Method for manufacturing a solar cell, solar cell and use thereof

Abstract

The application discloses a method for preparing a solar cell, the solar cell and application thereof, and the method comprises the following steps: (1) performing ALD deposition of an aluminum oxide layer on the surface of a silicon wafer, the ALD deposition of the aluminum oxide layer comprises a plurality of reaction cycles, each reaction cycle comprises sequentially performing a trimethylaluminum vapor pulse, a first nitrogen blowing, a water vapor pulse and a second nitrogen blowing; the ratio of the trimethylaluminum vapor pulse time to the water vapor pulse time is 1:(0.5-1.15); (2) performing annealing treatment on the silicon wafer in an oxidizing atmosphere; and (3) forming a silicon nitride layer on the surface of the aluminum oxide layer away from the silicon wafer. By optimizing the process conditions of the ALD deposition of the aluminum oxide layer, the content of hydrogen atoms in the aluminum oxide layer is reduced, so that the risk of film explosion of the aluminum oxide layer is reduced. Meanwhile, the oxidizing gas is introduced in the annealing process, so that a dense silicon oxide layer is formed between the silicon wafer and the aluminum oxide, and excellent chemical passivation effect is ensured.

Description

Technical Field

[0001] This application relates to the field of solar cells, and more particularly to a method for preparing solar cells, solar cells and their applications. Background Technology

[0002] Atomic layer deposition (ALD) of alumina utilizes the principle of self-confined surfaces, controlling the deposition process at the atomic layer scale by alternately exposing reactive gases to the substrate surface. Thermal ALD-deposited alumina is obtained by directly reacting trimethylaluminum as the aluminum source and water as the oxygen source at a specific temperature.

[0003] The advantage of atomic layer deposition (ALD) of alumina is that it can prepare uniform and dense alumina on large-area substrates, resulting in good passivation performance for solar cells. However, in actual production, when depositing silicon nitride on the surface of the alumina film using PECVD, the high temperature can cause excess hydrogen atoms in the alumina to escape, forming hydrogen gas that breaks through the silicon nitride film, causing a film explosion. This damages the integrity of the alumina and silicon nitride stack, ultimately leading to a decrease in passivation effect and a reduction in cell efficiency. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in related technologies. Therefore, the purpose of this application is to propose a method for fabricating solar cells, a solar cell, and its application. By optimizing the process conditions for ALD deposition of an alumina layer, this application effectively reduces the hydrogen atom content in the alumina layer, thereby reducing the possibility of H atoms in the alumina layer forming hydrogen gas during subsequent high-temperature processing, and lowering the risk of alumina layer delamination. Simultaneously, introducing oxidizing gas during annealing promotes the formation of a dense silicon oxide layer between the silicon wafer and the alumina, passivating the dangling bonds on the crystalline silicon surface, reducing the defect state density at the interface, and thus ensuring a superior chemical passivation effect.

[0005] In one aspect of this application, a method for fabricating a solar cell is provided. According to an embodiment of this application, the method includes:

[0006] (1) An ALD layer of aluminum oxide is deposited on the surface of a silicon wafer. The ALD deposition of aluminum oxide includes multiple reaction cycles. Each reaction cycle includes a trimethylaluminum vapor pulse, a first nitrogen purging, a water vapor pulse, and a second nitrogen purging in sequence. The ratio of the trimethylaluminum vapor pulse time to the water vapor pulse time is 1:(0.5~1.15).

[0007] (2) The silicon wafer is annealed in an oxidizing atmosphere;

[0008] (3) A silicon nitride layer is formed on the surface of the alumina layer away from the silicon wafer.

[0009] According to the method for fabricating solar cells in this application, by optimizing the process conditions for ALD deposition of the alumina layer, the hydrogen atom content in the alumina layer can be effectively reduced, thereby reducing the possibility of H atoms in the alumina layer forming hydrogen gas during subsequent high-temperature processing, and reducing the risk of alumina layer explosion. Simultaneously, introducing oxidizing gas during annealing promotes the formation of a dense silicon oxide layer between the silicon wafer and the alumina, passivating the dangling bonds on the crystalline silicon surface, reducing the defect state density at the interface, and thus ensuring a superior chemical passivation effect. In summary, this application reduces the risk of alumina layer explosion while ensuring the chemical passivation effect of the cell through oxidizing gas annealing.

