A boron doping method, a boron doped structure, and a back contact battery

Abstract

This invention discloses a boron doping method, a boron-doped structure, and a back contact battery. The method includes: step 1) pre-crystallization treatment; step 2) pre-oxidation; and step 3) boron diffusion. The pre-crystallization treatment is performed on an amorphous silicon layer in a silicon substrate under an inert gas atmosphere using a gradient voltage switching method. Before pre-oxidation and boron diffusion, this invention first transforms the amorphous silicon into microcrystalline silicon through a gradient voltage switching method, achieving gradual crystallization. This reduces lattice stress and enables a gradient distribution of grain size, avoiding the grain size inhomogeneity caused by single crystallization conditions and the doping concentration fluctuations caused by the disordered structure of amorphous silicon. This makes it easier for boron atoms to migrate to equilibrium positions, forming an ordered structure with a more uniform distribution. This results in a boron-doped structure with superior sheet resistance uniformity, thereby improving the photoelectric conversion efficiency of the back contact battery based on the boron-doped structure.

Description

Technical Field

[0001] This invention relates to the field of solar cells, and more particularly to a boron doping method, a boron doping structure, and a back contact cell. Background Technology

[0002] With the continuous development of photovoltaic technology, the pursuit of high-efficiency solar cells is becoming increasingly urgent. Traditional solar cell structures are gradually facing bottlenecks in improving conversion efficiency. Back contact (BC) cells, as a new generation of high-efficiency crystalline silicon solar cell technology, integrate all positive and negative electrodes on the back of the cell, completely eliminating the light loss caused by the grid lines on the front of the traditional cell, maximizing the utilization of incident photons, and significantly improving cell efficiency.

[0003] In the back-contact battery cathode structure, a tunneling oxide layer is first grown on the back side of the silicon wafer, followed by the deposition of an amorphous silicon layer to form selective carrier transport channels. At this point, boron diffusion diffuses boron into the amorphous silicon layer, modulating local electrical properties. This optimizes hole transport, improves the back surface field, reduces minority carrier recombination probability, increases open-circuit voltage, and ultimately significantly improves battery conversion efficiency. Therefore, the boron diffusion process is a crucial step in forming the P-type emitter region (cathode), and its quality directly affects the passivation effect and carrier transport efficiency of the battery.

[0004] However, current methods for fabricating boron-doped amorphous silicon layers still have many drawbacks. Due to the significant difference in diffusion kinetics between boron atoms and the silicon substrate, concentration gradient runaway is prone to occur during high-temperature diffusion, resulting in inconsistent boron doping concentrations across different regions of the silicon wafer surface. Even using traditional liquid or solid-state source diffusion processes, it is difficult to achieve uniform boron penetration on large-area silicon wafers. Local high / low concentration regions are often formed due to differences in diffusion rates, causing sheet resistance fluctuations far exceeding process requirements, thus leading to low efficiency of back-contact cells.

[0005] Therefore, how to solve the problem of uneven boron content distribution in the P-type emitter region in the prior art has become an important technical problem to be solved by those skilled in the art. Summary of the Invention

[0006] To address the above problems, the present invention aims to provide a boron doping method, a boron doping structure, and a back contact battery that can improve the uniformity of boron content distribution. The technical solution is as follows:

[0007] On the one hand, a boron doping method is provided, the method comprising:

[0008] Step 1) Pre-crystallization treatment;

[0009] Step 2) Pre-oxidation;

[0010] Step 3) Boron diffusion;

[0011] In step 1), the pre-crystallization process is performed by applying a gradient voltage to the amorphous silicon layer in the silicon wafer substrate under an inert gas atmosphere.

[0012] Before pre-oxidation in step 2), amorphous silicon is converted into microcrystalline silicon by gradient voltage transformation, thereby reducing lattice stress and achieving a gradient distribution of grain size. This avoids the problem of uneven grain size caused by single crystallization conditions and the fluctuation of doping concentration caused by the disordered structure of amorphous silicon, so that boron atoms can more easily migrate to the equilibrium position to form an ordered structure with a more uniform distribution.

[0013] In one exemplary embodiment, the gradient transformer ranges from 70 to 100 mBar.

