JP2001110568A - Organic light emitting device - Google Patents

Abstract

(57) [Problem] To provide a polymer-dispersed organic light-emitting device having high luminous efficiency. SOLUTION: The light emitting layer comprises a charge transporting polymer 3A having a specific hole transporting performance, a charge transporting material 3B having a specific electron transporting performance, and a light emitting material 3C,
A polymer-dispersed organic light-emitting device having high luminous efficiency can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting device used for a flat light source or a flat display.

[0002]

2. Description of the Related Art An electroluminescent element has attracted attention as a display element such as a flat display because it has high visibility due to self light emission and can be made thin. Above all, an organic EL element using an organic compound as a light-emitting element can achieve a desired emission color by being able to be driven at a low voltage, being easy to increase in area, and selecting an appropriate dye as compared with an inorganic EL element. It has features such as being easily obtained, and is being actively developed as a next-generation display.

As an EL element using an organic light-emitting material, blue light emission is obtained by applying a voltage of 30 V to an anthracene vapor-deposited film having a thickness of 1 μm or less (Thi).
n Solid Films, 94 (1982) 171). However, this device did not provide sufficient luminance even when a high voltage was applied, and it was necessary to further improve the luminous efficiency.

On the other hand, Tang et al. Have a transparent electrode (anode),
By stacking a hole transport layer, an electron transporting light emitting layer, and a cathode using a metal having a low work function, the luminous efficiency was improved, and a luminance of 1000 cd / m ² was realized with an applied voltage of 10 V or less ( Appl. Phys. Lett., 51 (1987) 913).

Further, a device having a three-layer structure in which a light emitting layer is sandwiched between a hole transport layer and an electron transport layer (Jpn. J. Appl Phys., 27
(1988) L269) and an element (J. Appl. Phys., 65 (1989) 3610) that obtains light emission from a dye doped in a light emitting layer.

On the other hand, while all the elements having the above-described structure form each layer by a dry process such as a vacuum evaporation method, there is a method of forming an element by a so-called wet film forming method such as a spin coating method or a casting method ( For example, Japanese Patent Laid-Open No. 3-7
No. 90, JP-A-3-171590 and the like).

That is, at least one of the materials for forming the hole transport layer, the electron transport layer, and the light emitting layer is dissolved in a suitable solvent together with a polymer binder, and the solution is applied to the electrode surface to form a light emitting layer. Thereafter, an electrode is further formed on the light emitting layer by a vapor deposition method or the like. Hereinafter, the organic light-emitting device thus manufactured is referred to as a polymer-dispersed light-emitting device with respect to a conventional stacked light-emitting device.

Advantages of the polymer-dispersed light-emitting device compared to an organic light-emitting device manufactured by a dry process include the following. (1) Materials that are difficult to form in a dry process such as vapor deposition can be used. (2) A small amount of doping, which is difficult to control in a dry process, can be easily realized. (3) Large area is easy. (4) It can be manufactured at low cost. (5) By introducing a plurality of light emitting materials, light emission from each light emitting material can be easily obtained simultaneously (white light emission is possible). (6) In the conventional stacked light emitting device, each layer is in an amorphous state, whereas in the polymer dispersed light emitting device, each material is dispersed in a polymer binder, so that it is thermally stable.

The structure of the light emitting layer of the conventional polymer dispersed light emitting device is a dispersion of a perinone derivative or tris (8-quinolinolato) aluminum as a light emitting material in polyvinyl carbazole, and tris (8-quinolinolato) as a light emitting material in polycarbonate. Aluminum and tetraphenylbenzidine are dispersed (for example, JP-A-3-790, JP-A-3-17159).
No. 0).

[0010]

The polymer-dispersed light-emitting device has the above-mentioned advantages, but has a problem that its luminous efficiency is lower than that of the conventional stacked-type light-emitting device.

That is, in the stacked light emitting device, holes are injected from the anode into the hole transport layer, and electrons are injected from the cathode into the electron transporting light emitting layer or the electron transport layer. And when these holes and electrons recombine in the light emitting layer,
Excitons are formed and emit light when the excitons transition to the ground state. Here, since electron transport and hole transport are functionally separated, recombination of electrons and holes occurs only near the interface between the layers. Therefore, exciton generation occurs efficiently, and luminous efficiency also improves.

