A back electrode of a double-sided solar cell and its preparation method and application

Abstract

The present invention discloses a back electrode of a double-sided solar cell and a preparation method and application thereof, belonging to the technical field of solar cells and back electrodes thereof. The back electrode of the double-sided solar cell of the present invention has an aluminum main grid composed of a straight-through aluminum main grid and a ring-shaped aluminum main grid distributed at intervals, a silver electrode located inside the ring-shaped aluminum main grid and electrically connected to the aluminum main grid, and the silver electrode is composed of a silver main region and silver fine main grids located at both ends of the silver main region, the two sides of the silver main region are electrically connected to the ring-shaped aluminum main grid, and the two ends are electrically connected to the straight-through aluminum main grid through the silver fine main grid. The present invention optimizes the structure of the back silver electrode, thereby effectively reducing the length and area ratio of the blank isolation area, while meeting the requirements of the double-sided battery for the double-sided rate and welding reliability.

Description

Technical Field

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

[0002] Bifacial solar cells can be produced with only minor changes to existing cell and module production lines, and can increase system power generation revenue by 5%-25% compared to single-sided cell and module products. As a result, bifacial cell technology has gradually become the mainstream technology for crystalline silicon cells and has been widely promoted and applied.

[0003] The design of the back electrode is intertwined with the optimization, constraints and compromises of factors such as the bifaciality, carrier collection, slurry consumption, and component welding of the bifacial cell. Figure 1 As shown in FIG. 1 , the entire back electrode is composed of uniformly and parallelly distributed sub-grids and main grids, which are vertically connected to each other to form a so-called H-shaped pattern. The sub-grid is often formed with aluminum paste, and an aluminum sub-grid 2 is used to replace the full-covering aluminum layer of the single-sided cell. The aluminum sub-grid 2 is connected to the silicon substrate through laser grooving to collect the current in the substrate area and then transmit it to the main grid; as shown in FIG. Figure 2 As shown, the main grid area is generally divided into an aluminum main grid area and a silver electrode area. The aluminum main grid area is directly connected to the aluminum sub-grid 2, collects the current collected by the sub-grid, and then transmits it to the silver electrode 3 to realize current extraction. At present, the back electrode pattern design generally adopts a 6-segment silver electrode 3, and the aluminum main grid 1 directly connected to the silver electrode area adopts a ring design (i.e., a ring-shaped aluminum main grid 102), and the aluminum main grid connecting the two silver electrodes 3 adopts a straight-through design (i.e., a straight-through aluminum main grid 101).

[0004] Since the resistivity of aluminum is much higher than that of silver, in order to meet the requirements of current transmission and back-side bifaciality, the aluminum electrode needs to have a narrower electrode width and a higher electrode height, just like the front electrode, that is, the aspect ratio should be as large as possible. However, the design of an aluminum electrode that is too high will cause a height difference of more than 15μm between the silver electrode 3 and the aluminum main grid 1 (such as Figure 3 As shown). When the MBB module uses ultra-thin solder strips, this height difference can easily cause problems such as cold soldering of the module, thereby affecting the module yield and product reliability. At present, in order to solve this problem, the industry mainly optimizes the design of the back electrode, that is, the back silver electrode and the aluminum electrode are isolated with a spacing of more than 1.5 mm, and a blank isolation area 4 is reserved to reduce the impact 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 the module welding.

[0005] However, the above-mentioned interval between the back silver electrode and the aluminum electrode, that is, the blank isolation area 4, will be a blank area for collecting back carriers. The current 6-segment graphic design, with different interval lengths, causes the area of ​​this collection blank area to account for about 1%-3%, thus affecting the conversion efficiency of the battery. Therefore, how to further improve the conversion efficiency of PERC cells while ensuring the quality and reliability of the components has become a difficult problem that solar cell technology continues to solve.

