JPH10144468A - Organic electroluminescence element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To radiate a heat of an organic EL element and provide sufficient humidity resistance by sequentially laminating at least an anode, a light emitting layer, and a cathode on a substrate having light transmitting property and employing quartz, crystal, or sapphire having thermal conductivity higher than ordinary soda glass for the substrate. SOLUTION: A substrate 61 is made of a material having thermal conductivity higher than an ordinary soda glass, and on the substrate 61, there are laminated in order an anode 2 made of a transparent conductive film, a positive hole transport layer 4 made of an organic compound, a light emitting layer 3, an electron transport layer 5, an electron injecting layer 10, and a cathode 1. Further, each layer can be interrupted from the outside atmosphere by the substrate 61 and a glass container 7a. Instead of the glass container 7a, sealing is made possible by a coating film 7b. The coating film 7b is formed by glass paste coating, moisture absorption of an element is prevented, however, thermal dispersion is degraded. Therefore, a quartz glass, a crystal or the like having thermal conductivity is employed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a material for a substrate of an organic electroluminescence device.

[0002]

2. Description of the Related Art Conventionally, there has been known an organic electroluminescent device (hereinafter, referred to as an organic EL device) which causes a phosphor formed on a glass plate or a transparent organic film to emit light by passing an electric current. As an organic EL device, as shown in FIG. 3A, a hole transport layer 4 made of an organic compound and a light emitting layer made of an organic compound are provided between a cathode 1 as a metal electrode and an anode 2 as a transparent electrode. 3. A structure in which an electron transport layer 5, an electron injection layer 10, and a cathode 1 made of an organic compound are sequentially stacked, or a two-layer structure in which a light emitting layer 3 made of an organic compound and a hole transport layer 4 made of an organic compound are arranged. Or a three-layer structure in which an electron transport layer 5 made of an organic compound, a light emitting layer 3 made of an organic compound, and a hole transport layer 4 made of an organic compound are stacked between the cathode 1 and the anode 2. Things are known. There is also known a device in which a hole injection layer is provided between the anode 2 and the hole transport layer 4 to improve luminous efficiency.

[0003] The hole transport layer 4 has a function of transporting holes from the anode 2 and a function of blocking electrons.
Has a function of transporting electrons from the cathode. In these organic EL devices, a glass substrate 6 is provided outside the anode 2 so that electrons injected from the metal cathode 1 and the anode 2
The exciton is generated by recombination with the hole injected into the light emitting layer 3 from the, and the exciton emits light in the process of radiation deactivation,
This light is emitted outside through the anode 2 and the glass substrate 6.

The anode 2 is provided with indium tin oxide (hereinafter referred to as "indium tin oxide").
A transparent conductive material having a large work function and emitting light to the outside, such as ITO, tin oxide, or the like, is used. The work function is the minimum energy required to extract one electron from the crystal surface of a metal or semiconductor to just outside the surface. The cathode 1 is made of a single metal of aluminum (Al), magnesium (Mg), indium (In), silver (Ag) or an alloy thereof such as Al-Mg or Ag-Mg and having a small work function. Is used.

Here, the important functions of the cathode are as follows: first, the role of efficiently injecting electrons into the light emitting layer 3; and, second, the line of the cathode 1 has a current flow in order to form an organic EL element having a matrix structure. Role as a bus line passing through. In order to fulfill these two functions, the properties required of the cathode material include the ability to form a conductor thin film having a small work function and a small resistance. For the glass substrate 6, a material having light transmittance is used to form a light emitting display surface, and soda glass, which is inexpensive, is used.

[0006] The above-mentioned cathode material is liable to be oxidized by moisture and deteriorated in light emission characteristics. Therefore, FIG.
As shown in (b) and (c), each of the functional layers is hermetically sealed with a glass container 7a, or a coating film 7b coated with a glass paste is provided, so that each of the functional layers is shut off from the surrounding air. Measures have been taken to prevent moisture absorption.

