JP4186101B2 - Organic EL display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic EL display device including a light emitting layer made of an organic EL material.
[0002]
[Prior art]
In recent years, next-generation displays have been actively developed in the field of display devices, and space saving, high brightness, low power consumption, and the like are demanded. An organic EL (Electro Luminescence) display device has attracted attention as a display that can realize these demands. This organic EL display device has features such as spontaneous light emission, high responsiveness, and no viewing angle dependency compared to a liquid crystal display device which is a typical flat panel display device. .
[0003]
Such an organic EL display device is configured by arranging a large number of organic EL elements, and each element corresponds to one pixel. The organic EL element has a configuration in which an anode layer, an organic EL layer, and a cathode layer, which are transparent electrodes, are sequentially laminated on a transparent substrate. In this organic EL element, by applying a predetermined voltage to the anode layer and the cathode layer, holes and electrons injected from the respective electrode layers are recombined in the organic EL layer, and energy is released at this time. Luminous phenomenon occurs. Since this light emission phenomenon is injection light emission similar to a light emitting diode, it is characterized by a low light emission voltage of 10 V or less.
[0004]
[Problems to be solved by the invention]
By the way, in the organic EL display device using the conventional organic EL element, in the element related to the pixel at the time of non-light emission, the external light passes through the transparent substrate, the anode layer and the organic EL layer, and reaches the cathode layer which is the back electrode. However, the external light reaching the cathode layer is reflected by the cathode layer as shown in FIG. 5 because the cathode layer is a metal electrode made of aluminum (Al). There was a problem that the contrast between light and darkness was lowered. In order to suppress such a decrease in contrast, methods have been proposed in which a colored filter, a polarizing filter, a quarter-wave plate, or the like is provided on the surface of the transparent substrate. As a result, the transmittance is lowered, and the screen brightness of the apparatus is lowered.
[0005]
Therefore, in order to solve such a problem, for example, in Patent Document 1, a black plate is installed other than the organic EL display unit and reflected light from the black plate is used, but this is a fundamental solution. Has not reached. Further, in Patent Document 2, although the black level is improved by the stacked cathode of Mg: Ag (18.5 nm) / ITO (84 nm) / Mg (50 nm), as shown in FIG. Since the reflection of the emitted light itself is also lowered, there is a problem that the luminance is lowered.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-148045
[Patent Document 2]
International Publication No. 01/08240 [0008]
The present invention has been made in view of such problems, and an object thereof is to provide an organic EL display device capable of improving contrast of light and dark and improving luminance.
[0009]
[Means for Solving the Problems]
The organic EL display device according to the present invention includes an anode layer, an organic EL layer including a light emitting layer, and a cathode layer in this order on a substrate, and light emission in the light emitting layer is taken out from the substrate side, The cathode layer has a configuration in which metal films and transparent conductive films are alternately laminated, the thickness of the transparent conductive film is 500 nm or more, and the cathode layer is each color of red, green and blue generated in the light emitting layer. The light has a reflection characteristic with respect to the light in the wavelength region, and has the absorption characteristic for light in at least the visible wavelength region other than the wavelength region of each color among the external light incident from the back surface of the substrate .
[0010]
In the organic EL display device according to the present invention, the light (emission wavelength) of the red, green, and blue wavelength regions generated in the light emitting layer is reflected on the cathode layer, while at least the visible wavelength region other than the wavelength regions of these colors. Light (external light) is absorbed in the reflective layer. That is, in the element related to the pixel at the time of light emission, the light emission wavelength from the organic EL layer is efficiently reflected in the cathode layer and the luminance is improved. Since it is absorbed, there is no reflection, and as a result, a display with improved contrast between light and dark is performed.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0012]
FIG. 1 is a configuration diagram showing an outline of an organic EL display device 10 according to an embodiment of the present invention. The organic EL display device 10 has a configuration in which organic EL elements 10R that emit red light, organic EL elements 10G that emit green light, and organic EL elements 10B that emit blue light are regularly arranged in a matrix. Each organic EL element 10R, 10G, 10B corresponds to one pixel. The organic EL display device 10 includes a substrate 11, and an anode layer 12 is formed on the substrate 11. An organic EL layer 13 is formed on the anode layer 12. A cathode layer 14 is formed on the organic EL layer 13, and the cathode layer 14 has a function as a so-called band filter. Details of this will be described later. A protective layer 15 is formed on the cathode layer 14.
