KR100643924B1 - Organic light emitting devices comprising emitting layer doped by wide energy gap impurity - Google Patents

Abstract

Provided are an organic light emitting device which is improved in the injection efficiency of electrons and holes and luminous efficiency and is remarkably enhanced in lifetime, and a method for preparing the device. The organic light emitting device comprises a light emitting layer containing 0.5-1.5 wt% of the impurities which has an energy gap greater than that of a light emitting host material. Preferably the light emitting host material is Alq3 (tris(8-hydroxyquinoline)aluminum); and the impurities is at least one selected from the group consisting of DPVBi (4,4-bis(2,2-diphenyl vinyl)-1,1-biphenyl), NPB (N,N'-diphenyl-N,N'-bis(1,1'-biphenyl)-4,4'-diamine) and BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline).

Description

Organic light emitting devices comprising emitting layer doped by wide energy gap impurity

1 is a schematic view showing the structure of a general organic light emitting device,

Figure 2 is a schematic diagram showing the layer configuration of the organic light emitting device according to an embodiment and a comparative example of the present invention,

Figure 3 is a schematic diagram showing the energy band structure of the organic light emitting device according to an embodiment of the present invention and Comparative Example, (a) is the energy band of the organic light emitting device to which 0.5% by weight of DPVBi is added to the light emitting layer, (b ) Represents the energy band structure of the basic element arranged based on the LUMO, HOMO of the organic material and the work function of the electrode,

Figure 4 is a graph showing the current density-voltage measurement results of the organic light emitting device manufactured according to the embodiment and the comparative example of the present invention,

FIG. 5 is a graph showing a result of measuring luminance intensity-voltage of organic light emitting diodes manufactured according to one embodiment and a comparative example of the present invention.

6 is a graph showing a result of measuring luminous efficiency-current density of organic light emitting diodes manufactured according to one embodiment and a comparative example of the present invention.

7 is a graph illustrating a result of measuring power efficiency-current density of organic light emitting diodes manufactured according to one embodiment and a comparative example of the present invention.

8 is a graph showing the life characteristics measurement results of the organic light emitting device manufactured according to the embodiment and the comparative example of the present invention.

<Explanation of symbols for the main parts of the drawings>

1: substrate

2: anode

3: hole transport layer

4: light emitting layer

5: electron transport layer

6: electron injection layer

7: cathode

The present invention relates to an organic light emitting device capable of increasing the light emitting efficiency and extending the light emitting life and a method of manufacturing the same.

Recently, as the size of the display device increases, the demand for a flat display device having less space is increasing. As one of the flat display devices, the technology of an organic light emitting device is rapidly developing. Currently, researches on organic light emitting devices are mainly focused on improving the efficiency and lifespan of the devices, and various structures and manufacturing methods are proposed to improve the light emission efficiency of the organic light emitting devices or to control the emission spectrum. It is becoming.

For example, an attempt has been made to add a light emitting impurity having an energy gap smaller than that of the light emitting host. The structure in which the light emitting impurity is added also reduces the effect of the light emitting host having a charge, thereby improving the life of the device.

In addition, there has been a study on a method of increasing the efficiency of an organic light emitting device by adding a new kind of phosphorous impurity to the organic light emitting device that enables the emission of triplet excitons other than singlet excitons. The development of phosphorous impurities has resulted in improved device efficiency.

However, in the conventional method of adding luminescent impurities to the host organic material, since luminescent impurities having an energy gap smaller than the energy gap of the luminescent host are used, efficiency decreases during energy transfer of exciton, or the luminescent region of the spectrum has a green or blue wavelength. There is a problem in that the wavelength is shorter than that of the region and the color of the desired wavelength region cannot be obtained. Accordingly, there is a need for an organic light emitting device having a high luminous efficiency and a long lifetime and capable of emitting light in a desired wavelength region.

