JP2692671B2 - Resonator type organic thin film EL device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic EL (electroluminescence) device which is a self-luminous type and is used as a high-definition display means on a thin flat surface, and more particularly to a resonator type organic thin film EL device.

[0002]

2. Description of the Related Art A new type of organic thin film EL device reported by Tang et al. Is an Applied Physics Letters.
s Letters), 51, 913 pages, 198
It has been disclosed in 7 years, and is composed of a flat substrate, an anode, a hole transport layer, a light emitting layer, and a cathode. As the anode, an indium tin oxide alloy (ITO) formed on a flat glass substrate, a hole transport layer 1,1′-bis (4-
N, N′-ditolylaminophenyl) cyclohexane (hereinafter abbreviated as DTAP), the light emitting layer is tris (8-
Hydroxyquinolinol aluminum) (hereinafter Alq
And a cathode are formed of a magnesium-silver alloy.

The light emitting operation principle of the organic thin film EL element of Tang et al. Is generally considered as follows. The holes injected from the anode into the hole transport layer move toward the light emitting layer interface. Electrons are injected into the light emitting layer from the cathode and move in the light emitting layer. Although holes are injected into the light-emitting layer through the hole-transporting layer, electrons are blocked by the hole-transporting layer, so that the electrons and holes recombine near the interface between the light-emitting layer and the hole-transporting layer. To do.
At this time, neutral stable excitons are generated, and the singlet excitons spontaneously emit, that is, spontaneously transition to the ground level with emission.

The organic thin film EL device currently being developed is
Basically, based on the concept of device structure and materials reported by Tung et al., Progress has been made by improving the device structure as well as organic materials and electrodes.

Dodaba lapur
Et al. Introduced a resonator structure into such an organic thin film EL element (US Pat. No. 5,405,710). A conceptual view of a conventional resonator type organic thin film EL element is shown in FIG. Referring to FIG.
In a conventional resonator type organic thin film EL element, a multilayer film reflecting mirror 2 and a SiN film 3 which are semi-transparent reflecting mirrors made of a dielectric multilayer film are formed on a glass substrate 1, and an ITO electrode 4 (anode) is formed thereon. , Triwenyldiamine derivative (hereinafter abbreviated as TAD) hole transport layer 5, Alq light emitting layer 6, Al electrode 7
(Cathode) is formed. The power supply 8 is connected between the TAD hole transport layer 5 and the Al electrode 7.

In the organic thin film EL element having such a layer structure, a resonator is constituted by the multilayer film reflecting mirror 2 and the Al electrode 7, and the effective resonance of the resonator determined by the thickness of the SiN film 3 is formed. Superposition of waves propagating at wavelengths according to the length of the vessel occurs, and an increase in EL emission is observed when viewed at a unit angle and unit spectrum.

[0007]

An organic thin film EL element similar to the structure of Tung et al. Can obtain high-luminance light emission at a low voltage, but on the other hand, since it is a current-driven element, it is necessary to obtain high luminance. The current density must be increased. As the current density increases, the power consumption increases, and as described above, the rate of decrease in brightness becomes remarkable. The cause of such a phenomenon is that the injected electrons and holes do not effectively lead to light emission, that is, the quantum efficiency of EL is small, and the light generated and emitted in the organic thin film is effectively used. It is considered that the light is not extracted to the outside, that is, the light extraction efficiency is low. Therefore, it is a practical problem of the organic thin film EL element to increase the light extraction efficiency and improve the efficiency by 1.5 times or more as compared with the current situation.

The causes of the low light extraction efficiency are as follows. When a flat substrate is used as the substrate, the light from the organic thin film layer, which is the isotropic emission source, is totally reflected when the incident angle to the substrate on the light extraction side or the transparent electrode surface exceeds the critical angle, so it is extracted to the outside. I can't. Therefore, the light extraction efficiency is limited to about 25%, which is a theoretical problem in a self-luminous light emitting element.

