Charge measurement method, program, and charge measurement system

Abstract

In this charge measurement method, with respect to a light-emitting element that has a pair of electrodes and a light-emitting layer disposed between the pair of electrodes, first data indicating a change in current flowing through the light-emitting element is acquired, the first data being obtained by applying a voltage between the pair of electrodes that periodically changes and that also periodically inverts polarity (S1). In the charge measurement method, second data indicating change in light emission intensity of the light-emitting element in accordance with the application of the voltage is acquired (S2). In the charge measurement method, charge that does not contribute to light emission in the light-emitting element is measured on the basis of the first data and the second data (S3).

Description

Charge measurement method, program, and charge measurement system

[0001] The present disclosure relates to a charge measurement method, a program, and a charge measurement system for measuring charges in a light-emitting element.

[0002] Non-Patent Document 1 discloses simultaneous measurement of the current density by measuring the displacement current of an organic light-emitting diode (OLED) and the light-emitting characteristics using a photodiode.

[0003] Masaru Inoue, Hideyuki Murata, "Simultaneous Measurement of Displacement Current and Emission Intensity of OLEDs," Proceedings of the 37th Regular Meeting of the Organic EL Symposium, S2-3 (2023)

[0004] The present disclosure provides a charge measurement method, a program, and a charge measurement system that make it easy to evaluate the light-emitting characteristics of a light-emitting element.

[0005] To achieve the above object, a charge measurement method according to one aspect of the present disclosure includes a light-emitting element having a pair of electrodes and a light-emitting layer disposed between the pair of electrodes, and acquires first data indicating a change in current flowing through the light-emitting element by applying a voltage between the pair of electrodes that periodically changes and whose polarity periodically reverses. The charge measurement method also acquires second data indicating a change in the light-emitting intensity of the light-emitting element due to the application of the voltage. The charge measurement method measures charge that does not contribute to light emission in the light-emitting element based on the first data and the second data.

[0006] In order to achieve the above object, a program according to one aspect of the present disclosure causes one or more processors to execute the charge measurement method.

[0007] To achieve the above object, a charge measurement system according to one aspect of the present disclosure includes a first acquisition unit, a second acquisition unit, and a charge measurement unit. The first acquisition unit acquires first data indicating a change in current flowing through a light-emitting element having a pair of electrodes and a light-emitting layer disposed between the pair of electrodes, the change being obtained by applying a voltage between the pair of electrodes that periodically changes and whose polarity periodically reverses. The second acquisition unit acquires second data indicating a change in the light-emitting intensity of the light-emitting element due to the application of the voltage. The charge measurement unit measures charges that do not contribute to light emission in the light-emitting element based on the first data and the second data.

[0008] The charge measurement method and the like according to the present disclosure have the advantage that the light-emitting characteristics of a light-emitting element can be easily evaluated.

[0009] FIG. 1 is a schematic diagram showing an overall configuration including a charge measurement system according to an embodiment. FIG. 2 is an explanatory diagram of charge measurement by a charge measurement unit of the charge measurement system according to an embodiment. FIG. 3 is a flowchart showing an example of operation of the charge measurement system according to an embodiment. FIG. 4 is a diagram showing measurement results of a blue organic light-emitting diode. FIG. 5 is a diagram showing measurement results of a red organic light-emitting diode. FIG. 6 is a diagram showing measurement results of a green organic light-emitting diode. FIG. 7 is a diagram showing measurement results of charges of a blue organic light-emitting diode, a red organic light-emitting diode, and a green organic light-emitting diode.

[0010] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0011] The embodiments described below are all comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement positions and connection forms of the components, etc. shown in the following embodiments are merely examples and are not intended to limit the scope of the claims. Furthermore, among the components in the following embodiments, components that are not described in the independent claims that represent the highest concepts are described as optional components. Furthermore, each drawing is not necessarily an exact illustration. In each drawing, substantially identical components are assigned the same reference numerals, and duplicate explanations are omitted or simplified.

[0012] 1 is a schematic diagram showing an overall configuration including a charge measurement system 200 according to an embodiment. The charge measurement system 200 is a system for measuring charges of a light-emitting element 100, more specifically, charges that do not contribute to light emission in the light-emitting element 100. Here, the light-emitting element 100 is an element that emits light by spontaneous emission or an element that emits light by stimulated emission due to current excitation.