[0010] In addition, the method for preparing solar cells according to the above embodiments of this application may also have the following additional technical features:

[0011] In some embodiments of this application, in step (1), the ratio of the trimethylaluminum vapor pulse time to the water vapor pulse time is 1:(0.7 to 1.1).

[0012] In some embodiments of this application, in step (1), during a single reaction cycle, the trimethylaluminum vapor pulse time accounts for 5% to 16% of the total time of the single reaction cycle; the water vapor pulse time accounts for 5% to 16% of the total time of the single reaction cycle; the first nitrogen purging time accounts for 30% to 40% of the total time of the single reaction cycle; and the second nitrogen purging time accounts for 35% to 50% of the total time of the single reaction cycle.

[0013] In some embodiments of this application, in step (1), the temperature for depositing the ALD alumina layer is 200°C to 350°C; and / or, the ALD alumina layer deposition includes 20 to 80 reaction cycles.

[0014] In some embodiments of this application, in step (2), the annealing temperature is 400℃~500℃ and the annealing time is 5min~15min.

[0015] In some embodiments of this application, in step (2), the oxidizing atmosphere includes at least one of oxygen and nitrous oxide.

[0016] In some embodiments of this application, in step (3), the silicon nitride layer is deposited on the surface of the alumina layer away from the silicon wafer using PECVD, and the deposition temperature is 400°C to 500°C.

[0017] In a second aspect, this application proposes a solar cell. According to an embodiment of this application, the solar cell includes:

[0018] Silicon wafers;

[0019] A silicon oxide layer is disposed on at least a portion of the surface of the silicon wafer;

[0020] An alumina layer is disposed on at least a portion of the surface of the silicon oxide layer away from the silicon wafer, wherein the percentage of hydrogen atoms in the alumina layer is 2.5 at.% to 3.6 at.%.

[0021] A silicon nitride layer is disposed on at least a portion of the surface of the alumina layer away from the silicon oxide layer.

[0022] According to the solar cell of this application embodiment, the hydrogen atom content in the alumina layer is low, only 2 at.% to 3 at.%, thereby reducing the possibility of H atoms in the alumina layer forming hydrogen gas during the subsequent high-temperature deposition of the silicon nitride layer on the alumina layer surface, and reducing the risk of alumina layer delamination. Simultaneously, a dense silicon oxide layer is formed between the silicon wafer and the alumina layer to passivate the dangling bonds on the crystalline silicon surface, reducing the defect state density at the interface, thus ensuring a superior chemical passivation effect. Therefore, this application reduces the risk of alumina layer delamination while ensuring the chemical passivation effect of the solar cell.

[0023] In addition, the solar cell according to the above embodiments of this application may also have the following additional technical features:

[0024] In some embodiments of this application, the thickness of the silicon oxide layer is 0.5 nm to 2 nm.

[0025] In some embodiments of this application, the thickness of the alumina layer is 3 nm to 10 nm; and / or, the thickness of the silicon nitride layer is 30 nm to 120 nm.

[0026] In a third aspect of the invention, a solar cell module is provided. According to embodiments of the invention, the solar cell module has the solar cells described in the above embodiments. Therefore, the solar cells in the solar cell module have superior open-circuit voltage (Voc), fill factor (FF), and power conversion efficiency (PCE).

[0027] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0029] Figure 1This is a schematic flowchart of a method for preparing a solar cell according to an embodiment of this application;

[0030] Figure 2 This is a schematic diagram of the structure of a solar cell according to an embodiment of this application.

