Passivation film, passivation film preparation method and solar cell

Abstract

The present application relates to a passivation film, a method for preparing the passivation film, and a solar cell. The passivation film includes two passivation layers. The first passivation layer is arranged on the surface of the substrate, and the second passivation layer is arranged on the surface of the first passivation layer away from the substrate. The field passivation effect of the first passivation layer is better than the field passivation effect of the second passivation layer, that is, the field passivation effect of the film layer close to the substrate is better than the field passivation effect of the top, which can prevent charge carriers of similar polarity from approaching the substrate, greatly reduce the number of carriers of one polarity reaching the surface, and significantly reduce the recombination loss on the substrate surface. The chemical passivation effect of the second passivation layer is better than the first passivation effect. The chemical passivation effect of the upper surface film layer of the outermost layer of the passivation film is the best, so that the atoms have enough time and energy to reach the optimal energy level, thereby saturating the surface dangling bonds, reducing their recombination effect on other positive and negative charges, and ensuring the passivation effect of the passivation film. That is, the passivation film in the present application can take into account both the field passivation effect and the chemical passivation effect.

Description

Technical Field

[0001] The present application relates to the technical field of solar cells, and in particular to a passivation film, a method for preparing the passivation film, and a solar cell. Background Art

[0002] The conversion efficiency of solar cells is an important parameter of solar cell performance. In order to improve the conversion efficiency of solar cells, in the field of solar cell technology, passivation technology is usually used to prepare passivation films during the preparation of solar cells. However, traditional passivation films cannot simultaneously guarantee a high fixed charge density and hydrogen atom percentage content, and it is difficult to take into account both field passivation effects and chemical passivation effects. Summary of the invention

[0003] Based on this, it is necessary to provide a passivation film, a passivation film preparation method and a solar cell that can take into account both field passivation effect and chemical passivation effect in order to solve the above technical problems.

[0004] In a first aspect, the present application provides a passivation film, the passivation film comprising:

[0005] A first passivation layer is provided on the surface of the substrate;

[0006] A second passivation layer is provided on a surface of the first passivation layer facing away from the substrate;

[0007] The field passivation effect of the first passivation layer is better than the field passivation effect of the second passivation layer, and the chemical passivation effect of the second passivation layer is better than the chemical passivation effect of the first passivation layer.

[0008] In one embodiment, the negative charge density of the first passivation layer is greater than the negative charge density of the second passivation layer.

[0009] In one embodiment, the hydrogen content of the second passivation layer is greater than the hydrogen content of the first passivation layer.

[0010] In one embodiment, a first thickness of the first passivation layer is less than a second thickness of the second passivation layer.

[0011] In one embodiment, it also includes:

[0012] A third passivation layer is provided on a surface of the second passivation layer facing away from the first passivation layer, wherein the negative charge density of the third passivation layer is less than the negative charge density of the first passivation layer and greater than the charge density of the second passivation layer;

[0013] The hydrogen content of the third passivation layer is less than the hydrogen content of the second passivation layer, and greater than the hydrogen content of the first passivation layer.

[0014] In one of the embodiments, the thickness of the first passivation layer is 15% to 25% of the thickness of the passivation film; the thickness of the passivation film is the sum of the thicknesses of the first passivation layer, the second passivation layer and the third passivation layer.

[0015] In one embodiment, the thickness of the second passivation layer is less than the thickness of the third passivation layer.

[0016] In one embodiment, the first passivation layer, the second passivation layer, and the third passivation layer are made of the same material.

[0017] In one embodiment, the first passivation layer, the second passivation layer, and the third passivation layer are all made of aluminum oxide.

[0018] In a second aspect, the present application further provides a method for preparing a passivation film, which is used to prepare the passivation film as described above; the method comprises:

[0019] forming a first passivation layer on the surface of the substrate;

[0020] forming a second passivation layer on a surface of the first passivation layer facing away from the substrate;

[0021] The field passivation effect of the first passivation layer is better than the field passivation effect of the second passivation layer, and the chemical passivation effect of the second passivation layer is better than the chemical passivation effect of the first passivation layer.

[0022] In a third aspect, the present application further provides a solar cell, comprising:

[0023] substrate;

[0024] As the above-mentioned passivation film, the passivation film is arranged on the surface of the substrate.

