KR20050042705A - Electro-luminescence device - Google Patents

Abstract

The present invention is to improve the brightness and color purity according to the optical resonance effect and to widen the viewing angle. To this end, the transparent substrate, first and second electrode layers sequentially formed on one surface of the transparent substrate, and the first An intermediate layer interposed between an electrode layer and a second electrode layer, the intermediate layer having a light emitting layer that emits light by electrical driving of the first electrode layer and the second electrode layer, and interposed between the transparent substrate and the first electrode layer; An electroluminescent light including a first refractive layer formed of a material having a higher refractive index, and having light resonance occurring between an interface between the second electrode layer and the intermediate layer and an interface between the transparent substrate and the first refractive layer Provided is an element.

Description

Electroluminescent device {Electro-luminescence device}

The present invention relates to an electroluminescent device, and more particularly, to an electroluminescent device with improved extraction efficiency of light generated by the optical resonance effect.

In general, electroluminescent devices are self-luminous displays that electrically excite fluorescent organic compounds to emit light, which can be driven at low voltage, are easy to thin, and are pointed out as problems in liquid crystal display devices such as wide viewing angle and fast response speed. It is attracting attention as the next generation display that can solve the problem.

The electroluminescent device may be classified into an inorganic electroluminescent device and an organic electroluminescent device according to whether the material forming the light emitting layer is an inorganic material or an organic material.

Meanwhile, in the organic EL device, an organic film having a predetermined pattern is formed on glass or other transparent insulating substrate, and electrode layers are formed on upper and lower portions of the organic film. The organic film consists of organic compounds. Materials for forming such organic films include phthalocyanine (CuPc: copper phthalocyanine), N, N-di (naphthalen-1-yl) -N, N'-diphenyl-benzidine (N, N'-Di (naphthalene-1) -yl) -N, N'-diphenyl-benzidine (NPB), tris-8-hydroxyquinoline aluminum (Alq3), etc. are used.

In the organic EL device configured as described above, as the anode and cathode voltages are applied to the electrodes, holes injected from the electrode to which the anode voltage is applied are moved to the light emitting layer via the hole transport layer, and the electrons are applied to the cathode voltage. It is injected into the light emitting layer via the electron transport layer from the electrode. In this light emitting layer, electrons and holes recombine to produce excitons, and as the excitons change from the excited state to the ground state, the fluorescent molecules in the light emitting layer emit light to form an image. The excitons, when classified into energy states, have one singlet state and three triplet states. Due to the bandgap energy characteristic, the singlet energy state emits light, but the triplet state energy is changed to thermal energy without emitting light.

As described above, the light efficiency of the organic EL device driven is divided into internal efficiency and external efficiency. Among these, the internal efficiency depends on the photoelectric conversion efficiency of the organic light emitting material. The external efficiency, also called light coupling efficiency, depends on the refractive index of each layer constituting the organic EL device. Among them, in the light extraction efficiency, which is an external efficiency, the organic EL device is lower than other display devices such as cathode ray tubes and PDPs, and thus, there is much room for improvement in characteristics of display devices such as brightness and lifetime.

As such, the biggest cause of the light extraction efficiency of the conventional organic EL device is lower than that of other display devices, such as a layer having a high refractive index, such as an ITO electrode layer, and a substrate, when light emitted by the organic film is emitted above a critical angle. This is because total reflection occurs at the interface between the layers having a low refractive index, and the extraction to the outside is prevented. Therefore, due to the total reflection problem at the interface, only about a quarter of the light generated in the organic light emitting layer in the organic EL device may be extracted to the outside.

An example of a conventional organic electroluminescent device for preventing such a decrease in light extraction rate is disclosed in Japanese Laid-Open Patent Publication No. 63-172691. The disclosed organic electroluminescent device includes a substrate having light condensation such as a protruding lens. However, such a convex lens for condensing is difficult to form on the substrate because the pixel according to the emission of the organic film is very small.

Japanese Laid-Open Patent Publication No. 62-172691 discloses an organic material having a first dielectric layer interposed between a transparent electrode layer and a light emitting layer and a second dielectric layer having a refractive index in the middle of the first dielectric layer and a transparent electrode on the transparent electrode side. An electroluminescent device is disclosed.