[0014] Considering that under normal pressure and high temperature processing, the silicon surface readily reacts with residual oxygen to form a silicon oxide layer (SiO2), while a low-pressure environment reduces the demand for this side reaction by decreasing the oxygen content, significantly lowering the oxygen partial pressure within the reaction chamber, thereby reducing the probability of amorphous silicon contacting oxygen and directly inhibiting the oxidation reaction. Therefore, it is preferable to reduce oxygen demand under low-pressure conditions to form highly uniform doped shallow junctions on the silicon substrate (amorphous / polycrystalline silicon), reducing BO (boron-oxygen) recombination and improving light absorption efficiency.

[0015] In one exemplary embodiment, the inert gas atmosphere comprises:

[0016] The inert gas flow rate is 1500-2000 sccm.

[0017] In one exemplary embodiment, the pre-oxidation conditions include: a pre-oxidation pressure of 90-100 mBar; an oxygen gas flow rate of 500-700 sccm; an inert gas flow rate of 2600-2800 sccm; and a pre-oxidation time of 200-300 s.

[0018] In one exemplary embodiment, in step 3), boron diffusion is performed using a gradient heating method; the gradient heating range is 800-1000℃.

[0019] In one exemplary embodiment, the method further includes a bonding process, the conditions of which include: a bonding pressure of 90-100 mBar; a bonding temperature of 900-1000℃; an inert gas flow rate of 1500-2500 sccm; and a bonding time of 180-360 s.

[0020] On the other hand, the present invention also provides a boron-doped structure, including a boron-doped structure prepared by any of the above methods.

[0021] On the other hand, the present invention also provides a back contact battery, including the aforementioned boron-doped structure.

[0022] This invention discloses a boron doping method, comprising: step 1) pre-crystallization treatment; step 2) pre-oxidation; and step 3) boron diffusion. The pre-crystallization treatment is performed on an amorphous silicon layer in a silicon wafer substrate using a gradient voltage regulation method under an inert gas atmosphere. Before pre-oxidation and boron diffusion, this invention first transforms the amorphous silicon into microcrystalline silicon through a gradient voltage regulation method, achieving gradual crystallization. This reduces lattice stress, enabling a gradient distribution of grain size. It avoids the grain size inhomogeneity problems caused by single crystallization conditions and the doping concentration fluctuations caused by the disordered structure of amorphous silicon, making it easier for boron atoms to migrate to equilibrium positions, forming an ordered structure with a more uniform distribution. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the present invention, the accompanying drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0024] Figure 1 This is a flowchart of a boron doping method provided in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of the structure of a back contact battery provided in an embodiment of the present invention.

[0026] The following is supplementary explanation of the attached figures:

[0027] 1-N-type silicon wafer; 2-P-region tunneling oxide layer; 3-P-poly layer; 4-N-region tunneling oxide layer; 5-N-poly layer; 6-alumina layer; 7-silicon nitride layer; 8-electrode. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This application provides a boron doping method; please refer to the specific steps. Figure 1 , Figure 1 The following is a flowchart of a boron doping method, which includes the following steps:

[0030] Step 1) Pre-crystallization treatment

[0031] Step 2) Pre-oxidation;

[0032] Step 3) Boron diffusion.

[0033] Specifically, the pre-crystallization process involves treating the amorphous silicon layer in the silicon wafer substrate using a gradient voltage method under an inert gas atmosphere.

[0034] For example, the silicon wafer substrate can be obtained by selecting an N-type silicon wafer as the substrate, polishing it, and preparing a first tunneling oxide layer and an amorphous silicon layer in LPCVD (Low Pressure Chemical Vapor Deposition). It should be noted that the pre-crystallization treatment, pre-oxidation, and boron diffusion in the embodiments of this application are all aimed at the amorphous silicon layer region in the silicon wafer substrate.

[0035] This application embodiment takes into account that if the amorphous silicon layer region in the silicon wafer substrate is pre-crystallized in the LPCVD process, then cooled and then transferred to a boron diffusion furnace for heating, pre-oxidation and boron diffusion, this second heating leads to a secondary heat treatment, which will change the ideal grain size and structure, affect the uneven distribution of the doped boron source, and thus reduce the defect state density and passivation effect of the doped polycrystalline silicon layer. Moreover, boron diffusion is carried out at a higher temperature than the LPCVD process, which is conducive to the complete crystallization of amorphous silicon and the formation of a polycrystalline silicon layer with fewer grain boundaries and lower defect density. Therefore, pre-crystallization, pre-oxidation and boron diffusion all need to be carried out in a boron diffusion furnace to improve the passivation effect.

