JP2004095549A - Organic electroluminescent element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL element in which current efficiency is improved, in which yield is superior, and which has low-cost, by introducing a new concept into the constitution of a conventional organic El element. <P>SOLUTION: This is the organic EL element having a first electrode 101 and a second electrode 102, an EL layer 103, and conductive particulates 104, and the organic EL element in which the conductive particulates 104 are dispersed in the EL layer 103 is used. Because the conductive particulates play the same role as a conventional electric charge generating layer, current efficiency becomes improved. Furthermore, because the conductive particulates and the EL layer can be film formed simultaneously, preparation process becomes easy and effective for cost reduction. <P>COPYRIGHT: (C)2004,JPO

Description

<< The present invention relates to an organic electroluminescent device having an organic compound layer capable of emitting light when an electric field is applied.

(4) Organic compounds have a wider variety of material systems than inorganic compounds, and there is a possibility that materials having various functions can be synthesized by suitable molecular design. In addition, there is a feature that a formed product such as a film is rich in flexibility and further excellent in workability by being polymerized. Due to these advantages, attention has recently been focused on photonics and electronics using functional organic materials.

 Photonics utilizing the optical properties of organic materials have already played an important role in current industrial technology. For example, a photosensitive material such as a photoresist is an indispensable material for a photolithography technique used for fine processing of a semiconductor. In addition, since the organic compound itself has the property of absorbing light and emitting light (fluorescence and phosphorescence), it is also widely used as a light-emitting material such as a laser dye.

 On the other hand, since the organic compound is a material having no carrier itself, it has essentially excellent insulating properties. Therefore, as for electronics using the electrical properties of organic materials, the function of an insulator has been mainly used in the past, and it has been used as an insulating material, a protective material, and a coating material.

 However, there exists a means for flowing a large amount of current through an organic material which is essentially an insulator, and is being used in the field of electronics. This means can be roughly divided into two types.

 One of them is that a π-conjugated organic compound is doped with an acceptor (electron acceptor) or a donor (electron donor), as represented by a conductive polymer, so that the π-conjugated organic compound has a carrier. (For example, see Non-Patent Document 1). By increasing the doping amount, carriers increase to a certain region, so that the dark conductivity also increases and a large amount of current flows.

Hideki Shirakawa, 4 others, Chemistry Communication, Vol. 16, 578-580 (1977)

 As described above, the means for increasing the dark conductivity by doping the acceptor or the donor and flowing a current to the organic material is already partially applied in the field of electronics. For example, there are a rechargeable secondary battery using polyaniline or polyacene, and an electric field capacitor using polypyrrole.

Another means for passing a large amount of current through an organic material is a means utilizing a space charge limited current (SCLC). The SCLC is a current flowing by injecting and moving a space charge from the outside, and its current density is represented by the child rule, that is, the following equation (1). J is the current density, ε is the relative dielectric constant, ε ₀ is the vacuum dielectric constant, μ is the carrier mobility, V is the voltage, and d is the interval at which V is applied.

(Equation 1)
J = 9/8 · εε ₀ μ · V ² / d ³ (1)

 The SCLC expressed by the above equation (1) is an equation that does not assume any carrier trap when the SCLC flows. The current limited by the carrier trap is called TCLC (Trap / Charge / Limited / Current) and is proportional to the power of the voltage. Since these are both bulk-limited currents, the same treatment will be applied hereinafter.

 Here, for the sake of comparison, the following equation (2) shows an equation representing the current density when an ohmic current flows according to the Ohm rule. σ is conductivity, and E is electric field strength.

(Equation 2)
J = σE = σ · V / d (2)

 Since the conductivity σ in the equation (2) is represented by σ = neμ (n is the carrier density and e is the electric charge), it is included in the controlling factor of the amount of current flowing through the carrier density. Therefore, unless an organic material having a certain carrier mobility is used to increase the carrier density by doping as described above, an ohmic current does not normally flow in an organic material having almost no carriers.

 However, as can be seen from Equation (1), the factors that determine SCLC are the dielectric constant, carrier mobility, voltage, and the interval at which the voltage is applied, and the carrier density is not relevant. That is, even if the organic material is an insulator having no carrier, the interval d to which a voltage is applied is made sufficiently thin and a material having a large carrier mobility μ is selected to inject a carrier and flow a current. You can do it.

 When this means is used, the amount of current can reach the level of a normal semiconductor or higher, so that an organic material having a large carrier mobility μ, that is, an organic material that can potentially transport carriers is an organic semiconductor. Can be called.

By the way, among such devices using SCLC, an organic electroluminescent device (hereinafter, referred to as an “organic EL device”) is a photoelectronic device that utilizes both optical and electrical properties of a functional organic material. ) Has made remarkable progress in recent years.

