Heterojunction solar cell

Abstract

The utility model discloses a heterojunction solar cell, and relates to the technical field of solar cells. The heterojunction solar cell provided by the utility model comprises a silicon substrate which comprises a first surface and a second surface which are opposite to each other along the thickness direction; the first passivation layer, the first doping layer, the first transparent conductive layer and the first electrode are sequentially stacked on the first surface side of the silicon substrate; the second passivation layer, the second doping layer, the second transparent conductive layer and the second electrode are sequentially stacked on the second surface side of the silicon substrate; the doping type of the second doping layer is opposite to that of the first doping layer; wherein the first surface and the second surface are different in morphology, the second doping layer comprises a plurality of sub-doping layers, and the refractive indexes of the sub-doping layers are different. The problems that a current heterojunction cell is low in double-sided rate and low in back cell efficiency can be solved at least, the back reflectivity of the cell can be reduced, and the double-sided rate and the back cell efficiency of the cell can be improved.

Description

Technical Field

[0001] The present application belongs to the technical field of solar cells and relates to heterojunction solar cells. Background Art

[0002] As a new type of efficient solar cell, heterojunction solar cells have become a new hot spot in the photovoltaic field in recent years. They have the advantages of simple structure, simple process, high conversion efficiency, high open circuit voltage, and low temperature coefficient.

[0003] In the related art, due to the insufficient passivation performance and low efficiency of the heterojunction solar cell with double-sided velvet, the back surface of the cell has been improved, such as by forming a surface with a micro-velvet structure on the back to increase the passivation effect of anti-epitaxial. In addition, the cell structure usually adopts a single-layer P-type doped layer structure. However, the refractive index of the back of the cell of this structure is high, and the optical utilization rate is low, resulting in a high reflectivity, so that the back current is low, resulting in a low bifaciality of the cell, such as a bifaciality of only 70% to 80%.

[0004] Therefore, there is an urgent need to find effective solutions to solve or alleviate the above problems. Utility Model Content

[0005] The utility model aims to solve at least one of the above technical problems to a certain extent. To this end, the utility model proposes a heterojunction solar cell, which can at least alleviate the problem of low bifaciality and low efficiency of the back cell of the current heterojunction cell, reduce the reflectivity of the back of the cell, and improve the bifaciality and efficiency of the back cell.

[0006] In order to solve the above technical problems, this application is implemented as follows:

[0007] According to an embodiment of the utility model, a heterojunction solar cell is provided, comprising:

[0008] The silicon substrate comprises a first surface and a second surface opposite to each other in a thickness direction;

[0009] A first passivation layer, a first doping layer, a first transparent conductive layer and a first electrode are sequentially stacked on the first surface side of the silicon substrate;

[0010] A second passivation layer, a second doping layer having a doping type opposite to that of the first doping layer, a second transparent conductive layer, and a second electrode are sequentially stacked on the second surface side of the silicon substrate;

[0011] The first surface and the second surface have different morphologies, the second doping layer includes multiple sub-doping layers, and the refractive index of each sub-doping layer is different.

[0012] In addition, the heterojunction solar cell according to the utility model may also have the following additional technical features:

[0013] In some of the embodiments, the first surface has a pyramid-shaped velvet structure;

[0014] The second surface is a polished surface, or the second surface is a surface with a refined microstructure.

[0015] In some of the embodiments, the refined microstructure comprises a plurality of block structures.

[0016] In some embodiments, the size of the block structure is 0.1 μm to 20 μm.

[0017] In some of the embodiments, the number of sub-doped layers is at least three;

[0018] Along the direction from the second passivation layer to the second transparent conductive layer, the refractive index of each of the sub-doped layers decreases sequentially.

