JP3236332B2 - Organic electroluminescence device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an organic electroluminescence device (hereinafter, referred to as an organic EL device).

[0002]

BACKGROUND ART As an organic EL device, as shown in FIG.
It has a two-layer structure in which an organic phosphor thin film 3 as a light emitting layer and an organic hole transport layer 4 which are made of an organic compound and are laminated on each other are disposed between a metal electrode 1 as a cathode and a transparent electrode 2 as an anode. There is something. Here, the organic hole transport layer 4 has a function of facilitating injection of holes from the anode and a function of blocking electrons. A glass substrate 6 is disposed outside the transparent electrode 2, and excitons are generated by recombination of electrons injected from the metal electrode 1 and holes injected from the transparent electrode 2, and the excitons are radiated by radiation. Light is emitted in the process of activation, and this light is emitted to the outside via the transparent electrode 2 and the glass substrate 6.

In the conventional organic EL device, it is desirable to use a metal material having a low work function of 3 electron volts or less (referred to as a low work function metal) as the metal electrode 1 of the cathode because it is a material effective for electron injection. However, this low work function metal cathode is easy to form,
Due to problems in stability and the like, metal materials having a high work function exceeding 3 electron volts (referred to as high work function metals) are currently used alone as aluminum, magnesium, magnesium indium alloy, magnesium aluminum alloy, magnesium silver alloy, etc. A material or a co-deposited alloy material is used for the cathode (Japanese Patent Application Laid-Open No. 63-63).
-295695).

In such a conventional organic EL device, a first metal is used as a low work function metal and a second metal is used as a high work function metal having film forming property and stability.
When a metal alloy material is used as the cathode, both are formed by co-evaporation. In this alloy cathode, the first metal is the main component and the second metal is present in about 1 to 10% of the whole metal. That is, a thin film is obtained in which the entire alloy cathode is uniformly mixed by co-evaporation. The second metal plays a role in assisting the deposition of the first metal in the co-deposition.

However, it is difficult to increase the luminance of a conventional organic EL device having an alloy cathode at a low driving voltage, and its environmental stability is not sufficient.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an organic EL device having high luminous efficiency and luminance and high environmental stability.

[0007]

The present invention relates to an organic compound between an anode and a cathode.
An organic electroluminescence device having an organic layer comprising: a cathode formed of a first metal that is a low work function metal having a work function of 3 electron volts or less and a second metal that stabilizes the first metal. Having an alloy region in contact with the interface between the organic layer and the cathode,
The first metal is lithium, the second metal is aluminum, and the alloy region includes one of the aluminum.
0.005 parts by weight of the lithium
It is characterized by containing 0.3 parts by weight, preferably 0.01 part by weight or more and 0.1 part by weight or less.

[0008] The present invention relates to an organic compound between an anode and a cathode.
An organic electroluminescence device having an organic layer comprising: a first metal which is a low work function metal having a work function of 3 electron volts or less and a second metal which stabilizes the first metal. And an alloy region in contact with the interface between the organic layer and the cathode, wherein the first metal is strontium, the second metal is magnesium, and the alloy region is based on 100 parts by weight of magnesium. The strontium concentration is 1
It is characterized in that it is contained in an amount of 0 to 40 parts by weight, preferably 10 to 25 parts by weight.

According to the present invention , an organic layer is disposed between an anode and a cathode.
Organic electroluminescent device, wherein
The pole has a low work function of less than 3 electron volts.
Stabilizing a first metal that is a work function metal and the first metal
Made of a second metal which is laminated on the cathode.
A protective electrode .

[0010]

According to the present invention, a high-luminance, low-voltage driven organic EL device having high environmental stability can be obtained.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the organic EL device according to the present invention shown in FIG. 2, between the alloy cathode 11 and the transparent electrode 12 as an anode, an organic phosphor thin film 13 as a light emitting layer, which is made of an organic compound and is laminated on each other, and an organic hole are formed. A transport layer 14 is provided. A glass substrate 16 is provided outside the transparent electrode 2. The protection electrode 17 is preferably formed of aluminum (Al) or magnesium (Mg) irrespective of the composition of the alloy cathode 11 in consideration of the work function, film formability and stability, and cost. The first metal is lithium (L
It is preferable to use low work function alkali metals or alkaline earth metals such as i) and strontium (Sr). Protection electrode 1
By virtue of the presence of 7, the component ratio of the second metal of the high work function metal in the alloy cathode 11 can be increased. Further, with such a configuration, in addition to stabilizing the first metal as an effect of the second metal, the sheet resistance of the entire cathode and protection electrode is reduced.

