Characterization method for organic light-emitting diode (OLED) devices

Abstract

An organic EL device (100) comprises a pair of electrodes (11, 12), a light emitting layer (15) disposed between the pair of electrodes (11, 12), and a carrier transport layer (positive hole transport layer (14)) disposed between one electrode (11) of the pair of electrodes (11, 12) and the light emitting layer (15). The carrier transport layer (positive hole transport layer (14)) contains ions (cations (17)) which are from a material different from a formation material forming the carrier transport layer (positive hole transport layer (14)) and have the same polarity as that of the carriers (positive holes) to be transported by the carrier transport layer (positive hole transport layer (14)).

Description

[Technical Field]

[0001] The present disclosure relates to an organic electroluminescence (EL) device, a method for manufacturing an organic EL device, and a method for evaluating the characteristics of an organic EL device. [Background technology]

[0002] Patent Document 1 discloses an optical input type organic EL element. This organic EL element has a structure in which a light-emitting display section made up of a light-emitting layer and a carrier injection layer, and a photoresponsive section are stacked between a pair of electrodes. This organic EL element emits light in response to information input to the photoresponsive section. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-175420 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides an organic EL device whose characteristics, including luminous efficiency, are likely to be improved, a method for manufacturing an organic EL device, and a method for evaluating the characteristics of an organic EL device. [Means for solving the problem]

[0005] To achieve the above object, an organic EL device according to one embodiment of the present disclosure includes a pair of electrodes, a light-emitting layer disposed between the pair of electrodes, and a carrier transport layer disposed between one of the pair of electrodes and the light-emitting layer, the carrier transport layer being derived from a material different from that constituting the carrier transport layer and containing ions of the same polarity as the carriers targeted by the carrier transport layer.

[0006] In order to achieve the above object, a method for manufacturing an organic EL device according to one embodiment of the present disclosure is a method for manufacturing an organic EL device including a pair of electrodes, a light-emitting layer disposed between the pair of electrodes, and a carrier transport layer disposed between one of the pair of electrodes and the light-emitting layer, the method including the step of adding, to the carrier transport layer, ions derived from a material different from a constituent material of the carrier transport layer and having the same polarity as the carriers targeted by the carrier transport layer.

[0007] To achieve the above object, a characteristic evaluation method for an organic EL device according to one embodiment of the present disclosure includes a pair of electrodes, a light-emitting layer disposed between the pair of electrodes, and a carrier transport layer disposed between one of the pair of electrodes and the light-emitting layer, the method including a step of performing a displacement current measurement. The displacement current measurement includes a measuring element including a constituent material constituting the carrier transport layer, an insulating layer disposed on only one of both sides of the constituent material in the thickness direction, and a pair of electrodes sandwiching the constituent material and the insulating layer in the thickness direction. A voltage that periodically changes and periodically reverses polarity is applied between the pair of electrodes, and ions contained in the constituent material are measured based on the current flowing through the measuring element as a result of the application of the voltage. The ions are derived from a material different from the constituent material and have the same polarity as the carriers targeted by the carrier transport layer. [Effects of the Invention]

[0008] The organic EL device according to the present disclosure has the advantage that its characteristics, including luminous efficiency, can be easily improved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing the structure of an organic EL device according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of a measurement system according to an embodiment. [Figure 3]FIG. 3 is a schematic diagram showing a measuring element according to an embodiment. [Figure 4] FIG. 4 is a flowchart showing an example of displacement current measurement according to the embodiment. [Figure 5] FIG. 5 is a diagram showing an example of measurement results of a material to be measured before and after sublimation purification, using displacement current measurement according to the embodiment. [Figure 6] FIG. 6 is a diagram showing a comparative example of measurement results of a material to be measured before and after sublimation purification, using displacement current measurement according to the embodiment. [Figure 7] FIG. 7 is a flowchart showing an example of a method for manufacturing an organic EL device according to an embodiment. [Figure 8] FIG. 8 is a diagram showing the measurement results of the driving voltage in the initial characteristics of the organic EL device according to the embodiment. [Figure 9] FIG. 9 is a diagram showing the measurement results of the emission spectrum in the initial characteristics of the organic EL device according to the embodiment. [Figure 10] FIG. 10 is a diagram showing the measurement results of the current efficiency in the initial characteristics of the organic EL device according to the embodiment. [Figure 11] FIG. 11 is a diagram showing the measurement results of the external quantum efficiency in the initial characteristics of the organic EL device according to the embodiment. [Figure 12] FIG. 12 is a diagram showing the measurement results of the driving voltage in the degradation analysis of the organic EL device according to the embodiment. [Figure 13] FIG. 13 is a diagram showing the measurement results of the luminance of emitted light in the degradation analysis of the organic EL device according to the embodiment. [Figure 14] FIG. 14 is a diagram showing the measurement results of current efficiency in degradation analysis of the organic EL device according to the embodiment. [Figure 15] FIG. 15 is a diagram showing the measurement results of power efficiency in the degradation analysis of the organic EL device according to the embodiment. [Figure 16] FIG. 16 is an enlarged view of the measurement results in the case where the driving time of the organic EL device in FIG. 15 is 0 to 100 hours. [Figure 17] FIG. 17 is an enlarged view of the measurement results in the case where the driving time of the organic EL device in FIG. 15 is 1500 to 2000 hours. DETAILED DESCRIPTION OF THE INVENTION

[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 redundant explanations are omitted or simplified.