[0013] As shown in FIG. 1 , the light-emitting element 100 includes a pair of electrodes 11 and 12 and a light-emitting layer 13 disposed between the pair of electrodes 11 and 12. In the embodiment, the light-emitting element 100 is an organic light-emitting diode and includes a pair of electrodes 11 and 12, a light-emitting layer 13 including a hole injection layer, a hole transport layer, and an electron transport layer, and an electron injection layer. The light-emitting element 100 may further include an electron blocking layer and a hole blocking layer. Note that FIG. 1 illustrates only the light-emitting layer 13 between the pair of electrodes 11 and 12, and does not illustrate carrier transport layers such as the hole injection layer, the hole transport layer, and the electron injection layer. The light-emitting element 100 may be a single-type light-emitting element having only one light-emitting layer, or a tandem-type light-emitting element having two or more light-emitting layers.

[0014] The first electrode 12, one of the pair of electrodes 11 and 12, is an anode and is mainly made of ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide). The thickness of the first electrode 12 is, for example, several tens of nanometers to several hundred nanometers.

[0015] The second electrode 11, which is the other of the pair of electrodes 11, 12, is a cathode and is mainly made of magnesium (Mg), silver (Ag), aluminum (Al), and alloys thereof. The thickness of the second electrode 11 is, for example, several nanometers to several hundred nanometers.

[0016] The hole injection layer is laminated on one surface of the first electrode 12 in the thickness direction (the upper surface in FIG. 1), and is generally formed using organic or inorganic compound-based constituent materials. An example of an organic compound-based material is a mixture system in which an electron-accepting material is added in the range of approximately 1 to 20% to a triarylamine-based hole transport material. An example of an electron-accepting material is mainly tetracyanoquinodimethane tetrafluoride. An example of an inorganic compound is MoO ３ (molybdenum(VI) oxide) is an example. The thickness of the hole injection layer is in the range of, for example, a few tenths of a nanometer to several tens of nanometers.

[0017] The hole transport layer is laminated on one surface of the hole injection layer in the thickness direction (the upper surface in FIG. 1 ) and is formed using a triarylamine compound such as α-NPD (N,N'-bis(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine) as its constituent material. The thickness of the hole transport layer is, for example, in the range of several tens of nanometers to several hundred nanometers. When an electron blocking layer is used, it is basically made of the same material as the material constituting the hole transport layer or a carbazole compound, and the work function is adjusted appropriately. The thickness of the electron blocking layer is, for example, in the range of several nanometers to several tens of nanometers.

[0018] The light-emitting layer 13 is laminated on one surface (top surface in FIG. 1 ) in the thickness direction of the hole transport layer or the electron blocking layer. For example, a dopant material responsible for emitting light is added to a host material in a range of 0.1 to several percent. Examples of the host material include a hole transport material, an electron transport material, or a mixture of a hole transport material and an electron transport material. Examples of the dopant material responsible for emitting light include fluorescent materials, phosphorescent materials, and thermally activated delayed fluorescence (TADF) materials. Examples of fluorescent materials include pyrene-, anthracene-, perylene-, quinacridone-, coumarin-, and rubrene-based compounds. Examples of phosphorescent materials include iridium-, palladium-, or platinum-based complexes. Examples of TADF materials include materials having both a donor and an acceptor within a single molecule. Examples of donors include carbazole groups, and examples of acceptors include cyanobenzene groups. The thickness of the light-emitting layer is, for example, in the range of several nm to several tens of nm.

[0019] The electron transport layer is laminated on one surface of the light-emitting layer in the thickness direction and is formed mainly from an oxadiazole-based or phenanthroline-based organic compound. A mixture of the organic compound and a lithium compound such as lithium quinoline (Liq) or lithium fluoride (LiF) may also be used. The mixing ratio of the electron-transporting organic compound to the lithium compound is typically in the range of 1:9 to 9:1. The thickness of the electron transport layer is, for example, in the range of several nanometers to several tens of nanometers. Furthermore, if a hole blocking layer is incorporated, the hole blocking layer is formed between the light-emitting layer and the electron transport layer. The material of the hole blocking layer is the same as that of the electron transport layer, and the work function is adjusted appropriately. The thickness of the hole blocking layer is, for example, in the range of several nanometers to several tens of nanometers.

