JP2009211994A - Inspection method for organic el element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection method can inspect open defects caused by aging and suitably determining its quality level, in an organic EL element having an upper electrode with film thickness of 135 nm or more. <P>SOLUTION: In the inspection method for the organic EL element wherein a lower electrode, an organic film including a light-emitting layer, and the upper electrode with film thickness of 135 nm or more are laminated in order on a substrate, voltage V is applied between both electrodes wherein a negative electrode side is set up to be a plus electrode and a positive electrode side is set up to be a minus electrode between the upper and lower electrodes, and leak current flowing between both electrodes is measured for a long period while making the defect section existed on the organic film evident. Thus, instantaneous current accompanied by the open defect can be detected, and it is determined on the basis of the measured leak current that what the instantaneous current is detected is a poor quality product and what the instantaneous current is not detected is a good quality product. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inspection method for an organic EL element.

  In general, an organic EL element is formed by laminating an anode as a lower electrode, an organic film including a light emitting layer, and a cathode as an upper electrode on a substrate. However, since an organic material is used, it is altered by an electric field or heat. And diffusion easily occur, which may cause a short circuit between the upper and lower electrodes. In particular, even if the initial leakage current is at the detection limit (for example, 1 nA or less), the upper and lower electrodes may be short-circuited suddenly during driving.

  On the other hand, in the method disclosed in Patent Document 1, after the organic EL element is formed, the cathode is the positive electrode and the anode is the negative electrode, and the reverse bias voltage is opposite to the forward voltage applied during light emission between the two electrodes. Then, apply a voltage in a voltage range between the breakdown voltage of the defect portion and the breakdown voltage of the organic EL element obtained in advance and equal to or higher than the reverse bias voltage during actual driving of the organic EL element to make the defect portion obvious. And aging to break open. According to this, a leakage current is generated in the defective portion by applying the reverse bias voltage, and the organic material is expanded by the Joule heat due to the leakage current and is scattered from the upper electrode, so that the defective portion is electrically opened, Leakage does not occur during driving. Note that. The defective part is a part where the organic film is locally thinned by a step such as a foreign substance and is easily short-circuited. The opened defective part (hereinafter referred to as an open defect) is caused by scattering of the upper electrode. It becomes a local non-light-emitting part.

  However, as a result of studies by the present inventors, when the film thickness of the upper electrode is 135 nm or more, most of the open defects caused by aging are of a size that can be visually confirmed (for example, the hole diameter is 150 μm or more). It became clear. Thus, an open defect having a size that can be visually confirmed causes a problem in display quality.

In the method disclosed in Patent Document 2, the first voltage V1 is applied as a reverse bias voltage between the upper and lower electrodes for an organic EL element having an upper electrode having a film thickness of 135 nm or more to reveal a defective portion. After the aging is performed, the second voltage V2 is applied as a reverse bias voltage between the upper and lower electrodes, and when this second voltage V2 is applied, the leakage current of the defective product is larger than the leakage current of the normal product. Within a certain time, the leakage current is measured. The quality of the organic EL element is determined based on the measured leakage current. According to this, it is possible to appropriately determine whether or not the organic EL element having the upper electrode having a film thickness of 135 nm or more is obvious by causing a defective portion that is likely to cause leakage.
Japanese Patent No. 3562522 JP 2007-66707 A

  However, as a result of further examination by the present inventor, the open defect manifested by aging in the organic EL element having the upper electrode having a film thickness of 135 nm or more has a film thickness of less than 135 nm regardless of its size (hole diameter). It has been clarified that the open defect is likely to cause a short circuit failure during driving, rather than the open defect that is manifested by aging in the organic EL element having the upper electrode.

  This is because the upper electrode is thick and difficult to scatter, so even if an open defect occurs due to aging, the structure (shape) of the open defect is likely to short-circuit (in other words, the structure where the upper electrode is close to the lower electrode). In addition, even if the upper and lower electrodes are short-circuited at the site of the open defect during driving, the voltage at the time of driving is smaller than the aging voltage, so that it is difficult to open again.

