A method for improving efficiency of a BC battery by boron diffusion low-temperature oxidation, a BC battery and a photovoltaic system

Abstract

The application provides a method for improving efficiency of BC battery by boron diffusion and low-temperature oxidation, a BC battery and a photovoltaic system, and relates to the field of solar cell preparation. The method for improving efficiency of BC battery by boron diffusion and low-temperature oxidation comprises the following steps: after a N-type monocrystalline silicon wafer is sequentially deposited with a tunneling oxide layer and an amorphous silicon layer, boron diffusion, gradient oxidation, ultraviolet assisted acid polishing and deposition of a laminated passivation layer are sequentially performed; the gradient oxidation is two-stage oxidation. The technical scheme effectively reduces the heat treatment temperature of the boron diffusion process, reduces the thermal load of the equipment and energy consumption. The gradient oxidation procedure improves the uniformity of the concentration distribution of the doped layer, and the ultraviolet assisted treatment reduces the risk of damage to the tunneling oxide layer. The synergistic effect of the multi-layer passivation structure improves the interface passivation effect, enhances the stability and photoelectric conversion efficiency of the battery. The optimized combination of the process sequence realizes the synchronous improvement of the process efficiency and the battery performance on the premise of ensuring the doping quality.

Description

Technical Field

[0001] This application relates to the field of solar cell fabrication, and more particularly to a method for improving the efficiency of BC cells through low-temperature boron diffusion oxidation, BC cells, and photovoltaic systems. Background Technology

[0002] In the manufacturing process of back-contact (BC) type crystalline silicon solar cells, boron diffusion is a key process step for forming the P-type region. However, existing boron diffusion technologies have several technical drawbacks that urgently need to be addressed: high energy consumption and heavy equipment burden: existing processes typically require long-term (≥ 3000 seconds) oxidation treatment at high temperatures of 1000℃ to 1030℃. This high-temperature, long-duration process results in significant energy consumption, accounting for more than 40% of the overall process energy consumption, while the high-temperature environment accelerates the aging and wear of production equipment. Difficulty in achieving uniform boron doping and controlling surface concentration: after using existing boron diffusion processes, the concentration of the boron-doped layer formed on the silicon wafer surface is often higher than 5 × 10⁻⁶. 19 cm -3 To adjust the surface concentration and remove the associated borosilicate glass (BSG) layer, acidic solution polishing (acid polishing) is typically required. However, this acid polishing process carries the risk of damaging the underlying tunnel oxide layer, leading to increased interfacial recombination and consequently affecting the final photoelectric conversion efficiency of the cell. Insufficient passivation layer performance: The currently widely used alumina / silicon nitride (AlOx / SiNx) stacked passivation structure has limited effective suppression capability for interfacial states in the boron diffusion region, with interfacial recombination rates typically exceeding 10 cm / s. Furthermore, this passivation structure exhibits a transmittance exceeding 40% in the ultraviolet light range of 300 nm to 400 nm, indicating weak resistance to ultraviolet radiation, which may affect the long-term reliability of the cell. To address these issues, existing technologies urgently need improvement. Summary of the Invention

[0003] The purpose of this application is to provide a method for improving the efficiency of BC battery by low-temperature boron diffusion oxidation, BC battery and photovoltaic system, so as to solve the above problems.

[0004] To achieve the above objectives, this application adopts the following technical solution: In a first aspect, this application provides a method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation, comprising: N-type monocrystalline silicon wafers with tunneling oxide layers and amorphous silicon layers are sequentially subjected to boron diffusion, gradient oxidation, UV-assisted acid polishing, and deposition of stacked passivation layers. The gradient oxidation is a two-stage oxidation process.

[0005] Optionally, the boron diffusion conditions are: introducing a first BCl3 and a pulse of O2, and reacting at a temperature of 780-820°C for 18-22 minutes.

[0006] Optionally, the flow rate of the first BCl3 is 280-320 sccm.

[0007] Optionally, the pulsed O2 has a flow rate of 750-1250 sccm and a duty cycle of 20-30%.

[0008] Optionally, the two-stage oxidation includes a first stage and a second stage: The first stage includes: introducing a mixture of first O2 and second BCl3 gases, and reacting at a temperature of 820-880℃ for 9-11 minutes; The second stage includes: introducing a second O2 and reacting at a temperature of 900°C for 4-6 minutes.

[0009] Optionally, in the first stage, the flow rate of the first O2 is 480-520 sccm; and the flow rate of the second BCl3 is 80-120 sccm.

[0010] Optionally, in the second stage, the flow rate of the second O2 is 750-1250 sccm.

[0011] Optionally, the UV-assisted acid polishing treatment time is 15-25 seconds.

[0012] Optionally, the acid polishing solution is a mixed solution of HF, HNO3, and H2O, and based on the total mass of the raw materials in the acid polishing solution being 100%, it includes: 10-14% HF, 30-38% HNO3, and 50-60% H2O.

[0013] Optionally, the ultraviolet wavelength is 280 nm, the photon energy is 4.43 eV, and the irradiation intensity is 40-60 mW / cm². 2 .

[0014] Optionally, the stacked passivation layer deposition includes sequential deposition of an AlOx layer, an AlN layer, and a SiNx layer.

[0015] Optionally, the AlOx layer is deposited using ALD under the following conditions: TEMAH precursor, TMA flow rate of 100-200 sccm, RF power of 145-155 W, and O2 ratio of 1-5%.

[0016] Optionally, the AlN layer is deposited by ICP under the following conditions: SiH4:NH3 = 1:6-10, Y2O3 doping 3-8wt%, and pressure 180-220 mTorr.

[0017] Optionally, the SiNx layer is deposited by PECVD under the following conditions: SiH4:NH3 = 1:3-5, and the bias voltage is -120~-180 V.

[0018] This application also provides a BC battery, the preparation method of which includes a boron diffusion low-temperature oxidation method for the BC battery.

[0019] Optionally, the BC cell includes a tunneling oxide layer, a boron-doped polycrystalline silicon layer, an AlOx layer, an AlN layer, and a SiNx layer arranged sequentially in the direction away from the N-type monocrystalline silicon wafer.

[0020] Optional: The thickness of the tunneling oxide layer is 1-2 nm; The thickness of the boron-doped polycrystalline silicon layer is 50-60 nm; The thickness of the AlOx layer is 2.5-3.5 nm; The thickness of the AlN layer is 1.5-2.5 nm; The thickness of the SiNx layer is 50-70 nm.

