Solar cell, method of manufacturing the same, apparatus for manufacturing the same, and photovoltaic module

Abstract

This application relates to the photovoltaic field, providing a solar cell, its fabrication method, its fabrication equipment, and a photovoltaic module. The solar cell includes a substrate, a first doped conductive layer, and a first electrode. The substrate includes a first doped region and a second doped region. The first doped region is located on the surface of the second doped region away from the first doped conductive layer. The doping type of the first doped region and the doping type of the second doped region are the same. In the direction from the first doped conductive layer to the substrate, the doping concentration of the first doped region gradually decreases, and the doping concentration of the second doped region gradually decreases, with the rate of decrease of the doping concentration of the second doped region being greater than the rate of decrease of the doping concentration of the first doped region. The solar cell provided by this application can at least improve the photoelectric conversion efficiency of the solar cell.

Description

Technical Field

[0001] This application relates to the photovoltaic field, and in particular to a solar cell, its preparation method, its preparation equipment, and a photovoltaic module. Background Technology

[0002] In crystalline silicon photovoltaic cells, such as passivated emitter and rear cell (PERC) cells, tunnel oxide passivated contact (TOPCon) cells, passivated contact (BC) cells, and heterojunction with intrinsic thin-layer (HTJ) solar cells, different wavelengths of light are absorbed at different depths within the silicon substrate. This leads to a spatial mismatch between the carrier generation location and the collection end (rear contact). Shallow carriers are easily lost due to surface recombination, while deep carriers undergo bulk recombination due to long-distance transport via inefficient thermal diffusion, limiting the improvement of full-spectrum quantum efficiency.

[0003] Therefore, there is an urgent need for a type of solar cell that can improve the photoelectric conversion efficiency of solar cells. Summary of the Invention

[0004] This application provides a solar cell, its preparation method, its preparation equipment, and a photovoltaic module, which at least helps to improve the photoelectric conversion efficiency of the solar cell.

[0005] According to some embodiments of this application, one aspect of this application provides a solar cell, including a substrate, a first doped conductive layer, and a first electrode. The first doped conductive layer is located on a surface of the substrate on one side, and the first electrode is located on a surface of the first doped conductive layer away from the substrate. The substrate includes a first doped region and a second doped region. The first doped region is located on a surface of the second doped region away from the first doped conductive layer. The doping type of the first doped region and the doping type of the second doped region are the same. In the direction from the first doped conductive layer to the substrate, the doping concentration of the first doped region gradually decreases, the doping concentration of the second doped region gradually decreases, and the rate of decrease of the doping concentration of the second doped region is greater than the rate of decrease of the doping concentration of the first doped region.

[0006] In some embodiments, the thickness of the first doped region is 80~180 μm in the direction in which the first doped conductive layer points toward the substrate.

[0007] In some embodiments, the thickness of the second doped region is 0.1~0.5 μm in the direction in which the first doped conductive layer points to the substrate.

[0008] In some embodiments, the doping concentration of the first doped region decreases linearly in the direction from the first doped conductive layer to the substrate.

[0009] In some embodiments, the doping concentration of the second doped region decreases exponentially in the direction from the first doped conductive layer to the substrate.

[0010] In some embodiments, the surface of the substrate near the first doped conductive layer is a first surface, the distance between a first predetermined position and the first surface is a first depth, the first predetermined position is any position in the second doped region, and the doping concentration at the first predetermined position and the first depth satisfy a Gaussian function or a complementary error function.

[0011] In some embodiments, the built-in electric field of the first doped region is 0.5~100V / cm.

[0012] In some embodiments, the built-in electric field of the second doped region is 10. 2 ~10 5 V / cm.

[0013] According to some embodiments of this application, another aspect of this application provides a method for fabricating a solar cell, for fabricating any of the aforementioned solar cells. The method for fabricating the solar cell includes: providing a substrate and processing the substrate to obtain a pre-doped region; processing a portion of the pre-doped region to obtain a second doped region, with the remaining pre-doped region forming a first doped region, wherein the first doped region and the second doped region form a substrate, the doping type of the first doped region and the doping type of the second doped region are the same, and in the direction from the first doped conductive layer to the substrate, the doping concentration of the first doped region gradually decreases, the doping concentration of the second doped region gradually decreases, and the rate of decrease of the doping concentration of the second doped region is greater than the rate of decrease of the doping concentration of the first doped region; forming a first doped conductive layer on a surface on one side of the substrate; and forming a first electrode on a surface of the first doped conductive layer away from the substrate.

[0014] In some embodiments, processing the substrate to obtain a pre-doped region includes: introducing a silicon source gas and a first doping source gas into a cavity containing the substrate and continuing for a first predetermined time to obtain the pre-doped region, wherein, during the first predetermined time, the flow rate of the first doping source gas is linearly reduced.

[0015] In some embodiments, processing a portion of the pre-doped region to obtain a second doped region includes: introducing a second doping source gas at a first flow rate into the chamber where the pre-doped region is located, and increasing the first flow rate to a second flow rate to obtain the second doped region, wherein the ratio of the second flow rate to the first flow rate is 100 to 1000.

[0016] In some embodiments, processing a portion of the pre-doped region to obtain a second doped region includes: performing a diffusion treatment on a portion of the pre-doped region at a predetermined temperature for a predetermined duration to obtain the second doped region.

[0017] According to some embodiments of this application, another aspect of this application provides a solar cell fabrication apparatus for fabricating any type of solar cell. The solar cell fabrication apparatus includes: a first doping device for providing a substrate and processing the substrate to obtain a pre-doped region; a second doping device for processing a portion of the pre-doped region to obtain a second doped region, with the remaining pre-doped region forming a first doped region, wherein the first doped region and the second doped region form a substrate, the doping type of the first doped region and the doping type of the second doped region are the same, and in the direction from the first doped conductive layer to the substrate, the doping concentration of the first doped region gradually decreases, the doping concentration of the second doped region gradually decreases, and the rate of decrease of the doping concentration of the second doped region is greater than the rate of decrease of the doping concentration of the first doped region; a first film growth device for forming a first doped conductive layer on a surface on one side of the substrate; and a second film growth device for forming a first electrode on a surface of the first doped conductive layer away from the substrate.

