Laser-assisted sintering method of TOPCon solar cell

Abstract

The invention provides a laser-assisted sintering method of a TOPCon solar cell, and relates to the technical field of TOPCon solar cells. The laser-assisted sintering method comprises the following steps that a battery piece subjected to light injection treatment is placed on an operation table, external voltage is applied to the battery piece to ensure that the front face of the battery piece is a negative electrode power source, and a laser is adopted to only conduct laser scanning treatment on a grid line area of the battery piece. The laser scanning treatment comprises the following specific steps of: scanning a laser beam along one side of the grid line, then scanning the end part of the grid line for the second time in an S shape along the other side of the grid line, and covering the position of the grid line by a light spot during each scanning; and all the grid lines are scanned by the laser. The laser-assisted sintering method has the advantages that the process time is shortened, the energy is finely controlled, and the conversion efficiency of the battery piece is improved.

Description

Technical Field

[0001] The present application relates to the technical field of TOPCon solar cells, and in particular to a laser-assisted sintering method for TOPCon solar cells. Background Art

[0002] TOPCon solar cells are a type of tunnel oxide passivated contact solar cell technology based on the principle of selective carriers. Its cell structure is an N-type silicon substrate, with an ultra-thin layer of silicon oxide prepared on the back of the cell, and then a thin layer of doped silicon is deposited. The two together form a passivated contact structure, effectively reducing surface recombination and metal contact recombination, thereby improving energy conversion efficiency.

[0003] Solar cells are electronic products with high precision and high cleanliness. They are one of the components of solar cell modules. Their main function is to convert light energy into electrical energy, thereby realizing solar power generation. Since solar energy is a renewable and clean energy, the market demand for solar cells is increasing, and higher requirements are placed on the quality and speed of solar cell production and processing.

[0004] Laser assisted sintering (LECO) is a process that utilizes the high energy density characteristics of lasers. It excites charge carriers by irradiating the cell with lasers, and at the same time applies high voltage to generate local current, thereby inducing mutual diffusion of silver paste and silicon, significantly reducing the contact resistance between metal and semiconductor. Therefore, the laser-assisted sintering process is currently introduced into the cell manufacturing process. It can reduce the contact resistivity between the grid line and the substrate of the solar cell by setting an external electric field, thereby achieving a better ohmic contact effect, and then the solar cell can have a higher photoelectric conversion efficiency. The current laser-assisted method uses an infrared continuous laser to scan the entire surface of the cell while combining it with a load voltage to complete the formation of ohmic contact. However, the use of infrared continuous laser to process the entire surface of the cell causes great damage to the non-grid line area, destroys the passivation layer, and limits the space for laser energy adjustment. Summary of the invention

[0005] The purpose of the present application is to provide a laser-assisted sintering method for TOPCon solar cells, which has the advantages of shortening process time, finely controlling energy and improving cell conversion efficiency.

[0006] In order to solve the above technical problems, the technical solution adopted in this application is:

[0007] The present application provides a laser-assisted sintering method for TOPCon solar cells, the steps of which are: placing a cell after light injection treatment on an operating table, applying an external voltage to the cell to ensure that the front of the cell is a negative power supply, and using a laser to perform laser scanning processing only on the grid line area of ​​the cell.

[0008] The specific steps of the laser scanning process are: scanning the laser beam along one side of the grid line, and then scanning the other side of the grid line in an "S" shape when scanning to the end of the grid line, and the light spot covers the grid line position each time; in this way, all the grid lines are scanned by the laser.

[0009] Compared with the prior art, the embodiments of the present application have at least the following advantages or beneficial effects:

[0010] 1. This application uses green visible lasers visible to the naked eye instead of traditional infrared lasers for laser-assisted sintering. The visible laser beam is easy to identify and facilitates accurate debugging of the scanning area on site. This application only scans the area around the grid lines, and does not scan the area without grid lines, which reduces the scanning time and shortens the process time. In addition, the laser does not scan the large area of ​​silicon nitride film layer not covered by the grid lines, and the laser does not damage the passivation layer.

