Secondary laser sintering method for battery piece

Abstract

The invention discloses a secondary laser sintering method for a battery piece, and belongs to the field of solar batteries. The secondary laser sintering method for the battery piece comprises the following steps: performing primary laser sintering on the battery piece at a first station, namely applying a first reverse voltage to the battery piece at the first station and applying first laser scanning treatment; and carrying out second laser sintering on the battery piece at a second station, wherein the second laser sintering comprises the steps of applying second reverse voltage to the battery piece at the second station and applying second laser scanning treatment. According to the invention, the laser enhancement efficiency-improving potential of the cell can be explored to a greater extent through secondary laser sintering, so that the solar power generation efficiency and yield of the cell are improved, and the method has the advantages of low cost and high compatibility.

Description

Technical Field

[0001] The embodiments of this application relate to the field of photovoltaic cell manufacturing technology, and more specifically, this application relates to a method for secondary laser sintering of solar cells. Background Technology

[0002] Laser-enhanced contact optimization (LECO) technology was first used by Cell Engineering GmbH in 2016 to repair under-sintered PERC cells and improve the contact between the metal electrodes and the silicon wafer in solar cells. This process occurs after the sintering process of screen-printed solar cells. After LECO treatment, the contact resistance of the solar cells is significantly reduced, and ohmic contacts can be formed even on lightly doped emitters.

[0003] Existing laser-enhanced contact optimization technology has limited effect on improving the power generation efficiency of solar cells and cannot fully optimize contact resistance. Summary of the Invention

[0004] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application provides a method for secondary laser sintering of solar cells, thereby solving the problem that existing processes cannot sufficiently improve the conversion efficiency of solar cells, without requiring changes to existing laser equipment or the configuration of new laser equipment.

[0005] To solve the above problems, the technical solution adopted in this application is as follows:

[0006] On one hand, this invention discloses a method for secondary laser sintering of solar cells, the method comprising:

[0007] Transport the battery cells to the first workstation;

[0008] The first laser sintering is performed on the solar cell at the first station. The first laser sintering includes applying a first reverse voltage to the solar cell located at the first station and applying a first laser sweeping process.

[0009] Transport the battery cells to the second workstation;

[0010] The second laser sintering is performed on the solar cell at the second station. The second laser sintering includes applying a second reverse voltage to the solar cell located at the second station and applying a second laser sweeping process.

[0011] The first reverse voltage is lower than the second reverse voltage.

[0012] The first reverse voltage used in the first laser sintering is lower than the second reverse voltage used in the second laser sintering. The first laser sintering can be normal or slightly under-sintered. The second laser sintering repairs the imaging defects of the first laser sintering and enhances the contact of the metal electrodes to improve filling. The second laser sintering can further explore the laser enhancement and efficiency improvement potential of the solar cell, thereby improving the solar power generation efficiency and yield of the solar cell. It also has the advantages of low cost and high compatibility.

[0013] In one embodiment, both the first laser sweeping process and the second laser sweeping process include: using multiple laser spots to perform laser sintering on the solar cell to which a first reverse voltage or a second reverse voltage is applied in a surface sweeping or line sweeping manner, wherein the number of laser spots is at least one.

[0014] Multiple light spots can be used to achieve surface scanning or line scanning. The more light spots there are, the larger the area that can be sintered at the same time, and the higher the sintering efficiency.

[0015] In one embodiment, the face scanning method includes:

[0016] Multiple light spots are moved side by side along a direction perpendicular to the fine grid lines of the solar cell, sweeping from the first side of the solar cell to the second side opposite to the first side.

[0017] The area scanning method has good compatibility, does not require consideration of the grid line distance of the solar cells themselves, does not require precise alignment, and can save scanning time and increase production capacity by scanning with multiple light spots.

[0018] Furthermore, the methods of surface scanning include:

[0019] After sweeping the solar cell once with multiple light spots arranged side by side in a direction perpendicular to the fine grid lines, the light spots move a preset distance along the length of the fine grid lines and then sweep the solar cell again in the opposite direction.

