Back contact solar cells, battery modules and photovoltaic systems

Abstract

This utility model relates to the field of solar cell technology, specifically disclosing a back-contact solar cell, a cell module, and a photovoltaic system. The back-contact solar cell includes: a silicon substrate having a first surface, a second surface, and a side surface, wherein the first surface and the second surface are disposed opposite to each other, and the side surface is connected to the first surface and the second surface respectively; an anti-reflection passivation composite layer including a first portion disposed on the first surface and a second portion extending from the edge of the first portion to the side surface; the anti-reflection passivation composite layer includes an ultrathin silicon oxide layer, an aluminum oxide layer, a silicon nitride layer, a silicon oxynitride layer, and a silicon oxide layer sequentially disposed along a direction away from the silicon substrate, wherein the refractive index of the silicon nitride layer, the silicon oxynitride layer, and the silicon oxide layer decreases sequentially. This utility model can effectively solve the influence of defects on the side surface of the silicon substrate, reduce parasitic absorption at the edge of the cell, and effectively improve the anti-reflection and passivation effect of the anti-reflection passivation composite layer through the interaction of multiple material layers, and improve stress problems, thereby effectively improving the overall conversion efficiency of the cell and ensuring the long-term reliability of the cell.

Description

Technical Field

[0001] This utility model relates to the field of solar cell technology, and in particular to a back-contact solar cell, a battery module and a photovoltaic system. Background Technology

[0002] Back-contact solar cells are a new type of solar cell structure. Unlike traditional solar cells that distribute the positive and negative electrodes on both sides of the cell, back-contact solar cells integrate both the positive and negative electrodes on the back of the cell. This eliminates electrode obstruction on the front of the cell, thereby increasing light absorption and effectively improving photoelectric conversion efficiency.

[0003] To maximize the use of sunlight, existing back-contact solar cells typically have a front composite film deposited on the front side. This composite film, for example, consists of multiple layers with different refractive indices, to enhance passivation and reduce reflection loss. However, current technology still has limitations:

[0004] On the one hand, silicon wafers have numerous defects such as dangling bonds on their sidewalls. These defects make the edges of the silicon wafers high-incidence areas for carrier recombination, increasing parasitic absorption. Current back-contact batteries often focus on improving the passivation and anti-reflection effects on the front side of the battery, while ignoring the impact of defects on the silicon wafer sidewalls, resulting in limited battery conversion efficiency of existing back-contact batteries. On the other hand, the poor matching degree of material properties such as thermal expansion coefficient and light characteristics between adjacent layers of the existing front film layer leads to poor overall passivation and reflection effects of the crystalline silicon battery front film layer, and it is prone to stress problems. The overall mechanical stability and adhesion of the film layer are poor, affecting the battery's conversion efficiency and reliability. Utility Model Content

[0005] The purpose of this invention is to provide a back-contact solar cell, battery module, and photovoltaic system in light of the existing technology.

[0006] This invention effectively addresses the impact of defects on the sides of the silicon substrate by setting an optimized anti-reflection passivation composite layer on the first surface and side surfaces of the silicon substrate. This reduces parasitic absorption at the battery edge and, through the cooperation between multiple material layers, effectively enhances the anti-reflection and passivation effects of the anti-reflection passivation composite layer and improves stress issues. As a result, the overall conversion efficiency of the battery is effectively improved, and the long-term reliability of the battery is ensured, thus enhancing the overall performance of the battery.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] First, this utility model provides a back-contact solar cell, comprising:

[0009] A silicon substrate has a first surface, a second surface, and side surfaces, wherein the first surface and the second surface are disposed opposite to each other, and the side surfaces are respectively connected to the first surface and the second surface;

[0010] The anti-reflection passivation composite layer includes a first portion disposed on the first surface and a second portion extending from the edge of the first portion to the outside of the side surface;

[0011] The anti-reflection passivation composite layer includes an ultrathin silicon oxide layer, an aluminum oxide layer, a silicon nitride layer, a silicon oxynitride layer, and a silicon oxide layer arranged sequentially in a direction away from the silicon substrate, wherein the refractive indices of the silicon nitride layer, the silicon oxynitride layer, and the silicon oxide layer decrease sequentially.

[0012] In some embodiments, the silicon nitride layer includes a first sublayer, a second sublayer, a third sublayer, and a fourth sublayer disposed sequentially in a direction away from the silicon substrate, wherein the refractive indices of the first sublayer, the second sublayer, the third sublayer, and the fourth sublayer decrease sequentially, and each sublayer has the same thickness.

[0013] In some embodiments, the refractive index difference between the first sublayer and the fourth sublayer is greater than or equal to 0.2, the refractive index difference between the first sublayer and the second sublayer is less than or equal to 0.3, and the refractive index difference between the second sublayer, the third sublayer, and the fourth sublayer, and between adjacent sublayers, is less than or equal to 0.2.

[0014] In some embodiments, the refractive index of the first sublayer is 2.15~2.35, the refractive index of the second sublayer is 2.05~2.15, the refractive index of the third sublayer is 1.95~2.05, and the refractive index of the fourth sublayer is 1.85~1.95.

[0015] In some embodiments, the difference in refractive index between the silicon oxynitride layer and the fourth sublayer is less than or equal to 0.2, and the difference in refractive index between the silicon oxide layer and the silicon oxynitride layer is less than or equal to 0.4.

[0016] In some embodiments, the refractive index of the silicon oxynitride layer is 1.75 to 1.85, and the refractive index of the silicon oxide layer is 1.45 to 1.6.

[0017] In some embodiments, the thickness of the ultrathin silicon oxide layer is less than 2 nm, and the thickness of the aluminum oxide layer is greater than the thickness of the ultrathin silicon oxide layer.

[0018] In some embodiments, the thickness of the ultrathin silicon oxide layer is 0.3 nm to 0.8 nm, and the thickness of the aluminum oxide layer is 3 nm to 10 nm.

[0019] In some embodiments, the total thickness of the silicon nitride layer is 5nm~30nm, the thickness of the silicon oxynitride layer is 20nm~60nm, and the thickness of the silicon oxide layer is 5nm~30nm.

[0020] In some embodiments, the thickness of the silicon oxynitride layer is greater than the total thickness of the silicon nitride layer.

[0021] In some embodiments, the thickness of the second portion is set to decrease along the direction from the first surface toward the second surface.

[0022] In some embodiments, the side surface includes a first sidewall, a second sidewall, a third sidewall, and a fourth sidewall connected in sequence, and the second portion is disposed on at least one of the first sidewall, the second sidewall, the third sidewall, and the fourth sidewall.

