JP2007242828A - Organic el device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL device capable of suppressing a leak current. <P>SOLUTION: The organic EL device A1 is provided with an anode electrode 2 and a cathode electrode 7 which are arranged oppositely each other, and a light-emitting element 5 provided between the anode electrode 2 and the cathode electrode 7 and made of an organic substance. A hole transport layer 4 containing an organic compound having a stereoscopic barrier structure is provided between the anode electrode 2 and the light-emitting layer 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an organic EL element that emits light by interposing an organic layer between a pair of electrodes and applying an electric field to the organic layer.

  FIG. 5 shows an example of a conventional organic EL element (see, for example, Patent Document 1). The organic EL element X shown in the figure has an anode electrode 92, a hole injection layer 93, a hole transport layer 94, a light emitting layer 95, an electron transport layer 96, a cathode buffer layer 97, and a cathode electrode 98 on a substrate 91. Is a laminated structure. The substrate 91 is made of transparent glass, and the anode electrode 92 is a transparent electrode made of, for example, ITO (Indium Tin Oxide). The hole injection layer 93 is a layer for injecting holes from the anode electrode 92 toward the light emitting layer 95, and is made of copper phthalocyanine (hereinafter, CuPc). The hole transport layer 94 is a layer for transporting holes from the hole injection layer 93 to the light emitting layer 95, and includes NPB (N, N-di (naphthalene-1-yl) -N, N-diphenyl). -benzidene). The light emitting layer 95 is made of an organic material and emits red light, green light, blue light and the like. The electron transport layer 96 is a layer for transporting electrons from the cathode electrode 98 to the light emitting layer 95. The cathode buffer layer 97 is a layer for stabilizing electron injection from the cathode electrode 98, and is made of, for example, LiF. The cathode electrode 98 is made of, for example, Al.

  The positive electrode of the power source P is connected to the anode electrode 92. The negative electrode of the power source P is connected to the cathode electrode 98. When a voltage is applied between the anode electrode 92 and the cathode electrode 98, holes and electrons are recombined in the light emitting layer 95. By this recombination, the light emitting layer 95 emits light. Light traveling upward in the figure from the light emitting layer 95 is reflected downward in the figure by the cathode electrode 98. The reflected light and the light emitted downward from the light emitting layer 95 are emitted downward through the anode electrode 92 and the substrate 91. Thus, the organic EL element X is configured as a so-called bottom emission type organic EL element.

  However, when the hole injection layer 93 is formed by using, for example, a vacuum deposition method, a protrusion 93a protruding in the thickness direction may be formed as shown in FIG. This is because CuPc, which is the material of the hole injection layer 93, is a substance that is relatively easy to grow crystals. When the hole transport layer 94 is formed on the hole injection layer 93 having such a protrusion 93 a, the tip of the protrusion 93 a is likely to protrude from the hole transport layer 94. This is because NPB, which is the material of the hole transport layer 94, is relatively easy to grow crystals like CuPc, and is formed relatively flat without depending on the shape of the protrusion 93a. If the light emitting layer 95 is formed with the protrusions 93a protruding, the hole injection layer 93 and the light emitting layer 95 are partially connected. Such a conductive portion tends to cause a so-called leakage current because current tends to flow intensively. Therefore, for example, when a display is configured using the organic EL element X, problems such as crosstalk light emission occur.

JP 2000-150171 A

  The present invention has been made under the circumstances described above, and an object thereof is to provide an organic EL element capable of suppressing a leakage current.

  An organic EL device provided by the present invention is an organic EL device comprising an anode electrode and a cathode electrode arranged to face each other, and a light emitting layer made of an organic material and interposed between the anode electrode and the cathode electrode. In addition, a layer containing an organic compound having a steric hindrance structure is interposed between the anode electrode and the light emitting layer.

