Back contact solar cell and preparation method and positioning method of mark point thereof

Abstract

This invention discloses a back-contact solar cell and its mark point fabrication and positioning method, belonging to the field of solar cells. The back side of the silicon substrate of this solar cell has several pads arranged in an array, several fine grid lines connecting the pads, and at least one pair of edge mark points. The edge mark points are located near the side of the cell perpendicular to the extension direction of the interconnects. The vertical distance from the geometric center of the edge mark point to the aforementioned side is 1.0~4.0 mm. The edge mark point is located between two rows of pads adjacent to it. Two fine grid lines adjacent to the edge mark point are separated by the edge mark point, and the distance between the edge mark point and the separating edge of the fine grid line is greater than or equal to 20 μm. The above-mentioned edge mark point setting can achieve high-precision positioning and enable the interconnects and pads to form a more complete metallurgical bond, improving pull strength and yield.

Description

Technical Field

[0001] This invention relates to the field of solar cell technology, and more specifically, to a back-contact solar cell and a method for preparing and positioning its Mark points. Background Technology

[0002] Back-contact solar cells have high photoelectric conversion efficiency due to the absence of grid lines obstructing the front side. In the module packaging process for back-contact solar cells, a wire-wound interconnect process is commonly used, where solder ribbons are wrapped around the edge of the cell and connected to the pads on the back. This process requires extremely high visual positioning accuracy. In existing technologies, the mark point is usually set in the central area of ​​the cell. The equipment needs to simultaneously locate both the "mark point" and the "cell edge" for coordinate calculation. This not only involves complex algorithms but also limits production cycle time due to the large-scale camera movement required, leading to inaccurate positioning and affecting the bonding strength between the pads and the fine grid lines, as well as the product yield. In view of this, the present invention is proposed. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing and positioning a back-contact solar cell and its Mark point.

[0004] This invention can be implemented as follows: In a first aspect, the present invention provides a back-contact solar cell, comprising a silicon substrate having a light-receiving surface and a back surface; the back surface is provided with a plurality of pads arranged in an array, a plurality of fine grid lines connecting the pads, and at least a pair of edge mark points, the edge mark points being disposed near the side of the cell perpendicular to the extension direction of the interconnect. The vertical distance from the geometric center of the edge mark point to the aforementioned side is 1.0mm to 4.0mm; the projection of the edge mark point on the cell is located in the area between the two rows of pads adjacent to the edge mark point; along the direction perpendicular to the extension direction of the interconnect, the two fine grid lines adjacent to the edge mark point are separated by the edge mark point, and the distance between the edge mark point and the edge of the separation side of the two fine grid lines is greater than or equal to 20μm.

[0005] In an optional embodiment, a recess is provided on the back side of the silicon substrate near the side edge, and an edge mark point is disposed in the recess.

[0006] In an optional implementation, the depth of the pit is 5 μm to 10 μm.

[0007] In an optional implementation, the distance between the projection of the edge mark point on the cell and any row of pads is greater than or equal to 0.2 mm.

[0008] In an optional implementation, the spacing between the fine grid lines is 1.2 to 1.5 times the length of the edge Mark point in a direction perpendicular to the direction of interconnect extension.

[0009] In an optional implementation, the pattern of the edge Mark point has at least one first positioning reference edge and at least one second positioning reference edge; wherein the first positioning reference edge is perpendicular to the extension direction of the interconnect, and the second positioning reference edge is parallel to the extension direction of the interconnect or has a non-right angle with the extension direction of the interconnect.

[0010] In a second aspect, the present invention provides a method for preparing a Mark point in a back-contact solar cell as described in any of the foregoing embodiments, comprising: Preparation of pits: Etching at predetermined positions on the back side of the silicon substrate to form pits as the bottom layer serving as edge mark points; Fabrication of fine gates: Fabricate fine gate lines and design the fine gate lines at the corresponding edge Mark point positions as interrupted states; Preparation of edge mark points and pads: Electrode paste is filled into the pits and pad areas, and after molding, a paste layer is obtained as the surface layer of edge mark points; the bottom layer and the surface layer together form the edge mark points; The thickness of the slurry layer is greater than the depth of the pit.

[0011] In an optional embodiment, the depth of the pit is 5μm to 10μm, and the depth of the slurry layer is 10μm to 15μm.

[0012] In an optional implementation, the etching step employs laser etching; the laser etching process parameters include: wavelength of 355nm~1064nm, pulse width of 10ns~100ns, and power density of 1.0×10⁻⁶. 5 W / cm 2 ~5.0×10 5 W / cm 2 .

[0013] In an optional implementation, the spacing between the fine grid lines along the extension direction perpendicular to the interconnect is 1.2 to 1.5 times the length of the edge mark point.

[0014] Thirdly, the present invention provides a positioning method for preparing a solar cell, comprising the following steps: The solar cell is transported to a predetermined position, and an image is acquired including the side area of ​​the solar cell perpendicular to the extension direction of the interconnect and the edge mark points; After preprocessing the acquired image, the first positioning reference edge of the edge Mark point is first identified to obtain the Y-direction position and rotation angle, and then the second positioning reference edge of the edge Mark point is identified to obtain the X-direction offset compensation amount. After positioning is complete, the interconnects are precisely laid in the center of the target pads, and a welding and curing process is performed to form a metallurgical connection between the interconnects and the pads.

