (11) and an intrinsic silicon thin film layer (12), and Step 11 includes: forming the intrinsic silicon thin film layer (12) on one main surface of the crystalline silicon wafer (11); forming a first silicon oxide layer (30) on the side of the intrinsic silicon thin film layer (12) away from the crystalline silicon wafer (11); Or, the battery substrate (10) comprises a crystalline silicon wafer (11) and an N+ region (13), and Step 11 includes: forming spaced-apart N+ regions (13) on one main surface of the crystalline silicon wafer (11); forming a first silicon oxide layer (30) on the region of the crystalline silicon wafer (11) adjacent to the N+ regions (13), and there is a spaced region (14) between the first silicon oxide layer (30) and the adjacent N+ regions (13); Or, The battery substrate (10) includes a crystalline silicon wafer (11), an N+ region (13), and an intrinsic silicon thin film layer (12). Step 11 includes: forming spaced-apart N+ regions (13) on a main surface of the crystalline silicon wafer (11); forming an intrinsic silicon thin film layer (12) in a region adjacent to the N+ regions (13) on the crystalline silicon wafer (11), with a spaced region (14) between the intrinsic silicon thin film layer (12) and the adjacent N+ regions (13); forming a first silicon oxide layer (30) on a side of the intrinsic silicon thin film layer (12) away from the crystalline silicon wafer (11).

4. The boron diffusion method of the solar cell according to claim 1, wherein Step 2 includes: Step 21: Cool the oxidation furnace tube to the standby temperature, and introduce nitrogen into the oxidation furnace tube at a flow rate of 20000 sccm to 30000 sccm for a duration of 10 min to 15 min; Step 22: Take out the initially boron-doped substrate (10') from the oxidation furnace tube and cool the initially boron-doped substrate (10') to room temperature.

5. The boron diffusion method of a solar cell according to claim 1, wherein Step 3 includes: Step 31: Re-put the cooled initially boron-doped substrate (10') into the oxidation furnace tube with a preheating temperature reaching 870 °C to 900 °C; Step 32: Under a nitrogen atmosphere, heat the oxidation furnace tube to 950 °C to 1050 °C and maintain for a duration of 5 min to 8 min, control the pressure inside the furnace tube to be 100 mbar to 200 mbar, and the nitrogen flow rate to be 2000 sccm to 3000 sccm.

6. The boron diffusion method for a solar cell according to any one of claims 1 to 4, characterized in that, Step 4 includes: Introduce oxygen into the oxidation furnace tube at a flow rate of 20000 sccm to 26000 sccm to form a second silicon oxide layer, and perform an oxidation and source absorption treatment on the boron-doped layer (20) based on the second silicon oxide layer. The conditions for the oxidation and source absorption treatment include: the temperature of the oxidation furnace tube is 1000 °C to 1050 °C, the pressure of the oxidation furnace tube is 800 mbar to 900 mbar, and the duration is 60 min to 150 min.

7. The boron diffusion method of the solar cell according to claim 1, characterized in that After step 4, it further includes: Step 5: Under an oxygen-free environment, cool the oxidation furnace tube to the standby temperature and restore the pressure of the oxidation furnace tube to atmospheric pressure for a duration of 40 min to 50 min.

8. The boron diffusion method for a solar cell according to claim 2, wherein, Step 12 includes: Step 121: Introduce oxygen, a boron source gas, boron-carrying nitrogen, and furnace door nitrogen into the oxidation furnace tube, control the pressure inside the oxidation furnace tube to be 100 mbar to 300 mbar, the temperature inside the oxidation furnace tube to be 830 °C to 850 °C, and maintain for a duration of 2 min to 3 min. Among them, the flow rate of oxygen is 400 sccm to 600 sccm; the flow rate of the boron source gas is 100 sccm to 400 sccm; the flow rate of the boron-carrying nitrogen is 3000 sccm to 4000 sccm; the flow rate of the furnace door nitrogen is 300 sccm to 700 sccm; restore the inside of the oxidation furnace tube to a nitrogen atmosphere for purging, and the temperature does not change between source introduction and purging; Step 122: Introduce oxygen, boron source gas, boron-carrying nitrogen gas, and furnace door nitrogen gas into the oxidation furnace tube. Control the pressure inside the oxidation furnace tube to be 100 mbar to 300 mbar, the temperature inside the oxidation furnace tube to be 830 °C to 850 °C, and the duration to be 2 min to 3 min. Among them, the flow rate of the oxygen is 400 sccm to 600 sccm; the flow rate of the boron source gas is 100 sccm to 400 sccm; the flow rate of the boron-carrying nitrogen gas is 3000 sccm to 4000 sccm; the flow rate of the furnace door nitrogen gas is 300 sccm to 700 sccm. Restore the inside of the oxidation furnace tube to nitrogen atmosphere purging, and the temperature does not change between source gas introduction and purging. Step 123: Introduce oxygen, boron source gas, boron-carrying nitrogen gas, and furnace door nitrogen gas into the oxidation furnace tube. Control the pressure inside the oxidation furnace tube to be 100 mbar to 300 mbar, the temperature inside the oxidation furnace tube to be 830 °C to 850 °C, and the duration to be 2 min to 3 min. Among them, the flow rate of the oxygen is 400 sccm to 600 sccm; the flow rate of the boron source gas is 100 sccm to 400 sccm; the flow rate of the boron-carrying nitrogen gas is 3000 sccm to 4000 sccm; the flow rate of the furnace door nitrogen gas is 300 sccm to 700 sccm. Restore the inside of the oxidation furnace tube to nitrogen atmosphere purging, and the temperature does not change between source gas introduction and purging. Preferably, Step 13 includes: Raise the temperature of the oxidation furnace tube to 880 °C to 920 °C, and control the nitrogen gas flow rate introduced into the oxidation furnace tube to be 2000 sccm to 4000 sccm; the pressure inside the oxidation furnace tube is 100 mbar to 300 mbar, and the duration is 5 min to 15 min to push the boron atoms to form the deep junction boron diffusion layer (21). and / or, The boron diffusion method further includes: removing the boron-silicate glass layer formed after the oxidation and source gas absorption treatment.

9. The boron diffusion method of a solar cell according to any one of claims 1 to 5, 7, and 8, characterized in that The junction depth of the PN junction formed by the boron diffusion method is 1 μm to 1.3 μm; and / or, The cell substrate (10) is formed based on an N-type monocrystalline silicon substrate.

10. A solar cell, characterized in that, including: A deep junction boron diffusion layer (21) formed by the boron diffusion method of a solar cell according to any one of claims 1 to 9.

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