Organic EL device, method for manufacturing organic EL device, and method for evaluating characteristics of organic EL device

Abstract

An organic EL device (100) is provided with: a pair of electrodes (11, 12); a light-emitting layer (15) disposed between the pair of electrodes (11, 12); and a carrier transport layer (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 (hole transport layer (14)) contains ions (cations (17)) that are derived from a material different from the constituent material constituting the carrier transport layer (hole transport layer (14)) and have the same polarity as the carrier (hole) that targets the carrier transport layer (hole transport layer (14)).

Description

Technical Field

[0001] The present disclosure relates to an organic EL (Electro-Luminescence) device, a method for manufacturing an organic EL device, and a method for evaluating characteristics of an organic EL device. Background Art

[0002] Patent Document 1 discloses a light input type organic EL element. The organic EL element has a structure in which a light emitting display section and a light response section layer are stacked between a pair of electrodes. The organic EL element performs light emitting display according to information input to the light response section.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Laid-Open No. 7-175420 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] The present disclosure provides an organic EL device, a method for manufacturing an organic EL device, and a method for evaluating characteristics of an organic EL device, which can easily improve characteristics including luminous efficiency.

[0008] Means for Solving the Problems

[0009] In order to achieve the above object, an organic EL device according to one aspect of the present disclosure includes: a pair of electrodes; a light emitting layer disposed between the pair of electrodes; and a charge transport layer disposed between one of the pair of electrodes and the light emitting layer. The charge transport layer contains ions from a material different from the constituent material of the charge transport layer and having the same polarity as the charge targeted by the charge transport layer.

[0010] In addition, in order to achieve the above object, a method for manufacturing an organic EL device according to one aspect of the present disclosure is a method for manufacturing an organic EL device including the following: a pair of electrodes; a light emitting layer disposed between the pair of electrodes; and a charge transport layer disposed between one of the pair of electrodes and the light emitting layer. The method for manufacturing the organic EL device includes a step of adding ions to the charge transport layer, the ions being from a material different from the constituent material of the charge transport layer and having the same polarity as the charge targeted by the charge transport layer.

[0011] In addition, in order to achieve the above object, a method for evaluating the characteristics of an organic EL device according to one aspect of the present disclosure is a method for evaluating the characteristics of an organic EL device including the following: a pair of electrodes; a light-emitting layer disposed between the pair of electrodes; and a charge transport layer disposed between one of the pair of electrodes and the light-emitting layer, the method for evaluating the characteristics of the organic EL device including a step of measuring a displacement current. In the measurement of the displacement current, the measurement is performed on a measurement element including: a constituent material constituting the charge transport layer; an insulating layer disposed only on one of both sides in the thickness direction of the constituent material; and a pair of electrodes sandwiching the constituent material and the insulating layer in the thickness direction. In the measurement of the displacement current, a voltage that periodically changes and periodically reverses in polarity is applied between the pair of electrodes, and ions contained in the constituent material are measured based on the current flowing through the measurement element by the application of the voltage, the ions being from a material different from the constituent material and having the same polarity as the charge carriers targeted for the charge transport layer.

[0012] Advantages of the Invention

[0013] The organic EL device and the like according to the present invention have the advantage of easily improving characteristics including luminous efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram showing the outline of the structure of the organic EL device of the embodiment.

[0015] Figure 2 It is a schematic structural diagram of the measurement system according to the embodiment.

[0016] Figure 3 It is a schematic diagram showing the outline of the measurement element of the embodiment.

[0017] Figure 4 It is a flowchart showing an example of the displacement current measurement of the embodiment.

[0018] Figure 5 It is a diagram showing an example of the measurement results of the material to be measured before and after sublimation purification obtained by the displacement current measurement of the embodiment.

[0019] Figure 6 It is a diagram showing a comparative example of the measurement results of the material to be measured before and after sublimation purification by the displacement current measurement of the embodiment.

[0020] Figure 7 It is a flowchart showing an example of the manufacturing method of the organic EL device of the embodiment.

[0021] Figure 8It is a graph showing the measurement results of the driving voltage in the initial characteristics of the organic EL device of the embodiment.

[0022] Figure 9 It is a graph showing the measurement results of the emission spectrum of the initial characteristics of the organic EL device of the embodiment.

[0023] Figure 10 It is a graph showing the measurement results of the current efficiency in the initial characteristics of the organic EL device of the embodiment.

[0024] Figure 11 It is a graph showing the measurement results of the external quantum yield in the initial characteristics of the organic EL device of the embodiment.

[0025] Figure 12 It is a graph showing the measurement results of the driving voltage in the degradation analysis of the organic EL device of the embodiment.

[0026] Figure 13 It is a graph showing the measurement results of the emission luminance in the degradation analysis of the organic EL device of the embodiment.

[0027] Figure 14 It is a graph showing the measurement results of the current efficiency in the degradation analysis of the organic EL device of the embodiment.

[0028] Figure 15 It is a graph showing the measurement results of the power efficiency in the degradation analysis of the organic EL device of the embodiment.

[0029] Figure 16 It is Figure 15 An enlarged view of the measurement results when the driving time of the organic EL device in [ ] is 0 to 100 hours.

[0030] Figure 17 It is Figure 15 An enlarged view of the measurement results when the driving time of the organic EL device in [ ] is 1500 to 2000 hours. Specific Embodiments

[0031] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0032] In addition, the embodiments described below all represent general or specific examples. The numerical values, shapes, materials, constituent elements, arrangement positions of the constituent elements, connection methods, etc. shown in the following embodiments are examples and are not intended to limit the claims. In addition, among the constituent elements in the following embodiments, the constituent elements not described in the independent claims representing the most general concept are described as optional constituent elements. In addition, the respective drawings are not necessarily strictly drawn figures. In each drawing, the same reference numerals are assigned to substantially the same structures, and redundant explanations are omitted or simplified.

