JP5484697B2 - Organic electronics luminescence element - Google Patents

Description

  The present invention relates to an organic EL (electroluminescence) element and a dopant material constituting a part of the light-emitting layer. By using a metal complex having a deuterium-substituted ligand as a dopant material, the emission efficiency of the organic EL element is improved. It is intended to increase.

Conventionally, research and development for increasing the luminous efficiency of organic EL elements have been actively conducted. As one means for improving the light emission efficiency, studies are being conducted on a light emitting material constituting a light emitting layer of an organic EL element.
With respect to a light-emitting material made of a metal complex, a material in which a hydrogen atom in a ligand constituting the metal complex is replaced with a deuterium atom has been studied.

  For example, Japanese Patent Application Laid-Open No. 2001-240854 discloses a light-emitting material composed of a metal complex using a deuterium-substituted pyrazolyl derivative as a ligand and terbium and cerium as a central metal. There is a description that the internal quantum efficiency of light emission is improved as compared with a light emitting material made of a terbium complex or a cerium complex having a pyrazolyl derivative not substituted with hydrogen as a ligand.

  In addition, J.H. Phy. Chem. C2007, 111, 3490-3494 (2007) includes an aluminum complex obtained by substituting hydrogen of 8-hydroxyquinoline which is a ligand of (8-quinolinolato) aluminum complex (Alq3) with deuterium, and bis (2- 2-methyl-8-hydroxyquinoline, which is a ligand of (methyl-8-quinolylate) (2,6-dimethyl-phenolate) aluminum (Q2AlOAr), and hydrogen of 2,6-dimethylphenol are substituted with deuterium. It has been reported that the external quantum efficiency is greatly improved to 200% or more by using an aluminum complex as a light emitting material.

  The reason why the emission efficiency is improved by using a light-emitting material comprising a metal complex having a deuterium-substituted ligand (hereinafter sometimes abbreviated as deuterium-substituted metal complex) is that the deuterium-substituted metal complex It is considered that this is because light emission inhibition factors such as quenching and heat deactivation in the light emission mechanism can be suppressed by replacing the C—H bond and the O—H bond in the middle with a CD bond and an OD bond.

However, in order to obtain the effect of improving the internal quantum efficiency by using this deuterium-substituted metal complex, it is necessary to use one in which all or most of the hydrogen atoms of the ligand in the metal complex are deuterated. is there.
This is because such an effect is hindered by thermal deactivation caused by a small amount of C—H bonds and O—H bonds remaining in the deuterium-substituted metal complex.

For this reason, a light-emitting material composed of a deuterium-substituted metal complex that is almost completely deuterium-substituted must be used as the light-emitting layer. However, this is very expensive and its practical use is substantially limited. There is a problem.
JP 2001-240854 A J. et al. Phy. Chem. C2007, 111, 3490-3494 (2007)

  Therefore, the subject in this invention is making it possible to comprise the organic EL element which has a cheap light emitting layer using the deuterium substitution metal complex which can anticipate high luminous efficiency.

To solve this problem,
The invention according to claim 1 has a light emitting layer including a dopant material made of a metal complex and a host material, and the dopant material has deuterated 8-hydroxyquinolines as a ligand, and the central metal is It is a metal complex which is aluminum, and the host material is 4,4′-N, N′-dicarbazole-biphenyl, 2-methyl-9,10-di (2-naphthyl) anthracene, or N, N— Organic electronic luminescence device which is di-[(1-naphthalene) -N, N-diphenyl] -1,1-biphenyl-4,4-diamine and the content of the dopant material is 0.01 wt% to 30 wt% It is.
The invention according to claim 2 is the organic electronic luminescence device according to claim 1 , wherein the deuteration rate of the ligand is 70% or more .

Since the dopant material of the present invention is composed of a metal complex having a deuterium-substituted ligand and having a central metal of aluminum or zinc, this is mixed with a host material to constitute a light emitting layer. Thus, the luminous efficiency of the organic EL device as a whole can be increased, and the amount of dopant material used in the light emitting layer can be reduced, so that an inexpensive organic EL device is obtained.
In addition, the durability as a light emitting material is improved and the power consumption is reduced.
For this reason, the organic EL element of the present invention is inexpensive, has high light emission efficiency, and has low power consumption and high durability.