[0023] In some embodiments, a doped layer is provided on the second surface, and a back anti-reflection passivation layer is provided on the side of the doped layer facing away from the silicon substrate. The back anti-reflection passivation layer includes an ultrathin SiO2 layer, an Al2O3 layer, and a SiN layer sequentially disposed along a direction away from the silicon substrate. x layer.

[0024] Second, this utility model provides a battery assembly, including the aforementioned back-contact solar cell.

[0025] Third, this utility model also provides a photovoltaic system, including the aforementioned battery module.

[0026] The beneficial effects of this utility model are as follows:

[0027] In this invention, an anti-reflection passivation composite layer is disposed on both the first surface and the outer side surface of a silicon substrate. The portion of the anti-reflection passivation composite layer on the first surface is designated as a first portion, and the portion on the outer side surface is designated as a second portion. Both the first and second portions include an ultrathin silicon oxide layer, an aluminum oxide layer, a silicon nitride layer, a silicon oxynitride layer, and a silicon oxide layer sequentially disposed along a direction away from the silicon substrate, with the refractive indices of the silicon nitride layer, silicon oxynitride layer, and silicon oxide layer decreasing sequentially. Specifically, the anti-reflection passivation composite layer of this invention effectively passivates the first surface and the outer side surface of the silicon substrate and effectively reduces reflection loss. Specifically, the anti-reflection passivation composite layer of this invention has an ultrathin silicon oxide layer disposed between the silicon substrate and the aluminum oxide layer. This ultrathin silicon oxide layer reduces the dangling bond density on the silicon substrate surface (first surface and outer side surface), reduces lattice defects, and constructs an ordered interface on the silicon substrate surface. The structure reduces the recombination probability of charge carriers, while the ultrathin silicon oxide layer provides a good growth surface for the subsequent alumina layer, making the subsequently grown alumina layer more uniform. The ultrathin silicon oxide layer and the alumina layer as a whole exhibit better chemical passivation effect. Subsequently, silicon nitride, silicon oxynitride, and silicon oxide layers with decreasing refractive indices are deposited sequentially on the alumina layer. The silicon nitride layer has a better field passivation effect. Combined with the chemical passivation effect of the aforementioned ultrathin silicon oxide and alumina layers, the overall passivation effect of the anti-reflection passivation composite layer is effectively improved. At the same time, the decreasing refractive indices of the silicon nitride, silicon oxynitride, and silicon oxide layers, with the silicon nitride layer transitioning to the silicon oxide layer via the silicon oxynitride layer, result in a higher degree of matching between adjacent materials. The overall combination can provide a better anti-reflection effect, allowing light of different wavelengths to enter the battery more easily, reducing reflection loss and effectively improving light utilization. On the other hand, the anti-reflection and passivation composite layer of this invention not only has good anti-reflection and passivation effects, but also has better matching between the material layers of the film, which can effectively improve stress problems. Specifically, by setting a thin ultra-thin silicon oxide layer, a buffer can be formed between the silicon substrate and the aluminum oxide layer, which can reduce the thermal stress between adjacent layers. At the same time, the silicon nitride layer adjacent to the aluminum oxide layer has a lower elastic modulus and better ability to adapt to deformation, which can buffer stress transmission. Combined with the silicon nitride layer, silicon oxynitride layer and silicon oxide layer with high material matching, stress is dispersed layer by layer. Thus, through the mutual cooperation between multiple material layers, the mechanical stability and adhesion of the anti-reflection and passivation composite layer are effectively improved.

[0028] Therefore, this invention effectively solves the impact of defects on the side of the silicon substrate by setting an optimized anti-reflection passivation composite layer on the first surface and side of the silicon substrate, reduces parasitic absorption at the edge of the battery, and effectively improves the anti-reflection and passivation effect of the anti-reflection passivation composite layer through the cooperation between multiple material layers, and improves stress problems, thereby effectively improving the overall conversion efficiency of the battery, ensuring the long-term reliability of the battery, and improving the overall performance of the battery. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the back-contact solar cell of this utility model.

[0030] Figure 2 for Figure 1 A magnified view of a portion of the image.

[0031] Figure 3 This is a schematic diagram of another embodiment of the back-contact solar cell of this utility model.

[0032] Figure 4 for Figure 3 A magnified view of part A.

[0033] Figure 5 This is a partial structural diagram of the first part of the anti-reflection passivation composite layer (silicon nitride layer with sublayer) of this utility model.

[0034] Figure 6 This is a flowchart of the preparation method of the back contact solar cell of this utility model.

[0035] Figure 7 This is a flowchart of the preparation method of the anti-reflection passivation composite layer of this utility model.

[0036] Figure 8 This is a schematic diagram of the improved ALD device of this utility model.

[0037] Figure 9 This is a comparison chart of reflectance curves for Embodiment 1 and Embodiment 2 of this utility model. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this utility model, and should not be construed as limiting this utility model. Furthermore, it should be understood that the specific embodiments described herein are merely for explaining this utility model and are not intended to limit this utility model.

[0039] In the description of this utility model, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first," "second," etc., may explicitly or implicitly include one or more of the stated features. In the description of this utility model, "multiple" or "several" means two or more, unless otherwise explicitly specified.

[0040] In the description of this utility model, unless otherwise expressly specified and limited, the first feature "above" or "below" the second feature may include the first feature and the second feature being in direct contact, or the first feature and the second feature not being in direct contact but being in contact through another feature between them.

[0041] First, see Figures 1 to 2 As shown, this utility model provides a back-contact solar cell, comprising:

[0042] The silicon substrate 1 has a first surface 11, a second surface 12 and a side surface 13, the first surface 11 and the second surface 12 are disposed opposite to each other, and the side surface 13 is connected to the first surface 11 and the second surface 12 respectively.

[0043] The anti-reflection passivation composite layer 2 includes a first portion 2A disposed on the first surface 11 and a second portion 2B extending from the edge of the first portion 2A to the outside of the side surface 13;

[0044] The anti-reflection passivation composite layer 2 includes an ultrathin silicon oxide layer 21, an aluminum oxide layer 22, a silicon nitride layer 23, a silicon oxynitride layer 24, and a silicon oxide layer 25 arranged sequentially along the direction away from the silicon substrate 1, and the refractive indices of the silicon nitride layer 23, the silicon oxynitride layer 24, and the silicon oxide layer 25 decrease sequentially.

