JP2002216945A - Organic electric field light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a long life organic electric field light-emitting element wherein a stable light emission is obtained even in the case of generation of heat by thermal relaxation in an electric field light-emitting process and driving of a long time is possible. SOLUTION: At a time of forming a transparent glass substrate 6 of the organic electric field light-emitting element, a prescribed amount of alumina or barium is kneaded in order to reduce heat expansion coefficient, and the heat expansion coefficient of the substrate 6 is made to be 40.0×10E-7/ deg.C or less. By this, stability of element property against the heat is enhanced, and luminance becomes stabilized also in the case of the thermal relaxation, and life-elongation of the element is realized, and driving for a long time can be made.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an organic electroluminescent device suitable for use in, for example, a self-luminous thin flat display.

[0002]

2. Description of the Related Art In recent years, the importance of interfaces between humans and machines, including multimedia-oriented products, has been increasing. In order for humans to operate a machine more comfortably and efficiently, a sufficient amount of information needs to be accurately, concisely, and instantaneously extracted from a machine to be operated. For this reason, various display elements for displays have been studied.

[0003] Further, with the miniaturization of machines, demands for miniaturization and thinning of display elements are increasing every day.

For example, there has been a remarkable progress in miniaturization of laptop information processing devices, such as notebook personal computers and notebook word processors, which are integrated with display elements. There are also great innovations regarding

A liquid crystal display is used as a display interface for various products, and is widely used not only for laptop-type information processing equipment but also for products such as small televisions, clocks, and calculators that are used daily. Have been.

[0006] These liquid crystal displays have been studied from the small size to the large capacity display devices as the main display elements, taking advantage of the characteristics of the liquid crystal driven at low voltage and low power consumption.

However, a liquid crystal display requires a backlight because it is not self-luminous, and requires more power to drive this backlight than to drive a liquid crystal. However, there is a drawback that the use time is shortened and the use is restricted.

Further, the liquid crystal display has a problem that it is not suitable for a display device such as a large display because the viewing angle is narrow.

Further, since the liquid crystal display is a display method based on the alignment state of liquid crystal molecules, there is a problem that the contrast changes depending on the angle even in the range of the viewing angle.

Considering the driving method, the active matrix method, which is one of the driving methods of the liquid crystal display, shows a response speed sufficient to handle moving images.
Since it is necessary to use a (thin film transistor) drive circuit, it has been difficult to increase the screen size due to the occurrence of pixel defects. In addition, using a TFT drive circuit is not very preferable in terms of cost.

On the other hand, the simple matrix system, which is another driving system of the liquid crystal display, has the features of being low in cost and relatively easy to enlarge the screen size, but has a sufficient response speed for handling moving images. There is a drawback that it does not have.

On the other hand, as a self-luminous display element, a plasma display element, an inorganic electroluminescent element, an organic electroluminescent element and the like have been studied.

The plasma display device uses plasma light emission in a low-pressure gas for display, and is suitable for increasing the size and capacity, but has problems in terms of thinning and cost. Further, since a high voltage AC bias is required for driving, it is not suitable for a portable device or the like.

As the inorganic electroluminescent device, a green light-emitting display or the like was first commercialized, but, like the plasma display device, was driven by an AC bias and required several hundred volts for driving, so that it was hardly accepted. Due to technological development, today, R
Although emission of the three primary colors (red), G (green), and B (blue) has been successful, since it is an inorganic material, for example, it is difficult to control the emission wavelength and the like by molecular design. Seems difficult.

On the other hand, the electroluminescence phenomenon caused by an organic compound is as follows.
It has been studied for a long time since the light emission phenomenon caused by carrier injection into an anthracene single crystal that emits strong fluorescence was discovered in the early 1960's. Was only at the stage of basic research called carrier injection.

However, in 1987 Eastman Kodak
Since Tang et al. Announced a stacked organic thin-film electroluminescent device with an amorphous light-emitting layer capable of low-voltage driving and high-brightness light emission, the RGB primary colors of light emission, stability, increased brightness, and a stacked structure have been developed in various fields. Research and development of manufacturing methods have been actively conducted.

Further, various novel materials have been invented by molecular design, which is a feature of organic materials, and application of organic electroluminescent devices having excellent characteristics such as low-voltage DC drive, thinness, and self-luminous properties to color displays. Research is also being actively conducted.

FIG. 7 shows an example of a conventional organic electroluminescent device.