[0031] Figure label:

[0032] 1-Silicon wafer, 2-Silicon oxide layer, 3-Aluminum oxide layer, 4-Silicon nitride layer. Detailed Implementation

[0033] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0034] In one aspect of this application, a method for fabricating a solar cell is provided. According to embodiments of this application, refer to the appendix... Figure 1 The method includes: S100: depositing an alumina layer on the surface of a silicon wafer using ALD, wherein the ALD deposition of the alumina layer includes multiple reaction cycles, each reaction cycle including a trimethylaluminum vapor (TMA) pulse, a first nitrogen purging, a water vapor pulse, and a second nitrogen purging in sequence; the ratio of the TMA pulse time to the water vapor pulse time is 1:(0.5~1.15); S200: annealing the silicon wafer under an oxidizing atmosphere; S300: forming a silicon nitride layer on the surface of the alumina layer away from the silicon wafer. Therefore, by optimizing the process conditions for ALD deposition of the alumina layer, this application can effectively reduce the hydrogen atom content in the alumina layer, thereby reducing the possibility of H atoms in the alumina layer forming hydrogen gas during subsequent high-temperature processing, and reducing the risk of alumina layer explosion. Simultaneously, the introduction of oxidizing gas during annealing promotes the formation of a dense silicon oxide layer between the silicon wafer and the alumina, passivating the dangling bonds on the crystalline silicon surface, reducing the defect state density at the interface, and thus ensuring a superior chemical passivation effect. In summary, this application reduces the risk of aluminum oxide layer explosion while ensuring the chemical passivation effect of the battery through oxidizing gas annealing.

[0035] The principle behind the method for preparing solar cells proposed in this invention, which enables the above-mentioned beneficial effects, will be explained in detail below:

[0036] This application effectively reduces the H atom content in the alumina layer (the percentage of hydrogen atoms in the alumina layer can be reduced to 2.5 at.% to 3.6 at.%) by adjusting the process parameters TMA and water pulse time of the ALD deposition alumina layer. This reduces the possibility of H atoms in the alumina layer forming hydrogen gas during subsequent high-temperature processing and reduces the risk of alumina layer bursting.

[0037] However, the reduction of H atoms in the alumina layer decreases the chemical passivation effect of the alumina layer, leading to a decrease in the battery's open-circuit voltage (Voc). The inventors discovered that introducing an oxidizing gas during annealing effectively promotes the formation of a denser silicon oxide layer at the interface between the alumina layer and crystalline silicon, passivating the dangling bonds on the crystalline silicon surface and reducing the defect state density at the interface, thereby ensuring the battery's chemical passivation effect. Therefore, this application reduces the risk of alumina layer explosion while ensuring the battery's chemical passivation effect through oxidizing gas annealing.

[0038] Specifically, see the attached document. Figure 1 The above method for preparing solar cells includes the following steps:

[0039] S100: ALD deposition of an alumina layer is performed on the surface of the silicon wafer.

[0040] In this step, an ALD (Alternating Current Deposition) layer of alumina is deposited on the surface of a texturized silicon wafer. This ALD deposition involves 20–80 reaction cycles, resulting in an alumina layer with a thickness of approximately 3 nm–10 nm. Each reaction cycle includes sequential trimethylaluminum vapor (TMA) pulses, a first nitrogen purging, a water vapor pulse, and a second nitrogen purging. During the TMA pulse, the TMA vapor undergoes a half-reaction with the OH- groups on the silicon wafer surface. The first nitrogen purging removes residual gases. The water vapor pulse completes the other half-reaction. The second nitrogen purging removes any remaining gases. The specific reaction process is as follows:

[0041] 1)Al(CH3)3+OH-=>O-Al-(CH3)2+CH4;

[0042] 2) Use N2 to purge and remove the remaining Al(CH3)3 gas and CH4 gas;

[0043] 3)O-Al-(CH3)2+H2O=>O-AlOH-(2)+(O)2-Al-CH3+CH4;

[0044] 4) Use N2 to purge and remove the remaining H2O and CH4. Complete one cycle.

[0045] In the embodiments of this application, the temperature for depositing the alumina layer by ALD is 200℃ to 350℃, for example, it can be 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, 330℃, 350℃, etc.

