Solar cell, photovoltaic module and photovoltaic system

Abstract

The utility model relates to a solar cell, a photovoltaic assembly and a photovoltaic system. The solar cell includes: a substrate; the tunneling oxide layer is arranged on one surface of the substrate; the at least one composite layer is arranged on the surface, away from the substrate, of the tunneling oxide layer, and when the number of the composite layers is larger than two, the composite layers are sequentially arranged on the surface, away from the substrate, of the tunneling oxide layer in a stacked mode; the composite layer comprises a first doped polycrystalline silicon layer, a second doped polycrystalline silicon layer and a third doped polycrystalline silicon layer which are sequentially stacked in the direction gradually away from the substrate; wherein the second doped polycrystalline silicon layer is doped with a carbon element. According to the solar cell, the photovoltaic assembly and the photovoltaic system, the surface passivation effect of the passivation contact structure can be improved, the surface recombination is reduced, and the conversion efficiency of the solar cell is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of photovoltaics, in particular to a solar cell, a photovoltaic component and a photovoltaic system. Background Art

[0002] With the continuous development of photovoltaic technology, people's requirements for the photoelectric conversion efficiency of crystalline silicon solar cells are getting higher and higher, but the improvement of the efficiency of industrial solar cells is still facing many challenges. In the solar cells of the related technology, in order to reduce the recombination rate, prolong the minority carrier lifetime, and improve the photoelectric conversion efficiency of the solar cell, the silicon substrate is generally passivated, and a passivation contact structure is formed on the surface of the silicon substrate to reduce the recombination of surface carriers, thereby reducing the impact caused by the internal defects of the silicon substrate. Among them, the common passivation contact structure combines the tunneling oxide layer with the heavily doped polysilicon layer, and reduces the interface recombination between the silicon substrate and the doped polysilicon layer through the chemical passivation of the tunneling oxide layer. At the same time, the tunneling oxide layer can also play a good tunneling role, so that the majority carriers are transported through the tunneling principle, while the minority carriers are difficult to tunnel through the tunneling oxide layer into the doped polysilicon layer due to the high potential barrier and be recombined. However, in the solar cells of the related technology, there are often problems of local structural peeling and film explosion of the doped polysilicon layer, which leads to poor surface passivation effect of the passivation contact structure, affecting the conversion efficiency of the solar cell. Utility Model Content

[0003] Based on this, it is necessary to provide a solar cell, a photovoltaic module and a photovoltaic system that can improve the surface passivation effect of the passivation contact structure, reduce surface recombination, and improve the conversion efficiency of the solar cell.

[0004] A first aspect of an embodiment of the present application provides a solar cell, comprising:

[0005] substrate;

[0006] A tunnel oxide layer is disposed on a surface of the substrate; and

[0007] At least one composite layer is disposed on the surface of the tunnel oxide layer away from the substrate. When the number of the composite layers is greater than two, the composite layers are sequentially stacked and disposed on the surface of the tunnel oxide layer away from the substrate.

[0008] The composite layer comprises: a first doped polysilicon layer, a second doped polysilicon layer and a third doped polysilicon layer sequentially stacked in a direction gradually away from the substrate;

[0009] The second doped polysilicon layer is further doped with carbon.

[0010] In one embodiment, in the same composite layer, the thickness of the first doped polysilicon layer is smaller than the thickness of the third doped polysilicon layer.

[0011] In one embodiment, the number of the composite layer is one, and in the same composite layer:

[0012] The thickness h1 of the first doped polysilicon layer satisfies: 10nm≤h1≤30nm;

[0013] The thickness h3 of the third doped polysilicon layer satisfies: 30nm<h3≤200nm.

[0014] In one embodiment, the thickness h2 of the second doped polysilicon layer satisfies: 10 nm≤h2≤30 nm.

[0015] In one embodiment, in the same composite layer, the doping concentration of the first doped polysilicon layer is less than the doping concentration of the third doped polysilicon layer.

