JPH03115486A - Organic electroluminescent element - Google Patents

Abstract

PURPOSE:To obtain a high yield of an organic electroluminescent element with good characteristics, having an organic thin film layer that withstands a process of forming an upper electrode by using a specified polymer as a luminescent organic dye. CONSTITUTION:An organic electroluminescent element having an organic thin film prepared by laminating a hole transfer layer and an electron transfer layer, which are made of an organic dye and at least one of which is luminescent, between two electrodes at least one of which is transparent, wherein a polymer having at least two organic dyes of a band gap of at least 3eV combined through a nonconjugated bond (e.g. a carbon-carbon single bond, a hydrocarbon residue, an ester linkage, a carbonyl residue, an amide linkage or an ether linkage) is used as a luminescent organic dye. For example, a luminescent bipyrenyl of formula I is used for the hole transfer layer, and dinitrobifluorenonyl of formula II for the electron transfer layer. This technique gives a high yield of an organic electroluminescent element with good characteristics without suffering a damage to the organic thin film layer when an upper electrode is formed and without causing a reduction in luminous intensity and short circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an organic electroluminescent device used as a display device, a lighting device, etc.

(Prior art) In recent years, with the increase in demand for portable TVs and computers,
Development of thin and lightweight display elements, mainly for flat panel displays, is progressing rapidly. Currently, liquid crystal display elements are the mainstream, but liquid crystal display elements have drawbacks such as difficulty in increasing the screen size and difficulty in viewing depending on the viewing angle.

Therefore, there is a demand for the development of a light-emitting display element that can be expected to have excellent display functions such as vivid colors, ease of displaying moving images, and the ability to display images even in dark places. As such light emitting display elements, plasma displays, inorganic electroluminescent elements, fluorescent display tubes, light emitting diodes, and the like are being studied. In order to realize a full color display with these elements, high brightness RGB light emission is required. However, at present, it is difficult for any of these devices to emit blue light, and a full-color display has not been realized.

Incidentally, many organic dye molecules emit fluorescence or phosphorescence in the blue region (near the wavelength 4BOr+m) during their photoluminescence. From this, an organic electroluminescent device having a structure in which a light-emitting layer made of a thin organic dye film is provided between two electrodes has a high possibility of realizing a full-color display device, and is highly anticipated. However, organic electroluminescent devices have a problem in that their luminance is so low that they cannot be recognized with the naked eye.

Therefore, in order to improve the brightness of organic electroluminescent devices, the basic structure of the device is an organic dye thin film containing organic dyes or a multilayer stacked structure of organic dye thin films. Organic electroluminescent devices having structures in which these are combined in various forms have been proposed (JP-A-61-43884, JP-A-61-44974, JP-A-61-44978, JP-A-61-Sho. No. 44981, JP-A-61-44988, etc.).

In addition, it has been reported that an organic electroluminescent device with a structure in which a hole transfer layer is provided between the positive electrode and the light emitting layer can emit high-intensity light with a low-voltage DC power source (Appl.
Phys, Lett, 51,913(1,987),
JP-A-83-49450, JP-A-63-284692
No., JP-A-63-295895).

In addition, Shogo Saito of Kyushu University and his colleagues have found that an organic electroluminescent device has a structure in which a hole transfer layer is provided between the positive electrode and the light emitting layer, and an electron transfer layer is provided between the negative electrode and the light emitting layer. It has been reported that the brightness is further improved (J, J,
Appl, Phys, 25. L775 (1986)
, 27. L289 (1988)). and,
For example, anthracene (B
), coronene (G), and perylene (R), RGB light emission can be obtained.

As mentioned above, organic electroluminescent devices have the following five properties: 1) good luminous efficiency, 2) high luminance, 2) blue short wavelength light emission, 2) drive at low voltage, and 4) high yield. It is required that two conditions be met. ■
, (2), it is important to control the electronic properties of the electron-donating dye and electron-accepting dye used in the hole-transfer layer and electron-transfer layer to optimal conditions. For (2), it is important to widen the band gap of the dye.

Here, the energy corresponding to blue light emission (λ-46Oni) is about 2.7 eV. Since the emission position is Stokes-shifted to the longer wavelength side than the absorption position, it is desirable that the absorption position of the dye, that is, the band gap, be set to 3 eV or more. Regarding (2), it is important to reduce the thickness of each organic thin film layer in order to apply a high electric field to the organic thin film layer.

