JPH053079A - Organic el element - Google Patents

Abstract

PURPOSE:To average the interference effect, and to reduce a visual angle dependent property and a membranous thickness dependent property. by laminating an organic electroluminescence(EL) layer and a metallic electrode, and making the surface contacting to either the EL layer or the metallic electrode in a rough surface. CONSTITUTION:A transparent electrode 2, an organic EL layer 3, and a metallic electrode 1 are laminated on a transparent base 6 in this order. In this case, the surface of the base 6 is made in a rough surface by a corrosion-processing with a medicine having a corrosive function such as a fluorate, or by sandblasting. Then, on the rough surface of the base 6, the layer of the transparent electrode 2 is formed by a spattering. After the electrode is formed, a TPD and an AIq3 are evaporated in order by a resistance-heating evaporation in a vacuum ambiance, so as to form the metallic electrode 1. As a result, the path differences of luminous points in the luminous layer 3 observed from the visual angle are different, and the interference effect is averaged. Consequently, the visual angle dependent property of the brightness and the luminous spectrum, and the variation owing to the uneven membranous thickness can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes an electroluminescence (hereinafter, referred to as EL) of a substance by injecting an electric current to form an E layer having a thin film of the substance.
L element, especially organic E whose light-emitting substance is an organic compound
Regarding the L element.

[0002]

2. Description of the Related Art As an organic EL device of this kind, as shown in FIG. 3, an EL layer 3 composed of light emitting thin films made of organic compounds and laminated between an organic compound and a transparent cathode 2 is provided. One having a two-layer structure in which the hole transport layer 4 is arranged, or as shown in FIG. 4, an electron transport layer 5 made of an organic compound laminated between the metal cathode 1 and the transparent anode 2,
A three-layer structure in which the EL layer 3 and the hole transport layer 4 are arranged is known. Here, the hole transport layer 4 has a function of facilitating the injection of holes from the anode and a function of blocking electrons, and the electron transport layer 5 has a function of facilitating the injection of electrons from the cathode and block holes. It has the function and.

For example, the metal cathode 1 may be made of a metal having a small work function such as aluminum, magnesium, indium, silver, or an alloy of each, and having a thickness of about 1000 to 5000 angstrom. Further, for example, in the anode 2, indium tin oxide (hereinafter referred to as ITO) is used.
Made of a conductive material with a large work function such as
A thickness of about 0 to 3000 angstroms or a thickness of gold of about 800 to 1500 angstroms can be used.

For the EL layer 3, an aluminum quinolinol complex, that is, an Al oxine chelate (hereinafter referred to as Alq ₃ ), a tetraphenyl butadiene derivative or the like can be used. In the hole transport layer 4, N, N′-diphenyl-N, N′-bis (3methylphenyl) -1,1′-biphenyl-4,4′-diamine (hereinafter referred to as TPD) which is a triphenyldiamine derivative. ) Is preferably used, and CT
M (Carrier Transporting Ma)
The compounds known as terials) can be used alone or as a mixture.

For the electron transport layer, for example, an oxadiazole derivative (PBD) or the like can be used. In these organic EL devices, a glass substrate 6 is arranged outside the transparent electrode 2 so that electrons injected from the metal cathode 1 and the transparent anode 2
Excitons are generated by recombination with holes injected from the EL layer 3 into the EL layer 3, and the excitons emit light in the process of radiation deactivation near the interface with the hole transport layer in the EL layer. It is emitted to the outside through the transparent anode 2 and the glass substrate 6 (Japanese Patent Laid-Open Nos. 59-194393 and 63-295).
695).

[0006]

By the way, the inventor
As a result of research on the EL layer film thickness, the emission spectrum and the brightness, and the viewing angle of the organic EL device having the layer structure, it was found that the brightness depends on the EL layer film thickness and the viewing angle.
That is, as shown in FIG. 5, the emission spectrum and the brightness change depending on the angle at which the viewer views the surface of the organic EL element on the glass substrate 6 side.

For a viewer, the light emitted from one point of the light emitting source P in the EL layer is divided into a path A directly directed to the substrate 6 in the figure and a path B reflected by the metal electrode 1 on the back surface to the substrate 6.
Includes two lights. The light of these two paths is expressed by the following Equation 1
Since the optical path difference L shown in Equation 1 and the phase difference ηy shown in Equation 2 are held, they interfere with each other (in both equations, n is the refractive index of the EL layer 3 and y is the light source P to the metal electrode 1). A distance, θ is a viewing angle deviating from a normal to the display surface in the EL layer, and λ is a wavelength. The same applies hereinafter.

