KR102001734B1 - Quantum dot light­emitting device and manufacturing method therefor - Google Patents

Abstract

The present invention relates to a quantum dot light emitting diode and a method of manufacturing the same, and more particularly, to a quantum dot light emitting diode and a method of manufacturing the same, which are capable of preventing electron leakage from a light emitting portion and improving electron- There is an effect of providing a quantum dot light emitting diode having improved lifetime and a manufacturing method thereof.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a quantum dot light emitting diode

The present invention relates to a quantum dot light emitting diode and a method of manufacturing the same, and more particularly, to a quantum dot light emitting diode and a method of manufacturing the same, And a method of fabricating the quantum dot light emitting diode.

The quantum dot is a colloidal semiconductor crystal having a size of several nanometers to tens of nanometers, and has been attracting attention as a next generation light emitting material due to its high color purity, color reproducibility and light stability. By controlling the particle size of semiconductor crystals, it is possible to control a wide range of emission wavelengths, and advantageous in that a solution process is possible and the manufacturing process is simple. As a result, a quantum dot light-emitting diode (QLED) using quantum dots as a light emitting material has been actively studied as a next generation device.

The general structure of a quantum dot light emitting diode includes an anode, a hole injection layer (HIL), a hole transport layer (HTL), a quantum dot light emitting layer, an electron transport layer (ETL) an electron injection layer (EIL), and a cathode. In the quantum dot light-emitting diode, a metal oxide formed mainly in the form of a nanoparticle or a sol-gel is used as an electron injection / transport layer. The hole transport layer is mainly composed of a deep homo (highest occupied molecular orbital) orbital: HOMO) energy level is formed by vacuum deposition. In this case, since the HOMO energy level of the hole transport layer and the valence band energy level of the quantum dot are larger than the energy level difference between the electron transport layer and the conduction band of the quantum dot, excessive electrons are injected into the light emitting layer There is a difficulty in fabricating a high-efficiency quantum dot light-emitting diode due to a non-luminescent transition phenomenon of the device.

Therefore, in order to realize the high efficiency of the quantum dot light-emitting diode, it is necessary to balance the electron-hole in the device effectively. However, the development of a technology for effectively balancing the electron-hole balance in the device by using a relatively simple processing method has not yet been sufficiently achieved, and development of the related technology is therefore continuously required.

Prior art information : Korean Patent Publication No. 10-2017-0117812

An object of the present invention is to provide a high-efficiency quantum dot light-emitting diode and a method of manufacturing the same.

It is a specific object of the present invention to provide a quantum dot light emitting diode having improved efficiency and lifetime by adjusting the balance of electron-hole in a device in a relatively simple manner in a conventional hole transporting structure and a method of manufacturing the same.

A quantum dot light emitting diode according to an embodiment of the present invention includes:

A light emitting portion provided between the first electrode and the second electrode,

An electron transferring portion for transferring electrons to the light emitting portion, and

And a hole transferring part for transferring holes to the light emitting part,

Wherein the hole transporting part comprises a first hole transporting material and a second hole transporting material, wherein the eu of the first hole transporting material is (1lu), the loops of the second hole transporting material is (2lu) , The following equation (1) may be satisfied.

[Equation 1]

1lu <2lu

A method of manufacturing a quantum dot light emitting diode according to another embodiment of the present invention includes:

A first hole material and a second hole material satisfying the relation of the following formula 1 when the loom (eV) of the first hole material is (1lu) and the loam (eV) of the second hole material is (2lu) Selecting,

[Equation 1]

1 <

Stacking a semiconductor material between the first electrode and the second electrode to provide a light emitting portion; And

The first hole transport material and the second hole transport material are mixed with the host material of the hole transport layer and the dopant material in a volume ratio of 1: 0.1 to 3 on the light emitting portion, respectively, and laminated to form a hole transport layer .

A method of fabricating a quantum dot light emitting diode according to another embodiment of the present invention includes:

A first hole material and a second hole material satisfying the relation of the following formula 1 when the loom (eV) of the first hole material is (1lu) and the loam (eV) of the second hole material is (2lu) Selecting,

[Equation 1]

1 <

Stacking a semiconductor material between the first electrode and the second electrode to provide a light emitting portion;

Forming an electron blocking layer for blocking electrons leaked from the light emitting portion by laminating the second hole transporting material on the light emitting portion; And

And forming a hole transport layer for transporting holes to the light emitting portion by laminating the first hole transporting material on the electron blocking layer.

A method of fabricating a quantum dot light emitting diode according to another embodiment of the present invention includes:

A first hole material and a second hole material satisfying the relation of the following formula 1 when the loom (eV) of the first hole material is (1lu) and the loam (eV) of the second hole material is (2lu) Selecting,

[Equation 1]

1 <

Depositing the semiconductor material between the first electrode and the second electrode to provide a light emitting portion;

Forming an electron blocking layer for blocking electrons leaked from the light emitting portion by laminating the second hole transporting material on the light emitting portion; And

Forming a hole transport layer by mixing and laminating the first hole transport material and the second hole transport material on the electron blocking layer in a volume ratio of 1: 0.1 ~ 3 as a host material of the hole transport layer and a dopant material, respectively; Lt; / RTI &gt;

According to the present invention, there is provided a quantum dot light-emitting diode having improved device lifetime by preventing electron leakage from a light-emitting portion and improving electron-hole balance in a light-emitting portion, .

