JP2001338761A - Organic el element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic EL element, where a positive hole is recombined with an electron even inside a luminescent layer, the thickness of a luminescent region in the luminescent layer and the position and the chromaticity of the luminescent region in the thickness direction can be controlled, and its luminescent color can be adjusted easily to a desired one. SOLUTION: This organic EL element 1 is provided, by forming a positive electrode 3 formed of ITO, an organic EL thin film, having the luminescent layer and a negative electrode 5 formed of an Al-Li alloy on a surface of a glass transparent substrate 2 in that order by a vacuum deposition method, and thereafter sealing them with a sealing member 6. In this case, the luminescent layer is provided with two kinds of luminescent regions, such as a first luminescent region 441 of perylene of a hole transporting blue dopant and a hole transport material TEL22 in an electron transport luminescent material BAlq, and a second luminescent region 442 including a hole transport red dopant DCJT therein.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention can increase the light emitting area in the thickness direction of the light emitting layer, can control the thickness of the light emitting area, etc., have high light emitting efficiency, and have sufficient luminance. The present invention relates to an organic electroluminescence (EL) device capable of reducing a voltage required for light emission in a device.

[0002]

2. Description of the Related Art A light emitting material used for a light emitting layer of an organic EL device is excellent in one of a hole transporting property and an electron transporting property. Light is emitted only in the region, which leads to a reduction in the life of the device. In addition, when light is emitted not only in the vicinity of one interface but also in a wide area including the inside of the light emitting layer, the thickness of the light emitting layer, the content of the dopant, and the like deviate from the optimum values at which the light emitting efficiency is maximized. In this case, the light emission region must be controlled by reducing the probability of recombination of holes and electrons, which leads to a decrease in light emission efficiency.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and the recombination region of holes and electrons can be extended to the inside of the light emitting layer, so that the lifetime is long. An object is to provide an organic EL device. In addition, the present invention can control the thickness, the position, and the chromaticity of the light-emitting region in the thickness direction of the light-emitting layer, and in particular, maintain the chromaticity of the light-emitting regions having different emission colors while maintaining high luminous efficiency. It is an object to provide an organic EL device which can be controlled and can easily adjust a light emission color of the device to a desired one.

[0004]

According to a first aspect of the present invention, there is provided an organic EL device comprising: a substrate; and an organic EL laminate formed by laminating an anode, an organic EL thin film, and a cathode in this order on a surface of the substrate. The organic EL thin film has at least a light emitting layer,
The light-emitting layer is made of an electron-transporting light-emitting material containing a hole-transporting material, or a hole-transporting light-emitting material containing at least one of an electron-transporting material and a hole-blocking material. Is expanded to the inside of the light emitting layer.

The above “organic EL thin film” is formed on the surface of the anode by
At least a hole transport layer, a light emitting layer, and an electron transport layer are sequentially laminated and formed. The light-emitting layer can contain a dopant for improving the luminous efficiency, the stability of the device, and the like, and the dopant can provide a desired luminescent color. Further, a hole injection layer can be provided between the anode and the hole transport layer, and an electron injection layer can be provided between the electron transport layer and the cathode.

The “electron transporting luminescent material” is Al
Aluminum quinolium complexes such as q3 and BAlq are often used, and a light emitting layer can be formed by adding a hole transport material to the aluminum quinolium complex. Examples of the “hole transporting material” include TPD, a dimer of triphenylamine, and a starburst amine derivative (m-MTDAT).
A), triallylamine derivatives such as HTM1 and NSD having a structure in which α-NPB and three triphenylamines are linked, and bisstyrylamine derivatives such as DPAVBi can be used.

In a light emitting layer made of an electron transporting light emitting material,
The recombination of holes and electrons is usually performed near the interface between the light emitting layer and the hole transport layer. For this reason, there are problems such as a long moving distance of electrons, a large resistance, a decrease in luminous efficiency, and the necessity of applying a high voltage to obtain a predetermined luminance. By including a hole transporting material in the light emitting layer, the hole transporting property of the light emitting layer is improved, and the probability of recombination of holes and electrons can be made more uniform in the light emitting layer. As a result, holes and electrons can be recombined inside the light emitting layer and also near the interface with the electron transport layer, and the light emitting region can be expanded in the thickness direction of the light emitting layer. Further, the efficiency of hole injection from the hole transport layer to the light emitting layer is improved, constant current driving can be performed at a lower voltage, and light can be emitted with sufficient luminance.