[0033] [1. Organic EL Device]

[0034] Figure 1 It is a schematic diagram showing the structure of the organic EL device 100 of the embodiment. In the embodiment, the organic EL device 100 is an organic light emitting diode. In addition, in the embodiment, the organic EL device 100 has a structure with an excess of holes as carriers.

[0035] As Figure 1 shown, the organic EL device 100 includes: a pair of electrodes 11, 12, a hole injection layer 13, a hole transport layer 14, a light 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 the first carrier transport layer and the second carrier transport layer. In addition, 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.

[0036] One of the pair of electrodes 11, 12, the first electrode 11, is an anode formed of ITO (Indium Tin Oxide). The thickness of the first electrode 11 is, for example, several tens of nm to about one hundred and several tens of nm.

[0037] The other of the pair of electrodes 11, 12, the second electrode 12, is a cathode formed of Al (aluminum). The thickness of the second electrode 12 is, for example, several tens of nm to about one hundred and several tens of nm.

[0038] The hole injection layer 13 is stacked on one surface in the thickness direction of the first electrode 11 ( Figure 1 the lower surface in it), and is formed of MoO3 (molybdenum(VI) oxide). The thickness of the hole injection layer 13 is, for example, a fraction of a nm.

[0039] The hole transport layer 14 is stacked on one surface in the thickness direction of the hole injection layer 13 ( Figure 1 the lower surface in it), and is formed of α-NPD as a constituent material, where α-NPD is N,N’-bis(1-naphthyl)-N,N’-diphenyl-1,1’-biphenyl-4,4’-diamine. In other words, α-NPD is the constituent material of the hole transport layer 14 (that is, the first carrier transport layer). The thickness of the hole transport layer 14 is, for example, several tens of nm. In other words, the hole transport layer 14 (carrier transport layer) is disposed between one of the pair of electrodes 11, 12 (the first electrode 11) and the light emitting layer 15.

[0040] In an embodiment, the hole transport layer 14 contains cations 17 as impurities (or additives). The cations 17 are not ions from α-NPD, but ions from a material different from α-NPD. Here, in the hole transport layer 14, an acceptor is usually added, and the acceptor extracts electrons, whereby α-NPD becomes a cationic state and the acceptor becomes an anion. In the embodiment, the cations 17 contained in the hole transport layer 14 are not α-NPD that has become a cationic state, but ions contained as impurities in α-NPD. In addition, the cations 17 are different from α-NPD that has become a cationic state and are mobile ions that can move by applying a voltage between the pair of electrodes 11 and 12.

[0041] Thus, in the embodiment, the first carrier transport layer (here, the hole transport layer 14) contains ions (here, cations 17) of the same polarity as the carriers (here, holes) targeted by the first carrier transport layer and from a material different from the constituent material (here, α-NPD) of the first carrier transport layer. Whether the first carrier transport layer contains the above ions can be measured by displacement current measurement. The displacement current measurement will be described in detail in [2. Displacement Current Measurement] described later.

[0042] The light-emitting layer 15 including an electron transport layer is laminated on one surface in the thickness direction ( Figure 1 the lower surface in) of the hole transport layer 14 and is formed with Alq3 (tris(8-hydroxyquinolinato)aluminium) as a constituent material. The thickness of the light-emitting layer 15 including an electron transport layer is, for example, several tens of nm. In other words, the light-emitting layer 15 is disposed between the pair of electrodes 11 and 12.

[0043] The electron injection layer 16 is laminated between one surface in the thickness direction ( Figure 1 the lower surface in) of the light-emitting layer 15 including an electron transport layer and one surface in the thickness direction ( Figure 1 the upper surface in) of the second electrode 12 and is formed with LiF (lithium fluoride) as a constituent material. The thickness of the electron injection layer 16 is, for example, a fraction of nm.

[0044] [2. Displacement Current Measurement]

[0045] Hereinafter, the displacement current measurement for measuring whether ions (here, cations 17) are contained in the first carrier transport layer (here, the hole transport layer 14) will be described. The displacement current measurement is performed using the Figure 2 shown measurement system 200.

[0046] Figure 2This is a schematic diagram showing the structure of the measurement system 200 according to the embodiment. The measurement system 200 according to the embodiment measures the polarity of ions (impurity ions) contained in the material 4 as the solid measurement object. Specifically, in the measurement system 200 according to the embodiment, for the measurement element 3 including the material 4 as the thin-film measurement object, by applying a voltage to a pair of electrodes 32 and 33 (described later) provided in the measurement element 3, the impurity ions contained in the material 4 to be measured are measured.

[0047] As Figure 2 shown, the measurement system 200 includes a voltage application unit 21 and a measurement unit 22.

[0048] The voltage application unit 21 is connected between a pair of electrodes 32 and 33 provided in the measurement element 3, and applies a voltage that periodically changes and whose polarity periodically reverses between the pair of electrodes 32 and 33. In the embodiment, the voltage application unit 21 is a function generator that generates a triangular wave voltage as the voltage that periodically changes and whose polarity periodically reverses, and applies the generated triangular wave voltage between the pair of electrodes 32 and 33. As an example, the frequency of the triangular wave voltage is 0.001 Hz, and the amplitude is ±10 V.