[0018] According to some embodiments of this application, another aspect of this application provides a photovoltaic module, including: a battery string, formed by connecting multiple solar cells prepared by any of the described methods or by any of the described methods; an encapsulating film for covering the surface of the battery string; and a cover plate for covering the surface of the encapsulating film facing away from the battery string.

[0019] The technical solution provided in this application has at least the following advantages:

[0020] By constructing two doped regions with different doping concentration change rates—a first doped region and a second doped region—within the substrate of a solar cell, the absorption depths of different wavelengths of light can be matched. For short-wavelength light, charge carriers generated by short-wavelength light tend to recombine in the surface region near the first doped conductive layer. By setting a second doped region with a larger doping concentration change rate, the surface repulsion efficiency of charge carriers generated by short-wavelength light can be improved. For long-wavelength light, charge carriers generated by long-wavelength light need to diffuse across the entire thickness of the substrate to reach the collection end. By setting a first doped region with a smaller doping concentration change rate, the bulk transport efficiency of long-wavelength charge carriers can be improved. Combining these methods, a substrate with a vertically varying bandgap can be constructed, reducing bulk recombination losses, improving the full-spectrum response, and thus enhancing the photoelectric conversion efficiency of the solar cell. Attached Figure Description

[0021] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the drawings 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 art, 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.

[0022] Figure 1 This is a schematic diagram of the structure of a solar cell according to an embodiment of this application;

[0023] Figure 2 This is a schematic diagram of the structure of another solar cell according to an embodiment of this application;

[0024] Figure 3 This is a schematic diagram of the doping distribution curve of a substrate for a solar cell according to an embodiment of this application;

[0025] Figure 4 This is a schematic diagram of the structure of another solar cell according to an embodiment of this application;

[0026] Figure 5 This is a schematic diagram of the doping distribution curve of a substrate for another solar cell according to an embodiment of this application;

[0027] Figure 6 This is a schematic flowchart illustrating a method for fabricating a solar cell according to an embodiment of this application.

[0028] Figure 7 This is a schematic diagram of the structure of a solar cell fabrication apparatus according to an embodiment of this application;

[0029] Figure 8 This is a schematic diagram of the structure of a photovoltaic module according to an embodiment of this application.

[0030] The above figures include the following reference numerals:

[0031] 10. Substrate; 11. First doped region; 12. Second doped region; 13. First doped conductive layer; 14. First electrode; 15. Tunneling dielectric layer; 16. Second doped conductive layer; 17. Second electrode; 18. Passivation layer; 19. Third doped region; 31. First doping device; 32. Second doping device; 33. First film growth device; 34. Second film growth device; 400. Solar cell; 402. Conductive strip; 41. Encapsulating film; 42. Cover plate. Detailed Implementation

[0032] As is known from the background technology, the absorption depth of light of different wavelengths within a silicon substrate varies, which limits the improvement of the photoelectric conversion efficiency of crystalline silicon photovoltaic cells.

[0033] To address the above problems and improve the photoelectric conversion efficiency of solar cells, this application provides a solar cell, its fabrication method, its fabrication equipment, and a photovoltaic module. The solar cell includes a substrate, a first doped conductive layer, and a first electrode. The first doped conductive layer is located on one side of the surface of the substrate, and the first electrode is located on the surface of the first doped conductive layer away from the substrate. The substrate includes a first doped region and a second doped region. The first doped region is located on the surface of the second doped region away from the first doped conductive layer. The doping types of the first and second doped regions are the same. In the direction from the first doped conductive layer to the substrate, the doping concentration of the first doped region gradually decreases, and the doping concentration of the second doped region gradually decreases, with the rate of decrease of the doping concentration of the second doped region being greater than the rate of decrease of the doping concentration of the first doped region.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0038] 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" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to 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.

[0039] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the 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.

[0040] 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. When describing a component (such as a layer, film, region, or substrate) on or on the surface of another component, the component may be "directly" located on the surface of the other component, or there may be a third component between the two components. Conversely, when describing a component on the surface of another component, or when another component is formed or disposed on the surface of a component, it indicates that there is no third component between the two components. Furthermore, when describing a component as being "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.

[0041] 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. Furthermore, when a component such as a layer, film, region, or plate is referred to as being "on / located" on another component, it can be "directly on" the other component (i.e., located on the surface of the other component with no other components between them), or another component may be present therein. Moreover, when a component such as a layer, film, region, or plate is "directly located" on another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it indicates that no other components are located therein.

[0042] The terminology used in the description of the various embodiments described 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 "foreword" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.

[0043] 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.

[0044] This application provides an exemplary embodiment of a solar cell, such as... Figure 1 and Figure 2As shown, the system includes a substrate 10, a first doped conductive layer 13, and a first electrode 14. The first doped conductive layer 13 is located on one side of the surface of the substrate 10, and the first electrode 14 is located on the side of the first doped conductive layer 13 away from the substrate 10. The substrate 10 includes a first doped region 11 and a second doped region 12. The first doped region 11 is located on the side of the second doped region 12 away from the first doped conductive layer 13. The doping type of the first doped region 11 and the doping type of the second doped region 12 are the same. In the direction from the first doped conductive layer 13 to the substrate 10, the doping concentration of the first doped region 11 gradually decreases, the doping concentration of the second doped region 12 gradually decreases, and the rate of decrease of the doping concentration of the second doped region 12 is greater than the rate of decrease of the doping concentration of the first doped region 11.

