Solar cell and photovoltaic module

Abstract

The invention provides a solar cell and a photovoltaic module, and relates to the technical field of photovoltaics. The battery includes: a silicon substrate including a surface having an N region and a P region; the N-type doped layer is positioned on the N region of the silicon substrate; the P-type doped layer is located on the P region of the silicon substrate; the first electrode is in contact with the P-type doped layer; the second electrode is in contact with the N-type doped layer; the first electrode and the second electrode both contain metal elements; the content of metal elements in a region corresponding to the first electrode in the P-type doped layer is greater than the content of metal elements in a region corresponding to the second electrode in the N-type doped layer. According to the invention, the contact resistance corresponding to the first electrode can be reduced, the contact difference between the P region and the N region can be reduced, good contact between the P region and the N region is realized at the same time, and the efficiency of the solar cell is improved.

Description

Technical Field

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

[0002] Solar cells can directly convert light energy into electrical energy through the photoelectric effect. Since they utilize clean energy, they have broad application prospects.

[0003] The electrodes in solar cells are primarily used to collect and conduct current. However, in existing solar cells, the electrodes have poor contact, which reduces the performance of the solar cell. Summary of the Invention

[0004] The present invention provides a solar cell and a photovoltaic module, aiming to solve the problem of poor contact of electrodes in existing solar cells.

[0005] A first aspect of the present invention provides a solar cell comprising:

[0006] A silicon substrate, comprising: a surface having an N region and a P region;

[0007] An N-type doped layer, located on the N region of the silicon substrate;

[0008] A P-type doped layer, located on the P region of the silicon substrate;

[0009] a first electrode, contacting the P-type doped layer;

[0010] a second electrode, contacting the N-type doped layer;

[0011] The first electrode and the second electrode both contain metal elements; the content of the metal elements in the region corresponding to the first electrode in the P-type doped layer is greater than the content of the metal elements in the region corresponding to the second electrode in the N-type doped layer.

[0012] Normally, the P-type doping layer is obtained by boron diffusion. Due to the diffusion characteristics of boron, it is difficult to obtain a high boron doping concentration. That is, normally, the doping concentration of the P-type doping layer is slightly low, which will result in a slightly higher contact resistance corresponding to the first electrode. In this application, the content of the metal element in the region corresponding to the first electrode in the P-type doping layer is greater than the content of the metal element in the region corresponding to the second electrode in the N-type doping layer. This indicates that more contact paths are formed in the region corresponding to the first electrode in the P-type doping layer, which improves the contact performance between the first electrode and the P-type doping layer, reduces the contact resistance corresponding to the first electrode, narrows the contact difference between the P region and the N region, achieves a good contact balance between the P region and the N region, and thus improves the efficiency of the solar cell.

[0013] Optionally, the content of the metal element in the first electrode is greater than the content of the metal element in the second electrode.

[0014] Optionally, the content of the metal element at the contact position between the first electrode and the P-type doped layer accounts for a first proportion of the content of the metal element in the first electrode; and the content of the metal element at the contact position between the second electrode and the N-type doped layer accounts for a second proportion of the content of the metal element in the second electrode.

[0015] The first ratio is smaller than the second ratio.

[0016] Optionally, the first ratio is 1:2.1 to 1:3.9;

[0017] The second ratio is 1:1.5 to 1:2.1.

[0018] Optionally, a diffusion depth of the metal element of the first electrode in the P-type doping layer is greater than a diffusion depth of the metal element of the second electrode in the N-type doping layer.

[0019] Optionally, a ratio of a diffusion depth of the metal element of the first electrode in the P-type doped layer to a diffusion depth of the metal element of the second electrode in the N-type doped layer is greater than 1 and less than or equal to 8.

[0020] Optionally, the diffusion depth of the metal element of the first electrode in the P-type doping layer is 100 nm to 450 nm;

[0021] The diffusion depth of the metal element of the second electrode in the N-type doping layer is 50 nm to 300 nm.

[0022] Optionally, the solar cell further comprises:

[0023] The P-type inner expansion layer is located inside the silicon substrate near the P-type doping layer and corresponds to the P region; the ratio of the doping concentration of the P-type doping layer to the doping concentration of the P-type inner expansion layer is 2 to 5×10 11 ;

[0024] The N-type inner expansion layer is located inside the silicon substrate near the N-type doping layer and corresponds to the N region; the ratio of the doping concentration of the N-type doping layer to the doping concentration of the N-type inner expansion layer is 2 to 6×10 11 .

[0025] Optionally, a ratio of the contact resistance between the first electrode and the P-type doped layer to the contact resistance between the second electrode and the N-type doped layer is 1.25 to 3.

[0026] Optionally, the solar cell further comprises:

[0027] a first passivation anti-reflection layer, located between the N-type doped layer and the second electrode, and

[0028] a second passivation anti-reflection layer, located between the P-type doped layer and the first electrode;

[0029] Wherein, the refractive index of the first passivation anti-reflection layer is greater than the refractive index of the second passivation anti-reflection layer.

[0030] Optionally, a difference between the refractive index of the first passivation anti-reflection layer and the refractive index of the second passivation anti-reflection layer ranges from 0.02 to 0.4.

[0031] Optionally, the P-type doped layer includes a first electrode region, and a surface of the first electrode region away from the silicon substrate has a plurality of first contact holes;

[0032] The N-type doped layer includes a second electrode region, and a surface of the second electrode region away from the silicon substrate has a plurality of second contact holes;

[0033] Wherein, along a thickness direction parallel to the silicon substrate, the depth of the first contact hole is greater than the depth of the second contact hole, and the first contact hole and the second contact hole are respectively suitable for accommodating metal crystals.

[0034] Optionally, along a thickness direction parallel to the silicon substrate, a depth of the first contact hole is 2 nm to 300 nm, and a depth of the second contact hole is 1 nm to 200 nm.

[0035] Optionally, the solar cell further comprises:

[0036] a first tunneling oxide layer, located between the silicon substrate and the P-type doped layer;

[0037] a second tunneling oxide layer, located between the silicon substrate and the N-type doped layer;

[0038] The thickness of the first tunnel oxide layer is greater than the thickness of the second tunnel oxide layer.

[0039] A second aspect of the present invention provides a photovoltaic assembly comprising: a plurality of cell strings, wherein the cell strings comprise any one of the aforementioned solar cells.

[0040] The solar cell and photovoltaic module of the present application achieve high field passivation, balanced PN region contact performance, and low recombination effects, thereby ensuring improved conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0042] Figure 1 and Figure 2 Schematic diagrams of the structures of two solar cells in the embodiments of the present invention are shown respectively;

[0043] Figure 3 An SEM image showing the contact position between an electrode and a doping layer in an embodiment of the present invention is shown;

[0044] Figure 4 shows an SEM image of a first electrode region in an embodiment of the present invention;

[0045] Figure 5 shows an SEM image of a second electrode region in an embodiment of the present invention;

[0046] Figure 6 A schematic diagram of determining the contact position between an electrode and a corresponding doping layer in an embodiment of the present invention is shown.

