Preparation method of superfine grid line of photovoltaic cell

Abstract

The invention provides a preparation method of a superfine grid line of a photovoltaic cell, relates to the technical field of photovoltaics, and aims to solve the technical problem that the high-quality superfine grid line is difficult to prepare by the photovoltaic cell. The method comprises the following steps: providing a photovoltaic cell; a plurality of fine grids are printed on the surface of the photovoltaic cell piece through a first screen printing plate, the fine grids are arranged at intervals in the first direction, each fine grid is provided with at least one discontinuous structure, the discontinuous structures corresponding to the fine grids are located at the same position in the second direction, and the first direction is perpendicular to the second direction; wherein the first screen printing plate is a metal casting screen printing plate, the viscosity of slurry adopted when the multiple thin grids are printed is 50 kpa.s to 70 kpa.s, and the value range of the line width of the multiple thin grids is 9 [mu] m to 10 [mu] m; at least one main grid structure extending in the first direction is printed on the surface of the photovoltaic cell piece through a second screen printing plate, each main grid structure is located on the discontinuous structure corresponding to each fine grid, and each main grid structure is electrically connected with each fine grid.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, and in particular to a method for preparing ultrafine grid lines for photovoltaic cells. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] In the fabrication of photovoltaic (PV) cells, most grid lines are produced using traditional screen printing, with linewidths ranging from 22μm to 28μm in mass production. For printing ultra-fine linewidth grid lines, traditional screen printing results in poor grid line morphology. Since the linewidth cannot be reduced, screen printing typically uses high-viscosity pastes to ensure low series resistance and lateral transport resistance in the PV cell, which increases silver loss. Therefore, there is an urgent need to develop a method for fabricating PV cells with high-quality ultra-fine grid lines. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing ultrafine grid lines for photovoltaic cells, so as to solve the technical problem that it is difficult to prepare high-quality ultrafine grid lines for photovoltaic cells.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for fabricating ultrafine grid lines in photovoltaic cells, comprising: Provide a photovoltaic cell; Multiple fine grids are printed on the surface of the photovoltaic cell using a first screen printing plate. The multiple fine grids are arranged at intervals along a first direction, and each fine grid has at least one discontinuous structure. The discontinuous structures corresponding to each fine grid are located at the same position in a second direction, and the first direction is perpendicular to the second direction. The first screen printing plate is a metal casting screen printing plate, and the viscosity of the paste used when printing the multiple fine grids is 50 kPa·s to 70 kPa·s. The linewidth of the multiple fine grids ranges from 9 μm to 10 μm. At least one main grid structure extending along the first direction is printed on the surface of the photovoltaic cell using a second screen printing plate, wherein each main grid structure is located on the discontinuous structure corresponding to each of the fine grids, and each main grid structure is electrically connected to each of the fine grids.

[0006] According to at least one embodiment of the present invention, the main gate structure includes two opposing and spaced-apart main gates and at least one connecting line, wherein the two ends of each connecting line are respectively connected to the two main gates; The two main gates are electrically connected to the two fine gate segments that form the corresponding discontinuous structure.

[0007] According to at least one embodiment of the present invention, the main gate structure includes a plurality of the connecting lines, the connecting lines extending along the second direction; The multiple connecting lines are evenly arranged along the first direction.

[0008] According to at least one embodiment of the present invention, the spacing between two adjacent connecting lines is consistent with the spacing between two adjacent fine grids; and / or, In the first direction, each of the connecting lines is located between the corresponding two fine grids.

[0009] According to at least one embodiment of the present invention, the main gate structure further includes at least one pad, each of the pads being electrically connected to both main gates.

[0010] According to at least one embodiment of the present invention, the second screen is a metal casting screen, the viscosity of the paste used when printing along the main grid structure is 50 kPa·s to 70 kPa·s, the linewidth of the main grid is in the range of 9 μm to 10 μm, and the linewidth of the connecting line is in the range of 9 μm to 10 μm.

