JP4881499B2 - Method for removing short circuit part of solar cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and method for removing a short-circuit portion generated in a thin film solar cell using an amorphous semiconductor or the like. More specifically, in the thin film solar cell, the present invention applies a reverse voltage equal to or lower than the withstand voltage between the substrate-side electrode and the back-side electrode sandwiching the photoelectric conversion semiconductor layer that contributes to power generation. The present invention relates to an apparatus and a method for insulating by removing or oxidizing a short-circuit portion by generated Joule heat.
[0002]
[Prior art]
FIG. 5 shows the structure of the thin film solar cell 10. As shown in FIG. 5, the thin-film solar cell 10 is formed by processing the first electrode 2, the photoelectric conversion semiconductor layer 3, and the second electrode 4 in a predetermined pattern on one surface of the insulating substrate 1. Thus, a plurality of solar cells 5 configured by sequentially stacking are provided. The photoelectric conversion semiconductor layer 3 is composed of, for example, an amorphous silicon semiconductor layer having a pin junction. With this structure, the second electrode 4b of the solar battery cell 5b adjacent to the first electrode 2a of the solar battery cell 5a, and the second electrode of the solar battery cell 5c adjacent to the first electrode 2b of the solar battery cell 5b. 4c are connected in series.
[0003]
In such a thin film solar cell, for example, if a pinhole is generated in the photoelectric conversion semiconductor layer during manufacturing, the first electrode and the second electrode of the solar cell may be short-circuited. Since the solar cell in which the short circuit has occurred does not contribute to power generation, the photoelectric conversion efficiency of the solar cell is reduced. In order to cope with this problem, a process (reverse bias process) is performed in which a reverse voltage (reverse bias voltage) is applied between the positive and negative electrodes of the solar battery cell to remove the short-circuit portion. In this process, by applying a reverse voltage to the photoelectric conversion semiconductor layer, the current is concentrated in the short circuit part, and the generated Joule heat scatters the metal in the short circuit part or oxidizes the metal to form an insulator. Remove the part.
[0004]
For example, in FIG. 5, the case where the short circuit part of the 1st electrode 2b and the 2nd electrode 4b which arose in the photoelectric conversion semiconductor layer 3b of the photovoltaic cell 5b is removed is demonstrated. In this case, the second electrode 4b of the solar battery cell 5b and the second electrode 4c of the adjacent solar battery cell 5c (this second electrode 4c is connected in series to the first electrode 2b of the solar battery cell 5b). The first and second probes 6a and 6b are in contact with each other, and a reverse voltage equal to or lower than the withstand voltage is applied between the first electrode 2b and the second electrode 4b sandwiching the photoelectric conversion semiconductor layer 3b contributing to power generation. Apply.
[0005]
Conventionally, reverse bias processing is performed by supplying a DC reverse voltage or a reverse voltage in the form of a pulsed rectangular wave between the first and second probes 6a and 6b.
[0006]
However, a solar cell is equivalent to a diode. For this reason, when a reverse voltage is applied between the first electrode 2 and the second electrode 4, the solar cell 5 including the first electrode 2, the photoelectric conversion semiconductor layer 3, and the second electrode 4 functions as a capacitor. Charges are likely to accumulate even after the applied voltage is removed. And the problem that weak parts other than the defect (short circuit part) of the photoelectric conversion semiconductor layer 3 may be destroyed due to the voltage by this stored charge has been found. Furthermore, recently, it has been found that charge accumulation due to application of a reverse voltage occurs very easily, and the adverse effect of the accumulated charge is greater than expected.
[0007]
[Problems to be solved by the invention]
The object of the present invention is to suppress the phenomenon that charges are accumulated between electrodes as much as possible when a reverse voltage is applied to a thin-film solar cell to remove the short-circuit portion, thereby avoiding destruction of portions other than the short-circuit portion. It is to provide an apparatus and method that can be used.
