CN106990120A - The quality determining method and its detection means of a kind of solar battery sheet - Google Patents

Abstract

The invention provides a kind of quality determining method of solar battery sheet and its detection means, this method is scanned using detection means to cell piece to be measured, obtains the OCT 3-D views of cell piece；Then gained OCT 3-D views are observed or handled the external appearance characteristic for obtaining cell piece, defective locations, thickness, gate line electrode size and cell piece and fall into the information such as light ability, contactless, not damaged on-line real-time measuremen to solar battery sheet can be achieved.Present invention detection is more comprehensive, and the detection of multiple parameters is only can be achieved with by single detection method and device, testing cost is greatly reduced, while the semi-manufactured goods quality in detectable production line each stage, reference index is provided for each technological process production.

Description

Quality detection method and detection device for a solar cell

technical field

The invention relates to the field of photovoltaics, in particular to a method for detecting the quality of solar cells and a detection device thereof.

Background technique

With the continuous reduction of fossil energy and the continuous aggravation of environmental degradation, the development of renewable energy represented by solar energy has received more and more attention. A solar cell is a device that converts solar energy into electrical energy based on the photovoltaic effect. It has the advantages of high reliability, long life, and no pollution. It can be used as a power source for artificial satellites, navigation lights, and transistor radios. Depending on the materials used, solar cells can be divided into silicon solar cells, compound solar cells, dye-sensitized cells, and organic thin-film cells. Among them, silicon solar cells are a fast-growing and more mature type of solar cells. Among the current industrialized solar cells, crystalline silicon solar cells account for nearly 90%.

The production of solar cells requires quite a lot of processes. In order to obtain solar cells with higher efficiency and longer service life, the detection of solar cells is an indispensable process. With the rapid growth of the global photovoltaic industry, higher requirements have been placed on the quality inspection of solar cells, which can be mainly divided into electrical performance testing and surface quality testing. At present, the vast majority of solar cell manufacturers still use manual methods for surface quality inspection, relying on the visual judgment of operators, which also brings many inspection problems, and at the same time, it is difficult to guarantee product quality. In addition, the time for manual inspection is short, and it is easy to fall into subjective opinions in the judgment of defects, so it is impossible to establish standards.

At present, there are many researches on solar cell detection methods, mainly including scanning electron microscopy (SEM), photoluminescence scanning (PL), electroluminescence scanning (EL), reflectivity measurement, and I-V characteristic test. Among them, the I-V characteristic test mainly detects the electrical properties of the cell, and the scanning electron microscope (SEM), photoluminescence scanning (PL) and electroluminescence scanning (EL) are used for the defect detection of the cell, which can detect the crack of the cell , Broken grid, etc., but the above method cannot obtain in-depth structural information, nor can it detect parameters such as the size of the grid electrode and the light trapping ability of the cell. Usually, it is necessary to cooperate with other detection methods such as reflectance to evaluate the quality of the cell and It is difficult to realize online real-time detection. Electroluminescence scanning (EL) is a contact detection, which is easy to cause damage to the battery. For example, a patent document (application number CN201110104821.6) discloses an integrated system of electroluminescence defect detection and IV detection of solar cells. Including the probe clamping mechanism for fixing the cell, the IV detection system, the EL detection system, and the circuit conversion device, etc., the structure is relatively complicated. cause damage and cannot achieve a more comprehensive detection. The patent document (Application No. 201410265102.6) discloses an online quality inspection method for solar cells, which uses multiple light sources, multiple imaging units, and flipping mechanisms to achieve online inspection. The structure is relatively complicated, and the cells need to be turned over during inspection. , other parameters other than defects cannot be detected. In addition, the scanning electron microscope (SEM) detection needs to process the cell sample, and the detection cost is high, which is not suitable for industrial application. Since silicon solar cells are fragile, they are more suitable for non-contact detection. Currently, there is no comprehensive non-contact detection method.

Contents of the invention

One of the objectives of the present invention is to provide a quality inspection method for solar cells to solve the problems that existing detection methods are destructive to cells, costly, or cannot obtain depth direction information.

The second object of the present invention is to provide a quality detection device for solar cells.