[0045] The substrate 10 is used to receive incident light and generate photogenerated carriers. In some embodiments, the material of the substrate 10 may include at least one of monocrystalline silicon, polycrystalline silicon, amorphous silicon, and microcrystalline silicon. In some embodiments, the substrate 10 may be doped with an N-type dopant or a P-type dopant. The N-type dopant may be any one of group V elements such as phosphorus (P), bismuth (Bi), antimony (Sb), or arsenic (As). The P-type dopant may be any one of group III elements such as boron (B), aluminum (Al), gallium (Ga), or indium (In). The doping type of the first doped conductive layer 13 is different from that of the substrate 10. If the substrate 10 is doped with N-type, then the first doped conductive layer 13 is doped with P-type. The first electrode 14 is in contact with the first doped conductive layer 13. The material of the first electrode 14 may include one or more of aluminum, silver, gold, nickel, molybdenum, and copper. This application does not limit the thickness of the first doped region 11 and the second doped region 12. The thickness of the first doped region 11 can be greater than or less than the thickness of the second doped region 12. The first doped region 11 is used to construct a slowly varying doping background, thereby forming a weak but persistent longitudinal guiding effect. This allows the transport of charge carriers within the substrate 10 to no longer rely solely on random diffusion, but to obtain a continuous and gentle transport bias in the thickness direction, thereby reducing bulk recombination losses and improving the collection conditions of deep charge carriers. The second doped region 12 is used to form a higher doping peak in the region adjacent to the light-receiving surface, which decays rapidly along the thickness direction of the substrate 10, thereby establishing a strong local built-in electric field near the surface. This accelerates the separation process of photogenerated charge carriers near the surface, reduces their residence time in the high surface recombination region, and suppresses front surface recombination losses.

[0046] Figure 3 A schematic diagram of the doping distribution curve of substrate 10 is shown, as follows. Figure 3As shown, the horizontal axis represents the depth of the first doped region 11 or the second doped region 12 into the substrate 10, and the vertical axis represents the doping concentration of the first doped region 11 or the second doped region 12. In the direction from the first doped conductive layer 13 to the substrate 10, the slope of the decreasing doping concentration gradient of the second doped region 12 is k1, and the slope of the decreasing doping concentration gradient of the first doped region 11 is k2, where |k1|>|k2|. Furthermore, the trends of the doping distribution curves of TOPCon cells and BC cells are not the same, such as... Figure 3 As shown, the solid line represents the doping distribution curve of the TOPCon cell, and the dashed line represents the doping distribution curve of the BC cell. The doping concentration of the TOPCon cell decays faster in the second doping region compared to the BC cell, and can continue to decrease significantly in the first doping region. Taking the N-type TOPCon cell as an example, the front surface p... + Emitter collects holes, back surface SiOx / n + Poly-Si passivated contacts collect electrons, with collection occurring on opposite sides of the front and back surfaces, and the front surface handling the collection function. The second doped region can relatively enhance the suppression of short-wavelength near-surface recombination, rapidly separate near-surface photogenerated carriers, and cooperate with the front surface hole collection. In other words, for majority carriers (holes) in the p+ emitter, the drift direction needs to be in the same direction as the electric field to facilitate their collection towards the front surface; for minority carriers (electrons) in the local p+ emitter, the drift direction is opposite to the electric field, facilitating their movement away from the front surface and entry into the first doped region. The doping concentration in the second doped region of the BC cell decreases more gradually compared to the TOPCon cell, and is closer to a gradual, weak change in the first doped region. In the BC cell, both polarity collection ends are placed on the back side. The second doped region can ensure the front surface's anti-recombination effect while avoiding excessive accumulation of majority carriers and the resulting enhanced Auger recombination. Excessive doping in the second doped region will enhance Auger recombination. The second doped region is a front surface protection zone primarily for suppressing front surface recombination; its strength should be sufficient to reduce the minority carrier concentration on the front surface, but avoid excessive accumulation of majority carriers on the front surface. The second doping region is a field that drives the minority holes away from the front surface. The majority carrier electrons drift in the opposite direction to the electric field to avoid excessive accumulation on the front surface. The minority carrier holes drift in the same direction as the electric field and enter the first doping region.

[0047] In some embodiments, such as Figure 1As shown, the aforementioned solar cell is a TOPCon cell, comprising: a substrate 10, a first doped conductive layer 13, a first electrode 14, a tunneling dielectric layer 15, a second doped conductive layer 16, and a second electrode 17. The substrate 10 includes a first surface and a second surface facing each other. The substrate 10 includes a first doped region 11 and a second doped region 12, with the first doped region 11 located near the second surface and the second doped region 12 located near the first surface. The first doped layer and the first electrode 14 are located on one side of the first surface, and the first doped layer and the first electrode 14 are in electrical contact. The tunneling dielectric layer 15, the second doped conductive layer 16, and the second electrode 17 are located on one side of the second surface, and the second electrode 17 is in electrical contact with the second doped conductive layer 16. The second doped conductive layer 16 can serve as a back interface, where the first doped region 11 and the second doped region 12 efficiently transport charge carriers to the back interface, and the second doped conductive layer 16 performs the final collection. The thickness of the second doped region 12 can be 0.1~0.2 μm.

[0048] In other embodiments, such as Figure 2 As shown, the aforementioned solar cell is a BC cell, comprising: a substrate 10, a passivation layer 18, a tunneling dielectric layer 15, a first doped conductive layer 13, a second doped conductive layer 16, a first electrode 14, and a second electrode 17. The substrate 10 includes a first surface and a second surface facing each other. The substrate 10 includes a first doped region 11 and a second doped region 12, with the first doped region 11 located near the second surface and the second doped region 12 located near the first surface. The passivation layer 18 is located on one side of the first surface. The tunneling dielectric layer 15, the first doped conductive layer 13, the second doped conductive layer 16, the first electrode 14, and the second electrode 17 are located on one side of the second surface. In the thickness direction perpendicular to the substrate 10, the first doped conductive layer 13 and the second doped conductive layer 16 are alternately arranged. The first electrode 14 is in electrical contact with the first doped conductive layer 13, and the second electrode 17 is in electrical contact with the second doped conductive layer 16. The thickness of the second doped region 12 can be 0.1~0.15 μm.

