JP2001332386A - Electric field-effect light emitting organic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric field-effect light emitting organic element which can be driven at a low voltage, with high luminous efficiency, and in which a stable luminous property can be maintained for a long term. SOLUTION: This is an electric field-effect light emitting organic element having a luminous layer 3 that is pinched by a positive electrode 2 and a negative electrode 5 on a substrate 1. Between the negative electrode 5 and the luminous layer 3, a negative electrode interface layer 4 to contain compound(s) expressed in a formula (1) is installed in contact with the negative electrode 5. (in the formula, R1 to R5 express hydrogen atom, halogen atom, alkyl group, aralkyl group, alkenyl group, cyano group, amino group, acyl group, alkoxycarbonyl group, carboxyl group, alkoxy group, haloalkyl group, hydroxyl group, aromatic hydrocarbon cyclic group or aromatic heterocyclic group which may have substituted group(s), and M shows either atom of sodium, potassium, rubidium, or cesium).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent device, and more particularly, to a thin film device which emits light by applying an electric field to a light emitting layer made of an organic compound.

[0002]

2. Description of the Related Art Conventionally, as a thin film type electroluminescent (EL) element, Zn, which is a group II-VI compound semiconductor of an inorganic material, is used.
In general, S, CaS, SrS, and the like are doped with Mn or a rare earth element (Eu, Ce, Tb, Sm, or the like) which is a luminescence center. However, EL devices manufactured from the above inorganic materials include: 1) AC drive is required (50-1000 Hz), 2) High drive voltage (up to 200 V), 3) Full color is difficult (especially blue), 4) Peripheral drive circuit has high cost. .

However, in recent years, in order to improve the above problems,
Development of EL devices using organic thin films has been started. In particular, in order to enhance the luminous efficiency, the type of the electrode was optimized for the purpose of improving the efficiency of carrier injection from the electrode, and a hole transport layer composed of an aromatic diamine and a luminescent layer composed of an aluminum complex of 8-hydroxyquinoline were used. Of an organic electroluminescent device equipped with an organic layer (Appl. Phys. Lett., Vol. 51,
913, 1987), the luminous efficiency has been greatly improved as compared with the conventional EL device using a single crystal such as anthracene or the like, and the practical characteristics have been approached.

In addition to the electroluminescent device using a low molecular material as described above, poly (p-phenylenevinylene) and poly [2-methoxy-5- (2-ethylhexyloxy)- Development of electroluminescent devices using polymer materials such as 1,4-phenylenevinylene] and poly (3-alkylthiophene), and devices in which a low molecular light emitting material and an electron transfer material are mixed with a polymer such as polyvinyl carbazole Is also being developed.

[0005] Under such circumstances, there are two problems with the organic electroluminescent device, namely, improvement of driving stability and lowering of driving voltage.

That is, the fact that the voltage at the time of driving the organic electroluminescent device is high and the driving stability including heat resistance is low is that:
This is a serious problem as a light source for a facsimile, a copying machine, a backlight of a liquid crystal display, etc., and is particularly undesirable as a display element for a full color flat panel display or the like.

The instability of the organic electroluminescent device during driving includes a decrease in light emission luminance, an increase in voltage during constant current driving, generation of a non-light emitting portion (dark spot), and the like. There are several sources of these instabilities, but mainly
It is considered that the deterioration of the cathode material, particularly the interface of the cathode on the light emitting layer side is a major factor. That is, in the case of an organic electroluminescent element, a low work function metal such as a magnesium alloy or calcium is usually used as a cathode material in order to easily perform electron injection from the cathode to the organic layer side. It is easily oxidized by moisture in the air, which is a major cause of instability during driving. A cathode using a low work function metal is effective for lowering the driving voltage of the device, but improvement is desired due to the instability described above.