  Therefore, in an organic EL element having an upper electrode having a film thickness of 135 nm or more, it is necessary to detect an open defect in order to prevent a short circuit failure in the market. As described above, an open defect can be detected by visually confirming a large hole diameter. However, since the open defect is in an electrically open state, an open defect having a size that cannot be visually confirmed (for example, the hole diameter is less than 150 μm) is also detected by leak current measurement after aging disclosed in Patent Document 2. I can't.

  In view of the above-mentioned problems, the present invention provides an organic EL element inspection method capable of detecting open defects caused by aging in an organic EL element having an upper electrode having a film thickness of 135 nm or more and appropriately determining pass / fail. The purpose is to provide.

  In order to achieve the above object, the present inventor has intensively studied. Although details will be described later, an organic EL element having a general configuration except that the film thickness of the cathode as the upper electrode is 135 nm or more is used, and a voltage V that makes a defective portion appear between the upper electrode and the lower electrode. Was applied. Then, the leakage current flowing between both electrodes was measured during the entire period in which the voltage V was applied (that is, during the aging process). As a result, the present inventors have newly found that an instantaneous current (a leak current that instantaneously shows a large value) is detected in an organic EL element in which an open defect has occurred due to aging.

  The invention according to claim 1 is based on the above knowledge, and is an inspection method of an organic EL element in which a lower electrode, an organic film including a light emitting layer, and an upper electrode having a thickness of 135 nm or more are sequentially laminated on a substrate. An aging step of applying a voltage V between both the upper and lower electrodes with the cathode side as a positive electrode and the anode side as a negative electrode to reveal a defective portion existing in the organic film, and between the two electrodes A leakage current measurement step for measuring a leakage current flowing between both electrodes in the entire period of applying the voltage V, and a determination step for determining the quality of the organic EL element based on the measured leakage current. Features.

  According to the present invention, as described above, it is possible to identify whether or not the organic EL element has an open defect based on the leak current measured during aging. it can.

  In the first aspect of the present invention, as described in the second aspect, in the leakage current measurement step, the leakage current flowing between the two electrodes is measured at a constant time interval S, and based on the measured leakage current. The quality of the organic EL element may be determined.

  As described above, when the leakage current is sampled during the application of the voltage V at the constant time interval S, the quality is determined based on the measured leakage current while reducing the number of data acquisition for detecting the instantaneous current. The configuration can be simplified.

  In the invention described in claim 2, as described in claim 3, the time interval S is preferably set to 28 μs or less. According to this, the instantaneous current can be reliably detected. This point has been confirmed by the present inventors.

  In the invention according to any one of claims 1 to 3, as described in claim 4, the voltage V in the aging process is preferably larger than the voltage applied during actual driving of the organic EL element. Since the aging process is a process of revealing defects generated during actual driving, according to the present invention, it is possible to promote the manifestation of defects.

  In the invention according to any one of claims 1 to 4, as described in claim 5, the voltage V in the aging process is preferably a DC voltage. According to this, the cost of the power supply for applying a voltage can be held down. Also, the voltage control is simplified.

  In the invention according to any one of claims 1 to 5, when a plurality of organic EL elements are formed in a matrix on the same substrate as described in claim 6, a plurality of organic EL elements are formed in the aging process. The voltage V is preferably applied to both electrodes in the organic EL element at once. According to this, open defects can be manifested in a lump for a plurality of organic EL elements.

  In the invention according to any one of claims 1 to 6, as in claim 7, the electrical connection state of both electrodes is inspected by lighting the organic EL element before and after the voltage V is applied. You may do it. Thus, when a forward voltage is applied to both electrodes before and after application of the voltage V and a lighting inspection is performed, the organic connection state between the electrodes becomes poor at the time before aging or during aging. An EL element can be detected. That is, it is possible to improve the reliability of the inspection for the presence or absence of open defects by the method described above.

  First, before describing the embodiment of the present invention, the background of the inventor's creation of the present invention will be described. The inventor of the present invention is an open defect (a part where an organic film is locally thinned by a step such as a foreign substance and is easily short-circuited as a defective part that has been manifested by aging. Intensive study was conducted on the local non-light-emitting portion scattered by the upper electrode. First, the relationship between the film thickness of the cathode as the upper electrode and the occurrence rate of short-circuit defects was investigated.

