JP3189438B2 - 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 an organic thin-film light-emitting device used as a light-emitting source of various display devices, and more particularly to a structure of an organic thin-film light-emitting device having excellent reliability.

[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. An electroluminescent element (hereinafter, referred to as an EL element) also meets this need, and in particular, as an all-solid spontaneous light emitting element,
It attracts attention due to its high resolution and high visibility not found in other displays. At present, an EL element made of an inorganic material using a ZnS / Mn-based material for the light-emitting layer is in practical use. However, this type of inorganic EL 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. In contrast, thin-film light-emitting devices using organic materials
In recent years, research has been actively conducted because the driving voltage required for light emission can be significantly reduced, and the application of various light-emitting materials has a sufficient possibility of full colorization.

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'-
Bis (4-N, N-ditriaminophenyl) cyclohex
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)).

[0004]

As described above, the thin-film light-emitting device using an organic material strongly suggests the possibility of low voltage driving and full colorization, but it must be solved in terms of performance. Many are left. In particular, the problem of characteristic deterioration due to long-time driving of about 10,000 hours is a problem that must be overcome. In addition, RGB in full color
Development of light-emitting materials that can emit light of three primary colors, and because the thickness of the organic layer is 1 μm or less, the film-forming properties are good, there are no electrical defects such as pinholes, and the ability to transport electrons and holes is improved. There is a development of an excellent organic material and a selection of an electrode material having an excellent charge injecting property into the organic layer.

Further, from the viewpoint of mass productivity, development of an inexpensive organic material which can be mass-produced and improvement of an element forming method are also important issues. Currently, research is focused on elucidation of the degradation mechanism, and from the examination of the atmosphere dependence during continuous driving, separation of the interface between the upper electrode and the organic film occurs due to moisture in the atmosphere, and it is speculated that this may cause deterioration, It has been learned that the reduction in current density during driving reduces the rate of deterioration, leading to an improvement in life.

The present invention has been made in view of the above points, and has as its object to develop an organic thin film which is excellent in reliability by developing an element structure which is hardly affected by moisture in the atmosphere and which can reduce the current density. It is to provide a light emitting element.

[0007]

According to the present invention, there is provided an insulating transparent substrate, an electrode, and a combination of a charge injection layer and a light emitting layer, wherein the combination is provided via an electrode. The electrodes are stacked in multiple stages on an insulating transparent substrate, and the electrodes are arranged such that positive electrodes and negative electrodes are alternately arranged via a combined body, and electrodes of the same polarity are electrically connected to each other on the insulating transparent substrate. The body is achieved by laminating the latter in such a way that the latter combines entirely with the former.

[0008]

Since the combination of the charge injection layer and the light emitting layer is stacked in multiple stages, the brightness of each stage can be reduced and the brightness of the combination of each stage can be integrated to increase the overall brightness. Therefore, it is possible to lower the voltage applied to the combined body of each stage and lower the current density of each stage for driving.

Further, since the former-stage combined body is entirely covered with the latter-stage combined body, the former-stage combined body does not diffuse water from the atmosphere, and thus can prevent the element from being deteriorated due to peeling of the electrode.

[0010]

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. 11,21,
31, 41 are insulating transparent substrates, 12, 18, 25, 3
6, 46, 52 are positive electrodes, 13, 17, 24, 26, 3
5, 37, 44, 47 and 51 are hole injection layers, and 14 and 1
6, 23, 27, 34, 38, 43, 48, 50 are light emitting layers, 15, 22, 28, 32, 42, 49, 300 are negative electrodes, 33, 39 are electron injection layers, 19, 29, 301, 4
Reference numeral 5 denotes a DC power supply.

As the insulating transparent substrate, glass, resin, or the like, which is a support for the element, is used. When a light emitting surface is used, a transparent material is used. The positive electrode is made of a semi-permeable film such as gold or nickel, or a transparent conductive film such as indium tin oxide (ITO) or tin oxide (SnO ₂ ), and is formed by resistance heating evaporation, electron beam evaporation, or sputtering. The thickness of the positive electrode is desirably 100 to 3000 ° in order to impart transparency.

The hole injection layer needs to transport and inject holes efficiently, and it is desirable that the hole injection layer be as transparent as possible in the maximum 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 between 100 and 2000 °, preferably between 200 and 800 °. As the hole injecting substance, a hydrazone compound, a pyrazoline compound, a stilbene compound, an amine compound or the like is used. Representative hole injecting materials are shown below.

[0014]

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The light emitting layer emits light efficiently 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 formation method includes spin coating, casting, LB method, resistance heating evaporation, electron beam evaporation, etc., but resistance heating evaporation is common. The film thickness is 100 to 2000 °, preferably 200 to 800 °. Representative luminescent materials are shown below.

[0016]

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It is desirable that the electron injection layer efficiently injects electrons into the light emitting layer. The film formation method includes spin coating, casting, LB method, resistance heating evaporation, electron beam evaporation, etc., but resistance heating evaporation is common. The film thickness is 100 to 2000 °, preferably 200 to 800 °. Oxadiazole derivatives,
A perylene derivative or the like is used. The following are representative electron injection materials.