[0020] The electron injection layer is laminated between one surface in the thickness direction of the light-emitting layer 13 (the upper surface in FIG. 1 ) including the electron transport layer and one surface in the thickness direction of the second electrode 11 (the lower surface in FIG. 1 ), and is formed using LiF (lithium fluoride) or ytterbium (Yb) as its constituent material. The thickness of the electron injection layer is, for example, in the range of a few tenths of a nanometer to several nanometers.

[0021] The charge measurement system 200 is an information processing device and includes a processor and a memory. The processor executes a program stored in the memory to function as the charge measurement system 200. In the embodiment, the information processing device is, for example, a desktop or laptop personal computer. In addition to a personal computer, the information processing device may also be a general-purpose information processing device such as a smartphone or a tablet terminal. As shown in FIG. 1 , the charge measurement system 200 includes a first acquisition unit 21, a second acquisition unit 22, and a charge measurement unit 23.

[0022] The first acquisition unit 21 acquires first data indicating a change in current flowing through the light-emitting element 100, which is obtained by applying a voltage that periodically changes and whose polarity periodically reverses between the pair of electrodes 11, 12 in the light-emitting element 100. In the embodiment, the first acquisition unit 21 acquires the first data by sequentially acquiring measurement results of a displacement current measured by a current measurement system 300, which will be described later.

[0023] The second acquisition unit 22 acquires second data indicating a change in the emission intensity of the light-emitting element 100 due to application of the voltage (i.e., the voltage applied to the light-emitting element 100 by the current measurement system 300). In the embodiment, the second acquisition unit 22 acquires the second data by sequentially acquiring measurement results of the emission intensity measured by the emission intensity measurement system 400, which will be described later.

[0024] The charge measuring unit 23 measures the charge that does not contribute to light emission in the light-emitting element 100 based on the first data acquired by the first acquiring unit 21 and the second data acquired by the second acquiring unit 22. In the embodiment, the charge measuring unit 23 measures the charge that does not contribute to light emission in the light-emitting element 100 based on the difference between the current density Id1 of the first current (see FIG. 2 ) and the current density Id2 of the second current (see FIG. 2 ).

[0025] Here, the first current is the current flowing through the light-emitting element 100 at time t1 (see FIG. 2 ) when charge injection into the light-emitting element 100 based on the first data begins. The charge injection here refers to behavior near a current change that occurs due to the recombination of charges (electrons and holes) in the light-emitting element 100. The second current is the current flowing through the light-emitting element 100 at time t2 (see FIG. 2 ) when light emission from the light-emitting element 100 begins based on the second data. The light emission start time t2 here does not refer to the time when a person becomes able to visually confirm the light emission of the light-emitting element 100, but rather refers to the time when the light emission intensity of the light-emitting element 100 becomes able to be measured by the light emission intensity measuring system 400.

[0026] Furthermore, in the embodiment, the charge measuring unit 23 measures the amount of charge that does not contribute to light emission in the light-emitting element 100 by integrating the difference between the current density Id1 of the first current and the current density Id2 of the second current over time.

[0027] The method of measuring charges by the charge measuring unit 23 will be described in detail below with reference to FIG. 2. FIG. 2 is an explanatory diagram of charge measurement by the charge measuring unit 23 of the charge measuring system 200 according to the embodiment. FIG. 2 is a diagram showing measurement results by the current measuring system 300 and measurement results by the emission intensity measuring system 400. In FIG. 2, the vertical axis on the left represents the current density (unit: mA / cm) of the current flowing through the light emitting element 100. ２"), and the vertical axis on the right represents the standardized intensity of light emitted by the light-emitting element 100, that is, the light emission intensity (unit: "a.u. (Arbitrary Unit)"). Also in FIG. 2, the horizontal axis represents the voltage (unit: "V") applied between the pair of electrodes 11, 12 of the light-emitting element 100. Also in FIG. 2, the solid line L1 represents the measurement results of the current measurement system 300, and the dashed line L2 represents the measurement results of the light emission intensity measurement system 400.

[0028] In the embodiment, the voltage applied to the pair of electrodes 11 and 12 is a periodically changing voltage, as described above. Therefore, the horizontal axis can also be said to represent time. For example, in the embodiment, the voltage applied to the pair of electrodes 11 and 12 changes at a rate of 0.02 V per second, as described below. Therefore, in the example shown in FIG. 2 , the start time t1 of charge injection in the light-emitting element 100 is approximately 100 (= 2 / 0.02) seconds, because the voltage applied to the pair of electrodes 11 and 12 at time t1 is approximately 2 V. Also, in the example shown in FIG. 2 , the start time t2 of light emission from the light-emitting element 100 is approximately 110 (= 2.2 / 0.02) seconds, because the voltage applied to the pair of electrodes 11 and 12 at time t2 is approximately 2.2 V.

