A laminated passivation structure, a preparation method thereof and a solar cell

Abstract

This application provides a stacked passivation structure, its fabrication method, and a solar cell. The stacked passivation structure includes a silicon substrate and an aluminum oxide layer, an aluminum nitride layer, and a silicon nitride layer sequentially disposed on the surface of the silicon substrate. The refractive index of the aluminum nitride layer gradually decreases along the stacking direction away from the silicon substrate. This stacked passivation structure simultaneously achieves a gradual change in refractive index and a gradual change in mechanical strength, thereby alleviating the stress mismatch between the aluminum nitride and silicon nitride layers, reducing the risk of interface delamination, and improving the overall passivation effect and mechanical stability of the passivation layer. When applied to a solar cell, it can effectively optimize the photoelectric conversion efficiency and lifespan of the cell. Furthermore, its fabrication method features a consistent process, excellent deposition effect, and environmental friendliness, making it suitable for industrial production.

Description

Technical Field

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

[0002] In the photovoltaic field, TOPCon (Top-Tunnel Oxide Passivated Contact) solar cells have become one of the core directions in high-efficiency cell research and development due to their excellent passivation performance and conversion efficiency potential. Among them, the back passivation film layer on the silicon substrate is a key structure affecting the efficiency and reliability of TOPCon cells. Current mainstream technologies often use a single alumina film layer or a composite film layer of alumina and other materials as the back passivation structure of TOPCon solar cells. However, traditional single alumina layers are difficult to simultaneously perform field passivation and anti-reflection functions, while composite films are prone to stress mismatch, increasing the risk of film peeling. It is difficult to balance passivation and mechanical integrity. Therefore, both single-layer and composite films have a technical contradiction of sacrificing one aspect for the other. This contradiction makes it difficult to further improve the open-circuit voltage and fill factor of the cell, which is not conducive to optimizing the photoelectric conversion efficiency of solar cells. Summary of the Invention

[0003] In view of this, embodiments of this application provide a stacked passivation structure, its preparation method, and a solar cell. By setting a double stack of aluminum nitride and silicon nitride on the surface of a silicon substrate to achieve a synergistic passivation effect, wherein the refractive index of the aluminum nitride layer gradually decreases along the stacking direction away from the silicon substrate, thereby simultaneously achieving a gradual change in refractive index and a gradual change in mechanical strength. This alleviates the stress mismatch between the aluminum nitride layer and the silicon nitride layer, reduces the risk of interface peeling, and improves the overall passivation effect and mechanical stability of the passivation layer. Applying this stacked passivation structure to TOPCon solar cells can effectively optimize the photoelectric conversion efficiency and lifespan of the cells.

[0004] In a first aspect, embodiments of this application provide a stacked passivation structure, including a silicon substrate and an aluminum oxide layer, an aluminum nitride layer, and a silicon nitride layer sequentially disposed on the surface of the silicon substrate; wherein, along the stacking direction away from the silicon substrate, the refractive index of the aluminum nitride layer gradually decreases.

[0005] In the embodiments of this application, the thickness of the aluminum nitride layer is 17nm-26nm; and / or, the refractive index of the aluminum nitride layer is 2.1-2.25; and / or, along the stacking direction away from the silicon substrate, the molar ratio of aluminum atoms to nitrogen atoms in the aluminum nitride layer decreases linearly from (1.2±0.1):1 to (0.8±0.1):1. In this embodiment, the thickness of the silicon nitride layer is 65nm-85nm, and the hydrogen content is 5at%-35at. In this embodiment of the application, along the stacking direction away from the silicon substrate, the aluminum nitride layer includes a first aluminum nitride layer, a second aluminum nitride layer, and a third aluminum nitride layer; The thickness of the first aluminum nitride layer is 5nm-8nm, and the refractive index of the first aluminum nitride layer decreases linearly from 2.23±0.02 to 2.2; and / or, the thickness of the second aluminum nitride layer is 7nm-10nm, and the refractive index of the second aluminum nitride layer decreases linearly from 2.2 to 2.15; and / or, the thickness of the third aluminum nitride layer is 5nm-8nm, and the refractive index of the third aluminum nitride layer decreases linearly from 2.15 to 2.12±0.02.

[0006] In this embodiment, along the stacking direction away from the silicon substrate, the silicon nitride layer includes a first silicon nitride layer, a second silicon nitride layer, and a third silicon nitride layer; the hydrogen content of the first silicon nitride layer, the second silicon nitride layer, and the third silicon nitride layer decreases sequentially.

[0007] In this embodiment of the application, the thickness of the first silicon nitride layer is 15nm-20nm and the hydrogen content is 25at%-35at; and / or, the thickness of the second silicon nitride layer is 20nm-25nm and the hydrogen content is greater than 15at% and less than 25at; and / or, the thickness of the third silicon nitride layer is 30nm-40nm and the hydrogen content is 5at%-15at.

[0008] Secondly, embodiments of this application provide a method for preparing a stacked passivation structure, comprising the following steps: providing a substrate, the substrate comprising a silicon substrate and an aluminum oxide layer; performing a first deposition using an aluminum source and a nitrogen source to deposit an aluminum nitride layer on the surface of the aluminum oxide layer, wherein the refractive index of the aluminum nitride layer gradually decreases along the stacking direction away from the silicon substrate; and performing a second deposition using a silicon source and a nitrogen source to deposit a silicon nitride layer on the surface of the aluminum nitride layer, thereby obtaining a stacked passivation structure.

[0009] In this embodiment, the molar ratio of aluminum in the aluminum source to nitrogen in the nitrogen source decreases linearly from (1.2±0.1):1 to (0.8±0.1):1.

[0010] In this embodiment of the application, the volumetric flow rate ratio of silicon source to nitrogen source in the second deposition is 1:(2-10).

[0011] Thirdly, embodiments of this application also provide a solar cell, including the stacked passivation structure provided in the first aspect of this application or the stacked passivation structure prepared by the preparation method provided in the second aspect of this application. Attached Figure Description

[0012] 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.

[0013] Figure 1 This is a cross-sectional schematic diagram of the stacked passivation structure provided in the embodiments of this application; Figure 2 This is a schematic cross-sectional view of the aluminum nitride layer in a stacked passivation structure provided in an embodiment of this application; Figure 3 This is a cross-sectional schematic diagram of a stacked passivation structure provided in an embodiment of this application; Figure 4 This is a schematic cross-sectional view of the silicon nitride layer in a stacked passivation structure provided in an embodiment of this application; Figure 5 This is a cross-sectional schematic diagram of a stacked passivation structure provided in an embodiment of this application; Figure 6 A flowchart illustrating the fabrication process of the stacked passivation structure provided in this application embodiment; Figure 7 This is a flowchart illustrating the fabrication process of a stacked passivation structure provided in another embodiment of this application. Figure 8 This is a cross-sectional schematic diagram of a solar cell provided in an embodiment of this application.

[0014] Explanation of icon numbers: 10 - Stacked passivation structure; 20 - Front passivation structure; 30 - Front electrode; 40 - Back electrode; 100 - Silicon substrate; 101 - Alumina layer; 102 - Aluminum nitride layer; 103 - Silicon nitride layer; 1021 - First aluminum nitride layer; 1022 - Second aluminum nitride layer; 1023 - Third aluminum nitride layer; 1031 - First silicon nitride layer; 1032 - Second silicon nitride layer; 1033 - Third silicon nitride layer. Detailed Implementation

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] Existing technologies often improve the passivation structure and fabrication process of silicon-based surfaces to enhance the back-side reliability of TOPCon solar cells, thereby improving photoelectric conversion efficiency. The most traditional and fundamental approach is to deposit an aluminum oxide (Al2O3) layer as a passivation layer on the back of the silicon substrate. Field-effect passivation is achieved by relying on the negative charge of aluminum oxide, and the formation of this negative charge depends on H2O. + or OH - The migration of H and O is a common problem in the preparation of single alumina films, which can lead to uneven H and O supply and charge density fluctuations. In particular, it is difficult to suppress interfacial recombination in highly doped regions. In addition, the dielectric constant of a single alumina layer has limited optimization space and it is difficult to form an ideal energy level match with the silicon substrate, which is not conducive to improving the open circuit voltage of the battery.

