Methods for preparing passivation layers for solar cells and solar cells

Abstract

A method for preparing a passivation layer for a solar cell and a solar cell are disclosed. The method for preparing the passivation layer includes: providing a substrate and forming a first passivation precursor on the substrate; introducing a first gas to perform a first repair on the first passivation precursor to obtain a second passivation precursor; introducing a second gas to perform a second repair on the second passivation precursor to obtain a passivation layer; wherein the first gas is nitrous oxide, and the second gas is a mixture of nitrous oxide and ammonia. This application employs a segmented gas repair method for the passivation layer of the solar cell. In the first segment, pure nitrous oxide is used to precisely oxygenate the shallow vacancies on the surface of the first passivation precursor. In the second segment, a mixture of nitrous oxide and ammonia is used to synergistically repair the deep vacancies in the bulk phase of the second passivation precursor, achieving simultaneous oxygen vacancy replenishment and dangling bond passivation. The repair coverage and oxygen vacancy repair rate of this two-stage repair method are both improved.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, specifically to a method for preparing a passivation layer for a solar cell and a solar cell. Background Technology

[0002] The passivation layer of solar cells is often formed using atomic layer deposition (ALD). However, insufficient chemical adsorption reactions may result in amorphous alumina films containing a large number of amorphous shapes and defects. Therefore, it is necessary to repair the alumina passivation film. The repair scheme often uses high-power single gas plasma for strong oxidation and oxygen replenishment, but the repair effect of single gas on alumina passivation layer is not ideal. Summary of the Invention

[0003] The purpose of this application is to provide a method for preparing a passivation layer for a solar cell and a solar cell, thereby solving the problem that the repair effect of a single gas on the alumina passivation layer is not ideal.

[0004] To achieve the objectives of this application, the following technical solution is provided: In a first aspect, this application provides a method for preparing a passivation layer for a solar cell, comprising: A substrate is provided, and a first passivation precursor is formed on the substrate; The first passivation precursor is repaired by introducing the first gas to obtain the second passivation precursor. A second gas is introduced to perform secondary repair on the second passivation precursor to obtain a passivation layer, which is used in solar cells. The first gas is nitrous oxide, and the second gas is a mixture of nitrous oxide and ammonia.

[0005] In one embodiment, the flow rate of the first gas is L1, and the flow rate of the second gas is L2, satisfying: L1 < L2.

[0006] In one embodiment, the flow rate of the nitrous oxide in the second gas is L3, and the flow rate of the ammonia in the second gas is L4, satisfying: L1 < L3, L1 < L4.

[0007] In one implementation, 5000 sccm ≤ L1 ≤ 6000 sccm; and / or, 7500sccm≤L3≤8500sccm; and / or, 7500sccm≤L4≤8500sccm.

[0008] In one embodiment, the radio frequency power of the single repair is 4500W-5500W; and / or, The radio frequency power of the secondary repair is 6500W-7500W; and / or, The cavity pressure during the first repair is 1000 mTorr - 1500 mTorr; and / or, The cavity pressure for the secondary repair is 1400 mTorr-2000 mTorr; and / or, The processing time for each repair is 20s-30s; and / or, The processing time for the secondary repair is 30s-50s.

[0009] In one embodiment, the thickness of the passivation layer is 4nm-8nm.

[0010] In one embodiment, forming a first passivation precursor on the substrate includes: A third passivation precursor is formed on the substrate; The third passivation precursor was annealed in a nitrogen atmosphere.

[0011] In one embodiment, the annealing operation is performed at a temperature of 450°C-550°C; and / or, The heating rate for the annealing operation is 2°C / min - 7°C / min; and / or, The holding time for the annealing operation is 15-30 minutes.

[0012] In one embodiment, the deposition cycle number for forming the third passivation precursor is 30-40; and / or, the deposition temperature for forming the third passivation precursor is 250°C-280°C.

[0013] Secondly, this application provides a solar cell including a passivation layer, said passivation layer being prepared using the method for preparing a solar cell passivation layer as described in any one of the various embodiments of the first aspect.

[0014] This application employs a segmented gas repair method for the passivation layer of solar cells. In the first segment, pure nitrous oxide is used to precisely oxygenate the shallow vacancies on the surface of the first passivation precursor. In the second segment, a mixture of nitrous oxide and ammonia is used to synergistically repair the deep vacancies in the bulk phase of the second passivation precursor, thereby achieving simultaneous oxygen vacancy replenishment and dangling bond passivation. The repair coverage and oxygen vacancy repair rate of the two-segment repair method in this application are both improved. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 This is a flowchart illustrating a method for preparing a passivation layer for a solar cell according to one embodiment. Detailed Implementation

[0017] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0018] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items.