[0021] This application also provides a photovoltaic system including the BC cell.

[0022] Compared with the prior art, the beneficial effects of this application include: The method for improving the efficiency of BC batteries through boron diffusion and low-temperature oxidation provided in this application achieves the equivalent treatment effect at a lower temperature by employing a two-stage gradient oxidation process after boron diffusion, thus solving the problem of excessively high thermal budget associated with the single-stage high-temperature oxidation method in existing technologies. By introducing UV-assisted acid polishing, the synergy between UV-assisted acid polishing and the boron diffusion process shortens the acid polishing time while preserving the tunneling layer thickness and reducing carrier recombination losses. The synergy between the gradient passivation layer and the low-temperature oxidation process reduces thermal damage during low-temperature oxidation, and combined with the stress release of the AlN layer, it improves the integrity of the passivation layer, thereby reducing the interface state density.

[0023] This application effectively reduces the heat treatment temperature of the boron diffusion process, thereby reducing equipment heat load and energy consumption. The gradient oxidation process improves the uniformity of the doped layer concentration distribution, and UV-assisted treatment reduces the risk of damage to the tunneling oxide layer. The synergistic effect of the multilayer passivation structure enhances the interface passivation effect, improving the stability and photoelectric conversion efficiency of the battery. The optimized combination of process sequences achieves simultaneous improvement in process efficiency and battery performance while ensuring doping quality. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0025] Figure 1 This is a schematic diagram of the BC battery structure provided for an embodiment.

[0026] The main labeling information is as follows: 100-N-type monocrystalline silicon wafer; 101-tunneling oxide layer; 102-boron-doped polycrystalline silicon layer; 103-AlOx layer; 104-AlN layer; 105-SiNx layer. Detailed Implementation

[0027] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0028] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0029] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1–5” is disclosed, the described range should be interpreted as including ranges “1–4”, “1–3”, “1–2”, “1–2 and 4–5”, “1–3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0030] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0031] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has "a" parts by mass and component B has "b" parts by mass, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it can mean that the mass of component A is aK and the mass of component B is bK (where K is any number representing a multiplier). It is important to understand that, unlike parts by mass, the sum of the mass parts of all components is not limited to 100 parts.

[0032] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0033] In existing technologies, the boron diffusion process for back-contact crystalline silicon solar cells faces challenges such as excessive energy consumption and equipment damage due to high-temperature processing. It also suffers from technical bottlenecks including uneven boron doping concentration, damage to the tunneling oxide layer during acid polishing, and insufficient interface suppression capability of the passivation layer. These shortcomings limit the improvement of cell efficiency and make it difficult to guarantee process stability.

[0034] To address the aforementioned issues, regarding the energy consumption of high-temperature processes, we consider reducing the overall thermal budget by optimizing temperature control and time management in the oxidation process. For controlling boron doping uniformity, we explore a staged oxidation process combined with improved surface treatment techniques. To address the insufficient performance of the passivation layer, we investigate methods for constructing multilayer composite passivation structures. Through adjustments to the process sequence and optimization of parameters, we aim to improve process efficiency while maintaining doping effectiveness.

[0035] Therefore, this application proposes a technical solution including boron diffusion treatment after the deposition of a tunnel oxide layer and an amorphous silicon layer. The treatment process includes a combination of boron diffusion, gradient oxidation, UV-assisted acid polishing and stacked passivation layer deposition, wherein the gradient oxidation adopts a two-stage oxidation process.

[0036] Among these processes, tunneling oxide layer refers to an ultrathin insulating dielectric layer formed on the silicon wafer surface, which can be achieved using thermal oxidation or chemical vapor deposition (CVD) to enable selective carrier transport. Amorphous silicon layer deposition refers to the formation of an amorphous silicon thin film on the surface of the tunneling oxide layer, which can be achieved using plasma-enhanced chemical vapor deposition (PECVD) as a carrier layer for boron doping. Gradient oxidation refers to a thermal treatment process that controls oxidation conditions in stages, which can be achieved using a two-stage program with different temperatures and gas ratios to progressively control the doping concentration distribution. UV-assisted acid polishing refers to introducing UV irradiation during acid polishing, which can be achieved using synchronous irradiation with a specific wavelength UV light source to selectively remove surface defect layers. Stacked passivation layer deposition refers to the continuous deposition of multiple dielectric thin films, which can be achieved using a combination of atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD) to construct composite passivation structures. A two-stage oxidation program refers to dividing the oxidation process into continuous processing stages with different parameters, which can be achieved using a segmented control method of first low temperature and then high temperature to optimize oxide layer quality and doping distribution.

[0037] Specifically, after forming a tunneling oxide layer and an amorphous silicon layer sequentially on the silicon wafer surface, boron doping is first performed to form a P-type region. Then, the doped layer is oxidized through a two-stage gradient oxidation process. In the gradient oxidation process, the first stage uses relatively low temperatures to achieve uniform oxidation, while the second stage uses high temperatures to complete the densification process. Subsequently, a UV-assisted acid polishing process is used to refine the surface, and finally, a multilayer composite passivation structure is deposited. This process combination controls the oxidation conditions in stages, ensuring doping quality while reducing the overall process temperature. The UV-assisted treatment effectively reduces damage to the tunneling oxide layer, and the multilayer passivation structure enhances the interface passivation effect.

[0038] Therefore, this application provides a method for improving the efficiency of BC battery by low-temperature boron diffusion oxidation, comprising: N-type monocrystalline silicon wafers with tunneling oxide layers and amorphous silicon layers are sequentially subjected to boron diffusion, gradient oxidation, UV-assisted acid polishing, and deposition of stacked passivation layers. The gradient oxidation is a two-stage oxidation process.

[0039] In an optional embodiment, the boron diffusion conditions are: introducing a first BCl3 and a pulse of O2, and reacting at a temperature of 780-820°C for 18-22 minutes.

[0040] Optionally, the reaction temperature for boron diffusion can be 780℃, 785℃, 790℃, 795℃, 800℃, 805℃, 810℃, 815℃, 820℃, or any value between 780℃ and 820℃; the reaction time for boron diffusion can be 18 min, 19 min, 20 min, 21 min, 22 min, or any value between 18 min and 22 min.

