Method for diffusing boron of solar cell

Abstract

A method for diffusing boron of a solar cell, having an upper surface and a lower surface opposite to each other, is provided. The method includes the following steps: forming a boron diffusion layer on the upper surface; selectively forming a boron-heavily-doped layer on a predetermined region of the upper surface, where the boron concentration in the boron-heavily-doped layer is greater than the boron concentration in the boron diffusion layer; introducing a semi-finished product of the solar cell, including the semiconductor substrate, the boron diffusion layer, and the boron-heavily-doped layer, into a chamber; maintaining the chamber in a nitrogen atmosphere, introducing oxygen into the chamber, and subjecting the semi-finished product to a temperature in the range of

Description

Technical Field

[0001] This invention relates to a method for boron diffusion in solar cells. Prior Technology

[0002] The semiconductor substrate used in solar cells is typically fabricated by diffusing impurities such as phosphorus or boron into the substrate. Taking an n-type tunnel oxide passivated contact (TOPCon) solar cell as an example, the n-type monocrystalline silicon substrate can be roughened (or texturing) before being doped with boron (B), forming a p+ boron emitter on its surface. A pn ​​junction is then formed between the boron emitter and the n-type monocrystalline silicon substrate. This allows for better formation of the passivation layer on the pn junction and the boron emitter in subsequent processes, thereby improving passivation and increasing photoelectric conversion efficiency.

[0003] However, the boron doping concentration (i.e., p+ concentration) is a key factor affecting the passivation effect and even the photoelectric conversion efficiency of an ideal TOPCon solar cell.

[0004] Therefore, determining the appropriate range of boron doping concentration to avoid negatively impacting the passivation effect or photoelectric conversion efficiency of the passivation layer (and even potentially producing positive effects) has become one of the technical problems that still need to be solved in this field.

[0005] In addition, how to optimize the boron diffusion process of solar cells to control the boron doping concentration within such a range is also one of the technical problems that need to be solved in this field. Summary of the Invention

[0006] In view of this, some embodiments propose a boron diffusion method for a solar cell, the solar cell comprising a semiconductor substrate having opposing upper and lower surfaces, the method comprising the following steps: forming a boron diffusion layer on the upper surface of the semiconductor substrate; selectively forming a heavily boron-doped region in a specific area on the upper surface of the semiconductor substrate, the boron concentration in the heavily boron-doped region being higher than the boron concentration in the boron diffusion layer; introducing a semi-finished solar cell comprising the semiconductor substrate, the boron diffusion layer, and the heavily boron-doped region into a cavity; subjecting the cavity to a nitrogen atmosphere, introducing oxygen into the cavity, and placing the semi-finished product in a temperature range of 1,000°C to 1,200°C for a time range of 80 to 120 minutes; stopping the introduction of oxygen into the cavity, and placing the semi-finished product in a temperature range of 700°C to 900°C for a time range of 10 to 15 minutes; and removing the semi-finished product from the cavity. Simple Explanation of the Diagram

[0007] The following figures are for illustrative purposes only, to provide a more complete understanding of some embodiments of the invention, but are not intended to limit the scope of the invention by virtue of these embodiments and the scale shown in the figures: Figure 1 is a schematic diagram of the structure of a solar cell according to the first embodiment; Figures 2A and 2B are schematic flowcharts of the boron diffusion method for solar cells as shown in Figure 1, based on some embodiments. Figure 3 is a schematic diagram of the structure of a solar cell according to the second embodiment; Figures 4A and 4B are schematic flowcharts of a boron diffusion method for a solar cell, as shown in Figure 3, based on some embodiments. Implementation

[0008] The following detailed description of the features and advantages of the present invention is sufficient to enable anyone skilled in the art to understand the technical content of the present invention and implement it accordingly. Based on the content disclosed in this specification, the scope of the patent application and the drawings, anyone skilled in the art can easily understand the relevant objectives and advantages of the present invention.

[0009] The term "between ... and ..." as used in this article refers to the upper limit, lower limit, and any value between these two limits. For example, the term "between 1,000℃ and 1,200℃" refers to any value that can be ≥1,000℃ and ≤1,200℃.

[0010] Please refer to Figures 1 and 2A. Figure 1 is a structural schematic diagram of the solar cell 1a according to the first embodiment; Figure 2A is a flowchart of the boron diffusion method S1a of the solar cell 1a as shown in Figure 1 according to some embodiments.

[0011] In Figure 2A, a boron diffusion method S1a for a solar cell 1a (as shown in Figure 1) is described. The solar cell 1a includes a semiconductor substrate 10, which has an upper surface 102 and a lower surface 101. A boron diffusion layer 131 and a heavily boron-doped region 132 are suitable for being disposed on the upper surface 102, and a tunneling oxide layer 11 is suitable for being disposed below the lower surface 101. As shown in Figure 2A, the above method S1a includes the following steps: Step S13: A boron diffusion layer 131 is formed on the upper surface 102 of the semiconductor substrate 10 (as shown in Figure 1; detailed later); Step S14: Selectively form a heavily boron-doped region 132 in a specific region A on the upper surface 102 of the semiconductor substrate 10, wherein the boron concentration in the heavily boron-doped region 132 is higher than the boron concentration in the boron diffusion layer 131 (details to follow); Step S15a: The semi-finished solar cell 1a, comprising a semiconductor substrate 10, a boron diffusion layer 131, and a boron heavily doped region 132, is introduced into a cavity (details to follow); Step S16a: Place the chamber in a nitrogen atmosphere, introduce oxygen into the chamber, and place the semi-finished product in a temperature range of 1,000°C to 1,200°C for 80 to 120 minutes (details to follow); Step S17a: Stop supplying oxygen to the chamber and place the semi-finished product in a temperature range of 700°C to 900°C for 10 to 15 minutes (details to follow); and Step S18: Remove the semi-finished product from the cavity (details to follow).

[0012] Through the above method S1a, the boron concentration of the boron diffusion layer 131 and / or the boron concentration of the heavily boron-doped region 132 of the semiconductor substrate 10 of the solar cell 1a can be respectively located within a specific doping concentration range (described in detail later).

[0013] The thickness H2 of the boron diffusion layer 131 (as shown in Figure 1 or Figure 3) can be defined according to a specific range of boron doping concentration. For example, by measuring the boron concentration at multiple locations on the upper surface 102 of the semiconductor substrate 10, the "thickness of the boron diffusion layer 131" can be defined as the shortest distance between any of the aforementioned locations where the boron concentration approaches the lower limit of a specific doping concentration range (e.g., a first doping concentration range) and the upper surface 102. Accordingly, the "thickness of the boron diffusion layer 131" is measured from the side of the boron diffusion layer 131 away from the upper surface 102 and the lower surface 101 of the semiconductor substrate 10, to the side adjacent to the upper surface 102 and the lower surface 101 of the semiconductor substrate 10.

