JP2003115390A - Light emitting element and its usage - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a contrast characteristic while raising light emitting efficiency of a light emitting element (an organic electric field light emitting element, an inorganic electric field light emitting element) and maintaining high luminosity. SOLUTION: In the light emitting element, in which a layer containing a light emitting domain is prepared between a positive electrode 2 and a negative electrode 9 on a substrate 1, the emitted light 11 generated in the light emitting domain is taken out from the negative electrode 9 side, the work function of the positive electrode 2 is 5.0 to 7.0 eV, and the visible light reflectance of the positive electrode 2 is 50% or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-luminous light emitting device used as a display device such as a color display, and its use.

[0002]

2. Description of the Related Art In recent years, especially in multimedia-oriented products and the like, the importance of human-machine interfaces has been increasing. In order to operate the machine more comfortably and efficiently, it is necessary to simply and instantly retrieve a sufficient amount of information from the side of the machine. Therefore, various display elements including a display have been studied. .

With the miniaturization of machines, demands for miniaturization and thinning of such display elements are increasing day by day. Hereinafter, specific examples of main display elements will be described.

Liquid crystal displays are used as interfaces of various products today as one of the typical display elements, and include laptop type information processing equipment, small television receivers, watches, electronic desk calculators. And so on, it is often used in daily life products.

This liquid crystal display has been researched as a dedicated interface from small size to large capacity display device by taking advantage of the characteristics that liquid crystal is driven at low voltage and low power consumption.

However, since this liquid crystal display is of a light receiving type, a backlight is indispensable, and the driving of the backlight requires electric power larger than that of the liquid crystal. Therefore, although the storage battery and the like are built in, there is a problem in that there is a limitation in use such as a limitation in power supply and a shortened operating time.

Further, it is possible to point out a particular problem with this liquid crystal display.

First, since the liquid crystal display is a display based on the alignment state of liquid crystal molecules, even within the viewing angle, the contrast changes depending on the angle. Therefore, the viewing angle is narrow and the display is large. The problem is that it is not suitable for large-scale display and that it is not suitable for displaying moving images due to the slow alignment speed of liquid crystal molecules.

On the other hand, in terms of the driving system, the active matrix system of the liquid crystal display has a response speed sufficient for handling a moving image, while it has a TFT (thin film transistor).
Since a drive circuit is used, it is difficult to increase the screen size due to pixel defects, and it is not a good idea from the viewpoint of cost reduction.

On the other hand, the simple matrix method, which is another driving method, is low in cost contrary to the above, and it is relatively easy to increase the screen size, but it has a sufficient response speed for handling moving images. There is a problem that you can not put it out.

In contrast to such a liquid crystal element, a plasma display element, an inorganic electroluminescent element (inorganic EL element), an organic electroluminescent element (organic EL element), etc. described below are display elements belonging to a self-luminous type. .

First, the plasma display element utilizes plasma light emission in a low-pressure gas for display, and is suitable for increasing size and capacity. However, it has problems in thinning and cost, and further requires a high-voltage AC bias for driving, and is not suitable for portable devices.

Further, as the inorganic electroluminescent device, a green light emitting display and the like have been commercialized, but like the plasma display device, several hundred V has been required for AC bias driving, and therefore it has not been accepted by users.

However, as a result of subsequent technological progress, R (red) and G, which are required for color display, are nowadays used.
Although it has succeeded in emitting light of the three primary colors of (green) and B (blue), it is impossible to control the emission wavelength by molecular design and the like because an inorganic material is indispensable for the configuration, and full colorization is difficult. It is expected to be.

On the other hand, the organic electroluminescence device utilizes electroluminescence from an organic compound, and this phenomenon has already been discovered about 30 years ago. That is, 196
In the first half of the 0's, it was observed that a peculiar luminescence phenomenon (due to the induction of luminescence) occurs when carriers are injected into an anthracene single crystal that strongly emits fluorescence. Since then,
Organic electroluminescent devices have been the subject of research for a long period of time, but because of their extremely low brightness, single color, and the use of single crystals, technical emphasis is placed mainly on the injection of carriers into organic materials. He went beyond the basic research stage.

The situation changes when the mid-1980s is reached. Eastm in 1987
Tang et al. of an Kodak Company announced an epoch-making organic thin film electroluminescent device at that time. This is a laminated structure having an amorphous light emitting layer, which can be driven at a low voltage and emit light with high brightness. With the invention of this laminated structure, the research and development of the organic electroluminescence device was further accelerated, and the emission of the three primary colors of RGB, stability, brightness increase, the laminated structure, and the manufacturing method and research were actively conducted in various fields. It has come to be seen, and it has come to today.

