Back contact solar cell and method of manufacturing the same

Abstract

The application provides a back contact type solar cell and a preparation method thereof. The solar cell comprises a substrate, the substrate has a first back surface and a side wall; a passivation film structure, the passivation film structure comprises a plurality of first film layers and a plurality of second film layers arranged in a stack, the first film layers are located on the first back surface and the side wall, the hydrogen content of any two first film layers is different, part of each second film layer is located on a side of the first film layer away from the first back surface, and the remaining part of each second film layer is located on a side of the first film layer away from the side wall, the material of the first film layer comprises silicon nitride, and the material of the second film layer comprises silicon oxynitride. The above solar cell solves the problem of insufficient passivation of the passivation film layer structure in the prior art.

Description

Technical Field

[0001] This application relates to the field of solar cell technology, and more specifically, to a back-contact solar cell and its fabrication method. Background Technology

[0002] N-type tunnel oxide back contact (TBC) crystalline silicon solar cells have extremely high theoretical photoelectric conversion efficiency. To maximize the utilization of sunlight, current N-type TBC crystalline silicon solar cells use silicon nitride prepared by plasma-enhanced chemical vapor deposition (PECVD) as the first back-side film structure. To reduce manufacturing costs, existing technologies use low-cost non-precious metals instead of precious metals like silver, employing coating techniques to electroplate the non-precious metals onto the cell to form electrodes. To form ohmic contacts, the passivation film on the cell surface needs to be laser ablated before electroplating. The refractive index and thickness of the film must be matched with the laser ablation process; excessively high refractive index and thickness lead to severe parasitic absorption in the film, affecting laser ablation.

[0003] Silicon nitride prepared by PECVD is relatively dense, and it is difficult to achieve a refractive index below 1.95. This results in low reflectivity and low bifaciality on the first back side, as well as severe parasitic absorption, which is detrimental to laser delamination. In addition, during the subsequent sintering process, the Si-H and NH bonds in the silicon nitride film are prone to breakage, leading to the escape of hydrogen atoms, increasing the interface state density, and even forming bubbles or rupturing, thus reducing the passivation effect. Summary of the Invention

[0004] The main objective of this application is to provide a back-contact solar cell and its fabrication method to solve the problem of insufficient passivation in the passivation film structure in the prior art.

[0005] To achieve the above objectives, according to one aspect of this application, a back-contact solar cell is provided, comprising:

[0006] A substrate having a first back surface and sidewalls;

[0007] A passivation film structure includes multiple layers of first film and multiple layers of second film stacked together. The first film layers are located on the first back side and the sidewall. The hydrogen content of any two first film layers is different. A portion of each second film layer is located on the side of the first film layer away from the first back side, and the remaining portion of each second film layer is located on the side of the first film layer away from the sidewall. The material of the first film layer includes silicon nitride, and the material of the second film layer includes silicon oxynitride.

[0008] Optionally, the hydrogen content at a first position in any first film layer is different from that at a second position in any second film layer. The first position and the second position overlap in a first direction or a second direction, where the first direction is perpendicular to the first back surface and the second direction is perpendicular to the sidewall.

[0009] Optionally, the hydrogen content of the multiple layers of the first film located on the first back side decreases in the direction away from the first back side; and / or the hydrogen content of the multiple layers of the first film located on the sidewall decreases in the direction away from the sidewall.

[0010] Optionally, the first film layer closest to the substrate is the first target film layer, and the first film layer closest to the second film layer is the second target film layer, wherein the thickness of the first target film layer is less than the thickness of the second target film layer.

[0011] Optionally, the multilayer second film has different refractive indices. The multilayer second film located on the first film away from the first back surface includes a refractive index that decreases in the direction away from the first back surface. The multilayer second film located on the first film away from the sidewall includes a hydrogen content that decreases in the direction away from the sidewall.

[0012] Optionally, the system further includes a third film layer, a portion of which is located on the side of the second film layer opposite to the first back surface, and the remaining portion of which is located on the side of the second film layer opposite to the sidewall. The material of the third film layer includes silicon oxide.

[0013] Optionally, the system further includes a first dielectric layer and a second dielectric layer stacked together, the first dielectric layer and the second dielectric layer being located between the first film layer and the substrate, wherein a portion of the first dielectric layer is located on one side of the first back surface, the remaining portion of the first dielectric layer is located on one side of the sidewall, the second dielectric layer covers the first dielectric layer, the material of the first dielectric layer includes one or more of silicon oxide and silicon nitride, and the material of the second dielectric layer includes aluminum oxide.

[0014] Optionally, the thickness of the first dielectric layer is 0.3 nm to 0.8 nm.

[0015] According to another aspect of this application, a method for fabricating a back-contact solar cell is provided, the method comprising:

[0016] A substrate is provided, the substrate having a first back surface and sidewalls;

[0017] A passivation film structure is formed on the first back surface and the sidewall. The passivation film structure includes multiple layers of first film and multiple layers of second film stacked together. The first film is located on the first back surface and the sidewall. The hydrogen content of any two layers of the first film is different in the thickness direction. A portion of each layer of the second film is located on the side of the first film away from the first back surface, and the remaining portion of each layer of the second film is located on the side of the first film away from the sidewall. The material of the first film includes silicon nitride, and the material of the second film includes silicon oxynitride.

[0018] Optionally, the step of forming the first film layer includes: forming multiple layers of the first film layer on the first back surface and the sidewall using a first deposition process, wherein the first deposition process uses a gas containing ammonia and silane as raw materials, the flow rate of the ammonia is in a first ratio to the flow rate of the silane, wherein the multiple layers of the first film layer include a third target film layer and a fourth target film layer, the third target film layer is located between the fourth target film layer and the substrate, the hydrogen content of the third target film layer is greater than the hydrogen content of the fourth target film layer, and the first ratio of the first deposition process for forming the third target film layer is greater than the first ratio of the first deposition process for forming the fourth target film layer.

[0019] Optionally, the first ratio satisfies 10 to 15.

[0020] Optionally, the step of forming the second film layer includes: forming multiple layers of the second film layer on the side of the first film layer away from the first back surface and on the side of the first film layer away from the sidewall using a second deposition process. The second deposition process uses a gas containing nitrous oxide and ammonia as raw material, and the flow rate of the nitrous oxide to the flow rate of the ammonia is a second ratio. The multiple layers of the second film layer include a fifth target film layer and a sixth target film layer. The fifth target film layer is located between the sixth target film layer and the substrate. The refractive index of the fifth target film layer is greater than the refractive index of the sixth target film layer. The second ratio of the second deposition process for forming the fifth target film layer is greater than the second ratio of the second deposition process for forming the sixth target film layer.

[0021] Optionally, the second ratio satisfies 5 to 9.

[0022] Optionally, before forming the first film layer, the preparation method further includes: forming a first dielectric layer on the first back surface and the sidewall using a third deposition process, wherein the third deposition process uses a gas containing nitrogen and ozone as raw material; forming a second dielectric layer on the side of the first dielectric layer opposite to the first back surface and on the side of the first dielectric layer opposite to the sidewall using a fourth deposition process, wherein the fourth deposition process uses a gas containing trimethylaluminum as raw material; and after the step of forming the second dielectric layer, forming the first film layer on the side of the second dielectric layer opposite to the first back surface and on the side of the second dielectric layer opposite to the sidewall.