[0019] It should be noted that the "range" disclosed in this invention is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for specific parameters, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this invention, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0020] All steps of the present invention can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0021] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0022] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0023] Please refer to Figure 1 This application provides a method for preparing a passivation layer for a solar cell, comprising: Step S10: Provide a substrate and form a first passivation precursor on the substrate; Step S20: Introduce the first gas to repair the first passivation precursor once, and obtain the second passivation precursor. Step S30: A second gas is introduced to perform secondary repair on the second passivation precursor to obtain a passivation layer, which is used in solar cells. The first gas is nitrous oxide, and the second gas is a mixture of nitrous oxide and ammonia.

[0024] Optionally, in step S10, the substrate can be an N-type silicon wafer.

[0025] Optionally, in step S10, providing the substrate includes: cleaning and texturing the silicon wafer, performing front-side boron diffusion treatment and BSG (borosilicate glass) removal process, alkaline polishing, depositing a tunneling oxide layer on the back side, depositing an intrinsic polycrystalline silicon layer, performing back-side phosphorus doping treatment and PSG (phosphosilicate glass) removal process, and RCA cleaning (wet chemical cleaning process).

[0026] Optionally, both primary and secondary repairs can be performed using plasma repair. Specifically, under plasma irradiation, nitrous oxide (N₂O) is decomposed into highly reactive groups such as oxygen (O) and nitrogen (N). Oxygen atoms fill oxygen vacancies and enhance field-effect passivation, while nitrogen atoms form dense aluminum oxynitride (AlO₂) on the passivation precursor. X N Y A hybrid layer such as silicon oxynitride (SiON) or silicon oxynitride (SiON) can be used to further enhance the passivation effect.

[0027] Specifically, ammonia (NH3) decomposes into hydrogen atoms (H) and nitrogen-hydrogen groups (NH*, etc.) in plasma. NH3 plasma treatment can nitrid the surface of the passivation precursor to form an aluminum oxynitride (AlON) film. Hydrogen atoms can diffuse to the Al2O3 / Si interface and combine with dangling bonds, effectively reducing the interface state density. Ammonia treatment can also reduce surface roughness and further improve interface quality.

[0028] Optionally, the passivation layer is an amorphous ultrathin aluminum oxide structure. The amorphous aluminum oxide structure contains a high density of fixed negative charges, which can form an electric field on the silicon surface and repel majority carriers (field-effect passivation), significantly reducing the surface recombination rate.

[0029] Optionally, in the secondary repair process, active oxygen atoms from nitrous oxide fill oxygen vacancies; while active hydrogen atoms from ammonia prevent excessive oxidation and simultaneously passivate the interface dangling bonds with hydrogen.

[0030] This application employs a segmented gas repair method for the passivation layer of solar cells. In the first segment, pure nitrous oxide is used to precisely oxygenate the shallow vacancies on the surface of the first passivation precursor. In the second segment, a mixture of nitrous oxide and ammonia is used to synergistically repair the deep vacancies in the bulk phase of the second passivation precursor, thereby achieving simultaneous oxygen vacancy replenishment and dangling bond passivation. The repair coverage and oxygen vacancy repair rate of the two-segment repair method in this application are both improved.

[0031] In one embodiment, the flow rate of the first gas is L1, and the flow rate of the second gas is L2, satisfying that L1 < L2.

[0032] The low-flow-rate first gas primarily repairs surface vacancies. At low flow rates, the concentration of active particles is low, and the energy is moderate, limiting the reaction depth to the shallow surface layer of the first passivation precursor. This layer is crucial for the passivation effect; the low-flow-rate first gas can gently fill shallow defects such as oxygen vacancies on the surface without excessively bombarding the surface of the first passivation precursor or introducing new damage.

[0033] The high-flow-rate second gas primarily repairs vacancies in the bulk phase. The high flow rate provides a sufficient concentration of active particles and a stronger diffusion driving force, enabling it to penetrate the surface of the repaired first passivation precursor and reach deep into the interior of the first passivation precursor to repair deep defects such as bulk oxygen vacancies buried within it.

[0034] In one embodiment, the flow rate of nitrous oxide in the second gas is L3, and the flow rate of ammonia in the second gas is L4, satisfying: L1 < L3, L1 < L4.

[0035] Optionally, L3 = L4. Equal supply of nitrous oxide and ammonia as the second gas allows for the simultaneous injection of the required hydrogen and oxygen atoms into the alumina film in the same process step. This saturates interfacial dangling bonds (chemical passivation) and increases the fixed negative charge (field-effect passivation), maximizing the passivation effect. The iso-flow design also allows for more precise control of the oxygen and hydrogen ratio injected into the passivation layer, achieving an ideal stoichiometric equilibrium point and maximizing the synergistic effect of the two passivation mechanisms. Compared to processes requiring complex flow ratio adjustments, iso-flow settings simplify process parameters, providing an easy-to-implement and reliable process starting point, which is beneficial for improving production yield and product consistency.

