TOPCon battery with laser slotting contact structure and preparation method of TOPCon battery

Abstract

The invention belongs to the technical field of solar cells, and provides a TOPCon cell with a laser slotting contact structure and a preparation method of the TOPCon cell. The method comprises the following steps of: firstly, forming a plurality of discontinuous micro contact pits which are arranged in an array on an anti-reflection passivation laminated layer on the front surface of a cell by adopting a non-thermal ablation mode, and exposing an emitting electrode below in a lossless manner; then, in-situ selective heavy doping is carried out on the emitting electrode at the bottom of the contact pit, and a high-concentration doped region is formed below each contact pit, so that the electrical environment of a contact interface is optimized, and a strong field passivation effect is provided; special front silver paste which is accurately matched with the microstructure and has low corrosivity is adopted for filling; and finally, a forward bias current is injected into the battery while a laser beam is used for instantaneous local heating, and due to the synergistic effect, interface defects possibly generated in the sintering process can be repaired in situ while low-resistance ohmic contact is formed.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology and relates to a TOPCon cell with a laser-grooved contact structure and its preparation method. Background Art

[0002] In recent years, tunnel oxide passivated contact (TOPCon) cell technology has rapidly become the mainstream technology route in the photovoltaic industry due to its excellent passivation performance and high conversion efficiency potential. However, the unstable contact quality between the front metal electrode and the semiconductor affects the performance of TOPCon cells.

[0003] Currently, the mainstream front-side metallization process is high-temperature screen printing sintering. This process relies on the melting of glass powder in conductive silver paste at high temperatures, "burning through" the anti-reflection passivation layer on the battery surface, thereby achieving physical and electrical connection between the silver electrode and the underlying silicon emitter. Although this "burn-through" mechanism achieves conductivity, the process has shortcomings: First, the chemical etching effect of the glass powder causes irreversible damage to the anti-reflection passivation layer, directly impairing the battery's open-circuit voltage; second, the intense reaction at high temperatures can easily form defects such as "silver nails" at the contact interface, piercing the silicon emitter and increasing the risk of leakage. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a TOPCon battery with a laser-grooved contact structure and its fabrication method. First, discontinuous contact pits are precisely fabricated on an anti-reflection passivation stack using a cold ablation method. Then, the bottom of the pits is selectively and in-situ heavily doped to form an N++ heavily doped region with both low barrier and strong field passivation effects. Subsequently, a specially formulated low-corrosion silver paste matching this structure is used for filling. Finally, a photoelectric synergistic sintering process is employed, simultaneously injecting a forward bias current to form a high-quality ohmic contact, thereby meeting the needs of actual production.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a method for fabricating a TOPCon battery with a laser-grooved contact structure, the method comprising:

[0007] S1, using a first laser beam to process and form discontinuous contact pits arranged in a single-row array along the grid line direction on the anti-reflection passivation stack on the front side of the TOPCon cell, so as to expose the emitter below;

[0008] S2, a second laser beam is used to selectively re-dop the emitter at the bottom of the contact pit to form an N++ heavily doped region under each contact pit;

[0009] S3, apply the front silver paste to the surface of the anti-reflection passivation stack and fill it into the contact pit;

[0010] S4 uses a third laser beam to scan the grid area filled with silver paste for local heating while injecting a forward bias current into the TOPCon cell to form an ohmic contact between the N++ heavily doped region and the silver paste.

[0011] Specifically, it includes:

[0012] S1, a TOPCon battery semi-finished product with an anti-reflection passivation stack already formed on the front side is placed in a laser processing equipment, and a first laser beam is used to process the anti-reflection passivation stack on the front side of the TOPCon battery to form discontinuous contact pits arranged in a single-row array along the grid line direction to expose the emitter below.