[0014] The thickness H3 of the heavily boron-doped region 132 (as shown in Figure 1 or Figure 3) can also be defined according to a specific range of boron doping concentration. For example, by measuring the boron concentration at multiple locations on the upper surface 102 of the semiconductor substrate 10, the "thickness of the heavily boron-doped region 132" can be defined as the shortest distance between any of the aforementioned locations where the boron concentration approaches the lower limit of another specific concentration range (e.g., a second doping concentration range) and the upper surface 102. Accordingly, the "thickness of the heavily boron-doped region 132" is measured from the side of the heavily boron-doped region 132 away from the upper surface 102 and the lower surface 101 of the semiconductor substrate 10, to the side adjacent to the upper surface 102 and the lower surface 101 of the semiconductor substrate 10.

[0015] In some embodiments, the lower limit of the boron concentration range (e.g., the second doping concentration range) of the heavily boron-doped region 132 is higher than the lower limit of the boron concentration range (e.g., the first doping concentration range) of the boron diffusion layer 131. In some embodiments, the lower limit of the boron concentration range (e.g., the second doping concentration range) of the heavily boron-doped region 132 is higher than the upper limit of the boron concentration range (e.g., the first doping concentration range) of the boron diffusion layer 131.

[0016] Compared to the boron concentration of the boron diffusion layer of a semiconductor substrate prepared by common or known techniques of the inventor, after the above method S1a, the boron doped in the boron diffusion layer 131 and / or the heavily boron-doped region 132 can diffuse into the cavity (or out-diffusion), thereby giving the boron diffusion layer 131 and / or the heavily boron-doped region 132 the following advantages: (1) lower boron concentration and reduced defect states; and (2) more ideal electric field distribution and current density.

[0017] When the boron concentration in the boron diffusion layer 131 and / or the heavily boron-doped region 132 is high, carriers (i.e., electrons and holes) easily recombine at the surface, resulting in a loss of photocurrent and a decrease in the short-circuit current (Jsc), thereby reducing the photoelectric conversion efficiency. Therefore, in some embodiments, by using a boron diffusion layer 131 and / or a heavily boron-doped region 132 with a lower boron concentration, carriers can avoid being consumed by recombination before reaching the electrode, thus preventing photocurrent loss. This allows the short-circuit current to be maintained or even increased, thereby enhancing the current density and improving the overall photoelectric conversion efficiency. Furthermore, in some embodiments, by using a boron diffusion layer 131 and / or a heavily boron-doped region 132 with a lower boron concentration, the electric field distribution of the boron diffusion layer 131 and / or the heavily boron-doped region 132 can be more ideal. This helps to separate electrons and holes, allowing photogenerated carriers to be collected more effectively, thereby improving the overall photoelectric conversion efficiency.

[0018] Regarding the known techniques for preparing TOPCon solar cells, TOPCon solar cells can be prepared, for example, by a method comprising the following steps: (1) cleaning and texturing; (2) front-side boron diffusion; (3) back-side treatment; (4) preparation of a tunneling oxide passivation structure; (5) front-side cleaning and removal of the coating; (6) front-side alumina passivation; (7) front-side and / or back-side silicon nitride passivation; (8) preparation of front-side and / or back-side metal electrodes; and (9) sintering to form an ohmic contact. The above method S1a can be used to at least replace step (2) (i.e., front-side boron diffusion) in the above-mentioned TOPCon solar cell preparation method, and after performing the remaining known TOPCon solar cell preparation methods (e.g., steps (1), (3) to (9)) in the above-mentioned TOPCon solar cell preparation method), solar cell 1a can be prepared (as shown in Figure 1, which will be described in detail later). The resulting solar cell 1a can have at least the advantages introduced by the aforementioned method S1a, namely: (1) lower boron concentration and reduced defect states; and (2) more ideal electric field distribution and current density, thereby improving the overall photoelectric conversion efficiency of the solar cell 1a.

[0019] Please continue to refer to Figures 1 and 2A. In some embodiments, method S1a may also include step S11 before proceeding to step S13. In step S11 of method S1a, the upper surface 102 of the semiconductor substrate 10 is texturized. This step S11 can be a texturing (or cleaning and texturing) process step familiar to those skilled in the art. Therefore, even if not described in detail here, those skilled in the art can clearly understand its detailed process steps, thereby preparing a semi-finished product (including the semiconductor substrate 10) that can proceed to step S13 (or step S12 of method S1c described later; detailed later).

[0020] Please continue referring to Figures 1 and 2A. In step S13 of method S1a, a boron diffusion layer 131 is formed on the upper surface 102 of the semiconductor substrate 10. This step S13 can be performed through at least one of the following processes: tubular diffusion process, ion implantation and annealing process, and coating source diffusion process. The tubular diffusion process can be performed in a low-pressure or atmospheric-pressure diffusion furnace, and the doping source can be boron chloride (BCl3) and / or boron bromide (BBr3), and the furnace temperature can be in the range of 700°C to 900°C. The coating source of the coating source diffusion process can be used to deposit the boron diffusion layer 131 on the upper surface 102 of the semiconductor substrate 10 for high-temperature annealing through at least one of the following processes: screen printing, spraying, spin coating, and roller printing. This step S13 is a process step familiar to those skilled in the art. Therefore, even without further details here, those skilled in the art can clearly understand its detailed process steps, thereby preparing a semi-finished product (including a semiconductor substrate 10 and a boron diffusion layer 131) that can proceed to step S14. For example, in the semi-finished product obtained by performing step S13 in a diffusion furnace (with BCl3 as the doping source) at a low pressure and an internal temperature of 700°C, the initial thickness of the boron diffusion layer 131 can be any thickness in the range of 0.2 μm to 0.4 μm (e.g., about 0.3 μm), and the boron concentration at any position within this initial thickness is in the range of 8 × 10¹⁹ / cm³ to 2 × 10²⁰ / cm³ (e.g., about 1 × 10²⁰ / cm³).

