Solar cell emitter precursor, method for preparing the same, and solar cell and method for preparing the same

Abstract

The present application relates to the field of solar cells, and discloses a solar cell emitter precursor, a preparation method thereof, a solar cell and a preparation method thereof. + The solar cell emitter precursor comprises, from bottom to top, a silicon wafer, a lightly doped P + layer and a borosilicate glass layer; wherein the thickness of the borosilicate glass layer is 5-10 nm. The borosilicate glass layer is obtained by boron diffusion deposition, and then the first push joint and the second push joint are performed to form the lightly doped P + layer, so that the surface doping concentration and the junction depth are optimized, the high sheet resistance drop is realized while the low reflectivity remains basically unchanged, sufficient boron source is provided for subsequent laser propulsion, selective boron heavy doping is realized, so that the emitter SE structure is formed, and the conversion efficiency of the solar cell is improved.

Description

Technical Field

[0001] This invention relates to the field of solar cells, specifically to a solar cell emitter precursor and its preparation method, and a solar cell and its preparation method. Background Technology

[0002] TOPCon (tunneling oxide passivated) solar cells, with efficiencies closest to the theoretical limit of crystalline silicon cells, have become one of the key research directions for the industrialization of high-efficiency solar cells. In current TOPCon cell technology, the selective emitter (SE) is considered the key to further improving the photoelectric conversion efficiency of solar cells.

[0003] Currently, TOPCon solar cell diffusion processes generally employ a multi-step deposition method.

[0004] CN110707178A discloses a method for preparing a boron-diffused SE structure for an N-type solar cell, which involves grooving the front boron diffusion surface using HF etching paste, followed by secondary deposition and diffusion.

[0005] CN110444631A discloses an N-type battery structure based on a selective emitter and its fabrication method, which uses a laser to open a boron wafer, and then performs secondary deposition and diffusion on the laser-opened silicon wafer.

[0006] CN111739794A discloses a boron diffusion method, a solar cell, and a method for fabricating the same. The method involves depositing a boron source at a low temperature, then raising the temperature for push-junction, and finally lowering the temperature again for a second diffusion deposition. However, existing diffusion processes often result in a very thick BSG (borosilicate glass) during the first boron source deposition, making it difficult to advance the boron source within the BSG, requiring higher laser power, causing greater damage to the silicon wafer, and resulting in only a minor improvement in cell efficiency.

[0007] Therefore, there is currently no simple and mature process for boron expansion SE, making the improvement of TOPCon battery efficiency a major challenge. Summary of the Invention

[0008] The purpose of this invention is to overcome the problem that the borosilicate glass layer of the diffusion sheet produced by the diffusion process in the prior art is relatively thick, making it difficult to reduce the damage of the laser to the textured surface while increasing the laser power. The invention provides a solar cell emitter precursor and its preparation method.

[0009] To achieve the above objectives, a first aspect of the present invention provides an emitter precursor for a solar cell, wherein the emitter precursor comprises, from bottom to top, a silicon wafer and a lightly doped P-coated silicon wafer. + The material comprises a borosilicate glass layer and a borosilicate glass layer; wherein the thickness of the borosilicate glass layer is 5-10 nm.

[0010] A second aspect of the present invention provides a method for preparing an emitter precursor for a solar cell, comprising the following steps:

[0011] (1) Nitrogen, oxygen and boron trichloride are introduced into the texturized silicon wafer to perform boron diffusion deposition and form a borosilicate glass layer. The flow rate of nitrogen is 500-1000 sccm, the flow rate of oxygen is 50-200 sccm, the flow rate of boron trichloride is 50-100 sccm, the temperature is 800-850℃, and the time is 200-400s.

[0012] (2) Under a protective atmosphere, the product obtained in step (1) is subjected to the first push-gathering;

[0013] (3) Under a protective atmosphere, the product obtained in step (2) is subjected to a second push-bonding to obtain a boron diffusion layer P. + ;

[0014] (4) Anneal the product obtained in step (3) to obtain the solar cell emitter precursor.

[0015] A third aspect of the present invention provides a method for fabricating a solar cell, wherein the method comprises: forming a heavily doped P-type solar cell emitter precursor obtained by the method described in the first aspect or the method described in the second aspect using a laser propulsion process. ++ The layers are then subjected to subsequent boron oxidation and metallization processes to obtain the solar cell.

