KR20220148634A - High-luminance quantum dot light-emitting device and method of manufacturing the same - Google Patents

Abstract

Disclosed are a high-luminance quantum dot light-emitting device and a method for manufacturing the same. The disclosed quantum dot light emitting device comprises: a substrate having a thermal conductivity of 100 W/mㆍK or more at 25℃; a first electrode disposed on the substrate; a second electrode disposed spaced apart from the first electrode on the substrate in a direction perpendicular to the substrate; and a quantum dot disposed between the first electrode and the second electrode and including a core portion and a shell portion. The shell portion includes: a quantum dot light-emitting layer having a composition gradient whose composition changes as moving away from the core portion; an electron transport layer disposed between the first electrode and the quantum dot light-emitting layer; a hole transport layer disposed between the second electrode and the quantum dot light-emitting layer and including a carbazole derivative; and a hole injection layer disposed between the hole transport layer and the second electrode and including a first layer and a second layer sequentially arranged from a side of the hole transport layer, wherein the first layer is provided with MoO_3 and the second layer is provided with hexaazatriphenylene hexacarbonitrile (HAT-CN). The quantum dot light-emitting device may have a top emission structure which emits light from the quantum dot light-emitting layer to a side opposite to where the substrate is disposed. The present invention aims to provide a quantum dot light-emitting device having excellent light extraction efficiency while stably emitting light at a high current density in a field requiring high luminance.

Description

High-luminance quantum dot light-emitting device and method of manufacturing the same

The present invention relates to an optical device and a manufacturing method thereof, and more particularly, to a quantum dot light emitting device and a manufacturing method thereof.

A quantum dot is a crystalline semiconductor having a size of several to tens of nanometers, and may be composed of hundreds to thousands of atoms. Because quantum dots are very small in size, they have a large surface area per unit volume, and most atoms exist on the crystal surface. Since these quantum dots have discontinuous energy levels due to a quantum confinement effect, they exhibit optical and/or electrical properties different from those of bulk semiconductors having continuous energy bands.

Recently, research has been conducted to apply quantum dots to various optical and electronic devices. In particular, interest in quantum dot light emitting devices using the electroluminescence phenomenon of quantum dots is increasing. The quantum dot light emitting device can be used as a high efficiency/low power light emitting device, and in particular, due to a narrow emission spectrum and easy wavelength control characteristics, it is attracting attention as one of the next generation light emitting devices.

However, in a self-luminous type quantum dot light-emitting device, that is, a self-emitting quantum dot light-emitting device (QLED), because electron and hole injection characteristics are different, a charge imbalance occurs in the light emitting layer, and this imbalance causes the excess charge to become exciton (exciton). ) resulting in Auger recombination, which inhibits luminescence. Auger recombination further increases as the current density increases, thus limiting the operation of the device under high current density/high luminance conditions. In addition, even if the above-described Auger recombination is suppressed, severe Joule heating of about 100° C. or more occurs in the device at high current density, which causes damage to the organic material layer and significantly degrades device performance. In televisions (TVs) and mobile phones that require relatively low luminance, there may be no problems in use if the charge is balanced only in the luminance region of about 1000 cd/m ² or less, but outdoor displays, AR (augmented reality)/VR In an application field requiring high luminance, such as a display for virtual reality or a light source of a device for medical/beauty, the above characteristics may be a big problem as disadvantages.

Therefore, a quantum dot light emitting device capable of stably emitting light with high current density in a field requiring high luminance and having excellent light extraction efficiency, overcoming the problem of performance degradation due to Joule heat, and securing durability and stable driving characteristics development is required.

The technical problem to be achieved by the present invention is to have excellent light extraction efficiency while stably emitting light at high current density in a field requiring high luminance, overcoming the problem of performance degradation due to Joule heat, durability (long life characteristics) and stability An object of the present invention is to provide a quantum dot light emitting device capable of securing driving characteristics.

In addition, the technical problem to be achieved by the present invention is to provide a method for manufacturing the above-described quantum dot light emitting device.

The problem to be solved by the present invention is not limited to the above-mentioned problems, and other problems not mentioned will be understood by those skilled in the art from the following description.

According to an embodiment of the present invention, a substrate having a thermal conductivity of 100 W / m · K or more at 25 ℃; a first electrode disposed on the substrate; a second electrode disposed on the substrate and spaced apart from the first electrode in a direction perpendicular to the substrate; A quantum dot light emitting layer disposed between the first electrode and the second electrode and including a quantum dot having a core portion and a shell portion, wherein the shell portion has a composition gradient in which the composition is changed as the distance from the core portion is increased. ; an electron transport layer disposed between the first electrode and the quantum dot emission layer; a hole transport layer disposed between the second electrode and the quantum dot emission layer and including a carbazole derivative; and a first layer and a second layer disposed between the hole transport layer and the second electrode in order from the hole transport layer side, wherein the first layer includes MoO ₃ and the second layer A quantum dot light emitting device having a top emission structure for emitting light from the quantum dot light emitting layer to the opposite side to the side on which the substrate is disposed is provided. do.

The substrate may include a silicon substrate part and a silicon oxide layer formed on a surface of the silicon substrate part. The thermal conductivity of the substrate may be dominantly determined by the silicon substrate portion.

The first electrode may be a reflective electrode, and the second electrode may be a transparent electrode. The spacing between the first electrode and the second electrode, the spacing between the first electrode and the quantum dot emitting layer, and the spacing between the quantum dot emitting layer and the second electrode may be controlled to generate optical constructive interference associated with the emission of light. can

The first electrode may include a first metal layer having a first thickness, and the second electrode may include a second metal layer having a second thickness smaller than the first thickness.

The hole transport layer may include CBP [4,4'-Bis(N-carbazolyl)-1,1'-biphenyl] as the carbazole derivative.

The first layer may be a MoO ₃ layer, and the second layer may be a HAT-CN layer.

The first layer may have a thickness in the range of about 3-7 nm, and the second layer may have a thickness in the range of about 3-7 nm.

The electron transport layer may include zinc oxide (ZnO)-based nanoparticles.

The shell portion of the quantum dot may include a continuous grading layer, a lattice adapter layer, and an injection barrier layer sequentially arranged from the side of the core portion.

The radius of the core part may be about 3.2±0.5 nm, the thickness of the continuous grading layer may be about 4.2±0.6 nm, the thickness of the grating adapter layer may be about 2.2±1.1 nm, and the thickness of the injection barrier layer is It may be on the order of 2.8±0.8 nm.

The thickness of the electron transport layer may be about 30 to 40 nm, the thickness of the quantum dot light emitting layer may be about 25 to 45 nm, the thickness of the hole transport layer may be about 30 to 50 nm, and the The thickness may be about 6-14 nm.

The quantum dot light emitting device may have a maximum luminance of about 3 million cd/m ² or more.

The quantum dot light emitting device may be configured to be driven with a current density of about 5 A/cm ² or more.

According to another embodiment of the present invention, providing a substrate having a thermal conductivity of 100 W / m · K or more at 25 ℃; forming a first electrode on the substrate; forming an electron transport layer on the first electrode; Forming a quantum dot light emitting layer comprising a quantum dot having a core portion and a shell portion on the electron transport layer, wherein the shell portion has a composition gradient that changes as the distance from the core portion increases; forming a hole transport layer including a carbazole derivative on the quantum dot emission layer; A hole injection layer including a first layer and a second layer sequentially disposed on the hole transport layer from the side of the hole transport layer, wherein the first layer includes MoO ₃ , and the second layer includes HAT-CN forming a; and forming a second electrode on the hole injection layer, the method of manufacturing a quantum dot light emitting device having a top emission characteristic to emit light from the quantum dot light emitting layer to the opposite side to the side on which the substrate is disposed this is provided

The substrate may include a silicon substrate part and a silicon oxide layer formed on a surface of the silicon substrate part. The thermal conductivity of the substrate may be dominantly determined by the silicon substrate portion.

