JPH03230584A - Organic-film light emitting element - Google Patents

Abstract

PURPOSE:To make one picture element emit rays of light of multiple colors by allowing electrons to be tunnel-injected into the second organic film and holes to be tunnel-injected into the first organic film to respectively make light emitting recombination. CONSTITUTION:This organic-film light emitting element is constituted of the first electrode (M1) 5, first organic film (O1) 4, second organic film (O2) 3, and second electrode (M2) 2 in the descending order. The second electrode 2 is a transparent electrode of ITO, etc., formed on, for example, a glass substrate 1 and light is taken out from the substrate 1 side. Barriers to electrodes and holes are formed at the joining boundary of the films 4 and 3 and, when a bias voltage which makes the electrode 2 positive is applied across the electrodes 5 and 2, electrons are injected into the first organic film 4 from the first electrode 5 and holes are injected into the second organic film 3 from the second electrode 2. Thus the electrons and holes are tunnel-injected into the organic films and make light emitting recombination in the organic films, resulting in the light emission of a wavelength determined by the first organic film and the light emission of another wavelength determined by the second organic film.

Description

Detailed Description of the Invention [Purpose of the Invention (Industrial Field of Application) The present invention relates to a light emitting device using an organic film, and in particular to a light emitting device that uses a combination of two or more six film layers to emit multicolor light per pixel. This invention relates to an organic film light emitting device that has been made possible.

(Prior Art) In recent years, research and development of organic film light emitting elements used as display elements, lighting elements, etc. has been actively conducted. For example, Shogo Saito of Bonyo University reported in 1986 an organic two-layer structure device using a metal electrode/aromatic dye/polythiophene/transparent electrode (J, J, Appl, Ph.
ys, 25. L773, 1988), here:
The thickness of the 6-layer membrane is 1 μm or more, and the applied voltage is as high as 100V. On the other hand, Kodak's C, W, Tang
etc. are Mg-Ag/AIq3/diamine/ITO
It has been reported that by reducing the thickness of the organic film to 1000 Å or less with the organic two-layer structure, an element that can be driven with an applied voltage of 10 V or less and exhibits sufficient brightness for practical use has been obtained (A P L .

51.913.1987). These light-emitting devices are based on an organic two-layer structure made by combining a hole-injecting dye and a hole-injecting dye. The main features include selecting a metal electrode with a small work function, and selecting a material that will not cause electrical defects when forming an organic film by vacuum evaporation or sublimation. Furthermore, in 1988, Shoto Saito of Bonyo University proposed an organic three-layer structure element consisting of a hole injection layer/emissive layer/hole injection layer, and by selecting a dye showing high photoluminescence for the emissive layer. It was shown that high-intensity luminescence could be obtained (J,
J. Appl. Phys., 27. L269
．． 198g).

Other research has been done so far, including the structure of a light-emitting device by combining various organic films, the fact that even a single-layer organic film can emit light to some extent by mixing a luminescent agent and a hole-injecting agent, and Studies on the deterioration of the characteristics of A iq3, which is a chemical compound, have been reported one after another, and many similar patent applications have been filed.

(Problems to be Solved by the Invention) Organic film light emitting devices have almost reached the practical stage in terms of luminance, but there are still many technical unresolved problems in terms of luminous efficiency, device lifespan, and device fabrication process. At present, the luminous efficiency is usually about 0.1% at best. Low luminous efficiency means that a current that does not contribute to luminescence flows between the electrodes, and this current generates Joule heat, which is a major cause of shortening the device life. Therefore, in order to put organic film light emitting devices into practical use, it is desirable to increase the luminous efficiency from at least a few percent to 10% or more.

In order to increase luminous efficiency, it is necessary to optimize the device structure and the electrical properties of the materials used. So far, the properties of organic materials have only been qualitatively defined, such as electron (hole) transport, electron (hole) injection, and luminescent properties. I can't say that.

The present invention combines a laminated structure of multiple organic films and metal electrodes, and by strictly defining the electrical properties of each of these materials, the present invention is a white-organic light emitting device that enables multicolor light emission per pixel. The purpose is to provide an element.

[Structure of the Invention (Means for Solving the Problems) Organic films can be regarded as a type of semiconductor, so in an element in which organic films are stacked, the electrical characteristics at the bonding surfaces of each layer govern the element characteristics. In other words, when considering the work function of the metal electrode and the conduction band level of the organic film, it is important to consider the relationship between the energy levels at each junction surface. Become. From this perspective, the present invention proposes a single pixel multicolor light emitting device structure using a semiconductor model.

That is, the light emitting device according to the present invention has a laminated structure of a first organic film and a second organic film that constitute a first layer for electrons and holes, and a first ladle with this laminated structure in between. Basically, the first electrode for hole injection is provided on the conductive film side, and the second electrode for hole injection is provided on the second organic film side.