[0046] In the embodiments of this application, the ratio of the above-mentioned trimethylaluminum vapor (TMA) pulse time to the above-mentioned water vapor pulse time is 1:(0.5 to 1.15), for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.15, etc. By limiting the ratio of the trimethylaluminum vapor (TMA) pulse time to the above-mentioned water vapor pulse time within the above range, the hydrogen atom content in the alumina layer can be effectively reduced (the percentage of hydrogen atom content in the alumina layer can be reduced to 2.5 at.% to 3.6 at.%), thereby reducing the possibility of H atoms in the alumina layer forming hydrogen gas during subsequent high-temperature treatment and reducing the risk of alumina layer bursting. The inventors discovered that if the proportion of the water vapor pulse time is too large, the percentage of hydrogen atoms in the deposited alumina layer will be too high. As a result, when silicon nitride is deposited on the surface of the alumina film using the PECVD method in the subsequent step, the high temperature will cause excess hydrogen atoms in the alumina to overflow and form hydrogen gas that breaks through the silicon nitride film, resulting in a film explosion. If the proportion of the water vapor pulse time is too small, the quality of the deposited alumina layer will be poor, thus affecting the passivation effect of the alumina layer.

[0047] As some preferred embodiments, the ratio of the above-mentioned trimethylaluminum vapor (TMA) pulse time to the above-mentioned water vapor pulse time is 1:(0.7~1.1), which can further effectively reduce the hydrogen atom content in the alumina layer, thereby further reducing the possibility of H atoms in the alumina layer forming hydrogen gas during subsequent high-temperature treatment, and further reducing the risk of alumina layer bursting.

[0048] In the embodiments of this application, there is no need to limit the pulse flow rates of TMA and water; the pulse flow rates of TMA and water are assumed to remain unchanged.

[0049] According to some specific embodiments of this application, in a single reaction cycle, the pulse time of the aforementioned trimethylaluminum vapor (TMA) accounts for 5% to 16% of the total time of the single reaction cycle (examples may be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc.); the pulse time of the aforementioned water vapor accounts for 5% to 16% of the total time of the single reaction cycle (examples may be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, etc.). The first nitrogen purging time accounts for 30% to 40% of the total time of a single reaction cycle (examples could be 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, etc.); the second nitrogen purging time accounts for 35% to 50% of the total time of a single reaction cycle (examples could be 35%, 36%, 38%, 39%, 40%, 42%, 44%, 46%, 48%, 50%, etc.). Therefore, by limiting the time percentage of each process, the hydrogen atom content in the alumina layer can be further effectively reduced, thereby further reducing the possibility of H atoms in the alumina layer forming hydrogen gas during subsequent high-temperature treatment, and further reducing the risk of alumina layer bursting.

[0050] S200: Annealing of silicon wafers under an oxidizing atmosphere.

[0051] In this step, the silicon wafer is annealed under an oxidizing atmosphere. The inventors discovered that reducing the number of hydrogen atoms in the alumina layer formed in step S100 decreases the chemical passivation effect of the alumina layer, leading to a decrease in the open-circuit voltage (Voc) of the battery. Therefore, this application introduces an oxidizing gas during the annealing process, which effectively promotes the formation of a denser silicon oxide layer at the interface between the alumina layer and the crystalline silicon, passivates the dangling bonds on the crystalline silicon surface, reduces the defect state density at the interface, and thus ensures the chemical passivation effect of the battery.

[0052] According to some specific embodiments of this application, the annealing temperature is 400℃~500℃ (examples can be 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, etc.), and the annealing time is 5min~15min (examples can be 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 14min, 15min, etc.). By limiting the annealing temperature and annealing time to the above range, it is possible to further effectively promote the formation of a denser silicon oxide layer at the interface between the alumina layer and the crystalline silicon, passivate the dangling bonds on the surface of the crystalline silicon, reduce the defect state density at the interface, and thus further ensure the chemical passivation effect of the battery.