[0013]
The substrate 11 is a transparent substrate made of, for example, a glass material and having a thickness of 1.1 mm. The substrate 11 preferably has good flatness. The substrate 11 may be made of a polymer material. Examples of the polymer material include polyethylene terephthalate (PET; Poly (Ethylene Terephthalate)), polycarbonate (PC; PolyCarbonate), polyolefin (PO; PolyOlefin), Polyethersulfone (PES; PolyEter Sulphone) etc. are mentioned. By using such a polymer material for the substrate 11, the substrate 11 becomes flexible.
[0014]
The anode layer 12 has a thickness of, for example, 150 nm, has a large work function from the vacuum level so that holes are efficiently injected into the organic EL layer 13, and transmits light so that light emitted from the organic EL layer 13 can be extracted. It is made of a material having optical properties. Examples of the anode material include indium tin oxide (ITO), tin oxide (SnO ₂ ), and zinc oxide (ZnO). In particular, ITO is preferable among these materials from the viewpoint of productivity and controllability.
[0015]
For example, the organic EL layer 13 is formed by laminating a hole transport layer 13A, a light emitting layer 13B, and an electron transport layer 13C in this order from the anode layer 12 side. The thickness of the organic EL layer 13 is 150 nm, for example.
[0016]
The hole transport layer 13A is provided to transport holes injected from the anode layer 12 to the light emitting layer 13B. Examples of the material for the hole transport layer 13A include benzine, styrylamine, triphenylamine, porphyrin, triazole, imidazole, oxadiazole, polyarylalkane, phenylenediamine, arylamine, oxazole, anthracene, fluorenone, hydrazone, stilbene. Alternatively, derivatives thereof, or heterocyclic conjugated monomers, oligomers, or polymers such as polysilane compounds, vinylcarbazole compounds, thiophene compounds, and aniline compounds can be used. Specifically, α-naphthylphenyldiamine, porphyrin, metal tetraphenylporphyrin, metal naphthalocyanine, 4,4,4-tris (3-methylphenylphenylamino) triphenylamine) triphenylamine, N, N, N , N-tetrakis (p-tolyl) p-phenylenediamine, N, N, N, N-tetraphenyl 4,4-diaminobiphenyl, N-phenylcarbazole, 4-di-p-tolylaminostilbene, poly (paraphenylene) Vinylene), poly (thiophene vinylene), poly (2,2-thienylpyrrole) and the like.
[0017]
When a potential difference occurs between the cathode layer 14 and the anode layer 12, the light emitting layer 13 </ b> B emits electrons and holes injected from the cathode layer 14 and the anode layer 12, and these electrons and holes recombine to emit light. It is an area to do. As the light emitting layer 13B, for example, the organic EL element 10R has a material that displays red light with a wavelength of 620 nm, the organic EL element 10G has a material that displays green light with a wavelength of 520 nm, and the organic EL element 10B has blue light with a wavelength of 460 nm. The material which shows is used. By arranging the light emitting layers 13B made of these materials in a matrix pattern, the organic EL display device 10 can perform color display.
[0018]
Such a light emitting layer 13B is made of a material having high luminous efficiency, for example, an organic material such as a low molecular fluorescent dye, a fluorescent polymer, or a metal complex. Specifically, for example, anthracene, naphthalene, phenanthrene, pyrene, chrysene, perylene, butadiene, coumarin, acridine, stilbene, tris (8-quinolinolato) aluminum complex, bis (benzoquinolinolato) beryllium complex, tri (dibenzoyl) And methyl) phenanthroline europium complex ditoluyl vinyl biphenyl.
[0019]
The electron transport layer 13C is provided to transport electrons injected from the cathode layer 14 to the light emitting layer 13B. Examples of the material for the electron transport layer 13C include quinoline, perylene, bisstyryl, pyrazine, and derivatives thereof. Specific examples include 8-hydroxyquinoline aluminum, anthracene, naphthalene, phenanthrene, pyrene, chrysene, perylene, butadiene, coumarin, acridine, stilbene, or derivatives thereof.
