JPH03230583A - Organic-film light emitting element - Google Patents

Abstract

PURPOSE:To make the light emitting efficiency of the title element higher by using a plurality of organic films and utilizing a carrier enclosing effect obtained by a band-gap difference. CONSTITUTION:This organic-film light emitting element is constituted of the first electrode (M1) 6, first organic film (O1) 5, third organic film (O3) 4, second organic film (O2) 3, and second electrode (M2) 2 in the order from the top. 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. The light emitting layer between the organic films 5 and 3 is constituted of a single or a plurality of organic films 4 having a narrow band gap and, when a bias voltage is applied across the electrodes 6 and 2, electrons and holes injected into the first and second organic films from the first and second electrodes, respectively, are enclosed in the light emitting layer. Therefore, light emission efficiently takes place in the light emitting layer due to the recombination of the carriers.

Description

[Detailed Description of the Invention] [Purpose of the Invention (Field of Industrial Application) The present invention relates to a light emitting device using an organic film, and in particular to a light emitting device that makes it possible to emit light with high efficiency by combining a plurality of organic films. The present invention relates to an organic film light emitting device.

(Prior Art) In recent years, research and development of f-conductive film light emitting elements used as display elements, lighting elements, etc. have 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, 198B). Here,
The thickness of the organic film 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/I
It has an organic two-layer structure called TO, and the thickness of the organic film is 1000 Å.
It has been reported that by doing the following, an element that can be driven with an applied voltage of 10 V or less and exhibits sufficient brightness for practical use was obtained (APL).

51.913.1987). These light-emitting devices are based on an organic two-layer structure that combines an electron-injecting dye and a hole-injecting dye, making the organic film as thin as possible, and using metal electrodes on the electron-injecting side. The main characteristics include selecting a material 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, Shogo Saito of Bonyo University proposed an organic three-layer structure element consisting of an electron injection layer, a light emitting layer, and a hole injection layer, and achieved high brightness by selecting a dye with high photoluminescence for the light emitting layer. It was shown that luminescence could be obtained (J, J
, Al) pl, Phys, 27. L26
9, 1988).

In addition, so far, it has been observed that light emitting device structures are created by combining various types of dielectric films, and that even a single layer organic film emits light to some extent by mixing a luminescent agent and a hole injection agent. , A1. which is a light emitter. Studies on the deterioration of the characteristics of q3 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 issues with luminous efficiency and device life.

There are still many unresolved technical problems in the device fabrication process. At present, the luminous efficiency is at best about 1% and usually about 0.1%. 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 been focused on electron (hole) transport and electron (hole) injection properties.

Only qualitative definitions such as luminescence have been made, and it cannot be said that the device conditions are sufficiently defined.

The present invention provides an organic film light emitting device that enables highly efficient light emission by strictly defining the electrical properties of each material in a combination of a stacked structure of a plurality of organic films and a metal electrode. The purpose is to

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

That is, the light emitting element according to the present invention has a basic structure in which a laminate of a plurality of organic films is sandwiched between first and second electrodes.

The first light emitting element of the present invention has such a basic structure, and includes a first organic film in contact with a first electrode.

A third organic film as a light emitting layer is provided between the second self-conducting film in contact with the second electrode, and the band gap of the third organic film is smaller than that of the first and second organic films. It is set.

Specifically, 1. The work function of the second electrode is E
MI + EM level) and the energy difference from the vacuum level at the top of the valence band (hereinafter simply referred to as the valence band level), respectively. 1. El
and Ev+, and the conduction band level, Fermi level and valence band level of the second organic film are Ec2 and E, respectively.
2 and Ev□, and the conduction band level of the third organic film.

Fermi level and valence band level are respectively Ec3
, E3 and Ev3, E M+ < E 1
...(1) E2<EM
2...(2)E c+>E
C2-(3) E vl> E V2-(4)
and E C3> E C2-(5) E v+> E V3 ''' (
The material is selected so as to satisfy [i]. Specifically, the relationship between equations (1) and (2) is that EMI EcI and Ev□-EM2 are each 1
eV or less, preferably 0.5 to 0.3 eV or less.

