CN101696942B - Multi-junction solar cell and each sub-cell AC electroluminescence test method and device - Google Patents

Abstract

The invention discloses a multi-junction solar cell and AC electroluminescence measuring method and device of each sub cell, relating to a solar cell AC electroluminescence test. The testing device is provided with an AC drive circuit, an optical module, a vidicon, a spectrograph and a computer. The output end of the AC drive circuit is connected with a solar cell array; the optical module is provided with a filter plate, a battery of lens and a speculum; the filter plate, the battery of lens, the speculum and the vidicon are on the same optical axis; reflecting beams of the speculum are transmitted to the receiving port of the spectrograph; and the output end of the vidicon is connected with the computer. A multi-junction solar cell sample is put on a sample table; the spectrograph is utilized to measure the electroluminescence light spectrum of the multi-junction solar cell to obtain the light-emitting band of each subjunction; a tested light spectrum is selected by the filter plate; the testing range of the cell sample is selected to obtain an AC electroluminescence image; and the computer processes data to obtain the information of the process injury and crystalline material defect of the solar cell and each sub cell component thereof.

Description

Multi-junction solar cell and each sub-cell AC electroluminescence test method and device

technical field

The present invention relates to a solar cell AC electroluminescence test, in particular to a multi-junction solar cell and each sub-battery AC electroluminescence test method and device, mainly by establishing a joint system of electroluminescence spectrum and spectroscopic imaging to realize the detection of each sub-cell Detection of material defects and device process damage.

Background technique

At present, under the double pressure of the depletion of non-renewable mineral energy such as oil and coal and the increasingly serious environmental pollution, more and more countries have begun to implement the Sunshine Plan to develop solar energy, a pure natural energy with large reserves, wide areas, and clean energy. Renewable and other advantageous resources. As a feasible and effective method of utilizing solar radiation energy, solar cells have opened up broad prospects for human beings to utilize solar energy extensively. With the improvement of battery manufacturing technology, compared with the first-generation solar cells of crystalline silicon and the second-generation thin-film solar cells such as amorphous silicon and copper indium gallium selenide, gallium arsenide-based semiconductor materials have good performance, and their multi-junction stack connections The formed solar cell can basically realize full-spectrum absorption, so that its photoelectric conversion efficiency is always far ahead of other solar cells. Coupled with its excellent radiation resistance and high temperature resistance, it further improves the reliability and service life of the space application of the battery, and it has increasingly shown the trend of replacing high-efficiency silicon solar cells and single-junction gallium arsenide solar cells.

The key to the design of multi-junction solar cells is to adjust the lattice matching of each sub-cell material, the bandgap matching between each heterojunction and the thickness of each sub-cell, so that the current matching between each sub-cell can meet the requirements of each sub-cell as much as possible. The condition that the photocurrent of the cell is equal to maximize the photoelectric conversion efficiency, otherwise, the photocurrent of the laminated cell will be limited to the sub-cell with the smallest photocurrent, resulting in the recombination loss of the current. A problem with any of the sub-cells will affect the characteristics of the whole battery, thereby reducing the photoelectric conversion efficiency of the battery. Therefore, for multi-junction solar cells, the separate detection of the characteristics of the whole cell and each sub-cell is a very critical technology.

Multi-junction solar cells are composed of different materials, and the mismatch stress at the heterointerface and the diffusion of impurities between layers increase the difficulty of material growth. Once the interface is not well controlled, a large number of defects such as dislocations and anti-phase domains will be generated to form recombination centers, which will seriously reduce the lifetime of minority carriers. However, with the increase of defect concentration, the recombination loss of photogenerated carriers occurs, and the leakage current increases, which seriously endangers the life and performance of solar cells. Especially for multi-junction solar cells for space applications, the radiation of high-energy particles in space will cause lattice matching defects, that is, radiation damage, which will gradually reduce the output power of the cells and seriously affect their service life. In addition, problems such as damage and electrode cracks introduced by the device process will also greatly weaken the photoelectric conversion efficiency of solar cells. In order to understand and control the defects in solar cells to improve the efficiency and service life of solar cells, the technology commonly used to detect solar cell defects is laser beam induced current (LBIC) technology (C.L.Zhou et.al., "Characterization of crystalline silicon solar cells by electrical parameters.", Optics and Precision Engineering, 7(2008) 1163.) and electron beam induced current (EBIC) technology (Y.Toshiki, et.al., "Noble Evaluation Method for Light Trapping Effect in Polycrystalline Silicon Solar Cells", Japanese Journal of Applied Physics, 43(2004) 439.). However, its test time is long, and it is mainly used for single-junction solar cells, and it is impossible to know the information of each sub-cell of multi-junction solar cells.