[0008]

[Equation 1]

[0009]

[Equation 2] Therefore, as an interference effect, the intensity I (y, λ) is
Can be expressed as

[0010]

[Equation 3]

The emission intensity f (y) distribution in the EL layer is shown in FIG.
As shown in, the boundary surface of the hole transport layer 4 strongly decreases toward the metal electrode 1, and can be expressed as an exponential function distribution with respect to the film thickness as in Expression 4, and the EL layer as a whole can be normalized as in Expression 5 ( In both equations, d is the distance from the light emitting source to the metal electrode, ε is the emission intensity distribution parameter, and k is a constant.

[0012]

[Equation 4]

[0013]

[Equation 5]

The intensity distribution F of the emission spectrum of the emission source itself
(Λ) can be expressed as a function of the wavelength λ peculiar to the light emitter. Therefore, the light emission intensity T (λ, θ, d) of the EL element that is actually observed by the viewer can be expressed by Expression 6.

[0015]

[Equation 6]

Here, the emission intensity T (λ, θ,
In order to confirm d), Alq ₃ having a film thickness d of 6000 angstroms is used. An organic EL device including an EL layer made of was prepared, and the emission intensity was tested under various viewing angles θ from 0 ° to 75 °. FIG. 7 shows the emission intensity distribution with respect to the emission wavelength. It was confirmed that the light emission intensity distribution and the light emission intensity T (λ, θ, d) of the above formula 6 are substantially the same. As is apparent from the figure, to the viewer, the colors seem to be sequentially different from the viewing angle of 0 ° to 75 ° depending on the viewing direction of the EL element display surface.

Further, in consideration of practical use, the visual sensitivity characteristic E (λ) of a viewer or a photodetector sensitive to the wavelength λ with a specific value is considered. For example, if the luminosity characteristic E (λ) is a normal distribution, the luminance characteristic L (d) of the EL element within the sensitivity characteristic can be expressed as a function of d as in Expression 7 (K indicates a constant).

[0018]

[Equation 7]

FIG. 8 shows Alq ₃ EL layer (θ =
(0, n = 1.7), the film thickness / brightness attenuation (characteristic) of the brightness / current characteristics with respect to the film thickness is shown when the film thickness is calculated from about 0 Å to 8000 Å. The film thickness dependence of the brightness in the element is shown.

From the above, in the organic EL element, the color (emission spectrum) and the luminance change depending on the viewing angle, and the luminance changes due to the variation in the film thickness. Therefore, when color display is performed, the color and the luminance change depending on the viewing angle. Change, and it becomes very inconvenient for a display, and its improvement is a major issue.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an organic EL element in which the viewing angle dependence of luminance and emission spectrum is reduced.

[0022]

The present invention has been completed on the basis of the above findings, and provides an organic EL element in which a transparent electrode, an organic EL layer and a metal electrode are laminated in this order on a transparent substrate. The surface of the organic EL layer that is in contact with the metal electrode or the surface of the metal electrode that is in contact with the organic EL layer is roughened.

[0023]

In the surface emitting device of the present invention, for example, in the organic EL layer including the hole transport layer and the light emitting layer, the luminance changes depending on the film thickness, and the emission spectrum and the luminance change depending on the viewing angle. It was found by experiments by the present inventors that the brightness decreases due to the above. Furthermore, it has been found that such changes can be explained by an interference model.

Therefore, by roughening the surface of the organic EL layer which is in contact with the metal electrode or the surface of the metal electrode which is in contact with the organic EL layer, the optical path difference of the light from the light emitting point in the light emitting layer is somewhat small. Differently, since the interference effect is averaged, the angle dependence and the film thickness dependence are reduced.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings described below, the same parts as those in FIG. 3 will be assigned the same reference numerals and overlapping explanations will be omitted.

FIG. 1 shows an embodiment in which the organic EL element of the present invention is applied to a two-layer structure. In ₂ O ₃ and SnO _{2 are formed} on the rough surface of the glass substrate 6. Transparent electrode 2, etc.
Triphenyldiamine derivative (T
(PD) hole transport layer 4 and aluminum quinolinome complex (Alq ₃ ) And a metal electrode 1 made of Mg-Al or the like are sequentially formed.

