Organic el element
The organic EL element with aligned energy levels in the acceptor and donor layers addresses the inefficiencies in conventional elements, achieving superior luminous efficiency and luminance through triplet annihilation and energy transfer mechanisms.
Patent Information
- Application Number
- JP2024012785
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-01-31
- Publication Date
- 2025-08-13
AI Technical Summary
Conventional organic EL elements have room for improvement in luminous efficiency and luminance.
An organic EL element comprising a laminate sandwiched between electrodes, with an acceptor layer and a donor layer forming an interface, where the acceptor layer contains acceptor molecules and the donor layer contains donor molecules that undergo triplet annihilation, and the energy levels of these molecules are specifically aligned to prevent non-radiative decay and enhance energy transfer.
The solution results in an organic EL element with enhanced luminous efficiency and luminance, as evidenced by improved light emission and reduced non-radiative deactivation pathways.
Smart Images
Figure 2025117840000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to an organic EL device. [Background technology]
[0002] An organic electroluminescence element (organic EL element) is an element that includes one or more organic semiconductor layers sandwiched between a pair of electrodes, and emits light by itself when a voltage is applied between the electrodes.
[0003] In recent years, research into improving the luminous efficiency and luminance of organic EL elements has been actively conducted. For example, the present inventors have proposed an organic EL element having a specific configuration and excellent luminous efficiency and luminance (see Patent Document 1). [Prior art documents] [Patent documents]
[0004] [Patent Document 1] International Publication No. 2022 / 211041 Summary of the Invention [Problem to be solved by the invention]
[0005] However, as a result of investigations by the present inventors, it has become clear that there is room for improvement in the luminous efficiency and luminance of conventional organic EL elements such as those disclosed in Patent Document 1.
[0006] Therefore, an object of the present invention is to provide an organic EL element that is excellent in luminous efficiency and luminance. [Means for solving the problem]
[0007] In view of the above circumstances, the present inventors have conducted extensive research and have come up with an organic EL element having the following configuration. That is, the organic EL element of the present invention is An organic EL element comprising a pair of electrodes and a laminate sandwiched between the electrodes, the stack includes an acceptor layer and a donor layer that forms an interface with the acceptor layer; the acceptor layer includes acceptor molecules; the donor layer comprises a donor molecule that undergoes triplet annihilation; The HOMO level of the acceptor molecule is lower than the HOMO level of the donor molecule, and the LUMO level of the acceptor molecule is lower than the LUMO level of the donor molecule, The excited triplet level of the donor molecule is smaller than the energy difference between the HOMO level of the donor molecule and the LUMO level of the acceptor molecule plus 0.1 eV. The excited triplet level of the acceptor molecule is greater than the energy difference between the HOMO level of the donor molecule and the LUMO level of the acceptor molecule. The energy difference between the HOMO level of the donor molecule and the LUMO level of the acceptor molecule is smaller than the energy difference between the HOMO level and the LUMO level of the donor molecule by 0.4 eV or more. However, this does not include the case where the acceptor layer is composed of an acceptor molecule represented by the following formula (A), the donor layer is composed of a first layer that forms an interface with the acceptor layer and a second layer laminated on the first layer, the first layer is composed of a donor molecule represented by the following formula (B) and a dopant molecule represented by the following formula (C), and the second layer is composed of a donor molecule represented by the following formula (B). [ka] [ka] [ka]
[0008] Such an organic EL element has excellent luminous efficiency and luminance, and although the reason for this is not entirely clear, the inventors' considerations will be explained with reference to FIGS.
[0009] Figure 1 is a conceptual diagram showing the mechanism by which light is emitted by the organic EL element of the present invention. In Figure 1, organic EL element 10 has acceptor layer 1, donor layer 2 forming an interface with acceptor layer 1, first electrode 3 formed on the acceptor layer 1 side, and second electrode 4 formed on the donor layer 2 side. In the explanation here, as in the examples, acceptor layer 1 corresponds to an electron transport layer, donor layer 2 corresponds to an emitting layer, first electrode 3 corresponds to a cathode, and second electrode 4 corresponds to an anode, respectively.
