JP7232140B2 - Organic electroluminescence device, display device, and lighting device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an organic electroluminescence (hereinafter, electroluminescence (electroluminescence) may be referred to as "EL") element, a display device, and a lighting device.

Organic EL elements are self-luminous, have a wide viewing angle, have excellent visibility, can be driven at a low voltage, can be made thinner and lighter due to surface emission, and can display multiple colors. are doing. Therefore, the organic EL element can be suitably used for a display device such as a display and a lighting device.

An organic EL device is generally constructed by laminating an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer and a cathode in this order on a transparent substrate. Light emission of the organic EL element occurs through processes (i) to (v) shown below.
(i) Holes and electrons are injected from the electrodes.
(ii) the injected holes and electrons are transported;
(iii) recombination of holes and electrons in the light-emitting layer;
(iv) the luminescent material forms an electronically excited state;
(v) the luminescent material emits light from an electronically excited state;

In organic EL devices, it has been proposed to use a phosphorescent material as a light-emitting material for the light-emitting layer in order to improve efficiency. A luminescent material generates a singlet excited state (S ₁ ) and a triplet excited state (T ₁ ) with a probability of 1:3 when it gains energy and becomes an electronically excited state. Then, when the light-emitting material returns from the electronically excited state to the ground state, it emits energy as light.

When a fluorescent material is used as the luminescent material, only the energy from _S1 is converted into light. In contrast, when a phosphorescent material is used as the light-emitting material, not only the energy from S ₁ but also the energy from T ₁ is converted into light. Therefore, an organic EL device using a phosphorescent material as a light-emitting material can be expected to have higher efficiency than an organic EL device using a fluorescent material (for example, see Non-Patent Document 1 and Non-Patent Document 2). ).

Phosphorescent materials are commonly used as guest materials together with host materials. In an organic EL device having a light-emitting layer containing a host material and a phosphorescent material (guest material), the energy of the host material excited by recombination of holes and electrons is transferred to the phosphorescent material. The energy excites the phosphorescent material and emits it as light energy. In order to enable efficient energy transfer from the host material to the phosphorescent material, the energy of the triplet excited state (T ₁ ) of the host material should be higher than the T ₁ energy of the phosphorescent material that is the guest material. (See, for example, Non-Patent Document 3). If the T ₁ energy of the guest material is higher than the T ₁ energy of the host material, reverse energy transfer from the guest material to the host material may occur, hindering efficient phosphorescence emission.

Many host materials used in the light-emitting layer have been reported so far. For example, host materials include carbazole-based compounds and the like, and the carbazole-based compounds have a relatively large T ₁ energy.

As a light-emitting material (guest material) of an organic EL device, an iridium complex is generally used because of which high external quantum efficiency can be obtained. However, an organic EL device using an iridium complex as a light-emitting material has a wide half width of the emission spectrum and low color purity. Therefore, in an organic EL device using an iridium complex as a light-emitting material, it is necessary to sharpen the emission spectrum using a color filter or the like, resulting in low light utilization efficiency.

In recent years, there has been a demand for organic EL elements that emit light with high color purity for use in displays. For example, in ultra-high-definition television (UHDTV), ITU-R Recommendation BT.2020 stipulates the use of a wide color gamut color system in which the three primary colors are positioned on the spectrum locus (for example, non-patent Reference 4).

Against this background, light-emitting materials with narrow half-value widths of emission spectra are being developed. For example, Non-Patent Document 5 below describes a platinum complex having a specific structure as a light-emitting material (guest material). According to the platinum complex, the half-width of the emission spectrum is 18 nm. Luminescence is obtained.

However, when a material having a 1,3,5-triazine group is used as the host material of the light-emitting layer combined with the platinum complex, an exciplex is likely to be formed between the host material and the light-emitting material (guest material). It has been reported that the half width of the emission spectrum of the organic EL device is widened and the color purity is lowered (see, for example, Non-Patent Document 6).

Organic EL display, Ohmsha Co., Ltd., pp. 83 (2011) Org. Electron, 14, 260 (2013) Appl. Phys. Lett. , 83, 569 (2003) Recommendation ITU-R BT. 2020-2 (2015) t. Fleetham, Arizona State University, PhD thesis, pp. 116-122 (2014) Molecules, 24, 454 (2019)

Organic EL elements are required to have low driving voltage while ensuring luminous efficiency. However, in conventional organic EL devices, the large energy barrier in the movement of holes and electrons from the electrode to the light-emitting layer has made it difficult to achieve a device that exhibits high external quantum efficiency while keeping the drive voltage sufficiently low. .
In addition, in conventional organic EL devices, it is difficult to achieve high external quantum efficiency, low power consumption, and high color purity when using a light emitting material (guest material) capable of emitting light with high color purity. was.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an organic EL device with high luminous efficiency (high external quantum efficiency) and low driving voltage (low power consumption).
In addition, the present invention further provides an organic EL device with high luminous efficiency, low driving voltage, and high color purity of light emission when a luminescent material (guest material) capable of emitting light with high color purity is used. It will be a challenge.

In order to solve the above problems, the present inventors have extensively studied and found that the light-emitting layer located between the two electrodes of the organic EL device has the following general formula that contributes to the hole-transport property and the electron-transport property. By including the compound represented by (1), the energy barrier in the movement of holes and electrons to the light-emitting layer is reduced, so that the driving voltage can be lowered, resulting in an organic EL device with high luminous efficiency and low driving voltage. The inventors have found that it can be realized, and conceived of the present invention.
Further, as a result of extensive studies, the present inventors have found that a compound represented by the following general formula (1) is used as the host material of the light-emitting layer, and a planar tetradentate compound having a coordination number of 4 is used as the guest material. The present inventors have found that by using a ligand-bonded complex, an organic EL device with high luminous efficiency, low driving voltage, and high color purity of emitted light can be realized.
The gist and configuration of the present invention for solving the above problems are as follows.