最 も The most basic structure of an organic EL device was disclosed in 1987 by C.I. W. Tang et al. (For example, see Non-Patent Document 2).

C. W. Ton, one outsider, Applied Physics Letters, Vol. 51, No. 12, 913-915 (1987)

The element reported in Non-Patent Document 2 is a type of diode element in which an organic thin film having a total thickness of about 100 nm, in which a hole transporting organic compound and an electron transporting organic compound are stacked, is sandwiched between electrodes. A light-emitting material (fluorescent material) is used as the transport compound. By applying a voltage to such an element, light can be extracted like a light-emitting diode.

The light-emitting mechanism is such that, when a voltage is applied to an organic thin film sandwiched between electrodes, holes and electrons injected from the electrodes recombine in the organic thin film and molecules in an excited state (hereinafter referred to as “molecular excitons”). It is believed that light is emitted when the molecular exciton returns to the ground state.

Note that the types of molecular excitons formed by an organic compound can be a singlet excited state and a triplet excited state, and the ground state is usually a singlet state, so that light emission from the singlet excited state is fluorescence or triplet. Light emission from the term excited state is called phosphorescence. In this specification, the case where either excited state contributes to light emission is also included.

に お い て In such an organic EL device, the organic thin film is usually formed as a thin film having a thickness of about 100 to 200 nm. Further, since the organic EL element is a self-luminous element in which the organic thin film itself emits light, there is no need for a backlight as used in a conventional liquid crystal display. Therefore, it is a great advantage that the organic EL element can be manufactured to be extremely thin and lightweight.

Further, for example, in an organic thin film of about 100 to 200 nm, the time from carrier injection to recombination is about several tens of nanoseconds in consideration of the carrier mobility of the organic thin film. Even in the process up to and including light emission, light is emitted within microsecond order. Therefore, one of the features is that the response speed is extremely fast.

か ら Due to these characteristics such as thinness, light weight, and high-speed response, organic EL elements are receiving attention as next-generation flat panel display elements. In addition, since it is a self-luminous type and has a wide viewing angle, it has relatively good visibility and is considered to be effective as an element used for a display screen of a portable device.

の 通 り As described above, the organic EL element is a device utilizing the flow of SCLC through an organic semiconductor, and the flow of SCLC accelerates the deterioration of the function of the organic semiconductor. It is known that in an organic EL element, the element life (half-life of emission luminance) is deteriorated in a manner that is almost inversely proportional to initial luminance, in other words, inversely proportional to the amount of flowing current (for example, see Non-Patent Document 3). .

Yoshiharu Sato, Japan Society of Applied Physics, Subgroup of Organic Molecules and Bioelectronics, Journal, Vol. 11, No. 1, 86-99 (2000)

Conversely, by improving the current efficiency of the organic EL element (luminance generated with respect to the flowing current), the amount of current required to achieve a certain luminance can be reduced, and thus such deterioration occurs. Is also thought to be smaller. Therefore, it can be said that current efficiency is an important factor not only from the viewpoint of power consumption but also from the viewpoint of element life.

However, the organic EL element has a problem in its current efficiency. As described above, the light emission mechanism of the organic EL element is converted into light by the recombination of the injected holes and electrons. Therefore, theoretically, one photon can be extracted at most from one hole and one electron recombination, and a plurality of photons cannot be extracted. That is, the internal quantum efficiency (the number of emitted photons with respect to the number of injected carriers) is 1 at the maximum.

However, in reality, it is difficult even to bring the internal quantum efficiency close to 1. For example, in the case of an organic EL device using a fluorescent material as a light emitter, the statistical generation ratio between the singlet excited state (S ^* ) and the triplet excited state (T ^* ) is S ^* : T ^* = 1: 3. Therefore, the theoretical limit of the internal quantum efficiency is 0.25 (for example, see Non-Patent Document 4). Further, as long as the fluorescent quantum yield phi _f the fluorescent material is not 1, the internal quantum efficiency is further lowered than 0.25.

Tetsuo Tsutsui, Japan Society of Applied Physics {Organic Molecules and Bioelectronics Subcommittee} 3rd Workshop Textbook, 31-37 (1993)

In recent years, attempts have been made to use a phosphorescent material to emit light from a triplet excited state to bring the theoretical limit of internal quantum efficiency closer to 0.75 to 1, and to improve the efficiency exceeding the fluorescent material actually. Has been achieved. However, this also requires the use of a phosphorescent material having a high phosphorescence quantum yield φ _p, so that the choice of materials is necessarily limited. This is because organic compounds that can emit phosphorescence at room temperature are extremely rare.

Therefore, as a method of overcoming the poor current efficiency of the device, the concept of a charge generation layer has recently been reported (for example, see Non-Patent Document 5).

