JP4837958B2 - Organic electroluminescence device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stacked organic electroluminescent (EL) element, using an inorganic semiconductor for a charge generating layer, in which a service life at the time of high-luminance emission can be prolonged although the prolongation of the service life is hardly achieved in a conventional organic EL element and which can be efficiently and stably manufactured. <P>SOLUTION: The present invention relates to an organic EL element which includes a plurality of light emitting units between electrode layers facing each other and in which a charge generating layer is formed between the adjacent light emitting units, wherein the charge generating layer includes an electron generating layer comprised of an inorganic semiconductor material with an electron injection property and a hole generating layer comprised of an inorganic semiconductor material with a hole injection property. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a stacked organic electroluminescence element called Multi Photon Emission.

2. Description of the Related Art In recent years, organic electroluminescence (hereinafter abbreviated as EL) elements having a light emitting layer made of an organic compound between an opposing anode and cathode have attracted attention as a means for realizing a large-area display element driven at a low voltage. .
However, the conventional organic EL element has only achieved a half-life exceeding 10,000 hours at a luminance of about 100 cd / m ² unit required for display device use from the viewpoint of element lifetime. , to obtain 1000cd ^{/ m 2} ~10000cd ^/ m 2 about brightness necessary for practical use element life required in lighting applications such as a (10,000 hours or more) are difficult at this stage, actually such high A luminance and long-life organic EL element has not been realized yet. In addition, the organic EL element can be driven at a low voltage of 10 V or less. However, in order to obtain high luminance light emission required for lighting applications, the organic EL element is changed from several tens mA / cm ² to several hundred mA / cm ² . There is also a problem that a high current density is required.

In order to solve such a problem, Patent Documents 1 to 5 propose organic EL elements in which light emitting units including a plurality of light emitting layers are stacked via an intermediate layer. In these organic EL elements, since a plurality of light emitting units are electrically connected in series via an intermediate layer, an improvement in current efficiency can be realized.
It is said that various materials can be used for this intermediate layer. Patent Document 3 discloses a laminate or mixed layer comprising an organic compound having a hole transporting property (having an electron donating property) and an inorganic substance or an organic substance capable of forming an electrophoretic transfer complex with this organic compound by an oxidation-reduction reaction. An intermediate layer that is an n-type doped organic layer, a p-type doped organic layer, or a combination thereof is disclosed in Patent Document 4. Further, Patent Document 5 discloses an intermediate layer that includes a semiconductor that is a matrix component and an additive, and in which the composition ratio of the matrix component and the additive varies in the film pressure direction.
As described above, an organic material, particularly an organic semiconductor, is mainly used as a material for the intermediate layer, and an intermediate layer using an inorganic material, particularly an inorganic semiconductor, has hardly been reported. Patent Document 5 discloses an example of an intermediate layer using an inorganic semiconductor. However, it achieves high current efficiency, which is impossible to achieve with conventional organic EL elements, and enables high luminance emission and long life. The inorganic material for obtaining the intermediate layer is not described in detail.

Japanese Patent Laid-Open No. 11-329748 JP 2003-45676 A JP 2003-272860 A JP 2004-39617 A JP-A-2005-135600

  The present invention has been made in view of the above-described problems, and is an organic EL element using an inorganic semiconductor for a charge generation layer (intermediate layer), which is difficult to achieve with conventional organic EL elements. It is a main object to provide a stacked organic EL element that can achieve a long life in time and can be manufactured efficiently and stably.

  In order to achieve the above object, the present invention provides an organic EL element having a plurality of light emitting units between opposing electrode layers, and a charge generation layer formed between adjacent light emission units, wherein the charge generation layer Provides an electron generating layer made of an inorganic semiconductor material having electron injecting properties and a hole generating layer made of an inorganic semiconductor material having hole injecting properties.

  According to the present invention, since a plurality of light emitting units are stacked via the charge generation layer, the light emitting units are connected in series when a voltage is applied, and emit light simultaneously. High current efficiency and high luminance can be obtained as compared with the organic EL element having the above. Further, in the organic EL element of the present invention, the luminance is improved when operated with the same current as the organic EL element having the conventional single light emitting unit, while the organic EL element having the conventional single light emitting unit is When operating at the same brightness, there is an advantage that the life is extended. Therefore, the organic EL element of the present invention can be suitably used for lighting applications that require high brightness and long life.

In the above invention, the inorganic semiconductor material having an electron injecting property contains a host material and an electron donating dopant, and the inorganic semiconductor material having the hole injecting property is a host material and an electron accepting dopant. It may contain.
The inorganic semiconductor material having an electron injecting property may contain a host material and an electron donating dopant, and the inorganic semiconductor material having the hole injecting property may contain an electron accepting material.
Further, the inorganic semiconductor material having electron injecting property may contain an electron donating material, and the inorganic semiconductor material having hole injecting property may contain a host material and an electron accepting dopant.

  In the present invention, the electron donating dopant is preferably at least one selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals. This is because these dopants have a relatively small ionization potential, so that the ionization potential is smaller than that of the host material, and the voltage increase in the electron generation layer can be suppressed.

  Furthermore, the electron donating material is preferably at least one selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals.

  In the present invention, the charge generation layer is preferably a vapor deposition film. In this case, it is preferable that at least one of the layers constituting the light emitting unit is a coating film. When the charge generation layer is formed by vapor deposition, the charge generation layer can be easily and stably stacked on the light emitting unit, so when forming the layer constituting the light emission unit by a wet method by coating, There is no need to select an organic material to be used for the layers constituting the light emitting unit so that the solubility in the solvent is different, the choice of organic materials to be used for the layers constituting the light emitting unit is widened, and the light emitting unit is stably formed. Because it can.

  The organic EL device of the present invention has a high luminance that cannot be realized by a conventional organic EL device while keeping a current density low by stacking a plurality of light emitting units between electrode layers via a charge generation layer. There is an effect that it is possible to extend the service life.

Hereinafter, the organic EL device of the present invention will be described in detail.
The organic EL device of the present invention is an organic EL device having a plurality of light-emitting units between opposing electrode layers, and a charge generation layer formed between adjacent light-emitting units, wherein the charge generation layer has electron injection. And an electron generating layer made of an inorganic semiconductor material having a property and a hole generating layer made of an inorganic semiconductor material having a hole injecting property.

The organic EL element of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view showing an example of the organic EL element of the present invention, and FIG. 2 is an explanatory view showing an operation mechanism of the organic EL element shown in FIG.
As illustrated in FIG. 1, the organic EL element of the present invention has an electrode layer (anode) 1, a light emitting unit 2-1, a charge generation layer 3, a light emitting unit 2-2, and an electrode layer (cathode) 4 stacked in this order. It has been done. In general, in an organic EL element, electrons (e) are injected from the cathode side and holes (h) are injected from the anode side, and electrons and holes are recombined in the light emitting unit to generate an excited state and emit light. In the organic EL element, two layers of light emitting units 2-1 and 2-2 are stacked via the charge generation layer 3, and as shown in FIG. 2, electrons (e) and anodes are formed from the cathode 4 side. Holes (h) are injected from the 1 side, holes (h) are injected in the direction of the cathode 4 by the charge generation layer 3, and electrons (e) are injected in the direction of the anode 1, and each light emitting unit 2-1 And 2-2, electron-hole recombination occurs, and a plurality of light emission occurs between the anode 1 and the cathode 4.

