JP5242976B2 - Organic electroluminescence device - Google Patents

Description

  The present invention relates to an organic electroluminescent device.

  Organic electroluminescent elements (hereinafter abbreviated as organic EL elements) are expected to be applied as promising next-generation display elements because they can emit light with high luminance and high efficiency at a low voltage. An organic EL element is a self-luminous light emitting device using an electroluminescence phenomenon (EL), which is similar in principle to an LED, but is characterized by using an organic material as a light emitting material.

From the viewpoint of putting organic EL elements into practical use, further reduction in voltage and further improvement in luminous efficiency are required. First, the use of triplet excitons is one of the methods for improving luminous efficiency. In the organic light emitting device, it is considered that singlet excitons and triplet excitons are generated in a ratio of 1: 3 due to recombination of holes and electrons in the organic layer.
In the conventional light-emitting material, the generated triplet exciton has a long excitation lifetime, and therefore, non-radiative thermal deactivation occurs preferentially over radiative deactivation in the deactivation process. Therefore, in the conventional organic light-emitting device, only radiation (fluorescence) from singlet excitons can be used as light emission, and radiation from triplet excitons (phosphorescence) cannot be used for light emission.

  However, a research group of Princeton University has disclosed organic light-emitting elements using phosphorescent organic materials that exhibit phosphorescence at room temperature as a light-emitting layer (Non-Patent Document 1), and these organic light-emitting elements use conventional fluorescent materials. It was shown that it has high luminous efficiency compared with the organic light emitting device. Accordingly, in principle, all the generated excitons can be used for light emission, and research on organic light-emitting devices using phosphorescent materials has been actively conducted. Such a phosphorescent organic material has a complex structure mainly having heavy metals such as platinum and iridium. A typical green phosphorescent material is tris (2-phenylpyridine) iridium.

  Further, organic EL elements using phosphorescent materials are expected from the viewpoint of high efficiency toward the practical application of next-generation display elements. However, the research has just begun, and many unsolved issues remain, such as improving the efficiency of the element, reducing the driving voltage, improving the color purity, and optimizing the element structure. Therefore, in order to solve these problems, optimization of element materials and element structures using phosphorescent materials is required. Furthermore, in consideration of the application of organic EL elements to future large screens and high-definition displays, it is possible to form a light emitting layer by a wet process using a solution such as a spin coating method, an ink jet method, or a printing method. Since it is considered to be suitable, it is required to develop a material that can be formed by a wet process, can be driven at a low voltage, and has high efficiency and a long life.

Here, when the light-emitting layer is composed of a mixture of a host material and a phosphorescent guest material, the process leading to phosphorescence from triplet excitons of the guest material is considered as follows. ing.
1. 1. Injection of holes and electrons into the light emitting layer Exciton generation of host material by recombination of holes and electrons (singlet and triplet)
3. Transfer of excitation energy from host material to guest material (singlet and triplet)
4). 4. Triplet exciton generation of guest material Phosphorescence emission associated with deactivation of triplet excitons in guest materials In addition to the above, processes involving trapping and recombination of holes or electrons in the guest material are also considered. Energy transfer and light emission in each process Occurs in competition with various deactivation processes that inhibit them.

  Therefore, in order to increase the light emission efficiency of the organic EL element, it is essential to use a light emitting material having a high emission quantum yield as a guest material. However, in order to efficiently emit the guest material in the organic EL element, The selection of the host material surrounding the guest material in the light emitting layer is also extremely important. That is, the host material is required to efficiently inject electrons and holes from the electrode and to efficiently transport the injected electrons and holes. Further, from the viewpoint of device durability, the host material is required to have high film stability.

  In addition, in order to realize an organic EL element capable of forming a light emitting layer by a wet process, solubility in an organic solvent and excellent film formation by a wet process are required. As a conventional host material in an organic EL element using a phosphorescent material as a guest material, N, N′-dicarbazolylbiphenyl (CBP) disclosed in Non-Patent Document 1 and Patent Document 1 are disclosed. Low molecular weight materials having a carbazole skeleton are widely known. However, these materials are effective for organic EL elements formed by vacuum deposition, but generally, when low molecular weight materials are formed by a wet process, there is a problem of film crystallization. It is considered that it is unsuitable for the production of organic EL devices by the above.

On the other hand, Patent Documents 2 to 4 are disclosed in relation to the present invention. In Patent Document 2, a side chain type non-conjugated polymer is disclosed as a host material, and an element using a non-conjugated polymer is also disclosed in Examples. However, the side chain type non-conjugated polymer has a poor conjugation spread and a low charge mobility. Thus, when a polymer material with low charge mobility is used as a host material of an organic EL element, there is a problem that the drive voltage of the element is increased. Although the main chain type polymer is also disclosed, specific examples are not disclosed.
Patent Document 3 discloses main chain type polycarbazole bonded at the 3 and 6 positions as a polymer host material. However, in the disclosed polymer host material, it is known that the conjugated system is difficult to spread due to the linkage at the 3,6-position. Further, Patent Document 4 discloses a main chain polymer having a repeating unit in which a benzene ring and fluorene are bonded, and an organic EL element using the main chain polymer. However, it is considered that the conjugated system does not spread sufficiently in a main chain polymer having a repeating unit of a benzene ring and fluorene bonded. A main chain type polymer having a benzene ring bonded to the 2-position of carbazole as a repeating unit is also disclosed, but it is considered that the conjugated system is not sufficiently widened, and specific examples are also shown. It has not been.
Therefore, although the polymer materials actually disclosed in Examples in Patent Document 3 and Patent Document 4 are main chain polymers, high charge mobility cannot be expected, and when used as a host of an organic EL element, As a result, the drive voltage of the element increases.
Patent WO01 / 072927 Japanese Patent Laid-Open No. 2001-257076 Japanese Patent Laid-Open No. 2003-076673 JP 2007-106990 A Appl. Phys. Lett. , 175, 4 (1999)

  The present invention has been made to solve the above-described problems, and provides an organic electroluminescent device and a display having high luminous efficiency, excellent stability, and capable of forming a light emitting layer by a wet process. With the goal.