An object of the present invention is to provide an organic light emitting device and a method of manufacturing the same that can increase the light emission efficiency and extend the light emission life.

In order to achieve the above object,

According to an aspect of the present invention, an organic light emitting device including an emission layer to which an impurity having an energy gap larger than that of an emission host material is added may be provided.

In addition, according to another aspect of the present invention,

1) forming an anode on the substrate;

2) forming a hole transport layer on the anode;

3) forming a light emitting layer on the hole transport layer;

4) forming an electron transport layer on the light emitting layer;

5) forming an electron injection layer on the electron transport layer; And

6) forming a cathode on the electron injection layer, wherein the step of forming the light emitting layer of the 3), the organic material is formed by adding impurities having an energy gap larger than the energy gap of the light emitting host material It is possible to provide a method of manufacturing a light emitting device.

Before describing the present invention in detail, the driving principle and structure of a general organic light emitting device will be briefly described.

Referring to FIG. 1, when a driving voltage is applied to the anode 2 and the cathode 7, holes and electrons proceed toward the light emitting layer 4 through the hole transport layer 3 and the electron transport layer 5, respectively, and they are organic. It is introduced into the light emitting layer to generate an exciton, and the exciton falls from the excited state to the ground state to generate visible light corresponding to the energy difference. In this way, the visible light generated from the light emitting layer displays an image or an image on the principle of escaping out through the transparent anode electrode.

The anode is a hole injection electrode, a transparent metal oxide is generally used so that the work function is high and the emitted light can come out of the device, the most widely used hole injection electrode is an indium tin oxide (ITO) electrode.

In addition, the light emitting layer is Alq ₃ Low molecular organic materials such as (tris- (8-hydrozyquinoline) aluminum) and anthracene, or high molecular organic materials such as poly (p-phenylenevinylene) (PPV), polythiophene (PT), and derivatives thereof are used.

The hole transport layer, the electron transport layer and the electron injection layer are formed between the anode and the light emitting layer or between the cathode and the light emitting layer to increase the mobility of holes and electrons, respectively, and these layers may be made of a low molecular or polymer organic material. . The combination of the transport layer and the injection layer increases the quantum efficiency, and the driving voltage can be lowered through a two-step injection process through which the carriers (electrons or holes) are not directly injected through the transport layer. In addition, since electrons and holes injected into the light emitting layer may be blocked by the opposite transport layer when the electrons and holes are moved to the opposite electrode through the light emitting layer, the light emission efficiency may be improved by controlling recombination.

As the hole transport layer, NPB (N, N'-diphenyl-N, N'-bis (1,1'-biphenyl) -4,4'-diamine), TPD (N, N'-diphenyl-N, N'- bis (3-methylphenyl)-(1,1'-biphenyl) -4,4'-diamine), 11,11,12,12-tetracyano-9,10-anthraquinodimethane (Synth. Met. 85, 1267 (1997) ) And Alq ₃ as the electron transport layer low molecular organic materials such as (tris- (8-hydrozyquinoline) aluminum), Anthracene, or poly (p-phenylenevinylene) (PPV), polythiophene (PT), TAZ (3- (4-biphenylyl) -4-phenyl-5- (4-tert-butylphenyl) -1,2,4-triazole), PBD ([2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole]), Bebq2 ( Bis (10-hydrozybenzo [h] qinolinatoberyllium), TPBI (2,2,2 '-(1,3,5-benzenetriyl) tris- [1-phenyl-1H-benzimidazole] and the like may be used.

The electron injection layer may be omitted, but in the case of formation, a thin layer of LiF or Liq (lithium quinolate) layer is formed, or an alkali metal or alkaline earth metal such as Li, Ca, Mg, Sr, etc. is used to improve electron injection performance.

As the cathode, Ca, Mg, Al, and the like, which have a small work function, are used.

According to an aspect of the present invention, an organic light emitting device including an emission layer to which an impurity having an energy gap larger than that of an emission host material is added may be provided.