The organic electroluminescent device 10 has an ITO (Indium Tin Oxide) transparent electrode 5 on a transparent glass substrate 6.
Hole transport layer 4, light emitting layer 3, electron transport layer 2, and cathode 1
Are sequentially formed by, for example, a vacuum evaporation method.

In this organic electroluminescent device 10, a DC voltage 11 is applied between the ITO transparent electrode 5 serving as an anode and the cathode 1.
Is applied, holes (holes) as carriers injected from the ITO transparent electrode 5 pass through the hole transport layer 4, while electrons injected from the cathode 1 move through the electron transport layer 2, respectively. At 3, recombination of these electron-hole pairs occurs, from which light emission 12 of a predetermined wavelength is generated, which can be observed from the transparent glass substrate 6 side.

For the light emitting layer 3, for example, light emitting substances such as anthracene, naphthalene, phenanthrene, pyrene, chrysene, perylene, butadiene, coumarin, acridine and stilbene can be used.

FIG. 8 shows another conventional organic electroluminescent device. In this organic electroluminescent device 20, the electron transport layer 2 also serves as a light emitting layer.

FIG. 9 shows a configuration example of a flat display using the organic electroluminescent device 20 of FIG.

As shown in the figure, an organic laminated structure including an electron transport layer 2 and a hole transport layer 4 is disposed between a cathode 1 and an anode 5. The cathode 1 and the anode 5 are provided in a stripe shape crossing each other, and selected by a luminance signal circuit 34 and a control circuit 35 with a built-in shift register, respectively, to which a signal voltage is applied. Thus, the selected cathode 1 and anode 5
The organic laminated structure at the position (pixel) where the light crosses emits light.

[0025]

In order to apply the above-mentioned organic electroluminescent device to a color display, stable light emission with a long life is an essential condition.

However, even in an organic electroluminescent device having an optimum structure, the process of electroluminescence necessarily involves thermal relaxation, and heat generated by the thermal relaxation process is one of the factors that cause deterioration of the device.

This is the result of research and development of organic materials.
Even if an organic electroluminescent element can be constituted by a combination of materials having high luminous efficiency, cracks may be generated between the organic material and the base constituting the organic electroluminescent element due to heat generated by a thermal relaxation process, There is a possibility of peeling, and it is difficult to extend the life of the element.

Accordingly, an object of the present invention is to provide an electroluminescent device which can obtain stable luminance even when generating heat and can be driven for a long time.

[0029]

That is, the present invention relates to an electroluminescent device in which an organic layer including a light emitting region is provided on a substrate, wherein the substrate has a thermal expansion coefficient of 40.0 × 10E-
The present invention relates to an electroluminescent device characterized by being at most 7 / ° C.

According to the electroluminescent device of the present invention, since the coefficient of thermal expansion of the base is 40.0 × 10E-7 / ° C. or less,
Provided is an electroluminescent element that can be driven for a long time by increasing the stability of the element against heat, thereby stabilizing the luminance even during heat generation such as thermal relaxation in the electroluminescent process, and extending the life of the element. Can be.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the above-mentioned electroluminescent device, it is preferable that a material for lowering the coefficient of thermal expansion is contained in the substrate, and that the material contains less than 30% by weight of alumina or barium.

It is preferable that the added amount of alumina or barium is kneaded into the raw material of the base when the base is formed.

Thus, a transparent electrode, desirably an organic hole injection layer, an organic hole transport layer, an organic light emitting layer and / or an organic electron transport layer, and a metal electrode are sequentially laminated on an optically transparent substrate. And an electroluminescent element can be formed.

The above-described embodiment will be specifically described with reference to the drawings.

The organic electroluminescent device of the present embodiment is similar to that of FIG.
As shown in (1), a transparent electrode 5 made of ITO is formed on a substrate 6 by sputtering, and a hole injection layer 7, a hole transport layer 4, a light emitting layer 3, an electron transport layer 2, and a cathode electrode 1 are vacuum deposited thereon. The organic electroluminescent device is manufactured by sequentially laminating the organic electroluminescent devices.

In order to extract light emission from the transparent electrode 5 on the anode side, it is common for the substrate 6 to use a glass substrate 6 such as soda glass for low cost.
A transparent substrate other than a glass substrate may be used as long as it can extract light emission, and is not limited by the light transmittance of the substrate.

Further, depending on the amount of alumina, barium, or the like mixed in the substrate 6 to lower the coefficient of thermal expansion,
In some cases, the transmittance may be extremely low. In this case, it is only necessary to use this substrate on the cathode side and to fabricate a device having an inverted structure such that a transparent electrode is formed at the end. It is not limited by value.