An example of a method for avoiding this problem is the introduction of a resonator structure. The introduction of the resonator allows the emitted light to have directivity, and the light emitted from the organic thin film can be effectively extracted to the outside of the glass substrate. For example, Takada et al. Applied Physics Letters (Applied Physics Letter)
s), Vol. 63, p. 2032, 1993, ITO anode, TAD hole transport layer, naphthostyrylamine (NSD) light emitting layer, oxadianol derivative (OXD) electron transport layer, MgAg cathode on a glass substrate. In an experiment using a resonator type organic thin film EL element having a laminated structure, it is reported that the divergence angle of emitted light is about 30 ° in half angle. Since the critical angle of total reflection of visible light at the above-mentioned glass-air interface is about 40 °, it means that the light emission from the organic thin film can be effectively extracted to the outside of the substrate.

On the other hand, however, the resonator type organic thin film EL
The directivity of the emitted light in the device simultaneously reduces the viewing angle. That is, as shown in FIG. 6, in the conventional resonator type organic thin film EL element, the directivity of emitted light is high,
The light is emitted within a range of about 30 ° in half angle. Glass substrate-The critical angle of total reflection in the visible light range of air is about 40
Therefore, the light emitted from the resonator type organic thin film light emitting layer is
It can be effectively taken out of the substrate without being totally reflected at the air interface. However, at the same time, in the organic thin film EL element having such a structure, the viewing angle is 3
This is 0 °, which is not sufficient when considering application to, for example, a display. From this, in the resonator type organic thin film EL element, it is a problem to widen the viewing angle while maintaining high light extraction efficiency.

[0011]

According to the present invention, a concave portion is formed on a substrate made of a transparent member, and a light emitting portion of a resonator structure is formed in the concave portion. The device is obtained.

Further, according to the present invention, in a resonator type organic thin film EL element in which a light emitting part having a resonator structure is formed on one surface side of a substrate by a transparent member, a light refracting part is provided on a light extraction part on the other surface side of the substrate. A resonator type organic thin film EL element characterized by being formed is obtained.

The photorefractive part is preferably formed by selective ion exchange by patterning a substrate containing high refractive index ions and immersing the substrate in a low refractive index ion molten salt.

According to the present invention, further, in the resonator type organic thin film EL element in which the light emitting portion of the resonator structure is formed on one surface side of the substrate by the transparent member, the light diffusion portion is formed on the other surface side of the substrate. A resonator type organic thin film EL element having the following features is obtained.

The light diffusing section is preferably formed by providing the other surface of the substrate with a surface roughness of the order of wavelength of the device.

[0016]

1 is a conceptual diagram showing a resonator type organic thin film EL element having a curved structure which is a first embodiment of the present invention. In the first embodiment, a concave portion is formed on the glass substrate 1, and a multilayer film reflecting mirror 2 and a SiN film 3 which are semitransparent reflecting mirrors made of a dielectric multilayer film are formed on the entire concave portion side. , ITO electrode 4 on it
(Anode) is formed. Furthermore, the TAD hole transport layer 5, the Alq light emitting layer 6, and the Al electrode 7 (cathode) are formed in the concave portion, so that the light emitting portion has a concave structure. The concave portion of the glass substrate 1 is obtained by forming the glass substrate 1 by injection molding or press molding, or by subjecting the glass substrate 1 to a treatment such as etching.

In the organic thin film EL device having such a layer structure, the resonator is constituted by the multilayer-film reflective mirror 2 and the Al electrode 7, and the resonator is determined by the thickness of the SiN film 3. Superposition of waves propagating at wavelengths according to the shaker length occurs, and an increase in EL emission is observed when viewed at a unit angle and a unit spectrum.

FIG. 4 (a) shows a schematic view of the optical path of the first embodiment. As is apparent from FIG. 4A, in the first embodiment of the present invention, since the light emitting portion has a concave surface, even if the spread of light emission from the unit area is 30 °, As a result, the total reflection critical angle can be expanded to 40 °. With such a concave surface structure, a desired outgoing light spread can be provided by optimizing the radius of curvature of the concave portion and the area of the light emitting layer.