[0023] Applying the technical solution of this application, in a back-contact solar cell, there are multiple first films located on the first back side and sidewall of the substrate, respectively. The hydrogen content of any two first films is different. By making the first film closer to the substrate have a higher hydrogen content, since hydrogen atoms can terminate unpaired electrons on the silicon surface, the dangling bonds on the substrate surface can be effectively passivated, reducing surface recombination centers, thereby improving the surface passivation effect of the solar cell and improving the photoelectric conversion efficiency of the cell. In addition, the first film with high H content can act as a barrier layer, confining hydrogen atoms to a region closer to the substrate, preventing hydrogen atoms from escaping at high temperatures and causing a decrease in cell performance. Furthermore, hydrogen atoms can fill defects on the substrate surface and at the interface. The first film with high H content close to the substrate can reduce interface defects between the substrate and subsequent film layers, thereby improving the reliability of the cell. Furthermore, a second film layer comprising silicon oxynitride is formed outside the first film layer comprising silicon nitride. The refractive index of the silicon oxynitride material can be below 1.95 or even lower. This low refractive index second film layer helps reduce parasitic absorption due to laser reflection, facilitating laser film opening and laying the foundation for subsequent coating and metallization. The second film layer comprising silicon oxynitride can also combine the anti-reflection effect of silicon nitride with the passivation effect of silicon dioxide. Silicon oxynitride has Si-O bonds at the silicon interface that are more stable than Si-H bonds, ensuring the stability of the interface properties. Hydrogen atoms escaping from silicon nitride during sintering can be bound by the second film layer, further enhancing the passivation effect. The aforementioned passivation film structure with enhanced passivation effect is located on the first back side and sidewalls of the substrate, achieving passivation protection for the first back side and sidewalls of the solar cell, further increasing the passivation effect. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0025] Figure 1 This is a cross-sectional structural diagram of a back-contact solar cell according to an embodiment of this application;

[0026] Figure 2 This is a flowchart of a method for fabricating a back-contact solar cell according to an embodiment of this application;

[0027] Figure 3 This is a cross-sectional structural diagram of a back-contact solar cell according to the comparative example of this application.

[0028] The above figures include the following reference numerals:

[0029] 10. Substrate; 101. First back side; 102. Sidewall; 103. Second back side; 105. Front side; 11. Substrate; 12. Tunneling oxide layer; 13. First doped region; 14. Second doped region; 15. Trench; 20. Passivation film structure; 21. First film layer; 211. First target film layer; 212. Second target film layer; 22. Second film layer; 221. Seventh target film layer; 222. Eighth target film layer; 30. Third film layer; 41. First dielectric layer; 42. Second dielectric layer; 43. Third dielectric layer; 44. Fourth dielectric layer; 50. Fourth passivation layer; 60. Fifth passivation layer. Detailed Implementation

[0030] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0031] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0032] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of the invention described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0033] It should be understood that when an element (such as a layer, film, region, or substrate) is described as being "on" another element, the element may be directly on the other element, or there may be an intermediate element present. Furthermore, in the specification and claims, when an element is described as being "connected" to another element, the element may be "directly connected" to the other element, or "connected" to the other element via a third element.

[0034] As described in the background section, in the prior art, the Si-H bonds and NH bonds in the silicon nitride film of the first back-side film layer structure of the back-contact crystalline silicon solar cell are easily broken, leading to the escape of hydrogen atoms, increasing the interface state density, and even forming bubbles or rupturing, thus reducing the passivation effect. In order to solve the above technical problems, the embodiments of this application provide a back-contact solar cell and a method for its preparation.

[0035] According to one aspect of this application, a back-contact solar cell is provided, such as... Figure 1 As shown, it includes: a substrate 10 having a first back surface 101 and a sidewall 102; a passivation film structure 20, the passivation film structure including multiple layers of first film 21 and multiple layers of second film 22 stacked together, the multiple layers of first film 21 being located on the first back surface 101 and the sidewall 102, any two layers of first film 21 having different hydrogen contents, a portion of each layer of second film 22 being located on the side of the first film 21 away from the first back surface 101, and the remaining portion of each layer of second film 22 being located on the side of the first film 21 away from the sidewall 102, the material of the first film 21 including silicon nitride, and the material of the second film 22 including silicon oxynitride.

[0036] For example, the hydrogen content at a first position in any first membrane layer 21 is different from that at a second position in any second membrane layer 22. The first position and the second position overlap in a first direction or a second direction. The first direction is perpendicular to the first back surface, and the second direction is perpendicular to the sidewall.

[0037] For example, the hydrogen content of the multilayer first film layer located on the first back surface 101 decreases in the direction away from the first back surface 101; and / or the hydrogen content of the multilayer first film layer located on the sidewall 102 decreases in the direction away from the sidewall 102.

[0038] In the aforementioned back-contact solar cell, multiple first films are located on the first back side and sidewall of the substrate, respectively. The first film layer closest to the substrate has a high hydrogen content. Since hydrogen atoms can terminate unpaired electrons on the silicon surface, they can effectively passivate dangling bonds on the substrate surface, reduce surface recombination centers, and thus improve the surface passivation effect of the solar cell, while also increasing the photoelectric conversion efficiency. The first film layer with high H content close to the substrate can act as a barrier layer, confining hydrogen atoms to a region closer to the substrate, preventing hydrogen atoms from escaping at high temperatures and causing a decline in cell performance. Furthermore, hydrogen atoms can fill defects on the substrate surface and at the interface. The first film layer with high H content close to the substrate can reduce interface defects between the substrate and subsequent film layers, thereby improving the reliability of the cell. Furthermore, a second film layer comprising silicon oxynitride is formed outside the first film layer comprising silicon nitride. The refractive index of the silicon oxynitride material can be below 1.95 or even lower. This low refractive index second film layer helps reduce parasitic absorption due to laser reflection, facilitating laser film opening and laying the foundation for subsequent coating and metallization. The second film layer comprising silicon oxynitride can also combine the anti-reflection effect of silicon nitride with the passivation effect of silicon dioxide. Silicon oxynitride has Si-O bonds at the silicon interface that are more stable than Si-H bonds, ensuring the stability of the interface properties. Hydrogen atoms escaping from silicon nitride during sintering can be bound by the second film layer, further enhancing the passivation effect. The aforementioned passivation film structure with enhanced passivation effect is located on the first back side and sidewalls of the substrate, achieving passivation protection for the first back side and sidewalls of the solar cell, further increasing the passivation effect.

[0039] In the above embodiments, the refractive index of the first film layer is greater than the refractive index of the second film layer.

[0040] Specifically, silicon nitride has a refractive index of 2.0–2.1. Furthermore, silicon nitride prepared by PECVD is relatively dense, making it difficult to reduce its refractive index. In contrast, the refractive index of silicon oxynitride can vary depending on the degree of oxidation and nitridation, and can be adjusted between 1.7 and 1.9. Forming a second film with a lower refractive index on the outer side of the first film layer away from the substrate reduces the refractive index of the passivation film structure, thereby increasing the reflectivity and bifaciality of the first back side of the back-contact solar cell, which is beneficial for subsequent laser-assisted film cutting.

[0041] In some alternative embodiments, the sum of the thicknesses of the first film layers is greater than the sum of the thicknesses of the second film layers.

[0042] Specifically, the first film layer can be made of silicon oxide, and the second film layer can be made of silicon oxynitride. The thickness of the silicon nitride layer is greater than that of the silicon oxynitride layer. Silicon nitride has a high hydrogen content, which allows it to form good interfacial properties with the substrate. The thicker silicon nitride layer can provide better surface and interface passivation, reduce surface recombination, and improve the photoelectric conversion efficiency of the battery. In the passivation film structure, the first film layer is close to the substrate and far from the laser irradiation surface, so the first film layer mainly affects the back reflection performance. The thicker silicon nitride layer can improve back reflection, reduce light transmission and absorption, and increase light reflection and capture inside the battery, thereby improving the bifaciality and overall photoelectric conversion efficiency of the battery.

[0043] In some alternative implementations, such as Figure 1 As shown, the first film layer 21 closest to the substrate 10 is the first target film layer 211, and the first film layer 21 closest to the second film layer 22 is the second target film layer 212. The thickness of the first target film layer 211 is less than the thickness of the second target film layer 212.

