Solar cell

Abstract

The utility model provides a kind of solar cell belongs to solar cell technical field, comprising: cell piece, passivation film layer is arranged on the front and / or back of cell piece, the thickness of passivation film layer exists thickness difference in the middle region of solar base and its edge region.The passivation film layer of thickness gradually changing is used in the front and / or back of cell of the application.When the film thickness of cell middle region is less than the film thickness of edge region, the incident light utilization of cell middle region can be increased while the passivation effect of cell edge region is enhanced.When light source mainly irradiates cell edge region, the amount of light of middle region is less, then the change trend that passivation film layer thickness in middle region is greater than edge region is used, to ensure the high incident light utilization of edge and the best passivation effect of middle region, improve the photoelectric conversion efficiency of overall cell.

Description

Technical Field

[0001] This utility model belongs to the field of photovoltaic cell technology, and specifically relates to a solar cell. Background Technology

[0002] Incident light utilization and surface recombination are two important factors affecting the photoelectric conversion efficiency of solar cells. Increasing the thickness of the passivation film usually enhances the effects of chemical and field passivation, better reducing the carrier surface recombination rate and improving cell efficiency. However, at the same time, the passivation film absorbs a certain amount of incident light, thus reducing the proportion of incident light reaching the cell substrate and causing optical losses. The thicker the passivation film, the higher the proportion of absorbed incident light, and the greater the optical losses.

[0003] Currently, the passivation film thickness on the surface of solar cells is uniform from the middle to the edge. However, when solar cells are manufactured, tested, or used, there may be uneven surface recombination efficiency or uneven light intensity. This uniform passivation film design will affect the photoelectric conversion efficiency of the cell.

[0004] Therefore, the current design of a passivation film layer with uniform thickness has not significantly improved the photoelectric conversion efficiency of photovoltaic cells, and the photoelectric conversion efficiency of the cells still needs to be improved. Utility Model Content

[0005] This utility model provides a solar cell designed to improve the photoelectric conversion efficiency of photovoltaic cells.

[0006] To achieve the above objectives, the technical solution adopted by this utility model is: to provide a solar cell, comprising: a cell, wherein a passivation film layer is provided on the front and / or back of the cell, and the thickness of the passivation film layer has a thickness difference between the middle region and the edge region of the solar cell substrate.

[0007] In one feasible approach, the thickness difference between the edge region and the intermediate region is ≤100nm.

[0008] In one feasible manner, the thickness of the passivation film gradually increases from the central region toward the edge region.

[0009] In one possible implementation, the surface of the passivation film layer on the solar cell substrate is a concave spherical shape, an inverted conical shape, or an inverted frustum shape.

[0010] In one feasible approach, the thickness of the passivation film gradually decreases from the middle region of the battery cell to its edge region.

[0011] In one feasible approach, the outermost part of the edge region has a section with uniform edge thickness.

[0012] In one feasible manner, the passivation film is a field passivation film and / or a field-free passivation film.

[0013] In one possible implementation, when the passivation film layer comprises a field passivation film layer and a non-field passivation film layer, the thickness of the field passivation film layer gradually increases from the middle region to the edge region, and the thickness of the non-field passivation film layer gradually decreases from the middle region to the edge region, to form a smooth surface; or

[0014] The thickness of the field passivation film gradually decreases from the middle region to the edge region, while the thickness of the non-field passivation film gradually increases from the middle region to the edge region, so as to form a smooth surface.

[0015] In one feasible embodiment, the field-free passivation film is any one or more layers of aluminum oxide, silicon nitride, and silicon oxide.

[0016] In one feasible embodiment, the field passivation film is any one or more layers of aluminum oxide, silicon nitride, and silicon oxide.

[0017] The solar cell provided by this invention has the following advantages compared with the prior art: the passivation film layer has a good passivation effect, which can effectively reduce the recombination rate on the cell surface, thereby increasing the cell efficiency. However, when the passivation film layer is too thick, it will absorb some incident light, resulting in optical loss and reducing the utilization rate of incident light. This application, through a passivation film layer with a thickness difference, by appropriately increasing or decreasing the thickness of the passivation film layer in the edge region, has practical significance in improving the overall efficiency of the cell.