[0053] In the embodiments of this application, the specific type of the above-mentioned oxidizing atmosphere is not particularly limited. Those skilled in the art can select it according to actual needs. As some preferred solutions, the above-mentioned oxidizing atmosphere includes at least one of oxygen and nitrous oxide. For example, a mixture of nitrogen and oxygen with different flow ratios or a mixture of nitrogen and nitrous oxide with different flow ratios can be used.

[0054] S300: A silicon nitride layer is formed on the surface of the alumina layer away from the silicon wafer.

[0055] In the embodiments of this application, the silicon nitride layer can be deposited on the surface of the alumina layer away from the silicon wafer using the PECVD method. Since the hydrogen atom content in the alumina layer is effectively reduced by optimizing the process conditions for ALD deposition of the alumina layer in step S100, when silicon nitride is deposited on the surface of the alumina film using the PECVD method in step S300, the high temperature will not cause excessive hydrogen atoms in the alumina to overflow and form hydrogen gas that breaks through the silicon nitride film, thus preventing the integrity of the alumina and silicon nitride stack from being compromised.

[0056] According to some specific embodiments of this application, the temperature at which the silicon nitride layer is deposited on the surface of the alumina layer by PECVD is 400°C to 500°C. Examples include 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, and 500°C.

[0057] In a second aspect, this application proposes a solar cell. According to embodiments of this application, the solar cell is prepared by the method described in the above embodiments. Specifically, refer to the appendix... Figure 2 The solar cell includes: a silicon wafer 1; a silicon oxide layer 2 disposed on at least a portion of the surface of the silicon wafer 1; an aluminum oxide layer 3 disposed on at least a portion of the surface of the silicon oxide layer 2 away from the silicon wafer 1, wherein the percentage of hydrogen atoms in the aluminum oxide layer 3 is 2 at.% to 3 at.%; and a silicon nitride layer 4 disposed on at least a portion of the surface of the aluminum oxide layer 3 away from the silicon oxide layer 2.

[0058] According to the solar cell of this application embodiment, the percentage of hydrogen atoms in the alumina layer is low, only 2.5 at.% to 3.6 at.%, thereby reducing the possibility of hydrogen gas formation from H atoms in the alumina layer during the subsequent high-temperature deposition of a silicon nitride layer on the alumina layer surface, and reducing the risk of alumina layer delamination. Simultaneously, a dense silicon oxide layer is formed between the silicon wafer and the alumina layer to passivate the dangling bonds on the crystalline silicon surface, reducing the defect state density at the interface, thus ensuring a superior chemical passivation effect. Therefore, this application reduces the risk of alumina layer delamination while ensuring the chemical passivation effect of the solar cell.

[0059] According to some specific embodiments of this application, the thickness of the silicon oxide layer is 0.5nm to 2nm, and for example, it can be 0.5nm, 0.6nm, 0.8nm, 1nm, 1.2nm, 1.4nm, 1.6nm, 1.8nm, 2nm, etc. This further ensures the passivation of dangling bonds on the silicon wafer surface, reduces the defect state density at the interface, and thus ensures a relatively excellent chemical passivation effect.

[0060] According to further specific embodiments of this application, the thickness of the aforementioned alumina layer is 3nm to 10nm, and examples include 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, etc. And / or, the thickness of the aforementioned silicon nitride layer is 30nm to 120nm, and examples include 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, etc.

[0061] In a third aspect of the invention, a solar cell module is provided. According to embodiments of the invention, the solar cell module has the solar cells described in the above embodiments. Therefore, the solar cells in the solar cell module have superior open-circuit voltage (Voc), fill factor (FF), and power conversion efficiency (PCE).

[0062] A battery module is a finished product with power generation output function, which is made by connecting multiple solar cells in series and / or in parallel and producing them through processes such as lamination and encapsulation. Specifically, a battery module includes photovoltaic glass, encapsulation film, solar cells, encapsulation film, backsheet, etc.

[0063] The embodiments of this application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. The concentrated sulfuric acid used below is 98% sulfuric acid by mass. Furthermore, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to methods described herein or known to the public. Reaction conditions not listed are also readily available to those skilled in the art.

