JP3226581B2 - 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).

However, the conventional organic EL device having an alloy cathode has insufficient environmental stability and film-forming properties. For example, in the case of an organic EL device having a cathode made of an aluminum-magnesium alloy, light emission is particularly high. Non-light-emitting area within the light-emitting area (1 dot: 2 x 2 mm)
(Hereinafter, referred to as a black spot) and grows with time. Also, depending on the material of the conventional alloy cathode,
It is difficult to increase the luminance at a low driving voltage, and an organic EL element with high luminous efficiency and high luminance has not been obtained.

[0005]

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.

[0006]

The organic EL device of the present invention is an organic electroluminescent device in which an anode, a hole transport layer made of an organic compound, a light emitting layer made of an organic compound, and a cathode are formed in this order on a substrate. The cathode has an alloy region made of indium and lithium and in contact with an interface between the light emitting layer and the cathode, and the alloy region has a lithium concentration of 0.1 part by weight with respect to 100 parts by weight of the indium.
It is characterized in that it is contained in a weight ratio of 005 parts by weight or more and 0.11 parts by weight or less.

[0007]

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

[0008]

Embodiments of the present invention will be described below in detail with reference to the drawings. As shown in FIG.
The L element is a cathode electrode 1 having an In-Li alloy region A.
, An anode transparent electrode 2 made of indium tin oxide (ITO), an organic phosphor thin film 3 made of, for example, tris (8-quinolinol) aluminum (Alq ₃ ) laminated between them, and N, N ′, for example. -Diphenyl-N,
An organic hole transport layer 4 made of N′-bis (3-methylphenyl) -1,1′-biphenyl-4,4′-diamine (TPD) is laminated on a glass substrate 6. In particular, the In-Li alloy region A of the cathode 1 is formed so as to be in contact with the interface between the light emitting layer 3 and the cathode 1. in this way,
The EL device according to the present embodiment has In as the cathode alloy region material.
-Li alloy is used.

With respect to the Li concentration in the In-Li alloy region A of the cathode 1, the thickness of the cathode film is set to 0 from the interface between the cathode film and the organic layer.
L contained within the following alloys region A range 10000Å beyond Å
The concentration of i is controlled to an extremely small amount of 0.005 wt% or more and 0.11 wt% or less. Note that the concentration of Li is set in the alloy region A.
In order to contain the alloy, it is preferable to form an Al-Li alloy base material in advance with an appropriate composition ratio instead of the co-evaporation method, and to form this by one-source resistance heating evaporation or an electron beam method. .

According to this embodiment, high-luminance and high-efficiency generation characteristics can be obtained, in particular, high environmental stability and excellent film-forming properties, which significantly suppress the generation and growth of black spots, can be obtained, and the stability of element production can be improved. This leads to advantages such as an increase in the number (ie, a stable element without variation) and a decrease in the luminance decay rate in the continuous light emission test. Further, the production of an alloy cathode film was performed using In
Rather than co-evaporation of simultaneously evaporating Li and Li from separate evaporation sources, if an In-Li alloy base material is prepared in advance with an appropriate composition ratio and this is used as a deposition material, control during film production becomes easier, Easy to supply stable elements, material storage,
There is also an advantage that the supply to the evaporation boat is facilitated. Further, it is possible to easily provide a concentration gradient in the film thickness direction with respect to the Li concentration in the In-Li cathode film. For example, L
The i 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 form an In-Li cathode film and a protective film from one evaporation source.

Specifically, an EL device having a two-layer structure shown in FIG. 1 was manufactured. In addition, the In-Li alloy region electrode 1 was set at 9000 ° (that is, the cathode electrode 1 consisting of only the In-Li alloy region), Alq ₃
The thin film 3 was laminated at a thickness of 550 ° and the TPD layer 4 was laminated at a thickness of 700 °. Table 1 shows L in the In-Li cathode film at this time.
i concentration of 0.025 wt%, 0.032 wt%, 0.067 wt%, and 0.12 w
The graph shows the efficiency when 300 cd / m ^{2 is} generated when the concentration is set to t% and when a pure In cathode is used.

FIG. 3 shows a Li concentration of 0 wt% (pure Al), 0.004 wt%, 0.00
8wt%, 0.017wt%, 0.025wt%, 0.032wt
300 corresponding to%, 0.067 wt%, and 0.12 wt%
4 shows a graph in which luminous efficiency during cd / m ² light emission is plotted.

[0013]

[Table 1] As is clear from Table 1 and FIG. 3, the emission at a luminance of 300 cd / m ^{2 was} observed.
Light efficiency is as high as 1.5 (lm / W) or higher.
i concentration is 0.005 to 0.11 wt%, preferably 0.01 wt% or more and 0.1 wt%
% , The maximum luminous efficiency can be obtained within the range, and it can be seen that if the cathode is formed within this range, a stable device with very small variation in the characteristics of the EL device can be obtained.

In FIG. 4, the In-L of such an EL device is shown.
Li concentration of i-cathode in the range of 0.01 wt% or more and 0.1 wt% or less,
The luminous efficiency (lm / W) with respect to the luminance (cd / m ² ) at 0.008 wt%, 0.12 wt% and the pure In cathode is shown in the graph. As is clear from the figure, 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 0.01 wt% or more and 0.1 wt% or less.