[0041] In an optional implementation, the flow rate of the first BCl3 is 280-320 sccm.

[0042] Optionally, the flow rate of the first BCl3 can be 280 sccm, 285 sccm, 290 sccm, 295 sccm, 300 sccm, 305 sccm, 310 sccm, 315 sccm, 320 sccm, or any value between 280 and 320 sccm.

[0043] In one optional implementation, the pulsed O2 flow rate is 750-1250 sccm and the duty cycle is 20-30%.

[0044] Optionally, the pulsed O2 flow rate can be 750 sccm, 800 sccm, 850 sccm, 900 sccm, 950 sccm, 1000 sccm, 1050 sccm, 1100 sccm, 1150 sccm, 1200 sccm, 1250 sccm, or any value between 750 and 1250 sccm; the duty cycle can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or any value between 20 and 30%.

[0045] In this process, the first BCl3 refers to the boron source gas, which can be achieved by mixing boron trichloride gas with a carrier gas. The boron doping concentration is controlled by adjusting the gas flow rate. Pulsed O2 refers to the intermittent introduction of oxygen, which can be achieved by periodically opening and closing gas valves. The oxidation rate is controlled by adjusting the pulse frequency and duty cycle. The temperature of 800℃ refers to the process temperature during the boron diffusion stage, which can be achieved using a tube furnace. This reduces the thermal budget by lowering the traditional process temperature. Furthermore, the time is optimized to balance the doping depth and defect density.

[0046] Specifically, during boron diffusion, boron trichloride gas, carried by a carrier gas, enters the reaction chamber and reacts with pulsed oxygen on the silicon wafer surface. By controlling the temperature at 800℃, the thermal load on the equipment from traditional high-temperature processes can be reduced, while simultaneously slowing down the boron atom diffusion rate. The intermittent pulsed oxygen introduction periodically creates an oxidizing atmosphere, inhibiting the overgrowth of the borosilicate glass layer. By controlling the reaction time, sufficient boron atom diffusion depth is ensured while avoiding lattice damage caused by prolonged high-temperature processing.

[0047] Through the aforementioned technical features, this application effectively reduces the energy consumption level of the boron diffusion process and minimizes the wear and tear on production equipment caused by high temperatures. The introduction of pulsed oxygen improves the uniformity of the boron doping layer concentration distribution, avoiding the risks associated with subsequent acid polishing processes due to excessively high surface concentration. The optimized reaction time window reduces the probability of lattice defect generation while ensuring the doping effect.

[0048] In an optional implementation, the two-stage oxidation includes a first stage and a second stage: The first stage includes: introducing a mixture of first O2 and second BCl3 gases, and reacting at a temperature of 820-880℃ for 9-11 minutes.

[0049] Optionally, the temperature of the first stage can be 820℃, 825℃, 830℃, 835℃, 834℃, 845℃, 850℃, 855℃, 860℃, 865℃, 870℃, 875℃, 880℃, or any value between 820℃ and 880℃; the reaction time can be 9 min, 10 min, 11 min, or any value between 9 and 11 min.

[0050] The second stage includes: introducing a second O2 and reacting at 900℃ for 4-6 minutes.

[0051] Optionally, the temperature of the second stage can be 900℃; the reaction time can be 4 min, 5 min, 6 min, or any value between 4 and 6 min.

[0052] Two-stage oxidation refers to dividing the oxidation process into two temperature stages, which can be achieved using different gas combinations and temperature gradients. The quality of the oxide layer is optimized by controlling the reaction conditions in each stage. The first stage involves introducing a mixture of oxygen and boron trichloride at a lower temperature. This mixture promotes boron atom diffusion and the initial formation of the oxide layer, while also slowing down the oxidation rate to avoid interface defects. The second stage involves introducing pure oxygen at a higher temperature. This high-temperature, pure oxygen environment accelerates the densification of the oxide layer, while the temperature gradient reduces the high-temperature exposure time.

[0053] Specifically, in the oxidation process, a mixture of oxygen and boron trichloride is first introduced at 850℃ to react. The boron trichloride in the mixture inhibits the oxidation rate, allowing boron atoms to diffuse uniformly on the silicon wafer surface and form a preliminary oxide layer. Subsequently, the temperature is raised to 900℃, and pure oxygen is introduced for rapid oxidation. This high-temperature environment promotes the densification of the oxide layer while shortening the high-temperature processing time. By controlling the gas composition and temperature in stages, the overall process temperature is reduced, while lattice damage caused by a single high-temperature environment is avoided.

[0054] Through the above-mentioned technical features, this application can reduce the overall temperature and equipment heat load of the boron diffusion process, reduce silicon wafer lattice defects caused by high temperature, and form a more uniform doped layer through staged oxidation, avoiding excessive erosion of the tunneling oxide layer by the acid polishing process, thereby improving the passivation effect of the battery interface and the photoelectric conversion efficiency.

[0055] In an optional implementation, during the first stage, the flow rate of the first O2 is 480-520 sccm; and the flow rate of the second BCl3 is 80-120 sccm.

[0056] Optionally, the flow rate of the first O2 can be 480 sccm, 485 sccm, 490 sccm, 495 sccm, 500 sccm, 505 sccm, 510 sccm, 515 sccm, 520 sccm, or any value between 480 and 520 sccm; the flow rate of the second BCl3 can be 80 sccm, 85 sccm, 90 sccm, 95 sccm, 100 sccm, 105 sccm, 110 sccm, 115 sccm, 120 sccm, or any value between 80 and 120 sccm.

[0057] In an optional implementation, during the second stage, the flow rate of the second O2 is 750-1250 sccm.

[0058] Optionally, the flow rate of the second O2 can be 750 sccm, 800 sccm, 850 sccm, 900 sccm, 950 sccm, 1000 sccm, 1050 sccm, 1100 sccm, 1150 sccm, 1200 sccm, 1250 sccm, or any value between 750 and 1250 sccm.

[0059] Specifically, in the low-temperature oxidation process, the first stage involves a reaction using a mixture of oxygen at 480-520 sccm and BCl3 at 80-120 sccm. Precise control of the gas ratio ensures a gradient distribution of boron atoms during oxide film formation. Subsequently, in the second stage, the oxygen flow rate is increased to 750-1250 sccm for high-temperature oxidation, promoting structural rearrangement within the oxide layer and eliminating interface defects. This synergistic control of the gas flow rates in both stages allows the oxidation reaction to be completed at a relatively low temperature, while avoiding uneven doping caused by excessively high local concentrations.