[0036] Both L3 and L4 must be greater than L1 for the second gas, nitrous oxide and ammonia, to penetrate the surface of the repaired first passivation precursor and repair deep defects.

[0037] In one embodiment, 5000 sccm ≤ L1 ≤ 6000 sccm. sccm is a unit of gas flow rate, meaning standard cubic centimeters per minute. Optionally, L1 can be 5000 sccm, 5100 sccm, 5200 sccm, 5300 sccm, 5400 sccm, 5500 sccm, 5600 sccm, 5700 sccm, 5800 sccm, 5900 sccm, 6000 sccm, etc., without limitation. The low-density active particles generated by the low flow rate naturally limit the reaction depth to the shallow surface layer of the film, allowing a single repair action to fill shallow defects such as surface oxygen vacancies without damaging the original structure of the film due to over-reaction.

[0038] In one embodiment, 7500 sccm ≤ L3 ≤ 8500 sccm. Optionally, L3 can be 7500 sccm, 7600 sccm, 7700 sccm, 7800 sccm, 7900 sccm, 8000 sccm, 8100 sccm, 8200 sccm, 8300 sccm, 8400 sccm, 8500 sccm, etc., without limitation. In another embodiment, 7500 sccm ≤ L4 ≤ 8500 sccm. Optionally, L4 can be 7500 sccm, 7600 sccm, 7700 sccm, 7800 sccm, 7900 sccm, 8000 sccm, 8100 sccm, 8200 sccm, 8300 sccm, 8400 sccm, 8500 sccm, etc., without limitation. High flow rates of L3 and L4 ensure that the second gas in the reaction chamber has a high density of active particles, allowing sufficient active particles to react with deep defects in the alumina film (such as bulk oxygen vacancies), achieving comprehensive repair from the surface to the core.

[0039] In the first gas within the L1 flow range, the particle energy distribution of the plasma is relatively mild, mainly acting on the outermost layer of the film. Through physical bombardment and chemical reaction, surface contaminants and dangling bonds are effectively removed, achieving surface activation and providing a stable and uniform substrate for subsequent secondary repair treatment.

[0040] The active particles (radicals and ions) generated by high-flow plasma also help optimize the interface between the second passivation precursor and the substrate and promote surface reactions to form a denser passivation layer with better stoichiometry, thereby improving the overall passivation effect and stability.

[0041] In one embodiment, the radio frequency (RF) power for a single repair is 4500W-5500W. Optionally, the RF power for a single repair can be 4500W, 4600W, 4700W, 4800W, 4900W, 5000W, 5100W, 5200W, 5300W, 5400W, 5500W, etc., without limitation. In the low power range of 4500W-5500W, the plasma is in a weakly ionized state, and the RF electric field is mainly used to accelerate electrons to obtain higher ionization efficiency. However, ions, due to their large mass and slow migration speed, are unlikely to obtain sufficient kinetic energy to cause lattice damage at low power. As the temperature of electrons in the plasma increases, they efficiently transfer energy to the first gas molecules through inelastic collisions, promoting their dissociation into active free radicals. The low-energy active free radicals first act on the outermost layer of the first passivation precursor, reacting with the unsaturated coordinating atoms on the surface to eliminate dangling bonds and form a highly activated chemisorption layer rich in hydroxyl groups (-OH) on the surface, providing a uniform distribution of reaction precursors for subsequent bulk phase repair.

[0042] In one embodiment, the radio frequency (RF) power for secondary repair is 6500W-7500W. Optionally, the RF power for secondary repair can be 6500W, 6600W, 6700W, 6800W, 6900W, 7000W, 7100W, 7200W, 7300W, 7400W, 7500W, etc., without limitation. With increased RF power, the ionization rate of the second gas significantly increases, the plasma density increases substantially, and the concentration of active free radicals and ions within the cavity increases simultaneously. The large number of active oxygen / hydrogen free radicals generated by the high-density plasma, driven by the concentration gradient, diffuse through the surface activation layer and penetrate deep into the bulk phase of the second passivation precursor, reacting chemically with oxygen vacancies buried deep within, thereby repairing bulk defects.

[0043] The primary repair process utilizes low-power, weak ionization treatment, while the secondary repair employs controlled ratios and flow rates of nitrous oxide and ammonia to create a redox equilibrium atmosphere. The entire process avoids high-energy bombardment, thus preventing thinning of the passivation layer and ensuring a complete passivation layer interface structure, preventing film damage issues common in existing processes. This step-by-step strategy of "repair first, then strengthen" effectively avoids damage to the ultrathin alumina film caused by a single high-power plasma, achieving high-quality passivation repair.

