JP3189480B2 - Organic thin film light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated structure of an organic thin-film light emitting device, and more particularly to a laminated structure of an organic thin-film layer and a translucent positive electrode.

[0002]

2. Description of the Related Art With the rapid increase in demand for flat displays that can replace conventional cathode ray tubes, various display elements are being developed and put into practical use. Electroluminescent elements (electroluminescent elements) are also in line with such needs, and are particularly attracting attention as all-solid-state spontaneous light-emitting elements due to high resolution and high visibility not found in other displays. At present, practically used materials include Z
This is an electroluminescent element made of an inorganic material using an nS / Mn system. However, this type of inorganic electroluminescent element has a problem that the driving voltage required for light emission is as high as 100 V or more, so that the driving method is complicated and the manufacturing cost is high. Also,
Since the efficiency of blue light emission is low, full colorization is difficult. On the other hand, a thin-film electroluminescent device using an organic material (hereinafter referred to as an organic thin-film light-emitting device) can drastically reduce the driving voltage required for light emission, and can be made full-color by applying various light-emitting materials. Research has become active in recent years because it has a sufficient amount of data.

In particular, the electrode / hole injection layer / light emitting layer / electrode
In the laminated type consisting of tris (8-hydroxy
Shiquinoline) aluminum was added to the hole injecting agent as 1,1-bi
(4-N, N-ditolylaminophenyl) cyclohexyl
By using sun, 10
00 cd / m^TwoThere was no report that the above brightness was obtained.
Since then, development has been spurred (Appl. Phys. Lett.Five
1, 913, (1987)).

FIG. 5 is a sectional view showing a conventional organic thin film light emitting device. On the insulating substrate 1, a translucent positive electrode 7, a hole injection layer 5, a light emitting layer 4, an electron injection layer 3, and a metal negative electrode 2 are laminated. 8 is a power supply. The hole injection layer 5, the light emitting layer 4, and the electron injection layer 3 are formed using an organic substance. The translucent positive electrode 7 is formed using indium tin oxide ITO, zinc oxide, or the like.

As the metal negative electrode 2, a metal, an alloy, or a laminate having a small work function is used.

[0006]

However, in the above-mentioned conventional organic thin-film light emitting device, the organic layer formed on the indium tin oxide ITO cathode on the insulating substrate has poor film smoothness due to poor surface smoothness. There has been a problem that the light emission stability and the light emission efficiency of the organic thin film light emitting element are impaired due to the reduction and the disturbance of the interface. In addition, there has been a problem in that the negative electrode is exposed to the environment, causing oxidation and peeling, which causes non-light emitting defects such as dark spots.

FIG. 6 is a sectional view showing a different conventional organic thin film light emitting device. This is the reverse of the stacking order of the above-mentioned conventional organic thin film light emitting device. In the organic thin-film light-emitting device having such a configuration, the metal negative electrode on the insulating support 1 has good surface smoothness, so that the film quality of the organic thin-film layer on the metal negative electrode is good. Further, the metal negative electrode is protected by the organic thin film layer, thereby eliminating unstable factors such as oxidation and peeling. The light-transmitting positive electrode in the uppermost layer is an oxide, and has high environmental resistance.

However, in such an organic thin-film light emitting device having an inverted structure, a high energy is applied to the organic thin-film layer when forming the light-transmitting positive electrode, so that the organic thin-film layer agglomerates or crystallizes. There has been a problem that the film thickness of the layer becomes non-uniform, the quality of the film is deteriorated, the electric field distribution is unbalanced, and light emission defects occur. Further, there is a problem that the imbalance of the electric field distribution causes local heat generation, which causes the translucent positive electrode to be separated from the organic thin film layer.

An object of the present invention is to provide an organic thin film light emitting device having an organic light emitting device having an inverted structure, which prevents deterioration of the quality of an organic thin film layer and has excellent light emission stability. .

