Broad-spectrum beam-induced current imaging device and its application

Abstract

The present invention discloses a wide-spectrum beam-induced current imaging device and its application. The depth of surface defects of solar cells is divided into four sections, and the detection wavelength range is divided according to the defect depth. A white light source is used in combination with interference filters of different wavelengths to obtain a quasi-monochromatic light source. The wide-spectrum beam-induced current imaging device is used to test solar cell defects, and the currents obtained by scanning four wavelengths are measured in turn. The cumulative distribution function diagram of the current is solved, and the quantile corresponding to the 0.05 quantile of the current distribution is determined through the cumulative distribution function diagram, and the optimal wavelength is selected according to the quantile size. The present invention has the following advantages: (1) Through four scans, a suitable detection wavelength can be quickly selected to maximize the number of solar cell defects detected and improve the detection efficiency. (2) A wide-spectrum light source is used, and different interference filters are equipped at the same time, which reduces the complexity of the system structure and the debugging problems caused by changing the light source.

Description

Technical Field

[0001] The invention relates to a light beam induced current scanning imaging device, in particular to a wide spectrum light beam induced current imaging device and application thereof. Background Art

[0002] Light beaminduced current mapping (LBIC mapping) is a method for detecting internal defects and optoelectronic properties of semiconductor photovoltaic devices. It has the advantages of high resolution and non-destructive testing, and is widely used in solar cell defect detection. LBIC technology focuses the measurement beam into a tiny spot, scans the sample surface, and detects the output current of the solar cell sample at the same time, reflecting the sample defects and optoelectronic properties according to the change in current. LBIC technology can measure short-circuit current distribution, quantum efficiency distribution, minority carrier diffusion length, PN junction depth, grain boundaries, dislocations and other information. In addition, by changing the wavelength of the detection light, defects at different depths can be detected.

[0003] The currently disclosed beam-induced current detection devices have the following deficiencies: (1) In order to detect defects at different depths, it is usually necessary to equip lasers with different wavelengths and even different laser power supplies. This method is inefficient and increases the structural complexity and volume of the LBIC device. In addition, the optical path needs to be re-adjusted after the laser is replaced. (2) Regarding the selection of the beam wavelength, it is only required that the wavelength be within the absorption band of the solar cell, and no selection plan is proposed. Summary of the invention

[0004] The present invention aims to provide a method for testing solar cell defects by using a wide-spectrum light beam induced current imaging device, which can quickly select the wavelength of the light beam and better detect the defects of the solar cell.

[0005] The technical scheme for implementing the present invention is: a wide-spectrum light beam induced current imaging device, comprising an LED light source, an optical fiber output collimating lens, a beam expansion system, an interference filter system, a spectroscope, a power meter, a two-dimensional galvanometer scanning system, an F-theta lens, an electric lifting slide, a source meter, and a PC; the LED light source is connected to the optical fiber output collimating lens through an optical fiber jumper, and the optical fiber output collimating lens, the beam expansion system, the interference filter system, the spectroscope, and the two-dimensional galvanometer scanning system are sequentially arranged on a common first optical axis, the power meter is arranged on the reflected light path of the spectroscope, the two-dimensional galvanometer scanning system is provided with an F-theta lens, the electric lifting slide is provided with a solar cell sample, the source meter is connected to the solar cell sample, and the PC is simultaneously connected to the power meter, the two-dimensional galvanometer scanning system, and the source meter.

[0006] The method for testing solar cell defects based on a wide spectrum beam induced current imaging device comprises the following steps:

[0007] Step 1: Adjust the electric lifting slide to place the solar cell sample at the focal plane of the F-theta lens, and proceed to step 2;

[0008] Step 2: perform hand-eye calibration on the two-dimensional galvanometer scanning system to obtain the conversion relationship between the galvanometer theoretical coordinates and the actual coordinates, and then proceed to step 3;

[0009] Step 3: Turn on the LED light source and adjust the beam splitter to make the splitting ratio of reflected light to transmitted light 1:9. Adjust the beam expansion system to make the spot diameter incident on the solar cell sample less than 100um, and then go to step 4;

[0010] Step 4: Adjust the interference filter system and select an interference filter to make the output quasi-monochromatic light beam wavelength 850nm, and then go to step 5;

[0011] Step 5: Control the two-dimensional galvanometer scanning system through the PC to perform a two-dimensional rough scan with a scanning step length greater than 100um, and at the same time trigger the source meter to measure the current I output by the solar cell sample and read the reference power P output by the power meter until the scan is completed, and then go to step 6;

