Solar cells and photovoltaic modules

Abstract

The application provides a solar cell and a photovoltaic module, and relates to the technical field of photovoltaics.The cell comprises a silicon substrate, the silicon substrate comprising a surface with an N region and a P region; an N-type doped layer on the N region of the silicon substrate; a P-type doped layer on the P region of the silicon substrate; a first electrode in contact with the P-type doped layer; a second electrode in contact with the N-type doped layer; the first electrode and the second electrode both comprising a metal element; the content of the metal element in the region corresponding to the first electrode in the P-type doped layer being greater than the content of the metal element in the region corresponding to the second electrode in the N-type doped layer.The application can reduce the contact resistance corresponding to the first electrode, thereby reducing the contact difference between the P region and the N region, and the P region and the N region can achieve good contact at the same time, thereby improving the efficiency of the solar cell.

Description

Technical Field

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

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

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

[0004] This invention provides a solar cell and a photovoltaic module, which aim to solve problems such as poor electrode contact in existing solar cells.

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

[0006] A silicon substrate, the silicon substrate comprising: a surface having N-regions and P-regions;

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

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

[0009] The first electrode is in contact with the P-type doped layer;

[0010] The second electrode is in contact with the N-type doped layer;

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

[0012] Typically, P-type doped layers are obtained by boron diffusion. Due to the diffusion characteristics of boron, it is difficult to achieve a high boron doping concentration. This means that a slightly lower doping concentration in the P-type doped layer usually results in a slightly higher contact resistance at the first electrode. In this application, the metal element content in the region corresponding to the second electrode in the P-type doped layer is higher than that in the region corresponding to the first electrode in the P-type doped layer. This indicates that more contact paths are formed in the region corresponding to the first electrode in the P-type doped layer, improving the contact performance between the first electrode and the P-type doped layer. This reduces the contact resistance at the first electrode, narrows the contact difference between the P and N regions, achieves a good contact balance between the P and N regions, and thus improves the efficiency of the solar cell.

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

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

[0015] Wherein, the first ratio is less than the second ratio.

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

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

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

[0019] Optionally, the ratio of the diffusion depth of the metal element of the first electrode in the P-type doped layer to the 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 in the first electrode in the P-type doped layer is 100 nm to 450 nm.

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

[0022] Optionally, the solar cell further includes:

[0023] The P-type inner extension layer is located inside the silicon substrate, close to the P-type doped layer, and corresponds to the P-region; the ratio of the doping concentration of the P-type doped layer to the doping concentration of the P-type inner extension layer is 2 to 5 × 10⁻⁶. 11 ;

[0024] An N-type inner extension layer is located inside the silicon substrate, close to the N-type doped layer, and corresponds to the N-region; the ratio of the doping concentration of the N-type doped layer to the doping concentration of the N-type inner extension layer is 2 to 6 × 10⁻⁶. 11 .

[0025] Optionally, the 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 includes:

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

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

[0029] The refractive index of the first passivation antireflection layer is greater than that of the second passivation antireflection layer.

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

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

[0033] Wherein, along the 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 the thickness direction parallel to the silicon substrate, the depth of the first contact hole is 2 nm to 300 nm, and the depth of the second contact hole is 1 nm to 200 nm.

[0035] Optionally, the solar cell further includes:

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

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

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

[0039] A second aspect of the present invention provides a photovoltaic module comprising: a plurality of battery strings, wherein the battery strings include any of the aforementioned solar cells.

[0040] The solar cells and photovoltaic modules of this application achieve high-field passivation, balanced PN region contact performance, and low recombination, thus ensuring improved conversion efficiency. Attached Figure Description

[0041] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

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

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

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

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

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

[0047] Explanation of the attached drawing numbers:

[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 and antireflection layer, 6-Second passivation and antireflection 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 Implementation