[0012] [1. Organic EL devices] 1 is a schematic diagram showing the structure of an organic EL device 100 according to an embodiment. In this embodiment, the organic EL device 100 is an organic light-emitting diode. In this embodiment, the organic EL device 100 has a configuration in which holes as carriers are in excess.

[0013] 1, the organic EL device 100 includes a pair of electrodes 11 and 12, a hole injection layer 13, a hole transport layer 14, an emitting layer 15 including an electron transport layer, and an electron injection layer 16. In the embodiment, the hole transport layer 14 and the electron transport layer correspond to a first carrier transport layer and a second carrier transport layer. In the embodiment, the first carrier transport layer is the hole transport layer 14, and the second carrier transport layer is the electron transport layer.

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

[0015] The second electrode 12, which is the other of the pair of electrodes 11, 12, is a cathode made of aluminum (Al) as its constituent material. The thickness of the second electrode 12 is, for example, several tens to several hundred nanometers.

[0016] The hole injection layer 13 is laminated on one surface of the first electrode 11 in the thickness direction (the lower surface in FIG. 1), and is formed using MoO3 (molybdenum (VI) oxide) as a constituent material. The thickness of the hole injection layer 13 is, for example, a few tenths of a nanometer.

[0017] The hole transport layer 14 is laminated on one surface of the hole injection layer 13 in the thickness direction (the lower surface in FIG. 1 ), and is formed using α-NPD (N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine) as its constituent material. In other words, α-NPD is the constituent material of the hole transport layer 14 (i.e., the first carrier transport layer). The thickness of the hole transport layer 14 is, for example, several tens of nanometers. In other words, the hole transport layer 14 (carrier transport layer) is disposed between one electrode (first electrode 11) of the pair of electrodes 11, 12 and the light-emitting layer 15.

[0018] In the embodiment, the hole transport layer 14 contains cations 17 as impurities (or additives). These cations 17 are not ions derived from α-NPD but are ions derived from a material other than α-NPD. Typically, an acceptor is added to the hole transport layer 14, and the acceptor extracts electrons, causing α-NPD to become cationic and the acceptor to become anionic. In the embodiment, the cations 17 contained in the hole transport layer 14 are not α-NPD in a cationic state but ions contained in α-NPD as impurities. Unlike α-NPD in a cationic state, the cations 17 are mobile ions that can move when a voltage is applied between the pair of electrodes 11 and 12.

[0019] As described above, in this embodiment, the first carrier transport layer (here, hole transport layer 14) is derived from a material different from the constituent material (here, α-NPD) of the first carrier transport layer, and contains ions (here, cations 17) of the same polarity as the carriers (here, holes) targeted by the first carrier transport layer. Whether or not the first carrier transport layer contains the above ions can be determined by displacement current measurement. Displacement current measurement will be described in detail below in [2. Displacement Current Measurement].

[0020] The light-emitting layer 15 including the electron transport layer is laminated on one surface of the hole transport layer 14 in the thickness direction (the lower surface in FIG. 1), and is formed using Alq3 (tris(8-hydroxyquinolinato)aluminum) as a constituent material. The thickness of the light-emitting layer 15 including the electron transport layer is, for example, several tens of nanometers. In other words, the light-emitting layer 15 is disposed between a pair of electrodes 11 and 12.

[0021] The electron injection layer 16 is laminated between one surface in the thickness direction of the light-emitting layer 15 including the electron transport layer (the lower surface in FIG. 1) and one surface in the thickness direction of the second electrode 12 (the upper surface in FIG. 1), and is formed using LiF (lithium fluoride) as a constituent material. The thickness of the electron injection layer 16 is, for example, a few tenths of a nanometer.

[0022] [2. Displacement current measurement] Hereinafter, a displacement current measurement for determining whether or not ions (cations 17 in this case) are contained in the first carrier transport layer (hole transport layer 14 in this case) will be described. The displacement current measurement is performed using a measurement system 200 shown in FIG.

[0023] 2 is a schematic diagram showing the configuration of a measurement system 200 according to an embodiment. The measurement system 200 according to an embodiment measures the polarity of ions (impurity ions) contained in a solid measurement target material 4. Specifically, the measurement system 200 according to the embodiment measures the impurity ions contained in the measurement target material 4 by applying a voltage to a pair of electrodes 32, 33 (described later) of a measurement element 3 including the measurement target material 4, which is a thin film.

[0024] As shown in FIG. 2, the measurement system 200 includes a voltage application unit 21 and a measurement unit 22.

[0025] The voltage application unit 21 is connected between a pair of electrodes 32, 33 of the measuring element 3, and applies a voltage that changes periodically and whose polarity periodically reverses between the pair of electrodes 32, 33. In the embodiment, the voltage application unit 21 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 32, 33. The triangular wave voltage has, for example, a frequency of 0.001 Hz and an amplitude of ±10 V.

[0026] Note that the frequency and amplitude of the triangular wave voltage are both 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 is high, the polarity of the voltage will be reversed before the ions contained in the material 4 to be measured reach the insulating layer 31 (described later), making it impossible to measure the current caused by the ions to be measured.

