A topcon cell structure and a preparation method thereof

Abstract

This invention discloses a TOPCon cell structure and its fabrication method, belonging to the field of photovoltaic technology. The TOPCon cell structure includes a boron-doped emitter, a first-phase Al2O3 amorphous layer, a second-phase γ-Al2O3 metastable layer, and a gradient composite film layer sequentially disposed on the surface of an N-type silicon substrate. In the TOPCon cell obtained by this invention, the first-phase Al2O3 amorphous state exhibits long-range disorder, non-periodic atomic arrangement, and contains numerous dangling bonds and structural defects. The second-phase γ-Al2O3 metastable state possesses high specific surface area and good thermal stability, enabling the synergistic formation of a high-density fixed negative charge. These charges effectively repel minority carriers, reducing surface recombination. The long-range disordered Al2O3 amorphous state and the partially ordered γ-Al2O3 form a metastable combination, which facilitates the formation of numerous dangling bonds at the alumina-silicon interface. These dangling bonds, with the assistance of hydrogen, effectively fix the negative charge, thereby achieving an extremely low surface recombination rate and exhibiting excellent passivation effects.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, specifically to a TOPCon cell structure and its fabrication method. Background Technology

[0002] TOPCon is a high-efficiency crystalline silicon solar cell technology, its core being its unique back-side passivated contact structure. By fabricating an oxide layer and a doped polycrystalline silicon thin film on the back of the cell to form the passivated contact structure, the metal electrode is completely separated from the silicon substrate, reducing the back-side recombination current density (J0) to below 10 fA / cm², achieving excellent passivation of the silicon wafer surface. This tunneling oxide layer utilizes the quantum tunneling effect, allowing majority carriers (such as electrons) to pass through smoothly while blocking the recombination of minority carriers (such as holes), thereby effectively reducing surface recombination and metal-contact recombination, improving the cell's open-circuit voltage and energy conversion efficiency. As one of the representative technologies of N-type cells, its single-junction theoretical efficiency reaches 28.7%. Compared to traditional P-type silicon wafers, N-type silicon has lower metal impurity sensitivity, higher minority carrier lifetime, and does not suffer from light-induced degradation (LID) problems caused by boron-oxygen recombination, providing a foundation for the cell's high-efficiency performance. The front side features a P-type emitter, silicon nitride antireflection film, and other structures to form a PN junction, reduce light reflection, and improve light absorption.

[0003] Improving passivation performance is crucial for high-efficiency solar cells because it directly relates to controlling the internal loss in the cell's conversion of photons into electrical energy. In existing cell passivation technologies, the low solid solubility of boron in silicon in the PN junction, which relies on boron diffusion for the front surface, results in poor surface passivation. Alumina thin films, due to their high density of fixed negative charges, are often paired with silicon nitride layers for front surface passivation of high-efficiency TOPCon cells. However, as high-efficiency solar cell technology enters a new phase driven by both efficiency improvements and cost reductions, performance and reliability face significant challenges. Ultraviolet (UV) light is one of the important environmental stress factors. When photovoltaic modules are exposed to high-energy UV light, the passivation formed by the single-layer alumina film and silicon nitride layer is damaged. UV light can activate defect states at the photovoltaic module interface, leading to an increase in defect state density, weakening the previously crucial chemical passivation effect, affecting the fixed charges at the interface, and degrading the field-effect passivation performance, ultimately resulting in a loss of photoelectric conversion efficiency in the photovoltaic module. Although the passivation performance can be improved by increasing the thickness of Al2O3, excessive Al2O3 thickness will increase the carrier penetration resistance to a certain extent, resulting in short-circuit current loss in the battery. Summary of the Invention

[0004] To address or partially address the problems existing in related technologies, this invention provides a TOPCon battery structure and its preparation method. The TOPCon battery structure prepared by this method can enhance the passivation performance of the battery through the combination of an Al2O3 amorphous layer and a γ-Al2O3 metastable phase layer.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a TOPCon battery structure is provided, the innovation of which is that the structure of the TOPCon battery includes a boron-doped emitter, a first crystalline phase Al2O3 amorphous layer, a second crystalline phase γ-Al2O3 metastable layer and a gradient composite film layer sequentially disposed on the surface of an N-type silicon substrate. The gradient composite film layer has a 3+2+1 structure, comprising three SiNx layers, two SiOxNy layers and one SiO2 layer.