[0025] The above-mentioned passivation film, passivation film preparation method and solar cell, the passivation film includes two passivation layers, wherein the first passivation layer is arranged on the surface of the substrate, and the second passivation layer is arranged on the surface of the first passivation layer away from the substrate, the field passivation effect of the first passivation layer is better than the field passivation effect of the second passivation layer, that is, the field passivation effect of the film layer close to the substrate is better than the field passivation effect of the top, which can prevent charge carriers of similar polarity from approaching the substrate, thereby greatly reducing the number of carriers of one polarity reaching the surface, and significantly reducing the recombination loss on the substrate surface. The chemical passivation effect of the second passivation layer is better than the first passivation effect, and the chemical passivation effect of the upper surface film layer of the outermost layer of the passivation film is the best, so that the atoms have enough time and energy to reach the optimal energy level, thereby saturating the surface dangling bonds, reducing their recombination effect on other positive and negative charges, and ensuring the passivation effect of the passivation film. That is, in the present application, the field passivation effect of the first passivation layer is better than the field passivation effect of the second passivation layer, and the chemical passivation effect of the second passivation layer is better than the chemical passivation effect of the first passivation layer, so that the overall field passivation effect and chemical passivation effect of the passivation film are improved, taking into account both the field passivation effect and the chemical passivation effect of the passivation film. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 One of the schematic diagrams of the structure of a passivation film in one embodiment;

[0027] Figure 2 The second schematic diagram of the structure of the passivation film in one embodiment;

[0028] Figure 3 The third schematic diagram of the structure of the passivation film in one embodiment;

[0029] Figure 4 The figure is a schematic diagram of a process for preparing a passivation film in one embodiment.

[0030] Description of reference numerals:

[0031] 10. passivation layer; 11. first passivation layer; 111. first aluminum oxide layer; 12. second passivation layer; 121. second aluminum oxide layer; 13. third passivation layer. DETAILED DESCRIPTION

[0032] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0034] It should be understood that when an element or layer is referred to as being "on, adjacent to, connected to or coupled to other elements or layers, it may be directly on, adjacent to, connected to or coupled to other elements or layers, or there may be intervening elements or layers. On the contrary, when an element is referred to as being "directly on, directly adjacent to, directly connected to or directly coupled to other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers, doping types and / or parts, these elements, components, regions, layers, doping types and / or parts should not be limited by these terms. These terms are merely used to distinguish one element, component, region, layer, doping type or part from another element, component, region, layer, doping type or part.

[0035] Spatially relative terms such as "under," "beneath," "below," "under," "above," "above," and the like may be used herein to describe the relationship of an element or feature shown in the figures to other elements or features. It should be understood that, in addition to the orientations shown in the figures, spatially relative terms also include different orientations of the device in use and operation. For example, if the device in the accompanying drawings is flipped, an element or feature described as "under other elements" or "under it" or "under it" will be oriented as being "above" the other elements or features. Thus, the exemplary terms "under" and "under" may include both upper and lower orientations. In addition, the device may also include additional orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptors used herein are interpreted accordingly.

[0036] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that when the terms "consisting of" and / or "comprising" are used in this specification, the presence of the features, integers, steps, operations, elements and / or parts can be determined, but the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups is not excluded. At the same time, when used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0037] Embodiments of the invention are described herein with reference to cross-sectional views which are schematic diagrams of ideal embodiments (and intermediate structures) of the present application, so that variations in the shapes shown due to, for example, manufacturing techniques and / or tolerances can be expected. Therefore, embodiments of the present application should not be limited to the specific shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing techniques. For example, an implanted region shown as a rectangle typically has rounded or curved features and / or an implant concentration gradient at its edges, rather than a binary change from an implanted region to a non-implanted region. Similarly, a buried region formed by implantation may result in some implantation in the region between the buried region and the surface through which the implantation is performed. Therefore, the regions shown in the figures are schematic in nature, their shapes do not represent the actual shape of the region of the device, and do not limit the scope of the present application.

[0038] The embodiment of the present application provides a passivation film, which is formed on the surface of the substrate and is used to improve the passivation effect of the passivation film. Furthermore, based on the application scenario of the passivation film, the performance of semiconductor devices, such as photovoltaic cells, semiconductor light-emitting devices, etc., can also be improved. Among them, the photovoltaic cell can be a solar cell. In this application, the application of the passivation film to a solar cell is used as an example for explanation.

