KR20050063659A - White organic light emitting device - Google Patents

Abstract

The present invention relates to a white organic light emitting device capable of realizing excellent color purity and high efficiency with a simple structure, including a light emitting layer, a factory wall layer, and an electron transporting layer between an anode and a cathode to which a bias voltage is applied, wherein the light emitting layer has a blue light emitting property. A host having a dopant and a first guest that emits orange or red light emission characteristics are doped, and the electron transport layer includes a material having green light emission characteristics.

Description

White organic light emitting device

The present invention relates to a white organic light emitting device used as a display device, and more particularly, to provide a white organic light emitting device that can exhibit excellent color purity and high efficiency with a simple structure.

As the information and communication industry develops, the use of display devices is rapidly increasing, and in recent years, display devices of light weight, thin film, and high resolution are required. In response to these demands, display devices using liquid crystal displays (LCDs) or organic light emitting characteristics have been developed.

In order to realize a lighter weight and a thinner display device, it is advantageous to use a light and thin plastic substrate, unlike a conventional display element using a glass substrate. As a next-generation display device using a plastic substrate, the organic light emitting device among the current display devices has been attracting attention as the most realistic, and intensive research has been made.

An organic light emitting element made of an organic material emits light by applying current or voltage to cathodes and anodes formed on both ends of the light emitting layer. In general, in order to obtain better light emission characteristics, a multilayer film structure is used in which a hole injection layer and / or a hole transport layer, an electron transport layer, and / or an electron injection layer are formed of a material that helps injection of holes and electrons to both sides of the light emitting layer.

The conventional monochromatic organic light emitting device has a structure in which an anode, a light emitting layer, and a cathode are stacked on a substrate. Such an organic light emitting device may emit various colors according to the type of material constituting the light emitting layer. In order to fabricate an organic light emitting device having a white light emitting property, the light emitting materials having the light emitting characteristics of red (R), green (G), and blue (B), which are three primary colors of light, are stacked or light emitting materials having complementary colors are stacked. The white organic light emitting diode can be classified into a three wavelength white organic light emitting diode and a two wavelength white organic light emitting diode.

The conventional three wavelength white organic light emitting diode has a structure in which an anode, a light emitting layer, and a cathode are stacked on a substrate, and the light emitting layer is formed of light emitting materials of red (R), green (G), and blue (B).

As described above, the three wavelength white organic light emitting diode using the three primary light emitting materials has excellent color purity. However, since the light emitting materials of red (R), green (G), and blue (B) are stacked, color stability changes due to an applied electric current or an energy potential according to time. Inserting an appropriate factory wall layer between the light emitting materials can improve color stability, but in this case, the structure is complicated, which makes it difficult to manufacture and lowers the efficiency.

On the other hand, the conventional two wavelength white organic light emitting device has a structure in which an anode, a light emitting layer and a cathode are stacked on a substrate, and the light emitting layers are made of light emitting materials having a complementary color relationship with each other.

The two-wavelength white organic light emitting diode is applied with a light emitting material having a complementary color relationship, for example, a combination of light blue and red or blue and orange light emitting materials. Therefore, it is easy to manufacture and high efficiency compared to the three wavelength white electroluminescent device. However, since the light emission characteristics of green are lower than those of red and blue, color reproducibility is not good, and thus, it is difficult to apply to applications requiring high color purity and color reproducibility such as display and lighting.

An object of the present invention is to implement an organic light emitting device having a white light emitting property of high efficiency with a simple structure using only a single light emitting layer.

Another object of the present invention is to implement a three-wavelength white organic light emitting diode having a high color reproducibility with a simple structure using only a single light emitting layer.

As a technical means for achieving the above object, an aspect of the present invention is the anode and cathode to which a bias voltage is applied; And a light emitting layer stacked between the anode and the cathode, the light emitting layer doped with a host having blue light emitting characteristics and a first guest emitting orange or red light emitting characteristics, a factory wall layer for confining holes in the light emitting layer, and a green light emitting characteristic. It provides a white organic light emitting device comprising an electron transport layer having a. Preferably, the second guest may be further doped to improve the efficiency of the blue light emitting material.

