JP2002289358A - Organic electroluminescence device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electroluminescence (E) having high luminous efficiency (light extraction efficiency), high luminance and low power consumption.
L) Providing a device. SOLUTION: The light emitted in the organic EL element has two paths, that is, light that goes directly to the front of the element and light that is reflected by the cathode 15 and then goes to the front of the element. These lights are
Since there is an optical path difference, they interfere with each other. The phase difference δ between the light coming out of the light emitting layer and going directly ahead of the device and the light reflected by the cathode
Is determined by δ = π + 4πL / λ in the normal direction of the substrate, λ is the wavelength, and L is the optical distance from the light emitting position to the reflecting surface. The optical distance L is given by the optical film thickness nd of the organic material existing from the light emitting position to the reflection surface (n is a refractive index, and d is a film thickness). When the organic material existing from the light emitting position to the reflecting surface is composed of a plurality of layers, the optical distance L
Is the sum of the optical distance (optical thickness) of each organic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat display device capable of multicolor display, and an organic electroluminescent device having a high luminous efficiency, which is a solid light emitting device usable also as a light source (hereinafter referred to as an organic EL device). About.

[0002]

2. Description of the Related Art In recent years, with the progress of information technology represented by the Internet, information devices such as notebook personal computers, portable terminals, and cellular phones have been rapidly spread. There is a demand for a high-quality, high-performance flat display device capable of instantaneously processing and displaying enormous information from these information devices. A typical flat display device is a liquid crystal display device. 2. Description of the Related Art Liquid crystal display devices have been used in many electronic products such as display devices for notebook personal computers and mobile phones, taking advantage of their features of low voltage driving and low voltage consumption. However, despite the low power consumption of the liquid crystal element itself, it is not a self-luminous type, so a bright and high-quality color display requires a backlight,
Driving this backlight requires large power. In addition, since the response speed is slow, it is difficult to display a moving image with satisfactory quality, and the viewing angle is narrow. On the other hand, organic EL elements are expected to be self-luminous display elements that can be driven at low voltage by direct current and have excellent performance as display elements such as a wide viewing angle, high visibility, and high-speed response. In addition, since low-voltage DC drive, high luminous efficiency, and high-luminance luminescence have been reported in a stacked-type device configuration, active research has been conducted toward practical use (Japanese Patent Publication No. Sho 64-7635, Japanese Patent Publication No. Hei 6-76). −32
No. 307, Appl. Phys. Lett. , 51,9
13 (1987)).

[0003] As a basic technical problem of an organic EL device,
There are low voltage driving, high luminous efficiency, high luminance, and multicolor light emission. The light emitting mechanism of the organic EL element is understood as follows. When an electric field is applied to the device, electrons are injected from the cathode and holes are injected from the anode as carriers. These carriers recombine in the light-emitting layer to generate excitons, and when energy is released, electrical energy is converted to light. Converts to energy and emits light. For the anode, a material having a large work function is generally considered to be good in order to increase the hole injection ability, and further, transparency for taking out light emission is required.
A transparent electrode such as ITO (indium tin oxide) is most often used as an anode material. A metal having a small work function or an alloy thereof is used for the cathode.

There are alkali metals, alkaline earth metals and Group 3 metals, but Al, Mg and their alloys, which are inexpensive and have relatively high chemical stability, are most often used. In order to improve luminous efficiency, it is important to efficiently inject and transport both electrons from the cathode and holes from the anode to the light-emitting layer, and to recombine as much of the injected carriers as possible. It is said that there is. Therefore, in a stacked type device, it is understood that there is a possibility that high efficiency can be realized by optimizing each material by sharing different functions of carrier injection, transport and light emission with different materials, Active research has begun. Further, in the stacked element, the recombination position of the carriers is concentrated at a position away from the electrode, so that the generated excitons are prevented from moving to the interface portion of the electrode and disappearing. It is preferable that the distance from the electrode to the light emission position does not become less than about 30 nm in order to prevent the exciton disappearance.

The structures of the organic EL elements proposed so far include a two-layer type, a three-layer type, and an improved type based on these, depending on the number of organic multilayer films. The two-layer type device has a light-emitting layer having both an electron-transport property and a hole-transport property, and is composed of a hole-transport layer / electron-transport light-emitting layer (see FIG. 13) and a hole-transport light-emitting element. Layer / electron transport layer (see FIG. 14). The two-layer element composed of the hole transport layer 3a / the electron transporting light emitting layer 4b has an electron transporting property between the anode 2 on the glass substrate 1 and the electron transporting layer 4a which is a light emitting layer having an electron transporting property. By providing the hole transport layer 3a having little or no holes, the holes can be efficiently injected and transported, and the electrons injected from the cathode 5 can be blocked at the interface between the hole transport layer 3a and the light emitting layer. The purpose is to improve the coupling efficiency. In this case, recombination of electrons and holes occurs only in the light emitting layer (light emitting position) 6 near the interface between the hole transporting layer light emitting layer 3b and the electron transporting light emitting layer 4b, and exhibits the maximum light emission intensity at that position. .

[0006] 2 comprising a hole transporting light emitting layer / electron transporting layer
Layer-type devices aim to improve the efficiency of electron-hole coupling by providing an electron-transporting layer between the cathode and the light-emitting layer having a hole-transporting property to block holes. It is a thing. In this case, recombination of electrons and holes occurs only in the light-emitting layer near the interface between the hole-transporting light-emitting layer and the electron-transporting layer, and exhibits the maximum light emission intensity at that position. The three-layer type element has a hole transport layer / light-emitting layer / carrier transport layer separated from each other.
It consists of a light emitting layer / electron transport layer. Alternatively, in order to lower the barrier against hole injection from the anode, another hole injection layer having a small difference in ionization potential between the hole transport layer and the anode may be provided. Also, Ap
pl. Phys. Lett. , 57, 531 (199
0), the thickness of the light emitting layer in the three-layer type device was 5 nm.
It is shown that the luminous efficiency does not decrease even if the thickness is reduced as far as possible. This indicates that light emission is occurring in the 5 nm thick light emitting layer. As described above, light emission of the multilayer organic EL element basically occurs only in the vicinity of the interface where electrons and holes recombine irrespective of the two-layer type or the three-layer type. The improvement of the luminous efficiency is still a fundamental problem of the organic EL element, and many materials and configurations have been proposed so far.

Japanese Unexamined Patent Publication (Kokai) No. 4-137485 discloses an electroluminescent device having a structure of anode / hole transporting light emitting layer / electron transporting layer / cathode in which the thickness of the electron transporting layer is 30 to 60 nm to obtain high brightness. An element is disclosed. Further, Japanese Patent Nos. 3065704 and 3065705 show a method of utilizing an interference effect of light reflected on a cathode. Japanese Patent No. 2,846,571 discloses an organic electroluminescence device that sets a total optical thickness and a refractive index of an anode (transparent electrode) and an organic multilayer film so as to enhance emission intensity at a selected wavelength. I have.
This does not define the optical distance from the position of the light emitting layer to the cathode, and also utilizes the interference between the reflected light at the interface between the anode (transparent electrode) and the substrate and the reflected light at the cathode. Therefore, in order to increase the reflectance at the interface between the transparent electrode and the substrate, it is described that a transparent electrode having a high refractive index of 1.8 or more is used as the transparent electrode. Patent No. 27
No. 97883 discloses a multicolor light emitting element which forms a microcavity with reflectors formed on both surfaces of a light emitting layer and performs multicolor display by controlling an optical distance between the reflectors, and a substrate thereof. ing.