  As illustrated in FIG. 1, the charge generation layer 3 includes an electron generation layer 3a and a hole generation layer 3b. The electron generating layer 3a is made of an inorganic semiconductor material having an electron injecting property. For example, when the electron generating layer 3a contains a host material and an electron donating dopant, the electron generating layer 3a receives electrons from the electron donating dopant. And becomes a radical anion state (electrons). On the other hand, the hole generating layer 3b is made of an inorganic semiconductor material having a hole injecting property. For example, when the hole generating layer 3b contains a host material and an electron-accepting dopant, The electrons are deprived, become oxidized, and become a radical cation state (holes). The radical anion state (electrons) and the radical cation state (holes) move toward the anode 1 and the cathode 4 respectively when a voltage is applied to the light emitting unit 2-1 in contact with the anode 1 side of the charge generation layer 3. Electrons are injected, and holes are injected into the light emitting unit 2-2 in contact with the cathode 4 side of the charge generation layer 3. That is, when a voltage is applied between the electrode layers, electrons are injected from the cathode side and holes are injected from the anode side. At the same time, electrons and holes are generated in the charge generation layer and separated from the charge generation layer. Electrons generated therein are directed toward the anode and injected into adjacent light emitting units, and holes generated in the charge generation layer are directed toward the cathode and injected into adjacent light emitting units. Subsequently, these electrons and holes recombine in the light emitting unit to generate light.

Therefore, according to the present invention, when a voltage is applied between the electrode layers, the light emitting units are connected in series and emit light simultaneously, and high current efficiency can be realized.
Further, according to the present invention, by appropriately selecting the inorganic semiconductor material used for the electron generation layer and the hole generation layer, the electron generation layer has a low hole injection energy barrier, and smooth hole injection into the light emitting unit. In the hole generation layer, the energy barrier for electron injection is low, and smooth electron injection into the light emitting unit can be realized.

  A conventional organic EL element has a structure in which a single light emitting unit is sandwiched between electrode layers (hereinafter referred to as a conventional organic EL element in this section), and “electrons (number) measured in an external circuit” The upper limit of the quantum efficiency, which is the ratio of photons (number) / second to / second, was theoretically 1 (= 100%). In contrast, the organic EL element of the present invention has no theoretical limit. This means that the hole (h) injection shown in FIG. 2 means the extraction of electrons from the valence band (or HOMO (highest occupied orbit)) of the light-emitting unit 2-2. The electrons extracted from the valence band of the light emitting unit 2-2 in contact with the side are injected into the conduction band (or LUMO (minimum unoccupied orbit)) of the light emitting unit 2-1 in contact with the anode side of the charge generation layer. This is because it is reused to create a luminescent excited state. Therefore, the quantum efficiency of each light emitting unit stacked via the charge generation layer (in this case, the number of electrons (number) / second that (apparently) passes through each light emitting unit, and the number of photons emitted from each light emitting unit (number ) / Second ratio is defined as the quantum efficiency of the organic EL device of the present invention, and there is no upper limit to the value.

  In addition, the luminance of the conventional organic EL element is substantially proportional to the current density, and a high current density is inevitably necessary to obtain high luminance. On the other hand, since the element lifetime is inversely proportional to the current density, not the driving voltage, high luminance light emission shortens the element lifetime. On the other hand, the organic EL element of the present invention increases the current density by, for example, n light emitting units having the same configuration existing between the electrode layers in order to obtain n times the luminance at a desired current density. It is possible to realize n times the luminance without causing it. N times the luminance can be realized without sacrificing the lifetime.

  Further, in the conventional organic EL element, the power conversion efficiency (W / W) is reduced due to the increase of the driving voltage. On the other hand, in the case of the organic EL element of the present invention, when n light emitting units are present between the electrode layers, the light emission start voltage (turn on voltage) is substantially n times, so that a voltage for obtaining a desired luminance is obtained. However, since the quantum efficiency (current efficiency) is also approximately n times, in principle, the power conversion efficiency (W / W) does not change.

  Further, according to the present invention, since there are a plurality of light emitting units, there is an advantage that the risk of an element short circuit can be reduced. Since the conventional organic EL element has only one light emitting unit, if an (electrical) short circuit occurs between electrode layers due to the influence of pinholes or the like existing in the light emitting unit, it becomes a non-light emitting element immediately. End up. On the other hand, in the case of the organic EL element of the present invention, a plurality of layers of light emitting units are laminated between electrode layers, so that the film is thick and the risk of short circuit is reduced. Furthermore, even if a specific light emitting unit is short-circuited, the other light emitting units can emit light, and the situation of no light emission can be avoided. In particular, in the case of constant current driving, the driving voltage is only reduced by a short-circuited light emitting unit, and a light emitting unit that is not short-circuited can emit light normally.

  Furthermore, for example, when a display device having a simple matrix structure is used as an application example, a decrease in current density means that a voltage drop due to wiring resistance and a substrate temperature increase can be greatly reduced as compared with the case of a conventional organic EL element. To do. Also in this respect, the organic EL element of the present invention is advantageous.

Similarly, the above-described characteristics work sufficiently advantageously when the application is used to uniformly illuminate a large area, particularly when illumination is considered as an application example of a product. In the conventional organic EL element, the specific resistance ( ^{-10 −4} Ω · cm) of an electrode material, particularly a transparent electrode material typified by ITO, etc. is compared with the specific resistance of a metal ( ^{−10 −6} Ω · cm). Since the voltage (V) (or electric field E (V / cm)) applied to the light emitting unit decreases as the distance from the power feeding portion increases, the luminance unevenness in the vicinity of the power feeding portion and in the distance (as a result) Brightness difference). On the other hand, when obtaining a desired luminance as in the organic EL element of the present invention, if the current value can be greatly reduced as compared with the conventional organic EL element, the potential drop can be reduced, and as a result, light emission with a substantially uniform large area is achieved. Can be obtained.

Furthermore, a conventional charge generation layer using an organic material can be formed by a wet method by coating. However, when a light emitting unit is formed by a wet method, a charge generation layer is further formed on the light emitting unit by a wet method. This is very difficult due to the relationship with the solvent. For this reason, it is necessary to devise organic materials for the light emitting unit and the charge generation layer so as to have different solubility in a solvent, or to combine a vacuum deposition method and the like, and the range of material selection has been narrowed. On the other hand, since the charge generation layer in the present invention uses an inorganic semiconductor material, it can be formed by a vacuum deposition method or the like and can be easily laminated on the light emitting unit. In addition, for example, it is not necessary to select an organic material to be used for the light emitting unit so that the solubility in a solvent is different, and the choice of the organic material of the light emitting unit is widened, and the light emitting unit can be stably formed by a wet method by coating. This has the advantage that the manufacturing process of the organic EL element is simplified.
Hereinafter, each structure of the organic EL element of this invention is demonstrated.

1. Charge generation layer The charge generation layer used in the present invention is formed between adjacent light emitting units, and includes an electron generation layer made of an inorganic semiconductor material having electron injection properties and holes made of an inorganic semiconductor material having hole injection properties. And a generation layer. This charge generation layer is not an electrode, but injects electrons in the anode direction and holes in the cathode direction.
In the present invention, since electrons and holes move as described in the example shown in FIG. 2 described above, it is preferable that the electron generation layer is disposed on the anode side and the hole generation layer is disposed on the cathode side. .

