Organic el element

Abstract

An organic EL element is an organic EL element provided with a first organic semiconductor layer held between a pair of electrodes and a second organic semiconductor layer forming an interface with the first organic semiconductor layer, the second organic semiconductor layer containing an organic semiconductor material generating triplet-triplet annihilation and one or more kinds of guest materials that emit light by energy transfer from energy generated by triplet-triplet annihilation based on the organic semiconductor material, the second organic semiconductor layer being capable of emitting white light by light emission from the plurality of kinds of guest materials or light emission from the organic semiconductor material and the one or more kinds of guest materials.

Description

Technical Field

[0001] This disclosure relates to organic EL devices. Background Technology

[0002] In organic EL devices having a light-emitting layer and a hole injection layer, it is known that a technique can emit light by applying a low voltage between a pair of electrodes holding the light-emitting layer and the hole injection layer (for example, refer to International Publication No. 2022 / 211041 (hereinafter referred to as Patent Document 1). The organic EL device described in Patent Document 1 has: a first organic semiconductor layer comprising a first organic semiconductor material; and a second organic semiconductor layer comprising a second organic semiconductor material and a guest material, and forming a junction with the first organic semiconductor. The second organic semiconductor material contained in the second organic semiconductor layer is a material that undergoes triplet-triplet annihilation, and the guest material contained in the second organic semiconductor layer is a material that generates light emission.

[0003] In the organic EL device described in Patent Document 1, when a voltage is applied between a pair of electrodes, a charge-transfer state is formed at the junction between the first organic semiconductor layer and the second organic semiconductor layer. The charges formed at the junction are recombinated, generating a triplet state of the second organic semiconductor material. The second organic semiconductor material, having generated a triplet state, undergoes triplet-triplet annihilation, thereby generating a high-energy excited state. Energy is transferred from the second organic semiconductor material to the guest material, resulting in luminescence originating from the guest material.

[0004] The organic EL element described in Patent Document 1 can reduce the voltage applied when generating light emission from the guest material by optimizing the relationship between the LUMO energy level of the first organic semiconductor material and the HOMO energy level of the second organic semiconductor material and the excited triplet energy level. Summary of the Invention

[0005] However, in the organic EL element described in Patent Document 1, the emitted light is only emitted from a single guest material, so it is not easy to emit white light.

[0006] This disclosure was made to solve such a problem, and its purpose is to provide an organic EL element capable of emitting white light.

[0007] The organic EL device disclosed herein is an organic EL device having a first organic semiconductor layer sandwiched between a pair of electrodes and a second organic semiconductor layer forming an interface with the first organic semiconductor layer. The second organic semiconductor layer includes an organic semiconductor material that generates triplet-triplet annihilation and one or more guest materials. The guest materials emit light through energy transfer generated by triplet-triplet annihilation based on the organic semiconductor material. The second organic semiconductor layer is capable of emitting white light through light emitted by a variety of guest materials or through light emitted by the organic semiconductor material and one or more guest materials.

[0008] Furthermore, in the organic EL element disclosed herein, it is preferable that white light has chromaticity contained in the following circular region: a circular region with a radius of 0.1 starting from the center point ((x, y) = (0.31, 0.316)) of the white region in the CIExy chromaticity diagram of JIS Z8110.

[0009] Furthermore, in the organic EL element disclosed herein, the organic semiconductor material preferably includes a compound that emits blue light by being excited through triplet-triplet annihilation, and the guest material preferably includes a compound that emits yellow or orange light by energy transfer generated by triplet-triplet annihilation based on the organic semiconductor material.

[0010] Furthermore, in the organic EL element disclosed herein, the guest material preferably includes a first guest material and a second guest material, wherein the first guest material emits blue light through energy transfer generated by triplet-triplet annihilation based on organic semiconductor materials, and the second guest material emits yellow or orange light through energy transfer from the first guest material.

[0011] Furthermore, in the organic EL element disclosed herein, it is preferred that: the organic semiconductor material comprises a compound that emits blue light by being excited through triplet-triplet annihilation, the guest material comprises a first guest material and a second guest material, the first guest material emits green light by energy transfer generated by triplet-triplet annihilation based on the organic semiconductor material, and the second guest material emits orange or red light by energy transfer from the first guest material.

[0012] Furthermore, in the organic EL element disclosed herein, the guest material preferably further includes a first guest material, a second guest material, and a third guest material. The first guest material emits blue light through energy transfer generated by triplet-triplet annihilation based on organic semiconductor materials, the second guest material emits green light through energy transfer from the first guest material, and the third guest material emits orange or red light through energy transfer from the second guest material.

[0013] Furthermore, in the method of using the organic EL element disclosed herein, it is preferable to set the current density supplied to the pair of electrodes within the following range: 100 mA / cm². 2 Above and 1000mA / cm 2 Below and within the range of white light emitted.

[0014] Furthermore, in the method of using the organic EL element disclosed herein, it is preferable that the current density supplied to the pair of electrodes is 1 mA / cm². 2 Above and 10mA / cm 2 the following.

[0015] public

[0016] The organic EL element disclosed herein is capable of emitting white light. Attached Figure Description

[0017] Figure 1 This is a diagram showing a light-emitting device having an organic EL element according to the first embodiment.

[0018] Figure 2 This is a diagram representing the area of ​​white.

[0019] Figure 3 It means Figure 1 The diagram shows the light-emitting mechanism of an organic EL element.

[0020] Figure 4 It indicates accompaniment Figure 3 The diagram shows the energy transfer of the emitted light.

[0021] Figure 5 This is a diagram showing a light-emitting device having an organic EL element according to the second embodiment.

[0022] Figure 6 It means Figure 5 The diagram shows the light-emitting mechanism of an organic EL element.

[0023] Figure 7 It indicates accompaniment Figure 6 The diagram shows the energy transfer of the emitted light.

[0024] Figure 8 This is a diagram showing a light-emitting device having an organic EL element according to the third embodiment.

[0025] Figure 9 It means Figure 8 The diagram shows the light-emitting mechanism of an organic EL element.

[0026] Figure 10 It indicates accompaniment Figure 9 The diagram shows the energy transfer of the emitted light.

[0027] Figure 11 This is a diagram showing a light-emitting device having an organic EL element according to the fourth embodiment.

[0028] Figure 12 It means Figure 11 The diagram shows the light-emitting mechanism of an organic EL element.

[0029] Figure 13 It indicates accompaniment Figure 12 The diagram shows the energy transfer of the emitted light.

[0030] Figure 14 This is a diagram showing a light-emitting device having an organic EL element according to the fifth embodiment.

[0031] Figure 15 It means Figure 14 The diagram shows the light-emitting mechanism of an organic EL element.

[0032] Figure 16 It indicates accompaniment Figure 15 The diagram shows the energy transfer of the emitted light.

[0033] Figure 17 This is a graph showing the light emission start voltage and white light emission characteristics of the organic EL element in Example 1.

[0034] Figure 18 This is a graph showing the light emission start voltage and white light emission characteristics of the organic EL element in Example 2.

[0035] Figure 19 This is a graph showing the light emission start voltage and white light emission characteristics of the organic EL element in Example 3.

[0036] Figure 20 This is a graph showing the light emission start voltage and white light emission characteristics of the organic EL element in Example 4.

[0037] Figure 21 This is a graph showing the light emission start voltage and white light emission characteristics of the organic EL element in Example 5.

[0038] Figure 22 This is a graph showing the light emission start voltage and white light emission characteristics of the organic EL element in Example 6.

[0039] Figure 23 This is a graph showing the light emission start voltage of the organic EL element in Comparative Example 1.

[0040] Figure 24 This is a graph showing the light emission start voltage of the organic EL element in Comparative Example 2.

[0041] Figure 25This is a graph showing the light emission start voltage and light emission characteristics of the organic EL element in Comparative Example 3.

[0042] Figure 26 This is a graph showing the light emission start voltage and light emission intensity characteristics of the organic EL element in Example 3.

[0043] Figure 27 This is a graph showing the light emission start voltage and light emission intensity characteristics of the organic EL element in Example 4.

[0044] Figure 28 This is a graph showing the light emission start voltage and light emission intensity characteristics of the organic EL element in Example 5.

[0045] Figure 29 This is a graph showing the light emission start voltage and light emission intensity characteristics of the organic EL element in Example 6.

[0046] Figure 30 This is a graph showing the light emission start voltage and light emission intensity characteristics of the organic EL element in Example 7.

[0047] Figure 31 This is a graph showing the light emission start voltage and light emission intensity characteristics of the organic EL element in Comparative Example 1.

[0048] Figure 32 This is a graph showing the light emission start voltage and light emission intensity characteristics of the organic EL element in Comparative Example 4.

[0049] Figure 33 This is a graph showing the light emission start voltage and light emission intensity characteristics of the organic EL element in Comparative Example 5. Detailed Implementation

[0050] The organic EL element involved in this disclosure will now be described with reference to the accompanying drawings. However, it should be noted that the scope of protection of this invention is not limited to these embodiments, but extends to the invention as described in the claims and its equivalents.