[0008] Jpn. J. Appl. Phys. Vo
l. 38 (1999) pp. 2799-2803, "E
evaluation of True Power L
uminous Efficiency from E
xperimental Luminance Val
es "(T. Tsutsui and K. Ya
In an organic EL device having a configuration of a transparent electrode (ITO) / hole injection / transport layer (TPD) / electron transport light-emitting layer (Alq) / cathode (MgAg), the electron transport light-emitting layer (Alq) Attempts have been made to correctly evaluate the light extraction efficiency from the change in the emission spectrum experimentally obtained by changing the film thickness and the viewing angle dependence of the luminance.

[0009]

As described above, for example, a plasma display element and an organic EL element are known as self-luminous display elements. However, the plasma display element utilizes plasma emission in a low-pressure gas, and is suitable for a large-sized display device. However, the plasma display element is not suitable for thinning and miniaturization, and a cost problem remains. I have. Further, high voltage AC driving of several hundred volts is required for plasma emission, which is not suitable for low power consumption. In addition, even if a light emitting material having a high internal quantum efficiency is used to improve the light emitting efficiency of the organic EL element, light emitted from the light emitting layer is not effectively extracted to the outside, that is, light extraction efficiency is low. For this reason, there is a problem that the luminous efficiency cannot be increased. This is mainly due to the fact that when the angle of incidence on the substrate surface on the light extraction side exceeds the critical angle, the light is totally reflected, so that light cannot be extracted from the substrate to the outside. For example, it is considered that an ordinary glass substrate has an extraction efficiency of about 25%. Therefore, the organic E
In order to improve the luminous efficiency of the L element, it is desired to provide an element configuration capable of effectively extracting light from the light emitting layer to the outside of the element.

Conventionally, luminous efficiency (light emission extraction efficiency)
One of the methods for improving the efficiency is to effectively use the light reflected from the cathode. In other words, if a metal material having a high reflectance in the visible light region is used as the cathode material,
The light emitted from the light-emitting layer can be effectively extracted by reflecting it in front of the device (on the anode side), but the light that goes out of the light-emitting layer and goes directly forward of the device and the light reflected by the cathode must interfere with each other. At present, accurate and detailed studies on this interference effect have not been made. Also,
In the above-mentioned Japanese Patent Application Laid-Open No. 4-137485, it is shown that the distance between the light emitting layer and the cathode is an important factor for improving the light emission intensity. The reason for the dependence is not fully understood. Further, there is no description about the relationship between the emission wavelength and the film thickness, and no study is made on the light interference effect.

In the prior arts of Japanese Patent No. 3065704 and Japanese Patent No. 3065705, the thickness of the EL layer or the electron transporting layer is determined by changing the film thickness including the secondary maximum value of the second highest luminance in the film thickness decay curve characteristic. It is described that the film thickness is set within a range that produces a luminance whose amplitude exceeds the convergent luminance value at which the amplitude converges.
“Equation 3” representing the light intensity as the light interference effect described in No. 704 is derived without considering the phase change of π radians of the light reflected by the cathode, and This would be against the law. In other words, according to Fresnel's law of reflection, when light is incident from an optically sparse substance (a substance with a small refractive index) to a dense substance (a substance with a large refractive index), the phase of the reflected light is only π radians. Known to change (eg, "interference and coherence"
(See the description of Lloyd's mirrors and coherence by Yoshiro Iinuma, Kyoritsu Shuppan). In general, a metal surface having a high reflectance is a so-called mirror surface, and the phase of reflected light changes by approximately π radians on the reflection surface. As described above, if the phase change of π radian of the reflected light at the cathode is ignored, not only the thickness of the EL layer that gives the maximum value of the emission intensity cannot be accurately obtained, but also the minimum value of the emission intensity. There is a possibility that the film thickness is set to a value.

It is generally considered that a metal surface having a high reflectance is a so-called mirror surface, and that the phase of reflected light changes by approximately π radian on the reflection surface. However, since an actual metal has a complex refractive index, The substantial phase change of the reflected light at the reflecting surface deviates from π radians. Similarly, in a semi-transmissive film formed of a metal thin film or a dielectric film having absorption, the substantial phase change of the reflected light on the reflecting surface similarly deviates from π radians. Therefore, when selecting a variety of cathode materials, it was necessary to consider the substantial phase change of the reflected light on the reflecting surface, but such a study has not been made so far. Further, in Japanese Patent No. 2846571, since EL emission is taken out of the element from the surface on the anode side, the anode is required to have a high transmittance in the visible light region, and is made of an anode material having a large reflectance like a cathode. Can not expect strong interference effects. Therefore, although the configuration shown in this prior art is effective for improving color purity, it is not possible to expect a great improvement in large luminous efficiency (light extraction efficiency). Similarly, Patent No. 279788
No. 3 does not specify the optical distance from the position of the light emitting layer to the cathode. Further, no detailed description is given of the light interference effect.

An object of the present invention is to provide an organic EL device having high luminous efficiency (light extraction efficiency), high luminance and low power consumption.
It is to provide an element.

[0014]

According to the first aspect of the present invention, there is provided an organic multilayer formed by forming an anode comprising a transparent electrode and at least two layers of a hole transport layer and an electron transport layer on the anode. And a cathode made of a specular reflection film made of a metal on the organic multilayer film. The optical film thickness nd of the electron transport layer of the organic multilayer film is nd = (2N-1) λ / 4,
The object is achieved by satisfying the following relationship (n is a refractive index, d is a film thickness, λ is a central wavelength of light emission, and N is a positive integer). According to the second aspect of the present invention, an anode formed of a transparent electrode, an organic multilayer film formed by stacking two layers on the anode in the order of a hole transporting layer and an electron transporting light emitting layer; A cathode made of a mirror-reflective film made of metal on the film layer, and an optical film thickness n of the electron transporting light emitting layer of the organic multilayer film.
The above object is achieved by satisfying the following relationship: d is nd = (2N-1) λ / 4, (n is a refractive index, d is a film thickness, λ is a central wavelength of light emission, and N is a positive integer). . According to the third aspect of the present invention, an organic multilayer film formed by laminating an anode composed of a transparent electrode and three layers on the anode in the order of a hole injection layer, a hole transport layer, and an electron transport light emitting layer And a cathode made of a specular reflection film made of metal on the organic multilayer film,
The optical film thickness nd of the electron transporting light emitting layer of the organic multilayer film is:
nd = (2N-1) λ / 4, (n is a refractive index, d is a film thickness,
The above object is achieved by satisfying the relationship of λ is the central wavelength of light emission and N is a positive integer. According to a fourth aspect of the present invention, in the second or third aspect, the electron transporting light emitting layer is doped with a small amount of a fluorescent material near an interface with the hole transporting layer. ,
The above objective is achieved.

According to a fifth aspect of the present invention, an anode composed of a transparent electrode, a hole transport layer, a light emitting layer having a thickness of 30 nm or less, and an electron transport layer are laminated on the anode in this order. And a cathode formed of a mirror-reflective film made of metal on the organic multilayer film. The optical thickness nd of the electron transport layer of the organic multilayer film is nd = (2N− 1) λ /
4, (n is the refractive index, d is the film thickness, λ is the central wavelength of light emission, N
Is a positive integer), thereby achieving the above object. According to a sixth aspect of the present invention, in the fifth aspect of the invention, the light-emitting layer achieves the object by being doped with a small amount of a fluorescent material.

