KR20090062085A - White organic light emitting device - Google Patents

Abstract

A white organic electroluminescent device is provided to increase efficiency and lifetime by reducing generation of exciton in an electron transport layer and a hole transport layer. An anode(2) is formed on a transparent substrate(1) by sputtering. A hole injection layer(3) and a hole transport layer(4) are successively vacuum-deposited on the anode. A light emitting layer(5-1) of anode side and a light emitting layer(5-2) of cathode side are successively vacuum-deposited on the hole transport layer. An electron transport layer(6) is vacuum-deposited on the light emitting layer of cathode side. An electron injection layer(7) and a cathode(8) are formed on the electron transport layer. A white is performed by mixing lights emitted in the light emitting layer of anode side and the light emitting layer of cathode side. A host material of the light emitting layer of anode side has hole transport performance higher than a host material of the light emitting layer of cathode side.

Description

White Organic Light Emitting Device

The present invention relates to a white organic electroluminescent device.

Organic electroluminescent devices that produce efficient white light are considered to be low-cost alternatives to many applications such as displays, paper-thin light sources, backlights in LCD displays, in-car interiors, and office lighting devices. Organic electroluminescent devices that produce white light should be bright, efficient and generally have a Commission International d'Eclairage (CIE) chromaticity coordinate of about (0.33, 0.33).

The light emitting mechanism of the organic light emitting display device is as follows. Holes injected from the anode into the valence band or highest occupied molecular orbital (HOMO) of the hole injection layer (HIL) proceed to the emitting layer through the hole transporting layer (HTL). At the same time, electrons move from the cathode to the emission layer through the electron injection layer to combine with holes to form excitons. The exciton falls to the ground and emits light.

By using the principle of the organic light emitting device as described above, Eastman Kodak Co., Ltd. in 1987 used TPD (N-N'-DiphenyI-N-N'-bis (methylphenyl-1,1'-biphenyl) as a hole transport layer. An organic light emitting device using Alq ₃ (tris (8-hydroxy- quinoline) aluminum complex) was developed as a light emitting layer using -4,4'-diamine. Since then, researches on organic light emitting devices using organic materials have been actively conducted. .

Conventional white organic electroluminescent devices have a hetero multilayer structure using two wavelengths including two light emitting layers using a complementary relationship between cyan, red, and blue and orange, or a three-wavelength hetero multilayer each including three primary light emitting layers of blue, green, and red. It is manufactured using the mixed color of a structure.

White organic light emitting diodes using three wavelengths are difficult to realize stable three wavelengths by energy transfer from blue to green or green to red, and have disadvantages of poor efficiency and short lifespan.

Conventional 2 wavelengths have advantages in efficiency than 3 wavelengths, but the color coordinates change greatly depending on the current density, and the charge balance between electrons and holes is not balanced. .

Also, in the case of the multi-layered light emitting structure, holes are more abundant than electrons in the light emitting layer adjacent to the anode, whereas in the light emitting layer adjacent to the cathode, the electrons are richer, so that the charge balance is not balanced. It occurs in the electron transport layer or the hole transport layer, and the organic layer is damaged, resulting in a shortened lifespan.

The present invention is to improve the above problems,

By using the host according to the hole and electron transfer characteristics in the light emitting layer of the multi-layer structure, the exciton is further generated in the light emitting layer, and the organic field having improved lifetime and efficiency by reducing the exciton generation in the electron transporting layer / hole transporting layer. It is an object to provide a light emitting element.

Further, an object of the present invention is to provide an organic electroluminescent device having excellent color coordinate characteristics by allowing excitons to be generated mostly in the light emitting layer.

As a means for achieving the above object,

A white organic electroluminescent device comprising an anode, an anode side emitting layer, a cathode side emitting layer, and a cathode, and implementing white color by mixing light emitted from the anode side emitting layer and the cathode side emitting layer, wherein the host material of the anode side emitting layer is Provided is a white organic electroluminescent device, which has better hole transfer performance than a host material of a cathode side light emitting layer.

In addition, an anode, an anode side light emitting layer, a cathode side light emitting layer, and a cathode, the white organic electroluminescent device which realizes white color by mixing of light emitted from the anode side light emitting layer and the cathode side light emitting layer, the host of the cathode side light emitting layer The material provides a white organic electroluminescent device, characterized in that the electron transfer performance is superior to the host material of the anode-side light emitting layer.

