JPH02213088A - Organic thin film el element and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent the deterioration of an EL element by laminating a hole conductive organic thin film or electron conductive organic thin film adjacent to at least one side of an organic phosphorus conductive film between electrodes as a pair containing at least one transparent electrode. CONSTITUTION:An organic compound having a porphylin ring or phthalocyanine ring skeleton, and an electron receptor molecule or donor molecule are co-deposited, thereby ensuring easy electron or hole implantation. A compound having a functional group such as cyano and nitro groups for easily taking in an electron added to phororanyl and other types of quinone and aromatic rings, is used as an electron receptor organic molecule. Also, a compound having a functional group such as an amino group for the easy emission of an electron added to tetrathiofurbaren and other types of polycyclic and aromatic rings is used as an electron donar organic molecule. An ITO electrode 2 is provided on a glass substrate 1 and a deposited film formed with a ratio of 10 magnesium phthalocyanine to 1 phororanyl is applied thereto as a hole implantation layer 2. Then, a phosphorus tris (8-hydroxynorine) aluminum 4 is provided and an indium electrode 5 is formed thereon. According to the aforesaid construction, it is possible to prevent the deterioration of luminous efficiency due to the deterioration of the implantation layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an organic thin film EL element used for flat light sources and displays.

(Prior Art) EL (electroluminescent) devices using organic materials as raw materials are attracting attention as they can realize inexpensive large-area full-color display devices. For example, DC-driven organic thin-film EL devices have been manufactured using condensed polycyclic aromatic systems such as anthracene and perylene as raw materials and made into thin films by the LB method, vacuum evaporation method, etc., and their light-emitting characteristics have been studied.

However, conventional organic thin film EL devices require a high driving voltage, and their luminance and efficiency are lower than those of inorganic thin film EL devices. In addition, the luminescent properties deteriorated significantly, making it impossible to achieve a practical level.

However, recently, a new type of organic thin film EL device with a two-layer organic thin film structure has been reported and is attracting strong interest (
Applied Physics Letters, Vol. 51, p. 913, 1987). As shown in Figure 3, they reported that bright green light was obtained by using a metal chelate complex that emits strong fluorescence as a hole-conducting organic material in the organic phosphor thin film layer 34 and an amine material 23 in the hole injection layer 33. ing. A brightness of several 100 cd/m is obtained by applying a DC voltage of 6 to 7 V. The maximum luminous efficiency is 1.5 (m/W), which is higher than the conventional Z
It has the same level of performance as nS thin film EL elements.

(Problems to be Solved by the Invention) As mentioned above, a new organic thin film EL element having a two-layer structure consisting of an organic phosphor thin film and an organic hole injection layer has a maximum luminance of 1000 cd/m. It emits bright green light. However, in order to obtain the above brightness,
A current of A/cm or more must be passed through the element. In conventional organic hole-conducting thin films, driving at such relatively high current densities deteriorates the electrical properties of the hole-conducting thin film as the current is applied, resulting in a decrease in luminous efficiency and an increase in luminescence-voltage. This caused the characteristics to shift to the higher voltage side.

It is also important to further improve luminous efficiency.

With the luminous efficiency of conventional devices, a large current of about 100 mA/cm must be passed in order to obtain sufficient luminance, but as the display area of the device increases, the heat generated by the device and the resulting decrease in luminous efficiency become a problem that cannot be ignored. ing.

Thus, it is very important to develop an organic thin film EL device that further improves device luminous efficiency and exhibits less device deterioration even when a relatively large current is applied.

(Means for Solving the Problems) A first means provided by the present invention to solve the above-mentioned problems is to provide an organic phosphor thin film layer between a pair of electrodes, at least one of which is transparent; A hole-conducting organic thin film layer in which at least one electron-accepting organic molecule is added to an organic compound having a porphyrin ring or phthalocyanine ring skeleton, or at least one electron-accepting organic molecule is added to the organic compound in contact with at least one surface of the thin film layer. This is an organic thin film EL device characterized by stacking electron conductive organic thin film layers to which the above electron-donating organic molecules are added.