[0020] To address this, those skilled in the art have attempted to combine or layer other materials (such as silicon nitride, silicon hydroxide, etc.) to overcome the inherent defects of the aforementioned alumina layer. Among these, the most widely used is a composite structure of an alumina layer with a silicon nitride layer and / or a silicon hydroxide layer. However, this presents new technical challenges. For instance, the significant differences in the thermal expansion coefficients and mechanical strengths of different materials can easily lead to interfacial stress concentration during subsequent annealing or battery cycling, causing film cracking or peeling. More importantly, the refractive index difference significantly hinders light absorption, resulting in a decrease in battery efficiency. Therefore, existing technologies struggle to simultaneously meet the combined requirements of high passivation, refractive index transition, and stress coordination. This contradiction has become one of the key bottlenecks restricting further improvements in the photoelectric efficiency of TOPCon batteries.

[0021] In view of this, embodiments of this application provide a stacked passivation structure 10, the cross-section of which is as follows: Figure 1As shown, it includes a silicon substrate 100 and an aluminum oxide layer 101, an aluminum nitride layer 102 and a silicon nitride layer 103 sequentially disposed on the surface of the silicon substrate, wherein the refractive index of the aluminum nitride layer 102 gradually decreases along the stacking direction away from the silicon substrate 100.

[0022] In this embodiment, the silicon substrate 100, the aluminum oxide layer 101, the aluminum nitride layer 102, and the silicon nitride layer 103 are all fully covered. Specifically, the aluminum oxide layer 101 fully covers the surface of the silicon substrate 100, the aluminum nitride layer 102 fully covers the surface of the aluminum oxide layer 101, and the silicon nitride layer 103 fully covers the surface of the aluminum nitride layer 102.

[0023] In this embodiment, the refractive index of the aluminum nitride layer 102 gradually decreases along the stacking direction away from the silicon substrate 100, meaning that the refractive index of the aluminum nitride layer 102 gradually decreases along the stacking direction away from the silicon substrate 100 to the silicon nitride layer 103.

[0024] In this embodiment, the refractive index of the aluminum nitride layer 102 gradually decreases along the stacking direction away from the silicon substrate 100. The gradual decrease includes a linear decrease, that is, the refractive index of the aluminum nitride layer 102 shows a continuous and uniform decreasing trend along the vertical direction away from the surface of the silicon substrate 100, and the refractive index change value is the same in any adjacent thickness region.

[0025] In this embodiment, an aluminum nitride layer 102 and a silicon nitride layer 103 are sequentially disposed on a silicon substrate 100. The aluminum nitride layer 102 mainly functions as a field-effect passivation layer, while the silicon nitride layer 103 synergistically enhances passivation and reduces light reflection. The aluminum nitride layer 102 also employs a gradient refractive index design. In reality, the refractive index of silicon nitride is lower than that of aluminum nitride, thus constructing a stacked passivation structure with a gradually decreasing refractive index from the inside out. This regular refractive index of the aluminum nitride layer 102 is beneficial for further enhancing field-effect passivation and light absorption, while also ensuring stress compatibility with the silicon nitride layer 103, effectively preventing delamination at the stack interface. The TOPCon cell composed of this stacked passivation structure exhibits a high open-circuit voltage and fill factor, excellent photoelectric conversion efficiency, and optimized structural stability and lifespan.

[0026] In this embodiment of the application, the silicon substrate 100 includes monocrystalline silicon and / or polycrystalline silicon, specifically N-type or P-type, and the front and / or back sides of the silicon substrate 100 may also include P-type and / or N-type doped regions.

[0027] In this embodiment, the thickness of the aluminum nitride (AlN) layer is 15nm-30nm, for example, but not limited to, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, and 30nm. The main function of the aluminum nitride layer 102 is to perform field-effect passivation on the silicon substrate 100. Having a suitable thickness is a fundamental condition for balancing passivation effectiveness and avoiding stress mismatch. This application uses elliptic polarization spectroscopy to measure the thickness; the instrument can be a JA Woollam M-2000 elliptic polarimeter.

[0028] In this embodiment, the refractive index of the aluminum nitride layer 102 is 2.1-2.25, for example, but not limited to, 2.1, 2.12, 2.14, 2.15, 2.17, 2.19, 2.2, 2.22, and 2.25. The refractive index is detected using elliptic polarization spectroscopy in this application.

[0029] In some embodiments of this application, the thickness of the aluminum nitride (AlN) layer is 17nm-26nm, and the refractive index of the aluminum nitride layer 102 decreases linearly from 2.23±0.02 to 2.12±0.02 along the stacking direction away from the silicon substrate 100.

[0030] In this embodiment of the application, along the stacking direction away from the silicon substrate 100, the molar ratio of aluminum atoms (Al) to nitrogen atoms (N) in the aluminum nitride layer 102 decreases linearly from (1.2±0.1):1 to (0.8±0.1):1. For example, it can be, but is not limited to, decreasing linearly from 1.3:1 to 0.7:1, from 1.3:1 to 0.8:1, from 1.2:1 to 0.8:1, from 1.18:1 to 0.9:1, from 1.1:1 to 0.9:1, and from 1.1:1 to 0.8:1. For example, in the aluminum nitride layer 102, the Al:N ratio at the edge closest to the aluminum oxide layer 101 is 1.2:1. Along the stacking direction away from the silicon substrate 100, the molar ratio of Al to N in the aluminum nitride layer 102 gradually decreases until the Al:N ratio at the edge closest to the silicon nitride layer 103 is 0.8:1. The molar ratio of aluminum to nitrogen atoms is positively correlated with the refractive index; the higher the proportion of aluminum atoms, the higher the refractive index. By controlling the Al / N atom ratio in this way, the refractive index of the aluminum nitride layer 102 can be linearly decreased along the stacking direction away from the silicon substrate 100. In this embodiment, elliptic polarization spectroscopy is used to analyze the molar ratio of Al to N atoms in the aluminum nitride layer 102.

[0031] In this embodiment, the molar ratio of Al to N in the aluminum nitride layer 102 is designed such that the AlN layer region near the aluminum oxide layer 101 is an Al-rich region, which is compatible with the Al2O3 material and forms a natural connection. The middle region of the AlN layer plays a transitional role, with Al / N approaching 1:1. At this time, the mechanical strength of the AlN layer approaches that of the silicon nitride layer 103, reducing the stress difference between the two materials and alleviating the interface separation caused by stress mismatch. Meanwhile, the AlN layer region near the silicon nitride layer 103 is an N-rich region, which can further improve the adhesion to the silicon nitride layer 103, enhance the interlayer bonding force and the long-term stability of the passivation structure, and help reduce light decay.

[0032] In this embodiment, along the stacking direction away from the silicon substrate 100, the aluminum nitride layer 102 includes a first aluminum nitride layer 1021, a second aluminum nitride layer 1022, and a third aluminum nitride layer 1023, with the refractive index decreasing sequentially among them. Furthermore, the refractive index within each aluminum nitride layer also exhibits a linear decreasing trend; that is, the change in refractive index is the same for any adjacent thickness regions within each aluminum nitride layer. In this case, the cross-section of the aluminum nitride layer 102 is as follows: Figure 2 As shown, the cross-section of the stacked passivation structure is as follows: Figure 3 As shown.