[0049] In addition, both the frequency and the amplitude of the triangular wave voltage are examples and are not limited thereto. However, the frequency of the triangular wave voltage is preferably a relatively low frequency. This is because if the frequency of the triangular wave voltage becomes high, the polarity of the voltage reverses before the ions contained in the material 4 to be measured reach the insulating layer 31 (described later), and thus the current caused by the ions to be measured cannot be measured.

[0050] The measurement unit 22 measures the physical properties of the material 4 to be measured based on the current flowing through the measurement element 3 by applying a voltage by the voltage application unit 21. In the embodiment, the physical properties of the material 4 to be measured at least include the polarity of the ions contained in the material 4 to be measured. In addition, 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.

[0051] In the embodiment, the measurement unit 22 includes an I-V converter 221 and a voltmeter 222. The I-V converter 221 is connected in series with a pair of electrodes 32 and 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 I-V converter 221. That is, the measurement unit 22 measures the current flowing through the measurement element 3 by measuring the voltage converted by the I-V converter 221 by the voltmeter 222.

[0052] Moreover, as will be described in detail later, the measurement unit 22 measures the polarity and the ion amount of the ions contained in the material 4 to be measured by measuring the current flowing through the measurement element 3.

[0053] Figure 3 It is a schematic diagram showing the measurement element 3 related to the embodiment. Figure 3 (a) of this is a plan view of the measurement element 3, Figure 3 (b) of this is a cross-sectional view of the measurement element 3. As Figure 3 shown, the measurement element 3 is composed of an insulating layer 31, a pair of electrodes 32, 33, a glass substrate 34, and a material 4 to be measured. In the embodiment, the measurement element 3 is in a square shape with a side length of several centimeters in the plan view.

[0054] The insulating layer 31 is a SiN (silicon nitride) insulating film. In addition, the material constituting the insulating layer 31 is not particularly limited. For example, the insulating layer 31 can also be a polyimide insulating film. The insulating layer 31 is formed on one side (here, the lower side) of the pair of electrodes 32, 33, specifically, on the upper surface of the electrode 33. Additionally, the material 4 to be measured is disposed on the other side (here, the upper side) of the insulating layer 31, that is, on the upper surface on the side of the electrode 32.

[0055] One of the pair of electrodes 32, 33 (here, the upper one) electrode 32 is an Al (aluminum) electrode. Additionally, the other of the pair of electrodes 32, 33 (here, the lower one) electrode 33 is an ITO electrode, which is a transparent electrode. In addition, the materials constituting the pair of electrodes 32, 33 are not particularly limited.

[0056] One of the pair of electrodes 32, 33 (here, the upper one) electrode 32 is disposed on one side (here, the upper surface) of the material 4 to be measured. Additionally, the other of the pair of electrodes 32, 33 (here, the lower one) electrode 33 is formed on one side (here, the upper surface) of the glass substrate 34. A part of the electrode 32 and the electrode 33 in the pair of electrodes 32, 33 is exposed to the outside, and the voltage application unit 21 and the measurement unit 22 can be electrically connected to the exposed part via wires.

[0057] As described above, the insulating layer 31 is only disposed on one side (here, the lower side) of the two sides in the thickness direction (here, the up and down direction) of the material 4 to be measured. Additionally, the pair of electrodes 32, 33 are disposed so as to sandwich the material 4 to be measured and the insulating layer 31 in the thickness direction. Therefore, one side (here, the lower surface) of the material 4 to be measured in the thickness direction is in contact with the insulating layer 31, and the other side (here, the upper surface) is in contact with the electrode 32 without passing through the insulating layer.

[0058] In addition, in the embodiment, in the lateral direction (here, the left - right direction) of the measurement element 3, the sizes of the electrode 32, the material 4 of the measurement object, the insulating layer 31, and the electrode 33 increase in sequence, but it is not intended to limit the sizes in the lateral direction. Further, in the embodiment, in the longitudinal direction (here, the depth direction of the paper surface) of the measurement element 3, the size of the material 4 of the measurement object is smaller than the sizes of the electrode 32 and the insulating layer 31, but it is not intended to limit the sizes in the longitudinal direction.

[0059] In the embodiment, the material 4 of the measurement object is a constituent material (here, α - NPD) of the first carrier transport layer (here, the hole transport layer 14) in the organic EL device 100. It should be noted that the material 4 of the measurement object may also be a constituent material of the second carrier transport layer (here, the electron transport layer) in the organic EL device 100.

[0060] In addition, in the embodiment, the material 4 of the measurement object is a solid, particularly a thin film. In the embodiment, the thickness of the material 4 of the measurement object is several tens of nm, but it may also be several hundreds of nm. Further, the material 4 of the measurement object only needs to be a solid and may not be a thin film.

[0061] Hereinafter, Figure 4 the operation of the measurement system 200 of the embodiment, that is, the displacement current measurement, will be described. Figure 4 is a flowchart showing an example of the displacement current measurement in the embodiment.

[0062] First, a measurement element 3 is fabricated (step S1). That is, an element is fabricated in which an electrode 33, an insulating layer 31, a thin film of the material 4 of the measurement object, and an electrode 32 are sequentially stacked on one surface (here, the upper surface) of a glass substrate 34.

[0063] Next, the measurement element 3 is heated (step S2). Here, the measurement element 3 is heated until the ambient temperature of the measurement element 3 becomes about 40 - 80 degrees Celsius. Then, while heating the measurement element 3, or in a state where the measurement element 3 is placed in a high - temperature environment, a voltage (here, a triangular - wave voltage) is applied between a pair of electrodes 32, 33 of the measurement element 3 by the voltage application unit 21 (step S3). That is, in the embodiment, the step S3 of applying a voltage between a pair of electrodes 32, 33 is performed at a temperature higher than room temperature (here, about 40 - 80 degrees Celsius).