The first electrode may be a reflective electrode, and the second electrode may be a transparent electrode. The spacing between the first electrode and the second electrode, the spacing between the first electrode and the quantum dot emitting layer, and the spacing between the quantum dot emitting layer and the second electrode may be controlled to generate optical constructive interference associated with the emission of light. can

The hole transport layer may include CBP [4,4'-Bis(N-carbazolyl)-1,1'-biphenyl] as the carbazole derivative.

The first layer may be a MoO ₃ layer, and the second layer may be a HAT-CN layer.

The first layer may have a thickness in the range of about 3-7 nm, and the second layer may have a thickness in the range of about 3-7 nm.

The shell portion of the quantum dot may include a continuous grading layer, a lattice adapter layer, and an injection barrier layer sequentially arranged from the side of the core portion.

The radius of the core part may be about 3.2±0.5 nm, the thickness of the continuous grading layer may be about 4.2±0.6 nm, the thickness of the grating adapter layer may be about 2.2±1.1 nm, and the thickness of the injection barrier layer is It may be on the order of 2.8±0.8 nm.

The quantum dot light emitting device may have a maximum luminance of about 3 million cd/m ² or more.

The quantum dot light emitting device may be configured to be driven with a current density of about 5 A/cm ² or more.

According to embodiments of the present invention, it has excellent light extraction efficiency while stably emitting light with high current density in a field requiring high luminance, and also overcomes the problem of performance degradation due to Joule heat, durability (long life characteristics) and It is possible to implement a quantum dot light emitting device capable of securing stable driving characteristics.

In particular, according to embodiments of the present invention, a multi-structured hole injection layer, a configuration of a hole transport layer combined with the hole injection layer, a substrate with high thermal conductivity, an optimized top emission structure, and a composition Through optimization of quantum dots with gradient and thickness conditions, etc., it can effectively suppress Auger recombination even at high current density, has a maximum luminance of about 3 million cd/m ² or more, and has high efficiency, excellent stability and durability It is possible to implement a quantum dot light emitting device having (long lifespan characteristics).

Quantum dot light emitting devices according to embodiments require high brightness such as outdoor displays, next-generation displays such as augmented reality (AR)/virtual reality (VR) displays, light sources of medical/beauty devices for phototherapy, and high-brightness lighting It can be usefully applied to various fields of application.

1 is a cross-sectional view showing a quantum dot light-emitting device according to an embodiment of the present invention.
2 is a view exemplarily showing a quantum dot light emitting device according to an embodiment of the present invention.
3 is a view for explaining a structure of a quantum dot that can be applied to a quantum dot light emitting device according to an embodiment of the present invention.
4A to 4D are cross-sectional views illustrating a method of manufacturing a quantum dot light emitting device according to an embodiment of the present invention.
5 is a graph showing results of evaluating current efficiency and luminance characteristics according to current density of quantum dot light emitting devices according to Examples and Comparative Examples of the present invention.
6 is a graph showing results of evaluating current efficiency and luminance characteristics according to current density of quantum dot light emitting devices according to Examples and Comparative Examples of the present invention.
7 is a graph showing a change in maximum pixel temperature according to time for each applied current density of a quantum dot light emitting device (S-QLED) according to an embodiment of the present invention.
8 is a graph showing a change in maximum pixel temperature according to time for each applied current density of a quantum dot light emitting device (G-QLED) according to a comparative example.
9 is an optical simulation result showing a change in emission intensity according to thickness conditions of a hole transport layer (HTL) and an electron transport layer (ETL) of a quantum dot light emitting device according to an embodiment of the present invention.
10 is a simulation result showing changes in the average QD occupancy <N> according to the QD areal density (ρ) and the applied current (J) of the quantum dot light emitting device according to an embodiment of the present invention; to be.
11 shows normalized electroluminescence (EL) of a quantum dot light emitting device (S-QLED) according to an embodiment having different QD areal densities (ρ) when the applied current (J) is 8.0 A cm ⁻² ) is a graph showing the spectrum.
12 is a graph showing a change in PL (photoluminescence) quantum yield (%) according to a process of growing a shell part of a quantum dot that can be applied to a quantum dot light emitting device according to an embodiment of the present invention.
13 is a graph showing the ensemble PL photoluminescence decay characteristics of CdSe QD (red), cg-QD (orange), cg/A-QD (green) and cg/A/B-QD (blue). to be.
14 is a graph showing the results of measuring changes in current density and luminance according to applied voltage of quantum dot light emitting devices according to Examples and Comparative Examples of the present invention.
15 is a graph showing the results of measuring changes in current efficiency and EQE (external quantum efficiency) according to the applied current density of quantum dot light emitting devices according to Examples and Comparative Examples of the present invention.
16 is a graph showing the results of evaluating the operational lifetime of quantum dot light emitting devices according to Examples and Comparative Examples of the present invention.
17 is a transient EL decay profile of a quantum dot light emitting device (S-QLED) according to an embodiment using time-resolved EL spectroscopy with a voltage pulse of 11.8V. A drawing showing the results.
18 is a transient EL normalized for various steady-state current densities (J) of 0.3, 1.6, 6.0 and 12.0 A cm ^-2 of a quantum dot light emitting device (S-QLED) according to an embodiment of the present invention. It is a graph showing the characteristics of normalized transient EL decay.
19 is a photograph showing the light emitting performance of a quantum dot light emitting device (S-QLED) according to an embodiment of the present invention.
20 is a photograph showing the result of evaluating the light emitting performance of a quantum dot light emitting device (S-QLED) according to an embodiment of the present invention.

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

Examples of the present invention to be described below are provided to more clearly explain the present invention to those of ordinary skill in the art, and the scope of the present invention is not limited by the following examples, The embodiment may be modified in many different forms.

The terminology used herein is used to describe specific embodiments, not to limit the present invention. As used herein, terms in the singular form may include the plural form unless the context clearly dictates otherwise. Also, as used herein, the terms "comprise" and/or "comprising" refer and does not exclude the presence or addition of one or more other shapes, steps, numbers, actions, members, elements, and/or groups thereof. In addition, as used herein, the term “connection” not only means that certain members are directly connected, but also includes indirectly connected members with other members interposed therebetween.

In addition, when a member is said to be located "on" another member in the present specification, this includes not only a case in which a member is in contact with another member but also a case in which another member is present between the two members. As used herein, the term “and/or” includes any one and any combination of one or more of the listed items. In addition, as used herein, terms such as "about", "substantially", etc. are used in the meaning of the range or close to the numerical value or degree, in consideration of inherent manufacturing and material tolerances, and to help the understanding of the present application The exact or absolute figures provided for this purpose are used to prevent the infringer from using the mentioned disclosure unfairly.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The size or thickness of the regions or parts shown in the accompanying drawings may be slightly exaggerated for clarity and convenience of description. Like reference numerals refer to like elements throughout the detailed description.

1 is a cross-sectional view showing a quantum dot light-emitting device according to an embodiment of the present invention.