[0015] In an optional implementation, the positioning method includes at least one of the following features: Feature 1: During acquisition, the edge Mark point is located in the center of the field of view; preferably, the absolute value of the deviation between the actual position of the edge Mark point and the center of the field of view is less than or equal to 0.5 mm; Feature 2: Preprocessing includes at least one of filtering and denoising, contrast enhancement, and binarization of the acquired image; Feature 3: The absolute value of the radial deviation between the center of the interconnect and the center of the pad is less than or equal to 0.1 mm; Feature 4: The contact length between the interconnect and the pad is greater than or equal to 80% of the pad diameter.

[0016] In an optional embodiment, the welding temperature is 200℃~350℃ and the welding time is 1.0s~5.0s.

[0017] The beneficial effects of this invention include: The back-contact solar cell provided by this invention achieves high-precision simultaneous positioning of the edge and the Mark point by controlling the vertical distance between the geometric center of the edge Mark point and the side of the cell perpendicular to the extension direction of the interconnect to 1mm~4mm, ensuring clear imaging of the cell edge and the Mark point within the same frame. In this invention, the projection of the edge Mark point onto the cell is located in the area between the two rows of pads adjacent to the edge Mark point, effectively avoiding interference from pad reflections. Along a direction perpendicular to the extension direction of the interconnect, the two fine grid lines adjacent to the edge Mark point are separated by the edge Mark point, and the distance between the edge Mark point and the edge of the separation between the two fine grid lines is greater than or equal to 20μm, thus creating sufficient physical space for the edge Mark point without sacrificing the effective power generation area.

[0018] This invention achieves precise positioning by setting specific edge mark points; at the same time, with specific welding conditions, it not only achieves high-precision positioning but also enables the interconnects and pads to form a more complete metallurgical bond, increasing the tensile strength between the interconnects and pads, thereby improving the product qualification rate. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A partial top view of the back-contact solar cell provided by the present invention; Figure 2 This is a partial schematic diagram of the pad gap in a back-contact solar cell provided by the present invention; Figure 3 This is a schematic diagram of the edge Mark point in the back contact solar cell provided by the present invention; Figure 4 The main process flow diagram of the positioning method for preparing solar cells provided by the present invention.

[0021] Reference numerals: 100-pad; 110-first row of pads; 120-second row of pads; 200-fine gate line; 300-edge mark point; 310-edge mark point projection; 400-silicon substrate; 410-recess; 420-paste layer. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0023] The following is a detailed description of the back-contact solar cell and its Mark point preparation and positioning method provided by the present invention.

[0024] This invention provides a back-contact solar cell, please refer to... Figure 1 and Figure 3 The back-contact solar cell includes a silicon substrate 400, which has a light-receiving surface and a back surface. The back surface is provided with a plurality of pads 100 arranged in an array, a plurality of fine grid lines 200 connecting the pads 100, and at least a pair of edge mark points 300, which are disposed near the side of the cell perpendicular to the direction of extension of the interconnect.

[0025] In this invention, the side of the battery cell perpendicular to the extension direction of the interconnect can be defined as the "long side of the battery cell", which is also parallel to the fine grid line 200; the side of the battery cell parallel to the extension direction of the interconnect can be defined as the "short side of the battery cell", and the interconnect can be understood as a solder strip.

[0026] In some alternative methods, a recess is provided on the back side of the silicon substrate near the long side of the solar cell, and an edge mark is set in the recess. The depth of the recess can be 5μm to 10μm, such as 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, or other values ​​in the range of 5μm to 10μm.

[0027] The geometric center of edge mark point 300 is perpendicularly distanced from the long side of the solar cell to 1.0mm~4.0mm; the projection of edge mark point 300 onto the solar cell (i.e., edge mark point projection 310) is located in the area between the two rows of pads 100 adjacent to edge mark point 300 (e.g., Figure 2 As shown); in a direction perpendicular to the extension direction of the interconnect, the two fine gate lines 200 adjacent to the edge Mark point 300 are separated by the edge Mark point 300, and the distance between the edge Mark point 300 and the isolation side edge of the two fine gate lines 200 is greater than or equal to 20 μm. In this article, "greater than or equal to" means "≥".

[0028] In some alternative implementations, the vertical distance between the geometric center of the edge Mark point 300 and the long side of the solar cell can be 1.0mm to 4.0mm, such as 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm or 4mm, or other values ​​within the range of 1.0mm to 4.0mm.

[0029] Because the back of the back-contact solar cell is densely covered with pads 100 and fine grid lines 200, the available blank area is extremely limited. If the edge mark point 300 completely avoids the fine grid lines 200 and pads 100, the distance between the edge mark point 300 and the long side of the cell will be too far, failing to meet the fast field of view requirements for edge positioning of the winding equipment. This invention controls the vertical distance between the geometric center of the edge mark point 300 and the long side of the cell to 1mm~4mm, which is beneficial to achieve high-precision simultaneous positioning of the long side of the cell and the mark point, ensuring that the edge of the cell and the mark point are clearly imaged in the same frame. If the vertical distance between the geometric center of the edge mark point 300 and the long side of the cell is less than 1mm, the micro-chipping and chamfering reflections caused by cell cutting can easily lead to visual misjudgment; if the vertical distance between the geometric center of the edge mark point 300 and the long side of the cell is greater than 4mm, the side-fixed camera cannot clearly image due to depth of field limitations, thus making it difficult to clearly image the edge of the cell and the mark point in the same frame, that is, it is difficult to simultaneously position the long side of the cell and the mark point.