[0047] Description of the accompanying figures:

[0048] 1-silicon substrate, 21-first tunneling oxide layer, 22-second tunneling oxide layer, 3-P-type doped layer, 4-N-type doped layer, 5-first passivation anti-reflection layer, 6-second passivation anti-reflection layer, 7-first electrode, 8-second electrode, 9-P-type inner expansion layer, 10-N-type inner expansion layer, 31-first contact hole, 41-second contact hole. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0050] The present invention provides a solar cell, referring to Figure 1 and Figure 2, the solar cell includes a silicon substrate 1, a P-type doping layer 3, an N-type doping layer 4, a first electrode 7 and a second electrode 8. The silicon substrate 1 can be N-type single crystal silicon or P-type single crystal silicon, which can provide long-life carriers; the silicon substrate can be obtained by cutting the silicon ingot with a diamond wire; in order to minimize the impact of the cutting line marks on the surface recombination, the surface of the silicon substrate can be cleaned and polished before preparing other structures. The silicon substrate 1 includes a surface with an N region and a P region, and can be a surface with both an N region and a P region. Then the solar cell is a back-contact solar cell, mainly with both an N region and a P region on the backlight surface, and an isolation region can be provided between the N region and the P region. As Figure 1 and Figure 2 As shown, on the backlight side of the silicon substrate 1, the area to the left of the dotted line L1 is the N region, and the area to the right of the dotted line L2 is the P region. An isolation region exists between the N and P regions to prevent short circuits within the solar cell. It should be noted that the dotted lines L1 and L2 do not actually exist in the solar cell; they are merely used to distinguish the P and N regions. During solar cell operation, the surface of the silicon substrate 1 that primarily receives light is its light-facing side, with the backlight side and the light-facing side facing each other. Figure 1 and Figure 2 In the figure, the backlight side is the lower surface of the silicon substrate 1, and the light-facing side is the upper surface of the silicon substrate 1. Alternatively, if a solar cell has an N region on one surface and a P region on the other surface, then the solar cell is a solar cell with electrodes on both sides, and the one surface and the other surface here refer to its light-facing side and backlight side.

[0051] The P-type doped layer 3 may contain one or more elements from Group IIIA (for example, boron). The N-type doped layer 4 may contain one or more elements from Group VA (for example, phosphorus). The materials of the N-type and P-type doped layers may include any semiconductor material, such as silicon, silicon germanium, germanium, or gallium arsenide. In terms of the arrangement of the materials, the crystalline phase of the doped layers may be amorphous, microcrystalline, nanocrystalline, single crystal, or polycrystalline. The materials of the N-type and P-type doped layers may be the same or different. For example, the materials of the N-type and P-type doped layers may both be doped polycrystalline silicon. For another example, the material of the P-type doped layer may include at least one of doped amorphous silicon, doped microcrystalline silicon, and doped nanocrystalline silicon, while the material of the N-type doped layer may be doped polycrystalline silicon. For another example, the material of the P-type doped layer may be doped single crystal silicon, i.e., formed by diffusion on the surface of the P region of the silicon substrate, while the material of the N-type doped layer may be doped polycrystalline silicon. The P-type doped layer 3 may be prepared by in-situ doping or ex-situ doping. The N-type doped layer 4 may also be prepared by in-situ doping or ex-situ doping.

[0052] The P-type doped layer 3 is located in the P region of the silicon substrate 1 surface, and the N-type doped layer 4 is located in the N region of the silicon substrate 1 surface. The relative sizes of the two regions are not specifically limited. The first electrode 7 contacts the P-type doped layer 3, and the second electrode 8 contacts the N-type doped layer 4 to respectively collect and conduct current.

[0053] Both the first electrode 7 and the second electrode 8 contain metal elements, and the metal elements here may include: silver (Ag) element, copper (Cu) element, aluminum (Al) element, etc. It should be noted that the type of metal element contained in the first electrode 7 is not specifically limited to whether the type of metal element contained in the second electrode 8 is the same as that of the metal element contained in the second electrode 8, and they may be the same or different. Generally, silver is more corrosive and more conductive, and it forms a silver-silicon alloy with silicon. Aluminum also has strong conductivity, and copper has lower cost. The content of metal elements in the corresponding area of the first electrode 7 in the P-type doped layer 3 is greater than the content of metal elements in the corresponding area of the second electrode 8 in the N-type doped layer 4. The content here may refer to the mass content.

[0054] The first electrode 7 and the second electrode 8 can be produced by printing, photolithography, or electroplating. The printing method can be, for example, screen printing or inkjet printing, preferably screen printing, which is relatively low-cost. In the process of screen printing electrodes, the first electrode 7 and the second electrode 8 can be printed in the same step or in different steps.

[0055] This application does not impose any restrictions on the measurement of the metal element content in the region corresponding to the electrode in the doping layer, and those skilled in the art can determine it by conventional methods in the art. For example, the metal element content in the region corresponding to the first electrode in the P-type doping layer can be measured by scanning electron microscope (SEM) surface scanning; the element distribution is tested in a cross-sectional view including the first electrode and the P-type doping layer, and the cross-sectional view can be a SEM test image obtained by cutting the solar cell at a certain angle to the extension direction of the first electrode, such as 90° (i.e., parallel to the electrode width). A single sub-region is taken from the region corresponding to the first electrode in the P-type doping layer, and then the element distribution in the sub-region is characterized by EDS surface scanning test, the proportion of the metal element in the sub-region to the element distribution in the sub-region is obtained, and the metal element content in the region corresponding to the first electrode in the P-type doping layer is obtained. Alternatively, multiple sub-regions of the same area are taken in the corresponding area of the first electrode in the P-type doped layer, and then the element distribution in each sub-region of the same area is tested and characterized by EDS surface scanning to obtain the proportion of the metal element in each sub-region in the element distribution in the sub-region, and then the average value is taken to obtain the metal element content in the corresponding area of the first electrode in the P-type doped layer. The multiple here can be 2, 3, 4, 5, 6, etc.

[0056] Here, the content of the metal element in the region corresponding to the first electrode 7 in the P-type doped layer 3 refers to the content of the metal element in the region corresponding to the first electrode 7 over the entire thickness of the P-type doped layer 3. The content of the metal element in the region corresponding to the second electrode 8 in the N-type doped layer 4 refers to the content of the metal element in the region corresponding to the second electrode 8 over the entire thickness of the N-type doped layer 4. The region corresponding to the electrode in the doped layer refers to the entire thickness region covered by the orthographic projection of the electrode in the doped layer. The orthographic projection here refers to the projection of the electrode in the doped layer when irradiating the electrode with light along the direction of the thickness of the silicon substrate. The sub-region here also corresponds to the entire thickness of the doped layer.

[0057] The metal element content in the region corresponding to the second electrode 8 in the N-type doped layer 4 can be tested using the same method as the metal element content in the region corresponding to the first electrode 7 in the P-type doped layer 3, and will not be further described here. It should be emphasized that when comparing metal content, the testing method must be consistent in both doped layers.

