Low-temperature laser synchronous welding method for main-grid-free structure of TOPCon battery

Abstract

The invention belongs to the technical field of laser material processing, and relates to a low-temperature laser synchronous welding method for a main-grid-free structure of a TOPCon battery, which comprises the following steps of: dividing and shaping incident laser into a plurality of paths of independent laser sub-beams matched with a fine grid line pattern through a spatial light modulator, and constructing a synchronous laser dot matrix energy field; the method comprises the following steps of: obtaining temperature distribution of a welding area in real time through a high-resolution infrared thermal imager, constructing a full-field temperature data set, performing temperature extraction and deviation analysis on the data set, generating power compensation amount of each sub-area, and judging whether to trigger power fine adjustment or not based on a preset temperature uniformity control judgment rule. And a fine adjustment object and a final compensation amount are determined during triggering, heat preservation and curing treatment are carried out on a fine-adjusted welding area, finally, a main-grid-free welding structure which is in uniform low-temperature connection with all the fine grid lines is formed, and uniform, reliable and low-damage synchronous connection between all the fine grid lines and the welding strip is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of laser material processing, and relates to a low-temperature laser synchronous welding method for a TOPCon cell without a main grid structure. BACKGROUND

[0002] As a representative of high-efficiency cell technology in the current photovoltaic field, the continuous optimization of the structure and process of the TOPCon cell is the key to improving the conversion efficiency. In recent years, in order to further reduce the shading loss of grid lines to sunlight and reduce the consumption of silver paste, the design of the main grid structure is widely used.

[0003] The main grid structure is connected to the solder strip covered with solder through multiple parallel micron-level fine grid lines to collect and export the photo-generated current. Laser welding technology has become a key process means for realizing precise connection between fine grid lines and solder strips due to its advantages of energy concentration, small heat-affected zone and high processing precision.

[0004] In the existing welding process of the TOPCon cell without the main grid structure, the commonly used technical solution is to use a single laser beam to perform high-speed sequential scanning on multiple fine grid lines. Specifically, the control system drives the scanning galvanometer to guide the single focused laser spot to quickly pass through the lap joint positions of dozens or even hundreds of fine grid lines and solder strips according to the preset path, one by one or in batches, to realize point-by-point or segment-by-segment welding by locally and quickly melting the low-temperature solder. This method has a relatively simple device structure and a relatively direct control mode, and is the mainstream technology currently applied in the industry.

[0005] However, the above welding method using a single laser beam for sequential scanning has inherent defects, which are specifically as follows: 1. Due to the time sequence in the scanning process, the thermal history experienced by the fine grid lines welded first is completely different from that experienced by the fine grid lines welded later, and the cumulative effect of heat in the cell will cause the background temperature of the welding area to continuously rise, making it difficult to keep the actual peak temperature and cooling rate of each welding point consistent.

[0006] 2. The existing open-loop processing method cannot respond to the microscopic differences in the material properties of the cell, the thickness of the grid paste and the uniformity of the solder coating in real time, which easily leads to significant fluctuations in the welding quality and affects the power output and long-term reliability of the final cell module.

[0007] It is particularly emphasized that under the combined action of the two key constraints of the main grid structure and the low-temperature welding process, the harmfulness of the above defects is dramatically amplified. The main grid structure means that each fine grid line is an indispensable independent current path, and the failure of any connection point will directly lead to permanent degradation of the cell performance. The low-temperature process window is narrow, and the requirements for heat input uniformity and accuracy are extremely strict. SUMMARY

[0008] In view of this, in order to solve the problems raised in the background art, a low-temperature laser synchronous welding method for TOPCon cell without main grid structure is proposed.

[0009] The purpose of the present application can be achieved by the following technical solutions: The present application provides a low-temperature laser synchronous welding method for TOPCon cell without main grid structure, which comprises: dividing and shaping the incident laser beam into multiple independent laser sub-beams matched with the fine grid line pattern of the TOPCon cell without main grid structure through a spatial light modulator to construct a synchronous laser dot array energy field.

[0010] The synchronous laser dot array energy field is projected onto the contact interface between the solder strip covered with low-temperature solder and the fine grid line of the cell to form an initial welding temperature field.

[0011] The temperature distribution of the welding area is obtained in real time by a high-resolution infrared thermal imager, and a full-field temperature dataset with fine grid line sub-area as the basic unit is constructed.

[0012] Temperature extraction and deviation analysis based on fine grid line sub-area are performed on the full-field temperature dataset to generate power compensation of each fine grid line sub-area.

