Solar cell and method of manufacturing the same, photovoltaic module

Abstract

The application relates to the field of solar cells, and discloses a solar cell, a preparation method thereof and a photovoltaic module. The solar cell comprises a substrate, and the surface of the substrate has a plurality of pyramid structures. The bottoms of two adjacent pyramid structures are separated by a first groove, and the ratio of the opening width to the depth of the first groove is 0.5:1-2:1. The pyramid structure in the solar cell has a high light trapping effect and can ensure the deposition effect of a film layer such as a passivation layer, thereby helping to improve the photoelectric conversion efficiency of the solar cell to a high degree.

Description

Technical Field

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

[0002] The utilization rate of light by a solar cell directly affects its ability to generate photogenerated carriers, while the recombination rate of the carriers in turn affects the effective utilization rate of the photogenerated carriers.

[0003] When the substrate surface of a solar cell is designed with a pyramid structure, the pyramid structure not only affects the absorption and utilization rate of sunlight but also the deposition quality of the subsequent passivation layer, thus affecting the passivation effect. Therefore, optimizing the pyramid structure to improve the absorption and utilization rate of sunlight while ensuring the passivation effect of the passivation layer is a pressing issue that needs to be addressed. Summary of the Invention

[0004] This application discloses a solar cell, its fabrication method, and a photovoltaic module. The pyramid structure in this solar cell not only has a high light-trapping effect but also ensures the deposition effect of passivation layers and other films, thereby contributing to a significant improvement in the photoelectric conversion efficiency of the solar cell.

[0005] In the first aspect, this application discloses a solar cell, which includes a substrate. The surface of the substrate has multiple pyramid structures, and the bases of two adjacent pyramid structures are separated by a first groove. The ratio of the opening width to the depth of the first groove is 0.5:1 to 2:1.

[0006] Furthermore, the depth of the first groove is 100 nm to 200 nm; and / or, The opening width of the first groove is 200 nm to 400 nm.

[0007] Furthermore, the inner wall of the first groove is an arc surface.

[0008] Furthermore, the curvature of the arc surface is 0.0025~0.005.

[0009] Furthermore, the solar cell also includes a conductive layer disposed on the substrate, the conductive layer having a second groove; The solar cell further includes electrodes, at least a portion of which are disposed within the second groove; and / or, The pyramid structure has an arched apex; and / or, The pyramid structure with the first groove is provided on the backlit surface of the substrate; and / or, On the surface having the first groove, a passivation layer is further disposed on the substrate, the passivation layer having an area coverage of 75%~85% on the top of the pyramid structure; and / or, On the surface having the first groove, a passivation layer is also provided on the substrate, the passivation layer having an area coverage of 80% to 90% at the base of the pyramid structure.

[0010] Furthermore, the solar cell is a heterojunction solar cell; The heterojunction solar cell further includes a passivation layer, a doped silicon layer, and a transparent conductive layer stacked sequentially on the substrate.

[0011] Secondly, this application discloses a method for fabricating a solar cell, the method comprising the following steps: The surface of the base is textured to create a pyramid structure; An oxide layer is prepared on the pyramid structure, wherein the thickness of the oxide layer located at the base of the pyramid structure is lower than that of the oxide layer located on the sidewall of the pyramid structure; Remove the oxide layer so that the base of two adjacent pyramid structures has a first groove, the ratio of the opening width to the depth of the first groove is 0.5:1 to 2:1; The solar cell is obtained through post-processing.

[0012] Furthermore, the preparation method shall satisfy at least one of the following conditions: (1) The thickness of the oxide layer at the bottom of the tower is 70 nm to 120 nm; (2) The thickness of the oxide layer at the sidewall is 90 nm to 130 nm; (3) The oxide layer is prepared on the pyramid structure by vapor deposition. The gas source includes oxygen, the gas flow rate is 4000 sccm~5000 sccm, the time is 2400 s~2600 s, the pressure is 800 mbar~850 mbar, and the temperature is 830℃~870℃. (4) In the step of removing the oxide layer: the removal reagent includes hydrofluoric acid, the mass percentage concentration of hydrofluoric acid is 8%~12%, and the time is 15 s~20 s.

[0013] Further, the substrate includes a first surface and a second surface disposed opposite to each other, wherein one of the first surface and the second surface is a light-receiving surface and the other is a light-repelling surface, and the oxide layer is disposed on the first surface. The step of removing the oxide layer includes: A protective layer is provided on the second surface of the substrate; The oxide layer on the first surface is etched to form the first groove at the base of the pyramid structure adjacent to the first surface; The top of the pyramid structure is rounded to make the top of the pyramid structure arc-shaped. Clean the first surface of the substrate.

[0014] Furthermore, when smoothing the top of the pyramid structure, the reagents include hydrofluoric acid and a smoothing additive, the mass percentage concentration of hydrofluoric acid is 8%~12%, the mass percentage concentration of the smoothing additive is 4%~6%, and the time is 15 s~20 s.