1 is a cross-sectional view illustrating a quantum dot light emitting diode according to an embodiment of the present invention.
2 is a cross-sectional view illustrating a quantum dot light emitting diode according to another embodiment of the present invention.
FIG. 3 is a graph comparing the current density-voltage-luminance of a quantum dot light emitting diode according to an embodiment of the present invention and a related art.
FIG. 4 is a graph illustrating a result of measurement of external quantum efficiency-current density of a quantum dot light emitting diode according to an embodiment of the present invention and a related art.
FIG. 5 is a graph illustrating a result of measuring lifetime characteristics of a quantum dot light-emitting diode according to an embodiment of the present invention and a related art.
6 is a graph showing a result of measurement of current density-voltage-luminance of a quantum dot light-emitting diode according to Reference Example 1. FIG.
FIG. 7 is a graph showing a result of measurement of external quantum efficiency-current density of a quantum dot light-emitting diode according to Reference Example 1. FIG.

BRIEF DESCRIPTION OF THE DRAWINGS The above objects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Rather, the embodiments disclosed herein are provided so that the disclosure can be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

In the present specification, when it is mentioned that a layer (or region (or portion)) is on another layer (or region (or region) or substrate), it may be formed directly on the other layer Or a third layer (or region (s)) may be interposed therebetween. Also, in the figures, the sizes and thicknesses of the structures and the like are exaggerated for clarity. Also, in various embodiments The terms first, second, etc. are used to describe various regions, layers (or regions), etc., but these regions and layers should not be limited by these terms. (Or layer) is distinguished from another region (portion) or a film (or layer) only by a region or portion. Thus, the layer referred to as the first layer in any one embodiment is, in another embodiment, May be referred to as the second floor have.

In the drawings, the thickness is enlarged to clearly represent the layers and regions. Like parts are designated with like reference numerals throughout the specification. It will be understood that when an element such as a layer, film, region, plate, or the like is referred to as being "on" another portion, it includes not only the element directly over another element, Conversely, when a part is "directly over" another part, it means that there is no other part in the middle.

Hereinafter, a structure of a quantum dot light emitting diode according to the present invention, a production example thereof, and a quantum dot light emitting diode using the same will be described in detail with reference to the accompanying drawings.

First, a quantum dot light emitting diode according to an embodiment of the present invention will be described in detail with reference to FIG. 1 is a cross-sectional view illustrating a quantum dot light emitting diode according to an embodiment of the present invention. Referring to FIG. 1, a quantum dot light emitting diode (QLED) according to an embodiment of the present invention includes a substrate 110, electrode layers 120 including a first electrode 120 and a second electrode 180 facing each other A quantum dot light emitting layer 140 disposed between the first electrode 120 and the second electrode 180 and an electron transferring part 130 disposed opposite to the quantum dot light emitting layer 140, And a transfer unit 160, 170.

The electron transporting part 130 may be a monolayer structure of an electron injection / transport layer or may be a bilayer structure of an electron injection layer and an electron transport layer. The hole transport part 160 and 170 may be a monolayer structure of a hole injection / Or may be a bilayer structure of a hole injecting layer and a hole transporting layer.

The first electrode 120 may be an anode electrode and the second electrode 180 may be a cathode electrode. Alternatively, the first electrode 120 may be a cathode electrode and the second electrode may be an anode electrode . The first electrode 120 and the second electrode 180 may be formed of a transparent conductive material or a semi-transmissive or reflective conductive material, respectively. For example, indium tin oxide (ITO), indium zinc oxide (IZO), indium zinc tin oxide (IZTO), aluminum zinc oxide (AZO), indium tin oxide-silver-indium tin oxide (ITO- (IZO-Ag-IZO), indium zinc tin oxide-silver-indium zinc tin oxide (IZTO-Ag-IZTO), aluminum zinc oxide- silver- aluminum zinc oxide (AZO- (Al), gold (Au), silver (Ag), copper (Cu), iridium (Ir), molybdenum (Mo), palladium (Pd), platinum LiF / Al), calcium and aluminum lamination (Ca / Al), or calcium and silver lamination (Ca / Ag). Depending on the kind of the material forming the first electrode 120 and the second electrode 180, the light emitting type may provide front emission, back emission, or both-sided emission. When the first electrode 120 is an anode, the first electrode 120 may include a material having a high work function to facilitate hole injection. For example, the work function of Al is 4.28 eV and the work function of ITO is 4.7 eV.

The first electrode 120 according to an exemplary embodiment of the present invention may include a transparent electrode such as indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO ₂ ), zinc oxide (ZnO) It may be formed to have a thin thickness by using the same conductive oxide or a metal such as aluminum (Al), silver (Ag), and magnesium (Mg). In addition, the first electrode 120 is not limited thereto, and may be formed in a stacked structure of two or more layers of a conductive oxide and a metal material.