In addition, the host material of the anode-side light emitting layer provides a white organic electroluminescent device, characterized in that at least one selected from CBP, TPD, TNATA, HMTPD, NPD.

In addition, the host material of the cathode-side light emitting layer provides a white organic electroluminescent device, characterized in that at least one selected from Alq3, TAZ, BAlq, BCP.

The cathode-side light emitting layer emits red light and the anode-side light emitting layer emits blue light.

Hereinafter, the present invention will be described in detail.

The white organic EL device of the present invention includes an anode, an anode side light emitting layer, a cathode side light emitting layer, and a cathode, and implements white color by mixing light emitted from the anode side emitting layer and the cathode side emitting layer.

The host of the anode-side light emitting layer near the anode side uses an excellent hole transfer performance compared to the host of the cathode-side light emitting layer near the cathode side, so that the holes can be transferred to the cathode-side light emitting layer well. Hosts with excellent hole-transporting properties generally have a strong tendency to block electrons, preventing electrons from passing through the light-emitting layer to other organic layers (hole transport layers, etc.), resulting in the formation of excitons in other organic layers. It is possible to improve this, and to improve the unstable change in color coordinates.

On the other hand, the host of the cathode side light emitting layer has better electron transfer performance than the host of the anode side light emitting layer to transfer electrons to the anode side emitting layer well, and the host having excellent electron transfer performance generally has a tendency to block holes. Since the hole is strong and reaches the other organic layer (electron transfer layer, etc.) through the light emitting layer, it is possible to improve the above problems caused by the formation of excitons.

1 is a cross-sectional view of a white organic light emitting diode according to an embodiment of the present invention. Briefly described as follows. First, the anode 2 is formed on the transparent substrate 1 by a method such as sputtering, and the hole injection layer 3 and the hole transport layer 4 are sequentially vacuum deposited on the anode. The anode-side light emitting layer 5-1 and the cathode-side light emitting layer 5-2 are again formed on the hole transport layer 4 by vacuum deposition, and then the electron transport layer 6 is formed by vacuum deposition. Thereafter, the electron injection layer 7 and the cathode 8 are formed on the electron transport layer 6.

In the above configuration, if necessary, one or more of a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer may be selectively omitted, and other configurations may be added and all are included in the present invention.

The substrate 1 is not particularly limited, and those commonly used in organic electroluminescent devices, for example, glass, transparent plastic, quartz, and the like may be used.

Examples of the anode (2) material include metal oxides or metal nitrides such as ITO, IZO, tin oxide, zinc oxide, zinc aluminum oxide, and titanium nitride; Metals such as gold, platinum, silver, copper, aluminum, nickel, cobalt, lead, molybdenum, tungsten, tantalum and niobium; Alloys of these metals or alloys of copper iodides; Conductive polymers such as polyaniline, polythiopine, polypyrrole, polyphenylenevinylene, poly (3-methylthiopine), and polyphenylenesulfagard. The anode 2 may be formed of only one type of the aforementioned materials or may be formed of a mixture of a plurality of materials. In addition, a multilayer structure composed of a plurality of layers of the same composition or different compositions can be formed.

The hole injection layer 3 of the present invention may use materials known in the art, but is not limited to PEDOT / PSS or copper phthalocyanine (CuPc), 4,4 ′, 4 ″ -tris (3-methylphenylphenylamino) Substances such as triphenylamine (m-MTDATA) can be used.

The hole transport layer 4 may be 4,4'-bis [N- (1-naphthyl) -N-phenyl-amino] -biphenyl (NPD) or N, N'-diphenyl-N, N'-bis Substances such as (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (TPD) can be used.

The anode light emitting layer 5-1 and the cathode light emitting layer 5-2 may be composed of a single material, but typically, light emission mainly comes from a dopant and has a guest compound or compounds that may have any color. Made of a doped host material.

As a host material of the anode-side light emitting layer 5-1, a host having excellent hole transporting performance is selected, and the host material is not limited as an example. , TPD (4,4'-bis [N- (1-naphthyl) -N-phenyl-amino] -biphenyl), TNATA (4,4 ', 4 "-tris (N- (2-naphthyl) -N-phenyl-amino) -triphenylamine), HMTPD (4,4'-bis [N, N '-(3-tolyl) amino] -3,3'-dimethylbiphenyl), NPD (4,4 At least one selected from '-bis [N- (1-naphthyl) -N-phenyl-amino] -biphenyl), AND (9,10-di- (2-naphthyl) anthracene)'.