[0016] In one embodiment, in the composite layer closest to the substrate, the doping concentrations of the P-type element or the N-type element in the first doped polysilicon layer, the second doped polysilicon layer, and the third doped polysilicon layer increase in sequence.

[0017] In one embodiment, the first doped polysilicon layer, the second doped polysilicon layer and the third doped polysilicon layer are all doped with the same type of P-type or N-type doping elements.

[0018] In one embodiment, the solar cell further comprises a passivation layer and an electrode, wherein the passivation layer is disposed on a surface of the outermost composite layer away from the substrate, and the electrode is disposed on the passivation layer and is in ohmic contact with the third doped polysilicon layer of the outermost composite layer;

[0019] The outermost composite layer is the composite layer farthest from the substrate among all the composite layers.

[0020] A second aspect of an embodiment of the present application provides a photovoltaic assembly, comprising at least one battery string, wherein the battery string comprises at least two of the above-mentioned solar cells.

[0021] A third aspect of an embodiment of the present application provides a photovoltaic system, comprising the above-mentioned photovoltaic component.

[0022] Beneficial effects of the above-mentioned solar cells, photovoltaic modules and photovoltaic systems:

[0023] Good passivation of the substrate is achieved by setting a tunneling oxide layer and at least one composite layer as a passivation contact structure. The composite layer includes a first doped polysilicon layer, a second doped polysilicon layer and a third doped polysilicon layer stacked in sequence in a direction gradually away from the substrate, wherein the second doped polysilicon layer is also doped with carbon elements, and carbon elements and hydrogen elements are not easy to combine. Thus, compared with the non-doped carbon element, the second doped polysilicon layer has less hydrogen elements. Therefore, during the high-temperature crystallization process, the gas overflow is reduced, the composite layer is not easy to peel off, and the occurrence of film explosion is reduced, which can improve the surface passivation effect of the passivation contact structure, reduce surface recombination, and improve the conversion efficiency of solar cells.

[0024] Furthermore, since a first doped polysilicon layer is provided between the second doped polysilicon layer and the tunneling oxide layer, it can block the second doped polysilicon layer and the tunneling oxide layer, thereby preventing the carbon element in the second doped polysilicon layer from diffusing into the tunneling oxide layer and destroying the structure of the tunneling oxide layer, which further improves the passivation effect of the passivation contact structure.

[0025] In addition, the second doped polysilicon layer is disposed between the first doped polysilicon layer and the third doped polysilicon layer, and the conductivity of the first doped polysilicon layer and the third doped polysilicon layer is higher than that of the second doped polysilicon layer, which can effectively solve the problem that the conductivity of the second doped polysilicon layer is low due to the introduction of carbon elements, thereby affecting the conductivity of the composite layer, so that the conductivity of the entire composite layer is improved. Of course, it can be understood that since the conductivity of the third doped polysilicon layer is higher than that of the second doped polysilicon layer, the third doped polysilicon layer is disposed on the side of the second doped polysilicon layer away from the substrate, and when the electrode is in ohmic contact with the third doped polysilicon layer, the contact resistance will also be lower than the contact resistance between the electrode and the second doped polysilicon layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the structure of a tunneling oxide layer and a composite layer stacked on each other in a solar cell provided in an embodiment of the present application;

[0027] Figure 2 A schematic diagram of another structure of a solar cell provided in an embodiment of the present application.

[0028] Description of Figure Numbers:

[0029] 100, solar cell; 10, substrate; 20, tunneling oxide layer; 30, composite layer;

[0030] 31. A first doped polysilicon layer; 32. A second doped polysilicon layer; 33. A third doped polysilicon layer; 40. A passivation layer; 50. An electrode. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned purposes, features and advantages of the utility model more obvious and easy to understand, the specific implementation methods of the utility model are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the utility model. However, the utility model can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the utility model, so the utility model is not limited by the specific embodiments disclosed below.

[0032] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0033] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present utility model, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0034] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] In the present utility model, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0036] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only implementation method.

