Boron diffusion method, solar cell, preparation method of solar cell and photovoltaic module

Abstract

The invention relates to the technical field of solar cells, in particular to a boron diffusion method, a solar cell, a preparation method of the solar cell and a photovoltaic module. The invention aims to solve the problem that the photoelectric conversion efficiency of a solar cell is affected due to poor sheet resistance consistency caused by poor diffusion uniformity of the existing boron diffusion method. In order to achieve the purpose, the boron diffusion method comprises the steps that a boron-doped amorphous silicon source layer with the thickness being 3-5 nm is prepared on one face of a silicon wafer through a hot filament chemical vapor deposition method, and oxygen-free boron diffusion treatment is conducted on the silicon wafer deposited with the boron-doped amorphous silicon source layer. And the uniform diffusion of the boron element is facilitated, so that the consistency of resistance after boron diffusion is improved, and the photoelectric conversion efficiency of the solar cell is further improved.

Description

Technical Field

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

[0002] In the process of solar cell manufacturing, the preparation of the PN junction is a crucial step. At present, the common method for preparing the PN junction is to perform boron diffusion on an N-type silicon wafer, so that boron atoms penetrate into the silicon wafer and react with silicon atoms to form a PN junction. Among them, the boron diffusion methods mainly include three types, namely boron tribromide liquid source diffusion, boron spin coating diffusion, and ion implantation. However, in the process of boron diffusion by the above methods, oxygen elements will inevitably be introduced, and the resulting boron-oxygen complexes will cause the phenomenon of light-induced degradation, which will further have an adverse impact on the photoelectric conversion efficiency of the solar cell.

[0003] In order to avoid the intervention of oxygen during boron diffusion, currently, the hot wire chemical vapor deposition method is generally used to deposit a heavily doped amorphous silicon source layer with a thickness of 10-30 nm on the surface of the silicon wafer, and then the boron diffusion and etching steps are carried out. Although this method can effectively prevent the intervention of oxygen during boron diffusion, the uniformity of boron element diffusion is poor, resulting in poor consistency of sheet resistance, which further has an adverse impact on the photoelectric conversion efficiency of the solar cell.

[0004] Correspondingly, a new technical solution is needed in this field to solve the above problems. Summary of the Invention

[0005] In order to solve at least one of the above problems in the prior art, that is, to solve the problem that the existing boron diffusion method has poor uniformity of boron element diffusion, resulting in poor consistency of sheet resistance, thereby affecting the photoelectric conversion efficiency of the solar cell, the present application provides a boron diffusion method, including:

[0006] Preparing a boron-doped amorphous silicon source layer on one side of the silicon wafer by using the hot wire chemical vapor deposition method; wherein, the thickness of the boron-doped amorphous silicon source layer is 3-5 nm;

[0007] Performing an oxygen-free boron diffusion treatment on the silicon wafer deposited with the boron-doped amorphous silicon source layer.

[0008] In a preferred technical solution of the above boron diffusion method, the gas sources used for preparing the boron-doped amorphous silicon source layer include a silicon source, a boron source, and hydrogen.

[0009] In a preferred technical solution of the above boron diffusion method, the flow rate of the silicon source is 120-160 sccm, the flow rate of the boron source is 100-150 sccm, and the flow rate of the hydrogen is 180-220 sccm.

[0010] In the preferred technical solution of the above boron diffusion method, it has one or both of the following characteristics:

[0011] The boron source includes at least one of borane, diborane and tetraborane;

[0012] The silicon source includes at least one of silane and disilane.

[0013] In the preferred technical solution of the above boron diffusion method, it is characterized in that in the hot wire chemical vapor deposition method, the hot wire temperature is 200 - 300 °C, the deposition pressure is 2.0 - 2.2 Pa, and the deposition time is 100 - 250 s.

[0014] In the preferred technical solution of the above boron diffusion method, the temperature of the anaerobic boron diffusion is 1000 - 1100 °C, the time is 0.8 - 1.5 h, and the pressure is (5 - 6)×10 -4 Pa.

[0015] In the preferred technical solution of the above boron diffusion method, the boron diffusion method further includes:

[0016] Performing a push - annealing treatment on the silicon wafer after the anaerobic boron diffusion treatment.

[0017] In the preferred technical solution of the above boron diffusion method, the temperature of the push - annealing is 800 - 900 °C, the time is 10 - 15 min, and the pressure is 120 - 150 mbar.

[0018] In the preferred technical solution of the above boron diffusion method, the boron diffusion method further includes:

[0019] Performing an etching treatment on the silicon wafer after the anaerobic boron diffusion treatment.

[0020] In the preferred technical solution of the above boron diffusion method, the etching method includes:

[0021] Performing a first etching on the boron - doped amorphous silicon source layer with a first etching solution;

[0022] Performing a second etching on the boron - doped amorphous silicon source layer with a second etching solution.

[0023] In the preferred technical solution of the above boron diffusion method, one of the first etching solution and the second etching solution is a mixed solution of HF and HNO 3 and the other is a NaOH solution or a KOH solution.

[0024] This application also provides a preparation method of a solar cell, including the following steps:

[0025] Processing the silicon wafer by using the boron diffusion method as described in any one of claims 1 to 10;

[0026] A passivation contact structure and an electrode layer are successively formed on the surface of the silicon wafer after boron diffusion treatment to obtain the solar cell.

[0027] This application also provides a solar cell, which is obtained by using the preparation method of the solar cell described in the above preferred technical solution.

[0028] This application also provides a photovoltaic module, which includes the solar cell described in the above preferred technical solution.

[0029] Those skilled in the art can understand that the boron diffusion method of this application deposits a 3-5 nm boron-doped amorphous silicon source layer on the surface of the silicon wafer by using the hot wire chemical vapor deposition method, and performs an oxygen-free boron diffusion treatment on the silicon wafer deposited with the boron-doped amorphous silicon source layer. This can not only avoid the intervention of oxygen during the boron diffusion process, but also facilitate the uniform diffusion of boron elements, thereby improving the consistency of the sheet resistance after boron diffusion, and further improving the photoelectric conversion efficiency of the solar cell.

[0030] Furthermore, by using a silicon source with a flow rate of 120-160 sccm, a boron source with a flow rate of 100-150 sccm, and hydrogen with a flow rate of 180-220 sccm to deposit a boron-doped amorphous silicon source layer on the surface of the silicon wafer, it is beneficial to improve the uniformity of boron elements in the boron-doped amorphous silicon source layer and ensure the doping uniformity of boron elements inside the silicon wafer after boron diffusion treatment.