[0015] Thirdly, this application discloses a photovoltaic module, which includes: a solar cell as described in any one of the first aspects, or a solar cell prepared by any one of the preparation methods described in the second aspect.

[0016] Compared with the prior art, the beneficial effects of this application are as follows: This application provides a solar cell and its fabrication method, as well as a photovoltaic module. The pyramid structure in the solar cell has both a high light trapping effect and ensures the deposition effect of films such as passivation layers, thereby helping to improve the photoelectric conversion efficiency of the solar cell to a greater extent.

[0017] In this application, the bases of two adjacent pyramid structures are separated by a first groove. This arrangement of the first groove preserves the overall shape and features of the pyramid structure to a high extent, thereby enabling the pyramid structure to effectively trap light.

[0018] Furthermore, by further controlling the ratio of the opening width to the depth of the first groove to be 0.5:1 to 2:1, on the one hand, within this range, sunlight can be reflected and refracted multiple times within the first groove, increasing the probability of sunlight being absorbed, thereby further improving the absorption rate of sunlight; on the other hand, within this range, it helps to form a first groove with a suitable morphology, which can effectively improve the uniformity of subsequent passivation layers and other films within the first groove, thereby effectively improving the passivation effect. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying 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.

[0020] Figure 1 This is a schematic diagram of an existing pyramid structure; Figure 2 This is a scanning electron microscope image of a pyramid structure with a first groove provided in an embodiment of this application; Figure 3 This is a schematic diagram of the first type of first groove structure provided in the embodiments of this application; Figure 4 This is a schematic diagram of the structure of the first type of substrate provided in the embodiments of this application; Figure 5 This is a schematic diagram of the structure of the second type of substrate provided in the embodiments of this application; Figure 6 This is a schematic diagram of the structure of the third type of substrate provided in the embodiments of this application; Figure 7 This is a schematic diagram of the structure of the second type of first groove provided in the embodiments of this application; Figure 8 This is a scanning electron microscope (SEM) schematic diagram of a longitudinal section of a pyramid structure with a first groove provided in an embodiment of this application, wherein... Figure 8 Figure b in the text is Figure 8 An enlarged view of the boxed area in Figure a; Figure 9 This is provided by the embodiments of this application. Figure 3 A schematic diagram of the longitudinal section; Figure 10 This is a schematic diagram of the structure of a solar cell provided in an embodiment of this application; Figure 11 This is a schematic diagram of the structure of the first type of second groove and electrode provided in the embodiments of this application; Figure 12 This is a schematic diagram of the structure of the second type of second groove and electrode provided in the embodiments of this application; Figure 13 This is a schematic diagram of the third type of second groove and electrode provided in the embodiments of this application; Figure 14 This is a schematic diagram of a pyramid structure provided in an embodiment of this application; Figure 15 This is a schematic diagram of another solar cell structure provided in an embodiment of this application.

[0021] Icons: 1. Substrate; 1a. Light-receiving surface; 1b. Backlight-receiving surface; 11. Pyramid structure; 12. First groove; 2. Transparent conductive layer; 2a. Second groove; 21. First transparent conductive layer; 22. Second transparent conductive layer; 3. Electrode; 31. First electrode; 32. Second electrode; 4. Passivation layer; 41. First passivation layer; 42. Second passivation layer; 5. Doped silicon layer; 51. First doped silicon layer; 52. Second doped silicon layer. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0024] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0025] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, components, or parts (which may be the same or different in specific type and construction), and are not intended to indicate or imply the relative importance or quantity of the indicated devices, components, or parts. Unless otherwise stated, "a plurality of" means two or more.

[0026] The technical solutions provided in this application will be further described below with reference to the embodiments and accompanying drawings.

[0027] In the field of solar cells, the absorption rate of sunlight can be improved by setting pyramid structures on the surface of the substrate. However, current pyramid structures often consist of several pyramids directly connected together, such as... Figure 1 As shown, the base edges of two adjacent pyramid structures 11 are shared. However, the light-trapping effect provided by this conventional pyramid structure 11 has reached its limit and it is difficult to improve it further.

[0028] While etching the sidewalls of a pyramid structure can increase its roughness and thus improve its absorption rate of sunlight, this increased roughness also creates more passivation dead zones. As a result, when passivation layers or other films are applied to such a rough pyramid structure, these dead zones make it difficult to deposit the films on the sidewalls with high quality. Consequently, the passivation effect of the passivation layer is poor, and the carrier recombination degree is high, making it difficult to effectively utilize the absorbed sunlight.

[0029] Based on the above problems, this application discloses a solar cell in which the pyramid structure has both a high light trapping effect and ensures the deposition effect of films such as passivation layers, thereby helping to improve the photoelectric conversion efficiency of the solar cell to a greater extent.

[0030] This application discloses a solar cell, such as Figures 2 to 3 As shown, the solar cell includes a substrate 1, the surface of which has multiple pyramid structures 11. The bases of two adjacent pyramid structures 11 are separated by a first groove 12. The ratio of the opening width W to the depth H of the first groove 12 is 0.5:1 to 2:1.