[0036] Therefore, preferably, pre-crystallization, pre-oxidation, and boron diffusion are performed sequentially in the diffusion furnace. On the one hand, this reduces the process temperature and time in LPCVD and extends the service life of the furnace tubes in LPCVD. On the other hand, it should be noted that the pre-crystallization is a preliminary crystallization and does not complete the entire crystallization process of the amorphous silicon layer. In the boron diffusion step, it is actually a process of simultaneous crystallization and boron deposition, so that the boron doping distribution and the final grain structure are formed and stabilized in the same controlled heat treatment process, which is more conducive to obtaining a uniform doping distribution and reducing the density of grain boundary defects and interface states.

[0037] In this embodiment of the application, the gradient transformer range is 70-100 mBar.

[0038] Specifically, under low-pressure conditions, gradient voltage-switching crystallization reduces oxidation requirements, forming highly uniform doped shallow junctions on the silicon substrate (amorphous / polycrystalline silicon), reducing BO recombination and improving light absorption efficiency. This application's embodiments consider that under normal pressure, during high-temperature processing, the silicon surface easily reacts with residual oxygen to form a silicon oxide layer (SiO2). The low-pressure environment reduces the need for this side reaction by decreasing oxygen content, significantly lowering the oxygen partial pressure within the reaction chamber, thereby reducing the probability of amorphous silicon contacting oxygen and directly inhibiting the oxidation reaction.

[0039] Specifically, the gradient transformation can be performed in two steps, three steps, or more steps, depending on the actual needs.

[0040] In this embodiment of the application, considering that conditions below 70 mBar cause significant wear and tear on the diffusion furnace, and to avoid instrument damage, tests below 70 mBar are no longer performed.

[0041] In this embodiment of the application, the inert gas atmosphere includes:

[0042] The inert gas flow rate is 1500-2000 sccm.

[0043] Specifically, the type and flow rate of the inert gas can be selected according to actual needs. For example, nitrogen is selected as the inert gas in this embodiment of the application, which achieves the experimental effect while saving costs. Preferably, in the pre-crystallization treatment step, an inert gas with a flow rate of 1500-2000 sccm can be introduced into the diffusion furnace (pre-crystallization treatment device) and kept for a certain period of time before the inert gas is stopped. Introducing inert gas in the early stage can reduce impurity contamination, stabilize the furnace pressure, inhibit oxidation and dangling bond defect formation, and promote uniform nucleation on the surface of amorphous silicon. In the later stage, the inert gas is not introduced, which can drive grain growth, form a more complete crystal lattice structure, and avoid interference of inert gas with crystallization kinetics. In addition, if the flow rate of inert gas is too small, it is difficult to maintain a stable balance of airflow in the diffusion furnace, which will cause uneven atmosphere in the diffusion furnace and thus uneven crystallization structure. On the other hand, if the flow rate of inert gas is too large, it may change the gas environment and pressure in the diffusion furnace, which will slow down the reaction rate of amorphous silicon to polycrystalline silicon too much, resulting in high time cost and energy consumption.

[0044] In this embodiment of the application, the pre-oxidation conditions include: a pre-oxidation pressure of 90-100 mBar; an oxygen gas flow rate of 500-700 sccm; an inert gas flow rate of 2600-2800 sccm; and a pre-oxidation time of 200-300 s.

[0045] Specifically, the purpose of this pre-oxidation step is to form a silicon oxide layer, which facilitates subsequent boron source deposition. Due to the different solid solubility of boron in Si and SiO2, boron readily diffuses in SiO2. Therefore, after amorphous silicon is converted into microcrystalline silicon, a SiO2 layer is formed on the surface, followed by boron source deposition, to ensure a more uniform distribution of the boron source in the surface SiO2 layer. Pre-oxidation pressure, oxygen gas flow rate, inert gas flow rate, and pre-oxidation time are all environmental factors that affect the performance of the silicon oxide layer.

[0046] In this embodiment of the application, in step 3), boron diffusion is carried out by gradient heating; the gradient heating range is 800-1000℃.

[0047] Specifically, in the boron diffusion step, the boron source can be BCl3 or BBr3. The embodiments of this application do not specifically limit the selection of the boron source.