Contents of the invention

The purpose of the present invention is to provide a multi-junction solar cell and each sub-cell alternating current electroluminescence testing device.

Another object of the present invention is to provide a multi-junction solar cell and a method for testing AC electroluminescence of each sub-cell.

The multi-junction solar battery and each sub-battery AC electroluminescence testing device of the present invention is provided with an AC drive circuit, an optical component, a camera tube, a spectrometer and a computer.

The input end of the AC drive circuit is connected to the AC mains, and the output end of the AC drive circuit is connected to the solar cell array; the optical component is provided with a filter for splitting the electroluminescent spectrum of the solar cell, a lens group and a mirror for changing the range of the test space, In order to realize the observation of the solar cell array and its single solar cell or even the tiny crystal defects, the filter is set above the solar cell array, the lens group is set above the filter, the reflector is set above the lens group, and the camera tube is set above the reflector , the optical axis of the filter, lens group, mirror and camera tube is the same optical axis, the reflected light beam of the mirror is transmitted to the receiving port of the spectrometer, and the electroluminescent spectrum measurement is performed on the solar cell to be tested, and the data output of the camera tube is The terminal is connected to the computer through the data line for analysis and processing.

The AC drive circuit can be a voltage regulator; the lens group can be a camera lens or a microscope.

The wavelength detection range of the spectrometer covers the spectral response range of the entire solar cell, and is used to measure the electroluminescence spectrum of the solar cell.

The camera tube includes infrared camera tube and visible light camera tube. According to the measurement object, infrared light or visible light camera tube is selected to realize the electroluminescence image measurement of multi-junction solar cell array, single solar cell and even each sub-cell.

The computer includes data acquisition and equipment control components, and data conversion, processing and analysis software. The equipment control part is mainly used to control the exposure time of the camera tube, the mode of image acquisition, the reading speed of the camera tube, etc.

The multi-junction solar cell and each sub-cell AC electroluminescence test method of the present invention adopts the multi-junction solar cell and each sub-cell AC electroluminescence test device, comprising the following steps:

1) The multi-junction solar cell sample is placed on the sample stage, and the mains power is applied to the battery sample after passing through the AC drive circuit;

2) Using a spectrometer to measure the electroluminescence spectrum of the multi-junction solar cell to obtain the luminescence band of each sub-junction;

3) According to the solar cell electroluminescence spectrum wavelength range known in step 2), select the imaging tube of the corresponding band, and pass the filter to select the spectral range of the test (can include multiple junctions or only contain a single sub-junction luminescence band );

4) Through different lens combinations, select the test range of the battery sample, and carefully adjust the focus to obtain a clear spatially resolved AC electroluminescence image; the AC electroluminescence image can use color or grayscale to represent the electroluminescent light intensity;

5) Use computer for data processing and analysis to obtain information on process damage and crystal material defects of solar cells and their sub-cells, and complete the AC electroluminescence test of multi-junction solar cells and their sub-cells.

In step 2), the electroluminescence spectrum of the multi-junction solar cell is measured. If the emission wavelength of the sub-cell is in the infrared range, the infrared filter is first used to split the light, and then the lens group is used to focus the image on the infrared light that can respond to this band. Optical camera tube; if the sub-battery with luminous spectrum in the visible light range, then directly select the visible light camera tube.

