JPH0541283A - Organic el element - Google Patents

Abstract

PURPOSE:To enhance light emitting efficiency as well as to enable light having desired wave length to be emitted by interposing an insulating thin film which is larger in band gap than each organic film, between a first and a second organic film. CONSTITUTION:When voltage is so applied that a second electrode 2 is positive, electrons are implanted into a first organic film 5 from a first electrode 6, so that positive holes are implanted into a second organic film 3 from the electrode 2. An electrical double layer is thereby formed out of the electrons and the positive holes across an insulating thin film 5. When the carrier density of the electrical double layer is made high with voltage further increased, electrons are implanted to the organic film 3 through the thin film 4 by means of tunnel effect so as to be combined with the positive holes within the organic film 3 again so as to be luminous. In addition, the positive holes are implanted into an organic film 5 through the thin film 4 by means of tunnel effect so as to be combined with the electrons within the organic film 5 again while being luminous. By this constitution, An EL element is provided, which functions ideally, is high in light emitting efficiency, and also enables light having desired wave length to be emitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic EL device capable of emitting light with high efficiency.

[0002]

2. Description of the Related Art In recent years, research and development of organic electroluminescent devices (organic EL devices) used as display devices, lighting devices, etc. have been actively conducted. For example, Shogo Saito of Kyushu University reports an EL device having an organic two-layer structure using a metal electrode / aromatic dye / polythiophene / transparent electrode (J.
J. Appl. Phys. , 25, L773, 198
6). However, in this element, the film thickness of the organic film is 1 μm or more, and the applied voltage is as high as 100 V or more. On the other hand, Kodak C.I. W. Tang et al.
It was reported that an element having an organic two-layer structure of Alq ₃ / diamine / ITO and having an organic film thickness of 100 nm or less, driven at an applied voltage of 10 V or less, and having practically sufficient brightness was obtained. (APL.51, 91
3, 1987). These EL elements have an organic two-layer structure in which an electron injecting dye and a hole injecting dye are combined, the organic film is made as thin as possible, and a metal electrode on the electron injecting side having a small work function is selected. The main feature is that a material that does not cause an electrical defect when an organic film is formed by a vacuum deposition method or a sublimation method is selected. Furthermore, Shogo Saito of Kyushu University proposed a device having an organic three-layer structure of an electron injection layer / a light emitting layer / a hole injection layer, and by selecting a dye showing a high photoluminescence as a light emitting layer, high brightness light emission was obtained. (J. J. Appl. Phys., 27, L269, 1
988).

Others Up to now, a certain amount of light emission is observed by mixing a light emitting agent and a hole injecting agent even in the case of an EL device structure formed by combining various organic films, and even a single-layer organic film. Research on the deterioration of the characteristics of the body Alq ₃ has been reported, and many patent applications have been filed.

By the way, in order to construct a full-color display using EL elements, red, green, and blue (RGB) EL elements, which are the three elements of light, are required. Of these, it is well known that blue light emission is particularly difficult to realize. This is because blue light has a wavelength of 460n
m is high energy emission of 2.7 eV in energy, it is very susceptible to impurities in the EL element, emission efficiency is low, and indirect emission from the impurity level (long wavelength emission) is prioritized. This is because it easily happens. As described above, there are various difficulties in realizing a practical EL element.

The present inventors have already proposed conditions for obtaining an organic EL device that exhibits desired characteristics such as highly efficient light emission (Japanese Patent Application No. 25101/1990). Since the organic film can be regarded as a kind of semiconductor, in the device in which the organic films are laminated, the device characteristics are governed by the electrical characteristics at the bonding surface of each layer. That is, the work function of the metal electrode,
Considering the energy level of the organic film, what relationship these have at each junction becomes important. In order to obtain highly efficient light emission in an organic EL device having an organic film having a two-layer structure, the following conditions must be satisfied:
It is preferable that the organic film and the second organic film form a barrier junction.

