A novel solar cell and a method for manufacturing the same

Abstract

The application provides a solar cell and a preparation method thereof. The solar cell comprises a silicon substrate having a first surface and a second surface arranged oppositely, the first surface comprising electrode regions and non-electrode regions arranged alternately; a first tunneling oxide layer, a first doped polysilicon layer, a second tunneling oxide layer and a second doped polysilicon layer arranged sequentially on the first surface and / or the second surface; wherein the first doped polysilicon layer is doped with a first dopant and a second dopant, and the second doped polysilicon layer is doped with the first dopant, and the doping concentration of the first dopant in the second doped polysilicon layer is greater than the doping concentration of the first dopant in the first doped polysilicon layer. The first doped polysilicon layer in the solar cell can achieve excellent passivation and significantly reduced free carrier absorption, and the second doped polysilicon layer can achieve rapid transport of carriers and excellent field passivation, which is helpful to improve the open-circuit voltage and the fill factor.

Description

Technical Field

[0001] This application belongs to the field of solar cell technology, specifically relating to a novel solar cell and its preparation method. Background Technology

[0002] Tunneling oxide passivated contact solar cells, as a new generation of high-efficiency solar cell technology that can be mass-produced, rely on an ultra-thin tunneling oxide layer and heavily doped polycrystalline silicon to achieve good passivation performance and selective collection of carriers, thereby obtaining ideal implicit open-circuit voltage, saturation current density and minority carrier lifetime.

[0003] In the mass production technology of tunneling oxide passivated contact solar cells, the back surface employs tunneling oxygen superimposed with doped polycrystalline silicon passivation, effectively solving the problems of metal recombination between the back metal and the semiconductor substrate, as well as passivation of non-metallic regions. However, metal recombination in the metal contact area of ​​the light-receiving side remains relatively high, limiting the improvement of cell efficiency. Furthermore, the balance between tunneling oxygen and polycrystalline silicon passivation, and between contact and free carrier absorption, is a major factor affecting cell efficiency improvement. Summary of the Invention

[0004] The purpose of this application is to provide a novel solar cell and a method for its fabrication.

[0005] Specifically, this application relates to the following aspects:

[0006] A solar cell, comprising:

[0007] A silicon substrate having a first surface and a second surface disposed opposite to each other, the first surface and / or the second surface including alternately disposed electrode regions and non-electrode regions;

[0008] A first tunneling oxide layer, a first doped polysilicon layer, a second tunneling oxide layer, and a second doped polysilicon layer are sequentially stacked on the first surface and / or the second surface.

[0009] The first doped polysilicon layer is doped with a first dopant and a second dopant, the second doped polysilicon layer is doped with a first dopant, and the doping concentration of the first dopant in the second doped polysilicon layer is greater than the doping concentration of the first dopant in the first doped polysilicon layer.

[0010] The first dopant is a Group IIIA or Group VA, and the second dopant is selected from one or more of carbon, oxygen, nitrogen, and sulfur.

[0011] Optionally, when the first dopant is phosphorus, the doping concentration of the first dopant in the first doped polysilicon layer is 1E+19 to 3E+19 cm⁻¹. -3The doping concentration of the second dopant is 8E+21 to 2E+22 cm⁻¹. -3 ;

[0012] When the first dopant is boron, the doping concentration of the first dopant in the first doped polysilicon layer is 1E+18 to 3E+18 cm⁻¹. -3 The doping concentration of the second dopant is 8E+21 to 2E+22 cm⁻¹. -3 .

[0013] Optionally, when the first dopant is phosphorus, the doping concentration of the first dopant in the second doped polysilicon layer is 3E+20 to 6E+20 cm⁻¹. -3 ,

[0014] When the first dopant is boron, the doping concentration of the first dopant in the second doped polysilicon layer is 6E+19 to 9E+19 cm⁻¹. -3 .

[0015] Optionally, when the first dopant is phosphorus, the sheet resistance of the passivation contact structure composed of the first tunneling oxide layer, the first doped polysilicon layer, the second tunneling oxide layer, and the second doped polysilicon layer is 20-80 Ω / sq.

[0016] When the first dopant is boron, the sheet resistance of the passivation contact structure composed of the first tunneling oxide layer, the first doped polysilicon layer, the second tunneling oxide layer, and the second doped polysilicon layer is 80-120 Ω / sq.

[0017] Optionally, the solar cell includes: a first tunneling oxide layer, a first doped polycrystalline silicon layer, a second tunneling oxide layer, and a second doped polycrystalline silicon layer sequentially stacked on the first surface.

[0018] The second tunneling oxide layer on the first surface is located in the electrode region, and the second doped polysilicon layer is formed on the second tunneling oxide layer.

[0019] Optionally, the solar cell further includes:

[0020] A first tunneling oxide layer, a first doped polysilicon layer, a second tunneling oxide layer, and a second doped polysilicon layer are sequentially stacked on the second surface;

[0021] The doping type of the first dopant on the first surface is different from that of the first dopant on the second surface.

[0022] Optionally, the electrode region includes alternating positive electrode regions and negative electrode regions, which are isolated by non-electrode regions;

[0023] In the positive electrode region, the solar cell includes a first tunneling oxide layer, a first doped polycrystalline silicon layer, a second tunneling oxide layer and a second doped polycrystalline silicon layer sequentially stacked on the second surface, wherein the first dopant is boron;

[0024] In the negative electrode region, the solar cell includes a first tunneling oxide layer, a first doped polycrystalline silicon layer, a second tunneling oxide layer, and a second doped polycrystalline silicon layer sequentially stacked on the second surface, wherein the first dopant is phosphorus.

