JP2007042875A - Organic electroluminescence element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescence element making compatible with a high luminous efficacy and a durability on a driving and enabling a low-voltage driving. <P>SOLUTION: The organic electroluminescence element has a hole transporting layer containing at least one kind of a hole transporting material, a luminous layer containing at least one kind of a luminous dopant and a plurality of host compounds, and an electron transporting layer containing at least one kind of an electron transporting material, between a pair of electrodes. In the organic electroluminescence element, a hole transportable host compound is used as at least one kind in a plurality of the host compounds and an electron transportable host compound as at least one kind. The organic electroluminescence element has a hole transportable intermediate layer composed only of the same compound as the hole transportable host compound between the hole transporting layer and the luminous layer, and/or an electron transportable intermediate layer composed only of the same compound as the electron transportable host compound between the electron transporting layer and the luminous layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic electroluminescent element that emits light by converting electric energy into light (hereinafter also referred to as “organic EL element”, “light emitting element”, or “EL element”).

An organic electroluminescence (EL) element has attracted attention as a promising display element because it can emit light with high luminance at a low voltage. Problems in the organic electroluminescence device include reduction of power consumption and improvement of driving durability. A hole transport material and an electron transport material are mixed as a host material of the light emitting layer, and the hole transport material and the electron transport are disposed between the light emitting layer and the hole transport layer and between the light emitting layer and the electron transport layer. It is disclosed to provide a mixed layer in which materials are mixed at a constant ratio (see Patent Document 1). However, in this device configuration, carriers are likely to leak from the light emitting layer to other layers, and the light emission efficiency is expected to decrease due to a decrease in the recombination probability between holes and electrons.
Therefore, a light emitting device with improved light emission efficiency, high drive durability, low voltage drive, and the like is desired.
JP 2002-313584 A

  An object of the present invention is to provide an organic electroluminescent device that achieves both high luminous efficiency and high driving durability and can be driven at a low voltage.

  As a result of intensive studies, the present inventors have found that a hole transport layer containing at least one kind of hole transport material, a light emitting layer containing at least one kind of luminescent dopant and a plurality of host compounds, and at least one kind of electron transport material. An electron transporting layer, wherein at least one of the plurality of host compounds is a hole transporting host, and at least one is an electron transporting host, between the hole transporting layer and the light emitting layer. Providing a hole transporting intermediate layer composed only of the same compound as the hole transporting host compound and / or the same compound as the electron transporting host compound between the electron transporting layer and the light emitting layer. It has been found that by providing an electron transporting intermediate layer consisting of only the above, it is possible to achieve improvement in luminous efficiency, improvement in driving durability, and reduction in driving voltage, and the present invention has been completed.

The above problems are solved by the following organic electroluminescent elements <1> to <23>.
<1> Between a pair of electrodes, a hole transport layer containing at least one kind of hole transport material, a light emitting layer containing at least one kind of luminescent dopant and a plurality of host compounds, and an electron containing at least one kind of electron transport material An organic electroluminescent device having a transport layer,
Among the plurality of host compounds, at least one is a hole transporting host compound, and at least one is an electron transporting host compound,
An organic electroluminescence device comprising a hole transporting intermediate layer made of only the same compound as the hole transporting host compound between the hole transporting layer and the light emitting layer.

<2> Between a pair of electrodes, a hole transport layer containing at least one kind of hole transport material, a light emitting layer containing at least one kind of luminescent dopant and a plurality of host compounds, and an electron containing at least one kind of electron transport material An organic electroluminescent device having a transport layer,
Among the plurality of host compounds, at least one is a hole transporting host compound, and at least one is an electron transporting host compound,
An organic electroluminescent element comprising an electron transporting intermediate layer made of only the same compound as the electron transporting host compound between the electron transporting layer and the light emitting layer.

<3> A hole transport layer containing at least one kind of hole transport material, a light emitting layer containing at least one kind of luminescent dopant and a plurality of host compounds, and an electron containing at least one kind of electron transport material between a pair of electrodes. An organic electroluminescent device having a transport layer,
Among the plurality of host compounds, at least one is a hole transporting host compound, and at least one is an electron transporting host compound,
Between the hole transport layer and the light emitting layer, it has a hole transport intermediate layer made of only the same compound as the hole transport host compound, and between the electron transport layer and the light emitting layer, An organic electroluminescent device comprising an electron-transporting intermediate layer comprising only the same compound as the electron-transporting host compound.

  <4> In any one of the above items <1> to <3>, in the light emitting layer, a region where the light emitting dopant is present is a part of a region composed of the plurality of host compounds. Organic electroluminescent element.

  <5> When the ionization potential of the light-emitting dopant is Ip (D) and the minimum ionization potential of the plurality of host compounds is Ip (H) min, ΔIp = Ip (D) −Ip ( H) The organic electroluminescence device according to any one of <1> to <4>, wherein ΔIp defined by min satisfies a relationship of ΔIp> 0 eV.

  <6> When the electron affinity of the luminescent dopant is Ea (D) and the maximum electron affinity of the plurality of host compounds is Ea (H) max, ΔEa = Ea (H) max−Ea ΔEa defined in (D) satisfies the relationship of ΔEa> 0 eV. The organic electroluminescent element according to any one of <1> to <4>, wherein

  <7> When the ionization potential of the light-emitting dopant is Ip (D) and the minimum ionization potential of the plurality of host compounds is Ip (H) min, ΔIp = Ip (D) −Ip ( H) ΔIp defined by min satisfies the relationship of ΔIp> 0 eV, and the electron affinity of the light-emitting dopant is Ea (D), and the maximum of the electron affinity of the plurality of host compounds is Ea ( Any one of <1> to <4> above, wherein ΔEa defined by ΔEa = Ea (H) max−Ea (D) satisfies a relationship of ΔEa> 0 eV when H) max The organic electroluminescent element according to one item.

<8> The organic electroluminescence device according to <5> or <7>, wherein the ΔIp satisfies a relationship of 1.2 eV>ΔIp> 0.2 eV.
<9> The organic electroluminescence device according to <6> or <7>, wherein the ΔEa satisfies a relationship of 1.2 eV>ΔEa> 0.2 eV.
<10> The organic electric field according to <7>, wherein ΔIp is 1.2 eV>ΔIp> 0.2 eV, and ΔEa satisfies a relationship of 1.2 eV>ΔEa> 0.2 eV. Light emitting element.

<11> The organic electroluminescent element according to any one of claims 5, 7, 8, and 10, wherein the Ip (H) min is 5.6 eV or more and 5.8 eV or less.
<12> The Ea (H) max is 2.8 eV or more and 3.1 eV or less, according to any one of the items <6>, <7>, <9>, and <10> Organic electroluminescent element.

<13> The organic electroluminescent element according to any one of <1> to <12>, wherein the luminescent dopant is a phosphorescent material.
<14> When the lowest excited triplet energy level of the luminescent dopant is T ₁ (D), and the lowest excited triplet energy level of the plurality of host compounds is T1 (H) min. The organic electroluminescent element according to any one of <1> to <13>, wherein T ₁ (H) min> T ₁ (D) is satisfied.

<15> Any one of the above <1> to <14>, wherein the light emitting dopant has a lowest excited triplet energy level T ₁ (D) of 251 kJ / mol (60 kcal / mol) or more. The organic electroluminescent element of description.
<16> Any one of the above <1> to <15>, wherein the light emitting dopant has a lowest excited triplet energy level T ₁ (D) of 272 kJ / mol (65 kcal / mol) or more. The organic electroluminescent element of description.

<17> Any one of <1> and <3> to <16>, wherein an ionization potential of the compound forming the hole transporting intermediate layer is 5.6 eV or more and 5.8 eV or less. The organic electroluminescent element according to item.
<18> The organic material according to any one of <2> to <16>, wherein an electron affinity of the compound forming the electron transporting intermediate layer is 2.8 eV or more and 3.1 eV or less. Electroluminescent device.
<19> The ionization potential of the compound forming the hole transporting intermediate layer is 5.6 eV to 5.8 eV, and the electron affinity of the compound forming the electron transporting intermediate layer is 2.8 eV to 3. It is 1 eV, The organic electroluminescent element as described in any one of said <3>-<16> characterized by the above-mentioned.
<20> The above <1> to <19>, wherein the content of the plurality of host compounds is 15% by mass or more and 85% by mass or less with respect to the total compound mass forming the light emitting layer, respectively. The organic electroluminescent element as described in any one.

<21> The organic electroluminescent element according to any one of <1> and <3> to <20>, wherein the hole transporting intermediate layer has a thickness of 1 nm to 10 nm. .
<22> The organic electroluminescent element as described in any one of <2> to <21>, wherein the electron-transporting intermediate layer has a thickness of 1 nm to 10 nm.
<23> The organic electroluminescent element according to any one of <1> to <22>, wherein the light emitting layer has a thickness of 5 nm to 20 nm.

  ADVANTAGE OF THE INVENTION According to this invention, the organic electroluminescent element which can make high luminous efficiency and high drive durability compatible, and can drive a low voltage can be provided.

  Hereinafter, the organic electroluminescence device of the present invention will be described in detail. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

In the first aspect of the present invention, a hole transport layer containing at least one kind of hole transport material, a light emitting layer containing at least one light emitting dopant and a plurality of host compounds, and at least one kind between a pair of electrodes An organic electroluminescent device having an electron transport layer containing an electron transport material,
Among the plurality of host compounds, at least one is a hole transporting host compound and at least one is an electron transporting host compound, and the hole transport is performed between the hole transporting layer and the light emitting layer. An organic electroluminescent device comprising a hole transporting intermediate layer composed only of the same compound as the conductive host compound.

  According to a second aspect of the present invention, a hole transport layer containing at least one kind of hole transport material, a light emitting layer containing at least one light emitting dopant and a plurality of host compounds, and at least one kind between a pair of electrodes. An organic electroluminescent device comprising an electron transport layer, wherein at least one of the plurality of host compounds is a hole transporting host compound, and at least one is an electron transporting host compound. And an organic electroluminescent element comprising an electron transporting intermediate layer made of only the same compound as the electron transporting host compound between the electron transporting layer and the light emitting layer.

  According to a third aspect of the present invention, a hole transport layer containing at least one kind of hole transport material, a light emitting layer containing at least one kind of luminescent dopant and a plurality of host compounds, and at least one kind between a pair of electrodes. An organic electroluminescent device comprising an electron transport layer, wherein at least one of the plurality of host compounds is a hole transporting host compound, and at least one is an electron transporting host compound. And having a hole transporting intermediate layer composed only of the same compound as the hole transporting host compound between the hole transporting layer and the light emitting layer, between the electron transporting layer and the light emitting layer. And an organic electroluminescent element comprising an electron transporting intermediate layer composed of only the same compound as the electron transporting host compound.

  The organic electroluminescent device of the present invention can achieve both high luminous efficiency and high driving durability by using the configuration of the first, second, or third aspect, and reduce the driving voltage. Is possible. Among the first, second, and third modes, the third mode is more preferable from the viewpoints of improving luminous efficiency, improving driving durability, and reducing driving voltage.

  The hole transporting intermediate layer in the present invention is preferably formed as an anode side adjacent layer of the light emitting layer. Moreover, it is preferable that the electron transport intermediate | middle layer in this invention is formed as a cathode side adjacent layer of a light emitting layer. The configuration of the organic electroluminescent element of the present invention will be described in detail later.