[0013] Based on the preset temperature uniformity control decision rule, it is determined whether to trigger the independent fine adjustment of the power of the subsequent multiple laser sub-beams, and when it is determined to trigger, the power fine adjustment object and the final power compensation of each object are confirmed.

[0014] The welding area after independent fine adjustment is subjected to heat preservation and solidification treatment to generate a main grid-free welding structure uniformly connected with all fine grid lines at low temperature.

[0015] Compared with the prior art, the present application has the following advantages: (1) The present application constructs a synchronous laser dot array energy field and projects it onto the welding interface at one time, which fundamentally eliminates the time difference inherent in the traditional sequential scanning welding process, ensures that all fine grid lines to be welded start at the same time and experience a highly consistent thermal cycle process, significantly improves the uniformity of the connection quality of each welding point, and effectively avoids defects such as virtual welding and overwelding caused by differences in thermal history.

[0016] (2) The present application integrates a full-field real-time temperature monitoring and feedback mechanism, dynamically senses the micro temperature distribution of the entire welding area, and independently and synchronously adjusts the power of the multiple sub-beams based on deviation analysis. This kind of closed-loop control mechanism gives the welding process unprecedented adaptive adjustment ability, enabling it to actively compensate for temperature field disturbances caused by random factors such as material non-uniformity or environmental fluctuations, greatly enhancing the stability and robustness of the process, and significantly improving the yield and reliability in large-scale production.

[0017] (3) The present application ensures that the entire welding process is always stable within the optimal process window of low-temperature solder by precise closed-loop temperature control, effectively avoiding local overheating. This not only achieves high-strength, low-ohmic contact between the solder ribbon and all fine grid lines, but more importantly, the connection is completed in a low-thermal-stress, low-damage-risk manner, maximizing the protection of heat-sensitive functional structures such as the passivation layer in the TOPCon cell, thereby ensuring the final high electrical performance and long-term stability of the battery module. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0019] Figure 1 The present application provides a method for implementing the steps of the process.

[0020] Figure 2 The present application provides a logic diagram for determining the temperature uniformity control rule.

[0021] Figure 3 The present application provides a power fine-tuning process flowchart. DETAILED DESCRIPTION

[0022] The technical solutions of the embodiments of the present application will be described in detail below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0023] Please refer to Figure 1 As shown in the drawings, the present application provides a low-temperature laser synchronous welding method for TOPCon cell without main grid structure, and the specific steps are as follows: S1, split and shape the incident laser beam into multiple independent laser sub-beams matched with the fine grid line pattern of the TOPCon cell without main grid by a spatial light modulator, to construct a synchronous laser dot array energy field.

[0024] In specific embodiments of the present application, the synchronous laser dot array energy field construction process includes: S11, obtaining the digital coordinate information of the fine grid line pattern of the TOPCon cell without main grid, and generating fine grid line pattern data.

[0025] It should be noted that the above fine grid line pattern data contains the geometric position, length, width and mutual spacing of each fine grid line to be welded, which can be obtained by directly importing the CAD file of the battery design, or generated by capturing the surface of the battery sheet through image recognition algorithm, which is a prior art and will not be described here.

[0026] S12, based on the fine grid line pattern data, a phase hologram is calculated and generated, and the phase hologram is loaded to the spatial light modulator to dynamically phase modulate the incident laser beam to generate multiple independent laser sub-beams.

[0027] The generation of the above phase hologram aims to convert a single incident laser beam into a target light intensity distribution on the Fourier lens focal plane, i.e. a laser dot array corresponding to the fine grid line pattern.

[0028] The generation of the phase hologram is mainly an iterative Fourier transform algorithm, which gradually approaches the target light intensity distribution by iterating between the phase modulation plane of the spatial light modulator and the Fourier lens focal plane, and the specific implementation process is as follows: According to the fine grid line pattern data, a target light intensity distribution on the Fourier lens focal plane is defined.

[0029] An initial complex amplitude field with uniform amplitude and random phase is initialized on the phase modulation plane of the spatial light modulator.

[0030] Based on the iterative Fourier transform algorithm, the cycle iteration process of performing forward Fourier transform, applying amplitude constraint on the focal plane, performing inverse Fourier transform, and applying amplitude constraint on the spatial light modulator plane is executed until the root mean square error of the focal plane light intensity and the target light intensity is less than the preset convergence threshold value, and the iteration is stopped, and the final phase distribution for generating the target light intensity distribution is obtained, and the preset convergence threshold value can be exemplarily set to 0.01.

[0031] The final phase distribution is quantized into discrete phase levels matched with the pixel array of the spatial light modulator to generate a phase hologram.

