Organic electroluminescence element, design method therefor and program

Abstract

To provide an organic electroluminescence element having high luminous efficiency and excellent operational stability by restraining quenching that occurs in a system using a delayed fluorescent material as an assist dopant for luminescence.SOLUTION: An organic electroluminescence element has a structure in which at least a light emission layer, a spacer layer, and an electron transport layer are laminated in this order between a pair of electrodes. The light emission layer contains a first delayed fluorescent material, a second delayed fluorescent material having a lower LUMO energy than the first delayed fluorescent material, and a light emission material. In addition, the lowest excited singlet energy of the second delayed fluorescent material is lower than the lowest excited singlet energy of the first delayed fluorescent material, the lowest excited singlet energy of the light emission material is lower than the lowest excited singlet energy of the second delayed fluorescent material, and the spacer layer contains a host material having a higher LUMO energy than the electron transport material and the second delayed fluorescent material, and a light emission material that is the same as the light emission material of the light emission layer.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an organic electroluminescence element that uses a delayed fluorescent material as an assist dopant for luminescence, a design method thereof, and a program for carrying out the design method. [Background technology]

[0002] There has been much research being conducted into improving the luminous efficiency and operational stability of organic electroluminescence devices, including research into improving luminous efficiency and operational stability by controlling the excited triplet state generated by current excitation of the emissive layer. That is, in the case of current excitation of an organic electroluminescent element, the excited singlet state and the excited triplet state occur with a probability of 25:75 according to the laws of spin statistics, so in order to obtain high luminous efficiency, it is necessary to effectively utilize the energy of the excited triplet state for luminescence. However, since the radiative transition from the excited triplet state to the ground singlet state is essentially a forbidden transition, in ordinary fluorescent materials, the excited triplet state has a long lifespan, during which it emits heat and is deactivated non-radiatively. Therefore, only 25% of the excited singlet energy is utilized for luminescence, and there is a theoretical limit to the luminous efficiency. In addition, there is a problem that the operation becomes unstable due to the accumulation of the long-lived excited triplet state, which causes losses due to exciton-exciton annihilation. For these reasons, it is important to control the excited triplet state in order to improve the luminous efficiency and operational stability of an organic electroluminescent element. From this point of view, for example, Non-Patent Document 1 proposes an organic electroluminescence element containing three components, a host material, a delayed fluorescent material, and a light-emitting material, in the light-emitting layer. Here, the delayed fluorescent material is an organic compound capable of undergoing reverse intersystem crossing from an excited triplet state to an excited singlet state, and having the lowest excited singlet energy intermediate between the host material and the light-emitting material. In such a light-emitting layer, the excited triplet state generated in the delayed fluorescent material and the excited triplet state generated by the energy transfer from the host material to the delayed fluorescent material are transferred to the light-emitting material by reverse intersystem crossing in the delayed fluorescent material, and are effectively used for the fluorescence emission of the light-emitting material. In addition, this process also suppresses the accumulation of the excited triplet state, and both the light-emitting efficiency and the operational stability are improved. In this way, the delayed fluorescent material here is called an "assist dopant" because it plays a role of assisting the fluorescence emission of the light-emitting material. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Uoyama et al., Nature 492, 234-238 (2012). Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, an organic electroluminescence element has been proposed that uses a delayed fluorescent material as an assist dopant for luminescence, thereby improving the luminous efficiency and operational stability. However, the present inventors have investigated the luminous properties of this organic electroluminescence element in detail and found that quenching occurs at the rise of voltage, and this quenching is a factor that impairs the luminous efficiency and operational stability.

[0005] Therefore, in order to solve such problems of the conventional technology, the present inventors have carried out research with the aim of providing an organic electroluminescence element having high luminous efficiency and excellent operational stability while using a delayed fluorescent material as an assist dopant for luminescence. [Means for solving the problem]

[0006] As a result of intensive research to solve the above problems, the present inventors have found that by using a delayed fluorescent material for host, a delayed fluorescent material for assist dopant, and a light-emitting material as components of the light-emitting layer, and by arranging a spacer layer containing a light-emitting material and a host material between the light-emitting layer and the electron transport layer to define the LUMO level of the host material, quenching is reduced, and the light-emitting efficiency and operation stability are improved. The present invention has been proposed based on these findings, and specifically has the following configuration.

[0007] [1] An organic electroluminescence element having a structure in which at least an emitting layer, a spacer layer, and an electron transport layer are laminated in this order between a pair of electrodes, the emitting layer containing a first delayed fluorescent material, a second delayed fluorescent material having a lower LUMO energy than the first delayed fluorescent material, and a emitting material, the minimum excited singlet energy of the second delayed fluorescent material being lower than the minimum excited singlet energy of the first delayed fluorescent material and the minimum excited singlet energy of the emitting material being lower than the minimum excited singlet energy of the second delayed fluorescent material, the electron transport layer being composed of an electron transport material, and the spacer layer containing a host material having a higher LUMO energy than the electron transport material and the second delayed fluorescent material, and a emitting material that is the same as the emitting material. [2] The organic electroluminescence element according to [1], wherein a difference in LUMO energy between the first delayed fluorescent material contained in the light-emitting layer and the host material contained in the spacer layer is within a range of 0 to 0.3 eV. [3] The organic electroluminescence element according to [1] or [2], wherein the first delayed fluorescent material and the host material are the same compound. [4] The organic electroluminescence element according to any one of [1] to [3], wherein the spacer layer consists only of the host material and the light-emitting material. [5] The organic electroluminescence device according to any one of [1] to [4], wherein the LUMO energy of the host material is higher than the LUMO energy of the electron transport material by a difference of 0.5 eV or less. [6] The organic electroluminescence element according to any one of [1] to [5], wherein the light-emitting layer is formed in contact with an electron blocking layer, and the HOMO energy of the first delayed fluorescent material is higher than the HOMO energy of the electron blocking material constituting the electron blocking layer. [7] The organic electroluminescent element according to any one of [1] to [6], wherein the difference between the HOMO energy of the first delayed fluorescent material and the HOMO energy of the electron blocking material is within a range of 0.5 eV or less. [8] The organic electroluminescence device according to any one of [1] to [7], wherein the difference between the HOMO energy and the LUMO energy of the first delayed fluorescent material is within a range of 1.6 to 4.0 eV. [9] The organic electroluminescence element according to any one of [1] to [8], wherein the thickness of the spacer layer is in the range of more than 0 μm and not more than 0.015 μm.

[10] The organic electroluminescence device according to any one of [1] to [9], wherein the concentration of the second delayed fluorescent material in the light-emitting layer is 50% by weight or less.