However, it is currently extremely difficult to satisfy the condition (2) of increasing the yield while reducing the thickness of the organic thin film layer. This is due to the following reasons. An organic electroluminescent device consists of a transparent electrode (for example, I) formed on a transparent substrate.
It is manufactured by sequentially vacuum-depositing a carrier injection layer and a light-emitting layer on top of TO (TO), and finally vacuum-depositing an upper metal electrode.

Here, the film thickness of the carrier injection layer and the light emitting layer is usually 100~
The range is 1.0000 people. In addition, when vacuum depositing the upper metal electrode, the vacuum degree is 10-5 to 10'' Torr.
By resistance heating or electron gun heating, the temperature is about 200~30℃.
A condition of 0°C is used. As a result, the carrier injection layer and the light emitting layer are affected by the radiant heat from the vapor deposition source and the heat transmitted by the incoming metal atom beam. The biggest influence among these is that when the dye has a low molecular weight, its vapor pressure is high, so the dye sublimes again under the influence of heat as described above, causing defects. Furthermore, the thin film is melted by the heat, which disturbs the film structure and causes defects, creating a short circuit bus between the upper electrode and the lower transparent electrode, making it impossible to apply a predetermined electric field to the organic thin film layer. This problem also occurs frequently.

In fact, when a low molecular weight luminescent dye such as anthracene, which emits blue light, is used, there is a problem in that the yield of devices is extremely low. In addition, relatively high yields can be expected if phthalocyanine with a high molecular weight is used, but since phthalocyanine is non-luminescent, this device uses phthalocyanine in the hole transfer layer and a luminescent electron-accepting dye in the electron transfer layer. must be used. However, the drawback is that there are very few luminescent electron-accepting dyes that have a wide band gap and are suitable for blue light emission.

(Problems to be Solved by the Invention) As described above, in conventional organic electroluminescent devices, the organic thin film layer is damaged during the formation of the upper electrode, resulting in a decrease in luminance and short circuits, resulting in a low yield. there were.

It is an object of the present invention to solve this problem and provide an organic electroluminescent device that has an organic thin film layer that can withstand the upper electrode formation process, has good characteristics, and has a high yield.

[Structure of the Invention] (Means and Effects for Solving the Problems) The organic electroluminescent device of the present invention comprises an organic dye between two electrodes, at least one of which is transparent, and at least one of which is luminescent. In an organic electroluminescent device having an organic thin film in which a hole transfer layer and an electron transfer layer are laminated, two organic dyes having a band gap of 3 eV or more are bonded to each other as the luminescent organic dye via a non-conjugated bond. This invention is characterized by using a multimer having the above-mentioned bonds.

The luminescent organic dye used in the present invention is a multimer in which two or more organic dyes with a band gap of 3 eV or more are bonded via non-conjugated bonds, so it has a high vapor pressure and can form the upper electrode. Re-sublimation can also be prevented in the vacuum evaporation process.

In the present invention, the molecular weight of the luminescent organic dye is preferably 400 or more. This is based on the vacuum degree fO-' to 1O-6 Torr and the temperature 200 to 300 when forming the upper electrode.
It is based on the knowledge obtained by measuring the vapor pressure of various condensed polycyclic aromatic dyes with different molecular weights under the general condition of ℃. In this case, even if the molecular weight is the same, the vapor pressure will differ slightly depending on the way the benzene rings are bonded, but the relationship between the molecule ff1M and the vapor pressure P is generally expressed by the following formula % formula % (where T is temperature and B and C are constants) The following relationship is satisfied.

From experimental results, it has been found that dyes with a molecular weight of 400 or more have a vapor pressure of 0-5 to -6 Torr per month at 200 to 300°C.

There are various types of such dye molecules having a large molecular weight, but in order to satisfy all of the conditions (1) to (4) described above, it is necessary to consider the molecular structure thereof. for example,
Examples of dye molecules having a large molecular weight include derivatives of condensed polycyclic aromatic molecules in which a π-electron conjugated system is expanded. Since these dyes are luminescent and generally electron-donating, they are used as hole transport layers. In order to use a derivative of a condensed polycyclic aromatic molecule as an electron transfer layer, it is necessary to induce the aromatic skeleton into a quinoid structure or to impart electron-accepting properties by introducing a nitro group, cyano group, halogen group, etc. is being carried out. Porphyrin metal complexes and phthalocyanine metal complexes are also known as dye molecules with large molecular weights.

