Method and system for detecting micro-area stress of crystalline silicon cell

Abstract

The invention relates to a method and a system for detecting micro-area stress of a crystalline silicon cell. The system for detecting the micro-area stress of the crystalline silicon battery comprises a micro-area Raman spectrometer system, a micro-area photocurrent imaging system, a sample bearing table and a probe table, the sample bearing table is vertically arranged right below the laser beam; a probe arm of the probe station is used for being connected with a crystalline silicon battery grid line so as to be connected with a voltmeter and a current amplifier in the microcell photocurrent imaging system; the micro-area Raman spectrometer system is used for testing stress distribution of a battery micro-area; and the micro-area photocurrent imaging system is used for detecting the photoelectric property of the battery micro-area. Compared with the prior art, the method can be used for carrying out mechanical and electrical same-region characterization on the micro-crack micro-region in the crystalline silicon battery piece so as to analyze the physical environment around the crack.

Description

Technical Field

[0001] The present invention relates to the technical field of tunneling oxide passivated contact batteries, and particularly to a method and system for detecting micro-area stress of crystalline silicon batteries. Background Art

[0002] Energy shortage and climate change are the main challenges faced by the current development of human society. In this context, vigorously developing clean energy technologies based on photovoltaic cells has become the consensus of the international community. Crystalline silicon solar cells have become the mainstream products in the current commercial photovoltaic power generation field due to their excellent optoelectronic performance and relatively low manufacturing cost. With the continuous development of photovoltaic technology, tunneling oxide passivated contact (TOPCon) batteries have gradually become the focus of research and application. TOPCon batteries significantly improve the efficiency and stability of the batteries by forming an ultra-thin tunneling oxide layer on the surface of crystalline silicon and combining with a polysilicon passivation layer. TOPCon batteries adopt the structure of tunneling oxide layer and polysilicon passivation layer, effectively reducing the carrier recombination, thus significantly increasing the open-circuit voltage and conversion efficiency of the batteries. Compared with traditional PERC batteries, the efficiency of TOPCon batteries under laboratory conditions has exceeded 25%, and their performance in actual applications is also very outstanding. At the same time, due to the good passivation effect, TOPCon batteries show excellent stability during long-term use, reducing power attenuation and improving the reliability and lifespan of the modules. In addition, very importantly, the compatibility of the manufacturing process is the key for TOPCon batteries to gain a large market share. Its manufacturing process can be compatible with the existing crystalline silicon battery production lines, only a few process steps need to be added to the existing production lines, avoiding large-scale equipment investment and technological transformation.

[0003] In order to further reduce production costs and improve battery efficiency, thinning the silicon wafer has become an important means. However, with the reduction of the silicon wafer thickness, the problems of light trapping and fragmentation become more prominent. Thin silicon wafers are more susceptible to mechanical stress during production, transportation and use, resulting in the generation of cracks and other defects. These defects will not only reduce the performance of the battery, but may also shorten its service life. During the production process of crystalline silicon batteries, cracks can occur in multiple links, such as silicon wafer cutting, surface treatment, electrode printing and module encapsulation, etc. The stress distribution and stress concentration areas in each link may become the origin of cracks. In addition, in order to increase the output voltage of the module, battery manufacturers usually divide the finished batteries into half-cell modules, and edge damage caused by cutting will be introduced during this process. These edge damages will also have a negative impact on the performance and reliability of the battery. In order to ensure the reliability and service life of crystalline silicon solar cells in actual applications, it is particularly important to analyze the defects caused by stress and propose effective solutions.