[0031] Wherein, the opening width W of the first groove 12 refers to the distance between the bases of the two pyramid structures 11 located on both sides of the first groove 12; the depth H of the first groove 12 refers to the vertical distance between the lowest point of the first groove 12 and the base of the pyramid structure 11.

[0032] Furthermore, this application can use a scanning electron microscope and an ion polisher to obtain the opening width and depth of the first groove 12. Specifically, to obtain the opening width of the first groove 12, a scanning electron microscope image of the first groove 12 is first obtained, and then the widths at both ends and the middle of the first groove 12 in the image are measured and averaged to obtain the opening width of the first groove 12. To obtain the depth of the first groove 12, the sample is first cut using an ion polisher to expose the cross-section of the first groove 12, and then a cross-sectional image of the first groove 12 is obtained using a scanning electron microscope. Then, the vertical distance between the base of the pyramid structure 11 forming the first groove 12 and the lowest point of the first groove 12 is measured to obtain the depth of the first groove 12. This application does not limit the specific testing method, as long as it achieves the effect of this application.

[0033] In this application, the bases of two adjacent pyramid structures 11 are separated by a first groove 12. This arrangement of the first groove 12 preserves the main structural features of the pyramid structure 11. That is, compared with the scheme of etching the sidewalls of the pyramid structure 11, the surface roughness of the sidewalls of the pyramid structure 11 in this application is relatively small. This allows the pyramid structure 11 to effectively exert its light-trapping effect and ensure the deposition quality of films such as passivation layers to a high degree.

[0034] Furthermore, this application further controls the ratio of the opening width to the depth of the first groove 12 to be 0.5:1 to 2:1. On the one hand, this range makes the shape of the first groove 12 suitable, allowing sunlight to undergo multiple reflections and refractions within the first groove 12, reducing the degree of sunlight escape from the opening of the first groove 12, thereby significantly improving the absorption rate of sunlight. On the other hand, this range helps to form a first groove 12 with a suitable morphology, reducing the existence of passivation dead zones, effectively reducing the difficulty of coating, and thus helping to improve the uniformity of subsequent passivation layers and other films within the first groove 12, thereby effectively improving the passivation effect and reducing carrier recombination losses. For example, the ratio of the opening width to the depth of the first groove 12 is 0.5:1, 0.9:1, 1.3:1, 1.6:1, or 2:1, etc.

[0035] In summary, the pyramid structure 11 in the solar cell of this application not only helps to further improve the absorption rate of sunlight, but also enhances the passivation effect of the passivation layer to a greater extent, thereby helping to improve the photoelectric conversion efficiency of the solar cell to a greater extent.

[0036] In one optional implementation, such as Figure 4 As shown, a pyramid structure 11 with a first groove 12 is disposed on the light-receiving surface 1a of the substrate 1; in a second optional embodiment, as... Figure 5 As shown, a pyramid structure 11 with a first groove 12 is disposed on the backlit surface 1b of the substrate 1; in a third alternative embodiment, as... Figure 6 As shown, the pyramid structure 11 with the first groove 12 is simultaneously disposed on the backlight surface 1b and the light-receiving surface 1a of the base 1.

[0037] More preferably, when the pyramid structure 11 with the first groove 12 is disposed on the back surface 1b of the substrate 1, it is more conducive to improving the photoelectric conversion efficiency of the solar cell. This is because the electric field of the back surface 1b is stronger. By providing the first groove 12 on the back surface 1b, it is not only helpful to improve the utilization of infrared light, but also to effectively reduce the influence of the presence of the first groove 12 on the recombination degree of the back surface 1b, thereby helping to optimize the photoelectric conversion efficiency of the solar cell.

[0038] Furthermore, the depth of the first groove 12 is 100 nm to 200 nm. When the depth of the first groove 12 is within the above range, sunlight reflected from the first groove 12 has a higher probability of being reflected to the inner wall of the first groove 12, rather than being emitted from the opening of the first groove 12, thereby significantly improving the absorption and utilization rate of sunlight. Moreover, this depth range also effectively ensures the deposition effect of passivation layers and other films in the first groove 12, thus further contributing to ensuring the passivation effect of the passivation layer. For example, the depth of the first groove 12 is 100 nm, 120 nm, 140 nm, 160 nm, or 200 nm, etc.

[0039] Furthermore, the opening width of the first groove 12 is 200 nm to 400 nm. When the width of the first groove 12 is within the above range, the light transmission distance of sunlight within the first groove 12 is larger, thereby increasing the probability of sunlight being absorbed by the substrate 1, and thus improving the absorption and utilization rate of sunlight to a greater extent. Moreover, this opening width range also effectively ensures the deposition effect of the passivation layer and other films in the first groove 12, thus further contributing to ensuring the passivation effect of the passivation layer. Furthermore, when the depth of the first groove 12 is in the range of 100 nm to 200 nm, it has a higher matching degree with the opening width of the first groove 12, which further helps to ensure the size of the formed first groove 12, thereby further contributing to improving the light absorption rate and ensuring the passivation effect of the passivation layer. For example, the width of the first groove 12 is 200 nm, 250 nm, 300 nm, 350 nm, or 400 nm, etc.

