JPH11176580A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescent element having sufficient contrast. SOLUTION: An organic multilayered film 7 containing an organic light emitting material is held by a pair of electrodes on a transparent board 1. One of the electrodes is formed with a negative electrode 8 containing the oxygen deficiency type oxide, and voltage is applied or current is carried between a pair of electrodes so as to make the organic light emitting material emit the light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an organic EL device used for a display or the like.

[0002]

2. Description of the Related Art In recent years, with the advancement of information, the need for a full-color flat panel display as a display element that is thinner, consumes less power, and is lighter than a CRT is increasing.
Non-self-luminous liquid crystal display (LCD) and self-luminous plasma display (P
DP), electroluminescence (EL) display and the like are known.

Further, the EL display has the following features: (1) Exciting a luminous body by local movement of electrons and holes in a luminescent layer, An intrinsic EL element that emits light; and (2) a charge injection type EL element that excites a luminous body by injecting electrons and holes from electrodes and recombines them in a light emitting layer to emit light by a DC electric field. Can be In the intrinsic EL element of (1), an inorganic substance is generally used as a light emitting body, and in the charge injection type EL element of (2), an organic substance is generally used as a light emitting layer.

[0004] Among them, EL displays using an organic substance have attracted a great deal of attention because they have characteristics such as self-emission, low power consumption, and various luminescent colors. .

As an example of the configuration of an organic EL element, one having a structure shown in FIG. 4 is well known. The conventional organic EL device shown in FIG. 4 is provided on a transparent substrate 1 made of glass or the like.
An anode 2, a hole transport layer 3, a light emitting layer 4, an electron transport layer 5, and a small work function such as Mg / Ag made of a transparent electrode material having a large work function such as indium-tin oxide (ITO). A cathode 6 made of an electrode material is sequentially laminated. A voltage is applied between the anode 2 and the cathode 6 of the organic EL element to inject electrons and holes into the light-emitting layer 4, and the recombination energy of electron-hole pairs formed in the light-emitting layer is converted into fluorescence or phosphorescence. Any color can be emitted by emitting light.

As a method of manufacturing an organic EL device, there are a vacuum deposition method in which an organic material is heated and sublimated in a vacuum to form a film on a substrate, and a Langmuir method in which an organic material is developed on a liquid surface and transferred onto the substrate. There are known a jet jet method (LB method), a spin coating method in which an organic material is dissolved in a solvent to prepare a solution, and this solution is dropped on a substrate and spin coated.

[0007]

SUMMARY OF THE INVENTION Organic E
In the case of the L element, the metal thin film used as the cathode is
The reflectivity of visible light is very high, so it easily reflects external light (ambient light), and there is a drawback that the contrast is not sufficient under high external light environment (outdoor direct sunlight, bright room, etc.). .

[0008]

Means for Solving the Problems In view of the above problems, the present inventors have conducted intensive studies, and as a result, have reached the present invention which achieves the above object. The organic EL device according to claim 1, wherein an organic single-layer film or an organic multilayer film containing an organic light-emitting material is sandwiched between a pair of electrodes including an anode and a cathode, and the pair of electrodes includes: In an organic EL element which emits the organic light emitting material by applying a voltage or injecting a current between the electrodes, one of the electrodes is an electrode containing an oxygen-deficient oxide. The organic EL device according to claim 2 of the present invention is characterized in that the electrode containing the oxygen-deficient oxide has a sheet resistance of 200 Ω / □ or less. The organic EL device according to claim 3, wherein the work function of the electrode containing the oxygen-deficient oxide is 5.0 eV or less. Is characterized by containing an electrically conductive substance simultaneously with the oxygen-deficient oxide. An organic EL device according to a fifth aspect of the present invention is characterized in that a conductive film having a sheet resistance lower than the sheet resistance of the electrode is disposed outside the electrode containing the oxygen-deficient oxide.

Hereinafter, the present invention will be described in detail. First, the organic EL device of the present invention will be described.
As described above, the element is an organic EL element in which an electrode made of a film containing an oxygen-deficient oxide is provided at a specific position. Components other than the electrode containing the oxygen-deficient oxide, that is, the organic single-layer film or the organic multilayer film sandwiched between a pair of electrodes, and on the side opposite to the electrode containing the oxygen-deficient oxide film The electrodes located are the same as those used in conventional organic EL elements.