[0004] Existing technologies for detecting defects in crystalline silicon cells, such as patent CN112991264B, describe a method for detecting cracks in monocrystalline silicon photovoltaic cells. This method analyzes edge feature points in images of defect-free monocrystalline silicon cells. Data analysis of the edge points in the image to be inspected identifies the location of the defect, enabling image-based detection of cracks in monocrystalline silicon cells. However, this detection method relies solely on pattern analysis and lacks characterization of the physical properties surrounding the cracks in the crystalline silicon cells. For example, patent CN117132844B describes a method for classifying cracks and scratches in photovoltaic panels based on image processing. By obtaining electroluminescence grayscale images and using an algorithm to determine the defect type within the abnormally connected domains based on the crack and scratch probabilities within those domains, this method enables non-destructive capture of defect images, effectively improving the accuracy of crack identification in photovoltaic modules. However, electroluminescence-based detection techniques often only characterize the device's electrical properties and can only observe the location of the defect. Further physical property analysis of the crack defect microregion is difficult for existing photovoltaic cell detection technologies. Summary of the Invention

[0005] To address the above technical issues, the present invention provides a method and system for detecting micro-region stress in crystalline silicon cells. This method and system utilizes a Raman spectrometer imaging system and integrates photocurrent imaging capabilities to characterize micro-region stress in crystalline silicon cells. Compared to existing technologies, this method and system can simultaneously characterize microcracks in crystalline silicon cells mechanically and electrically, thereby analyzing the physical environment surrounding the cracks.

[0006] The present invention is achieved through the following solutions:

[0007] The first object of the present invention is to provide a system for detecting micro-area stress of a crystalline silicon cell, comprising a micro-area Raman spectrometer system, a micro-area photocurrent imaging system, a sample carrier and a probe station;

[0008] The sample carrier is vertically positioned directly below the laser beam; the probe arm of the probe station is used to connect to the gate line of the crystalline silicon cell, thereby connecting to the voltmeter and current amplifier in the micro-area photocurrent imaging system;

[0009] The micro-area Raman spectrometer system is used to test the stress distribution of the battery micro-area; the micro-area photocurrent imaging system is used to detect the photoelectric performance of the battery micro-area.

[0010] In one embodiment of the present invention, the micro-Raman spectrometer system includes:

[0011] A spectrometer, used to collect scattered light signals generated by the laser;

[0012] Laser, a laser light source for generating Raman scattering;

[0013] A confocal microscope for sample positioning and laser focusing;

[0014] A white light source for sample illumination.

[0015] In one embodiment of the present invention, the wavelength of the laser beam of the micro-Raman spectrometer system is 325 nm - 1064 nm; preferably 532 nm; and the laser intensity is 1 mW - 10 mW.

[0016] In one embodiment of the present invention, the confocal microscope is a 50X - 100X short-focus microscope; and the numerical aperture is 0.6 - 0.9.

[0017] In one embodiment of the present invention, the micro-photocurrent imaging system includes

[0018] A current amplifier for amplifying the photo-electric signals generated by the device;

[0019] An amplifier power supply for grounding and powering the amplifier;

[0020] A voltmeter for measuring voltage.

[0021] In one embodiment of the present invention, the amplification factor of the amplifier is 1000 - 10000.

[0022] The second object of the present invention is to provide a method for detecting the micro-region stress of a crystalline silicon cell. Detection is carried out using the system for detecting the micro-region stress of a cell, and the method includes the following steps:

[0023] (1) Place the crystalline silicon cell sample on the sample carrier stage, and use the probe arm of the probe station to connect to the grid line of the crystalline silicon cell to achieve connection with the voltmeter and current amplifier of the micro-photocurrent imaging system;

[0024] (2) Locate the crystalline silicon cell sample under the confocal microscope, and focus the laser beam vertically on the micro-region of the crystalline silicon cell to obtain corresponding Raman spectrum data; meanwhile, obtain the photo-voltage data through the photocurrent imaging system;

[0025] (3) Move the sample carrier stage orderly along the horizontal or vertical direction through the controller, and focus the laser beam of the Raman spectrometer on different micro-regions of the crystalline silicon cell sample to obtain two-dimensional Raman spectrum data and photo-voltage imaging data;

[0026] (4) Calculate the micro-region stress distribution of the crystalline silicon cell based on the Raman spectrum data obtained in step (3).

[0027] In one embodiment of the present invention, in step (1), the surface roughness of the crystalline silicon cell sample is ≤ 1 μm.