[0051] (The structure and function of the organic EL element in the first embodiment)

[0052] Figure 1 This is a diagram showing a light-emitting device having an organic EL element according to the first embodiment.

[0053] The light-emitting device 100 includes a power supply 101 and an organic EL element 1, and is suitable for organic EL displays, organic EL lighting, digital signage, light sources for light sensors, laser light sources, and light sources for optical communication, etc. The power supply 101 supplies the desired current to the organic EL element 1 according to the instructions of a control device (not shown). The structure and function of the power supply 101 are well known, therefore a detailed description is omitted here.

[0054] The organic EL element 1 has a first electrode 11 and a second electrode 12 as a pair of electrodes, a first organic semiconductor layer 13 also called an electron transport layer, and a second organic semiconductor layer 14 also called a light-emitting layer and forming an interface 15 with the first organic semiconductor layer 13. The organic EL element 1 emits white light in response to a predetermined light-emitting start voltage being applied between the first electrode 11 and the second electrode 12 and a current I flowing from the first electrode 11 to the second electrode 12 being supplied from the power supply 101.

[0055] Figure 2 This is a diagram representing the area of ​​white. Figure 2 It is the CIExy chromaticity diagram specified by JIS Z8110.

[0056] White light has a chromaticity contained within a white region, which is a circular region with a radius of 0.1 originating from the center point (x, y) = (0.310, 0.316) in the CIExy chromaticity diagram of JIS Z8110. The chromaticity of white light is... Figure 2 The dashed line A is used to represent it.

[0057] The color of the fluorescence emitted by the material is defined by the peak wavelength of the fluorescence spectrum. Specifically, the peak wavelength is set to purple (380–430 nm), blue (430–490 nm), green (490–550 nm), yellow (550–590 nm), orange (590–640 nm), and red (640–770 nm).

[0058] The first electrode 11 is formed of a conductive component such as aluminum, and a first organic semiconductor layer 13 is stacked on one side. The film thickness of the first electrode 11 is 5 nm or more and 500 nm or less. The second electrode 12 is a thin film formed of a light-transmitting conductive component such as indium tin oxide (ITO) on a transparent substrate (not shown) such as glass. A second organic semiconductor layer 14 is stacked on the opposite side of the second electrode 12 to the side opposite to the transparent substrate. The film thickness of the second electrode 12 is 5 nm or more and 500 nm or less.

[0059] The first organic semiconductor layer 13 is disposed between the first electrode 11 and the second organic semiconductor layer 14, and contains a first organic semiconductor material 16 as an acceptor for transporting electrons. The thickness of the first organic semiconductor layer 13 is 0.1 nm or more, preferably 500 nm or less, more preferably 2 nm or more, and even more preferably 100 nm or less. The first organic semiconductor layer 13 may be formed solely of the first organic semiconductor material 16, or it may contain materials other than the first organic semiconductor material 16.

[0060] The first organic semiconductor material 16 can be a conventionally known electron transport material. The organic semiconductor that can be used as the first organic semiconductor material 16 is a compound as shown below.

[0061]

[0062]

[0063]

[0064]

[0065] The second organic semiconductor layer 14 is disposed between the second electrode 12 and the first organic semiconductor layer 13. The thickness of the second organic semiconductor layer 14 is 0.1 nm or more, preferably 500 nm or less, more preferably 2 nm or more, and even more preferably 100 nm or less. The second organic semiconductor layer 14 contains: a second organic semiconductor material 17, which is a hole donor and emits blue fluorescence; and a guest material 18, which emits light in a color that can be mixed with the blue fluorescence emitted by the second organic semiconductor material 17 to emit white light as mixed light. The second organic semiconductor layer 14 may be formed solely of the second organic semiconductor material 17 and the guest material 18, or it may contain materials other than the second organic semiconductor material 17 and the guest material 18. Furthermore, the second organic semiconductor layer 14 may have a pair of undoped layers formed of the second organic semiconductor material 17, and a doped layer comprising the second organic semiconductor material 17 and the guest material 18 and disposed between the pair of undoped layers. By having a pair of undoped layers and a doped layer, the luminous efficiency of the second organic semiconductor layer 14 can be improved. The thickness of the undoped layer can be, for example, 1 to 10 nm, preferably 1 to 5 nm.

[0066] The second organic semiconductor material 17 is a material that undergoes triplet-triplet annihilation (TTA) and returns to the ground state after emitting blue light from a high-energy excited state based on TTA. Organic semiconductors that can be used as the second organic semiconductor material 17 are compounds shown below.

[0067]

[0068]

[0069]

[0070] Guest material 18 is a material that emits fluorescence with a wavelength longer than that emitted by the second organic semiconductor material 17. Guest material 18 emits yellow, orange, or red fluorescence via Forster resonance energy transfer (FRET) from the second organic semiconductor material 17, which mixes with the blue light from the second organic semiconductor material 17 to generate white light. The organic semiconductor that can be used as guest material 18 is a compound as shown below. Guest material 18 is more preferably a material that emits yellow or orange fluorescence via FRET from the second organic semiconductor material 17.

[0071]

[0072]

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[0075]

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[0078] The first organic semiconductor material 16 and the second organic semiconductor material 17 are chosen such that the LUMO energy level of the first organic semiconductor material 16 is lower than the LUMO energy level of the second organic semiconductor material 17. From the viewpoint of highly preventing electron leakage and further improving luminous efficiency, the difference between the LUMO energy level of the first organic semiconductor material 16 and the LUMO energy level of the second organic semiconductor material 17 is preferably 0.5 eV or higher. It should be noted that there is no particular upper limit to the difference between the LUMO energy levels of the first organic semiconductor material and the second organic semiconductor material; for example, it can be set to 2 eV or lower.

[0079] In the following text, the energy difference between the HOMO energy level of the second organic semiconductor material 17 and the LUMO energy level of the first organic semiconductor material 16 is also referred to as the "CT energy level". The second organic semiconductor material 17 is selected such that the excited triplet energy level of the second organic semiconductor material 17 is lower than the CT energy level. The difference between the excited triplet energy level of the second organic semiconductor material 17 and the CT energy level is preferably less than 0.8 eV, more preferably less than 0.65 eV, and even more preferably less than 0.5 eV. By reducing the difference between the excited triplet energy level of the second organic semiconductor material 17 and the CT energy level, the emission voltage at which the organic EL element 1 begins to fluoresce, i.e., the emission onset voltage, can be reduced.

[0080] Hereinafter, the energy difference between the HOMO level and the LUMO level of a material will also be referred to as the "band gap" of that material. The CT level is preferably 0.5 eV or more smaller than the band gap of the second organic semiconductor material 17, more preferably 0.7 eV or more smaller. There is no particular upper limit to the energy difference between the CT level and the band gap of the second organic semiconductor material 17, for example, it may be 2 eV or less.

[0081] The guest material 18 is selected such that the value obtained by subtracting the band gap of the guest material 18 from the band gap of the second organic semiconductor material 17 (hereinafter referred to as the "first band gap difference") is 0 eV or more and 1.5 eV or less. When the first band gap difference is less than 0 eV, the guest material 18 does not emit fluorescence. When the first band gap difference is greater than 1.5 eV, the guest material 18 does not emit fluorescence.

[0082] In the organic EL element 1, the first organic semiconductor material 16, the second organic semiconductor material 17, and the guest material 18 can be combined in various ways. For example, the organic EL element 1 can use NDI-HF (2,7-bis(9H-fluoren-2-yl)benzo[lmn][3,8]-phenanthroline-1,3,6,8(2H,7H)-tetraone) as the first organic semiconductor material 16, 12ADN (9-(naphthyl-1-yl)-10-(naphthyl-2-yl)anthracene) as the second organic semiconductor material 17, and tbRub (2,8-di-tert-butyl-5,11-bis(4-tert-butylphenyl)-6,12-diphenyltetraphenyl) as the guest material 18.

[0083] Alternatively, the organic EL element 1 may, for example, use NDI-HF as the first organic semiconductor material 16, 12ADN as the second organic semiconductor material 17, and fluorene (C 42 H 28 ) as object material 18.

[0084] Organic EL device 1 is supplied with a current density of 100 mA / cm² from power source 101. 2 Above and 1000mA / cm 2 When the current is below, it can emit white light.

[0085] Figure 3 This is a diagram illustrating the light-emitting mechanism of organic EL element 1. Figure 4 It indicates accompaniment Figure 3 The diagram shows the energy transfer of the emitted light.

[0086] When a predetermined light-emitting start voltage is applied between the first electrode 11 and the second electrode 12, in response to the supply of current from the power supply 101 to the organic EL element 1, holes (+) are injected from the second electrode 12 into the second organic semiconductor layer 14, and electrons (-) are injected from the first electrode 11 into the first organic semiconductor layer 13. The light-emitting start voltage applied between the first electrode 11 and the second electrode 12 is a voltage of 1.0V or more and 2.0V or less. For the holes (+) injected into the second organic semiconductor layer 14 and the electrons (-) injected into the first organic semiconductor layer 13, the electrons (-) and holes (+) form charge-transfer (CT) states at the interface 15 between the first organic semiconductor layer 13 and the second organic semiconductor layer 14. 25% of the electrons (-) become excited singlet states, and 75% of the electrons (-) become excited triplet states. Through charge recombination by the excited triplet states, a second organic semiconductor material 17 in the triplet state (T1) is generated in the second organic semiconductor layer 14. The second organic semiconductor material 17 in the triplet state (T1) generates a high-energy excited state (S1) by generating a triplet-triplet annihilation (TTA) through the triplet state (T1) of the second organic semiconductor material 17.