[0049] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] This invention provides a solar cell, with reference to... Figure 1 and Figure 2The solar cell includes a silicon substrate 1, a P-type doped layer 3, an N-type doped layer 4, a first electrode 7, and a second electrode 8. The silicon substrate 1 can be either N-type or P-type monocrystalline silicon, providing long-lived charge carriers. The silicon substrate can be obtained by cutting a silicon ingot with diamond wire. To minimize the impact of cutting marks on surface recombination, the silicon substrate can be cleaned and polished before other structural fabrication. The silicon substrate 1 includes surfaces with both N- and P-regions; if a single surface simultaneously has both N- and P-regions, then the solar cell is a back-contact solar cell. Here, the back surface primarily has both N- and P-regions, and there can be an isolation region between the N- and P-regions. Figure 1 and Figure 2 As shown, in the back surface of silicon substrate 1, the area to the left of dashed line L1 is the N-region, and the area to the right of dashed line L2 is the P-region. An isolation region exists between the N-region and the P-region to prevent short circuits within the solar cell. It should be noted that dashed lines L1 and L2 are not actually present in the solar cell; they are merely illustrative to distinguish between the P-region and the N-region. During solar cell operation, the surface of silicon substrate 1 that primarily receives light is its light-facing side, while the back surface is opposite to the light-facing side. Figure 1 and Figure 2 In this context, the backlight side is the lower surface of silicon substrate 1, and the light-facing side is the upper surface of silicon substrate 1. Alternatively, if a solar cell has an N-region on one surface and a P-region on the other, then the solar cell is a solar cell with electrodes on both sides. Here, "one surface" and "other surface" 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 (e.g., boron). The N-type doped layer 4 may contain one or more elements from Group VA (e.g., phosphorus). The materials for both the N-type and P-type doped layers can include any semiconductor material such as silicon, germanium-silicon, germanium, or gallium arsenide. In terms of the arrangement of matter, the crystal phase of the doped layer can be amorphous, microcrystalline, nanocrystalline, single-crystal, or polycrystalline. The materials for the N-type and P-type doped layers can be the same or different. For example, both the N-type and P-type doped layers can be doped polycrystalline silicon. Another example: the P-type doped layer can include at least one of doped amorphous silicon, doped microcrystalline silicon, and doped nanocrystalline silicon, while the N-type doped layer can be doped polycrystalline silicon. Yet another example: the P-type doped layer can be doped single-crystal silicon, i.e., diffused onto the surface of the P-region of a silicon substrate, while the N-type doped layer can be doped polycrystalline silicon. The P-type doped layer 3 can be prepared by in-situ doping or ex-situ doping. Similarly, the N-type doped layer 4 can 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, and the N-type doped layer 4 is located in the N-region of the silicon substrate 1. The relative sizes of the two regions are not specifically defined. The first electrode 7 contacts the P-type doped layer 3, and the second electrode 8 contacts the N-type doped layer 4, respectively achieving current collection and conduction.

[0053] Both the first electrode 7 and the second electrode 8 contain metallic elements, which may include silver (Ag), copper (Cu), aluminum (Al), etc. It should be noted that there is no specific limitation on whether the types of metallic elements contained in the first electrode 7 and the second electrode 8 are the same; they can be the same or different. Generally, silver is more corrosive and has stronger conductivity, forming a silver-silicon alloy with silicon. Aluminum also has strong conductivity, while copper is less expensive. The content of metallic elements in the region corresponding to the first electrode 7 in the P-type doped layer 3 is greater than the content of metallic elements in the region corresponding to the second electrode 8 in the N-type doped layer 4. Here, "content" can refer to mass content.

[0054] The first electrode 7 and the second electrode 8 can be fabricated by methods such as printing, photolithography, or electroplating. The printing method can be, for example, screen printing or inkjet printing, with screen printing being preferred due to its lower cost. In the screen printing process for electrode fabrication, 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 doped layer, and those skilled in the art can determine it using conventional methods in the field. For example, the metal element content in the region corresponding to the first electrode in the P-type doped layer can be measured by scanning electron microscopy (SEM). The element distribution is tested in a cross-sectional image including the first electrode and the P-type doped layer. The cross-sectional image can be an SEM image obtained after 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 in the region corresponding to the first electrode in the P-type doped layer, and then the element distribution in the sub-region is characterized by EDS surface scanning to obtain the proportion of metal elements in the sub-region, thus obtaining the metal element content in the region corresponding to the first electrode in the P-type doped layer. Alternatively, multiple sub-regions of the same area can be selected from the corresponding region of the first electrode in the P-type doped layer. Then, the element distribution in each sub-region of the same area can be characterized by EDS surface scanning to obtain the proportion of metal elements in each sub-region. The average value can then be taken to obtain the metal element content in the region corresponding to the first electrode in the P-type doped layer. Here, multiple can be 2, 3, 4, 5, 6, etc.