Another aspect of the present invention is a white organic light emitting device comprising a hole injection layer, a hole transport layer, a light emitting layer, a factory wall layer, an electron transport layer, an electron injection layer formed by being laminated on the substrate with an anode and a cathode interposed therebetween, the light emitting layer A white organic light emitting diode including a host having a blue light emission property and a first guest having orange or red light emission properties is doped, and the electron transport layer includes a material having a green light emission property.

Preferably, the blue light emitting material is DPVBi or NPB and the like having a band gap between 3.5 and 2.5 eV, and the first guest is a red light emitting material such as DCM, DCJTB or DADB having a band gap between 2.2 and 1.7 eV. Doped to a concentration of 0.01 to 5%.

Preferably, the second guest is a blue light emitting material such as DSA-Amine or Perylene having a bandgap between 3.5 and 2.5 eV and is doped at a concentration of 0.1 to 10%.

The factory wall layer is formed of a material having a higher HOMO energy level than the light emitting layer, for example, BCP or TAZ, and has a thickness thinner than a Forster energy transition radius so that excitons can transfer Forster energy from the light emitting layer to the electron transport layer. .

Hereinafter, an embodiment of the present invention will be described in detail. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms, only the embodiments are to make the disclosure of the present invention complete and to those skilled in the art the scope of the invention It is provided for complete information.

1 is a cross-sectional view illustrating a white organic light emitting diode according to the present invention.

An anode 32 made of a transparent electrode material is formed on the transparent glass, quartz or plastic substrate 31. A hole injection layer (HIL) 33 is formed on the anode 32 to help inject holes. The hole injection layer 33 has a high hole mobility and holes in the light emitting layer 35. Hole transport layer (HTL) 34 to facilitate the transport of (HTL) 34 is formed.

A light emitting layer 35 doped with a blue light emitting material as a host and doped with a first guest capable of emitting orange or red light may be formed on the hole transport layer 34. Meanwhile, the light emitting layer 35 may further be doped with a second guest that may improve the efficiency of the blue light emitting material.

A hole blocking layer (HBL) 36 is formed on the light emitting layer 35 to confine holes in the light emitting layer 35. The light blocking layer 36 has a green light emission characteristic and has a light emission layer on the light emitting layer 35. 35) An Electron Transport Layer (ETL) 37 is formed that allows efficient electron transport into the vessel.

An electron injection layer (EIL) 38 is formed on the electron transport layer 37, and a cathode 39 is formed in a desired region on the electron injection layer 38.

Next, a method of manufacturing the white organic light emitting diode will be described.

The anode 32 is formed on the transparent glass, quartz or plastic substrate 31. The anode 32 is formed of a transparent electrode material, for example, an indium tin oxide (ITO), indium zinc oxide (IZO), or the like, and is formed of a transparent conductive material having a high work function. Go through the process.

A hole injection layer (HIL) 33 is formed to have a thickness of 10 nm to 50 nm using a material that helps injection of holes on the anode 32, for example, MTDATA, CuPc, PEDOT: PSS, or the like.

A hole transport layer (HTL) 34 having good mobility of holes on the hole injection layer 33 and facilitating the transport of holes to the light emitting layer 35 is formed to a thickness of 10 nm to 100 nm. The hole transport layer (HTL) 34 is TPD (N, N'-diphenyl-N, N'-bis- (3-methyl phenyl) -1,1'-biphenyl-4,4'-diamine) or NPB ( It is preferable to comprise a material having good hole mobility, such as 4,4'-bis [N- (1-naphthyl-1-)-N-phenyl-amino] -biphenyl).

A light emitting layer 35 doped with a blue light emitting material as a host on the hole transport layer 34 and doped with a first guest capable of emitting orange or red light may be formed. The second guest may be further doped to improve the efficiency of the blue light emitting material. The light emitting layer 35 may be deposited at a desired speed, and doping may be performed by simultaneously controlling the deposition rate. The thickness of the light emitting layer is preferably formed to a thickness of 10 to 100nm to maximize the efficiency of the device.

As the blue light emitting material, DPVBi, NPB, or the like having a band gap between 3.5 and 2.5 eV may be used.