[0010] When electrons (-) are injected from the cathode and holes (+) are injected from the anode into the organic EL device 10, electron (-)-hole (+) pairs form a charge transfer (CT) state at the interface between the acceptor layer 1 and the donor layer 2. The CT state undergoes charge recombination, resulting in the triplet state T of the donor molecule in the donor layer 2. 1D is generated. Triplet-triplet annihilation (TTA) occurs in the donor layer 2, generating a high-energy excited state (S1). When no dopant molecules are present in the donor layer 2, light emission originates from the donor molecules. When dopant molecules are present in the donor layer 2, energy transfer occurs from the donor molecules to the dopant molecules, resulting in light emission originating from the dopant molecules.
[0011] Figure 2 shows the energy levels of rubrene, perylene, NDI-HF, and NDI-Cy used in the examples. NDI-HF and NDI-Cy correspond to acceptor molecules, and rubrene and perylene correspond to donor molecules. The HOMO level of the acceptor molecule is lower than that of the donor molecule, the LUMO level of the acceptor molecule is lower than that of the donor molecule, and the energy difference between the HOMO level of the donor molecule and the LUMO level of the acceptor molecule is 0.4 eV or more smaller than the energy difference between the HOMO level and the LUMO level of the donor molecule. Therefore, it is believed that electron (-)-hole (+) pairs injected from the electrode can form a CT state at the interface between the acceptor layer 1 and the donor layer 2.
[0012] Fig. 3(A) is a schematic diagram showing the energy transfer mechanism up to light emission in the organic EL device of the present invention. The energy difference between the HOMO level of the donor molecule and the LUMO level of the acceptor molecule corresponds to the energy level of the CT3 state (hereinafter, also simply referred to as "CT"). In Fig. 3(A), the excited triplet level T 1A is larger than CT (for example, T 1A’ ), the excited triplet level T of the donor molecule 1D is smaller than CT plus 0.1 eV. On the other hand, as shown in Figure 3(B), when the excited triplet level of the acceptor molecule is smaller than CT (for example, T 1A’’ The energy efficiency of the organic EL device of the present invention is inferior to that of the organic EL device of the present invention. The reason for this is that, as shown in FIG. 3(B), the excited triplet state T 1D and energy transfer to the excited triplet state of the acceptor molecule, T 1A’’ One possible reason is that there is a route where the acceptor returns to its ground state S0 through non-radiative decay due to competition between the two. On the other hand, as shown in Figure 3(A), the excited triplet level T 1A T is greater than CT 1A’ In this case, non-radiative deactivation via the above route is sufficiently prevented, and energy efficiency is thought to be improved. Furthermore, in the organic EL device of the present invention, the excited triplet level T 1D is smaller than the value obtained by adding 0.1 eV to CT, it is thought that the electron (-)-hole (+) pair can pass through the CT state and generate a triplet state of the donor molecule in the donor layer 2. Note that although Figure 3(A) illustrates an example in which light emission originates from the donor molecule, if dopant molecules are present in the donor layer 2, energy transfer occurs from the donor molecule to the dopant molecule, resulting in light emission originating from the dopant molecule.
[0013] Excited triplet level T of the donor molecule 1Dis preferably equal to or smaller than CT from the viewpoint of further improving energy efficiency.
[0014] From the viewpoint of further improving the luminous efficiency, the donor layer preferably further contains dopant molecules.
[0015] The donor layer may have a first layer that forms an interface with the acceptor layer and a second layer stacked on the first layer, wherein the first layer contains donor molecules that cause triplet annihilation, and the second layer contains the donor molecules and dopant molecules.
