KR101726630B1 - Quantum-dot light emitting diode - Google Patents

Abstract

[0001] The present invention relates to a quantum-emitting device which realizes stable white even when a voltage applied to the quantum-emitting device changes, and the quantum-emitting device according to the present invention comprises a substrate; A positive electrode formed on the substrate; A hole transport layer formed on the anode; A quantum luminescent layer formed on the hole transport layer and comprising a red quantum dot, a green quantum dot, and a blue quantum dot, the core including a core, a shell surrounding the core, and a ligand surrounding the shell; An electron transport layer formed on the quantum luminescent layer; And a cathode formed on the electron transport layer, wherein the ligands of the red quantum dot, the green quantum dot, and the blue quantum dot are formed of materials having different HOMO levels from each other.

Description

QUANTUM-DOT LIGHT EMITTING DIODE [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantum-emitting device, and more particularly, to a quantum-emitting device that implements white using a plurality of quantum dots having different sizes.

In the information society, display has become more important as a visual information delivery medium, and it is necessary to meet requirements such as low power consumption, thinning, light weight, and high image quality in order to take a major position in the future.

Among these displays, a quantum luminescent device capable of being displayed using a light emitting material, capable of being slim, having high color purity, and capable of being driven for a long time has been studied recently.

Quantum dots (QDs) are semiconductor nanoparticles. Quantum dots with a diameter of nanometer size emit electrons in an unstable state from a conduction band to a valence band. The smaller the quantum dots, the shorter wavelength light is generated. The larger the particle, the longer wavelength light is generated. This is a unique electrical and optical property that is different from conventional semiconductor materials. Therefore, by regulating the size of the quantum dots, the visible light of a desired wavelength can be expressed, and various colors can be simultaneously realized by different quantum dots and quantum dots.

An organic light emitting display device uses an organic light emitting material as a light emitting layer material, and an organic light emitting diode (OLED) using a light emitting material has a single color such as white, red, and blue depending on the type of device , There is a limit to expressing a lot of light spectacularly.

On the other hand, the quantum dot light emitting element is a display element using quantum dots as a material of the light emitting layer, and can control the size of quantum dots to realize a desired natural color, has good color reproducibility and luminance, and is not lagging behind the light emitting diode. The light emitting diodes (LEDs) are well-known as materials that can overcome the disadvantages of the light emitting diodes (LEDs) and can realize white light using a plurality of quantum dots having different sizes.

Hereinafter, the structure of a general quantum dot light emitting device which emits white light will be described.

FIG. 1A is a cross-sectional view of a general quantum dot light emitting device, FIG. 1B is a band gap energy diagram of FIG. 1A, and FIG. 2 is a color coordinate diagram of a quantum dot light emitting device.

1A, a quantum dot light emitting device includes a positive electrode 10 and a negative electrode 50 opposed to each other on a substrate 100, a quantum luminescent layer 30 formed between the positive electrode 10 and the negative electrode 50, A hole transport layer 20 formed between the anode 10 and the quantum luminescent layer 30 and an electron transport layer 40 formed between the quantum luminescent layer 30 and the cathode 50.

The quantum luminescent layer 30 includes a plurality of quantum dots having a diameter of nanometer size and includes a red quantum dot 30R, a green quantum dot 30G and a blue quantum dot 30B. It can be mixed to realize white color.

The quantum dot has a core component that emits light at its center, and a shell surrounds the core surface to protect the surface.

The quantum luminescent layer 30 may be formed by dispersing a plurality of quantum dots in a solvent, applying a solvent in which the plurality of quantum dots are dispersed on the hole transport layer 20 by a solution process, A ligand is surrounded on the surface of the shell so that the quantum dots are dispersed well in the solvent.

The hole transport layer 20 facilitates injection of holes from the anode 10 and transmits holes to the quantum dots. The electron transport layer 40 facilitates injection of electrons from the cathode 50 , And to transfer electrons to the quantum dots.

The red quantum dot 30R, the green quantum dot 30G, and the blue quantum dot 30B differ only in the light emitting core component, and the shell and the ligand are formed of the same material. Since the HOMO (Highest Occupied Molecular Orbital) level of the red quantum dot 30R, the green quantum dot 30G and the blue quantum dot 30B is different, the driving voltages of the quantum dots are different.

Specifically, the HOMO level of the red quantum dot 30R is the highest and the HOMO level of the blue quantum dot 30B is the lowest. The higher the HOMO level of the quantum dot, the more easily the holes are injected into the quantum dots. Therefore, the driving voltage of the red quantum dot 30R is the lowest and the driving voltage of the blue quantum dot 30B is the highest.

That is, the quantum luminescent device having the quantum luminescent layer in which the red quantum dot 30R, the green quantum dot 30G and the blue quantum dot 30B are mixed to realize white differs in the white color realized according to the applied voltage.