As the first guest, a red light emitting material such as DCM, DCJTB, DADB, etc. having a band gap between 2.2 and 1.7 eV may be used, and a concentration such that the energy of blue does not move to the first guest of red, for example. For example, at a concentration of 0.01 to 5%, preferably 0.05%.

As the second guest, a blue light emitting material such as DSA-Amine or Perylene having a band gap between 3.5 and 2.5 eV may be used, and a concentration capable of obtaining an optimal blue efficiency, for example, 0.1 to 10%, Preferably it is doped at a concentration of 5%.

A factory wall layer (HBL) 36 is formed on the light emitting layer 35 to trap holes in the light emitting layer 35. The factory wall layer 36 may use a material having a higher HOMO energy level than the light emitting layer 35, for example, BCP, TAZ, or the like. The BCP, TAZ, and the like have a HOMO energy level about 0.5 to 1.0 eV higher than that of the emission layer 35.

The factory wall layer 36 is formed to a thickness thinner than the Forster energy transition radius, for example, 1 to 5 nm thick. The electron transport layer 37 may have light emission characteristics by setting a thickness such that excitons are capable of transferring Forster energy from the emission layer 35 to the electron transport layer 37. Regarding the Forster energy transition radius, for example, X.G. Jacek et al., "Electrophosphorescence from a polymer guest-host system with an Iridium Complex as guest: Forster Energy Transfer and Charge Trapping", Advanced Functional Materials 2003, 13, pp 439-444.

An electron transport layer (ETL) 37 is formed on the factory wall layer 36. The electron transport layer 37 has a green light emission characteristic and enables efficient electron transport into the light emitting layer 35. The electron transport layer (ETL) 37 is preferably composed of a person having green light emission characteristics such as tris (8-hydroxy quinoline) aluminum (Alq3) and 4,7-diphenyl-1,10-phenanthroline (BPhen).

An electron injection layer (EIL) 38 is formed on the electron transport layer 37. The electron injection layer (EIL) 38 is an organic thin film such as 1,3,4-oxadiazole dreivertive (PBD), 4,7-diphenyl-1,10-phenanthroline (BPhen), Li doped BPhen and LiF, NaF, Inorganic thin films such as AlO, CsF, and the like are used, and are preferably made of a material that facilitates injection of electrons from the cathode.

A cathode 39 is formed in a desired region on the electron injection layer 38. The cathode 39 may form Al, Ag, LiAl, Mg / Al, Mg / Ag, or the like.

In order to obtain a white light emitting property in a general manner, an orange light emitting material is laminated on blue or a red light emitting material is laminated on light blue. However, in this case, color reproducibility is inferior due to the low luminescence property of green. In addition, in order to easily implement the light emitting layer in a single layer structure, the orange guest should be directly doped to the blue host or the red guest to the sky blue host. In this case, the blue or light blue host should be orange or red guest with a small energy band gap. Energy transfer occurs easily, making white light emission difficult.

Therefore, the present invention uses the blue light emitting material as a host, and forms the light emitting layer 35 doped with a first guest that can exhibit orange or red light emission characteristics to have blue and red light emission characteristics. A second guest may be added to improve the efficiency of the blue light emitting material. In addition, in order to improve color purity, which remains a problem in the two wavelength white organic light emitting diode, a positive factory wall layer 36 is formed to effectively trap holes in the light emitting layer 35 in the light emitting layer to increase the light emission efficiency. At this time, the excitons are formed to have a regular wall layer 36 thinner than the Forster energy transition radius in order to enable Forster energy transfer from the light emitting layer 35 to the electron transport layer 37, so that the electron transport layer 37 has green light emission characteristics.

2 is a light emission spectrum of the white organic light emitting diode manufactured according to the present invention. The structure of the white organic light emitting diode used in the present measurement is a hole injection layer 33 between the anode ITO 32 and the cathode Al 39. 10 nm thick MTDATA, hole transport layer 34 30 nm thick NPB, and 0.05 wt.% DADB and 3.0 wt.% DSA-amine doped DPVBi doped with 300 nm thick. Subsequently, BCP having a thickness of 3 nm was deposited on the factory wall layer 36, Alq having a thickness of 30 nm was formed on the electron transport layer 37, and LiF of 1 nm on the electron injection layer 38. The luminescence (EL) spectrum measured by a Minolta CS1000 spectrometer for the luminescence properties of a white organic light emitting diode having the above structure at a room temperature with a current of 20 mA / cm ² applied between the anode 32 and the cathode 39. Is a graph. As described above, although the device is composed of one light emission, the light emission characteristics of the entire visible region are excellent, indicating excellent white characteristics.

