JPH05283169A - Organic thin-film el element - Google Patents

Abstract

PURPOSE:To provide luminescence having uniform and high intensity all over the luminescence face with good reproducibility by using an ion plating film made of metals containing Mg as the main constituent as a cathode. CONSTITUTION:The glass plate of a transparent insulating substrate 1 is coated with ITO as an anode 2. N,N'-diphenyl-N,N'-bis(3-methyl phenyl)-1,1'- bipheney-4,4'-diamine is deposited as a positive hole injection transporting layer 3. Tris(8-quinolinol)aluminum is deposited as an organic electron transporting luminescence layer 4, and an ion plating film of Mg is formed on it as a cathode 7. GeO is finally deposited as a sealing layer 8. The work function of the cathode 7 is lower than that of a conventional Mg-Ag alloy, it is illuminated in the yellow green color when DC voltage is applied, and uniform and high- intensity luminescence can be obtained all over the luminescence face.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EL device using electroluminescence, that is, electroluminescence (hereinafter simply referred to as EL), more specifically, an anode,
Hole injecting and transporting layer, organic electron transporting and light emitting layer, cathode, or anode, hole injecting and transporting layer, organic light emitting layer, electron injecting and transporting layer,
The present invention relates to an organic thin film EL element that is composed of a cathode in this order.

[0002]

2. Description of the Related Art Most conventional EL devices are of AC drive type in which a high resistance insulating layer is provided between electrodes, and they are classified into a dispersion type EL device and a thin film type EL device. Distributed EL
The device structure is such that powder of high dielectric constant barium titanate or the like dispersed in a resin binder is coated on an aluminum foil serving as a back electrode to a thickness of several tens of μm to form an insulating layer,
A zinc sulfide-based light emitting layer dispersed in a resin binder is provided thereon, and a transparent electrode is further laminated thereon. This type of element can be obtained at a low cost and has a large surface area and a surface light emitter having a thickness of 1 mm or less, and has applications such as a backlight for a liquid crystal display device, but at least the brightness is likely to decrease.

In a thin film EL device, a dielectric thin film layer of yttrium oxide or the like having a thickness of several hundreds nm is formed as an insulating layer by a sputtering method or the like on a transparent electrode substrate in which a glass plate is coated with indium tin oxide (hereinafter referred to as ITO). ZnS on it
-Based, ZnSe-based, SrS-based, CaS-based phosphor thin films of several hundred nm are stacked by electron beam evaporation, sputtering, etc., and then a dielectric thin film layer and a back electrode such as aluminum are stacked in this order. ing. The film thickness between electrodes is 1-2 μm
It is below. The thin film type EL device is long-lived and capable of high-definition display, and is suitable for applications such as displays for portable computers, but is expensive.

In either type of EL element, an AC high voltage of 100 V or more is required to obtain sufficient brightness. For example, since a step-up transformer is required when the EL element emits light with a battery, it is difficult to reduce the thickness of the entire device incorporated even if the EL element has a thin thickness of 1 mm or less.

Therefore, in recent years, research aiming at an unnecessary EL element of low voltage DC drive such as a step-up transformer has been conducted.
As one of them, researches on organic thin film EL devices have been conducted. JP-A-57-51781 and JP-A-59-19
4393, JP-A-63-264692, JP-A-63-295695, Japanese. journal. of. Applied. Physics Vol. 25, No. 9, p. 773 (1986), Applied. Physics.
Letter Vol. 51, No. 12, p. 913 (1987), Journal. of. Applied. Physics Volume 65 Volume 9
According to No. 3610 (1989), etc., an organic thin film EL device of this type has been conventionally manufactured as follows.