[0013] S2, a second laser beam is used to selectively re-dop the emitter at the bottom of the contact pit to form an N++ heavily doped region under each contact pit;

[0014] S3 uses a screen printing process to apply front-side silver paste to the surface of the anti-reflection passivation stack, filling the contact pits and forming fine grid lines. After printing, the solar cells are dried to obtain dried solar cells.

[0015] S4 uses a third laser beam to scan and dry the grid area filled with silver paste in the cell for local heating, while injecting a forward bias current into the TOPCon cell to form an ohmic contact between the N++ heavily doped region and the silver paste.

[0016] Step S1 utilizes a "cold processing" laser ablation method. The laser pulse time used in this step is extremely short, directly vaporizing and removing the material of the anti-reflection passivation layer. The heat hardly diffuses to the area around the contact pit, thus forming a very small heat-affected zone, which can perfectly preserve the passivation layer performance of the adjacent area.

[0017] In step S2, the laser briefly and locally heats the silicon surface at the bottom of the contact pit and the doped (boron) glass layer covering it, bringing them to a molten state. In this high-temperature liquid state, the diffusion ability of boron atoms is enhanced, and they rapidly migrate from the glass layer into the molten silicon. After laser irradiation ends, the molten region rapidly cools and re-solidifies, thereby fixing a high concentration of boron atoms within the silicon lattice, forming an N++ heavily doped region. This heavily doped layer has a dual function: firstly, it reduces the resistance at the contact between the semiconductor and the metal; secondly, by creating a strong electric field, it effectively blocks minority carriers from flowing to the contact interface, achieving a "field passivation" effect and reducing electrical losses in this region.

[0018] The silver paste used in step S3 can flow smoothly into and fill the micron-sized contact pits. At the same time, the content of glass powder in the silver paste is greatly reduced, and the chemical properties are milder. The role of glass powder is no longer to erode the passivation layer, but to act as a "flux" in the final sintering step, helping the silver particles to better bond with the heavily doped silicon surface and form a good metallurgical contact.

[0019] The mechanism of step S4 involves the simultaneous occurrence of heating and forming with defect repair. In this step, the laser beam causes silver and silicon to form an alloy, while the overall temperature of the battery remains at a low level, avoiding global thermal damage to battery performance. Simultaneously with laser heating, a positive current is injected into the battery. This generates auxiliary Joule heating, resulting in more uniform sintering. Furthermore, the charge carriers flowing through the interface actively repair or neutralize electronic defects that may arise during laser heating, ensuring extremely low interfacial recombination while forming low-resistance contacts.

[0020] As a preferred embodiment of the present invention, in S1, the contact pit is circular with a diameter of 5-10 μm and a depth of 0.5-1.5 μm. The edge spacing between two adjacent contact pits is 1-5 μm. For example, the diameter can be (5, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5 or 10) μm, the depth can be (0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5) μm, and the edge spacing between two adjacent contact pits can be (1.0, 1.4, 1.8, 2.2, 2.6, 3.0, 3.4, 3.8, 4.2, 4.6 or 5.0) μm. However, it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0021] In some optional embodiments, the single-row array of contact pits consists of multiple contact pit groups, each containing 10 contact pits, with passivation intervals between adjacent contact pit groups.

[0022] In some optional embodiments, the first laser beam is a deep ultraviolet picosecond laser with a wavelength of 266 nm, a pulse width of 10-30 ps, ​​a single pulse energy of 0.8-1.2 μJ, and an energy density of 8-12 J / cm². 2The repetition frequency is 1-2MHz, and the scanning method is a combination of galvanometer and platform. The galvanometer is responsible for the rapid scanning of the circular array within a single fine gate line, while the platform is responsible for silicon wafer stepping. The positioning accuracy is ±1μm. For example, the pulse width can be (10, 12, 14, 16, 18, 20, 22, 24, 26, 28, or 30) ps, the single pulse energy is (0.8, 0.84, 0.88, 0.92, 0.96, 1.0, 1.04, 1.08, 1.12, 1.16, or 1.2) μJ, and the energy density is (8, 8.4, 8.8, 9.2, 9.6, 10.0, 10.4, 10.8, 11.2, 11.6, or 12) J / cm². 2 The repetition frequency is (1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2.0) MHz, but is not limited to the listed values; other unlisted values ​​within this range also apply.