[0011] 2. The present application uses two laser processes for the same grid line, which can control the energy more precisely, making the microscopic cross-linking structure at the interface between the silver grid line and the silicon substrate more uniform, forming a better ohmic contact. The present application uses an S-shaped path to scan the grid line area to increase the continuity of the laser and facilitate operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0013] Figure 1 Schematic diagram of a single spot and a continuous spot scanned by a pulsed green laser in an embodiment of the present application;

[0014] Figure 2 This is a schematic diagram of a laser beam scanning a single grid line twice in an embodiment of the present application;

[0015] Figure 3 A schematic diagram of a scanning path of a laser beam on multiple grid lines according to an embodiment of the present application;

[0016] Figure 4 Schematic diagram of the scanning path of the conventional group of laser beams in the experimental example of this application. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0018] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to specific embodiments.

[0019] A laser-assisted sintering method for TOPCon solar cells comprises the following steps: placing a cell after light injection treatment on an operating table, applying an external voltage to the cell to ensure that the front of the cell is a negative power supply, and using a laser to perform laser scanning on only the grid line area of ​​the cell.

[0020] The specific steps of the laser scanning process are: scanning the laser beam along one side of the grid line, and then scanning the other side of the grid line in an "S" shape when scanning to the end of the grid line. The light spot covers the grid line position each time scanning; in this way, all the grid lines are scanned by the laser.

[0021] In some embodiments of the present application, the laser is a visible light laser.

[0022] In some embodiments of the present application, the laser is a pulsed green light laser.

[0023] In some embodiments of the present application, the energy of the laser scanning is 20-80w.

[0024] In some embodiments of the present application, the light output spot of the laser is a square spot of 70-100 μm.

[0025] In some embodiments of the present application, the external voltage is 12-17V.

[0026] In some embodiments of the present application, the laser beam is intermittently scanned, the light emission frequency of the laser beam is 10-50KHz, and the moving speed of the laser beam is 150-350m / s.

[0027] The features and performance of the present application are further described in detail below in conjunction with the embodiments.

[0028] Example 1

[0029] This embodiment provides a laser-assisted sintering method for a TOPCon solar cell, and the detailed process steps are as follows:

[0030] The cell that has been screen printed, sintered and light injected is placed on the workbench, and a pulsed green laser is used as the energy output. Only the grid line area of ​​the cell is laser scanned: the laser energy is 50W; the light spot size is 80μm square spot, the laser beam is intermittently scanned, the laser beam frequency is 20KHz, and the moving speed is 250m / s. The light frequency is adjusted so that each square spot is seamlessly connected at the edge. The single spot and the continuous spot are as follows: Figure 1 A 15V external voltage is applied to the cell to ensure that the front of the cell is a negative power supply. At the same time, the laser beam scans along one side of the grid line, and then scans along the other side of the grid line. Each time the light spot covers the grid line position, the schematic diagram of the two scans of a single grid line is shown in FIG. Figure 2 As shown, Figure 2 The middle gray is the grid line, and the green is the laser area. The entire grid line is scanned in a serpentine ("S" shape) shape. The scanning route is as follows: Figure 3 As shown, Figure 3 The medium grey is the grid line and the blue marker line is the laser scanning path.

[0031] Example 2

[0032] This embodiment provides a laser-assisted sintering method for a TOPCon solar cell, and the detailed process steps are as follows:

[0033] The cell that has been screen printed, sintered and light injected is placed on the workbench, and a pulsed green laser is used as the energy output. Only the grid line area of ​​the cell is laser scanned: the laser energy is 25W; the light spot size is 70μm square spot, the laser beam is intermittent scanning, the laser beam frequency is 25KHz, the moving speed is 200m / s, and the light frequency is adjusted to make each square spot seamlessly connected at the edge. A 16V external voltage is added to the cell to ensure that the front of the cell is a negative power supply. At the same time, the laser beam scans along one side of the grid line, and then scans along the other side of the grid line. During each scan, the light spot covers the grid line position; the entire grid line is scanned in a serpentine ("S" shape) afterwards.

[0034] Example 3

[0035] This embodiment provides a laser-assisted sintering method for a TOPCon solar cell, and the detailed process steps are as follows:

[0036] The cell that has been screen printed, sintered and light injected is placed on the workbench, and a pulsed green laser is used as the energy output. Only the grid line area of ​​the cell is laser scanned: the laser energy is 60W; the light spot size is 80μm square spot, the laser beam is intermittent scanning, the laser beam frequency is 20KHz, the moving speed is 250m / s, and the light frequency is adjusted to make each square spot seamlessly connected at the edge. A 16V external voltage is added to the cell to ensure that the front of the cell is a negative power supply. At the same time, the laser beam scans along one side of the grid line, and then scans along the other side of the grid line. During each scan, the light spot covers the grid line position; the entire grid line is scanned in a serpentine ("S" shape) afterwards.