Further, regarding the injection of holes and electrons, if the material of the layer in contact with each electrode is selected so that the injection barrier between the anode and the cathode is reduced, the injection can be easily performed and the driving at a low voltage is possible. Becomes

On the other hand, in the case of the polymer-dispersed light-emitting device, since it mainly has a single-layer structure, recombination of holes and electrons and generation of excitons occur locally, as in the above-described stacked light-emitting device. No hole from the electrode
Since the electron injection barrier is large, it has been difficult to improve the luminous efficiency.

The present invention solves the above-mentioned problems, and realizes high luminous efficiency and low driving voltage even in a polymer-dispersed organic light-emitting device.

[0015]

Means for Solving the Problems As a result of intensive studies to achieve the above object, we have found that a polymer-dispersed light emitting device contains a charge transport material having a specific carrier mobility in a polymer, or It has been found that by using a charge transporting polymer having a specific carrier mobility, current-luminance efficiency can be improved. Furthermore, it has been found that the drive voltage can be reduced by inserting a hole injection layer having a specific ionization potential between the positive electrode and the light emitting layer, or by including a hole transport material having a specific ionization potential in the light emitting layer. .

Specifically, the organic light-emitting device according to the first aspect of the present invention is an organic light-emitting device having at least one light-emitting layer between a positive electrode and a negative electrode, wherein the light-emitting layer is a charge transport material; An organic light emitting device comprising a light emitting material and a polymer for dispersing the light emitting material.

Further, the invention of claim 2 of the present application is an organic light emitting device wherein the polymer of claim 1 is a charge transporting polymer.

The invention according to claim 3 of the present application is an organic light-emitting device in which the polymer according to claim 1 is a hole transporting polymer.

The invention according to claim 4 of the present application is the organic light emitting device according to claim 3, wherein the charge transporting material is an electron transporting material.

According to a fifth aspect of the present invention, there is provided an organic light emitting device in which the hole transporting polymer according to the third or fourth aspect has a carrier mobility of 1 × 10 ⁻⁷ cm ² / V · s or more. is there.

According to the invention of claim 6 of the present application, the carrier mobility of the electron transporting material according to claim 4 or 5 is 5 × 10 ^−8.
An organic light-emitting device having a cm ² / V · s or more was obtained.

The invention of claim 7 of the present application is directed to claims 4 to
7. An organic light-emitting device according to item 6, wherein the content of the electron transporting material is 30 to 120% by weight based on the polymer.

The invention of claim 8 of the present application is directed to claims 4 to
7. The ion transport potential of the hole transporting polymer according to 7 is higher than the ion potential of the luminescent material,
In addition, the electron transport material has an electron affinity smaller than that of the light emitting material.

[0024] The invention of claim 9 of the present application is directed to claims 3 to
8. The organic light-emitting device according to item 8, wherein the polymer is poly-N-vinylcarbazole having a repeating unit represented by the general formula (Formula 1).

The invention of claim 10 of the present application is directed to claim 4
9. The electron transporting material according to any one of items 1 to 9, wherein the electron transporting material is an organic light emitting device comprising at least one of an oxazole derivative, an oxadiazole derivative, a triazole derivative, a pyrazine derivative, and an aldazine derivative.

The invention of claim 11 of the present application is directed to claim 4
9. The electron transporting material according to any one of items 1 to 9, wherein the electron transporting material is an organic light emitting device comprising a quinolinol complex or a derivative thereof.

The invention of claim 12 of the present application is directed to claim 1
The electron transporting material according to 1 is an organic light emitting device comprising tris (8-quinolinolato) aluminum or a derivative thereof.

Further, the invention of claim 13 of the present application is the invention of claim 1
13. The organic light-emitting device according to any one of items 12 to 12, further comprising a hole injection layer between the positive electrode and the light-emitting layer.

Further, the invention of claim 14 of the present application is the invention of claim 1
3. The ionization potential (Ip) of the hole injection layer described in 3.
(h)), the ionization potential (Ip
(p)), an organic light-emitting device in which the relationship between the ionization potential or work function (Ip (a)) of the positive electrode is represented by the following equation.