The thickness of the alloy cathode 11 is one half to two thirds of the total thickness of the alloy cathode 11 and the protection electrode 17.
It is preferable that the protective electrode 17 has a small thickness. The total thickness of the alloy cathode 11 and the protective electrode 17 is 1000
To 3,000 angstroms (Å). In addition, the alloy cathode 11 in which the first metal and the second metal are co-deposited accounts for 10 to 30% by weight of the entire deposited alloy.
Of the first metal component, and the remaining 70 to 90 wt% is the second metal component.
Metal. Also in this case, the first metal is a low work function metal, and the second metal is a high work function metal having film formability and stability.

The protection electrode 17 is preferably formed of aluminum or magnesium. However, it is also preferable that aluminum or magnesium is used as the second metal component of the alloy cathode 11 to form a single layer deposited from the second metal. Thus, the protective electrode 17 can be formed continuously from the alloy cathode 11 by the same apparatus. More specifically, as Examples 1 and 2, an organic EL device was manufactured by forming a film within the range of the film forming conditions of the alloy cathode and the protective electrode as shown in Tables 1 and 2, respectively.

[0014]

[Table 1]

[0015]

[Table 2] FIG. 3 is a graph showing a luminance characteristic with respect to a driving voltage of the manufactured organic EL element. Referring to FIG.
The luminance of the element having the lithium aluminum alloy cathode and the aluminum protective electrode of Example 2 is indicated by ○, and the luminance of the element having the strontium aluminum alloy cathode and the aluminum protective electrode of Example 2 is indicated by ◎. In FIG. 4, the luminance of the organic EL element having only the cathode made of aluminum alone prepared as a comparative example is indicated by ●.

As is apparent from FIG. 4, in the organic EL devices of these examples, high luminance was obtained at a low driving voltage. Thus, the driving voltage was reduced. Further, according to other tests, the rate of voltage rise during light emission of the element is reduced, and the rate of decay of luminance is also reduced. Also, even if lithium or strontium is present in the alloy cathode, hydroxylation and oxidation of the cathode are prevented. That is, lithium is used as the first metal and lithium as the second metal.
An alloy cathode was formed by changing the weight ratio of magnesium, and various organic EL devices having the above-described structure were prepared, and a test was conducted in which the devices were stored in a dry atmosphere for 200 hours. The lithium: magnesium weight ratio of the alloy cathode is 50: 1000, 90: 1.
000, 100: 1000, 115: 1000, 30
When the ratio is changed to 0: 1000, the weight ratio is 90: 100.
0, 100: 1000, 115: 1000 and 300:
The device having the 1000 alloy cathode could not be preserved while maintaining the luminous ability, but the device having the 50: 1000 alloy cathode by weight ratio could be preserved, and the luminous ability could be preserved for 600 hours. That is, the second metal magnesium is 100
It is preferable that the weight ratio of the first metal lithium is 50 parts by weight or less with respect to 0 parts by weight.

Similarly, an alloy cathode is formed by changing the weight ratio of strontium-magnesium with strontium as the first metal and magnesium as the second metal, and various organic EL devices having the above structure are prepared.
A time-saving test was performed. The strontium: magnesium weight ratio of the alloy cathode is 400: 1000,50.
When changing to 0: 1000 and 600: 1000,
The devices having the alloy cathodes with the weight ratios of 500: 1000 and 600: 1000 could not be preserved while maintaining the luminous ability, but the devices having the alloy cathodes with the weight ratio of 400: 1000 could be preserved. That is, it is preferable that the weight ratio of the first metal strontium is 400 parts by weight or less with respect to 1000 parts by weight of the second metal magnesium.