[0087] A portion of the second organic semiconductor material 17 in its high-energy excited state (S1) emits blue fluorescence, while the remaining portion does not emit blue fluorescence but instead transfers energy to the guest material 18 via FRET. The guest material 18, after energy transfer, becomes a high-energy excited state (S1) and emits yellow or orange light, which, when mixed with the blue emission, can generate white light. Through the mixing of the blue fluorescence emitted by the second organic semiconductor material 17 and the fluorescence emitted by the guest material 18, the organic EL element 1 emits white light.

[0088] (Method for manufacturing organic EL element according to the first embodiment)

[0089] First, in the substrate preparation process, a substrate with a transparent second electrode 12, such as ITO, formed on one surface is prepared. The substrate with the second electrode 12 formed on one surface can be a transparent substrate, including a glass substrate, a quartz substrate, a sapphire substrate, a plastic substrate, and a thin-film substrate. Next, in the second organic semiconductor layer stacking process, a second organic semiconductor layer 14 is stacked on the second electrode 12, and in the first organic semiconductor layer stacking process, a first organic semiconductor layer 13 is stacked on the second organic semiconductor layer 14. The first organic semiconductor layer 13 and the second organic semiconductor layer 14 are stacked using known stacking methods such as vacuum evaporation, sputtering, chemical vapor deposition, vapor deposition polymerization, spin coating, blade coating, rod coating, dip coating, and lamination. Then, in the first electrode stacking process, a first electrode 11 is stacked on the first organic semiconductor layer 13. The first electrode 11 is stacked using known stacking methods such as vacuum evaporation, sputtering, and plating to manufacture the organic EL device 1.

[0090] (Effects of the organic EL element in the first embodiment)

[0091] When the organic EL element 1 is supplied with current at a specified current density, the second organic semiconductor material 17 emits blue fluorescence and the guest material 18 emits yellow or orange fluorescence, thereby enabling the emission of white light.

[0092] Furthermore, the organic EL element 1 emits light when a light emission start voltage of 1.0V or higher and 2.0V or lower is applied, thus achieving low-voltage operation that can emit light using a typical primary or secondary battery with a rated voltage of 1.5V.

[0093] (The structure and function of the organic EL element in the second embodiment)

[0094] Figure 5 This is a diagram showing a light-emitting device having an organic EL element according to the second embodiment.

[0095] The light-emitting device 200 has a power supply 101 and an organic EL element 2. The power supply 101 supplies a desired voltage to the organic EL element 2 according to the instructions of a control device (not shown).

[0096] The organic EL element 2 has: a first electrode 21 and a second electrode 22 as a pair of electrodes; a first organic semiconductor layer 23, also called an electron transport layer, containing a first organic semiconductor material 26; and a second organic semiconductor layer 24, also called a light-emitting layer, forming an interface 25 with the first organic semiconductor layer 23. The organic EL element 2 emits white light in response to a current I supplied from the power source 101 flowing from the first electrode 21 to the second electrode 22. The structures and functions of the first electrode 21, the second electrode 22, the first organic semiconductor layer 23, and the first organic semiconductor material 26 are the same as those of the first electrode 11, the second electrode 12, the first organic semiconductor layer 13, and the first organic semiconductor material 16, respectively; therefore, detailed descriptions are omitted here.

[0097] The second organic semiconductor layer 24 comprises: a second organic semiconductor material 27, a first guest material 28, and a second guest material 29, which serve as donors for transporting holes. The second guest material 29 emits fluorescence of a color that can be mixed with the blue fluorescence emitted by the first guest material 28 to emit white light as mixed-color light. The second organic semiconductor layer 24 may be formed solely of the second organic semiconductor material 27, the first guest material 28, and the second guest material 29, or it may contain materials other than the second organic semiconductor material 27, the first guest material 28, and the second guest material 29.

[0098] The second organic semiconductor material 27 is a material that produces TTA, and the organic semiconductor that can be used as the second organic semiconductor material 27 is the same as the second organic semiconductor material 17.

[0099] The first guest material 28 is a material that emits fluorescence by transferring energy from the second organic semiconductor material 27 via FRET. The first guest material 28 is a compound whose absorption spectrum largely overlaps with the emission spectrum of the second organic semiconductor material 27. The fluorescence emitted by the first guest material 28 is blue light with a peak wavelength longer than that emitted by the second organic semiconductor material 27. Organic semiconductors that can be used as the first guest material 28 are compounds shown below.

[0100]

[0101]

[0102]

[0103]

[0104]

[0105]

[0106]

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[0112] The second guest material 29 is a material that emits fluorescence with a wavelength longer than that emitted by the first guest material 28 through FRET (Follicular Emission Transmission). The fluorescence emitted by the second guest material 29 is light of a color that can be mixed with blue light to produce white light, and is yellow, orange, or red light. The organic semiconductor that can be used as the second guest material 29 is the same as that of the guest material 18. The second guest material 29 is more preferably a material that emits yellow or orange fluorescence through FRET from the first guest material 28.

[0113] In the organic EL element 2, the first organic semiconductor material 26 and the second organic semiconductor material 27 are selected with reference to the HOMO and LUMO energy levels of the first organic semiconductor material 26 and the second organic semiconductor material 27, as well as the excited triplet energy level of the second organic semiconductor material 27. The first organic semiconductor material 26 and the second organic semiconductor material 27 are selected in the same way as the first organic semiconductor material 16 and the second organic semiconductor material 17.

[0114] The first guest material 28 is selected such that the difference between the band gap of the second organic semiconductor material 27 and the band gap of the first guest material 28 is less than 0.5 eV. When the difference between the band gap of the second organic semiconductor material 27 and the band gap of the guest material 28 is greater than 0.5 eV, the probability of energy migrating from the second organic semiconductor material 27 to the first guest material 28 via FRET varies depending on the supplied current, and the chromaticity of the emitted white light varies depending on the supplied current.

[0115] The second guest material 29 is selected such that the value obtained by subtracting the band gap of the second guest material 29 from the band gap of the first guest material 28 (hereinafter referred to as the "second band gap difference") is 0 eV or more and 1.5 eV or less. When the second band gap difference is less than 0 eV, the second guest material 29 does not emit fluorescence. When the second band gap difference is greater than 1.5 eV, the second guest material 29 does not emit fluorescence.

[0116] In the organic EL element 2, the first organic semiconductor material 26, the second organic semiconductor material 27, the first guest material 28, and the second guest material 29 can be combined in various ways. For example, the organic EL element 2 can use NDI-HF as the first organic semiconductor material 26, 12ADN as the second organic semiconductor material 27, TbPe (2,5,8,11-tetratert-butylperylene) as the first guest material 28, and tbRub as the second guest material 29.

[0117] Alternatively, the organic EL element 2 may use NDI-HF as the first organic semiconductor material 26, 12ADN as the second organic semiconductor material 27, TbPe as the first guest material 28, and rubrene (5,6,11,12-tetraphenyltetraphenyl) as the second guest material 29.

[0118] Alternatively, the organic EL element 2 may use NDI-HF as the first organic semiconductor material 26, 12ADN as the second organic semiconductor material 27, TbPe as the first guest material 28, and DBP (tetraphenyldibenzoperiflanthene) as the second guest material 29.

[0119] Organic EL element 2 is supplied with a current density of 1 mA / cm² from power source 101. 2 Up to 1000mA / cm 2 When the current is below, it can emit white light.

[0120] Figure 6 This is a diagram illustrating the light-emitting mechanism of organic EL element 2. Figure 7 It indicates accompaniment Figure 6 The diagram shows the energy transfer of the emitted light.

[0121] Similar to organic EL element 1, in response to the supply of current from power source 101 to organic EL element 2, a CT state is formed at the interface 25 between the first organic semiconductor layer 23 and the second organic semiconductor layer 24. In organic EL element 2, charge recombination occurs in the CT state, and a second organic semiconductor material 27 of T1 is generated in the second organic semiconductor layer 24. Through the second organic semiconductor material 27 of T1, TTA occurs, generating a high-energy excited state (S1) of the second organic semiconductor material 27.

[0122] Almost all of the second organic semiconductor material 27 in the high-energy excited state (S1) does not emit fluorescence, but its energy is transferred to the first guest material 28 via FRET. The first guest material 28, after energy transfer, becomes a high-energy excited state (S1). A portion of the first guest material 28 in the high-energy excited state (S1) emits blue fluorescence. The remaining portion of the first guest material 28 in the high-energy excited state (S1) transfers energy to the second guest material 29 via FRET. The second guest material 29, after energy transfer, becomes a high-energy excited state (S1). The second guest material 29 in the high-energy excited state (S1) emits light of colors such as yellow or orange, which can be mixed with the blue fluorescence to generate white light, as fluorescence. Through the mixing of the blue fluorescence emitted by the first guest material 28 and the yellow or orange fluorescence emitted by the second guest material 29, the organic EL element 2 emits white light.