[0011] According to at least one embodiment of the present invention, when printing multiple fine grids and printing the main grid structure, the solid content of the paste used is 87% to 89%; and / or, The fineness of the slurry used is 2μm to 8μm.

[0012] According to at least one embodiment of the present invention, the first screen has a first perforated structure of lines forming the fine grid, and the second screen has a second perforated structure of lines forming the main grid and the connecting line; The line width of the first hollow structure ranges from 6μm to 7μm; The line width of the second hollow structure ranges from 6μm to 7μm.

[0013] According to at least one embodiment of the present invention, both the first screen and the second screen are made of nickel alloy.

[0014] According to at least one embodiment of the present invention, the length of the discontinuous structure is 0.5 mm to 0.9 mm.

[0015] In one or more technical solutions provided in the exemplary embodiments of the present invention, at least one of the following beneficial effects can be achieved.

[0016] The method for preparing ultrafine grid lines for photovoltaic cells according to an exemplary embodiment of the present invention includes printing multiple fine grids on the surface of the photovoltaic cell using a first screen printing plate, and printing at least one main grid structure extending along a first direction using a second screen printing plate. Each fine grid forms an identical discontinuous structure at the same position in a second direction, while the main grid structure is disposed at the corresponding discontinuous structure of each fine grid, thereby forming an electrical connection (overlap) between the main grid structure and the multiple fine grids, i.e., the main grid structure extends along the first direction. Since the first screen printing plate is a metal casting screen printing plate, combined with a low-viscosity slurry (50 kPa·s ~ 70 kPa·s), high-quality ultrafine linewidth grid lines can be formed, wherein the linewidth of the fine grid ranges from 9 μm to 10 μm. Attached Figure Description

[0017] The accompanying drawings illustrate exemplary embodiments of the invention and, together with the description thereof, serve to explain the principles of the invention. These drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification. Figure 1 This is a schematic diagram of the structure of the fine grid according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the main gate structure according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the combination of the fine grid and the main grid structure according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the main gate structure in Comparative Example 3; Figure 5 This is a schematic flowchart of an ultrafine grid line fabrication method according to an embodiment of the present invention.

[0018] Figure label: 10. Fine grid; 11. Fine grid segment; 12. Discontinuous structure; 20. Main gate structure; 21. Main gate; 22. Connecting line; 23. Pad. Detailed Implementation

[0019] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0020] In the metallization process of photovoltaic cells' electrodes, the ultra-fine linewidth of traditional screen printing has always been limited by three factors: quality, appearance, and photoelectric conversion efficiency, making mass production impossible. Either producing excessively fine grid linewidths will result in poor morphology, or in order to ensure the photoelectric conversion efficiency of photovoltaic cells, using high-viscosity paste with ultra-fine screen printing linewidth will lead to quality abnormalities such as broken grids and incomplete printing.

[0021] For example, most screen printing in the industry currently uses 3D PI (polyimide) screens. The linewidth of the grid lines is limited by the material used to weave the screen, meaning the linewidth design limit cannot be lower than the wire diameter. Furthermore, the lower the wire diameter and the higher the mesh count, the higher the screen price. Moreover, conventional screen printing stencils can produce high-quality grid lines with linewidths above 18μm and aspect ratios below 60%, but these lines have relatively high resistance, thus affecting the photoelectric conversion efficiency of photovoltaic cells.

[0022] To address the aforementioned issues, the exemplary embodiment of this invention provides a method for preparing ultra-fine grid lines for photovoltaic cells. This method utilizes a first and second metal-cast screen and a pattern design different from traditional screen printing screens. This allows for the formation of high-quality ultra-fine grid lines to ensure high photoelectric conversion efficiency of the photovoltaic cells while reducing production costs.

[0023] Figure 5 This is a schematic flowchart of an ultrafine grid line fabrication method according to an embodiment of the present invention, as shown below. Figure 5 As shown, the method for fabricating ultrafine grid lines of a photovoltaic cell provided by an exemplary embodiment of the present invention includes: Step 101: Provide a photovoltaic cell, which can be a TOPCon cell without metal electrodes or a heterojunction cell, etc.