Ip (a) <Ip (h) <Ip (p) Further, the invention of claim 15 of the present application is directed to claim 13 or 14
The hole injection layer described above is an organic light emitting device comprising at least one of a polyaniline derivative, a polythiophene derivative, and amorphous carbon.

Further, the invention of claim 16 of the present application is the invention of claim 1
16. The organic light-emitting device according to any one of Items 15 to 15, further comprising an electron injection layer between the negative electrode and the light-emitting layer.

Further, the invention of claim 17 of the present application is the invention of claim 1
6. The electron affinity or work function of the electron injection layer according to item 6,
An organic light emitting device having a work function smaller than the work function of the negative electrode.

Further, the invention of claim 18 of the present application is the invention of claim 1
7. The electron injection layer according to item 7, wherein the electron injection layer is an organic light emitting device comprising at least one of dilithium phthalocyanine, disodium phthalocyanine, and an organic boron complex compound.

[0034] The invention of claim 19 of the present application is the invention of claim 1.
8. The organic light-emitting device according to item 8, wherein the electron injection layer comprises 4,4,8,8-tetrakis (1H-pyrazol-1-yl) pyraza ball.

Further, the invention of claim 20 of the present application is the invention of claim 1
20. The organic light-emitting device according to any one of Items 19 to 19, wherein the charge transporting material includes at least one or more hole transporting materials and at least one electron transporting material.

The invention of claim 21 of the present application is the invention of claim 2
0 is an organic light-emitting device in which the hole transport material has an ionization potential lower than the ionization potential of the polymer.

The invention of claim 22 of the present application is the invention of claim 2
An organic light-emitting device having a hole transport material content of 0 to 21 in an amount of 10 to 120% by weight based on the polymer.

[0038]

Embodiments of the present invention will be described below. FIG. 1 is a sectional view showing one example of the organic light emitting device according to the present invention. In FIG. 1, 1 is a substrate, 2 is a positive electrode, 3 is a light emitting layer, and 4 is a negative electrode.

The substrate 1 is only required to support the organic light-emitting device of the present invention. A transparent substrate such as glass or a resin film such as polycarbonate, polymethyl methacrylate, or polyethylene terephthalate, or an opaque substrate such as silicon is used. be able to.

At least one of the positive electrode 2 and the negative electrode 4 needs to be transparent or translucent, and light emitted from the light emitting layer is extracted to the outside through one or both electrodes. Usually, a transparent electrode such as indium tin oxide (ITO) or tin oxide is often used as the positive electrode 2, but a metal electrode such as NI, Au, Pt, or Pd may be used. For the purpose of improving the transparency or reducing the resistivity of the ITO film, a film forming method such as sputtering, electron beam evaporation, or ion plating is employed. The film thickness is determined from the required sheet resistance value and visible light transmittance. However, since the organic light emitting element has a relatively high driving current density, it is used at a thickness of 1000 mm or more to reduce the sheet resistance value. Is often done. Examples of the cathode 4 include alloys of metals such as Al, Ag, and Au, metals having low work functions such as MgAg alloys and AlLi alloys, and metals having relatively large work functions and stable metals.
A stacked electrode of a metal having a low work function and a metal having a high work function, such as / Al and LiF / Al, can be used.
A vapor deposition method or a sputtering method is preferred for forming these negative electrodes. In FIG. 1, although the structure is such that the substrate / positive electrode / light-emitting layer / negative electrode is arranged from the bottom, it is not always necessary to stack in this order. It may be in order. In FIG. 1, when only the electrode on the substrate 1 side, that is, the positive electrode 2 is transparent and the negative electrode 4 is opaque, the substrate 1 also needs to be a transparent substrate in order to extract light emission to the outside.

