KR20130013810A - Quantum-dot light emitting diode - Google Patents

Abstract

PURPOSE: A quantum light emitting diode is provided to improve the efficiency of the quantum light emitting diode by smoothly injecting an electron into a quantum dot by lowering an energy barrier of the electron. CONSTITUTION: A first electrode(110) is formed on a substrate. A phosphorescence host material layer(120b) is formed on the first electrode. A quantum light emitting layer is formed on the phosphorescence host material layer. The quantum light emitting layer includes a quantum dot(160). An electron transfer layer(140) is formed on the quantum light emitting layer to deliver an electron to the quantum light emitting layer. A second electrode(150) is formed on the electron transfer layer.

Description

Quantum light emitting device {QUANTUM-DOT LIGHT EMITTING DIODE}

The present invention relates to a quantum light emitting device, and relates to a quantum light emitting device capable of improving luminous efficiency by lowering an energy barrier of holes injected into quantum dots.

In the information society, display is emphasized as a visual information transmission medium, and in order to occupy a major position in the future, it is necessary to satisfy requirements such as low power consumption, thinness, light weight, and high definition. Among such displays, a quantum light emitting device capable of displaying, slimming, high color purity, and long driving time has been recently studied.

Quantum dots (QDs) are semiconductor nanoparticles. Quantum dots with a diameter of nanometers emit light when electrons in an unstable state descend from the conduction band to the valence band. Smaller particles of the quantum dots generate shorter wavelengths of light, and larger particles generate long wavelengths of light. This is a unique electrical and optical characteristic that differs from conventional semiconductor materials. Therefore, by adjusting the size of the quantum dot to represent the visible light of the desired wavelength, it is possible to implement a variety of colors at the same time by different quantum dot and quantum dot components of different sizes.

In general, an organic light emitting display device uses an organic light emitting material as a material of an emission layer, and an organic light emitting diode (OLED) using an organic light emitting material realizes a single color such as white, red, and blue according to the type of device. However, there is a limit to expressing a lot of light colorfully. On the other hand, the quantum light emitting device is a display device using quantum dots as a material of the light emitting layer, and can control the size of the quantum dots to achieve a desired natural color. It has been spotlighted as a material that can compensate for the shortcomings of light emitting diodes (LEDs).

Hereinafter, the structure of a general quantum light emitting device will be described in detail.

1A is a cross-sectional view of a general quantum light emitting device, and FIG. 1B is a bandgap energy diagram of a general quantum light emitting device.

Referring to FIG. 1A, a general quantum light emitting device is formed on a substrate 100, a substrate 100, and opposes the first electrode 10, the second electrode 50, the first electrode 10, and the second electrode 10. Between the quantum light emitting layer 30 formed between the electrode 50, the hole transport layer 20 formed between the first electrode 10 and the quantum light emitting layer 30, and between the quantum light emitting layer 30 and the second electrode 50. It includes the formed electron transport layer 40.

The quantum light emitting layer 30 is composed of a plurality of quantum dots 60 having a diameter of nanometer, a solvent in which a plurality of quantum dots 60 are dispersed in a solution process by dispersing the plurality of quantum dots 60 in a solvent. Is formed on the hole transport layer 20 and the solvent is volatilized.

The quantum dot 60 includes a core 60a, a shell 60b, and a ligand 60c. The shell 60b surrounding the core 60a serving to emit light and formed on the surface of the core 60a serves to protect the core 60a. In addition, a ligand 60c is formed on the surface of the shell 60b to surround the shell 60b, and the ligand 60c helps the quantum dot 60 to be well dispersed in the solvent when the quantum light emitting layer 30 is formed. Play a role.

However, as shown in FIG. 1B, a general quantum light emitting device has a high energy barrier between the quantum dot 60 and the hole transport layer 20, thereby making it easier to inject holes, resulting in high driving voltage and lower reliability of the device. In addition, since the energy barrier between the quantum dot 60 and the hole transport layer 20 is higher than the energy barrier between the quantum dot 60 and the electron transport layer 40, more electrons are injected into the quantum dot 60 than holes.

Therefore, electrons that do not participate in light emission among electrons injected into the quantum dot 60 are accumulated in the quantum dot 60, and the energy emitted by the electrons and holes is transferred to the stacked electrons without being used for light emission. (Auger Recombination) occurs to cause a problem that the efficiency of the quantum light emitting device is lowered.