Further, as the above-mentioned "hole transporting light emitting material", a triallylamine derivative, a bisstyrylamine derivative and the like are often used, and by incorporating at least one of an electron transporting material and a hole blocking material into the material. A light-emitting layer can be formed. As the above “electron transporting material”, oxadiazole-based compounds such as PBD and BND, compounds having a triazole structure, hydroxyflavone Be complexes, aluminum quinolium complexes frequently used as light emitting materials, and the like can be used. Furthermore,
A metal oxide such as Al ₂ O ₃ can be used as the “hole block material”.

In a light-emitting layer made of a hole-transporting light-emitting material, recombination of holes and electrons is usually performed in the vicinity of the interface between the light-emitting layer and the electron-transport layer, and the luminous efficiency is reduced.
There are problems such as that a high voltage must be applied to obtain a predetermined luminance. By including at least one of an electron transporting material and a hole blocking material in the light emitting layer, holes and electrons can be recombined inside the light emitting layer and also near the interface with the hole transporting layer, and the light emitting region It can be expanded in the thickness direction of the light emitting layer.

The quantitative ratio of the electron transporting luminescent material to the hole transporting material or the quantitative ratio of the hole transporting luminescent material to at least one of the electron transporting material and the hole blocking material is 99.9 / 0. It is preferably 1-50 / 50, more preferably 99.9 / 0.1-85 / 15. When the volume ratio of the electron-transporting light-emitting material or the hole-transporting light-emitting material exceeds 99.9, the light-emitting region cannot be sufficiently expanded in the thickness direction of the light-emitting layer, and in order to obtain sufficient light-emitting efficiency. There are problems such as the need to increase the applied voltage. On the other hand, if the volume ratio of the electron-transporting light-emitting material or the hole-transporting light-emitting material is less than 50, light emission from the electron-transporting layer or the hole-transporting layer starts to mix, which is not preferable. Note that the hole transporting material and the electron transporting material in the first invention do not include the dopant contained in a small amount in the light emitting layer.

In the organic EL device of the present invention, as in the second invention, the concentration of at least one of the hole transporting material or the electron transporting material and the hole blocking material contained in the light emitting layer varies in the thickness direction of the light emitting layer. At least the thickness of the light emitting region and its position can be controlled.

The concentration of the hole transport material or the like can be made substantially constant in the thickness direction of the light emitting layer, or the concentration can be inclined. If the concentration is almost constant,
Depending on the concentration, the probability of recombination of holes and electrons can be changed in the thickness direction of the light emitting layer, and the thickness of the light emitting region can be controlled. This thickness is 50% or more from the interface of the light emitting layer with the hole transport layer or the electron transport layer,
In particular, the thickness can be 70% or more, and the entire light emitting layer can emit light.

When the concentration is inclined, the probability that holes and electrons are recombined can be increased at a specific position in the thickness direction of the light emitting layer. Thereby,
Not only the thickness of the light-emitting region but also the position in the thickness direction can be controlled, and the thickness of the light-emitting layer at a predetermined position excluding the vicinity of the interface with the hole transport layer and the electron transport layer in the thickness direction of the light-emitting layer. The light emitting region can have a thickness of 20 to 80%, particularly 40 to 60% of the thickness. Further, in the second aspect, the chromaticity of the light emitting region can be controlled, and the light emitting color of the element can be easily adjusted to a desired one.

Further, in the organic EL device of the present invention, as in the third invention, two or more light-emitting regions having different chromaticities are formed in the thickness direction of the light-emitting layer, and at least one of these light-emitting regions is formed. The organic EL device may include a hole transport material or at least one of an electron transport material and a hole block material.

The two or more light emitting regions having different chromaticities can be usually formed by adding a specific dopant to the light emitting material. When a hole transporting material or the like is contained in the light emitting region or the concentration of the dopant, the ratio of the recombination of holes and electrons in each light emitting region can be controlled by the concentration.
The concentration can be substantially constant in the light emitting region, and can be inclined in the thickness direction of the light emitting region.
In any case, the chromaticity of each light emitting region can be controlled in a state where the dopant is contained at a concentration that provides the highest light emitting efficiency, and the light emitting color of the device can be controlled while maintaining the high light emitting efficiency. It can be easily adjusted to the desired one.