[0027] The measuring unit 22 measures the physical properties of the material 4 to be measured based on the current flowing through the measuring element 3 due to the application of a voltage by the voltage applying unit 21. In the embodiment, the physical properties of the material 4 to be measured include at least the polarity of the ions contained in the material 4 to be measured. Also, in the embodiment, the physical properties of the material 4 to be measured include the ion amount of the ions contained in the material 4 to be measured.

[0028] In this embodiment, the measurement unit 22 includes an IV converter 221 and a voltmeter 222. The IV converter 221 is connected in series with a pair of electrodes 32, 33 of the measurement element 3, and converts the current flowing through the measurement element 3 into a voltage. The voltmeter 222 measures the voltage converted by the IV converter 221. In other words, the measurement unit 22 measures the voltage converted by the IV converter 221 with the voltmeter 222, thereby measuring the current flowing through the measurement element 3.

[0029] As will be described in detail later, the measurement unit 22 measures the current flowing through the measurement element 3 to measure the polarity and amount of ions contained in the material 4 to be measured.

[0030] Fig. 3 is a schematic diagram showing a measuring element 3 according to an embodiment. Fig. 3(a) is a plan view of the measuring element 3, and Fig. 3(b) is a cross-sectional view of the measuring element 3. As shown in Fig. 3, the measuring element 3 is composed of an insulating layer 31, a pair of electrodes 32 and 33, a glass substrate 34, and a material 4 to be measured. In the embodiment, the measuring element 3 has a square shape of several centimeters on each side in plan view.

[0031] The insulating layer 31 is a SiN (silicon nitride) insulating film. The material constituting the insulating layer 31 is not particularly limited. For example, the insulating layer 31 may be a polyimide insulating film. The insulating layer 31 is formed on one surface (here, the upper surface) of one (here, the lower) electrode 33 of the pair of electrodes 32, 33. The material 4 to be measured is disposed on one surface (i.e., the upper surface) of the insulating layer 31 on the side of the other (here, the upper) electrode 32.

[0032] Of the pair of electrodes 32, 33, one (here, the upper) electrode 32 is an Al (aluminum) electrode. The other (here, the lower) electrode 33 of the pair of electrodes 32, 33 is an ITO electrode, which is a transparent electrode. The material constituting the pair of electrodes 32, 33 is not particularly limited.

[0033] One (here, the upper) electrode 32 of the pair of electrodes 32, 33 is disposed on one surface (here, the upper surface) of the material 4 to be measured. The other (here, the lower) electrode 33 of the pair of electrodes 32, 33 is formed on one surface (here, the upper surface) of a glass substrate 34. Of the pair of electrodes 32, 33, a portion of electrode 32 and electrode 33 are exposed to the outside, and the voltage application unit 21 and measurement unit 22 can be electrically connected to the exposed portions via electric wires.

[0034] As described above, the insulating layer 31 is disposed on only one side (here, the lower side) of both sides in the thickness direction (here, the vertical direction) of the material 4 to be measured. The pair of electrodes 32, 33 is disposed so as to sandwich the material 4 to be measured and the insulating layer 31 in the thickness direction. Therefore, the surface on one side (here, the lower surface) in the thickness direction of the material 4 to be measured is in contact with the insulating layer 31, and the surface on the other side (here, the upper surface) is in contact with the electrode 32 without an insulating layer interposed therebetween.

[0035] In the embodiment, in the horizontal direction (here, left-right direction) of the measuring element 3, the dimensions of the electrode 32, the dimension of the material 4 to be measured, the dimension of the insulating layer 31, and the dimension of the electrode 33 increase in this order, but this is not intended to limit the horizontal dimensions. Also, in the embodiment, in the vertical direction (here, depth direction on the paper) of the measuring element 3, the dimension of the material 4 to be measured is smaller than the dimensions of the electrode 32 and the insulating layer 31, but this is not intended to limit the vertical dimensions.

[0036] In this embodiment, the material 4 to be measured is a constituent material (here, α-NPD) that constitutes the first carrier transport layer (here, hole transport layer 14) in the organic EL device 100. Note that the material 4 to be measured may also be a constituent material that constitutes the second carrier transport layer (here, electron transport layer) in the organic EL device 100.

[0037] In the embodiment, the material 4 to be measured is a solid, and in particular a thin film. In the embodiment, the thickness of the material 4 to be measured is several tens of nanometers, but it may be several hundreds of nanometers. Note that the material 4 to be measured need only be a solid, and does not have to be a thin film.

[0038] The operation of measurement system 200 according to the embodiment, that is, displacement current measurement, will be described below with reference to Fig. 4. Fig. 4 is a flowchart showing an example of displacement current measurement according to the embodiment.

[0039] First, the measuring element 3 is fabricated (step S1). That is, an element is fabricated by laminating an electrode 33, an insulating layer 31, a thin film of the material 4 to be measured, and an electrode 32 in this order on one surface (here, the upper surface) of a glass substrate 34.

[0040] Next, the measuring element 3 is heated (step S2). Here, the measuring element 3 is heated until the ambient temperature of the measuring element 3 reaches about 40 to 80 degrees Celsius. Then, while the measuring element 3 is being heated, or while the measuring element 3 is placed in a high-temperature environment, a voltage (here, a triangular wave voltage) is applied between the pair of electrodes 32, 33 of the measuring element 3 by the voltage application unit 21 (step S3). That is, in this embodiment, step S3 of applying a voltage between the pair of electrodes 32, 33 is performed at a temperature higher than room temperature (here, about 40 to 80 degrees Celsius).