Of course, in the device having the above-described organic electroluminescent layer, the ITO anode electrode 5, the hole injection layer 7, the hole transport layer 4, the light emitting layer 3, the electron transport layer 2, and the cathode electrode 1
There is no particular limitation on the material. For example, the hole transport layer 4
If so, a hole transporting material such as a benzidine derivative, a styrylamine derivative, a triphenylmethane derivative, and a hydrazone derivative can also be used.

The ITO anode electrode 5, the hole injection layer 7, the hole transport layer 4, the light emitting layer 3, the electron transport layer 2, and the cathode electrode 1 may have a laminated structure composed of a plurality of layers.

Further, in order to control the emission spectrum of the light-emitting layer 3, an organic trace molecule may be co-deposited.
An organic thin film containing a trace amount of an organic substance such as a perylene derivative, a coumarin derivative, or a pyran dye may be used.

As for the material of the cathode electrode 1, in order to inject electrons efficiently, it is preferable to use a metal having a small work function from a vacuum level as an electrode material. For example, indium (In), magnesium (Mg) ), Low work function metals such as silver (Ag), calcium (Ca), barium (Ba), lithium (Li) and aluminum (Al) alone or as alloys with other metals (particularly Al) It may be used to enhance the performance.

In the present embodiment, in order to extract light emission from the anode electrode side, a transparent I
Was used TO, of course efficient for injecting holes, having a large work function from the vacuum level of the material of the anode electrode 5, for example, gold (Au), tin dioxide - antimony mixture (SnO ₂ + Sb), An electrode such as a zinc oxide-aluminum mixture (ZnO + Al) may be used.

Further, in order to enhance the stability, the entire organic layer including the cathode 1 may be sealed with germanium oxide or the like to eliminate the influence of atmospheric oxygen or the like. The element may be driven in the state.

The substrate having a coefficient of thermal expansion of 40.0 × 10E-7 / ° C. or less, which is a feature of the present embodiment, is not limited by a method of reducing the coefficient of thermal expansion.

The thermal expansion coefficient is 40.0 × 10E-7.
For example, considering a glass substrate,
This can be achieved by adding an inorganic oxide represented by alumina.

According to the present embodiment, the laminated structure of the substrate and the electrode layer and the organic layer laminated thereon and their materials are not limited, and the raw material of the substrate at the time of forming the substrate is made of alumina or barium. By adding less than 10% by weight, the coefficient of thermal expansion of the substrate is 40.0 × 10E-7 /
° C or less, whereby the stability of the characteristics of the element against heat can be improved.

[0047]

EXAMPLES Examples of the present invention and comparative examples for comparison with the examples will be described below. In each example, only the thermal expansion coefficient of the substrate is different.

[0048] On a glass substrate of Example 1 the thermal expansion coefficient of 37.8 × 10E-7 / ℃, an ITO substrate provided with ITO film (thickness: about 100 nm), on which, 2 mm × by SiO ₂ deposition 2mm
An ITO substrate for manufacturing an organic electroluminescent element was prepared by masking the area other than the light-emitting region.

Next, m-MTDATA (4,4 ′, 4 ″) having the structural formula shown in FIG. 3 was formed on the ITO substrate as a hole injection layer material.
-tris (3-methylphenylphenylamino) triphenylamine) was vacuum deposited to a thickness of 50 nm.

Next, α-NPD (4,4′-bis [N- (1-naphthyl) -N-phen) having the structural formula shown in FIG.
yl-amino] biphenyl) is vacuum-deposited to a thickness of 50 nm,
Finally, 50 n of Alq ₃ (8-hydroxyquinorine aluminum) having the structural formula shown in FIG.
m in vacuum. Then, as a cathode,
iF and Al (lithium fluoride / aluminum alloy) were laminated to produce an organic electroluminescent green light emitting device.

FIG. 2 shows a schematic configuration of the organic electroluminescent device (corresponding to one of the above-mentioned light emitting regions) manufactured as described above. That is, on the glass substrate 6, the ITO transparent electrode 5, the hole injection layer 7, the hole transport layer 4, the electron transport light emitting layer 8, and the Li
F and an Al electrode 1 were laminated in this order and produced. The same applies to other examples described later.

When the organic electroluminescent device thus manufactured was driven by a DC voltage, as shown in FIG.
2000 cd / m ² , and the voltage was 9.0 V.