[0006] Preferably, the thickness of both the first crystalline phase Al2O3 amorphous layer and the second crystalline phase γ-Al2O3 metastable layer is 2-4 nm.

[0007] Preferably, the total thickness of the three SiNx layers is 35-50 nm, the total thickness of the two SiOxNy layers is 10-30 nm, and the total thickness of the single SiO2 layer is 5-20 nm.

[0008] This invention also provides a method for preparing the above-mentioned TOPCon battery structure, the innovation of which lies in the following specific preparation method: S1. Randomly select an N-type silicon substrate wafer that has undergone pretreatment and clean and dry it using RCA. S2. An amorphous Al2O3 first crystalline phase layer is prepared on the front side of an N-type silicon substrate using a reactor. S3. Deposit a second crystalline phase γ-Al2O3 metastable layer on the first crystalline phase Al2O3 amorphous layer in the same reactor. S4. Transfer the silicon substrate wafer to another reactor for post-annealing. S5. After the treatment is completed, continue to deposit a gradient composite film layer on the front side at the same temperature. S6. The silicon substrate obtained in step S5 is used to make the finished TOPCon battery.

[0009] Preferably, in step S1, the pretreatment of the N-type silicon substrate includes: texturing and fabrication, boron diffusion, oxidation, LP / PE-Poly, removal of front and back phosphosilicate glass and borosilicate glass, and forming a boron-doped emitter on the front surface of the N-type silicon substrate after the pretreatment.

[0010] Preferably, in step S2, the precursor for preparing the first crystalline phase Al2O3 amorphous layer is an aluminum source, O3 and H2O(g), and the preparation temperature is 180-280 ℃.

[0011] Preferably, in step S3, the precursors for preparing the second crystalline phase γ-Al2O3 metastable phase layer are aluminum source and O3, and the preparation temperature is 270-370℃.

[0012] Preferably, the aluminum source is trimethylaluminum (TMA), aluminum chloride, or alkylaluminum.

[0013] Preferably, in step S4, the post-annealing process involves heating the inner cavity of the reactor from room temperature to 250-350°C at a heating rate of 5-10°C / min after loading, continuing to raise the cavity temperature to the holding temperature at a heating rate of 10-15°C / min, holding the temperature at 360-450°C for 5-15 minutes, and then raising the temperature to 460-550°C at a heating rate of 15-20°C / min after holding. The heat preservation process is carried out in an O2 atmosphere with an O2 flow rate of 1000~3000 scccm.

[0014] At a temperature of 460-550℃, continue to deposit a gradient composite film by vacuuming, leak detection, deposition, vacuuming, purging, nitrogen filling, and vacuum breaking. In the preparation of the SiNx bottom layer, the NH3:SiH4 flow ratio increases in a gradient from bottom to top, with the flow ratio of the bottom layer being 1.0:1 to 3.0:1, the flow ratio of the middle layer being 4.0:1 to 6.5:1, and the flow ratio of the top layer being 8.5:1 to 10.5:1. When preparing the SiOxNy layer, the flow ratio of SiH4:N2O:NH3 increases gradually from bottom to top. The flow ratio of the lower layer is set to 1:4:6 ~ 1:5:5, and the flow ratio of the upper layer is set to 2:7:3 ~ 3:7:3. When preparing the SiO2 layer, the N2O:SiH4 flow ratio is 10:1 to 13:1.

[0015] Preferably, in step S6, the process of making the finished battery cell from the silicon substrate includes back film preparation, front and back metallization, sintering, light injection annealing, and laser induction.