As a result of intensive investigations to realize a coating type organic EL device capable of obtaining high-efficiency light emission, excellent stability, and capable of forming a light-emitting layer by a wet process, the present inventors have substituted the N-position. Polycarbazole bonded at the 2,7-position with the carbazole group introduced as a repeating unit has high charge mobility due to the linear shape of the polymer and the development of conjugation, uniform by wet process And found that a thin film having excellent stability can be formed.
By using these polycarbazole as a host material and a light emitting material that emits fluorescence or phosphorescence as a guest material, it has been clarified that a coating type organic electroluminescent device capable of low voltage operation and extremely high efficiency can be obtained. It came to complete.

一般式（２）中、ｌ_２およびｍ_２はそれぞれ１〜９９の整数、ｎ_２は２〜１，０００，０００の整数であり、Ｒ_１，Ｒ_２，Ｒ_３およびＲ_４は、同一又は独立の置換基であって、水素原子、直鎖状アルキル基、分岐状アルキル基、またはアリール基である。 That is, the present invention adopts the following configuration.
An organic electroluminescent device of the present invention includes a pair of electrodes and a single-layer or multilayer organic thin film layer disposed between the pair of electrodes, and an organic layer having a light-emitting layer in at least one of the organic thin film layers. An electroluminescent device comprising:
The light emitting layer includes a charge transporting polymer host material which is a random copolymer of 3,6, N-substituted carbazole and N-substituted carbazole represented by the following general formula (2), platinum or a guest material is a ligand Toka Ranaru phosphorescent metal complex containing iridium atom and Kaoru aromatic hydrocarbons, but characterized in that it is contained at least.

In general formula (2), l ₂ and m ₂ are each an integer of 1 to 99, n ₂ is an integer of ₂ to 1,000,000, and R ₁ , R ₂ , R ₃ and R ₄ are the same or An independent substituent, which is a hydrogen atom, a linear alkyl group, a branched alkyl group, or an aryl group.

一般式（２）−（ａ）中、ｌ_３およびｍ_３はそれぞれ１〜９９の整数、ｎ_３は２〜１，０００，０００の整数であり、Ｒ_２、Ｒ_３、Ｒ_５およびＲ_６は、同一又は独立の置換基であって、水素原子、直鎖状アルキル基、分岐状アルキル基、またはアリール基である。 In the organic electroluminescent device of the present invention, the polymer host material is represented by the following general formula (2)-(a): high random copolymerization of 3,6, N-substituted carbazole and N-substituted carbazole It is preferably a molecule.

Formula (2) - in (a), an integer of _{l 3} and _{m 3} respectively 1 to 99, _{n 3} is an integer of _{2~1,000,000, R 2, R 3,} R 5 and _{R 6} Are the same or independent substituents, and are a hydrogen atom, a linear alkyl group, a branched alkyl group, or an aryl group.

The organic electroluminescent element of the present invention has an l ₂ : m ₂ or l ₃ : m _{3 in} the polymer host material represented by the general formula (2) or the general formula (2)-(a). The ratio is preferably in the range of 90:10 to 10:90.

The organic electroluminescent device of the present invention, prior to following general formula (2) or the general formula (2) - of the polymeric host material represented by (a), positive in an electric field intensity ^{1 × 10 5 (V / cm} ) The hole drift mobility is preferably 1 × 10 ⁻⁵ (cm ² / V · s) or more.

一般式（３）中、ｍ_４は０〜２の整数であり、ｎ_４は１〜３の整数である。また、Ｒ_９〜Ｒ_１６は、同一又は独立の置換基であって、水素原子、直鎖状アルキル基、分岐状アルキル基、アリール基またはベンゼン環もしくはピリジン環に縮合した芳香環である。さらに、Ｒ１７〜Ｒ１９は、同一又は独立の置換基であって、水素原子、直鎖状アルキル基、分岐状アルキル基、またはアリール基である。 In the organic electroluminescent element of the present invention, the phosphorescent metal complex is preferably an iridium complex composed of iridium represented by the following general formula (3) and a ligand phenylpyridine.

In the general formula (3), _{m 4} is an integer of 0 to 2, _{n 4} is an integer of 1-3. R _{9 to} R ₁₆ are the same or independent substituents and are a hydrogen atom, a linear alkyl group, a branched alkyl group, an aryl group, or an aromatic ring condensed with a benzene ring or a pyridine ring. Furthermore, R17 to R19 are the same or independent substituents, and are a hydrogen atom, a linear alkyl group, a branched alkyl group, or an aryl group.

As described above, according to the organic electroluminescence device of the present invention, carbazole having a substituent introduced at the N-position is used as a repeating unit, and polycarbazole bonded at the 2,7-position is used as a host material to emit fluorescence or phosphorescence. By using a light-emitting material as a guest material, a coating-type organic electroluminescent element that exhibits extremely high-efficiency light emission can be obtained.
Furthermore, according to the organic electroluminescent element of the present invention, low voltage operation is possible.

Hereinafter, an example of an organic electroluminescent element (organic EL element) according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an organic electroluminescent element (organic EL element) according to an embodiment of the present invention. FIG. 1 is for explaining the configuration of the organic EL element 10 of the present embodiment, and the size, thickness, dimensions, and the like of each part shown in the drawing are different from the dimensional relationships of the actual organic EL elements.
An organic electroluminescent element (organic EL element) 10 shown in FIG. 1 has an anode 2 formed on a substrate 1 and an organic thin film layer 8 composed of a hole injection layer 3 and a light emitting layer 4 formed thereon, Further, a cathode 5 is laminated. Furthermore, a sealing glass 7 is roughly constituted by being bonded by an ultraviolet curable resin 6.
By applying a voltage to the anode 2 and the cathode 5, holes are injected from the anode 2 into the hole injection layer 3. The holes move through the hole injection layer 3 and are then injected into the light emitting layer 4. On the other hand, electrons are injected from the cathode 5 into the light emitting layer 4. In the light emitting layer 4, the holes and the electrons are recombined to emit light.