On the other hand, lithium metal is added to aluminum in 0.01%.
A cathode made of an alloy containing 0.1 to 0.1 parts by weight is disclosed (JP-A-5-121172). In order to form this cathode, it is necessary to strictly control the content of lithium metal. However, in a vacuum deposition method, binary deposition using aluminum and lithium metal independently as deposition sources has a desired composition ratio. Forming a cathode layer of an aluminum-lithium alloy is difficult in terms of process. It has been considered that an alloy having a desired composition ratio of aluminum and lithium is prepared in the form of a pellet or a target in advance, and a cathode is formed by an electron beam evaporation method or a sputtering method. Due to differences in aluminum vapor pressure and sputtering efficiency, there is a practical problem that the composition ratio of the aluminum-lithium alloy as the vapor deposition source is fluctuated when film formation is repeated. In addition, since metal lithium atoms are easily diffused and diffuse into an adjacent organic layer to extinguish light emission, and because they are extremely sensitive to moisture, in a device in which a cathode containing lithium atoms is formed, sealing is performed. There is also a problem that the requirement for stopping accuracy is extremely severe.

On the other hand, a cathode made of an aluminum alloy containing at least 6 mol% of lithium has been disclosed (Japanese Patent Laid-Open No.
Such a device requires a strict protective film due to the instability of the lithium metal atoms described above, and cannot avoid the diffusion instability caused by the lithium atoms.

At the interface in contact with the organic light emitting layer side of the cathode, an extremely thin inorganic insulating layer (0.3
~ 10nm) is also being considered (Appl. Ph
ys. Lett., 70, 152, 1997; IEEE Trans. Electro
n. Devices, vol. 44, p. 1245, 1997), which has a problem in adhesion to an organic layer, and has a problem of dark spot generation due to peeling of a cathode.

It has also been reported that a layer of a lithium salt of benzoic acid is similarly inserted at the cathode interface (Jpn. J.
Appl. Phys., 38, L1348, 1999), the light emission performance is not sufficient.

[0012]

As described above, as a cathode material of an organic electroluminescent device, a material obtained by alloying lithium with aluminum metal or a material obtained by mixing a lithium compound has been proposed. Nothing effective for improving driving stability and lowering driving voltage has been provided, and furthermore, there is a practical problem in the manufacturing process.

Although it has been proposed to form an interface layer separately at the cathode interface, sufficient characteristics in light emission performance and the like have not been obtained.

The present invention solves the above-mentioned conventional problems and provides an organic electroluminescent device which can be driven at low voltage and high luminous efficiency and can maintain stable luminous characteristics for a long period of time. With the goal.

[0015]

According to the present invention, there is provided an organic electroluminescent device having a light emitting layer sandwiched between an anode and a cathode on a substrate, wherein the organic electroluminescent device is provided between the cathode and the light emitting layer. A cathode interface layer containing a compound represented by the following general formula (I) is provided in contact with the cathode.

[0016]

Embedded image

Wherein R ¹ , R ² , R ³ , R ⁴ , R
⁵ each independently represents a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an amino group, an acyl group, an alkoxycarbonyl group, a carboxyl group, an alkoxy group, a haloalkyl group, a hydroxyl group, and a substituent. Represents an aromatic hydrocarbon ring group which may have or an aromatic heterocyclic group which may have a substituent, M is sodium,
Shows any atom of potassium, rubidium, and cesium. )

That is, the present inventor has proposed that the organic light emitting device can emit light with high luminance at a low voltage, maintain stable light emitting characteristics even during driving, and have a wide range of process conditions that can be selected during device fabrication. As a result of intensive studies to provide a light-emitting element, an organic electroluminescent element having a light-emitting layer sandwiched between an anode and a cathode on a substrate, in contact with the cathode between the cathode and the light-emitting layer, benzoic acid or a derivative thereof It has been found that the above problems can be solved by providing a cathode interface layer containing a salt with a specific alkali metal, and the present invention has been completed.