[0123] (Method for manufacturing organic EL element according to the second embodiment)

[0124] The manufacturing method of organic EL element 2 is the same as that of organic EL element 1, so detailed descriptions are omitted here.

[0125] (Effects of the organic EL element in the second embodiment)

[0126] When the organic EL element 2 is supplied with a current at a specified current density, the first guest material 28 emits blue fluorescence and the second guest material 29 emits yellow or orange fluorescence, thereby emitting white light. By using a compound whose absorption spectrum largely overlaps with the emission spectrum of the second organic semiconductor material 27 as the first guest material 28, the organic EL element 2 can improve the FRET-based energy transfer efficiency from the second organic semiconductor material 27 to the first guest material 28. By improving the FRET-based energy transfer efficiency from the second organic semiconductor material 27 to the first guest material 28, the fluorescence emitted by the second organic semiconductor material 27, which is excited due to TTA, is suppressed, and the FRET-based fluorescence emitted by the first guest material 28 becomes dominant. Therefore, it can suppress chromaticity changes caused by variations in current intensity.

[0127] Furthermore, the organic EL element 2 emits light when a light emission start voltage of 1.0V or higher and 2.0V or lower is applied, thus achieving low-voltage operation that can emit light using a typical primary battery and secondary battery with a rated voltage of 1.5V.

[0128] (The structure and function of the organic EL element in the third embodiment)

[0129] Figure 8 This is a diagram showing a light-emitting device having an organic EL element according to the third embodiment.

[0130] The light-emitting device 300 has a power supply 101 and an organic EL element 3. The power supply 101 supplies a desired voltage to the organic EL element 3 according to the instructions of a control device (not shown).

[0131] The organic EL element 3 has: a first electrode 31 and a second electrode 32 as a pair of electrodes; a first organic semiconductor layer 33, also called an electron transport layer, containing a first organic semiconductor material 36; and a second organic semiconductor layer 34, also called a light-emitting layer, forming an interface 35 with the first organic semiconductor layer 33. The organic EL element 3 emits white light in response to a current I supplied from the power source 101 flowing from the first electrode 31 to the second electrode 32. The structures and functions of the first electrode 31, the second electrode 32, the first organic semiconductor layer 33, and the first organic semiconductor material 36 are the same as those of the first electrode 11, the second electrode 12, the first organic semiconductor layer 13, and the first organic semiconductor material 16, respectively; therefore, detailed descriptions are omitted here.

[0132] The second organic semiconductor layer 34 contains a second organic semiconductor material 37, a first guest material 38, a second guest material 39, and a third guest material 40 as donors for transporting holes. The first guest material 38, the second guest material 39, and the third guest material 40 emit fluorescence of a color that allows the mixed light, formed by mixing their respective fluorescence, to be emitted as white light. The second organic semiconductor layer 34 may be formed solely of the second organic semiconductor material 37, the first guest material 38, the second guest material 39, and the third guest material 40, or it may contain materials other than the second organic semiconductor material 37, the first guest material 38, the second guest material 39, and the third guest material 40.

[0133] The second organic semiconductor material 37 is a material that generates TTA, and the organic semiconductor that can be used as the second organic semiconductor material 37 is the same as the second organic semiconductor material 27.

[0134] The first guest material 38 is a material that emits fluorescence by transferring energy from the second organic semiconductor material 37 via FRET. The fluorescence emitted by the first guest material 38 is blue light with a peak wavelength. The organic semiconductor that can be used as the first guest material 38 is the same as that used for the first guest material 28.

[0135] The second guest material 39 is a material that emits fluorescence with a wavelength longer than that emitted by the first guest material 38 through FRET (Follicular Emission Transfer). The fluorescence emitted by the second guest material 39 is green light, which can be mixed with blue, orange, or red light to produce white light. Organic semiconductors that can be used as the second guest material 39 are compounds shown below.

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[0142]

[0143]

[0144] The third guest material 40 is a material that emits fluorescence with a wavelength longer than that emitted by the second guest material 39 through FRET (Follicular Emission Transmission). The fluorescence emitted by the third guest material 40 is white light that can be generated by mixing with the fluorescence emitted by the first guest material 38 and the second guest material 39; it is yellow, orange, or red light. The organic semiconductor that can be used as the third guest material 40 is the same as that of the guest material 18. More preferably, the third guest material 40 is a material that emits orange or red fluorescence through FRET from the second guest material 39.

[0145] In organic EL element 3, the first organic semiconductor material 36 and the second organic semiconductor material 37 are selected with reference to the HOMO and LUMO energy levels of the first organic semiconductor material 36 and the second organic semiconductor material 37, as well as the excited triplet energy level of the second organic semiconductor material 37. The first organic semiconductor material 36 and the second organic semiconductor material 37 are selected in the same way as the first organic semiconductor material 16 and the second organic semiconductor material 17. In addition, the first guest material 38 and the second guest material 39 are selected by the difference in band gap, just like the first guest material 28 and the second guest material 29 in organic EL element 2.

[0146] The third guest material 40 is selected such that the value obtained by subtracting the band gap of the third guest material 40 from the band gap of the second guest material 39 (hereinafter referred to as the "third band gap difference") is 0 eV or more and 1.5 eV or less. When the third band gap difference is less than 0 eV, the third guest material does not emit fluorescence. When the third band gap difference is greater than 1.5 eV, the third guest material does not emit fluorescence.

[0147] In the organic EL element 3, the first organic semiconductor material 36, the second organic semiconductor material 37, the first guest material 38, the second guest material 39, and the third guest material 40 can be combined in various ways. For example, the organic EL element 3 can use NDI-HF as the first organic semiconductor material 36, 12ADN as the second organic semiconductor material 37, TbPe as the first guest material 38, TTPA (tris[4-(2-thienyl)phenyl]amine) as the second guest material 39, and DBP as the third guest material 40.

[0148] Organic EL element 3 is supplied with a current density of 5 mA / cm² from power supply 101. 2 Up to 700mA / cm 2 When the current is below, it can emit white light.

[0149] Figure 9 This is a diagram illustrating the light-emitting mechanism of organic EL element 3. Figure 10 It indicates accompaniment Figure 9 The diagram shows the energy transfer of the emitted light.

[0150] Similar to organic EL element 1, in response to the supply of current from power source 101 to organic EL element 3, a CT state is formed at the interface 35 between the first organic semiconductor layer 33 and the second organic semiconductor layer 34. In organic EL element 3, the CT state undergoes charge recombination, thereby generating a second organic semiconductor material 37 of T1 in the second organic semiconductor layer 34. The generated second organic semiconductor material 37 of T1 undergoes TTA, thereby generating a high-energy excited state (S1) of the second organic semiconductor material 37.

[0151] Almost entirely, the second organic semiconductor material 37 in its high-energy excited state (S1) does not emit fluorescence, but its energy is transferred to the first guest material 38 via FRET. The first guest material 38, after energy transfer, becomes a high-energy excited state (S1). A portion of the first guest material 38 in its high-energy excited state (S1) emits blue fluorescence. The remaining portion of the first guest material 38 in its high-energy excited state (S1) transfers its energy to the second guest material 39 via FRET. The second guest material 39, after energy transfer, becomes a high-energy excited state (S1). A portion of the second guest material 39 in its high-energy excited state (S1) emits green or other light as fluorescence. The remaining portion of the second guest material 39 in its high-energy excited state (S1) transfers its energy to the third guest material 40 via FRET. The third guest material 40 in its high-energy excited state (S1) emits orange or red or other light as fluorescence. The organic EL element 3 emits white light by mixing the blue fluorescence emitted by the first guest material 38 with the fluorescence emitted by the second guest material 39 and the third guest material 40.

[0152] (Method for manufacturing organic EL element according to the third embodiment)

[0153] The manufacturing method of organic EL element 3 is the same as that of organic EL element 1, so detailed descriptions are omitted here.

[0154] (Effects of the organic EL element in the third embodiment)

[0155] When the organic EL element 3 is supplied with a current at a specified current density, the first guest material 38 emits blue fluorescence, the second guest material 39 emits green fluorescence, and the third guest material 40 emits orange or red fluorescence, thereby emitting white light. Furthermore, by using a compound whose absorption spectrum largely overlaps with the emission spectrum of the second organic semiconductor material 37 as the first guest material 38, the organic EL element 3 can improve the FRET-based energy transfer efficiency from the second organic semiconductor material 37 to the first guest material 38. By improving the FRET-based energy transfer efficiency from the second organic semiconductor material 37 to the first guest material 38, the fluorescence emitted by the second organic semiconductor material 37, which is excited due to TTA, is suppressed, and FRET-based fluorescence becomes dominant. Therefore, chromaticity changes caused by variations in current intensity can be suppressed.

[0156] Furthermore, the organic EL element 3 emits light when a light emission start voltage of 1.0V or higher and 2.0V or lower is applied, thus achieving low-voltage operation that can emit light using a typical primary battery and secondary battery with a rated voltage of 1.5V.