[0025] A photovoltaic module comprising any of the aforementioned solar cells.

[0026] A method for preparing a solar cell includes the following steps:

[0027] A first tunneling oxide layer is formed on at least one surface of a silicon substrate.

[0028] A first doped polycrystalline silicon layer, doped with a first dopant and a second dopant, is prepared on the tunneling oxide layer.

[0029] A second tunneling oxide layer is prepared on the first doped polycrystalline silicon layer.

[0030] A second doped polycrystalline silicon layer doped with the first dopant is prepared on the second tunneling oxide layer;

[0031] The doping concentration of the first dopant in the second doped polysilicon layer is greater than the doping concentration of the first dopant in the first doped polysilicon layer;

[0032] The first dopant is a Group IIIA or Group VA, and the second dopant is selected from one or more of carbon, oxygen, nitrogen, and sulfur.

[0033] Optionally, the preparation methods of the first tunneling oxide layer, the first doped polysilicon layer, the second tunneling oxide layer, and the second doped polysilicon layer are independently selected from LPCVD or PECVD.

[0034] Optionally, the solar cell is any of the above-mentioned types of solar cells.

[0035] The solar cell of this application includes a novel passivated contact structure, wherein a first polycrystalline silicon layer is co-doped with two elements, and a second polycrystalline silicon layer is doped with a single element. The first doped polycrystalline silicon layer optimizes the polycrystalline silicon bandgap, making the bandgap tunable, achieving excellent passivation and significantly reduced free carrier absorption; the dopant in the second doped polycrystalline silicon layer heavily dops the polycrystalline silicon, ensuring a sufficiently small contact barrier with the metal, enabling rapid carrier transport and excellent field passivation, which contributes to improving the open-circuit voltage and fill factor. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a TOPCon solar cell structure according to this application;

[0037] Figure 2 This is a schematic diagram of a back-contact solar cell structure according to this application. Attached image description:

[0039] 1. Silicon substrate; 2. Boron emitter; 3. First tunneling oxide layer on the light-receiving surface; 4. First doped polysilicon layer on the light-receiving surface; 5. Second tunneling oxide layer on the light-receiving surface; 6. Second doped polysilicon layer on the light-receiving surface; 7. Passivation layer on the light-receiving surface; 8. Anti-reflection layer on the light-receiving surface; 9. Positive electrode; 10. First tunneling oxide layer on the backlight surface; 11. First doped polysilicon layer on the backlight surface; 12. Second tunneling oxide layer on the backlight surface; 13. Second doped polysilicon layer on the backlight surface; 14. Passivation layer on the backlight surface; 15. Anti-reflection layer on the backlight surface; 16. Back electrode; 17. Positive electrode region. First tunneling oxide layer; 18 First doped polysilicon layer in positive electrode region; 19 Second tunneling oxide layer in positive electrode region; 20 Second doped polysilicon layer in positive electrode region; 21 First tunneling oxide layer in negative electrode region; 22 First doped polysilicon layer in negative electrode region; 23 Second tunneling oxide layer in negative electrode region; 24 Second doped polysilicon layer in negative electrode region; 25 Light-receiving electrode region; 26 Non-electrode region in light-receiving surface; 27 Backlight electrode region; 28 Non-electrode region in backlight surface; 29 Positive electrode region; 30 Negative electrode region; 31 Non-electrode region. Detailed Implementation

[0040] The present application is further illustrated below with reference to embodiments. It should be understood that the embodiments are only used to further illustrate and explain the present application and are not intended to limit the present application.

[0041] Unless otherwise defined, technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art. While similar or identical methods and materials may be applied in experimental or practical applications, materials and methods are described herein. In case of conflict, the definitions included herein shall prevail. Furthermore, materials, methods, and examples are for illustrative purposes only and are not intended to be limiting. The present application is further described below with reference to specific embodiments, but is not intended to limit the scope of the application.

[0042] In this application, the concentration of dopant in the doped polysilicon layer can be detected by any method known to those skilled in the art. Those skilled in the art can choose the appropriate method based on their needs; for example, it can be detected by methods such as ECV, SIMS, ICP-MS, GDMS, etc., with ECV & SIMS being preferred. Those skilled in the art will understand that the concentration of dopant in the doped polysilicon layer can refer to the concentration of dopant at any site on the surface of the doped polysilicon layer or at any site within the doped polysilicon layer. It can also be the average concentration of dopant at multiple sites or the average concentration of dopant across the entire doped polysilicon layer. Those skilled in the art can select any of the above-mentioned sites for detection based on the detection conditions and the instruments used, or they can detect multiple sites and calculate the average concentration of multiple sites as the dopant concentration. In a specific embodiment, the dopant concentration refers to the average value detected over the thickness of the doped polysilicon layer. For example, the ECV & SIMS method can be used to detect the concentration of dopant in the silicon wafer along one thickness direction and calculate the average value along that thickness direction.

[0043] In this application, the sheet resistance of the passivated contact structure can be detected by any method known to those skilled in the art. Those skilled in the art can choose based on their needs, such as by using a four-probe, non-contact sheet resistance tester, etc.

[0044] Currently, most studies improve metal recombination on the light-receiving surface by adding a tunneling oxide layer and a doped polysilicon passivation layer. Furthermore, by changing the doping concentration, film quality, and film thickness of the polysilicon layer, the passivation and contact properties of polysilicon are improved, and free carrier absorption is reduced, thereby increasing battery efficiency.

