A copper electrode laser curing system and method for a topcon solar cell

Abstract

The application discloses a kind of copper electrode laser curing system and method of TOPCon solar cell, the system includes mid-infrared laser generation module, beam shaping and energy management module, precision motion and positioning platform and synchronous control and monitoring module.The method used is: after coating copper paste on the back silver seed layer of TOPCon battery, laser beam is irradiated, by accurately controlling laser energy density and pulse width, energy is selectively resonant absorbed by copper paste organic matter, millisecond level rapid curing is realized, while ensuring that energy density is lower than the damage threshold of lower layer aluminum oxide / silicon nitride passivation film, so that the base temperature rise is lower than 200 DEG C.The application overcomes the defects of traditional thermal curing, such as low efficiency, high energy consumption and easy damage to passivation layer, and provides an efficient, reliable and non-damage battery performance industrialization solution for TOPCon battery low-cost "de-silverization".

Description

Technical Field

[0001] This invention relates to a copper electrode laser curing system and method, and more particularly to a copper electrode laser curing system and method for TOPCon solar cells. Background Technology

[0002] TOPCon cells based on N-type silicon wafers have become the next-generation mainstream photovoltaic technology due to their ultra-high theoretical conversion efficiency limit and excellent passivation performance. However, their production costs, especially the costs of the front silver paste and back silver-aluminum paste, which account for a significant proportion of non-silicon costs, severely restrict their large-scale market application. To address the challenge of high and volatile prices of the precious metal silver, the industry is actively exploring a "silver-free" technology route that replaces silver with the base metal copper.

[0003] The current mainstream TOPCon copper electrode solution typically adopts a stacked structure of "silver seed layer + copper paste": first, silver paste is printed and sintered at high temperature on the back of the cell to form a seed layer that ensures ohmic contact; then, a thicker copper paste is printed on the seed layer; finally, the copper paste is heated and cured as a whole using a hot air or infrared curing oven, causing the organic binder in it to crosslink. Although this solution avoids the problem of copper diffusion into silicon at high temperatures, it has the following inherent drawbacks: 1. The curing oven process is energy-intensive and time-consuming, resulting in a slow production cycle; 2. Overall heating causes the entire cell substrate to undergo unnecessary temperature rise, which not only wastes energy but may also cause irreversible thermal damage to the fine passivation layer on the front side (such as AL2O3 / SiNx stack), affecting long-term reliability; 3. The thermal curing process may lead to insufficient decomposition of organic components in the copper paste or the formation of pores, affecting the electrode density and conductivity.

[0004] Laser technology, due to its concentrated energy and precise controllability, has already seen mature applications in the photovoltaic field, such as laser grooving and laser doping. However, directly applying lasers to copper paste curing, especially to the heat-sensitive back passivation structure of TOPCon cells, faces significant technical challenges. The core dilemma lies in ensuring that the laser energy is sufficient to penetrate and effectively cure the surface copper paste, while also ensuring that the energy is strictly confined within the paste layer to avoid damaging the crucial underlying Al2O3 / SiNx passivation film. Summary of the Invention

[0005] To overcome the above-mentioned shortcomings, the present invention provides a laser curing system and method for copper electrodes of TOPCon solar cells, which can achieve selective, non-invasive copper paste curing.

[0006] To achieve this objective, the method employed in this invention is: a laser curing method for copper electrodes in TOPCon solar cells, comprising the following steps:

[0007] S1. Precursor preparation: A silver seed layer is formed on the back passivation structure of the TOPCon battery;

[0008] S2. Copper paste is applied to the silver seed layer;

[0009] S3. Laser selective curing uses a laser beam with a wavelength of 3μm-12μm to irradiate the copper paste area. The energy density and action time of the laser beam are controlled by the system so that the laser energy is selectively absorbed by the copper paste and causes it to solidify to form a copper electrode. At the same time, the energy density of the laser is ensured to be lower than the damage threshold of the aluminum oxide and / or silicon nitride film in the back passivation structure, and the peak temperature rise of the battery silicon substrate is kept below 200°C.

[0010] The wavelength of the laser is 9.6μm-10.6μm; the laser beam is shaped into a flat-top line spot or a square flat-top spot with energy uniformity greater than 90%.

