JP2011108473A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element having an electron injection layer which is in contact with a cathode and pinches the cathode with high electron injection efficiency and an organic cap layer, in which high voltage due to deterioration of the electron injection performance and deterioration of drive characteristics are suppressed. <P>SOLUTION: The organic EL element is provided with an electron injection layer 4 which is in contact with a cathode 5 and pinches the cathode 5 and contains an alkali metal, or alkali metal compound, or alkali earth metal or alkali earth metal compound, and an organic cap layer 6. The organic cap layer 6 is constructed of an organic compound consisting of a non-hetero carbon cyclic compound. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an organic electroluminescence (Electro Luminescence: hereinafter abbreviated as “EL”) element applied to a flat panel display, a projection display, illumination and the like.

  Research and development of organic EL elements using electroluminescence of organic materials are currently being actively conducted. In an organic EL element, an organic compound layer having at least a light emitting layer is disposed between an anode and a cathode, and the organic compound layer is energized so that holes and electrons injected from the respective electrodes are emitted from the light emitting layer. Recombination produces light emission.

  Improvement of luminous efficiency is mentioned as a subject of an organic EL element. In order to solve this problem, Patent Document 1 achieves high efficiency by forming an organic capping layer on the organic EL element by vapor deposition and controlling the refractive index or film thickness.

  Further, the organic EL element has a problem that it is vulnerable to moisture and oxygen. In order to protect from moisture and oxygen, a technique for forming a protective layer using a high energy film formation method such as sputtering or plasma CVD after forming an organic EL element is known. When the protective layer is formed by such a high energy film formation method, the organic compound layer of the organic EL element may be damaged. With respect to this problem, in Patent Document 2, in order to protect the organic compound layer, a first conductive layer is formed on the organic compound layer, and then a buffer layer is formed thereon by a vapor deposition method, and a sputtering method is formed thereon. The organic electroluminescent element provided with the 2nd conductive layer formed by is disclosed.

  On the other hand, Patent Document 3 proposes an organic EL element using an electron injection layer doped with alkali metal or alkaline earth metal. For this reason, the injection barrier from the cathode can be lowered to improve the electron injection property, and a long-life organic EL element is realized.

JP 2006-156390 A Japanese Patent Laid-Open No. 2005-63928 JP 2007-188870 A

  However, when the organic capping layer of Patent Document 1 or the buffer layer of Patent Document 2 is formed on an electrode having the electron injection layer of Patent Document 3 as a lower layer, there are the following problems. That is, the alkali metal or alkaline earth metal near the electrode gradually diffuses into the organic capping layer or the buffer layer under a high temperature environment. As a result, the electron injecting property is lowered, which may cause a high voltage and a deterioration in driving characteristics.

  An object of the present invention is due to a decrease in electron injection property in an organic EL element having an electron injection layer having high electron injection efficiency and a layer made of an organic compound (hereinafter referred to as an organic cap layer) sandwiching the cathode in contact with the cathode. The purpose is to suppress high voltage and deterioration of drive characteristics.

  The present invention includes an anode, a light-emitting layer, an electron injection layer containing an alkali metal, an alkali metal compound, an alkaline earth metal, or an alkaline earth metal compound, a cathode disposed in contact with the electron injection layer, An organic cap layer disposed in contact with the cathode, wherein the organic cap layer is composed of an organic compound composed of a non-heterocarbocyclic compound.

  In the present invention, since the organic cap layer is made of a specific material, diffusion of alkali metal and alkaline earth metal from the electron injection layer provided under the cathode to the organic cap layer is suppressed, and high electron injection property is achieved. Maintained. Therefore, according to the present invention, there is provided an organic EL element capable of suppressing high voltage and deterioration of drive characteristics due to a decrease in electron injection property.

It is a cross-sectional schematic diagram of one Embodiment of the organic EL element of this invention.

  The organic electroluminescence device of the present invention is disposed in contact with an anode, a light emitting layer, an electron injection layer containing an alkali metal, an alkali metal compound, an alkaline earth metal, or an alkaline earth metal compound, and an electron injection layer. And a cathode. Furthermore, the organic EL device of the present invention is provided with an organic cap layer on the side opposite to the electron injection layer in contact with the cathode, and the organic cap layer is composed of an organic compound made of a non-heterocarbocyclic compound.