Japanese Patent Application Laid-open No. Hei 1-220394 discloses an organic electroluminescent device in which a lower electrode, an insulating layer, a light emitting layer, and an upper electrode are formed on a substrate, and a mirror is formed to reflect light on one surface of the light emitting layer.

Since the thickness of the organic light emitting device is very thin, it is very difficult to install a mirror for reflection on the side surface, and as a result, the production cost increases.

In order to solve these problems, Japanese Laid-Open Patent Publication No. 11-283751 discloses an organic electroluminescent display device having one or more organic layers between an anode and a cathode, and includes a structure including a diffraction grating or a zone plate as a component. Is disclosed. This is to form a diffraction grating near the boundary where the refractive index is different and to extract the light of the organic layer by the light scattering effect. However, such a diffraction grating layer is complicated in actual manufacturing process, it is difficult to form a pattern of the upper layer of the thin film due to the surface curvature, there is a problem that a separate planarization process must be added to fill the surface curvature.

In addition, in order to improve the problems of the organic electroluminescent device, Japanese Unexamined Patent Application Publication Nos. 8-250786, 8-213174, and 10-177896 disclose an organic material using an optical microcavity concept. An electroluminescent device is disclosed. In the disclosed organic electroluminescent device, a transflective mirror having a multi-layer structure is formed between the glass substrate and the ITO electrode, and the transflective mirror functions as an optical resonator together with a metal cathode serving as a reflector. In this case, the transflective mirror is formed by alternately stacking a TiO ₂ layer having a high refractive index and a SiO ₂ layer having a low refractive index to form a multilayer, and controlling the reflectance as the number of the multilayer layers to provide a light resonance function. Design. However, the optical resonator needs to increase the number of layers because the reflection property is improved as the number of layers forming the transflective mirror increases, but in order to control the reflectance for a specific wavelength, it is necessary to design the number and thickness of stacked layers accurately. There is a disadvantage that the process of the electroluminescent element is complicated. In addition, this has the advantage that the luminance is increased and the color purity is improved, but the viewing angle is narrowed, and the spectrum is also narrowed.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide an electroluminescent device capable of improving light extraction efficiency by having a simple laminated structure causing a resonance effect.

Another object of the present invention is to provide an electroluminescent device capable of widening the viewing angle while improving luminance and color purity according to the optical resonance effect.

In order to achieve the above object, the present invention,

Transparent substrates;

First and second electrode layers sequentially formed on one surface of the transparent substrate;

An intermediate layer interposed between the first electrode layer and the second electrode layer, the intermediate layer having a light emitting layer that emits light by electrical driving of the first electrode layer and the second electrode layer; And

And a first refractive layer interposed between the transparent substrate and the first electrode layer, the first refractive layer including a material having a refractive index greater than that of the first electrode layer.

It provides an electroluminescent device characterized in that the optical resonance is generated between the interface between the second electrode layer and the intermediate layer and the interface between the transparent substrate and the first refractive layer.

In order to achieve the above object,

Transparent substrates;

First and second electrode layers sequentially formed on one surface of the transparent substrate;

An intermediate layer interposed between the first electrode layer and the second electrode layer, the intermediate layer having a light emitting layer that emits light by electrical driving of the first electrode layer and the second electrode layer; And

And a second refractive layer interposed between the transparent substrate and the first electrode layer and made of a material having a refractive index smaller than that of the transparent substrate.

It provides an electroluminescent device characterized in that the light resonance is generated between the interface between the second electrode layer and the intermediate layer and the interface between the first electrode layer and the second refractive layer.

The present invention also provides

Transparent substrates;

First and second electrode layers sequentially formed on one surface of the transparent substrate;

An intermediate layer interposed between the first electrode layer and the second electrode layer, the intermediate layer having a light emitting layer that emits light by electrical driving of the first electrode layer and the second electrode layer;

A first refractive layer interposed between the transparent substrate and the first electrode layer and formed of a material having a refractive index greater than that of the first electrode layer; And

And a second refractive layer interposed between the transparent substrate and the first refractive layer, the second refractive layer being made of a material having a smaller refractive index than the transparent substrate.