In step 5), the computer is used for data processing and analysis, and the analysis of the full-spectrum image of the AC electroluminescence of the solar cell array is to find and compare single cells that do not emit light and have weaker luminous intensity, wherein those that do not emit light at all are no Electrically injected single cells may be caused by problems in the process of assembly, packaging, electrodes, or electrical contacts, etc., while unevenly luminous single cells may be caused by crystal defects or device process damage, and further inspection is required; or

For the full-spectrum image analysis of AC electroluminescence of a single solar cell, the battery with strong luminous intensity and uniform spatial distribution is of good quality; the battery with weak luminous intensity and uneven spatial distribution has local material defects, sub-cell defects, or process damage. Batteries, which need to be further analyzed in conjunction with the AC electroluminescence images of each sub-cell; or

Process damage and material defect analysis of AC electroluminescence images of each sub-cell of a multi-junction solar cell.

The method for judging the process damage of the device is as follows: in a good solar cell electroluminescent image, the electrode and metal grid coverage areas on the battery surface appear as dark stripes, while the battery materials between the metal grids appear as uniform bright areas. Incomplete electrodes or device structures will lead to poor electrical injection and weak luminous intensity, which is shown as dark areas on the picture. By observing and comparing the AC electroluminescence images of different sub-cells, determine whether the shape of the weak light intensity area is the same as that of the electrode or other device structures, especially whether the luminescence image of the top cell is similar to the shape of the device structure, where the area of the same shape Damage to the device process.

The method for judging the defects of the crystal material is: in addition to the damage area related to the electrode, the weak light intensity area that is different from the shape of the electrode or other device structures can usually be observed. These dark areas have different shapes. In each sub-cell The positions of the subcells are not the same, and the weak light intensity areas that appear in each subcell and have similar shapes are crystal defects that run through each subcell, such as threading dislocations, grain boundaries, etc., which may originate from the bottom cell; The weak light intensity regions with different positions and shapes are local crystal defects in each sub-cell, such as impurity defects, heterostructure mismatch dislocations, etc., which are related to the material and structure of each sub-cell.

The observation of the above-mentioned damages and defects can increase the contrast of the luminescent image by increasing the voltage or current, so as to identify small defects in detail.

Since high-power solar panels are mostly used for power supply in daily life, the electroluminescent test of solar battery packs requires high current to drive. However, the DC stabilized power supply with high output power is bulky and expensive. The invention adopts an AC power supply, and utilizes commercial power combined with a voltage regulator to realize the high-current drive requirement of a high-power solar cell array, and avoids disadvantageous factors such as high price and large volume of the DC power supply. It can directly use the mains power, which is convenient and fast, and greatly reduces the cost, and can be widely used in industry. At the same time, the present invention combines electroluminescence and imaging technology, which can conveniently and quickly realize the separate detection of defect information in sub-cells of multi-junction solar cells in just a few seconds, and the test method is fast and convenient (the imaging time is about 1s) , to effectively distinguish the characteristics of multi-junction solar cell arrays, individual solar cells, and individual sub-cells. Therefore, it has broad application prospects in the research and development of multi-junction solar cells and even in large-scale production and preparation.

Description of drawings

FIG. 1 is a schematic diagram of the structure and composition of an embodiment of an alternating current electroluminescence test device for a multi-junction solar cell and each sub-cell according to the present invention.

FIG. 2 is a schematic diagram of the structure and composition of an embodiment of an AC electroluminescence test device for a single multi-junction solar cell and each sub-cell according to the present invention.

3 is a schematic diagram of the structure and composition of an embodiment of an alternating current electroluminescence test device for each sub-cell of a multi-junction solar cell according to the present invention.

Figure 4 is the AC electroluminescence spectrum of a single InGaP/GaAs/Ge triple-junction solar cell. In FIG. 4, the abscissa is the wavelength (nm), and the ordinate is the intensity (a.u.).

Fig. 5 is an AC electroluminescence image of an InGaP sub-cell of an InGaP/GaAs/Ge triple-junction solar cell. In Fig. 5, the scale bar is 1 mm.

Fig. 6 is an AC electroluminescence image of a GaAs sub-cell of an InGaP/GaAs/Ge triple-junction solar cell. In Fig. 6, the scale bar is 1 mm.

Detailed ways

The details of the method of the present invention will be described and demonstrated below in conjunction with the accompanying drawings, taking an InGaP/GaAs/Ge triple-junction solar cell as an example.