[0019] In some of the embodiments, the number of sub-doped layers is four;

[0020] Along the direction from the second passivation layer to the second transparent conductive layer, the sub-doped layers are sequentially a first sub-doped layer, a second sub-doped layer, a third sub-doped layer and a fourth sub-doped layer, the refractive index of the first sub-doped layer is 3.5 to 3.8, the refractive index of the second sub-doped layer is 3.3 to 3.5, the refractive index of the third sub-doped layer is 3.1 to 3.3, and the refractive index of the fourth sub-doped layer is 2.8 to 3.1.

[0021] In some embodiments, the refractive index of each of the sub-doped layers is different, and the total refractive index of the second doped layer is in the range of 2.8 to 3.8; and / or,

[0022] The refractive index of the sub-doped layer close to the second passivation layer is 3.5-3.8, and the refractive index of the sub-doped layer close to the second transparent conductive layer is 2.8-3.1.

[0023] In some embodiments, the total thickness of the second doping layer is 5 nm to 50 nm; and / or,

[0024] The thickness of each of the sub-doping layers is 0.5 nm to 5 nm.

[0025] In some embodiments, the silicon substrate is an N-type silicon substrate, the first doped layer is an N-type doped microcrystalline silicon layer, and the second doped layer is a P-type doped microcrystalline silicon layer;

[0026] Alternatively, the second doped layer is a P-type oxygen-doped microcrystalline silicon layer.

[0027] In some embodiments, the resistivity of the silicon substrate is 1-5 ohm·cm. Optionally, the thickness of the silicon substrate is 80-200 μm.

[0028] In some embodiments, the refractive index of the N-type doped microcrystalline silicon layer is 2.50 to 3.30. Optionally, the thickness of the N-type doped microcrystalline silicon layer is 15 to 30 nm.

[0029] In some embodiments, the first passivation layer and the second passivation layer are both amorphous silicon thin films with a thickness of 3 nm to 20 nm and a refractive index of 3.70 to 4.30; and / or,

[0030] The second transparent conductive layer has a thickness of 50 nm to 200 nm and a refractive index of 1.60 to 2.30.

[0031] Implementing the technical solution of this application has at least the following beneficial effects:

[0032] According to the heterojunction solar cell provided by the present application, the first surface and the second surface of the substrate have different morphologies, which helps to increase the passivation effect; at the same time, the second doping layer includes a plurality of stacked sub-doping layers, and the refractive index of each sub-doping layer is different. In this way, by setting up a plurality of sub-doping layers with different refractive indices, while ensuring conductivity, the optical band gap can be further widened, and the reflection of light at the interface can be effectively reduced, thereby reducing the reflectivity of the backlight surface, solving the problem of low anti-reflection effect of the backlight surface structure, and increasing the short-circuit current, thereby effectively improving the bifaciality of the battery and further improving the backlight surface efficiency.

[0033] Additional aspects and advantages of the present application will be given in part in the following description, and in part will become apparent from the following description, or will be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the structure of a heterojunction solar cell provided for some exemplary embodiments of the present application.

[0035] Figure 2 Schematic diagram of the structure of a heterojunction solar cell provided for some other exemplary embodiments of the present application.

[0036] Description of reference numerals:

[0037] 10-silicon substrate;

[0038] 21 - first passivation layer; 31 - first doping layer; 41 - first transparent conductive layer; 51 - first electrode;

[0039] 22 - second passivation layer; 32 - second doping layer; 320 - sub-doping layer; 321 - first sub-doping layer; 322 - second sub-doping layer; 323 - third sub-doping layer; 324 - fourth sub-doping layer; 42 - second transparent conductive layer; 52 - second electrode. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0041] The terms "first", "second", etc. in the specification and claims of the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable under appropriate circumstances, so that the embodiments of the present application can be implemented in an order other than those illustrated or described here, and the objects distinguished by "first", "second", etc. are generally of one type, and the number of objects is not limited. For example, the first object can be one or more. In addition, "and / or" in the specification and claims represents at least one of the connected objects, and the character " / " generally indicates that the objects associated with each other are in an "or" relationship.

[0042] The embodiments of the present application are described in detail below through specific embodiments and their application scenarios in conjunction with the accompanying drawings.