[0020] When a single area scan cannot cover the entire electrode area of ​​a solar cell, a bow-shaped, back-and-forth area scan path can minimize the overall scan path across the entire solar cell, thereby further saving scan time and increasing production capacity.

[0021] In one embodiment, the line scanning method includes:

[0022] Each of the multiple light spots is positioned on a fine grating line, and the light is swept from one end of the grating line to the other.

[0023] By using multiple light spots to perform line scanning on multiple fine grid lines, the process accuracy is high. The scanning time is the original time divided by the number of light spots. The more light spots, the shorter the scanning time.

[0024] Furthermore, the center-to-center distance between two adjacent light spots is equal to the distance between two adjacent fine grating lines.

[0025] The spacing between multiple light spots is set to be the same as the spacing between the fine grid lines, thus avoiding the trouble of aligning each light spot before each sweep.

[0026] In one embodiment, the shapes of the multiple light spots processed by the first laser sweep are different from those of the multiple light spots processed by the second laser sweep.

[0027] In one embodiment, the laser used in the secondary laser sintering has a wavelength of 200-1342nm, a power of 5-1000W, a sweep speed of 30-120m / s, a spot size of 30-1500μm, and a spot spacing of 1-2500μm.

[0028] By adjusting the parameters of secondary laser sintering, the laser enhancement effect of the solar cells can be improved, thereby increasing the power generation efficiency and yield of solar energy.

[0029] In one embodiment, a laser with a DOE lens is used to generate multiple light spots; or, at least two lasers are used to generate multiple light spots.

[0030] The more light spots there are, the faster the processing efficiency. The uniformity between multiple light spots obtained by the polarization reflection method of DOE lens is good, avoiding different laser sintering effects between different light spots.

[0031] In one embodiment, after sweeping multiple fine grid lines once, the system moves to one end of an adjacent unswept fine grid line and performs the next sweep until all fine grid lines are swept.

[0032] By using a bow-shaped reciprocating linear scanning path, the overall scanning path for the entire surface of the battery cell can be minimized, thereby further saving scanning time and increasing production capacity.

[0033] In another aspect, the present invention discloses a method for secondary laser sintering of battery cells, the method comprising:

[0034] Transport the battery cells to the first workstation;

[0035] The first laser sintering of the solar cell is performed at the first station. The first laser sintering includes applying a first reverse voltage to the solar cell located at the first station and applying a first laser sweeping process. The first laser sweeping process includes sweeping the solar cell with a first laser beam.

[0036] Transport the battery cells to the second workstation;

[0037] The second laser sintering is performed on the solar cell at the second station. The second laser sintering includes applying a second reverse voltage to the solar cell located at the second station and applying a second laser sweeping process. The second laser sweeping process includes sweeping the solar cell with a second laser beam.

[0038] The shape of the light spot formed by the first laser beam is different from the shape of the light spot formed by the second laser beam.

[0039] By using different spot shapes, the sweeping paths of the first and second laser sintering processes can be different. Through secondary laser sintering, the laser enhancement potential of the solar cell can be further explored, thereby improving the solar power generation efficiency and yield of the solar cell. It also has the advantages of low cost and high compatibility.

[0040] In one embodiment, both the first laser sweeping process and the second laser sweeping process include: using multiple laser spots to perform laser sintering on the solar cell to which a first reverse voltage or a second reverse voltage is applied in a surface sweeping or line sweeping manner, wherein the number of laser spots is at least one.

[0041] Multiple light spots can be used to achieve surface scanning or line scanning. The more light spots there are, the larger the area that can be sintered at the same time, and the higher the sintering efficiency.

[0042] In one embodiment, the face scanning method includes:

[0043] Multiple light spots are moved side by side along a direction perpendicular to the fine grid lines of the solar cell, sweeping from the first side of the solar cell to the second side opposite to the first side;

[0044] After sweeping the solar cell once, move a preset distance along the length of the fine grid lines and then sweep the solar cell again in the opposite direction.