[0056] Here, the metal element content in the region corresponding to the first electrode 7 in the P-type doped layer 3 refers to the metal element content in the region corresponding to the first electrode 7 across the entire thickness of the P-type doped layer 3. Similarly, the metal element content in the region corresponding to the second electrode 8 in the N-type doped layer 4 refers to the metal element content in the region corresponding to the second electrode 8 across 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. Here, orthographic projection refers to the projection of the electrode in the doped layer when illuminated by light along the direction of the silicon substrate's thickness. This sub-region also corresponds to the entire thickness of the doped layer.

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

[0058] The content of metal elements in the region corresponding to the first electrode 7 in the P-type doped layer 3 is greater than the content of metal elements in the region corresponding to the second electrode 8 in the N-type doped layer 4. This can be achieved by: the proportion of the corresponding metal element in the P-type doped layer 3 within the sub-region being greater than the proportion of the corresponding metal element in the N-type doped layer 4 within the sub-region; or by: the average proportion of the corresponding metal element in the P-type doped layer 3 within the sub-region being greater than the average proportion of the corresponding metal element in the N-type doped layer 4 within the sub-region; or by: the proportion of metal elements in a certain number of identical-area sub-regions corresponding to the first electrode in the P-type doped layer being greater than the proportion of metal elements in a certain number of identical-area sub-regions corresponding to the second electrode in the N-type doped layer. This certain proportion can be 50%, 60%, 70%, 80%, 90%, 100%, etc. The total number of identical area sub-regions taken from the corresponding region of the first electrode in the P-type doped layer can be equal to or unequal to the total number of identical area sub-regions taken from the corresponding region of the second electrode in the N-type doped layer; no specific limitation is imposed on this.

[0059] For example, in the P-type doped layer, five identical sub-regions are selected corresponding to the first electrode region, each corresponding to the entire thickness of the P-type doped layer. The elemental distribution in these five identical sub-regions is then characterized using EDS surface scanning to obtain the percentage of metal elements in each sub-region. The average of these percentages is then used to obtain the metal element content in the region corresponding to the first electrode in the P-type doped layer. The same method is used for the N-type doped layer, and the resulting average value is the metal element content in the region corresponding to the second electrode in the N-type doped layer. In this application, the average percentage of the metal element in the sub-region corresponding to the P-type doped layer 3 is greater than the average percentage of the metal element in the sub-region corresponding to the N-type doped layer 4.

[0060] For example, in the P-type doped layer, five identical sub-regions are selected corresponding to the first electrode, each sub-region corresponding to the entire thickness of the P-type doped layer. Then, EDS surface scanning is performed on the elemental distribution in each of these five identical sub-regions to obtain the proportion of metal elements in each sub-region. The same method is used for the N-type doped layer, determining the proportion of metal elements in each sub-region corresponding to the second electrode. In this application, the proportion of metal elements in three sub-regions of the P-type doped layer 3 can be greater than that in three sub-regions of the N-type doped layer 3; or the proportion of metal elements in four sub-regions of the P-type doped layer 3 can be greater than that in four sub-regions of the N-type doped layer 3; or the proportion of metal elements in five sub-regions of the P-type doped layer 3 can be greater than that in five sub-regions of the N-type doped layer 3.

[0061] Typically, P-type doped layers are obtained by boron diffusion. Due to the diffusion characteristics of boron, it is difficult to achieve a high boron doping concentration. This means that a slightly lower doping concentration in the P-type doped layer usually results in a slightly higher contact resistance at the first electrode. In this application, compared to the metal element content in the region corresponding to the second electrode in the N-type doped layer, the metal element content in the region corresponding to the first electrode in the P-type doped layer is higher. This indicates that more carrier transport paths are formed in the region corresponding to the first electrode in the P-type doped layer, improving the contact performance between the first electrode and the P-type doped layer. This reduces the contact resistance at 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 metal element content in the first electrode 7, which is in contact with the P-type doped layer 3, is greater than the metal element content in the second electrode 8, which is in contact with the N-type doped layer 4, in order to match the larger metal element content in the P-type doped layer. This helps the metal element in the first electrode 7 to diffuse into the P-type doped layer 3, thereby forming more contact paths and further improving the contact performance between the first electrode and the P-type doped layer.

[0063] Optionally, the proportion of the metal element content at the contact site between the first electrode 7 and the P-type doped layer 3 to the total metal element content of the first electrode 7 is defined as a first proportion, and the proportion of the metal element content at the contact site between the second electrode 8 and the N-type doped layer 4 to the total metal element content of the second electrode 8 is defined as a second proportion. Here, the first proportion is calculated by comparing the metal element content at the contact site between the first electrode 7 and the P-type doped layer 3 with the metal element content of the first electrode itself. The second proportion is obtained similarly, and will not be elaborated further here to avoid repetition.