The light emitting layer comprises a charge transport material 3B, a light emitting material 3C,
And polymer 3A for dispersing them.
As the polymer material, a charge transporting polymer is preferable, and among them, a hole transporting polymer is preferable. The hole transporting polymer has a carrier mobility of 1 × 10 ^−7.
cm ² / V · s or more is preferable, and poly-N-vinyl carbazole having a repeating unit represented by the general formula (Formula 1) is particularly preferable. When a hole transporting polymer is used, it is preferable to use an electron transporting material as the charge transporting material. Furthermore, the carrier mobility of the electron transport material is
It is preferably at least 5 × 10 ⁻⁸ cm ² / V · s. In particular, oxazole derivatives, oxadiazole derivatives, triazole derivatives, pyrazine derivatives, aldazine derivatives, quinolinol complexes and derivatives thereof are preferred. Further, the content of the electron transporting material is preferably 30 to 120% by weight based on the polymer. That is, when the content is less than 30% by weight, the electron transporting ability is not sufficient, and when the content is more than 120% by weight, the dispersibility in the polymer becomes poor. As the luminescent material, a fluorescent substance or a phosphorescent substance which emits light in response to hole / electron recombination may be used. Particularly, substances which exhibit strong fluorescence or phosphorescence include cyanine dyes, merocyanine dyes, styryl dyes, and anthracene derivatives. , Porphyrin derivative, phthalocyanine derivative, coumarin, D
Dyes such as CM and Nile Red and laser dyes can be used. Further, as the light emitting material, a substance in which the ionization potential of the light emitting material is lower than the ionization potential of the hole transporting polymer and the electron affinity of the light emitting material is higher than the electron affinity of the electron transporting material is preferable.

The light emitting mechanism of the organic light emitting device of the present invention is as follows. That is, in the organic light emitting device having the configuration shown in FIG. 1, when a voltage is applied between the positive electrode 2 and the negative electrode 4 in the direction shown in the figure, holes are injected from the positive electrode 2 and electrons are injected into the light emitting layer 3 from the negative electrode 4. You. The injected holes flow toward the negative electrode 4 and the electrons flow toward the positive electrode 2. The holes and electrons are recombined in the light emitting layer, and in response to this, the light emitting material in the light emitting layer emits fluorescence or phosphorescence. Here, the following factors can be cited as main factors for determining the current efficiency of light emission (the efficiency of light emission with respect to the injected current). (1) Recombination efficiency of holes and electrons with respect to injection current (2) Exciton generation efficiency of luminescent material due to recombination (3) Emission quantum efficiency from excitons of luminescent material Among the above, (2) and (3) ) Is substantially determined by the properties of the luminescent material itself. On the other hand, the recombination efficiency of holes and electrons in (1) is most affected by the balance between holes and electrons. In other words, if the balance between holes and electrons is poor, excess carriers reach the opposite electrode without recombination in the light-emitting layer even if injected from the electrode, resulting in a useless current that does not contribute to light emission. Therefore, if the mobility of each carrier in the light emitting layer is increased,
The holes and electrons flow in a well-balanced manner, and the luminous efficiency also improves. Specifically, the mobility of the hole is 1 × 10 ⁻⁷ cm ² / V · s
As described above, the electron mobility is preferably 5 × 10 ⁻⁸ cm ² / V · s or more.

FIGS. 2 to 4 are cross-sectional views showing another example of the organic light emitting device according to the present invention. 2 to 4, 5
Is a hole injection layer, 6 is an electron injection layer, 3D is a hole transport material, and 3E is an electron transport material.

The hole injection layer 5 is formed between the positive electrode 2 and the light emitting layer 3.
Inserted to assist hole injection into As the hole injection layer 5, its ionization potential (Ip (h))
And the ionization potential of the polymer (Ip (p)) and the ionization potential or work function (I
It is preferable to use a material that satisfies Ip (a) <Ip (h) <Ip (p) with respect to p (a)). In particular, it is preferable that the material be at least one of a polyaniline derivative, a polythiophene derivative, and amorphous carbon.

The electron injection layer 6 is inserted for the purpose of assisting electron injection from the negative electrode 4 into the light emitting layer 3. Electron injection layer 6
It is preferable to use a material whose electron affinity or work function is smaller than the work function of the negative electrode. In particular, it is preferable to be composed of at least one of dilithium phthalocyanine, disodium phthalocyanine, and an organic boron complex compound. The hole transporting material 3D is introduced for the purpose of assisting the hole injection from the positive electrode 2 to the light emitting layer 3 similarly to the hole injection layer. However, hole injection layer 5
Unlike this, instead of being inserted as a layer between the positive electrode 2 and the light emitting layer 3, they are dispersed directly in the light emitting layer. As the hole transport material 3D, it is preferable to use a material whose ionization potential is smaller than the ionization potential of the polymer. The content of the hole transport material is
It is preferably from 10 to 120% by weight based on the polymer. That is, if the amount is less than 10% by weight, sufficient hole injection cannot be performed, and if the amount is more than 120% by weight, dispersibility in a polymer becomes poor.

