Passivation structure, preparation method thereof and solar cell

Abstract

The application provides a passivation structure, a preparation method thereof and a solar cell. The passivation structure comprises a silicon oxide layer, a first passivation layer and a second passivation layer arranged on the surface of the silicon oxide layer in sequence. The first passivation layer comprises at least one first aluminum oxide layer and at least one second aluminum oxide layer arranged alternately. The second passivation layer comprises at least one third aluminum oxide layer and at least one fourth aluminum oxide layer arranged alternately. The densities of the first aluminum oxide layer, the second aluminum oxide layer, the third aluminum oxide layer and the fourth aluminum oxide layer gradually decrease. The passivation structure can balance good passivation effect and sintering efficiency, is applied to the field of solar cells, and can effectively improve photoelectric conversion performance such as open-circuit voltage and fill factor. The preparation method has simple and consecutive procedures, low process cost and is suitable for industrial production.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, and in particular to a passivation structure, its preparation method, and a solar cell. Background Technology

[0002] In Tunnel Oxide Passivated Contact (TOPCon) solar cells, the alumina (Al2O3) passivation layer plays a crucial role in passivation performance. Its density significantly impacts the cell's processing and performance; both excessively high and low densities can cause problems. For example, an overly dense Al2O3 layer hinders the etching of the passivation layer by metal pastes (such as silver paste), making it difficult for laser energy to fully penetrate or uniformly ablate, leading to incomplete sintering, increased contact resistance, or even open circuits. Conversely, a low-density, loose Al2O3 layer directly weakens the passivation effect or increases processing defects, thereby reducing the cell's open circuit voltage (Uoc) and fill factor (FF). Thus, high density affects contact formation, while low density impairs passivation reliability. This contradiction is one of the core challenges in optimizing TOPCon passivation technology, and current technologies struggle to achieve a balance between density and defect control. Summary of the Invention

[0003] In view of this, the present application provides a passivation structure, its preparation method and a solar cell. By designing multiple alternating layers of dense alumina and loose alumina, and controlling the density gradient of each layer, a passivation structure is formed that is generally dense in the inner layer and loose in the outer layer, with alternating density within the layers. This allows the density distribution to take into account both good passivation effect and facilitate subsequent sintering, achieving synergistic optimization of passivation performance and metallization process compatibility. The resulting solar cell has better photoelectric conversion efficiency and yield.

[0004] In a first aspect, embodiments of this application provide a passivation structure, including a silicon oxide layer and a first passivation layer and a second passivation layer sequentially disposed on the surface of the silicon oxide layer. The first passivation layer includes at least one layer of first aluminum oxide and at least one layer of second aluminum oxide, which are alternately stacked. The second passivation layer includes at least one layer of third aluminum oxide and at least one layer of fourth aluminum oxide, which are alternately stacked. The density of the first aluminum oxide layer, the second aluminum oxide layer, the third aluminum oxide layer, and the fourth aluminum oxide layer gradually decreases.

[0005] In this embodiment, the density of the first alumina layer is 2.9 g / cm³. 3 -3g / cm 3 The density of the second alumina layer is 2.75 g / cm³. 3 -2.85g / cm3 The density of the third alumina layer is 2.61 g / cm³. 3 -2.7g / cm 3 The density of the fourth alumina layer is 2.5 g / cm³. 3 -2.6g / cm 3 .

[0006] In this embodiment of the application, the difference in refractive index between the first passivation layer and the second passivation layer is 0.03-0.1.

[0007] In this embodiment of the application, the total number of the first alumina layer and the second alumina layer in the first passivation layer is 4 to 10 layers; the total number of the third alumina layer and the fourth alumina layer in the second passivation layer is greater than or equal to 20 layers; and the total thickness of the first passivation layer and the second passivation layer is 4 nm to 10 nm.

[0008] Secondly, embodiments of this application provide a method for preparing a passivation structure, comprising the following steps: A silicon oxide layer is provided, and a first deposition is performed using an aluminum source and ozone to deposit a first passivation layer on the surface of the silicon oxide layer. The first passivation layer includes at least one first aluminum oxide layer and at least one second aluminum oxide layer that are alternately stacked. A second deposition is performed using an aluminum source and water vapor to deposit a second passivation layer on the surface of the first passivation layer to obtain a passivation structure. The second passivation layer includes at least one third aluminum oxide layer and at least one fourth aluminum oxide layer that are alternately stacked. In the passivation structure, the density of the first alumina layer, the second alumina layer, the third alumina layer, and the fourth alumina layer gradually decreases.

[0009] In this embodiment of the application, the first deposition includes 2 to 5 deposition cycles, and each deposition cycle in the first deposition includes depositing a first alumina layer and a second alumina layer; In the first deposition, the purge flow rate of the aluminum source was 4000 sccm-6000 sccm; the purge flow rate of the ozone was kept constant, and the purge flow rate of the ozone was 6000 sccm-8000 sccm. During the deposition of the first alumina layer, the ratio of the purging time of the aluminum source to that of ozone is 1:(1-1.1); During the deposition of the second alumina layer, the ratio of the purging time of the aluminum source to that of ozone is 1:(1.15-1.2).

[0010] In this embodiment of the application, the second deposition includes 10 or more deposition cycles, and each deposition cycle in the second deposition includes depositing a third alumina layer and a fourth alumina layer. In the second deposition, the purging flow rate of the aluminum source is 4000 sccm-6000 sccm; the purging flow rate of water vapor is kept constant at 4000 sccm-6000 sccm. During the deposition of the third alumina layer, the ratio of the purging time of the aluminum source to that of water vapor is 1:(1.1-1.2). During the deposition of the fourth alumina layer, the ratio of the purging time of the aluminum source to that of water vapor is 1:(1.3-1.4).

[0011] In this embodiment of the application, a pre-water treatment is further included between the first deposition and the second deposition. The pre-water treatment includes 4 to 8 purging cycles, with the purging time of water vapor in each purging cycle being 5000ms-10000ms and the purging flow rate being 8000sccm-18000sccm.

[0012] In this embodiment, the first deposition, pre-water treatment, and second deposition are carried out at 190℃-260℃.

[0013] Thirdly, embodiments of this application also provide a solar cell, including a silicon substrate and a passivation structure as provided in the first aspect of this application or a passivation structure prepared by the preparation method provided in the second aspect of this application covering the surface of the silicon substrate, wherein a silicon oxide layer in the passivation structure is disposed between the silicon substrate and the first passivation layer. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0015] Figure 1 This is a cross-sectional schematic diagram of the passivation structure provided in an embodiment of this application; Figure 2 This is a cross-sectional schematic diagram of the first passivation layer in the passivation structure provided in the embodiments of this application; Figure 3 This is a cross-sectional schematic diagram of the second passivation layer in the passivation structure provided in the embodiments of this application; Figure 4 A flowchart illustrating the fabrication process of a passivation structure provided in one embodiment of this application; Figure 5 A flowchart illustrating the fabrication process of the passivation structure provided in another embodiment of this application; Figure 6 A cross-sectional schematic diagram of a solar cell provided in the embodiments of this application. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0017] Open Circuit Voltage (Uoc): also known as open voltage, refers to the potential difference between the two ends of a battery when no load is connected (open circuit state). It reflects the maximum voltage that the battery can generate under light, i.e., its photoelectric conversion performance.