[0021] In step S14 of method S1a, a heavily boron-doped region 132 is selectively formed in a specific region A of the upper surface 102 of the semiconductor substrate 10, and the boron concentration in the heavily boron-doped region 132 is higher than the boron concentration in the boron diffusion layer 131. This step S14 can be performed using various laser selective emitter process techniques, such as using laser heating technology to precisely guide the dopant (e.g., boron) to a specific region A of the upper surface 102 of the semiconductor substrate 10 (e.g., the position of the upper surface 102 corresponding to the subsequently fabricated upper electrode 18). For example, steps S13 to S14 described above can be performed through a process including the following steps: (a) covering the upper surface 102 of the semiconductor substrate 10 with a doping source (e.g., BCl3 and / or BBr3); (b) irradiating a portion of the upper surface 102 with a high-energy laser beam to locally heat the upper surface 102; and (c) heating to allow the doping source to penetrate into the interior of the upper surface 102 to form a boron diffusion layer 131 with a specific depth (i.e., thickness H2), and selectively controlling a portion of the boron diffusion layer 131 through laser irradiation so that local boron is guided to a specific region A and a heavily boron-doped region 132 with a specific depth (i.e., thickness H3) is formed in the specific region A. This step S14 can also be a process step familiar to those skilled in the art. Therefore, even if it is not described in detail here, those skilled in the art can clearly understand its detailed process steps, thereby preparing a semi-finished product (including semiconductor substrate 10, boron diffusion layer 131 and boron heavily doped region 132) that can continue to step S14. For example, in the semi-finished product obtained by performing step S14, the thickness of the boron diffusion layer 131 can be further adjusted to any thickness in the range of 0.2 μm to 0.4 μm (e.g., about 0.3 μm), and the boron concentration at any position within this thickness is in the range of 8×10 19 / cm 3 to 2×10 20 / cm 3 (e.g., about 1×10 20 / cm 3); while the initial thickness of the boron heavily doped region 132 can be any thickness in the range of 1.4 μm to 1.8 μm (e.g., about 1.6 μm), and the boron concentration at any position within this initial thickness is in the range of 1×10 19 / cm 3 to 8×10 19 / cm 3 (e.g., about 4×10 19 / cm 3).

[0022] In step S15a of method S1a, a semi-finished solar cell 1a comprising a semiconductor substrate 10, a boron diffusion layer 131, and a boron heavily doped region 132 is introduced into a cavity (not shown). This cavity may be, for example, the cavity of a diffusion furnace, and the dimensions of the cavity may be, for example, 50 cm * 50 cm * 390 cm. In step S15a, the cavity may be in a suitable state, which may include a suitable gas flow rate, such as nitrogen, and the nitrogen flow rate may be any flow rate in the range of 1,000 sccm to 5,000 sccm, 1,000 sccm to 4,000 sccm, 1,000 sccm to 3,000 sccm, 1,000 sccm to 2,000 sccm, 2,000 sccm to 5,000 sccm, 2,000 sccm to 4,000 sccm, 2,000 sccm to 3,000 sccm, 3,000 sccm to 5,000 sccm, 2,000 sccm to 4,000 sccm, 2,000 sccm to 3,000 sccm, 3,000 sccm to 5,000 sccm, 2,000 sccm to 4,000 sccm, 2,000 sccm to 4,000 sccm, 2,000 sccm to 5 ...5,000 sccm, 2,000 sc Any flow rate in the range of sccm to 3,000 sccm, any flow rate in the range of 3,000 sccm to 4,000 sccm, any flow rate in the range of 4,000 sccm to 5,000 sccm, or a flow rate curve consisting of any one or more flow rates in these ranges; for example, 2,000 sccm (±5%); the gas passage time may be, for example, in the range of 5 minutes to 10 minutes; for example, 7 minutes (±5%).

[0023] In some embodiments, the temperature of the cavity in step S15a may be any temperature in the range of 700°C to 900°C, any temperature in the range of 700°C to 850°C, any temperature in the range of 700°C to 800°C, any temperature in the range of 700°C to 750°C, any temperature in the range of 750°C to 900°C, any temperature in the range of 750°C to 850°C, any temperature in the range of 750°C to 800°C, any temperature in the range of 800°C to 900°C, any temperature in the range of 800°C to 850°C, any temperature in the range of 850°C to 900°C, or a temperature curve composed of any one or more of these ranges; for example, 800°C (±5%).

[0024] In some embodiments, the pressure in the cavity of step S15a is a third pressure, which may be, for example, any pressure in the range of 900 mbar to 1,200 mbar, any pressure in the range of 900 mbar to 1,100 mbar, any pressure in the range of 900 mbar to 1,000 mbar, any pressure in the range of 1,000 mbar to 1,200 mbar, any pressure in the range of 1,100 mbar to 1,200 mbar, or a pressure curve composed of any one or more pressures in these ranges; for example, 1,060 mbar (±5%).

[0025] In some embodiments, before proceeding to step S15a, the cavity may be brought into a preparatory state before being placed in the aforementioned appropriate state.

[0026] For example, the aforementioned preparatory state may include an appropriate cavity temperature state, such as any temperature in the range of 700°C to 900°C, any temperature in the range of 700°C to 850°C, any temperature in the range of 700°C to 800°C, any temperature in the range of 700°C to 750°C, any temperature in the range of 750°C to 900°C, any temperature in the range of 750°C to 850°C, any temperature in the range of 750°C to 800°C, any temperature in the range of 800°C to 900°C, any temperature in the range of 800°C to 850°C, any temperature in the range of 850°C to 900°C, or a temperature curve composed of any one or more of these ranges; for example, 800°C (±5%).

[0027] For example, the aforementioned preparatory state may include an appropriate gas flow rate, such as nitrogen, and the nitrogen flow rate may be any flow rate within the range of 10,000 sccm to 30,000 sccm, 10,000 sccm to 25,000 sccm, 10,000 sccm to 20,000 sccm, 10,000 sccm to 15,000 sccm, 15,000 sccm to 30,000 sccm, 15,000 sccm to 25,000 sccm, 15,000 sccm to 20,000 sccm, 20,000 sccm to 30,000 sccm, 20,000 sccm to 25,000 sccm. Any flow rate within the range of sccm, any flow rate within the range of 25,000 sccm to 30,000 sccm, or a flow rate curve consisting of any one or more flow rates within these ranges; for example, 20,000 sccm (±5%).

[0028] For example, the aforementioned preparatory state may include an appropriate pressure state, such as any pressure in the cavity within the range of 900 mbar to 1,200 mbar, any pressure within the range of 900 mbar to 1,100 mbar, any pressure within the range of 900 mbar to 1,000 mbar, any pressure within the range of 1,000 mbar to 1,200 mbar, any pressure within the range of 1,100 mbar to 1,200 mbar, or a pressure curve consisting of any one or more pressures within these ranges; for example, 1,060 mbar (±5%).