[0032] The specific execution process of the above dynamic phase modulation is as follows: The phase hologram is loaded to the pixel array of the spatial light modulator, so that each pixel unit applies a specific phase delay to the laser wavefront passing through it according to the corresponding phase value of the phase hologram.

[0033] The collimated incident laser beam is irradiated to the active surface of the spatial light modulator which has completed the phase hologram loading to obtain a phase-modulated diffracted laser field.

[0034] The phase-modulated diffraction laser field is passed through a Fourier lens, and at the focal plane of the Fourier lens, an array of multiple independent laser sub-beams corresponding to the fine grid pattern data is generated through optical diffraction and interference effects.

[0035] S13, the multiple independent laser sub-beams are spatially registered with the fine grid pattern to form the synchronous laser dot array energy field.

[0036] The embodiment of the present application fundamentally eliminates the time difference inherent in the traditional sequential scanning welding process by constructing a synchronous laser dot array energy field and projecting it onto the welding interface at one time, ensures that all fine grid lines to be welded start at the same time and undergo a highly consistent thermal cycle process, significantly improves the uniformity of the connection quality of each welding spot, and effectively avoids defects such as virtual welding and overwelding caused by differences in thermal history.

[0037] S2, the synchronous laser dot array energy field is projected onto the contact interface between the solder tape covered with low-temperature solder and the battery fine grid line to form an initial welding temperature field.

[0038] Due to the physical deviation between the laser transmission light path and the thermal imaging light path and the inherent aberration of the optical system, a spatial deviation between the actual projection position of the laser dot array on the focal plane and the theoretically designed position will occur. Based on this, in the specific embodiments of the present application, the synchronous laser dot array energy field projection further includes a calibration step: A pre-set standardized test pattern is projected onto the surface of a standard thermal target material through the spatial light modulator, and the test pattern includes a plurality of feature points distributed in a grid pattern.

[0039] An actual temperature field formed after the standard thermal target material is irradiated is collected by the high-resolution infrared thermal imager, and an initial spatial error between the actual temperature field and the expected temperature field is measured.

[0040] It should be noted that the initial spatial error measurement between the actual temperature field and the expected temperature field is based on the expected temperature value and the coordinate position of each feature point. Specifically, for each feature point in the expected temperature field, the expected coordinate is taken as the center, and within a set neighborhood, the minimum tolerance pixel point with a temperature value that meets the tolerance condition is searched in the actual temperature field, and the pixel point coordinate is taken as the actual coordinate of the feature point. If no temperature value that meets the tolerance condition is found in the neighborhood, the feature point is marked as invalid.

[0041] By calculating the Euclidean distance between the expected coordinate and the actual coordinate, the initial spatial error vector of each valid feature point is quantitatively obtained, and the error compensation functions in the x and y directions are constructed based on the two-dimensional interpolation method, so as to determine the spatial coordinate compensation amount of each pixel coordinate.

[0042] When the effective feature points are uniformly distributed, the two-dimensional interpolation method can exemplarily adopt bilinear interpolation or bicubic spline interpolation, and when the feature points are unevenly distributed, a piecewise interpolation based on Delaunay triangulation can be exemplarily adopted, and the above two-dimensional interpolation methods are all prior art and will not be described in detail here.

[0043] It should be noted that the determination process of the uniform distribution of the effective feature points is as follows: Delaunay triangulation is performed on all effective feature points, the edge length of all Delaunay triangles is calculated, and the edge length standard deviation is evaluated, and if the edge length standard deviation is less than or equal to 15% of the average edge length, it is determined that the effective feature points are uniformly distributed, otherwise it is determined that the effective feature points are unevenly distributed.

[0044] According to the initial spatial error, the fine grid line pattern data and the phase hologram calculation algorithm are dynamically corrected to eliminate inherent optical distortion.

[0045] It should be noted that the dynamic correction process is as follows: when calculating the phase hologram, according to the error compensation function constructed in the horizontal and vertical directions, each pixel coordinate in the fine grid line pattern data is pre-compensated by a corresponding coordinate compensation amount, and the corrected pattern data is used as the target light intensity distribution to recalculate the phase hologram.

[0046] S3, the temperature distribution of the welding area is acquired in real time by a high-resolution infrared thermal imager, and a full-field temperature data set with fine grid line sub-regions as basic units is constructed.

[0047] In specific embodiments of the present application, the full-field temperature data set construction process comprises: S31, the infrared image sequence of the welding area is continuously collected by a high-resolution infrared thermal imager.