[0037] In the solar cell of the related art, in the process of forming the passivation contact structure, hydrogen will be deposited in the crystalline silicon layer during the deposition of the doped polysilicon layer, and will be released in the form of gas when encountering a high temperature process in the subsequent process, destroying the adhesion between the crystalline silicon layer and the tunnel oxide layer, making it easy for the doped polysilicon layer finally formed to explode, thereby reducing the surface passivation effect of the passivation contact structure and affecting the conversion efficiency of the solar cell. In the embodiment of the present application, by providing multiple layers of doped polysilicon layers and doping carbon in the middle polysilicon doped layer, the explosion caused by the peeling of the film layer can be avoided as much as possible.

[0038] The solar cell, photovoltaic module and photovoltaic system of the embodiments of the present application are described below with reference to the accompanying drawings.

[0039] It should be noted that, in this application, the solar cell is taken as a TOPCon cell (Tunnel Oxide Passivated Contact) as an example for explanation, and the solar cell may also be other types of solar cells. The case where the solar cell is other types is similar to this and will not be repeated here.

[0040] Figure 1 A schematic diagram of the structure of a tunneling oxide layer and a composite layer stacked on each other in a solar cell provided in an embodiment of the present application, Figure 2 A schematic diagram of another structure of a solar cell provided in an embodiment of the present application.

[0041] Reference Figure 1 and Figure 2The solar cell 100 provided in the embodiment of the present application includes a substrate 10 , a tunneling oxide layer 20 and at least one composite layer 30 . Figure 2 In the figure, ellipsis is used to indicate the case where the number of the composite layer 30 is greater than two.

[0042] The tunnel oxide layer 20 is disposed on one surface of the substrate. At least one composite layer 30 is disposed on the surface of the tunnel oxide layer 20 that is away from the substrate 10. When the number of the composite layers 30 is greater than two, each composite layer 30 is sequentially stacked and disposed on the surface of the tunnel oxide layer 20 that is away from the substrate 10.

[0043] The composite layer 30 includes a first doped polysilicon layer 31, a second doped polysilicon layer 32 and a third doped polysilicon layer 33 which are sequentially stacked in a direction gradually away from the substrate 10. The second doped polysilicon layer 32 is also doped with carbon.

[0044] The substrate 10 is well passivated by providing a tunneling oxide layer 20 and at least one composite layer 30 as a passivation contact structure. The composite layer 30 includes a first doped polysilicon layer 31, a second doped polysilicon layer 32, and a third doped polysilicon layer 33 which are stacked in sequence in a direction gradually away from the substrate 10, wherein the second doped polysilicon layer 32 is also doped with carbon elements, and carbon elements and hydrogen elements are not easy to combine. Thus, compared with the non-doped carbon element, the second doped polysilicon layer 32 has less hydrogen elements. Therefore, during the high-temperature crystallization process, the gas overflow is reduced, the composite layer is not easy to peel off, the occurrence of film explosion is reduced, the surface passivation effect of the passivation contact structure can be improved, the surface recombination is reduced, and the conversion efficiency of the solar cell is improved.

[0045] Furthermore, since the first doped polysilicon layer 31 is also arranged between the second doped polysilicon layer 32 and the tunneling oxide layer 20, it can block the second doped polysilicon layer 32 and the tunneling oxide layer 20, thereby preventing the carbon element in the second doped polysilicon layer 32 from diffusing into the tunneling oxide layer 20 and destroying the structure of the tunneling oxide layer 20, which further improves the passivation effect of the passivation contact structure.

[0046] In addition, the second doped polysilicon layer 32 is disposed between the first doped polysilicon layer 31 and the third doped polysilicon layer 33. The conductivity of the first doped polysilicon layer 31 and the third doped polysilicon layer 33 is higher than that of the second doped polysilicon layer 32, which can effectively solve the problem that the conductivity of the second doped polysilicon layer 32 is low due to the introduction of carbon elements, thereby affecting the conductivity of the composite layer 30, so that the conductivity of the entire composite layer 30 is improved. Of course, it can be understood that, since the conductivity of the third doped polysilicon layer 33 is higher than that of the second doped polysilicon layer 32, the third doped polysilicon layer 33 is disposed on the side of the second doped polysilicon layer 32 away from the substrate 10, and when the electrode is in ohmic contact with the third doped polysilicon layer 33, the contact resistance will also be lower than the contact resistance between the electrode and the second doped polysilicon layer 32.

