Solar cell and manufacturing method therefor

Abstract

A solar cell and a manufacturing method therefor. The manufacturing method comprises: by means of a doping medium, performing doping diffusion on a first surface of a cell substrate; irradiating the surface of the cell substrate by means of laser having preset parameters, so as to form a heavily doped region and a doping transition region surrounding the heavily doped region; cleaning impurities formed after doping diffusion; manufacturing functional layers on the first surface of the cell substrate and a second surface facing away from the first surface thereof, the functional layers avoiding the heavily doped region and the doping transition region; and manufacturing metal gate lines along the heavily doped region on the first surface and the second surface of the cell substrate, the metal gate lines being arranged on the first surface along the heavily doped region. Laser is irradiated on the first surface of the cell substrate to form the heavily doped region and the doping transition region, the doping concentration of the doping transition region being smaller than that of the heavily doped region and greater than that of a lightly doped region. During manufacturing of the metal gate lines, if the metal gate lines are not aligned with the heavily doped region, the metal gate lines can still be in contact with the doping transition region, thus reducing the contact resistance, and improving the power generation efficiency of the solar cell.

Description

Solar cell and method for manufacturing the same

[0001] This disclosure claims priority to a Chinese patent application filed with the Patent Office of China on September 25, 2023, with application number 202311244725.0 and invention name “Solar Cells and Methods for Making Them,” the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present disclosure relates to the field of photovoltaic manufacturing, and in particular, to a solar cell and a method for preparing the same. Background Art

[0003] TOPCon is a tunnel oxide passivated contact (Tunnel Oxide Passivated Contact) solar cell technology based on the principle of selective carriers. A doped region is incorporated into the TOPCon cell, along which the grid lines are placed. The doped region reduces surface recombination and metal contact recombination in the TOPCon cell, thereby reducing the contact resistance between the metal grid lines and the TOPCon cell.

[0004] Currently, metal grid lines often have the problem of misalignment with doped regions, causing the grid lines to contact structures outside the doped regions, resulting in increased contact resistance and affecting the efficiency of the entire battery.

[0005] Therefore, how to improve the cell efficiency of photovoltaic cells is a technical problem that those skilled in the art urgently need to solve. Summary of the Invention

[0006] The present disclosure aims to solve at least one of the technical problems existing in the prior art, and proposes a solar cell and a preparation method thereof, which can reduce the contact resistance between the metal grid line and the cell, thereby improving the efficiency of the solar cell.

[0007] To achieve the purpose of the present disclosure, a method for preparing a solar cell is provided, comprising:

[0008] Performing doping diffusion on the first surface of the battery substrate through a doping medium;

[0009] Irradiating the surface of the battery substrate with a laser having preset parameters to form a heavily doped region and a doped transition region surrounding the heavily doped region;

[0010] Clean impurities formed after doping diffusion;

[0011] preparing a functional layer on the first surface of the battery substrate and a second surface away from the first surface, wherein the functional layer is arranged to avoid the heavily doped region and the doped transition region;

[0012] Metal grid lines are prepared along the heavily doped region on the first surface and the second surface of the battery substrate. The metal grid lines are arranged along the heavily doped region on the first surface.

[0013] In some embodiments, irradiating the surface of the battery substrate with a laser having preset parameters includes:

[0014] The surface of the battery substrate is irradiated with a laser having preset parameters for a preset time period, wherein the preset time period is 0.5s to 1s.

[0015] In some embodiments, the preset parameters of the laser include laser power and spot diameter, the laser power is 2000W~8000W, and the spot diameter is 5μm~150μm.

[0016] In some embodiments, the step of preparing functional layers on the front and back sides of the battery substrate includes:

[0017] A tunneling layer is prepared on the second surface.

[0018] In some embodiments, the step of preparing functional layers on the front and back sides of the battery substrate further comprises:

[0019] A passivation layer is prepared on the first surface.

[0020] In some embodiments, the step of preparing functional layers on the front and back sides of the battery substrate further comprises:

[0021] A passivation anti-reflection layer is prepared on a side of the passivation layer away from the battery substrate and a side of the tunneling layer away from the battery substrate.

[0022] In some embodiments, the doping medium is boron bromide or boron chloride;

[0023] The step of performing doping diffusion on the first surface of the battery substrate through a doping medium includes:

[0024] Boron is diffused on the first surface at a diffusion temperature of 900° C. to 1100° C.