[0006] The Chinese patent application No. 2017107571568 discloses a method for manufacturing a bifacial PERC solar cell with a silver grid on the back. The application makes grooves on the aluminum grid and replaces the original aluminum grid with silver grid in the groove, thereby reducing the overall resistivity, improving the cell fill factor, and reducing the back shading area. However, the use of silver grid on the back electrode will significantly increase the manufacturing cost, making it impossible to promote it in batches. Summary of the invention

[0007] 1. Problem to be solved

[0008] Aiming at the problem that the blank isolation area of ​​the existing 6-segment MBB bifacial cell back electrode structure is large, thus affecting the carrier collection effect and cell conversion efficiency, a back electrode of a bifacial solar cell and its preparation method and application are provided. The present invention optimizes the structure of the back silver electrode, thereby effectively reducing the length and area ratio of the blank isolation area, while meeting the requirements of the bifacial cell for the bifaciality and welding reliability.

[0009] 2. Technical solution

[0010] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0011] First, the back electrode of a double-sided solar cell of the present invention, its aluminum main grid is composed of a straight-type aluminum main grid and a ring-type aluminum main grid distributed at intervals, the silver electrode is located inside the ring-type aluminum main grid and is electrically connected to the aluminum main grid, and the length of the blank isolation area at both ends of the silver electrode is 0.1-1.4mm.

[0012] Furthermore, the silver electrode consists of a silver main area and silver fine main grids at both ends of the silver main area. The two sides of the silver main area are electrically connected to the annular aluminum main grid, and its two ends are electrically connected to the straight aluminum main grid through the silver fine main grid.

[0013] Furthermore, the silver fine main grid includes a central area silver fine main grid located in the middle of the silver main area and an edge area silver fine main grid located on both sides of the central area silver fine main grid.

[0014] Furthermore, the length of the silver main grid is the distance between 1-2 aluminum sub-grids, the width of the central area silver main grid and the edge area silver main grid are 0.05-0.1mm and 0.02-0.08mm respectively, and the distance between the two edge area silver main grids is consistent with the width of the silver main area.

[0015] Furthermore, the length of the silver thin main grid is 1.3 mm, and the widths of the silver thin main grid in the central area and the silver thin main grid in the edge area are 0.07 mm and 0.04 mm respectively.

[0016] Furthermore, the number of segments of the silver electrode on the same aluminum main grid is 8-50.

[0017] Furthermore, the width of a single silver electrode is 1.2-2.2 mm and the length is 1.5-5.5 mm.

[0018] Furthermore, the number of segments of the silver electrode on the same aluminum main grid is 12, and the width of a single silver electrode is 2.1 mm and the length is 2.7 mm.

[0019] Furthermore, the straight-through aluminum main grid is designed in an I-shape, and the ring-shaped aluminum main grid is designed in a long strip shape.

[0020] Furthermore, the width of the flange regions at both ends of the through-type aluminum main grid is greater than the width of the silver electrode, and the flange regions are overlapped and connected to the silver electrode.

[0021] Furthermore, the width of the flange areas at both ends of the straight-through aluminum main grid is 1.5-2.8 mm, and the width of the middle area is 0.5-1.2 mm.

[0022] Furthermore, the width of the flange areas at both ends of the straight-through aluminum main grid is 2.4 mm, and the width of the middle area is 1.0 mm.

[0023] Furthermore, the inner ring width of the annular aluminum main grid is smaller than the width of the silver electrode.

[0024] Furthermore, the annular width of the annular aluminum main grid is 0.2-0.5 mm, and the inner ring width is 1-2.1 mm.

[0025] Furthermore, the annular width of the annular aluminum main grid is 0.4 mm, and the inner ring width is 1.9 mm.

[0026] Furthermore, the aluminum sub-grid is perpendicular to the aluminum main grid and is spaced apart, the spacing between adjacent aluminum sub-grids is 0.8-1.5 mm, and the width is 60 μm-200 μm.

[0027] Furthermore, the spacing between adjacent aluminum sub-grids is 1.15 mm, and the width thereof is 120 μm.

[0028] Secondly, the method for preparing the back electrode of the present invention adopts screen printing to prepare silver electrodes and aluminum electrodes at corresponding positions on the back of the silicon wafer substrate.

[0029] Furthermore, laser grooving is performed at corresponding positions of the aluminum sub-grid region and the aluminum fine main grid region of the back electrode, while laser grooving is not performed at the silver electrode region and the annular aluminum main grid region.