[0008]

[11] A method for designing an organic electroluminescence element having a structure in which at least a light-emitting layer, a spacer layer, and an electron transport layer are laminated in this order between a pair of electrodes, comprising the steps of: [1] selecting a combination of a first delayed fluorescent material, a second delayed fluorescent material, and a light-emitting material that satisfy the following conditions (1) and (2), and designing a light-emitting layer using these materials; (1) The LUMO energy of the second delayed fluorescent material is lower than the LUMO energy of the first delayed fluorescent material. O has low energy. (2) The minimum excited singlet energy of the first delayed fluorescent material is smaller than the minimum excited singlet energy of the second delayed fluorescent material. The lowest excited singlet energy of the second delayed fluorescent material is lower than that of the first delayed fluorescent material. The lowest excited singlet energy of the luminescent material is low. [2] selecting an electron transport material and a host material having a LUMO energy higher than those of the electron transport material and the second delayed fluorescent material, designing the electron transport layer using the electron transport material, and designing a spacer layer using the host material and the light emitting material; A method for designing an organic electroluminescence element, comprising:

[0009]

[12] A program for implementing the design method described in

[11] . Effect of the Invention

[0010] According to the present invention, quenching that occurs in a system in which a delayed fluorescent material is used as an assist dopant for luminescence is reduced, and an organic electroluminescence element having high luminous efficiency and excellent operational stability can be realized. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is an energy level diagram of the EL device 1 prepared in Example 1. [Diagram 2] FIG. 2 is an energy level diagram of Comparative element 1 produced in Comparative Example 1. [Diagram 3] FIG. 11 is an energy level diagram of Comparative element 2 produced in Comparative Example 2. [Figure 4] 2 is a graph showing the change in luminescence intensity over time when a pulse voltage is applied to the EL element 1. [Diagram 5] 1 is a graph showing the change over time in emission intensity when a pulse voltage is applied to comparative element 1. [Figure 6] 13 is a graph showing the change in emission intensity over time when a pulse voltage is applied to comparative element 2. [Figure 7]1 is a graph showing the external quantum efficiency-luminance characteristics of EL element 1 and comparative element 1. [Figure 8] 1 is a graph showing the operational stability of EL element 1 and comparative elements 1 and 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will be described in detail below. The following description of the constituent elements may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range including the numerical values ​​before and after "to" as the lower and upper limits. In addition, the isotope species of hydrogen atoms present in the molecules of the compound used in the present invention are not particularly limited, and for example, all hydrogen atoms in the molecule may be 1 H, or part or all of 2 H (deuterium D). In this specification, the term "organic compound" refers to a compound containing one or more carbon atoms. The organic compound may be, for example, one consisting of only atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, sulfur atoms, boron atoms, and halogen atoms.

[0013] <Organic electroluminescence element> The organic electroluminescent element of the present invention is an organic electroluminescent element having a structure in which at least an emitting layer, a spacer layer, and an electron transport layer are laminated in this order between a pair of electrodes, in which the emitting layer contains a first delayed fluorescent material, a second delayed fluorescent material having a lower LUMO energy than the first delayed fluorescent material, and a emitting material, and the minimum excited singlet energy of the second delayed fluorescent material is lower than the minimum excited singlet energy of the first delayed fluorescent material and the minimum excited singlet energy of the emitting material is lower than the minimum excited singlet energy of the second delayed fluorescent material, the electron transport layer is made of an electron transport material, and the spacer layer contains a host material having a higher LUMO energy than the electron transport material and the second delayed fluorescent material, and the same emitting material as the emitting material contained in the emitting layer. That is, the organic electroluminescence device of the present invention satisfies the following conditions (a) to (d) regarding the lowest excited singlet energy and the LUMO (Lowest Unoccupied Molecular Orbital) energy. Condition (a) E S1 (T1) > E S1 (T2) > E S1 (E) (In the above formula, E S1 (T1) is the lowest excited singlet energy of the first delayed fluorescent material, E S1 (T2) is the lowest excited singlet energy of the second delayed fluorescent material, E S1 (E represents the lowest excited singlet energy of the luminescent material.) Condition (b) LUMO(T1) > LUMO(T2) Condition (c) LUMO(SH) > LUMO(T2) Condition (d): LUMO(SH) > LUMO(ET) (In the above formula, LUMO(T1) represents the LUMO energy of the first delayed fluorescent material, LUMO(T2) represents the LUMO energy of the second delayed fluorescent material, LUMO(SH) represents the LUMO energy of the host material, and LUMO(ET) represents the LUMO energy of the electron transport material.)

[0014] The "delayed fluorescent material" of the "first delayed fluorescent material" and "second delayed fluorescent material" in the present invention is a material composed of an organic compound, which undergoes reverse intersystem crossing from an excited triplet state to an excited singlet state, and is preferably a thermally activated delayed fluorescent material in which reverse intersystem crossing occurs due to the absorption of thermal energy. A delayed fluorescent material is determined by observing both fluorescence with a short emission lifetime and fluorescence with a long emission lifetime (delayed fluorescence) when the emission transient decay curves of a thin film (single film) made of the delayed fluorescent material or a mixed film made of the delayed fluorescent material and a host material are observed at 20°C. The "light-emitting material" in the present invention is preferably a fluorescent material or a delayed fluorescent material. Here, the "fluorescent material" is a light-emitting material that, when the emission of a thin film (single film) made of the fluorescent material or a mixed film made of the fluorescent material and a host material is observed at 20°C, has a higher fluorescence emission intensity than phosphorescence emission intensity. Ordinary fluorescence (fluorescence that is not delayed fluorescence) has an emission lifetime on the order of ns, while phosphorescence usually has an emission lifetime on the order of ms, so that fluorescence and phosphorescence can be distinguished by their emission lifetimes. For the definition of the "delayed fluorescent material", the definition of the "delayed fluorescent material" in the "first delayed fluorescent material" and "second delayed fluorescent material" above can be referred to. In the present invention, the "host material" refers to a material contained in a mixed film of organic compounds, and refers to an organic compound having the highest minimum excited singlet energy among the organic compounds constituting the mixed film. In the following description, a host material contained in the spacer layer and satisfying the conditions (c) and (d) may be referred to as a "host material for the spacer layer". In the present invention, the "electron transport material" refers to a material that is composed of an organic compound and that transports electrons by an electric field.

[0015] In the present invention, the "LUMO energy" is a value obtained by subtracting the band gap from the ionization potential measured for a thin film made of the compound to be measured (a film of the compound to be measured alone), and adding a "-" sign to the value. In this specification, the energy of the HOMO (Highest Occupied Molecular Orbital) is a value obtained by adding a "-" sign to the ionization potential. The band gap is estimated from the wavelength at the end of the absorption spectrum on the long wavelength side. The ionization potential is measured by photoelectron spectroscopy, and for example, a photoelectron spectrometer (AC-3 manufactured by Riken Keiki Co., Ltd.) can be used for the measurement. For the explanation of the "lowest excited singlet energy" in the present invention, see the following [Lowest excited singlet energy E S1 and the lowest excited triplet energy E T1 Please refer to the description in the "Measurement Method" column.

[0016] In the present invention, by satisfying the condition (a), the energy of the excited singlet state generated directly by carrier recombination (current excitation) in the first delayed fluorescent material and the second delayed fluorescent material, and the excited singlet energy generated by reverse intersystem crossing from the excited triplet state to the excited singlet state can be efficiently transferred to the light-emitting material and effectively utilized for the emission of the light-emitting material. Therefore, high luminous efficiency can be obtained. Here, the transfer of the excited singlet energy from the first delayed fluorescent material to the second delayed fluorescent material may or may not occur, but it is preferable to select a combination of the first delayed fluorescent material, the second delayed fluorescent material, and the light-emitting material so that (i) the transfer of the excited singlet energy from the first delayed fluorescent material to the second delayed fluorescent material is unlikely to occur, (ii) the transfer of the excited singlet energy from the first delayed fluorescent material to the light-emitting material is likely to occur, and (iii) the transfer of the excited singlet energy from the second delayed fluorescent material to the light-emitting material is likely to occur. As a result, the emission of the second delayed fluorescent material is suppressed, and the emission derived from the light-emitting material can be obtained with high purity. The combination of materials satisfying (i) to (iii) can be selected from combinations of materials in which the overlap between the emission peak of the first delayed fluorescent material and the absorption peak of the luminescent material and the overlap between the emission peak of the second delayed fluorescent material and the absorption peak of the luminescent material are greater than the overlap between the emission peak of the first delayed fluorescent material and the absorption peak of the luminescent material. A specific example of a combination of the first delayed fluorescent material, the second delayed fluorescent material, and the luminescent material that satisfies (i) to (iii) is the combination of PICTRZ2, 4CzIPN, and hBNCO shown below.