[0048] The gradient heating method can be two-step or multi-step. For example, a two-step gradient heating within 800-1000℃ can be performed to precisely control the diffusion depth and concentration distribution of boron.

[0049] In this embodiment of the application, the method further includes a bonding process, the conditions of which include: a bonding pressure of 90-100 mBar; a bonding temperature of 900-1000℃; an inert gas flow rate of 1500-2500 sccm; and a bonding time of 180-360 s.

[0050] Specifically, after the boron diffusion step, the silicon wafer undergoes a push-junction process in the boron diffusion furnace. The temperature of this push-junction process is generally higher than that of the boron diffusion process, providing conditions for the formation of the PN junction (where a P-type semiconductor and an N-type semiconductor come into contact, and through carrier diffusion and electric field drift, ultimately form an interface region with special electrical properties; in silicon-based N-type solar cells, the PN junction is formed by an N-type substrate and a P-type doped layer). N-type silicon wafers refer to semiconductor materials formed by doping single-crystal silicon with pentavalent impurity elements (such as phosphorus P, arsenic As, and antimony Sb); P-type silicon wafers refer to semiconductor materials formed by doping single-crystal silicon with trivalent impurity elements (such as boron B, aluminum Al, and gallium Ga).

[0051] This application also provides a boron-doped structure, including a boron-doped structure obtained by any of the boron doping methods provided in this application.

[0052] Specifically, the boron-doped structure includes a silicon wafer obtained by boron doping a silicon substrate using any of the boron doping methods provided in the embodiments of this application.

[0053] The present invention does not have any special requirements for the preparation method of other parts besides the boron-doped structure obtained by any of the boron doping methods provided in the embodiments of this application. Conventional silicon wafer substrate preparation methods in the art can be used. The specific preparation process is well known in the field of silicon wafer substrates and will not be described in detail here.

[0054] This application also provides a back contact battery, including a boron-doped structure provided in this application embodiment.

[0055] For example, please refer to Figure 2 , Figure 2 This is a schematic diagram of a back contact battery provided in this application. It should be noted that, in this embodiment, the silicon substrate (N-type silicon wafer 1, a P-region tunneling oxide layer 2 formed on the N-type silicon wafer, and an N-region amorphous silicon layer formed on the P-region tunneling oxide layer 2) undergoes pre-crystallization, pre-oxidation, boron diffusion, and junction pushing treatments sequentially to obtain the boron-doped structure provided in this embodiment. This boron-doped structure includes an N-type silicon wafer 1, a P-region tunneling oxide layer 2, and a P-poly layer 3 (Doped p-type Polycrystalline Silicon Layer). The boron-doped structure can be further processed using conventional back contact battery fabrication methods in the art to obtain the back contact battery provided in this embodiment.

[0056] This invention does not have any special requirements for the preparation method of the back contact battery. Conventional back contact battery preparation methods in the field can be used. The specific preparation process is well known in the field of back contact batteries and will not be described in detail here.

[0057] The technical solution of this application will be described below with reference to specific embodiments.

[0058] Example 1

[0059] In LPCVD, a first tunneling oxide layer is formed on an N-type silicon wafer at 560°C, 150 mtorr, and an oxygen gas flow rate of 28000 sccm. After maintaining the temperature at 560°C, the pressure is kept at 150 mtorr, and the SiH4 gas flow rate is 1300 sccm. After the first tunneling oxide layer and the amorphous silicon layer are prepared, the silicon wafer is loaded into a quartz boat and placed into an 800°C boron diffusion furnace.

[0060] Pre-crystallization treatment: Three-step gradient pressure change. At 75 mbar pressure, the temperature is raised to 900℃, the nitrogen gas flow rate is 2000 sccm, and the process time is 13 min. At 85 mbar pressure, the temperature remains constant, the nitrogen gas flow rate is 2000 sccm, and the process time is 13 min. At 95 mbar pressure, the temperature remains constant, the process time is 4 min, and no nitrogen is introduced.

[0061] Pre-oxidation: Maintain constant pressure and temperature (pressure 95 mbar, temperature 900℃), introduce oxygen at a flow rate of 600 sccm and nitrogen at a flow rate of 2700 sccm for pre-oxidation before boron deposition, with a process time of 210 s.