[0041] It is believed that heating the measuring element 3 in this manner can improve the mobility of ions contained in the measurement target material 4. Furthermore, in step S5 (described later) of measuring the amount of ions in the measurement target material 4, the measurement accuracy of the amount of ions contained in the measurement target material 4 can be further improved compared to when the measuring element 3 is not heated.

[0042] Next, the measuring unit 22 measures the current flowing between the pair of electrodes 32, 33 of the measuring element 3, and measures the polarity of the ions contained in the material 4 to be measured based on the measured current (step S4). Also, the amount of ions contained in the material 4 to be measured is measured based on the measured current (step S5).

[0043] Here, a specific example of measuring the polarity and amount of ions contained in the measurement target material 4 will be described with reference to FIG. 5. FIG. 5 is a diagram showing an example of measurement results for the measurement target material 4 before and after sublimation purification using displacement current measurement according to the embodiment. (a) of FIG. 5 is a diagram showing an example of measurement results for the measurement target material 4 after sublimation purification. (b) of FIG. 5 is a diagram showing an example of measurement results for the measurement target material 4 that has not been purified. That is, (a) of FIG. 5 is the measurement result for the measurement target material 4 from which impurities have been removed by sublimation purification, and (b) of FIG. 5 is the measurement result for the measurement target material 4 from which impurities have not been removed.

[0044] In the measurement results shown in Fig. 5, the vertical axis represents the current (unit: "A") flowing through the pair of electrodes 32, 33 and the measuring element 3, and the horizontal axis represents the voltage (unit: "V") applied between the pair of electrodes 32, 33. In Fig. 5, the dashed line represents the measurement result at room temperature (here, 25 degrees Celsius), the dashed line represents the measurement result when the measuring element 3 was heated to 40 degrees Celsius, the dotted line represents the measurement result when the measuring element 3 was heated to 60 degrees Celsius, and the solid line represents the measurement result when the measuring element 3 was heated to 80 degrees Celsius.

[0045] As shown in Figure 5(a), in the measurement results for the sublimation-purified measurement target material 4, slight peaks protruding from the parallelogram-shaped graph appear in both the first and third quadrants, but there is no significant difference between them. On the other hand, as shown in Figure 5(b), in the measurement results for the unpurified measurement target material 4, a prominent peak protruding from the parallelogram-shaped graph appears, particularly in the third quadrant (see the rectangular frame in Figure 5(b)). This peak becomes more prominent as the temperature of the measurement element 3 increases.

[0046] Therefore, by calculating the area of ​​the region including this peak, it is possible to measure the amount of ions (impurity ions) contained in the material 4 to be measured. This peak also appears prominently in the third quadrant, that is, during the period when the voltage applied to the measuring element 3 switches from a positive voltage to a negative voltage. That is, this peak is observed as ions move to the surface of the insulating layer 31 arranged on the side of the electrode 33, which is the negative electrode during this period, of the pair of electrodes 32, 33. Therefore, it is possible to determine that the ions (impurity ions) contained in the material 4 to be measured (here, α-NPD) are cations.

[0047] Furthermore, the ions measured by this displacement current measurement are mobile ions that move when a voltage is applied between the pair of electrodes 32 and 33. In other words, this displacement current measurement makes it possible to measure mobile ions (cations in this case) contained as impurities in the material 4 to be measured, rather than the material 4 to be measured that has become cationic.

[0048] The reason why no peak appears in the first quadrant is because no insulating layer is arranged on the electrode 32 side. That is, in the first quadrant, that is, during the period when the voltage applied to the measuring element 3 switches from a negative voltage to a positive voltage, the electrode 32 of the pair of electrodes 32, 33 becomes the negative electrode, but because no insulating layer is arranged on the electrode 32 side, ions contained in the material 4 to be measured are not detected. For this reason, no peak is observed in the first quadrant.

[0049] Furthermore, as described above, the peak becomes more pronounced as the temperature of the measuring element 3 increases. In other words, by increasing the temperature of the measuring element 3, it becomes easier to measure the amount of ions contained in the material 4 to be measured.

[0050] FIG. 6 shows comparative examples of measurement results for a measurement target material 4 before and after sublimation purification using displacement current measurement according to an embodiment. In the measurement results shown in FIG. 6, the vertical axis represents the current (unit: "A") flowing through the pair of electrodes 32, 33 and the measuring element 3, and the horizontal axis represents the voltage (unit: "V") applied between the pair of electrodes 32, 33. In FIG. 6, the dashed line represents the measurement result for the unpurified measurement target material 4, and the solid line represents the measurement result for the measurement target material 4 after sublimation purification. In addition, the measurement results shown in FIG. 6 are measurement results obtained when the temperature of the measuring element 3 is heated to 80 degrees Celsius. As shown in FIG. 6, by using displacement current measurement according to an embodiment, it is possible to observe peaks due to ions (impurity ions) contained in the measurement target material 4 in the first or third quadrant (here, the third quadrant).