[0018] This application employs a passivation film layer with gradually varying thickness on the front and / or back of the battery. When the film thickness in the middle region of the battery is less than that in the edge region, the passivation effect in the edge region can be enhanced while increasing the incident light utilization rate in the middle region. When the light source mainly illuminates the edge region of the battery, the light intensity in the middle region is less. Therefore, the passivation film layer thickness in the middle region is greater than that in the edge region to ensure high incident light utilization at the edge and optimal passivation effect in the middle region, thereby improving the overall photoelectric conversion efficiency of the battery. Attached Figure Description

[0019] Figure 1 A schematic diagram of the structure of a solar cell provided in this embodiment of the present invention, showing that the thickness of the passivation film layer increases from the middle region to the edge region (the thickness of the passivation film layer is zero in the middle region of the cell).

[0020] Figure 2 A schematic diagram of the structure of a solar cell provided in this embodiment of the present invention, showing that the thickness of the passivation film layer increases from the middle region to the edge region (the thickness of the passivation film layer is not zero in the middle region of the cell).

[0021] Figure 3 A schematic diagram of a solar cell provided in this embodiment of the present invention, showing that the thickness of the field passivation film increases from the middle region to the edge region, and the thickness of the non-field passivation film decreases from the middle region to the edge region.

[0022] Figure 4 A schematic diagram of the structure provided for an embodiment of this utility model, showing a thick passivation film layer at the edge and a thin passivation film layer in the middle region;

[0023] Figure 5 This invention provides a schematic diagram of a structure for preparing a passivation film with a thinner passivation film layer at the edge and a thicker passivation film layer in the middle region, as provided in an embodiment of the present invention. Figure 1 ;

[0024] Figure 6 This invention provides a schematic diagram of a structure for preparing a passivation film with a thinner passivation film layer at the edge and a thicker passivation film layer in the middle region, as provided in an embodiment of the present invention. Figure 2 ;

[0025] Explanation of reference numerals in the attached figures:

[0026] 1. Battery cell; 11. Middle area; 12. Edge area; 2. Passivation film; 21. Edge uniform thickness area; 22. Field passivation film; 23. Field-free passivation film; 3. Tray; 4. Column; 5. Side enclosure; 6. Top baffle; 61. Central air inlet. Detailed Implementation

[0027] To make the technical problems, technical solutions, and beneficial effects of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit the present utility model.

[0028] Passivation films have a good passivation effect and can effectively reduce the recombination rate on the battery surface, thereby increasing battery efficiency. However, when the passivation film is thick, it will absorb some incident light, resulting in optical loss and reducing the utilization rate of incident light.

[0029] Incident light utilization and surface recombination are two important factors affecting the photoelectric conversion efficiency of a battery. As the thickness of the field passivation film increases, the effects of chemical and field passivation are usually enhanced, which can better reduce the carrier surface recombination rate and improve battery efficiency. However, at the same time, the passivation film absorbs a certain amount of incident light, thereby reducing the proportion of incident light incident into the battery substrate, resulting in optical loss. The thicker the passivation film, the higher the proportion of absorbed incident light, and the greater the optical loss.

[0030] Therefore, appropriately increasing or decreasing the thickness of the passivation film layer in the edge region has practical significance in improving the overall efficiency of the battery.

[0031] Please see Figures 1 to 6 The solar cell provided by this utility model will now be described. The solar cell includes: a cell 1, and a passivation film layer 2 is provided on the front and / or back of the cell 1. The thickness of the passivation film layer 2 has a thickness difference between the middle region 11 and the edge region 12 of the solar cell substrate.

[0032] This application includes cases where a passivation film layer 2 is provided on the front side of the solar cell 1, a passivation film layer 2 is provided on both the front and back sides, and a passivation film layer 2 is provided only on the back side; the main one refers to the passivation film layer 2 on the light-receiving surface, which requires the use of a passivation film layer 2 with varying thickness.

[0033] This application utilizes a passivation film layer 2 with a thickness difference. By appropriately increasing or decreasing the thickness of the passivation film layer 2 in the edge region 12, it has practical significance in improving the overall efficiency of the battery.