[0012] Step 6: After the scan is completed, in order to eliminate the error caused by the unstable light source energy, the PC normalizes the reference power P at different measurement points to obtain P norm The measured current I is corrected using the normalized power value as the weight to obtain the corrected current I corr , where I corr =I×(1-P norm ), go to step 7;

[0013] Step 7, draw a current cumulative distribution function graph, and determine the quantile corresponding to the 0.05 quantile on the lower side of the current cumulative distribution function according to the current cumulative distribution function graph, and then proceed to step 8;

[0014] Step 8, by replacing the interference filter, readjusting the interference filter system, making the output quasi-monochromatic light beam wavelength between 750nm and 850nm, between 590nm and 690nm, and 470nm, respectively, returning to step 5, until the measurement is completed in the above three wavelength ranges, and then proceeding to step 9;

[0015] Step 9: Re-adjust the interference filter system and select the above four points I normi The wavelength corresponding to the minimum quantile point in the image is used to perform a two-dimensional fine scan by controlling the two-dimensional galvanometer scanning system through a PC. The scanning step length is less than 100um, and finally the current imaging of the solar cell sample is obtained for defect analysis.

[0016] Compared with the prior art, the present invention has the following significant advantages: (1) Through four scans, the appropriate detection wavelength can be quickly selected, so that more solar cell defects can be detected, thereby improving the detection efficiency. (2) A wide spectrum light source is used, and different interference filters are provided at the same time, avoiding the need to provide multiple lasers with different wavelengths, thereby reducing the complexity of the system structure and the debugging problems caused by replacing the laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The invention relates to a wide spectrum light beam induced current imaging device.

[0018] Figure 2 It is a schematic diagram of the intersection of the effective detection wavelength range of the second defect depth.

[0019] Figure 3 This is a schematic diagram of the intersection of the effective detection wavelength range of the third section defect depth.

[0020] Figure 4 It is the normalized current cumulative distribution function diagram.

[0021] In the figure, 1-LED light source, 2-fiber output collimating lens, 3-beam expansion system, 4-interference filter system, 5-beam splitter, 6-power meter, 7-two-dimensional galvanometer scanning system, 8-F-theta lens, 9-solar cell sample, 10-electric lifting slide, 11-source meter, 12-PC. DETAILED DESCRIPTION

[0022] The specific structure of the present invention is further described in detail below in conjunction with the accompanying drawings. The following embodiments can enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way.

[0023] Combination Figure 1 The invention discloses a device for imaging current induced by a wide spectrum beam, comprising an LED light source 1, an optical fiber output collimating lens 2, a beam expansion system 3, an interference filter system 4, a spectroscope 5, a power meter 6, a two-dimensional galvanometer scanning system 7, an F-theta lens 8, an electric lifting slide 10, a source meter 11, and a PC 12. The LED light source 1 is connected to the optical fiber output collimating lens 2 through an optical fiber jumper, and the optical fiber output collimating lens 2, the beam expansion system 3, the interference filter system 4, the spectroscope 5, and the two-dimensional galvanometer scanning system 7 are sequentially arranged on a common first optical axis. The power meter 6 is arranged on the reflection light path of the spectroscope 5, the two-dimensional galvanometer scanning system 7 is provided with an F-theta lens 8, the electric lifting slide 10 is provided with a solar cell sample 9, the source meter 11 is connected to the solar cell sample 9, and the PC 12 is simultaneously connected to the power meter 6, the two-dimensional galvanometer scanning system 7, and the source meter 11.

[0024] The LED light source 1 outputs continuous white light with a wavelength of 470nm to 850nm, and outputs a light beam with a power of 0.3mW to 1.2mW after passing through the optical fiber output collimating lens 2. The light beam is output after passing through the beam expansion system 3, and its spot diameter is greater than 8mm. The expanded light beam is converted into a quasi-monochromatic light beam through the interference filter system 4, and the quasi-monochromatic light beam is incident on the beam splitter 5. The power meter 6 measures the reflected light of the beam splitter 5 to obtain the reference power. After the light transmitted through the beam splitter 5 passes through the two-dimensional galvanometer scanning system 7 and the F-theta lens 8, the quasi-monochromatic light beam is focused on the solar cell sample 9, and the focused spot diameter is less than 100um. The source meter 11 measures the output current of the solar cell sample 9, and the PC 12 reads the measurement values ​​of the power meter 6 and the source meter 11. At the same time, the PC 12 controls the two-dimensional galvanometer scanning system 7 to move the quasi-monochromatic light beam to the next measurement point on the solar cell sample 9. After scanning the entire solar cell sample 9, the PC 12 normalizes the reference power at different measurement points, and uses the normalized power value as a weight to correct the measured current value. Finally, the PC 12 obtains the current distribution image of the solar cell sample 9, and determines whether there are defects on the solar cell sample 9 based on the current distribution image.