[0018] Short-circuit current (Isc): The output current when the battery terminal voltage is zero under illumination, which directly reflects the battery's carrier transport capability and photoelectric conversion efficiency.

[0019] Fill factor (FF): It is the ratio of the battery's maximum power to the product of its open-circuit voltage and short-circuit current. It measures how close the battery's actual output power is to its theoretical maximum power.

[0020] In existing tunnel oxide passivated contact (TOPCon) solar cells, an alumina layer is often placed on the silicon substrate surface as a passivation layer to reduce surface recombination and improve photoelectric conversion efficiency. However, the density of the alumina passivation layer has a significant impact on the stability of subsequent sintering processes and cell performance: low-density alumina layers have poor passivation reliability and contain more pores or defects. These pores and defects increase light scattering loss and reduce light absorption efficiency, and are also prone to causing metal ions (such as Ag in the electrode silver paste) to accumulate. + Leakage current can occur when the passivation layer penetrates into the silicon substrate or tunnels through the alumina layer, thereby reducing the cell's open-circuit voltage (Uoc) and fill factor (FF). While a high-density alumina layer can circumvent these issues, its excessive density makes it difficult for the glass phase in the electrode slurry to corrode or penetrate, hindering the formation of effective ohmic contact between the metal electrode and the underlying silicon substrate. This reduces subsequent sintering efficiency and cell yield. To alleviate the passivation-sintering compatibility imbalance, various auxiliary processes such as laser grooving or localized etching have been introduced. However, these processes not only increase complexity but may also damage the silicon substrate surface. Therefore, the existing alumina passivation layer cannot simultaneously meet the combined requirements of high passivation effect, sintering stability, and low process cost. This contradiction has become a key bottleneck restricting further efficiency improvements and mass production feasibility for TOPCon cells.

[0021] This application provides a passivation structure 10, the cross-section of which is shown in the figure. Figure 1As shown, it includes a silicon oxide layer 101 and a first passivation layer 102 and a second passivation layer 103 sequentially disposed on the surface of the silicon oxide layer 101; as Figure 2 As shown, the first passivation layer 102 includes at least one first aluminum oxide layer 1021 and at least one second aluminum oxide layer 1022 alternately stacked; as Figure 3 As shown, the second passivation layer 103 includes at least one third aluminum oxide layer 1031 and at least one fourth aluminum oxide layer 1032 that are alternately stacked. The density of the first alumina layer 1021, the second alumina layer 1022, the third alumina layer 1031, and the fourth alumina layer gradually decreases.

[0022] In this embodiment, the adjacent silicon oxide layer 101, the first passivation layer 102, and the second passivation layer 103 are all fully covered; the aluminum oxide in the first aluminum oxide layer 1021, the second aluminum oxide layer 1022, the third aluminum oxide layer 1031, and the fourth aluminum oxide layer 1032 are of the same crystal phase.

[0023] The passivation structure provided in this application embodiment exhibits an overall structure of dense inner layer and loose outer layer. That is, compared with the second passivation layer 103 which is far from the silicon oxide layer 101, the first passivation layer 102 which is close to the silicon oxide interface has a higher average density. The relatively dense first passivation layer 102 mainly contributes to the passivation effect and can protect the silicon substrate when applied to solar cells. The relatively loose second passivation layer 103 can alleviate the problem of "burn-through difficulty" of traditional fully dense layers. In the subsequent electrode sintering process of solar cell fabrication, the passivation structure provided in this application embodiment is beneficial to improving the effective ohmic contact between the metal electrode and the silicon substrate. On this basis, both the first passivation layer 102 and the second passivation layer 103 are composed of aluminum oxide layers with alternating dense and sparse layers. In this way, the overall density of the passivation structure can be reduced without affecting the protective function of the silicon substrate, thereby further improving the subsequent sintering efficiency.

[0024] In this embodiment, the thickness of the silicon oxide layer 101 is 1nm-2nm, for example, but not limited to 1nm, 1.2nm, 1.4nm, 1.5nm, 1.7nm, 1.8nm, and 2nm. The thin silicon oxide layer provides initial passivation for defects on the silicon surface while allowing electrons to pass through, thus enabling selective carrier transport.

[0025] Unsaturated chemical bonds (dangling bonds) formed due to lattice termination exist on the surface of the silicon substrate. These dangling bonds easily become centers for electron-hole recombination, affecting battery efficiency. In this embodiment, the silicon oxide layer 101 originates from the stable chemical bonds (Si-O-Si) formed by oxygen atoms combining with the dangling bonds on the silicon substrate surface. By controlling the thickness of the silicon oxide layer 101 within the aforementioned range, quantum tunneling of charge carriers can be allowed, achieving preliminary chemical passivation of the silicon substrate, while avoiding excessively thick silicon oxide layers 101 from affecting light absorption and subsequent sintering.

[0026] In this embodiment, the density of each alumina layer can be detected by X-ray reflectance method (XRR), and the average density of the first passivation layer and the second passivation layer can be measured by elliptic polarization spectroscopy.

[0027] In this embodiment, the densities of the first, second, third, and fourth alumina layers gradually decrease. That is, the density of any local area in the first passivation layer 102 is higher than the density of any local area in the second passivation layer 103, meaning the average density of the first passivation layer 102 is higher than the average density of the second passivation layer 103. This results in the passivation layer exhibiting a structure with a dense inner layer and a porous outer layer. The gradual decrease in density can be linear, parabolic, or irregular. This approach ensures a better passivation effect through the density of the inner layer while optimizing sintering compatibility through the porous outer layer.

[0028] In this embodiment, the density of the first alumina layer 1021 is 2.9 g / cm³. 3 -3g / cm 3 For example, it can be, but is not limited to, 2.91 g / cm³. 3 2.92g / cm 3 2.93g / cm 3 2.94 g / cm 3 2.95g / cm 3 2.96g / cm 3 2.97g / cm 3 2.98g / cm 3 2.99g / cm 3 3g / cm 3 The first alumina layer, 1021, contributes the most significant passivation effect in the overall passivation layer. Its high density determines its low defect state density (e.g., fewer oxygen vacancies and dangling bonds). Firstly, the Al2O3 layer can further saturate the dangling bonds on the substrate surface, thereby achieving chemical passivation. Secondly, it can facilitate the passage of aluminum ions (Al2O3). 3+The introduced positive charge layer repels holes on the silicon surface, achieving "field-effect passivation," thereby effectively reducing the carrier recombination rate on the silicon substrate surface and directly improving the cell's turn-on voltage and short-circuit current. In some specific embodiments of this application, the density of the first alumina layer 1021 is 2.92 g / cm³. 3 -2.97g / cm 3 .