[0030] Furthermore, when printing the aluminum electrode, the screen mesh number is 320-380 mesh, the wire diameter is 12-20 μm, the yarn thickness is 20-28 μm, and the film thickness is 18-22 μm.

[0031] Thirdly, the back electrode of the present invention is used in a double-sided solar cell.

[0032] 3. Beneficial effects

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The back electrode of a bifacial solar cell of the present invention optimizes the structure of the back electrode, especially optimizes the structure of the back silver electrode, thereby effectively improving the carrier collection effect of the back electrode while ensuring effective current conduction, and reducing the size of the blank isolation area. On the basis of ensuring the reliability of battery welding, the bifaciality and battery conversion efficiency are improved, which provides a possibility for a multi-silver electrode route.

[0035] (2) The back electrode of a bifacial solar cell of the present invention specifically improves the current collection effect of the blank area between silver and aluminum by setting a silver fine main grid at the silver electrode. At the same time, the use of a silver fine main grid instead of an aluminum main grid can reduce the shading area by 1.0%, thereby improving the bifaciality of the bifacial cell.

[0036] (3) The back electrode of a bifacial solar cell of the present invention can appropriately increase the width of the aluminum sub-grid while ensuring a certain bifacial rate (shading area) through structural optimization of the silver electrode. At the same time, while ensuring a certain collection effect, the height of the aluminum electrode can be appropriately reduced, thereby further reducing the limitations caused by the aspect ratio (height difference), achieving the reduction of the collection blank area and the establishment of multiple silver electrode routes.

[0037] (4) The method for preparing the back electrode of a bifacial solar cell of the present invention adopts screen printing to make silver electrodes and aluminum electrodes on the back of a silicon wafer substrate. Through the multi-segmented back electrode pattern design, the back electrode can significantly improve the carrier collection effect without negatively affecting the back shading area and slurry consumption, thereby improving the conversion efficiency of the cell. The back electrode prepared by the present invention is applied to solar cells, which can achieve an increase of more than 0.1% in the photoelectric conversion efficiency of PERC bifacial cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is the pattern of the back electrode of the existing MBB;

[0039] Figure 2 This is an enlarged view of the electrode area of ​​the existing MBB back electrode;

[0040] Figure 3 It is a cross-sectional view of the back electrode of an existing solar cell;

[0041] Figure 4 The pattern of the back electrode of the present invention;

[0042] Figure 5 It is an enlarged view of the electrode area of ​​the back electrode of the present invention;

[0043] Figure 6 It is a schematic structural diagram of the silver electrode of the present invention;

[0044] Figure 7 The laser groove pattern of the present invention;

[0045] Figure 8 The back silver pattern of the present invention;

[0046] Fig. 9 It is a schematic cross-sectional view of a double-sided solar cell of the present invention.

[0047] In the figure: 1. Aluminum main grid; 101. Straight-through aluminum main grid; 102. Ring-type aluminum main grid; 2. Aluminum sub-grid; 3. Silver electrode; 301. Silver main area; 302. Silver fine main grid; 3021. Silver fine main grid in the edge area; 3022. Silver fine main grid in the center area; 303. Silver antenna; 4. Blank isolation area; 5. Non-grooved area; 6. Laser grooved area; 7. Silicon wafer substrate; 8. Front emitter; 801. Heavily doped area; 802. Lightly doped area; 9. Front oxide layer; 10. Passivation and anti-reflection layer; 11. Positive electrode; 12. Back passivation layer; 13. Back laser groove; 14. Back electrode. DETAILED DESCRIPTION

[0048] In order to simultaneously meet the requirements of MBB bifacial cells for bifaciality and welding reliability, the blank isolation area between the silver and aluminum electrodes on the back electrodes of existing bifacial solar cells is relatively long, accounting for as much as 1%-3% of the area, which greatly limits the number of segments of the back silver electrode (currently mainly 6 segments), affecting the conversion efficiency of the cell. At the same time, the aluminum main grid width of the back electrode structure of the 6-segment MBB bifacial cell cannot be further reduced, and the bifaciality cannot be improved; and as the size of the silicon wafer increases, the problems of carrier collection effect, bifaciality, slurry consumption and component welding reliability caused by the 6-segment design will become more prominent.

