JP2004207000A - Organic el device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic EL device having charge-transporting layers of two or more, whose luminous efficiency and luminance lifetime are improved by improving adhesiveness between the adjacent charge-transporting layers. <P>SOLUTION: The organic EL device S1 has hole-transporting layers 3 and 4, luminous layers 5 and 6 and electron-transporting layers 7 and 8 which are laminated sequentially between an anode 2 and a cathode 10, wherein the charge-transporting layers of the hole-transporting layers 3 and 4 and the electron-transporting layers 7 and 8 are each composed of two or more layers. A mixed layer 11 made of a mixture of a material composing the hole-transporting layer 3 and a material composing the adjacent hole-transporting layer 4 is formed in an interface between the adjoining hole-transporting layers 3 and 4, in the hole-transporting layers 3 and 4 each formed of two or more layers. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
According to the present invention, an organic EL (a hole transporting layer, a light emitting layer, and an electron transporting layer are sequentially laminated between a pair of electrodes, and at least one of the hole transporting layer and the electron transporting layer is composed of two or more layers) (Electroluminescence) element.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in general, an organic EL element is generally formed by sequentially laminating a cathode composed of a hole transport layer, a light-emitting layer, an electron transport layer, a metal electrode and the like on an anode composed of a transparent electrode or the like by a vacuum deposition method.
[0003]
In this organic EL device, holes and electrons are injected from each electrode, and these injected charges are transported to the light emitting layer via each charge transport layer, that is, the hole transport layer and the electron transport layer. Then, light is emitted by recombination of holes and electrons in the light emitting layer.
[0004]
Further, in such an organic EL device, the hole transport layer and the electron transport layer usually have two or more layers in order to improve the transport efficiency of charges such as holes and electrons. For example, it is known that the hole transport layer has a two-layer structure including a layer made of copper phthalocyanine (CuPc) and a layer made of triphenylamine tetramer (TPTE) from the anode side (see Patent Document 1).
[0005]
[Patent Document 1]
JP 2001-148292 A (Page 3, FIG. 2)
[0006]
[Problems to be solved by the invention]
However, in the organic EL element, since each material of the light emitting layer and each charge transporting layer is formed by a vacuum deposition method, the adhesion at the interface between the layers is weak, and poor bonding at the interface due to stress such as heat is caused. It is presumed to happen.
[0007]
In particular, in the case where the charge transport layer is composed of two or more layers, when a bonding failure occurs at the interface between these two adjacent charge transport layers, the charge transport efficiency decreases. Then, there arises a problem that the luminous efficiency is reduced and the driving voltage is increased, and accordingly, the luminance life is shortened.
[0008]
In view of the above problems, it is an object of the present invention to improve the luminance life by improving the adhesion between two adjacent charge transport layers in an organic EL device having two or more charge transport layers. .
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a hole transport layer (3, 4), a light emitting layer (5, 6), and an electron transport layer (7, 8), and in an organic EL device in which at least one of both the charge transport layer of the hole transport layer and the electron transport layer is composed of two or more layers, the charge transport composed of two or more layers In the layer, mixed layers (11, 12) in which constituent materials of the adjacent charge transport layers are mixed are interposed at an interface between two adjacent charge transport layers.
[0010]
The present invention has been found as a result of an experimental study. The constituent materials of the adjacent charge transport layers are provided at the interface between two adjacent charge transport layers in the charge transport layer composed of two or more layers. By interposing a mixed layer in which is mixed, the adhesion between two adjacent charge transport layers can be improved, and the luminous efficiency and the luminance life can be improved as compared with the conventional one having no mixed layer. (See FIG. 3).
[0011]
This is because a mixed layer (11) is formed by mixing one layer (3, 7,) and the other layer (4, 8) of the two layers (3, 4, 7, 8) constituting the charge transport layer. , 12) between the two layers is presumed to improve the familiarity between the one layer and the other layer.