As another embodiment 3, as shown in FIG.
An electrode 1 having an l-Li alloy region A, an anode transparent electrode 2 made of indium tin oxide (ITO), and a tris (8-
Organic phosphor thin film 3 made of (quinolinol) aluminum (Alq3) and N, N'-diphenyl-N, N'-bis (3-methylphenyl) -1,1'-biphenyl-4,
An organic EL element having a two-layer structure without a protective electrode, which was formed by laminating an organic hole transport layer 4 made of 4'-diamine (TPD) on a glass substrate 6, was manufactured. Al of this element
-Regarding the Li concentration in the Li cathode thin film, the thickness of the cathode film from the interface between the cathode film and the organic layer, which is more than 0 ° and not more than 1500 ° and the Li concentration contained in the alloy region A is 0.00
It is controlled to a minute amount of 5 wt% or more and 0.3 wt% or less. In order to keep the concentration of Li within this alloy region, the co-evaporation method is not used, but the Al
It is desirable to prepare an alloy base material of -Li and form it by resistance heating evaporation of one source or an electron beam method.

According to this embodiment, by strictly controlling the range of the Li concentration in the Al-Li cathode thin film, the stability of device fabrication is increased, and furthermore, high-luminance and high-efficiency light-emitting characteristics can be obtained. Further, since the Li concentration is reduced to a small amount, an EL element having excellent environmental stability and film forming properties can be provided.
Further, instead of co-evaporation of simultaneously manufacturing Al and Li from separate evaporation sources to produce an alloy cathode film, if an Al-Li alloy base material is prepared in advance with an appropriate composition ratio and this is used as an evaporation material, There are advantages in that control during film formation is facilitated, stable elements can be easily supplied, materials can be easily stored, and materials can be easily supplied to a deposition boat. Further, it is possible to easily give a gradient of the Li concentration in the thickness direction of the alloy cathode film. For example, the Li concentration can be gradually increased or decreased toward the interface between the cathode film and the organic EL layer. This makes it possible to continuously produce an Al-Li cathode film and a protective film from one evaporation source.

More specifically, FIG.
An EL device having a layer structure was manufactured. The Al-Li alloy region electrode 1 was laminated to a thickness of 1500 Å (that is, the electrode 1 composed of only the Al-Li alloy region), the Alq ₃ thin film 3 was laminated to a thickness of 550 Å, and the TPD layer 4 was laminated to a thickness of 700 そ れ ぞ れ. Table 3 shows that the Li concentration of the Al—Li cathode in the EL device was 0.024 wt% and 0.58 wt%.
%, 5.6 wt%, and luminous efficiency at 300 cd / m ² when using a pure Al cathode. Table 4 shows that the concentration of Li in the alloy region in the EL element was 0.024 wt% and 0.048 wt%.
%, And 0.065 wt% when the emission efficiency is 300 cd / m ² .

FIG. 5 shows a Li concentration of 0 wt% (pure Al), 0.007 wt%, 0.01
6wt%, 0.024wt%, 0.048wt%, 0.065wt
%, 0.08 wt%, 0.2 wt%, 0.58 wt%, and 5.6
4 shows a graph in which luminous efficiency at 300 cd / m ² emission corresponding to wt% is plotted.

[0022]

[Table 3]

[0023]

[Table 4] Table 3 and 4 and as is clear from FIG. 5, the luminance 300
High efficiency of 1.5 (1 m / W) or more at cd / m ²
What is obtained is that the Li concentration is preferably 0.005 to 0.3 wt%.
Mashiku the Ri der within the following 0.1 wt% or more 0.01 wt%, and the maximum luminous efficiency is obtained when the 0.024Wt%, as is clear from Table 4 and FIG. 5, in the range It can be seen that the formation of the cathode makes it possible to obtain a stable element with a very small variation in the characteristics of the EL element.

In FIG. 6, the Li concentration of the Al—Li cathode of the EL element is in the range of 0.01 wt% to 0.1 wt%, 0.007 wt%, 0.58 wt%, and 5.6 wt%.
The luminous efficiency (1 m / W) with respect to the luminance (cd / m 2) in the case of using a pure Al cathode is shown in the graph. As is clear from the figures, high luminous efficiency was obtained in the organic EL devices in which the Li concentration in the alloy region of the electrodes of these examples was in the range of 0.005 wt% or more and 0.3 wt% or less. .