The present invention will be described in detail below.
[Dopant material]
The dopant material of the present invention is combined with a host material to constitute a light emitting layer.
The dopant material of the present invention comprises a metal complex having a deuterium-substituted ligand and having a central metal of aluminum or zinc.

  In the present invention, a deuterium-substituted ligand refers to a compound in which the abundance ratio of deuterium atoms in chemical species such as compounds and ions constituting the ligand exceeds the natural abundance ratio. The ratio of the number of deuterium atoms to the total number of deuterium atoms and hydrogen atoms in this chemical species is called deuteration rate. A preferable deuteration rate is 70% or more, more preferably 95% or more, and still more preferably 98% or more. When the deuteration rate is less than 70%, there is a possibility that the effect of improving the light emission efficiency as the light emitting material to be obtained may not be obtained due to the C—H bond or O—H bond remaining in the ligand.

Suitable deuterium-substituted ligands in the dopant material of the present invention include 8-hydroxyquinolines (for example, 8-hydroxyquinoline, 2-methyl-8-quinolines, 4-hydroxyphenanthridine, 2- Styryl-8-hydroxyquinolines, 2- (4-phenylstyryl) -8-hydroxyquinolines, 2-p- (N, N-dimethylaminostyryl) -8-hydroxyquinolines, 2- [β- (1 -Naphtyl) vinyl]}-8-hydroxyquinoline)), and the like. Among them, 8-hydroxyquinoline substituted with deuterium is preferable in terms of film-forming properties. is there.
8-hydroxyquinolines are represented by the following chemical formula (1).

In the compound represented by the chemical formula (1), the alkyl group in the alkyl group, alkoxy group, halogenated alkyl group, and dialkylamino group may be linear, branched, or cyclic. The linear and branched alkyl groups preferably have 1 to 5 carbon atoms. Specifically, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec Examples include -butyl group, tert-butyl group, n-pentyl group, and hexyl group.
It is preferable that all of the substituents R1 to R6 are substituted with deuterium.

The central metal of the metal complex is aluminum or zinc.
In general, a metal complex whose central metal is aluminum or zinc is employed in the present invention because it has good film formability and is easy to handle.

  In addition, aluminum complexes or zinc complexes such as tris (8-hydroxyquinoline) aluminum (Alq3) have been conventionally used as a light emitting material or an electron transport material alone because they have good film forming properties and are inexpensive. In addition, there are cases where tris (8-hydroxyquinoline-d6) aluminum substituted with deuterium as disclosed in Non-Patent Document 1 is also used alone as a light emitting material, but these are combined with a host material as a dopant material. There are no known examples that have been used.

Such a method for producing an aluminum complex or zinc complex having a deuterium-substituted ligand is carried out by reacting a deuterium-substituted ligand with an aluminum ion or zinc ion serving as a central metal.
A method for producing a deuterium-substituted ligand is performed by the method described in Non-Patent Document 1, for example.

  Since such a dopant material is made of an aluminum complex or zinc complex having a deuterium-substituted ligand, when the light emitting layer is formed by co-evaporation with the host material, the host material Thus, the electric energy is smoothly transferred from the dopant material to the dopant material, and the dopant material is efficiently excited to emit light with high efficiency.

