Laser-assisted TOPCon battery double-sided processing system and method

Abstract

The invention provides a laser-assisted TOPCon battery double-sided processing system and method.The system comprises a dual-wavelength laser source module, a three-dimensional galvanometer system and a vacuum reaction cavity, the dual-wavelength laser source module emits lasers of different wavelengths at the same time for sintering of grid lines on the front face of an electric sheet and etching of the back face of the electric sheet, and the three-dimensional galvanometer system is arranged in the vacuum reaction cavity; the vacuum reaction cavity is provided with an optical window, and the three-dimensional galvanometer system and the dual-wavelength laser source module are coupled through the optical window. The laser sintering front grid line adopts axial oscillation scanning, the contact interface is enlarged, the effective contact point density is improved, and the contact resistance is reduced; back annular etching pre-windowing reduces edge breakage, reduces edge microcrack density, and reduces recombination current; and in-situ passivation is performed within 5 seconds of etching, so that dangling bonds on the interface are saturated, and the state density of the interface is reduced. Physical damage of traditional mechanical cutting to the doping layer is avoided, meanwhile, the completeness of the doping structure is maintained through local treatment of laser, and finally efficiency improvement is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photovoltaic cell manufacturing, and particularly relates to a laser-assisted TOPCon cell double-sided processing system and method. BACKGROUND

[0002] Photovoltaic cell technology is undergoing a transformation from PERC (Passivated Emitter and Rear Cell) to TOPCon (Tunnel Oxide Passivated Contact). According to statistics from the China Photovoltaic Industry Association, in 2020, the newly built production lines still mainly used PERC cells, with a market share increasing from 65% in 2019 to 86.4%. As of 2023, despite the continuous emergence of new cell technologies, PERC technology still dominates the photovoltaic industry due to its mature process system and relatively low manufacturing cost. However, the rapid growth period of PERC cell efficiency has ended, with laboratory efficiency approaching the theoretical limit of 24%, and the room for improvement in mass production efficiency is increasingly narrow, usually stabilizing at 22.3%-22.8%.

[0003] TOPCon technology has become the most promising alternative route due to its excellent passivation contact characteristics. This technology prepares an ultra-thin tunnel oxide layer (SiOx, about 1.2 nm) on the back of the cell and deposits a heavily doped polysilicon layer (poly-Si, about 100 nm) on its surface, forming a highly efficient carrier selective contact structure. This structure allows most carriers to pass through the oxide layer through quantum tunneling, while blocking minority carriers from recombining, significantly reducing surface recombination rates. The mass production efficiency of N-type TOPCon cells has reached 24.5%-25.1%, an absolute increase of more than 1.5% compared to PERC cells, making it the mainstream direction of photovoltaic industry upgrading.

[0004] Current high-efficiency cell technology faces multiple technical bottlenecks, mainly in the following three aspects:

[0005] Balancing contact resistance and passivation performance: The contact quality between the metal electrode and the semiconductor silicon wafer directly affects the fill factor and open-circuit voltage of the cell. Traditional high-temperature sintering processes can easily over-etch the passivation layer when forming ohmic contacts, leading to increased recombination current. LECO (Laser Enhanced Contact Optimization) technology can significantly reduce contact resistance (ρc can be reduced to 1.8±0.58 mΩ·cm²) through laser-assisted sintering, but this technology has been patented globally by Qcells through the acquisition of Cell Engineering GmbH, posing a serious risk of patent barriers. In early 2025, Qcells has initiated patent infringement lawsuits against multiple leading TOPCon companies, demanding that they stop producing and selling related products.

[0006] Optical loss contradiction of double-sided structure: double-sided cells need to consider the efficiency of both sides, but if the full poly-Si passivation layer is used on the front side of the TOPCon cell, there will be significant parasitic light absorption loss (about 1.5 mA / cm²). The traditional solution adopts a local window structure, but it needs complex mask and etching processes (such as photolithography or laser slotting), which increases the process cost by about 0.12 yuan / watt410. The poly-Si layer on the back side is also too thick, which increases the absorption of infrared light, affecting the double-sided rate (usually only 75%-80%).

