A solar cell, its back electrode and preparation method

Abstract

The present invention discloses a solar cell, its back electrode and preparation method, belonging to the technical field of solar cells. The back electrode of the present invention includes an aluminum main grid, an aluminum sub-grid and a back silver electrode. The aluminum main grid is composed of annular aluminum main grids distributed at intervals and straight-through aluminum main grids connecting adjacent annular aluminum main grids. The back silver electrode is located inside the annular aluminum main grid and is electrically connected thereto. The straight-through aluminum main grid is composed of a central area straight-through aluminum main grid and a peripheral area straight-through aluminum main grid located above the central area straight-through aluminum main grid. By designing the back electrode pattern and adopting a step-by-step printing process, the present invention can significantly improve the carrier collection effect of the back electrode without negatively affecting the backlight shielding area and paste consumption, thereby improving the conversion efficiency of the cell.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar cells, and more specifically, relates to a solar cell, its back electrode and a preparation method thereof. Background Art

[0002] Multi-busbar (MBB) and bifacial cell technologies have become the mainstream technologies for current crystalline silicon cells and have been widely promoted and applied on a large scale. Among them, the MBB technology realizes a significant reduction in the light-shielding area and a substantial improvement in the current collection ability by increasing the number of main grids on the cell, narrowing the width of a single main grid, and the design of solder joints, thereby increasing the cell conversion efficiency by 0.3% and reducing the single consumption of silver paste by more than 10 mg. The bifacial cell technology has also been widely promoted and applied on a large scale due to advantages such as only requiring a small number of modifications to the existing single-sided cell and module production lines for production, and being able to increase the system power generation revenue of single-sided cell module products by 5%-25%.

[0003] Currently, the back electrode structure of existing MBB bifacial cells is usually as Figure 1 shown. Generally, a 6-segmented back silver electrode 11 is used on a single main grid, and an aluminum sub-grid 10 is used to replace the full-coverage aluminum layer of PERC cells. The aluminum sub-grid 10 is connected to the silicon substrate through laser grooving to achieve current collection; then the aluminum sub-grid 10 collects the current and transmits it to the aluminum main grid 9, and finally exports it through the back silver electrode 11. In addition, the aluminum main grid directly connected to the back silver electrode 11 area adopts a ring-shaped design, and the aluminum main grid connecting between two back silver electrodes 11 adopts a straight-through design (i.e., as Figure 2 shown, the aluminum main grid 9 is composed of a straight-through aluminum main grid 9-1 and a ring-shaped aluminum main grid 9-2, and a back silver electrode 11 is provided inside the ring-shaped aluminum main grid 9-2).

[0004] Since the resistivity of aluminum is much greater than that of silver, to meet the requirements of current transmission and the back bifacial ratio, the aluminum electrode, like the front electrode, needs to have a narrower electrode width and a higher electrode height, that is, the aspect ratio is required to be as large as possible. However, an overly high aluminum electrode design will cause a height difference of more than 15 μm between the back silver electrode 11 and the aluminum main grid 9 (as Figure 3 shown). When ultra-fine solder tapes are used in MBB modules, this height difference is extremely likely to cause problems such as false soldering of the module, thus affecting the module yield and product reliability. Currently, in the industry, to solve this problem, mainly through the design optimization of the back electrode, that is, isolating a spacing of more than 1.5 mm between the back silver electrode and the aluminum electrode to reserve a blank isolation area 12, thereby reducing the influence of the above height difference. At the same time, the length and width of the back silver electrode itself cannot be too small to ensure the reliability of module soldering.

[0005] However, the above-mentioned interval between the back silver electrode and the aluminum electrode, that is, the blank isolation area 12, will be a blank area for back carrier collection. In the current 6-segment graphic design, the area ratio of this collection blank area caused by different interval lengths is about 1%-3%, thus affecting the conversion efficiency of the battery. Therefore, how to further improve the conversion efficiency of PERC batteries while ensuring the quality and reliability of components has become a difficult problem that needs to be continuously solved in solar cell technology.