［一般式（１）中のＸ¹は、それぞれ独立にＮ又はＣ－Ｒ²を示し、少なくとも１つのＸ¹はＮであり、ここで、Ｒ²は、水素原子、炭素数１～１０のアルキル基、炭素数１～１０のアルコキシ基、炭素数１～１０のアルキルチオ基、炭素数１～１０のアルキルアミノ基、炭素数２～１０のアシル基、炭素数７～２０のアラルキル基、置換若しくは未置換の炭素数６～３０の芳香族炭化水素基、又は置換若しくは未置換の炭素数３～３０の芳香族複素環基であり、
Ｒ¹は、それぞれ独立に水素原子、炭素数１～１０のアルキル基、炭素数１～１０のアルコキシ基、炭素数１～１０のアルキルチオ基、炭素数１～１０のアルキルアミノ基、炭素数２～１０のアシル基、炭素数７～２０のアラルキル基、置換若しくは未置換の炭素数６～３０の芳香族炭化水素基、又は置換若しくは未置換の炭素数３～３０の芳香族複素環基であり、隣り合うＲ¹は一体となって環を形成していてもよい。］で表わされる化合物であることを特徴とする。
かかる本発明の有機エレクトロルミネッセンス素子は、発光効率が高く、駆動電圧が低い。 The organic electroluminescence device of the present invention comprises an anode, a light-emitting layer and a cathode in this order,
the light-emitting layer comprises a guest material and a host material;
The host material has the following general formula (1):

[X ¹ in general formula (1) each independently represents N or C—R ² , at least one X ¹ is N, where R ² is a hydrogen atom, a alkyl group, alkoxy group having 1 to 10 carbon atoms, alkylthio group having 1 to 10 carbon atoms, alkylamino group having 1 to 10 carbon atoms, acyl group having 2 to 10 carbon atoms, aralkyl group having 7 to 20 carbon atoms, substituted or an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms,
Each R ¹ is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, or 2 carbon atoms. ~10 acyl group, aralkyl group having 7 to 20 carbon atoms, substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms and adjacent R ^1s may be combined to form a ring. ] It is characterized by being a compound represented by.
Such an organic electroluminescence device of the present invention has high luminous efficiency and low driving voltage.

In a preferred embodiment of the organic electroluminescence device of the present invention, the guest material in the light-emitting layer is an organometallic complex. In this case, the luminous efficiency is further increased.

［一般式（２）中のＸ¹は、それぞれ独立にＮ又はＣ－Ｒ²を示し、少なくとも１つのＸ¹はＮであり、ここで、Ｒ²は、水素原子、炭素数１～１０のアルキル基、炭素数１～１０のアルコキシ基、炭素数１～１０のアルキルチオ基、炭素数１～１０のアルキルアミノ基、炭素数２～１０のアシル基、炭素数７～２０のアラルキル基、置換若しくは未置換の炭素数６～３０の芳香族炭化水素基、又は置換若しくは未置換の炭素数３～３０の芳香族複素環基であり、
Ｒ¹は、それぞれ独立に水素原子、炭素数１～１０のアルキル基、炭素数１～１０のアルコキシ基、炭素数１～１０のアルキルチオ基、炭素数１～１０のアルキルアミノ基、炭素数２～１０のアシル基、炭素数７～２０のアラルキル基、置換若しくは未置換の炭素数６～３０の芳香族炭化水素基、又は置換若しくは未置換の炭素数３～３０の芳香族複素環基であり、隣り合うＲ¹は一体となって環を形成していてもよく、
Ｒ³は、それぞれ独立に水素原子、炭素数１～１０のアルキル基、炭素数１～１０のアルコキシ基、炭素数１～１０のアルキルチオ基、炭素数１～１０のアルキルアミノ基、炭素数２～１０のアシル基、炭素数７～２０のアラルキル基、置換若しくは未置換の炭素数６～３０の芳香族炭化水素基、又は置換若しくは未置換の炭素数３～３０の芳香族複素環基である。］で示される化合物である。この場合、発光効率が更に高くなり、駆動電圧が更に低くなる。 In another preferred embodiment of the organic electroluminescence device of the present invention, the host material in the light-emitting layer has the following general formula (2):

[X ¹ in general formula (2) each independently represents N or C—R ² , at least one X ¹ is N, where R ² is a hydrogen atom, a alkyl group, alkoxy group having 1 to 10 carbon atoms, alkylthio group having 1 to 10 carbon atoms, alkylamino group having 1 to 10 carbon atoms, acyl group having 2 to 10 carbon atoms, aralkyl group having 7 to 20 carbon atoms, substituted or an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms,
Each R ¹ is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, or 2 carbon atoms. ~10 acyl group, aralkyl group having 7 to 20 carbon atoms, substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms and adjacent R ¹ may be united to form a ring,
Each R ³ is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, or 2 carbon atoms. ~10 acyl group, aralkyl group having 7 to 20 carbon atoms, substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms be. ] is a compound represented by In this case, the luminous efficiency is further increased and the driving voltage is further decreased.

Further, the organometallic complex is preferably a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4. In this case, an organic EL element with high luminous efficiency, low driving voltage, and high color purity of emitted light can be obtained.

［一般式（３）中のＭは、配位数が４の金属であり、
Ｒ⁴、Ｒ⁵、Ｒ⁶、Ｒ⁷は、それぞれ、置換されていてもよい炭素環基又は置換されていてもよい複素環基であり、
Ｌ¹は、Ｒ⁴とＲ⁵とを連結する連結基であり、
Ｌ²は、Ｒ⁵とＲ⁶とを連結する連結基であり、
Ｌ³は、Ｒ⁶とＲ⁷とを連結する連結基である。］で示される化合物であることが更に好ましい。この場合、発光の色純度が更に高くなる。 Here, the complex is represented by the following general formula (3):

[M in the general formula (3) is a metal with a coordination number of 4,
R ⁴ , R ⁵ , R ⁶ and R ⁷ are each an optionally substituted carbocyclic group or an optionally substituted heterocyclic group,
L ¹ is a linking group that links R ⁴ and R ⁵ ,
^L2 is a linking group that links ^R5 and ^R6 ,
L ³ is a linking group that links R ⁶ and R ⁷ . ] is more preferable. In this case, the color purity of emitted light is further enhanced.

で示されるいずれかの化合物であることがより一層好ましい。この場合、発光の色純度が更に高くなる。 Further, the compound represented by the general formula (3) has the following structural formulas (3-1) to (3-15):

Any one of the compounds represented by is even more preferable. In this case, the color purity of emitted light is further enhanced.

Further, it is particularly preferable that the guest material in the light-emitting layer is a compound represented by the structural formula (3-1) or (3-3). In this case, the color purity of emitted light is particularly high.

で示される化合物であることも好ましい。この場合、発光効率が更に高くなり、駆動電圧が更に低くなる。 Further, the organometallic complex has the following structural formula (4-1):

It is also preferable that it is a compound represented by. In this case, the luminous efficiency is further increased and the driving voltage is further decreased.

A display device of the present invention is characterized by comprising the organic electroluminescence element described above. Such a display device of the present invention has a low driving voltage and excellent luminous efficiency.

Further, a lighting device of the present invention is characterized by comprising the organic electroluminescence element described above. Such a lighting device of the present invention has a low driving voltage and excellent luminous efficiency.

According to the present invention, it is possible to provide an organic EL device in which the light-emitting layer positioned between two electrodes contains the compound represented by the general formula (1), has high light-emitting efficiency, and has a low driving voltage.
Further, according to a preferred embodiment of the present invention, the light-emitting layer contains the compound represented by the above general formula (1) and a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4, It is possible to provide an organic EL device with high luminous efficiency, low driving voltage, and high color purity of emitted light.

