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KR101687637B1 - White light-emitting device using the light-emitting layer and the color converting layer with a single quantum dot - Google Patents

White light-emitting device using the light-emitting layer and the color converting layer with a single quantum dot Download PDF

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KR101687637B1
KR101687637B1 KR1020150051815A KR20150051815A KR101687637B1 KR 101687637 B1 KR101687637 B1 KR 101687637B1 KR 1020150051815 A KR1020150051815 A KR 1020150051815A KR 20150051815 A KR20150051815 A KR 20150051815A KR 101687637 B1 KR101687637 B1 KR 101687637B1
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layer
light emitting
electrode
quantum dot
emitting layer
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KR1020150051815A
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KR20160122322A (en
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강신원
차승환
이재성
강병호
이상원
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경북대학교 산학협력단
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    • H01L51/502—
    • H01L51/5056—
    • H01L51/5072—
    • H01L51/5203—
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
    • H01L2924/10—Details of semiconductor or other solid state devices to be connected
    • H01L2924/11—Device type
    • H01L2924/12—Passive devices, e.g. 2 terminal devices
    • H01L2924/1204—Optical Diode
    • H01L2924/12044—OLED

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Abstract

The present invention relates to a white light emitting device using a light emitting layer and a color converting layer composed of a single quantum dot and including a light emitting layer composed of a single quantum dot and emitting a predetermined wavelength of light, Wherein a color filter layer is formed on one side of the outer surface of the first electrode, the color filter layer being positioned between the second electrode disposed on the upper portion of the electrode and having a wavelength higher than the wavelength of the light emitted from the light emitting layer. And a white light emitting device using the color conversion layer.
The present invention as described above forms a light emitting layer with a single quantum dot, absorbs light of a short wavelength emitted from the light emitting layer in a color filter layer formed outside the first electrode, emits white light, and the process is extinguished, And it is possible to minimize the life span due to the thermal degradation phenomenon.

Description

[0001] The present invention relates to a white light emitting device using a color conversion layer and a light emitting layer composed of a single quantum dot,

The present invention relates to a white light emitting device using a color conversion layer and a light emitting layer composed of a single quantum dot. More particularly, the present invention relates to a white light emitting device comprising a light emitting layer formed with a single quantum dot, A light emitting layer composed of a single quantum dot and a white light emitting layer using a color conversion layer capable of minimizing lifetime due to thermal degeneration phenomenon can be obtained by emitting white light by absorbing light of a short wavelength, Device.

In general, quantum dot light-emitting diodes (QLEDs) are light emitting devices made of semiconductor crystals of several nanometers, that is, quantum dots, which emit light in various sizes and voltages. Organic light emitting diodes OLED) process, high quantum efficiency, and excellent color purity. As a result, many researches have been carried out in connection with efforts to utilize the color clarity and excellent quantum efficiency characteristics of the quantum dot in the display lighting industry. .

1 is a view showing a conventional quantum dot light emitting device.

As shown in FIG. 1, the conventional quantum dot light emitting device 100 includes a first electrode 110 made of a transparent material and disposed on a base substrate 100 having a structure similar to a conventional organic light emitting device, A light emitting layer 130 stacked on the hole supply / transport layer 120, an electron transport / supply layer 140 stacked on the light emitting layer 130, and an electron transport / And a second electrode 150 stacked on the first electrode 140.

In order to realize white light, the conventional quantum dot light emitting device 100 requires a very precise thickness adjustment because the quantum dots are stacked in an intersecting manner in accordance with a bar stacking order formed by stacking a plurality of quantum dots having different band gaps in order to realize white light Thereby complicating the process.

In addition, since the conventional quantum dot light emitting device 100 needs to consider the problems of solubility and polarity between adjacent layers, it is not easy to manufacture and requires chemical treatment through the surface modification of the quantum dot, .

Some attempts have been made to produce a single luminescent layer in which a plurality of quantum dots are mixed in the same solvent. However, problems arise due to the thermal degradation phenomenon as heterogeneous quantum dots are used as the luminescent layer.

The conventional quantum dot light emitting device uses Alq3 as an electron transport layer and LiF as an electron supply layer. Such a structure has a feature of having excellent electron affinity, but it is essentially required to be manufactured by a vacuum deposition process When exposed to the atmosphere, the oxidation progresses rapidly and a life time is shortened.