[0023] In a preferred embodiment of the present invention, in S2, the second laser beam is a green laser or an infrared laser.

[0024] In some optional embodiments, the surface boron concentration of the N++ heavily doped region is (1-2) × 10⁻⁶. 20 cm -3 For example, it could be (1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, or 2.0) × 10 20 cm -3 However, this does not apply to all values ​​listed; other unlisted values ​​within the same range also apply.

[0025] In some alternative embodiments, the junction depth of the N++ heavily doped region is 0.6-0.7 μm, for example, it can be (0.6, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69 or 0.7) μm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0026] As a preferred embodiment of the present invention, in S3, the mass ratio of silver powder, glass powder, and silane coupling agent in the front-side silver paste is (96-97.5):(1-3):(0.5-1), the softening point of the glass powder is 400-500℃, and the silver powder comprises 90-95 wt.% spherical silver powder and 5-10 wt.% flake silver powder, the particle size of the spherical silver powder is 1-2 μm, and the particle size of the flake silver powder is 2-3 μm. For example, it can be silver powder from the front-side silver paste. The mass ratio of powder, glass powder, and silane coupling agent is (96, 96.15, 96.3, 96.45, 96.6, 96.75, 96.9, 97.05, 97.2, 97.35, or 97.5): (1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, or 3.0): (0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or 0.85). The glass powder has a softening point of (400, 410, 420, 430, 440, 450, 460, 470, 480, 490 or 500) °C, and the silver powder contains (90, 90.5, 91, 91.5, 92, 92.5, 93, 93.5, 94, 94.5 or 95) wt.% spherical silver powder and (5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5) wt. Or 10) wt.% of flake silver powder, with particle sizes of (1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2.0) μm for spherical silver powder and (2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.0) μm for flake silver powder, but not limited to the listed values; other unlisted values ​​within this range also apply.

[0027] In some optional embodiments, the drying temperature is 200-210°C, for example, it can be 200°C, 201°C, 202°C, 203°C, 204°C, 205°C, 206°C, 207°C, 208°C, 209°C or 210°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0028] As a preferred embodiment of the present invention, in S4, the third laser beam is a green laser with a wavelength of 532nm.

[0029] In some optional embodiments, the power density of the third laser beam is 10. 5 -10 7 W / cm 2 For example, it could be 10 5 W / cm 2 10 6 W / cm2 10 7 W / cm 2 However, this does not apply to all values ​​listed; other unlisted values ​​within the same range also apply.

[0030] In some alternative embodiments, the forward bias current density is 0.5-2 A / cm². 2 For example, it could be 0.5A / cm 2 0.65A / cm 2 0.8A / cm 2 0.95A / cm 2 1.1A / cm 2 1.25A / cm 2 1.4A / cm 2 1.55A / cm 2 1.7A / cm 2 1.85A / cm 2 Or 2.0A / cm 2 However, this does not apply to all values ​​listed; other unlisted values ​​within the same range also apply.

[0031] Secondly, the present invention provides a TOPCon battery with a laser-grooved contact structure prepared by the preparation method described in the first aspect.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention, through the laser selective doping step, pre-constructs a heavily doped region with both low barrier and strong field passivation effect at the bottom of the contact pit before metal contact, so that subsequent metal contact no longer needs to rely on the corrosive high temperature burn-through process, eliminating damage to the passivation layer from the source. Thus, while ensuring extremely low contact resistance, the interface recombination in the contact area is suppressed to a low level, improving the open circuit voltage and improving the battery conversion efficiency. Detailed Implementation

[0033] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The embodiments described herein are specific implementations of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limiting the implementation of the present invention or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0034] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone any further purification treatment.