[0007] Cutting process and edge recombination loss: mechanical cutting causes edge collapse and micro-cracks, resulting in a loss of cell efficiency of ≥0.5% and a high fragment rate of more than 6%. The heat damage caused by secondary cutting further aggravates edge recombination and reduces open-circuit voltage. Traditional edge passivation requires separate PECVD deposition, which is separate from the main grid sintering process, resulting in an increase in interface state density (>10¹¹eV⁻¹cm⁻²) and a leakage current of more than 0.5 mA / cm². SUMMARY

[0008] The purpose of the present application is to provide a laser-assisted TOPCon cell double-sided processing system to solve the above technical problems in the prior art.

[0009] Another purpose of the present application is to provide a laser-assisted TOPCon cell double-sided processing method to improve the existing laser sintering technology, and to improve the efficiency of the cell by ring etching windowing and in-situ SiN X deposition.

[0010] To this end, the technical solutions provided by the present application are as follows:

[0011] A laser-assisted TOPCon cell double-sided processing system, comprising a dual-wavelength laser source module, a three-dimensional galvanometer system and a vacuum reaction chamber, the dual-wavelength laser source module simultaneously emits laser beams of different wavelengths for front grid line sintering and back etching of the wafer, and the three-dimensional galvanometer system is arranged in the vacuum reaction chamber;

[0012] An optical window is arranged on the vacuum reaction chamber, the three-dimensional galvanometer system and the dual-wavelength laser source module are coupled through the optical window, the three-dimensional galvanometer system comprises a front scanning unit and a back control unit, the front scanning unit is used to control the reciprocating motion of the laser beam after receiving the laser beam, and the back control unit is used to control the scanning path of the laser beam.

[0013] A temperature control platform and a gas spray head are arranged in the vacuum reaction chamber.

[0014] A laser-assisted TOPCon cell double-sided processing method, which adopts a laser-assisted TOPCon cell double-sided processing system, comprises the following steps:

[0015] Sintering is performed by axial periodic oscillating laser scanning on the front grid lines of the battery.

[0016] Simultaneously perform closed-loop annular laser etching on the cutting area on the back of the battery;

[0017] A passivation layer is deposited on the etched surface within 5 seconds after etching is completed.

[0018] The laser scanning path for the axial periodic oscillation of the grid lines on the front of the battery is a sinusoidal oscillation trajectory with a frequency of 8 Hz to 12 Hz and an oscillation scanning power of 18 W to 22 W.

[0019] The laser etching path on the back of the battery is a concentric double-ring structure, with the inner diameter being 2mm shorter than the side length of the battery and the ring spacing being 30μm±5%.

[0020] The wavelength of the axial periodic oscillation laser scanning of the grid lines on the front of the battery is 1064nm, and the amplitude is 10μm~20μm; the wavelength of the laser etching on the back of the battery is 355nm.

[0021] After the back of the battery is etched, a passivation layer is deposited within 0.5s. A mixture of SiH4 and NH3 gas is introduced through a gas spray head, and the deposition rate is greater than 40nm / s.

[0022] The depth of the closed-loop ring etching is 120 nm to 180 nm, and the linewidth is 25 μm to 35 μm.

[0023] SiN was deposited by introducing a mixed gas of SiH4 and NH3 during the deposition of the passivation layer. X Passivation layer, with a thickness of 150nm~200nm.

[0024] During axial periodic oscillating laser scanning, the laser reciprocates along the grid lines on the front of the battery within ±15μm. When performing closed-loop annular laser etching on the cutting area on the back of the battery, the diameter of the laser spot is no greater than 1cm.

[0025] The beneficial effects of this invention are as follows:

[0026] The laser-assisted TOPCon battery bifacial processing system provided by this invention provides dual-wavelength lasers through a dual-wavelength laser source module. Under the control of a three-dimensional galvanometer system, the two laser beams of different wavelengths oscillate and scan along the grid line axis with an amplitude of ±15μm and a frequency of 10kHz, respectively, inducing local micro-melting zones to achieve sintering of the front grid lines. The ultraviolet laser scans in a ring path (linewidth 30μm) to directly vaporize the polycrystalline silicon layer, forming a passivation window with an inward shrinkage of 20μm to achieve back-side etching. Within ≤5 seconds after laser etching, passivation deposition is performed through a vacuum reaction chamber, eliminating interface exposure time and achieving "zero-delay passivation".

