Organic el element

Abstract

An organic EL element according to the present invention comprises: a first organic semiconductor layer that is sandwiched between a pair of electrodes; and a second organic semiconductor layer that forms an interface with the first organic semiconductor layer, wherein the second organic semiconductor layer includes an organic semiconductor material that causes triplet-triplet annihilation and one or more guest materials, the guest materials emit light by energy transfer due to the triplet-triplet annihilation caused by the organic semiconductor material, and the second organic semiconductor layer makes it possible to emit white light by light emission that is caused by two or more guest materials or light emission that is caused by the organic semiconductor material and one or more guest materials.

Description

organic EL element

[0001] The present disclosure relates to an organic electroluminescent device.

[0002] A technology is known in which an organic EL element having an emitting layer and a hole injection layer can emit light by applying a low voltage between a pair of electrodes sandwiching the emitting layer and the hole injection layer (see, for example, International Publication No. WO 2022 / 211041 (hereinafter referred to as Patent Document 1)). The organic EL element described in Patent Document 1 has a first organic semiconductor layer containing a first organic semiconductor material, and a second organic semiconductor layer containing a second organic semiconductor material and a guest material and forming a junction surface with the first organic semiconductor. The second organic semiconductor material contained in the second organic semiconductor layer is a material that causes triplet-triplet annihilation, and the guest material contained in the second organic semiconductor layer is a material that causes light emission.

[0003] In the organic EL element described in Patent Document 1, when a voltage is applied between a pair of electrodes, a charge transfer state is formed at the junction surface between the first organic semiconductor layer and the second organic semiconductor layer. The charges formed at the junction surface recombine to generate a triplet state in the second organic semiconductor material. The second organic semiconductor material in which the triplet state is generated undergoes triplet-triplet annihilation, generating a high-energy excited state, and energy transfer occurs from the second organic semiconductor material to the guest material, resulting in light emission originating from the guest material.

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

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

[0006] The present disclosure is intended to solve such problems, and has an object to provide an organic EL element capable of emitting white light.

[0007] The organic EL element according to the present disclosure is an organic EL element including 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, wherein the second organic semiconductor layer contains an organic semiconductor material that undergoes triplet-triplet annihilation and one or more types of guest materials, and the guest material emits light due to the transfer of energy generated by triplet-triplet annihilation caused by the organic semiconductor material, and the second organic semiconductor layer is capable of emitting white light due to the emission of the multiple types of guest materials or the emission of the organic semiconductor material and the one or more types of guest materials.

[0008] Furthermore, in the organic EL element according to the present disclosure, it is preferable that the white light has a chromaticity that is included in a circular region with a radius of 0.1 from the center point ((x, y) = (0.31, 0.316)) of the white region in the CIE xy chromaticity diagram of JIS Z8110.

[0009] Furthermore, in the organic EL element according to the present disclosure, it is preferable that the organic semiconductor material contains a compound that is excited by triplet-triplet annihilation and emits blue light, and the guest material contains a compound that emits yellow or orange light due to the transfer of energy generated by triplet-triplet annihilation in the organic semiconductor material.

[0010] Furthermore, in the organic EL element according to the present disclosure, the guest material preferably includes a first guest material that emits blue light due to energy transfer caused by triplet-triplet annihilation by the organic semiconductor material, and a second guest material that emits yellow or orange light due to energy transfer from the first guest material.

[0011] Furthermore, in the organic EL element according to the present disclosure, it is preferable that the organic semiconductor material includes a compound that is excited by triplet-triplet annihilation and emits blue light, and the guest material includes a first guest material that emits green light due to energy transfer caused by triplet-triplet annihilation in the organic semiconductor material, and a second guest material that emits orange or red light due to energy transfer from the first guest material.

[0012] Furthermore, in the organic EL element according to the present disclosure, it is preferable that the guest material further includes a first guest material that emits blue light due to energy transfer caused by triplet-triplet annihilation by the organic semiconductor material, a second guest material that emits green light due to energy transfer from the first guest material, and a third guest material that emits orange or red light due to energy transfer from the second guest material.

[0013] Furthermore, in a method for using an organic EL element according to the present disclosure, the current density of the current supplied between the pair of electrodes is set to 100 mA / cm ２ More than 1000mA / cm ２ It is preferable that the range be set to a value not larger than 1000 nm and that white light be emitted.

[0014] Furthermore, in the method for using the organic EL element according to the present disclosure, the current density of the current supplied between the pair of electrodes is 1 mA / cm ２ or more and 10 mA / cm ２ Preferably, the following is true:

[0015] The organic EL element according to the present disclosure can emit white light.

[0016] 1 is a diagram showing a light-emitting device having an organic EL element according to a first embodiment; FIG. 2 is a diagram showing a range of white light; FIG. 3 is a diagram showing the light-emitting mechanism of the organic EL element shown in FIG. 1; FIG. 4 is a diagram showing energy transition accompanying light emission shown in FIG. 3; FIG. 5 is a diagram showing a light-emitting device having an organic EL element according to a second embodiment; FIG. 6 is a diagram showing the light-emitting mechanism of the organic EL element shown in FIG. 7; FIG. 8 is a diagram showing energy transition accompanying light emission shown in FIG. 9; FIG. 10 is a diagram showing a light-emitting device having an organic EL element according to a third embodiment; FIG. 11 is a diagram showing the light-emitting mechanism of the organic EL element shown in FIG. 12; FIG. 13 is a diagram showing energy transition accompanying light emission shown in FIG. 15; FIG. 16 is a diagram showing the light-emitting mechanism of the organic EL element shown in FIG. 16; FIG. 17 is a diagram showing the light-emitting mechanism of the organic EL element shown in FIG. 17; 1 is a diagram showing the light emission start voltage and white light emission characteristics of an organic EL element according to Example 5. FIG. 2 is a diagram showing the light emission start voltage and white light emission characteristics of an organic EL element according to Example 6. FIG. 3 is a diagram showing the light emission start voltage of an organic EL element according to Comparative Example 1. FIG. 4 is a diagram showing the light emission start voltage of an organic EL element according to Comparative Example 2. FIG. 5 is a diagram showing the light emission start voltage and light emission characteristics of an organic EL element according to Comparative Example 3. FIG. 6 is a diagram showing the light emission start voltage and light emission intensity characteristics of an organic EL element according to Example 3. FIG. 7 is a diagram showing the light emission start voltage and light emission intensity characteristics of an organic EL element according to Example 4. FIG. 8 is a diagram showing the light emission start voltage and light emission intensity characteristics of an organic EL element according to Example 5. FIG. 9 is a diagram showing the light emission start voltage and light emission intensity characteristics of an organic EL element according to Example 6. FIG. 10 is a diagram showing the light emission start voltage and light emission intensity characteristics of an organic EL element according to Example 7. FIG. 11 is a diagram showing the light emission start voltage and light emission intensity characteristics of an organic EL element according to Comparative Example 1. FIG. 12 is a diagram showing the light emission start voltage and light emission intensity characteristics of an organic EL element according to Comparative Example 4.FIG. 10 is a diagram showing the light emission start voltage and light emission intensity characteristics of an organic EL element according to Comparative Example 5.

[0017] The organic EL device according to the present disclosure will be described below with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to the embodiments, but extends to the inventions set forth in the claims and their equivalents.

[0018] (Configuration and Function of Organic EL Element According to First Embodiment) FIG. 1 is a diagram showing a light emitting device having an organic EL element according to the first embodiment.

[0019] The light emitting device 100 has a power supply 101 and an organic EL element 1, and is applied to organic EL displays, organic EL lighting, digital signage, light sources for photosensors, laser light sources, light sources for optical communications, etc. The power supply 101 supplies a desired current to the organic EL element 1 in response to instructions from a control device (not shown). The configuration and function of the power supply 101 are well known, so a detailed description thereof will be omitted here.

[0020] The organic EL element 1 has a pair of electrodes, a first electrode 11 and a second electrode 12, a first organic semiconductor layer 13 also referred to as an electron transport layer, and a second organic semiconductor layer 14 also referred to as an emitting layer, which forms an interface 15 with the first organic semiconductor layer 13. The organic EL element 1 emits white light in response to a predetermined light emission 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 a power source 101.

