JP2008108995A - Organic light-emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic light-emitting diode that is driven by a lower voltage, and emits high-luminance and long-lived light. <P>SOLUTION: The organic light-emitting diode comprises at least a hole transport layer 13; a light-emitting layer 14; and an electron transport layer 15 in which a fluoride of an alkali metal is doped in a pyridyl-group containing oxadiazole derivative between an anode 12 and a cathode 16 that are provided on a substrate 11. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to organic light emitting diode devices.

  The organic light emitting diode device emits light with high luminance at a relatively low driving voltage, and can be made into a thin and light light emitting device. Therefore, application to a flat display is expected.

In order to make the organic light emitting diode emit light efficiently at a low driving voltage, a buffer that improves the electron injection efficiency into the light emitting layer is doped in the electron transport layer of the organic light emitting diode, or a buffer layer is provided in the organic light emitting diode. ing. As the buffer material, alkali metals and alkali metal compounds such as cesium and lithium are commonly used. Patent Document 1 discloses an organic light emitting diode device having an electron injecting dopant source layer containing an alkali metal compound such as lithium fluoride or a thermal decomposition product thereof. Further, Patent Document 2 discloses an organic EL diode including a buffer layer made of a component obtained by doping Alq ₃ as a host material with alkali fluoride or alkaline earth fluoride, and a cathode made of a noble metal. .

  However, since alkali metals are unstable in the atmosphere, an expensive vapor deposition source called an alkali dispenser must be used for doping. In addition, the layer doped with lithium fluoride as a buffer needs to be stacked as thin as 0.5 nm, and it is difficult to control the thickness.

JP 2004-14511 A JP 2006-157022 A

  An object of the present invention is to provide an organic light-emitting diode device which is driven at a lower voltage and which emits light with a high luminance and a long lifetime.

  An organic light-emitting diode device according to claim 1, which has been made to achieve the above object, includes at least a hole transport layer between an anode and a cathode provided on a substrate, It includes a light emitting layer and an electron transport layer in which pyridyl group-containing oxadiazole derivative is doped with an alkali metal fluoride.

  An organic light emitting diode device according to a second aspect is the one according to the first aspect, wherein the alkali metal fluoride is cesium fluoride.

  The organic light emitting diode device according to claim 3 is the one described in claim 1, wherein the pyridyl group-containing oxadiazole derivative has the following chemical formula:

で示される化合物であることを特徴とする。

It is a compound shown by these.

  The organic light-emitting diode device according to claim 4 is the device according to claim 1, wherein the molar ratio of the pyridyl group-containing oxadiazole derivative to the alkali metal fluoride is 1: 1 to 2: 1. It is characterized by being.

An organic light-emitting diode device according to a fifth aspect is the organic light-emitting diode device according to the first aspect, wherein the light-emitting layer is a layer made of aluminum tris 8-hydroxyquinoline (Alq ₃ ).

  The organic light-emitting diode device according to claim 6 is the device according to claim 1, wherein the hole transport layer is 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl. It is a layer made of (NPB).

  In the organic light-emitting diode device of the present invention, an oxadiazole derivative having a pyridyl group is used as an electron transport material, and an electron transport layer is constituted by a component doped with cesium fluoride. With this configuration, the energy gap between the cathode and the electron transport layer is lowered. As a result, the organic light-emitting diode of the present invention is driven at a low voltage equivalent to that of a light-emitting diode doped with an alkali metal as a buffer or a conventional light-emitting diode having a buffer layer, and obtains light emission with high brightness and long life. be able to.

  Since the cesium fluoride is a stable compound, it is easy to handle. Therefore, when producing an organic light emitting diode device, an expensive vapor deposition source such as an alkaline dispenser is not required.

  The organic light-emitting diode device of the present invention can be used for displays, lighting and the like.

Preferred form for carrying out the invention

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings, but the scope of the present invention is not limited to these embodiments.