(substrate)
The substrate 1 is preferably made of a material that is transparent and excellent in properties of shielding air, moisture, and the like. Examples of the material of the substrate 1 include inorganic materials such as glass and quartz, and organic materials such as a plastic film, but are not particularly limited in the present embodiment.
Moreover, when using organic materials, such as a plastic film, as the board | substrate 1, it is preferable to provide a gas barrier layer.
Here, the gas barrier layer refers to a thin film layer having an effect of shielding air, moisture, and the like, and can be exemplified by SiO ₂ or SiN formed by a CVD method or a high-frequency sputtering method. Furthermore, a hard coat layer can be provided on the substrate 1 as a gas barrier layer.

(anode)
The anode 2 is preferably made of a material that is transparent, has high conductivity, and a high work function, and more preferably has a work function of at least 4.2 eV.
Moreover, when taking out light emission of the organic EL element 10 from the anode 2 side, it is preferable that the material of the anode 2 is transparent.
Examples of the material of the anode 2 include conductive transparent oxides such as indium-tin-oxide (hereinafter referred to as ITO) or indium-zinc-oxide (hereinafter referred to as IZO). It is not limited to.

(Hole injection layer)
The hole injection layer 3 is preferably made of an organic material having a high hole injection capability. By applying an electric field, holes are taken into the hole injection layer 3 from the anode 2 with high efficiency, and further positive. A material capable of injecting holes from the hole injection layer 3 into the light emitting layer 4 with high efficiency is preferable.
The hole injection layer 3 is preferably an organic material that can stably exist as an organic thin film even when an electric field is applied.
Examples of the hole injection layer 3 include conductive polymer materials such as a mixed material of polyethylene dioxythiophene and polystyrene sulfonate (PEDOT / PSS mixed material), polyaniline, and polythiophene. The embodiment is not particularly limited to these.

The film thickness of the hole injection layer 3 is preferably 1 nm to 5 μm, more preferably 10 nm to 1 μm, and still more preferably 20 nm to 200 nm.
If the thickness of the hole injection layer 3 is less than 1 nm, the hole injection layer 3 is not preferable because it does not form a layer and has an island structure and cannot function as an organic EL element. On the other hand, if the thickness of the hole injection layer 3 exceeds 5 μm, the voltage required for light emission becomes too high due to the thick film thickness, which is not preferable because the light emission efficiency is lowered. Furthermore, when the voltage is increased, a short circuit occurs and the organic EL element 10 may be destroyed.

(Light emitting layer)
The light emitting layer 4 is composed of an organic material having at least two components, that is, a polymer host material and a guest compound made of a phosphorescent light emitting material.
By using the light emitting layer 4 as a host / guest system, concentration quenching is suppressed and the light emission efficiency of the organic EL element 10 can be improved. In addition, the generated excitons can be stably held at the triplet energy level of the guest compound. For this reason, the luminous efficiency of the organic EL element 10 can be improved.

<Polymer host material>
The polymer host material constituting the light emitting layer 4 is a charge transporting material that is a main component of the light emitting layer 4 described above.
The polymer host material is preferably a polymer material bonded at the 2,7-position represented by the following general formula (4) and having 3,6-, N-substituted carbazole as a repeating unit.

式中、ｎ_１は２〜１，０００，０００の整数であり、Ｒ_１，Ｒ_２およびＲ_３は、同一又は独立の置換基であって、水素原子；メチル基、エチル基等の直鎖状アルキル基；イソプロピル基、ｔ−ブチル基等の分岐状アルキル基；フェニル基、トリル基、キシリル基、メシチル基、ｔ−ブチルフェニル基、ビフェニル基等のアリール基等である。

In the formula, n ₁ is an integer of _{2 to} 1,000,000, and R ₁ , R ₂ and R ₃ are the same or independent substituents, and are hydrogen atoms; straight chain such as methyl group, ethyl group, etc. A branched alkyl group such as isopropyl group and t-butyl group; an aryl group such as phenyl group, tolyl group, xylyl group, mesityl group, t-butylphenyl group and biphenyl group.

式中、ｌ_２およびｍ_２はそれぞれ１〜９９の整数、ｎ_２は２〜１，０００，０００の整数であり、Ｒ_１，Ｒ_２，Ｒ_３およびＲ_４は、同一又は独立の置換基であって、水素原子；メチル基、エチル基等の直鎖状アルキル基；イソプロピル基、ｔ−ブチル基等の分岐状アルキル基；フェニル基、トリル基、キシリル基、メシチル基、ｔ−ブチルフェニル基、ビフェニル基等のアリール基等である。 In addition, the polymer host material is a random copolymer polymer bonded by the 2,7-position of the 3,6- and N-substituted carbazole and the N-substituted carbazole represented by the following general formula (5). preferable.

In the formula, l ₂ and m ₂ are each an integer of 1 to 99, n ₂ is an integer of ₂ to 1,000,000, and R ₁ , R ₂ , R ₃ and R ₄ are the same or independent substituents. A hydrogen atom; a linear alkyl group such as a methyl group or an ethyl group; a branched alkyl group such as an isopropyl group or a t-butyl group; a phenyl group, a tolyl group, a xylyl group, a mesityl group, or a t-butylphenyl group. Group, an aryl group such as a biphenyl group, and the like.