The present invention has been made to solve the above problems, and provides a quantum light emitting device that can be injected into the quantum dots smoothly through a phosphorescent host material layer having a low HOOC (Highest Occupied Molecular Orbital) level, the object There is this.

A quantum light emitting device of the present invention for achieving the above object, the first electrode formed on the substrate; A phosphorescent host material layer formed on the first electrode; A quantum light emitting layer formed on the phosphorescent host material layer and including a quantum dot; An electron transport layer formed on the quantum light emitting layer; And a second electrode formed on the electron transport layer.

The phosphorescent host material layer delivers holes to the quantum dots.

The phosphorescent host material layer is formed of CBP or mCP.

In addition, a quantum light emitting device of the present invention for achieving the same object, the first electrode formed on the substrate; A quantum light emitting layer formed on the first electrode and formed by mixing a phosphorescent host material and a quantum dot; An electron transport layer formed on the quantum light emitting layer; And a second electrode formed on the electron transport layer.

The quantum light emitting layer is formed by dispersing the phosphorescent host material and the quantum dots in a solvent.

The phosphorescent host material delivers holes to the quantum dots.

The phosphorescent host material is CBP or mCP.

The quantum light emitting device of the present invention as described above has the following effects.

First, since holes are injected into the quantum dots through a phosphorescent host material layer having a low HOOC (Highest Occupied Molecular Orbital) level, holes are smoothly injected into the quantum dots by lowering the energy barrier of the holes. Therefore, the efficiency of a quantum light emitting element can be improved.

Second, when the phosphorescent host material and the quantum dot are mixed to form the quantum light emitting layer, the structure and the process of the device can be simplified and the quantum light emitting layer can be formed thick, thereby increasing the light emitting area. In addition, since the quantum light emitting layer may be formed by a solution process, manufacturing costs may be reduced.

1A is a cross-sectional view of a typical quantum light emitting device.
1B is a bandgap energy diagram of a typical quantum light emitting device.
2A is a cross-sectional view of a quantum light emitting device according to a first embodiment of the present invention.
2B is a bandgap energy diagram of the quantum light emitting device of the first embodiment of the present invention.
3A is a cross-sectional view of a quantum light emitting device according to a second embodiment of the present invention.
3B is a bandgap energy diagram of a quantum light emitting device according to a second embodiment of the present invention.

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

* First Embodiment *

2A is a cross-sectional view of a quantum light emitting device according to a first embodiment of the present invention, and FIG. 2B is a bandgap energy diagram of the quantum light emitting device according to a first embodiment of the present invention.

As shown in FIG. 2A, the quantum light emitting device according to the first exemplary embodiment of the present invention includes a substrate 200, a first electrode 110 formed on the substrate 200, and a phosphorescent host material layer 120b formed on the first electrode 110. ), A quantum light emitting layer 130 formed on the phosphorescent host material layer 120b and including a quantum dot 160, an electron transport layer 140 formed on the quantum light emitting layer 130, and a second formed on the electron transport layer 140. Electrode 150.

The type of the substrate 200 is not particularly limited and may be variously used, and a glass substrate, a plastic substrate, or a silicon substrate may be used. Although not shown, a thin film transistor including an active layer, a gate electrode, a source electrode, and a drain electrode is formed on the substrate 200. The thin film transistor is electrically connected to the first electrode 110 as an anode.

Meanwhile, in the quantum light emitting display device of the present invention, the light emitted from the quantum light emitting layer 130 is emitted downward through the substrate 200 or the light generated from the quantum light emitting layer 130 is opposite to the substrate 200. It may be a top emission method emitted to. Therefore, when the quantum light emitting device is a bottom emission method, the first electrode 110 may include tin oxide (TO), indium tin oxide (ITO), indium zinc oxide (IZO), It is formed of a transparent conductive material such as indium tin zinc oxide (ITZO).

On the contrary, when the quantum light emitting device is a top emission type, the first electrode 110 is an opaque conductive material having high reflectance such as magnesium (Mg), silver (Ag), aluminum (Al), calcium (Ca), or the like having a low work function. It is preferable to form. The hole injection layer 120a is formed on the first electrode 110 to inject holes injected from the first electrode 110 into the quantum dots 160.

However, as described above, the general quantum light emitting device has a large energy barrier between the quantum dot and the hole transport layer, and thus it is difficult to easily inject holes into the quantum dots. Therefore, the general quantum light emitting device has a high driving voltage and low reliability.

