Method for forming Al2O3 / SiO2 bilayer on silicon wafer and photovoltaic device processed by plasma
By forming an Al2O3/SiO2 bimolecular layer on the silicon wafer and using plasma-assisted deposition technology, the problem of insufficient hydrogen content at lower temperatures of the Al2O3 film is solved, achieving efficient interface passivation and improved battery performance.
Patent Information
- Application Number
- CN202411713969.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-26
- Publication Date
- 2025-04-25
AI Technical Summary
In the prior art, when depositing Al2O3 films, it is difficult to obtain high film density and sufficient hydrogen content at lower temperatures, resulting in poor interface passivation effect.
Using the method of forming an Al2O3/SiO2 bilayer on a silicon wafer, the Al2O3 and SiO2 layers are deposited at higher temperatures through plasma-assisted deposition technology, and H2 gas is introduced during the annealing process to increase the hydrogen content.
A high hydrogen content Al2O3/SiO2 bilayer passivation film is achieved, which significantly improves the surface passivation effect and battery performance of photovoltaic devices.
Smart Images
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Abstract
Description
Technical Field
[0001] The present application belongs to the technical field of crystalline silicon photovoltaic devices, and in particular, relates to a method for forming an Al2O3 / SiO2 bilayer on a silicon wafer and a plasma-treated photovoltaic device. Background Art
[0002] Electronic passivation of c-Si surfaces with dielectric layers is particularly important for various semiconductor devices, especially crystalline silicon (c-Si) solar cells. Al2O3 is a material that has rapidly gained popularity in the past few years as a thin film passivation material for crystalline silicon (c-Si) photovoltaic devices (PV), and is therefore the most prominent and effective dielectric passivation layer. Its effectiveness is attributed to its high total fixed negative charge density. In combination with a low interface defect density, although the low density represents a fairly good chemical surface passivation, the high total fixed negative charge density leads to a reduction in the surface electron density, which has an important field effect contribution to the c-Si surface passivation.
[0003] But there are many technical issues to be solved in order to deposit Al2O3 in solar cells. For atomic layer (ALD) deposited thin films, ALD is less important for field effect passivation. The optimal deposition temperature is usually in the range of 150-250°C. Although the passivation level is not very sensitive to the deposition temperature, the optimal chemical passivation results in insufficient Al2O3 film density at lower temperatures, while Al2O3 has too low a hydrogen content at higher temperatures. In both cases, Al2O3 cannot provide enough hydrogen to passivate the Si dangling bonds at the interface, either because the hydrogen diffuses outward too much into the environment or because the hydrogen storage is too small to start deposition.
[0004] Considering that one of the steps in the annealing of Al2O3 is crucial for fully activating the surface passivation, the optimal temperature is about 400°C, at which sufficient hydrogen can be released from the film, and the hydrogen from the film can reduce the interface state density. In addition, relevant evidence shows that excellent surface passivation levels can also be provided by annealing in N2 gas, and the duration of the annealing step can be as short as 1 minute. Al2O3 is also stable enough in high-temperature firing steps, such as used in solar cells with screen-printed metallization. Therefore, there is an urgent need for a high-hydrogen passivation film based on Al2O3 to enhance the surface passivation effect of photovoltaic devices, thereby improving cell performance. Summary of the invention
[0005] In order to solve the problems existing in the prior art, the purpose of the present application is to provide a method for forming an Al2O3 / SiO2 bilayer on a silicon wafer and a plasma-treated photovoltaic device, wherein an Al2O3 / SiO2 bilayer passivation film is deposited on the surface of the silicon wafer, and the Al2O3 / SiO2 bilayer passivation film is treated with plasma to increase the hydrogen content so that it has a high passivation effect. The method can be applicable to various polycrystalline / single crystal solar cells, as well as the application of other types of passivation layers.
[0006] Specifically, this application involves the following aspects:
[0007] 1. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer, comprising the following steps:
[0008] (1) cleaning the surface of a silicon wafer and loading it on a graphite boat, placing the graphite boat loaded with the silicon wafer in a plasma-assisted deposition reaction chamber; (2) discharging the graphite boat through a radio frequency power supply, and introducing a first precursor and a second precursor into the plasma-assisted deposition reaction chamber respectively, wherein the first precursor is used to deposit an Al2O3 layer at a deposition temperature, and the second precursor is used to deposit an SiO2 layer at a deposition temperature; after depositing the Al2O3 layer and / or the SiO2 layer, introducing a passivation gas into the plasma-assisted deposition reaction chamber to ionize and generate plasma to treat the Al2O3 layer interface and / or the SiO2 layer interface to obtain an Al2O3 / SiO2 bilayer; (3) introducing H2 into the plasma-assisted deposition reaction chamber and annealing at an annealing temperature.
[0009] 2. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to item 1, wherein when the silicon wafer is a p-type silicon wafer, the method further comprises the following steps: repeating step (2) to obtain an i-layer Al2O3 / SiO2 bilayer.
[0010] 3. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to item 2, wherein the number of layers i of the i-layer Al2O3 / SiO2 bilayer is i=3.
[0011] 4. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to item 1, wherein the first precursor includes trimethylaluminum, and the discharge RF power discharged to the graphite boat by the RF power supply is in the range of 5000-12000w; the flow rate of trimethylaluminum is in the range of 80-150sccm, and the flow rate of nitrous oxide is in the range of 4000-8000sccm; the second precursor includes bis(diethylaminosilane); the flow rate of bis(diethylaminosilane) is in the range of 100-500sccm; the first precursor also includes nitrous oxide.
[0012] 5. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to item 1, wherein the passivation gas comprises a mixture of one or two of H2, N2, NH3, O2 or Ar; preferably, the passivation gas comprises H2; the flow rate of the passivation gas is in the range of 30-200sccm; preferably, the flow rate of the passivation gas is in the range of 50-100sccm; more preferably, the flow rate of the passivation gas is 100sccm.
[0013] 6. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to item 1, wherein the thickness of the Al2O3 layer of the Al2O3 / SiO2 bilayer is in the range of 2-5nm; preferably, the thickness of the Al2O3 layer of the Al2O3 / SiO2 bilayer is 3nm; the thickness of the SiO2 layer of the Al2O3 / SiO2 bilayer is in the range of 1-4nm; preferably, the thickness of the SiO2 layer of the Al2O3 / SiO2 bilayer is 2nm.