Further, in FIG. 7, the Al-Li
The Li concentration of the cathode was 0.065 wt%, 0.48 wt%,
The graphs show the ratios (luminance ratios) of the deterioration with the lapse of time of the respective luminances when 5.6 wt% and the pure Al cathode are used. As is clear from the figures, the Li concentration in the alloy region of the electrodes of these examples was 0.005 to 0.5.
Organic EL having a Li concentration of 0.065 wt% in a range of 3 wt%, preferably 0.01 wt% or more and 0.1 wt% or less.
In the device, the life was prolonged with less luminance deterioration due to aging.

On the other hand, in another embodiment 4, similarly to the organic EL device having the cathode having the alloy region A shown in FIG. 4, the composition of the alloy region A is changed to Mg-Sr instead of Al-Li.
Electrode 1, an anode transparent electrode 2 made of ITO, an organic phosphor thin film 3 made of Alq3 and TP
Thus, an EL device having a two-layer structure without the protective electrode and comprising the organic hole transport layer 4 made of D was manufactured. Regarding the Sr concentration in the Mg—Sr cathode thin film of this device, the thickness of the cathode film from the interface between the cathode film and the organic layer exceeds 0 ° and the thickness exceeds 150 °.
The concentration of Sr contained in the alloy region A of 0 ° or less is 1
The amount is controlled to be 0 wt% or more and 40 wt% or less. In order to keep the concentration of Sr within this alloy region, it is not necessary to use a co-evaporation method, but to use Mg—Sr
It is preferable to prepare an alloy base material and form it by a single source resistance heating evaporation or an electron beam method.

According to this embodiment, by strictly controlling the range of the Sr concentration in the Mg—Sr cathode thin film, the stability of the device fabrication is increased, and the light emission characteristics with higher luminance and higher efficiency are obtained. EL with excellent environmental stability and film forming properties
An element can be provided. Further, the production of the alloy cathode film was performed using Mg and S
Rather than co-evaporation in which r is simultaneously emitted from different evaporation sources, if a Mg-Sr alloy base material is prepared in advance with an appropriate composition ratio and this is used as the evaporation material, control during film formation becomes easy and stable. There are advantages in that the element can be easily supplied, that the material can be stored and that the material can be easily supplied to the evaporation boat.

Further, it is possible to easily provide a gradient of the Sr concentration in the thickness direction of the alloy cathode film. For example, the Sr concentration can be gradually increased or decreased toward the interface between the cathode film and the organic EL layer. This makes it possible to continuously produce the Mg—Sr cathode film and the protective film from one evaporation source. Specifically, an EL device having a two-layer structure without the protective electrode shown in FIG. 1 was manufactured. Note that M
The g-Sr alloy region electrode 1 was 1500 ° (that is, the electrode 1 consisting of only the Mg—Sr alloy region), the Alq ₃ thin film 3 was 550 °, and TP
D layer 4 was laminated in a thickness of 700 °. Table 5 shows the Sr concentration of the Mg—Sr cathode at this time as 20.5 wt% and 35.6 wt%.
The efficiency at the time of light emission of 300 cd / m ² is shown. In Table 6,
When the Sr concentration was 9.37 wt%, 20.5 wt%, 26.8 wt%
The efficiency at the time of light emission of 0 cd / m ² is shown.

FIG. 8 shows an Sr concentration of 3.0% by weight, 9.37% by weight, 14.0% by weight, 2% by weight in the alloy region in the EL device.
0.5 wt%, 26.8 wt%, 35.6 wt%, and 41.0 w
5 is a graph plotting luminous efficiency at the time of light emission of 300 cd / m ² corresponding to t%.

[0030]

[Table 5]

[0031]

[Table 6] Table 5 and 6 and as is clear from FIG. 8, intensity 300
High efficiency of 1.5 (1 m / W) or more at cd / m ²
What is obtained is that the Sr concentration in the Mg—Sr cathode film is 10 to 10.
This is the case where it is in the range of 40 wt%, preferably 10 wt% or more and 25 wt% or less . In this case, it is possible to obtain an EL device having a maximum luminous efficiency and having stable characteristics with very little variation in EL device characteristics. Understand.