[0035] Example 1

[0036] This embodiment provides a TOPCon battery with a laser-grooved contact structure and its fabrication method. The fabrication method specifically includes the following steps:

[0037] S1, a TOPCon battery semi-finished product with an anti-reflection passivation stack already formed on the front side is placed in a laser processing device. A first laser beam is used to process discontinuous contact pits arranged in a single-row array along the grid line direction on the anti-reflection passivation stack on the front side of the TOPCon battery to expose the emitter underneath. The first laser beam is a deep ultraviolet picosecond laser with a wavelength of 266nm, a pulse width of 12ps, a single pulse energy of 1.15μJ, and an energy density of 11.5J / cm². 2 The repetition frequency is 1.8MHz, and the scanning method is a combination of galvanometer and platform. The galvanometer is responsible for the rapid scanning of the circular array within a single fine gate line, and the platform is responsible for the silicon wafer stepping. The positioning accuracy is ±1μm. The processed contact pits are circular with a diameter of 9μm and a depth of 1.3μm. The edge spacing between two adjacent contact pits is 2μm. The contact pits arranged in the single column array are multiple contact pit groups, each contact pit group contains 10 contact pits, and there is a passivation zone between adjacent contact pit groups.

[0038] S2, a second laser beam is used to selectively re-dope the emitter at the bottom of the contact pit to form an N++ heavily doped region below each contact pit. The second laser beam is an infrared laser, and the surface boron concentration of the N++ heavily doped region reaches 1.9 × 10⁻⁶. 20 cm -3 The junction depth of the N++ heavily doped region is 0.68 μm;

[0039] S3. The front silver paste is applied to the surface of the anti-reflection passivation stack through screen printing and fills the contact pits to form fine grid lines. After printing, the battery cell is dried to obtain a dried battery cell. The mass ratio of silver powder, glass powder and silane coupling agent in the front silver paste is 97.2:1.8:0.5. The softening point of the glass powder is 420℃. The silver powder consists of 94wt.% spherical silver powder with a particle size of 1μm and 6wt.% flake silver powder with a particle size of 2μm. After printing, the battery cell is dried in an oven at 200℃.

[0040] S4, while using a third laser beam to scan and locally heat the grid area filled with silver paste in the dried solar cell, a forward bias current is injected into the TOPCon cell to form an ohmic contact between the N++ heavily doped region and the silver paste. The third laser beam is a green laser with a wavelength of 532nm and its power density is set to 5×10⁻⁶. 5 W / cm 2The forward bias current density is 1.8 A / cm². 2 A TOPCon battery with a laser-grooved contact structure was obtained.

[0041] Example 2

[0042] This embodiment provides a TOPCon battery with a laser-grooved contact structure and its fabrication method. The fabrication method specifically includes the following steps:

[0043] S1, a TOPCon battery semi-finished product with an anti-reflection passivation stack already formed on the front side is placed in a laser processing device. A first laser beam is used to process discontinuous contact pits arranged in a single-row array along the grid line direction on the anti-reflection passivation stack on the front side of the TOPCon battery to expose the emitter underneath. The first laser beam is a deep ultraviolet picosecond laser with a wavelength of 266nm, a pulse width of 28ps, a single pulse energy of 0.85μJ, and an energy density of 8.5J / cm². 2 The repetition frequency is 1.2MHz, and the scanning method is a combination of galvanometer and platform. The galvanometer is responsible for the rapid scanning of the circular array within a single fine gate line, and the platform is responsible for the silicon wafer stepping. The positioning accuracy is ±1μm. The processed contact pits are circular with a diameter of 6μm and a depth of 0.8μm. The edge spacing between two adjacent contact pits is 4.5μm. The contact pits arranged in the single column array are multiple contact pit groups, each contact pit group contains 10 contact pits, and there is a passivation zone between adjacent contact pit groups.