[0040] Furthermore, a passivation layer is also provided on the substrate 1 on the surface having the first groove 12, and the area coverage of the passivation layer at the top of the pyramid structure 11 is 75% to 85%. By controlling the area coverage of the passivation layer at the top of the pyramid structure 11 within the above range, the passivation effect of the passivation layer at the top of the pyramid can be effectively ensured, thereby reducing carrier recombination losses. For example, the area coverage is 75%, 77%, 79%, 81%, or 85%, etc.

[0041] Furthermore, a passivation layer is also provided on the substrate 1 on the surface having the first groove 12, and the area coverage of the passivation layer at the bottom of the pyramid structure 11 is 80% to 90%. By controlling the area coverage of the passivation layer at the bottom of the pyramid structure 11 within the above range, the passivation effect of the passivation layer at the bottom of the pyramid can be effectively ensured, thereby reducing the recombination loss of charge carriers. For example, the area coverage is 80%, 82.5%, 85%, 87.5%, or 90%, etc.

[0042] The area coverage is obtained using scanning electron microscopy and image processing software. Specifically, taking the area coverage at the top of the pyramid as an example, a high-resolution electron microscope (such as TEM) is first used to obtain an electron microscope image of the top of a single pyramid structure. Then, image processing software is used to obtain the area of ​​the top of the individual pyramid structure and the passivation layer, respectively. Finally, the area coverage is obtained by comparing the area of ​​the passivation layer with the area of ​​the pyramid structure. This application again does not limit the specific testing method, as long as it achieves the effect of this application.

[0043] Furthermore, in an alternative implementation, such as Figure 7 As shown, the inner wall of the first groove 12 is a plane; in another optional embodiment, as... Figure 3 , Figure 8 a in and Figure 8 As shown in b, the inner wall of the first groove 12 is curved. The curved design allows sunlight to be reflected in more directions, which helps to improve the absorption rate of sunlight; in addition, the curved design helps to reduce the passivation dead zone, thereby improving the deposition quality of the passivation layer and other films to a greater extent, and thus improving the photoelectric conversion efficiency of the solar cell to a greater extent.

[0044] Furthermore, the curvature of the arc surface is 0.0025~0.005. This curvature helps to increase the area coverage of films such as the passivation layer, reduce light reflection loss, and thus improve the photoelectric conversion efficiency of the solar cell to a greater extent. For example, the curvature is 0.0025, 0.003, 0.0036, 0.0041, or 0.005, etc.

[0045] Among them, such as Figure 9 As shown, curvature refers to the reciprocal of the radius R of the osculating circle of the arc surface, i.e., 1 / R, and the osculating circle is the circle that is closest to the arc surface. In this application, an image of the pyramid structure 11 can be obtained using a scanning electron microscope, and then the curvature at the top of the pyramid structure 11 in the obtained image can be tested using image processing software.

[0046] Furthermore, such as Figures 10 to 13 As shown, where, Figures 10 to 13 The conductive layer in the solar cell is a transparent conductive layer 2. The solar cell also includes a conductive layer disposed on the substrate 1, and the conductive layer has a second groove 2a. The solar cell also includes an electrode 3, and at least a portion of the electrode 3 is disposed at the second groove 2a.

[0047] In this application, a portion of the electrode 3 is disposed at the second groove 2a, so that the electrode 3 can contact the bottom and inner sidewall of the second groove 2a, thereby increasing the contact area between the electrode 3 and the conductive layer to a greater extent and improving the collection efficiency of the electrode 3 for charge carriers.

[0048] In addition, it is understood that the substrate 1 of this application is provided with a first groove 12, so according to the conformal characteristics, the transparent conductive layer 2 located on the substrate 1 will form a second groove 2a at the position corresponding to the first groove 12.

[0049] The conductive layer serves to connect with electrode 3 to establish an ohmic contact. This conductive layer can be either a transparent conductive layer 2 or a silicon-doped layer. (See also...) Figure 11 and Figure 12 "At least some of the electrodes 3 are located in the second groove 2a" means that some of the electrodes 3 are located in the second groove 2a, and the other part of the electrodes 3 are located on the side wall of the pyramid structure 11; or refer to the previous section. Figure 13 "At least some of the electrodes 3 are located in the second groove 2a" means that the electrodes 3 are not in contact with the side wall of the pyramid structure 11, and are all located in the second groove 2a.

[0050] Furthermore, such as Figure 14 As shown, the top of the pyramid structure 11 is arc-shaped. By setting the top of the pyramid structure 11 to be arc-shaped, it helps to improve the quality of the passivation layer and other films at the bottom of the pyramid, thereby further improving the photoelectric conversion efficiency of the solar cell.