[0006] The Chinese patent application No. 2017107571568 discloses a manufacturing method of a double-sided PERC solar cell with back silver grid lines. By making grooves on the aluminum grid lines and replacing the original aluminum grid lines with silver grid lines in the grooves in this application, the resistivity can be reduced as a whole, the fill factor of the battery can be improved, and the back shading area can be reduced at the same time. However, using the silver grid line method for the back electrode will significantly increase the manufacturing cost, resulting in its inability to be promoted in batches. Summary of the Invention

[0007] 1. Problems to be Solved

[0008] The purpose of the present invention is to solve the problem that the back electrode of the existing MBB double-sided battery has an insufficient collection effect on carriers and the bifaciality of the battery cannot meet the usage requirements and still needs to be further improved. A solar cell, its back electrode and a preparation method are provided. By adopting the technical solution of the present invention, a significant improvement in the carrier collection effect of the back electrode can be achieved without negative impacts on the back shading area and the paste consumption, thereby improving the conversion efficiency of the battery chip.

[0009] 2. Technical Solutions

[0010] To solve the above problems, the technical solutions adopted by the present invention are as follows:

[0011] Firstly, the back electrode of a solar cell of the present invention includes an aluminum main grid, an aluminum sub-grid and a back silver electrode. The aluminum main grid is composed of annular aluminum main grids distributed at intervals and straight-through aluminum main grids connecting adjacent annular aluminum main grids. The back silver electrode is located inside the annular aluminum main grid and is electrically connected thereto. The straight-through aluminum main grid is composed of a central area straight-through aluminum main grid and a peripheral area straight-through aluminum main grid located above the central area straight-through aluminum main grid.

[0012] Furthermore, the height of the back silver electrode corresponds to the height of the central area straight-through aluminum main grid, and its height is less than the height of the peripheral area straight-through aluminum main grid.

[0013] Further, the peripheral direct-through aluminum main grid is located on both upper sides of the central direct-through aluminum main grid, and its inner width is smaller than that of the central direct-through aluminum main grid; preferably, the inner width W4 of the peripheral direct-through aluminum main grid is 0.4 - 1.4 mm, and the width W3 of the central direct-through aluminum main grid is 0.5 - 1.5 mm.

[0014] Further, the number of segments of the back silver electrode corresponding to the same aluminum main grid is 8 - 50, the width W1 of a single back silver electrode is 1.2 - 2.2 mm, and the length H1 is 1.5 - 5.5 mm.

[0015] Further, the inner length of the annular aluminum main grid is greater than the length of the back silver electrode, and its inner width is smaller than the width of the back silver electrode; preferably, the inner length H2 of the annular aluminum main grid is 1.7 - 5.8 mm, and its inner width W2 is 1.0 - 2.1 mm.

[0016] Further, the number of aluminum main grids is greater than or equal to 9. The aluminum sub-grids are perpendicular to and evenly spaced from the aluminum main grids, with a width of 60 μm - 200 μm and a spacing of 0.8 - 1.5 mm.

[0017] Second, for the manufacturing method of the back electrode of the solar cell of the present invention, the aluminum main grid and the aluminum sub-grids adopt a step-by-step printing method, and the specific process is as follows: Through screen printing, the central direct-through aluminum main grid and the bottom aluminum sub-grids are printed simultaneously, so that the height of the central direct-through aluminum main grid matches that of the back silver electrode; then the peripheral direct-through aluminum main grid, the annular aluminum main grid and the upper aluminum sub-grids are printed simultaneously.

[0018] Further, during the first printing, a low-contact-resistance aluminum paste with a low solid content of 60% - 80% and a contact resistivity ≤ 10 mΩ·cm -2 is used, preferably the Ruxing 8401S double-sided aluminum paste; during the second printing, a high-conductivity aluminum paste with a grid line resistivity ≤ 1×10 -5 Ω·cm -2 is used, preferably the Ruxing 8401U-1 double-sided aluminum paste.

[0019] Further, during the first printing, the screen mesh count is 430 - 520 meshes, the wire diameter is 11 - 13 μm, the yarn thickness is 10 - 15 μm, and the film thickness is 4 - 10 μm; during the second printing, the screen mesh count is 325 - 360 meshes, the wire diameter is 15 - 20 μm, the yarn thickness is 22 - 28 μm, and the film thickness is 15 - 25 μm.

[0020] Third, a solar cell of the present invention adopts the above back electrode structure.