The first light emitting element of the present invention has the above-mentioned basic structure. When a positive bias is applied to the second organic film and the node 2 electrode side, electrons are injected from the first electrode into the first organic film and electrons are injected from the second 7111S pole into the second organic film. The holes are tunnel-injected into the second organic film, and the electrons injected into the first interface and the electrons into the second interface are tunnel-injected into the second organic film and recombined in the second organic film. , utilizes the fact that holes are tunnel-injected into the first organic film and recombined in light emission within the first organic film.

Specifically, 1. The work function of the second electrode is E
11, Ek+2, the energy difference from the vacuum level at the lower end of the conduction band of the first organic film (hereinafter this is referred to as the conduction band level at tB), and the energy difference from the vacuum level at the Fermi level (hereinafter simply referred to as tB). The energy difference from the vacuum level at the upper end of the valence band (hereinafter simply referred to as the valence band level) is EC1, respectively.
+ "" l and EVI, and the conduction band level of the second 9-organic film and the conduction band level of the third organic film of Fermile are respectively Ec1, E2 . When E2 and E y2, EMI<E+
... (1) E2<EM2 ・
...(2) ECI>EC2... (3) E v+> E V2
- Monthly charges are selected to satisfy (4). More specifically, equations (1) and (2) are EMI E
This means that CI and EVI/EV7 are 1 eV or less, preferably 0.5 to 0.3 eV or less, and (
Equations 3) and (4) are ECI EC2 and EV
, -EV2 is preferably 0.5 eV or more, for example 1 eV
The above shall apply.

In order to be able to control the emitted light color by the bias i pressure, Ec+-IECI< EVI EV2
(5) Or, Ec+-ECI> EVI EV2 (6
) is selected.

Further, the second light-emitting element of the present invention has a third eleventh layer between the second organic film and the second electrode in addition to the above-mentioned basic structure.
Interpose a membrane. And the first. Apply a positive bias to the second organic film and node 2 electrode side! When the organic membrane is exposed, electrons are injected from the first electrode into the first organic film and 71 electrons are injected from the second electrode into the second organic film through the third organic film. Holes or electrons injected into the first interface and the second
At the interface of electrons and holes, electrons are tunnel-injected into the second organic film at the first threshold and recombined in the second organic film. It is injected into the organic film and recombined radiatively within the third organic film.

Specifically, in order to make such multicolor light emission possible, in addition to the relationship between the electrical characteristics of each material in the first light emitting element,
The conduction band level of the third organic film and the Fermile conduction band level of the third organic film are EC3, Ej and EV, respectively.
, then E(l EC2< EVI EV2
° (7) EC2<EC3・ (8) E V2′++E V3 − (
9) EV2<EJ... (
The material is selected to satisfy lO).

Further, in the third light emitting element of the present invention, in the basic structure described above, a third organic film is interposed between the first organic films on the first electrode side. And the first. When a positive bias is applied to the second organic film and the electrode side of node 2, the electrons injected from the first electrode into the first AJ′ machine 11φ via the third organic film and the second Holes injected from the electrode into the second autoisotropic film, electrons injected into the first interface, electrons into the second interface, holes among the holes or the first at the first threshold. is tunnel-injected into the organic film and recombined in the first organic film, and further injected into the third organic film at the second threshold to emit light into the third organic film.
-1- Emission IIf is combined within Isogami.

In order to make such multicolor light emission possible, specifically, in addition to the relationship between the electrical characteristics of each material of the first optical element,
The conduction band level of the third organic film is EC, E, and EV.
3, 1:(l EC, > EVI EV
2-(If)Ect-Ex
−(12) E VJ< E v+
−(13) Ekll<EJ
...(14)! Materials are selected so as to

(Function) In the basic structure of the organic film light emitting device according to the present invention, first. A barrier for one electron and a barrier for holes are formed at the bonding interface of the second organic film (conditional expressions (3), (4)
) ). Furthermore, when a bias that makes the second electrode positive is applied, electrons are injected from the first electrode into the first organic film (conditional expression (1)), and electrons are injected from the second electrode into the second organic film. Holes are injected (conditional expression (2)). As a result, 1. Second
An electric double layer is formed at the first interface between the organic films.

Therefore, in the first light-emitting element, when the Asumi pressure exceeds a certain threshold, the electrons in the first organic film are transferred to the second organic film.
is tunnel-injected into the second organic film and recombined radiatively within the second organic film. Also, if you cross a certain threshold,
Holes in the second organic film are tunnel-injected into the first organic film and recombined radiatively within the first organic film. In this way, light emission with a wavelength determined by the first organic film and light emission with a wavelength determined by the second organic film can be obtained. When conditional expression (5) is satisfied (yo,
When the tunnel injection of electrons from the first organic film to the second organic film becomes dominant, and therefore the electron beam pressure is exceeded, the emission re-emission in the second organic film occurs at the first threshold value. Luminescence due to binding is observed, and at the second threshold, the first and second
One light emission from the organic film was observed at the same time. Conditional expression (6)
This relationship is reversed when .

