JPH0693256A - Organic thin-film luminescent element - Google Patents

Abstract

PURPOSE:To obtain an element having excellent surface-smoothness of positive electrode and exhibiting excellent luminescence stability and efficiency by successively applying a transparent laminate composed of successively laminated positive electrode and thin metallic layer, a luminescent layer and a negative electrode on an insulating substrate. CONSTITUTION:The element is produced by successively laminating a positive electrode 2 consisting of indium tin oxide and a thin metallic layer 3 consisting of platinum on an insulating substrate 1 and laminating the obtained transparent laminate with a hole-injection layer 4 consisting of the compounds of formula I, formula II, etc., a luminescent layer 5 consisting of an organic substance of formula III, formula IV, etc., an electron-injection layer 6 consisting of a compound of formula V, formula VI, etc., and a negative electrode 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode of an organic thin film light emitting device, and more particularly to an organic thin film light emitting device which has good positive electrode surface smoothness and excellent light emission stability and light emission efficiency.

[0002]

2. Description of the Related Art With the rapid increase in demand for flat displays replacing conventional cathode ray tubes, various display elements have been vigorously developed and put into practical use. An electroluminescence element (hereinafter referred to as an EL element) is also adapted to such a need, and in particular, as an all solid state spontaneous light emitting element,
It attracts attention due to its high resolution and high visibility that other displays do not have. At present, what has been put into practical use is an EL element made of an inorganic material using a ZnS / Mn system in the light emitting layer. However, this type of inorganic EL element has a problem that the driving method is complicated and the manufacturing cost is high because the driving voltage required for light emission is as high as 100 V or more. Also,
Since the efficiency of blue light emission is low, full colorization is difficult. On the other hand, a thin film light emitting device using an organic material is
Since the driving voltage required for light emission can be significantly reduced and the potential for full color conversion can be sufficiently obtained by applying various light emitting materials, research has been actively conducted in recent years.

In particular, in the laminated type composed of electrode / hole injection layer / light emitting layer / electrode, tris (8-hydroxyquinoline) aluminum is used as the light emitting agent and 1,1′-is used as the hole injection agent.
By using bis (4-N, N-ditriaminophenyl) cyclohexane, an applied voltage of 10 V or less
The development was spurred since it was reported that a brightness of more than 00 cd / cm ² was obtained (Appl.Phys.Lett.
51 , 913, (1987)).

FIG. 5 is a sectional view showing an example of a conventional organic thin film light emitting device. The positive electrode 2, the hole injection layer 4, the light emitting layer 5, and the negative electrode 7 are sequentially stacked on the insulating substrate 1. The hole injection layer and the light emitting layer are formed using an organic material.

[0005]

However, in the conventional organic thin film light emitting device, since the surface smoothness of the positive electrode on the insulating transparent substrate is poor, deterioration of the film quality and disorder of the interface are caused in the organic layer formed on the positive electrode. However, there is a problem in that the light emission stability and the light emission efficiency of the organic thin film light emitting device are deteriorated.

The present invention has been made in view of the above points, and an object thereof is to provide an organic thin film light emitting device which is excellent in light emission stability and light emission efficiency by improving the surface smoothness of a positive electrode.

[0007]

According to the present invention, the above-mentioned object has a transparent laminate, a light emitting layer, and a negative electrode, and the transparent laminate has a positive electrode and a metal thin film layer on an insulating transparent substrate. The light emitting layer is formed by sequentially laminating, and the light emitting layer is sandwiched between the metal thin film layer and the negative electrode of the transparent laminated body, and the light emitting layer is an organic material film.

[0008]

[Function] By providing the metal thin film layer, the surface of the positive electrode is flattened, an organic layer having a uniform thickness is formed, and local concentration and crystallization of the electric field are suppressed. As a result, conductivity and light transmittance of the positive electrode are suppressed. The light emission stability and light emission efficiency of the organic thin film light emitting device are improved without affecting the above.

[0009]

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 another embodiment of the present invention.

FIG. 4 is a sectional view showing an organic thin film light emitting device according to another embodiment of the present invention. 1 is an insulating substrate, 2 is a positive electrode, 3 is a metal thin film layer, 4 is a hole injection layer, 5 is a light emitting layer, 6 is an electron injection layer, 7 is a negative electrode, and 8 is a power supply.
The insulating substrate 1 is a support for the element and is made of a transparent material such as glass or resin. The positive electrode 2 is indium tin oxide (IT
O), tin oxide (SnO ₂ ), etc., and conductive heating polymers such as polypyrrole and resistance heating vapor deposition, electron beam
It is formed by vapor deposition, sputtering, electrolytic polymerization, or chemical polymerization. The positive electrode 2 has 5% in order to have transparency.
It is desirable to set the thickness to 0 to 300 nm.