In the organic electroluminescent device of the present invention, a reaction occurs during deposition between the cathode metal and the organic compound represented by the general formula (I) constituting the cathode interface layer, and as a result, electron injection is facilitated. Is formed at the cathode interface. Although the details of this reaction product are not clear, it is assumed that the alkali metal contained in the organic compound forming the cathode interface layer is partially released. As described above, in a conventional lithium-based compound, free lithium easily moves by diffusion or the like and causes instability of the device, whereas the organic compound used in the present invention has an atomic weight of more than lithium atom. The instability is avoided because an alkali metal atom is used which is difficult to diffuse.

In the present invention, the thickness of the cathode interface layer is
Preferably it is in the range of 0.3 to 10 nm.

The metal forming the cathode is preferably one or more selected from the group consisting of aluminum, indium, magnesium, calcium, zinc, vanadium, chromium and tin.

[0022]

Embodiments of the present invention will be described below in detail with reference to the drawings.

1 to 3 are cross-sectional views schematically showing examples of the structure of the organic electroluminescent device of the present invention, wherein 1 is a substrate, 2 is an anode, 3 is an organic light emitting layer, 3a is an anode buffer layer, and 3b is The hole transport layer, 3c represents an electron transport layer, 4 represents a cathode interface layer, and 5 represents a cathode.

The substrate 1 serves as a support for the organic electroluminescent device, and is made of a quartz or glass plate, a metal plate or a metal foil, a plastic film or a sheet, or the like. Particularly, a glass plate or a plate of a transparent synthetic resin such as polyester, polymethacrylate, polycarbonate, and polysulfone is preferable. When using a synthetic resin substrate, it is necessary to pay attention to gas barrier properties. If the gas barrier property of the substrate is too low, the organic air-emitting device may be deteriorated by outside air passing through the substrate, which is not preferable. Therefore, when a synthetic resin substrate is used, it is preferable to provide a dense silicon oxide film or the like on one or both surfaces to ensure gas barrier properties.

An anode 2 is provided on a substrate 1. Anode 2
Plays a role of injecting holes into the organic light emitting layer 3. The anode 2 is usually made of a metal such as aluminum, gold, silver, nickel, palladium, and platinum, a metal oxide such as an oxide of indium and / or tin, a metal halide such as copper iodide, carbon black, or It is composed of a conductive polymer such as poly (3-methylthiophene), polypyrrole, and polyaniline. Usually, the formation of the anode 2 is often performed by a sputtering method, a vacuum evaporation method, or the like. In the case of fine particles of metal such as silver, fine particles of copper iodide or the like, carbon black, fine particles of conductive metal oxide, fine particles of conductive polymer, etc., they are dispersed in an appropriate binder resin solution and To form the anode 2. Further, in the case of a conductive polymer, the anode 2 can also be formed by forming a thin film directly on the substrate 1 by electrolytic polymerization or by coating a conductive polymer on the substrate 1 (Appl. Phys. Let
t., 60, 2711, 1992). The anode 2 can be formed by laminating different materials. The thickness of the anode 2 depends on the required transparency. When transparency is required, the transmittance of visible light is usually 60% or more, preferably 80% or more.
% Or more, and in this case, the thickness is usually
It is about 5 to 1000 nm, preferably about 10 to 500 nm. If opaque, the anode 2 may be the same as the substrate 1. Further, it is also possible to laminate a different conductive material on the anode 2.

In the organic electroluminescent device of FIG. 1, an organic light emitting layer 3 is provided on the anode 2. The organic light emitting layer 3
It is made of a material that efficiently transports and recombines holes injected from the anode 2 and electrons injected from the cathode 4 between the electrodes to which an electric field is applied, and emits light efficiently by the recombination. Usually, in order to improve the luminous efficiency, the organic light emitting layer 3 is divided into a hole transport layer 3b and an electron transport layer 3c as shown in FIG. .Lett., 51, 913, 1987).