[0045] Studies have shown that in tunneling oxide passivated contact solar cell structures, the use of a tunneling oxide layer and a doped polycrystalline silicon layer passivation structure on the light-receiving surface leads to severe free carrier absorption in the doped polycrystalline silicon, hindering electron transport and significantly reducing photocurrent and fill factor. Furthermore, the doping level of the polycrystalline silicon layer determines the strength of the field passivation capability. Lower doping levels result in insufficient field passivation and higher contact resistance, leading to voltage turn-on and fill factor loss. Excessive doping concentration causes excessive diffusion of dopant atoms into the silicon substrate during high-temperature crystallization, resulting in severe Auger recombination and a significant decrease in passivation performance. In addition, the doping level and thickness of the polycrystalline silicon film significantly affect the absorption coefficient of long-wavelength light; higher doping concentration (thicker film) results in a larger absorption coefficient, corresponding to more severe free carrier absorption and greater photocurrent loss. Previous studies have shown that it is difficult to improve the passivation and contact performance of the doped polycrystalline silicon layer and reduce free carrier absorption using a single film structure.

[0046] To address the problems existing in the prior art, this application provides a novel solar cell, comprising:

[0047] A silicon substrate having a first surface and a second surface disposed opposite to each other, the first surface and / or the second surface including alternately disposed electrode regions and non-electrode regions;

[0048] A first tunneling oxide layer, a first doped polysilicon layer, a second tunneling oxide layer, and a second doped polysilicon layer are sequentially stacked on the first surface and / or the second surface.

[0049] The first doped polysilicon layer is doped with a first dopant and a second dopant, the second doped polysilicon layer is doped with a first dopant, and the doping concentration of the first dopant in the second doped polysilicon layer is greater than the doping concentration of the first dopant in the first doped polysilicon layer.

[0050] The first dopant is a Group IIIA or Group VA, and the second dopant is selected from one or more of carbon, oxygen, nitrogen, and sulfur.

[0051] The elements of Group IIIA and Group VA are known in the art. In one specific embodiment, the first dopant is phosphorus or boron.

[0052] As can be seen, the solar cell of this application includes a novel passivated contact structure, which includes a first tunneling oxide layer, a first doped polycrystalline silicon layer, a second tunneling oxide layer and a second doped polycrystalline silicon layer stacked sequentially.

[0053] The first doped polysilicon layer is co-doped with a first dopant and a second dopant. The second dopant can form chemical bonds with Si with high bond energy (C-Si bond, N-Si bond, O-Si bond or S-Si bond), which are difficult to break. This reduces the doping concentration of the first dopant in the doped polysilicon and reduces Auger recombination caused by high concentration of the first dopant. At the same time, doping with the second dopant reduces the work function of the polysilicon layer, thereby enhancing the built-in electric field of the first doped polysilicon layer, making it difficult for holes to reach the interface and improving the passivation capability of the first doped polysilicon layer.

[0054] However, co-doping of the first and second dopant in the first doped polysilicon layer reduces the contact performance between the doped polysilicon layer and the electrode. Therefore, this application improves the contact performance of the electrode by setting a second doped polysilicon layer with a high concentration of the first dopant. The heavy doping of the polysilicon in the second doped polysilicon layer ensures a sufficiently small contact barrier with the metal, enabling rapid carrier transport and contributing to the improvement of open-circuit voltage and fill factor.

[0055] In addition, the heavily doped polysilicon layer is placed on the outermost side, and the inner film layer can effectively block the diffusion of the first dopant into the silicon substrate. For example, it can block the first dopant, such as phosphorus or boron, in the second doped polysilicon layer from entering the silicon substrate, thereby reducing Auger recombination.

[0056] The first tunneling oxide layer is used to achieve interface passivation of the silicon substrate surface, achieving a chemical passivation effect. Specifically, due to the presence of interface state defects at the silicon substrate interface, the interface state density of the silicon substrate is relatively high. This increased interface state density promotes the recombination of photogenerated carriers, thereby reducing the fill factor and conversion efficiency of the solar cell. Therefore, by placing the first tunneling oxide layer on the silicon substrate surface, the dangling bonds on the saturated silicon substrate surface reduce the interface defect state density, thereby reducing recombination centers on the silicon substrate surface and lowering the carrier recombination rate. This allows the first tunneling oxide layer to achieve a chemical passivation effect on the silicon substrate surface. The second tunneling oxide layer acts as a barrier, preventing the diffusion of the first dopant element from the heavily doped second-doped polycrystalline silicon layer into the first-doped polycrystalline silicon layer, or even into the silicon substrate, increasing Auger recombination on the silicon substrate surface. Furthermore, during the formation of the polyfinger structure, the second tunneling oxide layer can reduce the possibility of damage to the first-doped polycrystalline silicon layer during etching. In some embodiments, the materials of the first tunneling oxide layer and / or the second tunneling oxide layer may be dielectric materials such as silicon oxide, magnesium fluoride, silicon oxide, amorphous silicon, polycrystalline silicon, silicon carbide, silicon nitride, silicon oxynitride, aluminum oxide, or titanium oxide.

[0057] In one specific embodiment, the first dopant is phosphorus, and the doping concentration of the first dopant in the first doped polycrystalline silicon layer is 1E+19 to 3E+19 cm⁻¹. -3 For example, it could be 1E+19cm -3 1.2E+19cm -3 1.5E+19cm -3 1.8E+19cm -3 2E+19cm -3 2.5E+19cm -3 2.8E+19cm -3 3E+19cm -3 And any value between these values; the doping concentration of the second dopant is 8E+21 to 2E+22 cm⁻¹. -3 For example, it could be 8E+21cm -3 8.5E+21cm -3 9E+21cm -3 9.5E+21cm -3 1E+22cm -3 1.5E+22cm -32E+22cm -3 , and any value between these values.