In addition to the above, new materials for displays have been developed one after another by utilizing the molecular design, which is a characteristic of organic materials, and have excellent characteristics such as DC voltage drive, thinness, and self-luminance. The organic electroluminescent elements possessed by this technology are successively emerging, and their applied research to color displays is being actively conducted.

[0018]

The advantages, disadvantages, and development history of typical display elements have been described above. The present invention is particularly concerned with organic electroluminescent elements and inorganic electric fields among these display elements. Since the present invention relates to the improvement of light emitting elements, the problems which these light emitting elements have today and are pointed out to be particularly important from various points of view will be described below.

The contrast characteristic is one of the main performances of the display, but in the self-luminous display elements such as the organic electroluminescent element and the inorganic electroluminescent element described above, the metal back (reflection of external light by the metal cathode), etc. Due to the influence of, sufficient contrast is not obtained. In particular, the contrast of an organic electroluminescence device is at most about 200: 1, and development of a display device having a sufficient contrast exceeding this is required from various fields.

Further, the luminous efficiency of the organic electroluminescent device is still insufficient. One of the causes is that the efficiency of carrier injection from the electrode to the organic layer is small, and the energy difference between the anode and the cathode is not sufficient, so that an energy barrier exists between the organic layers.

Further, since a general organic electroluminescence device has a device structure in which EL emission light is taken out from the anode side, the anode material is made of ITO (indium-tin-doped indium-
Almost limited to tin oxide), ZnO, SnO ₂ and their related substances, the hole injection material is largely restricted in energy matching with the anode material.

On the other hand, as another element structure of the organic EL element, there is an element structure in which EL emission light is taken out from the cathode side.

In this case, the cathode is a very thin metal having a low work function [eg Mg: Ag (3.5 eV) or Al: L].
i (2.9 eV)], and in some cases IT
Transparent electrodes such as O, ZnO, and SnO ₂ are laminated. In general, a metal having a high work function can be used for the anode.
TO, ZnO, may be used transparent electrode such as SnO _2. Selection of these anode materials depends on the smoothness of the anode thin film, compatibility with the patterning process, and the like.

Further, the order of laminating on the substrate may be from the anode to the organic material and then to the cathode, or vice versa.

In the former case, the substrate may be transparent to visible light such as glass or polymer, or opaque such as Si.

Since the TFT substrate has a large number of transistors and metal wirings on the substrate, the aperture ratio is inevitably small when light is to be extracted from the glass substrate side. However, as described above, the organic material from the anode on the TFT substrate,
The effect of the aperture ratio can be minimized by stacking the cathodes in this order and extracting the EL emission light from the cathode side.

When the anode is provided on the TFT substrate, a metal having a not so high work function such as Cr (work function of 4.5 eV) is often selected as the anode because of the above-mentioned material selection problem.

In such a case, the work function difference between the anode and the cathode is, for example, 1 eV for Cr-Mg: Ag and Cr-Al:
Li becomes 1.6 eV, which is smaller than the photon energies of RGB that should emit light, and the efficiency as an element is extremely low.

Therefore, an object of the present invention is to provide a light emitting device (organic electroluminescent device, inorganic electroluminescent device, etc.) in which the luminous efficiency is improved by the anode material and at the same time the contrast is improved while maintaining high brightness. is there.

[0030]

That is, according to the present invention, in a light emitting device in which a layer including a light emitting region is provided between an anode and a cathode, emitted light is taken out from the cathode side, The work function of the anode is 5.0 to 7.0 eV, which relates to a light emitting device (hereinafter referred to as a first light emitting device of the present invention). However, the layer including the light emitting region is composed of an organic compound layer and / or an inorganic compound layer having appropriate functions, as described later (the same applies hereinafter).

According to the first light emitting device of the present invention, the anode has a high work function material, that is, a work function of 5.0 eV to.
By using a material having a specific range of 7.0 eV (preferably 5.5 eV to 6.0 eV) and selecting an appropriate material for the material layer including the light emitting region, the energy difference between the anode and the cathode becomes sufficient. Thus, an electroluminescent device having a small energy barrier can be formed. As a result, the luminous efficiency is improved, and it is possible to realize a light emitting element that can extract light with low power consumption and high brightness from the cathode side. For this purpose, the work function of the anode must be 5.0 eV or more, and the upper limit must be 7.0 eV from the selectivity of the material of the light emitting region.