[0064] It is considered that by heating the measurement element 3 in this way, the mobility of the ions contained in the material 4 of the measurement object can be increased. Moreover, in step S5 (described later) of measuring the ion amount of the material 4 of the measurement object, the measurement accuracy of the ion amount of the ions contained in the material 4 of the measurement object can be further improved compared with the case where the measurement element 3 is not heated.

[0065] Next, the measurement unit 22 measures the current flowing between the pair of electrodes 32 and 33 of the measurement element 3, and measures the polarity of the ions contained in the material 4 to be measured based on the measured current (step S4). In addition, based on the measured current, the ion amount of the ions contained in the material 4 to be measured is measured (step S5).

[0066] Here, use Figure 5 A specific example of the measurement of the polarity and ion amount of the ions contained in the material 4 to be measured will be described. Figure 5 FIG. is a diagram showing an example of the measurement results of the material 4 to be measured before and after sublimation purification based on the displacement current measurement according to the embodiment. Figure 5 (a) of FIG. is a diagram showing an example of the measurement results of the material 4 to be measured after sublimation purification. Figure 5 (b) of FIG. is a diagram showing an example of the measurement results of the unpurified material 4 to be measured. That is, Figure 5 (a) of FIG. is the measurement result of the material 4 to be measured from which impurities have been removed by sublimation purification, Figure 5 (b) of FIG. is the measurement result of the material 4 to be measured from which impurities have not been removed.

[0067] In Figure 5 In the measurement results shown, the vertical axis represents the current (unit: A) flowing through the pair of electrodes 32 and 33 and the measurement element 3, and the horizontal axis represents the voltage (unit: V) applied between the pair of electrodes 32 and 33. In addition, in Figure 5 , the single-dot chain line represents the measurement result at room temperature (here, 25 degrees Celsius), the dashed line represents the measurement result when the measurement element 3 is heated to 40 degrees Celsius, the dotted line represents the measurement result when the measurement element 3 is heated to 60 degrees Celsius, and the solid line represents the measurement result when the measurement element 3 is heated to 80 degrees Celsius.

[0068] As Figure 5 (a) of FIG. shows, in the measurement results of the material 4 to be measured after sublimation purification, in either the first quadrant or the third quadrant, peaks slightly protruding from the parallelogram-shaped graph are generated, but no significant difference can be seen between them. On the other hand, as Figure 5 (b) of FIG. shows, in the measurement results of the unpurified material 4 to be measured, particularly in the third quadrant, a peak significantly protruding from the parallelogram-shaped graph appears (refer to the inside of the box on the rectangle in Figure 5 (b) of FIG.). This peak becomes more significant as the temperature of the measurement element 3 becomes higher.

[0069] Therefore, by calculating the area of the region containing the peak, the amount of ions (impurity ions) contained in the material 4 of the object to be measured can be determined. In addition, this peak appears significantly in the third quadrant, that is, during the period when the voltage applied to the measurement element 3 is switched from a positive voltage to a negative voltage. That is, ions move to the surface of the insulating layer 31 disposed on the side of the electrode 33 that becomes the negative electrode during this period among the pair of electrodes 32 and 33, and thus this peak is observed. Therefore, it can be determined that the ions (impurity ions) contained in the material 4 of the object to be measured (here α-NPD) are cations.

[0070] In addition, the ions measured by this displacement current measurement are mobile ions that move by applying a voltage between the pair of electrodes 32 and 33. That is, in this displacement current measurement, it is possible to measure the mobile ions (here cations) contained as impurities in the material 4 of the object to be measured, rather than the material 4 of the object to be measured in the cation state.

[0071] In addition, no peak appears in the first quadrant because no insulating layer is disposed on the electrode 32 side. That is, in the first quadrant, that is, during the period when the voltage applied to the measurement element 3 is switched from a negative voltage to a positive voltage, the electrode 32 among the pair of electrodes 32 and 33 becomes the negative electrode, but since no insulating layer is disposed on the electrode 32 side, the ions contained in the material 4 of the object to be measured cannot be detected. Therefore, no peak is observed in the first quadrant.

[0072] In addition, as described above, the above-mentioned peak becomes more significant as the temperature of the measurement element 3 becomes higher. That is, by raising the temperature of the measurement element 3, it is easy to measure the amount of ions contained in the material 4 of the object to be measured.

[0073] Figure 6 It is a diagram showing a comparative example of the measurement results of the material 4 of the object to be measured before and after sublimation purification based on the displacement current measurement of the embodiment. In Figure 6 In the shown measurement results, the vertical axis represents the current flowing through the pair of electrodes 32 and 33 and the measurement element 3 (unit: "A"), and the horizontal axis represents the voltage applied between the pair of electrodes 32 and 33 (unit: "V"). In addition, in Figure 6 , the dashed line represents the measurement results of the unpurified material 4 of the object to be measured, and the solid line represents the measurement results of the material 4 of the object to be measured after sublimation purification. In addition, Figure 6 The shown measurement results are the measurement results when the temperature of the measurement element 3 is heated to 80 degrees Celsius. As Figure 6 shown, by using the displacement current measurement of the embodiment, it is possible to observe a peak caused by the ions (impurity ions) contained in the material 4 of the object to be measured in the first quadrant or the third quadrant (here the third quadrant).