[0058] In one specific embodiment, the first dopant is boron, and the doping concentration of the first dopant in the first doped polycrystalline silicon layer is 1E+18 to 3E+18 cm⁻¹. -3 For example, it could be 1E+18cm -3 1.2E+18cm -3 1.5E+18cm -3 1.8E+18cm -3 2E+18, 2.2E+18cm -3 2.5E+18cm -3 2.8E+18cm -3 3E+18cm -3 And any value between these values; the doping concentration of the second dopant is 8E+21 to 2E+22 cm⁻¹. -3 For example, it could be 8E+21cm -3 8.5E+21cm -3 9E+21cm -3 9.5E+21cm -3 1E+22cm -3 1.5E+22cm -3 2E+22cm -3 , and any value between these values.

[0059] In one specific embodiment, the first dopant is phosphorus, and the doping concentration of the first dopant in the second doped polysilicon layer is 3E+20 to 6E+20 cm⁻¹. -3 For example, it can be 3E+20cm -3 3.2E+20cm -3 3.5E+20cm -3 3.8E+20cm -3 4E+20cm -3 4.2E+20cm -3 4.5E+20cm -3 4.8E+20cm -3 5E+20cm -3 5.2E+20cm -3 5.5E+20cm -3 5.8E+20cm -3 6E+20cm -3 , and any value between these values.

[0060] In one specific embodiment, the first dopant is boron, and the doping concentration of the first dopant in the second doped polysilicon layer is 6E+19 to 9E+19 cm⁻¹. -3 For example, it could be 6E+19cm -3 6.2E+19cm -3 6.5E+19, 6.8E+19cm -3 7E+19cm -3 7.2E+19cm -3 7.5E+19cm -3 7.8E+19cm -3 8E+19cm -3 8.2E+19cm -3 8.5E+19cm -3 8.8E+19cm -3 9E+19cm -3 , and any value between these values.

[0061] In one specific embodiment, the first dopant is phosphorus, and the doping concentration of the first dopant in the first doped polycrystalline silicon layer is 1E+19 to 3E+19 cm⁻¹. -3 The doping concentration of the second dopant is 8E+21 to 2E+22 cm⁻¹. -3 The doping concentration of the first dopant in the second doped polysilicon layer is 3E+20 to 6E+20 cm⁻¹. -3 .

[0062] In one specific embodiment, the first dopant is boron, and the doping concentration of the first dopant in the first doped polycrystalline silicon layer is 1E+18 to 3E+18 cm⁻¹. -3 The doping concentration of the second dopant is 8E+21 to 2E+22 cm⁻¹. -3 The doping concentration of the first dopant in the second doped polysilicon layer is 6E+19 to 9E+19 cm⁻¹. -3 .

[0063] Those skilled in the art will understand that for a first doped polysilicon layer and a second doped polysilicon layer located on one surface of a silicon substrate, the first dopant is of the same type, for example, both are phosphorus, or both are boron. When the second dopant in the first doped polysilicon layer is two or more types, for example, carbon and oxygen, then the doping concentration of the second dopant is the sum of the doping concentrations of carbon and oxygen.

[0064] In one specific embodiment, the thickness of the first doped polysilicon layer is 20 to 80 nm, for example, it can be 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, and any value between these values.

[0065] In one specific embodiment, the thickness of the first doped polycrystalline silicon layer is 20–50 nm.

[0066] In one specific embodiment, the thickness of the second doped polysilicon layer is 100–300 nm, for example, it can be 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm, and any value between these values.

[0067] In one specific embodiment, the thickness of the second doped polysilicon layer is 100–150 nm.

[0068] The materials of both the first and second tunneling oxide layers can be materials known in the art for tunneling oxide layers. In one specific embodiment, the material of the first tunneling oxide layer is silicon oxide, and the thickness is 1-2 nm. In another specific embodiment, the material of the second tunneling oxide layer is silicon oxide, and the thickness is 0.1-1 nm.

[0069] In one specific embodiment, the first dopant is phosphorus, and the sheet resistance of the passivation contact structure composed of the first tunneling oxide layer, the first doped polysilicon layer, the second tunneling oxide layer, and the second doped polysilicon layer is 20-80 Ω / sq, for example, it can be 20 Ω / sq, 25 Ω / sq, 30 Ω / sq, 35 Ω / sq, 40 Ω / sq, 45 Ω / sq, 50 Ω / sq, 55 Ω / sq, 60 Ω / sq, 65 Ω / sq, 70 Ω / sq, 75 Ω / sq, 80 Ω / sq, and any value between these values.

[0070] In one specific embodiment, the first dopant is boron, and the sheet resistance of the passivation contact structure composed of the first tunneling oxide layer, the first doped polysilicon layer, the second tunneling oxide layer, and the second doped polysilicon layer is 80-120 Ω / sq, for example, it can be 80 Ω / sq, 85 Ω / sq, 90 Ω / sq, 95 Ω / sq, 100 Ω / sq, 105 Ω / sq, 110 Ω / sq, 115 Ω / sq, 120 Ω / sq, and any value between these values.

[0071] Those skilled in the art will understand that any type of solar cell including the above-described passivated contact structure is included in the solar cells of this application, such as tunnel oxide passivated contact (TOPCon) cells, back contact cells, etc. The configuration of the passivated contact structure can also be flexible and diverse. For example, the first tunnel oxide layer, the first doped polycrystalline silicon layer, the second tunnel oxide layer, and the second doped polycrystalline silicon layer can be disposed on one surface of the silicon substrate, such as the light-receiving surface or the back-lighting surface. Alternatively, the first tunnel oxide layer, the first doped polycrystalline silicon layer, the second tunnel oxide layer, and the second doped polycrystalline silicon layer can be disposed on both surfaces of the silicon substrate, such as the light-receiving surface and the back-lighting surface. The first tunnel oxide layer, the first doped polycrystalline silicon layer, the second tunnel oxide layer, and the second doped polycrystalline silicon layer can be disposed in the entire area of ​​the light-receiving surface and / or the back-lighting surface of the silicon substrate, or in a partial area of ​​the light-receiving surface and / or the back-lighting surface of the silicon substrate.