In the above function-separated element, the material of the hole transport layer 3b is a material having a high hole injection efficiency from the anode 2 and capable of transporting the injected holes efficiently. It is necessary. For that purpose, it is required that the ionization potential is small, the hole mobility is large, the stability is further improved, and impurities serving as traps are hardly generated during production or use.

As such a hole transport material, for example, 4,4′-bis [N- (1-naphthyl) -N-phenylamino]
Including two or more tertiary amines represented by biphenyl;
Aromatic diamines in which two or more condensed aromatic rings are substituted with nitrogen atoms (JP-A-5-234681), 4,4 ', 4 "-tris (1-
Aromatic amine compounds having a starburst structure such as naphthylphenylamino) triphenylamine (J. Lumi
n., 72-74, 985, 1997), an aromatic amine compound composed of a tetramer of triphenylamine (Chem. Commun., 217).
5, p. 1996), spiro compounds such as 2,2 ', 7,7'-tetrakis- (diphenylamino) -9,9'-spirobifluorene (Syn
th.Metals, vol. 91, p. 209, 1997). These compounds may be used alone or as a mixture of two or more as necessary.

As a material for the hole transport layer 3b, in addition to the above compounds, polyarylene ether sulfone containing polyvinyl carbazole, polyvinyl triphenylamine (Japanese Patent Application Laid-Open No. 7-53953), and tetraphenylbenzidine (Polym. Adv. Tech., Vol. 7, p. 33, 1996).

The hole transport layer 3b is formed by laminating the above hole transport material on the anode 2 by a coating method or a vacuum deposition method.

In the case of the coating method, if necessary, an additive such as a binder resin or a coating property improving agent which does not trap holes is added to one or more of the hole transporting materials, and then dissolved to form a coating solution. Is prepared, coated on the anode 2 by a method such as spin coating, and dried to form the hole transport layer 3b. In this case, polycarbonate, polyarylate, polyester, or the like can be used as the binder resin. If the amount of the binder resin added is large, the hole mobility is reduced.
% By weight or less is preferred.

In the case of the vacuum evaporation method, the hole transporting material is put into a crucible placed in a vacuum vessel, and the inside of the vacuum vessel is evacuated to about 10 ⁻⁴ Pa by a suitable vacuum pump, and then the crucible is heated. Then, the hole transport material is evaporated to form a hole transport layer 3b on the anode 2 on the substrate 1 placed facing the crucible.

The thickness of the hole transport layer 3b is usually 10 to 300 n
m, preferably 30-100 nm. In order to uniformly form such a thin film, generally, a vacuum deposition method is often used.

For the purpose of further improving the efficiency of hole injection and improving the adhesion of the entire organic layer to the anode,
As shown in FIG. 3, an anode buffer layer 3a is also formed between the hole transport layer 3b and the anode 2. By forming such an anode buffer layer 3a, there is an effect that the initial drive voltage of the element is reduced, and at the same time, the voltage rise when the element is continuously driven with a constant current is suppressed. The conditions required for the material used for the anode buffer layer include:
A uniform thin film can be formed with good contact with the anode and thermally stable, that is, the melting point and glass transition temperature are high, the melting point is 300 ° C or more, and the glass transition temperature is
100 ° C or higher is required. Further, it is required that the ionization potential is low, holes are easily injected from the anode, and the hole mobility is high.

As such a material, a phthalocyanine compound such as copper phthalocyanine (JP-A-63-295695) is conventionally used.
Publication), polyaniline (Appl. Phys. Lett., 64, 1245)
P., 1994), polythiophene (Optical Materials, 9)
Vol. 125, 1998), sputtered carbon films (Synth. Met., Vol. 91, p. 73, 1997), and metal oxides such as vanadium oxide, ruthenium oxide and molybdenum oxide. (J. Phys. D, Vol. 29, p. 2750, 1996).

The anode buffer layer 3a can be formed as a thin film in the same manner as the hole transport layer 3b.
Furthermore, sputtering, electron beam evaporation, plasma CVD
Method can be used.

