Back contact solar cell, preparation method thereof and photovoltaic module

Abstract

The invention provides a back contact solar cell, a preparation method thereof and a photovoltaic module, and relates to the field of photovoltaic technology. The back contact solar cell comprises a silicon substrate, wherein the second conductive region is of a textured structure; the second transmission layer comprises a first part located in the insulating region and a second part located in the second conductive region; the thickness of the first part is greater than that of the second part; the barrier layer comprises a second surface far away from the silicon substrate and a first side surface connected with the second surface and close to the insulating region; and the first side surface sequentially extends towards the insulating region from the first end close to the second surface to the second end close to the insulating region. According to the back contact solar cell, deposition of the part, located on the first side face, in the second transmission layer is facilitated, the shape integrity of the formed second transmission layer is better, the thickness of the first part in the second transmission layer is large, various properties of the back contact solar cell are improved, and the passivation performance and the insulation performance are better.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic technology, and in particular to a back-contact solar cell and a preparation method thereof, and a photovoltaic module. Background Art

[0002] Solar cells are devices that directly convert light energy into electrical energy. After decades of development, crystalline silicon solar cells currently have an absolute advantage in the photovoltaic cell market, mainly due to their advantages such as wide sources of raw materials, high reliability, high power generation efficiency, and low cost. Crystalline silicon cells currently include passivated emitter and rear cells (PERC), tunnel oxide passivated contact cells (TOPcon), and heterojunction cells (HJT). Among them, crystalline silicon-amorphous silicon heterojunction solar cells (HJT) have gradually become one of the mainstream technologies of crystalline silicon cells due to their symmetrical structure, high open circuit voltage, low process temperature, and excellent temperature characteristics. They have received great attention from the industry and academia. At present, the efficiency of its certified large-area cell devices has reached 26.3%. In addition, the efficiency of TOPcon cells has also reached 25.7%, and TOPcon cells also have the advantage of low cost. HJT and TOPcon cells still have some problems. The light-entering surface of the cell is blocked by the grid line, which reduces the cell's absorption of sunlight, so the short-circuit current loss of the cell is large, which is also a problem faced by almost all silicon-based solar cells at present. Therefore, the research on solar cells without electrodes on the light-entering surface is particularly important. Based on this, interdigitated back contact solar cells (IBC) can solve this problem because their electrodes are set on the back of the cell, which can reduce the short-circuit current loss caused by the upper surface. The HBC (Hetero-Junction Back Contact) technology, which combines IBC technology with HJT technology, further reduces the metal recombination on the back of IBC. From the perspective of cell structure, HBC has the following advantages: ① The contact electrodes of the pn junction, substrate and emitter region are all on the back of the cell, and there is no metal electrode blocking the front, so it has a higher short-circuit current density; ② The front does not need to consider the contact resistance of the cell, and the front surface field and surface passivation can be optimally designed to increase the open circuit voltage of the cell; ③ The positive and negative electrodes are all on the back, and a wider metal grid line can be used to reduce the series resistance (Rs), thereby improving the fill factor (FF). The core issue of HBC is how to prepare high-quality p-regions and n-regions with interdigitated spacing on the back of the cell. Summary of the invention

[0003] The present invention provides a back-contact solar cell and a preparation method thereof and a photovoltaic module, aiming to solve the problem that the integrity of the second transmission layer in the existing back-contact solar cell is poor, which affects various performances of the back-contact solar cell.

[0004] A first aspect of the present invention provides a back-contact solar cell, comprising:

[0005] A silicon substrate, wherein the silicon substrate has a first surface; the first surface comprises: a first conductive region, a second conductive region, and an insulating region located between the first conductive region and the second conductive region; the second conductive region is a suede structure;

[0006] A first transmission layer, located on the first conductive area;

[0007] a barrier layer, located on the first transmission layer at an end region close to the insulating region;

[0008] a second transmission layer, located on the blocking layer, the insulating region and the second conductive region; the second transmission layer comprises: a first portion located in the insulating region and a second portion located in the second conductive region; a thickness of the first portion is greater than a thickness of the second portion;

[0009] The barrier layer includes a second surface away from the silicon substrate, and a first side surface connected to the second surface and close to the insulating region; the first side surface extends from a first end close to the second surface to a second end close to the insulating region, and then extends toward the insulating region.

[0010] In an embodiment of the present invention, the first transmission layer is located on the first conductive region. The barrier layer is located on the end region of the first transmission layer close to the insulating region. The second transmission layer is located on the barrier layer, the insulating region and the second conductive region. The barrier layer includes: a second surface away from the silicon substrate, and a first side surface connected to the second surface and close to the insulating region. The first side surface extends toward the insulating region from the first end close to the second surface to the second end close to the insulating region. That is, the first side surface has no concave portion toward the first conductive region, and the first side surface is conducive to the deposition of the second transmission layer, especially the deposition of the portion of the second transmission layer located on the first side surface, and the shape integrity of the formed second transmission layer is better, thereby improving the various performances of the back contact solar cell. The second conductive region is a velvet structure, and the other surfaces forming the second transmission layer are all non-velvet structures. The velvet structure has a larger specific surface area. Therefore, under the same deposition conditions, the thickness of the first part of the second transmission layer located in the insulating region will be greater than the thickness of the second part located in the second conductive region. Moreover, the second transmission layer, located in the first part of the insulating area, also has certain passivation and insulation properties. The thickness of the first part is greater than the thickness of the second part, which can improve the passivation and insulation properties of the back contact solar cell.

[0011] Optionally, the first side surface is a plane, or the first side surface is composed of a plurality of sub-regions, and the angles between adjacent sub-regions are less than or equal to 5°.

[0012] Optionally, a first angle between the first side surface and the first conductive region is an acute angle.

[0013] Optionally, the first side surface is a curved surface convex toward the second part.

[0014] Optionally, the second transmission layer further includes a third portion covering the first side surface and extending to an end portion close to the first portion, and the third portion has a shape of a continuous gentle slope.

[0015] Optionally, the first portion is composed of a continuous first sub-portion and a second sub-portion, the second sub-portion is connected to the second portion, and the third portion, the first sub-portion and the second sub-portion are sequentially connected to form a step shape;

[0016] A second angle between the first sub-portion away from the surface of the silicon substrate and the first conductive region is smaller than a third angle between the third sub-portion away from the surface of the silicon substrate and the first conductive region, and the second angle is smaller than a fourth angle between the second sub-portion away from the surface of the silicon substrate and the first conductive region.

[0017] Optionally, the first portion is in the shape of a continuous gentle slope.

[0018] Optionally, the thickness of the first part is 1.2 to 2 times the thickness of the second part.

[0019] Optionally, the second transmission layer includes: a back passivation layer and a doping layer stacked in sequence; the back passivation layer is closer to the silicon substrate than the doping layer; in the first part, the thickness of the back passivation layer is 1.2 to 2 times the thickness of the back passivation layer in the second part.

[0020] Optionally, the material of the barrier layer is selected from silicon nitride or silicon oxide.

[0021] Optionally, the barrier layer is a single-layer structure;

[0022] The refractive index of the barrier layer decreases from close to the silicon substrate to far away from the silicon substrate; or the refractive index at each position in the barrier layer is equal.

[0023] Optionally, the barrier layer is a multi-layer structure, and the etching rate of each layer structure decreases from close to the silicon substrate to away from the silicon substrate.

[0024] Optionally, the barrier layer is a multi-layer structure, and the refractive index of each layer structure decreases from close to the silicon substrate to away from the silicon substrate.

[0025] Optionally, the first end is farther away from the first conductive region than the second end; and along the thickness direction of the silicon substrate, a height difference between the first end and the second end is 30 nanometers to 200 nanometers.

[0026] Optionally, in a distribution direction parallel to the first conductive region and along the first conductive region and the insulating region, a size of the first sub-portion is less than or equal to 10 micrometers.

[0027] Optionally, the silicon substrate has a third surface opposite to the first surface, and the third surface is a suede structure; the first conductive region and the insulating region are both polished surface structures.

[0028] Optionally, the silicon substrate has a third surface opposite to the first surface; the first transmission layer comprises: a back passivation layer and a doping layer stacked in sequence; the back passivation layer is closer to the silicon substrate than the doping layer;

[0029] The back contact solar cell further comprises:

[0030] A transparent conductive layer, located on the second transmission layer and the exposed first transmission layer;

[0031] A first electrode is located on the transparent conductive layer, in the first conductive region outside the barrier layer;

[0032] a second electrode, located on the transparent conductive layer, in the second conductive region;

[0033] And a front passivation layer and a front anti-reflection layer are sequentially stacked on the third surface.

[0034] A second aspect of the present invention provides a method for preparing any of the aforementioned back-contact solar cells, comprising:

[0035] Step S1, providing a conductive substrate; the conductive substrate comprises: a silicon substrate, the silicon substrate having a first surface; the first surface comprises: a first conductive region, a second conductive region, and an insulating region located between the first conductive region and the second conductive region; a first transmission layer, a barrier layer, and a mask layer sequentially stacked on the first surface; the barrier layer is a single-layer structure, and the etching rate of the barrier layer decreases from the direction close to the silicon substrate to the direction away from the silicon substrate; or the barrier layer is a multi-layer structure, and the etching rate of each layer structure decreases from the direction close to the silicon substrate to the direction away from the silicon substrate;

[0036] Step S2, removing the mask layer located on the second conductive area and the insulating area, and removing the barrier layer located on the second conductive area, so that the first transmission layer located on the second conductive area is exposed, and the insulating area still has at least a partial thickness of the barrier layer;

[0037] Step S3, removing the first transmission layer exposed on the second conductive area, so that the second conductive area is exposed, and texturing the second conductive area under the condition that the barrier layer of at least a part of the thickness protects the insulating area, and the remaining mask layer protects the barrier layer on the first conductive area;

[0038] Step S4, removing the mask layer on the end region of the first conductive region close to the insulating region to expose the barrier layer thereunder, wet-etching at least a portion of the barrier layer on the insulating region to expose the insulating region, and wet-etching the exposed barrier layer on the end region of the first conductive region close to the insulating region to make the barrier layer on the end region of the first conductive region close to the insulating region include a second surface away from the silicon substrate, and a first side surface connected to the second surface and close to the insulating region; the first side surface extends from a first end close to the second surface to a second end close to the insulating region, and toward the insulating region in sequence;

[0039] Step S5, depositing a second transmission layer on the barrier layer, the insulating region and the second conductive region.