[0017] [ka]

[0018] The lowest excited triplet energy of each material is not particularly limited, but it is preferable that the lowest excited triplet energy of the second delayed fluorescent material is lower than the lowest excited triplet energy of the first delayed fluorescent material, and that the lowest excited triplet energy of the light-emitting material is lower than the lowest excited triplet energy of the second delayed fluorescent material.

[0019] As described above, among the three components of the light-emitting layer, the first delayed fluorescent material is the component with the highest minimum excited singlet energy. Therefore, a delayed fluorescent material having a relatively large difference between the HOMO energy and the LUMO energy is used as the first delayed fluorescent material. The difference between the HOMO energy and the LUMO energy of the first delayed fluorescent material is, for example, within a range of 1.6 to 4.0 eV, and may be within a range of 1.6 to 2.8 eV, or may be within a range of, for example, 2.8 to 4.0 eV. On the other hand, the second delayed fluorescent material is a delayed fluorescent material having a lower minimum excited singlet energy than the first delayed fluorescent material. In the present invention, the second delayed fluorescent material is a delayed fluorescent material that satisfies both condition (a) and condition (b), that is, a delayed fluorescent material having a lower LUMO energy and a lower minimum excited singlet energy than the first delayed fluorescent material. The HOMO energy of the second delayed fluorescent material is not particularly limited, but is preferably an energy value such that the energy difference between the HOMO and LUMO in the second delayed fluorescent material is smaller than the energy difference between the HOMO and LUMO in the first delayed fluorescent material. Here, if the light-emitting layer containing the first delayed fluorescent material and the second delayed fluorescent material is provided in contact with the electron transport layer, some of the electrons transported by the electron transport layer are trapped by the second delayed fluorescent material at the interface between the light-emitting layer and the electron transport layer and become non-luminescent electrons, causing quenching, because the LUMO energy of the second delayed fluorescent material is low. In the system using the delayed fluorescent material as an assist dopant for luminescence, it is presumed that this causes the luminous efficiency to decrease and the operation of the device to become unstable. In contrast, in the organic electroluminescence device of the present invention, a spacer layer containing a host material (host material for spacer layer) that satisfies conditions (c) and (d) is interposed between the light-emitting layer and the electron-transporting layer, so that the electrons transported in the electron-transporting layer reach the light-emitting layer via the LUMO of the host material for spacer layer. For example, referring to FIG. 1(b) showing a specific configuration of an embodiment, the electrons transported in the electron-transporting layer (ET) reach the light-emitting layer (EM) via the LUMO (upper solid line) of the spacer layer (SP). At this time, the electrons that have passed through the LUMO of the host material for spacer layer have a higher LUMO energy than the LUMO energy of the second delayed fluorescent material (upper dashed line in FIG. 1(b)) and are also higher than the LUMO energy of the electron-transporting material. Therefore, compared with the electrons transported in the electron-transporting layer, the electrons are more likely to be accommodated in the LUMO of the first delayed fluorescent material (upper solid line in FIG. 1(b)), which has a higher energy, and electron trapping in the second delayed fluorescent material is less likely to occur. Therefore, the occurrence of the above-mentioned quenching is suppressed, and the luminous efficiency and the operational stability are improved. In addition, since the spacer layer contains the same luminous material as the luminous material contained in the luminous layer, even if carrier recombination occurs in the host material for the spacer layer, this luminous material emits light, so that the luminous efficiency can be ensured. Note that FIG. 1(b) shows a case where the LUMO energy of the first delayed fluorescent material and the LUMO energy of the host material for the spacer layer are the same (energy difference is 0 eV), but as long as conditions (b) to (d) are satisfied, the same action and effect can be obtained.

[0020] In order to obtain such an effect more reliably, the difference between the LUMO energy of the first delayed fluorescent material and the LUMO energy of the host material for the spacer layer is preferably within a range of 0 to 0.3 eV. That is, it is preferable that the first delayed fluorescent material and the host material for the spacer layer satisfy the following condition (e). Condition (e) -0.3(eV) ≦ LUMO(T1)-LUMO(SH) ≦ 0.3(eV) This allows electrons to be efficiently transferred from the LUMO of the host material for the spacer layer to the LUMO of the first delayed fluorescent material, and electron trapping in the second delayed fluorescent material can be more reliably suppressed, and the driving voltage can be lowered. Here, the difference between the LUMO energy of the first delayed fluorescent material and the LUMO energy of the host material for the spacer layer may be, for example, in the range of 0 to 0.2 eV or in the range of 0 to 0.1 eV, or may be 0 eV. When the difference between the LUMO energy of the first delayed fluorescent material and the LUMO energy of the host material for the spacer layer is 0, the first delayed fluorescent material and the host material for the spacer layer may be the same compound or different compounds, but are preferably the same compound.

[0021] In addition, the LUMO energy of the host material for the spacer layer is preferably higher than the LUMO energy of the electron transport material within a range in which the difference is 0.5 eV or less. In other words, the host material for the spacer layer and the electron transport material preferably satisfy the following condition (d1). Condition (d1) 0(eV) < LUMO(SH)-LUMO(ET) ≦ 0.5(eV) This increases the efficiency of electron injection from the electron transport layer to the spacer layer, thereby lowering the driving voltage. The difference between the LUMO energy of the host material for the spacer layer and the LUMO energy of the electron transport material may be, for example, 0.4 eV or less or 0.3 eV or less, or 0.1 eV or more or 0.2 eV or more.