[0028] In one embodiment of the present invention, in step (2), the confocal microscope is a 50X - 100X short - focus microscope; the numerical aperture is 0.6 - 0.9.

[0029] In one embodiment of the present invention, in step (2), the wavelength of the laser beam is 325nm - 1064nm; the laser intensity is 1mW - 10mW.

[0030] In one embodiment of the present invention, in step (4), the micro - area stress of the crystalline silicon cell is calculated by the following formula:

[0031] σ = ω / -2.29×10 -9

[0032] In the formula, ω is the Raman shift; the Raman shift is obtained by fitting the Raman spectrum of each point to extract the peak position information of the characteristic peak.

[0033] The above - mentioned technical solution of the present invention has the following advantages compared with the prior art:

[0034] The method of the present invention can achieve micro - area optoelectronic and stress distribution with a spatial resolution of up to 300 nanometers. This technological breakthrough enables the present invention to extremely finely characterize the micro - cracks in crystalline silicon solar cells. By integrating the Raman spectroscopy and the photocurrent imaging system, the present invention can not only accurately detect the location of micro - cracks, but also detailedly analyze the stress distribution and optoelectronic properties in the surrounding micro - areas. Compared with the existing detection methods based on image processing or electroluminescence, the present invention significantly improves the spatial accuracy of stress and performance characterization, enabling in - depth revelation of the impact of microscopic stress changes on the overall performance of the battery. This characterization ability with a high spatial resolution of 3**00 nanometer level plays an important role in promoting the optimization of the manufacturing process of crystalline silicon cells and improving the reliability of components. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to the specific embodiments of the present invention in combination with the drawings, where

[0036] Figure 1 is a schematic diagram of the device for micro - area stress characterization and photocurrent testing of crystalline silicon cells of the present invention; where 1 is a laser beam focusing system (including a laser and a confocal microscope), 2 is a spectrometer, 3 is a probe station, 4 is a crystalline silicon solar cell, 5 is a sample carrier, 6 is a voltmeter, 7 is a current amplifier, 8 is a sample stage controller;

[0037] Figure 2 is a schematic diagram of the principle of stress testing using Raman spectroscopy of the present invention; where (a) is the principle of Raman scattering; (b) is the change of Raman spectra of silicon under different stress states;

[0038] Figure 3 are the morphological characterizations of the back pits of the TOPCon cells of the present invention; wherein, (a) 50X optical microscope photo, (b) 100X optical microscope photo corresponding to the central region of (a), (c) SEM microscope photo;

[0039] Figure 4 are the optoelectronic characterizations of the present invention; wherein, (a) photocurrent imaging, (b) photovoltage imaging;

[0040] Figure 5 are the micro-area Raman spectroscopy stress imaging of the present invention; wherein, (a) micro-area photovoltage distribution, (b) micro-area Raman frequency shift distribution, (c) micro-area stress distribution. Detailed implementation manners

[0041] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the specific embodiments cited are not intended to limit the present invention.

[0042] The present invention can implement the co-area characterization of the mechanics and electricity of the micro-cracks in the crystalline silicon cells, and then obtain the connection between the optoelectronic signals and the stress distribution. The principle of stress characterization is as follows:

[0043] (1) Raman is a light scattering technique. When the high-intensity incident light of a laser light source is scattered by molecules, most of the scattered light has the same wavelength (color) as the incident laser and cannot provide useful information. This kind of scattering is called Rayleigh scattering. However, there is still a very small part (about 10 -9 ) of the scattered light whose wavelength (color) is different from that of the incident light, and the change in its wavelength is determined by the chemical structure of the test sample (the so-called scattering substance). This part of the scattered light is called Raman scattering. And Raman spectroscopy is the technique for recording and analyzing this kind of light.