[0020]
The cathode layer 14 is a multilayer film in which metal films 14M _k and transparent conductive films 14T _m are alternately laminated from the organic EL layer 13 side (where k is a positive number from 1 to n, and m is 2 to n. Is a positive number). That is, the metal film 14M ₁ , the transparent conductive film 14T ₂ , the metal film 14M ₂ , the transparent conductive film 14T ₃ , the metal film 14M ₃ ,..., The transparent conductive film 14T _n , and the metal film 14M _n are sequentially stacked. Is.
[0021]
The metal film 14M ₁ has a thickness of, for example, 10 nm or more and 20 nm or less, a work function is small, electrons are efficiently injected into the organic EL layer 13, and a light-transmitting metal material is used. Examples of such metal materials include aluminum, indium (In), magnesium (Mg), silver (Ag), calcium (Ca), barium (Ba), and lithium (Li). These metals are used alone. It may also be used as an alloy with another metal in order to increase the stability. In particular, among these metal materials, it is preferable to use Al which is a material having a small work function and high reflectance, and the upper limit of the reflectance of the cathode layer 14 is determined by this Al. The metal film 14M _k (where k ≧ 2) has a thickness of, for example, 5 nm or more and 20 nm or less, and is made of niobium (Nb). The lower limit of the reflectance of the cathode layer 14 is determined by this Nb.
[0022]
The transparent conductive film 14T _m is indium tin oxide (ITO), tin oxide (SnO _2), zinc oxide (ZnO), or set to be a mixture comprising two or more of these materials. Among these metal materials, ITO is preferably used from the viewpoints of productivity and controllability. The thickness of the transparent conductive film 14T _m is 500nm or more. If the thickness of the transparent conductive film 14T _m is 500nm or more, the average absorption of visible light is larger than the average reflectance (Figure 2). In this case, as the thick transparent conductive film 14T _m, appear many peaks of the reflectance, the peak becomes sharper.
[0023]
Each film thickness of the cathode layer 14 has a reflectance of, for example, 60% or more with respect to light in the emission wavelength region of each organic EL element 10R, 10G, 10B, that is, light in the wavelength region of each color of red, green, and blue It is designed to have high absorption characteristics such as an average absorptance of 40% or more for light in a visible wavelength region other than these wavelength regions. Here, each film thickness of the cathode layer 14 is such that the thickness of each film is d, the refractive index of each film is n, and the wavelength of incident light incident on this multilayer film is λ. The thickness nd satisfies the formula shown in Equation 1 with respect to the wavelength λ of the incident light.
[0024]
[Expression 1]
nd = λ (α ± 1/4) (where α is a natural number)
[0025]
For example, Al is used for the metal film 14M ₁ , ITO is used for the transparent conductive film 14T ₂ , and Nb is used for the metal film 12M _{2. The} total number of layers is three, and the optical characteristics as shown in FIG. Designed to have. That is, for the light in the emission wavelength region of each organic EL element 10R, 10G, and 10B, that is, for the light of each color of red light having a wavelength of 620 nm, green light having a wavelength of 520 nm, and blue light having a wavelength of 460 nm, Layer 14 has a high reflectivity, for example, 70.9%, 71.3%, 68.8%, and a high absorptance, for example, average absorption, for light in the visible wavelength region other than these lights. It is designed to have an absorptance of 44% or higher and a transmittance of, for example, 5 to 10% with respect to light in the entire wavelength region. With this design, the thickness of the metal film 14M ₁ is 10 nm, the thickness of the transparent conductive film 14T ₂ is 898 nm, and the thickness of the metal film 14M ₂ is 5 nm.
[0026]
The protective layer 15 has a function of sealing the element and blocking oxygen and moisture in order to ensure the driving reliability of the organic EL element and prevent the element from deteriorating. The protective layer 15 has a thickness of 1000 nm, for example. The protective layer 15 can be made of a material that can maintain hermeticity, such as silicon oxide (SiO ₂ ), silicon nitride (SiN _x ), aluminum oxide (Al ₂ O ₃ ), aluminum nitride (AlN), and the like. Is mentioned.
[0027]
This organic EL display device 10 can be manufactured as follows, for example.