[0024] Step 102: Print multiple fine grids on the surface of the photovoltaic cell using a first screen printing plate.

[0025] Figure 1 This is a schematic diagram of the structure of the fine grid according to an embodiment of the present invention; as shown. Figure 1 As shown, the fine grid 10 formed on one surface of the photovoltaic cell by the first screen is specifically as follows: Multiple fine grids 10 are arranged at intervals along a first direction, each fine grid 10 having at least one discontinuous structure 12, and the discontinuous structures 12 corresponding to each fine grid 10 are located at the same position in a second direction, the first direction being perpendicular to the second direction.

[0026] For example, the length of the discontinuous structure 12 is 0.5mm to 0.9mm, such as 0.5mm, 0.55mm, 0.6mm, 0.65mm, 0.7mm, 0.75mm, 0.8mm, 0.85mm, 0.9mm or any two of the above values.

[0027] In practical applications, the printing press used can be a KLOON printing press, which uses a low-viscosity, low-solids silver paste to print fine grids 10 onto photovoltaic cells through a low-hardness squeegee and a metal-cast first screen.

[0028] For example, the first screen is made of a double-plated nickel alloy cast screen; Optionally, the second screen is made of a nickel alloy casting screen with secondary electroplating.

[0029] Printing parameters include: printing speed 360 mm / s~400 mm / s, ink return speed 300 mm / s~350 mm / s, printing pressure 35 N~55 N, and printing press compression 0.3~0.6. The low-hardness squeegee is a double-sided, double-attached squeegee; the hardness of the adhesive strip was tested using a Shore hardness tester, yielding a result of 65. The base plate used is carbon fiber. The printing head is an alloy printing head with a fixed angle of 60°.

[0030] For example, the viscosity of the slurry is 50 kPa·s to 70 kPa·s, such as 50 kPa·s, 52 kPa·s, 54 kPa·s, 56 kPa·s, 58 kPa·s, 60 kPa·s, 62 kPa·s, 64 kPa·s, 66 kPa·s, 68 kPa·s, 70 kPa·s, or within any two of the above values.

[0031] For example, the solid content of the slurry is 87% to 89%, such as 87%, 87.5%, 88%, 88.5%, 89%, or within any two of the above values.

[0032] For example, the fineness of the slurry is 2μm to 8μm, such as 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm or within any two of the above values.

[0033] It should be noted that the fineness of the paste is the reading of the scraper fineness gauge, which characterizes the size of the largest residual agglomerated particles in the silver paste.

[0034] It should be noted that when printing multiple fine grids or printing the main grid structure, the solid content, fineness, and viscosity of the paste used can be the same or different.

[0035] It is understandable that, corresponding to such Figure 1 The fine grid 10 shown has a first hollow structure with a roughly linear outline on the first screen.

[0036] like Figure 1As shown, after the first screen printing, multiple fine grids 10 are formed, evenly spaced along the first direction. The number of fine grids 10 depends on the size of the photovoltaic cell, for example, it can be 198. The spacing between the fine grids 10 can be 1.05 mm, and the linewidth of the fine grids 10 can be 9 μm to 10 μm, for example, 9 μm, 9.05 μm, 9.1 μm, 9.15 μm, 9.2 μm, 9.25 μm, 9.3 μm, 9.35 μm, 9.4 μm, 9.45 μm, 9.5 μm, 9.55 μm, 9.6 μm, 9.65 μm, 9.7 μm, 9.75 μm, 9.8 μm, 9.85 μm, 9.9 μm, 9.95 μm, 10 μm, or within any two of the above values.

[0037] Furthermore, the thickness of the first screen (measured as a patterned metal film) is 2μm to 5μm, and the aspect ratio of the resulting fine grid 10 is close to 1:1. On the one hand, the line width of the fine grid is reduced compared to that of a conventional fine grid, which can reduce the shading area; on the other hand, the ultra-fine grid 10 with an aspect ratio close to 1:1 can reduce line resistance and transmission resistance, thereby improving the photoelectric conversion efficiency of the photovoltaic cell.