Here, the work functions of the first and second electrodes are E _M1 and E _M2 , respectively, and the energy difference from the vacuum level at the lower end of the conduction band of the first organic film (hereinafter, simply referred to as the conduction band level). E), the energy difference from the vacuum level at the Fermi level (hereinafter simply referred to as the Fermi level) and the energy difference from the vacuum level at the upper end of the valence band (hereinafter simply referred to as the valence band level). _{Let C1} , E ₁ and E _V1 and the conduction band level, Fermi level and valence band level of the second organic film be E _C2 , E ₂ and E _V2 respectively, then E _M1 <E ₁ (1) E ₂ <E _M2 (2) E _C1 > E _C2 (3) E _V1 > E _V2 (4) The material is selected so as to satisfy.

FIG. 5 shows a band diagram in which each layer of the organic EL element satisfying such conditions is independent. FIG. 6 shows a band diagram in a state where the respective layers of this organic EL element are joined. In this element, the first and second
Barriers against electrons and holes are formed at the junction interface of the organic film. The operation of this organic EL element is shown in FIG.
A description will be given with reference to (a) and (b). FIG. 7A is a band diagram showing a state when a bias voltage is applied to this element so that the second electrode becomes positive. At this time the first
Electrons are injected from the electrode to the first organic film (conditional expression 1), and holes are injected from the second electrode to the second organic film (conditional expression 2). As a result, an electric double layer is formed at the bonding interface between the first and second organic films. As shown in FIG. 7B, when the voltage is further increased to increase the carrier density of the electric double layer, the electrons of the first organic film are tunnel-injected into the second organic film, and the second organic film is injected. Recombine within the luminescence. Alternatively, holes in the second organic film are tunnel-injected into the first organic film and are radiatively recombined in the first organic film.

As described above, if the electrical bonding conditions at the interface between the first organic film and the second organic film and the structural conditions of the thin film are satisfied, highly efficient light emission can be obtained and a predetermined value can be obtained. It is considered that blue light emission can be easily realized by forming an organic film using a molecule having a band gap of.
However, in an actual device, it is not always easy to form the above-mentioned ideal bonding interface. Hereinafter, what kind of problem occurs in an actual device will be described.

Consider a case where the first organic film is vapor-deposited on the second organic film. Inside the vapor deposition apparatus, the molecules of the first organic film collide with the surface of the second organic film at high speed, and the constituent molecules of the first organic film diffuse into the second organic film. The diffusion depth may reach several tens of nm. As a result,
The following various problems occur.

First, when the diffusion concentration of the constituent molecules of the first organic film into the second organic film is relatively low, FIG.
As shown in, an energy level is formed in the second organic film by the constituent molecules of the first organic film. In this case,
As shown in (b), it is similar to an ideal operation that electrons and holes are accumulated at the junction interface between the first organic film and the second organic film, an electric double layer is formed, and tunnel injection occurs. is there.
However, the electrons tunnel-injected into the conduction band of the second organic film go through two recombination paths. One of them is a path for recombining directly with holes in the valence band injected from the second electrode, as in the ideal operation. In this route,
Light emission of a short wavelength corresponding to the band gap of the second organic film can be obtained. The other is an indirect recombination path in which electrons injected into the conduction band transit to the level formed by diffusion of the first organic film and then recombine with holes in the valence band. This route gives longer wavelength emission than direct recombination. The resulting emission is a mixture of two types of emission. This indirect light emission can be used when white light emission is achieved by mixing two or more kinds of wavelengths, but this is an obstacle to obtaining pure blue light emission.