  Specifically, an anode as the lower electrode, an organic film, and a cathode as the upper electrode are stacked on the substrate, and a plurality of types of organic EL elements having different film thicknesses of the upper electrode are prepared. The number N1 of the generated open defects (including those that cannot be visually observed) was measured. Then, after applying an actual drive voltage of 15 V between the upper and lower electrodes for 10 h, among the open defects, the number N2 of the short-circuited by driving (the upper and lower electrodes are short-circuited at the site of the open defect) is measured. The occurrence rate of short circuit failure (N2 / N1) was determined.

  As a result, as shown in FIG. 1, when the film thickness of the upper electrode is 135 nm or more, the occurrence rate of short-circuit failure is larger than that when the film thickness of the upper electrode is less than 135 nm, and open defects may easily lead to short-circuit failure during driving. It became clear. In addition, the open defect manifested by aging in the organic EL element having a film thickness of 135 nm or more as the upper electrode is not more dependent on the size (hole diameter) than when the film thickness of the upper electrode is less than 135 nm. It became clear that open defects tend to lead to short-circuit defects. FIG. 1 is a diagram showing the relationship between the film thickness of the upper electrode and the incidence of short circuit failure.

  This is because even if an open defect occurs due to aging, the upper electrode, which is a thick film, is less likely to scatter compared to a thin upper electrode, and the upper electrode is located near the lower electrode through the open defect. Therefore, it is considered that one reason is that the upper and lower electrodes are easily short-circuited at the open defect portion during driving. In addition, even if a short circuit occurs at the open defect portion during driving, the voltage during driving is smaller than the aging voltage, and thus it is considered that it is difficult to open again.

  As described above, an open defect having a size that cannot be visually confirmed (for example, a hole diameter of less than 150 μm) that has not been affected in terms of display quality in the past has an upper electrode with a film thickness of 135 nm or more. It has been found that there is a possibility that a short circuit failure may occur in the market for EL elements.

  Therefore, the present inventor has intensively studied to find a method for detecting an open defect other than visual observation with respect to an organic EL element having a cathode film thickness of 135 nm or more as an upper electrode. Specifically, the leakage current flowing between the two electrodes was measured during the period of application of the voltage V while applying the voltage V that reveals the defective portion between the cathode and the anode as the lower electrode. As a result, as shown in FIG. 2, the leak current is almost constant in the organic EL element in which no open defect occurs due to aging. However, in the organic EL element in which the open defect occurs due to aging, a spike-like moment is generated as the leak current. Newly found that a large current (hereinafter referred to as an instantaneous current) flows. FIG. 2 is a diagram showing a change in leakage current flowing through the organic EL element during aging. The solid line indicates the result of the organic EL element in which an open defect occurs, and the broken line indicates the result of the organic EL element in which no open defect occurs. In addition, the horizontal axis represents the voltage application time, and the vertical axis represents the logarithmic value (log I) of the leakage current (I). This instantaneous current is considered to be caused by a phenomenon that the defective portion is electrically opened in a short period of time. When the leakage current flowing between the upper and lower electrodes after aging was measured, the above difference was not observed between the organic EL element in which no open defect occurred and the organic EL element in which the open defect occurred. The present invention is based on this finding, and hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 3 is a cross-sectional view showing a schematic configuration of the organic EL element according to the first embodiment of the present invention. An organic EL element 100 shown in FIG. 3 includes a substrate 10, an anode 20, an organic film 30 including a light emitting layer, and a cathode 40. The organic EL element 100 has a film configuration similar to that of a general organic EL element except that the thickness of the cathode 40 is 135 nm or more.

  The substrate 10 plays a role as a base material (base material), and is a transparent substrate made of glass or plastic. An anode 20 as a lower electrode is stacked on one surface of the substrate 10. As a constituent material of the anode 20, a material having conductivity and light transmittance such as indium tin oxide (ITO) can be employed. An organic film 30 is laminated on the surface of the anode 20 opposite to the substrate 10. As the organic film 30, a known configuration, that is, a single layer type including only a light emitting layer or a multilayer type including a hole injection layer other than the light emitting layer, a hole transport layer, an electron transport layer, an electron injection layer and the like is adopted. be able to. A cathode 40 as an upper electrode is laminated on the surface of the organic film 30 opposite to the anode 20. As a constituent material of the cathode 40, a conductive material such as aluminum can be employed.