FIG. 2 is an enlarged view of the rough surface portion. The maximum height of the roughened surface is about 1 μm, and the interval L between the roughened peaks is L. Is preferably about 3 μm. Then, the organic EL element roughened as described above is prepared as follows.

First, the surface of the glass substrate 6 is treated by, for example, a corrosive treatment with a chemical having a corrosive action such as a fluoric acid salt or a sandblast treatment. At this time, the maximum height of the roughened surface and the distance L between the peaks are about 1 μm and about 3 μm, respectively. These processing methods are the same as the so-called frosted glass manufacturing method.

Then, an ITO thin film of about 100 is sputtered on the roughened surface of the glass substrate 6.
A layer of the transparent electrode 2 having a thickness of 0 angstrom is formed.
In forming a layer of the transparent electrode 2, together with a mixed gas of Ar and O _2, 10 ^- carried out at ³ Torr vacuum degree of about in.

[0030] After finishing the formation of the transparent electrode 2, on the ^{surface, 10 - 6 ~10 - 7 Torr} TPD and Al in vacuum in the
q ₃ Are sequentially deposited by the resistance heating vapor deposition method, and
A 0 Å hole transport layer 4 and a light emitting layer 3 are formed. After finishing the formation of the light-emitting layer 3, thereon 10 ^{- 6} ~
10 ^{- 7} Torr by depositing Mg-Al in vacuum in, to form the metal electrode 1.

In this way, the interface of each layer is roughened to the above degree. As a result, the optical path difference of each light emitting point in the light emitting layer when viewed from a certain viewing angle is different and is not constant. Therefore, the interference effect is averaged, and changes due to viewing angle dependence of luminance and emission spectrum and variation in film thickness are suppressed.

Further, since the regular reflection is reduced, the contrast is also improved. In the present embodiment, the case where the surface of the glass substrate 1 is first roughened to roughen the surface in contact with the light emitting layer and the metal electrode has been described.
Not limited to this example, only the surface of the light emitting layer that is in contact with the metal electrode may be roughened.

Further, the present invention is not limited to the two-layer structure of the above-mentioned embodiment, and the interface between the respective layers can be roughened similarly in the case of the three-layer structure shown in FIG.

[0034]

As described above, the organic EL device of the present invention
According to the element, the surface of the organic EL layer on the side in contact with the metal electrode or the surface of the metal electrode on the side in contact with the organic EL layer is roughened so that the optical path difference of light from the light emitting point in the light emitting layer is made different. As a result, the interference effect is averaged and the angle dependence and the film thickness dependence are reduced, so that it is possible to prevent the decrease in luminance due to the viewing angle.

[Brief description of drawings]

FIG. 1 is a diagram showing an example in which the present invention is applied to an organic EL device having a two-layer structure.

FIG. 2 is a diagram showing a part of a rough surface portion of the organic EL element shown in FIG.

FIG. 3 is a structural diagram showing an organic EL device having a two-layer structure.

FIG. 4 is a structural diagram showing an organic EL device having a three-layer structure.

FIG. 5 is a partial enlarged cross-sectional view illustrating light interference in an organic EL element having a two-layer structure.

FIG. 6 is a graph illustrating the film thickness light emission intensity distribution of an EL layer in a two-layer structure organic EL element.

FIG. 7 is a graph illustrating a wavelength emission intensity distribution of an EL layer in an organic EL device having a two-layer structure.

FIG. 8 is a graph illustrating a film thickness luminance decay curve of a single layer of an EL layer in a two-layer structure organic EL element.

[Explanation of symbols]

 1 Metal Electrode 2 Transparent Electrode 3 EL Layer 4 Hole Transport Layer 5 Electron Transport Layer 6 Glass Substrate

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yukio Tanaka 465 Osato-cho, Kofu-shi, Yamanashi Pioneer Video Co., Ltd.Kokumo Factory (72) Inventor Keinobu Yonemoto 465 Osato-cho, Kofu-shi, Yamanashi Pioneer Video Co., Ltd. Kokumo Factory

Claims (1)

Claim: What is claimed is: 1. An organic EL device comprising a transparent substrate, a transparent electrode, an organic EL layer, and a metal electrode laminated in this order on a surface of the organic EL layer on the side in contact with the metal electrode or the metal electrode. 2. An organic EL element having a roughened surface on the side in contact with the organic EL layer.