JP2001196176A - Organic electric field light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To offer an organic electric field light emitting element with high light emitting efficiency and a small decrease in a brightness at the time of a drive life end. SOLUTION: The organic electric field light emitting element is characterized by a light emitting layer 4 which contains the light emitting organic and inorganic compounds, and film thickness being 5 nm or less. Or, the organic electric field light emitting element is characterized by the light emitting layer 4 containing the alkali metal compound. According to such composition, the organic electric field light emitting element which has a high light emitting efficiency and a possibility of emitting light in various colors is offered easily.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device widely used as various display devices such as a display, and more particularly to an organic electroluminescent device excellent in low driving voltage, high brightness and excellent stability. is there.

[0002]

2. Description of the Related Art An electroluminescent device is capable of displaying a brighter and clearer display than a liquid crystal device due to self-luminous light.
It has been studied by many researchers since ancient times.

At present, as an electroluminescent element which has reached a practical level and is commercialized, there is an element using ZnS as an inorganic material. However, since such an inorganic electroluminescent element requires a driving voltage of about 200 V for light emission,
It has not been widely used.

On the other hand, an organic electroluminescent device, which is an electroluminescent device using an organic material, is far from a practical level in the past. However, Applied Physics Letters, vol. 51, p. 1987 (App
l. Phys. Lett. , Vol. 51, Page 9
13, 1987), a layered structure element developed by CW Tang et al. Of Kodak Co., Ltd. has dramatically improved its characteristics. They stack a phosphor that has a stable structure and can transport electrons and an organic substance that can transport holes, and efficiently injects electrons and holes into the phosphor. We succeeded in emitting light. by this,
The luminous efficiency of the organic electroluminescent device was improved, and light emission of 1000 cd / m ² or more was obtained at a voltage of 10 V or less.

[0005] After that, the element structure and the organic compound to be used have been optimized, and the commercialization of the organic electroluminescent element has begun partially, but both the luminous characteristics and the life characteristics are insufficient.

[0006] In particular, improvement of life characteristics is a major problem.
Improving the heat resistance of the organic compound used for the device is still energetically performed. Further, Japanese Unexamined Patent Application Publication No.
Japanese Patent Application Laid-Open No. 02360 proposes dispersing an organic compound in an inorganic compound to improve heat resistance, but only one having low light emission characteristics is obtained.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an organic electroluminescent device having high luminous efficiency and excellent life characteristics.

[0008]

The present invention provides an organic electroluminescent device having at least a light emitting layer containing a light emitting organic compound between a pair of electrodes, wherein the light emitting layer contains an inorganic compound, An organic electroluminescent device having a thickness of 5 nm or less. Alternatively, an organic electroluminescent element having at least a light-emitting layer containing a light-emitting organic compound between a pair of electrodes, wherein the light-emitting layer contains an alkali metal compound It is.

According to such a configuration, an organic electroluminescent device having high luminous efficiency and excellent life characteristics can be easily provided.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The invention according to claim 1 has a light emitting layer containing a light emitting organic compound between a pair of electrodes,
The light emitting layer contains an inorganic compound and has a thickness of 0.05
An organic electroluminescent device having a thickness of not less than 5 nm and not more than 5 nm. By including an inorganic compound in the light emitting layer in this manner, heat resistance is improved, and further, the dispersed state of the light emitting organic compound is improved. Then, the thickness of the light emitting layer is set to 5
When the thickness is less than nm, highly efficient electroluminescence can be achieved.

As the inorganic compound used here, general inorganic compounds such as oxides, peroxides, composite oxides, halides and nitrides may be used. Specifically, SiO, Si
O ₂ , GeO, GeO ₂ , Li ₂ O, LiF, MgO, M
gF ₂ , CaO, CaF _{2 and the} like.

The luminescent material (luminescent organic compound used for the luminescent layer) used here is selected from various fluorescent organic compounds such as laser dyes. Particularly useful luminescent material is fluorescent metal. Complex compounds, quinacridone derivatives, coumarin derivatives, merocyanine derivatives, oxazole derivatives, thiazole derivatives, styryl derivatives,
Flavone derivatives, quinoline derivatives, acridine derivatives,
And condensed polycyclic compounds.

According to a second aspect of the present invention, there is provided the organic electroluminescent device according to the first aspect, wherein the fluorescence lifetime of the luminescent organic compound is shorter than the fluorescence lifetime of another organic compound used in the device. It is.