[0016] A fourth aspect of the present invention provides a solar cell prepared by the preparation method described in the third aspect above.

[0017] Through the above technical solution, the present invention can achieve the following technical effects:

[0018] (1) The solar cell emitter precursor provided by the present invention deposits a very thin (5-10nm) borosilicate glass layer on the surface of a silicon wafer. While optimizing the surface doping concentration and junction depth and reducing internal defects of the silicon wafer, it ensures lightly doped P + The layer can be laser-doped to form heavily doped P ++ The layer provides a sufficient boron source; in addition, the thin borosilicate glass layer can complete the boron doping process at a relatively low laser power, which helps to reduce the damage of boron diffusion to the textured surface of the silicon wafer, and can ensure that the low reflectivity remains basically unchanged while achieving high sheet resistance reduction.

[0019] (2) The solar cell emitter precursor provided by the present invention adopts a one-step deposition and two-step push-junction process, which can deposit boron source with less gas flow and lower temperature. The process method is simple, reduces the high temperature process, increases diffusion performance, and reduces process gas cost. The solar cell further obtained can provide a larger sheet resistance window, which can effectively reduce contact resistance, increase fill factor, increase short circuit current and open circuit voltage, and improve solar cell conversion efficiency. Attached Figure Description

[0020] Figure 1 The heavily doped P provided by this invention ++ A schematic diagram of the layer structure. Detailed Implementation

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] The first aspect of this invention provides an emitter precursor for a solar cell, wherein the emitter precursor, from bottom to top, comprises a silicon wafer and a lightly doped P-coated silicon wafer. + The material comprises a borosilicate glass layer and a borosilicate glass layer; wherein the thickness of the borosilicate glass layer is 5-10 nm.

[0023] In this invention, a thin layer of borosilicate glass is deposited on the surface of the silicon wafer in the solar cell emitter precursor, which can reduce the damage of boron diffusion to the textured surface of the silicon wafer. Furthermore, the high boron content provides sufficient boron diffusion source for subsequent laser propulsion, ensuring that the low reflectivity remains essentially unchanged while achieving high sheet resistance reduction.

[0024] In some embodiments of the present invention, preferably, the lightly doped P + The boron doping concentration in the layer is 0.5-1.5E+20cm. -3 As a non-limiting embodiment, lightly doped P + The boron doping concentration in the layer can be 0.5E+20cm. -3 0.7E+20cm -3 0.9E+20cm -3 1.1E+20cm -3 1.3E+20cm -3 1.5E+20cm -3And any value within a range formed by any two of these point values. Satisfying this range ensures that the laser doping provides a sufficient number of boron atoms without forming a dead layer. Preferably, the lightly doped P... + The junction depth in the layer is 0.2-0.6 μm. As a non-limiting embodiment, the junction depth can be 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, or any value within the range formed by any two of these values. Satisfying this range ensures the lightly doped P... + The emitter meets the requirements for a high-concentration shallow junction. In this invention, both the boron doping concentration and junction depth are measured using an electrochemical differential capacitance voltage (ECV) meter.

[0025] In some embodiments of the present invention, preferably, the reflectivity of the borosilicate glass layer is 8.5-9.8%. As a non-limiting embodiment, the reflectivity of the borosilicate glass layer can be any value within the range of 8.5%, 8.6%, 8.7%, 8.8%, 8.9%, 9.0%, 9.1%, 9.2%, 9.3%, 9.4%, 9.5%, 9.6%, 9.7%, 9.8%, or any two of these values. Meeting this range allows for the assessment that the thickness of the borosilicate glass film is between 5-10 nm. Preferably, the sheet resistance of the borosilicate glass layer is 100-130 Ω / □. As a non-limiting embodiment, the sheet resistance can be any value within the range of 100 Ω / □, 105 Ω / □, 110 Ω / □, 115 Ω / □, 120 Ω / □, 125 Ω / □, 130 Ω / □, or any two of these values. Meeting this range indicates that the boron atom doping concentration in the borosilicate glass layer is between 0.5 and 1.5E+20cm. -3 The junction depth is between 0.2 and 0.6 μm. In this invention, the reflectivity of the borosilicate glass layer is measured using a D8 reflectivity meter, and the sheet resistance is measured using a four-probe sheet resistance meter.