Referring to FIGS. 1-4 , the multi-junction solar cell and each sub-cell AC electroluminescence testing device of the present invention is provided with a voltage regulator (ie, an AC drive circuit) 9 , an optical component, a camera tube 13 , a spectrometer 17 and a computer 14 .

The input end of the voltage regulator 9 is connected to the AC mains, and the output end of the voltage regulator 9 is connected to the solar cell array 10; the optical assembly is provided with a filter 11 for splitting the electroluminescent spectrum of the solar cell, and a lens group for changing the range of the test space 12 and reflector 18, to realize the observation of solar cell array 10 and its single solar cell 15 or even fine crystal defects, the filter plate 11 is arranged on the top of the solar cell array 10, the lens group 12 is arranged on the top of the filter plate 11, and the reflector 18 Located on the top of the lens group 12, the camera tube 13 is arranged on the top of the mirror 18, the optical axis of the filter plate 11, the lens group 12, the mirror 18 and the camera tube 13 are the same optical axis, and the reflected light beam of the mirror 18 passes to the spectrometer 17 The receiving port is used to measure the electroluminescence spectrum of the solar cell to be tested, and the data output end of the camera tube 13 is connected to the computer 14 through the data line for analysis and processing.

The wavelength detection range of the spectrometer 17 covers the entire spectral response range of the solar cell, and is used for measuring the electroluminescent spectrum of the solar cell.

After the commercial power (AC) is adjusted to an appropriate voltage value by the voltage regulator 9, the solar cell array 10 and even a single multi-junction solar cell 16 and its sub-cells are driven. The camera tube 13 is connected with the lens group 12 and the filter 11, and placed above the solar cell to perform electroluminescence image measurement. The reflector 18 (above the lens group 12) is used to reflect the light to the receiving port of the spectrometer 17, and the electroluminescence spectrum measurement is performed on the solar cell to be tested (spectral measurement and image measurement are not carried out at the same time). The data is all transmitted to the computer 14 through the data line for analysis and processing.

The mains can use 220V or three-phase 380V voltage. According to the model specifications of the tested solar cell samples, adjust different voltages to change the size of the driving current. For example, the driving current required by a solar cell array is much higher than that of a single solar cell. During the test, the voltage value is gradually increased from small to large. Because the current of the diode increases exponentially with the voltage, the voltage should be fine-tuned after the solar cell starts to emit light, so as to prevent the battery from being burned out due to excessive current.

Different wavelength filters are used to split the electroluminescent spectrum of the solar cell. The lens group can choose camera lens, microscope, etc. Different focal length lens groups are used to change the scope of the test space, so as to realize the observation of the solar cell array and its single solar cell and even the tiny crystal defects.

The wavelength detection range of the spectrometer covers the spectral response range of the entire solar cell, and is used to measure the electroluminescence spectrum of the solar cell.

Camera tubes include infrared light and visible light. According to the measurement object, infrared light or visible light camera tube is selected to realize the electroluminescence image measurement of multi-junction solar cell array, single solar cell and even each sub-cell.

The computer mainly includes data acquisition and equipment control components, and data conversion, processing and analysis software. The equipment control part is mainly used to control the exposure time of the camera tube, the mode of image acquisition, the reading speed of the camera tube, etc.

The AC electroluminescence test of the InGaP/GaAs/Ge triple-junction solar cell and its sub-cells is given below.

Connect the high-power multi-junction solar cell array as shown in Figure 1. After passing through the voltage regulator 9, the commercial power is applied to the solar cell array 10 with an appropriate AC voltage value. Utilizing the forward conduction characteristics of the solar cell, electron-hole pairs are injected into the solar cell array 10, and radiative recombination of the electron-hole pairs occurs. The electroluminescence spectrum of the solar cell is obtained using a spectrometer 17 . Through the filter 11 and the lens group 12, the spectral range and the test range of the battery array are selected. Combining the camera tubes 13 with different detection wavelength bands, a luminescent image with spatial position resolution is obtained. Finally, a computer 14 is used for data processing and analysis. Observe the full-spectrum AC electroluminescence image of the solar cell array, find and compare single cells that do not emit light and have weaker luminous intensity. For a single cell 15 that does not emit light at all, there may be problems in its related assembly, packaging, electrodes, or electrical contacts; and for a single cell 16 with uneven light emission, it may be caused by crystal defects and device process damage. Further testing is required.