[0025] In some embodiments, before the doping diffusion is performed on the first surface of the battery substrate through the doping medium, the method further includes:

[0026] polishing the first surface and the second surface of the battery substrate;

[0027] Texturing the first surface and the second surface after polishing;

[0028] Cleaning the first surface and the second surface after texturing.

[0029] In some embodiments, the step of forming metal grid lines along the heavily doped region on the first surface and the second surface of the battery substrate includes:

[0030] Metal grid lines are prepared along the heavily doped region on the first surface and the second surface of the battery substrate by printing or sintering.

[0031] The present disclosure also provides a solar cell, which is prepared by any one of the above-mentioned preparation methods.

[0032] The present disclosure has the following beneficial effects:

[0033] The present disclosure provides a method for preparing a solar cell, comprising: performing doping diffusion on the first surface of a cell substrate through a doping medium; irradiating the cell substrate surface with a laser having preset parameters to form a heavily doped region and a doped transition region surrounding the heavily doped region; cleaning impurities formed after the doping diffusion; preparing a functional layer on the first surface of the cell substrate and a second surface facing away from the first surface, the functional layer being arranged to avoid the heavily doped region and the doped transition region; preparing metal grid lines on the first and second surfaces of the cell substrate along the heavily doped region, the metal grid lines being arranged along the heavily doped region on the first surface.

[0034] Doping diffusion is performed on the first surface of the cell substrate to form a lightly doped region. Subsequently, laser irradiation is performed on the first surface of the cell substrate to form a heavily doped region and a doped transition region. The doping concentration in the doped transition region is lower than that in the heavily doped region and higher than that in the lightly doped region. If the metal grid lines are misaligned with the heavily doped regions during fabrication, they can still contact the doped transition regions, reducing contact resistance and improving the power generation efficiency of the solar cell. Furthermore, the laser doping process for forming heavily doped and doped transition regions is simple and efficient, facilitating large-scale production of solar cells.

[0035] Another object of the present disclosure is to provide a solar cell prepared by the above preparation method, which has the above advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG1 is a flow chart of a method for preparing a solar cell provided by the present disclosure;

[0037] FIG2 is a schematic structural diagram of a solar cell provided by the present disclosure.

[0038] Wherein, the reference numerals in FIG1 and FIG2 are:

[0039] N-type silicon substrate 1, doping layer 2, passivation layer 3, first passivation anti-reflection layer 4, tunneling layer 5, phosphorus-doped polysilicon layer 6, second passivation anti-reflection layer 7, heavily doped region 8, doped transition region 9, and metal gate line 10. Modes for Carrying Out the Invention

[0040] In order to enable those skilled in the art to better understand the technical solution of the present disclosure, the solar cell and the preparation method thereof provided by the present disclosure are described in detail below with reference to the accompanying drawings.

[0041] The present disclosure provides a method for preparing a solar cell, comprising:

[0042] S1, performing doping diffusion on the first surface of the battery substrate through a doping medium;

[0043] The battery substrate can be a silicon substrate, specifically an N-type silicon substrate 1. The first surface of the N-type silicon substrate 1 can be specifically the front surface of the N-type silicon substrate 1, and the second surface is away from the first surface and can be specifically the back surface of the N-type silicon substrate 1.

[0044] Optionally, the doping medium can be boron bromide, boron chloride, or the like, and the corresponding doping diffusion process is boron diffusion. During the boron diffusion process, the diffusion medium reacts to generate boron atoms, which diffuse into the interior of the N-type silicon substrate 1, forming a lightly doped layer. The diffusion temperature can be 900°C to 1100°C, and after diffusion, the doped layer 2 is formed. The sheet resistance of the doped layer 2 can be 160Ω / □ to 260Ω / □, and the junction depth can be 0.6μm to 1.6μm.

[0045] Optionally, before the doping medium is used to diffuse the doping on the first surface of the battery substrate, the N-type silicon substrate 1 needs to be polished and textured to improve the adhesion of the surface of the N-type silicon substrate 1 .

