Photovoltaic cell

Abstract

The embodiment of the application relates to the field of photovoltaic cells, and provides a photovoltaic cell, which comprises a substrate; a doped conductive layer, which is located on one side of the substrate and comprises a lightly doped part and a heavily doped part arranged in a preset direction in sequence, the preset direction being a preset direction of the substrate; the heavily doped part is arranged on the side, away from the substrate, of the lightly doped part; and in the preset direction, the thickness of the heavily doped part is less than the thickness of the lightly doped part. The application can at least solve the problem that the doped conductive layer cannot simultaneously have excellent ohmic contact performance with an electrode and a low probability of causing Auger recombination characteristics.

Description

Technical Field

[0001] This application relates to the field of photovoltaic cells, and in particular to a photovoltaic cell. Background Technology

[0002] A photovoltaic cell is a semiconductor device that converts solar energy into electrical energy. Tunnel oxide passivating contact (TOPCon) solar cell technology, based on the selective carrier principle, significantly reduces electron-hole recombination due to its unique tunneling characteristics, thus greatly increasing the cell's on-state voltage and current density. More and more manufacturers are beginning to apply this technology.

[0003] To improve the ohmic contact capability between the electrode and the doped conductive layer, a common approach is to increase the doping concentration of the conductive layer. However, high-doping-concentration conductive layers are prone to Auger recombination, which significantly reduces the lifetime of minority carriers, leading to energy loss in the photovoltaic cell and consequently decreasing its photoelectric conversion efficiency and stability.

[0004] Therefore, how to design a photovoltaic cell that simultaneously possesses excellent ohmic contact performance with the electrodes and reduces Auger recombination is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This application provides a photovoltaic cell that at least helps to solve the problem that the doped conductive layer cannot simultaneously have high ohmic contact performance with the electrode and low probability of Auger recombination.

[0006] According to some embodiments of this application, one aspect of this application provides a photovoltaic cell, including:

[0007] Base;

[0008] A doped conductive layer is located on one side of the substrate. The doped conductive layer includes a lightly doped portion and a heavily doped portion sequentially disposed in a predetermined direction, wherein the predetermined direction is the thickness direction of the substrate; the heavily doped portion is disposed on the side of the lightly doped portion away from the substrate.

[0009] In a predetermined direction, the thickness of the heavily doped portion is less than the thickness of the lightly doped portion.

[0010] In some embodiments, the ratio between the thickness of the lightly doped portion and the thickness of the heavily doped portion ranges from 5 to 9.

[0011] In some embodiments, the thickness of the lightly doped portion ranges from 130 nm to 180 nm; and / or, the thickness of the heavily doped portion ranges from 20 nm to 30 nm.

[0012] In some embodiments, it also includes:

[0013] A tunneling layer is disposed between the doped conductive layer and the substrate.

[0014] In some embodiments, the thickness of the tunneling layer ranges from 1.5 nm to 2 nm.

[0015] In some embodiments, it also includes:

[0016] Multiple electrodes are spaced apart, and the electrodes are in electrical contact with the doped conductive layer.

[0017] In some embodiments, the electrode is embedded in the heavily doped portion, and the thickness of the portion of the electrode extending into the heavily doped portion is greater than or equal to half the thickness of the heavily doped portion.

[0018] In some embodiments, the doped conductive layer is a polycrystalline silicon passivation film, wherein the polycrystalline silicon passivation film is doped with an N-type dopant or a P-type dopant.

[0019] In some embodiments, a surface passivation layer is further included, the surface passivation layer being disposed on the side of the doped conductive layer away from the substrate.

[0020] In some embodiments, the doping concentration of the dopant element in the heavily doped portion is 1 × 10⁻⁶. 20 atoms / cm 3 ~3×10 20 atoms / cm 3 The doping concentration of the dopant element in the lightly doped portion is 6 × 10⁻⁶. 19 atoms / cm 3 ~1×10 20 atoms / cm 3 .