[0044] Specifically, the hydrogen content of the first film layer near the substrate is greater than that of the first film layer near the second film layer. Therefore, the hydrogen content of the first target film layer is greater than that of the second target film layer. The silicon nitride layer with a higher hydrogen content exhibits higher parasitic absorption and lower laser ablation efficiency. Forming a thinner first target film layer with a high hydrogen content near the substrate can improve the passivation effect. Conversely, the second target film layer with a low hydrogen content has higher laser ablation efficiency, making it more suitable for optimizing laser ablation and back reflection. A thicker second target film layer helps reduce material absorption during laser ablation and also optimizes the optical reflection characteristics of the back film structure. Furthermore, during sintering, hydrogen atoms in the high-hydrogen-content first target film layer diffuse into the substrate, improving the passivation effect. However, excessive hydrogen leakage can form unstable hydrogen bond structures, affecting the long-term stability of the battery. A thinner first target film layer can better control hydrogen release and diffusion, avoiding potential problems caused by excessive hydrogen content.

[0045] In some alternative implementations, the refractive index of the first target film layer is lower than that of the second target film layer, which further reduces the reflectivity of the passivation film structure, thereby reducing the difficulty of laser film opening, increasing the passivation effect, and improving the photoelectric conversion efficiency of the back contact solar cell.

[0046] Specifically, the refractive index of the first target film can be 2.0 to 2.1, and its thickness can be 10 to 30 nm; or the refractive index of the first target film can be 2.0 to 2.1, and its thickness can be 80 to 120 nm. This application does not impose any specific limitations. For example, the refractive index of the first target film is 2.05, and its thickness is 20 nm; or the refractive index of the first target film is 2.0, and its thickness is 100 nm.

[0047] In some alternative implementations, such as Figure 1 As shown, the multilayer second film layer 22 is located on the multilayer first film layer 21 away from the first back surface 101 and the sidewall 102. The multilayer second film layer has different refractive indices. The refractive index of the multilayer second film layer located on the first film layer 21 away from the first back surface 101 decreases in the direction away from the first back surface 101. The hydrogen content of the multilayer second film layer located on the first film layer 21 away from the sidewall 102 decreases in the direction away from the sidewall 102.

[0048] Specifically, on the side of the first film layer facing away from the substrate, a multilayer second film layer with a refractive index gradient is formed. The refractive index of the outermost second film layer is lower than that of the inner layers, reducing the reflectivity of the passivation film structure. This simplifies laser delamination, enhances the passivation effect, and improves the photoelectric conversion efficiency of the back-contact solar cell. Furthermore, the multilayer second film layer has a refractive index gradient. Because the refractive indices of the multiple second film layers are slightly different and gradually change, the reflection of incident light gradually decreases in each layer as it passes through them. This reduces reflection losses at the interfaces between different media, and also reduces scattering and absorption within the multilayer second film layer, improving light transmission efficiency and the efficiency and accuracy of laser delamination. Additionally, the stress difference between the second film layers with different refractive indices can be mitigated through the gradient refractive index design, thereby reducing film cracks caused by stress mismatch during sintering or temperature changes.

[0049] In some alternative implementations, such as Figure 1 As shown, the second film layer 22 closest to the substrate 10 is the seventh target film layer 221, and the second film layer 22 furthest from the substrate 10 is the eighth target film layer 222. The thickness of the seventh target film layer 221 is greater than the thickness of the eighth target film layer 222.

[0050] Specifically, the multilayer second film has different refractive indices, and the refractive indices of the multilayer second film decrease along the direction away from the first back surface 101 and along the direction away from the sidewall 102. Therefore, the refractive index of the seventh target film is greater than that of the eighth target film, and the thickness of the seventh target film is greater than that of the eighth target film. This can reduce film damage caused by laser reflection and absorption, ensure the accuracy and success rate of laser film opening, and the silicon oxynitride layers with different thicknesses and refractive indices can better match the stress between the film layers, avoid film cracking or peeling caused by uneven stress, and enhance the stability and reliability of the entire film structure.

[0051] For example, the refractive index of the seventh target film is 1.82 and its thickness is 10 nm, while the refractive index of the first target film is 1.75 and its thickness is 7 nm. This application does not make any specific limitations.

[0052] In some alternative implementations, such as Figure 1 As shown, the back-contact solar cell also includes a third film layer 30, a portion of which is located on the side of the second film layer 22 away from the first back surface 101, and the remaining portion of which is located on the side of the second film layer 22 away from the sidewall 102. The material of the third film layer 30 includes silicon oxide.

[0053] Specifically, a third layer of silicon oxide is formed outside the second film layer. Silicon oxide is an insulating material that can effectively passivate surface defects in the passivation film structure. During sintering, hydrogen atoms in the outer layer of the third film layer diffuse into the substrate. The Si-O bonds in silicon oxide are more stable than the Si-H bonds, and a small number of diffused hydrogen atoms can be bound by the silicon oxynitride layer, forming a stable passivation layer at the interface, further enhancing the bulk passivation effect. Simultaneously, it reduces surface recombination and improves the photoelectric conversion efficiency of the cell. Silicon oxide has a low refractive index (1.55–1.75), giving it good transparency and low reflectivity. Using silicon oxide as the outermost layer of the solar cell reduces light reflection from the backsheet structure and reduces parasitic absorption from laser reflection, which is beneficial for laser delamination and lays the foundation for subsequent metallization coating. Furthermore, the passivation film structure, from the inside out, consists of silicon nitride, silicon oxynitride, and silicon oxide. The gradual decrease in refractive index creates good optical matching, reduces scattering losses during light propagation between film layers, and improves the short-circuit current and bifaciality of the cell. In addition, silicon dioxide, as the outer layer, can withstand the physical and chemical erosion of the external environment, enhancing the overall stability of the backsheet structure.

[0054] For example, the refractive index of the third film layer can be 1.63 and its thickness is 7 nm, but this application does not make any specific limitation.

[0055] In some alternative implementations, such as Figure 1 As shown, the back-contact solar cell also includes a first dielectric layer 41 and a second dielectric layer 42 stacked together. The first dielectric layer 41 and the second dielectric layer 42 are located between the first film layer 21 and the substrate 10. A portion of the first dielectric layer 41 is located on one side of the first back surface 101, and the remaining portion of the first dielectric layer 41 is located on the sidewall 102. The second dielectric layer 42 covers the first dielectric layer 41. The material of the first dielectric layer 41 includes one or more of silicon oxide and silicon nitride, and the material of the second dielectric layer 42 includes aluminum oxide.

[0056] Specifically, a first dielectric layer, comprising silicon oxide, is located close to and in contact with the substrate. This allows charge carriers to tunnel through while providing sufficient charge blocking to reduce surface recombination and enhance the passivation effect of the passivation film structure. Silicon oxide possesses dangling bonds on the substrate surface, reducing the interface state density and decreasing non-radiative recombination of charge carriers on the surface, thereby increasing the open-circuit voltage of the cell and improving the photoelectric conversion efficiency of the solar cell. As the first layer between the substrate and other film layers, the first dielectric layer facilitates the penetration and fixation of hydrogen atoms, further enhancing the hydrogen passivation effect, improving the electrical properties of the silicon surface and interface, and increasing the adhesion between subsequent film layers (such as silicon nitride layers) and the substrate, contributing to the formation of a more robust film stack structure.