In the invention according to claim 7, an anode comprising a transparent electrode, an organic multilayer film formed by laminating two layers on the anode in the order of a hole transporting light emitting layer and an electron transporting layer, A cathode made of a specular reflection film made of a metal on the organic multilayer film; and an optical film thickness n of an electron transport layer of the organic multilayer film.
The above object is achieved by satisfying the following relationship: d is nd = (2N-1) λ / 4, (n is a refractive index, d is a film thickness, λ is a central wavelength of light emission, and N is a positive integer). . In the invention according to claim 8, in the invention according to any one of claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, and claim 7, the cathode comprises: The object is achieved by the metal film having a reflectance of 50% or more. According to the ninth aspect, the first, second, third,
In the invention according to any one of claims 4, 5, 6, 7, and 8, the positive integer N
Achieves the above object by being 1. In the invention according to claim 10, claim 1, claim 2, claim 3,
Claim 4, Claim 5, Claim 6, Claim 7, Claim 8,
The optical film thickness nd of the electron transporting layer or the electron transporting light emitting layer according to any one of claims 9 to 10.
Achieves the above object by being within the error range of the central wavelength of the light emission ± λ / 8.

In the eleventh aspect of the present invention, the transparent electrode
An anode, and at least a hole transport layer and an electron on the anode.
An organic multilayer film formed to have two transport layers,
Having a complex refractive index n '= nr-ikr on a multilayer film layer
And a cathode made of a metal film.
The optical thickness nd of the electron transport layer is nd = (λ / 4) (2N−
δr / π), δr = arctan (2nk_r/ (N^Two−
(N_r)^Two− (K_r)^Two)) + Π, (n^Two≤n_r ^Two+ K_r ^TwoIn
Where n is the refractive index, d is the film thickness, λ is the central wavelength of light emission, and N is
The above purpose is achieved by satisfying the relationship
To achieve. According to the twelfth aspect of the present invention, the transparent electrode is formed.
An anode, a hole transport layer on the anode, and an electron transporting light emitting layer.
An organic multilayer film formed by laminating two layers in this order,
Metal having complex refractive index n '= nr-ikr on multilayer film
A cathode made of a film, comprising:
The optical thickness nd of the transportable light emitting layer is nd = (λ / 4) (2
N−δr / π), δr = arctan (2nk_r/ (N^Two
− (N_r)^Two− (K _r)^Two)) + Π, (n^Two≤n_r ^Two+ K_r ^Twoso
Where n is the refractive index, d is the film thickness, λ is the central wavelength of light emission, N
Satisfies the relationship
Achieve. According to the thirteenth aspect of the present invention, a transparent electrode is used.
An anode, a hole injection layer, a hole transport layer, and an electron
Organic multilayer formed by stacking three layers in the order of transportable light emitting layer
Complex refractive index n '= nr-ik on the film and the organic multi-layer
and a cathode made of a metal film having r.
Film thickness nd of the electron transporting light emitting layer of the organic multilayer film is nd =
(Λ / 4) (2N−δr / π), δr = arctan
(2nk_r/ (N^Two− (N_r)^Two− (K_r)^Two)) + Π, (n
^Two≤n_r ^Two+ K_r ^TwoWhere n is the refractive index, d is the film thickness, and λ is the emission
Center wavelength of light, N is a positive integer)
Thus, the above object is achieved. According to the invention of claim 14,
Is the invention according to claim 12 or claim 13,
The electron transporting light emitting layer is near an interface with the hole transporting layer.
Is doped with a small amount of fluorescent material.
Achieve the above object.

According to the present invention, an anode comprising a transparent electrode, a hole transport layer on the anode, and a film thickness of 30 nm
An organic multilayer film formed by laminating three layers in the following order of a light emitting layer and an electron transport layer; and a complex refractive index n ′ on the organic multilayer film.
And a cathode made of a metal film having the following formula: nr-ikr, and the optical thickness nd of the electron transport layer of the organic multilayer film is:
nd = (λ / 4) (2N−δr / π), δr = arct
an (2nk _r / (n ² − (n _r ) ² − (K _r ) ² )) + π,
(N ² ≦ n _r ² + K _r ² , n is the refractive index, d is the film thickness, λ
Is the center wavelength of light emission, and N is a positive integer. In the invention according to claim 16, in the invention according to claim 15, the light-emitting layer comprises:
By doping a small amount of fluorescent material,
The above objective is achieved.

In the invention according to claim 17, an anode composed of a transparent electrode, an organic multilayer film formed by laminating two layers on the anode in the order of a hole-transporting light-emitting layer and an electron transport layer, A cathode made of a metal film having a complex refractive index n ′ = nr−ikr on the organic multilayer film, and the optical film thickness nd of the electron transport layer of the organic multilayer film is nd = (λ / 4) (2N
−δr / π), δr = arctan (2nk _r / (n ² −
(N _r ) ² − (K _r ) ² )) + π, (n ² ≦ n _r ² + K _r ² , where n is the refractive index, d is the film thickness, λ is the center wavelength of light emission, and N is a positive integer. The above object is achieved by satisfying the following relationship: In the invention according to claim 18, in the invention according to any one of claims 11, 12, 13, 14, 15, 16, and 17, the cathode comprises: The object is achieved by the metal film having a reflectance of 50% or more. In the invention according to claim 19, claim 11, claim 12, claim 13, and claim 1
4, Claim 15, Claim 16, Claim 17, Claim 18
In the invention described in any one of the above, the above object is achieved by the positive integer N being 1. According to the twentieth aspect of the present invention, any one of the eleventh, the twelfth, the thirteenth, the thirteenth, the fifteenth, the sixteenth, the seventeenth, the eighteenth and the nineteenth aspect is provided. In the invention, the optical film thickness nd of the electron transporting layer or the electron transporting light emitting layer is a central wavelength of the light emission ± λ / 8.
The above object is achieved by being within the error range of within.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to FIGS.
First, the organic EL device according to the first embodiment will be described. The organic EL device of the present embodiment is a mirror-reflective film in which the cathode is made of metal, and emits light so that light coming out of the light-emitting layer and directly traveling in front of the device and light reflected by the cathode are enhanced by an interference effect. The optical distance from the position to the cathode is set. Here, the fact that the cathode is a specular reflection film means that the phase of the reflected light at the interface with the organic layer changes substantially by π radian with respect to the incident light, and is limited to metal materials. However, a metal material having high reflectance and high electron injection efficiency is most suitable. In addition, an optimum device configuration is obtained for the center wavelength of the emission spectrum specific to the light emitting material, so that the strongest light is effectively extracted to the outside of the device.

FIG. 1 is a diagram showing light interference in an organic EL element. The light emitted in the organic EL element has two paths, that is, light that goes directly to the front of the element and light that is reflected by the cathode 15 and then goes to the front of the element. These lights interfere with each other due to the optical path difference. The phase difference δ between light emitted from the light-emitting layer and directed directly in front of the device and light reflected by the cathode is obtained by the following equation (1) in the direction normal to the substrate. δ = π + 4πL / λ (1)

Here, λ is the wavelength, and L is the optical distance from the light emitting position to the reflecting surface. The optical distance L is given by an optical film thickness nd of an organic material (for example, an electron transport layer in a two-layer element) existing from the light emitting position to the reflection surface (n is a refractive index, and d is a film thickness). . When the organic material existing from the light emitting position to the reflection surface is composed of a plurality of layers, the optical distance L is the sum of the optical distances (optical thicknesses) of the organic layers. The light emission position is the hole transport layer 13 showing the maximum light emission intensity.
a / the interface of the electron-transporting light-emitting layer 14b or the interface position of the light-emitting layer (hole-transporting) / electron-transporting layer. If the emission intensity distribution in the light emitting layer cannot be neglected, it can be dealt with by slightly adjusting the thickness of the electron transporting layer (to make it about half the emission intensity distribution thicker).