[0049] The solar cell of this application, by constructing two doped regions with different doping concentration change rates—a first doped region and a second doped region—within the solar cell substrate, can match the absorption depth of light of different wavelengths. For short-wavelength light, charge carriers generated by short-wavelength light tend to recombine in the surface region near the first doped conductive layer. By setting a second doped region with a larger doping concentration change rate, the surface repulsion efficiency of charge carriers generated by short-wavelength light can be improved. For long-wavelength light, charge carriers generated by long-wavelength light need to diffuse across the entire thickness of the substrate to the collection end. By setting a first doped region with a smaller doping concentration change rate, the bulk transport efficiency of long-wavelength charge carriers can be improved. Combining the above methods, a substrate with a vertically varying bandgap can be constructed, reducing bulk recombination losses, improving the full-spectrum response, and thus enhancing the photoelectric conversion efficiency of the solar cell.

[0050] In some embodiments, the thickness of the first doped region is 80-180 μm in the direction from the first doped conductive layer to the substrate. The thickness of the first doped region falls within this range, allowing for precise matching of the substrate to construct a gradually varying doping gradient for long-wavelength red light within this range. This further ensures that long-wavelength carriers are continuously driven by the drift electric field throughout the entire effective absorption layer, avoiding deep recombination losses caused by the lack of an electric field in traditional uniform doped structures, thereby further improving the photoelectric conversion efficiency of the solar cell.

[0051] The thickness of the first doped region can be any one of 80μm, 100μm, 120μm, 140μm, 160μm, and 180μm, or it can be between any two of the above values.

[0052] In other embodiments, the thickness of the second doped region is 0.1~0.5 μm in the direction from the first doped conductive layer to the substrate. A thickness within this range can cover the main absorption layer for short-wavelength light, reducing surface recombination of charge carriers. It also prevents excessive dilution of the doping concentration on the substrate surface and a decrease in the built-in electric field strength caused by an excessively thick second doped region.

[0053] That is, the thickness of the second doped region can be any one of 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, and 0.5 μm, or it can be between any two of the above values. In some embodiments, the thickness of the first doped region is greater than the thickness of the second doped region.

[0054] In some embodiments, the doping concentration of the first doped region decreases linearly in the direction from the first doped conductive layer to the substrate. The linear gradient doping of the first doped region allows the built-in electric field to remain constant within the substrate, thereby providing a uniform and continuous drift driving force. This avoids carrier accumulation or reverse drift caused by inflection points in the electric field due to nonlinear gradients, further improving the photoelectric conversion efficiency of the solar cell.

[0055] The doping concentration in the first doped region exhibits a slowly varying degradation distribution, with its concentration changing linearly or quasi-linearly with depth. The doping concentration at a certain point in the first doped region satisfies the following formula: ,in, The initial concentration of the substrate, in the case of the above solar cell being a TOPCon cell, It can be In the case where the aforementioned solar cell is a BC cell, It can be . This is the distance between this point and the surface of the substrate closest to the first doped conductive layer. In the case where the aforementioned solar cell is a TOPCon cell, The value can be 1.1 to 1.8. In the case where the aforementioned solar cell is a BC cell, It can be 1.0~1.5. D is the thickness of the substrate. It is a dimensionless, slowly varying coefficient, 0 < <1. In the case where the solar cell described above is a TOPCon cell, It can be 0.10~0.35. In the case where the above-mentioned solar cell is a BC cell, The value can be 0.02 to 0.12. In other embodiments, the above formula can be modified as follows: ,in, A value greater than or equal to D can be used to represent "slow change". In other embodiments, the doping concentration of the second doped region decreases exponentially in the direction from the first doped conductive layer to the substrate. This exponential concentration distribution naturally conforms to thermal diffusion kinetics, i.e., Fick's law, where the electric field intensity decreases exponentially with depth, perfectly matching the exponential decay distribution of photogenerated carriers near the surface. This distribution makes the electric field intensity positively correlated with the carrier concentration, forming a concentration-electric field self-reinforcing mechanism: the more carriers, the stronger the driving force, greatly suppressing recombination, thereby further improving the photoelectric conversion efficiency of the solar cell.

[0056] The doping concentration at a certain point in the second doped region described above satisfies the following formula: ,in, This refers to the surface peak concentration, specifically the dominant doping peak concentration of the second doped region at the light-receiving surface. For TOPCon cells, it corresponds to the front surface. Acceptor peak concentration at the emitter, for example: For BC / IBC batteries, it corresponds to the front surface. Donor peak concentration of the front surface field, for example: . The distance between the substrate and the surface closest to the first doped conductive layer. The surface attenuation characteristic length of the second doped region is given by this parameter, which determines the thickness of the second doped region and is responsible for near-surface attenuation. A strong built-in electric field is generated to control the rate of change of the curve in the second doped region. In the case of the aforementioned solar cell being a TOPCon cell, The thickness can be 0.01~0.05μm. In the case of the aforementioned solar cell being a BC cell, The thickness can be 0.03~0.08 μm. It should be noted that at the boundary between the first and second doped regions mentioned above... .

[0057] In some embodiments, the surface of the substrate closest to the first doped conductive layer is designated as the first surface, and the distance between the first predetermined position and the first surface is designated as the first depth. The first predetermined position can be any location within the second doped region. The doping concentration at the first predetermined position and the first depth satisfy a Gaussian function or a complementary error function. The Gaussian function or complementary error function ensures that the doping concentration is highest at the surface and decreases smoothly with depth, without abrupt changes or breaks, thus avoiding interface defects and stress concentration, and further improving the photoelectric conversion efficiency of the solar cell.