[0048] It should be noted that the high resolution of the high-resolution infrared thermal imager not only refers to the spatial resolution sufficient to clearly distinguish each micrometer-level fine grid line, but also refers to the time frame rate high enough to capture the millisecond-level temperature dynamic change in the laser heating process.

[0049] The welding area specifically refers to the contact interface between the welding strip and the battery fine grid line.

[0050] S32, noise filtering and temperature calibration are performed on the infrared image sequence to extract standardized temperature data.

[0051] Since the original infrared image sequence inevitably contains sensor thermal noise and environmental background radiation interference, image processing algorithms such as median filtering or Gaussian filtering are first used to smooth each frame of image to improve the signal-to-noise ratio.

[0052] In view of the fact that the infrared thermal imager directly measures the infrared radiation flux of the object rather than the temperature itself, it is necessary to calibrate the temperature according to the Planck radiation law, the core of which is to establish a nonlinear mapping relationship between the radiation intensity and the temperature, which can be simply represented as:

[0053] wherein, is the absolute temperature of the pixel point to be solved, is the radiation intensity value of the corresponding pixel point obtained from the infrared image sequence after noise filtering, is the infrared emissivity of the solder tape surface covered with low-temperature solder obtained through pre-experiment calibration, is the center wavelength of the working waveband of the infrared thermal imager, and are the first and second preset radiation constants, respectively.

[0054] S33, spatially align the standardized temperature data with the fine grid line pattern data, and extract the representative temperature values of each fine grid line sub-region by a weighted average algorithm to generate a full-field temperature data set.

[0055] The specific execution process of the spatial alignment is: the fine grid line pattern data is superimposed on each frame of the standardized temperature image as a digital mask, so that each fine grid line has a clear corresponding region of interest on the temperature image, and thus the temperature characteristic values and spatial position information of all fine grid lines are combined together.

[0056] The extraction of the representative temperature values of each fine grid line region by the weighted average algorithm specifically includes: For each fine grid line, a pixel set is defined in its corresponding spatial region.

[0057] The weighted average value of all pixel temperature values in the pixel set is calculated, wherein the weight is Gaussian distributed according to the distance between each pixel point and the center line of the fine grid line, and the closer the distance, the higher the weight.

[0058] The calculated weighted average value is taken as the representative temperature value of the fine grid line region.

[0059] S4, performing temperature extraction and deviation analysis based on the fine grid line sub-regions on the full-field temperature data set to generate power compensation amounts of each fine grid line sub-region.

[0060] In specific embodiments of the present application, the process of generating the power compensation amounts of each fine grid line sub-region includes: defining a process temperature range for the optimal soldering performance of the low-temperature solder.

[0061] It should be noted that the optimal welding performance process temperature range is determined in advance based on the following data sources: phase transition temperature data obtained by thermal analysis test on the low-temperature solder, performance statistical data of welding samples prepared at different process temperatures, the performance including interface wettability, degree of metallurgical reaction, joint mechanical strength and electrical connection performance, and material specification data provided by the solder supplier and relevant industry process standards.

[0062] The characteristic temperature value of each fine grid line sub-area is extracted from the full-field temperature data set, and the instantaneous temperature deviation of each fine grid line sub-area is calculated in real time based on the process temperature range.

[0063] It should be noted that the instantaneous temperature deviation is the difference between the characteristic temperature value and the median value of the process temperature range.

[0064] By inputting the instantaneous temperature deviation into the power compensation model, the power compensation amount of each fine grid line sub-area is generated, and the power compensation model is constructed by defining the dynamic functional relationship between the temperature deviation and the laser power compensation amount, which is configured to drive the laser power output according to the instantaneous temperature deviation, so that the actual temperature converges to the target temperature.

[0065] As an example, the power compensation model can be a proportional-integral-derivative control model, in which the formula of the dynamic functional relationship between the characteristic temperature deviation and the laser power compensation amount is: ; Wherein, represents the power compensation amount required by the i-th fine grid line sub-area, is the number of each fine grid line sub-area, , , represents the current time, represents the instantaneous temperature deviation at the current time, are proportional, integral and differential coefficients respectively, which are obtained by pre-adjusting according to the thermal response characteristics, and together determine the rapidity, stability and ability to eliminate steady-state error of the control response.

[0066] The model constitutes the main response of instantaneous control, and generates a proportional correction force according to the size of the temperature deviation measured at the current time. If the current temperature is low, this item will immediately increase the power and try to quickly pull back to the target temperature.