Junji Kido and 5 others, Proc. Of the 49th Annual Conference of the Japan Society of Applied Physics, 2002. 1308, 27p-YL-3

概念 The concept of the charge generation layer is described as shown in FIG. FIG. 6 is a schematic diagram of the organic EL device of Non-Patent Document 5 in which an anode, a first electroluminescent layer, a charge generation layer, a second electroluminescent layer, and a cathode are sequentially stacked. Note that an electroluminescent layer (hereinafter, referred to as an “EL layer”) is a layer containing an organic compound capable of electroluminescence or emitting light by carrier injection. In addition, the charge generation layer is not connected to an external circuit and serves as a floating electrode.

In such an organic EL device, when a voltage V is applied between the anode and the cathode, electrons are transferred from the charge generation layer to the first EL layer, and electrons are transferred from the charge generation layer to the second EL layer. Holes are injected respectively. According to the external circuit, holes flow from the anode to the cathode, and electrons flow from the cathode to the anode (Fig. 6 (a)). Both electrons and holes flow in the opposite direction from the charge generation layer. 6B, carrier recombination occurs in both the first EL layer and the second EL layer, which leads to light emission. At this time, if the current I is flowing, both the first EL layer and the second EL layer can emit photons corresponding to the current I. There is an advantage that twice the amount of light can be emitted with the same current (however, the voltage is more than twice that of a single organic EL element).

The organic EL device having such a charge generation layer can improve the current efficiency many times by laminating a number of EL layers (however, the voltage is required many times correspondingly). Become). Therefore, not only the theoretical current efficiency is improved but also the element life is expected to be greatly improved.

However, in order to further improve the current efficiency by using the charge generation layer, a number of EL layers must be stacked, and the work is complicated, so that a defect such as a pinhole may partially occur. The nature becomes high. Therefore, defects such as inter-element variation and eventually short-circuiting of the elements are likely to occur.

In addition, stacking a number of EL layers requires a corresponding amount of time for device fabrication, which has a large effect on throughput in consideration of mass production. This fact leads to higher costs.

In other words, in the conventional organic EL device using the charge generation layer, although the current efficiency is improved, a problem arises in the yield and cost of the device.

In view of the above, it is an object of the present invention to provide a low-cost organic EL element having a good yield while improving current efficiency by introducing a new concept into the configuration of a conventional organic EL element. I do.

As a result of intensive studies, the inventor of the present invention expresses conductivity and luminescence by using dispersed particles of a conductor (or semiconductor) having a carrier (hereinafter, referred to as “conductive particles”) and SCLC. Means that can solve the above problem by combining with an organic semiconductor have been devised. FIG. 1 shows the most basic configuration.

FIG. 1A shows an organic EL element including a first electrode 101 and a second electrode 102, an electroluminescent layer (hereinafter, simply referred to as an “EL layer”) 103, and conductive fine particles 104. The conductive fine particles 104 are dispersed in 103. Note that the EL layer 103 is a layer containing an organic compound which emits light when an electric field is applied.

What is important here is that the conductive fine particles 104 should be made of a material that can be almost ohmic-connected to the EL layer 103. In other words, the barrier between the conductive fine particles 104 and the material of the EL layer 103 is eliminated or extremely reduced.

こ と With this configuration, both holes and electrons are easily injected from the dispersed conductive fine particles. This is shown in FIG. As shown with respect to one of the conductive fine particles 104 ', application of a voltage causes both electrons and holes to be injected from the conductive fine particles into the EL layer in the opposite direction. The same occurs in fine particles). At the same time, holes are injected from the first electrode 101 (the anode in FIG. 1B) and electrons are injected from the second electrode 102 (the cathode in FIG. 1B). Become. That is, the phenomenon is similar in concept to the charge generation layer, but is characterized by fine particles instead of layers.

When such a basic structure of the present invention is applied, similarly to the organic EL device of Non-Patent Document 5 using the charge generation layer, the drive voltage is higher than that of a normal device, but the current efficiency is improved accordingly. Can be done. In addition, a structure in which the conductive fine particles are dispersed so as not to cause a short circuit in the EL layer (that is, uniformly) may be formed, so that a complicated operation of laminating many layers can be omitted. Therefore, the fabrication is easier than in the organic EL device of Non-Patent Document 5 using the conventional charge generation layer.

Therefore, according to the present invention, in an organic electroluminescent element provided with an electroluminescent layer containing an organic compound that emits light by applying a voltage between a first electrode and a second electrode, the electroluminescent layer It is characterized in that conductive fine particles are dispersed therein.