[0033] In some embodiments of this application, the thickness of the first aluminum nitride layer 1021 is 5nm-8nm, for example, but not limited to, 5nm, 5.3nm, 5.5nm, 5.8nm, 6nm, 6.2nm, 6.5nm, 6.7nm, 6.9nm, 7nm, 7.2nm, 7.5nm, 7.7nm, and 8nm. Along the stacking direction away from the silicon substrate 100, the refractive index of the first aluminum nitride layer 1021 linearly decreases from 2.23±0.02 to 2.2. Exemplarily, the range of the refractive index decrease of the first aluminum nitride layer 1021 may be linearly decreasing from 2.25 to 2.2, from 2.24 to 2.2, from 2.23 to 2.2, from 2.22 to 2.2, or from 2.21 to 2.2. The first aluminum nitride layer 1021 is in direct contact with the silicon substrate 100 and is a key interface for field-effect passivation. The high nitrogen content helps to break the lattice balance of AlN and fill vacancy defects, and its refractive index is close to that of silicon, which can avoid light reflection loss caused by abrupt changes in refractive index. Controlling its thickness between 5nm and 8nm can both meet the requirement of fixed positive charge density to achieve passivation and avoid excessive thickness that would significantly increase the series resistance.

[0034] In some embodiments of this application, the thickness of the second aluminum nitride layer 1022 is 7nm-10nm, for example, but not limited to, 7nm, 7.5nm, 7.8nm, 8nm, 8.2nm, 8.5nm, 8.7nm, 9nm, 9.4nm, 9.5nm, 9.9nm, and 10nm. Along the stacking direction away from the silicon substrate 100, the refractive index of the second aluminum nitride layer 1022 linearly decreases from 2.2 to 2.15. The second aluminum nitride layer 1022 is mainly used to connect the refractive index and internal stress of the first aluminum nitride layer 1021 and the third aluminum nitride layer 1023, alleviating interface conflicts at both ends. The thickness of 7nm-10nm is sufficient to support the gradient range and avoids side effects and unnecessary process costs caused by excessive thickness.

[0035] In some embodiments of this application, the thickness of the third aluminum nitride layer 1023 is 5nm-8nm, for example, but not limited to, 5nm, 5.3nm, 5.5nm, 5.8nm, 6nm, 6.2nm, 6.5nm, 6.7nm, 6.9nm, 7nm, 7.2nm, 7.5nm, 7.7nm, and 8nm. Along the stacking direction away from the silicon substrate 100, the refractive index of the third aluminum nitride layer 1023 linearly decreases from 2.15 to 2.12 ± 0.02. Exemplarily, the range of the refractive index decrease of the third aluminum nitride layer 1023 may be linearly decreasing from 2.15 to 2.14, from 2.15 to 2.13, from 2.12 to 2.12, from 2.15 to 2.11, or from 2.15 to 2.1. The refractive index of the third aluminum nitride layer 1023 is close to that of the silicon nitride layer 103, which can optimize the optical transition of AlN-Si3N4 to reduce light reflection loss. Furthermore, its high nitrogen content provides strong adhesion to silicon nitride, enhancing the bonding force between layers and helping to maintain structural stability. A thickness design of 5nm-8nm can form a continuous nitrogen-rich interface layer while controlling the total thickness of the aluminum nitride layer 102.

[0036] In some specific embodiments of this application, the total thickness of the aluminum nitride layer 102 is 20nm-25nm, and its refractive index decreases from 2.22±0.01 to 2.12±0.01. Specifically, in the aluminum nitride layer 102, the thickness of the first aluminum nitride layer 1021 is 5nm-7nm, and its refractive index decreases from 2.22±0.01 to 2.2; the thickness of the second aluminum nitride layer 1022 is 8nm-10nm, and its refractive index decreases from 2.2 to 2.15; and the thickness of the third aluminum nitride layer 1023 is 7nm-8nm, and its refractive index decreases from 2.15 to 2.12±0.01. When the aluminum nitride layer 102 meets the above limitations, it can maximize the passivation effect while taking into account strong light absorption and stacking adhesion.

[0037] In this embodiment, the thickness of the silicon nitride (Si3N4) layer 103 is 65nm-85nm, for example, but not limited to 65nm, 67nm, 70nm, 72nm, 75nm, 78nm, 80nm, 83nm, and 85nm. The silicon nitride layer 103 mainly serves to reduce reflection and passivate. The optical thickness (110nm-140nm) of the 65nm-85nm thick silicon nitride layer 103 is beneficial to increasing the proportion of incident light (especially infrared light) that is reflected back to the silicon substrate 100, while avoiding excessive light loss within the film layer due to excessive thickness. In some specific embodiments of this application, the thickness of the silicon nitride layer 103 is 65nm-70nm.

[0038] In some embodiments of this application, the silicon nitride layer 103 has a uniform hydrogen density, meaning that the hydrogen content is the same in any equal volume region within the silicon nitride layer 103. In this case, the hydrogen content of the silicon nitride layer 103 is 5at%-35at%, for example, but not limited to 5at%, 10at%, 12.5at%, 15at%, 18at%, 20at%, 25at%, 30at%, 32at%, 33.3at%, and 35at%. In this application, the hydrogen content is expressed as the atomic percentage of hydrogen atoms, with "at%" representing the atomic percentage. In fact, the refractive index of the silicon nitride layer 103 is positively correlated with the hydrogen content. When the silicon nitride layer 103 has a uniform hydrogen density, it has a uniform refractive index, which is any value between 2 and 2.1, for example, but not limited to 2, 2.01, 2.02, 2.03, 2.04, 2.05, 2.06, 2.07, 2.08, 2.09, and 2.1. In some specific embodiments of this application, the hydrogen content of the silicon nitride layer 103 can be 10at%-30at%, 15at%-30at%, 20at%-30at%, or 25at%-30at. This application uses elliptic polarization spectroscopy combined with Fourier transform infrared spectroscopy (FTIR) to detect the hydrogen content. FTIR can quantitatively analyze the concentration of Si-H bonds and NH bonds and convert it into atomic percentage content.

[0039] In other embodiments of this application, along the stacking direction away from the silicon substrate 100, the silicon nitride layer 103 includes two or more layers with decreasing hydrogen content, such as two, three, four, five, or six layers, etc., with no specific limitation on the number of layers. In this case, the hydrogen content of the silicon nitride layer 103 is 5 at%-35 at%, and the hydrogen density is the same in each hydrogen content decreasing layer. Designing a gradient hydrogen content within the silicon nitride layer 103 is beneficial for balancing the dual effects of passivation and anti-reflection, while also having a positive impact on reducing hydrogen-induced degradation.

[0040] In some embodiments of this application, along the stacking direction away from the silicon substrate 100, the silicon nitride layer 103 includes three layers with decreasing hydrogen content, that is, the silicon nitride layer 103 includes a first silicon nitride layer 1031, a second silicon nitride layer 1032, and a third silicon nitride layer 1033. In this case, the cross-section of the silicon nitride layer 103 is as follows: Figure 4 As shown, the cross-section of the stacked passivation structure is as follows: Figure 5 As shown, the atomic percentage of hydrogen atoms in the first silicon nitride layer 1031, the second silicon nitride layer 1032, and the third silicon nitride layer 1033 decreases sequentially. That is, the first silicon nitride layer 1031, which is closer to the aluminum nitride layer 102, has the highest hydrogen content, while the third silicon nitride layer 1033, which is farther away from the aluminum nitride layer 102, has the lowest hydrogen content. In this case, the refractive index of the silicon nitride layer 103 exhibits a gradient change in the range of 2-2.1, with the refractive index of the first silicon nitride layer 1031, the second silicon nitride layer 1032, and the third silicon nitride layer 1033 decreasing sequentially, and the refractive index within each silicon nitride layer is the same.