The host material of the cathode-side light emitting layer 5-2 is not limited to a host having excellent electron transfer performance, but Alq3 (tris (8-quinolinato) aluminum (III)) and TAZ (3-phenyl-4- (1'-naphthyl) -5-phenyl-1,2,4-triazole), BAlq (bis (2-methyl-8-quinolato) (p-phenyl-phenolato) aluminum), BCP (2 , 9-dimethyl-4,7-diphenyl-1,10-phenanthroline).

Further, the anode-side light emitting layer 5-1 and the cathode-side light emitting layer 5-2, together with the above-listed hosts, are not limited, but (4,4'-bis (2,2-diphenyl-ethene-1-). I) diphenyl (DPVBi), bis (styryl) amine (DSA) type, bis (2-methyl-8-quinolinolato) (triphenylsiloxy) aluminum (III) (SAlq), bis (2- Methyl-8-quinolinolato) (para-phenolato) aluminum (III) (BAlq), bis (salen) zin (II), 1,3-bis [4- (N, N-dimethylamino) phenyl- 1,3,4-oxadiazolyl] benzene (OXD8), 3- (biphenyl-4-yl) -5- (4-dimethylamino) 4- (4-ethylphenyl) -1,2,4-tria Sol (p-EtTAZ), 3- (4-biphenyl) -4-phenyl-5- (4-tert-butylphenyl) -1,2,4-triazole (TAZ), 2,2 ', 7 , 7'-tetrakis (non-phenyl-4-yl) -9,9'-spirofluorene (Spiro-DPVBI), tris (para-ter-phenyl-4-yl) amine (p-TTA), 5 , 5-bis (dimethylbutylboryl) -2,2-bithiophene (BMB-2T) and perylene, tris (8-quinolinato) aluminum (III) (Alq3), DCM1 (4-dish) Anomethylene-2-methyl-6- (para-dimethylami Stilyl) -4H-pyran), DCM2 (4-dicyanomethylene-2-methyl-6- (julolidin-4-yl-vinyl) -4H-pyran), DCJT (4- (dicyanomethylene)- 2-methyl-6- (1,1,7,7-tetramethylzulolidil-9-enyl) -4H-pyran), DCJTB (4- (dicyanomethylene) -2-tertbutylbutyl-6- ( 1,1,7,7-tetramethylzulolidil-9-enyl) -4H-pyran), DCJTI (4-dicyanomethylene) -2-isopropyl-6- (1,1,7,7-tetra One or more selected from methylzololidyl-9-enyl) -4H-pyran), nile red, rubrene, and the like can be used as a host or dopant. In addition, a blue dopant, a red dopant, a yellow dopant and the like known in the art may be used. For example, DSA-amine represented by Chemical Formula 1 may be used as a blue dopant, and Ir (piq) 3 represented by Chemical Formula 2 may be used as a red dopant.

<Formula 1>

<Formula 2>

In order to realize a white color, the anode-side light emitting layer 5-1 and the cathode-side light emitting layer 5-2 may be configured by mutually selecting a light emission of a complementary color. For example, red light emission and blue light emission may be selected. In addition, it can be varied and the configuration of a tandem white organic electroluminescent device well known in the art can be adopted.

Preferably, a red light emitting layer is used as the anode side emitting layer 5-1, and a blue light emitting layer is selected as the cathode side emitting layer 5-2. For this purpose, a red dopant is used for the anode layer emitting layer and blue is used for the cathode side emitting layer. Dopants may be used.

The electron transport layer 6 may include an aryl substituted oxadiazole, aryl-substituted triazole, aryl-substituted phenanthroline, benzoxazole, or benzoxazole compound, for example, 1,3 -Bis (N, Nt-butyl-phenyl) -1,3,4-oxadiazole (OXD-7); 3-phenyl-4- (1'-naphthyl) -5-phenyl-1,2,4-triazole (TAZ); 2,9-dimethyl-4,7-diphenyl-phenanthroline (vasocuproin or BCP); Bis (2- (2-hydroxyphenyl) -benzoxazolate) zinc; Or bis (2- (2-hydroxyphenyl) -benziazolate) zinc; As the electron transporting material, (4-biphenyl) (4-t-butylphenyl) oxydiazole (PDB) and tris (8-quinolinato) aluminum (III) (Alq3) can be used, preferably Tris ( Preference is given to 8-quinolinato) aluminum (III) (Alq3).