[0034] This application employs a passivation film layer 2 with a gradually varying thickness on the front and / or back of the battery cell 1. When the film thickness in the middle region 11 of the battery is less than that in the edge region 12, the passivation effect of the edge region 12 can be enhanced while increasing the incident light utilization rate of the middle region 11. However, if in a certain application scenario, the light source mainly illuminates the edge region 12 of the battery, and the light intensity in the middle region 11 is relatively low, then the thickness of the passivation film layer 2 in the middle region 11 is greater than that in the edge region 12 to ensure high incident light utilization at the edge and optimal passivation effect in the middle region 11, thereby improving the overall photoelectric conversion efficiency of the battery.

[0035] This application utilizes the difference in thickness of the passivation film 2 between the middle region 11 and the edge region 12 to improve the photoelectric conversion efficiency of the battery. Specific application scenarios are as follows: Typically, the thickness of the passivation film 2 in the edge region 12 is gradually increased compared to the thickness of the passivation film 2 in the middle region 11. This is because the passivation effect in the edge region 12 is generally considered more important than the incident light utilization rate, while the incident light utilization rate in the middle region 11 is more important than the passivation effect. For example, after fabricating a photovoltaic module from a solar cell and conducting electrical tests, black edges are often observed in the edge region 12 due to insufficient passivation. Therefore, in the fabrication of the passivation film 2, the thickness of the passivation film 2 in the edge region 12 should be greater than the thickness of the passivation film 2 in the middle region 11.

[0036] For example, during the cutting process of the battery substrate and the battery manufacturing process, the surface recombination rate of the battery edge region 12 is more likely to be greater than that of the middle region 11 due to process reasons. Therefore, appropriately increasing the thickness of the passivation film layer 2 in the edge region 12 has practical significance in improving the overall efficiency of the battery. Meanwhile, the incident light utilization rate of the battery middle region 11 is relatively more important. Appropriately reducing the thickness of the passivation film layer 2 in the middle region 11 can improve the incident light utilization rate of the middle region 11.

[0037] This application also protects the gradual change in the thickness of the passivation film 2 in the edge region 12 and the passivation film thickness in the middle region 11.

[0038] For example, if defects or impurities are found in the middle region 11 during the manufacturing process, the passivation effect of the middle region 11 is more important, thus requiring an increase in the passivation film thickness of the middle region 11. However, this would reduce the incident light utilization rate. Therefore, the passivation film thickness of the edge region 12 is reduced, and the incident light utilization rate of the edge region 12 is increased to compensate for the incident light loss in the middle region 11.

[0039] For example, in scenarios where the amount of light incident on the battery surface is uneven, with more light illuminating the edge region 12 of the battery cell 1, the middle region 11 of the battery is more likely to be blocked. Therefore, the thickness of the passivation film layer 2 in the edge region 12 should be less than that in the middle region 11.

[0040] To facilitate understanding, the influence of the thickness of the passivation layer 2 on the incident light utilization rate is analyzed below: The incident light utilization rate is directly related to the thickness of the passivation layer 2. Incident light illuminating the battery surface must first pass through the passivation layer 2 on the battery surface before reaching the single-crystal silicon substrate. Only after reaching the single-crystal silicon substrate can the incident light induce electron-hole pairs within the substrate, thereby forming a photocurrent and converting light energy into electrical energy. Therefore, the greater the proportion of light incident on the single-crystal silicon substrate, the higher the incident light utilization rate, and the higher the corresponding photoelectric conversion efficiency. However, the passivation layer 2 covering the battery surface—that is, the single-crystal silicon substrate—absorbs a portion of photons when incident light passes through. The photons absorbed by the passivation layer 2 cannot be used to generate free electron-hole pairs; instead, they are consumed in the lattice vibrations of the passivation layer 2 material, converting into heat energy. In other words, the incident light absorbed by the passivation layer 2 cannot be used to convert into electrical energy; it is useless absorption, also known as parasitic absorption. Parasitic absorption is a significant factor contributing to reduced incident light utilization and optical loss. Parasitic absorption is related to the thickness of the passivation film 2; the thicker the passivation film 2, the more incident light is absorbed. Reducing the thickness of the passivation film 2 can effectively reduce optical loss caused by parasitic absorption and improve incident light utilization. However, the thickness of the passivation film also affects its passivation effect; an excessively thin passivation film cannot form stable chemical and field passivation effects.