[0022] [Lowest excited singlet energy E S1 and the lowest excited triplet energy E T1 Measurement method] The lowest excited singlet energy E in the present invention S1 and the lowest excited triplet energy E T1 is a value measured by the following method, and ΔE ST is measured by the following method S1 and E T1 Using ΔE ST =E S1 -ET1 This value is calculated by: Ta. (1) The lowest excited singlet energy E S1 A sample with a thickness of 100 nm is prepared on a Si substrate by co-evaporating the compound to be measured and the host material so that the concentration of the compound to be measured is 6% by weight. The fluorescence spectrum of this sample is measured at room temperature (300K). Specifically, the emission is integrated from immediately after the excitation light is incident until 100 nanoseconds after the incident to obtain a fluorescence spectrum with the emission intensity on the vertical axis and the wavelength on the horizontal axis. A tangent line is drawn to the rising edge on the short wavelength side of this emission spectrum, and the wavelength value λedge [nm] at the intersection of this tangent line and the horizontal axis is obtained. This wavelength value is converted to an energy value using the following conversion formula, and the value E S1 Let us assume that. Conversion formula: E S1 [eV]=1239.85 / λedge For measuring the emission spectrum, a nitrogen laser (MNL200, manufactured by Lasertechnik Berlin) can be used as an excitation light source, and a streak camera (C4334, manufactured by Hamamatsu Photonics KK) can be used as a detector. (2) The lowest excited triplet energy E T1 Lowest excited singlet energy E S1 The same sample used in the measurement is cooled to 77[K], excitation light is irradiated onto the phosphorescence measurement sample, and the phosphorescence intensity is measured using a streak camera. Specifically, the emission is integrated from 1 ms to 10 ms after the excitation light is applied to obtain a phosphorescence spectrum with the emission intensity on the vertical axis and the wavelength on the horizontal axis. A tangent line is drawn to the rising edge of the phosphorescence spectrum on the short wavelength side, and the wavelength value λedge[nm] at the intersection of the tangent line and the horizontal axis is obtained. This wavelength value is converted to an energy value using the following conversion formula, and the value E T1 Let us assume that. Conversion formula: E T1 [eV]=1239.85 / λedge The tangent to the rising edge of the phosphorescence spectrum on the short wavelength side is drawn as follows. When moving along the spectral curve from the short wavelength side of the phosphorescence spectrum to the shortest maximum of the spectral maxima, consider the tangent at each point on the curve toward the long wavelength side. The slope of this tangent increases as the curve rises (i.e., as the vertical axis increases). The tangent drawn at the point where this slope is at its maximum value is considered to be the tangent to the rising edge of the phosphorescence spectrum on the short wavelength side. Note that a maximum point having a peak intensity of 10% or less of the maximum peak intensity of the spectrum is not included in the maximum value on the shortest wavelength side described above, and the tangent drawn at the point where the slope value is the maximum value that is closest to the maximum value on the shortest wavelength side is regarded as the tangent to the rising edge on the short wavelength side of the phosphorescence spectrum.

[0023] [Layer structure of organic electroluminescence element] The organic electroluminescence element of the present invention has a structure in which at least a light-emitting layer, a spacer layer, and an electron transport layer are laminated in this order between a pair of electrodes. In one embodiment of the present invention, the spacer layer is in contact with the light-emitting layer and the electron transport layer. In one embodiment of the present invention, the organic electroluminescence element has a structure in which an anode (one of a pair of electrodes), a light-emitting layer, a spacer layer, an electron transport layer, and a cathode (the other of the pair of electrodes) are laminated in this order. In this case, the layers disposed between the anode and the cathode may be only the light-emitting layer, the spacer layer, and the electron transport layer, or at least one organic layer may be provided between the light-emitting layer and the anode or between the electron transport layer and the cathode. For example, an example of an organic layer provided between the light-emitting layer and the anode is an electron blocking layer. The electron blocking layer is disposed so as to be in contact with the light-emitting layer, and is a layer for preventing electrons in the light-emitting layer from escaping to the outside of the light-emitting layer. An organic compound having a higher LUMO energy than the first delayed fluorescent material is used as the electron blocking material constituting the electron blocking layer. As for the HOMO, it is preferable that the HOMO energy of the first delayed fluorescent material is higher than that of the electron blocking material, and it is preferable that the HOMO energy of the first delayed fluorescent material is higher than that of the electron blocking material within a range in which the difference between the two is 0.5 eV or less. That is, it is preferable to satisfy the following condition (f). Condition (f) 0(eV) < HOMO(T1)-HOMO(EB) ≦ 0.5(eV) (In the above formula, HOMO(T1) represents the HOMO energy of the first delayed fluorescent material, and HOMO(EB) represents the HOMO energy of the electron blocking material.) This increases the efficiency of hole injection from the electron blocking layer to the light emitting layer, and reduces the driving voltage. The electron blocking layer may be an electron exciton blocking layer having an exciton blocking function. Other organic layers that may be provided between the pair of electrodes include a hole transport layer, a hole injection layer, a hole blocking layer, an exciton blocking layer, etc. The hole transport layer may be a hole injection transport layer having a hole injection function, and the hole blocking layer may be a hole exciton blocking layer having an exciton blocking function. Each component and each layer of the organic electroluminescence element will be described below. Here, the descriptions of the use examples, devices, displays, screens, and the like described in

[0141] to

[0169] and

[0192] to

[0242] of US2020 / 0168814A1 are hereby cited in their entirety as part of this specification, with the description of the "light-emitting layer" being replaced with the description of the "light-emitting layer" and "spacer layer" described below, to describe the present invention.

[0024] (Light Emitting Layer) The light-emitting layer of the organic electroluminescence device of the present invention contains the first delayed fluorescent material, the second delayed fluorescent material, and the light-emitting material, and satisfies the above conditions (a) to (c). The light-emitting layer is a layer that emits light after excitons are generated by recombination of holes and electrons injected from the anode and cathode, respectively. In a preferred embodiment of the present invention, the largest component of the light emitted from the element is light emitted from the light-emitting material. The fact that the largest component of the light emitted from the element is light emitted from the light-emitting material can be confirmed by the fact that the area of ​​the emission peak derived from the light-emitting material is more than 50% of the total emission peak area in the emission spectrum of the organic electroluminescence element. The first delayed fluorescent material and the second delayed fluorescent material are materials that can emit delayed fluorescence, but it is not essential that the first delayed fluorescent material and the second delayed fluorescent material emit delayed fluorescence when used in the organic electroluminescence element of the present invention. The light emitted from the first delayed fluorescent material and the second delayed fluorescent material is preferably less than 10% of the light emitted from the organic electroluminescence element of the present invention, and may be, for example, less than 1%, less than 0.1%, less than 0.01%, or below the detection limit.

[0025] The light-emitting layer may be composed of only the first delayed fluorescent material, the second delayed fluorescent material, and the light-emitting material, or may further contain other components. Examples of other components include a host material that does not emit delayed fluorescence. In a preferred embodiment of the present invention, the light-emitting layer does not contain any compound or metal element that transfers charge or energy other than the first delayed fluorescent material, the second delayed fluorescent material, and the light-emitting material. The light-emitting layer can also be composed of only the first delayed fluorescent material, the second delayed fluorescent material, and the light-emitting material. Furthermore, the light-emitting layer can also be composed of only a compound consisting of atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, boron atoms, oxygen atoms, sulfur atoms, and fluorine atoms. For example, the light-emitting layer can be composed of only a compound consisting of atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, boron atoms, oxygen atoms, and fluorine atoms. In a preferred embodiment of the present invention, the light-emitting layer contains carbon atoms, hydrogen atoms, nitrogen atoms, boron atoms, oxygen atoms, and fluorine atoms, and more preferably does not contain any other elements.

[0026] The concentration of the second delayed fluorescent material in the light-emitting layer is preferably 50% by weight or less based on the total amount of the materials constituting the light-emitting layer, which can provide the following effects: electron trapping in the second delayed fluorescent material can be more reliably suppressed, the recombination zone can be easily adjusted, and the energy of the second delayed fluorescent material can be almost completely transferred to the light-emitting material, thereby suppressing the decrease in color purity due to the emission of the second delayed fluorescent material. It is also preferable that the concentration of the first delayed fluorescent material is higher than the concentration of the second delayed fluorescent material, and the concentration of the luminescent material is higher than the concentration of the second delayed fluorescent material, i.e., the relationship of "concentration of the luminescent material < concentration of the second delayed fluorescent material < concentration of the first delayed fluorescent material" is satisfied. Specifically, the concentration of the second delayed fluorescent material in the light-emitting layer is preferably less than 50% by weight based on the total amount of the first delayed fluorescent material, the second delayed fluorescent material, and the light-emitting material, and can be, for example, less than 40% by weight, less than 30% by weight, less than 20% by weight, or less than 10% by weight. The concentration of the second delayed fluorescent material is preferably 0.1% by weight or more, and can be, for example, more than 1% by weight or more than 3% by weight. In addition, the concentration of the luminescent material in the luminescent layer can be 0.1% by weight or more or 1% by weight or more, or can be 30% by weight or less, 20% by weight or less, or 10% by weight or less, relative to the total amount of the first delayed fluorescent material, the second delayed fluorescent material, and the luminescent material.