[0064] Example 1

[0065] This embodiment provides a method for preparing a solar cell, including:

[0066] 1) Select an n-type silicon wafer with a thickness of 150μm and a resistivity of 2Ω as the substrate, and perform polishing to remove mechanical damage and dirt from the surface.

[0067] 2) Using methods such as laser thermal melting, wet etching, LPCVD, and PE-poly, p-poly-Si, n-poly-Si, and an isolation region are sequentially formed on the back side of the cell. A tunneling oxide layer exists between the p-poly-Si and n-poly-Si and the n-type silicon substrate. A pyramid-shaped textured structure is formed on the front side of the cell through texturing.

[0068] 3) The cleaned silicon wafer was placed in an atomic layer alumina deposition chamber to deposit an alumina layer at a deposition temperature of 290℃. The TMA pulse duration was 7s, the first nitrogen purging time was 15s, the water pulse duration was 5s, and the second nitrogen purging time was 20s. The resulting alumina layer was approximately 6nm thick.

[0069] 4) Place the silicon wafer with deposited alumina in a PECVD tube and anneal it at 450°C. During annealing, introduce a mixed gas of nitrogen and nitrous oxide at a flow rate ratio of 4:1 and maintain the temperature for 10 minutes to form a silicon oxide layer with a thickness of approximately 1 nm at the interface between the silicon wafer and the alumina layer. Then, deposit a silicon nitride film with a thickness of approximately 1 nm.

[0070] Example 2

[0071] The preparation methods of Example 2 and Example 1 are basically the same, with the only difference being:

[0072] 3) The pulse time of TMA is 7s, the first nitrogen purging time is 15s, the water pulse time is 4s, and the second nitrogen purging time is 20s.

[0073] Example 3

[0074] The preparation methods of Example 3 and Example 1 are basically the same, with the only difference being:

[0075] 3) The pulse time of TMA is 7s, the first nitrogen purging time is 15s, the water pulse time is 6s, and the second nitrogen purging time is 20s.

[0076] Example 4

[0077] The preparation method of Example 4 is basically the same as that of Example 1, the only difference being:

[0078] 3) The pulse time of TMA is 7s, the first nitrogen purging time is 15s, the pulse time of water is 7s, and the second nitrogen purging time is 20s.

[0079] Example 5

[0080] The preparation methods of Example 5 and Example 1 are basically the same, with the only difference being:

[0081] 3) The pulse time of TMA is 7s, the first nitrogen purging time is 15s, the water pulse time is 8s, and the second nitrogen purging time is 20s.

[0082] Example 6

[0083] The preparation methods of Example 6 and Example 1 are basically the same, with the only difference being:

[0084] 4) Heat to 400℃ for annealing. During the annealing process, a mixed gas of nitrogen and nitrous oxide with a flow rate ratio of 4:1 is introduced and kept at a constant temperature for 15 minutes to form a silicon oxide layer with a thickness of about 1nm at the interface between the silicon wafer and the alumina layer.

[0085] Example 7

[0086] The preparation methods of Example 7 and Example 1 are basically the same, with the only difference being:

[0087] 4) Heat to 500℃ for annealing. During the annealing process, a mixed gas of nitrogen and nitrous oxide with a flow rate ratio of 4:1 is introduced and kept at a constant temperature for 5 minutes to form a silicon oxide layer with a thickness of about 1nm at the interface between the silicon wafer and the alumina layer.

[0088] Example 8

[0089] The preparation methods of Example 8 and Example 1 are basically the same, with the only difference being:

[0090] 4) During the annealing process, a mixture of nitrogen and oxygen with a flow rate ratio of 4:1 is introduced.

[0091] Comparative Example 1

[0092] The preparation methods of Comparative Example 1 and Example 1 are basically the same, with the only difference being:

[0093] 3) The pulse time of TMA is 7s, the first nitrogen purging time is 15s, the water pulse time is 9s, and the second nitrogen purging time is 20s.