Here, the “organic monolayer film” is substantially 1
Functions as a light-emitting layer of an organic EL device, such as a layer composed of only one or more kinds of organic light-emitting materials or a layer composed of a mixture of one or more kinds of organic light-emitting materials and a hole transport layer and / or an electron transport layer. Means a single layer film. Further, the “organic multilayer film” means a laminated structure film having two or more layers having a hole transport layer, an electron transport layer, or an adhesive layer in addition to the light emitting layer, and the layers are laminated on the anode in the same manner as before. Is appropriately selected depending on whether an organic multilayer film is formed on the cathode or an organic multilayer film is formed on the cathode.

The constituent materials of the organic single layer film and the organic multilayer film are not particularly limited, and have conventionally been used as organic light emitting materials, hole transport materials, electron transport materials, and adhesive layer materials for organic EL devices. Substances can be used as they are. In addition, an inorganic semiconductor is also used as a hole transporting material and an electron transporting material for an organic EL device, and the inorganic semiconductor is also used as a hole transporting material and / or an electron transporting material in the organic EL device of the present invention. Can be. Therefore, the organic monolayer film also includes a layer made of a mixture of a hole transporting material and / or an electron transporting material made of an inorganic semiconductor and one or more kinds of organic light-emitting materials. And those having a hole transporting layer and / or an electron transporting layer.

The electrode disposed opposite to the electrode containing the oxygen-deficient oxide film sandwiching the organic single-layer film or the organic multilayer film described above emits light from the organic single-layer film or the organic multilayer film. 380 because it needs to be taken out
It is preferable to select the material and the film thickness so that the light transmittance is 10% or more in the wavelength range of ７780 nm. When the light transmittance is 10% or less, sufficient light emission cannot be taken out to the outside, and it is difficult to obtain an organic EL element having sufficient luminance for practical use. Examples of electrodes satisfying the above conditions include CuO, ITO, SnO ₂ , Z
100 to 500 nm thick made of transparent electrode material such as nO
Can be formed by the above film. The light transmittance in the wavelength range of 380 to 780 nm as referred to in the present invention means the lowest value of the spectral transmittance of light belonging to the above wavelength range among the light emitted from the organic light emitting material.

In the organic EL device of the present invention, the electrode on the side opposite to the light extraction side comprises an electrode containing an oxygen-deficient oxide, and the oxygen-deficient oxide is reduced by lowering the oxygen concentration of the oxygen-deficient oxide. , The sheet resistance of the electrode containing 200 .OMEGA ./. Quadrature.
/ □ or less and the work function is 5.0 eV or less. Furthermore, if the desired sheet resistance and work function cannot be obtained only by lowering the oxygen concentration, desired characteristics can be obtained by mixing an electrically conductive simple substance or compound with the oxygen-deficient oxide film. it can.

If the sheet resistance of the electrode containing the oxygen-deficient oxide is 200 Ω / □ or more, it is necessary to apply a high voltage in order to obtain practically sufficient luminance. When emitting light, the calorific value is large and not suitable for practical use,
When a panel is formed, there is a problem that a voltage drop occurs due to a resistance component of an electrode, and a difference in luminance occurs at both ends of the electrode. When the work function of the electrode containing the oxygen-deficient oxide is 5.0 eV or more, the efficiency of injecting electrons from the electrode containing the oxygen-deficient oxide into the organic monolayer film or the organic multilayer film becomes low. , The brightness when driven at a constant voltage is reduced.

As the electrically conductive element or compound mixed in the electrode containing the oxygen-deficient oxide, gold (A)
u) and platinum (Pt) are preferred because they are not easily oxidized. However, the present invention is not limited to these. Barium (Ba), calcium (Ca), magnesium (Mg), and zirconium (Zr) have a work function of 5.0 eV regardless of whether they are oxidized or not.
Therefore, it is preferable as a simple substance or a compound to be mixed in the electrode containing the oxygen-deficient oxide. However, the present invention is not limited to these.

In order to produce an element having a sufficient contrast for practical use, the oxygen-deficient oxide is
It is preferable to select a material and a film thickness so that the reflectance is 50% or less in a wavelength range of 380 to 780 nm. When the reflectance is 50% or more, it is difficult to sufficiently suppress the reflection of external light, and it is difficult to obtain an organic EL element having a sufficient contrast for practical use outdoors. The reflectance in the wavelength range of 380 to 780 nm in the present invention means the maximum value of the spectral reflection of light belonging to the above wavelength range among the external light incident through the substrate.

Examples of the substance forming an oxygen-deficient oxide satisfying the above conditions include Al, Cr, and Ta. The oxygen-deficient oxide according to the present invention is an oxygen-deficient oxide of the above oxide. It is not limited to a film. Further, these oxygen-deficient oxide films may be used alone or in combination.