[0027] The laser-assisted TOPCon cell double-sided processing system integrates laser sintering, back etching and passivation deposition, saves the cutting and passivation equipment cost, and optimizes the basic resistance and passivation quality.

[0028] The laser-assisted TOPCon cell double-sided processing method provided by the application adopts axial oscillation scanning for laser sintering of the front grid lines, expands the contact interface, improves the effective contact point density, and reduces the contact resistance; the back ring etching pre-windowing avoids stress damage, reduces edge collapse and edge micro-crack density, and reduces the recombination current; in-situ passivation within 5s of etching makes the interface dangling bond saturated and reduces the interface state density. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a flowchart of the method of the application;

[0030] Figure 2 is a time axis of the deposition of the passivation layer after etching. DETAILED DESCRIPTION

[0031] The following describes the embodiments of the application by specific examples, and those skilled in the art can easily understand other advantages and effects of the application from the disclosure.

[0032] The exemplary embodiments of the application will be described with reference to the accompanying drawings, however, the application can be implemented in many different forms, and is not limited to the embodiments described herein, which are provided to fully and completely disclose the application and to fully convey the scope of the application to those skilled in the art. The terms used in the exemplary embodiments represented in the accompanying drawings are not limitations of the application.

[0033] Unless otherwise defined, the terms used herein (including technical terms) have the meanings commonly understood by those skilled in the art. In addition, it can be understood that the terms defined in commonly used dictionaries should be understood in the context of the relevant art, and should not be understood in an idealized or overly formal sense.

[0034] Example 1

[0035] The application provides a laser-assisted TOPCon cell double-sided processing system, comprising a dual-wavelength laser source module, a three-dimensional galvanometer system and a vacuum reaction cavity, the dual-wavelength laser source module emits laser beams of different wavelengths simultaneously for sintering of front grid lines of an electric sheet and back etching, and the three-dimensional galvanometer system is arranged in the vacuum reaction cavity.

[0036] The vacuum reaction cavity is provided with an optical window, the three-dimensional galvanometer system and the dual-wavelength laser source module are coupled through the optical window, the three-dimensional galvanometer system comprises a front scanning unit and a back control unit, the front scanning unit is used for receiving a laser beam and controlling reciprocating movement of the laser beam, and the back control unit is used for controlling a scanning path of the laser beam.

[0037] The dual-wavelength laser source module can simultaneously emit laser beams of 1064 nm and 355 nm wavelengths. The infrared laser beam of 1064 nm is used for sintering of the battery front grid line, and is oscillated up and down along the grid line axis with an amplitude of ±15 μm and a frequency of 10 kHz to induce a local micro-melt zone (diameter ≤3 μm) to form an Ag-Si alloy lattice. The 355 nm ultraviolet laser is scanned in a ring-shaped path, and the photon energy (3.5 eV) is greater than the Si-Si bond energy (2.3 eV), so that the polycrystalline silicon layer is directly gasified to form an inwardly retracted passivation window. Within ≤5 seconds after laser etching, passivation deposition is performed through the vacuum reaction cavity to eliminate the interface exposure time, thereby realizing "zero-delay passivation". The front scanning unit controls reciprocating movement of the laser beam along the XY axis, and the back control unit controls the ring-shaped path of the laser beam.

[0038] The laser-assisted TOPCon battery double-sided processing system integrates laser sintering, back etching and passivation deposition, which not only saves the cost of cutting and passivation equipment, eliminates mechanical stress and reduces edge micro-cracks, but also optimizes the basic resistance and passivation quality.

[0039] Embodiment 2

[0040] Based on the embodiment 1, the embodiment provides a laser-assisted TOPCon battery double-sided processing system, and the vacuum reaction cavity is provided with a temperature control platform and a gas spraying head.

[0041] The temperature control platform is used for placing a processed silicon wafer for front and back double-sided processing, and the temperature can be controlled at 20℃-80℃. The gas spraying head is used for introducing SiH4 and NH3, and the inlet is ≤10 cm away from the silicon wafer.