[0046] Optionally, the first surface and the second surface of the battery substrate need to be polished first, and the polishing can be performed using an alkaline polishing process. After polishing, the first surface and the second surface are texturized, and the texturizing can be performed using an alkaline texturizing process. Specifically, an alkaline solution such as potassium hydroxide, sodium hydroxide or tetramethylamino hydroxide can be used, combined with polishing additives and texturizing additives, to clean the impurities of the silicon wafer and prepare the pyramid texturizing surface under conditions of 20°C to 80°C. After the texturizing is completed, the first surface and the second surface of the N-type silicon substrate 1 are cleaned to remove the alkaline solution, texturizing additives and other impurities. Of course, users can also use other processes for polishing and texturizing operations as needed, which is not limited here.

[0047] S2. Irradiating the surface of the battery substrate with a laser having preset parameters to form a heavily doped region 8 and a doped transition region 9 surrounding the heavily doped region;

[0048] After boron diffusion, boron atoms are deposited on the surface of the N-type silicon substrate 1. Laser light with preset parameters irradiates the surface of the N-type silicon substrate 1, causing the surface of the N-type silicon substrate 1 to melt, thereby causing the boron atoms to form a heavily doped region 8 in the N-type silicon substrate 1. The square resistance of the heavily doped region 8 can reach 40Ω / □~120Ω / □, and the junction depth can reach 1.0μm~2.6μm. The junction depth of the heavily doped region 8 is greater than the junction depth of the lightly doped region. In addition, the area near the direct irradiation range of the laser is also heated and melted, forming a doped transition region 9. The square resistance of the doped transition region 9 is greater than that of the heavily doped region 8, and smaller than that of the lightly doped region. The junction depth of the doped transition region 9 is smaller than the junction depth of the heavily doped region, and greater than the junction depth of the lightly doped region.

[0049] Laser irradiation forms a heavily doped region 8 and a doped transition region 9 surrounding the heavily doped region 8 on the surface of the N-type silicon substrate 1. The doped transition region 9 has a smaller square resistance than the lightly doped region. During the preparation of the metal grid line 10, if the metal grid line 10 deviates from the heavily doped region 8, the doped transition region 9 can contact the metal grid line 10. Since the doping concentration of the doped transition region 9 is higher than that of the lightly doped region, the square resistance of the doped transition region 9 is smaller than that of the lightly doped region. The connection resistance of the metal grid line 10 contacting the doped transition region 9 is smaller than that of the lightly doped region. This can reduce the internal resistance of the solar cell and improve the power generation efficiency of the solar cell. In addition, the addition of the doped transition region 9 outside the heavily doped region 8 provides a wider process window for the alignment of the metal grid line 10, reduces the difficulty of alignment, and thus reduces the difficulty of the process.

[0050] Optionally, the laser's preset parameters may include laser power and spot diameter. The laser power ranges from 2000W to 8000W, and the spot diameter ranges from 5μm to 150μm. Accordingly, the width of the heavily doped region 8 may be equal to the laser's spot diameter, and the width of the doped transition region 9 may be within 100μm. Of course, users can also set the laser's preset parameters as needed, and these are not limited here.

[0051] Optionally, the laser having preset parameters is used to irradiate the surface of the battery substrate, specifically for a preset duration of 0.5 to 1 second. Of course, the user can also set the preset duration as needed, which is not limited here.

[0052] S3, cleaning impurities formed by doping diffusion;

[0053] During the boron diffusion process, the dopant, oxygen, and silicon in the N-type silicon substrate 1 react to form silicon dioxide and boron atoms. Some of the boron atoms diffuse into the N-type silicon substrate 1, while the remaining boron atoms and silicon dioxide form BSG (Boron-Silicate Glass) on the surface of the N-type silicon substrate 1. The cleaning process removes the BSG and any metal or other impurities adsorbed on the surface of the N-type silicon substrate 1 during the aforementioned process. Methods for removing BSG and impurities can be found in existing technologies and are not detailed here.

[0054] S4. Functional layers are prepared on the first surface and the second surface of the battery substrate. The functional layers are arranged to avoid the heavily doped region 8 and the doped transition region 9.

[0055] Optionally, the functional layer may include a passivation layer 3 arranged on the first surface, a tunneling layer 5 arranged on the second surface, and a phosphorus-doped polysilicon layer 6 arranged on the side of the tunneling layer 5 away from the N-type silicon substrate 1, wherein the passivation layer 3 needs to be arranged to avoid the heavily doped region 8 and the doped transition region 9.