A second means provided by the present invention includes an organic phosphor thin film layer between a pair of electrodes, at least one of which is transparent, and a porphyrin ring or phthalocyanine ring skeleton in contact with at least one surface of the organic phosphor thin film layer. at least 1 part of
This is an organic thin film KL element characterized by laminating organic compounds substituted with the above electron-donating groups or electron-accepting groups.

A third means provided by the present invention includes an organic phosphor thin film layer between a pair of electrodes, at least one of which is transparent, and a porphyrin ring or phthalocyanine ring skeleton in contact with at least one surface of the organic phosphor thin film layer. at least 1 part of
A hole-conducting organic thin film layer in which at least one or more electron-accepting organic molecules are added to an organic compound substituted with the above electron-donating group, or a part of the porphyrin ring or phthalocyanine ring skeleton is added with at least one or more electron-accepting group. This is an organic thin film EL device characterized by laminating an electron conductive organic thin film layer in which at least one electron donating organic molecule is added to an organic compound substituted with .

A fourth means provided by the present invention is an organic compound having a porphyrin ring or phthalocyanine ring skeleton, or an organic compound in which a part of the porphyrin ring or phthalocyanine ring skeleton is substituted with at least one electron donating group or electron accepting group. , an organic thin film EL characterized in that electron-accepting organic molecules or electron-donating organic molecules are simultaneously supplied from separate evaporation sources in vacuum to form a hole-conducting organic thin film layer or an electron-conducting organic thin film layer. This is a method for manufacturing an element.

(Function) In an element driven with a relatively high current, such as an organic thin film EL element, the electrical properties of the materials constituting each layer must be stable. It has already been mentioned that in conventional organic thin film EL devices, electrical deterioration progresses in the charge injection layer, leading to device deterioration such as a shift to a higher voltage side of the driving voltage and a decrease in luminous efficiency.

We searched for materials for charge injection layers with stable electrical properties and found that thin films using metal-free or metal phthalocyanine, metal-free or metal porphyrin rings, and their derivatives are excellent. No change in electrical properties was observed even when a current of 100 mA/cm'' was continuously applied to a phthalocyanine film with a thickness of about 500 OA.

Furthermore, when an organic compound having a porphyrin ring or phthalocyanine ring skeleton and an electron-accepting molecule or an electron-donating molecule are co-deposited, a thin film containing an excess of electrons or holes can be formed. The resistance varied by about two orders of magnitude depending on the amount of electron-accepting molecules or electron-donating molecules added. When this thin film is used as a hole injection layer or an electron injection layer of an organic thin film EL device, electrons or holes are easily injected into the organic phosphor layer, and as a result, device characteristics can be significantly improved.

Examples of electron-accepting organic molecules include fluoranyl, trinitrofluorene, and tetracyanoquinodimethane (TCNQ).
, hexacyanobutadiene, tetracyanoethylene (T
CNE), methyltetracyanoquinodimethane, dimethyltetracyanoquinodimethane, and other organic compounds with quinones and aromatic rings attached with functional groups that easily absorb electrons, such as cyano groups and nitro groups. Examples of electron-donating organic molecules include tetrathiofulvalene (TTIF), tetrathiotetracene ('IvIwII), vercine, paraphenylenediamine, and tetramethyltetraselenofulvalene (TMTS).
F), phenothiazine, bis(ethylenedithio)tetrathiofulvalene, pentacene, etc. are organic compounds in which a functional group that easily releases electrons, such as an amino group, is attached to a polycyclic aromatic or aromatic ring.