[0157] (The structure and function of the organic EL element in the fourth embodiment)

[0158] Figure 11 This is a diagram showing a light-emitting device having an organic EL element according to the fourth embodiment.

[0159] The light-emitting device 400 has a power supply 101 and an organic EL element 4. The power supply 101 supplies a desired voltage to the organic EL element 4 according to the instructions of a control device (not shown).

[0160] The organic EL element 4 has: a first electrode 41 and a second electrode 42 as a pair of electrodes; a first organic semiconductor layer 43, also called an electron transport layer, containing a first organic semiconductor material 46; and a second organic semiconductor layer 44, also called a light-emitting layer, forming an interface 45 with the first organic semiconductor layer 43. The organic EL element 4 emits light in response to a current I supplied from the power source 101 flowing from the first electrode 41 to the second electrode 42. The structures and functions of the first electrode 41, the second electrode 42, the first organic semiconductor layer 43, and the first organic semiconductor material 46 are the same as those of the first electrode 11, the second electrode 12, the first organic semiconductor layer 13, and the first organic semiconductor material 16, respectively; therefore, detailed descriptions are omitted here.

[0161] The second organic semiconductor layer 44 contains a second organic semiconductor material 47, a first guest material 48, and a second guest material 49 as donors for transporting holes. The first guest material 48 and the second guest material 49 emit mixed light obtained by mixing their respective fluorescence. The second organic semiconductor layer 44 may be formed only of the second organic semiconductor material 47, the first guest material 48, and the second guest material 49, or it may contain materials other than the second organic semiconductor material 47, the first guest material 48, and the second guest material 49.

[0162] The second organic semiconductor material 47 is a material that generates TTA, and the organic semiconductor that can be used as the second organic semiconductor material 47 is the same as the second organic semiconductor material 17.

[0163] The first guest material 48 is a material that emits fluorescence through FRET, where energy migrates from the second organic semiconductor material 47. The organic semiconductor that can be used as the first guest material 48 is the same as the first guest material 28. The first guest material 48 is a compound whose absorption spectrum largely overlaps with the emission spectrum of the second organic semiconductor material 47.

[0164] The second guest material 49 is a material that emits fluorescence with a longer wavelength than that emitted by the first guest material 48 through FRET (Follicular Emission Transmission). The organic semiconductor that can be used as the second guest material 49 is the same as that used for guest material 18 or second guest material 39.

[0165] In organic EL element 4, the first organic semiconductor material 46 and the second organic semiconductor material 47 are selected with reference to the HOMO and LUMO energy levels of the first organic semiconductor material 46 and the second organic semiconductor material 47, as well as the excited triplet energy level of the second organic semiconductor material 47. The first organic semiconductor material 46 and the second organic semiconductor material 47 are selected in the same way as the first organic semiconductor material 16 and the second organic semiconductor material 17. In addition, the first guest material 48 and the second guest material 49 are selected by the difference in band gap, just like the first guest material 28 and the second guest material 29 of organic EL element 2.

[0166] In the organic EL element 4, the first organic semiconductor material 46, the second organic semiconductor material 47, the first guest material 48, and the second guest material 49 can be combined in various ways. For example, the organic EL element 4 can use NDI-HF as the first organic semiconductor material 46, 12ADN as the second organic semiconductor material 47, TbPe as the first guest material 48, and tbRub as the second guest material 49.

[0167] Alternatively, the organic EL element 4 may use NDI-HF as the first organic semiconductor material 46, 12ADN as the second organic semiconductor material 47, TbPe as the first guest material 48, and rubrene as the second guest material 49.

[0168] Alternatively, the organic EL element 4 may use NDI-HF as the first organic semiconductor material 46, 12ADN as the second organic semiconductor material 47, TbPe as the first guest material 48, and TTPA as the second guest material 49.

[0169] Figure 12 This is a diagram illustrating the light-emitting mechanism of organic EL element 4. Figure 13 It indicates accompaniment Figure 12 The diagram shows the energy transfer of the emitted light.

[0170] Similar to organic EL element 1, in response to the supply of current from power source 101 to organic EL element 4, a CT state is formed at the interface 45 between the first organic semiconductor layer 43 and the second organic semiconductor layer 44. In organic EL element 4, the CT state undergoes charge recombination, thereby generating a second organic semiconductor material 47 of T1 in the second organic semiconductor layer 44. The generated second organic semiconductor material 47 of T1 undergoes TTA, thereby generating a high-energy excited state (S1) of the second organic semiconductor material 47.

[0171] Almost all of the second organic semiconductor material 47 in the high-energy excited state (S1) does not emit fluorescence, but its energy is transferred to the first guest material 48 via FRET. The first guest material 48 after energy transfer becomes the high-energy excited state (S1). A portion of the first guest material 48 in the high-energy excited state (S1) emits fluorescence. The remaining portion of the first guest material 48 in the high-energy excited state (S1) transfers its energy to the second guest material 49 via FRET. The second guest material 49 after energy transfer becomes the high-energy excited state (S1). The second guest material 49 in the high-energy excited state (S1) emits fluorescence with a wavelength longer than that emitted by the first guest material 48.

[0172] (Method for manufacturing organic EL element according to the fourth embodiment)

[0173] The manufacturing method of organic EL element 4 is the same as that of organic EL element 1, so detailed descriptions are omitted here.

[0174] (Effects of the organic EL element in the fourth embodiment)

[0175] In the organic EL element 4, almost all of the second organic semiconductor material 47 does not emit fluorescence. Energy is transferred to the first guest material 48 via FRET, thus reducing the likelihood of changes in the amount of fluorescence emitted by the second organic semiconductor material 47 and consequently, changes in the chromaticity of the emitted light. By using a compound whose absorption spectrum largely overlaps with the emission spectrum of the second organic semiconductor material 47 as the first guest material 48, the organic EL element 4 can improve the FRET-based energy transfer efficiency from the second organic semiconductor material 47 to the first guest material 48. By increasing the FRET-based energy transfer efficiency from the second organic semiconductor material 47 to the first guest material 48, the fluorescence emitted by the second organic semiconductor material 47, which is excited by TTA, is suppressed, and FRET-based fluorescence becomes dominant. Therefore, chromaticity changes caused by variations in current intensity can be suppressed.

[0176] Furthermore, the organic EL element 4 emits light when a light emission start voltage of 1.0V or higher and 2.0V or lower is applied, thus achieving low-voltage operation that can emit light using a typical primary battery and secondary battery with a rated voltage of 1.5V.

[0177] (The structure and function of the organic EL element in the fifth embodiment)

[0178] Figure 14 This is a diagram showing a light-emitting device having an organic EL element according to the fifth embodiment.

[0179] The light-emitting device 500 has a power supply 101 and an organic EL element 5. The power supply 101 supplies a desired voltage to the organic EL element 5 according to the instructions of a control device (not shown).

[0180] The organic EL element 5 has: a first electrode 51 and a second electrode 52 as a pair of electrodes; a first organic semiconductor layer 53, also called an electron transport layer, containing a first organic semiconductor material 56; and a second organic semiconductor layer 54, also called a light-emitting layer, forming an interface 55 with the first organic semiconductor layer 53. The organic EL element 5 emits white light in response to a current I supplied from the power source 101 flowing from the first electrode 51 to the second electrode 52. The structures and functions of the first electrode 51, the second electrode 52, the first organic semiconductor layer 53, and the first organic semiconductor material 56 are the same as those of the first electrode 11, the second electrode 12, the first organic semiconductor layer 13, and the first organic semiconductor material 16, respectively; therefore, detailed descriptions are omitted here.

[0181] The second organic semiconductor layer 54 contains a second organic semiconductor material 57, a first guest material 58, a second guest material 59, and a third guest material 60 as donors for transporting holes. The first guest material 58, the second guest material 59, and the third guest material 60 emit fluorescence of a color capable of emitting mixed light obtained by mixing the individual fluorescencees. The second organic semiconductor layer 54 may be formed solely of the second organic semiconductor material 57, the first guest material 58, the second guest material 59, and the third guest material 60, or it may contain materials other than the second organic semiconductor material 57, the first guest material 58, the second guest material 59, and the third guest material 60.

[0182] The second organic semiconductor material 57 is a material that generates TTA, and the organic semiconductor that can be used as the second organic semiconductor material 57 is the same as the second organic semiconductor material 17.

[0183] The first guest material 58 is a material that emits fluorescence due to the transfer of energy from the second organic semiconductor material 57 via FRET. The fluorescence emitted by the first guest material 58 is blue light. The organic semiconductor that can be used as the first guest material 58 is the same as that of the first guest material 28.

[0184] The second guest material 59 is a material that emits fluorescence with a longer wavelength than that emitted by the first guest material 58 through FRET (Follicular Emission Transmission). The fluorescence emitted by the second guest material 59 is green. The organic semiconductors that can be used as the second guest material 59 are the same as those used for the second guest material 39.

[0185] The third guest material 60 is a material that emits fluorescence with a longer wavelength than that emitted by the second guest material 59 through FRET (Follicular Emission Transfer). The fluorescence emitted by the third guest material 60 is yellow, orange, or red. The organic semiconductor that can be used as the third guest material 40 is the same as that of the guest material 18.