[0047] The number of composite layers 30 can be set as required. Figure 1 The case where the number of the composite layer 30 is one layer is shown. When the number of the composite layer 30 is two or more layers, each composite layer 30 is sequentially stacked on the tunnel oxide layer, which will not be described in detail here.

[0048] In the embodiment of the present application, in the same composite layer 30 , the thickness of the first doped polysilicon layer 31 is less than the thickness of the third doped polysilicon layer 33 .

[0049] In specific implementation, preferably, the number of the composite layer 30 is one layer, and in the same composite layer 30:

[0050] The thickness h1 of the first doped polysilicon layer 31 satisfies: 10 nm ≤ h1 ≤ 30 nm;

[0051] The thickness h3 of the third doped polysilicon layer 33 satisfies: 30 nm<h3≤200 nm.

[0052] Such an arrangement can prevent the metal paste from burning through the outermost third doped polysilicon layer 33 and directly contacting the first doped polysilicon layer 31 during the manufacture of the electrode 50, thereby increasing the contact resistance.

[0053] In the embodiment of the present application, the thickness h2 of the second doped polysilicon layer 32 satisfies: 10 nm≤h2≤30 nm.

[0054] By controlling the thickness of the second doped polysilicon layer 32 within the above range, the film explosion can be reduced to the greatest extent and the conductivity of the composite layer 30 can be improved.

[0055] In the embodiment of the present application, in the same composite layer 30 , the doping concentration of the first doped polysilicon layer 31 is less than the doping concentration of the third doped polysilicon layer 33 .

[0056] The third doped polysilicon layer 33 has a high doping concentration, which can make it have good carrier transport performance and low resistance, thereby improving the conductivity of the solar cell 100. On the other hand, the first doped polysilicon layer 31 has a low doping concentration, which can further reduce parasitic absorption.

[0057] In addition, such a configuration can also minimize the diffusion of doping elements in the outer composite layer 30 to the tunnel oxide layer 20 when there are multiple composite layers 30, thereby avoiding adverse effects on the tunnel oxide layer 20 and improving the passivation quality.

[0058] In the embodiment of the present application, in the composite layer 30 closest to the substrate 10, the doping concentrations of the P-type element or the N-type element in the first doped polysilicon layer 31, the second doped polysilicon layer 32, and the third doped polysilicon are increased in sequence.

[0059] With such a configuration, compared with the case where the doping concentrations of the three doped polysilicon layers are the same, the first doped polysilicon layer 31 and the second doped polysilicon layer 32 with lower doping concentrations can act as barrier layers to a certain extent, thereby preventing more doping elements from entering the tunneling oxide layer 20 and destroying the tunneling oxide layer 20 as much as possible, thereby improving the passivation effect of the passivation contact structure formed by the tunneling oxide layer 20 and the composite layer 30.

[0060] In the embodiment of the present application, the first doped polysilicon layer 31 , the second doped polysilicon layer 32 , and the third doped polysilicon layer 33 are all doped with the same type of P-type or N-type doping elements.

[0061] In a specific implementation, the doping elements in the first doped polysilicon layer 31, the second doped polysilicon layer 32 and the third doped polysilicon layer 33 may be nitrogen, phosphorus, arsenic to provide electrons, or boron, aluminum, gallium to provide holes, wherein the doping concentration of the P-type element or the N-type element in the third doped polysilicon layer 33 is: 1E19-1E21cm -3 .

[0062] In the embodiment of the present application, the solar cell 100 further includes a passivation layer 40 and an electrode 50. The passivation layer 40 is disposed on the surface of the outermost composite layer 30 that is away from the substrate 10. The electrode 50 is disposed on the passivation layer 40 and is in ohmic contact with the third doped polysilicon layer 33 of the outermost composite layer 30. Here, the outermost composite layer 30 is the composite layer 30 that is farthest from the substrate 10 among all the composite layers 30.