It provides an electroluminescent device characterized in that the optical resonance is generated between the interface between the second electrode layer and the intermediate layer and the interface between the first refractive layer and the second refractive layer.

In the present invention, the transparent substrate is a glass material containing SiO 2 as a main component, the first electrode layer may be provided as a transparent electrode, the second electrode layer may be provided as a reflective electrode.

The first and second refractive layers may be transparent.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic cross-sectional view of an electroluminescent device according to a first exemplary embodiment of the present invention.

As shown in FIG. 1, in the electroluminescent device according to the first embodiment of the present invention, a first electrode layer 2 is formed on an upper surface of a transparent substrate 1 made of a transparent material, and the first electrode layer is formed. An intermediate layer 4 including at least a light emitting layer 41 is formed above the intermediate layer 2, and a second electrode layer 3 having a different polarity than the first electrode layer 2 is formed above the intermediate layer 4. do. Although not shown above the second electrode layer 3, a sealing member (not shown) for sealing the first electrode layer 2, the intermediate layer 4, and the second electrode layer 3 from the outside is further illustrated. It may be provided. Hereinafter, in the embodiments of the present invention to be described, convenience of description will be described based on a schematic structure in which the sealing member is omitted.

The transparent substrate 1 may be a substrate of a transparent glass material containing SiO ₂ as a main component. Although not shown in the drawings, the upper surface of the transparent substrate 1 may further include a buffer layer to block the smoothness of the substrate and the penetration of impurities, and the buffer layer may be formed of SiO ₂ or the like.

The first electrode layer 2 stacked on the transparent substrate 1 may be formed of a conductive material of a transparent material, and may be formed of indium tin oxide (ITO), and a predetermined pattern may be formed by a photolithography method. It may be formed to. In the case of the passive matrix type (PM), the pattern of the first electrode layer 2 may be formed as lines on stripe spaced apart from each other by a predetermined distance, and in the case of the active matrix type (AM) It may be formed in a form corresponding to the pixel. In the case of an active drive type, a TFT (Thin Film Transistor) layer further including at least one thin film transistor is further provided between the first electrode layer 2 and the transparent substrate 1, and the first electrode layer 2 is further provided. ) Is electrically connected to this TFT layer. This applies equally in all embodiments of the present invention to be described below.

Thus, the first electrode layer 2 provided with ITO may be connected to an external first electrode terminal (not shown) and serve as an anode electrode.

The second electrode layer 3 is positioned above the first electrode layer 2. The second electrode layer 3 may be a reflective electrode, is formed of aluminum / calcium, or the like, and is not illustrated. It may be connected to the second electrode terminal to act as a cathode electrode.

In the case of the passive driving type, the second electrode layer 3 may be formed as a line on a stripe orthogonal to the pattern of the first electrode layer 2, and in the case of the active driving type, the second electrode layer 3 may be formed in a shape corresponding to the pixel. . In the case of the active driving type, it may be formed over the entire active area where the image is implemented.

The polarity of the first electrode layer 2 and the second electrode layer 3 as described above may be opposite to each other.

The intermediate layer 4, which is interposed between the first electrode layer 2 and the second electrode layer 3, has a light emitting layer 41 that emits light by electrical driving of the first electrode layer 2 and the second electrode layer 3. . According to the kind of the intermediate layer 4, the electroluminescent device may be classified into an organic electroluminescent device or an inorganic electroluminescent device.

In the case of an organic light emitting device, low molecular weight organic materials or high molecular weight organic materials may be used.

In the case of the low molecular organic layer in which the intermediate layer 4 is formed of a low molecular organic material, the first layer 42 provided as a hole transport layer, a hole injection layer, etc. in the direction of the first electrode layer 2 with respect to the light emitting layer 41, It may have a structure of a second layer 43 provided as an electron transport layer, an electron injection layer, etc. in the direction of the second electrode layer 3. Of course, the hole injection layer, the hole transport layer, the electron transport layer, the electron injection layer and the like may be formed by stacking in a variety of complex structures.