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

[0065] The content of metal elements at the contact sites of the first electrode 7 and the P-type doped layer 3, and the second electrode 8 and the N-type doped layer 5, can be determined by analyzing the solar cell using scanning electron microscopy (SEM) and X-ray energy dispersive spectroscopy (EDS). Specifically, EDS is performed using line scanning, with the scanning direction perpendicular to the length or extension direction of the first electrode 7 and the second electrode 8. The contact sites of the first electrode 7 and the P-type doped layer 3, and the second electrode 8 and the N-type doped layer 4, can be determined based on the morphology and variations in Si (silicon) content. Specifically, the contact sites of the first electrode 7 and the P-type doped layer 3 are those where the metal content decreases compared to the first electrode itself, and where silicon and other elements decrease compared to the P-type doped layer 3 itself. Similarly, the contact sites of the second electrode 8 and the N-type doped layer 4 are those where the metal content decreases compared to the second electrode itself, and where silicon and other elements decrease 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, both the first electrode 7 and the second electrode 8 contain silver. Figure 3 In the diagram, the upper part is the first electrode, and the lower part consists of the P-type doped layer 3, silicon substrate, and other structures. The brighter, dot-like structures between them are silver-silicon alloys formed at the contact points between the first electrode and the P-type doped layer. Simultaneously, silver-silicon alloys are also formed at the contact points between the second electrode 8 and the N-type doped layer 4. These locations with silver-silicon alloys are the contact points. For example... Figure 6 This is a schematic diagram of the elemental distribution on the silicon substrate and one side of a solar cell. Figure 6 In the diagram, the horizontal axis represents the thickness of the solar cell, starting from the silicon substrate side, in nm, and the vertical axis represents the distribution ratio of elements at the corresponding thickness position in the scanned area. Figure 6 The metal element of the middle electrode is silver. The intersection of the silver and silicon curves represents the contact point between the electrode and the doped layer in contact with it. The ratio of the silver content at this intersection point to the silver content at the highest point to the right of the intersection point indicates the proportion of silver content at the contact point relative to the total silver content in the electrode. The thickness between this intersection point and the leftmost endpoint of the silver curve characterizes the tendency of silver to enter the doped layer. It should be noted that the line scan position needs to pass through the metal-silicon alloy formed by the metal element in the first electrode 7 and the silicon in the P-type doped layer 3, and the metal-silicon alloy formed by the metal element in the second electrode 8 and the silicon in the N-type doped layer 5; for example, regarding the aforementioned... Figure 3The scanning position needs to pass through the silver-silicon alloy position. One or more regions can be selected at the contact position between the first electrode and the P-type doped layer. Each region is formed with the aforementioned metallic silicon alloy. The content of metal elements in each region is measured separately. Then, the average value of the metal element content in multiple regions is taken to obtain the metal element content at the contact position between the first electrode and the P-type doped layer. Here, "multiple" 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 metal element content at the contact site between the second electrode and the N-type doped layer is similar, and will not be repeated here to avoid repetition. It is important to note that the method for obtaining the metal element content at the contact site between the second electrode and the N-type doped layer should be consistent with that for obtaining the metal element content at the contact site between the first electrode and the P-type doped layer. For example, three locations should be selected for measurement at both the contact site between the first electrode and the P-type doped layer and the contact site between the second electrode and the N-type doped layer, and the average metal element content at the three locations should be calculated.

[0067] The first ratio here is smaller than the second ratio, meaning the metal element content at the contact position between the first electrode 7 and the P-type doped layer 3 is relatively lower 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 that of the second electrode 8. Typically, the P-type doped layer 3 is obtained by boron diffusion. Due to the diffusion characteristics of boron, it is difficult to obtain a high boron doping concentration. That is, the doping concentration of the P-type doped layer 3 is usually slightly lower, resulting in a slightly higher contact resistance corresponding to the first electrode 7. In this application, the metal elements are formed at the two contact positions in the above distribution manner, which means that more metal elements in the first electrode 7 enter the P-type doped layer than metal elements in the second electrode 8. More contact paths are formed in the region corresponding to the first electrode in the P-type doped layer, 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 is in a first ratio of 1:2.1 to 1:3.9 to 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 is in a second ratio of 1:1.5 to 1:21 to the content of metal elements in the second electrode 8. When both ratios are within the above range, they are easy to process and prepare, and have a good effect on reducing the contact resistance corresponding to the first electrode 7.

