JPH11204266A - Organic electroluminescence element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescence (EL) element requiring a lower driving voltage and having higher efficiency than the conventional organic EL element. SOLUTION: A luminescent layer 4 made of an organic compound is pinched by an anode electrode 2 and a cathode electrode 5 to form this organic EL element. A hole injection layer 3 made of a π-conjugate oligomer is provided between the anode electrode 2 and the luminescent layer 4, the π-conjugate oligomer has a higher ionization potential than at least that of the anode electrode 2, and this molecule aggregate is made of multiple π-conjugate oligomers having the ionization potentials discretely distributed from near the ionization potential of the anode electrode 2 to near the ionization potential of the luminescent layer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an organic electroluminescence (EL) device having polarized light emission.

[0002]

2. Description of the Related Art In 1987, an organic electroluminescence device (hereinafter, also referred to as "organic EL device") using an organic compound thin film for a light emitting layer or a charge transport layer was developed.

[0003] For example, CW Tan
g) and SA VanSlyke
Written by Applied Physi Letters
cs Letters) 51 [12] (1987) pp. 913-915 discloses a basic structure of an organic EL device as shown in FIG.
FIG. 3 is a schematic sectional view showing a basic structure of a conventional organic EL element. 3, reference numeral 1 denotes a substrate, 2 denotes an anode electrode, 4 denotes an emission layer, 5 denotes a cathode electrode, and 6 denotes a hole transport layer. The conventional organic EL device has a structure in which a substrate 1, an anode electrode 2, a hole transport layer 6, a light emitting layer 4, and a cathode electrode 5 are sequentially laminated. The hole is the anode electrode 2
Is injected into the light emitting layer 4 via the hole transport layer 6, and electrons are injected from the cathode electrode 5 into the light emitting layer 4. Light emitting layer 4
The holes and the electrons injected into the light emitting layer recombine in the light emitting layer, and the energy when deactivated to the ground state is emitted as light (indicated by arrow B) to the outside. Generally, the anode electrode 2 is formed of a transparent thin film having a large work function such as ITO, and light is extracted to the outside from the transparent electrode side. The cathode electrode is composed of a thin film having a small work function such as Mg having a small work function, and the light emitting layer is generally made of a fluorescent material such as a quinolinol complex.
The hole transport layer 6 has a function of efficiently transporting holes from the anode electrode to the light-emitting layer, and further has a function of efficiently injecting holes into the light-emitting layer 4. Further, the hole transport layer also has a function of blocking the outflow of electrons from the light emitting layer to the hole transport layer. Thus, in the organic EL device having the above configuration, light emission with high luminance at a low voltage is obtained.

[0004]

As described above, the organic E
The L element can be driven at a low voltage, but for practical use, further lower voltage driving is required. At the same time, further improvement in luminous efficiency is required. Organic E
In the L element, an energy barrier exists at each interface between the cathode electrode and the light-emitting layer, the anode electrode and the hole transport layer, and at the interface between the hole transport layer and the light-emitting layer, and the charge must reach the light-emitting site beyond the energy barrier.

FIG. 4 is an energy diagram of a conventional organic EL device. In FIG. 4, the vertical axis indicates energy (eV). Further, 12 is the level of the anode electrode, 14 is the level of the light emitting layer, 15 is the level of the cathode electrode,
Reference numeral 16 denotes a level of the hole transport layer. Further, 17 indicates the energy difference between holes and electrons upon recombination,
Due to the recombination, light having a wavelength corresponding to the energy difference is emitted to the anode side. Reference numeral 18 indicates the emitted light. As shown in the figure, when the holes move from the anode electrode to the hole transport layer, they must cross the energy barrier 10a at the interface between the anode electrode and the hole transport layer. Must move over the energy barrier 10b at the interface between the hole transport layer and the light emitting layer. On the other hand, when electrons move from the cathode electrode to the light-emitting layer, they must cross the energy barrier 11 at the interface between the cathode electrode and the light-emitting layer. The higher the energy barrier, the more difficult it is for holes and electrons to move at the interface, and a higher driving voltage is required to obtain a predetermined light emission intensity.