[0026] A second aspect of the present invention provides a method for preparing an emitter precursor for a solar cell, comprising the following steps:

[0027] (1) Nitrogen, oxygen and boron trichloride are introduced into the texturized silicon wafer to perform boron diffusion deposition and form a borosilicate glass layer. The flow rate of nitrogen is 500-1000 sccm, the flow rate of oxygen is 50-200 sccm, the flow rate of boron trichloride is 50-100 sccm, the temperature is 800-850℃, and the time is 200-400s.

[0028] (2) Under a protective atmosphere, the product obtained in step (1) is subjected to the first push-gathering;

[0029] (3) Under a protective atmosphere, the product obtained in step (2) is subjected to a second push-bonding to obtain a boron diffusion layer P. + ;

[0030] (4) Anneal the product obtained in step (3) to obtain the solar cell emitter precursor.

[0031] This invention employs a single deposition and two push-junction methods to prepare solar cell emitter precursors. By controlling the gas flow rate, deposition temperature, and time during boron diffusion deposition, diffusion performance can be increased, process gas costs can be reduced, and the process method is simple, minimizing high-temperature processes. Furthermore, the lightly doped P formed after the second push-junction... + The layer has a high boron content, which can provide a sufficient boron source for subsequent laser propulsion.

[0032] In some embodiments of the present invention, preferably, in step (1), the nitrogen flow rate in the boron diffusion deposition is 800-1000 sccm, which can be any value within the range of 800 sccm, 840 sccm, 880 sccm, 920 sccm, 960 sccm, 1000 sccm, and any two of these values; the oxygen flow rate is 135-175 sccm, which can be any value within the range of 135 sccm, 145 sccm, 155 sccm, 165 sccm, 175 sccm, and any two of these values; the boron trichloride flow rate is 50-65 sccm, which can be any value within the range of 50 sccm, 53 sccm, 56 sccm, 59 sccm, 62 sccm, 65 sccm, and any two of these values. Meeting this range ensures a uniform distribution of the boron source from the furnace mouth to the furnace tail during the boron source deposition process. Furthermore, using boron trichloride as the boron source reduces the damage to quartz devices caused by byproducts during the boron diffusion process. The boron diffusion temperature is 800-825℃, and can be any value within the range of 800℃, 805℃, 810℃, 815℃, 820℃, 825℃, or any two of these values. Meeting this range provides temperature assurance for the series of chemical reactions required during the boron source deposition process. The boron diffusion pressure is 200-300 mBa, and the boron diffusion deposition time is 200-380 s, and can be any value within the range of 200 s, 230 s, 260 s, 290 s, 320 s, 350 s, 380 s, or any two of these values. Meeting this range ensures the formation of lightly doped P. + There is enough boron in the layer to be laser-doped.

[0033] In this invention, by simultaneously controlling the gas flow rate, boron diffusion temperature, pressure, and time during boron diffusion deposition within the range defined by this invention, a very thin borosilicate glass layer can be deposited on the surface of a silicon wafer, forming a lightly doped P with a large number of boron atoms. + The layer can facilitate the formation of heavily doped P-type lasers for subsequent laser doping. ++ The layer provides an ample boron source; furthermore, in this invention, the thin borosilicate glass layer enables the boron doping process to be completed at relatively low laser power, which helps reduce the damage of boron diffusion to the textured surface of the silicon wafer, and can maintain a low reflectivity while achieving a high sheet resistance reduction. Compared with traditional diffusion processes, it reduces the gas flow rate for boron diffusion deposition, lowers the boron diffusion deposition temperature, reduces high-temperature processes, increases diffusion performance, optimizes surface doping concentration and junction depth, and reduces process gas costs.

[0034] In some embodiments of the present invention, preferably, in step (2), the nitrogen flow rate during the first junction push is 2000-3000 sccm; the first junction push temperature is 900-950℃, the pressure is 800-1000 mba, and the time is 500-1000 s. In the present invention, controlling the first junction push temperature, pressure, and gas flow rate within the range defined by the present invention can push the boron on the surface of the silicon wafer after diffusion deposition into the silicon body to form a certain junction depth.

[0035] In some embodiments of the present invention, preferably, in step (3), the nitrogen flow rate during the second junction push is 2000-3000 sccm; the temperature of the second junction push is 900-950℃, the pressure is 750-980 mba, and the time is 500-1000 s. In the present invention, controlling the temperature, pressure, and gas flow rate of the second junction push within the range defined by the present invention can further push the boron source into the silicon body, increase the junction depth, and form lightly doped P. + layer.

