WO2013161515A1

WO2013161515A1 - Organic luminescent element

Info

Publication number: WO2013161515A1
Application number: PCT/JP2013/059819
Authority: WO
Inventors: 石原　慎吾; 広貴佐久間; 荒谷　介和
Original assignee: 株式会社日立製作所
Priority date: 2012-04-27
Filing date: 2013-04-01
Publication date: 2013-10-31
Also published as: JP2013229268A

Abstract

In cases when two luminescent layers are present, the excited states are concentrated and the surfaces of the luminescent layers on the side where the excited states are formed deteriorate. The purpose of the present invention is to inhibit the deterioration of luminescent layers. This organic luminescent element has three luminescent layers. In the first luminescent layer, injected electrons are transferred to a first emitter. The molecules of the first emitter that have come into an anionic state have a reduced HOMO energy level, which is lower than the level of the HOMO of a first host material, and are hence apt to trap holes. As a result, the anionic state of the first emitter results in an excited state.

Description

Organic light emitting device

The present invention relates to an organic light emitting device.

As a conventional example, Patent Document 1 discloses the following technique. That is, in the stacked light-emitting layer, the first light-emitting layer is added with a triplet emitter (an emitter is also referred to as a dopant) and has both polarities, but transports holes in particular. The second light-emitting layer has a bipolarity by adding a triplet emitter, and in particular has a structure that transports electrons and has a twist type II energy barrier at the interface between the first light-emitting layer and the second light-emitting layer. It is disclosed.

Special table 2008-509565 gazette

In the prior art, the excited state is concentrated on the interface between the two light emitting layers, and the light emitting emitter near the interface is deteriorated. An object of this invention is to provide the element structure which maintains a high efficiency and has a long life characteristic.

The features of the present invention for solving the above-described problems are as follows.

The organic light emitting device has three light emitting layers. In the first light emitting layer, the injected electrons are conducted through the first emitter. The energy position of the HOMO of the first emitter molecule in an anionic state is lowered, becomes smaller than the HOMO of the first host material, and easily traps holes. As a result, an excited state is generated from the anion state of the first emitter.

According to the present invention, deterioration of the light emitting layer can be suppressed. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is sectional drawing in one Embodiment of an organic light emitting element. It is an energy level conceptual diagram of the organic light emitting element of a conventional structure. It is an energy level conceptual diagram of the organic light emitting element which has three light emitting layers. It is an energy level conceptual diagram of the organic light emitting element which has three light emitting layers. It is an energy level conceptual diagram of the organic light emitting element which has two light emitting layers. It is an energy level conceptual diagram of the organic light emitting element which has two light emitting layers. It is an energy level conceptual diagram of the organic light emitting element which has one light emitting layer. This is an example in which a hole blocking layer is provided in the third light emitting layer. This is an example in which a hole blocking layer is provided in the second light emitting layer. This is an example in which a hole blocking layer is provided in the first light emitting layer.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the embodiments, the same reference numerals are given to those having the same function, and the repeated explanation thereof is omitted.

FIG. 1 is a cross-sectional view of an embodiment of an organic light emitting device. The organic light emitting element 100 includes a first substrate 101, a second substrate 102, a first electrode 103, a second electrode 104, and an organic layer 105. The first substrate 101, the first electrode 103, the organic layer 105, the second electrode 104, and the second substrate 102 are arranged in this order from the lower side of FIG. When the first electrode 103 is a reflective electrode serving as a cathode and the second electrode 104 is a transparent electrode serving as an anode, the organic light-emitting element in FIG. 1 is a top emission type that extracts light emitted from the organic layer 105 from the second electrode 104 side. It becomes. Further, when the first electrode 103 is a transparent electrode serving as an anode and the second electrode 104 is a reflective electrode serving as a cathode, the organic light-emitting element in FIG. 1 has a bottom that extracts light emitted from the organic layer 105 from the first electrode 103 side. It becomes an emission type. The first substrate 101, the first electrode 103, the first electrode 103, the organic layer 105, the organic layer 105, and the second electrode 104 may be in contact with each other. By including a red light emitting layer, a green light emitting layer, and a blue light emitting layer as the organic layer 105, white light is emitted from the organic layer 105 by red light emission, green light emission, and blue light emission. However, in the case of white light, the organic layer 105 includes a light emitting layer of two emission colors that are complementary colors. For example, a combination of a light blue light emitting layer and a yellow light emitting layer can be considered.

1 is provided with a driving device or the like in the organic light emitting device of FIG. Examples of the light source device using the present invention include, but are not limited to, household lighting, interior lighting, and backlights of liquid crystal display devices.

Fig. 2 shows a conceptual diagram of energy levels of a conventional organic light emitting device. In FIG. 2, the organic layer 105 includes a hole transport layer 14, a first light emitting layer 1, a second light emitting layer 2, and an electron transport layer 15. The first light emitting layer 1 includes a host and a light emitting emitter. The second light emitting layer 2 includes a host and a light emitting emitter. The light emitting emitter of the first light emitting layer 1 and the light emitting emitter of the second light emitting layer 2 are assumed to have the same main skeleton, the same substituent, or the same kind of substituent. When a voltage is applied between both electrodes of the organic light emitting device, holes 9 and electrons 10 are injected into the organic layer 105.

In the energy level conceptual diagram of FIG. 2, the relationship between the layers is described below, but the present invention is not limited to this. The highest occupied orbital (HOMO) energy is measured by photoelectron spectroscopy. Further, the lowest unoccupied orbit (LUMO) energy is directly measured by a method of calculating an HOMO-LUMO energy difference from an absorption spectrum, or by inverse photoelectron spectroscopy. HOMO3 of the hole transport layer 14 is smaller than HOMO4 of the host material of the first light emitting layer 1. The HOMO4 of the host material of the first light emitting layer 1 is smaller than the HOMO5 of the host material of the second light emitting layer 2. The LUMO8 of the host material of the second light emitting layer 2 is smaller than the LUMO6 of the electron transport layer 15. The LUMO7 of the host material of the first light emitting layer 1 is smaller than the LUMO8 of the host material of the second light emitting layer 2. The LUMO energy positions 11 of the emitter molecules dispersed in the first light-emitting layer 1 and the second light-emitting layer 2 are the LUMO 7 of the host material of the first light-emitting layer 1 and the LUMO 8 of the host material of the second light-emitting layer 2. Greater than. The HOMO energy positions 12 of the emitter molecules dispersed in the first light emitting layer 1 and the second light emitting layer 2 are HOMO4 of the host material of the first light emitting layer 1 and HOMO5 of the host material of the second light emitting layer 2. Smaller than.