[0051] Furthermore, solar cells include heterojunction solar cells, back-contact solar cells, or passivated contact solar cells.

[0052] In one alternative implementation, such as Figure 15 As shown, the solar cell is a heterojunction solar cell; The heterojunction solar cell also includes a passivation layer 4, a doped silicon layer 5, and a transparent conductive layer 2, which are stacked sequentially on the substrate 1.

[0053] Specifically, the light-receiving surface 1a of the substrate 1 is provided with a first passivation layer 41, a first doped silicon layer 51, a first transparent conductive layer 21 and a first electrode 31 stacked sequentially; the backlight surface 1b of the substrate 1 is provided with a second passivation layer 42, a second doped silicon layer 52, a second transparent conductive layer 22 and a second electrode 32 stacked sequentially. Among them, one of the first doped silicon layer 51 and the second doped silicon layer 52 is an N-type doped layer and the other is a P-type doped layer; one of the first electrode 31 and the second electrode 32 is a positive electrode and the other is a negative electrode.

[0054] This application discloses a method for fabricating a solar cell, the method comprising the following steps: The surface of the base is textured to create a pyramid structure; An oxide layer is prepared on a pyramid structure, wherein the thickness of the oxide layer at the base of the pyramid structure is lower than that of the oxide layer at the sidewalls of the pyramid structure. Remove the oxide layer so that the base of two adjacent pyramid structures has a first groove, the ratio of the opening width to the depth of the first groove is 0.5:1 to 2:1; Post-processing yields solar cells.

[0055] In this application, when preparing the oxide layer, the thickness of the oxide layer at the bottom of the pyramid structure is lower than that at the sidewalls. The difference in thickness makes the oxide layer at the bottom of the pyramid easier to etch, which in turn helps to prepare the first groove at the bottom of the pyramid structure while ensuring the integrity of the sidewalls of the pyramid structure.

[0056] Furthermore, the thickness of the oxide layer at the bottom of the tower is 70 nm to 120 nm. By controlling the thickness of the oxide layer at the bottom of the tower within the above range, it is easier to ensure the structure of the prepared first groove, thereby helping to improve the photoelectric conversion efficiency of the solar cell to a greater extent. For example, the thickness is 70 nm, 85 nm, 100 nm, 110 nm, or 120 nm, etc.

[0057] Furthermore, the thickness of the oxide layer at the sidewalls is 90 nm to 130 nm. By controlling the thickness of the oxide layer at the sidewalls within the above range, it is more helpful to ensure its protective effect on the sidewalls of the pyramid structure, thereby ensuring high structural integrity of the sidewalls. For example, the thickness is 90 nm, 100 nm, 110 nm, 120 nm, or 130 nm, etc.

[0058] The oxide layer is a silicon oxide layer. The lattice constant of the silicon oxide layer does not match that of the substrate, which will generate greater stress at the bottom of the pyramid structure. This makes the silicon oxide layer at the bottom of the pyramid easier to crack or peel off, which can quickly expose the substrate and then etch the substrate to form the first groove.

[0059] Furthermore, an oxide layer was prepared on the pyramid structure using a vapor deposition method. The gas source included oxygen, with a gas flow rate of 4000 sccm–5000 sccm, a time of 2400 s–2600 s, and a pressure of 800 mbar–850 mbar. Controlling the preparation parameters within these ranges helps ensure the quality of the first groove formed and effectively avoids impacting the sidewalls of the pyramid structure, thereby contributing to a higher degree of improvement in the photoelectric conversion efficiency of the solar cell.

[0060] In addition, when using the vapor deposition method, the substrate is first sent into the vapor deposition reactor. Before the gas source is introduced, the reactor is further checked for leaks and heated to ensure the effectiveness of the deposition reaction.

[0061] Furthermore, in the step of removing the oxide layer: the removal agent includes hydrofluoric acid, with a mass percentage concentration of 8% to 12%, and the time is 15 to 20 seconds. By controlling the removal agent within the above range, it is easier to ensure the removal effect, thereby ensuring the effect of the formed first groove to a greater extent.

[0062] Furthermore, the substrate includes a first surface and a second surface disposed opposite to each other, one of the first surface and the second surface being a light-receiving surface and the other a light-repelling surface, and an oxide layer is disposed on the first surface. The step of removing the oxide layer includes: A protective layer is provided on the second surface of the substrate; The oxide layer on the first surface is etched to form a first groove at the base of the adjacent pyramid structure on the first surface; The top of the pyramid structure is rounded off to make the top of the pyramid structure curved. Clean the first surface of the substrate.

[0063] The protective layer of the second surface is a water film, which does not react with the second surface, thus ensuring the integrity of the film layer on the second surface to a greater extent.