The effect of introducing the hole injection layer 5, the electron injection layer 6, and the hole transport material 3D will be described with reference to the drawings. 5 to 8 are energy diagrams of the organic light emitting device according to the present invention.

FIG. 5 shows an organic light-emitting device having a structure of a positive electrode / light-emitting layer (hole transporting polymer + electron transporting material + light-emitting material) / negative electrode, and FIG. 6 shows a positive electrode / hole injection layer / light-emitting layer (hole transporting property). 2 shows an energy diagram of an organic light-emitting device having a configuration of (polymer + electron transport material + light-emitting material) / negative electrode and its operation mechanism. As described above, when a voltage is applied to the organic light emitting device, holes are injected from the positive electrode and electrons are injected from the negative electrode into the light emitting layer. More specifically, as shown in FIG. 5, both carriers are injected into a substance having a smaller injection barrier, that is, holes are injected into the hole transporting polymer in the light emitting layer, and electrons are injected into the electron transporting material in the light emitting layer. Here, the smaller the injection barrier of both carriers (holes and electrons), the easier the injection occurs, and the lower the driving voltage. Therefore, even if the current efficiency is the same,
By reducing the driving voltage, the power efficiency of light emission (the efficiency of light emission with respect to input power) can be improved. Therefore,
For example, when inserting a hole injection layer where the ionization potential is between the positive electrode and the hole transporting polymer,
As shown in FIG. 6, the hole injection barrier is reduced, and the driving voltage can be reduced. Furthermore, when the hole injection barrier is larger than the electron injection barrier as shown in FIG. 5, the hole injection barrier is made smaller to improve the balance between the hole injection amount and the electron injection amount. Improvements in efficiency can also be expected.

FIG. 7 is an energy diagram of an organic light emitting device having a structure of a positive electrode / a light emitting layer (a hole transporting polymer + an electron transporting material + a light emitting material) / an electron injecting layer / a negative electrode. Similarly to the hole injection barrier, the electron injection barrier having an electron affinity smaller than that of the negative electrode can be inserted into the electron injection layer to reduce the barrier as shown in FIG. And luminous efficiency can be improved.

On the other hand, FIG. 8 is an energy diagram of an organic light emitting device having a structure of a positive electrode / a light emitting layer (a hole transporting polymer + a hole transporting material + an electron transporting material + a light emitting material) / a negative electrode. In this case, since the ion transport potential of the hole transport material is smaller than that of the hole transport polymer, holes are directly injected from the positive electrode into the hole transport material in the light emitting layer, as shown in the figure, and are injected into the hole transport polymer. The injection barrier is smaller than that of the first embodiment. Therefore, as in the case where the hole injection layer is inserted, the drive voltage can be reduced and the current efficiency can be improved.

Of course, a combination of the above constitutions, that is, both a hole injection layer and an electron injection layer are inserted, or an electron injection layer is further inserted by using a light emitting layer as a hole transporting polymer + a hole transporting material + an electron transporting material + a light emitting material. Alternatively, the configuration may be such that

Next, a more detailed description will be given based on specific embodiments.