  In the organic EL element 100, during actual driving, the organic film 30 emits light by applying a forward voltage between the electrodes 20 and 40 with the anode 20 as a positive pole and the cathode 40 as a negative pole. For example, light is extracted from the substrate 10 side.

  Here, in the present embodiment, a plurality of the organic EL elements 100 described above are formed in a matrix (matrix shape) on the same substrate 10. FIG. 4 is a schematic plan view showing a configuration in which a plurality of organic EL elements are formed in a matrix.

  As shown in FIG. 4, the anode 20 and the cathode 40 are formed in stripes so as to intersect with each other on the substrate 10, and the portions where the upper and lower electrodes 20, 40 intersect and overlap each other are pixels, It is configured as the organic EL element 100 shown in FIG.

  The organic EL elements 100 arranged in such a matrix can be used as a display panel by causing a desired one of the plurality of organic EL elements 100 to emit light by a drive circuit (not shown). Yes.

  Next, a method for manufacturing the organic EL element 100 will be described. FIG. 5 is a process flow diagram illustrating a method for manufacturing an organic EL element. FIG. 6 is a flowchart for explaining the inspection process in the manufacturing process. FIG. 7 is a diagram schematically showing an apparatus configuration for inspecting an organic EL element.

  As shown in FIG. 5, first, the organic EL element 100 having the above-described configuration is formed (step 10). Specifically, the anode 20 as a lower electrode is formed on the substrate 10 by sputtering or the like, and the organic film 30 is formed by an evaporation method using an organic light emitting material. Next, by depositing aluminum or the like, the cathode 40 as the upper electrode is formed to have a film thickness of 135 nm or more (for example, about 300 nm). Here, in the present embodiment, a plurality of organic EL elements 100 are formed in a matrix by patterning the anode 20 and the cathode 40 in a stripe shape as shown in FIG. 4 by photolithography or the like. The process up to this point is the element formation step, whereby the organic EL element 100 shown in FIGS. 3 and 4 is formed.

  And inspection is performed with respect to the formed organic EL element 100 (step 20). This inspection method is a characteristic part according to the present embodiment. In the present embodiment, as shown in FIG. 5, the inspection process is performed continuously as a process of manufacturing the organic EL element 100 following the above-described element formation process. In this inspection process, the cathode 40 in the organic EL element 100 is used as a positive electrode and the anode 20 is used as a negative electrode. An aging step for performing the process of making the material appear, and a leakage current measuring step for measuring the leakage current flowing between the electrodes 20 and 40 during the entire period of application of the voltage V in the aging step. That is, the leakage current is measured while aging.

  Specifically, as shown in FIG. 6, aging is first performed by applying a reverse bias voltage V between the electrodes 20 and 40 (step 21). The reverse bias voltage V is a voltage at which a defective portion existing in the organic EL element 100 becomes apparent. In this embodiment, by making the reverse bias voltage V larger than the voltage applied when the organic EL element 100 is actually driven, the manifestation of open defects is promoted. The reverse bias voltage V can be applied using a DC power supply 110 as shown in FIG. In the present embodiment, as shown in FIG. 7, the upper and lower electrodes 20, 40 in the plurality of organic EL elements 100 are connected to the DC power source 110 using a common wiring, and the control unit 130 controls the plurality of electrodes. The operation of the DC power supply 110 is controlled so that the reverse bias voltage V is applied to the organic EL elements 100 at once. Therefore, the plurality of organic EL elements 100 can be collectively inspected for the presence or absence of open defects (inspection process), and processing in a short time becomes possible. However, the application of the reverse bias voltage V (inspection process) may be performed for each organic EL element 100.

  Further, along with the application of the reverse bias voltage V, measurement of the leakage current flowing between the electrodes 20 and 40 is started (step 22). In the present embodiment, as shown in FIG. 7, a current measuring unit 120 that measures a direct current is electrically interposed between the cathode 40 and the direct current power source 110. Note that the current measurement unit 120 may be interposed between the anode 20 and the DC power supply 110. Then, the operation of the current measuring unit 120 is controlled by the control unit 130 so that the current measuring unit 120 measures the leakage current of the organic EL element 100 with the reverse bias voltage V applied to the organic EL element 100. Further, the leakage current measured by the current measuring unit 120 is sent to the control unit 130, and the control unit 130 compares the value of the leakage current with a predetermined threshold value to detect the presence or absence of an open defect. Therefore, the operation of the current measurement unit 120 is controlled by the control unit 130 so as to acquire data at a certain time interval S.