For example, TPD (N, N'-dipheny-N, N'-bis (3-methylphenyl)-(1,1 'biphenyl) -4,4'diamine), NTP (N, N'-diphenyl-N The highest Occupied Molecular Orbital (HOMO) levels of the hole transport layer, such as N'-bis (1-naphthylphenyl) -1,1'-biphenyl-4,4'-diamine, are 5.4 eV and 5.5 eV, respectively. The level is about 6.7 eV. In addition, since the energy barrier between the quantum dots and the hole transport layer is higher than the energy barrier between the quantum dots and the electron transport layer, more electrons are injected into the quantum dots than holes.

Accordingly, in the quantum light emitting device of the first embodiment of the present invention, in order to lower the energy barrier for injecting holes into the quantum dots 160, holes are injected into the quantum dots through the phosphorescent host material layer 120b having a low HOMO level, thereby emitting light emission efficiency. Can improve. That is, in the quantum light emitting device of the present invention, the phosphorescent host material layer 120b functions as a hole transport layer.

For example, the phosphorescent host material is a substance such as carbazole biphenyl (CBP) having a HOMO level of about 6.3 eV, mCP (1,3-bis (carbazol-9-yl), etc. having a HOMO level of about 5.9 eV, etc. The phosphorescent host material layer 120b disperses phosphorescent host materials such as CBP, mCP, and the like in a solvent, such as ink jet, nozzle coating, spray coating, roll printing, and the like. It is formed through a solution process (Soluble Process) or is formed by a vacuum deposition method.

That is, as shown in FIG. 2B, in the quantum light emitting device of the present invention, the difference between the HOMO level of the phosphorescent host material layer 120b and the HOMO level of the quantum dot 160 is reduced, so that an energy barrier is generated when holes are injected into the quantum dot 160. The hole may be easily injected into the quantum dot 160 by being lowered. Therefore, the driving voltage of the quantum light emitting device is lowered and the reliability is improved.

The quantum light emitting layer 130 formed on the phosphorescent host material layer 120b is formed of nanoscale quantum dots 160 having a diameter of 1 nm to 100 nm. The quantum light emitting layer 130 is formed by the above-described solution process, and the plurality of quantum dots 160 are dispersed in a solvent to apply a solvent having the plurality of quantum dots 160 dispersed on the phosphorescent host material layer 120b and to apply a solvent. It is formed by volatilization.

The quantum dot 160 includes nano semiconductor compounds of Groups 2-6 or 3-5. For example, the nano-semiconductor compound constituting the quantum dot 160 is cadmium selenide (CdSe), cadmium sulfide (CdS), cadmium telluride (CdTe), zinc selenide (ZnSe), zinc telluride (ZnTe), zinc sulfide (ZnS), mercury telluride (HgTe), indium arsenide (InAs), Cd1-xZnxSe1-ySy ', CdSe / ZnS, indium phosphorus (InP) and gallium arsenide (GaAs). The solvent is selected from various organic solvents such as hexane, toluene, chloroform and the like.

The quantum dot 160 is formed of a core that plays a role of emitting light, a shell surrounding the core and formed on the surface of the core to protect the core, and a ligand formed on the surface of the shell and surrounding the shell. The ligand serves to help the quantum dot 160 to be well dispersed in the solvent when forming the quantum light emitting layer 130.

The electron transport layer 140 and the electron injection layer for transferring electrons injected from the second electrode 150 to the quantum light emitting layer 130 are sequentially formed on the quantum light emitting layer 130, and only the electron transport layer 140 is illustrated in the drawing. . The electron transport layer 140 is formed of a material having excellent electron transport ability such as aluminum quinolate, and the electron injection layer may use a metal compound such as lithium fluoride (LiF).

The electron transport layer 140 and the electron injection layer may optionally be formed of one layer. In this case, one layer may perform the functions of the electron transport layer 140 and the electron injection layer to reduce the material cost, and improve productivity and yield. In addition, it is possible to reduce the driving voltage by reducing the interface (interface) through which the charge is moved, thereby reducing the power consumption of the quantum light emitting device.

The second electrode 150 formed on the electron transport layer 140 is a cathode for supplying electrons to the quantum dot 160 and is formed by a vacuum deposition method. The second electrode 150 may be formed of an opaque conductive material having a high reflectance such as magnesium (Mg), silver (Ag), aluminum (Al), calcium (Ca), or the like having a low work function when the quantum light emitting display device is a bottom emission method. Is formed. In the case of the top emission type, tin oxide (TO), indium tin oxide (ITO), indium zinc oxide (IZO), and indium tin zinc oxide (ITZO) It is formed of a transparent conductive material such as).