[0014] 7. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to item 1, wherein the deposition temperature ranges from 250-600°C; preferably, the deposition temperature is 400°C; the annealing temperature ranges from 350-600°C; preferably, the annealing temperature ranges from 450-550°C.
[0015] 8. A plasma-treated photovoltaic device according to any one of items 1-7, comprising: a silicon substrate and a dielectric passivation film; wherein the dielectric passivation film comprises i-layer Al2O3 / SiO2 bilayer; wherein the Al2O3 / SiO2 bilayer comprises an Al2O3 layer, an Al2O3 top interface, a SiO2 layer and a SiO2 top interface.
[0016] 9. A plasma-treated photovoltaic device according to item 8, wherein the thickness of the Al2O3 layer of the Al2O3 / SiO2 bilayer is in the range of 2-5nm; preferably, the thickness of the Al2O3 layer of the Al2O3 / SiO2 bilayer is 3nm; the thickness of the SiO2 layer of the Al2O3 / SiO2 bilayer is in the range of 1-4nm; preferably, the thickness of the SiO2 layer of the Al2O3 / SiO2 bilayer is 2nm.
[0017] 10. A plasma-treated photovoltaic device according to item 8, wherein the surface of the silicon substrate is a textured pyramid velvet surface or a pyramid base surface after alkali polishing.
[0018] Beneficial Effects
[0019] 1. The Al2O3 / SiO2 bilayer passivation film obtained by the method of forming an Al2O3 / SiO2 bilayer on a silicon wafer proposed in this application has a higher passivation effect than the ordinary Al2O3 / SiO2 bilayer due to the high hydrogen content of the deposition source.
[0020] 2. The SiO2 layer can enhance the chemical passivation effect. Since the Al2O3 layer is not suitable for field passivation of n-type silicon wafers, the multi-layer combination of Al2O3 / SiO2 can reduce the adverse field passivation effect of the Al2O3 layer on the n-type. In addition, PEALD can be used to efficiently deposit the Al2O3 / SiO2 bilayer. The deposition process is highly operable, the deposition process time is greatly reduced, and it has a high-temperature annealing function of 500-600℃.
[0021] 3. The special gas source used for multi-bilayer deposition can be kept consistent, so that it is easier to use in the photovoltaic industry; the Al2O3 / SiO2 bilayer is easy to expand different combinations of more materials, which is not only suitable for various polycrystalline / single crystal solar cells, but also for the use of other passivation layers. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1A A flow chart of a method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to an embodiment of the present application is illustrated;
[0023] Figure 1B Another flow chart of a method for depositing an Al2O3 / SiO2 bilayer on a silicon wafer according to an embodiment of the present application is illustrated;
[0024] Figure 2 The schematic diagram of the structure of a photovoltaic device treated by plasma according to an embodiment of the present application is shown;
[0025] Figure 3 The figure shows a schematic diagram of the relationship between annealing temperature and minority carrier lifetime in the process of preparing a plasma-treated photovoltaic device by a method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to an embodiment of the present application. DETAILED DESCRIPTION
[0026] The present application is further described below in conjunction with examples. It should be understood that the examples are only used to further describe and illustrate the present application and are not used to limit the present application.
[0027] Unless otherwise defined, the technical and scientific terms in this specification have the same meaning as those generally understood by those skilled in the art. Although similar or identical methods and materials as described herein may be used in experiments or practical applications, materials and methods are described herein below. In the event of a conflict, the present specification including the definitions therein shall prevail. In addition, materials, methods and examples are provided for illustration only and are not restrictive. The present application is further described below in conjunction with specific embodiments, but is not intended to limit the scope of the present application.
[0028] As mentioned above, in order to efficiently passivate the exposed, i.e., undiffused n / p-type c-Si front surface, the prior art generally uses ALD to deposit a single layer of Al2O3 film at a low temperature of 200-400°C; for the SiO2 layer, it is usually thermally oxidized and annealed at a temperature of 600-700°C on a p-type silicon wafer, and is applied to the emitter back passivation cell (PERC) cell to improve its surface passivation effect. Therefore, the two passivation films need to be deposited at different temperatures, which increases the deposition process time of the passivation layer from the equipment perspective; this also leads to larger quality defects at the interface of the Al2O3 / SiO2 bilayer and more unsaturated dangling bonds on the surface of the bilayer, which leads to poor stability of the deposited film; in addition, it is also difficult to effectively deposit the Al2O3 / SiO2 bilayer on the n-type c-Si front surface.
[0029] The Al2O3 / SiO2 bilayer can be deposited quickly based on plasma enhanced chemical vapor deposition (PECVD) technology. Therefore, the present application provides a method for forming an Al2O3 / SiO2 bilayer on a silicon wafer based on PECVD for preparing a plasma-treated photovoltaic device. The plasma-treated photovoltaic device can be used for n-type silicon wafers or p-type silicon wafers on the surface of solar cells, and can also be used for other single crystal or polycrystalline products. By improving the passivation performance of the bilayer during the preparation process to increase the minority carrier lifetime of the silicon wafer, the power conversion efficiency of the finished battery is improved.
[0030] Specifically, the method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to an embodiment of the present application may include the following steps: Figure 1A The following steps are shown:
[0031] S110, cleaning the surface of the silicon wafer and loading it on a graphite boat, placing the graphite boat loaded with the silicon wafer in a plasma-assisted deposition reaction chamber; S120, discharging a certain RF power to the graphite boat loaded with the silicon wafer through an RF power supply, and respectively introducing a first precursor and a second precursor into a plasma-assisted deposition (PE-ALD) reaction chamber, wherein the first precursor is used to deposit an Al2O3 layer at a deposition temperature, and the second precursor is used to deposit a SiO2 layer at a deposition temperature, and after depositing the Al2O3 layer and / or the SiO2 layer, introducing a passivation gas into the plasma-assisted deposition reaction chamber to ionize and generate plasma to treat the Al2O3 layer interface and / or the SiO2 layer interface to obtain an Al2O3 / SiO2 bilayer; S130, introducing a passivation gas into the plasma-assisted deposition reaction chamber and annealing at an annealing temperature.