[0056] Optionally, the tunneling layer 5 can be made of silicon oxide, with a thickness between 1 nm and 3 nm. The tunneling layer 5 can be formed by a deposition process. Silicon oxide chemically passivates the interface state density between the N-type silicon substrate 1 and the phosphorus-doped polysilicon layer 6, significantly increasing the majority carrier concentration compared to the minority carrier concentration, reducing the probability of electron-hole recombination and improving the solar cell's power generation efficiency. It also increases resistivity, creating selective contact for the majority carriers. Of course, the user can also adjust the thickness of the tunneling layer 5 as needed, and this is not a limitation here.

[0057] Furthermore, after the tunneling layer 5 is prepared, a phosphorus-doped polysilicon layer 6 can be prepared on its surface away from the N-type silicon substrate 1. Specifically, an intrinsic polysilicon layer can first be deposited on the side of the tunneling layer 5 away from the N-type silicon substrate 1. The intrinsic polysilicon layer can be prepared on the side of the tunneling layer 5 away from the N-type silicon substrate 1 by using LPCVD (Low Pressure Chemical Vapor Deposition) or PECVD (Plasma Enhanced Chemical Vapor Deposition) process. A polysilicon layer is then prepared on the side of the tunneling layer 5 away from the N-type silicon substrate 1, and then phosphorus is diffused into the polysilicon layer to form a phosphorus-doped polysilicon layer 6. The thickness of the phosphorus-doped polysilicon layer 6 can be greater than or equal to 20nm and less than or equal to 220nm, and the square resistance is between 30Ω / □ and 90Ω / □. The thickness of the phosphorus-doped polysilicon layer 6 can be set according to user needs and is not limited here.

[0058] Furthermore, during the phosphorus-doping process, PSG (Phospho Silicate Glass) is formed on the surface of the phosphorus-doped polysilicon layer 6 away from the N-type silicon substrate 1. After the phosphorus-doped polysilicon layer 6 is prepared, it is cleaned to remove the PSG on the surface of the phosphorus-doped polysilicon layer 6. The polysilicon plated around the first surface of the N-type silicon substrate 1, as well as metals or other impurities adsorbed on the surface of the N-type silicon substrate 1 during the preparation of the tunneling layer 5 and the phosphorus-doped polysilicon layer 6, are also removed. The cleaning method can be referred to the PSG and polysilicon removal methods, and will not be further described here.

[0059] Optionally, the primary material of passivation layer 3 can be aluminum oxide. Passivation layer 3 can be deposited using a plate-type device or a tube-type device, and the thickness of passivation layer 3 can specifically be 2 nm to 20 nm. Aluminum oxide is used to passivate the p-type semiconductor of the solar cell, reducing the recombination probability of electrons and holes on the front surface of the solar cell, further improving the power generation efficiency of the solar cell. The thickness of passivation layer 3 can also be set by the user as needed, and this is not limited here.

[0060] Optionally, the functional layer may also include a passivation anti-reflection layer. The passivation anti-reflection layer includes a first passivation anti-reflection layer 4 and a second passivation anti-reflection layer 7. The first passivation anti-reflection layer 4 can be disposed on the side of the passivation layer 3 away from the cell substrate, and the second passivation anti-reflection layer 7 can be disposed on the side of the tunneling layer 5 away from the cell substrate. The passivation anti-reflection layer can be made of materials such as silicon nitride, silicon oxynitride, and silicon oxide. After the passivation layer 3 and phosphorus-doped polysilicon layer 6 are prepared, the passivation anti-reflection layer can be deposited on their surfaces to form the passivation anti-reflection layer. The passivation anti-reflection layer can be a single or multi-layer thin film structure. The thickness of the first passivation anti-reflection layer 4 and the second passivation anti-reflection layer 7 can be greater than or equal to 40 nm and less than or equal to 100 nm. The passivation anti-reflection layer can reduce the reflection of sunlight by the solar cell, allowing more sunlight to be used for power generation, further improving the power generation efficiency of the solar cell. Of course, the thickness of the passivation anti-reflection layer can also be set according to user needs and is not limited here.

[0061] S5 , preparing metal gate lines 10 on the first surface and the second surface of the battery substrate. The metal gate lines 10 on the first surface are arranged along the heavily doped region 8 .