In the second light emitting element, the first. For the first between the second organic films, the barrier to electrons is set lower than the barrier to holes (conditional expression (7)).

(8)) Furthermore, the material is selected so that the holes injected from the second electrode into the third organic film flow to the second organic film with almost no hindrance (conditional expression (9)).

(10)). This allows the first . Among the carriers that are first accumulated between the second organic films to form an electric double layer, electrons are tunnel-injected into the second organic film and recombined in light emission in the second organic film. If the thickness of the second organic film is thinner than the mean free path of carriers, as the bias increases further, many electrons will flow to the third organic film and recombine in the third organic film. According to
A multicolor light emitting element whose emission color is controlled by bias is obtained.

In the third light emitting element, the first. For the first layer between the second organic films, the barrier to holes is set lower than the barrier to electrons (conditional expressions (11) and (12)), and the holes injected from the first electrode to the third organic film are The material is selected so that electrons can flow to the second organic film with almost no hindrance (conditional expressions (13>, (14)).As a result,
1st when bias is applied. Among the carriers that are accumulated in the first part between the second organic films to form an electric double layer, holes are tunnel-injected into the first organic film and recombined in light emission in the first organic film. As it rises, many holes flow to the third hexagonal film and are recombined by light emission within the third organic film. As a result, a multicolor light emitting element whose emission color is controlled by bias can be obtained.

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

FIG. 1 shows a cross-sectional structure of a light emitting device according to one embodiment.

This element has a first electrode (M+) of 5° as viewed from above.
Organic film (0+)4. It is composed of a second organic film (02) 3 and a second electrode i (M 2 ') 2. In this embodiment, the second electrode 2 is a transparent electrode made of ITO or the like formed on the glass substrate 1, and light is extracted from the substrate 1 side. A compound semiconductor may be used on the transparent electrode side. The manufacturing process for this element will be explained in detail later, but films are sequentially formed on a substrate by vacuum evaporation, vacuum sublimation, or the like.

FIG. 2 shows a band diagram in a state where each layer constituting this light emitting element is independent. The conduction band level of the first organic film 4 is E C1, the Fermi level is E l r, the valence band level is Ev, the conduction band level of the second organic film 3 is EC2t, and the Fermi level is E.

When the valence band level is set to E, 2, as shown in the figure,
A material satisfying E c+ > E C21E v+ > E V2 is selected. Further, the first electrode 5 has a work function E
MI is E, . second electrode 2
is the work function E1,2 or E,A2>E2, and the second
It is selected in such a manner that it is easy to inject holes into the organic film 3.

FIG. 3 is a band diagram of a light emitting device in which these layers are bonded together in a thermal equilibrium state. In thermal equilibrium, the Fermi levels of the system coincide. Therefore, from the magnitude relationship between the work function of the electrode and each energy level of the organic film shown in FIG. 2, as shown in FIG.
A junction is formed between which electrons can be easily injected from the first electrode 5.

A junction is formed between the second electrode 2 and the second electrode 3 through which holes can easily be injected from the second electrode 2. First organic film 4
and the second organic film 3, ΔEc-E(+
A barrier called EC2 is formed, and ΔEv'=
A barrier Ev+EV2 is formed.

The operating principle of the light emitting device of this example will be explained with reference to FIG. FIG. 4(a) is a band diagram of the device when a positive bias voltage V1 is applied to the second electrode 2 with respect to the first electrode 5. From the first electrode 5, the first organic film 4
Electrons are injected into the second organic film 3 from the second electrode 2.
Holes are injected into the first and second
is accumulated on the first interface of the organic film 3.4. The carriers will form an electric double layer at this interface. Since the thickness of this electric double layer is equal to the intermolecular distance of the dye (approximately 10 layers), a large electric field is generated here as a result. Then, as shown in FIG. 4(b), when the bias voltage exceeds a certain threshold value and reaches v2, carriers forming the electric double layer are tunnel-injected into the adjacent layer through the first layer. The holes injected from the second organic film 3 into the first organic film 4 recombine with electrons, which are majority carriers, within the first organic film 4, thereby emitting light with the first wavelength λ1. It will be done. The electrons injected from the first organic film 4 to the second Ij′ conductive film 3 are
It recombines with holes, which are majority carriers, within the second organic film 3, and thereby light emission of the second wavelength λ2 is obtained.

