Organic electroluminescent element, display device, lighting device

Abstract

To provide an organic electroluminescent element with a multi-photon emission structure that enables low-voltage driving with excellent element stability, and a display device and a lighting device equipped with such an organic electroluminescent element.SOLUTION: An organic electroluminescent device includes an anode and a cathode, and has a structure in which a plurality of light-emitting units each including a light-emitting layer containing an organic compound are laminated with a charge-generating layer sandwiched between the anode and the cathode, and at least one of the light-emitting units has at least one electron injection layer containing a lanthanide metal at a position closer to the cathode than the light-emitting layers included in the light-emitting unit, and a display device and a lighting device include the organic electroluminescent element.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an organic electroluminescent element, and a display device and a lighting device including the same. [Background technology]

[0002] An organic electroluminescent element (hereinafter sometimes abbreviated as "organic EL element" or simply "element") is a self-luminous element having a light-emitting layer made of an organic compound between a cathode and an anode facing each other. When a voltage is applied between the cathode and the anode, the organic EL element emits light due to excitons generated by the recombination in the light-emitting layer of electrons injected from the cathode side and holes injected from the anode side.

[0003] As an organic EL element that realizes high brightness and long life, an element with a multi-photon emission structure (hereinafter sometimes abbreviated as "MPE element") is known in which an emitting unit including at least one emitting layer is regarded as one unit, and an electrically insulating charge generating layer is arranged between a plurality of emitting units (see, for example, Patent Document 1). In this MPE element, when a voltage is applied between the cathode and the anode, the charges in the charge transfer complex move toward the cathode side and the anode side, respectively. As a result, holes are injected into one emitting unit located on the cathode side across the charge generating layer, and electrons are injected into another emitting unit located on the anode side across the charge generating layer. In such an MPE element, light is simultaneously emitted from a plurality of emitting units while maintaining the same amount of current, so that it is possible to obtain a current efficiency and an external quantum efficiency equivalent to the number of emitting units.

[0004] In addition, improving the efficiency of organic EL elements and lowering the driving voltage are important because they directly lead to a reduction in power consumption. For example, a method for realizing a lower driving voltage is to place an electron injection layer containing an alkali metal with a low work function (e.g., lithium, sodium, cesium, etc.) between the cathode and the light-emitting layer (see, for example, Patent Documents 2 to 4).

[0005] Patent Documents 5 to 8 describe organic EL devices equipped with one light-emitting unit (single unit) having an electron injection layer containing a lanthanoid metal. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2003-272860 A [Patent Document 2] JP 2004-200031 A [Patent Document 3] JP 2011-216688 A [Patent Document 4] JP 2019-087580 A [Patent Document 5] JP 2019-083187 A [Patent Document 6] JP 2019-021903 A [Patent Document 7] JP 2019-033192 A [Patent Document 8] JP 2019-009411 A Summary of the Invention [Problem to be solved by the invention]

[0007] As mentioned above, it is known that the driving voltage of an organic EL element can be reduced by using an electron injection layer containing an alkali metal with a low work function (e.g., lithium, sodium, cesium, etc.), but low-work-function alkali metals are highly active and easily react with moisture and oxygen contained in the element. For this reason, it was found that organic EL elements having an electron injection layer containing an alkali metal with a low work function have problems such as the occurrence of black spots (non-emitting areas) on the light-emitting surface and sudden short circuits in the element, resulting in poor element stability. In particular, the above problems are even more pronounced in MPE elements, since multiple electron injection layers must be arranged. The present invention has been proposed in view of the above circumstances, and aims to provide an organic electroluminescent element having a multi-photon emission structure that enables low-voltage driving with excellent element stability, as well as a display device and a lighting device that include such an organic electroluminescent element. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides the following means. <1> An organic electroluminescent element having an anode and a cathode, the element having a structure in which a plurality of light-emitting units, each including a light-emitting layer containing an organic compound, are stacked between the anode and the cathode with a charge generating layer interposed therebetween, at least one of the light-emitting units has at least one electron injection layer containing a lanthanoid metal located closer to the cathode than the light-emitting layer included in the light-emitting unit; The light-emitting unit has three or more of the above-mentioned light-emitting units, at least one of the light-emitting units is a blue light-emitting unit including a light-emitting layer that emits light having a peak wavelength in a blue wavelength region of 440 to 490 nm; at least one of the light-emitting units is a green light-emitting unit including a light-emitting layer that emits light having a peak wavelength in a green wavelength range of 500 to 560 nm; At least one of the light-emitting units is a red light-emitting unit including a light-emitting layer that emits light having a peak wavelength in a red wavelength range of 590 to 640 nm, the blue light-emitting unit, the green light-emitting unit, and the red light-emitting unit each have at least one electron injection layer located closer to the cathode than a light-emitting layer included in each of the light-emitting units; The organic electroluminescent device, wherein the lanthanide metal of the electron injection layer is ytterbium. <2> At least one of the electron injection layers is a single layer made of ytterbium. <1> The organic electroluminescent device according to claim 1. <3> At least one of the electron injection layers contains 3 to 70 mass % of ytterbium. <1> The organic electroluminescent device according to claim 1. <4> at least one of the light-emitting units has at least two electron injection layers located closer to the cathode than a light-emitting layer included in the light-emitting unit; At least one of the electron injection layers is a single layer made of ytterbium, At least one of the electron injection layers contains 3 to 70 mass % of ytterbium, the single layer made of ytterbium is in contact with the layer containing 3 to 70 mass % of ytterbium; <1> ~ <3> 13. The organic electroluminescent device according to claim 12 . <5> The electron injection layer has a thickness of 0.3 to 10 nm. <1> ~ <4> 13. The organic electroluminescent device according to claim 12 . <6> Among the light-emitting units, the light-emitting unit closest to the cathode has the electron injection layer, and the electron injection layer is in contact with the cathode. <1> ~ <5> 13. The organic electroluminescent device according to claim 12 . <7> At least one of the electron injection layers is in contact with the charge generation layer. <1> ~ <6> 13. The organic electroluminescent device according to claim 12 . <8> <1> ~ <7> 13. A display device comprising the organic electroluminescent element according to claim 12. <9> <1> ~ <7> 13. A lighting device comprising the organic electroluminescent element according to any one of claims 1 to 12. The present invention relates to the above <1> ~ <9> However, other matters (such as those described in (1) to (11) below) are also described in this specification for reference.

