Method for detecting sub-cell current and matching degree of multi-junction stacked photovoltaic cells

Abstract

The present invention discloses a method for detecting the current and matching degree of a sub-cell of a multi-junction stacked photovoltaic cell. The detection method comprises: obtaining the I-V curve of the multi-junction stacked photovoltaic cell by testing the I-V characteristics of the multi-junction stacked photovoltaic cell; obtaining the approximate value of the short-circuit current of each junction sub-cell in the multi-junction stacked photovoltaic cell by measuring the current corresponding to each current step in the I-V curve, and then obtaining the matching degree of the current of each junction sub-cell in the multi-junction stacked photovoltaic cell by calculating the discrete coefficient of the current value combination corresponding to all steps appearing in the I-V curve. The detection method provided by the present invention obtains the current matching degree of the sub-cell of the multi-junction stacked photovoltaic cell by calculating the discrete coefficient of the current value combination corresponding to all steps appearing in the I-V curve. The inspection process is fast and simple, and does not require a standard light source spectrum, does not require the addition of bias light, and does not require complex and time-consuming processes such as integration according to the standard light source spectrum.

Description

Technical Field

[0001] The present invention particularly relates to a method for detecting sub-cell current and matching degree of a multi-junction stacked photovoltaic cell, and belongs to the technical field of semiconductor testing. Background Art

[0002] The use of multi-junction stacking is an effective way to improve the conversion efficiency and voltage of solar cells and laser photovoltaic cells. The outstanding performance of multi-junction stacked photovoltaic cells in conversion efficiency has attracted much attention from researchers. The current of a multi-junction cell is mainly determined by the smallest sub-cell in each junction sub-cell current. If you want to obtain a cell with high conversion efficiency, you must ensure that the current of each junction sub-cell is equal, that is, matched. Under the above current matching requirements, the thickness of the absorption layer of each junction sub-cell is determined by the light flux of the corresponding band absorbed by the material. However, it is difficult to ensure that the current of each junction sub-cell is accurately matched in the manufactured photovoltaic cell structure. Therefore, checking whether the sub-cells of the manufactured multi-junction stacked photovoltaic cell are current matched has become a very important part of the test and analysis of multi-junction stacked photovoltaic cells.

[0003] In the prior art, the current matching of the sub-cells of a photovoltaic cell is mainly determined by measuring the quantum efficiency of the cell at different wavelengths, that is, the spectral response; however, for multi-junction solar cells, a bias laser needs to be added to make the current of the non-measured sub-cell in an oversaturated state to eliminate the influence of the non-measured sub-cell on the measured sub-cell. If you want to obtain the current of each sub-cell of a multi-junction solar cell, you need to add different bias lasers to test the spectral response in turn according to the number of sub-cells, and then calculate the short-circuit current of each sub-cell in combination with the standard spectral integral. The process of testing the current matching degree of the sub-cells of a multi-junction solar cell is relatively complicated and time-consuming. For multi-junction laser photovoltaic cells, the wavelength at the maximum value of the spectral response is compared with the deviation of the designed wavelength to determine whether the cell has reached the highest efficiency at the target wavelength, but it is impossible to quantitatively determine the short-circuit current of each sub-cell in a multi-junction laser photovoltaic cell at a certain wavelength. Since each sub-cell in a multi-junction laser photovoltaic cell generally uses the same absorption material, it is impossible to use the method of adding bias light to measure the spectral response to obtain information on the current matching degree between sub-cells, and there is currently no better method to test the current matching degree of sub-cells of a multi-junction laser photovoltaic cell at a certain wavelength. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for detecting the current and matching degree of sub-cells of a multi-junction stacked photovoltaic cell, so as to overcome the deficiencies in the prior art.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes:

[0006] The embodiment of the present invention provides a method for detecting the current and matching degree of sub-cells of a multi-junction stacked photovoltaic cell, which comprises:

[0007] By testing the IV characteristics of the multi-junction stacked photovoltaic cell, an IV curve of the multi-junction stacked photovoltaic cell is obtained;

[0008] By measuring the current corresponding to each current step in the IV curve, the approximate value of the short-circuit current of each junction sub-cell in the multi-junction stacked photovoltaic cell is obtained, and then by calculating the discrete coefficient of this group of currents, the matching degree of the current of each junction sub-cell in the multi-junction stacked photovoltaic cell is obtained.