[0045] The surface scanning method offers good compatibility, eliminating the need to consider the grid line spacing of the solar cells and precise alignment. Multiple light spots can be used for scanning, saving scanning time and increasing production capacity. The bow-shaped, reciprocating surface scanning path minimizes the overall scanning path across the entire solar cell surface, further reducing scanning time.

[0046] In one embodiment, the line scanning method includes:

[0047] Each of the multiple light spots is made to fall on a fine grating line, and the light is swept from one end of the fine grating line to the other end.

[0048] The center-to-center distance between two adjacent light spots in a multi-spot array is equal to the distance between two adjacent fine grating lines.

[0049] After sweeping multiple fine grid lines once, the system moves to one end of an adjacent unswept fine grid line and performs the next sweep until all fine grid lines are swept.

[0050] Multiple fine grid lines are scanned using multiple light spots, resulting in high process precision. The scanning time is calculated as the original time divided by the number of light spots; the more light spots, the shorter the scanning time. The spacing between the multiple light spots is set to be the same as the spacing between the fine grid lines, thus avoiding the hassle of aligning each light spot before each scan. The bow-shaped reciprocating scanning path minimizes the overall scanning path across the entire surface of the solar cell, further reducing scanning time. Attached Figure Description

[0051] Figure 1 This is a flowchart of a method for secondary laser sintering of battery cells according to an embodiment of this application;

[0052] Figure 2 This is a schematic diagram of the optical path design layout according to an embodiment of this application;

[0053] Figure 3 This is a schematic diagram of the surface scanning method according to an embodiment of this application;

[0054] Figure 4 This is a schematic diagram of the line scanning method according to an embodiment of this application;

[0055] In the picture:

[0056] 1-Laser head, 2-Beam expander, 3-Beam splitter DOE, 4-High-speed galvanometer, 5-Field mirror, 6-Battery cell, 7-Sweep path, 601-Fine grid line. Detailed Implementation

[0057] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0058] like Figure 1 As shown, this application discloses a method for secondary laser sintering of solar cells, comprising:

[0059] The solar cells are conveyed to the first station, where they undergo a first laser sintering process. This first laser sintering includes applying a first reverse voltage to the solar cells at the first station and performing a first laser sweeping process. The solar cells are then conveyed to the second station, where they undergo a second laser sintering process. This second laser sintering includes applying a second reverse voltage to the solar cells at the second station and performing a second laser sweeping process. Both the first and second stations are equipped with lasers and external power supplies. The external power supply provides a reverse voltage to the solar cells at the stations, and the laser emits a laser beam to sweep across the surface of the solar cells after receiving the reverse voltage. The first laser sintering may result in slight under-sintering or normal sintering. The second laser sintering can correct some imaging defects caused by the first laser sintering and enhance the contact between the metal electrodes to improve filling, ultimately improving power generation efficiency and yield.

[0060] In one embodiment, the difference between the two stations lies in the different voltage settings of the external power supply. The reverse voltage experienced by the battery cell in the second station is higher than that in the first station. The difference between the two reverse voltages can be set to 2V in this embodiment, for example.

[0061] In another embodiment, the laser beams used in the first and second laser sintering processes form different spot shapes. Therefore, the sweeping paths for both can also be designed differently according to actual needs. For example, the first laser sintering can use a line scan for precise sweeping, while the second laser sintering can use a surface scan for rapid sweeping. By forming a long strip of light spots from multiple spots, the entire electrode area (fine grid line distribution area) of the solar cell can be swept in one or two sweeps. As used in this application, "multiple" refers to at least one.

[0062] In other embodiments, the reverse voltage experienced by the solar cell at the second station may be higher than that at the first station, and the laser beams used in the secondary laser sintering may form different spot shapes. The "different spot shapes" referred to in this application mean that the dimensions of the laser spots used at the two stations are different along the horizontal direction perpendicular to the sweeping direction, resulting in different areas swept by the two spots each time. The areas of the two spots may be the same or different.