[0016] The donor layer may also have a first layer that forms an interface with the acceptor layer, a second layer stacked on the first layer, and a third layer stacked on the second layer, wherein the first layer contains a donor molecule that causes triplet annihilation, the second layer contains the donor molecule and a dopant molecule, and the third layer contains the donor molecule. [Effects of the Invention]
[0017] According to the present invention, it is possible to provide an organic EL element having excellent luminous efficiency and luminous brightness. [Brief explanation of the drawings]
[0018] [Figure 1] FIG. 1 is a conceptual diagram illustrating the mechanism by which light is emitted by the organic EL element of the present invention. [Figure 2] FIG. 1 shows the energy levels of rubrene, perylene, NDI-HF, and NDI-Cy used in the examples. [Figure 3] FIG. 1A is a schematic diagram showing the energy transfer mechanism up to light emission in an organic EL element of the present invention, and FIG. 1B is a schematic diagram showing the energy transfer mechanism in an organic EL element outside the scope of the present invention. [Figure 4] FIG. 1 is a diagram showing the measurement results of the excited triplet level T1 of NDI-HF. [Figure 5] FIG. 1 shows the measurement results of the excited triplet level T1 of NDI-Cy. [Figure 6]1 is a cross-sectional view of an organic EL element according to Example 1. FIG. [Figure 7] FIG. 1 is a graph showing the measurement results of applied voltage-luminance characteristics of the organic EL elements of Examples 1 and 2 and Comparative Example 1A. [Figure 8] FIG. 1 is a diagram showing the measurement results of the device lifetime of the organic EL elements of Reference Example 1 and Comparative Example 1B. [Figure 9] FIG. 1 is a graph showing the measurement results of the external quantum efficiency (EQE) of the organic EL devices of Examples 1 and 3 and Reference Example 1. [Figure 10] FIG. 10 is a graph showing the measurement results of applied voltage-luminance characteristics of the organic EL elements of Example 4 and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION
[0019] An embodiment of the present invention will be described in detail below, although the present invention is not limited to the following embodiment.
[0020] The organic EL element of this embodiment includes a laminate sandwiched between a pair of electrodes.
[0021] The laminate has an acceptor layer containing acceptor molecules and a donor layer containing donor molecules, and the acceptor layer and donor layer form an interface. The laminate may have an organic semiconductor layer other than the acceptor layer and the donor layer, and may further include an inorganic compound layer such as a molybdenum trioxide (MoO3) layer (hole transport layer or electron injection layer) or a lithium fluoride layer (electron injection layer) between the electrodes.
[0022] The acceptor layer may be formed only from acceptor molecules, or may contain materials other than acceptor molecules as long as the effects of the present invention are not significantly impaired.
[0023] The donor molecule is a material that causes triplet-triplet annihilation. The donor layer may be formed only from the donor molecule, or only from the donor molecule and the dopant molecule, or may contain materials other than the donor molecule and the dopant molecule as long as the effects of the present invention are not significantly impaired.
[0024] The donor layer may be formed from multiple layers. For example, the donor layer may be a two-layer donor layer having a first layer that forms an interface with the acceptor layer and a second layer stacked on the first layer (the second layer facing the acceptor layer across the first layer), or a three-layer donor layer having a first layer that forms an interface with the acceptor layer, a second layer stacked on the first layer (the second layer facing the acceptor layer across the first layer), and a third layer stacked on the second layer (the third layer facing the first layer across the second layer). When the donor layer is formed from multiple layers, each layer contains the same donor molecule.
[0025] When the donor layer contains donor molecules and dopant molecules, the donor layer preferably has an intermediate layer (hereinafter also referred to as "intermediate layer") that does not contain dopant molecules but contains donor molecules between the layer containing donor molecules and dopant molecules and the acceptor layer, from the viewpoint of further improving luminous efficiency. The reason why luminous efficiency is improved by the donor layer having an intermediate layer is not necessarily clear, but one reason is thought to be that light emission occurs away from the interface between the donor layer and the acceptor layer, thereby preventing interface quenching of excitons.
[0026] When an intermediate layer is present, its thickness can be, for example, 1 to 10 nm, preferably 1 to 5 nm.
[0027] The above-mentioned two-layer donor layer may have, for example, the first layer being the intermediate layer and the second layer being made up of the donor molecule and the dopant molecule.
