CN102788944A - Quick test method of solar battery electric performance and capable of removing internal capacitor effect - Google Patents

Abstract

The present invention proposes a quick test method for the electrical performance of solar cells that is not affected by the internal capacitance, which is characterized in that the voltage scan is performed in a single direction to measure the current at each voltage, and then the voltage scan in the opposite direction is performed to obtain the corresponding voltage again. Current, take the arithmetic mean of the current values under the same voltage in two scans as the final current measurement value under the voltage, and make an IV curve. The beneficial effect of the invention is that the test result is not affected by the internal capacitance of the solar cell, so the IV curve of the solar cell can be quickly and accurately measured, and then various electrical performance parameters of the solar cell can be obtained.

Description

A rapid test method for the electrical performance of solar cells that eliminates the influence of internal capacitance

technical field

The invention belongs to the field of solar cell production and research and development, in particular to a method for testing the electrical properties of a solar cell.

Background technique

The testing and characterization of solar cells play an important role in the development and production of solar cells. The measurement of electrical properties is an important aspect of solar cell testing. The IV curve can reflect many electrical performance parameters of solar cells, among which the maximum output efficiency P _m , voltage V _m and current I _m at maximum output power, open circuit voltage V _oc and short circuit current I _SC , fill factor FF, series resistance R _s and parallel resistance R _sh and other important parameters of solar cells can be obtained from the IV curve obtained directly or through simple processing.

Accurate and fast measurement of the I-V curve is the key to obtaining various important parameters of the solar cell. A common method for I-V curve testing is the balanced bridge compensation circuit method, that is, adding a scanning voltage to the battery to be tested and measuring the current passing through the battery. Make an I-V curve. Figure 1 is a schematic diagram of the solar cell I-V curve test. The dotted box in the figure is the equivalent circuit of the solar cell. This circuit is composed of diode D reflecting the characteristics of the P-N junction and constant current source Iph reflecting the photocurrent effect. The internal capacitance effect of can be equivalent to two capacitors Cs and Csh in the circuit. Figure 2 is a schematic diagram of the scanning voltage. After the voltage is changed, the current is measured after a certain delay time Td, and the elapsed time of the measurement action is Tt.

A quick test method for the electrical performance of solar cells that can eliminate the influence of internal capacitance. It is characterized in that two voltage scans in forward and reverse directions are performed under the same condition of keeping the scan speed and the voltage setting value of each measurement point the same.

For crystalline silicon solar cells, the internal capacitance effect is very small and can be ignored, while for some new types of batteries, such as thin-film solar cells such as copper indium gallium selenide (CIGS) and dye-sensitized solar cells (DSSC), the internal capacitance is relatively large , has a significant impact on the I-V curve, which shows that the results obtained by different scanning speeds and scanning directions have large errors, especially near the optimal power point, and the error is the largest, as shown in Figure 3. This is because when the scanning voltage changes, due to the existence of capacitance, the change of current will lag behind the change of voltage. Therefore, in order to obtain close to real measurement data, the scanning speed should be slowed down, that is, the delay time Td in Figure 2 should be increased. When the capacitance effect is strong, a larger Td will seriously affect the speed of I-V curve measurement, which is not conducive to Fast measurement in industry. In order to quickly and accurately measure the I-V curve of solar cells, we have innovated the measurement method on the basis of traditional I-V test hardware.

Contents of the invention

The purpose of the present invention is to provide a method for quickly measuring the electrical performance of a solar cell that can eliminate the influence of the internal capacitance of the solar cell. the

The technical solution of the present invention: a rapid test method for the electrical performance of solar cells that eliminates the influence of internal capacitance. The present invention mainly improves the measurement method, and performs voltage scanning in a single direction (scanning from large to small or from small to large) to measure the The current under each voltage is then scanned in the opposite direction (the voltage is scanned from small to large or from large to small), and the current under the corresponding voltage is obtained again, and the arithmetic mean of the current value under the same voltage of the two scans is taken As the final current measurement at this voltage, an I-V curve is made.

Based on this I-V curve, the key electrical performance parameters of the solar cell are calculated. In this way, although the I-V curve is measured twice, the final result is not affected by the internal capacitance of the solar cell to be tested, and the Td of each measurement can be small or without delay time, so the measurement speed is greatly improved.

From the monotonicity of the I-V curve, we can know that during the voltage scanning process of a certain measurement, the capacitor is in a single state of charging or discharging. If the voltage is scanned from high to low, the capacitor should be in a discharging state during the entire measurement process. , otherwise it is in charging state. Assuming that the battery performance does not change during the measurement, the equivalent circuit remains unchanged, the values of each parameter remain unchanged, and the changing law of the current over time during the charge and discharge process should also remain unchanged. Suppose the voltage changes from V1 to V2 when the capacitor is charged, and from V2 to V1 when it is discharged, then the current in the two processes is

（1）

(1)

（2）

(2)

visible

      （3）

(3)

Among them, _rc is the resistance value of the resistor connected in series with the capacitor, C is the capacitance of the capacitor, t is the time from the voltage change to the current measurement, and I ₀ is the stable current, that is, the current without the influence of the capacitance. Since the average value of the two is the stable current, the IV curve obtained by scanning the two directions to obtain the corresponding current average value during the measurement is the IV curve when the battery is in stable operation. Figure 4 shows the change of current when the voltage changes. When the voltage just changes, the current deviates from the balance value greatly, and slowly reaches the balance value after a period of time. However, the direction of the current deviation from the balance value in different scanning directions is different. The two directions The deviation value is exactly zero, which is consistent with the above formula.