Π in the first term on the right side of the equation (1) means a phase change of the light reflected on the reflecting surface. The intensity of light coming out of the device as an interference effect between direct light and reflected light is proportional to D (λ) given by the following equation (2). D (λ) = 1 + cos δ (2) Assuming that the emission spectrum of the light-emitting material itself is P (λ), the emission spectrum I (λ) observed outside the device is represented by Expression (3). I (λ) = P (λ) D (λ) (3) Therefore, the light intensity as the effect of interference is δ = 2Nπ
And the minimum when δ = (2N + 1) π (both N is a positive integer). This condition is as follows when rewritten using equation (1). Condition for maximum strength: L = (2N−1) λ / 4 (4) Condition for minimum strength: L = Nλ / 2 (5)

The organic EL device according to the present embodiment has the formula (4)
Is configured to satisfy the following condition. Equation (4)
If the amount of deviation from the optical distance L at which the maximum intensity obtained by the above is obtained is within the range of ± λ / 8, at least the convergence intensity value (the interference effect does not occur as in the case where the film thickness is greater than the interference length) (Intensity value of light at the time). That is, in the present embodiment, the element is configured to completely satisfy the expression (4), but at least ± λ /
It suffices that Expression (4) is substantially satisfied within the range of 8. Further, the optical distance at which the luminous intensity is maximized and the settable range thereof differ depending on the wavelength, and thus are set according to the luminous spectra of various luminescent materials.

Further, the configuration of the organic EL device of the present embodiment
Is disclosed in the prior art as shown in FIG. 13 and FIG.
The maximum emission intensity of the two-layer or three-layer element and the light-emitting layer
Applies to all cases where the indicated interface position is known
can do. In addition, a fluorescent material is
When doping, the cathode is
Is set so as to satisfy Expression (4).
You. The case where a positive integer N representing the order of interference is 1 is adopted.
And the thickness of the organic film (electron transport layer) can be reduced,
It is effective for pressure drive. Organic materials used for organic EL devices
The refractive index n of the material is about 1.6 to 1.8. For example,
In a two-layer element, the refractive index of the organic material is set to n = 1.7.
Then, the well-known luminescent material Almq _ThreeLuminous
Optimum film of electron transport layer for center wavelength λ = 510nm
The thickness is 75 nm. This film thickness can be sufficiently
A stable film can be formed, and the extinguishing
There is no light effect. Of emission spectrum specific to luminescent materials
As an example, FIG. 2 shows Al measured using a spectrofluorometer.
mq_ThreeThe photoluminescence spectrum P (λ) of
Show.

Using the photoluminescence spectrum P (λ) shown in FIG. 2 and equations (1), (2) and (3), the light emission position of the organic film having a refractive index n = 1.7 is calculated. Distance from the cathode to the cathode (film thickness of the electron transport layer) is 38 n
FIG. 3 shows emission spectra calculated for m, 75 nm, 112 nm, and 150 nm. 7 film thickness
The emission intensity is maximum at 5 nm, minimum at 150 nm, 38 n
It can be seen that the values at m and 112 nm are almost intermediate values.
FIG. 4 shows luminance values obtained by calculating the CIE color system in accordance with JIS-Z8701-1982 based on the spectrum calculated by gradually changing the film thickness.
It can be seen that when the film thickness is 400 nm or less, the maximum and minimum of the luminance are clearly reversed.

Next, a method for fabricating the organic EL device according to the present embodiment will be described, but a known method can be basically used. First, a transparent electrode such as ITO is formed on a glass substrate to a thickness of about 10 to 300 nm by vacuum evaporation or sputtering, and this is used as an anode. Commercially available glass substrates with ITO are readily available. Organic materials such as a hole transport layer, a light emitting layer, and an electron transport layer are sequentially formed on the ITO to a predetermined thickness by a vacuum deposition method, a spin coating method, or the like. In a two-layer device, a hole transport layer or an electron transport layer also functions as a light emitting layer.

As shown in FIG. 5, the material for forming the light emitting layer, the hole transporting layer, and the electron transporting layer used in the organic EL device of the present embodiment includes, for example, Triphenyldiamine derivative (TPD),
Triphenylamine derivatives (NSD), α-naphthylphenidylamine (α-NPD), phthalocyanines (C
uPc, H ₂ Pc), starburst polyamines (m
-MTDATA). Examples of the electron transport material include an aluminum quinolinol complex (Alq ₃ ) and a methyl aluminum quinolinol complex (4-methyl-8-hy).
droxyquinoline (Almq ₃ ), beryllium-quinoline complex (Beq ₂ ) and the like can be used, and these materials are also used as a light emitting material at the same time. Oxadiazole derivatives (PBD) are well known as excellent electron transport materials. If a material having a good electron transporting property such as PBD is used as the electron transporting layer, an element having a three-layer structure in which a light emitting layer and a carrier transporting layer are separated or a two-layer structure having a hole transporting light emitting layer can be realized. is there.

Further, as the doping material, coumarin derivatives, quinacridone, rubrene and the like can be used. As a doping method, a light emitting material such as Alq ₃ is used as a host material by co-evaporation using two heating boats, for example, near the interface with the hole transport layer (about 30 n).
m) or less, a fluorescent material can be doped by about several mol% to several tens mol%. Next, the cathode is formed by using a metal material by resistance heating, an evaporation method using an electron beam or the like, or a sputtering method using an alloy target.
It is formed with a film thickness of about 0 to 300 nm. In order to obtain a film having a sufficient reflectance and low resistance, it is preferable that the film thickness is preferably 100 nm or more. As the metal material used for the cathode, a metal having a small work function, for example, Li (lithium), Na (sodium), Mg (magnesium),
Ca (calcium), Sr (strontium), Al
(Aluminum), Ag (silver), In (indium),
A single metal element such as Sn (tin), Zn (zinc), Zr (zirconium), or an alloy thereof is used.
Further, LiF or the like may be formed on the cathode as an electrode protective film in the same manner as in the case of the cathode. Note that in this embodiment, as long as a cathode made of a metal film having a specular reflection interface whose phase changes substantially by π is used, regardless of the difference in the element stacking structure, from the position of the light emitting layer to the cathode By setting the optical distance of according to the present invention,
Luminous efficiency can be improved. In addition, organic EL
The basic concept of the present embodiment can be applied not only to the element but also to a similar surface emitting element using specular reflection.

Hereinafter, Modifications 1 and 2 of the first embodiment will be described. However, the organic EL element according to the present embodiment is not limited to the materials and element configurations in these embodiments. . (1) Modification 1 A glass substrate with ITO having a thickness of 1.1 mm is prepared, and an electrode pattern having a width of 2 mm is formed by a photolithography method using a general resist. Next, the substrate is washed with a surfactant, and the detergent is sufficiently rinsed off with pure water and then dried in the vapor of isopropyl alcohol.
Further, dirt from surface cleaning is sufficiently removed by oxygen plasma treatment. The substrate thus prepared is set in a vacuum deposition apparatus, and α-NPD as a hole transport material is vacuum deposited by resistance heating to form a hole transport layer having a thickness of 70 nm. The deposition conditions are as follows: the degree of vacuum is 2.7 × 10 −4.
Pa, the deposition rate was 1 nm / sec, and further continuously,
Almq ₃ is similarly vapor-deposited to form a 75 nm electron-transporting light-emitting layer.