[0040] Optionally, the blocking layer is a single-layer structure, and the reflectivity of the blocking layer decreases from close to the silicon substrate to away from the silicon substrate; or, the blocking layer is a multi-layer structure, and the refractive index of each layer structure decreases from close to the silicon substrate to away from the silicon substrate.

[0041] Optionally, the material of the barrier layer is selected from silicon nitride, and the step S1 comprises:

[0042] Preparing a barrier layer of a multilayer structure; in the process of preparing each layer structure, the flow rate of the nitrogen-containing gas increases successively from the direction close to the silicon substrate to the direction away from the silicon substrate;

[0043] Alternatively, a barrier layer with a single-layer structure is prepared; during the preparation process of the barrier layer, the flow rate of the gas containing nitrogen element is gradually increased.

[0044] Optionally, the step of preparing a barrier layer of a multilayer structure comprises:

[0045] Prepare a first layer structure close to the first transmission layer; the thickness of the first layer structure is 10 nm to 50 nm, and the refractive index of the first layer structure is 2.1 to 2.7;

[0046] Preparing a second layer structure located on the first layer structure; the thickness of the second layer structure is 10 nm to 50 nm, and the refractive index of the second layer structure is 1.9 to 2.5;

[0047] preparing a third layer structure located on the second layer structure; the thickness of the third layer structure is 10 nm to 50 nm, and the refractive index of the third layer structure is 1.7 to 2.3; the refractive indices of the first layer structure, the second layer structure and the third layer structure decrease in sequence;

[0048] The method for preparing a barrier layer with a single-layer structure comprises:

[0049] During the preparation of the single-layer structure, the flow rate of the nitrogen gas is 50 sccm to 300 sccm, and the flow rate of the nitrogen gas increases successively; or, during the preparation of the single-layer structure, the flow rate of the ammonia gas is 50 sccm to 400 sccm, and the flow rate of the ammonia gas increases successively.

[0050] Optionally, the material of the barrier layer is selected from silicon oxide, and the step S1 comprises:

[0051] Depositing a barrier layer of a multilayer structure; the deposition rate of each layer structure increases from close to the silicon substrate to away from the silicon substrate;

[0052] Alternatively, a barrier layer of a single-layer structure is deposited; during the deposition of the barrier layer, the deposition rate is increased.

[0053] Optionally, step S4 includes: first removing the mask layer on the end region of the first conductive region close to the insulating region, so that the barrier layer thereunder is exposed; then, wet etching at least a portion of the thickness of the barrier layer on the insulating region and the exposed barrier layer on the end region of the first conductive region close to the insulating region together, etching away at least a portion of the thickness of the barrier layer on the insulating region, so that the insulating region is exposed, and the barrier layer on the end region of the first conductive region close to the insulating region includes a second surface away from the silicon substrate, and a first side surface connected to the second surface and close to the insulating region; the first side surface extends from a first end close to the second surface to a second end close to the insulating region, and toward the insulating region in sequence;

[0054] Alternatively, step S4 includes: first, wet-etching at least part of the thickness of the barrier layer on the insulating region to etch away at least part of the thickness of the barrier layer on the insulating region to expose the insulating region; then, removing the mask layer on the end region of the first conductive region close to the insulating region to expose the barrier layer thereunder, and wet-etching the exposed barrier layer on the end region of the first conductive region close to the insulating region to make the barrier layer on the end region of the first conductive region close to the insulating region include a second surface away from the silicon substrate, and a first side surface connected to the second surface and close to the insulating region; the first side surface extends toward the insulating region in sequence from a first end close to the second surface to a second end close to the insulating region.

[0055] Optionally, step S2 includes:

[0056] Laser is used to remove the mask layer on the second conductive area and the barrier layer thereunder, so that the first transmission layer located in the second conductive area is exposed. At the same time, the heat-affected zone at the edge of the laser spot ablates the mask layer on the insulating area, or the mask layer on the insulating area and part of the thickness of the barrier layer thereunder, so that the insulating area still has at least part of the thickness of the barrier layer.

[0057] Optionally, in step S4, the wet etching solution includes: hydrofluoric acid, or phosphoric acid.

[0058] According to a third aspect of the present invention, there is provided a photovoltaic module, comprising: a plurality of any of the aforementioned back-contact solar cells.

[0059] The above-mentioned back-contact solar cell, method for preparing back-contact solar cell and photovoltaic module all have the same or similar beneficial effects, and will not be described again here to avoid repetition. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0061] Figure 1 A partial structural schematic diagram of a back-contact solar cell in an embodiment of the present invention is shown;

[0062] Figure 2 A partial structural schematic diagram of another back-contact solar cell in an embodiment of the present invention is shown;

[0063] Figure 3 A schematic diagram of a local structure of a barrier layer in an embodiment of the present invention is shown;

[0064] Figure 4 A schematic diagram of the partial structure of another barrier layer in an embodiment of the present invention is shown.

[0065] Description of the accompanying drawings:

[0066] 1-silicon substrate, 2-first transmission layer, 21-back passivation layer of the first transmission layer, 22-doping layer of the first transmission layer, 3-blocking layer, 31-second surface, 32-first side, 4-second transmission layer, 41-back passivation layer of the second transmission layer, 42-doping layer of the second transmission layer, 5-transparent conductive layer, 6-first electrode, 7-second electrode. DETAILED DESCRIPTION

[0067] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] The present invention provides a back contact solar cell. Figure 1 A partial structural schematic diagram of a back-contact solar cell in an embodiment of the present invention is shown. Figure 2 A partial structural schematic diagram of another back-contact solar cell in an embodiment of the present invention is shown. Figure 3 A schematic diagram of the local structure of a barrier layer in an embodiment of the present invention is shown. Figure 4 A schematic diagram of the partial structure of another barrier layer in an embodiment of the present invention is shown.

[0069] Reference Figure 1 , Figure 2 The upper side of the silicon substrate 1 is the first side of the silicon substrate 1, and the upper surface of the silicon substrate 1 is the first surface. The back contact solar cell includes a silicon substrate 1, and the first surface of the first side of the silicon substrate 1 includes: a first conductive region, a second conductive region, and an insulating region located between the first conductive region and the second conductive region. Figure 1 , Figure 2 In the figure, the area on the left side of the dotted line L4 in the first surface of the silicon substrate 1 is the first conductive area, the area between the dotted line L4 and the dotted line L2 in the first surface of the silicon substrate 1 is the insulating area, and the area on the right side of the dotted line L2 is the second conductive area. It should be noted that in the back-contact solar cell, the dotted lines L2, L3, L4, L5, and L6 do not actually exist, and are only used here to illustrate different areas. The second conductive area is a velvet structure, and the size of the velvet structure is not specifically limited. That is, the area on the right side of the dotted line L2 in the first surface of the silicon substrate 1 is a velvet structure.

[0070] The first transmission layer 2, the second transmission layer 4 and the barrier layer 3 are all located on the first side of the silicon substrate 1. The doping type of the silicon substrate 1 can be N-type doping or P-type doping, etc., and the doping type of the silicon substrate 1 is not specifically limited. The first side of the silicon substrate 1 is the side of the silicon substrate 1 close to the electrode of the back-contact solar cell, and the first surface of the first side of the silicon substrate 1 is the surface of the silicon substrate 1 close to the electrode of the back-contact solar cell. The first transmission layer 2 and the second transmission layer 4 have different doping types, that is, one of them is N-type doping and the other is P-type doping.

[0071] like Figure 1 , Figure 2 The first transmission layer 2 is located on the first conductive region. The barrier layer 3 is located on the end region of the first transmission layer 2 close to the insulating region. The second transmission layer 4 is located on the barrier layer 3, the insulating region and the second conductive region.

[0072] Reference Figures 1 to 4 The barrier layer 3 includes: a second surface 31 away from the silicon substrate 1, and a first side surface 32 connected to the second surface 31 and close to the insulating region. The first side surface 32 extends from a first end close to the second surface 31 to a second end close to the insulating region, and then extends toward the insulating region. Figures 1 to 4In the figure, the position of the first side surface 32 that coincides with the dotted line L3 is the position of the first end of the first side surface 32, and the position of the first side surface 32 that coincides with the dotted line L5 is the position of the second end of the first side surface 32. The first side surface 32 does not have a concave portion facing the first conductive region, and the first side surface 32 is conducive to the deposition of the second transmission layer 4, especially the deposition of the portion of the second transmission layer 4 located on the first side surface 32, so that the formed second transmission layer 4 has better shape integrity, thereby improving various performances of the back contact solar cell.