FIG. 2 is a conceptual view showing a resonator type organic thin film EL element having a photorefractive portion which is a second embodiment of the present invention. In the second embodiment, in addition to the structure of the conventional resonator-type organic thin film EL element, the glass substrate 1 has a light refraction portion by the low refractive index ion diffusion portion 9 on the light extraction side. Is characterized by. Such a light refraction part is formed by a selective ion exchange by patterning a flat substrate glass containing high refractive index ions and immersing it in a low refractive index ion molten salt.
There is a dimensional distribution refractive index lens or the like, but the present invention is not limited thereto.

FIG. 4 (b) shows a schematic view of the optical path of the second embodiment. In this case, the light emitted from the organic thin film light emitting layer has a spread of only 30 °, but this is an example in which the light is refracted by the low refractive index ion diffusion portion 9 and spread outside the glass substrate 1. Also in this case, the emitted light is not totally reflected at the substrate-air interface, so that high light extraction efficiency can be realized. In addition, the desired distribution of emitted light can be obtained by the distribution of low refractive index ions.

FIG. 3 is a conceptual diagram showing a resonator type organic thin film EL element having a light diffusing portion which is a third embodiment of the present invention. The third embodiment is characterized in that a light diffusing section 10 is formed on the light extraction side of the glass substrate 1 in addition to the structure of the conventional resonator type organic thin film EL element. This kind of light diffusing section 10 can be formed by giving the surface of the glass substrate 1 a surface roughness of a wavelength order.

FIG. 4 (c) shows a schematic view of the optical path of the third embodiment. Similar to the second embodiment, in this case as well, since the emitted light is spread on the back surface of the glass substrate 1, high light extraction efficiency can be realized. Further, in this case, since the diffusion is utilized, the viewing angle is 90 ° in half angle.

Although the present invention has been described above with reference to three preferred embodiments, the organic thin film E applicable to the present invention is described.
The organic thin film layer of the L element is not particularly limited, and any thin film structure such as a single layer structure having only a light emitting layer, a hole transport band layer, an electron transport band layer, an anode interface layer, a cathode interface layer, or the like is applied. It is possible. Further, the thin film layer other than the light emitting layer is not limited to an organic substance, but is effective even if it is a thin film using an inorganic substance or a thin film of a mixture of an organic substance and a metal.
In addition, the organic thin film layer is formed by vacuum vapor deposition or molecular beam vapor deposition (MB
E method) or a dipping method of a solution dissolved in a solvent,
It can be formed by a known method such as a spin coating method, a casting method, a bar coating method, or a roll coating method.

The material of the hole transporting zone layer in the present invention is not particularly limited, but for example, a triphenyldiamine derivative, an oxadiazole derivative, a porphyrin derivative, a stilbene derivative, an arylamine derivative and the like can be used. Further, the hole transport compound can be used as a layer in which a known polymer is used as a medium and dispersed therein. The polymer is preferably one that does not extremely hinder the hole transporting property, and examples thereof include poly- (N-vinylcarbazole), polycarbonate, polymethyl acrylate, polymethyl methacrylate, polystyrene-based polymer, polysilylene-based polymer, Polythiophene, polyaniline, polyphenylene vinylene, etc. can be applied.

The anode interface layer is introduced in order to achieve stable hole injection, but it must play a role of maintaining the adhesiveness between the organic thin film layer and the anode. Unnecessarily increasing the film thickness may increase the driving voltage for light emission and may cause unevenness on the surface of the thin film, which causes uneven light emission. The film thickness of the anode interface layer is preferably 30 nm or less. The anode interface layer applicable in the present invention is, for example, a spiro compound described in "Dye Handbook: Kodansha '86",
Fused polycyclic dyes such as azo compounds, quinone compounds, indigo compounds, diphenylmethane compounds, quinacridone compounds, polymethine compounds, acridine compounds and porphyrin compounds can be applied. In addition, "organic semiconductors such as aromatic amines: Ferlac Chemie (ORGANIC SEMICONDUCTOR
S: VERLAG CHEMIE) '74 ”is also applicable.