[0032] In step S110, the surface of the silicon wafer to be deposited with a bilayer can be first cleaned with a chemical solution, including using an alkaline solution to texturize the surface of the silicon wafer to form a pyramid velvet surface; or using an alkaline solution to polish the surface of the silicon wafer to obtain a tower base surface. The pyramid velvet surface is formed on the surface of the silicon wafer by chemical corrosion using an alkaline solution, such as sodium hydroxide. The silicon wafer is immersed in a tank containing an alkaline solution, and a pyramid structure of uniform size and moderate height is formed on the surface of the silicon wafer by controlling the temperature, concentration, and time of the alkaline solution and adding a specific texturing additive. In this way, the silicon wafer can effectively capture and refract sunlight, reduce the reflection loss of light, and improve the absorption efficiency of sunlight. In addition, an alkaline solution, such as sodium hydroxide or potassium hydroxide, can also be used to chemically react with impurities and oxide layers on the surface of the silicon wafer to generate soluble compounds and remove these defects and impurities, thereby forming a flat tower base surface, which is conducive to the absorption and conversion of light and the construction of a pyramid velvet surface.
[0033] After the silicon wafer is cleaned, an Al2O3 / SiO2 bilayer is deposited in the PE-ALD reaction chamber. PE-ALD is an improved thin film deposition method based on ALD. By alternately introducing precursors and / or reaction gases into the reaction chamber, a self-limiting interfacial chemical reaction can be used to deposit thin film layers on the surface of the silicon wafer layer by layer; during the deposition process, only one atomic layer is deposited in each reaction cycle, so highly accurate film thickness control can be achieved. In addition, at a certain temperature, the PEALD reaction chamber can also deposit an Al2O3 / SiO2 bilayer without additional temperature adjustment. Choosing a graphite boat as a carrier of the silicon wafer in the reaction chamber can ensure the stable placement of the silicon wafer during the deposition process, and transfer heat to the silicon wafer evenly through its excellent thermal conductivity, so that it reaches the required deposition temperature. Another benefit of choosing a graphite boat is that the active points on its surface are more evenly distributed in a saturated state, which is conducive to the uniform adsorption and reaction of the deposition gas on the surface of the loaded silicon wafer.
[0034] According to the plasma treated Al2O3 / SiO2 bilayer deposition method of the embodiment of the present application, the pressure range in the PE-ALD reaction chamber is set to 20-150mTorr, the deposition temperature range is 250-600°C, and the preferred deposition temperature is 400°C. The decomposition of the two precursors of aluminum and silicon can be avoided while maintaining the deposition rate.
[0035] In step S120, the RF power source discharges a certain RF power to the graphite boat, and the first precursor and the second precursor are introduced into the reaction chamber to deposit an Al2O3 layer and a SiO2 layer on the surface of the silicon wafer, respectively, to form an Al2O3 / SiO2 bilayer. The RF power source discharges a certain RF power to the carrier of the silicon wafer, that is, the graphite boat, to provide an energy source and excite the first precursor and the second precursor introduced to generate plasma, so that the plasma is deposited on the surface of the silicon wafer or the surface of the formed thin film layer to generate the required molecular layer.
[0036] In particular, according to a method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to an embodiment of the present application, a passivation gas is continuously and regularly introduced into a reaction chamber during the formation of the bilayer, and the passivation gas releases sufficient passivation atoms under the discharge of the RF power supply and enhances the passivation effect of the bilayer surface. That is, step S120 can be further divided into: S1201, the RF power supply discharges to the graphite boat, and the first precursor and the second precursor are respectively introduced into the plasma-assisted deposition reaction chamber, and the Al2O3 layer and the SiO2 layer are respectively deposited on the surface of the silicon wafer at the deposition temperature; S1202, after forming any one of the Al2O3 layer and the SiO2 layer, the passivation gas is continuously introduced into the plasma-assisted deposition reaction chamber to treat the Al2O3 layer interface and / or the SiO2 layer interface.
[0037] In step S1201, in order to deposit an Al2O3 layer on the surface of a silicon wafer, the first precursor selected according to the Al2O3 / SiO2 bilayer deposition method of an embodiment of the present application may be aluminum precursors such as trimethylaluminum (TMA), aluminum halide, and alkyl aluminum. Among them, the preferred first precursor is TMA with a higher saturated vapor pressure and thermal stability, which has strong reaction activity and higher deposition value. The RF power supply discharges to the graphite boat with a certain RF power and ionizes the first precursor in contact with the surface of the silicon wafer. The RF power may range from 5000 to 12000 W. For example, 5000 W, 5100 W, 5200 W, 5300 W, 5400 W, 5500 W, 5600 W, 5700 W, 5800 W, 5900 W, 6000 W, 6100 W, 6200 W, 6300 W, 6400 W, 6500 W, 6600 W, 6700 W, 6800 W, 6900 W, 7000 W, 7100 W, 7200 W, 7300 W, 7400 W, 7500 W, 7600 W, 7700 W, 7800 W, 7900 W, 8000 W, 8100 W ,8200W,8300W,8400W,8500W,8600W,8700W,8800W,8900W,9000W,9100W,920 0W,9300W,9400W,9500W,9600W,9700W,9800W,9900W,10000W,10100W,10200 W,10300W,10400W,10500W,10600W,10700W,10800W,10900W,11000W,11100W ,11200W,11300W,11400W,11500W,11600W,11700W,11800W,11900W,12000W.When the first precursor is TMA, the flow rate thereof can range from 80 to 150 sccm, for example, 80 sccm, 81 sccm, 82 sccm, 83 sccm, 84 sccm, 85 sccm, 86 sccm, 87 sccm, 88 sccm, 89 sccm, 90 sccm, 91 sccm, 92 sccm, 93 sccm, 94 sccm, 95 sccm, 96 sccm, 97 sccm, 98 sccm, 99 sccm, 100 sccm, 101 sccm, 102 sccm, 103 sccm, 104 sccm, 105 sccm, 106 sccm, 107 sccm, 108 sccm, 109 sccm, 110 sccm, 111 sccm, 112 sccm, 113 sccm, 114 sccm 14sccm,115sccm,116sccm,117sccm,118sccm,119sccm,120sccm,121sccm,122sccm,12 3sccm,124sccm,125sccm,126sccm,127sccm,128sccm,129sccm,130sccm,131sccm,132s ccm,133sccm,134sccm,135sccm,136sccm,137sccm,138sccm,139sccm,140sccm,141scc m,142sccm,143sccm,144sccm,145sccm,146sccm,147sccm,148sccm,149sccm,150sccm. The first precursor is introduced at a constant pressure and stably within the above-mentioned discharge RF power and flow rate range to ensure that there is sufficient reaction gas at the tail of the reaction chamber, which helps to improve the uniformity of the deposited aluminum oxide passivation film layer to achieve a better deposition effect while avoiding waste of precursor.