[0009] Compared with the prior art, the advantages of the present invention include: the detection method provided in the embodiment of the present invention obtains the current matching degree of the sub-cells of the multi-junction stacked photovoltaic cell by analyzing the IV curve of the multi-junction stacked photovoltaic cell obtained by scanning from reverse bias to forward bias voltage, and by calculating the discrete coefficient of the current value combination corresponding to all current steps appearing in the IV curve; and the detection method provided in the embodiment of the present invention has a fast and simple inspection process, and does not require complex and time-consuming processes such as standard light source spectrum, bias light, and integration according to the standard light source spectrum. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a structural schematic diagram of a detection system for sub-cell current and matching degree of a multi-junction stacked photovoltaic cell provided in a typical implementation case of the present invention;

[0011] Figure 2 This is an IV curve diagram of a six-junction 1550nm InGaAs laser photovoltaic cell in Example 1 of the present invention. DETAILED DESCRIPTION

[0012] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.

[0013] The present invention provides a method for detecting the current and matching degree of sub-cells of a multi-junction stacked photovoltaic cell. By measuring the IV characteristics of the multi-junction stacked photovoltaic cell, the approximate value of the photocurrent of each junction sub-cell (the short-circuit current is the current when the voltage is 0V. Ideally, it is generally believed that the short-circuit current of the sub-cell is equal to the photocurrent of the sub-cell) can be obtained. For a multi-junction laser photovoltaic cell, since the band gap of each junction sub-cell material is consistent, the reverse breakdown voltage of each junction sub-cell is determined by the doping concentration. If the doping concentration on the lightly doped side of the PN junction of each junction sub-cell is different, the short-circuit current of the PN junction sub-cell with a lower doping concentration corresponds to the current of the wider current step in the curve, and the short-circuit current of the PN junction sub-cell with a higher doping concentration corresponds to the current of the narrower current step in the curve. If the PN junctions of each junction sub-cell are doped the same, the sub-cell corresponding to each current step cannot be clearly identified, but a group of sub-cell short-circuit current values ​​can be quantitatively obtained. Regardless of whether it is a multi-junction solar cell or a multi-junction laser photovoltaic cell, the present invention can determine the matching degree of the sub-cell current through the current value of each junction sub-cell, without the need to analyze the matching degree of the current of each junction sub-cell through indirect means such as external quantum efficiency.

[0014] The invention discloses a method for detecting the current and matching degree of a sub-cell of a multi-junction stacked photovoltaic cell. The detection tools adopted by the detection method include a high-precision source meter, a light source with stable power (a solar simulator for a multi-junction solar cell and a power-adjustable laser for a laser photovoltaic cell), and a photovoltaic cell IV test system. The detection method includes connecting the multi-junction stacked photovoltaic cell with the high-precision source meter by a four-wire method, irradiating the multi-junction stacked photovoltaic cell with a light source with stable power, analyzing an IV curve obtained by scanning from a reverse bias to a forward bias voltage, measuring the discrete coefficients of the current value combinations corresponding to all current steps appearing in the IV curve, and obtaining the current matching degree of each junction sub-cell of the multi-junction stacked photovoltaic cell.

[0015] The embodiment of the present invention provides a method for detecting the current and matching degree of sub-cells of a multi-junction stacked photovoltaic cell, which comprises:

[0016] By testing the IV characteristics of the multi-junction stacked photovoltaic cell, an IV curve of the multi-junction stacked photovoltaic cell is obtained;

[0017] By measuring the current corresponding to each current step in the IV curve, the approximate value of the short-circuit current of each junction sub-cell in the multi-junction stacked photovoltaic cell is obtained, and then by calculating the discrete coefficient of this group of currents, the matching degree of the current of each junction sub-cell in the multi-junction stacked photovoltaic cell is obtained.

