A laser-induced sintering apparatus, method and n-type battery

Abstract

The application discloses a laser-induced sintering device, method and N-type battery, and belongs to the technical field of photovoltaic cell preparation. The laser-induced sintering device comprises an electric input assembly and at least two lasers; the electric input assembly acts on a cell to apply a reverse voltage to the cell; and the lasers emit laser beams which converge and jointly act on the surface of the cell. According to the structural design and related parameter adjustment of the application, the laser can act on the whole cell after the one-time probe array pressure combination, so that the component loss of the laser can be reduced, the time of the silicon wafer carrying operation can be obviously reduced, the production capacity can be improved, the surface damage of the silicon wafer caused by the laser can be obviously reduced, the laser-induced sintering effect can be improved, and the conversion efficiency of the cell can be improved.

Description

Technical Field

[0001] This application relates to the field of photovoltaic cell manufacturing technology, and more specifically, to a laser-induced sintering apparatus, method, and N-type cell. Background Technology

[0002] The mechanism of laser-induced sintering involves exciting charge carriers in the battery with a laser, causing them to flow directionally and form a circuit under the influence of a reverse voltage from an external electric field. After the laser irradiates the silicon wafer, the generated current propagates along a low-contact-resistance path through the photovoltaic effect, inducing silver-silicon interdiffusion and thus reducing the contact resistance. The duration of the entire sintering process is matched with the charge carrier lifetime, and the laser is stopped rapidly after it passes, thereby maximizing the preservation of the original passivation layer and avoiding charge carrier recombination caused by direct contact between the metal and silicon substrate. Essentially, it utilizes the high energy concentration and controllability of the laser to separate the two key steps of passivation layer erosion and contact formation during high-temperature sintering, thus achieving further precise control over the sintering process.

[0003] Laser-induced sintering is suitable for all high-temperature burn-through silver paste sintering processes, thus showing application potential for PERC, TOPCon, and even xBC cells. For TOPCon cells, since burn-through paste is used on both the front and back sides, the efficiency improvement potential of laser-induced sintering is higher than that of PERC cells.

[0004] The key to laser-induced sintering is to excite more free electrons to reduce silver ions, especially in TOPCon. Because the front side of a PERC cell already has many free electrons, precisely controlling the presence of only colloidal silver, without silver crystals, is very difficult. However, in TOPCon, the front side is naturally hole-conductive, ensuring that silver crystals will not form. Therefore, by increasing the reverse voltage to excite a large number of free electrons, when these free electrons encounter the glass layer of nano-colloidal silver, the high resistance generates instantaneous heat and high temperatures, exceeding 840 degrees Celsius or even higher, causing silver and silicon to eutecticly diffuse, forming a silver-silicon alloy junction. The contact quality of this silver-silicon alloy junction is higher than that of silver crystals before laser treatment (after simple sintering).

[0005] Therefore, based on the above mechanism of laser-induced sintering, the uniformity of the reverse bias voltage distribution effect and the magnitude of the laser energy at various points on the surface of the solar cell determine the peak current value under the photovoltaic effect, which becomes the core control point for the laser-induced sintering effect.

[0006] A search revealed patent number ZL202322179648.7, with an authorization announcement date of March 19, 2024, entitled "A Laser-Induced Sintering Processing Equipment." This application has at least two processing stations. The processing equipment includes a support device, and both processing stations are equipped with laser modules and electrical input modules. The support device includes at least one support unit and a first driving mechanism that drives the support unit to sequentially move to the first and second processing stations. Each of the two electrical input modules includes a conductive module and a second driving mechanism connected to the conductive module. The conductive module includes a first electrode and a second electrode, which are used for electrical contact with the upper and lower surfaces of the battery cell, respectively. The first electrode can have only one electrode contacting a single main grid line on the battery cell, or multiple electrodes arranged side-by-side can simultaneously contact multiple main grid lines on the battery cell. This processing equipment can solve the problem of poor contact resistivity uniformity caused by the conductive module blocking the laser. However, this application has two problems. First, setting a single laser in a fixed position, even with electrodes arranged side by side, cannot avoid the shadow problem caused by the laser hitting the vicinity of the electrodes. Second, this application requires processing the complete silicon wafer in half, which requires processing twice, increasing mechanical handling time and negatively impacting production capacity. Furthermore, processing the wafer in two separate steps, applying voltage and forming a loop current to the main gate of the other half, is conducted through the fine gate to the half of the probe array that has not been pressed together. This results in inherent current attenuation, leading to suboptimal laser-induced sintering.