[0009] (1) An organic electroluminescent element having an anode and a cathode, the element having a structure in which a plurality of light-emitting units, each including a light-emitting layer containing an organic compound, are stacked between the anode and the cathode with a charge generating layer interposed therebetween, At least one of the light-emitting units has at least one electron injection layer containing a lanthanoid metal, the electron injection layer being located closer to the cathode than the light-emitting layer included in the light-emitting unit. (2) 2. The organic electroluminescent device according to claim 1, wherein at least one of the electron injection layers is a single layer made of a lanthanoid metal. (3) 2. The organic electroluminescent device according to claim 1, wherein at least one of the electron injection layers contains 3 to 70% by mass of a lanthanoid metal. (4) The light-emitting unit has three or more of the above-mentioned light-emitting units, at least one of the light-emitting units is a blue light-emitting unit including a light-emitting layer that emits light having a peak wavelength in a blue wavelength region of 440 to 490 nm; at least one of the light-emitting units is a green light-emitting unit including a light-emitting layer that emits light having a peak wavelength in a green wavelength range of 500 to 560 nm; At least one of the light-emitting units is a red light-emitting unit including a light-emitting layer that emits light having a peak wavelength in a red wavelength range of 590 to 640 nm, The organic electroluminescent device according to any one of (1) to (3), wherein the blue light-emitting unit, the green light-emitting unit, and the red light-emitting unit each have at least one electron injection layer located closer to the cathode than an emitting layer included in each of the emitting units. (5) at least one of the light-emitting units has at least two electron injection layers located closer to the cathode than a light-emitting layer included in the light-emitting unit; At least one of the electron injection layers is a single layer made of a lanthanoid metal, At least one of the electron injection layers contains 3 to 70 mass % of a lanthanoid metal, The organic electroluminescent device according to any one of (1) to (4), wherein the single layer made of the lanthanoid metal and a layer containing 3 to 70% by mass of the lanthanoid metal are in contact with each other. (6) The organic electroluminescent device according to any one of (1) to (5), wherein the lanthanoid metal of the electron injection layer is ytterbium. (7) The organic electroluminescent device according to any one of (1) to (6), wherein the electron injection layer has a thickness of 0.3 to 10 nm. (8) The organic electroluminescent device according to any one of (1) to (7), wherein the light-emitting unit that is located closest to the cathode among the light-emitting units has the electron injection layer, and the electron injection layer is in contact with the cathode. (9) The organic electroluminescent device according to any one of (1) to (8), wherein at least one of the electron injection layers is in contact with the charge generation layer. (10) A display device comprising the organic electroluminescent element according to any one of (1) to (9). (11) A lighting device comprising the organic electroluminescent device according to any one of (1) to (9). Effect of the Invention