  Hereinafter, the organic EL element of the present invention will be described with reference to FIG. The organic EL element of FIG. 1 is a top emission type element, in which 1 is a substrate, 2 is an anode, 3 is a light emitting layer, 4 is an electron injection layer, 5 is a cathode, 6 is an organic cap layer, and 7 is an organic cap layer. A protective layer 8 is an organic compound layer. The organic compound layer 8 is composed of the light emitting layer 3 and the electron injection layer 4 in this example, but is not limited to this, and an electron transport layer, a hole transport layer, a hole injection layer, a hole is used as necessary. A block layer or the like is arranged.

  FIG. 1 schematically shows one pixel, and an organic EL device is configured by arranging a plurality of these pixels in parallel and providing a power source for energizing between the electrodes 2 and 3 as element driving means. .

  The anode 2 is preferably formed on a substrate 1 on which switching elements such as TFTs are formed, if necessary, and is formed of a light reflective member. Specifically, it is preferably made of a material such as Cr, Al, Ag, Au, or Pt. The higher the reflectance, the more the light extraction efficiency and the optical resonance effect can be improved. Further, a transparent electrode such as ITO or IZO may be laminated on the layer containing these metals to form the anode 2.

  An organic compound layer 8 is deposited on the substrate 1 on which the anode 2 is formed by a known means. The organic compound layer 8 is preferably an amorphous film from the viewpoint of luminous efficiency. The light emitting layer 3 is made of an organic light emitting material. Specific examples include triarylamine derivatives, stilbene derivatives, polyarylenes, aromatic condensed polycyclic compounds, aromatic heterocyclic compounds, aromatic heterocondensed ring compounds, metal complex compounds, etc., and single or composite oligos thereof. Well-known materials can be used.

  The hole transport layer and hole injection layer (both not shown) are composed of a hole transport material, and specifically include phthalocyanine compounds, triarylamine compounds, conductive polymers, perylene compounds, Eu complexes, and the like. Can be used.

  The electron transport layer (not shown) is made of an electron transport material. Specifically, Alq3 in which a trimer of 8-hydroxyquinoline is coordinated to aluminum, an azomethine zinc complex, a distyrylbiphenyl derivative system, an oxazole dielectric system, a triazole dielectric system, a phenanthroline compound, and the like can be used.

  In general, the organic compound layer 8 is laminated on the anode 2 in the order of a hole injection layer, a hole transport layer, a light emitting layer 3 and an electron transport layer, and then an electron injection layer 4 is formed. In this invention, it has at least the light emitting layer 3 and the electron injection layer 4, and can use another functional layer as needed.

  As the electron injection layer 4 according to the present invention, an organic compound layer doped with an alkali metal compound, an alkali metal, an alkaline earth metal compound, or an alkaline earth metal, which has a low work function in order to improve the electron injection property, is used. Alkali metals and alkaline earth metals contained in the electron injection layer 4 are intermolecular molecules that donate electrons to the heteroatoms of the heterocyclic compound or the metal atoms of the organometallic complex, thereby turning the organic molecule into a radical anion state. There is thought to be an interaction. Therefore, by using a layer formed by co-evaporation of an organic material and an alkali metal or alkaline earth metal as the electron injection layer 4, it is possible to smoothly transfer electrons between adjacent molecules, and an injection barrier from the cathode 5. And the electron injecting property is improved. As the organic material, the organic materials listed in the above electron transport materials can be used, and an alkali metal or alkaline earth metal having a low work function gives electrons, so that a heterocyclic compound or metal complex compound that easily becomes a radical anion state. Is preferably used. Moreover, Li, Na, Cs, Mg, or these compounds are preferably used as an alkali metal or an alkali metal compound, an alkaline earth metal compound or an alkaline earth metal. The weight ratio of the organic material in the electron injection layer to the alkali metal compound, alkali metal, alkaline earth metal compound, or alkaline earth metal is preferably 9: 1 to 1: 1. Moreover, the larger the proportion of the alkali metal compound, alkali metal, alkaline earth metal compound, or alkaline earth metal, the greater the effect obtained by the present invention. That is, if the weight ratio of the organic material in the electron injection layer to the alkali metal compound, alkali metal, alkaline earth metal compound, or alkaline earth metal is about 3: 1 to 1: 1, the obtained effect is large. Become.

  The film thickness of the organic compound layer constituting the organic compound layer 8 can be determined by optical calculation from the optical resonance effect.

  In the present invention, the cathode 5 made of a metal translucent thin film is formed so as to be in contact with the electron injection layer 4. The cathode 5 is preferably a transflective film that enables an optical resonance effect with the anode 2. As the metal that can be used in the present invention, Ag or an alloy containing Ag is preferable. This is because when Ag is included, the reflectance becomes high, so that the optical interference effect becomes strong. Further, as a forming method, a vapor deposition method or a sputtering method is generally used.