[0039] Specifically, a solar cell is a photoelectric semiconductor sheet that uses sunlight to generate electricity directly, also known as a "solar chip" or "photovoltaic cell". Under certain light conditions, sunlight shines on the semiconductor pn junction to form new hole-electron pairs. Under the action of the built-in electric field of the pn junction, photogenerated holes flow to the p region and photogenerated electrons flow to the n region. When the circuit is connected, current is generated, so the battery can output voltage and generate current in the presence of a loop. In the preparation process of solar cells, the problem of substrate surface passivation is usually solved by synthesizing a passivation film. The principle includes two aspects: one is to use the atoms generated in the passivation film to combine with the dangling bonds, thereby reducing its compounding effect on other positive and negative charges, forming a chemical passivation effect; the other is that there are certain charges in the passivation film, which will form a built-in electric field on the contact surface, thereby forming a field passivation effect. Its core function is to increase the open circuit voltage and short circuit current, thereby improving the fill factor, and further improving the photoelectric conversion efficiency.

[0040] In one embodiment, the present application provides a passivation film 10, such as Figure 1 One of the structural schematic diagrams of the passivation film 10 shown, the passivation film 10 includes a first passivation layer 11 and a second passivation layer 12, the first passivation layer 11 is arranged on the surface of the substrate; the second passivation layer 12 is arranged on the surface of the first passivation layer 11 away from the substrate; wherein the field passivation effect of the first passivation layer 11 is better than the field passivation effect of the second passivation layer 12, and the chemical passivation effect of the second passivation layer 12 is better than the chemical passivation effect of the first passivation layer 11.

[0041] The substrate may include a semiconductor substrate made of silicon or germanium, or a compound semiconductor substrate made of silicon carbide, silicon germanium, gallium arsenide, indium phosphide, zinc oxide, or gallium oxide. As an example, in this embodiment, the substrate is made of single crystal silicon. The substrate includes a light-receiving surface and a backlight surface that are arranged opposite to each other. The substrate surface may be a light-receiving surface that receives sunlight, or a backlight surface that is arranged opposite to the light-receiving surface.

[0042] The materials of the above-mentioned first passivation layer 11 and the second passivation layer 12 can be one or two of silicon oxide, aluminum oxide, silicon nitride, silicon oxynitride or carbon nitride silicon oxide, that is, the materials of the first passivation layer 11 and the second passivation layer 12 can be the same or different. For the first passivation layer 11 and the second passivation layer 12 of different materials, the passivation principle of the passivation film 10 formed is different from that of the passivation film 10 formed by the first passivation layer 11 and the second passivation layer 12 of the same material. For example, if the first passivation layer 11 is an aluminum oxide film layer and the second passivation layer 12 is a silicon oxide film layer, the passivation film 10 composed of the first passivation layer 11 and the second passivation layer 12 is a composite passivation film 10, and the aluminum oxide film layer and the silicon oxide film layer can passivate the dangling bonds on the substrate surface by adding atomic hydrogen, thereby ensuring the hydrogen passivation effect and improving the chemical passivation performance. When the first passivation layer 11 and the second passivation layer 12 are film layers of the same material, such as silicon oxide film layers, the field passivation effect and chemical passivation effect of the two passivation layers can be set to be different as in the present embodiment, thereby ensuring the field passivation effect and chemical passivation effect of the passivation layer at the same time, and improving the passivation effect of the passivation film 10 as a whole. For another example, if the two passivation layers are both silicon nitride film layers, the refractive index of the range silicon nitride film layers can be set to be different, thereby improving the anti-reflection effect of the passivation film 10. It can be understood that the above examples are only examples made to facilitate the understanding of the present embodiment, and are not specific limitations on the two passivation layers. In other examples, in order to achieve similar effects to the present embodiment, the passivation layers of different materials can also be set to have different field passivation effects and chemical passivation effects of each passivation layer.