[0186] In the organic EL element 5, the first organic semiconductor material 56 and the second organic semiconductor material 57 are selected with reference to the HOMO and LUMO energy levels of the first organic semiconductor material 56 and the second organic semiconductor material 57, as well as the excited triplet energy level of the second organic semiconductor material 57. The first organic semiconductor material 56 and the second organic semiconductor material 57 are selected in the same way as the first organic semiconductor material 16 and the second organic semiconductor material 17, respectively. In addition, the first guest material 58, the second guest material 59, and the third guest material 60 are selected by the difference in band gap, just like the first guest material 38, the second guest material 39, and the third guest material 40 of the organic EL element 3.

[0187] In the organic EL element 5, the first organic semiconductor material 56, the second organic semiconductor material 57, the first guest material 58, the second guest material 59, and the third guest material 60 can be combined in various ways. For example, the organic EL element 5 can use NDI-HF as the first organic semiconductor material 56, 12ADN as the second organic semiconductor material 57, TbPe as the first guest material 58, TTPA as the second guest material 59, and DBP as the third guest material 60.

[0188] Figure 15 This is a diagram illustrating the light-emitting mechanism of organic EL element 5. Figure 16 It indicates accompaniment Figure 15 The diagram shows the energy transfer of the emitted light.

[0189] Similar to organic EL element 1, in response to the supply of current from power source 101 to organic EL element 5, a CT state is formed at the interface 55 between the first organic semiconductor layer 53 and the second organic semiconductor layer 54. In organic EL element 5, charge recombination occurs in the CT state, thereby generating a second organic semiconductor material 57 of T1 in the second organic semiconductor layer 54. The generated second organic semiconductor material 57 of T1 undergoes TTA, thereby generating a high-energy excited state (S1) of the second organic semiconductor material 57.

[0190] Almost entirely of the second organic semiconductor material 57 in its high-energy excited state (S1) does not emit fluorescence, but its energy is transferred to the first guest material 58 via FRET. The first guest material 58, after energy transfer, becomes a high-energy excited state (S1). A portion of the first guest material 58 in its high-energy excited state (S1) emits fluorescence. The remaining portion of the first guest material 58 in its high-energy excited state (S1) transfers its energy to the second guest material 59 via FRET. The second guest material 59, after energy transfer, becomes a high-energy excited state (S1). A portion of the second guest material 59 in its high-energy excited state (S1) emits fluorescence with a wavelength longer than that emitted by the first guest material 58. The remaining portion of the second guest material 59 in its high-energy excited state (S1) transfers its energy to the third guest material 60 via FRET. The third guest material 60 in its high-energy excited state (S1) emits fluorescence with a wavelength longer than that emitted by the second guest material 59.

[0191] (Fifth embodiment of the method for manufacturing organic EL element)

[0192] The manufacturing method of organic EL element 5 is the same as that of organic EL element 1, so detailed descriptions are omitted here.

[0193] (Effects of the organic EL element in the fifth embodiment)

[0194] In the organic EL element 5, almost all of the second organic semiconductor material 57 does not emit fluorescence. Energy is transferred to the first guest material 58 through FRET. Therefore, the possibility of a change in the amount of fluorescence emitted by the second organic semiconductor material 57, thereby causing a change in the chromaticity of the emitted light, is low.

[0195] Furthermore, the organic EL element 5 emits light when a light emission start voltage of 1.0V or higher and 2.0V or lower is applied, thus achieving low-voltage operation that can emit light using a typical primary or secondary battery with a rated voltage of 1.5V.

[0196] (A variation of the organic EL element in the embodiment)

[0197] Organic EL elements 1-5 have a first electrode and a second electrode as a pair of electrodes, a first organic semiconductor layer, and a second organic semiconductor layer. However, the organic EL elements of the embodiments may also have other organic semiconductor layers or inorganic compound layers. For example, the organic EL elements of the embodiments may also have a hole transport layer disposed between the second organic semiconductor layer and the second electrode to transport holes. In addition, besides the hole transport layer, the organic EL elements of the embodiments may also have an electron injection layer disposed between the first organic semiconductor layer and the first electrode to inject electrons, and a hole injection layer disposed between the hole transport layer and the second electrode to inject holes.

[0198] Furthermore, in organic EL elements 1 to 5, the first organic semiconductor layer is an electron transport layer, but in the organic EL element of the embodiment, the first organic semiconductor layer may also be a hole blocking layer. Additionally, in the organic EL element of the embodiment, the first organic semiconductor layer, serving as a hole blocking layer, may function as an electron injection layer, and the light-emitting layer, serving as a second organic semiconductor layer, may function as a hole transport layer.

[0199] Furthermore, the organic EL element 3 has a first guest material 38 that emits blue fluorescence, a second guest material 39 that emits green fluorescence, and a third guest material 40 that emits red fluorescence. However, the organic EL element of the embodiment may also have a second organic semiconductor material that emits blue fluorescence, a first guest material that emits green fluorescence, and a second guest material that emits red fluorescence.

[0200] Furthermore, the organic EL element of the embodiment may also have multiple layers comprising the same organic semiconductor material. For example, when the organic EL element of the embodiment contains fluorene as the second organic semiconductor material in the second organic semiconductor layer, it may have a hole-blocking layer formed of fluorene.

[0201] Example

[0202] (Methods for determining luminescence properties)

[0203] Luminance, luminance, and chromaticity were measured for the organic EL elements of the examples and the comparative examples. Luminance was measured using a source measurement unit (B2902A, Keysight Technologies) and a luminance meter (BM-9, Topcom). Luminance was measured using a spectrophotometer (Fluorolog, HORIBA). Chromaticity was measured using a spectrophotometer (C-7000, SEKONIC CORPORATION). Note that the percentage of guest molecule content refers to volume percentage.

[0204] (Organic EL element of Example 1)

[0205] The organic EL device of Example 1 is formed by sequentially stacking a hole injection layer made of MoO3, a light-emitting layer corresponding to the second organic semiconductor layer, an electron transport layer corresponding to the first organic semiconductor layer, an electron injection layer made of LiF, and an Al electrode on an ITO-coated glass substrate. The hole injection layer, light-emitting layer, electron transport layer, electron injection layer, and Al electrode are deposited in a vacuum evaporation system at a density of 1×10⁻⁶. -4 The organic electroluminescent (EL) elements are laminated under high vacuum (Pa) via thermal evaporation. The resulting EL elements are then encapsulated in a glove box using a glass substrate and epoxy resin. The ITO-coated glass substrate is manufactured by Technoprint Co., Ltd., with an ITO thickness of 150 nm and a sheet resistance of 10.3 Ω sq. -1 The hole injection layer has a thickness of 10 nm and is deposited at a deposition rate of 0.1 nm / s.

[0206] The light-emitting layer comprises: a pair of undoped layers having 12ADN as a second organic semiconductor material; and a doped layer having 12ADN as the second organic semiconductor material and tbRub as a guest material, disposed between the pair of undoped layers. The pair of undoped layers each have a thickness of 10 nm and are deposited at a deposition rate of 1 nm / s. The tbRub content in the doped layer is 0.1%. The doped layer has a thickness of 50 nm and is deposited at a deposition rate of 1 nm / s. The electron transport layer has NDI-HF as a first organic semiconductor material. The electron transport layer has a thickness of 50 nm and is deposited at a deposition rate of 1 nm / s. The electron injection layer has a thickness of 1 nm and is deposited at a deposition rate of 0.1 nm / s. The Al electrode has a thickness of 100 nm and is deposited at a deposition rate of 3 nm / s.

[0207] (Organic EL elements in Examples 2-6)

[0208] The organic EL element in Example 2 differs from that in Example 1 in that it uses fluorene as the guest material instead of tbRub. The fluorene content in the doped layer is 0.1%. The doped layer has a thickness of 50 nm and is deposited at a deposition rate of 1 nm / s.

[0209] The organic EL element in Example 3 differs from that in Example 1 in that it has TbPe as the first guest material and tbRub as the second guest material. The content of TbPe in the doped layer is 0.5%, and the content of tbRub is 0.1%. The thickness of the doped layer is 65 nm, and the film is deposited at a film deposition rate of 1 nm / s.

[0210] The organic EL element in Example 4 differs from that in Example 3 in that it uses fluorene as the second guest material instead of tbRub. The doped layer contains 0.5% TbPe and 0.1% fluorene. The doped layer has a thickness of 50 nm and is deposited at a deposition rate of 1 nm / s.

[0211] The organic EL element in Example 5 differs from that in Example 3 in that it uses DBP as the second guest material instead of tbRub. The TbPe content in the doped layer is 0.5%, and the DBP content is 0.1%. The doped layer has a thickness of 50 nm and is deposited at a deposition rate of 1 nm / s.

[0212] The organic EL element of Example 6 differs from that of Example 3 in that it uses TTPA as the second guest material instead of tbRub, and DBP as the third guest material. The doped layer contains 0.5% TbPe, 0.1% TTPA, and 0.1% DBP. The doped layer has a thickness of 50 nm and is deposited at a deposition rate of 1 nm / s.