Referring to FIG. 1 , a quantum dot light emitting device according to an embodiment of the present invention may include a substrate 110 having a thermal conductivity of about 100 W/m·K or more at 25°C. The thermal conductivity of the substrate 110 is, for example, preferably about 100 W/m·K or more at 25°C, and a substrate material having a thermal conductivity of at least 350 W/m·K is also applicable. As a specific example, the substrate 110 may include a silicon (Si) substrate and a silicon oxide layer (SiO ₂ layer) formed on a surface (upper surface) of the silicon substrate. The thickness of the silicon oxide layer may be relatively very thin compared to the thickness of the silicon substrate portion. The thermal conductivity of the substrate 110 may be dominantly determined by the silicon substrate portion. Since the substrate 110 has excellent thermal conductivity, the substrate 110 may have excellent heat resistance and heat dissipation characteristics, and a high-density current may be applied to the quantum dot light emitting device. In some cases, a sapphire (Al ₂ O ₃ ) substrate having excellent thermal conductivity, a magnesium fluoride (MgF ₂ ) substrate, or the like may be used as the substrate 110 . In another embodiment, as a substrate having excellent thermal conductivity, a metal substrate having an electrically insulating surface in which an electric insulating layer is formed on the surface of a metal substrate such as copper or aluminum having high conductivity may be used.

The quantum dot light emitting device includes a first electrode 120 disposed on a substrate 110 and a second electrode ( 170 , and a quantum dot emission layer 140 disposed between the first electrode 120 and the second electrode 170 . In addition, the quantum dot light emitting device includes an electron transport layer (ETL) 130 disposed between the first electrode 120 and the quantum dot light emitting layer 140 , and between the second electrode 170 and the quantum dot light emitting layer 140 . It may include an disposed hole transport layer (HTL) 150 and a hole injection layer (HIL) 160 disposed between the hole transport layer 150 and the second electrode 170 . The quantum dot light emitting device includes a first electrode 120 , an electron transport layer 130 , a quantum dot light emitting layer 140 , a hole transport layer 150 , a hole injection layer 160 and a second electrode 170 on the upper surface of the substrate 110 . It may have a structure stacked in this order. The quantum dot light emitting device may have a top emission structure in which light is emitted from the quantum dot light emitting layer 140 to the opposite side of the side on which the substrate 110 is disposed (ie, toward the front side of the device).

The first electrode 120 may be a reflective electrode, and the second electrode 170 may be a transparent electrode (a light-transmitting electrode). Both the first electrode 120 and the second electrode 170 may be formed of a metal or a metallic material to generate an optical microcavity effect. In addition, the interval between the first electrode 120 and the second electrode 170 , the interval between the first electrode 120 and the quantum dot emission layer 140 , and the interval between the quantum dot emission layer 140 and the second electrode 170 . can be controlled to generate optical constructive interference associated with the emission of light. Accordingly, the light L1 emitted from the quantum dot light emitting layer 140 to the front surface of the device and the light L2 emitted from the quantum dot light emitting layer 140 and reflected from the first electrode 120 to the front surface of the device are subjected to constructive interference. can cause In addition, light L1 emitted from the quantum dot light emitting layer 140 to the front surface of the device and light L2 emitted from the quantum dot light emitting layer 140 and reflected from the first electrode 120 to the front surface of the device are formed in the microcavity. (microcavity) It is possible to show the reinforcement effect according to the resonance by the structure. Accordingly, the light extraction characteristics of the quantum dot light emitting device can be greatly improved.

The first electrode 120 may include a first metal layer having a first thickness, and the second electrode 170 may include a second metal layer having a second thickness smaller than the first thickness. As a specific example, an Ag layer (silver layer) having a thickness of about 80 nm or more or about 85 nm or more may be deposited as the first electrode 120 for high reflectance, and high transmittance as the second electrode 170 may be used. For this purpose, an Ag layer (silver layer) having a thickness of about 30 nm or less or about 25 nm or less may be deposited and used. The thickness of the first electrode 120 may be about 80 to 120 nm, and the thickness of the second electrode 170 may be about 15 to 30 nm. The material of the first electrode 120 and the second electrode 170 is not limited to Ag and may be variously changed.

The quantum dot emission layer 140 may include quantum dots having a core portion and a shell portion. Here, the shell part may have a composition gradient in which the composition is changed as the distance from the core part is increased. In addition, the shell part may have a plurality of shell layers forming the composition gradient. The thickness of the core part and the shell part (the plurality of shell layers) may be appropriately controlled. With respect to the configuration and thickness control characteristics of the quantum dots, extinction of excitons in the quantum dot light emitting layer 140 is minimized, quenching due to Auger recombination is suppressed, and luminescence characteristics and luminous efficiency are greatly improved. can be improved A specific structure that the quantum dots applied to the quantum dot light emitting layer 140 may have will be described in more detail later with reference to FIG. 3 . Meanwhile, the thickness of the quantum dot emission layer 140 may be, for example, about 25 to 45 nm or about 30 to 40 nm.

The hole injection layer 160 may have a multi-layer structure, for example, a double-layer structure. Specifically, the hole injection layer 160 may include a first layer 160a and a second layer 160b sequentially disposed from the hole transport layer 150 side. The first layer 160a may be disposed between the hole injection layer 160 and the second layer 160b. Here, the first layer 160a may include MoO ₃ , and the second layer 160b may include hexaazatriphenylene hexacarbonitrile (HAT-CN). The first layer 160a may be a MoO ₃ layer, and the second layer 160b may be a HAT-CN layer. In this case, the first layer 160a may have a thickness in the range of about 3-7 nm or in the range of about 4-6 nm, and the second layer 160b in the range of about 3-7 nm or in the range of about 4-6 nm may have a thickness of For example, the thickness of the first layer 160a may be 5 nm or 6 nm, and the thickness of the second layer 160b may be 5 nm or 6 nm. The thickness of the hole injection layer 160 may be about 6 to 14 nm or about 8 to 12 nm. As such, when the hole injection layer 160 has a structure in which the MoO ₃ layer and the HAT-CN layer are stacked, and their thickness is appropriately controlled, the hole injection barrier is greatly reduced by the hole injection layer 160, The hole injection characteristic is improved, and as a result, the luminescence characteristic and the luminous efficiency can be improved.

The hole transport layer 150 may include a carbazole derivative. As a specific example, the hole transport layer 150 may include CBP [4,4'-Bis(N-carbazolyl)-1,1'-biphenyl] as the carbazole derivative. The hole transport layer 150 may be, for example, a CBP layer. The CBP layer may be an organic material layer. The thickness of the hole transport layer 150 may be about 30 to 50 nm or about 35 to 45 nm. The configuration of the hole transport layer 150 may serve to improve hole movement characteristics together with the configuration of the hole injection layer 160 . In particular, when the CBP layer is applied as a material of the hole transport layer 150 and the CBP layer is used together with the MoO ₃ layer and the HAT-CN layer of the hole injection layer 160, it may be advantageous to secure excellent hole transport properties. Accordingly, the hole transport layer 150 and the hole injection layer 160 may preferably have a CBP/MoO ₃ /HAT-CN structure.

The electron transport layer 130 may include a metal oxide-based material. For example, the electron transport layer 130 may include a zinc oxide (ZnO)-based material or a titanium oxide-based material. The zinc oxide (ZnO)-based material may include a material in which zinc oxide (ZnO) or zinc oxide (ZnO) is doped with a metal, and the material in which zinc oxide (ZnO) is doped with a metal is, for example, , ZnMgO, ZnAlO, or the like. The titanium oxide-based material may include, for example, TiO ₂ . In addition, the metal oxide-based material included in the electron transport layer 130 may have a nanoparticle form. Here, the average particle diameter of the nanoparticles may be on the order of several nm to several tens of nm. For example, the average particle diameter of the nanoparticles may be about 2 nm to about 40 nm or about 2 nm to about 35 nm. As a specific example, the electron transport layer 130 may include zinc oxide (ZnO)-based nanoparticles. Here, the zinc oxide (ZnO)-based nanoparticles may be ZnO nanoparticles. The thickness of the electron transport layer 130 may be, for example, about 25 to 45 nm or about 30 to 40 nm. When the thickness of the electron transport layer 130 is appropriately controlled, the light emitting characteristics and light emitting efficiency of the quantum dot light emitting device may be further improved.