[0057] Furthermore, a second dielectric layer, comprising alumina, is located between the first dielectric layer and the first film layer. Alumina possesses excellent surface passivation capabilities, reducing recombination centers on the substrate surface and improving the open-circuit voltage of the battery. Simultaneously, alumina promotes hydrogen passivation. Hydrogen atoms in the first film layer, which has a high hydrogen content, may diffuse inward during sintering. The presence of the second dielectric layer effectively controls and guides the distribution of hydrogen atoms, further optimizing the passivation effect of the surface and interface. As a selective electron transport layer, alumina improves electron transport efficiency while preventing hole passage, effectively enhancing carrier separation and collection efficiency, thereby increasing the battery's short-circuit current and fill factor. The refractive index of the alumina layer is between that of the first dielectric layer and the first film layer, contributing to the formation of a favorable optical gradient, reducing light reflection and scattering, and improving light absorption, thus indirectly improving the battery's photoelectric conversion efficiency.

[0058] In some alternative implementations, the thickness of the first dielectric layer is 0.3 nm to 0.8 nm.

[0059] Specifically, the first dielectric layer can be an ultrathin silicon oxide layer with a thickness of 0.3 nm to 0.8 nm. This allows charge carriers (electrons or holes) to pass through the film layer via quantum tunneling, while effectively blocking unwanted charge flow and maintaining the good electrical performance of the PN junction. Although the first dielectric layer is extremely thin, silicon oxide can passivate dangling bonds on the substrate surface, reduce surface recombination centers, and improve the open-circuit voltage (Voc) of the battery. During subsequent high-temperature processing, the ultrathin first dielectric layer allows hydrogen atoms to penetrate into the substrate while limiting excessive hydrogen escape, optimizing the hydrogen passivation effect and further improving the passivation quality of the surface and interface. Compared to a thick silicon oxide layer, the ultrathin silicon oxide layer absorbs less incident light, reducing parasitic light absorption in the battery and helping to improve light utilization efficiency and short-circuit current. Furthermore, the ultrathin first dielectric layer provides a good foundation for the deposition of subsequent film layers, enhancing the adhesion between the film layers and the substrate and ensuring the integrity and stability of the film stack structure.

[0060] In some alternative embodiments, the aforementioned back-contact solar cell is an N-type TBC crystalline silicon solar cell, such as... Figure 1 As shown, the substrate 10 in this N-type TBC crystalline silicon solar cell has an N-type substrate 11. The substrate 11 has a second back side 103 and a front side 105. The second back side 103 of the substrate 11 has a tunneling oxide layer 12. On the side of the tunneling oxide layer 12 facing away from the substrate 11, there is a first doped region 13 and a second doped region 14. The first doped region 13 and the second doped region 14 have different doping types. The first doped region 13 and the second doped region 14 are isolated by a trench 15, and the trench 15 is in contact with the substrate 11 near the surface of the substrate 11. Figure 1 As shown, the substrate 10 has a first back surface 101 and a sidewall 102. A first dielectric layer 41 and a second dielectric layer 42 are respectively disposed on the first back surface 101 and the sidewall 102 of the substrate 10. A portion of the first dielectric layer 41 is located on one side of the first back surface 101, and the remaining portion of the first dielectric layer 41 is located on one side of the sidewall 102. The second dielectric layer 42 covers the first dielectric layer 41. The material of the first dielectric layer 41 includes one or more of silicon oxide and silicon nitride, and the material of the second dielectric layer 42 includes aluminum oxide. Passivation film structures 20 are respectively provided on the first back side and sidewall of the second dielectric layer 42 substrate. The passivation film structure 20 includes multiple first film layers 21 and multiple second film layers 22 stacked together. The multiple first film layers 21 are located on the first back side 101 and the sidewall 102. Any two first film layers have different hydrogen contents. The hydrogen contents of the multiple first film layers located on the first back side 101 decrease in the direction away from the first back side 101, and the hydrogen contents of the multiple first film layers located on the sidewall 102 decrease in the direction away from the sidewall 102. The multilayer second film layer 22 is located on the side of the first film layer 21 away from the first back surface 101 and on the side away from the sidewall 102. The multilayer second film layer has different refractive indices. The refractive index of the multilayer second film layer located on the first film layer 21 away from the first back surface 101 decreases in the direction away from the first back surface 101. The hydrogen content of the multilayer second film layer located on the first film layer 21 away from the sidewall 102 decreases in the direction away from the sidewall 102. The material of the first film layer 21 includes silicon nitride, and the material of the second film layer 22 includes silicon oxynitride.

[0061] Furthermore, such as Figure 1As shown, in the above-mentioned N-type TBC crystalline silicon solar cell, a third dielectric layer 43 and a fourth dielectric layer 44 are stacked on the front side 105 of the substrate 10. The third dielectric layer 43 is located on the side of the fourth dielectric layer 44 close to the substrate 10. The material of the third dielectric layer 43 includes one or more of silicon oxide and silicon nitride. The material of the fourth dielectric layer 44 includes aluminum oxide. The third dielectric layer 43 is in contact with the first dielectric layer 41, and the fourth dielectric layer 44 is in contact with the second dielectric layer 42. A fourth passivation layer 50 and a fifth passivation layer 60 are stacked on the side of the fourth dielectric layer 44 away from the substrate 10. The fourth passivation layer 50 is located on the side of the fifth passivation layer 60 close to the substrate. The material of the fourth passivation layer 50 includes silicon nitride, and the material of the fifth passivation layer 60 includes silicon oxide.

[0062] In the aforementioned N-type TBC crystalline silicon solar cell, a first dielectric layer, a second dielectric layer, and a passivation film structure are disposed on the sidewalls and the first back side of the cell. The multilayer first film is located on the first back side and sidewalls of the substrate. The first film layer closer to the substrate has a higher hydrogen content. Since hydrogen atoms can terminate unpaired electrons on the silicon surface, they can effectively passivate dangling bonds on the substrate surface, reduce surface recombination centers, and thus improve the surface passivation effect of the solar cell, while simultaneously enhancing the photoelectric conversion efficiency. The high-H content first film layer close to the substrate can act as a barrier layer, confining hydrogen atoms to a region closer to the substrate, preventing hydrogen atom escape at high temperatures that could lead to performance degradation. Furthermore, hydrogen atoms can fill defects on the substrate surface and at the interface. The high-H content first film layer close to the substrate can reduce interface defects between the substrate and subsequent film layers, thereby improving the reliability of the cell. Furthermore, a second film layer composed of silicon oxynitride is formed outside the first film layer composed of silicon nitride. The refractive index of the silicon oxynitride material can be below 1.95 or even lower. Moreover, the multiple second films have different refractive indices. The refractive index of the multiple second films located away from the first back surface of the first film layer decreases in the direction away from the first back surface. The hydrogen content of the multiple second films located away from the sidewall of the first film layer decreases in the direction away from the sidewall. The multiple second films have a refractive index gradient. Since the refractive indices of the multiple second films are slightly different and gradually change, the reflection of incident light gradually decreases in each layer when it passes through the multiple second films, thereby reducing the reflection loss of light at the interface between different media. At the same time, it also reduces the scattering and absorption of light in the multiple second films, improving the light transmission efficiency and the efficiency and accuracy of laser film opening. The low-refractive-index silicon oxynitride (SON) layer helps reduce parasitic absorption caused by laser reflection, facilitating laser film opening and laying the foundation for subsequent coating and metallization. SON films also combine the anti-reflection effects of silicon nitride with the passivation effects of silicon dioxide. SON exhibits stable Si-O bonds at the silicon interface compared to Si-H bonds, ensuring interface stability. Hydrogen atoms escaping from silicon nitride during sintering can be bound by the SON layer, further enhancing the passivation effect. This enhanced passivation film structure is located on the first back side and sidewalls of the substrate, providing passivation protection for the first back side and sidewalls of the solar cell, further increasing the passivation effect.