  The charge generation layer used in the present invention has an electron generation layer and a hole generation layer, and the electron generation layer is not particularly limited as long as it is made of an inorganic semiconductor material having an electron injection property. In addition, the hole generation layer is not particularly limited as long as it is made of an inorganic semiconductor material having hole injection properties, but there are three preferred embodiments. In the first embodiment, the electron generating layer is made of an inorganic semiconductor material containing a host material and an electron donating dopant, and the hole generating layer is an inorganic semiconductor material containing a host material and an electron accepting dopant. It is characterized by comprising. The second embodiment is characterized in that the electron generating layer is made of an inorganic semiconductor material containing a host material and an electron donating dopant, and the hole generating layer is made of an inorganic semiconductor material containing an electron accepting material. And In a third embodiment, the electron generating layer is made of an inorganic semiconductor material containing an electron donating material, and the hole generating layer is made of an inorganic semiconductor material containing a host material and an electron accepting dopant. And Each embodiment will be described below.

(1) First Embodiment A first embodiment of the charge generation layer used in the present invention is an electron generation layer comprising a host material and an electron injecting inorganic semiconductor material containing an electron donating dopant, a host material, and And a hole generating layer made of a hole-injecting inorganic semiconductor material containing an electron-accepting dopant.

FIG. 1 is a schematic cross-sectional view showing an example of an organic EL element having a charge generation layer according to this embodiment.
The electron generating layer 3a contains a host material and an electron donating dopant. In the electron generating layer 3a, the host material receives electrons from the electron donating dopant and is in a radical anion state (electrons). . On the other hand, the hole generation layer 3b contains a host material and an electron-accepting dopant, and in the hole-generation layer 3b, the host material is deprived of electrons by the electron-accepting dopant and becomes oxidized, thereby generating radical cations. It is in a state (hole). The radical anion state (electrons) and the radical cation state (holes) move toward the anode 1 and the cathode 4 respectively when a voltage is applied to the light emitting unit 2-1 in contact with the anode 1 side of the charge generation layer 3. Electrons are injected, and holes are injected into the light emitting unit 2-2 in contact with the cathode 4 side of the charge generation layer 3. That is, when a voltage is applied between the electrode layers, electrons are injected from the cathode side and holes are injected from the anode side. At the same time, electrons and holes are generated in the charge generation layer and separated from the charge generation layer. Electrons generated therein are directed toward the anode and injected into adjacent light emitting units, and holes generated in the charge generation layer are directed toward the cathode and injected into adjacent light emitting units. Subsequently, these electrons and holes recombine in the light emitting unit to generate light.

Therefore, according to this embodiment, when a voltage is applied between the electrode layers, the light emitting units are connected in series and emit light simultaneously, and high current efficiency can be realized.
In addition, according to this embodiment, by appropriately selecting the host material, the electron donating dopant, and the electron accepting dopant used for the electron generating layer and the hole generating layer, the electron generating layer has a hole injection energy barrier. Therefore, smooth hole injection into the light emitting unit can be realized, and the hole generation layer has a low energy barrier for electron injection, so that smooth electron injection into the light emitting unit can be realized.
Hereinafter, the electron generation layer and the hole generation layer will be described.

(I) Electron generation layer The electron generation layer used in this embodiment is composed of an electron injecting inorganic semiconductor material containing a host material and an electron donating dopant. The electron generating layer is semiconductive and the current through the electron generating layer is substantially carried by the electrons.

  It is preferable that the host material used for the electron generating layer is in a state in which electrons are received from an electron donating dopant to be in a radical anion state, that is, has an electron injecting property (electron transporting property). preferable. When the host material has both an electron injection property (electron transport property) and a hole injection property (hole transport property), the same host material can be used for the electron generation layer and the hole generation layer. . As such a host material, a material having a band gap of 2 eV or more is preferably used. Examples thereof include ZnS, ZnO, ZnSe, ZnTe, GaN, AlN, AlP, SiC, GaP, and AlAs. Of these, ZnS, ZnO, ZnSe, ZnTe, GaN, and SiC are preferable.

  Examples of the electron donating dopant used in this embodiment include metals and metal compounds. The metal compound includes inorganic salts, oxides and halides of metals. The electron donating dopant preferably has a smaller ionization potential than the host material. That is, the electron generating layer is preferably composed of a host material having a relatively large ionization potential and an electron donating dopant having a small ionization potential. This is because a voltage increase in the electron generation layer can be suppressed by using a highly conductive dopant. Specifically, the ionization potential of the electron donating dopant is preferably 4 eV or less, and more preferably 3 eV or less. Examples of such electron donating dopants include alkali metals, alkali metal compounds, alkaline earth metals, alkaline earth metal compounds, rare earth metals, rare earth metal compounds, and specifically Li, Na, K , Rb, Cs, Mg, Ca, Sr, Ba, La, Ce, Sm, Eu, Tb, Dy, Yb, and these compounds. Among these, Li and Cs are particularly preferable.

  The content of the electron-donating dopant can be set in the range of 1% by weight to 99% by weight in the electron generating layer, and particularly preferably in the range of 1% by weight to 50% by weight. .

Further, the electron generation layer may have a visible light transmittance of 1% or more, preferably 50% or more, and more preferably 70% or more. When the visible light transmittance is less than the above range, the generated light is absorbed when passing through the charge generation layer, and a desired quantum efficiency (current efficiency) is obtained even if the organic EL element has a plurality of light emitting units. It is because there is a possibility that it becomes impossible to obtain.
The visible light transmittance is an average value of values measured using UV-3100 manufactured by Shimadzu Corporation in the visible light region.

  Further, the thickness of the electron generating layer is appropriately selected depending on the visible light transmittance and the kind of the host material and electron donating dopant described above, but can be set within a range of 1 nm to 500 nm. Preferably, it exists in the range of 10 nm-100 nm.

The electron generating layer can be formed by co-evaporation of a host material and electron donating dopan. Examples of the method for forming the electron generating layer include a resistance heating vapor deposition method, an electron beam vapor deposition method, a vacuum vapor deposition method such as a laser beam vapor deposition method, and a sputtering method.
In this embodiment, the electron generating layer is preferably a co-deposited film (deposited film). By forming the electron generating layer by co-evaporation, the electron generating layer can be easily and stably laminated on the light emitting unit. Therefore, the light emitting unit can be stably formed by a wet method. It has the advantage that the organic material used is not restricted.

(Ii) Hole generation layer The hole generation layer used in the present embodiment is made of a hole-injecting inorganic semiconductor material containing a host material and an electron-accepting dopant. The hole generating layer is semiconductive and the current through the hole generating layer is substantially carried by the holes.

  The host material used for the hole-generating layer is preferably one that has been deprived of electrons by an electron-accepting dopant, becomes an oxidized state, and becomes a radical cation state. It is preferable to have (transportability). As described above, when the host material has both electron injection property (electron transport property) and hole injection property (hole transport property), the same host material is used for the electron generation layer and the hole generation layer. can do. As such a host material, those described in the section of the electron generation layer can be used.

Moreover, as an electron-accepting dopant used for this embodiment, a metal, a metal compound, etc. can be mentioned, for example. The metal compound includes inorganic salts, oxides and halides of metals. Among these, a metal oxide is preferably used as the electron-accepting dopant, and examples thereof include V ₂ O ₅ , WO ₃ , MoO ₃ , Re ₂ O ₇ , FeCl ₃ , and F4-TCNQ. In particular, V ₂ O ₅ and MoO ₃ are preferable.

  The content of the electron-accepting dopant can be set in the range of 1 wt% to 99 wt% in the hole generating layer, and preferably in the range of 1 wt% to 50 wt%.

  Note that the visible light transmittance, thickness, formation method, and the like of the hole generation layer are the same as those of the electron generation layer, and thus description thereof is omitted here.