[0029] In this embodiment, the density of the second alumina layer 1022 is 2.75 g / cm³. 3 -2.85g / cm 3 For example, it can be, but is not limited to, 2.75 g / cm³. 3 2.76 g / cm 3 2.77 g / cm 3 2.78g / cm 3 2.79 g / cm 3 2.8g / cm 3 2.81 g / cm 3 2.82 g / cm 3 2.83 g / cm 3 2.84 g / cm 3 2.85g / cm 3 The second alumina layer 1022 has a lower density than the first alumina layer 1021, contributing to the passivation effect. The second alumina layer 1022 is interspersed between the first alumina layers 1021, and its density is within the aforementioned range, which can neutralize the density of the first alumina layer 1021, allowing the first passivation layer 102 to avoid the problems of difficult sintering and difficult burn-through that are common in traditional single dense alumina layers. In some specific embodiments of this application, the density of the second alumina layer 1022 is 2.77 g / cm³. 3 -2.83g / cm 3 .

[0030] In this embodiment, the density of the third alumina layer 1031 is 2.61 g / cm³. 3 -2.7g / cm 3 For example, it can be, but is not limited to, 2.61 g / cm³. 3 2.62 g / cm 3 2.63 g / cm 3 2.64 g / cm 3 2.65g / cm 3 2.66 g / cm 3 2.67 g / cm 3 2.68g / cm 3 2.69 g / cm 3 2.7g / cm 3The more densely packed the atoms and molecules within each alumina layer of the passivation structure 10, the stronger the refractive effect on light; therefore, the refractive index is positively correlated with the packing density. Controlling the density of the third alumina layer 1031 within the aforementioned range can reduce the density difference between the fourth alumina layer 1032 and the first passivation layer 102, buffering the abrupt change in refractive index from the outside to the inside of the passivation structure 10, thereby reducing light reflection loss. In some specific embodiments of this application, the density of the third alumina layer 1031 is 2.62 g / cm³. 3 -2.68g / cm 3 .

[0031] In this embodiment, the density of the fourth alumina layer 1032 is 2.5 g / cm³. 3 -2.6g / cm 3 For example, it can be, but is not limited to, 2.5g / cm³. 3 2.51g / cm 3 2.52g / cm 3 2.53g / cm 3 2.54 g / cm 3 2.55g / cm 3 2.56 g / cm 3 2.57g / cm 3 2.58g / cm 3 2.59g / cm 3 2.6g / cm 3 The fourth alumina layer 1032 has a suitable amount of porosity. During subsequent sintering, the glass phase in the electrode silver paste can quickly penetrate and corrode the second passivation layer 103 through the pores, which helps to reduce the sintering temperature and accelerate the sintering rate. In addition, the fourth alumina layer 1032 moderately reduces the elastic modulus of the second passivation layer 103, which helps to buffer the internal stress caused by the difference in the thermal expansion coefficients of the materials during sintering, reduce the risk of cracking, and improve the mechanical reliability of the battery cell. In some specific embodiments of this application, the density of the fourth alumina layer 1032 is 2.53 g / cm³. 3 -2.58g / cm 3 .

[0032] In this embodiment, the total number of the first alumina layer 1021 and the second alumina layer 1022 is 4 to 10 layers, for example, but not limited to 4, 5, 6, 7, 8, 9, or 10 layers. For example, when the first passivation layer 102 includes 4 alumina layers, two are first alumina layers 1021 and two are second alumina layers 1022. The first alumina layers 1021 and 1022 are stacked alternately, specifically in a stacking form of first alumina layer 1021-second alumina layer 1022-first alumina layer 1021-second alumina layer 1022, i.e., there are three interfaces. This embodiment controls the total number of the first alumina layer 1021 and the second alumina layer 1022 within the above range. This is to construct a first passivation layer 102 with a preset thickness and to avoid excessive interfaces in the first passivation layer 102, which would increase the interlayer defect density and weaken the passivation effect. In some specific embodiments of this application, the total number of the first alumina layer 1021 and the second alumina layer 1022 is 4 to 6 layers.

[0033] In this embodiment, the total number of the third alumina layer 1031 and the fourth alumina layer 1032 is greater than or equal to 20 layers, for example, but not limited to 20, 21, 22, 23, 24, 25, 26, 27, 27, 28, 29, 30, 32, 35, 38, 40, and 50 layers. For example, when the second passivation layer 103 includes 30 alumina layers, 15 layers are the third alumina layer 1031, and 15 layers are the fourth alumina layer 1032. The third alumina layer 1031 and the fourth alumina layer 1032 are stacked alternately, specifically represented as third alumina layer 1031 - fourth alumina layer 1032 - (third alumina layer 1031 - 1032). 13 -The stacking configuration of the third alumina layer 1031-the fourth alumina layer 1032, (third alumina layer 1031-fourth alumina layer 1032) 13 This indicates that the third alumina layer 1031 and the fourth alumina layer 1032 are stacked and repeated 13 times. In this application embodiment, the total number of the third alumina layer 1031 and the fourth alumina layer 1032 is controlled within the above range to construct a second passivation layer 103 with a predetermined thickness. In some specific embodiments of this application, the total number of the third alumina layer 1031 and the fourth alumina layer 1032 is 20 to 40 layers.

[0034] In this embodiment, the thickness of the first passivation layer 102 is 2nm-4nm, for example, but not limited to 2nm, 2.3nm, 2.5nm, 2.8nm, 3nm, 3.2nm, 3.5nm, 3.7nm, and 4nm. The first passivation layer 102 mainly contributes to the passivation effect. By controlling its thickness within the above range, a sufficiently thick positive charge layer can be formed to exert field-effect passivation, effectively preventing the rapid recombination of photogenerated carriers on the silicon surface and thus increasing the open-circuit voltage. At the same time, it avoids the situation where the layer is too thick, causing short-wavelength photons (such as blue light) to be excessively absorbed and unable to reach the silicon substrate to generate carriers.

[0035] In this embodiment, the thickness of the second passivation layer 103 is 2nm-11nm, for example, but not limited to 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, and 11nm. Controlling the thickness of the second passivation layer 103 within the above range is beneficial for reducing the temperature required for electrode burn-through and accelerating the sintering rate, while simultaneously achieving refractive index transition. In some specific embodiments of this application, the thickness of the second passivation layer 103 is 3nm-6nm.

[0036] In this embodiment, the total thickness of the first passivation layer 102 and the second passivation layer 103 is 4nm-15nm, and can be, for example, not limited to, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, or 15nm. The thickness of the first passivation layer 102 directly affects the passivation effect, and the thickness of the second passivation layer 103 directly affects the electrode contact and optical transition. By controlling the total thickness of the passivation layers within the above range in this embodiment, a synergistic optimization of passivation effect and sintering efficiency can be achieved. In some specific embodiments of this application, the total thickness of the first passivation layer 102 and the second passivation layer 103 is 4nm-10nm. A passivation layer thickness within the range of 4nm-10nm is more conducive to balancing the passivation effect on the substrate, reducing the difficulty of subsequent electrode sintering, and improving the structural stability of the solar cell.