[0058] In some embodiments, the distance between the second predetermined position and the first surface is a second depth, the second predetermined position is any position in the first doped region, and the doping concentration of the second predetermined position and the second depth satisfy one of linear, quasi-linear, low-order polynomial or long-scale exponentially slowly varying function.

[0059] In other embodiments, the built-in electric field of the first doped region is 0.5~100V / cm. When the magnitude of the built-in electric field of the first doped region is within this range, the carrier drift velocity increases far beyond the thermal diffusion velocity, shortening the carrier transport time, reducing bulk recombination losses, and further improving the open-circuit voltage and photoelectric conversion efficiency of the solar cell.

[0060] The built-in electric field of the first doped region can be any value among 1V / cm, 10V / cm, 30V / cm, 40V / cm, 50V / cm, 80V / cm, and 100V / cm, or between any two of the above values. This built-in electric field provides a continuous directional drift velocity for the long-wavelength carriers generated deep within the region, transforming their transport mechanism from inefficient random thermal diffusion to efficient field-induced drift, significantly increasing the collection probability. In some embodiments, when the solar cell is a TOPCon cell, the built-in electric field of the first doped region can be 1~100V / cm. When the solar cell is a BC cell, the built-in electric field of the first doped region can be 0.5~30V / cm.

[0061] In some embodiments, the built-in electric field of the second doped region is 10. 2 ~10 5 V / cm. The built-in electric field of the second doped region is within the above range. This electric field can act as a shield, using a huge potential difference to instantly eject minority carriers from the highly recombination surface layer, solving the problem of surface state recombination, and thus further improving the photoelectric conversion efficiency of the solar cell.

[0062] In some embodiments, when the solar cell is a TOPCon cell, the built-in electric field of the second doped region can be 10. 3 ~10 5 V / cm. In the case of a BC solar cell, the built-in electric field of the second doped region can be 10 V / cm. 4 ~10 4 V / cm.

[0063] In other embodiments, such as Figure 4 As shown, the substrate further includes a third doped region 19, which is located on the side of the first doped region 11 away from the second doped region 12. The third doped region 19 can serve as a near-backside junction or matching region. Its main function is to readjust the distribution trend of the second region within a thickness range near the backside, thereby adjusting the local potential, electric field, and carrier concentration distribution in the near-backside region. This allows for a smoother transition of bulk transport to the backside collection structure and improves the initial conditions before backside junction, matching, or shunting.

[0064] The doping concentration at a certain point in the third doped region described above satisfies the following formula: ,in, The initial concentration of the substrate. The distance between the surface of the first doped region near the third doped region and the surface of the substrate near the first doped conductive layer is denoted as . , The thickness of the substrate. It is a dimensionless, slowly varying coefficient, 0 < <1, This refers to the readjustment intensity coefficient of the third doped region. In practical applications, for TOPCon cells, The value can be relatively large, for example: 0.20~0.80; for BC batteries, The value can be relatively small, for example: 0.03~0.20. This is the distance between this point and the surface of the substrate closest to the first doped conductive layer. The characteristic adjustment length is used to control the rate of change of the curve in the third doped region. For TOPCon cells, It can be 1~5μm; for BC batteries, The thickness can be 2~8μm. In other embodiments, the above formula can be modified as follows: ,in, This represents the initial background doping concentration parameter for the third doped region. It should be noted that at the boundary between the first and third doped regions, the aforementioned... .

[0065] In some embodiments, the thickness of the second doped region is greater than the thickness of the first doped region and the thickness of the second doped region, respectively. The thickness of the third doped region can be 2~20 μm. When the solar cell is a TOPCon cell, the thickness of the third doped region can be 5~20 μm. When the solar cell is a BC cell, the thickness of the third doped region can be 2~15 μm. The built-in electric field of the third doped region can be 10~300 V / cm.

[0066] In addition, the doping profile of the substrate, including the third doped region, is shown in the figure. Figure 5As shown, the solid line represents the doping distribution curve of the TOPCon cell, and the dashed line represents the doping distribution curve of the BC cell. The third doping region in the TOPCon cell is usually stronger than that in the BC cell to better match its electron-selective back contact. For TOPCon cells, the back contact is usually electron-selective, so the third doping region not only plays a role in the transition from bulk transport to the back contact, but also directly affects the electron extraction efficiency in the near-back region. In this case, if the third doping region exhibits a more significant local enhancement compared to the first doping region, it can further improve the electron transport conditions (i.e., carrier concentration distribution, carrier flux / current density distribution, residence time in the near-back region, the degree of accumulation of misdirected carriers at the wrong location, and the position and diffusion extent when entering the local potential field range of the back strip) within a limited thickness near the back, making it easier for electrons to migrate to the back contact and be effectively collected. At the same time, this near-back enhancement also helps to suppress the accumulation of holes near the back, thereby reducing recombination losses caused by non-target carriers reaching the contact interface. Therefore, for TOPCon, the more pronounced shoulder enhancement or upward trend of the third doped region essentially corresponds to further optimization of the near-backside electron extraction conditions. In other embodiments, the third doped region of the BC cell remains weak to avoid weakening the dominant role of the local two-dimensional shunting mechanism of the backside interdigitated strips. For BC cells, the backside is not a single type of collection end, but rather a final collection structure composed of interdigitated strips of different polarities. Although both electrons and holes need to reach the vicinity of the backside, their final separation and collection mainly depend on the local potential field established by the backside local structure and lateral distribution. Under this premise, the task of the third doped region is not to directly complete the final shunting, but to improve the transport conditions of charge carriers transitioning from the first doped region to the vicinity of the backside interdigitated structure, allowing them to enter the subsequent shunting region in a more suitable distribution state. Based on this role, the third doped region of the BC cell is more suitable to exhibit a slight shoulder or weak upward trend, that is, only to make limited adjustments to the near-backside transport without forming an excessively strong vertical enhancement. If the enhancement in this region is too strong, it may lead to excessive concentration of charge carriers near the back side, which in turn weakens the subsequent separation effect of the back interdigitated structure on electrons and holes.