[0008]
[Means for Solving the Problems]
The solar cell short-circuit removal method is a method of removing a short-circuit portion of a solar cell including one or a plurality of solar cells in which a first electrode layer, a semiconductor layer, and a second electrode layer are sequentially formed on a substrate. A reverse voltage having a waveform with a frequency of 20 to 1000 Hz and periodically changing within 0.2 seconds or less is applied between the positive and negative electrodes of the solar battery cell, and the waveform is 0 V And a plurality of periods approaching 0 V from the peak value, and the accumulated charges are discharged during the period . In this method, it is sufficient that the application time of the reverse voltage is (1 / reverse voltage frequency) or more. For example, when a sine wave having a frequency of 60 Hz is applied as the reverse voltage in the present invention, the reverse voltage application time corresponds to 1 to 12 cycle times.
[0010]
In the method of the present invention, the reverse voltage indicating a periodically changing waveform is applied between the first and second electrodes only for a short time of 0.2 seconds or less, so that accumulation of charges in the solar cell is suppressed as much as possible. The charge accumulated during the period when the reverse voltage is 0V and the period approaching 0V from the peak value can be effectively discharged, so that it is possible to suppress the destruction of the portion other than the short-circuit portion due to the accumulated charge. .
[0011]
In the method of the present invention, the operation of applying the reverse voltage indicating a periodically changing waveform for a time of 0.2 seconds or less may be repeated while sequentially increasing the peak value of the reverse voltage.
[0012]
In the method of the present invention, a sine wave, a half sine wave, a sawtooth wave, or a rectangular wave is used as the waveform of the reverse voltage. Note that the reverse voltage may mainly include a forward component, mainly a reverse component.
[0013]
The frequency of the reverse voltage is preferably matched with a time constant defined by the capacity C of the solar cell and the resistance R in the reverse direction. When the frequency of the reverse voltage is set as described above, the waveform of the applied voltage can be made to follow the waveform of the power supply voltage. Specifically, the frequency of the reverse voltage is set to a range of 20 to 1000 Hz, and further 50 to 120 Hz.
Another solar cell short-circuit portion removal method removes a short-circuit portion of a solar cell including one or a plurality of solar cells in which a first electrode layer, a semiconductor layer, and a second electrode layer are sequentially formed on a substrate. In this method, a reverse voltage and a DC forward voltage are alternately applied between the positive and negative electrodes of the solar battery cell, and a waveform in which the reverse voltage periodically changes within a time of 0.2 seconds or less. It is characterized by having.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
A solar cell short-circuit removing apparatus according to the present invention will be described with reference to FIG.
[0015]
As in FIG. 5, the thin film solar cell 10 in FIG. 1 is sequentially laminated on the insulating substrate 1 by processing the first electrode 2, the photoelectric conversion semiconductor layer 3, and the second electrode 4 in a predetermined pattern. Thus, the solar battery cells 5a and 5b are connected in series with each other.
[0016]
When a glass substrate or a transparent resin substrate is used as the insulating substrate 1, a transparent electrode material such as ITO (Indium Tin Oxide) is used as the second electrode as the first electrode 2. 4 is a metal electrode material. On the other hand, when a substrate material that does not transmit light is used as the insulating substrate 1, a metal electrode material is used as the first electrode 2, and a transparent electrode material is used as the second electrode 4.
[0017]
As the semiconductor layer 3, in the case of an amorphous silicon-based semiconductor, amorphous silicon, hydrogenated amorphous silicon, hydrogenated amorphous silicon carbide, amorphous silicon nitride, etc., as well as silicon and germanium or tin are used. A material such as an amorphous silicon alloy with another metal is used. Further, the semiconductor layer is not limited to a silicon system, and may be configured using a material such as a CdS system, a GaAs system, or an InP system. The amorphous semiconductor layer or the microcrystalline semiconductor layer may have a pin type, nip type, ni type, pn type, MIS type, heterojunction type, homojunction type, Schottky barrier type, or a combination thereof. Composed.
[0018]
An example of the solar cell short-circuit removing apparatus according to the present invention will be specifically described. As shown in FIG. 1, the first probe 6a and the second probe 6b are in contact with the first electrode 2a of the solar battery cell 5a and the second electrode 4b of the adjacent solar battery cell 5b, respectively. Pressed. A reverse bias voltage indicating a periodically changing waveform is applied to the probe 6 a and the probe 6 b via the amplifier (built-in current limiter) 12 from the function generator 11. The application time of the reverse voltage generated from the function generator 11 is controlled by the computer 13. A resistor 14 is inserted in the wiring between the probe 6 a and the amplifier 12, and the voltage applied to both ends of the resistor 14 is measured by the digital voltmeter 15. The peak value of the reverse voltage measured by the digital voltmeter 15 is input to the computer 13 and fed back to the function generator 11 so that a reverse voltage having a predetermined peak value is applied. Further, the computer 13 controls the XY movement of a table (not shown) on which the solar cell 10 is placed and the elevation of the table or probe mechanism.