[0042] The vacuum reaction cavity is further provided with a gas mist isolation device, an inert gas inlet and a residue suction port.

[0043] Embodiment 3

[0044] The embodiment provides a laser-assisted TOPCon battery double-sided processing method, as shown in Figure 1 The method comprises the following steps:

[0045] Sintering is performed on the battery front grid line by axial periodic oscillation laser scanning;

[0046] Synchronous closed-loop ring-shaped laser etching is performed on the battery back cutting area;

[0047] The passivation layer is deposited on the etching surface within 5s after the etching is completed.

[0048] Further, the axial periodic oscillation laser scanning path of the positive grid line of the battery is a sinusoidal oscillation trajectory, the frequency is 8HZ~12HZ, the oscillation scanning power is 18W~22W, the interval is 10μm, and the scanning speed is 2m / s.

[0049] Further, the laser etching path of the back of the battery is a concentric double-ring structure, the inner diameter is 2mm shorter than the length of the battery side, and the ring interval is 30μm±5%. The back ring laser etching pre-windowing (inner shrinkage design) completely avoids mechanical cutting damage, and the edge collapse width is less than 5μm.

[0050] Further, the wavelength of the axial periodic oscillation laser scanning of the positive grid line of the battery is 1064nm, and the amplitude is 10μm~20μm; the wavelength of the laser etching of the back of the battery is 355nm.

[0051] Further, after the etching of the back of the battery is completed, a passivation layer is deposited within 0.5s, SiH4 and NH3 mixed gas is introduced through a gas spraying head, and the deposition rate is greater than 40nm / s.

[0052] Further, the depth of the closed loop ring etching is 120nm~180nm, the line width is 25μm~35μm, and the inner shrinkage window is 20μm (compatible with 1cm cutting channel).

[0053] Further, when the passivation layer is deposited, SiH4 and NH3 mixed gas is introduced to deposit SiN X The passivation layer, the thickness of the passivation layer is 150nm~200nm. The passivation layer deposited on the fresh interface of the laser etching adopts PECVD technology, as shown in Figure 2 SiH4 and NH3 are introduced within 5s, the Si-H / N-H bond is activated by plasma, the Si3N4 network is formed by combining with the dangling bond, the dangling bond is saturated, the interface state density is reduced, and the interface state density is less than 10¹ 0 eV⁻¹cm⁻². Among them, the spraying head adopts turbulent flow control, the gas flow rate of the center area is greater than that of the edge area, the proportion is 1.2:1, the rotational flow angle is 15°, and the film thickness uniformity is improved by ±2%.

[0054] Further, when the axial periodic oscillation laser scanning is performed, the laser performs axial ±15μm reciprocating motion along the positive grid line of the battery, and when the closed loop ring laser etching is performed on the cutting area of the back of the battery, the diameter of the laser spot is not greater than 1cm.

[0055] The application simultaneously acts laser sintering and laser etching on the front and back of the battery, expands the contact interface, improves the effective contact point density, reduces the contact resistance (pc<2 mΩ·cm²) by using axial oscillation scanning for laser sintering of the front grid line; avoids stress damage, reduces the edge micro-crack density, and reduces the recombination current (J0<5 fA / cm²) by pre-windowing the back ring etching; in-situ passivation within 5s of etching makes the interface dangling bond saturated, and reduces the interface state density to <10 0 eV⁻¹cm⁻²

[0056] Compared with the battery piece prepared by the application and the traditional step-by-step process (LECO→cutting→PECVD), the loss of later cutting can be reduced. The mechanical cutting stress peak value is greater than 300Mpa, which is greater than the fracture strength of the super-polysilicon 250Mpa, so cracks are inevitably generated by mechanical cutting, leading to edge micro-cracks, and secondary repair laser burns passivation layer, resulting in passivation failure and efficiency decay. The heat affected zone of the laser etching of the application is <1 μm (355 nm cold etching), and the thermal stress is <50 MPa, which is lower than the damage threshold; the buffer distance of the inner shrinkage window is 20 μm, which is greater than the crack propagation length (average 15 μm), so physical isolation protection can be achieved.