[0010] According to the present invention, it is possible to provide an organic electroluminescent element having a multi-photon emission structure that enables low-voltage driving with excellent element stability, as well as a display device and a lighting device that include such an organic electroluminescent element. [Brief description of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of one embodiment of an organic EL element of the present invention. [Diagram 2] 1 is a cross-sectional view showing a device structure of an organic EL device according to Example 1. FIG. [Diagram 3] 1 is a cross-sectional view showing a device structure of an organic EL device of Comparative Example 1. FIG. [Figure 4] 1 is a cross-sectional view showing a device structure of an organic EL device of Comparative Example 2. FIG. [Diagram 5] FIG. 2 is a cross-sectional view showing the element structures of the organic EL elements of Examples 2 to 13. [Figure 6] FIG. 2 is a diagram showing an image of the light-emitting surface of the organic EL element of Example 1. [Figure 7] FIG. 2 is a diagram showing an image of the light-emitting surface of the organic EL element of Example 1. [Figure 8] FIG. 2 is a diagram showing an image of the light-emitting surface of the organic EL element of Example 1. [Figure 9] FIG. 1 is a diagram showing an image of the light-emitting surface of the organic EL element of Comparative Example 1. [Figure 10] FIG. 1 is a diagram showing an image of the light-emitting surface of the organic EL element of Comparative Example 1. [Figure 11] FIG. 13 is a diagram showing an image of the light-emitting surface of the organic EL element of Comparative Example 2. [Figure 12] FIG. 13 is a diagram showing an image of the light-emitting surface of the organic EL element of Comparative Example 2. [Figure 13] FIG. 13 is a diagram showing an image of the light-emitting surface of the organic EL element of Comparative Example 2. [Figure 14] FIG. 2 is a graph showing the luminance retention of the organic EL element of Example 1. [Figure 15] FIG. 2 is a graph showing the voltage change rate of the organic EL element of Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An organic electroluminescent element and a display device and a lighting device including the same according to embodiments of the present invention will be described in detail with reference to the drawings. In addition, the drawings used in the following description may show characteristic parts in an enlarged scale for the sake of convenience in order to make the characteristics easier to understand, and the dimensional ratios of each component may not necessarily be the same as in reality. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited to them, and may be appropriately modified and implemented within the scope of the present invention.

[0013] [Organic electroluminescent element (organic EL element)] The organic EL element of the present invention is an organic electroluminescent element having an anode and a cathode, and a structure in which a plurality of light-emitting units, each including an light-emitting layer containing an organic compound, are stacked between the anode and the cathode with a charge generation layer sandwiched therebetween, and at least one of the light-emitting units has at least one electron injection layer containing a lanthanoid metal located closer to the cathode than the light-emitting layer contained in the light-emitting unit.

[0014] The lanthanide metal contained in the electron injection layer of the organic EL element of the present invention is not particularly limited, but is preferably at least one selected from ytterbium (Yb), samarium (Sm), europium (Eu) and thulium (Tm), and more preferably ytterbium (Yb). The electron injection layer may contain a lanthanoid metal and other components, or may be a single layer made of a lanthanoid metal (i.e., the electron injection layer is a layer composed only of a lanthanoid metal). An embodiment in which at least one of the electron-injection layers is a single layer made of a lanthanoid metal is one of the preferred embodiments of the organic EL element of the present invention. One of the preferred embodiments of the organic EL device of the present invention is one in which at least one of the electron injection layers contains 3 to 70% by mass of a lanthanoid metal.

[0015] In one preferred embodiment of the organic EL element of the present invention, at least one of the light-emitting units has at least two electron injection layers containing a lanthanoid metal located closer to the cathode than the light-emitting layer contained in that light-emitting unit, at least one of the electron injection layers is a single layer made of a lanthanoid metal, at least one of the electron injection layers is a layer containing 3 to 70% by mass of a lanthanoid metal, and the single layer made of a lanthanoid metal and the layer containing 3 to 70% by mass of a lanthanoid metal are in contact with each other.

[0016] The thickness of the electron injection layer is not particularly limited, but is preferably 0.3 to 10 nm, and more preferably 1 to 10 nm.

[0017] The organic EL device of the present invention may have only one electron-injection layer containing a lanthanoid metal, or may have two or more electron-injection layers.

[0018] Of the light-emitting units in the organic EL device of the present invention, the light-emitting unit closest to the cathode preferably has an electron-injecting layer containing a lanthanoid metal, and the electron-injecting layer is in contact with the cathode.

[0019] In the organic EL device of the present invention, it is also preferred that at least one of the electron injection layers containing a lanthanoid metal is in contact with a charge generation layer. In particular, it is preferred that the electron injection layer in the light-emitting unit other than the light-emitting unit closest to the cathode is in contact with a charge generation layer located closer to the cathode than the electron injection layer.

[0020] The light-emitting unit includes a light-emitting layer containing an organic compound, and at least one of the plurality of light-emitting units has an electron injection layer containing a lanthanide metal located closer to the cathode than the light-emitting layer included in the light-emitting unit. In the organic EL device of the present invention, each of the plurality of light-emitting units preferably has an electron injection layer containing a lanthanoid metal at a position closer to the cathode than the light-emitting layer contained in the light-emitting unit.