[0030] In this invention, the projection of the edge mark point 300 onto the solar cell is located in the area between the two rows of pads 100 adjacent to the edge mark point 300. This can be understood as follows: when viewed from the side of the solar cell along its long side, the projection of the edge mark point 300 at this viewpoint is located between the two rows of pads 100 (e.g., ...). Figure 1 The gap between the first row of pads 110 and the second row of pads 120 (where the projection of the edge Mark point 300 falls completely into the gap of the pads 100) can effectively avoid the interference of reflection from the pads 100.

[0031] In some alternative implementations, the distance between the projection of the edge mark point 300 onto the solar cell and any row of pads 100 is greater than or equal to 0.2 mm. By setting the distance between the projection edge of the edge mark point 300 from the pads 100 on both sides at this viewpoint to not less than 0.2 mm, it can be ensured that the reflection of the pads 100 will not interfere with the camera's recognition of the edge mark point 300.

[0032] In some alternative embodiments, two fine gate lines 200 adjacent to the edge Mark point 300 are separated by the edge Mark point 300 in a direction perpendicular to the extension direction of the interconnect, and the distance between the edge Mark point 300 and the isolation side edge of the two fine gate lines 200 is greater than or equal to 20 μm, for example, 20 μm, 22 μm or 25 μm.

[0033] During the design process, the dimension of the edge Mark point 300 in the direction perpendicular to the long side of the solar cell can be larger than the spacing between the two adjacent fine grid lines 200, thereby allowing the edge Mark point 300 to cover part of the path of the two fine grid lines 200. On the covered fine grid line 200 path, the line segment corresponding to the overlapping area occupied by the edge Mark point 300 is missing, forming a partial interruption structure of the fine grid. The edge Mark point 300 does not contact the break points of the fine grid lines 200 on both sides of the interruption, and the distance between them is greater than or equal to 20 μm.

[0034] In this invention, the edge Mark point 300 simultaneously crosses and partially interrupts two adjacent fine grid lines 200, which can create sufficient physical space for the edge Mark point 300 without sacrificing the effective power generation area.

[0035] In some alternative embodiments, the spacing between the fine gate lines 200 is 1.2 to 1.5 times the length of the edge mark point 300, such as 1.2, 1.3, 1.4, or 1.5 times, in a direction perpendicular to the extension direction of the interconnect. By setting the spacing between the fine gate lines 200 to 1.2 to 1.5 times the length of the edge mark point 300, it can be ensured that the distance between the edge mark point 300 and the spacing side edge of both fine gate lines 200 is greater than or equal to 20 μm.

[0036] In some optional embodiments, the shape of the edge Mark point 300 can be a regular shape, such as a rectangle, cross, or circle; in other optional embodiments, the shape of the edge Mark point 300 can also be an irregular shape. According to other classification methods, the shape of the edge Mark point 300 can be a symmetrical shape or an asymmetrical shape.

[0037] As an example, the graphic of the edge Mark point has at least one first positioning reference edge and at least one second positioning reference edge; wherein the first positioning reference edge is perpendicular to the extension direction of the interconnect, and the second positioning reference edge is parallel to the extension direction of the interconnect or has a non-right angle with the extension direction of the interconnect.

[0038] The aforementioned edge mark point 300 has few limitations and wide applicability, ensuring both recognition accuracy and broadening practical setting methods. Furthermore, the edge mark point 300 can simultaneously provide the geometric information needed to calculate the Y-axis offset, rotation angle, and X-axis local drift of the solar cell in a single image captured by a side-mounted camera. Even when some areas of the edge mark point 300 are damaged by edge chipping of the solar cell, the remaining areas can still provide at least one complete positioning reference for visual algorithm fitting and completion. Accordingly, this invention also provides a method for preparing mark points in the aforementioned back-contact solar cell, comprising: S1: Prepare pit 410.

[0039] Etching is performed at a predetermined position on the back side of the silicon substrate 400 to form a pit 410 as the bottom layer of the edge Mark point 300.

[0040] In some alternative embodiments, the etching method may, by way of example but not limitation, include laser etching. The process parameters for laser etching may include: a wavelength of 355 nm to 1064 nm (e.g., 355 nm, 532 nm, or 1064 nm), a pulse width of 10 ns to 100 ns (e.g., 10 ns, 20 ns, 50 ns, 80 ns, or 100 ns), and a power density of 1.0 × 10⁻⁶. 5 W / cm 2 ~5.0×10 5 W / cm 2 (e.g., 1.0×10) 5 W / cm 2 2×10 5 W / cm 2 3×10 5 W / cm 2 4×10 5 W / cm 2 Or 5×10 5W / cm 2 wait).

[0041] In some alternative embodiments, the depth of the above-mentioned pit 410 can be 5μm to 10μm, such as 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, or other values ​​in the range of 5μm to 10μm.

[0042] S2: Fabrication of fine grids.

[0043] Fine gate lines 200 are prepared, and the fine gate lines 200 at the corresponding edge Mark point 300 are designed to be in a closed state.

[0044] In some alternative implementations, the fine grid lines 200 can be prepared by screen printing.

[0045] In some alternative embodiments, the spacing between the fine gate lines 200 along the extension direction perpendicular to the interconnect is 1.2 to 1.5 times the length of the edge mark point 300, such as 1.2, 1.3, 1.4, or 1.5 times. By setting the spacing between the fine gate lines 200 to 1.2 to 1.5 times the length of the edge mark point 300, it can be ensured that the distance between the edge mark point 300 and the spacing side edge of both fine gate lines 200 is greater than or equal to 20 μm.

[0046] S3: Prepare edge mark points and pads.