[0072] When the first tunneling oxide layer, the first doped polysilicon layer, the second tunneling oxide layer, and the second doped polysilicon layer are formed on both surfaces of a silicon substrate, such as the light-receiving surface and the back-light-receiving surface, the types of the first dopants on the two surfaces are different. When the first dopant on one surface is boron, the first dopant on the other surface is phosphorus, and vice versa.

[0073] Furthermore, the solar cell further includes a passivation layer and an antireflection layer sequentially stacked on one surface of the second doped polycrystalline silicon layer away from the silicon substrate. The materials of both the passivation layer and the antireflection layer can be various materials known in the art; for example, the passivation layer can be alumina with a thickness of 2-6 nm; the antireflection layer can be a stack of one or more of silicon nitride, silicon oxynitride, and silicon carbide with a thickness of 70-90 nm.

[0074] Figure 1This application illustrates the structure of a solar cell, specifically a TOPCon solar cell. The cell has any of the aforementioned passivation contact structures on both the light-receiving and back-light-receiving surfaces of a silicon substrate. Specifically, the solar cell includes a silicon substrate 1, such as an N-type silicon substrate 1, with a light-receiving surface and a back-light-receiving surface arranged opposite each other. The light-receiving surface includes alternating light-receiving electrode regions 25 and light-receiving non-electrode regions 26, and the back-light-receiving surface includes alternating back-light-receiving electrode regions 27 and back-light-receiving non-electrode regions 28. The light-receiving surface has a poly-finger structure, meaning that a first tunneling oxide layer 3, a first doped polycrystalline silicon layer 4, a second tunneling oxide layer 5, and a second doped polycrystalline silicon layer 6 are sequentially disposed on the light-receiving surface of the silicon substrate 1. The second tunneling oxide layer 5 partially covers the first doped polycrystalline silicon layer 4. Specifically, the second tunneling oxide layer 5 is located in the light-receiving electrode region 25. The second doped polysilicon layer 6 on the light-receiving surface is formed on the second tunneling oxide layer 5 on the light-receiving surface.

[0075] The poly-finger structure in the light-receiving surface has the following technical effects:

[0076] The addition of the second dopant to the first doped polysilicon layer increases the optical band gap of the first doped polysilicon layer. At the same time, the highly concentrated doped second doped polysilicon layer only covers the electrode area. The combined effect of the two can reduce the parasitic absorption problem of the polysilicon layer in the passivation contact structure.

[0077] A first tunneling oxide layer 10, a first doped polysilicon layer 11, a second tunneling oxide layer 12, and a second doped polysilicon layer 13 are sequentially disposed on the back surface of the silicon substrate 1.

[0078] The addition of a second dopant concentration to the first doped polysilicon layer in the stacked passivation contact structure of the backlight not only balances the issues of reducing Auger recombination on the silicon substrate surface and enhancing the contact performance between the polysilicon layer and the electrode, but also increases the band gap of the polysilicon layer, enhancing the absorption capacity of the battery backlight for short-wavelength light, improving light utilization, and increasing battery efficiency.

[0079] The thickness of the first doped polysilicon layer is 20–80 nm, for example, it can be 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, or any value between these values. Specifically, the thickness of the first doped polysilicon layer is 20–50 nm.

[0080] The thickness of the second doped polysilicon layer is 100–300 nm, for example, it can be 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, 250 nm, 260 nm, 270 nm, 280 nm, 290 nm, 300 nm, or any value between these. Specifically, the thickness of the second doped polysilicon layer is 100–150 nm.

[0081] The thickness of the first doped polysilicon layer is smaller than that of the second doped polysilicon layer, which can reduce parasitic absorption of polysilicon while ensuring the passivation and contact performance of the polysilicon layer with the electrode.

[0082] Wherein, the first dopant on the light-receiving side of the silicon substrate 1 is phosphorus, and the first dopant on the back-light side of the silicon substrate 1 is boron, or the first dopant on the light-receiving side of the silicon substrate 1 is boron, and the first dopant on the back-light side of the silicon substrate 1 is phosphorus.

[0083] Furthermore, the solar cell also includes a light-receiving passivation layer 7, a light-receiving anti-reflection layer 8, and a positive electrode 9 on the light-receiving side of the silicon substrate 1, and a back-light-receiving passivation layer 14, a back-light-receiving anti-reflection layer 15, and a back electrode 16 on the back-light-receiving side of the silicon substrate 1.

[0084] The positive electrode 9 and the back electrode 16 can be made of silver, aluminum, copper, tin, gold, lead, or nickel. For example, both the positive electrode and the back electrode can be made of silver.

[0085] Figure 2 This application illustrates another solar cell structure, specifically a back-contact solar cell. Any of the aforementioned passivated contact structures is provided on the back surface of a silicon substrate. Specifically, the solar cell includes a silicon substrate 1, which has a light-receiving surface and a back-contact surface disposed opposite to each other.

[0086] The light-receiving surface can have a textured surface, which can be prepared by solution texturing or laser texturing. The textured surface can include pyramidal structures, pyramid-like structures, or any other sloping structure with a high aspect ratio.