[0031] Furthermore, by performing oxygen-free boron diffusion at a temperature of 1000-1100 °C, a time of 0.8-1.5 h, and a pressure of (5-6)×10 -4 Pa, it is beneficial to promote the diffusion of boron elements into the silicon wafer and increase the junction depth of the PN junction.

[0032] Furthermore, by performing a push-junction treatment on the silicon wafer after oxygen-free boron diffusion, it is beneficial for boron elements to diffuse to a deeper position in the silicon wafer and increase the junction depth of the PN junction.

[0033] Furthermore, by performing an etching treatment on the silicon wafer after boron diffusion treatment, the residual boron-doped amorphous silicon source layer on the surface of the silicon wafer can be effectively removed, thereby avoiding the problem of reducing the photoelectric conversion efficiency of the solar cell caused by these residues and ensuring the efficient and stable operation of the solar cell. Description of the Drawings

[0034] The following describes the preferred technical solutions of this application with reference to the drawings. In the drawings:

[0035] Figure 1 is a flowchart of the boron diffusion method of this application;

[0036] Figure 2Boron-doped ECV curve graphs for Example 2 and Comparative Example 4. Detailed implementation manners

[0037] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.

[0038] In combination with Figure 1 , the boron diffusion method of this application will be described.

[0039] In order to solve the problem that the existing boron diffusion method has poor uniformity of boron element diffusion, resulting in poor consistency of sheet resistance and thus affecting the photoelectric conversion efficiency of solar cells, the boron diffusion method of this application includes the following steps:

[0040] On one side of the silicon wafer, a boron-doped amorphous silicon source layer is prepared by hot wire chemical vapor deposition; wherein, the thickness of the boron-doped amorphous silicon source layer is 3-5 nm;

[0041] The silicon wafer deposited with the boron-doped amorphous silicon source layer is subjected to an oxygen-free boron diffusion treatment.

[0042] By using hot wire chemical vapor deposition to deposit a 3-5 nm boron-doped amorphous silicon source layer on the surface of the silicon wafer and performing an oxygen-free boron diffusion treatment on the silicon wafer deposited with the boron-doped amorphous silicon source layer, this application can not only avoid the intervention of oxygen during the boron diffusion process, but also facilitate the uniform diffusion of boron elements, thereby improving the consistency of sheet resistance after boron diffusion and further improving the photoelectric conversion efficiency of solar cells.

[0043] Next, the preferred implementation manners of the boron diffusion method of this application will be introduced.

[0044] Step 101), on one side of the silicon wafer, a boron-doped amorphous silicon source layer is prepared by hot wire chemical vapor deposition; wherein, the thickness of the boron-doped amorphous silicon source layer is 3-5 nm.

[0045] Among them, by depositing a 3-5 nm boron-doped amorphous silicon source layer on one side of the silicon wafer, it is also conducive to the uniform diffusion of boron elements, thereby improving the consistency of sheet resistance after boron diffusion and further improving the photoelectric conversion efficiency of solar cells. If the thickness of the boron-doped amorphous silicon source layer is greater than 5 nm, it is easy to cause uneven distribution of boron elements after the oxygen-free boron diffusion treatment, resulting in an increase in recombination centers and affecting the photoelectric conversion efficiency of solar cells. If the thickness of the boron-doped amorphous silicon source layer is less than 3 nm, it will affect the depth of the PN junction and also affect the photoelectric conversion efficiency of solar cells.

[0046] Specifically, when preparing the boron-doped amorphous silicon source layer, using silicon source, boron source, and hydrogen as gas sources can avoid introducing oxygen during the deposition process. Among them, the flow rate of the silicon source is 120 - 160 sccm, the flow rate of the boron source is 100 - 150 sccm, and the flow rate of hydrogen is 180 - 220 sccm, which is beneficial to improving the uniformity of boron elements in the boron-doped amorphous silicon source layer and ensuring the doping uniformity of boron elements inside the silicon wafer after boron diffusion treatment.

[0047] It should be noted that this application has no specific restrictions on the silicon source and boron source, as long as it is beneficial to deposit and form a boron-doped amorphous silicon source layer on the silicon surface. For example, the boron source includes at least one of borane, diborane, and tetraborane. And / or, the silicon source includes at least one of silane and disilane.

[0048] In addition, in the hot wire chemical vapor deposition method, the hot wire temperature is 200 - 300 °C, the deposition pressure is 2.0 - 2.2 Pa, and the deposition time is 100 - 250 s. Under the above conditions, a uniform and dense boron-doped amorphous silicon source layer can be formed on the surface of the silicon wafer, which can reduce the defects on the surface and inside of the silicon wafer, providing a favorable environment for oxygen-free doping diffusion, thereby helping to improve the performance of the solar cell. If the hot wire temperature is less than 200 °C, the uniformity of the boron-doped amorphous silicon source layer is poor, the distribution of boron elements in the boron-doped amorphous silicon source layer is uneven, affecting the uniformity of boron element diffusion, resulting in poor sheet resistance consistency and an increase in recombination centers; while when the hot wire temperature is greater than 300 °C, it is easy to cause damage to the internal structure of the boron-doped amorphous silicon source layer, which is not conducive to the diffusion of boron elements, and thus affects the formation of the PN junction.

[0049] Step 102): Perform an oxygen-free boron diffusion treatment on the silicon wafer deposited with the boron-doped amorphous silicon source layer.

[0050] Among them, by adopting the oxygen-free boron diffusion method, the participation of oxygen in the boron diffusion process can be avoided, ensuring the photoelectric conversion efficiency of the solar cell. At the same time, it can also effectively promote the diffusion of boron elements into the silicon wafer and shorten the time of the boron diffusion process.

[0051] Specifically, this process is carried out in a high-temperature vacuum tube diffusion furnace. Among them, the temperature of boron diffusion is 1000 - 1100 °C, the time is 0.8 - 1.5 h, and the pressure is (5 - 6)×10 -4 Pa. By performing high-temperature oxygen-free diffusion on the boron-doped amorphous silicon source layer deposited on the silicon wafer under the above conditions, it is beneficial for boron elements to diffuse into the silicon wafer and increase the junction depth of the PN junction.

[0052] It should be noted that in order to increase the junction depth of the PN junction, this application further includes after the oxygen-free boron diffusion treatment:

[0053] Step 103): Perform a junction pushing treatment on the silicon wafer after the oxygen-free boron diffusion treatment.