[0073] Reference Figure 1 , Figure 2 , the second transmission layer 4 includes: a first part located in the insulating region, and a second part located in the second conductive region. The first part of the second transmission layer 4 is the part of the second transmission layer 4 located between the dotted lines L4 and L2, and the part of the second transmission layer 4 located to the right of the dotted line L2 is the second part located on the second conductive region. In the second transmission layer 4, the thickness of the first part located in the insulating region is greater than the thickness of the second part located in the second conductive region. The specific reason is that the second conductive region is a velvet structure, and the other surfaces forming the second transmission layer 4 are all non-velvet structures, for example, they can be polished surfaces. The velvet structure has a larger specific surface area. Therefore, under the same deposition conditions, the thickness of the first part of the second transmission layer 4 located in the insulating region will be greater than the thickness of the second part located in the second conductive region. Moreover, the first part of the second transmission layer 4 located in the insulating region also has certain passivation and insulation properties. The thickness of the first part is greater than the thickness of the second part, which can improve the passivation and insulation properties of the back contact solar cell.

[0074] It should be noted that how much greater the thickness of the first portion is than the thickness of the second portion is determined by the size of the suede structure of the second conductive region and actual process conditions.

[0075] Optional, see Figure 3 The first side surface 32 is a plane, or the first side surface 32 is composed of a plurality of sub-regions, and the angles between adjacent sub-regions are all less than or equal to 5°. The shape of the first side surface 32 is flexible and diverse, and it is easy to prepare a second transmission layer 4 with a more complete shape. For example, in the first side surface 32, the angles between adjacent regions can be: 5°, or 4°, or 3°, or 2.5°, or 2°, or 1°, or 0.5°, or 0.4°, etc.

[0076] Optional, see Figure 1 , Figure 2 , Figure 3The first side surface 32 is a plane, or the first side surface 32 is composed of a plurality of sub-regions, and the angles between adjacent sub-regions are less than or equal to 5°. The first angle a between the first side surface 32 and the insulating region is an acute angle, that is, the first angle a is greater than 0 and less than 90°. The shape of the first side surface 32 is flexible and diverse, and it is easy to prepare a second transmission layer 4 with a more complete shape.

[0077] Optional, see Figure 4 The first side surface 32 is a curved surface convex toward the second portion. The shape of the first side surface 32 is flexible and diverse, and it is easy to prepare a second transmission layer 4 with a more complete shape.

[0078] Reference Figure 1 , Figure 2 , the first part of the second transmission layer 4 is: the part of the second transmission layer 4 between the dotted line L4 and the dotted line L2. The second part of the second transmission layer 4 is: the part of the second transmission layer 4 on the right side of the dotted line L2. The second transmission layer 4 also includes: a third part covering the first side surface 32 and extending to the end close to the first part, the third part is the part of the second transmission layer 4 on the right side of the dotted line L3 and on the left side of the dotted line L4.

[0079] Optional, see Figure 1 The shape of the third part is a continuous gentle slope. The shape of the third part is flexible and diverse, and it is easy to prepare a second transmission layer 4 with a more complete shape.

[0080] Optional, see Figure 1 The first part is continuous with the third part, the first part is in a continuous gentle slope, the shape of the first part is flexible and diverse, and it is easy to prepare a second transmission layer 4 with a more complete shape.

[0081] Optional, see Figure 2, the first part of the second transmission layer 4 is composed of a first sub-portion between the dotted line L4 and the dotted line L6 in the second transmission layer 4, and a second sub-portion between the dotted line L6 and the dotted line L2 in the second transmission layer 4. The first sub-portion and the second sub-portion are continuous, and the third part between the dotted line L3 and the dotted line L4 in the second transmission layer 4, the first sub-portion between the dotted line L4 and the dotted line L6 in the second transmission layer 4, and the second sub-portion between the dotted line L6 and the dotted line L2 in the second transmission layer 4 are sequentially connected to form a step shape. The second angle between the first sub-portion between the dotted line L4 and the dotted line L6 in the second transmission layer 4, which is away from the surface of the silicon substrate 1, and the first conductive region, is smaller than the third angle b between the third part between the dotted line L3 and the dotted line L4 in the second transmission layer 4, which is away from the surface of the silicon substrate 1, and the insulating region, and the second angle is smaller than the fourth angle c between the second sub-portion between the dotted line L6 and the dotted line L2 in the second transmission layer 4, which is away from the surface of the silicon substrate 1, and the first conductive region. Whether the third angle b between the third portion, which is away from the surface of the silicon substrate 1, and the first conductive region, and the fourth angle c between the second sub-portion, which is away from the surface of the silicon substrate 1, and the first conductive region, are equal, has little effect on the shape integrity of the third portion, as well as the first sub-portion and the second sub-portion. Compared with the first portion and the third portion being continuous structures, the first portion and the third portion are stepped, which reduces the processing difficulty, expands the process window, and improves the product yield. It should be noted that if the third angle b and the fourth angle c are not equal, there is no limitation on which is larger. The second angle between the second sub-portion, which is away from the surface of the silicon substrate 1, and the first conductive region, can be 0°, or close to 0°. For example, Figure 2 The second angle may be 0°. For another example, the second angle may range from 0° to 10°.

[0082] Optional, see Figure 2 , in the distribution direction L7 parallel to the first conductive region and along the first conductive region and the insulating region, the size d1 of the first sub-portion located between the dotted line L4 and the dotted line L6 in the first portion is less than or equal to 10 micrometers (μm). The size of the first sub-portion within this range has a significant contribution to reducing the difficulty of processing, expanding the process window, and improving the product yield, and is easy to manufacture.

[0083] For example, along the direction L7 , in the first portion, a size d1 of the first subportion between the dotted line L4 and the dotted line L6 is 0.3 μm, 1 μm, 2 μm, 5 μm, 6 μm, 9 μm, or 10 μm.

[0084] Optional, see Figure 1 , Figure 2In the second transmission layer 4, the first part located in the insulating region is the part located between the dotted line L4 and the dotted line L2 in the second transmission layer 4, and the second part located in the second conductive region is the part located on the right side of the dotted line L2 in the second transmission layer 4. In the second transmission layer 4, the thickness of the first part located in the insulating region is 1.2 to 2 times the thickness of the second part in the second conductive region. When the thicknesses of the two parts are within this range, deposition is easy and the deposition process window is wide. For example, the thickness of the first part is 1.2 times, 1.3 times, 1.4 times, 1.5 times, 1.6 times, 1.68 times, 1.7 times, 1.71 times, 1.9 times, or 2 times the thickness of the second part in the second conductive region.

[0085] Optional, see Figure 1 , Figure 2 , the second transmission layer 4 includes: a back passivation layer 41 and a doping layer 42 stacked in sequence. The back passivation layer 41 is closer to the silicon substrate 1 than the doping layer 42. In the first part of the second transmission layer 4, the thickness of the back passivation layer 41 is 1.2 to 2 times the thickness of the back passivation layer 41 in the second part of the second transmission layer 4. Specifically, the back passivation layer 41 in the first part of the insulating region of the second transmission layer 4 mainly plays a role in avoiding the formation of leakage channels and back passivation. The thickness of the back passivation layer 41 in the first part of the insulating region of the second transmission layer 4 is relatively thick, thereby greatly reducing the probability of forming leakage channels and improving back passivation, thereby improving the photoelectric conversion efficiency of the back contact solar cell. At the same time, the thickness of the two is within this range. Since the velvet structure of the second conductive region has a large specific surface area, it is easy to deposit and obtain, and the window of the deposition process is wide.

[0086] For example, in the first part of the second transmission layer 4, the thickness of the back passivation layer 41 is 1.2 times, or 1.3 times, or 1.4 times, or 1.5 times, or 1.6 times, or 1.69 times, or 1.7 times, or 1.72 times, or 1.9 times, or 2 times the thickness of the back passivation layer 41 in the second part of the second transmission layer 4.

[0087] Optionally, the material of the barrier layer 4 is selected from silicon nitride or silicon oxide. The barrier layer 4 made of the above materials can be easily formed into the first side surface 32 of the aforementioned shape and has low cost.

[0088] Optionally, the barrier layer 4 is a single-layer structure, and the refractive index of the barrier layer 4 decreases in the direction L1 from close to the silicon substrate 1 to away from the silicon substrate 1. The barrier layer 4 of the above material and structure has a refractive index distributed according to this rule, which makes it particularly easy to form the first side surface 32 of the aforementioned shape and has low cost.

[0089] Optionally, the barrier layer 4 is a single-layer structure, and the refractive index at each position in the barrier layer 4 is equal. The barrier layer 4 of the above material and structure is also particularly easy to form the first side surface 32 of the above shape, and the cost is relatively low.

[0090] Optionally, the barrier layer 4 is a multi-layer structure, and the refractive index of each layer structure decreases from the direction L1 close to the silicon substrate 1 to the direction L1 away from the silicon substrate 1. The barrier layer 4 of the above material and structure has a refractive index distributed according to this rule, which is particularly easy to form the first side surface 32 of the above shape, and the cost is low. For example, the barrier layer is a two-layer structure, and the refractive index of each layer structure decreases along the direction L1. For another example, the barrier layer is a three-layer structure, and the refractive index of each layer structure decreases along the direction L1.

[0091] Optionally, the barrier layer 4 is a multi-layer structure, and the etching rate of each layer structure decreases from the direction L1 close to the silicon substrate 1 to the direction L1 away from the silicon substrate 1. The etching rate is distributed according to this rule, which makes it particularly easy to etch the first side surface 32 of the aforementioned shape, and the cost is relatively low.

[0092] Optional, see Figure 3 , Figure 4 , in the first side 32 of the barrier layer 3, the first end close to the second surface 31 is farther from the first conductive region than the second end close to the insulating region. In the thickness direction of the silicon substrate 1, in the first side 32, the height difference d2 between the first end and the second end is: 30 nanometers (nm) to 200 nanometers. The barrier layer 3 of the above size has a better barrier effect and is easy to obtain, and the first side 32 of the above size is easy to obtain a second transmission layer 4 with better shape integrity. Here, the thickness direction along the silicon substrate 1 is parallel to the aforementioned direction L1 from close to the silicon substrate 1 to away from the silicon substrate 1.