[0063] According to another aspect of this application, a method for fabricating a back-contact solar cell is provided, for fabricating any type of back-contact solar cell, such as... Figure 2 As shown, the preparation method includes:

[0064] Step S201: Provide a substrate having a first back surface and sidewalls;

[0065] Step S202: A passivation film structure is formed on the first back surface and sidewall. The passivation film structure includes multiple layers of first film and multiple layers of second film stacked together. The multiple layers of first film are located on the first back surface and sidewall. Any two layers of first film have different hydrogen contents. The hydrogen contents of the multiple layers of first film located on the first back surface decrease in the direction away from the first back surface. The hydrogen contents of the multiple layers of first film located on the sidewall decrease in the direction away from the sidewall. A portion of each second film is located on the side of the first film away from the first back surface, and the remaining portion of each second film is located on the side of the first film away from the sidewall. The material of the first film includes silicon nitride, and the material of the second film includes silicon oxynitride.

[0066] Using the fabrication method described in this application embodiment, during the fabrication of a back-contact solar cell, a passivation film structure is formed on the first back side and sidewall of the substrate. The first layer of the passivation film structure is located on the first back side and sidewall of the substrate. The first layer near the substrate has a high hydrogen content. Since hydrogen atoms can terminate unpaired electrons on the silicon surface, they can effectively passivate dangling bonds on the substrate surface, reduce surface recombination centers, thereby improving the surface passivation effect of the solar cell and simultaneously improving the photoelectric conversion efficiency of the cell. The first layer with high H content near the substrate can act as a barrier layer, confining hydrogen atoms to a region closer to the substrate, preventing the escape of hydrogen atoms at high temperatures that could lead to a decrease in cell performance. Furthermore, hydrogen atoms can fill defects on the substrate surface and at the interface. The first layer with high H content near the substrate can reduce interface defects between the substrate and subsequent layers, thereby improving the reliability of the cell. Furthermore, a second film layer comprising silicon oxynitride is formed outside the first film layer comprising silicon nitride. The refractive index of the silicon oxynitride material can be below 1.95 or even lower. This low refractive index second film layer helps reduce parasitic absorption due to laser reflection, facilitating laser film opening and laying the foundation for subsequent coating and metallization. The second film layer comprising silicon oxynitride can also combine the anti-reflection effect of silicon nitride with the passivation effect of silicon dioxide. Silicon oxynitride has Si-O bonds at the silicon interface that are more stable than Si-H bonds, ensuring the stability of the interface properties. Hydrogen atoms escaping from silicon nitride during sintering can be bound by the second film layer, further enhancing the passivation effect. The aforementioned passivation film structure with enhanced passivation effect is located on the first back side and sidewalls of the substrate, achieving passivation protection for the first back side and sidewalls of the solar cell, further increasing the passivation effect.

[0067] Exemplary embodiments of the method for fabricating a back-contact solar cell according to this application will now be described in more detail with reference to the accompanying drawings. However, these exemplary embodiments may be implemented in many different forms and should be construed as being limited to the embodiments set forth herein. It should be understood that these embodiments are provided so that the disclosure of this application is thorough and complete, and that the concept of these exemplary embodiments is fully conveyed to those skilled in the art.

[0068] First, proceed to step S201: provide the substrate.

[0069] Specifically, in the fabrication process of N-type TBC crystalline silicon solar cells, such as Figures 1 to 2 As shown, the provided substrate 10 has an N-type substrate 11, which has a first back side, sidewalls and a front side. The first back side of the substrate 11 has a tunneling oxide layer 12. On the side of the tunneling oxide layer 12 away from the substrate 11, there is a first doped region 13 and a second doped region 14. The materials of the first doped region 13 and the second doped region 14 may include polycrystalline silicon. The first doped region 13 and the second doped region 14 have different doping types. The first doped region 13 and the second doped region 14 are isolated from each other by a trench 15, and the trench 15 is in contact with the substrate 11 near the surface of the substrate 11.

[0070] The substrate fabrication process may include: First, using low-pressure chemical vapor deposition (LPCVD) to thermally oxidize an N-type silicon substrate, forming a tunneling oxide layer and a polycrystalline silicon layer on the first back side of the substrate; then, using a high-temperature diffusion furnace to perform boron and phosphorus diffusion in the polycrystalline silicon layer to obtain a first doped region and a second doped region, wherein the first doped region is a P-type polycrystalline silicon region and the second doped region is an N-type polycrystalline silicon region; then, using laser and wet isolation, a trench is formed between the first doped region and the second doped region to isolate the P-type polycrystalline silicon region and the N-type polycrystalline silicon region.

[0071] In some alternative embodiments, after the substrate is provided, step S2011 is performed: a first dielectric layer and a second dielectric layer are sequentially formed on the first back side and sidewall of the substrate.

[0072] Specifically, the steps of forming the first dielectric layer and the second dielectric layer may include: first, forming the first dielectric layer on the first back surface and sidewall using a third deposition process, wherein the third deposition process uses a gas containing nitrogen and ozone as raw material; then, forming the second dielectric layer on the side of the first dielectric layer opposite to the first back surface and on the side of the first dielectric layer opposite to the sidewall using a fourth deposition process, wherein the fourth deposition process uses a gas containing trimethylaluminum as raw material; then, after the step of forming the second dielectric layer, forming a first film layer on the side of the second dielectric layer opposite to the first back surface and on the side of the second dielectric layer opposite to the sidewall.

[0073] The third and fourth deposition processes both include atomic layer deposition (ALD) processes, which are not specifically limited in this application.

[0074] In some optional embodiments, the specific steps for forming the first dielectric layer using the third deposition process include: first, placing the substrate in an ALD cavity, evacuating the cavity, and setting the ozone generator to 5%–100% power; then, under reaction conditions of 50–450°C and reaction pressure of 0.3–0.8 mbar, introducing a mixture of high-purity nitrogen and ozone into the cavity for 1–300 s, with the ozone-to-gas flow ratio being 5%–50%; then, purging the cavity with high-purity nitrogen for 1–300 s; repeating the gas introduction and purging process 1–10 times to complete the preparation of the first dielectric layer, wherein the thickness of the first dielectric layer is approximately 0.3–0.8 nm.

[0075] The specific steps for forming the second dielectric layer using the fourth deposition process may include: under reaction temperatures of 50–450°C and reaction pressures of 0.6–1 mbar, alternatingly introducing trimethylaluminum and H2O vapor into the ALD cavity. Specifically, trimethylaluminum is introduced first for 1–20 s, followed by N2 purging for 1–10 s, then H2O vapor is introduced for 1–30 s, followed by N2 purging for 1–10 s. This alternating introduction of trimethylaluminum and H2O vapor is repeated 25–45 times to complete the preparation of the second dielectric layer, wherein the thickness of the second dielectric layer is approximately 3–10 nm.

[0076] Then, step S202 is performed: a passivation film structure is formed.

[0077] Specifically, the step of forming the first film layer may include: forming multiple layers of the first film layer on the first back side and sidewall using a first deposition process multiple times. The first deposition process uses a gas containing ammonia and silane as raw materials, with the flow rate of ammonia to the flow rate of silane being a first ratio. The multiple layers of the first film layer include a third target film layer and a fourth target film layer. The hydrogen content of the third target film layer is greater than that of the fourth target film layer. The first ratio of the first deposition process for forming the third target film layer is greater than the first ratio of the first deposition process for forming the fourth target film layer. For example, the first ratio is 10 to 15.

[0078] It should be noted that in some embodiments, the third target film layer and the first target film layer refer to the same film layer, and the fourth target film layer and the second target film layer refer to the same film layer.

[0079] Specifically, the steps for forming the first film layer may include: firstly, forming multiple layers of the first film layer on the first back side and sidewall using a first deposition process multiple times. The first deposition process uses a gas containing ammonia and silane as raw materials, and the flow rate of ammonia to the flow rate of silane is a first ratio. The multiple layers of the first film layer include a third target film layer and a fourth target film layer. The hydrogen content of the third target film layer is greater than the hydrogen content of the fourth target film layer. The first ratio of the first deposition process for forming the third target film layer is greater than the first ratio of the first deposition process for forming the fourth target film layer.