At this time, the substrate 110 may be made of a transparent material such as glass, quartz, plastic, or inorganic composite polymer having a first refractive index of about 1.4 to about 1.9. For example, the substrate 110 may be a glass substrate and may include borosilicate glass. In another example, the substrate 110 may be a flexible substrate, such as polyethylene terephthalide (PET), polyethylene naphthalate (PEN), polyethylene (PE), polyethersulfone (PES), polycarbonate , Polyarylate (PAR), or polyimide (PI). The substrate buffer layer may be positioned on the substrate 110, but may be omitted depending on the type of substrate and the process conditions. The substrate buffer layer may be formed of various materials capable of performing the function of flattening the surface while preventing penetration of impurity elements. For example, the substrate buffer layer may be any one of a silicon nitride (SiNx) film, a silicon oxide (SiOy) film, and a silicon oxynitride (SiOxNy) film.

Meanwhile, a light emitting portion 140 is formed between the first electrode 120 and the second electrode 180. The light emitting portion 140 includes a light emitting semiconductor material that displays a specific color. For example, the light emitting unit 140 may display basic colors such as blue, green, or red, or a combination thereof.

The semiconductor material included in the light emitting portion 140 according to an embodiment of the present invention may include quantum dots. For example, the light emitting unit 140 may include a red quantum dot having a wavelength of 570 nm to 780 nm, a green quantum dot having a wavelength of 480 nm to 570 nm, and a blue quantum dot having a wavelength of 380 to 480 nm And may include one or more species.

The quantum dot may comprise a Group II-VI compound, a Group III-V compound, a Group IV-VI compound, a Group IV compound, and combinations thereof. The II-VI compound may be selected from the group consisting of CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS and mixtures thereof; A trivalent element selected from the group consisting of CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, Small compounds; And a silane compound selected from the group consisting of HgZnTeS, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe and mixtures thereof.

The III-V compound is selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb and mixtures thereof; A trivalent compound selected from the group consisting of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP and mixtures thereof; And a photonic compound selected from the group consisting of GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb and mixtures thereof.

The III-V compound is selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb and mixtures thereof; A trivalent compound selected from the group consisting of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP and mixtures thereof; And a photonic compound selected from the group consisting of GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb and mixtures thereof.

Group IV-VI compounds are selected from the group consisting of SnS, SnSe, SnTe, PbS, PbSe, PbTe, and mixtures thereof; A triple compound selected from the group consisting of SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, and mixtures thereof; And a silane compound selected from the group consisting of SnPbSSe, SnPbSeTe, SnPbSTe, and mixtures thereof.

Group IV elements may be selected from the group consisting of Si, Ge and mixtures thereof, and the Group IV compounds may be selected from the group consisting of SiC, SiGe, and mixtures thereof. Oxides of group II in addition; Oxides of group III; Oxides of group VI; Oxides of group V; Or an oxide of group VI.

The average grain size of the core in the core / shell quantum dots may be between 2 nm and 6 nm. On the other hand, the average thickness of the shell may be from 3 nm to 7 nm. The average particle diameter of the quantum dots may be from 5 nm to 20 nm. When the core, shell and quantum dots satisfy the average particle diameter or the average thickness range as described above, characteristic behaviors as quantum dots can be obtained and, furthermore, excellent dispersibility can be obtained. By varying the particle diameter of the core, the average thickness of the shell, and the average particle diameter of the quantum dots within the ranges described above, the emission color of the quantum dots and / or the semiconducting characteristics of the quantum dots can be varied variously. The shape of the quantum dots is not limited to a specific one generally used in the art, but may be a spherical, pyramidal, multi-arm or cubic nanoparticle, a nanotube, a nanowire, Nanofibers, nano-sized particles, and the like are preferably used. The quantum dot may further include a ligand formed on the surface of the shell and chemically bonded thereto. The ligand may include an organic functional group, and the organic functional group may include, for example, oleate, trioctylphosphine, dendrimer, and the like.

At this time, the thickness of the light emitting portion 140 may be 15 to 35 nm, or 20 to 30 nm.

The hole transport layer 160 and the hole injection layer 170 may be disposed on the light emitting portion 140. The hole transport layer 160 is generally known to perform the function of smoothly transporting holes that are transferred from the hole injection layer. An electron blocking layer 150 may be formed between the light emitting portion 140 and the hole transporting layer 160 or a material for forming the electron blocking layer 150 may be formed on the hole transporting layer 160 The electrons leaked from the light emitting portion 140 to the hole transport layer 160 are blocked to confine the electrons to the quantum dot layer according to mixing as the dopant material, The voltage difference between the semiconductor material including the quantum dots and the anode is increased, and the electric field strength of the hole transporting layer is increased. Accordingly, the number of holes transported through the hole transport layer 160 increases, thereby efficiently adjusting the electron-hole balance in the device. As a result, it is possible to provide a low driving voltage, excellent efficiency and long life time compared to the device according to the prior art which does not form the electron blocking layer or does not include the hole transporting material constituting the electron blocking layer in the hole transporting layer Reference).