[0062] After the passivation anti-reflection layer is prepared, metal grid lines 10 are prepared on the first surface and the second surface of the N-type silicon substrate 1. The metal grid lines 10 can be formed by printing or sintering. Taking the printing of metal grid lines 10 as an example, during the printing process, the metal grid lines 10 on the front side need to be overprinted and corrected according to the heavily doped area 8. Specifically, the camera can be used to adjust the grab points of the laser marking points at multiple positions to print the metal grid lines 10 in the heavily doped metal area. The metal grid lines 10 may produce a certain offset during the printing process, but the offset will not exceed the width of the doping transition area 9, and the main part of the metal grid lines 10 is printed in the heavily doped area. The back metal grid lines 10 and the main gate electrodes on the front and back sides can be adjusted to have a symmetrical printing position. During the printing process, the sintering peak temperature is greater than or equal to 650°C and less than or equal to 900°C.

[0063] In a specific embodiment of the present disclosure, the solar cell manufacturing process first cleans and texturizes an N-type monocrystalline silicon wafer with a thickness of 130 μm. A boron diffusion process is then performed on the front surface of the N-type silicon substrate 1 to form a doped layer 2 with a diffusion square resistance of 220 Ω / □. Subsequently, a laser is applied to the area where the metal grid lines 10 are to be set to a locally heavily doped region 8, with a square resistance of 85 Ω / □. At the same time, a doped transition region 9 is formed between the lightly doped region and the heavily doped region, with a square resistance of 130 Ω / □ and a width of 30 μm. After the heavily doped region 8 and the doped transition region 9 are prepared, they are cleaned to remove the BSG. Subsequently, a tunneling layer 5 is prepared, and polycrystalline silicon is deposited on the surface of the tunneling layer 5 away from the N-type silicon substrate 1 to prepare a phosphorus-doped polycrystalline silicon layer 6. A passivation layer 3 is then deposited on the front surface of the N-type silicon substrate 1. Subsequently, a passivation anti-reflection layer is deposited on the front and back surfaces of the N-type silicon substrate 1. Finally, the metal grid lines 10 are prepared, which can be screen-printed. The metal grid lines 10 include a main grid and a fine grid, with the heavily doped region 8 primarily corresponding to the fine grid area. The local position of the fine grid on the front side may shift slightly during the printing process, but the fine grid must be located within the doping transition region 9. The peak sintering temperature of the metal grid lines 10 is 750°C, and the sintering time is 1 minute. After the solar cell is fabricated, the electrical performance of the cell is tested. The series resistance of the solar cell is consistent with normal levels, the fill factor is normal, and the average efficiency of the mass-produced solar cell is 25.5%.

[0064] The present disclosure also provides a solar cell, which is prepared by the preparation method in any one of the above embodiments. As shown in Figure 2, the front of the solar cell is prepared by the above method to form a heavily doped region 8 and a doped transition region 9, and the doped transition region 9 can provide a wider process window for the preparation of the metal grid line 10. Even if the metal grid line 10 on the front is slightly offset relative to the heavily doped region 8, it is still within the range of the doped transition region 9. The solar cell adopts an N-type silicon substrate 1, and the front of the solar cell is provided with a passivation layer 3 and a first anti-reflection passivation layer 4 in sequence along the direction away from the N-type silicon substrate 1, and the back of the solar cell is provided with a tunneling layer 5, a phosphorus-doped polysilicon layer 6 and a second passivation anti-reflection layer 7 in sequence along the direction away from the N-type silicon substrate 1. The front and back of the solar cell are provided with metal grid lines 10, and the structures of other parts of the solar cell can refer to the existing technology and will not be repeated here.

[0065] It is understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present disclosure, and the present disclosure is not limited thereto. Those skilled in the art may make various modifications and improvements without departing from the spirit and substance of the present disclosure, and such modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A method for preparing a solar cell, characterized in that: include: Performing doping diffusion on the first surface of the battery substrate through a doping medium; Irradiating the surface of the battery substrate with a laser having preset parameters to form a heavily doped region and a doped transition region surrounding the heavily doped region; Clean the impurities formed after doping diffusion; Prepare a functional layer on the first surface of the battery substrate and a second surface away from the first surface, wherein the functional layer is arranged to avoid the heavily doped region and the doped transition region; Metal grid lines are prepared along the heavily doped region on the first surface and the second surface of the battery substrate, and the metal grid lines are arranged along the heavily doped region on the first surface.