First, copper phthalocyanine, poly-3-methylthiophene, as a hole injecting and transporting layer, is formed on the anode of a transparent conductive film of gold or ITO formed on a transparent insulating substrate such as glass by vapor deposition or sputtering. Alternatively, 1,1-bis (4-di-para-tolylaminophenyl) cyclohexane (melting point: 181.4 ° C.
182.4 ° C.), or N, N ′ represented by (Chemical Formula 2)
-Diphenyl-N, N'-bis (3-methylphenyl)
-1,1'-biphenyl-4,4'-diamine (melting point 1
A layer of a tetraphenyldiamine derivative (59 ° C. to 163 ° C.) or the like is formed by vapor deposition, electrolytic polymerization or the like to have a thickness of about 1 μm or less in a single layer or laminated.

[0007]

[Chemical 1]

[0008]

[Chemical 2]

Next, on the hole injecting and transporting layer, tetraphenyl butadiene, anthracene, perylene, coronene, 12
-Phthaloperinone derivative, tris (8-quinolinol)
An organic phosphor such as aluminum is vapor-deposited or dispersed in a resin binder and coated to form an electron-transporting light-emitting layer with a thickness of about 1.0 μm or less. Finally, on top of that, Mg, In, Al single metal as a cathode,
Alternatively, an alloy of Mg and Ag (atomic ratio 10: 1) or the like is deposited.

In the device manufactured as described above, holes and electrons are injected into the light emitting layer by applying a direct current low voltage of 20 to 30 V or less with the transparent electrode side as an anode, and light is emitted by recombination thereof.

In addition, applied. Physics. Letter
According to Volume 57, No. 6, page 531 (1990), etc.
On the anode of ITO, Tachi et al.
N'-diphenyl-N, N'-bis (3-methylphenyi
Ru) -1,1'-biphenyl-4,4'-diamine, present
1- [4-N, N-bis (P-methoxy) as an organic light emitting layer
Phenyl) aminostyryl] naphthalene, electron injection transport
2- (4-biphenyl) -5- (4-t-butyl) as a layer
Ruphenyl) -1,3,4-oxadiazole (hereinafter referred to as
BPBD) and MgAg alloy as the cathode
The organic thin film EL device obtained by layering is prepared,
1000 cd / m at DC low voltage of V or less ² From the above EL
You are getting the light.

However, in this type of organic thin film EL device, in order to obtain a high brightness of 1000 cd / m ² or more at a low voltage of about 10 V or less, electrons are efficiently injected from the cathode to the organic electron transporting light emitting layer. There is a need to. For that purpose, it is necessary to use a cathode with a low work function having a high Fermi level higher than the energy level of the lowest unoccupied molecular orbital (hereinafter simply referred to as LUMO) of the organic phosphor used in the organic electron transporting light emitting layer.

The LUMO energy level of tris (8-quinolinol) aluminum, which is conventionally known as a typical organic electron-transporting light-emitting material capable of obtaining the highest brightness, has a work function measured by a photoelectron emission method in the atmosphere. The value obtained by subtracting the optical energy gap (2.75 eV) from the value is about 3.1 eV. Further, it is 2.7 eV in the case of BPBD used as an electron injecting and transporting material.
As a low work function metal having a work function of 3.1 eV or less and a high Fermi level, Li (work function 2.4e
V), Na (same 2.3eV), K (same 2.3eV) and other alkali metals, Mg (same 3.2eV), Ca (same 2.9).
eV), Sr (2.7 eV in the same), Ba (2.5 eV in the same)
Alkaline earth metals and the like, but except Mg, cannot be used as a cathode as a simple metal because they are extremely oxidizable and unstable in air.

Since Mg has a relatively high stability even though it has a low work function, it can be used as a single metal for the cathode by providing a sealing layer. However, it is difficult to obtain uniform light emission over the entire light emitting surface with good reproducibility because of poor adhesion to the organic thin film and lack of uniform thin film forming ability.

C. W. Tang et al. Realized an organic thin film EL device having a brightness of 1000 cd / m ² or more by applying a DC voltage of about 10 V by using a MgAg alloy (atomic ratio 10: 1, work function 3.8 eV) as a cathode. But Ag
Although the poor adhesion of Mg to the organic thin film and the poor uniformity of thin film formation were improved by alloying with Mg, the work function of MgAg alloy was Tris by mixing Ag (work function 4.6 eV). L of (8-quinolinol) aluminum
Since the energy level is lower than the UMO energy level, it is difficult to inject electrons.