[0044] In one embodiment, the cavity pressure for a single repair is 1000 mTorr-1500 mTorr. mTorr is a unit of pressure, meaning millitor. Optionally, the cavity pressure for a single repair can be 1000 mTorr, 1050 mTorr, 1100 mTorr, 1150 mTorr, 1200 mTorr, 1250 mTorr, 1300 mTorr, 1350 mTorr, 1400 mTorr, 1450 mTorr, 1500 mTorr, etc., without limitation. Excessive cavity pressure for a single repair can lead to excessively high ion energy, causing physical sputtering on the surface of the first passivation precursor, resulting in thinning of the first passivation precursor, and even breaking the Al-O-Si bonds at the interface, introducing new defects and deteriorating the passivation effect. Excessively high cavity pressure for a single repair may lead to plasma instability, uneven concentration and distribution of active particles, affecting the uniformity of surface repair of the first passivation precursor. Within a suitable cavity pressure range, the ion energy of the first gas is sufficient to activate the chemical reaction without causing physical damage. It can gently break and recombine the chemical bonds on the surface to achieve defect repair.

[0045] In one embodiment, the cavity pressure for secondary repair is 1400 mTorr-2000 mTorr. Optionally, the cavity pressure for secondary repair can be 1400 mTorr, 1450 mTorr, 1500 mTorr, 1550 mTorr, 1600 mTorr, 1650 mTorr, 1700 mTorr, 1750 mTorr, 1800 mTorr, 1850 mTorr, 1900 mTorr, 1950 mTorr, 2000 mTorr, etc., without limitation. The cavity pressure for secondary repair is greater than that for primary repair, allowing the second gas to penetrate into the bulk phase of the second passivation precursor for vacancy repair. However, the cavity pressure for secondary repair must also passivate the dangling bonds in the bulk phase of the second passivation precursor without causing physical damage.

[0046] In one embodiment, the treatment time for a single repair is 20-30 seconds. Optionally, the treatment time for a single repair can be 20 seconds, 21 seconds, 22 seconds, 23 seconds, 24 seconds, 25 seconds, 26 seconds, 27 seconds, 28 seconds, 29 seconds, 30 seconds, etc., without limitation. A short single repair is sufficient to break the chemical bonds between surface contaminants and weakly bonded atoms, forming a highly activated reaction precursor layer rich in dangling bonds and hydroxyl groups (-OH), providing uniform reaction sites for subsequent secondary repairs. Furthermore, if the treatment time is too long, although the power of the single repair is lower, prolonged particle bombardment may still cause slow changes in the surface physical and chemical properties.

[0047] In one embodiment, the secondary repair processing time is 30-50 seconds. Optionally, the secondary repair processing time can be 30 seconds, 32 seconds, 35 seconds, 38 seconds, 40 seconds, 42 seconds, 45 seconds, 48 ​​seconds, 50 seconds, etc., without limitation. The repair of bulk defects depends on the diffusion rate and reaction rate of active particles. Appropriately extending the secondary repair time ensures that after the surface reaction is saturated, excess active particles have sufficient time to diffuse inward, which helps to ensure that deep defects can be fully repaired, without being limited by the particle diffusion rate. If the secondary repair time is shortened, high concentrations of active particles may only react in the surface area, leading to excessive surface oxidation or nitriding, while the bulk defects remain unrepaired.

[0048] The processing time for a single repair is shorter than that for a second repair. This setting allows the two repairs to focus on the surface and the deep layers respectively. Furthermore, by coordinating the power and time settings, a complete repair path from the surface to the interior is formed.

[0049] In one embodiment, the thickness of the passivation layer is 4nm-8nm. Optionally, the thickness of the passivation layer is 4nm, 4.5nm, 5nm, 5.5nm, 6nm, 6.5nm, 7nm, 7.5nm, 8nm, etc., without limitation. An excessively thick passivation layer will significantly increase the resistance of charge carriers (electrons or holes) to reach the electrode through the tunneling effect, resulting in an increase in the series resistance of the battery, which is ultimately reflected in a significant decrease in the fill factor (FF). The passivation effect of the alumina passivation layer largely depends on the field effect generated by its fixed negative charge. If the passivation layer is too thin, it means that the total amount of effective material that can generate this effect is insufficient, and it is impossible to establish a sufficiently strong electric field on the silicon surface to effectively repel minority carriers, resulting in severe interfacial recombination and a significant reduction in the passivation effect. Limiting the thickness of the passivation layer can form a high-quality alumina film, ensuring that its fixed negative charge density and field effect passivation capability reach saturation, effectively reducing surface recombination, and also ensuring that the tunneling resistance of charge carriers is at a low level, thereby ensuring that the fill factor (FF) of the battery is not damaged due to an excessively thick passivation layer.