In the present invention, the content of the light-emitting dopant and the plurality of host compounds in the light-emitting layer may be a mode in which the light-emitting dopant is present in the entire region composed of the plurality of host compounds. The aspect which is a part of area | region which consists of a some host compound may be sufficient. The light emitting layer in the present invention includes any of the above-described inclusion modes.
Here, “part” means a region at either the end or the center of a region composed of a plurality of host compounds (relative to the thickness direction of the organic compound layer), preferably from a plurality of host compounds. The central portion of the region is more preferably 10% or more and less than 95%, further preferably 30% or more and less than 90%, particularly preferably 50% or more and less than 90%. In the light emitting layer, the concentration region (increase) of exciton density at the interface can be avoided because the region where the light emitting dopant exists is located in the center of the region composed of a plurality of host compounds.

  In the organic electroluminescent device of the present invention, when the ionization potential of the luminescent dopant is Ip (D) and the minimum of the ionization potentials of the plurality of host compounds is Ip (H) min, ΔIp = Ip It is preferable that ΔIp defined by (D) −Ip (H) min satisfy the relationship ΔIp> 0 eV.

Further, when the electron affinity of the luminescent dopant is Ea (D) and the maximum electron affinity of the plurality of host compounds is Ea (H) max, ΔEa = Ea (H) max−Ea ( It is preferable that ΔEa defined in D) satisfy the relationship ΔEa> 0 eV.
More preferably, ΔIp satisfies the relationship ΔIp> 0 eV, and ΔEa satisfies the relationship ΔEa> 0 eV.

  Furthermore, in the organic electroluminescent device of the present invention, the ΔIp satisfies the relationship of 1.2 eV> ΔIp> 0.2 eV and / or the ΔEa satisfies the relationship of 1.2 eV> ΔEa> 0.2 eV. In particular, it is preferable that the ΔIp satisfies a relationship of 1.2 eV> ΔIp> 0.4 eV and / or the ΔEa satisfies a relationship of 1.2 eV> ΔEa> 0.4 eV.

  The organic electroluminescent device of the present invention is configured such that the relationship of ΔIp and / or ΔEa satisfies the above conditions, thereby reducing the carrier injection barrier to the light emitting layer, thereby reducing the driving voltage, Since the carrier is mainly injected into the host material, the luminescent dopant can be suppressed from being deteriorated by the carrier, so that the durability can be improved.

  Furthermore, in the organic electroluminescent element of the present invention, the Ip (H) min is preferably 5.1 eV or more and 6.3 eV or less, and the Ip (H) min is 5.4 eV or more and 6.1 eV or less. Is more preferable, and the Ip (H) min is more preferably 5.6 eV or more and 5.8 eV or less.

In the organic electroluminescent device of the present invention, the Ea (H) max is preferably 2.6 eV or more and 3.3 eV or less, and the Ea (H) max is 2.8 eV or more and 3.2 eV or less. More preferably, the Ea (H) max is more preferably 2.8 eV or more and 3.1 eV or less.
Particularly preferably, the Ip (H) min is 5.6 eV or more and 5.8 eV or less, and the Ea (H) max is 2.8 eV or more and 3.1 eV or less.

One effect of satisfying such a condition is that hole injection or electron injection from the hole transporting intermediate layer and / or the electron transporting intermediate to the light emitting layer is likely to occur. Is possible.
Another effect is that the interaction between a plurality of host compounds in the light emitting layer is suppressed.
That is, when a charge transfer complex or exciplex having a lower excitation energy state is formed as a result of the interaction between a plurality of host compounds, the excited state that should originally be generated in any of the host compounds is the charge transfer. Energy transfer occurs in the charge transfer complex or exciplex from the excited state of the host compound once formed on the complex or exciplex. As a result, energy transfer to the luminescent dopant becomes insufficient, and predetermined light emission may not be obtained. Moreover, it is because there exists a concern about a drive durability fall by decomposition | disassembly from an excited state on a charge transfer complex and an exciplex.

Whether there is an interaction between a plurality of host compounds in the light emitting layer is determined by forming a single layer film consisting only of a plurality of host compounds contained in the light emitting layer in the same manner as the formation conditions of the light emitting layer, This can be determined by measuring the emission spectrum (fluorescence / phosphorescence spectrum) and comparing the obtained emission spectrum (fluorescence / phosphorescence spectrum) with the emission spectrum that each of the plurality of host compounds shows independently.
In other words, in the obtained emission spectrum (fluorescence / phosphorescence spectrum), if a long-wave emission spectrum component that cannot be attributed to each emission spectrum contained in a plurality of host compounds is observed, an interaction has occurred. Conceivable. In the present invention, it is particularly preferable that no emission spectrum component is observed on the longer wavelength side by 15 nm or more than any of the main peaks of the emission spectra of a plurality of host compounds alone.
For the measurement of the emission spectrum (fluorescence / phosphorescence spectrum), for example, RF-5300PC manufactured by Shimadzu Corporation can be used. As excitation light for measurement, light having a wavelength that each host compound has absorption alone is used. The measurement is performed at 25 ° C. in a nitrogen atmosphere.

Here, the ionization potential (Ip), electron affinity (Ea), and triplet state level (T ₁ ) in the present invention will be described.
The ionization potential (Ip), electron affinity (Ea), and triplet state level (T ₁ ) are values obtained by measuring a single layer film obtained by depositing each material on quartz by a vacuum deposition method. .
The ionization potential (Ip) is defined by a value measured at room temperature and in the atmosphere with an ultraviolet photoelectron analyzer “AC-1” or “AC-3” (manufactured by Riken Keiki Co., Ltd.). The measurement principle of the ultraviolet photoelectron analyzer is described in Chiba Adachi et al., “Collection of Organic Thin Film Work Function Data”, issued by CMC Publishing Co., Ltd. 2004.

  The electron affinity (Ea) is defined by a value obtained by calculating the band gap from the long wave end of the absorption spectrum of the single layer film and calculating the electron affinity (Ea) from the value of the ionization potential.

The lowest triplet excitation energy (triplet state level (T ₁ )) is defined by a value calculated from the short wave end of a phosphorescence emission spectrum measured at room temperature. Measurements can also be made at liquid nitrogen cooling temperatures.

As a factor that the light emitting device of the present invention is remarkably excellent in driving durability, it is presumed that the following light emitting mechanism is functioning.
That is, most of the holes injected from the anode are injected into the hole transporting host in the light emitting layer via the hole injection layer and the hole transport layer. On the other hand, most of the electrons injected from the cathode are injected into the electron transporting host in the light emitting layer via the electron injection layer and the electron transport layer. Holes are injected from the hole transporting host in the light emitting layer into the HOMO of the electron transporting host, and excitons are generated on the electron transporting host. Alternatively, electrons are injected from the electron transporting host into the LUMO of the hole transporting host, and excitons are generated on the hole transporting host. The excited state energy of the host moves to the luminescent dopant and emits light from the singlet and / or triplet state of the dopant.
Here, when holes and electrons are injected into the light-emitting layer, holes are mainly injected into the hole-transporting host and electrons are mainly injected into the electron-transporting host. Therefore, the electron transporting host can be released from the cationic state, and as a result, driving durability can be improved. In addition, when holes and electrons are injected into the light emitting layer, HOMO and LUMO of the light emitting dopant are formed by the hole transporting host and the electron transporting host, and Ip (H) min and Ea (H) max. Since it is on the outside, almost no carriers are injected into the dopant, and it is considered that deterioration of the light-emitting dopant having low resistance to cations or anions can be suppressed, and durability can be improved.

As another factor that the light emitting device of the present invention is remarkably excellent in driving durability, it is presumed as follows.
That is, by having a hole transporting intermediate layer composed of only the same compound as the hole transporting host between the hole transporting layer and the light emitting layer, the hole transporting intermediate layer material and the holes in the light emitting layer are provided. Ip difference from the transportable host does not occur, hole injection into the light emitting layer is facilitated, and at the interface between the light emitting layer and the anode side adjacent layer rather than the structure in which the hole transport layer and the light emitting layer are in direct contact with each other It is considered that the concentration of holes becomes difficult to occur, and this can suppress deterioration.
Similarly, by having an electron transporting intermediate layer made of only the same compound as the electron transporting host between the electron transporting layer and the light emitting layer, the electron transporting intermediate layer material and the electron transporting host in the light emitting layer Ea difference does not occur, and it becomes easier to inject electrons into the light emitting layer, and the concentration of electrons at the interface between the light emitting layer and its cathode side adjacent layer is less likely to occur than in the structure in which the electron transport layer and the light emitting layer are in direct contact. This is considered to be because the deterioration of the element can be suppressed.

As described in JP-A-2002-313584, the effect of suppressing carrier concentration at the interface is a mixture in which a hole transport material and an electron transport material are mixed at a constant ratio as a layer adjacent to the light emitting layer. Although there is a possibility of expression even by providing a layer, this element configuration causes the following problems.
For one, carrier leakage is likely to occur from the light-emitting layer, and the light-emitting efficiency is lowered by reducing the probability of recombination of holes and electrons. This is because a hole transporting material with a small Ip is included on the cathode side adjacent to the light emitting layer, so that holes are likely to leak, and since there is an electron transport material on the anode side adjacent to the light emitting layer, electrons leak. It is presumed to be easier.
On the other hand, in the present invention, a layer containing only an electron transporting material having a large Ip (low HOMO) (electron transporting intermediate layer) exists on the cathode side adjacent to the light emitting layer, and an anode adjacent to the light emitting layer is present. Since a layer containing only a hole transporting material having a small Ea (high LUMO) (hole transporting intermediate layer) exists on the side, both holes and electrons are difficult to leak from the light emitting layer. Thereby, it is considered that the recombination probability of holes and electrons in the light emitting layer is increased, and highly efficient light emission is possible.

In the light emitting device of the present invention, the factors that can reduce the drive voltage are estimated as follows.
That is, by having a hole transporting intermediate layer composed of only the same compound as the hole transporting host between the hole transporting layer and the light emitting layer, the hole transporting intermediate layer material and the holes in the light emitting layer are provided. Since there is no Ip difference with the transporting host, it is considered that there is no hole injection barrier to the light emitting layer, hole injection becomes easy, and low voltage driving is possible.
Similarly, by having an electron transporting intermediate layer made of only the same compound as the electron transporting host between the electron transporting layer and the light emitting layer, the electron transporting intermediate layer material and the electron transporting host in the light emitting layer Therefore, it is considered that there is no electron injection barrier to the light emitting layer, electron injection becomes easy, and low voltage driving is possible.

Here, when the hole transporting intermediate layer is a layer in which a hole transporting material and an electron transporting material are mixed as disclosed in JP-A-2002-313584, the electron transporting material is mixed. Since the hole mobility is lowered, the voltage applied to this layer is increased. Similarly, if the electron transporting intermediate layer is a layer in which a hole transporting material and an electron transporting material are mixed, the electron mobility decreases due to the mixing of the hole transporting material. However, a sufficient low voltage effect cannot be obtained.
As described above, the technique disclosed in Japanese Patent Laid-Open No. 2002-313584 is not sufficient, although the effect of reducing power consumption is sought.
On the other hand, the organic electroluminescence device of the present invention achieves improvement in luminous efficiency, improvement in driving durability, and reduction in driving voltage at the same time.