Referring to FIG. 2, as the high voltage is applied, the white color coordinates implemented are shifted to blue. When a low voltage is applied, electrons and holes are first injected into a red quantum dot (30R in FIG. 1B) having the lowest driving voltage to form an exciton, and when a high voltage is applied, a blue quantum dot 30B, many excitons are formed. Therefore, the white color realized by the voltage applied to the quantum-emitting device is different.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a quantum luminescent device which realizes a stable white color by matching drive voltages of a red quantum dot, a green quantum dot and a blue quantum dot.

According to an aspect of the present invention, there is provided a quantum-emitting device including: a substrate; A positive electrode formed on the substrate; A hole transport layer formed on the anode; A quantum luminescent layer formed on the hole transport layer and comprising a red quantum dot, a green quantum dot, and a blue quantum dot, the core including a core, a shell surrounding the core, and a ligand surrounding the shell; An electron transport layer formed on the quantum luminescent layer; And a cathode formed on the electron transport layer, wherein the ligands of the red quantum dot, the green quantum dot, and the blue quantum dot are formed of materials having different HOMO levels from each other.

The HOMO level of the ligand of the red quantum dot is lower than the HOMO level of the ligand of the green quantum dot.

The HOMO level of the ligand of the blue quantum dot is higher than the HOMO level of the ligand of the green quantum dot.

The ligand of the red quantum dot is octadecylamine.

The ligand of the green quantum dot is octylamine.

The ligand of the blue quantum dot is butylamine.

According to another aspect of the present invention, there is provided a quantum luminescent device comprising: a substrate; A positive electrode formed on the substrate; A hole transport layer formed on the anode; A quantum luminescent layer formed on the hole transport layer and comprising a red quantum dot, a green quantum dot, and a blue quantum dot, the core including a core, a shell surrounding the core, and a ligand surrounding the shell; An electron transport layer formed on the quantum luminescent layer; And a cathode formed on the electron transport layer, wherein the shells of the red quantum dot, the green quantum dot, and the blue quantum dot have different thicknesses.

The thickness of the shell of the red quantum dot is thicker than the thickness of the shell of the green quantum dot.

The shell thickness of the blue quantum dot is thinner than the shell thickness of the green quantum dot.

The quantum-emitting device of the present invention as described above realizes stable white regardless of the applied voltage by matching the driving voltages of the red quantum dot, the green quantum dot, and the blue quantum dot.

1A is a cross-sectional view of a general quantum dot light emitting device.
1B is a bandgap energy diagram of FIG. 1A. FIG.
2 is a view showing the color coordinates of a quantum-emitting device.
FIG. 3 is a bandgap energy diagram of a quantum dot light emitting device according to the first embodiment of the present invention
Figures 4a, 4b and 4c are bandgap energy diagrams of red, green, and blue quantum dots, respectively, according to the first embodiment of the present invention.
5a, 5b and 5c are bandgap energy diagrams of a red quantum dot, a green quantum dot and a blue quantum dot, respectively, according to a second embodiment of the present invention.

The quantum luminescent device of the present invention is characterized in that the red quantum dots, the green quantum dots and the blue quantum dots constituting the quantum luminescent layer have ligands different in balance band from each other, So that a stable white color can be realized.

Hereinafter, the quantum-emitting device of the present invention will be described in detail with reference to the accompanying drawings.

* First Embodiment *

FIG. 3 is a bandgap energy diagram of the quantum dot light emitting device according to the first embodiment of the present invention. FIGS. 4A, 4B and 4C are diagrams illustrating a red quantum dot, a green (green) A quantum dot, and a blue quantum dot.

3, a quantum luminescent device according to a first embodiment of the present invention includes a substrate (not shown), an anode 110 formed on the substrate (not shown), a hole formed on the anode 110 A red quantum dot 130R formed on the hole transport layer 120 and including a core, a shell surrounding the core and a ligand surrounding the shell, a green quantum dot 130G, The electron transport layer 140 formed on the quantum luminescent layer 130 and the cathode 150 formed on the electron transport layer 140 are formed of a quantum luminescent layer 130 in which the electron transport layer 140 and the blue quantum dot 130B are mixed, , The red quantum dot 130R, the green quantum dot 130G, and the blue quantum dot 130B are formed of materials having different HOMO levels from each other.

Although not shown, a hole injection layer may be further formed between the anode 110 and the hole transport layer 120. An electron injection layer and a hole blocking layer may be interposed between the electron transport layer 140 and the cathode 150 Can be formed. The hole blocking layer functions to prevent the holes injected into the quantum luminescent layer 130 from moving to the electron transporting layer.

The type of the substrate (not shown) is not particularly limited and may be various, and a glass substrate, a plastic substrate, a silicon substrate, or the like can be used.