式中、ｌ_３およびｍ_３はそれぞれ１〜９９の整数、ｎ_３は２〜１，０００，０００の整数であり、Ｒ_２、Ｒ_３、Ｒ_５およびＲ_６は、同一又は独立の置換基であって、水素原子；メチル基、エチル基等の直鎖状アルキル基；イソプロピル基、ｔ−ブチル基等の分岐状アルキル基；フェニル基、トリル基、キシリル基、メシチル基、ｔ−ブチルフェニル基、ビフェニル基等のアリール基等である。 Further, a random copolymer polymer in which the polymer host material is bonded at the 2,7-positions of 3,6-, N-substituted carbazole and N-substituted carbazole represented by the following general formula (5)-(a) It is preferable that

In the formula, l ₃ and m ₃ are each an integer of 1 to 99, n ₃ is an integer of _{2 to} 1,000,000, and R ₂ , R ₃ , R ₅ and R ₆ are the same or independent substituents. A hydrogen atom; a linear alkyl group such as a methyl group or an ethyl group; a branched alkyl group such as an isopropyl group or a t-butyl group; a phenyl group, a tolyl group, a xylyl group, a mesityl group, or a t-butylphenyl group. Group, an aryl group such as a biphenyl group, and the like.

Specific examples of the compound represented by the general formula (4) are shown below. However, these are merely representative examples, and the polymer host material represented by the general formula (4) used in the present invention is not limited thereto.

Moreover, the specific example of a compound shown by General formula (5) is shown. However, these are merely representative examples, and the polymer host material represented by the general formula (5) used in the present invention is not limited thereto.

Furthermore, the specific example of a compound represented by General formula (5)-(a) among the compounds shown by General formula (5) is shown. However, these are merely representative examples, and the polymer host material represented by the general formula (5)-(a) used in the present invention is not limited thereto.

In the case where the random copolymer polymer represented by the general formula (5) or the general formula (5)-(a) is used as the polymer host material of this embodiment, The composition ratio (l ₂ : m ₂ or l ₃ : m ₃ ) with the N-substituted carbazole is preferably in the range of 90:10 to 10:90. When the composition ratio l ₂ or l ₃ exceeds 90, it is not preferable because of a decrease in the light emission efficiency of the device, and when l ₂ or l ₃ is less than 10, it is preferable because the singlet and triplet energy decreases. Absent. On the other hand, when l ₂ or l ₃ is in the range of 10 to 90, the light emission efficiency of the device is preferably improved.

In addition, when the random copolymer polymer represented by the general formula (5) or the general formula (5)-(a) is used as the polymer host material of the present embodiment, the electric field strength is 1 × 10 ⁵ ( The hole drift mobility in (V / cm) is preferably 1 × 10 ⁻⁵ (cm ² / V · s) or more. When the hole drift mobility is less than 1 × 10 ⁻⁵ (cm ² / V · s), the driving voltage of the device increases, which is not preferable. On the other hand, 1 × 10 ⁻⁵ (cm ² / V · s) or more is preferable because the driving voltage of the element can be reduced.
In the present invention, the hole drift mobility is an index for evaluating the ease of transport of holes in the host material, and a voltage is applied to an element having a structure in which a thin film of material is sandwiched between two electrodes. The transient photocurrent when irradiated with pulsed light in the state is monitored with an oscilloscope or the like to calculate the transit time of holes. The hole drift mobility is estimated from the applied voltage, film thickness, and travel time.

<Guest materials>
The guest material constituting the light emitting layer 4 is preferably a material that emits fluorescence or phosphorescence, and more preferably a phosphorescent material. The phosphorescent material used as the guest material of this embodiment is preferably a metal complex having a transition metal, more preferably a phosphorescence comprising a platinum or iridium atom and a ligand containing an aromatic hydrocarbon. It is a luminescent metal complex. A phosphorescent metal complex is preferable because of its high quantum yield of phosphorescence.

式中、ｍ_４は０〜２の整数であり、ｎ_４は１〜３の整数である。また、Ｒ_９〜Ｒ_１６は、同一又は独立の置換基であって、水素原子、直鎖状アルキル基、分岐状アルキル基、アリール基またはベンゼン環もしくはピリジン環に縮合した芳香環である。さらに、Ｒ１７〜Ｒ１９は、同一又は独立の置換基であって、水素原子、直鎖状アルキル基、分岐状アルキル基、またはアリール基である。 Furthermore, in the guest material of this embodiment, the phosphorescent metal complex is preferably an iridium complex composed of iridium represented by the following general formula (6) and a ligand phenylpyridine.

In the formula, m ₄ is an integer of 0 to 2, and n ₄ is an integer of 1 to 3. R _{9 to} R ₁₆ are the same or independent substituents and are a hydrogen atom, a linear alkyl group, a branched alkyl group, an aryl group, or an aromatic ring condensed with a benzene ring or a pyridine ring. Furthermore, R17 to R19 are the same or independent substituents, and are a hydrogen atom, a linear alkyl group, a branched alkyl group, or an aryl group.

  Below, the concrete structural formula of the guest material used by this embodiment is shown. However, these are merely representative examples, and the guest material used in the present invention is not limited to these. In addition, Formula (6-1)-Formula (6-27) respond | corresponds to General formula (6).

The thickness of the light emitting layer 4 of the present embodiment is preferably 1 nm to 5 μm, more preferably 10 nm to 1 μm, and still more preferably 20 nm to 200 nm.
When the thickness of the light emitting layer 4 is less than 1 nm, the light emitting layer 4 is not preferable because it does not form a layer and has an island structure and cannot function as an organic EL element. On the other hand, if the thickness of the light emitting layer 4 exceeds 5 μm, the voltage required for light emission becomes too high due to the thick film thickness, which is not preferable because the light emission efficiency is lowered. Furthermore, when the voltage is increased, a short circuit occurs and the organic EL element 10 may be destroyed.