[0051] However, if the ions (impurity ions) contained in the material 4 to be measured are anions, a prominent peak protruding from the parallelogram-shaped graph will appear in the first quadrant, not the third quadrant. That is, during the period when the voltage applied to the measuring element 3 switches from a negative voltage to a positive voltage, the electrode 33 of the pair of electrodes 32, 33 becomes the negative electrode. Therefore, during this period, ions move to the surface of the insulating layer 31 arranged on the electrode 33 side, causing a peak to be observed. Therefore, in this case, it is possible to determine that the ions (impurity ions) contained in the material 4 to be measured are anions.

[0052] [3. Manufacturing method of organic EL device] A method for manufacturing an organic EL device 100 according to an embodiment will be described below with reference to FIG. 7. FIG. 7 is a flowchart showing an example of a method for manufacturing an organic EL device 100 according to an embodiment. Here, a method for manufacturing an organic EL device 100 in which the first carrier transport layer is a hole transport layer 14 will be described. In addition, although the organic EL device 100 is manufactured using a vacuum deposition method here, the organic EL device 100 may be manufactured using other methods.

[0053] First, a glass substrate having a first electrode 11, which is a pre-patterned transparent electrode, is prepared, and a hole injection layer 13 is formed so as to be laminated on one surface in the thickness direction of the first electrode 11 (Step S11). Next, a hole transport layer 14 is formed by doping with cations 17 so as to be laminated on one surface in the thickness direction of the hole injection layer 13, the surface opposite to the first electrode 11 side (Step S12).

[0054] Note that if the constituent material of the hole transport layer 14 (here, α-NPD) is doped with the cations 17 in advance, the step of doping with the cations 17 may be omitted. Also, if displacement current measurement shows that the constituent material of the hole transport layer 14 already contains the cations 17 as impurity ions, the step of doping with the cations 17 may be omitted.

[0055] Next, the light-emitting layer 15 including the electron transport layer is formed so as to be laminated on one surface in the thickness direction of the hole transport layer 14, on the surface opposite to the first electrode 11 side (Step S13). Note that Step S15 may be divided into a step of forming the electron transport layer and a step of forming the light-emitting layer 15. Next, the electron injection layer 16 is formed so as to be laminated on one surface in the thickness direction of the light-emitting layer 15 including the electron transport layer, on the surface opposite to the first electrode 11 side (Step S14). Then, the second electrode 12 is formed so as to be laminated on one surface in the thickness direction of the electron injection layer 16, on the surface opposite to the first electrode 11 side (Step S15). Through the above series of steps, the organic EL device 100 is manufactured.

[0056] [4. Characteristics of Organic EL Devices] The characteristics of organic EL device 100 according to the embodiment will be described below in comparison with an organic EL device of a comparative example. The organic EL device of the comparative example differs from organic EL device 100 according to the embodiment in that it uses a hole transport layer purified by sublimation, i.e., a hole transport layer that does not contain cations.

[0057] First, the results of comparing the initial characteristics of the organic EL device 100 according to the embodiment and the organic EL device of the comparative example will be described. FIG. 8 is a diagram showing the measurement results of the drive voltage in the initial characteristics of the organic EL device 100 according to the embodiment. In the measurement results shown in FIG. 8, the vertical axis on the left represents the current density (unit: mA / cm) of the organic EL device. 2 "), and the vertical axis on the right is the luminance of the organic EL device (unit: "cd / m 2 8, the horizontal axis represents the driving voltage (unit: "V") of the organic EL device, and in FIG. 8, curve L11 represents the measurement results of the luminance of the organic EL device of the comparative example, curve L12 represents the measurement results of the luminance of organic EL device 100 according to the embodiment, curve L13 represents the measurement results of the current density of the organic EL device of the comparative example, and curve L14 represents the measurement results of the current density of organic EL device 100 according to the embodiment.

[0058] 8, the driving voltage required for the same current density or luminance is higher for the organic EL device 100 according to the embodiment than for the organic EL device of the comparative example. Therefore, it was found that the driving voltage of the organic EL device increases slightly when the first carrier transport layer (hole transport layer 14 in this case) contains ions (impurity ions, cations 17 in this case).

[0059] Fig. 9 is a diagram showing the measurement results of the emission spectrum in the initial characteristics of organic EL device 100 according to the embodiment. In the measurement results shown in Fig. 9, the vertical axis represents the normalized intensity (unit: arb unit (arbitrary unit)) of light emitted by the organic EL device, and the horizontal axis represents the wavelength (unit: nm) of light emitted by the organic EL device. In Fig. 9, curve L21 represents the measurement results of the organic EL device of the comparative example, and curve L22 represents the measurement results of organic EL device 100 according to the embodiment.

[0060] 9, the results show that there is no significant difference in the emission spectrum between the organic EL device 100 according to the embodiment and the organic EL device of the comparative example. Therefore, it was found that even if the first carrier transport layer (here, the hole transport layer 14) contains ions (impurity ions, here, cations 17), there is almost no effect on the emission spectrum of the organic EL device.

[0061] 10 is a graph showing the measurement results of the current efficiency in the initial characteristics of the organic EL device 100 according to the embodiment. In the measurement results shown in FIG. 10, the vertical axis represents the current efficiency of the organic EL device (unit: "cd / A"), and the horizontal axis represents the current density of the organic EL device (unit: "mA / cm 2 10, curve L31 represents the measurement results of the organic EL device of the comparative example, and curve L32 represents the measurement results of the organic EL device 100 according to the embodiment.