Next, when the diffusion concentration of the constituent molecules of the first organic film into the second organic film is relatively high, FIG.
As shown in FIG. 5, the structure of the second organic film is disturbed by the collision of the molecules, and the intermediate layer in which the molecules forming the second organic film and the molecules forming the first organic film are mixed at the same concentration Is formed. In this intermediate layer, the density of energy levels due to the constituent molecules of each organic film is high. In this case,
As shown in (b), the electrons injected from the first electrode into the first organic film move to the energy level of the intermediate layer before being accumulated at the bonding interface, and the electrons are injected into the second organic film side. Is injected into the
It recombines with the holes in the valence band injected from the second electrode. At this time, all are indirect recombination, and only long-wavelength light emission can be obtained.

Further, even if there is no diffusion of molecules at the time of stacking the organic films, if the conduction band of the first organic film and the valence band of the second organic film are close to each other, the first organic film is formed. There is a possibility that electrons and holes accumulated at the junction interface between the film and the second organic film may be recombined indirectly through the junction interface. The emission wavelength at this time corresponds to the energy difference between the conduction band of the first organic film and the valence band of the second organic film.

As described above, various factors affect the electrical bonding conditions at the interface and the structural conditions of the thin film, so that it is difficult to fabricate an organic EL device that operates ideally.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an organic EL element which operates ideally, has high luminous efficiency, and can emit light of a desired wavelength.

[0015]

Means and Actions for Solving the Problems Organic EL of the Present Invention
The element includes first and second electrodes facing each other, a first organic film provided in contact with the first electrode, and a second organic film provided in contact with the second electrode. And the first,
When a positive bias is applied between the second electrodes on the side of the second electrode, electrons and holes are injected into the first and second organic films from the first and second electrodes, respectively. The electrons injected into the first organic film are tunnel-injected into the second organic film and radiatively recombine in the second organic film, or the holes injected into the second organic film are converted into the holes. In the organic EL element which is tunnel-injected into the first organic film and recombines by luminescence in the first organic film, between the first and second organic films,
It is characterized in that an insulating thin film having a larger band gap than the first and second organic films is provided.

FIG. 1 is a sectional view of an organic EL device according to the present invention. This element comprises a glass substrate 1, a second electrode 2,
Second organic film 3, insulating thin film 4, first organic film 5, first
The electrode 6 has a structure in which the electrodes 6 are sequentially formed.

In the organic EL device of the present invention, the work functions of the first and second electrodes are E _M1 and E _M2 , respectively, and the band gap of the first organic film is E _g1 , the conduction band level, the Fermi level and the valence. The electron band levels are E _C1 , E ₁ and E _V1 , the band gap of the second organic film is E _g2 , the conduction band level, the Fermi level and the valence band level are E _C2 , E ₂ and E _V2 , respectively, and the insulating property. If the band gap of the thin film is E _g3 , and the valence band level, Fermi level, and conduction band level are E _V3 , E ₃ , and E _C3 , respectively, then E _M1 <E ₁ … (1) E ₂ <E _M2 … (2) E _C1 > E _C2 (3) E _V1 > E _V2 (4) E _C1 > E _C3 (5) E _C2 > E _C3 (6) E _V3 > E _V1 (7) E _V3 > E _V2 The material is selected so as to satisfy (8).

More specifically, in the formulas (1) and (2), E _M1 -E _C1 and E _V2 -E _M2 are 1 eV or less,
It preferably means 0.5 to 0.3 eV or less. Further, in the expressions (3) and (4), E _C1 −E
_C2 and E _V1- E _V2 are 0.5 eV or more, and further 1 eV
The above is preferable. Further, if the formulas (5) to (8) are satisfied, E _g3 > E _g1 and E _g3 > E _g2 are inevitably obtained, and the band gap of the insulating thin film is the band of either the first organic film or the second organic film. It will be larger than the gap.