[0093] For example, along the thickness direction of the silicon substrate 1, in the first side 32, the height difference d2 between the first end and the second end is: 30nm, or 30nm, or 50nm, or 80nm, or 110nm, or 120nm, or 150nm, or 180nm, or 200nm.

[0094] Optionally, the third surface of the second side of the silicon substrate 1 is a velvet structure, the second side of the silicon substrate 1 is opposite to the first side of the silicon substrate 1, and the third surface is opposite to the first surface. Figure 1 , Figure 2 The second side of the silicon substrate 1 is the lower side of the silicon substrate 1. The third surface of the second side of the silicon substrate 1 is a suede structure, which can increase the light trapping effect and improve the photoelectric conversion efficiency.

[0095] Optionally, the first conductive region and the insulating region in the first surface of the silicon substrate 1 are both polished surface structures, and the first conductive region and the insulating region are relatively flat, so it is easy to prepare the first transmission layer 2 with good quality.

[0096] Optionally, the first transmission layer 2 includes: a back passivation layer 21 and a doping layer 22 stacked in sequence; the back passivation layer 21 is closer to the silicon substrate 1 than the doping layer 22. The doping type of the doping layer 22 in the first transmission layer 2 is different from the doping type of the doping layer 42 in the second transmission layer 4, that is, one of them is N-type doped and the other is P-type doped.

[0097] Optionally, the materials of the back passivation layer 21 of the first transmission layer 2 and the back passivation layer 41 of the second transmission layer 4 are both selected from: amorphous silicon, and the materials of the doping layer 22 of the first transmission layer 2 and the doping layer 42 of the second transmission layer 4 are both selected from: doped amorphous silicon or doped microcrystalline silicon, that is, the back contact solar cell is an HBC (Heterojunction back contact) cell, and the HBC cell has the following advantages: first, the pn junction, the silicon substrate 1 and the contact electrode of the emitter region are all on the back of the cell, and there is no metal electrode blocking the front, so it has a higher short-circuit current density; second, the light-facing side does not need to consider the contact resistance of the cell, and the front surface field and surface passivation can be optimally designed to increase the open circuit voltage of the cell; third, the positive and negative electrodes are all on the back, and a wider metal grid line can be used to reduce the series resistance (Rs), thereby improving the fill factor (FF). The back contact solar cell also has the advantages of low process temperature and excellent temperature characteristics.

[0098] Or, optionally, the materials of the back passivation layer 21 of the first transmission layer 2 and the back passivation layer 41 of the second transmission layer 4 are both selected from: silicon oxide, and the materials of the doping layer 22 of the first transmission layer 2 and the doping layer 42 of the second transmission layer 4 are both selected from: doped polycrystalline silicon, that is, the back contact solar cell is a TBC (Tunnel Oxide Passivated Contactbackcontact) cell, and the back contact solar cell also has the advantages of high open circuit voltage, low process temperature, excellent temperature characteristics and the like.

[0099] Optional, see Figure 1 , Figure 2 The back contact solar cell further includes: a transparent conductive layer 5, a first electrode 6, and a second electrode 7, all of which are located on the first side of the silicon substrate 1. The transparent conductive layer 5 is located on the second transmission layer and the exposed first transmission layer. The first electrode 6 is located on the transparent conductive layer 5 at a position outside the barrier layer 3 in the first conductive region, and the second electrode 7 is located on the transparent conductive layer 5 at a position corresponding to the second conductive region.

[0100] The back contact solar cell may further include: a front passivation layer and a front anti-reflection layer sequentially stacked on the third surface of the silicon substrate 1. The first surface and the third surface are arranged opposite to each other.

[0101] The present invention also provides a method for preparing a back-contact solar cell, comprising the following steps.

[0102] Step S1, providing a conductive substrate; the conductive substrate includes: a silicon substrate, the silicon substrate has a first surface; the first surface includes: a first conductive region, a second conductive region and an insulating region located between the first conductive region and the second conductive region; a first transmission layer, a barrier layer and a mask layer are sequentially stacked on the first surface; the barrier layer is a single-layer structure, and the etching rate of the barrier layer decreases from close to the silicon substrate to away from the silicon substrate; or, the barrier layer is a multi-layer structure, and the etching rate of each layer structure decreases from close to the silicon substrate to away from the silicon substrate; the portion of the barrier layer located in the second conductive region is disconnected, so that the first transmission layer on the second conductive region is exposed.

[0103] The silicon substrate 1 may be wet cleaned in advance to remove the cutting damage layer, foreign particles, metals, organic matter, moisture molecules, natural oxide film, etc.

[0104] The step S1 may be: using LPCVD (Low Pressure Chemical Vapor Deposition) or PECVD (Plasma Enhanced Chemical Vapor Deposition) to prepare a back passivation layer 21 and a back doping layer 22 of the first transmission layer 2 on the first side of the silicon substrate 1, and depositing a barrier layer 3 on the first transmission layer 2. The thickness of the back passivation layer 21 is 3nm (nanometer) to 15nm, for example, it can be 5nm-8nm. The thickness of the back doping layer 22 is 5nm to 25nm, for example, it can be 10nm-15nm. Then, a mask layer is deposited on the back doping layer 22. The mask layer can be an acid-resistant and alkali-resistant mask layer. For example, the material of the mask layer can be selected from polyurethane, etc., and the specific material of the mask layer is not limited.

[0105] Optionally, the blocking layer 3 is a single-layer structure, and the reflectivity of the blocking layer 3 decreases from close to the silicon substrate 1 to away from the silicon substrate 1; or, the blocking layer 3 is a multi-layer structure, and the reflectivity of each layer structure decreases from close to the silicon substrate 1 to away from the silicon substrate 1. The greater the reflectivity of the blocking layer 3, the slower the etching rate. The reflectivity of the above-mentioned blocking layer 3 is set according to this rule, and the above-mentioned first side 32 is easy to obtain.

[0106] Optionally, the barrier layer 3 can be divided into a multi-layer structure or a single-layer structure. The material of the barrier layer 3 is selected from silicon nitride (SiN x). A barrier layer with a single-layer structure is prepared. During the preparation process of the barrier layer, the flow rate of the nitrogen-containing gas is gradually increased, so that a barrier layer 3 with a decreasing refractive index or a decreasing etching rate from the direction L1 close to the silicon substrate 1 to the direction away from the silicon substrate can be simply prepared. There is no specific limitation on the degree of increase in the flow rate of the nitrogen-containing gas.

[0107] Optionally, the barrier layer 3 is a multi-layer structure. The material of the barrier layer 3 is selected from silicon nitride (SiN x ). In preparing a barrier layer of a multilayer structure, the flow rate of the nitrogen-containing gas increases successively from the direction L close to the silicon substrate 1 to the direction L far away from the silicon substrate 1 during the preparation of each layer structure, so that a barrier layer with a reduced refractive index or a reduced etching rate in each layer structure from the direction L close to the silicon substrate 1 to the direction L1 far away from the silicon substrate can be simply prepared. The degree of increase in the flow rate of the nitrogen-containing gas during the preparation of each layer structure is not specifically limited.

[0108] Optionally, the barrier layer 3 is a multi-layer structure. The material of the barrier layer 3 is selected from silicon nitride (SiN x ). Preparing the barrier layer 3 of the multilayer structure may include: preparing a first layer structure close to the silicon substrate 1, the first layer structure has a thickness of 10nm-50nm, for example, 15nm-40nm, and the refractive index of the first layer structure is 2.4±0.3, for example, 2.5-2.6. Preparing a second layer structure located on the first layer structure, the second layer structure has a thickness of 10nm-50nm, for example, 15nm-40nm, and the refractive index is 2.2±0.3, for example, 2.3-2.4. Preparing a third layer structure located on the second layer structure, the third layer structure has a thickness of 10nm-50nm, for example, 15nm-40nm, and the refractive index is 2.0±0.3, for example, 2.1-2.2.

[0109] Alternatively, the barrier layer 3 is a single-layer structure. The material of the barrier layer 3 is selected from silicon nitride (SiN x). During the preparation of a single-layer structure, the flow rate of nitrogen gas is 50sccm (standard cubic centimeter per minute) to 300sccm, and the flow rate of nitrogen gas is gradually increased; or, during the preparation of a single-layer structure, the flow rate of ammonia gas is 50sccm to 400sccm, and the flow rate of ammonia gas is gradually increased. In this way, a barrier layer with a single-layer structure whose refractive index decreases or whose etching rate decreases from the direction close to the silicon substrate 1 to the direction L1 away from the silicon substrate can be easily prepared. For example, when depositing silicon nitride, the flux of N2 or NH3 is gradually increased to form a silicon nitride film layer with a single-layer structure whose refractive index decreases or whose etching rate decreases. The thickness of the silicon nitride film layer of this single-layer structure is 20nm-200nm, for example, 30nm-90nm, and the flow rate of N2 is also gradually increased.

[0110] Optionally, the material of the barrier layer 3 is selected from silicon oxide (SiO x ), the aforementioned step S1 may include: depositing a barrier layer 3 of a multilayer structure, and the deposition rate of each layer structure increases from the direction L1 close to the silicon substrate 1 to the direction away from the silicon substrate 1. The higher the deposition rate, the lower the density of the formed silicon oxide, the lower the refractive index, and the lower the etching rate. Therefore, a barrier layer 3 with a lower refractive index in each layer structure can be obtained from the direction L1 close to the silicon substrate 1 to the direction away from the silicon substrate 1.