In the exemplary embodiment of the present invention, the material constituting the electron blocking layer 150 or the dopant material for modifying the hole transporting layer 160 may be a hole transporting material (CBP or the like, (MCP or the like, hereinafter referred to as a second hole transporting material) different from the first hole transporting material (hereinafter, referred to as a first hole transporting material) and the LUMO are included in the quantum dots constituting the light emitting portion 140 It is preferable not to cause agglomeration with semiconductor materials such as the above-mentioned material because the thin film coating property is excellent and the hole mobility is not adversely affected.

For example, the first hole transport material may satisfy the relationship of Equation 1 when the loom (eV) of the first hole transport material is (1lu) and the loam (eV) of the second hole transport material is (2lu)

[Equation 1]

1lu <2lu

For example, CBP used as the first hole transport material in the present invention is a material having a LUMO of -3.0 eV and a mum of LUMO of -2.4 eV used as a second hole transport material and a correlation Is satisfied.

Further, the second hole transporting material of the present invention has a surface energy and a hole density different from those of the first hole transporting material, and the semiconductor material including the quantum dots constituting the light emitting unit 140 aggregation is not caused, the thin film coating property is excellent, and the hole mobility is not adversely affected.

Here, the surface energy represents the contact angle measured by the sessile drop method, which is calculated by the Owen-Wendt method, g represents mJm ^{- 2} , and the hole density p represents the formula conductivity σ = pxe (1.602 × 10 ^-19 is C) x mobility as the unit is cm ^-3 calculated from (μ): as an example, the first surface energy (g) and the hole density (10 ¹¹ cm in a hole transport ^material-3), respectively (1se) and (1hd), and the surface energy (g) and the hole density (10 ¹¹ cm ^-3 ) of the second hole transporting material are (2se) and (2hd), respectively, Can be:

&Quot; (2) &quot;

2se <1se

&Quot; (3) &quot;

1h <2hd

For example, CBP used as the first hole transport material in the present invention has a surface energy of 32.12 g and a hole density of 1.85. As an example of the mCP used as the second hole transport material, the surface energy is 24.85 g and the hole density is 4.93, it can be confirmed that both of the expressions 2 and 3 are satisfied.

As another example, the surface energy g and the eV of the first hole transport material may be expressed as (1se) and (lu), respectively, and the surface energy (g) (2se) and (2lu), and the surface energy (g) and the root (eV) of the semiconductor material are respectively Qse and Qlu. For reference, Equation 4 below can also be confirmed.

&Quot; (4) &quot;

2se < 1se < Qse

&Quot; (5) &quot;

Qlu <1lu <2lu

For example, CBP used as the first hole transport material in the present invention has a surface energy of 32.12 g and a rumo of -3.0 eV. As an example of the mCP used as the second hole transport material, the surface energy is 24.85 g, -2.4 eV, the surface energy of CdZnS / ZnS as the semiconductor material is 33.12 g, and the ratios of most semiconductor materials (quantum dots) are -5.0 eV to -4.0 eV, confirming that Equations 4 and 5 are satisfied.

As a specific example, the first hole transporting material may be a donor (D) -connector (C) -linking material (C) -form (DCCD form) ) organic compound for hole transport having an n-type, D- (D) n-type, [DCDC] n-type, or DCD type, or an inorganic compound in the form of vacuum deposition, nanoparticle coating, . The electron donor material (donor: D) may include a carbazole derivative, an aromatic amine-based material, or an aromatic silane-based material. The connecting material (C) may include an arylene-based material including phenylene and naphthalene. And n may be an integer of 1 to 100.

For example, the first hole transport material may have a LUMO of -4.0 eV or more and a HOMO of -4.0 eV to -6.0 eV, and the ratio of the first hole transport material to the CBE of the quantum dot (Meaning that the absolute value is small because it is a negative number), and the homo is preferably positioned between the homo of the hole injection layer or the electrode and the homo of the second hole transport material. As another example, the first hole transporting material may be at least one selected from the compounds represented by the following formulas (1) to (6).

[Chemical Formula 1]

(2)

(3)

[Chemical Formula 4]

[Chemical Formula 5]

[Chemical Formula 6]

As a specific example, the second hole transporting material may be in the form of an electron donor (D) -linking material (C) -electron donor (D) (DCD form), a DCCCD form, a DCDCD form, An organic compound, or an inorganic material in the form of vacuum deposition, nanoparticle coating, or zeolite film formation. The electron donor material (donor: D) may include a carbazole derivative, an aromatic amine-based material, or an aromatic silane-based material. The connecting material (C) may include an arylene-based material including phenylene and naphthalene. And n may be an integer of 1 to 100.

For example, the first hole transport material may have a LUMO of -4.0 eV or more and a HOMO of -4.0 eV to -6.0 eV, and the ratio of the first hole transport material to the CBE of the quantum dot (Meaning that the absolute value is small because it is a negative number), and the homo is preferably positioned between the homo of the hole injection layer or the electrode and the homo of the second hole transport material. It is preferable that the second hole transport material is a material having a LUMO of -2.0 eV to -3.0 eV and a HOMO of -6.0 eV or more. The second hole transporting material may be at least one selected from compounds represented by the following formulas (7) to (11).