As shown in FIG. 1, the layer structure of the preferred organic light emitting diode device of the present invention is as follows: glass substrate 11 / anode 12 (ITO) / hole transport layer 13 (NPB) / light emitting layer 14 (Alq ₃ ) / electron transport layer 15. (BpyOXDm: cesium fluoride) / cathode 16 (Al).

  The electron transport layer 15 is a layer having a function of sending electrons injected from the cathode to the light emitting layer, and is a pyridyl group-containing oxadiazole derivative BpyOXDm (1,3-bis [2- (2,2'-bipyridin- 6-yl) -1,3,4-oxadiazol-5-yl] benzene) is composed of a component doped with cesium fluoride (CsF), which is an alkali metal fluoride. BpyOXDm has a structure represented by the following chemical formula.

  The electron transport layer is obtained by co-depositing BpyOXDm at a deposition rate of 1 Å / s and cesium fluoride at a deposition rate of 0.03 to 0.2 Å / s by a vacuum deposition method. It is preferable that the doping ratio of BpyOXDm and cesium fluoride is 1: 1 to 2: 1 in terms of molar ratio because driving at a lower voltage can be obtained. The thickness of the electron transport layer is preferably 20 to 50 nm.

The pyridyl group-containing oxadiazole derivative is not particularly limited as long as it has a pyridine ring, and may have a bipyridyl group. As a pyridyl group-containing oxadiazole derivative, in addition to the BpyOXDm,
2,6-bis [2- (2,2'-bipyridin-6-yl) -1,3,4-oxadiazol-5-yl] pyridine
(Phpy-OXDm), 1,3-bis [2- (2,2'-bipyridin-6-yl) -1,3,4-oxadiazol-5-yl] -5-cyanobenzene (CBPO) be able to.

The light emitting layer 14 is a layer having a function of emitting light by recombination of holes and electrons in the layer. The material constituting the light emitting layer is not particularly limited as long as it can exhibit the above functions, but aluminum tris 8-hydroxyquinoline (Alq ₃ ) is preferable.

  The hole transport layer 13 is a layer having a function of sending holes from the anode to the light emitting layer. The material constituting the hole transport layer is not particularly limited as long as it can exhibit the above functions, but 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPB). Is preferable.

  As the substrate 11, for example, a transparent substrate such as a glass substrate or a quartz substrate, or an opaque substrate such as a metal substrate or a ceramic substrate can be used.

  The material of the anode 12 is preferably a material having a large work function, for example, a simple metal such as gold, platinum, nickel, palladium, cobalt, selenium, vanadium; an alloy of these metals; tin oxide, zinc oxide, indium tin oxide. (ITO), and metal oxides such as zinc indium oxide. Of these, ITO is preferable. These anode materials may constitute an anode alone or may be used in combination.

  The material of the cathode 16 is preferably a material having a small work function, for example, simple metals such as lithium, sodium, potassium, calcium, magnesium, aluminum, indium and silver; and alloys of these metals. Of these, aluminum is preferable. These cathode materials may constitute a cathode alone or in combination.

  The formation method of the hole transport layer, the light emitting layer, the anode and the cathode is not particularly limited, and a known method such as a dry process such as a vacuum evaporation method, a wet process such as a spin coating method or an ink jet method is used. It can be used as appropriate.

  The organic light emitting diode device of the present invention may be provided with layers such as a hole injection layer, a hole blocking layer, and an electron injection layer in addition to the above layers. These layers may be a single layer or multiple layers.

  An example in which an organic light emitting diode device to which the present invention is applied is produced is shown in Examples 1 and 2, and an example in which an organic light emitting diode device to which the present invention is not applied is produced is shown in Comparative Example 1.

(Example 1)
The structure of the organic light emitting diode device of Example 1 is glass substrate / ITO / NPB / Alq ₃ / BpyOXDm: cesium fluoride / Al.

  On the glass substrate, ITO was formed into a film with a thickness of 150 nm by sputtering as an anode, and the surface was washed and dried.