The effect of the present invention is verified by using a dye-sensitized solar cell with a strong internal capacitance effect as the test object. The hardware part of the measurement system is shown in Figure 5, and the specific steps can be found in the "Specific Embodiments" section.

Figure 5 and Figure 6 show the I-V curve (Figure 5) and efficiency change curve (Figure 6) of the dye-sensitized solar cell measured by the method of the present invention. It can be seen from Figure 5 that the I-V curves measured by the same battery at the same time and the delay time Td are 1ms, 5ms, 50ms, and 1s are basically coincident, while the I-V curves measured by the traditional method in Figure 3 vary with Td. The different splits are relatively large, especially near the maximum power point (inside the small frame diagram in Figure 3).

Figure 6 is a comparison of the conversion efficiency of the dye-sensitized solar cell measured by the traditional method and the method of the present invention. The "Down" curve and the "Up" curve are the relationship between the conversion efficiency and the delay time Td measured by the unidirectional scanning method, and "Average" is With the relation of the conversion efficiency that the method of the present invention records and Td, the conversion efficiency that the method of the present invention records as seen has no obvious relation with Td, and the different scanning directions of the unidirectional scanning method and the same scanning direction draw under the different Td The conversion efficiencies are quite different. From the characteristics of the influence of the charge and discharge of the capacitor on the current, it can be seen that the longer the delay time Td, the closer the measured curve is to the real curve of the solar cell, and the closer the conversion efficiency is to the real efficiency.

The beneficial effects of the present invention are: as can be seen from the right side of Fig. 6, the efficiency measured when Td is 1ms with the method of the present invention is closer to the true value than the efficiency measured when Td is 1s by the traditional unidirectional scanning method, which fully proves It has been found that the method of the present invention can indeed measure the I-V curve and conversion efficiency of the solar cell quickly and accurately, and it is believed that this can provide a fast and accurate method for the detection on the solar cell module production line.

Description of drawings

Figure 1 The equivalent circuit inside the solar cell and the equivalent circuit for I-V curve measurement;

Figure 2 Schematic diagram of the scanning voltage when measuring the I-V curve of a solar cell;

Fig. 3 The influence of scanning direction and delay time Td on the I-V curve of large-capacitance solar cells;

Fig. 4 The change of current with time under different voltage scanning directions;

Fig. 5 is the result of testing the large internal capacitance solar cell of the present invention, and the measured I-V curve;

FIG. 6 shows the photoelectric conversion efficiency of the dye-sensitized solar cell measured in this embodiment.

Detailed ways

When the present invention is implemented, the hardware consists of the following parts: an analog solar light source, which provides solar energy for a solar cell with a mass of 1.5 atmospheres; Output the current through the solar cell; control the computer to control the measurement method and measurement parameters and read the measurement data and process and save the data.

The measurement method of the present invention is mainly realized by a computer control program. The program is written so that the source meter scans the voltage of the solar cell to be tested and then performs the same scan along the opposite direction. After measuring the corresponding two groups of data, the data is processed and output I-V curve and various electrical performance parameters of the solar cell to be tested.

We made a dye-sensitized solar cell with obvious internal capacitance effect to test our measurement method, and proved that the measurement method of the present invention can accurately and quickly measure the electrical properties of a solar cell with a large internal capacitance. A typical measurement includes the following step:

(1) Fabricate and package a dye-sensitized solar cell with N719 dye-sensitized TiO ₂ as the working electrode, I ^- /I ^3- acetonitrile solution as the electrolyte, and platinum-coated FTO conductive glass as the counter electrode. The working area is about 0.15cm ² .

(2) Turn on the simulated solar light source, calibrate with a standard silicon solar cell, and adjust the light source so that its optical power is equivalent to AM1.5 sunlight.

(3) Place the solar cell on the sample stage illuminated by the light source, connect the measuring wires, and place a mask to limit the illuminated area to a specific area.

(4) Turn on the digital source meter and the control computer, set the measurement parameters on the computer software and start the measurement.

The left side of Fig. 5 is the I-V curve obtained by this measurement, and Fig. 6 is the photoelectric conversion efficiency of the dye-sensitized solar cell obtained by this measurement. It can be seen that the method result of the present invention is not affected by the scanning speed and scanning direction, and realizes the elimination of solar energy. Electrical performance measurement of battery internal capacitance effects.

Claims (2)

1. eliminate the solar cell electrical property method for rapidly testing that internal capacitance influences for one kind; It is characterized in that first single direction carries out voltage scanning and measures after the electric current under each voltage; Carry out rightabout voltage scanning again; Draw the electric current under the corresponding voltage once more, the arithmetic mean of getting twice current value of depressing of scanning same electrical is made the I-V curve as the ultimate current measured value under this voltage.

2. the method for rapidly testing of the solar cell electrical property of elimination internal capacitance influence according to claim 1; The I-V curve that it is characterized in that using the mean value of the electric current of twice both forward and reverse directions scanning to make is the basis, draws each item unit for electrical property parameters of solar cell to be measured.

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