[0028]
First, the substrate 11 is prepared. An anode layer 12 made of ITO is formed on the substrate 11 by using, for example, a reactive DC sputtering method. Next, the anode layer 12 is formed into a predetermined pattern by a lithography method using a resist. Subsequently, a hole transport layer 13A, a light emitting layer 13B, and an electron transport layer 13C having a predetermined pattern are sequentially formed on the anode layer 12 by a vacuum deposition method using a metal mask, thereby forming an organic EL layer. 13 is formed. At this time, as the light emitting layer 13B, for example, a material that exhibits red light having a wavelength of 620 nm is formed in the formation region of the organic EL element 10R, a material that exhibits green light having a wavelength of 520 nm is formed in the formation region of the organic EL element 10G, In the formation region of 10B, materials showing blue light having a wavelength of 460 nm are used, and these materials are selectively formed.
[0029]
Next, the cathode layer 14 is formed on the organic EL layer 13 by a vacuum deposition method using a metal mask. The cathode layer 14 is a multilayer film in which a metal film 14M _k and the transparent conductive film 14T _m from the side of the organic EL layer 13 are alternately stacked. Each film thickness of the cathode layer 14 has high reflection characteristics such as a reflectance of 60% or more with respect to light in the emission wavelength region of each of the organic EL elements 10R, 10G, and 10B, and is visible outside the wavelength region. For light in the wavelength range, for example, it is designed to have a high absorption characteristic with an average absorption rate of 40% or more.
[0030]
Specifically, a three-layer structure of a metal film 14M ₁ made of Al, a transparent conductive film 14T _{2 made of} ITO, and a metal film 14M _{2 made} of Nb is used, and the thickness of each film is 10 nm, 898 nm, and 5 nm. Accordingly, as shown in FIG. 3, the cathode layer 14 has a high reflectance with respect to light of each color of red light having a wavelength of 620 nm, green light having a wavelength of 520 nm, and blue light having a wavelength of 460 nm, for example, 70 .9%, 71.3%, 68.8% reflectivity, and high absorptance with respect to light in the visible wavelength region other than these light, for example, average absorptance of 44% or more And has a transmittance of, for example, 5 to 10% with respect to light in the entire wavelength region. Finally, the organic EL display device 10 is completed by forming the protective layer 15 made of silicon nitride by the reactive DC sputtering method.
[0031]
In the organic EL display device 10 according to the present embodiment, when a positive or negative voltage is applied to each of the anode layer 12 and the cathode layer 14 of the selected element from a drive circuit (not shown), an electric field generated between the two electrodes is generated. Holes and electrons are injected into the light emitting layer 13B in the organic EL layer 13, recombination occurs, and so-called electroluminescence occurs. Light emitted from the light emitting layer 13B is extracted from the substrate 11 side.
[0032]
At this time, the cathode layer 14, since the work function from the vacuum level of the metal film 14M ₁ in contact with the organic EL layer 13 is small Al is used, electrons are efficiently injected into the organic EL layer 13, the light emission efficiency Will improve.
[0033]
When a single-layer electrode made of only Al is used as the cathode layer as in the prior art, when external light is incident from the substrate 11 side, reflection of external light occurs in the cathode layer as shown in FIG. Therefore, the contrast is deteriorated. On the other hand, in the present embodiment, since it has a three-layer structure of a metal film 14M ₁ made of Al, a transparent conductive film 14T _{2 made of} ITO, and a metal film 14M _{2 made} of Nb, as shown in FIG. The cathode layer 14 has high reflection characteristics with respect to light in the emission wavelength region of each of the organic EL elements 10R, 10G, and 10B, and has high absorption characteristics with respect to light in the visible wavelength region other than these wavelength regions. . Thereby, in the organic EL element which concerns on the pixel at the time of light emission, the light emission can be efficiently reflected by the cathode layer 14, and it becomes possible to improve a white level. In addition, in the organic EL element related to the non-light-emitting pixel, even if external light is incident on the cathode layer 14 from the back surface of the substrate 11, it is absorbed by the cathode layer 14 and reflection of external light is suppressed. It becomes possible to improve. Therefore, contrast between light and dark can be improved, and luminance can be improved.