[0064] In addition, when smoothing the top of the pyramid structure, the reagents include hydrofluoric acid and a smoothing additive. The mass percentage concentration of hydrofluoric acid is 8%~12%, and the mass percentage concentration of the smoothing additive is 4%~6%, with a time of 15 s~20 s. The smoothing additive is a reagent that promotes the etching of the top of the pyramid by hydrofluoric acid, resulting in an arc-shaped top after etching.

[0065] By controlling the smoothing parameters within the above range, it is easier to ensure the arc effect at the top of the pyramid structure, which in turn helps to improve the deposition effect of the film layer at the top of the pyramid.

[0066] Furthermore, when cleaning the first surface of the substrate, a mixture of hydrogen peroxide and sodium hydroxide is first used for cleaning, followed by cleaning with hydrofluoric acid and additives. Hydrogen peroxide and sodium hydroxide effectively remove organic matter from the second surface; while hydrofluoric acid and additives react with unreacted sodium hydroxide and effectively remove residual oxide layers, thereby significantly improving the surface cleanliness of the second surface.

[0067] Furthermore, after the step of etching the oxide layer on the first surface and before the step of smoothing the top of the pyramid structure, the step of removing the oxide layer also includes cleaning the first surface with hydrogen peroxide and sodium hydroxide.

[0068] The purpose of this step is to remove organic matter from the first surface so that the reagent used in the smoothing process can effectively act on the top of the pyramid structure, thereby improving the smoothing effect and making the arc at the top of the pyramid structure more pronounced.

[0069] Furthermore, the step of texturing the surface of the substrate includes: Pre-cleaning treatment of the substrate; The surface of the substrate is etched to fabricate a pyramid structure on the substrate; The base with the pyramid structure is then cleaned.

[0070] The pre-cleaning process for the substrate includes performing a first pre-cleaning treatment, a second pre-cleaning treatment, a third pre-cleaning treatment, and a fourth pre-cleaning treatment on the substrate surface in sequence. By employing these pre-cleaning treatments, the cleanliness of the membrane surface is ensured to a high degree, thereby effectively guaranteeing the quality of the formed pyramid structure.

[0071] The first pre-cleaning treatment consists of water at a temperature of 15℃~35℃ for 110 s~130 s. Its purpose is to rinse away impurities that have been desorbed from the substrate surface and any residual chemicals.

[0072] The second pre-cleaning treatment uses hydrofluoric acid, hydrochloric acid, and ozone for 110-150 seconds. Its purpose is to dissolve microorganisms and some organic matter, and to remove surface metallic impurities and microcrystalline films.

[0073] The third pre-cleaning treatment involves an alkali solution at a temperature of 67℃~73℃ for 90 s~100 s. These parameters allow the alkali to more effectively exert its isotropic etching effect, thereby further improving the surface cleanliness of the substrate.

[0074] The fourth pre-cleaning treatment uses alkali and hydrogen peroxide, at a temperature of 60℃~70℃, for 200 s~300 s. Its function is to use hydrogen peroxide to form an oxide film on the substrate surface, followed by etching of the oxide film with alkali. During the etching process, impurities adhering to the oxide film surface are removed along with the oxide film.

[0075] In the step of etching the substrate surface to fabricate the pyramid structure, the etching reagent includes an alkali and a texturing additive, the temperature is 80℃~83℃, and the time is 450 s~500 s. Its function is to further remove organic matter and metallic impurities from the silicon wafer surface, remove mechanical damage, and reduce recombination centers; it also enables the alkali to exhibit anisotropic etching, thereby fabricating the pyramid structure on the substrate.

[0076] The steps for post-cleaning a base with a pyramid structure include: performing a first post-cleaning treatment and a second post-cleaning treatment on the surface of the base in sequence.

[0077] The first post-cleaning treatment involves alkali and hydrogen peroxide, at a temperature of 60℃~70℃ for 200 s~300 s. Its purpose is to remove organic matter from the additives.

[0078] The second post-cleaning process involves hydrofluoric acid and additives, and lasts for 150-200 seconds. Its purpose is to remove any residual oxide layer from the previous step.

[0079] This application discloses a photovoltaic module, which includes the solar cell described above, or a solar cell prepared by the above-described method.

[0080] The technical solution of this application will be further explained below with reference to more specific embodiments and experimental test results.

[0081] Example 1: This application provides a heterojunction solar cell, the fabrication method of which includes: S1 involves texturing the surface of the substrate, including: S1.1 The pre-cleaning process for the substrate includes: S1.1.1 First pre-cleaning treatment, reagents include water, temperature is 20℃, time is 120 s; S1.1.2 Second pre-cleaning treatment, the reagents include hydrofluoric acid, hydrochloric acid and ozone, for 130 s; S1.1.3 Third pre-cleaning treatment, the reagent includes sodium hydroxide, the temperature is 70℃, and the time is 95 s; S1.1.4 Fourth pre-cleaning, reagents include sodium hydroxide and hydrogen peroxide, temperature is 65℃, time is 240 s.

[0082] S1.2 The surface of the substrate was etched to prepare a pyramid structure on the substrate. The etching reagent included sodium hydroxide and texturing additive. The temperature was 81°C and the time was 480 s.