The holes 9 are blocked by the energy barrier at the interface between the first light emitting layer 1 and the second light emitting layer 2 and accumulate on the first light emitting layer 1 side of the same interface. Similarly, the electrons 10 are blocked by the energy barrier at the interface between the first light emitting layer 1 and the second light emitting layer 2 and accumulate on the second light emitting layer 2 side. As the current density increases, the holes penetrating the first light emitting layer 1 are trapped in the light emitting emitter of the second light emitting layer 2. Further, electrons penetrating the second light emitting layer 2 are trapped in the light emitting emitter of the first light emitting layer 1. Therefore, carriers that do not contribute to light emission are reduced, resulting in high light emission efficiency. However, in the conventional structure, the recombination density is increased in the vicinity of the interface between the first light emitting layer 1 and the second light emitting layer 2 and the excited state is concentrated. Therefore, the first light emitting layer 1 and the second light emitting layer are concentrated. Deterioration of the emitter near the interface with 2 becomes a problem. Also, no means for improving the deterioration of the emitter is disclosed.

On the other hand, one embodiment of the present invention aims to suppress the deterioration of the light emitting emitter by not passing through the cation state of the light emitting emitter in the generation of the excited state. FIG. 3 is a conceptual diagram of energy levels of an organic light emitting device having three light emitting layers.

In FIG. 3, the organic layer 105 includes a first light emitting layer 141, a second light emitting layer 142, and a third light emitting layer 143. In the first light-emitting layer 141, the first emitter is dispersed in the first host material. In the second light-emitting layer 142, the second emitter is dispersed in the second host material. In the third light-emitting layer 143, the third emitter is dispersed in the third host material.

In the energy level conceptual diagram of FIG. 3, the relationship of each layer is described below, but is not limited to this.

First, the transport of holes in the light emitting layer will be described. The HOMO energy position 144 of the first host material is smaller than the HOMO energy position 145 of the first emitter molecule. Therefore, the holes injected into the first light emitting layer 141 are conducted between the first host molecules. The HOMO energy position 146 of the second host material is also smaller than the HOMO energy position 147 of the second emitter molecule. Similar to the first light-emitting layer 141, the holes injected into the second light-emitting layer 142 conduct between the second host molecules. On the other hand, the HOMO energy position 148 of the third host material is larger than the HOMO energy position 149 of the third emitter molecule. Therefore, the holes injected into the third light emitting layer 143 are trapped by the third emitter and conducted between the emitter molecules, or the hole traps to the third emitter molecule and the release to the third host molecule. To conduct between the third host molecules.

Next, the transport of electrons in the light emitting layer will be described. The LUMO energy position 154 of the third host material is smaller than the LUMO energy position 155 of the third emitter molecule. Therefore, the electrons injected into the third light emitting layer 143 are conducted between the third emitter molecules. The LUMO energy position 152 of the second host material is also smaller than the LUMO energy position 153 of the second emitter molecule. Similar to the third light-emitting layer 143, the electrons injected into the second light-emitting layer 142 are conducted between the second emitter molecules. The LUMO energy position 150 of the first host material is smaller than the LUMO energy position 151 of the first emitter molecule, and the electrons injected into the first light emitting layer 141 are conducted between the first emitter molecules. In the first light emitting layer, the second light emitting layer, and the third light emitting layer, electrons are conducted between the emitters. In order to improve the conduction characteristics, it is necessary to increase the concentration of the emitter. Specifically, 10% or more is desirable.

From the transport of holes and electrons, the recombination of carriers in each light emitting layer is as follows. In the first light emitting layer 141, the injected electrons are conducted through the first emitter. The energy position 145 ′ of the HOMO of the first emitter molecule in the anion state is lowered, becomes smaller than the HOMO of the first host material, and easily traps holes. As a result, an excited state is generated from the anion state of the first emitter. According to our simulation results, the triplet phosphorescent emitter molecule has an unstable cation state and is easily decomposed. In the first light-emitting layer 141, an excited state is generated without passing through the cation state of the emitter, so that deterioration due to decomposition of the emitter molecule is suppressed and high reliability can be secured.

Similarly, in the second light emitting layer 142, the injected electrons are conducted through the second emitter. The energy position 147 'of the HOMO of the second emitter molecule in the anion state is lowered, becomes smaller than the HOMO of the second host material, and tends to trap holes. As a result, an excited state is generated from the anion state of the second emitter. Also in the second light emitting layer 142, since a recombination state is formed without passing through the cation state of the second emitter, high reliability can be ensured.

On the other hand, in the third light-emitting layer 143, the third emitter functions as a hole trap. However, since the third light-emitting layer 143 is on the second electrode 104 side which is a cathode, There are many injected electrons, and the anion state of the third emitter is larger than the cation state. Therefore, the ratio of the excited state formed through the anion state of the third emitter is high, and high reliability is ensured even in the third light emitting layer. In particular, if the electron mobility of the third light-emitting layer is larger than the hole mobility of the first light-emitting layer 41 and the hole mobility of the second light-emitting layer, The cation state of the emitter is not formed, but an anion state is formed, and holes are trapped therein, and an excited state is generated. Therefore, high reliability is ensured also in the third light emitting layer. In the first light emitting layer and the second light emitting layer, the HOMO energy position of the emitter molecule is larger than the HOMO energy position of the host material. Therefore, it is desirable to use blue and green emitters having a large band gap, that is, a short emission center wavelength. On the other hand, in the third light emitting layer, the HOMO energy position of the emitter molecule is smaller than the HOMO energy position of the host material, and the LUMO energy position of the emitter molecule is larger than the LUMO energy position of the host material. Therefore, it is desirable to use a red emitter having a small band gap, that is, a long emission center wavelength.

Here, carrier mobility is measured by the TOF method or the IS method. In the TOF method, a sheet-like electric charge is generated on one electrode side by a light pulse, swept to the opposite side by an electric field, travel time is measured from a transient current waveform, and mobility is obtained using an average electric field. Is the method. The IS method applies a small sine wave voltage signal to the element and calculates the travel time, ie, mobility, by obtaining the impedance spectrum as a function of the frequency of the applied voltage signal from the amplitude and phase of the response current signal. It is a method to do.