Then, aluminum (Al) was vacuum-deposited on a film with a metal mask provided with a hole perpendicular to the ITO electrode pattern and having a width of 2 mm in close contact with the substrate and set in a vacuum deposition apparatus. A 160 nm thick metal film is formed and used as a cathode to obtain a 2 mm square lighting region. A protective film is formed by depositing LiF having a thickness of 300 nm on the Al electrode, and a protective film is formed on the device in an inert gas (Ar) atmosphere.
A layer of Pyrex (registered trademark) glass having a thickness of mm is laminated, and the periphery of the glass is sealed with an ultraviolet-curable adhesive to obtain an organic EL element. The position showing the maximum emission intensity is α-NP
The optical distance to the cathode near the interface between D and Almq ₃ satisfies the relational expression given by nd = (2N−1) λ / 4. Here, n is a refractive index, d is a film thickness, λ is a central wavelength of light emission, and N is a positive integer.

(2) Modification 2 As a hole injection layer, m-MTDATA is formed on an ITO electrode to a thickness of 30 nm, and then a hole transport layer is formed.
α-NPD is formed to a thickness of 50 nm, and Almq
_An electron transporting light emitting layer made of ₃ is formed with a thickness of 75 nm. In other respects, the organic EL device is manufactured in the same manner as in the first modification.

Next, an organic EL device according to a second embodiment will be described. In the organic EL device of the present embodiment, the cathode is a metal reflective film, as in the first embodiment, and the light that goes out of the light-emitting layer and goes directly in front of the device and the light reflected by the cathode reinforce by the interference effect. Thus, the optical distance from the light emitting position to the cathode is set. The cathode has light reflectivity and is made in consideration of the substantial phase change of the reflected light on the reflecting surface.It is not limited to metallic materials, but has high reflectivity and high electron injection efficiency. High metal materials are most suitable. Further, the most intense light is effectively extracted out of the device so that the device configuration is optimal for the center wavelength of the emission spectrum specific to the light emitting material.

The light emitted in the organic EL element has two paths, that is, light that goes directly to the front of the element and light that is reflected by the cathode and then goes to the front of the element (see FIG. 1). These lights interfere with each other because of the optical path difference. The phase difference δ between light emitted from the light-emitting layer and directed directly in front of the element and light reflected by the cathode is represented by the following equation (6) with respect to the direction normal to the substrate, where δr represents the phase change of the reflected light on the reflection surface. Given by δ = δr + 4πL / λ (6) where λ is the wavelength and L is the optical distance from the light emitting position to the reflecting surface. The optical distance L is given by an optical thickness nd of an organic material (for example, an electron transport layer in a two-layer element) existing from the light emitting position to the reflection surface (n is a refractive index,
d is the film thickness). When the organic material existing from the light emitting position to the reflection surface is composed of a plurality of layers, the optical distance L is the sum of the optical distances (optical thicknesses) of the organic layers. The light emission position is
Hole transport layer / light-emitting layer exhibiting maximum emission intensity (electron transportability)
Or an interface position of a light emitting layer (hole transporting property) / electron transporting layer. If the emission intensity distribution in the light emitting layer cannot be neglected, it can be dealt with by slightly adjusting the thickness of the electron transporting layer (to make it about half the emission intensity distribution thicker).

Here, the complex refractive index of the cathode material is n '= n
When r-ikr (nr and kr are called optical constants) and the refractive index of the transparent organic material in contact with the cathode are represented by n, the phase change δr of the reflected light on the reflecting surface is expressed by the Fresnel reflection equation Can be expressed by an equation as shown in FIG. Also, the energy reflectance R of light on the reflecting surface
Can be expressed by the equation in FIG. The optical constants of metals are measured by reflectance measurement, ellipsometry, or the like. (The optical constants of metal elements are described in "Thin Films" by Kanehara et al., Shokabo, p. 209, and "Optical Overview I" by Junpei Tsujiuchi.) Author, Asakura Shoten, 50 pages (American Ins
title of Physics Handbook
k (McGraw-Hill, 1972, p6-11
8). The intensity of light coming out of the device as an interference effect between direct light and reflected light is D (λ) given in FIG.
Is proportional to

The emission spectrum of the light emitting material itself is represented by P (λ)
Then, the emission spectrum I observed outside the device is
(Λ) is shown in FIG. Therefore, the intensity of light as an effect of interference is maximum when δ = 2Nπ,
= (2N + 1) π (N is a positive integer). This condition becomes as shown in FIG. 7 when rewritten using the equation (1). The organic EL device according to the present embodiment is shown in FIG.
The element is configured so as to satisfy the condition of the equation (a). If the deviation from the optical distance L at which the maximum intensity given in FIG. 7A is obtained is within the range of ± λ / 8, at least the convergence intensity value (when the film thickness is thicker than the interference length). (Intensity value of light when no interference effect occurs). That is, in the present embodiment,
The device is configured so as to completely satisfy FIG.
It suffices to satisfy at least the range of ± λ / 8. Further, the optical distance at which the luminous intensity is maximized and the settable range thereof differ depending on the wavelength, and thus are set according to the luminous spectra of various luminescent materials.

The configuration of the organic EL device according to the present embodiment is applied to all conventional devices of a two-layer or three-layer device, and in the case where the position of the interface showing the maximum emission intensity of the light emitting layer is known. be able to. When a fluorescent material is doped into the light emitting layer, the optical distance L to the cathode is set so as to satisfy the equation in FIG. If the case where the positive integer N representing the order of interference is 1 is adopted, the thickness of the organic film (electron transport layer) can be reduced, which is effective for low voltage driving. The refractive index n of the organic material used for the organic EL element is about 1.6 to 1.8.

As an example, the optical constant nr =
For 0.055 and kr = 3.32, the refractive index of the organic material (electron transport layer) in contact with Ag is n = 1.7, and the phase change and reflectance at the interface are shown in FIGS. 6 (a) and 6 (b). Δr = 2.195 [radian], R = 0.9
73. Based on this value, the center wavelength λ of light emission of Almq ₃ which is a light-emitting material (also serving as an electron transport layer) = 510
The optimum film thickness of the electron transport layer determined from FIG. 7A is 98 nm with respect to nm. Since it is 75 nm when calculated as δr = π radian, it is understood that the film thickness is as thick as 23 nm. This film thickness can be formed sufficiently stably by the vapor deposition method, and quenching does not occur due to the movement of the excitons to the cathode.

FIG. 2 shows a photoluminescence spectrum P (λ) of Almq ₃ measured using a spectrofluorometer as an example of an emission spectrum peculiar to the light emitting material, as in the first embodiment. The central wavelength of light emission is λ = 51
It is found at 0 nm. Using the photoluminescence spectrum P (λ) shown in FIG. 2 and FIGS. 6C and 6D,
For the organic film having a refractive index of n = 1.7, the distance from the light emitting position to the cathode (the thickness of the electron transport layer) was 61 nm, 9
FIG. 8 shows emission spectra calculated for the cases of 8 nm, 135 nm, and 173 nm. 98nm thick
(Corresponding to N = 1), the emission intensity is maximum, and the original emission spectrum of the material is reproduced. 173 film thickness
It can be seen that the emission intensity is minimum at 61 nm and almost at an intermediate value at 61 nm and 135 nm.