For the light emitting layer 3, for example, an aluminum complex of 8-hydroxyquinoline is used, and for the hole transporting layer 4, for example, N'-diphenyl-N, N'-bis (3-methylphenyl)- 1,1'-biphenyl-4,
4'-Diamine (TPD) is preferably used.
For the electron transport layer 5, for example, an aluminum complex of 8-hydroxyquinoline or the like is used.

[0008]

As described above, the organic E
The characteristic deterioration of the cathode layer of the L element due to moisture is remarkable,
When exposed to moisture in the air, there is a problem that a chemical change occurs, separation occurs between the organic material layer and the cathode, and a portion that does not emit light is generated. As a method of solving this moisture problem, FIG.
Sealing by a glass container 7a shown in FIG. 3B and sealing by a coating film 7b shown in FIG. 3C are known. According to this configuration, since each layer is shielded from the surroundings, it is possible to prevent an adverse effect of atmospheric moisture. On the other hand, there is also known a problem that heat is generated when the element is driven to cause oxidation or crystallization of the compound, thereby shortening the emission life. The above-described sealing structure has a structure in which the light emitting layer is shielded from the outside air, so that the heat generated from the light emitting layer is hardly released instead of preventing intrusion of moisture. In addition, as the thickness of the glass container or the coating film increases as the thickness of the glass container or the coating film increases, the heat generated from the light-emitting layer becomes more difficult to escape. Therefore, it is extremely difficult to solve the two problems at the same time. . The present invention has been made in view of the above problems, and an object of the present invention is to provide an organic EL element capable of dissipating heat generated in a light emitting layer of an organic EL element through a transparent substrate and sufficiently performing a measure against moisture. Aim.

[0009]

In order to solve the above-mentioned problems, an organic EL device according to a first aspect of the present invention comprises at least an anode, a light-emitting layer, and a cathode on a light-transmitting substrate. The substrate has a thermal conductivity of 0.75 W /
(M · deg).
Further, an organic EL device according to a second aspect of the present invention is the organic EL device according to the first aspect, wherein the substrate is made of quartz. The organic EL device according to claim 1, wherein the substrate is made of sapphire.

[0010]

According to the present invention, the organic EL device is constructed as described above.
The heat generated from the element can be radiated into the surrounding air through the transparent substrate, and sufficient measures against moisture can be taken.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is described below with reference to FIGS.
This will be described with reference to FIG. In the figure, components common to the prior art are denoted by the same reference numerals, and description thereof will be omitted. FIG. 1A shows that the heat generated by the organic EL element is efficiently dissipated to eliminate the deterioration of the organic EL element, and that each layer of the organic compound which is easily affected by the external atmosphere is shielded from the external atmosphere by a glass container. 1 shows an embodiment of a protected organic EL element whose performance is stabilized.
In FIG. 1A, a substrate 61 is made of a material having a higher thermal conductivity than ordinary soda glass such as sapphire or quartz, that is, quartz glass (also referred to as silica glass) or quartz, which has light transmittance. I have. An anode 2 made of a transparent conductive film, a hole transport layer 4 made of an organic compound, a light emitting layer 3 made of an organic compound, an electron transport layer 5 made of an organic compound, an electron injection layer 10 and a cathode 1 are formed on a substrate 61. It has a structure laminated in order. Further, each layer is shielded from the external atmosphere by the substrate 61 and the glass container 7a.

The electron injection layer 10 is made of, for example, the Al
_{q 3, Bu-PBD [2-} (4'-tert-Butylphenyl)
−5- (biphenyl) -1,3,4-oxadiazole) and the like are used.