[0047] Electrode paste is filled into the pit 410 and the pad 100 area, and after molding, a paste layer 420 is obtained as the surface layer of the edge mark point 300; the bottom layer and the surface layer together form the edge mark point 300.

[0048] In some alternative embodiments, the electrode paste simultaneously fills the pit 410 and the pad 100 area, and is then dried and sintered to obtain a paste layer 420 as the surface layer of the edge Mark point 300.

[0049] The thickness of the slurry layer 420 is greater than the depth of the pit 410, ensuring that the slurry fully fills the pit 410 and slightly protrudes above the surface. After sintering, a smooth, slightly convex structure is formed, which enhances diffuse reflection contrast and prevents contaminants from accumulating in the pit, thus improving visual recognition stability and process tolerance. If the thickness of the slurry layer 420 is less than the depth of the pit 410, the slurry cannot completely fill the pit 410, resulting in a recessed structure after sintering. This recess easily traps dust contaminants, and the edges of the pit 410 generate abnormal reflective interference, reducing visual recognition stability and positioning accuracy.

[0050] In some alternative embodiments, the depth of the slurry layer 420 can be 10μm to 15μm, such as 10μm, 11μm, 12μm, 13μm, 14μm or 15μm, or other values ​​within the range of 10μm to 15μm.

[0051] It should be noted that if the edge mark points are forcibly pressed onto the fine grid, it will cause the fine grid to break or the resistance to increase. If the edge mark points are pressed onto the solder pads, it will affect the soldering pull force and reduce the long-term reliability of the component.

[0052] Furthermore, the present invention also provides a positioning method for preparing solar cells, such as... Figure 4 As shown, it includes the following steps: (1) Transport the solar cell to a predetermined position and acquire an image containing the side (i.e. the long side of the solar cell) region perpendicular to the extension direction of the interconnect and the edge Mark point 300.

[0053] In some alternative implementations, an image containing the long side region of the battery cell and edge Mark points 300 can be acquired by a fixed-focus vision camera located on the side of the battery cell transport track.

[0054] In some alternative implementations, during acquisition, the edge Mark point 300 is located in the center of the field of view; preferably, the absolute value of the deviation between the actual position of the edge Mark point 300 and the center of the field of view is less than or equal to 0.5 mm (e.g., 0.5 mm, 0.4 mm, 0.3 mm, 0.2 mm, or 0.1 mm, etc.) to obtain more accurate positioning.

[0055] (2) After preprocessing the acquired image, first identify the first positioning reference edge of edge Mark point 300, obtain the Y-direction position and rotation angle, and then identify the second positioning reference edge of edge Mark point 300 to obtain the X-direction offset compensation amount.

[0056] In some alternative implementations, preprocessing includes at least one of filtering and denoising the acquired image, contrast enhancement, and binarization to highlight the outline of edge Mark point 300. This preprocessing also helps improve the accuracy of localization.

[0057] Since the edge Mark point 300 provided by the present invention has edge fault tolerance function, it can still be completed based on the remaining contour even when it is partially missing.

[0058] (3) After positioning is completed, the interconnect is laid on the center of the target pad 100 and the welding and curing process is performed to make the interconnect and the pad 100 form a metallurgical connection.

[0059] In some optional embodiments, the absolute value of the radial deviation between the center of the interconnect and the center of the pad 100 is less than or equal to 0.1 mm (e.g., 0.1 mm, 0.05 mm, or 0.01 mm, etc.). If the radial deviation between the center of the interconnect and the center of the pad 100 is greater than 0.1 mm, the effective contact length between the interconnect and the pad 100 will be less than 80% of the diameter of the pad 100, resulting in insufficient welding area, increased contact resistance, and decreased tensile strength. In severe cases, it may lead to poor soldering or desoldering, affecting the long-term reliability of the component. The contact length between the interconnect and the pad 100 is greater than or equal to 80% of the diameter of the pad 100, such as 80%, 85%, 90%, or 95% of the diameter of the pad 100, etc. If the contact length between the interconnect and the pad 100 is less than 80% of the diameter of the pad 100, the welding area is insufficient, resulting in increased contact resistance and decreased current transmission capacity; at the same time, the welding tensile strength is significantly reduced, making it prone to reliability failures such as solder strip desoldering and cracking under thermal cycling or mechanical loads, seriously affecting the long-term service life of the component.

[0060] In some alternative embodiments, the welding temperature can be 200℃~350℃, such as 200℃, 250℃, 300℃ or 350℃, or other values ​​within the range of 200℃~350℃. The welding time can be 1.0s~5.0s, such as 1s, 2s, 3s, 4s or 5s, or other values ​​within the range of 1.0s~5.0s.

[0061] If the welding temperature is below 200℃, the solder will not melt sufficiently, failing to form a continuous and uniform intermetallic compound layer. This results in insufficient welding pull, increased contact resistance, and a high risk of incomplete soldering. If the temperature is above 350℃, the silver layer on the solder pads will dissolve excessively, leading to an overly thick and brittle intermetallic compound layer. This makes the welding interface prone to microcracks, significantly reducing reliability. If the welding time is less than 1.0s, insufficient heat input and incomplete solder wetting result in a high porosity at the welding interface, making it impossible to achieve reliable pull. If the time is longer than 5.0s, excessive heat accumulation leads to excessive growth of the intermetallic compound, severely damaging the silver layer on the solder pads. Simultaneously, thermal stress may cause electrode detachment or microcracks in the silicon wafer.