In the organic EL device according to the first to third aspects of the present invention, the "substrate" may be a glass such as soda-lime glass, a synthetic resin such as polyethylene terephthalate, polyether sulfone, polycarbonate, or a transparent material such as quartz. Can be used. Of these, a substrate made of glass is particularly frequently used.

The "anode" can be formed of a simple metal such as gold or nickel, or a metal compound such as ITO, CuI, SnO ₂ , or ZnO. Of these, ITO is particularly preferred from the viewpoints of productivity, stable conductivity, and the like. The “cathode” is an Al—Li alloy, Mg—A
It can be formed of g alloy, Na-K alloy, sodium, magnesium, lithium, aluminum, or the like.
Among them, Al-Li alloy, Mg-Ag alloy and aluminum are particularly frequently used. Each layer constituting these organic EL elements can be formed by a vacuum evaporation method, and can also be formed by various other methods such as a spin coating method, a casting method, a sputtering method, and an LB method.

The organic EL laminate is sealed by a sealing member, and the sealing space is filled with a gas mainly composed of an inert gas such as nitrogen gas. As the sealing member, a member made of metal such as stainless steel, aluminum or an alloy thereof, glass such as soda-lime glass and silicate glass, and synthetic resin such as acrylic resin and styrene resin can be used.

The sealing member and the peripheral edge of the substrate can be joined with a thermosetting resin such as an epoxy resin or an acrylate resin, or with a sealing resin such as a photocurable resin. Among these, it is preferable to use a sealing resin that forms a cured body through which moisture or the like hardly permeates in order to suppress a decrease in luminance or the like. Further, a photocurable resin which can reduce the thermal stress applied to the element and has a high curing rate is more preferable.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by way of examples. Example 1 (Organic EL device in which DCJT which is a hole transporting dopant and TEL22 which is a hole transporting material are contained in a light emitting layer made of an electron transporting light emitting material) (1) Production of organic EL device FIG. An organic EL device whose vertical section was schematically shown was manufactured as follows. An anode 3 made of ITO and CuP are formed on the surface of a transparent substrate 2 made of glass by a vacuum evaporation method.
c, a hole transport layer 42 made of TEL22, Alq3 and TEL having a volume ratio of 10: 1.
22 and 0.8% by volume of DCJT with respect to Alq3 are uniformly dispersed and mixed in the thickness direction, the hole transporting light emitting layer 43, the electron transporting layer 45 composed of Alq3, and the Al—
A cathode 5 made of a Li alloy is formed in this order to form an organic EL.
After the formation of the laminate, the sealing member 6 was joined to the periphery of the transparent substrate 2 with a sealing resin, and the organic EL laminate was sealed, whereby the organic EL device 1 was manufactured.

The organic EL device was driven at a constant current so as to have a current density of 8.3 mA / cm ² .
A luminance of 507 cd / m ² was obtained at a voltage of 69 V. The luminous efficiency is 4.07 lm / W, and the chromaticity is x =
0.513 and y = 0.461. In this element,
In the light emitting layer, TEL22 as a hole transport material and DCJT as a red dopant are uniformly dispersed and contained. Therefore, the hole transporting property of the light emitting layer is improved, the area where light is actually emitted in the light emitting layer is widened, and holes and electrons are recombined near the interface between the light emitting layer and the electron transport layer. In addition, since the efficiency of injecting holes from the hole transport layer into the light emitting layer was increased, it was possible to emit light with high efficiency at a low voltage.

Example 2 (Organic EL device in which TEL 22 is contained in Example 1 with a gradient in the thickness direction) TEL 22 contained in the light emitting layer is highly concentrated on the interface side with the hole transport layer. An organic EL device was manufactured in the same manner as in Example 1, except that the concentration was inclined in the thickness direction of the light emitting layer so that the concentration was low on the interface side with the electron transport layer. When the organic EL element was driven at a constant current so as to have a current density of 8.3 mA / cm ² , 4.7 was obtained.
A luminance of 496 cd / m ² was obtained at a voltage of 3 V. The luminous efficiency is 3.95 lm / W, and the chromaticity is x =
0.542, y = 0.444. In this element,
The concentration of holes in the thickness direction of the light-emitting layer was almost constant, and light emission was efficiently performed using the entire light-emitting layer, and light was emitted with high efficiency at a low voltage.