[0041] Therefore, this application addresses different application scenarios or the personalized characteristics of batteries by creating a thickness difference between the middle region 11 and the edge region 12 of the passivation film layer 2 in the solar substrate. By thickening or thinning the edge region 12, the middle region 11 is correspondingly thinned and then thickened, thereby improving the efficiency of the battery.

[0042] In some embodiments, the thickness difference between the edge region 12 and the middle region 11 is ≤100nm.

[0043] In some embodiments, such as Figure 1 As shown, the thickness of the passivation film 2 gradually increases from the middle region 11 to the edge region 12. Moreover, the thickness of the passivation film 2 in the middle region 11 can be zero, that is, the passivation film 2 can exist only in the edge region 12.

[0044] Example 1: The edge region 12 on the back of the battery has a gradually thickening aluminum oxide layer, while the middle region 11 has no aluminum oxide layer. The aluminum oxide layer in the edge region 12 covers one-third of the area of ​​the battery cell 1. In the edge region 12, the aluminum oxide layer thickness near the outermost edge of the battery is greater than 5 nm, and the thickness gradually decreases to 0 nm from the outermost edge of the battery towards the middle region 11. "Gradually decreasing" means that the overall trend of the thickness is decreasing. Figure 1As shown, the alumina layer in the outermost region 12 can have a section of uniform edge thickness 21, and then the thickness gradually decreases to zero, while the middle region 11 has no alumina layer.

[0045] Example 2: The front of the battery has a silicon nitride layer with decreasing thickness from the edge region 12 to the middle region 11. The thickness of the silicon nitride film in the middle region 11 is not zero. Figure 2 As shown.

[0046] When the thickness of the passivation film layer 2 increases from the middle region 11 to the edge region 12, the shape of the passivation film layer 2 on the solar cell substrate is a concave spherical shape, an inverted cone shape, or an inverted frustum shape.

[0047] When the thickness of the passivation film layer 2 gradually decreases from the middle region 11 to the edge region 12 of the cell 1, the shape of the passivation film layer 2 on the solar cell substrate is a convex spherical shape, or a right conical shape, or a right frustum shape.

[0048] In some embodiments, the outermost edge region 12 has a section of edge thickness uniform region 21.

[0049] In some embodiments, the passivation film 2 is a field passivation film 22 and / or a non-field passivation film 23.

[0050] In some embodiments, when the passivation film layer 2 includes a field passivation film layer 22 and a field-free passivation film layer 23, the thickness of the field passivation film layer 22 gradually increases from the middle region 11 to the edge region 12, and the thickness of the field-free passivation film layer 23 gradually decreases from the middle region 11 to the edge region 12, so as to form a flat surface.

[0051] Example 3: such as Figure 3 As shown, the thickness of the aluminum oxide field passivation layer on the front side of the battery gradually decreases from the edge region 12 to the middle region 11. Other passivation layers or antireflective layers without field passivation function are paired with it, and their thickness gradually increases from the edge region 12 to the middle region 11 to form a smooth upper surface of the battery.

[0052] The field passivation film involved in this application carries a fixed positive or negative charge, and the absolute value of the fixed charge density is ≥1×10⁻⁶. 10 cm -2 .

[0053] Optionally, the thickness of the field passivation film 22 gradually decreases from the middle region 11 to the edge region 12, and the thickness of the non-field passivation film 23 gradually increases from the middle region 11 to the edge region 12 to form a smooth surface.

[0054] In some embodiments, the field-free passivation film 23 is one or more combinations of an aluminum oxide film, a silicon nitride film, and a silicon oxide film. For example, the field-free passivation film 23 may include stacked aluminum oxide films, silicon nitride films, and silicon oxide films, and may also include stacked amorphous silicon films and polycrystalline silicon films.

[0055] In some embodiments, the field passivation film 22 is one or more combinations of an aluminum oxide film, a silicon nitride film, and a silicon oxide film.

[0056] The passivation film 2 provided in this application also includes hydrogen atoms, and the hydrogen atom content gradually changes with the thickness of the passivation film 2. The thicker the passivation film 2, the higher the hydrogen atom content.