Example 1 An organic light-emitting device having the structure shown in FIG. 1 was manufactured as follows. A glass substrate having a thickness of 0.7 mm was used as a substrate 1, and ITO was formed thereon as a positive electrode 2 by a sputtering method. ITO film thickness is about 1000
(4) The sheet resistance was set to about 15 Ω / □, and patterned into a desired shape by photolithography. Light emitting layer 3
Are poly-N-vinylcarbazole (PVK) (molecular weight of about 28,000) as the polymer 3A, tris (8-quinolinolato) aluminum (Alq ₃ ) as the charge transporting material 3B, and Nile Red which is a laser dye as the light emitting material 3C. Was used. PVK is a hole transporting polymer having a carrier mobility of about 2 × 10 ⁻⁶ cm ² / V · s. Alq ₃ is an electron transporting material, and its carrier mobility is about 2 × 10 ⁻⁶ cm ² / V · s. The mixing ratio of each material is PVK: Alq ₃ : Nile Red = 100: 6
0: 0.2 (weight ratio). The light emitting layer was formed by the method described below. PVK 300 mg, Alq ₃ 180
mg and Nile Red (0.6 mg) were dissolved in a mixed solvent of toluene and chloroform (1: 1) (30 ml) and stirred for 1 day. This solution was spin-coated on the glass substrate with ITO, which had been previously washed and subjected to oxygen plasma treatment, to obtain a light-emitting layer 3. Spin coating is performed at 500 rpm for 10 seconds and 1000 rpm for 3 seconds in a state of being sealed using a spinner.
This was performed under the condition of 0 second, and then 1 hour using a hot plate.
Heat treatment was performed at 10 ° C. for 1 minute. The thickness of the light emitting layer 3 is about 1
000Å. Next, a Li / Al laminated electrode was formed as a cathode 4 by a vacuum evaporation method. Film formation is about 5 degrees of vacuum
Performed under × 10 ^-6 Torr, first, Li was added to about 0.5Å / s.
After depositing 10 ° at a rate of ec, Al was deposited at about 30 ° / s
Evaporated at 1500 ° C. The desired shape of the cathode was obtained using a mask.

On the other hand, regarding the energy level of each material, the ionization potential of ITO is 4.9 eV, PV
The ionization potential of K is 5.6 eV, the electron affinity is 2.0 eV, and the ionization potential of Alq3 is 5.7.
eV, electron affinity is 3.0 eV, ionization potential of Nile Red is 5.3 eV, electron affinity is 3.5 e
The work functions of V and Li are 2.9 eV, and the work function of Al is 4.3 eV.

When a voltage was applied to the organic light emitting device thus manufactured in the direction shown in FIG. 1, the device emitted orange light. At this time, current efficiency (cd / A) and luminance 100 cd /
Table 1 shows the drive voltage at m ² and the power efficiency (lm / W) at a luminance of 100 cd / m ² .

[0055]

[Table 1]

Example 2 An organic light emitting device having the structure shown in FIG. 2 was manufactured and evaluated. Substrate 1, positive electrode 2, light emitting layer 3, cathode 4
Has the same configuration and thickness as in Example 1, and a commercially available polythiophene derivative is inserted as the hole injection layer 5. The hole injection layer was formed by spin coating in the same manner as in the light emitting layer, and the film thickness was 150 °. The ionization potential of the polythiophene derivative used here is 5.3 eV. Table 1 shows the evaluation results of the device.

Example 3 As the hole injection layer 5 of Example 2, a commercially available polyaniline derivative having an ionization potential equivalent to that of the polythiophene derivative was used instead of the polythiophene derivative. The film formation of the polyaniline derivative was performed in the same manner as in Example 2, and the film thickness was 150 °. Table 1 shows the evaluation results of the device.

Example 4 As the hole injection layer 5 of Example 2, amorphous carbon was used instead of the polythiophene derivative. Amorphous carbon was formed by a sputtering method, and the film thickness was 100 °. The ionization potential of amorphous carbon is 5.2 eV.
Table 1 shows the evaluation results of the device.

Example 5 An organic light emitting device having the structure shown in FIG. 3 was manufactured and evaluated. The substrate 1, the positive electrode 2, and the light emitting layer 3 had the same configuration and film thickness as in Example 1. Dilithium phthalocyanine was formed as the electron injection layer 6 on the light emitting layer, and Al was formed as the negative electrode 4. . Dilithium phthalocyanine and Al are formed by a vacuum evaporation method, and dilithium phthalocyanine is deposited on the light emitting layer 3 at a rate of about 0.3 ° / sec.
After forming the film at 0 °, the Al is deposited at 1500 ° at approximately 30 ° / sec.
A film was formed. Dilithium phthalocyanine has an electron affinity of 3.0 eV. Table 1 shows the evaluation results of the device.

(Example 6) Instead of dilithium phthalocyanine, disodium phthalocyanine having the same electron affinity as the electron injection layer 6 of Example 5 was used. Film formation of disodium phthalocyanine was performed in the same manner as in Example 5, and the film thickness was 10 °. Table 1 shows the evaluation results of the device.