The anode 110 may be formed of a transparent material selected from indium tin oxide (ITO), zinc oxide, indium oxide, tin oxide, and indium tin oxide And the cathode 150 is made of one selected from the group consisting of Ca, Al, Mg, Ag, Ba and alloys thereof.

The hole transport layer 120 formed on the anode 110 facilitates injection of holes from the anode 110 and transmits holes to the quantum luminescent layer 130.

The quantum luminescent layer 130 is composed of nano-sized quantum dots having a diameter of 1 nm to 100 nm. The quantum luminescent layer 130 includes red quantum dots 130R, green quantum dots 130G And a blue quantum dot 130B are mixed.

The quantum dot has a core component that emits light at its center, and a shell surrounds the core surface to protect the surface.

The quantum luminescent layer 130 may be formed by dispersing a plurality of quantum dots in a solvent, applying a solvent in which the plurality of quantum dots are dispersed on the hole transport layer 120 by a solution process, A ligand is surrounded on the surface of the shell so that the quantum dots are dispersed well in the solvent.

The core and the shell are nano-sized inorganic semiconductors, and the shell is made of a material having a band gap larger than that of the core.

For example, the cores or shells of the quantum dots may be made of cadmium selenide (CdSe), cadmium sulfide (CdS), cadmium teleide (CdTe), zinc selenide (ZnSe), zinc teleride (ZsTe), zinc sulfide , And mercury teleride (HgTe), or a 3-5 group semiconductor compound such as indium arsenide (InAs) or indium phosphide (InP).

The HOMO (Highest Occupied Molecular Orbital) level of the red quantum dot 130R, the green quantum dot 130G, and the blue quantum dot 130B are different from each other. The HOMO level of the core of the red quantum dot 30R is the highest and the HOMO level of the core of the blue quantum dot 30B is the lowest. The higher the HOMO level of the quantum dot is, the more easily the holes are injected. Therefore, the driving voltage of the red quantum dot 130R is the lowest and the driving voltage of the blue quantum dot 130B is the highest.

As described above, since the drive voltages of the red quantum dot 130R, the green quantum dot 130G, and the blue quantum dot 130B are different from each other, when a low voltage is applied, the red quantum dot 130R having the lowest drive voltage generates electrons Holes are first injected to form an exciton. When a high voltage is applied, many excitons are formed even in the blue quantum dot 130B having the highest driving voltage. Thus, the white color realized according to the voltage applied to the quantum luminescent device is different.

Therefore, the quantum-efficiency light emitting device of the present invention is characterized in that the red quantum dot 130R, the green quantum dot 130G, and the blue quantum dot 130G are arranged so as to equalize the driving voltages of the red quantum dot 130R, the green quantum dot 130G, and the blue quantum dot 130B. The ligand of the quantum dot 130B is formed of a material having a different HOMO level.

When the hole is injected into the quantum dot in the hole transport layer 120, the ligand has a HOMO level lower than the HOMO level of the core, and functions as an energy barrier when the hole is injected into the quantum dot.

That is, the ligand of the red quantum dot 130R having the lowest driving voltage is formed of a material having a low HOMO level and the ligand of the blue quantum dot 130B having the highest driving voltage is formed of a material having a high HOMO level, The green quantum dot 130G, and the blue quantum dot 130B have the same driving voltage.

4A, the ligand of the red quantum dot 130R having the lowest driving voltage is formed of a material having a low HOMO level, and the ligand of the red quantum dot 130R is formed with respect to the hole injected into the red quantum dot 130R It functions as a high energy barrier. Accordingly, the driving voltage of the red quantum dot 130R is increased. As shown in FIG. 4C, the ligand of the blue quantum dot 130B having the highest driving voltage is formed of a material having a high HOMO level. Therefore, holes are well injected into the blue quantum dot 130B and the driving voltage of the blue quantum dot 130B is lowered.

4B, the ligand of the green quantum dot 130G has a HOMO level between the HOMO level of the ligand of the red quantum dot (130R in FIG. 4A) and the HOMO level of the ligand of the blue quantum dot (130B of FIG. 4C) .

  As described above, the driving voltages of the red quantum dot 130R, the green quantum dot 130G, and the blue quantum dot 130B are made equal to each other to prevent the color change phenomenon according to the applied voltage, thereby realizing a stable white color.

At this time, the ligand of the red quantum dot 130R is octadecylamine (ODA), the ligand of the green quantum dot 130G is octylamine (OA), the ligand of the blue quantum dot 130B is butyl It is preferable that it is an amine (Butylamine; BA).