In addition, in the case of the device shown in FIG. 1, the conductive fine particles 104 become partially non-uniform, and there is a risk of short circuit due to dielectric breakdown or the like. Therefore, as shown in FIG. 2A, an organic EL device including a first electrode 201 and a second electrode 202, an EL layer 203, and conductive fine particles 204, wherein the conductive fine particles are contained in the EL layer 203. An organic EL element in which insulating layers 205a and 205b are provided between the first electrode 201 and the EL layer 203 and between the second electrode 202 and the EL layer 203, respectively; Is preferred. With such a structure, short-circuiting of the element is easily prevented, and at the same time, the presence of the insulating layers 205a and 205b prevents generation of a leakage current, and is expected to improve efficiency.

Therefore, according to the present invention, in the organic electroluminescent device provided with an electroluminescent layer containing an organic compound which emits light by applying a voltage between a first electrode and a second electrode, the electroluminescent layer Conductive fine particles are dispersed therein, and insulating layers are provided between the first electrode and the electroluminescent layer and between the second electrode and the electroluminescent layer, respectively. It is characterized by.

As a more preferable configuration, in the organic EL device of the present invention shown in FIG. 2A, the thicknesses of the insulating layers 205a and 205b are sufficiently increased so that carriers are generated from the first electrode 201 and the second electrode 202. Design so that it is not injected. In this case, carrier injection from the outside cannot be performed, and a carrier injection source (generation source) exists only inside the EL layer 203 (that is, carriers are injected only from the conductive fine particles 204). (FIG. 2B). This method can extremely effectively prevent short-circuiting of the element, and can provide an element excellent in yield and driving stability.

Therefore, according to the present invention, in the organic electroluminescent element provided with an electroluminescent layer containing an organic compound which emits light by applying a voltage between the first electrode and the second electrode, Insulation for preventing carrier injection from the first electrode and the second electrode into the electroluminescent layer between an electrode and the electroluminescent layer and between the second electrode and the electroluminescent layer, respectively. It is characterized by having a layer.

Further, according to the present invention, in the organic electroluminescent element provided with an electroluminescent layer containing an organic compound which emits light by applying a voltage between a first electrode and a second electrode, the electroluminescent layer Conductive fine particles are dispersed therein, and an insulating layer is provided between the first electrode and the electroluminescent layer, and between the second electrode and the electroluminescent layer. And is operated by AC drive.

By the way, in the organic EL device of the present invention, it is preferable to form the EL layer with a single-layer structure (that is, a bipolar layer) in spite of the structure shown in FIGS. . In addition, when AC driving is performed with the configuration as shown in FIG. 2B, the layer is particularly preferably a bipolar layer.

(4) As a method of forming the EL layer as a bipolar layer, there is a method of forming an EL layer by mixing an organic compound having an electron transporting property and an organic compound having a hole transporting property. In addition, there is a method using a polymer compound having a π-conjugated system or a σ-conjugated system and being bipolar. In particular, the latter method has an advantage that the EL layer can be easily formed by wet coating simultaneously with the conductive fine particles, and is effective in simplicity of film formation.

Note that, as a material for all the conductive fine particles as described above, it is sufficient that a carrier can be injected. Therefore, it is not necessary to use a material having a low resistivity, and it is sufficient to have a certain amount of the carrier. Therefore, the conductive fine particles only need to include a material having a conductivity of 10 ⁻¹⁰ S / m or more.

手法 In addition, the method of applying the conductive fine particles simultaneously with the EL layer constituent material during wet application is the simplest in the film forming process. As a material suitable for the method, metal fine particles or inorganic semiconductor fine particles having an average diameter of 2 nm to 50 nm may be used. As metal fine particles, fine particles having a composition of gold or silver are useful. Further, as the inorganic semiconductor fine particles, CdS, CdSe, ZnO, ZnS, CuI, ITO and the like are useful. Further, in order to stabilize these fine particles, those having a surface coated with an organic compound may be used. Apart from these, it is also effective to use carbon fine particles, carbon fine particles surface-treated with a surfactant, or carbon nanotubes or fullerenes.

By implementing the present invention, it is possible to provide a low-cost organic EL element with improved yield while improving current efficiency.

Hereinafter, embodiments of the present invention will be described in detail with reference to an operation principle and a specific configuration example. Note that the organic EL element only needs to be transparent at one of the electrodes in order to extract light emission. Therefore, not only the conventional element structure in which a transparent electrode is formed on a substrate and light is extracted from the substrate side, but also a structure in which light is extracted from the opposite side of the substrate and a structure in which light is extracted from both sides of the electrode are actually applied. It is possible.

First, the operation mechanism of the organic EL device of the present invention shown in FIG. 1 will be described with reference to FIGS. FIG. 3A shows a normal organic EL element having an element structure in which an EL layer 303 is interposed between an anode 301 and a cathode 302. It is assumed that a current having a current density of J flows through the organic EL element by applying a voltage of V, and emits light at a luminance L corresponding to J. At this time, J is SCLC, which is a factor determined only by the film thickness d and the voltage V when the material of the EL layer 303 is determined in one way (see the above-described formula (1)).