FIG. 2 shows a band diagram in which each layer constituting the organic EL device according to the present invention is independent. FIG. 3 shows a band diagram in the state where these respective layers are joined.
The operating principle of this organic EL element is shown in FIGS. 4 (a) and 4 (b).
Will be described. As shown in FIG. 4A, when the bias voltage is applied so that the second electrode becomes positive,
Electrons are injected from the electrode to the first organic film, and holes are injected from the second electrode to the second organic film. Since there are barriers at the interface between the first organic film and the insulating thin film and the interface between the second organic film and the insulating thin film, the injected electrons are at the former interface and the injected holes are at the latter. Accumulates at the interface. Therefore, the electrons and the holes separate the insulating thin film and generate electricity.
A multilayer is formed. A strong electric field is induced in this electric double layer, and electrons and holes are easily tunnel-injected. As shown in FIG. 4B, when the voltage is further increased and the carrier density of the electric double layer is increased, electrons are tunnel-injected into the second organic film through the insulating thin film, and the electrons in the second organic film The holes are radiatively recombined with each other, or the holes are tunnel-injected into the first organic film through the insulating thin film and radiatively recombined with the electrons in the first organic film.

In the organic EL device of the present invention, since the insulating thin film is provided between the first organic film and the second organic film, when the upper organic film is formed by vapor deposition, its constituent molecules are formed. Can be prevented from diffusing into the lower organic film. Therefore, an energy level due to the constituent molecules of the upper organic film is not formed in the lower organic film, and long-wavelength light emission due to the formation of such an energy level is prevented. Furthermore, since the electrons and holes are accumulated through the insulating thin film as described above, there is no risk of these electrons and holes being recombined indirectly through the junction interface, and only by the direct transition light emission as described above. It is possible to realize the ideal operation. Therefore, it is possible to increase the light emission efficiency, and it is also easy to realize a desired light emission wavelength, for example, blue light emission, by using the organic molecule having a predetermined band gap.

In the present invention, the thickness of the insulating thin film is preferably as thin as possible in order to efficiently cause tunnel injection of carriers, and is preferably 10 nm or less, preferably 2.5 n.
m or less, and more preferably about 1 nm. On the contrary, the lower limit of the film thickness of the insulating thin film is not particularly limited, and a monomolecular film having a film thickness of about 0.5 nm may be used as long as a uniform film can be formed. The material forming the insulating thin film is required to have high thermal and mechanical resistance so as not to be damaged when forming the organic film on the upper side, and therefore it is preferable to use an organic polymer compound. The method of manufacturing this insulating thin film is
The method is not particularly limited as long as it is a method capable of forming a thin and uniform thin film, and for example, the Langmuir-Blodgett method, the vapor deposition method and the like are used. In the vapor deposition method, a polymer compound may be directly vapor deposited, or a vapor deposition polymerization method in which a monomer is vapor deposited and reacted on a substrate to obtain a polymer thin film.

In the organic EL device of the present invention,
In selecting a material that satisfies the expressions (1) to (8), it is necessary to use a method of measuring the magnitude relationship of energy levels at each joint surface. For this, the displacement current method as described below may be used.

10 (a) and 10 (b) show a sectional view of an element used in the displacement current method and a waveform diagram of an applied voltage, respectively. That is, this displacement current method forms an element composed of the metal electrode 11 / silicon 12 / silicon oxide film 13 / organic film 14 / metal electrode 15, applies a triangular wave voltage to this element, and changes the displacement current of the element at that time. Is measured. Now, assuming that the capacitance of the element is C, the displacement current is I = C · dV / dt

It is represented by Considering the case where the organic film 14 is not provided in the above-mentioned device structure, the device is generally known as M
It becomes an OS element, and its capacity is determined by the silicon oxide film 13. On the other hand, when the organic film 14 is provided,
The following displacement current is observed depending on the magnitude relationship between the Fermi level of the organic film 14 and the work function of the metal electrode 15.
The work function of the metal electrode 15 is E _M , the conduction band level of the organic film 14 is E _C , and the valence band level is E _V. (A) When the work function of the metal electrode 15 and the Fermi level of the organic film 14 are substantially equal.