[0019]
In this invention, the example of the waveform of the reverse voltage which shows the waveform which changes periodically and is supplied between the positive / negative poles of a photovoltaic cell through a 1st and 2nd probe from a function generator from FIG. Shown in (C). The reverse voltage waveform shown in FIG. 2A is a sine wave. The reverse voltage waveform shown in FIG. 2B is a half wave of a sine wave. The waveform of the reverse voltage shown in FIG. 2C is a sawtooth wave. In the present invention, the reverse voltage application time (indicated by T ₁ in FIG. 2) is set to 0.2 seconds or less.
[0020]
As described above, since the application time of the reverse voltage is as short as 0.2 seconds or less, it is difficult to accumulate charges. Further, by applying the reverse voltage having the waveform as described above, the charge accumulated between the first and second electrodes 2 and 4 as the reverse voltage value gradually approaches 0V from the peak value. Can be reduced, and destruction of normal parts can be suppressed.
[0021]
In the present invention, the reverse voltage, which is supplied between the positive and negative electrodes of the solar battery cell from the function generator through the first and second probes and shows a periodically changing waveform, is mainly partially in the reverse direction. A direction component may be included. Such reverse voltage waveforms are shown in FIGS. The waveform of the reverse voltage shown in FIG. 3A is a sine wave that partially includes a forward component. The waveform of the reverse voltage shown in FIG. 3B is a half wave of a sine wave that partially includes a forward component. The waveform of the reverse voltage shown in FIG. 3C is a rectangular wave partially including a forward component. The waveform of the reverse voltage shown in FIG. 3D is a sawtooth wave that partially includes a forward component.
[0022]
When a reverse voltage having the waveform as described above is applied, the charge accumulated between the first and second electrodes 2 and 4 when the forward component is applied can be further reduced, and the normal portion is destroyed. Can be suppressed.
[0023]
In the present invention, it is preferable to repeat the operation of applying a reverse voltage indicating a periodically changing waveform for a time of 0.2 seconds or less while sequentially increasing the peak value of the reverse voltage. Such a method provides the following advantages.
[0024]
Generally, the reverse breakdown voltage of the solar battery cell is 8 to 10V. If a relatively high reverse voltage of 4 V or higher (withstand voltage or lower) is applied to such a solar battery cell from the beginning, the short circuit portion may be difficult to remove. That is, in the state where the short-circuited portion is not removed, the reverse voltage and the leakage current (current flowing through the short-circuited portion) inherently show linear VI characteristics, and the short-circuited portion is removed. Later, the leakage current should decrease rapidly. However, when a reverse voltage having a high peak value is applied from the beginning, the observed leakage current may be larger than the assumed line of VI characteristics. Even when a reverse voltage having a peak value higher than the first peak value is applied to such a solar battery cell, the increase tendency of the leakage current becomes more remarkable, and it is often difficult to remove the short-circuit portion. .
[0025]
On the other hand, when the reverse bias processing for a short time according to the present invention is repeated while changing the peak value of the reverse voltage from a low value (specifically, 2 V or less) to a high value, the tendency of the change in the leakage current occurs. It is possible to determine whether the short circuit portion of the solar battery cell can be removed or is difficult to remove. Therefore, it is possible to appropriately determine whether to continue or end the reverse bias process and to perform an optimal reverse bias process.
[0026]
Further, as shown in FIG. 4, in such a process, the time of applying a reverse component at _one time (T ₁ ) and the application of the next reverse component having a peak value higher than the previous reverse voltage. A forward voltage of −0.5 V or less may be applied for a time T ₂ between the time (T ₁ ) time. Note that the method of changing the reverse voltage is not limited to the example shown in FIG. 4, and various modes are conceivable.
[0027]
If the forward voltage is applied in the time T _{2 in} this way, the charge accumulated between the first and second electrodes 2 and 4 can be further reduced, and the destruction of the normal part can be suppressed.