In the quantum light emitting device as described above, when a voltage is applied between the first electrode 110 and the second electrode 150, holes are injected from the first electrode 110, and electrons are injected from the second electrode 150 so that the quantum light emitting layer ( Recombination at 130 produces excitons. The exciton falls to the ground state and emits light.

* Second Embodiment *

Hereinafter, a quantum light emitting device according to a second embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3A is a cross-sectional view of a quantum light emitting device according to a second embodiment of the present invention, and FIG. 3B is a bandgap energy diagram of the quantum light emitting device according to a second embodiment of the present invention.

As shown in FIG. 3A, the quantum light emitting device according to the second embodiment of the present invention is formed on a substrate 300, a first electrode 210 formed on the substrate 300, a first electrode 210, and a phosphorescent host material ( And a second electrode 250 formed on the quantum light emitting layer 230, the electron transport layer 240 formed on the quantum light emitting layer 230, and the electron transport layer 240.

That is, the quantum light emitting device according to the second embodiment of the present invention forms the quantum light emitting layer 230 by mixing the phosphorescent host material 220b and the quantum dots 260 to simplify the structure and the process. At this time, the phosphorescent host material 220b delivers holes to the quantum dot 260.

Specifically, after the phosphorescent host material 220b and the quantum dot 260 are dispersed in a solvent, the dispersed mixture is formed on the first electrode 210 by a solution process and formed by volatilizing the solvent. In addition, a hole injection layer 220a may be further formed between the first electrode 210 and the quantum light emitting layer 230.

In general, the quantum light emitting device does not easily move holes and electrons injected into the quantum light emitting layer to other quantum dots due to the ligand of the quantum dot, so even when the quantum light emitting layer is formed thick, the interface between the quantum light emitting layer and the hole transport layer or the quantum light emitting layer and the electron transport layer The most luminescence occurs at. Therefore, since the load of the hole and the electron transporting layer interface is generated, the thickness of the quantum light emitting layer is made thinner than 30 nm, so that the light emitting area is narrowed and reliability is difficult to be secured.

However, the quantum light emitting device of the present invention may easily move holes and electrons to other quantum dots 260 through the phosphorescent host material 220b mixed with the quantum dots 260. Therefore, not only the interface between the quantum light emitting layer 260 and the hole injection layer 220a or the quantum light emitting layer 260 and the electron transport layer 240 but also holes and electrons may meet and emit light at the quantum dot 260 inside the quantum light emitting layer 230. Therefore, luminous efficiency can be improved.

Accordingly, the quantum light emitting device of the present invention forms the thickness of the quantum light emitting layer 230 to 30 nm or more, thereby widening the light emitting area. Therefore, not only can the reliability of the device be secured, but the process of forming the hole transport layer can be eliminated, thereby simplifying the process and reducing the manufacturing cost.

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.

200, 300: substrate 110, 210: first electrode
120a and 220a: hole injection layer 120b: phosphorescent host material layer
130, 230: quantum light emitting layer 140, 240: electron transport layer
150, 250: second electrode 160, 260: quantum dot
220b: phosphorescent host material

Claims (7)

A first electrode formed on the substrate;
A phosphorescent host material layer formed on the first electrode;
A quantum light emitting layer formed on the phosphorescent host material layer and including a quantum dot;
An electron transport layer formed on the quantum light emitting layer to transfer electrons to the quantum light emitting layer; And
And a second electrode formed on the electron transport layer. The method of claim 1,
The phosphorescent host material layer transfers holes to the quantum dots. The method of claim 1,
The phosphorescent host material layer is formed of CBP or mCP. A first electrode formed on the substrate;
A quantum light emitting layer formed on the first electrode and formed by mixing a phosphorescent host material and a quantum dot;
An electron transport layer formed on the quantum light emitting layer; And
And a second electrode formed on the electron transport layer. The method of claim 4, wherein
The quantum light emitting layer is formed by dispersing the phosphorescent host material and the quantum dots in a solvent. The method of claim 4, wherein
The phosphorescent host material transfers holes to the quantum dots. The method of claim 4, wherein
The phosphorescent host material is CBP or mCP, characterized in that the quantum light emitting device.

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