The quantum dot light emitting device according to an embodiment of the present invention may have a maximum luminance of about 3 million cd/m ² or more. The maximum luminance of the quantum dot light emitting device may be about 3 million to 4 million cd/m ² . The quantum dot light emitting device may be stably driven with little deterioration even under ultra-high luminance driving conditions of about 100,000 cd/m ² or more. In addition, the quantum dot light emitting device may be driven with a high current density of about 1 A/cm ² or more or about 5 A/cm ² or more. In the case of a conventional general quantum dot light emitting device, even when a current density of about 1 A/cm ² is applied, the function of the device is lost or the device is destroyed due to Joule heat and consequent damage to the thin film. occurs However, the quantum dot light emitting device according to an embodiment of the present invention may be stably driven even at a high current density of about 5 A/cm ² or more and up to about 12 A/cm ² . As described above, the substrate 110 having high thermal conductivity is used, the hole injection layer 160 having a multi-layer (double-layer) structure composed of specific materials is used, and a shell part having a composition gradient is included. By applying quantum dots that do this, adopting a top emission structure using constructive interference, and optimizing the thickness of the components, ultra-high luminance that can be stably driven even at high current densities (unprecedented ultra-high brightness of 3 million cd/m ² or more) A quantum dot light emitting device having high luminance) can be implemented. In particular, it may be important to maximize (maximize) light extraction efficiency as well as high current driving for ultra-high luminance characteristics. Extraction efficiency can be greatly improved.

In addition, the quantum dot light emitting device according to an embodiment of the present invention may have excellent device stability and durability, and, at the same time, may have high device efficiency. For example, based on the use of red quantum dots, the stability of the device may be about 100 million hours based on 100 cd/m ² , and the device efficiency may be about 75.6 cd/A. These stability and efficiency characteristics can be evaluated to greatly exceed the performance of the existing quantum dot light emitting device. In an embodiment of the present invention, by reducing/suppressing the problem of non-luminescent recombination such as exciton quenching due to Auger recombination, excellent light emitting characteristics can be secured and the stability/durability and efficiency of the device can be improved. have.

2 is a view exemplarily showing a quantum dot light emitting device according to an embodiment of the present invention. In FIG. 2 , the upper right perspective view shows an example of a quantum dot light emitting device, and the upper left cross-sectional image is a TEM (transmission electron microscope) image showing a cross section of the actually fabricated quantum dot light emitting device. Meanwhile, the lower view (perspective view) in FIG. 2 shows a Si/SiO ₂ substrate applicable to a quantum dot light emitting device according to an embodiment and a glass substrate applicable to a quantum dot light emitting device according to a comparative example.

Referring to the perspective view of the upper right of FIG. 2 , the quantum dot light emitting device according to the embodiment is sequentially provided on a substrate with a first electrode 120 , an electron transport layer 130 , a quantum dot light emitting layer 140 , and a hole transport layer 150 ). , the hole injection layer 160 and the second electrode 170 may be included, and the hole injection layer 160 may include a first layer 160a and a second layer 160b. Each of the first electrode 120 , the electron transport layer 130 , the quantum dot light emitting layer 140 , the hole transport layer 150 , the hole injection layer 160 ( 160a + 160b ) and the second electrode 170 is as described in FIG. 1 . It may have the same configuration and characteristics.

Referring to the lower drawing (perspective view) of FIG. 2 , a Si/SiO ₂ substrate may be applied to the quantum dot light emitting device according to the embodiment, and a glass substrate may be applied to the quantum dot light emitting device according to the comparative example. Here, the Si/SiO ₂ substrate may be an example of the substrate 110 of FIG. 1 . Through thermal simulation assuming the use of a heat source of 0.2 W, it was confirmed that the heat dissipation pattern (characteristics) of the glass substrate and the Si/SiO ₂ substrate showed a large difference.

3 is a view for explaining the structure of a quantum dot (QD) that can be applied to the quantum dot light emitting device according to an embodiment of the present invention. In FIG. 3 , the diagram on the right shows a band diagram (ie, an electrical structure) that the quantum dots QD may have, and the diagram on the left shows a TEM image of the quantum dots QD.

Referring to FIG. 3 , the quantum dot QD may have a core-shell structure including a core part 10 and a shell part 20 surrounding the core part 10 . Here, the shell part 20 may have a composition gradient in which the composition is changed as the distance from the core part is increased. In other words, the shell part 20 may have a configuration in which an energy band (energy barrier) is changed as it moves away from the core part 10 . The shell part 20 may include a plurality of shell layers 20a, 20b, and 20c forming the composition gradient. In addition, the thickness of the core portion 10 and the shell portion 20 (20a, 20b, 20c) can be appropriately controlled. With respect to the configuration and thickness conditions of the quantum dots (QDs), extinction of excitons in the quantum dot light emitting layer including the quantum dots (QDs) is minimized, quenching due to Auger recombination is suppressed, and light emission is achieved. Characteristics and luminous efficiency can be greatly improved.

More specifically, the shell portion 20 includes a continuous grading layer 20a, a lattice adapter layer 20b and an injection barrier layer ( It may include an injection barrier layer (20c). The continuous grading layer 20a may be a layer whose composition is continuously (gradually or stepwise) changed while going away from the core part 10 . If the composition change of the continuous grading layer 20a is used, light emission characteristics and light emission efficiency may be improved. The lattice adapter layer 20b may serve to control a lattice constant in the shell part 20 . When a lattice mismatch exists, instability increases and luminescence characteristics may deteriorate. This problem can be prevented/inhibited by controlling the lattice constant using the lattice adapter layer 20b. The injection barrier layer 20c may serve to improve an injection balance between electrons and holes. If the material of the quantum dot (QD) itself has electron-rich properties, the injection barrier layer 20c is used to somewhat suppress the injection of electrons, thereby balancing the injection of electrons and holes. can

When the quantum dot QD is a red quantum dot (ie, a red light emitting quantum dot), the core part 10 may be formed of CdSe, and the continuous grading layer 20a may be formed of Cd _x Zn _1-x Se, The lattice adapter layer 20b may be formed of ZnSe, and the injection barrier layer 20c may be formed of ZnSe _y S _1-y . In Cd _x Zn _1-x Se constituting the continuous grading layer 20a , the x value may decrease as the distance from the core part 10 increases. In ZnSe _y S _1-y constituting the injection barrier layer 20c, the y value may decrease as the distance from the core part 10 increases.

The radius of the core part 10 may be about 3.2±0.5 nm or 3.2±0.1 nm. The thickness (shell thickness) of the continuous grading layer 20a may be on the order of 4.2±0.6 nm. The thickness (shell thickness) of the grating adapter layer 20b may be about 2.2±1.1 nm. The thickness (shell thickness) of the injection barrier layer 20c may be about 2.8±0.8 nm. When these thickness conditions are satisfied, it is possible to obtain a result in which luminous properties and luminous efficiency are further improved.

4A to 4D are cross-sectional views illustrating a method of manufacturing a quantum dot light emitting device according to an embodiment of the present invention.