[0016] This invention provides a TOPCon battery structure and its fabrication method, which has the following beneficial effects: (1) The TOPCon battery obtained by the present invention includes a first crystalline phase Al2O3 amorphous layer and a second crystalline phase γ-Al2O3 metastable layer in its structure. The first crystalline phase Al2O3 amorphous layer is long-range disordered, with non-periodic atomic arrangement and contains a large number of dangling bonds and structural defects. The second crystalline phase γ-Al2O3 metastable layer has a high specific surface area and good thermal stability, and can synergistically form a high density of fixed negative charges. These charges can effectively repel minority carriers and reduce surface recombination. The long-range disordered Al2O3 amorphous layer and the partially ordered γ-Al2O3 are metastable and conducive to the formation of a large number of dangling bonds at the alumina and silicon interface. With the assistance of hydrogen, these dangling bonds can effectively fix negative charges, thereby achieving an extremely low surface recombination rate and having an excellent passivation effect.

[0017] (2) The present invention utilizes the first crystalline phase Al2O3 amorphous layer and the second crystalline phase γ-Al2O3 metastable layer, which work together with the composite film formed by the post-annealing process in an oxygen atmosphere to enhance the battery’s resistance to photothermal radiation. The combination of these properties, along with the adjustment of various core process parameters, optimizes the stoichiometry of the thin film, fills oxygen vacancies, and improves dielectric properties, forming a high-quality alumina thin layer interface on the silicon-based surface, enhancing chemical bond energy, and avoiding passivation failure caused by Si-H bond breakage under photothermal conditions.

[0018] (3) The temperature of the synthesis of the first crystalline phase Al2O3 amorphous layer and the second crystalline phase γ-Al2O3 metastable layer, the process and temperature of the post-annealing treatment, and the oxygen source atmosphere (post-annealing is carried out at a constant temperature in an oxygen atmosphere) in the preparation method of the present invention ensure the interface state density, avoid the destruction of Si-H bonds at high temperature, and the setting of low temperature oxygen annealing further improves the film density, effectively improves the quality of alumina film, greatly reduces the fluctuation of positive charge inside it, and promotes the formation of beneficial fixed negative charge in the film. Attached Figure Description

[0019] Figure 1 This is a flowchart of a TOPCon battery fabrication method provided by the present invention.

[0020] Figure 2 This is a schematic diagram of the TOPCon battery prepared in Example 1 of the present invention.

[0021] Among them, 1. N-type silicon substrate; 2. Boron-doped emitter; 3. First crystalline phase Al2O3 amorphous layer; 4. Second crystalline phase γ-Al2O3 metastable layer; 5. SiNx layer; 6. SiOxNy layer; 7. SiO2 layer; 8. Electrode. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the scope of protection of the present invention is not limited to the content described.

[0023] The reactor of this invention may specifically include a CVD reactor and an ALD reactor.

[0024] Example 1 This embodiment provides a method for fabricating a TOPCon battery structure, such as... Figure 1 As shown, the specific preparation method is as follows: S1. The N-type silicon substrate is subjected to pretreatment including texturing, boron diffusion, oxidation, LP / PE-Poly, and removal of front and back phosphosilicate glass and borosilicate glass. Any N-type silicon substrate that has undergone the pretreatment process is selected and subjected to RCA cleaning and drying. After the pretreatment, a boron-doped emitter is formed on the front surface of the N-type silicon substrate.

[0025] S2. Using trimethylaluminum (TMA), O3, and H2O (gaseous water molecules) as reaction precursors, the first crystalline phase Al2O3 amorphous layer is prepared on the front side of an N-type silicon substrate via an ALD tube furnace at a reaction temperature of 230℃.

[0026] S3. Using trimethylaluminum (TMA) and O3 as reaction precursors, a second crystalline phase γ-Al2O3 metastable layer is deposited on the first crystalline phase Al2O3 amorphous layer in an ALD tube furnace. The reaction temperature during preparation is 330℃.

[0027] S4. The silicon substrate wafer is transferred to a CVD tube furnace for post-annealing. Specifically, the post-annealing process involves heating the CVD tube furnace chamber from room temperature to 300°C at a rate of 8°C / min, then continuing to raise the chamber temperature to the holding temperature at a rate of 12°C / min, holding at 400°C for 10 minutes. After holding, the temperature is increased to 500°C at a rate of 18°C / min. The holding process is carried out in an O2 atmosphere with a flow rate of 2000 scccm.