[0043] As mentioned in the background technology, in the mass production process of single-sided texturing heterojunction cells in the related technology, in order to ensure a good passivation effect, the back doping layer such as the back microcrystalline P layer usually needs to use a single-layer oxygen-free film layer, and the refractive index is usually between 3.5 and 3.8, resulting in a higher reflectivity and a lower short-circuit current, resulting in a bifaciality of only 70% to 80%, and the efficiency of the back cell is also low. In addition, since the microcrystalline P adopts a single-layer oxygen-free process, the window for adjusting the refractive index is very narrow, which is not easy to match to the optimal range, and will seriously affect the light transmittance of the heterojunction cell. Or, on the other hand, while the existing technology improves the uniformity and flatness of the back morphology of the silicon wafer, it will also lead to a higher reflectivity on the back, which makes the back current low, reduces the bifaciality, and the efficiency of the back cell is also low.

[0044] Based on the above problems, the technical solution of the embodiment of the present application provides a heterojunction solar cell. The technical solution of the embodiment of the present application, by combining multiple layers of sub-doped layers with different refractive indices together, can give full play to the advantages of the doped thin film layer to a large extent, while ensuring passivation, it can also improve effective absorption, effectively reduce the reflection of light at the interface, thereby effectively improving the cell bifaciality and back cell efficiency. The specific technical solution is described below.

[0045] like Figure 1 to Figure 2 As shown, the provided heterojunction solar cell includes a silicon substrate 10, which includes a first surface and a second surface arranged opposite to each other along the thickness direction; wherein the first surface is a light-receiving surface (front surface) and the second surface is a backlight surface (back surface).

[0046] As an example, in this embodiment, the first surface of the silicon substrate 10 is the front surface, that is, the light-receiving surface (such as the N-type doped surface or N-surface); the second surface of the silicon substrate 10 is the back surface, that is, the backlight surface (such as the P-type doped surface or P-surface).

[0047] The heterojunction solar cell includes a first passivation layer 21 , a first doping layer 31 , a first transparent conductive layer 41 and a first electrode 51 which are sequentially stacked on the first surface side of a silicon substrate 10 .

[0048] The heterojunction solar cell further includes a second passivation layer 22 , a second doping layer 32 of opposite doping type to the first doping layer 31 , a second transparent conductive layer 42 and a second electrode 52 which are sequentially stacked on the second surface side of the silicon substrate 10 .

[0049] The first surface and the second surface have different morphologies, and the second doping layer 32 includes multiple sub-doping layers 320 , each of which has a different refractive index.

[0050] Optionally, when the first surface is the light-receiving surface and the second surface is the backlight surface, the first surface has a conventional suede structure, while the second surface does not have a conventional suede structure.

[0051] It should be noted that the present embodiment does not limit the specific type of the silicon substrate 10 (such as a silicon wafer), and may be, for example, a single crystal silicon substrate, a polycrystalline silicon substrate, or a quasi-single crystal silicon substrate, etc., and the silicon substrate may be P-type doped or N-type doped, that is, the silicon substrate may be an N-type silicon wafer, or may be a P-type silicon wafer. Optionally, the present embodiment uses an N-type single crystal silicon wafer as the silicon substrate 10.

[0052] Optionally, the first doping layer 31 may be an N-type doping layer, and the second doping layer 32 may be a P-type doping layer.

[0053] Therefore, the inventors of the present application set up multiple layers of sub-doped layers 320 with different refractive indices, such as combining stacked microcrystalline P structures with different refractive indices. This can maximize the advantages of the doped microcrystalline P thin film layer, while ensuring passivation and improving effective absorption, and reducing the reflectivity of the backlight surface, thereby effectively improving the battery bifaciality and back battery efficiency.

[0054] In addition, in a preferred embodiment, the second surface of the silicon substrate 10 is a plane or surface with a microstructure (micro-suede structure on the back side). The refined microstructure of the backlight side has a better anti-epitaxial passivation effect than ordinary suede, and exhibits a 1mV Voc gain effect on the battery cell.