[0016]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention uses a cathode material having a work function lower than that of a conventionally used MgAg alloy, a relatively stable and high uniformity, and a light emitting surface. The purpose of the present invention is to provide a high-brightness organic thin film EL element that is uniform over the entire area.

[0017]

That is, the present invention provides at least an anode, a hole injecting and transporting layer, an organic electron transporting and emitting layer,
Cathode, or at least an anode, a hole injecting and transporting layer, an organic light emitting layer, an electron injecting and transporting layer, and an organic thin film EL device comprising a cathode in this order, the ion plating using a metal whose main component is Mg. It is characterized by being formed of a film.

In the following, as shown in FIG. 1, the organic thin film EL device of the present invention comprises a substrate 1, an anode 2, a hole injecting and transporting layer 3, an organic electron transporting and emitting layer 4, and a cathode 7 in this order. Although described, the same structure can be formed on the substrate 1 in order from the cathode 7.

Further, as shown in FIG. 2, the organic electron transporting light emitting layer 4 is functionally separated into an organic light emitting layer 5 and an electron injecting and transporting layer 6, and an anode 2, a hole injecting and transporting layer 3, an organic layer is formed on a substrate 1. The light emitting layer 5, the electron injecting and transporting layer 6, and the cathode 7 may be arranged in this order.

The anode 2 is a transparent insulating substrate 1 such as glass.
A transparent electrode with a transparent conductive material such as ITO or zinc aluminum oxide coated on it by vacuum deposition or sputtering, with a surface resistance of 10 to 50 Ω / square and a visible light transmittance of 80% or more, or gold or platinum is thinly deposited. A semitransparent electrode is desirable.

However, in another case, the anode 2 is opaque, and a metal plate such as gold, platinum, nickel, or the like having a large work function that facilitates the injection of holes into the electron-transporting light-emitting layer, silicon, gallium phosphide, amorphous silicon carbide, or the like. Has a work function of 4.
It is also possible to use a semiconductor substrate of 8 eV or more, or an anode 2 in which a metal or semiconductor thereof is coated on an insulator substrate 1, and the cathode is a transparent electrode or a semitransparent electrode. When the cathode 7 is also opaque, at least one end of the light emitting layer 4 needs to be transparent.

Next, the hole injecting and transporting layer 3 is formed on the transparent anode 2. Preferred conditions for the hole injecting and transporting material are stable to oxidation, high hole mobility, and high ionization energy. It must be between the material and the light emitting layer material, have good film forming properties, and be substantially transparent at least in the fluorescence wavelength region of the light emitting layer material. A phthalocyanine such as copper phthalocyanine or metal-free phthalocyanine, or a tetraphenyldiamine derivative is used as a single layer or a laminated layer.

Typical materials for the tetraphenyldiamine derivative are 1,1-bis (4-di-para-tolylaminophenyl) cyclohexane and N, N'-diphenyl-N, N'-bis (3-methyl). Phenyl) -1,1'-
Biphenyl-4,4'-diamine, N, N'-diphenyl-N, N'-bis (para-tolyl) -1,1'-biphenyl-4,4'-diamine, N, N, N'N ' -Tetra (para-tolyl) -4,4'-diaminobiphenyl and the like can be mentioned, but not limited to the above examples.

Hole injecting and transporting layer 3 using these compounds
The film is formed mainly on the anode 2 of the transparent electrode by vapor deposition, but is formed by dispersing it in a resin such as polyester, polycarbonate or polymethylphenylsilane and coating it by a method such as spin coating. It is also possible.