[0018]

Embedded image

It is necessary for the negative electrode to efficiently inject electrons into the organic layer. As a film forming method, resistance heating evaporation, electron beam evaporation, and sputtering are used. Examples of the material for the negative electrode include Mg, Ag, In, Ca, Al, and the like, which have a small work function, alloys thereof, a laminate, zinc oxide to which Al is added, and the like. The zinc oxide to which Al has been added is preferably formed by electron beam evaporation and sputtering at a substrate temperature of 200 ° C. or lower, more preferably 100 ° C. or lower, with the Al addition in the range of 0.5 to 3%. 100 to 200 thickness
It is formed to a thickness of 0 °. The semi-permeable film of Al or the like is formed to a thickness of 300 to 800 ° by resistance heating evaporation. Embodiment 1 FIG. 1 is a sectional view showing an organic thin-film light emitting device according to an embodiment of the present invention. Positive electrode 1 made of ITO with a thickness of about 1000 Å
The glass substrate 11 provided with No. 2 was placed in a resistance heating evaporation apparatus, and a hole injection layer 13 and a light emitting layer 14 were sequentially formed. During the film formation, the internal pressure of the vacuum chamber was set to 8 × 10 ⁻⁴ Pa. The hole injecting layer 13 is made of the compound represented by the chemical formula (5-1) and has a boat temperature of 200 ° C. and a film forming rate of 2 ° / s.
形成 Formed to a thickness. Subsequently, the light emitting layer 14 is made of the compound represented by the chemical formula (6-1) and has a boat temperature of about 200.
The film was heated at a temperature of about 200.degree.

Thereafter, the substrate 11 is taken out of the vacuum chamber,
The sample was placed in a sputtering apparatus, and a sample in which an Al wire was placed on a zinc pellet was sputtered while flowing a mixed gas of Ar: O ₂ = 1: 1. It was formed to a thickness. The visible light transmittance of the Al-added zinc oxide transparent negative electrode 15 is about 85%. Next, remove the sample from the sputtering device,
Again placed in the resistance heating evaporation apparatus, using the same material as the light emitting layer 14 and the hole injection layer 13 and under the same conditions, the light emitting layer 16 and the hole injection layer 17 in the order of 500 mm thick. Formed. Finally, Ag was formed to a thickness of 1000 ° as the positive electrode 18. Comparative Example 1 An organic thin-film light emitting device was formed in the same manner as in Example 1 except that the light emitting layer 16, the hole injection layer 17, and the positive electrode 18 were not formed.

When a DC voltage was applied to both Example 1 and Comparative Example 1, uniform green (center wavelength: 550 nm) light emission was obtained. Voltage at a luminance of 100 cd / m ² ,
Table 1 shows the current density, luminous efficiency, and luminance half-life.

[0022]

[Table 1] In the present embodiment, since the combined body composed of the hole injection layer and the light emitting layer is stacked in two stages, the brightness borne by the single combined body can be low, and therefore a single combined body is required. Current density can be reduced, and the life of the organic thin film light emitting element as a whole can be improved. Further, the second-stage combined body entirely covers the first-stage combined body, so that the invasion of moisture into the first-stage combined body is prevented, and the reliability of the organic thin-film light emitting device is improved.

Since the voltage applied to the device can be reduced as compared with the one-stage device of the comparative example, the luminous efficiency is the same or slightly improved. Embodiment 2 FIG. 2 is a sectional view showing an organic thin-film light emitting device according to another embodiment of the present invention. A transparent negative electrode 22 made of Al-added zinc oxide was provided on a glass substrate 21 to a thickness of about 1000 °. Next, a light emitting layer 23 and a hole injection layer 24 were sequentially formed. The light emitting layer 23 and the hole injection layer 24 were formed under the same conditions as in Example 1.

The positive electrode 25 was made of Au and formed to a thickness of 700 ° using the same resistance heating evaporation apparatus. The light transmittance of this positive electrode is about 70%. Subsequently, a hole injection layer 26 and a light emitting layer 27 were sequentially formed in the same manner as described above. Finally, negative electrode 2
8 was formed to a thickness of 1000 ° by resistance heating evaporation using an alloy of Mg and Ag (Mg / Ag = 10: 1). Comparative Example 2 An organic thin-film light emitting device was formed in the same manner as in Example 2 except that the hole injection layer 26, the light emitting layer 27, and the negative electrode 28 were not formed.

When a DC voltage was applied to both Example 2 and Comparative Example 2, uniform green (center wavelength: 550 nm) light emission was obtained. Voltage at a luminance of 100 cd / m ² ,
Table 2 shows the current density, luminous efficiency, and luminance half-life.

[0026]

[Table 2] Embodiment 3 FIG. 3 is a sectional view showing an organic thin-film light emitting device according to still another embodiment of the present invention. A transparent negative electrode 32 made of Al-added zinc oxide is formed on a glass substrate 31 to a thickness of about 1000 Å.
Thickness. Next, an electron injection layer 33, a light emitting layer 34, and a hole injection layer 35 were sequentially formed. The electron injection layer was heated at a boat temperature of about 300 ° C. using the above-mentioned chemical formula (7-2) and formed to a thickness of 400 ° at a film forming rate of 2 ° / s. Light emitting layer 3
4 and the hole injection layer 35 were formed under the same conditions as in Example 1.