[0050] Furthermore, conventional repair solutions often employ high-power single nitrous oxide plasma for strong oxidation and oxygen replenishment. This process is suitable for films thicker than 8nm, but it does not match the 4nm-8nm passivation layer thickness of this application. This can easily lead to thinning of the film due to etching, breakage of Al-O-Si bonds at the interface, and deterioration of the passivation effect.

[0051] In one embodiment, step S10, forming a first passivation precursor on the substrate, includes: A third passivation precursor is formed on the substrate; The third passivation precursor was annealed in a nitrogen atmosphere.

[0052] Optionally, the nitrogen atmosphere must be ≥99.999% pure, with oxygen impurities <10ppm, and the annealing process must be completely oxygen-free.

[0053] Optionally, the third passivation precursor can be formed by depositing it on a substrate using an atomic layer deposition (ALD) process. The precursor is trimethylaluminum (TMA) and deionized water.

[0054] Annealing releases internal stress in the first passivation precursor, promotes interfacial atomic rearrangement, and activates the passivation properties of alumina, thereby significantly reducing the carrier recombination rate on the silicon wafer surface. Furthermore, annealing can utilize existing PECVD equipment to solidify the repair effect and suppress defect regeneration, eliminating the need for additional annealing equipment.

[0055] In one embodiment, the annealing temperature is 450℃-550℃. Optionally, the annealing temperature can be 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, etc., without limitation. If the annealing temperature is too low, sufficient thermal energy cannot be provided to drive atomic migration and rearrangement, resulting in incomplete passivation reaction and ineffective elimination of interface defects. If the annealing temperature is too high, the quality of the third passivation precursor will decrease, the density of fixed negative charges in the passivation layer will decrease, and the density of mobile positive charges will increase, thereby weakening the field-effect passivation effect. Limiting the annealing temperature can achieve high-quality passivation.

[0056] In one embodiment, the heating rate of the annealing operation is 2℃ / min-7℃ / min. Optionally, the heating rate of the annealing operation can be 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, etc., without limitation. A heating rate that is too slow will lead to increased process time and reduced production efficiency. A heating rate that is too fast will generate huge thermal stress inside the third passivation precursor, which may cause warping, cracking, or even peeling off from the substrate, and may introduce defects such as interface states.

[0057] In one embodiment, the holding time for the annealing operation is 15-30 minutes. Optionally, the holding time for the annealing operation can be 15 minutes, 18 minutes, 20 minutes, 22 minutes, 25 minutes, 28 minutes, 30 minutes, etc., without limitation. Insufficient holding time will lead to incomplete annealing reaction, and atoms will not have enough time to migrate to the correct positions, resulting in the inability to effectively eliminate interface defects. Prolonged annealing may cause changes in the composition of the third passivation precursor or decarburization and oxidation, and may also cause film grain growth, affecting its density and performance. A moderate holding time is sufficient for atoms to undergo sufficient rearrangement and diffusion, thereby achieving good interface optimization and reliable passivation effect.

[0058] Nitrogen high-temperature annealing can solidify the bonded structure, which significantly reduces the light-induced degradation and damp-heat degradation of solar cells. After the double 85 aging test, the degradation is only 1.7% (far lower than the industry standard ≤3%), and the Voc degradation of the aged solar cells is only 0.9mV.

[0059] In one embodiment, the deposition cycle number for forming the third passivation precursor is 30-40. Optionally, the deposition cycle number can be 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, etc., without limitation. Insufficient cycle number will result in the third passivation precursor failing to form a continuous and complete capping layer, failing to provide sufficient chemical passivation and field-effect passivation, leading to high interface defect state density, high surface recombination rate, and inability to improve the open-circuit voltage and efficiency of the battery. Excessive cycle number will result in an excessively thick third passivation precursor, which will significantly increase the resistance of charge carriers (electrons or holes) to reach the electrode through tunneling, leading to increased series resistance and decreased fill factor of the battery.

[0060] In one embodiment, the deposition temperature for forming the third passivation precursor is 250°C-280°C. If the deposition temperature is too low, the trimethylaluminum (TMA) precursor does not react completely with the surface, and the residual methyl (-CH3) groups become defect recombination centers as carbon impurities, impairing the passivation effect. Simultaneously, insufficient reaction between TMA and water leads to a higher residual hydroxyl and hydrogen content in the third passivation precursor, resulting in a lower density and looser structure of the passivation layer. If the deposition temperature is too high, the TMA molecules may thermally decompose before reaching the substrate surface, disrupting the basis of ALD self-limiting growth, causing uncontrolled growth of the third passivation precursor, uneven composition, and potentially introducing additional defects.