[0063] like Figure 2As shown in this application, the lasers at the first and second workstations include: a laser head 1, a beam expander 2, a beam splitter (DOE) 3, a high-speed galvanometer 4, and a field lens 5. The laser emitted from the laser head is expanded by the beam expander and then split by the DOE to obtain multiple desired laser spots. The number of these spots is at least one, and can be limited to 2-10, or more than 10 depending on the actual situation. The multiple lasers are directed by the high-speed galvanometer and focused onto the solar cell 6 by the field lens to form spots, following the movement path of the spots, i.e., the sweep path. In other embodiments, multiple lasers can also be used to form multiple spots.

[0064] The type of laser can be either a nanosecond laser or a picosecond laser. Laser sintering can be performed using nanosecond or picosecond lasers to ensure the effectiveness of secondary laser sintering.

[0065] The laser wavelength can be set in the range of 200-1342nm. In a preferred embodiment, it can be selected as 355-1064nm. In this embodiment, it is set to 1080nm.

[0066] The laser power can be set in the range of 5-1000W. In a preferred embodiment, any value in the range of 10-500W can be selected, such as 15W, 50W, 400W, 495W, etc. In this embodiment, it is set to 25W.

[0067] The laser speed can be set in the range of 30-120m / s. In a preferred embodiment, it can be selected as 50-100m / s. In this embodiment, it is set to 60m / s.

[0068] The laser spot size can be set in the range of 30-450μm or 30-1500μm. In a preferred embodiment, it can be selected as 50-300μm. In this embodiment, it is set to 100μm.

[0069] The spacing between multiple light spots can be set in the range of 0-2500μm (0-2.5mm). In a preferred embodiment, it can be selected as 0-2000μm. In this embodiment, it is set to 0.4mm (in the area scanning mode).

[0070] In one embodiment, multiple light spots are formed by the laser described above, and the solar cell subjected to a first reverse voltage or a second reverse voltage is laser sintered in a surface scanning or line scanning manner.

[0071] like Figure 3As shown, in the area scanning method, four light spots are used, which move side by side along the direction perpendicular to the fine grid lines 601 of the battery cell 6, sweeping from the first side of the battery cell to the second side opposite to the first side, forming the sweeping path 7 of the first sweep. After one sweep, the light spots move a preset distance (the width of the first sweeping path) along the length direction of the fine grid lines 601 to the adjacent area that has not been swept, and then perform the next row sweep on the battery cell in the opposite direction, thus sweeping the entire surface along the bow-shaped path.

[0072] like Figure 4 As shown, in the online scanning method, four light spots are used, each of which falls on a fine grid line 601 and is swept from one end to the other along the length of the fine grid line 601. After one sweep, the light spot moves laterally a preset distance (the width of the first sweep path) perpendicular to the fine grid line 601 and then sweeps the adjacent unswept fine grid lines 601 in the opposite direction for the next sweep, thus sweeping the entire surface along a bow-shaped path.

[0073] A test production line was set up, including a first station, a first IV test, a second station, and a second IV test. A large number of solar cells were supplied to the test production line. After the first laser sintering, the power generation efficiency of each cell was measured. After the second laser sintering, the power generation efficiency was measured again, resulting in the table below. The power generation efficiency of common solar cells is 21%–24%. The table shows that the average efficiency of all cells after the first laser sintering is 25.987%, and the average efficiency after the second laser sintering is 26.042%. Compared to cells without LECO treatment, cells with one LECO treatment have a power generation efficiency that is approximately 1–4% higher. Compared to cells with two LECO treatments (the latter using a higher reverse voltage), cells with one LECO treatment have an average efficiency improvement of 0.055%. The first LECO treatment may result in under-sintering; the second LECO treatment can correct some imaging defects caused by the first LECO treatment and further enhance electrode contact, ultimately further improving efficiency and yield.

[0074] Serial Number project efficiency 1 First laser sintering 25.987％ 2 Second laser sintering 26.042％ Increase 0.055％

[0075] Table 1. Results of power generation efficiency testing for secondary laser sintering.