The oxygen-deficient oxide referred to in the present invention refers to an oxide stoichiometrically deficient in oxygen. Specifically, as the properties of the oxygen-deficient oxide according to the present invention, as the amount of oxygen is larger and the stoichiometrically closer to the oxide, the amount of light absorption decreases, the electric resistance increases, and the work function of the oxide decreases. Become closer to that of. Conversely, if the amount of oxygen is too small, its properties become close to those of the metal, so that the reflectance increases, the electrical resistance decreases, and the work function approaches that of the metal. As described above, by appropriately adjusting the amount of oxygen in the oxygen-deficient oxide, the light absorption is high, that is, the reflectance is low,
In addition, an electrode having low electric resistance can be manufactured.

Further, more preferably, in order to prevent a problem such as a voltage drop due to a resistance component of the electrode when a panel or a display is formed, an electrode containing the oxygen-deficient oxide and various electric conductors having a lower resistance than the electrode. It is preferable to laminate with a simple substance or a compound.

[0020]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. (Embodiment 1) FIG. 1 is a diagram showing the structure of Embodiment 1 of the present invention. In the figure, 1 is a transparent substrate made of glass, 2 is an anode made of ITO, 7 is an organic multilayer film, and 8 is a cathode. The organic multilayer film 7 includes a hole transport layer and a light emitting layer.

The method for producing this element is as follows.
A 200-nm-thick ITO film formed by sputtering on a 50-mm-square transparent substrate 1 is patterned into a 2-mm-wide stripe.
0 minutes, acetone ultrasonic cleaning for 10 minutes, isopropyl alcohol vapor cleaning for 5 minutes, and drying at 100 ° C. for 1 hour. Next, this substrate was fixed to a substrate holder in a resistance heating evaporation apparatus, and the pressure was reduced to a vacuum of 1 × 10 ⁻⁴ Pa. Then, N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine represented by the following structural formula [1] is used as a hole transport layer. (TPD) at a deposition rate of 0.2 nm / sec and a film thickness of 50
nm, and tris (8-hydroxyquinolinato) aluminum (Alq ₃ ) represented by the following structural formula [2] was further stacked at a deposition rate of 0.2 nm / sec to a film thickness of 50 nm. .

[0022]

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[0023]

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Thereafter, cathodes of the following types of oxygen-deficient oxide films were prepared. The substrate prepared up to the above-mentioned organic multilayer film was fixed to a substrate holder in a sputtering apparatus having a stainless steel mask for forming a 2 mm-wide striped back electrode, and was subjected to a discharge current of 4 A, a gas pressure of 0.4 Pa, and an argon flow of 60 SCCM. Using Al, Ta, and Cr as raw materials for forming an oxygen-deficient oxide film, a cathode having a thickness of 200 nm was manufactured by changing the oxygen flow rate and the deposition rate.

As an evaluation of the characteristics of the manufactured organic EL device,
The reflectance was measured by a spectrophotometer (U-3410 type self-recording spectrophotometer:
The work function of the cathode was measured with a surface analyzer AC-1 (manufactured by Riken Keiki Co., Ltd.). The sheet resistance was also measured.

The contrast ratio of each device was measured by the following method. The method of measuring the luminance for obtaining the contrast ratio will be described below with reference to FIG. First, the organic EL element 12 is fixed on a predetermined table in a dark room, and light is incident on the element at an angle of 45 °, and the fluorescent lamp 10 is arranged so that the illuminance on the element becomes 400 lux.
Next, when a luminance meter (BM-7) 11 is arranged so as to be at 45 ° with the element and at 90 ° with the fluorescent lamp, and a voltage is applied to the organic EL element so as to have an emission luminance of 100 cd / m ^2. And the luminance when no voltage is applied. Then, a contrast ratio was calculated from the measurement results based on the following equation.

Contrast ratio = luminance at the time of light emission: luminance at the time of non-light emission The optical environment at the time of luminance measurement is a typical optical environment when the organic EL element is actually used indoors. It is.

Table 1 shows the manufacturing conditions and the results of the characteristic evaluation of each of the examples.

[0029]

[Table 1]

The results of the above examples are summarized below. When an electrode is manufactured using the oxygen-deficient oxide film according to the present invention, the contrast can be improved as compared with an element using an electrode used in a conventional organic EL element as shown in a comparative example.