[0067] This application also provides a method for preparing a solar cell, such as... Figure 6 As shown, the method for preparing any one of the above-mentioned solar cells includes:

[0068] Step S201: Provide a substrate and process the substrate to obtain a pre-doped region;

[0069] The substrate material may include at least one of monocrystalline silicon, polycrystalline silicon, amorphous silicon, and microcrystalline silicon. The resistivity of the substrate is less than [value missing]. After providing the substrate, it can be cleaned and pretreated to remove organic matter, metal ions, and the natural oxide layer from the substrate surface. Then, the substrate is placed in the epitaxial reaction chamber and the process is carried out in a hydrogen atmosphere. High-temperature baking for approximately 1-2 minutes is performed to thoroughly clean the surface and reconstruct the crystal lattice. The pre-doped region can be formed using methods such as doping or epitaxy. The substrate and the pre-doped region exhibit the same doping type.

[0070] Step S202: Process a portion of the pre-doped regions to obtain a second doped region, and the remaining pre-doped regions form a first doped region. The first doped region and the second doped region form a substrate. The doping type of the first doped region and the doping type of the second doped region are the same. In the direction from the first doped conductive layer to the substrate, the doping concentration of the first doped region gradually decreases, the doping concentration of the second doped region gradually decreases, and the rate of decrease of the doping concentration of the second doped region is greater than the rate of decrease of the doping concentration of the first doped region.

[0071] The second doped region can be formed using thermal diffusion or in-situ abrupt change. The thickness of the first doped region can be greater than or equal to the thickness of the second doped region. For example... Figure 3 As shown, the horizontal axis represents the depth of the first or second doped region into the substrate, and the vertical axis represents the doping concentration of the first or second doped region. In the direction from the first doped conductive layer to the substrate, the slope of the decreasing doping concentration gradient of the second doped region is k1, and the slope of the decreasing doping concentration gradient of the first doped region is k2, where |k1|>|k2|.

[0072] Step S203: A first doped conductive layer is formed on the surface of one side of the substrate;

[0073] A first doped conductive layer can be formed on the surface of one side of the substrate using methods such as ion implantation, thermal diffusion, and laser doping. The doping type of the first doped conductive layer is different from the doping type of the substrate.

[0074] Step S204: A first electrode is formed on the surface of the first doped conductive layer on the side away from the substrate.

[0075] The first electrode can be formed on the surface of the first doped conductive layer away from the substrate by means of screen printing, electroplating, vapor deposition and inkjet printing.

[0076] In the aforementioned method for fabricating solar cells, by constructing two doped regions with different rates of doping concentration change—namely, a first doped region and a second doped region—within the substrate of the solar cell, the absorption depths of different wavelengths of light can be matched. For short-wavelength light, charge carriers generated by short-wavelength light tend to recombine in the surface region near the first doped conductive layer. By setting a second doped region with a larger rate of doping concentration change, the surface repulsion efficiency of charge carriers generated by short-wavelength light can be improved. For long-wavelength light, charge carriers generated by long-wavelength light need to diffuse across the entire thickness of the substrate to the collection end. By setting a first doped region with a smaller rate of doping concentration change, the bulk transport efficiency of long-wavelength charge carriers can be improved. Combining these methods, a substrate with a vertically varying bandgap can be constructed, reducing bulk recombination losses, improving the full-spectrum response, and thus enhancing the photoelectric conversion efficiency of the solar cell.

[0077] In other embodiments, step S201 can be implemented by the following steps: Step S2011, introducing silicon source gas and first dopant source gas into the cavity containing the substrate and continuing for a first predetermined time to obtain the pre-doped region, wherein the flow rate of the first dopant source gas is linearly reduced during the first predetermined time. By linearly reducing the flow rate of the first dopant source gas, the doping concentration of the first doped region can be precisely controlled to decrease linearly with thickness, thereby achieving gradient doping.

[0078] The aforementioned pre-doped region can be formed using atmospheric or reduced-pressure chemical vapor deposition. Taking N-type doping as an example, the specific steps for forming the pre-doped region are as follows: Maintain the temperature at... Trichlorosilane is introduced as the silicon source gas, with the flow rate kept constant (10 SLM / min) to maintain a constant growth rate (approximately). And phosphine ( ). As an N-type dopant. In the early stages of growth, Traffic settings (corresponding to the baseline concentration) (With growth time) The shift (corresponding to growth thickness) (reduction), linearly reduced by the mass flow controller. The flow rate. Its governing equation can be: After about 30-40 minutes of growth, it forms a thickness of approximately... The N-type single-crystal silicon layer exhibits a linearly degenerate phosphorus concentration distribution due to the linear reduction of the dopant gas.

[0079] In some embodiments, step S202 can be implemented by the following steps: Step S2021, a second doping source gas with a first flow rate is introduced into the chamber where the pre-doped region is located, and the first flow rate is increased to a second flow rate to obtain the second doped region, wherein the ratio of the second flow rate to the first flow rate is 100 to 1000. By instantaneously increasing the flow rate of the second doping source gas by 100–1000 times, a local concentration surge is achieved at the end of the growth of the second doped region, which can save process steps.

[0080] After the aforementioned pre-doped region is formed, growth can be continued without interruption. The second doped region can be rapidly formed by instantaneously increasing the flow rate of the second doping source gas by an order of magnitude. Both the first and second doping source gases are... For example, the specific steps to form the second doped region are as follows: Instantly... The flow rate jumps instantaneously from 10 sccm to 2000 sccm and remains elevated for a very short time, ceasing growth after approximately 10-20 seconds. Subsequently, through a subsequent thermal process, the high-concentration impurities undergo extremely limited thermal diffusion, resulting in a steep exponential decay distribution.