(Example 7) As the electron injection layer 6 of Example 5, instead of dilithium phthalocyanine, 4,4,8,
8-Tetrakis (1H-pyrazol-1-yl) pyrazaball was used. 4,4,8,8-tetrakis (1H-
(Pyrazol-1-yl) pyraza ball was formed in Example 5.
And the film thickness was 10 °. 4,4,8,8-
The electron affinity of tetrakis (1H-pyrazol-1-yl) pyrazaball is 2.3 eV. Table 1 shows the evaluation results of the device.

Example 8 An organic light emitting device having the structure shown in FIG. 4 was manufactured and evaluated. The substrate 1, the positive electrode 2, and the negative electrode 4 had the same configuration and film thickness as those of the first embodiment. As the light emitting layer 3, PVK is used as the polymer 3A, and N,
N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine (T
PD), Alq ₃ as the electron transport material 3E, and the luminescent material 3
Nile red was used as C. The ionization potential of TPD is 5.4 eV. The mixing ratio of each material is
PVK: Alq ₃ : TPD: Nile red = 100: 6
0: 80: 0.2 (weight ratio). The formation of the light emitting layer
PVK 300mg, Alq ₃ 180mg, TPD240
mg and Nile Red (0.6 mg) were dissolved in a mixed solvent of toluene and chloroform (1: 1) (50 ml), stirred for one day, and then spin-coated on the glass substrate with ITO in the same manner as in Example 1. The thickness of the light emitting layer 3 was 1000 °. Further, a negative electrode 4 was formed thereon similarly to (Example 1).
, A Li / Al laminated electrode was vacuum deposited. Table 1 shows the evaluation results of the device.

(Example 9) An element having both a hole injection layer and an electron injection layer inserted was manufactured. That is, from the bottom, a substrate / a positive electrode / a hole injection layer / a light emitting layer / an electron injection layer / a negative electrode were used. The polythiophene derivative was used as the hole injection layer, and the dilithium phthalocyanine was used as the electron injection layer in Example 2, respectively. It was formed by the same manufacturing method and film thickness as in Example 5. The light emitting layer had the same structure as that of Example 1, and Al was formed at 1500 ° as a negative electrode. Table 1 shows the evaluation results of the device.

(Comparative Example 1) An organic light-emitting device similar to that of Example 1 was manufactured except that the light-emitting layer was made of only PVK and Nile Red in the structure of FIG. Table 1 shows the evaluation results of the device.

Comparative Example 2 An organic light-emitting device similar to that of Example 1 was manufactured except that the light-emitting layer was made of PVK, TPD, and Nile Red in the structure of FIG. TPD
Shows hole transport properties, but shows only extremely small electron transport properties. Table 1 shows the evaluation results of the device.

In comparison with Comparative Examples 1 and 2 which did not contain a charge transporting material having a high electron transporting ability, about 2 ×
When Alq ₃ having a high electron mobility of 10 ⁻⁶ cm ² / V · s was included, the current efficiency could be greatly improved. Further, as shown in Examples 2 to 9, the drive voltage is further reduced by inserting a hole injection layer and an electron injection layer, or by introducing a hole transporting material into the light emitting layer to assist hole injection. And improved power efficiency.

[0067]

As described above, according to the organic light-emitting device of the present invention, the light-emitting layer is made of a charge transporting material, a light-emitting material, and a polymer for dispersing the same, and these materials are made of a specific material. By having a carrier transporting property or an ionization potential, holes and electrons flow in the light emitting layer in a well-balanced manner, so that luminous efficiency can be improved.

Further, by inserting a hole injection layer or an electron injection layer, or introducing a hole transport material for assisting hole injection into the light emitting layer, the hole or electron injection barrier is relaxed and the driving voltage is further reduced. It can reduce the light emission efficiency.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an organic light-emitting device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of an organic light emitting device according to a second embodiment of the present invention.

FIG. 3 is a sectional view of an organic light emitting device according to a third embodiment of the present invention.

FIG. 4 is a sectional view of an organic light emitting device according to a fourth embodiment of the present invention.

FIG. 5 is a diagram showing an energy diagram of the organic light emitting device of the first embodiment according to the present invention.

FIG. 6 is a diagram showing an energy diagram of an organic light emitting device of a second embodiment according to the present invention.