[0010]

According to the present invention, there is provided an electroluminescent device using an organic thin film, comprising:
An insulating support, (2) a metal negative electrode, (3) an organic thin film layer, (4) a metal thin film layer, and (5) a translucent positive electrode, wherein the insulating support is a support of the device. The organic thin film layer comprises at least a light emitting layer of a light emitting layer and a charge injection layer, the metal negative electrode and the translucent positive electrode apply an electric field to the organic thin film layer to make the light emitting layer glow, and the metal thin film layer is a light emitting layer The light from the substrate is transmitted to the light-transmitting positive electrode, and the metal negative electrode, the organic thin film layer, the metal thin film layer, and the light-transmitting positive electrode are sequentially laminated on the insulating support. Is achieved by

[0011]

The high energy applied during the formation of the translucent positive electrode is absorbed and dispersed in the metal thin film layer. Therefore, crystallization of the organic thin film layer is prevented.

[0012]

FIG. 1 is a sectional view showing an organic thin-film light emitting device according to an embodiment of the present invention. FIG. 2 is a sectional view showing an organic thin-film light emitting device according to another embodiment of the present invention. FIG. 3 is a sectional view showing an organic thin-film light-emitting device according to still another embodiment of the present invention.

FIG. 4 is a sectional view showing an organic thin-film light emitting device according to still another embodiment of the present invention. 1 is an insulating substrate, 2 is a metal negative electrode, 3 is an electron injection layer, 4 is a light emitting layer, 5 is a hole injection layer, 6 is a metal thin film layer, 7 is a translucent positive electrode, and 8 is a power supply. The insulating substrate 1 is made of glass, resin, or the like as a support for the element. The translucent positive electrode 7 needs to be capable of efficiently injecting holes, having low resistance, being transparent at the maximum wavelength of light emission, and having high environmental stability. As the translucent positive electrode, a transparent conductive film such as indium tin oxide (ITO) or tin oxide (SnO ₂ ) is used. The film is formed by resistance heating evaporation, electron beam evaporation, or sputtering. The translucent positive electrode 7 is
In order to impart transparency, the thickness is desirably 10 to 500 nm.

The metal thin film layer 6 is formed on the light emitting layer 4 or the hole injection layer 5 by resistance heating evaporation, electron beam evaporation, or sputtering. Platinum, gold, silver, nickel, copper, and alloys or laminates thereof are used as materials for the metal thin film layer 6 from the viewpoints of hole injecting property, adhesion to the hole injecting layer 5 or the light emitting layer 4 serving as a base, and the like. Is appropriate. It is desirable that the transmittance of the metal thin film layer with respect to the maximum wavelength of light emission exceeds 80%.

The hole injection layer 5 needs to transport and inject holes efficiently, and it is desirable that the hole injection layer 5 is as transparent as possible in the maximum wavelength region of emitted light. As a film forming method, there are spin coating, casting, LB method, resistance heating evaporation, electron beam evaporation, etc., but resistance heating evaporation is common. The film thickness is 10 to 500 nm, preferably 10 to 100 nm. As the hole injecting substance, at least one of the organic substances represented by the chemical formulas (I-1) to (I-7) or derivatives thereof is used as a component. Representative hole injecting materials are shown below.

[0016]

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The light emitting layer 4 emits light efficiently by recombination of holes injected from the hole injection layer or the translucent positive electrode and electrons injected from the metal negative electrode or the electron injection layer. The film formation method includes spin coating, casting, LB method, resistance heating evaporation, electron beam evaporation, molecular beam epitaxy, etc., but resistance heating evaporation and molecular beam epitaxy are preferred. The film thickness is 1
0 to 500 nm, preferably 10 to 100 nm
nm. As the light-emitting substance, at least one kind of an organic substance represented by the chemical formulas (II-1) to (II-5) or a derivative thereof is used.