The purpose of the present invention is achieved by the following technical solutions: a quality detection method for solar cells, comprising the following steps:

1. Using a detection device to scan the cell to be tested to obtain an OCT three-dimensional image of the cell; the detection device includes an OCT detection system, and the OCT detection system uses a near-infrared light source that cannot be absorbed by a silicon chip;

2. Observe or process the obtained OCT three-dimensional image to obtain the quality parameters of the cell:

(a) Obtain the defect and impurity parameters of the cell: pure crystalline silicon is transparent in the image, but the defects and impurities will cause scattering or absorption and appear as bright spots or lines. The defects and impurity of the cell can be obtained by direct observation. impurity parameters;

(b) Obtain the thickness, warpage and battery grid parameters of the battery: observe the upper and lower surface structures of the battery from the OCT three-dimensional image, and directly obtain the surface evaporation and broken grid of the battery;

The position of the upper and lower surfaces of the silicon wafer is obtained through the boundary differential operator, and the height value h1 of the silicon wafer on the OCT three-dimensional image is obtained according to the pixel, and then the thickness of the silicon wafer h=h1/n is obtained from the refractive index n of the silicon wafer in the infrared band , according to the thickness of the silicon wafer and through the scale to obtain the distance between two adjacent grid line electrodes and the width and height of each grid line electrode;

The position of the center plane is obtained according to the position of the upper and lower surfaces of the silicon wafer, and then the maximum vertical distance between the center planes of different regions along the horizontal direction is obtained according to the pixels, which is the warpage of the cell.

(c) Obtain the light trapping ability parameters of the cell: average the OCT three-dimensional image of the cell along the depth direction to obtain the vertical one-dimensional average light intensity value, and use the light intensity value on the upper surface of the cell to characterize the light trapping ability of the cell , the light intensity value on the upper surface of the cell is inversely proportional to the light trapping ability of the cell.

The obtaining the defect parameters of the battery sheet includes obtaining information on surface and internal cracks of the battery sheet.

When testing the light-trapping ability of the cell, the original silicon wafer, the textured sheet, the diffusion sheet and the wafer after evaporation of the anti-reflection film are tested to obtain the light-trapping ability of the cell at different process stages.

A quality inspection device for solar cells, comprising an OCT measuring probe, an OCT integrated system and a computer;

The OCT measuring probe is connected with the OCT integrated system, the OCT measuring probe includes a self-focusing scanning lens and adopts a near-infrared light source that cannot be absorbed by silicon wafers, and the OCT measuring probe is used to perform laser scanning on the cell;

The OCT integrated system is respectively connected with the OCT measuring probe and the computer, and is used to collect the backscattered light of the cell introduced through the OCT measuring probe, and convert the obtained interference light signal into an electrical signal and transmit it to the computer;

The computer processes the input electric signal to obtain the scanned image of the cell, and processes the image to obtain the quality parameter information of the cell.

The detection device is installed on the cell production line to detect the quality of the cell in real time online.

The detection method of the present invention utilizes an OCT system and a near-infrared light source, which can realize non-contact and non-damage online real-time detection of solar cells. During detection, only a probe is needed to scan the cells without causing damage to the cells. Moreover, the operation is simple and easy to realize. Secondly, by detecting the backscattering signals at different depth levels, not only the surface information can be obtained, but also the information in the depth direction of the object to be tested can be obtained, which has a good detection effect on defects and impurities inside the cell. Thirdly, through the special light source design and image processing method, not only the inspection items are easy to observe, but also the appearance characteristics, defect position, thickness, grid line electrode size, light trapping ability of the cell and other information of the cell can be detected, making the inspection more comprehensive , Only a single detection method and device can realize the detection of multiple parameters, which greatly reduces the detection cost. At the same time, it can detect the quality of semi-finished products at each stage of the production line, and provide reference indicators for the production of various processes.

The detection device of the invention has a simple structure, can be configured in a cell production line for real-time imaging, is low in price, and has broad application prospects in actual production lines.

Description of drawings

Fig. 1 is a schematic structural diagram of the detection device of the present invention.

Fig. 2 is a three-dimensional image of a battery sheet collected by the detection device of the present invention.

Fig. 3 is a three-dimensional image of a battery sheet with cracks on the lower surface.

Figure 4 is a three-dimensional image of a battery sheet with cracks inside.

Figure 5 is a three-dimensional image of a battery sheet with internal impurities.

FIG. 6 is a schematic diagram of detecting the warpage of a battery sheet.

Fig. 7 is a graph showing the relationship between the light intensity signal and the depth of the semi-finished cell at each stage.