[0049] Based on the above situation, the present invention optimizes the structure of the silver electrode and adds silver fine main grids 302 at both ends of the silver main area 301. On the one hand, while ensuring effective current conduction, the current collection effect of the blank isolation area 4 between the silver and aluminum can be improved, and the length of the blank isolation area 4 can be shortened to 0.1-1.4mm (blank isolation areas 4 are provided at both ends of the silver main area 301, and the length of the blank isolation area 4 here refers to the distance between the end of the silver main area 301 and the end or edge of the non-laser grooved area 5 corresponding to the end), so that the shading area is reduced by about 1.0%, thereby improving the bifaciality of the bifacial battery; on the other hand, under the condition of ensuring a certain bifaciality and collection effect, the line width of the aluminum sub-grid 2 can be appropriately increased, and the height of the aluminum electrode can be reduced, thereby eliminating and reducing the limitations caused by the aspect ratio (height difference), and realizing the reduction of the collection blank area and multiple silver electrode routes.

[0050] By adopting the scheme of the present invention, the number of segments of the silver electrode 3 on the same main grid can be increased from the current 6 to 8-50. Specifically, the silver electrode 3 of the present invention is composed of a silver main area 301 and silver fine main grids 302 located at both ends of the silver main area 301. The two sides of the silver main area 301 are electrically connected to the ring-type aluminum main grid 102, and its two ends are electrically connected to the straight-through aluminum main grid 101 through the silver fine main grid 302. Among them, the silver fine main grid 302 includes a central area silver fine main grid 3022 located in the middle of the silver main area 301 and an edge area silver fine main grid 3021 located on both sides of the central area silver fine main grid 3022. The width of the silver main area 301 is 1.2-2.2mm, and the length is 1.5-5.5mm, so as to maintain the total silver electrode area basically unchanged. By significantly increasing the number of silver electrodes, the collection effect of back carriers is improved, thereby improving the conversion efficiency. The length of the silver thin main grid 302 is the distance between 1-2 aluminum sub-grids 2, the widths of the central area silver thin main grid 3022 and the edge area silver thin main grid 3021 are 0.05-0.1mm and 0.02-0.08mm respectively, and the distance between the two edge area silver thin main grids 3021 is consistent with the width of the silver main area 301. The preferred solution is: the number of segments of the silver electrode 3 on the same main grid is 12, the width of the silver main area 301 is 2.1mm, the length is 2.7mm, the length of the silver thin main grid 302 is 1.3mm, the widths of the central area silver thin main grid 3022 and the edge area silver thin main grid 3021 are 0.07mm and 0.04mm respectively.

[0051] Example 1

[0052] like Figure 4 As shown, the back electrode of this embodiment has an aluminum main grid 1 with a multi-main grid structure of 9 bars, and a single aluminum main grid 1 is a multi-segmented structure consisting of a straight aluminum main grid 101 and a ring-shaped aluminum main grid 102 that are spaced apart. The silver electrode 3 is located inside the ring-shaped aluminum main grid 102 and is electrically connected to the aluminum main grid 1 (the number of segments of the silver electrode 3 in this embodiment is 12). Figure 5 , Figure 6The silver electrode 3 of this embodiment is composed of a silver main region 301 and silver fine main grids 302 located at both ends of the silver main region 301. Both sides of the silver main region 301 are electrically connected to the ring-type aluminum main grid 102, and both ends thereof are electrically connected to the straight-through aluminum main grid 101 through the silver fine main grid 302. The silver fine main grid 302 includes a central area silver fine main grid 3022 located in the middle of the silver main region 301 and an edge area silver fine main grid 3021 located on both sides of the central area silver fine main grid 3022. Specifically, in this embodiment, the width of the silver main region 301 is 2.1 mm, the length is 2.7 mm, the length of the silver fine main grid 302 is 1.3 mm, the widths of the central area silver fine main grid 3022 and the edge area silver fine main grid 3021 are 0.07 mm and 0.04 mm respectively, and the length of the blank isolation area in this embodiment is 0.4 mm.