Referring to FIG. 4A , a substrate 110 may be prepared. The substrate 110 may have excellent thermal conductivity of about 100 W/m·K or more at 25°C. The thermal conductivity of the substrate 110 may be, for example, about 100 to 200 W/m·K at 25°C. As a specific example, the substrate 110 may include a silicon (Si) substrate and a silicon oxide layer (SiO ₂ layer) formed on a surface (upper surface) of the silicon substrate. The thickness of the silicon oxide layer may be relatively very thin compared to the thickness of the silicon substrate portion. The thermal conductivity of the substrate 110 may be dominantly determined by the silicon substrate portion. Since the substrate 110 has excellent thermal conductivity, it may have excellent heat resistance and heat dissipation properties. In some cases, a sapphire (Al ₂ O ₃ ) substrate or a magnesium fluoride (MgF ₂ ) substrate having excellent thermal conductivity may be used as the substrate 110 .

When the substrate 110 includes the silicon (Si) substrate portion and the silicon oxide layer (SiO ₂ layer) formed on a surface (upper surface) of the silicon substrate portion, the substrate 110 may be formed of acetone, isopropyl alcohol (IPA), after washing with distilled water (DI water) in order, it may be dried at a temperature of about 120 ℃. However, these washing and drying conditions are merely exemplary and may be variously changed.

Referring to FIG. 4B , the first electrode 120 may be formed on the substrate 110 . The first electrode 120 may be a reflective electrode. The first electrode 120 may be formed of a metal or a metallic material. As a specific example, an Ag layer (silver layer) having a thickness of about 80 nm or more or about 85 nm or more may be deposited and used as the first electrode 120 for high reflectivity. The thickness of the first electrode 120 may be about 80 to 120 nm. The material of the first electrode 120 is not limited to Ag and may be variously changed.

Next, the electron transport layer 130 may be formed on the first electrode 120 . The electron transport layer 130 may include a metal oxide-based material. For example, the electron transport layer 130 may include a zinc oxide (ZnO)-based material or a titanium oxide-based material. The zinc oxide (ZnO)-based material may include a material in which zinc oxide (ZnO) or zinc oxide (ZnO) is doped with a metal, and the material in which zinc oxide (ZnO) is doped with a metal is, for example, , ZnMgO, ZnAlO, and the like. The titanium oxide-based material may include, for example, TiO ₂ . In addition, the metal oxide-based material included in the electron transport layer 130 may have a nanoparticle form. Here, the average particle diameter of the nanoparticles may be on the order of several nm to several tens of nm. For example, the average particle diameter of the nanoparticles may be about 2 nm to about 40 nm or about 2 nm to about 35 nm. As a specific example, the electron transport layer 130 may include zinc oxide (ZnO)-based nanoparticles. Here, the zinc oxide (ZnO)-based nanoparticles may be ZnO nanoparticles. In this case, after a solution (nanoparticle solution) containing ZnO nanoparticles is applied on the first electrode 120 in a spin coating method, heat treatment is performed at a temperature of about 100° C. in a nitrogen atmosphere for about 30 minutes to form an electron transport layer ( 130) can be formed. The thickness of the electron transport layer 130 may be, for example, about 25 to 45 nm or about 30 to 40 nm.

Referring to FIG. 4C , the quantum dot emission layer 140 may be formed on the electron transport layer 130 . The quantum dot emission layer 140 may be formed by, for example, a spin coating method using a solution process. The quantum dot emission layer 140 may include quantum dots having a core part and a shell part. The shell part may have a composition gradient in which the composition is changed as the distance from the core part is increased. In addition, the shell part may have a plurality of shell layers forming the composition gradient. The thickness of the core part and the shell part (the plurality of shell layers) may be appropriately controlled. With respect to the configuration and thickness control characteristics of the quantum dots, extinction of excitons in the quantum dot light emitting layer 140 is minimized, quenching due to Auger recombination is suppressed, and luminescence characteristics and luminous efficiency are greatly improved. can be improved The thickness of the quantum dot emission layer 140 may be, for example, about 25 to 45 nm or about 30 to 40 nm.

Referring to FIG. 4D , the hole transport layer 150 , the hole injection layer 160 , and the second electrode 170 may be sequentially formed on the quantum dot emission layer 140 through a vacuum deposition process. The hole transport layer 150 may include a carbazole derivative. As a specific example, the hole transport layer 150 may include CBP [4,4'-Bis(N-carbazolyl)-1,1'-biphenyl] as the carbazole derivative. The hole transport layer 150 may be, for example, a CBP layer. The CBP layer may be an organic material layer. The thickness of the hole transport layer 150 may be about 30 to 50 nm or about 35 to 45 nm. The configuration of the hole transport layer 150 may serve to improve hole movement characteristics together with the configuration of the hole injection layer 160 . In particular, when the CBP layer is applied as a material of the hole transport layer 150, it may be advantageous to secure excellent hole transport properties.

The hole injection layer 160 may have a multi-layer structure, for example, a double-layer structure. Specifically, the hole injection layer 160 may include a first layer 160a and a second layer 160b sequentially disposed from the hole transport layer 150 side. The first layer 160a may be disposed between the hole injection layer 160 and the second layer 160b. Here, the first layer 160a may include MoO ₃ , and the second layer 160b may include hexaazatriphenylene hexacarbonitrile (HAT-CN). The first layer 160a may be a MoO ₃ layer, and the second layer 160b may be a HAT-CN layer. In this case, the first layer 160a may have a thickness in the range of about 3-7 nm or in the range of about 4-6 nm, and the second layer 160b in the range of about 3-7 nm or in the range of about 4-6 nm may have a thickness of For example, the thickness of the first layer 160a may be 5 nm or 6 nm, and the thickness of the second layer 160b may be 5 nm or 6 nm. The thickness of the hole injection layer 160 may be about 6 to 14 nm or about 8 to 12 nm. As such, when the hole injection layer 160 has a structure in which the MoO ₃ layer and the HAT-CN layer are stacked, and their thickness is appropriately controlled, the hole injection barrier is greatly reduced by the hole injection layer 160, The hole injection characteristic is improved, and as a result, the luminescence characteristic and the luminous efficiency can be improved. In the present embodiment, the hole transport layer 150 and the hole injection layer 160 may have a CBP/MoO ₃ /HAT-CN structure, and in this case, it may be advantageous to secure excellent hole transport characteristics.

The second electrode 170 may be a transparent electrode (a light-transmitting electrode). The second electrode 170 may be formed of a metal or a metallic material. As the second electrode 170 , an Ag layer (silver layer) having a thickness of about 30 nm or less or about 25 nm or less may be deposited and used for high transmittance. The thickness of the second electrode 170 may be about 15 to 30 nm. The material of the second electrode 170 is not limited to Ag and may be variously changed.

The first electrode 120 and the second electrode 170 may be configured to generate an optical microcavity effect. In addition, the interval between the first electrode 120 and the second electrode 170 , the interval between the first electrode 120 and the quantum dot emission layer 140 , and the interval between the quantum dot emission layer 140 and the second electrode 170 . can be controlled to generate optical constructive interference associated with the emission of light. Accordingly, the light emitted from the quantum dot emission layer 140 to the front surface of the device and the light emitted from the quantum dot emission layer 140 and reflected from the first electrode 120 to the front surface of the device may cause constructive interference. In addition, the light emitted from the quantum dot light emitting layer 140 to the front surface of the device and the light emitted from the quantum dot light emitting layer 140 and reflected from the first electrode 120 to the front surface of the device are generated by the microcavity structure. A reinforcing effect according to resonance may be exhibited. Accordingly, the quantum dot light emitting device may have excellent light extraction characteristics.

The quantum dot light emitting device of FIG. 4D may be the same as the quantum dot light emitting device described with reference to FIGS. 1 to 3 . Accordingly, the configuration and characteristics of the quantum dot light emitting device described in FIGS. 1 to 3 may be equally applied to the quantum dot light emitting device of FIG. 4D .