[0060] Through the above technical features, the overall thermal budget of the oxidation process can be effectively reduced, the number of interfacial recombination centers can be reduced while maintaining the uniformity of boron doping, and the adhesion performance of the subsequent passivation layer can be improved by optimizing the oxide layer structure, ultimately achieving a stable improvement in battery conversion efficiency.

[0061] In one optional embodiment, the UV-assisted acid polishing treatment time is 15-25 seconds.

[0062] Optionally, the UV-assisted acid polishing treatment time can be 15s, 16s, 17s, 18s, 19s, 20s, 21s, 22s, 23s, 24s, 25s, or any value between 15 and 25s.

[0063] In one optional embodiment, the acid polishing solution is a mixed solution of HF, HNO3, and H2O, wherein the mixing ratio of HF, HNO3, and H2O is 10-14:30-38:50-60.

[0064] Optionally, based on the total mass of the raw materials in the acid polishing solution as 100%, the amount of HF can be 10%, 11%, 12%, 13%, 14%, or any value between 10% and 14%; the amount of HNO3 can be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, or any value between 30% and 38%; and the amount of H2O can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, or any value between 50% and 60%.

[0065] In one optional implementation, the ultraviolet wavelength is 280 nm, the photon energy is 4.43 eV, and the irradiation intensity is 40-60 mW / cm². 2 .

[0066] Optionally, the irradiation intensity can be 40 mW / cm². 2 41 mW / cm 2 42 mW / cm 243 mW / cm 2 44 mW / cm 2 45 mW / cm 2 46 mW / cm 2 47 mW / cm 2 48 mW / cm 2 49 mW / cm 2 50 mW / cm 2 51 mW / cm 2 52 mW / cm 2 53 mW / cm 2 54 mW / cm 2 55 mW / cm 2 56 mW / cm 2 57 mW / cm 2 58 mW / cm 2 59 mW / cm 2 60 mW / cm 2 Or 40-60 mW / cm 2 Any value between.

[0067] Among them, UV-assisted acid polishing refers to the simultaneous application of UV light irradiation of a specific wavelength during the acid polishing process. Specifically, a 280nm wavelength UV light source combined with an irradiation intensity of 50mW / cm² can be used. 2 The parameters are configured to achieve this, and the photon energy in this band can excite the active groups in the acid solution. The acid polishing solution mixing ratio refers to the volume ratio of hydrofluoric acid, nitric acid, and deionized water, specifically a 12:38:50 ratio, which can balance the corrosion rate of the silicon wafer surface and the passivation layer protection requirements.

[0068] Specifically, within a 20-second processing time, ultraviolet irradiation increases the concentration of active particles in the acid solution, accelerating the selective etching of the borosilicate glass layer. Under ultraviolet excitation, the mixed acid solution forms hydroxyl radicals, which preferentially react with borosilicates, reducing the erosion of the tunneling oxide layer. It can also activate nitric acid molecules in the acid solution, causing them to decompose and generate oxidizing free radicals, thereby enhancing the etching efficiency for surface defects in the boron-doped layer.

[0069] Through the aforementioned technical features, the technical solution of this application can suppress excessive erosion of the tunneling oxide layer by the acid polishing process and maintain the quality of interface passivation. The active groups generated by ultraviolet-assisted irradiation can selectively remove the borosilicate glass layer without damaging the underlying structure, while specific wavelength irradiation can enhance the UV aging resistance of the subsequent passivation layer.

[0070] In an optional embodiment, the stacked passivation layer deposition includes sequential deposition of an AlOx layer, an AlN layer, and a SiNx layer.

[0071] In an optional implementation, the AlOx layer is deposited using ALD under the following conditions: TEMAH precursor, TMA flow rate of 100-200 sccm, RF power of 145-155 W, and O2 ratio of 1-5%.

[0072] Optionally, during ALD deposition, the TMA flow rate can be 100 sccm, 110 sccm, 120 sccm, 130 sccm, 140 sccm, 150 sccm, 160 sccm, 170 sccm, 180 sccm, 190 sccm, 200 sccm, or any value between 100 and 200 sccm; the RF power can be 145 W, 146 W, 147 W, 148 W, 149 W, 150 W, 151 W, 152 W, 153 W, 154 W, 155 W, or any value between 145 and 155 W.

[0073] The AlN layer was deposited by ICP under the following conditions: SiH4:NH3 = 1:6-10, Y2O3 doping 3-8wt%, and pressure 180-220mTorr.

[0074] Optionally, during the IPC deposition process, the SiH4:NH3 ratio can be 1:6, 1:7, 1:8, 1:9, 1:10, or any value between 1:6 and 10; the Y2O3 doping amount can be 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, or any value between 3 and 8wt%; the pressure can be 180 mTorr, 185 mTorr, 190 mTorr, 195 mTorr, 200 mTorr, 205 mTorr, 210 mTorr, 215 mTorr, 220 mTorr, or any value between 180 and 220 mTorr.

[0075] The SiNx layer was deposited using PECVD under the following conditions: SiH4:NH3 = 1:3-5, and the bias voltage was -120~-180V.

[0076] Optionally, during the PECVD deposition process, the SiH4:NH3 mixing ratio can be 1:3, 1:4, 1:5, or any value between 1:3 and 5; the bias voltage can be -120V, -125V, -130V, -135V, -140V, -145V, -150V, -155V, -160V, -165V, -170V, -175V, -180V, or any value between -120V and -180V.

[0077] Specifically, after boron diffusion and acid polishing, a multilayer passivation structure was constructed sequentially using three different deposition techniques: ALD, ICP, and PECVD. First, an ultrathin AlOx layer was formed at low temperature using the ALD process. Precise control of the precursor ratio and RF power ensured the formation of a dense, pinhole-free film, effectively covering surface defects in the boron diffusion region. Next, a Y2O3-doped AlN layer was deposited using the ICP process. By adjusting the reactant gas ratio and chamber pressure, a high-dielectric-constant intermediate layer was formed to enhance the field passivation effect. Finally, a thick SiNx layer was deposited using the PECVD process. The film stress state was controlled using a bias voltage to form a protective layer with both anti-reflection and anti-UV properties. The synergistic effect of the three-layer structure achieved a comprehensive improvement in interface state suppression, carrier transport optimization, and long-term stability.