Next, the structure in the organic electroluminescent element of this invention is demonstrated.
The organic electroluminescent element of the present invention has an organic compound layer including at least a light emitting layer between a pair of electrodes (anode and cathode), and further includes a hole transport layer between the anode and the light emitting layer, and a cathode. An electron transport layer is provided between the light-emitting layer.
In the present invention, the organic compound layer is preferably laminated in the order of the hole transport layer, the light emitting layer, and the electron transport layer from the anode side.
Further, a hole injection layer may be provided between the anode and the hole transport layer, and similarly, an electron injection layer may be provided between the cathode and the electron transport layer.
Furthermore, in the present invention, a hole transporting intermediate layer is provided between the hole transporting layer and the light emitting layer, and / or an electron transporting intermediate layer is provided between the light emitting layer and the electron transporting layer. It is.
From the nature of the light emitting element, it is preferable that at least one of the pair of electrodes is transparent.

  A preferred embodiment of the organic compound layer in the organic electroluminescence device of the present invention is, in order from the anode side, at least (1) a hole injection layer, a hole transport layer (the hole injection layer and the hole transport layer may serve as both). Good), a hole transporting intermediate layer, a light-emitting layer, an electron transport layer, and an electron injection layer (the electron transport layer and the electron injection layer may serve both), (2) hole injection layer, hole Transport layer (hole injection layer and hole transport layer may double), light-emitting layer, electron transport intermediate layer, electron transport layer, and electron injection layer (electron transport layer and electron injection layer may double) (3) a hole injection layer, a hole transport layer (a hole injection layer and a hole transport layer may serve both), a hole transport intermediate layer, a light emitting layer, an electron transport intermediate layer, It is an aspect which has an electron carrying layer and an electron injection layer (an electron carrying layer and an electron injection layer may serve as both).

The hole-transporting intermediate layer preferably has a function of promoting hole injection into the light-emitting layer and / or a function of blocking electrons.
Further, the electron transporting intermediate layer preferably has a function of promoting electron injection into the light emitting layer and / or a function of blocking holes.
Furthermore, the hole transporting intermediate layer and / or the electron transporting intermediate layer preferably has a function of blocking excitons generated in the light emitting layer.
In order to effectively express the functions of hole injection promotion, electron injection promotion, hole block, electron block, and exciton block, the hole transporting intermediate layer and the electron transporting intermediate layer are light emitting layers. It is preferable that it adjoins.
Each layer may be divided into a plurality of secondary layers.

Next, the elements constituting the organic electroluminescent element of the present invention will be described in more detail.
<Organic compound layer>
The organic compound layer in the present invention will be described.
The organic electroluminescent element of the present invention has an organic compound layer including at least one light emitting layer. As the organic compound layer other than the light emitting layer, as described above, a hole injection layer, a hole transport layer, and the like. , Hole transporting intermediate layer, light emitting layer, electron transporting intermediate layer, electron transporting layer, electron injection layer and the like.

-Formation of organic compound layer-
In the organic electroluminescent element of the present invention, each layer constituting the organic compound layer is preferably formed by any of dry film forming methods such as vapor deposition and sputtering, transfer methods, printing methods, coating methods, ink jet methods, and spray methods. Can be formed.

(Light emitting layer)
The light emitting layer receives holes from the anode, the hole injection layer, the hole transport layer, or the hole transport intermediate layer when an electric field is applied, and receives electrons from the cathode, the electron injection layer, the electron transport layer, or the electron transport intermediate layer. And a layer having a function of emitting light by providing a recombination field of holes and electrons.
The light emitting layer in the present invention contains at least one light emitting dopant and a plurality of host compounds.
Further, the light emitting layer may be a single layer or two or more layers, and each layer may emit light in different emission colors. Even when there are a plurality of light-emitting layers, it is preferable that each layer of the light-emitting layer contains at least one light-emitting dopant and a plurality of host compounds.

In the luminescent dopant contained in the light emitting layer and the plurality of host compounds in the present invention, it is preferable to satisfy the relationship of the following relationship (1).
Relationship (1): ΔIp (= Ip (D) −Ip (H) min)> 0 eV and / or ΔEa (= Ea (H) max−Ea (D))> 0 eV
That is, a phosphorescent dopant and a plurality of hosts that can emit light (phosphorescence) from a triplet exciton even in a combination of a fluorescence emitting dopant that can emit light (fluorescence) from a singlet exciton and a plurality of host compounds. A combination with a compound may be used, but among these, a combination of a phosphorescent dopant and a plurality of host compounds is preferable from the viewpoint of luminous efficiency.
The light emitting layer in the present invention can contain two or more kinds of light emitting dopants in order to improve color purity and to broaden the light emission wavelength region.

In the present invention, the luminescent dopant and the plurality of host compounds satisfying the relationship (1) will be described below.
When one luminescent dopant is used and a plurality of host compounds are used, Ip (D) of the luminescent dopant is larger than one ionization potential Ip (H) min of the host compound, that is, Ip (D)> Ip (H ) Satisfy the relationship of min and / or Ea (D) is smaller than the electron affinity Ea (H) max of the other host compound, that is, satisfy the relationship of Ea (H) max> Ea (D). preferable.
The host compound used as Ip (H) min at this time includes a hole transporting host compound, and the host compound used as Ea (H) max includes an electron transporting host compound.
When a plurality of light-emitting dopants are used, Ip (D) means the dopant having the smallest Ip, and Ea (D) means the dopant having the largest Ea.

-Luminescent dopant-
As the luminescent dopant in the present invention, any phosphorescent luminescent material, fluorescent luminescent material, etc. can be used as long as the relationship (1) is satisfied between the luminescent dopant and a plurality of host compounds. .
The luminescent dopant in the present invention is a dopant that further satisfies the relationship (2): 1.2 eV>ΔIp> 0.2 eV and / or 1.2 eV>ΔEa> 0.2 eV with the host compound. Is preferable from the viewpoint of driving durability.

In the luminescent dopant in the present invention, the lowest excited triplet energy level T ₁ (D) is preferably 251 kJ / mol (60 kcal / mol) or more, more preferably 272 kJ / mol (65 kcal / mol) or more. It is preferably 276 kJ / mol (66 kcal / mol) or more.

= Phosphorescent dopant =
In general, examples of the phosphorescent light-emitting dopant (phosphorescent dopant) include complexes containing a transition metal atom or a lanthanoid atom.
For example, the transition metal atom is not particularly limited, but preferably includes ruthenium, rhodium, palladium, tungsten, rhenium, osmium, iridium, and platinum, more preferably rhenium, iridium, and platinum. Preferred are iridium and platinum.
Examples of the lanthanoid atom include lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Among these lanthanoid atoms, neodymium, europium, and gadolinium are preferable.

Examples of the ligand of the complex include G.I. Wilkinson et al., Comprehensive Coordination Chemistry, Pergamon Press, 1987, H.C. Examples include ligands described in Yersin's "Photochemistry and Photophysics of Coordination Compounds" published by Springer-Verlag 1987, Akio Yamamoto "Organic Metal Chemistry-Fundamentals and Applications-" .
Specific ligands preferably include halogen ligands (preferably chlorine ligands), aromatic carbocyclic ligands (eg, cyclopentadienyl anion, benzene anion, naphthyl anion, etc.), Nitrogen heterocyclic ligands (eg, phenylpyridine, benzoquinoline, quinolinol, bipyridyl, phenanthroline, etc.), diketone ligands (eg, acetylacetone, etc.), carboxylic acid ligands (eg, acetic acid ligands, etc.), alcoholates A ligand (for example, a phenolate ligand), a carbon monoxide ligand, an isonitrile ligand, and a cyano ligand, and more preferably a nitrogen-containing heterocyclic ligand.
The complex may have one transition metal atom in the compound, or may be a so-called binuclear complex having two or more. Different metal atoms may be contained at the same time.

  Among these, specific examples of the luminescent dopant satisfying the relationship (1) include, for example, the specifications of US Pat. Nos. 6,303,238B1 and 6,097,147, and International Publication No. 00. / 57676, 00/70655, 01/08230, 01 / 39234A2, 01 / 41512A1, 02 / 02714A2, 02 / 15645A1, 02 / 44189A1, pamphlets, special Japanese Patent Application No. 2001-247859, Japanese Patent Application No. 2000-33561, Japanese Patent Application Laid-Open No. 2002-117978, Japanese Patent Application No. 2001-248165, Japanese Patent Application No. 2002-2335076, Japanese Patent Application No. 2001-239281, Japanese Patent Application Laid-Open No. 2002-170684, Europe Japanese Patent No. 12112257, Japanese Patent Application Laid-Open No. 2002-226495, Japanese Patent Application Laid-Open No. 02-234894, JP 2001-247659, JP 2001-298470, JP 2002-173675, JP 2002-203678, JP 2002-203679, JP 2003-157066, JP 2005-75340, JP Examples include phosphorescent compounds described in patent documents such as the specifications of Japanese Patent Application No. 2005-75341.

  As the luminescent dopant satisfying the relationship (2), Ir complex, Pt complex, Cu complex, Re complex, W complex, Rh complex, Ru complex, Pd complex, Os complex, Eu complex, Tb complex, Gd complex, Dy Complex and Ce complex are mentioned. Particularly preferred are Ir complexes, Pt complexes, and Re complexes. Among them, Ir complexes, Pt complexes, which include at least one coordination mode of metal-carbon bond, metal-nitrogen bond, metal-oxygen bond, and metal-sulfur bond, Re complexes are preferred.

= Fluorescent dopant =
As the fluorescent luminescent dopant (fluorescent luminescent dopant), generally, benzoxazole, benzimidazole, benzothiazole, styrylbenzene, polyphenyl, diphenylbutadiene, tetraphenylbutadiene, naphthalimide, coumarin, pyran, perinone, Oxadiazole, aldazine, pyralidine, cyclopentadiene, bisstyrylanthracene, quinacridone, pyrrolopyridine, thiadiazolopyridine, cyclopentadiene, styrylamine, aromatic dimethylidin compounds, condensed polycyclic aromatic compounds (anthracene, phenanthroline, pyrene, perylene) , Rubrene, pentacene, etc.), 8-quinolinol metal complexes, pyromethene complexes and various metal complexes represented by rare earth complexes, polythiophene, polyphenyle , Polyphenylene vinylene polymer compounds such as organosilanes, and the like can be given their derivatives.

  Among these, specific examples of the luminescent dopant satisfying the relationship (1) include the following compounds (D-1 to D-25), but are not limited thereto.

  Among the above, the luminescent dopant used in the present invention is D-2, D-3, D-4, D-5, D-6, D-7, D-8, from the viewpoint of luminous efficiency and durability. D-9, D-10, D-11, D-12, D-13, D-14, D-15, D-16, D-21, D-22, D-23, D-24, D- 25, D-2, D-3, D-4, D-5, D-6, D-7, D-8, D-12, D-14, D-15, D-16, D- 21, D-22, D-23, and D-24 are more preferable, and D-21, D-22, D-23, and D-24 are still more preferable.

  The light-emitting dopant in the light-emitting layer is preferably contained in an amount of 0.1 to 30% by mass with respect to the total mass of the compound generally forming the light-emitting layer in the light-emitting layer, from the viewpoint of durability and light emission efficiency. The content is more preferably 1 to 15% by mass, and further preferably 2 to 12% by mass.

  Although the thickness of the light emitting layer is not particularly limited, it is usually preferably 1 nm to 500 nm, more preferably 5 nm to 200 nm, and more preferably 5 nm to 100 nm from the viewpoint of light emission efficiency. More preferably, the thickness is 5 nm to 20 nm.