[0038] In particular, during the deposition process of aluminum precursors such as TMA, nitrous oxide, i.e., laughing gas, can also be introduced into the reaction chamber to assist the deposition process. The laughing gas reacts with TMA to generate aluminum oxide and also affects the charge distribution in the aluminum oxide layer. Specifically, the oxygen atoms in the laughing gas can react with the positively charged Al in the aluminum oxide layer. 3+ Reacts to generate negative charge, such as AlO 4- When there are more negative charges in the aluminum oxide layer, these negative charges move to the film surface under the action of the electric field, forming a negative charge layer to repel electrons from the inside of the solar cell, reducing the chance of electrons recombining with the film surface, thereby further reducing the recombination rate and improving the passivation effect.
[0039] In one example, the flow rate of nitrous oxide can range from 4000 to 8000 sccm, for example, 4000 sccm, 4100 sccm, 4200 sccm, 4300 sccm, 4400 sccm, 4500 sccm, 4600 sccm, 4700 sccm, 4800 sccm, 4900 sccm, 5000 sccm, 5100 sccm, 5200 sccm, 5300 sccm, 5400 sccm, 5500 sccm, 5600 sccm, 5700 sccm, 5800 sccm, 5900 sccm. The RF power of the laughing gas is consistent with the RF power of the TMA mentioned above. According to the Al2O3 / SiO2 bilayer deposition method of an embodiment of the present application, the thickness of the Al2O3 layer obtained by step S1201 is in the range of 2-5nm, for example 2nm, 3nm, 4nm, 5nm; preferably, the thickness of the Al2O3 layer is 3nm, and the top layer of Al2O3 is purged after deposition to effectively cover the surface defects of the silicon wafer and reduce charge recombination.
[0040] Similarly, in order to deposit the SiO2 layer, the second precursor selected according to the Al2O3 / SiO2 bilayer deposition method of the embodiment of the present application can be diethylaminosilane, trimethylsilylamine, triethylsilylamine, etc. The present application preferably uses diethylaminosilane as the second precursor. During the PE-ALD process, diethylaminosilane can stably exist in the reaction chamber and adapt to reaction conditions such as ionization. When the second precursor is diethylaminosilane, the value range of its inlet flow rate can be 100-500sccm, for example, 100sccm, 110sccm, 120sccm, 130sccm, 140sccm, 150sccm, 160sccm, 170sccm, 180sccm, 190sccm, 200sccm, 210sccm, 220sccm, 230sccm, 240sccm, 250sccm, 260sccm, 270sccm. The thickness of the SiO2 layer obtained by the Al2O3 / SiO2 bilayer deposition method according to the embodiment of the present application through step S1201 is in the range of 1-4nm, for example, 1nm, 2nm, 3nm, 4nm; preferably, the thickness of the SiO2 layer is 2nm, and the top layer of SiO2 is purged after deposition. In this way, the combined use of the formed Al2O3 / SiO2 bilayer can reduce the adverse field passivation effect of the Al2O3 layer on n-type silicon wafers, and improve the application range of plasma-treated photovoltaic devices prepared by the Al2O3 / SiO2 bilayer deposition method according to the embodiment of the present application.
[0041] It can be understood that the SiO2 layer is deposited on the upper surface of the Al2O3 layer, that is, on the top layer of the Al2O3 layer. As described above, in order to ensure that the Al2O3 layer and the SiO2 layer have a high hydrogen content, after each Al2O3 layer or SiO2 layer is prepared, a passivation gas can be introduced into the PE-ALD reaction chamber through step S1202. After the passivation gas is ionized, the dangling bonds on the interface surface are saturated at the top interface of the Al2O3 layer or the top interface of the SiO2 layer, so that each passivation layer can receive enough passivation atoms to passivate the dangling bonds on the interface.
[0042] In some specific embodiments, after first depositing the Al2O3 layer, a passivating gas is introduced for a certain period of time and ionized on the top interface surface of the Al2O3 layer, and then a SiO2 layer is deposited and a passivating gas is introduced for a certain period of time and ionized on the top interface surface of the SiO2 layer, so that the surface of each layer of the obtained Al2O3 / SiO2 bilayer has a good passivation effect.
[0043] Therefore, the Al2O3 / SiO2 bilayer deposition method according to the embodiment of the present application proposes to use plasma to excite and decompose substances containing saturated atoms to produce a large number of saturated atoms, so that high-concentration saturated atoms can more easily penetrate into the passivation layer, such as ionizing H2 on the surface of the Al2O3 layer and the SiO2 layer, and increasing the hydrogen content of the passivation layer to saturate the Si hanging bonds. Specifically, the passivation gas selected by the Al2O3 / SiO2 bilayer deposition method according to the embodiment of the present application can be a mixed gas of one or two of H2, N2, NH3, O2 or Ar. This is because nitrogen atoms, oxygen atoms or argon atoms are doped into the bilayer, which can passivate the surface of the layer to reduce surface defects and improve the life and quality of individual devices. Preferably, the passivation gas is H2, and a high-concentration hydrogen environment is obtained in the PE-ALD reaction chamber by directly ionizing and decomposing H2, so that each layer of the Al2O3 / SiO2 bilayer has an environmental condition that fully absorbs hydrogen atoms in the reaction chamber after deposition is completed.