[0029] The charge measurement unit 23 calculates the start time t1 of charge injection in the light-emitting element 100 based on the first data acquired by the first acquisition unit 21, i.e., the change in current (here, the change in current density) flowing through the light-emitting element 100. Specifically, the charge measurement unit 23 calculates the time when the current density changes sharply in association with the start of charge injection in the light-emitting element 100 as the start time t1 of charge injection in the light-emitting element 100. For example, the charge measurement unit 23 calculates the time when the differential value of the current density becomes equal to or greater than a threshold value for the first time since measurement by the current measurement system 300 started as the start time t1 of charge injection in the light-emitting element 100.

[0030] Furthermore, the charge measuring unit 23 calculates the start time t2 of light emission of the light-emitting element 100 based on the second data acquired by the second acquiring unit 22, i.e., the change in the light emission intensity of the light-emitting element 100. Specifically, the charge measuring unit 23 calculates the start time t2 of light emission of the light-emitting element 100 as the time when the measured light emission intensity is obtained for the first time since the emission intensity measuring system 400 started measuring.

[0031] Here, when electrons and holes recombine in the light-emitting layer 13 of the light-emitting element 100, electrically neutral excitons are generated. The excitons then emit light according to the quantum efficiency of light emission and undergo radiative deactivation. In this way, it is thought that the light-emitting element 100 emits light in response to recombination. However, in reality, as shown in FIG. 2 , there may be a discrepancy between the start time t1 of charge injection into the light-emitting element 100 and the start time t2 of light emission from the light-emitting element 100. For this reason, there is a discrepancy between the injection of charge into the light-emitting element 100 and the light emission from the light-emitting element 100, and it is thought that excitons generated by recombination do not emit light, that is, charges that do not contribute to the light emission of the light-emitting element 100 exist.

[0032] Therefore, the charge measurement unit 23 measures the charge that does not contribute to light emission in the light-emitting element 100 based on the difference between the current density Id1 of the first current, i.e., the current density Id1 of the current flowing through the light-emitting element 100 at the start time t1 of charge injection into the light-emitting element 100, and the current density Id2 of the second current, i.e., the current density Id2 of the current flowing through the light-emitting element 100 at the start time t2 of light emission of the light-emitting element 100. For example, the charge measurement unit 23 measures that the greater the difference between the current density Id1 of the first current and the current density Id2 of the second current, the more charge that does not contribute to light emission in the light-emitting element 100, and that the smaller the difference, the fewer charge that does not contribute to light emission in the light-emitting element 100.

[0033] In the embodiment, the charge measuring unit 23 measures the amount of charge that does not contribute to light emission in the light-emitting element 100 by integrating over time the difference between the current density Id1 of the first current and the current density Id2 of the second current. Specifically, the charge measuring unit 23 measures the amount of charge that does not contribute to light emission in the light-emitting element 100 (i.e., the area of ​​the region A1) by integrating over time the current density of the current flowing through the light-emitting element 100 in the section from the start time t1 of charge injection into the light-emitting element 100 to the start time t2 of light emission of the light-emitting element 100, as shown in FIG.

[0034] The charge measuring unit 23 may calculate the number of charges by dividing the amount of charges that do not contribute to light emission in the light emitting element 100 calculated by the above integration by the elementary charge.

[0035] 2. Current Measurement System Next, a current measurement system 300 according to an embodiment will be described with reference to Fig. 1. The current measurement system 300 includes a voltage application unit 31 and a current measurement unit 32.

[0036] The voltage application unit 31 is connected between the pair of electrodes 11, 12 of the light-emitting element 100, and applies a voltage that changes periodically and whose polarity periodically reverses between the pair of electrodes 11, 12. In the embodiment, the voltage application unit 31 is a function generator that generates a triangular wave voltage as a voltage that changes periodically and whose polarity periodically reverses, and applies the generated triangular wave voltage between the pair of electrodes 11, 12. As an example, the triangular wave voltage has a frequency of 0.001 Hz and an amplitude of ±5 V. Therefore, in the embodiment, the voltage applied between the pair of electrodes 11, 12 changes at a rate of 0.02 V per second.