[0080] The first deposition process may include PECVD process, but this application does not make specific limitations.

[0081] In some optional embodiments, the multilayer first film layer includes a third target film layer and a fourth target film layer, wherein the hydrogen content of the third target film layer is greater than that of the fourth target film layer. The steps of forming the first film layer using a PECVD process include: firstly, forming the third target film layer on the second dielectric layer using a PECVD process. In this PECVD process, a gas containing ammonia and silane is used as the feed gas, the gas flow ratio of ammonia to silane is (8-10):1, the flow rate of ammonia is 8000-15000 sccm, the flow rate of silane is 1000-1500 sccm, the reaction temperature is 450℃-550℃, the reaction time is 150-250 s, and the reaction pressure is 1000-2000 m³ / s. Torr, duty cycle (2-5):(60-70), RF power 1000-20000W; then, using PECVD process, a fourth target film layer is formed on the third target film layer. In this PECVD process, a gas containing ammonia and silane is used as the raw material gas, the gas flow ratio of ammonia to silane is (10-15):1, the flow rate of ammonia is 10000-22500 sccm, the flow rate of silane is 1000-1500 sccm, the reaction temperature is 450℃-550℃, the reaction time is 600-800s, the reaction pressure is 1000-2000mTorr, duty cycle (2-5):(60-70), RF power 20000-30000W.

[0082] In some optional embodiments, the multilayer second film is located on the side of the first film away from the first back surface and on the side away from the sidewall. The multilayer second film has different refractive indices. The refractive index of the multilayer second film located on the first film away from the first back surface decreases in the direction away from the first back surface, and the hydrogen content of the multilayer second film located on the first film away from the sidewall decreases in the direction away from the sidewall.

[0083] Specifically, the step of forming the second film layer may include: forming multiple layers of the second film layer on the side of the first film layer opposite to the first back surface and on the side of the first film layer opposite to the sidewall using a second deposition process. The second deposition process uses a gas containing nitrous oxide and ammonia as raw materials, and the flow rate of nitrous oxide to the flow rate of ammonia is a second ratio. The multiple layers of the second film layer include a fifth target film layer and a sixth target film layer. The refractive index of the fifth target film layer is greater than the refractive index of the sixth target film layer. The second ratio of the second deposition process for forming the fifth target film layer is greater than the second ratio of the second deposition process for forming the sixth target film layer. For example, the second ratio is 5 to 9.

[0084] The second deposition process may include PECVD process, which is not specifically limited in this application.

[0085] It should be noted that in some embodiments, the fifth target film layer and the seventh target film layer are the same second film layer, and the sixth target film layer and the eighth target film layer are the same second film layer.

[0086] In some optional embodiments, the multilayer first film layer includes a fifth target film layer and a sixth target film layer, wherein the refractive index of the fifth target film layer is greater than that of the fourth target film layer. The step of forming the second film layer using a PECVD process includes: firstly, forming the fifth target film layer on the fourth target film layer using a PECVD process. In this PECVD process, a gas containing nitrous oxide, ammonia, and silane is used as the feed gas. The flow rate ratio of nitrous oxide, ammonia, and silane is (8-10):(8-10):1. The flow rate of nitrous oxide is 8000-15000 sccm, the flow rate of ammonia is 8000-15000 sccm, the flow rate of silane is 1000-1500 sccm, the reaction temperature is 450℃-550℃, the reaction time is 30-80 s, and the reaction pressure is 1000-3000 sccm. mTorr, duty cycle (2-5):(100-120), RF power 1000-25000W; then, using PECVD process, a sixth target film layer is formed on the fifth target film layer. In this PECVD process, a gas containing nitrous oxide, ammonia and silane is used as the raw material gas. The gas flow ratio of nitrous oxide, ammonia and silane is (13-19):(1-6):1. The flow rate of nitrous oxide is 6000-10000 sccm, the flow rate of ammonia is 1000-2000 sccm, the flow rate of silane is 300-800 sccm, the reaction temperature is 450℃-550℃, the reaction time is 20-60s, the reaction pressure is 1000-3000 mTorr, the duty cycle (2-5):(100-120), and the RF power is 20000-30000W.

[0087] In some alternative embodiments, after forming the second film layer, step S2021 is further included: forming a third film layer.

[0088] Specifically, the step of forming the third film layer may include: forming the third film layer on the side of the second film layer away from the first back surface and on the side of the second film layer away from the sidewall using a fifth deposition process. The second deposition process uses a gas containing nitrous oxide as raw material. The fifth deposition process may include a PECVD process, which is not specifically limited in this application.

[0089] In some optional embodiments, the step of forming the third film layer using a PECVD process includes: forming the third film layer on the second film layer using a PECVD process, wherein a gas containing nitrous oxide and silane is used as the feed gas, the gas flow rate ratio of nitrous oxide to silane is (11-15):1, the flow rate of nitrous oxide is 7000-8500 sccm, the flow rate of silane is 400-800 sccm, the reaction temperature is 450°C-550°C, the reaction time is 30-80 s, the reaction pressure is 1000-3000 mTorr, the duty cycle is (2-5):(100-120), and the radio frequency power is 1000-25000 W.

[0090] The preparation method of the back-contact solar cell provided in this application will be further described below with reference to embodiments and comparative examples.

[0091] Example

[0092] The method for fabricating a tunneling oxide layer back contact crystalline silicon solar cell provided in this embodiment includes the following steps:

[0093] Step S701: Provide an N-type substrate;

[0094] Step S702: A tunneling oxide layer is formed on the second back side of the substrate using a thermal oxidation process, and a polycrystalline silicon layer is formed on the tunneling oxide layer using an LPCVD process.

[0095] Step S703: Boron diffusion and phosphorus diffusion are performed in the polycrystalline silicon layer using a high-temperature diffusion furnace to obtain the first P-type doped region and the second N-type doped region;

[0096] Step S704: A trench is formed between the first doped region and the second doped region using laser and wet isolation methods. The trench penetrates the polysilicon layer and the tunnel oxide layer to obtain the substrate.

[0097] Step S705: Place the above substrate in the ALD cavity, evacuate the cavity, and set the ozone generator to 50% power so that the temperature of the ALD cavity is 400°C and the pressure is 0.8 mbar.

[0098] Step S706: Introduce a mixture of high-purity nitrogen and ozone into the ALD cavity. The introduce time of the mixture is 30 seconds, the ozone flow rate is 20 sccm, and the flow rate ratio of ozone to the mixture is 10%.

[0099] Step S707: Purge the cavity with high-purity nitrogen for 10 seconds;

[0100] Step S708: Repeat steps S706 and S707 twice to complete the fabrication of the first dielectric layer. The thickness of the first dielectric layer is 0.5 nm. The first dielectric layer is located on the first back side, sidewall and front side of the substrate.

[0101] Step S709: Introduce trimethylaluminum into the ALD cavity at a flow rate of 20 sccm for 10 seconds, then purge with N2 for 10 seconds.

[0102] Step S710: Introduce H2O steam into the ALD cavity at a flow rate of 20 sccm for 10 seconds, then purge with N2 for 10 seconds.

[0103] Step S711: Repeat steps S709 and S710 25 times to complete the fabrication of the second dielectric layer. The thickness of the second dielectric layer is 5nm. The second dielectric layer is located on the side of the first dielectric layer away from the first back side, the side of the first dielectric layer away from the sidewall, and the side away from the front side.

[0104] Step S712: Place the above substrate in the PECVD chamber and evacuate the chamber to make the temperature of the PECVD chamber 500℃ and the pressure 2000mTorr.

[0105] Step S713: Introduce a mixture of ammonia and silane into the PECVD cavity for 200 seconds. The ammonia flow rate to silane flow rate ratio is 10:1, the silane flow rate is 1000 sccm, the ammonia flow rate is 10000 sccm, the duty cycle is 5:70, and the radio frequency power is 20000W to form a third target film layer. The third target film layer is located on the side of the second dielectric layer away from the first back surface and the side of the second dielectric layer away from the sidewall.