Next, another embodiment of the present invention will be described. FIG. 4 shows a conceptual diagram of energy levels of an organic light emitting device having three light emitting layers.

In FIG. 4, the organic layer 105 includes a first light emitting layer 241, a second light emitting layer 242, and a third light emitting layer 243. In the first light-emitting layer 241, the first emitter is dispersed in the first host material. In the second light-emitting layer 242, the second emitter is dispersed in the second host material. In the third light-emitting layer 243, the third emitter is dispersed in the third host material.

First, the transport of holes in the light emitting layer will be described. The HOMO energy position 244 of the first host material is smaller than the HOMO energy position 245 of the first emitter molecule. Therefore, the holes injected into the first light emitting layer 241 conduct between the first host molecules. The HOMO energy position 246 of the second host material is also smaller than the HOMO energy position 247 of the second emitter molecule. Similar to the first light-emitting layer 241, the holes injected into the second light-emitting layer 242 conduct between the second host molecules. The HOMO energy position 248 of the third host material is smaller than the HOMO energy position 249 of the third emitter molecule. Therefore, the holes injected into the third light emitting layer 243 are conducted between the third host molecules.

Next, the transport of electrons in the light emitting layer will be described. The LUMO energy position 254 of the third host material is smaller than the LUMO energy position 255 of the third emitter molecule. Therefore, the electrons injected into the third light emitting layer 243 are conducted between the third emitter molecules. The LUMO energy position 252 of the second host material is also smaller than the LUMO energy position 253 of the second emitter molecule. Similar to the third light emitting layer 243, the electrons injected into the second light emitting layer 242 conduct between the second emitter molecules. The LUMO energy position 250 of the first host material is smaller than the LUMO energy position 251 of the first emitter molecule, and the electrons injected into the first light emitting layer 241 conduct between the first emitter molecules. In the first light emitting layer, the second light emitting layer, and the third light emitting layer, electrons are conducted between the emitters. In order to improve the conduction characteristics, it is necessary to increase the concentration of the emitter. Specifically, 10% or more is desirable.

From the transport of holes and electrons, the recombination of carriers in each light emitting layer is as follows. In the first light emitting layer 241, the injected electrons are conducted through the first emitter. The energy position 245 ′ of the HOMO of the first emitter molecule in the anion state is lowered, becomes smaller than the HOMO of the first host material, and easily traps holes. As a result, an excited state is generated from the anion state of the first emitter. According to our simulation results, the triplet phosphorescent emitter molecule has an unstable cation state and is easily decomposed. In the first light emitting layer 241, an excited state is generated without passing through the cation state of the emitter, so that deterioration due to decomposition of the emitter molecule is suppressed, and high reliability can be secured.

Similarly, in the second light emitting layer 242, the injected electrons are conducted through the second emitter. The energy position 247 ′ of the HOMO of the second emitter molecule in the anion state is lowered, becomes smaller than the HOMO of the second host material, and easily traps holes. As a result, an excited state is generated from the anion state of the second emitter. Also in the second light emitting layer 242, a recombination state is formed without passing through the cation state of the second emitter, so that high reliability can be ensured.

Similarly, in the third light emitting layer 243, the injected electrons are conducted through the third emitter. The energy position 249 ′ of the HOMO of the third emitter molecule in the anion state is lowered, becomes smaller than the HOMO of the third host material, and easily traps holes. As a result, an excited state is generated from the anion state of the third emitter. Also in the third light emitting layer 243, a recombination state is formed without passing through the cation state of the third emitter, so that high reliability can be secured.

As shown in FIG. 8, the use of an element structure having a hole blocking layer 256 in the third light emitting layer 243 leads to higher efficiency. The HOMO energy position 257 of the hole blocking material is preferably larger than the HOMO energy position 248 of the third host material. Here, the HOMO of the host material refers to the HOMO of a thin film formed of the host material. In that case, the holes propagated in the third light-emitting layer remain at the interface between the third light-emitting layer and the hole blocking layer 256 and finally become an excited state, so that the reactive current that does not contribute to light emission is reduced. Therefore, high efficiency characteristics can be obtained.

Next, another embodiment of the present invention will be described. FIG. 5 shows a conceptual diagram of energy levels of an organic light emitting device having two light emitting layers.

In FIG. 5, the organic layer 105 includes a first light emitting layer 341 and a second light emitting layer 342. In the first light-emitting layer 341, a first emitter and a second emitter are dispersed in a first host material. In the second light-emitting layer 342, the third emitter is dispersed in the second host material.

First, the transport of holes in the light emitting layer will be described. The HOMO energy position 344 of the first host material is smaller than the HOMO energy position 345 of the first emitter molecule and the HOMO energy position 347 of the second emitter molecule. Therefore, the holes injected into the first light emitting layer 341 conduct between the first host molecules. The HOMO energy position 346 of the second host material is smaller than the HOMO energy position 349 of the third emitter molecule. Therefore, the holes injected into the second light emitting layer 342 are conducted between the third host molecules.

Next, the transport of electrons in the light emitting layer will be described. The LUMO energy position 352 of the second host material is smaller than the LUMO energy position 355 of the third emitter molecule. Therefore, the electrons injected into the second light emitting layer 342 are conducted between the third emitter molecules. The LUMO energy position 350 of the first host material is smaller than the LUMO energy position 351 of the first emitter molecule and the LUMO energy position 353 of the second emitter molecule, and is injected into the first light emitting layer 341. The electrons are conducted between the first emitter molecules, between the second emitter molecules, or between the first emitter molecule and the second emitter molecule. In both the first light emitting layer and the second light emitting layer, electrons are conducted between the emitter molecules. In order to improve the conduction characteristics, it is necessary to increase the concentration of the emitter. Specifically, 10% or more is desirable.

From the transport of holes and electrons, the recombination of carriers in each light emitting layer is as follows. In the first light emitting layer 341, the injected electrons are conducted through the first emitter or the second emitter. The energy position 345 ′ of the HOMO of the first emitter molecule in the anion state is lowered and becomes smaller than the energy position of the HOMO of the first host material, so that holes are easily trapped.