[0037] Note that the frequency and amplitude of the triangular wave voltage are merely examples and are not limited to these. However, it is preferable that the frequency of the triangular wave voltage is relatively low. This is because, if the frequency of the triangular wave voltage becomes high, it becomes difficult to observe the difference between the start time t1 of charge injection into the light-emitting element 100 and the start time t2 of light emission from the light-emitting element 100.

[0038] The current measuring unit 32 measures the current flowing through the light-emitting element 100 due to the application of a voltage by the voltage applying unit 31. In this embodiment, the current measuring unit 32 includes an I-V converter 321 and a voltmeter 322. The I-V converter 321 is connected in series with the pair of electrodes 11, 12 of the light-emitting element 100, and converts the current flowing through the light-emitting element 100 into a voltage. The voltmeter 322 measures the voltage converted by the I-V converter 321. In other words, the current measuring unit 32 measures the current flowing through the light-emitting element 100 by measuring the voltage converted by the I-V converter 321 with the voltmeter 322.

[0039] 3. Emission Intensity Measurement System Next, an emission intensity measurement system 400 according to an embodiment will be described with reference to Fig. 1. The emission intensity measurement system 400 includes a photodiode 41 and an emission intensity measurement unit 42.

[0040] The photodiode 41 is positioned opposite the light emitting surface of the light emitting element 100, and when it receives light emitted by the light emitting element 100, it outputs a current corresponding to the intensity of the received light (i.e., the light emitting intensity of the light emitting element 100).

[0041] The emission intensity measurement unit 42 measures the emission intensity of the light-emitting element 100 by measuring the current output from the photodiode 41. In this embodiment, the emission intensity measurement unit 42 includes an IV converter 421 and a voltmeter 422. The IV converter 421 is connected to the photodiode 41 and converts the current output from the photodiode 41 into a voltage. The voltmeter 422 measures the voltage converted by the IV converter 421. In other words, the emission intensity measurement unit 42 measures the current output from the photodiode 41 by measuring the voltage converted by the IV converter 421 with the voltmeter 422. The current output from the photodiode 41 has a correlation with the emission intensity of the light-emitting element 100, and therefore the emission intensity measurement unit 42 can indirectly measure the emission intensity of the light-emitting element 100.

[0042] The emission intensity of the light-emitting element 100 can also be measured using, for example, a general luminance meter. However, a general luminance meter has insufficient resolution for measuring the emission start time t2 of the light-emitting element 100. Therefore, in the embodiment, the emission intensity measurement unit 42 detects the emission of the light-emitting element 100 using the photodiode 41 and measures a current corresponding to the detected emission intensity of the light-emitting element 100, thereby indirectly measuring the emission intensity of the light-emitting element 100. In this embodiment, although the measurement result of the emission intensity measurement unit 42 is different from the emission intensity of the light-emitting element 100 in the strict sense, there is an advantage in that it is easy to ensure the resolution required to measure the emission start time t2 of the light-emitting element 100.

[0043] 4. Operation The operation (charge measurement method) of the charge measurement system 200 according to the embodiment will be described below with reference to Fig. 3. Fig. 3 is a flowchart showing an example of the operation of the charge measurement system 200 according to the embodiment.

[0044] First, the first acquisition unit 21 of the charge measurement system 200 acquires first data (S1). Here, as already described, the first acquisition unit 21 acquires the first data by sequentially acquiring measurement results of the displacement current measured by the current measurement system 300.

[0045] Furthermore, the second acquisition unit 22 of the charge measurement system 200 acquires second data (S2). Here, as already described, the second acquisition unit 22 acquires the second data by sequentially acquiring the measurement results of the luminescence intensity measured by the luminescence intensity measurement system 400. Here, steps S1 and S2 are executed simultaneously in parallel. That is, the start point of measurement by the current measurement system 300 and the start point of measurement by the luminescence intensity measurement system 400 are the same.

[0046] Next, the charge measurement unit 23 of the charge measurement system 200 measures the charge that does not contribute to light emission in the light-emitting element 100 based on the first data acquired in step S1 and the second data acquired in step S2 (S3). Here, as already described, the charge measurement unit 23 measures the amount of charge that does not contribute to light emission in the light-emitting element 100 by time-integrating the difference between the current density Id1 of the first current and the current density Id2 of the second current.