[0021] The technical solution provided in this application has at least the following advantages: the doped conductive layer of this application has stacked heavily doped and lightly doped portions. The heavily doped portion has excellent ohmic contact capability with the electrode, and the thickness of the lightly doped portion is greater than that of the lightly doped portion to reduce the initiation of Auger recombination, reduce the probability of carrier recombination, reduce energy loss, and thus improve the photoelectric conversion efficiency of photovoltaic cells. Attached Figure Description

[0022] One or more embodiments are illustrated by way of example with corresponding pictures in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the pictures in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional technology, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the structure of a photovoltaic cell according to an embodiment of this application;

[0024] Figure 2 This is a line graph showing the relationship between depth and doping concentration for a photovoltaic cell according to an embodiment of this application.

[0025] Figure 3 This is a schematic diagram of another photovoltaic cell structure provided according to an embodiment of this application.

[0026] In the figure: 100, substrate; 101, first surface; 102, second surface; 200, tunneling layer; 300, doped conductive layer; 310, lightly doped part; 320, heavily doped part; 400, electrode; 500, surface passivation layer. Detailed Implementation

[0027] As is known from the background technology, although a doped conductive layer with a high doping concentration has good ohmic contact capability with the electrode and reduces the contact resistance between the doped conductive layer and the electrode, it can also induce Auger recombination, which greatly reduces the lifetime of minority carriers, resulting in energy loss of photovoltaic cells, and consequently reducing the photoelectric conversion efficiency and stability of photovoltaic cells.

[0028] Analysis revealed that, in order for photovoltaic cells to simultaneously possess excellent ohmic contact capability with the electrodes and reduce Auger recombination, it is necessary to increase the doping concentration in the region of the doped conductive layer that contacts the electrodes to form an ohmic contact and reduce the contact resistance between the doped conductive layer and the electrodes. On the other hand, it is necessary to reduce the doping concentration in the regions of the doped conductive layer other than those that contact the electrodes to reduce Auger recombination and decrease the probability of carrier recombination.

[0029] This application provides a photovoltaic cell. The doped conductive layer of the photovoltaic cell includes a heavily doped portion and a lightly doped portion stacked on top of each other. The lightly doped portion is disposed away from the substrate from the heavily doped portion. The heavily doped portion with a high doping concentration is used to set electrodes to reduce contact resistance, increase the open-circuit voltage of the photovoltaic cell, and thus improve the photoelectric conversion efficiency. The lightly doped portion with a low doping concentration can, on the one hand, reduce the occurrence of Auger recombination, avoiding the reduction of the photoelectric conversion efficiency of the photovoltaic cell due to Auger recombination; on the other hand, the lightly doped portion with a low doping concentration can reduce the amount of dopant elements diffused into the substrate during its formation process, so as to avoid destroying the interface passivation effect. In particular, the thickness of the heavily doped portion is smaller than the thickness of the lightly doped portion, further reducing the occurrence of Auger recombination and lowering the probability of carrier recombination.

[0030] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined. Similarly, "multiple sets" refers to two or more sets (including two sets), and "multiple pieces" refers to two or more pieces (including two pieces).

[0031] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists, A and B exist simultaneously, and B exists. In addition, the character " / " in this document generally indicates that the related objects before and after it have an "or" relationship.

[0033] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application. For example, if the device or element in the illustration is inverted, then the element described as "below," "under," "below," or "bottom" of other elements or features will be oriented "above" or "top" of said other elements or features. Therefore, the term "below" may cover both above and below orientation depending on the context in which the term is used, which will be obvious to those skilled in the art. Materials may be oriented in other ways (e.g., rotated 90 degrees, inverted, flipped), and the spatial relative descriptive terms used herein may be interpreted accordingly.

[0034] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0035] In the accompanying drawings corresponding to the embodiments of this application, the thickness and area of ​​the layers are enlarged for better understanding and ease of description. Furthermore, when describing a component as "generally" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor is it formed on a portion of the edge of the entire surface.