[0021] The light-emitting unit may include a layer other than the light-emitting layer and the electron injection layer. The layer other than the light-emitting layer and the electron injection layer is not particularly limited, and examples thereof include an electron transport layer, a hole transport layer, a hole injection layer, a hole blocking layer, and an electron blocking layer.

[0022] The electron transport layer is preferably provided between the electron injection layer and the light emitting layer. Each light emitting unit may have only one electron transport layer, or two or more electron transport layers. The material constituting the electron transport layer is not particularly limited, and any known material (electron transporting material) may be used. The electron transporting material is not particularly limited, and for example, one having a relatively deep HOMO (Highest Occupied Molecular Orbital) level among electron transporting materials generally used in organic EL elements may be used. Specifically, an electron transporting material having a HOMO level of at least about 6.0 eV or more may be used.

[0023] The thickness of the electron transport layer is not particularly limited, and may be, for example, 15 to 100 nm, or 17 to 65 nm.

[0024] The hole transport layer is preferably provided between the light emitting layer and the charge generating layer, or between the light emitting layer and the anode. Each light emitting unit may have only one hole transport layer, or may have two or more hole transport layers. The material constituting the hole transport layer is not particularly limited, and any known material (hole transporting material) may be used. The hole transporting material is not particularly limited, but it is preferable to use, for example, an organic compound (electron donating material) having an ionization potential of less than 5.7 eV and hole transporting property, i.e., electron donating property. The thickness of the hole transport layer is not particularly limited, and may be, for example, 10 to 100 nm, or 20 to 70 nm.

[0025] The hole injection layer is preferably provided between the hole transport layer and the charge generation layer, or between the hole transport layer and the anode. Each light-emitting unit may have only one hole injection layer, or may have two or more hole injection layers. The material constituting the hole injection layer is not particularly limited, and any known material may be used. In general, an electron donating material having the same properties as the hole transport layer is used. The thickness of the hole injection layer is not particularly limited, and may be, for example, 10 to 100 nm, or 20 to 70 nm.

[0026] One preferred embodiment of the organic EL device of the present invention includes an embodiment having three or more light-emitting units, at least one of which is a blue light-emitting unit including an light-emitting layer (blue light-emitting layer) that emits light having a peak wavelength in the blue wavelength range of 440 to 490 nm, at least one of which is a green light-emitting unit including an light-emitting layer (green light-emitting layer) that emits light having a peak wavelength in the green wavelength range of 500 to 560 nm, and at least one of which is a red light-emitting unit including an light-emitting layer (red light-emitting layer) that emits light having a peak wavelength in the red wavelength range of 590 to 640 nm, and the blue, green, and red light-emitting units each have an electron-injection layer containing a lanthanoid metal located closer to the cathode than the light-emitting layers included in the respective light-emitting units.

[0027] The organic EL element of the above embodiment can obtain white light by the emission of light from the blue light-emitting unit, the green light-emitting unit, and the red light-emitting unit, and therefore can be suitably used in, for example, display devices and lighting devices.

[0028] The material constituting the light-emitting layer is not particularly limited, and any known material may be used.

[0029] The red, green, and blue light-emitting layers each contain, as organic compounds, a host material that is a major component and a guest material that is a minor component, and the red, green, and blue lights emitted are often due to the properties of the guest material in particular. A guest material is also called a dopant material, and a guest material that utilizes fluorescent emission is usually called a fluorescent material, and an emission layer composed of this fluorescent material is called a fluorescent layer. On the other hand, a guest material that utilizes phosphorescence is usually called a phosphorescent material, and an emission layer composed of this phosphorescent material is called a phosphorescent layer.

[0030] The guest material of the phosphorescent light-emitting layer is not particularly limited, and for example, a red phosphorescent light-emitting material such as Ir(piq)3 or Ir(btpy)3 can be used for the red phosphorescent light-emitting layer. Specific examples of the red phosphorescent light-emitting material include 688118-250MG and 680877-250MG manufactured by Sigma-Aldrich.

[0031] The green phosphorescent light-emitting layer may be made of a green phosphorescent material such as Ir(ppy)3. A specific example of the green phosphorescent light-emitting material is 694924-250MG manufactured by Sigma-Aldrich.

[0032] The host material for the red phosphorescent-emitting layer and the green phosphorescent-emitting layer may be an electron-transporting material, a hole-transporting material, or a mixture of both.Specific examples of the host material include 4,4'-biscarbazolylbiphenyl (CBP) and 2,9-dimethyl-4,7-diphenyl-9,10-phenanthroline (BCP).

[0033] The host material of the green fluorescent-emitting layer may be Alq, etc. The guest material of the green fluorescent-emitting layer may be Coumarin 6, etc.