  As described above, when the leakage current is measured (sampled) during the application of the reverse bias voltage V at the constant time interval S by the current measurement unit 120 whose operation is controlled by the control unit 130, the time interval is measured. The smaller S is, the higher the probability that an instantaneous current can be measured. However, as the time interval S is reduced, the number of data acquisition increases, and the cost of the inspection apparatus increases. Therefore, the present inventor scrutinized the relationship between the time interval S and the instantaneous current detection rate (open defect detection rate). The presence or absence of open defects was confirmed visually and with a microscope. As a result, as shown in FIG. 8, it has been found that if the time interval S is set to 28 μs or less, an instantaneous current, that is, an open defect can be reliably detected. Note that 28 μs substantially coincides with the measured half-value width of the instantaneous current, and in this embodiment, the time interval S is set to 28 μs. FIG. 8 is a diagram showing the relationship between the time interval S and the open defect detection rate (instantaneous current detection rate).

  As shown in step 23 of FIG. 6, the application of the reverse bias voltage V and the measurement of the leakage current are performed until the elapsed time from the application of the reverse bias voltage V passes a predetermined time for making the defective portion appear. Implemented. Since the elapsed time (predetermined time for making the defective portion visible) varies depending on the reverse bias voltage V, it is appropriately set according to the applied reverse bias voltage V. In this embodiment, the reverse bias voltage V is 28 V and the application time is 60 seconds.

  After a predetermined time has elapsed, the application of the reverse bias voltage and the measurement of the leakage current are finished (steps 24 and 25). Thus, the inspection process (aging process and leakage current measurement process) is completed. Then, as shown in FIG. 5, in the determination step, the quality of the organic EL element 100 is determined based on the leakage current measured in the inspection step (leakage current measurement step) (step 30). In the present embodiment, as described above, the leakage current measured by the current measuring unit 120 is compared with a predetermined threshold value by the control unit 130, and those that instantaneously exceed the threshold value are determined to have open defects. The In addition, it is determined that the anode 20 and the cathode 40 are short-circuited when the threshold value is exceeded until the application of the reverse bias voltage V is completed after the threshold value is exceeded once. Moreover, the thing below a threshold value determines with the anode 20 and the cathode 40 not being short-circuited, and not having an open defect. Note that the leakage current value of a normal element having no open defect differs depending on the structure of the organic EL element 100, and the peak value of the instantaneous current changes depending on the reverse bias voltage V. Therefore, a threshold value that is a criterion for determining the presence or absence of an open defect is appropriately set according to each condition. As described above, it is determined whether or not the organic EL element 100 has an open defect that causes a short circuit during actual driving. In the present embodiment, as described above, the inspection process and the determination process can be automated.

  Thus, according to the inspection method of the organic EL element 100 according to the present embodiment, the reverse bias voltage V is applied between the electrodes 20 and 40 to the organic EL element 100 having the cathode 40 having a film thickness of 135 nm or more. Thus, the defect portion (open defect and short-circuit defect between the anode 20 and the cathode 40) is made obvious, and the quality of the organic EL element 100 is determined based on the leak current measured at this time.

  Therefore, whether or not the organic EL element 100 has an open defect can be identified based on whether or not an instantaneous current as a leakage current is detected, and therefore it is possible to appropriately determine whether the organic EL element 100 has an open defect.

  In the present embodiment, since the leak current flowing between the electrodes 20 and 40 is sampled with the time interval S set to 28 μs or less, the instantaneous current is surely reduced while reducing the number of data acquisitions for detecting the instantaneous current. Can be detected. In addition, the configuration of the inspection apparatus can be simplified.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In the present embodiment, an example in which the reverse bias voltage V in the aging process is a DC voltage is shown. Thus, when it is set as a direct current voltage, the cost of the power supply for applying a voltage can be held down. Also, the voltage control is simplified. However, it may not be direct current and may be alternating current. The target voltage may be the effective voltage.