[0045] Understandably, the silicon substrate 1 has a first surface 11 and a second surface 12 disposed opposite to each other, wherein one is the light-receiving surface (usually referred to as the front side of the silicon substrate 1) and the other is the back side (usually referred to as the back side of the silicon substrate 1). The sidewalls of the perimeter of the silicon substrate 1 are side surfaces 13. In this specification, the first surface 11 is the light-receiving surface and the second surface 12 is the back side. The light-receiving surface generally refers to the side that receives light. In some embodiments, the light-receiving surface can also be set as a textured surface. It should be noted that in some embodiments, light incident through the back side can also be absorbed, thereby generating a photocurrent. Furthermore, in practical applications, this embodiment of the present invention does not specifically limit the material and conductivity type of the silicon substrate 1. For example, the material of the silicon substrate 1 can be monocrystalline silicon, microcrystalline silicon, polycrystalline silicon, or amorphous silicon, but is not limited thereto, and its conductivity can be N-type or P-type.

[0046] In this invention, an anti-reflection passivation composite layer 2 is provided on both the first surface 11 and the outer side 13 of the silicon substrate 1. The portion of the anti-reflection passivation composite layer 2 on the first surface 11 is designated as a first portion 2A, and the portion outside the side 13 is designated as a second portion 2B. Both the first portion 2A and the second portion 2B include an ultrathin silicon oxide layer 21, an aluminum oxide layer 22, a silicon nitride layer 23, a silicon oxynitride layer 24, and a silicon oxide layer 25 sequentially arranged along a direction away from the silicon substrate 1. Furthermore, the silicon nitride layer 23, the silicon oxynitride layer 24, and the silicon oxide layer 25 are... The refractive indices of the silicon oxide layer 24 and the silicon alumina layer 25 decrease sequentially. Specifically, the anti-reflection passivation composite layer 2 of this invention can effectively passivate the first surface 11 and side surface 13 of the silicon substrate 1 and effectively reduce reflection loss. Specifically, the anti-reflection passivation composite layer 2 of this invention has an ultrathin silicon oxide layer 21 disposed between the silicon substrate 1 and the aluminum oxide layer 22. The ultrathin silicon oxide layer 21 can reduce the dangling bond density on the surface of the silicon substrate 1 (first surface 11 and side surface 13), reduce lattice defects, and improve the performance of the silicon substrate 1. The orderly interface structure on the surface reduces the recombination probability of charge carriers. At the same time, the ultrathin silicon oxide layer 21 provides a good growth surface for the subsequent aluminum oxide layer 22, making the subsequently grown aluminum oxide layer 22 more uniform. The ultrathin silicon oxide layer 21 and the aluminum oxide layer 22 exhibit better chemical passivation effect. Subsequently, on the basis of the aluminum oxide layer 22, silicon nitride layer 23, silicon oxynitride layer 24 and silicon oxide layer 25 with decreasing refractive indices are deposited in sequence. The silicon nitride layer 23 has a better field passivation effect. Combined with the chemical passivation effect of the ultrathin silicon oxide layer 25 and the aluminum oxide layer 22, the overall passivation effect of the anti-reflection passivation composite layer 2 is effectively improved. At the same time, the decreasing refractive index of the silicon nitride layer 23, silicon oxynitride layer 24 and silicon oxide layer 25, and the transition from silicon nitride layer 23 to silicon oxide layer 25 via silicon oxynitride layer 24, results in a higher degree of matching between adjacent materials. The overall combination can provide a better anti-reflection effect, and light of different wavelengths can enter the battery more easily, reducing reflection loss and effectively improving light utilization. On the other hand, the anti-reflection and passivation composite layer 2 of this invention not only has good anti-reflection and passivation effects, but also has better matching between the material layers of the film, which can effectively improve stress problems. Specifically, by setting a thinner ultra-thin silicon oxide layer 21, a buffer can be formed between the silicon substrate 1 and the aluminum oxide layer 22, which can reduce the thermal stress between adjacent layers. At the same time, the silicon nitride layer 23 adjacent to the aluminum oxide layer 22 has a lower elastic modulus and better ability to adapt to deformation, which can buffer stress transmission. Combined with the silicon nitride layer 23, silicon oxynitride layer 24 and silicon oxide layer 25 with high material matching, stress is dispersed layer by layer. Thus, through the mutual cooperation between multiple material layers, the mechanical stability and adhesion of the anti-reflection and passivation composite layer 2 are effectively improved.

[0047] Therefore, by providing an optimized anti-reflection passivation composite layer 2 on the first surface 11 and side surface 13 of the silicon substrate 1, this utility model effectively solves the impact of defects on the side surface 13 of the silicon substrate 1, reduces parasitic absorption at the edge of the battery, and effectively improves the anti-reflection and passivation effect of the anti-reflection passivation composite layer 2 through the cooperation between multiple material layers, and improves stress problems, thereby effectively improving the overall conversion efficiency of the battery, ensuring the long-term reliability of the battery, and improving the overall performance of the battery.

[0048] In some embodiments, see Figure 3 and Figure 5 As shown, the silicon nitride layer 23 includes a first sublayer 231, a second sublayer 232, a third sublayer 233 and a fourth sublayer 234 arranged sequentially along the direction away from the silicon substrate 1. The refractive indices of the first sublayer 231, the second sublayer 232, the third sublayer 233 and the fourth sublayer 234 decrease sequentially, and the thickness of each sublayer is the same.

[0049] By using a multilayer sublayer design with progressively decreasing refractive indices, stress is further dispersed and buffered, improving the compatibility between adjacent material layers and enhancing the overall mechanical stability and adhesion of the anti-reflection passivation composite layer 2. At the same time, the highly matched refractive indices and thicknesses between adjacent material layers facilitate better interlayer optical transition, reducing light reflection loss at the interface. This effectively improves the overall conversion efficiency of the battery and ensures its long-term reliability.

[0050] In some embodiments, the difference in refractive index between the first sublayer 231 and the fourth sublayer 234 is greater than or equal to 0.2, the difference in refractive index between the first sublayer 231 and the second sublayer 232 is less than or equal to 0.3, and the difference in refractive index between the second sublayer 232, the third sublayer 233 and the fourth sublayer 234, and between adjacent sublayers is less than or equal to 0.2.