By providing such a light emitting layer, the energy of excitons generated by recombination of electrons and holes can be efficiently transferred to the material of the light emitting layer, and highly efficient electroluminescence can be obtained from the light emitting layer. It becomes possible. The term "fluorescence lifetime" as used herein refers to the time required for the fluorescence intensity to become 1 / e of the initial value, and is measured by a general-purpose fluorescence lifetime measuring device.

According to a third aspect of the present invention, there is provided an organic electric field comprising a light emitting layer containing a light emitting organic compound between a pair of electrodes, wherein the light emitting layer contains an alkali metal compound. It is a light emitting element. When the light-emitting layer contains an alkali metal compound, the light-emitting layer interacts with a light-emitting organic compound to change the light emission wavelength to a longer wavelength side.

As the invention of claim 4, as the alkali metal compound, an alkali metal oxide, peroxide, composite oxide, halide, nitride or alkali metal salt is useful. Specifically, LiF, LiCl, Li ₂ O,
Li ₂ O ₂ , LiAlO ₂ , LiCO ₃ , Li ₃ N, NaC
1, Na ₂ WO ₄ , KAlO ₂ , CsF, Cs ₂ O, Rb ₂
O, RbCl and the like.

Hereinafter, the present invention will be described with reference to specific embodiments.

In the following embodiment, N, N'-bis [4 '-(N, N'-diphenylamino) -4-biphenylyl] -N, N' represented by Chemical Formula 1 is used as a hole transport material. -Diphenylbenzidine (hereinafter referred to as TPT), tris (8-quinolinol) aluminum (hereinafter referred to as Alq) represented by Chemical Formula 2 as an electron transporting material, and an anode, a hole transporting layer, a light emitting layer, an electron transporting layer, The configuration of the element stacked in the order of the cathode is shown representatively,
The present invention is not limited to this configuration.
Also, usually laminated on the substrate in order from the anode to the cathode,
Conversely, the layers may be stacked on the substrate in order from the cathode to the anode.

[0019]

Embedded image

[0020]

Embedded image (Embodiment 1) The organic electroluminescent device of the present embodiment
As shown in FIG. 1, a hole transport layer 3, a light emitting layer 4, an electron transport layer 5, and a cathode 6 were formed on a glass substrate 1 on which an ITO electrode was formed as a transparent electrode 2 in advance. Having a configuration. As the luminescent organic compound, 4- (dicyanomethylene) -2-methyl-6 shown in Chemical formula 3 is used.
-(P-Aminostyryl) -4H-pyran (DCM) and GeO as the inorganic compound were used.

[0021]

Embedded image First, a sufficiently cleaned glass substrate with an ITO electrode, T
PT, DCM, Alq, GeO, aluminum and lithium were set in a vapor deposition device.

Then, after evacuating to 2 × 10 ^-4 Pa,
TPT set at a rate of 0.1 nm / sec was evaporated to form a hole transport layer of 50 nm. Then, the DCM of the luminescent material
And GeO, an inorganic compound, were deposited from different deposition sources to form a light emitting layer of 0.05 to 50 nm in thickness consisting of DCM and GeO. At this time, evaporation was performed by adjusting the evaporation rate so that the molar ratio of DCM to GeO was 1: 1.
Next, Alq as an electron transporting material is deposited at 0.1 nm / sec,
An electron transport layer having a thickness of 50 nm was laminated. Thereafter, aluminum and lithium were deposited from different deposition sources, and a co-deposited layer of aluminum and lithium was formed to a thickness of 150 nm to form a cathode. These depositions were continuously performed without breaking vacuum, and the film thickness was monitored with a quartz oscillator.

Immediately after the device was manufactured, the electrodes were taken out in dry nitrogen, and the characteristics were measured. Here, the luminous efficiency of the obtained device was 100 cd / luminance.
It was defined by the value for m ² . The drive life was defined as the time required for the luminance to reach half of the initial value, 500 cd / m ² , when the device was driven at a constant current with an initial luminance of 1000 cd / m ² .

The results are shown in the following (Table 1).

[0025]

[Table 1] From Table 1, it is confirmed that when the thickness of the light-emitting layer is 5 nm or less, the light-emitting characteristics and driving life are significantly improved, and the organic electroluminescent device of this embodiment has excellent light-emitting efficiency and driving life. Was.