The organic thin film according to the present invention includes: (1) a hole injection electrode, a hole conductive organic thin film layer, an organic phosphor thin film layer, an electron conductive organic thin film layer, and an electron injection electrode are sequentially laminated; (2) a hole injection electrode; A hole-conducting organic thin film layer, an organic phosphor thin film layer, and an electron injection electrode are sequentially laminated, or a hole-injecting electrode, an organic phosphor thin film layer, an electron-conducting organic thin film layer, and an electron injection electrode are sequentially laminated. Which structure of organic thin film EL is being used?
Even when used in devices, the effect of improving luminous efficiency was observed.

The skeleton is a porphyrin ring or a phthalocyanine ring,
Organic compound molecules partially substituted with at least one electron-donating group exhibit hole conductivity. Although the reason for this is not clear at present, it is thought to be as follows. The electron density at the center of the porphyrin ring or phthalocyanine ring of an organic compound molecule substituted with an electron-donating group increases, and the molecule becomes more likely to release electrons due to external changes such as an electric field. As a result, positively charged molecules or molecules in which holes are trapped are formed and exhibit hole conductivity. Its volume resistivity was about 10 Ω·am.

Similarly, an organic compound molecule that has a porphyrin ring or phthalocyanine ring as its backbone and has a portion thereof substituted with at least one electron-accepting group exhibits electron conductivity. The electron density at the center of the porphyrin ring or phthalocyanine ring of an organic compound molecule substituted with an electron-accepting group decreases, making it easier for the molecule to take in electrons due to external changes such as an electric field. As a result, negatively charged molecules are formed and are thought to exhibit electronic conductivity. Its volume resistivity was about 10 Ω·cm, which is almost the same as that of the above-mentioned one.

The organic thin film EL having the structure of ① to ② above is made using the materials constituting such a hole-conducting or electron-conducting organic thin film.
The device was manufactured. The efficiency of all of these organic thin film EL devices was improved by 2 to 5 times compared to conventional organic thin film EL devices.

In addition, a hole-conducting organic thin film layer consisting of an organic compound and an electron-accepting organic molecule with a porphyrin ring or phthalocyanine ring as the backbone, and a part of which is substituted with at least one electron donating group, or a hole-conducting organic thin film layer with a porphyrin ring or phthalocyanine ring as the backbone. The same effect can be obtained with an organic thin film EL element having the structure of (■) to (■) above, which uses an electron-conducting organic thin film layer consisting of an organic compound whose - part is substituted with at least one electron-accepting group and an electron-donating organic molecule. was recognized.

The skeleton is a porphyrin ring or a phthalocyanine ring,
As an electron donating group to partially substitute the alkoxy group,
Examples include aryl group, allyloxy group, alkylthio group, amino group, and methoxy group. Electron-accepting organic molecules mixed into this organic compound include fluoranyl, trinitrofluorene, tetracyanoquinodimethane (TCNQ), hexacyanobutadiene, and tetracyanoethylene (TCNQ).
E), methyltetracyanoquinodimethane, dimethyltetracyanoquinodimethane, and other organic compounds have quinones and aromatic rings attached with functional groups that easily absorb electrons, such as cyano groups and nitro groups.

On the other hand, examples of electron-accepting groups that have a porphyrin ring or phthalocyanine ring as a skeleton and substitute a part thereof include a cyano group, a nitro group, a pyridyl group, a quinolyl group, and a quinoxalyl group. Electron-donating organic molecules mixed into this organic compound include tetrathiofulvalene ('I'rF), tetrathiotetracene ('rr'r), perylene, paraphenylenediamine, and tetramethyltetraselenofulvalene (TMTSF). , phenothiazine, bis(ethylenedithio)tetrathiofulvalene, pentacene, etc. are organic compounds in which a functional group that easily releases electrons, such as an amino group, is attached to a polycyclic aromatic or aromatic ring.

As the efficiency is improved, less current is required to emit light than before, resulting in less Joule heat being generated.

As a result, the light emitting characteristics deteriorate due to element heat generation.

Shifts to the higher voltage side of the emission-applied voltage characteristics due to deterioration of the electrode-charge injection interface were also reduced.