[0053] The straight-through aluminum main grid 101 of the present embodiment is of I-shaped design, the ring-shaped aluminum main grid 102 is of long strip design, and the width of the flange areas at both ends of the straight-through aluminum main grid 101 is greater than the width of the silver electrode 3 (that is, greater than the spacing between the silver fine main grids 3021 in the edge area, so as to facilitate the overlap of the two). Specifically, in the present embodiment, the width of the flange areas at both ends of the straight-through aluminum main grid is 2.4 mm, the width of the middle area is 1.0 mm, the ring width of the ring-shaped aluminum main grid 102 is 0.4 mm, the inner ring width is 1.9 mm (smaller than the silver electrode width, so as to achieve connection with the silver electrode), the inner ring length is 3.0 mm, and silver antennae 303 are provided on both sides of the silver main area 301 for overlapping with the aluminum sub-grid.

[0054] In this embodiment, the aluminum auxiliary grid 2 is perpendicular to the aluminum main grid 1 and is spaced apart and parallel to the aluminum main grid 1. Most of the aluminum auxiliary grid 2 is connected to the aluminum main grid 1, and a part of the aluminum auxiliary grid 2 is directly connected to the ring-shaped aluminum main grid 102. The corresponding positions of the aluminum auxiliary grid 2 and the aluminum fine main grid are laser grooved, which is the laser groove area ( Figure 7 ), to realize current extraction, the corresponding positions of the silver electrode 3 and the annular aluminum main grid 102 are not laser grooved, that is, the non-grooved area. The spacing between adjacent aluminum sub-grids 2 is 1.15mm, and the width is 120μm.

[0055] The back electrode of this embodiment is applied to a double-sided solar cell, such as Fig. 9 As shown, the battery of this embodiment includes a back electrode 14, a back passivation layer 12, a silicon wafer substrate 7, a front emitter 8, a front oxide layer 9, a front passivation and anti-reflection layer 10 and a positive electrode 11 arranged in sequence from bottom to top, and its specific preparation process is as follows:

[0056] The specific preparation process of the bifacial battery of this embodiment is as follows:

[0057] 1. Texturing: Use single crystal P-type silicon wafers and use alkali to texturize the front and back sides to form a velvet structure.

[0058] 2. Diffusion: After texturing, the silicon wafer is reacted with phosphorus oxychloride and the silicon wafer at high temperature to diffuse on the front side to form a PN emitter junction. After diffusion, the square resistance of the thin layer on the front surface is between 160Ω / □.

[0059] 3. Laser SE: Using diffused phosphosilicate glass as a phosphorus source, laser doping is performed on the front side of the diffused silicon wafer and in the metallized area corresponding to the positive electrode gate line to form a heavily doped region 801, thereby realizing a selective emitter structure (heavily doped region 801 and lightly doped region 802) on the front side of the silicon wafer. The square resistance of the heavily doped region 801 is between 80Ω / □.

[0060] 4. Hot Oxygen: The silicon wafer after laser SE is oxidized by oxygen.

[0061] 5. Remove PSG: Use HF to remove PSG on the back and surrounding of the thermally oxidized silicon wafer.

[0062] 6. Alkali polishing: Polish the back and edges of the silicon wafer after PSG removal, and remove PSG from the front.

[0063] 7. Oxidation annealing: The alkali-polished silicon wafer is oxidized and annealed.

[0064] 8. Depositing a passivation film on the back side: A passivation film, i.e., a back side passivation layer 12, is prepared on the back side of the annealed silicon wafer.

[0065] 9. Deposition of anti-reflection film on the front side: Prepare a passivation and anti-reflection layer 10 on the front side of the silicon wafer.

[0066] 10. Back laser: Use the laser groove pattern corresponding to the aluminum electrode to perform laser grooves at the corresponding positions of the aluminum sub-grid area and the aluminum fine main grid area of ​​the back electrode ( Figure 7 ), to realize current extraction, while the silver electrode area and the annular aluminum main grid area are not laser grooved, and the non-grooved area 5 is rectangular with a width of 3.5mm and a length of 2.28mm.

[0067] 11. Preparation of back silver electrode: Use screen printing to prepare silver electrode 3 ( Figure 8 ), the back silver electrode uses Guangda GB21 silver paste.