[0057] Embodiment 4

[0058] In order to further illustrate the effect of the method of the application, the battery piece is prepared on the basis of embodiment 3, and the specific process is as follows:

[0059] Step 1) Texturing: an alkali solution is used to etch the silicon wafer to form a pyramid textured structure;

[0060] Step 2) Front boron expansion: surface diffusion is performed by a boron source;

[0061] Step 3) Back etching: remove the BSG layer on the back of the expansion, and polish by alkali solution;

[0062] Step 4) Preparation of tunnel oxide layer: 1nm~2nm ultra-thin silicon oxide layer is prepared by ALD;

[0063] Step 5) Polysilicon in-situ phosphorus doping: LPCVD is used for in-situ phosphorus doping of polysilicon on the back;

[0064] Step 6) Front etching: etch the edge and front plated polysilicon thin film and PSG layer, and perform RCA cleaning;

[0065] Step 7) Front aluminum oxide passivation: the front aluminum oxide thin film is stacked by ALD atomic deposition method;

[0066] Step 8) Front and back film: hydrogen passivation is performed on the front and back of the silicon wafer by chemical vapor deposition, and a silicon nitride film is deposited on the surface;

[0067] Step 9) printing and sintering;

[0068] Step 10) front side grid line laser sintering and back side laser ring etching simultaneously:

[0069] Front side grid line laser sintering: 1064nm laser, axial oscillation scanning (amplitude ±15μm, frequency 10kHz, power 20W), contact resistance reduced to 1.8 mΩ·cm².

[0070] Back side laser ring etching: 355nm laser, concentric double-ring path (inner diameter 2mm shorter than cell side length, ring spacing 30μm, depth 150nm, line width 30μm), edge collapse width <5μm.

[0071] In-situ passivation: SiH4 / NH3 mixed gas was introduced within 0.5 seconds after etching, and SiN was deposited X Passivation layer (thickness 180nm, deposition rate 45nm / s), interface state density <10¹ 0 eV⁻¹cm⁻².

[0072] Comparative example:

[0073] Different from Example 4, Step 10) was laser sintering, and other steps were the same.

[0074] The battery pieces prepared from Example 4 and the comparative example were tested, and the results are shown in Table 1.

[0075] Table 1 Performance parameters

[0076]

[0077] From Table 1, it can be seen that by using the laser-assisted double-sided synchronous processing technology, the following advantages are achieved:

[0078] 1. Efficiency improvement: the absolute value of conversion efficiency increased by 1.1% (26.16% vs 26.05%), mainly due to the reduction of contact resistance and recombination current.

[0079] 2. Process simplification: sintering, etching and passivation are integrated, saving equipment cost (reducing cutting and secondary passivation equipment).

[0080] 3. Reliability enhancement: edge micro-cracks reduced by 80%, passivation quality significantly improved (interface state density reduced by an order of magnitude).

[0081] 4. Compatibility: suitable for large-size silicon wafers (182 / 210mm), and the process parameters can be adapted to the existing TOPCon production line.

[0082] The performance bottleneck caused by mechanical cutting and passivation delay in the traditional process is completely broken, and the application provides an efficient and low-cost solution for mass production of TOPCon cells.

[0083] In summary, the laser-assisted TOPCon cell double-sided processing system provided by the application provides dual-wavelength laser through a dual-wavelength laser source module, and under the control of a three-dimensional galvanometer system, the laser beams of the two wavelengths are respectively oscillated and scanned along the grid line axis with an amplitude of ±15μm and a frequency of 10kHz, to induce a local micro-melt area to realize front grid line sintering, and the ultraviolet laser is scanned in a ring path (line width 30μm) to directly gasify the polycrystalline silicon layer, form a 20μm retracted passivation window to realize back etching, and within ≤5 seconds after laser etching, passivation deposition is performed through a vacuum reaction chamber to eliminate interface exposure time and realize "zero delay passivation".

[0084] The laser-assisted TOPCon cell double-sided processing system integrates laser sintering, back etching and passivation deposition, which not only saves the cost of cutting and passivation equipment, but also optimizes the basic resistance and passivation quality.