In addition, the HOMO energy position 347 ′ of the second emitter molecule in an anionic state is lowered in energy, and becomes smaller than the HOMO energy position of the first host material, and is easily trapped with holes. As a result, an excited state is generated from the anion state of the first emitter or the anion state of the second emitter. According to our simulation results, the triplet phosphorescent emitter molecule has an unstable cation state and is easily decomposed. In the first light-emitting layer 341, an excited state is generated without passing through the cation state of the emitter, so that deterioration due to decomposition of the emitter molecules is suppressed, and high reliability can be ensured. Also in the second light-emitting layer 342, the HOMO energy position 349 ′ of the third emitter molecule in an anionic state is reduced in energy and becomes smaller than the HOMO energy position of the second host material, and traps with holes. It becomes easy. As a result, an excited state is generated from the anion state of the third emitter. Therefore, since the recombination state is formed without passing through the cation state of the third emitter, high reliability can be ensured.

As shown in FIG. 9, the use of an element structure in which a hole blocking layer 356 is provided in the second light emitting layer 342 leads to higher efficiency. The energy position 357 of the HOMO of the hole blocking material is preferably larger than the HOMO of the second host material. In that case, the holes propagated in the second light-emitting layer remain at the interface between the second light-emitting layer and the hole blocking layer, and finally enter an excited state, so that the reactive current that does not contribute to light emission is reduced. Therefore, high efficiency characteristics can be obtained.

Next, another embodiment of the present invention will be described. FIG. 6 shows a conceptual diagram of energy levels of an organic light emitting device having two light emitting layers.

In FIG. 6, the light emitting layer of the organic layer 105 includes a first light emitting layer 441 and a second light emitting layer 442. Compared with FIG. 5, the stacking order of the first light-emitting layer 441 and the second light-emitting layer 442 is different. In the first light-emitting layer 441, a first emitter and a second emitter are dispersed in a first host material. In the second light-emitting layer 442, the third emitter is dispersed in the third host material.

First, the transport of holes in the light emitting layer will be described. The HOMO energy position 446 of the second host material is smaller than the HOMO energy position 449 of the third emitter molecule. Therefore, the holes injected into the second light emitting layer 442 conduct between the third host molecules. The HOMO energy position 444 of the first host material is smaller than the HOMO energy position 445 of the first emitter molecule and the HOMO energy position 447 of the second emitter molecule. Therefore, the holes injected into the first light emitting layer 441 conduct between the first host molecules.

Next, the transport of electrons in the light emitting layer will be described. The LUMO energy position 450 of the first host material is smaller than the LUMO energy position 451 of the first emitter molecule and the LUMO energy position 453 of the second emitter molecule, and is injected into the first light emitting layer 441. The electrons are conducted between the first emitter molecules, between the second emitter molecules, or between the first emitter molecule and the second emitter molecule. The LUMO energy position 452 of the second host material is smaller than the LUMO energy position 455 of the third emitter molecule. Therefore, the electrons injected into the second light emitting layer 442 conduct between the third emitter molecules. In both the first light emitting layer and the second light emitting layer, electrons are conducted between the emitters. In order to improve the conduction characteristics, it is necessary to increase the concentration of the emitter. Specifically, 10% or more is desirable.

From the transport of holes and electrons, the recombination of carriers in each light emitting layer is as follows. In the second light-emitting layer 442, a recombination state is formed without passing through the cation state of the third emitter, so that high reliability can be ensured. In the first light emitting layer 441, the injected electrons are conducted through the first emitter or the second emitter. The energy position 445 ′ of the HOMO of the first emitter molecule in the anion state is lowered and becomes smaller than the energy position of the HOMO of the first host material, so that holes are easily trapped. In addition, the HOMO energy position 447 ′ of the second emitter molecule in an anionic state is lowered in energy, and becomes smaller than the HOMO energy position of the first host material, and is easily trapped with holes. As a result, an excited state is generated from the anion state of the first emitter or the anion state of the second emitter. According to our simulation results, the triplet phosphorescent emitter molecule has an unstable cation state and is easily decomposed. In the first light-emitting layer 441, the HOMO energy position 445 ′ of the first emitter molecule in an anionic state is reduced in energy and becomes smaller than the HOMO energy position 444 of the first host material, and traps with holes. It becomes easy. In addition, the HOMO energy position 447 ′ of the second emitter molecule in an anionic state is reduced in energy, and becomes smaller than the HOMO energy position 444 of the first host material, so that it is easy to trap holes. As a result, an excited state is generated from the anion state of the first and second emitters. Therefore, an excited state is generated without passing through the cation state of the emitter, so that deterioration due to decomposition of the emitter molecule is suppressed, and high reliability can be secured.

As shown in FIG. 10, using an element structure in which a hole blocking layer 456 is provided next to the first light emitting layer 441 leads to higher efficiency. The HOMO energy position 457 of the hole blocking material is preferably larger than the HOMO energy position 444 of the first host material. In that case, the holes propagated in the first light-emitting layer remain at the interface between the first light-emitting layer and the hole blocking layer 456, and finally enter an excited state, thereby reducing reactive current that does not contribute to light emission. Therefore, high efficiency characteristics can be obtained.

Next, another embodiment of the present invention will be described. FIG. 7 shows a conceptual diagram of energy levels of an organic light emitting element having one light emitting layer.

In FIG. 7, the organic layer 105 is composed of a first light emitting layer 541. In the first light-emitting layer 541, a first emitter, a second emitter, and a third emitter are dispersed in a first host material. The third emitter is unevenly distributed on the second electrode 104 side.

First, the transport of holes in the light emitting layer will be described. The HOMO energy position 544 of the first host material is smaller than the HOMO energy position 545 of the first emitter molecule and the HOMO energy position 547 of the second emitter molecule. Moreover, it is larger than the HOMO energy position 549 of the third emitter molecule. Therefore, the holes injected into the first light-emitting layer 541 are conducted between the first host molecules and trapped by the third emitter unevenly distributed on the second electrode side.

Next, the transport of electrons in the light emitting layer will be described. The LUMO energy position 550 of the first host material is the LUMO energy position 555 of the third emitter molecule, the LUMO energy position 551 of the first emitter molecule, and the LUMO energy position 553 of the second emitter molecule. Smaller than that. Therefore, the electrons injected into the first light-emitting layer 541 are conducted between the third emitter molecule, the first emitter molecule, the second emitter molecule, or between the first emitter molecule and the second emitter molecule. In the first light emitting layer, electrons are conducted between the emitters. In order to improve the conduction characteristics, it is necessary to increase the concentration of the emitter. Specifically, 10% or more is desirable.