The anode buffer layer 3 thus formed
The thickness of a is usually 3 to 100 nm, preferably 10 to 50 nm.

An electron transport layer 3c is provided on the hole transport layer 3b. The electron transport layer 3c is formed to efficiently transport electrons from the cathode between the electrodes to which an electric field is applied in the direction of the hole transport layer 3b.
The electron transporting compound used for c needs to be a compound having high electron injection efficiency from the cathode 4 and capable of efficiently transporting the injected electrons. For this purpose, it is required that the compound has a high electron affinity, a high electron mobility, excellent stability, and hardly generates impurities serving as traps during production or use.

As materials satisfying such conditions, 8
Metal complexes such as aluminum complexes of -hydroxyquinoline (JP-A-59-194393);
[h] quinoline metal complex (JP-A-6-322362), bisstyrylbenzene derivative (JP-A-1-245087,
2-222484) and the like.

Electron transport layer 3c using these compounds
Can generally play a role of transporting electrons and a role of providing light emission upon recombination of holes and electrons. However, when the hole transport layer 3b has a light emitting function, the electron transport layer 3c may only play the role of transporting electrons.

The thickness of the electron transport layer 3c is usually 10 to 200 n
m, preferably 30-100 nm.

The electron transporting layer 3c can be formed by the same method as the hole transporting layer 3b, but usually, a vacuum deposition method is used.

For the purpose of improving the luminous efficiency of the device and changing the luminescent color, for example, doping a fluorescent dye for laser such as coumarin using an 8-hydroxyquinoline aluminum complex as a host material (J. Appl. Phy
s., 65, 3610, 1989). The advantages of this method are: 1) improved luminous efficiency by high-efficiency fluorescent dye, 2) variable emission wavelength by selecting fluorescent dye, 3) fluorescent dye which causes concentration quenching can be used, 4) fluorescent light with poor thin film property Dyes can also be used.

For the purpose of improving the driving life of the device, it is effective to dope a fluorescent dye by using the light emitting layer material as a host material. For example, using a metal complex such as an aluminum complex of 8-hydroxyquinoline as a host material, a naphthacene derivative represented by rubrene (Jpn.
J. Appl. Phys., 7A, L824, 1995), quinacridone derivative (Appl. Phys. Lett., 70, 1665, 1997) doped with 0.1 to 10% by weight based on the host material. Thereby, the light emission characteristics of the element, particularly the driving stability, can be greatly improved. As a method of doping the fluorescent material such as the naphthacene derivative and the quinacridone derivative into the light emitting layer host material, there are a method of co-evaporation and a method of previously mixing an evaporation source at a predetermined concentration.

Single-layer type organic light emitting layer 3 without function separation
The poly (p-phenylenevinylene) listed above
(Nature, 347, 539, 1990 et al.), Poly [2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylenevinylene] (Appl. Phys. Lett., 58, 1982, 1991 et al.), Poly (3-alkylthiophene) (Jpn. J. Appl.
Phys., 30, L1938, 1991, etc.)
A system in which a luminescent material and an electron transfer material are mixed with a polymer such as polyvinyl carbazole (Applied Physics, 61, 1044, 1992)
Year).

As a method for further improving the luminous efficiency of the organic electroluminescent device, an electron injection layer can be further laminated on such an organic luminescent layer 3. The compound used for the electron injection layer is required to be capable of easily injecting electrons from the cathode and having a higher electron transporting ability. As such an electron transporting material, 8 as already described as a light emitting layer material
-Hydroxyquinoline aluminum complex, oxadiazole derivative (Appl. Phys. Lett., Vol. 55, p. 1489, 1989, etc.) and a system in which they are dispersed in a resin such as polymethyl methacrylate (PMMA) (Appl. Phys. .Lett., 61, 2793, 1992
Year), phenanthroline derivatives (JP-A-5-331459) and the like. In this case, the thickness of the electron injection layer is
It is usually from 5 to 200 nm, preferably from 10 to 100 nm.