[0041] In some embodiments of this application, the hydrogen content of the first silicon nitride layer 1031 is 25at%-35at%, for example, but not limited to 25at%, 26at%, 27at%, 28at%, 29at%, 30at%, 31at%, 32at%, 33at%, 33.3at%, 34at%, and 35at; the thickness of the first silicon nitride layer 1031 is 15nm-20nm, for example, but not limited to 15nm, 16nm, 17nm, 18nm, 19nm, and 20nm. The first silicon nitride layer 1031 is in direct contact with the aluminum nitride layer 102. Its higher hydrogen content facilitates the diffusion of hydrogen atoms to the AlN-Si interface and the silicon substrate 100, filling lattice defects and reducing interfacial recombination. Meeting the above thickness range ensures that the silicon nitride region closest to the silicon substrate 100 has a sufficient supply of hydrogen atoms. In some specific embodiments of this application, the thickness of the first silicon nitride layer 1031 is 15nm-20nm, and the hydrogen content is 25at%-30at.

[0042] In some embodiments of this application, the hydrogen content of the second silicon nitride layer 1032 is greater than 15 at% and less than 25 at%, for example, but not limited to 15.1 at%, 16 at%, 16.67 at%, 17 at%, 18 at%, 19 at%, 20 at%, 21 at%, 22 at%, 23 at%, 24 at%, and 24.9 at%; the thickness of the second silicon nitride layer 1032 is 20 nm-25 nm, for example, but not limited to 20 nm, 21 nm, 22 nm, 23 nm, 24 nm, and 25 nm. The first silicon nitride layer 1031 exhibits an "expanded state" due to the large number of hydrogen atoms filling it, while the third silicon nitride layer 103 exhibits a relatively "contracted state." The second silicon nitride layer 1032, as a transition layer, retains some passivation capability and can alleviate the stress abrupt change between the two layers, preventing film cracking under battery thermal cycling. Its thickness within the aforementioned 20 nm-25 nm range ensures the formation of an effective buffer band, improving light absorption. In some specific embodiments of this application, the thickness of the second silicon nitride layer 1032 is 20nm-25nm, and the hydrogen content is 15at%-20at.

[0043] In some embodiments of this application, the hydrogen content of the third silicon nitride layer 1033 is 5at%-15at%, for example, but not limited to 5at%, 6at%, 7at%, 8at%, 9at%, 10at%, 11at%, 12at%, 14at%, and 15at%; the thickness of the third silicon nitride layer 1033 is 30nm-40nm, for example, but not limited to 30nm, 32nm, 35nm, 38nm, and 40nm. The third silicon nitride layer 1033 is the part closest to the external environment in the stacked passivation structure and is also the incident surface of light, receiving the strongest light. Its relatively low hydrogen content and relatively thick thickness can prevent hydrogen oxidative stress (H2O) on the silicon nitride surface under light. + Extensive migration leads to hydrogen-induced degradation, and low hydrogen content is more conducive to maintaining the chemical and structural stability of the material. In some specific embodiments of this application, the thickness of the third silicon nitride layer 1033 is 30nm-35nm, and the hydrogen content is 5at%-10at%.

[0044] In some specific embodiments of this application, the thickness of the first silicon nitride layer 1031 is 16nm-18nm, and the hydrogen content is 28at%-32at; the thickness of the second silicon nitride layer 1032 is 22nm-24nm, and the hydrogen content is 17at%-19at; the thickness of the third silicon nitride layer 1033 is 32nm-36nm, and the hydrogen content is 13at%-15at. When the silicon nitride layer 103 meets the above limitations, it can maximize its synergistic passivation effect with the aluminum nitride layer 102, while also taking into account strong light absorption and mechanical strength. This application designs the hydrogen content of the silicon nitride layer 103 in a segmented gradient and precisely matches the thickness of each gradient. In terms of effect, it is sufficient to achieve the core objectives of hydrogen management, stress buffering, and optical optimization, and can also avoid the problems of complex processes, soaring costs, and reduced production capacity associated with too many layers, which is more in line with the needs of economical mass production.

[0045] Traditional uniform composite passivation structures struggle to simultaneously meet the three major requirements of high passivation efficiency, low stress mismatch, and strong interfacial bonding. Pursuing high-field passivation can lead to excessive stress and film peeling, while prioritizing mechanical properties reduces the passivation effect. The AlN linear gradient layer provided in this application aims to overcome this contradiction, achieving both refractive index and mechanical strength transitions. Furthermore, by matching the thickness of different refractive indices, the passivation effect, light absorption, and structural stability are significantly improved. Moreover, the hydrogen content and thickness of the Si3N4 layer are designed with a gradient, achieving hydrogen passivation while preventing hydrogen-induced degradation, thus further optimizing the synergistic passivation and anti-reflection effects between the Si3N4 and AlN layers.

[0046] This application provides a method for preparing a stacked passivation structure, the preparation process of which is as follows: Figure 6 As shown, it includes the following steps: S1: Provide a substrate, which includes a silicon substrate and an aluminum oxide layer. A first deposition is performed using an aluminum source and a nitrogen source to deposit an aluminum nitride layer on the surface of the aluminum oxide layer. The refractive index of the aluminum nitride layer gradually decreases along the stacking direction away from the silicon substrate. S2: A second deposition is performed using silicon and nitrogen sources to deposit a silicon nitride layer on the surface of the aluminum nitride layer, resulting in a stacked passivation structure.

[0047] In this embodiment, aluminum nitride and silicon nitride layers are deposited sequentially on a silicon substrate using a first deposition and a second deposition process. During the first deposition, the molar ratio of Al to N in the deposited aluminum nitride layer is gradually reduced by progressively decreasing the nitrogen source supply, resulting in a gradual decrease in refractive index with increasing thickness. The resulting stacked passivation structure exhibits both good passivation quality and structural stability, which is beneficial for improving the photoelectric conversion efficiency and extending the lifespan of solar cells.

[0048] In step S1, the first deposition employs atomic layer deposition (ALD) technology, with alternating purging of aluminum and nitrogen sources to form an aluminum nitride layer. Specifically, the aluminum source is purged to react with hydroxyl groups or other active sites on the silicon substrate surface, forming surface-adsorbed Al(CH3)2; then, the nitrogen source is purged to react with the surface-adsorbed Al(CH3)2, oxidizing methyl ligands to volatile products (such as CO2, H2O) and generating Al-N bonds, thereby forming aluminum nitride (AlN). In some embodiments of this application, the ALD equipment used for the first deposition may be, but is not limited to, a Beneq-TFS-200 or a Picosun-R-200.

[0049] In some embodiments of this application, the thickness of the alumina (Al2O3) layer is 3nm-6nm, for example, but not limited to 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 5.5nm, and 6nm.

[0050] 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 TMA being preferred; the nitrogen source includes, but is not limited to, ammonia (NH3), aluminum trichloride (AlCl3), and hydrazine (N2H4), with NH3 being preferred.

[0051] In this embodiment of the application, the first deposition includes 100 to 150 deposition cycles, such as, but not limited to, 100, 110, 120, 130, 140, and 150 cycles, to deposit an aluminum nitride layer with a predetermined thickness.

[0052] In this embodiment, each deposition cycle includes sequential aluminum source purging, first inert gas purging, nitrogen source purging, and second inert gas purging. The inert gas purging is used to remove unreacted growth sources or byproducts. The purity of the inert gas is greater than or equal to 99.999% to ensure process purity. The inert gas includes nitrogen (N2) and / or argon (Ar).