The organic light emitting device formed by the method of the present invention is not particularly limited, and includes: a first electrode; Hole transport layer; Light emitting layer; Electron transport layer; Electron injection layer; And a second electrode / first electrode; Hole injection layer; Hole transport layer; Light emitting layer; Electron transport layer; Electron injection layer; And a second electrode / first electrode; Hole transport layer; Light emitting layer; Electron injection layer; And a second structure such as a second electrode.

In a preferred embodiment of the present invention, an anode formed on a substrate; Hole transport layer; Light emitting layer; Electron transport layer; Electron injection layer; And an organic light emitting device comprising a cathode.

In order to fabricate an organic light emitting device having a high luminous efficiency and a controllable emission spectrum, an attempt has been made to add a light emitting impurity having an energy gap smaller than that of the light emitting host (CW Tang, SA VanSlyke, and CH Chen,). J. Appl. Phys. 65 , 3610-3616 (1989)).

In addition, there has been a study on a method of increasing the efficiency of the organic light emitting device by adding a new kind of phosphorous impurities to the organic light emitting device to enable the emission of triplet excitons other than the singlet excitons to be formed (MA Baldo, DF O ' Brien, Y. You, A. Shoustikov, S. Sibley, ME Thompson, and SR Forrest, Nature 395 , 151-154 (1998)), which recently improved the efficiency with the development of new types of phosphorus impurities. (C. Adachi, MA Baldo, SR Forrest, and ME Thompson, Appl. Phys. Lett. 77 , 904-906 (2000)).

However, when an impurity smaller than the energy gap of the light emitting host material is added, there is a problem in that light does not emit in the spectral region of the light emitting host. In the present invention, in order to solve this problem and to improve the luminous efficiency and emission life of the light emitting layer host material of the organic light emitting device, an organic impurity having an energy gap larger than that of the light emitting layer host material is added to the light emitting layer.

Impurities having a smaller energy gap than the light emitting host material are directly emitted by the energy of excitons generated in the light emitting host, but impurities having a larger energy gap than the light emitting host do not participate in direct light emission. The non-emissive impurity serves to improve various characteristics of the device, which improves electron and hole injection characteristics, improves light emission characteristics and light emission efficiency, and delays deterioration of the device according to operation, thereby emitting light in a desired wavelength region. It provides an important structural basis for manufacturing high efficiency organic light emitting devices.

DPVBi (4,4-bis (2,2-diphenyl vinyl) -1,1 used as a blue light emitting organic material in the present invention in order to check the characteristics of the organic light emitting device with an impurity having a larger energy gap than the light emitting host material -biphenyl) was prepared by adding 0.5 wt% of Alq _{3 to the} light emitting host (Fig. 2A) and a basic device using only Alq _{3 as the} light emitting layer (Fig. 2B).

In the organic light emitting device comprising a light emitting layer to which an impurity having an energy gap larger than that of the light emitting host material is added,

The light emitting host material may vary depending on the color of the wavelength region desired to emit light, and is selected from the group consisting of Alq ₃ , anthracene, poly (p-phenylenevinylene) (PPV), and polythiophene (PT), and Alq _3. It is more preferable that is.

Further, the impurity is not particularly limited as long as the energy gap of the impurity is larger than the energy gap of the light emitting host, and may be DPVBi, NPB and BCP (2,9-dimethyl-4,7diphenyl-1,10-phenanthroline). It is preferable to select from the group which consists of, and it is more preferable that it is DPVBi.

In addition, the concentration to which the impurity is added is preferably 0.5 to 1.5% by weight, more preferably 0.5% by weight. If it is added less than 0.5% by weight, the growth rate of the host organic material is increased, there is a problem in the uniformity of the organic matter, when added to more than 1.5% by weight there is a problem that the charge transfer efficiency is lowered by impurities.