[0087] The backlight surface includes alternating electrode regions and non-electrode regions 31. The electrode regions include alternating positive electrode regions 29 and negative electrode regions 30, which are isolated by the non-electrode regions 31. In the positive electrode region 29, the solar cell includes a first tunneling oxide layer 17, a first doped polycrystalline silicon layer 18, a second tunneling oxide layer 19, and a second doped polycrystalline silicon layer 20, which are sequentially stacked on the backlight surface. The first dopant is boron. In the negative electrode region 30, the solar cell includes a first tunneling oxide layer 21, a first doped polycrystalline silicon layer 22, a second tunneling oxide layer 23, and a second doped polycrystalline silicon layer 24, which are sequentially stacked on the backlight surface. The first dopant is phosphorus.

[0088] The passivated contact structure of this application in the back-contact solar cell can achieve the following technical effects: Firstly, the passivation effect of the first tunneling oxide layer and the first doped polycrystalline silicon layer on the electrode region improves the problem of severe carrier recombination in the electrode region. At the same time, the second dopant can adjust the band gap of the first doped polycrystalline silicon layer, improve the absorption of short-wavelength light by the back surface of the cell, and thus improve the utilization rate of transmitted and reflected light by the back surface. Secondly, the high concentration of the first dopant in the second doped polycrystalline silicon layer improves the contact performance between the electrode and the silicon substrate, reduces the contact resistance between the electrode and the cell, and improves the carrier collection efficiency. Thirdly, when both the positive and negative electrode regions are located on the back of the cell, the addition of the second dopant will increase the band gap of the polycrystalline silicon layer, enhance the absorption capacity of the back surface of the cell for short-wavelength light, improve the light utilization rate, and improve the cell efficiency.

[0089] This application also provides a photovoltaic module, which includes any of the above-mentioned solar cells.

[0090] This application also provides a method for preparing a solar cell, comprising the following steps:

[0091] A first tunneling oxide layer is formed on at least one surface of a silicon substrate.

[0092] A first doped polycrystalline silicon layer, doped with a first dopant and a second dopant, is prepared on the tunneling oxide layer.

[0093] A second tunneling oxide layer is prepared on the first doped polycrystalline silicon layer.

[0094] A second doped polycrystalline silicon layer doped with the first dopant is prepared on the second tunneling oxide layer;

[0095] The doping concentration of the first dopant in the second doped polysilicon layer is greater than the doping concentration of the first dopant in the first doped polysilicon layer.

[0096] The types of the first dopant and the second dopant are as described above.

[0097] The first tunneling oxide layer, the first doped polysilicon layer, the second tunneling oxide layer, and the second doped polysilicon layer can all be prepared using methods known in the art, such as LPCVD or PECVD.

[0098] In the preparation of the first doped polycrystalline silicon layer and the second doped polycrystalline silicon layer, the selection of dopant and the concentration of dopant can be adjusted according to the specific structure of the solar cell.

[0099] Those skilled in the art will understand that the preparation method may further include the preparation steps of a passivation layer, an antireflection layer, and an electrode, all of which can be performed using techniques known in the art.

[0100] In one specific embodiment, the solar cell is any of the above-described solar cells.

[0101] Example

[0102] Example 1

[0103] This embodiment provides the above-described Figure 1 The TOPCon solar cell shown is fabricated using the following steps:

[0104] (b1) Polishing: The original silicon wafer is treated with alkali and additives to remove the damaged layer;

[0105] (b2) Preparation of the first tunneling oxide layer on the front side: A tunneling oxide layer is formed by reacting oxygen generated from the decomposition of N₂O with silicon using a PECVD machine. Preparation of the first doped polycrystalline silicon layer: Silane is decomposed at 400–500°C to generate polycrystalline silicon with a low degree of crystallinity. Precursor gases of the first dopant (BH₃) and the second dopant (NH₃) are simultaneously introduced to form the first doped polycrystalline silicon layer. Preparation of the second tunneling oxide layer: A tunneling oxide layer is formed by reacting oxygen generated from the decomposition of N₂O with polycrystalline silicon. Preparation of the second doped polycrystalline silicon layer: Silane is decomposed at 400–500°C to generate polycrystalline silicon with a low degree of crystallinity. Simultaneously, the first dopant (BH₃) is introduced to form the second doped polycrystalline silicon layer. The concentration of boron in the first doped polycrystalline silicon layer is 1E+18–3E+18 cm⁻¹. -3 The nitrogen doping concentration is 8E+21 to 2E+22 cm⁻¹ -3 The thickness of the first doped polysilicon layer is 20–50 nm, the thickness of the second doped polysilicon layer is 100–150 nm, the thickness of the first tunneling oxide layer is 1–2 nm, and the thickness of the second tunneling oxide layer is 0.1–1 nm.

[0106] (b3) High-temperature crystallization: After (b2), a high-temperature crystallization treatment of 850-900℃ is performed;

[0107] (b4) Removal of borosilicate glass (BSG) and winding plating: Remove the boron diffusion layer and BSG winding plating from the back and surface of the silicon wafer body, and then remove the winding plating using NaOH / KOH alkaline solution and additives;