[0067] The integral term is used to eliminate the steady-state error of the system, which responds to the cumulative amount of temperature deviation from the past to the present, and can correct the persistent small deviation that cannot be completely eliminated by the proportional term alone. For example, if a certain area is slightly lower than the target temperature for a long time due to faster heat dissipation, the integral term will continuously accumulate this negative deviation over time and output a continuously increasing power compensation until the temperature is finally stabilized at the target value, making the steady-state error zero.

[0068] The derivative term is used to provide damping and prediction functions, responding to the rate of change of temperature deviation, and sensing whether the temperature is rapidly deviating or tending towards the target. When the temperature starts to drop rapidly, the derivative term will output a positive power compensation in advance to stop the temperature drop trend before the deviation becomes large. Conversely, when the temperature rises rapidly, it will reduce the power in advance to prevent overshoot.

[0069] After the model calculation, a specific power compensation result is output for each fine grid sub-area, which indicates the power value that needs to be increased or decreased for the corresponding sub-beam to drive its actual temperature to converge towards the target temperature.

[0070] S5, based on the preset temperature uniformity control determination rule, determine whether to trigger the subsequent independent fine adjustment of the power of multiple laser sub-beams, when it is determined to trigger, confirm the power fine adjustment object and the final power compensation of each object.

[0071] Please refer to Figure 2 In the specific embodiments of the present application, the content of the temperature uniformity control determination rule includes: traversing all fine grid sub-areas, if the absolute value of the instantaneous temperature deviation of a sub-area is greater than the preset individual temperature deviation threshold, the sub-area is determined as an out-of-tolerance unit.

[0072] For each sub-area of the non-out-of-tolerance unit, based on the time series data, the temperature variation trend in the future preset window is fitted, if there is a condition greater than the preset individual temperature deviation threshold in the future preset window, the sub-area is pre-judged as a near-instability unit.

[0073] The sum of the near-instability unit and the out-of-tolerance unit is counted, if the ratio of the sum to the total number of fine grid lines is greater than the preset tolerance, it is determined that the subsequent independent fine adjustment of the power of multiple laser sub-beams is triggered, otherwise it is determined not to be triggered.

[0074] It should be noted that the above-mentioned preset individual temperature deviation threshold defines the maximum temperature deviation allowed for a single fine grid sub-area, which is at least greater than the difference between the median value and the lower limit value of the process temperature range.

[0075] The preset tolerance defines the upper limit of the proportion of the number of fine grid sub-areas that exceed the preset individual temperature deviation threshold in the entire welding area.

[0076] Both of the two preset parameters are set and stored in the WEB cloud according to the requirements of the welding process on the connection quality and the control accuracy of the equipment.

[0077] In the specific embodiment of the present application, when the determination trigger is determined, the following steps are performed to confirm the power fine-tuning objects and the final power compensation amounts of each object: The laser sub-beams corresponding to the out-of-tolerance units and the units at risk of instability are determined as the power fine-tuning objects.

[0078] For each fine grid line sub-region that is pre-determined as a unit at risk of instability, the feedforward power compensation amount required to offset the temperature change trend is quantified according to the temperature change rate of the future preset window, and the feedforward power compensation amount is superimposed with the power compensation amount generated based on the instantaneous temperature deviation of the unit at risk of instability, to obtain the final power compensation amount of the sub-region.

[0079] It should be noted that the quantification process of the feedforward power compensation amount required to offset the temperature change trend is as follows: the temperature change rate of the unit at risk of instability in the future preset window is multiplied by a pre-set feedforward compensation coefficient to calculate the basic value of the feedforward power compensation amount.

[0080] The basic value is given a direction opposite to the temperature change rate, that is, if the temperature change rate is positive, the basic value is negative, to obtain the final feedforward power compensation amount.

[0081] For each fine grid line sub-region that is determined as an out-of-tolerance unit, the power compensation amount generated based on the instantaneous temperature deviation of the unit is directly used as the final power compensation amount of the sub-region.

[0082] Please refer to Figure 3 In the specific embodiment of the present application, the independent fine-tuning process of the power of the multiple laser sub-beams includes: mapping the final power compensation amounts of each object into the multiple control signals of the spatial light modulator.

[0083] It should be noted that the mapping of the multiple control signals of the spatial light modulator is realized through a pre-set lookup table, and the construction method of the lookup table includes: In the invention calibration stage, the actual laser output power of each control unit of the spatial light modulator under different control signals is measured.

[0084] The mapping relationship from the target power compensation amount to the control signal of the spatial light modulator is established, and the mapping relationship is stored as a lookup table.

[0085] In real-time control, the power compensation amount result is directly converted into the corresponding multiple control signals by querying the lookup table.