[0062] By precisely positioning and coordinating the aforementioned welding conditions, a reliable metallurgical connection can be ensured between the interconnect and the pad 100, thereby effectively improving welding pull and meeting the long-term reliability requirements of the component. Furthermore, the positioning method provided by this invention can be integrated into existing production lines with low modification costs and has broad industrial application value.

[0063] Example 1 This embodiment provides a back-contact solar cell, which includes a silicon substrate 400, the silicon substrate 400 having a light-receiving surface and a back surface; the back surface is provided with a plurality of pads 100 arranged in an array, a plurality of fine grid lines 200 connecting the pads 100, and at least a pair of edge Mark points 300, and the long side of the back surface of the silicon substrate is provided with a pit with a depth of 8μm, and the edge Mark points are disposed in the pit.

[0064] The geometric center of the edge mark point 300 is 2.5 mm perpendicularly to the long side of the solar cell. The projection of the edge mark point 300 onto the solar cell is located in the area between the two rows of pads 100 adjacent to the edge mark point 300, and the distance between the projection of the edge mark point 300 onto the solar cell and the adjacent pad 100 is 0.2 mm. Along the direction perpendicular to the extension of the interconnect, two fine grid lines 200 adjacent to the edge mark point 300 are separated by the edge mark point 300, and the distance between the edge mark point 300 and the separation edge of the two fine grid lines 200 is 20 μm (the separation interval of the fine grid lines 200 is 1.2 times the length of the edge mark point 300). The shape of the edge mark point 300 is rectangular, that is, the edge mark point 300 has two first positioning reference edges perpendicular to the extension direction of the interconnect, and two second positioning reference edges parallel to the extension direction of the interconnect.

[0065] The method for preparing the Mark points in this back-contact solar cell includes: S1: Prepare pit 410.

[0066] Laser etching is performed at a predetermined location on the back side of the silicon substrate 400 to form a pit 410 as the underlying layer of the edge mark point 300. The laser etching process parameters include: wavelength of 532 nm, pulse width of 50 ns, and power density of 3.0 × 10⁻⁶. 5 W / cm 2 The depth of pit 410 is 8 μm.

[0067] S2: Fabrication of fine grids.

[0068] Fine gate lines 200 are fabricated using screen printing, and the fine gate lines 200 at the corresponding edge Mark points 300 are designed to be in a spaced-out state. Specifically, along the direction perpendicular to the extension of the interconnect, the spacing of the fine gate lines 200 is 1.3 times the length of the edge Mark points 300. S3: Prepare edge mark points and pads.

[0069] Electrode paste is simultaneously filled into the pit 410 and the pad 100 area, and then dried and sintered to obtain a paste layer 420 as the surface layer of the edge mark point 300; the bottom layer and the surface layer together form the edge mark point 300; wherein, the thickness of the paste layer 420 is 12μm.

[0070] Example 2 This embodiment provides a back-contact solar cell, which includes a silicon substrate 400, the silicon substrate 400 having a light-receiving surface and a back surface; the back surface is provided with a plurality of pads 100 arranged in an array, a plurality of fine grid lines 200 connecting the pads 100, and at least a pair of edge Mark points 300, and the long side of the back surface of the silicon substrate is provided with a pit with a depth of 5μm, and the edge Mark points are disposed in the pit.

[0071] The geometric center of the edge mark point 300 is 1 mm perpendicularly to the long side of the solar cell. The projection of the edge mark point 300 onto the solar cell is located in the area between the two rows of pads 100 adjacent to the edge mark point 300, and the distance between the projection of the edge mark point 300 onto the solar cell and the adjacent pad 100 is 0.25 mm. Along the direction perpendicular to the extension of the interconnect, two fine grid lines 200 adjacent to the edge mark point 300 are separated by the edge mark point 300, and the distance between the edge mark point 300 and the separation edge of the two fine grid lines 200 is 25 μm (the separation interval of the fine grid lines 200 is 1.2 times the length of the edge mark point 300). The shape of the edge mark point 300 is a regular hexagon, that is, the edge mark point 300 has two first positioning reference edges perpendicular to the extension direction of the interconnect, and four second positioning reference edges with non-right angles to the extension direction of the interconnect.

[0072] The method for preparing the Mark point in this back-contact solar cell includes the following steps: S1: Prepare pit 410.

[0073] Laser etching is performed at a predetermined location on the back side of the silicon substrate 400 to form a pit 410 as the underlying layer of the edge mark point 300. The laser etching process parameters include: wavelength of 355 nm, pulse width of 10 ns, and power density of 1.0 × 10⁻⁶. 5 W / cm 2 The depth of pit 410 is 5 μm.

[0074] S2: Fabrication of fine grids.

[0075] Fine gate lines 200 are fabricated using screen printing, and the fine gate lines 200 at the corresponding edge Mark points 300 are designed to be in a spaced-out state. Specifically, along the direction perpendicular to the extension of the interconnect, the spacing of the fine gate lines 200 is 1.2 times the length of the edge Mark points 300. S3: Prepare edge mark points and pads.

[0076] Electrode paste is simultaneously filled into the pit 410 and the pad 100 area, and then dried and sintered to form a paste layer 420 that serves as the edge mark point 300. The bottom layer and the top layer together form the edge mark point 300. The thickness of the paste layer 420 is 10 μm.

[0077] Example 3 This embodiment provides a back-contact solar cell, which includes a silicon substrate 400, the silicon substrate 400 having a light-receiving surface and a back surface; the back surface is provided with a plurality of pads 100 arranged in an array, a plurality of fine grid lines 200 connecting the pads 100, and at least a pair of edge Mark points 300, and the long side of the back surface of the silicon substrate is provided with a pit with a depth of 10μm, and the edge Mark points are disposed in the pit.