[0051] To ensure a smooth optical transition between the silicon nitride layer 23 and the aluminum oxide layer 22 and silicon oxynitride layer 24, which have significantly different refractive indices, the refractive index difference between the first sub-layer 231 and the fourth sub-layer 234 of the silicon nitride layer 23 is set to be greater than or equal to 0.2. Simultaneously, to ensure better optical property matching between the sub-layers of the silicon nitride layer 23, the refractive index difference between the first sub-layer 231 and the second sub-layer 232 is set to be less than or equal to 0.3, and the refractive index difference between adjacent sub-layers (second sub-layer 232, third sub-layer 233, and fourth sub-layer 234) is set to be less than or equal to 0.2. This results in a better anti-reflection passivation composite layer 2, thereby effectively improving battery conversion efficiency.

[0052] In some embodiments, the refractive index of the first sublayer 231 is 2.15 to 2.35, the refractive index of the second sublayer 232 is 2.05 to 2.15, the refractive index of the third sublayer 233 is 1.95 to 2.05, and the refractive index of the fourth sublayer 234 is 1.85 to 1.95.

[0053] Within this range, the silicon nitride layer 23 can form a good optical transition between the aluminum oxide layer 22 and the silicon oxynitride layer 24, which have a large difference in refractive index. The anti-reflection passivation composite layer 2 has a better anti-reflection effect overall, thereby effectively improving the battery conversion efficiency.

[0054] For example, the refractive index of the first sublayer 231 may be 2.15, 2.16, 2.17, 2.18, 2.19, 2.20, 2.21, 2.22, 2.23, 2.24, 2.25, 2.26, 2.27, 2.28, 2.29, 2.30, 2.31, 2.32, 2.33, 2.34, or 2.35, but is not limited thereto.

[0055] For example, the refractive index of the second sublayer 232 is 2.05, 2.06, 2.07, 2.08, 2.09, 2.10, 2.11, 2.12, 2.13, 2.14 or 2.15, but is not limited thereto.

[0056] For example, the refractive index of the third sublayer 233 is 1.95, 1.96, 1.97, 1.98, 1.99, 2.00, 2.01, 2.02, 2.03, 2.04 or 2.05, but is not limited thereto.

[0057] For example, the refractive index of the fourth sublayer 234 is 1.85, 1.86, 1.87, 1.88, 1.89, 1.90, 1.91, 1.92, 1.93, 1.94 or 1.95, but is not limited thereto.

[0058] In some embodiments, the difference in refractive index between the silicon oxynitride layer 24 and the fourth sublayer 234 is less than or equal to 0.2, and the difference in refractive index between the silicon oxide layer 25 and the silicon oxynitride layer 24 is less than or equal to 0.4.

[0059] Within this range, the silicon nitride layer 23 can form a good optical transition between the aluminum oxide layer 22 and the silicon oxynitride layer 24, which have a large difference in refractive index. The anti-reflection passivation composite layer 2 has a better anti-reflection effect overall, thereby effectively improving the battery conversion efficiency.

[0060] In some embodiments, the refractive index of the silicon oxynitride layer 24 is 1.75 to 1.85, and the refractive index of the silicon oxide layer 25 is 1.45 to 1.6.

[0061] For example, the refractive index of the silicon oxynitride layer 24 is 1.75, 1.76, 1.78, 1.79, 1.80, 1.81, 1.82, 1.83, 1.84 or 1.85, but is not limited thereto.

[0062] For example, the refractive index of the silicon oxide layer 25 is 1.45, 1.46, 1.47, 1.48, 1.49, 1.50, 1.51, 1.52, 1.53, 1.54, 1.55, 1.56, 1.57, 1.58, 1.59 or 1.60, but is not limited thereto.

[0063] In this invention, by setting the refractive index between the above-mentioned material layers, the optical property matching degree between adjacent material layers in the anti-reflection passivation composite layer 2 is effectively improved, which effectively increases the absorption of sunlight by the battery, reduces reflection loss, and improves the battery conversion efficiency.

[0064] In some embodiments, the thickness of the ultrathin silicon oxide layer 21 is less than 2 nm, and the thickness of the aluminum oxide layer 22 is greater than the thickness of the ultrathin silicon oxide layer 21.

[0065] When the thickness of the ultrathin silicon oxide layer 21 is too thick, it is difficult to play a good stress buffering role between the aluminum oxide layer 22 and the silicon substrate 1, which affects the mechanical stability and adhesion of the anti-reaction passivation composite layer 2, and also affects the passivation effect of subsequent material layers. Alumina has excellent passivation performance. By combining a thinner ultrathin silicon oxide layer 21 with a thicker aluminum oxide layer 22, the dangling bond density on the surface of the silicon substrate 1 can be effectively reduced, carrier recombination can be reduced, and more sufficient passivation can be provided, which helps to improve the open circuit voltage and fill factor of the battery, thereby improving the conversion efficiency of the battery.

[0066] In some embodiments, the thickness of the ultrathin silicon oxide layer 21 is 0.3 nm to 0.8 nm, and the thickness of the aluminum oxide layer 22 is 3 nm to 10 nm.

[0067] Within this thickness range, the bonding between the ultrathin silicon oxide layer 21, the aluminum oxide layer 22 and the silicon substrate 1 is better, the ultrathin silicon oxide layer 21 can play a good stress buffering role, and the passivation effect of the anti-reflection passivation composite layer 2 is better.

[0068] For example, the thickness of the ultrathin silicon oxide layer 21 is 0.3nm, 0.35nm, 0.4nm, 0.45nm, 0.5nm, 0.55nm, 0.6nm, 0.65nm, 0.7nm, 0.75nm or 0.8nm, but is not limited thereto.

[0069] For example, the thickness of the alumina layer 22 is 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 5.5nm, 6nm, 6.5nm, 7nm, 7.5nm, 8nm, 8.5nm, 9nm, 9.5nm or 10nm, but is not limited thereto.

[0070] In some embodiments, the total thickness of the silicon nitride layer 23 is 5 nm to 30 nm, the thickness of the silicon oxynitride layer 24 is 20 nm to 60 nm, and the thickness of the silicon oxide layer 25 is 5 nm to 30 nm.

[0071] Within this thickness range, the refractive index of each material layer, including silicon nitride layer 23, silicon oxynitride layer 24, and silicon oxide layer 25, decreases progressively. This results in a higher degree of matching between the refractive index and thickness of the silicon nitride layer 23, silicon oxynitride layer 24, and silicon oxide layer 25. Consequently, the anti-reflection passivation composite layer 2 exhibits better optical property matching, effectively increasing the absorption of sunlight by the battery, reducing reflection loss, and improving battery conversion efficiency.

[0072] For example, the total thickness of the silicon nitride layer 23 is 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, or 30nm, but is not limited thereto.