[0061] Choosing 30-40 cycles ensures the formation of a complete, dense, and appropriately thick third passivation precursor layer, effectively passivating the interface without affecting carrier transport due to excessive thickness. Selecting a deposition temperature of 250℃-280℃ maximizes the fixed negative charge density of the film while ensuring sufficient TMA reaction and avoiding carbon contamination, thus achieving optimal chemical and field-effect passivation effects.

[0062] In one embodiment, the method for preparing the passivation layer of a solar cell further includes: depositing front-side SiN within the same PECVD cavity. X :H Antireflective coating (the thickness of the antireflective coating can be 70nm-80nm, and the refractive index is 2.0-2.1), SiN deposited on the back side. X The passivation film (thickness 80nm-90nm, refractive index 2.05-2.15) is laser-grooved (groove width 30±5μm), silver electrodes are screen-printed (front grid line width 20μm-30μm, back grid line width 35μm-45μm), and sintering is performed (peak temperature 750℃-850℃, holding time 10s-20s). After sorting and testing, the solar cell is obtained.

[0063] This application provides a solar cell including a passivation layer, which is formed using the method for preparing a solar cell passivation layer as described in any of the foregoing embodiments.

[0064] The method for preparing the passivation layer of solar cells in this application does not use hydrogen throughout the entire process, thus avoiding the risk of hydrogen-induced degradation and further improving long-term reliability and process safety. All processes can reuse existing ALD and PECVD equipment, requiring no new equipment or changes to the main process. The ionization parameters for the two repair stages are fixed, adapting to standardized mass production line operations and allowing for direct implementation in production. Furthermore, FTIR testing shows that the passivation layer in this application exhibits a passivation performance at 1080 cm⁻¹. -1 The absence of intensity decay in the characteristic peak at the interface indicates that the Al-O-Si bonding at the passivation layer of this application is intact. Furthermore, the solar cell of this application possesses an ultrathin and complete alumina passivation layer, which helps reduce the defect density at the Al2O3 / Si interface and decreases the probability of photogenerated carrier recombination at the interface. By reducing recombination, the open-circuit voltage of the solar cell is increased, and the fill factor and conversion efficiency are improved.

[0065] The technical solution of the present invention will be described in detail below through specific embodiments.

[0066] Example 1 The method for preparing the passivation layer of the solar cell in this embodiment includes: providing a substrate (N-type silicon wafer with a resistivity of 0.6 to 1.6 Ω·cm and a thickness of 130 ± 5 μm). Substrate pretreatment: N-type silicon wafers undergo conventional RCA cleaning, texturing (pyramid size 0.8–1.2 μm), front-side boron diffusion (sheet resistance 170 ± 5 Ω / sq), BSG removal with HF + H₂O₂ mixture, back-side polishing (weight reduction controlled at 0.19–0.21 g), and LPCVD deposition of tunneled SiO₂. X (Thickness 1.2nm), intrinsic polycrystalline silicon (thickness 150±5nm) was deposited by LPCVD, phosphorus doped (sheet resistance 60±5Ω / sq), PSG was removed by HF to obtain the substrate; A first passivation precursor was formed on the substrate: ALD ultrathin alumina deposition was performed at a deposition temperature of 260℃ and a deposition cycle of 34 cycles. The precursors were TMA (pulse time 0.15s) and deionized water (pulse time 0.2s), and the carrier gas was high-purity nitrogen (flow rate 2000sccm). The chamber pressure was 0.8Torr. Finally, a third passivation precursor with an Al2O3 passivation layer with a thickness of 6nm was prepared. The substrate was then fed into the PECVD chamber for annealing. High-purity nitrogen (purity 99.999%, oxygen impurity content <10ppm) was introduced, and the heating rate was 5℃ / min. After heating to 500℃, the substrate was held at that temperature for 30min to obtain the first passivation precursor. The first passivation precursor is repaired by introducing the first gas to obtain the second passivation precursor. The first gas is pure N2O gas ionization, the flow rate of nitrous oxide is 5500 sccm, the radio frequency power is 5000W, the chamber pressure is 1200mTorr, the processing time is 30s, and no hydrogen is introduced throughout the process. The second passivation precursor was repaired by introducing a second gas. The flow rate of the second gas was 8000 sccm for N2O and 8000 sccm for NH3, the radio frequency power was 7000W, the chamber pressure was 1400mTorr, the processing time was 40s, and no hydrogen was introduced throughout the process, resulting in the repaired passivation layer. The subsequent fabrication process for solar cells includes: depositing front-side SiN within the PECVD chamber. X :H antireflective coating (75nm thickness, refractive index 2.05), back side SiN X :H passivation film (thickness 85nm, refractive index 2.10); laser grooving (groove width 30±5μm); screen printing silver electrodes (front grid line width 25μm, back grid line width 40μm); co-firing (peak temperature 800℃, holding time 10s), sorting and testing, to obtain solar cells.