[0038] For the same fine grid 10, a corresponding number of discontinuous structures 12 are provided according to the number of main grid structures 20 required for the size of the photovoltaic cell. For example, if the number of main grid structures 20 of the photovoltaic cell is designed to be 12, then there are also 12 discontinuous structures 12 on each fine grid 10, and the corresponding discontinuous structures 12 of each fine grid 10 in the second direction are all in the same position, so that after the main grid structure 20 is printed, it is approximately perpendicular to each fine grid 10 to form an electrical connection with each fine grid 10. Figure 3 As shown, Figure 3 This is a schematic diagram of the combination of fine grid and main grid structures according to an embodiment of the present invention.

[0039] Because there are many fine grids 10, the corresponding number of first perforated structures on the first screen is also large. When the length 'a' of the discontinuous structure 12 of the fine grid 10 in the second direction is not less than 0.5 mm, the first screen will not undergo large deformation during use, exhibiting high dimensional stability and significantly improved service life. For a metal-cast first screen, if designed with a conventional fine grid pattern, the resulting fine grid 10 will not have discontinuous structures 12, or the length of the discontinuous structure 12 will be less than 0.1 mm. In this case, the deformation of the first screen during use will be large, the quality and morphology of the fine grid 10 will be difficult to guarantee, and the service life will be reduced by more than 50%.

[0040] When the length a of the discontinuous structure 12 of the fine grid 10 in the second direction is greater than 0.9 mm, it will cause an increase in line resistance, thereby reducing the photoelectric conversion efficiency of the photovoltaic cell.

[0041] Step 103: Print at least one main grid structure 20 extending in the first direction on the surface of the photovoltaic cell using a second screen printing plate.

[0042] In practical applications, the number of main busbar structures 20 depends on the size of the solar cell. Figure 2 This is a schematic diagram of the main gate structure according to an embodiment of the present invention, combined with... Figure 2 and Figure 3 As shown, only a portion of the main gate structure 20 is shown, and it is only a partial view.

[0043] It is understandable that, corresponding to such Figure 2 The main grid structure 20 shown has a second hollow structure with a roughly linear outline on the second screen.

[0044] The main grid structure 20 is located on the discontinuity structure 12 (the discontinuity structure 12 at the same position in the second direction) corresponding to each fine grid 10, and each main grid structure 20 is electrically connected to each fine grid 10. Specifically, each fine grid 10 is divided into multiple fine grid segments 11 by the discontinuity structure 12.

[0045] For example, the main grid structure 20 includes two opposing and spaced main grids 21 and at least one connecting line 22, with each end of the connecting line 22 connected to the two main grids 21 respectively; the two main grids 21 are electrically connected to the two fine grid segments 11 forming the corresponding discontinuous structure 12 respectively.

[0046] For example, the main gate structure 20 includes a plurality of connecting lines 22 extending along a second direction; the plurality of connecting lines 22 are evenly arranged along a first direction. For example, the spacing c between two adjacent connecting lines 22 is the same as the spacing between two adjacent fine gates 10.

[0047] The main grid structure 20 is equivalent to spanning each of the fine grids 10 at the location of the discontinuous structure 12. One main grid 21 overlaps with the fine grid segments 11 of each of the fine grids 10 on the same side of the discontinuous structure 12, and the other main grid 21 overlaps with the fine grid segments 11 of each of the fine grids 10 on the other side of the discontinuous structure 12. Furthermore, with the connection of multiple connecting lines 22 between the two main grids 21, the fine grid segments 11 of each of the fine grids 10 are electrically connected through the main grid structure 20.

[0048] To minimize the resistance of the photovoltaic cell, the number of multiple connecting lines 22 in the same main grid structure 20 is approximately the same as the number of fine grids 10. In the first direction, each connecting line 22 is located between two corresponding fine grids 10. For example, in the first direction, each connecting line 22 is located in the middle of the upper and lower fine grids 10; that is, in the first direction, the connecting lines 22 and the fine grids 10 are staggered. This arrangement, compared to having the position of each connecting line 22 in the first direction the same as the fine grid 10, can avoid the connecting lines 22 overlapping on the corresponding fine grid segments 11 during printing, which would cause the main grid 21, fine grid segments 11, and connecting lines 22 to overlap, resulting in poor morphology at that position and thus causing quality abnormalities.