[0034]
While the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment, and various modifications can be made. For example, as in the organic EL display device 20 shown in FIG. 4, in each organic EL element 20R, 20G, 20B, as the cathode layer 21, a metal film 14M _k (where k is 1 to n) and a transparent conductive film 14T. _m (where, m is 2- through n) alternately laminated on the metal film 14M _n, for example, may be a metal film 14M n + ₁ consisting of Al. Thereby, the average transmittance of light in the visible wavelength region can be reduced, and the reflectance of red light, green light, and blue light can be increased while maintaining the black level. Further, a light emission auxiliary layer made of lithium oxide (LiO) having a thickness of, for example, 0.1 to 0.3 nm may be formed between the organic EL layer 13 and the cathode layer 14. This light emission auxiliary layer can reduce the light emission starting voltage.
[0035]
Furthermore, in the above embodiment, the cathode layer 14 has high reflection characteristics with respect to light in the wavelength regions of the three primary colors of red, green, and blue. This wavelength region depends on the emission wavelength of the organic EL element. It can be changed as appropriate. For example, the cathode layer 14 may have high reflection characteristics with respect to light in at least one wavelength region of these three primary colors.
[0036]
【The invention's effect】
As described above, according to the organic EL display device of the present invention, the cathode layer has reflection characteristics with respect to light in the wavelength region of each color of red, green, and blue generated in the light emitting layer, and the wavelength of each color. Since it has absorption characteristics for light in at least the visible wavelength region other than the region, the element related to the pixel at the time of light emission can efficiently reflect light in the specific wavelength region by the cathode layer. The level can be improved. Further, in the element related to the pixel at the time of non-light emission, even if external light is incident on the cathode layer, it is absorbed in the cathode layer, so that the black level can be improved. Accordingly, contrast between light and dark can be improved, and luminance can be improved.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an organic EL display device according to an embodiment of the present invention.
2 shows the film thickness dependence of a transparent conductive film in the optical characteristics of the cathode layer of the organic EL display device shown in FIG.
3 shows the optical characteristics of the cathode layer of the organic EL display device shown in FIG.
FIG. 4 is a modification of the organic EL display device.
FIG. 5 shows optical characteristics of a cathode layer of a conventional organic EL display device.
FIG. 6 shows optical characteristics of a cathode layer of a conventional organic EL display device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Organic EL display apparatus, 10R, 10G, 10B ... Organic EL element, 11 ... Substrate, 12 ... Anode layer, 13 ... Organic EL layer, 13A ... Hole transport layer, 13B ... Light emitting layer, 13C ... Electron transport layer, 14 ... Cathode layer

Claims (6)

An organic EL display device comprising an anode layer on a substrate, an organic EL layer including a light emitting layer, and a cathode layer in this order, wherein light emitted from the light emitting layer is extracted from the substrate side ,
The cathode layer has a configuration in which metal films and transparent conductive films are alternately laminated,
The transparent conductive film has a thickness of 500 nm or more,
The cathode layer has reflection characteristics with respect to light in the wavelength regions of each color of red, green, and blue generated in the light emitting layer, and other than the wavelength region of each color out of the external light incident from the back surface of the substrate Has absorption characteristics at least for light in the visible wavelength region
Organic EL display device. The cathode layer has a reflectance of 60% or more with respect to light in a wavelength region of each color of red, green, and blue generated in the light emitting layer, and other than the wavelength region of each color in external light incident from the back surface of the substrate The absorption coefficient for light in at least the visible wavelength region is 40% or more
The organic EL display device 請 Motomeko 1 wherein. The metal film is made of niobium (Nb), aluminum (Al), magnesium (Mg), or silver (Ag).
The organic EL display device 請 Motomeko 1 wherein. The transparent conductive film is made of indium tin oxide (ITO), tin oxide (SnO2), zinc oxide (ZnO), or a mixture containing two or more of these materials.
The organic EL display device 請 Motomeko 1 wherein. The cathode layer is to first metal film made of aluminum (Al), a transparent conductive film made of indium tin oxide (ITO), a second metal film made of niobium (Nb) are laminated in this order
The organic EL display device 請 Motomeko 1 wherein. Each film thickness of the cathode layer is defined as follows: d is the thickness of each film, n is the refractive index of each film, and λ is the wavelength of incident light incident on this multilayer film. Satisfies the equation shown in Equation 1 with respect to the wavelength λ of the incident light.
The organic EL display device according to claim 1.
(Equation 1)
nd = λ (α ± 1/4) (where α is a natural number)

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