[0078] Through the aforementioned technical features, this application effectively reduces the interfacial recombination rate in the boron diffusion region, enhances the passivation layer's ability to confine charge carriers, and significantly improves the stability of the passivation structure in the ultraviolet band. The bandgap matching of the three-layer material optimizes the charge carrier transport path, and the introduction of Y2O3 doping and bias voltage further strengthens the dielectric properties and mechanical strength of the thin film, thereby achieving simultaneous improvement in battery efficiency and reliability while maintaining process compatibility.

[0079] Secondly, this application also provides a BC battery, the preparation method of which is the boron diffusion low-temperature oxidation method for the BC battery described above.

[0080] In an optional embodiment, the BC cell includes, in the direction away from the N-type monocrystalline silicon wafer, a tunneling oxide layer, a boron-doped polycrystalline silicon layer, an AlOx layer, an AlN layer, and a SiNx layer arranged sequentially.

[0081] The thickness of the tunneling oxide layer is 1-2 nm.

[0082] Optionally, the thickness of the tunneling oxide layer can be 1 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm, 2 nm, or any value between 1 and 2 nm.

[0083] The thickness of the boron-doped polycrystalline silicon layer is 50-60 nm.

[0084] Optionally, the thickness of the boron-doped polycrystalline silicon layer can be 50 nm, 51 nm, 52 nm, 53 nm, 54 nm, 55 nm, 56 nm, 57 nm, 58 nm, 59 nm, 60 nm, or any value between 50 and 60 nm.

[0085] The thickness of the AlOx layer is 2.5-3.5 nm.

[0086] Optionally, the thickness of the AlOx layer is 2.5 nm, 2.6 nm, 2.7 nm, 2.8 nm, 2.9 nm, 3 nm, 3.1 nm, 3.2 nm, 3.3 nm, 3.4 nm, 3.5 nm, or any value between 2.5 and 3.5 nm.

[0087] The thickness of the AlN layer is 1.5-2.5 nm.

[0088] Optionally, the thickness of the AlN layer can be 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2 nm, 2.1 nm, 2.2 nm, 2.3 nm, 2.4 nm, 2.5 nm, or any value between 1.5 and 2.5 nm.

[0089] The thickness of the SiNx layer is 50-70 nm.

[0090] Optionally, the thickness of the SiNx layer can be 50 nm, 55 nm, 60 nm, 65 nm, or 70 nm, with the thickness being any value between 50 and 70 nm.

[0091] Through the above technical solutions, this application solves the problems of high interfacial recombination rate and insufficient UV resistance in existing passivation layers. Specifically, the synergistic thickness reduction of the AlOx and AlN layers decreases the interfacial state density and reduces the recombination rate; the optimized SiNx layer thickness reduces the UV transmittance to below 20% while improving the visible light transmittance. Precise matching of the thicknesses of each layer also avoids film cracking caused by stress mismatch, thus ensuring the long-term reliability of the battery.

[0092] Thirdly, this application also provides a photovoltaic system including the BC battery.

[0093] Through the above technical solutions, this application effectively reduces the energy consumption and equipment wear of the boron diffusion process and solves the problem of energy waste caused by high-temperature oxidation; through the synergistic effect of UV-assisted acid polishing and gradient oxidation, it avoids tunneling layer damage and improves doping uniformity; through the design of stacked passivation layers, it significantly reduces the interface recombination rate and enhances the resistance to UV radiation, thereby improving the long-term stability and photoelectric conversion efficiency of the photovoltaic system.

[0094] The specific method for preparing the BC battery provided in this application is as follows: S1: Silicon wafer pretreatment: N-type monocrystalline silicon wafers (resistivity 1-3 Ω·cm, thickness 130μm) are selected, and surface contaminants are removed using the RCA standard cleaning method.

[0095] S2: Deposition of tunneling oxide layer and amorphous silicon layer: Tunneling oxide layer: A SiOx layer with a thickness of 1.5 nm and a refractive index of 1.95 was deposited by PECVD.

[0096] Amorphous silicon layer: An intrinsic amorphous silicon layer with a thickness of 25nm was deposited using LPCVD.

[0097] S3: Boron diffusion.

[0098] S4: Low-temperature gradient oxidation.

[0099] S5: UV-assisted acid polishing.

[0100] S6: Deposition of stacked passivation layers.

[0101] S7: Metallization and Laser Grooving: Metal grid lines: screen-printed Ag back field (30 μm line width) and Al grid lines (50 μm line width), co-sintered at 780℃.

[0102] Laser grooving: wavelength 1064 nm, energy density 1.0 J / cm² 2 The etching depth penetrates the passivation layer to the silicon substrate.

[0103] S8: IV test.

[0104] The following examples and comparative examples are all implemented on N-type monocrystalline silicon wafers that have a tunneling oxide layer and an amorphous silicon layer after step S2.

[0105] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0106] Example 1 This embodiment provides a method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation: the specific steps are as follows. (1) Boron diffusion: BCl3 (flow rate of 300 sccm) and pulsed O2 (flow rate of 800 sccm, duty cycle of 25%) were introduced into a tube furnace by PECVD and diffused at 800℃ for 20 minutes.

[0107] (2) Low-temperature gradient oxidation: First stage: Oxidation was carried out in a tube furnace using the PECVD method with a flow rate of 500 sccm for O2 and 100 sccm for BCl3, and the oxidation was carried out at 850℃ for 10 minutes.

[0108] Second stage: Pure O2 at a flow rate of 1000 sccm is introduced into a tube furnace using the PECVD method, and the temperature is raised to 900℃ for 5 minutes for oxidation.

[0109] (3) UV-assisted acid polishing: The silicon wafers that have undergone gradient oxidation are treated by combining acid polishing solution with UV irradiation, wherein the wavelength of UV irradiation is 280 nm and the irradiation intensity is 50 mW / cm. 2 The processing time was 20 seconds, removing the BSG layer to a thickness of <3nm. The acid polishing solution formulation was: HF 12 vol%, HNO3 38 vol%, H2O 50 vol%.

[0110] (4) Deposition of stacked passivation layers: AlOx layer 103: ALD deposition (TEMAH precursor, RF power 150 W, TMA content 150 sccm, O2 ratio 3%).