[0106] Step S714: A mixture of ammonia and silane is introduced into the PECVD cavity for 200 seconds. The ammonia flow rate to silane flow rate ratio is 15:1, the silane flow rate is 1000 sccm, the ammonia flow rate is 15000 sccm, the duty cycle is 5:70, and the radio frequency power is 20000W. A fourth target film is obtained, wherein the fourth target film is located on the side of the third target film away from the first back side and on the side of the third target film away from the sidewall.

[0107] Step S715: A mixture of nitrous oxide, ammonia, and silane is introduced into the PECVD cavity for 60 seconds. The flow rate of nitrous oxide, ammonia, and silane is in the ratio of 9:1:1. The flow rate of nitrous oxide is 8100 sccm, the flow rate of ammonia is 8100 sccm, the flow rate of silane is 900 sccm, the duty cycle is 5:70 (the ratio of RF power supply on / off), and the RF power is 20000W. The fifth target film layer is obtained. The fifth target film layer is located on the side of the first film layer away from the first back surface and on the side of the first film layer away from the sidewall.

[0108] Step S716: A mixture of nitrous oxide, ammonia, and silane is introduced into the PECVD cavity for 40 seconds. The flow rate of nitrous oxide, ammonia, and silane is in the ratio of 16:3:1. The flow rate of nitrous oxide is 8000 sccm, the flow rate of ammonia is 1500 sccm, the flow rate of silane is 500 sccm, the duty cycle is 5:110, and the radio frequency power is 20000W. The sixth target film layer is obtained. The sixth target film layer is located on the side of the fifth target film layer away from the first back side and on the side of the third target film layer away from the sidewall.

[0109] Step S717: A mixture of nitrous oxide and silane is introduced into the PECVD cavity for 55 seconds. The ratio of nitrous oxide flow rate, ammonia flow rate and silane flow rate is 13:1. The nitrous oxide flow rate is 7800 sccm, the silane flow rate is 600 sccm, the duty cycle is 5:110, and the radio frequency power is 20000W. A third film layer is obtained. The third film layer is located on the side of the second film layer away from the first back side and on the side of the second film layer away from the sidewall.

[0110] Step S718: Introduce a mixture of ammonia and silane into the PECVD chamber for 200 seconds. The ammonia flow rate to silane flow rate ratio is 15:1, the silane flow rate is 1000 sccm, the ammonia flow rate is 10000 sccm, the duty cycle is 5:70, and the RF power is 20000W. A fourth passivation layer is formed on the front side of the substrate.

[0111] Step S719: A mixture of nitrous oxide and silane is introduced into the PECVD chamber for 55 seconds. The flow rate ratio of nitrous oxide, ammonia, and silane is 13:1. The nitrous oxide flow rate is 7800 sccm, and the silane flow rate is 600 sccm. The duty cycle is 5:110, and the radio frequency power is 20000W. A fifth passivation layer is formed on the fourth passivation layer, resulting in the following... Figure 1 The back-contact crystalline silicon solar cell shown.

[0112] Specifically, such as Figure 1As shown, the back-contact solar cell includes a substrate 11, which has a second back side 103 and a front side 105. The second back side 103 of the substrate 11 has a tunneling oxide layer 12. On the side of the tunneling oxide layer 12 facing away from the substrate 11, there is a first doped region 13 and a second doped region 14. The first doped region 13 and the second doped region 14 have different doping types. The substrate 11, the tunneling oxide layer 12, the first doped region 13 and the second doped region 14 constitute a substrate 10. The first doped region 13 and the second doped region 14 are isolated from each other by a trench 15. The trench 15 is in contact with the substrate 11 near the surface of the substrate 11. The substrate 10 has a first back surface 101 and a sidewall 102. A first dielectric layer 41 and a second dielectric layer 42 are respectively disposed on the first back surface 101 and the sidewall 102 of the substrate 10. A portion of the first dielectric layer 41 is located on one side of the first back surface 101, and the remaining portion of the first dielectric layer 41 is located on one side of the sidewall 102. The second dielectric layer 42 covers the first dielectric layer 41. The material of the first dielectric layer 41 includes one or more of silicon oxide and silicon nitride, and the material of the second dielectric layer 42 includes aluminum oxide. Passivation film structures 20 are respectively disposed on the first back side and sidewall of the second dielectric layer 42 substrate. The passivation film structure 20 includes multiple layers of first film 21 and multiple layers of second film 22 stacked together. The multiple layers of first film 21 are located on the first back side 101 and the sidewall 102. Any two layers of first film have different hydrogen contents. The hydrogen contents of the multiple layers of first film located on the first back side 101 decrease in the direction away from the first back side 101, and the hydrogen contents of the multiple layers of first film located on the sidewall 102 decrease in the direction away from the sidewall 102. The refractive index of the multilayer second film layer 22 is located on the side of the first film layer 21 away from the first back surface 101 and the sidewall 102. The multilayer second film layer has different refractive indices. The refractive index of the multilayer second film layer located on the first film layer 21 away from the first back surface 101 decreases in the direction away from the first back surface 101. The hydrogen content of the multilayer second film layer located on the first film layer 21 away from the sidewall 102 decreases in the direction away from the sidewall 102. The material of the first film layer 21 includes silicon nitride, and the material of the second film layer 22 includes silicon oxynitride.

[0113] Furthermore, such as Figure 1As shown, in the aforementioned back-contact solar cell, a third dielectric layer 43 and a fourth dielectric layer 44 are stacked on the front side 105 of the substrate 10. The third dielectric layer 43 is located on the side of the fourth dielectric layer 44 closest to the substrate 10. The material of the third dielectric layer 43 includes one or more of silicon oxide and silicon nitride. The material of the fourth dielectric layer 44 includes aluminum oxide. The third dielectric layer 43 is in contact with the first dielectric layer 41, and the fourth dielectric layer 44 is in contact with the second dielectric layer 42. A fourth passivation layer 50 and a fifth passivation layer 60 are stacked on the side of the fourth dielectric layer 44 away from the substrate 10. The fourth passivation layer 50 is located on the side of the fifth passivation layer 60 closest to the substrate. The material of the fourth passivation layer 50 includes silicon nitride, and the material of the fifth passivation layer 60 includes silicon oxide.

[0114] Comparative Example

[0115] The difference between this comparative example and the embodiment is that the preparation process of the comparative example does not include steps S715 to S717, resulting in the following... Figure 3 The back-contact crystalline silicon solar cell shown.

[0116] Specifically, such as Figure 3 As shown, the back-contact solar cell fabricated in the comparative example includes a substrate 11. The substrate 11 has a second back side 103 and a front side 105. The second back side 103 of the substrate 11 has a tunneling oxide layer 12. On the side of the tunneling oxide layer 12 facing away from the substrate 11, there is a first doped region 13 and a second doped region 14. The first doped region 13 and the second doped region 14 have different doping types. The substrate 11, the tunneling oxide layer 12, the first doped region 13 and the second doped region 14 constitute a substrate 10. The first doped region 13 and the second doped region 14 are connected by a trench 15. The trench 15 is isolated and contacts the surface of the substrate 11. The substrate 10 has a first back surface 101 and a sidewall 102. A first dielectric layer 41 and a second dielectric layer 42 are respectively disposed on the first back surface 101 and the sidewall 102 of the substrate 10. A portion of the first dielectric layer 41 is located on one side of the first back surface 101, and the remaining portion of the first dielectric layer 41 is located on one side of the sidewall 102. The second dielectric layer 42 covers the first dielectric layer 41. The material of the first dielectric layer 41 includes one or more of silicon oxide and silicon nitride, and the material of the second dielectric layer 42 includes aluminum oxide. Passivation film structures 20 are respectively provided on the first back side and sidewall of the second dielectric layer 42 substrate. The passivation film structure 20 includes multiple first film layers 21 and multiple second film layers 22 stacked together. The multiple first film layers 21 are located on the first back side 101 and the sidewall 102. Any two first film layers 21 have different hydrogen contents. The hydrogen content of the multiple first film layers located on the first back side 101 decreases in the direction away from the first back side 101, and the hydrogen content of the multiple first film layers located on the sidewall 102 decreases in the direction away from the sidewall 102.