In particular, in the case of an organic electroluminescent device, the work function of the anode can be specified within the range of 5.0 eV to 7.0 eV, and the hole injection layer as the anode material can achieve energy matching (that is, between the both). By optimizing energy matching), hole injection efficiency can be improved and light emission efficiency can be increased. Moreover, by doing so, the selection range of the anode material is widened, the restriction on the hole injection material is eliminated, and the restriction on the anode material is also eliminated for the hole injection material, both of which are wider than before. It is possible to use various materials.

Further, according to the present invention, in a light emitting element in which a layer including a light emitting region is provided between an anode and a cathode, emitted light is extracted from the cathode side, and visible light reflection of the anode is performed. Also provided is a light emitting element characterized by having a ratio of 50% or less (hereinafter referred to as a second light emitting element of the present invention).

According to the second light-emitting element of the present invention, the visible light reflectance of the anode is 50% or less, and therefore the influence of reflection by visible external light when the emitted light is extracted from the cathode side (by the anode It is possible to suppress the metal back) and surely improve the contrast while maintaining high brightness. For this purpose, the visible light reflectance of the anode must be 50% or less. Note that the visible light reflectance of a general metal anode material is about 70% or more, but with this, there is a large amount of reflection at the anode, and the contrast is greatly reduced.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION First and second light emitting elements of the present invention
In order to exert the effect of maintaining high brightness and improving the contrast in the light emitting device, the work function of the anode is specified in the range of 5.0 eV to 7.0 eV, and the visible light range (usually, the wavelength is It is important to keep the reflectivity of the anode below 50% over the entire wavelength range (380 to 780 nm).

For this purpose, as the constituent material of the anode, there are IIIA group, IVA group, VA group, VIA group, VII of the periodic table.
It is preferable to use one or more metals, alloys or compounds thereof selected from Group A, Group VIII and Group IB.

Specific examples of the above metals include Ni, Ru,
Ir, Rh, Pt, Pd, Re, Ti, Zr, Nb, M
There are o and W.

The above compounds include intermetallic compounds.
Preferred are oxides, oxides, nitrides or oxynitrides. these
To give a specific example, LiNiO₂, PtRhO_x, TiN
bO_x, WReO_x, NiO, RuO_x, IrO_x, PtO
_x, RhO_x, PdO_x, ReO _x, WO_x, NiNO, L
iNiNO, RuNO, IrNO, PtNO, RhN
O, ReNO, WNO, TiNO, TiN and ZrN
and so on.

In addition, a dopant may be added to the anode material in order to improve the physicochemical properties of the anode. The main examples of the anode material added with the dopant are R
_X NiO (R = H, Li, Na, K, Rb, Cs, C
u, Ag, Au), R _x WO ₃ (R = H, Li, Na,
K, Rb, Cs, Cu, Ag, Au), TiNb _x O _y and the like.

However, the composition of the above anode material does not necessarily have to be a stoichiometric composition, and may be a nonstoichiometric ratio.

Further, the crystal phase of the anode material may be either a single phase or a plurality of phases.

Of course, the morphology of the anode layer (Morp
The hology: form) is not particularly limited. A film having a high smoothness and uniformity, such as an amorphous film, a microcrystal film, an epitaxial film, a single crystal film, or a film similar to these is desirable.

In order to increase the hole injection efficiency,
The anode material preferably has p-type electrical conductivity.

The anode may be a single layer or a plurality of layers. In particular, in the case of forming a laminated structure with a transparent electrode such as ITO, by optimizing the composition and layer thickness, the visible light reflectance, the work function, and the electrical resistivity are impaired in other characteristics. Can be controlled as desired.

Preferred examples of the anode structure relating to the above-mentioned phases and layers include a structure in which the phase containing the metal or metal compound described above and the phase containing zinc, indium or tin are monolayered or laminated. .

Alternatively, the structure in which the phase containing the metal or the metal compound described above and the phase containing Cr, Au, W, etc. are formed into a single layer or laminated layers makes the anode opaque, has a low resistance, and has a smooth surface. It is preferable in terms of conversion.

When these conditions are satisfied, the difference in work function between the anode and the cathode can be increased, and the energy level of the light emitting device constituent material such as an organic material between the electrodes can be optimized to improve the luminous efficiency. Can be increased. Further, by increasing the work function between the anode and the cathode, it is possible to eliminate the constraint of constraining the constituent material of the light emitting device such as an organic material, and it is possible to use a wider range of material systems.