However, dye molecules whose basic skeletons are large condensed polycyclic aromatic molecules, or dye molecules whose basic skeletons are porphyrin metal complexes or phthalocyanine metal complexes have narrow band gaps, making it difficult to emit blue light. There is a drawback. Furthermore, it is difficult to synthesize the dye molecules, making it difficult to control the electron-accepting or electron-donating properties of the dye.

In contrast, in the present invention, an organic dye with a band gap of 3 eV or more is used as a luminescent organic dye with a structure that does not narrow the band gap while satisfying the condition of having a large molecular weight. through 2
It uses multimers in which two or more molecules are linked together. Organic dyes with a band gap of 3 eV or more as a monomer have a molecular weight of 1
oo to 400 may be sufficient. This organic dye has a band gap of 3 eV or more and emits short wavelength blue light, but it is also desirable that it has good luminous efficiency and high luminance.

Examples of non-conjugated bonds that bind these organic dyes include carbon-carbon single bonds, hydrocarbon residues, ester bonds, carbonyl residues, amide bonds, and ether bonds. Further, these organic dyes may be bonded to the linear polymer in a pendant manner.

In this case, the non-conjugated bond becomes a repeating unit that constitutes a linear chain.

As mentioned above, Tables 1 to 3 show examples of luminescent organic dyes made of multimers in which two or more organic dyes having a band gap of 3 eV or more are bonded via non-conjugated bonds.

Table 1 shows examples of luminescent organic dyes in which the non-conjugated bond is a carbon-carbon single bond or a hydrocarbon residue (-CH-CH-). (a) is the donor (b) is the acceptor.

Table 2 shows the constituents of the luminescent organic dye: (a) Donor, which becomes the monomer; (b) Acceptor, which becomes the monomer; (C) Ester bonds, carbonyl residues, and amide bonds as non-conjugated bonds. , which shows examples of combinations such as ether bonds. Here, R represents a donor or an acceptor.

Table 3 shows examples of luminescent organic dyes in which donors or acceptors R are bonded pendantly to a linear polymer serving as a monomer.

The luminescent organic dye according to the present invention is multimerized by bonding two or more organic dyes as described above through non-conjugated bonds, so compared to the original organic dye, its electron It exhibits good properties, with no major effects on physical properties such as electron-accepting properties, electron-donating properties, band gap width, etc. Moreover, since it has a large molecular weight,
The vacuum deposition process for forming the upper metal electrode also suffers from damage, leading to a decline in the yield of organic electroluminescent devices.
d.

No. Table (Part 1) (a) donor Visipenza Atofuna I Norha V Ni~ No. Table (Part 2) (b) Acceptor Czs Hs N 60 + b (c) Non-conjugated bond ○ 0- Table (Part 2) R A non-conjugated bond may be introduced.

Li -CI-(2-0- No. 3 table CH.

■-be CH2CH soup 7-1 ( -0 H-HCHz-CHh-H -0 rl-3~10 (Example) The present invention will be explained in detail below.

FIG. 1 shows a configuration diagram of an organic electroluminescent device according to the present invention. In FIG. 1, an ITO electrode 2 is placed on a glass substrate 1,
A hole transfer layer 3, an electron transfer layer 4, and an Ag electrode 5 are formed in this order. Further, a DC power supply 6 is connected between the ITO electrode 2 and the Al electrode 5.

The ITO electrode 2 was formed by sputtering.

The hole transfer layer 3 and the electron transfer layer 4 were formed by vacuum sublimation of an organic compound. The Ag electrode 5 was formed by vacuum evaporation. At this time, heating is performed using a resistance heating method,
The degree of vacuum was 10-6 Torr.

Example 1 The organic electroluminescent device shown in FIG. 1 was produced using luminescent bibyrenyl as the hole transfer layer and dinitrobifluorenonyl as the electron transfer layer. The absorption edge of bibyrenyl is 40
It is near 0 nm and satisfies the band gap of 3 eV or more. The film thickness of the hole transfer layer and electron transfer layer is 5
000.2000.1000.500.250 people fabricated a device and applied a DC voltage, and the film thickness was 50%.
Until 0 people, there was no short-circuit wrestler to Motoko.