[0021] 2 is a diagram showing the range of white, and is a CIE xy chromaticity diagram defined by JIS Z8110.

[0022] White light has chromaticity that falls within the white region, which is a circular region with a radius of 0.1 from the center point of the white region ((x, y) = (0.310, 0.316)) in the CIE xy chromaticity diagram of JIS Z8110. The chromaticity of white is indicated by dashed line A in Figure 2. The color of fluorescence emitted by a material is defined by the peak wavelength of the fluorescence spectrum. Specifically, if the peak wavelength is between 380 and 430 nm, it is purple; if it is between 430 and 490 nm, it is blue; if it is between 490 and 550 nm, it is green; if it is between 550 and 590 nm, it is yellow; if it is between 590 and 640 nm, it is orange; and if it is between 640 and 770 nm, it is red.

[0023] The first electrode 11 is formed of a conductive material such as aluminum, and a first organic semiconductor layer 13 is laminated on one surface. 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 material such as indium tin oxide (ITO), and is formed on a transparent substrate (not shown) such as glass. A second organic semiconductor layer 14 is laminated on the surface of the second electrode 12 opposite to the surface facing the transparent substrate. The film thickness of the second electrode 12 is 5 nm or more and 500 nm or less.

[0024] 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 that is an acceptor that transports electrons. The film thickness of the first organic semiconductor layer 13 is preferably 0.1 nm or more and 500 nm or less, and more preferably 2 nm or more and 100 nm or less. The first organic semiconductor layer 13 may be formed only from the first organic semiconductor material 16, or may contain materials other than the first organic semiconductor material 16.

[0025] A conventionally known electron transporting material can be used as the first organic semiconductor material 16. The organic semiconductors that can be used as the first organic semiconductor material 16 are the compounds shown below.

[0026]

[0027] The second organic semiconductor layer 14 is disposed between the second electrode 12 and the first organic semiconductor layer 13. The film thickness of the second organic semiconductor layer 14 is preferably 0.1 nm or more and 500 nm or less, and more preferably 2 nm or more and 100 nm or less. The second organic semiconductor layer 14 contains a second organic semiconductor material 17 that is a hole-transporting donor and emits blue fluorescence, and a guest material 18 that emits light of 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 only from the second organic semiconductor material 17 and the guest material 18, or may contain materials other than the second organic semiconductor material 17 and the guest material 18. The second organic semiconductor layer 14 may also include a pair of non-doped layers formed from the second organic semiconductor material 17, and a doped layer that includes the second organic semiconductor material 17 and the guest material 18 and is disposed between the pair of non-doped layers. The second organic semiconductor layer 14 can improve the luminous efficiency by having a pair of an undoped layer and a doped layer. The thickness of the undoped layer can be, for example, 1 to 10 nm, and preferably 1 to 5 nm.

[0028] The second organic semiconductor material 17 is a material that undergoes triplet-triplet annihilation (TTA) and emits blue light from a high-energy excited state due to TTA and returns to a ground state. Organic semiconductors that can be used as the second organic semiconductor material 17 include the following compounds.

[0029]

[0030] The guest material 18 is a material that emits fluorescence having a longer wavelength than the fluorescence emitted by the second organic semiconductor material 17. The guest material 18 emits yellow, orange, or red fluorescence due to Förster resonance energy transfer (FRET) from the second organic semiconductor material 17, and generates white light by mixing with the blue light of the second organic semiconductor material 17. Organic semiconductors that can be used as the guest material 18 are the compounds listed below. It is more preferable that the guest material 18 is a material that emits yellow or orange fluorescence due to FRET from the second organic semiconductor material 17.

[0031]

[0032] The first organic semiconductor material 16 and the second organic semiconductor material 17 are selected so that the LUMO level of the first organic semiconductor material 16 is lower than the LUMO 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 levels of the first organic semiconductor material 16 and the second organic semiconductor material 17 is preferably 0.5 eV or more. Note that the upper limit of the difference between the LUMO levels of the first organic semiconductor material and the second organic semiconductor material is not particularly limited, but can be, for example, 2 eV or less.

[0033] Hereinafter, the energy difference between the HOMO level of the second organic semiconductor material 17 and the LUMO level of the first organic semiconductor material 16 is also referred to as the "CT level." The second organic semiconductor material 17 is selected so that the excited triplet level of the second organic semiconductor material 17 is smaller than the CT level. The difference between the excited triplet level of the second organic semiconductor material 17 and the CT 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 level of the second organic semiconductor material 17 and the CT level, the light emission onset voltage, which is the voltage at which the organic EL element 1 starts to emit fluorescence, can be reduced.

[0034] Hereinafter, the energy difference between the HOMO level and the LUMO level of a material is also 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, and more preferably 0.7 eV or more smaller. The upper limit of the energy difference between the CT level and the band gap of the second organic semiconductor material 17 is not particularly limited, but is, for example, 2 eV or less.

[0035] The guest material 18 is selected so 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.

[0036] Various combinations of the first organic semiconductor material 16, the second organic semiconductor material 17, and the guest material 18 are possible in the organic EL element 1. For example, the organic EL element 1 may use NDI-HF (2,7-di(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-(naphthalen-1-yl)-10-(naphthalen-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-diphenyltetracene) as the guest material 18.

[0037] The organic EL element 1 uses, for example, NDI-HF as the first organic semiconductor material 16, 12ADN as the second organic semiconductor material 17, and Rubrene (C 42 H 28 The organic EL element 1 may be a thin film transistor having a current density of 100 mA / cm ２ or more and 1000 mA / cm ２When a current of less than or equal to 100 W is supplied from the power supply 101, white light can be emitted.

[0038] FIG. 3 is a diagram showing the light-emitting mechanism of the organic EL element 1, and FIG. 4 is a diagram showing the energy transition accompanying the light emission shown in FIG.

[0039] When a predetermined light emission start voltage is applied between the first electrode 11 and the second electrode 12, 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 in response to the current supplied from the power source 101 to the organic EL element 1. The light emission start voltage applied between the first electrode 11 and the second electrode 12 is a voltage of 1.0 V or more and 2.0 V or less. The holes (+) injected into the second organic semiconductor layer 14 and the electrons (-) injected into the first organic semiconductor layer 13 form a charge transfer (CT) state at the interface 15 between the first organic semiconductor layer 13 and the second organic semiconductor layer 14, with pairs of electrons (-) and holes (+). 25% of the electrons (-) are in an excited singlet state, and 75% of the electrons (-) are in an excited triplet state. Charge recombination in the excited triplet state generates the second organic semiconductor material 17 in a triplet state (T1) in the second organic semiconductor layer 14. Triplet-triplet annihilation (TTA) of the second organic semiconductor material 17 in the triplet state (T1) generates the second organic semiconductor material 17 in a high-energy excited state (S1).

[0040] A portion of the second organic semiconductor material 17 in the high-energy excited state (S1) emits blue fluorescence, and the remainder of the second organic semiconductor material 17 in the high-energy excited state (S1) transfers energy to the guest material 18 by FRET without emitting blue fluorescence. The guest material 18 to which energy has been transferred enters the high-energy excited state (S1) and emits fluorescent light of a color that can be mixed with blue emitted light such as yellow and orange to produce white light. The blue fluorescence emitted by the second organic semiconductor material 17 and the fluorescence emitted by the guest material 18 mix together, causing the organic EL element 1 to emit white light.