[0044] See Figure 2, the principle of Raman scattering can be explained with reference to Figure (a). The figure shows an incident light source (usually a laser), and this light interacts with the sample molecules. When the laser beam irradiates the molecules, most of the scattered light has the same energy (or wavelength) as the incident light. This process is called Rayleigh scattering. This scattered light cannot provide useful information about the molecular structure because it only reflects the same energy as the incident light. Molecules have different vibrational energy levels, denoted as E0 (ground state) and E1 (excited state). When light interacts with molecules, it can cause transitions between these vibrational energy levels. Only a small fraction of the scattered light's energy changes. This change in energy is due to the interaction of light with the vibrational modes of the molecules, resulting in an increase or decrease in the energy of the scattered light. Stokes Raman scattering: If the energy of the scattered light is lower than that of the incident light (i.e., the molecule absorbs a portion of energy and transitions to a higher vibrational energy level E1), this is called Stokes Raman scattering. Anti-Stokes Raman scattering: If the energy of the scattered light is higher than that of the incident light (i.e., the molecule loses a portion of energy and transitions to a lower vibrational energy level E0). The energy difference between the incident light and the scattered light corresponds to the vibrational energy levels of the molecules. This change in energy provides valuable information for Raman scattering because it reflects the vibrational modes of the molecules in the sample. This information is utilized in Raman spectroscopy for identifying and analyzing the chemical structure of materials.

[0045] (2) Raman spectroscopy is used for stress characterization.

[0046] Specifically refer to Figure 2 in (b). The Raman spectra of silicon at different sample positions are different. One important parameter is the change in the Raman peak position. Generally speaking, the change in the peak position reflects the change in stress and strain. Taking silicon as an example, the phonon vibration mode of silicon belongs to the vibration of a diatomic chain, which can be simply understood as the vibration of two spring oscillators. If the atoms are squeezed, that is, an external compressive stress is applied, the distance between the atoms will become smaller, the vibration of the spring oscillator will become more intense, and the corresponding vibration of the silicon atoms will also become more intense. That is to say, compressive stress will cause the Raman frequency shift to move towards higher wavenumbers. Conversely, tensile stress will cause the Raman frequency shift to move towards lower wavenumbers. Therefore, the local stress and strain distribution can be obtained by analyzing the change in the peak position of silicon.

[0047] To ensure that the image has a high resolution, a short-focus and high-magnification lens should be used. The present invention employs a 50X - 100X short-focus microscope with a numerical aperture parameter of 0.6 - 0.9. Additionally, for the laser used, a laser with a short wavelength should be preferably selected. In this test, a highly collimated laser with a wavelength of 325nm - 1064nm is used. Since the wavelength of the laser is positively correlated with the imaging resolution, a short wavelength can achieve high-precision imaging at a smaller resolution. Moreover, during the test, effective contact between the probe and the battery grid line needs to be ensured to avoid fluctuations in the measured electrical signals, which may lead to a decline in the imaging quality. Additionally, the surface roughness of the test area should not exceed 1μm; otherwise, defocusing problems will occur, significantly degrading the imaging quality.

[0048] (1) High-spatial-resolution stress characterization technology: By integrating Raman spectroscopy and a photocurrent imaging system, the present invention achieves high-spatial-resolution characterization at the 300-nanometer level for microcracks in crystalline silicon solar cells. This innovation enables precise analysis of the stress distribution and optoelectronic properties around microcracks, significantly improving the detection accuracy.

[0049] (2) Simultaneous mechanical and electrical analysis in the same area: The present invention can simultaneously characterize the mechanical and electrical properties in the same microarea, revealing the relationship between stress changes and optoelectronic properties in the microarea. This ability of simultaneous analysis is crucial for optimizing the performance and reliability of the battery.

[0050] (3) Coupling of microarea Raman spectroscopy and photocurrent imaging: By combining microarea Raman spectroscopy and photocurrent imaging techniques, the present invention achieves comprehensive characterization of the microcrack region in crystalline silicon cells, providing richer physical and electrical information and significantly enhancing the application value of the characterization technology.