In FIG. 9, the Sr concentration of the Mg—Sr cathode of the EL element is in the range of 10% to 25% by weight, 3% by weight, and 36% by weight.
Luminous efficiency (lm) for luminance (cd / m ² ) when t% and 63 wt%
/ W) is shown in the graph. As is apparent from the figure, the Sr concentration in the alloy region of the electrodes of these examples is 10 wt% or more and 25 wt% or more.
High luminous efficiency was obtained in the organic EL device within the range of wt% or less.

Further, in FIG. 10, the Mg-S
The Sr concentration of the r cathode was 13.9 wt%, 17.8 wt%,
The graphs show the ratios (luminance ratios) of deterioration due to the temporal change of the respective luminances at 24.8 wt% and 33.2 wt%. As is clear from the figure, the Sr concentration in the alloy region of the electrodes of these examples is 10 to 40 watts.
In the organic EL element in the range of t%, preferably in the range of 10 wt% or more and 25 wt% or less, there was little luminance deterioration due to aging and the life was extended.

When the Sr concentration exceeds 40 wt%, Sr
As the concentration increases, the luminous efficiency decreases and the environmental stability rapidly deteriorates. Further, when the Sr concentration is less than 10 wt%, it is difficult to improve the poor film formability of Mg, and a stable EL element cannot be provided. In the above-described embodiment of the present invention, in order to preserve the organic EL element during manufacture, the periphery of the element is sealed and sealed with an inert gas such as argon or nitrogen, or the atmosphere is evacuated. When both are sealed, they are cut off from the element in the vicinity of the element, and diphosphorus pentoxide is present and sealed.

In the above-described embodiment of the present invention, the organic EL device having a two-layer structure has been described, but the present invention is not limited to this. The present invention provides a three-layer structure including an organic phosphor thin film and an organic hole transport layer as an organic layer, and an organic electron transport layer between the organic phosphor thin film and the cathode to facilitate injection of electrons from the alloy cathode. Can also be applied to

[0036]

As described above, according to the present invention, the first metal
The concentration of the first metal Li contained in the alloy region of a predetermined film thickness (0 ° or more and 1500 ° or less) from the interface between the alloy cathode composed of Li and the stabilized second metal Al and the organic layer is 0.01 w
Since it is controlled to a very small amount of not less than t% and not more than 0.1 wt% , the luminous efficiency at a luminance of 300 cd / m ² is 1.5 (1
m / W) or more and high luminous efficiency and luminance, and manufacture of devices
An organic EL element having high environmental stability and capable of suppressing the above variation can be obtained. Also, according to the present invention, the first metal
A predetermined thickness from the interface between the organic cathode and the alloy cathode composed of Sr and the stabilized second metal Mg (more than 0 ° and 1500 ° or less)
The concentration of the first metal Sr contained in the alloy region of
% To 40 wt% or less.
Organic EL with high luminous efficiency, high brightness and high environmental stability
An element is obtained.

Further, in the organic EL device of the present invention,
In a device composed of a transparent anode, a hole transport layer, a light emitting layer, and an alloy cathode composed of a first metal and a second metal laminated on a substrate, the protective electrode is laminated on the alloy cathode. In this case, the brightness can be increased, and the environmental stability can be enhanced by completely covering the alloy cathode.

[Brief description of the drawings]

FIG. 1 is a structural diagram showing an organic EL element.

FIG. 2 is a structural diagram showing the organic EL elements of Examples 1 and 2.

FIG. 3 is a graph showing luminance driving voltage characteristics of the organic EL elements of Examples 1 and 2 and Comparative Example.

FIG. 4 is a structural diagram showing the organic EL elements of Examples 3 and 4.

FIG. 5 is a graph showing luminous efficiency characteristics with respect to Li concentration in an alloy region of Example 3.

FIG. 6 is a graph showing luminous efficiency characteristics with respect to luminance in Example 3.

FIG. 7 is a graph showing a change over time in luminance of the EL element of Example 3.