[0053] In this embodiment, a residence (wait) time is set after each purging of the growth source (TMA or NH3) and before the purging of the inert gas to ensure that TMA diffuses to all active sites to achieve monolayer saturated adsorption, and to ensure that NH3 fully contacts the Al-CH3 group and is completely converted into Al-N. The residence time can be 2s-5s, for example, but not limited to 2s, 3s, 4s, 5s, to ensure saturated adsorption.

[0054] In some embodiments of this application, the purging time of TMA in each deposition cycle of the first deposition is a constant value, which can be any value between 5 and 10 s, such as, but not limited to, 6 s, 7 s, and 8 s. Starting from the second deposition cycle, the purging time of TMA in each deposition cycle is reduced by 0.01-0.05 s compared to the previous deposition cycle, and the reduction time can be, for example, 0.01 s, 0.02 s, 0.03 s, 0.04 s, and 0.05 s. For example, the first deposition includes 120 deposition cycles, and the purging time of NH3 in each deposition cycle is always 6 s. The purging time of TMA in the first deposition cycle is 7.2 s, the purging time of TMA in the second deposition cycle is 7.18 s, the purging time of TMA in the third deposition cycle is 7.16 s, and so on, with the purging time of NH3 in the 120th deposition cycle being 4.82 s. Thus, as the thickness of the formed alumina layer increases, the molar ratio of aluminum atoms to nitrogen atoms decreases linearly from 1.2:1 to 0.8:1, which also causes the refractive index of the alumina layer to gradually decrease along the direction of thickness increase.

[0055] In some embodiments of this application, the temperature of the first deposition is 250°C-300°C, for example, but not limited to, 250°C, 260°C, 270°C, 280°C, 290°C, and 300°C. This temperature allows the growth source to decompose and be adsorbed, while avoiding adverse effects of high temperature on the silicon substrate. The power of the first deposition is 50W-200W, for example, but not limited to, 50W, 80W, 100W, 120W, 150W, 170W, and 200W.

[0056] In some embodiments of this application, during the first deposition process, the purge flow rates of the aluminum source and the nitrogen source remain constant. Specifically, the purge flow rate of TMA in each deposition cycle is any constant value between 50 sccm and 100 sccm, such as, but not limited to, 50 sccm, 60 sccm, 70 sccm, 80 sccm, 90 sccm, and 100 sccm; the purge flow rate of NH3 in each deposition cycle is any constant value between 100 sccm and 200 sccm, such as, but not limited to, 100 sccm, 120 sccm, 150 sccm, 180 sccm, and 200 sccm.

[0057] In some embodiments of this application, the purging time of the first inert gas is greater than or equal to 2 seconds, for example, but not limited to 2 seconds, 3 seconds, 4 seconds, 5 seconds, 6 seconds, 7 seconds, or 8 seconds, and the purging flow rate is 50 sccm-100 sccm, for example, but not limited to 50 sccm, 60 sccm, 70 sccm, 80 sccm, 90 sccm, or 100 sccm. In some specific embodiments of this application, the purging time of the first inert gas is 3 seconds to 5 seconds, which is sufficient to purify the TMA or byproducts remaining within the aforementioned preset TMA purging time, while saving energy.

[0058] In some embodiments of this application, the purging time of the second inert gas is greater than or equal to 5 seconds, for example, but not limited to 5 seconds, 6 seconds, 7 seconds, 8 seconds, 9 seconds, 10 seconds, 20 seconds, or 30 seconds, and the purging flow rate is 80 sccm-150 sccm, for example, but not limited to 80 sccm, 90 sccm, 100 sccm, 110 sccm, 120 sccm, 130 sccm, 140 sccm, or 150 sccm. Preferably, starting from the second deposition cycle, the purging time of the second inert gas in each deposition cycle is reduced by 0.02 seconds to 0.03 seconds compared to the previous deposition cycle. Essentially, this reduction is synchronized with the decrease in the TMA purging time. This approach can minimize process time and reduce energy consumption and emissions while ensuring the removal of unreacted growth sources and byproducts.

[0059] In step S2, the second deposition employs plasma-enhanced chemical vapor deposition (PECVD). An electric field is applied via radio frequency or other means, and the electric field energy ionizes silicon and nitrogen source molecules, generating active ions such as ions and free radicals, for example, SiH3. + NH2 - H + These active particles adsorb onto the substrate surface and undergo a chemical reaction to generate silicon nitride (Si3N4), while releasing byproducts such as H2. The byproducts detach from the substrate surface and eventually form a silicon nitride layer.

[0060] In this application, the silicon source includes, but is not limited to, one or more of silane (SiH4), silane, propane, and butane, with SiH4 being preferred; the nitrogen source includes, but is not limited to, ammonia (NH3); and the equipment for the second deposition can be a tubular PECVD furnace or a plate PECVD furnace.

[0061] In this embodiment, the temperature of the second deposition is 400℃-500℃, for example, but not limited to 400℃, 420℃, 450℃, 480℃, and 500℃. Here, the temperature of the second deposition refers to the chamber temperature of the PECVD equipment. During the deposition process, a large amount of hydrogen is introduced into the Si3N4 layer, which exists in the form of Si-H and NH. A suitable deposition temperature can give hydrogen atoms enough energy for hydrogen passivation and ensure the density and uniformity of the deposition layer.

[0062] In some embodiments of this application, during the second deposition, the SiH4 flow rate is 1000 sccm-2000 sccm, for example, but not limited to, 1000 sccm, 1500 sccm, 1800 sccm, or 2000 sccm; the NH3 flow rate is 2000 sccm-8000 sccm, for example, but not limited to, 2000 sccm, 3000 sccm, 4500 sccm, 5000 sccm, 7200 sccm, or 8000 sccm; and the SiH4 to NH3 flow rate ratio is 1:(2-10), for example, but not limited to, 1:2, 1:2.5, 1:2.8, 1:3, 1:3.5, 1:3.6, 1:4, 1:5, 1:6, 1:6.4, 1:7, 1:7.6, or 1: 8, 1:9, 1:10; the second deposition time is 600s-700s, for example, but not limited to 600s, 620s, 650s, 680s, 700s, so as to deposit a silicon nitride layer with a preset thickness and hydrogen content; the furnace pressure of the second deposition is 200Pa-250Pa, for example, but not limited to 200Pa, 210Pa, 220Pa, 230Pa, 240Pa, 250Pa; the radio frequency power of the second deposition is 10000W-18000W, for example, but not limited to 10000W, 12000W, 14000W, 15000W, 18000W. Appropriate furnace pressure and radio frequency power help control the generation rate and deposition rate of active free radicals, and avoid the silicon nitride layer from being deposited too quickly locally, resulting in protrusions or agglomerations. When the process parameters of the second deposition meet the above limitations, the deposition rate of the silicon nitride layer is 0.1 nm / s - 0.13 nm / s, which means that the thickness of the silicon nitride layer increases by 0.1 nm - 0.13 nm per second. The silicon nitride layer deposited in this way has a uniform overall texture, with a preset thickness and uniform refractive index and hydrogen content.

[0063] In other embodiments of this application, the second deposition includes two or more SiH4 decreasing depositions. By changing the deposition process, the hydrogen content of the silicon nitride layer decreases in a gradient, thereby obtaining two or more silicon nitride sublayers. The number of silicon nitride sublayers is not limited.

[0064] In some specific embodiments of this application, the second deposition includes three SiH4 decreasing depositions, that is, the second deposition S2 successively includes high-hydrogen deposition S201, medium-hydrogen deposition S202, and low-hydrogen deposition S203. In this case, the preparation process of the stacked passivation structure is as follows: Figure 7 As shown. Correspondingly, a first silicon nitride layer is obtained by high hydrogen deposition, a second silicon nitride layer is obtained by medium hydrogen deposition, and a third silicon nitride layer is obtained by low hydrogen deposition, with the hydrogen content of the first, second, and third silicon nitride layers decreasing sequentially.