-Host compound-
The light emitting layer in the present invention is a light emitting layer containing at least one light emitting dopant and a plurality of host compounds. As the plurality of host compounds, a hole-transporting host compound having excellent hole-transporting properties (hereinafter referred to as “hole-transporting host” as appropriate) and an electron-transporting host compound having excellent electron-transporting properties (hereinafter referred to as appropriate). Each of which is referred to as an “electron transporting host”.
Moreover, as a some host compound, what satisfy | fills the said relationship (1) is preferable, and it can select in consideration of the relationship with a luminescent dopant, etc. from what satisfy | fills this relationship. Among host compounds satisfying the range of the relationship (1), a host compound satisfying the relationship (2) is more preferable.

= Hole-transporting host =
In the present invention, the hole-transporting host contained in the light emitting layer is preferably one that satisfies the relationship (1). Depending on the relationship with the luminescent dopant, the ionization potential Ip is preferably 5.1 eV or more and 6.3 eV or less from the viewpoint of durability improvement and driving voltage reduction. More preferably, it is 5.6 eV or more and 5.8 eV or less. Further, from the viewpoint of improving durability and lowering driving voltage, the electron affinity Ea is preferably 1.2 eV or more and 3.1 eV or less, more preferably 1.4 eV or more and 3.0 eV or less, and 1.8 eV or more. More preferably, it is 2.8 eV or less.

Specific examples of the hole transporting host that satisfies the relationship (1) include the following materials.
Pyrrole, carbazole, triazole, oxazole, oxadiazole, pyrazole, imidazole, polyarylalkane, pyrazoline, pyrazolone, phenylenediamine, arylamine, amino-substituted chalcone, styrylanthracene, fluorenone, hydrazone, stilbene, silazane, aromatic tertiary Amine compounds, styrylamine compounds, aromatic dimethylidin compounds, porphyrin compounds, polysilane compounds, poly (N-vinylcarbazole), aniline copolymers, thiophene oligomer thiophene oligomers, conductive polymer oligomers such as polythiophene, organic Examples thereof include silane, carbon film, and derivatives thereof.
Among these, as the hole-transporting host satisfying the relationship (2), carbazole derivatives, aromatic tertiary amine compounds, and thiophene derivatives are preferable, and in particular, a plurality of carbazole skeletons and / or aromatic tertiary amine skeletons are included in the molecule. Those having one are preferred.
Specific examples of the hole transporting host include, but are not limited to, the following compounds (H-1 to H-23).

= Electron transporting host =
As the electron transporting host in the light emitting layer used in the present invention, those satisfying the relationship (1) are preferable. Although it depends on the relationship with the luminescent dopant, the electron affinity Ea is preferably 2.5 eV or more and 3.5 eV or less from the viewpoint of improving durability and lowering driving voltage, among which 2.6 eV or more and 3.2 eV. More preferably, it is more preferably 2.8 eV or more and 3.1 eV or less. Further, from the viewpoint of improving durability and reducing driving voltage, the ionization potential Ip is preferably 5.7 eV or more and 7.5 eV or less, more preferably 5.8 eV or more and 7.0 eV or less, and 5.9 eV or more. More preferably, it is 6.5 eV or less.

Specific examples of such an electron transporting host include the following materials.
Pyridine, pyrimidine, triazine, imidazole, pyrazole, triazole, oxazole, oxadiazol, fluorenone, anthraquinodimethane, anthrone, diphenylquinone, thiopyran dioxide, carbodiimide, fluorenylidenemethane, distyrylpyrazine, Fluorine-substituted aromatic compounds, heterocyclic tetracarboxylic anhydrides such as naphthaleneperylene, phthalocyanines, and derivatives thereof (which may form condensed rings with other rings), metal complexes and metals of 8-quinolinol derivatives Examples thereof include various metal complexes represented by metal complexes having phthalocyanine, benzoxazole or benzothiazol as a ligand.

Preferred examples of the electron transporting host include metal complexes, azole derivatives (benzimidazole derivatives, imidazopyridine derivatives, etc.), and azine derivatives (pyridine derivatives, pyrimidine derivatives, triazine derivatives, etc.). To metal complex compounds are preferred. The metal complex compound (A) is more preferably a metal complex having a ligand having at least one nitrogen atom, oxygen atom or sulfur atom coordinated to the metal.
The metal ion in the metal complex is not particularly limited, but is preferably beryllium ion, magnesium ion, aluminum ion, gallium ion, zinc ion, indium ion, tin ion, platinum ion, palladium ion, more preferably beryllium ion, aluminum. Ion, gallium ion, zinc ion, platinum ion, and palladium ion, and more preferably aluminum ion, zinc ion, and palladium ion.

  There are various known ligands contained in the metal complex. For example, “Photochemistry and Photophysics of Coordination Compounds” Springer-Verlag H. Examples include ligands described in Yersin's 1987 issue, “Organometallic Chemistry: Fundamentals and Applications”, Hankabo Publishing Company, Akio Yamamoto, 1982 issue, and the like.

The ligand is preferably a nitrogen-containing heterocyclic ligand (preferably having 1 to 30 carbon atoms, more preferably 2 to 20 carbon atoms, particularly preferably 3 to 15 carbon atoms, and a monodentate ligand. Alternatively, it may be a bidentate or higher ligand, preferably a bidentate or higher and a hexadentate or lower ligand, or a bidentate or higher and lower 6 or lower ligand and a monodentate mixed ligand. preferable.
Examples of the ligand include an azine ligand (for example, pyridine ligand, bipyridyl ligand, terpyridine ligand, etc.), a hydroxyphenylazole ligand (for example, hydroxyphenylbenzimidazole coordination). And a hydroxyphenyl benzoxazole ligand, a hydroxyphenyl imidazole ligand, a hydroxyphenylimidazopyridine ligand, etc.), an alkoxy ligand (preferably having 1 to 30 carbon atoms, more preferably 1 carbon atom). To 20, particularly preferably 1 to 10 carbon atoms, such as methoxy, ethoxy, butoxy, 2-ethylhexyloxy), aryloxy ligands (preferably 6 to 30 carbon atoms, more preferably 6-20 carbon atoms, particularly preferably 6-12 carbon atoms, for example phenyl Carboxymethyl, 1-naphthyloxy, 2-naphthyloxy, 2,4,6-trimethylphenyl oxy, and 4-biphenyloxy and the like.),

Heteroaryloxy ligand (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, and examples thereof include pyridyloxy, pyrazyloxy, pyrimidyloxy, quinolyloxy, etc.) An alkylthio ligand (preferably having 1 to 30 carbon atoms, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as methylthio and ethylthio), arylthio ligand ( Preferably, it has 6 to 30 carbon atoms, more preferably 6 to 20 carbon atoms, particularly preferably 6 to 12 carbon atoms, and examples thereof include phenylthio, etc., a heteroarylthio ligand (preferably 1 to 1 carbon atoms). 30, more preferably 1 to 20 carbon atoms, particularly preferably 1 to 12 carbon atoms, such as pyridylthio, 2 Benzimidazolylthio, 2-benzoxazolylthio, 2-benzthiazolylthio, etc.), siloxy ligands (preferably having 1 to 30 carbon atoms, more preferably 3 to 25 carbon atoms, particularly preferably C6-C20, for example, a triphenylsiloxy group, a triethoxysiloxy group, a triisopropylsiloxy group etc.), an aromatic hydrocarbon anion ligand (preferably C6-C30, more preferable) Has 6 to 25 carbon atoms, particularly preferably 6 to 20 carbon atoms, and examples thereof include a phenyl anion, a naphthyl anion, an anthranyl anion, etc.), an aromatic heterocyclic anion ligand (preferably 1 to 30 carbon atoms). , More preferably 2 to 25 carbon atoms, particularly preferably 2 to 20 carbon atoms, such as pyrrole anion, pyr ), An indolenine anion ligand, etc., preferably a nitrogen-containing ligand, an indolenine anion ligand, and the like. Heterocyclic ligand, aryloxy ligand, heteroaryloxy group, siloxy ligand, more preferably nitrogen-containing heterocyclic ligand, aryloxy ligand, siloxy ligand, aromatic hydrocarbon Anionic ligands and aromatic heterocyclic anionic ligands.
Examples of the metal complex electron transporting host include, for example, Japanese Patent Application Laid-Open No. 2002-235076, Japanese Patent Application Laid-Open No. 2004-214179, Japanese Patent Application Laid-Open No. 2004-221106, Japanese Patent Application Laid-Open No. 2004-221068, Japanese Patent Application Laid-Open No. 2004-221313, Japanese Patent Application Laid-Open No. The compound described in each gazette is mentioned.

  Specific examples of such an electron transporting host include, but are not limited to, the following compounds (E-1 to E-22).

  Examples of the electron transporting host satisfying the relationship (2), which is a preferable electron transporting host material in the present invention, include E-1 to E-6, E-8, E-9, E-21, and E-22. Preferably, E-3, E-4, E-6, E-8, E-9, E-10, E-21, E-22 are more preferable, E-3, E-4, E-21, E -22 is more preferable.

In the light emitting layer of the present invention, when a phosphorescent dopant is used as the luminescent dopant, the lowest triplet excitation energy T ₁ (D) of the phosphorescent dopant and the lowest excited triplet energy of the plurality of host compounds It is preferable in terms of color purity, luminous efficiency, and driving durability that the minimum T ₁ (H) min satisfies the relationship of T ₁ (H) min> T ₁ (D).

  In addition, the content of the plurality of host compounds in the present invention is not particularly limited, but from the viewpoint of light emission efficiency and driving voltage, 15% by mass or more and 85% by mass with respect to the total compound mass forming the light emitting layer, respectively. It is preferable that it is below mass%.

The carrier mobility in the light emitting layer is generally 10 ⁻⁷ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less. From the point, it is preferably 10 ⁻⁶ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less, preferably 10 ⁻⁵ cm ² · V ⁻¹ · s ⁻¹ or more. ^-1 cm ² · V ^-1 · s ^-1 or less is more preferable, and 10 ^-4 cm ² · V ^-1 · s ^-1 or more and 10 ^-1 cm ² · V ^-1 · s ^-1 or less is particularly preferable.
The carrier mobility of the light emitting layer is preferably smaller than the carrier mobility of the carrier transport layer (hole transport layer, electron transport layer, etc.) described later, from the viewpoints of light emission efficiency and driving durability.
The carrier mobility was measured by the Time of Flight method, and the obtained value was defined as the carrier mobility.

(Hole transporting intermediate layer)
As described above, the hole transporting intermediate layer according to the present invention includes only the same compound as the hole transporting host among the plurality of host materials included in the light emitting layer, and the hole transporting layer, the light emitting layer, It is a layer formed between.
The details of the compound forming the hole transporting intermediate layer are the same as those described above as the hole transporting host used in the light emitting layer.
The thickness of the hole transporting intermediate layer is preferably 1 nm or more and 10 nm or less, more preferably 2 nm or more and 8 nm or less, more preferably 3 nm or more, from the viewpoints of driving voltage reduction, light emission efficiency improvement, and durability improvement. More preferably, it is 5 nm or less.

(Electron transporting intermediate layer)
As described above, the electron transporting intermediate layer in the present invention uses only the same compound as the electron transporting host among the plurality of host materials contained in the light emitting layer, and is between the electron transporting layer and the light emitting layer. It is a layer to be formed.
The details of the compound forming the electron transporting intermediate layer are the same as those described above as the electron transporting host used in the light emitting layer.
The thickness of the electron transporting intermediate layer is preferably from 1 nm to 10 nm, more preferably from 2 nm to 8 nm, more preferably from 3 nm to 5 nm, from the viewpoints of lowering driving voltage, improving luminous efficiency, and improving durability. More preferably, it is as follows.