In order to manufacture the anode of the light emitting device of the present invention, a film forming method known in this field, such as sputtering, electron beam evaporation, ion plating,
A method such as laser ablation may be used.

Next, a preferable example of the actual structure of the light emitting device of the present invention will be specifically described with reference to the drawings.

First, a preferred practical basic structure of the light emitting device of the present invention is that a positive electrode and a light emitting region are provided on a TFT (thin film transistor) substrate or a transparent or semitransparent (or opaque) substrate such as glass. The organic or inorganic layer including the cathode and the cathode are sequentially laminated. "Opaque" here
Is a transmittance of several% or less, and "translucent" is a few% or more.
It means 80% (hereinafter the same).

Further, the organic layer may be modified in various layers according to the purpose. For example, a hole transport layer may be provided on the anode side and an electron transport layer may be provided on the cathode side.
Can be provided.

A hole injection layer may be provided between the anode and the hole transport layer.

An electron injection layer may be provided between the cathode and the electron transport layer.

Furthermore, a light emitting layer can be provided between the hole transport layer and the electron transport layer.

FIG. 1 shows an example 10 of the light emitting device of the present invention. This is called an organic electroluminescence device (organic EL device), and here, a device in which the layer structure described above is slightly modified is shown. That is, in the light emitting element of FIG. 1A, the anode 2, the hole injection layer 3, the hole transport layer 4, the light emitting layer 5, the electron transport layer 6, the electron injection layer 7, the TFT substrate (or the glass substrate) 1, The buffer layer 8 and the cathode 9 are sequentially laminated by vacuum deposition or the like (however, the hole injection layer, the electron injection layer, and the buffer layer may not necessarily be provided, and the electron transport layer or the hole transport layer is the light emitting layer. May also serve as). The emitted light 11 is extracted from the cathode 9 side.

On the other hand, the light emitting element 12 shown in FIG. 1 (B) has a structure in which each layer is just reverse to that of the light emitting element shown in FIG. 1 (A).

The light emitting device shown in FIG. 2 is a so-called inorganic electroluminescent device, in which an anode 2, a light emitting layer 5 and a cathode 9 are sequentially laminated on a transparent substrate 1. .

As the materials for the hole injecting layer, hole transporting layer, light emitting layer, electron transporting layer, electron injecting layer, buffer layer and cathode described above, materials known in this kind of field can be used without any particular limitation.

For example, as the constituent material of the hole transport layer,
A benzidine derivative, a styrylamine derivative, a triphenylmethane derivative, a triphenyl (or aryl) amine derivative, a hydrazone derivative and the like are used. Among them, α-NPD (α-naphtyl phenyl diami) shown in FIG.
ne) is a commonly used hole transport material.

Further, a beryllene derivative, a bisstyryl derivative, a pyrazine derivative or the like is used as a constituent material of the electron transport layer. For example, Alq ₃ (8-hydro shown in FIG.
xyquinoline aluminum) is a preferred electron transport material.

The constituent material of the hole injection layer is, for example, m-MTDATA (4,4 ', 4 "-tris (3-me shown in FIG.
thylphenylphenylamino) triphenylamine) is a preferred hole injection material.

As a constituent material of the electron injection layer, an oxydiazole derivative, a triazole derivative or the like is used.

As the constituent material of the light emitting layer, the above-mentioned Alq is used.
₃ etc. are used. In order to control the emission spectrum of this light emitting layer, co-evaporation with another organic material may be performed,
Examples include perylene derivatives, coumarin derivatives, and benzidine derivatives. Of course, it may be an organic film containing a material such as a pyran derivative.

As the cathode material, it is preferable to use a metal having a small work function from the vacuum level of the material in order to efficiently inject electrons into the other layer. For example, In, Mg,
It is preferable to use Ca, Sr, Ba, Li or the like as an alloy with another metal to improve stability.

For the buffer layer, in order to efficiently inject electrons into another layer, for example, an alkali metal oxide such as Li ₂ O, LiF, SrO or CaF ₂ or an alkali metal fluoride is provided between the cathode and the electron injection layer. It is advisable to interpose a halide, an alkaline earth metal oxide, or an alkaline earth metal fluoride.