[0044] In some specific embodiments, the flow rate of the passivation gas is in the range of 30-200sccm, for example, 30sccm, 31sccm, 32sccm, 33sccm, 34sccm, 35sccm, 36sccm, 37sccm, 38sccm, 39sccm, 40sccm, 41sccm, 42sccm, 43sccm, 44sccm, 45sccm, 46sccm, 47sccm, 48sccm, 49sccm, 50sccm, 51sccm, 52sccm, 53sccm, 54sccm, 55sccm, 56sccm, 57sccm, 58sccm, 59sccm cm,60sccm,61sccm,62sccm,63sccm,64sccm,65sccm,66sccm,67sccm,68sccm,69sccm,70sccm,71sccm,72sccm,73sccm,74sccm,75sccm,76sccm,77 sccm,78sccm,79sccm,80sccm,81sccm,82sccm,83sccm,84sccm,85sccm,86sccm,87sccm,88sccm,89sccm,90sccm,91sccm,92sccm,93sccm,94sccm,9 5sccm,96sccm,97sccm,98sccm,99sccm,100sccm,101sccm,102sccm,103sccm,104sccm,105sccm,106sccm,107sccm,108sccm,109sccm,110sccm,11 1sccm,112sccm,113sccm,114sccm,115sccm,116sccm,117sccm,118sccm,119sccm,120sccm,121sccm,122sccm,123sccm,124sccm,125sccm,126sccm ,127sccm,128sccm,129sccm,130sccm,131sccm,132sccm,133sccm,134sccm,135sccm,136sccm,137sccm,138sccm,139sccm,140sccm,141sccm,142 sccm,143sccm,144sccm,145sccm,146sccm,147sccm,148sccm,149sccm,150sccm,151sccm,152sccm,153sccm,154sccm,155sccm,156sccm,157sccm,158sccm,159sccm,160sccm,161sccm,162sccm,163sccm,164sccm,165sccm,166sccm,167sccm,168scc m,169sccm,170sccm,171sccm,172sccm,173sccm,174sccm,175sccm,176sccm,177sccm,178sccm,179s ccm,180sccm,181sccm,182sccm,183sccm,184sccm,185sccm,186sccm,187sccm,188sccm,189sccm,19 0sccm, 191sccm, 192sccm, 193sccm, 194sccm, 195sccm, 196sccm, 197sccm, 198sccm, 199sccm or 200sccm. Preferably, the flow rate of the passivation gas is in the range of 50-100sccm. Pure H2 is introduced at a certain temperature and ionized at the top interface of the Al2O3 / SiO2 bilayer. As the flow rate of H2 increases gradually, the passivation effect is significantly improved. After the hydrogen concentration in the reaction chamber reaches the threshold, the passivation effect of the passivation layer tends to be flat. After the flow rate exceeds 100sccm, the passivation effect is greatly reduced. In order to avoid ineffective use of plasma, the plasma flow rate is further preferably 100sccm to balance the passivation performance and preparation cost.
[0045] In some advantageous examples, the bilayer obtained after the passivation gas treatment of the Al2O3 layer interface and the SiO2 layer interface can be further stacked, that is, step S140: repeat the deposition method of step S120 above i-1 times to obtain a total of i Al2O3 / SiO2 bilayers and obtain a passivation film structure of a multi-layer passivation layer to improve the passivation performance of the Al2O3 / SiO2 bilayer on the p-type silicon wafer. The preparation process is as shown in the attached Figure 1B As shown. For n-type silicon wafers and p-type silicon wafers, the thickness and composition of the optimal passivation layer required on their surfaces are not the same. According to the Al2O3 / SiO2 bilayer deposition method of the embodiment of the present application, the number of plasma-treated Al2O3 / SiO2 bilayers prepared on the surface of n-type silicon wafers is preferably 1 layer, while the number of plasma-treated Al2O3 / SiO2 bilayers prepared on the surface of p-type silicon wafers is preferably i=3 layers. The specific effects achieved by the bilayers under the preferred number of layers are detailed in the following embodiments.
[0046] Finally, in step S130, the passivation gas is continuously introduced into the reaction chamber and annealing is performed at an annealing temperature. Since annealing requires a higher temperature than the deposition process of the aluminum source and the silicon source to promote the chemical bond reaction that has not been completely reacted, for example, at the annealing temperature, the Al-OH bond in the Al2O3 layer is converted into an Al-O bond and hydrogen atoms are released to enhance the passivation effect of the passivation layer, the annealing temperature needs to be increased. Advantageously, this is the first time that the reaction chamber temperature is adjusted during the deposition process of the Al2O3 / SiO2 bilayer deposition method according to the embodiment of the present application, so the deposition method as a whole is still efficient and concise.
[0047] In some embodiments, the annealing time is 20 minutes, and the annealing temperature ranges from 350 to 600°C, for example, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C or 600°C. The preferred range further obtained by experiment is 450-550°C, as shown in the following embodiments. It can be understood that the deposition temperature and the annealing temperature can be an overlapping temperature range or temperature value, which is also conducive to the rapid temperature control of the PE-ALD reaction device.
[0048] In particular, the purpose of continuously introducing the passivation gas during the annealing process is to provide passivation atoms to saturate the dangling bonds on the surface of the bilayer in the passivation gas atmosphere to further enhance the passivation effect. In one example, when H2 is preferably used as the passivation gas during the passivation process, H2 may also be preferably used as the passivation gas during the annealing process to provide hydrogen atoms to saturate the dangling bonds on the surface of the material.
[0049] In another advantageous embodiment, the Al2O3 / SiO2 bilayer deposition method according to the embodiment of the present application can also deposit the Al2O3 layer and the SiO2 layer in different devices to expand the flexibility of bilayer preparation; the process of plasma ionization treatment of the top interface of the Al2O3 / SiO2 bilayer can be after the Al2O3 layer, after the SiO2 layer, or both, and the time of plasma ionization treatment for increasing the hydrogen content of the passivation gas in the reaction chamber can be appropriately adjusted according to the actual needs of technicians in this field. In addition, in the example of preparing a bilayer on a silicon-based battery, the Al2O3 / SiO2 bilayer deposition method according to the embodiment of the present application can be, but not limited to, forming a plasma-treated Si, Al2O3, SiO2 or SiNx layer, and can be any passivation layer or passivation film optimized based on the plasma treatment process of the Al2O3 / SiO2 bilayer deposition method according to the embodiment of the present application.