In this case, the junction between the metal electrode 15 and the organic film 14 has a high barrier against both electrons and holes. Since the organic film 14 can be regarded as an insulating film, the device capacitance becomes a serial capacitance of the silicon oxide film 13 and the organic film 14, and shows a constant value smaller than that of the MOS device. Therefore, the displacement current when the triangular wave voltage is applied is shown in FIG.
As shown in, it shows a constant small value regardless of the voltage. (B) The work function of the metal electrode 15 is smaller than the Fermi level of the organic film 14.

In this case, the metal electrode 15 and the organic film 14 form a junction in which electrons are easily injected from the metal electrode 15 to the organic film 14. Therefore, when the triangular wave voltage is applied and the metal electrode 15 side becomes negative, the metal electrode 1
Electrons are injected from 5 into the organic film 14, and the electrons are accumulated at the interface between the organic film 14 and the silicon oxide film 13. In this state, the element capacitance has a value determined by the silicon oxide film 13, and the displacement current increases to the level of the MOS element. On the other hand, when the side of the metal electrode 15 becomes positive, the electrons in the organic film 14 flow away to the metal electrode 15, and the displacement current decreases to a value as small as when the organic film 14 can be regarded as an insulator. At this time, _assuming that the voltage at which the above-mentioned electron injection starts is V _th1 and the flat band potential is V _FB as shown in FIG. 12, the voltage V applied to the organic film is
_{th, org} is V _{th, org} = V _th1 [C _ox / (C _ox + C _org )] (V _th1 −V _FB ) (where C _org is the capacitance of the organic film 14 and C _ox is the silicon oxide film 13). capacity.)

[0027] Here, the V _{th, org} is approximately equivalent metal electrode 15 to the barrier height for electron injection into the organic film 14 (E _M -E _C). Therefore, E _M
If is known, E _C can be obtained by measuring V _th1 and V _FB . Further, if E _C is obtained, E _V can also be obtained by measuring the band gap of the organic film 14 by optical measurement. (C) When the work function of the metal electrode 15 is higher than the Fermi level of the organic film 14.

In this case, the metal electrode 15 and the organic film 14 form a junction in which holes are easily injected from the metal electrode 15 to the organic film 14. Therefore, when the triangular wave voltage is applied and the metal electrode 15 side becomes positive, the metal electrode 1
Holes are injected from 5 to the organic film 14, and the holes are accumulated at the interface between the organic film 14 and the silicon oxide film 13. In this state, the element capacitance has a value determined by the silicon oxide film 13, and the displacement current increases to the level of the MOS element as shown in FIG. On the other hand, when the side of the metal electrode 15 becomes negative, the holes in the organic film 14 flow away to the metal electrode 15, and the displacement current decreases to a value as small as when the organic film 14 can be regarded as an insulator. Further, at this time, E _V can be obtained by measuring the voltages V _th2 and V _{FB at} which the injection of holes starts, and E _C can be obtained by further measuring the band gap of the organic film 14. ..

When the organic film 14 has a very wide band gap, the metal electrode 15 and the organic film 14 are bonded to each other regardless of the work function of the metal electrode 15 and the Fermi level of the organic film 14. Is a junction having a high barrier against both electrons and holes. In this case, even if a metal having a small E _M such as Mg (E _M is about 3.0 eV) is used as the metal electrode 15, a metal having a large E _M , such as Au, is used.
Even when (E _M is about 5.0 eV) is used, the organic film can be regarded as an insulating film, so that the displacement current when a triangular wave voltage is applied shows a constant small value. Therefore, regardless of the work function of the metal electrode 15, the organic film 14 that can always obtain such a displacement current has a wide band gap and can be applied as an insulating thin film in the device structure of the present invention.

The above is the relationship between the metal electrode and the organic film, but if the same measurement is performed with the organic film portion of the element structure described above as a laminated structure of the organic film and the insulating thin film, the conduction of the two is conducted. The relationship between the band level, the Fermi level, and the valence band level becomes clear.