[0036] In the description of the embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and other components may be further included. The formation or provision of a second component above or on a first component, or on the surface of a first component, or on one side of a first component, may include embodiments where the first and second components are in direct contact, and may also include embodiments where an additional component may be present between the first and second components, thereby preventing direct contact between the first and second components. For simplicity and clarity, various components may be drawn at different scales. In the drawings, some layers / components may be omitted for simplicity. Unless otherwise specified, the formation or provision of a second component on the surface of a first component refers to direct contact between the first and second components. The term "component" may refer to a layer, film, region, portion, structure, etc.

[0037] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "component" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.

[0038] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0039] Figure 1 This is a schematic diagram of the structure of a photovoltaic cell provided in an embodiment of this application.

[0040] refer to Figure 1 Photovoltaic cells include:

[0041] 100 for the substrate;

[0042] A doped conductive layer 300 is located on one side of the substrate 100. The doped conductive layer 300 includes a lightly doped portion 310 and a heavily doped portion 320 sequentially disposed in a preset direction Y, where the preset direction Y is the thickness direction of the substrate 100. The heavily doped portion 320 is disposed on the side of the lightly doped portion 310 away from the substrate 100.

[0043] In the preset direction Y, the thickness of the heavily doped portion 320 is less than the thickness of the lightly doped portion 310.

[0044] This application designs the doped conductive layer 300 as a two-layer structure comprising a heavily doped layer and a lightly doped layer stacked on top of each other. A heavily doped portion 320 with a high doping concentration is disposed on the side of the lightly doped portion 310 away from the substrate 100 for mounting the electrode 400. This ensures good ohmic contact between the heavily doped portion 320 and the electrode 400, reducing contact resistance and thus improving the photoelectric conversion efficiency of the photovoltaic cell. The lightly doped portion 310 is disposed on the side of the heavily doped portion 320 closer to the substrate 100. The low doping concentration of the light doping provides good passivation and prevents Auger recombination, ensuring the photoelectric conversion efficiency of the photovoltaic cell. The thickness of the heavily doped portion 320 is greater than the thickness of the lightly doped portion 310, further ensuring the good passivation effect and preventing Auger recombination characteristic of the light doping.

[0045] The embodiments of this application will be described in more detail below with reference to the accompanying drawings.

[0046] Reference Figure 1 As shown, Figure 1 A schematic diagram of a photovoltaic cell according to an embodiment of this application is shown. The photovoltaic cell has intersecting and perpendicular predetermined directions Y, X, and Z. The photovoltaic cell includes a substrate 100, which has opposing first surfaces 101 and second surfaces 102 in the predetermined direction Y. The substrate 100 can receive incident light and generate photogenerated carriers.

[0047] In some embodiments, the substrate 100 may be a silicon substrate material, which may include one or more of monocrystalline silicon, polycrystalline silicon, amorphous silicon, or microcrystalline silicon. The substrate 100 may be an N-type substrate or a P-type substrate.

[0048] In other embodiments, the substrate 100 may be made of elemental carbon, organic materials, or multi-component compounds. Multi-component compounds may include, but are not limited to, perovskite, gallium arsenide, cadmium telluride, and copper indium selenide.

[0049] In some embodiments, the second surface 102 of the substrate 100 may be configured as a pyramidal textured surface to reduce light reflection on the second surface 102 of the substrate 100, increase the absorption and utilization rate of light, and thereby improve the photoelectric conversion efficiency of the photovoltaic cell.

[0050] It should be noted that the substrate 100 has a first surface 101 and a second surface 102. For a single-sided battery, the first surface 101 can be the backlight surface and the second surface 102 can be the light-receiving surface. For a double-sided battery, both the first surface 101 and the second surface 102 can be the light-receiving surface.