As described above, as a material constituting the electron injection layer 10, various proposals have already been made, but as a novel material which has not been proposed in the past, an alkaline earth metal compound which is not an oxide (for example, CaMoO ₄ , BaTi
O ₃ , SrCl ₂ , SrB ₆ , BaAl ₂ O ₄ , BaW
O ₄ , SrMoO ₄ , SrWO ₄ ) or rare earth compounds (for example, CeO ₂ , CeCl ₃ , EuCl ₃ , SmF)
₃ ) or an alkali metal compound can be used. Since the thin film layer is transparent and has a very small work function, the thin film layer functions as an insulator but can emit light with high luminance by optimizing its thickness. That is, the first and second cathode layers described above are used.
Since the electron injection layer performing only the first function is provided separately from the cathode layer, the degree of freedom of the stacking order of each functional layer is increased, and the range of selection of the material for forming the electrode layer is expanded. .

That is, the cathode layer has a function of efficiently injecting electrons from the cathode layer to the light-emitting layer and a role as a bus line for passing a current for forming an organic EL element having a matrix structure. The role of electron injection that separates the function and performs only the former function can be provided separately from the cathode layer, expanding the range of choices for the material for forming the electrode layer, and enabling continuous light emission with high luminance at low applied voltage Will be able to

The electron injection layer 10 is omitted and the substrate 6
1, the anode 2, the hole transport layer 4, the light emitting layer 3, the electron transport layer 5, and the cathode 1 do not have the above advantages, but function as an organic EL device.

The light emitting layer 3 is made of, for example, an aluminum complex of 8-hydroxyquinoline, which has an electron transporting ability and a light emitting ability. Further, in the light emitting layer 3, for the carrier hole transport layer 4, for example, TPD is preferably used.

Further, the light emitting layer 3 is composed of an organic host substance having a carrier transporting property and an organic guest substance capable of emitting light in response to energy transfer from the host substance or carrier recombination. A guest-host type light-emitting layer may be used. For example, a light-emitting layer in which a guest substance such as Alq ₃ or a coumarin derivative is added with a guest substance such as a dicyanomethylenepyran derivative or a quinacudrine derivative is used.

Next, for the hole transport layer 4, for example, TPD is preferably used, and in addition, CTM (Carrier Transporting) is used.
Materials) can be used alone or as a mixture.

FIG. 1B shows the glass container 7 shown in FIG.
An organic EL element sealed with a coating film 7b instead of a is shown. The coating film 7b is formed by coating with a glass paste, and prevents moisture absorption of the organic EL element, but reduces heat dissipation of heat generated by the organic EL element. Therefore, the substrate 61 is made of quartz having a higher thermal conductivity than ordinary soda glass, that is, quartz glass, quartz, or sapphire, and heat is radiated from the light emitting display surface of the substrate 61 to the outside atmosphere through the substrate 61. Thus, it is possible to take a heat radiation measure after taking a sufficient moisture resistance measure. Sapphire has the ideal chemical composition A
A single crystal of l ₂ O ₃ (aluminum oxide) which is blue. Quartz has an ideal chemical composition of SiO ₂ and is a representative of silica minerals. Often used for ceramics and glass industry materials, quartz is particularly versatile. Quartz glass has a network structure of silica (SiO ₂ ). Soda-lime glass, also called soda glass, is the most commonly used glass and has a composition centered on Na ₂ O.CaO.5SiO ₂ .

Generally, the thermal conductivity of soda glass is 0.7
It is about 5 W / (m · deg). On the other hand, the thermal conductivity of quartz glass is 1.25 to 1.45 W / (m
By using quartz such as quartz glass for the substrate 61 as high as about deg), heat dissipation can be improved. In addition, since the light transmission wavelength region (light transmittance of 80% or more) of quartz glass is 0.2 to 9.2 (μm), it can be sufficiently used as a light-emitting and transmitting surface to the outside. Also, when sapphire in alumina is used, the cost is high, but the thermal conductivity is higher, and the heat dissipation can be further improved. The thermal conductivity of sapphire is 42 W / (m · d
eg), which is extremely high, and the light transmission wavelength range is 0.22.
４4.7 (μm). By using a material having optical transparency and high thermal conductivity as the material of the substrate in this way, the transparent substrate can be used as a heat sink, and the heat can be radiated after taking moisture resistance measures. .
The substrate material is not limited to the above-mentioned quartz and sapphire. If a material having a desired light transmittance and a heat conductivity higher than that of the conventional soda glass is used, moisture and heat radiation measures can be reduced as compared with the conventional technology. Can provide an organic EL device excellent in the above.