[0111] AlN layer 104: ICP deposition (SiH4:NH3=1:8, Y2O3 doping 5wt%, pressure 200 mTorr).

[0112] SiNx layer 105: PECVD deposition (SiH4:NH3=1:4, bias voltage -150V).

[0113] This embodiment also provides a BC battery, the fabrication process of which is as described above. The BC battery is fabricated from the N-type monocrystalline silicon wafer 100 in the direction away from the N-type monocrystalline silicon wafer 100 as follows: Tunneling oxide layer 101: 1 nm thick; Boron-doped polycrystalline silicon layer 102: 55 nm thick; AlOx layer 103: thickness is 3nm; AlN layer 104: thickness is 2nm; SiNx layer 105: thickness is 60nm.

[0114] Example 2 This embodiment provides a method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation: the specific steps are as follows. (1) Boron diffusion: BCl3 (flow rate of 280 sccm) and pulsed O2 (flow rate of 780 sccm, duty cycle of 25%) were introduced into a tube furnace and diffused at 800°C for 18 minutes.

[0115] (2) Low-temperature gradient oxidation: First stage: O2 with a flow rate of 480 sccm and BCl3 with a flow rate of 80 sccm were introduced into a tube furnace using the PECVD method, and oxidation was carried out at 850℃ for 9 minutes.

[0116] Second stage: Pure O2 at a flow rate of 750 sccm is introduced into a tube furnace using the PECVD method, and the temperature is raised to 900℃ for 4 minutes for oxidation.

[0117] (3) UV-assisted acid polishing: The silicon wafers that have undergone gradient oxidation are treated by combining acid polishing solution with UV irradiation, wherein the wavelength of UV irradiation is 280 nm and the irradiation intensity is 50 mW / cm. 2 The processing time was 20 seconds, removing the BSG layer to a thickness of <3nm. The acid polishing solution formulation was: HF 12 vol%, HNO3 38 vol%, H2O 50 vol%.

[0118] (4) Deposition of stacked passivation layers: AlOx layer 103: ALD deposition (TEMAH precursor, RF power 145 W, O2 ratio 3%).

[0119] AlN layer 104: ICP deposition (SiH4:NH3=1:6, Y2O3 doping 5wt%, pressure 180 mTorr).

[0120] SiNx layer 105: PECVD deposition (SiH4:NH3=1:3, bias voltage -150V).

[0121] This embodiment also provides a BC battery, the fabrication process of which is as described above. The BC battery is fabricated from the N-type monocrystalline silicon wafer 100 in the direction away from the N-type monocrystalline silicon wafer 100 as follows: Tunneling oxide layer 101: 1 nm thick; Boron-doped polycrystalline silicon layer 102: 50 nm thick; AlOx layer 103: thickness is 2.5nm; AlN layer 104: thickness is 1.5nm; SiNx layer 105: thickness is 50nm.

[0122] Example 3 This embodiment provides a method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation: the specific steps are as follows. (1) Boron diffusion: BCl3 (flow rate 320 sccm) and pulsed O2 (flow rate 1250 sccm, duty cycle 25%) were introduced and diffused at 800℃ for 22 minutes.

[0123] (2) Low-temperature gradient oxidation: First stage: O2 with a flow rate of 520 sccm and BCl3 with a flow rate of 120 sccm were introduced into a tube furnace using the PECVD method, and oxidation was carried out at 850℃ for 11 minutes.

[0124] Second stage: Pure O2 at a flow rate of 1250 sccm is introduced into a tube furnace using the PECVD method, and the temperature is raised to 900℃ for 6 minutes for oxidation.

[0125] (3) UV-assisted acid polishing: The silicon wafers that have undergone gradient oxidation are treated by combining acid polishing solution with UV irradiation, wherein the wavelength of UV irradiation is 280 nm and the irradiation intensity is 50 mW / cm. 2 The processing time was 20 seconds, removing the BSG layer to a thickness of <3nm. The acid polishing solution formulation was: HF 12 vol%, HNO3 38 vol%, H2O 50 vol%.

[0126] (4) Deposition of stacked passivation layers: AlOx layer 103: ALD deposition (TEMAH precursor, RF power 155 W, O2 ratio 3%).

[0127] AlN layer 104: ICP deposition (SiH4:NH3=1:10, Y2O3 doping 5wt%, pressure 220 mTorr).

[0128] SiNx layer 105: PECVD deposition (SiH4:NH3=1:5, bias voltage -150V).

[0129] This embodiment also provides a BC battery, the fabrication process of which is as described above. The BC battery is fabricated from the N-type monocrystalline silicon wafer 100 in the direction away from the N-type monocrystalline silicon wafer 100 as follows: Tunneling oxide layer 101: 2 nm thick; Boron-doped polycrystalline silicon layer 102: 60 nm thick; AlOx layer 103: thickness is 3.5nm; AlN layer 104: thickness is 2.5nm; SiNx layer 105: thickness is 70nm.

[0130] Comparative Example 1 This comparative example provides a conventional BC battery fabrication process, including conventional boron diffusion, oxidation, and passivation processes. The specific steps are as follows: (1) Silicon wafer pretreatment: N-type single crystal silicon wafers (resistivity 1-3Ω·cm, thickness 130μm) were selected, and surface contaminants were removed by RCA standard cleaning method.

[0131] (2) Deposition of tunneling oxide layer and amorphous silicon layer: Tunneling layer: A SiOx layer with a thickness of 1.5 nm and a refractive index of 1.95 was deposited by PECVD.

[0132] Amorphous silicon layer: An intrinsic amorphous silicon layer with a thickness of 25nm (20-30nm) is deposited using LPCVD.

[0133] (3) Boron diffusion: BCl3 flow rate of 500 sccm and pulsed O2 flow rate of 1500 sccm were introduced, with a duty cycle of 30%, and diffusion was carried out at 910℃ for 25 minutes. The temperature was then raised to 1010℃, and pure O2 flow rate of 3000 sccm was used for oxidation for 20 minutes.

[0134] (4) Graphicalization: Selective printing of the BSG area is performed using a green laser 45W.

[0135] (5) Pickling: The pickling solution is HF 30%, HNO3 20%, H2O 50%, and the pickling time is 30 seconds to remove the BSG dead layer.

[0136] (6) Deposited passivation layer: AlOx layer: 5 nm deposited using conventional ALD method.

[0137] SiNx layer: 75nm deposited using conventional PECVD method.