[0094] Comparative Example 2

[0095] The preparation methods of Comparative Example 2 and Example 1 are basically the same, with the only difference being:

[0096] 3) The pulse time of TMA is 7s, the first nitrogen purging time is 15s, the water pulse time is 3s, and the second nitrogen purging time is 20s.

[0097] Comparative Example 3

[0098] The preparation methods of Comparative Example 3 and Example 1 are basically the same, with the only difference being:

[0099] 4) No oxidizing gas is introduced during the annealing process.

[0100] The percentage of hydrogen atoms in the alumina layers deposited in Examples 1-8 and Comparative Examples 1-3 was tested, the film bursting of the alumina layers deposited in Examples 1-8 and Comparative Examples 1-3 was observed, and the short-circuit current (Isc), open-circuit voltage (Voc), fill factor (FF), and photoelectric conversion efficiency (Eta) of the solar cells deposited in Examples 1-8 and Comparative Examples 1-3 were tested. The results are shown in Table 1.

[0101] Table 1

[0102]

[0103] As shown in Table 1, the alumina layer in Comparative Example 1 has a higher percentage of hydrogen atoms and exhibits film bursting, while the alumina layers in Examples 1-8 all have lower percentages of hydrogen atoms and do not exhibit film bursting. This indicates that if the proportion of water vapor pulse time is too large, it will lead to an excessively high percentage of hydrogen atoms in the deposited alumina layer, resulting in film bursting. Furthermore, compared to Comparative Example 1, the open-circuit voltage (Voc) and Eta of Examples 1-8 are improved.

[0104] As can be seen from Table 1, compared with Comparative Example 2, the open-circuit voltage (Voc) and Eta of Examples 1 to 8 were significantly improved. This shows that if the proportion of water vapor pulse time is too small, the quality of the deposited alumina layer will be poor, thus affecting the passivation effect of the alumina layer.

[0105] As can be seen from Table 1, compared with Comparative Example 3, the open circuit voltage (Voc) and Eta of Examples 1 to 8 were significantly improved. This shows that if oxidizing gas is not introduced during the annealing process, the chemical passivation effect of the alumina layer will be reduced.

[0106] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0107] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing a solar cell, characterized in that, include: (1) An ALD layer of aluminum oxide is deposited on the surface of a silicon wafer. The ALD deposition of aluminum oxide includes multiple reaction cycles. Each reaction cycle includes a trimethylaluminum vapor pulse, a first nitrogen purging, a water vapor pulse, and a second nitrogen purging in sequence. The ratio of the trimethylaluminum vapor pulse time to the water vapor pulse time is 1:(0.5~1.15). (2) The silicon wafer is annealed in an oxidizing atmosphere; (3) A silicon nitride layer is formed on the surface of the alumina layer away from the silicon wafer. In step (1), in a single reaction cycle, the trimethylaluminum vapor pulse time accounts for 5% to 16% of the total time of the single reaction cycle; the water vapor pulse time accounts for 5% to 16% of the total time of the single reaction cycle; the first nitrogen purging time accounts for 30% to 40% of the total time of the single reaction cycle; and the second nitrogen purging time accounts for 35% to 50% of the total time of the single reaction cycle.

2. The method according to claim 1, characterized in that, In step (1), the ratio of the trimethylaluminum vapor pulse time to the water vapor pulse time is 1:(0.7~1.1).

3. The method according to claim 1, characterized in that, In step (1), the temperature for depositing the alumina layer by ALD is 200℃~350℃; And / or, the ALD deposited alumina layer comprises 20 to 80 reaction cycles.

4. The method according to any one of claims 1 to 3, characterized in that, In step (2), the annealing temperature is 400℃~500℃ and the annealing time is 5min~15min.

5. The method according to any one of claims 1 to 3, characterized in that, In step (2), the oxidizing atmosphere includes at least one of oxygen and nitrous oxide.

6. The method according to any one of claims 1 to 3, characterized in that, In step (3), the silicon nitride layer is deposited on the surface of the alumina layer away from the silicon wafer using the PECVD method at a deposition temperature of 400℃~500℃.

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