(2) Second Embodiment A second embodiment of the charge generation layer used in the present invention is an electron generation layer comprising an electron injecting inorganic semiconductor material containing a host material and an electron donating dopant, and an electron accepting property. And a hole generating layer made of a hole-injecting inorganic semiconductor material containing the material.

FIG. 3 is a schematic cross-sectional view showing an example of an organic EL element having a charge generation layer of this embodiment.
The electron generating layer 23a contains a host material and an electron donating dopant. In the electron generating layer 23a, the host material receives electrons from the electron donating dopant and is in a radical anion state (electrons). . On the other hand, the hole generation layer 23b contains an electron-accepting material, and at the interface between the hole generation layer 23b and the electron generation layer 23a, the host material in the electron generation layer 23a is an electron in the hole generation layer 23b. Electrons are taken away by the accepting material, become oxidized, and are in a radical cation state (holes). When the radical anion state (electrons) and the radical cation state (holes) move in the anode direction and the cathode direction, respectively, when a voltage is applied, electrons are transferred to the light emitting unit 22-1 in contact with the anode 21 side of the charge generation layer 23. Then, holes are injected into the light emitting unit 22-2 in contact with the cathode 4 side of the charge generation layer 23. The electrons and holes recombine at the light emitting units 22-1 and 22-2 to generate light.
Therefore, according to this embodiment, when a voltage is applied between the electrode layers, the light emitting units are connected in series and emit light simultaneously, and high current efficiency can be realized.
In addition, by appropriately selecting the host material, electron donating dopant, and electron accepting material used for the electron generating layer and the hole generating layer, the electron generating layer has a low hole injection energy barrier, so that Smooth hole injection is realized, and the hole generation layer has a low energy barrier for electron injection, and smooth electron injection into the light emitting unit can be realized.

  Since the electron generating layer is the same as that described in the section of the first embodiment, description thereof is omitted here. Hereinafter, the hole generation layer will be described.

(I) Hole generation layer The hole generation layer used in this embodiment is made of a hole-injecting inorganic semiconductor material containing an electron-accepting material. The hole generating layer is semiconductive and the current through the hole generating layer is substantially carried by the holes.

Examples of the electron-accepting material used in this embodiment include metals and metal compounds that can be electron-accepting dopants. The metal compound includes inorganic salts, oxides and halides of metals. Among these, a metal oxide is preferably used as the electron-accepting material, and examples thereof include V ₂ O ₅ , WO ₃ , MoO ₃ , and Re ₂ O ₇ . In particular, V ₂ O ₅ and MoO ₃ are preferable.

  The hole generating layer is preferably a deposited film. By forming the hole generating layer by vapor deposition, the hole generating layer can be easily and stably laminated on the light emitting unit. Therefore, the light emitting unit can be stably formed by a wet method, and light emission can be achieved. It has the advantage that the organic material used for the unit is not restricted. Examples of the method for forming the hole generating layer include a resistance heating vapor deposition method, an electron beam vapor deposition method, a vacuum vapor deposition method such as a laser beam vapor deposition method, and a sputtering method.

  The thickness of the hole generating layer is appropriately selected depending on the visible light transmittance and the type of the electron-accepting material, but is preferably in the range of 1 nm to 100 nm.

  The visible light transmittance and the like of the hole generation layer are the same as those of the hole generation layer in the first embodiment, and thus description thereof is omitted here.

(3) Third Embodiment A third embodiment of the charge generation layer used in the present invention is an electron generation layer made of an electron injecting inorganic semiconductor material containing an electron donating material, a host material, and an electron accepting layer. And a hole generating layer made of a hole injecting inorganic semiconductor material containing a dopant.

FIG. 4 is a schematic cross-sectional view showing an example of an organic EL element having a charge generation layer of this embodiment.
The hole generating layer 33b contains a host material and an electron-accepting dopant, and in the hole generating layer 33b, the host material is deprived of electrons by the electron-accepting dopant and becomes an oxidized state, and a radical cation state. (Hole). On the other hand, the electron generation layer 33a contains an electron donating material. At the interface between the electron generation layer 33a and the hole generation layer 33b, the host material in the hole generation layer 33b is donated in the electron generation layer 33a. In this state, electrons are received from the functional material and are in the radical anion state (electrons). When the radical anion state (electrons) and the radical cation state (holes) move in the anode direction and the cathode direction, respectively, when a voltage is applied, electrons are transferred to the light emitting unit 32-1 in contact with the anode 31 side of the charge generation layer 33. Then, holes are injected into the light emitting unit 32-2 in contact with the cathode 34 side of the charge generation layer 33. The electrons and holes recombine in the light emitting units 32-1 and 32-2, and generate light.
Therefore, according to this embodiment, when a voltage is applied between the electrode layers, the light emitting units are connected in series and emit light simultaneously, and high current efficiency can be realized.
In addition, by appropriately selecting the host material, electron accepting dopant and electron donating material used for the electron generating layer and the hole generating layer, the electron generating layer has a low hole injection energy barrier, so Smooth hole injection is realized, and the hole generation layer has a low energy barrier for electron injection, and smooth electron injection into the light emitting unit can be realized.

  The hole generation layer is the same as that described in the section of the first embodiment, and a description thereof is omitted here. Hereinafter, the electron generation layer will be described.

(I) Electron generation layer The electron generation layer used in the present embodiment is made of an electron injecting inorganic semiconductor material containing an electron donating material. The electron generating layer is semiconductive and the current through the electron generating layer is substantially carried by the electrons.

  Examples of the electron donating material used in this embodiment include metals and metal compounds that can serve as an electron donating dopant. The metal compound includes inorganic salts, oxides and halides of metals. Examples of such electron donating materials include alkali metals, alkali metal compounds, alkaline earth metals, alkaline earth metal compounds, rare earth metals, rare earth metal compounds, and specifically Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, La, Ce, Sm, Eu, Tb, Dy, Yb, and these compounds can be mentioned. Among these, Li and Cs are particularly preferable.

  The thickness of the electron generating layer is appropriately selected depending on the visible light transmittance and the type of the electron donating material, but is preferably in the range of 1 nm to 500 nm, more preferably in the range of 10 nm to 100 nm. is there.

  The visible light transmittance of the electron generation layer is the same as that of the electron generation layer in the first embodiment, and the formation method of the electron generation layer is the same as that of the hole generation layer in the second embodiment. Therefore, explanation here is omitted.

(4) Others In the present invention, a plurality of light emitting units are stacked via the charge generation layer. FIG. 5 is a schematic cross-sectional view of an organic EL element in which n layers of light emitting units are stacked via a charge generation layer. As illustrated in FIG. 5, in the organic EL element of the present invention, on the electrode layer (anode) 1, the light emitting unit 2-1, the charge generation layer 3-1, the light emission unit 2-2, and the charge generation layer are sequentially formed. 3-2,..., The charge generation layer 3- (n-1) and the light emission unit 2-n are repeatedly laminated with the light emitting unit and the charge generation layer, and the electrode layer (cathode) 4 is formed on the uppermost surface. ing. In such an organic EL device, as illustrated in FIG. 6, electron-hole recombination occurs in a plurality of light emitting units stacked via a charge generation layer, and a plurality of light emission occurs.
Thus, as the number of stacked light emitting units increases, the number of charge generation layers interposed between the light emitting units also increases. In this case, the structure of the charge generation layer provided between the light emitting units may be the same or different. For example, the inorganic semiconductor materials used for the charge generation layer may be the same or different.