[0028] S5. After the treatment is completed, continue to deposit a gradient composite film on the front side at the same temperature; specifically, continue to deposit a gradient composite film at 500℃ by vacuuming, leak detection, deposition, vacuuming, purging, nitrogen filling and vacuum breaking.

[0029] In the preparation of the SiNx bottom layer, the NH3:SiH4 flow ratio (setting the SiNx layer using NH3 and SiH4 is an existing technology) shows a gradient increase from bottom to top, with the first layer having a flow ratio of 2.0:1, the second layer having a flow ratio of 5.0:1, and the third layer having a flow ratio of 9.5:1.

[0030] The flow ratio of SiH4:N2O:NH3 used to prepare the SiOxNy layer (using NH3, SiH4, and N2O to set the SiOxNy layer is an existing technology) increases from bottom to top, with the flow ratio of the lower layer set to 1:4.5:5.5 and the flow ratio of the upper layer set to 2.5:7:3.

[0031] The flow ratio of N2O to SiH4 (using SiH4 and N2O to set the SiO2 layer is an existing technology) for preparing the SiO2 layer is 11:1.

[0032] The purpose of gradient setting is to improve the density, uniformity, chemical stability of the film and optimize interface defects.

[0033] S6. The silicon substrate obtained in step S5 is used to make a finished TOPCon cell. The process of making the finished cell from the silicon substrate includes back film preparation, front and back metallization, sintering, light injection annealing, and laser induction.

[0034] The structure of the TOPCon battery obtained by the above preparation method in this embodiment is as follows: Figure 2 As shown, the structure includes a boron-doped emitter 2, a first-phase Al2O3 amorphous layer 3 (3 nm thick), a second-phase γ-Al2O3 metastable layer 4 (3 nm thick), and a gradient composite film layer sequentially disposed on the surface of an N-type silicon substrate 1. The gradient composite film layer has a 3+2+1 structure, comprising three SiNx layers 5, two SiOxNy layers 6, and one SiO2 layer 7. The total thickness of the three SiNx layers is 45 nm, the total thickness of the two SiOxNy layers is 22 nm, and the total thickness of the one SiO2 layer is 13 nm. The formation of three, two, and one layers respectively achieves good optical management and interface passivation balance. The TOPCon cell obtained in this embodiment has 16 electrodes 8 uniformly and vertically interspersed in each layer.

[0035] Example 2 This embodiment provides a method for fabricating a TOPCon battery structure, the specific fabrication method is as follows: S1. The N-type silicon substrate is subjected to pretreatment including texturing, boron diffusion, oxidation, LP / PE-Poly, and removal of front and back phosphosilicate glass and borosilicate glass. Any N-type silicon substrate that has undergone the pretreatment process is selected and subjected to RCA cleaning and drying. After the pretreatment, a boron-doped emitter is formed on the front surface of the N-type silicon substrate.

[0036] S2. Using trimethylaluminum (TMA), O3, and H2O (gaseous water molecules) as reaction precursors, the first crystalline phase Al2O3 amorphous layer is prepared on the front side of an N-type silicon substrate by CVD tube furnace. The reaction temperature during preparation is 180℃.

[0037] S3. Using trimethylaluminum (TMA) and O3 as reaction precursors, a second crystalline phase γ-Al2O3 metastable layer is deposited on the first crystalline phase Al2O3 amorphous layer in a CVD tube furnace. The reaction temperature during preparation is 370℃.

[0038] S4. The silicon substrate wafer is transferred to an ALD tube furnace for post-annealing. Specifically, the post-annealing process involves heating the CVD tube furnace chamber from room temperature to 250°C at a rate of 5°C / min, then continuing to raise the chamber temperature to the holding temperature at a rate of 15°C / min, holding at 450°C for 5 minutes. After holding, the temperature is raised to 460°C at a rate of 15°C / min. The holding process is conducted in an O2 atmosphere with a flow rate of 3000 scccm.

[0039] S5. After the treatment is completed, continue to deposit a gradient composite film on the front side at the same temperature; specifically, at a temperature of 460℃, a gradient composite film is deposited by vacuuming, leak detection, deposition, vacuuming, purging, nitrogen filling, and vacuum breaking.