[0074] However, assuming that the ions (impurity ions) contained in the material 4 to be measured are anions, a peak protruding from the parallelogram-shaped graph appears significantly not in the third quadrant but in the first quadrant. That is, during the period when the voltage applied to the measurement element 3 is switched from a negative voltage to a positive voltage, the electrode 33 in the pair of electrodes 32 and 33 becomes the negative electrode. Therefore, during this period, the ions move to the surface of the insulating layer 31 disposed on the electrode 33 side, and thus a peak is observed. Therefore, in this case, it is possible to measure that the ions (impurity ions) contained in the material 4 to be measured are anions.

[0075] [3. Manufacturing Method of Organic EL Device]

[0076] Hereinafter, Figure 7 a method for manufacturing the organic EL device 100 of the embodiment will be described. Figure 7 FIG. is a flowchart showing an example of a method for manufacturing the organic EL device 100 of the embodiment. Here, a method for manufacturing the organic EL device 100 in which the first carrier transport layer is the hole transport layer 14 will be described. In addition, here, the organic EL device 100 is manufactured by a vacuum evaporation method, but the organic EL device 100 can also be manufactured by other methods.

[0077] First, a glass substrate having a pre-patterned transparent electrode, i.e., the first electrode 11, 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, i.e., the surface on the side opposite to the first electrode 11 side (step S12).

[0078] It should be noted that when cations 17 are pre-doped in the constituent material (here, α-NPD) constituting the hole transport layer 14, the process of doping with cations 17 can be omitted. In addition, when cations 17 are already contained as impurity ions in the constituent material constituting the hole transport layer 14 through displacement current measurement, the process of doping with cations 17 can also be omitted.

[0079] Next, a light-emitting layer 15 including an electron transport layer is formed so as to overlap with a surface on the opposite side of the first electrode 11 in the thickness direction of the hole transport layer 14 (step S13). In addition, step S15 may be divided into a step of forming an electron transport layer and a step of forming the light-emitting layer 15. Next, an electron injection layer 16 is formed so as to overlap with a surface on the opposite side of the first electrode 11 in the thickness direction of the light-emitting layer 15 including the electron transport layer (step S14). Then, a second electrode 12 is formed so as to overlap with a surface on the opposite side of the first electrode 11 in the thickness direction of the electron injection layer 16 (step S15). Through the above series of steps, the organic EL device 100 is manufactured.

[0080] [4. Characteristics of Organic EL Device]

[0081] Hereinafter, the characteristics of the organic EL device 100 of the embodiment will be described in combination with a comparison with the organic EL device of the comparative example. The organic EL device of the comparative example is different from the organic EL device 100 of the embodiment in that it uses a hole transport layer purified by sublimation, that is, a hole transport layer containing no cations.

[0082] First, the comparison results of the initial characteristics of the organic EL device 100 of the embodiment and the organic EL device of the comparative example will be described. Figure 8 is a graph showing the measurement results of the driving voltage in the initial characteristics of the organic EL device 100 of the embodiment. In Figure 8 the shown measurement results, the left vertical axis represents the current density of the organic EL device (unit: "mA / cm 2 "), the right vertical axis represents the luminance of the organic EL device (unit: "cd / m 2 "), and the horizontal axis represents the driving voltage of the organic EL device (unit: "V"). In addition, in Figure 8 , the curve L11 represents the measurement results of the luminance of the organic EL device of the comparative example, the curve L12 represents the measurement results of the luminance of the organic EL device 100 of the embodiment, the curve L13 represents the measurement results of the current density of the organic EL device of the comparative example, and the curve L14 represents the measurement results of the current density of the organic EL device 100 of the embodiment.

[0083] As Figure 8 shown, the following results are obtained: compared with the organic EL device of the comparative example, the driving voltage of the organic EL device 100 of the embodiment is higher for the same current density or the same luminance. Therefore, the following insight is obtained: by including ions (impurity ions, here cations 17) in the first carrier transport layer (here the hole transport layer 14), the driving voltage of the organic EL device slightly increases.

[0084] Figure 9This is a graph showing the measurement results of the emission spectrum in the initial characteristics of the organic EL device 100 of the embodiment. In Figure 9 In the measurement results shown, the vertical axis represents the intensity of the light emitted by the organic EL device after normalization (unit: "arbunit (Arbitrary Unit)"), and the horizontal axis represents the wavelength of the light emitted by the organic EL device (unit: "nm"). In addition, in Figure 9 , the curve L21 represents the measurement results of the organic EL device of the comparative example, and the curve L22 represents the measurement results of the organic EL device 100 of the embodiment.

[0085] As Figure 9 shown, regarding the emission spectrum, a result was obtained in which no significant difference was observed between the organic EL device 100 of the embodiment and the organic EL device of the comparative example. Therefore, the following insight was obtained: Even if the first charge transport layer (here, the hole transport layer 14) contains ions (impurity ions, here, cations 17), it has almost no effect on the emission spectrum of the organic EL device.

[0086] Figure 10 This is a graph showing the measurement results of the current efficiency in the initial characteristics of the organic EL device 100 of the embodiment. In Figure 10 In the measurement results shown, 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 "). In addition, in Figure 10 , the curve L31 represents the measurement results of the organic EL device of the comparative example, and the curve L32 represents the measurement results of the organic EL device 100 of the embodiment.

[0087] As Figure 10 shown, a result was obtained in which the current efficiency of the organic EL device 100 of the embodiment is higher than that of the organic EL device of the comparative example. Therefore, the following insight was obtained: By including ions (impurity ions, here, cations 17) in the first charge transport layer (here, the hole transport layer 14), the current efficiency of the organic EL device increases.