In addition, usable organic materials are copper phthalocyanine (CuPc), N, N-di (naphthalen-1-yl) -N, N'-diphenyl-benzidine (N, N'-Di (naphthalene-1-) yl) -N, N'-diphenyl-benzidine (NPB), tris-8-hydroxyquinoline aluminum (Alq3) and the like can be variously applied. When the intermediate layer 4 is a full color organic EL device, the emission layer 41 may be formed in various patterns so as to correspond to the color of each pixel. The low molecular weight organic layer may be formed by heating and depositing an organic material in a vacuum, wherein the emission layer 41 may be formed through a mask having a slit of a predetermined pattern so as to correspond to each pixel. It can be formed by sequentially depositing each star.

Meanwhile, in the case of the polymer organic layer formed of the polymer organic material, only a hole transport layer (HTL) may be provided as the first layer 42 in the direction of the first electrode layer 2 around the light emitting layer 41. The second layer 43 can be omitted. The polymer hole transport layer is made of polyethylene dihydroxythiophene (PEDOT: poly- (2,4) -ethylene-dihydroxy thiophene), polyaniline (PANI: polyaniline), or the like by inkjet printing or spin coating. It is formed on the first electrode layer 2 of the substrate (1), the polymer organic light emitting layer may be PPV, Soluble PPV's, Cyano-PPV, polyfluorene (Polyfluorene), etc., using inkjet printing or spin coating or laser The color pattern can be formed by a conventional method such as a thermal transfer method.

In the case of the inorganic electroluminescent device, the light emitting layer 41 includes metal sulfides such as ZnS, SrS, CsS, or alkaline earth potassium sulfides such as CaCa2S4, SrCa2S4, and Mn, Ce, Tb, Eu, Tm, Er, Pr, Pb, and the like. It is formed of light emitting center atoms such as transition metal or alkali rare earth metals. In addition, both the first layer 42 and the second layer 43 may be formed of an insulating layer.

The upper part of the second electrode layer 3 is provided with a sealing member (not shown), the sealing member may be provided with a metal cap having a moisture absorbent therein, or by applying a sealing resin material to the inside Allow moisture ingress to be blocked. In addition, the sealing member may be formed using a substrate.

In the first embodiment of the present invention, a first refractive layer 51 is further interposed between the transparent substrate 1 and the first electrode layer 2. The first refractive layer 51 is formed of a material having a higher refractive index than the material forming the first electrode layer 2. As a result, the interface reflecting surface is formed due to the difference in refractive index at the interface between the first electrode layer 2 and the first refractive layer 51, thereby further increasing the optical resonance effect. Thus, as shown in FIG. 1, the optical resonance effect is the resonance region C of the interface between the second electrode layer 3 and the intermediate layer 4 and the interface between the transparent substrate 1 and the first refractive layer 51. Happened in).

As described above, in the present invention, the first refraction layer 51 is interposed between the transparent substrate 1 and the first electrode layer 2, thereby causing an optical resonance effect, thereby improving luminance and improving color purity. have. In addition, since the first refractive layer 51 is formed as a single layer, the process can be simplified, unlike the above-described multilayer of the prior art.

On the other hand, in the present invention to achieve the resonance effect by using the interfacial reflectance at the interface between the layers having different refractive indices, which can be seen in the second embodiment of the present invention as shown in FIG. It may be implemented by the third embodiment of the present invention.

The second embodiment of the present invention as seen in FIG. 2 has the same basic configuration as the first embodiment described above, but instead of the first refractive layer, between the transparent substrate 1 and the first electrode layer 2 The second refractive layer 52 having a smaller refractive index than the transparent substrate 1 is interposed. Due to the second refractive layer 52, the resonance region C is formed between the interface between the first electrode layer 2 and the second refractive layer 52 and the interface between the second electrode layer 3 and the intermediate layer 4. Is formed.