FIG. 3B shows an example of an element having a charge generation layer described in Non-Patent Document 5, in which three EL layers (303a to 303c) are stacked. By applying a triple voltage 3V across the charge generation layers 304a and 304b, a voltage of V is applied to each EL layer having a film thickness d. Electric current flows. Then, since each EL layer emits light at a luminance L corresponding to the current density J, an organic EL element which emits a total of 3 L of luminance is obtained.

Here, for example, if the charge generation layers 304a and 304b in FIG. 3B are made thinner, a layer (film) cannot be finally formed, and a cluster-like structure as shown in FIG. The charge generation regions 305a and 305b are formed. Even in this case, if the cluster-like charge generation regions are formed of the same material as the charge generation layers 304a and 304b, it is considered that the same organic EL element as that of FIG. 3B can be obtained.

{Circle around (3)} In the structure of FIG. 3 (c), the organic EL element of the present invention is one in which the cluster-like charge generation regions 305a and 305b are dispersed evenly over the entire EL layer. FIG. 4 shows a schematic diagram of the operation. In FIG. 4, reference numerals in FIG. 1 are cited.

As shown in FIG. 4, if the conductive fine particles 104 are substantially uniformly dispersed at intervals of about d (“中 d” in the figure), larger than V according to the basic principle shown in FIG. By applying the voltage V ′, a current having a current density J sufficient to obtain light emission can flow. At this time, the film thickness D of the element can of course be made larger than the film thickness level (about d) of a normal organic EL element. Moreover, unlike the conventional organic EL device using the charge generation layer, there is no need to laminate any layers, and the device can be manufactured with a simple configuration in which only the conductive fine particles are dispersed in the single-layer organic EL device.

{Circle around (2)} If the insulating layers 205a and 205b are thin enough to inject carriers, the organic EL device of the present invention shown in FIG. 2A operates exactly the same as the operation principle shown in FIG. Further, even if the insulating layers 205a and 205b are made sufficiently thick so that carriers are not injected from the first electrode 201 or the second electrode 202, light emission can be obtained by AC driving (see FIG. 2 (b) element). Such an element can most effectively prevent a defect such as a short circuit of the element. The operation principle of the device shown in FIG. 2B will be described with reference to FIG.

FIG. 5 shows an organic EL device of the present invention in which an AC power supply is attached to the first electrode 201 and the second electrode 202 of the organic EL device shown in FIG. In addition, the code | symbol of FIG. 2 is quoted. Here, it is assumed that a bipolar light-emitting body is used as the EL layer 203. The potential of the first electrode is V ₁ , and the potential of the second electrode is V ₂ .

When an AC voltage is applied to this element, first, at the moment when a bias of V ₁ > V ₂ is applied, electrons from each conductive fine particle 204 toward the first electrode 201 and electrons toward the second electrode 202. Holes are respectively injected into the EL layer 203 (FIG. 5A). At this time, in a relatively central region (for example, 501) in the EL layer 203, electrons and holes can recombine to emit light. (Eg, 502 and 503).

On the other hand, since the insulating layers 205a and 205b exist, carriers are not injected into the EL layer 203 from the first electrode 201 or the second electrode 202. As a result, some electrons or holes are accumulated at the interface between the insulating layer 205a and the EL layer 203 or at the interface between the insulating layer 205b and the EL layer 203 (FIG. 5B).

Since the applied voltage is an AC bias, a voltage of V ₁ <V ₂ is applied to the element at the next moment. At this time, although not shown, carriers are injected from each conductive fine particle 204 in a direction opposite to that in the case of FIG. On the other hand, the carriers accumulated in FIG. 5B also flow in the opposite direction as before (FIG. 5C). As a result, the accumulated carriers can contribute to recombination.

This organic EL device is different from the device shown in FIG. 1 in that carriers are not injected from external electrodes because the insulating layers 205a and 205b are present, and the carrier injection is entirely performed by conductive fine particles embedded inside. This is the point that is made from 204. That is, only an apparent AC current flows (appears to behave like an intrinsic EL). This makes it possible to easily prevent a short circuit or the like of the element, which is extremely useful.

In the element of the present invention, no leakage current occurs due to the presence of the insulating layers 205a and 205b. Therefore, one of the features is that the efficiency is expected to be more improved.

波形 Further, as the waveform of the AC bias described above, a sine wave, a rectangular wave, and a triangular wave are preferable, but it is not necessary to be limited to these. The maximum value of the voltage is preferably 300 V or less.

The above has described the basic operation principle of the present invention. In the following, preferable materials for the conductive fine particles used in the present invention and preferable materials for the EL layer are listed. However, the present invention is not limited to these.