The film thickness of the hole injecting and transporting layer 3 is 1 μm or less, preferably 0.03 to 0.1 μm even when it is formed by a single layer or a laminated layer. When a hole injecting and transporting material that melts by heating, such as a tetraphenyldiamine derivative, is used, defects in the deposited film may be removed during or after the vapor deposition of the hole injecting and transporting material in a vacuum or in an inert gas atmosphere. In order to remove it, the substrate heat treatment may be performed at a temperature equal to or lower than the melting point.

When a hole injecting and transporting material such as copper phthalocyanine that is crystalline and has a surface on which the deposited film is likely to be uneven is used, the substrate may be cooled during the deposition to obtain an amorphous deposited film. it can.

Next, the organic electron transporting light emitting layer 4 is formed on the hole injecting and transporting layer 3. The phosphor used for the organic electron transporting light emitting layer 4 has fluorescence in the visible region and is formed by an appropriate method. Any phosphor that can be filmed can be used. For example, anthracene, salicylate, pyrene, coronene, perylene, tetraphenylbutadiene, 9,10-bis (phenylethynyl) anthracene, tris (8-quinolinol) aluminum, bis (8-quinolinol) zinc, tris (5-fluoro-). Examples include 8-quinolinol) aluminum complex, bis [8- (para-tosyl) aminoquinoline] zinc, and cadmium complex.

As the phosphors in the organic electron transporting light emitting layer 4, two or more kinds of phosphors are mixed in order to convert emission wavelength and improve light emission efficiency, or two or more light emitting layers of various kinds of phosphors are laminated. One of them may exhibit fluorescence in the infrared region or the ultraviolet region. The method of forming the organic electron transporting light emitting layer 4 is performed by a vacuum vapor deposition method, a cumulative film method, or a method in which the organic electron transporting light emitting layer 4 is dispersed in an appropriate resin binder and coated by spin coating or the like.

The film thickness of the organic electron transporting light emitting layer 4 is 1 μm or less, preferably 0.03 to 0.1 μm even when it is formed by a single layer or a laminated layer. Next, when the organic electron transporting light emitting layer 4 is functionally separated into the organic light emitting layer 5 and the electron injecting and transporting layer 6 as shown in FIG. 2, a preferable condition of the electron injecting and transporting material is that the electron mobility is large. , L
The UMO energy level is between the LUMO energy level of the organic light emitting material and the Fermi level of the cathode material, and the film forming property is good. Further, in the element in which the anode 2 is opaque and the light is extracted from the transparent or semitransparent cathode 7, it is necessary that it is substantially transparent at least in the fluorescence wavelength region of the organic light emitting layer material. Examples include BPBD, 3,4,9,10-perylenetetracarboxyl-bis-benzimidazole and the like, but are not particularly limited to the above examples.

The electron injecting and transporting layer 6 is formed by a vacuum vapor deposition method, a cumulative film method, or by dispersing the electron injecting and transporting layer 6 in an appropriate resin binder and coating it by spin coating or the like. The film thickness of the electron injecting and transporting layer 6 is 1 μm or less, preferably 0.01 to 0.1 μm.

When the organic electron transporting light emitting layer 4 or the organic light emitting layer 5 and the electron injecting and transporting layer 6 are formed by the vacuum vapor deposition method, non-electron attracting properties such as hydrogen and ammonia or electron donating can be obtained during or immediately after vapor deposition. It is also possible to introduce a volatile gas into the vacuum chamber and allow it to be adsorbed by the organic molecules, which prevents the organic molecules from adsorbing oxygen in the air and increasing the electrical resistance of the membrane.

Next, the cathode 7 according to the present invention is formed on the organic electron transporting light emitting layer 4 or the electron injecting and transporting layer 6. The main component of the cathode according to the present invention is Mg, but other than the main component, for example, Ag, Al, In, Sn, Li, Na, C
Impurities and additives such as a, Sr, and Ba may be contained, but are not particularly limited to the above examples.