[0111] Alternatively, the material of the barrier layer 3 is selected from silicon oxide (SiO x ), the aforementioned step S1 may include: depositing a barrier layer 3 of a single-layer structure, during the deposition process of the barrier layer 3, the deposition rate increases, the higher the deposition rate, the lower the density of the formed silicon oxide, the lower the refractive index, and the lower the etching rate, so that a barrier layer 3 with a decreasing refractive index or a decreasing etching rate from the direction L1 close to the silicon substrate 1 to the direction away from the silicon substrate 1 can be obtained.

[0112] Step S2, removing the mask layer located in the second conductive area and the insulating area, and removing the blocking layer located in the second conductive area, so that the first transmission layer located in the second conductive area is exposed, and the insulating area still has at least a partial thickness of the blocking layer.

[0113] Laser, special etching agent, etc. can be used to remove the mask layer located in the second conductive area and the insulating area, and remove the blocking layer 3 located in the second conductive area, so that the first transmission layer located in the second conductive area is exposed, and the insulating area still has at least a partial thickness of the blocking layer 3.

[0114] Optionally, step S2 may include: using laser to remove the mask layer on the second conductive area and the barrier layer 3 thereunder, so that the first transmission layer on the second conductive area is exposed. The laser may be adjusted so that a heat-affected zone exists at the edge of the laser spot. While the laser removes the mask layer on the second conductive area and the barrier layer 3 thereunder, the heat-affected zone at the edge of the laser spot ablates the mask layer on the insulating area, or the mask layer on the insulating area and the barrier layer 3 of a part of its thickness thereunder, so that the insulating area still has at least a part of its thickness of the barrier layer 3. That is, the heat-affected zone at the edge of the laser spot may be the zone that only ablates the mask layer on the insulating area, or the heat-affected zone at the edge of the laser spot may be the zone that ablates the mask layer on the insulating area and the barrier layer 3 of a part of its thickness thereunder, depending on the energy of the heat-affected zone at the edge of the laser spot. When the energy of the heat-affected zone at the edge of the laser spot is relatively large, the heat-affected zone at the edge of the laser spot may ablate the mask layer on the insulating area and the barrier layer 3 of a part of its thickness thereunder. When the energy of the heat-affected zone at the edge of the laser spot is small, the heat-affected zone at the edge of the laser spot can only ablate the mask layer on the insulating area.

[0115] It should be noted that after the laser is used to complete the patterning process, if there is a little barrier layer 3 left on the second conductive area, hydrofluoric acid or phosphoric acid can be used to clean the barrier layer 3 that may remain on the second conductive area after the patterning process. The hydrofluoric acid here can be at room temperature, and the phosphoric acid can be greater than or equal to 158°C. Since the barrier layer on the second conductive area has been etched by the laser spot, the barrier layer 3 that may remain on the second conductive area is less or thinner. Even if the heat-affected zone at the edge of the laser spot ablates the mask layer on the insulating area and the barrier layer 3 of a certain thickness thereunder, the energy of the heat-affected zone at the edge of the laser spot is much smaller than the energy of the laser spot. Therefore, the thickness of the barrier layer 3 left on the insulating area is much greater than the thickness of the barrier layer 3 that may remain on the second conductive area. By controlling the cleaning time, etc., the barrier layer 3 that may remain on the second conductive area is completely cleaned, the first transmission layer on the second conductive area is exposed, and there is still a barrier layer 3 of a certain thickness on the insulating area. During the cleaning process, the barrier layer 3 on the first transmission layer on the first conductive region is substantially unaffected because of the protection of the mask layer.

[0116] It should be noted that when the area of ​​the heat affected zone at the edge of the laser spot is large, Figure 2The structure of the first part shown in the figure, that is, in the first part formed, the second angle between the first sub-part and the surface of the silicon substrate 1 is smaller than the third angle b between the third sub-part and the surface of the silicon substrate 1, and the first conductive region, and the second angle is smaller than the fourth angle c between the second sub-part and the surface of the silicon substrate 1, and the first conductive region, and the third part, the first sub-part and the second sub-part are connected in sequence to form a step shape. When the area of ​​the heat-affected zone at the edge of the laser spot is small, it can form Figure 1 The structure of the first part shown in , that is, the first part is in a continuous gentle slope shape, and the first part and the third part are continuous and form a gentle slope shape.

[0117] Step S3, removing the first transmission layer exposed on the second conductive area, exposing the second conductive area, and texturing the second conductive area while at least part of the thickness of the barrier layer protects the insulating area, and the remaining mask layer protects the barrier layer on the first conductive area.

[0118] A texturing liquid can be used to remove the exposed first transmission layer on the second conductive area, so that the second conductive area is exposed, and the second conductive area is texturized. During the texturing process, at least a portion of the thickness of the barrier layer located on the insulating area will protect the insulating area, and the remaining mask layer will protect the barrier layer on the first conductive area. For example, the texturing liquid is an alkaline texturing liquid, the barrier layer is silicon nitride and / or silicon oxide, the alkaline texturing liquid has basically no damage to the barrier layer, the mask layer is acid-resistant and alkali-resistant, and the alkaline texturing liquid has basically no effect on the mask layer. The main purpose of texturing the second conductive area is that the velvet structure can provide a larger specific surface area, and then under the same deposition conditions, the second part of the second transmission layer obtained on the second conductive area has a smaller thickness, and the first part located on the insulating area has a larger thickness, thereby providing better insulation performance and passivation performance, etc.

[0119] It should be noted that the third surface of the second side of the silicon substrate 1 is exposed, and the third surface can also be textured while the second conductive area is textured. The third surface is textured after the first side of the silicon substrate 1 has the first transmission layer 2 and the barrier layer 3. The barrier layer 3 can be used as a mask for the remaining areas except the second conductive area, which saves the process and improves the production efficiency. There is no specific limitation on the texturing liquid for texturing.

[0120] Step S4, removing the mask layer on the end region of the first conductive region close to the insulating region to expose the barrier layer thereunder, and wet-etching at least part of the thickness of the barrier layer on the insulating region to expose the insulating region, and wet-etching the exposed barrier layer on the end region of the first conductive region close to the insulating region to make the barrier layer on the end region of the first conductive region close to the insulating region include a second surface away from the silicon substrate, and a first side surface connected to the second surface and close to the insulating region; the first side surface extends toward the insulating region from a first end close to the second surface to a second end close to the insulating region.

[0121] The mask layer on the end region of the first conductive region close to the insulating region may be removed by using laser, special etchant or the like.

[0122] During the wet etching process, at least part of the thickness of the barrier layer in the insulating region will be completely etched away. The barrier layer 3 on the end region of the first conductive region close to the insulating region has a slower etching rate as the refractive index is larger. Therefore, during the wet etching process, the etching rate of the portion of the barrier layer 3 far from the silicon substrate 1 is fast, while the etching rate of the portion close to the silicon substrate 1 is slow. Further, the barrier layer 3 after wet etching includes: a second surface 31 far from the silicon substrate 1, and a first side surface 32 connected to the second surface 31 and close to the insulating region. The first side surface 32 extends toward the insulating region from a first end close to the second surface 31 to a second end close to the insulating region.

[0123] Optionally, in step S4, the wet etching etchant may include: hydrofluoric acid, or phosphoric acid. The hydrofluoric acid may be etched at room temperature, and the phosphoric acid may be etched at a temperature of 158° C. or above. The above-mentioned etchant has a slow etching rate for the barrier layer 3 with a large refractive index, and a fast etching rate for the barrier layer 3 with a small refractive index. It is easy to form the first side surface 32 of the aforementioned shape, and the cost is low, and the impact on other film layers of the back contact solar cell is small.

[0124] Optionally, the aforementioned step S4 may include: first removing the mask layer on the end region of the first conductive region close to the insulating region to expose the barrier layer 3 thereunder; then, wet etching at least a portion of the thickness of the barrier layer 3 on the insulating region and the exposed barrier layer 3 on the end region of the first conductive region close to the insulating region together to etch away at least a portion of the thickness of the barrier layer 3 on the insulating region to expose the insulating region, and making the barrier layer 3 on the end region of the first conductive region close to the insulating region include a second surface 31 away from the silicon substrate 1, and a first side surface 32 connected to the second surface 31 and close to the insulating region; the first side surface 32 extends toward the insulating region from a first end close to the second surface 31 to a second end close to the insulating region. That is, the barrier layer 3 on the insulating region and the barrier layer 3 exposed on the end region of the first conductive region close to the insulating region are etched together. Due to the protective effect of the mask layer on the barrier layer 3 exposed on the end region of the first conductive region close to the insulating region, the barrier layer 3 on the insulating region is affected by the ablation effect of the heat affected zone at the edge of the laser spot, and the influence of the texturing liquid, the barrier layer 3 on the insulating region will be thinner than the barrier layer 3 exposed on the end region of the first conductive region close to the insulating region. Therefore, in the same wet etching environment, by controlling the etching conditions, etc., it can be achieved that the barrier layer 3 on the insulating region has been completely etched, while the barrier layer 3 exposed on the end region of the first conductive region close to the insulating region still remains. Moreover, since the etching rate or refractive index of the barrier layer 3 decreases from close to the silicon substrate 1 to away from the silicon substrate, the barrier layer on the end region of the first conductive region close to the insulating region is easy to form the aforementioned required morphology.