BRIEF DESCRIPTION OF THE DRAWINGS It is a cross-sectional schematic diagram for demonstrating an example of the organic EL element of this embodiment. 4 is a graph showing the results of measuring the emission spectra at 300K and 77K of the thin film formed in Experiment 1. FIG. 10 is a graph showing the results of measuring the emission spectra at 300K and 77K of the thin film formed in Experiment 2. FIG. 4 is a graph showing the relationship between applied voltage and luminance in the organic EL elements of Example 1 and Comparative Example 1. FIG. 4 is a graph showing the relationship between current density and power efficiency in the organic EL devices of Example 1 and Comparative Example 1. FIG. 10 is a graph showing emission spectra of thin films formed in Experiments 4 and 5. FIG. 5 is a graph showing the relationship between applied voltage and luminance in the organic EL devices of Example 2 and Comparative Example 2. FIG. 5 is a graph showing the relationship between current density and power efficiency in the organic EL devices of Example 2 and Comparative Example 2. FIG.

The organic electroluminescence element, the display device, and the lighting device of the present invention will be illustrated and described in detail below based on the embodiments thereof.

<Organic electroluminescence element>
The organic electroluminescence device of the present invention comprises an anode, a light-emitting layer and a cathode in this order, the light-emitting layer comprising a guest material and a host material, the host material comprising the above general formula (1 ) is a compound represented by

で示される４，４’－ビス（９－カルバゾリル）－２，２’－ビフェニル（ＣＢＰ）が最も一般に用いられている。ＣＢＰは、正孔輸送性のみを示し、Ｓ₁（一重項励起状態）エネルギーとＴ₁（三重項励起状態）エネルギーとの差が大きい材料であり、エネルギーギャップが大きい。このため、ＣＢＰを用いた発光層を有する従来の有機ＥＬ素子では、電極から発光層への正孔及び電子の移動におけるエネルギー障壁が大きく、駆動電圧が高かった。
ここで、駆動電圧を低くするには、発光層のホスト材料として、ＣＢＰを用いた場合と同程度のＴ₁エネルギーを有し、ＣＢＰと比較してＳ₁エネルギーとＴ₁エネルギーとの差が小さい化合物を用いればよい。このことにより、ＣＢＰと比較してホスト材料のエネルギーギャップを小さくできる。
そこで、本発明者らは鋭意検討を重ね、発光層のホスト材料として、上記一般式（１）で示される化合物を用いればよいことを見出した。一般式（１）で示される化合物においては、ジヒドロアクリジン骨格又はジヒドロアントラセン骨格が正孔輸送性に寄与し、フェナントロイミダゾール骨格が電子輸送性に寄与する。このため、一般式（１）で示される化合物は、正孔輸送性と電子輸送性の両方を兼ね備え、Ｓ₁エネルギーとＴ₁エネルギーとの差が小さい。従って、一般式（１）で示される化合物をホスト材料として含む発光層を有する有機ＥＬ素子では、ホスト材料のエネルギーギャップが小さくなる。その結果、電極から発光層への正孔移動及び／又は電極から発光層への電子移動におけるエネルギー障壁が小さくなり、有機ＥＬ素子の駆動電圧が低くなる。しかも、一般式（１）で示される化合物をホスト材料として含む発光層を有する有機ＥＬ素子では、ホスト材料としてＣＢＰを用いた場合と同等の高い発光効率が得られる。
従って、発光層が、ホスト材料として、上記一般式（１）で表わされる化合物を含む本発明の有機ＥＬ素子は、発光効率が高く、駆動電圧が低い。 As described above, in conventional organic EL devices, carbazole compounds are generally used as the host material of the light-emitting layer. Among the carbazole compounds, the following structural formula (5):

4,4'-bis(9-carbazolyl)-2,2'-biphenyl (CBP) represented by is most commonly used. CBP is a material that exhibits only hole-transporting properties, has a large difference between S ₁ (singlet excited state) energy and T ₁ (triplet excited state) energy, and has a large energy gap. For this reason, conventional organic EL devices having a light-emitting layer using CBP have a large energy barrier in the movement of holes and electrons from the electrode to the light-emitting layer, and require a high driving voltage.
Here, in order to lower the driving voltage, the host material of the light-emitting layer should have the same T ₁ energy as when CBP is used, and the difference between the S ₁ energy and the T ₁ energy compared to CBP should be A small compound may be used. This makes it possible to reduce the energy gap of the host material compared to CBP.
Accordingly, the present inventors have made extensive studies and found that the compound represented by the general formula (1) may be used as the host material for the light-emitting layer. In the compound represented by the general formula (1), the dihydroacridine skeleton or dihydroanthracene skeleton contributes to hole-transport properties, and the phenanthroimidazole skeleton contributes to electron-transport properties. Therefore, the compound represented by the general formula (1) has both hole-transporting property and electron-transporting property, and the difference between S ₁ energy and T ₁ energy is small. Therefore, in an organic EL device having a light-emitting layer containing the compound represented by formula (1) as a host material, the energy gap of the host material is small. As a result, the energy barrier in the transfer of holes from the electrode to the light-emitting layer and/or the transfer of electrons from the electrode to the light-emitting layer is reduced, and the driving voltage of the organic EL element is lowered. Moreover, an organic EL device having a light-emitting layer containing the compound represented by the general formula (1) as a host material can obtain a high luminous efficiency equivalent to that in the case of using CBP as the host material.
Therefore, the organic EL device of the present invention, in which the light-emitting layer contains the compound represented by the general formula (1) as a host material, has high luminous efficiency and low driving voltage.

Next, one aspect of the organic electroluminescence device of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view for explaining an example of the organic EL element of this embodiment.

The organic EL element 1 of this embodiment shown in FIG. ), a laminated structure including a light-emitting layer 6 is formed.
The layered structure of the organic EL element 1 of the present embodiment includes a hole injection layer 4, a hole transport layer 5, a light emitting layer 6, an electron transport layer 7, and an electron injection layer 8, which are formed in this order. It is.
The organic EL element 1 shown in FIG. 1 may be of a top emission type in which light is extracted to the side opposite to the substrate 2, or may be of a bottom emission type in which light is extracted to the substrate 2 side.

(substrate)
Examples of materials for the substrate 2 include resin materials and glass materials. Only one type of material for the substrate 2 may be used, or two or more types may be used in combination.
Resin materials used for the substrate 2 include polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyarylate, and the like. When a resin material is used as the material of the substrate 2, it is preferable because the organic EL element 1 having excellent flexibility can be obtained.
On the other hand, examples of glass materials used for the substrate 2 include quartz glass, soda glass, and Pyrex (registered trademark).

When the organic EL device 1 is of the bottom emission type, a transparent substrate is used as the material of the substrate 2 .
On the other hand, when the organic EL element 1 is of the top emission type, the material of the substrate 2 may be not only a transparent substrate but also an opaque substrate. Examples of opaque substrates include substrates made of ceramic materials such as alumina, substrates made of metal plates such as stainless steel with an oxide film (insulating film) formed thereon, and substrates made of resin materials.