[0051] A doped conductive layer 300 is disposed on the side of the substrate 100 facing the first surface 101. The doped conductive layer 300 includes a lightly doped portion 310 and a heavily doped portion 320 stacked together. The heavily doped portion 320 is disposed on the side of the lightly doped portion 310 away from the substrate 100. The doping concentration of the dopant element in the heavily doped portion 320 is greater than that in the lightly doped portion 310. The heavily doped portion 320 is used to set the electrode 400. The high doping concentration of the heavily doped portion 320 provides excellent ohmic contact capability with the electrode 400, resulting in lower contact resistance and improved photoelectric conversion efficiency of the photovoltaic cell. The lower doping concentration of the lightly doped portion 310 reduces Auger recombination, thus reducing energy loss and improving the photoelectric conversion efficiency of the photovoltaic cell. Furthermore, the amount of dopant element diffused into the substrate 100 during the doping process of the lightly doped portion 310 is less, avoiding disruption of the interface passivation effect.

[0052] Furthermore, the thickness of the heavily doped portion 320 is less than that of the lightly doped portion 310. The thicker lightly doped portion 310 further reduces the occurrence of Auger recombination, thereby reducing energy loss caused by Auger recombination and improving the photoelectric conversion efficiency of the photovoltaic cell.

[0053] In some embodiments, the ratio between the thickness of the lightly doped portion 310 and the thickness of the heavily doped portion 320 ranges from 5 to 9. Optionally, the ratio between the thickness of the lightly doped portion 310 and the thickness of the heavily doped portion 320 can be 6.5, 7, 7.5, or 8. Maintaining a suitable ratio between the thickness of the lightly doped portion 310 and the thickness of the heavily doped portion 320 ensures the passivation effect of the lightly doped portion 310 on the substrate; and the thicker lightly doped portion 310 reduces the amount of dopant elements diffusing into the substrate 100 during its formation, thereby avoiding damage to the interface passivation effect.

[0054] In some embodiments, the thickness of the lightly doped portion 310 ranges from 130 nm to 180 nm. Optionally, the thickness of the lightly doped portion 310 ranges from 140 nm to 170 nm, and the thickness of the lightly doped portion 310 can be 140 nm, 150 nm, 160 nm, or 170 nm.

[0055] In some embodiments, the thickness of the heavily doped portion 320 ranges from 20 to 30 nm. Optionally, the thickness of the heavily doped portion 320 ranges from 22 to 28 nm, and the thickness of the heavily doped portion 320 can be 22 nm, 24 nm, 26 nm, or 28 nm.

[0056] In some embodiments, the doped conductive layer 300 includes a polycrystalline silicon passivation film, in which N-type or P-type doping elements are doped. The doping concentration of the polycrystalline silicon passivation film can be greater than that of the substrate 100, thereby forming a sufficiently high barrier on the first surface 101 of the substrate 100. This barrier can induce band bending on the first surface 101 of the substrate 100, achieving the aggregation of majority carriers and the depletion of minority carriers on the first surface 101 of the substrate, and reducing carrier recombination on the back side of the substrate.

[0057] In some embodiments, the material of the doped conductive layer 300 includes doped polycrystalline silicon. Both the heavily doped portion 320 and the lightly doped portion 310 are made of doped polycrystalline silicon, but the concentrations of the doping elements differ between them.

[0058] It should be noted that the types of doping elements in the heavily doped section 320 are the same as those in the lightly doped section 310, and the doping elements can be P-type or N-type doping elements.

[0059] Furthermore, the types of doping elements in the heavily doped portion 320 and the lightly doped portion 310 are the same as the types of doping elements in the substrate 100.

[0060] In some embodiments, the doping element can be a P-type doping element or an N-type doping element. The P-type doping element includes at least one of boron, chlorine, gallium, indium, or thallium, and the N-type doping element includes at least one of phosphorus, arsenic, antimony, or bismuth. Optionally, the doping element in the doped conductive layer 300 is of the same type as the doping element in the substrate 100, and the doped conductive layer 300 serves as a passivation structure to achieve a passivation effect.