[0049] In other embodiments, the number of connecting lines 22 in the same main gate structure 20 may be different from the number of fine gates 10. For example, the number of connecting lines 22 in the same main gate structure 20 may be greater than the number of fine gates 10 or less than the number of fine gates 10, depending on the actual line resistance.

[0050] For example, the length of the connecting line 22, that is, the distance b between the two main grids 21, can be greater than the length a of the discontinuity structure 12. Thus, the ends of the fine grid segments 11 located on both sides of the main grid structure 20 can extend to the space between the two main grids 21, that is, each fine grid segment 11 overlaps with the corresponding main grid 21, thus avoiding poor contact between the main grid structure 20 and the fine grid 10.

[0051] In some implementations, continue as Figure 3 As shown, in the method for preparing ultrafine grid lines of photovoltaic cells provided by the exemplary embodiment of the present invention, the linewidth of the main grid 21 ranges from 9μm to 10μm, for example, it can be 9μm, 9.05μm, 9.1μm, 9.15μm, 9.2μm, 9.25μm, 9.3μm, 9.35μm, 9.4μm, 9.45μm, 9.5μm, 9.55μm, 9.6μm, 9.65μm, 9.7μm, 9.75μm, 9.8μm, 9.85μm, 9.9μm, 9.95μm, 10μm or within any two of the above values.

[0052] For example, the line width of the connecting line 22 is in the range of 9μm to 10μm, such as 9μm, 9.05μm, 9.1μm, 9.15μm, 9.2μm, 9.25μm, 9.3μm, 9.35μm, 9.4μm, 9.45μm, 9.5μm, 9.55μm, 9.6μm, 9.65μm, 9.7μm, 9.75μm, 9.8μm, 9.85μm, 9.9μm, 9.95μm, 10μm or within any two of the above values.

[0053] It should be noted that the parameters and paste used when printing the main grid structure 20 on the surface of the photovoltaic cell forming the fine grid 10 using the second screen are the same as those in step S2, and will not be repeated here.

[0054] In some implementations, continue as Figure 3 As shown, in the method for preparing ultrafine grid lines of photovoltaic cells provided by the exemplary embodiment of the present invention, the main grid structure 20 further includes at least one pad 23, and each pad 23 is electrically connected to two main grids 21.

[0055] In practical applications, each main gate structure 20 is provided with multiple pads 23 made of the same material as the main gate 21, also called pad points. For example, the size of the pad points can be... It is usually set near the end of the main grid structure 20; the size of the Pad point can also be Typically located in the middle of the main grid structure 20, the aforementioned Pad point is used for welding with the solder strip to form an effective electrical connection between the main grid structure 20 and a solder strip.

[0056] For example, the outline of the Pad point is roughly rectangular, with its two sides overlapping the two main gates 21. It can be understood that at the Pad point location, the Pad point can replace the connecting line 22 at that location to form an electrical connection between the two main gates 21.

[0057] As can be seen from the above, the photovoltaic cell ultrafine grid line preparation method provided by the exemplary embodiment of the present invention adopts a screen pattern different from that of traditional screen printing. By using a screen pattern cast with a secondary electroplated nickel alloy, the line width of the grid line can be reduced to 9μm to 10μm. If a traditional screen printing screen is used to prepare a line width of 9μm to 10μm (ultra-high mesh count with ultra-fine steel wire), the cost is dozens of times that of a screen pattern cast with a secondary electroplated nickel alloy. If a traditional screen printing screen is directly reduced in line width of the screen's hollow structure and combined with a high-viscosity paste, it will lead to a large number of broken grid lines, false printing and other quality abnormalities. However, the first and second screens of the present invention benefit from the smooth sidewalls of the screen, which allows for better plasticity of the paste and avoids abnormalities such as inkjet printing. Low solid content and low viscosity silver paste can be used, reducing silver paste consumption by 25-40%, and the steepness of the grid line edge reaches 88°±2°.