[0058] The content of the metal element in the region corresponding to the first electrode 7 in the P-type doped layer 3 is greater than the content of the metal element in the region corresponding to the second electrode 8 in the N-type doped layer 4. This can be the aforementioned ratio of the metal element in the P-type doped layer 3 to the element distribution in the sub-region, which is greater than the ratio of the metal element in the N-type doped layer 4 to the element distribution in the sub-region. Alternatively, it can be the average ratio of the metal element in the P-type doped layer 3 to the element distribution in the sub-region, which is greater than the average ratio of the metal element in the N-type doped layer 4 to the element distribution in the sub-region. Alternatively, it can be the ratio of the metal element in the element distribution in a certain proportion of the total number of sub-regions of the same area corresponding to the region of the first electrode in the P-type doped layer to the element distribution in the sub-region, which is greater than the ratio of the metal element in the element distribution in a certain proportion of the total number of sub-regions of the same area corresponding to the region of the second electrode in the N-type doped layer. The certain proportion here can be 50%, 60%, 70%, 80%, 90%, 100%, etc. The total number of sub-regions of the same area corresponding to the first electrode in the P-type doped layer may be equal to or different from the total number of sub-regions of the same area corresponding to the second electrode in the N-type doped layer, and there is no specific limitation on this.

[0059] For example, in the corresponding area of the first electrode in the P-type doped layer, 5 sub-areas of the same area are taken, each sub-area corresponds to the entire thickness of the P-type doped layer, and then the element distribution in these 5 sub-areas of the same area is characterized by EDS surface scanning test to obtain the proportion of the metal element in each sub-area in the element distribution in the sub-area, and then the proportion of the metal element in the element distribution in the 5 sub-areas of the same area in the sub-area is averaged to obtain the metal element content in the area corresponding to the first electrode in the P-type doped layer. The same method is used for the N-type doped layer, and the average value obtained is the metal element content in the area corresponding to the second electrode in the N-type doped layer. In this application, the average value of the proportion of the corresponding metal element in the P-type doped layer 3 in the element distribution in the sub-area is greater than the average value of the proportion of the corresponding metal element in the N-type doped layer 4 in the element distribution in the sub-area.

[0060] For another example, five sub-regions of equal area are taken from the region corresponding to the first electrode in the P-type doped layer, each of which corresponds to the entire thickness of the P-type doped layer. Then, an EDS surface scan test is performed on the element distribution in each of the five sub-regions of equal area to obtain the proportion of the metal element in the element distribution within the sub-region. The same method is used for the N-type doped layer, and the proportion of the metal element in the element distribution within the sub-region corresponding to the second electrode in the N-type doped layer is obtained. In the present application, the proportion of the metal element in the element distribution within the three sub-regions of the P-type doped layer 3 can be greater than the proportion of the metal element in the element distribution within the three sub-regions of the N-type doped layer 3; the proportion of the metal element in the element distribution within the four sub-regions of the P-type doped layer 3 can be greater than the proportion of the metal element in the element distribution within the four sub-regions of the N-type doped layer 3; or the proportion of the metal element in the element distribution within the five sub-regions of the P-type doped layer 3 can be greater than the proportion of the metal element in the element distribution within the five sub-regions of the N-type doped layer 3.

[0061] Normally, the P-type doping layer is obtained by boron diffusion. Due to the diffusion characteristics of boron, it is difficult to obtain a high boron doping concentration. That is, normally, the doping concentration of the P-type doping layer is slightly low, which will result in a slightly higher contact resistance corresponding to the first electrode. In this application, the content of the metal element in the region corresponding to the first electrode in the P-type doping layer is greater than the content of the metal element in the region corresponding to the second electrode in the N-type doping layer. This indicates that more carrier transmission paths are formed in the region corresponding to the first electrode in the P-type doping layer, which improves the contact performance between the first electrode and the P-type doping layer, reduces the contact resistance corresponding to the first electrode, narrows the contact difference between the P region and the N region, achieves a good contact balance between the P region and the N region, and thus improves the efficiency of the solar cell.

[0062] Optionally, the content of metal elements in the first electrode 7 in contact with the P-type doped layer 3 is greater than the content of metal elements in the second electrode 8 in contact with the N-type doped layer 4, to match the larger content of metal elements in the P-type doped layer, which helps the metal elements in the first electrode 7 to diffuse into the P-type doped layer 3 to form more contact paths, further improving the contact performance between the first electrode and the P-type doped layer.

[0063] Optionally, the content of the metal element at the contact position between the first electrode 7 and the P-type doped layer 3 accounts for a first proportion of the content of the metal element in the first electrode 7, and the content of the metal element at the contact position between the second electrode 8 and the N-type doped layer 4 accounts for a second proportion of the content of the metal element in the second electrode 8. The first proportion here is the content of the metal element at the contact position between the first electrode 7 and the P-type doped layer 3. Compared with the metal element content of the first electrode itself, the first proportion can be calculated. The second proportion is obtained in a similar manner and will not be described again here to avoid repetition.

[0064] The contact position between the first electrode 7 and the P-type doped layer 3 may be a contact region between the first electrode 7 and the P-type doped layer 3. The thickness of the contact region may be about 5 nm, and the direction of the thickness of the contact region is parallel to the thickness direction of the silicon substrate. Figure 1 and Figure 2 The thickness direction of the silicon substrate is the vertical direction. In the contact position between the first electrode 7 and the P-type doped layer 3, the metal elements in the first electrode 7 and the silicon in the P-type doped layer 3 form a metal-crystalline silicon alloy. The contact position between the second electrode 8 and the N-type doped layer 4 can be the contact area between the second electrode 8 and the N-type doped layer 4. The thickness of the contact area can also be about 5nm, and the direction of the thickness of the contact area is parallel to the thickness direction of the silicon substrate. In the contact position between the second electrode 8 and the N-type doped layer 4, the metal elements in the second electrode 8 and the silicon in the N-type doped layer 4 form a metal-crystalline silicon alloy. For example, if both the first electrode and the second electrode contain silver elements, a silver-silicon alloy is formed at the contact position between the first electrode 7 and the P-type doped layer 3, and at the contact position between the second electrode 8 and the N-type doped layer 4.