[0062] Boron diffusion: Under constant pressure and temperature, the first boron source deposition was performed with a boron source gas flow rate of 200 sccm, an oxygen gas flow rate of 600 sccm, and a nitrogen gas flow rate of 3000 sccm, for a process time of 150 s; the temperature was then increased to 920℃, and the second boron source deposition was performed with a boron source gas flow rate of 210 sccm, an oxygen gas flow rate of 630 sccm, and a nitrogen gas flow rate of 3150 sccm, for a process time of 150 s.

[0063] Bonding treatment: The temperature is raised to 940℃, and nitrogen gas is introduced at a flow rate of 2000 sccm for heating and bonding treatment, with a process time of 300s.

[0064] After cooling to 800℃ and operating at normal pressure, the vessel is unloaded.

[0065] Example 2

[0066] Compared with Example 1, the pre-crystallization treatment conditions were changed, while other conditions remained unchanged.

[0067] Pre-crystallization treatment: Two-step gradient pressure change, at 85 mbar pressure, the temperature is raised to 900℃, the process time is 26 min, and the nitrogen gas flow rate is 2000 sccm; at 95 mbar pressure, the temperature remains unchanged, no gas is introduced, and the process time is 4 min.

[0068] Example 3

[0069] Compared with Example 1, the pre-crystallization treatment conditions were changed, while other conditions remained unchanged.

[0070] Pre-crystallization treatment: Under constant pressure of 95 mbar, the temperature is raised to 900℃, and nitrogen gas is introduced at a flow rate of 2000 sccm for 26 min; with constant pressure and temperature, no gas is introduced for 4 min.

[0071] Example 4

[0072] Compared with Example 1, the pre-crystallization treatment conditions were changed, while other conditions remained unchanged.

[0073] Pre-crystallization treatment: Three-step gradient pressure change, at 75 mbar pressure, the temperature is raised to 900℃, the process time is 13 min, and the nitrogen gas flow rate is 2000 sccm; at 85 mbar pressure, the temperature is constant, the nitrogen gas flow rate is 2000 sccm, and the process time is 13 min; at 95 mbar pressure, the temperature is constant, the nitrogen gas flow rate is 2000 sccm, and the process time is 4 min.

[0074] Example 5

[0075] Compared with Example 1, the pre-crystallization treatment conditions were changed, while other conditions remained unchanged.

[0076] The flow rate of nitrogen gas introduced in the first two steps is 1500 sccm.

[0077] Example 6

[0078] Compared to Example 1, the pre-crystallization treatment was performed at a bar greater than 100 mBar, while other conditions remained unchanged.

[0079] At a pressure of 100 mbar, the temperature is raised to 900℃, the nitrogen gas flow rate is 2000 sccm, and the process time is 13 min; at a pressure of 110 mbar, the temperature remains constant, the nitrogen gas flow rate is 2000 sccm, and the process time is 13 min; at a pressure of 120 mbar, the temperature remains constant, the process time is 4 min, and no nitrogen is introduced.

[0080] Example 7

[0081] Compared with Example 1, the pre-crystallization treatment conditions were changed, while other conditions remained unchanged.

[0082] The flow rate of nitrogen gas in the first two steps is 1000 sccm.

[0083] Example 8

[0084] Compared with Example 1, the pre-crystallization treatment conditions were changed, while other conditions remained unchanged.

[0085] The flow rate of nitrogen gas in the first two steps is 3000 sccm.

[0086] Comparative Example 1

[0087] Compared to Example 1, there was no pre-crystallization step, and other conditions remained unchanged.

[0088] Comparative Example 2

[0089] Compared to Example 1, in LPCVD, a first tunneling oxide layer was first formed on an N-type silicon wafer at 560°C, 150 mtorr, and an oxygen gas flow rate of 28000 sccm. Then, the temperature was increased to 620°C, the pressure was maintained at 150 mtorr, and a SiH4 gas flow rate of 1300 sccm was introduced to form a polycrystalline silicon layer on the tunneling oxide layer. After the first tunneling oxide layer and the polycrystalline silicon layer were prepared, the silicon wafer was loaded into a quartz boat and placed in an 800°C boron diffusion furnace. No pre-crystallization treatment step was performed, and other conditions remained unchanged.