The cathode interface layer 4 is laminated on the organic light emitting layer 3, the electron transport layer 3c, or the electron injection layer. The present invention is characterized in that the organic compound represented by the general formula (I) is used as a material for forming the cathode interface layer 4.

In the general formula (I), R¹~ R⁵When
Preferably, each independently represents a hydrogen atom;
Halogen atom such as atom, bromine atom and iodine atom; methyl
An alkyl group having 1 to 6 carbon atoms such as an alkyl group or an ethyl group; benzyl
Aralkyl groups such as phenyl and phenethyl groups;
Kenyl group; cyano group; amino group; dimethylamino group, di
A dialkylamino group such as an ethylamino group; diphenyla
Amino group; acyl group such as acetyl group; methoxycarbonyl
Alkoxy having 2 to 6 carbon atoms, such as
Cicarbonyl group; carboxyl group; methoxy group, ethoxy
A C1-C6 alkoxy group such as a thio group;
Haloalkyl group such as tyl group; hydroxyl group; phenyl group, naph
Aromatic carbonization such as tyl group, acenaphthyl group and anthryl group
Hydrogen group; pyridyl group, quinolyl group, thienyl group, carba
Aromatic heterocyclic groups such as zolyl group, indolyl group and furyl group
And the like. These aromatic hydrocarbon groups or aromatics
Substituents for the heterocyclic group include methyl and ethyl
C1-C6 alkyl group such as methoxy group;
1 to 6 alkoxy groups; aryloxy such as phenoxy groups
An arylalkoxy group such as a benzyloxy group;
Aryl groups such as phenyl and naphthyl; dimethylamino
And substituted amino groups such as a group. R¹~ R ⁵As
Is particularly preferably an alkyl having 1 to 6 carbon atoms.
, A C 1-6 alkoxy group, a phenyl group, a naph
And an aryl group such as a tyl group.

M is sodium, potassium, rubidium,
Indicates any alkali metal atom of cesium.

Preferred specific examples of the compound represented by formula (I) are shown in the following Tables 1 and 2, but are not limited thereto.

[0051]

[Table 1]

[0052]

[Table 2]

The above compound has a stable thin film shape even after thinning, and contributes to stabilization of the device. The cathode interface layer of the present invention may contain other components as long as the characteristics of the compound represented by the general formula (I) are not impaired.

The thickness of the cathode interface layer 4 is preferably 0.3 to 1
0 nm, particularly preferably 0.5 to 5 nm. In order to form such a thin film, a vacuum evaporation method is generally used.

The cathode 5 plays a role of injecting electrons into the organic light emitting layer 3 via the cathode interface layer 4. In the present invention, examples of the metal forming the cathode include aluminum, indium, magnesium, calcium, zinc, vanadium, chromium, tin, and copper, and particularly preferably aluminum.

In the organic electroluminescent device of the present invention, as described above, a reaction occurs during the deposition between the cathode metal and the organic compound constituting the cathode interface layer, and as a result, a reaction product which facilitates electron injection is produced by the cathode. Formed at the interface.

The thickness of the cathode 4 is usually the same as that of the anode 2.

For the purpose of protecting the cathode 4, it is preferable to further laminate a protective layer made of a metal material having a high work function and being stable to the atmosphere in order to increase the stability of the device. Aluminum, copper, chromium, gold and silver metals are used for this purpose. The metal material used for the protective layer may be the same as or different from the metal material used for the cathode 4.

FIGS. 1 to 3 show an embodiment of the organic electroluminescent device of the present invention, and do not limit the structure of the organic electroluminescent device of the present invention.
For example, the structure opposite to that of FIG.
It is also possible to laminate the cathode interface layer 4, the organic light emitting layer 3, and the anode 2 in this order. As described above, the organic electroluminescent element of the present invention is provided between two substrates, at least one of which has high transparency. It is also possible. Similarly, the organic electroluminescent devices shown in FIGS. 2 and 3 can be stacked in a structure opposite to the above-described respective layer configurations.