Adjust the lens combination to focus the test range on a single multi-junction solar cell 16 (see FIG. 2 ) to be further tested. Using the spectrometer 17 to obtain the electroluminescence spectrum of a single solar cell, the emission wavelengths are 685nm and 886nm, respectively corresponding to the interband emission of InGaP and GaAs sub-cells. An infrared camera tube (400-1800nm) was used to obtain the AC electroluminescence image of the whole battery.

According to the luminescent spectrum of each sub-cell, select the visible light camera tube (400-800nm), then only the information of the top layer InGaP is received and sent to the data processing center of the computer 14, and the electroluminescent image of the InGaP sub-cell as shown in Figure 5 is obtained . A 750nm infrared filter 11 is selected to filter visible signals, and an infrared camera tube is used to obtain electroluminescent images of GaAs and Ge sub-cells as shown in FIG. 6 . Then select the 1700nm infrared filter 11 to filter the luminescence signals of InGaP and GaAs sub-cells, and use an infrared camera tube to obtain the electroluminescence image of Ge sub-cells. Because Ge is an indirect band semiconductor, the electroluminescence signal is weak at room temperature, and it cannot be observed. Effective glowing images. Therefore, Figure 6 is actually an electroluminescence image of a GaAs subcell.

Since the device of a multi-junction solar cell has a certain shape, its process damage is closely related to the shape, which can be judged by the light-emitting image of the cell. As shown in Figure 5, the regular dark area 1 and dark area 2 are related to the shape of the electrode, mainly due to the damage of the preparation process, which leads to poor carrier injection and weak electroluminescence intensity in the corresponding area.

For the defects of the material itself, its shape is usually different from that of the electrodes or other device structures, resulting in different shapes of dark areas of light emission, and different positions in each sub-cell. The dark area 3 marked in Figure 5 and Figure 6 appears at the same longitudinal position of each sub-cell and has a similar shape, which is a crystal defect penetrating through each sub-cell, such as a threading dislocation. The dark areas marked 4, 5, and 6 in Figure 5 appear only in the InGaP sub-cell image, and they are InGaP material defects; the dark areas marked 7 and 8 in Figure 6 are GaAs material defects.

Therefore, the present invention can quickly and clearly display information such as material defects and process damages of multi-junction solar cells and their sub-cells, and provide scientific basis for the design, growth, and device technology of high-efficiency multi-junction solar cells.

Claims (10)