[0061] In some embodiments, a high-low junction is formed between the heavily doped portion 320 and the lightly doped portion 310. Taking the example that both the heavily doped portion 320 and the lightly doped portion 310 contain N-type dopants, the high-low junction between them is of type N+ / N. Under the built-in electric field of the N+ / N type high-low junction, electrons in the lightly doped portion 310 migrate more easily to the heavily doped portion 320, and the electrode 400 connected to the heavily doped portion 320 can easily collect more electrons, i.e., the electron current is larger, thereby improving the photoelectric conversion efficiency of the photovoltaic cell. Similarly, taking the example that both the heavily doped portion 320 and the lightly doped portion 310 contain P-type dopants, the high-low junction between them is of type P+ / P. Under the built-in electric field of the P+ / P type high-low junction, holes in the lightly doped portion 310 migrate more easily to the heavily doped portion 320, i.e., the hole current is larger, thereby improving the photoelectric conversion efficiency of the photovoltaic cell.

[0062] In some embodiments, the doping concentration of the dopant element in the heavily doped portion 320 is in the range of 1 × 10⁻⁶. 20 atoms / cm 3 ~3×10 20 atoms / cm 3 Optionally, the doping concentration of the dopant element in the heavily doped section 320 ranges from 1.2 × 10⁻⁶. 20 atoms / cm 3 ~2.8×10 20 atoms / cm 3 The doping concentration of the dopant element in the heavily doped section 320 can be 1.2 × 10⁻⁶. 20 atoms / cm 3 1.6×10 20 atoms / cm 3 2×10 20 atoms / cm 3 Or 2.5×10 20 atoms / cm 3 .

[0063] In some embodiments, the doping concentration of the dopant element in the lightly doped portion 310 is in the range of 6 × 10⁻⁶. 19 atoms / cm 3 ~1×10 20 atoms / cm 3 Optionally, the doping concentration of the dopant element in the lightly doped portion 310 ranges from 7 × 10⁻⁶. 19 atoms / cm 3 ~9.5×10 19 atoms / cm 3 The doping concentration of the dopant element in the lightly doped portion 310 can be 7 × 10⁻⁶. 19 atoms / cm 3 8×10 19 atoms / cm 3 9×10 19 atoms / cm 3 Or 9.5×10 19 atoms / cm 3 .

[0064] In some embodiments, the lightly doped portion 310 and the heavily doped portion 320 are an integral structure, which helps to improve the interface state defects between the lightly doped portion 310 and the heavily doped portion 320. Therefore, when the carriers migrate between the lightly doped portion 310 and the heavily doped portion 320, it helps to reduce the probability of carrier recombination due to interface defects, thereby improving the photoelectric conversion efficiency of the photovoltaic cell.

[0065] Furthermore, the dislocation density of the heavily doped portion 320 is less than that of the lightly doped portion 310, meaning the density of the heavily doped portion 320 is less than that of the lightly doped portion 310. In the doping process that forms the heavily doped portion 320 and the lightly doped portion 310, the diffusion rate of the dopant element in the more dense lightly doped portion 310 is less than the diffusion rate of the dopant element in the less dense heavily doped portion 320, resulting in a difference in doping concentration between the heavily doped portion 320 and the lightly doped portion 310 after the doping process is completed.

[0066] It should be noted that dislocation density refers to the total length of dislocation lines per unit volume of a crystal or the number of dislocation lines passing through a unit cross-sectional area. In other words, the higher the dislocation density of a crystal, the better its compactness, and the more difficult it is for dopant elements to diffuse within the crystal during the doping process.

[0067] Furthermore, the process for forming the doped conductive layer 300 includes LPCVD (Low Pressure Chemical Vapor Deposition) process. The process parameters of LPCVD include deposition temperature and deposition time. By adjusting the deposition temperature and the corresponding deposition time, heavily doped portions 320 and lightly doped portions 310 with different thicknesses and densities can be formed, thus constituting an integral structure of the heavily doped portions 320 and lightly doped portions 310.