In FIG. 4, it is necessary to prevent the electrons injected into the light emitting layer from moving from the light emitting layer to the hole transport layer so that the electrons do not exceed the energy barrier at the interface between the light emitting layer and the hole transport layer. As the energy barrier at the interface between the light emitting layer and the hole transport layer for the electrons is lower, the electrons flow out of the light emitting layer to the hole transport layer, and the probability of recombination with holes is reduced, thereby lowering the luminous efficiency.

The conventional organic EL device has such a problem.

The height of the energy barrier is the difference between the work function of the material of the anode electrode for holes and the ionization potential of the material of the hole transport layer and the light emitting layer, and the height of the energy barrier for electrons. , And the electron affinity of the material of the hole transport layer and the light emitting layer, and is determined by the material used. To solve the above problem, Japanese Patent Application Laid-Open No. 8-31574 discloses an organic light emitting device having a structure in which a material having an ionization potential smaller than the hole transport layer and containing a material larger than the anode electrode is provided near the anode electrode side of the hole transport layer. EL
An element is disclosed. However, the above problem has not been sufficiently solved.

In view of the above facts, an object of the present invention is to provide a highly efficient organic electroluminescent device having a lower driving voltage than conventional organic EL devices.

[0010]

The organic EL device according to claim 1 of the present invention is an organic electroluminescence device comprising a light emitting layer made of an organic compound sandwiched between an anode electrode and a cathode electrode. A hole injection layer comprising a π-conjugated oligomer is provided between the light-emitting layer and the light-emitting layer,
The π-conjugated oligomer has a higher ionization potential than at least the anode electrode, and is composed of a plurality of π-conjugated oligomers whose ionization potential is discretely distributed from the vicinity of the ionization potential of the anode electrode to the vicinity of the ionization potential of the light emitting layer. It is composed of molecular assemblies.

In the organic EL device according to the second aspect of the present invention, the plurality of π-conjugated systems in which the electron affinity of the hole injection layer is at least smaller than the electron affinity of the light emitting layer and the electron affinity is discretely distributed. It is composed of a molecular assembly composed of oligomers.

Further, the organic EL according to claim 3 of the present invention.
The device is provided with a hole injection layer made of a plurality of π-conjugated oligomers having different numbers of repeating units between the anode electrode and the light emitting layer.

Further, the organic EL according to claim 4 of the present invention.
In the device, the hole injection layer is obtained by mixing a plurality of kinds of π-conjugated oligomers having different repeating unit structures.

The organic EL according to claim 5 of the present invention.
In the device, the hole injection layer is formed by mixing a plurality of π-conjugated oligomers having different numbers of repeating units and a compound molecule having a hole transporting property different from the π-conjugated oligomer.

Further, the organic EL according to claim 6 of the present invention.
The device has a structure in which a hole transport layer made of a compound molecule having a hole transport property is inserted between at least one of the hole injection layer and the anode electrode or between the hole injection layer and the light emitting layer.

Further, in the organic EL device according to a seventh aspect of the present invention, the hole injection layer is formed by co-evaporation using a vacuum evaporation method.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to an organic electroluminescent device comprising a light emitting layer made of an organic compound sandwiched between an anode electrode and a cathode electrode, wherein a hole injection layer is inserted between the anode electrode and the light emitting layer. The present invention relates to an organic electroluminescence device comprising:

FIG. 1 shows each layer of the organic EL device of the present invention.
It will be described according to. FIG. 1 is a schematic sectional view showing the basic structure of the organic EL device of the present invention. In FIG. 1, 1 is a substrate, 2 is an anode electrode, 3 is a hole injection layer, 4 is a light emitting layer, and 5 is a cathode electrode. The organic EL device of the present invention has a structure in which a substrate 1, an anode electrode 2, a hole injection layer 3, a light emitting layer 4, and a cathode electrode 5 are sequentially laminated. Holes are injected from the anode electrode 2 to the light emitting layer 4 via the hole injection layer 3, and electrons are injected from the cathode electrode 5 to the light emitting layer 4. The holes and the electrons injected into the light emitting layer 4 recombine in the light emitting layer, and the energy when deactivated to the ground state is emitted as light (indicated by an arrow A) to the outside.