[0011] In step S3, the laser beam is controlled to operate in a pulsed manner, with a single pulse energy density of 0.5 J / cm²-2.0 J / cm² and a pulse width of 0.1 ms-20 ms.

[0012] The temperature of the laser-irradiated area is monitored in real time by an infrared thermal imager, and the laser power or scanning speed is dynamically adjusted based on the monitoring results to achieve closed-loop control.

[0013] Step S3 is performed under an inert gas protective atmosphere.

[0014] After post-treatment, laser curing is performed, followed by a brief thermal annealing at a low temperature.

[0015] A TOPCon solar cell copper electrode laser curing system for implementing the above method includes a mid-infrared laser generation module, a beam shaping and energy management module, a precision motion platform, and a synchronous control and monitoring module.

[0016] The mid-infrared laser generating module includes a laser for generating continuous or pulsed laser beams with wavelengths of 3μm-12μm;

[0017] The beam shaping and energy management module is used to shape the laser beam into a uniform spot of a preset shape and modulate the laser energy;

[0018] A precision motion platform for carrying and transporting TOPCon batteries to be processed;

[0019] The synchronous control and monitoring module is communicatively connected to the mid-infrared laser generation module, beam shaping and energy management module, and precision motion platform, and is used to control laser parameters and motion coordination.

[0020] The laser is a carbon dioxide laser.

[0021] The beam shaping and energy management module includes a beam feeding and collimating lens group, an acousto-optic modulator, and a beam homogenizer arranged in sequence; the beam homogenizer is a diffractive optical element or a compound eye lens integrator.

[0022] The synchronous control and monitoring module includes a process control unit, a real-time feedback unit, and an environmental control unit. The process control unit pre-stores multiple process recipes and can coordinate the control of laser power, pulse parameters, scanning speed, and platform movement. The real-time feedback unit includes one or more of an infrared thermal imager for monitoring the temperature of the processing area and a photodetector for monitoring optical signals. The environmental control unit includes a nozzle that provides inert gas protection to the laser processing area.

[0023] Its beneficial effects are:

[0024] 1. Creatively Resolving the "Cure vs. Damage" Contradiction: This invention is the first to explicitly propose utilizing the selective absorption characteristics and precise energy management of mid-infrared lasers to achieve safe curing of copper paste on TOPCon batteries. By controlling the laser energy density and interaction time within a precise window below the passivation film damage threshold but above the copper paste curing threshold, and employing uniform laser spot and closed-loop temperature control, the risk of damaging the AL2O3 / SiNx passivation layer is fundamentally eliminated—something that traditional thermosetting ovens cannot achieve.

[0025] 2. Ultimate Performance and Efficiency: The instantaneous localized heating of the laser enables rapid and complete cross-linking of the organic matter in the copper paste, resulting in electrodes with high density and low porosity, exhibiting superior contact resistance and line resistance compared to traditional thermosetting electrodes. Simultaneously, the processing speed, measured in seconds or even milliseconds, increases production efficiency by tens of times compared to minute-level thermosetting processes, while significantly reducing energy consumption.

[0026] 3. Excellent process compatibility and reliability: This process results in a minimal heat-affected zone, avoiding overall thermal stress on the battery and improving long-term reliability under harsh environments such as damp heat and thermal cycling. The system can be seamlessly integrated into existing TOPCon production lines as a standalone module.

[0027] 4. Driving cost reduction in the industry: This method removes key technical obstacles for the large-scale adoption of low-cost copper paste to replace precious metal silver paste in TOPCon cells, and provides an efficient and stable solution with industrialization prospects, which is of great significance for reducing the levelized cost of electricity (LCOE) of photovoltaics. Attached Figure Description

[0028] The present invention will be described by way of example and with reference to the accompanying drawings, wherein:

[0029] Figure 1This is a system structure diagram of the present invention;

[0030] Figure 2 This is a schematic diagram of the cross-sectional structure of a TOPCon battery prepared using the method of this invention;

[0031] Figure 3 This is a schematic diagram comparing the heat distribution of traditional thermosetting and the laser-curing process of this invention;

[0032] Figure 4 This is a schematic diagram of energy deposition and thermally affected depth in the laser curing process. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0034] In the description of the invention, it should be noted that the terms "upper," "lower," "inner," "outer," "front end," "rear end," "both ends," "one end," and "the other end," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0035] In the description of the invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "connected," etc., should be interpreted broadly. For example, "connection" can be 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; it can be a connection within two components; a fixed connection can be welded or glued. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0036] like Figure 1 The copper electrode laser curing system for a TOPCon solar cell shown includes a mid-infrared laser generation module, a beam shaping and energy management module, a precision motion platform 9, and a synchronous control and monitoring module.