[0068] 12. Preparation of back aluminum electrode: The back aluminum electrode pattern of this embodiment is used to prepare the back aluminum electrode. The electrode is prepared by screen printing and alignment of laser MARK points captured by a high-precision camera. The screen plate specifications use low yarn thickness and low film thickness screen plates, preferably 360 mesh, 16 μm wire diameter, 22 yarn thickness, and 20 μm film thickness. The aluminum paste uses Ruxing RX8401E-9B double-sided aluminum paste.

[0069] 13. Printing of the positive electrode main grid area: Using a front silver paste, the positive electrode 11 is prepared by screen printing on the silicon wafer with the back electrode printed.

[0070] 14. Sintering: Co-sinter the silicon wafer with the printed front electrode, with a sintering peak temperature of 760°C.

[0071] 15. Electrical injection: The sintered battery cells are subjected to electrical injection treatment.

[0072] 16. Finished products: Test, sort, package and store the battery cells.

[0073] The solar cell prepared in this embodiment can significantly improve the carrier collection effect of the back electrode without negatively affecting the back shading area, slurry consumption and component welding performance, and achieve an increase of about 0.15% in the photoelectric conversion efficiency of the PERC cell.

[0074] Example 2

[0075] like Figure 4 As shown, the structure of the back electrode of this embodiment is basically the same as that of embodiment 1, and the main difference lies in that: in this embodiment, the main grid adopts a multi-main grid structure with 12 main grids, the number of segments of the back silver electrode is 9, the width of the silver main area 301 is 1.2mm, the length is 5.5mm, the length of the silver thin main grid 302 is 1.5mm, the width of the central area silver thin main grid 3022 and the edge area silver thin main grid 3021 are 0.05mm and 0.02mm respectively, and the length of the blank isolation area at both ends of the silver main area 301 is 1.2mm; the width of the flange areas at both ends of the straight-through aluminum main grid is 1.5mm, the width of the middle area is 0.5mm, the ring width of the annular aluminum main grid 102 is 0.4mm, the inner ring width is 1mm, and the inner ring length is 5mm; the spacing between adjacent aluminum sub-grids 2 is 1.2mm, and its width is 100μm.

[0076] The back electrode of this embodiment is applied to a double-sided solar cell, and its specific preparation process is basically the same as that of embodiment 1, and the main difference is that: in this embodiment, the square resistance of the thin layer on the front surface after diffusion is between 120Ω / □, the square resistance of the heavily doped region 801 is between 50Ω / □, the sintering peak temperature is 720℃, and the screen mesh number is 360 mesh, the wire diameter is 16μm, the yarn thickness is 26, and the film thickness is 20μm when printing the aluminum electrode. The solar cell prepared in this embodiment can achieve a significant improvement in the carrier collection effect of the back electrode without negatively affecting the back shading area, slurry consumption, and component welding, and achieve an increase of about 0.12% in the photoelectric conversion efficiency of the PERC cell.

[0077] Example 3

[0078] The structure of the back electrode of this embodiment is basically the same as that of Embodiment 1, and the main difference lies in that: in this embodiment, the main grid adopts a multi-main grid structure with 14 main grids, the number of segments of the back silver electrode is 16, the width of the silver main area 301 is 1.7 mm, the length is 3.3 mm, the length of the silver thin main grid 302 is 1.8 mm, the widths of the central area silver thin main grid 3022 and the edge area silver thin main grid 3021 are 0.1 mm and 0.08 mm respectively, and the length of the blank isolation area at both ends of the silver main area 301 is 1.4 mm; the width of the flange areas at both ends of the straight-through aluminum main grid is 2.3 mm, the width of the middle area is 0.8 mm, the ring width of the annular aluminum main grid 102 is 0.3 mm, the inner ring width is 1.5 mm, and the inner ring length is 2.9 mm; the spacing between adjacent aluminum sub-grids 2 is 1.5 mm, and its width is 60 μm.