FIG. 7 is a diagram showing an energy diagram of an organic light emitting device of a third embodiment according to the present invention.

FIG. 8 is a diagram showing an energy diagram of an organic light emitting device of a fourth embodiment according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Positive electrode 3 Light emitting layer 3A polymer 3B Charge transport material 3C Light emitting material 3D Hole transport material 3E Electron transport material 4 Negative electrode 5 Hole injection layer 6 Electron injection layer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tetsuya Sato 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Terms (reference) 3K007 AB03 AB06 CA00 CA01 CA05 CA06 CB01 DA00 DB03 EB00 FA01

Claims (22)

[Claims] 1. An organic light emitting device having at least one light emitting layer between a positive electrode and a negative electrode, wherein the light emitting layer comprises:
An organic light-emitting device comprising a charge transport material, a light-emitting material, and a polymer for dispersing these materials. 2. The organic light emitting device according to claim 1, wherein the polymer is a charge transporting polymer. 3. The organic light emitting device according to claim 1, wherein the polymer is a hole transporting polymer. 4. The organic light emitting device according to claim 3, wherein the charge transporting material is an electron transporting material. 5. The carrier transfer of the hole transporting polymer.
Mobility is 1 × 10^-7cm ^Two/ V · s or more
The organic light-emitting device according to claim 3 or 4, wherein 6. The carrier mobility of the electron transport material is 5
^{5. The method according} to claim 4, wherein the pressure is not less than × 10 ⁻⁸ cm ² / V · s.
Or the organic light-emitting device according to 5. 7. The organic light emitting device according to claim 4, wherein the content of the electron transporting material is 30 to 120% by weight based on the weight of the polymer. 8. The method according to claim 1, wherein an ionization potential of the hole transporting polymer is higher than an ionization potential of the light emitting material, and an electron affinity of the electron transporting material is smaller than an electron affinity of the light emitting material. Item 8. The organic light-emitting device according to any one of Items 4 to 7. 9. The organic light-emitting device according to claim 3, wherein the polymer is poly-N-vinylcarbazole having a repeating unit represented by the following general formula (Formula 1). . Embedded image 10. The method according to claim 4, wherein the electron transporting material comprises at least one of an oxazole derivative, an oxadiazole derivative, a triazole derivative, a pyrazine derivative, and an aldazine derivative. Organic light emitting device. 11. The method according to claim 4, wherein the electron transporting material comprises a quinolinol complex or a derivative thereof.
10. The organic light-emitting device according to any one of 9. 12. The organic light emitting device according to claim 11, wherein the electron transporting material is made of tris (8-quinolinolato) aluminum or a derivative thereof. 13. The organic light emitting device according to claim 1, further comprising a hole injection layer between the positive electrode and the light emitting layer. 14. The relationship among the ionization potential (Ip (h)) of the hole injection layer, the ionization potential of the polymer (Ip (p)), the ionization potential of the positive electrode or the work function (Ip (a)) is as follows: The organic light emitting device according to claim 13, wherein the organic light emitting device is represented by the following formula. Ip (a) <Ip (h) <Ip (p) 15. The method according to claim 1, wherein the hole injection layer is made of at least one of a polyaniline derivative, a polythiophene derivative, and amorphous carbon.
15. The organic light-emitting device according to 3 or 14. 16. The organic light emitting device according to claim 1, further comprising an electron injection layer between the cathode and the light emitting layer. 17. The organic light emitting device according to claim 16, wherein an electron affinity or a work function of the electron injection layer is smaller than a work function of the negative electrode. 18. The organic light emitting device according to claim 17, wherein the electron injection layer is made of at least one of dilithium phthalocyanine, disodium phthalocyanine, and an organic boron complex compound. 19. The method according to claim 19, wherein the electron injection layer comprises 4,4,8,8-
The organic light-emitting device according to claim 18, comprising tetrakis (1H-pyrazol-1-yl) pyrazaball. 20. The organic light emitting device according to claim 1, wherein the charge transporting material includes at least one kind of hole transporting material and at least one electron transporting material. 21. The organic light emitting device according to claim 20, wherein an ionization potential of the hole transport material is smaller than an ionization potential of the polymer. 22. The organic light emitting device according to claim 20, wherein the content of the hole transport material is 10 to 120% by weight based on the weight of the polymer.