  Next, NPB was deposited on the anode as a hole transport layer to a thickness of 50 nm by a vacuum deposition method.

Next, on the hole transport layer, Alq ₃ was deposited to a thickness of 20 nm as a light emitting layer by vacuum deposition.

Next, on the light emitting layer, as an electron transport layer, BpyOXDm and cesium fluoride are formed at a deposition rate of 1 Py / s of BpyOXDm by vacuum deposition so that the molar ratio is 1: 1, and cesium fluoride is formed. Co-evaporation was performed at a film speed of 0.1 蒸 着 / s at a vacuum degree of 2.0 × 10 ⁻⁴ Pa or more to form a film with a thickness of 30 nm.

  Next, on the electron transport layer, aluminum as a cathode was formed into a film having a film thickness of 200 nm by a vacuum vapor deposition method and dried to obtain the device of Example 1.

(Example 2)
A device of Example 2 was obtained in the same manner as Example 1 except that the molar ratio of BpyOXDm to cesium fluoride was 2: 1.

(Comparative Example 1)
The structure of the organic light emitting diode device of Comparative Example 1 is glass substrate / ITO / NPB / Alq ₃ / BpyOXDm / LiF / Al.

  On the glass substrate, ITO was formed into a film with a thickness of 150 nm by sputtering as an anode, and the surface was washed and dried.

  Subsequently, NPB was formed into a film thickness of 50 nm as a positive hole transport layer on the said anode by the vacuum evaporation method.

Next, on the hole transport layer, Alq ₃ was deposited as a light emitting layer to a thickness of 20 nm by vacuum deposition.

  Next, BpyOXDm was deposited as an electron transport layer on the light emitting layer to a thickness of 30 nm by vacuum deposition.

  Next, lithium fluoride (LiF) was deposited as a buffer layer on the electron transport layer to a thickness of 0.5 nm by a vacuum deposition method.

  Next, on the buffer layer, aluminum as a cathode was formed into a film having a film thickness of 200 nm by a vacuum vapor deposition method and dried to obtain a device of Comparative Example 1.

  The devices prepared in Examples 1 and 2 and Comparative Example 1 were subjected to the following measurements and evaluated for physical properties.

(Current density measurement)
The current density of each device was measured using an organic EL luminous efficiency measuring device EL1003 (manufactured by Play Size Gauge). The measurement results are shown in FIG.

  As is clear from FIG. 2, the device of the example was able to obtain a current density equivalent to that of the device of the comparative example at a lower voltage than the device of the comparative example.

It is a cross-sectional schematic diagram which shows the layer structure of the organic light emitting diode device to which this invention is applied.

It is a graph which shows the relationship between the voltage and current density in each device obtained by the Example and comparative example of this invention.

Explanation of symbols

  1 is an organic light emitting diode device, 11 is a substrate, 12 is an anode, 13 is a hole transport layer, 14 is a light emitting layer, 15 is an electron transport layer, and 16 is a cathode.

Claims (6)

  Between the anode and the cathode provided on the substrate, at least a hole transport layer, a light emitting layer, and an electron transport layer doped with an alkali metal fluoride in a pyridyl group-containing oxadiazole derivative are provided. An organic light-emitting diode device characterized by that.   2. The organic light emitting diode device according to claim 1, wherein the alkali metal fluoride is cesium fluoride. The pyridyl group-containing oxadiazole derivative has the following chemical formula:

The organic light-emitting diode device according to claim 1, wherein the organic light-emitting diode device is a compound represented by the formula:   2. The organic light emitting diode device according to claim 1, wherein a molar ratio of the pyridyl group-containing oxadiazole derivative and the alkali metal fluoride is 1: 1 to 2: 1. The organic light emitting diode device of claim 1, wherein the light emitting layer, characterized in that a layer consisting of aluminum tris 8-hydroxyquinoline (Alq _3).   2. The organic light emitting diode according to claim 1, wherein the hole transport layer is a layer made of 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (NPB). device.

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