(Hole injection layer, hole transport layer)
The hole injection layer and the hole transport layer are layers having a function of receiving holes from the anode or the anode side and transporting them to the cathode side.
Specifically, the hole injection layer and the hole transport layer are pyrrole derivatives, carbazole derivatives, pyrazole derivatives, triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, Phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, thiophene derivatives, silazane derivatives, aromatic tertiary amine compounds, styrylamine compounds, aromatic dimethylidin compounds, A layer containing a porphyrin compound, a phthalocyanine compound, an organic silane derivative, carbon, or the like is preferable.

Among the materials for the hole injection layer and the hole transport layer as described above, preferably a pyrrole derivative, a carbazole derivative, a phenylenediamine derivative, an arylamine derivative, a thiophene derivative, and a phthalocyanine compound, more preferably a carbazole derivative, Arylamine derivatives, thiophene derivatives, and phthalocyanine compounds, more preferably, hole injection layer materials are arylamine derivatives, thiophene derivatives, and phthalocyanine compounds, and hole transport layer materials include carbazole derivatives and arylamine derivatives. It is.
The Ip of the hole injection layer material is preferably 4.6 eV or more and 5.8 eV or less, more preferably 4.8 eV or more and 5.6 eV or less, and still more preferably, from the viewpoint of driving voltage reduction, light emission efficiency improvement, and durability improvement. It is 5.1 eV or more and 5.4 eV or less.
In addition, the Ip of the hole transport layer material is preferably 5.1 eV or more and 5.8 eV or less, more preferably 5.2 eV or more and 5.6 eV or less, from the viewpoints of lowering driving voltage, improving luminous efficiency, and improving durability. Preferably they are 5.2 eV or more and 5.5 eV or less.

The thicknesses of the hole injection layer and the hole transport layer are not particularly limited, but the thickness is preferably 1 nm to 5 μm from the viewpoint of driving voltage reduction, light emission efficiency improvement, durability improvement, The thickness is further preferably 5 nm to 1 μm, and particularly preferably 10 nm to 500 nm.
Note that the driving voltage of the hole injection layer and the hole transport layer can be reduced by chemical doping or the like.
The hole injection layer and the hole transport layer may have a single-layer structure composed of one or more of the materials described above, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions. .

From the viewpoint of driving durability, it is preferable that Ip (HTL) of the hole transport layer is smaller than Ip (D) of the luminescent dopant contained in the light emitting layer.
The Ip (HTL) in the hole transport layer can be measured by the Ip measurement method.

In addition, the carrier mobility in the hole transport layer is generally 10 ⁻⁷ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less. From the viewpoint of efficiency, it is preferably 10 ⁻⁵ cm ² · V ⁻¹ · s ⁻¹ or more and preferably 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less, and 10 ⁻⁴ cm ² · V ⁻¹ · s ⁻¹ or more. 10 ^-1 cm ² · V ^-1 · s ^-1 or less is more preferable, and 10 ^-3 cm ² · V ^-1 · s ^-1 or more and 10 ^-1 cm ² · V ^-1 · s ^-1 or less is particularly preferable.
As the carrier mobility in the hole transport layer, a value measured by the same method as the method for measuring the carrier mobility of the light emitting layer is adopted.
In addition, the carrier mobility of the hole transport layer is preferably larger than the carrier mobility of the light emitting layer from the viewpoint of driving durability and light emission efficiency.

(Electron injection layer, electron transport layer)
The electron injection layer and the electron transport layer are layers having any one of a function of injecting electrons from the cathode, a function of transporting electrons, and a function of blocking holes that can be injected from the anode.
Specific examples of the material for the electron injection layer and the electron transport layer include pyridine, pyrimidine, triazine, imidazole, triazole, oxazole, oxadiazol, thiazole, thiadiazole, fluorenone, anthraquinodimethane, anthrone, Heterocyclic tetracarboxylic acid anhydrides such as diphenylquinone, thiopyran dioxide, carbodiimide, fluorenylidenemethane, distyrylpyrazine, fluorine-substituted aromatic compounds, naphthaleneperylene, phthalocyanines, siloles and their derivatives (condensed with other rings) A metal complex of an 8-quinolinol derivative, a metal phthalocyanine, a metal complex having a benzoxazole or a benzothiazol as a ligand, and the like. .

Among the materials for the electron injection layer and the electron transport layer as described above, pyridine derivatives, pyrimidine derivatives, pyrazine derivatives, triazine derivatives, imidazole derivatives, triazole derivatives, oxazole derivatives, oxadiazol derivatives, thiazole derivatives, thiadiazoles are preferable. Derivatives, fluorine-substituted aromatic compounds, silole derivatives, metal complexes of 8-quinolinol derivatives (these may form condensed rings with other rings), more preferably pyridine derivatives, pyrimidine derivatives, pyrazine derivatives. , Triazine derivatives, imidazole derivatives, triazole derivatives, silole derivatives, metal complexes of 8-quinolinol derivatives (these may form condensed rings with other rings), more preferably pyridine derivatives, pyrazine derivatives, triazine derivatives , Imi Tetrazole derivatives, triazole derivatives, silole derivatives, metal complexes of 8-quinolinol derivatives (which may form a condensed ring with another ring.).
Ea of the electron injection layer material is preferably 2.5 eV or more and 3.8 eV or less, more preferably 2.8 eV or more and 3.6 eV or less, more preferably 2 from the viewpoint of driving voltage reduction, light emission efficiency improvement, and durability improvement. .8 eV or more and 3.5 eV or less. The Ea of the electron transport layer material is preferably 2.3 eV or more and 3.6 eV or less, more preferably 2.5 eV or more and 3.5 eV or less, and still more preferably, from the viewpoints of driving voltage reduction, light emission efficiency improvement, and durability improvement. Is 2.6 eV or more and 3.3 eV or less.

The thicknesses of the electron injecting layer and the electron transporting layer are not particularly limited, but the thickness is preferably 1 nm to 5 μm from the viewpoint of lowering driving voltage, improving luminous efficiency, and improving durability. It is more preferably 1 μm, and particularly preferably 10 nm to 500 nm.
Note that the driving voltage of the electron injection layer and the electron transport layer can be reduced by chemical doping or the like.
The electron injection layer and the electron transport layer may have a single layer structure composed of one or more of the above-described materials, or may have a multilayer structure composed of a plurality of layers having the same composition or different compositions.

The Ea (ETL) of the electron transport layer is preferably larger than the dopant Ea (D) contained in the light emitting layer from the viewpoint of driving durability.
As Ea (ETL), a value measured by the same method as the method for measuring Ea is used.

The carrier mobility in the electron transport layer is generally 10 ⁻⁷ cm ² · V ⁻¹ · s ⁻¹ or more and 10 ⁻¹ cm ² · V ⁻¹ · s ⁻¹ or less. From the point of 10 ^-5 cm ² · V ^-1 · s ^-1 or more, preferably 10 ^-1 cm ² · V ^-1 · s ^-1 or less, preferably 10 ^-4 cm ² · V ^-1 · s ^-1 or more. ^-1 cm ² · V ^-1 · s ^-1 or less is more preferable, and 10 ^-3 cm ² · V ^-1 · s ^-1 or more and 10 ^-1 cm ² · V ^-1 · s ^-1 or less is particularly preferable.
Moreover, it is preferable from the viewpoint of driving durability that the carrier mobility of the electron transport layer is larger than the carrier mobility of the light emitting layer. The carrier mobility was measured in the same manner as the hole transport layer measurement method.
In the carrier mobility of the light-emitting element in the present invention, the carrier mobility in the hole transport layer, electron transport layer, and light-emitting layer is (electron transport layer ≧ hole transport layer)> light-emitting layer. From the viewpoint of sex.

(Hole blocking layer)
The hole blocking layer is a layer having a function of preventing holes transported from the anode side to the light emitting layer from passing through to the cathode side. In the present invention, a hole blocking layer can be provided as the organic compound layer provided on the cathode side of the light emitting layer. The hole blocking layer is preferably formed between the light-emitting layer and the electron transport layer, and when an electron transport intermediate layer is used, it is preferably formed between the electron transport intermediate layer and the electron transport layer.
Although a hole block layer is not specifically limited, Specifically, aluminum complexes, such as BAlq, a triazole derivative, a pyraza ball derivative, etc. can be contained.
Further, the thickness of the hole blocking layer is generally preferably 50 nm or less, preferably 1 to 50 nm, and more preferably 5 to 40 nm in order to lower the driving voltage.

(anode)
The anode usually has a function as an electrode for supplying holes to the organic compound layer, and there is no particular limitation on the shape, structure, size, etc., depending on the use and purpose of the light-emitting element. , Can be appropriately selected from known electrode materials. As described above, the anode is usually provided as a transparent anode.

  As a material of the anode, for example, a metal, an alloy, a metal oxide, a conductive compound, or a mixture thereof can be suitably cited, and a material having a work function of 4.0 eV or more is preferable. Specific examples of the anode material include conductive metals such as tin oxide (ATO, FTO) doped with antimony or fluorine, tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), etc. Metals such as oxides, gold, silver, chromium, nickel, and mixtures or laminates of these metals and conductive metal oxides, inorganic conductive materials such as copper iodide and copper sulfide, polyaniline, polythiophene, polypyrrole, etc. Organic conductive materials, and a laminate of these and ITO. Among these, conductive metal oxides are preferable, and ITO is particularly preferable from the viewpoints of productivity, high conductivity, transparency, and the like.

  The anode is composed of, for example, a wet method such as a printing method and a coating method, a physical method such as a vacuum deposition method, a sputtering method, and an ion plating method, and a chemical method such as a CVD and a plasma CVD method. It can be formed on the substrate according to a method appropriately selected in consideration of suitability with the material to be processed. For example, when ITO is selected as the anode material, the anode can be formed according to a direct current or high frequency sputtering method, a vacuum deposition method, an ion plating method, or the like.

  In the organic electroluminescent element of the present invention, the formation position of the anode is not particularly limited and can be appropriately selected according to the use and purpose of the light emitting element. The anode may be formed on the entire one surface of the substrate, or may be formed on a part thereof.

  The patterning for forming the anode may be performed by chemical etching such as photolithography, or may be performed by physical etching such as laser, or vacuum deposition or sputtering with a mask overlapped. It may be performed by a lift-off method or a printing method.

  The thickness of the anode can be appropriately selected depending on the material constituting the anode and cannot be generally defined, but is usually about 10 nm to 50 μm, and preferably 50 nm to 20 μm.

The resistance value of the anode is preferably 10 ³ Ω / □ or less, and more preferably 10 ² Ω / □ or less. When the anode is transparent, it may be colorless and transparent or colored and transparent. In order to take out light emission from the transparent anode side, the transmittance is preferably 60% or more, and more preferably 70% or more.

  The transparent anode is described in detail in the book “New Development of Transparent Electrode Films” published by CMC (1999), supervised by Yutaka Sawada, and the matters described here can be applied to the present invention. In the case of using a plastic substrate having low heat resistance, a transparent anode formed using ITO or IZO at a low temperature of 150 ° C. or lower is preferable.

(cathode)
The cathode usually has a function as an electrode for injecting electrons into the organic compound layer, and there is no particular limitation on the shape, structure, size, etc., depending on the use and purpose of the light-emitting element, It can select suitably from well-known electrode materials.