[0138] (7) Metallization sintering: screen printing Ag back field (line width 30μm) and Al grid line (line width 50μm), co-sintering temperature 780℃.

[0139] This comparative example also provides a BC battery, with the structure as follows: Figure 1 As shown, its fabrication process is as described above. The BC cell proceeds sequentially from the N-type monocrystalline silicon wafer towards the direction away from the N-type monocrystalline silicon wafer: Tunneling oxide layer: 1.5 nm thick; Boron-doped polycrystalline silicon layer: 100 nm thick; AlOx layer: 5nm thick; SiNx layer: 75nm thick.

[0140] Comparative Example 2 This comparative example provides a method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation: the specific steps are as follows. This embodiment provides a method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation: the specific steps are as follows. (1) Boron diffusion: BCl3 (flow rate of 300 sccm) and pulsed O2 (flow rate of 800 sccm, duty cycle of 25%) were introduced into a tube furnace and diffused at 800℃ for 20 minutes.

[0141] (2) High-temperature oxidation: Pure O2 with a flow rate of 1000 sccm was introduced by PECVD and the temperature was raised to 900℃ for 5 minutes.

[0142] (3) UV-assisted acid polishing: The silicon wafers that have undergone gradient oxidation are treated by combining acid polishing solution with UV irradiation, wherein the wavelength of UV irradiation is 280 nm and the irradiation intensity is 50 mW / cm. 2 The processing time was 20 seconds, removing the BSG layer to a thickness of <3nm. The acid polishing solution formulation was: HF 12 vol%, HNO3 38 vol%, H2O 50 vol%.

[0143] (4) Deposition of stacked passivation layers: AlOx layer: ALD deposition (TEMAH precursor, RF power 150 W, O2 ratio 3%).

[0144] AlN layer: ICP deposition (SiH4:NH3=1:8, Y2O3 doping 5wt%, pressure 200 mTorr).

[0145] SiNx layer: PECVD deposition (SiH4:NH3=1:4, bias voltage -150V).

[0146] This embodiment also provides a BC battery, the fabrication process of which is as described above. The BC battery is prepared by moving from the N-type monocrystalline silicon wafer away from the N-type monocrystalline silicon wafer in the following order: The thickness of the tunneling oxide layer is 1 nm; The thickness of the boron-doped polycrystalline silicon layer is 40 nm; The AlOx layer has a thickness of 3 nm; The thickness of the AlN layer is 2 nm; The SiNx layer has a thickness of 60 nm.

[0147] Comparative Example 3 This embodiment provides a method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation: the specific steps are as follows. This embodiment provides a method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation: the specific steps are as follows. (1) Boron diffusion: BCl3 (flow rate of 300 sccm) and pulsed O2 (flow rate of 800 sccm, duty cycle of 25%) were introduced and diffused at 800℃ for 20 minutes.

[0148] (2) Low-temperature gradient oxidation: First stage: Introduce O2 at a flow rate of 500 sccm and BCl3 at a flow rate of 100 sccm, and oxidize at 850℃ for 10 minutes.

[0149] Second stage: Introduce 1000 sccm of pure O2 and heat to 900℃ for 5 minutes for oxidation.

[0150] (3) Acid polishing: The silicon wafer that has undergone gradient oxidation is treated with acid polishing solution to remove the BSG layer to a thickness of <3nm. The acid polishing solution formula is: HF 12 vol%, HNO3 38 vol%, H2O 50 vol%.

[0151] (4) Deposition of stacked passivation layers: AlOx layer: ALD deposition (TEMAH precursor, RF power 150 W, O2 ratio 3%).

[0152] AlN layer: ICP deposition (SiH4:NH3=1:8, Y2O3 doping 5wt%, pressure 200 mTorr).

[0153] SiNx layer: PECVD deposition (SiH4:NH3=1:4, bias voltage -150V).

[0154] This embodiment also provides a BC battery, the fabrication process of which is as described above. The BC battery is prepared by moving from the N-type monocrystalline silicon wafer away from the N-type monocrystalline silicon wafer in the following order: The thickness of the tunneling oxide layer is 1 nm; The thickness of the boron-doped polycrystalline silicon layer is 85 nm; The AlOx layer has a thickness of 3 nm; The thickness of the AlN layer is 2 nm; The SiNx layer has a thickness of 60 nm.

[0155] Comparative Example 4 This embodiment provides a method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation: the specific steps are as follows. This embodiment provides a method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation: the specific steps are as follows. (1) Boron diffusion: BCl3 (flow rate of 300 sccm) and pulsed O2 (flow rate of 800 sccm, duty cycle of 25%) were introduced and diffused at 800℃ for 20 minutes.

[0156] (2) Low-temperature gradient oxidation: First stage: Introduce O2 at a flow rate of 500 sccm and BCl3 at a flow rate of 100 sccm, and oxidize at 850℃ for 10 minutes.

[0157] Second stage: Introduce 1000 sccm of pure O2 and heat to 900℃ for 5 minutes for oxidation.

[0158] (3) UV-assisted acid polishing: The silicon wafers that have undergone gradient oxidation are treated by combining acid polishing solution with UV irradiation, wherein the wavelength of UV irradiation is 280 nm and the irradiation intensity is 50 mW / cm. 2The processing time was 20 seconds, removing the BSG layer to a thickness of <3nm. The acid polishing solution formulation was: HF 12 vol%, HNO3 38 vol%, H2O 50 vol%.

[0159] (4) Deposition of stacked passivation layers: AlOx layer: ALD deposition (TEMAH precursor, RF power 150 W, O2 ratio 3%).

[0160] SiNx layer: PECVD deposition (SiH4:NH3=1:4, bias voltage -150V).

[0161] This embodiment also provides a BC battery, the fabrication process of which is as described above. The BC battery is prepared by moving from the N-type monocrystalline silicon wafer away from the N-type monocrystalline silicon wafer in the following order: The thickness of the tunneling oxide layer is 1 nm; The thickness of the boron-doped polycrystalline silicon layer is 25 nm; The AlOx layer has a thickness of 3 nm; The SiNx layer has a thickness of 60 nm.

[0162] The BC batteries provided in the above embodiments and comparative examples were subjected to IV tests, and the test results are shown in Table 1.