The cathode 36 was made of Au, and was formed to a thickness of 700 ° using the same resistance heating evaporation apparatus. The light transmittance of this positive electrode is about 70%. Subsequently, a hole injection layer 37, a light emitting layer 38, and an electron injection layer 39 were sequentially formed in the same manner as described above. Finally, the negative electrode 300 is made of an alloy of Mg and Ag (Mg / A
g = 10: 1) to a thickness of 1000 ° by resistance heating evaporation. Comparative Example 3 An organic thin-film light emitting device was formed in the same manner as in Example 3 except that the hole injection layer 37, the light emitting layer 38, and the negative electrode 300 were not formed.

When a DC voltage was applied to both Example 3 and Comparative Example 3, uniform green (center wavelength: 550 nm) light emission was obtained. Voltage at a luminance of 100 cd / m ² ,
Table 3 shows the current density, luminous efficiency, and luminance half-life.

[0029]

[Table 3] Embodiment 4 FIG. 4 is a sectional view showing an organic thin-film light emitting device according to a further different embodiment of the present invention. A transparent negative electrode 42 made of Al-added zinc oxide was formed on a glass substrate 41 to a thickness of about 1000 Å.
Thickness. Next, a light emitting layer 43 and a hole injection layer 44 were sequentially formed. The light emitting layer 43 and the hole injection layer 44 are the same as those of the first embodiment.
Created under the same conditions as

The positive electrode 46 was made of Au and formed to a thickness of 700 ° using the same resistance heating evaporation apparatus. The light transmittance of this positive electrode is about 70%. Subsequently, a hole injection layer 47, a light emitting layer 48, a negative electrode 49, a light emitting layer 50, and a hole injection layer 51 were formed in the same manner as described above. The positive electrode 52 was formed of Ag at 1000 °. In this element, three sets of a combined body of a hole injection layer and a light emitting layer are laminated. Comparative Example 4 Same as Comparative Example 2.

When a DC voltage was applied to both Example 4 and Comparative Example 4, uniform emission of green light (center wavelength: 550 nm) was obtained. Voltage at a luminance of 100 cd / m ² ,
Table 4 shows the current density, luminous efficiency, and luminance half-life.

[0032]

[Table 4]

[0033]

According to the present invention, there is provided an insulating transparent substrate, an electrode, and a combined body of a charge injection layer and a light emitting layer, and the combined body is stacked on the insulating transparent substrate in a multi-stage manner via the electrode. And
The electrodes are arranged such that the positive electrode and the negative electrode are alternately arranged via a combination, and the electrodes of the same polarity are electrically connected to each other on the insulating transparent substrate. Since the former-stage combined body is entirely covered, it is possible to lower the luminance of each stage of the combined body of the charge injection layer / light-emitting layer and to increase the luminance of the whole device by integrating the luminance of the combined body of each stage. it can. Accordingly, an organic thin-film light-emitting device having excellent reliability can be obtained, which can be driven by lowering the voltage applied to the combined body of each stage and reducing the current density of each stage.

Further, in the laminate of the organic thin-film light-emitting element, the former stage is entirely covered with the latter stage, so that the former stage does not diffuse moisture from the atmosphere and the electrodes are separated. An organic thin-film light-emitting device which can prevent deterioration and has excellent reliability can be 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.

[Description of Signs] 11, 21, 31, 41 Insulating transparent substrate 12, 18, 25, 36, 46, 52 Positive electrode 13, 17, 24, 26, 35, 37, 44, 47, 5
1 hole injection layer 14, 16, 23, 27, 34, 38, 43, 48, 5
0 light emitting layer 15, 22, 28, 32, 42, 49, 300 negative electrode 33, 39 electron injection layer 19, 29, 301, 45 DC power supply

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H05B 33/00-33/28

Claims (5)

(57) [Claims] 1. An insulating transparent substrate, an electrode, a charge injection layer,
A combination of light-emitting layers, wherein the combination is stacked in multiple layers on an insulating transparent substrate via an electrode, and the electrodes have the same polarity with positive electrodes and negative electrodes being alternately arranged via the combination The electrodes are electrically connected to each other on an insulative transparent substrate, and the combined body is formed by laminating the combined body in the subsequent stage so as to entirely cover the combined body in the preceding stage. . 2. The organic thin film light emitting device according to claim 1, wherein the combination of the charge injection layer and the light emitting layer is a hole injection layer and a light emitting layer. 3. The organic thin-film light-emitting device according to claim 1, wherein the combined charge injection layer / light-emitting layer is a light-emitting layer sandwiched between a hole injection layer, an electron injection layer and the former. Organic thin film light emitting device. 4. The organic thin-film light-emitting device according to claim 1, wherein each light-emitting layer is made of the same light-emitting substance. 5. The organic thin-film light-emitting device according to claim 1, wherein each charge injection layer is made of the same charge injection material.