SUMMARY OF THE INVENTION The present invention has been conceived to solve such problems as described above. It is an object of the present invention to provide a light emitting device having a light emitting layer formed by a single quantum dot, absorbing light of a short wavelength emitted from a light emitting layer in a color filter layer formed outside the first electrode And a white light emitting device using a color conversion layer and a light emitting layer made of a single quantum dot that can greatly improve productivity and minimize life span due to thermal degradation phenomenon by emitting white light.

In addition, the present invention can manufacture the electroluminescent part except for the electrode using the ZnO nanoparticles dispersed in the polar solvent as the electron transport layer, thereby further shortening the manufacturing process and thereby significantly improving the productivity A light emitting layer made of a single quantum dot and a white light emitting element using a color conversion layer.

According to an aspect of the present invention, there is provided a light emitting device including: a first electrode including an emissive layer including a single quantum dot and emitting a predetermined short wavelength light; And a color filter layer formed between the two electrodes and having a wavelength higher than the wavelength of the light emitted from the light emitting layer, the color filter layer absorbing the short wavelength light and causing the white light to emit light is formed on one side of the outer surface of the first electrode. A light emitting layer made of a single quantum dot and a white light emitting element using a color conversion layer.

The electroluminescent unit is disposed between the first electrode and the second electrode. The electroluminescent unit is formed of a single quantum dot, and emits light having a predetermined wavelength. The electroluminescent unit is positioned between the first electrode and the electroluminescent layer. A hole transporting layer disposed between the hole transporting layer and the light emitting layer and reducing a potential barrier between the light emitting layer and the hole transporting layer and a hole transporting layer disposed between the hole transporting layer and the light emitting layer, An electron supply layer which is located between the electron supply layer and the light emitting layer and which transports electrons supplied to the second electrode to the light emitting layer and an electron transport layer which is located in the electron supply layer and the light emitting layer, And an electron transport layer for transferring the light to the light emitting layer.

The light emitting layer may be a single quantum dot having a wavelength band of 440 to 490 nm.

In addition, it is preferable that the color filter layer includes a single quantum dot having a wavelength band of 580 to 620 nm.

The color filter layer may be formed on one side of the outer surface of the first electrode after mixing a single quantum dot with the resin.

It is preferable that the first electrode is indium tin oxide mixed with indium oxide and a predetermined amount of tin oxide.

delete

The electron transport layer is preferably formed of ZnO nanoparticles synthesized by dissolving a zinc compound and a basic substance in a polar solvent.

In addition, the electron transport layer may be coated with the ZnO nanoparticles dispersed in a predetermined amount of a polar solvent and the light emitting layer.

In addition, the electroluminescent unit is preferably fabricated by a solution process method between the first electrode and the second electrode.

The present invention as described above forms a light emitting layer with a single quantum dot, absorbs light of a short wavelength emitted from the light emitting layer in a color filter layer formed outside the first electrode, emits white light, and the process is extinguished, And it is possible to minimize the life span due to the thermal degradation phenomenon.

In addition, the present invention can manufacture the electroluminescent part except for the electrode using the ZnO nanoparticles dispersed in the polar solvent as the electron transport layer, thereby further shortening the manufacturing process and thereby significantly improving the productivity There is an effect that can be made.

1 is a view showing a conventional quantum dot light emitting device,
FIG. 2 illustrates a white light emitting device using a color conversion layer and a light emitting layer composed of a single quantum dot according to an embodiment of the present invention.
FIG. 3 is a graph showing energy band gaps of a white light emitting device using a color conversion layer and a conventional quantum dot light emitting device according to an embodiment of the present invention,
FIG. 4 is a flow chart showing a process of manufacturing an electron transport layer according to an embodiment of the present invention,
5 is a view illustrating an operation of a white light emitting device using a color conversion layer and a light emitting layer composed of a single quantum dot according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a view illustrating a white light emitting device using a color conversion layer and a light emitting layer composed of a single quantum dot according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a light emitting layer having a single quantum dot according to an embodiment of the present invention. FIG. 4 is a flowchart illustrating a process of fabricating an electron transport layer according to an embodiment of the present invention. Referring to FIG. 4, the energy band gap of a white light emitting device using a color conversion layer and a conventional quantum dot light emitting device is shown.

As shown in FIG. 2, the white light emitting device using the color conversion layer 40 and the light emitting layer 31 composed of a single quantum dot according to an embodiment of the present invention includes a first electrode 10, a second electrode 20, And an electroluminescence unit 30 disposed between the first electrode 10 and the second electrode 20 and a color conversion layer 40 formed on the outside of the first electrode 10.