[0054] Among them, by performing diffusion pushing on the silicon wafer after the anaerobic boron diffusion treatment, the boron element can be diffused to a deeper position of the silicon wafer, increasing the junction depth of the PN junction and improving the consistency of the PN junction depth. Specifically, the temperature of the diffusion pushing is 800 - 900 °C, the time is 10 - 15 min, and the pressure is 120 - 150 mbar.

[0055] It should be noted that during the boron diffusion process of the boron-doped amorphous silicon source layer, the amorphous silicon on the silicon wafer surface is transformed into polycrystalline silicon, and the polycrystalline silicon will cause the boron atoms remaining on the silicon wafer surface to aggregate, resulting in an increase in surface defects of the silicon wafer, thus having an adverse impact on the battery performance. Therefore, after the anaerobic boron diffusion treatment or the oxidation diffusion pushing treatment, it further includes:

[0056] Step 104): Etching the silicon wafer after the anaerobic boron diffusion treatment.

[0057] Among them, by etching the silicon wafer after the boron diffusion treatment, the polycrystalline silicon on the silicon wafer surface can be removed, solving the problem that the increase in surface defects of the silicon wafer caused by the polycrystalline silicon affects the battery performance.

[0058] Specifically, the etching method includes:

[0059] Step 1041): First etching the boron-doped amorphous silicon source layer with a first etching solution.

[0060] It should be noted that the boron-doped amorphous silicon source layer here refers to the source layer after depositing the boron-doped amorphous silicon source layer by the hot wire chemical vapor deposition method and then undergoing anaerobic boron diffusion and diffusion pushing treatment.

[0061] Among them, the first etching solution can be a mixed solution of nitric acid and hydrofluoric acid, or an alkaline solution. The alkaline solution can be a NaOH solution or a KOH solution.

[0062] Taking the first etching solution as a mixed solution of nitric acid and hydrofluoric acid as an example, HNO 3 can oxidize the polycrystalline silicon to form SiO 2 , and SiO 2 is soluble in the HF solution, so the polycrystalline silicon on the silicon surface can be removed. Among them, the chemical reactions involved in the above process are as follows:

[0063] 3Si + 4HNO 3 = 3Si 2 O + 2H 2 O + 4NO;

[0064] SiO 2 + 6HF = H 2 SiF 6 + 2H 2 O.

[0065] It should be noted that the present application places no restrictions on the concentrations of nitric acid and hydrofluoric acid in the mixed solution, the etching time, and the etching temperature of the mixed solution, as long as the polysilicon on the silicon surface can be removed. For example, the volume concentration of HNO 3 in the mixed solution can be 40%, and the volume concentration of HF can be 0.5%. And / or, the etching time can be 120 - 180 s. And / or, the etching temperature can be 10°C.

[0066] Taking the first etching solution as the NaOH solution for illustration, the NaOH solution can oxidize the polysilicon to form Na 2 SiO 3 , thereby being able to remove the polysilicon on the silicon surface. Among them, the chemical reactions involved in the above process are as follows:

[0067] Si + H 2 O + 2NaOH = Na 2 SiO 3 + 2H 2 .

[0068] It should be noted that the present application places no restrictions on the concentrations of KOH or NaOH in the alkali solution, the etching time, and the temperature of the alkali solution, as long as the polysilicon on the silicon surface can be removed. For example, the mass concentration of KOH or NaOH can be 5%. And / or, the etching time can be 40 - 60 s. And / or, the etching temperature can be 20°C.

[0069] Step 1042): Use the second etching solution to perform a second etching on the boron-doped amorphous silicon source layer.

[0070] It should be noted that the boron-doped amorphous silicon source layer here refers to the source layer after being etched by the first etching solution. By etching the boron-doped amorphous silicon source layer with the second etching solution, the remaining polysilicon on the silicon wafer surface can be removed.

[0071] Among them, the second etching solution can be a mixed solution of nitric acid and hydrofluoric acid, or an alkali solution. Among them, the alkali solution is an NaOH solution or a KOH solution. It should be noted that the second etching solution and the first etching solution are different etching solutions from each other. Specifically, when the first etching solution is a mixed solution of nitric acid and hydrofluoric acid, the second etching solution is an alkali solution; and when the second etching solution is a mixed solution of nitric acid and hydrofluoric acid, the first etching solution is an alkali solution. It should be noted that the mixed solution of nitric acid and hydrofluoric acid and the alkali solution are the same as the first etching, and will not be elaborated here.

[0072] It should also be noted that after etching is completed with the first etching solution, the first etching solution remains on the silicon wafer. To avoid the influence of the first etching solution remaining on the silicon wafer surface on the second etching, before the second etching with the second etching solution, it is preferred to clean the silicon wafer with ultrapure water. Herein, there is no limitation on the number of cleaning times in this application, as long as the influence of the remaining first etching solution on the second etching solution can be avoided. For example, the number of cleaning times can be 1 - 3 times.

[0073] Next, to ensure the cleanliness of the silicon wafer surface after etching, the silicon wafer needs to be cleaned. Herein, there is no limitation on the cleaning method in this application, as long as the cleanliness of the silicon wafer surface can be improved. For example, after the second etching of the silicon wafer, the silicon wafer can be cleaned successively with the following solutions: HF solution, SC1 solution, SC2 solution, and HF solution. It should be noted that before cleaning with the above solutions, in order to completely eliminate the residual influence of the previous step solution, the silicon wafer will be pre-cleaned with ultrapure water. Regarding the number of times of ultrapure water cleaning, there is no limitation in this application, as long as the cleaning solution of the previous step does not interfere with the influence of the next cleaning solution. For example, the number of cleaning times can be 1 - 3 times. In addition, there is no limitation on the cleaning time, cleaning temperature, and concentration of HF in this application for the HF solution. For example, the concentration of HF in the two HF solution cleanings of the silicon wafer can both be 5%, the cleaning time is 2 min, and the cleaning temperature can be room temperature. There is no limitation on the cleaning time, cleaning temperature, and concentrations of H2O2 and NH3·2H2O in this application for the SC1 solution. For example, the cleaning time is 10 min, the cleaning temperature is 70 °C, the volume concentration of H2O2 in the SC1 solution is 14.3%, and the volume and concentration of NH3·2H2O are 14.3%. There is no limitation on the cleaning time, cleaning temperature, and concentrations of H2O2 and NH3·2H2O in this application for the SC2 solution. For example, the cleaning time is 10 min, the cleaning temperature is 70 °C, the volume concentration of H2O2 in the SC2 solution is 14.3%, and the volume concentration of HCl is 14.3%.