[0060]

EXAMPLES Next, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the following examples unless it exceeds the gist.

Example 1 An organic electroluminescent device having the structure shown in FIG. 2 was manufactured by the following method.

A transparent conductive film of indium tin oxide (ITO) having a thickness of 150 nm (manufactured by Sanyo Vacuum; sheet resistance of 15Ω) having a width of 3 mm was formed on the glass substrate 1 by using ordinary photolithography and hydrochloric acid etching. The anode 2 was formed by patterning into a stripe. Patterned IT
The O substrate was cleaned in the order of ultrasonic cleaning with acetone, water cleaning with pure water, and ultrasonic cleaning with isopropyl alcohol, dried with nitrogen blow, and finally cleaned with ultraviolet and ozone, and set in a vacuum evaporation apparatus.

[0063] After the crude exhaust oil rotary pump of the device, the vacuum degree in the apparatus 2 × 10 ^{- 6} Torr (about 2.7 × 10
^-4 Pa) or less using an oil diffusion pump equipped with a liquid nitrogen trap, and then the following 4,4'-bis [N-
(M-tolyl) -N-phenylamino] biphenyl was deposited by heating a tantalum boat with electric current. The degree of vacuum at the time of vapor deposition was 3 × 10 ⁻⁶ Torr (about 4.0 × 10 ⁻⁴ Pa), and the vapor deposition rate was 0.
The hole transport layer 3b having a thickness of 75 nm was formed at 2 nm / sec.

[0064]

Embedded image

Subsequently, the electron transport layer 3 having a light emitting function
As the material of c, 8 of aluminum represented by the following structural formula:
-Hydroxyquinoline complex, Al (C ₉ H ₆ NO) ₃ was deposited in the same manner as the hole transport layer 3b. The degree of vacuum during deposition is 3 × 10
The electron transport layer 3c having a thickness of 75 nm was formed at ^-6 Torr (about 4.0 × 10 ^-4 Pa) at a deposition rate of 0.25 nm / sec.

[0066]

Embedded image

Subsequently, the compound (1) shown in Table 1 was similarly deposited on the electron transporting layer 3c at a deposition rate of 0.05 nm / sec to form a cathode interface layer 4 having a thickness of 2 nm. The degree of vacuum at the time of vapor deposition was 3 × 10 ⁻⁶ Torr (about 4 × 10 ⁻⁴ Pa).

The substrate temperature during vacuum deposition of the above-described hole transport layer 3b, electron transport layer 3c and cathode interface layer 4 was kept at room temperature.

Here, a stripe-shaped shadow mask having a width of 3 mm as a mask for the cathode deposition was adhered to the device on which the vapor deposition up to the cathode interface layer 4 was performed so as to be orthogonal to the ITO stripe of the anode 2. . This mask replacement operation was performed without breaking the vacuum.

Subsequently, aluminum was formed as the cathode 5 on the cathode interface layer 4 at a deposition rate of 1 nm / sec to a thickness of 100 nm. The degree of vacuum during the deposition is 6.0 × 10 ⁻⁵ Torr (about 8 × 10 ⁻⁴ P
a). The substrate temperature during the cathode deposition was kept at room temperature.

As described above, an organic electroluminescent device having a size of 3 mm × 3 mm was obtained.

After taking out the device from the cathode vapor deposition apparatus, a forward voltage was applied between the anode and the cathode in the air, and the light emission characteristics were measured. FIG. 4 is a graph showing the luminance-current density characteristics of this device. The current emission efficiency obtained from the slope of the graph was 3.0 cd / A.