[0031]

Embodiments of the present invention will be described below with reference to the drawings. Example 1

As shown in FIG. 1, the organic EL element in this embodiment has a second electrode 2 made of an ITO film on a glass substrate 1, a second organic film 3 made of S144 shown in Chemical formula 1, and a chemical formula 2. The insulating thin film 4 made of polyisobutylmethacrylate shown in FIG. 1, the first organic film 5 made of DNIBPO shown in Chemical formula 3, and the first electrode 6 made of samarium (Sm) are sequentially formed. ..

This organic EL device was produced as follows. First, the glass substrate 1 is sputtered to form a second
Sheet resistance of 10 Ω / cm ² as the electrode 2 of The ITO film of was formed. Furthermore, the degree of vacuum is about 10 ^-6 T by the vacuum sublimation method.
Sublimate S144 by orr to obtain a second film with a thickness of 100 nm.
The organic film 3 of was formed. Next, polyisobutyl methacrylate (PIBM) having a molecular weight of 100,000 was dissolved in toluene, spread on the water surface of the LB trough, and compressed by a movable barrier until the surface pressure became 12 dyn / cm. After that, the substrate on which the second organic film was formed was attached to the accumulator, and 5 mm / m was formed so as to vertically cross the monomolecular film on the water surface.
The substrate was submerged at a rate of in, and then the substrate was lifted from the water to the surface of the water at the same rate and taken out. By this operation, two PIBM monomolecular films were accumulated to form the insulating thin film 4. The film thickness of this insulating thin film 4 was 2.2 nm. Subsequently, after the substrate was sufficiently dried, DNIBPO was sublimated on the insulating thin film 4 by the vacuum sublimation method to form the first organic film 5 having a film thickness of 100 nm. Finally, the S
m was vapor-deposited to form a first electrode 6 having a film thickness of 100 nm. Each layer constituting the organic EL device of the present invention comprises (1) to
It was confirmed by the above-mentioned displacement current method that the relation of the expression (8) was satisfied.

[0034]

[Chemical 1]

[0035]

[Chemical 2]

[0036]

[Chemical 3]

Whether or not the constituent molecules of the first organic film diffuse into the second organic film can be confirmed by the absorption spectrum. The presence or absence of indirect light emission can be confirmed by a photoluminescence (PL) spectrum. These measurements were performed in a state where the transparent electrode, the second organic film, the insulating thin film, and the first organic film were formed on the quartz substrate.

The absorption spectrum can be evaluated as follows. That is, if the constituent molecules of the first organic film are diffused in the second organic film and interact with the constituent molecules of the second organic film in the ground state, the second wavelength is on the long wavelength side of the absorption spectrum.
A new charge transfer absorption based on the electronic transition from the constituent molecule of the organic film to the constituent molecule of the first organic film appears.

The PL spectrum can be evaluated as follows. That is, when the device as designed is manufactured, the second organic film is excited by light irradiation to generate an electron-hole pair (exciton), and the exciton corresponds to the band gap of the S144 film by direct transition. Wavelength 4
Emission of 70 nm occurs. However, when the constituent molecules of the first organic film diffuse into the second organic film to form the indirect light emission level, the exciton electrons once transit to the indirect level and then become holes. Because of recombination, indirect light emission occurs. The emission wavelength at this time corresponds to the energy difference between the conduction band of the first organic film and the valence band of the second organic film.

Regarding the device of this example, no charge transfer absorption was observed in the absorption spectrum, and only the light emission based on the direct transition was observed and the indirect light emission was not observed in the PL spectrum. From these results, in the device of this example,
It can be seen that the constituent molecules of the first organic film do not diffuse into the second organic film.