The metal thin film layer 3 is formed on the positive electrode 2 by resistance heating vapor deposition,
It is formed by electron beam evaporation and sputtering. As the material of the metal thin film layer 3, platinum, gold, silver, nickel, copper and alloys containing these are suitable from the viewpoint of hole injection properties and adhesion to the positive electrode. The thickness of the metal thin film layer is equal to or more than the average surface roughness of the positive electrode 2, and the transmittance of the emission center wavelength is 80%.
It is desirable to be able to maintain above.

The hole injection layer 4 is required to efficiently transport and inject holes, and it is desirable that the hole injection layer 4 be as transparent as possible in the emission maximum wavelength region of the emitted light. The film forming method includes spin coating, casting, LB method, resistance heating evaporation, electron beam evaporation and the like, but resistance heating evaporation is common. The film thickness is 200 to 5000Å, preferably 300 to 800Å. As the hole injecting substance, at least one kind of the organic substances represented by the chemical formulas (I-1) to (I-7) or the derivatives thereof is used as a component. Representative hole injecting materials are shown below.

[0013]

[Chemical 1]

The light emitting layer 5 efficiently emits light by recombination of holes injected from the hole injection layer or the positive electrode and electrons injected from the negative electrode or the electron injection layer. The film forming method includes spin coating, casting, LB method, resistance heating evaporation, electron beam evaporation, molecular beam epitaxy and the like, but resistance heating evaporation and molecular beam epitaxy are preferable. The film thickness is 200 to 5000Å, preferably 300 to 800Å. The luminescent substance contains at least one kind of the organic substances represented by the chemical formulas (II-1) to (II-5) or the derivatives thereof.

[0015]

[Chemical 2]

It is desirable for the electron injection layer 6 to efficiently inject electrons into the light emitting layer. The film forming method is spin coating, casting, LB method, resistance heating vapor deposition, electron beam vapor deposition,
Although there are molecular beam epitaxy and the like, resistance heating vapor deposition and molecular beam epitaxy are common. Film thickness is 200 to 5000Å
However, it is preferably 300 to 800Å. As the electron injecting substance, the chemical formula (III -1) to the chemical formula (III
-3) At least one kind of the organic substances or their derivatives is used as a component.

[0017]

[Chemical 3]

The negative electrode 7 efficiently injects electrons into the organic layer.
It is necessary. Resistance heating vapor deposition and electric
Sub-beam evaporation and sputtering methods are used. Material for negative electrode 7
As for, Mg, Ag, In, Ca, which have a small work function,
Al and the like, alloys of these and laminated bodies are used. Example 1 A 1.1 mm thick glass provided with ITO having a film thickness of about 1000 Å
As shown in Fig. 1, platinum, gold, silver or copper on the lath substrate
Was deposited to a thickness of 10 nm by an electron beam evaporation method. Next hole
The injection layer is formed by using the substance represented by the chemical formula (I-1).
It was The light emitting layer is formed by using the substance represented by the chemical formula (II-1).
Filmed Mg-Sc alloy (9: 1 weight ratio as negative electrode)
Was prepared by the electron beam evaporation method. The above film formation
1-5 × 10 ^-FiveThe vacuum was maintained at Pa.

A DC voltage was applied to the obtained organic thin film light emitting device to continuously drive it. Voltage has an initial brightness of 200 cd / m
Adjusted to be ² . The continuous emission time until the initial luminous efficiency and the luminance become 1/2 of the initial luminance was defined as the luminance half life. The results are shown in Table 1. 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.

[0020]

[Table 1] The organic thin film light emitting device of this example had an initial luminous efficiency of 3.7 times at maximum and a half-life of luminance of 5.9 times at most as compared with Comparative Example 1. Example 2 As shown in FIG. 2, platinum, gold, silver, or copper was deposited to a thickness of 10 nm on a 1.1 mm-thick glass substrate provided with ITO having a film thickness of about 1000 Å by an electron beam evaporation method. The light emitting layer was formed by using the substance represented by the chemical formula (II-1). A Mg—Sc alloy (weight ratio of 9: 1) was prepared as an anode by an electron beam evaporation method. The above film formation is 1 to 5 × 10 ⁻⁵ P
The vacuum degree of a was maintained.

A DC voltage was applied to the obtained organic thin film light emitting device to continuously drive it. Voltage has an initial brightness of 200 cd / m
Adjusted to be ² . The continuous emission time until the initial luminous efficiency and the luminance become 1/2 of the initial luminance was defined as the luminance half life. The results are shown in Table 2. Comparative Example 2 An organic thin film light emitting device was prepared in the same manner as in Example 2 except that the metal thin film layer was not provided.