[0027] The light-emitting layer may be formed by a wet process or a dry process using a light-emitting composition containing at least the first delayed fluorescent material, the second delayed fluorescent material, and the light-emitting material. In the wet process, a solution containing a light-emitting composition is applied to a surface, and after removal of the solvent, a light-emitting layer is formed. Examples of the wet process include, but are not limited to, spin coating, slit coating, inkjet (spray) printing, gravure printing, offset printing, and flexographic printing. In the wet process, an appropriate organic solvent capable of dissolving the light-emitting composition is selected and used. In an embodiment, a substituent (e.g., an alkyl group) that increases the solubility in an organic solvent can be introduced into a compound contained in the light-emitting composition.

[0028] As the dry process, a vacuum deposition method can be preferably adopted. When a vacuum deposition method is adopted, each compound constituting the light-emitting layer may be co-deposited from an individual deposition source, or may be co-deposited from a single deposition source in which all compounds are mixed. When a single deposition source is used, a mixed powder in which all compounds are mixed in powder may be used, a compression molded body in which the mixed powder is compressed may be used, or a mixture in which each compound is heated, melted, mixed, and then cooled may be used. In an embodiment, a light-emitting layer having a composition ratio corresponding to the composition ratio of the multiple compounds contained in the deposition source can be formed by performing co-deposition under conditions in which the deposition rates (weight reduction rates) of the multiple compounds contained in a single deposition source are the same or almost the same. If a multiple compound is mixed in the same composition ratio as the composition ratio of the light-emitting layer to be formed and used as a deposition source, a light-emitting layer having a desired composition ratio can be easily formed. In an embodiment, a temperature at which each compound to be co-deposited has the same weight reduction rate can be specified, and the temperature can be adopted as the temperature during co-deposition. When the light-emitting layer is formed by a vapor deposition method, the molecular weight of each of the first delayed fluorescent material, the second delayed fluorescent material, and the light-emitting material is preferably 1500 or less, more preferably 1200 or less, even more preferably 1000 or less, and even more preferably 900 or less. The lower limit of the molecular weight may be, for example, 200, 400, or 600.

[0029] The thickness of the light-emitting layer is preferably from 10 to 100 nm, more preferably from 20 to 60 nm, and further preferably from 30 to 50 nm.

[0030] (Spacer layer) The spacer layer contains a host material (host material for spacer layer) that satisfies the above conditions (c) and (d) and a light-emitting material that is the same as the light-emitting material contained in the light-emitting layer. The spacer layer is disposed between the light-emitting layer and the electron transport layer, and suppresses electron trapping (quenching) in the second delayed fluorescent material in the light-emitting layer, thereby improving the luminous efficiency and operational stability of the element. The spacer layer may be composed of only a host material for the spacer layer and the same light-emitting material as the light-emitting material contained in the light-emitting layer, or may contain a material other than these materials. For preferred examples of the constituent elements of the compound that can constitute the spacer layer, the corresponding description of the light-emitting layer can be referred to. For example, the luminescent material contained in the spacer layer may contain a luminescent material different from the luminescent material contained in the light-emitting layer in addition to the same luminescent material as the luminescent material contained in the light-emitting layer, but it is preferable that the luminescent material is composed only of the same luminescent material as the luminescent material contained in the light-emitting layer. The spacer layer may contain the same delayed fluorescent material as the second delayed fluorescent material contained in the light-emitting layer, but the concentration of the delayed fluorescent material in the spacer layer is lower than the concentration of the second delayed fluorescent material in the light-emitting layer. When the delayed fluorescent material is contained in the spacer layer, the concentration of the delayed fluorescent material may be uniform in the spacer layer, but may have a concentration gradient. For example, by providing a concentration gradient in which the electron transport layer side is low and the light-emitting layer side is high, it is possible to suppress electrons from being trapped in the delayed fluorescent material that is the same as the second delayed fluorescent material at the interface between the spacer layer and the electron transport layer. In a preferred embodiment of the present invention, the spacer layer is composed only of a host material for the spacer layer and a light-emitting material that is the same as the light-emitting material contained in the light-emitting layer.

[0031] The concentration of the light-emitting material in the spacer layer can be 0.1% by weight or more, or 1% by weight or more, relative to the total amount of materials constituting the spacer layer, and can be 30% by weight or less, 20% by weight or less, or 10% by weight or less.

[0032] The thickness of the spacer layer is preferably in the range of more than 0 μm and not more than 0.015 μm, and may be, for example, in the range of more than 0 μm and not more than 0.008 μm or more than 0.008 μm and not more than 0.015 μm, which can effectively improve the light emission efficiency and operational stability of the element.

[0033] (electron transport layer) The "electron transport layer" in the present invention means a layer that is composed of an electron transport material and has an electron transport function. The electron transport layer may have an electron injection function, a hole blocking function, or an exciton blocking function in addition to the electron transport function. That is, the electron transport layer may be an electron transport / electron injection layer, an electron transport / hole blocking layer, an electron transport / exciton blocking layer, or an electron transport / hole exciton blocking layer. In addition, in the name of a layer used in this specification, a layer that includes "electron transport / " means a layer that has both an electron transport function and the function to the right of " / ", and is classified as an "electron transport layer". In addition, in an organic electroluminescence element having a plurality of layers that correspond to the electron transport layer, the electron transport layer closest to the spacer layer is the "electron transport layer" in the "structure in which a light-emitting layer, a spacer layer, and an electron transport layer are laminated in order".

[0034] In the organic electroluminescence device of the present invention, the electron transport layer (when the organic electroluminescence device has a plurality of electron transport layers, the electron transport layer closest to the spacer layer) is composed of an electron transport material that satisfies the above condition (d). The electron transport layer may be composed of only an electron transport material that satisfies the condition (d), or may contain an electron transport material that does not satisfy the condition (d) in addition to the electron transport material that satisfies the condition (d). However, when the electron transport material contains an electron transport material that does not satisfy the condition (d), the concentration of the electron transport material that satisfies the condition (d) is preferably 50% by weight or more, for example, 70% by weight or more, 80% by weight or more, or 90% by weight or more, based on the total amount of the materials that constitute the electron transport layer. In a preferred embodiment of the present invention, the electron transport layer (when the organic electroluminescence device has a plurality of electron transport layers, the electron transport layer closest to the spacer layer) is composed of only an electron transport material that satisfies the condition (d).

[0035] The spacer layer, the electron transport layer, and each layer provided as necessary can be formed by a wet process or a dry process. For an explanation of the wet process and the dry process, see the above (Light Emitting Layer) section.