When driving the light emitting device of the present invention, in order to eliminate the influence of oxygen and the like in the atmosphere and enhance the stability, for example, germanium oxide or Si is previously prepared.
It is desirable to seal with Nx or the like, or to keep the surrounding space in a vacuum.

The light emitting device of the present invention is used for a display or a display device, a computer, a television receiver, a billboard, a studio screen, a facsimile, a mobile phone,
It is suitable for use in mobile terminals, luminescent nameplates, vehicles, audio equipment or vehicle-mounted audio equipment.

For example, FIG. 6 shows a display comprising an organic EL element of active matrix drive incorporating a TFT, and the above-mentioned amorphous organic compound layers 3,
Organic EL layer consisting of 4, 5, 6, 7 (this is ZnS: M
It may be replaced with an inorganic EL layer using n. ) 13 is provided on the substrate 1, the above-mentioned anode 2 is formed below the substrate 1, and the cathode 9 is formed above the buffer layer via the buffer layer. By applying a voltage between these electrodes, the emitted light 11 of a predetermined color is filtered ( It is obtained from the cathode 9 side through (not shown).

In order to apply a data voltage to the anode 2 by active matrix driving, for example, it is partitioned into a gate electrode 14, a gate insulating film 15, and a source region S, a drain region D, and a channel region Ch formed on the substrate 1. Bottom-gate MOSTF composed of semiconductor thin film 16
T (Metal Oxide Semiconductor Thin Film Transisto
r) The TFT 1 is built on the substrate 1. In the figure, 17 is an interlayer insulating film, 18 is a source electrode, 19 is a drain electrode, and 20 is an interlayer insulating film. Although such a bottom-gate type is known, a known top-gate type or dual-gate type MOSTFT may be used instead.

FIG. 7 is an equivalent circuit of the pixel portion PXL having the organic EL element 10, and the organic EL element 1 shown in FIG.
X to the gate of the transistor TFT1 which drives 0
A gate connected to the scanning line and a source connected to the Y data line
The drain of the FT transfer gate TFT2 is connected, and the stop control transistor TFT3 is connected between this drain and the Z stop control line (note that Cs is an auxiliary capacitance for compensating for the voltage drop due to the leak current).

Here, since the TFT substrate 1 has many transistors and metal wirings on the substrate, the glass substrate 1
If you try to extract light from the side, the aperture ratio will decrease. However, as described above, since the organic material 13 and the cathode 9 are laminated in this order on the TFT substrate 1 and the EL light emission 11 is extracted from the cathode 9 side, the influence of the aperture ratio is minimized and the efficiency is improved. The emitted light 11 can be extracted.

Also in this case, from the above-mentioned reason, in order to exert the effect of maintaining the high brightness and improving the contrast,
The work function of the anode 2 is specified in the range of 5.0 eV to 7.0 eV, and the visible light range (usually, the wavelength is 380 to 78).
0 nm), the anode 2 has a reflectance of 50
It is important to keep the percentage below.

[0073]

EXAMPLES The present invention will be described in more detail based on the following examples.

Example 1 Cr (thickness: about 200 nm) was deposited as an anode layer on a 30 mm × 30 mm transparent glass substrate by DC sputtering, and LiNiO ₂ (thickness: about 100 nm) was deposited by RF sputtering. The visible light reflectance of this anode is 52
18% at 0 nm (see FIG. 8), work function 5.80 eV
Met.

On this substrate, SiO₂2 mm by vapor deposition
An organic electroluminescence device in which a region other than a 2 mm emission region is masked
A cell for production was produced. Next, the hole transport layer
As α-NPD (α-naphtyl phenyl diamine)
Vapor deposition of 50 nm under vacuum (vacuum deposition rate 0.2
nm / s), followed by Alq as an electron-transporting light-emitting layer. ₃
(8-hydroxy quinoline aluminum) deposited to 50 nm
Then, Mg: Ag is vapor-deposited as a cathode by about 15 nm,
An organic electroluminescent device was produced.

The characteristics of the organic electroluminescent device thus produced were measured by taking out emitted light from the cathode side.
The maximum emission wavelength was 520 nm, the coordinates on the CIE chromaticity coordinate were (0.32, 0.55), and good green emission was exhibited. Moreover, the current density when the driving voltage is 6 V is 39.6 mA.
/ Cm ² , and the brightness was 1200 cd / m ² (see FIG. 9). Also, the non-luminous brightness at 300 l _X irradiation is 2.92c.
d / m ² and the contrast was 410: 1.