From the transport of holes and electrons, the recombination of carriers in each light emitting layer is as follows. In the first light emitting layer 541, the injected electrons are conducted through the first emitter or the second emitter. The HOMO energy position 545 ′ of the first emitter molecule in an anionic state is lowered in energy, and becomes smaller than the HOMO energy position of the first host material, so that holes are easily trapped. In addition, the HOMO energy position 547 ′ of the second emitter molecule in an anionic state is reduced in energy, and becomes smaller than the HOMO energy position of the first host material, so that holes are easily trapped. As a result, an excited state is generated from the anion state of the first emitter or the anion state of the second emitter. In addition, since the recombination state is formed without passing through the cation state even in the third emitter unevenly distributed on the second electrode 104 side, high reliability can be ensured. In the first light emitting layer, the HOMO energy position of the third emitter molecule is smaller than the HOMO energy position of the first host material, and the LUMO energy position of the third emitter molecule is the LUMO energy position of the first host material. Greater than energy position. Therefore, it is desirable to use a red emitter having a small band gap, that is, a long emission center wavelength, as the third emitter.

The organic layer will be described below.

<Light emitting layer host>
As the host, it is preferable to use a carbazole derivative, a fluorene derivative, an arylsilane derivative, or the like. In order to obtain efficient light emission, the excitation energy of the host is preferably sufficiently larger than the excitation energy of the blue emitter. The excitation energy is measured using an emission spectrum.

<Blue emitter>
The blue emitter has a maximum PL spectrum intensity at room temperature between 400 nm and 500 nm. Examples of the main skeleton of the blue emitter include perylene and iridium complexes (Bis (3,5-difluoro-2- (2-pyrylyl) phenyl- (2-carbopyrylyl) iridium (III)): FIrpic and the like). Among them, the iridium complex represented by (Chemical Formula 11) is more preferable in terms of light emission characteristics. In the formula, X1 represents an aromatic heterocycle containing N, and X2 represents an aromatic hydrocarbon ring or an aromatic heterocycle.

Examples of the aromatic heterocycle represented by X1 include quinoline ring, isoquinoline ring, pyridine ring, quinoxaline ring, thiazole ring, pyrimidine ring, benzothiazole ring, oxazole ring, benzoxazole ring, indole ring and isoindole ring. It is done. Examples of the aromatic hydrocarbon ring or aromatic heterocycle represented by X2 include a benzene ring, naphthalene ring, anthracene ring, thiophene ring, benzothiophene ring, furan ring, benzofuran ring, and fluorene ring. In the formula, X3 includes acetylacetonate derivatives, picolinate derivatives, tetrakispyrazolyl borate derivatives and the like. X3 may be the same as X1-X2.

From the viewpoint of luminous efficiency and carrier conduction, the concentration of the blue emitter is preferably 10 wt% or more with respect to the host. The weight average molecular weight of the blue emitter is preferably 500 or more and 3000 or less.

<Green emitter>
The green emitter has a maximum PL spectrum intensity at room temperature between 500 nm and 590 nm. Examples of the main skeleton of the green emitter include coumarin and derivatives thereof, and iridium complexes (Tris (2-phenylpyridine) iridium (III): hereinafter Ir (ppy) ₃ , etc.). Among them, the iridium complex represented by (Chemical Formula 11) is more preferable in terms of light emission characteristics. In the formula, X1 represents an aromatic heterocycle containing N, and X2 represents an aromatic hydrocarbon ring or an aromatic heterocycle.

Examples of the aromatic heterocycle represented by X1 include quinoline ring, isoquinoline ring, pyridine ring, quinoxaline ring, thiazole ring, pyrimidine ring, benzothiazole ring, oxazole ring, benzoxazole ring, indole ring and isoindole ring. It is done. Examples of the aromatic hydrocarbon ring or aromatic heterocycle represented by X2 include a benzene ring, naphthalene ring, anthracene ring, thiophene ring, benzothiophene ring, furan ring, benzofuran ring, and fluorene ring. X3 is an acetylacetonate derivative, and the same as X1-X2.

As described above, the HOMO energy position of the green emitter molecule is preferably larger than the HOMO energy position of the host material to which the emitter is added. Further, it is desirable that the energy position of the anionic HOMO in which electrons are supplied to the green emitter is smaller than the energy position of the HOMO of the host material to which the emitter is added. Specific examples include (Chemical Formula 14), (Chemical Formula 15), and (Chemical Formula 16).

Regarding the HOMO energy position of the green emitter molecule and the HOMO energy position of the host material,
LUMO (host1) <LUMO (emit1)
In the cationic state,
LUMO (host1) ≧ LUMO (emit1)
Satisfy the relationship. This relationship also holds for the HOMO energy position of the blue emitter molecule and the HOMO energy position of the host material.

From the viewpoint of luminous efficiency, suppression of energy transfer from the blue emitter, and carrier conduction, the concentration of the green emitter is preferably 1 wt% or less with respect to the host. The weight average molecular weight of the green emitter is preferably 500 or more and 3000 or less.

<Red emitter>
The red emitter has a maximum PL spectrum intensity at room temperature between 590 nm and 780 nm. The main skeleton of the red emitter includes, for example, rubrene, (E) -2- (2- (4- (dimethylamino) styryl) -6-methyl-4H-pyran-4-ylidene) malononitrile (DCM) and its derivatives, iridium Complexes (such as Bis (1-phenylisoquinoline) (acetylacetonate) iridium (III)), osmium complexes, and europium complexes can be given. Among them, the iridium complex represented by (Chemical Formula 11) is more preferable in terms of light emission characteristics. In the formula, X1 represents an aromatic heterocycle containing N, and X2 represents an aromatic hydrocarbon ring or an aromatic heterocycle.

Examples of the aromatic heterocycle represented by X1 include quinoline ring, isoquinoline ring, pyridine ring, quinoxaline ring, thiazole ring, pyrimidine ring, benzothiazole ring, oxazole ring, benzoxazole ring, indole ring and isoindole ring. It is done. Examples of the aromatic hydrocarbon ring or aromatic heterocycle represented by X2 include a benzene ring, naphthalene ring, anthracene ring, thiophene ring, benzothiophene ring, furan ring, benzofuran ring, and fluorene ring. X3 is preferably an acetylacetonate derivative or the like.

From the viewpoint of suppressing energy transfer from the blue emitter and carrier conduction, the concentration of the red emitter is preferably 1 wt% or less with respect to the host. The weight average molecular weight of the red emitter is preferably 500 or more and 3000 or less.