[0036] Preferred materials that can be used in organic electroluminescence elements are described below, and specific examples thereof are given. However, the materials that can be used in the present invention are not limited to the following exemplary compounds. In addition, even if a compound is exemplified as a material having a specific function, it can also be used as a material having other functions.

[0037] [First delayed fluorescent material and second delayed fluorescent material] The first delayed fluorescent material and the second delayed fluorescent material have a difference ΔE ST is preferably 0.3 eV or less, more preferably 0.25 eV or less, more preferably 0.2 eV or less, more preferably 0.15 eV or less, even more preferably 0.1 eV or less, even more preferably 0.07 eV or less, even more preferably 0.05 eV or less, even more preferably 0.03 eV or less, and particularly preferably 0.01 eV or less. ΔE ST If the excited triplet state is small, reverse intersystem crossing from the excited singlet state to the excited triplet state is easily caused by absorption of thermal energy. Therefore, reverse intersystem crossing from the excited triplet state to the excited singlet state is relatively easily caused by absorbing heat generated by the device, and the excited triplet energy can be contributed to the light emission of the light-emitting material. As the first delayed fluorescent material and the second delayed fluorescent material, for example, paragraphs 0008 to 0048 and 0095 to 0133 of WO2013 / 154064, paragraphs 0007 to 0047 and 0073 to 0085 of WO2013 / 011954, paragraphs 0007 to 0033 and 0059 to 0066 of WO2013 / 011955, paragraphs 0008 to 0071 and 0118 to 0133 of WO2013 / 081088, paragraphs 0009 to 0046 and 0093 to 0134 of JP2013-256490A, and JP2013-116975A Paragraphs 0008 to 0020 and 0038 to 0040 of WO2013 / 133359, paragraphs 0007 to 0032 and 0079 to 0084 of WO2013 / 161437, paragraphs 0008 to 0054 and 0101 to 0121 of JP2014-9352A, paragraphs 0007 to 0041 and 0060 to 0069 of JP2014-9224A, paragraphs 0008 to 0048 and 0067 to 0076 of JP2014-9224A, paragraphs 0013 to 0025 of JP2017-119663A, paragraphs 0013 to 0026 of JP2017-119664A, Compounds included in the general formulas described in paragraphs 0012 to 0025 of JP 2017-226838 A, paragraphs 0010 to 0050 of JP 2017-226838 A, paragraphs 0012 to 0043 of JP 2018-100411 A, and paragraphs 0016 to 0044 of WO 2018 / 047853 A, JP 2013-253121 A, WO 2013 / 133359 A, WO 2014 / 034535 A, WO 2014 / 115743 A, WO 2014 / 122895 A, WO 2014 / 126200 A, WO 2014 / 136758 A, WO 20 14 / 133121, WO2014 / 136860, WO2014 / 196585, WO2014 / 189122 WO2014 / 168101, WO2015 / 008580, WO2014 / 203840, WO2015 / 002 213 Publication, WO2015 / 016200 Publication, WO2015 / 019725 Publication, WO2015 / 072470 Publication, WO201 5 / 108049 publication, WO2015 / 080182 publication, WO2015 / 072537 publication, WO2015 / 080183 publication,Luminescent materials that emit delayed fluorescence and are described in JP2015-129240A, WO2015 / 129714A, WO2015 / 129715A, WO2015 / 133501A, WO2015 / 136880A, WO2015 / 137244A, WO2015 / 137202A, WO2015 / 137136A, WO2015 / 146541A, and WO2015 / 159541A can be used. The above publications described in this paragraph are hereby incorporated by reference as part of this specification. Of these delayed fluorescent materials, it is preferable to adopt a DA-type delayed fluorescent material as the first delayed fluorescent material. The DA-type delayed fluorescent material means a delayed fluorescent material having a structure in which a donor group (D) and an acceptor group (A) are linked via a single bond or a linking group (e.g., an aromatic ring group such as a benzene ring). Here, the donor group (D) can be selected from a group of substituents having a negative Hammett σp value, and the acceptor group (A) can be selected from a group of substituents having a positive Hammett σp value. When a DA-type delayed fluorescent material is used as the first delayed fluorescent material, the carrier recombination region can be easily adjusted to a position away from the interface of the light-emitting layer, and effects such as a significant reduction in driving voltage, mitigation of roll-off (reduction in light-emitting efficiency during high current density driving), and improvement of element life can be obtained. For an explanation of Hammett's σp value and the numerical values ​​of each substituent, refer to Hansch, C. et.al., Chem. Rev., 91, 165-195 (1991). Examples of donor groups include substituted or unsubstituted diarylamino groups (two aryl groups may be bonded to each other via a single bond or a linking group to form a ring), such as substituted or unsubstituted diphenylamino groups, substituted or unsubstituted 9-carbazolyl groups, and fused ring groups having a structure in which an indole ring is condensed to a substituted or unsubstituted 9-carbazolyl group. Examples of acceptor groups include groups containing a nitrogen-containing aromatic 6-membered ring, such as substituted or unsubstituted pyridyl groups, substituted or unsubstituted pyrimidyl groups, and substituted or unsubstituted triazyl groups. Examples of the substituent include alkyl groups having 1 to 20 carbon atoms, aryl groups having 6 to 40 carbon atoms, and groups formed by combining two or more alkyl groups having 1 to 20 carbon atoms and aryl groups having 6 to 40 carbon atoms.

[0038] [Luminescent materials] The luminescent material is preferably a fluorescent material or a delayed fluorescent material. Among them, it is preferable that the luminescent material is a multiple resonance type luminescent material that multiple resonance occurs between one or more atoms selected from the group consisting of nitrogen atoms, oxygen atoms, and sulfur atoms and boron atoms, because the emission bandwidth is narrow and the color purity is high. As the multiple resonance type luminescent material, for example, compounds represented by the general formulas and specific compounds described in paragraphs

[0011] to

[0032] of WO2020 / 039930, and compounds represented by the following formulas can be preferably used as the luminescent material. The above publications described in this paragraph are hereby cited as part of this specification.

[0039] [ka]

[0040] [Host material (host material for spacer layer)] The host material for the spacer layer is preferably the same compound as the first delayed fluorescent material. For the preferred range and specific examples of the first delayed fluorescent material, the description in the above [First delayed fluorescent material and second delayed fluorescent material] can be referred to. In addition, the host material for the spacer layer can be selected from known host materials that satisfy the conditions (c) and (d). The host material for the spacer layer preferably does not contain metal atoms, and can be selected from, for example, a compound consisting of atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, and sulfur atoms, and can be selected from, for example, a compound consisting of atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, and oxygen atoms, and can be selected from, for example, a compound consisting of carbon atoms, hydrogen atoms, and nitrogen atoms. Specific examples include the host materials described in paragraph 0036 of JP 2022-132140 A. The above publications described in this paragraph are hereby cited as part of this specification.

[0041] [Other materials] As the hole transport material, for example, the following compounds can be used. [ka]

[0042] As the electron blocking material, for example, the following compounds can be used, and compounds that satisfy the condition (f) can be selected from the following compounds and used. [ka]

[0043] As the electron transport material, for example, one that satisfies the condition (d) can be selected from the following compounds. [ka]

[0044] As the hole injection material, for example, the following compounds can be used. [ka]

[0045] As the electron injection material, for example, the following compounds can be used. [ka]

[0046] Furthermore, examples of compounds that can be added to the organic layers of the organic electroluminescence element are given below, which may be used as stabilizing materials, for example.