[0036] According to the present invention, in the preparation process of the solar cell emitter precursor, a low-temperature diffusion deposition and high-temperature propulsion process is adopted, which can increase diffusion performance and diffusion sheet resistance uniformity, reduce the damage of boron diffusion to the textured surface of the silicon wafer, and the process method is simple.

[0037] In some embodiments of the present invention, preferably, in step (4), the nitrogen flow rate during annealing is 2000-3000 sccm; the annealing temperature is 800-850℃, the pressure is 800-1000 mba, and the time is 180-240 s. In the present invention, introducing nitrogen gas for annealing can repair the crystal lattice and activate more boron atoms; furthermore, controlling the nitrogen flow rate, annealing time, and temperature within the range defined by the present invention is beneficial to ensuring the efficiency of silicon wafer fabrication and reducing resource waste.

[0038] A third aspect of the present invention provides a method for fabricating a solar cell, wherein the method comprises a solar cell emitter precursor as described in the first aspect or a solar cell emitter precursor obtained by the method described in the second aspect, and a heavily doped P-type solar cell is formed by laser propulsion. ++ The layers are then subjected to subsequent boron oxidation and metallization processes to obtain the solar cell.

[0039] This invention uses laser propulsion to prepare the solar cell emitter precursor, forming a heavily doped P-type solar cell. ++ The selective emitter (SE) structure is obtained by layering layers, which not only optimizes the surface doping concentration and junction depth and reduces internal defects in the silicon wafer, but also provides sufficient boron diffusion sources for subsequent laser propulsion. The resulting solar cells can effectively reduce contact resistance, increase fill factor, increase short-circuit current and open-circuit voltage, and improve the conversion efficiency of solar cells.

[0040] In some embodiments of the present invention, preferably, the laser power in the laser propulsion process is 35-60W, and the laser scanning speed is 20-50m / s. In this invention, the laser power and scanning speed in the laser propulsion process are controlled within the above ranges to ensure the fabrication efficiency of the solar cell.

[0041] In some embodiments of the present invention, preferably, the heavily doped P ++ In the layer, the boron doping concentration is 1-3E+19cm -3 The junction depth is 1.5-1.8μm.

[0042] In this invention, the specific conditions for the post-boron oxidation and metallization processes in the solar cell fabrication method are not particularly limited. They can be referenced from existing technologies or adjusted by those skilled in the art according to actual conditions. These conditions will not be described in detail here. Furthermore, the fabrication method may also include other post-processing steps. The specific procedures for these post-processing steps are not particularly limited and can be carried out in a manner well-known in the art. These procedures will not be described in detail here.

[0043] A fourth aspect of the present invention provides a solar cell prepared by the preparation method described in the third aspect above.

[0044] In some embodiments of the present invention, preferably, the short-circuit current of the solar cell is 41.6-41.95mA; the open-circuit voltage is 718-725mV; and the conversion efficiency is 25.01-25.6%.

[0045] The present invention will be described in detail below through this embodiment.

[0046] The thickness of the borosilicate glass layer was measured using an ellipsometry; the sheet resistance was measured using a four-probe sheet resistance meter; the reflectivity was measured using a D8 reflectivity meter; the boron doping concentration and junction depth were measured using an electrochemical differential capacitance voltage (ECV) meter; and the efficiency parameters of the solar cell were measured using an IV meter.

[0047] Example 1

[0048] (1) After cleaning and texturing, the silicon wafer was purged with nitrogen, oxygen, and boron trichloride for boron diffusion deposition. The nitrogen flow rate was 1000 sccm, the oxygen flow rate was 145 sccm, and the boron trichloride flow rate was 55 sccm. The boron diffusion deposition temperature was 830℃, the pressure was 300 mba, and the deposition time was 330 s. Nitrogen was then purged at a flow rate of 2800 sccm for the first push-junction, at a temperature of 915℃, a pressure of 850 mba, and a time of 500 s. Nitrogen was then purged at a flow rate of 3000 sccm for the second push-junction, forming lightly doped P. + The second push-bonding layer was performed at a temperature of 915℃, a pressure of 845 mba, and a time of 500 s. Annealing was then carried out with nitrogen gas at a flow rate of 2000 sccm at a temperature of 800℃, a pressure of 1000 mba, and a time of 200 s. The silicon wafer was then removed and its performance was tested. The test results are shown in Table 1.