[0021] Fourthly, in the preparation method of the solar cell of the present invention, a step-by-step printing method is adopted to prepare the aluminum grid lines of the back electrode. Specifically, first, the direct-through aluminum main grid in the central area and the aluminum sub-grid at the bottom layer are printed simultaneously, so that the height of the direct-through aluminum main grid in the central area matches the back silver electrode; then, the direct-through aluminum main grid in the peripheral area, the annular aluminum main grid, and the aluminum sub-grid at the upper layer are printed simultaneously.

[0022] 3. Beneficial effects

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The back electrode of a solar cell of the present invention includes an aluminum main grid, an aluminum sub-grid, and a back silver electrode. By optimizing the design of the multi-segmented back electrode pattern, it is possible to significantly improve the carrier collection effect of the back electrode without negatively affecting the backlight shielding area and paste consumption, thus improving the conversion efficiency of the cell.

[0025] (2) The back electrode of a solar cell of the present invention. Specifically, the direct-through aluminum main grid is designed to be composed of a direct-through aluminum main grid in the central area and a direct-through aluminum main grid in the peripheral area located above the direct-through aluminum main grid in the central area, and the height of the direct-through aluminum main grid in the central area corresponds to the height of the back silver electrode. Thus, it is possible to effectively avoid problems such as component virtual soldering caused by the height difference between the aluminum main grid and the back silver electrode in the welding direction, thereby significantly reducing the isolation collection blank area between the aluminum main grid and the back silver electrode, improving the carrier collection effect of the back electrode, and further improving the conversion efficiency of the cell. At the same time, through the graphic optimization of the back electrode of the present invention, the limitation of the multi-segmented design is broken, providing a greater optimization space for the design and promotion of large-sized cells.

[0026] (3) In the manufacturing method of the back electrode of the solar cell of the present invention, by step-by-step printing the aluminum grid lines of the back electrode and controlling the height of the direct-through aluminum main grid in the central area to correspond to the height of the back silver electrode, the isolation collection blank area between the aluminum main grid and the back silver electrode can be reduced, and the number of segments of the back silver electrode can be increased, thus improving the carrier collection effect of the back electrode and the conversion efficiency of the cell.

[0027] (4) In the manufacturing method of the back electrode of the solar cell of the present invention, by selecting the step-by-step printing process of the aluminum grid lines, different aluminum pastes can be matched according to needs, thereby further improving the current transmission effect of the aluminum electrode, reducing the lateral corrosion of the aluminum paste on the passivation layer in the laser grooving area, which is beneficial to further improving the conversion efficiency of the cell and improving the reliability of the bifacial cell.

[0028] (5) For the solar cell of the present invention, through the graphic design of the back electrode, it is possible to achieve an improvement in the photoelectric conversion efficiency of the PERC bifacial cell by more than 0.08% and an improvement in the back PID of the bifacial cell by more than 0.2%. Brief Description of the Drawings

[0029] Figure 1 It is a schematic diagram of the back electrode of an existing solar cell;

[0030] Figure 2 It is a partially enlarged schematic diagram of the back electrode of an existing solar cell;

[0031] Figure 3 It is a sectional view of the back electrode of an existing solar cell;

[0032] Figure 4 It is a schematic diagram of the back electrode of the solar cell of the present invention;

[0033] Figure 5 It is a partially enlarged schematic diagram of the back electrode of the present invention;

[0034] Figure 6 It is a sectional view of the back electrode of the present invention;

[0035] Figure 7 It is a distribution schematic diagram of the back silver electrode (12 segments) of the present invention;

[0036] Figure 8 It is the first printing pattern of the aluminum back surface field of the present invention;

[0037] Figure 9 It is the second printing pattern of the aluminum back surface field of the present invention;

[0038] Figure 10 It is a schematic diagram of the structure of the solar cell of the present invention.

[0039] In the figure: 1. silicon wafer substrate; 2. front emitter; 2-1. lightly doped region; 2-2. heavily doped region; 3. oxide layer; 4. passivation and antireflection layer; 5. positive electrode; 6. back passivation layer; 7. back electrode; 8. back laser grooving; 9. aluminum main grid; 9-1. straight-through aluminum main grid; 9-1-1. central area straight-through aluminum main grid; 9-1-2. peripheral area straight-through aluminum main grid; 9-2. ring-shaped aluminum main grid; 10. aluminum sub-grid; 11. back silver electrode; 12. blank isolation area. Detailed Description of the Invention