In addition, the light emitting layer 4 containing the polymer host material and the guest material shown in the above specific examples may contain other components. That is, other metal complex materials, light emitting materials such as fluorescent materials or phosphorescent materials, or compounds used for a hole transport layer, an electron injection layer, or an electron transport layer can be used.

(cathode)
The cathode 5 of this embodiment preferably uses a metal having a low work function, and is preferably at least 4.0 eV or less. By using a metal having a low work function for the cathode 5, the electron injection barrier between the cathode 5 and the light emitting layer 4 is lowered, and electrons are easily injected from the cathode 5 into the light emitting layer 4. Examples of the metal having a low work function include alkali metals such as Li and Cs, and alkaline earth metals such as Ca, Ba, and Mg, but the present embodiment is not particularly limited thereto. .
However, since a metal having a low work function easily reacts with oxygen or moisture in the air, it is preferably formed as an alloy such as MgAg or a compound such as LiF, LiO2, or CsF. Alternatively, it is preferable to stack a metal having a high work function such as Al and Au on the alkali metal and the alkaline earth metal.

(Sealing glass)
The device portion of the organic EL element 10 can be shielded from the outside by adhering the sealing glass 7 of the present embodiment to the substrate 1 using the ultraviolet curable resin 6. For this reason, the influence of oxygen, moisture, etc. in the air is reduced, and the durability and element life as an organic EL element can be greatly improved. Further, when sealing with glass, the air inside the sealing glass 7 and the substrate 1 is replaced with nitrogen gas, and the desiccant is further introduced into the interior, thereby further enhancing the above-described effects. Can do.

(Production method)
Below, an example of the manufacturing method of the organic EL element 10 of this embodiment is demonstrated in detail.
The manufacturing process of the organic EL element generally includes an anode forming process, an organic thin film layer forming process, and a cathode forming process.

(Anode formation process)
First, the anode 2 is formed on the substrate 1 by sputtering, vacuum deposition, or the like. The anode 2 may be formed in a pattern, and the pattern may be formed by using a mask when forming the anode 2, or after forming the anode 2 over the entire surface, a resist is applied and a glass mask is formed. Then, an exposure process is performed to form a pattern.

(Organic thin film layer forming process)
Next, the organic thin film layer 8 is formed on the anode 2.
Although the formation method of the organic thin film layer 8 of this embodiment is not specifically limited, It can form by methods, such as vacuum evaporation, an electron beam, sputtering, a molecular lamination method, the inkjet method, and the printing method. In addition, vacuum deposition, spin coating, ink jetting, and printing are particularly preferable in view of the characteristics and manufacturing aspects of the formed organic thin film layer 8. Furthermore, when the organic EL element is applied to a future large screen or high-definition display, it is preferable to form the organic thin film layer 8 by a wet process such as a spin coating method, an ink jet method, or a printing method.

(Hole injection layer)
When the above-mentioned PEDOT / PSS mixed material is used as the hole injection layer 3, a formation method using a spin coating method can be exemplified.
For example, first, a predetermined amount of PEDOT / PSS is contained in an organic solvent to prepare a hole injection layer solution. Next, the substrate 1 is set at a predetermined position of the spin coater, set to a predetermined rotation speed, and then the hole injection layer solution is applied. The hole injection layer 3 having a predetermined thickness is formed by introducing it into a chamber at 180 ° C., performing a drying process, and removing the organic solvent.
The organic solvent is preferably a polar solvent, and examples thereof include N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, ethylene glycol, diethylene glycol, and glycerin.

(Light emitting layer)
The light emitting layer 4 is exemplified by a method in which the light emitting layer solution is first prepared, and then the light emitting layer solution is applied and dried on the hole injection layer 3 by a wet process such as a spin coating method or an ink jet method. can do.
More specifically, for example, the substrate 1 on which the hole injection layer 3 is formed is set at a predetermined position of a spin coater, and after the light emitting layer solution is dropped, the substrate is rotated and applied at a predetermined speed. The rotation is stopped, and the substrate 1 taken out from the spin coater is introduced into the chamber and held for 1 hour. By this drying step, the organic solvent is removed, and the light emitting layer 4 having a predetermined thickness is formed.

  The organic thin film layer 8 is composed of a plurality of layers including the hole injection layer 3 and the light emitting layer 4. Examples of the organic thin film layer 8 other than the hole injection layer 3 and the light emitting layer 4 include a hole transport layer, an electron injection layer, and an electron transport layer. For the formation of the other layers, various materials known for constituting each layer can be used.

(Cathode formation process)
Finally, the cathode 5 is formed by sputtering, vacuum deposition, or the like. Below, the formation method of the cathode 5 by a vacuum evaporation method is illustrated, However It does not specifically limit to this.
First, the substrate 1 on which the organic thin film layer 8 has been formed is attached to a predetermined position in a chamber of a vacuum evaporator, and then the inside of the chamber is decompressed and a metal material is vacuum-deposited. A cathode 5 is formed on the substrate 1.

Hereinafter, effects of the embodiment of the present invention will be described.
In the organic EL device of this embodiment, since the material of two or more components constituting the light emitting layer is composed of a polymer host material and a guest compound made of a phosphorescent light emitting material, electrons, holes and electrons And excitons generated by hole recombination can be accumulated in the light emitting layer. Moreover, since the generated excitons can be held at the triplet energy level of the guest compound, the light emission efficiency of the organic EL element can be improved.

  In the organic EL device of this embodiment, the polymer host material has a linear shape and has developed conjugation, so that the charge transport ability is excellent, and the carbazole having a substituent introduced at the N-position is a repeating unit. As described above, since it is a polycarbazole bonded at positions 2 and 7, many holes can be accumulated in the light emitting layer. As a result, the light emission efficiency of the organic EL element can be improved.