[0086] The multi-channel control signals are synchronously sent to the spatial light modulator, and the diffraction efficiency of each laser sub-beam is changed by adjusting its phase hologram in real time, thereby achieving independent and synchronous fine-tuning of the power.

[0087] This invention integrates a real-time temperature monitoring and feedback mechanism across the entire welding area. By dynamically sensing the microscopic temperature distribution of the entire welding zone and independently and synchronously fine-tuning the power of multiple sub-beams based on deviation analysis, this closed-loop control mechanism endows the welding process with unprecedented adaptive adjustment capabilities. It enables the process to actively compensate for temperature field disturbances caused by random factors such as material inhomogeneity or environmental fluctuations, greatly enhancing the stability and robustness of the process, thereby significantly improving the yield and reliability in large-scale production.

[0088] S6. After independent fine-tuning, the welding area is subjected to heat preservation and curing treatment to generate a masterless welding structure that is uniformly and low-temperature connected to all fine grid lines.

[0089] In a specific embodiment of the present invention, the heat preservation and curing treatment includes: After power fine-tuning, the heat preservation power is dynamically set based on the thermal capacity difference of the fine grid sub-region, and the synchronous laser array energy field is maintained at this power level for heat preservation treatment.

[0090] It should be noted that the above-mentioned dynamic setting of insulation power based on the thermal capacity difference of the fine grid line sub-regions is specifically: for fine grid line regions with wider linewidths or larger connection areas, a higher insulation power level is set, and for fine grid lines with narrower linewidths or end regions, a lower insulation power level is set. Based on this principle, the process of obtaining the insulation power of each fine grid line sub-region can be: quantifying the linewidth and connection area of ​​each sub-region.

[0091] Based on the known specific heat capacity and density of the solar cell, an accumulation operation is performed using linewidth and connection area to estimate the heat capacity coefficient of each sub-region.

[0092] The heat capacity coefficient is input into a linear function. The logic of this function is as follows: the product of the preset proportional coefficient and the heat capacity coefficient is used as the adaptive heat preservation power. The adaptive heat preservation power is added to the preset basic heat preservation power common to all sub-regions to obtain the differentiated heat preservation power of each sub-region.

[0093] After the heat preservation treatment is completed, the laser irradiation is stopped, and the welding area is cooled in a controlled environment to complete the curing process.

[0094] The aforementioned controllable environment specifically refers to a sealed chamber filled with high-purity nitrogen, maintained at a temperature of 15-25°C, and with a relative humidity of less than 10%. The welded parts are cooled to below 50°C within this chamber at a controlled rate of 0.5-2°C / second.

[0095] The welding structure after the solidification treatment is evaluated in electrical and mechanical performance to confirm the qualification of the main grid-free welding structure.

[0096] It is to be noted that the electrical performance evaluation process includes: measuring the contact resistance between the solder strip and all the fine grid lines by using a four-probe tester, and if the contact resistance value is lower than the preset resistance threshold and the resistance distribution uniformity between the fine grid lines is within 10%, the electrical performance is determined to be qualified.

[0097] The mechanical performance evaluation process includes: using a tensile testing machine to apply a tensile force perpendicular to the surface of the battery to the solder strip, and if the solder strip does not fall off or the fine grid lines do not break at a preset strength threshold, the mechanical performance is determined to be qualified.

[0098] Only when both the electrical performance and the mechanical performance evaluation are qualified, the qualified main grid-free welding structure is finally confirmed to be generated.

[0099] The embodiment of the present application ensures that the entire welding process is always stable within the optimal process window of low-temperature solder by precise closed-loop temperature control, effectively avoiding local overheating. This not only realizes high-strength, low-ohmic contact between the solder strip and all the fine grid lines, but more importantly, the connection is completed in a low thermal stress and low damage risk manner, which maximizes the protection of the functional structures such as the passivation layer in the TOPCon battery that are sensitive to heat, thereby ensuring the final high electrical performance and long-term service stability of the battery module.

[0100] In specific embodiments of the present application, after the independent fine adjustment of the power of the multiple laser sub-beams, it further includes: Again, the temperature distribution of the updated welding area is obtained from the high-resolution infrared thermal imager.

[0101] Based on the updated temperature distribution data, the full-field temperature data set is reconstructed, and the steps of generating power compensation and triggering the demand determination are repeated until it is determined that the subsequent independent fine adjustment of the power of the multiple laser sub-beams is not triggered.

[0102] The core technical principle of the present application is to construct a space-time collaborative control mechanism to solve the problem of thermal uniformity in multi-fine grid line synchronous welding.