In the present invention, the charge generation layer may have an intervening layer formed between the electron generation layer and the hole generation layer. This intervening layer is made of an inorganic semiconductor material having an electron injecting property and a hole injecting property. As such an inorganic semiconductor material, those used as a host material having electron injecting property and hole injecting property described in the section of the electron generating layer in the first embodiment are preferably used.
The thickness of the intervening layer, the visible light transmittance, the formation method, and the like are the same as those of the hole generating layer in the second embodiment, and thus the description thereof is omitted here.

2. Light-Emitting Unit The light-emitting unit used in the present invention is composed of one or more organic layers including at least a light-emitting layer. That is, the light emitting unit includes at least a light emitting layer, and has a layer configuration of one or more organic layers. Usually, when a light emitting unit is formed by a wet method by coating, it is difficult to stack a large number of layers in relation to the solvent, so that it is often formed by one or two organic layers. Further, it is possible to further increase the number of layers by devising an organic material so that the solubility in a solvent is different or by combining a vacuum deposition method.

Examples of the organic layer formed in the light emitting unit other than the light emitting layer include charge injection layers such as a hole injection layer and an electron injection layer. Furthermore, examples of the other organic layers include a charge transport layer such as a hole transport layer that transports holes to the light-emitting layer and an electron transport layer that transports electrons to the light-emitting layer. In many cases, it is formed integrally with the charge injection layer by imparting a charge transporting function. In addition, as the organic layer formed in the light emitting unit, by preventing the penetration of holes or electrons like the carrier block layer, further preventing the diffusion of excitons and confining excitons in the light emitting layer, Examples include a layer for increasing the recombination efficiency.
Hereinafter, each structure of such a light emission unit is demonstrated.

(1) Light emitting layer The light emitting layer used in the present invention has a function of emitting light by providing a recombination field of electrons and holes. As the material for forming the light emitting layer, a dye-based light-emitting material, a metal complex-based light-emitting material, or a polymer-based light-emitting material can be generally used.

  Examples of dye-based luminescent materials include cyclopentadiene derivatives, tetraphenylbutadiene derivatives, triphenylamine derivatives, oxadiazole derivatives, pyrazoloquinoline derivatives, distyrylbenzene derivatives, distyrylarylene derivatives, silole derivatives, thiophene ring compounds, pyridine Examples thereof include a ring compound, a perinone derivative, a perylene derivative, an oligothiophene derivative, a trifumanylamine derivative, a coumarin derivative, an oxadiazole dimer, and a pyrazoline dimer.

Examples of the metal complex light emitting material include aluminum quinolinol complex, benzoquinolinol beryllium complex, benzoxazole zinc complex, benzothiazole zinc complex, azomethyl zinc complex, porphyrin zinc complex, europium complex, iridium metal complex, platinum metal complex, etc. The center metal has a rare earth metal such as Al, Zn, Be, Ir, Pt, or Tb, Eu, Dy, etc., and the ligand has an oxadiazole, thiadiazole, phenylpyridine, phenylbenzimidazole, quinoline structure, etc. The metal complex etc. which have can be mentioned. Specifically, tris (8-quinolinol) aluminum complex (Alq ₃ ) can be used.

  Furthermore, examples of the polymer light emitting material include polyparaphenylene vinylene derivatives, polythiophene derivatives, polyparaphenylene derivatives, polysilane derivatives, polyacetylene derivatives, polyvinylcarbazole, polyfluorenone derivatives, polyfluorene derivatives, polyquinoxaline derivatives, polydialkylfluorene derivatives. , And copolymers thereof. Moreover, what polymerized the said pigment-type luminescent material and metal complex type | system | group luminescent material is also mentioned.

  Among the above, the light emitting material used in the present invention is preferably a metal complex light emitting material or a polymer light emitting material, and more preferably a polymer light emitting material. Of the polymer light emitting materials, a conductive polymer having a π-conjugated structure is preferable. Examples of the conductive polymer having such a π-conjugated structure include polyparaphenylene vinylene derivatives, polythiophene derivatives, polyparaphenylene derivatives, polysilane derivatives, polyacetylene derivatives, polyfluorenone derivatives, polyfluorene derivatives, polyquinoxaline derivatives as described above. , Polydialkylfluorene derivatives, and copolymers thereof.

  The thickness of the light emitting layer is not particularly limited as long as it can provide a function of emitting light by providing a recombination field between electrons and holes, and can be, for example, about 1 nm to 200 nm. .

  Further, a dopant that emits fluorescence or phosphorescence may be added to the light emitting layer for the purpose of improving the light emission efficiency and changing the light emission wavelength. Examples of such dopants include perylene derivatives, coumarin derivatives, rubrene derivatives, quinacridone derivatives, squalium derivatives, porphyrin derivatives, styryl dyes, tetracene derivatives, pyrazoline derivatives, decacyclene, phenoxazone, quinoxaline derivatives, carbazole derivatives, fluorene derivatives, and the like. Can be mentioned.

The method for forming the light emitting layer is not particularly limited as long as it can be patterned. For example, dry methods such as vacuum deposition method, sputtering method, etc., printing method, ink jet method, spin coating method, casting method, dipping method, bar coating method, blade coating method, roll coating method, gravure coating method, flexographic printing method, Examples thereof include a wet method such as a spray coating method. Among these, it is preferable to use a spin coat method or an ink jet method.
Further, when the light emitting layer is patterned, it may be applied separately by a masking method for pixels having different light emission colors, or a partition may be formed between the light emitting layers. As a material for forming such a partition, a photocurable resin such as a photosensitive polyimide resin or an acrylic resin, a thermosetting resin, an inorganic material, or the like can be used. Furthermore, you may perform the process which changes the surface energy (wetting property) of the material which forms these partition walls.

  In the present invention, the light emitting layer is preferably a coating film. The “coating film” refers to a film formed by a wet method.

(2) Charge Injection / Transport Layer In the present invention, a charge injection / transport layer may be formed between the electrode layer and the light emitting layer. The charge injecting and transporting layer here has a function of stably transporting charges from the electrode layer to the light emitting layer, and such a charge injecting and transporting layer is provided between the electrode layer and the light emitting layer. Thus, the injection of charges into the light emitting layer is stabilized, and the light emission efficiency can be increased.

  Examples of the charge injection transport layer include a hole injection transport layer that transports holes injected from the anode into the light emitting layer, and an electron injection transport layer that transports electrons injected from the cathode into the light emitting layer. Hereinafter, the hole injection / transport layer and the electron injection / transport layer will be described.

(I) Hole Injecting and Transporting Layer The hole injecting and transporting layer used in the present invention is either a hole injecting layer for injecting holes into the light emitting layer or a hole transporting layer for transporting holes. The hole injection layer and the hole transport layer may be laminated, or a single layer having both the hole injection function and the hole transport function may be used.

  The material used for the hole injecting and transporting layer is not particularly limited as long as it can stably transport holes injected from the anode into the light emitting layer. In addition to the exemplified compounds, phenylamine, starburst amine, phthalocyanine, vanadium oxide, molybdenum oxide, ruthenium oxide, aluminum oxide and other oxides, amorphous carbon, polyaniline, polythiophene, polyphenylene vinylene derivatives, etc. may be used. it can. Specifically, bis (N- (1-naphthyl-N-phenyl) benzidine (α-NPD), 4,4,4-tris (3-methylphenylphenylamino) triphenylamine (MTDATA), poly 3, 4-ethylenedioxythiophene-polystyrene sulfonic acid (PEDOT-PSS), polyvinyl carbazole (PVCz), etc. are mentioned.