  In the organic EL device of the present embodiment, the guest compound is a phosphorescent light-emitting material having platinum or iridium atoms that can stably hold excitons at the triplet energy level. Excitons can be accumulated at the triplet energy level of the guest compound, and light can be emitted with high efficiency. As a result, the light emission efficiency of the organic EL element can be improved.

  Since the organic EL element of this embodiment can form organic thin film layers, such as a light emitting layer, with a wet process, it does not require the large vacuum chamber etc. which are required by a dry process, but is a large-sized organic EL display. Manufacturing can be simplified.

As described above, according to the organic electroluminescent device of this embodiment, carbazole having a substituent introduced at the N-position is used as a repeating unit, polycarbazole bonded at the 2,7-position is used as a host material, and fluorescence or phosphorescence is emitted. By using a light emitting material that emits light as a guest material, it is possible to obtain a coating type organic electroluminescent element that exhibits extremely high efficiency light emission.
Furthermore, according to the organic electroluminescent element of the present embodiment, since a polymer host material having a high charge transport capability is used, low voltage operation is possible.

  Hereinafter, the production and characteristics of the organic EL elements of Examples and Comparative Examples will be described in detail, and the effects of the present invention will be described. However, the present invention is not limited to these Examples.

Monomers used for the production of the polycarbazole derivatives of the present invention, such as 2,7-dichloro-N-alkylcarbazole, 2,7-dichloro-3,6-dimethyl-N-alkylcarbazole, 2,7-dichloro- N- (4-alkyloxyphenyl) carbazole and 2,7-dichloro-3,6-dimethyl-N- (4-alkyloxyphenyl) carbazole have been described by James-Francois et al., Macromolecules, Vol. 34, p4680, (2001), Gianni et al., Macromolecules, Vol. 35, p2122, (2002), Kijima et al., Chemistry Letter, Vol. 34, p900, (2005), Ahmed et al., Chemistry of Materials, Vol. 18, p1007, (2006). The structure of the obtained product was confirmed by mass spectrum and ¹ H-NMR analysis, and used for the synthesis of the following polycarbazole derivatives.

<Example 1>
As a polymer host material of the light emitting layer, 2,7-position bonded 3,6-dimethyl-N- (4- (2-ethylhexyloxy) phenyl) carbazole and 2,7-position bonded-N- (4- (2- (2- A random copolymer (compound (5) -17) was synthesized with ethylhexyloxy) phenyl) carbazole in a molar ratio of l: m = 50: 50.

First, 0.79 g (2.88 mmol) of bis (1,5-cyclooctadiene) nickel (0) and 0.45 g (2.88 mmol) of 2,2′-bipyridyl were added to an argon-substituted Schlenk. The mixture was placed in an argon stream, 6.0 mL of N, N-dimethylformamide (DMF) was added, and the mixture was stirred at room temperature for 30 minutes. There 0.28 g (0.60 mmol) 2,7-dichloro-3,6-dimethyl-N- (4- (2-ethylhexyloxy) phenyl) carbazole and 0.26 g (0.60 mmol) 2,7 A solution of -dichloro-N- (4- (2-ethylhexyloxy) phenyl) carbazole in 15 mL of tetrahydrofuran (THF) was added, and the vessel was sealed and stirred at 65 ° C. for 72 hours.
Next, 0.17 g (0.60 mmol) of 4-chlorotriphenylamine as an end cap agent was added to the reaction solution, and the container was sealed and stirred at 65 ° C. for 8 hours. The reaction solution was added dropwise to a mixed solvent of 2000 mL of methanol and 80 mL of concentrated hydrochloric acid and stirred for 12 hours. The precipitate was collected by filtration, dissolved in 150 mL of toluene, washed twice with 150 mL of 3N-HCl, and further repeatedly washed with ultrapure water until neutral.
Subsequently, it was washed twice with 150 mL of ammonia water and washed with ultrapure water until neutral. The toluene solution was concentrated and dropped into 2000 mL of methanol for reprecipitation. The precipitate was collected by filtration to obtain 0.42 g of polymer (recovery rate 77%).

The molecular weight of the polymer measured by gel permeation chromatography (GPC) is, in terms of polystyrene, weight average molecular weight (Mw) 638,804, number average molecular weight (Mn) 92,604, and polydispersity (Mw / Mn). 90.
FIG. 2 shows a ¹ H-NMR spectrum (CDCl ₃ , 400 MHz) of this polymer.

<Example 2>
As a polymer host material of the light emitting layer, 2,7-position bonded 3,6-dimethyl-N- (4- (2-ethylhexyloxy) phenyl) carbazole and 2,7-position bonded-N- (4- (2- (2- A random copolymer (compound (5) -17) was synthesized so that ethylhexyloxy) phenyl) carbazole was in a molar ratio of 1: m = 30: 70.

  As used in Example 1, 0.28 g (0.60 mmol) of 2,7-dichloro-3,6-dimethyl-N- (4- (2-ethylhexyloxy) phenyl) carbazole and 2,7-dichloro-N -(4- (2-ethylhexyloxy) phenyl) carbazole instead of 0.26 g (0.60 mmol), 2,7-dichloro-3,6-dimethyl-N- (4- (2-ethylhexyloxy) phenyl) Carbasol 0.16 g (0.36 mmol) and 2,7-dichloro-N- (4- (2-ethylhexyloxy) phenyl) carbazole 0.37 g (0.84 mmol) were used, and the other conditions were the same as in Example 1. Thus, a copolymer was synthesized to obtain 0.41 g of a polymer (recovery rate 78%).

The molecular weight of the polymer measured by GPC was weight average molecular weight (Mw) 418,649, number average molecular weight (Mn) 124,461, and polydispersity (Mw / Mn) 3.36 in terms of polystyrene.
FIG. 3 shows the ¹ H-NMR spectrum (CDCl ₃ , 400 MHz) of this polymer.