[Light emitting layer]
The light emitting layer referred to in the present invention is composed of the above-described dopant material and host material, and is formed into a thin film by co-evaporation or the like. The light emitting layer is formed by forming the light emitting material into a thin film having a thickness of 10 to 100 nm on the hole transport layer or the like of the transparent substrate by thin film forming means such as vacuum deposition. When the thickness is increased, the applied voltage is increased, and when the thickness is decreased, problems such as interlayer short circuit and optical interference occur. Therefore, the thickness is preferably about 20 to 50 nm. The host material constituting the light emitting layer in the present invention is not particularly limited as long as energy transfer to the dopant material proceeds smoothly.
For example, aluminum complexes such as tris (8-hydroxyquinoline) aluminum (Alq3), gallium complexes, beryllium complexes such as bis (benzoquinolinolato) beryllium (BeBq2), zinc such as bis (8-quinolato) zinc (Znq2) Metal complexes such as complexes, 4,4′-bis (2,2-diphenylvinyl) biphenyl (DPVBi), 4,4 ′-(bis (9-ethyl-3-carbazovinylene) -1,1′-biphenyl (BCzVBi) ) And the like.

In addition, compounds containing arylethynylbenzene, sexiphenyl, benzimidazole, bipyridine derivatives and the like can also be used.
p-iodophenylcarbazole, diaminocarbazole, 4-carbazole-3 ′, 5′-dicarbazolebiphenyl, 4,4′-N, N′-dicarbazole-diphenyl, 4,4′-N, N′-dicarbazole Carbazole derivatives such as -biphenyl (CBP) can also be used.

Furthermore, 9,9- (bis (4-hydroxyphenyl)) fluorene, 3- (4-biphenyl) -4-phenyl-5- (4-tert-butylphenyl) -1,2,4-triazole (TAZ) Diphenylfluorene compounds such as 3-phenyl-4- (1′-naphthyl) -5-phenyl-1,2,4-triazole, perylene derivatives, N, N′-dicarbazoyl-3,5-benzene, 2-methyl -9,10-di (2-naphthyl) anthracene (MADN) can also be used.
Among these, 4,4′-N, N′-dicarbazole-biphenyl (CBP) and 2-methyl-9,10-di (2-naphthyl) anthracene (MADN) are preferable in terms of film formability and energy transfer. ) Is preferred.

  The dopant material of the present invention is a powdery solid at room temperature, and a light emitting layer as referred to in the present invention can be prepared by co-evaporation with a host material that is also a powdered solid.

  The content of the dopant material in the light emitting layer is 0.01 wt% to 30 wt%, preferably 0.1 to 30 wt%, more preferably 3 wt% to 20 wt%, more preferably 6 wt% to 20 wt%. If it is less than 0.01 wt%, the effect of improving the light emission efficiency cannot be obtained. If it exceeds 30 wt%, the film formability cannot be ensured, and the price of the whole organic EL element is increased, which is disadvantageous.

  In such a light emitting layer, it is composed of a dopant material made of an aluminum complex or zinc complex having a deuterium-substituted ligand and a host material. The high luminous efficiency originally possessed by the aluminum complex or zinc complex having a different ligand is exhibited as it is.

In addition, since the amount of the aluminum complex or zinc complex having an expensive deuterium-substituted ligand can be suppressed to 30 wt% or less, preferably 20 wt% or less of the total amount of the light emitting material, the cost can be reduced. .
Furthermore, in the case of an organic EL element, it is possible to reduce power consumption by reducing the applied voltage required for light emission at a predetermined light amount, for example, 100 cd / m ² .

[Organic EL device]
The organic EL element of this invention has the above-mentioned light emitting layer. The structure of the organic EL element here is such that an anode made of a transparent conductive thin film such as ITO (indium tin oxide) or IZO (indium zinc oxide) is provided on a transparent substrate such as a glass plate or a transparent plastic film. Hole injection layer made of phthalocyanine compound, etc. on the anode, hole transport layer made of triphenylamine derivative, light emitting layer, electron transport layer made of quinolinol aluminum complex, oxadiazole derivative, triazole derivative, electron injection layer In addition, there is a structure in which cathodes made of lithium fluoride, aluminum, and the like are sequentially stacked.

In addition, other structures may be used, such as a structure in which the light emitting layer also serves as an electron transport layer, a structure in which the hole injection layer or the electron injection layer is omitted, a structure in which a buffer layer is provided, and the like. There is no limitation as long as it includes at least an anode, a light emitting layer, and a cathode.
Furthermore, not only the bottom emission structure but also a top emission structure may be used.