5 is a graph showing results of evaluating current efficiency and luminance characteristics according to current density of quantum dot light emitting devices according to Examples and Comparative Examples of the present invention. The quantum dot light emitting device according to the embodiment has the structure of FIG. 1 , a MoO ₃ layer (thickness: 5 nm) is applied as the first layer 160a of the hole injection layer 160, and the second layer 160b is formed. This is a case where a HAT-CN layer (thickness: 5 nm) is applied. The quantum dot light emitting device according to the comparative example was a case in which a MoO ₃ single layer was applied as a hole injection layer, and other conditions were the same as in the above embodiment. A CBP layer was used as the hole transport layer in both the Examples and Comparative Examples. On the other hand, a voltage was applied to the quantum dot light emitting device using a Keithley 2400 source meter to obtain a current characteristic, and a Keithley 2000 multimeter and a silicon photodiode were used. The light intensity was measured. In addition, emission spectra were obtained using a spectroradiometer, Minolta CS-2000, and efficiency and luminance were calculated through current-voltage characteristics, light intensity, and emission spectrum. This measurement method was also the same for FIG. 6 below.

Referring to FIG. 5 , when using a hole injection layer having a double-layer structure (MoO ₃ /HAT-CN) according to an embodiment, a hole injection layer having a single-layer structure (MoO ₃ ) according to a comparative example When using It can be seen that the current efficiency and luminance are significantly improved. Through these results, it can be confirmed that when a hole injection layer having a double layer structure (MoO ₃ /HAT-CN) is used as in the embodiment, hole injection characteristics can be greatly improved.

6 is a graph showing results of evaluating current efficiency and luminance characteristics according to current density of quantum dot light emitting devices according to Examples and Comparative Examples of the present invention. The quantum dot light emitting device according to the embodiment has the structure of FIG. 1 , and a Si/SiO ₂ substrate is used as the substrate 110 . The quantum dot light emitting device according to the comparative example was a case in which a glass substrate was used as a substrate, and other conditions were the same as in the above embodiment. The quantum dot light emitting device according to the embodiment was represented by S-QLED, and the quantum dot light emitting device according to the comparative example was represented by G-QLED.

Referring to FIG. 6 , it can be seen that the quantum dot light emitting device according to the embodiment using a Si/SiO ₂ substrate exhibits improved current efficiency and luminance characteristics than the quantum dot light emitting device according to the comparative example using a glass substrate. In particular, since the Si/SiO ₂ substrate of the embodiment has excellent thermal conductivity and rapidly diffuses heat generated from the driving pixel to the periphery, a quantum dot light emitting device to which it is applied may be operated up to an extremely high current density.

7 is a graph showing a change in maximum pixel temperature according to time for each applied current density of a quantum dot light emitting device (S-QLED) according to an embodiment of the present invention. Here, the substrate of the quantum dot light emitting device (S-QLED) according to the embodiment is a Si/SiO ₂ substrate.

8 is a graph showing a change in maximum pixel temperature according to time for each applied current density of a quantum dot light emitting device (G-QLED) according to a comparative example. Here, the substrate of the quantum dot light emitting device (G-QLED) according to the comparative example is a glass substrate. The ON period in FIGS. 7 and 8 was between 5 and 15 seconds.

7 and 8 , it can be seen that the maximum pixel temperature of the quantum dot light emitting device (S-QLED) according to the embodiment is relatively very lower than the maximum pixel temperature of the quantum dot light emitting device (G-QLED) according to the comparative example. have. Accordingly, the quantum dot light emitting device (S-QLED) according to the embodiment may be stably driven without a problem due to heat generation even at a high current density.

9 is an optical simulation result showing a change in emission intensity according to thickness conditions of a hole transport layer (HTL) and an electron transport layer (ETL) of a quantum dot light emitting device according to an embodiment of the present invention. The quantum dot light emitting device according to the embodiment has a top emission structure as described with reference to FIG. 1 . On the other hand, a small graph (ie, insert) inserted inside the large graph in FIG. 9 shows the simulation results for the quantum dot light emitting device according to the comparative example. The quantum dot light emitting device according to the comparative example has a bottom emission structure.

Referring to FIG. 9 , in the quantum dot light emitting device according to the embodiment, the thickness of the hole transport layer (HTL) may be preferably about 30 to 50 nm or about 35 to 45 nm, and the thickness of the electron transport layer (ETL) is about It may be on the order of 25-45 nm or about 30-40 nm. In particular, the thickness of the hole transport layer (HTL) may preferably be about 35 to 45 nm, and the thickness of the electron transport layer (ETL) may be about 30 to 40 nm. When these conditions are satisfied, the light emitting characteristics and light emitting efficiency of the quantum dot light emitting device according to the embodiment may be further improved. On the other hand, in the case of the quantum dot light emitting device according to the comparative example having a bottom emission structure (see insert), it can be seen that the light emission intensity is relatively very low.

10 is a simulation result showing changes in the average QD occupancy <N> according to the QD areal density (ρ) and the applied current (J) of the quantum dot light emitting device according to an embodiment of the present invention; to be. Here, the dotted line indicates a contour (contour line) in the case of <N> = 1, 2 and 3. Meanwhile, the inserted graph shows the calculated internal quantum efficiency (IQE) of QLED as a function of J with ρ varying from 1×10 ¹¹ cm ^-2 (black) to 5×10 ¹¹ cm ^-2 (blue). show

11 shows normalized electroluminescence (EL) of a quantum dot light emitting device (S-QLED) according to an embodiment having different QD areal densities (ρ) when the applied current (J) is 8.0 A cm ⁻² ) is a graph showing the spectrum. The inset graph shows 1S _e -1S _hh conversion (S) and 1P _e -1S _hh conversion (P). As the QD areal density (ρ) increases to a predetermined level within a given range, it can be seen that a peak corresponding to P-emission, not main emission, is suppressed. This may mean that the light emitting characteristics can be improved by adjusting the thickness of the QD layer.

12 is a graph showing a change in PL (photoluminescence) quantum yield (%) according to a process of growing a shell part of a quantum dot that can be applied to a quantum dot light emitting device according to an embodiment of the present invention. The result of FIG. 12 is for a quantum dot (QD) having the structure described with reference to FIG. 3 .

Referring to FIG. 12, as described in FIG. 3, the quantum dot may have a core part and a shell part surrounding it, and the shell part is a continuous grading layer (cg) sequentially disposed from the core part side, a grating adapter layer (A) and an injection barrier layer (B). As a result of measuring the quantum yield (%) according to the process of growing the shell part, as shown in FIG. 12 , the continuous grading layer (cg), the lattice adapter layer (A), and the injection barrier layer (B) were respectively applied to an appropriate thickness. When all are formed, it can be seen that a high quantum yield (%) can be secured.

13 is a graph showing the ensemble PL photoluminescence decay characteristics of CdSe QD (red), cg-QD (orange), cg/A-QD (green) and cg/A/B-QD (blue). to be. Here, CdSe QD means a QD having only a core part, cg-QD means a QD in which only a cg layer is added to the core part, and cg/A-QD is a QD having a cg layer and an A layer added to the core part. Meaning, cg/A/B-QD means a QD in which a cg layer and both A and B layers are added to the core part. cg/A/B-QD may be applied to the quantum dot light emitting device according to an embodiment of the present invention. Each trace has been rescaled for clarity. The inset provides a single exciton lifetime (τ _X ) as a function of shell thickness, where the color-encoded arrows correspond to the decay curves.