[0040] To meet the requirements of current transmission and the rear double-sided rate, the main grid lines of the rear electrode of the MBB double-sided battery are required to have as large an aspect ratio as possible, resulting in a large height difference (more than 15 μm) between the rear silver electrode 11 and the aluminum main grid 9, causing problems such as component soldering voids and affecting the component yield and product reliability. Currently, in the prior art, the problem caused by the above height difference is mainly overcome by increasing the distance between the rear silver electrode and the aluminum electrode, that is, by setting the blank isolation area 12, which limits the number of rear silver electrodes 11 (the rear silver electrodes of the existing MBB double-sided battery are usually designed in 6 segments), affecting the current collection effect and the conversion efficiency of the battery. At the same time, the width of the aluminum main grid cannot be further reduced, so the double-sided rate of the battery cannot be further improved. With the increase in the size of the silicon wafer, the problems such as the carrier collection effect, double-sided rate, paste consumption, and component soldering reliability caused by the 6-segment design will be further highlighted.

[0041] To solve the above problems, on the one hand, the present invention designs the rear electrode pattern, that is, the straight-through aluminum main grid is designed to be composed of a central area straight-through aluminum main grid and a peripheral area straight-through aluminum main grid located above the central area straight-through aluminum main grid, and controls the height of the rear silver electrode to correspond to the height of the central area straight-through aluminum main grid, and its height is less than the height of the peripheral area straight-through aluminum main grid. Thus, on the basis of ensuring current transmission and the rear double-sided rate, the component soldering voids and the impact on product reliability caused by the height difference between the rear silver electrode and the aluminum main grid can be effectively avoided. Therefore, the distance between the rear silver electrode and the aluminum main grid, that is, the length of the blank isolation area 12, can be greatly reduced, and the number of segments of the rear silver electrode can be effectively increased, which can be increased from the current 6 to 8 - 50. At the same time, the width W1 of a single silver electrode is 1.2 - 2.2 mm, and the length H1 is 1.5 - 5.5 mm, so as to maintain the total silver electrode area basically unchanged. By greatly increasing the number of silver electrodes, the collection effect of the rear carriers is improved, thereby improving the conversion efficiency of the battery.

[0042] On the other hand, the present invention prints the aluminum grid lines by adopting a step-by-step printing process. The first-step printing: first print the central area straight-through aluminum main grid and the bottom aluminum sub-grid at the same time, so that the height of the central area straight-through aluminum main grid matches the rear silver electrode; then the second-step printing: print the peripheral area straight-through aluminum main grid, the annular aluminum main grid, and the upper aluminum sub-grid at the same time. Thus, different aluminum pastes can also be matched as needed. Through the mesh plate specifications and paste matching, the height difference between the aluminum main grid and the rear silver electrode can be effectively reduced, providing the possibility for the realization of multiple silver electrodes (8 - 50) on the rear electrode, further improving the current transmission effect of the aluminum electrode, reducing the lateral corrosion of the aluminum paste on the passivation layer of the laser grooving area, being beneficial to further improving the conversion efficiency of the battery and improving the reliability of the double-sided battery.

[0043] Specifically, the back electrode of the solar cell of the present invention includes an aluminum main grid 9, an aluminum sub-grid 10, and a back silver electrode 11. The aluminum main grid 9 is composed of annular aluminum main grids 9-2 distributed at intervals and straight-through aluminum main grids 9-1 connecting adjacent annular aluminum main grids 9-2. The back silver electrode 11 is located inside the annular aluminum main grid 9-2 and is electrically connected thereto. The straight-through aluminum main grid 9-1 is composed of a central area straight-through aluminum main grid 9-1-1 and a peripheral area straight-through aluminum main grid 9-1-2 located above the central area straight-through aluminum main grid 9-1-1. The height of the back silver electrode 11 corresponds to the height of the central area straight-through aluminum main grid 9-1-1, and its height is less than the height of the peripheral area straight-through aluminum main grid 9-1-2. The number of segments of the back silver electrode 11 corresponding to the same aluminum main grid 9 is 8-50. The width W1 of a single back silver electrode 11 is 1.2-2.2 mm, and the length H1 is 1.5-5.5 mm. The peripheral area straight-through aluminum main grid 9-1-2 is located on both sides above the central area straight-through aluminum main grid 9-1-1, and its internal width is less than the width of the central area straight-through aluminum main grid 9-1-1. Preferably, the internal width W4 of the peripheral area straight-through aluminum main grid 9-1-2 is 0.4-1.4 mm, and the width W3 of the central area straight-through aluminum main grid 9-1-1 is 0.5-1.5 mm. The internal length of the annular aluminum main grid is greater than the length of the back silver electrode 11, and its internal width is less than the width of the back silver electrode 11; preferably, the internal length H2 of the annular aluminum main grid is 1.7-5.8 mm, and its internal width W2 is 1.0-2.1 mm. Its length is slightly greater than the length of the silver electrode, so as to achieve the isolation of silver and aluminum in the direction of the main grid and avoid the component welding problem caused by the height difference of the overlap in this area. The number of the aluminum main grids 9 is greater than or equal to 9. The aluminum sub-grids 10 are perpendicular to the aluminum main grids 9 and are evenly distributed at intervals. Their width is 60 μm-200 μm, and the spacing is 0.8-1.5 mm.