[0007] Patent application number 202310217621.4, publication date October 10, 2023, invention title: A dual-laser solar cell sintering device. This application uses a laser sintering device to replace the chain sintering furnace to thermally melt, solidify, and sinter the electrode patterns on the solar cell. On the one hand, it reduces the space occupied by the equipment; on the other hand, it reduces the area of ​​the solar cell exposed to high temperature, avoiding the amplification of internal defects in the solar cell caused by high temperature. Although this application uses dual lasers, it still processes the silicon wafer twice, which is equivalent to two lasers processing the solar cell completely twice. The laser spot energy cannot be superimposed, and the requirements for the use and selection of individual lasers are still relatively high. Summary of the Invention

[0008] 1. The technical problem that the invention aims to solve

[0009] In view of the problems existing in the prior art, this application provides a laser-induced sintering device, method and N-type battery; in the laser-induced sintering process of finished battery, this application designs a more reasonable probe pressing method and a more reasonable laser prototyping method, which can better achieve the voltage division effect and the laser effect.

[0010] 2. Technical Solution

[0011] The summary section of this application is intended to provide a brief overview of the concepts, which will be described in detail in the detailed description section below. This summary section is not intended to identify key or essential features of the claimed technical solutions, nor is it intended to limit the scope of the claimed technical solutions.

[0012] To achieve the above objectives, the technical solution provided in this application is as follows:

[0013] As a first aspect of this application, this application provides a laser-induced sintering apparatus, including an electrical input component and N lasers, where N≥2; the electrical input component acts on a solar cell to apply a reverse voltage to the solar cell; the lasers emitted by the N lasers converge and act together on the surface of the solar cell.

[0014] Furthermore, the electrical input component includes a power supply and a probe array. The probe array is provided with a power transmission electrode connected to the power supply and probes that make electrical contact with the battery cell. Multiple probes are provided, and the multiple probes are arranged in a strip or matrix.

[0015] Furthermore, the probe array is provided with a frame, which is composed of multiple horizontally and vertically arranged connecting ribs. The probes are disposed on the connecting ribs, and the power transmission electrodes are electrically connected to the connecting ribs.

[0016] Furthermore, the width of the connecting rib is smaller than the width of the main grid of the battery cell, and the connecting rib is made of precious metal material or superconducting material.

[0017] Furthermore, the position and number of probes on the frame correspond to the position and number of PAD points on the main grid of the solar cell.

[0018] Furthermore, the laser emitted by the laser is focused on the surface of the battery cell to form a spot shape including a linear spot, a rectangular spot, a square spot, or a circular spot.

[0019] Furthermore, a calibration device is provided on the laser to ensure that the lasers remain parallel and equidistant from each other.

[0020] Furthermore, the calibration device includes a laser emitting device, a reflector, and a laser receiving device; the laser emitting device and the laser receiving device are mounted on the same laser, the reflector is mounted on another laser, and the laser emitted by the laser emitting device is reflected back to the laser receiving device in parallel by the reflector; at least two sets of the calibration device are set between the two lasers.

[0021] Furthermore, two lasers are provided, positioned above the solar cell and symmetrically arranged along the bisector of the solar cell.

[0022] As a second aspect of this application, this application provides a laser-induced sintering method, in which a probe is pressed onto the corresponding main grid PAD point of the solar cell and a reverse bias voltage is applied; while the reverse voltage is applied, the laser emitted by the laser is focused and acts on the surface of the solar cell to perform an all-round scan of the solar cell, thereby realizing laser-induced sintering.

[0023] As a third aspect of this application, this application provides an N-type battery that is laser-induced sintered using the method described in the second aspect of this application.

[0024] 3. Beneficial effects

[0025] Compared with existing known technologies, the technical solution provided in this application has the following significant advantages:

[0026] The current drawback of laser-induced sintering is that when a reverse voltage is applied, the probe array blocks the laser, allowing only half of the cell to be lasered at a time. Therefore, for a complete cell, lasers need to be applied to both sides once to achieve the full process effect. According to the structural design and related parameter adjustments of this application, lasers can be applied to the entire cell after the probe array is pressed together in one go. This not only reduces the component loss of the laser, but also significantly reduces the time spent on silicon wafer handling, increasing production capacity. Furthermore, it significantly reduces surface damage to the silicon wafer caused by the laser, improving the effect of laser-induced sintering and increasing the conversion efficiency of the cell. Attached Figure Description

[0027] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application.

[0028] Furthermore, throughout the accompanying drawings, the same or similar reference numerals denote the same or similar elements. It should be understood that the drawings are schematic, and the elements are not necessarily drawn to scale.