Hereinafter, a method for fabricating the organic EL device according to the second embodiment will be described. Note that a known method can be basically used as a method for manufacturing the organic EL element. First, a transparent electrode such as ITO is formed on a glass substrate to a thickness of about 10 to 300 nm by vacuum evaporation or sputtering, and this is used as an anode. Alternatively, a commercially available glass substrate with ITO can be easily obtained. Organic materials such as a hole transport layer, a light emitting layer, and an electron transport layer are sequentially formed on the ITO to a predetermined thickness by a vacuum deposition method, a spin coating method, or the like. In a two-layer element, the hole transport layer or the electron transport layer also functions as the light emitting layer.

As a material for forming the light emitting layer, the hole transport layer, and the electron transport layer used in the organic EL device of the present embodiment, conventional materials can be used. For example, as shown in FIG. 5, as a hole transporting material, triphenyldiamine derivative (TPD), triphenylamine derivative (NSD), α-naphthylphenidylamine (α
-NPD), phthalocyanines (CuPc, H ₂ P)
c), starburst polyamines (m-MTDAT)
A) is used. Examples of the electron transport material include an aluminum quinolinol complex (Alq ₃ ) and a methyl aluminum quinolinol complex (4-Methyl-8-hydroxyqu).
inoline: Almq3), include beryllium over quinoline complex (Beq _2), these materials are also used as a light emitting material at the same time. Oxadiazole derivatives (PBD) are well known as excellent electron transport materials. If a material having a good electron transporting property such as PBD is used as the electron transporting layer, an element having a three-layer structure in which a light emitting layer and a carrier transporting layer are separated or a two-layer structure having a hole transporting light emitting layer can be realized. is there.

Further, as a doping material, a coumarin derivative, quinacridone, rubrene or the like can be used. As a doping method, a light emitting material such as Alq ₃ is used as a host material by co-evaporation using two heating boats, for example, near the interface with the hole transport layer (about 30 n).
m) or less, a fluorescent material can be doped by about several mol% to several tens mol%. Next, the cathode is formed by a method such as evaporation of a metal material by resistance heating or an electron beam, or sputtering using an alloy target.
It is formed with a film thickness of about 0 to 300 nm. In order to obtain a film having a sufficient reflectance and low resistance, it is preferable that the film thickness is preferably 100 nm or more. As the metal material used for the cathode, a metal having a small work function, for example, Li, N
a, Mg, Ca, Sr, Ba, Ti, Mn, Al, A
A single metal element such as g, In, Sn, Zn, Zr, or an alloy thereof is used. Alkali metals are used as an alloy with Ag, Al, or the like in order to improve adhesion to an organic film and avoid deterioration due to oxygen, moisture, or the like. Further, LiF, SiO2 or the like may be formed on the cathode as an electrode protection film in the same manner as in the case of the cathode.

FIG. 9 shows the optical constants of various metal elements, the phase change at the reflecting surface, and the reflectivity. The refractive index of the organic material in contact with the metal surface is set to n = 1.7. All of these metals have a δr in the range of π / 2 to π. When an organic EL element is formed by using these metal elements as a cathode,
FIG. 10 shows the result of calculating the optimum film thickness of the electron transport layer from the equation of FIG. 6A when the order of interference is N = 1, 2, and 3.
Shown in Optical constants of metals and other alloys other than these, or wavelength dispersion of the optical constants can be measured by an ellipsometry method or the like.

Hereinafter, modified examples 1 to 3 of the second embodiment will be described, but the modified examples of the second embodiment are not limited to only these materials and element configurations. (1) Modification 1 Aluminum (A) is used as the metal material forming the cathode.
Use l). A glass substrate with ITO having a thickness of 1.1 mm is prepared, and an electrode pattern having a width of 2 mm is formed by a photolithography method using a general resist.
Next, the substrate is washed with a surfactant, the detergent is sufficiently washed away with pure water, dried in the vapor of isopropyl alcohol, and the surface cleaning stain is sufficiently removed by oxygen plasma treatment. The substrate thus prepared was set in a vacuum deposition apparatus, and α-NPD was vacuum-deposited as a hole transporting material by resistance heating to have a film thickness of 7 mm.
A 0 nm hole transport layer is formed.

The deposition conditions are as follows: the degree of vacuum is 2.7 × 10 −4 P
a, The deposition rate is 1 nm / sec. More continuously,
Almq ₃ was similarly deposited to form an electron transporting light emitting layer.
The film thickness of Almq ₃ is set so as to substantially coincide with the optimum film thickness value of 87 nm obtained as N = 1 in equation (1). That is, the position showing the maximum emission intensity is α-N
It is near the interface between PD and Almq ₃ and the optical distance to the cathode satisfies the relational expression as shown in FIG. Next, a metal mask having a hole that is orthogonal to the ITO electrode pattern with a width of 2 mm is closely attached to the substrate and set in a vacuum evaporation apparatus.
1) is vacuum-deposited to form a 160-nm-thick metal film, which is used as a cathode to obtain a 2-mm square lighting region. LiF having a thickness of 300 nm is deposited on the Al electrode to form a protective film. Further, in an inert gas (Ar) atmosphere, Pyrex glass having a thickness of 1 mm is stacked on the element, and the periphery of the glass is sealed with an ultraviolet-curable adhesive to obtain an organic EL element.

(2) Modification 2 As a hole injection layer, m-MTDATA is formed on an ITO electrode to a thickness of 30 nm, and then as a hole transport layer.
α-NPD is formed with a thickness of 50 nm, and further modified example 1
The electron transporting light emitting layer made of Almq3
m. In other respects, the organic EL device is manufactured in the same manner as in the first modification.

(3) Modification 3 As a metal material for forming the cathode, M having a thickness of 150 nm
An organic EL element is formed using the same organic material as in Modification Example 2 except that a gAg alloy is used. The cathode is formed by co-evaporation using Mg and Ag. The optical constants of the MgAg alloy were measured by an ellipsometry method using a sample formed on a glass substrate under the same conditions as when forming the element. As a result, nr = 0.3 and kr = 5. Using this optical constant, the phase change of the reflected light on the reflecting surface obtained from the equation in FIG. 12 is δr = 2.5 (radian). From the equation shown in FIG.
The film is formed so as to have a film thickness of 91 nm.

[0048]

According to the first aspect of the present invention, the optical thickness nd of the electron transport layer of the organic multilayer film is nd = (2N-1) λ /
4, (n is the refractive index, d is the film thickness, λ is the central wavelength of light emission, N
Satisfies the following relationship: the external light extraction efficiency can be increased, and the power consumption can be effectively reduced. According to the second aspect of the invention, the optical film thickness nd of the electron transporting light emitting layer of the organic multilayer film is nd = (2N−
1) Since the relationship of λ / 4, where n is the refractive index, d is the film thickness, λ is the center wavelength of light emission, and N is a positive integer, the external light extraction efficiency can be increased and the power consumption can be increased. Can be easily reduced. In the invention according to claim 3, the optical thickness nd of the electron transporting light emitting layer of the organic multilayer film is:
nd = (2N-1) λ / 4, (n is a refractive index, d is a film thickness,
[lambda] satisfies the relationship of emission center wavelength and N is a positive integer), so that the external extraction efficiency of light can be increased and power consumption can be easily reduced. Claim 4
In the described invention, the electron-transporting light-emitting layer is doped with a small amount of fluorescent material near the interface with the hole-transporting layer, so that the luminous efficiency can be increased and the recombination region of carriers, that is, the light-emitting position is doped. And the interference effect due to the optical thickness of the electron transport layer can be further enhanced.