[0018] Furthermore, the detection method includes: irradiating the multi-junction stacked photovoltaic cell with a light source having a stable output power, and scanning the multi-junction stacked photovoltaic cell within a set voltage scanning range to obtain the IV curve.

[0019] Furthermore, the setting voltage scanning range is from reverse bias to forward bias.

[0020] Furthermore, the set voltage scanning range is from reverse breakdown voltage to forward open circuit voltage.

[0021] Furthermore, the detection method specifically includes:

[0022] Connect the positive and negative electrodes of the multi-junction stacked photovoltaic cell to a high-precision source meter using the four-wire method;

[0023] Placing the multi-junction stacked photovoltaic cell within the light spot coverage of the light source;

[0024] The light source is set and turned on, and the multi-junction stacked photovoltaic cell is scanned from a reverse bias voltage to a forward bias voltage to obtain an IV curve.

[0025] Furthermore, the multi-junction stacked photovoltaic cell includes an N-junction laser photovoltaic cell, an N-junction solar cell or an N-junction thermal photovoltaic cell, where N≥2.

[0026] Furthermore, the multi-junction stacked photovoltaic cell is a laser photovoltaic cell, and the light source is a laser with stable output power.

[0027] Furthermore, the multi-junction stacked photovoltaic cell is a multi-junction solar cell, and the light source is a steady-state solar simulator.

[0028] Furthermore, the detection method specifically includes:

[0029] Analyze each current step in the IV curve to obtain the current values ​​I1, I2, I3, ... I corresponding to each current step. N , where N is the number of junctions of the multi-junction stacked photovoltaic cell, and the current value corresponding to each current step is approximately equal to the short-circuit current value of each junction sub-cell;

[0030] The dispersion coefficient of the current is calculated using the following formula (1):

[0031]

[0032] Thus, the current matching degree of each junction sub-battery in the multi-junction stacked photovoltaic cell is obtained, wherein the smaller the M value is, the better the current matching degree of each junction sub-battery is, and vice versa.

[0033] Furthermore, the wavelength of the incident light provided by the light source is the same as or different from the design target wavelength of the multi-junction stacked photovoltaic cell.

[0034] The technical solution, its implementation process and principle will be further explained below in conjunction with the accompanying drawings.

[0035] according to Figure 1 The detection system for the current matching degree of sub-cells of the assembled multi-junction stacked photovoltaic cell shown in the figure comprises: a light source 3 / 8, a high-precision digital source meter 5 and a computer 7; wherein the light source 3 / 8 is at least used to provide light for irradiating the multi-junction stacked photovoltaic cell 1, the high-precision digital source meter 5 is connected to the multi-junction stacked photovoltaic cell 1 to be tested, and is at least used to measure and collect IV data of the multi-junction stacked photovoltaic cell to be tested when it is irradiated by the light source 3 / 8; the computer 7 is respectively connected to the light source 3 / 8 and the high-precision digital source meter 5, and is at least used to draw an IV curve based on the IV data.

[0036] Specifically, the high-precision digital source meter 5 is the electronic load of the multi-junction stacked photovoltaic cell. The high-precision digital source meter 5 is connected to the positive and negative electrodes of the multi-junction stacked photovoltaic cell 1 to be tested by a four-wire connection method. The four-wire connection method is used to eliminate the voltage test error caused by the lead series resistance, and the voltage scanning range of the high-precision digital source meter 5 meets the voltage scanning range required for the test; the computer 7 is used to control the light source and the digital source meter, mainly including sending voltage scanning instructions to the high-precision digital source meter, issuing opening and closing instructions to the light source, and collecting IV data measured by the high-precision digital source meter, and drawing an IV curve based on the IV data.

[0037] Specifically, the multi-junction stacked photovoltaic cell under test can be a multi-junction laser photovoltaic cell or a multi-junction solar cell. When the multi-junction stacked photovoltaic cell 1 under test is a multi-junction laser photovoltaic cell, the light source is a power-adjustable laser 3. The power of the power-adjustable laser 3 is stable, and the central wavelength is the target application wavelength designed for the multi-junction laser photovoltaic cell. When testing the laser photovoltaic cell, the optical fiber 4 light head should not be too close to the surface of the multi-junction stacked photovoltaic cell to avoid tunnel junction current limiting. When the multi-junction stacked photovoltaic cell 1 under test is a multi-junction solar cell, a steady-state solar simulator 8 can be used as the light source.