[0090] Comparative Example 3

[0091] In LPCVD, a first tunneling oxide layer is formed on an N-type silicon wafer at 560°C, 150 mtorr, and an oxygen gas flow rate of 28,000 sccm. After maintaining the temperature at 560°C, the pressure is kept at 150 mtorr, and a SiH4 gas flow rate of 1300 sccm is introduced. Following the formation of an amorphous silicon layer on the first tunneling oxide layer, a pre-crystallization treatment is performed in LPCVD: a three-step gradient pressure change. At 130 mtorr, the temperature is raised to 700°C, and a nitrogen gas flow rate of 1400 sccm is introduced for 13 minutes. At 140 mtorr, the temperature remains constant, and a nitrogen gas flow rate of 1400 sccm is introduced for 13 minutes. At 150 mtorr, the temperature remains constant for 4 minutes, without nitrogen introduction. The wafer is then transferred to a diffusion furnace for subsequent steps under the same conditions as in Example 1. It should be noted that, due to the limitations of the LPCVD process, it is not possible to maintain the same conditions as the pre-crystallization treatment in Example 1.

[0092] Comparative Example 4

[0093] Compared to Example 1, the pre-crystallization treatment was performed under near-normal pressure conditions, while other conditions remained unchanged.

[0094] At a pressure of 750 mBar, the temperature was raised to 900℃, the nitrogen gas flow rate was 2000 sccm, and the process time was 13 min; at a pressure of 850 mBar, the temperature remained constant, the nitrogen gas flow rate was 2000 sccm, and the process time was 13 min; at a pressure of 950 mBar, the temperature remained constant, the process time was 4 min, and no nitrogen was introduced.

[0095] The performance of the boron-doped structures obtained in the examples and comparative examples was tested, and the results of their sheet resistance and uniformity are shown in Table 1.

[0096] Table 1. Performance test results of boron-doped structures obtained from different embodiments and comparative examples

[0097] Case Point 1 Point 2 Point 3 Point 4 5 points Mean (Ω) Uniformity Example 1 132.6 138.4 136.9 141.2 136.5 137.1 3.1％ Example 2 134.5 130.8 141.2 139.0 137.4 136.6 3.8％ Example 3 129.8 133.5 138.9 132.5 142.3 135.4 4.6％ Example 4 132.3 140.3 140.6 133.2 130.7 135.4 3.7％ Example 5 131.6 138.7 136.4 133.6 140.5 136.2 3.3％ Example 6 136.8 135.9 143.4 130.8 137.9 137.0 4.6％ Example 7 129.8 136.7 139.5 142.8 131.8 136.1 4.8％ Example 8 140.3 135.4 129.6 128.6 139.5 134.7 4.3％ Comparative Example 1 130.5 127.6 142.6 129.5 141.9 134.4 5.6％ Comparative Example 2 133.9 140.5 143.0 128.2 126.9 134.5 6.0％ Comparative Example 3 128.1 133.2 142.3 141.3 135.6 136.1 5.2％ Comparative Example 4 127.9 143.8 126.9 139.5 140.1 135.6 6.2％

[0098] As shown in Table 1, compared with the conventional boron diffusion process, the process of this invention, through gradient voltage transformer crystallization of amorphous silicon, has a lower surface concentration (the lower the surface concentration, the higher the sheet resistance) and effectively improves the uniformity of the boron diffusion sheet resistance. Example 1 shows an increase in sheet resistance of approximately 2.7 Ω / m² compared to Comparative Example 1. □ Sheet resistance uniformity was improved by 2.5%.

[0099] Taking the fabrication of a back-contact battery as an example, an N-type silicon wafer is selected as the substrate. The process includes polishing, deposition of a P-region tunneling oxide layer and an amorphous silicon layer on the back side, boron diffusion according to the examples and comparative examples, first grooving and cleaning, deposition of an N-region tunneling oxide layer and a polycrystalline silicon layer on the back side, phosphorus diffusion, second grooving and cleaning, double-sided alumina and silicon nitride, screen printing, sintering, light injection, and testing and sorting to fabricate a TBC battery. Performance tests were conducted on the back-contact batteries fabricated based on the boron-doped structures obtained in the examples and comparative examples. The performance test results are shown in Table 2. It should be noted that the process conditions for fabricating the back-contact batteries based on the boron-doped structures obtained in the examples and comparative examples in this application are the same.

[0100] Table 2. Performance test results of boron-doped back contact batteries obtained based on different embodiments and comparative examples.