(7)

[Chemical Formula 8]

[Chemical Formula 9]

[Chemical formula 10]

(11)

When the electron blocking layer 150 is formed between the light emitting portion 140 and the hole transporting layer 160, the total thickness of the hole transporting layer 160 and the electron blocking layer 150 may range from 20 to 100 nm, . The thickness of the hole transport layer 160 provided by mixing the material of the electron blocking layer 150 as a dopant material for modifying the hole transport layer 160 may be 20 to 80 nm or 40 to 60 nm.

A hole injection layer 170 may be disposed on the hole transport layer 160. At this time, the long hole injection layer 170 may function to improve injection of holes from the electrode for injecting holes in the electrode layers 120 and 180 into the hole transport layer 160. The hole injecting material constituting the hole injecting layer 170 is not particularly limited as long as it is a substance that facilitates injection of holes from the anode, and conventional organic or inorganic materials are applicable. For example, HAT-CN (hexaazatriphenylene-hexanitrile), molybdenum oxide (MoO ₃ ), tungsten oxide (WO ₃ ), vanadium oxide (V ₂ O ₅ ) and the like. The thickness of the hole injection layer 170 may be 2 to 20 nm, or 10 to 20 nm. The hole injecting layer 170 and the hole transporting layer 160 are stacked in the present invention. However, the present invention is not limited thereto. The hole injecting layer 170 and the hole transporting layer 160 may be formed as a single layer .

In particular, the hole transporting portions 150, 160, and 170 may include a hole transporting layer 160 disposed on the light emitting portion 140; And a hole injection layer 170 disposed on the hole transport layer 160. The hole transport layer 160 may be formed using the first hole transport material as a host material and the second hole transport material as a dopant material, It is an aspect of the present invention that the leakage of electrons from the light emitting unit 140 is blocked. The volume of the second hole-transporting material is sufficient to exhibit electrical characteristics at a volume ratio of the host material and the dopant material in a volume ratio of 1: 0.1 to 3, or 1: 0.1 to 1, It is preferable that the leakage of electrons from the light emitting part 140 is effectively blocked while preventing aggregation with the semiconductor material constituting the light emitting part 140 and does not greatly affect the hole mobility. The hole transport units 150, 160, and 170 may be disposed between the light emitting unit 140 and the electrodes 120 and 180.

The hole transporting part 150, 160, and 170 may include an electron blocking layer 150 disposed on the light emitting part 140; A hole transport layer 160 located on the electron blocking layer 150; And a hole injection layer 170 disposed on the hole transport layer 160. The electron blocking layer 150 may include a hole transport material as the host material, The hole transporting material is included as a bilayer structure using a host material. Here, the electron blocking layer 150 also effectively prevents the leakage of electrons from the light emitting portion 140, prevents aggregation with the semiconductor material constituting the light emitting portion 140, and does not significantly affect hole mobility, Do.

On the other hand, the electron transport layer and the electron injection layer may be disposed on the light emitting portion 140 as electron transport portions in the layer direction in which the hole transport portions 150, 160, and 170 are not formed. The electron transporting layer can transfer electrons from the electron injecting electrode to the light emitting portion. Further, the electron transporting layer can prevent the holes injected from the hole injecting electrode from passing through the light emitting portion and moving to the electron injecting electrode. That is, the electron transporting layer serves as a hole blocking layer, which helps to bond holes and electrons in the light emitting portion. The electron injection layer can also function to improve the injection of electrons from the electron transfer electrode into the electron transport layer.

The electron transport layer and the electron injection layer of the present invention may be formed in a laminated structure or may be formed as a single layer, and the total thickness may be 30 to 60 nm, or 30 to 50 nm. Further, at least one of the electron transporting layer and the electron injecting layer may further include a group III transition metal. That is, at least one of the electron transport layer and the electron injection layer contains at least any one of scandium (Sc), yttrium (Y), lanthanum (La), acatanium (Ac), ruthenium (Ru), and rhodium can do. These Group III transition metals may contain 1 to 10% by weight based on the total weight of the electron transport layer and / or the electron injection layer.

1, the electron transporting / injecting layer 130 may include a metal oxide, an organic material, or an organic compound. For example, In ₂ S ₃ , Cu ₂ S, Ag2S, may include ZnSe, ZnS, ZnO, ZnTe, ZnSe, TiO _2, SnO ₂ and at least one selected from ZnS, but not limited to this. The electron transporting / injecting layer 130 may be formed, for example, by spin coating in a solution state in which zinc oxide synthesized by a nanoparticle method is dispersed in an alcohol solvent such as butanol, May be used at a concentration of 5 to 40 mg / ml, or 5 to 20 mg / ml.

In the quantum dot light emitting diode according to the present invention, when a current is supplied to the quantum dot light emitting diode, electrons are moved from the transparent electrode 120 to the light emitting portion 140 through the electron transporting / injecting layer 130, The electrons may be transferred from the metal electrode 180 to the light emitting unit 140 through the hole injection layer 170, the electron transport layer 160, and the electron blocking layer 150. At this time, electrons and holes are formed in the light emitting part 140 to form an exciton, and light can be emitted in the process of recombining the excitons.

The quantum dot light emitting diode according to the present invention exhibits an EQE efficiency of 0.1 to 20%, a driving voltage of 2 to 8 V, and may be a red quantum dot light emitting diode, a green quantum dot light emitting diode, a blue quantum dot light emitting diode, or a white quantum dot light emitting diode.