  The thickness of the hole injecting and transporting layer is not particularly limited as long as the hole injecting holes from the anode and transporting the holes to the light emitting layer is sufficiently exhibited. It is preferable to be in the range of 5 nm to 1000 nm, especially in the range of 10 nm to 500 nm.

In the present invention, the hole injecting and transporting layer is preferably a coating film.
The method for forming the hole injecting and transporting layer is the same as that of the light emitting layer, and thus the description thereof is omitted here.

(Ii) Electron Injection / Transport Layer The electron injection / transport layer used in the present invention may be either an electron injection layer for injecting electrons into the light emitting layer or an electron transport layer for transporting electrons. A layer and an electron transport layer may be laminated, or a single layer having both an electron injection function and an electron transport function may be used.

  The material used for the electron injection layer is not particularly limited as long as the material can stabilize the injection of electrons into the light emitting layer. In addition to the compounds exemplified as the light emitting material of the light emitting layer, Aluminum lithium alloy, lithium fluoride, strontium, magnesium oxide, magnesium fluoride, strontium fluoride, calcium fluoride, barium fluoride, aluminum oxide, strontium oxide, calcium, polymethyl methacrylate, sodium polystyrene sulfonate, lithium, cesium, Alkali metals, alkali metal halides, alkali metal organic complexes, and the like, such as cesium fluoride, can be used.

  In addition, the thickness of the electron injection layer is not particularly limited as long as the electron injection function is sufficiently exerted.

On the other hand, the material used for the electron transport layer is not particularly limited as long as it is a material capable of transporting electrons injected from the electrode layer into the light emitting layer. For example, bathocuproine, bathophenanthroline, phenanthroline derivatives , A triazole derivative, an oxadiazole derivative, or a tris (8-quinolinol) aluminum complex (Alq ₃ ).

  Furthermore, as an electron injecting and transporting layer composed of a single layer having both an electron injecting function and an electron transporting function, a metal doped layer in which an alkali metal or an alkaline earth metal is doped on an electron transporting organic material is formed. This can be used as an electron injecting and transporting layer. Examples of the electron-transporting organic material include bathocuproin, bathophenanthroline, and phenanthroline derivatives. Examples of the metal to be doped include Li, Cs, Ba, and Sr.

In the present invention, the electron injecting and transporting layer is preferably a coating film.
Further, the method for forming the electron injecting and transporting layer is the same as that of the light emitting layer, and thus the description thereof is omitted here.

(3) Others In the present invention, a plurality of light emitting units are stacked via the charge generation layer. The number of stacked light emitting units is not particularly limited as long as it is a plurality, that is, two or more layers, and may be, for example, three layers, four layers, or more. It is preferable that the number of stacked light emitting units is a number with which high luminance can be obtained.

Moreover, the structure of each light emitting unit may be the same or different.
For example, three layers of light emitting units that emit red light, green light, and blue light can be stacked. In this case, white light with greatly improved current efficiency and lifetime can be generated as compared with the conventional organic EL element. When such an organic EL element that generates white light is used for illumination, for example, high luminance generated from a large area can be obtained.
FIG. 7 shows an example of an organic EL element that generates white light. In this organic EL element, light emitting units 2B, 2G, and 2R are respectively stacked on an electrode layer (anode) 1 via a charge generation layer 3, and an electrode layer (cathode) 4 is formed on the uppermost surface. ing. Among these light emitting units, the light emitting unit 2B emits blue light, the light emitting unit 2G emits green light, and the light emitting unit 2R emits red light.

  In the case of an organic EL element that generates white light, the intensity and hue of light emitted from each light emitting unit are selected so that they combine to produce white light or light close to white light. There are many combinations of light emitting units that can be used to generate light that appears white, in addition to the combinations of red light, green light, and blue light described above. For example, a combination of blue light and yellow light, red light and cyan light, or green light and magenta light can be cited. Thus, white light is emitted using a two-layer light emitting unit that emits two colors of light. Light can be generated. Moreover, an organic EL element can be obtained by using a plurality of these combinations.

  In addition, it can be applied to a color display device by a color conversion method using an organic EL element that generates blue light. Conventionally, a light emitting material that generates blue light has a disadvantage that its lifetime is short. However, the organic EL element of the present invention has a good current efficiency and a long lifetime, and thus is advantageous for such a color display device.

3. Electrode Layer The electrode layer used in the present invention is not particularly limited as long as one is an anode and the other is a cathode, but the electrode layer on the light extraction surface side needs to be a transparent electrode. For example, when light is extracted from the anode side, the cathode may not be transparent, but when light is extracted from both sides of the anode and the cathode, both are required to be transparent.

  For the anode, a conductive material having a large work function is preferably used so that holes can be easily injected. The anode preferably has as low resistance as possible. Generally, a metal material is used, but an organic substance or an inorganic compound may be used. Specific examples include tin oxide, indium tin oxide (ITO), and indium zinc oxide (IZO).

In addition, it is preferable to use a conductive material having a small work function for the cathode so that electrons can be easily injected. The cathode preferably has as little resistance as possible, and generally a metal material is used, but an organic substance or an inorganic compound may be used. Specifically, Al, Cs, Er, etc. as a simple substance, MgAg, AlLi, AlLi, AlMg, CsTe, etc. as an alloy, Ca / Al, Mg / Al, Li / Al, Cs / Al, Cs ₂ O / Al, LiF / Al, include _ErF 3 / Al or the like.

The electrode layer can be formed using a general electrode forming method, and examples thereof include a sputtering method, a vacuum deposition method, and an ion plating method.
The thickness of the electrode layer is appropriately selected depending on the target resistance value, visible light transmittance, and type of conductive material.

4). Applications The organic EL element of the present invention can be applied to, for example, full-surface illumination, display devices, or various devices, and is preferably used for illumination applications.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

Hereinafter, the present invention will be specifically described using examples and comparative examples.
[Example 1]
(Formation of anode)
A transparent glass substrate (non-alkali glass NA35 manufactured by NH Techno Glass Co., Ltd.) having a length and width of 40 mm × 40 mm and a thickness of 0.7 mm was prepared as a base material, and the transparent glass substrate was washed according to a conventional method. Thereafter, a thin film (thickness 130 nm) of indium zinc oxide compound (IZO) was formed on the transparent glass substrate by a sputtering method. In the above IZO thin film formation, a mixed gas of Ar and O ₂ (volume ratio Ar: O ₂ = 100: 1) was used as the sputtering gas, and the pressure was 0.1 Pa and the DC output was 150 W.
Next, a photosensitive resist (OFPR-800 manufactured by Tokyo Ohka Kogyo Co., Ltd.) is applied onto the IZO thin film, mask exposure, development (using NMD3 (developer) manufactured by Tokyo Ohka Kogyo Co., Ltd.), and etching are performed. Then, the anode was patterned.

(Formation of hole injection transport layer)
Next, the transparent glass substrate provided with the anode and the insulating layer is washed, subjected to UV ozone treatment, and then in the air, the polyethylene dioxythiophene represented by the following structural formula is formed on the transparent glass substrate so as to cover the anode. -Polystyrene sulfonate (PEDOT-PSS) was apply | coated by the spin coat method, and it dried and formed the positive hole injection transport layer (thickness 80nm).

  Here, in the above formula, n is 10,000 to 500,000.