4 to 7 show the current density-voltage, emission intensity-voltage, emission efficiency-current density and power efficiency-current density characteristics of the organic light emitting diode and the basic element of the present invention to which 0.5 wt% DPVBi is added to the light emitting layer. have. DPVBi added to the light emitting layer of the organic light emitting device of the present invention serves to reduce the electron-electron interaction in Alq ₃ negatively charged by the transported electrons to reduce the amount of space charge. As the amount of space charge decreases, the injection of electrons and holes is facilitated, and the energy barrier for electrons transferred through the hole transport layer to be transferred to the light emitting layer is relatively high, thereby increasing the probability of generating excitons, thereby increasing luminous efficiency.

FIG. 8 shows the results of measuring lifetime characteristics of an organic light emitting diode and a basic element having 0.5 wt% DPVBi added to the light emitting layer at an initial brightness of 1000 cd / m ² . When the initial brightness is converted to 100 cd / m ² , the half life of the organic light emitting diode of the present invention to which 0.5 wt% DPVBi is added to the light emitting layer is 2017 hours, and the half lifetime of the basic device is 734 hours. DPVBi added to the light emitting layer controls the amount of holes injected into the Alq ₃ light emitting layer by increasing the injection barrier through which holes passing through the hole transport layer are injected into the light emitting layer, and facilitates the injection of electrons due to the effect of reducing the space charge. Reduce the amount of holes staying at ₃ . As a result, deterioration caused by holes staying in Alq ₃ is reduced, thereby extending the life of the device.

In addition, the present invention

1) forming an anode on the substrate;

2) forming a hole transport layer on the anode;

3) forming a light emitting layer on the hole transport layer;

4) forming an electron transport layer on the light emitting layer;

5) forming an electron injection layer on the electron transport layer; And

6) forming a cathode on the electron injection layer, wherein the step of forming the light emitting layer of the 3), the organic light emitting device is formed by adding an impurity having a larger energy gap than the energy gap of the light emitting host material The manufacturing method of can be presented.

Hereinafter, preferred embodiments of the organic light emitting device according to the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the following examples, and many variations are possible by those skilled in the art within the spirit of the present invention.

Example 1 Fabrication of Organic Light Emitting Diode

<1-1> Preparation of Anode

An Indium-Tin-Oxide (ITO) thin film having a small surface resistance (˜30 μs / □) and high transmittance (˜90%) was deposited on a glass substrate using an organic molecular beam evaporator.

<1-2> Preparation of Hole Transport Layer

NPB was deposited on the prepared anode under a vacuum condition of 10 ⁻⁷ to 10 ⁻⁹ Torr to prepare a hole transport layer having a thickness of 40 nm.

<1-3> Preparation of Light Emitting Layer

At a growth rate of about 0.1 nm / sec in a vacuum condition of 10 ^-7 to 10 ^-9 Torr, Alq ₃ was added so that the doping concentration of DPVBi was 0.5% by weight. Mixing deposition to a thickness of 30nm to form a light emitting layer.

<1-4> Preparation of Electron Transport Layer

At a growth rate of about 0.1 nm / sec under vacuum conditions of 10 ⁻⁷ to 10 ⁻⁹ Torr, Alq ₃ was vacuum deposited to a thickness of 30 nm on the light emitting layer to form an electron transport layer.

<1-5> Preparation of Liq Electron Injection Layer and Cathode

At a growth rate of about 0.1 nm / sec in a vacuum condition of 10 ⁻⁷ to 10 ⁻⁹ Torr, Liq was deposited to a thickness of 2 nm on the light emitting layer and the electron transport layer, and Al was deposited to a thickness of 100 nm as a cathode.

Comparative Example 1 Fabrication of Organic Light-Emitting Element (Basic Element) Having a Light-Emitting Layer Without Impurity Added

An organic light emitting device was manufactured in the same manner as in Example 1, except that the Alq ₃ layer having a thickness of 60 nm was deposited as the emission layer and the electron transport layer (see FIG. 2B).