When the element forming the oxygen-deficient oxide film is Al, as can be seen from Examples 1 and 2 and Comparative Example 1,
If the oxygen-oxygen concentration in the oxygen-deficient oxide film is high, the surface resistance of the electrode formed of the oxygen-deficient oxide film increases, and charge cannot be efficiently injected into the light-emitting layer, so that light emission from the organic EL element cannot be observed. By appropriately controlling the concentration, the surface resistance of the electrode formed of the oxygen-deficient oxide film can be reduced, light emission can be observed, and an organic EL device with good contrast can be obtained.

Further, when the element forming the oxygen-deficient oxide film is Ta, the sheet resistance cannot be sufficiently reduced only by controlling the oxygen concentration as shown in Comparative Examples 2 and 3, and light emission is observed. However, by co-evaporating a metal and an oxygen-deficient oxide film as shown in Example 4 and Example 5, the sheet resistance can be reduced, light emission can be observed, and an organic EL device having good contrast can be obtained. Obtainable. In this case, as shown in Example 5, in addition to Au as shown in Example 5, a metal (Au) having a higher work function than an oxygen-deficient oxide film and an electrode co-evaporated with an oxygen-deficient oxide film are used. Also, an electrode co-deposited with a metal (Mg) having a lower work function than an oxygen-deficient oxide film can lower the work function of the electrode itself, so that charges can be efficiently injected into the organic EL element, and Driving by voltage can be performed. Where Mg
It is also conceivable that Mg also becomes an oxide, but in the case of Mg, the work function is lower when it becomes an oxide, so that even if Mg becomes an oxide, the work function of the cathode can be lowered.

Also, when the element forming the oxygen-deficient oxide film is Cr, as shown in Comparative Example 4, since the work function of the electrode formed of the oxygen-deficient oxide film is high, charge is efficiently stored in the organic EL device. Cannot be injected and no light emission is observed, but as shown in Example 6, a metal (M
By co-evaporating g), the work function of the cathode can be lowered and light emission can be observed, so that an organic EL device with good contrast can be obtained.

(Embodiment 2) FIG. 3 is a view showing the structure of another embodiment of the present invention. The difference from the structure of the first embodiment is that a conductive film 9 is provided on the cathode 8 of the oxygen-deficient oxide film of the first embodiment. The device of the present invention was manufactured in the same manner as in Embodiment 1 up to the organic multilayer film 7, and then the cathodes and conductive films shown in Table 2 were manufactured.

[0035]

[Table 2]

With respect to these devices, the reflectance, the sheet resistance of the cathode, the work function, and the sheet resistance, the work function, and the contrast ratio of the conductive film were measured in the same manner as in the first embodiment.

Embodiment 7 and Embodiment 1, Embodiment 8 and Embodiment 6
As can be seen from the comparison, by laminating a metal electrode having a low sheet resistance on a film made of an oxygen-deficient oxide film, the wiring resistance of the cathode can be reduced, so that the driving voltage can be reduced.

[0038]

According to the structure of the present invention, an electrode suitable for an organic EL device can be manufactured, and the contrast of the organic EL device can be improved. Therefore, a high-contrast organic EL device that can be seen even in a bright place. Can be manufactured.

[Brief description of the drawings]

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

FIG. 2 is a contrast measurement system.

FIG. 3 is a sectional view showing another embodiment of the organic EL device of the present invention.

FIG. 4 is an example of a cross-sectional view of a conventional organic EL element.

[Description of Signs] 1 Transparent substrate 2 Anode 7 Organic multilayer film 8 Cathode 9 Conductive film 10 Fluorescent lamp 11 Luminance meter 12 Organic EL device

Claims (5)

[Claims] 1. An organic single-layer film or an organic multilayer film containing an organic light-emitting material is sandwiched between a pair of electrodes comprising an anode and a cathode, and a voltage is applied or a current is injected between the pair of electrodes. An organic EL device that emits light from the organic light-emitting material by doing so, wherein one of the electrodes is an electrode containing an oxygen-deficient oxide. 2. An electrode containing the oxygen-deficient oxide has a sheet resistance of 200 Ω / □ or less.
3. The organic EL device according to claim 1. 3. The work function of the electrode containing the oxygen-deficient oxide is 5.0 eV or less.
Or the organic EL device according to 2. 4. The electrode containing an oxygen-deficient oxide contains an electrically conductive substance.
The organic EL device according to any one of the above. 5. The electrode according to claim 1, wherein a conductive film having a sheet resistance lower than the sheet resistance of the electrode is arranged outside the electrode containing the oxygen-deficient oxide. Organic EL device.