Comparative Example 1 A device was prepared in the same manner as in Example 1 except that a lithium salt of benzoic acid was used as a constituent material of the cathode interface layer, and the light emitting characteristics of the obtained device were measured. FIG. 4 is a graph showing the luminance-current density characteristics of this device. The current emission efficiency obtained from the slope of the graph was 1.7 cd / A.

Example 2 A device was prepared in the same manner as in Example 1 except that each of the compounds (17) in Table 1 was used as a constituent material of the cathode interface layer, and the emission characteristics of the obtained device were measured. FIG. 4 is a graph showing the luminance-current density characteristics of this device. The current emission efficiency obtained from the slope of the graph was 2.3 cd / A.

Comparative Example 2 A device was prepared in the same manner as in Example 1 except that a lithium fluoride layer was formed to a thickness of 0.8 nm as a cathode interface layer, and the light emitting characteristics of the obtained device were measured. FIG. 4 is a graph showing the luminance-current density characteristics of this device. The current emission efficiency obtained from the slope of the graph was 1.8 cd / A.

Comparative Example 3 A device was prepared in the same manner as in Example 1 except that the cathode interface layer was not provided, and the light emitting characteristics of the obtained device were measured. FIG. 4 is a graph showing the luminance-current density characteristics of this device. The current emission efficiency obtained from the slope of the graph was 0.95 cd / A.

As is clear from the values of the current luminous efficiencies of the devices manufactured in Examples 1 and 2 and Comparative Examples 1 to 3, the organic electroluminescent device of the present invention has a cathode interface layer made of a conventionally known material. It can be seen that the luminous efficiency is superior to the element having the luminous efficiency.

[0078]

As described in detail above, by forming the cathode interface layer according to the present invention, it is possible to emit light with high luminance and high efficiency at a low voltage, and to stably operate at a high current density. Thus, an element with less deterioration during storage can be obtained.

Therefore, the organic electroluminescent device according to the present invention can be used as a light source (for example, a copier) for a flat panel display (for example, for an OA computer or a wall-mounted television), an on-vehicle display device, a mobile phone display, or a surface illuminator. , Light sources for liquid crystal displays and backlights for instruments and the like, display boards, and sign lamps, and their technical value is great.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating an embodiment of an organic electroluminescent device of the present invention.

FIG. 2 is a schematic sectional view showing another embodiment of the organic electroluminescent device of the present invention.

FIG. 3 is a schematic cross-sectional view showing another embodiment of the organic electroluminescent device of the present invention.

FIG. 4 shows luminance in Examples 1 and 2 and Comparative Examples 1 to 3.
4 is a graph showing current density characteristics.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 anode 3 organic light emitting layer 3a anode buffer layer 3b hole transport layer 3c electron transport layer 4 cathode interface layer 5 cathode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K007 AB02 AB03 AB06 AB11 BA06 CA01 CB01 DA01 DB03 EA02 EB00

Claims (3)

[Claims] 1. An organic electroluminescent device having a light-emitting layer sandwiched between an anode and a cathode on a substrate, wherein, between the cathode and the light-emitting layer, the following general formula (I)
An organic electroluminescent device comprising a cathode interface layer containing a compound represented by the formula: Embedded image (Wherein, R ¹ , R ² , R ³ , R ⁴ , and R ⁵ each independently represent a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an alkenyl group, a cyano group, an amino group, an acyl group, an alkoxy group, A carbonyl group, a carboxyl group, an alkoxy group, a haloalkyl group, a hydroxyl group, an optionally substituted aromatic hydrocarbon ring group or an optionally substituted aromatic heterocyclic group, and M is sodium , Potassium, rubidium, or cesium.) 2. The organic electroluminescent device according to claim 1, wherein the thickness of the cathode interface layer is in the range of 0.3 to 10 nm. 3. The method according to claim 1, wherein the metal forming the cathode is at least one member selected from the group consisting of aluminum, indium, magnesium, calcium, zinc, vanadium, chromium, and tin. 3. The organic electroluminescent device according to 2.