[0055] In some embodiments, the first surface is the light-receiving surface (front side), the second surface is the backlight surface (back side), and the first surface has a pyramid-shaped velvet structure; while the second surface is a polished plane, or the second surface is a surface with a refined microstructure.

[0056] In this embodiment, the first surface of the silicon substrate 10 has a velvet structure, such as a pyramid-shaped velvet structure. Generally, the pyramid-shaped velvet structure has a pyramid structure. By performing a velvet treatment on the silicon substrate 10, the light-receiving surface can have a light-trapping structure with a consistent velvet surface, such as a pyramid-shaped velvet structure formed by alkaline corrosion.

[0057] The second surface of the silicon substrate 10 can be a polished plane, or the second surface is a surface with a refined microstructure. Preferably, the second surface of the silicon substrate 10 is a surface with a refined microstructure. Compared with ordinary velvet, the refined microstructure has a better anti-epitaxial passivation effect, and exhibits a 1mV Voc gain effect on the battery cell. In addition, the refined microstructure of the backlight surface has sufficient adhesion for subsequent printed grid lines, which can alleviate the problem of grid debonding caused by direct polishing on the back. In addition, the refined microstructure is easier to passivate, which has an improvement effect on the battery opening voltage, thereby improving the battery efficiency. The refined microstructure of the backlight surface can reduce the surface area of ​​the back side, which helps to shorten the coating time.

[0058] In some embodiments, the refined microstructure includes a plurality of block structures, wherein at least some of the block structures have partially overlapping surfaces. The embodiment of the present invention does not limit the number or range of overlapping block structures.

[0059] The surface feature of the backlight surface of the silicon wafer of this embodiment is a fine small square structure, that is, a microstructure surface composed of multiple small squares, some of which have overlapping parts, and the structure is flatter, which can reduce the surface area of ​​the back surface and make it easier to passivate. Therefore, compared with the existing pyramid-shaped back surface or polished back surface structure, the small square-shaped refined microstructure back surface of this embodiment has a better anti-epitaxial passivation effect and has sufficient adhesion, which helps to improve battery performance and shorten the back coating time.

[0060] In some embodiments, the size of the block structure is 0.1μm to 20μm. That is, in a plurality of blocks, the size of each independent unit is 0.1μm to 20μm. The size refers to the average length or average width of the square cross section of the block. Preferably, the size of the block structure is 1μm to 10μm; more preferably, the size of the block structure is 1μm to 2μm; for example, the size of the block structure can be 0.1μm, 0.5μm, 1μm, 1.5μm, 2μm, 3μm, 5μm, 6μm, 8μm, 10μm, 12μm, 15μm, 20μm, etc. By making the size of the block within the above range, it is helpful to obtain a more suitable reflectivity, improve the utilization rate of light, and also improve the adhesion, ensure the reliability of the structure, and help improve the performance of the battery.

[0061] Optionally, the first doping layer 31 and the second doping layer 32 are prepared by chemical vapor deposition.

[0062] In some embodiments, the silicon substrate 10 is an N-type silicon substrate, the first doped layer 31 is an N-type doped layer, and the second doped layer 32 is a P-type doped layer. For example, the first doped layer 31 is an amorphous silicon or microcrystalline silicon layer doped with a Group VA element, and the second doped layer 32 is an amorphous silicon or microcrystalline silicon layer doped with a Group IIIA element. The Group VA elements include one or more of nitrogen, phosphorus, arsenic, and antimony. Preferably, in this embodiment, the Group VA element is phosphorus. The Group IIIA elements include one or more of indium, boron, aluminum, and gallium. Preferably, in this embodiment, the Group IIIA element is boron.

[0063] Optionally, the first doped layer 31 , ie, the N-type doped layer, is an amorphous silicon or microcrystalline silicon layer doped with phosphorus, preferably a microcrystalline silicon layer, called an N-type doped microcrystalline silicon layer, also called a microcrystalline N layer.