[0029] In the attached diagram:

[0030] Figure 1 This is a schematic diagram of the battery cell structure;

[0031] Figure 2 This is a top view of the probe array;

[0032] Figure 3 This is a schematic diagram of the probe array from the left.

[0033] Figure 4 This is a schematic diagram of laser line intersection;

[0034] Figure 5 This is a schematic diagram of the current mass-produced pressing probe method and laser ablation method.

[0035] Explanation of the labels in the diagram:

[0036] 1. Main grid; 2. Fine grid; 3. PAD point; 4. Frame; 5. Probe; 6. Transmission electrode; 7. Laser. Detailed Implementation

[0037] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While some embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this application. It should be understood that the drawings and embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0038] It should also be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. Unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0039] The present application will now be described in detail with reference to the accompanying drawings and embodiments.

[0040] Example 1

[0041] like Figure 5 As shown, this is the current mass-produced pressing probe and laser application method. The first step involves pressing the probe onto the leftmost main grid line of the silicon wafer half. Because the upper frame and lines of the probe array have a large cumulative shading area, the probe is pressed onto the leftmost probe array first, and the laser is applied to the right half of the cell, performing laser-induced sintering only on the right half of the cell. The second step involves rotating the cell onto another process stage, which is equipped with a set of probes and lasers that are mirrored to the left side, pressing it onto the rightmost main grid line, and applying the laser to the left half of the cell to achieve the laser-induced sintering process.

[0042] The above method has obvious drawbacks: (1) When the probe is pressed on the leftmost grid and a reverse voltage is applied to the cell, because the horizontal grid has obvious line resistance, the voltage is transferred from the left to the right. During the voltage division process, the applied reverse voltage shows a decreasing trend. That is, the reverse voltage on the right side of the cell is obviously low. The front of the N-type cell is boron expanded, and the positively charged holes are driven by the reverse voltage, which is obviously weak. The current generated is obviously low on the right side, and the instantaneous heat reached in a short time is obviously low. It is easy to have obvious deviations in the quality of the silver-silicon alloy junction. It is easy to have EL abnormalities such as cloudiness on the right side of the half cell or poor silver-silicon alloy junction quality leading to poor cell contact. Similarly, when applied to the second step, it will cause cloudiness on the left side of the half cell or poor silver-silicon alloy junction quality leading to poor cell contact. (2) Because the reverse voltage is applied to the cell twice, if there is an obvious difference in the initial voltage of each applied voltage, it will cause obvious EL difference between the left and right halves of the cell.

[0043] To overcome the above-mentioned defects, this embodiment draws inspiration from the working principle of shadowless lamps and designs a laser-induced sintering device. The device includes an electrical input component and N lasers. The electrical input component includes a power supply, a power transmission electrode 6 connected to the power supply, and a probe 5 that is in electrical contact with the battery cell. The probe 5 acts on the battery cell to apply a reverse voltage to the battery cell. The lasers emitted by the N lasers converge and act together on the surface of the battery cell.

[0044] This embodiment can achieve a shadowless mode by adjusting the height of the laser and the processing table, as well as the relative distance between the lasers, so that when the laser from different directions shines on the probe, at most only one direction of the laser is blocked. Although there will be areas blocked by the grid lines, where only one laser source is irradiated, resulting in efficiency loss, the efficiency improvement in other completely unblocked areas is much greater than the specific blocked area. The cumulative effect is still a significant improvement in efficiency, thus achieving the goal of increasing production.

[0045] Furthermore, because the laser emitted by the laser is focused and acts on the surface of the solar cell, scanning the entire surface of the solar cell, the laser emitted by the laser has a wider range of usable wavelengths and the advantage of being able to select optical wavelengths according to the laser line energy requirements of different cells.

[0046] Laser focusing also allows for a greater variety of laser spot morphologies, enabling the laser spot to be any of the following shapes: linear, rectangular, square, or circular. In actual processing, the laser spot morphology can be determined by considering the laser's energy density, its actual stable output power, the size of the laser beam, and the area and location of the processing surface. Matching any given morphology allows for a wider range of laser power and wavelength options.

[0047] As the above analysis shows, in order to obtain a wider range of laser power and wavelength selection, and a richer variety of laser spot morphologies, theoretically, two, three, four, or even more lasers can be set. Even with multiple lasers, the energy density per unit area after the laser spots intersect can be no less than that of a structure where the laser spot is not linear as described in this application. However, considering the feasibility and cost-effectiveness of practical implementation, this embodiment uses two lasers, positioned above the solar cell and symmetrically arranged along the bisector of the solar cell.