[0041] (Method of Manufacturing an Organic EL Element According to the First Embodiment) First, in a substrate preparation step, a substrate is prepared having a transparent second electrode 12 made of ITO or the like formed on one surface. The substrate having the second electrode 12 formed on one surface is a transparent substrate, including a glass substrate, a quartz substrate, a sapphire substrate, a plastic substrate, and a film substrate. Next, in a second organic semiconductor layer lamination step, a second organic semiconductor layer 14 is laminated on the second electrode 12. In a first organic semiconductor layer lamination step, a first organic semiconductor layer 13 is laminated on the second organic semiconductor layer 14. The first organic semiconductor layer 13 and the second organic semiconductor layer 14 are laminated by a known lamination method such as vacuum deposition, sputtering, chemical vapor deposition, vapor deposition polymerization, spin coating, blade coating, bar coating, dip coating, or laminating. Then, in a first electrode lamination step, a first electrode 11 is laminated on the first organic semiconductor layer 13. The first electrode 11 is laminated by a known lamination method such as vacuum deposition, sputtering, or plating, to manufacture the organic EL element 1 .

[0042] (Action and effect of the organic EL element according to the first embodiment) When a current is supplied at a predetermined current density, the organic EL element 1 can emit white light by causing the second organic semiconductor material 17 to emit blue fluorescence and the guest material 18 to emit yellow or orange fluorescence.

[0043] Furthermore, the organic EL element 1 emits light when a light emission start voltage of 1.0 V or more and 2.0 V or less is applied, thereby realizing low-voltage operation that allows light emission using general primary and secondary batteries with a rated voltage of 1.5 V.

[0044] (Configuration and Function of Organic EL Element According to Second Embodiment) FIG. 5 is a diagram showing a light emitting device having an organic EL element according to a second embodiment.

[0045] The light emitting device 200 includes a power supply 101 and an organic EL element 2. The power supply 101 supplies a desired voltage to the organic EL element 2 in response to an instruction from a control device (not shown).

[0046] The organic EL element 2 has a pair of electrodes, a first electrode 21 and a second electrode 22, a first organic semiconductor layer 23 also referred to as an electron transport layer and containing a first organic semiconductor material 26, and a second organic semiconductor layer 24 also referred to as an emitting layer and 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 flowing from the first electrode 21 to the second electrode 22, which is supplied from a power source 101. The first electrode 21, the second electrode 22, the first organic semiconductor layer 23, and the first organic semiconductor material 26 have the same configurations and functions as the first electrode 11, the second electrode 12, the first organic semiconductor layer 13, and the first organic semiconductor material 16, respectively, and therefore will not be described in detail here.

[0047] The second organic semiconductor layer 24 contains a second organic semiconductor material 27 that is a donor that transports holes, a first guest material 28, and a second guest material 29 that 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 light. The second organic semiconductor layer 24 may be formed only from the second organic semiconductor material 27, the first guest material 28, and the second guest material 29, or may contain materials other than the second organic semiconductor material 27, the first guest material 28, and the second guest material 29.

[0048] The second organic semiconductor material 27 is a material that causes TTA, and the organic semiconductor that can be used as the second organic semiconductor material 27 is the same as that of the second organic semiconductor material 17 .

[0049] The first guest material 28 is a material that emits fluorescence when energy is transferred from the second organic semiconductor material 27 by FRET. The first guest material 28 is a compound whose absorption spectrum overlaps largely with the emission spectrum of the second organic semiconductor material 27. The fluorescence emitted by the first guest material 28 is blue light whose peak wavelength is longer than that of the fluorescence emitted by the second organic semiconductor material 27. Organic semiconductors that can be used as the first guest material 28 are the compounds shown below.

[0050]

[0051] The second guest material 29 is a material that emits fluorescence having a longer wavelength than the fluorescence emitted by the first guest material 28 due to energy transfer from the first guest material 28 by FRET. The fluorescence emitted by the second guest material 29 is yellow, orange, or red light that can be mixed with blue light to generate white light. The organic semiconductor that can be used as the second guest material 29 is the same as the guest material 18. The second guest material 29 is more preferably a material that emits yellow or orange fluorescence due to FRET from the first guest material 28.

[0052] 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 levels and LUMO levels of the first organic semiconductor material 26 and the second organic semiconductor material 27, and the excited triplet 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 manner as the first organic semiconductor material 16 and the second organic semiconductor material 17, respectively.

[0053] The first guest material 28 is selected so 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 0.5 eV or less. 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 transition from the second organic semiconductor material 27 to the first guest material 28 by FRET changes depending on the supplied current, and the chromaticity of the emitted white light changes depending on the supplied current.

[0054] The second guest material 29 is selected so 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.

[0055] In the organic EL element 2, various combinations of the first organic semiconductor material 26, the second organic semiconductor material 27, the first guest material 28, and the second guest material 29 are possible. For example, 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 (2,5,8,11-tetra-tert-butylperylene) as the first guest material 28, and tbRub as the second guest material 29.

[0056] Furthermore, the organic EL element 2 may use, for example, 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-Tetraphenylnaphthacene) as the second guest material 29.

[0057] The organic EL element 2 may also use, for example, 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. The organic EL element 2 may be configured such that the current density is 1 mA / cm. ２ to 1000mA / cm ２ When a current of less than or equal to 100 W is supplied from the power supply 101, white light can be emitted.

[0058] FIG. 6 is a diagram showing the light-emitting mechanism of the organic EL element 2, and FIG. 7 is a diagram showing the energy transition accompanying the light emission shown in FIG.

[0059] Similar to the organic EL element 1, the organic EL element 2 forms a CT state at the interface 25 between the first organic semiconductor layer 23 and the second organic semiconductor layer 24 in response to a current being supplied to the organic EL element 2 from the power source 101. In the organic EL element 2, the CT state undergoes charge recombination to generate the second organic semiconductor material 27 in T1 in the second organic semiconductor layer 24, and the second organic semiconductor material 27 in T1 undergoes TTA to generate the second organic semiconductor material 27 in a high-energy excited state (S1).

[0060] Substantially all of the second organic semiconductor material 27 in the high-energy excited state (S1) transfers energy to the first guest material 28 by FRET without emitting fluorescence. The first guest material 28 to which energy has been transferred enters the high-energy excited state (S1). A portion of the first guest material 28 in the high-energy excited state (S1) emits blue fluorescence. The remainder of the first guest material 28 in the high-energy excited state (S1) transfers energy to the second guest material 29 by FRET. The second guest material 29 to which energy has been transferred enters the high-energy excited state (S1). The second guest material 29 in the high-energy excited state (S1) emits fluorescent light of a color that can be mixed with blue emission, such as yellow or orange, to produce white light. The blue fluorescence emitted by the first guest material 28 and the yellow or orange fluorescence emitted by the second guest material 29 are mixed, causing the organic EL element 2 to emit white light.

[0061] (Method for Manufacturing Organic EL Element According to Second Embodiment) The method for manufacturing the organic EL element 2 is the same as the method for manufacturing the organic EL element 1, and therefore a detailed description thereof will be omitted here.

[0062] (Action and Effect of Organic EL Element According to Second Embodiment) When a current is supplied at a predetermined current density to the organic EL element 2, the first guest material 28 emits blue fluorescence and the second guest material 29 emits yellow or orange fluorescence, thereby enabling the organic EL element 2 to emit white light. The organic EL element 2 uses, as the first guest material 28, a compound whose absorption spectrum overlaps largely with the emission spectrum of the second organic semiconductor material 27, thereby increasing the efficiency of energy transfer by FRET from the second organic semiconductor material 27 to the first guest material 28. By increasing the efficiency of energy transfer by FRET from the second organic semiconductor material 27 to the first guest material 28, the organic EL element 2 suppresses the fluorescence emitted by the second organic semiconductor material 27 excited by TTA, and the fluorescence emitted by the first guest material 28 due to FRET becomes dominant, thereby suppressing changes in chromaticity caused by changes in current intensity.

[0063] Furthermore, the organic EL element 2 emits light when a light emission start voltage of 1.0 V or more and 2.0 V or less is applied, thereby realizing low-voltage operation that allows light emission using general primary and secondary batteries with a rated voltage of 1.5 V.

[0064] (Configuration and Function of Organic EL Element According to Third Embodiment) FIG. 8 is a diagram showing a light emitting device having an organic EL element according to a third embodiment.

[0065] The light emitting device 300 includes a power supply 101 and an organic EL element 3. The power supply 101 supplies a desired voltage to the organic EL element 3 in response to an instruction from a control device (not shown).