[0079] The back electrode of this embodiment is applied to a double-sided solar cell, and its specific preparation process is basically the same as that of embodiment 1, and the main difference is that: in this embodiment, the square resistance of the thin layer on the front surface after diffusion is between 200Ω / □, the square resistance of the heavily doped region 801 is between 90Ω / □, the sintering peak temperature is 800℃, and the screen mesh number is 325 mesh, the wire diameter is 16μm, the yarn thickness is 26μm, and the film thickness is 20μm when printing the aluminum electrode. The photoelectric conversion efficiency of the solar cell prepared in this embodiment can be improved by about 0.13%.

[0080] Example 4

[0081] The structure of the back electrode of this embodiment is basically the same as that of Embodiment 1, and the main difference lies in that: in this embodiment, the main grid adopts a multi-main grid structure with 22 main grids, the number of segments of the back silver electrode is 26, the width of the silver main area 301 is 1.8 mm, the length is 3.0 mm, the length of the silver thin main grid 302 is 1.1 mm, the width of the central area silver thin main grid 3022 and the edge area silver thin main grid 3021 are 0.1 mm and 0.03 mm respectively, and the length of the blank isolation area at both ends of the silver main area 301 is 0.2 mm; the width of the flange areas at both ends of the straight-through aluminum main grid is 2.2 mm, the width of the middle area is 0.9 mm, the ring width of the annular aluminum main grid 102 is 0.5 mm, the inner ring width is 1.6 mm, and the inner ring length is 2.7 mm; the spacing between adjacent aluminum sub-grids 2 is 0.8 mm, and its width is 150 μm.

[0082] The back electrode of this embodiment is applied to a double-sided solar cell, and its specific preparation process is basically the same as that of embodiment 1, and the main difference is that: in this embodiment, the square resistance of the thin layer on the front surface after diffusion is between 140Ω / □, the square resistance of the heavily doped region 801 is between 65Ω / □, the sintering peak temperature is 740℃, and the screen mesh number is 360 mesh, the wire diameter is 16μm, the sand thickness is 22, and the film thickness is 20μm when printing the aluminum electrode. The photoelectric conversion efficiency of the solar cell prepared in this embodiment can be improved by about 0.12%.

[0083] Example 5

[0084] The structure of the back electrode of this embodiment is basically the same as that of Embodiment 1, and the main difference lies in that: in this embodiment, the main grid adopts a multi-main grid structure with 15 main grids, the number of segments of the back silver electrode is 30, the width of the silver main area 301 is 2.0 mm, the length is 2.4 mm, the length of the silver thin main grid 302 is 1.4 mm, the widths of the central area silver thin main grid 3022 and the edge area silver thin main grid 3021 are 0.09 mm and 0.04 mm respectively, and the length of the blank isolation area at both ends of the silver main area 301 is 1.0 mm; the width of the flange areas at both ends of the straight-through aluminum main grid is 2.3 mm, the width of the middle area is 0.8 mm, the ring width of the annular aluminum main grid 102 is 0.5 mm, the inner ring width is 1.7 mm, and the inner ring length is 2.1 mm; the spacing between adjacent aluminum sub-grids 2 is 1.2 mm, and its width is 200 μm.

[0085] The back electrode of this embodiment is applied to a double-sided solar cell, and its specific preparation process is basically the same as that of embodiment 1, and the main difference is that: in this embodiment, the square resistance of the thin layer on the front surface after diffusion is between 130Ω / □, the square resistance of the heavily doped region 801 is between 65Ω / □, the sintering peak temperature is 770℃, and the screen mesh number is 480 mesh, the wire diameter is 11μm, the yarn thickness is 15μm, and the film thickness is 5μm when printing the aluminum electrode. The photoelectric conversion efficiency of the solar cell prepared in this embodiment can be improved by about 0.10%.

Claims

1. A back electrode of a bifacial solar cell, wherein the aluminum main grid (1) is composed of a straight aluminum main grid (101) and a ring-shaped aluminum main grid (102) that are spaced apart, and the silver electrode (3) is located inside the ring-shaped aluminum main grid (102) and is electrically connected to the aluminum main grid (1), characterized in that: The lengths of the blank isolation regions (4) at both ends of the silver electrode (3) are 0.1-1.4 mm; the silver electrode (3) is composed of a silver main region (301) and silver fine main grids (302) located at both ends of the silver main region (301); both sides of the silver main region (301) are electrically connected to the annular aluminum main grid (102), and both ends of the silver main grid (302) are electrically connected to the straight aluminum main grid (101); the annular aluminum main grid (102) is designed as a long strip.