[0065] Solar cells can be analyzed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to determine the metal element content at the contact point between the first electrode 7 and the P-type doped layer 3, as well as the metal element content at the contact point between the second electrode 8 and the N-type doped layer 5. Specifically, EDS characterization testing is performed in the form of a line scan, with the line scan direction perpendicular to the length or extension direction of the first electrode 7 and the second electrode 8. The contact point between the first electrode 7 and the P-type doped layer 3, as well as the contact point between the second electrode 8 and the N-type doped layer 4, can be determined based on the morphology and changes in Si (silicon) content. Specifically, the contact point between the first electrode 7 and the P-type doped layer 3 is a location where the metal element content is reduced compared to the first electrode itself, and elements such as silicon are reduced compared to the P-type doped layer 3 itself. The contact point between the second electrode 8 and the N-type doped layer 4 is a location where the metal element content is reduced compared to the second electrode itself, and elements such as silicon are reduced compared to the N-type doped layer 4 itself. Figure 3 This is a partial SEM image of a back-contact solar cell. For example, the first electrode 7 and the second electrode 8 both contain silver. Figure 3 In the figure, the top is the first electrode, the bottom is the P-type doped layer 3, the silicon substrate and other structures, and the brighter dot structure between the two is the silver-silicon alloy formed at the contact position between the first electrode and the P-type doped layer. At the same time, the silver-silicon alloy is also formed at the contact position between the second electrode 8 and the N-type doped layer 4. The position where the silver-silicon alloy is formed is the contact position. For another example, Figure 6 Schematic diagram of the element distribution on the silicon substrate and one side of the silicon substrate in a solar cell. Figure 6 In the figure, the horizontal axis is the thickness of the solar cell starting from the silicon substrate side, in nm, and the vertical axis is the distribution ratio of the elements at the corresponding thickness position in the scanning area. Figure 6 The metal element of the middle electrode is silver. The intersection of the silver and silicon curves can be the contact position between the electrode and the doped layer in contact with the electrode. The silver content at the intersection and the ratio of the silver content at the highest point on the right side of the intersection can indicate the proportion of the silver content at the contact position to the silver content in the electrode. The thickness between the intersection and the leftmost endpoint of the silver curve can characterize the tendency of the silver element to enter the doped layer. It should be noted that the line scanning position needs to pass through the metal crystal silicon alloy formed by the metal element in the first electrode 7 and the silicon of the P-type doped layer 3, as well as the metal crystal silicon alloy formed by the metal element in the second electrode 8 and the silicon of the N-type doped layer 5; for example, for the aforementioned Figure 3The scanning position needs to pass through the position of the silver-silicon alloy. One or more regions can be selected at the contact position between the first electrode and the P-type doped layer, each region being formed with the aforementioned metal-crystalline silicon alloy. The metal element content is measured for each region, and then the metal element content of the multiple regions is averaged to obtain the metal element content at the contact position between the first electrode and the P-type doped layer. The "multiple" here can be greater than or equal to 2, for example, 2, 3, 4, 5, 6, 7, 8, 9, or 10.

[0066] The method for obtaining the content of the metal element at the contact position between the second electrode and the N-type doped layer is similar to this, and will not be repeated here to avoid repetition. It should be noted that the method for obtaining the content of the metal element at the contact position between the second electrode and the N-type doped layer should be consistent with the method for obtaining the content of the metal element at the contact position between the first electrode and the P-type doped layer. For example, three positions are selected for measurement at the contact position between the first electrode and the P-type doped layer and the contact position between the second electrode and the N-type doped layer, and the average value of the metal element content at the three positions is calculated.

[0067] The first ratio here is smaller than the second ratio, and the metal element content at the contact position between the first electrode 7 and the P-type doped layer 3 is less than that of the first electrode 7; at the contact position between the second electrode 8 and the N-type doped layer 4, the metal element content is relatively close to the second electrode 8; normally, the P-type doped layer 3 is obtained by boron diffusion, and due to the diffusion characteristics of boron, it is difficult to obtain a higher boron doping concentration, that is, normally the doping concentration of the P-type doped layer 3 is slightly low, resulting in a slightly higher contact resistance corresponding to the first electrode 7. In the present application, the metal elements are formed at the two contact positions in the above-mentioned distribution manner, which means that the metal elements in the first electrode 7 enter the P-type doped layer more than the metal elements in the second electrode 8, and more contact paths are formed in the P-type doped layer corresponding to the first electrode, which can reduce the contact resistance corresponding to the first electrode 7, thereby reducing the contact difference between the P region and the N region, achieving a good contact balance between the P region and the N region, and thus improving the efficiency of the solar cell.

[0068] Optionally, the content of metal elements at the contact position between the first electrode 7 and the P-type doped layer 3 accounts for a first ratio of 1:2.1 to 1:3.9 of the content of metal elements in the first electrode 7, and the content of metal elements at the contact position between the second electrode 8 and the N-type doped layer 4 accounts for a second ratio of 1:1.5 to 1:21 of the content of metal elements in the second electrode 8. The two ratios are within the above ranges, are easy to process and prepare, and have a better effect on reducing the contact resistance corresponding to the first electrode 7.

[0069] For example, the first ratio may be 1:2.1, 1:2.2, 1:2.5, 1:2.7, 1:2.8, 1:3, 1:3.1, 1:3.3, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9, and the second ratio may be 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:1.55, 1:1.65, 1:1.75, 1:1.85, 1:1.95, 1:2, or 1:21.

[0070] Optionally, the diffusion depth of the metal element of the first electrode 7 in the P-type doped layer 3 is greater than the diffusion depth of the metal element of the second electrode 8 in the N-type doped layer 4. Typically, due to the difficulty in obtaining a high boron doping concentration, the contact resistance between the first electrode 7 and the P-type doped layer 3 is slightly high. In the present application, the diffusion depth of the metal element in the P-type doped layer 3 is deeper, which can reduce the contact resistance between the first electrode 7 and the P-type doped layer 3, thereby reducing the contact difference between the P region and the N region, achieving good contact between the P region and the N region at the same time, and thereby improving the efficiency of the solar cell.

[0071] It should be noted that, in the present application, the diffusion depth of the metal element of the first electrode 7 in the P-type doped layer 3 refers to the approximate distance from the position where the first electrode 7 and the P-type doped layer 3 begin to contact in the direction away from the silicon substrate to the position of the first electrode 7 in the diffusion region within the P-type doped layer 3 that is closest to the silicon substrate. The diffusion depth of the metal element of the second electrode 8 in the N-type doped layer 4 refers to the approximate distance from the position where the second electrode 8 and the N-type doped layer 4 begin to contact in the direction away from the silicon substrate to the position of the second electrode 8 in the diffusion region within the N-type doped layer 4 that is closest to the silicon substrate.

[0072] Optionally, the ratio of the diffusion depth of the metal element of the first electrode 7 in the P-type doped layer 3 to the diffusion depth of the metal element of the second electrode 8 in the N-type doped layer 4 is greater than 1 and less than or equal to 8. In the present application, the ratio of the diffusion depth of the metal element in the P-type doped layer 3 to the diffusion depth of the metal element of the second electrode 8 in the N-type doped layer 4 is within the above-mentioned numerical range. This ratio is relatively appropriate, which not only reduces the contact resistance between the first electrode 7 and the P-type doped layer 3, but also reduces the contact difference between the P region and the N region, thereby achieving good contact between the P region and the N region, thereby improving the efficiency of the solar cell, and is also compatible with existing processes and easy to implement.

[0073] For example, the ratio of the diffusion depth of the metal element of the first electrode 7 in the P-type doped layer 3 to the diffusion depth of the metal element of the second electrode 8 in the N-type doped layer 4 can be 1.01, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, or 8.