[0064] Optionally, the second doped layer 32, ie, the P-type doped layer, is an amorphous silicon or microcrystalline silicon layer doped with boron, preferably a microcrystalline silicon layer, called a P-type doped microcrystalline silicon layer, also called a microcrystalline P layer (not doped with oxygen).

[0065] Alternatively, in other embodiments, the second doped layer 32 is an oxygen-doped microcrystalline silicon layer doped with Group IIIA elements, such as the second conductive type doped layer is an oxygen-doped microcrystalline silicon layer doped with boron, called a P-type oxygen-doped microcrystalline silicon layer, also called an oxygen-doped microcrystalline P layer.

[0066] The second doping layer 32 of the embodiment of the present invention may be a microcrystalline P layer (without oxygen doping) or an oxygen-doped microcrystalline P layer. For example, in some embodiments, the second doping layer 32 is an oxygen-doped microcrystalline P layer. 2 O is doped, and since the nitrogen element has little effect on crystallinity, it will not deteriorate the passivation performance. In addition, the stacked microcrystalline P layer is doped with nitrous oxide (N 2 The refractive index of each film layer is adjusted by the flow rate of N 2 O can be dissociated at a relatively low output power of the CVD power supply, so that the refractive index of each layer can be easily matched to a more optimal range, and the production cost is very low.

[0067] In some embodiments, the number of sub-doped layers 320 is at least three; that is, the number of sub-doped layers 320 is three or more. As an example, the number of sub-doped layers 320 can be three to ten layers, further can be three to eight layers, further can be three to six layers, such as the number of sub-doped layers 320 can be three, four, five, six or more layers.

[0068] In some embodiments, the refractive index of each sub-doped layer 320 decreases in sequence along the direction from the second passivation layer 22 to the second transparent conductive layer 42. In this embodiment, the refractive index of each sub-doped layer 320 decreases gradually along the direction from close to the second passivation layer 22 to far away from the second passivation layer 22. In comparison, the refractive index of the sub-doped layer 320 close to the second passivation layer 22 is the largest, while the refractive index of the sub-doped layer 320 close to the second transparent conductive layer 42 is the smallest, and the refractive index of the sub-doped layer 320 located in the middle is between the maximum value and the minimum value.

[0069] In some embodiments, the refractive index of each sub-doped layer 320 is different, and the total refractive index of the second doped layer 32 is in the range of 2.8 to 3.8.

[0070] The present embodiment adopts N≥3 layers of microcrystalline P structure with different refractive indexes and thicknesses, wherein the refractive index of the sub-doped layer 320 close to the second passivation layer 22 is greater than the refractive index of the middle layer, the refractive index of the sub-doped layer 320 in the middle layer is greater than the refractive index of the sub-doped layer 320 close to the second transparent conductive layer 42, and the total refractive index range of the second doped layer 32 is 2.8 to 3.8, thereby further widening the optical band gap while ensuring conductivity, effectively reducing light reflection at the interface, and increasing the short-circuit current, thereby improving the cell bifaciality and bifacial equivalent cell efficiency.

[0071] Optionally, the refractive index of the sub-doped layer 320 close to the second passivation layer 22 is 3.5-3.8, and the refractive index of the sub-doped layer 320 away from the second passivation layer 22 is 2.8-3.1, that is, the refractive index of the sub-doped layer 320 close to the second transparent conductive layer 42 is 2.8-3.1.

[0072] like Figure 2 As shown, in a specific embodiment, the number of layers of the sub-doping layer 320 may be four;

[0073] Optionally, along the direction from the second passivation layer 22 to the second transparent conductive layer 42, the sub-doping layers 320 are sequentially a first sub-doping layer 321, a second sub-doping layer 322, a third sub-doping layer 323 and a fourth sub-doping layer 324, the refractive index of the first sub-doping layer 321 is 3.5 to 3.8, the refractive index of the second sub-doping layer 322 is 3.3 to 3.5, the refractive index of the third sub-doping layer 323 is 3.1 to 3.3, and the refractive index of the fourth sub-doping layer 324 is 2.8 to 3.1.