[0037] In this embodiment, the refractive index of the first passivation layer 102 is greater than that of the second passivation layer 103. Thus, the passivation structure 10 provided in this embodiment constructs a refractive index gradient that decreases sequentially from the silicon substrate, the first passivation layer 102 to the second passivation layer 103. This helps to avoid the increased light reflection caused by the "refractive index jump" phenomenon and helps to improve the light absorption of the silicon substrate.

[0038] In this embodiment, the refractive index difference between the first passivation layer 102 and the second passivation layer 103 is 0.03-0.1, for example, but not limited to 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, and 0.1. By controlling the refractive index difference between the first passivation layer 102 and the second passivation layer 103 within a suitable range, optical loss can be reduced firstly, a smoother refractive index transition can be achieved, and interface reflection can be reduced, thereby enhancing the transmission and absorption of light within the battery; secondly, it can avoid the introduction of defect states due to excessive interlayer refractive index difference, which would increase the carrier recombination probability, thus helping to reduce interface defect density and maintain a good passivation effect. In some specific embodiments of this application, the refractive index difference between the first passivation layer 102 and the second passivation layer 103 is 0.04-0.07.

[0039] In this embodiment, the refractive index of the first passivation layer 102 is 1.71-1.75, for example, but not limited to, 1.71, 1.72, 1.73, 1.74, and 1.75; the refractive index of the second passivation layer 103 is 1.65-1.7, for example, but not limited to, 1.65, 1.66, 1.67, 1.68, 1.69, and 1.7. By limiting the refractive indices of the first passivation layer 102 and the second passivation layer 103 to the above ranges while satisfying the refractive index difference requirement, the refractive indices can be matched with the thickness of each layer. This facilitates the "cancellation" of reflections through interference effects, thereby increasing the amount of light transmitted to the silicon substrate and improving the photoelectric conversion efficiency of the battery.

[0040] In the passivation structure provided in this application embodiment, the silicon oxide layer 101 and the relatively dense first passivation layer 102 synergistically endow the passivation structure with better passivation performance. The second passivation layer 103 has a relatively low density, but it is located on the outer layer far from the silicon substrate and does not affect the passivation effect. It mainly undertakes the functions of refractive index transition and assisting burn-through. Moreover, both the first passivation layer 102 and the second passivation layer 103 are composed of a cross-layer of loose alumina and dense alumina, which greatly reduces the difficulty of subsequent sintering. This allows the passivation structure provided in this application embodiment to overcome the contradiction between passivation effect and sintering stability. On this basis, the density, number of layers, thickness and refractive index of each alumina layer are further designed in a synergistic manner, systematically improving the efficiency, yield and reliability of the battery.

[0041] This application provides a method for preparing a passivation structure, the preparation process of which is as follows: Figure 4 As shown, it includes the following steps: S101: Provide a silicon oxide layer, and perform a first deposition using an aluminum source and ozone to deposit a first passivation layer on the surface of the silicon oxide layer. The first passivation layer includes at least one layer of first aluminum oxide and at least one layer of second aluminum oxide that are alternately stacked. S102: A second deposition is performed using an aluminum source and water vapor to deposit a second passivation layer on the surface of the first passivation layer, thereby obtaining a passivation structure. The second passivation layer includes at least one third aluminum oxide layer and at least one fourth aluminum oxide layer that are alternately stacked. In the passivation structure provided in the embodiments of this application, the density of the first alumina layer, the second alumina layer, the third alumina layer, and the fourth alumina layer gradually decreases.

[0042] The passivation structure preparation method provided in this application adopts atomic layer deposition (ALD). Using ozone (O3) and water (H2O) as oxygen sources, alumina layers with different densities are deposited sequentially. First, an overall framework with a dense inner layer and a loose outer layer is constructed. Second, during the intralayer deposition process of the inner and outer layers, a deposition mode of alternating loose and dense alumina layers is further designed. The passivation structure is obtained by following the cross-density rule of "the density of the first alumina layer, the second alumina layer, the third alumina layer, and the fourth alumina layer gradually decreases". This passivation structure has both good passivation quality and burn-through resistance, which is beneficial to improving the open circuit voltage and fill factor.

[0043] In step S101, aluminum oxide is deposited using TMA as the aluminum source and O3 as the oxygen source. The specific formation process of aluminum oxide is as follows: TMA is purged to react with hydroxyl groups or other active sites on the substrate surface to form surface-adsorbed Al(CH3)2; then the oxygen source (O3) is purged to react with the surface-adsorbed Al(CH3)2, oxidizing the methyl ligand into volatile products (such as CO2, H2O) and generating Al-O bonds, thereby forming aluminum oxide (Al2O3).

[0044] In the embodiments of this application, the aluminum source includes, but is not limited to, one or more of trimethylaluminium (TMA), aluminum trichloride, dimethylaluminium chloride, triisobutylaluminum, dimethylaminoaluminum, aluminum tritert-butoxide, and aluminum triisopropoxide, with trimethylaluminium being preferred.

[0045] In this embodiment, the first deposition includes 2 to 5 deposition cycles, each deposition cycle including the deposition of one first alumina layer and one second alumina layer. Therefore, the first passivation layer formed after the first deposition includes 4 to 10 alumina layers, wherein the first alumina layer and the second alumina layer are alternately stacked. In some embodiments of this application, the number of deposition cycles for the first deposition can be, for example, 2, 3, 4, or 5. Correspondingly, the number of alumina layers in the first passivation layer formed after the first deposition can be 4, 6, 8, or 10. By controlling the number of deposition cycles for the first deposition to be 2 to 5, a first passivation layer with a preset thickness can be obtained to meet the passivation requirements and light absorption requirements. In some specific embodiments of this application, the first deposition includes 2 to 3 deposition cycles.

[0046] In this embodiment of the application, during the deposition of the first alumina layer, the purging time ratio of TMA to O3 is 1:(1-1.1), for example, but not limited to, 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, and 1:1.1. When the purging time ratio of TMA to O3 is within the above range, that is, the purging amount of TMA and the purging amount of O3 are similar during the deposition of the first alumina layer, a relatively dense first alumina layer can be formed.

[0047] In some embodiments of this application, during the deposition of the first alumina layer, the TMA purge time is 5000ms-7000ms, for example, but not limited to, 5000ms, 5300ms, 5500ms, 5700ms, 6000ms, 6200ms, 6500ms, 6800ms, and 7000ms. For example, the purge time is set according to the range of the ratio of TMA to O3 purge time. When the TMA purge time is 6000ms, the O3 purge time can specifically be 6000ms, 6100ms, 6120ms, 6200ms, 6240ms, 6300ms, 6360ms, 6400ms, 6480ms, 6500ms, and 6600ms.

[0048] In the embodiments of this application, during the deposition of the second alumina layer, the purging time ratio of TMA to O3 is 1:(1.15-1.2), for example, but not limited to, 1:1.15, 1:1.16, 1:1.17, 1:1.18, 1:1.19, and 1:1.2. When the purging time ratio of TMA to O3 is within the above range, that is, when the amount of O3 purged during the deposition of the second alumina layer is slightly more than the amount of TMA, a second alumina layer with a lower density than the first alumina layer can be formed.