[0044] S2, a second laser beam is used to selectively re-dope the emitter at the bottom of the contact pit to form an N++ heavily doped region below each contact pit. The second laser beam is a green laser, and the surface boron concentration of the N++ heavily doped region reaches 1.2 × 10⁻⁶. 20 cm -3 The junction depth of the N++ heavily doped region is 0.62 μm;

[0045] S3. Through screen printing, the front silver paste is applied to the surface of the anti-reflection passivation stack and fills the contact pits to form fine grid lines. After printing, the battery cell is dried to obtain a dried battery cell. The mass ratio of silver powder, glass powder and silane coupling agent in the front silver paste is 96.2:2.8:0.9. The softening point of the glass powder is 490℃. The silver powder consists of 91wt.% spherical silver powder with a particle size of 2μm and 9wt.% flake silver powder with a particle size of 2μm. After printing, the battery cell is dried in an oven at 210℃.

[0046] S4, while using a third laser beam to scan and locally heat the grid area filled with silver paste in the dried solar cell, a forward bias current is injected into the TOPCon cell to form an ohmic contact between the N++ heavily doped region and the silver paste. The third laser beam is a green laser with a wavelength of 532nm and its power density is set to 10. 5 W / cm 2 The forward bias current density is 0.7 A / cm². 2 A TOPCon battery with a laser-grooved contact structure was obtained.

[0047] Example 3

[0048] This embodiment provides a TOPCon battery with a laser-grooved contact structure and its fabrication method. The fabrication method specifically includes the following steps:

[0049] S1, a TOPCon battery semi-finished product with an anti-reflection passivation stack already formed on the front side is placed in a laser processing device. A first laser beam is used to process discontinuous contact pits arranged in a single-row array along the grid line direction on the anti-reflection passivation stack on the front side of the TOPCon battery to expose the emitter underneath. The first laser beam is a deep ultraviolet picosecond laser with a wavelength of 266nm, a pulse width of 20ps, a single pulse energy of 1.0μJ, and an energy density of 10J / cm². 2 The repetition frequency is 1.5MHz, and the scanning method is a combination of galvanometer and platform. The galvanometer is responsible for the rapid scanning of the circular array within a single fine gate line, and the platform is responsible for the silicon wafer stepping. The positioning accuracy is ±1μm. The processed contact pits are circular with a diameter of 10μm and a depth of 0.6μm. The edge spacing between two adjacent contact pits is 1.5μm. The contact pits arranged in the single column array are multiple contact pit groups, each contact pit group contains 10 contact pits, and there is a passivation zone between adjacent contact pit groups.

[0050] S2, a second laser beam is used to selectively re-dope the emitter at the bottom of the contact pit to form an N++ heavily doped region below each contact pit. The second laser beam is a green laser, and the surface boron concentration of the N++ heavily doped region reaches 1.5 × 10⁻⁶. 20 cm -3 The junction depth of the N++ heavily doped region is 0.7 μm;

[0051] S3. Through screen printing, the front silver paste is applied to the surface of the anti-reflection passivation stack and fills the contact pits to form fine grid lines. After printing, the battery cell is dried to obtain a dried battery cell. The mass ratio of silver powder, glass powder and silane coupling agent in the front silver paste is 97:2:0.8. The softening point of the glass powder is 450℃. The silver powder consists of 95wt.% spherical silver powder with a particle size of 1μm and 5wt.% flake silver powder with a particle size of 3μm. After printing, the battery cell is dried in an oven at 206℃.

[0052] S4, while using a third laser beam to scan and locally heat the grid area filled with silver paste in the dried solar cell, a forward bias current is injected into the TOPCon cell to form an ohmic contact between the N++ heavily doped region and the silver paste. The third laser beam is a green laser with a wavelength of 532nm and its power density is set to 3×10⁻⁶. 6 W / cm 2 The forward bias current density is 1.0 A / cm². 2 A TOPCon battery with a laser-grooved contact structure was obtained.