[0081] In some embodiments, step S202 can also be implemented in other ways, such as step S2022, where a portion of the pre-doped region is diffused at a predetermined temperature for a predetermined duration to obtain the second doped region. Forming the second doped region through thermal diffusion can reduce the complexity of the co-process.

[0082] After the epitaxial growth of the pre-doped region is completed, the surface concentration is low, and the silicon wafer can be moved into a diffusion furnace for shallow phosphorus diffusion. Set temperature to 800~ The process lasted for 10 minutes. Due to the diffusion following Fick's law, high concentrations of phosphorus atoms diffused inward from the surface, naturally forming an exponential distribution.

[0083] This application also provides an apparatus for fabricating solar cells, such as... Figure 7 As shown, the apparatus for fabricating any one of the above-mentioned solar cells includes:

[0084] The first doping device 31 is used to provide a substrate and process the substrate to obtain a pre-doped region;

[0085] The substrate material may include at least one of monocrystalline silicon, polycrystalline silicon, amorphous silicon, and microcrystalline silicon. The resistivity of the substrate is less than [value missing]. After providing the substrate, it can be cleaned and pretreated to remove organic matter, metal ions, and the natural oxide layer from the substrate surface. Then, the substrate is placed in the epitaxial reaction chamber and the process is carried out in a hydrogen atmosphere. High-temperature baking for approximately 1-2 minutes is performed to thoroughly clean the surface and reconstruct the crystal lattice. The pre-doped region can be formed using methods such as doping or epitaxy. The substrate and the pre-doped region exhibit the same doping type.

[0086] The second doping device 32 is used to process a portion of the pre-doped region to obtain a second doped region, and the remaining pre-doped region forms a first doped region. The first doped region and the second doped region form a substrate. The doping type of the first doped region and the doping type of the second doped region are the same. In the direction from the first doped conductive layer to the substrate, the doping concentration of the first doped region gradually decreases, the doping concentration of the second doped region gradually decreases, and the rate of decrease of the doping concentration of the second doped region is greater than the rate of decrease of the doping concentration of the first doped region.

[0087] The second doped region can be formed using thermal diffusion or in-situ abrupt change. The thickness of the first doped region can be greater than or equal to the thickness of the second doped region. For example... Figure 3 As shown, the horizontal axis represents the depth of the first or second doped region into the substrate, and the vertical axis represents the doping concentration of the first or second doped region. In the direction from the first doped conductive layer to the substrate, the slope of the decreasing doping concentration gradient of the second doped region is k1, and the slope of the decreasing doping concentration gradient of the first doped region is k2, where |k1|>|k2|.

[0088] The first film growth apparatus 33 is used to form a first doped conductive layer on the surface of the substrate.

[0089] A first doped conductive layer can be formed on the surface of one side of the substrate using methods such as ion implantation, thermal diffusion, and laser doping. The doping type of the first doped conductive layer is different from the doping type of the substrate.

[0090] The second film growth apparatus 34 is used to form a first electrode on the surface of the first doped conductive layer away from the substrate.

[0091] The first electrode can be formed on the surface of the first doped conductive layer away from the substrate by means of screen printing, electroplating, vapor deposition and inkjet printing.

[0092] like Figure 8 As shown, embodiments of this application also provide a photovoltaic module, including:

[0093] The battery string is formed by connecting multiple solar cells 400 of any one of the above embodiments;

[0094] Specifically, two adjacent battery strings can be electrically connected via conductive strips 402. In some embodiments, the electrodes of the same polarity of the solar cells 400 face the same direction, and the conductive strips 402 connect the electrodes of different polarities of two adjacent solar cells 400 respectively. In other embodiments, the solar cells 400 can also be arranged according to electrodes of different polarities, that is, the electrodes of multiple adjacent cells are arranged in the order of first polarity, second polarity, and first polarity, respectively, and the conductive strips 402 connect two adjacent cells on the same side. In some embodiments, there is no gap between the cells, that is, the cells overlap each other.

[0095] Encapsulating film 41 is used to cover the surface of the battery string;

[0096] Specifically, the encapsulating film 41 includes a first encapsulating layer and a second encapsulating layer. The first encapsulating layer covers either the front or back of the stacked battery string, and the second encapsulating layer covers the other side of the front or back of the battery string. Specifically, the material of the encapsulating film 41 can be at least one of organic encapsulating films such as polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), polyvinyl octene coelastomer (POE), or polyethylene terephthalate (PET). In practical applications, there is a gap between the first and second encapsulating layers during lamination, but after lamination, the first and second encapsulating layers together form the encapsulating film 41.

[0097] Cover plate 42 is used to cover the surface of the encapsulating film 41 away from the battery string.

[0098] Specifically, the material of the cover plate 42 may include light-transmitting materials such as glass or plastic. Furthermore, the surface of the cover plate 42 facing the encapsulating film 41 may be an uneven surface, thereby increasing the utilization rate of incident light. The cover plate 42 includes a first cover plate and a second cover plate, the first cover plate being disposed opposite to the first encapsulation layer, and the second cover plate being disposed opposite to the second encapsulation layer.

[0099] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0100] 1) The solar cell of this application, by constructing two doped regions with different doping concentration change rates inside the solar cell substrate—namely, a first doped region and a second doped region—can match the absorption depth of light of different wavelengths. For short-wavelength light, charge carriers generated by short-wavelength light tend to recombine in the surface region near the first doped conductive layer. By setting a second doped region with a larger doping concentration change rate, the surface repulsion efficiency of charge carriers generated by short-wavelength light can be improved. For long-wavelength light, charge carriers generated by long-wavelength light need to diffuse across the entire thickness of the substrate to the collection end. By setting a first doped region with a smaller doping concentration change rate, the bulk transport efficiency of long-wavelength charge carriers can be improved. Combining the above methods, a substrate with a vertically varying bandgap can be constructed, reducing bulk recombination losses, improving the full-spectrum response, and thus enhancing the photoelectric conversion efficiency of the solar cell.