[0069] For example, the first ratio can 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, or 1:3.9. The second ratio can 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 in the first electrode 7 within the P-type doped layer 3 is greater than the diffusion depth of the metal element in the second electrode 8 within the N-type doped layer 4. Typically, due to the difficulty in achieving a high boron doping concentration, the contact resistance between the first electrode 7 and the P-type doped layer 3 is slightly higher. In this application, the diffusion depth of the metal element within the P-type doped layer 3 is greater, 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. This achieves good contact between the P-region and the N-region simultaneously, thus improving the efficiency of the solar cell.

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

[0072] Optionally, the ratio of the diffusion depth of the metal element in the P-type doped layer 3 of the first electrode 7 to the diffusion depth of the metal element in the N-type doped layer 4 of the second electrode 8 is greater than 1 and less than or equal to 8. In this 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 in the N-type doped layer 4 of the second electrode 8 is within the above-mentioned numerical range. This ratio is more suitable, which can not only 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, thus improving the efficiency of the solar cell, but also be 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 element in the first electrode 7 in the P-type doped layer 3 is 100 nm to 450 nm, and the diffusion depth of the metal element in the second electrode 8 in the N-type doped layer 4 is 50 nm to 300 nm. This not only reduces the contact resistance corresponding to the first electrode 7, but also reduces 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. Moreover, it is compatible with existing processes and easy to implement.

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

[0076] Optionally, the thickness of the P-type doped layer 3 can be greater than the thickness of the N-type doped layer 4. Increasing the thickness of the P-type doped layer facilitates higher concentrations of P-type dopant dissolved in the corresponding doped layer and allows for greater diffusion depth of metal elements in the P-type doped layer, minimizing the diffusion of metal elements into the silicon substrate and thus reducing recombination. It also ensures the electric field strength within the region, achieving good field effects in both the P- and N-regions, thus guaranteeing the effectiveness of the heterojunction and high / low junction structures. Furthermore, the difference between the thickness of the P-type doped layer 3 and the N-type doped layer 4 can be from 10 nm to 150 nm. For example, the thickness of the P-type doped layer 3 can be 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, or 600nm, while the thickness of the N-type doped layer 4 can be 90nm, 100nm, 150nm, 200nm, 250nm, 300nm, 330nm, 400nm, or 450nm. It should be noted that in selecting these values, the thickness of the P-type doped layer 3 must be greater than the thickness of the N-type doped layer 4.

[0077] Optional, refer to Figure 2The solar cell may further include a P-type inner extension layer 9 and an N-type inner extension layer 10. The P-type inner extension layer 9 is the portion of the dopant element in the P-type doped layer 3 that diffuses into the silicon substrate. The N-type inner extension layer 10 is the portion of the dopant element in the N-type doped layer 4 that diffuses into the silicon substrate. It should be noted that, regardless of whether the silicon substrate 1 itself has N-type or P-type doping, the doping concentration of the P-type inner extension layer 9 and the N-type inner extension layer 10 is usually higher than the doping concentration of the silicon substrate 1 itself. Furthermore, the location of the P-type inner extension layer 9 and the N-type inner extension layer 10 allows for convenient and accurate differentiation between the silicon substrate itself and the P-type and N-type inner extension layers 9 and 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 close to the back surface of the silicon substrate. The P-type inner expansion layer 9 corresponds to the P-region, and the N-type inner expansion layer 10 corresponds to the N-region. For bifacial electrode solar cells, 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 close to the surface of the silicon substrate adjacent to the P-type doped layer 3, and the N-type inner expansion layer 10 is positioned close to 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, close to the P-type doped layer 3, and corresponds to the P-region. The ratio of the doping concentration of the P-type doped layer 3 to the doping concentration of the P-type inner extension layer 9 is 2 to 5 × 10⁻⁶. 11 The N-type inner extension layer 10 is located inside the silicon substrate 1, close to the N-type doped layer 4, and corresponds to the N-region. The ratio of the doping concentration of the N-type doped layer 4 to the doping concentration of the N-type inner extension layer 10 is 2 to 6 × 10⁻⁶. 11 The ratio of the doping concentration of the P-type doped layer 3 to the doping concentration of the P-type inner extension layer 9, and the ratio of the doping concentration of the N-type doped layer 4 to the doping concentration of the N-type inner extension layer 10 are controlled within the above range 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 doped layer 3 to the doping concentration of the p-type inner extension layer 9 can be 2, 10, 100, 1000, 5000, or 1 × 10⁻⁶. 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 doped layer 4 to the doping concentration of the N-type inner extension layer 10 can be 2, 50, 10, 1000, or 1 × 10⁻⁶. 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 doped layer 3 is 1×10⁻⁶. 17 cm -3 Up to 5×10 21 cm -3 The doping concentration of the P-type inner extension layer 9 is 1×10⁻⁶. 10 cm -3 Up to 5×10 16 cm -3 The doping concentrations of both the P-type doped layer 3 and the P-type inner extension layer 9 are within the aforementioned range, resulting in a suitable doping concentration or amount of the P-type inner extension layer 9 within the silicon substrate. This ensures low contact resistance between the electrode and the P-type doped region. Furthermore, the variation in doping concentration between the P-type doped layer 3 and the P-type inner extension layer 9 along the depth direction of the silicon substrate is appropriate, ensuring effective carrier separation, improving the efficiency of the solar cell, and enhancing compatibility with existing processes.