A method of forming the cathode 7 will be described with reference to the illustration of the ion plating apparatus shown in FIG. After the chamber 11 is once evacuated to a vacuum of the order of 10 ^-6 Torr or less, an inert gas such as Ar or Ne is introduced through the gas introduction valve 12 and stabilized at a pressure of 10 ^-4 to 10 ^-3 Torr. Plasma is generated by applying high-frequency power from the RF power supply 13 to the coil electrode 15 via the matching circuit 14. While monitoring with a crystal oscillator type film thickness meter, vapor deposition was performed from the resistance heating vapor deposition source 16 to the substrate 17,
The ion plating film is formed with a film thickness of about 0.3 μm, but plasma can be generated even on the order of 10 ⁻⁵ Torr by using an electron beam evaporation source or a microwave power source. Further, by applying a negative voltage from the substrate bias power source 18 to the substrate 17, implantation of positively charged particles such as Mg ions can be promoted, but the substrate 17 is not required to be positively applied. The implantation effect due to the sheath bias generated in the vicinity can be expected.

In order to prevent the organic layer material from being decomposed by plasma, the electron temperature near the substrate 17 is 10e.
It is important to control the applied power so that the sheath bias voltage is about V or less and the sheath bias voltage is about 10 V or less.
In the ion plating method, it is relatively easy to control by the geometrical arrangement of the coil electrode 15 and the substrate 17.

Finally, a sealing layer 8 is formed on the element in order to prevent oxidation of the organic layers and electrodes of the element. The sealing layer 8 is formed of SiO ₂ , SiO, GeO, MoO ₃ immediately after the formation of the cathode 7.
Oxides such as MgF ₂ , LiF, BaF ₂ , AiF ₃ ,
An inorganic material such as fluoride such as FeF _{3 is} formed by vapor deposition, sputtering, etc., and a glass plate, etc. is adhered and sealed by using a low hygroscopic UV-curing adhesive, epoxy adhesive, etc. to prevent the entry of moisture. To do.

The organic thin film EL element constructed as described above emits light when a positive voltage is applied to the anode 2 and a DC voltage is applied. Emits light.

[0037]

In vacuum deposition, since Mg is a sublimable metal, when the input power of the deposition source is small, it is deposited as a relatively large cluster. Further, since Mg particles are likely to move on most substrates and tend to be a non-uniform and non-smooth polycrystalline thin film, it is difficult to obtain uniform light emission over the entire light emitting surface with good reproducibility.

Therefore, in the present invention, by using a Mg ion plating thin film for the cathode, uniform light emission is realized over the entire light emitting surface. Mg due to electron impact in plasma
The clusters are decomposed and crystal growth is suppressed on the substrate. Further, since the Mg ions are accelerated by the bias electric field, a uniform and smooth amorphous thin-film Mg cathode having high adhesion is obtained by the implantation effect. Further, since it can be used with Mg alone, it becomes a cathode having a lower work function than the MgAg alloy.

[0039]

【Example】

Example 1 An example of the EL device of the present invention will be described below with reference to FIG. First, a 1.1 mm-thick glass plate was used as the transparent insulating substrate 1, and 0.12 μm of ITO was coated thereon to form the anode 2. This transparent conductive glass substrate was washed with alcohol and then heated at about 400 ° C. for 10 minutes to degrease it. Next, as the hole injecting and transporting layer 3, N,
N′-diphenyl-N, N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine was vapor-deposited by 0.05 μm.

Next, tris (8-quinolinol) aluminum was vapor-deposited in an amount of 0.05 μm as the organic electron transporting light-emitting layer 4, and an Mg ion plating film was formed in a thickness of 0.2 μm as the cathode 7 on the upper surface thereof. The plasma conditions were Ar plasma with an atmospheric pressure of 5 × 10 ⁻⁴ Torr and an RF power of 0.3 W. The work function of the cathode 7 was about 3.2 eV as measured by the photoelectron emission method. Finally, GeO was vapor-deposited to a thickness of 2 μm as the sealing layer 8.

This element emits yellowish green light when a DC voltage of 2.4 V or more is applied, and the maximum brightness is 69 V at 16 V.
The current density was 48 cd / m ² and the current density was 241 mA / cm ² , and uniform high-luminance light emission was obtained over the entire light emitting surface.