[0047] [ka] <Design method of organic electroluminescence element> The method for designing an organic electroluminescence element of the present invention is a method for designing an organic electroluminescence element having a structure in which at least a light-emitting layer, a spacer layer, and an electron transport layer are laminated in this order between a pair of electrodes, the method comprising the steps of: [1] selecting a combination of a first delayed fluorescent material, a second delayed fluorescent material, and a light-emitting material that satisfies the following conditions (1) and (2), and designing a light-emitting layer using these materials; (1) The LUMO energy of the second delayed fluorescent material is lower than the LUMO energy of the first delayed fluorescent material. (2) The minimum excited singlet energy of the second delayed fluorescent material is lower than the minimum excited singlet energy of the first delayed fluorescent material, and the minimum excited singlet energy of the light-emitting material is lower than the minimum excited singlet energy of the second delayed fluorescent material. [2] selecting an electron transport material and a host material (host material for spacer layer) having a LUMO higher than those of the electron transport material and the second delayed fluorescent material selected in step [1], designing an electron transport layer using the electron transport material, and designing a spacer layer using the host material for spacer layer and a light-emitting material. The condition (1) in step [1] corresponds to the above condition (b), and the condition (2) corresponds to the above condition (a). The relationship between the LUMO energies of the materials in step (2) corresponds to the above conditions (c) and (d). For the options and preferred energy conditions of the first delayed fluorescent material, the second delayed fluorescent material, the light-emitting material, the host material (host material for the spacer layer) and the electron transport material used in the design method of the present invention, as well as the layer structure of the organic electroluminescence element, the corresponding descriptions in the above <Organic electroluminescence element> section can be referred to.

[0048] <Program> The program of the present invention is a program for carrying out the design method described in the above section <Design method of organic electroluminescence element>. In one embodiment of the present invention, the program includes a step (S11) of selecting a combination of a first delayed fluorescent material, a second delayed fluorescent material, and a light-emitting material that satisfies the conditions (1) and (2) (conditions (a) and (b)) by referring to, for example, a database in which the LUMO energies and the lowest excited singlet energies of delayed fluorescent materials and a database in which the lowest excited singlet energies of light-emitting materials are stored; a step (S12) of selecting a specific combination from the list of combinations selected in step (S11) and designing an emission layer using the first delayed fluorescent material, the second delayed fluorescent material, and the light-emitting material; and a step (S13) of selecting a specific combination from the list of combinations selected in step (S11) and designing an emission layer using the first delayed fluorescent material, the second delayed fluorescent material, and the light-emitting material. the step (S13) of selecting a host material that satisfies the condition (c) in relation to the specific second delayed fluorescent material selected in step (S12) with reference to the above; the step (S14) of selecting a combination of a host material and an electron transport material that satisfies the condition (d) with reference to the list of the host materials selected in step (S13) and a database in which the LUMO energies of the electron transport materials are accumulated; and the step (S15) of selecting a specific combination from the list of combinations selected in step (S14), designing an electron transport layer using the electron transport material, and designing a spacer layer using the host material and the specific light-emitting material selected in step (S12).

[0049] In one embodiment of the present invention, the program includes a step (S21) of selecting a combination of a first delayed fluorescent material, a second delayed fluorescent material, and a light-emitting material that satisfies conditions (1) and (2) (conditions (a) and (b)) by referring to, for example, a database in which the LUMO energies and the lowest excited singlet energies of delayed fluorescent materials and a database in which the lowest excited singlet energies of light-emitting materials are stored; a step (S22) of selecting a specific combination from the list of combinations selected in step (S21) and designing an emission layer using the first delayed fluorescent material, the second delayed fluorescent material, and the light-emitting material; the step (S23) of selecting a combination that satisfies the condition (d) by referring to a database in which the LUMO energies of the host material and the database in which the LUMO energies of the host material are accumulated; the step (S24) of selecting a combination that satisfies the condition (c) in relation to the specific second delayed fluorescent material selected in step (S22) from the list of combinations selected in step (S23); and the step of selecting a specific combination from the list of combinations selected in step (S24), designing an electron transport layer using the electron transport material, and designing a spacer layer using the host material and the specific light-emitting material selected in step (S22).

[0050] The above step (S11) can be performed, for example, as follows. That is, one or more combinations of the first delayed fluorescent material, the second delayed fluorescent material, and the luminescent material are assumed (S101), and it is determined whether or not the conditions (a) and (b) are satisfied for each combination (S102). If it is desired to determine other combinations, steps S11 and S12 are repeated one or more times (S103). The determination results can be output by displaying or printing as a list of combinations that satisfy the conditions (a) and (b). Steps (S13), (S14), (S21), (S23), and (S24) can also be performed in the same manner by changing the materials of the combination to the corresponding materials. The judgment result may be output for each cycle of steps (S101) and (S102), or may be output together after all cycles are completed. In step (S103), a subprogram may determine whether or not to repeat the cycle. For example, a subprogram may be used that issues a command to repeat the cycle until a specific number or more of combinations that satisfy the conditions are found. When the cycle is repeated one or more times, a new combination different from the previously assumed combination is assumed in step (S101). In this case, in step (S11), only one of the first organic compound, the second organic compound, and the third organic compound may be changed, or two of them may be changed, or all three may be changed. Also, a subprogram that reads candidate first organic compound, second organic compound, and third organic compound in advance and outputs combinations of the candidate compounds in order may be used in step (S101). Other modifications obvious to those skilled in the art may be appropriately performed. EXAMPLES

[0051] The features of the present invention will be described in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. The light emission performance was evaluated using a source meter (Keithley: 2400 series), a semiconductor parameter analyzer (Agilent Technologies: E5273A), an optical power meter (Newport: 1930C), an optical spectrometer (Ocean Optics: USB2000), a spectroradiometer (Topcon: SR-3), and a streak camera (Hamamatsu Photonics K.K.: C4334). The first and second delayed fluorescent materials, the light-emitting material, the host material for the spacer layer, the electron transporting material, and the electron blocking material used in this example are shown below.

[0052] [ka] JPEG2025044371000010.jpg190159Energy level diagrams of the organic electroluminescence elements prepared in Example 1 and Comparative Examples 1 and 2 are shown in Figures 1 to 3. In each figure, EB represents an electron exciton blocking layer (electron blocking layer), EM represents an emission layer, SP represents a spacer layer, and ET represents an electron transport / hole exciton blocking layer (electron transport layer). The upper and lower solid lines in EM and SP represent the LUMO and HOMO levels of PICTRZ2 (first delayed fluorescent material), the upper and lower dashed lines represent the LUMO and HOMO levels of 4CzIPN (second delayed fluorescent material), and the upper and lower dotted lines represent the LUMO and HOMO levels of hBNCO (emitting material). Also, Figure 1(b) shows the injection of electrons from the electron transport layer (ET) to the spacer layer (SP) and the injection of holes from the electron blocking layer (EB) to the emission layer (EM). This embodiment satisfies the conditions (d1) and (f) and is designed to reduce the driving voltage. The LUMO energy, HOMO energy, and lowest excited singlet energy of each material are summarized in Table 1.