According to the fifth aspect of the invention, the optical film thickness nd of the electron transport layer of the organic multilayer film is nd = (2N-1) λ /
4, (n is the refractive index, d is the film thickness, λ is the central wavelength of light emission, N
Satisfies the relationship of (a positive integer), the light extraction efficiency can be increased, and power consumption can be easily reduced. According to the sixth aspect of the present invention, since the light emitting layer is doped with a trace amount of fluorescent material, the light emitting efficiency can be increased, the recombination region of carriers, that is, the light emitting position can be controlled by doping, and the optical transport layer The interference effect due to the film thickness can be further enhanced. In the invention according to claim 7, the optical film thickness nd of the electron transport layer of the organic multilayer film is nd = (2N-1) λ / 4, (n is the refractive index, d is the film thickness, and λ is the central wavelength of light emission. , N are positive integers), the external light extraction efficiency can be increased, and power consumption can be easily reduced.

According to the eighth aspect of the present invention, since the cathode is a metal film having a reflectance of 50% or more, the interference effect can be effectively taken out. According to the ninth aspect of the present invention, since the positive integer N is 1, that is, the first-order interference is used, the thickness of the organic film can be reduced, which is effective for low-voltage driving. At this time, the thickness of the electron transport layer is not so thin as to be affected by quenching due to the movement of the excitons to the cathode, and can be easily controlled by a normal vapor deposition method. In the invention according to claim 10, the optical thickness nd of the electron transporting layer or the electron transporting light emitting layer is equal to the central wavelength of light emission ± λ /.
Since it is within the error range of 8 or less, the effect of enhancing the emission intensity due to the interference effect is ensured, an intensity larger than the convergence intensity value is obtained, and by indicating a substantial allowable range of the film thickness,
The quality control of the manufacturing process and the product can be facilitated.

According to the eleventh aspect, the organic multilayer film
The optical thickness nd of the electron transport layer is nd = (λ / 4) (2N
−δr / π), δr = arctan (2nk_r/ (N^Two−
(N _r)^Two− (K_r)^Two)) + Π, (n^Two≤n_r ^Two+ K_r ^TwoIn
Where n is the refractive index, d is the film thickness, λ is the central wavelength of light emission, and N is
Satisfies the relationship of
Rate can be increased, effectively reducing power consumption.
be able to. In the invention according to claim 12, an organic multilayer film
The optical film thickness nd of the electron transporting light emitting layer of nd is nd = (λ /
4) (2N−δr / π), δr = arctan (2nk
_r/ (N^Two− (N_r)^Two− (K_r)^Two)) + Π, (n^Two≤n_r ^Two
+ K_r ^TwoWhere n is the refractive index, d is the film thickness, and λ is the center of light emission.
Wavelength and N are positive integers).
Extraction efficiency can be increased, reducing power consumption.
It can be easily realized. According to the invention of claim 13,
Is the optical thickness nd of the electron transporting light emitting layer of the organic multilayer film,
nd = (λ / 4) (2N−δr / π), δr = arct
an (2nk_r/ (N^Two− (N_r)^Two− (K_r)^Two)) + Π,
(N^Two≤n_r ^Two+ K_r ^TwoWhere n is the refractive index, d is the film thickness, λ
Is the central wavelength of light emission, and N is a positive integer.
The light extraction efficiency can be increased,
Power reduction can be easily realized. Claim 14
In the described invention, the electron-transporting light-emitting layer is
A small amount of fluorescent material is doped near the interface
Luminous efficiency can be increased, and the carrier recombination region,
In other words, the emission position can be controlled by doping, and electron transport
The interference effect due to the optical thickness of the layer can be further enhanced
You.

In the invention according to claim 15, the organic multilayer film
The optical thickness nd of the electron transport layer is nd = (λ / 4) (2N
−δr / π), δr = arctan (2nk_r/ (N^Two−
(N _r)^Two− (K_r)^Two)) + Π, (n^Two≤n_r ^Two+ K_r ^TwoIn
Where n is the refractive index, d is the film thickness, λ is the central wavelength of light emission, and N is
Satisfies the relationship of
Rate can be increased, reducing power consumption easily.
can do. According to the sixteenth aspect, the light emitting layer
Has a small amount of fluorescent material doped,
The light efficiency can be increased, and the carrier recombination region,
The light position can be controlled by doping, and the light in the electron transport layer
The interference effect due to the film thickness can be further enhanced. Contract
In the invention according to claim 17, the light in the electron transport layer of the organic multilayer film is
The theoretical film thickness nd is nd = (λ / 4) (2N−δr / π),
δr = arctan (2nk_r/ (N^Two− (N _r)^Two− (K
_r)^Two)) + Π, (n^Two≤n_r ^Two+ K_r ^TwoWhere n is refraction
Rate, d is the film thickness, λ is the central wavelength of light emission, N is a positive integer)
To improve light extraction efficiency
Power consumption can be easily reduced.
Wear.

According to the eighteenth aspect, the cathode is a metal film having a reflectance of 50% or more, so that the interference effect can be effectively taken out. According to the nineteenth aspect of the present invention, since the positive integer N is 1, that is, the thickness of the organic film can be reduced by using the first-order interference, which is effective for low-voltage driving. The thickness of the electron transport layer is not so thin as to be affected by quenching due to the movement of excitons to the cathode, and can be easily controlled by a normal vapor deposition method. In the twentieth aspect, the optical thickness nd of the electron transporting layer or the electron transporting light emitting layer is determined by the following equation: the central wavelength of light emission ± λ /
Since the error is within the error range of 8 or less, the effect of enhancing the emission intensity due to the interference effect is ensured, an intensity larger than the convergence intensity value is obtained, and the production process and the product Quality control can be facilitated.

[Brief description of the drawings]

FIG. 1 is a diagram showing light interference in an organic EL element.

FIG. 2 is a diagram showing a photoluminescence spectrum of Almq ₃ .

FIG. 3 is a diagram showing a difference in emission spectrum when the thickness of an electron transport layer is changed in the first embodiment.

FIG. 4 is a diagram showing a relationship between a film thickness of an electron transport layer and a luminance value.

FIG. 5 is a diagram showing structural formulas of an electron transporting material and a hole transporting material.

FIG. 6 is a diagram showing equations for calculating a phase change δr, an energy reflectance R, light intensity, and an emission spectrum I (λ).

FIG. 7 is a diagram showing an equation for calculating an optical distance from a light emitting position to a reflecting surface according to an intensity condition.

FIG. 8 is a diagram showing a difference in emission spectrum when the thickness of the electron transport layer is changed in the second embodiment.

FIG. 9 is a diagram showing optical constants of various metal elements, phase change on a reflection surface, and reflectance.

FIG. 10 is a diagram showing an optimum film thickness of an electron transport layer when various metals having different optical constants are used as a cathode.

FIG. 11 is a view showing a setting condition (1) of an optical film thickness of an electron transport layer of an organic EL element.

FIG. 12 is a view showing a setting condition (2) of an optical film thickness of an electron transport layer of an organic EL element.

FIG. 13 shows a two-layer organic EL having an electron transporting light emitting layer.
FIG. 2 is a schematic cross-sectional view illustrating a layer configuration of an element.

FIG. 14 shows a two-layer organic EL having a hole-transporting light-emitting layer.
FIG. 2 is a schematic cross-sectional view illustrating a layer configuration of an element.