[0073] For example, the thickness of the silicon oxynitride layer 24 is 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm or 60nm, but is not limited thereto.

[0074] For example, the thickness of the silicon oxide layer 25 is 5nm, 8nm, 10nm, 12nm, 15nm, 18nm, 20nm, 22nm, 25nm, 28nm or 30nm, but is not limited thereto.

[0075] In some embodiments, preferably, the thickness of the silicon oxynitride layer 24 is greater than the total thickness of the silicon nitride layer 23, which helps to further reduce reflection loss and improve stress distribution.

[0076] In some embodiments, the thickness of the second portion 2B is set to decrease along the direction from the first surface 11 toward the second surface 12, which helps to improve the stress distribution at the edge of the battery, effectively reduce stress concentration, and thereby improve the overall performance of the anti-reflection passivation composite layer 2.

[0077] In some embodiments, side 13 includes a first side wall, a second side wall, a third side wall and a fourth side wall connected in sequence, and a second portion 2B is disposed on at least one of the first side wall, the second side wall, the third side wall and the fourth side wall.

[0078] Preferably, the second portion 2B is disposed on the first side wall, the second side wall, the third side wall and the fourth side wall.

[0079] In some embodiments, see Figure 1 and Figure 3 As shown, a doped layer 3 is provided on the second surface 12. A back anti-reflection passivation layer 5 is provided on the side of the doped layer 3 facing away from the silicon substrate 1. The back anti-reflection passivation layer 5 includes an ultrathin SiO2 layer 51, an Al2O3 layer 52, and a SiN layer sequentially disposed along the direction away from the silicon substrate 1. x Layer 53.

[0080] By setting a back anti-reflection passivation layer 5, the anti-reflection and passivation effects on the back of the battery are improved, further enhancing the battery conversion efficiency.

[0081] In some embodiments, the doped layer 3 includes a first doped layer 31 and a second doped layer 32 with opposite polarities. In some embodiments, the first doped layer 31 and the second doped layer 32 are arranged alternately. In another embodiment, a portion of the second doped layer 32 may be stacked on a portion of the first doped layer 31. In this case, an insulating protective layer exists in the region where the first doped layer 31 and the second doped layer 32 are stacked.

[0082] Understandably, in terms of conductivity type, the polarity of the first doped layer 31 and the polarity of the second doped layer 32 can be the same as or opposite to the polarity of the silicon substrate 1, as long as it is ensured that the polarity of the first doped layer 31 is opposite to the polarity of the second doped layer 32. Either the first doped layer 31 and / or the second doped layer 32 is made of monocrystalline silicon, polycrystalline silicon, or amorphous silicon doped with Group III elements (e.g., B, Ga, or In), and the other is made of monocrystalline silicon, microcrystalline silicon, polycrystalline silicon, or amorphous silicon doped with Group V elements (e.g., P, As, Sb).

[0083] In some embodiments, a passivation layer 4 may be disposed between the doped layer 3 and the silicon substrate 1 to improve the passivation effect and carrier transport effect. The passivation layer 4 may be an intrinsic amorphous silicon layer or a tunneling oxide layer (e.g., silicon oxide, titanium oxide, etc.). For example, when the doped layer 3 is polycrystalline silicon, the passivation layer 4 may be a tunneling oxide layer, but it is not limited to this.

[0084] Second, see Figure 6 and Figure 7 As shown, this utility model provides a method for fabricating a back-contact solar cell, comprising:

[0085] S100. A silicon substrate 1 is provided, the silicon substrate 1 having a first surface 11, a second surface 12 and a side surface 13, the first surface 11 and the second surface 12 being disposed opposite to each other, and the side surface 13 being connected to the first surface 11 and the second surface 12 respectively;

[0086] S200. Deposit an anti-reflection passivation composite layer 2 on a silicon substrate 1. The anti-reflection passivation composite layer 2 includes a first portion 2A disposed on a first surface 11 and a second portion 2B extending from the edge of the first portion 2A to the outside of the side surface 13.

[0087] The step of depositing the anti-reflection passivation composite layer 2 on the silicon substrate 1 includes:

[0088] An ultrathin silicon oxide layer 21, an aluminum oxide layer 22, a silicon nitride layer 23, a silicon oxynitride layer 24, and a silicon oxide layer 25 are sequentially deposited on the first surface 11 and the outer side surface 13, with the refractive indices of the silicon nitride layer 23, the silicon oxynitride layer 24, and the silicon oxide layer 25 decreasing sequentially.

[0089] For details, see Figure 7 As shown, step S200, which involves depositing an anti-reflection passivation composite layer 2 on the silicon substrate 1, includes:

[0090] S210. An ultrathin silicon oxide layer 21 is deposited on the first surface 11 and the outer side surface 13;

[0091] S220. Deposit an aluminum oxide layer 22 on the ultrathin silicon oxide layer 21;

[0092] S230. Deposit silicon nitride layer 23 on alumina layer 22;

[0093] S240. Deposit silicon oxynitride layer 24 on silicon nitride layer 23;

[0094] S250. Deposit silicon oxide layer 25 on silicon oxynitride layer 24.

[0095] In some embodiments, see Figure 8 As shown, the ultrathin silicon oxide layer 21 and aluminum oxide layer 22 are both fabricated using a modified ALD equipment. The modified ALD equipment includes a process chamber and an ozone generator, and a connecting pipeline is provided between the ozone generator and the process chamber.

[0096] By continuously preparing an ultrathin silicon oxide layer 21 and an aluminum oxide layer 22 using a modified ALD equipment, the silicon substrate 1 can be treated with ozone provided by an ozone generator before depositing the aluminum oxide layer 22, thereby cleaning and oxidizing it. This forms an ultrathin silicon oxide layer 21 between the silicon substrate 1 and the aluminum oxide layer 22, which not only improves the passivation performance of the aluminum oxide layer 22, but also plays a good role in stress buffering. The anti-reaction passivation composite layer 2 as a whole exhibits better passivation performance and mechanical stability.

[0097] Preferably, in this preparation method, an ultrathin silicon oxide layer 21 and an aluminum oxide layer 22 are prepared using a modified ALD equipment, and a silicon nitride layer 23, a silicon oxynitride layer 24, and a silicon oxide layer 25 are prepared using PECVD.