Which of the first wavelength light emission and the second wavelength light emission is dominant depends on the first. The barrier height ΔEC of the second organic films 4 and 3 to the first electron and the barrier height ΔEv to the hole
determined by the relationship between

Therefore, by selecting the material, ■ the first . A light-emitting element that can simultaneously obtain light of the second wavelength; ■ At the first threshold, only the light of the first wavelength is emitted;
A multicolor light emitting element that obtains multiple light emission at a threshold of
It is possible to obtain any of the following multicolor light emitting elements that obtain multiple light emission at a threshold value of .

Figures 5(a) and 5(b) show Ec+ EC2<EVI
FIG. 3 is a band diagram for explaining the operation of a multicolor light emitting element whose materials are selected to satisfy Ell-1. As is clear from the previous explanation of the principle, electrons are generated by bias voltage V.

Holes are injected and an electric double layer is formed,
When the bias voltage V exceeds the first threshold value v thx, electrons are tunnel-injected from the first organic film into the second organic film, as shown in FIG. The light is recombined and light with a wavelength λ2 is generated. When the bias voltage V is further increased and it exceeds the second threshold value V th2, tunnel injection of holes from the second organic film to the first organic film also begins, as shown in FIG. 5(b). , the emitted light is recombined at the first nail guiding film, and the emitted light with the wavelength λl overlaps.

Figure 6<a) (b) is E c+ E C2>E
FIG. 2 is a diagram for explaining the operation of a multicolor light emitting element whose material is selected to satisfy v+E V2. In this case, contrary to FIG. 5, at the first threshold value v tht, the first
The light emission (wavelength λ1) in the organic film occurs, and the light emission (wavelength λ2) in the second organic film overlaps at the second threshold value V th2. Note that 1. in Figure 6. Second threshold V Lhl
V Lh2, wavelength λ1. λ2 are generally not the same as those in FIG.

In addition, in selecting a material having a magnitude relationship of energy levels at each bonding surface as in the light emitting element of the second embodiment, a method for measuring the magnitude relationship of the energy levels is required. This can be done by using the method discovered by the present invention, which will be described below.

As shown in FIG. 15, metal electrode 11 / silicone electrode 12 /
silicon oxide film 13/organic film 14/metal ni D 15
An element consisting of is formed. A square wave voltage as shown in FIG. 16 is applied to this element, and the displacement current of the element at that time is measured. Now, if the capacitance of the element is C, the displacement current is expressed as 1-C-dV/dt. Considering the device shown in FIG. 15 without the organic film 14, the device becomes a commonly known MOS device, the capacitance of which is determined by the silicon oxide film 13. On the other hand, when the organic film 14 is present, the following displacement current 71'P1 is obtained depending on the magnitude relationship between the Fermi level of the Fa-containing film 14 and the work function of the metal electrode 15.

(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 becomes a junction with a high barrier to both electrons and holes. Therefore, since the organic film 14 can be regarded as an insulator, the device capacitance is the series capacitance of the silicon oxide film and the organic film, and exhibits a constant value smaller than that of the MOS device. As a result, when a triangular wave voltage is applied to the element as shown in FIG. 16, the displacement current exhibits a constant small value as shown in FIG. 17.

(b) When the work function of the metal electrode 15 is smaller than the Fermi level of organic film ] 4 In this case, the junction between the metal electrode 15 and the organic film 14 is a junction where electrons are easily injected from the metal electrode 15 into the organic film 14. form. Therefore, when the diagonal wave voltage shown in FIG. 15 is applied to the device, when the metal electrode 15 side becomes negative, electrons are injected from the metal electrode 5 into the organic film 14, and these electrons are transferred to the interface between the organic film 14 and the oxide film 13. Accumulated. In this state, the element capacitance becomes a value determined by the oxide film 13, and the displacement current increases to the level of the MO3 element, as shown in FIG.

When the applied voltage is positive on the metal electrode]5 side, f-t
``Electrons in the conductive film 4 flow away to the metal electrode] 5, resulting in a displacement 7
This current decreases to a small value when it is an organic film]4 or an insulator.

(C) When the work function of the metal iL electrode]5 is larger than the Fermi level of the +i-mechanical film 14, in this case, the metal electrode 15 and the a-mechanism]4 are connected from the metal electrode 15 to the white conductive film]4. Forms a junction into which holes are easily injected. Therefore, when the triangular wave voltage shown in FIG. 15 is applied to the device, when the metal electrode 15 side becomes positive, holes are injected from the metal electrode 15 into the organic film 14, and these holes are accumulated at the interface between the organic film 14 and the oxide film 13. be done. In this state, the element capacitance becomes a value determined by the oxide film 13, and the displacement current increases to the level of the MO5 element, as shown in FIG.

When the applied voltage has a negative polarity on the metal electrode 15 side, the holes in the organic film 14 flow away to the metal electrode 15, and the displacement current decreases to a small value when the organic film 14 is an insulator.