[0028] The above-mentioned three-layer donor layer may have, for example, the first layer being the intermediate layer, the second layer consisting of the donor molecule and the dopant molecule, and the third layer consisting of the donor molecule.
[0029] The HOMO level of the acceptor molecule is lower than that of the donor molecule. From the viewpoint of highly preventing hole leakage and further improving luminous efficiency, the difference between the HOMO levels of the acceptor molecule and the donor molecule is preferably 0.5 eV or more. Note that the upper limit of the difference between the HOMO levels of the acceptor molecule and the donor molecule is not particularly limited, but can be, for example, 2 eV or less.
[0030] The LUMO level of the acceptor molecule is lower than that of the donor molecule. The difference between the LUMO levels of the acceptor molecule and the donor molecule is preferably 0.3 eV or more from the viewpoint of highly preventing electron leakage and further improving luminous efficiency. The upper limit of the difference between the LUMO levels of the acceptor molecule and the donor molecule is not particularly limited, but can be, for example, 2 eV or less.
[0031] Excited triplet level T of the donor molecule 1D is preferably smaller than CT plus 0.1 eV, and is equal to or smaller than CT. 1D The difference between CT and CT is preferably less than 0.8 eV, more preferably less than 0.7 eV, and even more preferably less than 0.6 eV. If these differences are small, the light emission start voltage can be reduced.
[0032] The CT is at least 0.4 eV smaller than the energy difference between the HOMO level and the LUMO level of the donor molecule. There is no particular upper limit to the CT, but it can be set to, for example, 2 eV or less.
[0033] When the donor layer contains donor molecules and dopant molecules, it is preferable that the energy difference between the HOMO level and the LUMO level of the dopant molecules is smaller than the energy difference between the HOMO level and the LUMO level of the donor molecules. When the dopant molecules are used, energy transfer occurs from the donor molecules to the dopant molecules, and light emission originating from the dopant molecules can be realized.
[0034] The content of the dopant molecules in the donor layer can be, for example, 0.01 to 50% by volume, and preferably 0.1 to 10% by volume, relative to 100% by volume of the total amount of the donor layer.
[0035] As the acceptor molecule, for example, a conventionally known electron transporting material can be used, and specific examples thereof include the compounds shown below.
[0036] [ka]
[0037] [ka]
[0038] [ka]
[0039] [ka]
[0040] As the donor molecule, for example, the following compounds that have been reported to produce TTA can be used.
[0041] [ka]
[0042] [ka]
[0043] [ka] (Chem. Rev. 2015, 115, 395-465 reference)
[0044] The energy levels of these compounds, such as the HOMO level, LUMO level, and excited triplet level T1, are specific to the material, and reference values can be used.
[0045] As the dopant molecule, a conventionally known light-emitting material can be used. Specific examples of the dopant molecule include the compounds shown below.
[0046] [ka]
[0047] [ka]
[0048] [ka]
[0049] The organic EL element of the present embodiment may be formed from a pair of electrodes, an acceptor layer, and a donor layer, as shown in FIG. 1, or may include other conventionally known organic semiconductor layers, inorganic compound layers, etc.
[0050] The organic EL device of this embodiment may have, between a pair of electrodes, layers such as a hole injection layer, an electron blocking layer, a hole transport layer, an emitting layer, an electron transport layer, a hole blocking layer, and an electron injection layer, in this order from the anode. Among these, the acceptor layer may be the electron transport layer, and the donor layer may be the emitting layer.
[0051] The functions of these layers are not strictly distinguished. For example, the light-emitting layer, which is a donor layer, may also function as a hole-transporting layer, and the hole-blocking layer may also function as an electron-injecting layer.
[0052] The order of the layers in the organic EL element is not limited to the above. For example, the hole injection layer may be located between the electron blocking layer and the hole transport layer, or the electron injection layer may be located between the hole blocking layer and the electron transport layer.
[0053] The layers in the organic EL device may contain the same organic semiconductor material. For example, when the organic EL device contains rubrene as a donor molecule in the donor layer (light-emitting layer), the organic EL device may have a hole-blocking layer formed from rubrene.