[0081] For example, the doping concentration of the p-type doped layer 3 can be 1 × 10⁻⁶. 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 1×10⁹. 10 cm -3 5×10 10 cm -3 1×10 11 cm -3 5×10 11 cm -31×10 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 doping concentrations for both must meet the aforementioned ratio constraints. Along the depth direction of the P-type doped layer 3, the doping concentration at various points in the P-type doped layer 3 can remain essentially constant, which can be characterized by surface concentration. That is to say, along the depth direction of the P-type doped layer 3, the doping concentration at various points in the P-type doped layer 3 is relatively uniform.

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

[0083] For example, the doping concentration of the N-type doped layer 4 can be 1 × 10⁻⁶. 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 1×10⁻⁶. 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 selection of doping concentrations for both must meet the aforementioned ratio constraints. Along the depth direction of the N-type doped layer 4, the doping concentration at various points in the N-type doped layer 4 can remain essentially constant, which can be characterized by the surface concentration. That is to say, along the depth direction of the N-type doped layer 4, the doping concentration at various points in the N-type doped layer 4 is relatively uniform.

[0084] In solar cells, the ratio of the doping concentration of the N-type doped layer 4 to the doping concentration of the P-type doped layer 3 ranges from 10 to 6 × 10⁻⁶. 5 To ensure compatibility with existing processes and reduce the damage to the battery caused by the high-temperature boron expansion process of the P-type doped layer, the design, which combines the difference in metal element concentration between the P-type and N-type doped layers, can effectively control the balance of carrier transport effects in the N-region and P-region, ultimately improving battery performance.

[0085] The depth of the P-type inner layer 9 can be 50 nm to 100 nm greater than the depth of the N-type inner layer 10. This depth difference ensures passivation while reducing recombination and improves contact matching with the electrode, enabling efficient carrier separation. It should be noted that multiple sites can be selected in the N-type doped layer 4 to obtain the doping concentration at each site. The average doping concentration at each site is then taken to obtain the total doping concentration of the N-type doped layer 4. These multiple sites can be 2, 3, 4, 5, 6, 7, 8, 9, or 10. The doping concentration of the P-type doped layer 3 is determined similarly. The ratio of the doping concentration of the N-type doped layer 4 to the doping concentration of the P-type doped layer 3 indicates how much higher the doping concentration of the N-type doped layer 4 is compared to the P-type doped 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. Typically, the P-type doped layer 3 is obtained by boron diffusion, and it is difficult to obtain a high boron doping concentration. The P-type doped layer 3 will result in a slightly higher contact resistance between the first electrode 7 and the P-type doped layer 3. In this application, the ratio of the contact resistances 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 2.5 Ω / cm to 4 Ω / cm; the contact resistance between the second electrode 8 and the N-type doped layer 4 is 0.5 Ω / cm to 2 Ω / cm. The contact resistance of the two is within the corresponding range mentioned above, which reduces 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.

[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 antireflection layer 5 located between the N-type doped layer 4 and the second electrode 8, and a second passivation antireflection layer 6 located between the P-type doped layer 3 and the first electrode 7. The refractive index of the first passivation antireflection layer 5 is greater than that of the second passivation antireflection layer 6. The first and second passivation antireflection layers provide surface passivation; they can be formed in the same process step or in different process steps, both achieving the aforementioned refractive index distribution. Factors affecting the refractive index include the thickness, density, or composition of the passivation antireflection layer, such as the silicon-to-nitrogen ratio. The refractive index is positively correlated with density to a certain extent. The lower density of the second passivation antireflection layer in the P-region facilitates corrosion of the second passivation antireflection 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 diffuse more easily into the P-type doped layer, thereby achieving contact balance between the P-region and the N-region.