The above is the relationship between the organic films on the metal electrode side.
．． A similar displacement current 4pj for the laminated structure of the second organic film
Make a decision. As a result, the conduction band level of the two organic films,
The relationship between Fermi level and valence band level becomes clear.

For example, in the device structure shown in FIG. 15, the portion of the organic film 14 in contact with the metal electrode 15 is the first organic film 14 □,
The second organic film is below] 4□. It is assumed that electrons are injected from the metal electrode 15 into the first a-structure 14. This has been investigated using the previously mentioned organic film or single-layer devices. If the displacement current or the metal electrode 15 side is in a negative state, the MOS
If the electrons flow to the device level, the electrons injected into the first organic film 14 are further injected into the second organic film 142. As a result, the second FF conductive film 4
It can be seen that the conduction band level of □ is lower than that of the first organic film 14. If such a displacement current at the MOS element level is not observed, it can be seen that the conduction band level of the second organic film]4□ is higher than that of the first organic film]4.

Regarding the valence band level, the magnitude relationship can also be determined by a similar displacement current 71P+ constant using hole injection.

A more specific example of an a-mode multicolor light emitting device using the device structure shown in FIG. 1 will be described below.

Example 1 In the element of Fig. 1, First electrode 5: Erbium film First organic film 4: Second organic film 3: bipyrenyl Second electrode 2: ITO film was used.

This material system satisfies the conditions shown in Figure 2, and E, 1-E C
It has been confirmed by the displacement current M1 method described above that the condition 2<EVI E V2 is satisfied.

The device fabrication process is as follows. First, a vacuum sublimation method (vacuum degree ~10-
6 Torr), and then 1000 layers of the second organic film were formed on top of it using the vacuum sublimation method.
Finally, 1,000 erbium films are formed by vacuum evaporation.

When a bias that makes the ITO electrode positive is applied to the obtained device, a current of 5 mA at 3 V flows, and the brightness is 500 Cd.
/m2 orange luminescence was observed. This is light emission from the first organic film. When the bias voltage was increased to 15 V, the luminance increased to 200 Cd/m2 and the luminescent color changed to yellow-green. This is the result of color mixing of the blue light emitted by the second E+-membrane.

Example 2 In the element of Fig. 1, First electrode 5: Erbium film 1st 9 machine membrane 4: Second organic film 3: Second electrode 2: IT○ membrane was used.

The device fabrication process and the film thickness of each layer are the same as in Example 1.

A bias voltage was applied to the obtained device so that the ITO electrode became positive, and yellow light emission was observed after 5 seconds. This is the first
This is due to light emission from the organic film 4. Further increase the bias voltage to 15
When V was increased, the luminescent color changed to reddish-orange. This is the second
This is the result of the light emission from mechanism 3 overlapping.

FIG. 1 shows an example of a multicolor light emitting device using two organic films, but based on this, a multicolor light emitting device can be made by further combining a third six-layer film. Such an embodiment will now be described.

FIG. 7 is a sectional view of an organic film multicolor light emitting device of such an embodiment. Unlike FIG. 1, in this embodiment, a third organic film 6 is sandwiched between the second organic film 3 and the second electrode 2.

FIG. 8 shows the work function and other electrical characteristics of each layer of the device shown in FIG. First electrode5. First organic film 4. Second organic film 3. The relationship between the material properties of the second electrode 2 is basically the same as in the embodiment of FIG. However, the first 9
The construction pressure levels of the organic membrane 4 and the second organic membrane 3 are set to the relationship E c+ E C2< E v+ E V2. Regarding the third organic film 6, the second
In relation to the organic film 3 and the second electrode 2, the conduction band level Ecq, the Fermi levels Ec1, E, and the valence band level EV3 are set as follows.

LCI>EC2 El·, ~Ev□E+<E), 12 Therefore, the band diagram in the thermal equilibrium state of the element in which these layers are joined is as shown in FIG. First and second corners -
As in the previous example, a +2't barrier is formed between the structures 4 and 3 for both electrons and holes.

However, the barrier ΔE for electrons on the conduction band side is smaller than the barrier ΔE■ for holes on the valence band side.