[0047] [5. Advantages] Advantages of the charge measurement system 200 (charge measurement method) according to the embodiment will be described below. As described above, the charge measurement system 200 according to the embodiment measures the charge that does not contribute to light emission in the light-emitting element 100 based on the first data (i.e., data indicating a change in the current flowing through the light-emitting element 100) and the second data (i.e., data indicating a change in the light-emitting intensity of the light-emitting element 100). Therefore, the charge measurement system 200 according to the embodiment has the advantage that it is easy to evaluate the light-emitting characteristics of the light-emitting element 100, such as the degree of deterioration of the light-emitting element 100, by referring to the measured charge that does not contribute to light emission in the light-emitting element 100.

[0048] Below, we will explain the results of an experiment conducted on the correlation between the charge that does not contribute to light emission in light-emitting element 100 and the degree of deterioration of light-emitting element 100. In the experiment, a blue organic light-emitting diode, a red organic light-emitting diode, and a green organic light-emitting diode were used as light-emitting elements 100 to be measured, and the charge that does not contribute to light emission in the initial state and the charge that does not contribute to light emission in the deteriorated state were measured using charge measurement system 200.

[0049] Here, the initial state refers to a state in which the light-emitting element 100 has not yet been used. The deteriorated state refers to a state in which the light-emitting element 100 has deteriorated due to use. In this experiment, the luminance of the light-emitting element 100 in the deteriorated state was approximately 90% of the luminance of the light-emitting element 100 in the initial state. The light-emitting element 100 in the deteriorated state was prepared by performing an accelerated test on the light-emitting element 100 in the initial state. The accelerated test was performed by continuously flowing a relatively large current through the light-emitting element 100 for a predetermined period (e.g., several thousand hours).

[0050] 4 shows the measurement results of a blue organic light-emitting diode. The device configuration of the blue organic light-emitting diode is as described for the light-emitting element 100. (a) of FIG. 4 shows the measurement results of a blue organic light-emitting diode in an initial state using the current measurement system 300, and (b) of FIG. 4 shows the measurement results of a blue organic light-emitting diode in a deteriorated state using the current measurement system 300.

[0051] Fig. 5 shows the measurement results of a red organic light-emitting diode. The device configuration of the red organic light-emitting diode is as described for the light-emitting element 100. Fig. 5(a) shows the measurement results of a red organic light-emitting diode in an initial state using the current measurement system 300, and Fig. 5(b) shows the measurement results of a red organic light-emitting diode in a deteriorated state using the current measurement system 300.

[0052] 6A and 6B are diagrams showing measurement results of a green organic light-emitting diode. The device configuration of the green organic light-emitting diode is the same as that described for the light-emitting element 100. Fig. 6A shows the measurement results of a green organic light-emitting diode in an initial state using the current measurement system 300, and Fig. 6B shows the measurement results of a green organic light-emitting diode in a deteriorated state using the current measurement system 300.

[0053] 4, 5, and 6, the vertical axis represents the current (unit: "A") flowing through the organic light-emitting diode, and the horizontal axis represents the voltage (unit: "V") applied to a pair of electrodes of the organic light-emitting diode. In addition, in each of Fig. 4, 5, and 6, the solid line L3 represents the measurement results of the current measurement system 300, and the area of ​​the region A2 represents the amount of charge that does not contribute to light emission, measured by the charge measurement system 200.

[0054] 4, 5, and 6, although it appears that there are two solid lines L3, in reality there is only one line, and the portions not shown are connected. That is, the upper solid line L3 represents the measurement results of the current measurement system 300 when the voltage applied to the pair of electrodes is increasing, and the lower solid line L3 represents the measurement results of the current measurement system 300 when the voltage applied to the pair of electrodes is decreasing.

[0055] As shown in Fig. 4, in the blue organic light-emitting diode in the initial state, there is almost no charge that does not contribute to light emission, but in the blue organic light-emitting diode in the deteriorated state, the charge that does not contribute to light emission increases. Also, as shown in Fig. 5, in the red organic light-emitting diode in the initial state, there is almost no charge that does not contribute to light emission, but in the red organic light-emitting diode in the deteriorated state, the charge that does not contribute to light emission increases. Also, as shown in Fig. 6, in the green organic light-emitting diode in the initial state, there is almost no charge that does not contribute to light emission, but in the green organic light-emitting diode in the deteriorated state, the charge that does not contribute to light emission increases.