[0049] (2) The silicon wafer described in step (1) is laser-driven to form an SE structure, and its performance is tested. The test results are shown in Table 1.

[0050] (3) The silicon wafer after laser propulsion was subjected to boron oxidation process and its performance was tested. The test results are shown in Table 1.

[0051] (4) The silicon wafer after boron oxidation is processed by the battery process to obtain the solar cell. The performance of the solar cell is tested and the test results are shown in Table 1.

[0052] Example 2

[0053] (1) After cleaning and texturing, the silicon wafer was purged with nitrogen, oxygen, and boron trichloride for boron diffusion deposition. The nitrogen flow rate was 900 sccm, the oxygen flow rate was 150 sccm, and the boron trichloride flow rate was 50 sccm. The boron diffusion deposition temperature was 825℃, the pressure was 290 mba, and the deposition time was 350 s. Nitrogen gas was then purged at a flow rate of 2800 sccm for the first push-junction, at a temperature of 905℃, a pressure of 850 mba, and a time of 830 s. Nitrogen gas was then purged at a flow rate of 3000 sccm for the second push-junction, forming lightly doped P. +The second push-bonding layer was performed at a temperature of 900℃, a pressure of 845 mba, and a time of 850 s. Annealing was then carried out with nitrogen gas at a flow rate of 2000 sccm at a temperature of 800℃, a pressure of 1000 mba, and a time of 200 s. The silicon wafer was then removed and its performance was tested. The test results are shown in Table 1.

[0054] (2) The silicon wafer described in step (1) is laser-driven to form an SE structure, and its performance is tested. The test results are shown in Table 1.

[0055] (3) The silicon wafer after laser propulsion was subjected to boron oxidation process and its performance was tested. The test results are shown in Table 1.

[0056] (4) The silicon wafer after boron oxidation is processed by the battery process to obtain the solar cell. The performance of the solar cell is tested and the test results are shown in Table 1.

[0057] Example 3

[0058] (1) After cleaning and texturing, the silicon wafer was purged with nitrogen, oxygen, and boron trichloride for boron diffusion deposition. The nitrogen flow rate was 900 sccm, the oxygen flow rate was 155 sccm, and the boron trichloride flow rate was 60 sccm. The boron diffusion deposition temperature was 835℃, the pressure was 280 mba, and the deposition time was 330 s. Nitrogen gas was then purged at a flow rate of 2800 sccm for the first push-junction, at a temperature of 915℃, a pressure of 850 mba, and a time of 850 s. Nitrogen gas was then purged at a flow rate of 3000 sccm for the second push-junction, forming lightly doped P. + The second push-bonding layer was performed at a temperature of 915℃, a pressure of 845 mba, and a time of 900 s. Annealing was then carried out with nitrogen gas at a flow rate of 2000 sccm at a temperature of 800℃, a pressure of 1000 mba, and a time of 200 s. The silicon wafer was then removed and its performance was tested. The test results are shown in Table 1.

[0059] (2) The silicon wafer described in step (1) is laser-driven to form an SE structure, and its performance is tested. The test results are shown in Table 1.

[0060] (3) The silicon wafer after laser propulsion was subjected to boron oxidation process and its performance was tested. The test results are shown in Table 1.

[0061] (4) The silicon wafer after boron oxidation is processed by the battery process to obtain the solar cell. The performance of the solar cell is tested and the test results are shown in Table 1.

[0062] Comparative Example 1

[0063] The method of Example 1 was followed, except that in step (1), the nitrogen flow rate for boron diffusion deposition was 2500 sccm, the oxygen flow rate was 700 sccm, the boron trichloride flow rate was 200 sccm, the temperature for boron diffusion deposition was 840°C, the pressure was 300 mba, and the deposition time was 550 s.

[0064] Table 1

[0065]

[0066] As can be seen from the results in Table 1, the solar cell emitter precursor provided by this invention, employing a one-step deposition and two-step junction push process, deposits a boron source with a lower gas flow rate and temperature, enabling the deposition of a very thin (5-10 nm) borosilicate glass layer on the silicon wafer surface. This optimizes the surface doping concentration and junction depth, and also lightly dops with P. + The layer has a high boron content, which can facilitate laser doping to form P. ++ The heavily doped region provides a sufficient boron source, enabling the boron doping process to be completed at relatively low laser power. This helps reduce the damage of boron diffusion to the textured surface of the silicon wafer, and while achieving a high sheet resistance drop, it ensures that the low reflectivity remains essentially unchanged. The resulting solar cell can effectively reduce contact resistance, increase fill factor, and improve short-circuit current and open-circuit voltage, thereby improving the conversion efficiency of the solar cell. In contrast, the borosilicate glass layer of the emitter precursor of the solar cell obtained in document 1 is thicker because it does not use the boron diffusion deposition conditions within the scope of this invention. This is not conducive to laser propulsion and textured surface protection, and makes it difficult to improve the conversion efficiency of the solar cell.