Further, the second light emitting element of the present invention has a third light emitting element of the first light emitting element.
The organic film portion is further composed of a plurality of layers of organic films. That is, a two-layer laminate of at least third and fourth organic films is provided as a light emitting layer between a first organic film in contact with the first electrode and a second organic film in contact with the second electrode. , the third and fourth organic films are characterized in that the band gaps are set smaller than those of the first and second organic films.

Specifically, when the conduction band level, Fermi level, and valence band level of the fourth organic film are respectively Ec, E4 and Ev4, E u+ < E +
...(A) E4<EM□
...(8) is satisfied, and E cl-E C3> E (4> E C2...(9
)E V2~E V4< E v3< E v+
-' The material is selected so as to satisfy (10).

(Function) In the organic film light emitting device r according to the present invention, the light emitting layer between the first and second organic films is composed of a single layer or multiple layers of organic films with a narrow band gap. Therefore, the first
．． When a bias voltage is applied between the second 71ti, the first
．． from the second electrode to the first electrode, respectively. Electrons and holes injected into the second organic film are confined within the light emitting layer. As a result, light is efficiently emitted by carrier recombination within the light emitting layer. That is, due to the effect of carrier confinement, there is no current that does not contribute to radiative recombination, resulting in higher luminous efficiency and longer device life.

Specifically, the above conditional expression for the first light emitting element is
If a suitable material is selected, there is a junction between the first electrode and the first organic film where electrons are easily injected from the first electrode to the first organic film (conditional expression (1)), and the second The space between the electrode and the second organic film is a quality junction in which holes are injected from the second electrode to the second organic film (conditional expression (2)). Therefore, the first. When a bias voltage is applied between the second electrodes so that the second electrode side is positive, electrons are injected from the first electrode into the first organic film, and holes are injected from the second electrode into the second organic film. Injected.

According to conditional expression (3), the second organic film blocks electrons from the first organic film, and according to conditional expression (4), the first organic film blocks holes from the second organic film. On the other hand, it becomes a block, and electrons and holes are confined in the third hexagonal film according to conditional expressions (5) and (6).

This enables highly efficient light emission.

Furthermore, in the second light emitting element, conditional expressions (9) (10>
The third layer is a light-emitting layer. The conditions for carrier confinement within the fourth organic film are satisfied. and a third organic film and a fourth organic film.
According to conditional expression (9), a barrier is formed in the flow of electrons from the third organic film to the fourth organic film, and a barrier is formed between the organic films from the third A barrier is formed in the flow of holes into the organic film. Then, when the bias voltage exceeds a certain value, the electrons in the third organic film recombine within the fourth organic film tunnel-injected into the fourth organic film, and the electrons in the third organic film recombine.
Holes in the organic film are tunnel-injected into the third organic film and recombined within the third organic film. These recombination processes produce light emission at wavelengths determined by the materials of the third and fourth angular guiding films, respectively.

(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 6 degrees and a first membrane (0+) of 5 degrees when viewed from above. 3rd number of planes 4. The second membrane (
0, ) 4 and a second electrode (M2) 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. 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. first organic film (0,)5
The conduction band level of E. 1. The Fermi level is E11, the valence band level is Evl, and the conduction band level of the second organic film (0□)3 is E. 2. When the Fermi level is E21, the valence band level is Ev2, and the conduction band level of the third organic film (0,)4 is Ec3+Fermi level is E32, the valence band level is Ev3, as shown in the figure, Ec3>E.
cl>E C21E v+>E V2>E V
Three materials have been selected. Further, the first electrode 5 has a work function EMI of EM, <E, and is selected in such a manner that electrons are easily injected into the first a-mechanical film 5. The second electrode 2 has a work function EM2 such that EM2>E2, and is selected so that holes can be easily injected into the second organic film 3.

The operation of the device of this embodiment will be explained using FIG. FIG. 3(a) is a band diagram of the light emitting device of this example in a thermal equilibrium state. In thermal equilibrium, the Fermi levels of the system coincide. Therefore, from the size relationship between the electrode function 11 and each energy level of the organic film shown in FIG. 2, as shown in FIG. 3(a), the distance between the first electrode 6 and the first organic film 5 is An electronic junction is formed from the first electrode 6.