The basic layer structure of the organic EL device of the present invention is the same as the conventional organic EL device shown in FIG.

In the present invention, as described above, the hole injection layer inserted between the anode electrode and the light emitting layer has the greatest feature.

In the present invention, for convenience, a layer made of a π-conjugated oligomer having an ionization potential designed between an anode electrode and a light emitting layer is called a “hole injection layer”, and a conventionally used anode injection layer is used. The hole transporting layer (hole injecting layer) inserted between the electrode and the light emitting layer was called a “hole transporting layer” and distinguished.

The conventional organic EL device shown in FIG. 3 has a hole transporting layer for transporting holes to the light emitting layer.
In this case, one or both of the energy barrier when holes move from the anode electrode to the hole transport layer and the energy barrier when holes move from the hole transport layer to the light emitting layer are increased, and the driving voltage is increased. Was. Furthermore, the energy barrier when electrons move from the light emitting layer to the cathode electrode is reduced, and the luminous efficiency is reduced accordingly. In contrast, in the hole injection layer of the present invention,
It is composed of a plurality of types of oligomer molecules having different numbers of repeating units, and therefore has excellent driving voltage and luminous efficiency. FIG. 2 is an energy diagram showing the energy state of the organic EL device of the present invention.
In FIG. 2, the vertical axis indicates energy (eV). The same parts as those in FIG. 4 are indicated by the same reference numerals. Further, reference numeral 13 denotes a vacuum level of the hole injection layer.

In order to efficiently inject holes into the light-emitting layer or the electron-transporting layer, the anode electrode used in the present invention may be any one which is made of an electric conductor having a work function of 4.0 eV or more. And any one of inorganic substances such as metals, inorganic oxides and semiconductors, and organic substances. More specifically, in an organic EL element, in order to extract light from the substrate side, that is, the anode electrode side, ITO (indium tin oxide), In ₂ O ₃ (indium oxide), S
It is preferably a transparent electrode made of nO ₂ (tin oxide) or the like.

As the cathode electrode in the present invention, any conventional electric conductor having a work function of 4.5 eV or less from the viewpoint of efficiently injecting electrons into the light emitting layer or the electron transporting layer is used. It may be made of any of inorganic materials such as metals, inorganic oxides and semiconductors, and organic materials. More specifically, from the viewpoint of injection efficiency, an electrode made of Al, Mg: Ag alloy, or the like is preferable.

The organic compound constituting the light emitting layer of the present invention is represented by the following formula (1):

[0026]

Embedded image

A quinolinol complex represented by tris (8-hydroxyquinoline) aluminum (Alq ₃ ), a distyrylarylene derivative and poly (2,5-phenylenevinylene) or poly (9,
Conventional polymers such as π-conjugated polymers typified by 9-dihexylfluorene) and those doped with a laser dye may be used.

The substrate used in the present invention may be any substrate that has been conventionally used. In an organic EL device, light is extracted from the substrate side. For example, sapphire crystal, quartz, various types of glass, polycarbonate, etc. It is preferable to use a transparent substrate in a light emitting region such as plastic.

The organic EL device of the present invention comprises a substrate, an anode electrode, a light emitting layer, a hole injection layer, and a cathode electrode in principle. The organic EL device efficiently injects holes into the light emitting layer and further blocks electrons. A hole transport layer may be provided between the anode electrode and the light emitting layer,
An electron transport layer may be provided between the light emitting layer and the cathode electrode in order to efficiently inject electrons into the light emitting layer and to block holes. In this case, the materials constituting the hole transport layer and the electron transport layer may be conventional ones.