[0074] Therefore, this gradual change of the refractive index from 2.8-3.1 to 3.1-3.3 to 3.3-3.5 to 3.5-3.8 can further reduce the reflectivity and increase the light transmittance compared to a single-layer microcrystalline P layer, which helps to improve the efficiency of the battery.

[0075] In addition, it should be understood that Figure 1 or Figure 2 The structure of the multi-layer sub-doping layer shown is only an example. In actual application, a suitable structure can be selected according to the battery performance effect or the convenience of the coating process operation. For example, the number of sub-doping layers can also be three, five or more layers.

[0076] Optionally, the total thickness of the second doping layer 32 is 5 nm to 50 nm; for example, the total thickness of the second doping layer 32 may be 5 nm, 6 nm, 8 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, etc.

[0077] Optionally, the thickness of each sub-doping layer 320 is 0.5 nm to 5 nm; the thicknesses of different sub-doping layers 320 may be the same or different, such as by making different sub-doping layers 320 have different thicknesses, which helps to adjust different sub-doping layers 320 to have different refractive indices.

[0078] Thus, through the microcrystalline P anti-reflection structure in this embodiment, that is, through the setting of multiple layers of sub-doped layers 320 with different refractive indices, the back reflectivity can be effectively reduced, solving the problem of low anti-reflection effect of the back micro-suede structure, effectively improving the bifaciality of the back micro-suede structure heterojunction battery, and further improving the back efficiency, which is suitable for industrial applications.

[0079] In some embodiments, the resistivity of the silicon substrate is 1 to 5 ohm·cm; for example, it can be 1 ohm·cm, 2 ohm·cm, 3 ohm·cm, 4 ohm·cm, 5 ohm·cm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0080] In some embodiments, the thickness of the silicon substrate is 80-200 μm; for example, it can be 80 μm, 100 μm, 120 μm, 150 μm, 160 μm, 180 μm, or 200 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0081] In some embodiments, the first passivation layer 21 and the second passivation layer 22 are both amorphous silicon films with thicknesses of 3 nm to 20 nm, for example, 3 nm, 5 nm, 8 nm, 10 nm, 15 nm, 18 nm, and 20 nm, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0082] Optionally, the refractive index of the first passivation layer 21 and the second passivation layer 22 is 3.70-4.30, for example, 3.7, 3.8, 3.9, 4.0, 4.1, 4.2, 4.3, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0083] Optionally, the first doped layer is an N-type doped microcrystalline silicon layer, and the refractive index of the N-type doped microcrystalline silicon layer is 2.50 to 3.30, for example, it can be 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.3, but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable. Optionally, the thickness of the N-type doped microcrystalline silicon layer is 15 to 30nm; for example, it can be 15nm, 18nm, 20nm, 25nm, 30nm, but it is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0084] In some embodiments, the thickness of the second transparent conductive layer 42 is 50 nm to 200 nm; for example, it can be 50 nm, 60 nm, 80 nm, 100 nm, 150 nm, 180 nm, or 200 nm, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0085] Optionally, the refractive index of the second transparent conductive layer 42 is 1.60-2.30, for example, 1.6, 1.8, 2.0, 2.1, 2.2, 2.3, but is not limited to the listed values, and other values ​​not listed within the range are also applicable.

[0086] In summary, the embodiment of the present application sets a multilayer sub-doping layer 320, so that, compared with the single-layer microcrystalline P structure which can only provide a good passivation effect but a poor optical utilization rate, the film thickness and refractive index of each dielectric film of the stacked microcrystalline P structure are matched and designed, while ensuring passivation, the optical utilization rate can be increased, and the short-circuit current Isc of the cell is increased by 200 to 400 mA, thereby increasing the cell efficiency on the back of the cell by 0.3% to 0.8%, and the bifaciality by 2% to 6%. Furthermore, the adjustable refractive index window of the multilayer sub-doping layer 320, such as the stacked microcrystalline P, is wider, and the sensitivity to deposition temperature, power, and gas flow is low, which can reduce the impact of equipment fluctuations on cell efficiency.