[0091] Both the first and second passivation antireflection layers are made of monolayers of silicon dioxide, aluminum dioxide, silicon nitride, or silicon oxynitride, or stacked films of one or more of these materials. The materials of the first and second passivation antireflection layers can be the same or different. It should be noted that when at least one of the first and second passivation antireflection layers is a stacked structure, the refractive index is the refractive index measured for the entire passivation antireflection layer. For example, if at least one of the first and second passivation antireflection layers is a stacked structure of aluminum dioxide and silicon nitride, the refractive index is the refractive index measured for the entire passivation antireflection layer. In this case, the passivation antireflection layer can simultaneously protect and passivate the underlying silicon substrate or functional layer, such as a P-type or N-type doped layer, as well as reduce the reflection of light incident on the light-receiving or backlighting surface.

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

[0093] Optionally, the difference between the refractive index of the first passivation antireflection layer and the refractive index of the second passivation antireflection layer ranges from 0.02 to 0.4. By controlling the difference in refractive index between the first and second passivation antireflection layers within this range, the relatively low density of the second passivation antireflection layer 6 in the P-region facilitates the formation of contact between the first electrode and the P-type doped layer in the P-region, and makes it easier for metal elements to diffuse into the P-type doped layer, thereby achieving contact balance in the P-region and N-region. Within the range of the difference design, the passivation and antireflection effects in the P-region and N-region can be guaranteed simultaneously. For example, the refractive index of the first passivation antireflection layer is greater than that of the second passivation antireflection 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 example, the refractive index of the second passivation antireflection layer can be 1.95, 1.97, 1.98, 2, 2.05, 1.96, 1.99, 2.01, 2.02, 2.03, or 2.04. The refractive index of the first passivation antireflection layer can 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, as shown in the figure. Figure 4 The surface of the first electrode region away from the silicon substrate has multiple 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, as shown in the figure. Figure 5 The surface of the second electrode region away from the silicon substrate has multiple second contact holes 41. To observe the contact hole structure more clearly, other layers above the doped layer in the solar cell can be removed and acid-washed, for example, with a mixed acid of nitric acid and hydrofluoric acid, and then the solar cell electrode region can be measured by SEM. The depth of the first contact hole 31 is greater than the depth of the second contact hole 41 along the thickness direction parallel to the silicon substrate. Both the first and second contact holes 31 are suitable for accommodating metal crystals, which are mainly metal-silicon alloys formed by the metal elements entering the doped layer from the electrode and the silicon in the doped layer. When measuring the depth of the contact holes, the second electrode region of the N-type doped layer can be the cross-sectional morphology formed after cleaning, removal of metal crystals and glass frit. Setting the depth of the first contact hole to be greater than the depth of the second contact hole allows for a greater diffusion depth of metal elements in the P-doped layer. This increases the contact depth of metal elements in the P-doped layer, compensating for the higher contact resistance in the P-region compared to the N-region, thereby achieving a balance between the current transport and collection performance of the N-region and the P-region.

[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 and second contact holes within the above ranges, the problem of excessive recombination caused by direct burn-through due to excessive corrosion depth of the first and second electrodes can be effectively avoided; at the same time, the problem of increased contact resistance caused by poor contact due to insufficient 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 2nm, 5nm, 10nm, 50nm, 80nm, 100nm, 120nm, 150nm, 190nm, 200nm, 220nm, 250nm, or 300nm, and the depth of the second contact hole 41 can be 1nm, 10nm, 20nm, 50nm, 90nm, 100nm, 130nm, 150nm, 170nm, 180nm, 190nm, or 200nm. It should be noted that during the setting of 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 the thickness of the second tunneling oxide layer 22. In the case of a back-contact solar cell, such as... Figure 1 The first tunneling oxide layer 21 and the second tunneling oxide layer 22 are both located on the back surface of the silicon substrate, with the first tunneling oxide layer 21 corresponding to the P-region and the second tunneling oxide layer 22 corresponding to the N-region. The thickness of the first tunneling oxide layer 21 is greater than that of the second tunneling oxide layer 22, mainly to accommodate the different effects of Group IIIA elements such as boron and Group VA elements such as phosphorus on the tunneling silicon oxide. Specifically, boron diffuses into the silicon substrate more easily through the tunneling oxide layer than phosphorus. Therefore, a thicker first tunneling oxide layer is needed to control the diffusion concentration of boron during diffusion, reducing recombination caused by excessively high doping concentration. The matching relationship between the thicknesses of the first and second tunneling oxide layers can simultaneously achieve coordination and fine control of the diffusion depth of the two doping types, achieving good contact and carrier separation effects in both the N-region and the P-region, which can further improve the efficiency of the solar cell. At the same time, the first and second tunneling oxide layers can also passivate the surface recombination of the silicon substrate.