[0050] In this way, a plasma-treated photovoltaic device can be prepared according to the Al2O3 / SiO2 bilayer deposition method of the embodiment of the present application, which can significantly improve the minority carrier lifetime of the silicon wafer and improve the conversion efficiency of the finished battery after being treated with plasma ionization to optimize the passivation performance. The plasma-treated photovoltaic device can be used for n-type silicon wafers or p-type silicon wafers of solar cells, and can also be used for other single crystal or polycrystalline products. The surface passivation film of the plasma-treated photovoltaic device is as shown in the attached Figure 2 As shown, it may include a silicon substrate 1 and a dielectric passivation film; wherein the silicon substrate 1 may be a silicon wafer of different shapes and sizes, and the dielectric passivation film may include the aforementioned i-layer Al2O3 / SiO2 bilayer; the Al2O3 / SiO2 bilayer further includes an Al2O3 layer 2, an Al2O3 top interface 3-1, a SiO2 top interface 3-2 and a SiO2 layer 4; the Al2O3 top interface and the SiO2 top interface are both subjected to a plasma ionization passivation treatment of a passivation gas, preferably H2, thereby stably increasing the hydrogen content of the Al2O3 layer and the SiO2 layer during the preparation stage.
[0051] In some feasible examples of the Al2O3 / SiO2 bilayer deposition method according to the embodiments of the present application, the thickness of the Al2O3 layer in the Al2O3 / SiO2 bilayer is in the range of 2-5nm; preferably, the thickness of the Al2O3 layer in the Al2O3 / SiO2 bilayer is 3nm, so as to effectively cover the surface defects of the silicon substrate and reduce charge recombination. The thickness of the SiO2 layer in the Al2O3 / SiO2 bilayer is in the range of 1-4nm; preferably, the thickness of the SiO2 layer in the Al2O3 / SiO2 bilayer is 2nm, so as to effectively compensate for the adverse field passivation effect of the Al2O3 layer on the n-type silicon substrate. The surface of the silicon substrate can be a textured pyramid velvet surface or a tower base surface after alkali polishing, which can be prepared in different ways by using alkali solutions.
[0052] Thus, the present application obtains a c-Si photovoltaic device with a better passivation effect according to the method of forming an Al2O3 / SiO2 bilayer on a silicon wafer. During the annealing process, hydrogen from the bilayer saturates Si dangling bonds, reducing the interface state density, thereby reducing the silicon wafer surface recombination rate when the plasma-treated photovoltaic device is used in a solar cell panel, and improving the minority carrier life and open circuit voltage of the battery. At the same time, the passivation layer can further prevent the recombination of photogenerated electrons and back charges, reducing the loss in the photoelectric conversion process. The application of the plasma-treated photovoltaic device of the present application in the large-scale application of solar cells significantly improves the power generation efficiency, which helps to further promote the application of such clean power generation equipment; the process of preparing plasma-treated photovoltaic devices does not need to be carried out in multiple devices or different environments, and the specific gas source used in the multi-layer passivation process of silicon wafers is easy to obtain and can be kept consistent with the passivation parameters in the passivation process, so that the method of forming an Al2O3 / SiO2 bilayer on a silicon wafer is easy to apply and promote in the photovoltaic industry.
[0053] That is, the plasma-treated photovoltaic device obtained by the method of forming an Al2O3 / SiO2 bilayer on a silicon wafer according to an embodiment of the present application, that is, the above-mentioned c-Si photovoltaic device can be used as a single crystal silicon cell or a polycrystalline silicon cell, and a solar cell with high power generation efficiency is formed based on such a cell. In one example, a plasma-treated photovoltaic device is used as an n-type / p-type cell together with glass, a junction box, and a battery backplane to form an n-type / p-type solar cell; the n-type / p-type solar cells formed in this way are connected in series and in parallel to form an n-type / p-type photovoltaic module. In this way, the n-type / p-type photovoltaic module is set in an area with sufficient light, and is irradiated by light that meets the illumination conditions, and can output voltage quickly and stably, and generate current in the presence of a loop. Under the action of a series of circuit components such as an inverter, the generated current can be used in daily life.
[0054] Example
[0055] This application provides a general and / or specific description of the materials and test methods used in the experiment. The raw materials or instruments used without indicating the manufacturer are all conventional raw materials or instruments that can be obtained through commercial purchase.
[0056] Example 1 Photovoltaic device based on plasma treatment of n-type silicon wafer
[0057] 1. An n-type silicon wafer was selected, and the surface was textured using an alkaline solution to form a pyramid velvet surface;
[0058] 2. Load the textured silicon wafer onto a graphite boat, place the graphite boat into the PE-ALD reaction chamber, set the pressure to 50-150 mTorr, and the deposition temperature to 400°C;
[0059] 3. TMA was introduced with a flow rate of 80-150 sccm and nitrous oxide with a flow rate of 4000-8000 sccm; the RF power was set to 5000-12000 W, and a 3 nm Al2O3 layer was deposited. After deposition, a purge was performed for 10 seconds.
[0060] 4. Pure H2 gas is introduced for ionization, with the flow rate set to 50-100 sccm, to treat the top interface of the Al2O3 layer;
[0061] 5. Add bis(diethylaminosilane) with a flow rate of 100-500 sccm to deposit a 2 nm thick SiO2 layer, and purge for 10 seconds after deposition;
[0062] 6. Pure H2 gas is introduced for ionization, with the flow rate set to 50-100 sccm, to treat the interface and obtain a single Al2O3 / SiO2 bilayer;
[0063] 7. Pure H2 was introduced with a flow rate of 100 sccm, and annealing was performed at 350-550°C for 20 min to obtain an n-type c-Si photovoltaic device.
[0064] 8. Photoconductance degradation (PCD) measurements were performed using a lifetime tester WCT-120 (Sinton Instruments) to determine the effective minority charge carrier lifetime of the single Al2O3 / SiO2 bilayer.
[0065] The obtained c-Si photovoltaic device is used as a cell to prepare an n-type solar cell. Several n-type solar cells are connected in series and in parallel to form an n-type photovoltaic module. When the n-type photovoltaic module is irradiated by light that meets certain illumination conditions, it can instantly output voltage to generate current. These clean energies are delivered to daily electrical equipment through a series of actions such as inverters.