The present invention will be explained in detail below with reference to Examples.

(Example 1) Tris(8-hydroxyquinoline) as an organic phosphor
Aluminum (Alq3) was used. As shown in FIG. 1, an ITO transparent electrode 2 is formed on a glass substrate 1, and then magnesium phthalocyanine and fluoranil are deposited at a evaporation rate ratio of 10:1 as an organic hole injection (organic hole conductive thin film) layer 3. 150 people died. Thereafter, 900 people formed the organic phosphor thin film 4. An organic thin film EL device is completed by forming 1,500 In back metal electrodes 5.

FIG. 2 shows the vacuum evaporation equipment used to manufacture the device. Second
As shown in the figure, the manufacturing apparatus used in this example evaporates organic substances from three evaporation sources 21, and the evaporation rate is detected by a crystal oscillator 22. Before film formation, vacuum gauge 2
When the degree of vacuum was checked at 7, it was on the order of 10-7 Torr. Further, during film formation, the vacuum was on the order of 10 Torr. Although this manufacturing apparatus is capable of heating the substrate with a heater 26, the substrate was not particularly heated. The start and end of vapor deposition is performed by a shutter 24 located just in front of the substrate 23. When forming an organic hole conductive layer, evaporation source 2
Add magnesium phthalocyanine and fluoranil to Step 3 and heat and evaporate them at the same time.

When the luminescent properties of this element were measured in dry nitrogen, a luminescence of 300 cd/m was obtained when a DC voltage of about 8 V was applied. It can be seen that the luminance and efficiency are improved by 2 to 5 times compared to conventional elements. When this organic thin film EL element was subjected to an aging test at a current density of 0.5 mA/am, the luminance half-life was over 1000 hours. The reliability of this device is significantly improved compared to 100 to 300 hours for conventional devices.

In the present invention, similar effects can be obtained not only with tris(8-hydroxyquinoline)aluminum organic phosphors but also with other organic phosphors such as tetraphenylbutadiene, bis(8-hydroxyquinoline)magnesium, and stilbene derivatives. Furthermore, the transparent hole injection electrode is not limited to ITO, but may also be made of 5n203, ZnO:Al, Au, or the like.

Furthermore, a similar effect could be obtained by combining an organic compound having two or more types of porphyrin rings or phthalocyanine ring skeletons with an electron-accepting molecule.

(Examples 2 to 8) An organic compound having a porphyrin ring or phthalocyanine ring skeleton and an electron-accepting molecule were simultaneously supplied from separate evaporation sources using the apparatus shown in Fig. 2 to form a hole-conducting organic thin film layer ( Examples a to g in Table 1 were formed, and an organic thin film EL device was manufactured in the same manner as in Example 1.

Table 1 Pc in the margin below shows metal-free phthalocyanines. TPP represents tetraphenylporphyrin, and P represents porphyrin.

(Example 9) As shown in FIG. 3, an ITO transparent electrode 32 is formed on a glass substrate 31, and then an organic hole injection (organic hole conductive thin film) layer 33 is formed using magnesium phthalocyanine and fluoranyl in 10: At a deposition rate ratio of 1, 150 people were evaporated.

Thereafter, 900 organic phosphor (A1q3) thin films 34 were formed. As the electron injection layer 35, 300 layers of 3.4.9.10-perylenetetracarboxylic-bis-benzimidazole were formed. Finally, 1,500 Mg back metal electrodes 36 are formed to complete the organic thin film EL device.

When the luminescent properties of this element were measured in dry nitrogen, a luminescence of 300 cd/m was obtained when a DC voltage of about 8 V was applied. It can be seen that the luminance and efficiency are improved by 2 to 5 times compared to conventional elements. When this organic thin film EL element was subjected to an aging test at a current density of 0.5 mA/cm, the luminance half-life was over 1000 hours. The reliability of this device is significantly improved compared to 100 to 300 hours for conventional devices.