[0040] In the preparation of the SiNx bottom layer, the NH3:SiH4 flow ratio increases in a gradient from bottom to top, with the first layer having a flow ratio of 1.0:1, the second layer having a flow ratio of 4.0:1, and the third layer having a flow ratio of 10.5:1.

[0041] When preparing the SiOxNy layer, the flow ratio of SiH4:N2O:NH3 increases from bottom to top, with the flow ratio of the lower layer set to 1:5:5 and the flow ratio of the upper layer set to 2:7:3.

[0042] The flow ratio of N2O:SiH4 during the preparation of the SiO2 layer is 10:1.

[0043] S6. The silicon substrate obtained in step S5 is used to make a finished TOPCon cell. The process of making the finished cell from the silicon substrate includes back film preparation, front and back metallization, sintering, light injection annealing, and laser induction.

[0044] In this embodiment, the TOPCon battery obtained by the above preparation method has the same structure as that in the previous embodiment. The first crystalline phase Al2O3 amorphous layer 3 has a thickness of 2 nm, the second crystalline phase γ-Al2O3 metastable layer 4 has a thickness of 4 nm, and a gradient composite film layer has a 3+2+1 structure, including three SiNx layers 5, two SiOxNy layers 6, and one SiO2 layer 7. The total thickness of the three SiNx layers is 35 nm, the total thickness of the two SiOxNy layers is 30 nm, and the total thickness of the one SiO2 layer is 20 nm.

[0045] Example 3 This embodiment provides a method for fabricating a TOPCon battery structure, the specific fabrication method is as follows: S1. The N-type silicon substrate is subjected to pretreatment including texturing, boron diffusion, oxidation, LP / PE-Poly, and removal of front and back phosphosilicate glass and borosilicate glass. Any N-type silicon substrate that has undergone the pretreatment process is selected and subjected to RCA cleaning and drying. After the pretreatment, a boron-doped emitter is formed on the front surface of the N-type silicon substrate.

[0046] S2. Using aluminum chloride, O3 and H2O (gaseous water molecules) as reaction precursors, the first crystalline phase Al2O3 amorphous layer is prepared on the front side of an N-type silicon substrate via an ALD tube furnace. The reaction temperature during preparation is 280℃.

[0047] S3. Using aluminum chloride and O3 as reaction precursors, a second crystalline phase γ-Al2O3 metastable layer is deposited on the first crystalline phase Al2O3 amorphous layer in an ALD tube furnace. The reaction temperature during preparation is 270℃.

[0048] S4. The silicon substrate wafer is transferred to a CVD tube furnace for post-annealing. Specifically, the post-annealing process involves heating the CVD tube furnace chamber from room temperature to 350°C at a rate of 10°C / min after wafer loading, then continuing to raise the chamber temperature to the holding temperature at a rate of 10°C / min, maintaining the temperature at 360°C for 15 minutes. After holding, the temperature is increased to 550°C at a rate of 20°C / min. The holding process is carried out in an O2 atmosphere with a flow rate of 1000 scccm.

[0049] S5. After the treatment is completed, continue to deposit a gradient composite film on the front side at the same temperature; specifically, at a temperature of 550℃, a gradient composite film is deposited by vacuuming, leak detection, deposition, vacuuming, purging, nitrogen filling, and vacuum breaking.

[0050] In the preparation of SiNx, the NH3:SiH4 flow ratio of the bottom layer increases in a gradient from bottom to top, with the first layer having a flow ratio of 3.0:1, the second layer having a flow ratio of 6.5:1, and the third layer having a flow ratio of 8.5:1.

[0051] When preparing the SiOxNy layer, the flow ratio of SiH4:N2O:NH3 increases from bottom to top, with the flow ratio of the lower layer set to 1:4:6 and the flow ratio of the upper layer set to 3:7:3.

[0052] The flow rate ratio of N2O:SiH4 for preparing the SiO2 layer was 13:1.