[0034] The host material and guest material of the blue fluorescent-emitting layer may be, for example, the blue fluorescent-emitting materials described in paragraphs

[0052] to

[0061] of International Publication No. 2012 / 053216. The guest material may be, for example, a styrylamine compound, a fluoranthene compound, an aminopyrene compound, a boron complex, or the like.

[0035] From the viewpoint of improving the element life and realizing high color rendering, it is preferable to use a blue fluorescent material as the guest material of the blue light-emitting layer. On the other hand, when a blue phosphorescent light-emitting layer is used instead of the blue fluorescent light-emitting layer, a blue phosphorescent light-emitting material such as Ir(Fppy)3 can be used. In addition, a specific example of the phosphorescent light-emitting material is 682594-250MG manufactured by Sigma-Aldrich.

[0036] The type of the light-emitting unit of the organic EL element of the present invention is not limited to the above embodiment. For example, the organic EL element of the present invention may have a light-emitting unit other than the blue light-emitting unit, the green light-emitting unit, and the red light-emitting unit, for example, an orange light-emitting unit, a yellow light-emitting unit, etc. In addition, for example, when the organic EL element has two green light-emitting units, the organic EL element may have only a plurality of light-emitting layers that emit light of the same color.

[0037] Generally, it is preferable to use a metal having a small work function, or an alloy or metal oxide thereof, etc. As the metal forming the cathode, for example, an elemental metal such as an alkali metal such as lithium (Li), an alkaline earth metal such as magnesium (Mg) or calcium (Ca), or a rare earth metal such as europium (Eu), or an alloy containing these metals and aluminum (Al), silver (Ag), indium (In), etc. can be used.

[0038] The cathode may be configured to use a metal-doped organic layer at the interface between the cathode and the organic layer, as described in, for example, JP-A-10-270171 and JP-A-2001-102175. In this case, the cathode may be made of a conductive material, and the properties thereof, such as the work function, are not particularly limited.

[0039] In addition, the cathode may be formed of an organic layer in contact with the cathode, as described in, for example, JP-A-11-233262 and JP-A-2000-182774, which contains at least one selected from the group consisting of alkali metal ions, alkaline earth metal ions, and rare earth metal ions. In this case, the cathode may be made of a metal capable of reducing the metal ions contained in the organometallic complex compound to metal in vacuum, such as (thermally reducible) metals such as aluminum (Al), zirconium (Zr), titanium (Ti), and silicon (Si), or an alloy containing these metals. Among these, Al, which is generally and widely used as a wiring electrode, is particularly preferred from the viewpoints of ease of deposition, high light reflectance, chemical stability, and the like.

[0040] There are no particular limitations on the material of the anode, and when light is extracted from the anode side, for example, a transparent conductive material such as ITO (indium tin oxide) or IZO (indium zinc oxide) can be used.

[0041] Contrary to the case of general organic EL elements, it is also possible to extract light from the cathode side by using a metal material for the anode and a transparent conductive material for the cathode. For example, the method described in "JP Patent Publication 2002-332567A" can be used to form the cathode from the above-mentioned transparent conductive material such as ITO or IZO by a sputtering method that does not damage the organic film.

[0042] The organic EL element of the present invention has a structure in which a plurality of light-emitting units are laminated with a charge generation layer sandwiched therebetween, that is, the organic EL element of the present invention has a structure in which the organic EL element has at least two light-emitting units and at least one charge generation layer, and the charge generation layer is disposed between the two light-emitting units. The organic EL device of the present invention may have only one charge generating layer, or may have two or more charge generating layers. The charge generating layer is preferably an electrically insulating layer made of an electron accepting material and an electron donating material. The resistivity of this electrically insulating layer is preferably 1.0×10 2 It is preferable that the resistance is Ω·cm or more, and 1.0×105 It is more preferable that the resistivity is Ω·cm or more. The charge generating layer may be made of a mixture of different materials, one of which may form a charge transfer complex by oxidation-reduction reaction. The charge generating layer may be made of a laminate of an electron accepting substance and an electron donating substance.

[0043] Materials constituting the charge generating layer may be, for example, materials described in JP-A-2003-272860. Among them, materials described in paragraphs

[0019] to

[0021] may be preferably used. Materials constituting the charge generating layer may be materials described in paragraphs

[0023] to

[0026] of WO 2010 / 113493. Among them, a strong electron accepting material (HATCN6) described in paragraph

[0059] may be preferably used.

[0044] The method for forming each layer constituting the light-emitting unit is not particularly limited, but for example, a vacuum deposition method, a spin coating method, or the like can be used.

[0045] The organic EL device of the present invention may have a substrate on the outer side of at least one of the anode and the cathode. The substrate may be a glass substrate or a plastic substrate. As the glass substrate, for example, soda lime glass, non-alkali glass, borosilicate glass, silicate glass, or the like can be used. As the plastic substrate, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), etc. can be used.