[0088] Figure 11 This is a graph showing the measurement results of the external quantum yield in the initial characteristics of the organic EL device 100 of the embodiment. In Figure 11 In the measurement results shown, 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 "). In addition, in Figure 11 , the curve L41 represents the measurement results of the organic EL device of the comparative example, and the curve L42 represents the measurement results of the organic EL device 100 of the embodiment.

[0089] As Figure 11 shown, the following results were obtained: The external quantum yield of the organic EL device 100 of the embodiment is higher than that of the organic EL device of the comparative example. Therefore, the following insight was obtained: By including ions (impurity ions, here cations 17) in the first charge transport layer (here the hole transport layer 14), the external quantum yield of the organic EL device increases.

[0090] As described above, the following insight was obtained: By including ions (impurity ions, here cations 17) in the first charge transport layer (here the hole transport layer 14), although the driving voltage of the organic EL device slightly increases, the current efficiency and the external quantum yield (i.e., the luminous efficiency) increase.

[0091] Next, the comparison results of the lifetimes of the organic EL device 100 of the embodiment and the organic EL device of the comparative example will be described. The measurements of the organic EL device 100 of the embodiment and the organic EL device of the comparative example were both carried out by measuring the time changes of the voltage, luminous brightness, current efficiency, and power efficiency when a current flows at a constant current density of 50 mA / cm 2 at room temperature.

[0092] Figure 12 is a graph showing the measurement results of the driving voltage in the degradation analysis of the organic EL device 100 of the embodiment. In Figure 12 the shown measurement results, the vertical axis represents the driving voltage of the organic EL device (unit: "V"), and the horizontal axis represents the driving time of the organic EL device (unit: "h"). In addition, in Figure 12 , the curve L51 represents the measurement results of the organic EL device of the comparative example, and the curve L52 represents the measurement results of the organic EL device 100 of the embodiment.

[0093] As Figure 12 shown, the following results were obtained: Before the driving time elapsed 2000 hours, the rising tendency of the driving voltage was almost the same in the organic EL device of the comparative example and the organic EL device 100 of the embodiment. Therefore, it was found that including ions (impurity ions, here cations 17) in the first charge transport layer (here the hole transport layer 14) has almost no effect on the driving voltage of the organic EL device.

[0094] Figure 13 is a graph showing the measurement results of the luminous brightness in the degradation analysis of the organic EL device 100 of the embodiment. In Figure 13In the measurement results shown, the vertical axis represents the relative luminance (unit: "arb unit") when the luminance of the organic EL device at the initial driving (driving time: 0 hours) is set to "100", and the horizontal axis represents the driving time of the organic EL device (unit: "h"). Additionally, in Figure 13 the curve L61 represents the measurement results of the organic EL device of the comparative example, and the curve L62 represents the measurement results of the organic EL device 100 of the embodiment.

[0095] As Figure 13 shown, the following results were obtained: In the period before the driving time elapsed 2000 hours, compared with the organic EL device of the comparative example, the tendency for the luminance of the organic EL device 100 of the embodiment to decrease was less likely to decrease. Therefore, the following insight was obtained: By including ions (impurity ions, here cations 17) in the first charge transport layer (here the hole transport layer 14), the luminance of the organic EL device is less likely to decrease as the driving time elapses.

[0096] Figure 14 is a graph showing the measurement results of the current efficiency in the degradation analysis of the organic EL device 100 of the embodiment. In Figure 14 the measurement results shown, 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"). Additionally, in Figure 14 the curve L71 represents the measurement results of the organic EL device of the comparative example, and the curve L72 represents the measurement results of the organic EL device 100 of the embodiment.

[0097] As Figure 14 shown, the following results were obtained: In the period before the driving time elapsed 2000 hours, compared with the organic EL device of the comparative example, the tendency for the current efficiency of the organic EL device 100 of the embodiment to decrease was less likely to decrease. Therefore, the following insight was obtained: By including ions (impurity ions, here cations 17) in the first charge transport layer (here the hole transport layer 14), the current efficiency of the organic EL device is less likely to decrease as the driving time elapses.

[0098] Figure 15 is a graph showing the measurement results of the power efficiency in the degradation analysis of the organic EL device 100 of the embodiment. In Figure 15 the measurement results shown, the vertical axis represents the power efficiency of the organic EL device (unit: "lm / W"), and the horizontal axis represents the driving time of the organic EL device (unit: "h"). Additionally, Figure 16 is a graph obtained by magnifying the measurement results when the driving time of the organic EL device in Figure 15 is from 0 to 100 hours, Figure 17 is Figure 15Figure showing the measurement results of the organic EL device magnified when the driving time is 1500 to 2000 hours. In addition, in Figures 15 to 17 In each figure, the curve L81 represents the measurement results of the organic EL device of the comparative example, and the curve L82 represents the measurement results of the organic EL device 100 of the embodiment.

[0099] As Figure 15 and Figure 16 shown, in the period before 25 hours of driving time, compared with the organic EL device of the comparative example, the power efficiency of the organic EL device 100 of the embodiment is lower. However, as Figure 15 and Figure 17 shown, when the driving time exceeds 25 hours, the power efficiency of the organic EL device 100 of the embodiment is higher than that of the organic EL device of the comparative example. Therefore, the following insight is obtained: by including ions (impurity ions, here cations 17) in the first charge transport layer (here the hole transport layer 14), the power efficiency of the organic EL device is not easily reduced as the driving time elapses.

[0100] As described above, the following insight is obtained: by including ions (impurity ions, here cations 17) in the first charge transport layer (here the hole transport layer 14), the luminance, current efficiency, and power efficiency of the organic EL device are not easily reduced as the driving time elapses, that is, long life of the organic EL device can be achieved.