[0066] The organic EL element 3 has a pair of electrodes, a first electrode 31 and a second electrode 32, a first organic semiconductor layer 33 also referred to as an electron transport layer and containing a first organic semiconductor material 36, and a second organic semiconductor layer 34 also referred to as an emitting layer and 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 flowing from the first electrode 31 to the second electrode 32, which is supplied from a power source 101. The configurations 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 the configurations and functions of the first electrode 11, the second electrode 12, the first organic semiconductor layer 13, and the first organic semiconductor material 16, respectively, and therefore will not be described in detail here.

[0067] The second organic semiconductor layer 34 contains a second organic semiconductor material 37 which is a donor that transports holes, a first guest material 38, a second guest material 39, and a third guest material 40. The first guest material 38, the second guest material 39, and the third guest material 40 emit fluorescence of a color that allows mixed light obtained by mixing the fluorescence of each material to be emitted as white light. The second organic semiconductor layer 34 may be formed only from the second organic semiconductor material 37, the first guest material 38, the second guest material 39, and the third guest material 40, or 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.

[0068] The second organic semiconductor material 37 is a material that causes TTA, and the organic semiconductor that can be used as the second organic semiconductor material 37 is the same as that of the second organic semiconductor material 27 .

[0069] The first guest material 38 is a material that emits fluorescence when energy is transferred from the second organic semiconductor material 37 by FRET. The fluorescence emitted by the first guest material 38 is light with a blue peak wavelength. The organic semiconductors that can be used as the first guest material 38 are the same as those of the first guest material 28.

[0070] The second guest material 39 is a material that emits fluorescence having a longer wavelength than the fluorescence emitted by the first guest material 38 as a result of energy transfer from the first guest material 38 by FRET. The fluorescence emitted by the second guest material 39 is green light, a color that can be mixed with blue light and orange or red light to generate white light. Organic semiconductors that can be used as the second guest material 39 are the compounds shown below.

[0071]

[0072] The third guest material 40 is a material that emits fluorescence having a longer wavelength than the fluorescence emitted by the second guest material 39 due to energy transfer from the second guest material 39 by FRET. The fluorescence emitted by the third guest material 40 is yellow, orange, or red light that can be mixed with the fluorescence emitted by the first guest material 38 and the second guest material 39 to generate white light. The organic semiconductor that can be used as the third guest material 40 is the same as the guest material 18. The third guest material 40 is more preferably a material that emits orange or red fluorescence due to FRET from the second guest material 39.

[0073] In the organic EL element 3, the first organic semiconductor material 36 and the second organic semiconductor material 37 are selected with reference to the HOMO levels and LUMO levels of the first organic semiconductor material 36 and the second organic semiconductor material 37, and the excited triplet 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 manner as the first organic semiconductor material 16 and the second organic semiconductor material 17, respectively. Furthermore, the first guest material 38 and the second guest material 39 are selected based on the difference in band gap, similar to the first guest material 28 and the second guest material 29 in the organic EL element 2.

[0074] The third guest material 40 is selected so 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.

[0075] In the organic EL element 3, various combinations of 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 are possible. The organic EL element 3 may, for example, 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. The organic EL element 3 may be configured such that a current density of 5 mA / cm ２ to 700mA / cm ２ When a current of less than or equal to 100 W is supplied from the power supply 101, white light can be emitted.

[0076] FIG. 9 is a diagram showing the light emission mechanism of the organic EL element 3, and FIG. 10 is a diagram showing the energy transition accompanying the light emission shown in FIG.

[0077] Similar to the organic EL element 1, the organic EL element 3 forms a CT state at the interface 35 between the first organic semiconductor layer 33 and the second organic semiconductor layer 34 in response to a current being supplied to the organic EL element 3 from the power source 101. In the organic EL element 3, the CT state recombines with charges to generate the second organic semiconductor material 37 in T1 in the second organic semiconductor layer 34, and the generated second organic semiconductor material 37 in T1 undergoes TTA to generate the second organic semiconductor material 37 in a high-energy excited state (S1).

[0078] Substantially all of the second organic semiconductor material 37 in the high-energy excited state (S1) transfers energy to the first guest material 38 by FRET without emitting fluorescence. The first guest material 38 to which energy has been transferred enters a high-energy excited state (S1). A portion of the first guest material 38 in the high-energy excited state (S1) emits blue fluorescence. The remainder of the first guest material 38 in the high-energy excited state (S1) transfers energy to the second guest material 39 by FRET. The second guest material 39 to which energy has been transferred enters a high-energy excited state (S1). A portion of the second guest material 39 in the high-energy excited state (S1) emits green or other light as fluorescence. The remainder of the second guest material 39 in the high-energy excited state (S1) transfers energy to the third guest material 40 by FRET. The third guest material 40 in the high-energy excited state (S1) emits orange, red, or other light as fluorescence. The blue fluorescence emitted by the first guest material 38 and the fluorescence emitted by the second guest material 39 and the third guest material 40 are mixed together, so that the organic EL element 3 emits white light.

[0079] (Method for Manufacturing Organic EL Element According to Third Embodiment) The method for manufacturing the organic EL element 3 is the same as the method for manufacturing the organic EL element 1, and therefore a detailed description thereof will be omitted here.

[0080] (Effects of the Organic EL Element According to the Third Embodiment) When a current is supplied at a predetermined current density to the organic EL element 3, 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 enabling the organic EL element 3 to emit white light. Furthermore, by using, as the first guest material 38, a compound whose absorption spectrum overlaps largely with the emission spectrum of the second organic semiconductor material 37, the organic EL element 3 can increase the efficiency of energy transfer by FRET from the second organic semiconductor material 37 to the first guest material 38. By increasing the efficiency of energy transfer by FRET from the second organic semiconductor material 37 to the first guest material 38, the organic EL element 3 suppresses the fluorescence emitted by the second organic semiconductor material 37 excited by TTA, and the fluorescence by FRET becomes dominant, thereby making it possible to suppress changes in chromaticity due to changes in current intensity.

[0081] Furthermore, the organic EL element 3 emits light when a light emission start voltage of 1.0 V or more and 2.0 V or less is applied, thereby realizing low-voltage operation that allows light emission using general primary and secondary batteries with a rated voltage of 1.5 V.

[0082] (Configuration and Function of Organic EL Element According to Fourth Embodiment) FIG. 11 is a diagram showing a light emitting device having an organic EL element according to a fourth embodiment.

[0083] The light emitting device 400 includes a power supply 101 and an organic EL element 4. The power supply 101 supplies a desired voltage to the organic EL element 4 in response to an instruction from a control device (not shown).

[0084] The organic EL element 4 has a pair of electrodes, a first electrode 41 and a second electrode 42, a first organic semiconductor layer 43 also referred to as an electron transport layer and containing a first organic semiconductor material 46, and a second organic semiconductor layer 44 also referred to as an emitting layer and forming an interface 45 with the first organic semiconductor layer 43. The organic EL element 4 emits light in response to a current I flowing from the first electrode 41 to the second electrode 42, which is supplied from a power source 101. The configurations 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 the configurations and functions of the first electrode 11, the second electrode 12, the first organic semiconductor layer 13, and the first organic semiconductor material 16, respectively, and therefore will not be described in detail here.

[0085] The second organic semiconductor layer 44 contains a second organic semiconductor material 47 that is a donor that transports holes, a first guest material 48, and a second guest material 49. The first guest material 48 and the second guest material 49 emit mixed-color light by mixing the fluorescent lights of the first and second guest materials 48 and 49. The second organic semiconductor layer 44 may be formed only from the second organic semiconductor material 47, the first guest material 48, and the second guest material 49, or may contain materials other than the second organic semiconductor material 47, the first guest material 48, and the second guest material 49.

[0086] The second organic semiconductor material 47 is a material that causes TTA, and the organic semiconductor that can be used as the second organic semiconductor material 47 is the same as that of the second organic semiconductor material 17 .