(anode)
The anode 3 injects holes into the hole injection layer 4 or the hole transport layer 5 . For this reason, as the material of the anode 3, various metal materials having a relatively large work function, various alloys, and the like are used. Examples of materials for the anode 3 include gold, copper iodide, tin oxide, aluminum-doped zinc oxide (ZnO:Al), indium tin oxide (ITO), indium zinc oxide (IZO), fluorine tin oxide (FTO), and the like. is mentioned. Among these, ITO, IZO, and FTO are preferable as the material for the anode 3 from the viewpoint of transparency and work function.

When the organic EL device 1 is of the bottom emission type, a transparent conductive material is used as the material of the anode 3 .
On the other hand, when the organic EL element 1 is of the top emission type, the material of the anode 3 may be not only a transparent conductive material, but also an opaque material or a reflective material.

(hole injection layer)
The material used for the hole injection layer 4 is selected according to the relationship between the work function of the anode 3 and the ionization potential (IP) of the hole transport layer 5, charge transport properties, and the like. The material of the hole injection layer 4 may be a compound having appropriate IP and charge transport properties, and various organic compounds and inorganic compounds can be selected and used regardless of whether they are low-molecular-weight or high-molecular-weight. The material of the hole injection layer 4 may be used alone or in combination of two or more.

Examples of inorganic compounds used for _the hole injection layer 4 include molybdenum oxide (MoOx) and vanadium oxide ( _V2O5 ). Inorganic compounds are stable compared to organic compounds. Therefore, when an inorganic compound is used for the hole injection layer 4, it is easier to obtain high resistance to oxygen and water compared to when an organic compound is used.

Examples of organic compounds used for the hole injection layer 4 include compounds represented by the following structural formulas (6-1) to (6-19).

Among the compounds represented by the above structural formulas (6-1) to (6-19), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT) represented by the structural formula (6-11) :PSS), poly(3,4-ethylenedioxythiophene) (PEDOT) represented by the structural formula (6-12), and copper phthalocyanine (CuPc) represented by the structural formula (6-4) are preferred, and the structural formula ( PEDOT shown in 6-12) is particularly preferred.

(Hole transport layer)
Materials used for the hole transport layer 5 include, for example, compounds represented by the following structural formulas (7-1) to (7-37).

Among the compounds represented by the above structural formulas (7-1) to (7-37), N,N'-di(1-naphthyl)-N,N'-diphenyl- represented by the structural formula (7-1) 1,1′-biphenyl-4,4′-diamine (α-NPD) and structural formula (7-36) or (7-37) having a large bandgap and excellent electrical and thermal stability It is particularly preferred to use in combination with the indicated compounds.

The material of the hole transport layer 5 may be used alone or in combination of two or more. Moreover, the hole transport layer 5 may be formed of only one layer, or may be formed by stacking two or more layers. For example, the hole-transporting layer 5 includes a layer composed of a compound represented by structural formula (7-36) or (7-37) arranged on the light-emitting layer 6 side and a structural formula ( 7-1) and a layer made of α-NPD shown in 7-1) can be laminated.

(Light emitting layer)
The light-emitting layer 6 included in the organic EL device 1 of this embodiment includes a host material that performs charge transport and charge recombination, and a guest material that is a light-emitting material.

で表わされる化合物を用いる。
一般式（１）で示される化合物中のジヒドロアクリジン骨格又はジヒドロアントラセン骨格は、正孔輸送性に寄与するドナー性を有する。また、一般式（１）で示される化合物中のフェナントロイミダゾール骨格は、電子輸送性に寄与するアクセプター性の置換基である。 "Host material"
In this embodiment, the host material is represented by the following general formula (1):

A compound represented by is used.
The dihydroacridine skeleton or dihydroanthracene skeleton in the compound represented by general formula (1) has a donor property that contributes to hole transport properties. In addition, the phenanthroimidazole skeleton in the compound represented by general formula (1) is an acceptor substituent that contributes to electron transport properties.

Each X ¹ in general formula (1) independently represents N or CR ² , and at least one X ¹ is N. Here, R ² is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, or 2 carbon atoms. ~10 acyl group, aralkyl group having 7 to 20 carbon atoms, substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms be.

Each R ¹ in the general formula (1) is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, or an alkylthio group having 1 to 10 carbon atoms. alkylamino group, acyl group having 2 to 10 carbon atoms, aralkyl group having 7 to 20 carbon atoms, substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or substituted or unsubstituted 3 to 30 carbon atoms is an aromatic heterocyclic group, and adjacent R ¹ may be combined to form a ring.
Here, “adjacent R ¹ ” includes two R ¹ bonded to the same carbon atom and R ¹ bonded to each of the two bonded carbon atoms. .

で示される化合物が好ましい。この場合、発光効率が更に高くなり、駆動電圧が更に低くなる。 As the compound represented by the general formula (1), the following general formula (2):

A compound represented by is preferred. In this case, the luminous efficiency is further increased and the driving voltage is further decreased.

Each X ¹ in general formula (2) independently represents N or CR ² , and at least one X ¹ is N. Here, R ² is a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, or 2 carbon atoms. ~10 acyl group, aralkyl group having 7 to 20 carbon atoms, substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms be.

Each R ¹ in the general formula (2) is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, or a alkylamino group, acyl group having 2 to 10 carbon atoms, aralkyl group having 7 to 20 carbon atoms, substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or substituted or unsubstituted 3 to 30 carbon atoms is an aromatic heterocyclic group, and adjacent R ¹ may be combined to form a ring.
Here, “adjacent R ¹ ” includes two R ¹ bonded to the same carbon atom and R ¹ bonded to each of the two bonded carbon atoms. .

Each R ³ in the general formula (2) is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, or an alkylthio group having 1 to 10 carbon atoms. alkylamino group, acyl group having 2 to 10 carbon atoms, aralkyl group having 7 to 20 carbon atoms, substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or substituted or unsubstituted 3 to 30 carbon atoms is an aromatic heterocyclic group.

Regarding R ¹ , R ² and R ³ described above, the alkyl group having 1 to 10 carbon atoms includes methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group and nonyl group. and the like, and examples of alkoxy groups having 1 to 10 carbon atoms include methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, tert-butoxy, pentyloxy, hexyloxy, heptyloxy Examples of alkylthio groups having 1 to 10 carbon atoms include methylthio, ethylthio, propylthio, butylthio, pentylthio, hexylthio, heptylthio, octylthio, and nonylthio groups. Examples of alkylamino groups having 1 to 10 carbon atoms include methylamino group, ethylamino group, propylamino group, butylamino group, pentylamino group, hexylamino group, heptylamino group, octylamino group, nonylamino group and the like. Examples of acyl groups having 2 to 10 carbon atoms include acetyl group, propionyl group, and butyryl group. Examples of aralkyl groups having 7 to 20 carbon atoms include benzyl group, phenethyl group, phenylpropyl group, and naphthyl. Examples of substituted or unsubstituted aromatic hydrocarbon groups having 6 to 30 carbon atoms include methyl group, phenyl group, 2,6-xylyl group, mesityl group, duryl group, biphenyl group, terphenyl group and naphthyl. group, anthryl group, pyrenyl group, toluyl group, anisyl group, fluorophenyl group, diphenylaminophenyl group, dimethylaminophenyl group, diethylaminophenyl group, pyridylphenyl group, phenanthrenyl group, etc., and substituted or unsubstituted carbon number Examples of aromatic heterocyclic groups of 3 to 30 include pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl and triazine groups.