[0062] 10, the current efficiency of the organic EL device 100 according to the embodiment is higher than that of the organic EL device of the comparative example. Therefore, it was found that the current efficiency of the organic EL device is increased by including ions (impurity ions, cations 17 in this case) in the first carrier transport layer (hole transport layer 14 in this case).

[0063] 11 is a graph showing the measurement results of the external quantum yield in the initial characteristics of the organic EL device 100 according to the embodiment. In the measurement results shown in FIG. 11, the vertical axis represents the external quantum yield of the organic EL device (unit: "%)" and the horizontal axis represents the current density of the organic EL device (unit: "mA / cm 2 11, curve L41 represents the measurement results of the organic EL device of the comparative example, and curve L42 represents the measurement results of the organic EL device 100 according to the embodiment.

[0064] 11, the organic EL device 100 according to the embodiment has a higher external quantum yield than the organic EL device of the comparative example. Therefore, it was found that the external quantum yield of the organic EL device increases when the first carrier transport layer (hole transport layer 14 in this case) contains ions (impurity ions, cations 17 in this case).

[0065] As described above, it has been found that when the first carrier transport layer (here, the hole transport layer 14) contains ions (impurity ions, here, cations 17), the driving voltage of the organic EL device increases slightly, but the current efficiency and external quantum yield (i.e., luminous efficiency) increase.

[0066] Next, the results of comparing the lifetime of the organic EL device 100 according to the embodiment and the organic EL device of the comparative example will be described. The measurements of the organic EL device 100 according to the embodiment and the organic EL device of the comparative example were performed at a constant current density of 50 mA / cm. 2 The changes over time in voltage, luminance, current efficiency, and power efficiency when a current was passed through the device were measured at room temperature.

[0067] Fig. 12 is a diagram showing measurement results of the driving voltage in a degradation analysis of organic EL device 100 according to the embodiment. In the measurement results shown in Fig. 12, the vertical axis represents the driving voltage (unit: "V") of the organic EL device, and the horizontal axis represents the driving time (unit: "h") of the organic EL device. In Fig. 12, curve L51 represents the measurement results of the organic EL device of the comparative example, and curve L52 represents the measurement results of organic EL device 100 according to the embodiment.

[0068] 12, the results show that the increasing trend of the driving voltage is almost the same for the organic EL device of the comparative example and the organic EL device 100 according to the embodiment until the driving time reaches 2000 hours. Therefore, it was found that the inclusion of ions (impurity ions, cations 17 in this case) in the first carrier transport layer (hole transport layer 14 in this case) has almost no effect on the driving voltage of the organic EL device.

[0069] Fig. 13 is a diagram showing measurement results of emission luminance in a degradation analysis of organic EL device 100 according to an embodiment. In the measurement results shown in Fig. 13, the vertical axis represents relative luminance (unit: arb unit) when the luminance of the organic EL device at the initial driving time (driving time 0 hours) is set to "100", and the horizontal axis represents the driving time of the organic EL device (unit: h). In Fig. 13, curve L61 represents the measurement results of the organic EL device of the comparative example, and curve L62 represents the measurement results of organic EL device 100 according to an embodiment.

[0070] 13, the results show that the luminance of the organic EL device 100 according to the embodiment is less likely to decrease compared to the organic EL device of the comparative example until the driving time reaches 2000 hours. Therefore, it was found that the luminance of the organic EL device is less likely to decrease with the passage of driving time when the first carrier transport layer (hole transport layer 14 in this case) contains ions (impurity ions, cations 17 in this case).

[0071] Fig. 14 is a diagram showing the measurement results of current efficiency in a degradation analysis of organic EL device 100 according to the embodiment. In the measurement results shown in Fig. 14, the vertical axis represents the current efficiency of the organic EL device (unit: "cd / A"), and the horizontal axis represents the driving time of the organic EL device (unit: "h"). In Fig. 14, curve L71 represents the measurement results of the organic EL device of the comparative example, and curve L72 represents the measurement results of organic EL device 100 according to the embodiment.

[0072] 14, the results show that the current efficiency of the organic EL device 100 according to the embodiment is less likely to decrease over 2000 hours of operation time than that of the organic EL device of the comparative example. Therefore, it was found that the current efficiency of the organic EL device is less likely to decrease over operation time when the first carrier transport layer (hole transport layer 14 in this case) contains ions (impurity ions, cations 17 in this case).

[0073] FIG. 15 is a diagram showing measurement results of power efficiency in a degradation analysis of organic EL device 100 according to an embodiment. In the measurement results shown in FIG. 15, the vertical axis represents the power efficiency of the organic EL device (unit: "lm / W"), and the horizontal axis represents the drive time of the organic EL device (unit: "h"). FIG. 16 is a diagram showing an enlargement of the measurement results in FIG. 15 when the drive time of the organic EL device is 0 to 100 hours, and FIG. 17 is a diagram showing an enlargement of the measurement results in FIG. 15 when the drive time of the organic EL device is 1500 to 2000 hours. In each of FIGS. 15 to 17, curve L81 represents the measurement results of the organic EL device of the comparative example, and curve L82 represents the measurement results of organic EL device 100 according to an embodiment.