[0103] In the spatial dimension, a spatial light modulator is used to instantaneously convert a single laser source into a synchronous laser dot array energy field that accurately matches the fine grid line array of the battery, fundamentally eliminating the inherent timing differences of traditional scanning methods and achieving synchronous heating of all welding points.

[0104] In the time dimension, high-resolution infrared thermal imaging technology is integrated to conduct full-field real-time temperature monitoring, converting the physical temperature field into an analyzable full-field temperature dataset, which is subjected to deviation analysis based on the position of the fine grid lines to generate accurate power compensation instructions for each sub-beam. Through temperature uniformity control decision rules, independent and synchronous fine tuning of the power of multiple sub-beams is triggered, forming a rapid closed-loop feedback loop. This loop continues to iterate, dynamically offsetting various non-uniformity factors, until the temperature of the entire welding area stabilizes within the optimal process window, and finally a high-quality connection is completed through a controlled holding and solidification process.

[0105] Firstly, the present application realizes true sense of thermal synchronous welding, ensuring that all fine grid lines experience highly consistent thermal history throughout the welding process, greatly improving the consistency of solder joint quality and effectively avoiding defects such as false welding and overwelding. Secondly, the closed-loop independent power fine tuning mechanism provides unprecedented process control precision and robustness, enabling it to actively adapt to material batch differences, equipment state fluctuations and other uncertainty factors, significantly improving the stability and yield of the welding process. Finally, since the entire process is carried out within the optimal process window of low-temperature solder and avoids local overheating, the present application realizes high-strength, low-resistance connections while greatly reducing the risk of thermal damage to the sensitive structure of TOPCon cells, thereby ensuring the electrical performance and long-term reliability of the cells, providing a solution for large-scale, high-quality manufacturing of busbar-free cell modules.

[0106] The above is merely an example and explanation of the concept of the present application, and those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, as long as they do not deviate from the concept of the present application or exceed the scope defined by the present application, which shall fall within the protection scope of the present application.

Claims

1. A low-temperature laser synchronous welding method for TOPCon batteries without a main grid structure, characterized in that: include: The incident laser beam is split and shaped into multiple independent laser sub-beams that match the gridless fine grid pattern of the TOPCon cell by using a spatial light modulator to construct a synchronous laser array energy field. The synchronous laser array energy field is projected onto the interface between the solder ribbon coated with low-temperature solder and the fine grid line of the battery in one go, forming an initial welding temperature field; The temperature distribution of the welding area is acquired in real time using a high-resolution infrared thermal imager, and a full-field temperature dataset is constructed with the fine grid line sub-region as the basic unit. Temperature extraction and deviation analysis based on fine grid line sub-regions are performed on the full-field temperature dataset to generate power compensation amounts for each fine grid line sub-region. Based on the preset temperature uniformity control judgment rules, it is determined whether to trigger the independent fine-tuning of the power of subsequent multi-channel laser sub-beams. When the determination is triggered, the power fine-tuning object and the final power compensation amount of each object are confirmed. The welded areas after independent fine-tuning are subjected to heat preservation and curing treatment to generate a masterless welded structure that is uniformly and low-temperature connected to all fine grid lines.

2. The low-temperature laser synchronous welding method for a TOPCon battery without a main grid structure according to claim 1, characterized in that, The process of constructing the energy field of the synchronous laser array includes: Obtain the digital coordinate information of the grid-less fine grid pattern of the TOPCon battery and generate the fine grid pattern data; A phase hologram is calculated and generated based on the fine grid pattern data, and the phase hologram is loaded by the spatial light modulator to dynamically modulate the phase of the incident laser beam, generating multiple independent laser sub-beams. The multiple independent laser sub-beams are spatially registered with the fine grating pattern to form the synchronous laser dot array energy field.

3. The low-temperature laser synchronous welding method for a TOPCon battery without a main grid structure according to claim 1, characterized in that, The process of constructing the full-field temperature dataset includes: A sequence of infrared images of the welding area is continuously acquired using a high-resolution infrared thermal imager; The infrared image sequence is subjected to noise filtering and temperature calibration to extract standardized temperature data; The standardized temperature data is spatially aligned with the fine grid pattern data, and the characteristic temperature value of each fine grid sub-region is extracted one by one using a weighted average algorithm to generate a full-field temperature dataset.