[0028]
Actually, according to the method of the present invention and the conventional method as described below, reverse bias treatment was performed on each cell of solar cells in which 60 solar cells were integrated in series, and the effects were compared.
[0029]
According to the method of the present invention, reverse bias treatment was performed by applying a reverse voltage and a forward voltage according to the following schedule. (1) A reverse voltage composed of a sine wave having a frequency of 60 Hz and a peak value of 2 V is applied for 0.17 seconds, (2) a DC forward voltage of -0.1 V is applied for 0.17 seconds, and (3) a frequency of 60 Hz, peak A reverse voltage consisting of a sine wave having a value of 4V is applied for 0.17 seconds, a DC forward voltage of (4) -0.1V is applied for 0.17 seconds, and (5) a sine wave having a frequency of 60 Hz and a peak value of 6V. A reverse voltage was applied for 0.17 seconds, and a DC forward voltage of (6) -0.1 V was applied for 0.17 seconds (total processing time 1.02 seconds). In this case, good photoelectric conversion characteristics were recognized in 58 cells out of 60 cells.
[0030]
On the other hand, according to a conventional method, a reverse bias process was performed by applying a rectangular wave pulse having a frequency of 60 Hz and a peak value of 4 V for 1.0 second. In this case, only 50 cells had good photoelectric conversion characteristics among the 60 cells. From these results, it can be seen that the method for removing a short-circuit portion according to the present invention is extremely effective.
[0031]
【Effect of the invention】
As described above in detail, by using the solar cell short-circuit removing device and the short-circuit removing method of the present invention, it is possible to suppress the phenomenon of charge accumulation between the electrodes as much as possible and avoid destruction of portions other than the short-circuited portion. In addition, since the short-circuit portion can be reliably removed, it greatly contributes to the improvement of the photoelectric conversion characteristics of the solar cell.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a solar cell short-circuit removing apparatus according to the present invention.
FIG. 2 is a diagram showing a waveform of a reverse voltage according to the present invention.
FIG. 3 is a diagram showing a waveform of a reverse voltage according to the present invention.
FIG. 4 is a diagram showing a waveform of a reverse voltage according to the present invention.
FIG. 5 is a diagram for explaining a configuration of a solar cell and a method for removing a short-circuit portion.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Insulating substrate 2 ... 1st electrode 3 ... Photoelectric conversion semiconductor layer 4 ... 2nd electrode 5 ... Solar cell 6 ... Probe 10 ... Solar cell 11 ... Function generator 12 ... Amplifier 13 ... Computer 14 ... Resistance 15 ... Digital voltmeter

Claims (6)

A method of removing a short-circuit portion of a solar battery including one or a plurality of solar cells in which a first electrode layer, a semiconductor layer, and a second electrode layer are sequentially formed on a substrate, wherein the positive and negative of the solar cells A reverse voltage having a waveform having a frequency of 20 to 1000 Hz and periodically changing within a time of 0.2 seconds or less is applied between the electrodes, and the waveform has a period of 0V and a period in which the peak value approaches 0V. A method for removing a short-circuited portion of a solar cell, comprising: a plurality, wherein the accumulated charge is discharged during the period .   The operation of applying the reverse voltage is repeated while sequentially increasing the peak value of the reverse voltage, and each reverse voltage has a waveform that periodically changes within a time of 0.2 seconds or less. The short circuit part removal method of the solar cell of Claim 1 characterized by the above-mentioned.   3. The method for removing a short circuit portion of a solar cell according to claim 1, wherein the reverse voltage is a sine wave, a half wave of a sine wave, a sawtooth wave, or a rectangular wave. Short circuit portion removing method of the solar cell according to claim 1, wherein the frequency of the reverse voltage is 50～120Hz.   A method of removing a short-circuit portion of a solar battery including one or a plurality of solar cells in which a first electrode layer, a semiconductor layer, and a second electrode layer are sequentially formed on a substrate. A reverse voltage and a DC forward voltage are alternately applied between the electrodes, and the reverse voltage has a waveform that periodically changes within a time of 0.2 seconds or less. Of removing the short circuit. The method of claim 5 , wherein the reverse voltage is a sine wave, a half sine wave, a sawtooth wave, or a rectangular wave.

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