[0074] Optionally, the diffusion depth of the metal elements of the first electrode 7 in the P-type doping layer 3 is 100nm to 450nm, and the diffusion depth of the metal elements of the second electrode 8 in the N-type doping layer 4 is 50nm to 300nm. This can not only reduce the contact resistance corresponding to the first electrode 7, but also reduce the contact difference between the P region and the N region, and achieve good contact between the P region and the N region at the same time, thereby improving the efficiency of the solar cell. Moreover, it is compatible with existing processes and easy to implement.

[0075] For example, the diffusion depth of the metal element of the first electrode 7 in the P-type doped layer 3 can be 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 130nm, 270nm, 390nm, 410nm, 430nm, 440nm, or 450nm. For example, the diffusion depth of the metal element of the second electrode 10 in the N-type doped layer 4 can be 50nm, 90nm, 100nm, 150nm, 170nm, 200nm, 250nm, 280nm, or 300nm. It should be noted that in the process of selecting the values of the two, it is necessary to satisfy the diffusion depth of the metal element of the first electrode 7 in the P-type doped layer 3 that is greater than the diffusion depth of the metal element of the second electrode 8 in the N-type doped layer 4.

[0076] Optionally, the thickness of the P-type doping layer 3 here can be greater than the thickness of the N-type doping layer 4. By increasing the thickness of the P-type doping layer, it is beneficial for the P-type doping to be dissolved in the corresponding doping layer at a higher concentration, and to match the greater diffusion depth of the metal elements in the P-type doping layer, so as to avoid the diffusion of metal elements into the silicon substrate as much as possible, thereby reducing recombination. The electric field strength in the region can be guaranteed, and the P region and the N region can simultaneously achieve a good field effect, thereby ensuring the effectiveness of the heterojunction and high-low junction structure. Furthermore, the difference between the thickness of the P-type doping layer 3 and the thickness of the N-type doping layer 4 can be 10nm to 150nm. For example, the thickness of the P-type doped layer 3 can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, or 600 nm, and the thickness of the N-type doped layer 4 can be 90 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 330 nm, 400 nm, or 450 nm. It should be noted that, in the process of selecting the respective values of the two, it is necessary to ensure that the thickness of the P-type doped layer 3 is greater than the thickness of the N-type doped layer 4.

[0077] Optional, see Figure 2, the solar cell may also include: a P-type inner expansion layer 9 and an N-type inner expansion layer 10. The P-type inner expansion layer 9 is the portion where the doping elements in the P-type doping layer 3 are diffused into the silicon substrate. The N-type inner expansion layer 10 is the portion where the doping elements in the N-type doping layer 4 are diffused into the silicon substrate. It should be noted that, regardless of whether the silicon substrate 1 itself has N-type doping or P-type doping, the doping concentrations of the P-type inner expansion layer 9 and the N-type inner expansion layer 10 are usually higher than the doping concentration of the silicon substrate 1 itself. Moreover, the positions of the P-type inner expansion layer 9 and the N-type inner expansion layer 10 can be used to conveniently and accurately distinguish the silicon substrate itself from the P-type inner expansion layer 9 and the N-type inner expansion layer 10. For back-contact solar cells, such as Figure 2 As shown, both the P-type inner expansion layer 9 and the N-type inner expansion layer 10 are located within the silicon substrate and are positioned near the backlight surface of the silicon substrate. The P-type inner expansion layer 9 corresponds to the P region, while the N-type inner expansion layer 10 corresponds to the N region. For a double-sided electrode solar cell, both the P-type inner expansion layer 9 and the N-type inner expansion layer 10 are located within the silicon substrate. The P-type inner expansion layer 9 is positioned near the surface of the silicon substrate, adjacent to the P-type doped layer 3, while the N-type inner expansion layer 10 is positioned near the surface of the silicon substrate, adjacent to the N-type doped layer 4.

[0078] The P-type inner extension layer 9 is located inside the silicon substrate 1 near the P-type doping layer 3 and corresponds to the P region. The ratio of the doping concentration of the P-type doping layer 3 to the doping concentration of the P-type inner extension layer 9 is 2 to 5×10 11 The N-type inner expansion layer 10 is located inside the silicon substrate 1 near the N-type doping layer 4 and corresponds to the N region. The ratio of the doping concentration of the N-type doping layer 4 to the doping concentration of the N-type inner expansion layer 10 is 2 to 6×10 11 The ratio of the doping concentration of the P-type doping layer 3 to the doping concentration of the P-type inner extension layer 9, as well as the ratio of the doping concentration of the N-type doping layer 4 to the doping concentration of the N-type inner extension layer 10, is controlled within the above ranges in order to ensure that the electric field strength in the region has a good carrier shunting effect.

[0079] For example, the ratio of the doping concentration of the P-type doping layer 3 to the doping concentration of the P-type inner extension layer 9 can be 2, 10, 100, 1000, 5000, 1×10 4 , 1×10 5 , 5×10 6 , 8×10 7 , 1×10 8 , 1×10 9 , 1×10 10 , 1×10 11 , 5×10 11 The ratio of the doping concentration of the N-type doping layer 4 to the doping concentration of the N-type inner extension layer 10 can be 2, 50, 10, 1000, 1×10 4 , 5×10 5 , 1×106 , 5×10 7 , 1×10 8 , 1×10 9 , 1×10 10 , 1×10 11 , 5×10 11 , 6×10 11 .

[0080] Optionally, the doping concentration of the P-type doping layer 3 is 1×10 17 cm -3 to 5×10 21 cm -3 The doping concentration of the P-type inner extension layer 9 is 1×10 10 cm -3 to 5×10 16 cm -3 The doping concentrations of both the P-type doped layer 3 and the P-type inner expansion layer 9 are within the aforementioned range, resulting in a suitable doping concentration or doping amount for the P-type inner expansion layer 9 within the silicon substrate, ensuring low contact resistance between the electrode and the P-type doped region. Furthermore, along the depth direction of the silicon substrate, the doping concentration of the P-type doped layer 3 and the doping content of the P-type inner expansion layer 9 vary appropriately, ensuring effective carrier separation and improving the efficiency of the solar cell while also enhancing compatibility with existing processes.

[0081] For example, the doping concentration of the P-type doping layer 3 can be 1×10 17 cm -3 , 5×10 17 cm -3 , 1×10 18 cm -3 , 5×10 18 cm -3 , 1×10 19 cm -3 , 5×10 19 cm -3 , 1×10 20 cm -3 , 5×10 20 cm -3 , 1×10 21 cm -3 , 5×10 21 cm -3 The doping concentration of the P-type inner extension layer 9 can be 1×10 10 cm -3 , 5×10 10 cm -3 , 1×10 11 cm -3 , 5×10 11 cm -3, 1×10 12 cm -3 , 1×10 13 cm -3 , 5×10 13 cm -3 , 1×10 14 cm -3 , 1×10 15 cm -3 , 1×10 16 cm -3 , 5×10 16 cm -3 It should be noted that the selection of the doping concentrations of the two must meet the aforementioned ratio restrictions. Along the depth direction of the P-type doping layer 3, the doping concentration at each location of the P-type doping layer 3 can remain basically unchanged, which can be specifically characterized by the surface concentration. That is, along the depth direction of the P-type doping layer 3, the doping concentration at each location of the P-type doping layer 3 is relatively uniform.