[0163] Table 1 IV Test Results

[0164] As shown in Table 1: In different embodiments, the conversion efficiencies (Eta) of the BC cells prepared by the technical solution of this application are 25.67%, 25.66%, and 25.65%, respectively. Compared with the BC cells prepared by conventional methods, the conversion efficiency is 25.25%, indicating that the technical solution provided by this application has a higher power generation per unit area and a higher power output of the photovoltaic modules. It also has a lower system cost compared to the BC cells prepared by conventional methods. Compared with Comparative Examples 2-4, whose preparation methods employ conventional high-temperature oxidation, conventional acid polishing, and conventional passivation layer setups, the conversion efficiencies of these methods are all lower than those of the technical solution provided by this application. This means that the technical solution provided by this application improves the conversion efficiency of the prepared BC cells to varying degrees through the synergistic effect of low-temperature gradient oxidation, UV-assisted acid washing, and stacked passivation layers. The BC cells prepared by the technical solution of this application have a higher open-circuit voltage (Uoc), indicating that they can support lower current transmission, reduce line loss, and mitigate voltage decay caused by temperature increases. The higher short-circuit current (Isc) compared to the comparative schemes indicates that the BC cell prepared by the method of this application can improve the maximum output power and maintain a high current output even under low irradiance. The lower overall fill factor (FF) indicates that the BC cell prepared by the comparative schemes exhibits low series resistance and high parallel resistance in practical applications, while the technical solution provided by this application is beneficial for reducing carrier transport losses.

[0165] In summary, this application utilizes the synergy of a gradient passivation layer and a low-temperature oxidation process. Low-temperature oxidation reduces thermal damage, and combined with stress release in the AlN layer, it enhances the integrity of the passivation layer, thereby increasing the interface state density from 1.2 × 10⁻⁶. 10 Reduced to 3.8×10 9 cm -2 ·eV -1 By synergistically combining UV-assisted acid polishing with boron diffusion, the acid polishing time was reduced from 30 seconds to 20 seconds, and the plating removal rate was increased from 95% to 99%, while preserving the tunneling layer thickness and reducing carrier recombination losses. Through the synergy of doped Y₂O₃ wt. 5% and a gradient passivation layer, the minority carrier lifetime was increased from 2200 μs to 3100 μs, and the open-circuit voltage (Voc) increased from 732 mV to 745 mV. Through the synergy of low-temperature gradient oxidation and UV acid polishing, the reflectivity was reduced from 3.8% to 2.1% (optimized to 16%), while also reducing the corrosion of the tunneling layer by the acid polishing solution.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0167] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, in the foregoing claims, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation, characterized in that, include: N-type monocrystalline silicon wafers with tunneling oxide layers and amorphous silicon layers are sequentially subjected to boron diffusion, gradient oxidation, UV-assisted acid polishing, and deposition of stacked passivation layers. The gradient oxidation is a two-stage oxidation process.

2. The method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation according to claim 1, characterized in that, The conditions for boron diffusion are: introducing a first BCl3 and a pulse of O2, and reacting at a temperature of 780-820℃ for 18-22 minutes.

3. The method for improving the efficiency of BC batteries through low-temperature boron diffusion oxidation according to claim 2, characterized in that, At least one of the following conditions must be met: A. The flow rate of the first BCl3 is 280-320 sccm; B. The flow rate of the pulsed O2 is 750-1250 sccm, and the duty cycle is 20-30%.

4. The method for improving the efficiency of BC battery by low-temperature oxidation with boron diffusion according to claim 1, characterized in that, The two-stage oxidation process includes a first stage and a second stage: The first stage includes: introducing a mixture of first O2 and second BCl3 gases, and reacting at a temperature of 820-880℃ for 9-11 minutes; The second stage includes: introducing a second O2 and reacting at a temperature of 900°C for 4-6 minutes.

5. The method for improving the efficiency of BC battery by low-temperature oxidation with boron diffusion according to claim 4, characterized in that, At least one of the following conditions must be met: C. In the first stage, the flow rate of the first O2 is 480-520 sccm; the flow rate of the second BCl3 is 80-120 sccm; D. In the second stage, the flow rate of the second O2 is 750-1250 sccm.

6. The method for improving the efficiency of BC battery by low-temperature oxidation with boron diffusion according to claim 1, characterized in that, The UV-assisted acid polishing treatment time is 15-25 seconds, and meets at least one of the following conditions: E. The acid polishing solution is a mixed solution of HF, HNO3, and H2O, and based on the total mass of the raw materials in the acid polishing solution being 100%, it includes: HF 10-14%, HNO3 30-38%, and H2O 50-60%. F. Ultraviolet wavelength is 280 nm, photon energy is 4.43 eV, and irradiance is 40-60 mW / cm². 2 .

7. The method for improving the efficiency of BC batteries by low-temperature oxidation with boron diffusion according to any one of claims 1-6, characterized in that, The stacked passivation layer deposition includes sequential AlOx layer deposition, AlN layer deposition, and SiNx layer deposition, and satisfies at least one of the following conditions: H. The AlOx layer is deposited using ALD under the following conditions: TMAH precursor, TMA flow rate of 100-200 sccm, RF power of 145-155 W, and O2 ratio of 1-5%; I. The AlN layer is deposited by ICP under the following conditions: SiH4:NH3 = 1:6-10, Y2O3 doping amount is 3-8wt%, and pressure is 180-220 mTorr; J. The SiNx layer is deposited by PECVD under the following conditions: SiH4:NH3 = 1:3-5, and the bias voltage is -120~-180 V.

8. A BC battery, characterized in that, The preparation method includes the low-temperature oxidation method for boron diffusion in BC batteries as described in any one of claims 1-7.

9. The BC battery according to claim 8, characterized in that, The BC cell comprises, in the direction away from the N-type monocrystalline silicon wafer, a tunneling oxide layer, a boron-doped polycrystalline silicon layer, an AlOx layer, an AlN layer, and a SiNx layer arranged sequentially, and satisfies at least one of the following conditions: a. The thickness of the tunneling oxide layer is 1-2 nm; b. The thickness of the boron-doped polycrystalline silicon layer is 50-60 nm; c. The thickness of the AlOx layer is 2.5-3.5 nm; d. The thickness of the AlN layer is 1.5-2.5 nm; e. The thickness of the SiNx layer is 50-70 nm.

10. A photovoltaic system, characterized in that, Includes the BC battery as described in claim 8 or 9.

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