[0063] The passivation layer 40 may be a single layer or a multilayer structure, and the material of the passivation layer 40 may be aluminum oxide, silicon oxide, silicon nitride or silicon oxynitride. The passivation layer 40 may include, for example, at least one first anti-reflection layer. Thus, the passivation layer 40 plays the role of passivation and anti-reflection at the same time.

[0064] In addition, although not shown in the figure, the solar cell 100 further includes a first passivation layer, a doped conductive layer, and a first electrode.

[0065] The doped conductive layer and the first passivation layer are sequentially stacked on a surface of the substrate away from the tunnel oxide layer 20 .

[0066] In actual situations, the solar cell 100 may include an N-type cell and a P-type cell. The substrate of the N-type cell is doped with an N-type element, and the doped conductive layer is doped with a P-type element. The substrate of the P-type cell is doped with a P-type element, and the doped conductive layer is doped with an N-type element. The doped conductive layer is used to form a PN junction with the substrate. In the embodiment of the present application, the substrate 10 is an N-type substrate as an example. In this case, the doped conductive layer may be a P-type doped layer, for example, a boron-doped doped conductive layer (also called a P+ type emitter).

[0067] The first passivation layer is stacked on the doped conductive layer. The first passivation layer plays a surface passivation and anti-reflection role in the solar cell 100 . It can better chemically passivate the dangling bonds on the surface of the substrate 10 and play an anti-reflection effect on the front side of the solar cell 100 .

[0068] The first passivation layer may be a single-layer structure or a multi-layer structure, and the material of the first passivation layer may be at least one of aluminum oxide, silicon oxide, silicon nitride or silicon oxynitride. In addition, the first electrode is disposed in the first passivation layer and is in ohmic contact with the doped conductive layer.

[0069] The following is a brief introduction to a method for manufacturing a solar cell according to an embodiment of the present application, the method comprising:

[0070] S10, preparing a layer of silicon dioxide with a thickness of less than 3 nm as a tunneling oxide layer 20 on one surface of the substrate 10 in the thickness direction. The preparation method is thermal oxidation, and the thickness of the silicon dioxide is preferably 1.5 mm.

[0071] S20, using chemical vapor deposition (PECVD) method, using silane, hydrogen, and methane as reaction gases, to prepare a doped or intrinsic first amorphous silicon film on the surface of the tunneling oxide layer 20 away from the substrate 10, the thickness of which is preferably 10-30nm, and the doping elements are nitrogen, phosphorus, arsenic that provide electrons or boron, aluminum, and gallium that provide holes, and the doping concentration is 1E19-1E21cm -3 .

[0072] S30, using chemical vapor deposition (PECVD) to prepare a doped or intrinsic second amorphous silicon film on the surface of the first amorphous silicon film, preferably with a thickness of 10-30nm and a carbon atom concentration of 5-50%, that is, the atomic ratio of carbon atoms to silicon atoms is 5-50%. The doping elements are carbon, nitrogen, phosphorus, arsenic that provide electrons, or boron, aluminum, and gallium that provide holes, and the doping concentration is 1E19-1E21cm-3 When the doping element is an n-type element, the reaction gas is silane, phosphine, hydrogen, or methane. When the doping element is a p-type element, the reaction gas is silane, borane, hydrogen, or methane.

[0073] S40, using chemical vapor deposition (PECVD) to prepare a doped or intrinsic third amorphous silicon film on the surface of the second amorphous silicon film, the thickness of which is preferably 30-200 nm, and the doping elements are nitrogen, phosphorus, arsenic that provide electrons or boron, aluminum, gallium that provide holes, and the doping concentration is 1E19-1E21cm -3 When the doping element is n-type, the reaction gas is silane, phosphine, hydrogen, and methane. When the doping element is p-type, the reaction gas is silane, borane, hydrogen, and methane.