  In such an organic EL element, since the light emitting layer is composed of a light emitting material containing a dopant material made of an aluminum complex or zinc complex having a deuterium-substituted ligand, luminous efficiency is improved. , High power consumption, low durability, and low cost.

Specific examples are shown below.
(Example 1) Preparation of deuterium-substituted ligand
Using commercially available 8-hydroxyquinoline (special grade reagent, manufactured by Wako Pure Chemical Industries, Ltd.), 8-hydroxyquinoline-d6 was produced by the method described in Non-Patent Document 1.
The deuteration rate was 98% as measured with a Fourier transform infrared spectrometer, a nuclear magnetic resonance apparatus, and a mass spectrometer.

(Example 2) Preparation example of aluminum complex (dopant material) having a deuterium-substituted ligand
While stirring 8-hydroxyquinoline-d6, aluminum chloride hexahydrate, deuterated ethanol (CH ₃ OD), and heavy water, a neutral aqueous solution of sodium hydroxide was added for neutralization. After completion of the reaction, the precipitate was collected by filtration, dispersed and washed with heavy water and deuterated ethanol, and further purified by train sublimation. This gave tris- (8-hydroxyquinoline-d6) aluminum.
For comparison, a commercially available tris- (8-hydroxyquinoline) aluminum (Alq3) (manufactured by Dojin Chemical Co., Ltd.) was separately prepared.

(Example 3 Measurement of fluorescence lifetime of an aluminum complex having a deuterium-substituted ligand)
The tris- (8-hydroxyquinoline-d6) aluminum obtained in Example 2 was added to PMMA as a dopant material at 3 wt%, 5 wt%, 10 wt%, and 20 wt%, formed into a film by a cast method, and a fluorescence lifetime (PLQE) ) Was measured.
As a comparison, the same measurement was performed on tris- (8-hydroxyquinoline) aluminum obtained in Example 1.
For comparison, only tris- (8-hydroxyquinoline-d6) aluminum and only tris- (8-hydroxyquinoline) aluminum were used to form a film by a casting method, and the same measurement was performed. Table 1 shows the results.

  From Table 1, PLQE (%) was also improved when the dopant amount of deuterated Alq3 in PMMA was 3 to 20 wt%. Moreover, PLQE (%) improved when the dopant amount was reduced.

(Example 4 Production Example 1 of Light-Emitting Layer)
An organic EL device having a light emitting layer in which tris- (8-hydroxyquinoline-d6) aluminum obtained in Example 2 and 4,4′-N, N′-dicarbazole-biphenyl (CBP) are co-evaporated is prepared. did. The content of tris- (8-hydroxyquinoline-d6) aluminum was 10 wt%.
Similarly, an organic EL device having a light-emitting layer in which commercially available tris- (8-hydroxyquinoline) aluminum and CBP were co-evaporated was prepared for comparison. Similarly, the content of tris- (8-hydroxyquinoline) aluminum was 10 wt%.

  For comparison, an organic EL device having a light-emitting layer made of only tris- (8-hydroxyquinoline-d6) aluminum (deuterated Alq3) and light emission made only of tris- (8-hydroxyquinoline) aluminum (Alq3). Organic EL device having a layer, organic EL device having a light emitting layer composed of deuterated Alq3 as a host material and C545T having a concentration of 1 wt% as a dopant material, C545T having a host material as Alq3 and a concentration of 1 wt% as a dopant material An organic EL element having a light emitting layer made of was prepared. The structure of the element is as follows.