The thickness of the second organic film 3 is thinner than the mean free path of carriers, and no barrier is formed against the flow of electrons from the second organic film 3 to the third organic film 6. In addition, holes are easily injected from the second electrode 2 to the third organic film 6, and the holes injected into the third organic film 6 are transferred to the second organic film 3 without any hindrance.
It is designed to be able to flow up to

The operation of multicolor light emission in this light emitting element will be explained using FIG. 10. By applying the same bias as in the previous example, electrons are injected from the first electrode 5 into the first organic film 4, and are injected from the second electrode 2 through the third six-layer organic film 6. Holes are injected into the organic film 3 of the first. second organic film 4,
First, an electric double layer is formed between 3 and 3. When the bias voltage exceeds the first threshold value VthL, FIG. 10(a)
As shown in FIG. 3, electrons are tunnel-injected from the first organic film 4 to the second organic film 3, recombine with holes in the second organic film 3, and emit light. When the bias voltage is further increased to exceed the threshold value V th2, many of the electrons injected from the first organic film 4 to the second organic film 3 recombine, as shown in FIG. 10(b). The third organic film 6 is implanted without being implanted.
It recombines with holes in the organic film 6 and emits light. In other words, under low bias conditions, the second organic film 3 with a wide bandgap
At high bias, short-wavelength light emission from the third organic film 6 having a narrow bandgap is mixed with the short-wavelength light emission from the third organic film 6 having a narrow bandgap. For example, if the second organic film 3 is made of a blue light-emitting agent and the third organic film 6 is made of a yellow light-emitting agent, blue light will be emitted at a low applied voltage, and white light will be emitted at a high applied voltage.

FIG. 11 shows another example of a multicolor light emitting device using a three-layer organic film. In this embodiment, a third organic film 6 is provided between the first electrode 5 and the first organic film 4.

FIG. 12 shows the energy level of each layer before bonding. Concerning the energy levels of the first organic film 4 and the second organic film 3, E CI E c2>
The relationship is set as E yl E V2. Regarding the third organic film 6, the first organic film 4 and the first
With respect to the electrode 2, the conduction band levels Ec1, E3 . The Fermi level E3 and the valence band level EV3 are set as follows.

EC3~ECI E　v、＜　E　V2 E3>E,.

Therefore, the band diagram of an element in which these layers are bonded together in a thermal equilibrium state is as shown in FIG. 13.

As in the previous embodiment, a barrier is formed between the first and second organic films 4 and 3 for both electrons and holes. However, the barrier ΔEC for electrons on the conduction band side is larger than the barrier ΔEv for holes on the valence band side.

The thickness of the second organic film 3 is thinner than the mean free path of carriers, and no barrier is formed against the flow of holes from the second organic film 3 to the third organic film 6. Further, electrons are easily injected from the first electrode 5 to the third organic film 6, and the electrons injected into the third organic film 6 can flow to the second corner structure 3 with almost no hindrance. ing.

FIG. 14 is a band diagram showing the operation of multicolor light emission in this light emitting element. By applying a bias, the 1st degree and the second rJ-
As in the previous embodiment, an electric double layer is formed in the first part between structure 4.3. When the bias voltage exceeds the first threshold value VLhl, the holes in the second organic film 3 are tunnel-injected into the first (-j゛ mechanical film 4) as shown in FIG. When the bias is further increased to exceed the threshold value V th2, many holes are recombined within the third organic film 6 as shown in FIG. 14(b).
The third organic film 6 emits light and recombines. Therefore, this embodiment also allows multicolor light emission in which the color of the emitted light is controlled by the bias. A specific example using the device structure shown in FIGS. 7 and 11 will be described below.

Example 3 In the device shown in FIG. 7, first RF conductive film: bis(dicyano-9-fluorenonyl)ethane second organic film 3 bibyrenyl third organic film 6. Bicoronenyl first electrode 5: erbium second electrode: ITO was used. It has been confirmed by displacement current measurement that this material system satisfies the conditions shown in FIG.

The device fabrication process is similar to that described in the previous example.

When a bias is applied to the obtained device, approximately 5 mA at 5 V
A current of 1000 Cd/m' was passed, and blue light emission with a brightness of 1000 Cd/m' was obtained. This light emission is due to the second organic film 3.

When the bias voltage is increased to 15V, the current is approximately 20mA.
A white-yellow emission with a brightness of 2000 Cd/m2 was obtained. This is because the orange light emitted by the third organic film 6 is mixed with the blue light emitted by the second organic film 3.

Example 4 In the device shown in FIG. 11, first organic film 4 second organic film 3 third organic film 6 first electrode 5: erbium second electrode: TO was used. It has been confirmed by displacement current measurement that this material system satisfies the conditions shown in FIG. The device fabrication process is similar to that described in the previous example.

When a bias is applied to the obtained device, approximately 5 mA at 5 V
A current of 1000 Cd/m2 was passed, and yellow light emission with a brightness of 1000 Cd/m2 was obtained. This light emission is due to the second organic film 3. When the bias voltage was increased to 15 V, the current flowed about 20 mA and red-orange luminescence with a brightness of 2000 Cd/m2 was obtained. This is because the red light emitted by the third organic film 6 is mixed with the yellow light emitted by the second organic film 3.

In the above examples, two layers in a two-layer organic film stack structure are both light-emitting layers, and two layers in a three-layer organic film stack structure are light-emitting layers, that is, in the case of two-color light emission. However, by expanding the application of these principles, it is possible to obtain a multicolor light-emitting element with an even larger number of light-emitting layers.