[0038] Specifically, the computer 7 and the high-precision digital source meter 5, the computer 7 and the light source 3 are connected via a serial communication data line 6, and the high-precision digital source meter 5 is connected to the positive and negative electrodes of the multi-junction laminated photovoltaic cell 1 via a wire 2.

[0039] Specifically, a method for detecting the current and matching degree of a sub-cell of a multi-junction stacked photovoltaic cell mainly includes the following steps:

[0040] 1) Provide Figure 1 The detection system of sub-cell current and matching degree of multi-junction stacked photovoltaic cells shown in FIG.

[0041] 2) The multi-junction laminated photovoltaic cell is attached to the heat sink to ensure that the multi-junction laminated photovoltaic cell has good heat dissipation conditions, and the irradiation time of the incident light during the test should be short enough to avoid a significant increase in the temperature of the multi-junction laminated photovoltaic cell during the test;

[0042] 3) Connect the computer to the high-precision digital source meter via a serial line;

[0043] 4) Connect the positive and negative electrodes of the multi-junction stacked photovoltaic cell to a high-precision source meter using the four-wire method;

[0044] 5) Placing the multi-junction stacked photovoltaic cell within the light spot coverage of the light source;

[0045] 6) Turn on the laser or solar simulator with the set power, so that the multi-junction stacked photovoltaic cell is exposed to stable light, and perform voltage scanning on the multi-junction stacked photovoltaic cell at the same time, and obtain IV data of the multi-junction stacked photovoltaic cell after the voltage scanning is completed. The starting point of the voltage scanning in the multi-junction stacked photovoltaic cell IV test system is set to the reverse breakdown voltage of the photovoltaic cell, and the end point of the voltage scanning is set to the open circuit voltage of the multi-junction stacked photovoltaic cell;

[0046] 7) Analyze each current step in the IV curve to obtain the current value I1, I2, I3 ... I corresponding to each current step N , where N is the number of junctions of the multi-junction stacked photovoltaic cell, and the current value corresponding to each current step is approximately equal to the short-circuit current value of each junction sub-cell;

[0047] 8) The discrete coefficient of the current is calculated using the following formula (1):

[0048]

[0049] Thus, the current matching degree of each junction sub-battery in the multi-junction stacked photovoltaic cell is obtained, wherein the smaller the M value is, the better the current matching degree of each junction sub-battery is, and vice versa.

[0050] Specifically, for multi-junction laser photovoltaic cells, the corresponding relationship between the short-circuit current of each junction sub-cell and each step in the IV curve is determined by the breakdown voltage of the sub-cell, that is, the doping concentration on the low-doped side of the PN junction; if the doping concentration on the low-doped side that affects the reverse breakdown voltage of the sub-cell PN junction is different, then the current value corresponding to the wider step corresponds to the short-circuit current of the sub-cell with the low-doping concentration, and the current value corresponding to the narrower step corresponds to the short-circuit current of the sub-cell with the higher doping concentration.

[0051] Specifically, the wavelength of the incident light provided by the light source is the same as or different from the designed target wavelength of the multi-junction stacked photovoltaic cell, that is, for a multi-junction laser photovoltaic cell, the wavelength of the incident laser can be a wavelength other than the designed target wavelength. At this time, the detection method obtains the current matching degree between each sub-cell at the wavelength of the incident laser.

[0052] It should be noted that the detection method provided in the embodiment of the present invention is mainly aimed at the matching degree at the target wavelength of the multi-junction stacked photovoltaic cell, but the detection method provided in the embodiment of the present invention is also applicable to a wavelength other than the target wavelength of the multi-junction stacked photovoltaic cell (i.e., non-target wavelength). This is because in the actual production process of the battery device, the material parameters used are different from the design parameters, resulting in the optimal response wavelength of the battery device finally prepared deviating from the target wavelength. At this time, at the target wavelength, the sub-cell current of the multi-junction stacked photovoltaic cell is not matched.