2. The preparation method according to claim 1, characterized in that: The step of irradiating the surface of the battery substrate with a laser having preset parameters comprises: The surface of the battery substrate is irradiated with a laser having preset parameters for a preset time period, wherein the preset time period is 0.5s to 1s.

3. The preparation method according to claim 1, characterized in that: The preset parameters of the laser include laser power and spot diameter. The laser power is 2000W-8000W, and the spot diameter is 5μm-150μm.

4. The preparation method according to claim 1, characterized in that: The method of preparing functional layers on the front and back sides of the battery substrate comprises: A tunneling layer is prepared on the second surface.

5. The preparation method according to claim 2, characterized in that: The method of preparing functional layers on the front and back sides of the battery substrate comprises: A tunneling layer is prepared on the second surface.

6. The preparation method according to claim 3, characterized in that: The method of preparing functional layers on the front and back sides of the battery substrate comprises: A tunneling layer is prepared on the second surface.

7. The preparation method according to claim 4, characterized in that: The method of preparing functional layers on the front and back sides of the battery substrate further includes: A passivation layer is prepared on the first surface.

8. The preparation method according to claim 7, characterized in that: The method of preparing functional layers on the front and back sides of the battery substrate further includes: A passivation anti-reflection layer is prepared on a side of the passivation layer away from the battery substrate and a side of the tunneling layer away from the battery substrate.

9. The preparation method according to claim 1, characterized in that: The doping medium is boron bromide or boron chloride; The step of performing doping diffusion on the first surface of the battery substrate through a doping medium includes: Boron diffusion is performed on the first surface at a diffusion temperature of 900° C.-1100° C.

10. The preparation method according to claim 2, characterized in that: The doping medium is boron bromide or boron chloride; The step of performing doping diffusion on the first surface of the battery substrate through a doping medium includes: Boron diffusion is performed on the first surface at a diffusion temperature of 900° C.-1100° C.

11. The preparation method according to claim 3, characterized in that: The doping medium is boron bromide or boron chloride; The step of performing doping diffusion on the first surface of the battery substrate through a doping medium includes: Boron diffusion is performed on the first surface at a diffusion temperature of 900° C.-1100° C.

12. The preparation method according to claim 1, characterized in that: Before the doping diffusion is performed on the first surface of the battery substrate through the doping medium, the method further includes: polishing the first surface and the second surface of the battery substrate; Texturing the first surface and the second surface after polishing; Cleaning the first surface and the second surface after texturing.

13. The preparation method according to claim 2, characterized in that: Before the doping diffusion is performed on the first surface of the battery substrate through the doping medium, the method further includes: polishing the first surface and the second surface of the battery substrate; Texturing the first surface and the second surface after polishing; Cleaning the first surface and the second surface after texturing.

14. The preparation method according to claim 3, characterized in that: Before the doping diffusion is performed on the first surface of the battery substrate through the doping medium, the method further includes: polishing the first surface and the second surface of the battery substrate; Texturing the first surface and the second surface after polishing; Cleaning the first surface and the second surface after texturing.

15. The preparation method according to claim 12, characterized in that: The step of preparing metal grid lines along the heavily doped region on the first surface and the second surface of the battery substrate comprises: Metal grid lines are prepared along the heavily doped regions on the first surface and the second surface of the battery substrate by printing or sintering.

16. The preparation method according to claim 10, characterized in that: After the first surface of the battery substrate is doped and diffused by a doping medium, a doping layer is formed, the sheet resistance of the doping layer is 160Ω / □-260Ω / □, and the junction depth of the doping layer is 0.6μm-1.6μm.

17. The preparation method according to claim 1, characterized in that: The square resistance of the heavily doped region is 40Ω / □-120Ω / □, and the junction depth of the heavily doped region is 1.0μm-2.6μm.

18. The preparation method according to claim 1, characterized in that: The sheet resistance of the doped transition region is greater than the sheet resistance of the heavily doped region, and is smaller than the sheet resistance of the lightly doped region.

19. The preparation method according to claim 1, characterized in that: The junction depth of the doped transition region is smaller than the junction depth of the heavily doped region, and larger than the junction depth of the lightly doped region.

20. A solar cell, characterized in that: The method is prepared according to claim 1.

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