[0083] S1.3 The post-cleaning process for the base with a pyramid structure includes: S1.3.1 The first post-cleaning treatment includes sodium hydroxide and hydrogen peroxide, the temperature is 65℃, and the time is 240s; S1.3.2 Second post-cleaning treatment, using reagents including hydrofluoric acid and additives, for 180 s.

[0084] In step S2, the oxide layer is prepared on the pyramid structure using a vapor deposition method to prepare a silicon oxide layer on the back side of the pyramid structure. The gas source includes oxygen, the gas flow rate is [value missing], the time is 2500 s, and the pressure is 820 mbar. The thickness of the oxide layer at the base of the pyramid structure is 100 nm, and the thickness of the oxide layer at the side wall of the pyramid structure is 100 nm.

[0085] The steps for removing the oxide layer using S3 include: S3.1 A water film is placed on the light-receiving surface of the substrate as a protective layer; S3.2 Etch the silicon oxide layer on the backlight surface to form a first groove at the base of the adjacent pyramid structure on the backlight surface; the etching reagent includes hydrofluoric acid, the average ratio of the opening width to the depth of the first groove is 1.4:1, the average depth of the first groove is 150 nm, the average opening width is 210 nm, the inner wall of the first groove is an arc surface with a curvature of 0.00375, and the top of the pyramid structure is arc-shaped.

[0086] S3.3 uses hydrogen peroxide and sodium hydroxide to clean the back surface; S3.4 The top of the pyramid structure on the backlit side is rounded to make the top of the pyramid structure arc-shaped; wherein the reagents include hydrofluoric acid and a smoothing additive, the mass percentage concentration of hydrofluoric acid is 9%, the mass percentage concentration of the smoothing additive is 5%, and the time is 18s.

[0087] S3.5 Clean the backlight surface of the substrate. First, clean the backlight surface with sodium hydroxide and hydrogen peroxide, then clean the backlight surface with hydrofluoric acid and additives.

[0088] The steps of S4 post-processing include: S4.1 A first passivation layer with a thickness of 5 nm is prepared on the light-receiving side of the silicon substrate using PECVD; a second passivation layer with a thickness of 6 nm is prepared on the back-light-receiving side of the silicon substrate using PECVD. S4.2 An N-type doped layer with a thickness of 20 nm is prepared on the second passivation layer. The process gases used for depositing the N-type doped layer include SiH4, N2O, PH3, and H2 in a gas flow ratio of 1:4:4:240. The passivation layer has an area coverage of 80% at the top of the pyramid structure and an area coverage of 85% at the bottom of the pyramid structure.

[0089] S4.3 A P-type doped layer with a thickness of 30 nm is prepared on the first passivation layer, wherein the process gas used to deposit the P-type doped layer includes SiH4, N2O, B2H6 and H2 with a gas flow ratio of 1:0.4:0.5:300.

[0090] S4.4 A first transparent conductive layer is prepared on an N-type doped layer using PVD; a second transparent conductive layer is prepared on a P-type doped layer.

[0091] S4.5 A first electrode is fabricated on a first transparent conductive layer, and a second electrode is fabricated on a second transparent conductive layer to obtain a solar cell, wherein a portion of the second electrode is located in a second groove of the second transparent conductive layer.

[0092] Example 2: The only difference between this embodiment and Embodiment 1 is that the average ratio of the opening width to the depth of the first groove is 2:1.

[0093] Example 3: The only difference between this embodiment and Embodiment 1 is that the average ratio of the opening width to the depth of the first groove is 0.5:1.

[0094] Example 4: The only difference between this embodiment and Embodiment 1 is that the curvature of the first groove is 0.0025.

[0095] Example 5: The only difference between this embodiment and Embodiment 1 is that the curvature of the first groove is 0.005.

[0096] Example 6: The only difference between this embodiment and Embodiment 1 is that the curvature of the first groove is 0.002.

[0097] Example 7: The only difference between this embodiment and Embodiment 1 is that the curvature of the first groove is 0.006.

[0098] Comparative Example 1: The only difference between this comparative example and Example 1 is that neither the pyramid structure on the light-receiving surface nor the backlight surface has a first groove.

[0099] Comparative Example 2: The only difference between this comparative example and Example 1 is that the average ratio of the opening width to the depth of the first groove is 0.2:1.

[0100] Comparative Example 3: The only difference between this comparative example and Example 1 is that the average ratio of the opening width to the depth of the first groove is 4:1.

[0101] Performance testing The solar cells prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to the following related tests: This application describes the performance testing of a solar cell using a GIV-60 testing machine manufactured by Zhongsen Electric Technology Co., Ltd., covering aspects such as open-circuit voltage, short-circuit current, and fill factor. The tested solar cell has a silicon wafer size of 210.6 mm × 71 mm, and the calibrated light intensity is 1000 ± 5 W / m². The experimental test results are shown in Table 1, which presents the performance test results of the solar cell.