[0043] In this embodiment, a passivation film 10 is provided including two passivation layers, wherein the first passivation layer 11 is provided on the surface of the substrate, and the second passivation layer 12 is provided on the surface of the first passivation layer 11 away from the substrate. The field passivation effect of the first passivation layer 11 is better than the field passivation effect of the second passivation layer 12, that is, the field passivation effect of the film layer close to the substrate is better than the field passivation effect of the top, which can prevent charge carriers of similar polarity from approaching the substrate, thereby greatly reducing the number of carriers of one polarity reaching the surface, and significantly reducing the recombination loss on the substrate surface. The chemical passivation effect of the second passivation layer 12 is better than the first passivation effect, and the chemical passivation effect of the outermost upper surface film layer of the passivation film 10 is the best, so that the atoms have enough time and energy to reach the optimal energy level, thereby saturating the surface dangling bonds, reducing their recombination effect on other positive and negative charges, and ensuring the passivation effect of the passivation film 10. That is, in this embodiment, the field passivation effect of the first passivation layer 11 is better than the field passivation effect of the second passivation layer 12, and the chemical passivation effect of the second passivation layer 12 is better than the chemical passivation effect of the first passivation layer 11, so that the overall field passivation effect and chemical passivation effect of the passivation film 10 are improved, while ensuring the field passivation effect and chemical passivation effect of the passivation film 10.

[0044] In one embodiment, the negative charge density of the first passivation layer is greater than the negative charge density of the second passivation layer. Specifically, the higher the negative charge density of the contact surface between the passivation layer and the substrate, the stronger the ability to shield minority carriers on the surface of the substrate, and thus has a better field passivation effect. For example, the negative charge density of the first passivation layer can be greater than 2×10 12 cm -2 , and is greater than the negative charge density of the second passivation layer. In other examples, the negative charge density of the first passivation layer may also be greater than 2.1×10 12 cm -2 , 2.2×10 12 cm -2 , 2.3×10 12 cm -2 , 2.4×10 12 cm -2 , 2.5×10 12 cm -2 , 3×10 12 cm -2 , 3.5×10 12 cm -2 , etc., but not limited to these.

[0045] In this embodiment, by setting the negative charge density of the first passivation layer to be greater than the negative charge density of the second passivation layer, the passivation effect of the first passivation layer close to the surface of one side of the substrate is better than the passivation effect of the second passivation layer on the surface of one side of the first passivation layer, which can more effectively ensure the field passivation effect of the passivation film, thereby improving the photoelectric conversion efficiency of the solar cell.

[0046] In one embodiment, the hydrogen content of the second passivation layer is greater than the hydrogen content of the first passivation layer. Specifically, the higher the hydrogen content on the upper surface of the passivation film, the stronger its ability to reduce the recombination effect of dangling bonds on other positive and negative charges, and thus has a better chemical passivation effect. Exemplarily, the hydrogen content of the second passivation layer may be greater than 3% and greater than the hydrogen content of the first passivation layer. In other examples, the hydrogen content of the second passivation layer may also be greater than 3.1%, 3.2%, 3.3%, 3.4%, 3.4%, 4%, 5%, etc., without limitation thereto.

[0047] In this embodiment, by setting the hydrogen content of the second passivation layer to be greater than the hydrogen content of the first passivation layer, the chemical passivation effect of the second passivation layer on the surface of the first passivation layer facing away from the substrate is better than the chemical passivation effect of the first passivation layer. On the one hand, the chemical passivation effect of the passivation film can be effectively guaranteed, thereby improving the photoelectric conversion efficiency of the solar cell; on the other hand, the first passivation layer has a low hydrogen content, which can also effectively avoid the occurrence of film explosion and improve the quality of the passivation film.

[0048] In one embodiment, a first thickness of the first passivation layer is less than a second thickness of the second passivation layer.

[0049] For the sake of convenience, the total thickness of the passivation film in the embodiment of the present application is referred to as the passivation film thickness, wherein, in order to avoid the problem that the passivation layer that is difficult for the silver paste to burn through reaches the substrate surface during the preparation of the solar cell, the passivation film thickness should not be too thick, and illustratively, it can be 1nm to 30nm. In other examples, it can also be 2nm to 20nm, 3nm to 18nm, 4nm to 15nm, etc., without limitation thereto.