[0101] [5. Advantages]

[0102] Hereinafter, the advantages of the organic EL device 100 of the embodiment will be described in conjunction with the insight that completes the present disclosure. Conventionally, it has been known that when ionic impurities are contained in a liquid crystal display, a decrease in voltage holding ratio, image sticking, a decrease in response speed, or luminance unevenness occurs, thereby reducing the function of the liquid crystal display. However, for the ionic impurities contained in the organic EL device, it is not clear whether the function of the organic EL device is reduced.

[0103] Therefore, the inventors of the present application fabricated an organic EL device using a hole transport layer before sublimation purification and an organic EL device using a hole transport layer after sublimation purification. Moreover, the inventors of the present application evaluated how the presence or absence of ionic impurities (here cations) affects the characteristics of the organic EL device by comparing the characteristics of these organic EL devices.

[0104] Here, as described above, in view of the understanding that ionic impurities reduce the performance of liquid crystal displays, it is assumed that in an organic EL device, ionic impurities also reduce the performance of the organic EL device. However, in reality, as described in [4. Characteristics of Organic EL Devices] above, by including ionic impurities (here, cations 17) in the first carrier transport layer (here, the hole transport layer 14), the characteristics of the organic EL device 100 including luminous efficiency are improved, and long-term operation of the organic EL device 100 can be achieved. It is considered that this is because, by the presence of cations 17 from materials other than α-NPD in the hole transport layer 14, the driving voltage increases and excess holes are suppressed.

[0105] As described above, the organic EL device 100 of the embodiment contains ions (here, cations 17) from a material different from the constituent material (here, α-NPD) of the carrier transport layer in the carrier transport layer (here, the hole transport layer 14), and thus has the advantage of easily improving the characteristics including luminous efficiency. In addition, the organic EL device 100 of the embodiment has the advantage of being able to further achieve long-term operation because it contains the above ions in the carrier transport layer.

[0106] [6. Method for Evaluating Characteristics of Organic EL Device]

[0107] Hereinafter, a method for evaluating the characteristics of the organic EL device 100 of the embodiment will be described. As described above, the characteristics of the organic EL device 100 vary depending on whether ions (impurity ions, here, cations 17) are included in the first carrier transport layer (here, the hole transport layer 14). That is, by measuring whether ions (impurity ions) are included in the first carrier transport layer using displacement current measurement, the characteristics of the organic EL device 100 (particularly, the characteristics including luminous efficiency and lifespan) can be evaluated.

[0108] Therefore, it can be said that the method for evaluating the characteristics of the organic EL device 100 of the embodiment includes a step of performing displacement current measurement. In addition, the step of performing displacement current measurement is the same as the Figure 4 step shown, and thus the description thereof is omitted here.

[0109] (Modification Example)

[0110] As described above, based on the embodiment, the organic EL device 100, the manufacturing method of the organic EL device 100, and the method for evaluating the characteristics of the organic EL device 100 according to the present disclosure have been described, but the present disclosure is not limited to the embodiment. As long as it does not deviate from the gist of the present disclosure, various modified forms conceived by those skilled in the art for the embodiment, or other forms constructed by combining some constituent elements in the embodiment, are also included in the scope of the present disclosure.

[0111] In an embodiment, the first charge transport layer may be an electron transport layer, and the ions (impurity ions) contained in the first charge 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 constitution with an excess of electrons. In this case, if the electron transport layer does not contain ions derived from F8BT but contains anions, which are ions derived from a material different from F8BT, as impurities, the organic EL device can be expected to have the advantage of easily improving characteristics including luminescence characteristics.

[0112] (Summary)

[0113] As described above, the organic EL device 100 according to the first 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 charge transport layer (first charge transport layer) disposed between one of the pair of electrodes 11 and 12 (first electrode 11) and the light-emitting layer 15. The charge transport layer contains ions of the same polarity as the charge that is the object of the charge transport layer and that are derived from a material different from the constituent material of the charge transport layer.

[0114] Thereby, there is an advantage of easily improving the characteristics including the luminous efficiency of the organic EL device 100.

[0115] In addition, in the organic EL device 100 according to the second aspect of the present disclosure, in the first aspect, the charge transport layer (first charge transport layer) is a hole transport layer 14. The ions are cations 17.

[0116] Thereby, there is an advantage of easily improving the characteristics including the luminous efficiency of the organic EL device 100 having a constitution with an excess of holes.

[0117] Further, in the organic EL device 100 according to the third aspect of the present disclosure, in the first or second aspect, the ions are ions measured by displacement current measurement. In the displacement current measurement, the measurement is performed on a measurement element 3, and the measurement element 3 includes: a constituent material (material 4 to be measured); an insulating layer 31 disposed only on one of the two sides in the thickness direction of the constituent material; and a pair of electrodes 32 and 33 sandwiching the constituent material and the insulating layer 31 in the thickness direction. In the displacement current measurement, a voltage that periodically changes and whose polarity periodically reverses is applied between the pair of electrodes 32 and 33 (step S3), and based on the current flowing through the measurement element 3 due to the application of the voltage, the ions contained in the constituent material are measured (steps S4 and S5).

[0118] Thereby, the charge transport layer contains ions that can be measured by displacement current measurement, and thus there is an advantage of easily improving the characteristics including the luminous efficiency of the organic EL device 100.

[0119] In addition, the manufacturing method of the organic EL device 100 according to the fourth aspect of the present disclosure is a manufacturing method of an organic EL device including the following: 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 manufacturing method of the organic EL device 100 includes a step of adding ions to the carrier transport layer, and the ions are from a material different from the constituent material of the carrier transport layer and have the same polarity as the carriers targeted by the carrier transport layer.