1. A multi-junction solar cell and each sub-cell AC electroluminescence testing device, characterized in that it is provided with an AC drive circuit, an optical assembly, a camera tube, a spectrometer and a computer; The input end of the AC drive circuit is connected to the AC mains, and the output end of the AC drive circuit is connected to the solar cell array; the optical component is provided with a filter for splitting the electroluminescent spectrum of the solar cell, a lens group and a mirror for changing the range of the test space, In order to realize the observation of the solar cell array and its single solar cells and fine crystal defects, the filter is set above the solar cell array, the lens group is set above the filter, the reflector is set above the lens group, and the camera tube is set above the reflector , the optical axis of the filter, lens group, mirror and camera tube is the same optical axis, the reflected light beam of the mirror is transmitted to the receiving port of the spectrometer, and the electroluminescent spectrum measurement is performed on the solar cell to be tested, and the data output of the camera tube is The terminal is connected to the computer through the data line for analysis and processing. 2 . The multi-junction solar cell and each sub-cell AC electroluminescence testing device according to claim 1 , wherein the AC drive circuit adopts a voltage regulator. 3 . 3. The multi-junction solar cell and each sub-cell AC electroluminescence testing device according to claim 1, characterized in that said lens group adopts a camera lens or a microscope. 4. The multi-junction solar cell and each sub-cell AC electroluminescence testing device as claimed in claim 1, wherein the wavelength detection range of the spectrometer covers the spectral response range of the whole solar cell, and is used for measuring the electroluminescent spectrum of the solar cell. 5 . The multi-junction solar cell and each sub-cell AC electroluminescence testing device according to claim 1 , wherein the imaging tube is an infrared imaging tube or a visible imaging tube. 6 . 6. multi-junction solar cell and each sub-cell alternating current electroluminescence testing method, it is characterized in that adopting multi-junction solar cell and each sub-cell alternating current electroluminescence testing device as claimed in claim 1, comprises the following steps: 1) Place the multi-junction solar cell on the sample stage, and apply the mains power to the multi-junction solar cell after passing through the AC drive circuit; 2) Using a spectrometer to measure the electroluminescence spectrum of the multi-junction solar cell to obtain the luminescence band of each sub-junction; 3) According to the multi-junction solar cell electroluminescent spectrum wavelength range known in step 2), select the camera tube of the corresponding wave band, and select the spectral range of the test through the filter; 4) Through different lens combinations, select the test range of the multi-junction solar cell, and adjust the focus to obtain a clear spatially resolved AC electroluminescence image; 5) Use computer for data processing and analysis to obtain device process damage and crystal material defect information of the multi-junction solar cell and its sub-cells, and complete the AC electroluminescence test of the multi-junction solar cell and its sub-cells. 7. multi-junction solar cell as claimed in claim 6 and each sub-battery AC electroluminescence test method, it is characterized in that in step 2) in, described measurement multi-junction solar cell electroluminescence spectrum, if luminescence wavelength is in infrared light For the sub-battery in the range of visible light, the infrared filter is used to split the light first, and then the lens group is used to focus the image on the infrared light imaging tube that can respond to this band; if the emission spectrum of the sub-cell is in the visible light range, the visible light imaging tube is directly selected. 8. The multi-junction solar cell and each sub-cell AC electroluminescence test method according to claim 6, characterized in that in step 4), the AC electroluminescence image uses color or gray scale to represent the electroluminescent light intensity. 9. multijunction solar cell as claimed in claim 6 and each sub-battery AC electroluminescence test method, it is characterized in that in step 5) in, described adopting computer to carry out data processing and analysis, to solar cell array AC electroluminescence all Spectrum image analysis is to find and compare single cells that do not emit light and have weaker luminous intensity. Among them, the single cells that do not emit light at all are those without electric injection, which are caused by problems in assembly, packaging, electrodes or electrical contact processes. , the single cells with uneven light emission are caused by crystal defects and device process damage, which need further inspection; For the full-spectrum image analysis of AC electroluminescence of a single solar cell, the battery with strong luminous intensity and uniform spatial distribution is of good quality; the battery with weak luminous intensity and uneven spatial distribution has local material defects, sub-cell defects, or process damage. The battery needs to be further analyzed in combination with the AC electroluminescence images of each sub-battery; Process damage and material defect analysis of AC electroluminescence images of each sub-cell of a multi-junction solar cell. 10. multi-junction solar cell as claimed in claim 6 and each sub-cell alternating current electroluminescence test method, it is characterized in that in step 5), the judging method of described device process damage is: good solar cell electroluminescence image , the electrode and metal grid coverage areas on the battery surface appear as dark stripes, while the battery material between the metal grids appears as uniform bright areas; incomplete electrodes or device structures will lead to poor electrical injection and weak luminous intensity. It is shown as a dark area on the picture; by observing and comparing the AC electroluminescence images of different sub-cells, determine whether the shape of the weak light intensity area is the same as that of the electrode or other device structures, and the area with the same shape is the device process damage; The method for judging the defects of the crystal material is: in addition to the electrode-related damage area, weak light intensity areas that are different from the shape of the electrode or other device structures can also be observed. These dark areas have different shapes. The positions are not the same, and the weak light intensity regions with similar positions and shapes that appear in each sub-cell are crystal defects that run through each sub-cell, and the crystal defects include threading dislocations, grain boundaries, and weak light intensity regions with different positions and shapes. The light intensity region is the local crystal defect in each sub-cell, and the local crystal defect in each sub-cell includes impurity defect and heterostructure mismatch dislocation.

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