[0050] Specifically, the first thickness mentioned above can be understood as the thickness of the first passivation layer when it can achieve sufficient field passivation effect on the substrate, and the second thickness can be understood as the thickness of the second passivation layer when it can achieve the target chemical passivation effect on the basis of achieving sufficient field passivation effect in the first passivation layer. Furthermore, according to the different materials of the passivation layer, the corresponding thickness when the field passivation effect / chemical passivation effect is optimal is also different. For example, the first passivation layer and the second passivation layer are both aluminum oxide as an example for explanation. When the aluminum oxide film layer is usually about 2nm thick, the increase in the fixed charge of its surface dielectric layer reaches a saturation value, and the field passivation effect reaches a peak value at this time; when the aluminum oxide thickness is greater than about 10nm, its surface recombination rate no longer decreases. Therefore, in this embodiment, the first thickness of the first passivation layer is set to be less than the second thickness of the second passivation layer, which can simultaneously ensure the field passivation effect and chemical passivation effect of different passivation layers in the passivation film. Exemplarily, the thickness of the first passivation layer is 15% to 25% of the thickness of the passivation film. For example, when the thickness of the passivation film is 4nm, the first thickness of the first passivation layer is set to 0.6nm to 1nm, and the second thickness of the second passivation layer is set to 3nm to 3.4nm; for example, when the thickness of the passivation film is 15nm, the first thickness of the first passivation layer is set to 2.25nm to 3.75nm, and the second thickness of the second passivation layer is set to 11.25nm to 12.75nm, etc., but is not limited to this.

[0051] In the present embodiment, by setting the first thickness of the first passivation layer to be smaller than the second thickness of the second passivation layer, on the one hand, the internal stress inside the passivation film can be reduced, so that the thermal stress can be relieved, and the electrical properties of the passivation film and the substrate can be significantly improved, thereby significantly improving the photoelectric conversion efficiency of the solar cell; on the other hand, according to the performance requirements of the passivation film, an appropriate first thickness is selected, so that the difference between the first thickness of the first passivation layer and the second thickness of the second passivation layer is a threshold difference, and while meeting the passivation requirements of the passivation film, the first passivation layer and the second passivation layer are prepared respectively by preparation processes with different preparation efficiencies, thereby being compatible with the overall preparation time of the passivation film and the passivation effect of the passivation film.

[0052] In one embodiment, Figure 2 As shown in the second structural schematic diagram of the passivation film 10, the passivation film 10 also includes a third passivation layer 13, and the third passivation layer 13 is arranged on the surface of the second passivation layer 12 away from the first passivation layer 11, and the negative charge density of the third passivation layer 13 is less than the negative charge density of the first passivation layer 11, and greater than the charge density of the second passivation layer 12; the hydrogen content of the third passivation layer 13 is less than the hydrogen content of the second passivation layer 12, and greater than the hydrogen content of the first passivation layer 11.

[0053] It can be understood that the passivation film 10 in this embodiment also includes a third passivation layer 13, and the thickness of the passivation film 10 described in the previous embodiment is the sum of the thicknesses of the first passivation layer 11, the second passivation layer 12, and the third passivation layer 13. Similar to the first passivation layer 11 and the second passivation layer 12, the material of the third passivation layer 13 can also be one of silicon oxide, aluminum oxide, silicon nitride, silicon oxynitride, or carbon nitride silicon oxide, which can be the same as or different from the material of the first passivation layer 11 and the second passivation layer 12.

[0054] In this embodiment, the third passivation layer 13 is arranged on the surface of the second passivation layer 12 away from the first passivation layer 11, and the negative charge density of the third passivation layer 13 is set to be less than the negative charge density of the first passivation layer 11, and greater than the charge density of the second passivation layer 12, so that the field passivation effect of the third passivation layer 13 is inferior to that of the first passivation layer 11 and better than that of the second passivation layer 12. At the same time, the hydrogen content of the third passivation layer 13 is set to be less than the hydrogen content of the second passivation layer 12, and greater than the hydrogen content of the first passivation layer 11, so that the chemical passivation effect of the third passivation layer 13 is inferior to that of the second passivation layer 12 and due to the first passivation layer 11, therefore, this embodiment can optimize the passivation effect of the overall passivation film 10 by adding a passivation layer with different passivation effects on the surface of the second passivation layer 12 away from the first passivation film 10.

[0055] In one embodiment, the thickness of the first passivation layer is 15% to 25% of the thickness of the passivation film; the thickness of the passivation film is the sum of the thicknesses of the first passivation layer, the second passivation layer, and the third passivation layer. Specifically, in order to ensure the passivation effect of the passivation film while avoiding the problem that the silver paste is difficult to burn through the passivation film, the first thickness of the first passivation layer, the second thickness of the second passivation layer, and the third thickness of the third passivation layer can be set to gradually increase, that is, the thickness of the second passivation layer is less than the thickness of the third passivation layer, thereby improving the electrical properties of the passivation film and the substrate, and significantly improving the photoelectric conversion efficiency of the solar cell. For example, when the thickness of the passivation film is 4nm, the first thickness of the first passivation layer is set to 0.6nm~1nm, the second thickness of the second passivation layer is set to 1.2nm~1.4nm, and the third thickness of the third passivation layer is set to 1.6nm~2.2nm; if the thickness of the passivation film is 15nm, the first thickness of the first passivation layer is set to 2.25nm~3.75nm, the second thickness of the second passivation layer is set to 4nm~4.75nm, the third thickness of the third passivation layer is set to 7.25nm~8nm, etc., but not limited to this.