[Explanation of symbols]

 Reference Signs List 1 glass substrate 2 anode (transparent electrode) 3a, 13a hole transport layer 3b hole transport light emitting layer 4a electron transport layer 4b, 14b electron transport light emitting layer 5, 15 cathode (metal electrode) 6 light emitting position

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yumi Matsuki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Yoshitomo Kimura 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Takashi Okada 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Takuji Kato 1-3-6 Nakamagome, Ota-ku, Tokyo Ricoh Co., Ltd. F term (reference) 3K007 AB03 CA01 CB01 CC01 DA01 DB03 EB00

Claims (20)

[Claims] An anode comprising a transparent electrode; an organic multilayer film having at least two layers of a hole transport layer and an electron transport layer on the anode; and a metal on the organic multi-layer. A cathode made of a specular reflection film, wherein the optical film thickness nd of the electron transport layer of the organic multilayer film is nd = (2N-1) λ / 4 (n is a refractive index, d is a film thickness, An organic electroluminescence device characterized by satisfying a relationship of λ is a central wavelength of light emission and N is a positive integer. 2. An anode comprising a transparent electrode; an organic multilayer film formed by stacking two layers on the anode in the order of a hole transporting layer and an electron transporting light emitting layer; And a cathode made of a specular reflection film made of metal. The optical film thickness nd of the electron transporting light emitting layer of the organic multilayer film is nd = (2N-1) λ / 4 (n is a refractive index, An organic electroluminescence device, wherein d is a film thickness, λ is a central wavelength of light emission, and N is a positive integer. 3. An anode comprising a transparent electrode; an organic multilayer film formed by stacking three layers on the anode in the order of a hole injection layer, a hole transport layer, and an electron transporting light emitting layer; A cathode made of a mirror-reflective film made of metal on the organic multilayer film, and the optical film thickness nd of the electron transporting light emitting layer of the organic multilayer film is nd = (2N-1) λ / 4 ( An organic electroluminescence device, wherein n is a refractive index, d is a film thickness, λ is a center wavelength of light emission, and N is a positive integer. 4. The organic electroluminescence according to claim 2, wherein the electron transporting light emitting layer is doped with a small amount of a fluorescent material near an interface with the hole transporting layer. element. 5. An anode comprising a transparent electrode; and an organic multilayer film formed by stacking three layers on the anode in the order of a hole transport layer, a light emitting layer having a thickness of 30 nm or less, and an electron transport layer. A cathode made of a specular reflection film made of a metal on the organic multilayer film; and an optical film thickness nd of an electron transport layer of the organic multilayer film, nd = (2N-1) λ / 4 ( An organic electroluminescence device, wherein n is a refractive index, d is a film thickness, λ is a center wavelength of light emission, and N is a positive integer. 6. The organic electroluminescence device according to claim 5, wherein the light emitting layer is doped with a trace amount of a fluorescent material. 7. An anode comprising a transparent electrode; an organic multilayer film formed by laminating two layers on the anode in the order of a hole transporting light emitting layer and an electron transport layer; And a cathode made of a specular reflection film made of metal. The optical film thickness nd of the electron transport layer of the organic multilayer film is as follows: nd = (2N-1) λ / 4 (n is a refractive index, d is An organic electroluminescence device characterized by satisfying a relationship of film thickness, λ is a central wavelength of light emission, and N is a positive integer. 8. The method according to claim 1, wherein the cathode is a metal film having a reflectance of 50% or more. Item 8. The organic electroluminescent device according to any one of Items 7 to 7. 9. The method of claim 1, wherein the positive integer N is 1. Any one of 8
3. The organic electroluminescent device according to 1.). 10. The optical film thickness nd of the electron transporting layer or the electron transporting light emitting layer may be set at a central wavelength ± λ / 8 of the light emission.
Any one of claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, claim 8, claim 9, and claim 9 within an error range of 2. The organic electroluminescent device according to item 1. 11. An anode made of a transparent electrode, an organic multilayer film formed on the anode having at least two layers of a hole transport layer and an electron transport layer, and a complex refraction on the organic multilayer film. A cathode made of a metal film having a ratio n ′ = nr−ikr, and the optical thickness nd of the electron transport layer of the organic multilayer film is as follows: nd = (λ / 4) (2N−δr / π) δr = arctan (2nk _r / (n ² − (n _r ) ² − (K
_r ) ² )) + π (n ² ≦ n _r ² + K _r ² , where n is the refractive index, d is the film thickness, λ
Is a central wavelength of light emission, and N is a positive integer). 12. An anode comprising a transparent electrode; an organic multilayer film formed by laminating two layers on the anode in the order of a hole transport layer and an electron transporting light emitting layer; And a cathode made of a metal film having a complex refractive index n ′ = nr-ikr. The optical film thickness nd of the electron transporting light emitting layer of the organic multilayer film is nd = (λ / 4) (2N −δr / π) δr = arctan (2nk _r / (n ² − (n _r ) ² − (K
_r ) ² )) + π (n ² ≦ n _r ² + K _r ² , where n is the refractive index, d is the film thickness, λ
Is a central wavelength of light emission, and N is a positive integer). 13. An anode comprising a transparent electrode, an organic multilayer film formed by stacking three layers on the anode in the order of a hole injecting layer, a hole transporting layer, and an electron transporting light emitting layer; A cathode made of a metal film having a complex refractive index n ′ = nr−ikr on an organic multilayer film, wherein the optical film thickness nd of the electron transporting light emitting layer of the organic multilayer film is nd = (λ / 4) (2N-δr / π) δr = arctan (2nk r / (n 2 - (n r) 2 - (K
_r ) ² )) + π (n ² ≦ n _r ² + K _r ² , where n is the refractive index, d is the film thickness, λ
Is a central wavelength of light emission, and N is a positive integer). 14. The organic electroluminescence according to claim 12, wherein the electron transporting light emitting layer is doped with a small amount of a fluorescent material near an interface with the hole transporting layer. element. 15. An anode comprising a transparent electrode; and an organic multilayer film formed by stacking three layers on the anode in the order of a hole transport layer, a light emitting layer having a thickness of 30 nm or less, and an electron transport layer. A cathode made of a metal film having a complex refractive index n ′ = nr−ikr on the organic multilayer film; and the optical film thickness nd of the electron transport layer of the organic multilayer film is nd = (λ / 4) (2N-δr / π) δr = arctan (2nk r / (n 2 - (n r) 2 - (K
_r ) ² )) + π (n ² ≦ n _r ² + K _r ² , where n is the refractive index, d is the film thickness, λ
Is a central wavelength of light emission, and N is a positive integer). 16. The organic electroluminescence device according to claim 15, wherein the light emitting layer is doped with a trace amount of a fluorescent material. 17. An anode comprising a transparent electrode; an organic multilayer film formed by laminating two layers on the anode in the order of a hole-transporting light-emitting layer and an electron transport layer; And a cathode made of a metal film having a complex refractive index n ′ = nr−ikr. The optical thickness nd of the electron transport layer of the organic multilayer film is as follows: nd = (λ / 4) (2N−δr / π) δr = arctan (2nk r / (n 2 - (n r) 2 - (K
_r ) ² )) + π (n ² ≦ n _r ² + K _r ² , where n is the refractive index, d is the film thickness, λ
Is a central wavelength of light emission, and N is a positive integer). 18. The cathode according to claim 11, wherein the cathode is a metal film having a reflectance of 50% or more.
The organic electroluminescent device according to any one of claims 13, 14, 15, 15, 16, and 17. 19. The method of claim 11, wherein the positive integer N is 1. 1
8. The organic electroluminescent device according to any one of 8 above. 20. The optical film thickness nd of the electron transporting layer or the electron transporting light emitting layer is a central wavelength of the light emission ± λ / 8.
12. The method according to claim 11, wherein
The organic electroluminescence device according to any one of claims 12, 13, 13, 14, 15, 16, 16, 17, 18, and 19.