Example 2 Cr (thickness: about 200 nm) and W (thickness: about 100 nm) were used as an anode layer on a transparent glass substrate of 30 mm × 30 mm.
Were laminated by DC sputtering. This anode has a visible light reflectance of 70% at 520 nm and a work function of 5.2 eV.
Met.

[0078] 2mm on the substrate, the SiO ₂ deposition
A cell for producing an organic electroluminescence device was produced by masking a portion other than the emission region of × 2 mm. Next, as a hole transport layer, α-
Vapor deposition of NPD (α-naphtyl phenyl diamine) in vacuum by vacuum deposition method to 50 nm (deposition rate 0.2 nm / s)
As an electron-transporting light-emitting layer, Alq ₃ (8-hydroxy quino
line aluminum) is deposited to a thickness of 50 nm, and M is used as a cathode.
g: Ag was vapor-deposited with a thickness of about 15 nm to prepare an organic electroluminescence device.

The characteristics of the organic electroluminescent device thus produced were measured by taking out the emitted light from the cathode side. The maximum emission wavelength was 520 nm, and the coordinates on the CIE chromaticity coordinate were (0.32, 0.55). And exhibited good green emission. The current density at a driving voltage of 6 V is 39.6 mA /
cm ² , and the brightness was 750 cd / m ² . Also, 300
The non-luminous luminance at the time of 1x irradiation was 4.2 cd / m ² , and the contrast was 180: 1.

Example 3 An organic electroluminescence device was prepared in the same manner as in Example 1, except that an opaque silicon substrate was used instead of the glass substrate. This light emitting device also showed the same maximum emission wavelength, emission color, current and luminance characteristics, and contrast as those of the device of Example 1.

Example 4 Cr was used as an anode on a glass substrate of 30 mm × 30 mm.
(Film thickness of about 200 nm) by DC sputtering
iNiO ₂ (film thickness of about 10 nm) was laminated by RF sputtering. The reflectance of this anode is 1 at a wavelength of 520 nm.
The work function was 8% and the work function was 5.80 eV.

On this laminated body, SiO₂2m by vapor deposition
For making light emitting device with masking other than the light emitting area of mx 2 mm
The cell of was produced. On top of this, the luminescent center phosphor is Ca
Ga ₂S_Four: Inorganic EL composed of Ce and Mg: Ag cathode
Inorganic electroluminescent device is prepared by vapor deposition (thickness: about 15 nm).
did.

The inorganic electroluminescent device thus prepared was
When driven at V and 60 Hz, the maximum brightness is 15 cd /
It was m ² . Non-luminous brightness at 300l _X irradiation is 2.55
The contrast was 6: 1 at cd / m ² .

Comparative Example 1 Cr (thickness: about 200 nm) was deposited as an anode layer on a 30 mm × 30 mm transparent glass substrate by DC sputtering. The visible light reflectance of this anode is 6 at 520 nm.
8% (see FIG. 8) and the work function was 4.60 eV.

On this substrate, SiO₂2 mm by vapor deposition
An organic electroluminescence device in which a region other than a 2 mm emission region is masked
A cell for production was produced. Next, the hole transport layer
As α-NPD (α-naphtyl phenyl diamine)
Vapor deposition of 50 nm under vacuum (vacuum deposition rate 0.2
nm / s), followed by Alq as an electron-transporting light-emitting layer. ₃
(8-hydroxy quinoline aluminum) deposited to 50 nm
As a buffer layer₂O is vapor-deposited to 0.5 nm and
Al as a cathode is vapor-deposited with about 200 nm to generate an organic electric field.
An optical device was produced.

The characteristics of the organic electroluminescent device thus produced were measured by extracting emitted light from the cathode side.
The maximum emission wavelength was 520 nm, the coordinates on the CIE chromaticity coordinate were (0.32, 0.55), and good green emission was exhibited. Moreover, the current density when the driving voltage is 6 V is 21.9 mA.
/ Cm ² , and the brightness was 556 cd / m ² (see FIG. 9). In addition, the non-luminous brightness at 300 l _X irradiation is 3.92c.
d / m ² and the contrast was 140: 1.

Comparative Example 2 C was used as an anode layer on a 30 mm × 30 mm glass substrate.
r (film thickness of about 200 nm) was laminated by DC sputtering. The reflectance of this anode was 68% at 520 nm, and the work function was 4.60 eV.