[0037] The mid-infrared laser generating module includes a laser 1 for generating a continuous or pulsed laser beam with a wavelength of 3μm-12μm, preferably a carbon dioxide laser with an output wavelength of 10.6μm, because it has stable output, high power, and this wavelength matches well with the absorption peaks of CO and CH bond vibrations of most organic polymers.

[0038] The beam shaping and energy management module, connected to the output optical path of the mid-infrared laser generation module, is used to collimate, expand, homogenize, and focus the original laser beam. It includes a beam guard and collimating lens group 2, an acousto-optic modulator 3, and a beam homogenizer 4, arranged sequentially. The beam homogenizer 4 is a diffractive optical element or a compound eye lens integrator. The beam homogenizer 4 is used to convert the Gaussian spot into a flat-topped spot or a uniform line spot with highly uniform energy distribution, thereby eliminating local hot spots and ensuring uniform curing. The acousto-optic modulator can be replaced with an electro-optic modulator, both used for high-speed, precise modulation of the laser pulse width, frequency, and intensity.

[0039] The precision motion platform 9 is used to carry and precisely transport the TOPCon cells 8 that have undergone back-side silver seed layer sintering and copper paste printing. This platform features micron-level positioning accuracy and stable vacuum adsorption capabilities, ensuring no cell displacement during processing.

[0040] The synchronous control and monitoring module is communicatively connected to the mid-infrared laser generation module, beam shaping and energy management module, and precision motion platform, and is used to control laser parameters and motion coordination.

[0041] The synchronous control and monitoring module includes a process control unit 11, a real-time feedback unit 10, and an environmental control unit 12. The process control unit 11 pre-stores multiple process recipes and can coordinate and control laser power, pulse parameters, scanning speed, and platform movement. The real-time feedback unit 10 includes one or more of an infrared thermal imager for monitoring the temperature of the processing area and a photodetector for monitoring optical signals. The environmental control unit 12 includes a nozzle that provides inert gas protection to the laser processing area.

[0042] The method for laser curing using the copper electrode laser curing system of the above-mentioned TOPCon solar cell comprises the following steps:

[0043] S1. Precursor preparation provides an N-type TOPCon cell silicon wafer, on which a silver paste pattern is formed by screen printing in the back electrode area and then sintered by high-temperature (>750°C) rapid thermal annealing (RTP) to form a dense silver seed layer with good ohmic contact.

[0044] S2. Copper paste is coated onto the silver seed layer, and a layer of copper paste with a specific formulation is applied by screen printing. This copper paste formulation is optimized to contain organic carriers or infrared absorbers that have strong absorption of 10.6μm wavelength laser light to enhance the selective absorption effect;

[0045] S3. Selective Laser Curing: The coated battery is placed on the precision motion platform 9. A laser beam with a wavelength of 3μm-12μm generated by laser 1 is used to irradiate the copper paste area. Preferably, the laser wavelength is 9.6μm-10.6μm, and more preferably, the laser wavelength is 10.6μm. The laser beam passes sequentially through the beam guide and collimating lens group 2, the acousto-optic modulator 3, the beam homogenizer 4, the galvanometer 5, and the field lens 6 to shape the laser beam into a flat-top line spot or a square flat-top spot 7 with an energy uniformity greater than 90%. The energy density and action time of the laser beam are controlled by the process control unit 11, so that the laser energy is selectively absorbed by the copper paste and causes it to solidify to form a copper electrode. At the same time, it is ensured that the laser energy density is lower than the damage threshold of the alumina and / or silicon nitride film in the back passivation structure, and that the peak temperature rise of the battery silicon substrate is lower than 200°C.

[0046] S4. After post-treatment laser curing, a short-term (<30s) thermal annealing at a low temperature (<200℃) can be performed to further remove residual solvent and enhance the bonding force between copper particles and electrode adhesion.

[0047] In step S3, the laser beam is controlled to operate in a pulsed manner, with a single pulse energy density of 0.5 J / cm²-2.0 J / cm² and a pulse width of 0.1 ms-20 ms, to ensure shallow heat penetration depth.