<Example 3>
As a polymer host material for the light-emitting layer, 2,7-position bonded 3,6-dimethyl-N-decylcarbazole and 2,7-position bonded-N-decylcarbazole were used in a molar ratio of l: m = 40: 60. Thus, a random copolymer (compound (5) -2) was synthesized.

First, 0.66 g (2.40 mmol) of bis (1,5-cyclooctadiene) nickel (0) and 0.38 g (2.40 mmol) of 2,2′-bipyridyl were added to an argon-substituted Schlenk. After putting in an argon stream and adding 8.0 mL of DMF, the mixture was stirred at room temperature for 30 minutes. There, 0.16 g (0.40 mmol) 2,7-dichloro-3,6-dimethyl-N-decylcarbazole and 0.23 g (0.60 mmol) 2,7-dichloro-N-decylcarbazole. Then, a solution dissolved in 20 mL of THF was added, the vessel was sealed, and stirred at 65 ° C. for 72 hours.
Next, the reaction solution was dropped into a mixed solvent of 1000 mL of methanol and 40 mL of concentrated hydrochloric acid and stirred for 12 hours. The precipitate was collected by filtration, dissolved in 150 mL of toluene, washed twice with 150 mL of 3N-HCl, and further repeatedly washed with ultrapure water until neutral.
Subsequently, it was washed twice with 150 mL of ammonia water and washed with ultrapure water until neutral. The toluene solution was concentrated and dropped into 1000 mL of methanol for reprecipitation. The precipitate was collected by filtration to obtain 0.13 g of polymer (recovery rate 65%).

The molecular weight of the polymer measured by GPC was weight average molecular weight (Mw) 490,920, number average molecular weight (Mn) 102,884, and polydispersity (Mw / Mn) 4.77 in terms of polystyrene.
FIG. 4 shows the ¹ H-NMR spectrum (CDCl ₃ , 400 MHz) of this polymer.

The solution optical properties and thin film optical properties of the polymers obtained in Examples 1 to 3 were measured. Table 1 shows the characteristics of the polymers synthesized according to Examples 1 to 3, respectively.
The solution optical properties were obtained by dissolving the polymers obtained in Examples 1 to 3 in chloroform and measuring the absorption spectrum (UV) to 1.0 × 10 ⁻⁵ (mol / l), the fluorescence spectrum (PL ) At the time of measurement, the concentration was adjusted to 1.0 × 10 ⁻⁷ (mol / l) and then measured.
The thin film optical characteristics were obtained by preparing a toluene or xylene solution of the polymer obtained in Examples 1 to 3 and forming a film by spin coating. Film formation conditions were 2000 rpm (60 seconds) after 500 rpm (5 seconds), and the film thickness of the thin film was adjusted to 30 to 40 (nm).

In Table 1, λmax indicates the maximum wavelength (nm) of the absorption spectrum, and PL indicates the maximum wavelength (nm) of the fluorescence.
Moreover, the fluorescence quantum yield ((PHI) sol) in the solution state of the polymer of Examples 1 to 3 was calculated based on 9,10-diphenylanthracene ([Phi] = 0.90).
Further, the highest occupied orbit (HOMO) was calculated from onset of the oxidation potential of the thin film measured by cyclic voltammetry.
Furthermore, the lowest empty orbit (LUMO) was calculated from the difference between the optical band gap and HOMO.
The optical band gap (Eg) was determined from the absorption edge of the UV spectrum of the polymer thin film obtained in Examples 1 to 3.

Moreover, the spin coat film | membrane (solvent: toluene) was formed using the polymer of Examples 1-3, and the hole drift mobility was measured by the time-of-flight method.
Table 2 shows the measurement results of the hole drift mobility of the polymer films of Examples 1 to 3. It was shown that all the polymers of Examples 1 to 3 have a high hole drift mobility of 10 ⁻⁴ (cm 2 / V · s) or more.

<Example 4>
As Example 4, an organic EL element having the structure shown in FIG. 1 was produced as follows.
First, an anode 2 made of indium-tin oxide (ITO) was formed on a substrate 1 made of glass.
Next, PEDOT: PSS (Baytron P CH8000) was formed as a hole injection layer on the anode 2 to a thickness of 35 nm by a spin coating method and dried at 180 ° C.
Further, the mass ratio of the polymer (5) -17 shown in Example 1 as a polymer host material and Ir (ppy) ₃ represented by the structural formula of the compound (6) -2 exemplified as the guest compound And a toluene solution was prepared by mixing in a ratio of 94: 6. Using this toluene solution, the light emitting layer 4 was formed by spin coating.
Furthermore, a cathode 5 made of CsF (2 nm) / Al (100 nm) was formed on the light emitting layer 4 by vacuum deposition.
Further, after the cathode 5 was formed, sealing glass 7 was adhered to the element with ultraviolet curable resin 6 in a glove box filled with nitrogen gas, and sealing was performed.

When the voltage was applied to the organic EL element of Example 4 so as to be positive on the ITO anode side and negative on the aluminum cathode side, the current, luminance, and emission spectrum were measured. When voltage was applied, green light emission from a guest having an emission peak of 516 nm was obtained. The voltage at a luminance of 100 (cd / m ² ) is 4.9 (V), and the external light emission quantum efficiency and the power efficiency at a luminance of 100 (cd / m ² ) are 3.3 (%) and 7 respectively. 4 l (m / W).

<Example 5>
In the organic EL device of Example 5, the polymer (5) -17 (monomer charge ratio 50:50) shown in Example 1 and the electron transport material OXD-7 are 70:30 in mass ratio. The mixture was used as a polymer host material.
This polymer host material and Ir (ppy) ₃ as a guest compound were mixed at a mass ratio of 94: 6 to prepare a toluene solution. Using this toluene solution, the light emitting layer 4 was formed by spin coating. In addition, it has the same structure as the element of the above-mentioned Example 4 except the composition of the light emitting layer.