[0074] In addition, this application also provides a method for manufacturing a solar cell, including the following steps:

[0075] Treat the silicon wafer with the boron diffusion method described in any of the above embodiments;

[0076] Form a passivated contact structure and an electrode layer on the surface of the silicon wafer after boron diffusion treatment in sequence to obtain the solar cell.

[0077] Among them, before the boron diffusion method treatment of the silicon wafer, texturing treatment is carried out, then the silicon wafer is treated with the boron diffusion method, and subsequently, a tunneling oxide layer, a polysilicon layer, a passivation layer, and an electrode layer are formed on the silicon wafer surface in sequence, which can improve the photoelectric conversion efficiency of the solar cell.

[0078] It should be noted that the tunneling oxide layer is formed on the surface of the silicon wafer after boron diffusion treatment. In addition, the methods of texturing the silicon wafer and sequentially forming the tunneling oxide layer, poly-silicon layer, passivation layer, and electrode layer on the silicon wafer surface are all conventional solutions in the art, and the above solutions will not be described in detail herein.

[0079] In addition, the present application also provides a solar cell, which is prepared according to the above-mentioned preparation method of the solar cell.

[0080] Furthermore, the present application also provides a photovoltaic module, which includes the solar cell of any of the above embodiments.

[0081] The boron diffusion method of the present application will be described in conjunction with the following embodiments.

[0082] Example 1

[0083] The boron diffusion method includes the following steps:

[0084] Step 101): Place the silicon wafer in the reaction chamber of a hot wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 280 °C, introduce 150 sccm of silane, 150 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot wire voltage of 55 V and a hot wire current of 32 A, and deposit for 150 s to form a 4-nm boron-doped amorphous silicon source layer on the front side of the silicon wafer.

[0085] Step 102): Place the silicon wafer deposited with the boron-doped amorphous silicon source layer in a diffusion furnace tube, and raise the temperature in the furnace to 1000 °C and evacuate to 5×10 -4 Pa for oxygen-free boron diffusion for 1 h.

[0086] Step 103): Continue to evacuate the diffusion furnace, and introduce nitrogen and oxygen to form a pressure of 120 mbar, adjust the temperature to 900 °C, push and anneal for 10 min, and then cool the silicon wafer to 850 °C and take it out of the diffusion furnace.

[0087] Step 104): Perform an etching treatment on the silicon wafer after oxidation and pushing. The etching method includes:

[0088] Step 1041): Perform the first etching on the boron-doped amorphous silicon source layer with a mixed solution of nitric acid and hydrofluoric acid. Among them, the volume concentration of HNO 3 is 40%, the volume concentration of HF is 0.5%, the etching time is 150 s, and the etching temperature is 10 °C.

[0089] Step 1042): The silicon wafer after the first etching is cleaned twice with ultrapure water, and then the boron-doped amorphous silicon source layer is etched for the second time with a KOH solution. Among them, the mass concentration of KOH is 5%, the etching time is 50 s, and the etching temperature is 20 °C.

[0090] Step 1043): The silicon wafer after the second etching is cleaned twice with ultrapure water, and then cleaned with an HF solution with a volume concentration of 5% at room temperature for 2 min; after being cleaned twice with ultrapure water at room temperature, it is cleaned with an SC1 solution with a volume concentration of 14.3% of H 2 O 2 and a volume concentration of 14.3% of NH 3 ·2H 2 O at 70 °C for 10 min; then after being cleaned twice with ultrapure water at room temperature, it is cleaned with an SC2 solution with a volume concentration of 14.3% of H 2 O 2 and a volume concentration of 14.3% of HCl at 70 °C for 10 min; finally, after being cleaned twice with ultrapure water, it is dried to obtain a silicon wafer after boron diffusion treatment.

[0091] Example 2

[0092] The boron diffusion method includes the following steps:

[0093] Step 101), place the silicon wafer in the reaction chamber of the hot wire chemical vapor deposition equipment, evacuate the reaction chamber to 2 Pa, heat the hot wire to 250 °C, and then introduce 150 sccm of silane, 150 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot wire voltage of 55 V and a hot wire current of 32 A, and deposit for 120 s to form a 3-nm boron-doped amorphous silicon source layer on the front surface of the silicon wafer.

[0094] Step 102): Place the silicon wafer deposited with the boron-doped amorphous silicon source layer in a diffusion furnace tube, raise the temperature in the furnace to 1000 °C, and evacuate to 5×10 -4 Pa for oxygen-free boron diffusion for 1 h.

[0095] Step 103): Continue to evacuate the diffusion furnace, introduce nitrogen and oxygen to form a pressure of 120 mbar, adjust the temperature to 900 °C, push and anneal for 10 min, and then cool the silicon wafer to 850 °C and take it out of the diffusion furnace.

[0096] Step 104): Etch the silicon wafer after oxidation and push-annealing, and the etching method includes:

[0097] Step 1041): The boron-doped amorphous silicon source layer is etched for the first time with a mixed solution of nitric acid and hydrofluoric acid. Among them, HNO 3The volume concentration is 40%, the volume concentration of HF is 0.5%, the etching time is 150 s, and the etching temperature is 10 °C.

[0098] Step 1042): The silicon wafer after the first etching is cleaned twice with ultrapure water, and then the boron-doped amorphous silicon source layer is etched for the second time with a KOH solution. Among them, the mass concentration of KOH is 5%, the etching time is 50 s, and the etching temperature is 20 °C.

[0099] Step 1043): The silicon wafer after the second etching is cleaned twice with ultrapure water, and then cleaned with an HF solution with a volume concentration of 5% at room temperature for 2 min; after being cleaned twice with ultrapure water at room temperature, it is cleaned with an SC1 solution with a volume concentration of 14.3% of H 2 O 2 and a volume concentration of 14.3% of NH 3 ·2H 2 O at 70 °C for 10 min; then after being cleaned twice with ultrapure water at room temperature, it is cleaned with an SC2 solution with a volume concentration of 14.3% of H 2 O 2 and a volume concentration of 14.3% of HCl at 70 °C for 10 min; finally, after being cleaned twice with ultrapure water, it is dried to obtain a silicon wafer after boron diffusion treatment.