A third embodiment of the present invention as seen in FIG. 3 is provided with a first refractive layer 51 interposed between the transparent substrate 1 and the first electrode layer 2, and is transparent with the first refractive layer 51. The second refractive layer 52 is interposed between the substrate 1. As a result, a resonance region C is formed between the interface between the first refractive layer 51 and the second refractive layer 52 and the interface between the second electrode layer 3 and the intermediate layer 4.

As described above, according to the present invention, the optical resonance effect is further increased by the interfacial reflectance at the interface between the layers, and the first refractive layer 51 and the second refractive layer 52 According to the refractive index of the first electrode layer 2, various materials may be used.

Table 1 below shows the refractive index of the layers that can be applied to the organic EL device according to an embodiment of the present invention. The refractive index shown in Table 1 represents the case where the thickness is 530 nm.

ITO Nb ₂ O ₅ TiO ₂ SiO ₂ Porous Silica (NPS) Refractive index (n) 1.79 2.1 2.2 1.53 1.2

In Table 1, the porous silica (Nano Poros Silica, hereinafter referred to as "NPS") is provided with a plurality of pores, and has the property of absorbing moisture or oxygen, at this time, even if the moisture or oxygen is absorbed, its transparency It is said to have the characteristics to be maintained. In addition, since the absorbed moisture may affect the life of the organic EL, the NPS layer is preferably hydrophobic.

Such an NPS layer can be manufactured by various methods, one of which is as follows.

First, a first mixture of 0.3 g of a surfactant and 0.6 g of a solvent is prepared. In this case, a surfactant is used as a polymer material, and the solvent is formed by mixing propanol and butanol in a ratio of 1 to 2. In addition, a second mixture of 5 g of Tetra-Ethyl-Ortho-Silicate (TEOS) and 1.85 g of 10.65 g of HCL was prepared.

Stir the second mixture for about 1 hour and mix 2.1 g of the second mixture with the first mixture to form a third mixture. This third mixture is applied to the substrate. The coating may be spin coating, spray coating, roll coating, or the like, and in the case of spin coating, the coating may be performed by turning at about 30 seconds at 2000 rpm. Thereafter, aged for about 24 hours at room temperature or 5 hours at 40-50 degrees Celsius. The polymer is burned by baking for about 2 hours in an oven at about 400 degrees Celsius to form a hygroscopic hole. The thickness of the NPS formed under such conditions is about 7000 GPa. By repeating the above process, a desired thin film is formed. The amount of material used in the above description is used to indicate the ratio and is not significant in the absolute amount.

As another method, ammonia water (NH 4 OH) is added to 30 g of H 2 O to show basicity, and then 10 g of TEOS (tetraethyl ortho silicate) is added thereto, followed by heating for 3 hours or more, followed by hydrolysis and polycondensation. Proceed. An acid such as an organic acid or an inorganic acid is added to the solution thus obtained.

To the mixture thus obtained, 13.2 g of a 30% by weight aqueous acrylic resin solution was added for stability, followed by stirring to obtain a uniform solution.

The solution is applied onto a substrate, which is then spin coated at 180 rpm for 120 seconds and then dried in a drying oven for about 2 minutes to remove unevaporated solvent. This process is repeated to make the film thicker.

 The resulting product may be heat-treated at 500 ° C. for 30 minutes to remove polymers and organic materials and to cure silica. The amount of the substance used above is used to indicate the ratio, and it is not meaningful to the absolute amount.

The NPS prepared through the above process contains large pores in its structure. The size of these pores is usually about 2 ~ 30 nm, this size can be adjusted by adjusting the size of the polymer used in the first mixture. The density of the pores can be prepared to be about 80%. The NPS layer may be prepared using spin coating, spray coating, roll coating, or the like as described above, and may be manufactured by a process having excellent mechanical and thermal stability and relatively easy to control.

Referring to Table 1, in the first embodiment of the present invention, since the transparent substrate 1 is a glass material having SiO ₂ as a main component, and the first electrode layer 2 is ITO, the first refractive layer 51 Silver Nb ₂ O ₅ , TiO ₂ and the like can be used. In the second embodiment, the second refractive layer 52 may be an NPS layer.