[0074] 15 and 16, the power efficiency of the organic EL device 100 according to the embodiment is lower than that of the organic EL device of the comparative example until the driving time reaches 25 hours. However, as shown in Fig. 15 and 17, after the driving time reaches 25 hours, the power efficiency of the organic EL device 100 according to the embodiment is higher than that of the organic EL device of the comparative example. Therefore, it has been found that the power efficiency of the organic EL device is less likely to decrease with the elapse of driving time when the first carrier transport layer (here, the hole transport layer 14) contains ions (impurity ions, here, cations 17).

[0075] As described above, it has been discovered that when the first carrier transport layer (here, the hole transport layer 14) contains ions (impurity ions, here, the cations 17), the luminance, current efficiency, and power efficiency of the organic EL device are less likely to decrease with the passage of operating time, that is, the life of the organic EL device can be extended.

[0076] 5. Advantages The advantages of the organic EL device 100 according to the embodiment will be described below, taking into account the findings that led to the creation of the present disclosure. It has been known that the inclusion of ionic impurities in a liquid crystal display reduces the performance of the liquid crystal display by causing problems such as a reduction in voltage holding ratio, image sticking, a reduction in response speed, and uneven brightness. However, it has been unclear whether ionic impurities contained in an organic EL device reduce the performance of the organic EL device.

[0077] Therefore, the inventors of the present application fabricated organic EL devices using a hole transport layer before purification by sublimation and organic EL devices using a hole transport layer after purification by sublimation, and compared the characteristics of these organic EL devices to evaluate how the presence or absence of ionic impurities (here, cations) affects the characteristics of the organic EL devices.

[0078] Considering the above-mentioned finding that ionic impurities degrade the performance of liquid crystal displays, it is expected that ionic impurities also degrade the performance of organic EL devices. However, as described above in [4. Characteristics of Organic EL Devices], in fact, the inclusion of ionic impurities (here, cations 17) in the first carrier transport layer (here, hole transport layer 14) improved the characteristics of organic EL device 100, including its luminous efficiency, and extended its lifespan. This is thought to be due to the fact that the presence of cations 17 derived from a material other than α-NPD in hole transport layer 14 increased the driving voltage and suppressed excess holes.

[0079] As described above, the organic EL device 100 according to the embodiment has an advantage that the characteristics including the luminous efficiency are easily improved because the carrier transport layer (here, the hole transport layer 14) contains ions (here, the cations 17) derived from a material different from the constituent material of the carrier transport layer (here, α-NPD). Furthermore, the organic EL device 100 according to the embodiment has an advantage that the lifetime can be further extended because the carrier transport layer contains the ions.

[0080] [6. Characterization methods for organic EL devices] A method for evaluating the characteristics of organic EL device 100 according to an embodiment will be described below. As described above, the characteristics of organic EL device 100 vary depending on whether or not ions (impurity ions, here cations 17) are contained in the first carrier transport layer (here, hole transport layer 14). That is, by measuring whether or not ions (impurity ions) are contained in the first carrier transport layer by displacement current measurement, it is possible to evaluate the characteristics of organic EL device 100 (particularly characteristics including luminous efficiency and lifetime).

[0081] Therefore, it can be said that the characteristic evaluation method for the organic EL device 100 according to the embodiment includes a step of measuring the displacement current. Note that the step of measuring the displacement current is the same as the step shown in FIG. 4, and therefore a description thereof will be omitted here.

[0082] (Variation) The organic EL device 100, the manufacturing method of the organic EL device 100, and the characteristic evaluation method of the organic EL device 100 according to the present disclosure have been described above based on the embodiments, but the present disclosure is not limited to the embodiments. As long as they do not deviate from the gist of the present disclosure, various modifications that a person skilled in the art can make to the embodiments, or other modifications constructed by combining some of the components of the embodiments, are also included within the scope of the present disclosure.

[0083] In the embodiment, the first carrier transport layer may be an electron transport layer, and the ions (impurity ions) contained in the first carrier transport layer may be anions. For example, when the electron transport layer is formed using F8BT (poly(9,9-dioctylfluorene-alt-benzothiazole)) as a constituent material, the organic EL device has a configuration in which electrons are in excess. In this case, if the electron transport layer contains, as an impurity, anions that are ions derived from a material other than F8BT, rather than ions derived from F8BT, the organic EL device is expected to have an advantage in that its properties, including its light-emitting properties, are more likely to be improved.

[0084] (summary) As described above, the organic EL device 100 according to the first embodiment of the present disclosure includes a pair of electrodes 11 and 12, an emitting layer 15 disposed between the pair of electrodes 11 and 12, and a carrier transport layer (first carrier transport layer) disposed between one of the pair of electrodes 11 and 12 (first electrode 11) and the emitting layer 15. The carrier transport layer is made of a material different from the constituent materials of the carrier transport layer and contains ions of the same polarity as the carriers targeted by the carrier transport layer.

[0085] This has the advantage that the properties of the organic EL device 100, including the luminous efficiency, can be easily improved.

[0086] In the organic EL device 100 according to the second embodiment of the present disclosure, the carrier transport layer (first carrier transport layer) in the first embodiment is the hole transport layer 14. The ions are cations 17.