[0066] Example 2 Photovoltaic device based on plasma treatment of p-type silicon wafer
[0067] 1. A p-type silicon wafer was selected, and the surface was textured using an alkaline solution to form a polished tower base morphology;
[0068] 2. Load the polished silicon wafer into a graphite boat, place the graphite boat in the PE-ALD reaction chamber, set the pressure to 50-150mTorr, and the deposition temperature to 400°C;
[0069] 3. TMA was introduced at a flow rate of 80-150 sccm, and nitrous oxide was introduced at a flow rate of 4000-8000 sccm; the RF power was set to 5000-12000 W, and a 2 nm Al2O3 layer was deposited, and a purge was performed for 10 seconds after deposition;
[0070] 4. Pure H2 gas is introduced for ionization, with the flow rate set to 50-100 sccm, to treat the top interface of the Al2O3 layer;
[0071] 5. Add bis(diethylaminosilane) with a flow rate of 100-500 sccm to deposit a 2 nm thick SiO2 layer, and purge for 10 seconds after deposition;
[0072] 6. Introduce pure H2 gas ionization with a flow rate of 50-100 sccm to treat the interface;
[0073] 7. Repeat steps 3-6 to deposit 3 Al2O3 / SiO2 bilayers;
[0074] 8. Pure H2 was introduced with a flow rate of 100 sccm, and annealing was performed at 350-550°C for 20 min to obtain a p-type c-Si photovoltaic device.
[0075] 9. PCD measurements were performed using a lifetime tester WCT-120 (Sinton Instruments) to determine the effective minority charge carrier lifetime of the 3-layer Al2O3 / SiO2 bilayer.
[0076] The obtained p-type c-Si photovoltaic device is used as a cell to prepare a p-type solar cell. Several p-type solar cells are connected in series and in parallel to form a p-type photovoltaic module. After being irradiated by light that meets certain illumination conditions, the p-type photovoltaic module can instantly output voltage to generate current. These clean energies are delivered to daily electrical equipment through a series of actions such as inverters.
[0077] Comparative Example 1 Photovoltaic device based on n-type silicon wafer
[0078] 1. The same n-type silicon wafer as in Example 1 was selected, and the surface was textured using the same alkaline solution as in Example 1 to form a pyramid velvet surface;
[0079] 2. Load the textured silicon wafer into the same graphite boat as in Example 1, and place the graphite boat into the same PE-ALD reaction chamber as in Example 1, set the pressure to 50-150 mTorr, and the deposition temperature to 400° C.;
[0080] 3. TMA was introduced with a flow rate of 80-150 sccm and nitrous oxide with a flow rate of 4000-8000 sccm; the RF power was set to 5000-12000 W, and a 3 nm Al2O3 layer was deposited. After deposition, a purge was performed for 10 seconds.
[0081] 4. Add bis(diethylaminosilane) with a flow rate of 100-500 sccm to deposit a 2 nm thick SiO2 layer, and purge for 10 seconds after deposition;
[0082] 5. Anneal at the same time for 20 min in an atmosphere of 350-550° C. to obtain an n-type c-Si photovoltaic device.
[0083] 6. Photoconductivity degradation (PCD) measurements were performed using a lifetime tester WCT-120 (Sinton Instruments) to determine the effective minority charge carrier lifetime of the single Al2O3 / SiO2 bilayer.
[0084] The minority charge carrier lifetimes at different annealing temperatures measured for the c-Si photovoltaic devices of Example 1, Example 2 and Comparative Document 1 are compared. The comparison results are shown in the attached figure. Figure 3 As shown. The Al2O3 / SiO2 bilayer of the c-Si photovoltaic device of Example 1 and Example 2 corresponds to the Al2O3 / SiO2 bilayer after single-layer treatment and the Al2O3 / SiO2 bilayer after three-layer treatment in the figure, respectively, and the Al2O3 / SiO2 bilayer of the c-Si photovoltaic device of Comparative Example 1 corresponds to the Al2O3 / SiO2 bilayer without plasma treatment in the figure.
[0085] Depend on Figure 3 It can be seen that the minority charge carrier lifetime of the plasma-treated n-type c-Si photovoltaic device in Example 1 is significantly higher than that of the non-plasma-treated n-type c-Si photovoltaic device in Comparative Example 1 starting from the annealing temperature of 350°C. As the annealing temperature increases, the performance of the plasma-treated n-type c-Si photovoltaic device also increases, while the performance of the non-plasma-treated n-type c-Si photovoltaic device reaches the highest at about 500°C, but is still inferior to the plasma-treated n-type c-Si photovoltaic device annealed at the same temperature. It can be seen that at 500°C, the passivation performance of the Al2O3 / SiO2 bilayer is enhanced by 70% after plasma treatment, which will greatly enhance the power generation efficiency and long-term stability of the c-Si photovoltaic device.
[0086] In addition, compared with c-Si photovoltaic devices that have not been treated with plasma, c-Si photovoltaic devices that have been treated with plasma still have the potential to improve the passivation effect after the annealing temperature exceeds 500°C.
[0087] Comparative Example 2 Photovoltaic devices based on plasma treatment of n-type and p-type silicon wafers
[0088] 1. Select the n-type silicon wafer of Example 1 and the p-type silicon wafer of Example 2 respectively, and perform texturing treatment on the surfaces thereof using an alkaline solution to form a pyramid velvet surface;
[0089] 2. Load the textured n-type silicon wafer and p-type silicon wafer into graphite boats respectively. Place the graphite boats in the PE-ALD reaction chamber. Set the pressure to 50-150 mTorr and the deposition temperature to 400°C.
[0090] 3. TMA was introduced at a flow rate of 80-150 sccm, and nitrous oxide was introduced at a flow rate of 4000-8000 sccm; the RF power was set to 5000-12000 W, and a 3 nm Al2O3 layer was deposited on the n-type silicon wafer, and a 2 nm Al2O3 layer was deposited on the p-type silicon wafer, and each was purged for 10 seconds after deposition;
[0091] 4. Pure NH3 gas is introduced for ionization, with the flow rate set to 50-100 sccm, to treat the top interface of the Al2O3 layer;
[0092] 5. Introduce bis(diethylamino)silane with a flow rate of 100-500 sccm to deposit a 2 nm thick SiO2 layer on the Al2O3 layer of the n-type silicon wafer and the p-type silicon wafer, respectively, and purge for 10 seconds after deposition;
[0093] 6. Pure NH3 gas is introduced for ionization, and the flow rate is set to 50-100 sccm to treat the interface and obtain a single Al2O3 / SiO2 bilayer;
[0094] 7. Repeat steps 3-6 for the p-type silicon wafer to deposit three Al2O3 / SiO2 bilayers;
[0095] 8. Pure NH3 was introduced with a flow rate of 100 sccm, and the single-layer Al2O3 layer of the n-type silicon wafer and the three-layer Al2O3 / SiO2 bilayer of the p-type silicon wafer were annealed for 20 min at an atmosphere of 350-550°C to obtain n-type c-Si photovoltaic devices and p-type c-Si photovoltaic devices, respectively.