FIG. 8 is a graph showing luminous efficiency characteristics with respect to Sr concentration in an alloy region of Example 4.

FIG. 9 is a graph showing luminous efficiency characteristics with respect to luminance in Example 4.

FIG. 10 is a graph showing a change over time in luminance of the EL element of Example 3.

[Description of Signs of Main Parts]

 Reference Signs List 1 cathode 2 transparent electrode 3 organic phosphor thin film 4 organic hole transport layer 6 glass substrate 11 alloy cathode 12 transparent electrode 13 organic phosphor thin film 14 organic hole transport layer 16 glass substrate 17 protective electrode A alloy region

──────────────────────────────────────────────────続 き Continuing on the front page (72) Kenichi Nagayama 6-11, Fujimi, Tsurugashima-shi, Saitama Prefecture Pioneer Corporation (72) Inventor Teruichi Watanabe 6-1-1, Fujimi, Tsurugashima-shi, Saitama (56) References JP-A-60-166571 (JP, A) JP-A-2-139893 (JP, A) JP-A-2-15595 (JP, A) JP-A-4 −212287 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 33/00-33/28

Claims (11)

(57) [Claims] 1. An organic electroluminescence device having an organic layer made of an organic compound disposed between an anode and a cathode, wherein the cathode is a low work function metal having a work function of 3 electron volts or less. An alloy region made of one metal and a second metal for stabilizing the first metal and having an interface with an interface between the organic layer and the cathode, wherein the first metal is lithium, and the second metal is aluminum; , the alloy region, the lithium concentration 0.005 part by weight to 0.3 parts by weight of the weight ratio containing Mikatsu per 100 parts by weight of the aluminum, the organic layer and
Exists in a thickness range of 1500 ° or less from the interface of the cathode.
And a protective electrode laminated on the alloy cathode
Having a thickness of the alloy cathode and the protection of the alloy cathode
An organic electroluminescent device, wherein the thickness of the organic electroluminescent device is one half to two thirds of the total thickness of the electrode . 2. An organic electroluminescence device having an organic layer disposed between an anode and a cathode, wherein the cathode has 3 layers.
A first metal that is a low work function metal having a work function of less than electron volts and a second metal that stabilizes the first metal;
An alloy region made of metal and in contact with an interface between the organic layer and the cathode, wherein the first metal is strontium, the second metal is magnesium, and the alloy region is 100 parts by weight of the magnesium. An organic electroluminescence device comprising the strontium concentration in a weight ratio of 10 parts by weight or more and 40 parts by weight or less. 3. The organic electroluminescence device according to claim 2 , wherein the alloy region exists in a thickness range of 1500 ° or less from an interface between the light emitting layer and the cathode. 4. The organic electroluminescent device according to claim 2 , further comprising a protective electrode laminated on said alloy cathode. 5. An organic electroluminescence device having an organic layer disposed between an anode and a cathode, wherein the cathode comprises 3
An alloy cathode made of a second metal which allowed to stabilize a first metal and the first metal is a low work function metal having a work function of electron volts, have a protective electrode which is stacked on the alloy cathode, thickness of the alloy negative electrode is the case
1/2 to 3 times the thickness of the gold cathode and the entire protective electrode
The organic electroluminescence Nemi net sensing element, wherein the minute is 2. 6. The organic electroluminescence device according to claim 5, wherein the first metal is lithium. 7. The weight ratio of the first metal and the second metal in the alloy cathode is such that the weight ratio of the second metal is 1000 parts by weight and lithium is 50 parts by weight or less. 7. The organic electroluminescent device according to 6 . 8. The method according to claim 1, wherein the first metal is strontium.
The organic electroluminescent device according to claim 5, wherein the door. 9. The weight ratio of the first and second metals in the alloy cathode is such that the weight ratio of strontium to the second metal is 1000 parts by weight and that of strontium is 400 parts by weight or less. 9. The organic electroluminescence device according to 8 . 10. The organic electroluminescence device according to claim 5, wherein the second metal is aluminum or magnesium. 11. The organic electroluminescence device according to claim 5, wherein the protection electrode is made of the second metal.