[0029] In step S16a of method S1a, the chamber is placed in a nitrogen atmosphere, oxygen is introduced into the chamber, and the semi-finished product is placed in a temperature range of 1,000°C to 1,200°C for 80 to 120 minutes. Since boron has low solid solubility in silicon, the heat treatment process in step S16a allows boron to diffuse outward from the upper surface 102 of a semiconductor substrate 10, for example, based on silicon, and escape into the gas phase. This allows the doping concentration of boron on the upper surface 102 to be adjusted, and a boron diffusion layer 131 and / or a heavily doped boron region 132 with a specific concentration range to be formed. For example, in the semi-finished product obtained by performing step S16a, the thickness of the boron diffusion layer 131 can be further adjusted to any thickness in the range of 0.4 μm to 1.2 μm (e.g., about 0.8 μm), and the boron concentration (or surface boron doping concentration, the same below) at any position within this thickness is any concentration in the range of 1×10 17 / cm 3 to 1×10 19 / cm 3 (e.g., about 1×10 18 / cm 3); while the thickness of the boron heavily doped region 132 can be further adjusted to any thickness in the range of 1.4 μm to 2.4 μm (e.g., about 2.1 μm), and the boron concentration at any position within this thickness is any concentration in the range of 1×10 17 / cm 3 to 1×10 19 / cm 3 (e.g., about 4×10 18 / cm 3).

[0030] In some embodiments, the flow rate of nitrogen in step S16a can be any flow rate within the range of 1,000 sccm to 5,000 sccm, 1,000 sccm to 4,000 sccm, 1,000 sccm to 3,000 sccm, 1,000 sccm to 2,000 sccm, 2,000 sccm to 5,000 sccm, 2,000 sccm to 4,000 sccm, 2,000 sccm to 3,000 sccm, 3,000 sccm to 5,000 sccm, 3,000 sccm to 4,000 sccm, 4,000 sccm to 5,000 sccm. Any flow rate within a range of sccm, or a flow rate curve consisting of any one or more flow rates within these ranges; for example, 3,500 sccm (±5%).

[0031] In some embodiments, the oxygen flow rate in step S16a can be any flow rate between 5,000 sccm and 20,000 sccm. Controlling the oxygen flow rate within this range can facilitate the formation of silicon oxide on the surface of the boron diffusion layer 131 and / or the boron heavily doped region 132 due to contact with oxygen, thereby providing excellent passivation effects and reducing surface recombination and carrier loss. In some embodiments, the oxygen flow rate may be any flow rate in the range of 5,000 sccm to 15,000 sccm, any flow rate in the range of 5,000 sccm to 10,000 sccm, any flow rate in the range of 10,000 sccm to 20,000 sccm, any flow rate in the range of 10,000 sccm to 15,000 sccm, any flow rate in the range of 15,000 sccm to 20,000 sccm, or a flow rate curve consisting of any one or more flow rates within these ranges; for example, 10,000 sccm (±5%).

[0032] In some embodiments, the temperature of the cavity in step S16a can be any temperature between 1,000°C and 1,200°C. Controlling the cavity temperature within this range allows for better control of the thickness and doping concentration of the boron diffusion layer 131 and / or the heavily doped boron region 132 within an appropriate range. For example, within this temperature range, a lower cavity temperature (e.g., 1,000°C) will result in a thinner boron diffusion layer 131 and / or a higher boron doping concentration than the original boron diffusion layer 131 and / or the heavily doped boron region 132. Therefore, depending on different process requirements, the desired thickness and doping concentration of the boron diffusion layer 131 and / or the heavily doped boron region 132 can be obtained by adjusting the cavity temperature. In some embodiments, the temperature of the cavity may be any temperature in the range of 1,000°C to 1,150°C, any temperature in the range of 1,000°C to 1,100°C, any temperature in the range of 1,000°C to 1,050°C, any temperature in the range of 1,050°C to 1,200°C, any temperature in the range of 1,050°C to 1,150°C, any temperature in the range of 1,050°C to 1,100°C, any temperature in the range of 1,100°C to 1,200°C, any temperature in the range of 1,100°C to 1,150°C, any temperature in the range of 1,150°C to 1,200°C, or a temperature curve consisting of any one or more of these ranges; for example, 1,080°C (±5%).

[0033] In some embodiments, the pressure of the cavity in step S16a is a first pressure, which can be any pressure in the range of 500 mbar to 900 mbar. Controlling the first pressure of the cavity within this pressure range can help shorten the process time and make the doping distribution of the boron diffusion layer 131 and / or the boron heavily doped region 132 more uniform. In some embodiments, the pressure of the cavity in step S16a (i.e., the first pressure) can be any pressure in the range of 500 mbar to 800 mbar, any pressure in the range of 500 mbar to 700 mbar, any pressure in the range of 500 mbar to 600 mbar, any pressure in the range of 600 mbar to 900 mbar, any pressure in the range of 600 mbar to 800 mbar, any pressure in the range of 600 mbar to 700 mbar, any pressure in the range of 700 mbar to 900 mbar, any pressure in the range of 700 mbar to 800 mbar, any pressure in the range of 800 mbar to 900 mbar, or a pressure curve composed of any one or more pressures in these ranges; for example, 600 mbar (±5%).

[0034] In some embodiments, the process time of step S16a can be, for example, between 80 and 120 minutes. Controlling the process time of step S16a within this range helps to control the thickness and doping concentration of the boron diffusion layer 131 and / or the heavily doped boron region 132 within an appropriate range. For example, within this process time range, a shorter process time (e.g., 80 minutes) will result in a thinner boron diffusion layer 131 and / or a higher boron doping concentration. Therefore, depending on different process requirements, the desired thickness and doping concentration of the boron diffusion layer 131 and / or the heavily doped boron region 132 can be obtained by adjusting the process time of step S16a. In some embodiments, the process time of step S16a can be any time within the range of 80 minutes to 110 minutes, any time within the range of 80 minutes to 100 minutes, any time within the range of 80 minutes to 100 minutes, any time within the range of 80 minutes to 90 minutes, any time within the range of 90 minutes to 120 minutes, any time within the range of 90 minutes to 110 minutes, any time within the range of 90 minutes to 100 minutes, any time within the range of 100 minutes to 120 minutes, any time within the range of 100 minutes to 110 minutes, or any time within the range of 110 minutes to 120 minutes; for example, 105 minutes (±5%).