[0088] 2mm on the substrate, the SiO ₂ deposition
A cell for producing a light emitting element was produced by masking the area other than the light emitting area of × 2 mm. On top of this, the luminescent center phosphor is CaG.
An inorganic EL device made of a ₂ S ₄ : Ce and a Mg: Ag cathode (film thickness of about 15 nm) were vapor-deposited to prepare an inorganic electroluminescent device.

The inorganic electroluminescent device thus prepared was
When driven at V and 60 Hz, the maximum brightness is 8 cd / m
^{Was 2} . Non-luminous brightness at 300 lx irradiation is 3.9c
The contrast was 2: 1 at d / m ² .

As described above, according to the light emitting devices (Examples 1 to 4) according to the present invention, the work function is 5.0 eV.
Or more and 7.0 eV or less (preferably 5.5 eV or more,
It is possible to construct an organic or inorganic electroluminescent device having a small energy barrier by using an anode having a visible light reflectance of 50% or less and selecting an appropriate material for the organic material layer. The luminous efficiency can be improved and the contrast characteristics can be improved.

[0091]

As described above, the present invention uses an anode having a work function of 5.0 eV or more and 7.0 eV or less and a visible light reflectance of 50% or less.
By selecting an appropriate material for the organic or inorganic material layer, an electroluminescence device with a small energy barrier can be constructed,
Luminous efficiency can be improved and contrast characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of an organic electroluminescent device according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing the configuration of an inorganic electroluminescent device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a structural formula of α-NPD used in a hole transport layer of an organic electroluminescent device.

FIG. 4 is an Alq used in an electron transport layer of a light emitting device.
FIG. ₃ is a diagram showing a structural formula of ₃ .

[FIG. 5] Similarly, m-MTDAT used for the hole injection layer.
It is a figure which shows the structural formula of A.

FIG. 6 is a cross-sectional view of a main part of a display including a TFT driven organic EL element according to the present invention.

FIG. 7 is an equivalent circuit diagram of the pixel portion of the display.

FIG. 8 is a graph showing the wavelength dependence of the light reflectance of the anode of the light emitting device.

FIG. 9 is a graph showing voltage dependence of luminance of a light emitting element.

[Explanation of symbols]

1 ... Substrate, 2 ... Anode, 3 ... Hole injection layer, 4 ... Hole transport layer, 5 ... Light emitting layer, 6 ... Electron transport layer, 7 ... Electron injection layer,
8 ... Buffer layer, 9 ... Cathode, 10 ... Organic EL element, 11
… Emitting light, 12… Inorganic EL element

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinichiro Tamura             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation F term (reference) 3K007 AB02 AB03 CB00 DB03

Claims (44)