[0087] The first guest material 48 is a material that emits fluorescence when energy is transferred from the second organic semiconductor material 47 by FRET. Organic semiconductors that can be used as the first guest material 48 are the same as those for the first guest material 28. The first guest material 48 is a compound whose absorption spectrum overlaps largely with the emission spectrum of the second organic semiconductor material 47.

[0088] The second guest material 49 is a material that emits fluorescence having a longer wavelength than the fluorescence emitted by the first guest material 48 when energy is transferred from the first guest material 48 by FRET. The organic semiconductor that can be used as the second guest material 49 is the same as the guest material 18 or the second guest material 39.

[0089] In the organic EL element 4, the first organic semiconductor material 46 and the second organic semiconductor material 47 are selected with reference to the HOMO levels and LUMO levels of the first organic semiconductor material 46 and the second organic semiconductor material 47, and the excited triplet 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 manner as the first organic semiconductor material 16 and the second organic semiconductor material 17, respectively. Furthermore, the first guest material 48 and the second guest material 49 are selected based on the difference in band gap, similar to the first guest material 28 and the second guest material 29 of the organic EL element 2.

[0090] Various combinations of the first organic semiconductor material 46, the second organic semiconductor material 47, the first guest material 48, and the second guest material 49 are possible in the organic EL element 4. For example, 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 tbRub as the second guest material 49.

[0091] Furthermore, the organic EL element 4 may use, for example, 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.

[0092] Furthermore, the organic EL element 4 may use, for example, 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.

[0093] FIG. 12 is a diagram showing the light emitting mechanism of the organic EL element 4, and FIG. 13 is a diagram showing the energy transition accompanying the light emission shown in FIG.

[0094] Similar to the organic EL element 1, the organic EL element 4 forms a CT state at the interface 45 between the first organic semiconductor layer 43 and the second organic semiconductor layer 44 in response to a current being supplied to the organic EL element 4 from the power source 101. In the organic EL element 4, the CT state recombines with charges to generate a second organic semiconductor material 47 in T1 in the second organic semiconductor layer 44, and the generated second organic semiconductor material 47 in T1 undergoes TTA to generate the second organic semiconductor material 47 in a high-energy excited state (S1).

[0095] Substantially all of the second organic semiconductor material 47 in the high-energy excited state (S1) transfers energy to the first guest material 48 by FRET without emitting fluorescence. The first guest material 48 to which energy has been transferred enters the high-energy excited state (S1). A portion of the first guest material 48 in the high-energy excited state (S1) emits fluorescence. The remainder of the first guest material 48 in the high-energy excited state (S1) transfers energy to the second guest material 49 by FRET. The second guest material 49 to which energy has been transferred enters the high-energy excited state (S1). The second guest material 49 in the high-energy excited state (S1) emits fluorescence having a wavelength longer than the wavelength of the fluorescence emitted by the first guest material 48.

[0096] (Method for Manufacturing Organic EL Element According to Fourth Embodiment) The method for manufacturing the organic EL element 4 is the same as the method for manufacturing the organic EL element 1, and therefore a detailed description thereof will be omitted here.

[0097] (Effects of the Organic EL Element According to the Fourth Embodiment) In the organic EL element 4, substantially all of the second organic semiconductor material 47 does not emit fluorescence and transfers energy to the first guest material 48 by FRET, so there is little risk of a change in the amount of fluorescence emitted by the second organic semiconductor material 47 and a change in the chromaticity of the emitted light. The organic EL element 4 can increase the efficiency of energy transfer by FRET from the second organic semiconductor material 47 to the first guest material 48 by using, as the first guest material 48, a compound whose absorption spectrum overlaps largely with the emission spectrum of the second organic semiconductor material 47. In the organic EL element 4, by increasing the efficiency of energy transfer by FRET from the second organic semiconductor material 47 to the first guest material 48, the fluorescence emitted by the second organic semiconductor material 47 excited by TTA is suppressed, and the fluorescence by FRET becomes dominant, so that changes in chromaticity due to changes in current intensity can be suppressed.

[0098] Furthermore, the organic EL element 4 emits light when a light emission start voltage of 1.0 V or more and 2.0 V or less is applied, thereby realizing low-voltage operation that allows light emission using general primary and secondary batteries with a rated voltage of 1.5 V.

[0099] (Configuration and Function of Organic EL Element According to Fifth Embodiment) FIG. 14 is a diagram showing a light emitting device having an organic EL element according to a fifth embodiment.

[0100] The light emitting device 500 includes a power supply 101 and an organic EL element 5. The power supply 101 supplies a desired voltage to the organic EL element 5 in accordance with instructions from a control device (not shown).

[0101] The organic EL element 5 has a pair of electrodes, a first electrode 51 and a second electrode 52, a first organic semiconductor layer 53 also referred to as an electron transport layer and containing a first organic semiconductor material 56, and a second organic semiconductor layer 54 also referred to as an emitting layer and 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 flowing from the first electrode 51 to the second electrode 52, which is supplied from a power source 101. The configurations 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 the configurations and functions of the first electrode 11, the second electrode 12, the first organic semiconductor layer 13, and the first organic semiconductor material 16, respectively, and therefore will not be described in detail here.

[0102] The second organic semiconductor layer 54 contains a second organic semiconductor material 57 which is a donor that transports holes, a first guest material 58, a second guest material 59, and a third guest material 60. 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-color light obtained by mixing the fluorescence of each material. The second organic semiconductor layer 54 may be formed only from the second organic semiconductor material 57, the first guest material 58, the second guest material 59, and the third guest material 60, or 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.

[0103] The second organic semiconductor material 57 is a material that causes TTA, and the organic semiconductor that can be used as the second organic semiconductor material 57 is the same as that of the second organic semiconductor material 17 .

[0104] The first guest material 58 is a material that emits fluorescence when energy is transferred from the second organic semiconductor material 57 by FRET. The fluorescence emitted by the first guest material 58 is blue light. The organic semiconductors that can be used as the first guest material 58 are the same as those of the first guest material 28.

[0105] The second guest material 59 is a material that emits fluorescence having a longer wavelength than the fluorescence emitted by the first guest material 58 due to energy transfer from the first guest material 58 by FRET. The fluorescence emitted by the second guest material 59 is green light. The organic semiconductors that can be used as the second guest material 59 are the same as those for the second guest material 39.

[0106] The third guest material 60 is a material that emits fluorescence having a longer wavelength than the fluorescence emitted by the second guest material 59 due to energy transfer from the second guest material 59 by FRET. The fluorescence emitted by the third guest material 60 is yellow, orange, or red light. The organic semiconductors that can be used as the third guest material 40 are the same as those of the guest material 18.

[0107] 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 levels and LUMO levels of the first organic semiconductor material 56 and the second organic semiconductor material 57, and the excited triplet 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 manner as the first organic semiconductor material 16 and the second organic semiconductor material 17, respectively. Furthermore, the first guest material 58, the second guest material 59, and the third guest material 60 are selected based on the difference in band gap, similar to the first guest material 38, the second guest material 39, and the third guest material 40 of the organic EL element 3.

[0108] In the organic EL element 5, various combinations are possible for 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. The organic EL element 5 may use, for example, 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.

[0109] FIG. 15 is a diagram showing the light emission mechanism of the organic EL element 5, and FIG. 16 is a diagram showing the energy transition accompanying the light emission shown in FIG.

[0110] Similar to the organic EL element 1, the organic EL element 5 forms a CT state at the interface 55 between the first organic semiconductor layer 53 and the second organic semiconductor layer 54 in response to a current being supplied to the organic EL element 5 from the power source 101. In the organic EL element 5, the CT state recombines with charges to generate the second organic semiconductor material 57 in T1 in the second organic semiconductor layer 54, and the generated second organic semiconductor material 57 in T1 undergoes TTA to generate the second organic semiconductor material 57 in a high-energy excited state (S1).