[0022]

[Table 2] The organic thin-film light emitting device of this example had an initial luminous efficiency of up to 3.4 times and a luminance half life of up to 5.2 times compared to Comparative Example 2. Example 3 As shown in FIG. 3, platinum, gold, silver or copper was deposited to a thickness of 10 nm on a 1.1 mm-thick glass substrate provided with ITO having a film thickness of about 1000 Å by an electron beam evaporation method. The light emitting layer was formed by using the substance represented by the chemical formula (II-1). The electron injection layer was formed by using the substance represented by the chemical formula (III-1). A Mg—Sc alloy (weight ratio of 9: 1) was prepared as an anode by an electron beam evaporation method. The above film formation is 1 to 5
It was carried out while maintaining a vacuum degree of × 10 ^-5 Pa.

A DC voltage was applied to the obtained organic thin film light emitting device to continuously drive it. Voltage has an initial brightness of 200 cd / m
Adjusted to be ² . The continuous emission time until the initial luminous efficiency and the luminance become 1/2 of the initial luminance was defined as the luminance half life. Comparative Example 3 An organic thin film light emitting device was prepared in the same manner as in Example 3 except that the metal thin film layer was not provided.

The results are shown in Table 3.

[0025]

[Table 3] The organic thin film light emitting device of this example had an initial luminous efficiency of up to 1.6 times and a luminance half life of up to 3.0 times compared to Comparative Example 3. Example 4 As shown in FIG. 4, platinum, gold, silver or copper was deposited to a thickness of 10 nm on a 1.1 mm-thick glass substrate provided with ITO having a film thickness of about 1000 Å by an electron beam evaporation method. Next, the hole injection layer was formed using the substance represented by the chemical formula (I-1). The light emitting layer was formed by using the substance represented by the chemical formula (II-1). The electron injection layer was formed by using the substance represented by the chemical formula (III-1). A Mg—Sc alloy (weight ratio of 9: 1) was prepared as an anode by an electron beam evaporation method. The above film formation was performed while maintaining a vacuum degree of 1 to 5 × 10 ⁻⁵ Pa.

A DC voltage was applied to the obtained organic thin film light emitting device to continuously drive it. Voltage has an initial brightness of 200 cd / m
Adjusted to be ² . The continuous emission time until the initial luminous efficiency and the luminance become 1/2 of the initial luminance was defined as the luminance half life. Comparative Example 4 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.

The results are shown in Table 4.

[0028]

[Table 4] The organic thin-film light emitting device of this example had an initial emission efficiency of 3.5 times at maximum and a luminance half life of 4.3 times at most, as compared with Comparative Example 4.

[0029]

According to the present invention, it has a transparent laminate, a light emitting layer, and a negative electrode, and the transparent laminate is formed by sequentially laminating a positive electrode and a metal thin film layer on an insulating substrate. The light emitting layer is sandwiched between the metal thin film layer and the negative electrode, and the light emitting layer is assumed to be a film of an organic substance.Therefore, by providing the metal thin film layer, the surface of the positive electrode is flattened and the uniform film thickness The organic layer is formed to suppress local concentration of electric field and crystallization,
As a result, it is possible to obtain an organic thin film light emitting device having improved light emission stability and light emission efficiency without affecting the conductivity or light transmittance of the positive electrode.

[Brief description of 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 another embodiment of the present invention.

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

[Explanation of symbols]

 1 Insulating substrate 2 Positive electrode 3 Metal thin film layer 4 Hole injection layer 5 Light emitting layer 6 Electron injection layer 7 Negative electrode 8 Power supply

Claims (5)

[Claims] 1. A transparent laminated body, a light emitting layer, and a negative electrode, wherein the transparent laminated body is formed by sequentially laminating a positive electrode and a metal thin film layer on an insulating substrate, and a metal thin film layer of the transparent laminated body. An organic thin film light emitting device characterized in that a light emitting layer is sandwiched between negative electrodes, and the light emitting layer is a film of an organic substance. 2. The organic thin film light emitting device according to claim 1, wherein the positive electrode is made of indium tin oxide. 3. The organic thin film light emitting device according to claim 1, wherein the metal thin film layer is made of platinum. 4. The organic thin film light emitting device according to claim 1, wherein a hole injection layer is provided between the metal thin film layer and the light emitting layer. 5. The organic thin film light emitting device according to claim 1, wherein an electron injection layer is provided between the light emitting layer and the negative electrode.