[0012]
Here, it is considered that even if the mixed layers (11, 12) are too thick, the charge transporting ability of the charge transporting layer is impaired, and the luminance life is deteriorated. Then, when the thickness of the mixed layer was studied, it was found that the brightness life can be appropriately improved if the thickness is 10 nm or less as in the invention described in claim 2.
[0013]
It should be noted that reference numerals in parentheses of the above-described units are examples showing the correspondence with specific units described in the embodiments described later.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention shown in the drawings will be described. In the following embodiments, the same portions are denoted by the same reference numerals in the drawings.
[0015]
(1st Embodiment)
FIG. 1 is a diagram showing a schematic sectional configuration of an organic EL element S1 according to the first embodiment of the present invention.
[0016]
The substrate 1 is a transparent substrate such as glass or resin, on which an anode 2 is formed. The anode 2 is made of a transparent conductive film such as indium tin oxide (ITO).
[0017]
On the anode 2, hole transport layers 3 and 4 made of an organic material having a hole transport property, light emitting layers 5 and 6 made of an organic EL material, electron transport layers 7 and 8 made of an organic material having an electron transport property, and electron injection An electron injection layer 9 made of a conductive material and a cathode 10 made of a metal electrode and the like are sequentially formed and deposited by a vacuum evaporation method.
[0018]
Here, in the organic EL element S1, each of the charge transport layers 3, 4, 7, and 8, that is, the hole transport layers 3, 4 and the electron transport layers 7, 8 are each composed of two layers.
[0019]
That is, the hole transport layer is formed by laminating two layers made of different materials, that is, the first hole transport layer 3 and the second hole transport layer 4 from the anode 2 side. , 6 from the side, the first electron transport layer 7 and the second electron transport layer 8 are formed by laminating two layers made of different materials.
[0020]
When the charge transport layer has two or more layers, the energy barrier between the layers can be reduced as compared with the single layer structure. , 4 can be improved in the efficiency of charge transport.
[0021]
The light emitting layer is also formed by laminating the first light emitting layer 5 and the second light emitting layer from the side of the hole transport layers 3 and 4. When the light emitting layers 5 and 6 have a multilayer structure, mixed color light emission is possible.
[0022]
In the organic EL device S1, in the charge transport layers 3 and 4 composed of two or more layers, the constituent materials of the adjacent charge transport layers are mixed at the interface between the two adjacent charge transport layers. A unique configuration in which a mixed layer 11 is interposed is employed.
[0023]
In the present embodiment, the configuration of the first and second hole transport layers 3 and 4 is provided at the interface between the adjacent first hole transport layer 3 and second hole transport layer 4 in the hole transport layers 3 and 4. A mixed layer 11 in which materials are mixed is interposed. For example, the material of the first hole transport layer 3 and the material of the second hole transport layer 4 can be mixed at a volume mixing ratio of about 1: 1.
[0024]
The mixed layer 11 can be formed by a co-evaporation method. Specifically, in the vacuum chamber, the constituent material of the first hole transport layer 3 and the constituent material of the second hole transport layer 4 are separately put into two crucibles, and a shutter is provided on each crucible. The co-evaporation is performed by adjusting the opening and closing of each shutter. The mixing ratio is determined by the film formation rate of each material.
[0025]
An example in which the effect of providing such a mixed layer 11 is specifically examined will be described. A glass substrate was used as the substrate 1, and ITO was formed as the anode 2 on the substrate 1 by a sputtering method or the like.
[0026]
On the anode 2 made of ITO, copper phthalocyanine (CuPc) having a film thickness of 15 nm as the first hole transport layer 3, a mixed layer 11, and triphenylamine 4 as the second hole transport layer 4 were formed by a vacuum evaporation method. The body (TPTE) is 40 nm thick, the first light emitting layer 5 is 1 nm thick doped with rubrene using TPTE as a host and 5% doped, and the second light emitting layer 6 is 6% doped distyramine with a pyrene compound as a host. These were sequentially formed to a thickness of 40 nm.