A junction is formed between the second electrode 2 and the second organic film 3 to which holes can easily be injected from the second electrode 2. A third angular conductive film 4 having a smaller band gap than these is sandwiched between the first organic film II'2.5 and the second organic film 3.

FIG. 3(l) is a band diagram of the light emitting device of this example when a positive bias voltage V is applied to the second electrode 2 with respect to the first electrode 6.

Electrons are injected from the first electrode 6 into the first organic film 5,
Holes are injected from the second electrode 2 into the second organic film 3, and these electrons and holes are injected into the third organic film, which serves as a potential well for both electrons and holes. be trapped in 4.

This trapped electron.

Light is emitted when holes recombine with each other.

Since the first and second organic films 5 and 3 have a larger band gap than the third organic film 4, the light emitted from the third organic film 3 is transmitted to the first. It is taken out to the outside without being reabsorbed by the second organic film 53.

Note that when selecting a material with a set energy level magnitude relationship at each bonding surface as in the light emitting element of this example, the energy level magnitude relationship is determined by
A method is needed to determine the This can be done by using a method discovered by the inventors as described below.

As shown in FIG. 11, metal electrode 11/silicon 12/
A device consisting of silicon oxide film 13/organic film 14/metal electrode 15 is formed. A triangular wave voltage as shown in Fig. 12 is applied to this element, and the displacement current of the element at that time is 7Ill.
i decide. 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. 11 without the organic film 14, the device becomes a commonly known MO3 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 is observed depending on the magnitude relationship between the Fermi level of the 6' machine 112.14 and the work function of the metal electrode 15.

<a) Metal electrode] When the work function of 5 and the Fermi level of the organic film 14 are approximately strong In this case, the junction between the metal electrode 15 and the organic film 14 is a junction with a high barrier to both electrons and holes. Become. 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 is reduced to a constant value smaller than that of the MOS device. As a result, when a triangular wave voltage as shown in FIG. 12 is applied to the element, the displacement current exhibits a constant small value as shown in FIG. 13.

(b) When the work function of the metal electrode 15 is smaller than the Fermi level of the organic film 14 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 to the H-machine film 14. form. Therefore, when the triangular wave voltage shown in FIG. 12 is applied to the device, when the metal electrode 15 side becomes negative, electrons are injected from the metal electrode 15 into the organic film 14, and these electrons are accumulated at the interface between the organic film 14 and the oxide film 13. . 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 positive polarity on the metal electrode 15 side, electrons 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.

(c) When the work function of the metal electrode 15 is larger than the Fermi level of the organic film 14 In this case, the junction between the metal electrode 15 and the organic film 14 is a junction where holes are easily injected from the metal electrode 15 into the organic film 14. form. Therefore, when the triangular wave voltage shown in FIG. 12 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 metal electrode and the organic film.Next, the organic film 14 portion in the device structure of FIG. A similar displacement current measurement is performed for a second layered structure of several membranes. This clarifies the relationship between the conduction band level, Fermi level, and valence band level of the two white conductive films.

For example, in the device structure shown in FIG. 11, the portion of the membrane 14 in contact with the metal electrode 15 has the first a! It is assumed that there is a film 141 and a second organic film 142 underneath it. It is assumed that electrons are injected from the metal electrode 15 into the first organic film 14. This has been investigated using the aforementioned device with an organic film in the middle layer. If the displacement current is negative on the metal electrode 15 side, the MO
If it flows to the three-element level, the first H mechanism 14
, are further injected into the second a mechanism 41□. As a result, the second h#1 film 1
It can be seen that the conduction band level at 4° is lower than that of the first organic film 14. If such a displacement current at the MO3 element level is not observed, the conduction band level of the second organic film 14° is the same as that of the first organic film 14. It can be seen that it is higher than that of .

Regarding the valence band level, the magnitude relationship can also be determined by similarly determining the displacement current A111 using hole injection.

A more specific example of an organic multicolor light emitting device using the device structure shown in FIG. 1 will be described next.

Example 1 In the element of Fig. 1, The first electricity! 6: Erbium film First organic film 5: Second what machine film 3: Third organic film 4: Second electrode 2: ITO film was used.

That this material system satisfies the conditions shown in FIG. 2 has been confirmed by the previously explained displacement current M [standard method].