[0096] 9. Photoconductivity degradation (PCD) measurements were performed using a lifetime tester WCT-120 (Sinton Instruments) to determine the effective minority charge carrier lifetime for a single Al2O3 / SiO2 bilayer of an n-type c-Si photovoltaic device and a 3-layer Al2O3 / SiO2 bilayer of a p-type c-Si photovoltaic device, respectively.
[0097] 10. Adjust the flow rate of pure NH3 introduced in steps 4, 6 and 8 so that the minority charge carrier lifetimes of the single-layer Al2O3 / SiO2 bilayer of the n-type c-Si photovoltaic device and the three-layer Al2O3 / SiO2 bilayer of the p-type c-Si photovoltaic device obtained in this embodiment reach the same values as the minority charge carrier lifetimes of the single-layer Al2O3 / SiO2 bilayer of the n-type c-Si photovoltaic device in Example 1 and the minority charge carrier lifetimes of the three-layer Al2O3 / SiO2 bilayer of the p-type c-Si photovoltaic device in Example 2 at an annealing temperature of 550°C.
[0098] Finally, the passivation gas used at this time, that is, the mean of the three times of the flow rate of pure NH3, is recorded, and compared with the mean of the three times of the flow rate of the passivation gas used in Example 1 and Example 2. The results are shown in the following table:
[0099] Table 1 Passivation gas flow rates required in the preparation of different c-Si photovoltaic devices with the same minority carrier lifetime
[0100]
[0101] As shown in Table 1, in order to ensure the same passivation effect, the pure NH3 flow rate required to passivate the Al2O3 and SiO2 top interface of n-type photovoltaic devices is 30 times or more than the pure H2 flow rate; and the pure NH3 flow rate required to passivate the Al2O3 and SiO2 top interface of p-type photovoltaic devices is about 50 times the pure H2 flow rate. It can be predicted that the introduction of passivation gases such as N2 may require a larger flow rate, which is unrealistic in the actual production process of photovoltaic devices. Only by continuously introducing a certain amount of pure H2 can the passivation performance of photovoltaic devices be significantly improved, while ensuring the feasibility of photovoltaic device production and avoiding high costs and material waste.
Claims
1. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer, comprising the following steps: (1) performing surface cleaning on a silicon wafer and loading the silicon wafer onto a graphite boat, and placing the graphite boat loaded with the silicon wafer into a plasma-assisted deposition reaction chamber; (2) discharging to the graphite boat through a radio frequency power supply, and respectively introducing a first precursor and a second precursor into a plasma-assisted deposition reaction chamber, wherein the first precursor is used to deposit an Al2O3 layer at a deposition temperature, and the second precursor is used to deposit an SiO2 layer at the deposition temperature, and after depositing the Al2O3 layer and / or the SiO2 layer, a passivation gas is introduced into the plasma-assisted deposition reaction chamber to ionize and generate plasma to treat the Al2O3 layer interface and / or the SiO2 layer interface to obtain an Al2O3 / SiO2 bilayer; (3) H2 is introduced into the plasma assisted deposition reaction chamber and annealing is performed at an annealing temperature.
2. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to claim 1, wherein: When the silicon wafer is a p-type silicon wafer, the method further comprises the following steps: Repeat step (2) to obtain i-layer Al2O3 / SiO2 bilayer.
3. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to claim 2, wherein: The number of layers of the i-layer Al2O3 / SiO2 bilayer is i=3.
4. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to claim 1, wherein: The first precursor includes trimethylaluminum, and the discharge radio frequency power discharged to the graphite boat by the radio frequency power supply has a value range of 5000-12000w; The flow rate of trimethylaluminum is in the range of 80-150 sccm, and the flow rate of nitrous oxide is in the range of 4000-8000 sccm; The second precursor includes bis(diethylaminosilane); The flow rate of bis(diethylaminosilane) is in the range of 100-500 sccm; The first precursor also includes nitrous oxide.
5. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to claim 1, wherein: The passivation gas includes one or a mixture of two of H2, N2, NH3, O2 or Ar; Preferably, the passivating gas comprises H2; The flow rate of the passivation gas is in the range of 30-200 sccm; Preferably, the flow rate of the passivation gas is in the range of 50-100 sccm; More preferably, the flow rate of the passivation gas is 100 sccm.
6. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to claim 1, wherein: The thickness of the Al2O3 layer of the Al2O3 / SiO2 bilayer is in the range of 2-5nm; Preferably, the thickness of the Al2O3 layer of the Al2O3 / SiO2 bilayer is 3 nm; The thickness of the SiO2 layer of the Al2O3 / SiO2 bilayer is in the range of 1-4 nm; Preferably, the thickness of the SiO2 layer of the Al2O3 / SiO2 bilayer is 2 nm.
7. A method for forming an Al2O3 / SiO2 bilayer on a silicon wafer according to claim 1, wherein: The deposition temperature ranges from 250 to 600°C; Preferably, the deposition temperature is 400°C; The annealing temperature ranges from 350 to 600°C; Preferably, the annealing temperature ranges from 450°C to 550°C.
8. A plasma-treated photovoltaic device according to any one of claims 1 to 7, comprising: Silicon substrate and dielectric passivation film; Wherein, the dielectric passivation film comprises a layer of Al2O3 / SiO2 bilayer; Wherein, the Al2O3 / SiO2 bilayer includes an Al2O3 layer, an Al2O3 top interface, a SiO2 layer and a SiO2 top interface.
9. The plasma treated photovoltaic device of claim 8, wherein: The thickness of the Al2O3 layer of the Al2O3 / SiO2 bilayer is in the range of 2-5nm; Preferably, the thickness of the Al2O3 layer of the Al2O3 / SiO2 bilayer is 3 nm; The thickness of the SiO2 layer of the Al2O3 / SiO2 bilayer is in the range of 1-4 nm; Preferably, the thickness of the SiO2 layer of the Al2O3 / SiO2 bilayer is 2 nm.
10. The plasma treated photovoltaic device of claim 8, wherein: The surface of the silicon substrate is a textured pyramid velvet surface or a pyramid base surface after alkali polishing.