4. The low-temperature laser synchronous welding method for a TOPCon battery without a main grid structure according to claim 1, characterized in that, The power compensation generation process for each fine-grid sub-region includes: Define the process temperature range for optimal welding performance of low-temperature solders; The characterization temperature values ​​of each fine grid line sub-region are extracted from the full-field temperature dataset, and the instantaneous temperature deviation of each fine grid line sub-region is calculated in real time based on the process temperature range. By inputting the instantaneous temperature deviation into the power compensation model, the power compensation amount of each fine grid sub-region is generated. The power compensation model is constructed by defining a dynamic functional relationship between the temperature deviation and the laser power compensation amount. This functional relationship is configured to drive the laser power output according to the instantaneous temperature deviation, so that the actual temperature converges to the target temperature.

5. The low-temperature laser synchronous welding method for a TOPCon battery without a main grid structure according to claim 4, characterized in that, The temperature uniformity control judgment rules include: Traverse all fine grid line sub-regions. If the absolute value of the instantaneous temperature deviation of a certain sub-region is greater than the preset individual temperature deviation threshold, then the sub-region is determined to be an out-of-tolerance unit. For each sub-region of a non-out-of-tolerance unit, the temperature change trend within a future preset window is fitted based on time series data. If there is a situation within the future preset window where the temperature deviation exceeds the preset individual temperature deviation threshold, the sub-region is predicted to be a unit on the verge of instability. If the sum of the units on the verge of instability and the units exceeding the tolerance is greater than a preset tolerance, then it is determined that the independent fine-tuning of the power of the subsequent multi-path laser sub-beams will be triggered; otherwise, it is determined that it will not be triggered.

6. The low-temperature laser synchronous welding method for a TOPCon battery without a main grid structure according to claim 5, characterized in that, When a trigger is detected, the following steps are performed to confirm the power fine-tuning objects and the final power compensation amount for each object: The laser sub-beams corresponding to the out-of-tolerance unit and the near-instability unit are identified as the power fine-tuning targets; For each fine grid sub-region that is predicted to be on the verge of instability, the feedforward power compensation amount required to offset the temperature change trend is quantified according to the temperature change rate of its future preset window. The feedforward power compensation amount is then superimposed with the power compensation amount generated based on its instantaneous temperature deviation to obtain the final power compensation amount for that sub-region. For each fine grid line sub-region that is determined to be an out-of-tolerance cell, the power compensation amount generated by its instantaneous temperature deviation is directly used as the final power compensation amount for that sub-region.

7. The low-temperature laser synchronous welding method for a TOPCon battery without a main grid structure according to claim 1, characterized in that, The independent fine-tuning process for the power of the multi-channel laser sub-beams includes: The final power compensation amount of each object is mapped to the multiplex control signal of the spatial light modulator; The multi-channel control signals are synchronously sent to the spatial light modulator, and the diffraction efficiency of each laser sub-beam is changed by adjusting its phase hologram in real time, thereby achieving independent and synchronous fine-tuning of the power.

8. The low-temperature laser synchronous welding method for a TOPCon battery without a main grid structure according to claim 1, characterized in that, The heat preservation and curing treatment includes: After power fine-tuning, the heat preservation power is dynamically set based on the thermal capacity difference of the fine grid line sub-region, and the synchronous laser array energy field is maintained at this power level for heat preservation treatment. After the heat preservation treatment is completed, the laser irradiation is stopped, and the welding area is cooled in a controlled environment to complete the curing process; The electrical and mechanical properties of the welded structure after curing were evaluated to confirm the qualification of the main grid-less welded structure.

9. The low-temperature laser synchronous welding method for a TOPCon battery without a main grid structure according to claim 1, characterized in that, After the independent fine-tuning of the power of the multiple laser sub-beams, the following is also included: The updated temperature distribution of the welded area was obtained again from a high-resolution infrared thermal imager; Based on the updated temperature distribution data, the full-field temperature dataset is reconstructed, and the steps of generating power compensation and triggering demand determination are repeated until it is determined that the independent fine-tuning of the power of subsequent multi-path laser sub-beams will not be triggered.

10. The low-temperature laser synchronous welding method for a TOPCon battery without a main grid structure according to claim 1, characterized in that, The synchronous laser array energy field projection also includes a calibration step: A pre-defined standardized test pattern is projected onto the surface of a standard thermal target material through the spatial light modulator. The test pattern contains multiple feature points distributed in a grid pattern. The actual temperature field formed by the standard thermal target material after irradiation is acquired by the high-resolution infrared thermal imager, and the initial spatial error between the actual temperature field and the expected temperature field is measured. Based on the initial spatial error, the fine grating pattern data and phase hologram calculation algorithm are dynamically corrected to eliminate inherent optical distortion.

Images