When a DC voltage of IOV is applied, 5rrA
/cm' current flows, maximum brightness 5000c d
/m'' blue luminescence was obtained.

Comparative Example 1 An organic electroluminescent device as shown in FIG. 1 was prepared using pyrene having a molecular weight of 400 or less as a hole transfer layer and dinitrofluorenone as an electron transfer layer. Example 1
Similarly, when the film thickness of the hole transfer layer and the γ-ton transfer layer is made thinner, short circuits occur in the device by 2000 people, and 500
I needed a film thickness of 0 people.

Even if a DC voltage of 100 μ is applied, 1 “Alc
Only II+2 current flows and maximum brightness is 500C/m
It was as low as 2.

Example 2 Luminescent bis(anthrylthyroxy) as hole transport layer
The organic electroluminescent device shown in FIG. 1 was prepared by using terephthalic acid ester and bis(troanthrylmethyloxy)terephthalic acid ester as an electron and auxiliary layer. The film thicknesses of the hole transfer layer and electron transfer layer were respectively 5000.2000.
When a device was prepared with a thickness of 1000, 500, and 250 and a DC voltage was applied, no short circuit occurred in the device until the film thickness reached 500.

When a DC voltage of 1OV is applied, 5mA/
cm2 current flows, maximum brightness 5000c d/
A blue emission of m 2 was obtained.

Comparative Example 2 The organic electroluminescent device shown in FIG. 1 was produced using luminescent anthracene having a molecular weight of 400 or less as the hole transfer layer and dinitroanthracene as the electron transfer layer. As in Example 1, when the film thicknesses of the hole transfer layer and electron transfer layer were made thinner, a short circuit occurred in the device even with 2000 people.
A film thickness of 5,000 people was required.

Even if 100 V DC voltage is applied, 1 mA/
Only -2 current was flowing, and the maximum brightness was low at 500 cd7m2.

Example 3 The organic electroluminescent device shown in FIG. 1 was produced using luminescent tetraphenylpyrene as the front plate transfer layer and tetranitrophenylanthraquinone as the electron transfer layer. The film thickness of the hole transfer layer and electron transfer layer is 5000.20, respectively.
When a device was fabricated with a thickness of 00.1000.500.250 and a DC voltage was applied, no short circuit occurred in the device up to a film thickness of 500.

And when IOV DC voltage is applied, 5mA/
cm' current flows, maximum brightness 5000c d/
A blue emission of m 2 was obtained.

Comparative Example 3 The organic electroluminescent device shown in FIG. 1 was produced using luminescent pyrene having a molecular weight of 400 or less as the hole transfer layer and nitroanthraquinone as the electron transfer layer. Example 1
Similarly, when the film thickness of the hole transfer layer and electron transfer layer is made thinner, a short circuit occurs in the device even with 2000 people, and 500 people
A film thickness of 0 was required.

Even if 100v DC voltage is applied, 1mA/
Only a current of cm2 flows and the maximum brightness is 500cd
/ m2.

[Effects of the Invention] As detailed above, since the organic electroluminescent device of the present invention uses an organic dye with a large molecular weight, it is not susceptible to damage even during the vacuum deposition process for forming the upper metal electrode. Even if the organic thin film layer is made thinner and driven at a lower voltage, high brightness can be obtained, and the yield is also significantly improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an organic electroluminescent device in an example of the present invention. DESCRIPTION OF SYMBOLS 1... Glass substrate, 2... ITO electrode, 3... Hole transfer layer, 4... Electron transfer layer, 5... AJ2
Electrode, 6...DC power supply.

Claims (2)

[Claims] (1) In an organic electroluminescent device having an organic thin film in which a hole transfer layer and an electron transfer layer made of an organic dye and at least one of which is luminescent are laminated between two electrodes, at least one of which is transparent. An organic electroluminescent device characterized in that, as the luminescent organic dye, a multimer in which two or more organic dyes having a band gap of 3 eV or more are bonded via non-conjugated bonds is used. (2) The organic electroluminescence according to claim (1), wherein the non-conjugated bond is a carbon-carbon single bond, a hydrocarbon residue, an ester bond, a carbonyl residue, an amide bond, or an ether bond. element.