The electron transport layer 140 formed on the quantum luminescent layer 130 facilitates electron injection from the cathode 150 and transmits electrons to the quantum luminescent layer 130. The hole transport layer 120 may be formed of a material selected from the group consisting of TPD (N, N'-bis- (3-methylphenyl) -N, N'- N-vinylcarbazole), NPD (N, N'-diphenylbenzidine), CBP (4,4'-N, N'- dicarbazole- biphenyl), DNA-CTMA (cetyl trimethylammonium-Deoxyribonucleic acid ), mCP (1,3-bis (carbazol-9-yl), PEDOT: PSS, poly (3,4- ethylenedioxythiophene) (3- (4-biphenylyl) -4-phenyl-5-t-butylphenyl-1,2,4-triazole), BCP (basocuproine), TPBI (1,3,5-tris (N-phenylbenzimidazol- ) benzene), Alq ₃ (tris (8-quinolinolato) aluminum complex) and the like.

* Second Embodiment *

FIGS. 5A, 5B, and 5C are band diagram energy diagrams of a red quantum dot, a green quantum dot, and a blue quantum dot, respectively, according to the second embodiment of the present invention.

In order to avoid redundant explanations, the same reference numerals are assigned to the same parts that have the same functions as those in FIG. 3 described above, and only the characteristic contents will be described.

5A, 5B and 5C, the quantum dot light emitting device according to the second embodiment of the present invention includes a substrate (not shown), an anode 110 formed on the substrate (not shown) A red quantum dot 130R formed on the hole transport layer 120 and composed of a core, a shell surrounding the core and a ligand surrounding the shell, a red quantum dot 130R formed on the hole transport layer 120, An electron transport layer 140 formed on the quantum luminescent layer 130 and a cathode 150 formed on the electron transport layer 140. The quantum luminescent layer 130 includes a quantum dot 130G and a blue quantum dot 130B, And the shells of the red quantum dot 130R, the green quantum dot 130G, and the blue quantum dot 130B have different thicknesses.

Although not shown, a hole injection layer may be further formed between the anode 110 and the hole transport layer 120. An electron injection layer and a hole blocking layer may be interposed between the electron transport layer 140 and the cathode 150 Can be formed. The hole blocking layer functions to prevent the holes injected into the quantum luminescent layer 130 from moving to the electron transporting layer.

In the quantum luminescent device according to the second embodiment of the present invention, the thickness of the shell surrounding the cores of the red quantum dot 130R, the green quantum dot 130G and the blue quantum dot 130B is made different, The shell functions as an energy barrier of holes injected into the red quantum dot 130R, the green quantum dot 130G and the blue quantum dot 130B to drive the red quantum dot 130R, the green quantum dot 130G and the blue quantum dot 130B The voltages can be matched equally.

Specifically, as shown in FIG. 5A, the shell of the red quantum dot 130R having the lowest drive voltage has the thickest thickness. Therefore, the shell functions as a high energy barrier for holes injected into the red quantum dot 130R, and the driving voltage of the red quantum dot 130R is increased. As shown in FIG. 5C, the shell of the blue quantum dot 130B having the highest driving voltage has the smallest thickness, so that holes are well injected into the blue quantum dot 130B and the driving voltage of the blue quantum dot 130B is lowered. 5B, the shell of the green quantum dot 130G is formed to be thicker than the shell of the red quantum dot (130R in FIG. 5A) and thinner than the shell of the blue quantum dot (130B in FIG. 5C).

  Accordingly, the driving voltage of the red quantum dot 130R, the green quantum dot 130G, and the blue quantum dot 130B are matched to each other to prevent a color change phenomenon according to a voltage applied to realize a stable white color.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Will be apparent to those of ordinary skill in the art.

110: anode 120: hole transport layer
130R: red quantum dot 130G: green quantum dot
130B: blue quantum dot 130: quantum luminescent layer
140: electron transport layer 150: cathode

Claims (9)

Board;
A positive electrode formed on the substrate;
A hole transport layer formed on the anode;
A quantum luminescent layer formed on the hole transport layer and comprising a red quantum dot, a green quantum dot, and a blue quantum dot, the core including a core, a shell surrounding the core, and a ligand surrounding the shell;
An electron transport layer formed on the quantum luminescent layer; And
And a cathode formed on the electron transporting layer,
Wherein the HOMO level of the ligand of the red quantum dot is lower than the HOMO level of the ligand of the green quantum dot and the HOMO level of the ligand of the blue quantum dot is higher than the HOMO level of the ligand of the green quantum dot,
Wherein the shell of the red quantum dot is thicker than the shell of the green quantum dot and the shell of the blue quantum dot is thinner than the shell of the green quantum dot. delete delete The method according to claim 1,
When the HOMO level of the ligand of the red quantum dot is lower than the HOMO level of the ligand of the green quantum dot and the HOMO level of the ligand of the blue quantum dot is higher than the HOMO level of the ligand of the green quantum dot,
The ligand of the red quantum dot is octadecylamine,
The ligand of the green quantum dot is octylamine,
And the ligand of the blue quantum dot is butylamine. delete delete delete delete delete

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