2. The back electrode of a bifacial solar cell according to claim 1, characterized in that: The silver fine main grid (302) comprises a central area silver fine main grid (3022) located in the middle of the silver main area (301) and edge area silver fine main grids (3021) located on both sides of the central area silver fine main grid (3022).

3. The back electrode of a bifacial solar cell according to claim 2, characterized in that: The length of the silver main grid (302) is the distance between 1-2 aluminum sub-grids (2), the widths of the central area silver main grid (3022) and the edge area silver main grid (3021) are 0.05-0.1 mm and 0.02-0.08 mm respectively, and the distance between the two edge area silver main grids (3021) is consistent with the width of the silver main area (301).

4. The back electrode of a bifacial solar cell according to claim 3, characterized in that: The length of the silver thin main grid (302) is 1.3 mm, and the widths of the central area silver thin main grid (3022) and the edge area silver thin main grid (3021) are 0.07 mm and 0.04 mm respectively.

5. A back electrode of a bifacial solar cell according to any one of claims 1 to 4, characterized in that: The number of segments of the silver electrode (3) on the same aluminum main grid (1) is 8-50.

6. The back electrode of a bifacial solar cell according to claim 5, characterized in that: The width of a single silver electrode (3) is 1.2-2.2 mm, and the length is 1.5-5.5 mm.

7. The back electrode of a bifacial solar cell according to claim 6, characterized in that: The number of segments of the silver electrode (3) on the same aluminum main grid (1) is 12, and the width of a single silver electrode (3) is 2.1 mm and the length is 2.7 mm.

8. A back electrode of a bifacial solar cell according to any one of claims 1 to 4, characterized in that: The width of the flange regions at both ends of the through-type aluminum main grid (101) is greater than the width of the silver electrode (3), and the flange regions are overlapped and connected to the silver electrode (3).

9. The back electrode of a bifacial solar cell according to claim 8, characterized in that: The width of the flange regions at both ends of the straight-through aluminum main grid (101) is 1.5-2.8 mm, and the width of the middle region is 0.5-1.2 mm.

10. The back electrode of a bifacial solar cell according to claim 9, characterized in that: The width of the flange regions at both ends of the straight-through aluminum main grid (101) is 2.4 mm, and the width of the middle region is 1.0 mm.

11. A back electrode of a bifacial solar cell according to any one of claims 1 to 4, characterized in that: The inner ring width of the annular aluminum main grid (102) is smaller than the width of the silver electrode (3).

12. The back electrode of a bifacial solar cell according to claim 11, characterized in that: The annular width of the annular aluminum main grid (102) is 0.2-0.5 mm, and the inner ring width is 1-2.1 mm.

13. The back electrode of a bifacial solar cell according to claim 12, characterized in that: The annular width of the annular aluminum main grid (102) is 0.4 mm, and the inner ring width is 1.9 mm.

14. A back electrode of a bifacial solar cell according to any one of claims 1 to 4, characterized in that: The aluminum auxiliary grid (2) is perpendicular to the aluminum main grid (1) and is spaced apart. The spacing between adjacent aluminum auxiliary grids (2) is 0.8-1.5 mm, and the width is 60 μm-200 μm.

15. The back electrode of a bifacial solar cell according to claim 14, characterized in that: The spacing between adjacent aluminum sub-grids (2) is 1.15 mm, and their width is 120 μm.

16. A method for preparing a back electrode according to any one of claims 1 to 15, characterized in that: A silver electrode (3) and an aluminum electrode are respectively prepared at corresponding positions on the back side of a silicon wafer substrate (7) by screen printing.

17. The method for preparing a back electrode according to claim 16, characterized in that: When printing aluminum electrodes, the screen mesh is 320-380 mesh, the wire diameter is 12-20 μm, the yarn thickness is 20-28 μm, and the film thickness is 18-22 μm.

18. Use of the back electrode according to any one of claims 1 to 15 in a bifacial solar cell.

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