で示される化合物が特に好ましい。上記構造式（１－１）又は（１－２）で示される化合物は、一重項励起状態（Ｓ₁）と三重項励起状態（Ｔ₁）とのエネルギー差が小さく、且つエネルギーギャップが小さいため、外部量子効率が高い有機ＥＬ素子１が得られ易く、好ましい。 As the compound represented by the general formula (1), the following structural formula (1-1) or (1-2):

Compounds represented by are particularly preferred. The compound represented by the above structural formula (1-1) or (1-2) has a small energy difference between the singlet excited state (S ₁ ) and the triplet excited state (T ₁ ), and has a small energy gap. , the organic EL device 1 having a high external quantum efficiency can be easily obtained, which is preferable.

By measuring the fluorescence spectrum of the compound, the S ₁ (singlet excited state) energy of the compound can be obtained. Also, the T ₁ (triplet excited state) energy of the compound can be obtained by measuring the phosphorescence spectrum of the compound.

The compound represented by the general formula (1) can be obtained by synthesizing by a known method. The method for synthesizing the compound represented by the general formula (1) is not particularly limited. For example, a dihydroacridine compound or a dihydroanthracene compound is coupled with a phenanthroimidazole compound having a bromophenyl group. can be synthesized by Here, a compound having a desired structure can be appropriately synthesized by introducing a desired substituent into a dihydroacridine compound or dihydroanthracene compound and/or a phenanthroimidazole compound having a bromophenyl group.

"Guest Materials"
A fluorescent material and/or a phosphorescent material is preferably used as the guest material. The guest material preferably has an absorption wavelength that overlaps with the emission wavelength of the host material in order to effectively transfer energy from the host material.
The content of the guest material in the host material is preferably 1-10% by mass. When the content of the guest material is within the above range, energy transfer from the host material to the guest material occurs efficiently, and the luminous efficiency of the organic EL device 1 is improved.

- Phosphorescent materials -
When the guest material is a phosphorescent material, the T ₁ energy of the guest material is preferably less than the T ₁ energy of the host material.
Phosphorescent materials used as guest materials include, for example, compounds represented by the following structural formulas (4-1) to (4-29).

In this embodiment, since the compound represented by the general formula (1) is used as the host material, among the phosphorescent materials represented by the structural formulas (4-1) to (4-29), the structural formula (4 Green light-emitting materials such as Ir(mppy) ₃ represented by -1) are particularly preferred.

Since Ir(mppy) ₃ represented by the above structural formula (4-1) has a relatively small T ₁ energy, the compound represented by the general formula (1) is used as the host material and Ir(mppy) ₃ is used as the guest material. , efficient energy transfer from the host material to the guest material occurs. As a result, the organic EL device 1 with a lower driving voltage is obtained. Moreover, since Ir(mppy) ₃ has an absorption wavelength that overlaps with the emission wavelength of the compound represented by the general formula (1), the organic EL element 1 has a higher emission efficiency.

When the compound represented by the general formula (1) is used as the host material and Ir(mppy) ₃ is used as the guest material, the content of the guest material in the host material is preferably 1 to 6% by mass. When the content of the guest material is within the above range, energy transfer from the host material to the guest material occurs efficiently, and a decrease in efficiency due to triplet-triplet annihilation (TTA) due to an increase in the guest material concentration can be prevented. can. Therefore, the luminous efficiency of the organic EL element 1 is improved.

-Fluorescent materials-
Fluorescent materials used as guest materials include, for example, compounds represented by the following structural formulas (4-30) to (4-51).

-organometallic complexes-
As the guest material in the light-emitting layer 6, it is preferable to use an organometallic complex. When an organometallic complex is used as the guest material, the luminous efficiency is further enhanced.
Examples of the organometallic complex include phosphorescent materials represented by the structural formulas (4-1) to (4-29) described above, and planar tetradentate ligands to metals having a coordination number of 4, which will be described later. conjugated complexes, and the like.

The guest material in the light-emitting layer 6 preferably contains a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4, from the viewpoint of obtaining light emission with high color purity. By using the compound represented by the above general formula (1) as the host material of the light-emitting layer 6 and using a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4 as a guest material, the luminous efficiency is increased. The organic EL element 1 can have a high driving voltage, a low driving voltage, and a high color purity of emitted light.
The compound represented by the general formula (1) has a small energy gap and a higher T ₁ energy than the guest material. High external quantum efficiencies can be obtained when used with complexes bound by .
In addition, the compound represented by the general formula (1) has a phenanthroimidazole skeleton as a skeleton having an electron-transporting property, and the phenanthroimidazole skeleton is different from the 1,3,5-triazine skeleton, guest Even if a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4 is used as the material, exciplex formation between the host material and the guest material as described in Non-Patent Document 6 can be suppressed. . Therefore, by using the compound represented by the general formula (1) as a host material and using a complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4 as a guest material, the half width of the emission spectrum is reduced to Narrow, high color purity emission can be obtained.

で示される化合物が好ましい。
上記一般式（３）で示される化合物は、四座配位子が、金属を囲むように略同一平面上に配置された４つの環状構造を有する基と、隣接する環状構造を有する基の間のうちの３箇所をそれぞれ連結する連結基とを有する。このため、一般式（３）で示される化合物は、安定であり、分子の振動に伴う光の放射が効果的に抑制され、発光スペクトルの半値幅が狭く、高色純度の発光が得られるものと推定される。 A complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4 may contain only one type, or may contain two or more types. A complex in which a planar tetradentate ligand is bonded to a metal having a coordination number of 4 is represented by the following general formula (3):

A compound represented by is preferred.
The compound represented by the general formula (3) has a tetradentate ligand between a group having four cyclic structures arranged substantially on the same plane so as to surround the metal and a group having an adjacent cyclic structure. It has a connecting group that connects each of the three sites. Therefore, the compound represented by the general formula (3) is stable, effectively suppresses light emission associated with molecular vibration, has a narrow half width of the emission spectrum, and provides light emission with high color purity. It is estimated to be.

M in the general formula (3) is a metal with a coordination number of 4. M in the general formula (3) may be any metal having a coordination number of 4, and examples thereof include Pt, Pd, Cu, etc. Pt and Pd are preferred, and Pt is particularly preferred.