[0044] The manufacturing method of the back electrode of the solar cell of the present invention. The aluminum main grid 9 and the aluminum sub-grid 10 adopt a step-by-step printing method. The specific process is as follows: By screen printing, in the first step, the central area straight-through aluminum main grid 9-1-1 and the bottom aluminum sub-grid 10 are printed simultaneously, so that the height of the central area straight-through aluminum main grid 9-1-1 matches the back silver electrode 11; then in the second step, the peripheral area straight-through aluminum main grid 9-1-2, the annular aluminum main grid 9-2, and the upper aluminum sub-grid 10 are printed simultaneously. Among them, when printing for the first time, the double-sided aluminum paste uses a low solid content of 60%-80% and the contact resistivity ≤ 10 mΩ·cm -2Low-contact-resistance aluminum paste is used to reduce the contact resistance. Preferably, Ruxing 8401S double-sided aluminum paste is used. When printing for the first time, the screen mesh count is 430 - 520 meshes, the wire diameter is 11 - 13 μm, the yarn thickness is 10 - 15 μm, and the film thickness is 4 - 10 μm. Preferably, the screen mesh count is 430 meshes, the wire diameter is 13 μm, the yarn thickness is 15 μm, and the film thickness is 5 μm. Secondly, the screen mesh count is 480 or 520 meshes, the wire diameter is 11 μm, the yarn thickness is 15 μm, and the film thickness is 5 μm. When printing for the second time, the double-sided aluminum paste with a grid line resistivity ≤ 1×10 -5 Ω·cm -2 High-conductivity aluminum paste is used to reduce the resistivity and the lateral corrosion of the aluminum paste to the passivation layer in the laser opening area. Preferably, Ruxing 8401U-1 double-sided aluminum paste is used. When printing for the second time, the screen mesh count is 325 - 360 meshes, the wire diameter is 15 - 20 μm, the yarn thickness is 22 - 28 μm, and the film thickness is 15 - 25 μm. Preferably, the screen mesh count is 360 meshes, the wire diameter is 16 μm, the yarn thickness is 22, 26 or 28 μm, and the film thickness is 20 μm. Secondly, the screen mesh count is 325 meshes, the wire diameter is 16 μm, the yarn thickness is 26 or 28 μm, and the film thickness is 20 μm.

[0045] Example 1

[0046] Combined with Figures 4 - 6 , the back electrode of the solar cell in this embodiment includes an aluminum main grid 9, an aluminum sub-grid 10, and a back silver electrode 11. The aluminum main grid 9 is composed of annular aluminum main grids 9-2 distributed at intervals and straight-through aluminum main grids 9-1 connecting adjacent annular aluminum main grids 9-2. The back silver electrode 11 is located inside the annular aluminum main grid 9-2 and is electrically connected to it. The straight-through aluminum main grid 9-1 is composed of a central area straight-through aluminum main grid 9-1-1 and a peripheral area straight-through aluminum main grid 9-1-2 located above the central area straight-through aluminum main grid 9-1-1. The height of the back silver electrode 11 corresponds to the height of the central area straight-through aluminum main grid 9-1-1, and its height is less than the height of the peripheral area straight-through aluminum main grid 9-1-2. Specifically, as shown in Figure 7 , in this embodiment, the number of segments of the back silver electrode 11 corresponding to the same aluminum main grid 9 is 12. The width W1 of a single back silver electrode 11 is 2.1 mm, and the length H1 is 2.7 mm. The internal width W4 of the peripheral area straight-through aluminum main grid 9-1-2 is 1.0 mm, and the width W3 of the central area straight-through aluminum main grid 9-1-1 is 1.1 mm. The internal length H2 of the annular aluminum main grid is 3.0 mm, and its internal width W2 is 1.9 mm. The number of aluminum main grids 9 is 9. The aluminum sub-grid 10 is perpendicular to the aluminum main grid 9 and is evenly distributed at intervals, and its width is 110 μm, and the spacing is 1.106 mm.