[0058] An exemplary embodiment of the present invention provides a screen printing plate set for a method of preparing ultrafine grid lines, comprising a first screen plate and a second screen plate, both of which are metal casting screen plates; The first screen is used to print multiple fine grids 10 on the surface of a photovoltaic cell. The multiple fine grids 10 are arranged at intervals along a first direction. Each fine grid 10 has at least one discontinuous structure 12. The discontinuous structures 12 corresponding to each fine grid 10 are located at the same position in a second direction. The first direction is perpendicular to the second direction. The length of the discontinuous structure 12 is 0.5 mm to 0.9 mm, for example, it can be 0.5 mm, 0.55 mm, 0.6 mm, 0.65 mm, 0.7 mm, 0.75 mm, 0.8 mm, 0.85 mm, 0.9 mm or within any two of the above values.

[0059] The second screen is used to print at least one main grid structure 20 extending along a first direction on the surface of the photovoltaic cell, wherein each main grid structure 20 is located on the discontinuous structure 12 corresponding to each fine grid 10, and each main grid structure 20 is electrically connected to each fine grid 10.

[0060] In some embodiments, the main gate structure 20 includes two opposing and spaced-apart main gates 21 and at least one connecting line 22, with each end of the connecting line 22 connected to the two main gates 21 respectively. The two main grids 21 are electrically connected to the two fine grid segments 11 that form the corresponding discontinuous structure 12.

[0061] In some embodiments, the main gate structure 20 includes a plurality of connecting lines 22 extending along a second direction; Multiple connecting lines 22 are evenly arranged along the first direction.

[0062] In some embodiments, the first screen has a first cutout structure forming the fine grid 10, and the second screen has a second cutout structure forming the main grid 21 and the connecting line 22.

[0063] For example, the line width of the first hollow structure ranges from 6μm to 7μm, and can be, for example, 6μm, 6.05μm, 6.1μm, 6.15μm, 6.2μm, 6.25μm, 6.3μm, 6.35μm, 6.4μm, 6.45μm, 6.5μm, 6.55μm, 6.6μm, 6.65μm, 6.7μm, 6.75μm, 6.8μm, 6.85μm, 6.9μm, 6.95μm, 7μm, or within any two of the above values.

[0064] For example, the line width of the second hollow structure ranges from 6μm to 7μm, and can be, for example, 6μm, 6.05μm, 6.1μm, 6.15μm, 6.2μm, 6.25μm, 6.3μm, 6.35μm, 6.4μm, 6.45μm, 6.5μm, 6.55μm, 6.6μm, 6.65μm, 6.7μm, 6.75μm, 6.8μm, 6.85μm, 6.9μm, 6.95μm, 7μm, or within any two of the above values.

[0065] For example, the second cutout structure also includes a portion forming a border line that extends around the perimeter of the cell near the edge. This border line is equivalent to the main grid used to connect the fine grids. Forming the second cutout structure forming the border line on the second screen results in a longer lifespan compared to forming it on the first screen (which has more fine grids than the main grid structure).

[0066] In some embodiments, both the first and second screens are made of nickel alloy. For example, the two screens are subjected to secondary electroplating (nickel + copper or copper + nickel) followed by heat treatment diffusion to form a nickel alloy layer on the substrate.

[0067] The screen printing plate assembly provided in the exemplary embodiment of the present invention can utilize special processes such as covering the first and second screens with a PI layer during their formation to ensure a direct isolation layer between the screen and the photovoltaic cell, thereby reducing the impact on the photoelectric conversion efficiency of the photovoltaic cell. Compared to traditional screen printing plates, the screen printing plate assembly of the present invention does not suffer from the problem of steel wires, mesh knots, or other obstructions affecting ink permeability.