<Hole injection layer>
The hole injection layer is used for the purpose of improving luminous efficiency and lifetime. Moreover, although it is not essential, it is used for the purpose of relaxing the unevenness of the anode. A single hole injection layer or a plurality of hole injection layers may be provided. The hole injection layer is preferably a conductive polymer such as PEDOT (poly (3,4-ethylenedioxythiophene)): PSS (polystyrene sulfonate). In addition, polypyrrole-based or triphenylamine-based polymer materials can be used. Further, phthalocyanine compounds and starburst amine compounds that are often used in combination with a low molecular weight (weight average molecular weight 10,000 or less) material system are also applicable.

<Hole transport layer>
The hole transport layer is a layer that supplies holes to the light emitting layer. In a broad sense, a hole injection layer and an electron blocking layer are also included in the hole transport layer. A single hole transport layer or a plurality of hole transport layers may be provided. As the hole transport layer, a starburst amine compound, a stilbene derivative, a hydrazone derivative, a thiophene derivative, a fluorene derivative, or the like can be used. Further, the present invention is not limited to these materials, and two or more of these materials may be used in combination. In order to lower the resistance of the hole transport layer and reduce the driving voltage, an electron accepting material may be added to the hole transport layer.

<Electron blocking layer>
An electron blocking layer for confining electrons in the light emitting layer may be provided between the hole transport layer and the light emitting layer. The electron blocking layer material preferably has a small LUMO energy position. Specifically, TAPC ((Chemical Formula 1)) and NPB ((Chemical Formula 2)) are desirable, but are not limited to these materials. Moreover, the material which can be used together among the above may be contained in the electron blocking layer of 1 type, or 2 or more types.

<Electron transport layer>
The electron transport layer is a layer that supplies electrons to the light emitting layer. In a broad sense, an electron injection layer and a hole blocking layer are also included in the electron transport layer. A single layer or a plurality of electron transport layers may be provided. Examples of the material for the electron transport layer include bis (2-methyl-8-quinolinolato) -4- (phenylphenolato) aluminum (BAlq), tris (8-quinolinolato) aluminum (Alq ₃ ), Tris (2 4,6-trimethyl-3- (pyridin-3-yl) phenyl) borane (3TPYMB), 1,4-Bis (triphenylsilyl) benzene (UGH2), oxadiazole derivatives, triazole derivatives, fullerene derivatives, phenanthroline derivatives, A quinoline derivative, a silole derivative, or the like can be used. In order to lower the resistance of the electron transport layer and reduce the driving voltage of the device, an electron donating material may be added to the electron transport layer.

<Hole blocking layer>
In order to confine holes in the light emitting layer between the light emitting layer and the electron transport layer, a hole blocking layer may be provided. The hole blocking layer material preferably has a deep HOMO energy position. Specific examples include 3TPYMB ((Chemical Formula 3)) and Alq ₃ ((Chemical Formula 4)), but are not limited to these materials. Moreover, the material which can be used together among the above may be contained in the 1 or 2 or more types of hole-blocking layer.

<Electron injection layer>
The electron injection layer improves the electron injection efficiency from the cathode to the electron transport layer. Specifically, lithium fluoride, magnesium fluoride, calcium fluoride, strontium fluoride, barium fluoride, magnesium oxide, and aluminum oxide are desirable. Of course, the material is not limited to these materials, and two or more of these materials may be used in combination.

<Board>
Examples of the first substrate 101 and the second substrate 102 include a glass substrate, a metal substrate, a plastic substrate on which an inorganic material such as SiO ₂ , SiN _x , and Al ₂ O ₃ is formed. Examples of the metal substrate material include alloys such as stainless steel and alloy. Examples of the plastic substrate material include polyethylene terephthalate, polyethylene naphthalate, polymethyl methacrylate, polysulfone, polycarbonate, and polyimide.

<Anode>
As the anode material, any material having transparency and a high work function can be used. Specifically, conductive oxides such as ITO and IZO and metals having a large work function such as thin Ag can be used. In general, the electrode pattern can be formed on a substrate such as glass by using photolithography.

<Cathode>
The cathode material is a reflective electrode for reflecting light from the light emitting layer. Specifically, a laminate of LiF and Al, an Mg: Ag alloy, or the like is preferably used. Moreover, it is not limited to these materials, For example, a Cs compound, Ba compound, Ca compound etc. can be used instead of LiF.

The contents of the present invention will be described in more detail below by showing specific examples.

As a first example of the present invention, an organic light-emitting device having three light-emitting layers shown in FIGS. 3 and 4 was fabricated by the following procedure using a vapor deposition method.

A glass substrate with an ITO (150 nm) electrode was immersed in acetone and subjected to ultrasonic cleaning for 10 minutes. Next, pure water cleaning and rotary drying were performed using an ultrasonic spin cleaning machine using pure water. Thereafter, the substrate was heated at 200 ° C. for 10 minutes in an air atmosphere using a hot plate. After heating, the substrate was cooled for 10 minutes, and UV / O ₃ treatment was performed at an irradiation intensity of 8 mW / cm ^{2 for} 30 minutes.

On the substrate subjected to these treatments, α-NPD ((Chemical Formula 2)) was formed as a hole injection layer by a vacuum deposition apparatus. The thickness of the hole injection layer was 5 nm.

Next, TAPC ((Chemical Formula 1)) was formed as a hole transport layer on the substrate. The thickness of the hole injection layer was 85 nm.

Next, on the hole transport layer, an organic film having a thickness of 10 nm is formed as a first light emitting layer by doping the host material TCZ-1 ((Chemical Formula 5)) with 1 wt% of the green emitter (Chemical Formula 6). did. On top of that, an organic film having a thickness of 10 nm was formed by doping the host material mCP ((Chemical Formula 7)) with 10 wt% of the blue emitter FIr6 (Chemical Formula 8) as the second light emitting layer. On top of that, an organic film having a thickness of 10 nm was formed by doping the host material CBP ((Chemical Formula 9)) with 1 wt% of the red emitter (Chemical Formula 10) as the third light emitting layer.

Here, the green light emitter is placed in the first light emitting layer and the blue light emitter is put in the second light emitting layer. However, the blue light emitter is placed in the first light emitting layer and the second light emitting layer is reversed. The organic light emitting device of the present invention can also be manufactured with a configuration in which a green emitter is inserted in the green light emitter.