[0035] In step S17a of method S1a, oxygen supply to the chamber is stopped, and the semi-finished product is placed in a temperature range of 700°C to 900°C for 10 to 15 minutes. This allows the temperature of the chamber to decrease and the pressure to increase, and minimizes changes in the doping concentration of the boron diffusion layer 131 and / or the heavily boron-doped region 132 during this stage, facilitating the removal of the semi-finished product from the chamber in the subsequent step S18. For example, in the semi-finished product obtained by performing step S17a, the thickness of the boron diffusion layer 131 can be maintained at any thickness between 0.4 μm and 1.2 μm (e.g., about 0.8 μm), and the boron concentration at any position within this thickness is at any concentration between 1×10 17 / cm 3 and 1×10 19 / cm 3 (e.g., about 1×10 18 / cm 3); while the thickness of the boron heavily doped region 132 is maintained at any thickness between 1.4 μm and 2.4 μm (e.g., about 2.1 μm), and the boron concentration at any position within this thickness is at any concentration between 1×10 17 / cm 3 and 1×10 19 / cm 3 (e.g., about 4×10 18 / cm 3).

[0036] In some embodiments, the temperature of the cavity in step S17a may be any temperature in the range of 700°C to 850°C, any temperature in the range of 700°C to 800°C, any temperature in the range of 700°C to 750°C, any temperature in the range of 750°C to 900°C, any temperature in the range of 750°C to 850°C, any temperature in the range of 750°C to 800°C, any temperature in the range of 800°C to 900°C, any temperature in the range of 800°C to 850°C, any temperature in the range of 850°C to 900°C, or a temperature curve composed of any one or more of these ranges; for example, 850°C (±5%).

[0037] In some embodiments, the process time of step S17a may be in the range of 10 to 15 minutes, for example, 13 minutes (±5%). By controlling the process time of step S17a within this time range, the doping concentration of the boron diffusion layer 131 and / or the boron heavily doped region 132 is minimized during this stage.

[0038] In some embodiments, the flow rate of nitrogen in step S17a can be any flow rate within the range of 10,000 sccm to 30,000 sccm, any flow rate within the range of 10,000 sccm to 25,000 sccm, any flow rate within the range of 10,000 sccm to 20,000 sccm, any flow rate within the range of 10,000 sccm to 15,000 sccm, any flow rate within the range of 15,000 sccm to 30,000 sccm, any flow rate within the range of 15,000 sccm to 25,000 sccm, any flow rate within the range of 15,000 sccm to 20,000 sccm, any flow rate within the range of 20,000 sccm to 30,000 sccm, any flow rate within the range of 20,000 sccm to 25,000 sccm, any flow rate within the range of 25,000 sccm to 30,000 sccm. Any flow rate within a range of sccm, or a flow rate curve consisting of any one or more flow rates within these ranges; for example, 20,000 sccm (±5%).

[0039] In some embodiments, the pressure of the cavity in step S17a is a second pressure, which may be any pressure in the range of 900 mbar to 1,200 mbar, any pressure in the range of 900 mbar to 1,100 mbar, any pressure in the range of 900 mbar to 1,000 mbar, any pressure in the range of 1,000 mbar to 1,200 mbar, any pressure in the range of 1,100 mbar to 1,200 mbar, or a pressure curve composed of any one or more pressures in these ranges; for example, 1,060 mbar (±5%).

[0040] In step S18 of method S1a, the semi-finished product is extracted from the cavity. The condition parameters of this step S18 (such as cavity temperature, gas flow rate, pressure and process time) can be the same as the condition parameters of the cavity in the preparatory state before entering step S15a; therefore, please refer to the specific implementation of the preparatory state as described above, which will not be described in detail here. For example, in the semi-finished product obtained by performing step S18, the thickness H2 of the boron diffusion layer 131 (as shown in Figure 1) can be maintained at any thickness between 0.4 μm and 1.2 μm (e.g., about 0.8 μm), and the boron concentration at any position in this thickness H2 is at any concentration between 1×10 17 / cm 3 and 1×10 19 / cm 3 (e.g., about 1×10 18 / cm 3); while the thickness H3 of the boron heavily doped region 132 (as shown in Figure 1) is maintained at any thickness between 1.4 μm and 2.4 μm (e.g., about 2.1 μm), and the boron concentration at any position in this thickness H3 is at any concentration between 1×10 17 / cm 3 and 1×10 19 / cm 3 (e.g., about 4×10 18 / cm 3). The semi-finished product obtained by performing step S18 can be further processed by performing other known TOPCon solar cell preparation methods (such as steps (3) to (9) in the above-mentioned TOPCon solar cell preparation method) to prepare solar cell 1a (as shown in Figure 1).

[0041] Referring to Figure 1, a solar cell 1a includes a semiconductor substrate 10, a boron diffusion layer 131, a passivation layer 14, an upper antireflection layer 15, an upper electrode 18, a boron heavily doped region 132, a tunneling oxide layer 11, a semiconductor thin film layer 12, a lower antireflection layer 16, and a lower electrode 17. The semiconductor substrate 10 has an upper surface 102 and a lower surface 101 opposite to each other. The boron diffusion layer 131 is located on the upper surface 102 of the semiconductor substrate 10, and the thickness H2 of the boron diffusion layer 131 (as shown in Figure 1) is any thickness in the range of 0.4 μm to 1.2 μm, and the boron concentration at any position within this thickness H2 is any concentration in the range of 1×10¹⁷ / cm³ to 1×10¹⁹ / cm³. The passivation layer 14 is located on the boron diffusion layer 131. The upper antireflection layer 15 is located on the passivation layer 14. A portion of the upper electrode 18 penetrates the passivation layer 14 and the upper antireflective layer 15 to be electrically connected to the boron diffusion layer 131. Multiple heavily boron-doped regions 132 are individually located between the upper electrode 18 and the semiconductor substrate 10, and the thickness H3 of each heavily boron-doped region 132 (as shown in Figure 1) is any thickness between 0.4 μm and 1.2 μm, with a boron concentration at any location within this thickness H3 ranging from 1 × 10¹⁷ / cm³ to 1 × 10¹⁹ / cm³. A tunneling oxide layer 11 is located below the lower surface 101 of the semiconductor substrate 10. A semiconductor thin film layer 12 is located below the tunneling oxide layer 11. A lower antireflective layer 16 is located below the semiconductor thin film layer 12. A portion of the lower electrode 17 penetrates the lower antireflective layer 16 to be electrically connected to the semiconductor thin film layer 12. Therefore, in some embodiments, the solar cell 1a obtained through the process including the above method S1a may have at least the following advantages: (1) lower boron concentration and reduced defect states; and (2) more ideal electric field distribution and current density, thereby improving the overall photoelectric conversion efficiency of the solar cell 1a.