[0067] Example 2 The difference between this embodiment and Embodiment 1 is that: in the first repair, the nitrous oxide flow rate L1 = 6000 sccm, and in the second repair, the N2O flow rate L3 = 7500 sccm and the NH3 flow rate L4 = 7500 sccm. The remaining plasma power, cavity pressure, processing time, ALD deposition, nitrogen annealing, and subsequent battery fabrication process parameters are completely consistent with those in Example 1.

[0068] Example 3 The difference between this embodiment and Embodiment 1 is that the N2O flow rate L3 = 8000 sccm and the NH3 flow rate L4 = 7500 sccm in the secondary remediation. The remaining plasma power, cavity pressure, processing time, ALD deposition, nitrogen annealing, and subsequent battery fabrication process parameters are completely consistent with those in Example 1.

[0069] Example 4 The difference between this embodiment and Embodiment 1 is that the N2O flow rate L3 = 7500 sccm and the NH3 flow rate L4 = 8000 sccm in the secondary remediation. The remaining plasma power, cavity pressure, processing time, ALD deposition, nitrogen annealing, and subsequent battery fabrication process parameters are completely consistent with those in Example 1.

[0070] Example 5 The difference between this embodiment and Embodiment 1 is that the N2O flow rate L3 = 7750 sccm and the NH3 flow rate L4 = 7750 sccm in the secondary remediation. The remaining plasma power, cavity pressure, processing time, ALD deposition, nitrogen annealing, and subsequent battery fabrication process parameters are completely consistent with those in Example 1.

[0071] Comparative Example 1 The difference between this comparative example and Example 1 is that the two-stage progressive repair is cancelled, and only a single high-power pure N2O plasma is used for treatment: the N2O flow rate is 8000 sccm, the radio frequency power is 13000W, the cavity pressure is 1200 mTorr, the treatment time is 60s, no NH3 is involved, and there is no segmented treatment.

[0072] The remaining parameters and procedures are the same as in Example 1.

[0073] Comparative Example 2 The difference between this comparative example and Example 1 is that the two-stage progressive repair is cancelled, and only pure NH3 plasma treatment is used: the NH3 flow rate is 8000 sccm, the radio frequency power is 7000W, the cavity pressure is 1400mTorr, the treatment time is 70s, no N2O is involved, and there is no segmented treatment.

[0074] The remaining parameters and procedures are the same as in Example 1.

[0075] Comparative Example 3 The difference between this comparative example and Example 1 is that the second gas is a mixture of N2O and H2, the N2O flow rate is 8000 sccm, the H2 flow rate is 8000 sccm, the radio frequency power is 7000W, and the processing time is 40s.

[0076] The remaining parameters and procedures are the same as in Example 1.

[0077] The solar cells and their passivation layers obtained in the above embodiments and comparative examples were tested under the following conditions: 1. Oxygen vacancy test: XPS test, by analyzing the binding energy of Al2p orbitals, to identify the chemical composition and chemical state of the passivation layer; 2. Battery electrical performance testing: Under standard test conditions (STC), sunlight irradiation was simulated using a solar simulator (AM1.5G spectrum, 1000W / m²). 2 Irradiance and 25°C battery temperature) were used to measure the key electrical performance parameters of the battery, obtaining open-circuit voltage (Voc), short-circuit current (Isc), fill factor (FF), and photoelectric conversion efficiency (Eff). 3. Long-term stability test: Simulates extreme humid and hot environment (85℃ / 85%RH), accelerates aging within 1000 hours, with the industry standard being less than or equal to 3%, to evaluate the long-term reliability of the battery; 4. Film thickness integrity test: The physical thickness of the passivation layer is measured using an ellipsometry.

[0078] Table 1

[0079] Table 2

[0080] As shown in Tables 1 and 2, compared with Comparative Example 1, the oxygen vacancy repair rate of the two-stage repair method of this application is significantly improved compared with the single nitrous oxide repair. Oxygen vacancies, as recombination centers of photogenerated electron-hole pairs, severely impair carrier lifetime and transport efficiency. Reducing the oxygen vacancy defect concentration can reduce carrier recombination (increasing Voc and Isc) and optimize internal resistance (increasing FF and Eff). Therefore, solar cells with lower oxygen vacancy defect concentrations have better cell performance. Thus, the solar cells obtained by the preparation method of this application have higher open-circuit voltage, short-circuit current, fill factor, and conversion efficiency. Moreover, the solar cells of this application have lower degradation efficiency (far below the industry standard ≤3%), and the thickness of the passivation layer after repair shows no obvious etching thinning phenomenon. In contrast, the high-power single nitrous oxide repair process of Comparative Example 1 causes severe damage to the 6nm ultrathin passivation layer, resulting in incomplete repair and extremely poor stability.