[0087] This has the advantage that the characteristics, including the luminous efficiency, of the organic EL device 100 having a configuration in which holes are in excess are likely to be improved.

[0088] In the organic EL device 100 according to the third aspect of the present disclosure, the ions are ions measured by displacement current measurement in the first or second aspect. In the displacement current measurement, a measuring element 3 includes a constituent material (a material 4 to be measured), an insulating layer 31 disposed on only one of both sides of the constituent material in the thickness direction, and a pair of electrodes 32 and 33 sandwiching the constituent material and the insulating layer 31 in the thickness direction. A voltage that periodically changes and periodically reverses polarity is applied between the pair of electrodes 32 and 33 (step S3), and ions contained in the constituent material are measured based on a current that flows through the measuring element 3 due to the applied voltage (steps S4 and S5).

[0089] This has the advantage that the characteristics of the organic EL device 100, including the luminous efficiency, can be easily improved by including ions that can be measured by displacement current measurement in the carrier transport layer.

[0090] A method for manufacturing an organic EL device 100 according to a fourth embodiment of the present disclosure is a method for manufacturing an organic EL device including a pair of electrodes 11 and 12, a light-emitting layer 15 disposed between the pair of electrodes 11 and 12, and a carrier transport layer (first carrier transport layer) disposed between one of the pair of electrodes 11 and 12 (first electrode 11) and the light-emitting layer 15. The method for manufacturing organic EL device 100 includes a step of adding, to the carrier transport layer, ions derived from a material different from the constituent material of the carrier transport layer and having the same polarity as the carriers targeted by the carrier transport layer.

[0091] This has the advantage that it is possible to manufacture an organic EL device 100 whose characteristics, including luminous efficiency, are easily improved.

[0092] In the method for producing the organic EL device 100 according to the fifth embodiment of the present disclosure, the carrier transport layer (first carrier transport layer) in the fourth embodiment is the hole transport layer 14. The ions are cations 17.

[0093] This has the advantage that it is possible to manufacture an organic EL device 100 having a configuration in which the properties including the luminous efficiency are easily improved and holes are in excess.

[0094] A characteristic evaluation method for an organic EL device 100 according to a sixth aspect of the present disclosure includes a pair of electrodes 11 and 12, a light-emitting layer 15 disposed between the pair of electrodes 11 and 12, and a carrier transport layer (first carrier transport layer) disposed between one of the pair of electrodes 11 and 12 (first electrode 11) and the light-emitting layer 15, and includes a step of measuring a displacement current. In the displacement current measurement, a measuring element 3 includes a constituent material (a material to be measured 4) constituting the first carrier transport layer, an insulating layer 31 disposed on only one of both sides of the constituent material in the thickness direction, and a pair of electrodes 32 and 33 sandwiching the constituent material and the insulating layer 31 in the thickness direction. A voltage that periodically changes and periodically reverses polarity is applied between the pair of electrodes (step S3), and ions contained in the constituent material are measured based on a current that flows through the measuring element 3 due to the applied voltage (steps S4 and S5). The ions are derived from a material different from the constituent material and have the same polarity as the carriers targeted by the carrier transport layer.

[0095] This has the advantage that the characteristics of the organic EL device 100, including the luminous efficiency, can be easily evaluated by measuring the displacement current to determine whether or not ions are contained in the carrier transport layer.

[0096] In the method for evaluating the characteristics of the organic EL device 100 according to the seventh embodiment of the present disclosure, the carrier transport layer (first carrier transport layer) in the sixth embodiment is the hole transport layer 14. The ions are cations 17.

[0097] This has the advantage that by measuring the displacement current to determine whether or not ions are present in the carrier transport layer, it is easy to evaluate the characteristics, including the luminous efficiency, of the organic EL device 100 having a configuration in which there is an excess of holes. [Industrial Applicability]

[0098] The present disclosure can be applied to organic EL devices such as organic light-emitting diodes. [Explanation of symbols]

[0099] 100 Organic EL Devices 11 1st electrode 12 Second electrode 13 Hole injection layer 14 Hole transport layer 15 Light-emitting layer 16 Electron injection layer 17 Cation 200 Measurement System 21 Voltage application section 22 Measuring part 221 IV Converter 222 Voltmeter 3. Measuring element 31 Insulating layer 32,33 electrode 34 Glass substrate 4. Materials to be measured

Claims

1. A method for evaluating characteristics of an organic EL device comprising a pair of electrodes, a light-emitting layer disposed between the pair of electrodes, and a carrier transport layer disposed between one of the pair of electrodes and the light-emitting layer, the method comprising: measuring a displacement current; In the displacement current measurement, In a measuring element including a constituent material that constitutes the carrier transport layer, an insulating layer disposed on only one of both sides of the constituent material in the thickness direction, and a pair of electrodes that sandwich the constituent material and the insulating layer in the thickness direction, a voltage that periodically changes and periodically reverses polarity is applied between the pair of electrodes, and ions contained in the constituent material are measured based on a current that flows through the measuring element due to the application of the voltage, the ions are derived from a material different from the constituent material and have the same polarity as the carriers targeted by the carrier transport layer; A method for evaluating the characteristics of an organic electroluminescent device.

2. The carrier transport layer is a hole transport layer, the ions are cations; The method for evaluating characteristics of an organic EL device according to claim 1 .

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