[Claims] 1. In a light emitting device in which a layer including a light emitting region is provided between an anode and a cathode, emitted light is extracted from the side of the cathode, and the work function of the anode is 5.
A light-emitting device having a voltage of 0 to 7.0 eV. 2. The anode is a group IIIA or IVA of the periodic table.
The light emitting device according to claim 1, which contains one or more metals, alloys, or compounds thereof selected from Group, VA, VIA, VIIA, VIII, and IB groups. 3. The light emitting device according to claim 2, wherein the compound is an intermetallic compound, an oxide, a nitride or an oxynitride. 4. The light emitting device according to claim 2, wherein the metal, alloy, or compound thereof is formed into a single layer or laminated to form the anode. 5. The phase according to claim 2, wherein the phase containing the metal, alloy, or a compound thereof and the phase containing zinc, indium, or tin are formed into a single layer or laminated to form the anode. The light emitting device described. 6. The light emitting device according to claim 1, wherein the visible light reflectance of the anode is 50% or less. 7. The light emitting device according to claim 1, wherein the anode, an organic or inorganic layer including the light emitting region, and the cathode are laminated on a thin film transistor substrate. 8. The light emitting device according to claim 7, wherein the organic layer has a hole transport layer on the anode side and an electron transport layer on the cathode side. 9. The light emitting device according to claim 7, wherein the organic layer has a hole injection layer between the anode and the hole transport layer. 10. The light emitting device according to claim 7, wherein the organic layer has a light emitting layer between the hole transport layer and the electron transport layer. 11. The light emitting device according to claim 7, wherein the organic layer has an electron injection layer between the cathode and the electron transport layer. 12. The light emitting device according to claim 1, wherein the anode, the organic or inorganic layer including the light emitting region, and the cathode are laminated on an opaque or semitransparent substrate. 13. The organic layer has a hole transport layer on the anode side and an electron transport layer on the cathode side, respectively.
2. The light emitting device according to 2. 14. The light emitting device according to claim 12, wherein the organic layer has a hole injection layer between the anode and the hole transport layer. 15. The light emitting device according to claim 12, wherein the organic layer has a light emitting layer between the hole transport layer and the electron transport layer. 16. The light emitting device according to claim 12, wherein the organic layer has an electron injection layer between the cathode and the electron transport layer. 17. The light emitting device according to claim 1, wherein the anode, the organic or inorganic layer including the light emitting region, and the cathode are laminated on a transparent substrate. 18. The organic layer has a hole transport layer on the anode side and an electron transport layer on the cathode side, respectively.
7. The light emitting device according to 7. 19. The light emitting device according to claim 17, wherein the organic layer has a hole injection layer between the anode and the hole transport layer. 20. The light emitting device according to claim 17, wherein the organic layer has a light emitting layer between the hole transport layer and the electron transport layer. 21. The light emitting device according to claim 17, wherein the organic layer has an electron injection layer between the cathode and the electron transport layer. 22. A display or a display device using the light emitting device according to claim 1, a computer, a television receiver, a billboard, a studio screen, a facsimile, a mobile phone, a mobile terminal. ,
Luminescent nameplates, vehicles, audio equipment or vehicle audio equipment. 23. In a light emitting device having a layer including a light emitting region provided between an anode and a cathode, emitted light is extracted from the side of the cathode, and the visible light reflectance of the anode is 50%. A light emitting device characterized by the following: 24. The visible light is 380 nm to 780 n
24. The light emitting device according to claim 23, having a wavelength of m. 25. The anode is a group IIIA or IVA of the periodic table.
24. The light emitting device according to claim 23, which contains one or more metals, alloys, or compounds thereof selected from Group, VA, VIA, VIIA, VIII and IB. 26. The compound is an intermetallic compound, an oxide,
The light emitting device according to claim 25, which is a nitride or an oxynitride. 27. The light emitting device according to claim 25, wherein the metal, alloy, or compound thereof is formed into a single layer or laminated to form the anode. 28. The anode according to claim 25, wherein the phase containing the metal, alloy, or compound thereof and the phase containing zinc, indium, or tin are monolayered or laminated to form the anode. The light emitting device described. 29. The light emitting device according to claim 23, wherein the anode, the organic or inorganic layer including the light emitting region, and the cathode are stacked on a thin film transistor substrate. 30. The organic layer has a hole transport layer on the anode side and an electron transport layer on the cathode side, respectively.
9. The light emitting device according to item 9. 31. The light emitting device according to claim 29, wherein the organic layer has a hole injection layer between the anode and the hole transport layer. 32. The light emitting device according to claim 29, wherein the organic layer has a light emitting layer between the hole transport layer and the electron transport layer. 33. The light emitting device according to claim 29, wherein the organic layer has an electron injection layer between the cathode and the electron transport layer. 34. The light emitting device according to claim 23, wherein the anode, the organic or inorganic layer including the light emitting region, and the cathode are laminated on an opaque or semitransparent substrate. 35. The organic layer has a hole transport layer on the anode side and an electron transport layer on the cathode side, respectively.
4. The light emitting device according to item 4. 36. The light emitting device according to claim 34, wherein the organic layer has a hole injection layer between the anode and the hole transport layer. 37. The light emitting device according to claim 34, wherein the organic layer has a light emitting layer between the hole transport layer and the electron transport layer. 38. The light emitting device according to claim 34, wherein the organic layer has an electron injection layer between the cathode and the electron transport layer. 39. The light emitting device according to claim 23, wherein the anode, the organic or inorganic layer including the light emitting region, and the cathode are laminated on a transparent substrate. 40. The organic layer has a hole transport layer on the anode side and an electron transport layer on the cathode side, respectively.
9. The light emitting device according to item 9. 41. The light emitting device according to claim 39, wherein the organic layer has a hole injection layer between the anode and the hole transport layer. 42. The light emitting device according to claim 39, wherein the organic layer has a light emitting layer between the hole transport layer and the electron transport layer. 43. The light emitting device according to claim 39, wherein the organic layer has an electron injection layer between the cathode and the electron transport layer. 44. A display or display device using the light-emitting element according to claim 23,
Computers, televisions, billboards, studio screens, facsimiles, mobile phones, mobile terminals, luminescent nameplates, vehicles, audio equipment or vehicle audio equipment.