[0027]
Further, on the second light-emitting layer 6, a first thickness 5nm pyrene compound as an electron-transporting layer 7, Alq ₃ as a second electron transport layer 8 (tris (8-quinolinolato) aluminum) film thickness 20nm Then, lithium fluoride (LiF) was formed to a thickness of 0.5 nm as the electron injection layer 9, and aluminum (Al) was formed to a thickness of 100 nm as the cathode 10 by a vacuum evaporation method.
[0028]
Here, the mixed layer 11 is formed such that CuPc, which is a constituent material of the first hole transport layer 3, and TPTE, which is a constituent material of the second hole transport layer 4, are mixed at a volume mixing ratio of 1: 1 by co-evaporation. Mixtures having thicknesses of 1 nm, 5 nm, 10 nm, and 50 nm were produced. Hereinafter, these are referred to as a 1 nm mixed layer element, a 5 nm mixed layer element, a 10 nm mixed layer element, and a 50 nm mixed layer element, respectively.
[0029]
As a comparative example, a device having a conventional configuration without the mixed layer 11 was also manufactured. FIG. 2 shows a schematic cross-sectional configuration of the organic EL element of this comparative example. In the examples having the light emitting layers 3 and 4 in these examples, the first light emitting layer 5 emits yellow and the second light emitting layer 6 emits blue at the same time, and a mixed color of these light is emitted.
[0030]
With respect to each of the manufactured organic EL devices, initial characteristics and a luminance deterioration evaluation after 200 hours at 100 Hz, 1/64 duty pulse driving, and 400 cd / m ² luminance in an atmosphere of 85 ° C. were performed.
[0031]
In the initial characteristics, the luminous efficiency of the comparative example was 6.8 cd / A, whereas that of the 1 nm mixed layer device was 8.5 cd / A, which was improved by about 25%, and that of the 5 nm mixed layer device was 6 cd / A. It is almost equal to 0.8 cd / A, and in the 10 nm mixed layer element, it is reduced by about 5% to 6.4 cd / A, and in the 50 nm mixed layer element, it is decreased by about 20% to 5.3 cd / A.
[0032]
The driving voltage of the comparative example was about 14 V, whereas the 1 nm mixed layer device reduced the driving voltage by about 10% to 12.5 V, and the 5 nm mixed layer element reduced the driving voltage by about 14% to 12 V, thereby reducing the 10 nm mixed layer element. In the layer device, the voltage was reduced by about 14% to 12 V, and in the 50 nm mixed-layer element, the voltage was increased by about 10% to 15.3 V.
[0033]
Regarding the luminance degradation, the comparative example deteriorated 30% after 200 hours, whereas the 1 nm mixed layer element had 17%, the 5 nm mixed layer element had 20%, the 10 nm mixed layer element had 23%, and the 50 nm mixed layer element had. The deterioration was 30%.
[0034]
FIG. 3 is a diagram showing the relationship between the luminance and the durability time (time) for the 1 nm mixed layer element (1 nm mixed layer 11), the 50 nm mixed layer element (50 nm mixed layer 11), and the element of the comparative example. The luminance is shown by standardizing the initial luminance to 1.
[0035]
As described above, according to the present embodiment, the mixed layer 11 is provided by interposing the mixed layer 11 at the interface between the adjacent two layers 3 and 4 in the hole transport layers 3 and 4 formed of two layers. Compared with the conventional case, the adhesion between the two adjacent hole transport layers 3 and 4 can be improved, and the luminance life can be improved.
[0036]
And, as shown in the above results, even if the mixed layer 11 is too thick, the hole transporting ability of the hole transporting layers 3 and 4 is impaired, and the luminance life is deteriorated. From the above results, when the thickness of the mixed layer 11 of the present embodiment is 10 nm or less, the driving voltage and the luminance life can be appropriately improved, and when the thickness is 1 nm, the luminous efficiency can be improved. I understood.