[0042] In Figure 1, the semiconductor substrate 10 is a type-1 doped semiconductor (e.g., n-type) and has opposing upper and lower surfaces 102 and 101. The material of the semiconductor substrate 10 may be silicon, such as monocrystalline silicon, polycrystalline silicon, amorphous silicon, or a combination thereof. In some embodiments, the two surfaces 102 and 101 may be texturized (e.g., step (1) or step S11 described above). Therefore, it will be understood by those skilled in the art that Figure 1 illustrates the two surfaces 102 and 101 as planar only for ease of explanation; however, it will be understood that the two surfaces 102 and 101 may have uneven or serrated structures rather than being planar, for example, having multiple pyramidal structures. In some embodiments, the thickness of the semiconductor substrate 10 is any thickness in the range of 100 μm to 160 μm.

[0043] In Figure 1, the emitter thin film layer 13 includes a boron diffusion layer 131 and a boron heavily doped region 132, both of which are type II doped semiconductors (e.g., p-type, different from type I doped semiconductors), and is located on the upper surface 102 of the semiconductor substrate 10. The emitter thin film layer 13 can be formed by the aforementioned method S1a, which will not be described in detail here.

[0044] In Figure 1, an upper protective layer (not shown) is located on the emitter thin film layer 13. The material of the upper protective layer may be at least one of aluminum oxide (AlOx), silicon oxide (SiOx), silicon nitride (SiNx), and silicon oxynitride (SiOxNy). In some embodiments, the upper protective layer includes a passivation layer 14 and an upper antireflection layer 15, which may be formed on the emitter thin film layer 13 by, for example, the aforementioned step (6) (i.e., front aluminum oxide passivation), step (7) (i.e., front and / or back silicon nitride passivation), or steps (6)-(7). The formation of the upper protective layer may be performed without affecting the upper surface 102, the boron diffusion layer 131, and the boron heavily doped region 132 by common or inventor-known methods such as thermal oxidation, low-pressure chemical vapor deposition (LPCVD), PECVD, or combinations thereof, which will not be described in detail here. In some embodiments, the passivation layer 14 contains aluminum oxide (AlOx) and its thickness is any thickness in the range of 5 nm to 15 nm, and the upper antireflection layer 15 contains silicon nitride (SiNx) and its thickness is any thickness in the range of 55 nm to 95 nm. Accordingly, in some embodiments, the upper protective layer comprising the passivation layer 14 and the upper antireflection layer 15 may have the functions of passivation, antireflection, or both.

[0045] In Figure 1, a portion of the upper electrode 18 extends from the outside of the upper protective layer (e.g., the outside of the upper antireflective layer 15) towards the semiconductor substrate 10, penetrating the passivation layer 14 and the upper antireflective layer 15, so that the upper electrode 18 and the boron diffusion layer 131 are electrically connected to each other. The material of the upper electrode 18 can be various metals, such as metals with good conductivity; for example, at least one of gold, silver, copper, platinum, tin, and various alloys thereof. The upper electrode 18 and the boron diffusion layer 131 can be electrically connected through, for example, the aforementioned step (8) (i.e., preparing the front and / or back metal electrodes). The formation of the above-mentioned upper electrode 18 can be carried out through a metallization process of gate line printing and sintering, which is common or known to the inventors, without affecting the upper surface 102, the boron diffusion layer 131, and the boron heavily doped region 132, and will not be described in detail here.

[0046] In Figure 1, the tunneling oxide layer 11 is located below the lower surface 101 of the semiconductor substrate 10. The material of the tunneling oxide layer 11 can be at least one of silicon oxide (SiOx) and silicon oxynitride (SiOxNy). The tunneling oxide layer 11 can be formed below the lower surface 101 of the semiconductor substrate 10 by, for example, step (4) described above (i.e., preparing the tunneling oxide passivation structure). The formation of the tunneling oxide layer 11 can be carried out by common or inventor-known methods such as thermal oxidation, LPCVD, PECVD, or combinations thereof without affecting the upper surface 102, the boron diffusion layer 131, and the boron heavily doped region 132, which will not be described in detail here. In some embodiments, the tunneling oxide layer 11 comprises silicon oxide (SiOx) and its thickness is any thickness in the range of 0.3 nm to 3.0 nm.

[0047] In Figure 1, the semiconductor thin film layer 12 is a type-1 doped semiconductor (e.g., the same as the n-type doped semiconductor substrate 10) and is located under the tunneling oxide layer 11. The material of the semiconductor thin film layer 12 can be silicon, such as monocrystalline silicon, polycrystalline silicon, amorphous silicon, or a combination thereof. The semiconductor thin film layer 12 can be formed under the tunneling oxide layer 11 by, for example, the aforementioned step (4) (i.e., preparing the tunneling oxide passivation structure); or it can be selectively formed under the tunneling oxide layer 11 by the aforementioned step (5) (i.e., front cleaning and de-coating). In some embodiments, the semiconductor thin film layer 12 is a highly doped polycrystalline silicon thin layer, which is formed by crystallizing an initial doped amorphous silicon thin layer (e.g., hydrogenated amorphous silicon (a-Si:H)) through an annealing process (or other heat treatment process). Through this annealing process (or other heat treatment process), lattice (grain boundary) defects and stresses of the doped amorphous silicon thin layer can be eliminated. The semiconductor thin film layer 12 can be formed without affecting the upper surface 102, the boron diffusion layer 131, and the boron heavily doped region 132, by means of common or inventor-known thermal oxidation, LPCVD, PECVD, or combinations thereof, which will not be described in detail here. In some embodiments, the semiconductor thin film layer 12 is formed under the tunneling oxide layer 11 by at least a PECVD and annealing process. In some embodiments, the thickness of the semiconductor thin film layer 12 is any thickness in the range of 70 nm to 150 nm.

[0048] In Figure 1, the lower antireflective layer 16 is located below the semiconductor thin film layer 12. The material of the lower antireflective layer 16 can be at least one of silicon nitride (SiNx) and silicon oxynitride (SiOxNy). The lower antireflective layer 16 can be formed below the semiconductor thin film layer 12 by, for example, the aforementioned step (7) (i.e., front and / or back silicon nitride passivation). The formation of the lower antireflective layer 16 can be performed by common or inventor-known methods such as thermal oxidation, LPCVD, PECVD, or combinations thereof without affecting the upper surface 102, the boron diffusion layer 131, and the boron heavily doped region 132, which will not be described in detail here. In some embodiments, the thickness of the lower antireflective layer 16 is any thickness in the range of 55 nm to 95 nm. Accordingly, in some embodiments, the lower antireflective layer 16 may have a passivating effect.