[0051] (4) Application to defect detection and optimization of crystalline silicon solar cells: The present invention focuses on stress analysis and performance optimization of microcracks and their surrounding areas in crystalline silicon solar cells, providing key technical support for improving the battery manufacturing process and extending the service life of components.

[0052] Example 1

[0053] Refer to Figure 1As shown in the figure, the system for detecting the stress in the micro-region of the battery includes a micro-region Raman spectrometer system, a micro-region photocurrent imaging system, a sample carrier stage, and a probe station. Among them, the sample carrier stage is vertically below the laser beam; the material of the sample carrier stage is copper; the probe arm of the probe station is used to connect to the grid line of the crystalline silicon battery to realize the connection with the voltmeter and current amplifier in the micro-region photocurrent imaging system; the Raman spectrometer among them analyzes the stress distribution in the micro-region of the crystalline silicon battery based on Raman scattering. On the other hand, the photocurrent and photovoltage of the device are measured by applying an external resistance to obtain the optoelectronic signal of the device. The specific micro-region Raman spectrometer system consists of four parts, namely:

[0054] (1) A spectrometer for collecting the scattered light signals generated by the laser;

[0055] (2) A laser for generating the laser light source for Raman scattering;

[0056] (3) A confocal microscope for sample positioning and laser focusing;

[0057] (4) A white light source for sample illumination;

[0058] In addition, the micro-region photocurrent imaging system consists of the following three parts, namely:

[0059] (1) A current amplifier for amplifying the optoelectronic signals generated by the device;

[0060] (2) An amplifier power supply for grounding and powering the amplifier;

[0061] (3) A voltmeter for measuring the voltage of the device;

[0062] Finally, the control system of the entire system is controlled by the piezoelectric ceramic scanner of the micro-region Raman spectrometer system, which can achieve precise control at the sub-micron level.

[0063] Example 2

[0064] This example provides a method for detecting the stress in the micro-region of a crystalline silicon battery, which is as follows:

[0065] When the laser of the micro-region Raman spectrometer irradiates the surface of the crystalline silicon battery, Raman scattering signals and optoelectronic signals will be generated. On the one hand, this device collects Raman signals through a high-precision spectrometer, and on the other hand, collects electrical signals through a voltmeter and current amplifier connected by an external circuit.

[0066] By moving the sample stage, the laser scans each position of the selected area point by point, thereby obtaining the Raman spectra and the values of photocurrent and photovoltage corresponding to each point.

[0067] Further data processing is performed on the Raman spectrum. For the obtained Raman spectrum, the peak position information of the Raman peak can be extracted through fitting, corresponding to the numerical value of the Raman shift, that is, Raman shift imaging is obtained.

[0068] Finally, numerical calculations are performed on the Raman shift imaging data, and stress distribution imaging is obtained through the formula of Raman shift and stress, thus realizing the synchronous collection of stress distribution and optoelectronic information in the micro-region.

[0069] Formula for Raman shift and stress: σ = ω / -2.29×10 -9 ,

[0070] In the formula, ω is the Raman shift; the Raman shift is obtained by fitting the peak position information of the characteristic peak from the Raman spectrum of each point.

[0071] The micro-region Raman spectrometer in this embodiment uses the WITecα300R confocal Raman imaging system of the German company witec.

[0072] Specifically, the device that combines micro-region Raman spectroscopy and photocurrent imaging technology in the present invention is used for defect characterization of tunnel oxide passivated contact (TOPCon) cells. The specific data is as Figure 3 shown:

[0073] As Figure 3 shown in (a), the device of the present invention can obtain a microscopic image under a 50X lens. It can be seen from the image that the defect is located on the back of the TOPCon cell. From (b), it can be seen that the defect presents a pit structure, and the specific morphology can be seen from the SEM microscope photo in (c).

[0074] Subsequently, micro-region photocurrent and photovoltage characterizations are performed on the defect region. The data is as Figure 4 shown. Figure 4 (a) corresponds to photocurrent imaging, Figure 4 (b) corresponds to photovoltage imaging. The data results show that serious defect recombination centers are formed around the pit, resulting in serious attenuation of photocurrent and photovoltage.