[0048] The infrared thermal imager of the real-time feedback unit 10 monitors the temperature of the laser-irradiated area in real time, controls the laser spot to scan the copper paste area at a speed of 1000-20000 mm / s, and dynamically adjusts the laser power or scanning speed according to the monitoring results to ensure that the peak temperature is always below 150℃, preferably below 120℃, thus achieving closed-loop control.

[0049] The environmental control unit 12 is used to ensure that step S3 is performed in an inert gas protective atmosphere, such as nitrogen or argon, to prevent the copper paste from oxidizing under high-temperature instantaneous heating.

[0050] Example 1

[0051] A radio-frequency excited sealed-off CO2 laser with a maximum power of 300W is used to output pulsed or continuous laser light with a wavelength of 10.6μm. After passing through a beam expander and collimator, the laser light is modulated by an acousto-optic modulator into a pulse sequence with an adjustable frequency of 1-50kHz and a pulse width of 0.1-20ms. The pulsed laser light passes through a beam homogenizer based on a microlens array to convert the Gaussian beam into a flat-top beam with energy uniformity >95% on the focal plane. Then, it is focused by an F-θ scanning field lens into a uniform line spot with a length of 20mm and a width of 0.5mm.

[0052] The back of the TOPCon battery to be processed has a pre-formed silver seed layer and is printed with a special copper paste with a thickness of approximately 15μm, which is then adsorbed onto a precision platform. An infrared thermal imager monitors the temperature of the area behind the laser spot's point of application in real time at an oblique incidence angle. All equipment is integrated and controlled by a synchronous control cabinet with built-in process software. During processing, an inert gas nozzle sprays a nitrogen curtain to cover the processing area. The precision motion platform moves at a uniform speed along the Y-axis, allowing the linear laser spot to scan the entire back of the battery, completing the copper paste curing.

[0053] Battery structure and curing effect

[0054] like Figure 2 As shown, the laser-cured TOPCon cell 8 structure includes an N-type silicon substrate 13. The front side of the N-type silicon substrate 13 consists of a P+ diffused emitter 20, an aluminum oxide (Al2O3) passivation layer 16, and a silicon nitride (SiN) layer, in sequence. x A capping layer 17 is formed, and a silver electrode 22 is disposed thereon. The back side of the N-type silicon substrate 13 consists, in sequence, a tunneling oxide layer (SiO2) 14, an N+ polycrystalline silicon layer 15, an aluminum oxide (Al2O3) passivation layer 16, and a silicon nitride (SiN) layer. x The capping layer 17 and the silver seed layer 18 are sintered at high temperature in a sintering furnace to form an ohmic contact with the N+ polycrystalline silicon layer 15. A laser-cured copper electrode 19 is then placed on the silver seed layer 18. The alumina (Al2O3) passivation layer 16 provides excellent field-effect passivation, and the silicon nitride (SiN) layer... x The capping layer 17 serves as an anti-reflection and protective layer. The laser-cured copper electrode 19 formed by the method of the present invention is dense and well bonded to the silver seed layer 18. Due to precise process control, the underlying alumina (Al2O3) passivation layer 16 and silicon nitride (SiN) passivation layer are... x The capping layer 17 remains intact, without cracks, ablation, or changes in crystal phase.

[0055] Process parameter window and comparison data

[0056] Through extensive experiments, we determined that for a typical ~10nm Al2O3 / ~80nm SiNx passivation structure, the damage threshold under a 10.6μm laser with a 1ms pulse width in our system is approximately 1.8 J / cm². The energy density threshold required for complete curing of the copper paste used is 0.7 J / cm².

[0057] Therefore, the preferred process parameters are set as follows: laser energy density 1.2 J / cm², pulse width 1 ms, and line spot scanning speed 100 mm / s.

[0058] Under these parameters: the instantaneous temperature of the copper paste surface is approximately 320℃, but the substrate silicon nitride (SiN) xThe peak temperature of the cover layer 17 was successfully suppressed to below 105°C, far below the damage threshold. Using a traditional hot air curing oven, it would take 3 minutes to cure at 180°C, and the temperature of the entire battery cell would rise uniformly to 180°C.