  According to such a configuration, the organic compound having the steric hindrance structure is relatively difficult to grow a crystal, and the film formation process proceeds in a so-called amorphous state. For this reason, even if there is a steep protrusion in the portion where the layer containing the organic compound having the steric hindrance structure is formed, it is possible to completely cover it. Thereby, it is possible to prevent the light emitting layer from being unduly conducted to other layers without going through the layer containing the organic compound having the steric hindrance structure. Therefore, the leakage current of the organic EL element can be suppressed.

  In a preferred embodiment of the present invention, the organic compound having a steric hindrance structure is a phenylenediamine type compound. According to such a structure, it is suitable for making the layer containing the organic compound having the steric hindrance structure amorphous.

  In a preferred embodiment of the present invention, the layer containing an organic compound having a steric hindrance structure has a thickness of 100 to 1000 mm. According to such a configuration, the injection and transport of holes from the anode electrode are appropriately promoted while covering the steep protrusion generated in the portion where the layer containing the organic compound having the steric hindrance structure is formed. be able to.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

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

  FIG. 1 shows a first embodiment of an organic EL element according to the present invention. The organic EL element A1 of this embodiment includes a substrate 1, an anode electrode 2, a hole injection layer 3, a hole transport layer 4, a light emitting layer 5, an electron transport layer 6, and a cathode electrode 7. The organic EL element A1 is configured as a so-called bottom emission type organic El element that emits light from the lower surface of the substrate 1 in the figure.

  The substrate 1 is a transparent substrate made of glass, for example. The substrate 1 is for supporting the anode electrode 2, the hole injection layer 3, the hole transport layer 4, the light emitting layer 5, the electron transport layer 6, and the cathode electrode 7.

  The anode electrode 2 is connected to the positive electrode of the power source P and is an electrode for supplying holes. The anode electrode 2 is a transparent electrode made of, for example, ITO. The surface of the anode electrode 2 is polished, for example, and is a relatively flat surface.

  The hole injection layer 3 has a role of improving the efficiency of hole injection from the anode electrode 2 to the light emitting layer 5. The hole injection layer 3 is made of CuPc, for example.

  The hole transport layer 4 has a role of efficiently transferring holes to the light emitting layer 5 and increasing the recombination efficiency of electrons and holes in the light emitting layer 5. The hole transport layer 4 contains an organic compound having a steric hindrance structure. As the organic compound having this steric hindrance structure, for example, a phenylenediamine type compound is used.

The light-emitting layer 5 contains a light-emitting substance, and is a field where excitons are generated by recombination of holes from the anode electrode 2 and electrons from the cathode electrode 7. In the process in which the excitons move in the light emitting layer 5, the light emitting material emits light. By selecting the type of the luminescent material contained in the light emitting layer 5, red light, green light, blue light and the like are self-luminous. Examples of the light-emitting substance include tris (8-quinolinolato) aluminum complex, bis (benzoquinolinolato) beryllium complex, ditoluylvinylbiphenyl, tri (dibenzoylmethyl) phenanthroline europium complex (Eu (DBM) ₃ (Phen)) And fluorescent or phosphorescent emissive materials such as phenylpyridine iridium compounds can be used. Of course, polymer light-emitting substances such as poly (p-phenylene vinylene), polyalkylthiophene, polyfluorene, and derivatives thereof may be used.

  The electron transport layer 6 has a role of efficiently transferring electrons to the light emitting layer 5 and increasing the recombination efficiency of electrons and holes in the light emitting layer 5. As a material constituting the electron transport layer 6, for example, anthraquinodimethane, diphenylquinone, perylenetetracarboxylic acid, triazole, oxazole, oxadiazole, benzoxazole, and derivatives thereof can be used. A cathode buffer layer 81 is formed on the electron transport layer 6. The cathode buffer layer 81 is made of, for example, LiF, and is a layer for increasing electron injection efficiency. An electron injection layer may be further formed between the electron transport layer 6 and the cathode buffer layer 81.