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

[0099] In the case of a bifacial electrode solar cell, the first tunneling oxide layer and the second tunneling oxide layer are located on opposite sides of the silicon substrate. The technical effect of the difference in thickness between the first tunneling oxide layer and the second tunneling oxide layer is the same as described above, and will not be repeated here.

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

[0101] For example, if the thickness of the first tunneling oxide layer 21 is greater than the thickness of the second tunneling oxide layer 22, the difference between the thickness of the first tunneling oxide layer 21 and the thickness of the second tunneling 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 solar cells, the thickness of the first tunneling 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 、 The thickness of the second tunneling 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, or 9nm. When selecting the thickness of both layers within the corresponding range, it is necessary to ensure that the thickness of the first tunneling oxide layer 21 is greater than the thickness of the second tunneling oxide layer 22.

[0103] It should be noted that this application does not limit the specific fabrication process of solar cells.

[0104] This application also provides a photovoltaic module comprising a plurality of the aforementioned solar cells. The photovoltaic module may further include encapsulating films or the like located on both sides of the solar cells; no specific limitations are made therein. This photovoltaic module has the same or similar beneficial effects as any of the aforementioned solar cells, and related aspects can be referred to each other. To avoid repetition, further details are omitted here.

[0105] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0106] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A solar cell, characterized by, The solar cell comprises: a silicon substrate, the silicon substrate comprising a surface with an N region and a P region; an N-type doped layer on the N region of the silicon substrate; a P-type doped layer on the P region of the silicon substrate; a first electrode in contact with the P-type doped layer; a second electrode in contact with the N-type doped layer; the first electrode and the second electrode each contain a metal element; the content of the metal element in the P-type doped layer in the region corresponding to the first electrode is greater than the content of the metal element in the N-type doped layer in the region corresponding to the second electrode.

2. The solar cell according to claim 1, characterized in that, 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 of 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 of 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 proportion is less than the second proportion.

4. The solar cell according to claim 3, characterized in that, The first proportion is 1:2.1 to 1:3.

9. The second proportion is 1:1.5 to 1:2.

1.

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

6. The solar cell of claim 1, wherein The ratio of the diffusion depth of the metal element of the first electrode in the P-type doped layer to the 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.

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

8. The solar cell of claim 1, wherein, Further comprising: The P-type inner extension layer is located inside the silicon substrate and close to the P-type doped layer, and corresponds to the P-type region; the ratio of the doping concentration of the P-type doped layer to the doping concentration of the P-type inner extension layer is 2 to 5×10 11 ; The N-type inner extension layer is located inside the silicon substrate and close to the N-type doped layer, and corresponds to the N region; the ratio of the doping concentration of the N-type doped layer to the doping concentration of the N-type inner extension layer is 2 to 6×10 11 .

9. The solar cell of claim 1, wherein, The 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.

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

11. The solar cell of claim 10, wherein, The difference between the refractive index of the first passivation and anti-reflection layer and the refractive index of the second passivation and anti-reflection layer is 0.02 to 0.

4.

12. The solar cell of claim 11, wherein: the P-type doped layer comprises a first electrode region, the surface of the first electrode region away from the silicon substrate has a plurality of first contact holes; the N-type doped layer comprises a second electrode region, the surface of the second electrode region away from the silicon substrate has a plurality of second contact holes; wherein, along the 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 adapted to accommodate metal crystals.

13. The solar cell of claim 12, wherein, Along the thickness direction parallel to the silicon substrate, the depth of the first contact hole is 2 nm to 300 nm, and the 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, 4 to 13, characterized in that, Further comprising: a first tunneling oxide layer between the silicon substrate and the P-type doped layer; a second tunneling oxide layer between the silicon substrate and the N-type doped layer; the first tunneling oxide layer has a thickness greater than the thickness of the second tunneling oxide layer.

15. A photovoltaic module, characterized by comprising: a plurality of cell strings, the cell strings comprising the solar cell of any one of claims 1 to 14.

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