Resonating organic membrane el element

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an organic EL (electroluminescence) element that is self-luminous and is used, for example, as a high-definition display means on a thin flat surface, and particularly to a resonator type organic thin film EL element.

【0002】

[Conventional technology]

A new type of organic thin-film EL device reported by Tang et al., Published in Applied Physics Letters, Vol. 51, p. 913, 1987, is a flat substrate, anode, hole. It is composed of a transport layer, a light emitting layer, and a cathode. The anode is an indium tin oxide alloy (ITO) formed on a flat glass substrate, a hole transport layer 1,1'-bis (4-N, N'-ditrilaminophenyl) cyclohexane (hereinafter abbreviated as DTAP). The light emitting layer is made of tris (8-hydroxyquinolinol aluminum) (hereinafter abbreviated as Alq), and the cathode is made of magnesium-silver alloy.

【0003】

The light emitting operation principle of the organic thin film EL element of Tang et al. Is roughly 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. Holes are injected into the light emitting layer via the hole transport layer, but electrons are blocked by the hole transport layer, so that the electrons and holes recombine near the interface of the light emitting layer with the hole transport layer. To do. At this time, neutral stable excitons are generated, of which the singlet excitons spontaneously transition to the basal level with spontaneous emission, that is, light emission.

【0004】

The organic thin-film EL device currently being developed is basically based on the concept of the device configuration and materials reported by Tang et al., And has been improved by improving the organic materials and electrodes, including the improvement of the device configuration. There is.

【0005】

Dodabalapur et al. Introduced a resonator structure into such an organic thin film EL device (US Pat. No. 5405710). Figure 5 shows a conceptual diagram of a conventional resonator-type organic thin-film EL device. With reference to FIG. 5, the conventional resonator-type organic thin film EL element forms a multilayer film reflector 2 and a SiN film 3 which are translucent reflectors made of a dielectric multilayer film on a glass substrate 1, and on the glass substrate 1. An ITO electrode 4 (aluminum), a triwenyldiamine derivative (hereinafter abbreviated as TAD) hole transport layer 5, an Alq light emitting layer 6, and an Al electrode 7 (cathode) are formed therein. The power supply 8 is connected between the TAD hole transport layer 5 and the Al electrode 7.

【0006】

In an organic thin film EL element having such a layer structure, the resonator is composed of the multilayer film reflector 2 and the Al electrode 7, and the effective resonator length of the resonator is determined by the thickness of the SiN film 3. Waves propagating at the corresponding wavelengths are superposed, and an increase in EL emission is observed when viewed at a unit angle and a unit spectrum.

【0007】

[Problems to be Solved by the Invention]

An organic thin-film EL device similar to the structure of Tang et al. Can emit high-luminance light at a low voltage, but since it is a current-driven device, the current density must be increased in order to obtain high brightness. 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 are not effectively linked 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 conceivable that the light is not taken out to the outside, that is, the light taking out 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 of the current level.

【0008】

The causes of 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 an isotropic light emitting source, is totally reflected when the incident angle to the substrate on the light extraction side or the surface of the transparent electrode exceeds the critical angle, so that the light is taken out to the outside. Can't. Therefore, the light extraction efficiency remains at about 25%, which is a principle problem in the self-luminous light emitting element.

【0009】

One example of a method of avoiding this problem is the introduction of a resonator structure. By introducing a resonator, it is possible to give directivity to the emitted light, and it is possible to effectively take out the light emitted from the organic thin film to the outside of the glass substrate. For example, in Applied Physics Letters, Vol. 63, p. 2032, 1993, Takada et al., On a glass substrate, an ITO anode, a TAD hole transport layer, a naphthostyrylamine (NSD) light emitting layer, In an experiment using a resonator-type organic thin-film EL device with a structure in which an oxadianol derivative (OXD) electron transport layer and an MgAg cathode are laminated, it was reported that the spread angle of the emitted light was about 30 ° in half angle. ing. Since the total reflection critical angle of visible light at the glass-air interface described above is about 40 °, it means that the light emitted from the organic thin film can be effectively extracted to the outside of the substrate.