Fig. 8 is a graph of the reflectance of semi-finished cells of cells at various stages measured by an infrared spectrometer.

detailed description

As shown in FIG. 1 , the structure of the detection device of the present invention includes an OCT measurement probe 103 , a computer 102 and an OCT integrated system 10 . Wherein, the OCT measuring probe 103 and the computer 102 are respectively connected with the OCT integrated system 101. The OCT measuring probe 103 includes a self-focusing scanning lens, and the OCT measuring probe 103 performs laser scanning on the solar cell sheet 104 through the self-focusing scanning lens. The backscattered light of the film is collected by the OCT integrated system 101 through the OCT measuring probe 103, and the OCT integrated system 101 converts the obtained interference light signal into an electrical signal and transmits it to the computer 102 for analysis and processing, and finally obtains the image data of the scanned object. Fig. 2 is a three-dimensional image obtained by scanning the finished battery sheet 104 with a detection device. The central wavelength of the light source of the detection device is the near-infrared band, and the silicon wafer does not absorb light in this wavelength band. From Figure 2, we can clearly see the upper and lower surfaces of the solar cell, while the inside of the silicon wafer shows transparency.

Use the above detection device to scan the cell to be tested to obtain the OCT three-dimensional image of the cell; then observe or process the obtained OCT three-dimensional image to obtain the quality parameters of the solar cell in three aspects. The specific detection and processing are described as follows:

1. Realize the detection of defects and impurities in the cell

Pure crystalline silicon should be transparent in 3D images, but defects and impurities can cause scattering or absorption, appearing as bright spots or lines, which show up on the image. During the production process, some external forces will cause different degrees of damage to the silicon wafer, and slight collisions may form cracks that are not easy to detect. The invention can easily detect the hidden cracks of the cell, as well as internal impurities and defect information. and easy to observe. Figure 3 is a three-dimensional image of a cell with cracks on the lower surface. It can be clearly seen from the figure that there are two intersecting bright lines on the lower surface of the cell, and the position and specific shape of the crack can be distinguished. Figure 4 is The three-dimensional image of the cell with cracks inside, its specific shape and position can also be clearly seen from the figure. Figure 5 is a three-dimensional image of a battery sheet with internal impurities, and an impurity defect located inside the battery can be clearly seen. If the inside of the battery is a homogeneous silicon medium, it should be transparent and invisible on the image, but there are bright spots inside the battery, indicating that light scattering occurs at the bright spots, which proves that this is not a uniform silicon medium.

2. Realize the detection of battery thickness, warpage and battery grid

From Figure 1, you can clearly see the upper and lower surfaces of the solar cell, and the inside of the silicon wafer is transparent, so you can directly observe the grid electrode on the surface and its vapor deposition, and judge whether there is a broken grid. According to the parameters set by the scan and the refractive index of the solar cell in the infrared band, the thickness of the solar cell can be obtained, and the distance between two adjacent grid electrodes, as well as the width and height of each electrode can be obtained. The position of the upper and lower surfaces of the silicon wafer can be found through the boundary differential operator, and then the height value h1 of the silicon wafer on the three-dimensional image can be obtained according to the pixel size, and then the thickness h= of the silicon wafer can be obtained from the refractive index n of the silicon wafer in the infrared band h1/n. Then, according to the thickness of the silicon wafer and through the scale, the distance between the adjacent grid line electrodes and the height and width of each grid line electrode can be obtained, so as to better judge the evaporation of the electrodes.

The maximum vertical distance difference between the center planes of different areas along the horizontal direction of the silicon wafer is defined as the warpage. According to the position of the upper and lower surfaces of the silicon wafer, the position of the center plane can be obtained, and then the maximum vertical distance between the center planes of different areas along the horizontal direction can be obtained according to the pixels. distance. As shown in Figure 6, the OCT images of two different positions along the horizontal direction of the silicon wafer are shown. The central planes are H1 and H2 respectively. The distance between H1 and H2 is 13 pixels, and the size of each pixel is 5 microns. The warpage is 丨H1-H2丨=65 microns.

3. Realize the detection of the light trapping ability of the cell

The light intensity signal on the surface of the cell in the three-dimensional image is proportional to the backscattered light of the detected cell, and the backscattered light is inversely proportional to the light trapping ability of the cell, so the light trapping can be evaluated by the light intensity value on the upper surface of the cell ability.