[0120] Accordingly, there is an advantage that an organic EL device 100 having characteristics including easily improved luminous efficiency can be manufactured.

[0121] In addition, the manufacturing method of the organic EL device 100 according to the fifth aspect of the present invention is such that, in the fourth aspect, the carrier transport layer (first carrier transport layer) is a hole transport layer 14. The ions are cations 17.

[0122] Accordingly, there is an advantage that an organic EL device 100 having characteristics including easily improved luminous efficiency and having a structure with hole excess can be manufactured.

[0123] In addition, the characteristic evaluation method of the organic EL device 100 according to the sixth aspect of the present disclosure is a characteristic evaluation method of the organic EL device 100 including the following: 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 characteristic evaluation method of the organic EL device includes a step of measuring displacement current. In the displacement current measurement, the measurement is performed on a measurement element 3, and the measurement element 3 includes: a constituent material (material 4 to be measured) constituting the first carrier transport layer; an insulating layer 31 disposed only on one side of the two sides in the thickness direction of the constituent material; and a pair of electrodes 32 and 33 sandwiching the constituent material and the insulating layer 31 in the thickness direction. In the displacement current measurement, a voltage that periodically changes and periodically reverses in polarity is applied between the pair of electrodes (step S3), and ions contained in the constituent material are measured based on the current flowing through the measurement element 3 due to the application of the voltage (steps S4 and S5). The ions are from a material different from the constituent material and have the same polarity as the carriers targeted by the carrier transport layer.

[0124] Accordingly, by measuring whether ions are contained in the carrier transport layer using displacement current measurement, there is an advantage that it is easy to evaluate the characteristics including luminous efficiency of the organic EL device 100.

[0125] Further, in the method for evaluating the characteristics of the organic EL device 100 according to the seventh aspect of the present invention, in the sixth aspect, the carrier transport layer (the first carrier transport layer) is the hole transport layer 14, and the ion is the cation 17.

[0126] Accordingly, there is an advantage that it is easy to evaluate the characteristics including the luminous efficiency of the organic EL device 100 having a configuration with an excess of holes by measuring whether ions are contained in the carrier transport layer by using displacement current measurement.

[0127] [Industrial Applicability]

[0128] The present disclosure can be applied to organic EL devices such as organic light-emitting diodes.

[0129] Symbol Explanation

[0130] 100 Organic EL device

[0131] 11 First electrode

[0132] 12 Second electrode

[0133] 13 Hole injection layer

[0134] 14 Hole transport layer

[0135] 15 Light-emitting layer

[0136] 16 Electron injection layer

[0137] 17 Cation

[0138] 200 Measurement system

[0139] 21 Voltage application unit

[0140] 22 Measurement unit

[0141] 221 I-V converter

[0142] 222 Voltmeter

[0143] 3 Measurement element

[0144] 31 Insulating layer

[0145] 32, 33 Electrodes

[0146] 34 Glass substrate

[0147] 4 Material to be measured

Claims

1. An organic EL device, comprising: a pair of electrodes; a light-emitting layer disposed between the pair of electrodes; and a charge transport layer disposed between one of the pair of electrodes and the light-emitting layer, wherein the charge transport layer contains ions having the same polarity as the charges targeted by the charge transport layer and derived from a material different from the constituent material of the charge transport layer.

2. The organic EL device according to claim 1, wherein the charge transport layer is a hole transport layer and the ions are cations.

3. The organic EL device according to claim 1 or 2, wherein the ions are ions measured by displacement current measurement, in the displacement current measurement, the measurement is performed in a measurement element having: the constituent material; an insulating layer disposed only on one of the two sides in the thickness direction of the constituent material; and a pair of electrodes sandwiching the constituent material and the insulating layer in the thickness direction, and in the displacement current measurement, a voltage that periodically changes and periodically reverses in polarity is applied between the pair of electrodes, and based on the current flowing through the measurement element by the application of the voltage, the ions contained in the constituent material are measured.

4. A method for manufacturing an organic EL device, which is a method for manufacturing an organic EL device having: a pair of electrodes; a light-emitting layer disposed between the pair of electrodes; and a charge transport layer disposed between one of the pair of electrodes and the light-emitting layer, the method for manufacturing the organic EL device includes a step of adding ions to the charge transport layer, the ions being derived from a material different from the constituent material of the charge transport layer and having the same polarity as the charges targeted by the charge transport layer.

5. The method for manufacturing an organic EL device according to claim 4, wherein the charge transport layer is a hole transport layer and the ions are cations.

6. A method for evaluating characteristics of an organic EL device, which is a method for evaluating characteristics of an organic EL device having: a pair of electrodes; a light-emitting layer disposed between the pair of electrodes; and a charge transport layer disposed between one of the pair of electrodes and the light-emitting layer, the method for evaluating characteristics of the organic EL device includes a step of performing displacement current measurement, in the displacement current measurement, the measurement is performed in a measurement element having: a constituent material constituting the charge transport layer; an insulating layer disposed only on one of the two sides in the thickness direction of the constituent material; and a pair of electrodes sandwiching the constituent material and the insulating layer in the thickness direction, and in the displacement current measurement, a voltage that periodically changes and periodically reverses in polarity is applied between the pair of electrodes, and based on the current flowing through the measurement element by the application of the voltage, the ions contained in the constituent material are measured, the ions being derived from a material different from the constituent material and having the same polarity as the charges targeted by the charge transport layer.

7. The method for evaluating characteristics of an organic EL device according to claim 6, wherein The carrier transport layer is a hole transport layer, and the ion is a cation.

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