  The cathode 5 according to the present invention is preferably 10 nm or more from the viewpoint of reducing sheet resistance, and is preferably a thin film of 20 nm or less from the viewpoint of effectively extracting light from the cathode 5 side without absorbing light. On the other hand, when a single Ag or an Ag alloy is formed into a thin film of 20 nm or less, the film is not formed uniformly and is formed in a discontinuous state in which the film is partially cut. Therefore, the alkali metal and alkaline earth metal contained in the electron injection layer 4 may diffuse into the organic cap layer 6 described later from the film break. This is particularly remarkable in a film made of Ag alone. However, in the present invention, diffusion of the metal is prevented for the reasons described later.

  The organic cap layer 6 is formed in contact with the cathode 5. As described above, since the cathode 5 is a thin film, when the organic cap layer 6 is formed by a sputtering method or a plasma CVD method, the underlying organic compound layer 8 is damaged and the life characteristics are deteriorated. Therefore, the organic cap layer 6 is a layer made of an organic compound formed to a thickness of about 10 nm to 150 nm by an evaporation method with little damage.

  The organic cap layer 6 according to the present invention is a layer for preventing an influence on the organic compound layer 8 under the cathode 5 when a thick protective layer 7 is formed thereon by a sputtering method or a plasma CVD method. is there. The intermolecular interaction in the electron injection layer 4 according to the present invention is not so strong as to retain alkali metals and alkaline earth metals. In particular, in the high temperature environment, the alkali metals and alkaline earth metals in the vicinity of the interface of the electron injection layer 4 are different. Will diffuse into the organic compound layer. At this time, when an organic material having a structure causing an intermolecular interaction with an alkali metal or alkaline earth metal, that is, a heterocyclic compound or an organometallic complex is used for the organic compound layer in contact with the electron injection layer 4, This causes problems. That is, alkali metal and alkaline earth metal easily enter the organic compound layer due to intermolecular interaction, and diffusion proceeds. Although the cathode 5 exists between the electron injection layer 4 and the organic cap layer 6 of the present invention, it is discontinuous and is insufficient to prevent the diffusion of alkali metal and alkaline earth metal.

  Therefore, the organic compound constituting the organic cap layer 6 according to the present invention has a structure in which alkali metals and alkaline earth metals are less likely to cause intermolecular interactions and are less likely to diffuse than heterocyclic compounds and organometallic complexes. Consists of heterocarbocyclic compounds. Examples of non-heterocarbocyclic compounds used for organic compounds in the organic cap layer include fluoranthene compounds, pyrene compounds, chrysene compounds, anthracene compounds, naphthalene compounds, fluorene compounds, phenanthrene compounds, and the like. It is done. The present invention is not limited to these. Specific examples are given below. The organic cap layer 6 may contain a small amount of an inorganic material in addition to the above organic compound.

  The organic cap layer 6 according to the present invention may have a multilayer structure in which two or more kinds of carbocyclic compound layers are laminated as necessary, and the film thickness may be determined by optical calculation. The present invention does not necessarily require the protective layer 7, and as disclosed in Patent Document 1, a layer made of an organic compound is laminated on the cathode 5 to increase efficiency from a moisture etc. by a glass cap. It may be in a protected form.

  A functional film such as a protective layer can be formed on the organic cap layer as necessary. Usually, the protective layer is thick and is formed by sputtering or plasma CVD, but in the present invention, since the organic cap layer 6 is formed on the cathode 5, even if sputtering or plasma CVD is performed, There is no fear of affecting the organic compound layer 8 under the cathode 5.

  The protective layer that can be used in the present invention is preferably an inorganic compound that is transparent from the viewpoint of light extraction and hardly permeates moisture. Specifically, a known moisture-proof film such as SiN, SiO, or SiON or a transparent conductive film such as ITO or IZO can be used, and the film is formed by sputtering or plasma CVD to have a thickness of about 50 to 500 nm.

  In the present invention, sealing is not particularly limited, and a glass cap may be used. However, when SiN or the like is used for the protective layer, the protective layer is thickened to about 1 μm to 10 μm and sealed. It may be stopped. Alternatively, a multilayer structure with different structures such as SiO and SiN may be used, and a resin may be applied on a protective layer such as SiN with a thickness of 10 μm, and SiN or the like may be further formed to seal the film.

  In the organic EL device obtained as described above, the organic cap layer 6 prevents the organic compound layer 8 from being affected when a protective layer or the like is formed on the cathode 5, and at the same time, to the organic cap layer 6. The alkali metal diffusion is suppressed, and stable light emission characteristics can be obtained.