[0101] 2) The method for fabricating the solar cell of this application constructs two doped regions with different doping concentration change rates inside the solar cell substrate, namely a first doped region and a second doped region, which can match the absorption depth of light of different wavelengths. For short-wavelength light, charge carriers generated by short-wavelength light tend to recombine in the surface region near the first doped conductive layer. By setting a second doped region with a larger doping concentration change rate, the surface repulsion efficiency of charge carriers generated by short-wavelength light can be improved. For long-wavelength light, charge carriers generated by long-wavelength light need to diffuse across the entire thickness of the substrate to the collection end. By setting a first doped region with a smaller doping concentration change rate, the bulk transport efficiency of long-wavelength charge carriers can be improved. Combining the above methods, a substrate with a vertical bandgap can be constructed, reducing bulk recombination losses, improving the full-spectrum response, and thus improving the photoelectric conversion efficiency of the solar cell.

[0102] 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 solar cell, characterized by, It includes a substrate, a first doped conductive layer, and a first electrode. The first doped conductive layer is located on a surface of the substrate on one side, and the first electrode is located on a surface of the first doped conductive layer on the side away from the substrate. The substrate includes a first doped region and a second doped region. The first doped region is located on the surface of the second doped region away from the first doped conductive layer. The doping type of the first doped region and the doping type of the second doped region are the same. In the direction from the first doped conductive layer to the substrate, the doping concentration of the first doped region gradually decreases, the doping concentration of the second doped region gradually decreases, and the rate of decrease of the doping concentration of the second doped region is greater than the rate of decrease of the doping concentration of the first doped region.

2. The solar cell according to claim 1, characterized in that, In the direction from the first doped conductive layer to the substrate, the thickness of the first doped region is 80~180μm.

3. The solar cell according to claim 1, characterized in that, In the direction from the first doped conductive layer to the substrate, the thickness of the second doped region is 0.1~0.5μm.

4. The solar cell according to claim 1, characterized in that, In the direction from the first doped conductive layer to the substrate, the doping concentration of the first doped region decreases linearly.

5. The solar cell according to claim 1, characterized in that, In the direction from the first doped conductive layer to the substrate, the doping concentration of the second doped region decreases exponentially.

6. The solar cell according to claim 5, characterized in that, The surface of the substrate near the first doped conductive layer is the first surface, the distance between the first predetermined position and the first surface is the first depth, the first predetermined position is any position in the second doped region, and the doping concentration at the first predetermined position and the first depth satisfy a Gaussian function or a complementary error function.

7. The solar cell according to any one of claims 1 to 6, characterized in that, The built-in electric field of the first doped region is 0.5~100V / cm.

8. The solar cell according to any one of claims 1 to 6, characterized in that, The built-in electric field of the second doped region is 10 2 ~10 5 V / cm.

9. A method for preparing a solar cell, characterized in that, The method for preparing the solar cell according to any one of claims 1 to 8 comprises: A substrate is provided, and the substrate is processed to obtain a pre-doped region; A portion of the pre-doped regions are processed to obtain a second doped region, and the remaining pre-doped regions form a first doped region. The first doped region and the second doped region form a substrate. The doping type of the first doped region and the doping type of the second doped region are the same. In the direction from the first doped conductive layer to the substrate, the doping concentration of the first doped region gradually decreases, the doping concentration of the second doped region gradually decreases, and the rate of decrease of the doping concentration of the second doped region is greater than the rate of decrease of the doping concentration of the first doped region. A first doped conductive layer is formed on the surface of one side of the substrate; A first electrode is formed on the surface of the first doped conductive layer on the side away from the substrate.

10. The method for preparing a solar cell according to claim 9, characterized in that, The substrate is processed to obtain a pre-doped region, including: A silicon source gas and a first doping source gas are introduced into the cavity containing the substrate and continued for a first predetermined time to obtain the pre-doped region, wherein the flow rate of the first doping source gas is linearly reduced during the first predetermined time.

11. The method for preparing a solar cell according to claim 9, characterized in that, The pre-doped region is processed to obtain a second doped region, including: A second doping source gas with a first flow rate is introduced into the chamber where the pre-doped region is located, and the first flow rate is increased to a second flow rate to obtain the second doped region, wherein the ratio of the second flow rate to the first flow rate is 100~1000.

12. The method for preparing a solar cell according to claim 9, characterized in that, The pre-doped region is processed to obtain a second doped region, including: A portion of the pre-doped region is diffused at a predetermined temperature for a predetermined duration to obtain the second doped region.

13. An apparatus for fabricating solar cells, characterized in that, The apparatus for preparing the solar cell according to any one of claims 1 to 8 includes: A first doping device is used to provide a substrate and process the substrate to obtain a pre-doped region; A second doping device is used to process a portion of the pre-doped region to obtain a second doped region, and the remaining pre-doped region forms a first doped region. The first doped region and the second doped region form a substrate. The doping type of the first doped region and the doping type of the second doped region are the same. In the direction from the first doped conductive layer to the substrate, the doping concentration of the first doped region gradually decreases, the doping concentration of the second doped region gradually decreases, and the rate of decrease of the doping concentration of the second doped region is greater than the rate of decrease of the doping concentration of the first doped region. A first film growth apparatus is used to form a first doped conductive layer on the surface of one side of the substrate; A second film growth apparatus is used to form a first electrode on the surface of the first doped conductive layer away from the substrate.

14. A photovoltaic module, characterized in that, include: A battery string is formed by connecting multiple solar cells prepared by any one of claims 1 to 8 or by any one of claims 9 to 12. An encapsulating film is used to cover the surface of the battery string; A cover plate is used to cover the surface of the encapsulating film that faces away from the battery string.

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