Effects of the Invention As described above, according to the present invention, by combining a plurality of organic films, it is possible to obtain a single pixel multicolor light emitting element whose emission color can be controlled by bias.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an organic film light emitting device according to an embodiment of the present invention, Fig. 2 is a band diagram showing the electrical characteristics of each layer of the device before bonding, and Fig. 3 is a thermal equilibrium state of the device. Band diagram of Fig. 4 (
a) (b) are band diagrams to explain the operating principle of the device, and Figures 5 (a) and (b) are band diagrams to explain the operation when light emission from the second organic film is dominant. Figure, Figure 6 (a
) (b) is a band diagram for explaining the operation when light emission from the first organic film is dominant, FIG. 7 is a cross-sectional view showing an organic film light emitting device of another example, and FIG. A band diagram showing the electrical characteristics of each layer of the element before bonding. Figure 9 is a band diagram of the element in a thermal equilibrium state. Figures 10 (a) and (b) are band diagrams to explain the operation of the element. Fig. 11 is a cross-sectional view showing an organic film light emitting device according to another example, Fig. 12 is a band diagram showing the electrical characteristics of each layer of the device before bonding, and Fig. 13 is a thermal equilibrium state of the device. Band diagram, No. 14
Figures (a) and (b) are band diagrams to explain the operation of the device, Figure 15 is a diagram showing the displacement current measurement method for understanding the material properties of organic films, and Figure 16 is the applied voltage waveform. Figure 17 is a diagram showing the displacement current-voltage characteristics when there is no organic film, Figure 18 is a diagram showing the displacement current-voltage characteristics when the electrode-organic film junction is hole-injecting, and Figure 19 is a diagram showing the displacement current-voltage characteristics when the electrode-organic film junction is hole-injecting. The figure is a diagram showing displacement current-voltage characteristics when the electrode-organic film junction is hole-injecting. DESCRIPTION OF SYMBOLS 1...Glass substrate, 2...2nd electrode, 3...2nd 6-layer film, 4...1st organic film, 5...1st electrode, 6... Third organic film.

Claims (1)