[0076] More specifically, the principle / purpose of the first LECO treatment is: to use a high-intensity laser to irradiate the grid lines of the solar cell to excite charge carriers, while applying a reverse voltage of more than 10V, thereby generating a local current of several amperes. Sintering occurs at the corresponding location, initiating the interdiffusion of silver paste and silicon. The silver-silicon interface melts and interdiffused to form a silver-silicon alloy. When the silver-silicon alloy appears, it forms an interface breakthrough, which significantly reduces the contact resistance between the metal and the semiconductor, increases the fill factor, and thus improves efficiency.

[0077] The principle / purpose of the second LECO treatment is to perform a second, different LECO treatment based on the first LECO treatment, thereby increasing the number of silver-silicon junctions, creating more interface breakthroughs, and further improving the fill factor, thus enhancing efficiency. Currently, battery manufacturers have relatively high efficiency requirements. In mass production, defects have been found during the sintering of battery edges, resulting in poor EL (electroluminescence) test results. Therefore, it is necessary to reduce the primary laser sintering voltage or optimize the sintering furnace temperature to improve edge defects; and then combine this with a secondary laser treatment to further optimize and improve the defects and efficiency gains from the primary sintering.

[0078] In this application, the more or larger the light spot, the shorter the scanning time. Technicians can design the number of light spots according to actual needs.

[0079] The secondary laser sintering method for solar cells proposed in this application does not require strict temperature control, does not require the use of special gases and chemicals, has high production capacity, high laser precision, and a wide range of applications. It can be used for cells including BC and TOPCon, and can also be integrated into existing production processes to form production lines compatible with other processes without requiring significant modifications to existing production lines.

[0080] The above provides various embodiments, which can be combined and implemented without conflict, and simultaneously achieve the corresponding technical effects. For example, the voltage set for the LECO processing at the second station is higher than the voltage set for the LECO processing at the first station, and the laser spot shapes used in the two LECO processes are different.

[0081] In the foregoing description of this application, unless otherwise expressly specified and limited, the terms "fixed," "installed," "connected," or "linked" should be interpreted broadly. For example, the term "linked" can refer to a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; or it can refer to the internal communication of two components or the interaction between two components. Therefore, unless otherwise expressly limited in this application, those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0082] Based on the above description of this application, those skilled in the art will also understand that the terms used, such as "upper," "lower," "front," "rear," "left," "right," "length," "width," "thickness," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," "circumferential," "center," "longitudinal," "transverse," "clockwise," or "counterclockwise," are based on the orientation or positional relationship shown in the accompanying drawings of this application. They are only for the purpose of facilitating the explanation of the solution of this application and simplifying the description, and do not explicitly or implicitly suggest that the device or element involved must have the specific orientation, or be constructed and operated in a specific orientation. Therefore, the above-mentioned orientation or positional relationship terms should not be understood or interpreted as a limitation on the solution of this application.

[0083] Furthermore, the terms "first" or "second," etc., used in this application to refer to numbers or ordinal numbers are for descriptive purposes only and should not be construed as explicitly or implicitly indicating relative importance or specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include multiple such features. In the description of this application, "multiple" means at least two, such as two, three, or more, unless otherwise explicitly specified.

[0084] While numerous embodiments of this application have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will arise for those skilled in the art without departing from the spirit and intent of this application. It should be understood that various alternatives to the embodiments of this application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A method for secondary laser sintering of solar cells, characterized in that, The method includes: Transport the battery cells to the first workstation; The first laser sintering is performed on the battery cell at the first station. The first laser sintering includes applying a first reverse voltage to the battery cell located at the first station and applying a first laser sweeping process. Transport the battery cells to the second workstation; The second laser sintering is performed on the battery cell at the second station. The second laser sintering includes applying a second reverse voltage to the battery cell located at the second station and applying a second laser sweeping process. The first reverse voltage is lower than the second reverse voltage.