[0037] Example 4

[0038] This embodiment provides a laser-assisted sintering method for a TOPCon solar cell, and the detailed process steps are as follows:

[0039] The cell that has been screen printed, sintered and light injected is placed on the workbench, and a pulsed green laser is used as the energy output. Only the grid line area of ​​the cell is laser scanned: the laser energy is 80W; the light spot size is 80μm square spot, the laser beam is intermittent scanning, the laser beam frequency is 20KHz, the moving speed is 250m / s, and the light frequency is adjusted to make each square spot seamlessly connected at the edge. A 17V external voltage is added to the cell to ensure that the front of the cell is a negative power supply. At the same time, the laser beam scans along one side of the grid line, and then scans along the other side of the grid line. During each scan, the light spot covers the grid line position; the entire grid line is scanned in a serpentine ("S" shape) afterwards.

[0040] Example 5

[0041] This embodiment provides a laser-assisted sintering method for a TOPCon solar cell, and the detailed process steps are as follows:

[0042] The cell that has been screen printed, sintered and light injected is placed on the workbench, and a pulsed green laser is used as the energy output. Only the grid line area of ​​the cell is laser scanned: the laser energy is 70W; the light spot size is 100μm square spot, the laser beam is intermittent scanning, the laser beam frequency is 30KHz, the moving speed is 300m / s, and the light frequency is adjusted to make each square spot seamlessly connected at the edge. A 15V external voltage is added to the cell to ensure that the front of the cell is a negative power supply. At the same time, the laser beam scans along one side of the grid line, and then scans along the other side of the grid line. During each scan, the light spot covers the grid line position; the entire grid line is scanned in a serpentine ("S" shape) afterwards.

[0043] Example 6

[0044] This embodiment provides a laser-assisted sintering method for a TOPCon solar cell, and the detailed process steps are as follows:

[0045] The cell that has been screen printed, sintered and light injected is placed on the workbench, and a pulsed green laser is used as the energy output. Only the grid line area of ​​the cell is laser scanned: the laser energy is 80W; the light spot size is 100μm square spot, the laser beam is intermittent scanning, the laser beam frequency is 30KHz, the moving speed is 300m / s, and the light frequency is adjusted to make each square spot seamlessly connected at the edge. A 12V external voltage is added to the cell to ensure that the front of the cell is a negative power supply. At the same time, the laser beam scans along one side of the grid line, and then scans along the other side of the grid line. During each scan, the light spot covers the grid line position; the entire grid line is scanned in a serpentine ("S" shape) afterwards.

[0046] Example 7

[0047] This embodiment provides a laser-assisted sintering method for a TOPCon solar cell, and the detailed process steps are as follows:

[0048] The cell that has been screen printed, sintered and light injected is placed on the workbench, and a pulsed green laser is used as the energy output. Only the grid line area of ​​the cell is laser scanned: the laser energy is 40W; the light spot size is 70μm square spot, the laser beam is intermittent scanning, the laser beam frequency is 15KHz, the moving speed is 180m / s, and the light frequency is adjusted to make each square spot seamlessly connected at the edge. A 15V external voltage is added to the cell to ensure that the front of the cell is a negative power supply. At the same time, the laser beam scans along one side of the grid line, and then scans along the other side of the grid line. During each scan, the light spot covers the grid line position; the entire grid line is scanned in a serpentine ("S" shape) afterwards.

[0049] Example 8

[0050] This embodiment provides a laser-assisted sintering method for a TOPCon solar cell, and the detailed process steps are as follows:

[0051] The cell that has been screen printed, sintered and light injected is placed on the workbench, and a pulsed green laser is used as the energy output. Only the grid line area of ​​the cell is laser scanned: the laser energy is 40W; the light spot size is 80μm square spot, the laser beam is intermittent scanning, the laser beam frequency is 20KHz, the moving speed is 250m / s, and the light frequency is adjusted to make each square spot seamlessly connected at the edge. A 17V external voltage is added to the cell to ensure that the front of the cell is a negative power supply. At the same time, the laser beam scans along one side of the grid line, and then scans along the other side of the grid line. During each scan, the light spot covers the grid line position; the entire grid line is scanned in a serpentine ("S" shape) afterwards.