[0065] In some embodiments of this application, during high-hydrogen deposition, the flow rate of SiH4 is 1600 sccm-2000 sccm, for example, but not limited to 1600 sccm, 1700 sccm, 1800 sccm, or 2000 sccm; and the flow rate of NH3 is 2000 sccm-3200 sccm, for example, but not limited to 2000 sccm, 2100 sccm, 2200 sccm, 2500 sccm, 2800 sccm, 3000 sccm, or 3200 sccm. The high-hydrogen deposition time is 100s-150s, for example, but not limited to 100s, 120s, 130s, 140s, or 150s; the furnace pressure for high-hydrogen deposition is 200Pa-220Pa, for example, but not limited to 200Pa, 210Pa, or 220Pa; and the power is 10000W-14000W, for example, but not limited to 12000W, 13000W, or 14000W. When the process parameters for high-hydrogen deposition meet the above limitations, the deposition rate of the first silicon nitride layer is 0.12nm / s-0.14nm / s, for example, but not limited to 0.13nm / s. The first silicon nitride layer obtained in this way has a uniform texture, a thickness of 15nm-20nm, and a hydrogen content of 25at%-35at%.

[0066] In the embodiments of this application, during hydrogen deposition, the flow rate of SiH4 is 1400 sccm-1600 sccm, for example, but not limited to 1400 sccm, 1500 sccm, 1590 sccm, and 1600 sccm; the flow rate of NH3 is 4200 sccm-4800 sccm, for example, but not limited to 4200 sccm, 4300 sccm, 4400 sccm, 4500 sccm, 4600 sccm, and 4800 sccm. The deposition time for intermediate hydrogen is 150s-250s, for example, but not limited to 150s, 180s, 200s, 230s, and 250s; the furnace pressure for intermediate hydrogen deposition is 210Pa-230Pa, for example, but not limited to 210Pa, 220Pa, and 230Pa; and the power is 13000W-16000W, for example, but not limited to 13000W, 15000W, and 16000W. When the intermediate hydrogen deposition process parameters meet the above limitations, the deposition rate of the second silicon nitride layer is 0.1nm / s-0.12nm / s, for example, but not limited to 0.11nm / s. The second silicon nitride layer obtained in this way has a uniform texture, a thickness of 20nm-25nm, and a hydrogen content greater than 15at% and less than 25at%.

[0067] In the embodiments of this application, during low-hydrogen deposition, the flow rate of SiH4 is 1000 sccm-1200 sccm, for example, but not limited to 1000 sccm, 1100 sccm, or 1200 sccm; the flow rate of NH3 is 6400 sccm-7200 sccm, for example, but not limited to 6400 sccm, 6500 sccm, 6600 sccm, 6700 sccm, 6800 sccm, 6900 sccm, 7000 sccm, 7100 sccm, or 7200 sccm. The low-hydrogen deposition time is 280s-320s, for example, but not limited to 280s, 290s, 300s, 310s, and 320s; the furnace pressure for low-hydrogen deposition is 220Pa-240Pa, for example, but not limited to 220Pa, 230Pa, and 240Pa; and the power is 13000W-16000W, for example, but not limited to 13000W, 14000W, 15000W, and 16000W. When the process parameters for low-hydrogen deposition meet the above limitations, the deposition rate of the third silicon nitride layer is 0.09nm / s-0.11nm / s, for example, but not limited to 0.1nm / s. The resulting third silicon nitride layer has a uniform texture, a thickness of 30nm-40nm, and a hydrogen content of 5at%-15at%.

[0068] The stacked passivation structure prepared by the preparation method provided in the embodiments of this application is as described above, and will not be repeated here.

[0069] This application first employs an ALD process to deposit an aluminum nitride layer on a silicon substrate. By dynamically decreasing the supply of TMA (Total Molecular Mass Activated), the molar ratio of Al to N in the aluminum nitride layer is varied from high to low, resulting in a linear decrease in the refractive index of the aluminum nitride layer along the stacking direction away from the silicon substrate. Next, a PECVD process is used to deposit a silicon nitride layer on the aluminum nitride layer. Further, by gradually reducing the SiH4 flow rate, the hydrogen content in the silicon nitride layer is varied from high to low, resulting in a gradient decrease in the hydrogen content of the silicon nitride layer along the stacking direction away from the silicon substrate, while simultaneously controlling the film growth rate. The resulting stacked passivation structure can simultaneously meet the requirements of refractive index transition and mechanical strength adaptation, exhibiting both excellent passivation effect and mechanical stability. Furthermore, this fabrication method is continuous, has low temperature requirements, is environmentally friendly, and is suitable for industrial production.

[0070] This application also provides a solar cell, which includes the stacked passivation structure provided above or the stacked passivation structure prepared by the preparation method provided above.

[0071] In some embodiments of this application, solar cells, such as Figure 8 As shown, the structure includes a stacked passivation structure 10, a front passivation structure 20, a front electrode 30, and a back electrode 40. The aluminum nitride layer 102 and silicon nitride layer 103 in the stacked passivation structure 10 are the back structure of the solar cell. The front passivation structure 20 is disposed on the surface of the silicon substrate 100 in the stacked passivation structure 10 that is away from the aluminum nitride layer 102. The front electrode 30 may also include a main grid and a fine grid. The back electrode 40 may include a metal layer (such as aluminum, silver, etc.) that fully covers or partially contacts the back electrode. This application also provides a method for fabricating a solar cell, including providing a silicon substrate, performing a first deposition and a second deposition on the surface of the silicon substrate to obtain a stacked passivation structure, thereby forming a solar cell.

[0072] 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.

[0073] Example 1 1) Preparation: The back-to-back full-boat substrate is sent into the cavity. The substrate includes a silicon wafer and an aluminum oxide layer with a thickness of 3nm on the silicon wafer. The process is started. The process cavity is evacuated and the furnace temperature is set to 280℃. The subsequent process maintains a constant temperature of 280℃.

[0074] 2) First deposition: The total number of deposition cycles was 120, with the purging flow rates of TMA, NH3, and N2 remaining constant. The first deposition cycle consisted of sequential TMA purging for 7.2 s, N2 purging for 3 s, NH3 purging for 6 s, and N2 purging for 8 s. The TMA purging flow rate was 80 sccm, the NH3 purging flow rate was 150 sccm, and the N2 purging flow rate was 80 sccm. At this time, the atomic molar ratio of TMA and NH3 supplied was Al:N = 1.2:1. The second deposition cycle consisted of TMA purging for 7.18 s, N2 purging for 3 s, NH3 purging for 6 s, and N2 purging for 7.98 s. Similarly, the TMA purging time and N2 purging time for each deposition cycle are reduced by 0.02 s compared to the previous deposition cycle. The 120th deposition cycle consisted of a TMA purging cycle of 4.82 s, an N2 purging cycle of 3 s, an NH3 purging cycle of 6 s, and an N2 purging cycle of 5.6 s. At this time, the molar ratio of atoms supplied by TMA and NH3 was Al:N = 0.8:1. An aluminum nitride layer with a thickness of 20 nm was obtained, and the refractive index gradually decreased from 2.22 to 2.11 along the stacking direction away from the silicon substrate.