[0025] The beam expansion system 3, the beam splitter 5, and the F-theta lens 8 are all broadband models.

[0026] The interference filter system 4 includes a plurality of interference filters, and interference filters of different wavelengths are switched by rotating a component.

[0027] The incident angle of the beam splitter 5 is 45 degrees, the beam splitting ratio is 1:9, and the reflected light is 10%.

[0028] The two-dimensional galvanometer scanning system 7 includes two galvanometers whose axes are perpendicular to each other, and the galvanometer lens used in the galvanometer mirrors reflects wavelengths of 400nm to 900nm. The focal length of the F-theta lens 8 is 100mm.

[0029] The present invention can measure surface defects of solar cell sample 9, and the measurable defect depth is less than 18um. The defect depth is divided into four sections: the first section defect depth range is less than 0.3um, and the detection wavelength is 470nm; the second section defect depth range is [0.3um, 2.4um), and the detection wavelength range is [590nm, 690nm]; the third section defect depth range is [2.4um, 9.3um), and the detection wavelength range is [750nm, 850nm); the fourth section defect depth range is [9.3um, 18um), and the detection wavelength is 850nm.

[0030] Combined with Table 1, Figure 2 , Figure 3, for further detailed description. In the first section, the peak wavelength of defect detection is 470nm, as shown in Table 1. Using 470nm as the detection wavelength can obtain more obvious defect signals. In the second section, the intersection of the effective detection wavelength ranges of defects at different depths is 590nm to 690nm, as shown in Table 1. Figure 2 As shown in Figure 1, the detection wavelength range of 590nm to 690nm can detect the largest range of defect depths. In the third section, the intersection of the effective detection wavelength ranges of defects at different depths is 750nm to 850nm, as shown in Figure 1. Figure 3 As shown in FIG. 1 , the detection wavelength in the range of 750nm to 850nm can detect the largest defect depth range. In the fourth section, the peak wavelength of defect detection is 850nm. As shown in Table 1, using 850nm as the detection wavelength can obtain more obvious defect signals.

[0031] Table 1 shows the effective detection wavelengths for defects at different depths.

[0032]

[0033]

[0034] The present invention discloses a method for testing solar cell defects using a wide spectrum beam induced current imaging device, and the method steps are as follows:

[0035] Step 1: Adjust the electric lifting slide 10 so that the solar cell sample 9 is located at the focal plane of the F-theta lens 8, and then proceed to step 2.

[0036] Step 2: perform hand-eye calibration on the two-dimensional galvanometer scanning system 7 to obtain the conversion relationship between the galvanometer theoretical coordinates and the actual coordinates, and then proceed to step 3.

[0037] Step 3: Turn on the LED light source 1 and adjust the beam splitter 5 to make the splitting ratio of reflected light to transmitted light 1:9. Adjust the beam expansion system 3 to make the spot diameter incident on the solar cell sample 9 less than 100um, and then go to step 4.

[0038] Step 4: Adjust the interference filter system 4 and select an interference filter to make the output quasi-monochromatic light beam wavelength 850nm, and then go to step 5.

[0039] Step 5: Control the two-dimensional galvanometer scanning system 7 through the PC 12 to perform a two-dimensional rough scan with a scanning step length greater than 100um. At the same time, trigger the source meter 11 to measure the current I output by the solar cell sample 9 and read the reference power P output by the power meter 6 until the scan is completed and go to step 6.

[0040] Step 6: After the scan is completed, in order to eliminate the error caused by the unstable light source energy, the PC 12 normalizes the reference power P at different measurement points to obtain P norm The measured current I is corrected using the normalized power value as the weight to obtain the corrected current I corr , where I corr =I×(1-P norm ), go to step 7.

[0041] Step 7: Draw a current cumulative distribution function graph. According to the current cumulative distribution function graph, determine the quantile corresponding to the 0.05 quantile on the lower side of the current cumulative distribution function, such as Figure 4 As shown, the calculation process is as follows:

[0042] 7-1) For the corrected current I corr Normalize to get the normalized current I norm , making the current values ​​induced by beams of different wavelengths comparable.