[0078] The geometric center of the edge mark point 300 is 4 mm perpendicularly to the long side of the solar cell. The projection of the edge mark point 300 onto the solar cell is located in the area between the two rows of pads 100 adjacent to the edge mark point 300, and the distance between the projection of the edge mark point 300 onto the solar cell and the adjacent pad 100 is 0.3 mm. Along the direction perpendicular to the extension of the interconnect, the two fine grid lines 200 adjacent to the edge mark point 300 are separated by the edge mark point 300, and the distance between the edge mark point 300 and the separation edge of the two fine grid lines 200 is 30 μm (the separation interval of the fine grid lines 200 is 1.5 times the length of the edge mark point 300). The shape of the edge mark point 300 is a right trapezoid, that is, the edge mark point 300 has two first positioning reference edges perpendicular to the extension direction of the interconnect, one second positioning reference edge parallel to the extension direction of the interconnect, and one second positioning reference edge with a non-right angle to the extension direction of the interconnect.

[0079] The method for preparing the Mark point in this back-contact solar cell includes the following steps: S1: Prepare pit 410.

[0080] Laser etching is performed at a predetermined location on the back side of the silicon substrate 400 to form a pit 410 as the bottom layer of the edge mark point 300. The laser etching process parameters include: wavelength of 1064 nm, pulse width of 100 ns, and power density of 5.0 × 10⁻⁶ ns. 5 W / cm2 The depth of pit 410 is 10 μm.

[0081] S2: Fabrication of fine grids.

[0082] Fine gate lines 200 are fabricated using screen printing, and the fine gate lines 200 at the corresponding edge Mark points 300 are designed to be in a spaced-out state. Specifically, along the direction perpendicular to the extension of the interconnect, the spacing of the fine gate lines 200 is 1.5 times the length of the edge Mark points 300. S3: Prepare edge mark points and pads.

[0083] Electrode paste is simultaneously filled into the pit 410 and the pad 100 area, and then dried and sintered to obtain a paste layer 420 as the surface layer of the edge mark point 300; the bottom layer and the surface layer together form the edge mark point 300; wherein, the thickness of the paste layer 420 is 15μm.

[0084] Application Example 1 This application example provides a method for positioning the solar cell in Example 1, including the following steps: (1) The solar cell is transported to a predetermined position, and a fixed-focus vision camera located on the side of the solar cell transport track acquires an image containing the long side area of ​​the solar cell and the edge Mark point 300.

[0085] During data acquisition, edge Mark point 300 is located in the center of the field of view, and the actual position of edge Mark point 300 deviates from the center of the field of view by 0.05mm.

[0086] (2) After preprocessing the acquired image, the first positioning reference edge of edge Mark point 300 is first identified to obtain the Y-direction position and rotation angle, and then the second positioning reference edge of edge Mark point 300 is identified to obtain the X-direction offset compensation amount. Among them, the preprocessing includes filtering and denoising, contrast enhancement and binarization of the acquired image to highlight the contour of edge Mark point 300.

[0087] (3) After positioning is completed, the solder strip is precisely laid on the center of the target pad 100, and the welding curing process is performed to make the solder strip and the pad 100 form a metallurgical connection.

[0088] The radial deviation between the center of the solder strip and the center of the pad 100 is 0.05 mm. The contact length between the solder strip and the pad 100 is 80% of the diameter of the pad 100. The soldering temperature is 300℃ and the soldering time is 3.0 s.

[0089] Application Example 2 This application example provides a method for positioning the solar cell in Example 2, including the following steps: (1) The solar cell is transported to a predetermined position, and a fixed-focus vision camera located on the side of the solar cell transport track acquires an image containing the long side area of ​​the solar cell and the edge Mark point 300.

[0090] During data acquisition, edge Mark point 300 is located in the center of the field of view, and the actual position of edge Mark point 300 deviates from the center of the field of view by 0.1mm.

[0091] (2) After preprocessing the acquired image, the first positioning reference edge of edge Mark point 300 is first identified to obtain the Y-direction position and rotation angle, and then the second positioning reference edge of edge Mark point 300 is identified to obtain the X-direction offset compensation amount. Among them, the preprocessing includes filtering and denoising, contrast enhancement and binarization of the acquired image to highlight the contour of edge Mark point 300.

[0092] (3) After positioning is completed, the solder strip is precisely laid on the center of the target pad 100, and the welding curing process is performed to make the solder strip and the pad 100 form a metallurgical connection.

[0093] The radial deviation between the center of the solder strip and the center of the pad 100 is 0.05 mm. The contact length between the solder strip and the pad 100 is 85% of the diameter of the pad 100. The soldering temperature is 200℃ and the soldering time is 5.0 s.

[0094] Application Example 3 This application example provides a positioning method for preparing the solar cell in Example 3, including the following steps: (1) The solar cell is transported to a predetermined position, and a fixed-focus vision camera located on the side of the solar cell transport track acquires an image containing the long side area of ​​the solar cell and the edge Mark point 300.

[0095] During data acquisition, edge Mark point 300 is located in the center of the field of view, and the actual position of edge Mark point 300 deviates from the center of the field of view by 0.5mm.