Example 1
On the substrate on which the anode was formed, an organic compound layer was formed in the order of hole transport layer / light emitting layer / electron transport layer / electron injection layer. In the electron injection layer, a phenanthroline compound and Cs ₂ CO ₃ were co-deposited at a weight ratio of 9: 1 to a thickness of 20 nm.

Thereafter, a cathode was formed on the electron injection layer. Ag was vapor-deposited and used for the cathode. Ag was deposited to a thickness of 12 nm by resistance heating with a tungsten metal boat in a vacuum chamber having a degree of vacuum of 5 × 10 ⁻⁵ Pa.

  An organic cap layer was formed on the cathode. The organic cap layer was formed by vapor deposition of the fluorene compound (1).

  Thereafter, SiN having a thickness of 5 μm was stacked as a protective layer by a plasma CVD method to obtain an organic EL element.

  The organic EL device was stored in a high-temperature environment of 80 ° C., and the driving characteristics were observed while changing the storage time. However, no voltage increase or change in driving characteristics was observed over time.

(Example 2)
An organic EL device was produced in the same manner as in Example 1 except that the cathode was formed to a thickness of 15 nm by a sputtering method and the fluoranthene compound (1) was used for the organic cap layer.

  The organic EL device was stored in a high-temperature environment of 80 ° C., and the driving characteristics were observed while changing the storage time. However, no voltage increase or change in driving characteristics was observed over time.

(Example 3)
The same method as in Example 1 except that pyrene-based compound (2) is used for the organic cap layer, IZO is deposited as a protective layer to a thickness of 50 nm, and then sealed with a glass cap to which a hygroscopic agent is attached. Thus, an organic EL element was produced.

  The organic EL device was stored in a high-temperature environment of 80 ° C., and the driving characteristics were observed while changing the storage time. However, no voltage increase or change in driving characteristics was observed over time.

Example 4
The naphthalene compound (1) was used for the organic cap layer, SiN was deposited as a protective layer to a thickness of 1 μm, a resin layer made of epoxy resin was deposited to a thickness of 10 μm, and SiN was further formed to 1 μm. Except for the above, an organic light emitting device was produced in the same manner as in Example 1.

  The organic EL device was stored in a high-temperature environment of 80 ° C., and the driving characteristics were observed while changing the storage time. However, no voltage increase or change in driving characteristics was observed over time.

(Comparative Example 1)
An organic EL device was produced in the same manner as in Example 1 except that Alq3, which is a metal complex, was formed as an organic cap layer on the cathode in Example 1 to a thickness of 50 nm by vapor deposition.

  When the organic EL element was stored in a high temperature environment of 80 ° C. and the drive characteristics were observed while changing the storage time, there was a case where a voltage increase occurred or the drive characteristics were deteriorated. Further, when this organic EL element was analyzed with a secondary ion mass spectrometer (SIMS), it was confirmed that Cs was diffused in the Alq3 layer near the cathode.

(Comparative Example 2)
An organic EL device was produced in the same manner as in Example 1 except that 50 nm of the heterocyclic compound, bathophenanthroline, was formed on the cathode as an organic cap layer by vapor deposition.

  When the organic EL element was stored in a high temperature environment of 80 ° C. and the drive characteristics were observed while changing the storage time, there was a case where a voltage increase occurred or the drive characteristics were deteriorated. Further, when this organic EL element was analyzed with a secondary ion mass spectrometer (SIMS), it was confirmed that Cs was diffused in the Alq3 layer near the cathode.

  1: substrate, 2: anode, 3: light emitting layer, 4: electron injection layer, 5: cathode, 6: organic cap layer, 8: organic compound layer

Claims (4)

  An anode, a light-emitting layer, an electron injection layer containing an alkali metal, an alkali metal compound, an alkaline earth metal, or an alkaline earth metal compound, a cathode disposed in contact with the electron injection layer, and in contact with the cathode An organic cap layer, wherein the organic cap layer is made of an organic compound made of a non-heterocarbocyclic compound.   The organic electroluminescence element according to claim 1, further comprising a protective layer formed in contact with the organic cap layer by a sputtering method or a plasma CVD method.   The organic electroluminescent element according to claim 1, wherein the cathode is made of a metal containing Ag and has a thickness of 10 nm to 20 nm.   The organic compound constituting the organic cap layer is any one of a fluoranthene compound, a pyrene compound, a chrysene compound, an anthracene compound, a naphthalene compound, a fluorene compound, and a phenanthrene compound. The organic electroluminescent element according to any one of 1 to 3.

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