The production steps of crystalline silicon solar cells mainly include: cleaning texture, diffusion junction, edge etching, anti-reflection film deposition, evaporation electrode. The purpose of the process is to reduce the reflectivity of the surface of the battery sheet and enhance the light trapping ability, thereby improving the photoelectric conversion efficiency of the battery. Usually, the main steps that have a greater impact on the surface reflectance of the cell are texturing and anti-reflection film deposition. Installing the device of the present invention on the cell production line can realize online real-time detection of the cell, such as using the present invention to scan the solar cell semi-finished products at various stages online to obtain the light intensity values on the surface of the cell at different preparation stages, and then obtain its The light trapping ability is used to evaluate the quality of different processes in solar cell production. The main operation steps are as follows:

1) Under the same test environment, use the detection device to scan the original silicon wafer, textured wafer, diffuser wafer and the wafer after evaporation of the anti-reflection film;

2) Surface alignment of the obtained OCT 3D images;

3) Average all the A-SCANs in the three-dimensional image along the depth direction to obtain the longitudinal one-dimensional average light intensity signal;

4) From step 3), the light intensity values on the upper surface of the cell at each stage (used to characterize its light trapping ability) can be calculated. As shown in Figure 7, it can be clearly seen that the light trapping capabilities of different cells are different. At the same time, the reflectance of the above samples is measured by using the current relatively mature detection technology (infrared spectrometer), as shown in Figure 8, it can be seen from the figure , using the detection method of the present invention is consistent with the test results of the prior art. Since the main purpose of silicon wafer processing in different technological processes is to improve its light-trapping ability and thereby improve cell efficiency, the detection method of the present invention can be used to detect the light-trapping ability of cells at each stage to evaluate the quality of different technological processes for solar cell production , not only convenient and quick, but also reliable.

Claims (5)

1. a kind of quality determining method of solar battery sheet, it is characterised in that comprise the following steps：

1. cell piece to be measured is scanned using detection means, obtains the OCT 3-D views of cell piece；The detection means bag OCT detecting systems are included, the OCT detecting systems use the nonabsorbable near-infrared light source of silicon chip；

2. gained OCT 3-D views are observed or handled the mass parameter for obtaining cell piece：

（a）Obtain defect, the impurity parameter of cell piece：OCT 3-D views are observed, pure crystalline silicon is transparent in the picture , but defect and impurity can cause scattering or absorb and be rendered as speck or bright line, by directly observe obtain cell piece lack Sunken, impurity parameter；

（b）Obtain thickness, warped degree and the battery grid parameter of cell piece：The upper following table of cell piece is observed by OCT 3-D views Face structure, directly obtains cell piece surface evaporation and grid situation of breaking；

The upper and lower surface position of silicon chip is obtained by border differential operator, and silicon chip is obtained on OCT 3-D views according to pixel Height value h1, then thickness h=h1/n of silicon chip is obtained by silicon chip in the refractive index n of infrared band, according to the thickness of silicon chip and led to Cross engineer's scale and obtain the spacing of adjacent two gate line electrodes and the width of every gate line electrode and height；

Its median plane position is obtained according to the upper and lower surface position of silicon chip, then tried to achieve according to pixel in different zones in the horizontal direction Maximum normal distance between heart face is the warped degree of cell piece；

（c）Obtain cell piece and fall into luminous energy force parameter：The OCT 3-D views of cell piece are averaged along depth direction, indulged To one-dimensional average intensity values, the sunken light ability of cell piece, cell piece upper surface are characterized with the light intensity value of cell piece upper surface Light intensity value and the sunken light ability of cell piece be inversely proportional.

2. the quality determining method of solar battery sheet according to claim 1, it is characterised in that the acquisition cell piece Defect parameters include obtaining the surface of cell piece and internal hidden split situation information.

3. the quality determining method of solar battery sheet according to claim 1, it is characterised in that fallen into detection cell piece During light ability, the chip after former silicon chip, making herbs into wool piece, diffusion sheet and evaporation antireflective coating is detected, different process rank is obtained The sunken light ability of the cell piece of section.

4. a kind of quality detection device of solar battery sheet, it is characterised in that the detection means include OCT measuring probes, OCT integrated systems and computer；

The OCT measuring probes are connected with OCT integrated systems, and OCT measuring probes are comprising self-focusing scanning lens and use silicon chip Nonabsorbable near-infrared light source, OCT measuring probes are used to carry out laser scanning to cell piece；

The OCT integrated systems are connected with OCT measuring probes and computer respectively, incoming via OCT measuring probes for gathering Cell piece rear scattered light, and obtained interference light signal is converted into electric signal transmission to computer；

Electric signal progress of the computer to input handles the scan image for obtaining cell piece, and image is handled The quality parameter information of cell piece.

5. the quality detection device of solar battery sheet according to claim 4, it is characterised in that the detection means peace Loaded on battery slice assembly line, on-line real-time measuremen is carried out to battery tablet quality.