[0018]

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The metal anode 2 needs to efficiently inject electrons into the organic layer. As a film forming method, resistance heating evaporation, electron beam evaporation, and sputtering are used. As a material for a metal anode, Mg, Ag, I having a small work function is used.
n, Ca, Al, etc., and their alloys and laminates are used. The electron injection layer 3 needs to transport and inject electrons efficiently, and it is desirable that the electron injection layer 3 is as transparent as possible in the emission maximum wavelength region of emitted light. As a film forming method, there are spin coating, casting, LB method, resistance heating evaporation, electron beam evaporation, etc., but resistance heating evaporation is common. The film thickness is 5 to 500 nm, preferably l
0-100 nm. As the electron injection layer material, at least one of the organic substances represented by the chemical formulas (III-1) to (III-3) or derivatives thereof is used. Representative electron injection layer qualities are shown below.

[0020]

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Example 1 A 1.1 m thick MgIn metal negative electrode having a thickness of about 100 nm was provided.
As shown in FIG. 1, a light emitting layer 4 and a hole injection layer 5 were sequentially formed on a m glass substrate. The light emitting layer has the above chemical formula (II-
Using the luminescent material shown in 1), the resistance heating evaporation method
A film was formed to a thickness of 0 nm. The hole injection layer 5 has the chemical formula (I −
Using the compound shown in 1), 50
The film was formed to have a thickness of nm. Platinum, gold, silver or copper was formed as the metal thin film layer 6 to a thickness of 10 nm by an electron beam evaporation method. The above film formation method was performed while maintaining the degree of vacuum of 1 to 5 × 10 ⁻⁵ Pa. Finally, indium tin oxide ITO was formed as a light-transmitting positive electrode to a thickness of 100 nm by electron beam evaporation under an oxygen gas. Comparative Example 1 An organic thin-film light-emitting device was prepared in the same manner as in Example 1, except that the metal thin-film layer was not provided and the stacking order was reversed. Comparative Example 2 An organic thin-film light-emitting device was prepared in the same manner as in Example 1, except that no metal thin-film layer was provided.

The organic thin film light emitting device prepared as described above was continuously driven by applying a DC voltage. The drive voltage was adjusted so that the initial luminance was 200 cd / m ² . As a measure of light emission stability, the time required for the light emission luminance of the element to become 1/2 of the initial value was defined as the luminance half life. The presence or absence of a light emission defect was measured at the initial stage and after 1000 hours. The results are shown in Table 1.

[0023]

[Table 1] Luminescence defects are observed with the naked eye. The luminance is measured using a measuring device. The luminance half life and the light emission defect do not always match. By using platinum or gold for the metal thin film layer, the luminance half-life was increased 31 times at the maximum. No light emission defect is detected even after continuous driving for 1000 hours. Example 2 A thickness of 1.1 m provided with a MgIn metal negative electrode having a thickness of about 100 nm
The light emitting layer 4 was formed on the m glass substrate as shown in FIG. The light-emitting layer was formed to a thickness of 70 nm using a light-emitting substance represented by the above chemical formula (II-1) by a resistance heating evaporation method. Platinum, gold, silver or copper was deposited as the metal thin film layer 6 to a thickness of 10 nm by an electron beam evaporation method. The above film formation method was performed while maintaining the degree of vacuum of 1 to 5 × 10 ⁻⁵ Pa. Finally, indium tin oxide ITO was formed as a light-transmissive positive electrode 7 to a thickness of 100 nm by an electron beam evaporation method under an oxygen gas. Comparative Example 3 An organic thin-film light-emitting device was produced in the same manner as in Example 2, except that there was no metal thin-film layer and the order of lamination was reversed. Comparative Example 4 An organic thin-film light-emitting device was prepared in the same manner as in Example 2, except that there was no metal thin-film layer.