The organic compound constituting the hole injection layer of the present invention includes phenylene oligomer, thiophene oligomer, selenophene oligomer, aniline oligomer,
A π-conjugated oligomer molecule such as a phenylene vinylene oligomer, a thienylene vinylene oligomer, a phenylene ethynylene oligomer, a thienylene ethynylene oligomer, a pyridine oligomer, a pyrrole oligomer, a mixture thereof, or a copolymer thereof is used. Further, these π-conjugated oligomers may be mixed with a triphenyldiamine derivative or the like conventionally used as a hole transport layer to form a hole injection layer.

Next, a method for manufacturing the organic EL device of the present invention will be described.

First, an anode electrode is formed on a substrate by a dry process in a vacuum such as a sputtering method, and then a hole injection layer is formed on the anode electrode. In this case, a glass substrate provided with an anode electrode in advance may be used. Before forming the hole injection layer, a conventionally used hole transport layer may be formed. Further, a light emitting layer is formed on the hole injection layer. Then, a cathode electrode is formed on the light emitting layer. Further, a conventional electron transport layer may be formed on the light emitting layer before forming the cathode electrode. The anode electrode, the hole transport layer, the light emitting layer, the electron transport layer, and the cathode electrode are conventionally used materials, and may be manufactured by a conventional method.

The hole injection layer is formed by a vacuum evaporation method,
Molecular beam deposition, molecular beam epitaxial growth, cluster ion beam, ion deposition, ion plating, various chemical vapor deposition (CVD) methods, plasma polymerization,
A dry process such as a pulse laser deposition method may be used, but it is preferable to use a vacuum deposition method or a molecular beam deposition method in that a thin film to be a hole injection layer is formed under mild conditions. Furthermore, a vacuum deposition method is most preferable in that a hole injection layer is easily formed.

In the present invention, the hole injection layer is constituted by a plurality of types of molecules. Therefore, in the above-mentioned dry process, it is preferable to deposit molecules from a plurality of evaporation sources at the same time. Furthermore, from the viewpoint of easily producing a light emitting layer,
It is preferable to perform co-evaporation in a vacuum evaporation method. Less than,
The method for manufacturing the light-emitting layer of the present invention will be described typified by co-evaporation of a vacuum evaporation method. However, those skilled in the art can also manufacture the light-emitting layer of the present invention by other methods.

One evaporation source is charged with one kind of compound molecule, and a plurality of such evaporation sources are prepared. Further, a plurality of types of compound molecules having similar evaporation temperatures may be loaded in one evaporation source. A plurality of kinds of vapor deposition are performed at the same time so that the thin film composition includes a plurality of molecular species. The degree of vacuum at this time is 10 ^−2.
What is necessary is just to be higher than Pa. The deposition rate is controlled for each evaporation source using, for example, a film thickness sensor having a quartz oscillator. The deposition rate is not particularly limited, but the molecular species that is easily crystallized should not be higher than others. The substrate temperature is, for example, liquid nitrogen for cooling, and a heater for heating, which may be monitored by a thermocouple and controlled by a temperature controller. The temperature is preferably from -196 to + 300 ° C from the viewpoint of the efficiency of the organic molecules adhering to the substrate surface, and from 20 to 300 from the viewpoint that the temperature can be easily controlled.
C. is particularly preferred.

[0036]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1 First, a glass substrate (sheet resistance 15Ω / □) coated with ITO as an anode electrode was ultrasonically washed with isopropyl alcohol, then washed with pure water, rinsed with isopropyl alcohol, and immediately dried. I let it. This substrate was introduced into a substrate holder in a vacuum chamber, and 10
^The chamber was evacuated to ^-5 Pa. The evaporation cell is heated, and the number of repeating units on the substrate is different from the formula (2):

[0038]

Embedded image

A hole injection layer (thickness: 50 nm) was prepared by co-evaporation of the phenylene oligomer shown in FIG. At this time, the substrate temperature was 25 ° C.

Table 1 shows the ionization potential (eV) and electron affinity (eV) of the phenylene oligomer with respect to the number of repeating units.