[0108] (b5) Preparation of the first tunneling oxide layer on the back side: A tunneling oxide layer is generated by reacting oxygen produced by the decomposition of N2O with silicon on a PECVD machine. Preparation of the first doped polycrystalline silicon layer: Silane is decomposed at 400–500°C to generate polycrystalline silicon with a low degree of crystallinity. Precursor gases of the first dopant (PH3) and the second dopant (NH3) are simultaneously introduced to generate the first doped polycrystalline silicon layer. Preparation of the second tunneling oxide layer: A tunneling oxide layer is generated by reacting oxygen produced by the decomposition of N2O with polycrystalline silicon. Preparation of the second doped polycrystalline silicon layer: Silane is decomposed at 400–500°C to generate polycrystalline silicon with a low degree of crystallinity. Simultaneously, the first dopant (PH3) is introduced to generate the second doped polycrystalline silicon layer. The phosphorus doping concentration in the first doped polycrystalline silicon layer is 1E+19–3E+19 cm⁻¹. -3 The nitrogen doping concentration is 8E+21 to 2E+22 cm⁻¹ -3 The thickness of the first doped polysilicon layer is 20–50 nm, the thickness of the second doped polysilicon layer is 100–150 nm, the thickness of the first tunneling oxide layer is 1–2 nm, and the thickness of the second tunneling oxide layer is 0.1–1 nm.

[0109] (b6) High-temperature crystallization, (b5) followed by high-temperature crystallization treatment at 850-900℃;

[0110] (b7) Removal of phosphorus-silicon glass (PSG) and winding plating: Remove the phosphorus diffusion layer and PSG layer that are wound around the back and surface of the silicon wafer body, and then remove the winding plating by NaOH / KOH alkaline solution and additives;

[0111] (b8) Patterning: Local laser grooving is performed on the boron-doped second passivation layer;

[0112] (b9) Texturing: Alkali texturing is performed on the laser-processed area of ​​the silicon wafer;

[0113] (b10) Deposition of passivation and antireflection layers: Passivation and antireflection layers are deposited on the front and back sides of the cell using PECVD. In this embodiment, the passivation layer is aluminum oxide with a thickness of 2-6 nm, and the antireflection layer is a stack of one or more of silicon nitride, silicon oxynitride, and silicon carbide with a thickness of 70-90 nm;

[0114] (b11) Metallization: Print front and back electrodes, perform sintering, light injection, and laser-induced sintering (LECO) processes to obtain a solar cell. In this embodiment, the electrodes are silver electrodes.

[0115] Example 2

[0116] This embodiment provides the above-described Figure 2 The back-contact solar cell shown is described. The method for fabricating the solar cell includes the following steps:

[0117] (b1) Polishing: The original silicon wafer is treated with alkali and additives to remove the damaged layer;

[0118] (b2) Preparation of the initial first tunneling oxide layer in the positive electrode region: The tunneling oxide layer is generated by the decomposition of N2O on the PECVD machine to produce oxygen and react with silicon; Preparation of the initial first doped polycrystalline silicon layer in the positive electrode region: Silane is decomposed at 400-500℃ to produce polycrystalline silicon with a low degree of crystallinity, and the precursor gases of the first dopant (BH3) and the second dopant (NH3) are introduced to generate the first doped polycrystalline silicon layer; Preparation of the initial second tunneling oxide layer in the positive electrode region: The tunneling oxide layer is generated by the decomposition of N2O to produce oxygen and react with polycrystalline silicon; Preparation of the initial second doped polycrystalline silicon layer in the positive electrode region: Silane is decomposed at 400-500℃ to produce polycrystalline silicon with a low degree of crystallinity, and the first dopant (BH3) is introduced to generate the second doped polycrystalline silicon layer.

[0119] A first laser process is used to remove the first tunneling oxide layer, the first doped polysilicon layer, the second tunneling oxide layer, and the second doped polysilicon layer in the positive electrode region, located in both the negative and non-electrode regions. The remaining initial first tunneling oxide layer in the positive electrode region is termed the first tunneling oxide layer, the remaining initial first doped polysilicon layer in the positive electrode region is termed the first doped polysilicon layer, the initial second tunneling oxide layer in the positive electrode region is termed the second tunneling oxide layer, and the remaining initial second doped polysilicon layer in the positive electrode region is termed the second doped polysilicon layer. The boron concentration in the first doped polysilicon layer is between 1E+18 and 3E+18 cm⁻¹. -3 The nitrogen doping concentration is 8E+21 to 2E+22 cm⁻¹ -3 The thickness of the first doped polysilicon layer is 20–50 nm, the thickness of the second doped polysilicon layer is 100–150 nm, the thickness of the first tunneling oxide layer is 1–2 nm, and the thickness of the second tunneling oxide layer is 0.1–1 nm.

[0120] (b3): ​​Forming a first mask layer, the first mask layer being located on the side of the second doped polysilicon layer in the positive electrode region away from the silicon substrate;

[0121] (b4): A first tunneling oxide layer, a first doped polysilicon layer, a second tunneling oxide layer, and a second doped polysilicon layer are sequentially formed covering the first surface and the first mask layer in the initial negative electrode region;

[0122] In a PECVD machine, oxygen generated by the decomposition of N2O reacts with silicon to form the first tunneling oxide layer in the initial negative electrode region. The first doped polycrystalline silicon layer in the initial negative electrode region is prepared by decomposing silane at 400–500°C to generate polycrystalline silicon with a low degree of crystallinity, while simultaneously introducing precursor gases of the first dopant (PH3) and the second dopant (NH3) to generate the first doped polycrystalline silicon layer in the initial negative electrode region. The second tunneling oxide layer in the negative electrode region is prepared by reacting oxygen generated by the decomposition of N2O with polycrystalline silicon to form a tunneling oxide layer. The second doped polycrystalline silicon layer in the negative electrode region is also prepared by decomposing silane at 400–500°C to generate polycrystalline silicon with a low degree of crystallinity, while simultaneously introducing the first dopant (PH3) to generate the second doped polycrystalline silicon layer in the initial negative electrode region.