The organic thin-film light-emitting device prepared as described above was continuously driven by applying a DC voltage. The drive voltage was adjusted so that the initial luminance was 200 cd / m ² . As a measure of light emission stability, the time required for the light emission luminance of the element to become 1/2 of the initial value was defined as the luminance half life. The presence or absence of a light emission defect was measured at the initial stage and after 1000 hours. The results are shown in Table 2.

[0025]

[Table 2] By using platinum or gold for the metal thin film layer, the luminance half time was increased 34 times at the maximum. No light emission defect is detected even after continuous driving for 1000 hours. Example 3 1.1 m thick provided with a MgIn metal negative electrode having a thickness of about 100 nm
m on a glass substrate as shown in FIG.
The light emitting layer 4 was formed. The electron injection layer 3 has the chemical formula (III-
50 nm by resistance heating evaporation using the compound shown in 1)
Was formed to a thickness of The light emitting layer 4 has the above chemical formula (II-1)
70n by resistance heating evaporation using the luminescent material shown in
The film was formed to a thickness of m. Platinum, gold, silver or copper was deposited as the metal thin film layer 6 to a thickness of 10 nm by electron beam evaporation. The above film formation method was performed while maintaining the degree of vacuum of 1 to 5 × 10 ⁻⁵ Pa. Finally, indium tin oxide ITO was used as a translucent positive electrode 7 by electron beam evaporation under oxygen gas.
0 nm was formed. Comparative Example 5 An organic thin-film light-emitting device was prepared in the same manner as in Example 3, except that there was no metal thin-film layer and the order of lamination was reversed. Comparative Example 6 An organic thin-film light-emitting device was prepared in the same manner as in Example 3, except that there was no metal thin-film layer.

The organic thin film light emitting device prepared as described above was continuously driven by applying a DC voltage. The drive voltage was adjusted so that the initial luminance was 200 cd / m ² . As a measure of light emission stability, the time required for the light emission luminance of the element to become 1/2 of the initial value was defined as the luminance half life. The presence or absence of a light emission defect was measured at the initial stage and after 1000 hours. The results are shown in Table 3.

[0027]

[Table 3] By using platinum or gold for the metal thin film layer, the luminance half-life was increased 30 times at the maximum. No light emission defect is detected even after continuous driving for 1000 hours. Example 4 1.1 m thick provided with a MgIn metal negative electrode having a thickness of about 100 nm
m on a glass substrate as shown in FIG.
The light emitting layer 4 and the hole injection layer 5 were formed. The electron injection layer 3 was formed to a thickness of 50 nm using a compound represented by the chemical formula (III-1) by a resistance heating evaporation method. The light-emitting layer 4 was formed to a thickness of 70 nm using a light-emitting substance represented by the above chemical formula (II-1) by a resistance heating evaporation method. The hole injection layer 5 was formed using a compound represented by the chemical formula (I-1) to a thickness of 50 nm by a resistance heating evaporation method. Platinum as the metal thin film layer 6,
Gold, silver or copper was deposited to a thickness of 10 nm by electron beam evaporation. The above film formation method was performed while maintaining the degree of vacuum of 1 to 5 × 10 ⁻⁵ Pa. Finally, a 100 nm indium tin oxide ITO film was formed as a light-transmissive positive electrode 7 by an electron beam evaporation method under an oxygen gas. Comparative Example 8 An organic thin film light emitting device was prepared in the same manner as in Example 4, except that the metal thin film layer was not provided and the order of lamination was reversed. Comparative Example 7 An organic thin-film light-emitting device was prepared in the same manner as in Example 4, except that no metal thin-film layer was provided.

The organic thin-film light emitting device prepared as described above was continuously driven by applying a DC voltage. The drive voltage was adjusted so that the initial luminance was 200 cd / m ² . As a measure of light emission stability, the time required for the light emission luminance of the element to become 1/2 of the initial value was defined as the luminance half life. The presence or absence of a light emission defect was measured at the initial stage and after 1000 hours. The results are shown in Table 4.