[0068] For example, in the LPCVD process for forming the doped conductive layer 300, amorphous silicon is first deposited on the side of the substrate 100 facing the first surface 101 using a first deposition temperature and a first deposition time. The first deposition temperature is 400°C to 500°C, and the first deposition time is 30 min to 50 min, forming a lightly doped portion 310 with a thickness of 130 nm to 180 nm. Then, amorphous silicon is deposited using a second deposition temperature and a second deposition time. The second deposition temperature is 500°C to 700°C, and the second deposition time is 5 min to 20 min, forming a heavily doped portion 320 with a thickness of 20 to 30 nm. Since both the lightly doped portion 310 and the heavily doped portion 320 are deposited using the LPCVD process and are made of the same material, the lightly doped portion 310 and the heavily doped portion 320 are a single integrated structure. However, the different process parameters of the two result in different dislocation densities in the lightly doped part 310 and the heavily doped part 320. The dislocation density of the lightly doped part 310 is greater than that of the heavily doped part 320, and the lightly doped part 310 has higher density than the heavily doped part 320.

[0069] It is important to understand that the lightly doped portion 310 and the heavily doped portion 320 formed after the deposition of amorphous silicon by the LPCVD process are both made of elemental amorphous silicon. The lightly doped portion 310 and the heavily doped portion 320 need to undergo subsequent doping processes and thermal annealing processes to transform their materials into doped polycrystalline silicon materials.

[0070] In some embodiments, the ratio between the dislocation density of the lightly doped portion 310 and the dislocation density of the heavily doped portion 320 ranges from 2 to 4. Optionally, the ratio between the dislocation density of the lightly doped portion 310 and the dislocation density of the heavily doped portion 320 can range from 2.5 to 3.5, and the ratio between the dislocation density of the lightly doped portion 310 and the dislocation density of the heavily doped portion 320 can be 2.5, 2.8, 3, or 3.2.

[0071] In some embodiments, the dislocation density of the lightly doped portion 310 is 10 / μm. 2 ~20 / μm 2 Optionally, the dislocation density of the lightly doped portion 310 is 120 / μm. 2 ~18 / μm 2 The dislocation density of the lightly doped portion 310 can be 12 / μm. 2 14 / μm 2 16 / μm 2 Or 18 / μm 2 .

[0072] In some embodiments, the dislocation density of the heavily doped portion 320 is 2 μm. 2 ~10 / μm 2 Optionally, the dislocation density of the heavily doped portion 320 is 4 μm. 2 ~8 / μm 2 The dislocation density of the heavily doped 320 can be 4 / μm. 2 6 / μm 2 7 / μm 2 or 8 / μm 2 .

[0073] Furthermore, the process for forming the doped conductive layer 300 also includes a doping process. The process parameters of the doping process include doping temperature and doping time. By adjusting the corresponding doping temperature and doping time, heavily doped portions 320 and lightly doped portions 310 with different doping concentrations can be formed.

[0074] For example, in the doping process, the conductive layer 300 is first doped using a first doping temperature and a first doping time. The first doping temperature is 700℃~900℃, and the first doping time is 5min~15min. Because the density of the lightly doped portion 310 in the conductive layer 300 is greater than that of the heavily doped portion 320, a large amount of dopant accumulates in the heavily doped portion 320 near the boundary with the lightly doped portion 310. Then, the conductive layer 300 is doped using a second doping temperature and a second doping time. The second doping temperature is 850℃~950℃, and the second doping time is 20min~30min, so that the doping concentrations of the lightly doped portion 310 and the heavily doped portion 320 in the conductive layer 300 reach the first target concentration and the second target concentration, respectively. The first doping temperature is lower than the second doping temperature, and the doping concentration of the heavily doped portion 320 after doping is greater than that of the lightly doped portion 310. It should be noted that the first target concentration of the lightly doped portion 310 is the doping concentration of the lightly doped portion 310 in this embodiment, and the second target concentration of the heavily doped portion 320 is the doping concentration of the heavily doped portion 320 in this embodiment.