[0048] Thus, the selection of laser wavelength can be broadened from the previous 650nm-1400nm to a range of 400-1800nm. Regarding spot morphology, for example, to achieve a spot length or width within 5-20mm, the minimum spot length using a single laser (not applicable to this application) is 5mm. However, by using the method of stitching together two laser spots as described in this application, a smaller side length of 3mm can be achieved, resulting in a minimum side length of 5mm. In terms of power selection, for example, if a 500W output power is required, a single laser can only output 500W. However, two lasers can be combined and their power distributed, allowing the use of two 250W lasers. This significantly improves the lifespan of optical components, reduces costs, and provides more flexibility for process debugging.

[0049] Example 2

[0050] Combination Figure 1 , Figure 2 and Figure 3 The electrical input component provided in this embodiment includes a power supply and a probe array. The probe array is provided with a frame 4, which is composed of multiple horizontally and vertically arranged connecting ribs. The probes 5 are disposed on the connecting ribs, and the power transmission electrodes 6 are electrically connected to the connecting ribs.

[0051] The main busbar 1 of the solar cell is widened at a specific location to provide welding points for better tensile strength during welding. Figure 2The PAD point 3 is shown in the diagram. In this embodiment, the position and number of probes 5 on the frame 4 correspond to the position and number of PAD points 3 on the main grid 1 of the solar cell. The probes 5 are vertically pressed onto the PAD points 3 on the main grid 1 of the solar cell. The width of the main grid 1 of the solar cell is generally within 60-100 micrometers. In this embodiment, the width of the connecting ribs is set to be smaller than the width of the main grid 1 of the solar cell, so that the area other than the main grid 1 is not obscured when viewed from above. The connecting ribs are made of precious metal materials such as gold or superconducting materials. The width of the connecting ribs can be set between 25-60 micrometers, which is larger than the width of the fine grid 2 of the solar cell (the width of the fine grid is about 15-25 micrometers). That is, when using this whole-surface integrated probe array, it is possible to achieve uniform voltage division when applying reverse voltage to various positions of the solar cell, thus avoiding the EL defects caused by voltage division. At the same time, it also realizes that the laser-induced sintering process of the entire solar cell can be completed by applying a reverse bias voltage once without adding a mechanical rotation device.

[0052] This embodiment utilizes two lasers, enabling simultaneous laser action from all directions on the battery cell. It achieves zero shadow area when lasers are applied from the left and right, and overcomes the drawback of the frame and probes blocking the laser line even in a large probe array frame structure.

[0053] Example 3

[0054] Compared to Example 2, which utilizes a single probe array and two lasers, this example designs multiple probes in a strip arrangement. Although this design is slightly inferior in terms of voltage uniformity, it still possesses the advantages of Example 1 in terms of laser power, wavelength selection, and laser spot morphology.

[0055] Example 4

[0056] Focusing the emitted laser light from two lasers onto a single point with perfect precision is relatively difficult. This is because the two lasers are controlled independently, and it is challenging to synchronize and precisely control their relative positions. Therefore, this embodiment adds a calibration device between the lasers to ensure they remain parallel and equidistant.

[0057] Combination Figure 4 , Figure 4The dashed lines represent the emitted laser beams 7. The calibration device includes a laser emitting device, a reflector, and a laser receiving device. At position A on the opposite surface of the first and second lasers, the laser emitting device and the laser receiving device are installed. At the corresponding position on the opposite surface of the second and first lasers, a single-sided reflector capable of high-speed and stable rotation is installed. The first laser emits a laser beam 7 of a fixed frequency (the laser pulse duration is fixed) to the second laser, which is perpendicularly reflected onto the reflector on the second laser. The reflector reflects the light parallel to the laser receiving device on the first laser. By controlling the time difference, the distance between the two lasers at this position is controlled.

[0058] Similarly, at position B on the opposite side of the second laser and the first laser, a laser emitting device and a laser receiving device are set up. At the corresponding position on the opposite side of the first laser and the second laser, a single-sided reflector capable of high-speed and stable rotation is installed. The second laser emits a laser beam 7 of a fixed frequency (the laser pulse duration is fixed) to the first laser, which is perpendicularly irradiated by the reflector on the first laser. The reflector reflects the light parallel to the laser receiving device on the second laser. By controlling the time difference, the distance between the two lasers at this position is controlled.

[0059] By controlling the time monitoring of the two positions above, the lasers can be made parallel and equidistant, which can greatly improve the relative positional accuracy error of the two lasers relative to the workpiece.