[0213] (Organic EL elements in Comparative Examples 1-3)

[0214] The organic EL element in Comparative Example 1 differs from the organic EL element in Example 1 in that it uses DBP as the guest material instead of tbRub. The DBP content in the doped layer is 0.1%. The thickness of the doped layer is 50 nm, and the film is deposited at a deposition rate of 1 nm / s.

[0215] The organic EL element in Comparative Example 2 differs from the organic EL element in Example 1 in that it uses TTPA as the guest material instead of tbRub. The TTPA content in the doped layer is 0.1%. The thickness of the doped layer is 50 nm, and the film is deposited at a deposition rate of 1 nm / s.

[0216] The organic EL element in Comparative Example 3 differs from that in Example 3 in that it uses TTPA as the second guest material instead of tbRub. The TTPA content in the doped layer is 0.1%. The thickness of the doped layer is 50 nm, and the film is deposited at a deposition rate of 1 nm / s.

[0217] (Evaluation of luminescence onset voltage and white luminescence characteristics)

[0218] Figure 17 This is a graph showing the light-emitting start voltage and white light-emitting characteristics of the organic EL element in Example 1. Figure 18 This is a graph showing the light-emitting start voltage and white light-emitting characteristics of the organic EL element in Example 2. Figure 19This is a graph showing the light emission start voltage and white light emission characteristics of the organic EL element in Example 3. Figure 20 This is a graph showing the light emission start-up voltage and white light emission characteristics of the organic EL element in Example 4. Figure 21 This is a graph showing the light emission start-up voltage and white light emission characteristics of the organic EL element in Example 5. Figure 22 This is a graph showing the light emission start voltage and white light emission characteristics of the organic EL element in Example 6. Figure 23 This is a graph showing the light emission start voltage of the organic EL element in Comparative Example 1. Figure 24 This is a graph showing the light emission start-up voltage of the organic EL element in Comparative Example 2. Figure 25 This is a graph showing the light-emitting onset voltage and light-emitting characteristics of the organic EL element in Comparative Example 3. Figures 17-22 and Figure 25 In the diagram, (a) represents the applied voltage-luminance characteristic, and (b) represents the supplied current density-chromaticity characteristic. Figures 17-22 and Figure 25 In (a), the horizontal axis represents the applied voltage, and the vertical axis represents the luminance. Figures 17-22 and Figure 25 In (b), the horizontal axis represents the x-coordinate of the CIExy chromaticity diagram of JIS Z8110, and the vertical axis represents the y-coordinate of the CIExy chromaticity diagram of JIS Z8110. Figure 23 and 24 This indicates the applied voltage-luminance characteristic.

[0219] Table 1 shows the evaluation results of the emission start voltage and white emission characteristics of the organic EL elements of Examples 1-6 and Comparative Examples 1-3. Table 2 shows the relationship between the supply current density and the chromaticity of the emitted light of the organic EL elements of Examples 1-6 and Comparative Example 3.

[0220] [Table 1]

[0221]

[0222] [Table 2]

[0223]

[0224] In Table 1, the "Emission Start Voltage [V]" column indicates the voltage at which the organic EL elements of Examples 1-6 and Comparative Examples 1-3 begin to emit light. The "Chromaticity Characteristics" column indicates the evaluation results of the chromaticity of the light emitted from the organic EL elements of Examples 1-6 and Comparative Examples 1-3. The "Evaluation Results" column indicates the evaluation results of the emission start voltage and white emission characteristics of the organic EL elements of Examples 1-6 and Comparative Examples 1-3.

[0225] In the "Colorimetric Characteristics" column of Table 1, "◎" indicates that the supply current density should be at least 5 mA / cm². 2 Up to 500mA / cm 2 When the chromaticity of the emitted light varies within a certain range, it is included in... Figure 2 The white area is shown. Additionally, "0" indicates that the supply current density is from 1 mA / cm². 2 Up to 1000mA / cm 2 When the chromaticity changes, at least a portion of the emitted light contains... Figure 2 The white area is shown. Additionally, "×" indicates that the supply current density is from 1 mA / cm². 2 Up to 1000mA / cm 2 When changes occur, the chromaticity of the emitted light is not included. Figure 2 Within the white area shown.

[0226] In the "Evaluation Results" column of Table 1, "〇" indicates that the voltage at which light emission begins is less than 2.0V, and the evaluation in the "Chromaticity Characteristics" column is "◎" or "〇", indicating that the organic EL element emitting white light has good characteristics. Conversely, "×" indicates that the voltage at which light emission begins is greater than 2.0V, or the evaluation in the "Chromaticity Characteristics" column is "×", indicating that the organic EL element emitting white light does not have good characteristics.

[0227] In Table 2, under the columns “Example 1” to “Comparative Example 3”, the “x-coordinate” and “y-coordinate” columns represent the chromaticity of the emitted light as specified in the CIExy chromaticity diagram according to JIS Z8110. Additionally, in the “Evaluation” column, “0” indicates that the light is included in… Figure 2 In the white area indicated by the dashed line A, an "×" indicates that it is not included. Figure 2 The white area indicated by the dashed line A.

[0228] The organic EL device of Example 1 has a low-voltage operating characteristic that allows it to start emitting light at a voltage of 1.1V, and the current density of the supplied current is 100mA / cm². 2 Up to 1000mA / cm 2 White light emanates from within its range.

[0229] The organic EL element in Example 2 has a low-voltage operating characteristic, starting to emit light at 1.0V, and the supplied current density is 100mA / cm². 2 Up to 1000mA / cm 2 White light emanates from within its range.

[0230] The organic EL device of Example 3 has a low-voltage operating characteristic that begins to emit light at a voltage of 1.6V, and the current density of the supplied current is 3mA / cm². 2 Up to 1000mA / cm 2 White light emanates from within its range.

[0231] The organic EL device of Example 4 has a low-voltage operating characteristic that begins to emit light at 1.5V, and the current density supplied is 10mA / cm². 2 It emits white light at times.

[0232] The organic EL device of Example 5 has a low-voltage operating characteristic that begins to emit light at a voltage of 1.4V, and the current density supplied is 1mA / cm². 2 It emits white light at times.

[0233] The organic EL device of Example 6 has a low-voltage operating characteristic that begins to emit light at a voltage of 1.9V, and the current density of the supplied current is 5mA / cm². 2 Up to 700mA / cm 2 White light emanates from within its range.

[0234] Although the organic EL device in Comparative Example 1 has a low-voltage operating characteristic of starting to emit light at 1.3V, the current density of the supplied current is 1mA / cm². 2 Up to 1000mA / cm 2 It does not emit white light within its range.

[0235] Although the organic EL device in Comparative Example 2 has a low-voltage operating characteristic of starting to emit light at 1.6V, the current density of the supplied current is 1mA / cm². 2 Up to 1000mA / cm 2 It does not emit white light within its range.

[0236] Although the organic EL device in Comparative Example 3 has a low-voltage operating characteristic of starting to emit light at 1.4V, the current density supplied is 5mA / cm². 2 Up to 1000mA / cm 2 It does not emit white light within its range.

[0237] (Organic EL element of Example 7 and organic EL elements of Comparative Examples 4-5)

[0238] The organic EL element of Example 7 has the same structure as the organic EL element of Comparative Example 3, the organic EL element of Comparative Example 4 has the same structure as the organic EL element of Example 1, and the organic EL element of Comparative Example 5 has the same structure as the organic EL element of Example 2.

[0239] (Evaluation of luminescence onset voltage and luminescence intensity characteristics)

[0240] Figure 26 This is a graph showing the emission onset voltage and emission intensity characteristics of the organic EL element in Example 3. Figure 27 This is a graph showing the emission onset voltage and emission intensity characteristics of the organic EL element in Example 4. Figure 28 This is a graph showing the light emission start voltage and light emission intensity characteristics of the organic EL element in Example 5. Figure 29 This is a graph showing the emission onset voltage and emission intensity characteristics of the organic EL element in Example 6. Figure 30 This is a graph showing the light emission start voltage and light emission intensity characteristics of the organic EL element in Example 7. Figure 31 This is a graph showing the emission onset voltage and emission intensity characteristics of the organic EL element in Comparative Example 1. Figure 32 This is a graph showing the emission onset voltage and emission intensity characteristics of the organic EL element in Comparative Example 4. Figure 33 This is a graph showing the emission onset voltage and emission intensity characteristics of the organic EL element in Comparative Example 5. Figures 26-33 In the diagram, (a) represents the voltage-luminance characteristic, and (b) represents the change in emission wavelength-luminance characteristic caused by current density. Figures 26-33 In (a), the horizontal axis represents the applied voltage, and the vertical axis represents the luminance. Figures 26-33 In (b), the values ​​of 1, 10, 100, 1000, etc., represent the supply current density (mA / cm²). 2 The horizontal axis represents the emission wavelength, and the vertical axis represents the emission intensity.

[0241] Table 3 shows the evaluation results of the emission start voltage and emission intensity characteristics of the organic EL elements of Examples 3-7 and the organic EL elements of Comparative Examples 1 and 4-5. Table 4 shows the relationship between the current density and emission intensity of the supplied current for the organic EL elements of Examples 3-7 and the organic EL elements of Comparative Examples 1 and 4-5.