[0056] In one embodiment, the first passivation layer, the second passivation layer, and the third passivation layer are made of the same material. Exemplarily, the first passivation layer, the second passivation layer, and the third passivation layer are all made of aluminum oxide. Because the aluminum oxide film layer and the substrate interface have a low interface defect state density and a high fixed negative charge density. The fixed negative charge will induce a space charge region within a certain depth range on the semiconductor surface and form a built-in electric field. The built-in electric field will make it difficult for carriers (such as electrons) in the semiconductor to approach the semiconductor surface, thereby reducing the possibility of interface defect states and carrier recombination, and playing a field passivation role. The aluminum oxide film contains a high content of hydrogen atoms, and the hydrogen atoms will bond with the dangling bonds on the semiconductor surface, thereby reducing the interface defect states and playing a role in chemical passivation. Therefore, in this embodiment, the material of each passivation layer in the passivation film is set to aluminum oxide, which can improve the passivation effect of the passivation film.

[0057] In one embodiment, the present application further provides a passivation film 10, such as Figure 3 The third structural schematic diagram of the passivation film 10 shown in the figure, the passivation film 10 includes a first aluminum oxide layer 111 and a second aluminum oxide layer 121, the first aluminum oxide layer 111 is arranged on the surface of the substrate 20, and the second aluminum oxide layer 121 is arranged on the surface of the first aluminum oxide layer 111 away from the substrate 20, the total thickness of the first aluminum oxide layer 111 and the second aluminum oxide layer 121 is 4nm to 15nm, the thickness of the first aluminum oxide layer 111 is 15% to 25% of the total thickness of the first aluminum oxide layer 111 and the second aluminum oxide layer 121, the thickness of the second aluminum oxide layer 121 is 75-85% of the total thickness of the first aluminum oxide layer 111 and the second aluminum oxide layer 121, and the negative charge density of the first aluminum oxide layer 111 is greater than 2×10 12 cm-2 and higher than the negative charge density of the second aluminum oxide layer 121 ; the hydrogen content in the second aluminum oxide layer 121 is greater than 3% and higher than the hydrogen content in the first aluminum oxide layer 111 .

[0058] In this embodiment, the passivation film 10 includes a two-layer aluminum oxide structure. Among them, the negative charge density of the first aluminum oxide layer 111 disposed on the surface of the substrate 20 is higher than the negative charge density of the second aluminum oxide layer 121 disposed on the surface of the first aluminum oxide layer 111 away from the substrate 20, so the first aluminum oxide layer 111 has a better field passivation effect, and the hydrogen content of the second aluminum oxide layer 121 is higher than that of the first aluminum oxide layer 111, so the chemical passivation effect of the second aluminum oxide layer 121 is better. By combining the two aluminum oxide layers, an aluminum oxide passivation film 10 with excellent field passivation effect and chemical passivation effect can be obtained; in addition, the first aluminum oxide layer 111 has a low hydrogen content, which can reduce the occurrence of film explosion and improve the quality of the passivation film 10.

[0059] In one embodiment, the present application also provides a method for preparing a passivation film, such as Figure 4The schematic diagram of the passivation film preparation method shown in FIG. Figure 1 The passivation film preparation method is used to prepare the passivation 10 in any of the above embodiments, and can usually be prepared by atomic layer deposition (ALD) and plate-type PERC (Passivated Emitter Rear Contact). In this embodiment, the passivation film 10 prepared by atomic layer deposition technology is used as an example for explanation. The passivation film preparation method in this embodiment includes the following steps 402 to 404.

[0060] Step 402 , forming a first passivation layer 11 on the surface of the substrate 20 .