  Examples of the material constituting the cathode include metals, alloys, metal oxides, electrically conductive compounds, and mixtures thereof, and those having a work function of 4.5 eV or less are preferable. Specific examples include alkali metals (eg, Li, Na, K, Cs, etc.), alkaline earth metals (eg, Mg, Ca, etc.), gold, silver, lead, aluminum, sodium-potassium alloys, lithium-aluminum alloys, magnesium. -Rare earth metals such as silver alloys, indium, ytterbium, and the like. These may be used alone, but two or more can be suitably used in combination from the viewpoint of achieving both stability and electron injection.

Among these, as a material constituting the cathode, an alkali metal or an alkaline earth metal is preferable from the viewpoint of electron injecting property, and a material mainly composed of aluminum is preferable from the viewpoint of excellent storage stability.
The material mainly composed of aluminum is aluminum alone, an alloy of aluminum and 0.01 to 10% by mass of alkali metal or alkaline earth metal, or a mixture thereof (for example, lithium-aluminum alloy, magnesium-aluminum alloy, etc.) Say.

  The materials for the cathode are described in detail in JP-A-2-15595 and JP-A-5-121172, and the materials described in these public relations can also be applied in the present invention.

  There is no restriction | limiting in particular about the formation method of a cathode, According to a well-known method, it can carry out. For example, the cathode described above is configured from a wet method such as a printing method or a coating method, a physical method such as a vacuum deposition method, a sputtering method, or an ion plating method, or a chemical method such as CVD or plasma CVD method. It can be formed according to a method appropriately selected in consideration of suitability with the material. For example, when a metal or the like is selected as the cathode material, one or more of them can be simultaneously or sequentially performed according to a sputtering method or the like.

  Patterning when forming the cathode may be performed by chemical etching such as photolithography, physical etching by laser, or the like, or by vacuum deposition or sputtering with the mask overlaid. It may be performed by a lift-off method or a printing method.

In the present invention, the cathode formation position is not particularly limited, and may be formed on the entire organic compound layer or a part thereof.
Further, a dielectric layer made of an alkali metal or alkaline earth metal fluoride or oxide may be inserted between the cathode and the organic compound layer with a thickness of 0.1 to 5 nm. This dielectric layer can also be regarded as a kind of electron injection layer. The dielectric layer can be formed by, for example, a vacuum deposition method, a sputtering method, an ion plating method, or the like.

The thickness of the cathode can be appropriately selected depending on the material constituting the cathode and cannot be generally defined, but is usually about 10 nm to 5 μm, and preferably 50 nm to 1 μm.
Further, the cathode may be transparent or opaque. The transparent cathode can be formed by depositing a thin cathode material to a thickness of 1 to 10 nm and further laminating a transparent conductive material such as ITO or IZO.

(substrate)
In the present invention, a substrate can be used. The substrate used is preferably a substrate that does not scatter or attenuate light emitted from the organic compound layer. Specific examples thereof include zirconia stabilized yttrium (YSZ), inorganic materials such as glass, polyesters such as polyethylene terephthalate, polybutylene phthalate, and polyethylene naphthalate, polystyrene, polycarbonate, polyethersulfone, polyarylate, polyimide, and polycycloolefin. , Organic materials such as norbornene resin and poly (chlorotrifluoroethylene).
For example, when glass is used as the substrate, it is preferable to use non-alkali glass as the material in order to reduce ions eluted from the glass. Moreover, when using soda-lime glass, it is preferable to use what gave barrier coatings, such as a silica. In the case of an organic material, it is preferable that it is excellent in heat resistance, dimensional stability, solvent resistance, electrical insulation, and workability.

  There is no restriction | limiting in particular about the shape of a board | substrate, a structure, a magnitude | size, It can select suitably according to the use, purpose, etc. of a light emitting element. In general, the shape of the substrate is preferably a plate shape. The structure of the substrate may be a single layer structure, a laminated structure, may be formed of a single member, or may be formed of two or more members.

  The substrate may be colorless and transparent or colored and transparent, but is preferably colorless and transparent in that it does not scatter or attenuate light emitted from the organic light emitting layer.

The substrate can be provided with a moisture permeation preventing layer (gas barrier layer) on the front surface or the back surface.
As a material for the moisture permeation preventive layer (gas barrier layer), inorganic materials such as silicon nitride and silicon oxide are preferably used. The moisture permeation preventing layer (gas barrier layer) can be formed by, for example, a high frequency sputtering method.
When a thermoplastic substrate is used, a hard coat layer, an undercoat layer, or the like may be further provided as necessary.

(Protective layer)
In the present invention, the entire organic EL element may be protected by a protective layer.
As a material contained in the protective layer, any material may be used as long as it has a function of preventing materials that promote device deterioration such as moisture and oxygen from entering the device.
Specific examples thereof include metals such as In, Sn, Pb, Au, Cu, Ag, Al, Ti, and Ni, MgO, SiO, SiO ₂ , Al ₂ O ₃ , GeO, NiO, CaO, BaO, and Fe ₂ O. ₃ , metal oxides such as Y ₂ O ₃ and TiO ₂ , metal nitrides such as SiN _x and SiN _x O _y , metal fluorides such as MgF ₂ , LiF, AlF ₃ and CaF ₂ , polyethylene, polypropylene, polymethyl Monomer mixture containing methacrylate, polyimide, polyurea, polytetrafluoroethylene, polychlorotrifluoroethylene, polydichlorodifluoroethylene, copolymer of chlorotrifluoroethylene and dichlorodifluoroethylene, tetrafluoroethylene and at least one comonomer A copolymer obtained by copolymerization of a copolymer having a cyclic structure in the copolymer main chain. Copolymer, 1% by weight of the water absorbing water absorption material, water absorption of 0.1% or less of moisture-proof material, and the like.

  The method for forming the protective layer is not particularly limited, and for example, vacuum deposition, sputtering, reactive sputtering, MBE (molecular beam epitaxy), cluster ion beam, ion plating, plasma polymerization (high frequency) Excited ion plating method), plasma CVD method, laser CVD method, thermal CVD method, gas source CVD method, coating method, printing method, transfer method can be applied.

(Sealing)
Furthermore, the organic electroluminescent element of this invention may seal the whole element using a sealing container.
Further, a moisture absorbent or an inert liquid may be sealed in a space between the sealing container and the light emitting element. Although it does not specifically limit as a moisture absorber, For example, barium oxide, sodium oxide, potassium oxide, calcium oxide, sodium sulfate, calcium sulfate, magnesium sulfate, phosphorus pentoxide, calcium chloride, magnesium chloride, copper chloride Cesium fluoride, niobium fluoride, calcium bromide, vanadium bromide, molecular sieve, zeolite, magnesium oxide and the like. The inert liquid is not particularly limited, and examples thereof include fluorinated solvents such as paraffins, liquid paraffins, perfluoroalkanes, perfluoroamines, perfluoroethers, chlorinated solvents, and silicone oils. It is done.

  The organic electroluminescence device of the present invention emits light by applying a direct current (which may include an alternating current component as necessary) voltage (usually 2 to 15 volts) or a direct current between the anode and the cathode. Obtainable.

The driving durability of the organic electroluminescent element in the present invention can be measured by the luminance half time at a specific luminance. For example, using a source measure unit 2400 manufactured by KEITHLEY, a direct current voltage is applied to an organic EL element to emit light, and a continuous driving test is performed under the condition of an initial luminance of 2000 cd / m ² , and the luminance becomes 1000 cd / m ² . The brightness half-life time can be determined by comparing the brightness half-life time with a conventional light emitting device. This numerical value was used in the present invention.

  An important characteristic value of the organic electroluminescence device is external quantum efficiency. The external quantum efficiency is calculated by “external quantum efficiency φ = number of photons emitted from the device / number of electrons injected into the device”, and it can be said that the larger this value, the more advantageous the device in terms of power consumption.

  The external quantum efficiency of the organic electroluminescent element is determined by “external quantum efficiency φ = internal quantum efficiency × light extraction efficiency”. In an organic EL device using fluorescence emission from an organic compound, the limit value of the internal quantum efficiency is 25%, and the light extraction efficiency is approximately 20%. Therefore, the limit value of the external quantum efficiency is approximately 5%. Has been.

The external quantum efficiency of the organic electroluminescent element is preferably 6% or more, and particularly preferably 12% or more from the viewpoint of reducing power consumption and driving durability.
Numerical external quantum efficiency, the maximum value of the external quantum efficiency when the device is driven at 20 ° C., or in the vicinity 100~300cd / m ² when the device is driven at 20 ° C. (preferably 200 cd / m ²⁾ The external quantum efficiency value can be used.
In the present invention, using a source measure unit type 2400 manufactured by Toyo Technica, a DC constant voltage is applied to the EL element to emit light, and the luminance is measured using a luminance meter BM-8 manufactured by Topcon Corporation, and is 200 cd / m ^2. A value obtained by calculating the external quantum efficiency at is used.

  Further, the external quantum efficiency of the organic electroluminescence device can be calculated from the result and the relative visibility curve obtained by measuring the emission luminance, emission spectrum, and current density. That is, the number of input electrons can be calculated using the current density value. The emission luminance can be converted into the number of photons emitted by integral calculation using the emission spectrum and the relative visibility curve (spectrum). From these, the external quantum efficiency (%) can be calculated by “(number of emitted photons / number of electrons input to the device) × 100”.

  With respect to the driving method of the organic electroluminescent device of the present invention, for example, JP-A-2-148687, JP-A-6-301355, JP-A-5-29080, JP-A-7-134558, JP-A-8-234585, and JP-A-8-241047. No. 2,784,615, U.S. Pat. Nos. 5,828,429, 6023308, and the like, and the like can be applied.

  The organic electroluminescence device of the present invention can be suitably used for display devices, displays, backlights, electrophotography, illumination light sources, recording light sources, exposure light sources, reading light sources, signs, signboards, interiors, optical communications, and the like.

  EXAMPLES Hereinafter, although this invention is demonstrated using an Example, this invention is not limited to these at all.

1. Production of organic electroluminescence device (1) Production of light-emitting device A1 of the present invention Using an ITO target having an In ₂ O ₃ content of 95% by mass on a glass substrate of 0.5 mm thickness and 2.5 cm square, An ITO thin film (thickness 0.2 μm) as a transparent anode was formed by DC magnetron sputtering (conditions: substrate temperature 100 ° C., oxygen pressure 1 × 10 ⁻³ Pa). The surface resistance of the ITO thin film was 10Ω / □.
Next, the substrate on which the transparent anode was formed was placed in a cleaning container, washed with 2-propanol, and then subjected to UV-ozone treatment for 30 minutes. The following organic compound layers were sequentially deposited on the transparent anode (ITO film) by vacuum deposition.
The vapor deposition rate in the examples of the present invention was measured using a crystal resonator. The film thicknesses described below were also measured using a crystal resonator.
Table 1 shows values of ionization potential (Ip), electron affinity (Ea), and lowest excited triplet energy level (T ₁ ) of the organic compound in each layer.

[Hole injection layer]
Copper phthalocyanine: film thickness 10 nm (deposition rate: 0.5 nm / second)
[Hole transport layer]
α-NPD: film thickness 30 nm (deposition rate: 0.3 nm / second)
[Hole transporting intermediate layer]
CBP: film thickness 10 nm (deposition rate: 0.3 nm / second)
[Light emitting layer]
The deposition rates of CBP (hole transporting host) and ETM-1 (electron transporting host) are each 0.3 nm / second, and the phosphorescent dopant EM-1 is 8 masses with respect to the whole organic material in the light emitting layer. The ternary co-evaporation is performed so as to be%. The thickness of the light emitting layer is 30 nm.
[Electron transport layer 1]
BAlq: film thickness 10 nm (deposition rate: 0.3 nm / second)
[Electron transport layer 2]
Alq: film thickness 30 nm (deposition rate: 1 nm / second)
[Electron injection layer]
A patterned mask (a mask with a light emitting area of 2 mm × 2 mm) is placed on the electron transport layer 2 and lithium fluoride is deposited at a deposition rate of 0.1 nm / second to form an electron injection layer having a thickness of 1 nm. Is provided.
[cathode]
Aluminum is deposited on the electron injection layer at a deposition rate of 3 nm, and a cathode having a thickness of 150 nm is provided.
Aluminum lead wires are respectively connected from the anode and the cathode to form a light emitting laminate.