[0111] Substantially all of the second organic semiconductor material 57 in the high-energy excited state (S1) transfers energy to the first guest material 58 by FRET without emitting fluorescence. The first guest material 58 to which energy has been transferred enters a high-energy excited state (S1). A portion of the first guest material 58 in the high-energy excited state (S1) emits fluorescence. The remainder of the first guest material 58 in the high-energy excited state (S1) transfers energy to the second guest material 59 by FRET. The second guest material 59 to which energy has been transferred enters a high-energy excited state (S1). A portion of the second guest material 59 in the high-energy excited state (S1) emits fluorescence having a wavelength longer than the wavelength of the fluorescence emitted by the first guest material 58. The remainder of the second guest material 59 in the high-energy excited state (S1) transfers energy to the third guest material 60 by FRET. The third guest material 60 in the high-energy excited state (S1) emits fluorescence having a wavelength longer than the wavelength of the fluorescence emitted by the second guest material 59.

[0112] (Method for Manufacturing Organic EL Element According to Fifth Embodiment) The method for manufacturing the organic EL element 5 is the same as the method for manufacturing the organic EL element 1, and therefore a detailed description thereof will be omitted here.

[0113] (Action and effect of organic EL element according to fifth embodiment) In the organic EL element 5, almost all of the second organic semiconductor material 57 does not emit fluorescence and transfers energy to the first guest material 58 by FRET, so there is little risk that the amount of fluorescence emitted by the second organic semiconductor material 57 will change and the chromaticity of the emitted light will change.

[0114] Furthermore, the organic EL element 5 emits light when a light emission start voltage of 1.0 V or more and 2.0 V or less is applied, thereby realizing low-voltage operation that allows light emission using general primary and secondary batteries with a rated voltage of 1.5 V.

[0115] (Variations of Organic EL Elements According to Embodiments) Organic EL elements 1 to 5 each include a pair of electrodes, namely, a first electrode and a second electrode, a first organic semiconductor layer, and a second organic semiconductor layer. However, the organic EL elements according to the embodiments may further include other organic semiconductor layers or inorganic compound layers. For example, the organic EL elements according to the embodiments may further include a hole transport layer that is disposed between the second organic semiconductor layer and the second electrode and transports holes. Furthermore, the organic EL elements according to the embodiments may further include, in addition to the hole transport layer, an electron injection layer that is disposed between the first organic semiconductor layer and the first electrode and injects electrons, and a hole injection layer that is disposed between the hole transport layer and the second electrode and injects holes.

[0116] In the organic EL elements 1 to 5, the first organic semiconductor layer is an electron transport layer, but in the organic EL element according to the embodiment, the first organic semiconductor layer may be a hole blocking layer. In the organic EL element according to the embodiment, the first organic semiconductor layer, which is a hole blocking layer, may also function as an electron injection layer, and the light-emitting layer, which is the second organic semiconductor layer, may also function as a hole transport layer.

[0117] The organic EL element 3 also includes 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 according to the embodiment may include 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.

[0118] The organic EL device according to the embodiment may have a plurality of layers containing the same organic semiconductor material. For example, when the second organic semiconductor layer contains rubrene as the second organic semiconductor material, the organic EL device according to the embodiment may have a hole-blocking layer formed of rubrene.

[0119] (Method for measuring light-emitting characteristics) The light luminance, luminance intensity, and chromaticity were measured for each of the organic EL elements according to the examples and the organic EL elements according to the comparative examples. The luminance was measured using a source measure unit (B2902A, manufactured by Keysight Technologies) and a luminance meter (BM-9, manufactured by Topcom). The luminance intensity was measured using a spectrofluorometer (Fluorolog, manufactured by HORIBA). The chromaticity was measured using a spectrophotometer (C-7000, manufactured by Sekonic Corporation). Note that the "%" in the guest molecule content refers to volume %.

[0120] (Organic EL element according to Example 1) The organic EL element according to Example 1 is formed by forming a MoO ３ The hole injection layer, the light emitting layer, the electron transport layer, and the Al electrode were sequentially stacked in a vacuum deposition system at 1×10 -4 The organic EL device was laminated by thermal evaporation under high vacuum of 100 Pa. The formed organic EL device was encapsulated in a glove box with a glass substrate and epoxy resin. The ITO-coated glass substrate was manufactured by Technoprint Co., Ltd., and the ITO thickness was 150 nm and the sheet resistance was 10.3 Ω sq. -１ The thickness of the hole injection layer was 10 nm, and the layer was formed at a film formation rate of 0.1 nm / s.

[0121] The light-emitting layer includes a pair of non-doped layers having 12ADN as a second organic semiconductor material, and a doped layer having 12ADN as a second organic semiconductor material and tbRub as a guest material, disposed between the pair of non-doped layers. Each of the pair of non-doped layers had a thickness of 10 nm and was deposited at a deposition rate of 1 nm / s. The doped layer had a tbRub content of 0.1%. The doped layer had a thickness of 50 nm and was deposited at a deposition rate of 1 nm / s. The electron transport layer had NDI-HF as a first organic semiconductor material. The electron transport layer had a thickness of 50 nm and was deposited at a deposition rate of 1 nm / s. The electron injection layer had a thickness of 1 nm and was deposited at a deposition rate of 0.1 nm / s. The Al electrode had a thickness of 100 nm and was deposited at a deposition rate of 3 nm / s.

[0122] (Organic EL Elements of Examples 2 to 6) The organic EL element of Example 2 differs from the organic EL element of Example 1 in that it uses Rubrene as the guest material instead of tbRub. The content of Rubrene in the doped layer is 0.1%. The thickness of the doped layer is 50 nm and it was formed at a film formation rate of 1 nm / s. The organic EL element of Example 3 differs from the organic EL element of Example 1 in that it uses 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 it was formed at a film formation rate of 1 nm / s. The organic EL element of Example 4 differs from the organic EL element of Example 3 in that it uses Rubrene as the second guest material instead of tbRub. The doped layer had a TbPe content of 0.5%, and a Rubrene content of 0.1%. The doped layer had a thickness of 50 nm and was formed at a deposition rate of 1 nm / s. The organic EL element of Example 5 differs from the organic EL element of Example 3 in that DBP was used as the second guest material instead of tbRub. The doped layer had a TbPe content of 0.5%, and a DBP content of 0.1%. The doped layer had a thickness of 50 nm and was formed at a deposition rate of 1 nm / s. The organic EL element of Example 6 differs from the organic EL element of Example 3 in that TTPA was used as the second guest material instead of tbRub and DBP was used as the third guest material. The doped layer had a TbPe content of 0.5%, a TTPA content of 0.1%, and a DBP content of 0.1%. The doped layer had a thickness of 50 nm and was deposited at a deposition rate of 1 nm / s.

[0123] (Organic EL Elements of Comparative Examples 1 to 3) The organic EL element of Comparative Example 1 differs from the organic EL element of Example 1 in that DBP is used as the guest material instead of tbRub. The content of DBP in the doped layer is 0.1%. The thickness of the doped layer is 50 nm and the layer was formed at a deposition rate of 1 nm / s. The organic EL element of Comparative Example 2 differs from the organic EL element of Example 1 in that TTPA is used as the guest material instead of tbRub. The content of TTPA in the doped layer is 0.1%. The thickness of the doped layer is 50 nm and the layer was formed at a deposition rate of 1 nm / s. The organic EL element of Comparative Example 3 differs from the organic EL element of Example 3 in that TTPA is used as the second guest material instead of tbRub. The content of TTPA in the doped layer is 0.1%. The thickness of the doped layer is 50 nm and the layer was formed at a deposition rate of 1 nm / s.