The device fabrication process is as follows. First, on the glass substrate on which the ITO film was formed, a vacuum sublimation method (Okado ~ 10-
The second organic film 3 was heated to a temperature of 200 to 1000
A third organic film 4. is then formed by a similar vacuum sublimation method. The first organic film 5 is sequentially formed by 200 to 1,000 people, and finally the erbium film is deposited by 200 to 1,000 people by vacuum evaporation.
~1000 people will be formed.

When a bias that makes the ITO electrode positive is applied to the resulting device, a current of 1.0 mA at 5 V flows, and the brightness is 1000 C.
Luminescence of d/m2 was observed. The luminous efficiency was about 10%.

By the way, No. 1. When the second organic film is not provided and a third organic film single layer is used as a light emitting layer, the brightness is low and 20V
Even if a current of 100mA is applied, 500Cd/m2
(Luminescence efficiency 0.5%) No deer was obtained. From now on, the first. It is understood that carrier confinement by sandwiching the light-emitting layer between the second organic films contributes to improving the light-emitting efficiency.

Two embodiments using different material systems based on the element structure shown in FIG. 1 will now be described.

FIG. 4 shows a band diagram of each layer of one element before bonding, corresponding to FIG. 2. As is clear from a comparison with FIG. 2, in this embodiment, the second organic film 3 and the third
satisfies the conditions Ev2 to E0, and the first
The condition EcI<Ec3 is satisfied between the organic film 5 and the third organic film 4. Other conditions are the same as in the previous example.

FIGS. 5(a) and 5(b) are explanatory views of the operation of the light emitting device of this embodiment. FIG. 5(a) is a band diagram in a thermal equilibrium state, and as shown in the figure, in this embodiment, between the first organic film 5 and the third organic film 4, A barrier (ΔEc-E(l E
c3) is formed. This barrier to electrons is smaller than the barrier to holes (ΔEv=Ev□−E VJ). The state in which a bias is applied to this is shown in FIG. 5(b). Electrons injected from the first electrode 6 into the first organic film 5 are accumulated in the barrier junction with the third organic film 4, and
The holes injected from the electrode 2 into the second organic film 3 flow to the third organic film 4 without being blocked in any way, and are accumulated in the barrier junction with the first organic film 5.

The carriers thus accumulated at the junction between the first organic film 5 and the third organic film 4 form an electric double layer. Since the thickness of this electric double layer is the intermolecular distance of the dye (~10 people), as a result, a large electric field of about 10'V/CDI or more is formed here.

Due to this strong electric field, electrons in the first organic film 5 are tunnel-injected into the third organic film 4 and recombined within the third organic film 4 .

FIG. 6 is a band diagram of each layer of another element before bonding. In the case of this embodiment, as shown in the figure, the first organic film 5
and the third organic film 4, the conditions are set to EcI to Ec3, and between the second organic film 3 and the third organic film 4, Ev
The condition is set such that 2<Ev3. Other than that, the second
It is similar to the figure.

FIGS. 7(a) and 7(b) are explanatory views of the operation of the light emitting element of this embodiment. FIG. 7(a) is a band diagram in a thermal equilibrium state, and as shown in FIG. A barrier (ΔEv=Evs
Ev□) is formed. This barrier to holes is smaller than the barrier to electrons (ΔEc-E C3E C2). The state in which a bias is applied to this is shown in FIG. 7(b). Electrons injected from the first electrode 6 into the first white conductive film 5 flow to the third BM film 4 without being blocked in any way and are accumulated in the barrier junction between it and the second organic film 3. °, second
The holes injected from the electrode 2 into the second H mechanism 3 are
Organic p! is accumulated in the barrier junction between 4 and 4.

The carriers thus accumulated at the junction between the second organic film 3 and the third organic film 4 form an electric double layer. When the bias voltage exceeds a certain value, the holes in the second organic film 3 are tunnel-injected into the third organic film 4 and are recombined within the third organic film 4 .

Also in these embodiments, a large number of carriers are confined in the third organic film, resulting in highly efficient light emission.

Next, an example in which the light emitting layer has a stacked structure of a plurality of organic films will be described.