(Embodiment 2) An organic electroluminescent device according to the present embodiment is similar to that of Embodiment 1, except that LiF is used instead of GeO as an inorganic material contained in the light emitting layer. It was fabricated and its characteristics were evaluated. Note that the thickness of the light-emitting layer was 1 nm.

As a result, the luminous efficiency was 2.5 lm / W, and the driving life was 360 hours. It was confirmed that the organic electroluminescent device of this embodiment had excellent luminous efficiency and driving life. Further, the peak wavelength of the emission spectrum is 620
nm, which is a 35 nm longer wavelength shift than 585 nm when LiF is not used. Thus, it was confirmed that the emission wavelength could be controlled by including the alkali metal compound in the light emitting layer.

(Embodiment 3) As shown in FIG. 1, the organic electroluminescent device of this embodiment has a hole transport layer on a glass substrate 1 on which an ITO electrode is formed in advance as a transparent electrode 2. 3, a light emitting layer 4, an electron transporting layer 5, and a cathode 6 in that order. DCM is used as the luminescent organic compound, and Li is used as the alkali metal compound.
F was used.

First, a sufficiently cleaned glass substrate with an ITO electrode, TPT, DCM, Alq, LiF, aluminum and lithium were set in a vapor deposition apparatus.

Then, after evacuating to 2 × 10 ^-4 Pa,
TPT set at a rate of 0.1 nm / sec was evaporated to form a hole transport layer of 50 nm. Then, the DCM of the luminescent material
And LiF as an inorganic compound and Alq as an electron transporting material were respectively deposited from different evaporation sources to form a 25 nm-thick light emitting layer composed of DCM, LiF and Alq. At this time, D
Vapor deposition was performed by adjusting the vapor deposition rate so that the concentrations of CM and LiF became 1 mol%. Next, Alq as an electron transporting material was deposited at a rate of 0.1 nm / sec, and an electron transporting layer having a thickness of 25 nm was laminated. Thereafter, aluminum and lithium were deposited from different deposition sources, and a co-deposited layer of aluminum and lithium was formed to a thickness of 150 nm to form a cathode. These depositions were continuously performed without breaking the vacuum, and the film thickness was monitored with a quartz oscillator.

Immediately after the device was manufactured, the electrodes were taken out in dry nitrogen, and the same characteristic measurement as in the first embodiment was performed.

As a result, the luminous efficiency was 4.5 lm / W, and the driving life was 460 hours. It was confirmed that the organic electroluminescent device of this embodiment had excellent luminous efficiency and driving life. Further, the peak wavelength of the emission spectrum is 630.
nm, which is 40 nm longer than 590 nm when LiF was not used. Thus, it was confirmed that the emission wavelength could be controlled by including the alkali metal compound in the light emitting layer.

[0033]

As described above, according to the present invention, the organic electroluminescent device or the light emitting layer in which the light emitting layer contains a light emitting organic compound and an inorganic compound and has a thickness of 0.05 nm or more and 5 nm or less. By using an organic electroluminescent device containing an alkali metal compound, an organic electroluminescent device having high luminous efficiency and capable of emitting various colors can be easily provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an organic electroluminescent device according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Transparent electrode 3 Hole transport layer 4 Light emitting layer 5 Electron transport layer 6 Cathode

Continued on the front page F term (reference) 3K007 AB00 AB03 AB04 AB14 CA01 CB01 DA00 DA02 DB03 EB00 FA01 5F041 AA03 CA45 CA46 CA88 CA98 FF01

Claims (4)

[Claims] 1. A light-emitting layer containing a light-emitting organic compound is provided between a pair of electrodes, wherein the light-emitting layer contains an inorganic compound and has a thickness of 0.05 nm or more and 5 nm or less. Organic electroluminescent device. 2. The organic electroluminescent device according to claim 1, wherein the fluorescence lifetime of the luminescent organic compound is shorter than the fluorescence lifetime of another organic compound used in the device. 3. An organic electroluminescent device having a light emitting layer containing a light emitting organic compound between a pair of electrodes, wherein the light emitting layer contains an alkali metal compound. 4. The organic electric field according to claim 3, wherein the alkali metal compound is selected from alkali metal oxides, peroxides, complex oxides, halides, nitrides and alkali metal salts. Light emitting element.