Referring to FIG. 13 , it can be seen that cg/A/B-QD, which can be applied to the quantum dot light emitting device according to the embodiment, exhibits the best optical properties. Accordingly, the quantum dot light emitting device according to the embodiment to which cg/A/B-QD is applied may exhibit excellent light emitting performance in relation to the configuration and thickness conditions of the quantum dots.

14 is a graph showing the results of measuring changes in current density and luminance according to applied voltage of quantum dot light emitting devices according to Examples and Comparative Examples of the present invention. The quantum dot light emitting device according to the embodiment has the structure of FIG. 1 , and a Si/SiO ₂ substrate is used as the substrate 110 . The quantum dot light emitting device according to the comparative example was a case in which a glass substrate was used as a substrate, and other conditions were the same as in the above embodiment. The quantum dot light emitting device according to the embodiment was represented by S-QLED, and the quantum dot light emitting device according to the comparative example was represented by G-QLED.

Referring to FIG. 14 , it can be seen that the quantum dot light emitting device according to the embodiment using a Si/SiO ₂ substrate has relatively higher maximum current density and luminance than the quantum dot light emitting device according to the comparative example using a glass substrate. Since the Si/SiO ₂ substrate of the embodiment has excellent thermal conductivity and rapidly diffuses heat generated from the driving pixel to the surroundings, a quantum dot light emitting device to which it is applied may be operated up to an extremely high current density. In addition, the Si/SiO ₂ substrate may contribute to realization of high luminance.

15 is a graph showing the results of measuring changes in current efficiency and EQE (external quantum efficiency) according to the applied current density of quantum dot light emitting devices according to Examples and Comparative Examples of the present invention. The quantum dot light emitting device according to the embodiment has the structure of FIG. 1 , and a Si/SiO ₂ substrate is used as the substrate 110 . The quantum dot light emitting device according to the comparative example was a case in which a glass substrate was used as a substrate, and other conditions were the same as in the above embodiment. The quantum dot light emitting device according to the embodiment was represented by S-QLED, and the quantum dot light emitting device according to the comparative example was represented by G-QLED.

15 , it can be seen that the quantum dot light emitting device according to the embodiment using a Si/SiO ₂ substrate has relatively higher current efficiency and EQE than the quantum dot light emitting device according to the comparative example using a glass substrate. In addition, the quantum dot light emitting device according to the embodiment may be operated up to an extremely high current density.

16 is a graph showing the results of evaluating the operational lifetime of quantum dot light emitting devices according to Examples and Comparative Examples of the present invention. Here, the initial brightness (L ₀ ) of the quantum dot light emitting device according to the Examples and Comparative Examples was 200000 cd m ^-2 . The quantum dot light emitting device according to the embodiment is an S-QLED, and the quantum dot light emitting device according to the comparative example is a G-QLED. The graph inserted in FIG. 16 shows the half-lifetime (T ₅₀ ) and acceleration factor of 1.8 of G-QLED (blue) and S-QLED (red) at various L ₀ values. Estimate of T ₅₀ (dotted line) used is shown.

Referring to FIG. 16 , it can be seen that the quantum dot light emitting device according to the embodiment may have a relatively very long operating life than the quantum dot light emitting device according to the comparative example. In particular, the quantum dot light emitting device according to the embodiment may have stability and lifespan of about 100 million hours or more based on 100 cd/m ² . This is an increase of about 10 times compared to the quantum dot light emitting device according to the comparative example.

17 is a quantum dot light emitting device according to an embodiment using time-resolved EL spectroscopy having a voltage pulse of 11.8 V (which corresponds to a steady-state current density of 12.0 A cm ⁻² ). -QLED) is a diagram showing the evaluation result of the transient EL decay profile.

18 is a transient EL normalized for various steady-state current densities (J) of 0.3, 1.6, 6.0 and 12.0 A cm ^-2 of a quantum dot light emitting device (S-QLED) according to an embodiment of the present invention. It is a graph showing the characteristics of normalized transient EL decay. The inset graph shows the current density (J) dependent EL decay time constant (τ _EL ) compared to the PL lifetime (τ _X ) of cg/A/B-QD.

17 and 18, it can be seen that the quantum dot light emitting device according to an embodiment of the present invention can be stably driven at a high current density up to about 12 A/cm ² .

19 is a photograph showing the light emitting performance of a quantum dot light emitting device (S-QLED) according to an embodiment of the present invention, and shows an S-QLED pixel emitting different light under strong daylight conditions (about 100000 lux). Since the quantum dot light emitting device (S-QLED) according to the embodiment can generate light having very high luminance, the emitted light can be clearly identified even under strong sunlight conditions.

20 is a photograph showing the result of evaluating the light emitting performance of a quantum dot light emitting device (S-QLED) according to an embodiment of the present invention. In Fig. 20, the upper left photo shows the light emission of an S-QLED having a single pixel, and the lower left photo shows the light emission of an S-QLED having 10 pixels. Meanwhile, the right photo of FIG. 20 shows the letter (Q, L, E, D) structures illuminated by a single pixel of the S-QLED. Here, the letter (Q, L, E, D) structures are separated by 2.0, 3.5, 5.0 and 6.5 m respectively from the single pixel illuminating them. In all the photos of FIG. 20 , the area of each light emitting pixel was 1.4 mm × 1.4 mm. It can be seen from FIG. 20 that the quantum dot light emitting device (S-QLED) according to the embodiment emits light having high luminance (ultra-high luminance).

Table 1 below summarizes various physical properties and performances of the quantum dot light emitting device (S-QLED) according to an embodiment of the present invention and the quantum dot light emitting device (G-QLED) according to the comparative example.

In Table 1, EL peak means the emission wavelength (center wavelength), FWHM means the full width at half maximum of the emission spectrum, Max L means maximum luminance, Max CE means maximum current efficiency, and Max EQE is the maximum external quantum efficiency (external quantum efficiency).

Referring to Table 1, the quantum dot light emitting device (S-QLED) according to an embodiment has a maximum luminance (Max L) of 3 million cd/m ² or more, and a maximum current efficiency (Max CE) of 70 cd A ^-1 or more. and has a maximum external quantum efficiency (Max EQE) of 20% or more. These values can be said to be significantly better or significantly improved than the quantum dot light emitting device (G-QLED) according to the comparative example and the conventional quantum dot light emitting device. However, the characteristics of the quantum dot light emitting device (S-QLED) according to the embodiment disclosed in Table 1 are exemplary, and the characteristics may be variously changed according to the material or composition used.

According to the embodiments of the present invention described above, it has excellent light extraction efficiency while stably emitting light at high current density in a field requiring high luminance, and overcomes the problem of performance degradation due to Joule heat and durability (long lifespan) characteristics) and a quantum dot light emitting device capable of securing stable driving characteristics can be implemented. In particular, a multi-structured hole injection layer, a configuration of a hole transport layer combined with the hole injection layer, a substrate with high thermal conductivity, an optimized top emission structure, quantum dots with a composition gradient, and thickness conditions Through optimization, etc., it is possible to effectively suppress Auger recombination even at high current density, and to have a maximum luminance of about 3 million cd/m ² or more, and a quantum dot light emitting device having high efficiency, excellent stability and durability (long life characteristics) can be implemented. The quantum dot light emitting device according to the embodiments has all aspects such as maximum luminance (about 3 million cd/m ² or more), device stability (about 100 million hours or more based on 100 cd/m ² ), and device efficiency (about 75.6 cd/A) can have significantly superior performance than the conventional quantum dot light emitting device.

The quantum dot light emitting device according to the above embodiments is an outdoor display, a next-generation display such as an AR/VR display that requires a super-resolution and high brightness of 2000 ppi or more at the same time, a light source of a medical/beauty device for phototherapy, high-brightness lighting It can be usefully applied to various application fields requiring high luminance, such as.