[0082] Optionally, the doping concentration of the N-type doping layer 4 is 1×10 18 cm -3 to 6×10 21 cm -3 The doping concentration of the N-type inner extension layer 10 is 1×10 11 cm -3 to 5×10 17 cm -3 The doping concentrations of both layers are within the aforementioned range, resulting in a suitable doping concentration or doping amount for the N-type inner extension layer 10 within the silicon substrate, ensuring low contact resistance between the second electrode and the N-type doped layer. Furthermore, along the depth direction of the silicon substrate, the doping concentration of the N-type doped layer 4 and the doping content of the N-type inner extension layer 10 vary appropriately, ensuring effective carrier separation and improving the efficiency of the solar cell. This also enhances compatibility with existing processes.

[0083] For example, the doping concentration of the N-type doping layer 4 can be 1×10 18 cm -3 , 5×10 18 cm -3 , 1×10 19 cm -3 , 5×10 19 cm -3 , 1×10 20 cm -3 , 5×10 20 cm -3 , 1×10 21 cm -3 , 5×10 21 cm -3 , 6×1021 cm -3 The doping concentration of the N-type inner extension layer 10 can be 1×10 11 cm -3 , 5×10 11 cm -3 , 1×10 12 cm -3 , 1×10 13 cm -3 , 5×10 13 cm -3 , 1×10 14 cm -3 , 1×10 15 cm -3 , 1×10 16 cm -3 , 5×10 16 cm -3 , 1×10 17 cm -3 , 5×10 17 cm -3 It should be noted that the doping concentrations of the two must meet the aforementioned ratio restrictions. Along the depth direction of the N-type doping layer 4, the doping concentration at each location in the N-type doping layer 4 can remain essentially unchanged. This can be specifically characterized by the surface concentration. That is, along the depth direction of the N-type doping layer 4, the doping concentration at each location in the N-type doping layer 4 is relatively uniform.

[0084] In the solar cell, the ratio of the doping concentration of the N-type doping layer 4 to the doping concentration of the P-type doping layer 3 is in the range of 10 to 6×10 5 , in order to be compatible with existing processes and reduce the damage to the battery caused by the high-temperature process of boron diffusion in the P-type doped layer. In addition, combined with the difference in the concentration of metal elements in the P-type doped layer and the N-type doped layer, the balance of carrier transport effects in the N-region and the P-region can be effectively regulated, ultimately improving battery performance.

[0085] The depth of the P-type inner expansion layer 9 can be 50nm to 100nm greater than the depth of the N-type inner expansion layer 10. The difference in depth between the two can ensure the passivation effect while reducing recombination, and can also improve the contact matching effect between the electrodes, so as to achieve efficient separation of carriers. It should be noted that multiple positions can be selected in the N-type doping layer 4 to obtain the doping concentration of each position, and then the doping concentration of each position is averaged to obtain the doping concentration of the N-type doping layer 4. The multiple positions can be 2, 3, 4, 5, 6, 7, 8, 9, or 10. The determination of the doping concentration of the P-type doping layer 3 is similar to this, and then the ratio obtained by dividing the doping concentration of the N-type doping layer 4 by the doping concentration of the P-type doping layer 3 is how much higher the doping concentration of the N-type doping layer 4 is than the doping concentration of the P-type doping layer 3.

[0086] Optionally, the ratio of the contact resistance between the first electrode 7 and the P-type doped layer 3 to the contact resistance between the second electrode 8 and the N-type doped layer 4 is 1.25 to 3. Normally, the P-type doped layer 3 is obtained by boron diffusion, and it is difficult to obtain a higher boron doping concentration. The P-type doped layer 3 will cause the contact resistance between the first electrode 7 and the P-type doped layer 3 to be slightly higher. In the present application, the ratio of the contact resistance of the two is within the above range, which reduces the contact resistance between the first electrode 7 and the P-type doped layer 3, thereby reducing the contact difference between the P region and the N region. The P region and the N region achieve good contact at the same time, thereby improving the efficiency of the solar cell. At the same time, it is also easier to implement while being compatible with existing processes.

[0087] For example, the ratio of the contact resistance between the first electrode 7 and the P-type doped layer 3 to the contact resistance between the second electrode 8 and the N-type doped layer 4 can be 1.25, 1.5, 1.8, 2, 2.25, 2.125, 2.5, 2.7, 2.8, 2.9, or 3.

[0088] Optionally, the contact resistance between the first electrode 7 and the P-type doped layer 3 is 2.5Ω / cm to 4Ω / cm; the contact resistance between the second electrode 8 and the N-type doped layer 4 is 0.5Ω / cm to 2Ω / cm. The contact resistances of the two are within the above corresponding ranges, which reduces the contact difference between the P region and the N region, and achieves good contact between the P region and the N region at the same time, thereby improving the efficiency of the solar cell. At the same time, it is also easier to implement while being compatible with existing processes.

[0089] For example, the contact resistance between the first electrode 7 and the P-type doped layer 3 can be 2.5Ω / cm, 2.6Ω / cm, 2.8Ω / cm, 2.9Ω / cm, 3Ω / cm, 3.3Ω / cm, 3.5Ω / cm, 3.7Ω / cm, 3.9Ω / cm, or 4Ω / cm; the contact resistance between the second electrode 8 and the N-type doped layer 4 can be 0.5Ω / cm, 0.8Ω / cm, 1Ω / cm, 1.2Ω / cm, 1.5Ω / cm, 1.75Ω / cm, 1.9Ω / cm, 1.8Ω / cm, or 2Ω / cm.

[0090] Optionally, the solar cell may further include: a first passivation anti-reflection layer 5 located between the N-type doped layer 4 and the second electrode 8; and a second passivation anti-reflection layer 6 located between the P-type doped layer 3 and the first electrode 7. The refractive index of the first passivation anti-reflection layer 5 is greater than that of the second passivation anti-reflection layer 6. The first and second passivation anti-reflection layers serve to passivate the surface. They can be formed in the same process step or in different process steps, and both can produce the aforementioned refractive index profile. Factors influencing the refractive index include the thickness, density, or composition of the passivation anti-reflection layer, such as the silicon-nitrogen ratio. The refractive index is positively correlated with density to a certain extent. The lower density of the second passivation anti-reflection layer in the P region facilitates corrosion of the second passivation anti-reflection layer by the first electrode. Compared to the second electrode, the first electrode is more likely to form contact with the P-type doped layer, and metal elements are more likely to diffuse into the P-type doped layer, thereby achieving contact balance between the P and N regions.