[0125] Alternatively, optionally, the aforementioned step S4 may include: first, wet-etching at least a portion of the thickness of the barrier layer 3 on the insulating region to etch away at least a portion of the thickness of the barrier layer 3 on the insulating region to expose the insulating region; then, removing the mask layer on the end region of the first conductive region close to the insulating region to expose the barrier layer 3 thereunder, and wet-etching the exposed barrier layer 3 on the end region of the first conductive region close to the insulating region to make the barrier layer 3 on the end region of the first conductive region close to the insulating region include a second surface 31 away from the silicon substrate 1, and a first side surface 32 connected to the second surface 31 and close to the insulating region, the first side surface 32 extending from a first end close to the second surface 32 to a second end close to the insulating region, and then toward the insulating region. That is to say, the barrier layers 3 in the two regions are etched separately, and first, at least a portion of the thickness of the barrier layer 3 on the insulating region is wet-etched. During the wet etching process, the remaining mask layer will protect the barrier layer 3 on the end region of the first conductive region close to the insulating region. After at least a portion of the thickness of the barrier layer 3 on the insulating region is completely etched, the mask layer on the end region of the first conductive region close to the insulating region is removed. The mask layer on the region can also be removed by laser, special etching agent, etc., and then the barrier layer 3 on the end region of the first conductive region close to the insulating region is wet-etched. Since the etching rate or refractive index of the barrier layer 3 decreases from close to the silicon substrate 1 to away from the silicon substrate, the barrier layer on the end region of the first conductive region close to the insulating region is easy to form the aforementioned required morphology.

[0126] It should be noted that etching the barrier layer 3 on the insulating region together with the exposed barrier layer 3 on the end region of the first conductive region close to the insulating region reduces one etching step, but the process window is narrow. Etching the barrier layer 3 on the insulating region separately from the barrier layer 3 on the end region of the first conductive region close to the insulating region has a wider process window and is easy to implement.

[0127] Step S5, depositing a second transmission layer on the barrier layer, the insulating region and the second conductive region.

[0128] The first side surface 32 of the aforementioned shape extends from the first end close to the second surface 31 to the second end close to the insulating region, and then extends toward the insulating region in sequence, and then the second transmission layer 4 is deposited from the side away from the barrier layer 3 and away from the silicon substrate 1. The first side surface 32 of the barrier layer 3 will not affect the deposition of the second transmission layer 4, so a second transmission layer with good shape integrity can be formed, especially the first part of the formed second transmission layer 4 located in the insulating region has good shape integrity, and the first part usually has the function of blocking the leakage path and passivation. Since the shape integrity of the first part is better, the short circuit risk is lower and the passivation effect is better in the back contact solar cell, thereby improving the photoelectric conversion efficiency. At the same time, since the velvet structure of the second conductive region has a larger specific surface area, under the same deposition conditions, the second part of the second transmission layer 4 obtained on the second conductive region has a smaller thickness, while the first part located on the insulating region has a larger thickness, thereby providing better insulation performance and passivation performance, etc., further improving the photoelectric conversion efficiency.

[0129] The second transmission layer 4 can be deposited by LPCVD / PECVD or the like. The thickness of the back passivation layer 41 in the second transmission layer 4 is 3nm-15nm, for example, 5nm-8nm, and the thickness of the doping layer 42 in the second transmission layer 4 is 5nm-25nm, for example, 10nm-15nm. After the step S5, the method may further include: opening the second transmission layer 4 and the lower barrier layer 3 of the first conductive region by photolithography or laser. Using LPCVD / PECVD equipment, a front passivation layer and a front anti-reflection layer are sequentially deposited on the second side of the silicon substrate 1. Next, a transparent conductive layer 5 is deposited, and the thickness of the conductive layer 5 may be 80±30nm TCO. TCO may use indium-free or low-indium materials, mainly ITO (indium tin oxide), AZO (aluminum zinc oxide), IO:H (indium hydroxide doped), IWO (indium tungsten oxide), etc. For example, the material of the transparent conductive layer 5 may be ITO (indium tin oxide). TCO insulation treatment is performed by using laser ablation technology, printing ink or photolithography technology, etc., to complete TCO insulation. The first electrode 6 and the second electrode 7 are prepared by any one of screen printing, inkjet printing, laser transfer, chemical plating, electroplating and PVD.

[0130] The present invention also provides a photovoltaic module, including: a plurality of any of the aforementioned back-contact solar cells, and whether the photovoltaic module also includes other structures is not specifically limited. For example, the photovoltaic module may also include: a front encapsulation film and a cover plate sequentially located on the light-facing side of the back-contact solar cell, and a rear encapsulation film and a back plate sequentially located on the backlight-repellent side of the back-contact solar cell.

[0131] It should be noted that the preparation method of the back-contact solar cell, the photovoltaic module, and the back-contact solar cell can be referenced to each other and have the same or similar beneficial effects as any of the aforementioned back-contact solar cells. In order to avoid repetition, they will not be described here.

[0132] The present invention is further explained below in conjunction with specific embodiments.

[0133] Example 1

[0134] The silicon substrate 1 is an N-type 1.3±0.3Ωcm 166×166 silicon wafer with a thickness of 150um.

[0135] The first step is polishing and cleaning: the silicon substrate 1 enters the slot-type polishing and texturing machine, and the silicon substrate 1 is first pre-cleaned to remove organic and other contaminants generated during the cutting and transportation of the silicon substrate 1. The pre-cleaning can be performed using the standard RCA-cleaned SC1. That is: NH4OH-H2O2-H2O composition, the volume ratio of the three is (1:1:5), and the cleaning temperature is 65°C. After water washing and neutralization of the residual chemicals in the previous process, alkaline polishing treatment is performed. The alkaline polishing formula is: 5.00%wt KOH, the concentration of KOH stock solution is (45%), the temperature is 80°C, and the time is 300s, to remove damage and prepare for polishing. Then, high-efficiency SC1 cleaning is performed, with the volume ratio of NH4OH-H2O2-H2O being (1:1:5), 65°C for 300s, SC2 metal residue removal cleaning (in SC2, HCL:H2O2:H2O, the volume ratio of the three is 1:1:5, temperature is 65°C, and the cleaning time is 200s), and finally 5%wt hydrofluoric acid cleaning is performed to complete the preparation of the polishing sheet. The first surface of the first side of the silicon substrate 1 includes: a first conductive region, a second conductive region, and an insulating region located between the first conductive region and the second conductive region.

[0136] In the second step, a 7 nm back passivation layer 21 and a 25 nm doping layer 21 are deposited on the first surface of the first side of the silicon substrate 1 using a PECVD device at a temperature of 240°C. Subsequently, a first layer of SiN x , thickness 40nm, refractive index 2.5, second layer SiN x , thickness 40nm, refractive index 2.3, the third layer SiN x , thickness 40nm, refractive index 2.0, first layer SiN x , the second layer SiN x And the third layer SiN x The barrier layer 3 is formed. Finally, a 20 nm acid and alkali resistant mask layer A is deposited. The mask layer A can be polyurethane or the like.

[0137] The third step is laser film opening. Green light nanoseconds are used to open the barrier layer 3 on the second conductive area, i.e., SiN x The mask layer A is vaporized and ablated to open the film. At the same time, the heat-affected zone at the edge of the laser spot ablates the mask layer A on the insulating area and the partial thickness of the barrier layer 3 thereunder, so that the insulating area still has a partial thickness of the barrier layer 3.

[0138] Step 4: Post-texturing cleaning solution: First sub-step: Use 1% wt hydrofluoric acid (HF) to clean the remaining SiN in the second conductive area opened by the laser. x After 120 seconds of cleaning, the first transmission layer on the second conductive area is exposed. The second sub-step is texturing cleaning: using the TS53V01:KOH:DIW system, wherein the TS53V01wt% concentration is 0.2%-1.5%, the KOHwt concentration is 1%-3%, and the temperature is 75℃-85℃. For example, the TS53V01wt% concentration is 0.5℃-1%, and the KOHwt concentration is 1.5℃-2%. During the texturing cleaning process, the texturing liquid cleans away the first transmission layer on the second conductive area, exposing the second conductive area, and the texturing liquid texturing the second conductive area. The third sub-step is to perform high-efficiency SC1 cleaning, with the volume ratio of KOH-H2O2-H2O being (2:1:5) at 65℃ for 300s; SC2 metal residue removal cleaning (SC2 uses a volume ratio of 1:1:5 HCL:H2O2:H2O, a temperature of 65℃, and a cleaning time of 200s). Then, 4% HF was used to treat the partial thickness of the barrier layer 3, i.e., SiN x Etch the side surface to completely etch away the barrier layer in the insulating area. Then use an etchant to remove the remaining mask layer A, and then use 4% HF to remove the third SiN layer on the first conductive area. x Remove, the first layer of SiNx and the second layer of SiNx as the barrier layer 3 after etching to form a gentle slope morphology, forming a step-shaped morphology formed by the third part, the first sub-part, and the second sub-part connected in sequence. In the distribution direction L7 parallel to the first conductive area and along the first conductive area and the insulating area, the size or width of the first sub-part is 1μm, and finally slowly pull and dry, the barrier layer 3 after etching is obtained as shown Figure 2 The structure shown in .

[0139] In the fifth step, a 5 nm thick back passivation layer 41 and a 15 nm thick doping layer 42 are deposited on the first side of the silicon substrate 1 using a PECVD device at a temperature of 185° C.

[0140] The sixth step is laser film opening, using green light nanoseconds to open the second transmission layer 4 in the first conductive layer area.

[0141] Step 7: Clean the exposed barrier layer 3, i.e., SiN xThe exposed SiN layer was coated with 4% wt hydrofluoric acid solution for 450 s. x The layer is completely removed, and then the silicon substrate 1 is efficiently cleaned. Optionally, standard RCA cleaning is used, namely SC1 cleaning, the volume ratio of NH4OH-H2O2-H2O is (1:1:5) 65°C time 300s, SC2 metal residue removal cleaning (SC2 uses a volume ratio of 1:1:5HCL:H2O2:H2O, temperature 65°C, cleaning time 200s), and finally after 4%wt hydrofluoric acid cleaning, the velvet surface on the third surface of the silicon substrate 1 and the second conductive area, the oxide layer in the patterned area is removed and hydrophobic.