[0043] 7-2) to I norm Perform histogram statistics.

[0044] 7-3) According to the histogram statistical results, that is, the probability density function, I is calculated norm The cumulative distribution function F(I norm ).

[0045] 7-4) Let F(I normi )=0.05, solve for the quantile I corresponding to the 0.05 quantile normi , I normi The smaller it is, the more I norm The peak value moves toward the direction of decreasing current, indicating that the number of detected defects increases. Wherein, the sequence number of different wavelengths i=1, 2, 3, 4; proceed to step 8.

[0046] Step 8: Re-adjust the interference filter system 4 by replacing the interference filter, so that the wavelength of the output quasi-monochromatic light beam is between 750nm and 850nm, between 590nm and 690nm, and 470nm respectively, and return to step 5 until the measurement in the above three wavelength ranges is completed, and then go to step 9.

[0047] Step 9: Re-adjust the interference filter system 4 and select the above four points I normi The wavelength corresponding to the minimum quantile point in the image is used to control the two-dimensional galvanometer scanning system 7 through the PC 12 to perform two-dimensional fine scanning, and the scanning step length is less than 100um. Finally, the current imaging of the solar cell sample 9 is obtained for defect analysis.

[0048] Example 1

[0049] In this embodiment, the length, width and height of the solar cell sample 9 are 20mm*20mm*200um, and the spot size incident on the surface of the solar cell sample 9 is 30um. Adjust the interference filter system 4 and select an interference filter so that the output quasi-monochromatic light beam wavelength is 850nm. The two-dimensional galvanometer scanning system 7 is controlled by the PC 12 to perform a two-dimensional rough scan with a scanning step of 100um. At the same time, the source meter 11 is triggered to measure the current output by the solar cell sample 9 and read the reference power output by the power meter 6 until the scan is completed. After the scan is completed, the PC 12 corrects the measured current value. Draw the corrected current cumulative distribution function diagram, and determine the quantile corresponding to the 0.05 quantile on the lower side of the current cumulative distribution function according to the current cumulative distribution function diagram. By replacing the interference filter and re-adjusting the interference filter system 4, the output quasi-monochromatic light beam wavelengths are 780nm, 650nm, and 470nm respectively, and the above steps are repeated until the above three wavelength ranges are measured. The interference filter system 4 is readjusted, the wavelength corresponding to the smallest quantile among the four quantiles is selected, and the two-dimensional galvanometer scanning system 7 is controlled by the PC 12 to perform two-dimensional fine scanning with a scanning step length of 10 um. Finally, the current imaging of the solar cell sample 9 is obtained for defect analysis.

Claims

1. A wide spectrum beam induced current imaging device, characterized in that: The invention comprises an LED light source (1), an optical fiber output collimating lens (2), a beam expansion system (3), an interference filter system (4), a beam splitter (5), a power meter (6), a two-dimensional galvanometer scanning system (7), an F-theta lens (8), an electric lifting slide (10), a source meter (11), and a PC (12); the LED light source (1) is connected to the optical fiber output collimating lens (2) via an optical fiber jumper, the optical fiber output collimating lens (2), the beam expansion system (3), the interference filter system (4), the beam splitter (5), and the two-dimensional galvanometer scanning system (7) are arranged in sequence on a common first optical axis, the power meter (6) is arranged on the reflection light path of the beam splitter (5), the two-dimensional galvanometer scanning system (7) is provided with an F-theta lens (8), the electric lifting slide (10) is provided with a solar cell sample (9), the source meter (11) is connected to the solar cell sample (9), and the PC (12) is simultaneously connected to the power meter (6), the two-dimensional galvanometer scanning system (7), and the source meter (11); The LED light source (1) outputs continuous white light with a wavelength of 470 nm to 850 nm, and outputs a light beam with a power of 0.3 mW to 1.2 mW after passing through an optical fiber output collimating lens (2). The light beam is outputted after passing through a beam expansion system (3), and its spot diameter is greater than 8 mm. The beam after expansion is converted into a quasi-monochromatic light beam through an interference filter system (4), and the quasi-monochromatic light beam is incident on a beam splitter (5). A power meter (6) measures the reflected light of the beam splitter (5) to obtain a reference power. The light transmitted through the beam splitter (5) is scanned by a two-dimensional galvanometer scanning system (7) and an F-th After passing through the eta lens (8), the quasi-monochromatic light beam is focused onto the solar cell sample (9), and the focused spot diameter is less than 100um. The source meter (11) measures the output current of the solar cell sample (9), and the PC (12) reads the measurement values ​​of the power meter (6) and the source meter (11). At the same time, the PC (12) controls the two-dimensional galvanometer scanning system (7). After scanning the entire solar cell sample (9), the PC (12) normalizes the reference power at different measurement points. Finally, the PC (12) obtains the current distribution image of the solar cell sample (9).