(Formation of first light emitting unit)
Poly (9,9 dioctylfluorene-co-benzoate represented by the following structural formula on the hole injecting and transporting layer in a low oxygen (oxygen concentration 1 ppm or less), low humidity (water vapor concentration 1 ppm or less) glove box. A polymer (5BTF8) composed of thiazole) (F8BT) and poly (9,9 dioctylfluorene) (PF8) was applied by spin coating and dried to form a first polymer light emitting layer (thickness 80 nm). The polymer (5BTF8) is a light emitting material in which F8BT and PF8 are blended at a weight ratio of 5:95.

  Here, in the above formula, n is 100,000 to 1,000,000.

(Formation of charge generation layer)
A ZnS: Cs co-evaporated film (thickness 50 nm) is formed as an electron generating layer on the first polymer light emitting layer by a resistance heating vapor deposition method, and ZnS: V ₂ O _{5 is} formed thereon as a hole generating layer. The co-deposited film (thickness 50 nm) was formed by resistance heating vapor deposition.

(Formation of second light emitting unit)
Similar to the formation of the first polymer light-emitting layer, a second polymer light-emitting layer (thickness 80 nm) was formed on the charge generation layer.

(Formation of cathode)
On the second polymer light emitting layer, Ca (thickness 10 nm) and Ag (thickness 150 nm) were sequentially deposited as a cathode to form a cathode. The deposition conditions were a degree of vacuum of 5 × 10 ⁻⁵ Pa and a film formation rate of 2 to 3 liters / second.

Thereafter, sealing was performed with alkali-free glass in a glove box in a low oxygen (oxygen concentration 1 ppm or less) and low humidity (water vapor concentration 1 ppm or less) state.
As described above, an organic EL element having an anode patterned in a line shape having a width of 2 mm and a cathode formed in a line shape having a width of 2 mm so as to be orthogonal to the anode, and having four light emitting areas (area 4 mm ² ). Was made.

(Evaluation)
When a voltage of 12 V was applied to the organic EL element, a current density of about 200 mA / cm ² and a luminance of about 10,000 cd / m ₂ observed from the anode side were obtained. The luminous efficiency was 5 cd / A.

[Comparative Example 1]
In the same manner as in Example 1, an anode, a hole injection transport layer, and a first polymer light emitting layer were formed on a transparent glass substrate. Next, in the same manner as in Example 1, a cathode was formed on the first polymer light emitting layer and sealed with alkali-free glass to produce an organic EL device.
In this organic EL element, the applied current was 5 V, the current density was about 200 mA / cm ² , the luminance was about 5000 cd / m ² observed from the anode side, and the light emission efficiency was 2.5 cd / A.
From Example 1 and Comparative Example 1, it was confirmed that multi-photon emission was realized by using the charge generation layer of the present invention.

[Example 2]
In the same manner as in Example 1, an anode, a hole injecting and transporting layer, and a first polymer light emitting layer were formed on a transparent glass substrate.

(Formation of charge generation layer)
A ZnS: Cs co-deposited film (thickness 40 nm) is formed as an electron generating layer on the first polymer light emitting layer by resistance heating deposition, and then the ZnS deposition film (thickness 20 nm) is formed by resistance heating deposition. Furthermore, a ZnS: V ₂ O ₅ co-evaporated film (thickness 40 nm) was formed as a hole generating layer by a resistance heating vapor deposition method.

(Formation of second light emitting unit)
Similar to the formation of the first polymer light-emitting layer, a second polymer light-emitting layer (thickness 80 nm) was formed on the charge generation layer.

(Formation of cathode)
On the second polymer light emitting layer, LiF (thickness 0.2 nm) and Al (thickness 150 nm) were sequentially deposited as a cathode to form a cathode. The deposition conditions were a degree of vacuum of 5 × 10 ⁻⁵ Pa and a film formation rate of 2 to 3 liters / second.

Thereafter, sealing was performed with alkali-free glass in a glove box in a low oxygen (oxygen concentration 1 ppm or less) and low humidity (water vapor concentration 1 ppm or less) state.
As described above, an organic EL device having an anode patterned in a line shape having a width of 2 mm and a cathode formed in a line shape having a width of 2 mm so as to be orthogonal to the anode, and having four light emitting areas (area 4 mm ² ). Was made.

(Evaluation)
When a voltage of 13 V was applied to the organic EL element, a current density of about 200 mA / cm ² and a luminance of about 10,000 cd / m ² observed from the anode side were obtained. The luminous efficiency was 5 cd / A.

[Comparative Example 2]
In the same manner as in Example 1, an anode, a hole injection transport layer, and a first polymer light emitting layer were formed on a transparent glass substrate. Next, in the same manner as in Example 2, a cathode was formed on the first polymer light emitting layer and sealed with alkali-free glass to produce an organic EL device.
In this organic EL element, the applied current was 5 V, the current density was about 200 mA / cm ² , the luminance was about 5000 cd / m ² observed from the anode side, and the light emission efficiency was 2.5 cd / A.
From Example 2 and Comparative Example 2, it was confirmed that multiphoton emission was realized by using the charge generation layer of the present invention.

[Example 3]
In the same manner as in Example 1, an anode was formed on a transparent glass substrate.

(Formation of hole injection transport layer)
Next, after the transparent glass substrate provided with the anode and the insulating layer is washed and subjected to UV ozone treatment, α-NPD (Chemipro Chemical Sublimation Products) is deposited by resistance heating, and a hole injection transport layer ( A thickness of 40 nm) was formed.

(Formation of first light emitting unit)
On the hole injection layer, a co-deposited film having a ratio of Alq3 to coumarin 6 of 10: 1 was formed as a first low molecular light emitting layer by resistance heating vapor deposition.

(Formation of charge generation layer)
A ZnS: Cs co-evaporated film (thickness 50 nm) is formed as an electron generating layer on the first low-molecular light emitting layer by resistance heating vapor deposition, and then ZnS: V ₂ O ₅ is co-deposited as a hole generating layer. A film (thickness 50 nm) was formed by resistance heating vapor deposition.

(Formation of second light emitting unit)
In the same manner as the formation of the first low molecular light emitting layer, a second low molecular light emitting layer (thickness 80 nm) was formed on the charge generation layer.

(Formation of cathode)
On the second low-molecular light emitting layer, LiF (thickness 0.5 nm) and Al (thickness 150 nm) were sequentially deposited as a cathode to form a cathode.

Thereafter, sealing was performed with alkali-free glass in a glove box in a low oxygen (oxygen concentration 1 ppm or less) and low humidity (water vapor concentration 1 ppm or less) state.
As described above, an organic EL device having an anode patterned in a line shape having a width of 2 mm and a cathode formed in a line shape having a width of 2 mm so as to be orthogonal to the anode, and having four light emitting areas (area 4 mm ² ). Was made.

(Evaluation)
When a voltage of 14 V was applied to the organic EL element, a current density of about 300 mA / cm ² and a luminance of about 2000 cd / m ² observed from the anode side were obtained. The luminous efficiency was about 7 cd / A.

[Comparative Example 3]
In the same manner as in Example 3, an anode, a hole injecting and transporting layer, and a first low molecular light emitting layer were formed on a transparent glass substrate. Next, in the same manner as in Example 3, a cathode was formed on the first low molecular light emitting layer and sealed with non-alkali glass to produce an organic EL device.
In this organic EL element, the applied voltage was 6 V, the current density was about 300 mA / cm ² , the luminance was about 1000 cd / m ² observed from the anode side, and the luminous efficiency was 3.5 cd / A.
From Example 3 and Comparative Example 3, it was confirmed that multi-photon emission was realized by using the charge generation layer of the present invention.