[0075] 3) Second deposition: at a temperature of 450℃, consisting of high-hydrogen deposition, medium-hydrogen deposition, and low-hydrogen deposition in sequence. High-hydrogen deposition: deposition time was 120 s, SiH4 flow rate was 1700 sccm, NH3 flow rate was 3000 sccm, furnace pressure was 200 Pa, and RF power was 12000 W. The deposition rate was 0.13 nm / s, resulting in a first silicon nitride layer with a thickness of 16 nm and a hydrogen content of 25 at%. Hydrogen deposition: deposition time was 200 s, SiH4 flow rate was 1600 sccm, NH3 flow rate was 4500 sccm, furnace pressure was 210 Pa, and RF power was 15000 W. The deposition rate was 0.11 nm / s, resulting in a second silicon nitride layer with a thickness of 22 nm and a hydrogen content of 17 at%. Low-hydrogen deposition: deposition time was 300 s, SiH4 flow rate was 1100 sccm, NH3 flow rate was 7000 sccm, furnace pressure was 220 Pa, and RF power was 15000 W. The deposition rate was 0.09 nm / s, resulting in a 30 nm thick third silicon nitride layer with a hydrogen content of 8 at%. This process yields a stacked passivation structure.

[0076] Example 2 1) Preparation: The only difference from Example 1 is that the furnace temperature is 270°C.

[0077] 2) First deposition: The total number of deposition cycles was 130, with the purging flow rates of TMA, NH3, and N2 remaining constant. First deposition cycle: The only difference from Example 1 is that the TMA purging time is 7s, and the atomic molar ratio of TMA and NH3 supplied is Al:N=1.18:1; Starting from the second deposition cycle, the TMA purging time and N2 purging time were reduced by 0.01 s compared to the previous deposition cycle in each deposition cycle. This continued until the 150th deposition cycle, when the TMA purging time decreased to 5.51 s and the N2 purging time decreased to 6.51 s, at which point the atomic molar ratio of TMA and NH3 supplied was Al:N = 0.9:1. An aluminum nitride layer with a thickness of 25 nm was obtained, and the refractive index gradually decreased from 2.21 to 2.13 along the stacking direction away from the silicon substrate.

[0078] 3) Secondary deposition: This includes, in sequence, high-hydrogen deposition, medium-hydrogen deposition, and low-hydrogen deposition. High-hydrogen deposition: The difference from Example 1 is that the flow rate of SiH4 is 1800 sccm and the flow rate of NH3 is 3000 sccm, resulting in a first silicon nitride layer with a thickness of 15 nm and a hydrogen content of 26 at%. Hydrogen deposition: The difference from Example 1 is that the deposition time is 210s, the SiH4 flow rate is 1600sccm, and the NH3 flow rate is 4600sccm, resulting in a second silicon nitride layer with a thickness of 23nm and a hydrogen content of 16at%. Low-hydrogen deposition: The difference from Example 1 is that the deposition time is 310s, the SiH4 flow rate is 1000sccm, and the NH3 flow rate is 7000sccm, resulting in a third silicon nitride layer with a thickness of 32nm and a hydrogen content of 7at%. This process yields a stacked passivation structure.

[0079] Example 3 1) Preparations are the same as in Example 1; 2) The first deposition is the same as in Example 1; 3) The difference between the second deposition and Example 1 is that the thickness of the silicon nitride layer is 90 nm, wherein the first silicon nitride layer is 20 nm, the second silicon nitride layer is 25 nm, and the third silicon nitride layer is 45 nm. This process yields a stacked passivation structure.

[0080] Example 4 1) Preparations are the same as in Example 1; 2) The first deposition is the same as in Example 1; 3) The difference between the second deposition and Example 1 is that the hydrogen content of the first silicon nitride layer is 36 at%, the hydrogen content of the second silicon nitride layer is 22 at%, and the hydrogen content of the third silicon nitride layer is 18 at%. This process yields a stacked passivation structure.

[0081] Example 5 1) Preparations are the same as in Example 1; 2) The difference between the first deposition and Example 1 is that the refractive index of the aluminum nitride layer decreases linearly from 2.3 to 2.0 along the stacking direction away from the substrate; 3) The second deposition is the same as in the example; This process yields a stacked passivation structure.

[0082] Example 6 1) Preparations are the same as in Example 1; 2) The difference between the first deposition and Example 1 is that the thickness of the aluminum nitride layer is 30 nm; 3) The second deposition is the same as in Example 1; This process yields a stacked passivation structure.

[0083] Example 7 1) Preparations are the same as in Example 1; 2) The first deposition is the same as in Example 1; 3) Second deposition: Temperature 450℃, deposition time 650s, SiH4 flow rate 1800sccm, NH3 flow rate 4500sccm, furnace pressure 230Pa, RF power 14000W. Deposition rate 0.11nm / s, yielding a silicon nitride layer with a thickness of 65nm and a hydrogen content of 25at%. This process yields a stacked passivation structure.

[0084] Example 8 1) Preparations are the same as in Example 1; 2) The first deposition is the same as in Example 5; 3) The second deposition is the same as in Example 7; This process yields a stacked passivation structure.

[0085] Example 9 1) Preparations are the same as in Example 1; 2) The first deposition is the same as in Example 6; 3) The second deposition is the same as in Example 7; This process yields a stacked passivation structure.

[0086] Example 10 1) Preparations are the same as in Example 1; 2) The first deposition is the same as in Example 1; 3) The difference between the second deposition and Example 7 is that the SiH4 flow rate is 1500 sccm and the NH3 flow rate is 5400 sccm. The hydrogen content of the silicon nitride layer is 30 at%; This process yields a stacked passivation structure.

[0087] Example 11 1) Preparations are the same as in Example 1; 2) The first deposition is the same as in Example 1; 3) The difference between the second deposition and Example 7 is that the SiH4 flow rate is 1000 sccm, the NH3 flow rate is 8000 sccm, and the hydrogen content of the silicon nitride layer is 10 at%; This process yields a stacked passivation structure.

[0088] Example 12 1) Preparations are the same as in Example 1; 2) The first deposition is the same as in Example 1; 3) The difference between the second deposition and Example 7 is that the deposition time is 780s, resulting in a silicon nitride layer with a thickness of 87 nm; This process yields a stacked passivation structure.

[0089] Example 13 1) Preparations are the same as in Example 1; 2) The first deposition is the same as in Example 1; 3) The difference between the second deposition and Example 7 is that the deposition time is 580s, resulting in a silicon nitride layer with a thickness of 63nm; This process yields a stacked passivation structure.

[0090] Comparative Example 1 1) Preparations are the same as in Example 1; 2) The difference between the first deposition and Example 1 is that each deposition cycle includes TMA purging for 6 seconds, N2 purging for 3 seconds, NH3 purging for 5 seconds, and N2 purging for 5 seconds. The TMA purging flow rate is 80 sccm, the NH3 purging flow rate is 150 sccm, and the N2 purging flow rate is 80 sccm. Under these conditions, the atomic molar ratio of TMA and NH3 supplied is Al:N=1:1. After 100 cycles, a first aluminum nitride layer with a thickness of 20 nm and a refractive index of 2.18 is obtained.

[0091] 3) The second deposition is the same as in Example 1; This process yields a stacked passivation structure.

[0092] Comparative Example 2 1) Preparations are the same as in Example 1; 2) The first sedimentary sediment is the same as that in Comparative Example 1; 3) Second deposition: Same as in Example 7; This process yields a stacked passivation structure.

[0093] Comparative Example 3 1) Preparations are the same as in Example 1; 2) The difference between the first deposition and Example 1 is that NH3 is replaced with O3, and a 20nm aluminum oxide Al2O3 layer is deposited.

[0094] 3) The second deposition is the same as in Example 1; This process yields a stacked passivation structure.

[0095] Comparative Example 4 The difference from Example 1 is that no second deposition is performed, the pretreatment and the first deposition are the same as in Example 1, and the final passivated structure only contains a substrate and an aluminum nitride layer.

[0096] Comparative Example 5 The difference from Example 1 is that the first deposition is not performed, and the pretreatment and second deposition are the same as in Example 1. The final passivation structure only contains a substrate and a silicon nitride layer.