[0049] In some embodiments of this application, during the deposition of the second alumina layer, the TMA purging time is 5000ms-9000ms, for example, but not limited to, 5000ms, 6000ms, 7000ms, 8000ms, and 9000ms. For example, based on the range of the TMA to O3 purging time ratio, when the TMA purging time is 6000ms, the O3 purging time can specifically be 6900ms, 6960ms, 7000ms, 7020ms, 7080ms, 7140ms, 7150ms, and 7200ms. The embodiments of this application, by controlling the TMA to O3 purging time ratio, further limit the purging times of both, which helps to comprehensively optimize the density, thickness, and refractive index of the first passivation layer.

[0050] In step S102, alumina is deposited using TMA as the aluminum source and H2O as the oxygen source. The specific formation process of the alumina is similar to that in step S101, and will not be described again here. Compared to step S102, which uses O3 as the oxygen source to deposit alumina, the H2O in step S102 has milder oxidizing and reactive properties than the O3 in step S101. Therefore, the deposited alumina layer has a lower density and a more porous structure.

[0051] In this application, the second deposition includes 10 or more deposition cycles, each deposition cycle including the deposition of one third alumina layer and one fourth alumina layer. The second passivation layer formed after the second deposition includes at least 20 alumina layers. In some embodiments of this application, the number of deposition cycles for the second deposition can be, for example, but not limited to, 10, 11, 12, 13, 14, 15, 18, or 20 times. Correspondingly, the number of alumina layers in the second passivation layer formed after the second deposition can be 20, 22, 24, 26, 28, 30, 36, or 40 layers. In summary, some embodiments of this application indicate that the second deposition includes 13 to 18 deposition cycles, which can produce a second passivation layer with a predetermined thickness to meet the requirements of refractive index transition and sintering.

[0052] In this embodiment of the application, during the deposition of the third alumina layer, the purging time ratio of TMA to H2O is 1:(1.1-1.2), for example, but not limited to, 1:1.1, 1:1.12, 1:1.14, 1:1.16, 1:1.18, and 1:1.2. Based on the difference between H2O and O3 oxygen sources, when the purging time ratio of TMA to H2O is within the above range, a third alumina layer with a lower density than the second alumina layer can be formed.

[0053] In this embodiment of the application, during the deposition of the third alumina layer, the TMA purging time is 6000ms-9000ms, for example, but not limited to, 6000ms, 6500ms, 7000ms, 7500ms, 8000ms, 8500ms, and 9000ms. For example, based on the range of the TMA to H2O purging time ratio, when the TMA purging time is 6000ms, the O3 purging time can specifically be 6600ms, 6700ms, 6800ms, 6900ms, 7000ms, 7100ms, and 7200ms.

[0054] In this embodiment of the application, during the deposition of the fourth alumina layer, the purging time ratio of TMA to H2O is 1:(1.3-1.4), for example, but not limited to, 1:1.3, 1:1.32, 1:1.35, 1:1.38, and 1:1.4. When the purging time ratio of TMA to H2O is within the above range, a fourth alumina layer with a lower density than the third alumina layer can be formed.

[0055] In this embodiment, during the deposition of the fourth alumina layer, the TMA purge time is 6000ms-10000ms, for example, but not limited to, 6000ms, 7000ms, 8000ms, 9000ms, and 10000ms. For example, based on the range of the TMA to H2O purge time ratio, when the TMA purge time is 6000ms, the O3 purge time can specifically be 7800ms, 7900ms, 8000ms, 8100ms, 8200ms, 8300ms, and 8400ms. This embodiment, by controlling the TMA to H2O purge time ratio and further limiting the purge times of both, helps to comprehensively optimize the density, thickness, and refractive index of the second passivation layer.

[0056] In steps S101 and S102, the purge flow rates of the three growth sources (TMA, O3, and H2O) remain constant. Specifically, the purge flow rate of TMA is any fixed value between 4000 sccm and 6000 sccm, the purge flow rate of O3 is any fixed value between 6000 sccm and 8000 sccm, and the purge flow rate of H2O is any fixed value between 4000 sccm and 6000 sccm.

[0057] In steps S101 and S102, a residence (wait) time and a purging (purge) time must be set after each purging of the growth source (TMA, O3, or H2O). The residence time is used to ensure that TMA has sufficient time to diffuse to all active sites to achieve monolayer saturation adsorption, and to ensure that O3 or H2O fully contacts all Al-CH3 groups and completely converts them to Al-OH. Purging is performed by purging with an inert gas to remove unreacted growth sources and byproducts. The purity of the inert gas is greater than or equal to 99.999% to ensure process purity.

[0058] In this embodiment of the application, the dwell time is 500ms-5000ms, for example, but not limited to 500ms, 800ms, 1000ms, 1200ms, 1500ms, 2000ms, 2500ms, 3000ms, 4000ms, and 5000ms.

[0059] In this embodiment, the inert gas includes nitrogen (N2) and / or argon (Ar), and the purging time of the inert gas is 5000ms-9000ms, for example, but not limited to 5000ms, 6000ms, 7000ms, 8000ms, and 9000ms; the purging flow rate of the inert gas is 20000-30000sccm, for example, but not limited to 22000sccm, 25000sccm, and 28000sccm.

[0060] Please see Figure 5 A flowchart of a method for preparing a passivation structure according to another embodiment of this application is provided, including: S201: Provide a silicon oxide layer, and perform a first deposition using an aluminum source and ozone to deposit a first passivation layer on the surface of the silicon oxide layer. The first passivation layer includes at least one layer of first aluminum oxide and at least one layer of second aluminum oxide that are alternately stacked. S202: Pre-water treatment; S203: A second passivation layer is formed on the surface of the first passivation layer by using an aluminum source and water vapor to obtain a passivation structure. The second passivation layer includes at least one third aluminum oxide layer and at least one fourth aluminum oxide layer that are alternately stacked.

[0061] S201 and S203 can be referred to in the descriptions of S101 and S102 above, and will not be repeated here.

[0062] In this embodiment of the application, step S202 is included between steps S201 and S203, namely, after the first deposition is completed and before the second deposition begins, water vapor is blown out to pre-water treat the material, such as... Figure 5As shown. Under the ozone treatment of the first deposition, the alumina surface of the first passivation layer itself has hydroxyl groups that can serve as deposition sites for subsequent TMA. However, nitrogen purging may cause some hydroxyl groups to desorb. In this embodiment, the material is pre-hydrated before changing the oxygen source to introduce water molecules, which compensate for the hydroxyl defects on the material surface through physical adsorption, or through chemical adsorption with Al. 3+ Coordination forms a hydroxylated layer, providing sufficient active sites for subsequent TMA deposition, which is beneficial to improving the deposition efficiency of the second passivation layer.