[0091] The materials of the first passivation anti-reflection layer and the second passivation anti-reflection layer both include a single layer formed of silicon dioxide, aluminum dioxide, silicon nitride, or silicon oxynitride, or may be a stacked layer formed by a combination of one or more of the foregoing materials. The materials of the first passivation anti-reflection layer and the second passivation anti-reflection layer may be the same or different. It should be noted that when at least one of the first passivation anti-reflection layer and the second passivation anti-reflection layer is a stacked structure, the refractive index is the refractive index measured for the passivation anti-reflection layer as a whole. For example, when at least one of the first passivation anti-reflection layer and the second passivation anti-reflection layer is a stacked structure of aluminum dioxide and silicon nitride, the refractive index is the refractive index measured for the passivation anti-reflection layer as a whole. In this case, the passivation anti-reflection layer can take into account both the protective and passivation effects of the underlying silicon substrate or functional layer, such as the P-type doped layer or the N-type doped layer, as well as the anti-reflection effect on light incident on the light-receiving surface or the backlight surface.

[0092] It should be noted that, in the case where the solar cell is a back contact solar cell, Figure 1 As shown, the first passivation anti-reflection layer 5 and the second passivation anti-reflection layer 6 are both located on the backlight side of the silicon substrate 1. The first passivation anti-reflection layer 5 corresponds to the N region, and the second passivation anti-reflection layer 6 corresponds to the P region. The back-contact solar cell may also include a third passivation anti-reflection layer located on the light-facing side of the silicon substrate. The surface of the silicon substrate may also have a suede structure for light trapping. In the case of a double-sided electrode solar cell, the first passivation anti-reflection layer and the second passivation anti-reflection layer are located on different sides of the silicon substrate, respectively, existing as the front passivation anti-reflection layer and the back passivation anti-reflection layer.

[0093] Optionally, the difference in refractive index between the first passivation anti-reflection layer and the second passivation anti-reflection layer ranges from 0.02 to 0.4. By controlling the difference in refractive index between the first passivation anti-reflection layer and the second passivation anti-reflection layer within this range, the relatively low density of the second passivation anti-reflection layer 6 in the P region facilitates contact between the first electrode in the P region and the P-type doped layer, and facilitates diffusion of metal elements into the P-type doped layer, thereby achieving contact balance between the P region and the N region. Within the range of the designed difference, the passivation anti-reflection effect in both the P region and the N region can be maintained. For example, the refractive index of the first passivation anti-reflection layer is greater than the refractive index of the second passivation anti-reflection layer, and the difference between the two can be 0.02, 0.04, 0.07, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or 0.4. For another example, the refractive index of the second passivation anti-reflection layer may be 1.95, 1.97, 1.98, 2, 2.05, 1.96, 1.99, 2.01, 2.02, 2.03, or 2.04, and the refractive index of the first passivation anti-reflection layer may be 2.05, 2.06, 2.09, 2.1, 2.12, 2.15, 2.16, 2.18, or 2.2.

[0094] Optionally, the P-type doped layer includes a first electrode region, which is a region on the P-type doped layer 3 that can contact the first electrode 7. Figure 4 The surface of the first electrode region away from the silicon substrate has a plurality of first contact holes 31. The N-type doped layer 4 includes a second electrode region, which is a region on the N-type doped layer 4 that can contact the second electrode 8. Figure 5 The surface of the second electrode region facing away from the silicon substrate has multiple second contact holes 41. To more clearly observe the contact hole structure, the other layers above the doped layer in the solar cell can be removed and then pickled, for example, with a mixture of nitric acid and hydrofluoric acid. The electrode region of the solar cell can then be measured using an SEM. The depth of the first contact hole 31, parallel to the thickness of the silicon substrate, is greater than the depth of the second contact hole 41. Furthermore, the first contact hole 31 and the second contact hole 41 are each adapted to accommodate metal crystals, primarily metal elements from the electrode that enter the doped layer and form a metal-silicon alloy with silicon in the doped layer. When measuring the contact hole depth, the cross-sectional morphology of the second electrode region of the N-type doped layer can be obtained after cleaning and removal of the metal crystals and glass frit. Setting the depth of the first contact hole greater than the depth of the second contact hole allows for a greater diffusion depth of the metal elements in the P-doped layer. This, in turn, can compensate for the higher contact resistance of the P region compared to the N region by increasing the contact depth of the metal elements in the P-doped layer, thereby achieving a balance in current transmission and collection performance between the N and P regions.

[0095] Optionally, along the thickness direction parallel to the silicon substrate, the depth of the first contact hole 31 is 2nm to 300nm, and the depth of the second contact hole 41 is 1nm to 200nm. By setting the depths of the first contact hole and the second contact hole within the above range, the problem of excessive composite caused by direct burn-through due to excessive corrosion depth of the first electrode and the second electrode can be effectively avoided; at the same time, the problem of increased contact resistance caused by poor contact due to too shallow corrosion depth can be avoided.

[0096] For example, along the thickness direction parallel to the silicon substrate, the depth of the first contact hole 31 can be 2 nm, 5 nm, 10 nm, 50 nm, 80 nm, 100 nm, 120 nm, 150 nm, 190 nm, 200 nm, 220 nm, 250 nm, or 300 nm, and the depth of the second contact hole 41 can be 1 nm, 10 nm, 20 nm, 50 nm, 90 nm, 100 nm, 130 nm, 150 nm, 170 nm, 180 nm, 190 nm, or 200 nm. It should be noted that when setting the depths of the first contact hole 31 and the second contact hole 41, it is necessary to ensure that the depth of the first contact hole 31 is greater than the depth of the second contact hole 41.

[0097] Optionally, the solar cell may further include: a first tunneling oxide layer 21 located between the silicon substrate 1 and the P-type doped layer 3; and a second tunneling oxide layer 22 located between the silicon substrate 1 and the N-type doped layer 4. The thickness of the first tunneling oxide layer 21 is greater than that of the second tunneling oxide layer 22. In the case where the solar cell is a back contact solar cell, as shown in FIG. Figure 1 The first tunnel oxide layer 21 and the second tunnel oxide layer 22 are both located on the backlight side of the silicon substrate, and the first tunnel oxide layer 21 corresponds to the P region, while the second tunnel oxide layer 22 corresponds to the N region. The thickness of the first tunnel oxide layer 21 is greater than that of the second tunnel oxide layer 22, mainly to adapt to the difference in the interaction between Group IIIA elements such as boron and Group VA elements such as phosphorus and tunnel oxide. Specifically, boron is easier to diffuse into the silicon substrate through the tunnel oxide layer than phosphorus. Therefore, during the diffusion process, a thicker first tunnel oxide layer is required to control the diffusion concentration of boron and reduce the recombination caused by excessive doping concentration. The matching of the thickness relationship between the first tunnel oxide layer and the second tunnel oxide layer can simultaneously achieve the coordination and fine control of the depth of the two doping extensions, achieve good contact effect and carrier separation effect in both the N region and the P region, and further improve the efficiency of the solar cell. At the same time, the first tunnel oxide layer and the second tunnel oxide layer can also play a passivation role in reducing the surface recombination of the silicon substrate.