[0053] Example 4

[0054] This embodiment provides a TOPCon battery with a laser-grooved contact structure and its fabrication method. The fabrication method specifically includes the following steps:

[0055] S1, a TOPCon battery semi-finished product with an anti-reflection passivation stack already formed on the front side is placed in a laser processing device. A first laser beam is used to process the anti-reflection passivation stack on the front side of the TOPCon battery to form discontinuous contact pits arranged in a single-row array along the grid line direction, so as to expose the emitter underneath. The first laser beam is a deep ultraviolet picosecond laser with a wavelength of 266nm, a pulse width of 15ps, a single pulse energy of 0.9μJ, and an energy density of 9J / cm². 2 The repetition frequency is 1.1MHz, and the scanning method is a combination of galvanometer and platform. The galvanometer is responsible for the rapid scanning of the circular array within a single fine gate line, and the platform is responsible for silicon wafer stepping. The positioning accuracy is ±1μm. The processed contact pits are circular with a diameter of 5μm and a depth of 1.5μm. The edge spacing between two adjacent contact pits is 5μm. The contact pits arranged in the single column array are multiple contact pit groups, each contact pit group contains 10 contact pits, and there is a passivation zone between adjacent contact pit groups.

[0056] S2, a second laser beam is used to selectively re-dope the emitter at the bottom of the contact pit to form an N++ heavily doped region below each contact pit. The second laser beam is an infrared laser, and the surface boron concentration of the N++ heavily doped region reaches 1.7 × 10⁻⁶. 20 cm-3 The junction depth of the N++ heavily doped region is 0.61 μm;

[0057] S3. Through screen printing, the front silver paste is applied to the surface of the anti-reflection passivation stack and fills the contact pits to form fine grid lines. After printing, the battery cell is dried to obtain a dried battery cell. The mass ratio of silver powder, glass powder and silane coupling agent in the front silver paste is 96:1.5:1. The softening point of the glass powder is 470℃. The silver powder consists of 90wt.% spherical silver powder with a particle size of 2μm and 10wt.% flake silver powder with a particle size of 3μm. After printing, the battery cell is dried in an oven at 204℃.

[0058] S4, while using a third laser beam to scan and locally heat the grid area filled with silver paste in the dried solar cell, a forward bias current is injected into the TOPCon cell to form an ohmic contact between the N++ heavily doped region and the silver paste. The third laser beam is a green laser with a wavelength of 532nm and its power density is set to 10. 7 W / cm 2 The forward bias current density is 2.0 A / cm². 2 A TOPCon battery with a laser-grooved contact structure was obtained.

[0059] Comparative Example 1

[0060] This comparative example provides a TOPCon battery with a laser-grooved contact structure and its fabrication method. The difference between this example and Example 1 is that S2 is skipped and the emitter at the bottom of the contact pit is not selectively heavily doped. Other process parameters and operating conditions are exactly the same as in Example 1.

[0061] Comparative Example 2

[0062] This comparative example provides a TOPCon battery with a laser-grooved contact structure and its preparation method. The difference between this example and Example 1 is that S4 is not used; instead, a conventional high-temperature sintering furnace is used. Other process parameters and operating conditions are exactly the same as in Example 1.

[0063] Comparative Example 3

[0064] This comparative example provides a TOPCon battery with a laser-grooved contact structure and its preparation method. The difference between this example and Example 1 is that a conventional silver paste containing a high proportion of corrosive glass powder is used instead of the front silver paste in S3. Other process parameters and operating conditions are exactly the same as in Example 1.

[0065] Performance tests were conducted on a TOPCon battery with a laser-grooved contact structure prepared in Examples 1-4 and Comparative Examples 1-3, wherein:

[0066] The test methods for open-circuit voltage and fill factor include:

[0067] Test equipment: A solar simulator that meets the Class AAA standard defined in IEC 60904-9, ensuring that spectral matching, irradiance inhomogeneity, and temporal instability meet Class A specifications; an IV measurement unit equipped with a four-point probe measurement system to eliminate the influence of measurement leads and probe contact resistance on test results; a temperature-controlled test platform capable of precisely controlling the temperature of the tested battery at 25.0±1.0℃; and a standard reference battery calibrated by a calibration institution and possessing a traceable calibration certificate.