  The cathode electrode 7 is connected to the negative pole of the power source P and is an electrode for supplying electrons. The cathode electrode 7 is made of, for example, Al and is a layer having a relatively high reflectance.

  Next, the operation of the organic EL element A1 will be described.

  FIG. 2 shows a stacked portion of the hole injection layer 3, the hole transport layer 4, and the light emitting layer 5 of the organic EL element A1. CuPc forming the hole injection layer 3 is a material that relatively easily grows crystals. For this reason, for example, when the hole injection layer 3 is formed by a vacuum deposition method, the degree of crystal growth of CuPc tends to vary locally in the in-plane direction of the substrate 1, that is, in the horizontal direction in the figure. When the degree of crystal growth varies, the thickness of each part of the hole injection layer 3 varies. A portion where this thickness is significantly larger than the surrounding portion becomes a protrusion 3a shown in FIG.

  In this embodiment, the hole transport layer 4 formed on the hole injection layer 3 is made of a phenylenediamine type compound. A phenylenediamine type compound is an organic compound having a steric hindrance structure. For this reason, when the hole transport layer 4 is formed by, for example, a vacuum deposition method, crystal growth is extremely difficult to progress as compared with CuPc or NPB. Such a hole transport layer 4 is easily formed in an amorphous state. In the film formation in an amorphous state, the thickness distribution of the hole transport layer 4 depends greatly on the shape of the hole injection layer 3 such as the protrusion 3a. As a result, the hole transport layer 4 is formed to follow the shape of the hole injection layer 3 and completely covers the protrusion 3a. Accordingly, it is possible to avoid the protrusion 3a from entering the light emitting layer 5, and it is possible to prevent the hole injection layer 3 and the light emitting layer 5 from being directly conducted. Therefore, it is possible to suppress the leakage current of the organic EL element A1, and for example, it is possible to reduce a possibility that crosstalk light emission or the like occurs in a display using the organic EL element A1.

  Hereinafter, the Example of organic EL element A1 and the comparative example of this were produced, and the characteristic of these elements was measured.

  In Example 1, organic EL element A1 was produced by the following method. First, an anode electrode 2 made of ITO is formed on a glass substrate 1. A hole injection layer 3 made of CuPc having a thickness of 200 mm is formed on the anode electrode 2 by a vacuum deposition method. Next, a hole transport layer 4 made of a phenylenediamine type compound having a thickness of 400 mm is formed on the hole injection layer 3 by a vacuum deposition method. Further, the light emitting layer 5 having a thickness of 400 mm is formed on the hole transport layer 4 by a vacuum deposition method. Further, an electron transport layer 6 having a thickness of 200 mm and a cathode buffer layer 81 having a thickness of 5 mm are formed on the light emitting layer 5 by a vacuum deposition method. Then, a cathode electrode 7 made of Al having a thickness of 1500 mm is formed.

  In the comparative example, an organic EL element was produced by the same method as in Example 1 described above except that the hole transport layer 4 was formed using NPB.

  A leakage current was measured when a voltage of −15 V serving as a reverse bias was applied to each of the organic EL elements of Example 1 and Comparative Example 1. The measurement results are shown in Table 1.

  As shown in Table 1, when comparing the organic EL elements of Example 1 and the comparative example, the magnitude of the leakage current was −257 nA in the comparative example, but the leakage current was −103 nA in Example 1. Met. According to Example 1, the leak current could be reduced to half or less of the comparative example. As shown in FIG. 2, this is because the protrusion 3a generated in the hole injection layer 3 is completely covered by the hole transport layer 4 made of a phenylenediamine type compound. 3 and the light emitting layer 5 are considered to be prevented from conducting directly. In addition, when the thickness of the hole transport layer 4 is set to 100 to 1000 mm, it is possible to appropriately exhibit such a leakage current suppressing effect and a hole transport effect.

  3 and 4 show another embodiment of the present invention. In these drawings, the same or similar elements as those in the above embodiment are denoted by the same reference numerals as those in the above embodiment.