[0098] It should be noted that, in the solar cell, the side surface of the silicon substrate 1 may also be covered with a tunneling oxide layer, and the side surface of the silicon substrate 1 connects the light-facing surface and the backlight surface of the silicon substrate.

[0099] In the case of a double-sided electrode solar cell, the first tunnel oxide layer and the second tunnel oxide layer are located on either side of the silicon substrate. The technical effect of the thickness difference between the first tunnel oxide layer and the second tunnel oxide layer is the same as described above and will not be repeated here.

[0100] Optionally, on the basis that the thickness of the first tunnel oxide layer 21 is greater than the thickness of the second tunnel oxide layer 22, the difference between the thickness of the first tunnel oxide layer 21 and the thickness of the second tunnel oxide layer 22 is 0.1nm to 2nm, which is easy to implement while being compatible with existing processes.

[0101] For example, on the basis that the thickness of the first tunnel oxide layer 21 is greater than the thickness of the second tunnel oxide layer 22, the difference between the thickness of the first tunnel oxide layer 21 and the thickness of the second tunnel oxide layer 22 can be 0.1nm, 0.2nm, 0.5nm, 0.8nm, 1nm, 1.1nm, 1.05nm, 1.3nm, 1.5nm, 1.8nm, 1.9nm, or 2nm.

[0102] It should be noted that in the solar cell, the thickness of the first tunnel oxide layer 21 can be 1.1 nm. 、 1.3nm 、 1.5nm 、 2nm 、 2.5nm 、 3nm 、 3.5nm 、 4nm 、 4.5nm 、 5nm 、 5.5nm 、 6nm 、 6.5nm 、 7nm 、 7.5nm 、 8nm 、 8.5nm 、 9nm 、 9.5nm 、 10nm, the thickness of the second tunnel oxide layer 22 can be 1nm, 1.1nm, 1.4nm, 1.5nm, 2nm, 2.5nm, 2.8nm, 3nm, 3.5nm, 4.2nm, 5nm, 5.6nm, 6nm, 6.7nm, 7nm, 7.5nm, 8nm, 8.5nm, 9nm. In the process of selecting the thickness of the two within the corresponding range, it is necessary to ensure that the thickness of the first tunnel oxide layer 21 is greater than the thickness of the second tunnel oxide layer 22.

[0103] It should be noted that, in this application, the specific preparation process of the solar cell is not limited.

[0104] The present application also provides a photovoltaic assembly, comprising any of the aforementioned solar cells. The photovoltaic assembly may also include adhesive films located on both sides of the solar cells, without specific limitation. The photovoltaic assembly has the same or similar beneficial effects as any of the aforementioned solar cells, and relevant aspects may be referenced in conjunction with each other. To avoid repetition, the details will not be repeated here.

[0105] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0106] 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 methods. The above-mentioned specific implementation methods are merely illustrative and not 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 protected by the present invention.

Claims

1. A solar cell, characterized in that: include: A silicon substrate, comprising: a surface having an N region and a P region; An N-type doped layer, located on the N region of the silicon substrate; A P-type doped layer, located on the P region of the silicon substrate; a first electrode, contacting the P-type doped layer; a second electrode, contacting the N-type doped layer; The first electrode and the second electrode both contain metal elements; the content of the metal elements in the region corresponding to the first electrode in the P-type doped layer is greater than the content of the metal elements in the region corresponding to the second electrode in the N-type doped layer.

2. The solar cell according to claim 1, wherein The content of the metal element in the first electrode is greater than the content of the metal element in the second electrode.

3. The solar cell according to claim 1 or 2, characterized in that The content of the metal element at the contact position between the first electrode and the P-type doped layer accounts for a first proportion of the content of the metal element in the first electrode; the content of the metal element at the contact position between the second electrode and the N-type doped layer accounts for a second proportion of the content of the metal element in the second electrode; The first ratio is smaller than the second ratio.

4. The solar cell according to claim 3, characterized in that The first ratio is 1:2.1 to 1:3.9; The second ratio is 1:1.5 to 1:2.

1.

5. The solar cell according to claim 1, wherein The diffusion depth of the metal element of the first electrode in the P-type doping layer is greater than the diffusion depth of the metal element of the second electrode in the N-type doping layer.

6. The solar cell according to claim 1, wherein The ratio of the diffusion depth of the metal element of the first electrode in the P-type doping layer to the diffusion depth of the metal element of the second electrode in the N-type doping layer is greater than 1 and less than or equal to 8.

7. The solar cell according to claim 1, wherein The diffusion depth of the metal element of the first electrode in the P-type doping layer is 100 nm to 450 nm; The diffusion depth of the metal element of the second electrode in the N-type doping layer is 50 nm to 300 nm.

8. The solar cell according to claim 1, wherein Also includes: The P-type inner expansion layer is located inside the silicon substrate near the P-type doping layer and corresponds to the P region; the ratio of the doping concentration of the P-type doping layer to the doping concentration of the P-type inner expansion layer is 2 to 5×10 11 ; The N-type inner expansion layer is located in the silicon substrate near the N-type doping layer and corresponds to the N region; the ratio of the doping concentration of the N-type doping layer to the doping concentration of the N-type inner expansion layer is 2 to 6×10 11 .

9. The solar cell according to claim 1, wherein A ratio of a contact resistance between the first electrode and the P-type doped layer to a contact resistance between the second electrode and the N-type doped layer is 1.25 to 3.

10. The solar cell according to claim 1, wherein Also includes: a first passivation anti-reflection layer, located between the N-type doped layer and the second electrode, and a second passivation anti-reflection layer, located between the P-type doped layer and the first electrode; Wherein, the refractive index of the first passivation anti-reflection layer is greater than the refractive index of the second passivation anti-reflection layer.

11. The solar cell according to claim 10, characterized in that The difference between the refractive index of the first passivation anti-reflection layer and the refractive index of the second passivation anti-reflection layer is in a range of 0.02 to 0.

4.

12. The solar cell according to claim 11, characterized in that The P-type doped layer includes a first electrode region, and a surface of the first electrode region away from the silicon substrate has a plurality of first contact holes; The N-type doped layer includes a second electrode region, and a surface of the second electrode region away from the silicon substrate has a plurality of second contact holes; Wherein, along a thickness direction parallel to the silicon substrate, the depth of the first contact hole is greater than the depth of the second contact hole, and the first contact hole and the second contact hole are respectively suitable for accommodating metal crystals.

13. The solar cell according to claim 12, wherein: Along a thickness direction parallel to the silicon substrate, a depth of the first contact hole is 2 nm to 300 nm, and a depth of the second contact hole is 1 nm to 200 nm.

14. The solar cell according to any one of claims 1 to 2 and 4 to 13, characterized in that: Also includes: a first tunneling oxide layer, located between the silicon substrate and the P-type doped layer; a second tunneling oxide layer, located between the silicon substrate and the N-type doped layer; The thickness of the first tunnel oxide layer is greater than the thickness of the second tunnel oxide layer.

15. A photovoltaic module, characterized in that: include: A plurality of cell strings, each cell string comprising the solar cell according to any one of claims 1 to 14.

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