【0010】

However, on the other hand, the directivity of the emitted light in the resonator type organic thin film EL element also brings about a reduction in the viewing angle. That is, as shown in FIG. 6, in the conventional resonator type organic thin film EL element, the directivity of the emitted light is high, and the emitted light is emitted within a range of about 30 ° in half-width. Since the critical angle of total reflection of glass substrate-air in the visible light region is about 40 ° in half angle, light emission from the resonator type organic thin film light emitting layer is effectively outside the substrate without total reflection at the substrate-air interface. It will be possible to take it out. However, at the same time, in an organic thin film EL device having such a structure, the viewing angle is 30 ° in half angle, which is not sufficient considering application to a display or the like, for example. For this reason, in the resonator type organic thin film EL device, it is an issue to expand the viewing angle while maintaining high light extraction efficiency.

【0011】

[Means for solving problems]

According to the present invention, a resonator-type organic thin film EL element characterized in that a recess is formed on a substrate made of a transparent member and a light emitting portion having a resonator structure is formed in the recess can be obtained.

【0012】

According to the present invention, in a resonator type organic thin film EL element in which a light emitting portion having a resonator structure is formed on one surface side of a substrate made of a transparent member, a light refracting portion is formed on a light extraction portion on the other surface side of the substrate. A resonator-type organic thin-film EL device characterized by this can be obtained.

【0013】

The light refraction portion 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.

【0014】

According to the present invention, further, in a resonator type organic thin film EL element in which a light emitting portion having a resonator structure is formed on one surface side of a substrate made of a transparent member, a light diffusing portion is formed on the other surface side of the substrate. A resonator-type organic thin-film EL device can be obtained.

【0015】

The light diffusing portion is preferably formed by giving the other surface of the substrate a surface roughness on the order of the wavelength of the element.

【0016】

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a conceptual diagram showing a resonator-type organic thin film EL device having a curved structure, which is the first embodiment of the present invention. In the first embodiment, a recess is formed on the glass substrate 1, and a multilayer reflector 2 and a SiN film 3 which are translucent reflectors made of a dielectric multilayer film are formed on the entire recess side. , ITO electrode 4 (anode) is formed on it. Further, 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 recesses of the glass substrate 1 can be 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.

【0017】

In an organic thin film EL element having such a layer structure, a resonator is composed of a multilayer film reflector 2 and an Al electrode 7, and the actual public resonator length of the resonator is determined by the thickness of the SiN film 3. Waves propagating at wavelengths corresponding to the above are superimposed, and an increase in EL emission is observed when viewed at a unit angle and a unit spectrum.

【0018】

FIG. 4A shows a schematic diagram of the optical path of the first embodiment. As is clear from FIG. 4 (a), in the first embodiment of the present invention, since the light emitting portion has a concave surface, the spread of light emission from a unit area is 30 ° as a whole. It can be expanded up to the total reflection critical angle of 40 °. According to such a concave surface structure, a desired emission light spread can be provided by optimizing the radius of curvature of the concave portion, the area of the light emitting layer, and the like.

【0019】

FIG. 2 is a conceptual diagram showing a resonator-type organic thin film EL device having a light refracting portion, which is the second embodiment of the present invention. In this second embodiment, in addition to the structure of the conventional resonator type organic thin film EL element, a light refraction part by a low refractive index ion diffusion part 9 is provided on the light extraction side of the glass substrate 1. It is characterized by. As such a light refraction part, an embedded three-dimensional distributed refractive index lens formed by selective ion exchange by patterning a flat plate substrate glass containing high refractive index ions and immersing it in a low refractive index ion molten salt. Etc., but this is not the case.

【0020】

FIG. 4 (b) shows a schematic diagram of the optical path of this 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 unit 9 and spreads outside the glass substrate 1. In this case as well, high light extraction efficiency can be realized because the emitted light is not totally reflected at the substrate-air interface. Further, the distribution of low refractive index ions also makes it possible to obtain a desired emission light spread.

【0021】

FIG. 3 is a conceptual diagram showing a resonator-type organic thin film EL device having a light diffusing portion according to the third embodiment of the present invention. The third embodiment is characterized in that a light diffusing portion 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 type of light diffusing portion 10 can be formed by giving a surface roughness on the order of wavelength to the surface of the glass substrate 1.

【0022】

FIG. 4 (c) shows a schematic diagram of the optical path of the third embodiment. Similar to the second embodiment, in this case as well, since the structure is such that 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 diffusion is used, the viewing angle is 90 ° in half angle.