[0068] Test conditions: Irradiation intensity: 1000 W / m 2 Spectral distribution: AM1.5G (IEC 60904-3 standard); Battery temperature: 25.0±1.0℃;

[0069] Test Procedure: Before the test begins, the irradiance of the solar simulator is calibrated using a standard reference cell to ensure that its setpoints are consistent with the STC requirements. The sample of the battery under test is placed on a temperature-controlled test platform. Once the sample reaches the set test temperature and achieves thermal equilibrium, the four probes of the IV measurement unit are precisely and reliably brought into contact with the positive and negative main grid lines of the battery under test, and the test sequence is initiated. At the instant the solar simulator emits a stable light pulse, the IV measurement unit rapidly scans the load, recording a series of current-voltage data points from the open-circuit state (I≈0) to the short-circuit state (V≈0), generating a complete IV curve. Based on the acquired IV curve, the test software calculates and extracts the open-circuit voltage and fill factor performance parameters.

[0070] Methods for testing saturation current density include:

[0071] Test equipment: The quasi-steady-state photoconductance (Suns-Voc) measurement system is used. The system is equipped with a high-intensity flash lamp source, an RF induction coil for non-contact measurement of minority carrier concentration, and a probe for measuring open-circuit voltage.

[0072] Test Procedure: The battery sample to be tested was placed on the measurement platform of the Suns-Voc system. The measurement program was started, and the system's flash lamp emitted a light pulse with exponentially decaying intensity to illuminate the sample. Throughout the entire process of light intensity decay, the system synchronously and at high frequency recorded the instantaneous photogenerated minority carrier concentration and the corresponding instantaneous open-circuit voltage. Based on the collected data points, the system plotted the relationship curve between the injection level (minority carrier concentration) and the open-circuit voltage (i.e., the Suns-Voc curve). The saturation current density was calculated by fitting and analyzing this curve using an ideal diode model. The test results are shown in Table 1.

[0073] Table 1. Test results of a TOPCon battery with a laser-grooved contact structure prepared in Examples 1-4 and Comparative Examples 1-3.

[0074] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Open circuit voltage (mV) 730 734 735 732 718 720 724 Fill factor (%) 84.8 84.5 85.0 84.7 80.5 82.0 78.0 <![CDATA[Saturation current density (fA / cm 2 ).]]> 6.8 7.2 7.1 7.4 10.5 12.0 8.7

[0075] As shown in Table 1, compared to Example 1, Comparative Example 1 exhibits a decrease in open-circuit voltage, a decrease in fill factor, and an increase in saturation current density; Comparative Example 2 shows a decrease in open-circuit voltage, a decrease in fill factor, and an increase in saturation current density; and Comparative Example 3 shows a decrease in open-circuit voltage, a decrease in fill factor, and an increase in saturation current density. This is because Comparative Example 1 does not selectively heavily dope the emitter at the bottom of the contact pit. When the metal (silver) directly contacts the n-type semiconductor, a Schottky barrier is formed at the interface due to the difference in work function, hindering the flow of majority carriers (electrons) from the semiconductor to the metal. Macroscopically, this manifests as a high contact resistivity, leading to a decrease in fill factor. Simultaneously, the N++ heavily doped region forms a built-in electric field that inhibits interface recombination. Therefore, Comparative Example 1 lacks a field passivation effect, increasing the interface recombination rate, resulting in an increase in saturation current density and a decrease in open-circuit voltage. Comparative Example 2 uses a conventional high-temperature sintering furnace, where the global high temperature causes severe thermal damage to battery life and surface passivation, thus resulting in a decrease in open-circuit voltage, a decrease in fill factor, and an increase in saturation current density. In Comparative Example 3, a traditional silver paste containing a high proportion of corrosive glass powder was used. The laser energy of the third laser beam was insufficient to completely melt the glass powder and complete its etching / wetting function. Unmelted or semi-melted glass powder remained at the interface, forming an insulating or semi-insulating physical barrier layer. This severely hindered the charge transfer between silver and N++ silicon, resulting in extremely high contact resistance. Consequently, the open-circuit voltage decreased, the fill factor decreased, and the saturation current density increased.