[0085] The laser-assisted TOPCon cell double-sided processing method provided by the application expands the contact interface by using axial oscillation scanning for laser sintering of the front grid line, improves the effective contact point density, reduces the contact resistance, pre-opens the window by ring etching on the back, avoids stress damage, reduces the edge collapse, reduces the edge micro-crack density and reduces the recombination current, and in-situ passivation within 5s of etching makes the interface dangling bond saturated and reduces the interface state density. The application avoids the physical damage of the doped layer caused by traditional mechanical cutting, and at the same time maintains the integrity of the doped structure through local processing of the laser, finally realizes the efficiency improvement.

[0086] The above examples are only illustrative of the application and do not constitute a limitation on the protection scope of the application, and any design identical or similar to the application falls within the protection scope of the application.

Claims

1. A laser-assisted double-sided processing system for TOPCon batteries, characterized in that: It includes a dual-wavelength laser source module, a three-dimensional galvanometer system, and a vacuum reaction chamber. The dual-wavelength laser source module emits lasers of different wavelengths simultaneously for sintering the front grid lines and etching the back side of the electrode sheet. The three-dimensional galvanometer system is located inside the vacuum reaction chamber. The vacuum reaction chamber is provided with an optical window, and the three-dimensional galvanometer system and the dual-wavelength laser source module are coupled through the optical window. The three-dimensional galvanometer system includes a front scanning unit and a back control unit. The front scanning unit is used to receive the laser beam and control its reciprocating motion, and the back control unit is used to control the laser beam scanning path.

2. The laser-assisted TOPCon battery double-sided processing system according to claim 1, characterized in that: The vacuum reaction chamber is equipped with a temperature-controlled platform and a gas spray head.

3. A laser-assisted double-sided processing method for TOPCon batteries, characterized in that: The laser-assisted TOPCon battery double-sided processing system described in claim 1 or 2 includes the following steps: Sintering is performed by axial periodic oscillating laser scanning on the front grid lines of the battery. Simultaneously perform closed-loop annular laser etching on the cutting area on the back of the battery; A passivation layer is deposited on the etched surface within 5 seconds after etching is completed.

4. The laser-assisted double-sided processing method for TOPCon batteries according to claim 3, characterized in that: The laser scanning path for the axial periodic oscillation of the grid lines on the front of the battery is a sinusoidal oscillation trajectory with a frequency of 8 Hz to 12 Hz and an oscillation scanning power of 18 W to 22 W.

5. The laser-assisted double-sided processing method for TOPCon batteries according to claim 3, characterized in that: The laser etching path on the back of the battery is a concentric double-ring structure, with the inner diameter being 2mm shorter than the side length of the battery and the ring spacing being 30μm±5%.

6. The laser-assisted double-sided processing method for TOPCon batteries according to claim 3, characterized in that: The wavelength of the axial periodic oscillation laser scanning of the grid lines on the front of the battery is 1064nm, and the amplitude is 10μm~20μm; the wavelength of the laser etching on the back of the battery is 355nm.

7. The laser-assisted double-sided processing method for TOPCon batteries according to claim 3, characterized in that: After the back of the battery is etched, a passivation layer is deposited within 0.5s. A mixture of SiH4 and NH3 gas is introduced through a gas spray head, and the deposition rate is greater than 40nm / s.

8. The laser-assisted double-sided processing method for TOPCon batteries according to claim 3, characterized in that: The depth of the closed-loop ring etching is 120 nm to 180 nm, and the linewidth is 25 μm to 35 μm.

9. The laser-assisted double-sided processing method for TOPCon batteries according to claim 3, characterized in that: SiN was deposited by introducing a mixed gas of SiH4 and NH3 during the deposition of the passivation layer. X Passivation layer, with a thickness of 150nm~200nm.

10. A laser-assisted double-sided processing method for TOPCon batteries according to claim 3, characterized in that: During axial periodic oscillating laser scanning, the laser reciprocates along the grid lines on the front of the battery within ±15μm. When performing closed-loop annular laser etching on the cutting area on the back of the battery, the diameter of the laser spot is no greater than 1cm.

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