Comparative Example 1 (Organic EL device not containing TEL22 in Example 1) FIG. 2 is a schematic cross-sectional view of the organic EL device in the same manner as in Example 1 except that the light-emitting layer did not contain TEL22. The organic EL device shown in FIG. This organic EL device was 8.3 mA
When driving at a constant current with a current density of / cm ² , a luminance of 467 cd / m ² was obtained at a voltage of 5.29 V. The luminous efficiency was 3.33 lm / W, and the chromaticity was x = 0.543 and y = 0.439. In this device, since the light-emitting layer has a strong electron-transport property, recombination of holes and electrons occurs only in the vicinity of the interface between the hole-transport layer and the light-emitting layer, and light is intensively emitted at this interface. And
DCJT, which is often present near the interface with the electron transport layer, not only does not contribute to light emission, but also increases the resistance of the light emitting layer,
The luminance decreased slightly, the required voltage increased, and the luminous efficiency decreased.

Example 3 (having light emitting regions of different chromaticities,
Organic EL in which one light emitting region contains a hole transport material
Element) A first light-emitting region 441 containing 0.8% by volume of perylene as a blue dopant in BAlq as an electron-transporting light-emitting material, and a second light-emitting region containing 0.8% by volume of DCJT as a red dopant. A light emitting layer including the region 442, and only the first light emitting region has a volume ratio of 10% to BAlq.
An organic EL device was manufactured in the same manner as in Example 1, except that the TEL 22 was contained in the ratio of / 1. FIG. 3 schematically shows a longitudinal section thereof.

When the organic EL device was driven at a constant current so as to have a current density of 8.3 mA / cm ² , the current density was 7.
A luminance of 398 cd / m ² was obtained at a voltage of 1 V. The luminous efficiency is 2.11 lm / W, and the chromaticity is x =
0.348, y = 0.356. In this element,
While maintaining the optimal content of perylene in the first light-emitting region at an optimum content for obtaining high light-emitting efficiency, holes can be injected into the second light-emitting region, and the second light-emitting region can also emit light with high efficiency. It was possible to make the emission color white as desired. Further, since holes can be easily injected from the hole transport layer into the first light emitting region, light can be emitted with high efficiency at a low voltage.

Comparative Example 2 (Organic EL device in which TEL22 was not contained in the first light emitting region in Example 3) An organic EL device was produced in the same manner as in Example 3 except that TEL22 was not contained in the first light emitting region. Was manufactured. When the organic EL device was driven at a constant current so as to have a current density of 8.3 mA / cm ² , a voltage of 9.2 V and a voltage of 249 c
A luminance of d / m ² was obtained. The luminous efficiency is 1.02
lm / W, chromaticity x = 0.210, y = 0.30
It was 8. In this device, since the hole transporting property of the first light emitting region is low, light is emitted only in the vicinity of the interface between the hole transport layer and the first light emitting region, and the efficiency of hole injection into the second light emitting region is low. The light emitting region emits little light. Therefore, the emission color of the device is blue, and the purpose of adjusting the emission color to white from the blue and the red emission color of the second emission region has not been achieved.

Comparative Example 3 (Organic EL Device with Perylene Concentration Reduced in Comparative Example 2) An organic EL device was manufactured in the same manner as in Comparative Example 2, except that the perylene concentration was 0.3% by volume. When the organic EL device was driven at a constant current so as to have a current density of 8.3 mA / cm ² , a voltage of 8.9 V and 279 cd / m ^{2 were obtained.}
Was obtained. The luminous efficiency is 1.18 lm / W
And the chromaticity was x = 0.295 and y = 0.371. In this device, although the chromaticity could be controlled, the luminous efficiency in the first luminescent region was reduced due to the small content of perylene, and the luminescent efficiency of the entire luminescent layer was also reduced. In addition, since the emission intensity of blue light by perylene was lowered and the emission of BAlq was mixed, the chromaticity was shifted to the green direction, and the purpose of making the emission color white was not achieved.