The light emitting layer material of the organic thin film EL element is not particularly limited, and known light emitting materials can be applied. For example, metal complexes of 8-hydroxyquinolinol and its derivatives, tetraphenylbutadiene derivatives, distyrylaryl derivatives, coumarin derivatives, quinacridone derivatives, perylene derivatives, polymethine derivatives, anthracene derivatives,
Examples thereof include polyvinylcarbazole. The light emitting layer may be a single component or a system doped with another light emitting material.

In the present invention, an electron transport band may be provided between the light emitting layer and the cathode, if necessary. The electron transport material is not particularly limited, but 8-hydroxyquinolinol and its derivatives, oxadiazole derivatives, diphenylquinone derivatives and the like can be applied.

The anode of the organic thin film EL element plays a role of injecting holes into the hole transport zone layer, and it is effective that it has a work relationship of 4.5 eV or more. Specific examples of the anode material include indium tin oxide alloy (ITO), tin oxide (NESA), gold, silver, platinum, and copper.
The cathode is preferably a material having a small work relationship for the purpose of injecting electrons into the electron transport band or the light emitting layer, and is not particularly limited, but specifically, indium, aluminum, magnesium, magnesium-indium alloy, magnesium-aluminum alloy. , Aluminum-lithium alloy,
A metal containing aluminum-scandium alloy or the like as a main component can be used. In order to protect the device from oxygen and moisture, it is also effective to provide a sealing layer formed of a known sealing material such as a metal oxide, a metal sulfide, a metal fluoride or an organic compound.

[0029]

As described above with reference to a plurality of embodiments, in the resonator type organic thin film EL element of the present invention, the resonator type organic thin film E has a very simple structure.
While maintaining the high light extraction efficiency, which is a characteristic of the L element, it is possible to simultaneously increase the viewing angle. Therefore,
It is also suitable for application to a light emitting device such as a matrix type organic thin film EL display, and enables the production of a high-definition device with low power consumption.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a resonator type organic EL element having a curved structure which is a first embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a resonator type organic EL element having a photorefractive portion which is a second embodiment of the present invention.

FIG. 3 is a conceptual diagram showing a resonator type organic EL element having a light diffusing portion, which is a third embodiment of the present invention.

FIG. 4 is a conceptual diagram showing an optical path of a resonator type organic EL element according to first to third embodiments of the present invention.

FIG. 5 is a conceptual diagram showing a conventional resonator type organic thin film EL element.

FIG. 6 is a conceptual diagram showing an optical path of a conventional resonator type organic EL element.

[Explanation of symbols]

 1 Glass Substrate 2 Multilayer Reflector 3 SiN Film 4 ITO Electrode 5 TAD Hole Transport Layer 6 Alq Light Emitting Layer 7 Al Electrode 8 Power Supply 9 Low Refractive Index Ion Diffuser 10 Light Diffuser

Claims (5)

(57) [Claims] 1. A recess is formed on a substrate made of a transparent member,
A resonator-type organic thin film EL element characterized in that a light emitting portion having a resonator structure is formed in this recess. 2. In a resonator type organic thin film EL element in which a light emitting part of a resonator structure is formed on one surface side of a substrate by a transparent member, a light refraction part is formed on a light extraction part on the other surface side of the substrate. Characteristic resonator type organic thin film EL element. 3. The resonator type organic thin film EL element according to claim 2, wherein the photorefractive part is selected by patterning a substrate containing high refractive index ions and immersing it in a low refractive index ion molten salt. Resonator type organic thin film EL device characterized by being formed by selective ion exchange. 4. A resonator-type organic thin film EL device in which a light emitting portion having a resonator structure is formed on one surface side of a substrate made of a transparent member, wherein a light diffusion portion is formed on the other surface side of the substrate. Organic thin film EL device. 5. The resonator type organic thin film EL element according to claim 4, wherein the light diffusing portion is formed by providing the other surface of the substrate with a surface roughness in the order of wavelength of the element. Resonator type organic thin film EL device.