FIG. 8 is a sectional view showing the element structure of such an embodiment. As is clear from a comparison with FIG. 1, in this example,
The light emitting layer region sandwiched between the first organic film 5 and the second organic film 3 is a laminate of the third organic film 4 and the fourth organic Wk7.

FIG. 9 is a band diagram of each constituent layer of this device before bonding. As shown in the figure, in this example, E, >E, >E4>
E2 E C3E vi< E c I E
The materials are combined so as to satisfy the following conditions: v+Ec4Ev4<Ec2Ev2 ECI=EC3>EC4EV2 to Eva<EV3.

FIG. 10(a) is a band diagram of the device of this example in a thermal equilibrium state. Between the first and second organic films 5 and 3 having a large band gap, there is a third organic film having a small band gap. Fourth organic films 4 and 7 are sandwiched between them.

Looking at the conduction band, the space between the first organic film 5 and the third organic film 4 is smooth, and there is a barrier between the third organic film 4 and the fourth organic film 7 (ΔEc=Ec4 Ec3). is formed. This barrier to electrons is formed by the fourth organic film 7 and the second
is smaller than that between membranes 3 and 3. -h Looking at the valence band, there is a smooth transition between the second several-layer film 5 and the fourth f-i mechanism 7, and between the third several-layer film 4 and the fourth a-layer p&7. A barrier (ΔE, -Ev3 to E V4) is formed.

This barrier to holes is smaller than that between the third organic film 4 and the first organic film 5.

FIG. 10(b) is a band diagram when a bias voltage such that the second electrode 2 side is positive is applied to the element of this example.

767- is injected from the first electrode 6 into the second organic film 5, and these electrons are transferred to the third organic film 4 and accumulated in the open barrier junction with the fourth organic film 7. . second electrode 2
From then on, holes are injected into the second organic film 3, and these holes are transferred to the fourth organic film 7 and accumulated in the barrier junction with the third organic film 4. Thus, in this example, the third
An electric double layer is formed at the junction between the fourth organic films 4 and 7. When the bias voltage exceeds a certain value, the third
Electrons are tunnel-injected from the organic film 4 to the fourth organic film 7 and recombined in the fourth organic film 7, and holes are tunnel-injected from the fourth organic film 7 to the third organic film 4. The light is tunnel-injected and recombined to emit light within the third organic film 4.

In this case, if the threshold values for the luminescent recombination in the third organic film 4 and the luminescent recombination in the fourth organic film 7 are the same, the luminescent recombination in the third organic film 4 and the fourth organic film 7 are the same. This results in color mixture of light emitted from the organic film 7. If the threshold values are different, light emission from one of them takes priority. For example, light emission occurs in the third organic film 4 at the first threshold, and by further increasing the bias, light emission occurs at the fourth organic film at the second threshold.
The light emission from the organic film 7 overlaps with this. When choosing materials, this order of priority is reversed. In any case, in this case, single pixel multicolor display in which the emitted light color can be controlled by bias is possible.

In this example as well, the third and fourth organic films, which are light-emitting layers, are sandwiched between the first and second organic films having a wide bandgap, and therefore highly efficient light emission is achieved due to the carrier confinement effect. I can get it.

An example in which two layers are used as the light-emitting layer will be specifically described.

Example 2 In the device shown in FIG. 8, first electrode 6: erbium film first organic film 5: tetranitrobifluorenonyl third organic film 4: fourth organic film 7: bicoronenyl second organic film Film 3: Same as Example 1 First electrode 2: ITO The device fabrication process is basically the same as that described in Example 1 above. When a bias was applied to the obtained element, a current of about 10 mA flowed at an applied voltage of 5 V, and a current of about 20 mA flowed.
Light emission with a brightness of 00 Cd/m2 was observed. The luminous efficiency was about 20%.