The first electrode 10 is provided as an anode to provide holes. The first electrode 10 is formed of ITO (indium tin oxide), which is a transparent electrode having a large work function to facilitate the supply of holes to the HOMO level of the light emitting layer 31, (indium tin oxide) glass, and when formed from an ITO glass, a pattern can be formed through a phto-lithography process.

The second electrode 20 is positioned above the first electrode 10 and serves to receive the first electrode 10 and the other electrode where the second electrode 20 can be provided as a cathode, An electrode of a metal having a low work function and having a high internal reflectivity is used so that electrons can be easily injected into the LUMO level of the electrode 31.

In one embodiment of the present invention, Al may be used as the second electrode 20.

The electroluminescence unit 30 includes a light emitting layer 31 positioned between the first electrode 10 and the second electrode 20 and a hole supply / transport layer 31 located between the first electrode 10 and the light emitting layer 31 And an electron supply / transport layer 33 positioned between the light emitting layer 31 and the second electrode 20 and having a hole and a hole provided from the first electrode 10 and the second electrode 20, respectively, It emits light through electrons.

The light emitting layer 31 is located above the hole supply layer 32a to be described later and is composed of a single quantum dot. In this embodiment, the quantum dot includes a quantum dot having a wavelength band of 440 to 490 nm to fabricate a white light emitting device.

The quantum dots are CdSe / ZnS II-VI compounds composed of a hetero-junction of a core having a trioctyl phosphine oxide (TOPO) ligand and a shell, and have various emission wavelengths depending on the particle size.

The emissive layer 31 is formed on the hole supply layer 32a. The emissive layer 31 is formed by dispersing the quantum dots at 20 mg / mL and using a PVDF filter of 0.45 μm in order to minimize the flatness of the interface and the hydrofluoric acid. After refining, the poly-TPD thin film was spin-coated at 3,000 rpm for 60 seconds, and then heat-treated in a vacuum oven at 80 ° C for 30 minutes.

At this time, in order to optimize the device, the film thickness of the light emitting layer 31 can be selected according to the concentration of the quantum dots, and it is most preferable that the film thickness is 30 nm.

The hole supplying and transporting layer 32 includes a hole supplying layer 32a and a hole transporting layer 32b positioned between the first electrode 10 and the light emitting layer 31 and between the hole supplying layer 32a and the light emitting layer 31, And transmits the holes injected from the first electrode 10, that is, the anode, to the light emitting layer 31.

The hole supply layer 32a functions to planarize the roughness of the ITO generated through exposure and etching and to inject holes from the first electrode 10 into the hole transport layer 32b. Here, the hole supply layer 32a, May be provided as PEDOT: poly (ethylenedioxythiophene): poly-styrenesulphonate.

The hole transport layer 32b is located between the hole supply layer 32a and the light emitting layer 31 and reduces the potential barrier between the light emitting layer 31 and the hole injection layer to reduce holes injected through the hole supply layer 32a into the light emitting layer 31), which may be poly-TPD (poly (N, N'-bis (4-butylphenyl) -N, N'-bis (phenyl) benzidine).

The electron supply / transport layer 33 includes an electron supply layer 33a located between the second electrode 20 and the light emitting layer 31 and an electron transport layer 33b located between the electron supply layer 33a and the light emitting layer 31 And serves to transmit electrons injected from the cathode to the light emitting layer 31. [

The electron supply layer 33a serves to transfer the electrons injected from the cathode to the electron transport layer 33b and is formed in the form of a thin film of several nanometers

The electron transport layer 33b serves to transmit electrons injected from the cathode to the light emitting layer 31 and to form a hole blocking layer In this embodiment, ZnO nanoparticles dispersed in a polar solvent such as ethanol may be used as the electron transport layer 33b.

The electron transport layer 33b including the ZnO nanoparticles as the oxide semiconductor functions to prevent the potential barrier between the LUMO level from the second electrode 20 and the electron transport layer 33b to enable effective electron transfer. This will be described in more detail with reference to FIG.