The obtained light emitting laminate was put in a glove box substituted with argon gas, and a stainless steel sealing can provided with a desiccant and an ultraviolet curable adhesive (XNR5516HV, manufactured by Nagase Ciba Co., Ltd.) were used. To obtain the light-emitting element A1 of the example.
The operations from the deposition of copper phthalocyanine to the sealing are performed in a vacuum or nitrogen atmosphere, and the device is manufactured without exposure to the air.

(2) Production of Light Emitting Element A2 of Example (1) Substrate treatment was performed in the same manner as production of light emitting element A1 of Example, and then the following organic compound layers were sequentially deposited on the transparent anode (ITO film) by vacuum deposition. Vapor deposited.
Table 1 shows values of ionization potential (Ip), electron affinity (Ea), and lowest excited triplet energy level (T ₁ ) of the organic compound in each layer.

[Hole injection layer]
Copper phthalocyanine: film thickness 10 nm (deposition rate: 0.5 nm / second)
[Hole transport layer]
α-NPD: film thickness 30 nm (deposition rate: 0.3 nm / second)
[Light emitting layer]
The vapor deposition rates of CBP (hole transporting host) and ETM-1 (electron transporting host) were each 0.3 nm / second, and the phosphorescent dopant EM-1 was 8 wt% with respect to the entire organic material in the light emitting layer. Ternary co-evaporation is performed so that The thickness of the light emitting layer is 30 nm.
[Electron transporting intermediate layer]
ETM-1: film thickness 10 nm (deposition rate: 0.3 nm / second)
[Electron transport layer 1]
BAlq: film thickness 10 nm (deposition rate: 0.3 nm / second)
[Electron transport layer 2]
Alq: film thickness 30 nm (deposition rate: 1 nm / second)
[Electron injection layer]
A patterned mask (a mask with a light emitting area of 2 mm × 2 mm) is placed on the electron transport layer 2 and lithium fluoride is deposited at a deposition rate of 0.1 nm / second to form an electron injection layer having a thickness of 1 nm. Is provided.
[cathode]
Aluminum is deposited on the electron injection layer at a deposition rate of 3 nm, and a cathode having a thickness of 150 nm is provided.
Aluminum lead wires are respectively connected from the anode and the cathode to form a light emitting laminate.

The obtained light emitting laminate was put in a glove box substituted with argon gas, and a stainless steel sealing can provided with a desiccant and an ultraviolet curable adhesive (XNR5516HV, manufactured by Nagase Ciba Co., Ltd.) were used. To obtain a light emitting element A2 of the example.
The operations from the deposition of copper phthalocyanine to the sealing are performed in a vacuum or nitrogen atmosphere, and the device is manufactured without exposure to the air.

(3) Production of Light-Emitting Element B1 of Comparative Example Using an ITO target having an In ₂ O ₃ content of 95% by mass on a 0.5 mm thick, 2.5 cm square glass substrate, DC magnetron sputtering (conditions: An ITO thin film (thickness 0.2 μm) as a transparent anode was formed at a substrate temperature of 100 ° C. and an oxygen pressure of 1 × 10 ⁻³ Pa. The surface resistance of the ITO thin film was 10Ω / □.
Next, the substrate on which the transparent anode was formed was placed in a cleaning container, washed with 2-propanol, and then subjected to UV-ozone treatment for 30 minutes. The following organic compound layers were sequentially deposited on the transparent anode (ITO film) by vacuum deposition.
The vapor deposition rate in the examples of the present invention was measured using a crystal resonator. The film thicknesses described below were also measured using a crystal resonator.
Table 1 shows values of ionization potential (Ip), electron affinity (Ea), and lowest excited triplet energy level (T ₁ ) of the organic compound in each layer.

[Hole injection layer]
Copper phthalocyanine: film thickness 10 nm (deposition rate: 0.5 nm / second)
[Hole transport layer]
α-NPD: film thickness 30 nm (deposition rate: 0.3 nm / second)
[Mixed layer 1 of hole transport material and electron transport material]
The deposition rate of CBP is fixed at 0.3 nm / second, the shutter of the deposition source of ETM-1 which is an electron transport material is gradually opened, and a mixed region having a concentration gradient is formed to 10 nm. When the mixed region reaches 10 nm, the deposition rate of ETM-1 is set to 0.3 nm / second.
[Light emitting layer]
The vapor deposition rates of CBP (hole transporting host) and ETM-1 (electron transporting host) were each 0.3 nm / second, and the phosphorescent dopant EM-1 was 8 wt% with respect to the entire organic material in the light emitting layer. Ternary co-evaporation is performed so that The thickness of the light emitting layer is 20 nm.
[Mixed layer 2 of hole transport material and electron transport material]
The deposition rate of ETM-1 is fixed at 0.3 nm / second, the shutter of the CBP deposition source is gradually closed, and a mixed region having a concentration gradient is formed to 10 nm. When the mixed region reaches 10 nm, the CBP deposition rate is finished.
[Electron transport layer 1]
BAlq: film thickness 10 nm (deposition rate: 0.3 nm / second)
[Electron transport layer 2]
Alq: film thickness 30 nm (deposition rate: 1 nm / second)
[Electron injection layer]
A patterned mask (a mask with a light emitting area of 2 mm × 2 mm) is placed on the electron transport layer 2 and lithium fluoride is deposited at a deposition rate of 0.1 nm / second to form an electron injection layer having a thickness of 1 nm. Is provided.
[cathode]
Aluminum is deposited on the electron injection layer at a deposition rate of 3 nm, and a cathode having a thickness of 150 nm is provided.
Aluminum lead wires are respectively connected from the anode and the cathode to form a light emitting laminate.

The obtained light emitting laminate is put in a glove box substituted with argon gas, and sealed with a stainless steel sealing can provided with a desiccant and an ultraviolet curable adhesive (XNR5516HV, manufactured by Chiba Nagase). Thus, the comparative light emitting device 1 is obtained.
The operations from the deposition of copper phthalocyanine to the sealing are performed in a vacuum or nitrogen atmosphere, and the device is manufactured without exposure to the air.

(4) Production of Light-Emitting Element B2 of Comparative Example In the light-emitting element B1 of the comparative example, instead of [the mixed layer 1 of hole transport material and electron transport material], α-NPD was 10 nm (deposition rate was 0.3 nm / In the same manner as in Comparative Example 1 except that BAlq was changed to 10 nm (deposition rate was 0.3 nm / second) instead of [mixed layer 2 of hole transport material and electron transport material]. A light emitting element B2 of a comparative example is obtained.

(5) Production of Light-Emitting Element A3 of Example In the light-emitting element B1 of the comparative example, instead of [the mixed layer 1 of hole transport material and electron transport material], CBP was 10 nm (deposition rate was 0.3 nm / second, The present invention is changed to a hole transporting intermediate layer in the present invention, and instead of [mixed layer 2 of hole transport material and electron transport material 2], BAlq is 10 nm (deposition rate is 0.3 nm / second). The light-emitting element A3 of the example is obtained in the same manner as the light-emitting element B1 of the comparative example except that the above is changed.

(6) Production of Light-Emitting Element A4 of Example In the light-emitting element B1 of the comparative example, α-NPD was changed to 10 nm instead of [the mixed layer 1 of hole transport material and electron transport material] (deposition rate was 0.3 nm / In addition, instead of [Hole transport material and electron transport material mixed layer 2], ETM-1 was changed to 10 nm (deposition rate was 0.3 nm / second, the electron transporting intermediate layer in the present invention). Except for the change to the equivalent), the light emitting element A4 of the example is obtained in the same manner as the light emitting element B1 of the comparative example.

(7) Production of Light-Emitting Element A5 of Example In the light-emitting element B1 of the comparative example, instead of [mixed layer 1 of hole transport material and electron transport material], CBP was 10 nm (deposition rate was 0.3 nm / second, ETM-1 is changed to 10 nm (deposition rate is 0.3 nm / second) instead of [mixed layer 2 of hole transport material and electron transport material]. The light emitting device A5 of the example is obtained in the same manner as the light emitting device B1 of the comparative example, except that it is changed to the electron transporting intermediate layer in the present invention.

(8) Production of Light-Emitting Element B3 of Comparative Example In the light-emitting element A3 of the example, ETM-1 (electron transporting host) in the light-emitting layer was not used, and the others were compared in the same manner as the light-emitting element A3 of the example. An example light emitting device B3 is obtained.

(9) Production of Light-Emitting Element B4 of Comparative Example In the light-emitting element A3 of the example, the CBP (hole transporting host) in the light-emitting layer was not used, and the others were the same as those of the light-emitting element A3 of the example. The light emitting element B4 is obtained.

(10) Production of Light-Emitting Elements B5 to B8 of Comparative Examples and Light-Emitting Elements A6 to A8 of Examples In the light-emitting elements B1 to B5 of Comparative Examples and the light-emitting elements A3 to A5 of Examples, Instead, the devices manufactured in the same manner as the above light emitting devices except that EM-2 was used are obtained as light emitting devices B5 to B8 of comparative examples and light emitting devices A6 to A8 of examples, respectively.

(11) Production of Light-Emitting Elements B9 to B12 of Comparative Examples and Light-Emitting Elements A9 to A11 of Examples In the light-emitting elements B1 to B5 of Comparative Examples and the light-emitting elements A3 to A5 of Examples, MCP is used instead of CBP. The light-emitting elements B9 to B12 of the comparative examples and the light-emitting elements A9 to A11 of the examples were prepared in the same manner as the above light-emitting elements except that EM-3 was used instead of the light-emitting dopant EM-1. Get as.

(12) Production of light-emitting elements A12 to A-14 of Example In the light-emitting element A-11 of the examples, D-22, D-23, and D-24 were used instead of the light-emitting dopant EM-3, respectively. Fabricated in the same manner as the light-emitting element A11, and obtained as light-emitting elements A12 to A-14 of the examples.

(13) Production of Light-Emitting Element A15 of Example The light-emitting element A-8 was produced in the same manner as the light-emitting element A-8 except that D-21 was used instead of the light-emitting dopant EM-2. Thus, a light emitting element A15 of the example is obtained.

  The structure of the compound used for each light emitting element is shown below.

2. Evaluation of compound physical properties Table 1 shows measurement methods and measurement results of ionization potential, electron affinity, and T ₁ energy of the compounds used in the examples.

(1) Ionization potential Each compound used for the organic compound layer was deposited on a glass substrate so as to have a thickness of 50 nm. The ionization potential of this membrane was measured with an ultraviolet photoelectron analyzer AC-1 or AC-3 manufactured by Riken Keiki Co., Ltd. under normal temperature and normal pressure.

(2) Electron affinity The ultraviolet-visible absorption spectrum of the film used for measuring the ionization potential was measured with a UV3100 spectrophotometer manufactured by Shimadzu Corporation, and the excitation energy was determined from the energy at the long wavelength end of the absorption spectrum. The electron affinity was calculated from the excitation energy and the value of the ionization potential.