[0057] Hydrogen Atom Content: Hydrogen atoms can be incorporated into the passivation film layer 2 using a hydrogen-containing reaction gas. Hydrogen is commonly used in the reaction gases for silicon nitride and aluminum oxide passivation films layer 2. Hydrogen plays a crucial role in the passivation film layer 2; hydrogen atoms can bind to dangling bonds on the surface of the crystalline silicon substrate, passivating these bonds. Dangling bonds on the surface of the crystalline silicon substrate are an important type of defect. Appropriately increasing the hydrogen content in the passivation film layer 2 increases the number of hydrogen atoms reaching the surface of the crystalline silicon substrate and passivating the dangling bonds, thereby reducing the dangling bond defect density and improving the passivation quality. The thicker the passivation film layer 2, the larger its volume per unit area, and the higher the total hydrogen content per unit area. After the battery undergoes high-temperature processing, more hydrogen atoms migrate from the passivation film layer 2 to the surface of the crystalline silicon substrate, resulting in better passivation quality.

[0058] Furthermore, the textured surface size beneath the passivation film layer 2 provided in this application gradually changes synchronously with the thickness of the passivation film layer 2. That is, the textured surface size beneath the passivation film layer 2 in thicker regions is also larger. The textured surface shape includes a pyramid shape or a polished base shape, and the textured surface size refers to the height of the pyramid or the height of the center point of the polished base.

[0059] The purpose of the textured surface is to address the issue that a large textured surface size can negatively impact the deposition quality of the passivation film 2. Depositing a thin passivation film 2 on a large textured surface may result in exposed peaks where the passivation film 2 fails to cover them, or the passivation film 2 at the peaks may be rubbed off during cell stacking, thus affecting the passivation effect. Therefore, in areas where the passivation film 2 is thinner, the textured surface size can be appropriately reduced to improve the deposition quality. Conversely, in areas where the passivation film 2 is thicker, appropriately increasing the textured surface size can reduce the total surface area of ​​the textured surface, thereby reducing surface recombination.

[0060] Controlling the gradient of textured surface height: The concentration of the texturing solution and the reaction time both affect the textured surface size. A mask layer of uneven thickness is formed on the surface of the crystalline silicon substrate. When reacting with the texturing solution, in areas where the mask layer is thicker, the solution needs to etch the mask layer first before contacting the silicon substrate surface. This shortens the reaction time between the texturing solution and the substrate in areas with thicker mask layers. The shorter the reaction time, the smaller the textured surface size.

[0061] The solar cell fabrication process provided in this application is as follows: When depositing the passivation film 2 using chemical vapor deposition methods such as PECVD or LPCVD, the gas source is usually located above the cell 1, the cell 1 is placed on the tray 3, the gas undergoes a chemical reaction on the upper surface of the cell 1 and forms the passivation film 2, and the lower surface of the cell does not come into contact with the reaction gas, thereby achieving the deposition of a passivation film 2 of uniform thickness only on the upper surface of the cell 1.

[0062] PECVD: PECVD stands for Plasma Enhanced Chemical Vapor Deposition, a core technology that uses plasma-assisted reactions to deposit thin film materials at low temperatures.

[0063] LPCVD – Low Pressure Chemical Vapor Deposition.

[0064] See Figure 4 The preparation process of the passivation film layer 2, which has a gradually changing thickness from thicker at the edges to thinner in the middle, is as follows:

[0065] To form a passivation film layer 2 with a gradually varying thickness, thicker at the edges and thinner in the middle, the tray 3 of the solar cell 1 can be modified by placing four corner pillars 4 between the four corners of the solar cell 1 and the tray 3 (pillars 4 are only placed at the four corners). The solar cell 1 is supported by the four pillars 4, forming a gap between the solar cell 1 and the tray 3 below. The reactive gas can enter the gap below the solar cell 1 through the pillars 4 and contact the lower surface of the solar cell 1. Due to the high gas density at the edge of the lower surface and the low gas density in the middle region 11, a gradually varying passivation film layer 2 with a thicker edge region 12 and a thinner middle region 11 can be formed on the lower surface of the solar cell 1. By adjusting the height of the four pillars 4, the gas density entering the gap below the solar cell 1 can be controlled, thereby controlling the gradual thickness trend of the passivation film layer 2 on the lower surface of the cell based on experimental data. The uniformly thick passivation film layer 2 formed simultaneously on the upper surface of the cell during this process can be removed using a single-sided cleaning process.