[0054] The organic EL device of this embodiment can be manufactured by forming an acceptor layer and a donor layer by a conventionally known method, such as vacuum deposition, chemical vapor deposition, sputtering, vapor deposition polymerization, spin coating, blade coating, bar coating, dip coating, or laminating. Specifically, the organic EL device of this embodiment can be manufactured by, for example, laminating a first electrode, an acceptor layer, a donor layer, a second electrode, and any other layers on a substrate. The method for forming each organic semiconductor layer can be appropriately selected depending on the compound. Examples of substrates that can be used include glass substrates, quartz substrates, sapphire substrates, plastic substrates, and film substrates.
[0055] The thickness of the acceptor layer and the donor layer in the organic EL device of this embodiment is not particularly limited, but is preferably 0.1 nm to 500 nm, more preferably 2 nm to 200 nm.
[0056] Organic EL elements are expected to be applied to, for example, organic EL displays, organic EL lighting, digital signage, light sources for photosensors, laser light sources, light sources for optical communications, and the like. [Example]
[0057] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples. The structures of the compounds used in the examples are shown below.
[0058] [ka]
[0059] (Measurement of excited triplet level T1 of NDI-HF and NDI-Cy) The excited triplet level T1 was determined from the peak intensity of the phosphorescence spectrum measured at liquid nitrogen temperature using a spectrofluorometer (JASCO Corporation, Model FP-8650). When multiple peaks were detected, the peak on the higher energy side was used. For NDI-HF, a 50 nm-thick thin film was deposited on a quartz substrate as a sample, and for NDI-Cy, a 10 -5 A chloroform solution of 100 mol / L concentration was placed in a sample tube with a diameter of 5 mm to serve as a sample. The measurement results of the excited triplet level T1 for NDI-HF and NDI-Cy are shown in Figures 4 and 5, respectively.
[0060] Example 1 On a glass substrate coated with indium tin oxide (ITO) (ITO thickness: 150 nm, sheet resistance: 10.3 Ω / □, Technoprint Co., Ltd.), a MoO hole transport layer (10 nm), a rubrene layer (undoped) (10 nm), a rubrene layer (DBP-doped) (100 nm), a rubrene layer (undoped) (2 nm), an NDI-HF layer (50 nm), a LiF electron injection layer (3 nm), a MoO electron injection layer (3 nm), and an Al electrode (100 nm) were deposited in this order in a vacuum deposition system under high vacuum (~10 -5 The device was thermally evaporated at 1000 kJ / cm² (Pa). The device was then sealed with a glass substrate and epoxy resin in a glove box to obtain an organic EL device. The rubrene layer (DBP-doped) was formed by adding DBP as a dopant at 0.5% by volume relative to the entire rubrene layer and introducing DBP into the rubrene layer by co-evaporation. The mixed concentration was controlled by the ratio of the evaporation rates. The obtained organic EL device had the following configuration. ITO electrode / MoO3 hole transport layer / Rubrene layer (undoped) / Rubrene layer (DBP doped) / Rubrene layer (undoped) / NDI-HF layer / LiF electron injection layer / MoO3 electron injection layer / Al electrode Fig. 6 is a cross-sectional view of the organic EL device of Example 1. The organic EL device 100 shown in Fig. 6 has a structure in which a glass substrate 11, an ITO electrode 12, a MoO hole transport layer 13, an undoped rubrene layer 14A, a DBP-doped rubrene layer 14B, an undoped rubrene layer 14C, an NDI-HF layer 15, a LiF electron injection layer 16, a MoO electron injection layer 17, and an Al electrode 18 are laminated in this order. In the organic EL device 100, the rubrene (undoped) layer 14A, the rubrene (DBP-doped) layer 14B, and the rubrene (undoped) layer 14C correspond to the donor layer 14, and the NDI-HF layer 15 corresponds to the acceptor layer.