[0100] Example 3

[0101] The boron diffusion method includes the following steps:

[0102] Step 101), place the silicon wafer in the reaction chamber of the hot wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 250 °C, 150 sccm of silane, 150 sccm of diborane, and 200 sccm of hydrogen are introduced under the conditions of a hot wire voltage of 55 V and a hot wire current of 32 A, and deposited for 150 s to form a 4-nm boron-doped amorphous silicon source layer on the front surface of the silicon wafer.

[0103] Step 102): Place the silicon wafer deposited with the boron-doped amorphous silicon source layer in a diffusion furnace tube, and raise the temperature in the furnace to 1000 °C and evacuate to 5×10 -4 Pa for oxygen-free boron diffusion for 1 h.

[0104] Step 103): Continue to evacuate the diffusion furnace and introduce nitrogen and oxygen to form a pressure of 120 mbar, adjust the temperature to 900 °C, push and anneal for 10 min, and then cool the silicon wafer to 850 °C and take it out of the diffusion furnace.

[0105] Step 104): The silicon wafer after oxidation and push annealing is etched, and the etching method includes:

[0106] Step 1041): The boron-doped amorphous silicon source layer is etched for the first time with a mixed solution of nitric acid and hydrofluoric acid. Among them, the volume concentration of HNO 3 is 40%, the volume concentration of HF is 0.5%, the etching time is 150 s, and the etching temperature is 10 °C.

[0107] Step 1042): The silicon wafer after the first etching is cleaned twice with ultrapure water, and then the boron-doped amorphous silicon source layer is etched for the second time with a KOH solution. Among them, the mass concentration of KOH is 5%, the etching time is 50 s, and the etching temperature is 20 °C.

[0108] Step 1043): The silicon wafer after the second etching is cleaned twice with ultrapure water, and then cleaned with an HF solution with a volume concentration of 5% at room temperature for 2 min; after being cleaned twice with ultrapure water at room temperature, it is cleaned with an SC1 solution with a volume concentration of 14.3% of H 2 O 2 and a volume concentration of 14.3% of NH 3 ·2H 2 O at 70 °C for 10 min; then, after being cleaned twice with ultrapure water at room temperature again, it is cleaned with an SC2 solution with a volume concentration of 14.3% of H 2 O 2 and a volume concentration of 14.3% of HCl at 70 °C for 10 min; finally, after being cleaned twice with ultrapure water again, it is dried to obtain a silicon wafer after boron diffusion treatment.

[0109] Example 4

[0110] The boron diffusion method includes the following steps:

[0111] Step 101), place the silicon wafer in the reaction chamber of a hot wire chemical vapor deposition equipment, evacuate the reaction chamber to 2 Pa, heat the hot wire to 250 °C, and then introduce 150 sccm of silane, 150 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot wire voltage of 55 V and a hot wire current of 32 A, and deposit for 180 s to form a 5-nm boron-doped amorphous silicon source layer on the front side of the silicon wafer.

[0112] Step 102): Place the silicon wafer deposited with the boron-doped amorphous silicon source layer in a diffusion furnace tube, raise the temperature in the furnace to 1000 °C, evacuate to 5×10 -4 Pa, and perform oxygen-free boron diffusion for 1 h.

[0113] Step 103): Continue to evacuate the diffusion furnace, introduce nitrogen and oxygen to form a pressure of 120 mbar, adjust the temperature to 900 °C, push and sinter for 10 min, and then cool the silicon wafer to 850 °C and take it out of the diffusion furnace.

[0114] Step 104): Etch the silicon wafer after oxidation and push - knotting. The etching method includes:

[0115] Step 1041): Use a mixed solution of nitric acid and hydrofluoric acid to perform the first etching on the boron - doped amorphous silicon source layer. Among them, the volume concentration of HNO 3 is 40%, the volume concentration of HF is 0.5%, the etching time is 150 s, and the etching temperature is 10 °C.

[0116] Step 1042): Wash the silicon wafer after the first etching twice with ultrapure water, and then use a KOH solution to perform the second etching on the boron - doped amorphous silicon source layer. Among them, the mass concentration of KOH is 5%, the etching time is 50 s, and the etching temperature is 20 °C.

[0117] Step 1043): Wash the silicon wafer after the second etching twice with ultrapure water, and then use an HF solution with a volume concentration of 5% to wash at room temperature for 2 min; then wash twice with ultrapure water at room temperature, and then use an SC1 solution with a volume concentration of 14.3% of H 2 O 2 and a volume concentration of 14.3% of NH 3 ·2H 2 O to wash at 70 °C for 10 min; then wash twice with ultrapure water at room temperature again, and then use an SC2 solution with a volume concentration of 14.3% of H 2 O 2 and a volume concentration of 14.3% of HCl to wash at 70 °C for 10 min; finally, wash twice with ultrapure water and then dry to obtain the silicon wafer after boron diffusion treatment.

[0118] Example 5

[0119] The boron diffusion method includes the following steps:

[0120] Step 101), Place the silicon wafer in the reaction chamber of a hot - wire chemical vapor deposition device. After evacuating the reaction chamber to 2.2 Pa and heating the hot wire to 200 °C, introduce 120 sccm of silane, 100 sccm of diborane, and 180 sccm of hydrogen under the conditions of a hot - wire voltage of 55 V and a hot - wire current of 32 A, and deposit for 250 s to form a 5 - nm boron - doped amorphous silicon source layer on the front side of the silicon wafer.

[0121] Step 102): Place the silicon wafer deposited with the boron - doped amorphous silicon source layer in a diffusion furnace tube, raise the temperature in the furnace to 1100 °C, and evacuate to 6×10 -4 Pa for oxygen - free boron diffusion for 0.8 h.

[0122] Step 103): Continue to evacuate the diffusion furnace, introduce nitrogen and oxygen to form a pressure of 150 mbar, adjust the temperature to 800 °C, perform pushing and sintering for 12 minutes, and then take out the wafer from the diffusion furnace.

[0123] Step 104): Etch the wafer after pushing and sintering. The etching method includes:

[0124] Step 1041): Perform the first etching on the boron-doped amorphous silicon source layer using a KOH solution. Among them, the mass concentration of KOH is 5%, the etching time is 60 s, and the etching temperature is 20 °C.

[0125] Step 1042): Wash the wafer after the first etching twice with ultrapure water, and then perform the second etching on the boron-doped amorphous silicon source layer using a mixed solution of nitric acid and hydrofluoric acid. Among them, the volume concentration of HNO 3 is 40%, the volume concentration of HF is 0.5%, the etching time is 120 s, and the etching temperature is 10 °C.