<Example 2> As in Example 1, the hole injecting and transporting layer 3 and the organic electron transporting and emitting layer 4 were sequentially deposited on the transparent conductive glass substrate, and an Mg ion plating film was used as the cathode 7. A film having a thickness of 0.2 μm was formed. The plasma conditions were Ar plasma with an atmospheric pressure of 5 × 10 ⁻⁴ Torr and RF power of 1 W. The work function of the cathode 7 was about 3.2 eV as measured by the photoelectron emission method. Finally the sealing layer 8
Was deposited to a thickness of 2 μm.

This device emits yellowish green light when a DC voltage of 2.4 V or more is applied, and the maximum brightness is 608 at 16 V.
0 cd / m ² , current density is 223 mA / cm ² ,
Uniform high-brightness light emission was obtained over the entire light emitting surface.

<Comparative Example 1> In the same manner as in Example 1, the hole injecting and transporting layer 3 and the organic electron transporting and emitting layer 4 were sequentially deposited on the transparent conductive glass substrate, and then the cathode 7 was co-deposited with MgAg alloy. Formed. The work function of the cathode 5 was about 3.8 eV as measured by the photoelectron emission method. Finally, MgF ₂ was deposited by 0.33 μm as the sealing layer 8.

This device emits yellow-green light when a DC voltage of 3 V or more is applied, and the maximum brightness is 5990 c at 17 V.
The d / m ² and the current density were 268 mA / cm ² , and uniform high brightness light emission was obtained over the entire light emitting surface.

Comparative Example 2 As in Comparative Example 1, the hole injecting and transporting layer 3 and the organic electron transporting and emitting layer 4 were sequentially deposited on the transparent conductive glass substrate, and then Mg was deposited as the cathode 7 to a thickness of 0.2 μm. .. The work function of the cathode 5 was about 3.2 eV as measured by the photoelectron emission method. Finally, GeO was vapor-deposited to a thickness of 2 μm as the sealing layer 8.

This device emits yellowish green light when a DC voltage of 2.4 V or more is applied, and the maximum brightness is 252 at 16 V.
Although the current density was 0 cd / m ² and the current density was 252 mA / cm ² , uneven brightness occurred on the light emitting surface, and uniform light emission could not be obtained over the entire light emitting surface.

[0048]

As described above, by using the ion plating film using a metal containing Mg as a main component as the cathode of the organic thin film EL element, the conventionally used Mg
Since it is possible to obtain a uniform and smooth amorphous-like Mg thin film cathode having a work function lower than that of an Ag alloy and high adhesion, it is effective in obtaining a uniform high-brightness organic thin film EL element over the entire light emitting surface with good reproducibility. is there.

[0049]

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an organic thin film EL element of the present invention.

FIG. 2 is an explanatory view showing another embodiment of the organic thin film EL element of the present invention.

FIG. 3 is an explanatory view of an apparatus for forming an ion plating thin film cathode in the organic thin film EL element of the present invention.

[Explanation of symbols]

 1 Substrate 2 Anode 3 Hole Injecting and Transporting Layer 4 Organic Electron Transporting and Emitting Layer 5 Organic Emitting Layer 6 Electron Injecting and Transporting Layer 7 Cathode 8 Sealing Layer 11 Chamber 12 Gas Introducing Valve 13 RF Power Supply 14 Matching Circuit 15 Coil Electrode 16 Resistance Heating Vapor Deposition Source 17 Substrate 18 Substrate bias power supply

Claims (1)

[Claims] 1. An organic thin film comprising at least an anode, a hole injecting and transporting layer, an organic electron transporting and emitting layer, a cathode, or at least an anode, a hole injecting and transporting layer, an organic light emitting layer, an electron injecting and transporting layer, and a cathode in this order. In the EL element, the organic thin film EL element is characterized in that the cathode is formed of an ion plating film using a metal containing Mg as a main component.