[0068] The following specific embodiments further illustrate the above-mentioned method for fabricating ultrafine grid lines in photovoltaic cells.

[0069] Example 1 The Kronway printing press has a printing speed of 360 mm / s to 400 mm / s, an ink return speed of 300 mm / s to 350 mm / s, a printing pressure of 35 N to 55 N, and a press compression of 0.3 to 0.6. The low-hardness squeegee is a double-sided, double-attached squeegee; the hardness of the adhesive strip was tested using a Shore hardness tester, yielding a result of 65. The base plate used is made of carbon fiber. The print head is an alloy print head with a fixed angle of 60°.

[0070] The silver paste has a viscosity of 60 kPa·s, a solid content of 88%, and a fineness of 5 μm.

[0071] The fine grid formed by printing using the first screen printing plate, such as Figure 1 As shown, the linewidth of the fine grid 10 is 9.5 μm, the spacing between two adjacent fine grids is 1.05 mm, the number of fine grids is 198, and the length of the discontinuous structure 12 of the fine grid 10 is 0.6 mm.

[0072] The main grid structure formed using the second screen printing plate is as follows: Figure 2 As shown, the linewidth of the two main gates 21 and the linewidth of the connecting line 22 in the main gate structure 20 are both 9.5 μm. The spacing between the two main gates 21 is 0.65 mm, and the spacing between two adjacent connecting lines 22 is 1.05 mm. The number of connecting lines 22 is the same as the number of fine gates 10. The size of the Pad point near the end of the main gate structure 20 is... ， The size of the middle Pad point is .

[0073] Both the first and second screen printing plates are metal casting screen printing plates. After printing on a printing press, the grid lines are sintered and metallized to obtain the finished photovoltaic cells.

[0074] Comparative Example 1 The only difference between this comparative example and Example 1 is that the length of the discontinuous structure 12 of the fine grid 10 is 0.4 mm.

[0075] Comparative Example 2 The only difference between this comparative example and Example 1 is that the length of the discontinuous structure 12 of the fine grid 10 is 1 mm.

[0076] Comparative Example 3 The only difference between this comparative example and Example 1 is that the main grid structure 20 formed using the second screen printing plate is as follows: Figure 4 As shown. The main grid structure 20 consists of a single main grid spanning across each connecting line 22, and is located in the middle of the connecting line 22 in the second direction. The connecting lines 22 are positioned in the same direction as the fine grids 10 and correspond one-to-one, that is, the two ends of the connecting line 22 overlap with the fine grid segments 11 on both sides of the discontinuous structure 12. The size and distribution of the Pad points on the main grid structure 20 are the same as in Embodiment 1.

[0077] Test case The finished solar cells formed by the above embodiments and comparative examples were tested using an IV tester, where Isc is the short-circuit current (mA), Voc is the open-circuit voltage (V), FF is the fill factor, Eta is the conversion efficiency, Irev12 is the reverse current (mA), Rs is the series resistance (Ω), and Rp is the parallel resistance (Ω).

[0078] Table 1. Test data for Example 1, Comparative Example 1, and Comparative Example 2 ; Referring to Table 1, the test data of Example 1 and Comparative Example 1 show that when the discontinuous structure of the fine grid 10 formed by the first screen is less than 0.5mm, the service life of the first screen is drastically reduced from 180,000 solar cells in Example 1 to 80,000 solar cells, which significantly increases the production cost.

[0079] Referring again to Table 1 above, the test data from Example 1 and Comparative Example 2 show that when the discontinuity of the fine grid 10 formed by the first screen is greater than 0.9 mm, the short-circuit current Isc of the finished solar cell decreases, the current collection capacity decreases, and the fill factor FF and cell conversion efficiency Eta also decrease. Based on this, the exemplary embodiment of the present invention uses a fine grid with a discontinuity length in the range of 0.5 mm to 0.9 mm, which can both ensure the service life of the screen, reduce production costs, and improve the photoelectric conversion efficiency of the finished photovoltaic cell.