The electron injection layer 7 and the cathode 8 may be made of a material known in the art, but are not limited to LiF as an electron injection layer and a metal having a low work function such as Al, Ca, Mg, Ag, or the like. It is possible to use, preferably Al is preferred.

Each layer constituting the organic electroluminescent element of the present invention can be formed by applying a known method, such as a vapor deposition method, a spin coating method, a cast method, or the like, to a material which should constitute each layer, to form a thin film. The film thickness of each of the layers thus formed, for example, the light emitting layer, is not particularly limited and can be appropriately selected depending on the situation.

The white organic electroluminescent device of the present invention classifies the host according to the hole and electron transfer characteristics in the light emitting layer having a multilayer structure, and has a good hole transfer characteristic in the light emitting layer on the anode side, and a host having good electron transfer characteristics in the light emitting layer on the cathode side. By using this, the transfer efficiency is increased, so that the excitons are generated more efficiently in the light emitting layer.

In addition, by blocking the opposite characteristics, it is possible to reduce the generation of excitons in the electron transporting layer / hole transporting layer through the light emitting layer, thereby improving lifespan and efficiency, and improving color coordinate unstable change.

Hereinafter, the present invention will be described in more detail with reference to Examples. The following examples are specific examples of the present invention, but the present invention is not limited thereto even though there is a certain or definite expression.

EXAMPLE

The light emitting area of the ITO gliss was patterned to have a size of 3 mm × 3 mm and then washed. After mounting the substrate in the vacuum chamber, the basic pressure was 1 X 10 ^-6 torr, and the organic material was ADN (250Å) / Ir doped with 3% by weight of DNTPD (500Å) / NPD (500Å) / DSA-amine on ITO. The film was formed in the order of BAlq (250 mm 3) / Balq (350 mm 3) / LiF (50 mm 3) / Al (1,000 mm 3) doped with (piq) 3 by weight. That is, ADN having a hole transporting property was used as a host for the anode-side light emitting layer, and BAlq having an electron transporting property was used as the host for the cathode-side light emitting layer.

Efficiency characteristics and color coordinates of the organic electroluminescent device manufactured according to the example are shown in Table 1, and the EL spectrum is shown in FIG. As can be seen, it can be seen that the organic electroluminescent device of the embodiment is excellent in efficiency and the color coordinates and the EL spectrum provide white which is close to natural light.

TABLE 1

   10000 (㏅ / ㎡) standard Voltage (V) Measures 8.8 Current density (㎃ / ㎠) Measures 113 Efficiency (cd / A) Measures 8.85 Light efficiency (lm / W) Measures 3.16 Color coordinates x 0.3235 y 0.3844

1 is a cross-sectional view of a white organic electroluminescent device according to an embodiment of the present invention;

2 is an EL spectrum of an embodiment of the present invention.

** Description of the main symbols in the drawings **

1: substrate 2: anode

3: hole injection layer 4: hole transport layer

5-1: anode side light emitting layer 5-2: cathode side light emitting layer

6: electron transport layer

7: electron injection layer 8: cathode

Claims (4)

A white organic electroluminescent device comprising an anode, an anode side emitting layer, a cathode side emitting layer, and a cathode, and implementing white color by mixing light emitted from the anode side emitting layer and the cathode side emitting layer, The host material of the anode-side light emitting layer is a hole transport performance is superior to the host material of the cathode-side light emitting layer, the white organic electroluminescent device, characterized in that at least one selected from CBP, TPD, TNATA, HMTPD, NPD, ADN. A white organic electroluminescent device comprising an anode, an anode side emitting layer, a cathode side emitting layer, and a cathode, and implementing white color by mixing light emitted from the anode side emitting layer and the cathode side emitting layer, The host material of the cathode side light emitting layer has a better electron transport performance than the host material of the anode side light emitting layer, the white organic electroluminescent device, characterized in that the hole block performance is superior. The white organic electroluminescent device according to claim 2, wherein the host material of the cathode side light emitting layer is at least one selected from Alq3, TAZ, BAlq, and BCP. The white organic electroluminescent device according to any one of claims 1 to 3, wherein the cathode light emitting layer emits red light and the anode light emitting layer emits blue light.

Images