Example 1: [ITO / TAPC (40 nm) / CBP: DAlq3 (10 wt%) (30 nm) / BCP (10 nm) / Alq3 (20 nm) / LiF (0.5 nm) / Al (80 nm)]
Comparative Example 1: [ITO / TAPC (40 nm) / CBP: Alq3 (10 wt%) (30 nm) / BCP (10 nm) / Alq3 (20 nm) / LiF (0.5 nm) / Al (80 nm)]
Comparative Example 2: [ITO: Br / NPD (40 nm) / DAlq3 (60 nm) / LiF (0.5 nm) / Al (80 nm)]
Comparative Example 3: [ITO: Br / NPD (40 nm) / Alq3 (60 nm) / LiF (0.5 nm) / Al (80 nm)]
Comparative Example 4: [ITO: Br / NPD (20 nm) / DAlq3: C545T (1 wt%) (20 nm) / DAlq3 (40 nm) / LiF (0.5 nm) / Al (80 nm)]
Comparative Example 5: [ITO: Br / NPD (20 nm) / Alq3: C545T (1 wt%) (20 nm) / Alq3 (40 nm) / LiF (0.5 nm) / Al (80 nm)]

  “DAlq3” is tris- (8-hydroxyquinoline-d6) aluminum, “Alq3” is tris- (8-hydroxyquinoline) aluminum, and “C545T” is 10- (2-benzothiazolyl) -2,3, 6,7-tetrahydro-1,1,7,7-tetramethyl-1H, 5H, 11H- (1) -benzopyrrolopyrano (6,7-8-i, j) quinolidin-11-one, “TAPC” Is 1,1-bis ((di-6triamino) phenyl) cyclohexane, “NPD” is N, N-di-[(1-naphthalene) -N, N-diphenyl] -1,1-biphenyl-4 4-diamine.

About the obtained organic EL element, applied voltage (V), power luminous efficiency PE (lm / W), current luminous efficiency CE (cd / A), and external quantum efficiency EQE (%) were measured.
The applied voltage is a voltage necessary for setting the light amount during light emission to 100 cd / m ² or 1000 cd / m ² .
The applied voltage is measured by applying a DC voltage from the variable voltage DC power supply device between the anode and cathode of the produced organic EL element, and the voltage when the light quantity during light emission is 100 cd / m ² or 1000 cd / m ^2. Was measured.

The current luminous efficiency (CE) was calculated by dividing the front luminance by the current density.
Regarding the calculation of power luminous efficiency (PE), first, the organic EL element was assumed to be a complete diffusion surface light source, and the total luminous flux emitted from the element was determined from the front luminance. Thereafter, the total luminous flux obtained was divided by the electric power to obtain PE.

The external quantum yield (EQE) is measured by vapor-depositing the above six kinds of light emitting materials on a quartz substrate to form a thin film, and using a PLQY measuring device manufactured by Hamamatsu Photonics, the light emitting quantum yield at an excitation wavelength of 325 nm is measured. It was measured.
With respect to EQE, it was first assumed that the organic EL element was a completely diffusing surface light source and the emission spectrum had no angular dependence. Then, EQE was obtained from the measured current density, luminance, and EL spectrum.
The results are shown in Table 2.

  From Table 2, in the comparative example using all the light emitting layers as deuterated Alq3, the applied voltage is higher than using non-deuterated Alq3. However, Example 1 using deuterated Alq3 as a dopant is equivalent to the applied voltage compared to Comparative Example 1 using non-deuterated Alq3 as a dopant. In addition, power luminous efficiency (PE), current luminous efficiency (CE), and external quantum efficiency (EQE) were improved. Moreover, the increase rate of EQE with respect to the comparative example 1 of Example 1 is a raise with respect to the comparative example 3 (all the light emitting layers are normal Alq3) of the comparative example 2 (all the light emitting layers are deuterated Alq3). A high value almost equal to the rate was obtained. From the results of Comparative Example 4 and Comparative Example 5, no improvement in performance was observed even when deuterated Alq3 was used as the host material.