[0053] [Table 1]

[0054] Example 1 Each thin film was deposited on a glass substrate with an anode made of indium tin oxide (ITO) with a thickness of 100 nm by vacuum deposition at a vacuum degree of 1×10 -4The film was fabricated by laminating at 1000 Pa. First, HAT-CN was evaporated on ITO to a thickness of 10 nm to form a hole injection layer, and TrisPCz was evaporated on top of that to a thickness of 30 nm to form a hole transport layer. Next, mCBP was evaporated to a thickness of 5 nm to form an electronic exciton blocking layer. Next, PICTRZ2, 4CzIPN, and hBNCO were co-evaporated from different evaporation sources to form a layer with a thickness of 20 nm to serve as the light-emitting layer. At this time, the concentration of 4CzIPN was 6 wt%, and the concentration of hBNCO was 1 wt%. On top of that, PICTRZ2 and hBNCO were co-evaporated from different evaporation sources to form a layer with a thickness of 10 nm to serve as the spacer layer. At this time, the concentration of hBNCO was 1 wt%. Next, SF3-TRZ was evaporated to a thickness of 10 nm to form an electron transport / hole exciton blocking layer, on which SF3-TRZ and Liq were co-evaporated from different evaporation sources to form a layer with a thickness of 40 nm to serve as an electron transport layer. At this time, the concentration of Liq was set to 30% by weight. Furthermore, Liq was evaporated to a thickness of 2 nm to form an electron injection layer, on which Al was evaporated to a thickness of 100 nm to form a cathode, to provide an organic electroluminescence element (EL element 1). Note that here, the "electron transport / hole exciton blocking layer" corresponds to the "electron transport layer" in the "structure in which a light-emitting layer, a spacer layer, and an electron transport layer are laminated in this order."

[0055] Comparative Example 1 An organic electroluminescence element (comparative element 1) was produced in the same manner as in Example 1, except that the light-emitting layer was formed to a thickness of 30 nm and no spacer layer was formed.

[0056] Comparative Example 2 Except for forming the light-emitting layer by co-evaporation of PICTRZ2 and hBNCO, an organic electroluminescence element (comparative element 2) was produced in the same manner as in Comparative Example 1. At this time, the concentration of hBNCO was 1% by weight. Table 2 shows the compositions and thicknesses of the light-emitting layers and spacer layers of the devices fabricated in Example 1 and Comparative Examples 1 and 2, as well as the presence or absence of a spacer layer.

[0057] [Table 2]

[0058] [evaluation] For EL element 1 and comparative elements 1 and 2, the results of measuring the change in luminance over time when a pulse voltage was applied are shown in Figures 4 to 6, the results of measuring the external quantum efficiency (EQE)-luminance characteristics of EL element 1 and comparative element 1 are shown in Figure 7, and the results of measuring the luminance lifetime of EL element 1 and comparative elements 1 and 2 are shown in Figure 8. In Figure 8, L / L0 represents the relative value of luminance with respect to the initial luminance. As shown in Figures 4 and 5, among the elements using 4CzIPN (second delayed fluorescent material), the EL element 1 having a spacer layer exhibits a steep rise in emission intensity, whereas the comparative element 1 not having a spacer layer exhibits a sluggish and broad rise in emission intensity. This is presumably because electrons transported in the SF3TRZ layer were trapped by m4CzIPN at the interface between the layers, causing quenching. In addition, as shown in Figures 5 and 6, the EL element 1 had a higher external quantum efficiency than the comparative element 1, and had a longer lifespan with less deterioration of luminance over time than the comparative elements 1 and 2. From these results, it was found that the use of a second delayed fluorescent material and the provision of a spacer layer reduced quenching and improved emission efficiency and operation stability.

[0059] [ka] [Industrial Applicability]

[0060] According to the present invention, it is possible to suppress quenching that occurs in a system in which a delayed fluorescent material is used as an assist dopant for luminescence. Therefore, by using the present invention, it is possible to realize an organic electroluminescence element having high luminous efficiency and excellent operational stability. Therefore, the present invention has a high industrial applicability.

Claims

1. An organic electroluminescence element having a structure in which at least a light-emitting layer, a spacer layer, and an electron transport layer are laminated in this order between a pair of electrodes, the light-emitting layer includes a first delayed fluorescent material, a second delayed fluorescent material having a lower LUMO energy than the first delayed fluorescent material, and a light-emitting material, and the minimum excited singlet energy of the second delayed fluorescent material is lower than the minimum excited singlet energy of the first delayed fluorescent material, and the minimum excited singlet energy of the light-emitting material is lower than the minimum excited singlet energy of the second delayed fluorescent material; the electron transport layer is made of an electron transport material, the spacer layer includes a host material having a LUMO energy higher than those of the electron transport material and the second delayed fluorescent material, and the light emitting material. Organic electroluminescent element.

2. 2. The organic electroluminescence element according to claim 1, wherein a difference in LUMO energy between the first delayed fluorescent material contained in the light-emitting layer and the host material contained in the spacer layer is within a range of 0 to 0.3 eV.

3. The organic electroluminescence device according to claim 2 , wherein the first delayed fluorescent material and the host material are the same compound.

4. 2. The organic electroluminescence device according to claim 1, wherein the spacer layer consists essentially of the host material and the light-emitting material.

5. 2 . The organic electroluminescence device according to claim 1 , wherein the LUMO energy of the host material is higher than the LUMO energy of the electron transporting material by a difference of 0.5 eV or less.

6. 2. The organic electroluminescence element according to claim 1, wherein the light-emitting layer is formed in contact with an electron blocking layer, and the HOMO energy of the first delayed fluorescent material is higher than the HOMO energy of the electron blocking material constituting the electron blocking layer.

7. 2 . The organic electroluminescence device according to claim 1 , wherein the HOMO energy of the first delayed fluorescent material is higher than the HOMO energy of the electron blocking material by a difference of 0.5 eV or less.

8. 2. The organic electroluminescence element according to claim 1, wherein a difference between the HOMO energy and the LUMO energy of the first delayed fluorescent material is within a range of 1.6 to 4.0 eV.

9. 2. The organic electroluminescence device according to claim 1, wherein the spacer layer has a thickness in the range of more than 0 μm to 0.015 μm or less.

10. The organic electroluminescence element according to any one of claims 1 to 9, wherein the concentration of the second delayed fluorescent material in the light-emitting layer is 50% by weight or less.

11. A method for designing an organic electroluminescence element having a structure in which at least a light-emitting layer, a spacer layer, and an electron transport layer are laminated in this order between a pair of electrodes, comprising the steps of: [1] selecting a combination of a first delayed fluorescent material, a second delayed fluorescent material, and a light-emitting material that satisfy the following conditions (1) and (2), and designing a light-emitting layer using these materials; (1) The LUMO energy of the second delayed fluorescent material is lower than the LUMO energy of the first delayed fluorescent material. O has low energy. (2) The minimum excited singlet energy of the second delayed fluorescent material is smaller than the minimum excited singlet energy of the first delayed fluorescent material. The lowest excited singlet energy of the second delayed fluorescent material is lower than the lowest excited singlet energy of the second delayed fluorescent material. The lowest excited singlet energy of the luminescent material is low. [2] selecting an electron transport material and a host material having a LUMO energy higher than those of the electron transport material and the second delayed fluorescent material, designing the electron transport layer using the electron transport material, and designing a spacer layer using the host material and the light emitting material; A method for designing an organic electroluminescence element, comprising:

12. A program for implementing the design method according to claim 11.

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