2. The wide spectrum beam induced current imaging device according to claim 1, characterized in that: The interference filter system (4) comprises a plurality of interference filters, and interference filters of different wavelengths are switched by rotating components.

3. The wide spectrum beam induced current imaging device according to claim 2, characterized in that: The incident angle of the beam splitter (5) is 45 degrees, the beam splitting ratio is 1:9, and the reflected light is 10%.

4. The wide spectrum beam induced current imaging device according to claim 3, characterized in that: The surface defect depth of the solar cell sample (9) measured by the device is less than 18um, and the defect depth is divided into four sections: the first section defect depth range is less than 0.3um, and the detection wavelength is 470nm; the second section defect depth range is [0.3um, 2.4um), and the detection wavelength range is [590nm, 690nm]; the third section defect depth range is [2.4um, 9.3um), and the detection wavelength range is [750nm, 850nm); the fourth section defect depth range is [9.3um, 18um), and the detection wavelength is 850nm.

5. A method for testing solar cell defects based on a wide spectrum beam induced current imaging device according to any one of claims 1 to 4, characterized in that: Here are the steps: Step 1, adjust the electric lifting slide (10) so that the solar cell sample (9) is located at the focal plane of the F-theta lens (8), and proceed to step 2; Step 2, perform hand-eye calibration on the two-dimensional galvanometer scanning system (7), obtain the conversion relationship between the galvanometer theoretical coordinates and the actual coordinates, and proceed to step 3; Step 3, turn on the LED light source (1), adjust the beam splitter (5) so that the splitting ratio of reflected light to transmitted light is 1:9; adjust the beam expansion system (3) so that the diameter of the light spot incident on the solar cell sample (9) is less than 100 um, and proceed to step 4; Step 4, adjust the interference filter system (4), select an interference filter, make the output quasi-monochromatic light beam wavelength 850nm, and go to step 5; Step 5, controlling the two-dimensional galvanometer scanning system (7) to perform a two-dimensional rough scan through the PC (12), with a scanning step length greater than 100 μm, and at the same time triggering the source meter (11) to measure the current I output by the solar cell sample (9), and read the reference power P output by the power meter (6), until the scan is completed, and then proceeding to step 6; Step 6: After the scan is completed, in order to eliminate the error caused by the unstable light source energy, the PC (12) normalizes the reference power P at different measurement points to obtain P norm The measured current I is corrected using the normalized power value as the weight to obtain the corrected current I corr , where I corr =I×(1-P norm ), go to step 7; Step 7, draw a current cumulative distribution function graph, and determine the quantile corresponding to the 0.05 quantile on the lower side of the current cumulative distribution function according to the current cumulative distribution function graph, and then proceed to step 8; Step 8, by replacing the interference filter, readjusting the interference filter system (4), making the output quasi-monochromatic light beam wavelength between 750nm and 850nm, between 590nm and 690nm, and 470nm, respectively, and returning to step 5 until the measurement in the above three wavelength ranges is completed, and then proceeding to step 9; Step 9: Re-adjust the interference filter system (4) and select the above four points I normi The wavelength corresponding to the minimum quantile point in the image is used to control a two-dimensional galvanometer scanning system (7) through a PC (12) to perform two-dimensional fine scanning with a scanning step length of less than 100 um, and finally obtain current imaging of the solar cell sample (9) for defect analysis.

6. The method for testing solar cell defects based on a wide spectrum beam induced current imaging device according to claim 5, characterized in that: In step 7, a current cumulative distribution function graph is drawn, and according to the current cumulative distribution function graph, the quantile corresponding to the 0.05 quantile on the lower side of the current cumulative distribution function is determined, as follows: 7-1) For the corrected current I corr Normalize to get the normalized current I norm ; 7-2) to I norm Perform histogram statistics; 7-3) According to the histogram statistical results, that is, the probability density function, I is calculated norm The cumulative distribution function F(I norm ); 7-4) Let F(I normi )=0.05, solve for the quantile I corresponding to the 0.05 quantile normi , i represents the serial number of different wavelengths, i = 1, 2, 3, 4; I normi The smaller it is, the more I norm The peak value moves toward the direction of decreasing current, indicating that the number of detected defects increases.

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