[0063] In some embodiments of this application, the pre-water treatment includes 2 to 8 purging cycles, with each purging cycle including one steam purging. In some embodiments of this application, the number of purging cycles for the pre-water treatment can be, for example, 2, 3, 4, 5, 6, 7, or 8. In some specific embodiments of this application, the number of purging cycles for the pre-water treatment is 2 to 5.

[0064] In some embodiments of this application, the steam purging time in the pre-water treatment is 5000ms-10000ms, and the steam purging flow rate is 8000sccm-18000sccm.

[0065] In this embodiment, the preparation of the silicon oxide layer includes pre-oxidation treatment of the silicon substrate to remove surface impurities and passivate surface dangling bonds. The resulting silicon oxide layer reduces the surface hydrogen concentration and increases the surface hydroxyl groups, laying the foundation for the subsequent deposition of a higher density alumina layer.

[0066] The pre-oxidation treatment includes 2 to 5 purging cycles, with each purging cycle including one ozone purging. In some embodiments of this application, the number of purging cycles for the pre-oxidation treatment may be, for example, 2, 3, 4, or 5. A suitable pre-oxidation treatment can generate a silicon oxide layer of appropriate thickness on the silicon substrate surface, thereby achieving preliminary chemical passivation of the silicon substrate, while avoiding an excessively thick silicon oxide layer that could lead to uneven distribution of surface hydroxyl groups or increased contact resistance. In some specific embodiments of this application, the number of purging cycles for the pre-oxidation treatment is 2 to 3.

[0067] In this embodiment of the application, the ozone purging time in the pre-oxygenation treatment is 15000ms-25000ms, for example, but not limited to 15000ms, 18000ms, 20000ms, 22000ms, and 25000ms; the ozone purging flow rate is 6000sccm-10000sccm (standard cubic centimeters per minute), for example, but not limited to 6000sccm, 7000sccm, 8000sccm, 9000sccm, and 10000sccm.

[0068] In some embodiments of this application, a silicon substrate is pre-oxidized to obtain a silicon oxide layer, and a first deposition, a pre-water treatment, and a second deposition are performed on the surface of the silicon oxide layer to obtain a passivation structure.

[0069] In this embodiment, the pre-oxidation treatment, first deposition, pre-hydration treatment, and second deposition are all performed at a constant temperature between 190℃ and 260℃, for example, but not limited to 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, and 260℃. Controlling the reaction temperature within this range ensures sufficient reaction between the TMA and the silicon substrate surface, while avoiding excessively high temperatures that could exacerbate desorption between the TMA and the silicon substrate growth surface, thus achieving a better alumina growth rate. In some specific embodiments of this application, the constant temperature is 200℃-230℃.

[0070] In other embodiments of this application, the pre-oxidation treatment, first deposition, pre-hydration treatment, and second deposition are performed at varying temperatures within a range of 190°C to 260°C. Specifically, the temperatures for the pre-oxidation treatment and first deposition are 190°C to 230°C, for example, but not limited to, 190°C, 200°C, 210°C, 220°C, and 230°C; the temperatures for the pre-hydration treatment and second deposition are 240°C to 260°C, for example, but not limited to, 240°C, 245°C, 250°C, 255°C, and 260°C. This variable-temperature preparation process is suitable for preparing passivation structures with a total thickness exceeding 15 nm, and helps alleviate problems such as defects, uneven nucleation, and stress cracking encountered in thick film growth during isothermal deposition.

[0071] The passivated structure prepared by the method provided in the embodiments of this application is as described above, and will not be repeated here.

[0072] Compared to the traditional alternating pulse method for depositing a single-density alumina passivation layer, the preparation method provided in this application uses a dual-cycle process with two oxygen sources to deposit alumina layers of different densities. Furthermore, by designing the number of deposition cycles for the first and second depositions, as well as the ratio and range of purging time for the aluminum and oxygen sources within each deposition cycle, a passivation structure with the density regularity, refractive index, and thickness described above can be obtained. This preparation method is continuous, simple in process, and suitable for industrial production.

[0073] This application also provides a solar cell, which includes a silicon substrate and a passivation structure provided above in this application or a passivation structure prepared by the preparation method provided above in this application covering the surface of the silicon substrate, wherein a silicon oxide layer in the passivation structure is disposed between the silicon substrate and the first passivation layer.

[0074] In some embodiments of this application, solar cells, such as Figure 6As shown, it includes a passivation structure 10, a silicon substrate 20, a front electrode 30, and a back electrode 40. The silicon substrate 20 includes monocrystalline silicon and / or polycrystalline silicon, specifically N-type or P-type. The front or back of the silicon substrate 20 may also include P-type or N-type doped regions. The passivation structure 10 covers the front of the silicon substrate. The front electrode 30 may also include a main gate and a fine gate. The back electrode 40 includes a metal layer (such as aluminum, silver, etc.) that is fully covered or partially contacted. This application also provides a method for fabricating a solar cell, including providing a silicon substrate, pre-oxidizing the silicon substrate to obtain a silicon oxide layer, performing a first deposition and a second deposition on the surface of the silicon oxide layer to obtain a passivation structure, and forming a solar cell.

[0075] The effects of the technical solution of this application will be further illustrated below with several specific examples. Unless otherwise specified, the raw materials used in the embodiments of this invention are all commercially available products.

[0076] Example 1 Preparation: Place the back-to-back full-boat silicon wafers into the cavity and start the operation; evacuate the process cavity and set the furnace temperature to 220℃, and maintain a constant temperature of 220℃ for subsequent processes.

[0077] Pre-oxidation treatment 2Cy: 1)-3) below is one deposition cycle, and two consecutive deposition cycles are performed to form a silicon oxide layer on the front side of the silicon wafer.

[0078] 1) O3: Set the O3 flow rate to 8000 sccm and the purge time to 20000 ms; 2) wait: Set time to 3000ms; 3) N2: Set the N2 flow rate to 8000 sccm and the purge time to 20000 ms; First deposition 2Cy: Using O3 as the oxygen source, 1)-16) below constitute one deposition cycle, and two consecutive deposition cycles are performed to form a first passivation layer on top of the silicon oxide layer. The first passivation layer includes two first aluminum oxide layers and two second aluminum oxide layers. 1) TMA: Set the TMA purge flow rate to 5000 sccm and the purge time to 6000 ms; 2) wait: Set time to 3000ms; 3) TMA Purge: Purge high-purity N2 into the TMA and O3 pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms for both. 4) wait: Set time to 3000ms; 5) O3: Set the O3 purge flow rate to 8000 sccm and the purge time to 6000 ms; 6) wait: Set time to 3000ms; 7) O3Pruge: Purge high-purity N2 into the TMA and O3 pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms for both. 8) wait: Set the purge time to 3000ms; 9) TMA: Set the purge time to 6000ms; 10) wait: Set time to 3000ms; 11) TMA Purge: Purge high-purity N2 into the TMA and O3 pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 12) wait: Set time to 3000ms; 13) O3: Set the purge time to 7000ms; 14) wait: Set time to 3000ms; 15) O3Pruge: Purge high-purity N2 into the TMA and O3 pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 16) wait: Set time to 3000ms; Second deposition 15Cy: Using H2O as the oxygen source, the following 1)-16) constitute one deposition cycle, and the deposition cycle is repeated 15 times to form a second passivation layer on top of the first passivation layer. The second passivation layer includes 15 third alumina layers and 15 fourth alumina layers. 1) TMA: Set the purge time to 6000ms; 2) wait: Set time to 3000ms; 3) TMA Purge: Purge high-purity N2 into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 4) wait: Set time to 3000ms; 5) H2O: Set the H2O purging flow rate to 5000 sccm and the purging time to 7000 ms; 6) wait: Set time to 3000ms; 7) H2O Purge: Purge high-purity N2 into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 8) wait: Set time to 3000ms; 9) TMA: Set the purge time to 6000ms; 10) wait: Set time to 3000ms; 11) TMA Purge: Purge high-purity N2 into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 12) wait: Set time to 3000ms; 13) H2O: Set the purging time to 8000ms; 14) wait: Set time to 3000ms; 15) H2O Purge: Purge high-purity N2 into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 16) wait: Set the time to 3000ms to obtain the passivation structure.