[0102] Table 1 Performance test results of solar cells

[0103] Comparing the data from Examples 1 to 3 with those from Comparative Examples 1 to 3, it can be seen that the photoelectric conversion efficiency of Examples 1 to 3 is superior to that of Comparative Examples 1 to 3. It is evident that by using the first groove to isolate two adjacent pyramid structures and setting the ratio of the opening width to depth of the first groove within a specific range, it helps to improve the absorption and utilization rate of sunlight and also helps to improve the uniformity of subsequent passivation layers and other coatings within the first groove, thereby effectively improving the passivation effect.

[0104] Comparing the data from Examples 1, 4 to 7, it can be seen that the photoelectric conversion efficiency of Examples 1, 4, and 5 is better than that of Examples 6 and 7. This indicates that the curvature of Examples 1, 4, and 5 is more suitable. A more suitable curvature helps to increase the area coverage of the passivation layer and other films, thereby helping to reduce recombination loss and light reflection loss, and further improving the absorption and utilization rate of sunlight.

[0105] The solar cells, their preparation methods, and photovoltaic modules disclosed in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the solar cells, their preparation methods, and photovoltaic modules. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A solar cell, characterized in that, The solar cell includes a substrate, the surface of which has multiple pyramid structures. The bases of two adjacent pyramid structures are separated by a first groove, the ratio of the opening width to the depth of the first groove being 0.5:1 to 2:

1.

2. The solar cell according to claim 1, characterized in that, The depth of the first groove is 100 nm to 200 nm; and / or, The opening width of the first groove is 200 nm to 400 nm.

3. The solar cell according to claim 1, characterized in that, The inner wall of the first groove is an arc surface.

4. The solar cell according to claim 3, characterized in that, The curvature of the arc surface is 0.0025~0.

005.

5. The solar cell according to claim 1, characterized in that, The solar cell further includes a conductive layer disposed on the substrate, the conductive layer having a second groove; The solar cell further includes electrodes, at least a portion of which are disposed at the second groove; and / or, The pyramid structure has an arched apex; and / or, The pyramid structure with the first groove is provided on the backlit surface of the substrate; and / or, On the surface having the first groove, a passivation layer is further disposed on the substrate, the passivation layer having an area coverage of 75%~85% on the top of the pyramid structure; and / or, On the surface having the first groove, a passivation layer is also provided on the substrate, the passivation layer having an area coverage of 80% to 90% at the base of the pyramid structure.

6. The solar cell according to claim 1, characterized in that, The solar cell is a heterojunction solar cell; The heterojunction solar cell further includes a passivation layer, a doped silicon layer, and a transparent conductive layer stacked sequentially on the substrate.

7. A method for fabricating a solar cell, characterized in that, The preparation method includes the following steps: The surface of the base is textured to create a pyramid structure; An oxide layer is prepared on the pyramid structure, wherein the thickness of the oxide layer located at the base of the pyramid structure is lower than that of the oxide layer located on the sidewall of the pyramid structure; Remove the oxide layer so that the base of two adjacent pyramid structures has a first groove, the ratio of the opening width to the depth of the first groove is 0.5:1 to 2:1; The solar cell is obtained through post-processing.

8. The preparation method according to claim 7, characterized in that, The preparation method must satisfy at least one of the following conditions: (1) The thickness of the oxide layer at the bottom of the tower is 70 nm to 120 nm; (2) The thickness of the oxide layer at the sidewall is 90 nm to 130 nm; (3) The oxide layer is prepared on the pyramid structure by vapor deposition. The gas source includes oxygen, the gas flow rate is 4000 sccm~5000 sccm, the time is 2400 s~2600 s, the pressure is 800 mbar~850 mbar, and the temperature is 830℃~870℃. (4) In the step of removing the oxide layer: the removal reagent includes hydrofluoric acid, the mass percentage concentration of hydrofluoric acid is 8%~12%, and the time is 15 s~20 s.

9. The preparation method according to claim 7, characterized in that, The substrate includes a first surface and a second surface disposed opposite to each other, wherein one of the first surface and the second surface is a light-receiving surface and the other is a light-repelling surface, and the oxide layer is disposed on the first surface. The step of removing the oxide layer includes: A protective layer is provided on the second surface of the substrate; The oxide layer on the first surface is etched to form the first groove at the base of the pyramid structure adjacent to the first surface; The top of the pyramid structure is rounded to make the top of the pyramid structure arc-shaped. Clean the first surface of the substrate.

10. The preparation method according to claim 9, characterized in that, When smoothing the top of the pyramid structure, the reagents include hydrofluoric acid and a smoothing additive. The mass percentage concentration of hydrofluoric acid is 8%~12%, and the mass percentage concentration of the smoothing additive is 4%~6%. The time is 15 s~20 s.

11. A photovoltaic module, characterized in that, The photovoltaic module includes: the solar cell according to any one of claims 1 to 6, or the solar cell prepared by the preparation method according to any one of claims 7 to 10.

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