[0080] Table 2 Test data for Example 1 and Comparative Example 3 ; Referring to Table 2, the test data from Example 1 and Comparative Example 3 show that the dual-main-grid structure formed by the second screen of the exemplary embodiment of the present invention, combined with the fine grid formed by the first screen, has a significantly lower rate of poor overlap compared to the main-grid structure with only a single main grid in Comparative Example 3. The short-circuit current Isc, fill factor FF, and cell conversion efficiency Eta of the finished solar cell formed by the screens (including the first and second screens) of the exemplary embodiment of the present invention are all improved. Based on this, the method for preparing ultra-fine grid lines for photovoltaic cells according to the exemplary embodiment of the present invention can achieve the production of ultra-fine linewidth grid lines using low-viscosity slurry, reducing the rate of poor overlap between the main grid structure and the fine grid, improving the photoelectric conversion efficiency of the photovoltaic cell while reducing production costs.

[0081] Those skilled in the art should understand that the above embodiments are merely for illustrating the present invention and are not intended to limit the scope of the invention. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of the present invention.

Claims

1. A method for fabricating ultrafine grid lines in a photovoltaic cell, characterized in that, include: Provide a photovoltaic cell; Multiple fine grids are printed on the surface of the photovoltaic cell using a first screen printing plate. The multiple fine grids are arranged at intervals along a first direction, and each fine grid has at least one discontinuous structure. The discontinuous structures corresponding to each fine grid are located at the same position in a second direction, and the first direction is perpendicular to the second direction. The first screen printing plate is a metal casting screen printing plate, and the viscosity of the paste used when printing the multiple fine grids is 50 kPa·s to 70 kPa·s. The linewidth of the multiple fine grids ranges from 9 μm to 10 μm. At least one main grid structure extending along the first direction is printed on the surface of the photovoltaic cell using a second screen printing plate, wherein each main grid structure is located on the discontinuous structure corresponding to each of the fine grids, and each main grid structure is electrically connected to each of the fine grids.

2. The method for fabricating ultrafine grid lines according to claim 1, characterized in that, The main grid structure includes two opposing and spaced-apart main grids and at least one connecting line, with each end of the connecting line connected to the two main grids respectively; The two main gates are electrically connected to the two fine gate segments that form the corresponding discontinuous structure.

3. The method for preparing ultrafine grid lines according to claim 2, characterized in that, The main gate structure includes a plurality of the connecting lines, which extend along the second direction; The multiple connecting lines are evenly arranged along the first direction.

4. The method for preparing ultrafine grid lines according to claim 3, characterized in that, The spacing between two adjacent connecting lines is the same as the spacing between two adjacent fine grids; and / or, In the first direction, each of the connecting lines is located between the corresponding two fine grids.

5. The method for preparing ultrafine grid lines according to claim 2, characterized in that, The main gate structure also includes at least one pad, each of which is electrically connected to both main gates.

6. The method for preparing ultrafine grid lines according to claim 2, characterized in that, The second screen is a metal casting screen. The viscosity of the paste used when printing along the main grid structure is 50 kPa·s to 70 kPa·s. The line width of the main grid ranges from 9 μm to 10 μm, and the line width of the connecting lines ranges from 9 μm to 10 μm.

7. The method for preparing ultrafine grid lines according to claim 6, characterized in that, When printing multiple fine grids and the main grid structure, the solid content of the paste used is 87% to 89%; and / or, The fineness of the slurry used is 2μm to 8μm.

8. The method for preparing ultrafine grid lines according to claim 6, characterized in that, The first screen has a first cutout structure of linear shape forming the fine grid, and the second screen has a second cutout structure of linear shape forming the main grid and the connecting line; The line width of the first hollow structure ranges from 6μm to 7μm; The line width of the second hollow structure ranges from 6μm to 7μm.

9. The method for preparing ultrafine grid lines according to any one of claims 1-8, characterized in that, Both the first and second screen printing plates are made of nickel alloy.

10. The method for fabricating ultrafine grid lines according to any one of claims 1-8, characterized in that, The length of the discontinuous structure is 0.5 mm to 0.9 mm.

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