[0126] Step 1043): Wash the wafer after the second etching twice with ultrapure water, and then wash it with an HF solution with a volume concentration of 5% at room temperature for 2 minutes; then wash it twice with ultrapure water at room temperature, and then use an SC1 solution with a volume concentration of 14.3% of H 2 O 2 and a volume concentration of 14.3% of NH 3 ·2H 2 O to wash it at 70 °C for 10 minutes; then wash it twice with ultrapure water at room temperature again, and then use an SC2 solution with a volume concentration of 14.3% of H 2 O 2 and a volume concentration of 14.3% of HCl to wash it at 70 °C for 10 minutes; finally, wash it twice with ultrapure water again and then dry it to obtain the boron-diffused wafer.

[0127] Example 6

[0128] The boron diffusion method includes the following steps:

[0129] Step 101), place the wafer in the reaction chamber of the hot wire chemical vapor deposition equipment, evacuate the reaction chamber to 2.1 Pa, heat the hot wire to 300 °C, and then introduce 160 sccm of disilane, 120 sccm of diborane, and 220 sccm of hydrogen under the conditions of a hot wire voltage of 55 V and a hot wire current of 32 A, and deposit for 100 s to form a 3-nm boron-doped amorphous silicon source layer on the front side of the wafer.

[0130] Step 102): Place the wafer deposited with the boron-doped amorphous silicon source layer in the diffusion furnace tube, raise the temperature in the furnace to 1050 °C, and evacuate the vacuum to 5.5×10-4 Pa, with an oxygen-free boron diffusion for 1.5 h.

[0131] Step 103): Continue to evacuate the diffusion furnace, and introduce nitrogen and oxygen to form a pressure of 130 mbar. Adjust the temperature to 850 °C, push and sinter for 15 min, and then take out from the diffusion furnace.

[0132] Step 104): Etch the silicon wafer after oxidation and push-sintering. The etching method includes:

[0133] Step 1041): Use a mixed solution of nitric acid and hydrofluoric acid to perform the first etching on the boron-doped amorphous silicon source layer. Among them, the volume concentration of HNO 3 is 40%, the volume concentration of HF is 0.5%, the etching time is 180 s, and the etching temperature is 10 °C.

[0134] Step 1042): Wash the silicon wafer after the first etching twice with ultrapure water, and then use a NaOH solution to perform the second etching on the boron-doped amorphous silicon source layer. Among them, the mass concentration of NaOH is 5%, the etching time is 40 s, and the etching temperature is 20 °C.

[0135] Step 1043): Wash the silicon wafer after the second etching twice with ultrapure water, and then use an HF solution with a volume concentration of 5% to wash for 2 min at room temperature; then wash twice with ultrapure water at room temperature, and then use an SC1 solution with a volume concentration of 14.3% of H 2 O 2 and a volume concentration of 14.3% of NH 3 ·2H 2 O to wash for 10 min at 70 °C; then wash twice with ultrapure water at room temperature again, and then use an SC2 solution with a volume concentration of 14.3% of H 2 O 2 and a volume concentration of 14.3% of HCl to wash for 10 min at 70 °C; finally, wash twice with ultrapure water again and then dry to obtain the silicon wafer after boron diffusion treatment.

[0136] Comparative Example 1

[0137] The difference from Examples 1-4 is only in Step 101), and specifically, Step 101) is as follows:

[0138] Place the silicon wafer in the reaction chamber of a hot wire chemical vapor deposition device. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 250 °C, introduce 150 sccm of silane, 150 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot wire voltage of 55 V and a hot wire current of 32 A, and deposit for 90 s to form a 2-nm boron-doped amorphous silicon source layer on the front side of the silicon wafer.

[0139] Comparative Example 2

[0140] It is only different from Examples 1 - 4 in Step 101), and specifically, Step 101) is as follows:

[0141] Place the silicon wafer in the reaction chamber of a hot - wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 250 °C, introduce 150 sccm of silane, 150 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot - wire voltage of 55 V and a hot - wire current of 32 A, and deposit for 240 s to form a 7 - nm boron - doped amorphous silicon source layer on the front side of the silicon wafer.

[0142] Comparative Example 3

[0143] It is only different from Examples 1 - 4 in Step 101), and specifically, Step 101) is as follows:

[0144] Place the silicon wafer in the reaction chamber of a hot - wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 250 °C, introduce 150 sccm of silane, 150 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot - wire voltage of 55 V and a hot - wire current of 32 A, and deposit for 330 s to form a 10 - nm boron - doped amorphous silicon source layer on the front side of the silicon wafer.

[0145] Comparative Example 4

[0146] It is only different from Examples 1 - 4 in Step 101), and specifically, Step 101) is as follows:

[0147] Place the silicon wafer in the reaction chamber of a hot - wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 250 °C, introduce 150 sccm of silane, 150 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot - wire voltage of 55 V and a hot - wire current of 32 A, and deposit for 930 s to form a 30 - nm boron - doped amorphous silicon source layer on the front side of the silicon wafer.

[0148] Comparative Example 5

[0149] It is only different from Examples 1 - 4 in Step 101), and specifically, Step 101) is as follows:

[0150] Place the silicon wafer in the reaction chamber of a hot - wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 100 °C, introduce 150 sccm of silane, 150 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot - wire voltage of 55 V and a hot - wire current of 32 A, and deposit for 150 s to form a 4 - nm boron - doped amorphous silicon source layer on the front side of the silicon wafer.

[0151] Comparative Example 6

[0152] It is only different from Examples 1-4 in Step 101), where Step 101) is specifically as follows:

[0153] Place the silicon wafer in the reaction chamber of a hot-wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 400 °C, introduce 150 sccm of silane, 150 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot-wire voltage of 55 V and a hot-wire current of 32 A, and deposit for 150 s to form a 4-nm boron-doped amorphous silicon source layer on the front side of the silicon wafer.

[0154] Comparative Example 7

[0155] It is only different from Examples 1-4 in Step 101), where Step 101) is specifically as follows:

[0156] Place the silicon wafer in the reaction chamber of a hot-wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 250 °C, introduce 200 sccm of silane, 150 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot-wire voltage of 55 V and a hot-wire current of 32 A, and deposit for 150 s to form a 4.5-nm boron-doped amorphous silicon source layer on the front side of the silicon wafer.