Comparative Example 4 (Organic EL Device with First Light Emitting Region Thinned in Comparative Example 2) An organic EL device was manufactured in the same manner as in Comparative Example 2 except that the thickness of the first light emitting region was reduced from 30 nm to 15 nm. Manufactured.
When the organic EL device was driven at a constant current so as to have a current density of 8.3 mA / cm ² , a luminance of 336 cd / m ² was obtained at a voltage of 8.4 V. The luminous efficiency is 1.51 lm / W, the chromaticity is x = 0.362, and y =
0.365. In this device, although the chromaticity could be controlled by changing the film thickness, holes were blocked between the hole transport layer and the first light emitting region, and the voltage required for constant current driving was high. Since light was emitted even in the layer, the luminous efficiency was not sufficient.

The results of luminance, driving voltage, luminous efficiency and chromaticity of Examples 1 to 3 and Comparative Examples 1 to 4 are summarized in Table 1.

[0030]

[Table 1]

Example 4 (Organic EL device in which the content of TEL22 was changed in Example 3) In Example 3, the content of TEL22 in the first light emitting region was 99.5: 0. 5, 9
An organic EL device was manufactured in the same manner as in Example 3, except that the ratio was 9: 1, 90:10, and 50:50. FIG. 4 is a graph showing the chromaticity of these elements, where ○ indicates the case of only BAlq and perylene, and ● indicates the case of only BAlq and DCJT. This graph shows that the chromaticity can be easily controlled by the content of TEL22.

It should be noted that the present invention is not limited to the above embodiment, but may be variously modified within the scope of the present invention depending on the purpose and application. For example, if necessary, an electron injection layer made of a fluoride or oxide of an alkali metal such as LiF, or a fluoride of an alkaline earth metal such as BaF ₂ can be formed.

[0033]

According to the first aspect of the invention, the light emitting region in the light emitting layer can be a wide region including not only the interface with the hole transport layer or the electron transport layer but also the inside of the light emitting layer.
According to the second aspect, the thickness and the position of the light emitting region in the thickness direction of the light emitting layer can be easily controlled, and the chromaticity can be controlled. Further, according to the third aspect, by forming two or more kinds of light emitting regions having different chromaticities in the light emitting layer and controlling these chromaticities, an organic EL element having a desired light emitting color can be obtained. it can.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a vertical cross section of an organic EL element in Example 1.

FIG. 2 is a schematic diagram showing a vertical cross section of an organic EL element in Comparative Example 1.

FIG. 3 is a schematic view showing a vertical cross section of an organic EL device in Example 3.

FIG. 4 is a graph showing a change in chromaticity in Example 4 in which the content of TEL 22 was changed in Example 3;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1; Organic EL element, 2; Transparent substrate, 3; Anode, 41; Hole injection layer, 42; Hole transport layer, 43; Hole transport light emitting layer, 441; First light emitting area, 442; Second light emitting area, 45 Electron transport layer, 5; cathode, 6; sealing member, 6
1; joint.

Claims (3)

[Claims] 1. A substrate and an anode and an organic E on the surface of the substrate.
L thin film and cathode are laminated in this order to form organic E.
L stacked body, wherein the organic EL thin film has at least a light emitting layer, and the light emitting layer is an electron transporting light emitting material containing a hole transporting material, or a hole containing at least one of an electron transporting material and a hole blocking material. An organic EL device comprising a transportable light-emitting material, wherein a recombination region of holes and electrons in the light-emitting layer is extended to the inside of the light-emitting layer. 2. The thickness of the light emitting region in the thickness direction of the light emitting layer and the position thereof depending on the concentration of the hole transporting material or at least one of the electron transporting material and the hole blocking material contained in the light emitting layer. The organic EL device according to claim 1, wherein at least the thickness of the organic EL device is controlled. 3. The light-emitting layer having different chromaticities in the thickness direction.
2. The organic EL device according to claim 1, wherein at least one kind of light emitting region is formed, and at least one of the light emitting regions contains the hole transporting material or at least one of the electron transporting material and the hole blocking material.