[Example 4]
An anode was formed on the transparent glass substrate in the same manner as in Example 1, and then a hole injecting and transporting layer and a first low molecular light emitting layer were formed in the same manner as in Example 3.

(Formation of charge generation layer)
A ZnS: Cs co-deposited film (thickness 40 nm) is formed as an electron generating layer on the first low-molecular light-emitting layer by a resistance heating deposition method, and then a ZnS deposition film (thickness 20 nm) is formed by a resistance heating deposition method. Furthermore, a ZnS: V ₂ O ₅ co-evaporated film (thickness 40 nm) was formed as a hole generating layer by a resistance heating vapor deposition method.

(Formation of second low-molecular light-emitting layer)
In the same manner as the formation of the first low molecular light emitting layer, a second low molecular light emitting layer (thickness 80 nm) was formed on the charge generation layer.

(Formation of cathode)
On the second low-molecular light emitting layer, LiF (thickness 0.5 nm) and Al (thickness 150 nm) were sequentially deposited as a cathode to form a cathode.

Thereafter, sealing was performed with alkali-free glass in a glove box in a low oxygen (oxygen concentration 1 ppm or less) and low humidity (water vapor concentration 1 ppm or less) state.
As described above, an organic EL device having an anode patterned in a line shape having a width of 2 mm and a cathode formed in a line shape having a width of 2 mm so as to be orthogonal to the anode, and having four light emitting areas (area 4 mm ² ). Was made.

(Evaluation)
When a voltage of 15 V was applied to the organic EL element, a current density of about 300 mA / cm ² and a luminance of about 2000 cd / m ² observed from the anode side were obtained. The luminous efficiency was about 7 cd / A.

[Comparative Example 4]
In the same manner as in Example 4, an anode, a hole injecting and transporting layer, and a first low molecular light emitting layer were formed on a transparent glass substrate. Next, in the same manner as in Example 4, a cathode was formed on the first low-molecular light emitting layer and sealed with non-alkali glass to produce an organic EL device.
In this organic EL element, the applied voltage was 6 V, the current density was about 300 mA / cm ² , the luminance was about 1000 cd / m ² observed from the anode side, and the luminous efficiency was 3.5 cd / A.
From Example 4 and Comparative Example 4, it was confirmed that multi-photon emission was realized by using the charge generation layer of the present invention.

[Example 5]
An organic EL device was produced in the same manner as in Example 1 except that the charge generation layer was formed as follows.

(Formation of charge generation layer)
On the first polymer light-emitting layer, a ZnS: Cs co-deposited film (thickness: 50 nm) is formed as an electron generating layer by resistance heating vapor deposition, and V ₂ O ₅ is deposited thereon as a hole generating layer. A film was formed by resistance heating vapor deposition.

Compared with the light emission efficiency of 2.5 cd / A at the current density of 200 mA / cm ² of the organic EL element of Comparative Example 1, the organic EL element of Example 5 has doubled light emission efficiency of 5 cd / A at the same current density. And confirmed the realization of multi-photon emission.

[Example 6]
An organic EL element was produced in the same manner as in Example 3 except that the charge generation layer was formed as follows.

(Formation of charge generation layer)
A ZnS: Cs co-deposited film (thickness: 50 nm) is formed as an electron generating layer on the first low-molecular light emitting layer by resistance heating vapor deposition, and V ₂ O ₅ is deposited thereon as a hole generating layer. A film was formed by resistance heating vapor deposition.

Compared with the luminous efficiency of 3.5 cd / A at the current density of 300 mA / cm ² of the organic EL element of Comparative Example 3, the organic EL element of Example 6 has doubled luminous efficiency of 7 cd / A at the equivalent current density. And we confirmed the realization of the multi-photon emission element.

It is a schematic sectional drawing which shows an example of the organic EL element of this invention. It is explanatory drawing which shows the operation mechanism of the organic EL element of this invention. It is a schematic sectional drawing which shows the other example of the organic EL element of this invention. It is a schematic sectional drawing which shows the other example of the organic EL element of this invention. It is a schematic sectional drawing which shows the other example of the organic EL element of this invention. It is explanatory drawing which shows the operation mechanism of the organic EL element of this invention. It is a schematic sectional drawing which shows the other example of the organic EL element of this invention.

Explanation of symbols

1 ... Electrode layer (anode)
2, 2-1, 2-2, 2-n, 22-1, 22-2, 32-1, 32-2 ... Light-emitting units 3, 3-1, 3-2, 3- (n-1), 23, 33 ... Charge generation layer 3a, 23a, 33a ... Electron generation layer 3b, 23b, 33b ... Hole generation layer 4 ... Electrode layer (cathode)

Claims (7)

An organic electroluminescence element having a plurality of light emitting units between opposing electrode layers, and a charge generation layer formed between the adjacent light emitting units,
The charge generation layer has an electron generation layer made of an inorganic semiconductor material having electron injection properties and a hole generation layer made of an inorganic semiconductor material having hole injection properties,
The inorganic semiconductor material having an electron injecting property contains a host material and an electron donating dopant, and the inorganic semiconductor material having the hole injecting property contains a host material and an electron accepting dopant,
The charge generating layer is between the electron-generating layer and the hole generating layer, and further have the intervening layer of inorganic semiconductor material having electron injecting property and a hole injecting property,
The host material contained in the inorganic semiconductor material constituting the electron generating layer; the host material contained in the inorganic semiconductor material constituting the hole generating layer; and the inorganic semiconductor material constituting the intervening layer; Are the same, The organic electroluminescent element characterized by the above-mentioned. An organic electroluminescence element having a plurality of light emitting units between opposing electrode layers, and a charge generation layer formed between the adjacent light emitting units,
The charge generation layer has an electron generation layer made of an inorganic semiconductor material having electron injection properties and a hole generation layer made of an inorganic semiconductor material having hole injection properties,
The inorganic semiconductor material having an electron injecting property contains a host material and an electron donating dopant, and the inorganic semiconductor material having the hole injecting property contains an electron accepting material,
The charge generating layer is between the electron-generating layer and the hole generating layer, and further have the intervening layer of inorganic semiconductor material having electron injecting property and a hole injecting property,
The organic electroluminescent element , wherein the host material contained in the inorganic semiconductor material constituting the electron generating layer and the inorganic semiconductor material constituting the intervening layer are the same . An organic electroluminescence element having a plurality of light emitting units between opposing electrode layers, and a charge generation layer formed between the adjacent light emitting units,
The charge generation layer has an electron generation layer made of an inorganic semiconductor material having electron injection properties and a hole generation layer made of an inorganic semiconductor material having hole injection properties,
The inorganic semiconductor material having electron injecting property contains an electron donating material, the inorganic semiconductor material having hole injecting property contains a host material and an electron accepting dopant,
The charge generating layer is between the electron-generating layer and the hole generating layer, and further have the intervening layer of inorganic semiconductor material having electron injecting property and a hole injecting property,
The organic electroluminescence element , wherein the host material contained in the inorganic semiconductor material constituting the hole generating layer and the inorganic semiconductor material constituting the intervening layer are the same .   3. The organic electroluminescence device according to claim 1, wherein the electron donating dopant is at least one selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals.   4. The organic electroluminescence device according to claim 3, wherein the electron donating material is at least one selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals.   The organic electroluminescence device according to claim 1, wherein the charge generation layer is a vapor deposition film.   The organic electroluminescent element according to any one of claims 1 to 6, wherein at least one of the layers constituting the light emitting unit is a coating film.

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