[0053] S6. The silicon substrate obtained in step S5 is used to make a finished TOPCon cell. The process of making the finished cell from the silicon substrate includes back film preparation, front and back metallization, sintering, light injection annealing, and laser induction.

[0054] In this embodiment, the TOPCon battery obtained by the above preparation method has the same structure as that in the previous embodiment. The first crystalline phase Al2O3 amorphous layer 3 has a thickness of 4 nm, the second crystalline phase γ-Al2O3 metastable layer 4 has a thickness of 2 nm, and a gradient composite film layer has a 3+2+1 structure, including three SiNx layers 5, two SiOxNy layers 6, and one SiO2 layer 7. The total thickness of the three SiNx layers is 50 nm, the total thickness of the two SiOxNy layers is 10 nm, and the total thickness of the one SiO2 layer is 5 nm.

[0055] Comparative Example 1 The comparative example uses existing solar cell fabrication methods, including the following steps: N-type silicon substrates that have undergone conventional pretreatment processes were selected. A single-phase alumina passivation layer was prepared using an ALD tube furnace, with trimethylaluminum (TMA) and H₂O(g) as raw materials. The reaction temperature in the tube furnace was set to 230℃, and the thickness was 3 nm. The layer was then transferred to a CVD tube furnace to prepare the front-side thin film. The front-side film preparation process included heating, vacuuming, leak detection, deposition, vacuuming, purging, nitrogen purging, and vacuum breaking. The solar cell then underwent subsequent processes including back-side film preparation, front and back metallization, sintering, photo-injection annealing, and laser-induced formation of the finished solar cell.

[0056] The batteries prepared in Example 1 and Comparative Example 1 were tested using the quasi-steady-state photoconductivity decay method. Specifically, a Sinton WCT-120 instrument was used to test silicon wafers that had only completed double-sided deposition of the front and back films but had not yet had metal electrodes sintered. The test results are shown in Table 1, which compares the passivation performance of the multiphase alumina structure battery of Example 1 with that of the single-phase alumina structure battery of Comparative Example 1.

[0057] Table 1 Minority carrier lifetime, interfacial recombination current density (J0), and simulated open-circuit voltage (iVoc) are three key parameters for evaluating the passivation effect of a battery. These three parameters directly reflect the quality of the passivation performance, characterizing it from different perspectives. The underlying mechanism is closely related to suppressing carrier recombination. A longer lifetime indicates a lower probability of carriers being captured and recombinating due to surface / interface defects, and a better suppression effect of the passivation layer on recombination centers. A lower J0 value indicates a slower recombination rate per unit surface area, and a higher overall quality of the passivation layer (including chemical passivation and field-effect passivation). A higher iVoc indicates a higher upper limit of voltage output that the battery can achieve under ideal conditions, directly reflecting the limiting potential difference that the passivation structure can achieve. As shown in Table 1, compared with the existing single-phase alumina structure battery, the multiphase alumina structure battery of Example 1 of this invention has a higher minority carrier lifetime, lower interfacial recombination current density (J0), and higher simulated open-circuit voltage (iVoc), indicating that its surface passivation effect is significantly improved.

[0058] The multiphase alumina structure battery of Example 1 and the comparative single-phase alumina structure battery were subjected to module power decay tests, i.e., ultraviolet aging tests (UV aging tests are one of the common methods to evaluate the stability and passivation of battery devices). The power decay test comparison is shown in Table 2. As can be seen from Table 2, the power decay of the multiphase alumina structure battery of Example 1 before and after the test is 0.11% compared with the comparative single-phase alumina structure battery of the prior art. Compared with the 1.76% power decay of the comparative single-phase alumina structure battery, the passivation performance is significantly better, indicating that the passivation performance of the battery obtained by the method of the present invention is significantly improved (because the fundamental reason behind the UV-induced battery power decay is the deterioration of the battery's passivation performance, which can be indirectly reflected by the results of the UV aging test). Table 2 The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A TOPCon battery structure, characterized in that: The TOPCon cell structure includes a boron-doped emitter, a first crystalline phase Al2O3 amorphous layer, a second crystalline phase γ-Al2O3 metastable layer, and a gradient composite film layer sequentially disposed on the surface of an N-type silicon substrate. The gradient composite film layer has a 3+2+1 structure, comprising three SiNx layers, two SiOxNy layers, and one SiO2 layer.