[0081] As shown in Tables 1 and 2, compared with Example 1 and Example 2, with the other parameters unchanged, only the gas flow rate for repair will affect the oxygen vacancy repair rate and battery degradation efficiency to a certain extent. This is because the oxygen vacancy defect concentration of the battery will affect the carrier recombination and internal resistance of the battery. However, the repair efficiency of Example 2 is still better than that of Comparative Examples 1-3.

[0082] As shown in Tables 1 and 2, compared with Comparative Example 1 and Comparative Example 2, the oxygen vacancy repair rate of the preparation method using the two-stage repair method of this application is significantly improved compared with single ammonia repair. This is because single ammonia repair cannot repair oxygen vacancy and can only achieve surface dangling bond passivation. The repair effect is significantly worse than the synergistic mechanism of "oxygen supplementation + passivation" of this application.

[0083] As shown in Tables 1 and 2, compared with Comparative Example 3, the oxygen vacancy repair rate of the preparation method using the two-stage repair method of this application is higher than that of nitrous oxide and hydrogen repair, and the relevant performance of the solar cell is also better. Furthermore, compared with Comparative Example 3, Example 1 does not require the introduction of hydrogen, thus avoiding the increased process safety risks caused by hydrogen introduction.

[0084] As shown in Tables 1 and 2, compared with Examples 3-5 (where L3+L4 is the same) and Example 5 (where gas flow rate is equal (L3=L4)), the oxygen vacancy defect concentration of the solar cells repaired by Examples 3 (more nitrous oxide) and 4 (more ammonia) is slightly increased, the oxygen vacancy repair rate is slightly decreased, and the corresponding performance of the solar cells is also reduced. This indicates that the synergistic effect of equal flow rates of nitrous oxide and ammonia can further improve the oxygen vacancy repair capability. Furthermore, the repair efficiency and corresponding performance of the solar cells in Examples 3-5 are superior to those in Comparative Examples 1-3.

[0085] In the description of the embodiments of this application, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and other indicators are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0086] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. A method for preparing a passivation layer for a solar cell, characterized in that, include: A substrate is provided, and a first passivation precursor is formed on the substrate; The first passivation precursor is repaired by introducing the first gas to obtain the second passivation precursor. A second gas is introduced to perform secondary repair on the second passivation precursor to obtain a passivation layer. The first gas is nitrous oxide, and the second gas is a mixture of nitrous oxide and ammonia.

2. The method for preparing the passivation layer of a solar cell according to claim 1, characterized in that, The flow rate of the first gas is L1, and the flow rate of the second gas is L2, satisfying the condition: L1 < L2.

3. The method for preparing the passivation layer of a solar cell according to claim 2, characterized in that, The flow rate of the nitrous oxide in the second gas is L3, and the flow rate of the ammonia in the second gas is L4, satisfying: L1 < L3, L1 < L4.

4. The method for preparing the passivation layer of a solar cell according to claim 3, characterized in that, 5000sccm≤L1≤6000sccm; and / or, 7500sccm≤L3≤8500sccm; and / or, 7500sccm≤L4≤8500sccm.

5. The method for preparing a passivation layer for a solar cell according to claim 1, characterized in that, The radio frequency power of the single repair is 4500W-5500W; and / or, The radio frequency power of the secondary repair is 6500W-7500W; and / or, The cavity pressure during the first repair is 1000 mTorr - 1500 mTorr; and / or, The cavity pressure for the secondary repair is 1400 mTorr-2000 mTorr; and / or, The processing time for each repair is 20s-30s; and / or, The processing time for the secondary repair is 30s-50s.

6. The method for preparing a passivation layer for a solar cell according to claim 1, characterized in that, The passivation layer has a thickness of 4nm-8nm.

7. The method for preparing a passivation layer for a solar cell according to any one of claims 1 to 6, characterized in that, Forming a first passivation precursor on the substrate includes: A third passivation precursor is formed on the substrate; The third passivation precursor was annealed in a nitrogen atmosphere.

8. The method for preparing a passivation layer for a solar cell according to claim 7, characterized in that, The annealing operation is performed at a temperature of 450℃-550℃; and / or, The heating rate for the annealing operation is 2°C / min - 7°C / min; and / or, The holding time for the annealing operation is 15-30 minutes.

9. The method for preparing a passivation layer for a solar cell according to claim 6, characterized in that, The deposition cycle number for forming the third passivation precursor is 30-40; and / or the deposition temperature for forming the third passivation precursor is 250℃-280℃.

10. A solar cell, characterized in that, It includes a passivation layer, which is formed using the method for preparing a solar cell passivation layer as described in any one of claims 1-9.

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