[0098] In some embodiments, see Figure 1 , Figure 3 , Figure 7 and Figure 8 As shown, the deposition step (step S210) of the ultrathin silicon oxide layer 21 includes:

[0099] The silicon substrate 1 is transferred into the process chamber, and N2 / O3 mixed gas and purge gas are alternately circulated into the process chamber. In the N2 / O3 mixed gas, the flow rate of O3 accounts for 5%~50%, the deposition temperature is 50℃~400℃, and the pressure is 0.3mbar~0.8mbar. The process is repeated N times until the thickness of the ultrathin silicon oxide layer 21 reaches 0.3nm~0.8nm.

[0100] The deposition step of the alumina layer 22 (step S220) includes:

[0101] After the ultrathin silicon oxide layer 21 is deposited, the same deposition temperature and pressure are maintained to complete N growth cycles until the thickness of the aluminum oxide layer 22 reaches 3nm~10nm. In each growth cycle, TMA, purge gas, H2O vapor and purge gas are sequentially introduced into the process chamber. The purge gas is nitrogen.

[0102] Specifically, in step S210, the silicon substrate 1 is placed in the process chamber, a vacuum is drawn, and the ozone generator is turned on at 5%~100% power. Under the temperature range of 50℃~400℃ and the pressure of 0.3mbar~0.8mbar, an N2 / O3 mixed gas is introduced into the chamber for 1s~300s, and the flow rate of O3 in the N2 / O3 mixed gas is controlled to be 5%~50%. Then, the process chamber is purged with high-purity nitrogen for 1s~300s. This process is repeated 1~10 times to complete the preparation of ultrathin silicon oxide.

[0103] Specifically, in step S220, after the ultrathin silicon oxide layer 21 is deposited, the same deposition temperature and pressure are maintained. First, TMA is introduced for 1 to 20 seconds, then nitrogen is introduced for 1 to 10 seconds, then H2O vapor is introduced for 1 to 30 seconds, and then nitrogen is introduced for 1 to 10 seconds. This process is repeated 25 to 45 times to complete the deposition of the alumina thin film.

[0104] In some embodiments, the deposition step of the silicon nitride layer 23 (step S230) includes:

[0105] The silicon substrate 1 with the deposited alumina layer 22 is transferred into the PECVD chamber, and ammonia and silane are introduced to sequentially deposit the first sublayer 231, the second sublayer 232, the third sublayer 233, and the fourth sublayer 234.

[0106] The refractive indices of the first sublayer 231, the second sublayer 232, the third sublayer 233, and the fourth sublayer 234 decrease sequentially, and the thickness of each sublayer is the same.

[0107] In some embodiments, during the deposition of the first sublayer 231, the second sublayer 232, the third sublayer 233 and the fourth sublayer 234, the ratio of ammonia flow rate to silane flow rate increases layer by layer, and the ratio of ammonia flow rate to silane flow rate for each sublayer is 5~8, 8~11, 11~15 and 16~20 respectively.

[0108] By controlling the ratio of ammonia flow rate to silane flow rate in each sublayer to increase layer by layer, the nitrogen content in each sublayer is increased, thereby improving the refractive index layer by layer.

[0109] In some embodiments, the deposition step of the silicon nitride layer 23 (step S230) includes:

[0110] S231. Deposit the first sublayer 231 on the alumina layer 22:

[0111] Temperature is controlled at 450℃~550℃, ammonia flow rate to silane flow rate ratio is 5~8, silane flow rate is 1500sccm~2000sccm, ammonia flow rate is 7500sccm~16000sccm, pressure is 1000Torr~2000mTorr, duty cycle is (2~5):(60~90), RF power is 6000W~30000W, duration is 150s~300s.

[0112] S232. Deposit the second sublayer 232 on the first sublayer 231:

[0113] Temperature is controlled at 450℃~550℃, ammonia flow rate to silane flow rate ratio is 8~11, silane flow rate is 1000sccm~1500sccm, ammonia flow rate is 8000sccm~16500sccm, pressure is 1000Torr~2000mTorr, duty cycle is (2~5):(60~90), RF power is 6000W~30000W, duration is 150s~300s.

[0114] S233. Deposit the third sublayer 233 on the second sublayer 232:

[0115] Temperature is controlled at 450℃~550℃, ammonia flow rate to silane flow rate ratio is 11~15, silane flow rate is 500sccm~1000sccm, ammonia flow rate is 5500sccm~15000sccm, pressure is 1000Torr~2000mTorr, duty cycle is (2~5):(60~90), RF power is 6000W~30000W, duration is 150s~300s.

[0116] S234. Deposit the fourth sublayer 234 on the third sublayer 233:

[0117] Temperature is controlled at 450℃~550℃, ammonia flow rate to silane flow rate ratio is 16~20, silane flow rate is 300sccm~900sccm, ammonia flow rate is 4800sccm~18000sccm, pressure is 1000Torr~2000mTorr, duty cycle is (2~5):(60~90), RF power is 6000W~30000W, duration is 150s~300s.

[0118] In some embodiments, the step of preparing the silicon oxynitride layer 24 by PECVD (step S240) includes:

[0119] The temperature is controlled at 450℃~550℃, the flow ratio of nitrous oxide, ammonia and silane is (15~18):(2~4):1, the flow rate of silane is 300sccm~1000sccm, the flow rate of ammonia is 600sccm~4000sccm, the flow rate of nitrous oxide is 4500sccm~18000sccm, the pressure is 1000Torr~2000mTorr, the duty cycle is (2~5):(60~90), the radio frequency power is 6000W~3000W, and the duration is 150s~300s.

[0120] In some embodiments, the step of preparing the silicon oxide layer 25 by PECVD (step S250) includes:

[0121] The temperature is controlled at 450℃~550℃, the flow ratio between nitrous oxide and silane is (15~20):1, the silane flow rate is 300sccm~1000sccm, the nitrous oxide flow rate is 4500sccm~20000sccm, the pressure is 1000Torr~2000mTorr, the duty cycle is (2~5):(60~90), the radio frequency power is 6000W~3000W, and the duration is 150s~300s.

[0122] In some embodiments, the refractive index of the first sublayer 231 is 2.15 to 2.35, the refractive index of the second sublayer 232 is 2.05 to 2.15, the refractive index of the third sublayer 233 is 1.95 to 2.05, and the refractive index of the fourth sublayer 234 is 1.85 to 1.95.

[0123] In some embodiments, the refractive index of the silicon oxynitride layer 24 is 1.75 to 1.85, and the refractive index of the silicon oxide layer 25 is 1.45 to 1.6.

[0124] Third, this utility model provides a battery assembly, including the aforementioned back-contact solar cell; or,

[0125] This includes back-contact solar cells prepared by the methods described above.