(3) T ₁ energy The phosphorescence spectrum of the film used for measuring the ionization potential was measured at a temperature condition of 77 K using F4500 manufactured by Hitachi, Ltd., and the T ₁ energy was calculated from the energy at the short wavelength end of the phosphorescence spectrum. Asked.

3. Evaluation of organic electroluminescent element The organic electroluminescent element obtained above was evaluated by the following method.
(1) External quantum efficiency The waveform of the emission spectrum of the produced light emitting device is measured using a multi-channel analyzer PMA-11 manufactured by Hamamatsu Photonics. The wavelength value of the emission peak is determined from this measurement data. Further, the external quantum efficiency is calculated from the waveform of the emission spectrum and the current / brightness (300 cd / m ² ) at the time of measurement. The results are shown in Table 2, Table 3, Table 4, and Table 5.

(2) Driving durability test Using a source measure unit 2400 manufactured by KEITHLEY, a direct current voltage is applied to the light emitting element to emit light. The luminance is measured using a luminance meter BM-8 manufactured by Topcon Corporation, and the external quantum efficiency at 300 cd / m ² is calculated.
Subsequently, this light-emitting element is subjected to a continuous driving test under the condition of constant initial luminance, and the time when the luminance is reduced to half is defined as a luminance half time T (1/2). The results are shown in Table 2, Table 3, Table 4, and Table 5.
(Initial luminance 300 cd / m ² the element described in Table 2, evaluated in Table 3, the initial luminance 2000 cd / m ² the element described in Table 4, the elements described in Table 5 Initial luminance 360 cd / m ^2.)

(3) Driving voltage Using a source measure unit 2400 manufactured by KEITHLEY, a direct current voltage is applied to the light emitting element to emit light. The voltage is measured when the luminance (measured with a luminance meter BM-8 manufactured by Topcon Corporation) is 300 cd / m ² . The results are shown in Table 2, Table 3, Table 4, and Table 5.

All of the elements shown in Table 2 can emit red light derived from the light emission of the luminescent dopant EM-1.
As is apparent from Table 2, the light-emitting elements A1 and A2 of the examples have low voltage drive, high efficiency light emission, and high drive durability.

All of the elements shown in Table 3 can emit red light derived from the light emission of the luminescent dopant EM-1.
As is apparent from Table 3, the element having the layer in which the hole transport material and the electron transport material are mixed with a concentration gradient as the layer adjacent to the light emitting layer (the light emitting element B1 of the comparative example) does not have the mixed layer. Although the drive voltage is lower than that of the light emitting elements B2 to B4 of the comparative example, the light emission efficiency is significantly lowered.
On the other hand, the light emitting elements A3 to A5 of the example can simultaneously improve the light emission efficiency and the drive durability simultaneously with the decrease in the drive voltage. In addition, as shown in the results of the light emitting element A5, the element having both the hole transporting intermediate layer and the electron transporting intermediate layer is particularly excellent in any of driving voltage reduction, light emission efficiency, and driving durability. It is.

All of the elements shown in Table 4 can emit green light derived from the light emission of the luminescent dopant EM-2.
As is apparent from Table 4, the element having the layer in which the hole transport material and the electron transport material are mixed with a concentration gradient as the layer adjacent to the light emitting layer (the light emitting element B5 of the comparative example) does not have the mixed layer. Although the drive voltage is lower than that of the light emitting elements B6 to B8 of the comparative example, the light emission efficiency is significantly reduced.
On the other hand, the light emitting elements A6 to A8 of the embodiment can simultaneously improve the light emission efficiency and the drive durability simultaneously with the decrease of the drive voltage. In addition, as shown in the results of the light-emitting element A8, the element having both the hole transporting intermediate layer and the electron transporting intermediate layer is particularly excellent in any of driving voltage reduction, light emission efficiency, and driving durability. It is.

Among the elements shown in Table 5, all of the light-emitting elements A9 to A11 of Examples can obtain blue light emission derived from the light emission of the light-emitting dopant EM-3. In contrast, the light emitting elements B9 and B10 of the comparative example can emit blue-green light. This is presumably because holes leaked from the light emitting layer to the electron transport layer, so that the holes and electrons recombined in the electron transport layer, causing BAlq and / or Alq to emit light, and the green component was mixed. . Thus, it can be said that the light-emitting elements of the examples are excellent in terms of color purity.
Further, as is apparent from Table 5, an element having a layer in which a hole transport material and an electron transport material are mixed with a concentration gradient as a layer adjacent to the light emitting layer (light emitting element B9 of the comparative example) Although the drive voltage is lower than other comparative light emitting elements that do not have the light emitting elements B10 to B11 of the comparative examples that do not have the mixed layer, the light emission efficiency is significantly reduced.
On the other hand, the light emitting elements A9 to A11 of the embodiment can simultaneously improve the light emission efficiency and the drive durability simultaneously with the decrease in the drive voltage. In addition, as shown in the results of the light emitting element A11, the element having both the hole transporting intermediate layer and the electron transporting intermediate layer is particularly excellent in any of driving voltage reduction, light emission efficiency, and driving durability. It is.

In the elements described in Table 6, blue light emission derived from the light emission of the light emitting dopants D-22 to D-23 can be obtained.
These elements are those using the preferred luminescent dopant used in the present invention, and in this case, they exhibit excellent effects in any of the driving voltage reduction, the luminous efficiency, and the driving durability. The effect is more remarkable in terms of efficiency and driving durability.

In the element described in Table 7, green light emission derived from the light emission of the luminescent dopant D-21 is obtained.
This device uses a preferable luminescent dopant used in the present invention, and in this case, the device exhibits excellent effects in all aspects of reduction in driving voltage, luminous efficiency, and driving durability. In addition, the effect is more remarkable in terms of driving durability.

Claims (23)

Between a pair of electrodes, a hole transport layer containing at least one kind of hole transport material, a light emitting layer containing at least one kind of luminescent dopant and a plurality of host compounds, and an electron transport layer containing at least one kind of electron transport material, An organic electroluminescent device having
Among the plurality of host compounds, at least one is a hole transporting host compound, and at least one is an electron transporting host compound,
An organic electroluminescence device comprising a hole transporting intermediate layer made of only the same compound as the hole transporting host compound between the hole transporting layer and the light emitting layer. Between a pair of electrodes, a hole transport layer containing at least one kind of hole transport material, a light emitting layer containing at least one kind of luminescent dopant and a plurality of host compounds, and an electron transport layer containing at least one kind of electron transport material, An organic electroluminescent device having
Among the plurality of host compounds, at least one is a hole transporting host compound, and at least one is an electron transporting host compound,
An organic electroluminescent element comprising an electron transporting intermediate layer made of only the same compound as the electron transporting host compound between the electron transporting layer and the light emitting layer. Between a pair of electrodes, a hole transport layer containing at least one kind of hole transport material, a light emitting layer containing at least one kind of luminescent dopant and a plurality of host compounds, and an electron transport layer containing at least one kind of electron transport material, An organic electroluminescent device having
Among the plurality of host compounds, at least one is a hole transporting host compound, and at least one is an electron transporting host compound,
Between the hole transport layer and the light emitting layer, it has a hole transport intermediate layer made of only the same compound as the hole transport host compound, and between the electron transport layer and the light emitting layer, An organic electroluminescent device comprising an electron-transporting intermediate layer comprising only the same compound as the electron-transporting host compound.   4. The organic electroluminescent element according to claim 1, wherein in the light emitting layer, the region where the light emitting dopant is present is a part of a region formed of the plurality of host compounds.   ΔIp = Ip (D) −Ip (H) min, where Ip (D) is the ionization potential of the luminescent dopant and Ip (H) min is the minimum of the ionization potentials of the plurality of host compounds. The organic electroluminescent element according to claim 1, wherein ΔIp defined by the above satisfies a relationship of ΔIp> 0 eV.   ΔEa = Ea (H) max−Ea (D) where Ea (D) is the electron affinity of the luminescent dopant and Ea (H) max is the maximum of the electron affinity of the plurality of host compounds. The organic electroluminescent element according to claim 1, wherein ΔEa defined by the above satisfies a relationship of ΔEa> 0 eV.   ΔIp = Ip (D) −Ip (H) min, where Ip (D) is the ionization potential of the luminescent dopant and Ip (H) min is the minimum of the ionization potentials of the plurality of host compounds. ΔIp satisfies the relationship of ΔIp> 0 eV, the electron affinity of the luminescent dopant is Ea (D), and the maximum of the electron affinity of the plurality of host compounds is Ea (H) max The ΔEa defined by ΔEa = Ea (H) max−Ea (D) satisfies the relationship of ΔEa> 0 eV. 5. The organic according to claim 1, Electroluminescent device.   8. The organic electroluminescent device according to claim 5, wherein the ΔIp satisfies a relationship of 1.2 eV> ΔIp> 0.2 eV.   The organic electroluminescent element according to claim 6 or 7, wherein the ΔEa satisfies a relationship of 1.2 eV> ΔEa> 0.2 eV.   The organic electroluminescence device according to claim 7, wherein the ΔIp satisfies 1.2eV> ΔIp> 0.2eV, and the ΔEa satisfies a relationship of 1.2eV> ΔEa> 0.2eV.   11. The organic electroluminescence device according to claim 5, wherein the Ip (H) min is 5.6 eV or more and 5.8 eV or less.   11. The organic electroluminescent element according to claim 6, wherein the Ea (H) max is 2.8 eV or more and 3.1 eV or less.   The organic electroluminescent element according to claim 1, wherein the luminescent dopant is a phosphorescent material. When the lowest excited triplet energy level of the luminescent dopant is T ₁ (D) and the lowest excited triplet energy level of the plurality of host compounds is T ₁ (H) min, The organic electroluminescent element according to claim 1, wherein a relationship of T ₁ (H) min> T ₁ (D) is satisfied. The organic electroluminescence according to any one of claims 1 to 14, wherein the lowest excited triplet energy level T ₁ (D) of the luminescent dopant is 251 kJ / mol (60 kcal / mol) or more. element. The organic electroluminescence according to any one of claims 1 to 15, wherein the lowest excited triplet energy level T ₁ (D) of the luminescent dopant is 272 kJ / mol (65 kcal / mol) or more. element.   The organic electroluminescence device according to any one of claims 1 and 3 to 16, wherein an ionization potential of the compound forming the hole transporting intermediate layer is 5.6 eV or more and 5.8 eV or less. .   The organic electroluminescence device according to any one of claims 2 to 16, wherein an electron affinity of the compound forming the electron transporting intermediate layer is 2.8 eV to 3.1 eV.   The ionization potential of the compound forming the hole transporting intermediate layer is 5.6 eV or more and 5.8 eV or less, and the electron affinity of the compound forming the electron transporting intermediate layer is 2.8 eV or more and 3.1 eV or less. The organic electroluminescent element according to any one of claims 3 to 16, wherein the organic electroluminescent element is.   20. The content of the plurality of host compounds is 15% by mass or more and 85% by mass or less, respectively, with respect to the total compound mass forming the light emitting layer. Organic electroluminescent element.   21. The organic electroluminescent element according to claim 1, wherein the thickness of the hole transporting intermediate layer is 1 nm or more and 10 nm or less.   The thickness of the said electron transport intermediate | middle layer is 1 nm or more and 10 nm or less, The organic electroluminescent element as described in any one of Claims 2-21 characterized by the above-mentioned. The thickness of the said light emitting layer is 5 nm or more and 20 nm or less, The organic electroluminescent element as described in any one of Claims 1-22 characterized by the above-mentioned.