[0041]

[Table 1]

The molar composition ratio of the hole injection layer is approximately (n−2 = 1) :( n−2 = 2) :( n−2 = 3):
(N-2 = 4): (n-2 = 5): (n-2 = 6) =
1: 2: 2: 2: 2: 2. Subsequently, Alq3 represented by the formula (1) was deposited on the hole injecting layer to form a light emitting layer (50 nm in thickness). Next, Mg and Ag were co-deposited to form a cathode electrode (thickness: 50 nm, Mg: Ag = 10:
1 weight ratio) to obtain an organic EL device of the present invention having the structure shown in FIG. 1 described above.

(Evaluation Method) The emission luminance when a DC voltage was applied to the obtained organic EL device was measured with a normal luminance meter.
It was examined by a method of evaluating a light emission start voltage at which light emission luminance becomes 1 cd / m ² . Table 2 shows the obtained results.

[0044]

[Table 2]

Example 2 An organic compound used for producing a hole injection layer was prepared by using a compound represented by the following formula (3) having a different number of repeating units:

[0046]

Embedded image

The hole injection layer (50 nm thick) was prepared by co-evaporation of the phenylene vinylene oligomer shown in FIG. At this time, the substrate temperature was 25 ° C.

Table 3 shows the ionization potential (e) of the phenylene vinylene oligomer with respect to the number of repeating units.
V) and a table showing electron affinity (eV).

[0049]

[Table 3]

The molar composition ratio of the hole injection layer is approximately (n−2 = 1) :( n−2 = 2) :( n−2 = 3):
(N-2 = 4) = 1: 1: 1: 1: 1. Otherwise in the same manner as in Example 1, an organic EL device according to the present invention was manufactured.

The same evaluation as in Example 1 was performed on the obtained organic EL device. Table 2 shows the results.

Example 3 An organic compound used to form a hole injection layer was co-deposited with a phenylene oligomer represented by the formula (2) and a phenylene vinylene oligomer represented by the formula (3) having different numbers of repeating units to form a hole injection layer ( (Thickness: 50 nm). At this time, the substrate temperature was 25 ° C. Further, the molar composition ratio of the hole injection layer is approximately phenylene oligomer (n-
2 = 1) :( n−2 = 2) :( n−2 = 3) :( n−2)
= 4) = 1: 2: 2: 2, phenylene vinylene oligomer (n−2 = 1) :( n−2 = 2) :( n−2 = 3) =
2: 2: 2. Otherwise in the same manner as in Example 1, an organic EL device according to the present invention was manufactured.

The same evaluation as in Example 1 was performed on the obtained organic EL device. Table 3 shows the results.

Example 4 An organic compound used for producing a hole injection layer was prepared by using a phenylene oligomer represented by the formula (2) having a different number of repeating units and a formula (4):

[0055]

Embedded image

N, N'-diphenyl-N, N'-
Bis (3-methylphenyl)-[1,1'-biphenyl] -4,4'-diamine (TPD) was co-deposited to form a hole injection layer (50 nm thick). At this time, the substrate temperature was 25 ° C. The molar composition ratio of the hole injection layer is approximately (n−2 = 1) :( n−2 = 2) :( n−2 =
3): (n−2 = 4): (n−2 = 5): (n−2 =
6) = 1: 2: 2: 2: 2: 2. Otherwise in the same manner as in Example 1, an organic EL device according to the present invention was manufactured.

The same evaluation as in Example 1 was performed on the obtained organic EL device. Table 2 shows the results.

Example 5 An organic compound used for producing a hole injection layer was co-deposited with a phenylene vinylene oligomer represented by the formula (3) having a different number of repeating units and a TPD represented by the formula (4) to form a hole injection layer (thickness). 50 nm). At this time, the substrate temperature was 25 ° C. The molar composition ratio of the hole injection layer is approximately (n−2 = 1) :( n−2 = 2) :( n−2)
= 3): (n−2 = 4) = 1: 1: 1: 1: 1. Otherwise in the same manner as in Example 1, an organic EL device according to the present invention was manufactured.

The same evaluation as in Example 1 was performed on the obtained organic EL device. Table 4 shows the results.