Further, regarding the element of this embodiment, an EL element
The ITO electrode becomes positive in order to evaluate the operation as
If a bias voltage is applied, the voltage will be 50mA / c at 20V.
m² Current flows, emission wavelength 470 nm, brightness 1000
cd / cm² The electric field emission of
It was

As a comparative example, an organic EL element having the same structure as that of the example except that the insulating thin film was not formed was prepared. In the case of this element, the PL spectrum shows a wavelength 470 corresponding to the band gap of the S144 film due to direct transition.
Along with the emission of nm, strong indirect emission of wavelength 600 nm was observed on the long wavelength side. From this measurement result, it is estimated that the constituent molecules of the first organic film are diffused into the second organic film when the first organic film is formed on the second organic film by vapor deposition. Further, when the operation as an EL element was evaluated under the same conditions as in the example, no electroluminescence at 470 nm was observed, only electroluminescence corresponding to indirect emission at 600 nm was observed, and blue emission could not be realized. Example 2

Instead of using the PIBM film as the insulating thin film, the substrate temperature was set to −100 ° C., and the insulating thin film was formed by directly heating and sublimating polyisopropylene in vacuum. Organic E as in 1
An L element was produced. The thickness of the insulating thin film is 4 nm,
It was composed of a polymer having an average molecular weight of 5000.

When a bias voltage was applied to the obtained device so that the ITO electrode was positive, 50 mA / cm at 50V.
² Current flows, emission wavelength 470 nm, brightness 1000c
d / cm ² It was possible to obtain blue light emission.

[0045]

As described above in detail, according to the present invention, it is possible to provide an organic EL element that operates ideally, has high luminous efficiency, and can emit light of a desired wavelength.

[Brief description of drawings]

FIG. 1 is a sectional view of an organic EL element according to the present invention.

FIG. 2 is a band diagram in which each layer constituting the organic EL element according to the present invention is independent.

FIG. 3 is a band diagram showing a state in which layers constituting an organic EL element according to the present invention are joined.

4 (a) and 4 (b) are band diagrams explaining the operation principle of the organic EL element according to the present invention.

FIG. 5 is a band diagram in which each layer constituting the conventional organic EL element is independent.

FIG. 6 is a band diagram showing a state in which layers constituting a conventional organic EL element are joined.

7 (a) and 7 (b) are band diagrams explaining an ideal operation principle of a conventional organic EL element.

8 (a) and 8 (b) are band diagrams for explaining the operation principle when the constituent molecules of the first organic film are diffused into the second organic film at a low concentration in the conventional organic EL device.

9 (a) and 9 (b) are band diagrams for explaining the operation principle when the constituent molecules of the first organic film are diffused into the second organic film at a high concentration in the conventional organic EL device.

10A is a sectional view of an element used in the displacement current method, and FIG. 10B is a waveform diagram of a voltage applied by the displacement current method.

FIG. 11 is a diagram showing a displacement current when a triangular wave voltage is applied when the work function of the metal electrode and the Fermi level of the organic film are substantially equal.

FIG. 12 is a diagram showing a displacement current when a triangular wave voltage is applied when the work function of the metal electrode is smaller than the Fermi level of the organic film.

FIG. 13 is a diagram showing a displacement current when a triangular wave voltage is applied when the work function of the metal electrode is larger than the Fermi level of the organic film.

[Explanation of symbols]

1 ... glass substrate, 2 ... second electrode, 3 ... second organic film,
4 ... Insulating thin film, 5 ... 1st organic film, 6 ... 1st electrode.

Claims (1)

[Claims] 1. A first and a second electrode facing each other, a first organic film provided in contact with the first electrode, and the second electrode.
A second organic film provided in contact with the first electrode, and when a positive bias is applied to the second electrode side between the first and second electrodes, the first and second electrodes are formed. From the electrode to the first and second
Electrons and holes are respectively injected into the organic film, and the electrons injected into the first organic film are tunnel-injected into the second organic film to recombine radiatively in the second organic film, or In the organic EL device in which the holes injected into the second organic film are tunnel-injected into the first organic film to recombine in the first organic film by light emission, An organic EL device characterized in that an insulating thin film having a band gap larger than those of the first and second organic films is provided therebetween.