Further, in FIG. 5, the result of examining the luminance decay rate by the continuous light emission test of this embodiment is shown in FIG.
The Li concentration of the Li cathode was 0.017 wt%, 0.025 wt%, and 0.10 wt%.
The graph shows the ratio (luminance ratio) of the deterioration due to the temporal change of the luminance when wt% is used. As is apparent from the figure, L in the alloy region of the electrodes of these examples was
It can be seen that in the organic EL device having the i concentration of 0.01 wt% or more and 0.1 wt% or less, the luminance is less deteriorated due to the aging and the life is extended.

Further, FIGS. 6 and 7 show the results obtained by examining the environmental stability and film formability of this embodiment by a light-emitting area observation test of an EL element. FIG. 6A shows an enlarged photograph of the state of the light-emitting portion (within the dot) immediately after the EL device of this example was manufactured. FIG. 6B shows an enlarged photograph of the state of the light emitting portion 700 hours after the EL element of this example. In addition, FIG. 7 shows the EL element composed of a Mg—Al alloy cathode immediately after the production (FIG. 7A) and after 600 hours (FIG. 7).
(B) shows an enlarged photograph of the state inside the light emitting dot. Each EL element was observed and photographed in a state where it was stored in a vacuum desiccator.

As is apparent from FIGS. 6 and 7, in the device using Mg-Al as the cathode material, the black spots grow and grow with the passage of time, whereas In-Li is used as the cathode material.
In the present embodiment using, no black spots are observed. FIG.
As shown in another embodiment, it is preferable that the protective electrode 17 is laminated on the cathode 1. The protection electrode 17 is preferably made of aluminum or magnesium. The presence of the protective electrode 17 has the effect of stabilizing the cathode 1 and reducing the sheet resistance of the cathode and the entire protective electrode.

Further, 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 when the atmosphere is sealed together. It is preferable that diphosphorus pentoxide be present in the vicinity of the element and sealed off. In the embodiments of the present invention described above, the organic EL device having the two-layer structure is 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

[0019]

As described above, according to the present invention, an anode, an organic compound hole transporting layer, a light emitting layer made of an organic compound, and an interface between the light emitting layer made of indium and lithium are formed on a substrate. In an organic EL device in which a cathode having an alloy region in contact with the cathode is formed in order, the cathode has a predetermined thickness (more than 0 ° and not more than 10000 °) from the interface between the cathode and the organic layer (light emitting layer or electron transport layer). Since the concentration of Li contained is controlled to a very small amount of 0.005 wt% or more and 0.11 wt% or less, the luminous efficiency can be increased, and an organic EL element driven by a high luminance and low voltage with high environmental stability can be obtained. Be chosen.

[Brief description of the drawings]

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

FIG. 2 is a structural view showing an organic EL device of an example according to the present invention.

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

FIG. 4 is a graph showing luminous efficiency characteristics with respect to luminance in an example.

FIG. 5 is a graph showing a change over time in luminance of an EL element of an example.

FIG. 6 is an enlarged plan photograph of a light emitting portion (in a dot) immediately after (FIG. 6 (a)) and after 700 hours (FIG. 6 (b)) of the EL element of the example.

FIG. 7 is an enlarged plan photograph of a light emitting portion (in a dot) immediately after the fabrication of the EL element of the comparative example (FIG. 7A) and after 600 hours (FIG. 7B).

FIG. 8 is a structural view showing an organic EL device according to another embodiment of the present invention.

[Description of Signs of Main Parts]

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

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Teruichi Watanabe 6-1-1, Fujimi, Tsurugashima-shi, Saitama Pioneer Corporation General Research Institute (56) References JP-A-3-203982 (JP, A) JP-A-60-166571 (JP, A) JP-A-4-212284 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H05B 33/00-33/28

Claims (3)

(57) [Claims] 1. An organic electroluminescence device in which an anode, a hole transport layer made of an organic compound, a light emitting layer made of an organic compound, and a cathode are formed in this order on a substrate, wherein the cathode is made of indium and An alloy region made of lithium and in contact with the interface between the light emitting layer and the cathode, wherein the alloy region has a lithium concentration of 0.005 parts by weight or more with respect to 100 parts by weight of indium;
1 parts by weight or less of the weight ratio containing Mikatsu, the light-emitting layer and the
An organic electroluminescent device characterized by being present in a thickness range of 10,000 ° or less from an interface of a cathode . 2. The alloy region is made of an Al-Li alloy base material.
And use this as a source of resistance heating evaporation or electron
The concentration of lithium within the alloy region by the beam method
The organic material according to claim 1, wherein the organic material is formed.
Electroluminescence element. 3. The method according to claim 1, wherein the alloy region is preliminarily provided with the lithium alloy.
In-Li alloy base material is made in the composition ratio of the concentration of the
It is characterized by being formed by vapor deposition as a vapor deposition material
The organic electroluminescent element according to claim 1,
Child.