[0060] Example 5

[0061] The laser-induced sintering method of this embodiment includes the following steps:

[0062] Step 1: Move the battery cell under the probe array, press probe 5 to the corresponding main grid PAD point 3 of the battery cell, and apply a certain amount of reverse bias voltage, basically between 5 and 20V.

[0063] Step 2: While applying reverse voltage, the two lasers emit laser lines. After the lasers converge, they act together on the surface of the solar cell to perform laser scanning on the position of the printed grid lines. This can be done by scanning the solar cell in all directions along or perpendicular to the grid lines.

[0064] Step 3: After laser scanning, the battery cells are transported out of the laser processing process and left for subsequent efficiency testing and grading.

[0065] Example 6

[0066] An N-type battery of this embodiment is obtained by laser-induced sintering using any one of the devices described in Embodiments 1-4 and the method described in Embodiment 5.

[0067] In summary, the laser-induced sintering apparatus and method provided in this application can achieve the production of uniform and dense silver-silicon alloys, significantly reducing contact resistivity, and achieving a reduction in contact resistivity of fine grids of more than 0.8 Ω*m. This opens a window for reducing doping in the front-side boron expansion process to achieve high sheet resistance, and enables SE heavily doped structures without matching the high and low junction structures of the front-side boron expansion to directly make ohmic contact with the higher sheet resistance non-SE structures in the shallowly doped region, achieving a breakthrough in higher open-circuit voltage for solar cells. Simultaneously, it provides a direction for improving efficiency by reducing the corrosivity of the front-side slurry to increase open-circuit voltage, and can also be matched with sintering furnace temperatures to significantly reduce peak temperatures and thus increase open-circuit voltage.

[0068] It can achieve an average efficiency improvement of at least 0.08% per cell.

[0069] Eta / % Uoc / V Isc / A FF / % Increase 0.08 0.09 0.019 0.3

[0070] As can be seen from the table above, the conversion efficiency Eta, open-circuit voltage Uoc, short-circuit current Isc, and fill factor FF of the solar cells have all been significantly improved.

[0071] The above description is merely a selection of preferred embodiments of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in the embodiments of this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in the embodiments of this application.

Claims

1. A laser-induced sintering apparatus, characterized in that: It includes an electrical input component and N lasers, where N≥2; the electrical input component acts on the battery cell to apply a reverse voltage to the battery cell; the lasers emitted by the N lasers converge and act together on the surface of the battery cell; The electrical input component includes a power supply and a probe array. The probe array is provided with a power transmission electrode (6) connected to the power supply and a probe (5) that makes electrical contact with the battery cell. Multiple probes (5) are provided, and the multiple probes (5) are arranged in a strip or matrix. The probe array is provided with a frame (4), which is composed of multiple horizontal and vertical connecting ribs. The probe (5) is placed on the connecting ribs, and the power transmission electrode (6) is electrically connected to the connecting ribs. The width of the connecting rib is smaller than the width of the main grid (1) of the battery cell, and the connecting rib is made of precious metal material or superconducting material.

2. The laser-induced sintering apparatus according to claim 1, characterized in that: The position and number of probes (5) on the frame (4) correspond to the position and number of PAD points (3) on the main grid (1) of the battery cell.

3. A laser-induced sintering apparatus according to claim 1 or 2, characterized in that: The laser emitted by the laser is focused on the surface of the solar cell to form a spot shape including a linear spot, a square spot, or a circular spot.

4. The laser-induced sintering apparatus according to claim 3, characterized in that: The laser is equipped with a calibration device that ensures that the lasers remain parallel and equidistant from each other.

5. The laser-induced sintering apparatus according to claim 4, characterized in that: The calibration device includes a laser emitting device, a reflector, and a laser receiving device; the laser emitting device and the laser receiving device are mounted on the same laser, and the reflector is mounted on another laser. The laser emitted by the laser emitting device is reflected back to the laser receiving device in parallel by the reflector; at least two sets of the calibration device are set between the two lasers.

6. The laser-induced sintering apparatus according to claim 5, characterized in that: Two lasers are provided, positioned above the solar cell and symmetrically arranged along the bisector of the solar cell.

7. A method for laser-induced sintering using the apparatus according to any one of claims 1-5, characterized in that: The probe (5) is pressed onto the corresponding PAD point (3) of the main grid of the battery cell and a reverse bias voltage is applied. At the same time as the reverse voltage is applied, the laser emitted by the laser converges and acts on the surface of the battery cell to perform an all-round scan of the battery cell and realize laser-induced sintering.

8. An N-type battery, characterized in that: Laser-induced sintering is performed using the method described in claim 7.

Images