[Claims] (1) A first structure forming a barrier junction for electrons and holes.
A laminated structure of an organic film and a second organic film, a first electrode for electron injection provided on the first organic film side with this laminated structure in between, and a positive electrode provided on the second organic film side. and a second electrode for hole injection, and when a positive bias is applied between the first and second electrodes to the second electrode side, the first electrode flows from the first electrode to the first organic film. Electrons injected into the second organic film and holes injected into the second organic film from the second electrode are accumulated at the interface of the barrier junction, and out of these accumulated electrons and holes, electrons are injected into the second organic film. tunnel injection into the organic film of 2.
An organic film light-emitting device characterized in that the holes are tunnel-injected into the first organic film and emitted and recombined within the first organic film. (2) The work functions of the first and second electrodes are each E_
M_1, E_M_2, the energy difference from the vacuum level at the lower end of the conduction band, the Fermi level, and the upper end of the valence band of the first organic film are respectively E_c_1, E_1, and E_v_1, and the conduction of the second organic film is The energy difference from the vacuum level at the bottom of the band, the Fermi level, and the top of the valence band is expressed as E
Claim 1 characterized in that, when _c_2, E_2 and E_v_2, the material is selected so that E_M_1<E_1 E_2<E_M_2 E_c_1>E_c_2 E_v_1>E_v_2 and E_c_1-E_c_2<E_v_1-E_v_2. The organic film light emitting device described above. (3) The work functions of the first and second electrodes are each E_
M_1, E_M_2, the energy difference from the vacuum level at the lower end of the conduction band, the Fermi level, and the upper end of the valence band of the first organic film are respectively E_C_1, E_1, and E_V_1, and the conduction of the second organic film is The energy difference from the vacuum level at the bottom of the band, the Fermi level, and the top of the valence band is expressed as E
Claim 1 characterized in that, when _C_2, E_2 and E_V_2, the material is selected so that E_M_1<E_1 E_2<E_M_2 E_C_1>E_C_2 E_V_1>E_V_2 and E_C_1-E_C_2>E_V_1-E_V_2 are satisfied. The organic film light emitting device described above. (4) The first layer that forms a wall junction for electrons and holes
A laminated structure of an organic film and a second organic film, a first electrode for electron injection provided on the first organic film side with this laminated structure in between, and a third organic film on the second organic film side. and a second electrode for hole injection provided through a membrane, and a material is selected so that a positive charge is filled between the first and second electrodes on the second electrode side. Claim 4 characterized by
The organic film light emitting device described above. (6) The first layer that forms a wall junction for electrons and holes
a laminated structure of an organic film and a second organic film, a first electrode for electron injection provided via a third organic film provided on the first organic film side with this laminated structure in between, and a second electrode for hole injection provided on the second organic film side, and when a positive bias is applied between the first and second electrodes to the second electrode side, the When a front bias is applied from the first electrode, electrons injected from the first electrode into the first organic film and electrons transferred from the second electrode to the second organic film via the third organic film. Holes injected into the film are accumulated at the interface of the wall junction, and among these accumulated electrons and holes, electrons are tunnel-injected into the second organic film and are generated within the second organic film. An organic film light emitting device characterized in that the light emitted from the light emitted is recombined, and further injected into a third organic film and recombined within the third organic film. (5) The work functions of the first and second electrodes are each E_
M_1, E_M_2, the energy difference from the vacuum level at the lower end of the conduction band, the Fermi level, and the upper end of the valence band of the first organic film are respectively E_C_1, E_1, and E_V_1, and the conduction of the second organic film is The energy difference from the vacuum level at the bottom of the band, the Fermi level, and the top of the valence band is expressed as E
Let _C_2, E_2 and E_V_2 be the energy differences from the vacuum level at the lower end of the conduction band, the Fermi level and the upper end of the valence band of the third organic film, respectively.
3. When E_3 and E_V_3, E_M_1<E_1 E_2<E_M_2 E_C_1>E_C_2 E_V_1>E_V_2 and E_C_1-E_C_2<E_V_1-E_V_2E_
C_2<E_C_3 E_V_2~E_V_3 E_M_2<E_3 The electrons injected into the first organic film through the third organic film and the holes injected into the second organic film from the second electrode The holes are accumulated at the interface of the wall junction, and among these accumulated electrons and holes, holes are tunnel-injected into the first organic film and recombined in light emission within the first organic film. An organic film light emitting device characterized in that the organic film is injected into an organic film and emitted and recombined within a third organic film. (7) The work functions of the first and second electrodes are each E_
M_1, E_M_2, the energy difference from the vacuum level at the lower end of the conduction band, the Fermi level, and the upper end of the valence band of the first organic film are respectively E_C_1, E_1, and E_V_1, and the conduction of the second organic film is The energy difference from the vacuum level at the bottom of the band, the Fermi level, and the top of the valence band is expressed as E
Let _C_2, E_2 and E_V_2 be the energy differences from the vacuum level at the lower end of the conduction band, the Fermi level and the upper end of the valence band of the third organic film, respectively.
3. When E_3 and E_V_3, E_M_1<E_1 E_2<E_1 E_C_1>E_C_2 E_V_1>E_V_2 and E_C_1-E_C_2>E_V_1-E_V_2E_
7. The organic film light emitting device according to claim 6, wherein the material is selected so as to satisfy C_3 to E_C_1 E_V_3<E_V_1 E_M_1<E_3. (8) It has a structure in which a plurality of organic films are sandwiched between a first electrode for electron injection and a second electrode for hole injection, and a second electrode is sandwiched between the first and second electrodes. The organic film is selected so that when a positive bias voltage is applied to the electrode side of the organic film, different colors of light are emitted from different organic films depending on the magnitude of the bias voltage. element. (9) The plurality of organic films include a stacked structure of a first organic film and a second organic film in which a barrier junction is formed with respect to electrons and holes, and when the bias voltage is applied, the first organic film
An electric double layer in which electrons and holes are accumulated is formed at the interface between the organic film of Node 2 and the organic film of Node 2, and at a certain threshold, light emission is re-injected from the first organic film to the second organic film. 9. The organic film light emitting device according to claim 8, wherein bonding occurs and luminescent recombination occurs due to hole injection from the second organic film to the first organic film at another threshold value. (10) The plurality of organic films include a first organic film on the first electrode side and a second organic film on the second electrode side, in which wall junctions are formed for electrons and holes. and a third organic film provided between the multilayer structure and the second electrode, and the interface between the first organic film and the second organic film is formed by applying the bias voltage. An electric double layer in which electrons and holes are accumulated is formed, and a second
radiative recombination occurs in the organic film, and the second
9. The organic film light emitting device according to claim 8, wherein emission recombination occurs in the third organic film due to electron injection from the organic film to the third organic film. (11) The plurality of organic films include a first organic film on the first electrode side and a second organic film on the second electrode side, where a wall junction is formed for electrons and holes. It has a laminated structure and a third organic film provided between the laminated structure and the first electrode, and when the bias voltage is applied, the interface between the first organic film and the second organic film is An electric double layer in which electrons and holes are accumulated is formed, and at a first threshold, a second
Luminescent recombination occurs in the first organic film due to hole injection from the organic film to the first organic film, and holes inject from the first organic film to the third organic film at the second threshold. 9. The organic film light emitting device according to claim 8, wherein luminescent recombination occurs in the third organic film due to injection.