In order to confirm the above-mentioned effects, an organic EL device using soda glass for a conventionally known substrate 61 and an organic EL device using sapphire according to the present invention were experimentally manufactured and compared. The constituent materials are soda glass or sapphire for the substrate 61, ITO for the anode 2, copper phthalocyanine for the hole injection layer, TPD for the hole transport layer 4, and Al for the light emitting layer 3.
q ₃ , Li ₂ O was used for the electron transport layer 5, and Al was used for the cathode 1. FIG. 2 shows the time course of the DC light emission characteristics of the organic EL devices of the prototype soda glass substrate and sapphire substrate.

The vertical axis in FIG. 2 represents the light emission luminance 11 at the start of operation.
The percentage represents 50 cd / m ² , and the horizontal axis represents elapsed time. That is, the emission luminance after 100 hours has elapsed is 78% for soda glass and 83% for sapphire. After the elapse of 500 hours, the characteristics are deteriorated at 54% and 64%, respectively.

Next, a destructive test of the prototyped organic EL device,
That is, when a part of or almost all of the device electrode is sublimated and disappears, the ambient temperature is 20%.
In an environment of 80 ° C. and a humidity of 80%, the drive current density of the organic EL element at the time of luminance saturation immediately before destruction is 1.2 A / cm ² (terminal voltage of 16.
9V, luminance 45000 cd / m ² )
5.88 A for an organic EL device having a sapphire substrate 61
/ Cm ² (terminal voltage 55 V, luminance 90900 cd /
m ₂ ), and it was confirmed that the characteristics were improved with respect to the element destruction due to heat generation.

As described above, the organic EL element requires a measure against moisture and a measure against heat radiation due to the characteristics of the organic compound. However, the present invention provides a light-transmitting substrate for forming a light-emitting display surface.
By using a light-transmitting material having a higher thermal conductivity than conventionally used soda glass such as quartz and sapphire, heat is radiated without impairing the sealing effect, and the above two measures are taken.

[0025]

As described above, according to the present invention, the organic E
The heat generated from the L element can be effectively radiated into the surrounding air through the transparent substrate serving as the display surface, and sufficient measures against moisture can be taken, so that the deterioration of the characteristics of the organic EL element can be improved.

[Brief description of the drawings]

FIG. 1 is a view showing the structure of an organic EL device according to the present invention.

FIG. 2 is a diagram showing a comparison between the emission characteristics of the organic EL device of the present invention and a conventional organic EL device.

FIG. 3 is a view showing a structure of a conventional organic EL element.

[Explanation of symbols]

 1 ··· Cathode 2 ··· Anode 3 ··· Emitting layer 4 ··· Hole transport layer 5 ··· Electron transport layer 6 ··· Glass substrate 61 ··· Substrate 7a ···· Glass container 7b ··· Coating film 10 ··· Electron injection layer

 ──────────────────────────────────────────────────の Continuation of the front page (72) Inventor Yoshinori Fukuda 6-1-1, Fujimi, Tsurugashima-shi, Saitama Pref.

Claims (3)

[Claims] 1. An organic electroluminescence device comprising a light-transmitting substrate, on which at least an anode, a light-emitting layer, and a cathode are sequentially laminated, wherein the substrate has a thermal conductivity of 0.75 W / (m · deg). 2. The organic electroluminescence device according to claim 1, wherein the substrate is made of quartz. 3. The organic electroluminescence device according to claim 1, wherein the substrate is made of sapphire.