[0157] Comparative Example 8

[0158] It is only different from Examples 1-4 in Step 101), where Step 101) is specifically as follows:

[0159] Place the silicon wafer in the reaction chamber of a hot-wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 250 °C, introduce 100 sccm of silane, 150 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot-wire voltage of 55 V and a hot-wire current of 32 A, and deposit for 150 s to form a 3-nm boron-doped amorphous silicon source layer on the front side of the silicon wafer.

[0160] Comparative Example 9

[0161] It is only different from Examples 1-4 in Step 101), where Step 101) is specifically as follows:

[0162] Place the silicon wafer in the reaction chamber of a hot-wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 250 °C, introduce 150 sccm of silane, 80 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot-wire voltage of 55 V and a hot-wire current of 32 A, and deposit for 150 s to form a 3.2-nm boron-doped amorphous silicon source layer on the front side of the silicon wafer.

[0163] Comparative Example 10

[0164] It is only different from Examples 1-4 in Step 101), where Step 101) is specifically as follows:

[0165] Place the silicon wafer in the reaction chamber of a hot-wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 250 °C, introduce 150 sccm of silane, 180 sccm of diborane, and 200 sccm of hydrogen under the conditions of a hot-wire voltage of 55 V and a hot-wire current of 32 A, and deposit for 150 s to form a 4.2-nm boron-doped amorphous silicon source layer on the front side of the silicon wafer.

[0166] Comparative Example 11

[0167] It is only different from Examples 1-4 in Step 101), where Step 101) is specifically as follows:

[0168] Place the silicon wafer in the reaction chamber of a hot-wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 250 °C, introduce 150 sccm of silane, 150 sccm of diborane, and 150 sccm of hydrogen under the conditions of a hot-wire voltage of 55 V and a hot-wire current of 32 A, and deposit for 150 s to form a 3.8-nm boron-doped amorphous silicon source layer on the front side of the silicon wafer.

[0169] Comparative Example 12

[0170] It is only different from Examples 1-4 in Step 101), where Step 101) is specifically as follows:

[0171] Place the silicon wafer in the reaction chamber of a hot-wire chemical vapor deposition equipment. After evacuating the reaction chamber to 2 Pa and heating the hot wire to 250 °C, introduce 150 sccm of silane, 150 sccm of diborane, and 240 sccm of hydrogen under the conditions of a hot-wire voltage of 55 V and a hot-wire current of 32 A, and deposit for 150 s to form a 4.2-nm boron-doped amorphous silicon source layer on the front side of the silicon wafer.

[0172] I. Solar Cell Performance Test

[0173] Fabricate solar cells from the silicon wafers obtained in Examples 1-6 and Comparative Examples 1-12 according to the following method, and test the photoelectric conversion efficiency (EFF), fill factor (FF), open-circuit voltage (V OC ) and short-circuit current (I SC ) of these solar cells. The results are shown in Table 1.

[0174] Among them, the preparation method of the solar cell includes the following steps:

[0175] S1. Select an N-type silicon wafer as the initial sample and texture the front side of the silicon wafer;

[0176] S2. The front sides of the textured silicon wafers are respectively subjected to boron diffusion treatment by using the boron diffusion methods provided in Examples 1-6 and Comparative Examples 1-6 to form PN junctions;

[0177] S3. A tunneling SiO 2 layer is deposited on the front side of the silicon wafer after boron diffusion treatment by PECVD. The reaction gas used is N 2 O, the reaction temperature is 450 °C, the flow rate of N 2 O is 10000 sccm, the deposition time is 60 s, and the deposition time can be adjusted to control the thickness of the tunneling SiO 2 layer; the thickness of the tunneling SiO 2 layer is 3 nm;

[0178] S4. An AlOx thin film is deposited on the front side of the silicon wafer in the form of ALD. The thickness of the AlOx thin film is 9 nm, and it is formed by reacting Al(CH 3 ) 3 with water vapor. The process temperature is controlled at 260 °C; then a SiNx thin film is deposited on the AlOx thin film in the form of tube PECVD to form a stacked passivation film; the thickness of the front SiNx thin film is 90 nm and the refractive index is 2.1; the thickness of the back SiNx thin film is 100 nm and the refractive index is 2.0; the specific operation steps are as follows: a SiNx film is deposited by using a tube PECVD device (frequency 40 KHz); the reaction gases in the tube cavity are SiH 4 , NH3, the working pressure is 1600 mtorr, the power is 12000 W, the temperature is 500 °C, the flow rate of the SiH 4 gas is 1500 sccm, the flow rate of the NH 3 gas is 10000 sccm, the silicon-nitrogen ratio is 0.15, and the deposition time is 15 min. A 90 / 100 nm SiNx film is deposited on the front / back sides of the silicon wafer.

[0179] S5. The silicon wafers with the passivation film formed are successively subjected to screen printing process to print conductive paste on the front / back sides of the battery, and then subjected to sintering process to make the conductive paste form a good ohmic contact with the silicon substrate, and finally a solar cell is obtained.

[0180] Table 1 Performance parameters of the solar cell

[0181] It can be seen from the data in Table 1 that during the preparation of the boron-doped amorphous silicon source layer, the hot wire temperature, the thickness of the boron-doped amorphous silicon source layer, and the flow rates of the silicon source, boron source, and hydrogen all have a significant impact on the performance of the solar cell. Specifically as follows:

[0182] 1) When the thickness of the boron-doped amorphous silicon source layer is in the range of 3 - 5 nm, the fabricated solar cells have higher photoelectric conversion efficiency and fill factor compared to the products obtained with boron-doped amorphous silicon source layers of other thicknesses. This indicates that when the thickness of the boron-doped amorphous silicon source layer is in the range of 3 - 5 nm, it is beneficial for the uniform diffusion of boron elements, thereby improving the consistency of the sheet resistance after boron diffusion, and thus enhancing the photoelectric conversion efficiency and fill factor of the solar cells.

[0183] 2) When the hot wire temperature is in the range of 200 - 300 °C, the fabricated solar cells exhibit higher photoelectric conversion efficiency and fill factor compared to the products obtained under other hot wire temperature conditions. The reason may be that when the hot wire temperature is maintained in the range of 200 - 300 °C, it is conducive to the formation of a dense amorphous silicon layer. This dense structure can reduce the defects on the surface and inside of the silicon wafer, providing a favorable environment for oxygen-free doping diffusion, and thus contributing to the improvement of the performance of the solar cells. However, when the hot wire temperature is greater than 300 °C, it is easy to cause damage to the internal structure of the boron-doped amorphous silicon source layer, which is not conducive to the diffusion of boron elements, and thus affects the formation of the PN junction. When the hot wire temperature is less than 200 °C, the distribution of boron elements in the boron-doped amorphous silicon source layer is uneven, resulting in an increase in recombination centers, thereby affecting the performance of the solar cells.