Experimental Example 1 Efficiency Measurement of Organic Light Emitting Diode

<1-1> Current Density-Voltage Measurement of Organic Light Emitting Diode

In order to determine the efficiency of the organic light emitting diode according to Example 1 and Comparative Example 1 of the present invention, the current density-voltage was measured in 0.5V units from 0 to 15V using KEITHELY (model: 236 SOURCE MESURE UNIT). 4 is a graph showing the results.

<1-2> Luminescence intensity-voltage measurement of the organic light emitting device

The anodes and cathodes of the organic light emitting diodes manufactured in Example 1 and Comparative Example 1 were lighted with a luminance meter (CHROMA METER CS-100A) in a dark box while applying KEITHELY (model: 236 SOURCE MEASURE UNIT) to 0-15V. Intensity was measured. 5 is a graph showing the results.

<1-3> Luminous efficiency-current density measurement of organic light emitting device

From the current density-voltage characteristics and the emission intensity-current density characteristics of the organic light emitting diodes manufactured in Example 1 and Comparative Example 1, the spectral luminance efficiency and the emission intensity of the visual system curve are integrated in the visible range and divided by the current density. One luminous efficiency is shown according to the current density. 6 is a graph showing the results.

<1-4> Current Density-Power Efficiency Measurement of Organic Light Emitting Diode

From the current density-voltage characteristics and the light emission intensity-current density characteristics of the organic light emitting diodes manufactured in Example 1 and Comparative Example 1, the spectral luminance efficiency and luminance emission amount of the visual system curve were integrated in the visible light region and converted into electric power. Power efficiency is shown according to the current density. 7 is a graph showing the results.

<1-5> Lifespan Measurement of Organic Light Emitting Diode

In order to measure the lifespan of the organic light emitting diode, a change in the photocurrent of the luminance meter is measured with time while supplying a constant current of 1000 cd / m ² to the device. 8 is a graph showing the standardized photocurrent measured with time. The half life can be obtained by fitting with an exponential function from the change characteristic of the photocurrent measured with time. 8 is a graph showing the results.

As described above, the organic light emitting device manufactured by adding impurities having a larger energy gap than the light emitting host material used as the light emitting layer has improved the injection efficiency and emission efficiency of electrons and holes, and delays deterioration of the light emitting material. It was confirmed that the life was greatly extended. From these results, the organic light emitting device having the structure of the present invention can be usefully used to manufacture a high efficiency, long life organic light emitting device required for the production of an active large display.

Claims (9)

An organic light emitting device comprising a light emitting layer to which impurities are added having an energy gap larger than that of the light emitting host material. The device of claim 1, further comprising: an anode on the substrate; Hole transport layer; Light emitting layer; Electron transport layer; Electron injection layer; And an organic light emitting element comprising a cathode. The organic light emitting diode of claim 1 or 2, wherein the light emitting host material is Alq ₃ . The organic light emitting device of claim 1 or 2, wherein the impurities are at least one material selected from the group consisting of DPVBi, NPB, and BCP. The organic light emitting device of claim 1 or 2, wherein the concentration of the impurity is 0.5 to 1.5 wt%. 1) forming an anode on the substrate; 2) forming a hole transport layer on the anode; 3) forming a light emitting layer on the hole transport layer; 4) forming an electron transport layer on the light emitting layer; 5) forming an electron injection layer on the electron transport layer; And 6) forming a cathode on the electron injection layer, wherein the step of forming the light emitting layer of the 3), the organic light emitting device is formed by adding an impurity having a larger energy gap than the energy gap of the light emitting host material Manufacturing method. The method of claim 6, wherein the light emitting host material is Alq ₃ . The method of claim 7, wherein the impurity is at least one material selected from the group consisting of DPVBi, NPB, and BCP. The method of claim 8, wherein the concentration of the impurity is 0.5 to 1.5 wt%.

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