[0061] Example 2 An organic EL device was produced in the same manner as in Example 1, except that an NDI-Cy layer (50 nm) was formed by thermal evaporation instead of the NDI-HF layer. This organic EL device had the following configuration. ITO electrode / MoO3 hole transport layer / Rubrene layer (undoped) / Rubrene layer (DBP doped) / Rubrene layer (undoped) / NDI-Cy layer / LiF electron injection layer / MoO3 electron injection layer / Al electrode
[0062] (Comparative Example 1A) An organic EL device was produced in the same manner as in Example 1, except that a PTCDI-C8 layer (50 nm) was formed by thermal evaporation instead of the NDI-HF layer. This organic EL device had the following configuration. ITO electrode / MoO3 hole transport layer / Rubrene layer (undoped) / Rubrene layer (DBP doped) / Rubrene layer (undoped) / PTCDI-C8 layer / LiF electron injection layer / MoO3 electron injection layer / Al electrode
[0063] (Comparative example 1B) An organic EL device was fabricated in the same manner as in Comparative Example 1A, except that the rubrene layer (undoped) in contact with the PTCDI-C8 layer was omitted. This organic EL device had the following configuration. ITO electrode / MoO3 hole transport layer / Rubrene layer (undoped) / Rubrene layer (DBP doped) / PTCDI-C8 layer / LiF electron injection layer / MoO3 electron injection layer / Al electrode
[0064] <Evaluation of organic EL elements 1> The applied voltage-luminance characteristics of the organic EL devices of Examples 1 and 2 and Comparative Example 1A were measured using a source measure unit (B2902A manufactured by Keysight Technologies) and a luminance meter (BM-9 manufactured by Topcom). The results are shown in FIG. As is clear from FIG. 7, the organic EL elements of Examples 1 and 2 are superior in luminance compared to the organic EL element of Comparative Example 1A.
[0065] (Example 3: Study of Intermediate Layer Thickness) An organic EL device was fabricated in the same manner as in Example 1, except that the thickness of the intermediate layer (rubrene layer (undoped)) corresponding to the first layer of the donor layer was changed from 2 nm to 4 nm.
[0066] (Reference Example 1: Consideration of the case where there is no intermediate layer) An organic EL device was produced in the same manner as in Example 1, except that the intermediate layer (rubrene layer (undoped)) corresponding to the first layer of the donor layer was omitted. The obtained organic EL device had the following configuration. ITO electrode / MoO3 hole transport layer / Rubrene layer (undoped) / Rubrene layer (DBP doped) / NDI-HF layer / LiF electron injection layer / MoO3 electron injection layer / Al electrode
[0067] <Lifespan evaluation> The device lifetimes (assessed as LT95, the time it takes for the brightness to decrease to 95%, assuming the initial brightness to be 100%) of the organic EL elements of Reference Example 1 and Comparative Example 1B are shown in Figure 8. As is clear from Figure 8, the organic EL element of Reference Example 1 had an LT95 of 20 hours or more, which is about twice as long as the organic EL element of Comparative Example 1B, which had an LT95 of 10 hours.
[0068] <Evaluation of Organic EL Elements 2> The external quantum yields (EQEs) of the organic EL devices of Examples 1 and 3 and Reference Example 1 were measured using a calibrated high-sensitivity broadband spectrometer (AvaSpec-UV / VIS / NIR, manufactured by Avantes), and the results are shown in FIG. As is clear from FIG. 9, the luminous efficiency is highest when the thickness of the intermediate layer is 2 nm.
[0069] Example 4 On a glass substrate coated with indium tin oxide (ITO) (ITO thickness: 150 nm, sheet resistance: 10.3 Ω / □, Technoprint Co., Ltd.), a MoO hole transport layer (10 nm), a perylene layer (undoped) (50 nm), an NDI-HF layer (50 nm), a LiF electron injection layer (3 nm), a MoO electron injection layer (3 nm), and an Al electrode (100 nm) were deposited in this order in a vacuum deposition system under high vacuum (~10 -5 The device was thermally evaporated at 2000 K (Pa). The device was encapsulated with a glass substrate and epoxy resin in a glove box to obtain an organic EL device. The obtained organic EL device had the following configuration. ITO electrode / MoO3 hole transport layer / perylene layer (undoped) / NDI-HF layer / LiF electron injection layer / MoO3 electron injection layer / Al electrode In the organic EL device of Example 4, the "perylene layer (undoped)" corresponds to the donor layer, and the NDI-HF layer corresponds to the acceptor layer.