As mentioned above, although the preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment, A various deformation | transformation is performed by a person with ordinary skill in the art within the technical idea of this invention. It is possible.

In the case of a general white organic light emitting diode, two white light emitting layers having a complementary color relationship or three light emitting layers having three primary colors are stacked to derive white characteristics. However, in this case, there is a difficulty in depositing a multilayer organic thin film and there is a problem in that luminous efficiency is low.

The present invention is easy to manufacture and the manufacturing cost is reduced by implementing a white organic light emitting device having a simple structure having a single light emitting layer. The white organic light emitting diode of the present invention has a three-wavelength white color, which is excellent in color reproducibility, thereby enabling the implementation of a general-purpose organic light emitting diode that can realize high efficiency white. In addition, the application of the white organic light emitting device of the present invention can easily implement a liquid crystal display, a lighting plate, a white organic LED, and the like including a white light backlight plate and a color filter.

1 is a cross-sectional view for explaining a white organic light emitting device according to the present invention.

Figure 2 is a graph for explaining the light emission (EL) characteristics of the white organic light emitting device according to the present invention.

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

31 substrate 32 anode

33: hole injection layer 34: hole transport layer

35: light emitting layer 36: factory wall layer

37: electron transport layer 38: electron injection layer

39: cathode

Claims (14)

An anode and a cathode to which a bias is applied; And The light emitting layer is stacked between the anode and the cathode and includes a light emitting layer doped with a host having blue light emission characteristics and a first guest that emits orange or red light, a factory wall layer for confining holes in the light emitting layer, and a green light emission characteristic. White organic light emitting device comprising an electron transport layer having. According to claim 1, The white organic light emitting diode further doped with a second guest that can improve the efficiency of the blue light emitting material. The white organic light emitting diode of claim 1, wherein the blue light emitting material is DPVBi or NPB having a band gap between 3.5 and 2.5 eV. The white organic light emitting diode of claim 1, wherein the first guest is any one of DCM, DCJTB, or DADB having a band gap between 2.2 and 1.7 eV, and is doped at a concentration of 0.01 to 5%. The white organic light emitting diode of claim 1, wherein the second guest is SA-Amine or Perylene having a band gap between 3.5 and 2.5 eV and is doped at a concentration of 0.1 to 10%. The white organic light emitting diode of claim 1, further comprising a hole injection layer and a hole transport layer stacked between the anode and the light emitting layer. The method of claim 1 The white organic light emitting device further comprises an electron injection layer on the electron transport layer. The white organic light emitting diode of claim 1, wherein the regular wall layer is formed of a material having a higher HOMO energy level than the light emitting layer. The white organic light emitting diode of claim 8, wherein the material is any one of BCP and TAZ. The white organic light emitting diode of claim 1, wherein the factory wall layer is formed to have a thickness thinner than a Forster energy transition radius so that excitons can transfer Forster energy from the light emitting layer to the electron transport layer. The white organic light emitting diode of claim 10, wherein the regular wall layer is formed to a thickness of 1 to 5 nm. In a white organic light emitting device comprising a hole injection layer, a hole transport layer, a light emitting layer, a factory wall layer, an electron transport layer, an electron injection layer formed by being laminated on the substrate with an anode and a cathode interposed therebetween, The light emitting layer is doped with a host having blue light emission characteristics and a first guest having orange or red light emission characteristics, The organic light emitting device comprising a material having a green light emitting property in the electron transport layer. The white organic light emitting diode of claim 12, wherein the regular wall layer is formed to a thickness thinner than a Forster energy transition radius so that excitons can transfer Forster energy from the light emitting layer to the electron transport layer. The method of claim 12, The white organic light emitting diode further doped with a second guest that can improve the efficiency of the blue light emitting material.