[0079] Example 2 (Pre-oxygenation 2Cy + 2CyO3 + Pre-water 3Cy + 15CyH2O) The only difference from Example 1 is that a pre-water treatment is added after the first deposition and before the second deposition begins. Pre-water treatment 3Cy: 1)-3) below is one deposition cycle, and three consecutive deposition cycles are performed to form a silicon oxide layer on the front side of the silicon wafer.

[0080] 1) H2O: Set the H2O flow rate to 8000 sccm and the purging time to 10000 ms; 2) wait: Set time to 3000ms; 3) N2: Set the N2 flow rate to 8000 sccm and the purge time to 20000 ms.

[0081] Example 3 The difference from Example 1 is that: the first deposition cycle is 7 times, and the first passivation layer formed includes 7 layers of first alumina and 7 layers of second alumina; the first deposition cycle is 10 times, and the second passivation layer formed includes 10 layers of third alumina and 10 layers of fourth alumina.

[0082] Comparative Example 1 The preparations are the same as in Example 1; Single-cycle 34Cy: Using H2O as the oxygen source, 1)-8) below constitute one deposition cycle, and 34 consecutive deposition cycles are performed to obtain a passivation structure. This passivation layer consists of 34 layers of alumina with the same density. 1) TMA: Set the TMA purge flow rate to 5000 sccm and the purge time to 6000 ms; 2) wait: Set time to 3000ms; 3) TMA Purge: Purge high-purity nitrogen into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 4) wait: Set time to 3000ms; 5) H2O: Set the H2O purging flow rate to 5000 sccm and the purging time to 6000 ms; 6) wait: Set time to 3000ms; 7) H2O Purge: Purge high-purity nitrogen into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 8) wait: Set the time to 3000ms to obtain the passivation structure.

[0083] Comparative Example 2 The pre-treatment and pre-oxygenation process are the same as in Example 1; First deposition 12Cy: Using H2O as the oxygen source, 1)-8) below constitute one deposition cycle. 12 consecutive deposition cycles are performed to obtain the first passivation layer, which consists of 12 layers of alumina with the same density. 1) TMA: Set the TMA purge flow rate to 5000 sccm and the purge time to 6000 ms; 2) wait: Set time to 30000ms; 3) TMA Purge: Purge high-purity nitrogen into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 1000 ms. 4) wait: Set the time to 1000ms; 5) H2O: Set the H2O purging flow rate to 5000 sccm and the purging time to 6000 ms; 6) wait: Set the time to 1000ms; 7) H2O Purge: Purge high-purity nitrogen into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 3000 ms. 8) wait: Set time to 1000ms; The second deposition, 22Cy: using O3 as the oxygen source, 1)-8) below constitute one deposition cycle, and 22 consecutive deposition cycles are performed to obtain the second passivation layer. This second passivation layer consists of 22 layers of alumina with the same density. 1) TMA: Set the purge time to 6000ms; 2) wait: Set time to 3000ms; 3) TMA Purge: Purge high-purity nitrogen into the TMA and O3 pipelines, setting the purging flow rate to 25000 sccm and the purging time to 1000 ms. 4) wait: Set time to 3000ms; 5) O3: Set the O3 purge flow rate to 8000 sccm and the purge time to 8000 ms; 6) wait: Set time to 3000ms; 7) O3Pruge: Purge high-purity nitrogen into the TMA and O3 pipelines, setting the purging flow rate to 25000 sccm and the purging time to 3000 ms. 8) wait: Set the time to 3000ms to obtain the passivation structure.

[0084] Comparative Example 3 The pre-treatment and pre-oxygenation process are the same as in Example 1; First deposition 4Cy: Using O3 as the oxygen source, 1)-8) below constitute one deposition cycle. Four consecutive deposition cycles are performed to obtain the first passivation layer, which consists of four layers of alumina with the same density. 1) TMA: Set the TMA purge flow rate to 5000 sccm and the purge time to 6000 ms; 2) wait: Set time to 3000ms; 3) TMA Purge: Purge high-purity nitrogen into the TMA and O3 pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 4) wait: Set time to 3000ms; 5) O3: Set the O3 purge flow rate to 8000 sccm and the time to 6000 ms; 6) wait: Set time to 3000ms; 7) O3Pruge: Purge high-purity nitrogen into the TMA and O3 pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 8) wait: Set time to 3000ms; Second deposition 30Cy: Using H2O as the oxygen source, 1)-8) below constitute one deposition cycle, and 30 consecutive deposition cycles are performed to form a second passivation layer on top of the first passivation layer. This second passivation layer consists of 30 layers of alumina with the same density. 1) TMA: Set the purge time to 6000ms; 2) wait: Set time to 3000ms; 3) TMA Purge: Purge high-purity nitrogen into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 4) wait: Set time to 3000ms; 5) H2O: Set the H2O purging flow rate to 5000 sccm and the time to 8000 ms; 6) wait: Set time to 3000ms; 7) H2O Purge: Purge high-purity nitrogen into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 8) wait: Set the time to 3000ms to obtain the passivation structure.