[0053] Specifically, taking laser photovoltaic cells as an example, an ideal laser photovoltaic cell only has the best response to a laser of a single wavelength (target wavelength). For example, under the irradiation of an 808nm laser of the same power, the short-circuit current of a multi-junction laser photovoltaic cell is the largest, and under the irradiation of 830nm, the short-circuit current becomes smaller. However, the laser photovoltaic cells actually manufactured do not necessarily have the best response at 808nm.

[0054] Specifically, in the specific detection process, in order to avoid interference from ambient light, the detection process should be carried out in a dark room, and the test environment temperature parameters should be recorded at the same time, because the matching degree of each sub-cell current is related to the temperature, and the temperature will affect the band gap width of the material, thereby affecting the material's absorption coefficient of light of a specific wavelength; specifically, the sub-cell current and matching degree of a multi-junction stacked photovoltaic cell are related to the material's absorption coefficient of light, and the absorption coefficient is related to the photon energy. Therefore, under the irradiation of light of different wavelengths, the absorption coefficient of the material is different; and thus the matching degree of the sub-cell current is also different at different wavelengths; the above situations can all obtain the sub-cell current and its matching degree of the multi-junction stacked photovoltaic cell through the detection method provided in the embodiment of the present invention.

[0055] Example 1

[0056] Taking a six-junction 1550nm InGaAs laser photovoltaic cell chip as an example, the detection method of the sub-cell current and its matching degree of a multi-junction stacked photovoltaic cell is described. The detection method of the sub-cell current and matching degree of an InGaAs laser photovoltaic cell includes the following steps:

[0057] 1) Roughly measure the forward IV characteristics of the photovoltaic cell, select an InGaAs laser photovoltaic cell with a small series resistance and no serious leakage, use conductive silver paste to paste the InGaAs laser photovoltaic cell (sheet) 1 on a ceramic copper-clad sheet that can dissipate heat well, and use a wire bonding machine to bond the gold wire;

[0058] 2) Connecting the InGaAs laser photovoltaic cell to the high-precision digital source meter 5 by a four-wire method, the positive electrode of the InGaAs laser photovoltaic cell 1 is connected to the positive wiring port of the high-precision digital source meter, and the negative electrode is connected to the negative wiring port of the high-precision digital source meter 5, and the working mode of the high-precision digital source meter 5 is set to four-wire;

[0059] 3) The head of the output optical fiber 4 of the laser 3 is fixed above the InGaAs laser photovoltaic cell 1 with a bracket. In order to avoid the current limiting phenomenon of the InGaAs laser photovoltaic cell due to excessive local light intensity density resulting in excessive local photocurrent density, the head of the optical fiber 4 should maintain an appropriate distance from the surface of the InGaAs laser photovoltaic cell (the height of 3 cm is used in this embodiment);

[0060] 4) Open the multi-junction stacked photovoltaic cell fast IV test program on the computer 7. Since the reverse breakdown voltage of the single-junction InGaAs PN junction with the same doping concentration as the PN junction of each sub-cell in the multi-junction cell obtained during the detection process is about -1.5V, the reverse breakdown voltage of the six-junction InGaAs laser photovoltaic cell is about -9V, and the open circuit voltage is close to 3V, the starting point of the voltage scan is set to -9V and the end point is set to 3V;

[0061] 5) Start voltage scanning on the InGaAs laser photovoltaic cell and get the following results: Figure 2 The IV curve shown is Figure 2 It can be seen that the IV curve has several current steps in the scanned voltage range where the current remains stable when the voltage changes. These steps approximately correspond to the photocurrents of sub-cells with different junctions. Read the ordinate values ​​corresponding to each step, i.e., the current values ​​"I1", "I2", "I3", "I4", "I5" and "I6", and calculate the discrete coefficients C of multiple current values ​​corresponding to all steps. v (C v =σ / μ, σ is the standard deviation, μ is the mean), the dispersion coefficient is used to determine the matching degree of each sub-cell in the multi-junction stacked photovoltaic cell, and the dispersion coefficient C v It represents the matching degree of each sub-battery current. The smaller the dispersion coefficient, the higher the sub-battery current matching degree. Conversely, the lower the sub-battery current matching degree.