Examples of the conductive fine particles include gold fine particles, gold colloid fine particles coated with an organic compound having a thiol group such as alkanethiol, silver fine particles, platinum fine particles, metal fine particles protected with an amphiphilic organic compound, ITO fine particles, silane cups. Examples include ITO fine particles coated with a ring agent, inorganic semiconductor fine particles such as CdS, CdSe, ZnO, ZnS, and CuI, carbon fine particles, carbon fine particles treated with a surfactant, carbon nanotube, and fullerene.

Next, the configuration of the EL layer will be exemplified below. As a structure of the EL layer, a generally used organic EL element constituent material may be used. However, considering operation with an AC bias, it is preferable to form a bipolar EL layer.

One method of obtaining a bipolar EL layer is to form a bipolar layer by mixing a hole transporting material and an electron transporting material. As the hole transporting material, an aromatic amine compound (that is, a compound having a benzene ring-nitrogen bond) is widely used, and 4,4′-bis (diphenylamino) -biphenyl (abbreviation: TAD) is used. And its derivatives such as 4,4′-bis [N- (3-methylphenyl) -N-phenyl-amino] -biphenyl (abbreviation: TPD) and 4,4′-bis [N- (1-naphthyl) —N-phenyl-amino] -biphenyl (abbreviation: α-NPD). 4,4 ′, 4 ″ -tris (N, N-diphenyl-amino) -triphenylamine (abbreviation: TDATA), 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N -Phenyl-amino] -triphenylamine (abbreviation: MTDATA) and the like. As the electron transporting material, a metal complex is often used, and tris (8-quinolinolato) aluminum (abbreviation: Alq), tris (4-methyl-8-quinolinolato) aluminum (abbreviation: Almq), bis (10- A metal complex having a quinoline skeleton or a benzoquinoline skeleton such as hydroxybenzo [h] -quinolinato) beryllium (abbreviation: Bebq) or bis (2-methyl-8-quinolinolato)-(4-hydroxy) which is a mixed ligand complex -Biphenylyl) -aluminum (abbreviation BAlq) and the like. In addition, bis [2- (2-hydroxyphenyl) -benzoxazolat] zinc (abbreviation: Zn (BOX) ₂ ), bis [2- (2-hydroxyphenyl) -benzothiazolato] zinc (abbreviation: Zn (BTZ)) There is also a metal complex having an oxazole-based or thiazole-based ligand such as ₂ ). Further, in addition to the metal complex, 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis [5- Oxadiazole derivatives such as (p-tert-butylphenyl) -1,3,4-oxadiazol-2-yl] benzene (abbreviation: OXD-7), 3- (4-tert-butylphenyl) -4 -Phenyl-5- (4-biphenylyl) -1,2,4-triazole (abbreviation: TAZ), 3- (4-tert-butylphenyl) -4- (4-ethylphenyl) -5- (4-biphenylyl) ) Triazole derivatives, such as -1,2,4-triazole (abbreviation: p-EtTAZ), and phenanthrolines, such as bathophenanthroline (abbreviation: BPhen) and bathocuproine (abbreviation: BCP) Derivative has an electron transporting property.

ＥＬ In addition, many materials for EL devices using a polymer compound exhibit bipolar properties and are suitable. Specifically, a polyparaphenylene-based polymer such as poly (2,5-dialkoxy-1,4-phenylene) (abbreviation: RO-PPP), poly (2,5-dialkoxy-1,4-phenylene) There are polyparaphenylene vinylene-based polymers such as vinylene (abbreviation: RO-PPV) and polyfluorene-based polymers such as poly (9,9-dialkylfluorene) (abbreviation: PDAF).

When the first electrode and the second electrode are operated by DC drive, one of them becomes an anode and the other becomes a cathode. As a material of the anode, if light is extracted from the anode, a transparent conductive inorganic compound such as ITO (indium tin oxide) or IZO (indium zinc oxide) is often used. Ultra-thin films such as gold are also possible. When non-transparent (light is extracted from the cathode side), a metal / alloy or a conductor that does not transmit light but has a large work function may be used, and examples thereof include W, Ti, and TiN. A metal or an alloy having a small work function is usually used for the cathode, and an alkali metal, an alkaline earth metal, or a rare earth metal is used, and an alloy containing such a metal element is also used. For example, Mg: Ag alloy, Al: Li alloy, Ba, Ca, Yb, Er and the like can be used. When light is extracted from the cathode, an ultrathin film of these metals and alloys may be applied.

In the case where the insulating layer is made thicker and operated by alternating current, the first electrode and the second electrode may be any ordinary conductors, such as aluminum, chromium, and titanium. However, since at least one of them needs to have a light-transmitting property, it is preferable to use a transparent conductive film such as ITO for at least one of them.