2. The method for secondary laser sintering of battery cells according to claim 1, characterized in that, Both the first laser scanning process and the second laser scanning process include: using multiple laser spots to perform laser sintering on the solar cell to which the first reverse voltage or the second reverse voltage is applied in a surface scanning or line scanning manner, wherein the number of the multiple laser spots is at least one.

3. The method for secondary laser sintering of battery cells according to claim 2, characterized in that, The surface scanning method includes: Multiple light spots are moved side by side along a direction perpendicular to the fine grid lines of the solar cell, sweeping from the first side of the solar cell to the second side opposite to the first side.

4. The method for secondary laser sintering of battery cells according to claim 3, characterized in that, The surface scanning method includes: After sweeping the solar cell once with multiple light spots arranged side by side in a direction perpendicular to the fine grid lines, the light spots move a preset distance along the length of the fine grid lines and then sweep the solar cell again in the opposite direction.

5. The method for secondary laser sintering of battery cells according to claim 2, characterized in that, The line scanning method includes: Each of the multiple light spots is positioned on a fine grating line, and the light is swept from one end of the grating line to the other.

6. The method for secondary laser sintering of battery cells according to claim 5, characterized in that, The center-to-center distance between two adjacent light spots is equal to the distance between two adjacent fine grid lines.

7. The method for secondary laser sintering of battery cells according to claim 2, characterized in that, The shapes of the plurality of light spots processed by the first laser scanning process are different from those of the plurality of light spots processed by the second laser scanning process.

8. The method for secondary laser sintering of battery cells according to claim 1, characterized in that, The laser used in the secondary laser sintering has a wavelength of 200-1342nm, a power of 5-1000W, a sweep speed of 30-120m / s, a spot size of 30-1500μm, and a spot spacing of 1-2500μm.

9. The method for secondary laser sintering of battery cells according to claim 2, characterized in that, The plurality of light spots are generated using a laser with a DOE lens; or, the plurality of light spots are generated using at least two lasers.

10. The method for secondary laser sintering of battery cells according to claim 5 or 7, characterized in that, After sweeping multiple fine grid lines once, the system moves to one end of an adjacent unswept fine grid line and performs the next sweep until all fine grid lines are swept.

11. A method for secondary laser sintering of solar cells, characterized in that, The method includes: Transport the battery cells to the first workstation; The first laser sintering is performed on the battery cell at the first station. The first laser sintering includes applying a first reverse voltage to the battery cell located at the first station and applying a first laser sweeping process. The first laser sweeping process includes sweeping the battery cell with a first laser beam. Transport the battery cells to the second workstation; The second laser sintering is performed on the battery cell at the second station. The second laser sintering includes applying a second reverse voltage to the battery cell located at the second station and applying a second laser sweeping process. The second laser sweeping process includes sweeping the battery cell with a second laser beam. The shape of the light spot formed by the first laser beam is different from the shape of the light spot formed by the second laser beam.

12. The method for secondary laser sintering of solar cells according to claim 11, characterized in that, Both the first laser scanning process and the second laser scanning process include: using multiple laser spots to perform laser sintering on the solar cell to which the first reverse voltage or the second reverse voltage is applied in a surface scanning or line scanning manner, wherein the number of the multiple laser spots is at least one.

13. The method for secondary laser sintering of battery cells according to claim 12, characterized in that, The surface scanning method includes: Multiple light spots are moved side by side along a direction perpendicular to the fine grid lines of the solar cell, sweeping from the first side of the solar cell to the second side opposite to the first side; After sweeping the solar cell once, move a preset distance along the length of the fine grid lines and then sweep the solar cell again in the opposite direction.

14. The method for secondary laser sintering of solar cells according to claim 12, characterized in that, The line scanning method includes: Each of the multiple light spots is made to fall on a fine grating line, and the light is swept from one end of the fine grating line to the other end. The center-to-center distance between two adjacent light spots in a multi-spot array is equal to the distance between two adjacent fine grating lines. After sweeping multiple fine grid lines once, the system moves to one end of an adjacent unswept fine grid line and performs the next sweep until all fine grid lines are swept.

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