[0075] Reference Figure 2 As shown, Figure 2 A line graph showing the relationship between depth and doping concentration for a photovoltaic cell according to an embodiment of this application is shown. Furthermore, considering the difference in density between the heavily doped portion 320 and the lightly doped portion 310 (the lightly doped portion 310 is more dense than the heavily doped portion 320), the doping process causes the dopant element to accumulate in the heavily doped portion 320 near the boundary with the lightly doped portion 310. That is, the doping concentration of the heavily doped portion 320 gradually increases along its depth direction (i.e., the opposite direction of the preset direction Y), reaching its maximum doping concentration at the boundary between the heavily doped portion 320 and the lightly doped portion 310. This increased doping concentration improves the ohmic contact performance between the heavily doped portion 320 and the electrode 400, reduces the contact resistance between them, and thus improves the photoelectric conversion efficiency of the photovoltaic cell. Compared with the prior art, the doping concentration and maximum doping concentration of the heavily doped part 320 in the embodiments of this application are greater, so as to improve the ohmic contact performance between the heavily doped part 320 and the electrode 400, reduce the contact resistance between the heavily doped part 320 and the electrode 400, and thus improve the photoelectric conversion efficiency of the photovoltaic cell.

[0076] In some embodiments, the maximum doping concentration of the heavily doped portion 320 is 2.5 × 10⁻⁶. 20 atoms / cm 3 ~3×10 20 atoms / cm 3 .

[0077] Continue to refer to Figure 1The photovoltaic cell also includes an electrode 400, which is disposed on the side of the heavily doped portion 320 opposite to the lightly doped portion 310, and the electrode 400 is in metallized contact with the heavily doped portion 320. It should be noted that the number of electrodes 400 can be one or multiple. When there are multiple electrodes 400, the electrodes 400 are uniformly spaced along the first direction X.

[0078] In some embodiments, electrode 400 can be as follows: Figure 1 The electrode is embedded on the surface of the heavily doped portion 320; in other embodiments, the electrode may also be a cover on the surface of the heavily doped portion.

[0079] In the embodiment where the electrode 400 is embedded in the heavily doped portion 320, since the doping concentration of the heavily doped portion 320 gradually increases along its depth direction (i.e., the opposite direction of the preset direction Y), the ohmic contact performance between the heavily doped portion 320 and the electrode 400 is further improved, the contact resistance between the heavily doped portion 320 and the electrode 400 is reduced, and thus the photoelectric conversion efficiency of the photovoltaic cell is improved.

[0080] Furthermore, the thickness of the portion of electrode 400 embedded in the heavily doped portion 320 is greater than or equal to half the thickness of the heavily doped portion 320, that is, the embedding depth of electrode 400 is greater than or equal to half the thickness of the heavily doped portion 320. This further improves the ohmic contact performance between the heavily doped portion 320 and electrode 400, reduces the contact resistance between the heavily doped portion 320 and electrode 400, and thereby improves the photoelectric conversion efficiency of photovoltaic cells.

[0081] It should be noted that the structure of the doped conductive layer 300 of this application, which includes a heavily doped portion 320 and a lightly doped portion 310, can be applied to various photovoltaic cells with passivated contact structures. The types of photovoltaic cells can be TOPCon cells or BC cells, etc.

[0082] Continue to refer to Figure 1 The photovoltaic cell also includes a surface passivation layer 500, which is disposed on the side of the doped conductive layer 300 facing away from the substrate 100. The electrode 400 penetrates the surface passivation layer 500 in a predetermined direction Y and is embedded in the heavily doped portion 320. The surface passivation layer 500 has excellent insulation properties and protects the doped conductive layer 300.

[0083] In some embodiments, the surface passivation layer 500 is made of at least one of silicon oxide, aluminum oxide, silicon nitride, silicon carbide, or silicon oxynitride.

[0084] Reference Figure 1 As shown, in some embodiments, the doped conductive layer 300 is in direct contact with the substrate 100, and the lightly doped portion 310 covers the first surface 101 of the substrate 100.