Further, the green light emitting device was set to an initial luminance of 200
When driving at a constant current of cd / m ² , the actual driving time was 100
The luminance at 00 hours was about 140 cd / m ² , and a long-life organic electroluminescent device could be obtained.

[0054] On a glass substrate of Example 2 thermal expansion coefficient of 37.0 × 10E-7 / ℃, an ITO substrate provided with ITO film (thickness: about 100 nm), on which, 2 mm × by SiO ₂ deposition 2mm
An ITO substrate for manufacturing an organic electroluminescent element was prepared by masking the area other than the light-emitting region.

Next, m-MTDATA (4,4 ′, 4 ″) having the structural formula shown in FIG. 3 was formed on the ITO substrate as a hole injection layer material.
-tris (3-methylphenylphenylamino) triphenylamine) was vacuum deposited to a thickness of 50 nm.

Next, α-NPD (4,4′-bis [N- (1-naphthyl) -N-phen) having the structural formula shown in FIG.
yl-amino] biphenyl) is vacuum-deposited to a thickness of 50 nm,
Finally, 50 n of Alq ₃ (8-hydroxyquinorine aluminum) having the structural formula shown in FIG.
m in vacuum. Then, as a cathode,
iF and Al (lithium fluoride / aluminum alloy) were laminated to produce an organic electroluminescent green light emitting device.

When the organic electroluminescent device thus manufactured was driven by a DC voltage, the highest luminance was 65000 cd /.
m ² , and the voltage was 9.0 V, which was almost the same as in Example 1.

Further, the green light emitting element was set to an initial luminance of 200
When driving at a constant current of cd / m ² , the actual driving time was 100
The luminance at 00 hours was about 143 cd / m ² , and a long-life organic electroluminescent device could be obtained.

[0059] On a glass substrate of Comparative Example 1 thermal expansion coefficient of 46.7 × 10E-7 / ℃ (for LCD), an ITO substrate provided with ITO film (thickness: about 100 nm), on which, SiO ₂ 2m by evaporation
An ITO substrate for manufacturing an organic electroluminescent device was prepared by masking a region other than the light emitting region of mx 2 mm.

Next, m-MTDATA (4,4 ′, 4 ″) having the structural formula shown in FIG. 3 was formed on the ITO substrate as a hole injection layer material.
-tris (3-methylphenylphenylamino) triphenylamine) was vacuum deposited to a thickness of 50 nm.

Next, α-NPD (4,4′-bis [N- (1-naphthyl) -N-phen) having the structural formula shown in FIG.
yl-amino] biphenyl) is vacuum-deposited to a thickness of 50 nm,
Finally, 50 n of Alq ₃ (8-hydroxyquinorine aluminum) having the structural formula shown in FIG.
m in vacuum. Then, as a cathode,
iF and Al (lithium fluoride / aluminum alloy) were laminated to produce an organic electroluminescent green light emitting device.

When the organic electroluminescent device thus manufactured was driven by a DC voltage, the highest luminance was 1 as shown in FIG.
The voltage was 7000 cd / m ² and the voltage was 8.0 V.

As compared with Example 1, the stability of the device in the high luminance region, that is, the region where the amount of heat generated in the thermal relaxation process was large, was poor, and the characteristics near the maximum luminance varied and deteriorated quickly. .

Further, the green light emitting element was set to an initial luminance of 200
When driving at a constant current of cd / m ² , the actual driving time was 100
The luminance at the time of 00 hours was about 50 cd / m ² , and the stability to heat in long-term driving was poor.

Comparative Example 2 An ITO substrate (thickness: about 100 nm) provided on a glass substrate having a coefficient of thermal expansion of 48.0 × 10E-7 / ° C. was used, and 2 mm × 2 mm was deposited thereon by SiO ₂ evaporation. For manufacturing organic electroluminescent devices masking areas other than the light emitting region
An O substrate was produced.

Next, m-MTDATA (4,4 ′, 4 ″) having the structural formula shown in FIG. 3 was formed on the ITO substrate as a hole injection layer material.
-tris (3-methylphenylphenylamino) triphenylamine) was vacuum deposited to a thickness of 50 nm.

Next, α-NPD (4,4′-bis [N- (1-naphthyl) -N-phen) having the structural formula shown in FIG.
yl-amino] biphenyl) is vacuum-deposited to a thickness of 50 nm,
Finally, 50 n of Alq ₃ (8-hydroxyquinorine aluminum) having the structural formula shown in FIG.
m in vacuum. Then, as a cathode,
iF and Al (lithium fluoride / aluminum alloy) were laminated to produce an organic electroluminescent green light emitting device.