Referring to FIG. 3, the electron transport layer 33b using the conventional alunicinium complex (Alq3) has a LUMO level of 3.1 eV and a HOMO level of 5.8 eV. Since the work function of the second electrode 20 used as the cathode, that is, the Al electrode, forms a high energy barrier at the interface with Alq3, a buffer layer such as Calcium (Ca) or Lithium fluoride (LiF) And the electron injection barrier between the cathode and the electron transport layer 33b is lowered.

For example, as shown in FIG. 3, an ultra thin film of LiF having a thickness of 1 nm or less can be formed through vacuum thermal deposition to be used as an electron injection layer. The HOMO level (5.5 eV) of the aluminum quinolium complex (Alq3) is lower than the HOMO level of CdSe, so that the hole transported to the light emitting layer (31) is lowered to the HOMO level of the aluminum quinolium complex (Alq3) The probability of moving is relatively large. In addition, the high LUMO level of the aluminum quinolium complex (Alq3) is not significantly different from the LUMO level of the poly-TPD adjacent to CdSe, and electrons transferred from Alq3 are highly likely to migrate to the poly-TPD interface.

On the other hand, referring to FIG. 4, ZnO nanoparticles according to an embodiment of the present invention have a LUMO level of 4.2 eV and a HOMO level of 7.6 eV, and a barrier function between the LUMO levels of Al and ZnO having a work function of 4.3 eV there is no potential barrier, and effective electron transfer is possible at the LUMO level of CdSe corresponding to 4.4 eV.

In addition, since the high HOMO level (7.7 eV) of ZnO is larger than the HOMO level (6.7 eV) of CdSe, the probability of excess holes that can not bond in the light emitting layer (31) 140 is lowered to the HOMO level of ZnO .

Therefore, it is possible to increase the recombination rate of electron-hole by inducing efficient charge confinement in CdSe. Therefore, it is possible to improve the characteristics of the device, but it is also excellent in dispersion property in polar solvent. Thus, the problem of solubility in quantum dots dispersed in non- It is possible to spin-coat by a solution process, so that all the components of the electroluminescence portion 30 except for the electrode can be manufactured based on the solution process.

Here, the electron transport layer 33b according to the present embodiment is prepared by dispersing the synthesized ZnO nanoparticles in ethanol at a constant concentration, refining using a filter of 0.45 um PVDF, spin coating at 1,500 rpm for 30 seconds To form a film of about 30 nm thick, followed by heat treatment in a 90 ° C vacuum oven for 30 minutes.

Meanwhile, a method of synthesizing ZnO nanoparticles as described above will be described below.

 First, Zn (CH3COO) 2 is dissolved in methanol, and methanol is heated to 60 占 폚, which is a temperature below the boiling point (S120)

Then, KOH dissolved in methanol is dropped at a rate of 1 ml / sec into the solution in which Zn (CH3COO) 2 is dissolved (S130).

After about 5 minutes, ZnO nuclei are slowly formed. After 60 minutes, about 3 to 5 nm uniform ZnO nanoparticles are synthesized (S140).

IPA and hexane are added at a ratio of 1: 1: 5 to remove extra ions such as K + and ZnO nanoparticles synthesized after the reaction, followed by aging for 24 hours (S150, S160).

Subsequently, ions and mixed solvents other than the ZnO nanoparticles in the solvent are removed using a centrifugal separator to obtain purified colloidal ZnO nanoparticles (S170).

The color conversion layer 40 is formed of a single quantum dot having a wavelength band higher than that of the light emitting layer 31 and is formed outside the first electrode 10 and is formed in the same manner as the light emitting window layer described above. In the example, it includes quantum dots in a wavelength band of 580 to 620 nm.

The reason why the color conversion layer 40 includes the quantum dots in the wavelength band of 580 to 620 nm is to absorb the light of the short wavelength of 500 nm or less and it is preferable that the color conversion layer 40 emits light having a wavelength of 440 to 490 nm Absorbs light and causes white light to appear.

FIG. 5 is a diagram illustrating the operation of a white light emitting device using a color conversion layer and a light emitting layer composed of a single quantum dot according to an embodiment of the present invention.

Referring to the accompanying drawings, the operation of a light emitting layer composed of a single quantum dot and a white light emitting element using a color conversion layer according to an embodiment of the present invention having such a structure will be described. Transporting layer 32 and the electrons injected from the second electrode 20 are transferred to the light-emitting layer 31 through the electron supply / transport layer 33. The light-

As holes and electrons are transferred to the light emitting layer 31, the light emitting layer 31 emits light having a wavelength band of 440 to 490 nm, that is, short wavelength light. The emitted short wavelength light is transmitted through the first electrode 10 formed of a transparent TIO glass, Where the short wavelength light is absorbed by the color conversion layer 40 while overlapping with the absorption wavelength of the color conversion layer 40.