[0046] FIG. 1 is a cross-sectional view showing a schematic configuration of one example of a preferred embodiment of the organic EL element of the present invention. 1 has a structure in which light-emitting units 10A, 10B, and 10C are stacked with charge generation layers 7A and 7B sandwiched between a cathode 1 and an anode 2. More specifically, the organic EL element 100 has a structure in which the charge generation layer 7A is sandwiched between the light-emitting units 10A and 10B, and the charge generation layer 7B is sandwiched between the light-emitting units 10B and 10C. The light-emitting unit 10A includes, from the cathode 1 side, an electron injection layer 3A, an electron transport layer 4A, a light-emitting layer 5A, and a hole transport layer 6A in this order. The light-emitting unit 10B has, from the charge generation layer 7A side, an electron injection layer 3B, an electron transport layer 4B, a light-emitting layer 5B, and a hole transport layer 6B in this order. The light-emitting unit 10C includes, from the charge generation layer 7B side, an electron injection layer 3C, an electron transport layer 4C, a light-emitting layer 5C, a hole transport layer 6C, and a hole injection layer 8 in this order.

[0047] The present invention also relates to a display device comprising the above-mentioned organic EL element of the present invention. The present invention also relates to a lighting device comprising the above-mentioned organic EL element of the present invention. For information on the display device, please refer to the descriptions in paragraphs

[0084] to

[0098] of JP 2019-145474 A. For information on the lighting device, please refer to the description in paragraphs

[0074] to

[0083] of JP 2019-145474 A. EXAMPLES

[0048] The effects of the present invention will be made clearer by the following examples. The present invention is not limited to the following examples, and can be modified as appropriate within the scope of the present invention.

[0049] Example 1 <Fabrication of organic EL elements> In Example 1, an organic EL element having the element structure shown in FIG. 2 was produced. Specifically, first, a soda-lime glass substrate having a thickness of 0.7 mm and an ITO film (anode) having a thickness of 100 nm, a width of 2 mm, and a sheet resistance of about 20 Ω / □ was prepared. The substrate was then ultrasonically cleaned with neutral detergent, ion-exchanged water, acetone, and isopropyl alcohol for 5 minutes each, spin-dried, and then subjected to UV / O3 treatment.

[0050] Next, the materials for each layer shown in FIG. 2 were filled into each of the evaporation crucibles (made of tantalum or alumina) in the vacuum evaporation apparatus. Then, the above substrate was set in the vacuum evaporation apparatus, and the vacuum degree was 1×10 -4 The evaporation crucible was heated by passing an electric current through it in a reduced pressure atmosphere of less than 1 Pa, and each layer was evaporated to a specified thickness at a deposition rate of 0.1 nm / sec. In addition, layers consisting of two or more materials, such as the light-emitting layer, were co-evaporated by passing an electric current through the evaporation crucible so that they were formed in a specified mixture ratio. The cathode was deposited at a deposition rate of 1 nm / sec. As shown in Table 1 below, the first electron injection layer, the second electron injection layer, and the third electron injection layer were all single layers (thickness 1 nm) made of ytterbium (Yb). The thickness of each layer other than the electron injection layer is as shown in Figure 2. The concentration of the guest material in the red light-emitting layer was 3 mass %, the concentration of the guest material in the blue light-emitting layer was 5 mass %, and the concentration of the guest material in the green light-emitting layer was 10 mass %. After the deposition was completed, the organic EL element was attached to a glass substrate for sealing using a UV-curable epoxy resin, and then the resin was irradiated with UV light to harden it for sealing. The sealing process was carried out in a glove box with an oxygen concentration of 0.1 ppm or less and a moisture concentration of 0.5 ppm or less.

[0051] <Evaluation of organic EL elements> A power supply control unit (product name: PEL-100TB, manufactured by EHC) was connected to the organic EL element. A current density of 10 mA / cm was applied to the organic EL element. 2A constant current of 10 ... Images of the light-emitting surface of the organic EL element of Example 1 are shown in Figures 6 to 8. Figure 6 is the image before light emission (0 hours), Figure 7 is the image 500 hours after the start of light emission, and Figure 8 is the image 1000 hours after the start of light emission. In the organic EL element of Example 1, no black spots were observed on the light-emitting surface even 1000 hours after the start of light emission. It should be noted that the black dots seen in the center of the images in Figs. 6 to 8 are reflections of the measurement field of the luminance meter, and are not black dots that represent non-luminous areas. The luminance retention rate and voltage change rate of the organic EL element of Example 1 over time are shown in Fig. 14 and Fig. 15, respectively. The luminance retention rate and voltage change rate are shown as relative values ​​with the initial luminance or driving voltage set to 1.00. Figs. 14 and 15 show that 1000 hours after the start of light emission, the amount of change in the luminance retention rate is less than 10% of the initial state, and the voltage change rate also increases by only about 10%. This shows that it is possible to drive the organic EL element stably for a long period of time.