[0124] (Evaluation of Light-Emitting Diode and White Light-Emitting Characteristics) FIG. 17 shows the light-emitting voltage and white light-emitting characteristics of the organic EL element according to Example 1, FIG. 18 shows the light-emitting voltage and white light-emitting characteristics of the organic EL element according to Example 2, and FIG. 19 shows the light-emitting voltage and white light-emitting characteristics of the organic EL element according to Example 3. FIG. 20 shows the light-emitting voltage and white light-emitting characteristics of the organic EL element according to Example 4, FIG. 21 shows the light-emitting voltage and white light-emitting characteristics of the organic EL element according to Example 5, and FIG. 22 shows the light-emitting voltage and white light-emitting characteristics of the organic EL element according to Example 6. FIG. 23 shows the light-emitting voltage of the organic EL element according to Comparative Example 1, FIG. 24 shows the light-emitting voltage of the organic EL element according to Comparative Example 2, and FIG. 25 shows the light-emitting voltage and light-emitting characteristics of the organic EL element according to Comparative Example 3. In FIGS. 17 to 22 and 25, (a) shows the applied voltage-light-emitting luminance characteristics, and (b) shows the supplied current density-chromaticity characteristics. In Figures 17 to 22 and 25(a), the horizontal axis represents applied voltage, and the vertical axis represents luminance. In Figures 17 to 22 and 25(b), the horizontal axis represents the x-coordinate of the JIS Z8110 CIE xy chromaticity diagram, and the vertical axis represents the y-coordinate of the JIS Z8110 CIE xy chromaticity diagram. Figures 23 and 24 show applied voltage-luminance characteristics.

[0125] Table 1 shows the evaluation results of the light emission start voltage and white light emission characteristics of the organic EL elements according to Examples 1 to 6 and the organic EL elements according to Comparative Examples 1 to 3. Table 2 shows the relationship between the supply current density and the chromaticity of the emitted light of the organic EL elements according to Examples 1 to 6 and the organic EL element according to Comparative Example 3.

[0126]

[0127]

[0128] In Table 1, the "Light Emission Start Voltage [V]" column indicates the voltage at which the organic EL elements according to Examples 1 to 6 and the organic EL elements according to Comparative Examples 1 to 3 start to emit light. The "Chromaticity Characteristics" column indicates the evaluation results of the chromaticity of the light emitted from the organic EL elements according to Examples 1 to 6 and the organic EL elements according to Comparative Examples 1 to 3. The "Evaluation Results" column indicates the evaluation results of the light emission start voltage and white light emission characteristics of the organic EL elements according to Examples 1 to 6 and the organic EL elements according to Comparative Examples 1 to 3.

[0129] In the "chromaticity characteristics" column of Table 1, "◎" indicates a current of at least 5 mA / cm ２ to 500mA / cm ２ When the supply current density is changed in the range from 1 mA / cm to 1 mA / cm, the chromaticity of the emitted light falls within the white range shown in FIG. ２ to 1000mA / cm ２ This indicates that when the supply current density is changed up to 1 mA / cm, the chromaticity of at least a part of the emitted light falls within the white range shown in FIG. 2. ２ to 1000mA / cm ２ 2. This shows that when the supply current density is changed up to

[0130] In the "Evaluation Results" column of Table 1, "◯" indicates that the light emission starting voltage is less than 2.0 V, and the evaluation in the "Chromaticity Characteristics" column is "◎" or "◯", and the element has good characteristics as an organic EL element that emits white light. "X" indicates that the light emission starting voltage is 2.0 V or more, or the evaluation in the "Chromaticity Characteristics" column is "X", and the element does not have good characteristics as an organic EL element that emits white light.

[0131] In each of the "Example 1" to "Comparative Example 3" columns in Table 2, the "x coordinate" and "y coordinate" columns indicate the "x coordinate" and "y coordinate" of the chromaticity of the emitted light in the CIE xy chromaticity diagram defined by JIS Z8110. In addition, in the "Evaluation" column, "◯" indicates that the result is included in the white region indicated by dashed line A in FIG. 2, and "×" indicates that the result is not included in the white region indicated by dashed line A in FIG. 2.

[0132] The organic EL element according to Example 1 has low-voltage operating characteristics, in which light emission begins at a voltage of 1.1 V, and the current density of the supplied current is 100 mA / cm. ２ to 1000mA / cm ２ It emits white light in the range of

[0133] The organic EL element according to Example 2 has low voltage operation characteristics in which light emission starts at a voltage of 1.0 V, and the current density of the supplied current is 100 mA / cm. ２ to 1000mA / cm ２ It emits white light in the range of

[0134] The organic EL element according to Example 3 has low voltage operation characteristics in which light emission starts at a voltage of 1.6 V, and the current density of the supplied current is 3 mA / cm. ２ to 1000mA / cm ２ It emits white light in the range of

[0135] The organic EL element according to Example 4 has low voltage operation characteristics in which light emission starts at a voltage of 1.5 V, and the current density of the supplied current is 10 mA / cm. ２ It emits white light.

[0136] The organic EL element according to Example 5 has low voltage operation characteristics in which light emission starts at a voltage of 1.4 V, and the current density of the supplied current is 1 mA / cm ２ It emits white light.

[0137] The organic EL element according to Example 6 has low-voltage operation characteristics in which light emission starts at a voltage of 1.9 V, and the current density of the supplied current is 5 mA / cm. ２ to 700mA / cm ２It emits white light in the range of

[0138] The organic EL element according to Comparative Example 1 has low-voltage operation characteristics, in which light emission begins at a voltage of 1.3 V, but the current density of the supplied current is 1 mA / cm ２ to 1000mA / cm ２ It does not emit white light in the range

[0139] The organic EL element according to Comparative Example 2 has low-voltage operation characteristics, in which light emission begins at a voltage of 1.6 V, but the current density of the supplied current is 1 mA / cm ２ to 1000mA / cm ２ It does not emit white light in the range

[0140] The organic EL element according to Comparative Example 3 has low-voltage operation characteristics, in which light emission begins at a voltage of 1.4 V, but the current density of the supplied current is 5 mA / cm ２ to 1000mA / cm ２ It does not emit white light in the range

[0141] (Organic EL element according to Example 7 and organic EL elements according to Comparative Examples 4 and 5) The organic EL element according to Example 7 has the same configuration as the organic EL element according to Comparative Example 3, the organic EL element according to Comparative Example 4 has the same configuration as the organic EL element according to Example 1, and the organic EL element according to Comparative Example 5 has the same configuration as the organic EL element according to Example 2.

[0142] (Evaluation of Emission Start Voltage and Emission Intensity Characteristics) FIG. 26 shows the emission start voltage and emission intensity characteristics of the organic EL element according to Example 3, FIG. 27 shows the emission start voltage and emission intensity characteristics of the organic EL element according to Example 4, and FIG. 28 shows the emission start voltage and emission intensity characteristics of the organic EL element according to Example 5. FIG. 29 shows the emission start voltage and emission intensity characteristics of the organic EL element according to Example 6, and FIG. 30 shows the emission start voltage and emission intensity characteristics of the organic EL element according to Example 7. FIG. 31 shows the emission start voltage and emission intensity characteristics of the organic EL element according to Comparative Example 1, FIG. 32 shows the emission start voltage and emission intensity characteristics of the organic EL element according to Comparative Example 4, and FIG. 33 shows the emission start voltage and emission intensity characteristics of the organic EL element according to Comparative Example 5. In FIGS. 26 to 33 (a), (a) shows the applied voltage-emission luminance characteristics, and (b) shows the change in emission wavelength-emission intensity characteristics with current density. In (a) of FIGS. 26 to 33 (a), the horizontal axis shows the applied voltage, and the vertical axis shows the emission luminance. In (b) of Figures 26 to 33, the numerical values ​​in the legends such as 1, 10, 100, and 1000 represent the supplied current density (mA / cm ２ ), the horizontal axis represents the emission wavelength, and the vertical axis represents the emission intensity.

[0143] Table 3 shows the evaluation results of the light emission start voltage and light emission intensity characteristics of the organic EL elements according to Examples 3 to 7 and the organic EL elements according to Comparative Examples 1 and 4 to 5. Table 4 shows the relationship between the current density of the supplied current and the light emission intensity of the organic EL elements according to Examples 3 to 7 and the organic EL elements according to Comparative Examples 1 and 4 to 5.

[0144]

[0145]

[0146] In Table 3, the "Light Emission Start Voltage [V]" column indicates the voltage at which the organic EL elements according to Examples 3 to 7 and the organic EL elements according to Comparative Examples 1 and 4 to 5 start to emit light. The "Intensity Change Characteristics" column indicates the evaluation results of the rate of change, depending on the supplied current density, of the light emission intensity of light emitted from the organic EL elements according to Examples 3 to 7 and the organic EL elements according to Comparative Examples 1 and 4 to 5. The "Evaluation Results" column indicates the evaluation results of the light emission start voltage and light emission intensity characteristics of the organic EL elements according to Examples 3 to 7 and the organic EL elements according to Comparative Examples 1 and 4 to 5.