[0085] Reference Figure 3 As shown, Figure 3 A schematic diagram of a photovoltaic cell according to other embodiments of this application is shown. The photovoltaic cell further includes a tunneling layer 200 sandwiched between a substrate 100 and a doped conductive layer 300. The tunneling layer 200 can chemically passivate the substrate 100. Furthermore, the tunneling layer 200 can cause an asymmetric shift in the energy band of the second surface 102 of the substrate 100, making the barrier for majority carriers lower than the barrier for minority carriers. Therefore, majority carriers can more easily tunnel through the tunneling layer 200, while minority carriers have difficulty passing through, thus achieving selective carrier transport.

[0086] In some embodiments, the thickness of the tunneling layer 200 ranges from 1 nm to 2 nm. Optionally, the thickness of the tunneling layer 200 ranges from 1.2 nm to 1.8 nm, and the thickness of the tunneling layer 200 can be 1.2 nm, 1.4 nm, 1.6 nm, or 1.8 nm. The nanometer-scale thickness of the tunneling layer 200 allows electrons or holes to pass through the tunneling layer 200 using the tunneling effect.

[0087] In some embodiments, the material of the tunneling layer 200 includes at least one of silicon oxide, silicon nitride, and silicon oxynitride.

[0088] In some embodiments, the method for forming the tunneling layer 200 includes an LPCVD (Low Pressure Chemical Vapor Deposition) process.

[0089] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.

Claims

1. A photovoltaic cell, characterized in that, include: Base (100); A doped conductive layer (300) is located on one side of the substrate (100). The doped conductive layer (300) includes a lightly doped portion (310) and a heavily doped portion (320) sequentially disposed in a predetermined direction, wherein the predetermined direction is the thickness direction of the substrate (100); the heavily doped portion (320) is disposed on the side of the lightly doped portion (310) away from the substrate (100). In the preset direction, the thickness of the heavily doped portion (320) is less than the thickness of the lightly doped portion (310).

2. The photovoltaic cell as described in claim 1, characterized in that, The ratio between the thickness of the lightly doped portion (310) and the thickness of the heavily doped portion (320) is in the range of 5 to 9.

3. The photovoltaic cell according to claim 1, characterized in that, The thickness of the lightly doped portion (310) ranges from 130 nm to 180 nm; and / or the thickness of the heavily doped portion (320) ranges from 20 nm to 30 nm.

4. The photovoltaic cell as described in claim 1, characterized in that, Also includes: A tunneling layer (200) is disposed between the doped conductive layer and the substrate (100).

5. The photovoltaic cell as described in claim 4, characterized in that, The thickness of the tunneling layer (200) ranges from 1.5 nm to 2 nm.

6. The photovoltaic cell as described in claim 1, characterized in that, Also includes: Multiple electrodes (400) are spaced apart, and the electrodes (400) are in electrical contact with the doped conductive layer (300).

7. The photovoltaic cell as described in claim 6, characterized in that, The electrode (400) is embedded in the heavily doped portion (320), and the thickness of the portion of the electrode (400) extending into the heavily doped portion (320) is greater than or equal to half the thickness of the heavily doped portion.

8. The photovoltaic cell as described in claim 1, characterized in that, The doped conductive layer (300) includes a polycrystalline silicon passivation film, wherein the polycrystalline silicon passivation film is doped with an N-type dopant or a P-type dopant.

9. The photovoltaic cell as described in claim 8, characterized in that, It also includes a surface passivation layer (500) disposed on the side of the doped conductive layer (300) away from the substrate (100).

10. The photovoltaic cell as described in claim 1, characterized in that, The doping concentration of the doped element in the heavily doped section (320) is 1×10⁻⁶. 20 atoms / cm 3～ 3×10 20 atoms / cm 3 The doping concentration of the doped element in the lightly doped portion (310) is 6 × 10⁻⁶. 19 atoms / cm 3 ~1×10 20 atoms / cm 3 .

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