[0067] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing an emitter precursor for a solar cell, characterized in that, Includes the following steps: (1) Nitrogen, oxygen and boron trichloride are introduced into the texturized silicon wafer to perform boron diffusion deposition and form a borosilicate glass layer. The flow rate of nitrogen is 500-1000 sccm, the flow rate of oxygen is 50-200 sccm, the flow rate of boron trichloride is 50-100 sccm, the temperature is 800-850℃, the pressure is 200-300 mba, and the time is 200-400 s. (2) Under a protective atmosphere, the product obtained in step (1) is subjected to a first push-bonding; in the first push-bonding, the nitrogen flow rate is 2000-3000 sccm; the temperature of the first push-bonding is 900-950℃, the pressure is 800-1000 mba, and the time is 500-1000 s. (3) Under a protective atmosphere, the product obtained in step (2) is subjected to a second push-junction to obtain lightly doped P. + Layer; In the second push-junction, the nitrogen flow rate is 2000-3000 sccm; The temperature of the second push-junction is 900-950℃, the pressure is 750-980 mba, and the time is 500-1000 s; (4) Anneal the product obtained in step (3) to obtain the solar cell emitter precursor; The emitter precursor consists of a silicon wafer and a lightly doped P-type silicon wafer from bottom to top. + A layer and a borosilicate glass layer; wherein the thickness of the borosilicate glass layer is 5-10 nm; the lightly doped P + The boron doping concentration in the layer is 0.5-1.5E+20cm. -3 The junction depth is 0.2-0.6μm.

2. The method according to claim 1, characterized in that, In step (1), during the boron diffusion deposition process, the nitrogen flow rate is 800-1000 sccm, the oxygen flow rate is 135-175 sccm, and the boron trichloride flow rate is 50-65 sccm.

3. The preparation method according to claim 1, characterized in that, The boron diffusion temperature is 800-825℃, and the time is 200-380s.

4. The method according to claim 1, characterized in that, In step (4), the nitrogen flow rate during annealing is 2000-3000 sccm.

5. The preparation method according to claim 1, characterized in that, The annealing temperature is 800-850℃, the pressure is 800-1000mba, and the time is 180-240s.

6. A solar cell emitter precursor prepared by the method for preparing a solar cell emitter precursor according to any one of claims 1-5, characterized in that, The emitter precursor consists of a silicon wafer and a lightly doped P-type silicon wafer from bottom to top. + The material comprises a borosilicate glass layer and a borosilicate glass layer; wherein the thickness of the borosilicate glass layer is 5-10 nm.

7. The emitter precursor according to claim 6, characterized in that, The lightly doped P + The boron doping concentration in the layer is 0.5-1.5E+20cm. -3 The junction depth is 0.2-0.6μm.

8. The emitter precursor according to claim 6, characterized in that, The borosilicate glass layer has a reflectivity of 8.5-9.8% and a sheet resistance of 100-130 Ω / □.

9. A method for preparing a solar cell, characterized in that, The preparation method includes: forming a heavily doped P-type solar cell emitter precursor obtained by the preparation method according to any one of claims 1-5 using a laser propulsion process. ++ The layers are then subjected to subsequent boron oxidation and metallization processes to obtain the solar cell.

10. The preparation method according to claim 9, characterized in that, In the laser propulsion process, the laser power is 35-60W and the laser scanning speed is 20-50m / s.

11. The preparation method according to claim 9, characterized in that, In the heavily doped P++ layer, the boron doping concentration is 1-3E+19cm-3, and the junction depth is 1.5-1.8μm.

12. A solar cell prepared by the preparation method according to any one of claims 9-11.

13. The solar cell according to claim 12, characterized in that, The short-circuit current of the solar cell is 41.6-41.95mA; the open-circuit voltage is 718-725mV; and the conversion efficiency is 25.01-25.6%.

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