[0056] 7 shows the measurement results of the electric charges of a blue organic light-emitting diode, a red organic light-emitting diode, and a green organic light-emitting diode. In FIG. 7 , "Blue initial" represents the blue organic light-emitting diode in its initial state, "Blue degraded" represents the blue organic light-emitting diode in its degraded state, "Red initial" represents the red organic light-emitting diode in its initial state, "Red degraded" represents the red organic light-emitting diode in its degraded state, "Green initial" represents the green organic light-emitting diode in its initial state, and "Green degraded" represents the green organic light-emitting diode in its degraded state. Also in FIG. 7 , "charge injection voltage" represents the voltage applied to a pair of electrodes at the start of charge injection into the organic light-emitting diode, and "light-emitting voltage" represents the voltage applied to a pair of electrodes at the start of light emission from the organic light-emitting diode. Also in FIG. 7 , "charge amount" represents the amount of charge that does not contribute to light emission in the organic light-emitting diode, and "number of charges" represents the number of such charges.

[0057] 7, the amount of charge that does not contribute to light emission increases due to deterioration of the organic light-emitting diode for all emitting colors. Thus, there is a correlation between the amount of charge that does not contribute to light emission in the organic light-emitting diode and the degree of deterioration of the organic light-emitting diode.

[0058] While the charge measurement system 200 (charge measurement method) according to the present disclosure has been described above based on the embodiment, the present disclosure is not limited to the embodiment. As long as it does not deviate from the gist of the present disclosure, various modifications conceivable by a person skilled in the art to the embodiment, or other modifications constructed by combining some of the components of the embodiment, are also included within the scope of the present disclosure.

[0059] In the embodiment, the light-emitting element 100 to be measured by the charge measurement method (charge measurement system 200) may be a light-emitting device with a so-called side-by-side structure, in which materials emitting red, green, and blue light are respectively formed on a substrate by vapor deposition. The light-emitting element 100 may also be a light-emitting device in which, for example, three white organic light-emitting diodes are combined with red, green, and blue color filters. The light-emitting element 100 may also be a light-emitting device with a so-called tandem structure, in which a plurality of light-emitting units and charge generation layers (hole transport layer, intermediate electrode, and electron transport layer) are stacked in series, with each light-emitting unit having three light-emitting layers, each divided into red, blue, and green. The light-emitting element 100 may also be a light-emitting device using, for example, quantum dots as an electroluminescent material. The light-emitting element 100 may also be a light-emitting device in which, for example, a plurality of blue organic light-emitting diodes are each combined with a quantum dot for color conversion. Of course, the light emitting device 100 is not limited to the light emitting devices listed above, but may be other light emitting devices.

[0060] In the embodiment, the charge measurement system 200 is realized by a single information processing device, but this is not limiting. For example, the charge measurement system 200 may be realized by multiple information processing devices. As an example, the charge measurement system 200 may be realized by an information processing device that executes the function of the first acquisition unit 21, an information processing device that executes the function of the second acquisition unit 22, and an information processing device that executes the function of the charge measurement unit 23 cooperating with each other.

[0061] In addition, in the embodiments, the charge measurement method may be realized by a computer program, or may be realized by a computer-readable non-transitory recording medium such as a semiconductor memory in which the computer program is stored.

[0062] (Summary) As described above, the charge measurement method according to the first aspect of the present disclosure involves obtaining first data indicating a change in current flowing through light-emitting element 100, which includes a pair of electrodes 11, 12 and a light-emitting layer 13 disposed between the pair of electrodes 11, 12, by applying a voltage that periodically changes and periodically reverses polarity between the pair of electrodes 11, 12 (S1). The charge measurement method also obtains second data indicating a change in the light-emitting intensity of light-emitting element 100 as the voltage is applied (S2). The charge measurement method then measures the charge that does not contribute to light emission in light-emitting element 100 based on the first and second data (S3).

[0063] This has the advantage that the light-emitting characteristics of the light-emitting element 100, such as the degree of degradation of the light-emitting element 100, can be easily evaluated by referring to the charge that does not contribute to light emission in the measured light-emitting element 100.

[0064] In addition, in the charge measurement method according to the second aspect of the present disclosure, in the first aspect, charge that does not contribute to light emission in the light-emitting element 100 is measured based on the difference between the current density Id1 of the first current and the current density Id2 of the second current. The first current is the current flowing through the light-emitting element 100 at the start time t1 of charge injection into the light-emitting element 100 based on the first data. The second current is the current flowing through the light-emitting element 100 at the start time t2 of light emission of the light-emitting element 100 based on the second data.