[0075] Then, the micro-region Raman spectroscopy imaging technology is used to characterize the local stress distribution. The data is as Figure 5 shown. Through the characterization of Figure 5 the stress distribution in the black square area (50μm×50μm) in (a), the Figure 5 Raman shift distribution in (b) is obtained, and the stress distribution in (c) is obtained through formula conversion. Finally, the characterization of the local stress distribution is realized. Figure 5 (c)

[0076] Through the above description, it is verified that the designed device based on micro-Raman spectroscopy and the combination of micro-photocurrent / photovoltage can realize the co-regional characterization of the mechanics and electricity of the micro-cracks in the crystalline silicon cell, and then obtain the relationship between the optoelectronic signal and the stress distribution. In addition, through the high-precision optical system, the device of the present invention can achieve high-spatial-resolution imaging at the level of 300 nanometers, which is also difficult to achieve by the previous defect characterization means.

[0077] Obviously, the above embodiments are only examples for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A system for detecting the micro-region stress of a crystalline silicon cell, characterized in that, It includes a micro-Raman spectrometer system, a micro-photocurrent imaging system, a sample stage, and a probe station; The sample stage is vertically below the laser beam; the probe arm of the probe station is used to connect to the grid line of the crystalline silicon cell to achieve connection with the voltmeter and current amplifier in the micro-photocurrent imaging system; The micro-Raman spectrometer system is used to test the stress distribution in the micro-region of the cell; the micro-photocurrent imaging system is used to detect the optoelectronic performance of the micro-region of the cell.

2. The system according to claim 1, wherein The micro-Raman spectrometer system includes a spectrometer for collecting the scattered light signals generated by the laser; a laser for generating the laser light source for Raman scattering; a confocal microscope for sample positioning and laser focusing; a white light source for sample illumination.

3. The system according to claim 1, wherein The wavelength of the laser beam of the micro-Raman spectrometer system is 325nm - 1064nm; the laser intensity is 1mW - 10mW.

4. The system according to claim 1, wherein The confocal microscope is a 50X - 100X short-focus microscope; the numerical aperture is 0.6 - 0.

9.

5. The system according to claim 1, characterized in that The micro-photocurrent imaging system includes a current amplifier for amplifying the optoelectronic signals generated by the device; an amplifier power supply for grounding and powering the amplifier; a voltmeter for measuring voltage.

6. The system according to claim 5, wherein The amplification factor of the amplifier is 1000 - 10000.

7. A method for detecting the micro-region stress of a crystalline silicon cell, characterized in that, Using the system for detecting the stress in the micro-region of the cell according to any one of claims 1 - 6 for detection, includes the following steps: (1) Place the crystalline silicon cell sample on the sample stage, and use the probe arm of the probe station to connect to the grid line of the crystalline silicon cell to achieve connection with the voltmeter and current amplifier in the micro-photocurrent imaging system; (2) Locate the crystalline silicon cell sample under the confocal microscope, and focus the laser beam vertically on the micro-region of the crystalline silicon cell to obtain corresponding Raman spectral data; meanwhile, obtain the photovoltage data through the photocurrent imaging system; (3) Move the sample stage orderly in the horizontal or vertical direction through the controller, and focus the laser beam of the Raman spectrometer on different micro-regions of the crystalline silicon cell sample to obtain two-dimensional Raman spectral data and photovoltage imaging data; (4) Calculate the stress distribution in the micro-region of the crystalline silicon cell through the Raman spectral data obtained in step (3).

8. The method according to claim 7, wherein In step (1), the surface roughness of the crystalline silicon cell sample is ≤ 1μm.

9. The method according to claim 7, characterized in that, In step (2), the confocal microscope is a 50X - 100X short-focus microscope; the numerical aperture is 0.6 - 0.

9.

10. The method according to claim 7, wherein In step (2), the wavelength of the laser beam is 325nm - 1064nm; the laser intensity is 1mW - 10mW.

Images