R ⁴ , R ⁵ , R ⁶ and R ⁷ in general formula (3) are each an optionally substituted carbocyclic group or an optionally substituted heterocyclic group. The carbocyclic group or heterocyclic group as R ⁴ , R ⁵ , R ⁶ and R ⁷ is a 5-membered or 6-membered ring because it becomes a compound that further suppresses molecular vibrations accompanying light emission. is preferred. R ⁴ , R ⁵ , R ⁶ and R ⁷ in general formula (3) may all be the same, or may be partially or wholly different from each other.

Carbocyclic groups for R ⁴ , R ⁵ , R ⁶ and R ⁷ described above include cyclopentyl, cyclohexyl, phenyl, biphenyl, terphenyl, naphthyl, anthryl, pyrenyl and phenanthrenyl. Examples of heterocyclic groups include imidazolyl, pyrazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, benzimidazolyl, and carbazolyl groups. Substituents for the carbocyclic and heterocyclic groups include alkyl groups having 1 to 10 carbon atoms, alkoxy groups having 1 to 10 carbon atoms, alkylthio groups having 1 to 10 carbon atoms, and alkylamino groups having 1 to 10 carbon atoms. groups, acyl groups having 2 to 10 carbon atoms, and the like.

L ¹ in general formula (3) is a linking group that links R ⁴ and R ⁵ , L ² is a linking group that links R ⁵ and R ⁶ , and L ³ is R ⁶ and It is a connecting group that connects with ^R7 . L ¹ , L ² and L ³ in general formula (3) may be those that connect adjacent groups having a cyclic structure (R ⁴ , R ⁵ , R ⁶ and R ⁷ ). It may be a ring structure formed together with atoms forming a group having an adjacent cyclic structure, or a single bond between atoms forming a group having an adjacent cyclic structure, It may be an ether bond. L ¹ , L ² and L ³ in general formula (3) may all be the same, or may be partially or wholly different from each other.

As the compound represented by the general formula (3), compounds represented by the following structural formulas (3-1) to (3-15) are preferable. Compounds represented by (3-1) and compounds represented by Structural Formula (3-3) are particularly preferred.

When the compound represented by the general formula (1) is used as the host material and the compound represented by the general formula (3) is used as the guest material, the content of the guest material in the host material is 3 to 10% by mass. is preferably When the content of the guest material is within the above range, energy transfer from the host material to the guest material occurs efficiently, and a decrease in efficiency due to triplet-triplet annihilation (TTA) due to an increase in guest concentration can be prevented. . Therefore, the luminous efficiency of the organic EL element 1 is further improved.

(Electron transport layer)
An electron-transporting layer 7 having an appropriate lowest unoccupied molecular orbital (LUMO) level is provided between the cathode 9 or electron-injecting layer 8 and the light-emitting layer 6 so that the electron-transporting layer 7 from the cathode 9 or electron-injecting layer 8 , and the electron injection barrier from the electron-transporting layer 7 to the light-emitting layer 6 is relaxed. Also, if the material used for the electron-transporting layer 7 has an appropriate highest occupied molecular orbital (HOMO) level, holes are blocked from recombining in the light-emitting layer 6 and flowing to the counter electrode. As a result, holes are confined within the light-emitting layer 6 and the recombination efficiency within the light-emitting layer 6 is enhanced.
The electron-transporting layer 7 may be omitted when the electron injection barrier is not a problem and the electron-transporting ability of the light-emitting layer 6 is sufficiently high.

Materials used for the electron transport layer 7 include, for example, compounds represented by the following structural formulas (8-1) to (8-28).

Among the compounds represented by the above structural formulas (8-1) to (8-28), 2,2′,2″-(1,3,5-benzenetriyl) represented by the structural formula (8-4) -tris(1-phenyl-1-H-benzimidazole) (TPBi) is particularly preferred.

(Electron injection layer)
The material used for the electron injection layer 8 is selected from the viewpoint of the work function of the cathode 9, the LUMO level of the electron transport layer 7, and the like. The material used for the electron injection layer 8 is selected in consideration of the LUMO levels of the guest material and the host material of the light emitting layer 6 when the electron transport layer 7 is not provided.

The material used for the electron injection layer 8 may be an organic compound or an inorganic compound. When the electron injection layer 8 is made of an inorganic compound, for example, alkali metals, alkaline earth metals, lithium fluoride, sodium fluoride, potassium fluoride, cesium fluoride, cesium carbonate, etc. can be used, preferably lithium fluoride.

(cathode)
Cathode 9 injects electrons into electron injection layer 8 or electron transport layer 7 . For this reason, as the material of the cathode 9, various metal materials, various alloys, and the like having a relatively small work function are used. Examples of materials for the cathode 9 include aluminum, silver, magnesium, calcium, gold, indium tin oxide (ITO), indium zinc oxide (IZO), magnesium indium alloy (MgIn), and silver alloy.

When the organic EL element 1 is of the bottom emission type, the material of the cathode 9 can be an opaque electrode made of metal, or a reflective material.
On the other hand, when the organic EL element 1 is of the top emission type, a transparent conductive material is used as the material of the cathode 9 . When ITO is used as the material of the cathode 9, electron injection becomes difficult because of the large work function of ITO. In addition, since the ITO film is formed using a sputtering method or an ion beam vapor deposition method, there is a possibility that the electron injection layer 8 and the like may be damaged during film formation. Therefore, when ITO is used as the material of the cathode 9, it is preferable to provide a magnesium layer or a copper phthalocyanine layer between the electron injection layer 8 and ITO.

(Formation method)
The organic EL element 1 shown in FIG. It can be manufactured by forming the cathode 9 in this order. The method of forming each layer of the anode 3, the hole injection layer 4, the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, the electron injection layer 8, and the cathode 9 is not particularly limited, and the characteristics of the materials used for each layer. It can be formed by appropriately using various conventionally known forming methods.

Specifically, for example, methods for forming the anode 3 and the cathode 9 include a sputtering method, a vacuum deposition method, a sol-gel method, a spray pyrolysis (SPD) method, an atomic layer deposition (ALD) method, and a vapor deposition method. , a liquid phase deposition method, and the like.
As a method for forming each layer of the hole injection layer 4, the hole transport layer 5, the light emitting layer 6, the electron transport layer 7, and the electron injection layer 8, an organic compound solution containing an organic compound for each layer is applied. method, vacuum deposition method, ESDUS (Evaporative Spray Deposition from Ultra-dilute Solution) method, and the like. Among these formation methods, it is particularly preferable to use the coating method.
Further, when any one of the hole injection layer 4, the hole transport layer 5, the electron transport layer 7, and the electron injection layer 8 is made of an inorganic material, the layer made of the inorganic material is formed by, for example, a sputtering method. , a vacuum deposition method, or the like.