【0023】

Although the three preferred embodiments of the present invention have been described above, the organic thin film layer of the organic thin film EL device applicable to the present invention is not particularly limited, and a single-layer structure having only a light emitting layer or a hole transport zone is used. Any thin film structure such as one having a layer, an electron transport zone layer, an anode interface layer, a cathode interface layer, etc. can be applied. Further, as the thin film layer forming other than the light emitting layer, not only an organic substance but also a thin film using an inorganic substance or a thin film such as a mixture of an organic substance and a metal is effective. Further, the organic thin film layer is known by a coating method such as a vacuum vapor deposition method, a molecular beam vapor deposition method (MBE method), a dipping method of a solution dissolved in a solvent, a spin coating method, a casting method, a bar coating method, or a roll coating method. It can be formed by a method.

【0024】

The material of the hole transport zone layer in the present invention is not particularly limited, and for example, a triphenyldiamine derivative, an oxadiazole derivative, a porphyrin derivative, a stilben derivative, an arylamine derivative and the like can be used. Further, the hole transport compound can be used as a layer dispersed in a known polymer as a medium. It is desirable that the polymer does not extremely inhibit the hole transport property, and for example, poly- (N-vinylcarbazole), polycarbonate, polymethylacrylate, polymethylmethacrylate, polystyrene-based polymer, polysilylene-based polymer, and the like. Polythiophene, polyaniline, polyphenylene vinylene, etc. can be applied.

【0025】

The anode interface layer is introduced to achieve stable hole injection, but it must play a role of maintaining the adhesion between the organic thin film layer and the anode. Unnecessarily increasing the film thickness may increase the driving voltage for light emission or cause unevenness on the surface of the thin film that causes non-uniform light emission, and it is desirable that the anode interface layer has a film thickness of 30 nm or less. The anode interface layer applicable in the present invention is, for example, a spiro compound, an azo compound, a quinone compound, an indigo compound, a diphenylmethane compound, a quinacridone compound, a polymethine compound, an acrydin compound, or a porphyrin compound described in "Dye Handbook: Kodansha 1986". Condensed polycyclic dyes such as, etc. can be applied. In addition, low-molecular-weight organic P-type semiconductors described in "ORGANIC SEMICONDUCTORS: VERLAG CHEMIE ́74" such as aromatic amines can also be applied.

【0026】

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

【0027】

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.

【0028】

The anode of the organic thin film EL device plays a role of injecting holes into the hole transport zone layer, and it is effective to have 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, copper and the like. The cathode is preferably a material having a small work relationship for the purpose of injecting electrons into the electron transport zone or the light emitting layer, and is not particularly limited, but specifically, indium, aluminum, magnesium, magnesium-indium alloy, magnesium-aluminum alloy. , Aluminum-lithium alloy, aluminum-scandium alloy, etc. as the main component can be used. For the purpose of protecting the element from oxygen and moisture, it is also effective to provide a sealing layer formed of a known sealing material composed of a metal oxide, a metal sulfide, a metal boiled product, an organic compound, or the like.

【0029】

[Effect of the invention]

As described above with reference to a plurality of embodiments, the resonator-type organic thin-film EL device of the present invention has an extremely simple structure and has a high light extraction efficiency, which is a feature of the resonator-type organic thin-film EL device. While maintaining it, the viewing angle can be expanded at the same time. Therefore, it is also suitable for application to a light emitting device such as a matrix type organic thin film EL display, and it is possible to create a high-definition device with low power consumption.

[Simple explanation of drawings]

[Figure 1]

It is a conceptual diagram which shows the resonator type organic EL element which has a curved structure which is 1st Embodiment of this invention.

[Figure 2]

It is a conceptual diagram which shows the resonator type organic EL element which has the optical refraction part which is the 2nd Embodiment of this invention.

[Fig. 3]

It is a conceptual diagram which shows the resonator type organic EL element which has a light diffusion part which is the 3rd Embodiment of this invention.

[Fig. 4]

It is a conceptual diagram which shows the optical path of the resonator type organic EL element of 1st to 3rd Embodiment of this invention.

[Fig. 5]

It is a conceptual diagram which shows the conventional resonator type organic thin film EL element.

[Fig. 6]

It is a conceptual diagram which shows the optical path of the conventional resonator type organic EL element.

[Explanation of symbols]

1 Glass substrate 2 Multilayer film reflector 3 SiN membrane 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