[0097] Solar cells were fabricated using the stacked passivation structures or passivation structures of Examples 1-13 and Comparative Examples 1-5, and tested under standard test conditions (STC: irradiance 1000 W / m²). 2 Battery performance was tested at 25℃ and AM1.5G spectrum, including open-circuit voltage Uoc, circuit density, fill factor FF, and light decay LID using the current-voltage (IV) characteristic test method. The test results are shown in Table 1. Table 1. Summary of efficiency and yield of batteries from Examples 1-13 and Comparative Examples 1-5

[0098] As shown in Table 1, the stacked passivation structures prepared in Examples 1 and 2 exhibit the best performance. The solar cells assembled from these two structures have an open-circuit voltage higher than 735 mV, a photoelectric conversion efficiency exceeding 26%, and a light decay of less than 0.1%, significantly outperforming other examples and all comparative examples. This is because Examples 1 and 2 achieve a smooth transition in refractive index and mechanical strength through a graded refractive index aluminum nitride layer, alleviating stress mismatch with the silicon nitride layer. Simultaneously, the graded hydrogen content silicon nitride layer synergistically performs passivation and anti-reflection effects, effectively reducing interfacial recombination and light reflection losses. Therefore, the open-circuit voltage, current density, and fill factor of the cells are all at high levels, with extremely low light decay and excellent long-term stability.

[0099] Comparing Examples 3-6 with Examples 1-2, it is evident that altering the thickness and refractive index of the aluminum nitride layer, as well as the thickness and hydrogen content of the silicon nitride layer, can all affect battery performance. Compared to Example 3, the silicon nitride layer in Example 1 has a suitable thickness, which avoids increasing light loss within the film layer, thus preventing a decrease in current density and fill factor. Compared to Example 4, the silicon nitride layer in Example 1 has a suitable hydrogen content, which avoids exacerbating hydrogen-induced degradation and increasing light decay. Compared to Example 5, the aluminum nitride layer in Example 1 exhibits a suitable refractive index variation pattern, effectively reducing light reflection loss. Compared to Example 6, the aluminum nitride layer in Example 1 has a suitable thickness, which is beneficial for reducing series resistance and promoting carrier transport.

[0100] Comparing Examples 7-13 and Examples 1-2, it can be seen that the silicon nitride layer with gradient hydrogen content can better balance the passivation effect and the resistance to hydrogen-induced degradation compared to the silicon nitride layer with single hydrogen content. Therefore, the batteries in Examples 1 and 2 have higher efficiency and lower light decay.

[0101] The battery performance of each comparative example was significantly worse than that of the example: Comparative Example 1 used an aluminum nitride layer with a single refractive index, which could not achieve a gradual transition in refractive index and mechanical strength, and the stress mismatch problem was not alleviated, resulting in increased interfacial recombination and decreased efficiency and stability; In Comparative Example 2, the refractive index of the aluminum nitride layer was uniform and the hydrogen content of the silicon nitride layer was uniform, with neither a gradual change in refractive index nor a gradient in hydrogen content, resulting in poor passivation and stress coordination, and the highest light decay; Comparative Example 3 used an aluminum oxide layer instead of an aluminum nitride layer, but the field effect passivation effect of aluminum oxide was weaker than that of aluminum nitride, and the interfacial bonding with the silicon nitride layer was poor, resulting in insufficient efficiency and stability; Comparative Example 4 had no silicon nitride layer, so the anti-reflection and passivation effects were missing, resulting in the lowest photoelectric conversion efficiency and severe light decay; Comparative Example 5 had no aluminum nitride layer, which not only failed to achieve an effective gradual change in refractive index and stress coordination, but also increased the risk of interfacial peeling, resulting in unsatisfactory photoelectric conversion efficiency and stability.

[0102] In summary, the stacked passivation structure provided in this application features an aluminum nitride layer with a gradient refractive index and a silicon nitride layer with a gradient hydrogen content. This design simultaneously solves the problems of passivation effect, refractive index transition, and stress imbalance in traditional passivation structures, effectively improving the photoelectric conversion efficiency and stability of solar cells.

[0103] 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 can understand that implementing all or part of the processes of the above embodiments and making equivalent changes in accordance with the claims of this application still fall within the scope of this application.

Claims

1. A stacked passivation structure, characterized in that, It includes a silicon substrate and an aluminum oxide layer, an aluminum nitride layer, and a silicon nitride layer sequentially disposed on the surface of the silicon substrate; In particular, along the stacking direction away from the silicon substrate, the refractive index of the aluminum nitride layer gradually decreases.

2. The stacked passivation structure as described in claim 1, characterized in that, The thickness of the aluminum nitride layer is 17nm-26nm; and / or, the refractive index of the aluminum nitride layer is 2.10-2.25; and / or, along the stacking direction away from the silicon substrate, the molar ratio of aluminum atoms to nitrogen atoms in the aluminum nitride layer decreases linearly from (1.2±0.1):1 to (0.8±0.1):

1.

3. The stacked passivation structure as described in claim 1 or 2, characterized in that, The thickness of the silicon nitride layer is 65nm-85nm, and the hydrogen content is 5at%-35at.

4. The stacked passivation structure according to any one of claims 1-3, characterized in that, Along the stacking direction away from the silicon substrate, the aluminum nitride layer includes a first aluminum nitride layer, a second aluminum nitride layer, and a third aluminum nitride layer; The thickness of the first aluminum nitride layer is 5nm-8nm, and the refractive index of the first aluminum nitride layer linearly decreases from 2.23±0.02 to 2.2; and / or, The thickness of the second aluminum nitride layer is 7nm-10nm, and the refractive index of the second aluminum nitride layer decreases linearly from 2.2 to 2.15; and / or, The thickness of the third aluminum nitride layer is 5nm-8nm, and the refractive index of the third aluminum nitride layer decreases linearly from 2.15 to 2.12±0.

02.

5. The stacked passivation structure according to any one of claims 1-4, characterized in that, Along the stacking direction away from the silicon substrate, the silicon nitride layer includes a first silicon nitride layer, a second silicon nitride layer, and a third silicon nitride layer; The hydrogen content of the first silicon nitride layer, the second silicon nitride layer, and the third silicon nitride layer decreases sequentially.

6. The stacked passivation structure as described in claim 5, characterized in that, The thickness of the first silicon nitride layer is 15nm-20nm, and the hydrogen content is 25at%-35at%; and / or, The second silicon nitride layer has a thickness of 20nm-25nm and a hydrogen content greater than 15at% and less than 25at%; and / or, The thickness of the third silicon nitride layer is 30nm-40nm, and the hydrogen content is 5at%-15at.

7. A method for preparing a stacked passivation structure, characterized in that, Includes the following steps: A substrate is provided, the substrate comprising a silicon substrate and an aluminum oxide layer, a first deposition is performed using an aluminum source and a nitrogen source, an aluminum nitride layer is deposited on the surface of the aluminum oxide layer, and the refractive index of the aluminum nitride layer gradually decreases along the stacking direction away from the silicon substrate; A second deposition is performed using silicon and nitrogen sources to deposit a silicon nitride layer on the surface of the aluminum nitride layer, resulting in a stacked passivation structure.

8. The method for preparing the stacked passivation structure as described in claim 7, characterized in that, In the first deposition, the molar ratio of aluminum in the aluminum source to nitrogen in the nitrogen source decreases linearly from (1.2±0.1):1 to (0.8±0.1):

1.

9. The method for preparing the stacked passivation structure as described in claim 7 or 8, characterized in that, In the second deposition, the volumetric flow rate ratio of the silicon source to the nitrogen source is 1:(2-10).

10. A solar cell, characterized in that, This includes the stacked passivation structure as described in any one of claims 1-6 or the stacked passivation structure prepared by the preparation method described in any one of claims 7-9.

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