  In the present embodiment, an example has been shown in which the inspection process is performed continuously as a process of the manufacturing process of the organic EL element 100 following the element formation process. However, it may be implemented as an independent process with a gap from the element forming process.

  In this embodiment, the example which performs a determination process after the inspection process (leakage current measurement process) was shown. However, the leakage current measurement process and the determination process may be performed simultaneously. That is, pass / fail determination may be performed simultaneously with measurement of the leakage current. The method for detecting the instantaneous current is not limited to the above example. For example, a voltage generated in a current measuring resistor connected between the DC power supply 110 and the cathode 40 is compared with a reference voltage by a comparator, and the output of the comparator is “1” or “0” depending on the presence or absence of an instantaneous current. It is good also as a structure which becomes either of these. In this case, since the leakage current can be measured continuously during the application of the reverse bias voltage V, not the sampling, the instantaneous current can be reliably detected. Alternatively, the inspection process may be terminated when an instantaneous current is detected without waiting for the elapse of a predetermined time.

  In the present embodiment, an example in which the inspection process and the determination process are automated has been described. However, the present invention is not particularly limited to automation.

  Although not particularly mentioned in the present embodiment, before and after the application of the reverse bias voltage V, the cathode 40 in the organic EL element 100 is a negative electrode and the anode 20 is a positive electrode. The electrical connection state of both electrodes 20 and 40 may be inspected by applying the voltage of 1 and turning on the organic EL element 100. When the lighting inspection is performed in this way, the organic EL element 100 in which the electrical connection state between the electrodes 20 and 40 is already defective before the aging, or the electrical connection between the electrodes 20 and 40 during aging is performed. The organic EL element 100 in which the connection state is defective can be detected. That is, it is possible to improve the reliability of the inspection for the presence or absence of open defects shown in this embodiment.

It is a figure which shows the relationship between the film thickness of an upper electrode, and a short circuit defect incidence. It is a figure which shows the change of the leakage current which flows into an organic EL element during aging. It is sectional drawing which shows schematic structure of the organic EL element which concerns on 1st Embodiment. It is a schematic plan view which shows the structure which formed the some organic EL element in the matrix form. It is a process flow figure showing a manufacturing method of an organic EL element. It is a flowchart explaining an inspection process among manufacturing processes. It is a figure which shows typically the apparatus structure for test | inspecting an organic EL element. It is a figure which shows the relationship between the time interval S and an open defect detection rate (instantaneous current detection rate).

Explanation of symbols

10 ... Substrate 20 ... Anode (lower electrode)
30 ... Organic film 40 ... Cathode (upper electrode)
DESCRIPTION OF SYMBOLS 100 ... Organic EL element 110 ... DC power supply 120 ... Current measurement part 130 ... Control part

Claims (7)

A method for inspecting an organic EL element in which a lower electrode, an organic film including a light emitting layer, and an upper electrode having a thickness of 135 nm or more are sequentially stacked on a substrate,
Among the upper and lower electrodes, an aging step in which the cathode side is a positive electrode and the anode side is a negative electrode, and a voltage V is applied between the two electrodes to reveal a defective portion existing in the organic film;
A leakage current measurement step for measuring a leakage current flowing between the electrodes in the entire period in which the voltage V is applied between the electrodes;
And a determination step of determining whether the organic EL element is good or not based on the measured leakage current. In the leakage current measurement step, the leakage current flowing between the electrodes at a constant time interval S is measured,
The inspection method for an organic EL element according to claim 1, wherein the quality of the organic EL element is determined based on the measured leakage current.   The organic EL element inspection method according to claim 2, wherein the time interval S is 28 μs or less.   The method for inspecting an organic EL element according to any one of claims 1 to 3, wherein the voltage V in the aging step is larger than a voltage applied during actual driving of the organic EL element.   5. The method for inspecting an organic EL element according to claim 1, wherein the voltage V in the aging step is a DC voltage. A plurality of the organic EL elements are formed in a matrix on the same substrate, and in the aging step, the voltage V is collectively applied to the electrodes of the plurality of organic EL elements. The inspection method of the organic EL element according to any one of claims 1 to 5.   The electrical connection state of the electrodes is inspected by lighting the organic EL element before and after applying the voltage V between the electrodes. The inspection method of the organic EL element of 1 item | term.

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