As shown in FIG. 1, the quantum dot light emitting diode of the present invention can be manufactured in the order of a back cathode, an electron injection and transport layer, a quantum dot light emitting layer, an electron blocking layer, a hole transport layer, a hole injection layer, and a cathode in this order, As described above, the anode, the hole injecting layer, the hole transporting layer, the electron blocking layer, the quantum dot light emitting layer, the electron injecting and transporting layer, and the cathode can be fabricated in this order. 1, the lower electrode is fabricated as a back light emitting structure using a transparent electrode, but the lower electrode may be replaced with a metal electrode and the upper electrode may be replaced with a dielectric / metal / dielectric multilayer thin film or a transparent electrode And can be manufactured with a top emission structure.

The method of manufacturing a quantum dot light emitting diode according to another embodiment of the present invention is not limited thereto, but it can be simply manufactured while maintaining the basic structure in the following manner: First, the rho (eV) 1lu) and the loam (eV) of the second hole material is (2lu), the first hole material and the second hole material satisfying the relationship of the following formula (1) are selected.

[Equation 1]

1 <

Then, the selected semiconductor material is stacked between the first electrode and the second electrode to provide a light emitting portion. The first hole transport material and the second hole transport material selected on the light emitting portion are mixed with the host material of the hole transport layer and the dopant material in a volume ratio of 1: 0.1 ~ 3, respectively, and laminated to form a hole transport layer.

The method of manufacturing a quantum dot light emitting diode according to another embodiment of the present invention is not limited thereto but may be simply manufactured while maintaining the basic structure in the following manner: (1lu) and the loam (eV) of the second hole material is (2lu), the first hole material and the second hole material satisfying the relationship of the following formula (1) are selected.

[Equation 1]

1 <

The selected semiconductor material is stacked between the first electrode and the second electrode to provide a light emitting portion. And a second hole transport material selected on the light emitting portion is stacked to form an electron blocking layer for blocking electrons leaked from the light emitting portion. Then, a selective hole transporting material is laminated on the electron blocking layer to form a hole transporting layer for transporting holes to the light emitting portion.

The method of manufacturing a quantum dot light emitting diode according to another embodiment of the present invention is characterized in that when the first hole material eu is 1lu and the second hole material eu is 2u, The first hole material and the second hole material satisfying the relationship of the formula (1) are selected.

[Equation 1]

1 <

The semiconductor material is laminated between the first electrode and the second electrode to provide a light emitting portion. An electron blocking layer is formed by stacking the second hole transporting material on the light emitting portion to block electrons leaking from the light emitting portion. The first hole transporting material and the second hole transporting material are mixed with the host material of the hole transporting layer and the dopant material at a volume ratio of 1: 0.1 to 3, respectively, on the electron blocking layer and laminated to form a hole transporting layer.

Hereinafter, the structure and effect of the present invention will be described in more detail with reference to examples and comparative examples. However, this embodiment is intended to explain the present invention more specifically, and the scope of the present invention is not limited to these embodiments.

Example

Example  1: Selecting the first hole transport material, the second hole transport material

Among the various hole transport materials constituting the conventional hole transport layer, materials satisfying the following condition (1) were selected. That is, the materials satisfying the relation of the following formula 1 were selected when the rumo (eV) of the first hole material was (1lu) and the loam (eV) of the second hole material was (2lu).

[Equation 1]

1lu <2lu

Then, it was confirmed whether the conditions of the following equations (1) and (2) were satisfied among the selected materials. Specifically, the surface energy (g) of the first hole transport material and the hole density (10 ¹¹ cm ^-3 ) are set to (1se) and (1hd) It was selected a material that satisfies the relationship of ^- (10 ¹¹ cm ^3), respectively to to to (2se) and (2hd) equation 2 and equation 3.

&Quot; (2) &quot;

1se> 2se

&Quot; (3) &quot;

2hd> 1hd

Further, the relationship between the surface energy of CdZnS / ZnS selected as a semiconductor material and the rumen among the selected materials is confirmed by the following equations (4) and (5). That is, the surface energy g and the eV of the first hole transport material are expressed as (1se) and (1lu), respectively, and the surface energy (g) 2se) and (2lu), and the surface energy (g) and the root (eV) of the semiconductor material are respectively Qse and Qlu.

&Quot; (4) &quot;

2se < 1se < Qse

&Quot; (5) &quot;

Qlu <1lu <2lu

Finally, it was confirmed that the LUMO of the second hole transport material was within the range of -2.0 eV to -3.0 eV.