[0096] (2) After preprocessing the acquired image, the first positioning reference edge of edge Mark point 300 is first identified to obtain the Y-direction position and rotation angle, and then the second positioning reference edge of edge Mark point 300 is identified to obtain the X-direction offset compensation amount. Among them, the preprocessing includes filtering and denoising, contrast enhancement and binarization of the acquired image to highlight the contour of edge Mark point 300.

[0097] (3) After positioning is completed, the solder strip is precisely laid on the center of the target pad 100, and the welding curing process is performed to make the solder strip and the pad 100 form a metallurgical connection.

[0098] The radial deviation between the center of the solder strip and the center of the pad 100 is 0.1 mm. The contact length between the solder strip and the pad 100 is 90% of the diameter of the pad 100. The soldering temperature is 350℃ and the soldering time is 1.0 s.

[0099] Comparative Example 1 The difference between this comparative example and application example 1 is that in the back-contact solar cell, the geometric center of the edge Mark point 300 is 0.5mm away from the long edge of the cell.

[0100] Comparative Example 2 The difference between this comparative example and application example 1 is that in the back-contact solar cell, the geometric center of the edge Mark point 300 is 4.5mm away from the long side of the cell.

[0101] Comparative Example 3 The difference between this comparative example and application example 1 is that the distance between the edge Mark point 300 and the partition edge of the two fine grid lines 200 is 15μm.

[0102] Comparative Example 4 The difference between this comparative example and application example 1 is that the distance between edge Mark point 300 and the isolation side edge of one fine gate line 200 is 15 μm, and the distance between it and the isolation side edge of another fine gate line 200 is 20 μm.

[0103] Comparative Example 5 The difference between this comparative example and application example 1 is that the distance between the projection of the edge Mark point 300 on the cell and its adjacent pad 100 is 0.1 mm.

[0104] Comparative Example 6 The difference between this comparative example and application example 1 is that the thickness of the slurry layer 420 is equal to the depth of the pit 410.

[0105] Comparative Example 7 The difference between this comparative example and application example 1 is that the welding temperature is 180℃.

[0106] Comparative Example 8 The difference between this comparative example and application example 1 is that the welding temperature is 380℃.

[0107] Comparative Example 9 The difference between this comparative example and application example 1 is that the welding time is 0.5s.

[0108] Comparative Example 10 The difference between this comparative example and application example 1 is that the welding time is 6 seconds.

[0109] Test case The success rate of identification and the welding pull force of back-contact solar cells in Application Examples 1-3 and Comparative Examples 1-10 were compared.

[0110] The method for testing the recognition success rate is as follows: Ten back-contact battery samples were subjected to a wire-wound positioning test under the same conditions. The parameters of the side fixed-focus camera were fixed, and the visual recognition success rate and positioning time of each sample were recorded. The average value of all test samples was taken as the final test result.

[0111] The welding tensile test method is as follows: Ten back contact battery samples are subjected to a universal tensile tester, and the welding strip is pulled vertically at a speed of 50 mm / min. The maximum tensile force when the solder pad is detached is recorded, and the average value of the ten samples is taken as the welding tensile force.

[0112] The test results are shown in Table 1.

[0113] Table 1 Test Results

[0114] As can be seen from Table 1, Application Examples 1-3 of the present invention are significantly better than the comparative examples in terms of recognition success rate (greater than or equal to 98%), positioning time (less than or equal to 158ms), and welding pull force (greater than or equal to 1.35N / mm). This proves that the position constraint, preparation process, and positioning method proposed in the present invention can achieve precise positioning and enable excellent welding pull force between the solder strip and the solder pad, thereby improving the product qualification rate.

[0115] As can be seen from the comparison between Application Example 1 and Comparative Examples 1 and 2, if the geometric center of the edge Mark point 300 in the back-contact solar cell is too small and the vertical distance between it and the long side of the cell is too small, the edge Mark point 300 will be easily affected by edge chipping and chamfer reflection, and the recognition success rate will drop to 82%. If the geometric center of the edge Mark point 300 in the back-contact solar cell is too large and the vertical distance between it and the long side of the cell is too large, the edge Mark point 300 will exceed the depth of field range of the side fixed-focus camera, and the image will be blurred, resulting in a recognition success rate of only 88%.

[0116] As can be seen from the comparison of Application Example 1 and Comparative Examples 3-4, if the distance between the edge Mark point 300 and the edge of the two fine grid lines is <20μm, and the distance between the edge Mark point 300 and the fine grid break is insufficient, on the one hand, the leakage current may increase due to damage to the fine grid caused by the laser heat-affected zone, and on the other hand, the residual reflection of the fine grid will interfere with visual recognition, reducing the recognition success rate to 91%~93% and the welding pull force to 1.25N / mm~1.28N / mm.

[0117] As can be seen from the comparison between Application Example 1 and Comparative Example 5, if the distance between the projection of the edge Mark point 300 on the cell and the adjacent pad 100 is less than 0.2mm, the reflection of the pad 100 will enter the recognition area of ​​the edge Mark point 300, the background noise of the image will increase, the visual recognition success rate will drop to 90%, the average positioning time will increase to 165ms, and the welding pull force will drop to 1.20N / mm due to the decrease in positioning accuracy.

[0118] As can be seen from the comparison between Application Example 1 and Comparative Example 6, if the thickness of the slurry layer 420 is not greater than the depth of the pit 410, the slurry will not be able to completely fill the pit 410 after sintering, forming a recessed structure. This recess is prone to trapping dust and the edges produce abnormal reflective interference, which reduces the visual recognition success rate to 94% and the welding tensile force to 1.30 N / mm.