[0123] (b5) A second laser process is used to remove the first tunneling oxide layer, the first doped polysilicon layer, the second tunneling oxide layer, and the second doped polysilicon layer in the initial negative electrode region located in the positive electrode region and the non-electrode region. The remaining first tunneling oxide layer in the initial negative electrode region on the negative electrode region is the first tunneling oxide layer in the negative electrode region, the remaining first doped polysilicon layer in the initial negative electrode region on the negative electrode region is the first doped polysilicon layer in the negative electrode region, the initial second tunneling oxide layer in the initial negative electrode region on the negative electrode region is the second tunneling oxide layer in the negative electrode region, and the remaining second doped polysilicon layer in the initial negative electrode region on the negative electrode region is the second doped polysilicon layer in the negative electrode region. The phosphorus doping concentration in the first doped polysilicon layer is 1E+19 to 3E+19 cm⁻¹. -3 The nitrogen doping concentration is 8E+21 to 2E+22 cm⁻¹ -3 The thickness of the first doped polysilicon layer is 20–50 nm, the thickness of the second doped polysilicon layer is 100–150 nm, the thickness of the first tunneling oxide layer is 1–2 nm, and the thickness of the second tunneling oxide layer is 0.1–1 nm.

[0124] (b6): Remove the first mask layer. The mask layer can be removed using conventional wet processes or laser processes.

Claims

1. A solar cell, comprising: A silicon substrate having a first surface and a second surface disposed opposite to each other, the first surface and / or the second surface including alternately disposed electrode regions and non-electrode regions; A first tunneling oxide layer, a first doped polysilicon layer, a second tunneling oxide layer, and a second doped polysilicon layer are sequentially stacked on the first surface and / or the second surface. The first doped polysilicon layer is doped with a first dopant and a second dopant, the second doped polysilicon layer is doped with a first dopant, and the doping concentration of the first dopant in the second doped polysilicon layer is greater than the doping concentration of the first dopant in the first doped polysilicon layer. The first dopant is boron or phosphorus, and the second dopant is selected from one or more of carbon, oxygen, nitrogen, and sulfur. When the first dopant is phosphorus, the doping concentration of the first dopant in the first doped polysilicon layer is 1E+19~3E+19 cm⁻¹. -3 The doping concentration of the second dopant is 8E+21~2E+22 cm⁻¹. -3 The doping concentration of the first dopant in the second doped polysilicon layer is 3E+20~6E+20 cm⁻¹. -3 ; When the first dopant is boron, the doping concentration of the first dopant in the first doped polysilicon layer is 1E+18~3E+18 cm⁻¹. -3 The doping concentration of the second dopant is 8E+21~2E+22 cm⁻¹. -3 The doping concentration of the first dopant in the second doped polysilicon layer is 6E+19~9E+19 cm⁻¹. -3 .

2. The solar cell according to claim 1, wherein when the first dopant is phosphorus, the sheet resistance of the passivation contact structure composed of the first tunneling oxide layer, the first doped polycrystalline silicon layer, the second tunneling oxide layer, and the second doped polycrystalline silicon layer is 20-80 Ω / sq. When the first dopant is boron, the sheet resistance of the passivation contact structure composed of the first tunneling oxide layer, the first doped polysilicon layer, the second tunneling oxide layer, and the second doped polysilicon layer is 80-120 Ω / sq.

3. The solar cell according to claim 1, wherein the solar cell comprises: A first tunneling oxide layer, a first doped polysilicon layer, a second tunneling oxide layer, and a second doped polysilicon layer are sequentially stacked on the first surface. The second tunneling oxide layer on the first surface is located in the electrode region, and the second doped polysilicon layer is formed on the second tunneling oxide layer.

4. The solar cell according to claim 3, wherein the solar cell further comprises: A first tunneling oxide layer, a first doped polysilicon layer, a second tunneling oxide layer, and a second doped polysilicon layer are sequentially stacked on the second surface; The doping type of the first dopant on the first surface is different from that of the first dopant on the second surface.

5. The solar cell according to any one of claims 1-4, wherein The electrode region includes alternating positive electrode regions and negative electrode regions, which are isolated by non-electrode regions. In the positive electrode region, the solar cell includes a first tunneling oxide layer, a first doped polycrystalline silicon layer, a second tunneling oxide layer and a second doped polycrystalline silicon layer sequentially stacked on the second surface, wherein the first dopant is boron; In the negative electrode region, the solar cell includes a first tunneling oxide layer, a first doped polycrystalline silicon layer, a second tunneling oxide layer, and a second doped polycrystalline silicon layer sequentially stacked on the second surface, wherein the first dopant is phosphorus.

6. A photovoltaic module comprising the solar cell according to any one of claims 1-5.

7. A method for preparing a solar cell according to any one of claims 1-5, comprising the following steps: A first tunneling oxide layer is formed on at least one surface of a silicon substrate. A first doped polycrystalline silicon layer, doped with a first dopant and a second dopant, is prepared on the tunneling oxide layer. A second tunneling oxide layer is prepared on the first doped polycrystalline silicon layer. A second doped polycrystalline silicon layer doped with the first dopant is prepared on the second tunneling oxide layer; The doping concentration of the first dopant in the second doped polysilicon layer is greater than the doping concentration of the first dopant in the first doped polysilicon layer; The first dopant is boron or phosphorus, and the second dopant is selected from one or more of carbon, oxygen, nitrogen, and sulfur.

8. The preparation method according to claim 7, wherein the preparation methods of the first tunneling oxide layer, the first doped polysilicon layer, the second tunneling oxide layer, and the second doped polysilicon layer are independently selected from LPCVD or PECVD.

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