Next, a 3TPYMB ((Chemical Formula 3)) film was formed as an electron transport layer on the third light-emitting layer. The film thickness of the electron transport layer was 30 nm.

Next, LiF was formed as an electron injection layer on the hole blocking layer. The thickness of the electron injection layer was 0.5 nm. Next, Al was deposited as a cathode on the electron injection layer. The film thickness of the cathode was 150 nm.

Finally, sealing was performed using a sealing substrate with a sealing agent made of a photo-curing resin, to produce an organic light emitting device.

In the present organic light emitting device, in the first light emitting layer and the second light emitting layer, since the HOMO energy position of the emitter molecule is deeper than the HOMO energy position of the host material, holes propagate between the host materials. . Further, since the LUMO energy position of the emitter molecule is deeper than the LUMO energy position of the host material, electrons are repeatedly captured and emitted by the emitter and propagated through the light emitting layer. For this reason, the excited states of the green and blue emitters were generated without passing through cations, so that the deterioration of the emitters was reduced. Further, in the third light emitting layer, holes are injected in a state where there are many anions of the red emitter, so that the excited state of the red emitter was generated without passing through the cation, so that deterioration of the emitter was reduced. Due to the above effects, the lifetime of the organic light emitting device was improved.

Next, as a second example of the present invention, an organic light-emitting device having two light-emitting layers shown in FIGS. 5 and 6 was fabricated according to the following procedure using a vapor deposition method.

The pretreatment method of the glass substrate with ITO electrode and the formation method of the hole injection layer and the hole transport layer are the same as in Example 1.

Next, 10 wt% of the green emitter ((Chemical Formula 12)) and 10 wt% of the red emitter ((Chemical Formula 10)) are added to the host material TCZ-1 ((Chemical Formula 5)) as the first light emitting layer on the hole transport layer. % Doped organic film was formed. The thickness of the first light emitting layer was 15 nm. Next, an organic film having a film thickness of 15 nm was formed by doping the host material mCP ((Chemical Formula 7)) with 10 wt% of the blue emitter FIr6 ((Chemical Formula 8)) as the second light emitting layer in the first light emitting layer. In addition, the electron transport layer, electron injection layer, cathode, sealing formation method, and conditions are the same as in Example 1.

In the present organic light emitting device, in the first light emitting layer, the HOMO energy position of the emitter molecule is deeper than the HOMO energy position of the host material, and the LUMO energy position of the emitter molecule is deeper than the LUMO energy position of the host material. The excited states of the green and red emitters were generated without passing through cations, and the deterioration of the emitters was reduced. In the third light emitting layer, the excited state of the blue emitter is generated without passing through the cation, and the deterioration of the emitter is reduced. Due to the above effects, the lifetime of the organic light emitting device was improved.

Next, as a third example of the present invention, an organic light-emitting device having one light-emitting layer shown in FIG. 7 was prepared according to the following procedure using a coating method.

An ITO electrode was used for the lower electrode, and a polymer material was used for the hole transport layer. For the light emitting layer, TCZ-1 ((Chemical formula 5)) was used as the host material, FIr6 ((Chemical formula 8)) was used as the blue emitter, (Chemical formula 6) was used as the green emitter, and (Chemical formula 13) was used as the red emitter. The weight ratio of each material was 100: 10: 1: 1.

These coating materials were prepared by dissolving the host material, blue emitter, green emitter, and red emitter material in toluene. The solid component concentration of the coating liquid was set to 1 wt.%. Using this coating solution, a light emitting layer was formed by spin coating.

Next, an electron transport layer was formed. An electron transport layer was formed by spin coating using a coating solution in which (Chemical Formula 6) was dissolved in 2-propanol. Subsequently, a laminate of LiF and Al was formed as an electron injection layer / cathode, and a target organic light emitting device was produced. The sealing method is the same as in Example 1.

In the present organic light emitting device, in the light emitting layer, the red emitter was localized on the upper surface side serving as the electron transport layer side due to the substituent. Since the HOMO energy position of the blue emitter and the green emitter molecule is deeper than the HOMO energy position of the host material, and the LUMO energy position of the blue emitter and the green emitter molecule is deeper than the LUMO energy position of the host material, the blue emitter and the green emitter The excited state of was generated without going through the cation, and the deterioration of the emitter was reduced. In addition, the HOMO energy position of the red emitter molecule is shallower than the HOMO energy position of the host material, but the LUMO energy position of the red emitter molecule is deeper than the LUMO energy position of the host material. A state was formed and emitter degradation was reduced. Due to the above effects, the lifetime of the organic light emitting device was improved.

1, 141, 241, 341, 441, 541 First

light emitting layer

2, 142, 242, 342, 442 Second light emitting layer 3 HOMO of hole transport layer 14
4 HOMO of the host material of the first light emitting layer 1
5 HOMO of the host material of the second light emitting layer 2
6 LUMO of electron transport layer 15
7 LUMO of the host material of the first light emitting layer 1
8 LUMO of the host material of the second light emitting layer 2
9 hole 10 electron 11 LUMO energy position 12 of the emitter molecule dispersed in the first light emitting layer 1 and the second light emitting layer 2 emitter molecule dispersed in the first light emitting layer 1 and the second light emitting layer 2 HOMO energy position 14 hole transport layer 15 electron transport layer 101 first substrate 102 second substrate 103 first electrode 104 second electrode 105 organic layers 143, 243 third light emitting layers 144, 244, 344 445, 544 HOMO energy position of the first host material 145, 245, 345, 445, 545 HOMO energy position of the first emitter molecule 146, 246, 346, 446 HOMO energy position of the second host material 147, 247, 347, 447, 547 HOMO energy positions 148, 248 of the second emitter molecule HOMO energy positions 149, 249, 349, 449, 549 of the third material HOMO energy positions 150, 250, 350, 450, 550 of the third emitter molecule LUMO energy positions 151, 251, 351 of the first host material , 451, 551 LUMO energy position of the first emitter molecule 152, 252, 352, 452 LUMO energy position of the second host material 153, 253, 353, 453, 553 LUMO energy position of the second emitter molecule 154, 254 LUMO energy position of the third host material 155, 255, 355, 455, 555 LUMO energy position of the third emitter molecule