In the present specification, preferred embodiments of the present invention have been disclosed, and although specific terms are used, they are only used in a general sense to easily describe the technical content of the present invention and help the understanding of the present invention, and to limit the scope of the present invention. It is not meant to be limiting. It will be apparent to those of ordinary skill in the art to which the present invention pertains that other modifications based on the technical spirit of the present invention can be implemented in addition to the embodiments disclosed herein. For those of ordinary skill in the art, the quantum dot light emitting device and its manufacturing method according to the embodiments described with reference to FIGS. 1 to 20 are variously substituted without departing from the technical spirit of the present invention. , it will be appreciated that changes and modifications may be made. As a specific example, in FIG. 1, the electron transport layer 130 is disposed under the quantum dot light emitting layer 140, and the hole transport layer 150 and the hole injection layer 160 are disposed on the quantum dot light emitting layer 140. In some cases, the hole transport layer 150 and the hole injection layer 160 may be disposed under the quantum dot emission layer 140 , and the electron transport layer 130 may be disposed on the quantum dot emission layer 140 . In addition, various modifications may be possible. Therefore, the scope of the invention should not be determined by the described embodiments, but should be determined by the technical idea described in the claims.

* Explanation of symbols for the main parts of the drawing *
10: core part 20: shell part
20a: continuous grading layer 20b: grid adapter layer
20c: injection barrier layer 110: substrate
120: first electrode 130: electron transport layer
140: quantum dot light emitting layer 150: hole transport layer
160: hole injection layer 160a: first layer
160b: second layer 170: second electrode
QD: Quantum dots

Claims (19)

a substrate having a thermal conductivity of 100 W/m·K or more at 25°C;
a first electrode disposed on the substrate;
a second electrode disposed on the substrate and spaced apart from the first electrode in a direction perpendicular to the substrate;
A quantum dot light emitting layer disposed between the first electrode and the second electrode and including a quantum dot having a core portion and a shell portion, wherein the shell portion has a composition gradient in which the composition is changed as the distance from the core portion is increased. ;
an electron transport layer disposed between the first electrode and the quantum dot emission layer;
a hole transport layer disposed between the second electrode and the quantum dot emission layer and including a carbazole derivative; and
It is disposed between the hole transport layer and the second electrode, and includes a first layer and a second layer sequentially arranged from the hole transport layer side, wherein the first layer includes MoO ₃ , and the second layer comprises: A hole injection layer having a HAT-CN (hexaazatriphenylene hexacarbonitrile);
A quantum dot light emitting device having a top emission structure for emitting light from the quantum dot light emitting layer to the opposite side of the side on which the substrate is disposed. The method of claim 1,
The substrate includes a silicon substrate portion and a silicon oxide layer formed on a surface of the silicon substrate portion, and the thermal conductivity of the substrate is dominantly determined by the silicon substrate portion. The method of claim 1,
The first electrode is a reflective electrode, the second electrode is a transparent electrode,
The spacing between the first electrode and the second electrode, the spacing between the first electrode and the quantum dot light emitting layer, and the spacing between the quantum dot light emitting layer and the second electrode are controlled to generate optical constructive interference associated with the emission of light. Quantum dot light emitting device. The method of claim 1,
The first electrode comprises a first metal layer having a first thickness,
The second electrode is a quantum dot light emitting device including a second metal layer having a second thickness smaller than the first thickness. The method of claim 1,
The hole transport layer is a quantum dot light emitting device comprising CBP [4,4'-Bis(N-carbazolyl)-1,1'-biphenyl] as the carbazole derivative. The method of claim 1,
The first layer is a MoO ₃ layer, the second layer is a HAT-CN layer,
The first layer has a thickness in the range of 3 to 7 nm, the second layer has a thickness in the range of 3 to 7 nm quantum dot light emitting device. The method of claim 1,
The electron transport layer is a quantum dot light emitting device including zinc oxide (ZnO)-based nanoparticles (nanoparticles). The method of claim 1,
A quantum dot light emitting device comprising a continuous grading layer, a lattice adapter layer, and an injection barrier layer disposed in sequence from the side of the core part in the shell part of the quantum dot. 9. The method of claim 8,
The radius of the core part is 3.2±0.5 nm,
The thickness of the continuous grading layer is 4.2±0.6 nm,
The thickness of the grating adapter layer is 2.2±1.1 nm,
A quantum dot light emitting device having a thickness of the injection barrier layer of 2.8±0.8 nm. The method of claim 1,
The thickness of the electron transport layer is 30-40 nm,
The thickness of the quantum dot light emitting layer is 25 to 45 nm,
The thickness of the hole transport layer is 30-50 nm,
A quantum dot light emitting device having a thickness of the hole injection layer of 6 to 14 nm. The method of claim 1,
The quantum dot light emitting device is a quantum dot light emitting device having a maximum luminance of 3 million cd / m ² or more. The method of claim 1,
The quantum dot light emitting device is a quantum dot light emitting device configured to be driven with a current density of 5 A / cm ² or more. providing a substrate having a thermal conductivity of 100 W/m·K or more at 25°C;
forming a first electrode on the substrate;
forming an electron transport layer on the first electrode;
Forming a quantum dot light emitting layer comprising a quantum dot having a core portion and a shell portion on the electron transport layer, wherein the shell portion has a composition gradient that changes as the distance from the core portion increases;
forming a hole transport layer including a carbazole derivative on the quantum dot emission layer;
A hole injection layer including a first layer and a second layer sequentially disposed on the hole transport layer from the side of the hole transport layer, wherein the first layer includes MoO ₃ , and the second layer includes HAT-CN forming a; and
Comprising the step of forming a second electrode on the hole injection layer,
A method of manufacturing a quantum dot light emitting device having a top emission characteristic for emitting light from the quantum dot light emitting layer to the opposite side of the side on which the substrate is disposed. 14. The method of claim 13,
The substrate includes a silicon substrate portion and a silicon oxide layer formed on a surface of the silicon substrate portion, and the thermal conductivity of the substrate is dominantly determined by the silicon substrate portion. 14. The method of claim 13,
The first electrode is a reflective electrode, the second electrode is a transparent electrode,
The spacing between the first electrode and the second electrode, the spacing between the first electrode and the quantum dot light emitting layer, and the spacing between the quantum dot light emitting layer and the second electrode are controlled to generate optical constructive interference associated with the emission of light. A method of manufacturing a quantum dot light emitting device. 14. The method of claim 13,
The hole transport layer is a method of manufacturing a quantum dot light emitting device comprising CBP [4,4'-Bis(N-carbazolyl)-1,1'-biphenyl] as the carbazole derivative. 14. The method of claim 13,
The first layer is a MoO ₃ layer, the second layer is a HAT-CN layer,
The first layer has a thickness in the range of 3 to 7 nm, the second layer is a method of manufacturing a quantum dot light emitting device having a thickness in the range of 3 to 7 nm. 14. The method of claim 13,
The shell portion of the quantum dot includes a continuous grading layer, a lattice adapter layer and an injection barrier layer sequentially arranged from the side of the core portion,
The radius of the core part is 3.2±0.5 nm, the thickness of the continuous grading layer is 4.2±0.6 nm, the thickness of the grating adapter layer is 2.2±1.1 nm, and the thickness of the injection barrier layer is 2.8±0.8 nm. A method of manufacturing a light emitting device. 14. The method of claim 13,
The quantum dot light emitting device is a method of manufacturing a quantum dot light emitting device having a maximum brightness of 3 million cd / m ² or more.

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