(another example)
The organic EL element of the present invention is not limited to the organic EL elements described in the above embodiments.
Specifically, in the above-described embodiment, the organic EL element 1 having the forward structure in which the anode 3 is arranged between the substrate 2 and the light-emitting layer 6 was described as an example. may have an inverted structure in which the cathode is arranged between the substrate and the light-emitting layer.

In addition, in the organic EL device of the present invention, the hole injection layer, the hole transport layer, the electron transport layer, and the electron injection layer may be formed as required, and may not be provided.
Each layer of the anode, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, the electron injection layer, and the cathode may be formed of one layer, or may be formed of two or more layers. can be anything.
Further, the organic EL device of the present invention may have another layer between each layer of the anode, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer, the electron injection layer and the cathode. good. Specifically, for reasons such as further improving the characteristics of the organic EL element, it may have an electron blocking layer or the like, if necessary.

<Display device>
A display device of the present invention is characterized by comprising the organic electroluminescence element described above. Since the display device of the present invention includes the above-described organic EL element with high luminous efficiency and low driving voltage, the luminous efficiency is high and the driving voltage is low. The display device of the present invention can comprise other components commonly used in display devices, in addition to the organic EL elements described above.

<Lighting device>
A lighting device of the present invention is characterized by comprising the organic electroluminescence element described above. Since the lighting device of the present invention includes the above-described organic EL element with high luminous efficiency and low driving voltage, the luminous efficiency is high and the driving voltage is low. In addition to the organic EL elements described above, the lighting device of the present invention can comprise other components commonly used in lighting devices.

EXAMPLES Examples and comparative examples of the present invention will be described below. It should be noted that the present invention is not limited to the examples shown below.

<Experiment 1>
A thin film having a thickness of 50 nm made of a compound represented by the following structural formula (1-1) was formed on a substrate made of a glass material by a vacuum deposition method.

Incidentally, the compound represented by the structural formula (1-1) {2-(4-(9,9-diphenylacridin-10(9H)-yl)phenyl)-1-(4-methoxyphenyl)-1H-phenanthro[ 9,10-d]imidazole (PhImEn)} is described in J. Am. Mater. Chem. C, 2018, 6, 9363-9377.

<Experiment 2>
A thin film of CBP represented by the structural formula (5) having a thickness of 50 nm was formed on a substrate made of a glass material by a vacuum deposition method.

<Experiment 3>
A 50 nm-thick thin film of Ir(mppy) ₃ represented by the structural formula (4-1) was formed on a substrate made of a glass material by vacuum deposition.

(Measurement of emission spectrum)
For the thin film formed in Experiment 1, the emission spectrum was measured at 300K and 77K using FluoroMax-4 manufactured by HORIBA, using an excitation light source with a wavelength of 300 nm. Further, for the thin film formed in Experiment 2, the emission spectra at 300K and 77K were measured using a similar device and an excitation light source with a wavelength of 300 nm. The results are shown in FIGS. 2 and 3. FIG. 2 is a graph showing measurement results of the thin film formed in Experiment 1. FIG. 3 is a graph showing measurement results of the thin film formed in Experiment 2. FIG.

The emission spectrum at normal temperature (300K) shows fluorescence emission. Therefore, from the emission spectrum at normal temperature (300 K), knowledge corresponding to S ₁ (singlet excited state) energy can be obtained.
As shown in FIGS. 2 and 3, the fluorescence emission of the compound represented by the structural formula (1-1) (Experiment 1) is seen on the longer wavelength side than the fluorescence emission of CBP (Experiment 2). Therefore, the S ₁ energy of the compound represented by structural formula (1-1) is smaller than that of CBP.

In addition, for the thin films formed in Experiments 1 and 2, phosphorescence emission was observed by emission spectrum measurement at a low temperature (77 K or lower), and the energy of the triplet excited state (T ₁ ) of the thin films was determined. In addition, the emission spectrum measurement at a low temperature was performed with a delay of 50 ms after irradiation of the excitation light in order to remove the fluorescence emission component and observe the phosphorescence spectrum. Table 1 shows the energy of the triplet excited state (T ₁ ) of the thin films formed in Experiments 1 and 2 thus obtained.
Also, for the thin film (Ir(mppy) ₃ ) formed in Experiment 3, the energy of the triplet excited state (T ₁ ) of the thin film was obtained in the same manner as in Experiments 1 and 2. Table 1 shows the energy of the triplet excited state (T ₁ ) of the thin film formed in Experiment 3.

As mentioned above, the S ₁ energy of the compound represented by Structural Formula (1-1) is smaller than that of CBP. Further, as shown in Table 1, the T ₁ energy of the compound represented by the structural formula (1-1) (Experiment 1) is approximately the same as that of CBP (Experiment 2). Therefore, the compound represented by Structural Formula (1-1) has a smaller energy gap than CBP. Therefore, it can be seen that the compound represented by Structural Formula (1-1) is preferable to CBP as the host material for the light-emitting layer.

Further, as shown in _Table 1, the T ₁ energy of the compound represented by the structural formula (1-1) (Experiment 1) is higher than that of Ir(mppy) ₃ , which is a general green phosphorescent material. Not small, the compound represented by the structural formula (1-1) is suitable for the host material of the light-emitting layer.

<Example 1>
An organic EL device of Example 1 was produced by the method shown below using the materials shown below.
A hole injection layer, a second hole transport layer, a first hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a cathode are formed on the anode of the substrate by vacuum deposition, were formed in this order to fabricate an organic EL device of Example 1.

(substrate, anode)
A commercially available transparent glass substrate with an average thickness of 0.7 mm with 3 mm wide patterned electrodes made of ITO (indium tin oxide).

(hole injection layer)
PEDOT (Clevios HIL1.5) (thickness 30 nm) represented by the structural formula (6-12)

(Hole transport layer)
"First hole transport layer": a compound represented by the structural formula (7-36) (thickness: 10 nm)
"Second hole transport layer": α-NPD (thickness 20 nm) represented by structural formula (7-1)

(Light emitting layer)
A compound represented by structural formula (1-1), which is a compound represented by general formula (1), is used as a host material, and Ir(mppy ) ₃ % by mass (thickness 25 nm)

(Electron transport layer)
TPBi (thickness 35 nm) represented by the structural formula (8-4)

(Electron injection layer)
LiF film (thickness 0.8 nm)

(cathode)
Al film (thickness 100 nm)

<Comparative Example 1>
An organic EL device of Comparative Example 1 was produced in the same manner as in Example 1, except that CBP represented by Structural Formula (5) was used as the host material of the light-emitting layer.

(Measurement of external quantum efficiency)
For the organic EL devices of Example 1 and Comparative Example 1 obtained as described above, the external quantum efficiency was measured at a current density of 10 mA/cm ² . Table 2 shows the results.

As shown in Table 2, the external quantum efficiency of the organic EL device of Example 1 was higher than that of the organic EL device of Comparative Example 1.