Moreover, the organic EL element was similarly produced except having changed the dopant density | concentration of the light emitting layer. The structure of the element is as follows.
Example 2: [ITO / TAPC (40 nm) / CBP: DAlq3 (6 wt%) (30 nm) / BCP (10 nm) / Alq3 (20 nm) / LiF (0.5 nm) / Al (80 nm)]
Comparative Example 6: [ITO / TAPC (40 nm) / CBP: Alq3 (6 wt%) (30 nm) / BCP (10 nm) / Alq3 (20 nm) / LiF (0.5 nm) / Al (80 nm)]
Example 3: [ITO / TAPC (40 nm) / CBP: DAlq3 (20 wt%) (30 nm) / BCP (10 nm) / Alq3 (20 nm) / LiF (0.5 nm) / Al (80 nm)]
Comparative Example 7: [ITO / TAPC (40 nm) / CBP: Alq3 (20 wt%) (30 nm) / BCP (10 nm) / Alq3 (20 nm) / LiF (0.5 nm) / Al (80 nm)]

  About the obtained organic EL element, applied voltage (V), power luminous efficiency PE (lm / W), current luminous efficiency CE (cd / A), and external quantum efficiency EQE (%) were measured. The results of Example 1 and Comparative Example 1 are also shown in Table 3.

  From Table 3, when the dopant amount of deuterated Alq3 is 6 wt% to 20 wt%, the applied voltage is equal or reduced compared to the non-deuterated Alq3 dopant, and the power emission efficiency PE (lm / W), The current luminous efficiency CE (cd / A) and the external quantum efficiency EQE (%) were improved.

(Example 5: Production example 2 of light emitting layer)
An organic EL device having a light emitting layer obtained by co-evaporation of tris- (8-hydroxyquinoline-d6) aluminum obtained in Example 2 and 2-methyl-9,10-di (2-naphthyl) anthracene (MADN) Created.
The structure of the element is as follows.
Example 4: ITO: Br / NPD (20 nm) / NPD: DAlq3 (20 wt%) (20 nm) / MADN: DAlq3 (20 wt%) (50 nm) / DAlq3 (10 nm) / LiF (0.5 nm) / Al (80 nm) )
Comparative Example 8: ITO: Br / NPD (20 nm) / NPD: Alq3 (20 wt%) (20 nm) / MADN: Alq3 (20 wt%) (50 nm) / DAlq3 (10 nm) / LiF (0.5 nm) / Al (80 nm) )

  About the obtained organic EL element, applied voltage (V), power luminous efficiency PE (lm / W), current luminous efficiency CE (cd / A), and external quantum efficiency EQE (%) were measured. The results of Example 4 and Comparative Example 8 are shown in Table 4.

  From Table 4, even if the host material is MADN and the electron transport layer, which is another component of the organic EL element, is changed, the organic EL element having a light-emitting layer using deuterated Alq3 as a dopant material, Compared with the organic EL element having a light emitting layer using Alq3 which is not deuterated as a dopant material, the applied voltage is reduced, the power light emitting efficiency PE (lm / W), the current light emitting efficiency CE (cd / A) and the external The quantum efficiency EQE (%) was improved. Furthermore, the applied voltage (V) was reduced.

By deuterating the luminescent material, it is possible to improve the luminous efficiency while maintaining the color purity of the light emitted from the original material and other chemical characteristics, as described in the above-mentioned known documents (Patent Document 1, Non-Patent Document 1). ).
In the present invention, from the result of the experiment, by deuterating the material added as a dopant material, 6 to 20 wt%, the luminous efficiency is improved to be equal to or higher than that when using 100 wt% of the deuterated material. Confirmed to do. Furthermore, it was confirmed that the improvement in applied voltage observed when a deuterated material was used for the light emitting layer was suppressed. That is, it was confirmed that it is very useful to use a deuterated luminescent material as a dopant.

Claims (2)

It has a light emitting layer containing a dopant material made of a metal complex and a host material,
The dopant material is a metal complex in which deuterium-substituted 8-hydroxyquinolines are used as a ligand and the central metal is aluminum.
The host material is 4,4′-N, N′-dicarbazole-biphenyl, 2-methyl-9,10-di (2-naphthyl) anthracene, or N, N-di-[(1-naphthalene). -N, N-diphenyl] -1,1-biphenyl-4,4-diamine,
The organic electronics luminescence element whose content rate of the said dopant material is 0.01 wt%-30 wt%. The organic electronics luminescence device according to claim 1, wherein the deuteration rate of the ligand is 70% or more.