[0061] Specifically, after setting the reaction chamber temperature and precursors (such as water, trimethylaluminum) of the atomic layer deposition system, the substrate 20 is placed in the reaction chamber, trimethylaluminum is introduced into the reaction chamber at a first preset flow rate within a first preset time, the reaction chamber is evacuated, and water is introduced into the reaction chamber at a second preset flow rate within a second preset time, the reaction chamber is evacuated again, and the above steps are repeated for a first preset number of times to obtain the first passivation layer 11. The first preset time, the second preset time, the first preset flow rate, the second preset flow rate, and the first preset number of times can be flexibly set according to the actual operation scenario, and are not specifically limited in this embodiment.

[0062] Step 404 , forming a second passivation layer 12 on the surface of the first passivation layer 11 facing away from the substrate 20 ; wherein the field passivation effect of the first passivation layer 11 is better than the field passivation effect of the second passivation layer 12 , and the chemical passivation effect of the second passivation layer 12 is better than the chemical passivation effect of the first passivation layer 11 .

[0063] Specifically, the reaction chamber temperature and precursor of the atomic layer deposition system are reset according to actual needs. After the first passivation layer 11 is prepared, trimethylaluminum is introduced into the reaction chamber at a third preset flow rate within a third preset time, and water is introduced into the reaction chamber at a fourth preset flow rate within a fourth preset time after vacuuming. The reaction chamber is vacuumed again, and the above steps are repeated for a second preset number of times to obtain the second passivation layer 12. The third preset time, the fourth preset time, the third preset flow rate, the fourth preset flow rate, and the second preset number of times can be flexibly set according to the actual operation scenario, and are not specifically limited here.

[0064] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps does not have a strict order restriction, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily to be carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0065] Based on the aforementioned passivation film and passivation film preparation method, this embodiment also provides a solar cell with a passivation film having both excellent field passivation effect and chemical passivation effect, the solar cell includes a substrate and a passivation film in any of the above embodiments, and the passivation film is arranged on the surface of the substrate. The substrate is used to receive incident light and generate photogenerated carriers. For example, in some embodiments, the solar cell is a bifacial cell, that is, both surfaces of the substrate are used to receive sunlight. The substrate can be a silicon substrate, and the material of the silicon substrate can include monocrystalline silicon, polycrystalline silicon, amorphous silicon and microcrystalline silicon. The passivation film includes a first passivation layer and a second passivation layer, and the first passivation layer is arranged on the surface of the substrate. The second passivation layer is arranged on the surface of the first passivation layer away from the substrate, the field passivation effect of the first passivation layer is better than the field passivation effect of the second passivation layer, and the chemical passivation effect of the second passivation layer is better than the chemical passivation effect of the first passivation layer.

[0066] In one embodiment, the negative charge density of the first passivation layer is greater than the negative charge density of the second passivation layer.

[0067] In one embodiment, the hydrogen content of the second passivation layer is greater than the hydrogen content of the first passivation layer.

[0068] In one embodiment, a first thickness of the first passivation layer is less than a second thickness of the second passivation layer.

[0069] In one embodiment, the thickness of the first passivation layer is 15% to 25% of the thickness of the passivation film; the thickness of the passivation film is the sum of the first thickness of the first passivation layer and the second thickness of the second passivation layer.

[0070] In one embodiment, the first passivation layer and the second passivation layer are made of the same material.

[0071] In one embodiment, the first passivation layer and the second passivation layer are both made of aluminum oxide.

[0072] In one embodiment, the passivation film also includes a third passivation layer, which is arranged on the surface of the second passivation layer away from the first passivation layer, the negative charge density of the third passivation layer is less than the negative charge density of the first passivation layer, and is greater than the charge density of the second passivation layer; the hydrogen content of the third passivation layer is less than the hydrogen content of the second passivation layer, and is greater than the hydrogen content of the first passivation layer.

[0073] In one embodiment, the thickness of the second passivation layer is less than the thickness of the third passivation layer.

[0074] In one embodiment, the material of the third passivation layer is the same as the material of the first passivation layer and the second passivation layer.

[0075] In one embodiment, the third passivation layer, the second passivation layer and the first passivation layer are all made of aluminum oxide.

[0076] Correspondingly, an embodiment of the present application further provides a photovoltaic module, which includes a battery string, and the battery string is formed by connecting the solar cell provided by any of the above embodiments or multiple solar cells using the passivation film provided by any of the above embodiments.