[0029]

[Table 4] By using platinum or gold for the metal thin film layer, the luminance half time was increased 27 times at the maximum. No light emission defect is detected even after continuous driving for 1000 hours.

[0030]

According to the present invention, there is provided an electroluminescent device using an organic thin film, comprising (1) an insulating support, (2) a metal negative electrode, (3) an organic thin film layer, and (4) a metal thin film. Layers and
(5) a light-transmitting positive electrode, wherein the insulating support is a support of the device, the organic thin-film layer comprises at least a light-emitting layer of a light-emitting layer and a charge injection layer, and a metal negative electrode and a light-transmitting positive electrode Applies an electric field to the organic thin-film layer to illuminate the light-emitting layer, the metal thin-film layer transmits light from the light-emitting layer and guides the light-transmitting positive electrode, and a metal negative electrode and an organic thin-film layer are placed on an insulating support. Since the metal thin film layer and the light-transmitting positive electrode are sequentially laminated, high energy applied during the formation of the light-transmitting positive electrode is absorbed and dispersed in the metal thin film layer. As a result, deterioration of the film quality of the organic thin film layer is prevented, the occurrence of light emission defects is prevented, and an organic thin film light emitting device having excellent light emission stability is obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an organic thin-film light emitting device according to an embodiment of the present invention.

FIG. 2 is a sectional view showing an organic thin-film light emitting device according to another embodiment of the present invention.

FIG. 3 is a sectional view showing an organic thin-film light-emitting device according to still another embodiment of the present invention.

FIG. 4 is a sectional view showing an organic thin-film light-emitting device according to still another embodiment of the present invention.

FIG. 5 is a sectional view showing a conventional organic thin film light emitting device.

FIG. 6 is a cross-sectional view showing a different conventional organic thin film light emitting device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Metal negative electrode 3 Electron injection layer 4 Light emitting layer 5 Hole injection layer 6 Metal thin film layer 7 Translucent positive electrode 8 Power supply

Continuation of the front page (56) References JP-A-4-363896 (JP, A) JP-A-6-93256 (JP, A) JP-A-4-254887 (JP, A) JP-A-2-253593 (JP) , A) JP-A-6-5365 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 33/00-33/28

Claims (6)

(57) [Claims] 1. An electroluminescent device using an organic thin film, comprising: (1) an insulating support; (2) a metal negative electrode; (3) an organic thin film layer; (4) a metal thin film layer; A) a light-transmissive positive electrode, wherein the insulating support is a support of the device, the organic thin film layer comprises at least a light-emitting layer of a light-emitting layer and a charge injection layer, and the metal negative electrode and the light-transmissive positive electrode are organic. An electric field is applied to the thin film layer to illuminate the light emitting layer. The metal thin film layer transmits light from the light emitting layer and guides the light to the light-transmitting positive electrode. On the insulating support, a metal negative electrode, an organic thin film layer, An organic thin-film light-emitting element comprising a metal thin-film layer and a light-transmitting positive electrode which are sequentially stacked. 2. The organic thin film light emitting device according to claim 1, wherein the charge injection layer is a hole injection layer and is provided between the metal thin film layer and the light emitting layer. 3. The organic thin-film light-emitting device according to claim 1, wherein the charge injection layer is an electron injection layer and is provided between the metal negative electrode and the light-emitting layer. 4. The organic thin film light emitting device according to claim 1, wherein the charge injection layer is a hole injection layer and an electron injection layer, wherein the hole injection layer is between the metal thin film layer and the light emitting layer, and the electron injection layer. Is an organic thin-film light-emitting device provided between the metal negative electrode and the light-emitting layer. 5. The organic thin-film light-emitting device according to claim 1, wherein the metal thin-film layer is made of platinum or gold. 6. The organic thin-film light-emitting device according to claim 1, wherein the metal thin-film layer is a laminate of different metals.