[0076] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for fabricating a TOPCon battery with a laser-grooved contact structure, characterized in that, The preparation method includes: S1, using a first laser beam to process and form discontinuous contact pits arranged in a single-row array along the grid line direction on the anti-reflection passivation stack on the front side of the TOPCon cell, so as to expose the emitter below; S2, a second laser beam is used to selectively re-dop the emitter at the bottom of the contact pit to form an N++ heavily doped region under each contact pit; S3, apply the front silver paste to the surface of the anti-reflection passivation stack and fill it into the contact pit; S4 uses a third laser beam to scan the grid area filled with silver paste for local heating while injecting a forward bias current into the TOPCon cell to form an ohmic contact between the N++ heavily doped region and the silver paste.

2. The method for fabricating a TOPCon battery with a laser-grooved contact structure according to claim 1, characterized in that, In S1: The contact pit is circular, with a diameter of 5-10 μm and a depth of 0.5-1.5 μm. The distance between the edges of two adjacent contact pits is 1-5 μm.

3. The method for fabricating a TOPCon battery with a laser-grooved contact structure according to claim 1, characterized in that, In S1: The single-row array of contact pits consists of multiple contact pit groups, each containing 10 contact pits, with passivation intervals between adjacent contact pit groups.

4. The method for fabricating a TOPCon battery with a laser-grooved contact structure according to claim 1, characterized in that, In S1: The first laser beam is a deep ultraviolet picosecond laser with a wavelength of 266 nm, a pulse width of 10-30 ps, ​​a single pulse energy of 0.8-1.2 μJ, and an energy density of 8-12 J / cm². 2 The repetition frequency is 1-2MHz, and the scanning method is a combination of galvanometer and platform. The galvanometer is responsible for the rapid scanning of the circular array within a single fine gate line, and the platform is responsible for the silicon wafer stepping. The positioning accuracy is ±1μm.

5. The method for fabricating a TOPCon battery with a laser-grooved contact structure according to claim 1, characterized in that, In S2: The second laser beam is a green laser or an infrared laser.

6. The method for fabricating a TOPCon battery with a laser-grooved contact structure according to claim 1, characterized in that, In S2: The surface boron concentration of the N++ heavily doped region is (1-2)×10 20 cm -3 ; The junction depth of the N++ heavily doped region is 0.6-0.7 μm.

7. The method for fabricating a TOPCon battery with a laser-grooved contact structure according to claim 1, characterized in that, In S3: The mass ratio of silver powder, glass powder and silane coupling agent in the front silver paste is (96-97.5):(1-3):(0.5-1). The softening point of the glass powder is 400-500℃. The silver powder contains 90-95wt.% spherical silver powder and 5-10wt.% flake silver powder. The particle size of the spherical silver powder is 1-2μm and the particle size of the flake silver powder is 2-3μm.

8. The method for fabricating a TOPCon battery with a laser-grooved contact structure according to claim 1, characterized in that, In S4: The third laser beam is a green laser with a wavelength of 532nm; The power density of the third laser beam is 10. 5 -10 7 W / cm 2 .

9. The method for fabricating a TOPCon battery with a laser-grooved contact structure according to claim 1, characterized in that, In S4: The forward bias current density is 0.5-2 A / cm². 2 .

10. A TOPCon battery with a laser-grooved contact structure is obtained by the preparation method according to any one of claims 1-9.