As the insulating layer, an inorganic insulator such as aluminum oxide or calcium fluoride or an insulating organic material such as polyparaxylylene can be used. However, the insulating layer on the light extraction side needs to have at least a light-transmitting property. There is.

In this example, the organic EL element of FIG. 1 manufactured by using wet coating is specifically exemplified. First, an aqueous solution of polyethylene dioxythiophene / polystyrene sulfonic acid (abbreviation: PEDOT / PSS) is applied by spin coating on a glass substrate on which ITO is formed to a thickness of about 100 nm as a first electrode, and a 50 nm hole injection layer is formed. Form a film.

Next, poly [2-methoxy-5- (2′-ethylhexoxy) -1,4-phenylenevinylene] (abbreviation: MEH-PPV) and gold fine particles having an average diameter of 5 nm stabilized with alkylthiol were added to toluene. Mix in the solution and sonicate to prepare a well dispersed solution. This solution is spin-coated on the hole injection layer to form a 300 nm EL layer.

(4) Finally, an Al: Li alloy is deposited to a thickness of 100 nm as a second electrode to obtain the organic EL device of the present invention. This device emits light by DC drive using the ITO electrode as an anode, but can also emit light by AC voltage drive.

In this example, the organic EL device of FIG. 2 will be specifically exemplified. First, a 200-nm-thick polyvinyl phenol film is formed as an insulating layer by spin coating on a glass substrate on which ITO is formed to a thickness of about 100 nm as a first electrode. Note that isopropanol may be used as the solvent.

Next, 50 wt% of polycarbonate as a binder, 29 wt% of TPD as a hole transport material, and 2,5-bis (1-naphthyl) -1,3,4-oxadiazole (abbreviation: A toluene solution is prepared so that BND) is 20 wt% and coumarin 6 as a luminescent dye is 1.0 wt%. After further mixing a toluene solution of alkanethiol-stabilized gold fine particles (average diameter: 5 nm) with the toluene solution, spin coating is performed on the insulating layer to form a 300 nm EL layer.

Further, as an insulating layer, polyvinyl phenol is formed to a thickness of 200 nm by spin coating. Finally, 200 nm of aluminum is deposited as an electrode to obtain the organic EL device of the present invention. This element emits light by AC driving.

In this example, the organic EL element of the present invention, which is manufactured by a bonding method using no coating and using a polymer composite film containing a luminescent dye and gold fine particles, using a coating method, is specifically exemplified.

{Circle over (1)} First, a 200-nm-thick polyvinylphenol film is formed as an insulating layer by spin coating on a plastic substrate (a polyester substrate, a polyimide substrate, or the like) on which ITO as the first electrode is formed to a thickness of about 100 nm. Isopropanol is used as the solvent.

Next, 50 wt% of polycarbonate as a binder, 29 wt% of TPD as a hole transport material, and 2,5-bis (1-naphthyl) -1,3,4-oxadiazole (abbreviation: A toluene solution is prepared so that BND) is 20 wt% and coumarin 6 as a luminescent dye is 1.0 wt%. After further mixing a toluene solution of alkanethiol-stabilized gold fine particles (average diameter: 5 nm) with the toluene solution, spin coating is performed on the insulating layer to form a 300 nm EL layer. In the following, the substrate formed so far is referred to as a “first substrate”.

(4) Apart from the above, a substrate on which the configuration of the plastic substrate / ITO / insulating layer / EL layer is formed is prepared in exactly the same manner as the first substrate. Hereinafter, this substrate is referred to as a “second substrate”. Then, a spacer film corresponding to a thickness of 1.0 μm is arranged on the periphery of the previously prepared first substrate, and the second substrate is bonded with the electroluminescent layer inside.

置 き Place the laminated film-shaped substrate on a stainless steel plate on a hot plate, and place a weight on the stainless steel plate. In this state, it is heated to 80 ° C. Then, after cooling while applying a load, the film-shaped substrate is taken out, and lead wires are attached to the ITO electrodes (that is, the first electrode and the second electrode) on both sides to complete the organic EL device of the present invention. This element emits light by AC driving.

で は In this embodiment, the organic EL device shown in FIG.

(4) Poly (4-vinylphenol) as an insulating layer was formed to a thickness of 200 nm from an isopropanol solution by spin coating on a glass substrate on which ITO was formed, and dried under vacuum at 60 ° C. for 30 minutes. Next, polyvinyl carbazole (64.3 mol%) as a hole transport material, and 2,5-bis (1-naphthyl) -1,3,4-oxadiazole (abbreviation: BND) (electron transport material) 35.1 mol%) and a dichloromethane solution (polymer composition solution) comprising coumarin-6 dye (0.6 mol%) as a luminescent dye. On the other hand, as a fine particle supply source, an isopropanol suspension of ITO fine powder (average particle diameter: 50 nm) was prepared.