[0142] Step 8: Deposit hydrogenated amorphous silicon and silicon nitride anti-reflection film on the front side. Use PECVD equipment to deposit 10nm hydrogenated amorphous silicon at 200℃ as the front passivation layer, and deposit 80nm 2.1 refractive index SiN x Anti-reflection film, used as the front anti-reflection layer.

[0143] In the ninth step, a transparent conductive layer 5 is deposited, wherein the thickness of the deposited layer is 50 nm ITO (indium tin oxide).

[0144] Step 10: Insulate the first transmission layer 2 and the second transmission layer 4, and use laser film opening to insulate the transparent conductive layer 5 to prevent leakage caused by the interconnection of the first transmission layer 2 and the second transmission layer 4. After opening by UV picosecond, the insulation resistance of the insulation area can be tested to be > 2MΩ, and the laser width is 100um.

[0145] The eleventh step is electrode preparation, which uses screen printing technology to complete the preparation of the back metallized electrode.

[0146] The back contact solar cell prepared in Example 1 is as follows Figure 2 shown.

[0147] Table 1 shows the distribution table of chemicals used in each tank and their corresponding functions in the wet cleaning of Example 1. Referring to Table 1, there may be 12 tanks for wet cleaning of Example 1, each tank is numbered from 1 to 12, each tank corresponds to a small step, and the chemicals used in each tank and their functions are recorded below the number corresponding to the tank.

[0148] Table 1: Chemicals used in each tank in wet cleaning of Example 1 and corresponding function distribution table

[0149]

[0150] Example 2

[0151] The third step of Example 2 is slightly different from that of Example 1, and the remaining steps are the same. In the third step of Example 2, the area of ​​the heat-affected zone at the edge of the laser spot is smaller than that of the heat-affected zone at the edge of the laser spot in the third step of Example 1. Figure 1 The structure of the first part is shown in FIG. 2. The back contact solar cell prepared in Example 2 is as shown in FIG. Figure 1 shown.

[0152] Example 3

[0153] The only difference between Example 3 and Example 1 is the second step, and the remaining steps are the same.

[0154] In the second step, a 7nm back passivation layer 21 and a 25nm doping layer 21 are deposited on the first surface of the first side of the silicon substrate using PECVD equipment at a temperature of 240°C. Subsequently, a silicon nitride film layer with a gradient refractive index is deposited, and the N content gradually increases. The film is divided into three time periods, with NH3 50sccm in the first time period, NH3 100sccm in the second time period, and NH3 150sccm in the third time period, and a total deposition of 90nm. The duration of the first time period, the duration of the second time period, and the duration of the third time period can be equal, all of which are 10 minutes to 30 minutes.

[0155] The back contact solar cell prepared in Example 3 is as follows Figure 2 shown.

[0156] Comparative Example 1

[0157] The first step is polishing and cleaning. The first step in Comparative Example 1 is the same as the first step in Example 1.

[0158] In the second step, a mask is fabricated on the first side of the silicon substrate, a second side of the silicon substrate is textured, and the mask on the first side is removed.

[0159] In the third step, a 7nm back passivation layer 21 and a 25nm doping layer 21 are deposited on the first surface of the first side of the silicon substrate using a PECVD device at a temperature of 240°C. Subsequently, a SiN layer with a thickness of 120nm and a refractive index of 2.2 and uniform structure and reflectivity is obtained. x As a barrier layer.

[0160] The fourth step is laser film opening, using green light nanoseconds to vaporize and ablate the barrier layer 3 to open the film.

[0161] Step 5: Use 1% wt hydrofluoric acid to remove residual SiN in the laser-opened area. x After cleaning for 120 seconds, an alkaline solution was used to remove the exposed first transfer layer, and finally the film was slowly pulled to dry.

[0162] The subsequent steps of Comparative Example 1 are the same as the fifth to eleventh steps of Example 1.

[0163] Comparative Example 2

[0164] The difference between Comparative Example 2 and Comparative Example 1 is only the third step, and the remaining steps are the same.

[0165] In the third step, a 7nm back passivation layer 21 and a 25nm doping layer 21 are deposited on the first surface of the first side of the silicon substrate using a PECVD device at a temperature of 240°C. Subsequently, a SiN layer with a thickness of 120nm and a refractive index of 2.3 and uniform structure and reflectivity is obtained. x As a barrier layer.

[0166] Comparative Example 3

[0167] The difference between Comparative Example 3 and Comparative Example 1 is only the third step, and the remaining steps are the same.

[0168] In the third step, a 7nm back passivation layer 21 and a 25nm doping layer 21 are deposited on the first surface of the first side of the silicon substrate using a PECVD device at a temperature of 240°C. Subsequently, a SiN layer with a thickness of 90nm and a refractive index of 2.1 and uniform structure and reflectivity is obtained. x As a barrier layer.

[0169] The back-contact solar cells formed in each embodiment and each comparative example were subjected to performance tests under the same test conditions. The test results are shown in Table 2 below.

[0170] Table 2: Performance comparison of back-contact solar cells formed in various embodiments and comparative examples

[0171] <![CDATA[Jsc(A / cm 2 )]]> Voc(V) FF(%) Eff(%) Rs(Ω) Rsh_D(Ω) IVRV2(A) Example 1 41.66 0.7443 80.77 25.045 0.0028 158 0.26 Example 2 41.79 0.7429 80.57 25.014 0.0021 107 0.35 Example 3 41.64 0.7438 80.33 25.880 0.0034 198 0.21 Comparative Example 1 41.61 0.7402 80.05 24.655 0.003 36 0.78 Comparative Example 2 41.59 0.7412 79.15 24.399 0.0029 44 0.81 Comparative Example 3 41.63 0.7392 79.91 24.590 0.0038 42 0.90

[0172] In Table 1, Jsc represents the short-circuit current density of the back-contact solar cell, and Voc represents the open-circuit voltage of the back-contact solar cell. FF represents the fill factor of the back-contact solar cell, Eff represents the photoelectric conversion efficiency of the back-contact solar cell, Rs represents the series resistance of the back-contact solar cell, Rsh_D represents the parallel resistance of the back-contact solar cell, and IVRV2 represents the reverse current of the back-contact solar cell. It can be concluded from Table 1 above that, relative to Comparative Examples 1 to 3, the parallel resistance of the back-contact solar cells of Examples 1 to 3 is large, and the reverse current is small. Therefore, the insulation resistance value of the back-contact solar cells of Examples 1 to 3 is large, and the insulation effect is better. At the same time, relative to Comparative Examples 1 to 3, the short-circuit current density, open-circuit voltage, fill factor, and photoelectric conversion efficiency of the back-contact solar cells of Examples 1 to 3 are large, and the electrical performance of the back-contact solar cells of Examples 1 to 3 is better. The main reason is that in Examples 1 to 3, the barrier layer 3 includes: a second surface 31 away from the silicon substrate 1, and a first side surface 32 connected to the second surface 31 and close to the insulating area. The first side surface 32 extends from the first end close to the second surface 31 to the second end close to the insulating area, and then extends toward the insulating area. The first side surface 32 does not have a concave portion toward the first conductive area. The first side surface 32 is conducive to the deposition of the second transmission layer 4, especially the deposition of the portion of the second transmission layer 4 located on the first side surface 32. The shape integrity of the formed second transmission layer 4 is better, thereby improving the various performances of the back contact solar cell. Since the second conductive area is a velvet structure, the velvet structure has a large specific surface area. Therefore, under the same deposition conditions, the thickness of the first part of the second transmission layer 4 located in the insulating area will be greater than the thickness of the second part located in the second conductive area. Moreover, the second transmission layer 4, located in the first part of the insulating area, also has certain passivation and insulation properties. The thickness of the first part is greater than the thickness of the second part, which can improve the passivation and insulation properties of the back contact solar cell.

[0173] It should be noted that, for the method embodiments, for the sake of simplicity of description, they are all expressed as a series of action combinations, but those skilled in the art should be aware that the embodiments of the present application are not limited by the described order of actions, because according to the embodiments of the present application, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions involved are not necessarily required by the embodiments of the present application.

[0174] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0175] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, a magnetic disk, or an optical disk), and includes a number of instructions for enabling a terminal (which can be a mobile phone, a computer, a server, an air conditioner, or a network device, etc.) to execute the methods described in each embodiment of the present invention.

[0176] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A back contact solar cell, characterized in that: include: A silicon substrate having a first surface; The first surface includes: a first conductive area, a second conductive area, and an insulating area between the first conductive area and the second conductive area; the second conductive area is a suede structure; A first transmission layer, located on the first conductive area; a barrier layer, located on the first transmission layer at an end region close to the insulating region; a second transmission layer, located on the blocking layer, the insulating region and the second conductive region; the second transmission layer comprises: a first portion located in the insulating region and a second portion located in the second conductive region; a thickness of the first portion is greater than a thickness of the second portion; The barrier layer includes a second surface away from the silicon substrate, and a first side surface connected to the second surface and close to the insulating region; the first side surface extends from a first end close to the second surface to a second end close to the insulating region, and then extends toward the insulating region.

2. The back contact solar cell according to claim 1, characterized in that: The first side surface is a plane, or the first side surface is composed of a plurality of sub-regions, and the angles between adjacent sub-regions are all less than or equal to 5°.

3. The back contact solar cell according to claim 2, characterized in that: A first angle between the first side surface and the first conductive region is an acute angle.