[0047] The manufacturing method of the back electrode of the solar cell in this embodiment. The aluminum main grid 9 and the aluminum sub-grid 10 adopt a step-by-step printing method. Combined with Figure 8 、 Figure 9, the specific process is as follows: Through screen printing, first synchronously print the central area direct aluminum main grid 9-1-1 and the bottom aluminum sub-grid 10, so that the height of the central area direct aluminum main grid 9-1-1 matches that of the back silver electrode 11; then synchronously print the peripheral area direct aluminum main grid 9-1-2, the annular aluminum main grid 9-2 and the upper aluminum sub-grid 10. Among them, for the first printing, 8401S double-sided aluminum paste is used, and the screen mesh count is 430 meshes, wire diameter is 13μm, yarn thickness is 15μm, and film thickness is 5μm. For the second printing, Ruxing 8401U-1 double-sided aluminum paste is used, and the screen mesh specifications are: screen mesh count is 360 meshes, wire diameter is 16μm, yarn thickness is 28μm, and film thickness is 20μm.

[0048] As Figure 10 shown, the solar cell of this embodiment includes a back electrode 7, a back passivation layer 6, a silicon wafer substrate 1, a front emitter 2, a front oxide layer 3, a front passivation and antireflection layer 4, and a positive electrode 5 which are arranged in sequence from bottom to top. Its specific preparation process is as follows:

[0049] 1. Texturing: Use a single-crystalline P-type silicon wafer (this embodiment takes single-crystalline silicon as an example for illustration, but it is not limited to single-crystalline silicon actually), and perform front and back texturing with an alkali to form a textured surface structure.

[0050] 2. Diffusion: React the textured silicon wafer with phosphorus oxychloride at high temperature, so that a PN emitter junction (i.e., the front emitter 2) is formed on the front surface by diffusion. The sheet resistance of the positive surface thin layer after diffusion is between 160Ω / □.

[0051] 3. Laser SE: Use the phosphorus silicate glass after diffusion as a phosphorus source, and perform laser doping on the front surface of the silicon wafer after diffusion and in the metallization area corresponding to the positive electrode grid lines to form a heavily doped region 2-2, thereby realizing the structure of a selective emitter on the front surface of the silicon wafer (composed of the heavily doped region 2-2 and the lightly doped region 2-1). The sheet resistance of the heavily doped region is between 80Ω / □.

[0052] 4. Thermal oxidation: Pass oxygen through the silicon wafer after laser SE for oxidation.

[0053] 5. Remove PSG: Use HF to remove the back and peripheral PSG of the silicon wafer after thermal oxidation.

[0054] 6. Alkaline polishing: Polish the back and edges of the silicon wafer after removing PSG, and remove PSG on the front surface.

[0055] 7. Oxidation annealing: Perform oxidation and annealing treatment on the silicon wafer after alkaline polishing to form the oxide layer 3.

[0056] 8. Deposit a passivation film on the back: Prepare a passivation film on the back of the annealed silicon wafer, that is, the back passivation layer 6.

[0057] 9. Front deposition of antireflection film: Prepare the passivation and antireflection layer 4 on the front side of the silicon wafer.

[0058] 10. Backside laser: Perform laser drilling on the silicon wafer with a passivation film prepared on the backside to form the backside laser grooving 8.

[0059] 11. Preparation of backside electrode: Adopt the above-mentioned backside electrode preparation process, where the aluminum sub-gates 10 are parallel and evenly distributed, and their positions correspond to the positions of the backside laser grooving 8. The aluminum sub-gates 10 are in contact with the silicon wafer substrate 1 through the backside laser grooving 8.