The color conversion layer 40 formed of quantum dots in the 580 to 620 nm wavelength band absorbs a short wavelength by photoluminescence and emits white light.

As described above, the white light emitting device using the color conversion layer 40 and the light emitting layer 31 composed of a single quantum dot according to an embodiment of the present invention is superior to the conventional technology of the R, G, B quantum dot laminating structure or the mixed structure Since the process is simple and the homogeneous quantum dots are dispersed in the light emitting layer 31, the thermal degradation phenomenon can be relatively reduced as compared with the device in which the different quantum dots are used as the light emitting layer 31.

In addition, by using ZnO nanoparticles dispersed in a polar solvent such as ethanol as an electron transport layer 33b, it is possible to realize a white light device based on a solution process by eliminating the vacuum evaporation type common layer material, which is essential in the conventional quantum dot electroluminescent device, Not only the process can be shortened but also the productivity can be remarkably improved.

Although the present invention has been described in connection with the above-mentioned preferred embodiments, it is possible to make various modifications and variations without departing from the spirit and scope of the invention. Accordingly, the appended claims are intended to cover such modifications or changes as fall within the scope of the invention.

10: first electrode 20: second electrode
30: electroluminescent element 31: light emitting layer
32: hole supplying / transporting layer 32a: hole supplying layer
32b: hole transport layer 33: electron supply / transport layer
33a: electron supply layer 33b: electron transport layer
40: Color conversion layer

Claims (10)

And a second electrode disposed on an upper portion of the first electrode, wherein the electroluminescent portion comprises a single quantum dot and includes a light emitting layer that emits light having a predetermined short wavelength, and is disposed between the first electrode and the second electrode, And a color filter layer composed of quantum dots having a high wavelength and absorbing the short wavelength light to emit white light is formed on one side of the outer surface of the first electrode. device.
The method according to claim 1,
The electroluminescent portion
A light emitting layer which is located between the first electrode and the second electrode and is formed of a single quantum dot and emits light having a predetermined wavelength;
A hole supply layer located between the first electrode and the light emitting layer and reducing a surface roughness of the first electrode;
A hole transport layer positioned between the hole supply layer and the emission layer and reducing a potential barrier between the emission layer and the hole supply layer;
An electron supply layer positioned between the light emitting layer and the second electrode and transferring electrons supplied to the second electrode to the light emitting layer; And
And an electron transport layer which is located in the electron supply layer and the light emitting layer and transfers electrons transferred by the electron supply layer to the light emitting layer so that light is emitted from the light emitting layer. Layer light emitting device.
3. The method of claim 2,
Wherein the light emitting layer is a single quantum dot having a wavelength band of 440 to 490 nm, wherein the light emitting layer comprises a single quantum dot and the color conversion layer.
3. The method of claim 2,
Wherein the color filter layer comprises a single quantum dot having a wavelength band of 580 to 620 nm, wherein the color filter layer comprises a single quantum dot and a color conversion layer.
3. The method of claim 2,
Wherein the color filter layer is formed on one side of the outer surface of the first electrode after mixing a single quantum dot with the resin.
The method according to claim 1,
Wherein the first electrode is indium tin oxide mixed with indium oxide and a predetermined amount of tin oxide, and the white light emitting device using the color conversion layer and the light emitting layer composed of a single quantum dot.
delete 3. The method of claim 2,
Wherein the electron transport layer is formed of ZnO nanoparticles synthesized by dissolving a zinc compound and a basic substance in a polar solvent, wherein the electron transport layer is composed of a single quantum dot and a color conversion layer.
9. The method of claim 8,
Wherein the electron transport layer is formed by dispersing the ZnO nanoparticles in a predetermined amount of a polar solvent and coating the light emitting layer with a light emitting layer made of a single quantum dot and a color conversion layer.
10. The method of claim 9,
Wherein the electroluminescent unit is fabricated by a solution process method between the first electrode and the second electrode, wherein the electroluminescent unit comprises a single quantum dot and the color conversion layer.
KR1020150051815A 2015-04-13 2015-04-13 White light-emitting device using the light-emitting layer and the color converting layer with a single quantum dot KR101687637B1 (en)

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