{Circle around (1)} First, a polymer composition solution was applied on an insulating layer by a spin coating method in an amount equivalent to a thickness of 50 nm at room temperature. Without drying the polymer composition layer, the ITO fine powder suspension was sprayed by a spin coating method to a thickness not forming a film. Further, application of the polymer composition (equivalent to 50 nm) and spraying of the ITO fine powder suspension were repeated a total of eight times. By this operation, mutual mixing of the polymer composition and the fine particles was promoted, and a state in which the fine particles were dispersed in the polymer composition was realized.

(4) The polymer composition was formed to a thickness of 50 nm, and then vacuum dried at 60 ° C. for 1 hour. Poly (4-vinylphenol) was formed thereon as an insulating layer to a thickness of 200 nm from an isopropanol solution by spin coating, and vacuum-dried at 60 ° C. for 30 minutes. Finally, an aluminum electrode having a thickness of 60 nm was formed on the upper portion by a vacuum evaporation method.

An AC power supply that generates a sine wave was connected between the electrodes, and an AC voltage was applied at a drive frequency in the range of 1 kHz to 100 kHz. In the case of a driving frequency of 100 kHz, when observed from the ITO electrode side, green emission of the coumarin dye was observed as a rectangular uniform emission corresponding to the shape of the electrode from the emission start voltage of 60 V (peak voltage). When the light emission luminance was measured with a luminance meter (Topcon BM-5A), it showed a luminance of 60 cd / m ² at an applied voltage of 180 V. Since no more voltage could be applied due to the limitation of the AC power source, it was confirmed that continuous light emission with almost no luminance decay for 1 hour was maintained when 180 V was applied. Light emission was observed even when the driving frequency was reduced to 1 kHz.

FIG. 1 is a diagram showing a basic configuration of the present invention. FIG. 1 is a diagram showing a basic configuration of the present invention. FIG. 3 is a diagram illustrating the concept of a charge generation layer. The figure which shows the operation | movement principle of this invention. The figure which shows the operation | movement principle of this invention. The figure which shows the organic EL element using the conventional charge generation layer.

Claims (14)

In an organic electroluminescent element provided with an electroluminescent layer containing an organic compound which emits light by applying a voltage between a first electrode and a second electrode, conductive fine particles are provided in the electroluminescent layer. Organic electroluminescent element, wherein is dispersed. 2. The organic electroluminescent device according to claim 1, wherein the first electrode is provided between the first electrode and the electroluminescent layer and between the second electrode and the electroluminescent layer. 3. And an insulating layer for preventing carrier injection from the second electrode into the electroluminescent layer. The organic electroluminescent device according to claim 1, wherein an insulating layer is provided between the first electrode and the electroluminescent layer, and between the second electrode and the electroluminescent layer. Organic luminescent device characterized by operating with an AC bias (4) The organic electroluminescent device according to any one of (1) to (3), wherein the electroluminescent layer is bipolar. 4. The organic electroluminescent device according to claim 1, wherein the electroluminescent layer is a bipolar mixture in which an electron transporting organic compound and a hole transporting organic compound are mixed. 5. An organic electroluminescent element, which is a layer. 4. The organic electroluminescent device according to claim 1, wherein the electroluminescent layer has a π-conjugated system or a σ-conjugated system and includes a polymer compound having a bipolar property. 5. An organic electroluminescent device, comprising: The organic electroluminescent device according to claim 1, wherein the conductive fine particles include a material having a conductivity of 10 ⁻¹⁰ S / m or more. Luminescent element. The organic electroluminescent device according to any one of claims 1 to 6, wherein the conductive fine particles have an average diameter of 2 nm or more and 50 nm or less, and are metal fine particles. Organic electroluminescent device. The organic electroluminescent device according to claim 8, wherein the metal fine particles have a composition of gold, silver, or platinum. The organic electroluminescent device according to claim 8, wherein the metal fine particles are fine particles coated with an organic compound. The organic electroluminescent device according to any one of claims 1 to 6, wherein the conductive fine particles have an average diameter of 2 nm or more and 50 nm or less, and are inorganic semiconductor fine particles. Organic electroluminescent device. 12. The organic electroluminescent device according to claim 11, wherein the inorganic semiconductor fine particles are cadmium sulfide, or selenium sulfide, or zinc oxide, or zinc sulfide, or copper iodide, or indium tin oxide. Organic electroluminescent element. The organic electroluminescent device according to claim 11 or 12, wherein the inorganic semiconductor fine particles are fine particles coated with an organic compound. 7. The organic electroluminescent device according to claim 1, wherein the conductive fine particles are carbon fine particles, carbon fine particles surface-treated with a surfactant, carbon nanotubes, or fullerene. An organic electroluminescent device, characterized in that:

Images