[0126] Fourth, this utility model also provides a photovoltaic system, including the aforementioned battery module.

[0127] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0128] Example 1

[0129] See Figures 3 to 5 As shown, this embodiment discloses a back-contact solar cell, comprising:

[0130] A silicon substrate has a first surface, a second surface, and side surfaces, wherein the first surface and the second surface are disposed opposite to each other, and the side surfaces are respectively connected to the first surface and the second surface;

[0131] The anti-reflection passivation composite layer includes a first portion disposed on a first surface and a second portion extending from the edge of the first portion to the outside of the side surface;

[0132] The anti-reflection passivation composite layer includes an ultrathin silicon oxide layer, an aluminum oxide layer, a silicon nitride layer, a silicon oxynitride layer, and a silicon oxide layer arranged sequentially in a direction away from the silicon substrate, with the refractive indices of the silicon nitride layer, silicon oxynitride layer, and silicon oxide layer decreasing sequentially.

[0133] In this embodiment, the silicon nitride layer includes a first sublayer, a second sublayer, a third sublayer, and a fourth sublayer disposed sequentially along a direction away from the silicon substrate. The refractive indices of the first sublayer, the second sublayer, the third sublayer, and the fourth sublayer decrease sequentially, and each sublayer has the same thickness.

[0134] In this embodiment, the refractive index difference between the first sublayer and the fourth sublayer is greater than or equal to 0.2, the refractive index difference between the first sublayer and the second sublayer is less than or equal to 0.3, and the refractive index difference between the second sublayer, the third sublayer, and the fourth sublayer, and between adjacent sublayers, is less than or equal to 0.2.

[0135] In this embodiment, the refractive index of the first sublayer is 2.2, the refractive index of the second sublayer is 2.15, the refractive index of the third sublayer is 2.05, and the refractive index of the fourth sublayer is 1.95.

[0136] In this embodiment, the refractive index difference between the silicon oxynitride layer and the fourth sublayer is less than or equal to 0.2, and the refractive index difference between the silicon oxide layer and the silicon oxynitride layer is less than or equal to 0.4.

[0137] In this embodiment, the refractive index of the silicon oxynitride layer is 1.85, and the refractive index of the silicon oxide layer is 1.6.

[0138] In this embodiment, the thickness of the ultrathin silicon oxide layer is less than 2 nm, and the thickness of the aluminum oxide layer is greater than the thickness of the ultrathin silicon oxide layer.

[0139] In this embodiment, the thickness of the ultrathin silicon oxide layer is 0.5 nm, and the thickness of the aluminum oxide layer is 5 nm.

[0140] In this embodiment, the total thickness of the silicon nitride layer is 15 nm, the thickness of the silicon oxynitride layer is 40 nm, and the thickness of the silicon oxide layer is 15 nm.

[0141] In this embodiment, the thickness of the silicon oxynitride layer is greater than the total thickness of the silicon nitride layer.

[0142] In this embodiment, the side includes a first sidewall, a second sidewall, a third sidewall, and a fourth sidewall connected in sequence, and the second portion is disposed on the first sidewall, the second sidewall, the third sidewall, and the fourth sidewall.

[0143] In this embodiment, a doped layer is provided on the second surface, and a back anti-reflection passivation layer is provided on the side of the doped layer facing away from the silicon substrate. The back anti-reflection passivation layer includes an ultrathin SiO2 layer, an Al2O3 layer, and a SiN layer sequentially arranged in a direction away from the silicon substrate. x layer.

[0144] Second, this embodiment discloses a method for fabricating a back-contact solar cell, including:

[0145] S100. A silicon substrate is provided, the silicon substrate having a first surface, a second surface and a side surface, the first surface and the second surface being disposed opposite to each other, and the side surface being connected to the first surface and the second surface respectively;

[0146] S200. Deposit an anti-reflection passivation composite layer on a silicon substrate, the anti-reflection passivation composite layer including a first portion disposed on a first surface and a second portion extending from the edge of the first portion to the outside of the side surface;

[0147] The steps of depositing an anti-reflection passivation composite layer on a silicon substrate include:

[0148] An ultrathin silicon oxide layer, an aluminum oxide layer, a silicon nitride layer, a silicon oxynitride layer, and a silicon oxide layer are sequentially deposited on the first surface and the outer side surface, with the refractive indices of the silicon nitride layer, silicon oxynitride layer, and silicon oxide layer decreasing sequentially.

[0149] Specifically, step S200, which involves depositing an anti-reflection passivation composite layer on a silicon substrate, includes:

[0150] S210. An ultrathin silicon oxide layer is deposited on the first surface and the outer side surface;

[0151] S220. Depositing an aluminum oxide layer on an ultrathin silicon oxide layer;

[0152] S230. Deposit a silicon nitride layer on the alumina layer;

[0153] S240. Deposit a silicon oxynitride layer on the silicon nitride layer;

[0154] S250. Deposit a silicon oxide layer on a silicon oxynitride layer.

[0155] In this embodiment, both the ultrathin silicon oxide layer and the aluminum oxide layer are prepared using a modified ALD equipment. The modified ALD equipment includes a process chamber and an ozone generator, and a connecting pipeline is provided between the ozone generator and the process chamber.

[0156] In this embodiment, the deposition step of the ultrathin silicon oxide layer (step S210) includes:

[0157] The silicon substrate is placed in the process chamber, a vacuum is drawn, and the ozone generator is turned on at 50% power. Under a temperature range of 400℃ and a pressure of 0.8mbar, an N2 / O3 mixed gas is introduced into the chamber for 30s, and the flow rate of O3 in the N2 / O3 mixed gas is controlled to be 10%. Then, the process chamber is purged with high-purity nitrogen for 10s. This process is repeated twice to complete the preparation of ultrathin silicon oxide.

[0158] The alumina layer deposition step (step S220) includes:

[0159] After the ultrathin silicon oxide layer is deposited, the same deposition temperature and pressure are maintained. First, TMA is introduced for 10 seconds, then nitrogen is introduced for 10 seconds, then H2O vapor is introduced for 10 seconds, and then nitrogen is introduced for 10 seconds. This process is repeated 25 times to complete the deposition of the alumina thin film.

[0160] Example 2

[0161] See Figures 1 to 2 As shown, the difference between this embodiment and Embodiment 1 is that the silicon nitride layer in this embodiment is a material layer with a single refractive index, a thickness of 60 nm, and a refractive index of 2.1.