(Measurement of voltage-luminance characteristics)
Voltage was applied to the organic EL elements of Example 1 and Comparative Example 1 using Keithley's "2400 type source meter", and luminance was measured using Konica Minolta's "LS-100". , investigated the relationship between applied voltage and luminance. The results are shown in FIG.

As shown in FIG. 4, in the organic EL device of Example 1, as compared with the organic EL device of Comparative Example 1, high luminance was obtained at the same applied voltage, and the driving voltage was low. This is presumably because the compound represented by the structural formula (1-1) used in Example 1 as the host material for the light-emitting layer has a smaller energy gap than CBP used in Comparative Example 1. be done.

(Measurement of current density-power efficiency characteristics)
The current density and power efficiency of the organic EL devices of Example 1 and Comparative Example 1 were examined using a Keithley Model 2400 source meter. The results are shown in FIG.

As shown in FIG. 5, the organic EL device of Example 1 provides higher power efficiency than the organic EL device of Comparative Example 1 at the same current density. This is presumably because the compound represented by the structural formula (1-1) used in Example 1 as the host material for the light-emitting layer has a smaller energy gap than CBP used in Comparative Example 1. be done.

<Experiment 4>
A thin film having a thickness of 30 nm containing 1 mass % of the compound represented by the structural formula (3-1) in the compound represented by the structural formula (1-1) was formed on a quartz substrate by vacuum deposition.

で示される化合物を用いたこと以外は、実験４と同様にして、実験５の薄膜を作製した。 <Experiment 5>
Instead of the compound represented by the structural formula (1-1), the following structural formula (9):

A thin film of Experiment 5 was prepared in the same manner as in Experiment 4, except that the compound represented by was used.

(Measurement of emission spectrum)
For the thin films obtained in Experiments 4 and 5, the emission spectra at 300 K were measured using FluoroMax-4 manufactured by HORIBA, using an excitation light source with a wavelength of 350 nm. The results are shown in FIG.

As shown in FIG. 6, in the emission spectrum of the thin film of Experiment 4, it was confirmed that the emission intensity of the peak seen around 560 nm was smaller than that of the thin film of Experiment 5, and the color purity of the emitted light was high. This is because the compound represented by Structural Formula (1-1) having a phenanthroimidazole group is more preferable than the compound represented by Structural Formula (9) having a triazine group as the host material. This is because exciplex formation is less likely to occur between the material and the guest material (the compound represented by the structural formula (3-1)), and the resulting increase in emission spectrum width can be reduced.

<Example 2>
Using the materials shown below, an organic EL device of Example 2 was produced by the method shown below.
A hole injection layer, a second hole transport layer, a first hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a cathode are formed on the anode of the substrate by vacuum deposition, were formed in this order to fabricate an organic EL device of Example 2.

(substrate, anode)
A commercially available transparent glass substrate with an average thickness of 0.7 mm with a 3 mm wide patterned electrode (anode) made of ITO (indium tin oxide).

(hole injection layer)
PEDOT (Clevios HIL1.3N) (thickness 30 nm) represented by the structural formula (6-12)

(Hole transport layer)
"First hole transport layer": a compound represented by the structural formula (7-37) (thickness: 10 nm)
"Second hole transport layer": α-NPD (thickness 20 nm) represented by structural formula (7-1)

(Light emitting layer)
The compound represented by the structural formula (1-1) is used as a host material, and the host material contains 6% by mass of the compound represented by the structural formula (3-1) as a guest material (thickness: 25 nm).

(Electron transport layer)
TPBi (thickness 35 nm) represented by the structural formula (8-4)

(Electron injection layer)
LiF film (thickness 0.8 nm)

(cathode)
Al film (thickness 100 nm)

<Comparative Example 2>
An organic EL device of Comparative Example 2 was fabricated in the same manner as in Example 2, except that CBP represented by Structural Formula (5) was used as the host material of the light-emitting layer.

(Measurement of external quantum efficiency)
The organic EL devices of Example 2 and Comparative Example 2 obtained as described above were measured for external quantum efficiency at a current density of 10 mA/cm ² in the same manner as described above. Table 3 shows the results.

As shown in Table 3, the external quantum efficiency of the organic EL device of Example 2 was higher than that of the organic EL device of Comparative Example 2.

(Measurement of voltage-luminance characteristics)
Voltage was applied to the organic EL elements of Example 2 and Comparative Example 2 using Keithley's "2400 type source meter", and luminance was measured using Konica Minolta's "LS-100". , investigated the relationship between applied voltage and luminance. The results are shown in FIG.

As shown in FIG. 7, in the organic EL device of Example 2, high luminance was obtained at the same applied voltage as compared with the organic EL device of Comparative Example 2, and the driving voltage was low.

(Measurement of current density-power efficiency characteristics)
The current density and power efficiency of the organic EL devices of Example 2 and Comparative Example 2 were examined in the same manner as described above. The results are shown in FIG.

As shown in FIG. 8, even in the organic EL element of Example 2 in which the light-emitting material (guest material) of Example 1 was changed, the current Higher power efficiency is obtained for the same density.

1: Organic EL (electroluminescence) element 2: Substrate 3: Anode 4: Hole injection layer 5: Hole transport layer 6: Light emitting layer 7: Electron transport layer 8: Electron injection layer 9: Cathode

Claims (4)

comprising an anode, a light-emitting layer, and a cathode in this order;
the light-emitting layer comprises a guest material and a host material;
The host material has the following general formula ( 2 ):

[X ¹ in the general formula ( 2 ) each independently represents N or C—R ² , at least one X ¹ is N, where R ² is a hydrogen atom, a alkyl group, alkoxy group having 1 to 10 carbon atoms, alkylthio group having 1 to 10 carbon atoms, alkylamino group having 1 to 10 carbon atoms, acyl group having 2 to 10 carbon atoms, aralkyl group having 7 to 20 carbon atoms, substituted or an unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms,
Each R ¹ is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, or 2 carbon atoms. ~10 acyl group, aralkyl group having 7 to 20 carbon atoms, substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms and adjacent R ¹ may be united to form a ring,
Each R ³ is independently a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkylthio group having 1 to 10 carbon atoms, an alkylamino group having 1 to 10 carbon atoms, or 2 carbon atoms. ~10 acyl group, aralkyl group having 7 to 20 carbon atoms, substituted or unsubstituted aromatic hydrocarbon group having 6 to 30 carbon atoms, or substituted or unsubstituted aromatic heterocyclic group having 3 to 30 carbon atoms There is . ] is a compound represented by
The guest material has the following structural formulas (3-1) to (3-15):

An organic electroluminescence device characterized by being any one of the compounds represented by : 2. The organic electroluminescence device according to claim 1 , wherein the guest material in said light-emitting layer is a compound represented by said structural formula (3-1) or (3-3). A display device comprising the organic electroluminescence device according to claim 1 . A lighting device comprising the organic electroluminescence device according to claim 1 .

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