[0087] Parts not described in detail in the utility model specification are well known to those skilled in the art.

[0088] For ease of explanation, spatial relative terms such as "upper", "lower", "left", "right", etc. are used in the embodiments to illustrate the relationship between an element or feature shown in the figure and another element or feature. It should be understood that, in addition to the orientation shown in the figure, the spatial terms are intended to include different orientations of the device in use or operation. For example, if the device in the figure is inverted, the elements described as being "under" other elements or features will be positioned "on" other elements or features. Therefore, the exemplary term "under" can include both upper and lower orientations. The device can be positioned in other ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used here can be interpreted accordingly.

[0089] The embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present application, ordinary technicians in this field can also make many forms without departing from the purpose of the present application and the scope of protection of the claims, all of which are within the protection of the present application.

Claims

1. A heterojunction solar cell, characterized in that: include: The silicon substrate comprises a first surface and a second surface opposite to each other in a thickness direction; A first passivation layer, a first doping layer, a first transparent conductive layer and a first electrode are sequentially stacked on the first surface side of the silicon substrate; A second passivation layer, a second doping layer having a doping type opposite to that of the first doping layer, a second transparent conductive layer, and a second electrode are sequentially stacked on the second surface side of the silicon substrate; Wherein, the first surface has a pyramid-shaped velvet structure; the second surface is a polished plane, or the second surface is a surface with a refined microstructure; The second doping layer includes a plurality of sub-doping layers, and the refractive index of each of the sub-doping layers decreases in sequence along a direction from the second passivation layer to the second transparent conductive layer.

2. The heterojunction solar cell according to claim 1, characterized in that: The refined microstructure includes a plurality of block structures.

3. The heterojunction solar cell according to claim 2, characterized in that: The size of the block structure is 0.1 μm to 20 μm.

4. The heterojunction solar cell according to any one of claims 1 to 3, characterized in that: The number of the sub-doping layers is at least three.

5. The heterojunction solar cell according to claim 4, characterized in that: The number of sub-doping layers is four; Along the direction from the second passivation layer to the second transparent conductive layer, the sub-doped layers are sequentially a first sub-doped layer, a second sub-doped layer, a third sub-doped layer and a fourth sub-doped layer, the refractive index of the first sub-doped layer is 3.5 to 3.8, the refractive index of the second sub-doped layer is 3.3 to 3.5, the refractive index of the third sub-doped layer is 3.1 to 3.3, and the refractive index of the fourth sub-doped layer is 2.8 to 3.

1.

6. The heterojunction solar cell according to any one of claims 1 to 3, characterized in that: The total refractive index of the second doped layer is in the range of 2.8 to 3.8; and / or, The refractive index of the sub-doped layer close to the second passivation layer is 3.5-3.8, and the refractive index of the sub-doped layer close to the second transparent conductive layer is 2.8-3.

1.

7. The heterojunction solar cell according to any one of claims 1 to 3, characterized in that: The total thickness of the second doping layer is 5 nm to 50 nm; and / or, The thickness of each of the sub-doping layers is 0.5 nm to 5 nm.

8. The heterojunction solar cell according to any one of claims 1 to 3, characterized in that: The silicon substrate is an N-type silicon substrate, the first doped layer is an N-type doped microcrystalline silicon layer, and the second doped layer is a P-type doped microcrystalline silicon layer; Alternatively, the second doped layer is a P-type oxygen-doped microcrystalline silicon layer.

9. The heterojunction solar cell according to claim 8, characterized in that: The first passivation layer and the second passivation layer are both amorphous silicon thin films with a thickness of 3nm to 20nm; and / or, The thickness of the second transparent conductive layer is 50 nm to 200 nm.

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