4. The back contact solar cell according to claim 1, characterized in that: The first side surface is a curved surface convex toward the second portion.

5. The back-contact solar cell according to any one of claims 1 to 4, characterized in that: The second transmission layer also includes a third portion covering the first side surface and extending to an end portion close to the first portion, and the third portion is in a shape of a continuous gentle slope.

6. The back contact solar cell according to claim 5, characterized in that: The first part is composed of a continuous first sub-part and a second sub-part, the second sub-part is connected to the second part, and the third part, the first sub-part and the second sub-part are connected in sequence to form a step shape; A second angle between the first sub-portion away from the surface of the silicon substrate and the first conductive region is smaller than a third angle between the third sub-portion away from the surface of the silicon substrate and the first conductive region, and the second angle is smaller than a fourth angle between the second sub-portion away from the surface of the silicon substrate and the first conductive region.

7. The back-contact solar cell according to any one of claims 1 to 4, characterized in that: The first portion is in the shape of a continuous gentle slope.

8. The back-contact solar cell according to any one of claims 1 to 4, characterized in that: The thickness of the first part is 1.2 to 2 times the thickness of the second part.

9. The back contact solar cell according to claim 8, characterized in that: The second transmission layer includes: a back passivation layer and a doping layer stacked in sequence; the back passivation layer is closer to the silicon substrate than the doping layer; in the first part, the thickness of the back passivation layer is 1.2 to 2 times the thickness of the back passivation layer in the second part.

10. The back contact solar cell according to any one of claims 1 to 4, characterized in that: The material of the barrier layer is selected from silicon nitride or silicon oxide.

11. The back contact solar cell according to claim 10, characterized in that: The barrier layer is a single-layer structure; The refractive index of the barrier layer decreases from close to the silicon substrate to far away from the silicon substrate; or the refractive index at each position in the barrier layer is equal.

12. The back contact solar cell according to claim 10, characterized in that: The barrier layer is a multi-layer structure, and the etching rate of each layer structure decreases from the direction close to the silicon substrate to the direction away from the silicon substrate.

13. The back contact solar cell according to claim 10, characterized in that: The barrier layer is a multi-layer structure, and the refractive index of each layer structure decreases from the direction close to the silicon substrate to the direction away from the silicon substrate.

14. The back-contact solar cell according to any one of claims 1 to 4, characterized in that: The first end is farther away from the first conductive region than the second end; along the thickness direction of the silicon substrate, the height difference between the first end and the second end is 30 nanometers to 200 nanometers.

15. The back contact solar cell according to claim 6, characterized in that: In a distribution direction parallel to the first conductive region and along the first conductive region and the insulating region, a size of the first sub-portion is less than or equal to 10 micrometers.

16. The back-contact solar cell according to any one of claims 1 to 4, characterized in that: The silicon substrate has a third surface opposite to the first surface, and the third surface is a suede structure; the first conductive region and the insulating region are both polished surface structures.

17. The back-contact solar cell according to any one of claims 1 to 4, characterized in that: The silicon substrate has a third surface opposite to the first surface; The first transmission layer comprises: a back passivation layer and a doping layer stacked in sequence; the back passivation layer is closer to the silicon substrate than the doping layer; The back contact solar cell further comprises: A transparent conductive layer, located on the second transmission layer and the exposed first transmission layer; A first electrode is located on the transparent conductive layer, in the first conductive region outside the barrier layer; a second electrode, located on the transparent conductive layer, in the second conductive region; And a front passivation layer and a front anti-reflection layer are sequentially stacked on the third surface.

18. A method for preparing a back contact solar cell according to any one of claims 1 to 17, characterized in that: include: Step S1, providing a conductive substrate; The conductive substrate comprises: a silicon substrate, the silicon substrate having a first surface; the first surface comprising: a first conductive region, a second conductive region, and an insulating region located between the first conductive region and the second conductive region; a first transmission layer, a barrier layer, and a mask layer sequentially stacked on the first surface; the barrier layer is a single-layer structure, and the etching rate of the barrier layer decreases from the direction close to the silicon substrate to the direction away from the silicon substrate; or the barrier layer is a multi-layer structure, and the etching rate of each layer structure decreases from the direction close to the silicon substrate to the direction away from the silicon substrate; Step S2, removing the mask layer located on the second conductive area and the insulating area, and removing the barrier layer located on the second conductive area, so that the first transmission layer located on the second conductive area is exposed, and the insulating area still has at least a partial thickness of the barrier layer; Step S3, removing the first transmission layer exposed on the second conductive area, so that the second conductive area is exposed, and texturing the second conductive area under the condition that the barrier layer of at least a part of the thickness protects the insulating area, and the remaining mask layer protects the barrier layer on the first conductive area; Step S4, removing the mask layer on the end region of the first conductive region close to the insulating region to expose the barrier layer thereunder, wet-etching at least a portion of the barrier layer on the insulating region to expose the insulating region, and wet-etching the exposed barrier layer on the end region of the first conductive region close to the insulating region to make the barrier layer on the end region of the first conductive region close to the insulating region include a second surface away from the silicon substrate, and a first side surface connected to the second surface and close to the insulating region; the first side surface extends from a first end close to the second surface to a second end close to the insulating region, and toward the insulating region in sequence; Step S5, depositing a second transmission layer on the barrier layer, the insulating region and the second conductive region.

19. The method for preparing a back contact solar cell according to claim 18, characterized in that: The barrier layer is a single-layer structure, and the reflectivity of the barrier layer decreases from close to the silicon substrate to away from the silicon substrate; or, the barrier layer is a multi-layer structure, and the refractive index of each layer structure decreases from close to the silicon substrate to away from the silicon substrate.

20. The method for preparing a back contact solar cell according to claim 18 or 19, characterized in that: The material of the barrier layer is selected from silicon nitride, and the step S1 comprises: Preparing a barrier layer of a multilayer structure; in the process of preparing each layer structure, the flow rate of the nitrogen-containing gas increases successively from the direction close to the silicon substrate to the direction away from the silicon substrate; Alternatively, a barrier layer with a single-layer structure is prepared; during the preparation process of the barrier layer, the flow rate of the gas containing nitrogen element is gradually increased.

21. The method for preparing a back contact solar cell according to claim 20, characterized in that: The method for preparing a barrier layer of a multilayer structure comprises: Prepare a first layer structure close to the first transmission layer; the thickness of the first layer structure is 10 nm to 50 nm, and the refractive index of the first layer structure is 2.1 to 2.7; Preparing a second layer structure located on the first layer structure; the thickness of the second layer structure is 10 nm to 50 nm, and the refractive index of the second layer structure is 1.9 to 2.5; preparing a third layer structure located on the second layer structure; the thickness of the third layer structure is 10 nm to 50 nm, and the refractive index of the third layer structure is 1.7 to 2.3; the refractive indices of the first layer structure, the second layer structure and the third layer structure decrease in sequence; The method for preparing a barrier layer with a single-layer structure comprises: During the preparation of the single-layer structure, the flow rate of the nitrogen gas is 50 sccm to 300 sccm, and the flow rate of the nitrogen gas increases successively; or, during the preparation of the single-layer structure, the flow rate of the ammonia gas is 50 sccm to 400 sccm, and the flow rate of the ammonia gas increases successively.

22. The method for preparing a back-contact solar cell according to claim 18 or 19, characterized in that: The material of the barrier layer is selected from silicon oxide, and the step S1 comprises: Depositing a barrier layer of a multilayer structure; the deposition rate of each layer structure increases from close to the silicon substrate to away from the silicon substrate; Alternatively, a barrier layer of a single-layer structure is deposited; during the deposition of the barrier layer, the deposition rate is increased.

23. The method for preparing a back-contact solar cell according to claim 18 or 19, characterized in that: The step S4 comprises: first removing the mask layer on the end region of the first conductive region close to the insulating region, so that the barrier layer thereunder is exposed; then, wet etching at least a portion of the thickness of the barrier layer on the insulating region and the exposed barrier layer on the end region of the first conductive region close to the insulating region together, etching away at least a portion of the thickness of the barrier layer on the insulating region, so that the insulating region is exposed, and the barrier layer on the end region of the first conductive region close to the insulating region includes a second surface away from the silicon substrate, and a first side surface connected to the second surface and close to the insulating region; the first side surface extends from a first end close to the second surface to a second end close to the insulating region, and sequentially toward the insulating region; Alternatively, step S4 includes: first, wet-etching at least part of the thickness of the barrier layer on the insulating region to etch away at least part of the thickness of the barrier layer on the insulating region to expose the insulating region; then, removing the mask layer on the end region of the first conductive region close to the insulating region to expose the barrier layer thereunder, and wet-etching the exposed barrier layer on the end region of the first conductive region close to the insulating region to make the barrier layer on the end region of the first conductive region close to the insulating region include a second surface away from the silicon substrate, and a first side surface connected to the second surface and close to the insulating region; the first side surface extends toward the insulating region in sequence from a first end close to the second surface to a second end close to the insulating region.

24. The method for preparing a back-contact solar cell according to claim 18 or 19, characterized in that: The step S2 comprises: Laser is used to remove the mask layer on the second conductive area and the barrier layer thereunder, so that the first transmission layer located in the second conductive area is exposed. At the same time, the heat-affected zone at the edge of the laser spot ablates the mask layer on the insulating area, or the mask layer on the insulating area and part of the thickness of the barrier layer thereunder, so that the insulating area still has at least part of the thickness of the barrier layer.

25. The method for preparing a back-contact solar cell according to claim 18 or 19, characterized in that: In the step S4, the wet etching solution includes hydrofluoric acid or phosphoric acid.

26. A photovoltaic module, characterized in that: include: A back-contact solar cell as claimed in any one of claims 1 to 17.

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