[0037]
(2nd Embodiment)
FIG. 4 is a diagram showing a schematic cross-sectional configuration of an organic EL element S2 according to the second embodiment of the present invention. Hereinafter, points different from the first embodiment will be mainly described.
[0038]
Also in the organic EL element S2 shown in FIG. 4, in the charge transport layers 7 and 8 composed of two or more layers, the constituent materials of the adjacent charge transport layers are mixed at the interface between the two adjacent charge transport layers. It has a unique configuration in which a mixed layer 12 is interposed.
[0039]
In the present embodiment, in the two electron transport layers 7 and 8, the first and second electron transport layers 7 and 8 are disposed at the interface between the adjacent first and second electron transport layers 7 and 8. The mixed layer 12 formed by mixing the constituent materials 8 is interposed.
[0040]
The mixed layer 12 can be, for example, a material in which the constituent material of the first electron transport layer 7 and the constituent material of the second electron transport layer 8 are mixed at a volume mixing ratio of about 1: 1. Further, the mixed layer 12 can be formed by a co-evaporation method as in the first embodiment.
[0041]
An example of specifically examining the effect of providing such a mixed layer 12 will be described. An anode 2 is formed on a substrate 1 with the same material and thickness as in the specific example of the first embodiment, and the first and second hole transport layers 3 are formed on the anode 2 by a vacuum deposition method. , 4, and the first and second light emitting layers 5 and 6 were formed.
[0042]
After forming a pyrene compound as the first electron transporting layer 7 with a thickness of 5 nm and the mixed layer 12 and the second electron transporting layer 8 with Alq ₃ as the 20 nm thickness on the second light emitting layer 6, An electron injection layer 9 and a cathode 10 were formed.
[0043]
Here, the mixed layer 12 is a 1: 1 volume mixture of a pyrene compound as a constituent material of the first electron transport layer 7 and an Alq _{3 as} a constituent material of the second electron transport layer 8 by co-evaporation. Mixing was performed at a ratio of 1 nm, 5 nm, 10 nm, and 50 nm. Hereinafter, these are referred to as a 1 nm mixed layer element, a 5 nm mixed layer element, a 10 nm mixed layer element, and a 50 nm mixed layer element, respectively.
[0044]
As in the first embodiment, each of the organic EL elements manufactured in the present embodiment and the element of the comparative example are 100 Hz, 1/64 duty pulse drive in an 85 ° C. atmosphere, and 400 cd / The luminance degradation evaluation after 200 hours was performed at a luminance of m ² .
[0045]
In the initial characteristics, the luminous efficiency was improved by about 25% in the 1 nm mixed layer element, decreased by about 10% in the 5 nm and 10 nm mixed layer elements, and decreased by about 60% in the 50 nm mixed layer element with respect to the comparative example.
[0046]
The drive voltage was reduced by about 10% for the 1 nm and 5 nm mixed layer elements, decreased by about 5% for the 10 nm mixed layer element, and increased by about 30% for the 50 nm mixed layer element compared to the comparative example.
[0047]
Regarding the luminance degradation, the comparative example deteriorated 30% after 200 hours, whereas the 1 nm mixed layer element had 17%, the 5 nm mixed layer element had 11%, the 10 nm mixed layer element had 26%, and the 50 nm mixed layer element had. The deterioration was 50%.
[0048]
FIG. 5 is a diagram showing the relationship between the luminance and the durability time (time) for the 1 nm mixed layer element (1 nm mixed layer 12), the 50 nm mixed layer element (50 nm mixed layer 12), and the element of the comparative example in the present embodiment. It is. The luminance is shown by standardizing the initial luminance to 1.
[0049]
As described above, even in the present embodiment, the mixed layer 12 is not provided by interposing the mixed layer 12 at the interface between the adjacent two layers 7 and 8 in the electron transport layers 7 and 8 formed of two layers. Compared with the conventional one, the adhesion between two adjacent electron transport layers 7 and 8 can be improved, and the luminance life can be improved.