[0070] (Comparative Example 2) An organic EL device was produced in the same manner as in Example 4, except that a PTCDI-C8 layer (50 nm) was formed by thermal evaporation instead of the NDI-HF layer. This organic EL device had the following configuration. ITO electrode / MoO3 hole transport layer / perylene layer (undoped) / PTCDI-C8 layer / LiF electron injection layer / MoO3 electron injection layer / Al electrode
[0071] <Evaluation of Organic EL Elements 3> The applied voltage-luminance characteristics of the organic EL elements of Example 4 and Comparative Example 2 were measured using a source measure unit (B2902A manufactured by Keysight Technologies) and a luminance meter (BM-9 manufactured by Topcom). The results are shown in FIG. As is clear from FIG. 10, the organic EL element of Example 4 is superior to the organic EL element of Comparative Example 2 in luminance. [Explanation of symbols]
[0072] 1...acceptor layer, 2...donor layer, 3...first electrode, 4...second electrode, 10,100...organic EL element, 11...glass substrate, 12...ITO electrode, 13...MoO3 hole transport layer, 14...donor layer, 14A,14C...rubrene (undoped) layer, 14B...rubrene (DBP doped) layer, 15...NDI-HF layer, 16...LiF electron injection layer, 17...MoO3 electron injection layer, 18...Al electrode.
Claims
1. An organic EL element comprising a pair of electrodes and a laminate sandwiched between the electrodes, the stack includes an acceptor layer and a donor layer that forms an interface with the acceptor layer; the acceptor layer includes acceptor molecules; the donor layer comprises a donor molecule that undergoes triplet annihilation; the HOMO level of the acceptor molecule is lower than the HOMO level of the donor molecule, and the LUMO level of the acceptor molecule is lower than the LUMO level of the donor molecule; the excited triplet level of the donor molecule is smaller than the energy difference between the HOMO level of the donor molecule and the LUMO level of the acceptor molecule plus 0.1 eV; The excited triplet level of the acceptor molecule is larger than the energy difference between the HOMO level of the donor molecule and the LUMO level of the acceptor molecule, An organic EL element in which the energy difference between the HOMO level of the donor molecule and the LUMO level of the acceptor molecule is smaller by 0.4 eV or more than the energy difference between the HOMO level and the LUMO level of the donor molecule (excluding the case where the acceptor layer is made of an acceptor molecule represented by the following formula (A), the donor layer is made of a first layer forming an interface with the acceptor layer and a second layer laminated on the first layer, the first layer is made of a donor molecule represented by the following formula (B) and a dopant molecule represented by the following formula (C), and the second layer is made of a donor molecule represented by the following formula (B)). 【Chemical 1】 【Chemistry 2】 【Chemistry 3】
2. 2. The organic EL device according to claim 1, wherein the excited triplet level of the donor molecule is equal to or smaller than the energy difference between the HOMO level of the donor molecule and the LUMO level of the acceptor molecule.
3. The organic electroluminescent device according to claim 1 , wherein the donor layer further comprises dopant molecules.
4. the donor layer has a first layer that forms an interface with the acceptor layer and a second layer stacked on the first layer; the first layer comprises a donor molecule that undergoes triplet annihilation; 3. The organic electroluminescent device according to claim 1, wherein the second layer comprises the donor molecules and the dopant molecules.
5. the donor layer has a first layer forming an interface with the acceptor layer, a second layer stacked on the first layer, and a third layer stacked on the second layer; the first layer comprises a donor molecule that undergoes triplet annihilation; the second layer includes the donor molecule and the dopant molecule; 3. The organic electroluminescent device according to claim 1, wherein the third layer comprises the donor molecule.
Citation Information
Patent Citations
Organic electroluminescent element
WO2022211041A1