[0101]

[0102]

[0103] The results above show that, compared to the comparative example, the conversion efficiency of the embodiments achieved a gain of 0.1-0.21%. By using gradient voltage switching crystallization, amorphous silicon is converted into microcrystalline silicon in advance, thereby reducing lattice stress and achieving a gradient distribution of grain size. This avoids the grain size inhomogeneity caused by single crystallization conditions and the doping concentration fluctuations caused by the disordered structure of amorphous silicon, making it easier for boron atoms to migrate to their equilibrium positions. During boron diffusion, the pre-crystallized silicon layer continues to crystallize, with boron deposition and crystallization occurring simultaneously, forming an ordered structure with a more uniform distribution. Ultimately, boron doping is completed while converting to polycrystalline silicon. Secondly, gradient voltage switching crystallization reduces oxidation requirements, forming highly uniform doped shallow junctions on the silicon substrate (amorphous / polycrystalline silicon), reducing BO recombination and improving light absorption efficiency. Finally, by pre-stabilizing the structure of the doped region, a polycrystalline silicon layer with low defect density is formed, which improves the doping unevenness during boron diffusion and makes the crystal structure of the boron-doped polycrystalline silicon layer more uniform and dense. This step can reduce the density of grain boundary defects and interface states, and has better sheet resistance uniformity, thereby reducing the recombination loss of charge carriers at the interface. The recombination effect of photogenerated charge carriers is weak, which improves the open-circuit voltage and short-circuit current of the battery, and thus improves the photoelectric conversion efficiency of the battery.

[0104] As can be seen from the above technical solutions of the embodiments of the present invention, the present invention discloses a boron doping method, wherein the method includes: step 1) pre-crystallization treatment; step 2) pre-oxidation; step 3) boron diffusion; the pre-crystallization treatment is performed on the amorphous silicon layer in the silicon wafer substrate under an inert gas atmosphere using a gradient voltage transformation method; before pre-oxidation and boron diffusion, the method first transforms the amorphous silicon into microcrystalline silicon through a gradient voltage transformation method, thereby reducing lattice stress, realizing a gradient distribution of grain size, avoiding the problem of uneven grain size caused by single crystallization conditions and the problem of doping concentration fluctuation caused by the disordered structure of amorphous silicon, making it easier for subsequent boron atoms to migrate to the equilibrium position, forming an ordered structure with a more uniform distribution, thereby obtaining a boron-doped structure with better sheet resistance uniformity, and thus improving the photoelectric conversion efficiency of the back contact based on the boron-doped structure.

[0105] The foregoing description has fully disclosed the specific embodiments of the present invention. It should be noted that any modifications made to the specific embodiments of the present invention by those skilled in the art do not depart from the scope of the claims. Accordingly, the scope of the claims is not limited to the foregoing specific embodiments.

Claims

1. A boron doping method, the method comprising the following steps: Step 1) Pre-crystallization treatment; In an inert gas atmosphere, an amorphous silicon layer in a silicon wafer substrate is subjected to gradient voltage transformation to convert the amorphous silicon layer into a microcrystalline silicon layer; and the gradient voltage transformation range is 70-100 mBar. Step 2) Pre-oxidation; The obtained microcrystalline silicon layer is pre-oxidized to form a silicon oxide layer on its surface; Step 3) Boron diffusion; Boron source deposition is performed on the surface of the obtained silicon oxide layer, and boron diffusion is carried out based on a gradient temperature increase; the gradient temperature increase range is 800-1000℃.

2. The boron doping method according to claim 1, wherein the inert gas atmosphere comprises: The inert gas flow rate is 1500-2000 sccm.

3. The boron doping method according to claim 1, wherein the pre-oxidation conditions include: The pre-oxidation pressure is 90-100 mBar; the oxygen gas flow rate is 500-700 sccm; the inert gas flow rate is 2600-2800 sccm; and the pre-oxidation time is 200-300 s.

4. The boron doping method according to claim 1, further comprising a junction push-back process, wherein the conditions for the junction push-back process include: The push-off pressure is 90-100 mBar; The bonding temperature is 900-1000℃; the inert gas flow rate is 1500-2500 sccm; and the bonding time is 180-360s.

5. A boron-doped structure, characterized in that, Including boron-doped structures prepared by any one of claims 1 to 4.

6. A back-contact battery, characterized in that, Including the boron-doped structure as described in claim 5.

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