Note that the organic hole injection layer (first layer) used in Examples 2 to 8
Similar effects were observed even when ag) in the table were used as the hole injection layer in this example.

In addition to the electron injection layer materials used in this example, various perylene derivatives, 3-methylthiophene, α-bithiophene, α-tertiniel, chenothiophene, dichenothiophene, and 2,2-thienylvirol starting materials were also used. Any material with a low oxidation potential, such as polythiophene, could be used.

(Example 10) As shown in FIG. 4, an ITO transparent electrode 42 was formed on a glass substrate 41, and then an organic phosphor thin film 43 was formed over a 90°
Form 0 people. Subsequently, an electron injection layer (organic electron conductive thin film) 44 was formed using TeCo (p-CI) 5, 10, 15.
20-tetraphenylporphyrin (tetraph
1Co (p-CI
) and tetrathiotetracene (abbreviated as TPP) and tetrathiotetracene, the second
Using the apparatus shown in the figure, 300 people were formed at the same time at a deposition rate of 5:1. Finally, 1,500 back metal electrodes 45 having an atomic ratio of Mg and Ag of 10:1 are formed to complete the organic thin film EL device.

When the luminescent properties of this element were measured in dry nitrogen, a luminescence of 300 cd/m was obtained when a DC voltage of about 8 V was applied. Compared to conventional elements, luminance and efficiency are improved by 2 to 5 times. This organic thin film EL element has a current density of 0.5 m.
When an aging test was conducted under the condition of A/cm, the luminance half-life was over 1000 hours. 10 for conventional elements
0 to 300 hours, the reliability of this device is greatly improved.

(Examples 11 to 16) An electron-conductive organic thin film layer (h-m in Table 2) was formed by simultaneously supplying an organic compound having a porphyrin ring or phthalocyanine ring skeleton and an electron-donating organic molecule from separate evaporation sources. An organic thin film EL device was manufactured in the same manner as in Example 10.

Table 2'r(4-py)p represents tetra(4-pyridyl)porphyrin, T(6-Q) represents tetra(6-quinolyl)porphyrin, P represents porphyrin, and Pc represents phthalocyanine.

(Example 17) As shown in FIG. 3, after forming an ITO transparent electrode 32 on a glass substrate 31, magnesium phthalocyanine and fluoranyl were used as an organic hole injection (organic hole conductive thin film) layer 33. At a deposition rate ratio of 1, there were 150 deposition ports.

Thereafter, 900 organic phosphor (A1q3) thin films 34 were formed. 'r(4-py)p and TT as the electron injection layer 35
An electronically conductive organic thin film made of F at a ratio of 5:l,
300 people were formed. Finally, attach the Mg back metal electrode 36 to 1
After 500 people formed, the organic thin film EL device was completed.

When the luminescent properties of this element were measured in dry nitrogen, a luminescence of 300 cd/m was obtained when a DC voltage of about 8 V was applied. It can be seen that the luminance and efficiency are improved by 2 to 5 times compared to conventional elements. When this organic thin film EL element was subjected to an aging test at a current density of 0.5 mA/cm, the luminance half-life was over 1000 hours. The reliability of this device is significantly improved compared to 100 to 300 hours for conventional devices.

In addition, magnesium phthalocyanine and fluoranyl are used as hole conductive organic thin films and electron conductive organic thin films.
Similar effects were also obtained by using a-b in Table 1 and hm shown in Table 2 instead of T(4-Py)P and TTF.

(Example 18) In Example 17, hole injection (organic hole conductive thin film)
An organic thin film EL device was manufactured using an organic molecule such as triphenyldiamine or a polymer such as polycarbazole as the layer 33. The characteristics are the same as those of the device of Example 17, and the reliability of the light emitting characteristics is greatly improved compared to the conventional device.