[0147] In the "Intensity change characteristics" column of Table 3, "◯" indicates that the supply current density is 100 mA / cm ２ The supply current density for the light emission intensity when ２ The symbol "x" indicates that the ratio of the luminous intensity when the supply current density is 100 mA / cm ２ The supply current density for the light emission intensity when ２ This indicates that the ratio of the luminescence intensity when

[0148] In the "Evaluation Results" column of Table 3, "Good" indicates that the light emission starting voltage is less than 2.0 V, and the "Intensity Change Characteristics" column is evaluated as "Good," indicating that the organic EL element has good characteristics for emitting light whose chromaticity is unlikely to change in response to changes in the supply current density. "Poor" indicates that the light emission starting voltage is 2.0 V or more, or the "Intensity Change Characteristics" column is evaluated as "Poor," indicating that the organic EL element does not have good characteristics for emitting light whose chromaticity is unlikely to change in response to changes in the supply current density.

[0149] The "Emission Intensity Ratio" column in Table 4 shows the emission intensity of the peak wavelength of the fluorescence of the guest material when the emission intensity of the emitted light is normalized, with the intensity at a wavelength of 465 nm being set to "1." The fluorescence peak wavelength of the guest material was measured by a fluorescence spectrum using a fluorescence spectrophotometer. In the "Emission Intensity Ratio" column, "10 mA / cm ２ " column indicates the supply current density is 10 mA / cm ２ The luminous intensity ratio when ２ The " column indicates the supply current density of 100 mA / cm２ The "Intensity change rate" column shows the emission intensity ratio when the supplied current density is 100 mA / cm ２ The emission intensity ratio when the supply current density is 10 mA / cm ２ The "Evaluation" column shows the evaluation results of the emission intensity change characteristics of the organic EL elements according to Examples 3 to 7 and the organic EL elements according to Comparative Examples 1 and 4 to 5.

[0150] The organic EL element according to Example 3 has a low voltage operating characteristic in which light emission starts at 1.6 V. In the organic EL element according to Example 3, the intensity change rate of the second guest material is 1.55. The organic EL element according to Example 3 has a current density of 10 mA / cm ２ and 100mA / cm ２ Since the rate of change in intensity of the second guest material when the supplied current density is changed between 0.1 and 1.0 is less than 2.00, it is possible to emit light with little change in chromaticity due to changes in the supplied current density.

[0151] The organic EL element according to Example 4 has a low voltage operating characteristic in which light emission starts at 1.5 V. In the organic EL element according to Example 4, the intensity change rate of the second guest material is 1.46. The organic EL element according to Example 4 has a current density of 10 mA / cm ２ and 100mA / cm ２ Since the rate of change in intensity of the second guest material when the supplied current density is changed between 0.1 and 1.0 is less than 2.00, it is possible to emit light with little change in chromaticity due to changes in the supplied current density.

[0152] The organic EL element according to Example 5 has a low voltage operating characteristic in which light emission starts at 1.4 V. In the organic EL element according to Example 5, the intensity change rate of the second guest material is 1.94. The organic EL element according to Example 5 has a current density of 10 mA / cm ２ and 100mA / cm ２ Since the rate of change in intensity of the second guest material when the supplied current density is changed between 0.1 and 1.0 is less than 2.00, it is possible to emit light with little change in chromaticity due to changes in the supplied current density.

[0153] The organic EL element according to Example 6 has low voltage operation characteristics, starting to emit light at 1.9 V. In the organic EL element according to Example 6, the intensity change rate of the second guest material is 1.00. The intensity change rate of the third guest material is 1.98. The organic EL element according to Example 6 exhibited a low current of 10 mA / cm. ２ and 100mA / cm ２ Since the intensity change rate of the second guest material and the third guest material when the supply current density is changed between 0.01 and 0.1, it is possible to emit light with little change in chromaticity due to changes in the supply current density.

[0154] The organic EL element according to Example 7 has a low voltage operating characteristic in which light emission starts at 1.0 V. In the organic EL element according to Example 7, the intensity change rate of the second guest material is 1.06. The organic EL element according to Example 7 has a current density of 10 mA / cm ２ and 100mA / cm ２ Since the rate of change in intensity of the second guest material when the supplied current density is changed between 0.1 and 1.0 is less than 2.00, it is possible to emit light with little change in chromaticity due to changes in the supplied current density.

[0155] The organic EL element according to Comparative Example 1 has a low voltage operating characteristic in which light emission starts at 1.3 V. In the organic EL element according to Comparative Example 1, the intensity change rate of the guest material is 2.58. The organic EL element according to Comparative Example 1 has a current density of 10 mA / cm ２ and 100mA / cm ２ Since the intensity change rate of the guest material when the supplied current density is changed between 0.01 and 0.1, the chromaticity of the emitted light changes greatly in response to changes in the supplied current density.

[0156] The organic EL element according to Comparative Example 4 has a low voltage operating characteristic in which light emission starts at 1.1 V. In the organic EL element according to Comparative Example 4, the intensity change rate of the guest material is 3.29. The organic EL element according to Comparative Example 4 has a current density of 10 mA / cm ２ and 100mA / cm ２ Since the intensity change rate of the guest material when the supplied current density is changed between 0.01 and 0.1, the chromaticity of the emitted light changes greatly in response to changes in the supplied current density.

[0157] The organic EL element according to Comparative Example 5 has a low voltage operating characteristic in which light emission starts at 1.0 V. In the organic EL element according to Comparative Example 5, the intensity change rate of the guest material is 3.63. The organic EL element according to Comparative Example 5 has a low voltage operating characteristic in which light emission starts at 10 mA / cm ２ and 100mA / cm ２ Since the intensity change rate of the guest material when the supplied current density is changed between 0.01 and 0.1, the chromaticity of the emitted light changes greatly in response to changes in the supplied current density.

Claims

1. An organic EL device comprising 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, wherein the second organic semiconductor layer contains an organic semiconductor material that undergoes triplet-triplet annihilation and one or more types of guest materials, the guest material emitting light due to the transfer of energy generated by triplet-triplet annihilation caused by the organic semiconductor material, and the second organic semiconductor layer is capable of emitting white light due to the emission of the multiple types of guest materials or the emission of the organic semiconductor material and the one or more types of guest materials.

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

3. The organic EL device according to claim 1 or 2, wherein the organic semiconductor material comprises a compound that is excited by triplet-triplet annihilation and emits blue light, and the guest material comprises a compound that emits yellow or orange light due to the transfer of energy generated by triplet-triplet annihilation in the organic semiconductor material.

4. The organic EL element according to claim 1 or 2, wherein the guest material comprises a first guest material that emits blue light due to energy transfer generated by triplet-triplet annihilation in the organic semiconductor material, and a second guest material that emits yellow or orange light due to energy transfer from the first guest material.

5. The organic EL device according to claim 1 or 2, wherein the organic semiconductor material comprises a compound that is excited by triplet-triplet annihilation and emits blue light, and the guest material comprises a first guest material that emits green light due to energy transfer caused by triplet-triplet annihilation in the organic semiconductor material, and a second guest material that emits orange or red light due to 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 that emits blue light due to energy transfer generated by triplet-triplet annihilation in the organic semiconductor material, a second guest material that emits green light due to energy transfer from the first guest material, and a third guest material that emits orange or red light due to energy transfer from the second guest material.

7. A method for using the organic EL element according to claim 3, wherein the current density of the current supplied between the pair of electrodes is 100 mA / cm ２ More than 1000mA / cm ２ A method in which the wavelength is within the range below and white light is emitted.

8. A method for using the organic EL element according to claim 4, wherein the current density of the current supplied between the pair of electrodes is 1 mA / cm ２ More than 1000mA / cm ２ A method in which the wavelength is within the range below and white light is emitted.

Images