[0050]
And, as shown in the above results, even if the mixed layer 12 is too thick, the electron transporting ability of the electron transporting layers 7 and 8 is impaired, and the luminance life is deteriorated. From the above results, when the thickness of the mixed layer 12 of the present embodiment is 10 nm or less, the driving voltage and the luminance life can be appropriately improved, and when the thickness is 1 nm, the luminous efficiency can be improved. all right.
[0051]
From the above embodiments, it can be said that the brightness lifetime can be appropriately improved if the thickness of the hole transport layer side mixed layer 11 and the electron transport layer side mixed layer 12 is at least 10 nm or less.
[0052]
Further, the mixed layers 11 and 12 of the above embodiments are layers made of a mixture of hole transporting materials or electron transporting materials. Usually, since the film-forming rates of hole transporting materials and electron transporting materials are almost the same, when forming a mixed layer by a co-evaporation method, a material having a volume mixing ratio of about 1: 1 is formed. It can be said that the mixing ratio is easy.
[0053]
(Other embodiments)
In the first and second embodiments, each of the hole transport layers 3, 4 and the electron transport layers 7, 8 is composed of two or more charge transport layers, of which only the hole transport layer side or only the electron transport layer side is included. Mixed layers 11 and 12 are interposed.
[0054]
That is, the mixed layer does not need to be interposed in all of the charge transport layers composed of two or more layers, and the mixed layer may be interposed in the charge transport layer in which a bonding failure is likely to occur. Needless to say, a configuration in which the mixed layer 11 is interposed between the hole transport layers 3 and 4 and the mixed layer 12 is also interposed between the electron transport layers 7 and 8 is shown in FIG. As described above, when the thickness is 10 nm or less, the same results as those of the first and second embodiments are obtained.
[0055]
In the above embodiment, both the hole transport layers 3 and 4 and both the electron transport layers 7 and 8 are composed of two layers, but may be composed of three or more layers. In that case, a mixed layer in which constituent materials of adjacent layers are mixed at the interface of three or more layers may be interposed.
[0056]
Further, only one of the charge transporting layers of the hole transporting layers 3 and 4 and the electron transporting layers 7 and 8 may be constituted by two or more layers, and the other may be constituted by a single layer. In that case, it goes without saying that the mixed layer is interposed in the charge transport layer composed of two or more layers.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an organic EL device according to a first embodiment of the present invention.
FIG. 2 is a schematic sectional view of an organic EL device of a comparative example.
FIG. 3 is a diagram showing a relationship between luminance and a durability time for a 1 nm mixed layer element, a 50 nm mixed layer element, and an element of a comparative example in the first embodiment.
FIG. 4 is a schematic sectional view of an organic EL device according to a second embodiment of the present invention.
FIG. 5 is a diagram showing a relationship between luminance and a durability time for a 1 nm mixed layer element, a 50 nm mixed layer element, and a comparative example element in the second embodiment.
FIG. 6 is a table showing experimental results according to another embodiment together with the first embodiment and the second embodiment.
[Explanation of symbols]
2 ... Anode, 3 ... First hole transport layer, 4 ... Second hole transport layer,
5 ... first light emitting layer, 6 ... second light emitting layer, 7 ... first electron transport layer,
8: second electron transport layer, 10: cathode, 11, 12 ... mixed layer.

Claims (2)

A hole transport layer (3, 4), a light emitting layer (5, 6), and an electron transport layer (7, 8) are sequentially laminated between a pair of electrodes (2, 10);
In an organic EL device, at least one of the charge transport layer of the hole transport layer and the electron transport layer is composed of two or more layers.
In the charge transport layer composed of two or more layers, a mixed layer (11, 12) in which constituent materials of the adjacent charge transport layers are mixed is interposed at an interface between two adjacent charge transport layers. An organic EL device, comprising: The organic EL device according to claim 1, wherein the thickness of the mixed layer (11, 12) is 10 nm or less.

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