[0065] This has the advantage that the light-emitting characteristics of the light-emitting element 100, such as the degree of degradation of the light-emitting element 100, can be easily evaluated by referring to the charge that does not contribute to light emission in the measured light-emitting element 100.

[0066] In addition, in the charge measurement method according to the third aspect of the present disclosure, in the second aspect, the amount of charge that does not contribute to light emission in the light-emitting element 100 is measured by integrating over time the difference between the current density Id1 of the first current and the current density Id2 of the second current.

[0067] This has the advantage that by referring to the amount of charge that does not contribute to light emission in the measured light-emitting element 100, it is easy to quantitatively evaluate the light-emitting characteristics of the light-emitting element 100, such as the degree of deterioration of the light-emitting element 100.

[0068] A program according to a fourth aspect of the present disclosure causes one or more processors to execute the charge measurement method according to any one of the first to third aspects.

[0069] This has the advantage that the light-emitting characteristics of the light-emitting element 100, such as the degree of degradation of the light-emitting element 100, can be easily evaluated by referring to the charge that does not contribute to light emission in the measured light-emitting element 100.

[0070] Moreover, a charge measurement system 200 according to a fifth aspect of the present disclosure includes a first acquisition unit 21, a second acquisition unit 22, and a charge measurement unit 23. The first acquisition unit 21 acquires first data indicating a change in current flowing through a light-emitting element 100 having a pair of electrodes 11, 12 and a light-emitting layer 13 disposed between the pair of electrodes 11, 12, the first data being obtained by applying a voltage that periodically changes and whose polarity periodically reverses between the pair of electrodes 11, 12. The second acquisition unit 22 acquires second data indicating a change in the light-emitting intensity of the light-emitting element 100 resulting from the application of the voltage. The charge measurement unit 23 measures charges that do not contribute to light emission in the light-emitting element 100 based on the first data and the second data.

[0071] This has the advantage that the light-emitting characteristics of the light-emitting element 100, such as the degree of degradation of the light-emitting element 100, can be easily evaluated by referring to the charge that does not contribute to light emission in the measured light-emitting element 100.

[0072] The present disclosure can be used to measure the charge on a light emitting element, such as an organic light emitting diode.

[0073] 100 Light-emitting element 11 Second electrode 12 First electrode 13 Light-emitting layer 200 Charge measurement system 21 First acquisition unit 22 Second acquisition unit 23 Charge measurement unit 300 Current measurement system 31 Voltage application unit 32 Current measurement unit 321 I-V converter 322 Voltmeter 400 Emission intensity measurement system 41 Photodiode 42 Emission intensity measurement unit 421 I-V converter 422 Voltmeter A1, A2 Region Id1 Current density of first current Id2 Current density of second current L1, L3 Solid line L2 Dashed line t1 Start time of charge injection t2 Start time of emission

Claims

1. A charge measurement method comprising the steps of: acquiring first data indicating a change in current flowing through a light-emitting element having a pair of electrodes and a light-emitting layer disposed between the pair of electrodes, the first data being obtained by applying a voltage between the pair of electrodes that changes periodically and whose polarity is periodically reversed; acquiring second data indicating a change in the light-emitting intensity of the light-emitting element due to the application of the voltage; and measuring charges that do not contribute to light emission in the light-emitting element based on the first data and the second data.

2. The charge measurement method according to claim 1, wherein charges that do not contribute to light emission in the light-emitting element are measured based on the difference between the current density of a first current flowing through the light-emitting element at the start of charge injection into the light-emitting element based on the first data and the current density of a second current flowing through the light-emitting element at the start of light emission from the light-emitting element based on the second data.

3. The charge measurement method according to claim 2, wherein the amount of charge that does not contribute to light emission in the light-emitting element is measured by integrating the difference between the current density of the first current and the current density of the second current with respect to time.

4. A program causing one or more processors to execute the charge measurement method according to any one of claims 1 to 3.

5. A charge measurement system comprising: a first acquisition unit that acquires first data indicating a change in current flowing through a light-emitting element having a pair of electrodes and a light-emitting layer disposed between the pair of electrodes, the first data being obtained by applying a voltage between the pair of electrodes that changes periodically and whose polarity is periodically reversed; a second acquisition unit that acquires second data indicating a change in the light-emitting intensity of the light-emitting element due to the application of the voltage; and a charge measurement unit that measures charges that do not contribute to light emission in the light-emitting element based on the first data and the second data.

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