[Effects of the Invention] As described above, according to the present invention, a plurality of layers can be used. It is possible to provide an organic film light-emitting element that uses a film and makes it possible to obtain high luminous efficiency by utilizing the effect of carrier confinement due to a difference in band gap.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing a light emitting device according to an embodiment of the present invention. Fig. 2 is a band diagram showing the electrical characteristics of each layer before bonding. Fig. 3 (a) and (b) explain the operation of the device. Figure 4 is a band diagram showing the electrical characteristics of each layer of a light emitting device of another example before bonding, and Figures 5(a) and (b) are band diagrams of the device in thermal equilibrium state and bias state. Band diagrams for the thermal equilibrium state and bias state are used to explain the operation, and FIG. 6 is a band diagram showing the electrical characteristics of each layer of the light emitting device of another embodiment before bonding. FIG. 7(a) (b) are band diagrams in a thermal equilibrium state and a bias state to explain the operation of the device, FIG. 8 is a cross-sectional view showing a light emitting device of another example, and FIG. 9 is a diagram showing the electrical characteristics of each layer before bonding. Figures 10(a) and 10(b) are band diagrams for the thermal equilibrium state and bias state, respectively, to explain the device operation. Figure 11 explains the displacement current measurement method for understanding the characteristics of organic films. Figure 12 is a diagram showing the applied voltage waveform, Figure 13 is a diagram showing the displacement current-voltage characteristics when there is no organic film, and Figures 14 and 15 are diagrams showing the displacement current-voltage characteristics when there is an organic film. FIG. 3 is a diagram showing displacement current-voltage characteristics. DESCRIPTION OF SYMBOLS 1...Glass substrate, 2...2nd electrode, 3...2nd organic film, 4...3rd organic film, 7...4th organic film, 5... first organic film, 6... first electrode;

Claims (7)

[Claims] (1) In an organic light emitting device having a structure in which a plurality of organic films are sandwiched between first and second electrodes facing each other, the plurality of organic films are provided in contact with the first electrode. a first organic film provided in contact with the second electrode; and a second organic film provided in contact with the second electrode.
and a third organic film having a bandgap smaller than that of the first and second organic films, which is sandwiched between the first organic film and the second organic film and serves as a light emitting layer. organic film light emitting device. (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
_c_2, E_2 and E_v_2, and the energy difference from the vacuum level at the lower end of the conduction band and the upper end of the valence band of the third organic film is E_c_3 and E_v_, respectively.
3. The organic film light emitting device according to claim 1, wherein 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_3>E_c_2 E_v_1>E_v_3 are satisfied. element. (3) When the energy difference from the Fermi level vacuum level of the third organic film is E_3, E_M_1<E
3. The organic film light emitting device according to claim 2, wherein _3<E_M_2 and E_c_1≦E_c_3 E_v_3≦E_v_2 are satisfied. (4) When the energy difference from the Fermi level vacuum level of the third organic film is E_3, E_3<E_
The organic film light emitting device according to claim 2, wherein the organic film light emitting device satisfies M_2 and E_c_1>E_c_3 E_v_3≦E_v_2. (5) When the energy difference from the Fermi level vacuum level of the third organic film is E_3, E_M_1<
The organic film light emitting device according to claim 2, wherein E_3 is satisfied, and E_c_1≦E_c_3 E_v_3>E_v_2. (6) In an organic light emitting device having a structure in which a plurality of organic films are sandwiched between first and second electrodes facing each other, the plurality of organic films are provided in contact with the first electrode. a first organic film provided in contact with the second electrode; and a second organic film provided in contact with the second electrode.
an organic film, and a laminate of third and fourth organic films having a smaller band gap than the first and second organic films, which are sandwiched between the first organic film and the second organic film and serve as a light emitting layer. An organic film light emitting device comprising: (7) The work functions of the first and second electrodes are each E_
M_1 and E_M_2, and the energy difference from the vacuum level at the lower end of the conduction band and the upper end of the valence band of the first organic film is E_c_1, respectively.
and E_v_1, and the energy difference from the vacuum level at the lower end of the conduction band and the upper end of the valence band of the second organic film is E_c_2, respectively.
and E_v_2, and 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 are respectively E_c_3, E_3, and E_v_3, and the conduction band of the fourth organic film is When the energy differences from the vacuum level at the lower end of the Fermi level and the upper end of the valence band are respectively E_c_4, E_4 and E_v_4, E_M_1<E_3 E_4<E_M_2 is satisfied, and E_c_1~E_c_4>E_c_4>E_c_2
7. The organic film light emitting device according to claim 6, wherein the material is selected so as to satisfy E_v_2 to E_v_4<E_v_3<E_v_1.