Claims

An anode, a cathode,
An organic light emitting device having a first light emitting layer, a second light emitting layer, and a third light emitting layer disposed in order between the anode and the cathode,
In the first light emitting layer, the first emitter is dispersed in the first host material,
In the second light emitting layer, the second emitter is dispersed in the second host material,
In the third light emitting layer, the third emitter is dispersed in the third host material,
In the first light emitting layer, holes are conducted between the first host materials of the light emitting layer,
In the second light emitting layer, holes are conducted between the second host materials of the light emitting layer,
In the first light emitting layer, electrons are conducted between the first emitters of the light emitting layer,
In the second light emitting layer, electrons are conducted between the second emitters of the light emitting layer,
In the third light emitting layer, an electron is conducted between the third emitters of the light emitting layer.
The organic light-emitting device according to claim 1,
In the third light emitting layer, the organic light emitting element is characterized in that holes are trapped by a third emitter.
The organic light-emitting device according to claim 1,
The hole mobility of the first light emitting layer is smaller than the electron mobility of the third light emitting layer,
The organic light emitting device, wherein the hole mobility of the second light emitting layer is smaller than the electron mobility of the third light emitting layer.
The organic light emitting device according to claim 1,
HOMO of the first host material is HOMO (host 1),
HOMO of the first emitter molecule is HOMO (emit1),
HOMO of the second host material is HOMO (host 2),
HOMO of the second emitter molecule is HOMO (emit2),
An organic light-emitting element satisfying the following formula:
HOMO (host1) <HOMO (emit1)
HOMO (host2) <HOMO (emit2)
The organic light emitting device according to claim 2,
HOMO of the third host material is HOMO (host 3),
The HOMO of the third emitter molecule is HOMO (emit3),
An organic light-emitting element satisfying the following formula:
HOMO (host3)> HOMO (emit3)
The organic light emitting device according to claim 1,
LUMO of the first host material is LUMO (host 1),
The LUMO of the first emitter molecule is LUMO (emit1),
LUMO of the second host material is LUMO (host 2),
LUMO of the second emitter molecule is LUMO (emit2),
LUMO of the third host material is LUMO (host 3),
LUMO of the third emitter molecule is LUMO (emit3),
An organic light-emitting element satisfying the following formula:
LUMO (host1) <LUMO (emit1)
LUMO (host2) <LUMO (emit2)
LUMO (host3) <LUMO (emit3)
The organic light-emitting device according to claim 1,
An organic light emitting device comprising a hole blocking layer.
An anode, a cathode,
An organic light emitting device having a first light emitting layer and a second light emitting layer disposed in order between the anode and the cathode,
In the first light emitting layer, the first emitter and the second emitter are dispersed in the first host material,
In the second light emitting layer, the third emitter is dispersed in the second host material,
In the first light emitting layer, holes are conducted between the first host materials of the light emitting layer,
In the second light emitting layer, holes are conducted between the second host materials of the light emitting layer,
In the first light emitting layer, electrons are conducted between the first emitters of the light emitting layer, between the second emitter molecules, or between the first emitter and the second emitter,
In the second light-emitting layer, an electron is conducted between the third emitters of the light-emitting layer.
The organic light emitting device according to claim 8,
HOMO of the first host material is HOMO (host 1),
HOMO of the first emitter molecule is HOMO (emit1),
HOMO of the second emitter molecule is HOMO (emit2),
HOMO of the second host material is HOMO (host 2),
The HOMO of the third emitter molecule is HOMO (emit3),
An organic light-emitting element satisfying the following formula:
HOMO (host1) <HOMO (emit1)
HOMO (host1) <HOMO (emit2)
HOMO (host2) <HOMO (emit3)
The organic light emitting device according to claim 8,
LUMO of the first host material is LUMO (host 1),
The LUMO of the first emitter molecule is LUMO (emit1),
LUMO of the second emitter molecule is LUMO (emit2),
LUMO of the second host material is LUMO (host 2),
LUMO of the third emitter molecule is LUMO (emit3),
An organic light-emitting element satisfying the following formula:
LUMO (host1) <LUMO (emit1)
LUMO (host1) <LUMO (emit2)
LUMO (host2) <LUMO (emit3)
An anode, a cathode,
An organic light-emitting device having a first light-emitting layer sequentially disposed between the anode and the cathode,
In the first light emitting layer, the first emitter, the second emitter, and the third emitter are dispersed in the first host material,
In the first light-emitting layer, holes are conducted between the first host molecules and trapped by a third emitter that is unevenly distributed on the second electrode side,
In the first light emitting layer, electrons are conducted between the first emitter, the second emitter, the first emitter and the second emitter, or the third emitter of the light emitting layer. Organic light emitting device.
The organic light emitting device according to claim 11,
HOMO of the first host material is HOMO (host 1),
HOMO of the first emitter molecule is HOMO (emit1),
HOMO of the second emitter molecule is HOMO (emit2),
The HOMO of the third emitter molecule is HOMO (emit3),
An organic light-emitting element satisfying the following formula:
HOMO (host1) <HOMO (emit1)
HOMO (host1) <HOMO (emit2)
HOMO (host1)> HOMO (emit3)
The organic light emitting device according to claim 11,
LUMO of the first host material is LUMO (host 1),
The LUMO of the first emitter molecule is LUMO (emit1),
LUMO of the second emitter molecule is LUMO (emit2),
LUMO of the third emitter molecule is LUMO (emit3),
An organic light-emitting element satisfying the following formula:
LUMO (host1) <LUMO (emit1)
LUMO (host1) <LUMO (emit2)
LUMO (host1) <LUMO (emit3)
The organic light emitting device according to any one of claims 1 to 13,
The concentration of the first emitter is m (emit1),
The concentration of the second emitter is m (emit2),
The concentration of the third emitter is m (emit3),
An organic light-emitting element satisfying the following formula:
m (emit1) ≧ 10%
m (emit2) ≧ 10%
m (emit3) ≧ 10%
The organic light emitting device according to any one of claims 1 to 7, 11 to 13,
An organic light emitting element, wherein the emission color of the third emitter is red.
The organic light emitting device according to any one of claims 1 to 7,
LUMO of the first host material is LUMO (host 1),
The LUMO of the first emitter molecule is LUMO (emit1),
LUMO of the second host material is LUMO (host 2),
LUMO of the second emitter molecule is LUMO (emit2),
An organic light-emitting element satisfying the following formula:
In the neutral state,
LUMO (host1) <LUMO (emit1)
LUMO (host2) <LUMO (emit2)
In the cationic state,
LUMO (host1) ≧ LUMO (emit1)
LUMO (host2) ≧ LUMO (emit2)