[0052] Comparative Example 1 <Fabrication of organic EL elements> In Comparative Example 1, an organic EL element having the element structure shown in FIG. As shown in Table 1 below, the first electron injection layer, the second electron injection layer, and the third electron injection layer were all single layers (film thickness 0.5 nm) made of lithium (Li). The constituent materials of each layer other than the electron injection layer were the same as in Example 1. The film thicknesses of each layer other than the electron injection layer are as shown in FIG.

[0053] <Evaluation of organic EL elements> The organic EL device was evaluated in the same manner as in Example 1. Images of the light-emitting surface of the organic EL element of Comparative Example 1 are shown in Figures 9 and 10. Figure 9 is the image before light emission (0 hours), and Figure 10 is the image 50 hours after the start of light emission. In the organic EL element of Comparative Example 1, black spots were already appearing on the light-emitting surface before the start of light emission, and the number of black spots further increased 50 hours after the start of light emission. It should be noted that the black dots seen in the center of the images in Figures 9 and 10 are reflections of the measurement field of the luminance meter, and are not black dots representing non-luminous areas.

[0054] Comparative Example 2 <Fabrication of organic EL elements> In Comparative Example 2, an organic EL element having the element structure shown in FIG. As shown in Table 1 below, the first electron injection layer, the third electron injection layer, and the fifth electron injection layer were all single layers (thickness 0.4 nm) made of calcium (Ca), and the second electron injection layer, the fourth electron injection layer, and the sixth electron injection layer were all single layers (thickness 3 nm) made of 8-hydroxyquinolinolato-lithium (Liq), which is a quinolinol complex. The materials constituting each layer other than the electron injection layer were the same as in Example 1. The thickness of each layer other than the electron injection layer is as shown in FIG. 4.

[0055] <Evaluation of organic EL elements> The organic EL device was evaluated in the same manner as in Example 1. Images of the light-emitting surface of the organic EL element of Comparative Example 2 are shown in Figures 11 to 13. Figure 11 is the image before light emission (0 hours), Figure 12 is the image 100 hours after the start of light emission, and Figure 13 is the image 200 hours after the start of light emission. In the organic EL element of Comparative Example 2, no black spots were observed on the light-emitting surface before the start of light emission, but black spots appeared 100 hours after the start of light emission, and the number of black spots further increased 200 hours after the start of light emission. It should be noted that the black dots seen in the center of the images in Figs. 11 to 13 are reflections of the measurement field of the luminance meter, and are not black dots that represent non-luminous areas.

[0056] The materials constituting the electron injection layer and the film thicknesses of the electron injection layer in Example 1, Comparative Example 1, and Comparative Example 2 are summarized in Table 1 below.

[0057] [Table 1]

[0058] A measuring device driver (product name: KEITHLEY2425, manufactured by KEITHLEY) was connected to the organic EL devices of Example 1 and Comparative Example 2 prepared as described above, and a current of 3 mA / cm 2 The voltage value was measured when the organic EL element was lit by passing a constant current of 1000 V. Furthermore, the emission spectrum, luminance, and current efficiency of the organic EL element were measured using a spectroradiometer (product name: CS-2000, manufactured by Konica Minolta, Inc.), and the power efficiency and external quantum efficiency of the organic EL elements of Example 1 and Comparative Example 2 were calculated based on the measurement results. In Table 2 below, the power efficiency, external quantum efficiency, and voltage are expressed as relative values ​​with the value in Example 1 being set to "1.00."

[0059] [Table 2]

[0060] The element of Comparative Example 1 had black spots at an early stage, so the light emission characteristics were not evaluated. In the element of Example 1, an external quantum efficiency equivalent to that of Comparative Example 2 was obtained, and the driving voltage was lower than that of Comparative Example 2, realizing low-voltage driving. Therefore, it is shown that the element of Example 1 can achieve both low-voltage driving and high element stability.

[0061] (Examples 2 to 13) <Fabrication of organic EL elements> In Examples 2 to 13, organic EL devices having the device structure shown in FIG. The "electron injection layer (Yb)" in FIG. 5 is a single-layer electron injection layer made of ytterbium (Yb). The film thickness of the electron injection layer (Yb) in contact with the cathode is Znm, and the value of Z in each example is as shown in Table 3 below. In Table 3, the examples (Examples 7 to 13) in which the value of Z is "-" indicate that the single-layer electron injection layer (Yb) in contact with the cathode shown in FIG. 5 was not provided. The film thicknesses (X, Y) of the electron injection layer (Yb) other than the electron injection layer (Yb) in contact with the cathode shown in FIG. 5 are as shown in Table 3. "Electron injection layer: Yb αnm β%" in Fig. 5 is an electron injection layer having a film thickness of αnm, containing β mass% of ytterbium (Yb) in a material exhibiting electron transport properties. In Table 3, the examples (Examples 2 to 5) with a value of "-" for α indicate that the "electron injection layer: Yb αnm β%" shown in Fig. 5 was not provided. The constituent materials of each layer other than the electron injection layer are the same as those in Example 1. However, in Examples 2 to 13, the concentration of the guest material in the red light-emitting layer was 4 mass %, the concentration of the guest material in the blue light-emitting layer was 8 mass %, and the concentration of the guest material in the green light-emitting layer was 10 mass %. The film thickness of each layer other than the electron injection layer is as shown in FIG. 5.