[0184] 3) When the flow rate of the silicon source is in the range of 120 - 160 sccm, the flow rate of the boron source is in the range of 100 - 150 sccm, and the flow rate of hydrogen is in the range of 180 - 220 sccm, the fabricated solar cells have higher photoelectric conversion efficiency and fill factor compared to the products obtained under other gas source flow rates. This indicates that when the flow rate of the silicon source is 120 - 160 sccm, the flow rate of the boron source is 100 - 150 sccm, and the flow rate of hydrogen is 180 - 220 sccm, it is beneficial to improve the uniformity of boron elements in the boron-doped amorphous silicon source layer, ensure the uniform doping of boron elements inside the silicon wafer after boron diffusion treatment, and contribute to the improvement of the photoelectric conversion efficiency and fill factor of the solar cells.

[0185] II. Boron Doping Concentration Test

[0186] Taking the silicon wafers obtained in Example 2 and Comparative Example 4 as examples, the concentration distribution of boron doping on the surface of the silicon wafers was tested, and the results are shown in Figure 2 . Among them, the depth of the boron doping ECV curve in Example 2 and Comparative Example 4 is from the front surface of the silicon wafer to the inside of the silicon wafer.

[0187] Through Figure 2It can be seen that Example 2 exhibits a higher boron doping concentration in the silicon wafer than that in Comparative Example 4. This phenomenon indicates that, compared with Comparative Example 4, the boron diffusion method provided in Example 2 is more conducive to the diffusion of boron elements into the interior of the silicon wafer. Therefore, the solar cells obtained according to Example 2 are significantly superior to the solar cells prepared according to Comparative Example 4 in terms of electrical performance, including photoelectric conversion efficiency, fill factor, open-circuit voltage, and short-circuit current.

[0188] III. Sheet Resistance Uniformity Test

[0189] Taking the silicon wafers obtained in Example 3 and Comparative Example 4 as examples, a probe tester was used to measure the sheet resistance values of the test points at the same positions on the above two groups of silicon wafers. The test points included Test Point 1 located at the center of the silicon wafer and Test Points 2, 3, 4, 5, 6, 7, 8, and 9 that were arranged in a circular array around Test Point 1, and the sheet resistance uniformity was calculated. The results are shown in Table 2.

[0190] Among them, non-uniformity = (maximum value - minimum value) / (maximum value + minimum value)

[0191] Table 2 Sheet Resistance and Uniformity of the Silicon Wafers Obtained in Example 3 and Comparative Example 4

[0192] It can be seen from Table 2 that, compared with Comparative Example 4, Example 3 has better consistency in sheet resistance, which indicates that the boron diffusion method of the present application can improve the uniformity of boron element diffusion. And it can also be seen from the data in Table 1 that by using the boron diffusion method of the present application, while improving the uniformity of boron element diffusion, the photoelectric conversion efficiency of the solar cell is also improved.

[0193] Those skilled in the art can understand that although some of the embodiments described herein include certain features included in other embodiments rather than other features, the combination of the features of different embodiments means that it is within the scope of the present application and forms different embodiments. For example, in the claims of the present application, any one of the claimed embodiments can be used in any combination.

[0194] It should be noted that although the detailed steps of the method of the present application are described in detail above, on the premise of not deviating from the basic principle of the present application, those skilled in the art can combine, split, and change the order of the above steps. The technical solutions modified in this way do not change the basic concept of the present application, so they also fall within the protection scope of the present application.

[0195] So far, the technical solutions of the present application have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present application is obviously not limited to these specific embodiments. Without departing from the principle of the present application, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present application.

Claims

1. A boron diffusion method, characterized in that: include: A boron-doped amorphous silicon source layer is prepared on one side of a silicon wafer by hot wire chemical vapor deposition method; wherein the thickness of the boron-doped amorphous silicon source layer is 3-5 nm; The silicon wafer on which the boron-doped amorphous silicon source layer is deposited is subjected to oxygen-free boron diffusion treatment.

2. The boron diffusion method according to claim 1, characterized in that: The gas sources used to prepare the boron-doped amorphous silicon source layer include silicon source, boron source and hydrogen.

3. The boron diffusion method according to claim 2, characterized in that: The flow rate of the silicon source is 120-160 sccm, the flow rate of the boron source is 100-150 sccm, and the flow rate of the hydrogen is 180-220 sccm.

4. The boron diffusion method according to claim 2, characterized in that: Possess one or both of the following characteristics: The boron source comprises at least one of borane, diborane and tetraborane; The silicon source includes at least one of silane and disilane.

5. The boron diffusion method according to any one of claims 1 to 4, characterized in that: In the hot wire chemical vapor deposition method, the hot wire temperature is 200-300° C., the deposition pressure is 2.0-2.2 Pa, and the deposition time is 100-250 s.

6. The boron diffusion method according to claim 1, characterized in that: The temperature of oxygen-free boron diffusion is 1000-1100°C, the time is 0.8-1.5h, and the pressure is (5-6)×10 -4 Pa.

7. The boron diffusion method according to claim 1, characterized in that: The boron diffusion method further comprises: The silicon wafer after the oxygen-free boron diffusion treatment is subjected to a push-in treatment.

8. The boron diffusion method according to claim 7, characterized in that: The pushing temperature is 800-900° C., the time is 10-15 minutes, and the pressure is 120-150 mbar.

9. The boron diffusion method according to claim 1, characterized in that: The boron diffusion method further comprises: Using a first etching solution to perform a first etching on the boron-doped amorphous silicon source layer; The boron-doped amorphous silicon source layer is etched for a second time using a second etching solution.

10. The boron diffusion method according to claim 9, characterized in that: One of the first etching solution and the second etching solution is a mixed solution of HF and HNO 3 , and the other is a NaOH solution or a KOH solution.

11. A method for preparing a solar cell, characterized in that: The following steps are involved: Treating the silicon wafer using the boron diffusion method according to any one of claims 1 to 10; A passivation contact structure and an electrode layer are sequentially formed on the surface of the silicon wafer after the boron diffusion treatment to obtain the solar cell.

12. A solar cell, characterized in that: A solar cell manufactured by the method for manufacturing a solar cell according to claim 11.

13. A photovoltaic module, characterized in that: Comprising the solar cell according to claim 12.

Images