[0077] The photovoltaic module also includes an encapsulation layer and a cover plate, wherein the encapsulation layer is used to cover the surface of the battery string, and the cover plate is used to cover the surface of the encapsulation layer away from the battery string. The solar cells are electrically connected in the form of a whole piece or multiple pieces to form a plurality of battery strings, and the plurality of battery strings are electrically connected in series and / or in parallel. Specifically, in some embodiments, the plurality of battery strings can be electrically connected by a conductive tape. The encapsulation layer covers the surface of the solar cell. For example, the encapsulation layer can be an organic encapsulation film such as an ethylene-vinyl acetate copolymer film, a polyethylene octene co-elastic film, or a polyethylene terephthalate film. The cover plate can be a cover plate with a light-transmitting function such as a glass cover plate, a plastic cover plate, etc.

[0078] In one embodiment, the present application further provides a photovoltaic system, comprising the photovoltaic assembly in any of the above embodiments.

[0079] It can be understood that the photovoltaic system can be used in photovoltaic power stations, such as ground power stations, rooftop power stations, water power stations, etc., and can also be used in equipment or devices that use solar energy to generate electricity, such as user solar power supplies, solar street lights, solar cars, solar buildings, etc. Of course, it can be understood that the application scenarios of the photovoltaic system are not limited to this, that is to say, the photovoltaic system can be used in all fields that require solar energy to generate electricity. Taking the photovoltaic power generation system network as an example, the photovoltaic system may include a photovoltaic array, a junction box and an inverter. The photovoltaic array can be an array combination of multiple photovoltaic components. For example, multiple photovoltaic components can form multiple photovoltaic arrays. The photovoltaic array is connected to the junction box. The junction box can converge the current generated by the photovoltaic array. The converged current flows through the inverter and is converted into the alternating current required by the mains power grid. After that, it is connected to the mains network to realize solar power supply.

[0080] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0081] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A solar cell, characterized in that: The solar cell comprises: substrate; A passivation film, comprising a first passivation layer, a second passivation layer and a third passivation layer, wherein the first passivation layer is disposed on the surface of the substrate; the second passivation layer is disposed on the surface of the first passivation layer away from the substrate; and the third passivation layer is disposed on the surface of the second passivation layer away from the first passivation layer; Among them, the field passivation effect of the first passivation layer is better than the field passivation effect of the second passivation layer, and the chemical passivation effect of the second passivation layer is better than the chemical passivation effect of the first passivation layer; the first thickness of the first passivation layer, the second thickness of the second passivation layer and the third thickness of the third passivation layer gradually increase; the total thickness of the passivation film is 4nm~15nm.

2. The solar cell according to claim 1, characterized in that The negative charge density of the first passivation layer is greater than the negative charge density of the second passivation layer.

3. The solar cell according to claim 1, characterized in that The hydrogen content of the second passivation layer is greater than the hydrogen content of the first passivation layer.

4. The solar cell according to claim 1, characterized in that A first thickness of the first passivation layer is less than a second thickness of the second passivation layer.

5. The solar cell according to claim 1, characterized in that: The negative charge density of the third passivation layer is less than the negative charge density of the first passivation layer, and greater than the charge density of the second passivation layer; The hydrogen content of the third passivation layer is less than the hydrogen content of the second passivation layer, and greater than the hydrogen content of the first passivation layer.

6. The solar cell according to claim 5, characterized in that: The thickness of the first passivation layer is 15% to 25% of the thickness of the passivation film; the thickness of the passivation film is the sum of the thicknesses of the first passivation layer, the second passivation layer and the third passivation layer.

7. The solar cell according to claim 5, characterized in that: The thickness of the second passivation layer is smaller than the thickness of the third passivation layer.

8. The solar cell according to claim 5, characterized in that: The first passivation layer, the second passivation layer and the third passivation layer are made of the same material.

9. The solar cell according to claim 8, characterized in that The first passivation layer, the second passivation layer, and the third passivation layer are all made of aluminum oxide.

10. A method for preparing a passivation film, characterized in that: Used for preparing a passivation film in a solar cell according to any one of claims 1 to 9; the method comprises: forming a first passivation layer on the surface of the substrate; forming a second passivation layer on a surface of the first passivation layer facing away from the substrate; forming a third passivation layer on a surface of the second passivation layer facing away from the first passivation layer; Among them, the field passivation effect of the first passivation layer is better than the field passivation effect of the second passivation layer, and the chemical passivation effect of the second passivation layer is better than the chemical passivation effect of the first passivation layer; the first thickness of the first passivation layer, the second thickness of the second passivation layer and the third thickness of the third passivation layer gradually increase; the total thickness of the passivation film is 4nm~15nm.

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