  FIG. 3 shows a second embodiment of the organic EL element according to the present invention. The organic EL element A2 of this embodiment is different from the first embodiment described above in that it does not include a single hole transport layer and in that it includes a filter 82 and a color conversion layer 83. As shown in this figure, only the hole injection layer 3 is formed between the anode electrode 2 and the light emitting layer 5. The hole injection layer 3 is formed of a phenylenediamine type compound. In the present embodiment, the hole injection layer 3 is configured to also function as the hole transport layer 4 of the first embodiment.

  The filter 82 and the color conversion layer 83 are stacked on the substrate 1 and are covered with a protective layer 84. The color conversion layer 83 is a layer for transmitting light emitted from the light emitting layer 5 as wavelength-converted light by performing wavelength conversion, and is generally made of an organic substance. For example, the blue light emitted from the light emitting layer 5 is emitted as red light or green light by performing wavelength conversion. The filter 82 is a layer for selectively transmitting light in a wavelength band specific to red light or green light, for example, thereby increasing the saturation of these lights.

  In such an embodiment, since the color conversion layer 83 made of an organic substance is fragile, when the polishing process is performed on the anode electrode 2, the color conversion layer 83 is destroyed even though the protective layer 84 is interposed. There is a high risk of For this reason, it is difficult to polish the anode electrode 2. ITO employed to make the anode electrode 2 a transparent electrode is relatively easy to grow crystals. Therefore, like the hole injection layer 3 in the first embodiment described above, the protrusion 2a shown in FIG. 4 is easily formed. When the protrusion 2a enters the light emitting layer 5, the leakage current increases.

  In the present embodiment, the hole injection layer 3 on the anode electrode 2 is formed of a phenylenediamine type compound. For this reason, the protrusion 2 a can be completely covered by the hole injection layer 3. Therefore, direct conduction between the anode electrode 2 and the light emitting layer 5 can be prevented, and the leakage current of the organic EL element A2 can be suppressed.

  The organic EL device according to the present invention is not limited to the above-described embodiment. The specific configuration of each part of the organic EL element according to the present invention can be varied in design in various ways.

  The organic compound having a steric hindrance structure referred to in the present invention is a material formed in an amorphous state to such an extent that it can completely cover the protrusion 3a shown in FIG. 2 and the protrusion 2a shown in FIG. Any material suitable for facilitating the injection and transportation of holes may be used. Of these materials, the phenylenediamine type compound is a material that is particularly preferable for exhibiting the effect intended by the present invention. Other organic compounds having a steric hindrance structure include spiro derivatives and orthotetraphenylene derivatives. And triphenylamine derivatives.

It is sectional drawing which shows 1st Embodiment of the organic EL element which concerns on this invention. It is a principal part expanded sectional view of the organic EL element shown in FIG. It is sectional drawing which shows 2nd Embodiment of the organic EL element which concerns on this invention. It is a principal part expanded sectional view of the organic EL element shown in FIG. It is sectional drawing which shows an example of the conventional organic EL element. It is a principal part expanded sectional view of the organic EL element shown in FIG.

Explanation of symbols

A1, A2 Organic EL element 1 Substrate 2 Anode electrode 3 Hole injection layer 4 Hole transport layer 5 Light emitting layer 6 Electron transport layer 7 Cathode electrode

Claims (3)

An anode electrode and a cathode electrode arranged opposite to each other;
A light-emitting layer interposed between the anode electrode and the cathode electrode and made of an organic substance;
An organic EL device comprising:
An organic EL element, wherein a layer containing an organic compound having a steric hindrance structure is interposed between the anode electrode and the light emitting layer.   The organic EL device according to claim 1, wherein the organic compound having a steric hindrance structure is a phenylenediamine type compound.   The organic EL device according to claim 1, wherein the layer containing the organic compound having a steric hindrance structure has a thickness of 100 to 1000 mm.

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