[0060]

[Table 4]

Example 6 First, a glass substrate (sheet resistance 15 Ω / □) coated with ITO as an anode electrode was ultrasonically cleaned with isopropyl alcohol, then washed with pure water, rinsed with isopropyl alcohol, and immediately dried. I let it. This substrate was introduced into a substrate holder in a vacuum chamber, and 10
^The chamber was evacuated to ^-5 Pa. The evaporation cell was heated and TPD was deposited on the anode electrode to form a hole transport layer (thickness 5).
0 nm). Next, a hole injection layer (thickness: 30 nm) was formed by co-evaporating an organic compound used for forming a hole injection layer on the hole transport layer with a phenylene oligomer represented by the formula (2) having a different number of repeating units. . At this time, the substrate temperature was 25 ° C. The molar composition ratio of the hole injection layer is approximately (n−2 = 1) :( n−2 = 2):
(N-2 = 3): (n-2 = 4): (n-2 = 5):
(N−2 = 6) = 1: 2: 2: 2: 2: 2. Otherwise in the same manner as in Example 1, an organic EL device according to the present invention was manufactured.

The same evaluation as in Example 1 was performed on the obtained organic EL device. Table 4 shows the results.

Example 7 First, a glass substrate (sheet resistance: 15 Ω / □) coated with ITO as an anode electrode was ultrasonically cleaned with isopropyl alcohol, then washed with pure water, rinsed with isopropyl alcohol, and immediately dried. I let it. This substrate was introduced into a substrate holder in a vacuum chamber, and 10
^The chamber was evacuated to ^-5 Pa. The evaporation cell was heated, and a phenylene vinylene oligomer represented by the formula (3) having a different number of repeating units was co-deposited on the anode electrode to form a first hole injection layer (thickness: 20 nm). Next, a phenylene oligomer represented by the formula (2) having a different number of repeating units was co-evaporated on the first hole injection layer to form a second hole injection layer (20 nm thick). At this time, the substrate temperature is 2
5 ° C. The molar composition ratio of the first hole injection layer is approximately (n−2 = 1) :( n−2 = 2) :( n−2 =
3): (n−2 = 4) = 1: 1: 1: 1: 1. The molar composition ratio of the second hole injection layer is approximately (n−2 = 1):
(N-2 = 2): (n-2 = 3): (n-2 = 4):
(N−2 = 5) :( n−2 = 6) = 1: 2: 2: 2:
2: 2. Otherwise in the same manner as in Example 1, an organic EL device according to the present invention was manufactured.

The same evaluation as in Example 1 was performed on the obtained organic EL device. Table 4 shows the results.

Comparative Example 1 A phenylene hexamer having a repeating unit number of n−2 = 4 among the phenylene oligomers represented by the formula (2) was deposited to form a hole transport layer (50 nm thick). At this time, the substrate temperature was 25 ° C. Otherwise in the same manner as in Example 1, an organic EL device according to the present invention was manufactured.

The same evaluation as in Example 1 was performed on the obtained organic EL device. Table 4 shows the results.

COMPARATIVE EXAMPLE 2 TPD represented by the formula (4) was vapor-deposited to form a hole transport layer (thickness: 5).
0 nm). At this time, the substrate temperature was 25 ° C. In this comparative example, no hole injection layer was provided. Otherwise in the same manner as in Example 1, an organic EL device according to the present invention was manufactured.

The same evaluation as in Example 1 was performed on the obtained organic EL device. Table 4 shows the results.

[0069]

The organic EL device according to the first aspect of the present invention is an organic electroluminescence device in which a light emitting layer made of an organic compound is sandwiched between an anode electrode and a cathode electrode. A hole injection layer comprising a π-conjugated oligomer between the π-conjugated oligomer, the π-conjugated oligomer having an ionization potential higher than at least the anode electrode, and the ionization potential of the light-emitting layer is changed from near the ionization potential of the anode electrode. Since it is composed of a molecular assembly composed of a plurality of π-conjugated oligomers discretely distributed to the vicinity, it is possible to provide an organic electroluminescence device that can be driven at a low voltage.