[0117] Furthermore, such as Figure 3 As shown, in the aforementioned back-contact solar cell, a third dielectric layer 43 and a fourth dielectric layer 44 are stacked on the front side 105 of the substrate 10. The third dielectric layer 43 is located on the side of the fourth dielectric layer 44 closest to the substrate 10. The material of the third dielectric layer 43 includes one or more of silicon oxide and silicon nitride. The material of the fourth dielectric layer 44 includes aluminum oxide. The third dielectric layer 43 is in contact with the first dielectric layer 41, and the fourth dielectric layer 44 is in contact with the second dielectric layer 42. A fourth passivation layer 50 and a fifth passivation layer 60 are stacked on the side of the fourth dielectric layer 44 away from the substrate 10. The fourth passivation layer 50 is located on the side of the fifth passivation layer 60 closest to the substrate. The material of the fourth passivation layer 50 includes silicon nitride, and the material of the fifth passivation layer 60 includes silicon oxide.

[0118] The difference between the back-contact solar cell prepared in the comparative example and the back-contact solar cell prepared in the embodiment is that the back-contact solar cell prepared in the comparative example does not have a second film layer and a third film layer.

[0119] Experimental data:

[0120] Using a non-contact PL camera, the battery efficiency was fitted by testing the PL brightness values ​​(the magnitude of the PL brightness value represents the passivation quality) under conditions of 1 sun and 0.1 sun. The results are shown in the table below.

[0121]

[0122] The above are merely preferred embodiments of this application and are not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A back-contact solar cell, characterized in that, include: The substrate has a first back surface and sidewalls, and the substrate has a substrate, a tunneling oxide layer, a first doped region and a second doped region; A passivation film structure includes multiple layers of first film and multiple layers of second film stacked together. The first film layers are located on the first back surface and the sidewall. The hydrogen content of any two first film layers is different. The hydrogen content of the first film layer closer to the substrate is greater than the hydrogen content of the first film layer closer to the second film layer. A portion of each second film layer is located on the side of the first film layer away from the first back surface, and the remaining portion of each second film layer is located on the side of the first film layer away from the sidewall. The material of the first film layer includes silicon nitride, and the material of the second film layer includes silicon oxynitride.

2. The back-contact solar cell according to claim 1, characterized in that, The hydrogen content at a first position in any first film layer is different from that at a second position in any second film layer. The first position and the second position overlap in a first direction or a second direction. The first direction is perpendicular to the first back surface, and the second direction is perpendicular to the sidewall.

3. The back-contact solar cell according to claim 1, characterized in that, The hydrogen content of the multiple layers of the first film located on the first back side decreases in the direction away from the first back side; and / or The hydrogen content of the multiple first membrane layers located on the sidewall decreases in the direction away from the sidewall.

4. The back-contact solar cell according to claim 1, characterized in that, The first film layer closest to the substrate is the first target film layer, and the first film layer closest to the second film layer is the second target film layer. The thickness of the first target film layer is less than the thickness of the second target film layer.

5. The back-contact solar cell according to claim 1, characterized in that, The multilayer second film has different refractive indices. The multilayer second film located away from the first back surface of the first film includes a refractive index that decreases in the direction away from the first back surface. The multilayer second film located away from the sidewall of the first film includes a hydrogen content that decreases in the direction away from the sidewall.

6. The back-contact solar cell according to claim 1, characterized in that, It also includes a third film layer, a portion of which is located on the side of the second film layer away from the first back surface, and the remaining portion of which is located on the side of the second film layer away from the sidewall. The material of the third film layer includes silicon oxide.

7. The back-contact solar cell according to claim 1, characterized in that, It also includes a first dielectric layer and a second dielectric layer stacked together, the first dielectric layer and the second dielectric layer being located between the first film layer and the substrate, wherein a portion of the first dielectric layer is located on one side of the first back surface, the remaining portion of the first dielectric layer is located on one side of the sidewall, the second dielectric layer covers the first dielectric layer, the material of the first dielectric layer includes one or more of silicon oxide and silicon nitride, and the material of the second dielectric layer includes aluminum oxide.

8. The back-contact solar cell according to claim 7, characterized in that, The thickness of the first dielectric layer is 0.3 nm to 0.8 nm.

9. A method for fabricating a back-contact solar cell, characterized in that, The method for preparing the back-contact solar cell according to any one of claims 1 to 8 comprises: A substrate is provided having a first back surface and sidewalls, and the substrate having a substrate, a tunneling oxide layer, a first doped region, and a second doped region; A passivation film structure is formed on the first back surface and the sidewall. The passivation film structure includes multiple layers of first film and multiple layers of second film stacked together. The first film layers are located on the first back surface and the sidewall. Any two layers of the first film have different hydrogen contents in the thickness direction. The hydrogen content of the first film layer closer to the substrate is greater than the hydrogen content of the first film layer closer to the second film layer. A portion of each second film layer is located on the side of the first film layer away from the first back surface, and the remaining portion of each second film layer is located on the side of the first film layer away from the sidewall. The material of the first film layer includes silicon nitride, and the material of the second film layer includes silicon oxynitride.

10. The preparation method according to claim 9, characterized in that, The steps for forming the first film layer include: Multiple layers of the first film are formed on the first back side and the sidewall using a first deposition process. The first deposition process uses a gas containing ammonia and silane as raw materials, and the flow rate of the ammonia is in a first ratio to the flow rate of the silane. The multiple layers of the first film include a third target film and a fourth target film. The third target film is located between the fourth target film and the substrate. The hydrogen content of the third target film is greater than the hydrogen content of the fourth target film. The first ratio of the first deposition process for forming the third target film is greater than the first ratio of the first deposition process for forming the fourth target film.

11. The preparation method according to claim 10, characterized in that, The first ratio satisfies 10 to 15.

12. The preparation method according to claim 10, characterized in that, The steps for forming the second film layer include: Multiple second deposition processes are used to form a multilayer second film layer on the side of the first film layer opposite to the first back surface and on the side of the first film layer opposite to the sidewall. The second deposition process uses a gas containing nitrous oxide and ammonia as raw materials, and the flow rate of the nitrous oxide to the flow rate of the ammonia is a second ratio. The multilayer second film layer includes a fifth target film layer and a sixth target film layer. The fifth target film layer is located between the sixth target film layer and the substrate. The refractive index of the fifth target film layer is greater than the refractive index of the sixth target film layer. The second ratio of the second deposition process for forming the fifth target film layer is greater than the second ratio of the second deposition process for forming the sixth target film layer.

13. The preparation method according to claim 12, characterized in that, The second ratio satisfies 5 to 9.

14. The preparation method according to claim 9, characterized in that, Before forming the first film layer, the preparation method further includes: A first dielectric layer is formed on the first back surface and the sidewall using a third deposition process, wherein the third deposition process uses a gas containing nitrogen and ozone as raw material; A second dielectric layer is formed on the side of the first dielectric layer away from the first back surface and on the side of the first dielectric layer away from the sidewall using a fourth deposition process, wherein the fourth deposition process uses a gas containing trimethylaluminum as a raw material. After the step of forming the second dielectric layer, the first film layer is formed on the side of the second dielectric layer opposite to the first back surface and on the side of the second dielectric layer opposite to the sidewall.

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