[0074] The doping types of the doping elements of the first amorphous silicon film, the second amorphous silicon film, and the third amorphous silicon film are the same.

[0075] S50 , performing a crystallization treatment at 700-1000° C. to form the first amorphous silicon film into a first polysilicon doped layer 31 , the second amorphous silicon film into a second polysilicon doped layer 32 , and the third amorphous silicon film into a third doped polysilicon layer 33 .

[0076] S60 , using a chemical vapor deposition method (PECVD) or an atomic deposition method (ALD) to deposit a passivation layer 40 of aluminum oxide, silicon nitride, or a single layer or a stacked layer of silicon oxide on the third polysilicon doped layer 33 , thereby forming a passivation contact structure.

[0077] A second aspect of an embodiment of the present application provides a photovoltaic module (not shown), including at least one battery string, the battery string including at least two solar cells 100 as described above, and the solar cells 100 can be connected together by series welding.

[0078] A third aspect of an embodiment of the present application provides a photovoltaic system (not shown), comprising the above-mentioned photovoltaic assembly.

[0079] Photovoltaic systems 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 is understandable that the application scenarios of photovoltaic systems are not limited to this, that is to say, photovoltaic systems 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 may 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, and then connected to the mains network to realize solar power supply.

[0080] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described 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-mentioned embodiments only express several implementation methods of the utility model, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the utility model patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the utility model, which all belong to the protection scope of the utility model. Therefore, the protection scope of the utility model patent shall be based on the attached claims.

Claims

1. A solar cell, characterized in that: include: substrate; A tunneling oxide layer is disposed on a surface of the substrate; as well as At least one composite layer is arranged on the surface of the tunnel oxide layer away from the substrate. When the number of the composite layers is greater than two, each of the composite layers is sequentially stacked and arranged on the surface of the tunnel oxide layer away from the substrate. The composite layer includes: a first doped polysilicon layer, a second doped polysilicon layer, and a third doped polysilicon layer sequentially stacked in a direction gradually away from the substrate. Wherein, the second doped polysilicon layer is also doped with carbon element.

2. The solar cell according to claim 1, characterized in that In the same composite layer, the thickness of the first doped polysilicon layer is smaller than the thickness of the third doped polysilicon layer.

3. The solar cell according to claim 2, characterized in that: The number of the composite layer is one, and in the same composite layer: The thickness h1 of the first doped polysilicon layer satisfies: 10nm≤h1≤30nm; The thickness h3 of the third doped polysilicon layer satisfies: 30nm<h3≤200nm.

4. The solar cell according to claim 1, characterized in that The thickness h2 of the second doped polysilicon layer satisfies: 10 nm≤h2≤30 nm.

5. The solar cell according to claim 1, characterized in that: In the same composite layer, the doping concentration of the first doped polysilicon layer is less than the doping concentration of the third doped polysilicon layer.

6. The solar cell according to claim 1, characterized in that In the composite layer closest to the substrate, the doping concentrations of the P-type element or the N-type element in the first doped polysilicon layer, the second doped polysilicon layer, and the third doped polysilicon layer increase in sequence.

7. The solar cell according to any one of claims 1 to 5, characterized in that: The first doped polysilicon layer, the second doped polysilicon layer and the third doped polysilicon layer are all doped with the same type of P-type or N-type doping elements.

8. The solar cell according to any one of claims 1 to 5, characterized in that: The solar cell further comprises a passivation layer and an electrode, wherein the passivation layer is arranged on a surface of the outermost composite layer away from the substrate, and the electrode is arranged on the passivation layer and is in ohmic contact with the third doped polysilicon layer of the outermost composite layer; The outermost composite layer is the composite layer farthest from the substrate among all the composite layers.

9. A photovoltaic module, characterized in that: The invention comprises at least one battery string, wherein the battery string comprises at least two solar cells according to any one of claims 1 to 8.

10. A photovoltaic system, characterized in that: Comprising the photovoltaic module as claimed in claim 9.

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