[0162] Comparative Example 1

[0163] The difference between this comparative example and Example 1 is that the anti-reflection passivation composite layer of this comparative example is only disposed on the first surface, that is, it does not have a second portion disposed on the side.

[0164] Comparative Example 2

[0165] The difference between this comparative example and Example 1 is that this comparative example uses a front composite layer to replace the anti-reflection passivation composite layer. The front composite layer is only disposed on the first surface. Specifically, the front composite layer consists of an ultrathin silicon oxide sublayer, an aluminum oxide sublayer, and a silicon nitride sublayer arranged sequentially along the direction away from the silicon substrate. Each sublayer is prepared by PECVD. The thickness of the ultrathin silicon oxide sublayer is 2nm, the thickness of the aluminum oxide sublayer is 5nm, the thickness of the silicon nitride sublayer is 60nm, and the refractive index is 2.1.

[0166] The performance of the solar cells prepared in Examples 1 to 2 and Comparative Examples 1 to 2 was tested, and the test results are as follows:

[0167]

[0168] The experimental results show that, compared with Comparative Examples 1 and 2, Examples 1 and 2 have higher conversion efficiencies. This demonstrates that the anti-reflection passivation composite layer of this invention can effectively improve battery conversion efficiency.

[0169] A comparison of reflectance curves was performed between Example 1 and Example 2. Figure 9 The reflectance curve comparison chart shows that, compared to Example 2, the reflectance of long-wavelength and short-wavelength light in Example 1 is reduced by 10% to 30%. A comparison of the passivation PL brightness, fitting efficiency, and testing efficiency of the two examples yields the following results:

[0170]

[0171] Table 1 Comparison of passivated PL brightness and fitting efficiency

[0172]

[0173] Table 2 Comparison of Test Efficiency

[0174] Compared to Example 2, the passivation PL brightness value of Example 1 is increased by about 1000, the passivation effect is more obvious, the fitting efficiency is increased by 0.26%, and the testing efficiency is increased by 0.23%. It can be seen that in this utility model, the silicon nitride layer is composed of multiple sub-layers with decreasing refractive index and the same thickness, which can effectively improve the passivation effect, reduce reflection loss, and improve the battery conversion efficiency.

[0175] In the description of this specification, references to terms such as "some embodiments," "exemplary," "example," or "for example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0176] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any way. Although the present utility model has been disclosed above with reference to a preferred embodiment, it is not intended to limit the present utility model. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present utility model. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present utility model without departing from the scope of the present utility model shall still fall within the scope of the present utility model.

Claims

1. A back contact solar cell, characterized by, include: A silicon substrate has a first surface, a second surface, and side surfaces, wherein the first surface and the second surface are disposed opposite to each other, and the side surfaces are respectively connected to the first surface and the second surface; The anti-reflection passivation composite layer includes a first portion disposed on the first surface and a second portion extending from the edge of the first portion to the outside of the side surface; The anti-reflection passivation composite layer includes an ultrathin silicon oxide layer, an aluminum oxide layer, a silicon nitride layer, a silicon oxynitride layer, and a silicon oxide layer arranged sequentially in a direction away from the silicon substrate, wherein the refractive indices of the silicon nitride layer, the silicon oxynitride layer, and the silicon oxide layer decrease sequentially.

2. The back contact solar cell of claim 1, wherein, The silicon nitride layer includes a first sublayer, a second sublayer, a third sublayer, and a fourth sublayer arranged sequentially in a direction away from the silicon substrate. The refractive indices of the first sublayer, the second sublayer, the third sublayer, and the fourth sublayer decrease sequentially, and each sublayer has the same thickness.

3. The back contact solar cell of claim 2, wherein, The refractive index difference between the first sublayer and the fourth sublayer is greater than or equal to 0.2, the refractive index difference between the first sublayer and the second sublayer is less than or equal to 0.3, and the refractive index difference between the second sublayer, the third sublayer, and the fourth sublayer, and between adjacent sublayers, is less than or equal to 0.

2.

4. The back contact solar cell of claim 3, wherein, The refractive index of the first sublayer is 2.15 to 2.35, the refractive index of the second sublayer is 2.05 to 2.15, the refractive index of the third sublayer is 1.95 to 2.05, and the refractive index of the fourth sublayer is 1.85 to 1.

95.

5. The back contact solar cell of claim 2, wherein, The difference in refractive index between the silicon oxynitride layer and the fourth sublayer is less than or equal to 0.2, and the difference in refractive index between the silicon oxide layer and the silicon oxynitride layer is less than or equal to 0.

4.

6. The back-contact solar cell according to claim 5, characterized in that, The refractive index of the silicon oxynitride layer is 1.75 to 1.85, and the refractive index of the silicon oxide layer is 1.45 to 1.

6.

7. The back-contact solar cell according to claim 1, characterized in that, The thickness of the ultrathin silicon oxide layer is less than 2 nm, and the thickness of the aluminum oxide layer is greater than the thickness of the ultrathin silicon oxide layer.

8. The back-contact solar cell according to claim 7, characterized in that, The thickness of the ultrathin silicon oxide layer is 0.3 nm to 0.8 nm, and the thickness of the aluminum oxide layer is 3 nm to 10 nm.

9. The back-contact solar cell according to claim 1, characterized in that, The total thickness of the silicon nitride layer is 5nm to 30nm, the thickness of the silicon oxynitride layer is 20nm to 60nm, and the thickness of the silicon oxide layer is 5nm to 30nm.

10. The back-contact solar cell according to claim 9, characterized in that, The thickness of the silicon oxynitride layer is greater than the total thickness of the silicon nitride layer.

11. The back-contact solar cell according to claim 1, characterized in that, The thickness of the second portion decreases along the direction from the first surface toward the second surface.

12. The back-contact solar cell according to claim 1, characterized in that, The side surface includes a first side wall, a second side wall, a third side wall, and a fourth side wall connected in sequence, and the second portion is disposed on at least one of the first side wall, the second side wall, the third side wall, and the fourth side wall.

13. The back-contact solar cell according to claim 1, characterized in that, The second surface is provided with a doped layer, a backside anti-reflection passivation layer is arranged on the side of the doped layer away from the silicon substrate, and the backside anti-reflection passivation layer comprises, in sequence from the direction away from the silicon substrate, an ultrathin SiO2 layer, an Al2O3 layer and a SiN x layer.

14. A battery assembly, characterized in that, Including the back-contact solar cell according to any one of claims 1 to 13.

15. A photovoltaic system, characterized in that, Includes the battery assembly as described in claim 14.

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