When the organic electroluminescent device thus manufactured was driven by a DC voltage, the maximum luminance was 15,000 cd /
m ² , and the voltage was 8.0 V.

Compared with Example 1, the stability of the element against heat in the high luminance region, that is, the region where the amount of heat generated in the thermal relaxation process was large, was poor, and the characteristics near the maximum luminance varied and deteriorated quickly. .

Further, this green light emitting element was set to an initial luminance of 200
When driving at a constant current of cd / m ² , the actual driving time was 100
The luminance at the time of 00 hours was about 45 cd / m ² , and the stability to heat during long-term driving was poor.

According to this embodiment, the thermal expansion coefficient is 40.0 × 10E-7, as in the above-described first and second embodiments.
By using a substrate having a temperature of / ° C. or lower, the stability of the organic electroluminescent device against heat in a high-luminance region is improved,
In particular, the improvement of the maximum luminance is remarkable, the maximum luminance is improved several times, the life of the element is extended, and the initial luminance is increased by 200 times.
10 drive times from cd / m ² until the life is halved
Over 000 hours can be achieved.

That is, since the luminance is stable even when heat is generated due to thermal relaxation in the electroluminescent process, an electroluminescent element which can be driven for a long time is realized, and a crack between the substrate and the organic material due to the conventional thermal relaxation is realized. And concerns about deterioration of the element due to peeling.

The above embodiment can be modified based on the technical concept of the present invention.

For example, a material other than alumina or barium can be used as a material for lowering the thermal expansion coefficient of the substrate.

Further, the layer structure of the organic layer in the above-mentioned electroluminescent device is not limited to the embodiment, but can be appropriately implemented.

The formation of each of the organic layers described above is not limited to vapor deposition, and a film forming method involving sublimation or vaporization can be applied.

[0077]

As described above, the present invention relates to an electroluminescent device in which an organic layer including a light emitting region is provided on a substrate, wherein the substrate has a thermal expansion coefficient of 40.0 × 10E-7.
/ ° C or less, the stability of the element against heat is enhanced, so that the luminance is stable even during heat generation such as thermal relaxation in the electroluminescent process, and the element has a long life and can be driven for a long time. An electroluminescent element can be provided.

[Brief description of the drawings]

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

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

FIG. 3 is a diagram showing the MM used in the organic electroluminescent device of the example.
It is a structural formula of TDATA.

FIG. 4 shows the α-N used in the organic electroluminescent device of the example.
3 is a structural formula of PD.

FIG. 5 shows an Alq used in the organic electroluminescent device of the example.
_{3 is} a structural formula.

FIG. 6 is a graph showing characteristics of Example 1 and Comparative Example 1.

FIG. 7 is a schematic cross-sectional view illustrating a configuration of an organic electroluminescent device according to a conventional example.

FIG. 8 is a schematic cross-sectional view showing the configuration of another organic electroluminescent device.

FIG. 9 is a schematic diagram showing a configuration of a flat panel display using the organic electroluminescent device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cathode, 2 ... Electron transport layer, 3 ... Light emitting layer, 4 ... Hole transport layer, 5 ... ITO transparent electrode, 6 ... Substrate, 7 ... Hole injection layer, 8 ... Electron transport light emitting layer, 10, 20 ... Organic EL device

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shinichiro Tamura 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation F-term (reference) 3K007 AB02 AB04 AB14 CA01 CB01 DA01 DB03 EB00

Claims (6)

[Claims] 1. An electroluminescent device in which an organic layer including a light emitting region is provided on a substrate, wherein the substrate has a thermal expansion coefficient of 40.0 × 10E-7 / ° C. or less. Light emitting element. 2. The electroluminescent device according to claim 1, wherein the base contains a material for lowering a coefficient of thermal expansion. 3. The electroluminescent element according to claim 2, wherein less than 30% by weight of alumina or barium is added as a material for lowering the coefficient of thermal expansion. 4. The electroluminescent device according to claim 3, wherein said alumina or barium is kneaded into a raw material of said base when said base is formed. 5. The electric field according to claim 1, wherein a transparent electrode, an organic hole transport layer, an organic light emitting layer and / or an organic electron transport layer, and a metal electrode are sequentially laminated on an optically transparent substrate. Light emitting element. 6. The electroluminescent device according to claim 5, wherein an organic hole injection layer is provided between the transparent electrode and the organic hole transport layer.