[0049] In Figure 1, a portion of the lower electrode 17 extends from the outside of the lower antireflective layer 16 toward the semiconductor substrate 10, penetrating the lower antireflective layer 16 to electrically connect the lower electrode 17 to the semiconductor thin film layer 12. The material of the lower electrode 17 can be various metals, such as metals with good conductivity; for example, at least one of gold, silver, copper, platinum, tin, and various alloys thereof. In some embodiments, the material of the lower electrode 17 is the same as the material of the upper electrode 18. The lower electrode 17 and the semiconductor thin film layer 12 can be electrically connected through, for example, the aforementioned step (8) (i.e., preparing the front and / or back metal electrodes). The formation of the lower electrode 17 can be performed through a metallization process of gate line printing and sintering, which is common or known to the inventors, without affecting the upper surface 102, the boron diffusion layer 131, and the boron heavily doped region 132, and will not be described in detail here.

[0050] Please refer to Figure 2B, which is a schematic flowchart of the boron diffusion method S1b for solar cell 1a in Figure 1, based on some embodiments. The main difference between method S1b shown in Figure 2B and method S1a shown in Figure 2A is, for example, that the cavity pressure in step S16b is a first pressure, and the cavity pressure in step S17b is a second pressure, with the second pressure being greater than the first pressure. In some embodiments, the cavity pressure in step S15b is a third pressure, with the third pressure being greater than the first pressure. For example, the first pressure is in the range of 500 mbar to 900 mbar, the second pressure is in the range of 1,000 mbar to 1,100 mbar, and the third pressure is in the range of 1,000 mbar to 1,100 mbar. Therefore, in some embodiments, the surface boron doping concentration of the boron diffusion layer 131 and / or the heavily boron-doped region 132 can be kept as low as possible during this stage, facilitating the extraction of the semi-finished product from the cavity in the subsequent step S18. The semi-finished product obtained by method S1b as shown in Figure 2B can be further processed by other known TOPCon solar cell preparation methods (such as steps (3) to (9) in the above-mentioned TOPCon solar cell preparation method) to obtain solar cell 1a (as shown in Figure 1); please refer to the above-mentioned specific implementation as described above, and will not be described in detail here.

[0051] Please refer to Figures 3 and 4A. Figure 3 is a schematic diagram of the structure of the solar cell 1b according to the second embodiment; Figure 4A is a flowchart of the boron diffusion method S1c of the solar cell 1b as shown in Figure 3 according to some embodiments. The main difference between method S1a shown in Figure 2A and method S1c shown in Figure 4A is that, before performing step S13, method S1c also includes step S12, forming a silicon oxide layer 19 (as shown in Figure 3) on the upper surface 102 of the semiconductor substrate 10. Therefore, in step S13, boron can first cover the silicon oxide layer 19 located on the upper surface 102 of the semiconductor substrate 10, and after performing step S13, boron diffuses into the lower silicon oxide layer 19 due to the high-temperature atmosphere, thereby forming a boron diffusion layer 131 between the silicon oxide layer 19 and the upper surface 102. Through the provision of the silicon oxide layer 19, the diffusion rate of boron can be effectively improved, thereby slowing down the rate at which boron forms a pn junction with the upper surface 102 of the semiconductor substrate 10. Therefore, in some embodiments, the thickness of the boron diffusion layer 131 (e.g., the thickness H2 shown in FIG3) can be made uneven or unstable (e.g., too thick or too thin) due to the excessively fast boron diffusion rate, thereby avoiding affecting the performance of the boron diffusion layer 131 and even the overall photoelectric conversion efficiency of the solar cell 1b. In addition, in some embodiments, since the silicon oxide layer 19 has a passivation effect, the surface recombination and carrier loss can be reduced by setting the silicon oxide layer 19, thereby improving the open-circuit voltage (V OC) of the solar cell 1b. The above-mentioned semi-finished product obtained by the method S1c shown in FIG4A (including steps S11-S14, S15b, S16a, S17a and S18) can be further processed by performing other known TOPCon solar cell preparation methods (e.g., steps (3) to (9) in the above-mentioned TOPCon solar cell preparation method) to prepare the solar cell 1b (as shown in FIG3).

[0052] In some embodiments, step S12 of method S1c may form a silicon oxide layer 19 on the upper surface 102 of the semiconductor substrate 10 by at least one of the following methods: thermal oxidation, UV irradiation, atmospheric pressure chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), and plasma-assisted chemical vapor deposition (PECVD).

[0053] Referring to Figure 3, in some embodiments, the thickness H1 of the silicon oxide layer 19 of the solar cell 1b fabricated according to the aforementioned process (including method S1c or method S1d described later) is any thickness ranging from 1 nm to 20 nm. Controlling the thickness H1 of the silicon oxide layer 19 within this thickness range can improve the diffusion of boron and avoid affecting the performance of the boron diffusion layer 131 and the pn junction, thereby avoiding affecting the overall photoelectric conversion efficiency of the solar cell 1b. In some embodiments, the thickness H1 of the silicon oxide layer 19 can be any thickness ranging from 1 nm to 15 nm, 1 nm to 10 nm, 1 nm to 5 nm, 5 nm to 20 nm, 5 nm to 15 nm, 5 nm to 10 nm, 10 nm to 20 nm, 10 nm to 15 nm, or 15 nm to 20 nm; for example, 3 nm (±5%).

[0054] Please refer to Figures 4A and 4B. Figure 4B is a flowchart illustrating the boron diffusion method S1d of the solar cell 1b in Figure 3, based on some embodiments. The main difference between method S1d shown in Figure 4B and method S1c shown in Figure 4A is, for example, that the cavity pressure in step S16b is a first pressure, and the cavity pressure in step S17b is a second pressure, with the second pressure being greater than the first pressure. In some embodiments, the cavity pressure in step S15b is a third pressure, with the third pressure being greater than the first pressure. For example, the first pressure is in the range of 500 mbar to 900 mbar, the second pressure is in the range of 1,000 mbar to 1,100 mbar, and the third pressure is in the range of 1,000 mbar to 1,100 mbar. Therefore, in some embodiments, the surface boron doping concentration of the boron diffusion layer 131 and / or the heavily boron-doped region 132 can be kept as low as possible during this stage, facilitating the extraction of the semi-finished product from the cavity in the subsequent step S18. The semi-finished product obtained by method S1b as shown in Figure 4B can be further processed by other known TOPCon solar cell preparation methods (such as steps (3) to (9) in the above-mentioned TOPCon solar cell preparation method) to prepare solar cell 1b (as shown in Figure 3); please refer to the above-mentioned specific implementation as described above, and will not be described in detail here.