Example 2

The materials selected in the above Example 1 were manufactured as follows with reference to the sectional view of FIG. Specifically, ITO having a resistance of 10 to 15? /? And a thickness of 150 nm was formed as a first electrode 120 on a glass substrate 110 having a thickness of 0.7 mm. A zinc oxide solution having a concentration of 20 mg / ml, which was synthesized by nanoparticle method and dispersed in a butanol solvent, was spin-coated on the first electrode 120 at 2000 rpm for 40 seconds and then heat-treated at 100 ° C for 1 hour under a nitrogen atmosphere. An electron transporting / injecting layer 130 formed of a zinc oxide thin film was formed. A quantum dot having a CdZnS core as a core on the electron transporting / injecting layer 130 and a ZnS shell surrounding the surface thereof was spin-coated at 4000 rpm for 30 seconds and dried at 100 ° C for 10 minutes to form a light- (140). Then, the compound of Formula 1 (corresponding to CBP) as a host material and the compound of Formula 7 (corresponding to mCP) as a dopant material were doped in a volume ratio of 1: 1 as a host material and deposited on the light emitting portion 140 through vacuum deposition to form a 60 nm thick And a molybdenum oxide (MoO ₃ ) was deposited on the hole transport layer 160 through vacuum deposition to form a hole injection layer 170 having a thickness of 10 nm. Next, aluminum was vacuum-deposited on the hole injection layer 170 to form a second electrode 180 having a thickness of 130 nm to manufacture a quantum dot light-emitting diode.

Example  3

The same process as in Example 2 was repeated except that the second hole-transporting material among the materials selected in Example 2 was used as the host material constituting the electron blocking layer 150 in the sectional view of FIG. Specifically, the light emitting portion 140 is formed in Embodiment 2, CBP as a host material and mCP as a dopant material are mixed at a volume ratio of 1: 1, and then vapor deposition is performed on the light emitting portion 140 through a vacuum deposition method to form a 60 nm thick The step of forming the hole transporting layer 160 is omitted. Instead, mCP is deposited as a host material on the light-emitting portion 140 through vacuum deposition to form an electron blocking layer 150 having a thickness of 20 nm. Then, on the electron blocking layer 150, A hole transporting layer 160 having a thickness of 40 nm was formed. Subsequently, the hole injection layer 170 and the metal electrode 180 were successively stacked in the manner as described in Example 2.

Example  4

A hole transport layer 160 was formed on the electron blocking layer 150 in Example 3 and a material obtained by mixing the host material CBP and the dopant mCP in the 1: 1 volume ratio as the hole transport layer 160 A quantum dot light-emitting diode was fabricated by repeating the same procedure as in Example 3, except that a hole transport layer 160 having a thickness of 60 nm was additionally formed by vacuum deposition.

Comparative Example 1

A quantum dot light-emitting diode was produced in the same manner as in Example 3 except that the electron blocking layer was not formed in Example 3.

Experimental Examples 1 to 3

The electrical characteristics of the quantum dot LEDs of Example 2 and Comparative Example 1 were measured using a Keithley 237 source meter while measuring the electrical characteristics using a Keithley 2000 multimeter, a silicon photodiode, and a photomultiplier tube. Electroluminescence (EL) spectra were also obtained using a Minolta CS-2000A spectrometer. The driving lifetime of the device was measured using McScience and MC620S until the luminance decreased to 40% of the initial luminance by applying a current having a constant luminance value to the device.

The measured current density-voltage-luminance results are shown in Fig. For reference, Device A represents an embodiment and Device B represents a comparative example. As shown in FIG. 3, according to the present invention, it was confirmed that the current density was increased twice (Example: 206 mA / cm ² , Comparative Example: 105 mA / cm ² ) at the same voltage (6 V) .

The measured external quantum efficiency-current density results are also shown in FIG. For reference, Device A represents an embodiment and Device B represents a comparative example. As shown in FIG. 4, according to the present invention, the maximum external quantum efficiency is doubled (2.5% in the embodiment, 1.3% in the comparative example) compared with the conventional device.

Furthermore, the measured life characteristic results are shown in Fig. For reference, Device A represents an embodiment and Device B represents a comparative example. Both devices were subjected to a measurement by applying a constant current so that the initial luminance value was 200 cd / m ² . The period until the initial luminance value reached 50% was measured by measuring until the driving luminance of the device reached 40% of the initial luminance value. As shown in FIG. 5, according to the present invention, it was confirmed that the time for 50% of the initial luminance value is increased by 25% than that of the conventional device.

Reference example  One

Except that only the electron blocking layer 150 was formed in Example 3 and the hole transporting layer 160 was not formed so that the hole blocking material 150 constituting the electron blocking layer 150 functions as a hole transporting layer. The quantum dot light-emitting diode was fabricated. The quantum dot light-emitting diode thus manufactured was measured in the same manner as in Figs. 3 to 5, and is summarized in Fig. 6 and Fig. As it is shown in Figures 6 and 7, the maximum luminance 45cdm ^- was was ^2, the maximum external quantum efficiency was 0.01%. It can be deduced that mCP is aggregated due to surface energy difference with quantum dots as only mCP is formed as a hole transport layer without CBP.

From the above experiments, it can be seen that in the case of the quantum dot light emitting diode according to the present invention, electrons leaked from the light emitting portion to the hole transport layer in a simple manner are deposited or doped with hole transporting materials satisfying the correlation between the high LUMO energy level and the specific surface energy and the hole density It is confirmed that the electron-hole balance in the device is matched and the efficiency and lifetime of the device are increased accordingly.