[0060] 12. Printing of the front electrode main grid area: Use positive silver paste to screen-print and prepare the front electrode 5 on the silicon wafer printed with the backside electrode.

[0061] 13. Sintering: Co-sinter the silicon wafer printed with the front electrode, and the sintering peak temperature is 760 °C.

[0062] 14. Electrical injection: Perform electrical injection treatment on the sintered solar cell.

[0063] 15. Finished product: Test, sort, and package the product solar cell and store it in the warehouse.

[0064] Example 2

[0065] Combined with Figures 4 - 6 , the backside electrode of the solar cell in this embodiment has basically the same structure as that in Example 1. The main difference is that: in this embodiment, the number of segments of the back silver electrode 11 corresponding to the same aluminum main grid 9 is 10, the width W1 of a single back silver electrode 11 is 2.0 mm, the length H1 is 3.0 mm, the internal length H2 of the ring-shaped aluminum main grid is 3.4 mm, and its internal width W2 is 1.8 mm. The internal width W4 of the peripheral area leading to the aluminum main grid 9-1-2 is 1.2 mm, and the width W3 of the central area leading to the aluminum main grid 9-1-1 is 1.3 mm. The number of aluminum main grids 9 is 9, the aluminum sub-gates 10 are perpendicular to and evenly spaced from the aluminum main grids 9, and their width is 110 μm, and the spacing is 1.106 mm.

[0066] The manufacturing method of the backside electrode of the solar cell in this embodiment is basically the same as that in Example 1. The main difference is that: in this embodiment, the screen mesh specifications for the first printing are: screen mesh count 480 meshes, wire diameter 11 μm, yarn thickness 15 μm, film thickness 5 μm, and the screen mesh specifications for the second printing are: screen mesh count 325 meshes, wire diameter 16 μm, yarn thickness 26 μm, film thickness 20 μm.

[0067] The preparation method of the solar cell in this embodiment has basically the same process as that in Example 1. The main difference is that: in this embodiment, the sheet resistance of the positive surface thin layer after diffusion is between 140 Ω / □, and the sheet resistance of the heavily doped region is between 60 Ω / □, and the sintering peak temperature is 720 °C.

[0068] Example 3

[0069] Combined Figures 4 - 6 , the back electrode of the solar cell in this embodiment has basically the same structure as that in Embodiment 1, and the main difference is that: in this embodiment, the number of segments of the back silver electrode 11 corresponding to the same aluminum main grid 9 is 20, the width W1 of a single back silver electrode 11 is 1.4 mm, the length H1 is 1.9 mm, the internal length H2 of the annular aluminum main grid is 2.2 mm, and its internal width W2 is 1.3 mm. The internal width W4 of the peripheral area leading to the inside of the aluminum main grid 9-1-2 is 1.0 mm, and the width W3 of the central area leading to the aluminum main grid 9-1-1 is 0.9 mm. The number of the aluminum main grids 9 is 12, the aluminum sub-grids 10 are perpendicular to and evenly spaced from the aluminum main grids 9, and their width is 80 μm and the spacing is 1.0 mm.

[0070] The manufacturing method of the back electrode of the solar cell in this embodiment is basically the same as that in Embodiment 1, and the main difference is that: in this embodiment, the screen specifications for the first printing are: screen mesh number 520, wire diameter 11 μm, yarn thickness 15 μm, film thickness 5 μm, and the screen specifications for the second printing are: screen mesh number 360, wire diameter 16 μm, yarn thickness 26 μm, film thickness 20 μm.

[0071] The preparation method of the solar cell in this embodiment has basically the same process as that in Embodiment 1, and the main difference is that: in this embodiment, the sheet resistance of the positive surface thin layer after diffusion is between 135 Ω / square, and the sheet resistance of the heavily doped region is between 90 Ω / square, and the sintering peak temperature is 800 °C.

Claims

1. The back electrode of a solar cell includes an aluminum main grid (9), an aluminum sub-grid (10), and a back silver electrode (11). It is characterized in that: The aluminum main grid (9) is composed of annular aluminum main grids (9-2) distributed at intervals and straight-through aluminum main grids (9-1) connecting adjacent annular aluminum main grids (9-2). The back silver electrode (11) is located inside the annular aluminum main grid (9-2) and is electrically connected to it. The straight-through aluminum main grid (9-1) is composed of a central area straight-through aluminum main grid (9-1-1) and peripheral area straight-through aluminum main grids (9-1-2) located on both sides above the central area straight-through aluminum main grid (9-1-1), and the height of the central area straight-through aluminum main grid (9-1-1) corresponds to the height of the back silver electrode (11). The number of segments of the back silver electrode (11) corresponding to the same aluminum main grid (9) is 8 - 50, and the number of aluminum main grids (9) is greater than or equal to 9.