[0055] In summary, by subjecting a semi-finished solar cell containing at least a semiconductor substrate, a boron diffusion layer, and heavily boron-doped regions to a specific environment (e.g., any temperature or temperature profile between 1,000°C and 1,200°C, with an atmosphere containing nitrogen and oxygen) for a specific time (e.g., any time between 80 and 120 minutes) as part of a heat treatment process, the boron doping concentration of the boron diffusion layer and / or the heavily boron-doped regions can be adjusted. Consequently, the surface doping thickness of the boron diffusion layer and / or the heavily boron-doped regions becomes more uniform, and the resulting solar cell, after subsequent processing, can at least have fewer defect states, a more ideal electric field distribution, and a higher current density, thereby improving the overall photoelectric conversion efficiency.

[0056] Although the present invention has been disclosed above with reference to the foregoing embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make some modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of patent protection of the present invention shall be determined by the scope of the patent application attached to this specification.

[0057] 1a, 1b: Solar cells 10: Semiconductor substrate 101: Lower surface 102: Upper surface 11: Tunneling Oxide Layer 12: Semiconductor thin film layer 13: Emitter thin film layer 131: Boron diffusion layer 132: Boron heavily doped region 14: Passivation layer 15: Upper anti-reflective layer 16: Lower anti-reflective layer 17: Lower electrode 18: Upper electrode 19: Silicon oxide layer A: Specific area H1-H3: Thickness S1a-S1d: (Boron diffusion method in solar cells) S11, S12, S13, S14, S18: Steps S15a, S15b, S16a, S16b, S17a, S17b: Steps X: X-axis of coordinates Y: Y-axis coordinates Z: Z-axis of coordinates

Claims

1. A boron diffusion method for a solar cell, the solar cell comprising a semiconductor substrate having an upper surface and a lower surface opposite to each other, the method comprising the steps of: forming a boron diffusion layer on the upper surface of the semiconductor substrate; selectively forming a heavily boron-doped region in a specific region of the upper surface of the semiconductor substrate, wherein the boron concentration in the heavily boron-doped region is higher than the boron concentration in the boron diffusion layer; introducing a semi-finished product of the solar cell comprising the semiconductor substrate, the boron diffusion layer and the heavily boron-doped region into a cavity; subjecting the cavity to a nitrogen atmosphere, introducing oxygen into the cavity, and placing the semi-finished product in a temperature range of 1,000°C to 1,200°C for a time range of 80 minutes to 120 minutes; stopping the introduction of oxygen into the cavity, and placing the semi-finished product in a temperature range of 700°C to 900°C for a time range of 10 minutes to 15 minutes; and removing the semi-finished product from the cavity.

2. The boron diffusion method for a solar cell as described in claim 1, wherein, Prior to the step of forming the boron diffusion layer on the upper surface of the semiconductor substrate, the method further includes forming a silicon oxide layer on the upper surface of the semiconductor substrate.

3. The boron diffusion method for a solar cell as described in claim 2, wherein, After the step of placing the semi-finished product in the range of 700°C to 900°C, or after the step of removing the semi-finished product from the cavity, the thickness of the silicon oxide layer is in the range of 1 nm to 20 nm.

4. The boron diffusion method for a solar cell as described in claim 2, wherein, The silicon oxide layer is formed by at least one of the following methods: thermal oxidation, UV irradiation, atmospheric pressure chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), and plasma-assisted chemical vapor deposition (PECVD).

5. The boron diffusion method for a solar cell as described in claim 2, wherein, Before the step of forming the silicon oxide layer on the upper surface of the semiconductor substrate, the method further includes texturing the upper surface of the semiconductor substrate.

6. The boron diffusion method for a solar cell as described in claim 2, wherein, Before the step of forming the boron diffusion layer on the upper surface of the semiconductor substrate, the method further includes texturing the upper surface of the semiconductor substrate.

7. The boron diffusion method for a solar cell as described in claim 1, wherein: In the step of placing the semi-finished product in the range of 1,000°C to 1,200°C, the cavity system is under a first pressure; and in the step of placing the semi-finished product in the range of 700°C to 900°C, the cavity system is under a second pressure; wherein the second pressure is greater than the first pressure.

8. The boron diffusion method for a solar cell as described in claim 7, wherein, In the step of introducing the semi-finished solar cell into the cavity, the cavity system is under a third pressure, and the third pressure is greater than the first pressure.

9. The boron diffusion method for a solar cell as described in claim 8, wherein, The first pressure is in the range of 500 mbar to 900 mbar, the second pressure is in the range of 1,000 mbar to 1,100 mbar, and the third pressure is in the range of 1,000 mbar to 1,100 mbar.

10. The boron diffusion method for a solar cell as described in claim 1, wherein, In the step of placing the semi-finished product at a temperature between 1,000°C and 1,200°C, the oxygen flow rate is between 5,000 sccm and 20,000 sccm, and the nitrogen flow rate is between 1,000 sccm and 5,000 sccm.

11. The boron diffusion method for a solar cell as described in claim 1, wherein, In the step of placing the semi-finished product at a temperature between 700°C and 900°C, the flow rate of nitrogen is between 10,000 sccm and 30,000 sccm.

12. The boron diffusion method for a solar cell as described in claim 1, wherein, During the step of introducing the semi-finished solar cell into the cavity, the temperature of the cavity is in the range of 700°C to 900°C.

13. The boron diffusion method for a solar cell as described in claim 1, wherein, After the step of placing the semi-finished product in the range of 700°C to 900°C, or after the step of removing the semi-finished product from the cavity, the thickness of the boron diffusion layer is in the range of 0.4 μm to 1.2 μm.

14. The boron diffusion method for a solar cell as described in claim 1, wherein, After the step of placing the semi-finished product in the range of 700°C to 900°C, or after the step of removing the semi-finished product from the cavity, the thickness of the boron-doped region is in the range of 1.4 μm to 2.4 μm.

15. The boron diffusion method for a solar cell as described in claim 1, wherein, After the step of placing the semi-finished product in the range of 700°C to 900°C, or after the step of removing the semi-finished product from the cavity, the boron doping concentration on the side of the boron diffusion layer away from the upper surface of the semiconductor substrate is in the range of 1×10¹⁷ / cm³ to 1×10¹⁹ / cm³.

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