[0062] Among them, C v“Coefficient of variation” is the abbreviation of dispersion coefficient. The aforementioned M (Match) is the current matching degree. In the present invention, the dispersion coefficient of a set of step current values ​​is defined as the sub-cell current matching degree of the multi-junction laser photovoltaic cell. Therefore, M = C v .

[0063] The detection method provided by the present invention, combined with the actual structure of a multi-junction stacked photovoltaic cell, compares the doping concentration on the lightly doped side of the PN junction of each sub-cell with the width of each step in the IV curve, and obtains the current value corresponding to the step corresponding to each junction sub-cell according to the principle that the higher the doping concentration, the smaller the step width.

[0064] It should be noted that the above embodiments are only preferred application examples of the present invention and do not constitute any limitation to the protection scope of the present invention. The method of detecting the current matching degree of sub-cells using IV characteristics proposed in the present invention can be applied not only to multi-junction laser photovoltaic cells, but also to multi-junction solar cells.

[0065] The detection method provided in the embodiment of the present invention analyzes the IV curve of the multi-junction stacked photovoltaic cell obtained by scanning the voltage from reverse bias to forward bias, and calculates the discrete coefficient of the current value combination corresponding to all current steps appearing in the IV curve to obtain the current matching degree of the sub-cells of the multi-junction stacked photovoltaic cell.

[0066] The detection method provided by the embodiment of the present invention has a fast and simple inspection process, and does not require a standard light source spectrum, does not require the addition of bias light, and does not require complex and time-consuming processes such as integration based on the standard light source spectrum; the detection method provided by the embodiment of the present invention is suitable for extracting the short-circuit current value of each sub-cell of a multi-junction stacked photovoltaic cell under the irradiation of a stable power light source and for quantitatively evaluating the current matching degree of the sub-cells of the multi-junction stacked photovoltaic cell.

[0067] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting the current and matching degree of sub-cells of a multi-junction stacked photovoltaic cell, characterized in that include: Irradiating the multi-junction stacked photovoltaic cell with a light source having a stable output power, and scanning the multi-junction stacked photovoltaic cell within a set voltage scanning range, thereby obtaining an IV curve of the multi-junction stacked photovoltaic cell, wherein the set voltage scanning range is from a reverse breakdown voltage to a forward open circuit voltage; Analyze each current step in the IV curve to obtain the current values ​​I1, I2, I3, ... I corresponding to each current step. N , where N is the number of junctions of the multi-junction stacked photovoltaic cell, and the current value corresponding to each current step is approximately equal to the short-circuit current value of each junction sub-cell; The dispersion coefficient of the current is calculated using the following formula (1): Thus, the current matching degree of each junction sub-battery in the multi-junction stacked photovoltaic cell is obtained, wherein the smaller the M value is, the better the current matching degree of each junction sub-battery is, and vice versa, the worse the current matching degree of each junction sub-battery is.

2. The detection method according to claim 1, characterized in that Specifically include: Connect the positive and negative electrodes of the multi-junction stacked photovoltaic cell to a high-precision source meter using the four-wire method; Placing the multi-junction stacked photovoltaic cell within the light spot coverage of the light source; The light source is set and turned on, and the multi-junction stacked photovoltaic cell is scanned from a reverse bias voltage to a forward bias voltage to obtain an IV curve.

3. The detection method according to claim 1, characterized in that: The multi-junction stacked photovoltaic cell includes an N-junction laser photovoltaic cell, an N-junction solar cell or an N-junction thermal photovoltaic cell, wherein N≥2.

4. The detection method according to claim 1, characterized in that: The multi-junction stacked photovoltaic cell is a laser photovoltaic cell, and the light source is a laser with stable output power.

5. The detection method according to claim 1, characterized in that: The multi-junction stacked photovoltaic cell is a multi-junction solar cell, and the light source is a steady-state solar simulator.

6. The detection method according to claim 1, characterized in that: The wavelength of the incident light provided by the light source is the same as or different from the design target wavelength of the multi-junction stacked photovoltaic cell.

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