[0085] Comparative Example 4 The pre-treatment and pre-oxygenation process are the same as in Example 1; First deposition 4Cy: Using O3 as the oxygen source, 1)-8) below constitute one deposition cycle. Four consecutive deposition cycles are performed to obtain the first passivation layer, which consists of four layers of alumina with the same density. 1) TMA: Set the TMA purge flow rate to 5000 sccm and the purge time to 6000 ms; 2) wait: Set time to 3000ms; 3) TMA Purge: Purge high-purity nitrogen into the TMA and O3 pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 4) wait: Set time to 3000ms; 5) O3: Set the O3 purge flow rate to 8000 sccm and the purge time to 8000 ms; 6) wait: Set time to 3000ms; 7) O3Pruge: Purge high-purity nitrogen into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 8) wait: Set time to 3000ms; Second deposition 30Cy: Using H2O as the oxygen source, 1)-8) below constitute one deposition cycle, and 30 consecutive deposition cycles are performed to obtain the second passivation layer, which consists of 30 layers of alumina with the same density. 1) TMA: Set the purge time to 6000ms; 2) wait: Set time to 3000ms; 3) TMA Purge: Purge high-purity nitrogen into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 4) wait: Set time to 3000ms; 5) H2O: Set the H2O purging flow rate to 5000 sccm and the purging time to 6000 ms; 6) wait: Set time to 3000ms; 7) H2O Purge: Purge high-purity nitrogen into the TMA and H2O pipelines, setting the purging flow rate to 25000 sccm and the purging time to 6000 ms. 8) wait: Set the time to 3000ms to obtain the passivation structure. For the passivated structures obtained in Examples 1-3 and Comparative Examples 1-4, the density of each alumina layer was detected by X-ray reflectance method (XRR); the refractive index of the first passivation layer and the refractive index of the second passivation layer were detected by elliptic polarization spectroscopy.

[0086] The test results are shown in Table 1: Table 1 Summary of passivation structure parameters for Examples 1-3 and Comparative Examples 1-4

[0087] The passivated structures of Examples 1-3 and Comparative Examples 1-4 were used to fabricate solar cells, which were then tested under standard test conditions (STC: light intensity 1000 W / m²). 2 The tests were conducted at 25°C under AM1.5G light. The tests included measuring the Eta conversion efficiency, Rs series resistance, Rsh parallel resistance, and Irev2 reverse leakage current using a current-voltage (IV) characteristic testing method.

[0088] The test results are shown in Table 2: Table 2 Summary of Efficiency & Yield of Examples 1-3 and Comparative Examples 1-4

[0089] As shown in Table 1, the passivation structure obtained in Comparative Example 1 is a single-density alumina layer; in the passivation structure obtained in Comparative Example 3, the intralayer densities of the first and second passivation layers are uniform; in the passivation structures obtained in Comparative Examples 2 and 4, the intralayer densities of the first and second passivation layers are uniform, and the density and refractive index follow the rule: first passivation layer < second passivation layer. Applying the passivation structure to solar cells, as shown in Table 2, Examples 1-3, compared to Comparative Examples 1-4, impart superior electrical performance to the solar cells, especially improving the open-circuit voltage (Uoc), short-circuit current (Isc), and fill factor (FF), which further contributes to improving the photoelectric conversion efficiency of the solar cells.

[0090] In summary, the embodiments of this application use ozone and water as oxygen sources sequentially, and prepare passivation structures by controlling the purging time ratio of aluminum and oxygen sources. The passivation structure generally exhibits a dense inner layer and a porous outer layer, with alternating dense and porous layers within the layers. This density distribution achieves synergistic optimization of passivation performance and sintering efficiency, resulting in superior photoelectric conversion efficiency when applied to solar cells. Furthermore, the preparation method is simple and sequential, yields high product yield, and is suitable for industrial production.

Claims

1. A passivation structure, characterized in that, It includes a silicon oxide layer and a first passivation layer and a second passivation layer sequentially disposed on the surface of the silicon oxide layer. The first passivation layer includes alternating layers of first aluminum oxide and second aluminum oxide, wherein the total number of the first aluminum oxide and second aluminum oxide layers in the first passivation layer is 4 to 10 layers. The second passivation layer includes alternating layers of a third alumina layer and a fourth alumina layer, wherein the total number of the third alumina layer and the fourth alumina layer in the second passivation layer is greater than or equal to 20 layers; The density of the first alumina layer, the second alumina layer, the third alumina layer, and the fourth alumina layer gradually decreases.

2. The passivation structure as described in claim 1, characterized in that, The density of the first alumina layer is 2.9 g / cm³. 3 -3g / cm 3 The density of the second alumina layer is 2.75 g / cm³. 3 -2.85g / cm 3 The density of the third alumina layer is 2.61 g / cm³. 3 -2.7g / cm 3 The density of the fourth alumina layer is 2.5 g / cm³. 3 -2.6g / cm 3 .

3. The passivation structure as described in claim 1, characterized in that, The difference in refractive index between the first passivation layer and the second passivation layer is 0.03-0.

1.

4. The passivation structure as described in claim 1, characterized in that, The total thickness of the first passivation layer and the second passivation layer is 4nm-10nm.

5. A method for preparing a passivation structure, characterized in that, Includes the following steps: A silicon oxide layer is provided, and a first deposition is performed using an aluminum source and ozone. A first passivation layer is deposited on the surface of the silicon oxide layer. The first deposition includes 2 to 5 deposition cycles. Each deposition cycle in the first deposition includes depositing a first aluminum oxide layer and a second aluminum oxide layer. The first passivation layer includes alternating layers of first aluminum oxide and second aluminum oxide. A second deposition is performed using an aluminum source and water vapor to deposit a second passivation layer on the surface of the first passivation layer to obtain a passivation structure. The second deposition includes 10 or more deposition cycles. Each deposition cycle in the second deposition includes depositing a third alumina layer and a fourth alumina layer. The second passivation layer includes alternating layers of third alumina and fourth alumina. In the passivation structure, the density of the first alumina layer, the second alumina layer, the third alumina layer, and the fourth alumina layer gradually decreases.

6. The method for preparing the passivation structure as described in claim 5, characterized in that, In the first deposition, the purge flow rate of the aluminum source is 4000 sccm-6000 sccm; the purge flow rate of the ozone is kept constant, and the purge flow rate of the ozone is 6000 sccm-8000 sccm. During the deposition of the first alumina layer, the ratio of the purging time of the aluminum source to that of the ozone is 1:(1-1.1); During the deposition of the second alumina layer, the ratio of the purging time of the aluminum source to that of the ozone is 1:(1.15-1.2).

7. The method for preparing the passivation structure as described in claim 5, characterized in that, In the second deposition, the purging flow rate of the aluminum source is 4000 sccm-6000 sccm; the purging flow rate of the water vapor remains constant, and the purging flow rate of the water vapor is 4000 sccm-6000 sccm. During the deposition of the third alumina layer, the ratio of the purging time of the aluminum source to that of the water vapor is 1:(1.1-1.2). During the deposition of the fourth alumina layer, the ratio of the purging time of the aluminum source to that of the water vapor is 1:(1.3-1.4).

8. The method for preparing the passivation structure as described in claim 5, characterized in that, Between the first deposition and the second deposition, a pre-water treatment is also included, which includes 4 to 8 purging cycles, wherein the purging time of water vapor in each purging cycle is 5000ms-10000ms and the purging flow rate is 8000sccm-18000sccm.

9. The method for preparing the passivation structure as described in claim 8, characterized in that, The first deposition, the pre-water treatment, and the second deposition were carried out at 190°C-260°C.

10. A solar cell, characterized in that, The present invention includes a silicon substrate and a passivation structure as described in any one of claims 1-4 or a passivation structure prepared by any one of claims 5-9 covering the surface of the silicon substrate, wherein the silicon oxide layer in the passivation structure is disposed between the silicon substrate and the first passivation layer.

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