110: substrate
120: transparent electrode
130: electron injection / transport layer
140:
150: electron blocking layer
160: hole transport layer
170: Hole injection layer
180: metal electrode

Claims (18)

A light emitting portion provided between the first electrode and the second electrode, the light emitting portion including a quantum dot semiconductor material,
An electron transferring portion for transferring electrons to the light emitting portion, and
And a hole transferring part for transferring holes to the light emitting part,
The hole transporting portion includes an electron blocking layer located on the light emitting portion; A hole transport layer located on the electron blocking layer; And a hole injection layer disposed on the hole transport layer,
Wherein the electron blocking layer comprises a second hole transporting material, wherein the hole transporting layer comprises a first hole transporting material and a second hole transporting material in a volume ratio of 1: 0.1 to 3,
(Eu) of the first hole transporting material is set to (1lu), the loom (eV) of the second hole transporting material is set to (2lu), and the loom (eV) of the quantum dot semiconductor material is set to (Qlu) The quantum dot light emitting diode satisfies the following formula (5).
&Quot; (5) &quot;
Qlu <1lu <2lu The method according to claim 1,
The first hole transport material surface energy (g) and the hole density (10 ¹¹ cm ^{- 3)} to, and to each (1se) and (1hd) and the second surface energy, (g) and the hole density of the hole transport material ( 10 ¹¹ cm ^{- 3)} for each (2se) and the quantum dot light-emitting diode, characterized in that to satisfy the relation of the following formula 2 and formula 3 to a (2hd).
&Quot; (2) &quot;
1se> 2se
&Quot; (3) &quot;
2hd> 1hd delete The method according to claim 1,
Wherein the hole transport layer shields electrons leaked from the light emitting portion using the first hole transport material as a host material and the second hole transport material as a dopant material. delete The method according to claim 1,
Wherein the electron blocking layer comprises the second hole transporting material as a host material and the hole transporting layer comprises a bi-layer structure using the first hole transporting material as a host material. The method according to claim 1,
The first hole transporting material may be in the form of a donor (D) -connector (C) -connecting material (C) -form of a donor (D) , D- (D) n form, [DCDC] n form, or DCD form; Or an inorganic material in the form of vacuum deposition, nanoparticle coating, or forming a thin film of a zeolite. The method according to claim 1,
The second hole transporting material may be an electron blocking organic compound having a form of an electron donor (D) -linking substance (C) -electron donor (D), a DCCCD form, a DCDCD form or a DDD form ; (LUMO) is in the range of -2.0 eV to -3.0 eV, and the homo (HOMO) is in the range of -6.0 eV or more. Light emitting diode. The method according to claim 7 or 8,
Wherein the donor (D) comprises a carbazole derivative, an aromatic amine or an aromatic silane-based material, the connecting material (C) comprises an arylene-based material including phenylene and naphthalene, and n Lt; RTI ID = 0.0 &gt; 1 &lt; / RTI &gt; The method according to claim 1,
Wherein the first hole transporting material is a material having a LUMO of -4.0 eV or more and a HOMO of -4.0 eV to -6.0 eV. The method according to claim 1,
Wherein the second hole transporting material is a material having a LUMO of -2.0 eV to -3.0 eV and a HOMO of -6.0 eV or more. The method according to claim 1,
Wherein the first hole transporting material is at least one selected from compounds represented by Chemical Formulas 1 to 6 below.
[Chemical Formula 1]

(2)

(3)

[Chemical Formula 4]

[Chemical Formula 5]

[Chemical Formula 6]

The method according to claim 1,
Wherein the second hole transporting material is at least one selected from compounds represented by the following general formulas (7) to (11).
(7)

[Chemical Formula 8]

[Chemical Formula 9]

[Chemical formula 10]

(11)

The method according to claim 1,
Wherein the light emitting portion includes at least one selected from the group consisting of a red quantum dot having a wavelength of 570 nm to 780 nm in a luminescent region, a green quantum dot having a wavelength of 480 nm to 570 nm, and a blue quantum dot having a wavelength of 380 to 480 nm And a quantum dot light emitting diode. The method according to claim 1,
Wherein the quantum dot light emitting diode has an EQE efficiency of 0.1 to 20% and a driving voltage of 2V to 8V and is a red quantum dot light emitting diode, a green quantum dot light emitting diode, a blue quantum dot light emitting diode, or a white quantum dot light emitting diode. . delete delete When the luminous (eV) of the first hole transport material is (1lu), the luminous (eV) of the second hole transport material is (2lu), and the loam (eV) of the quantum dot semiconductor material is (Qlu) Selecting a first hole transporting material, a second hole transporting material, and a quantum dot semiconductor material satisfying the relationship of the following formula (5)
&Quot; (5) &quot;
Qlu <1lu <2lu
Depositing the quantum dot semiconductor material between a first electrode and a second electrode to provide a light emitting portion;
Forming an electron blocking layer for blocking electrons leaked from the light emitting portion by laminating the second hole transporting material on the light emitting portion; And
Forming a hole transport layer by mixing and laminating the first hole transport material and the second hole transport material on the electron blocking layer in a volume ratio of 1: 0.1 ~ 3 as a host material of the hole transport layer and a dopant material, respectively; Method of manufacturing a quantum dot light emitting diode.

Images