[0059] like Figure 3 , Figure 4 As shown, traditional hot air curing ovens provide overall heating, with heat penetrating evenly and causing the entire surface to heat up. The passivation layer is in a hot environment. In contrast, laser curing provides localized selective heating, with highly concentrated heat and shallow penetration. The passivation layer is in a near-room temperature environment. Therefore, laser curing can effectively control the temperature rise of the substrate, keeping its energy density below the damage threshold of the passivation layer.

[0060] Table 1 shows a comparison of the battery performance using laser curing versus traditional thermosetting.

[0061]

[0062] Table 1

[0063] This invention is superior to traditional technologies in terms of efficiency, energy consumption, electrode performance, and long-term reliability.

[0064] Based on the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of this invention. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for laser curing copper electrodes in a TOPCon solar cell, characterized in that, Includes the following steps: S1. Precursor preparation: A silver seed layer is formed on the back passivation structure of the TOPCon battery; S2. Copper paste is applied to the silver seed layer; S3. Laser selective curing uses a laser beam with a wavelength of 3μm-12μm to irradiate the copper paste area. The energy density and action time of the laser beam are controlled by the system so that the laser energy is selectively absorbed by the copper paste and causes it to solidify to form a copper electrode. At the same time, the energy density of the laser is ensured to be lower than the damage threshold of the aluminum oxide and / or silicon nitride film in the back passivation structure, and the peak temperature rise of the battery silicon substrate is kept below 200°C.

2. The method for laser curing copper electrodes of a TOPCon solar cell according to claim 1, characterized in that, The wavelength of the laser is 9.6μm-10.6μm; the laser beam is shaped into a flat-top line spot or a square flat-top spot with energy uniformity greater than 90%.

3. A method for laser curing copper electrodes in a TOPCon solar cell according to claim 1 or 2, characterized in that, In step S3, the laser beam is controlled to operate in a pulsed manner, with a single pulse energy density of 0.5 J / cm²-2.0 J / cm² and a pulse width of 0.1 ms-20 ms.

4. The method for laser curing of copper electrodes in a TOPCon solar cell according to claim 3, characterized in that, The temperature of the laser-irradiated area is monitored in real time by an infrared thermal imager, and the laser power or scanning speed is dynamically adjusted based on the monitoring results to achieve closed-loop control.

5. The method for laser curing copper electrodes of a TOPCon solar cell according to claim 1, characterized in that, After post-treatment, laser curing is performed, followed by a brief thermal annealing at a low temperature.

6. The method for laser curing copper electrodes of a TOPCon solar cell according to claim 1, characterized in that, Step S3 is performed under an inert gas protective atmosphere.

7. A laser curing system for copper electrodes of TOPCon solar cells for implementing the method of any one of claims 1-6, characterized in that, It includes a mid-infrared laser generation module, a beam shaping and energy management module, a precision motion platform (9), and a synchronous control and monitoring module; A mid-infrared laser generating module includes a laser (1) for generating continuous or pulsed laser beams with wavelengths of 3μm-12μm. The beam shaping and energy management module is used to shape the laser beam into a uniform spot of a preset shape and modulate the laser energy; A precision motion platform (9) is used to carry and transport the TOPCon battery 8 to be processed; The synchronous control and monitoring module is connected in communication with the mid-infrared laser generation module, beam shaping and energy management module and precision motion platform (9) to control laser parameters and motion coordination.

8. The TOPCon solar cell copper electrode laser curing system according to claim 7, characterized in that, The laser (1) is a carbon dioxide laser.

9. The TOPCon solar cell copper electrode laser curing system according to claim 7, characterized in that, The beam shaping and energy management module includes a beam guard and collimating lens group (2), an acousto-optic modulator (3), and a beam homogenizer (4) arranged in sequence; the beam homogenizer (4) is a diffractive optical element or a compound eye lens integrator.

10. The TOPCon solar cell copper electrode laser curing system according to claim 7, characterized in that, The synchronous control and monitoring module includes a process control unit, a real-time feedback unit, and an environmental control unit; the process control unit (11) pre-stores multiple sets of process recipes and can coordinate and control laser power, pulse parameters, scanning speed and platform movement; the real-time feedback unit (10) includes one or more of an infrared thermal imager for monitoring the temperature of the processing area and a photoelectric detector for monitoring optical signals; the environmental control unit (12) includes a nozzle that provides inert gas protection to the laser processing area.

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