[0066] The number of columns 4 can also be increased; for example, one column 4 can be installed at the center of each of the four sides of the battery cell 1. The columns are connected as a whole by connecting rods to prevent the support structure from wobbling.

[0067] See Figure 5 and Figure 6 The preparation process of the passivation film layer 2, which has a gradually increasing thickness from thin at the edges to thick in the middle, is as follows:

[0068] To form a passivation film layer 2 with a gradually changing thickness from thin at the edges to thick in the middle, the tray 3 of the battery cell 1 can be modified in another way. A side enclosure 5 is set between the battery cell 1 and the tray 3, and a top baffle 6 with a central air inlet 61 is set on the top of the side enclosure 5, forming a sealed cavity with only the central air inlet 61. The side enclosure 5 blocks the airflow from the side, so that the airflow can only enter from the central air inlet 61, which directly contacts the middle area 11 of the battery cell 1. The airflow density in the middle area 11 of the upper surface of the battery cell 1 is high, and the passivation film layer 2 formed by the gas reaction in the middle area 11 of the battery cell 1 is also thicker. The edge area 12 of the battery cell 1 has a lower gas density, and the passivation film layer 2 formed by the reaction is also thinner, thus forming a gradually changing trend of thick in the center and thin at the edges.

[0069] By adjusting the height of the side enclosure 5, the size of the central air inlet 61 of the top baffle 6, and the angle between the top baffle 6 and the horizontal plane based on experimental data, the airflow density on the upper surface of the battery cell 1 can be controlled, thereby controlling the gradual change in thickness. For example, Figure 5 The top baffle 6 is placed horizontally, while Figure 6 A top baffle 6 is installed at an angle to the horizontal plane.

[0070] The terms used in this article are explained as follows:

[0071] Fixed charge: Some films formed by certain materials will carry a certain amount of fixed charge due to the material properties. For example, aluminum oxide films usually carry a negative fixed charge, while silicon nitride films usually carry a positive fixed charge.

[0072] Field passivation: When the electron and hole concentrations on the battery surface are similar, the surface recombination rate is the highest. If the concentration of a certain type of charge carrier on the surface decreases, the surface recombination rate will decrease significantly. The fixed charges in the field passivation film will repel like-charge carriers and attract opposite-charge carriers, thereby changing the surface charge carrier concentration and reducing the probability of electron-hole recombination. This process is called field-effect passivation.

[0073] Chemical passivation: The passivation film can saturate the dangling bonds and various defect states on the surface of the battery, reduce the interface defect density, and reduce the recombination centers in the band gap, which is the effect of chemical passivation.

[0074] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0075] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A solar cell, characterized in that, include: A battery cell (1) has a passivation film layer (2) provided on the front and / or back sides of the battery cell (1), and the thickness of the passivation film layer (2) has a thickness difference between the middle region (11) and the edge region (12) of the battery cell (1). The thickness of the passivation film (2) gradually increases from the middle region (11) to the edge region (12); or The thickness of the passivation film (2) gradually decreases from the middle region (11) of the battery cell (1) to its edge region (12).

2. The solar cell as described in claim 1, characterized in that, The thickness difference between the edge region (12) and the middle region (11) is ≤100nm.

3. The solar cell as described in claim 1, characterized in that, The outermost edge region (12) has a section of uniform edge thickness (21).

4. The solar cell according to claim 1, characterized in that, The passivation film (2) is a field passivation film (22) and / or a non-field passivation film (23).

5. The solar cell as described in claim 4, characterized in that, When the passivation film layer (2) includes a field passivation film layer (22) and a non-field passivation film layer (23), the thickness of the field passivation film layer (22) gradually increases from the middle region (11) to the edge region (12), and the thickness of the non-field passivation film layer (23) gradually decreases from the middle region (11) to the edge region (12) to form a smooth surface; or The thickness of the field passivation film (22) gradually decreases from the middle region (11) to the edge region (12), and the thickness of the field-free passivation film (23) gradually increases from the middle region (11) to the edge region (12) to form a smooth surface.

6. The solar cell as described in claim 4, characterized in that, The field-free passivation film (23) is any one or more of the following: aluminum oxide film, silicon nitride film, and silicon oxide film.

7. The solar cell as claimed in claim 4, characterized in that, The field passivation film (22) is any one or more of the following: aluminum oxide film, silicon nitride film, and silicon oxide film.

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