(Example 19) As shown in FIG.
The first hole injection layer is 0 and N, N, N', N
A hole injection layer formed by laminating a second hole injection layer in which 20OA of ,-tetraphenyl-4,4-diaminobiphenyl was vapor-deposited was used, and then 900 organic phosphor (Alq3) thin films 34 were formed.

When the luminescent properties of this element were measured in dry nitrogen, a luminescence of 300 cd/m was obtained when a DC voltage of about 6.5 V was applied. Compared to conventional elements, luminance and efficiency are improved by about five times. This organic thin film EL element has a current density of 0.5
When an aging test was conducted under the condition of mA/cm, the luminance half-life time was more than 1000 hours. The reliability of this device is significantly improved compared to 100 to 300 hours for conventional devices.

A similar effect could be obtained by appropriately combining the materials shown in Table 1 to form two or more hole entry layers.

(Effects of the Invention) As explained above, the present invention was able to significantly improve the light emission characteristics and reliability.

As described above, the present invention makes it possible to raise the organic thin film EL device to a practical level, and the industrial scale of FIG. 1 shows the cross-sectional structure of the organic thin film EL device used in Examples 1 to 8 of the present invention. FIG. 2 shows an apparatus for manufacturing an organic thin film EL device used in the present invention. FIG. 3 is an embodiment of the present invention 9.17.18
The cross-sectional structure of the organic thin film EL device used in this figure is shown. FIG. 4 shows the cross-sectional structure of the organic thin film EL device used in Examples 10 to 16 of the present invention. FIG. 5 shows a cross-sectional structure of an organic thin film EL device used in Example 19 of the present invention.

1, 31.41.51...Glass substrate, 2.32.4
2.52...Transparent electrode, 3', 33...Hole injection layer, 4.34.43.54...Organic phosphor thin film, 35.
44... Electron injection layer, 5.36.45.55... Metal electrode, 53... First hole injection layer, 53'... Second hole injection layer, 21... Vapor deposition source, 22... Crystal resonator, 23... Substrate, 24... Shutter, 26...
...Heater, 27...Vacuum gauge.

Claims (1)

[Claims] 1) An organic phosphor thin film layer between a pair of electrodes, at least one of which is transparent, and an organic phosphor having a porphyrin ring or phthalocyanine ring skeleton in contact with at least one surface of the organic phosphor thin film layer. A hole-conducting organic thin film layer in which at least one electron-accepting organic molecule is added to a compound, or an electron-conducting organic thin film layer in which at least one electron-donating organic molecule is added to the organic compound. An organic thin film EL device featuring 2) An organic phosphor thin film layer is placed between a pair of electrodes, at least one of which is transparent, and a part of the porphyrin ring or phthalocyanine ring skeleton is in contact with at least one surface of the organic phosphor thin film layer, and at least one electron An organic thin film EL device characterized by stacking organic compounds substituted with a donating group or an electron accepting group. 3) An organic phosphor thin film layer is placed between a pair of electrodes, at least one of which is transparent, and a part of the porphyrin ring or phthalocyanine ring skeleton is in contact with at least one surface of the organic phosphor thin film layer, and at least one electron A hole-conducting organic thin film layer made by adding at least one electron-accepting organic molecule to an organic compound substituted with a donor group, or an organic compound in which a part of the porphyrin ring or phthalocyanine ring skeleton is substituted with at least one electron-accepting group. An organic thin film EL device characterized by laminating an electron conductive organic thin film layer in which at least one electron donating organic molecule is added to a compound. 4) Organic compounds having a porphyrin ring or phthalocyanine ring skeleton, organic compounds in which a part of the porphyrin ring or phthalocyanine ring skeleton is substituted with at least one electron-donating group or electron-accepting group, and electron-accepting organic molecules or electron-donating A method for manufacturing an organic thin film EL device, characterized in that organic molecules are simultaneously supplied in vacuum from separate evaporation sources to form a hole conductive organic thin film layer or an electron conductive organic thin film layer.