2. The TOPCon battery structure according to claim 1, characterized in that: The thickness of the first crystalline phase Al2O3 amorphous layer and the second crystalline phase γ-Al2O3 metastable layer is 2-4 nm.

3. A TOPCon battery structure according to claim 1, characterized in that: The total thickness of the three-layer SiNx is 35-50 nm, the total thickness of the two-layer SiOxNy is 10-30 nm, and the total thickness of the single-layer SiO2 is 5-20 nm.

4. A method for preparing the TOPCon battery structure according to any one of claims 1-3, characterized in that: The specific preparation method is as follows: S1. Randomly select an N-type silicon substrate wafer that has undergone pretreatment and clean and dry it using RCA. S2. An amorphous Al2O3 first crystalline phase layer is prepared on the front side of an N-type silicon substrate using a reactor. S3. A second crystalline phase γ-Al2O3 metastable layer is deposited on the first crystalline phase Al2O3 amorphous layer in the same reactor. S4. Transfer the silicon substrate wafer to another reactor for post-annealing. S5. After the treatment is completed, continue to deposit a gradient composite film layer on the front side at the same temperature. S6. The silicon substrate obtained in step S5 is used to make the finished TOPCon battery.

5. The TOPCon battery structure and its fabrication method according to claim 4, characterized in that: In step S1, the pretreatment of the N-type silicon substrate includes: texturing and fabrication, boron diffusion, oxidation, LP / PE-Poly, removal of front and back phosphosilicate glass and borosilicate glass, and forming a boron-doped emitter on the front surface of the N-type silicon substrate after the pretreatment.

6. The TOPCon battery structure and its preparation method according to claim 4, characterized in that: In step S2, the precursors for preparing the first crystalline phase Al2O3 amorphous layer are aluminum source, O3 and H2O(g), and the preparation temperature is 180-280 ℃.

7. The TOPCon battery structure and its fabrication method according to claim 4, characterized in that: In step S3, the precursors for preparing the second crystalline phase γ-Al2O3 metastable phase layer are aluminum source and O3, and the preparation temperature is 270-370℃.

8. A TOPCon battery structure and its preparation method according to claim 6 or 7, characterized in that: The aluminum source is trimethylaluminum (TMA), aluminum chloride, and alkylaluminum.

9. The TOPCon battery structure and its preparation method according to claim 4, characterized in that: In step S4, the post-annealing process involves heating the reactor cavity from room temperature to 250-350°C at a heating rate of 5-10°C / min after loading, continuing to raise the cavity temperature to the holding temperature at a heating rate of 10-15°C / min, holding the temperature at 360-450°C for 5-15 minutes, and then raising the temperature to 460-550°C at a heating rate of 15-20°C / min after holding. The heat preservation process is carried out in an O2 atmosphere with an O2 flow rate of 1000~3000 scccm; At a temperature of 460-550℃, continue to deposit a gradient composite film by vacuuming, leak detection, deposition, vacuuming, purging, nitrogen filling, and vacuum breaking. In the preparation of the SiNx bottom layer, the NH3:SiH4 flow ratio increases in a gradient from bottom to top, with the flow ratio of the bottom layer being 1.0:1 to 3.0:1, the flow ratio of the middle layer being 4.0:1 to 6.5:1, and the flow ratio of the top layer being 8.5:1 to 10.5:

1. When preparing the SiOxNy layer, the SiH4:N2O:NH3 flow ratio increases in a gradient from bottom to top, with the lower layer flow ratio set to 1:4:6 ~ 1:5:5 and the upper layer flow ratio set to 2:7:3 ~ 3:7:

3. When preparing the SiO2 layer, the N2O:SiH4 flow ratio is 10:1 to 13:

1.

10. The TOPCon battery structure and its preparation method according to claim 4, characterized in that: In step S6, the process of making the finished solar cell from the silicon substrate includes back film preparation, front and back metallization, sintering, light injection annealing, and laser induction.

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