[0062] <Evaluation of organic EL elements> A measuring device driver (product name: KEITHLEY2425, manufactured by KEITHLEY) was connected to the organic EL devices of Examples 2 to 13 fabricated as described above, and a current of 3 mA / cm 2 The voltage value was measured when the organic EL element was lit by passing a constant current of 1000 V. Furthermore, the emission spectrum, luminance, and current efficiency of the organic EL element were measured using a spectroradiometer (product name: CS-2000, manufactured by Konica Minolta, Inc.), and the power efficiency and external quantum efficiency of the organic EL elements of Examples 2 to 13 were calculated based on the measurement results. In Table 3 below, the power efficiency, external quantum efficiency, and voltage are expressed as relative values ​​with the value in Example 2 being set to "1.00."

[0063] [Table 3]

[0064] From the results of Examples 2 to 13, the electron injection layer: When Yb was used as a single layer (Examples 2 to 5), When Yb was mixed with an electron transport material (Examples 7 to 13), When a single layer of Yb and a layer mixed with an electron transport material were used in combination (Example 6), From this, it is understood that regardless of the structural form of the electron injection layer using Yb, good luminescence properties are exhibited in any of the forms. [Explanation of symbols]

[0065] 100 Organic EL element 1...Cathode 2...Anode 10A, 10B, 10C... Light emitting unit 3A, 3B, 3C...electron injection layer 4A, 4B, 4C...electron transport layer 5A, 5B, 5C: Light-emitting layer 6A, 6B, 6C: Hole transport layer 7A, 7B: Charge generating layer 8. Hole injection layer

Claims

1. An organic electroluminescent element having an anode and a cathode, the element having a structure in which a plurality of light-emitting units, each including a light-emitting layer containing an organic compound, are stacked between the anode and the cathode with a charge generating layer interposed therebetween, at least one of the light-emitting units has at least one electron injection layer containing a lanthanoid metal located closer to the cathode than the light-emitting layer included in the light-emitting unit; The light-emitting unit has three or more light-emitting units, at least one of the light-emitting units is a blue light-emitting unit including a light-emitting layer that emits light having a peak wavelength in a blue wavelength region of 440 to 490 nm; at least one of the light-emitting units is a green light-emitting unit including a light-emitting layer that emits light having a peak wavelength in a green wavelength range of 500 to 560 nm; at least one of the light-emitting units is a red light-emitting unit including a light-emitting layer that emits light having a peak wavelength in a red wavelength region of 590 to 640 nm; the blue light-emitting unit, the green light-emitting unit, and the red light-emitting unit each have at least one electron injection layer located closer to the cathode than a light-emitting layer included in each of the light-emitting units; The organic electroluminescent device, wherein the lanthanide metal of the electron injection layer is ytterbium.

2. 2. The organic electroluminescent device according to claim 1, wherein at least one of the electron injection layers is a single layer made of ytterbium.

3. 2. The organic electroluminescent device according to claim 1, wherein at least one of the electron injection layers contains 3 to 70% by mass of ytterbium.

4. at least one of the light-emitting units has at least two electron injection layers located closer to the cathode than a light-emitting layer included in the light-emitting unit; at least one of the electron injection layers is a single layer made of ytterbium, At least one of the electron injection layers contains 3 to 70 mass % of ytterbium, 4. The organic electroluminescent device according to claim 1, wherein the single layer made of ytterbium and the layer containing 3 to 70% by mass of ytterbium are in contact with each other.

5. 5. The organic electroluminescent device according to claim 1, wherein the electron injection layer has a thickness of 0.3 to 10 nm.

6. 6. The organic electroluminescent device according to claim 1, wherein the light-emitting unit that is closest to the cathode among the light-emitting units has the electron injection layer, and the electron injection layer is in contact with the cathode.

7. 7. The organic electroluminescent device according to claim 1, wherein at least one of the electron injection layers is in contact with the charge generation layer.

8. A display device comprising the organic electroluminescent element according to any one of claims 1 to 7.

9. A lighting device comprising the organic electroluminescent device according to any one of claims 1 to 7.

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