In the organic EL device according to a second aspect of the present invention, a plurality of π-conjugated systems in which the electron affinity of the hole injection layer is at least smaller than the electron affinity of the light emitting layer and the electron affinity is discretely distributed. Since it is composed of a molecular assembly composed of an oligomer, it is possible to provide organic electroluminescence with high luminous efficiency.

The organic EL according to claim 3 of the present invention.
The device includes a hole injection layer composed of a plurality of π-conjugated oligomers having different numbers of repeating units between the anode electrode and the light-emitting layer. An electroluminescent element can be provided.

The organic EL according to claim 4 of the present invention.
In the device, since the hole injection layer is formed by mixing a plurality of kinds of π-conjugated oligomers having different repeating unit structures, it is possible to provide an organic electroluminescent device having high luminous efficiency and capable of driving at a low voltage. it can.

The organic EL according to claim 5 of the present invention.
In the device, since the hole injection layer is formed by mixing a plurality of π-conjugated oligomers having different numbers of repeating units and a compound molecule having a hole-transport property different from the π-conjugated oligomer, low-voltage driving is possible. An organic electroluminescence element having high luminous efficiency can be provided.

The organic EL according to claim 6 of the present invention.
The device has a structure in which a hole transport layer made of a hole transport compound molecule is inserted between at least one of the hole injection layer and the anode electrode or between the hole injection layer and the light emitting layer. It is possible to provide an organic electroluminescent device having a high luminous efficiency and capable of performing the above.

Further, in the organic EL device according to claim 7 of the present invention, since the hole injection layer is formed by co-evaporation of a vacuum evaporation method, the organic EL device having high luminous efficiency which can be driven at a low voltage. An electroluminescent element can be easily provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a basic structure of an organic EL device of the present invention.

FIG. 2 is an energy diagram showing an energy state of the organic EL device of the present invention.

FIG. 3 is a schematic sectional view showing a basic structure of a conventional organic EL element.

FIG. 4 is an energy diagram showing an energy state of a conventional organic EL element.

[Explanation of symbols]

1 substrate, 2 anode electrode, 3 hole injection layer, 4
Light emitting layer, 5 cathode electrode, 6 hole transport layer.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C07C 211/54 C07C 211/54 C08G 61/02 C08G 61/02 61/10 61/10 C09K 11/06 610 C09K 11/06 610 615 615 620 620 680 680

Claims (7)

[Claims] 1. An organic electroluminescent device comprising a light emitting layer made of an organic compound sandwiched between an anode electrode and a cathode electrode, comprising a hole injection layer made of a π-conjugated oligomer between the anode electrode and the light emitting layer. A plurality of π-conjugated oligomers, wherein the π-conjugated oligomer has at least an ionization potential higher than that of the anode electrode, and the ionization potential is discretely distributed from near the ionization potential of the anode electrode to near the ionization potential of the light emitting layer. An organic electroluminescent device composed of a molecular assembly comprising: 2. The method according to claim 1, wherein the hole injecting layer has a smaller electron affinity than at least the light emitting layer and has a plurality of π-conjugated oligomers in which the electron affinity is discretely distributed. 2. The organic electroluminescent device according to 1. 3. The organic electroluminescence device according to claim 1, further comprising a hole injection layer made of a plurality of π-conjugated oligomers having different numbers of repeating units between the anode electrode and the light emitting layer. 4. The organic electroluminescence device according to claim 1, wherein the hole injection layer is formed by mixing a plurality of kinds of π-conjugated oligomers having different repeating unit structures. 5. The organic electroluminescence device according to claim 1, wherein the hole injection layer is formed by mixing a plurality of π-conjugated oligomers having different numbers of repeating units and a compound molecule having a hole transporting property different from the π-conjugated oligomer. . 6. A hole transport layer comprising a compound molecule having a hole transport property is inserted between at least one of the hole injection layer and the anode electrode or between the hole injection layer and the light emitting layer. 6. The organic electroluminescence device according to 5. 7. The organic electroluminescence device according to claim 3, wherein the hole injection layer is formed by co-evaporation of a vacuum evaporation method.