When a voltage was applied to the organic EL element of Example 5 so as to be positive on the ITO anode side and negative on the aluminum cathode side, green light emission from a guest having an emission peak of 516 nm was obtained. The voltage at a luminance of 100 (cd / m ² ) is 6.0 (V), and the external light emission quantum efficiency and the power efficiency at a luminance of 100 (cd / m ² ) are 4.4 (%) and 7 respectively. 0.8 l (m / W).

<Comparative Example 1>
In the organic EL device of Comparative Example 1, the mass ratio of poly (N-vinylcarbazole), which is a non-conjugated polymer having a carbazole group in the side chain, and the electron transport material OXD-7 is 70:30. The mixture was used as a polymer host material.
This polymer host and Ir (ppy) ₃ as a guest compound were mixed at a mass ratio of 94: 6 to prepare a toluene solution. Using this toluene solution, the light emitting layer 4 was formed by spin coating. In addition, except for the composition of the light emitting layer, it has the same structure as the device of Example 5 described above.

When a voltage was applied to the organic EL element of Comparative Example 1 so as to be positive on the ITO anode side and negative on the aluminum cathode side, green light emission from a guest having an emission peak of 512 nm was obtained. The voltage at luminance 100 (cd / m ² ) is 5.3 (V), and the external light emission quantum efficiency and power efficiency at luminance 100 (cd / m ² ) are 3.1 (%) and 6 respectively. 0.6 l (m / W).

Table 3 shows the composition of the light emitting layer of the organic EL devices of Examples 5 to 6 and Comparative Example 1, and Table 4 shows the evaluation results.
The organic EL element of Example 5 emitted light at a lower voltage than the organic EL element of Comparative Example 1. In addition, the organic EL device of Example 6 had higher external quantum efficiency than the organic EL device of Comparative Example 1.

  From the above results, it is shown that by using the polymer material of the present invention as a host and the phosphorescent material as a guest, a coating type organic EL element capable of being driven at a low voltage and obtaining high efficiency light emission can be produced. It was.

  The present invention relates to an organic electroluminescent device that emits high-efficiency phosphorescence, and can be suitably used in the fields of display devices, displays, backlights, electrophotography, illumination light sources, exposure light sources, signs, signboards, and interiors. It can be used in the lighting equipment and display industries. In particular, it can be suitably used for energy saving and highly visible flat panel displays.

1 shows the ¹ H-NMR spectrum of Compound (5) -17 (monomer charge ratio: 50:50), which is a polymer according to Example 1. ¹ shows the ¹ H-NMR spectrum of Compound (5) -17 (monomer charge ratio 70:30), which is a polymer according to Example 2. ¹ shows the ¹ H-NMR spectrum of Compound (5) -2 (monomer charge ratio 40:60) which is a polymer according to Example 3. The cross-sectional schematic diagram of the organic electroluminescent element (organic EL element) which is embodiment of this invention is shown.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Anode, 3 ... Hole injection layer, 4 ... Light emitting layer, 5 ... Cathode, 6 ... UV curable resin, 7 ... Glass for sealing , 8 ... Organic thin film layer, 10 ... Organic electroluminescence device (organic EL device)

Claims (5)

An organic electroluminescent device comprising a pair of electrodes and a single-layer or multi-layer organic thin film layer disposed between the pair of electrodes, and having a light emitting layer in at least one of the organic thin film layers,
The light emitting layer includes a charge transporting polymer host material which is a random copolymer of 3,6, N-substituted carbazole and N-substituted carbazole represented by the following general formula (2), platinum or a guest material is a ligand Toka Ranaru phosphorescent metal complex containing iridium atom and Kaoru aromatic hydrocarbon, but the organic electroluminescent device, characterized in that it is contained at least.

In general formula (2), l ₂ and m ₂ are each an integer of 1 to 99, n ₂ is an integer of ₂ to 1,000,000, and R ₁ , R ₂ , R ₃ and R ₄ are the same or An independent substituent, which is a hydrogen atom, a linear alkyl group, a branched alkyl group, or an aryl group. The polymer host material is a random copolymer polymer of 3,6, N-substituted carbazole and N-substituted carbazole represented by the following general formula (2)-(a): The organic electroluminescent element according to claim 1.

Formula (2) - in (a), an integer of _{l 3} and _{m 3} respectively 1 to 99, _{n 3} is an integer of _{2~1,000,000, R 2, R 3,} R 5 and _{R 6} Are the same or independent substituents, and are a hydrogen atom, a linear alkyl group, a branched alkyl group, or an aryl group. The ratio of l ₂ : m ₂ or l ₃ : m _{3 in} the polymer host material represented by the general formula (2) or the general formula (2)-(a) is 90:10 to 10: The organic electroluminescent element according to claim 1 or 2, wherein the organic electroluminescent element is in a range of 90. The hole drift mobility in the electric field strength of 1 × 10 ⁵ (V / cm) of the polymer host material represented by the general formula (2) or the general formula (2)-(a) is 1 × 10 ^−5. The organic electroluminescent element according to any one of claims 1 to 3, wherein the organic electroluminescent element is (cm ² / V · s) or more. 5. The phosphorescent metal complex is an iridium complex composed of iridium represented by the following general formula (3) and a ligand phenylpyridine. Organic electroluminescent element.

In the general formula (3), _{m 4} is an integer of 0 to 2, _{n 4} is an integer of 1-3. R _{9 to} R ₁₆ are the same or independent substituents and are a hydrogen atom, a linear alkyl group, a branched alkyl group, an aryl group, or an aromatic ring condensed with a benzene ring or a pyridine ring. Furthermore, R17 to R19 are the same or independent substituents, and are a hydrogen atom, a linear alkyl group, a branched alkyl group, or an aryl group.

Images