On the other hand, the reflectance at each interface when the layers are combined is shown in Table 2.

ITO / SiO ₂ TiO ₂ / SiO ₂ TiO ₂ / NPS ITO / NPS Nb ₂ O ₅ / SiO ₂ Nb ₂ O ₅ / NPS Interfacial reflectance 0.078 0.180 0.294 0.197 0.157 0.273

Referring to Table 2, TiO ₂ / NPS or Nb ₂ O ₅ / NPS may be used for the first refractive layer 51 and the second refractive layer 52 of the third embodiment of the present invention.

On the other hand, as described above, when the refractive layers are formed, the reflectance between the substrate and the first refractive layer 51 or the second refractive layer 52 is small, so that the viewing angle is reduced despite the luminance improvement due to the resonance effect. As it is not big, a viewing angle of 100 degrees or more can be secured.

According to the organic electroluminescent device of the present invention made as described above, the following effects can be obtained.

First, it is possible to amplify the light emitted by configuring a light resonance layer of a simple structure, thereby increasing the light extraction efficiency.

Second, by forming a single layer structure of the optical resonant layer that microresonates the light emitted from the organic light emitting layer, the device layer design structure can be made simpler, and the overall manufacturing process can be simplified.

Third, it is possible to obtain an effect of increasing brightness and improving color purity according to the optical resonance effect, and at the same time, securing a wide viewing angle.

Fourth, efficiency can be improved.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary and one of ordinary skill in the art will understand that various modifications and variations are possible. Therefore, the present invention will be defined by the technical spirit of the appended claims the true technical protection scope of the present invention.

1 is a cross-sectional view of an electroluminescent device according to a preferred embodiment of the present invention.

2 is a cross-sectional view of an electroluminescent device according to another exemplary embodiment of the present invention.

3 is a cross-sectional view of an electroluminescent device according to another exemplary embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

1: transparent substrate 2: first electrode layer

3: second electrode layer 4: intermediate layer

41: light emitting layer 51: first refractive layer

52: second refractive layer

Claims (5)

Transparent substrates; First and second electrode layers sequentially formed on one surface of the transparent substrate; An intermediate layer interposed between the first electrode layer and the second electrode layer, the intermediate layer having a light emitting layer that emits light by electrical driving of the first electrode layer and the second electrode layer; And And a first refractive layer interposed between the transparent substrate and the first electrode layer, the first refractive layer including a material having a refractive index greater than that of the first electrode layer. And an optical resonance between an interface between the second electrode layer and the intermediate layer and an interface between the transparent substrate and the first refractive layer. Transparent substrates; First and second electrode layers sequentially formed on one surface of the transparent substrate; An intermediate layer interposed between the first electrode layer and the second electrode layer, the intermediate layer having a light emitting layer that emits light by electrical driving of the first electrode layer and the second electrode layer; And And a second refractive layer interposed between the transparent substrate and the first electrode layer and made of a material having a refractive index smaller than that of the transparent substrate. And an optical resonance between an interface between the second electrode layer and the intermediate layer and an interface between the first electrode layer and the second refractive layer. Transparent substrates; First and second electrode layers sequentially formed on one surface of the transparent substrate; An intermediate layer interposed between the first electrode layer and the second electrode layer, the intermediate layer having a light emitting layer that emits light by electrical driving of the first electrode layer and the second electrode layer; A first refractive layer interposed between the transparent substrate and the first electrode layer and formed of a material having a refractive index greater than that of the first electrode layer; And And a second refractive layer interposed between the transparent substrate and the first refractive layer, the second refractive layer being made of a material having a smaller refractive index than the transparent substrate. And an optical resonance is generated between an interface between the second electrode layer and the intermediate layer and an interface between the first refractive layer and the second refractive layer. The method according to any one of claims 1 to 3, The transparent substrate is a glass material containing SiO 2 as a main component, the first electrode layer is provided as a transparent electrode, the second electrode layer is an electroluminescent device, characterized in that provided as a reflective electrode. The method of claim 4, wherein And the first and second refractive layers are transparent.