[0242] [Table 3]

[0243]

[0244] [Table 4]

[0245]

[0246] In Table 3, the "Emission Start Voltage [V]" column indicates the voltage at which the organic EL elements of Examples 3-7 and Comparative Examples 1 and 4-5 begin to emit light. The "Intensity Variation Characteristics" column shows the evaluation results of the rate of change of the luminous intensity of light emitted from the organic EL elements of Examples 3-7 and Comparative Examples 1 and 4-5 based on the supply current density. The "Evaluation Results" column indicates the evaluation results of the emission start voltage and luminous intensity characteristics of the organic EL elements of Examples 3-7 and Comparative Examples 1 and 4-5.

[0247] In the "Intensity Variation Characteristics" column of Table 3, "0" indicates that the supplied current density is 10 mA / cm². 2 The luminous intensity at that time is relative to the supplied current density of 100 mA / cm². 2 The ratio of luminous intensity at that time is less than 2.00. Additionally, "×" indicates a supply current density of 10 mA / cm². 2 The luminous intensity at that time is relative to the supplied current density of 100 mA / cm². 2 The ratio of luminous intensity at that time is above 2.00.

[0248] In the "Evaluation Results" column of Table 3, "〇" indicates that the organic EL element with an initial emission voltage of less than 2.0V and an evaluation of "〇" in the "Intensity Variation Characteristics" column has good characteristics, meaning that the emitted light intensity is difficult to change with variations in the supply current density. Conversely, "×" indicates that the organic EL element with an initial emission voltage of 2.0V or higher, or an evaluation of "×" in the "Intensity Variation Characteristics" column, does not have good characteristics, meaning that the emitted light intensity is difficult to change with variations in the supply current density.

[0249] The “Luminescence Intensity Ratio” column in Table 4 shows the luminescence intensity at the peak wavelength of the guest material's fluorescence when the intensity at a wavelength of 465 nm is set to “1” and the luminescence intensity of the emitted light is normalized. The peak wavelength of the guest material's fluorescence was determined by fluorescence spectroscopy based on a fluorescence spectrophotometer. In the “Luminescence Intensity Ratio” column, “10 mA / cm²” is used. 2 The column indicates that the supply current density is 10 mA / cm². 2 The ratio of luminous intensity at time, "100mA / cm 2 The column indicates that the supply current density is 100 mA / cm². 2 The ratio of luminous intensity at that time. The "Intensity Change Rate" column indicates the supply current density of 10 mA / cm². 2 The ratio of luminous intensity at that time to the supply current density of 100 mA / cm² 2 The value is obtained by comparing the luminous intensity at different times. The "Evaluation" column shows the evaluation results of the luminous intensity variation characteristics of the organic EL elements of Examples 3-7 and the organic EL elements of Comparative Examples 1 and 4-5.

[0250] The organic EL element of Example 3 exhibits a low-voltage operating characteristic, starting to emit light at 1.6V. In the organic EL element of Example 3, the intensity variation rate of the second guest material is 1.55. The organic EL element of Example 3 achieves a supply current density of 10 mA / cm². 2 With 100mA / cm 2 The rate of change of the strength of the second object material when the current density changes is less than 2.00, so it can emit light with small chromaticity changes caused by changes in the supply current density.

[0251] The organic EL element of Example 4 exhibits a low-voltage operating characteristic, starting to emit light at 1.5V. In the organic EL element of Example 4, the intensity variation rate of the second guest material is 1.46. The organic EL element of Example 4 enables a supply current density of 10 mA / cm². 2 With 100mA / cm 2 The rate of change of the strength of the second object material when the current density changes is less than 2.00, so it can emit light with small chromaticity changes caused by changes in the supply current density.

[0252] The organic EL element of Example 5 exhibits low-voltage operation, starting to emit light at 1.4V. In the organic EL element of Example 5, the intensity variation rate of the second guest material is 1.94. The organic EL element of Example 5 enables a supply current density of 10 mA / cm². 2 With 100mA / cm 2 The rate of change of the strength of the second object material when the current density changes is less than 2.00, so it can emit light with small chromaticity changes caused by changes in the supply current density.

[0253] The organic EL element of Example 6 exhibits a low-voltage operating characteristic, starting to emit light at 1.9V. In the organic EL element of Example 6, the intensity variation rate of the second guest material is 1.00. Furthermore, the intensity variation rate of the third guest material is 1.98. The organic EL element of Example 6 provides a supply current density of 10 mA / cm². 2 With 100mA / cm 2 The rate of change of the intensity of the second and third guest materials when they change is less than 2.00, so they can emit light with small chromaticity changes caused by changes in the supply current density.

[0254] The organic EL element of Example 7 exhibits a low-voltage operating characteristic, starting to emit light at 1.0V. In the organic EL element of Example 7, the intensity variation rate of the second guest material is 1.06. The organic EL element of Example 7 enables a supply current density of 10 mA / cm². 2 With 100mA / cm 2The rate of change of the strength of the second object material when the current density changes is less than 2.00, so it can emit light with small chromaticity changes caused by changes in the supply current density.

[0255] The organic EL device of Comparative Example 1 exhibits a low-voltage operating characteristic, starting to emit light at 1.3V. In the organic EL device of Comparative Example 1, the intensity variation rate of the guest material is 2.58. The organic EL device of Comparative Example 1 operates at a supply current density of 10 mA / cm². 2 With 100mA / cm 2 The rate of change of the strength of the object material during the change is greater than 2.00, therefore, the change in the chromaticity of the emitted light increases with the change in the supply current density.

[0256] The organic EL device of Comparative Example 4 exhibits a low-voltage operation characteristic, starting to emit light at 1.1V. In the organic EL device of Comparative Example 4, the intensity variation rate of the guest material is 3.29. The organic EL device of Comparative Example 4 achieves a supply current density of 10 mA / cm². 2 With 100mA / cm 2 The rate of change of the strength of the object material during the change is greater than 2.00, therefore, the change in the chromaticity of the emitted light increases with the change in the supply current density.

[0257] The organic EL device of Comparative Example 5 exhibits a low-voltage operation characteristic, starting to emit light at 1.0V. In the organic EL device of Comparative Example 5, the intensity variation rate of the guest material is 3.63. The organic EL device of Comparative Example 5 achieves a supply current density of 10 mA / cm². 2 With 100mA / cm 2 The rate of change of the strength of the object material during the change is greater than 2.00, therefore, the change in the chromaticity of the emitted light increases with the change in the supply current density.

Claims

1. An organic EL element, characterized in that, It has a first organic semiconductor layer sandwiched between a pair of electrodes and a second organic semiconductor layer forming an interface with the first organic semiconductor layer. The second organic semiconductor layer comprises an organic semiconductor material that generates triplet-triplet annihilation, and one or more guest materials. The guest material emits light through energy transfer resulting from triplet-triplet annihilation based on the organic semiconductor material. The second organic semiconductor layer can emit white light through light emission generated by the various guest materials, or through light emission generated by the organic semiconductor material and one or more guest materials.

2. The organic EL element according to claim 1, wherein, The white light has chromaticity contained in the following circular region: a circular region with a radius of 0.1 starting from the center point ((x, y) = (0.31, 0.316)) of the white region in the CIExy chromaticity diagram of JIS Z8110.

3. The organic EL element according to claim 1 or 2, wherein, The organic semiconductor material contains a compound that emits blue light when excited by triplet-triplet annihilation. The guest material comprises a compound that emits yellow or orange light through the transfer of energy generated by triplet-triplet annihilation based on the organic semiconductor material.

4. The organic EL element according to claim 1 or 2, wherein, The guest material comprises a first guest material and a second guest material, wherein the first guest material emits blue light through energy transfer resulting from triplet-triplet annihilation based on the organic semiconductor material, and the second guest material emits yellow or orange light through energy transfer from the first guest material.

5. The organic EL element according to claim 1 or 2, wherein, The organic semiconductor material contains a compound that emits blue light when excited by triplet-triplet annihilation. The guest material comprises a first guest material and a second guest material, wherein the first guest material emits green light through energy transfer resulting from triplet-triplet annihilation based on the organic semiconductor material, and the second guest material emits orange or red light through energy transfer from the first guest material.

6. The organic EL element according to claim 1 or 2, wherein, The guest material further comprises a first guest material, a second guest material, and a third guest material, wherein the first guest material emits blue light through energy transfer resulting from triplet-triplet annihilation based on the organic semiconductor material, the second guest material emits green light through energy transfer from the first guest material, and the third guest material emits orange or red light through energy transfer from the second guest material.

7. A method of using the organic EL element according to claim 3, wherein, The current density supplied to the pair of electrodes is set within the following range: 100 mA / cm². 2 Above and 1000mA / cm 2 Below and within the range of white light emitted.

8. A method of using the organic EL element according to claim 4, wherein, The current density supplied to the pair of electrodes is set within the following range: 1 mA / cm². 2 Above and 1000mA / cm 2 Below and within the range of white light emitted.

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