[0052] Experimental example

[0053] This application experimentally compares the traditional infrared laser continuous sintering with the laser sintering method of Example 1 of this application, wherein the infrared laser continuous sintering process specifically uses 30W laser energy, a spot width of 150μm, an external voltage of 15V, and a moving speed of 600m / s. In addition, the traditional infrared laser group also performs serpentine scanning, but the difference is that the traditional group covers the entire cell in a serpentine path, including the gate line and non-gate line areas. In order to prevent large-scale damage to the passivation layer on the surface of the cell, the laser energy is relatively small, and the gate line area is only covered once. Its scanning path is as follows: Figure 4 shown.

[0054] The experimental group (process of Example 1) and the traditional group (infrared laser continuous sintering process) have the same pre-process (screen printing, sintering and light injection) and post-process (sorting test and packaging) for the cells. The prepared cells were tested, and the results are shown in Table 1.

[0055] Table 1

[0056]

[0057] As can be seen from Table 1, compared with the traditional group, the conversion efficiency Eta of the experimental group increased by 0.046, which is a significant improvement. The reason is that the infrared laser itself is invisible to the naked eye, and it is difficult to adjust the accuracy. It only performs rough scanning and is fast. It uses a large light plate with fixed energy to scan the entire surface of the battery in a serpentine path. In order to avoid causing large-scale damage to the passivation layer on the surface of the battery, the energy is usually relatively small (20-40W). After the experimental group uses green light, it can control the laser energy more accurately and increase the energy limit (up to 80W). Under high-energy conditions, it can open up more effective contact areas and form more local sub-micron junction contacts, greatly increasing the contact area, improving the contact ability, and thus improving FF.

[0058] In summary, the laser-assisted sintering method of a TOPCon solar cell in the embodiment of the present application has the following advantages: 1. The present application adopts green visible laser visible to the naked eye instead of the traditional infrared laser for laser-assisted sintering, and the visible laser beam facilitates the precise debugging of the scanning area on site. The present application only scans the area around the grid lines, and does not scan the area without grid lines, thereby reducing the scanning time and shortening the process time. In addition, the laser does not scan the large area of ​​silicon nitride film layer not covered by the grid lines, and the laser does not damage the passivation layer.

[0059] 2. The present application uses two laser processes for the same grid line, which can control the energy more precisely, making the microscopic cross-linking structure at the interface between the silver grid line and the silicon substrate more uniform, forming a better ohmic contact. The present application uses an S-shaped path to scan the grid line area to increase the continuity of the laser and facilitate operation.

[0060] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present application.

Claims

1. A laser-assisted sintering method for TOPCon solar cells, characterized in that: The method comprises the following steps: placing the cell after light injection treatment on an operating table, applying an external voltage to the cell to ensure that the front of the cell is a negative power supply, and using a laser to perform laser scanning treatment only on the grid line area of ​​the cell; The specific steps of the laser scanning process are: scanning the laser beam along one side of the grid line, and then scanning the other side of the grid line in an "S" shape when scanning to the end of the grid line. The light spot covers the grid line position each time scanning; in this way, all the grid lines are scanned by the laser.

2. The laser-assisted sintering method of a TOPCon solar cell according to claim 1, characterized in that: The laser is a visible light laser.

3. The laser-assisted sintering method of a TOPCon solar cell according to claim 2, characterized in that: The laser is a pulsed green laser.

4. The laser-assisted sintering method of a TOPCon solar cell according to claim 1, characterized in that: The energy of the laser scanning is 20-80w.

5. The laser-assisted sintering method of a TOPCon solar cell according to claim 1, characterized in that: The light output spot of the laser is a square spot of 70-100 μm.

6. The laser-assisted sintering method of a TOPCon solar cell according to claim 1, characterized in that: The external voltage is 12-17V.

7. The laser-assisted sintering method of a TOPCon solar cell according to claim 5, characterized in that: The laser beam is intermittently scanned, the light emission frequency of the laser beam is 10-50KHz, and the moving speed of the laser beam is 150-350m / s.

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