2. The back electrode of a solar cell according to claim 1, It is characterized in that: The height of the back silver electrode (11) is less than the height of the peripheral area straight-through aluminum main grid (9-1-2).

3. The back electrode of a solar cell according to claim 2, It is characterized in that: The inner width of the peripheral area straight-through aluminum main grid (9-1-2) is less than the width of the central area straight-through aluminum main grid (9-1-1); the inner width W4 of the peripheral area straight-through aluminum main grid (9-1-2) is 0.4 - 1.4 mm, and the width W3 of the central area straight-through aluminum main grid (9-1-1) is 0.5 - 1.5 mm; the inner length of the annular aluminum main grid is greater than the length of the back silver electrode (11), and its inner width is less than the width of the back silver electrode (11); the inner length H2 of the annular aluminum main grid is 1.7 - 5.8 mm, and its inner width W2 is 1.0 - 2.1 mm.

4. The back electrode of a solar cell according to any one of claims 1 - 3, It is characterized in that: The width W1 of a single back silver electrode (11) is 1.2 - 2.2 mm, and the length H1 is 1.5 - 5.5 mm.

5. The back electrode of a solar cell according to any one of claims 1 - 3, It is characterized in that: The aluminum sub-grid (10) is perpendicular to and evenly spaced from the aluminum main grid (9), its width is 60 μm - 200 μm, and the spacing is 0.8 - 1.5 mm.

6. A method for manufacturing the back electrode of a solar cell according to any one of claims 1 - 5, It is characterized in that, The aluminum main grid (9) and the aluminum sub-grid (10) adopt a step-by-step printing method, and the specific process is as follows: Through screen printing, first print the central area straight-through aluminum main grid (9-1-1) and the bottom aluminum sub-grid (10) simultaneously, so that the height of the central area straight-through aluminum main grid (9-1-1) matches the back silver electrode (11); then print the peripheral area straight-through aluminum main grids (9-1-2), the annular aluminum main grids (9-2), and the upper aluminum sub-grid (10) simultaneously.

7. The method for manufacturing the back electrode of a solar cell according to claim 6, It is characterized in that: For the first printing, the double-sided aluminum paste uses a low solid content of 60%-80% and has a contact resistivity ≤ 10 mΩ·cm -2 of the low contact resistance type aluminum paste. For the second printing, the double-sided aluminum paste uses a grid line resistivity ≤ 1×10 -5 Ω·cm -2 of the high conductivity aluminum paste.

8. The manufacturing method of the back electrode of a solar cell according to claim 7, characterized in that: When printing for the first time, the double-sided aluminum paste used is 8401S double-sided aluminum paste, and when printing for the second time, the double-sided aluminum paste used is 8401U-1 double-sided aluminum paste.

9. The manufacturing method of the back electrode of a solar cell according to claim 6, characterized in that: When printing for the first time, the screen mesh count is 430-520 meshes, the wire diameter is 11-13μm, the yarn thickness is 10-15μm, and the film thickness is 4-10μm; when printing for the second time, the screen mesh count is 325-360 meshes, the wire diameter is 15-20μm, the yarn thickness is 22-28μm, and the film thickness is 15-25μm.

10. A solar cell, characterized in that: The back electrode described in any one of claims 1-5 is adopted.

11. A manufacturing method of a solar cell as described in claim 10, characterized in that: A step-by-step printing method is adopted to prepare the aluminum grid lines of the back electrode. Specifically, first, the direct-through aluminum main grid (9-1-1) in the central area and the aluminum sub-grid (10) at the bottom layer are printed simultaneously, so that the height of the direct-through aluminum main grid (9-1-1) in the central area matches that of the back silver electrode (11); then, the direct-through aluminum main grid (9-1-2) in the peripheral area, the ring-shaped aluminum main grid (9-2), and the aluminum sub-grid (10) at the upper layer are printed simultaneously.

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