[0119] As can be seen from the comparison between Application Example 1 and Comparative Examples 7-8, if the welding temperature is too low, the solder will not melt sufficiently, and a continuous and uniform intermetallic compound layer cannot be formed. The welding pull force is only 0.95 N / mm, and it is easy to cause cold solder joints. If the welding temperature is too high, the silver layer on the pad will be excessively dissolved, the intermetallic compound layer will be too thick and brittle, the welding pull force will be only 0.88 N / mm, and microcracks will easily form at the interface.

[0120] As can be seen from the comparison between Application Example 1 and Comparative Examples 9-10, if the welding time is too short, it will lead to insufficient heat input, incomplete solder wetting, high porosity at the welding interface, and a welding tensile strength of only 0.82 N / mm; if the welding time is too long, it will lead to excessive heat accumulation, excessive growth of intermetallic compounds and increased brittleness, severe damage to the silver layer of the solder pad, and a welding tensile strength of only 0.91 N / mm.

[0121] In summary, the present invention can achieve precise positioning by setting specific edge Mark points 300; at the same time, with specific welding conditions, it can achieve high-precision positioning while enabling the interconnect and the pad 100 to form a more complete metallurgical bond, increasing the tension between the interconnect and the pad 100, thereby improving the product qualification rate.

[0122] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A back-contact solar cell, characterized in that, The device includes a silicon substrate having a light-receiving surface and a back surface; the back surface is provided with a plurality of pads arranged in an array, a plurality of fine grid lines connecting the pads, and at least a pair of edge mark points, the edge mark points being disposed near the side of the cell perpendicular to the extension direction of the interconnect. The vertical distance from the geometric center of the edge mark point to the side is 1.0mm to 4.0mm; the projection of the edge mark point on the cell is located in the area between two rows of pads adjacent to the edge mark point; along a direction perpendicular to the extension direction of the interconnect, two fine grid lines adjacent to the edge mark point are separated by the edge mark point, and the distance between the edge mark point and the edge of the separation side of the two fine grid lines is greater than or equal to 20μm; The back side of the silicon substrate near the side has a recess that serves as the bottom layer for the edge mark point, and the edge mark point is disposed in the recess.

2. The back-contact solar cell according to claim 1, characterized in that, The depth of the pit is 5μm~10μm.

3. The back-contact solar cell according to claim 1 or 2, characterized in that, The edge Mark point also has at least one of the following characteristics: Feature 1: The distance between the projection of the edge Mark point on the solar cell and any row of pads is greater than or equal to 0.2 mm; Feature 2: Along a direction perpendicular to the extension direction of the interconnect, the spacing between the fine grid lines is 1.2 to 1.5 times the length of the edge Mark point; Feature 3: The graphic of the edge Mark point has at least one first positioning reference edge and at least one second positioning reference edge; wherein, the first positioning reference edge is perpendicular to the extension direction of the interconnect, and the second positioning reference edge is parallel to the extension direction of the interconnect or has a non-right angle with the extension direction of the interconnect.

4. A method for preparing a Mark point in a back-contact solar cell as described in any one of claims 1 to 3, characterized in that, include: Preparation of pits: Etching at a predetermined position on the back side of the silicon substrate to form pits that serve as the bottom layer for the edge Mark points; Fabrication of fine gates: The fine gate lines are fabricated, and the fine gate lines at the corresponding edge Mark point positions are designed to be in a closed state; Preparation of edge mark points and pads: Electrode paste is filled into the pits and the pad areas, and after molding, a paste layer is obtained as the surface layer of the edge mark points; the bottom layer and the surface layer together form the edge mark points; The thickness of the slurry layer is greater than the depth of the pit.

5. The preparation method according to claim 4, characterized in that, The depth of the pit is 5μm~10μm, and the depth of the slurry layer is 10μm~15μm.

6. The preparation method according to claim 4, characterized in that, The etching is performed using laser etching; the process parameters for the laser etching include: wavelength of 355nm~1064nm, pulse width of 10ns~100ns, and power density of 1.0×10⁻⁶. 5 W / cm 2 ~5.0×10 5 W / cm 2 .

7. The preparation method according to claim 4, characterized in that, Along the extension direction perpendicular to the interconnect, the spacing between the fine gate lines is 1.2 to 1.5 times the length of the edge mark point.

8. A positioning method for preparing a back-contact solar cell as described in any one of claims 1 to 3, characterized in that, Includes the following steps: The solar cell is transported to a predetermined position, and an image is acquired including the side area of ​​the solar cell perpendicular to the extension direction of the interconnect and the edge mark points; After preprocessing the acquired image, the first positioning reference edge of the edge Mark point is first identified to obtain the Y-direction position and rotation angle, and then the second positioning reference edge of the edge Mark point is identified to obtain the X-direction offset compensation amount. After positioning is complete, the interconnect is laid in the center of the target pad, and a soldering and curing process is performed to form a metallurgical connection between the interconnect and the pad.

9. The positioning method according to claim 8, characterized in that, The positioning method includes at least one of the following features: Feature 1: During the acquisition, the edge Mark point is located in the center region of the field of view; Feature 2: The preprocessing includes at least one of filtering and denoising, contrast enhancement, and binarization of the acquired image; Feature 3: The absolute value of the radial deviation between the center of the interconnect and the center of the pad is less than or equal to 0.1 mm; Feature 4: The contact length between the interconnect and the pad is greater than or equal to 80% of the pad diameter.

10. The positioning method according to claim 8, characterized in that, The welding temperature is 200℃~350℃, and the welding time is 1.0s~5.0s.

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